North American Mesoscale Model Verification on January 26-27...

By: Zachary Labe , 10:34 PM GMT on January 29, 2011

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The North American Mesoscale Model (NAM) is a high resolution model courtesy of the National Center for Environmental Prediction. Another very common and referenced name for the model is the Weather Research and Forecasting Model (WRF). They are the same model and run out to 84 hours. The purpose of the model is to run a higher resolution determining mesoscale features that often cannot be picked up by the global models due to their larger scale. The NAM can be run on an 80km resolution with a broad view of the United States, or 40km which allows the viewer to zoom in on a localized region to put up on mesoscale features. Also a very high resolution form of the NAM exists using a 12km parametric and can zoom into different states. The model is released four times a day at 0z, 6z, 12z, and 18z. Keep in mind that time is zulu or more commonly known as greenwich mean time.

Computer models are critical to forecasting the weather as they use parametric and other mathematical equations to derive the current and predicted state of the atmosphere using a physical and chemical explanation as the background for the predictions. The NCEP is associated with the National Oceanic Atmospheric Administration (NOAA) to be the developer of these computer models. Each meteorological organization worlwide uses their own developed computer models to serve as a basis for the forecasts. Without computer models, we are not able to derive predictions on the weather greater than 24 hours out.

Like all computer models, the NAM shows all layers of the atmosphere in maps determining positioning and speed of the jet stream, surface precipitation amounts (quantitive precipitation forecast QPF), temperatures throughout the entire core of the atmosphere, convective indices, simulated radars, etc. Due to the higher resolution of the NAM, several problems do exist. It often produces convective elements in many middle latitude cyclones and these are known as convective feedback problems. This is where it developed these unstable regions and often associates them as surface lows causing the surface depiction to be distorted. This was a problem in the recent prediction of the January 26-27 winter storm and will be noted below. Also the NAM has a tendency to produce higher than normal precipitation amounts. I typically find myself cutting totals nearly by 30% as shown on the NAM. Finally the NAM has a bias to overamplify a low pressure and close them off to early particularily on eastern United States cyclogenesis off the coast.

The January 26-27 winter storm featured many model headaches do to some interesting variables. Early on it appeared likely for a low pressure to track up inland along the coastal plain. There was a lacking 50/50 low, unfavorable position of the western trough axis, neutral NAO, natural baroclinicity along the coastline, and stale antecedent cold air mass. This would produce rain along I-95 with heavy snows inland. The 500mb synoptic pattern showed very strong signals for this time of setup with most computer model guidance also in support. The GGEM and ECMWF led the pack with the heavy snows from I-81 on westward. The GFS suffered major problems with varying solutions for each run. But then the computer models began to delay the storm. In fact it was delayed nearly 48-60 hours from the original starting time. This caused a different scenario to unfold. The lacking high pressure to the north was still a problem as the anticyclone zoomed east-northeast, but now a high pressure and associated shortwave out ahead of it allowed sunk east-southeast across the Midwest and western Great Lakes. This acted as a 'kicker' helping to push the cyclonegenesis farther off the coast. This in turn allowed for a colder scenario along with precipitation to occur farther east. Therefore a turn of events allowed for a major I-95 snowstorm with 6in+ totals from Washington DC to Boston. This was very fortunate for snow lovers in that corridor due to pure luck given the poor synoptic setup.

Given the NAM's high resolution, it often overanalyzes prognostics post hour 60. It tends to enhance QPF, overamplify lows, and pick up on mesoscale features that really do not exist. Therefore I typically throw out hours 60-84. It would be a rare event where you would find the NAM 84 hour verifying anywhere close to accurate. But in the near term range, the NAM does an excellent job locating temperature thermals, QPF ranges, and picking up on mesoscale features; coastal fronts, enhanced convection, deformation bands, etc. But in this recent storm, it suffered a plethora of problems and even the 6 and 12 hour surface maps had poor verification especially in the QPF department.

