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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517. 900MB
Quoting Blizzard92:

You won't get any more snow probably. I never understand why Upton had that much snow forecast. There will be some freezing rain tonight, but I think you change to plain rain relatively quickly. New York City is not a good location for ice storm formation.


You can't win em all! We've been snow hogs here! Speaking of which, are we getting our snow back on Saturday?
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Quoting 900MB:


Seems like a dud in NYC so far, snowed pretty good to our north, but only about a half inch of snow/sleet and it has been drizzling at around 30 degrees for the past couple of hours. Don't see how we are going to get the 5" forecast by NWS considering that the storm will likely be rain when the main event gets here. Ideas?

You won't get any more snow probably. I never understand why Upton had that much snow forecast. There will be some freezing rain tonight, but I think you change to plain rain relatively quickly. New York City is not a good location for ice storm formation.
Member Since: December 14, 2007 Posts: 284 Comments: 15112
Quoting TheRasberryPatch:
temp 27.7F

Campbelltown, PA

do you expect the temps to continue to climb and then stabilize by evening?

I expect them to rise and then actually fall maybe a degree or two after sunset.
Member Since: December 14, 2007 Posts: 284 Comments: 15112
514. 900MB
Quoting Blizzard92:
Light freezing drizzle here with 1.25in of snow here 10mi northeast of Harrisburg, PA; 25.6F. Still not sure how tonight will pan out as far as temperatures. NAM is steady and cold, while other guidance is not. But past experience with cold air damming says to believe the NAM.


Seems like a dud in NYC so far, snowed pretty good to our north, but only about a half inch of snow/sleet and it has been drizzling at around 30 degrees for the past couple of hours. Don't see how we are going to get the 5" forecast by NWS considering that the storm will likely be rain when the main event gets here. Ideas?
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Bellmawr, NJ
31F
Overcast
Misty, dreary day
Sporadic icing, still expecting overnight accumulation of ice through Wednesday afternoon.
Member Since: Posts: Comments:
2" of a fine, powdery snow as of 11am
light Snow
14.5 °F
Windchill: 7 °F
Humidity: 88%
Dew Point: 12 °F
Wind: 5.0 mph from the NNE
Wind Gust: 6.0 mph
Pressure: 30.39 in (Falling)
Visibility: 0.5 miles
Member Since: January 26, 2007 Posts: 15 Comments: 922
Quoting Hoynieva:
Thanks, Matlack. You're one of the only ones who are, I'm certain. Haha.


Yeah, you know where I stand on this issue!
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temp 27.7F

Campbelltown, PA

do you expect the temps to continue to climb and then stabilize by evening?
Member Since: January 26, 2007 Posts: 72 Comments: 6260
Here 10mi northeast of Harrisburg...

up to 26.3F
Member Since: December 14, 2007 Posts: 284 Comments: 15112
New Milford, CT

4.5" and the snow is picking up a bit at this moment.
21.1 °F
Snow Freezing Fog
Windchill: 21 °F
Humidity: 84%
Dew Point: 17 °F
Wind: 0.0 mph

Wind Gust: 0.0 mph
Pressure: 30.25 in (Steady)
Visibility: 0.5 miles
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Thanks, Matlack. You're one of the only ones who are, I'm certain. Haha.
Member Since: January 20, 2009 Posts: 0 Comments: 1509
Persistence of this pattern?

So now that my little corner of central MA is having another foot (or two?) of snow added to its already 36-40" snowpack, with another noreaster possible this this weekend, it begs the question: Is it possible that we're in for a few more weeks of winter storms every few days? What are the long term models saying about this conveyor belt?
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Hoynieva - I'm hoping it changes for you to be able to get out of there. Good Luck and enjoy your trip!
Member Since: January 1, 2006 Posts: 0 Comments: 358
Quoting Blizzard92:
Looks like the GFS already a tad too warm...


