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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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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Heavy snow here in Smithfield Ri at work, it was snowing very hard when I left sutton, ma with about 3" on the ground from this second half at about 16-17 degrees. Very light fluffy snow. Not sure if we'll change over before we get a decent amount up here though....
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Good Morning all here is sending some warm air to everyone north of me. Crossed the 32 barrier at 2am this morning and now close to 36.5 degrees at the shore. Good luck to all hoping that your power stays on.
Member Since: January 1, 2006 Posts: 0 Comments: 358
I keep double posting!
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Sleeting here this morning in coastal Ma.
Member Since: May 28, 2008 Posts: 38 Comments: 5303
Good morning. New site will take a while to get used to. Wunderground has been in that other format forever.

@6:00 am

31.8F, Freezing Drizzle

0.52" freezing rain has fallen overnight.

Temperature has risen from 27.8F at Midnight to 31.8F at 6:00am

Haven't been outside yet.
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Good luck to all of you caught in the ice storm. We are lucking out up in northern Vermont. +6F at BTV with moderate snow. We are forecasted to stay all snow with up to 18" here and maybe a couple feet in the Green Mountains and Adirondacks. Another storm Saturday and another coming Tuesday. Quite a winter so far. Stay safe in the ice zones!
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Just woke up. Omigod.
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Temp. up to 29F here at my house in Stamford CT. Looks like a mess outside, hope it creeps up to 33F by day-break!
Member Since: January 31, 2009 Posts: 0 Comments: 8010
808. Gaara
I stayed at a friends place in Hamden. This is very very bad. I do not want to be near trees. What was supposed to be sleet is freezing rain AND sleet.
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Naugatuck, CT
18 degrees
Heavy Freezing Rain
Temperature has not risen at all

This is looking epic for all the wrong reasons.
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802. Gaara
$25 to the person who lives closest to the highest
Observed QP. Please substantiate.
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801. Gaara
Gaara here in Hamden CT at 230am. This will be the worst am commute of the year. This will end poorly for southern CT
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Cannot sleep at all. Knew I shouldn't have taken that nap. Whoa new site setup. Anyway, I'm actually with heavy, I think things are back to normal :(

Bellmawr, NJ
Steady freezing rain
32F
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Blizz, what are your thoughts about this, from Joe over at "that site which must not be named":

Joe Bastardi does feel that storms hitting the eastern half of the nation will trend warmer in the period beyond mid-February into part of March.

"That would mean more rain events over snow events," Bastardi said.

"Before the end of February, Washington, D.C., will hit 70 and Dallas will hit 80 degrees," Bastardi added Tuesday afternoon.

Joe is calling for a "big flip" in the weather pattern across the U.S. in a couple of weeks.
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Steady freezing rain in West Chester. Looks like it's warming slightly, temp now near 30F.
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Looks like we are still holding steady at 30 degrees. Ice is everywhere. New look for Wunderground - finally.
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Officially 32 and switched to plain rain here in State College.
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Quoting HeavySnow:


Time to go huff a cat.
I'm reporting you to PETA
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Quoting Hoynieva:


Oh, my fault, you're a copycat.

Stan, lay off the cough syrup dude, I’m worried about you man.


Time to go huff a cat.
Member Since: July 7, 2004 Posts: 18 Comments: 2990
Freezing drizzle in West Chester, PA. My apt lot is an ice-skating rink. It sucks since we're under new management this year--last year, our maintenance crews actively battled the storms, and this year, they're being highly reactive, so there's no salt, nothing, on our lots.

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31 in State College. We may change to plain rain soon.
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KMUI looks like it has icing issues already:


KMUI 020434Z AUTO 07005KT 4SM -FZDZ BR OVC006 M03/M03 A3010 RMK AO2 FZDZEMMB0357 FZDZEMMB0359 FZDZEMMB0401 FZDZEMMB0403 FZDZEMMB0405 FZDZEMMB0416 FZDZEMMB0418 FZDZEMMB0420 FZDZEMMB0422 FZDZEMMB0424 FZDZEMMB0426 FZDZEMMB0428 FZDZEMMB0430 FZDZEMMB0432 FZDZE
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i think my thermometer has frozen up. Its been bouncing all over the place the past few minutes... 3000+ now without power according to met-eds outage website in PA.
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Quoting HeavySnow:


This is my first declaration Mr. Slave. You must be thinking of Mr. Hat or Mr. Stick. It's actually one of the ships, ssa or shipweather. I never cancel winter. But the long range says finito! Crud, crap, I hate you Kyle.


Oh, my fault, you're a copycat.

Stan, lay off the cough syrup dude, I’m worried about you man.
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Quoting Blizzard92:

I had that problem, but fixed it. Make sure your compatibility view is not on. The button is located next to the refresh button on the internet.


Thanks Blizz. I'm right about winter at least for DC aren't I? :(
Member Since: July 7, 2004 Posts: 18 Comments: 2990
Quoting Hoynieva:


How many times have you declared winter over this year? Sorry DC area is bag to their usual cold rain storms.

You should have upgraded that igloo into a time machine so you could go back to last winter...indefinitely.