Let us first look at the actual accumulated precipitation totals for the storm.

Given this is a 24 hour accumulated precipitation amount, about .01-.1in of additional precipitation fell south of the Mason-Dixon line in the previous 24 hours.

Here are the preceeding NAM total QPF forecasts...


(January 24; 18z) (January 25; 6z)


(January 25; 12z) (January 25; 18z)


(January 26; 0z) (January 26; 6z)

As you can see, the NAM had a lot of variance with the northwestern sharp precipitation gradients. These tight gradients this year have been caused by the rapid intensification of the coastal lows allowing the heaviest moisture to be confined closer to the center of circulation. Also in this instance, a very cold and dry air mass along with associated cold front was quickly advancing southeast across the Great Lakes and was even picked up on by the 700mb RH charts. This allowed the flow out of the northwest to dry up some moisture for areas more inland.

The NAM simulated radar vs. the forecast QPF did not match up. Often the NAM simulated radar showed the heavier mesoscale bands lining up in northern Maryland and southern Pennsylvania where as it only showed total QPF to be .25in-.5in. In fact looking at total verification, the NAM did very well for its simulated radar.


(Actual NEXRAD National Radar) (6z NAM January 26 Simulated Radar)

The NAM did seem to have a hold on the 500mb map showing the negatively tilted trough producing the coastal low along with the placement of the upper level low and associated shortwave kicker just to the west.


(18z NAM January 24; 500mb) (0z NAM January 26; 500mb)

In general the differences in the 500mb maps were very subtle with just a general strengthening in the closed 500mb low, which verified a tad north of the January 24 18z model run.

The NAM did a very excellent job in identifying mesoscale band using the UUV/700mb RH charts.

(6z NAM January 26; 700mb)

It indentifed the enhanced snow growth over southeastern Pennsylvania up through New Jersey and New York City. The problems with the NAM generally existed in the QPF fields. The model likely suffered a very convective feedback issues in QPF totals. This is why it is important to note other maps than surface maps to help locate the heaviest precipitation. The 700mb map screamed that snow totals would be farther inland with the enhanced deformation band and UUV rates. In general the high resolution models handled this the best with the HRR scoring an amazing victory for QPF along with the ECMWF. The GFS/NAM did a very poor job for QPF, but as noted above QPF does not always tell the story. Sometimes it is important to note other layers of the atmosphere to help make a forecast. This point is why many forecasters missed the boat. Many forecasters (especially broadcoast meteorologists) are drawn to the easy to understand QPF/surface maps, but one has to look at all layers of the atmosphere to make a prediction.

Lower Susquehanna Valley Doppler...

(Courtesy of WGAL)

"Here northeast of Harrisburg 2010-2011 winter statistics"
(Snow Stats)
Current Snow Cover- 0-3in
Monthly Total (November)- Trace
Monthly Total (December)- 0.6in
Monthly Total (January)- 18.90in
Monthly Total (February)- 1.35in
Seasonal Total- 20.85in
Winter Weather Advisories- 7
Winter Storm Warnings- 2
Ice Storm Warnings- 0
Blizzard Warnings- 0
Freezing Rain Advisories- 1
Winter Storm Watches- 2

(Temperature Stats)
Lowest High Temperature- 23.7F
Lowest Low Temperature- -1.7F
Wind Chill Advisories- 0
Wind Chill Warnings- 0

(Snow Storms Stats)
First accumulating snow - December 10 - 0.50in of snow
Clipper light snow - January 7-8 - 2.25in then another 1in of snow
Double Barrel Low - January 11 - 4.5in of snow
Coastal Low - January 17-17 - 1.8in of snow/sleet
Arctic Front - January 20-21 - 2.1in of snow
Upper level/coastal low - January 26 - 5.75in of snow
Two clippers - January 28-29 - 1.5in of snow

