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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Lt i was looking at the wrong thursday! oops
Member Since: Posts: Comments:
1316. hurigo
Quoting absurfer:
the nws is calling for 1 to 3 for my area and 2 to 4 to my west with some standouts of 5 or more im interested in the qpf which each run seems to put out more everytime they forecast totals we always double the amount so im keeping my fingers crossed for a half a foot ha ha


Good luck with that neighbor. We had a foot the day after Christmas. I'll keep my fingers crossed for you but I'm not sure I want that much at my end -- although it would offer up some good photo ops. If you do get that much can you get to my (beloved) Atlantic and take some photos on the Oceanside?
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the nws is calling for 1 to 3 for my area and 2 to 4 to my west with some standouts of 5 or more im interested in the qpf which each run seems to put out more everytime they forecast totals we always double the amount so im keeping my fingers crossed for a half a foot ha ha
Quoting hurigo:
Hey Absurfer! I just saw the WSW myself. Not sure where the dividing line is. Maybe the snow this time will be further north and I'll see some. You sure did capture some great photos with the last one.
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1314. KEEPEROFTHEGATE (Mod)
we may have the cold now but the warmer weather is coming



SIGNIFICANT WARM-UP COMING
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1313. hurigo
Hey Absurfer! I just saw the WSW myself. Not sure where the dividing line is. Maybe the snow this time will be further north and I'll see some. You sure did capture some great photos with the last one.
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1312. hurigo
Hello Blizz, et al.
Hubby and I were sitting on the front (north facing) covered porch and it got cold all of a sudden. Beautiful sunset reflected in the windows of the opposite structures.

Just checked the weathercast and see this has been posted:

... Winter Storm Watch in effect from late Wednesday night through
Thursday morning...

The National Weather Service in Wakefield has issued a Winter
Storm Watch... which is in effect from late Wednesday night
through Thursday morning.

* Areas affected: portions of northeast North Carolina.

* Precipitation types: snow.

* Accumulation: 2 to 3 inches... locally higher amounts up to 4
inches possible.

* Timing: light snow or flurries are expected to begin between 10
PM Wednesday and 2 am Thursday... with the snow forecast to continue
through the late morning hours. The heaviest snow is expected
between 3 am and 9 am EST Thursday.

* Temperatures: will range from the mid 20s to around 30 degrees.

* Visibilities: locally one quarter of a mile or less at times.

* Impacts: hazardous driving conditions... impacting the morning
rush hour.

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winter storm watch for eastern nc again can u believe it
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Just a note, I've been following the national radar picture all day, from the early morning, and an area of snow has been over the entire state of Kansas and has hardly moved all day. That seems alittle strange, virtually no movement!
Member Since: January 31, 2009 Posts: 0 Comments: 8011
1309. crowe1
Same (Broadalbin,NY)here, we went from a balmy 31F to 15F. High gust of 42mph so far, wind chill -2ish.

edited to add location
Member Since: January 26, 2007 Posts: 15 Comments: 953
wow is it bitter outside. the temps have been dropping all day and the winds have picked up

a high gust of 35mph just recently. temps is 27.2F

Campbelltown, PA

edited: now a gust of 41mph at 430pm and just noted the dewpt is -1F
Member Since: January 26, 2007 Posts: 72 Comments: 6285
1307. crowe1
Wind and pressure up, temperature down.

Member Since: January 26, 2007 Posts: 15 Comments: 953
TheF1Man, which Wed. and Thurs. are they talking about, next week? Could be by then.
Member Since: January 31, 2009 Posts: 0 Comments: 8011
Quoting nesnow383:
Winter just died, everyone is mourning......


Come to Vermont! Winter still going strong. 8" new at my house as of noon and still snowing hard. Went skiing at Smugglers Notch and there was still untouched 16-20" powder stashes in the woods and a fresh 8-10 on the slopes. Barn collapses are the main news item and BTV has well exceeded the normal yearly snowfall already. I have no room to plow the snow. A brief break would be welcome but we do have another 7 weeks of winter.
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Accuweather thinks it will be 50 and 51 here Wednesday and Thurs...are you kidding me? TWC has me in the 20s..go figure
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Very quiet here indeed. We had maybe 2-3 inches last night
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Quoting originalLT:
Hoy, your post, # 1298, the pic. did not come through. What was it?


Haha, really? Odd. Wonder why it shows on mine. It was nothing, just rainforest of the Na'vi people being destroyed in Avatar. Yeah, I saw the cold temps starting tonight, but looking forward to the warm up. I got a taste of warmth and now I want more of it. Ready to plant my seeds and see life rise from the earth again.

