Tropical Tidbits from the Tundra

Severe weather tonight and tomorrow

By: Levi32, 8:41 PM GMT on February 28, 2007

Wednesday update 3pm eastern:

A near repeat of last week's severe weather outbreak over the plains will begin tonight. The only big difference between the two is that the severe weather with this system will cover a much larger area. An upper trough will move into the plains this afternoon, causing cyclogenesis over northern Texas, with a warm front forming through southern Kansas and Missouri. Thunderstorms will begin to develop late tonight along the dryline which will set up over Texas extending north through Oklahoma and SE Kansas. T-storms will also get going along the warm frontal boundary. These storms shouldn't get too severe tonight, due to the main activity taking place during diurnal cooling, and jet stream cirrus have already limited daytime heating over the western gulf coast states today. The SPC has a moderate risk area over southern Missouri and northern Arkansas for tonight, with a fairly large risk for tornadoes. There will be plenty of directional shear for the formation of tornadoes with a very strong jet moving into the plains, along with a good low-level jet bringing plenty of moisture northwards. Dew points will be even higher than with the last outbreak, with 60+ values making it all the way up to SE Kansas and southern Missouri. The deep moisture will also cover a bigger area with this system. Once again convective activity will be limited somewhat by cool temperatures tonight, but some storms will still become very dangerous.

By tomorrow morning things will really be heating up over Louisiana, Arkansas, and Missouri. Instability will be peaking at that time, and the low will be deepening rapidly over northern Missouri. This low is a fast mover, and will already be moving into southern Wisconsin at peak intensity tomorrow night. Throughout the afternoon tomorrow storms will spread east across Mississippi, Tennessee, and Alabama. Some severe storms will even make it as far north as Illinois, Indiana, and western Kentucky. The SPC has a moderate risk area tomorrow covering the entire southeast except Florida, which should once again escape with just a few isolated severe storms. The storms should gradually start to decrease in intensity once they get into Georgia and South Carolina, but the SPC has a moderate risk for those areas as well. Instability will decrease the farther east you go, so I expect that the tornado threat will be greatly lessened for these areas.

Once again this system has the potential to be an explosive outbreak, depending on how much daytime heating we get tomorrow. This is probably a more significant outbreak than last week's, and also a much bigger one, so be careful everybody.

We shall see what happens!




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Updated: 9:40 PM GMT on February 28, 2007

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Severe weather tonight and tomorrow

By: Levi32, 8:41 PM GMT on February 28, 2007

Wednesday update 3pm eastern:

A near repeat of last week's severe weather outbreak over the plains will begin tonight. The only big difference between the two is that the severe weather with this system will cover a much larger area. An upper trough will move into the plains this afternoon, causing cyclogenesis over northern Texas, with a warm front forming through southern Kansas and Missouri. Thunderstorms will begin to develop late tonight along the dryline which will set up in Texas and along the warm frontal boundary. These storms shouldn't get too severe tonight, due to the main activity taking place during diurnal cooling, and jet stream cirrus have already limited daytime heating over the western gulf coast states today. The SPC has a moderate risk area over southern Missouri and northern Arkansas for tonight, with a fairly large risk for tornadoes. There will be plenty of directional shear for the formation of tornadoes with a very strong jet moving into the plains, along with a good low-level jet bringing plenty of moisture northwards. Dew points will be even higher than with the last outbreak, with 60+ values making it all the way up to SE Kansas and southern Missouri. The deep moisture will also cover a bigger area with this system. Once again convective activity will be limited somewhat by cool temperatures tonight, but some storms will still become very dangerous.

By tomorrow morning things will really be heating up over Louisiana, Arkansas, and Missouri. Instability will be peaking at that time, and the low will be deepening rapidly over northern Missouri. This low is a fast mover, and will already be moving into southern Wisconsin at peak intensity tomorrow night. Throughout the afternoon tomorrow storms will spread east across Mississippi, Tennessee, and Alabama. Some severe storms will even make it as far north as Illinois, Indiana, and western Kentucky. The SPC has a moderate risk area tomorrow covering the entire southeast except Florida, which should once again escape with just a few isolated severe storms. The storms should gradually start to decrease in intensity once they get into Georgia and South Carolina, but the SPC has a moderate risk for those areas as well. Instability will decrease the farther east you go, so I expect that the tornado threat will be greatly lessened for these areas.