Ice Storm 2011... (Blizzard92)
.4-.5in of freezing rain
Ice Storm 2011...
Ice Storm 2011... (Blizzard92)
.4-.5in of freezing rain
Ice Storm 2011...
Ice Storm 2011... (Blizzard92)
.4-.5in of freezing rain
Ice Storm 2011...
Ice Storm 2011... (Blizzard92)
.4-.5in of freezing rain
Ice Storm 2011...
Ice Storm 2011... (Blizzard92)
.4-.5in of freezing rain
Ice Storm 2011...
Ice Storm 2011... (Blizzard92)
.4-.5in of freezing rain
Ice Storm 2011...
Ice Storm 2011 (Blizzard92)
Melting begins...
Ice Storm 2011
Ice Storm 2011 (Blizzard92)
Melting begins...
Ice Storm 2011

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Quoting TheRasberryPatch:
Great pictures Blizz and Mason.

717Weather - i have like 5 boxwoods that were destroyed last year that i need to replace. the holes are so big. talking to a landscaper he said the boxwoods aren't great for snow and ice. i would look for another bush this spring that won't be so susceptible to winter damage


Thanks! Believe me I would NEVER plant another boxwood. We bought the house when it was 9 months old and it was already in. In our 100 year old house in Ewing, NJ before we moved here we had them on either side of the front door and they were a mess. I had this whole intricate support system for a while be for I finally gave up. My homeowners association says I have to have 5 shrubs/bushes so I will have to come up with something to put there.
Member Since: December 18, 2009 Posts: 0 Comments: 270
Nice pics everyone....

Anybody had a chance to look at Saturday's potential
storm?

I'm thinking this system was the "trend breaker".
Member Since: March 1, 2009 Posts: 0 Comments: 209
Oh, just noticed your pics Blizz. Nice. Looks like a similar amount of ice to what we received.

BTW, is that Japanese Maple? Im kind of worried about mine.
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just herd across the scanner that trees and powerlines are down in the same area where i took those pics above. i guess life is all about timing lol
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Great pictures Blizz and Mason.

717Weather - i have like 5 boxwoods that were destroyed last year that i need to replace. the holes are so big. talking to a landscaper he said the boxwoods aren't great for snow and ice. i would look for another bush this spring that won't be so susceptible to winter damage
Member Since: January 26, 2007 Posts: 72 Comments: 6233
Quoting 717WeatherLover:
Mason, guess the mountains to your east really kept the cold air bottled up and kept the warm from coming over the top from the west. Here in Lower Paxton Twp, east of Hbg it is quite amusing to look out the eastern fasing windows as the freezing rain froze on the screens in a big way. It is so thick that it is totally opaque. I should try to take some pictures. The ice destroyed my boxwood in front of my house. It was coming out this spring anywasy as I had gotten too big and leggy.


yeah these pics were all taken on the east facing slope of south mountain. you can see how basiclly one side of the tree limbs have the ice accertion
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Mason, guess the mountains to your east really kept the cold air bottled up and kept the warm from coming over the top from the west. Here in Lower Paxton Twp, east of Hbg it is quite amusing to look out the eastern fasing windows as the freezing rain froze on the screens in a big way. It is so thick that it is totally opaque. I should try to take some pictures. The ice destroyed my boxwood in front of my house. It was coming out this spring anywasy as I had gotten too big and leggy.
Member Since: December 18, 2009 Posts: 0 Comments: 270
PPL reporting almost 40,000 power outages...
Link
Member Since: December 14, 2007 Posts: 278 Comments: 15045
Got about .2-.3in of ice last night. No delays or anything up here go figure.
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Quoting Mason803:
1" accertion just west of cashtown. very impressive



















Wild pictures! I love the second one...
Member Since: December 14, 2007 Posts: 278 Comments: 15045
Quoting Blizzard92:
Decent sized limb just came down off our willow tree.


willow trees don't do well with ice. we had one in our yard but had to cut it down due to all the damage from ice storms and also t-storm damage
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Quoting Blizzard92:
Decent sized limb just came down off our willow tree.


