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 a statement to Father Winter..."it's over now drink your big black cow and get out of here" hahahahaha
Member Since: January 26, 2007 Posts: 72 Comments: 6256
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.
Member Since: January 31, 2009 Posts: 0 Comments: 7500
BTW, nice new pic. of Blizz on the main directory page, handsome guy! TV weathermen , lookout!!
Member Since: January 31, 2009 Posts: 0 Comments: 7500
Thanks Zotty for those posts, sounds interesting both short term and medium term--the next 2-3 weeks!
Member Since: January 31, 2009 Posts: 0 Comments: 7500
963. zotty
Link

that's an article on a tennis club that collapsed in Connecthedot. pretty scary. good thing they closed b/c of the ice storm, or people would have been killed.
Member Since: August 19, 2009 Posts: 0 Comments: 738
962. zotty
steve dimartino at NYNJPAweather.com has a new video blog out- says that the pattern that has given us such s stormy winter on the coast is not breaking down, it is reloading! -EPO and -NAO should redevelop in the middle of Feb, bringing us back to the cold and stormy weather. I am not a premium subscriber but he says he goes into more details there for those who are..
Member Since: August 19, 2009 Posts: 0 Comments: 738
961. zotty
not even 10 posts yet this morning?  well, closing in on another 1000 post blog for blizz, but it seems our winter weather warriors are getting tired.  or they have to start working!
Here in lower westchester we are under another HWO.  
SREF/GFS ENSEMBLE MEAN TRACK THE LOW OVER THE 40/70
BENCHMARK...ALTHOUGH GREATER DISTRIBUTION OF MEMBERS IS INSIDE
BENCHMARK. THE GFS/ECMWF ARE JUST INSIDE. THE NAM/UKMET BOTH TAKE
THE LOW OVER LI. THE GEM KEEPS THIS MAINLY AS A SOUTHERN LOW IN A
SPLIT UPPER FLOW...TRACKING WELL SOUTH OF THE 40/70 BENCHMARK. WHILE
ALL OF THESE ARE WITHIN THE REALM OF POSSIBILITIES...WILL WORK THE
HIGHEST CLUSTERING AND CONTINUITY AND CONTINUE WITH A TRACK JUST
INSIDE OF THE 40/70 BENCHMARK BY 00Z SUN.

THE TRACK WILL BE CRITICAL AS TEMPS PROFILES ARE ONLY MARGINALLY
COLD FOR WINTRY PRECIP ACROSS THE REGION. MODELS ARE ALL SIGNALING
A FRONTOGENETIC/DEFORMATION BAND ON THE NE SIDE OF THE LOW AS
SHORTWAVE ENERGY APPROACHES...WHICH WILL SUPPORT ENOUGH DYNAMIC
COOLING FOR A PERIOD OF MDT TO LOCALLY HEAVY SNOW AS IT SLIDES NE.
CURRENT FORECAST TRACK WOULD HAVE HIGHEST PROB OF THIS SNOW BAND
ACROSS INTERIOR NE NJ...INTERIOR LOWER HUDSON VALLEY AND INTERIOR SW
CONN. A GENERAL 4-8 INCHES OF SNOW WOULD BE POSSIBLE IN THE SNOW
BAND...WITH AMOUNTS QUICKLY TAPERING TO LITTLE OR NOTHING WORKING
SE.

THERMAL PROFILES LOOK TO BE COLD ENOUGH FOR A START AS SNOW
EVERYWHERE LATE FRI NIGHT...THEN LIKELY CHANGING TO RAIN ACROSS SE
SECTIONS AND A ZONE OF A MIX OF RAIN/SLEET/SNOW ACROSS THE NY/NJ
METRO AND COASTAL CONN BY SATURDAY AFTERNOON. THE HEAVIEST PCPN LATE
SAT MORNING INTO SAT AFTN...TAPERING OFF FROM SW TO NE SAT EVE
Member Since: August 19, 2009 Posts: 0 Comments: 738
Wooo!
Member Since: Posts: Comments:
In southern NH and northern MA there is now 32" of packed down snow, probably 5 inches worth of water content, with 2 more storms predicted. This means that any warmup will send the Merrimack river to flood stage, and if there is a heavy rainstorm (like there was last year) it will be a major flood. Here is the link to the flood prediction service in Lowell which monitors the river level:


http://water.weather.gov/ahps2/hydrograph.php?wfo=box&gage=lowm3
Member Since: Posts: Comments:
Quoting pittsburghnurse:
I do think the core of winter is going to be done in a couple of weeks. More rain, less snow accumulating, some temps sneaking above the freezing mark. All signs of coming Spring and waning winter. I'm sure a lot of it is wishful thinking because Lord knows, I do wish.