Once again this system has the potential to be an explosive outbreak, depending on how much daytime heating we get tomorrow. This is probably a more significant outbreak than last week's, and also a much bigger one, so be careful everybody.

We shall see what happens!




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Severe weather on Wed/Thu?

By: Levi32, 5:47 PM GMT on February 25, 2007

Sunday morning update:

Our severe weather outbreak over the southern states has for the most part ended this morning. There are no severe watches or warnings at this time, and storms should steadily weaken throughout the day. A total of 14 tornadoes were reported and 88 total reports of severe weather. Today the low responsible for this will continue to weaken over Indiana and southern Michigan. There is a slight risk of an isolated severe storm over northern Florida, but I doubt they'll get anything bad. In fact they could really use the rain, so this is a good thing.

Looking ahead we could have a repeat this Wednesday/Thursday with another low coming across the plains. Right now it looks like the trough associated with it will dig a bit further south than this last one, which could put the gulf coast areas at greater risk. We'll have a better idea of the potential impact in the coming days.

We shall see what happens!




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Severe weather in the southern states today

By: Levi32, 4:25 PM GMT on February 24, 2007

Update 7pm eastern:

7 tornadoes have been reported so far today, with 22 total reports of severe weather. Not the largest outbreak we've ever seen, but not the weakest either. Everything from 2 feet of snow in Wisconsin to hurricane force winds in Kansas to tornadoes and severe weather in the southern states is with this storm. The cold front and associated squall line has moved for the most part out of Arkansas, leaving behind 5 reported tornadoes in the state. The squall line now extends from NE Louisiana to NW Mississippi, and will continue to progress eastward tonight. The tornado threat in Kansas has ended with the upper low now over the eastern part of the state, and instability has moved off the the south and east. By the time the surface low makes it to Missouri it will have begun to weaken as it loses upper-level support. T-storms will diminish in intensity the further east they go, and the areas of Georgia, Florida panhandle, and southern Alabama shouldn't see too much severe weather with this. Northern Florida could still get some severe storms, but right now it doesn't look like conditions will favor more than an isolated severe storm here and there. Tonight the worst impacted area will be NE Louisiana and the state of Mississippi. Southern Louisiana could see some severe storms pop up later tonight with the arrival of a jet streak over the northern Gulf of Mexico. Instability will still be fairly favorable, and residents in that area should watch the skies. The worst tornado threat will be tonight for central and northern MS, but will diminish greatly by tomorrow morning as the storms lose support from the LLJ. Stay safe everyone!

We shall see what happens!

Update 1:45pm eastern:

Severe t-storms continue to intensify over northern Louisiana and Arkansas. An impressive return flow from the GOM is bringing very warm moist air northward to feed these storms. The surface low over Kansas continues to deepen, and the upper trough is beginning to really enhance instability throughout these areas. New storms with tornado warnings have also popped up in central Kansas. These t-storms are located in the dry slot of the low. Temperatures and Dewpoints are quite low, but there is enough instability and upper-level vorticity to spawn some low-top supercells. All these areas will see increased storm coverage and intensity during the next several hours, with the storms in LA and AR moving eastward with time, eventually affecting Mississippi later tonight.

Saturday morning severe weather update:

Model-wise little has changed this morning. The surface low has made it into the plains, and will quickly deepen during the day today to about 985mb. The low will move across Kansas and then move ENE through Missouri and Illinois, where it will begin to fill as it loses upper-level support tomorrow. A strong jet is accompanying the upper trough associated with this low. The trough is now moving across the plains, and will serve as the main kick-starter for supercells this afternoon. Late tonight another jet streak will develop over the western Gulf of Mexico and head east along the gulf coast. On Sunday this jet streak combined with the tail-end of the cold front from the low over northern Illinois will produce a marginal threat for severe storms over southern Alabama, Georgia, and northern Florida. As we have seen with the last couple storms it doesn't take much beyond a low-level jet and that jet streak to make severe storms pop up. Right now it is very uncertain what Florida will get, but we'll have a better idea late tonight.