I bet it's weeping even harder now...
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Decent sized limb just came down off our willow tree.
Member Since: December 14, 2007 Posts: 278 Comments: 15045
Thanks, Zotty.

Mason - I was just about to post some pics, but your ice is more impressive. Guess it's kind of pointless, haha.

Poor trees.
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1" accertion just west of cashtown. very impressive

















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852. zotty

Quoting Blizzard92:
Temperatures will warm up above freezing today with increasingly gusty winds throughout the day. About .4-.5in of freezing rain here this morning with some tree damage in my immediate view. We definitely were cold enough for more ice, but it appears surprisingly the precipitation moved through quicker than expected with lower QPF.
thank goodness for that.  in white plains ny the roads are mostly all right.  i scraped another quarter inch of ice off my car this morning.  i've really had enough of ice.  driveway was a skating rink, and not a lot better not after I shoveled part of it.  temperature at 32 now, though.  the hard freeze tonight is going to be pretty awful.  
i just hope the ice melts off the trees and lines before the wind rolls through, or things are going to snap all over the place.
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851. zotty

Quoting Hoynieva:



Nope, I think I'll be good :) The temperature just went above freezing and there's melting occurring. It's 32.7 and supposed to get to 40. It looks bad out there, but I just went for a walk and the sidewalks are walkable if you have tread on your boots. Streets are fine, just soaking wet with huge puddles. I'm assuming the runways must be fine also. I'll let you know if I get stuck in the airport for hours though. My only concern is the effect delays last night and early this morning might have on flights later in the day.

Thanks :)
good luck 
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Quoting sunnysmum:
Hoy, I hate to bring this up but what has become of your travel plans? Were you able to reschedule?



Nope, I think I'll be good :) The temperature just went above freezing and there's melting occurring. It's 32.7 and supposed to get to 40. It looks bad out there, but I just went for a walk and the sidewalks are walkable if you have tread on your boots. Streets are fine, just soaking wet with huge puddles. I'm assuming the runways must be fine also. I'll let you know if I get stuck in the airport for hours though. My only concern is the effect delays last night and early this morning might have on flights later in the day.

Thanks :)
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Moderate to heavy snow falling here in Brunswick, ME. Forecast calls for an additional 8 to 12 on top of the 4.5 we got yesterday. Looks like this second round has deposited about 2 inches since 6 this morning. Though it has picked up in intensity, this storm appears to be moving thru quickly so I will be anxious to see if we can squeeze out the additional 6 to 10 inches they are forecasting.

Does anyone have early thoughts on the Saturday storm? Local mets are in disagreement as to whether it will make it to Maine.

Hoy, I hate to bring this up but what has become of your travel plans? Were you able to reschedule?
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I see now that Central Dauphin is closed.
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Very icy here in Warwick, NY. Stayed home - decided against the commute to the city. Trees are covered in ice, not sure how thick, and the freezing rain is coming down still.
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A new format that will take some time to get used to.

It looks like about 1/4 inch of ice/glaze on everything in Lawnton, 5 miles east of Harrisburg, PA. Power went out about 3:30 AM and came back on abut 5:00 AM. Doors on the drivers side of the car (facing east) were completly frozen and would not open. Had to crawl in on the pasenger side after breaking off some of the ice. Trees are heavely weighted down with ice.

I can't beleive that they had only a two hour delay for Central Dauphin School. It will take them a day to get the ice off of the busses.
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Quoting wxgeek723:
Well I do have a delay from school but the weather is hardly inclement.

Snow accumulation since Monday: Trace
Ice accumulation since Monday: Trace
Rain accumulation since Monday: Way too much.

Grrrr. Someone reassure me that winter is not over and that La Nina isn't trying to get a grip on things!

Although with around 9 feet of snow since December 2009, I think Mother Nature may have a painfully long snow drought in store for the Mid Atlantic.


