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
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Forecast calls for low 50's tomorrow, which likely means 60+ and Friday, well, I was hoping to get near 70, but clouds will likely keep it below that.
Regardless, loving this weather.
Hopefully blizz makes an appearance soon, I want to know what's happening next week for the possible storm.
Thanks, TRP and P451 - It is definitely different with Blizz not giving his excellent insight. And I agree with you, P, Blizz is likely going to be very busy with schooling, and they'll probably want him to do a blog for Cornell's weather next year! *sigh* If Blizz can't do the blog next year, perhaps one of our many weather-savvy folk will take it over? Or take turns doing posts to give Blizz somewhat of a break? The blog might actually be comfortingly familiar to a new college student away in a totally new society. In any case, however it pans out, it'd be a shame to let the community disappear.
"All eyes will be on Tuesday as there is growing support for the threat for accumulating snowfall on Tuesday morning throughout the New York City and Philadelphia metropolitan areas. At this time, details are still uncertain about the exact track of the low pressure system and precipitation type, however the threat is clearly growing for another round of snow for early next week."
Yay!
Snow for the week is forecasted to remain to our north, however the threat remains for flurries. With the ground so warm, whatever comes down has little chance of sticking. There still remains some patches of snow on the grassy slopes but they should be gone by tomorrow afternoon.
Glad you delurked Blizz. Really good to hear from you.
I know some may be winter weary this season, but remember it's only February 17th. As far as I'm concerned, we're in the heart of snow season. Don't let the premature spring tease fool ya.
That's unfortunate you remain so cold, F1, we only went down to 45 last night. Already at 50 with mostly overcast skies. I'll go with 62 for a high today and 68 tomorrow, even though they predict 56 and 61, respectively.
The snow is basically gone, and what remains is soggy ground and extremely dirty piles of what is hard to believe is snow. If you want to see dirty snow, visit NYC. This place is full of filth.
Pittnurse: You've been ready for spring since January lol. Don't put your money on a big snowfall, that's only per the 06Z GFS.
I can see what may be starting to happen with the early week system. There may be an intitial low that tracks east-northeast through New England spreading precip as all snow for the northern half up there, and snow/rain for southern New England. Then, a second low forms behind low #1 along the leading edge of the progressive cold air trough, bringing low #2 on a east or east-southeast track through the southern mid-atlantic with a band of heavy snow just north of the center.
I'm trying not to model hug here, but just giving an idea as to the evolution of guidance on this system for those who are not following or whatever. Just something to talk about really.
Sure is. I'm at 64F at 1:30. Today may end up being warmer than tomorrow. Friday afternoon cumulus and a slight chance of an afternoon shower way limit the maximums. We'll see though.
I agree, more sunshine today than tomorrow, I was just thinking the same thing.
Not sure the reason, maybe too much weight given to the snowcover? I don't know...
As of 2:00 pm, a few areas in southenr NJ begining to enter low-70's. I'd say today was a completely busted forecast temperature wise.
Good job on the temp predictions hoy now get busy on that snow forecast.
LT- The sound is a killer!
I went outside at lunchtime today and have to admit I felt alive for the first time since that big snow after Christmas. Monday back in the freezer- oh well.
I'm officialy calling it a 0" snowcover after noon today for the first time since January 7th. Since I believe 7am this morning should be considered T" depth, that means 42 straight days with snowcover. That's an enormous consecutive stretch for these parts. There's still some snow around out there, but 0" for flat, open & untouched areas. Snow evidence (drifts/shade/snow mounds) have been consistent since December 26th.
Area forecast discussion
National Weather Service Mount Holly New Jersey
342 PM EST Thursday Feb 17 2011
Long term /Sunday night through Thursday/...
there is better model consensus today for the first half of the long
term than there was yesterday as most medium range models have a
double shot of precipitation affecting our County Warning Area from Sunday night
into Tuesday. It looks like wintry precipitation will return but at
this forecast juncture the ability to have the ptype exactly correct
should be viewed as less than average.
Most of the models are ejecting the closed low from the southwestern Continental U.S.
Faster than yesterday. If anything most of the medium range models
trended toward yesterday's 12z GFS solution. Thus we have slid the
precipitation event forward in time about 12 to 24 hours. Still feel
uncomfortable about the GFS northernmost track because it is predicated
on a piece of energy coming from the baffin island polar vortex.
Both the GFS and European model (ecmwf) models initialized it well, so its more of a
function of its interaction/track down the Road.
At any rate, probability of precipitation were started on Sunday night. The idea of consensus
warm air advection would change snow over to rain or non snow (could be freezing
rain) for most of our County Warning Area as Sunday night continues. Monday would
spend time either in the warm sector or being warm enough for
mainly rain. As the first low exits, a second wave of low pressure
is forecast to form on its frontal boundary and give our area a
second shot or precipitation. Because its expected to get colder
behind the departing first low and the general farther south
forecast track of the second low, we bring wintry precipitation
deeper into our County Warning Area. We end precipitation as snow throughout our County Warning Area
on Tuesday morning. While the models are much closer than they were
yesterday, the details on how this will transpire will hopefully
become clearer over the next couple of days. The GFS and European model (ecmwf)
ensemble means are a bit more progressive and muted with the
second wave, but as ensembles go, this would be expected given
some members have flatter solutions than the op model.
