Saturday, March 2, 2013

"We have a situation..." 
- Actor John Amos in Die Hard 2

11:55 AM EST 3/3/12 (Mid-Atlantic & Southeast Winter Stormcast Teams


  • UPDATE: A major winter weather event is possible for the upper Midwest to the Mid-Atlantic region by mid-week. The storm is currently onshore east of Canada's Coast Range as shown left in the Surface Low Tracks map.
  • Black Ice event overnight as reported by our North Georgia Team indicates overnight low temperatures in other regions are conducive to winter weather.
SNOWFALL PROBABILITY OF 4" OR GREATER WITHIN 72 HOURS

SITUATION: Although the Mid-Atlantic region has been rather tranquil lately, regarding winter weather, that may change drastically into the first full week of March. Indications continue to suggest a possible snowstorm for the region from Wednesday into Thursday. At this point there is high uncertainty with the track of this system, with one scenario going south of the region, and another delivering the mid-Atlantic with a late season snowstorm. 

ANALYSIS: We do expect better consensus later this weekend as the storm is still offshore from the Pacific Northwest and should move inland this weekend. This will allow NOAA ground-based data collection systems to provide more inputs to computer models, and in turn this data  should help projections gain more clarity on potential outcomes. 



Another reason for uncertainty is that this storm would be one part of multiple storms that will have to come together to deliver a major event. Computer models at times, have difficulty  modeling these types of complex systems. Below we outline the two scenarios for this system that we see at the moment. At this time, given the current available projections, we will way each of these scenarios has a 50% chance of occurring as stated.


Scenario A (Storm stays south) In this scenario, the storms do not fully come together until they are off the coast and so the storm pushes off the GA coast. 
This would lead to a minimal effect to the mid-Atlantic region with portions of central & northern VA possibly receiving light snow from the system. 
Scenario B (Storm comes north) With this scenario, the storm systems come together early enough to move north into the mid-Atlantic and provide a snowstorm for portions of MD, WV, DE, NJ, and PA. Depending on how far north the system moves there could be some areas of mixing across portions of the mid-Atlantic, limiting any snow accumulations that may fall for the areas with a mix. Another concern with this scenario is that being late in the Winter season, the higher sun angle could also limit snow accumulations.  
Some areas could receive a significant snowfall from this system. 
WHAT WILL MAKE OR BREAK THIS STORM? – There are several factors that are both working for and against this storm. The atmospheric pattern is more favorable than anything we have seen since January 2011, but since we are in the month of March, a lot of issues prevent large snowstorms. 
  • Sun Angle – If snowfall occurs during the day while the sun is up, it will be very difficult to stick. As a result, even if a lot of snow falls during the day, it may have trouble sticking. We are rapidly approaching the equinox, and the sun angle is currently equivalent to early October. If snow falls at night, the impact is relatively insignificant.

  • Temperatures – Average temperatures for March during the day in the Mid-Atlantic are  already into the 50s for some places. It is possible that even if the upper atmosphere pattern is conducive to snow, the surface temperatures may promote rain.

  • North Atlantic Oscillation – This is a measure that we look to often, especially the winter. It is basically a measure of the pressure differences in the north Atlantic Ocean, and can create blocking when in the negative phase. A negative NAO often forces a trough and cold air into the eastern United States and increases chances for snow. Currently, the NAO is in the negative phase. However, we have found that the direction the NAO is going is equally important. A negative NAO that is dropping tends to suppress storms further south, while a negative NAO that is rising can pull the storm up the coast. It remains to be seen what direction it will be going next week. 

  • Arctic & Pacific patterns  – The other teleconnections are very important as well. The Arctic Oscillation is currently in the negative phase (forces cold air south) and the PNA is in the positive phase (a ridge in the west pushes a trough into the east). With favorable indices for snowstorms in all three major teleconnections for the first time since January 2011, this does bear close watching.

So what does this mean? Well don’t go buy your bread and milk yet, but stay close to your authentic local teams here with Foot’s Forecast as we work to determine where this storm will track next week.

Lead Writers:
Mid-Atlantic Winter Stormcast Director Zach Fasnacht  (State College, PA)
Central Maryland Lead Forecaster Mike Natoli (College Park, MD)


15 comments:

ravensbbr said...

Still a good ways out...but love how it's looking for us MD/PA folk!!!

http://coolwx.com/cgi-bin/getptype.cgi?region=us&model=gfs&run=18&fhr=99&field=ptype

Andy, Southern York County Pa said...

Looks massive. Potential foot +. We will know better by sunday night as to details etc.

Unknown said...

Hmm.....the temps under-performed quite well today. Do you believe that this could be a sign that the airmass is cooler than we think? If so, than this could be beneficiary to the storm on Tuesday/Wednesday. BTW how much are you concerned with the temps. I've heard that if the storm takes too much of a north shift, Baltimore would see more rain. You're take?

BioPat said...

Lookin' good, let's hear it for a significant snow storm to catch us up to where we should be this year. Still too far out we've watched many storms stay south and off they go, OTS. Let's hope this one holds the course fo us.

BioPat said...

This should prove to be an interesting week. It appears the models are falling into alignment with a mid-Atlantic snow storm at mid-week. I love the television "meteorologists" that are advising people to prep - as if we won't be back in the stores on Friday.
I for one really look forward to a snow day or 2, but I won't be greedy; Id be overjoyed with just a day. However, I do need to lesson plan a bit to be ready for the event. My guys will be overjoyed at just the planning changes in anticipation of the "snow feast".
I am concerned about a March snow storm bringing us a heavy wet snow. These are the ones that bring on heart attacks from those shoveling and also cause significant damage just by the weight of the snow. If, in fact, this is coming together; prepare well and be careful.

Andy, Southern York County Pa said...

Models continue to support a general 12 inch snowfall for the region. Details will come into better focus by tonight. I could see some reports as high as 18 inches if trends continue.

Andy, Southern York County Pa said...

12z GFS is taking the storm slightly further north placing Baltimore in a better position. This is starting to solidify and has the makings of a truly historic March storm. Foot plus idea is looking really good.

Foot's Forecast said...

Winter Stormcast Team will be adding more sticks to the drumbeat later today... time to get ready for a last hurrah of Winter 2012-13.

(Mr. Foot)

NeedaSnowday said...

Trying to temper my excitement....

ravensbbr said...

Sooooooo...does anyone know how to get snowthrower shoes back ON after you took them off to inspect them?


Andy, Southern York County Pa said...

The 18z GFS crushes central md with a solid 18 inch region wide snow. I am impressed.

Unknown said...

The 12z EURO: Should we be concerned?

Andy, Southern York County Pa said...

I always pay attention to the Euro Op. The op is the outlier though as its ensembles have been north. The storm is entering into a data rich environment now and we have a better data set in the model. With the GFS and Nam getting wetter and more north as time goes on the Euro OP will likely shift north. Anything is possible and who knows it may score a grim win of sorts, but it is increasingly the outlier and we are getting to the 48 hour time range for the storm. The Euro Op shifted North with the Feb 2010 blizzard inside 48 hours where the GFS scored a big win, so it is not without precedent.

I think the Euro OP will shift and if it does welcome to the Great Mid Atlantic March blizzard of 2013. TIME WILL TELL.

NeedaSnowday said...

me thinks I better test the generator... GFS unloads a heap o' snow!

BioPat said...

Andy I do like the way you're talking! I think we're due for a record setting March, we definitely need something to chat about over the next few days. This winter has been far too quiet on FF chat, perhaps the whole old gang will join us by tomorrow!