Tornadoes, extreme flooding, unprecedented heat expected in U.S. today

By: Dr. Jeff Masters , 3:04 PM GMT on March 19, 2012

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Widespread and potentially catastrophic areal flooding and river flooding is expected this afternoon through Wednesday morning in Eastern Oklahoma, Western Arkansas, Western Louisiana, and Southwest Missouri, warns the National Weather Service in Tulsa, Oklahoma, in their latest flood watch for the region. The storm system responsible is a massive, slow-moving trough of low pressure over the Western U.S. that dumped heavy snows that closed several interstate highways in Arizona over the weekend. This storm system will collide with the warmest and moistest air mass ever recorded in March in the Central and Eastern U.S. According to the NWS in Minneapolis, Minnesota, moisture flowing northwards into Minnesota along the cold front yesterday had the highest levels of moisture ever recorded so early in the year, and moisture levels are expected to remain at record levels today. At the boundary between the Western U.S. trough of low pressure and Central U.S. ridge of high pressure, a cold front will lift huge quantities of moisture-laden air aloft, forcing record rains to fall. A wide region of 4 - 8 inches of rain is expected in the flood watch area, and isolated amounts as high as 15 inches could fall by Wednesday, as numerous rounds of thunderstorms repeatedly track over the same area. The cold front is also expected to trigger a Moderate Risk of severe weather over much of Texas today, including the Dallas-Fort Worth area, says NOAA's Storm Prediction Center. Damaging winds, large hail, flash flooding, and few strong tornadoes are expected to affect the area late this afternoon. Severe thunderstorm watches are already posted for much of West Texas, as seen on our Severe Weather Map. Eleven tornadoes were reported yesterday in Oklahoma, Nebraska, and South Dakota.


Figure 1. Predicted rainfall amounts for the 3-day period Monday morning through Thursday morning show an area of 7+ inches (yellow colors) is expected over Eastern Oklahoma, Western Arkansas, Western Louisiana, and Southwest Missouri. Image credit: NOAA HPC.


Figure 2. NOAA's Storm Prediction Center has highlighted a Moderate Risk area for severe weather over much of Texas today, including the Dallas-Fort Worth area.

Summer in March for the Midwest
The ongoing March heat wave in the Midwest is one of the most extreme heat events in U.S. history. With so many records being shattered, it is difficult to cover in detail just how widespread, long-lasting, and extreme the event is, and I offer just a few highlights:

Winner, South Dakota hit 94°F yesterday, the earliest 90°+ reading ever recorded in the Northern Plains, according to wunderground's weather historian, Christopher C. Burt. The 94°F reading was just 2°F short of the all-time state record for South Dakota in March, which was 96°F in Tyndall in 1943. However, subsequent analysis by NOAA questioned this 94°F reading, and it is now believed that 87°F is the appropriate high for Winner.

International Falls, Minnesota hit 79°F yesterday, the hottest March temperature on record in the Nation's Icebox. At midnight this morning, the temperature was 66°F there, breaking the record high for March 19 (set in 1910) by 6°F. The low temperature for International Falls bottomed out near 60°F this morning, so low for today is (unofficially) the same as the previous record high for the date. This is the seventh consecutive day that International Falls has broken or tied a daily record. That is spectacularly hard to do for a station with a century-long weather record. The longest string of consecutive records being broken I'm aware of is nine days in a row, set June 2 - 10, 1911 in Tulsa, Oklahoma (with weather records going back to 1905.) International Falls has a good chance of surpassing nine consecutive records this week.

Houghton, Michigan, near the frigid shores of Lake Superior, hit 76°F both Saturday and Sunday. It was the hottest March temperature on record, and an astonishing 44°F above the average high for the date (Saturday) of 32°. Huron, South Dakota also recorded a high temperature (88°F) that was 44° above the average high for the date, on Sunday. Most of the cities in Northern Michigan set all-time March high temperature records over the weekend.

Chicago, Illinois now has a string of five consecutive days of 80°+ temperatures, and the hottest temperature on record for so early in the year (82°F on Friday, and tied again on Saturday). The average high temperature in August is 82°F in Chicago, so this week is basically summer weather. Prior to this year, there had only been 10 days in March with highs in the 80s in Chicago, going back to 1871. The last time Chicago saw an 80 degree temperature during the month of March (prior to this year) was over 22 years ago back on March 12, 1990 when the high temperature hit 81. This morning's Public Information Statement from the National Weather Service in Chicago had this to say about this unprecedented March heat:

Chicago and Rockford have now both broken high temperature records 5 days in a row. There is even the potential they could tie or break record highs for up to an unbelievable 8 days in a row depending on how warm temperatures get Monday through Wednesday. It is extraordinarily rare for climate locations with 100+ year long periods of records to break records day after day after day.


