North American Mesoscale Model Verification on January 26-27...
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
Reader Comments
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Missed ya P.....while it seems that we may have some rain mixed in on we'd afternoon, sounds like we have a long term icing event for the northern nj up through coastal ct and ri area. This could get ugly.......
It really makes you wonder how Syracuse NY handles 120" per season average. I mean, that's a pretty decent sized city. They already have 115" this season, average to date is 67" so they are running at 48" above average.
I realize that parts of the Tughill average over 200" mostly way out in the sticks, but 120" in a city like Syracuse? How do they do it? They've been above freezing only 4 times this month, 3 of those times during the first 4 days. And to think they could see 15" - 20" from this storm alone next week.
It happens...
Good to see you back, P, this blog has been missing you.
LT, I hope that's correct. As much as I know most people don't want rain on Wed, I would love rain. It can turn back to ice and snow in the evening/night for all I care.
This winter is crazy.
Monday Night
Mostly cloudy. A chance of snow after midnight. Lows around 19. Northeast winds 5 to 10 mph. Chance of snow 50 percent.
Tuesday
Snow likely. Highs in the lower 30s. Northeast winds 5 to 10 mph. Chance of snow 60 percent.
Tuesday Night
Freezing rain and snow likely. Sleet likely after midnight. Lows in the upper 20s. Chance of precipitation 70 percent.
Wednesday
Freezing rain likely in the morning. Rain likely. Highs in the upper 30s. Chance of precipitation 70 percent.
Wednesday Night
A chance of rain in the evening. Mostly cloudy with a chance of snow. Breezy with lows in the lower 20s. Chance of precipitation 50 percent.
mess to the south of me
4 PM :(
NATIONAL WEATHER SERVICE CHICAGO IL
1134 AM CST SUN JAN 30 2011
...MAJOR WINTER STORM TO IMPACT THE REGION TUESDAY INTO WEDNESDAY...
.THE FIRST PHASE OF THE UPCOMING WINTER STORM WILL BEGIN MONDAY
AFTERNOON THROUGH EARLY TUESDAY MORNING FOR NORTHERN ILLINOIS AND
NORTHWEST INDIANA. SNOWFALL TOTALS FROM THE FIRST PHASE APPEARS TO
BE BETWEEN 2 AND 4 INCHES ACROSS NORTHERN ILLINOIS AND NORTHWEST
INDIANA. THE FOCUS TURNS TOWARDS THE LARGER EVENT THAT PUSHES INTO
THE REGION TUESDAY AFTERNOON AND WILL PERSIST THROUGH WEDNESDAY.
A DEVELOPING AREA OF LOW PRESSURE IS EXPECTED TO SLIDE EAST OF THE
ROCKIES INTO EASTERN TEXAS MONDAY NIGHT AND RAPIDLY STRENGTHEN AS
IT SLIDES NORTH TUESDAY. THE PRECISE TRACK OF THE LOW CONTINUES TO
WOBBLE WITH EACH NEW MODEL RUN...HOWEVER RELATIVE CONSISTENCY OF A
TRACK FROM CENTRAL ARKANSAS NORTH TO CENTRAL INDIANA BY WEDNESDAY
MORNING LOOKS TO BE THE MOST PROBABLE TRACK. THIS WOULD PLACE THE
AXIS OF THE HEAVIEST SNOWFALL TO THE NORTHWEST OF THE TRACK OF THE
LOW PRESSURE...OR ACROSS MUCH OF NORTHERN ILLINOIS AND NORTHWEST
INDIANA.
