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
Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 — Blog Index
NATIONAL WEATHER SERVICE STATE COLLEGE PA
913 PM EST TUE FEB 1 2011
PAZ004>006-010>012-017>019-024>028-033>037-041-042-045-046-049>053-
056>059-063>066-020813-
ADAMS-BEDFORD-BLAIR-CAMBRIA-CAMERON-CLEARFIELD-COLUMBIA-CUMBERLAND-
DAUPHIN-ELK-FRANKLIN-FULTON-HUNTINGDON-JUNIATA-LANCASTER-LEBANON-
MCKEAN-MIFFLIN-MONTOUR-NORTHERN CENTRE-NORTHERN CLINTON-
NORTHERN LYCOMING-NORTHUMBERLAND-PERRY-POTTER-SCHUYLKILL-SNYDER-
SOMERSET-SOUTHERN CENTRE-SOUTHERN CLINTON-SOUTHERN LYCOMING-SULLIVAN-
TIOGA-UNION-WARREN-YORK-
INCLUDING THE CITIES OF...ALTOONA...HARRISBURG...JOHNSTOWN...
LANCASTER...STATE COLLEGE...WILLIAMSPORT...YORK
913 PM EST TUE FEB 1 2011
.NOW...
BANDS OF HEAVY FREEZING RAIN WILL BE ACROSS THE REGION OVERNIGHT.
TEMPERATURES WILL REMAIN BELOW FREEZING OVERNIGHT. TRAVEL WILL
LIKELY BE DIFFICULT AND DANGEROUS IN MANY PLACES. AVOID TRAVEL
IF POSSIBLE. THE BANDS OF FREEZING RAIN ARE MOVING NORTHEAST
AT 35 MPH.
Blizz,
I have a steady freezing drizzle here. Everything seems to be a sheet of ice. Is everything going like you thought it would? I see the schools are already being cancelled for tomorrow in Mifflin County.
So far everything is going exactly according to plan.
When's the last time we had a storm drawing moisture from the Pacific like that?
Looks iffy (I'd stay home!)...
http://www.wunderground.com/cgi-bin/findweather/getForecast?query=02101&hourly=1&yday=32&weekday=We dnesday
Said with a Dr. Evil laugh.
School in many areas has already been declared closed for tomorrow.
And here's something funny I found on the Chatham (Cape Cod) Squire Pub page:
http://sphotos.ak.fbcdn.net/hphotos-ak-snc6/hs023.snc6/165390_484695520965_86384660965_6357990_7990 402_n.jpg
We need a version for this storm (possibly a tad less vulgar. LOL!).
Thanks Breald. That's the new family addition, Clifford. He's not so sure what to make of all this snow-pack.
I'm feeling optimistic about the folks. Boy, they sure are stubborn.
You've got that exactly right. I was in the midst of (one of?) those little Brooklyn tornadoes this Summer, one touched down right behind my apartment while I, naturally, was looking out the front, and is documented here: Link along with much amusing YouTube commentary. You can imagine that was the highpoint of my career as a weather buff.
Not to distract from the main story. Temp here at 9:45 pm is 27 and holding pretty steady. Blizz's post at 686 makes me think we could really get iced tonight.
We might be able to get there but I doubt we could get home. Do you have room for all of us to stay for a sleep over?
I posted this on my facebook earlier!
It's a complex. You could just barge into random people's apartments and throw them out of their beds...
All single females 22-30 are welcome to stay in my royal quarters.
Back to the weather.
Camp Hill, PA - 27.3F
Freezing Rain
It's not a drizzle but not a downpour, which as Blizz stated, is better for accumulation. Trees are glazed and sidewalks are coated.
I give electricity 2 hours...
Blizz, will this continue to be a major issue through CT during most of tomorrow? What do you think think the liquid total equivalent will be? Thanks.
I am just south of you in Tarrytown. We had about two inches of snow and sleet and a crust of freezing drizzle.
Looks like we are in for a tough one tonight. I just put down a ton of salt on my driveway and have loaded up on the wood for the potbelly in case we lose power.
Best of luck.
Yeah, I've watched some of those videos, but not that one in particular until now. One of my friends who lives in Park Slope had a portion of his roof ripped off at the apt building where he is the super. I went for a walk a few days later through the area of Queens that was hit by one during the same storm and it was even worse. You could actually see the path the tornado took, just sawing off trees half way up the trunk and twisting fences around nearby objects. Hundreds of cars and houses decorated with trees. Definitely some wicked weather last summer.
Yea, I'm sure that 2 hour delay tomorrow will give everyone time to get the roads and schools set for you guys to go to school. Sounds like they took heat today for not using the 2 hour delay to see how the roads turned out.
Precipitation starts in cold air aloft as ice crystals/snowflakes that have formed via heterogeneous nucleation, deposition, and ice multiplication and grown through aggregation and riming. Crystals then fall through a melting (warm) layer that is sufficiently deep or warm enough to completely melt the crystals to water drops. The drops then become supercooled as they fall through a subfreezing (refreezing) layer near the surface and freeze on contact if ground objects are colder than 0 C (32 F). A typical freezing rain sounding is shown in Figure 2.
Melting layers greater than 1200 ft deep usually cause complete melting, although for large flakes or for maximum melting layer temperatures less than or equal to 1 C, a deeper melting layer may be required for complete melting.
If the ground temperature is warmer than 0 C but the air temperature is colder than 0 C, then heat conduction may prevent freezing on the ground/streets, but freezing will occur on elevated cold surfaces, i.e., trees, power lines, and cars. If the ground is frozen, then freezing rain can occur despite air temperatures above 0 C (at least for awhile).
Brooklyn, NY
I highly doubt we have school tomorrow. An ice storm of this potential will cause major problems through tomorrow evening with widespread power outages and tree damage. Now if we have temperatures warm up tonight, then this eliminates the threat of course.
Can't you just rub your magic 8 ball and tell us if it warms up tonight? JK, I fully understand the complex nature of the battles of the different layers of warm and cold air that is taking place tonight. It just cracks me up how many people still want you to tell us if it will happen.
Hahaha... yep, I try to provide all of the options and highlight one as the most likely forecast according to my thoughts. That is essentially what forecasting is.
26.9F, Fog
First convective looking freezing rain showers knocking on the door.
Mount Pocono is 20F with light freezing rain
Thanks!
I still think the sleet will prevent major ice accretions towards your region. I have heard there has been nearly .2in of sleet recently in State College.
Yeah maybe. She's a huge wuss and would be extra sensitive to that sort of thing.
I still think it is too high for the Laurel Highlands and State College region, but not high enough in the northern Dauphin County latitude going west to east.
Been basically all freezing rain here so far. Little sleet mixing but not accumulating.
23.5 degrees
IP/ZR mix falling
0.5-0.75" of ice in the forecast.
Ice storm warning now for metropolitan Philadelphia...
One thing possibly pushing up total in State College is the freezing rain we got from the front running precip earlier this evening at like 6:30. Prob got .05in of ice at least out of it.
From my 3rd story window everything looks like glass.
Viewing: 701 - 751
Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 — Blog Index