well it certainly has been a cold winter. nothing extreme, but since Thanksgiving we haven't had much of a reprieve with the temps. The shortlived couple of days before New Years Day and that has been it. I couldn't tell you the last time we hit 40F and nothing close to 50F.
Member Since: January 26, 2007 Posts: 72 Comments: 6256
I do think the core of winter is going to be done in a couple of weeks. More rain, less snow accumulating, some temps sneaking above the freezing mark. All signs of coming Spring and waning winter. I'm sure a lot of it is wishful thinking because Lord knows, I do wish.
Member Since: October 14, 2006 Posts: 1 Comments: 639
We got 16 inches here, with drifts up to 14 feet!
(northern illinois)

some good pix on here, thnx for sharing













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Member Since: Posts: Comments:
Seems that my declaration of the end of winter was a bit premature. The models seem to have flopped back to no warm up! Right on you stupid models!
Member Since: July 7, 2004 Posts: 18 Comments: 2989
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?????
Member Since: January 1, 2006 Posts: 0 Comments: 358
Quoting jrzyshore:
The anti-christ is preaching in a Baptist church....what blasphemy !!!

Link


He's so banned!
Member Since: July 7, 2004 Posts: 18 Comments: 2989
Wow 60's are a dream up here, it hit 20 or 21 for a high up this way. I think our local mets are just trying to give everyone hope, they are sticking with rain for us up in SNE for both sat and tuesday with temps well into the upper 30's/low 40's.
Member Since: February 10, 2010 Posts: 0 Comments: 223
My post earlier meant to say 60's in NJ, not Pa. Went back n changed it
Member Since: December 17, 2009 Posts: 0 Comments: 796
Quoting jrzyshore:
The anti-christ is preaching in a Baptist church....what blasphemy !!!

Link


AMEN!!!!!!!!
Member Since: Posts: Comments:
Quoting HeavySnow:
I don't know the temperature but it was balmy here today.


And now for the howling winds...
Member Since: Posts: Comments:
The anti-christ is preaching in a Baptist church....what blasphemy !!!

Link
Member Since: Posts: Comments:
I don't know the temperature but it was balmy here today.
Member Since: July 7, 2004 Posts: 18 Comments: 2989
high of 38.1F
a high wind gust of 33mph
Member Since: January 26, 2007 Posts: 72 Comments: 6256
Quoting Blizzard92:

Wow! Only got up to 37F here.


Hit 39.9 here.
Member Since: Posts: Comments:
Wow! Only got up to 37F here.

Yeah, huge temperature gradient. Outside shot at some strong thunderstorms in those areas today never came to fruition.
Member Since: December 17, 2009 Posts: 0 Comments: 796
Quoting TrentonThunder:


Yup, got into the low 60's in far southeastern PA & towards the Del-Mar-Va. Trenton got up to 40F. Got pretty foggy this afternoon as that warm air tried to surge over the snowpack.

Wow! Only got up to 37F here.
Member Since: December 14, 2007 Posts: 284 Comments: 15112
CPC has pretty much all of as at below average temperatures and above average precipitation into mid-February. Much below average temperatures on Feb 8th & 9th.
Member Since: December 17, 2009 Posts: 0 Comments: 796
Quoting breald:


64 degrees?? Is that right?


Yup, got into the low to mid 60's in some spots in far southeastern NJ & towards the Del-Mar-Va. Trenton got up to 40F. Got pretty foggy this afternoon as that warm air tried to surge over the snowpack.
Member Since: December 17, 2009 Posts: 0 Comments: 796
Anemometer finally unfroze late this afternoon. I have been registering gusts in the 20s, although it is in a sheltered location.
Member Since: December 14, 2007 Posts: 284 Comments: 15112
Quoting cicadaknot:
Power still out across parts of southeastern PA:

Link


Outage in Penn Twp. is just up the road from me. Power flickered a few times today - nothing more.
Member Since: Posts: Comments:
Windy here all day. I'd say gusting 30+, but I don't have any equipment - just an estimate.
Member Since: Posts: Comments:
Power still out across parts of southeastern PA:

Link
Member Since: July 17, 2004 Posts: 0 Comments: 74
Quoting TrentonThunder:
Some huge temperature disparities today in this neck of the woods...