AS THE LOW PRESSURE CONTINUES TO SLIDE NORTH AND STRENGTHEN...NORTHEAST
WINDS OF 20 TO 30 MPH ARE EXPECTED TO DEVELOP AND BRING A FLOW OF
COLD AIR ACROSS LAKE MICHIGAN AIDING IN THE GENERATION OF LAKE
EFFECT SNOW TUESDAY EVENING. WINDS WILL CONTINUE TO RAMP UP WITH
SUSTAINED WINDS TUESDAY EVENING BETWEEN 25 AND 35 MPH WITH GUSTS
UP TO 40 MPH POSSIBLE. NORTHEAST WINDS THEN CONTINUE TO STRENGTHEN
TUESDAY NIGHT INTO EARLY MORNING WEDNESDAY WITH GUSTS UP TO 45 MPH
POSSIBLE. THIS IN COMBINATION WITH THE FALLING SNOWFALL MAY CREATE
BLIZZARD CONDITIONS AND WHITE OUT CONDITIONS. AS THE LOW PRESSURE
CONTINUES TO LIFT NORTH INTO CENTRAL INDIANA WEDNESDAY
MORNING...WINDS WILL BEGIN TO TURN NORTHERLY AND BRING THE LAKE
ENHANCED SNOWFALL TO NORTHWEST INDIANA.
BY LATER WEDNESDAY THE SNOW FROM THE DEPARTING WINTER STORM WILL
BE WINDING DOWN ACROSS THE AREA BUT A BAND OF SIGNIFICANT LAKE
EFFECT SNOW IS EXPECTED IN NORTHWEST INDIANA WHERE SEVERAL
ADDITIONAL INCHES OF SNOW ARE POSSIBLE BEFORE THE LAKE EFFECT
SHIFTS FURTHER OFF TO THE EAST INTO SOUTHWESTERN LOWER MICHIGAN
AND NORTH CENTRAL INDIANA.
BETWEEN THE INITIAL LIGHTER SNOW MONDAY INTO TUESDAY MORNING...
THE HEAVY SNOWFALL FROM THE MAJOR WINTER STORM DURING TUESDAY
AFTERNOON THROUGH WEDNESDAY MORNING...AND THE INCREASINGLY INTENSE
LAKE EFFECT SNOW DEVELOPING DURING WEDNESDAY...IN EXCESS OF A FOOT
AND A HALF OR MORE OF SNOW WILL NOT BE UNCOMMON OVER MUCH OF
NORTHERN ILLINOIS AND FAR NORTHWEST INDIANA. SNOWFALL RATES UP TO
3 INCHES PER HOUR WILL BE PROBABLE AT THE HEIGHT OF THE STORM
TUESDAY NIGHT.
THE STORM SYSTEM WILL BE AFFECTING A LARGE PORTION OF THE
SOUTHERN GREAT LAKES...MIDWEST AND OHIO VALLEY REGIONS. ANYONE
WITH TRAVEL PLANS TUESDAY AND WEDNESDAY...INCLUDING THOSE
TRAVELING THROUGH CHICAGO OHARE AND MIDWAY AIRPORTS...SHOULD
CONTINUE TO MONITOR LATER FORECASTS REGARDING THE DEVELOPMENT OF
THIS WINTER STORM..
ILZ003>006-008-010>014-019>023-032-033-039-INZ001-002-010-011-019-
310145-
/O.CAN.KLOT.WS.A.0001.110201T1800Z-110203T0000Z/
/O.NEW.KLOT.BZ.A.0001.110201T1800Z-110203T0000Z/
WINNEBAGO-BOONE-MCHENRY-LAKE IL-OGLE-LEE-DE KALB-KANE-DUPAGE-COOK-
LA SALLE-KENDALL-GRUNDY-WILL-KANKAKEE-LIVINGSTON-IROQUOIS-FORD-
LAKE IN-PORTER-NEWTON-JASPER-BENTON-
INCLUDING THE CITIES OF...ROCKFORD...BELVIDERE...WOODSTOCK...
WAUKEGAN...OREGON...DIXON...DEKALB...AURORA...WHEATON...CHICAGO...
OTTAWA...OSWEGO...MORRIS...JOLIET...KANKAKEE...PONTIAC...
WATSEKA...PAXTON...GARY...VALPARAISO...MOROCCO...RENSSELAER...
FOWLER
1134 AM CST SUN JAN 30 2011 /1234 PM EST SUN JAN 30 2011/
...BLIZZARD WATCH IN EFFECT FROM TUESDAY AFTERNOON THROUGH
WEDNESDAY AFTERNOON...
...WINTER STORM WATCH IS CANCELLED...