Ok, so what's happening today? Well the dryline is over eastern Texas, and the cold front is over western Texas. The warm front is over NE Texas, and is responsible for the current storms firing over Arkansas. Both these fronts will trigger severe storms throughout the afternoon. Lots of mid-level dry air is invading Texas and Arkansas, and you can already see some high cloud tops blowing up on satellite imagery. The main focus of worst weather today will be over eastern Texas, northern Louisiana, southern Arkansas, and parts of Mississippi. A strong jet will be moving over the area during the course of this afternoon, which will enhance the already strong shear profiles. As the day progresses colder temperatures aloft will be advecting into the area from the upper-level trough. This will increase instability further. Daytime temperatures will once again be somewhat hindered by clouds and existing storms, but the areas of Texas and Louisiana should see highs in the lower-mid 70s, with low 70s even extending up into parts of Arkansas. The return flow from the Gulf of Mexico is very strong, and is bringing 60+ degree dewpoints all the way into Arkansas. The gulf coasts of Louisiana and Mississippi may get in on some bad storms tonight as the jet streak forms over the northern gulf. Mid-level lapse rates are quite high over the entire affected area, and instability will continue to increase throughout the day. The conditions are setting up for potential strong and severe tornadoes, along with 2+ inch hail. Everyone should be very careful today. Stay safe!

We shall see what happens!




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-Discussion and debate are allowed. Argueing is NOT allowed

If you break any of these rules:

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Updated: 12:10 AM GMT on February 25, 2007

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Severe weather in the plains tonight....moving into the SE U.S. this weekend

By: Levi32, 3:11 AM GMT on February 23, 2007

Bedtime Update:

Thunderstorms have increased in coverage, but remain for the most part on the quiet side....for now. The main upper low and surface low haven't made it into the plains yet, and until they do, I think diurnal cooling will tame the storms down to mostly a hail threat with hail diameters not exceeding 1.25 inches. Tomorrow morning things will start to heat up again with the upper trough moving into the picture, and the surface low deepening over Kansas. The strong left front quad of the jet will provide ample upper-level support for the developing storms over the course of the afternoon. Squall lines along the dryline and cold front will advance eastward across Louisiana, Arkansas, and Mississippi throughout the day. Late Saturday and Sunday the low will lose upper-level support and begin to fill near southern Michigan. There is a marginal severe weather threat for northern Florida due to a strong jet streak forecasted to move across the Gulf of Mexico on Sunday. It is still uncertain how favorable conditions will be at this time, but considering the last two storms which have affected the Florida area, it only takes a low-level jet and some moisture to get severe weather going.

We shall see what happens!

8pm Update:

Strong t-storms have begun to develop over northern Texas, Oklahoma, and southern Kansas. Severe weather threat will increase as the night goes on from SW Texas to southern Nebraska. Right now diurnal cooling is setting in, but the upper trough to the west will be steadily advancing east throughout the night, cooling upper-level temperatures and therefore increasing atmospheric instability over the entire area. I think the moist inflow from the Gulf of Mexico, the strong dryline, and upper dynamics coming into play will keep a tornado threat going throughout the night, but the main problem will be hail and damaging straight-line winds until tomorrow when the tornado threat will be renewed during afternoon heating. This is only the beginning of the outbreak. The storm system responsible isn't even entirely over the rockies yet. Tomorrow the low will be deepening over Kansas with a strong jet streak in the left front quad of the jet. All these factors will combine to produce more severe storms over parts of Arkansas, Louisiana, and the eastern plains tomorrow.

Update 4pm eastern:

The dryline is beginning to set up in extreme west Texas, and instability will continue to increase as the afternoon goes on. Clouds have limited daytime heating in central/northern Texas into southeast Oklahoma, but all other areas are heating up to near 70 degrees even up into Kansas. Dewpoints are also climbing as the southerly flow starts to grab moisture from the GOM. The first storms are still a few hours away. Be on your guard!

Friday morning update:

There is little change in the models since yesterday. The SPC outlook for today has a moderate risk area focused over Oklahoma, which is where the worst instability will set up late this afternoon. They have also issued a moderate risk area for Louisiana, Arkansas, and Mississippi tomorrow. Severe storms should start developing late this afternoon into tonight over northern Texas, Oklahoma, and Kansas. Some upper-level clouds are drifting northeastward over Texas into Oklahoma, and these could limit daytime heating somewhat, we'll have to see how that goes. The big question will be if the storms break the cap tonight. The main part of this event will be during the night, making it a very dangerous situation for residents.

