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 breald:
The immediate coast from RI east to Cape Cod is the only area without a watch in SNE. I think we are going to get much of anything from this storm.

I dont know Breald, you could see 3-6 inches there before icing. Suprised you dont have a watch yet. Wouldnt be suprised if one pops up there soon.

Member Since: December 17, 2009 Posts: 0 Comments: 796
Ok been out of it for a few days but possibly crippling ice storm in the next few days while Im off work? go figure
Member Since: August 29, 2006 Posts: 0 Comments: 168
Quoting Mason803:
quite a temp spread out there with york at 3f and dc at 31f. that's a temp gradient


that is amazing because northern Baltimore suburbs were in the mid teens.
Member Since: January 26, 2007 Posts: 72 Comments: 6248
The immediate coast from RI east to Cape Cod is the only area without a watch in SNE. I think we are going to get much of anything from this storm.
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Wales, i think you will be alright. They are calling for sleet to mix in around the mass pike, but even there for it to be mostly snow. Add to that the fact that these storms have been ending up colder then modeled and I think that you and I, just south of Worcester, will be in the snow for a while!
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CtWX: Where do you think the freezing rain (ice storm?) vs. mostly snow line is going to be? Obviously somewhere in CT/MA, but where?

Quoting ConnecticutWXGuy:


depends on if it's an inch of freezing rain or an inch of sleet. An inch of freezing rain is huge. I think only New London and points east change to plain rain.
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Quoting ConnecticutWXGuy:


depends on if it's an inch of freezing rain or an inch of sleet. An inch of freezing rain is huge. I think only New London and points east change to plain rain.


Well that is me.
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Quoting breald:
2-5 inches for my area Tuesday and less then an inch of mixture on Wednesday. This storm doesn't seem too bad for the SNE coast.


depends on if it's an inch of freezing rain or an inch of sleet. An inch of freezing rain is huge. I think only New London and points east change to plain rain.
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5 below zero in Jeffersonville, VT. WSW in effect. They're calling for 8-18" of snow. No mixing up here! Bout time we got a real snowstorm!!! I went through the ice storm in 98' and I hope none of you guys get anything like that. We did better than Quebec but it was really bad nonetheless. Many had no power for weeks. Good luck to all in the bullseye of the ice.
Member Since: January 9, 2011 Posts: 0 Comments: 83
Lotsa H2o.

Member Since: January 26, 2007 Posts: 15 Comments: 921
GTO: You can keep the negatives, I'm not a very negative guy:)
Member Since: January 26, 2007 Posts: 15 Comments: 921
WSW up for us. 2-8" by Tues night, 2 day totals over 1 ft. Looks like they think the mix line will stay safely south of I-90.
Member Since: January 26, 2007 Posts: 15 Comments: 921
I saw -2 on my ride in this morning in Uxbridge, MA.
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Mason803: Wow, that sure is a very tight gradient! 2.3F up here in the SE Adirondacks.
Member Since: January 26, 2007 Posts: 15 Comments: 921
2-5 inches for my area Tuesday and less then an inch of mixture on Wednesday. This storm doesn't seem too bad for the SNE coast.
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quite a temp spread out there with york at 3f and dc at 31f. that's a temp gradient
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NAM seems to be handling the cold air damming better than the warmer GFS. Therefore this likely leads to the scenario of a damaging ice storm from the Mason-Dixon line on northward to I-80. Areas in this region should stay tuned to the latest forecasts throughout today and tonight.
Member Since: December 14, 2007 Posts: 281 Comments: 15085
Quoting PalmyraPunishment:
Any chance this thing trends much colder and we end up with more snow or all snow, blizz? I know it's unlikely given the set up, but it seems as if the models have trended colder from where they were, right?

No, there is not enough time for that big of a shift. Crazy 6z NAM never gets us above 30F with all freezing rain of nearly 1in!
Member Since: December 14, 2007 Posts: 281 Comments: 15085
don't look now both NAM and GFS just trended colder for SNE
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I doubt the rain is going to make it much past I-95 in SNE. The low looks to redevelop off the NJ coast just in time to stop the northward progression of the rain/frozen precipitation line. Keep in mind that the models are likely running a bit too warm, as well... as they have been all winter.

Meh, I'm not ready for rain yet anyway. Bring on more winter weather! I've already seen some things this winter that I've never seen before, like 35 inches of snow on the ground at one time. I'm ready for more. We've had 70+ inches in a month, let's see if we can get another 70 in here. Now that'd be a winter to remember even if March and April turned out to be busts.

What can I say, I'm a storm lover. There's nothing good about cold weather unless it's stormy.
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That's true, LT. Even trickier up that way. Either way all eyes are on this potentially enormous and far reaching storm.
Member Since: January 20, 2009 Posts: 0 Comments: 1503
Quoting KEEPEROFTHEGATE:
not to get to far ahead of myself but feb is looking to come in with serveral events 4 or five systems for the first 10 days of feb things appear to show a stormy period setting up for awhile


It's already been setup for over a month. Basically it appears to continue to be a volatile pattern for the indefinite future.
Member Since: January 20, 2009 Posts: 0 Comments: 1503
Quoting bwi:
I'm hoping we don't get the freezing rain in DC. Sleet would be OK -- rain I can deal with. Freezing rain is tough though. Even a light glaze makes my commute near impossible, and I've used up all my work-at-home days. There's a lot of cold air to the north waiting to be dragged down into a cold air damming situation. Highs in the single digits and lows below zero in upstate NY, SW Quebec, E Ontario.