HIGH'S
35F Andover, NJ
36F Teterboro, NJ
36F Wilkes Barre, PA
36F Quakertown, PA
37F Mount Pocono, PA
37F Sussex, NJ

64F Breakwater Harbor, NJ
60F Atlantic City Inland, NJ
59F Wildwood, NJ
54F Millville, NJ
54F North Wildwood, NJ


64 degrees?? Is that right?
Member Since: May 28, 2008 Posts: 38 Comments: 5303
Awsome pictures...
Member Since: December 17, 2009 Posts: 0 Comments: 796
For what it's worth, 18Z NAM & GFS looking a little better for early this weekend.

18Z GFS has a 3" - 6" bullseye from the central Susquehanna River Valley in Pennsylvania and northeast through the southern tip of Maine. Higher end over the Poconos - Catskills - Litchfield Hills - Berkshires - and the hills of central Mass.
Member Since: December 17, 2009 Posts: 0 Comments: 796
About 18" and still snowing pretty hard here in northern VT. Never got any sleet or frzing rain. Supposed to get another 3-6" overnight. Hearing some reports of 24"+ in the higher terrain. I'll try and post some pics.
Member Since: January 9, 2011 Posts: 0 Comments: 83
Some huge temperature disparities today in this neck of the woods...

HIGH'S
35F Andover, NJ
36F Teterboro, NJ
36F Wilkes Barre, PA
36F Quakertown, PA
37F Mount Pocono, PA
37F Sussex, NJ

64F Breakwater Harbor, NJ
60F Atlantic City Inland, NJ
59F Wildwood, NJ
54F Millville, NJ
54F North Wildwood, NJ
Member Since: December 17, 2009 Posts: 0 Comments: 796
929. Gaara
Ended up with .35" from the second half of the storm.. The right tires on my car got a pretty glaze:


Took half a vacation day, too!
Member Since: December 27, 2010 Posts: 0 Comments: 375
Great pictures everyone!

IceCoast- Wow, that fourth picture really shows how deep it is.
Member Since: December 14, 2007 Posts: 284 Comments: 15112
Blizz - I thought leaving the snow on the ground would make things easier and not have just a layer of black ice which can be very difficult to chop

i will have to remember that next time. you know how sometimes it is with just freezing rain. like i said the amount of water under the ice was incredible. i haven't seen it like that before.

Icecoast - great pictures. looks like you have a lot of snow on the roof. great neighborhood
Member Since: January 26, 2007 Posts: 72 Comments: 6256
Great pictures IceCoast!!
Member Since: May 28, 2008 Posts: 38 Comments: 5303
Turned out to be a pretty good storm yet again here in Northeast MA. Measured 15 inches at my house in Methuen between the two systems and NWS just put us under a WWA for another 1-3. On top of the 2+ ft we already on the ground, I think this is the most snow I have seen here.

Some pics i took..



There's a bench in between these trees somewhere!



Out of places to put the snow...





Member Since: Posts: Comments:
All the slush we have is now freezing. I was out walking the dogs earlier this afternoon and the streets will be very dangerous tomorrow morning. I hope everyone drives safe and slow.
Member Since: May 28, 2008 Posts: 38 Comments: 5303
I will have my forecast out for Friday night by later tomorrow.

Quoting TheRasberryPatch:


but Pardon Me Pete didn't see his shadow. What are you saying Blizz?

did you enjoy shoveling? all that water under the ice?

Lol, I shoveled the snow yesterday and then put down some excellent ice melt. So no struggles here; although had to get the snowblower out when the plow came by.
Member Since: December 14, 2007 Posts: 284 Comments: 15112
Just saw on local (WTEN) weather, there is a band of thunder-snow S of Albany, NY.
Member Since: Posts: Comments:
Also, in the 18Z GFS run the low has trended further East. We'll see, it's a good 2-3days out.
Member Since: January 31, 2009 Posts: 0 Comments: 7500
Thanks for the info P451 and Crowe1. P, I just feel if the FRI. nite/Sat storm is all snow, it will put down more than 2-3", because it is a Gomex originating low. Just a feeling.
Member Since: January 31, 2009 Posts: 0 Comments: 7500
Quite foggy here also.
Member Since: Posts: Comments:
It's actually a kind of freezing rain/sleet now. We have about toatl 20-22" on the ground now
Sacandaga Lake, Broadalbin, New York (PWS):

Overcast
22.3 °F
Overcast
Windchill: 16 °F
Humidity: 94%
Dew Point: 21 °F
Wind: 4.0 mph from the SW
Wind Gust: 5.0 mph
Pressure: 29.73 in (Rising)
Visibility: 10.0 miles
Member Since: Posts: Comments:

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About Blizzard92

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

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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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