THE NATIONAL WEATHER SERVICE IN CHICAGO HAS ISSUED A BLIZZARD
WATCH...WHICH IS IN EFFECT FROM TUESDAY AFTERNOON THROUGH
WEDNESDAY AFTERNOON. THE WINTER STORM WATCH HAS BEEN CANCELLED.
* TIMING...HEAVY SNOWFALL WILL SPREAD NORTHEASTWARD ACROSS THE
AREA MIDDAY TUESDAY AND CONTINUE THROUGH TUESDAY NIGHT. AS THE
SNOWFALL FROM THE STORM SYSTEM STARTS TO WIND DOWN DURING
WEDNESDAY MORNING AND EARLY AFTERNOON...LAKE EFFECT SNOW WILL
HAVE DEVELOPED ON THE ILLINOIS SIDE OF THE LAKE. INCREASINGLY
HEAVY AND MORE CONCENTRATED LAKE EFFECT SNOW WILL SHIFT INTO
FAR NORTHWEST INDIANA DURING WEDNESDAY AFTERNOON AND PERSIST
INTO WEDNESDAY EVENING BEFORE SHIFTING FURTHER OFF TO THE EAST
INTO SOUTHWEST LOWER MICHIGAN AND NORTH CENTRAL INDIANA.
* ACCUMULATIONS...TOTAL ACCUMULATIONS FROM MONDAY MORNING THROUGH
WEDNESDAY EVENING ARE EXPECTED TO BE IN EXCESS OF 8 INCHES IN
NORTH CENTRAL ILLINOIS...AND IN EXCESS OF 18 INCHES OVER
NORTHEAST AND EAST CENTRAL ILLINOIS...AS WELL AS NORTHWEST
INDIANA. LOCAL AMOUNTS IN EXCESS OF 24 INCHES ARE POSSIBLE IN
FAR NORTHWEST INDIANA...DEPENDING ON EXACTLY WHERE THE LAKE
EFFECT SNOW BAND SETS UP AND HOW PERSISTENT IT IS OVER ANY ONE
LOCATION.
* HAZARDS...BLIZZARD CONDITIONS WITH CONSIDERABLE BLOWING AND
DRIFTING SNOW AND FREQUENT WHITE OUT CONDITIONS.
* IMPACTS...NEARLY IMPOSSIBLE TRAVEL CONDITIONS AS SNOW WILL BE
ACCUMULATING AT A RAPID RATE DURING THE PEAK OF THE SNOW STORM
TUESDAY AFTERNOON AND NIGHT. HEAVY LAKE EFFECT SNOW IN NORTHWEST
INDIANA LATER WEDNESDAY AND WEDNESDAY EVENING WILL CONTINUE TO
SNARL TRAVEL THERE.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
A BLIZZARD WATCH MEANS THERE IS A POTENTIAL FOR FALLING AND/OR
BLOWING SNOW WITH STRONG WINDS AND EXTREMELY POOR VISIBILITIES.
THIS CAN LEAD TO WHITEOUT CONDITIONS AND MAKE TRAVEL VERY
DANGEROUS.
The 18Z WTF shows polar opposites colliding on the blog at this time.
This could be cause for concern.
We'll have to keep an eye on it.
We appreciate it - but you know us illiterate snow-fiends. All we want or care about is snow, snow, snow so a tease of a forecast will win out to your thoughtful postcast.
But still, thats not to say we dont appreciate it!
18Z
12Z
Doesn't look like the Harrisburg area sees that much rain...looks ugly!
Good, I always wonder how you guys find them earlier than me, but that was even earlier still.
That's correct, LT. It's going to be a wet sloppy mess.
12Z NAM Precip Type:
This looks like something John Madden would draw - "And, if you're in the red zone, then BOOM! it's gonna snow."
Where's my chicken wings/!!??!!
You must mean the "Turducken" with 10 legs.
KMDT...
1.217in of pure freezing rain with the temperature stay below 30F
What about jersey? Says the high is 32 but rain on Wednesday. Seems like west of i95 may stay below freezing. Thoughts?
Viewing: 51 - 101
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