Figure 3. March's month-to-date average temperature compared to the other top 5 warmest months of March in Chicago. The dotted blue lines are month-to-date average temperatures based on the current predicted temperatures. The hashed black line is the average month to date temperature for March. These graphs really illustrate just how far above the previous warmest top 5 Marches this month really has been and assuming no major pattern change the last week of the month gives some indication of just how far above the record March 2012 could end up being. Image credit: NWS Chicago.

Record heat in Canada
Record-breaking heat has also penetrated into the Prairie provinces of Canada over the past week. Winnipeg, Manitoba broke its record high for the past four days in a row, and hit 21°C yesterday, its hottest temperature on record so early in the year. With today's forecast by Environment Canada and wunderground both calling for highs near 25°C (77°F), Winnipeg is likely to record its highest March temperature on record. Previous record: 23.3°C on March 27, 1946. The earliest date for a 25°C+ temperature in Winnipeg is April 9, 1977.


Figure 4. The jet stream pattern features a large, southwards dipping bulge over the Western U.S., creating a trough of low pressure with cold and snow, and a large, northwards looping bulge over the Central U.S., creating a record-strength ridge of high pressure.

Why the record early-season warmth?
The unusual warmth is due to a loop in the jet stream that has created a large upper-level ridge of high pressure that is stuck in place over the Eastern U.S.--a phenomenon known as a "blocking pattern." Since the jet stream acts as the boundary between cold air to the north and warm air to the south, and the large loop in the jet places its axis far to the north of the eastern U.S., summer-like warmth has developed over the eastern half of the U.S. Conversely, colder than average temperatures have developed over the western third of the U.S. behind the southwards-dipping loop of the jet stream. There are at least three large-scale patterns working together right now to create an unusually strong ridge over the eastern half of the U.S.:

1) La Niña. The on-going La Niña event in the Eastern Pacific has weakened considerably over the past month, but ocean temperatures there are still cool enough to affect the jet stream pattern, favoring high pressure and warm temperatures over the Eastern U.S., and low pressure and cold temperatures over the Western U.S.

2) The Madden-Julian Oscillation( MJO). The MJO is a 2-month cycle of thunderstorm activity that travels west to east along the Equator. The MJO is currently in phase with La Niña, and is helping create warmer temperatures over the Eastern U.S.

3) The North Atlantic Oscillation (NAO.) The NAO is in its positive phase, which means the difference in pressure between the Icelandic Low and the Azores High is stronger than usual. This tends to increase the jet stream winds and keeps the jet from sagging southwards over the Eastern U.S.

While the blocking pattern responsible for the heat wave is natural, it is very unlikely that the intensity of the heat would have been so great unless we were in a warming climate. Climate scientist Dr. James Hansen has posted an interesting (as yet unpublished) paper discussing how the odds of such extreme heat events have shifted in recent years.

Extreme jet stream patterns like this often lead to tornado outbreaks in the Midwest, at the boundary of where warm, moist air flowing north from the Gulf of Mexico collides with cold, dry air flowing south. Cold dry air aloft, combined with warm, moist air at the surface, makes the atmosphere unstable, since air rising in thunderstorm updrafts will be less dense than the surroundings, allowing the air to accelerate upwards and increase the intensity of the thunderstorm. This will be the case today, when NOAA's Storm Prediction Center has highlighted a Moderate Risk area for severe weather over much of Texas today, including the Dallas-Fort Worth area.

Flood risk low this year for the Northern Plains
For the first time in four years, the Northern Plains are not expecting major to record snow melt flooding, said NOAA's National Weather Service in their annual spring flood outlook issued last week. Residents along the Mississippi, Missouri, Red, and Souris Rivers have endured a punishing series of bad flood years, but this year is unlikely to continue that trend, due to a lack of snow cover. The Northern Plains states of Minnesota, Wisconsin, North Dakota, and South Dakota recorded their 3rd - 8th warmest winter in the 117-year record, and are on pace to crush the record for warmest March in history. Winter snowfall was below average over most of the region, and what snow was on the ground at the beginning of March has mostly melted, thanks to the record-breaking March heat this week. The Souris and Red River basins contain about one-third the amount of water in the snow as last year, ranking this season in the lower half of the last 60 years. Precipitation this water year (since Oct 1, 2011) has been less than 50% of the normal across the Upper Mississippi and Upper Missouri Valleys, and much of the region is under moderate to severe drought, according to the latest Drought Monitor.


Figure 5. What a difference a year makes! Snow cover on March 15 of last year (top) was heavy over Minnesota, Wisconsin, and the Dakotas, and caused massive flooding problems on the Mississippi and Missouri Rivers during spring melt season. In contrast, there is almost no snow pack in the Upper Midwest this year (bottom), significantly reducing the odds of spring flooding on the Missouri and Mississippi Rivers. Image credit: NOAA/NOHRSC.


