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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Quoting originalLT:
Hi Silver Ships, well thats all I could remember in a short period of time while responding to you. I do agree, the back of winter has been broken, but just sayin, don't let your guard down.


If letting my guard down means a higher risk for a three-foot snowfall, then consider my guard down. Way down.
Member Since: December 1, 2008 Posts: 0 Comments: 600
^ That's not to say I wouldn't love a huge Spring snowstorm...
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56.3 here! Other than tomorrow's hiccup, this week is a welcome tease.

Bring on Spring.
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Hi Silver Ships, well thats all I could remember in a short period of time while responding to you. I do agree, the back of winter has been broken, but just sayin, don't let your guard down.
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I've been in Chicago for a week, I'll be here for one more and then I'll be home in Shippensburg for 2 days then back here again. When I got here it had snowed 3" on top of the 25" they already had. The on Monday snowed 3" on top of that. Last Firday they were still digging places out, WAY over a week after. It's crazy how much snow there was. It's been warm though and the melting is occurring quickly. Hopefully it snows again while I'm here because things aren't looking good back east.
Member Since: December 15, 2007 Posts: 19 Comments: 987
Quoting originalLT:
Not yet Silver Ships! Tomorrow will feel like an ice box, then of course warmer starting Wed. but Blizz hinted, look out for March! We've had some big snows in March.--Super Storm of 1993, Blizzard of 1888, Big snow of March 3-4th, 1961 0r 62(can't remember which!)


Three storms in 123 years? That hardly worries me. Are we looking at a hot/cold/hot/cold 70s/30s/70s/30s pattern March through April? When can I plant my garden, play golf, and go mountain biking?
Member Since: December 1, 2008 Posts: 0 Comments: 600
Quoting zotty:


I like Syracuse- 95 straight hours of snowfall. Maybe Heavy should consider moving to that hotbed of economic and social activity...


My dang family won't go. Jerks. hahahahahaha.
Syracuse? Hmmmmmm, Rochester maybe. Glens Falls? Okay. Tug Hill Plateau, I'm there!
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1460. crowe1
Rapid warm up. low 23F at 8am to 43F at 10am!

putting a few test taps for sap today.

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thanks MG. I keep thinking it will run its course in a few days

Blizz - said back in early January I think that March and April will be warmer than normal. Then a few weeks later he changed his prediction.

Did anyone see those pictures of Lead, South Dakota back in early January of the snow they got. Truly amazing.

Anyone having a problem with having to sign in all the time here on Wunderground? It happens to me all the time the last couple of weeks. What a PIA.
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Not yet Silver Ships! Tomorrow will feel like an ice box, then of course warmer starting Wed. but Blizz hinted, look out for March! We've had some big snows in March.--Super Storm of 1993, Blizzard of 1888, Big snow of March 3-4th, 1961 0r 62(can't remember which!)
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Winter is over? Can we call it officially?
Member Since: December 1, 2008 Posts: 0 Comments: 600
RP-I called my dr and described what I had and they are going to call in meds. Guess so many people are sick that the dr does not have any appt open.
http://www.webmd.com/cold-and-flu/cold-guide/cold -becomes-sinus-infection
I read about it here and you need to call your dr. gotta be well soon cause it is almost time to start planting!
Member Since: September 10, 2001 Posts: 2 Comments: 486
1455. zotty
Quoting Hoynieva:
Some of you have probably seen it already, but in case you haven't TWC made a snow report card: Link

Pretty interesting to see some of the totals across the nation.


I like Syracuse- 95 straight hours of snowfall. Maybe Heavy should consider moving to that hotbed of economic and social activity...
Member Since: August 19, 2009 Posts: 0 Comments: 747
1454. anduril
Quoting TrentonThunder:
I posted this question a while back but got no response. My aunt and uncle just moved from here to Mechanicsburg PA a couple weeks ago. They're curious as to which television station provides the best weather forecasts for that area. Anyone? Anyone?
WGAL is probably the better of the big three I'd say. The CBS affiliate can be decent for weather but for news they seem to be more into shock and terrible stuff than anything else. Fox, well, I just avoid fox
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Quoting P451:


There is however it will pull it down over the western states while we get the ridge and the warmer weather. In the long term it should migrate eastward but also moderate as it does so. Not looking good through the rest of February for winter weather enthusiasts.