Thursday evening update:

Some very active weather could be in store for the plains and southeastern states this weekend. An upper trough and associated low pressure system currently moving inland over northern California will move east over the Rockies tonight. By tomorrow morning the low will emerge over western Kansas, and begin to strengthen as the upper-level dynamics intensify. Plenty of low-level moisture is expected to be present due to good inflow from the Gulf of Mexico, with 55 degree dewpoints making it all the way up into northern Kansas tomorrow afternoon. Right now the models are forecasting decent instability down through northern Texas, but exactly how unstable the atmosphere becomes will rest on how much daytime heating will take place. There is a possibility of some clouds moving into the area prior to the arival of the warm front, which could limit daytime heating somewhat. If this is the case then the storms may find it hard to break the inversion cap, but I don't think the cap will be strong enough to hold down the instability that will be developing as the afternoon goes on.

As the low moves east, an impressive dry-line is forecast to develop over western Texas late tomorrow night, and steadily advance eastward through Louisiana and Mississippi. This is a classic setup with plenty of moisture over eastern Texas and Louisiana and very dry air over western Texas and New Mexico. A strong squall line will likely develop along the dry-line Friday night with embedded supercells. Plenty of shear will be present, and tornadoes are definitely a threat. Severe storms will continue on Saturday over Louisiana, Mississippi, Arkansas, and even Tennessee could see some action Saturday night. By Sunday morning the low will be rapidly losing upper-level support, and will begin to fill while moving northeast over southern Michigan. Thunderstorms will continue to affect Alabama, Georgia, and maybe even Florida Sunday afternoon. The storms will gradually diminish in intensity as they move east, and the tornado threat should be minimal by the time they get into Georgia. However things are a little more complicated for northern and central Florida. Depending on how far south the trough digs, thunderstorms could make it down as far south as Orlando, providing some much needed rain for those areas. The forecast challenge is whether or not these storms will become severe. The 18z model runs are now showing a second jet streak forming over the Gulf of Mexico and moving east during Sunday. We still need to see a few more runs to be sure, but if the models are correct, the chances of severe weather in northern and central Florida will be greatly increased.

Right now the SPC has a moderate risk area for the plains tomorrow, and a slight risk area for the gulf coast states on Saturday, which may get upgraded depending on how the storm develops. Bottom line this has the potential to be a significant outbreak, and residents should be ready for a rough ride over the next couple days.

We shall see what happens!




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-No bad-mouthing others or putting anyone down
-Respect everyone and their forecasts/opinions
-Discussion and debate are allowed. Argueing is NOT allowed

If you break any of these rules:

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Second Offense - You get a timeout for 15 minutes
Third Offense - You get banned/blocked for 3 days
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Updated: 7:06 AM GMT on February 24, 2007

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Bad signs for hurricane season/Severe weather outbreak this weekend

By: Levi32, 3:16 AM GMT on February 22, 2007

Hints at what hurricane season might hold in store for us this year keep popping up everywhere lately. The ENSO has officially plunged into neutral, and I believe a coming La Nina is a strong possibility this spring. The latest ENSO report from Australia came out today. As always it's full of good information so I encourage you to read it. Also skyepony found an interesting link to an experimental product, the ESPI (ENSO Precipitation Index). It's just like the SOI (Southern Oscillation Index), but it measures precipitation instead of air pressure. The numbers are similar to most ENSO indices. The 30-day average ESPI has plunged from +0.61 to -0.14 in only two weeks, which supports the current trend towards La Nina.

Another thing that I'm concerned about is the wind shear values in the Atlantic. The SSD Tropical Genesis data page shows that the wind shear in the eastern Atlantic, and both the western and eastern Caribbean have all been decreasing rapidly over the last 3 weeks, and are now well below normal for this time of year. In fact the wind shear in these areas is so low that if it were summer they would be favorable for tropical development. This is a bad sign to me, as it is once again supporting a developing La Nina, and could mean an early start to the hurricane season due to more favorable conditions in the upper atmosphere. We'll have to see if the SST anomalies fall in line as well this spring, but right now it looks like we are going to have a more active season than last year at any rate.

On another note, a potentially significant severe weather outbreak could be in the works as early as Friday night for Texas, Oklahoma, and Kansas. A low coming down out of the pacific northwest will deepen over the plains with the support of a strong (110+ knot) jetstream aloft. A classic setup with good, moist, low-level inflow from the gulf of Mexico, strong upper level dynamics, and plenty of instability is what the models are forecasting at this time. The storms will begin to decrease in intensity as the low loses upper-level support by the time they get past the Mississippi River, but some potent storms could still threaten the areas of Tennessee, Mississippi, and Georgia on Saturday and the early part of Sunday. The SPC 3-day outlook already has a slight risk area posted for the plains.

