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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Any early estimates for Central PA?
NWS Forecast up here at University Park
Monday Night: Snow. Low around 16. Calm wind becoming east around 6 mph. Winds could gust as high as 20 mph. Chance of precipitation is 100%. New snow accumulation of 2 to 4 inches possible.
Tuesday: Snow before 1pm, then snow and freezing rain. High near 28. East wind around 6 mph. Chance of precipitation is 80%. New precipitation amounts between a quarter and half of an inch possible.
Tuesday Night: Freezing rain. Low around 22. East wind around 7 mph. Chance of precipitation is 90%. New precipitation amounts between a half and three quarters of an inch possible.
Wednesday: Freezing rain before 1pm, then snow and freezing rain likely, possibly mixed with sleet. High near 33. Chance of precipitation is 80%. New precipitation amounts between a quarter and half of an inch possible.
Wednesday Night: A chance of snow. Cloudy, with a low around 11. Chance of precipitation is 40%.
Cold air typically does not hold well in your area. I would not expect the ice to get too bad like it will for the cold air damming spots east of the mountains. But an ice storm is bad and can cause major problems both for transportation and communication.
Yeah I'm about 60 or 70 miles north of you. My high for the 48 hrs says 33 right now. If this trends any further south and or the coastal takes over sooner and south then I could be looking at a big mess along with you!
That makes me wonder...what is the highest qpf that has ever fallen as all freezing rain. I just can't fathom an inch of frozen rain.
danielb1023- Given your proximity a bit closer to the coast, that will help you a bit dislodging the cold air and avoiding a more severe ice storm at least. Areas just to your northwest will definitely get hit a lot worse. Although if this coastal develops, you may be able to squeeze out some more sleet/snow.
For our area, I am not sure about the most freezing rain. But there have been several terrible and horrific ice storms with accretions well over 1in. Remember how bad it was in northern Kentucky last year. I think that terrible ice storm in Canada and northern Maine (I forget the year) had ice accretions of nearly 4in.
Didn't they get hammered up in Montreal like a decade ago?
The Canadian one was in 1998. Also, here's an interesting fact: the ice storm in Kentucky actually had flash flood warnings on it too!
That just boggles the mind. I guess my son and husband picked a bad time to replace the valve cover gasket on my van. While it sits toasty in the garage awaiting the replacement piece that my son broke, our 1982 Porsche 928 will have to endure this storm out in the elements. My son is gonna be very worried about his baby if we get ice.
Sorry, long way out, one thing at a time.
That's barely even in the realm of imagination. Those poor souls.
here's a pic of the '94 ice storm in b-more
Oh yeah....that's the one where I told you all that I swallowed my pride and crawled across my front yard to get to the front door
it was HARD HARD work just trying to clear the sidewalk. as you can see from your picture
I did that last November in a much less situation. I went to go outside to get something from my car and was not aware of the ice accumulation on the sidewalk. Took one step and went down. Twisted the crap out of my knee, it immediately began swelling. I had to Vietnam-crawl up 2 flights of stairs. I didn't walk on that knee for a month.
They were actually extremely frequent in the 90's. Not so much / pretty rare since 2000's. I remember in the Blizzard of '96 that it was pretty weird we were seeing all snow and no ice. Ice may be a problem for us Tuesday night/Wednesday morning.
.75" of ice on south mountain
luckily i was @ Disney. I actually left a day early in anticipation of the storm. my house was without power for 2 1/2 days. It ended up killing my sewer pump, the spike of having the power come back on
Just in my neighborhood there were over 10 ornamental pear trees that split in half. not good trees for this area anyway.
after 3 years of being a coop observer, i finally made the daily temp. and precip. summary.
Link
adams county
cashtown 1s
Hahaha... yay! Maybe the had to do some sort of accuracy verification over time.
i think they wanted to make sure i was the real deal before showcasing my site lol
OF THE NORTHEAST USA...
.SNOW TUESDAY MORNING WILL TURN TO RAIN...SLEET AND FREEZING DRIZZLE
SOMETIME TUESDAY AFTERNOON AND THEN RESUME AS HEAVY RAIN OR FREEZING
RAIN EARLY WEDNESDAY BEFORE TAPERING OFF LATE WEDNESDAY.