Fine with me. If it's not going to snow, it might as well be warm, and anything else in between just isn't fun.
Member Since: February 23, 2010 Posts: 0 Comments: 677
MG - The sinus infection is a pain. I am starting my fourth week of it coming and going...mostly with me. I will probably go to the Dr. this week. Usually these things last maybe a week, but this one is just hanging on. I wonder how much Dr can do though, since it is probaby a virus.
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1449. bwi
Cloudy most of the day in DC. Probably kept temps down a little. South and SW winds didn't bring as much warmth as I expected. Supposed to be breezy tomorrow too. Maybe later this week some real warmth.
Member Since: September 4, 2007 Posts: 0 Comments: 1389
Started moving the last of the fall oak leaves and found daffodils up about 3-4 inches......need to transplant some lilies but ground is to wet and cold. Some of my plants are showing signs of spring! My sign of spring, sinus infection. Dr. tomorrow. I see we are still waiting on 'surprise'.
I had not sprayed deer repellant (homemade and worked last year) and my rhod. blossoms are gone, should have sprayed earlier....
Member Since: September 10, 2001 Posts: 2 Comments: 486
1447. KEEPEROFTHEGATE (Mod)

Member Since: July 15, 2006 Posts: 174 Comments: 54627
1446. KEEPEROFTHEGATE (Mod)


warm up in progress with increasing temps towards end of week with rain will be good now we just need a good strong breeze to get a good melt going

today i have for the first time since end of december seen some small grassy areas showing up from the snow melt if temps go the way its forecasted by friday we may have nothing here but some dirty snowbanks to deal with hopefully we are done but i say there is still a chance for at least 2 or 3 more storms before spring truly takes hold

as always we wait watch and see
Member Since: July 15, 2006 Posts: 174 Comments: 54627
I just looked it up online TT, and they still get DC stations, but they also get A station or two from Hagerstown, Johnstown and I think Harrisburg too.
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Back then before cable, Harrisburg stations weren't powerful enough to be seen in Chambersburg but the big DC transmitters were. I'm interested in finding out what they watch now.
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49.1 degrees, but feels cooler due to the wind. Still, nicest weather in a long time around here.

Brooklyn, NY
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Quoting HeavySnow:
Hey TT. I was born in Chambersburg and still have family there. Growing up, they watched the DC channels believe it or not. It's an hour and a half away. I'll check with my cousins who still live there.


Yeah ok thanks. I think they'd be more interested in a local Harrisburg station.
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Quoting h2oskt:
Posting from Central CT here. Light flurries at the moment and approximately eighteen inches of snow pack across the yard. I am now looking to the future as all interested in weather do. :-)

It seems a forgone conclusion that we will loose the snow pack to a thaw through the end of this week. Is there any guess as to a long term forecast through the end of the month and into March? Any discussion on the long term outlook would be greatly appreciated. :-)


Temperature wise, we should be well above average for the rest of February with 1 or 2 very short lived knocks back to average/slightly below over the entire span. Will probably see a couple early buds down here before months end.

I still have a 2" snowpack that just won't budge. As soon as it's gone, it might green up a little around here.
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Hey TT. I was born in Chambersburg and still have family there. Growing up, they watched the DC channels believe it or not. It's an hour and a half away. I'll check with my cousins who still live there.
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I posted this question a while back but got no response. My aunt and uncle just moved from here to Mechanicsburg PA a couple weeks ago. They're curious as to which television station provides the best weather forecasts for that area. Anyone? Anyone?
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Time to put the snowblower away for the season. It didn't get used as much as I thought with some of those storms. And the shovels also, except for one shovel should we get some nuisance snow in March. It will be nice to walk around the yard again.
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There's an east/west split for ya
Member Since: February 23, 2010 Posts: 0 Comments: 677
Welcome h20ski! Glad to have another CT person here. You think 18 inches of snow will melt in a week? Everything refreezes at night into ice on top, protecting what's underneath...I'm no expert though so it's just a thought.
Member Since: February 23, 2010 Posts: 0 Comments: 677
1435. h2oskt
Posting from Central CT here. Light flurries at the moment and approximately eighteen inches of snow pack across the yard. I am now looking to the future as all interested in weather do. :-)