Figure 6. The U.S. spring flood risk, as predicted by the National Weather Service on March 15, 2012.

Jeff Masters

March 18th sundown (rosana)
Today it was warm, sunny & calm water with clouds matching the mood of the people just enjoying this view.
March 18th sundown
Mullet Lake ice melting (JeffMasters)
I pulled a piece of ice out of Mullet Lake in Northern Michigan during my bike ride along the shore. It was so strange riding shirtless in 82°F heat along the shore of a frozen lake. The ground still had some snow patches from the 16" snow storm from last week. The lake ice is breaking up weeks ahead of usual due to our warm winter and incredible March heat.
Mullet Lake ice melting
Come have a glass of wine on the patio! (RedRoxx)
LOL woke up to MORE snow, in the VOC (Sedona) are today, want to have a drink on the patio with us?
Come have a glass of wine on the patio!
End of the Icefishing Season (bbend)
One last beautiful day on the ice but it's beginning to weaken and get unsafe- another 60 plus degree day. Normally we'd have about 3' of ice or more but this season it was about 24" at the most.
End of the Icefishing Season

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400. Patrap
11:58 PM GMT on March 19, 2012
Member Since: July 3, 2005 Posts: 419 Comments: 127377
399. MAweatherboy1
11:56 PM GMT on March 19, 2012
TORNADO WARNING
OKC061-077-121-200015-
/O.NEW.KTSA.TO.W.0003.120319T2344Z-120320T0015Z/

BULLETIN - EAS ACTIVATION REQUESTED
TORNADO WARNING
NATIONAL WEATHER SERVICE TULSA OK
644 PM CDT MON MAR 19 2012

THE NATIONAL WEATHER SERVICE IN TULSA HAS ISSUED A

* TORNADO WARNING FOR...
SOUTHWESTERN HASKELL COUNTY IN SOUTHEAST OKLAHOMA
WESTERN LATIMER COUNTY IN SOUTHEAST OKLAHOMA
NORTHEASTERN PITTSBURG COUNTY IN SOUTHEAST OKLAHOMA

* UNTIL 715 PM CDT

* AT 641 PM CDT...A SEVERE THUNDERSTORM CAPABLE OF PRODUCING A
TORNADO WAS LOCATED 5 MILES SOUTH OF HIGGINS...MOVING NORTH AT 45
MPH.

* SOME LOCATIONS IN OR NEAR THE PATH OF THIS STORM INCLUDE...
HIGGINS...DAMON...WILBURTON...ROBBERS CAVE STATE PARK...QUINTON AND
KINTA.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

IF YOU ARE NEAR THE PATH OF THIS STORM...TAKE COVER NOW! IF NO
UNDERGROUND SHELTER IS AVAILABLE MOVE TO AN INTERIOR ROOM ON THE
LOWEST FLOOR. MOBILE HOMES AND VEHICLES SHOULD BE ABANDONED FOR MORE
SUBSTANTIAL SHELTER. AVOID WINDOWS!

&&

LAT...LON 3468 9551 3524 9546 3519 9519 3468 9534
TIME...MOT...LOC 2344Z 191DEG 40KT 3478 9543

$$
Member Since: February 11, 2012 Posts: 82 Comments: 7566
398. redwagon
11:56 PM GMT on March 19, 2012
Quoting ScottLincoln:


Also seems to have ~150kts of storm-top divergence. Yikes... nice updraft.


'Yikes' - Scott Lincoln
Member Since: August 4, 2007 Posts: 0 Comments: 3091
397. Patrap
11:55 PM GMT on March 19, 2012
College of DuPage Meteorology
Severe Weather and Flash Flood Warnings


Note: This page will reload every 2 minutes. Warnings are listed with the most recent first.

Click on the station ID to bring up list of recent severe weather statements.

SVR T-STORM WARNING AUSTIN/SAN ANTONIO TX - KEWX 654 PM CDT MON MAR 19 2012

SVR T-STORM WARNING CORPUS CHRISTI TX - KCRP 649 PM CDT MON MAR 19 2012

SVR T-STORM WARNING CHARLESTON WV - KRLX 745 PM EDT MON MAR 19 2012

SVR T-STORM WARNING AUSTIN/SAN ANTONIO TX - KEWX 645 PM CDT MON MAR 19 2012

TORNADO WARNING TULSA OK - KTSA 644 PM CDT MON MAR 19 2012
Member Since: July 3, 2005 Posts: 419 Comments: 127377
396. hurricanehunter27
11:54 PM GMT on March 19, 2012
Quoting redux:
hurricane hunter 27, where can one go to generate such imagery?