However all this could change as the low which will spawn this outbreak is still in its formation stages off the California coast, and the models usually don't handle these storms well until they're inland and crossing the Rockies. Right now I think the SPC is on the right track putting a slight risk area down for the plains on Friday. I think the ingredients will be there for a bad outbreak, but how it actually turns out could be much different considering the last two outbreaks which looked like they might be bad but in reality turned out not to be so awful.

We shall see what happens!
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What is El Nino?

El Nino is a reversal of the normal trade wind flow over the equatorial Pacific. When conditions are normal, trade winds flow from east to west. This usually sets up high pressure over northwestern South America, and low pressure in the western Pacific near Australia. A normal rainfall pattern with moist in Australia and dry in the eastern Pacific and South America is the result.

However when El Nino pops up, those trade winds can be reversed or greatly slowed down. The flow is then from west to east, which sets up the low pressure over NW South America and the high pressure over Australia. This is the total opposite of normal conditions. If El Nino sticks around for several months, Australia experiences severe droughts, and NW South America experiences heavy tropical rains. SSTs in the eastern equatorial Pacific are warmer than normal because no upwelling is occurring due to the reversed trade winds. Upwelling is brining up colder water from the deeper ocean to the surface. When the trade winds are from the east like normal, they "push" the ocean water westward from the coast of South America. As the warm surface water is pushed westward, the cold water from deep down moves up to replace it in response. But when the trade winds are reversed, upwelling is shut down, and the SSTs near the South American coast are warmed greatly. Warming of the SSTs near the equator is one of the first signs of an El nino, and is an easy signature to recognize on an SST anomaly map. El Nino is also known to cause global weather pattern changes which can be very severe. Where I live in Alaska, El Nino causes winters to be extremely mild and rainy, and summers to be very hot and dry. The affects are different for different parts of the world.

El Nino also has a large impact on the Atlantic and eastern Pacific Hurricane seasons. Warming of the SSTs in the eastern equatorial Pacific tends to be counter-acted by a cooling of the SSTs in the Gulf of Mexico, the Caribbean, and the western Atlantic. It also tends to increase wind shear. This lowers the average intensity and number of hurricanes. A classic example is last year, when even a weak El Nino greatly reduced the number and strength of hurricanes. The affects of El Nino can reduce the number of U.S. hurricane landfalls as well. When low pressure sets up over NW South America, high pressure sets up over the Caribbean, which directs tropical waves south and west over South America. These waves then pop out on the other side in the eastern Pacific, where they have a much better chance to develop. This results in a much more active eastern Pacific hurricane season. Therefore El Nino decreases hurricane activity in the Atlantic, and increases activity in the eastern Pacific.

La Nina is the opposite of El Nino, and is simply an intensification of normal conditions. Easterly trade winds are stronger, which causes more upwelling of colder deeper water in the eastern equatorial Pacific. SSTs are colder than normal, which is the signature of a La Nina on an SST anomaly map. Rainfall in Australia is increased, and NW South America experiences very dry conditions. La Nina, like El Nino, also has major impacts on weather patterns across the globe, though usually the opposite of El Nino. Likewise the affects on the eastern Pacific and Atlantic hurricane seasons are opposite. Strong high pressure builds in the eastern equatorial Pacific, which results in low pressure over the Caribbean. Tropical waves in the Atlantic are steered northwest towards the U.S. and Mexican coasts, increasing the number of storm landfalls. The cooling of the SSTs in the equatorial Pacific also tends to warm the SSTs in the western Atlantic. Wind shear is also decreased. This results in a more active Atlantic hurricane season. On the other end the eastern Pacific sees very little tropical activity, as SSTs are lowered and few tropical waves make it across into the pacific basin.

El Nino and La Nina are some of the toughest pieces of the weather to forecast. Either one could pop up any time without us foreseeing it. However lots of research is being put into these phenomenon, and hopefully some day we will be able to accurately predict these climate-changing events.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

WUHOUND Rules of Behavior:

-No cuss words, cursing, or swearing of any sort
-No bad-mouthing others or putting anyone down
-Respect everyone and their forecasts/opinions
-Discussion and debate are allowed. Argueing is NOT allowed

If you break any of these rules:

First Offense - I give you a Warning
Second Offense - You get a timeout for 15 minutes
Third Offense - You get banned/blocked for 3 days
Fourth Offense - You get banned permanently until I or the majority of members decides that you can be un-banned

Updated: 3:21 AM GMT on February 22, 2007

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A Peek into Hurricane Season

By: Levi32, 9:08 PM GMT on February 11, 2007

Hurricane Season 2007 is rapidly approaching, and there are many things to keep track of when trying to forecast how active a season we are to have in the Atlantic. Probably the most important variable to consider is the ENSO (El Nino Southern Oscillation).