Sunnysmum, sure, I can email you some pics, but it was hard to capture most of the life on film. Especially the birds, such as toucans. All I was able to get were some silhouettes of them and parrots were even more difficult. I need a professional camera but can't afford it. I was going to paste a few of the pics up here, but yeah, I can email you.

Member Since: January 20, 2009 Posts: 0 Comments: 1783
Hoy, your post, # 1298, the pic. did not come through. What was it?
Member Since: January 31, 2009 Posts: 0 Comments: 8011
Welcome back safe and sound! And also welcome back to some REAL COLD temps. by Wed. AM!
Member Since: January 31, 2009 Posts: 0 Comments: 8011
Quoting Hoynieva:
Hello all.

Weather in Costa Rica was perfect. Mid 80's everyday with plenty of sunshine during the day and a soaking rain each night. Saw all sorts of crazy animals I'd previously only seen on television or in zoos.

The rainforest is teeming with life, as expected.


Hey welcome back. I would love to see some pics of the rainforest those crazy animals if you want to share.
you can send by email NLCHIPMAN@yahoo.com. :)
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Clever, PP, but it was actually more like this:


Member Since: January 20, 2009 Posts: 0 Comments: 1783
Quoting Hoynieva:
The rainforest is teeming with life, as expected.




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1295. bwi
Wind advisory, and they weren't kidding. Hopefully it'll die down this afternoon.
Member Since: September 4, 2007 Posts: 0 Comments: 1647
Hello all.

Weather in Costa Rica was perfect. Mid 80's everyday with plenty of sunshine during the day and a soaking rain each night. Saw all sorts of crazy animals I'd previously only seen on television or in zoos.

The rainforest is teeming with life, as expected.
Member Since: January 20, 2009 Posts: 0 Comments: 1783
Quoting TheRasberryPatch:


more snow? well it better happen soon. Come March I want the snow gone so the daffodils can bloom and for the garden to dry out a bit to prepare it for some cold weather vegetables.

I was just thinking that myself - late frosts can also be a problem.
Member Since: Posts: Comments:
A break can be okay; agreed. Hopefully Blizz will have some time soon to explain what's happening in the longer term.
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Quoting testbenchdude:
I love winter as much as anyone on here does, but a short break sounds pretty darn good right about now. I'm just getting over my second chest cold of the season so it'd be nice to warm up for a bit...just so long as we all understand I still want more snow before winter ends. Just to be clear. :)


more snow? well it better happen soon. Come March I want the snow gone so the daffodils can bloom and for the garden to dry out a bit to prepare it for some cold weather vegetables.
Member Since: January 26, 2007 Posts: 72 Comments: 6285
I love winter as much as anyone on here does, but a short break sounds pretty darn good right about now. I'm just getting over my second chest cold of the season so it'd be nice to warm up for a bit...just so long as we all understand I still want more snow before winter ends. Just to be clear. :)
Member Since: October 19, 2005 Posts: 0 Comments: 252
Well, I don't know if winter has died, it will be real cold the next couple of days, but it will definitelly be on hold for a while , starting Friday or Sat. Blizz said it could come back in 2-3 weeks.
Member Since: January 31, 2009 Posts: 0 Comments: 8011
Winter just died, everyone is mourning......
Member Since: Posts: Comments:
Wow - this is one quiet blog these days.

Wind is starting to kick up, and it's quite dark out there. Still warm, 38.9F. Gonna be nasty when there's wind and cold!
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1286. crowe1
3" of wet snow so far, snowing lightly, very pretty.