That's quite enough out of you. hahahaha
Member Since: July 7, 2004 Posts: 18 Comments: 2989
Well I do have a delay from school but the weather is hardly inclement.

Snow accumulation since Monday: Trace
Ice accumulation since Monday: Trace
Rain accumulation since Monday: Way too much.

Grrrr. Someone reassure me that winter is not over and that La Nina isn't trying to get a grip on things!

Although with around 9 feet of snow since December 2009, I think Mother Nature may have a painfully long snow drought in store for the Mid Atlantic.
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Just lots of rain and now fog down here. Speaking of the 'new' look for WU, it is cutting off comments on the right hand side. Few letters missing on some, like the old view better.

Not a drop of snow left around here......
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Temperatures will warm up above freezing today with increasingly gusty winds throughout the day. About .4-.5in of freezing rain here this morning with some tree damage in my immediate view. We definitely were cold enough for more ice, but it appears surprisingly the precipitation moved through quicker than expected with lower QPF.
Member Since: December 14, 2007 Posts: 278 Comments: 15045
841. RkTec
Lots of ice here in Emmaus. Power has been off since 6:30 a.m. every 15 seconds or so I hear a pop followed by a tree and/or branches falling in the woods. Thank goodness for smart phones!
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Current PPL Power outages:
Link
Member Since: July 17, 2004 Posts: 0 Comments: 73
Quoting TrentonThunder:


To add, snow season in Trenton averages November 22nd to April 1st

Freeze-free season averages October 23rd to April 15th.

If you seperated the coldest 3 month period into 3 parts (early-mid-late winter), mid-winter is about January 7th - February 7th, which means we're still in mid-winter temperture wise.



I will have wintry conditions till about April. "Last" frost is June 1st. I also don't suspect winter is over.


Current conditions.
Overcast
Light sleet.
Temp 20F
Breezy
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The long range did look good and then it abruptly flipped to a warmer regime. :(
Member Since: July 7, 2004 Posts: 18 Comments: 2989
Oh BTW - Pardon Me Pete (my backyard Groundhog) didn't see his shadow. HURRAY.
"Clouds portend warmth and rain that would thaw the fields and have them ready for planting" taken from the Farmers Almanac.
HURRAY
Member Since: January 26, 2007 Posts: 72 Comments: 6233
I'm just looking at all the models, etc, when it appears somewhat obvious that they think La Nina is kicking in finally in the long range especially. It looks depressingly warm and wet. I know that February is the snnowiest month and everything else you guys have been saying, and I hope I'm terribly wrong.
Member Since: July 7, 2004 Posts: 18 Comments: 2989
temp is 32.1F

icy everywhere. if Blizz is around - what do you expect for today? I am debating on clearing the ice from the driveway and sidewalks. What a job this will be to remove it all UGH

Campbelltown, PA
Member Since: January 26, 2007 Posts: 72 Comments: 6233
Quoting anduril:
I go to bed expecting some serious icing for central PA and it looks like we didn't get it that bad (guess we warmed up fairly well?) but even worse Wunderground looks completely different. Almost like an old version of weather.com...


some areas may have warmed but here along south mountain we are still below freezing with over 0.3" of glaze accertion.
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Quoting Hoynieva:


Yep, I was going to respond to that, but I already have the last two times someone said it.

It's wishful thinking at best.

The majority of our 50 plus inches last year occurred in February. Not to mention March winter storms are not all that uncommon and it can snow into late April if it feels like it.


To add, snow season in Trenton averages November 22nd to April 1st

Freeze-free season averages October 23rd to April 15th.

