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 Blizzard92:

Good call by them. Some of us may even see a few inches of sleet accumulation. This storm is going to be nasty.


Any predictions yet?
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Quoting Blizzard92:

Good call by them. Some of us may even see a few inches of sleet accumulation. This storm is going to be nasty.


i'd rather see sleet than fz-rain because sleet counts as snow when measuring which would increase my ytd
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Quoting Mason803:
ctp went all in with warnings


I'm not even under a watch, but we have a parking ban starting tomorrow afternoon..LOL
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NOAA must be getting a lot of hits today. I can't get into the regional forecast.
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Quoting Mason803:
ctp went all in with warnings

Good call by them. Some of us may even see a few inches of sleet accumulation. This storm is going to be nasty.
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ctp went all in with warnings
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Quoting TheF1Man:


Link

Where do you live in CT again? Somewhere near my house i believe?


I'm in Norwalk
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Member Since: July 15, 2006 Posts: 187 Comments: 57781
Member Since: July 15, 2006 Posts: 187 Comments: 57781
Quoting IceCoast:

They updated that map pretty quick!! They have me at 20 inches now. Are you down by the CT/MA border?


Yep exactly, I'm in springfield for school
Member Since: February 23, 2010 Posts: 0 Comments: 738
Quoting danielb1023:
All, I think Joe Lundberg does a nice job on (the site that shall not be mentioned) describing the severity of this storm. Goes through all of the components and the dangers they present. I didnt bother with the video but the written portion is a good read.


I agree that he does a nice job. Some of the individual meteorologist do a good job on their blogs but have you ever noticed that the maps that they show on the blogs never agree with what the "site" forcast is. For example it is currently showing for Harrisburg 1.2 inches of snow and a "bit of ice" for Wednesday. A BIT? I'd say a quarter-half and inch of freezing rain is a bit.
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Quoting TheF1Man:
IceCoast they've updated it again, and that one was only a couple of hours old. They've moved increased overall amounts and i'm now at about 14"

They updated that map pretty quick!! They have me at 20 inches now. Are you down by the CT/MA border?
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Quoting SilverShipsofAndilar:


What makes you say that?

Totals all shifted south.  11:35am map from Taunton had the 10in line across extreme northern RI and CT.  the 12:48 update puts those same areas in 13-14 and moved the 10 inch line much closer to the coast.
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Quoting SilverShipsofAndilar:


What makes you say that?


1)wishful thinking and
2) wishful thinking!
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Quoting danielb1023:


That looks colder no?


What makes you say that?
Member Since: December 1, 2008 Posts: 0 Comments: 600
Quoting TheF1Man:
Yeah Lt I can't wait!

I'm not sure if this is the new NAM as i'm still learning the models. 60 hours.



That looks colder no?
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Quoting SnowinCT:

do you have a link for this map?


Link

Where do you live in CT again? Somewhere near my house i believe?
Member Since: February 23, 2010 Posts: 0 Comments: 738
Yeah Lt I can't wait!

I'm not sure if this is the new NAM as i'm still learning the models. 60 hours.

Member Since: February 23, 2010 Posts: 0 Comments: 738
Quoting TheF1Man:
IceCoast they've updated it again, and that one was only a couple of hours old. They've moved increased overall amounts and i'm now at about 14"





do you have a link for this map?
Member Since: Posts: Comments:
All, I think Joe Lundberg does a nice job on (the site that shall not be mentioned) describing the severity of this storm. Goes through all of the components and the dangers they present. I didnt bother with the video but the written portion is a good read.
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Quoting Hoynieva:


Southern Maine should get a lot of snow. At least a foot, probably closer to two.


Whoo hooo, I'm ready!
But I do feel a little guilty wishing this upon the wildlife, so I'll whip up a double batch of peanut butter suet tomorrow for the birds - as a peace offering :)
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Quoting crowe1:


Big time slow.


It's all jammed up!
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Quoting bwi:
Winter storm watch extended further south into Maryland.


WSWatch for MoCo MD up Tues PM through Wed. 1/4" of ice expected. Tonight should be minor w/light sleet/ice, so they are saying.
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TheF1man, you are going to get a real good snow total--cancelled classes anyone! Good luck.LT
Member Since: January 31, 2009 Posts: 0 Comments: 8011
Quoting sunnysmum:



Just huff and puff and blow it up here to Maine! I'm still waiting for my big storm.