Download the trial: Link

Once downloaded put this source in your polling.
http://mesonet.agron.iastate.edu/data/nexrd2/raw/
Member Since: July 22, 2010 Posts: 1 Comments: 3841
395. Thundercloud01221991
11:53 PM GMT on March 19, 2012
Quoting redux:
hurricane hunter 27, where can one go to generate such imagery?



Link
Member Since: August 1, 2006 Posts: 28 Comments: 3716
394. ScottLincoln
11:52 PM GMT on March 19, 2012
Quoting KoritheMan:


The average person knows next to nothing about the dynamics of weather. My grandmother was saying after we had a cold front two weeks ago, that she was witnessing tornado formation because the sky was dark with relatively low clouds. I tried explaining that you don't get severe weather (typically) after cold fronts. My aunt was also present and said "Yeah but with how bad the storms have been this year, you never know."


Someone should try that reasoning on a synoptic meteorology exam.
Member Since: September 28, 2002 Posts: 5 Comments: 3159
393. redux
11:52 PM GMT on March 19, 2012
hurricane hunter 27, where can one go to generate such imagery?
Member Since: June 28, 2010 Posts: 0 Comments: 226
392. DavidHOUTX
11:51 PM GMT on March 19, 2012
Quoting KoritheMan:


The average person knows next to nothing about the dynamics of weather. My grandmother was saying after we had a cold front two weeks ago, that she was witnessing tornado formation because the sky was dark with relatively low clouds. I tried explaining that you don't get severe weather (typically) after cold fronts. My aunt was also present and said "Yeah with how bad the storms have been this year, you never know."


You are so right about that. Sometimes my fiance is wondering why I am always on the computer when big weather systems head our way. Mother Nature is something that we can do nothing about. It is intriguing as well as fascinating how amazing Mother Nature can be. I have been obsessed since I was 5 years old and I always will be :)
Member Since: August 18, 2011 Posts: 0 Comments: 598
391. hurricanehunter27
11:49 PM GMT on March 19, 2012
Member Since: July 22, 2010 Posts: 1 Comments: 3841
390. Patrap
11:48 PM GMT on March 19, 2012
Member Since: July 3, 2005 Posts: 419 Comments: 127377
389. KoritheMan
11:48 PM GMT on March 19, 2012
Quoting DavidHOUTX:
Boy will this be an ugly evening. Im here in Houston for the ride. I just hope people are alert and understand what is happening. Not all people are weather fanatics like us on here nor do they know anything about it.


The average person knows next to nothing about the dynamics of weather. My grandmother was saying after we had a cold front two weeks ago, that she was witnessing tornado formation because the sky was dark with relatively low clouds. I tried explaining that you don't get severe weather (typically) after cold fronts. My aunt was also present and said "Yeah but with how bad the storms have been this year, you never know."
Member Since: March 7, 2007 Posts: 550 Comments: 19798
388. DavidHOUTX
11:47 PM GMT on March 19, 2012
Quoting Patrap:


Sabinal should have a tornado warning right now as well. That cell is nasty and certainly looks to have a tornado imminent. Then again, that is just based off radar imagery
Member Since: August 18, 2011 Posts: 0 Comments: 598
387. GeorgiaStormz
11:46 PM GMT on March 19, 2012
Quoting DavidHOUTX:


That has tornado written all over it


not yet, but it is starting to get some weak rotation.
Member Since: February 11, 2012 Posts: 0 Comments: 9718
386. Patrap
11:46 PM GMT on March 19, 2012
People have eyes, the net, and Local TV,..

...but always relay any info to your neighbors, and those like the elderly, shut-ins and those you can reach who may not be aware of approaching Severe weather.

Be pro-active,,as reactive may be too late. .

Member Since: July 3, 2005 Posts: 419 Comments: 127377
385. jamesrainier
11:46 PM GMT on March 19, 2012
TORNADO WARNING
NATIONAL WEATHER SERVICE TULSA OK
644 PM CDT MON MAR 19 2012

THE NATIONAL WEATHER SERVICE IN TULSA HAS ISSUED A

* TORNADO WARNING FOR...
SOUTHWESTERN HASKELL COUNTY IN SOUTHEAST OKLAHOMA
WESTERN LATIMER COUNTY IN SOUTHEAST OKLAHOMA
NORTHEASTERN PITTSBURG COUNTY IN SOUTHEAST OKLAHOMA

* UNTIL 715 PM CDT

* AT 641 PM CDT...A SEVERE THUNDERSTORM CAPABLE OF PRODUCING A
TORNADO WAS LOCATED 5 MILES SOUTH OF HIGGINS...MOVING NORTH AT 45
MPH.

