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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This is so weird, I just checked the member blog main page again , and I still get the old pic. of Blizz standing in front of those grey shingles, I don't get it?
Member Since: Posts: Comments:
1016. breald
I only see his new picture.
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1015. hurigo
Thanks, Ya'll: LT and JRzy. Neither the old nor the new seem to show the new Blizz--oh I do hope they didn't media-te him too much. I'll check back later. Leftovers for suppa calling me now.
Member Since: Posts: Comments:
No Hurigo, WU has put the old picture back up on the main blog directory page, it's not you. Also the 18Z GFS has the storm right in or near the bench mark on Sat. but shows the 0C line pretty far North and West, even most of PA it shows to be above freezing, at 18Z on Sat. I guess there's not enough cold air to the North of the storm for it to pull down and keep us cold enough.
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Below is a link to the thread introducing the changes made here. On post #1077 there is a link to the old site. Apparently the old version is running parallel to the new one.



Link
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1012. hurigo
Quoting originalLT:
Wow, just went to the member blogs page, and Blizz's OLD picture is back up! What's going on?


Thanks LT for letting us know. So maybe I wasn't mashing the wrong keys. Maybe the mysterious on and off is part of the promo for Blizz's big news "not yet set in stone."
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1011. hurigo
Thanks Jrzy, I really appreciate you trying to help but I am seeing the old photo (the cropped one of him in front of the cedar shake place). I tried following your instructions twice. It is probably one of those things where I think I am doing what you said but I'm not really.
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Wow, just went to the member blogs page, and Blizz's OLD picture is back up! What's going on?
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Quoting hurigo:
Hey Blizz, et al.
Very intriguing commentary here. So, you will keep your audience on the edge. Please don't tell me you are going to become a talking head; no, I cannot believe that will be it. Cornell is more important and I just know you would not do anything to interrupt that stream.

AND, folks, I cannot see the new Blizz picture. Somebody help this hearty fellow(a) out!

Go to the wunderground home page and click on "member blogs" ....Zach is one of the featured blogs at the top of the listings...His new picture is there.
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1008. hurigo
Hey Blizz, et al.
Very intriguing commentary here. So, you will keep your audience on the edge. Please don't tell me you are going to become a talking head; no, I cannot believe that will be it. Cornell is more important and I just know you would not do anything to interrupt that stream.

AND, folks, I cannot see the new Blizz picture. Somebody help this hearty fellow(a) out!
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Quoting PalmyraPunishment:


This intrigues and disturbs me. Both at the same time.
LOL Got me snortin' with that one PP....I'm thinkin' Mr. Labe?....Dr. Labe?.... The Labenator ?
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Quoting Matlack:
Hit 52 at the Jersey Shore yesterday - but I couldn't get out to enjoy it. Looks like a line of snow moving through shortly. The Wunderradar is showing lightning strikes with it?????

I went to a driving range in Toms River yesterday and hit 2 large buckets. (Cabin Fever) Every shot was right down the middle! (not)
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My forecast for Friday and Saturday: rain and sleet

-_-

Welcome back, La Nina...
Member Since: August 28, 2008 Posts: 79 Comments: 3714
Quoting PalmyraPunishment:


This intrigues and disturbs me. Both at the same time.


Why don't you have a seat over there....
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Quoting Blizzard92:
Good afternoon everyone! Boy this place is quiet, did everyone go over to Americanwx forum? hahahaha


Nah, Just PP & I over there stirring things up while you are in school. Did you see the crazyness with them trying to put the Central PA subforum under the "new" Phili subforum? Looks like the majority of the Central PA folks plan on staying under the Upper NY/PA. I see you posting over there occasionally.

We'd never leave the Wunderblog of Blizzard92 as there is no better sense of community anywhere.
Member Since: December 18, 2009 Posts: 0 Comments: 270
Quoting Blizzard92:
Lol, you will all just have to wait and see.