Weather Station
Sacandaga Lake, Broadalbin
Elevation
770 ft

Light Snow
Temperature: 30.1 °F
Windchill: 30 °F
Pressure: 29.56 in
Humidity: 98%
Dew Point: 30 °F
Wind Speed / Dir: Calm
Wind Gust: 0.0 mph
Visibility: 1.0 miles
Clouds: Mostly Cloudy 300 ft
Overcast 1600 ft
Member Since: January 26, 2007 Posts: 15 Comments: 953
another reason you can tell Spring is coming. The past two nights skunk smelling the neighborhood. oh what a delight, huh hahahaaha
Member Since: January 26, 2007 Posts: 72 Comments: 6285
1282. hurigo
P451 so nice to see you again. Glad you got to see the robins fest and I wonder if it proceeded the big storm. Sorry no birds for you now. We were at the beach a couple weekends ago and there were crowds of crows jabbering. They were after some greyish bush berry. Hubby reached up and picked off a twig of it. Not sure what it was but the crows were loving it
Member Since: Posts: Comments:
1280. hurigo
MG: you have buds? I have been attentive to the possibility but none spotted yet. I didn't realize you still had some ice. Did you plant your bulbs (or am I confusing you with someone else?)
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1278. hurigo
WOW. Patch and Mat (nice to meet you): There was a storm of robins today. They were maneuvering haphazardly everywhere and they were chirping as though they had a lot to say to one another. I think they may have been feeding on some of the berry bushes. I do recall having seen this activity before, but my memory is pale as to what happened afterward. I want to say that last time I saw this was before the November n'oyster of 09, but it also could have been before February snow. Makes it especially interesting with the forecast of snow Wed eve through Thur.

P.S. Patch: I made broccoli onion garlic soup tonight. Turned out well but I know it would have been better with local, fresh produce. AND re our earlier exchange re Blizz's future, no, I did not think your comments harsh and I appreciate that it made me think more about my biases. You've always been a gentleman
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TRP thanks for the feedback. You know the old saying: March goes in like a lion and out like a lamb. Hopefully the middle is lamby.

Meanwhile, just watched the rain turn to snow. For a few 10ths of a second, everything just stops. A winter weather advisory is calling for 2-5". I'm thinking it will be closer to the 2", and low ratio.

It was warm today and melted most of the remaining snow but the ice in my back yard is still thick. Anyone care to skate?

Member Since: October 14, 2006 Posts: 1 Comments: 639
Quoting MarylandGirl:
Just came in from raking. 57 here right now. Sedum is growing, min.roses have new leaves, weeds are growing! Buds on my lilacs (tiny) and azaleas. Spring must be around the corner! Can't wait to see what else as I move more leaves!
Thanks RP-I am a little anxious! I know it is to early but fun to think about it!


Oh sounds heavenly
Member Since: October 14, 2006 Posts: 1 Comments: 639
Quoting hurigo:
Hey Blizz, et al.
NWS says we'll have snow (snow/rain mix) starting Wed night, Thursday and Thursday night. Hope it stays warm enough. Saw a field of robins today don't know if they've come up from south or down from north. Also saw an osprey coming in to land and making a lot of racket. I think the birds are ready and I know I am too for spring


Am I correct thinking Osprey's migrate south? and do they migrate south of the outer banks?
Member Since: January 26, 2007 Posts: 72 Comments: 6285
1274. Matlack
Quoting hurigo:
Hey Blizz, et al.
NWS says we'll have snow (snow/rain mix) starting Wed night, Thursday and Thursday night. Hope it stays warm enough. Saw a field of robins today don't know if they've come up from south or down from north. Also saw an osprey coming in to land and making a lot of racket. I think the birds are ready and I know I am too for spring


I was shocked as well on my way home this afternoon saw robins in a grassy patch. Nature has a funny way of letting us know when the worst of the winter is over. But I agree with many of those who think that March and even April may be rough.
Member Since: January 1, 2006 Posts: 0 Comments: 358
Yeah, P451, that arctic high which is moving in is just forcing anything forming, off the coast and out to sea. Just too strong and it's(the arctic high) placement is just too far South and East in my opinion to allow anything up the coast. It does look cold thru Friday.
Member Since: January 31, 2009 Posts: 0 Comments: 8011
Quoting TheF1Man:


At first I thought you meant raking your roof like I was yesterday!

It's that fun time of the year when I'm just about almost willing to be happy for spring and still enjoying/wishing for snow.

DiMartino says winter is definitely not over, but his discussion so far is for premium members.
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Quoting MarylandGirl:
Just came in from raking. 57 here right now. Sedum is growing, min.roses have new leaves, weeds are growing! Buds on my lilacs (tiny) and azaleas. Spring must be around the corner! Can't wait to see what else as I move more leaves!
Thanks RP-I am a little anxious! I know it is to early but fun to think about it!


At first I thought you meant raking your roof like I was yesterday!
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Quoting TrentonThunder:


You had a good 10" or so storm in December though right?


No Richmond got 5".
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Just came in from raking. 57 here right now. Sedum is growing, min.roses have new leaves, weeds are growing! Buds on my lilacs (tiny) and azaleas. Spring must be around the corner! Can't wait to see what else as I move more leaves!
Thanks RP-I am a little anxious! I know it is to early but fun to think about it!
Member Since: Posts: Comments:

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