How do you think we'll far in State College?
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Bliz - looks like only the 13Z RUC is right on target so far based on the chart you posted. Could this mean the colder air will have a better foothold tonight?
Member Since: January 1, 2006 Posts: 0 Comments: 358
Snow report for mid-Hudson Valley, NY - Rhinebeck in Dutchess County.

As of 10:30 am had right around 6 inches of nice powder. Still snowing hard. Supposed to turn to a mix later but as of now it is very cold out there.

Definitely bummed that this isn't going to stick around as powder.
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Snowing very heavily in Smithfield, RI 3 inches on the ground now, temps still around 15 degrees.
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Blizz, you think they're right about this transitioning to rain by tomorrow afternoon for NYC? I need it to.

We're under a winter storm warning for 3-6" of snow and sleet followed by .40" of freezing rain and then plain rain.
Member Since: January 20, 2009 Posts: 0 Comments: 1509
Looks like the GFS already a tad too warm...
Member Since: December 14, 2007 Posts: 284 Comments: 15112
Light freezing drizzle here with 1.25in of snow here 10mi northeast of Harrisburg, PA; 25.6F. Still not sure how tonight will pan out as far as temperatures. NAM is steady and cold, while other guidance is not. But past experience with cold air damming says to believe the NAM.
Member Since: December 14, 2007 Posts: 284 Comments: 15112
West Chester, PA current obs:

Fog, 29F, winds calm

Had about 1/8" of ice on my car this morning and on the ground, but the roads have been heavily treated and are simply wet. Looks like the overnight forecast for Philly metro area was a bust, but all the same, WCU opened 90 minutes late.
Member Since: October 19, 2005 Posts: 0 Comments: 217
Snowing pretty hard now, then looks like a break for a bit. I'll take a measurement when it stops.

Sacandaga Lake, Broadalbin, New York
Heavy Snow
13.0 °F
Heavy Snow Freezing Fog
Windchill: 13 °F
Humidity: 90%
Dew Point: 11 °F
Wind: 2.0 mph from the NE
Wind Gust: 5.0 mph
Pressure: 30.40 in (Steady)
Visibility: 0.2 miles
Member Since: January 26, 2007 Posts: 15 Comments: 922
Worcester MA checking in:

Tiny snow flakes, falling fast. Visibility is down to .5 miles (top of my hill = best guess) and we've got 2.5 in. snow...

that means they have to start plowing, right??
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at least we got a layer of snow and sleet on the sidewalks and driveways before the freezing rain hits. it won't be as difficult to clear, I hope. At least not like plain freezing rain on the surface
Member Since: January 26, 2007 Posts: 72 Comments: 6260
Blizz - what happened to the WGAL radar?

there it is
Member Since: January 26, 2007 Posts: 72 Comments: 6260
Some really heavy precipitation falling along I80 according to the NWS radar. Loading so slow however that it could have been hours ago ;)
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Excited for my family near Detroit. This looks to be at least their 3rd biggest snowfall of all time.
Member Since: January 20, 2009 Posts: 0 Comments: 1509
Quoting GTOSnow:
Looks like the models have trended the storm north, is that what everyone else sees?
By the looks of the radar, everything (wave 1) seems to be going North of Harrisburg....was it supposed to do this?
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Quoting Matlack:
NWS Mount Holly Storm Snow Total Forecast.

Their maps havent matched their wording in the Philly and immediate suburbs and south. Maps closer to reality, though they have toned wording down to an inch, which is still high maybe for continuity purposes.
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Light snow here in Stamford CT. 26F, we've had about 1", NE wind 2-7mph. Baro.30.32F Lookslike this batch of precip will be ending here by 10AM or so. Then probably just flurries or freezing drizzle for awhile.
Member Since: January 31, 2009 Posts: 0 Comments: 7731
Quoting ConnecticutWXGuy:
was checking Chicago's NWS site and they actually have a video storm briefing. WOW! I wish our NWS would at least do that. I've never seen NYC NWS do anything close to that for storms.