What is El Nino?

El Nino is a reversal of the normal trade wind flow over the equatorial Pacific. When conditions are normal, trade winds flow from east to west. This usually sets up high pressure over northwestern South America, and low pressure in the western Pacific near Australia. A normal rainfall pattern with moist in Australia and dry in the eastern Pacific and South America is the result.

However when El Nino pops up, those trade winds can be reversed or greatly slowed down. The flow is then from west to east, which sets up the low pressure over NW South America and the high pressure over Australia. This is the total opposite of normal conditions. If El Nino sticks around for several months, Australia experiences severe droughts, and NW South America experiences heavy tropical rains. SSTs in the eastern equatorial Pacific are warmer than normal because no upwelling is occurring due to the reversed trade winds. Upwelling is brining up colder water from the deeper ocean to the surface. When the trade winds are from the east like normal, they "push" the ocean water westward from the coast of South America. As the warm surface water is pushed westward, the cold water from deep down moves up to replace it in response. But when the trade winds are reversed, upwelling is shut down, and the SSTs near the South American coast are warmed greatly. Warming of the SSTs near the equator is one of the first signs of an El nino, and is an easy signature to recognize on an SST anomaly map. El Nino is also known to cause global weather pattern changes which can be very severe. Where I live in Alaska, El Nino causes winters to be extremely mild and rainy, and summers to be very hot and dry. The affects are different for different parts of the world.

El Nino also has a large impact on the Atlantic and eastern Pacific Hurricane seasons. Warming of the SSTs in the eastern equatorial Pacific tends to be counter-acted by a cooling of the SSTs in the Gulf of Mexico, the Caribbean, and the western Atlantic. It also tends to increase wind shear. This lowers the average intensity and number of hurricanes. A classic example is last year, when even a weak El Nino greatly reduced the number and strength of hurricanes. The affects of El Nino can reduce the number of U.S. hurricane landfalls as well. When low pressure sets up over NW South America, high pressure sets up over the Caribbean, which directs tropical waves south and west over South America. These waves then pop out on the other side in the eastern Pacific, where they have a much better chance to develop. This results in a much more active eastern Pacific hurricane season. Therefore El Nino decreases hurricane activity in the Atlantic, and increases activity in the eastern Pacific.

La Nina is the opposite of El Nino, and is simply an intensification of normal conditions. Easterly trade winds are stronger, which causes more upwelling of colder deeper water in the eastern equatorial Pacific. SSTs are colder than normal, which is the signature of a La Nina on an SST anomaly map. Rainfall in Australia is increased, and NW South America experiences very dry conditions. La Nina, like El Nino, also has major impacts on weather patterns across the globe, though usually the opposite of El Nino. Likewise the affects on the eastern Pacific and Atlantic hurricane seasons are opposite. Strong high pressure builds in the eastern equatorial Pacific, which results in low pressure over the Caribbean. Tropical waves in the Atlantic are steered northwest towards the U.S. and Mexican coasts, increasing the number of storm landfalls. The cooling of the SSTs in the equatorial Pacific also tends to warm the SSTs in the western Atlantic. Wind shear is also decreased. This results in a more active Atlantic hurricane season. On the other end the eastern Pacific sees very little tropical activity, as SSTs are lowered and few tropical waves make it across into the pacific basin.

Current Conditions:

Right now there are strong signs that El Nino is weakening, and we are currently on our way into a neutral phase of the ENSO. I believe that a La Nina is possible by the time hurricane season starts. Evidence of this is shown in these two charts:



In the top image you can see the cold water bulging upward towards the surface. This is further shown in the bottom anomaly image by a large cold area near 125w at 100 meters. This spot has been migrating towards the surface over the last month or so. If this were to surface the SST anomalies would go down dramatically.