* SOME LOCATIONS IN OR NEAR THE PATH OF THIS STORM INCLUDE...
HIGGINS...DAMON...WILBURTON...ROBBERS CAVE STATE PARK...QUINTON AND
KINTA.
Member Since: June 1, 2010 Posts: 0 Comments: 159
384. DavidHOUTX
11:45 PM GMT on March 19, 2012
Quoting hurricanehunter27:
Leakey TX needs a tornado warning.


you are not kidding
Member Since: August 18, 2011 Posts: 0 Comments: 598
383. 1900hurricane
11:45 PM GMT on March 19, 2012
The new cell appears to be acquiring rotation rather quickly.

Member Since: August 2, 2006 Posts: 46 Comments: 11660
382. Patrap
11:44 PM GMT on March 19, 2012

343
WUUS54 KFWD 192341
SVRFWD
TXC281-200030-
/O.NEW.KFWD.SV.W.0019.120319T2341Z-120320T0030Z/

BULLETIN - EAS ACTIVATION REQUESTED
SEVERE THUNDERSTORM WARNING
NATIONAL WEATHER SERVICE FORT WORTH TX
641 PM CDT MON MAR 19 2012

THE NATIONAL WEATHER SERVICE IN FORT WORTH HAS ISSUED A

* SEVERE THUNDERSTORM WARNING FOR...
SOUTHERN LAMPASAS COUNTY IN NORTH CENTRAL TEXAS...

* UNTIL 730 PM CDT

* AT 641 PM CDT...NATIONAL WEATHER SERVICE METEOROLOGISTS DETECTED A
SEVERE THUNDERSTORM CAPABLE OF PRODUCING QUARTER SIZE HAIL...AND
DAMAGING WINDS IN EXCESS OF 60 MPH. THIS STORM WAS LOCATED 19 MILES
WEST OF LAMPASAS...MOVING EAST AT 45 MPH.

* THE SEVERE THUNDERSTORM WILL BE NEAR...
LAMPASAS AROUND 705 PM...

PRECAUTIONARY/PREPAREDNESS ACTIONS...

IF YOU ARE CAUGHT OUTSIDE...SEEK SHELTER IN A STRONG BUILDING AND
STAY INSIDE...AWAY FROM WINDOWS UNTIL THE STORM HAS PASSED.

A TORNADO WATCH IS IN EFFECT FOR THE WARNING AREA. SEVERE
THUNDERSTORMS CAN PRODUCE TORNADOES WITH LITTLE OR NO WARNING.



LAT...LON 3118 9852 3125 9804 3106 9791 3104 9792
3103 9844
TIME...MOT...LOC 2341Z 255DEG 38KT 3102 9848
Member Since: July 3, 2005 Posts: 419 Comments: 127377
381. DavidHOUTX
11:44 PM GMT on March 19, 2012
Boy will this be an ugly evening. Im here in Houston for the ride. I just hope people are alert and understand what is happening. Not all people are weather fanatics like us on here nor do they know anything about it.
Member Since: August 18, 2011 Posts: 0 Comments: 598
380. hurricanehunter27
11:43 PM GMT on March 19, 2012
Leakey TX needs a tornado warning.
Member Since: July 22, 2010 Posts: 1 Comments: 3841
379. Patrap
11:42 PM GMT on March 19, 2012
Member Since: July 3, 2005 Posts: 419 Comments: 127377
378. hurricanehunter27
11:42 PM GMT on March 19, 2012
Quoting 1900hurricane:
Big time watch!



WWUS40 KWNS 192321
WWP7

TORNADO WATCH PROBABILITIES FOR WT 0087
NWS STORM PREDICTION CENTER NORMAN OK
0621 PM CDT MON MAR 19 2012

WT 0087
PROBABILITY TABLE:
PROB OF 2 OR MORE TORNADOES : 70%
PROB OF 1 OR MORE STRONG /F2-F5/ TORNADOES : 50%
PROB OF 10 OR MORE SEVERE WIND EVENTS : 80%
PROB OF 1 OR MORE WIND EVENTS >= 65 KNOTS : 50%
PROB OF 10 OR MORE SEVERE HAIL EVENTS : 80%
PROB OF 1 OR MORE HAIL EVENTS >= 2 INCHES : 80%
PROB OF 6 OR MORE COMBINED SEVERE HAIL/WIND EVENTS : >95%

&&
ATTRIBUTE TABLE:
MAX HAIL /INCHES/ : 3.0
MAX WIND GUSTS SURFACE /KNOTS/ : 70
MAX TOPS /X 100 FEET/ : 550
MEAN STORM MOTION VECTOR /DEGREES AND KNOTS/ : 24030
PARTICULARLY DANGEROUS SITUATION : NO

&&
FOR A COMPLETE GEOGRAPHICAL DEPICTION OF THE WATCH AND
WATCH EXPIRATION INFORMATION SEE WOUS64 FOR WOU7.

$$
Thats pretty high.
Member Since: July 22, 2010 Posts: 1 Comments: 3841
377. DavidHOUTX
11:41 PM GMT on March 19, 2012
Member Since: August 18, 2011 Posts: 0 Comments: 598
376. DavidHOUTX
11:41 PM GMT on March 19, 2012
Quoting 1900hurricane:
New storm just about came from nowhere along US 83!