If you seperated the coldest 3 month period into 3 parts (early-mid-late winter), mid-winter is about January 7th - February 7th, which means we're still in mid-winter temperture wise.
Member Since: December 17, 2009 Posts: 0 Comments: 796
I go to bed expecting some serious icing for central PA and it looks like we didn't get it that bad (guess we warmed up fairly well?) but even worse Wunderground looks completely different. Almost like an old version of weather.com...
Member Since: August 29, 2006 Posts: 0 Comments: 168
Newcomer here. Like the new format, I've been a weather junky for years.
One thing that's missing from this blog package is the location of commenters. So unless you've been here long enough to figure out (and REMEMBER) where everyone is from, a lot of the posts lose some of their impact/meaning.
Would be great if they could change that.
I'm just East of Worcester, Ma. Had snow here at 4-5am, now it's pretty quiet out, not much precip at all.
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Quoting johnbluedog69:
47.8degrees and light drizzle currently in seaford de.hope everyone stays safe up there!


You might see some thunderstorms later today
Member Since: December 17, 2009 Posts: 0 Comments: 796
@ 7:23am

32.6F, moderate rain

Temperature rose to 32.1F at 6:35 am.
Member Since: December 17, 2009 Posts: 0 Comments: 796
826. bwi
33.5 in Greenbelt Maryland, and I think it stayed above freezing all night. We dodged the ice -- best wishes to those further north.
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Quoting TrentonThunder:


Winter's not out, it's only February 2nd. February on average is the snowiest month of the season in my area. Spring temperatures don't arrive (in my mind) until March 7th. The coldest 91/92 day average temperature period in Philadelphia PA is December 7th through March 7th.

Sorry!

I


Yep, I was going to respond to that, but I already have the last two times someone said it.

It's wishful thinking at best.

The majority of our 50 plus inches last year occurred in February. Not to mention March winter storms are not all that uncommon and it can snow into late April if it feels like it.
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47.8degrees and light drizzle currently in seaford de.hope everyone stays safe up there!
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very icy in south central pa. here in cashtown 0.30" of glaze with many trees and wires down. temp is still 31f
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Quoting pittsburghnurse:
Winter is on its way out. Rain here in Pittsburgh. Expecting snow later. Looks like a mix of rain and snow events in the upcoming weekly forecast. Honestly, I am so ready.


Winter's not out, it's only February 2nd. February on average is the snowiest month of the season in my area. Spring temperatures don't arrive (in my mind) until March 7th. The coldest 91/92 day average temperature period in Philadelphia PA is December 7th through March 7th.

Sorry!

I accidentally scheduled a sleep study for myself this Sunday. Super Bowl Sunday! What an idiot...
Member Since: December 17, 2009 Posts: 0 Comments: 796
Well, sidewalks are a mess. The main roads are fine, but penguins are walking around the neighborhood, trying to make it to work.
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Looks like a big dry slot working into the MA area. Funny thing is the local mets aren't even mentioning it! It is now sleeting pretty hard here in Smithfield, but the dry slot looks to already have advanced pretty far into CT and western, MA. Maybe a few more hours of precip before it stops up this way. How is everyone else making out?
Member Since: February 10, 2010 Posts: 0 Comments: 223
Winter is on its way out. Rain here in Pittsburgh. Expecting snow later. Looks like a mix of rain and snow events in the upcoming weekly forecast. Honestly, I am so ready.
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Icing is substantial in Brooklyn. Still freezing rain coming down. Interesting that they went from a Freezing Rain Advisory for up to .25" of ice accrual to an Ice Storm Warning for up to .75" while everyone was asleep. They should have seen this coming from the beginning with the temps never getting out of the 20's yesterday.

Change over will probably occur in an hour or so, but, damage done.
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About Blizzard92

Cornell University- Atmospheric Sciences Student; Central PA SKYWARN Storm Spotter; American Meteorological Society Member; PA CoCoRaHS Branch Member

Local Weather

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47 °F
Mostly Cloudy

Personal Weather Stations

Linglestown, PA
Elevation: 520 ft
Temperature: 24.2 °F
Dew Point: 15.2 °F
Humidity: 68%
Wind: Calm
Wind Gust: 9.0 mph
Updated: 10:37 AM EST on January 18, 2014

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