Model analogs
have been showing many La Nina years and very few El Nino years lately. This could also be evidence of a developing La Nina. Also this January was very warm in the eastern U.S., unlike the cool fall season. This is also evidence of a weakening El Nino. Further more, if this pattern continues to develop, a ridge in the east would mean more hurricane landfalls in the U.S. this season.

MJO (Madden-Julian Oscillation)

Not much is known about this fascinating oscillation, but there is a lot being learned about it all the time. What it is basically, is a fluctuation of upward motion, convection, and precipitation near the equator all around the globe. Areas of more or less convection migrate west to east across the tropics, and can enhance or decrease tropical development. A chart of the MJO phase over the last 90 days can be found here. Each phase is a different part of the world, and this chart shows which phase the MJO is in right now, where it has been over the past 3 months, and its strength. For example right now the MJO isn't very strong, but it appears to be in phase 6. This means that you can probably find above normal convection in the Western Pacific. Eventually this convection will move eastward. A good site for monitoring the MJO is here. The MJO won't become very useful until hurricane season is actually in progress, but we can still draw patterns from it in correlation with the upper air patterns and El Nino.



The above image shows the vertical velocity anomalies at 200mb for the world. Areas under green lines have above normal convection or convection potential. Areas under brown lines have below normal convection. When the MJO is pronounced (right now it is very weak), you can see a main area of convection which migrates west to east with time. This becomes very important during hurricane season because when that area moves over the Atlantic chances for hurricane development are greatly increased.

Models:

Global models are forecasting above normal precipitation in the ITCZ over the Atlantic this summer, along with very dry conditions over the eastern equatorial Pacific. The dry Pacific indicates La Nina, and the wet ITCZ obviously points to more TC formations.



This is the average forecast of the 6 models. The same models are forecasting at least a small La Nina during the summer.





The first image is the average of the 6 models, where you can see a weak La Nina is forecast. The second image is an individual model which is forecasting a very strong La Nina to develop. Other models are also forecasting the same thing, along with above normal heights over the western Atlantic, indicating a more western position of the Bermuda High.

Right now I see a more active year than last year shaping up, with a La Nina instead of El Nino. The big key this year will be where the Bermuda High sets up. Right now global models are showing a chance that it will set up pretty far west close the eastern seaboard, which wouldn't be good news. If that does happen there will be a corridor leading every storm towards the US. The SSTs in the Caribbean and off the eastern Seaboard should also be warmer this year than they were last season. In short: Be ready for a ride!



We shall see what happens!

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-No cuss words, cursing, or swearing of any sort
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-Discussion and debate are allowed. Argueing is NOT allowed

If you break any of these rules:

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Third Offense - You get banned/blocked for 3 days
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Updated: 3:09 PM GMT on February 14, 2007

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Watching El Nino

By: Levi32, 4:52 PM GMT on February 08, 2007

Hurricane season is only 3 months away, and like any year, the SSTs in the equatorial Pacific play a huge role in what the season will be like. Last year El Nino was partially responsible for the unexpected low number and intensity of storms. There has been an El Nino since last summer and through this winter, but there are signs of it weakening. The latest official update from Australia reflects this, and I encourage you to read it as it has some interesting information. Here are some maps and charts:

30-Day SOI (Southern Oscillation Index):



Here is a link to a 3-year chart with a brief explanation of the SOI.

SSTs and anomalies in the equatorial Pacific from the surface to 500 meters deep:



Near 125w at about 100 meters you can see a good-sized ball of cold water moving closer and closer to the surface in the anomaly map(bottom chart) over the last couple months. If this cold water does make it to the surface SST anomalies will go down dramatically. Also notice the cold water bulging upward towards the surface in the SST map (top chart). This is the area of cold water shown in the anomaly map above. This could be evidence of upwelling, which is bringing colder water up from the deep ocean closer to the surface.

Global SST Anomaly Map:



Experimental seasonal forecast models are all showing some sort of trend toward La Nina in their SST forecasts, some more dramatic that others. These same models are also forecasting precipitation patterns this summer which correspond to a La Nina pattern.

All these signs point to a weakening El Nino, and I think a La Nina could be in the making by the beginning of the hurricane season. Of course there's no way to tell how strong it will be, or exactly what impacts it will have. Predicting El Nino and La Nina is one of the toughest aspects of forecasting.

We shall see what happens!
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What is El Nino?

El Nino is a reversal of the normal trade wind flow over the equatorial Pacific. When conditions are normal, trade winds flow from east to west. This usually sets up high pressure over northwestern South America, and low pressure in the western Pacific near Australia. A normal rainfall pattern with moist in Australia and dry in the eastern Pacific and South America is the result.