That has tornado written all over it
Member Since: August 18, 2011 Posts: 0 Comments: 598
375. DavidHOUTX
11:40 PM GMT on March 19, 2012
That storm heading straight towards San Antonio is going to cause some problems. People in San Antonio need to watch this closely
Member Since: August 18, 2011 Posts: 0 Comments: 598
374. ScottLincoln
11:39 PM GMT on March 19, 2012
Quoting GeorgiaStormz:
The severe thunderstorm furthest west has the highest cloud tops on GRLevel2, excess of 50000 feet


Also seems to have ~150kts of storm-top divergence. Yikes... nice updraft.
Member Since: September 28, 2002 Posts: 5 Comments: 3159
373. 1900hurricane
11:39 PM GMT on March 19, 2012
New storm just about came from nowhere along US 83!

Member Since: August 2, 2006 Posts: 46 Comments: 11660
372. KEEPEROFTHEGATE (Mod)
11:38 PM GMT on March 19, 2012
Member Since: July 15, 2006 Posts: 168 Comments: 53286
371. GeorgiaStormz
11:36 PM GMT on March 19, 2012
The severe thunderstorm furthest west has the highest cloud tops on GRLevel2, excess of 50000 feet
Member Since: February 11, 2012 Posts: 0 Comments: 9718
370. TomTaylor
11:35 PM GMT on March 19, 2012
Quoting ScottLincoln:


Depends. If you assume the other 2 of the 3 categories are split evenly, it would be 40% below 30% near avg 30% above avg. Sometimes it wouldnt be the best choice to split them evenly. Those graphics are tough for the general public to understand, and many times trained mets use them incorrectly.
Well it's not assuming, it's deducing. The chance of above average precipitation has to be less than 40% or else we would have equal chances (or alternatively, the chance of above average precipitation could be greater than 40% but then above average precipitation would be shaded, not below average like the graphic is showing).

Anyway, yeah those graphics are easy to misinterpret. The way I look at it now is if a category is shaded and it's percentage is also above 50% then it is the most likely condition. However, between 33%-50%, the shaded category is not necessarily the most likely individual category. Instead, the shaded category and normal conditions are most likely to occur over the opposite anomaly and normal conditions. Reason for that is below average conditions could be at 40%, but normal conditions could also be at 50% even though below average conditions are shaded.
Member Since: August 24, 2010 Posts: 19 Comments: 4357
369. hurricanehunter27
11:35 PM GMT on March 19, 2012
Storm near Leaky TX has a huge hail core.
Member Since: July 22, 2010 Posts: 1 Comments: 3841
368. 1900hurricane
11:33 PM GMT on March 19, 2012
Big time watch!



WWUS40 KWNS 192321
WWP7

TORNADO WATCH PROBABILITIES FOR WT 0087
NWS STORM PREDICTION CENTER NORMAN OK
0621 PM CDT MON MAR 19 2012

WT 0087
PROBABILITY TABLE:
PROB OF 2 OR MORE TORNADOES : 70%
PROB OF 1 OR MORE STRONG /F2-F5/ TORNADOES : 50%
PROB OF 10 OR MORE SEVERE WIND EVENTS : 80%
PROB OF 1 OR MORE WIND EVENTS >= 65 KNOTS : 50%
PROB OF 10 OR MORE SEVERE HAIL EVENTS : 80%
PROB OF 1 OR MORE HAIL EVENTS >= 2 INCHES : 80%
PROB OF 6 OR MORE COMBINED SEVERE HAIL/WIND EVENTS : >95%

&&
ATTRIBUTE TABLE:
MAX HAIL /INCHES/ : 3.0
MAX WIND GUSTS SURFACE /KNOTS/ : 70
MAX TOPS /X 100 FEET/ : 550
MEAN STORM MOTION VECTOR /DEGREES AND KNOTS/ : 24030
PARTICULARLY DANGEROUS SITUATION : NO

&&
FOR A COMPLETE GEOGRAPHICAL DEPICTION OF THE WATCH AND
WATCH EXPIRATION INFORMATION SEE WOUS64 FOR WOU7.

$$
Member Since: August 2, 2006 Posts: 46 Comments: 11660
367. ScottLincoln
11:32 PM GMT on March 19, 2012
Quoting SPLbeater:
Dangerous cell headed for San Antonio...Likely has hail in it. VIL gives reflection of 60


Looks like the core just fell out of it. VIL is almost minimal for a supercell now. Might be indicative of an RFD forming.