NJZ001-007>010-012-015-PAZ054-055-060>062-068-069-310945-
/O.NEW.KPHI.WS.A.0004.110201T0800Z-110202T2200Z/
SUSSEX-WARREN-MORRIS-HUNTERDON-SOMERSET-MIDDLESEX-MERCER-CARBON-
MONROE-BERKS-LEHIGH-NORTHAMPTON-MONTGOMERY-BUCKS-
INCLUDING THE CITIES OF...NEWTON...WASHINGTON...MORRISTOWN...
FLEMINGTON...SOMERVILLE...NEW BRUNSWICK...TRENTON...JIM THORPE...
STROUDSBURG...READING...ALLENTOWN...BETHLEHEM...EASTON...
NORRISTOWN...DOYLESTOWN
835 PM EST SUN JAN 30 2011
...WINTER STORM WATCH IN EFFECT FROM LATE MONDAY NIGHT THROUGH
WEDNESDAY AFTERNOON...
THE NATIONAL WEATHER SERVICE IN MOUNT HOLLY HAS ISSUED A WINTER
STORM WATCH...WHICH IS IN EFFECT FROM LATE MONDAY NIGHT THROUGH
WEDNESDAY AFTERNOON.
* GEOGRAPHICAL COVERAGE: EAST CENTRAL AND NORTHEAST PENNSYLVANIA
AS WELL AS MUCH OF NORTHERN NEW JERSEY.
* PRECIPITATION TYPE: SNOW TUESDAY MORNING CHANGES TO SLEET OR
FREEZING DRIZZLE DURING THE AFTERNOON OR EVENING. PERIODS OF
HEAVY SLEET OR FREEZING RAIN ARE EXPECTED LATE TUESDAY NIGHT
INTO WEDNESDAY.
* ACCUMULATIONS: 2 TO 6 INCHES OF SNOW AND SLEET TUESDAY. GLAZE
MAY ACCUMULATE FROM ONE QUARTER TO THREE QUARTERS OF AN INCH.
* TIMING: SNOW BEGINS BETWEEN MIDNIGHT AND 4 AM TUESDAY. THE
CHANGE TO SLEET OR FREEZING DRIZZLE SHOULD OCCUR BETWEEN NOON
AND 6 PM TUESDAY.
* IMPACTS: THE TUESDAY MORNING COMMUTE WILL LIKELY BE HAZARDOUS
WITH AT LEAST SOME SNOW AND TEMPERATURES NEAR 20. THE WEDNESDAY
MORNING COMMUTE IS ALSO LIKELY TO BE HAZARDOUS DUE TO ICE AND
THE WEDNESDAY EVENING COMMUTE MAY STILL BE HAZARDOUS FOR ALL
UNTREATED PAVEMENTS. IF GLAZE REACHES OR EXCEEDS ONE HALF
INCH...POWER OUTAGES MAY OCCUR. ALSO...THE WATER EQUIVALENT
PRECIPITATION FOR THIS STORM MAY EXCEED ONE INCH AND THIS ADDED
TO SNOW LOADS ON SOME ROOFS AND ATTEMPTING TO RUN OFF INTO ICE
ALREADY ICE CLOGGED ROOF GUTTERS MAY CONTRIBUTE TO STRUCTURE LEAKS.
* CONFIDENCE: ABOVE AVERAGE ON BOTH SNOW AND GLAZE OCCURRING BUT
TOP END AMOUNTS OF 6 INCHES OF SNOW AND SLEET AND THREE
QUARTERS OF AN INCH OF GLAZE ARE BELOW AVERAGE CONFIDENCE.
http://www1.whdh.com/images/weather/producer_uploads/special-560x389.jpg?01301722
Are we talking about this whole thing shifting a little SW in latest models? That would put me in the 20-25" area. (Per their current map, I'm about 20 miles SW of it.)
I have to fly on Wed afternoon and I was wondering what you think about precip type. It's looking to me like it will be all rain by late afternoon, but maybe you see something different. Hoping for rain...
My nick implies my location; I'm in Wales, MA.
If the coastal low develops a bit sooner, then yes it will probably be considered a southeast trend as thermals will be colder.
We do NOT need another 20 inches of snow.
Yeah, It sure does seem that way. It's been relentless and it doesn't look to end anytime soon.
Banned!
Ugh it's almost like a New England Snowmaggedon, which bothers me because I take pride in experiencing the true Snowmaggedon in the Mid Atlantic, lol.
I'm supposed to root for the snow?
My wife and I were saying tonight that if we get another big one, we might just have to hang a white flag out the window.
We surrender!
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