After the lows depart, fair but colder weather will return Tuesday
night and Wednesday. A cold front is forecast to approach our County Warning Area on
Thursday. Showers are possible as the front approaches. There will
be some temperature recovery, so the mention of snow for now was
confined northwest of the i95 corridor.
Temperatures in the long term are expected to average around or
colder than normal. The one exception might be Monday if parts of
our County Warning Area get into the warm sector. There is considerable uncertainty
though about the maximum temperatures. This can be seen as there was a 6
Standard deviation spread on phl's maximum temperature off the 00z ensemble
run. Or to put it another way, there was a 25 degree spread among
the ensemble MOS members for monday's maximum temperature at phl.
Sunday Night
Mostly cloudy. A chance of rain and snow after midnight. Lows in the lower 30s. Chance of precipitation 40 percent.
Washingtons Birthday
Mostly cloudy with a 40 percent chance of rain. Highs in the upper 40s.
Monday Night
Mostly cloudy with a chance of snow. A chance of rain in the evening. Lows in the lower 20s. Chance of precipitation 40 percent.
Tuesday
Mostly cloudy with a chance of snow in the morning... then partly sunny in the afternoon. Highs in the mid 30s. Chance of snow 40 percent.
For my S. PA brethern, Weatherworld is favoring an accumlating snow fall for PA - south of I-80 as per their Sure Bets segment in tonight's broadcast. In last night's Extended Forecast, Paul Knight was favoring a Canadian-like solution with the LP riding the frontal boundry to our South - wintry mix, possible all snow, possibly all ice, possibly mixed.
WW is 92% accurate with their Sure Bets calls this winter season and overall a very solid forecasting crew for our region.
Edit: forgot to give ya al link or web addy: www.weatherworld.psu.edu
This post has been edited by Undertakers
(T) = Tied
* = Broken
Huntington WV: 70 (T)
Harrisburg PA: 67*
Trenton NJ: 67 (T)
Beckley WV: 66*
Bluefield WV: 66*
Newark NJ: 66 (T)
Reading PA: 64 (T)
a bit rural so not much concrete and pavement to warm as Harrisburg
55F right now....warm for this time of day and this time of the year
Current:
Sacandaga Lake, Broadalbin, New York (PWS)
Clear
33.8 °F
Clear
Windchill: 34 °F
Humidity: 90%
Dew Point: 31 °F
Wind: 0.0 mph
Wind Gust: 0.0 mph
Pressure: 29.96 in (Falling)
Storm Warning
URGENT - MARINE WEATHER MESSAGE
NATIONAL WEATHER SERVICE MARQUETTE MI
1005 PM EST THU FEB 17 2011
A STORM WARNING REMAINS IN EFFECT FROM 7 AM TO 10 PM EST FRIDAY.
* WIND AND WAVES DURING THE STORM WARNING: EXPECT SUSTAINED
WINDS OF UP TO 42 KNOTS FROM THE WEST...WITH GUSTS UP TO 54
KNOTS. THE LARGEST EXPECTED SIGNIFICANT WAVES WILL BE 27 FEET
WITH A MAXIMUM WAVE HEIGHT OF UP TO 40 FEET POSSIBLE.
Oh I'm sure I'm not alone. Once Christmas is over and the decorations are put away, winter can become a bit of a drudge for me. This year especially with trying to renovate and protect an empty home wintering over. Worrying about freezing pipes, etc. and making sure the contractors don't slip and fall on icy surfaces.
Monday looks like it will be mostly rain around here before changing to snow Monday night, though I doubt there'd be much if any accumulation now that the surface has warmed. We'll see though. There's little doubt we'll have more snow this winter.
Looks like our best chance for a light snow is Tuesday morning. Otherwise just a cold rain. Oh well; I'll enjoy spring today! I like the variety, and I'd love more snow. :)
A couple of low pressure systems will move through the northern Mid Atlantic on Monday and Tuesday. The first low pressure system will move from the Ohio Valley into the southern Hudson Valley on Monday morning. Most locations will be on the warm side of this low pressure system, however portions of the northern interior like northeastern Pennsylvania, northwestern New Jersey, the Hudson Valley, and interior Connecticut; will be on the cold side of this storm track initially with a period of light to moderate snow on Monday morning. Accumulations will be limited as warm air will overwhelm the region changing any snow in these locations over to rain, however a 1 to 3 inch or 2 to 4 inch accumulation of snow is possible before any change over to rain. The cold front with this low pressure will move through on Monday afternoon. Ahead of the cold front temperatures will warm into the 40′s for most locations, possibly touching 50 degrees.
Behind the cold front, another Polar/Arctic air mass will move into the region. A second wave of low pressure will develop over the Ohio Valley, however this low pressure system is expected to track towards the Delaware coast on Tuesday morning. With a cold air mass in place, a period of light to moderate snow and sleet is expected on Tuesday morning with minor to moderate snowfall accumulations possible. There is still some uncertainty about this low pressure system, however most guidance agrees with the timing of this low pressure system impacting the region in the morning hours of Tuesday.
Agreed. Can't last for too long this time, though, with temps rising again by the end of the week.
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