This is my first declaration Mr. Slave. You must be thinking of Mr. Hat or Mr. Stick. It's actually one of the ships, ssa or shipweather. I never cancel winter. But the long range says finito! Crud, crap, I hate you Kyle.
Member Since: July 7, 2004 Posts: 18 Comments: 2990
Pretty excited about that big bass clef headed our way but our estimated totals have dropped from 20" to 13", now with a chance of ice mixed in even though all maps have us above the ice/sleet line. Hoping for the best. Memories of our '08 ice storm very fresh. 6 days of no electricity=noooo fun.

Seacoast(SE)NH
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I wish they'd bring back the feature that marks each of your favorite cities on the radar. That was one of the best little features I've ever seen on a weather site. It really helped with city-by-city nowcasting.
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Quoting HeavySnow:
Some of your comments lose some of their words at the end of the lines. Is that happening for everyone? Stinkin' new format. Boooooo. Rain here with some sleet. 33 degrees.

Winter is over. :(

I had that problem, but fixed it. Make sure your compatibility view is not on. The button is located next to the refresh button on the internet.
Member Since: December 14, 2007 Posts: 285 Comments: 15140
It's a bit cleaner looking, as long as it eventually fits the screen I will be satisfied. Not much going on here in springfield, ma
Member Since: February 23, 2010 Posts: 0 Comments: 685
Quoting HeavySnow:
Some of your comments lose some of their words at the end of the lines. Is that happening for everyone? Stinkin' new format. Boooooo. Rain here with some sleet. 33 degrees.

Winter is over. :(


How many times have you declared winter over this year? Sorry DC area is back to their usual cold rain storms.

You should have upgraded that igloo into a time machine so you could go back to last winter...indefinitely.
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Some of your comments lose some of their words at the end of the lines. Is that happening for everyone? Stinkin' new format. Boooooo. Rain here with some sleet. 33 degrees.

Winter is over. :(
Member Since: July 7, 2004 Posts: 18 Comments: 2990
Quoting PalmyraPunishment:


I actually like the new version, but as a developer, it's pretty friggin stupid to unleash a new version during high traffic periods. Morons.


Perhaps they forgot to check the weather?
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26.9F now
Member Since: December 14, 2007 Posts: 285 Comments: 15140
New layout cuts off text on right side in Safari on my iPhone, oh joy.
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Quoting Blizzard92:

They are still working out the bugs and I am sure it will eventually be fixed or something.


Again... this really was the worst time to go through with all this lol.
Member Since: January 31, 2007 Posts: 9 Comments: 2250
Quoting testbenchdude:
I just want to repost this here, sry Blizz, but am I the only one who has this issue? Physically measured with a ruler on my 21" 1650x1080 screen. You HD users have got to be even worse off than I am!



Yikes.

They are still working out the bugs and I am sure it will eventually be fixed or something.
Member Since: December 14, 2007 Posts: 285 Comments: 15140
I just want to repost this here, sry Blizz, but am I the only one who has this issue? Physically measured with a ruler on my 21" 1650x1080 screen. You HD users have got to be even worse off than I am!



Yikes.
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It will also be interesting to see how many of the automated sensors freeze up and show winds coming from the same dir and speed for hours on end.
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fire up the generators good luck guys up north
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Quoting Hoynieva:


Maybe it is. I heard there was a glass warning out for your area.


Hahahahaha!!!!!
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Temperature falling a bit with moderate freezing rain; 27.0F
Member Since: December 14, 2007 Posts: 285 Comments: 15140
Quoting Hoynieva:
Not sure I care for this new layout. I need to prepare for change, not have it thrust at me when I'm least expecting it...

alas...i'll get used to it.


Yeah, I could do without the left 3" and right 7" of whitespace on my widescreen monitor. Fark did the same thing when they "upgraded" several years ago, so I hope WU fixes this.

Interestingly off topic, all the Gawker sites "upgraded" today and Slashdot "upgraded" yesterday, and now WU...

I'm all for progress, but I really, really hate when sites foist "upgrades" upon unsuspecting users. It's just rude.


Back on topic--29.5F (down a degree from an hour ago) and freezing fog still in place here in West Chester. Looks like it won't start to pick up until after midnight here. A little concerned about school tomorrow--WCU has a history of less-than-timely closure announcements.
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Quoting Blizzard92:

Keep in mind for sleet that surface temperatures do not matter. It is a matter of how thick the cold layer is aloft. Given your higher latitude and elevation, the cold layer is a bit more aloft allowing for the potential for sleet. Don't get me wrong, I still think significant freezing rain is likely for State College.


Crack me up! We said the same thing but yours was much more technical, while mine was layman terms. Maybe I should translate for you sometime. JK Did you pull qpf amounts off of the 0Z NAM?
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Quoting Hoynieva:
Not sure I care for this new layout. I need to prepare for change, not have it thrust at me when I'm least expecting it...

alas...i'll get used to it.


You had from 2006 until now to prepare for the concept of "Change" and that covers everything known to man. This is entirely on you.

I actually like the new version, but as a developer, it's pretty friggin stupid to unleash a new version during high traffic periods. Morons.
Member Since: January 31, 2007 Posts: 9 Comments: 2250
Not sure if anybody heard of the supercooled warm rain process, but it is freezing rain within a column of saturated air that is dry from about 700mb up and can be completely below freezing, with no warm layer. Happens out in the plains states fairly often and is a real headache to forecast. I can't say that i've ever seen it in the northeast, fortunately.


Check out an example sounding.

Link

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Cornell University- Atmospheric Sciences Undergrad; Research Assist.- Onset of Spring Indices Toolbox; Interests- Small spatial scale climatolology

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