My problem with the big storm next week, is that without the excellent blocking we had back in December and January, La Nina climatology favors a farther west track. That will be our problem; definitely not going out to sea.


isn't that the problem in winter? some storms track to our west and some too far to our east and some up the coast. from the 70's to now....it didn't happen very often, a storm coming up the coast for over 12" of snow. a lot of winters are brown and cold. we have been lucky the past 20 years. the 70's were very brown as well as the 80's.
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Quoting anduril:
Wow, for some reason my mental picture of blizz was COMPLETELY wrong :) Oh well


This intrigues and disturbs me. Both at the same time.
Member Since: January 31, 2007 Posts: 9 Comments: 2250
1000. anduril
Wow, for some reason my mental picture of blizz was COMPLETELY wrong :) Oh well
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Why are we getting so much mix in this year in the Northeast? It seem excessive.
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Thanks Blizz with the idea of next weeks storm potential, and possible track, but as you know, weather does not always follow the "text book"! At least I can hope!
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Blizz - what's going on...it's nice to have the sun out today. it's been awhile since the sun has been out all day.
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Lol, you will all just have to wait and see.

My problem with the big storm next week, is that without the excellent blocking we had back in December and January, La Nina climatology favors a farther west track. That will be our problem; definitely not going out to sea.
Member Since: December 14, 2007 Posts: 285 Comments: 15140
Yeah--who would be really surprised to find out that Blizz was offered a job as a forecaster and decided to skip college?
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Well the hint from Blizz that we might have a storm next weekend might be enough to get the chat started up again in here.
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Also I may have some surprising news, although I won't announce it yet until it is set in stone.

ABC27 fired their dope and hired you? Yussssss. I knew my letter of recommendation would be strongly worded and threatening enough to put you over the top!
Member Since: January 31, 2007 Posts: 9 Comments: 2250
Now, the "surprising news" thing is really a tease! Zotty, you can see the new pic. of Blizz on the main WU blog directory page.
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Thanks! I am just teasing about the lack of comments today, lol. Yea you can call me Zack or blizz, lol. I think the potential is definitely set as we have an NAO phase change. In fact I did a research blog a year or two ago on phase changes associated with NAO regimes correlating to large nor'easters. Given the pattern though, I cannot rule out this track farther west. But I do think the eastern half of the nation will face a major low pressure storm system during the end of next week. This will signal a relaxation in the pattern towards mid month before it gets colder again later in the month towards early March. As for the Saturday, low pressure. I am still a bit at odds with it, but I can so I highly doubt accumulations along I-95. For those of us northwest, it will be close to rain or a decent accumulating snow. I will have more tomorrow. New blog will be coming Saturday. Also I may have some surprising news, although I won't announce it yet until it is set in stone.
Member Since: December 14, 2007 Posts: 285 Comments: 15140
Quoting MarylandGirl:
The new picture of Blizz is great, our boy has grown up! We may have to start calling him Zach! College man and all you know.
Heavy, I think our snow time may be over.....
Going to go check the crocus!
to me he will always be known as The Blizz he has come far and has far to go
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989. zotty
Quoting Matlack:
Good afternoon all - doing my part to reach the 1000 post mark.

Zach Great new picture - can't call you blizz anymore!
when do you expect your forecast on the upcoming week to be posted?


where is this picture you and LT are commenting on? I see the same ol' hooded sweatshirted blizz...
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Good afternoon all - doing my part to reach the 1000 post mark.

Zach Great new picture - can't call you blizz anymore!
when do you expect your forecast on the upcoming week to be posted?
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TheF1Man, the precip. for the Fri/Sat storm should not start in CT untill well after midnight, Friday night/Sat.AM If you drive home on Friday you should be OK. LT.
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986. zotty
Blizz- thoughts on predictions of reappearance of a negative NAO regime for the middle of the month? Thanks-
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985. zotty
Quoting Blizzard92:
Good afternoon everyone! Boy this place is quiet, did everyone go over to Americanwx forum? hahahaha


yes, i commented on that earlier. 983 posts are not enough for you?

some of us have to work, you know! :)
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984. zotty
The southern most city in the continental US- Browsville, TX- is currently under a winter storm warning. now that is something you don't see everyday. the people vacationing at South Padre Island must be thrilled...
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Good afternoon everyone! Boy this place is quiet, did everyone go over to Americanwx forum? hahahaha
Member Since: December 14, 2007 Posts: 285 Comments: 15140
982. zotty
Quoting TheF1Man:
Read an article from Bastardi over at Accu...he said he expects the next 2 winters to be even colder because following a La Nina cycle, the first winter is usually warm. Then the next 2 become subsequently colder, however we've already started with a cold winter. I'm not sure if the pattern will come true, but I thought I'd share.