It seems a forgone conclusion that we will loose the snow pack to a thaw through the end of this week. Is there any guess as to a long term forecast through the end of the month and into March? Any discussion on the long term outlook would be greatly appreciated. :-)
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P451 - it only takes a week of dry weather and/or windy conditions to dry out most grassy areas. good drainage also helps.

as for the cold air still in Canada....is there a mechanism to bring it down into the lower 48?
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Quoting HeavySnow:
It was muddy as hell on the course I saw. Iced over ponds still.


that isn't fun no thanks. I can't stand those conditions.
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Quoting pittsburghnurse:
Blizz, where are you? You OK?

He's around. He posted in my blog earlier today.
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It was muddy as hell on the course I saw. Iced over ponds still.
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Quoting HeavySnow:
Isawpeople golfing today TRP. I thought of you


it's going to be at least another week here for any golf. we have had a good snowpack for a month now. once the snow melts, then the grounds have to dry. it would be nice. I've been watching the pros at Pebble Beach. The weather there is amazing. I'd love to be out there. Spyglass and Pebble Beach are two fantastic courses to play
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cchamp all of our hedges/bushes at home are bent over/broken and I don't even know what else. You're not alone
Member Since: February 23, 2010 Posts: 0 Comments: 677
Quoting originalLT:
Hoy, on Feb. 4th, Blizz gave us a "Teaser" about a "surprise" If you go back to blog posts, 1000-1050, on page 21 of this current blog, you can see some of his posts about the "Surprise". Snow never made it to me in Stamford, had plenty of "virga" though!


Thanks, LT, missed that one because I was away at the time. If his surprise was disappearing for a week, he has succeeded.

Heavy, it's ok, it was just a weakened squall line passing through, we didn't end up with accumulation. No need to get your panties in a bunch...again.

cchamp, crazy amounts of snow, you weren't kidding. Sorry about your trees :(
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Isawpeople golfing today TRP. I thought of you
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cchamp - that is a shame you have lost your hemlocks. like you said it is nice to have snow, but not to where things get damaged
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Crowe it looks intense and a squall looks to be headed my way soon. We'll see what happens
Member Since: February 23, 2010 Posts: 0 Comments: 677
1421. crowe1
Quoting TheF1Man:
I wonder if that current line of showers over central ny is expected to keep moving east?


The main band moving thru now is pretty intense, visibility down to maybe .1mi. We've had scattered squalls/flurries all day with maybe .5" accumulation but its hard to tell because it's blowing pretty hard too.

Sacandaga Lake, Broadalbin, New York (PWS)
Updated: 0 sec ago
Scattered Clouds
29.1 °F
Scattered Clouds
Windchill: 16 °F
Humidity: 86%
Dew Point: 26 °F
Wind: 20.0 mph from the WSW
Wind Gust: 26.0 mph (peak G35)
Pressure: 29.77 in (Rising)
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1420. cchamp6
img src="Photobucket">


img src="Photobucket">


img src="Photobucket">


img src="Photobucket">



So this is the snow that has accumulated since the day after Christmas. There has been no melting. My hemlock hedges are all destroyed. 60% of them are broken. I have been here since 99 and this has never happened. I love snow and a good storm but this year has worn me down.
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1419. cchamp6
img src="Photobucket">
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Quoting Hoynieva:
It's snowing :)



I hate you guys. Cthulhu will now banish you to a dark oblivion.
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Hi, TheF1Man, looks like it's moving ESE but alot of the precip. out there on radar is virga, although that line seems alittle stronger.
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