Quoting hurricanehunter27:
As the storm matures there is also a decent chance it could produce a tornado. Classic supercell.


Perhaps. But <50% of supercells ever produce a tornado. Needs something a bit more than just looking like a classic supercell.
Member Since: September 28, 2002 Posts: 5 Comments: 3159
366. hurricanehunter27
11:31 PM GMT on March 19, 2012
Quoting SPLbeater:
Dangerous cell headed for San Antonio...Likely has hail in it. VIL gives reflection of 60
As the storm matures there is also a decent chance it could produce a tornado. Classic supercell.
Member Since: July 22, 2010 Posts: 1 Comments: 3841
365. IceCoast
11:31 PM GMT on March 19, 2012


URGENT - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 87
NWS STORM PREDICTION CENTER NORMAN OK
625 PM CDT MON MAR 19 2012

THE NWS STORM PREDICTION CENTER HAS ISSUED A
TORNADO WATCH FOR PORTIONS OF

SOUTH CENTRAL TEXAS

EFFECTIVE THIS MONDAY NIGHT AND TUESDAY MORNING FROM 625 PM UNTIL
100 AM CDT.

TORNADOES...HAIL TO 3 INCHES IN DIAMETER...THUNDERSTORM WIND
GUSTS TO 80 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE
AREAS.

THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 60 STATUTE
MILES EAST AND WEST OF A LINE FROM 25 MILES WEST SOUTHWEST OF
LAREDO TEXAS TO 25 MILES NORTHEAST OF AUSTIN TEXAS. FOR A
COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE
UPDATE (WOUS64 KWNS WOU7).

REMEMBER...A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FOR
TORNADOES AND SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH
AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR
THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS
AND POSSIBLE WARNINGS.

OTHER WATCH INFORMATION...CONTINUE...WW 85...WW 86...

DISCUSSION...SEVERAL DISCRETE SUPERCELLS HAVE FORMED TO THE WEST AND
SOUTHWEST OF SAN ANTONIO...AND APPEAR LIKELY TO MAINTAIN INTENSITY
THROUGH MUCH OF THE EVENING. A MOIST AND VERY UNSTABLE AIR
MASS...COUPLED WITH STRONG LOW LEVEL AND DEEP LAYER SHEAR...WILL
PROMOTE THE RISK OF TORNADIC SUPERCELLS ALSO CAPABLE OF DAMAGING
WINDS AND VERY LARGE HAIL.

AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL
SURFACE AND ALOFT TO 3 INCHES. EXTREME TURBULENCE AND SURFACE
WIND GUSTS TO 70 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO
550. MEAN STORM MOTION VECTOR 24030.


...HART
Member Since: October 17, 2010 Posts: 0 Comments: 1267
364. 1900hurricane
11:29 PM GMT on March 19, 2012


MESOSCALE DISCUSSION 0294
NWS STORM PREDICTION CENTER NORMAN OK
0605 PM CDT MON MAR 19 2012

AREAS AFFECTED...SCNTRL THROUGH NCNTRL TX

CONCERNING...TORNADO WATCH 85...

VALID 192305Z - 200030Z

THE SEVERE WEATHER THREAT FOR TORNADO WATCH 85 CONTINUES.

GREATEST SEVERE THREAT IS EXPECTED TO PERSIST OVER CNTRL AND SCNTRL
TX PORTION OF TORNADO WATCH 86 THROUGH 01Z. TENDENCY HAS BEEN FOR
STORMS TO DEVELOP FARTHER SOUTH AND A NEW WW WILL BE ISSUED SHORTLY
FOR PORTIONS OF SCNTRL TX.


LINE OF STORMS FROM NCNTRL THROUGH SCNTRL TX IS MOVING SLOWLY EWD AT
AROUND 15 KT OR LESS. STRONGEST AND MORE DISCRETE STORMS PERSIST
OVER SCNTRL TX NORTHWEST AND WEST OF SAN ANTONIO WHERE THE
ATMOSPHERE REMAINS VERY UNSTABLE WITH MLCAPE FROM 2500-3000 J/KG AND
EFFECTIVE BULK SHEAR FROM 40-50 KT. TREND HAS BEEN FOR STORM TO
INCREASE IN COVERAGE...POSSIBLY IN RESPONSE TO AN IMPULSE MOVING
THROUGH BASE OF UPPER TROUGH. THIS ACTIVITY WILL POSE A THREAT FOR
VERY LARGE HAIL AND TORNADOES INTO THE EVENING AS IT DEVELOPS NEWD.