Southern Maine should get a lot of snow. At least a foot, probably closer to two.
Member Since: January 20, 2009 Posts: 0 Comments: 1763
IceCoast they've updated it again, and that one was only a couple of hours old. They've moved increased overall amounts and i'm now at about 14"




Member Since: February 23, 2010 Posts: 0 Comments: 738
Quoting bwi:
NWS websites running slow for me. Maybe they need to take down some graphics or buy more bandwidth for big storms.


Big time slow.
Member Since: January 26, 2007 Posts: 15 Comments: 953
Quoting CTfireman:
connecticut shoreline
36.0 f
sunny and melting nicely
hoping this whole thing goes out and hits the fish



Just huff and puff and blow it up here to Maine! I'm still waiting for my big storm.
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289. bwi
NWS websites running slow for me. Maybe they need to take down some graphics or buy more bandwidth for big storms.
Member Since: September 4, 2007 Posts: 0 Comments: 1586
connecticut shoreline
36.0 f
sunny and melting nicely
hoping this whole thing goes out and hits the fish
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Quoting 900MB:
One more rose colored glasses observation.
High for Weds now forecast for 35 degrees (was 38 earlier). Much of the storm forecast is for 29 degrees and freezing rain. The only hours above freezing for the next few days is from 2pm-8pm weds (33-35 degrees). Just saying, a slight shift East or slightly colder air and who knows? After all, 48 hours ago we were in the blizzard target.

Now, back to reality....


The trend all winter has been to be colder than what is shown 36-48 hours prior to the event. Not saying that will happen but wouldnt shock me. Once the low forms off the coast I would suspect that temps along the coast will stop rising and begin their descent. Like you said, it could be only about 6 or so hours above freezing although those are likely the 6 hours with the highest precip amounts. Interesting storm...........
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286. bwi
Winter storm watch extended further south into Maryland.
Member Since: September 4, 2007 Posts: 0 Comments: 1586
285. 900MB
One more rose colored glasses observation.
High for Weds now forecast for 35 degrees (was 38 earlier). Much of the storm forecast is for 29 degrees and freezing rain. The only hours above freezing for the next few days is from 2pm-8pm weds (33-35 degrees). Just saying, a slight shift East or slightly colder air and who knows? After all, 48 hours ago we were in the blizzard target.

Now, back to reality....
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284. 900MB
Quoting Hoynieva:
900MB, this will not be anything like the storm from last week (for us anyhow). But, we will likely add about 4 to 6 inches of snow on top of our annual total before the change over occurs. Sleet on top of that before freezing rain and rain turns the snow to cement. That will put us past 60" with a lot of winter left still.


It's been quite a year!!! Still think we'll sneak 6-8" before changeover. Looks like 24 hours of snow, sleet, and freezing rain (6am tues-6am weds) before straight rain.
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NWS Taunton MA first take on totals. I'll take another 18 inches!! Still must have close to a 30 inch base on the ground here in Methuen.

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Not to mention there are several more storms on the conveyor belt following this one.
Member Since: January 20, 2009 Posts: 0 Comments: 1763
900MB, this will not be anything like the storm from last week (for us anyhow). But, we will likely add about 4 to 6 inches of snow on top of our annual total before the change over occurs. Sleet on top of that before freezing rain and rain turns the snow to cement. That will put us past 60" with a lot of winter left still.
Member Since: January 20, 2009 Posts: 0 Comments: 1763
280. 900MB
Quoting originalLT:
Hi 900mb, I guess what they are figuring is that the primary low will be strong enough and positioned so that it will pull in enough warmer air from the East and Southeast, before the secondary forms and takes over and pulls the cold air back in again. I really don't see anything like another 19" in NYC, maybe a half a foot when all is said and done , with plenty of ice and some sleet. I hope I'm wrong though, I'd rather see alot more snow.