I think we're hosed, I'm expecting ice, more and longer than the local mets are calling for. They were all very blase about it on the broadcasts tonight.
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Quoting Mason803:
patch,

here's a pic of the '94 ice storm in b-more



I was in school at Towson for that series of ice storms (winter 93-94). I somehow made it to campus the one morning they opened at 10AM and by the time I got to the science building the maintenance staff were pulling people up the hill on ropes because they couldn't get the stairs and walkways deiced. Towson then closed campus because during the 30 min they were open at least 3 people had fallen and broken bones.

I also remember trying to chip inches of built up ice off the windshield of my car and my ice scraper broke. My roommate and I couldn't get enough traction to walk, neither one of us had crampons, so we tied socks around the outside of our shoes to try and get traction. It didn't really work.
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not to get to far ahead of myself but feb is looking to come in with serveral events 4 or five systems for the first 10 days of feb things appear to show a stormy period setting up for awhile
Member Since: July 15, 2006 Posts: 169 Comments: 53296
Member Since: July 15, 2006 Posts: 169 Comments: 53296
Member Since: July 15, 2006 Posts: 169 Comments: 53296
Member Since: July 15, 2006 Posts: 169 Comments: 53296
00z gfs run up next
Member Since: July 15, 2006 Posts: 169 Comments: 53296
Yeah I was thinking the same thing Hoy, but Hartford could be even more difficult, being further North and much more inland.
Member Since: January 31, 2009 Posts: 0 Comments: 7410
Quoting Rhodyguy:
Can anyone help, my kids have flights out of Bradley (Hartford CT) Wed at 2pm. It looks like that will be in the middle of the storm. Any guesses what is the error factor on this event? slower, faster, warmer ?...


I'm in the same boat as your son. Actually, if it was a boat we'd probably be better off. Stay tuned.
Member Since: January 20, 2009 Posts: 0 Comments: 1503
Member Since: July 15, 2006 Posts: 169 Comments: 53296
Quoting Rhodyguy:
Can anyone help, my kids have flights out of Bradley (Hartford CT) Wed at 2pm. It looks like that will be in the middle of the storm. Any guesses what is the error factor on this event? slower, faster, warmer ?...
we will know more during the daylight hours as system gets its act together on the ground and see just how big this is going to be
Member Since: July 15, 2006 Posts: 169 Comments: 53296
Member Since: July 15, 2006 Posts: 169 Comments: 53296
Member Since: July 15, 2006 Posts: 169 Comments: 53296
Member Since: July 15, 2006 Posts: 169 Comments: 53296


remember black line is the freeze line north of it ice and snow south of it rain
Member Since: July 15, 2006 Posts: 169 Comments: 53296
Quoting originalLT:
Palmyra, just looked at the 00Z GFS, and at the 66 hour mark it shows the low's center right over the Harrisburg area. That's not so good, it also pushes the 0 degree C line almost to the NY State border, that's not good either. This is of course one model and one model run, alot can change. We do need a coastal to form and take over like DM125 noted in post #220.


Well to be honest, I'll take rain over that damn much ice any day lol, so if this thing is going to give me the option of crippling ice, or rain, i'll take rain. I think.
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Palmyra, just looked at the 00Z GFS, and at the 66 hour mark it shows the low's center right over the Harrisburg area. That's not so good, it also pushes the 0 degree C line almost to the NY State border, that's not good either. This is of course one model and one model run, alot can change. We do need a coastal to form and take over like DM125 noted in post #220.
Member Since: January 31, 2009 Posts: 0 Comments: 7410
Can anyone help, my kids have flights out of Bradley (Hartford CT) Wed at 2pm. It looks like that will be in the middle of the storm. Any guesses what is the error factor on this event? slower, faster, warmer ?...
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Member Since: July 15, 2006 Posts: 169 Comments: 53296
Any chance this thing trends much colder and we end up with more snow or all snow, blizz? I know it's unlikely given the set up, but it seems as if the models have trended colder from where they were, right?
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at centre top right of sat image low level se moisture flow is detected
Member Since: July 15, 2006 Posts: 169 Comments: 53296
HIGH IMPACTING WIDESPREAD WINTER WEATHER EVENT ON THE WAY

Member Since: July 15, 2006 Posts: 169 Comments: 53296
220. DM125
WE NEED SOUTH WESTERN COASTAL LOW DEVELOPEMENT
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Peng, I would expect delays. Both cities are set up for significant ice. If you can postpone travel to Wednesday, I would consider it.
Member Since: October 14, 2006 Posts: 1 Comments: 639
Quoting Blizzard92:
It does not even get to freezing on the 0z NAM here in the Harrisburg area with likely over .75in of freezing rain verbatum on this recent run.


Yup, 00Z NAM low #1 only makes it to eastern Ohio and transfers its energy to a new low on the central New Jersey coast. Another trend of earlier and southwestward coastal low development.
Member Since: December 17, 2009 Posts: 0 Comments: 796
Quoting SoLanCo96:
Hello to everyone im new to your blog...


Nice to see you here!!
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