FARTHER NORTH INTO NCNTRL TX STORMS HAVE BEEN MORE LINEAR IN
NATURE...BUT STILL MAY POSE A THREAT FOR ISOLATED DAMAGING WIND...AN
ISOLATED TORNADO OR TWO AS WELL AS VERY HEAVY RAIN.

..DIAL.. 03/19/2012


ATTN...WFO...FWD...OUN...CRP...EWX...SJT...

LAT...LON 30949966 31859855 33589731 33749595 32939612 30959786
30319689 29179698 28069968 28750015 29170043 29580095
30949966
Member Since: August 2, 2006 Posts: 46 Comments: 11660
363. SPLbeater
11:28 PM GMT on March 19, 2012
Dangerous cell headed for San Antonio...Likely has hail in it. VIL gives reflection of 60
Member Since: August 4, 2011 Posts: 46 Comments: 4481
362. KEEPEROFTHEGATE (Mod)
11:28 PM GMT on March 19, 2012
Member Since: July 15, 2006 Posts: 168 Comments: 53286
361. hurricanehunter27
11:26 PM GMT on March 19, 2012
Quoting ScottLincoln:


...and now we just had another split south of the first one. Splitting and merging going on all over the place. Major radar eye-candy.
Yah this radar set may be used in Met 101 videos.
Member Since: July 22, 2010 Posts: 1 Comments: 3841
360. ScottLincoln
11:26 PM GMT on March 19, 2012
Quoting hurricanehunter27:
Lol was just making sure cause earlier I was talking about the lefty.


...and now we just had another split south of the first one. Splitting and merging going on all over the place. Major radar eye-candy.
Member Since: September 28, 2002 Posts: 5 Comments: 3159
359. hurricanehunter27
11:24 PM GMT on March 19, 2012
Quoting ScottLincoln:


The one NW of Pearsall. The other supercell is the left-moving anticyclonic one near Vanderpool.
Lol was just making sure cause earlier I was talking about the lefty.
Member Since: July 22, 2010 Posts: 1 Comments: 3841
358. ScottLincoln
11:23 PM GMT on March 19, 2012
Quoting hurricanehunter27:
Are you talking about the right mover?


The one NW of Pearsall. The other supercell is the left-moving anticyclonic one near Vanderpool.
Member Since: September 28, 2002 Posts: 5 Comments: 3159
357. hurricanehunter27
11:22 PM GMT on March 19, 2012
Quoting ScottLincoln:


Very characteristic supercell signature on radar. See the reflectivity of the forward flank splitting like a "V"? See how it abruptly slowed down and started to turn right? Even a hail spike evident from New Braunfels NEXRAD now. Probably worst threat would be south half of San Antonio area.

And the left-moving splitter looks like an anticyclonic supercell. Classic.
Quoting hurricanehunter27:
Supercells need to split to acquire a MESO. Typically it happens so early on you never see it on radar. One of them typically dies.
Mentioned it earlier. Nearly jumped out of my seat when I saw it.
Member Since: July 22, 2010 Posts: 1 Comments: 3841
356. TampaSpin
11:22 PM GMT on March 19, 2012
JUST WEST OF BANDERA, TEXAS

Member Since: September 2, 2007 Posts: 178 Comments: 20439
355. GeoffreyWPB
11:22 PM GMT on March 19, 2012
Member Since: September 10, 2007 Posts: 0 Comments: 10932
354. hurricanehunter27
11:21 PM GMT on March 19, 2012
Quoting ScottLincoln:


Very characteristic supercell signature on radar. See the reflectivity of the forward flank splitting like a "V"? See how it abruptly slowed down and started to turn right? Even a hail spike evident from New Braunfels NEXRAD now.
.
Member Since: July 22, 2010 Posts: 1 Comments: 3841
353. 1900hurricane
11:21 PM GMT on March 19, 2012
Quoting KoritheMan:
Closest skew-t I could find to San Antonio:


This is from the RUC, so it's not an actual sounding, but it should probably be a good representation.



Looks kinda like a loaded gun sounding to me.
Member Since: August 2, 2006 Posts: 46 Comments: 11660
352. Patrap
11:19 PM GMT on March 19, 2012
..always watch the severe right mover.. it usually spells trouble..
Member Since: July 3, 2005 Posts: 419 Comments: 127377
351. KEEPEROFTHEGATE (Mod)
11:19 PM GMT on March 19, 2012
Member Since: July 15, 2006 Posts: 168 Comments: 53286
There are a great many warnings going up now.

Member Since: August 2, 2006 Posts: 46 Comments: 11660

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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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