Link


What is your thought for Eastern, CT
we live in Hebron
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NWS Mount Holly Storm Snow Total Forecast.
Member Since: January 1, 2006 Posts: 0 Comments: 358
Is anyone any good at looking at the soundings to see when/if we get above freezing for tomorrow? I have trouble finding them.
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Quoting pittsburghnurse:
Precip thinning out here in Pgh. Event has been mostly rain with heavier concentrations of sleet and freezing rain increasing north as you get to I-80. Right now 32 degrees at the airport with mist. So far, a few accidents but generally no problems.
Member Since: October 14, 2006 Posts: 1 Comments: 639
Precip thinning out here in Pgh. Event has been mostly rain with heavier concentrations of sleet and freezing increasing north as you get to I-80. Right now 32 degrees at the airport with mist. So far, a few accidents but generally no problems.
Member Since: October 14, 2006 Posts: 1 Comments: 639
Current conditions here (40 mi NNW of Albany):
11.6 °F
light/moderate snow
Windchill: 5 °F
Humidity: 89%
Dew Point: 9 °F
Wind: 5.0 mph from the NE
Wind Gust: 6.0 mph
Pressure: 30.41 in (Steady)
Visibility: 0.5 miles
Snow flakes are very small, about .5" so far.
Member Since: January 26, 2007 Posts: 15 Comments: 922
Wow, look at Texas on the WunderMap. Link
Like Doc pointed out, it's an amazing gradient.
Member Since: January 26, 2007 Posts: 15 Comments: 922
Actually, stepped out and its a thin but hard mixture of snow sleet frz rain on untreated surfaces. Highways just wet, untreated backroads slick, icy mixture tough to get off car. Steady freezing mist not being detected by radar, 27F. Mixing was not expected until late morning. Some schools delayed, most schools normal. 8 to 12 inch snowpack leftover from previous storms. Plenty of cement snow amazingly still stuck to some trees, especially pines and large bushes.
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--Naugatuck, CT--
16 degrees
Moderate Snow
3/4 of an inch on the ground
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Moderate snow here in Warwick, NY. Roughly 2-3" on the ground. 15 degrees. The local mets are saying it's supposed to stop for a while today, so I am venturing into the city for work via NJ Transit. I hope I'm not making a mistake.
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Quoting Mason803:
not much snow down here. looks to be a heavy layer of sleet and fzrain. already a report of wires down near caledonia state park


I love Caledonia.

28 here with a freezing mist.
Member Since: July 7, 2004 Posts: 18 Comments: 2989
473. 900MB
NYC- 27 degrees and a light icy coating of sleet on the ground. Moderate sleet right now.
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About 1" snow on the ground in Brooklyn, NY, and nothing happening now. Still waiting for the second leg to start Weds., or the second half of the first leg yet today? The front seems to be just north and west of the City.
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Just got to work and it was raining pretty hard on the way here. Although I had scrapped my windows they were ice coated by the time I got here. I only live 7 min from work so the car doesn't really have time to warm all the way up. Roads were for the most part snow covered back roads and not too slippery. Is certainly raining harder than drizzle.
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0.5" of snow and sleet water equivalent 0.21"

current observations
light drizzle
temp 25.2F
dewpt. 23.7F
winds out of East
barometer 1025.1mb and falling

Campbelltown, PA 5 miles East of Hershey
Member Since: January 26, 2007 Posts: 72 Comments: 6260
469. bwi
30 degrees in DC area, looks like a decent glaze on the driveway. Joy.
Member Since: September 4, 2007 Posts: 0 Comments: 1390
Looks like the first bust of the season to me snowfall wise in extreme southeast PA and the southern 2/3 of New Jersey today.

I couldn't see how they arrived at 2" - 4" last night. I told anyone who asked me 1" - 3". The only reason I didn't say 1" - 2" was because NWS was higher. The overall warning that came out recently still sais 2" - 5", I'd tone that down to a coating south and 1" north right about now.
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offically @ cashtown 1s

snow 0.2"

lquid equiv. 0.13"

currently 23f
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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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