What time frame are we looking at for the Fri/sat storm, I'm trying to decide when i should drive home.


hmmm. kind of like creighton's state of fear- bad things sell and bring people back. if he said things will be tranquil for the next two years, would you check his site as often? maybe i'm too skeptical...
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981. zotty
Quoting PalmyraPunishment:
I'm high on Culture. I just think Seattle's culture su-su-su-sucks.

You're flying free? You bangin' a stewardess? Is this like the episode of Family Guy where Peter went on all kinds of free trips, like Kentucky, just to get some chicken?

"I'm lookin' for Mr. Sanders..."

"No, I say you, he dead."

"THE COLONEL!"


haha! classic. good south park on col sanders, too
Member Since: Posts: Comments:
Read an article from Bastardi over at Accu...he said he expects the next 2 winters to be even colder because following a La Nina cycle, the first winter is usually warm. Then the next 2 become subsequently colder, however we've already started with a cold winter. I'm not sure if the pattern will come true, but I thought I'd share.


What time frame are we looking at for the Fri/sat storm, I'm trying to decide when i should drive home.
Member Since: February 23, 2010 Posts: 0 Comments: 685
Quoting PalmyraPunishment:
I'm high on Culture. I just think Seattle's culture su-su-su-sucks.

You're flying free? You bangin' a stewardess? Is this like the episode of Family Guy where Peter went on all kinds of free trips, like Kentucky, just to get some chicken?

"I'm lookin' for Mr. Sanders..."

"No, I say you, he dead."

"THE COLONEL!"


Working for an airline.
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Quoting originalLT:
BTW, nice new pic. of Blizz on the main directory page, handsome guy! TV weathermen , lookout!!

had Blizz never mentioned he was going off to college in the fall, who would've ever thought a weather wiz like him was only 18! And yes, he's got the looks for tv too.
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The new picture of Blizz is great, our boy has grown up! We may have to start calling him Zach! College man and all you know.
Heavy, I think our snow time may be over.....
Going to go check the crocus!
Member Since: Posts: Comments:
Member Since: Posts: Comments:
Member Since: Posts: Comments:
I'm high on Culture. I just think Seattle's culture su-su-su-sucks.

You're flying free? You bangin' a stewardess? Is this like the episode of Family Guy where Peter went on all kinds of free trips, like Kentucky, just to get some chicken?

"I'm lookin' for Mr. Sanders..."

"No, I say you, he dead."

"THE COLONEL!"
Member Since: January 31, 2007 Posts: 9 Comments: 2250
Quoting PalmyraPunishment:


You're better off not. Aside from Coffee, Seattle blows.


Oh quit yer bitchin'. I fly for free so it's no biggie and it's better than Shippensburg. Culture up PP!!
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Leave it to Palmyra to, "Tell it like it is!"
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Quoting shipweather:


I was going to fly to Seattle in that time frame. Hopefully I can...


You're better off not. Aside from Coffee, Seattle blows.
Member Since: January 31, 2007 Posts: 9 Comments: 2250
Quoting originalLT:
Hi Shipweather, well being that it's out there so early on that model, I think you are safe!. Like I said, I'll believe it when I see it!


I was just figuring it was my luck...
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Hi Shipweather, well being that it's out there so early on that model, I think you are safe!. Like I said, I'll believe it when I see it!
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Quoting originalLT:
The 12Z GFS shows a big storm for us, the NE and Middle Atlantic States for next Thurs./Fri. That would be nice , but I'll believe it when I see it! Henry M. on Accu. is hinting that too.


I was going to fly to Seattle in that time frame. Hopefully I can...
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this is a statement to Father Winter..."it's over now drink your big black cow and get out of here" hahahahaha
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