I guess it all comes down to where the low sets up and I am getting mixed signals. Some see a low over Eastern PA, and with that I understand our warm up and rain, but others are pointing to off the Delmarva or off Jersey. Off Jersey I can see how we'd get a might mix, but a little further out and I think we are in the same boat as the last storm. So, I guess the consensus has the low too close or West of NYC.
But, how can I complain- 56" of snow and counting this season!
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Breald,you shouldn't be too bad down there,but for me north of I-90,whole different story,I think the cold high pressure is going to have a lot more influence on this system then we think.
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12z NAM still has over 1" of ice for all of central PA, with up to 1.25" in some locations. Hopefully the NAM is overdoing the QPF as it usually does and these amounts will be somewhat less. The last ice storm we had was around .5" accretion and I lost power for three days. I don't want to see what an inch of ice would cause.
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Everything I find puts me between 15-20". As many have said all ready, "I'd rather have lots of snow than a little ice."
Member Since: January 26, 2007 Posts: 15 Comments: 953
Quoting originalLT:
Hi 900mb, I guess what they are figuring is that the primary low will be strong enough and positioned so that it will pull in enough warmer air from the East and Southeast, before the secondary forms and takes over and pulls the cold air back in again. I really don't see anything like another 19" in NYC, maybe a half a foot when all is said and done , with plenty of ice and some sleet. I hope I'm wrong though, I'd rather see alot more snow.


I agree. This obviously not going to be that big of a deal for most of Southern New England and the coastal Mid Atlantic states.
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Hi 900mb, I guess what they are figuring is that the primary low will be strong enough and positioned so that it will pull in enough warmer air from the East and Southeast, before the secondary forms and takes over and pulls the cold air back in again. I really don't see anything like another 19" in NYC, maybe a half a foot when all is said and done , with plenty of ice and some sleet. I hope I'm wrong though, I'd rather see alot more snow.
Member Since: January 31, 2009 Posts: 0 Comments: 8011
274. 900MB
Quoting ConnecticutWXGuy:
I doubt the rain is going to make it much past I-95 in SNE. The low looks to redevelop off the NJ coast just in time to stop the northward progression of the rain/frozen precipitation line. Keep in mind that the models are likely running a bit too warm, as well... as they have been all winter.

Meh, I'm not ready for rain yet anyway. Bring on more winter weather! I've already seen some things this winter that I've never seen before, like 35 inches of snow on the ground at one time. I'm ready for more. We've had 70+ inches in a month, let's see if we can get another 70 in here. Now that'd be a winter to remember even if March and April turned out to be busts.

What can I say, I'm a storm lover. There's nothing good about cold weather unless it's stormy.


My forecast is pretty darned similar to the last storm- snow, ice, sleet, rain, and then snow for NYC with accumulations of 2"-5" and up to a half inch of ice. Last time we had this forecast we ended up with 19" in the Park!

Can I believe that it will really warm to 38 degrees on Weds? Thoughts?
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I know, Sorry Dan....I don't even like me this week

TRP, I wish I could do that, but this is pretty much a turbo trip I'm doing and our rainforest zip line/jungle trek and snorkeling outing have been booked. At most I could be delayed 18 hours and still make it in time. Fortunately it's a direct flight so I won't have to worry about delays in any other airport.

And as for moving it to tomorrow, well, that would cost too much. If they were offering, I'd definitely do it, but they're not.
Member Since: January 20, 2009 Posts: 0 Comments: 1763
Quoting Hoynieva:
Allow me to be the voice of insanity.

Not liking the trend toward colder temps...

Need it to change to rain here for wed afternoon.



Hoy - just curious did you look into moving your flight out up a day? i did that in the Dec. 2007 storm and was so glad I did. just something to consider, even if it is for a few bucks.
Member Since: January 26, 2007 Posts: 72 Comments: 6276
Quoting Hoynieva:
Allow me to be the voice of insanity.

Not liking the trend toward colder temps...

Need it to change to rain here for wed afternoon.



Have I mentioned I dont like you this week!?!
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Allow me to be the voice of insanity.

Not liking the trend toward colder temps...

Need it to change to rain here for wed afternoon.

Member Since: January 20, 2009 Posts: 0 Comments: 1763
Springfield, MA channel 40 (WGGB) is being very pessimistic and calling for a major ice storm in south central MA and northern CT. Their discussion suggests up to an inch of ice accretion, which means power outages. I'll take 6 feet of snow over 1 inch of ice any day! Someone, tell me this map won't be so!

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S
Quoting breald:
The immediate coast from RI east to Cape Cod is the only area without a watch in SNE. I think we are going to get much of anything from this storm.

I dont know Breald, you could see 3-6 inches there before icing. Suprised you dont have a watch yet. Wouldnt be suprised if one pops up there soon.

Member Since: December 17, 2009 Posts: 0 Comments: 796

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Cornell University- Atmospheric Sciences Undergrad; Research Assist.- Onset of Spring Indices Toolbox; Interests- Small spatial scale climatolology

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