However when El Nino pops up, those trade winds can be reversed or greatly slowed down. The flow is then from west to east, which sets up the low pressure over NW South America and the high pressure over Australia. This is the total opposite of normal conditions. If El Nino sticks around for several months, Australia experiences severe droughts, and NW South America experiences heavy tropical rains. SSTs in the eastern equatorial Pacific are warmer than normal because no upwelling is occurring due to the reversed trade winds. Upwelling is brining up colder water from the deeper ocean to the surface. When the trade winds are from the east like normal, they "push" the ocean water westward from the coast of South America. As the warm surface water is pushed westward, the cold water from deep down moves up to replace it in response. But when the trade winds are reversed, upwelling is shut down, and the SSTs near the South American coast are warmed greatly. Warming of the SSTs near the equator is one of the first signs of an El nino, and is an easy signature to recognize on an SST anomaly map. El Nino is also known to cause global weather pattern changes which can be very severe. Where I live in Alaska, El Nino causes winters to be extremely mild and rainy, and summers to be very hot and dry. The affects are different for different parts of the world.

El Nino also has a large impact on the Atlantic and eastern Pacific Hurricane seasons. Warming of the SSTs in the eastern equatorial Pacific tends to be counter-acted by a cooling of the SSTs in the Gulf of Mexico, the Caribbean, and the western Atlantic. It also tends to increase wind shear. This lowers the average intensity and number of hurricanes. A classic example is last year, when even a weak El Nino greatly reduced the number and strength of hurricanes. The affects of El Nino can reduce the number of U.S. hurricane landfalls as well. When low pressure sets up over NW South America, high pressure sets up over the Caribbean, which directs tropical waves south and west over South America. These waves then pop out on the other side in the eastern Pacific, where they have a much better chance to develop. This results in a much more active eastern Pacific hurricane season. Therefore El Nino decreases hurricane activity in the Atlantic, and increases activity in the eastern Pacific.

La Nina is the opposite of El Nino, and is simply an intensification of normal conditions. Easterly trade winds are stronger, which causes more upwelling of colder deeper water in the eastern equatorial Pacific. SSTs are colder than normal, which is the signature of a La Nina on an SST anomaly map. Rainfall in Australia is increased, and NW South America experiences very dry conditions. La Nina, like El Nino, also has major impacts on weather patterns across the globe, though usually the opposite of El Nino. Likewise the affects on the eastern Pacific and Atlantic hurricane seasons are opposite. Strong high pressure builds in the eastern equatorial Pacific, which results in low pressure over the Caribbean. Tropical waves in the Atlantic are steered northwest towards the U.S. and Mexican coasts, increasing the number of storm landfalls. The cooling of the SSTs in the equatorial Pacific also tends to warm the SSTs in the western Atlantic. Wind shear is also decreased. This results in a more active Atlantic hurricane season. On the other end the eastern Pacific sees very little tropical activity, as SSTs are lowered and few tropical waves make it across into the pacific basin.

El Nino and La Nina are some of the toughest pieces of the weather to forecast. Either one could pop up any time without us foreseeing it. However lots of research is being put into these phenomenon, and hopefully some day we will be able to accurately predict these climate-changing events.
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Updated: 6:05 PM GMT on February 11, 2007

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Nice weekend ahead

By: Levi32, 4:50 AM GMT on February 08, 2007

Wednesday Evening Alaska Weather Update:

Alaska is finally coming out of the week-long warm spell during which most areas lost several feet of snowpack to the sun. Temperatures in Palmer sored to an unbelievable 56 degrees late last week. However temps are now coming back down below freezing, though still well above average. A weak but persistent low has been sustaining a strong onshore flow out of the SE over the area, producing some light overrunning snow during the last couple days. This will continue through Friday as another storm system moves in from the west, however the models are now coming into agreement on high pressure building in from the north by Saturday, which should keep the lows far enough south to allow some fairly pleasant partly-cloudy weather to move in for the weekend over most of the mainland. The high pressure will break down again middle of next week, but we'll take all the sun we can get!

We shall see what happens!











^Click for larger version^

Updated: 4:53 AM GMT on February 08, 2007

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About Levi32

Levi Cowan has been tracking tropical systems since 2002, and is currently working on his bachelor's degree in physics at UAF.

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