Friday, March 22, 2013

The Winter That Wasn't...Won't Leave

9:45 PM EDT 3/22 (Forecaster Mike & Winter Stormcast Team) The calendar may have flipped to spring, but the weather is stuck in winter. With highly unusual cold for this time of year, across  much of the U.S., all it takes is a storm to form and rare spring snows may start. As a result of this chill and wintry pattern, there may be another winter storm in the works at the end of spring’s first weekend to impact the Mid-Atlantic Sunday night into Monday. The good news? We currently do not expect a major, high impact snowstorm is at this point, but some inland areas are likely to receive accumulating snow. 
(Photo credit: Fusion Photographer Emily R., Carroll County MD)

WHY SO COLD? - This excessive cold pattern of late has been caused in part by a near record low value of the Arctic Oscillation (AO). When the AO goes so negative like it is currently (shown by the sharply decreases on the graphic to the right)  it creates an upper level “block” in the atmosphere at high latitudes, and this displaces the cold air. In response, the cold air has nowhere to go, so it floods southward into the United States. 

We have limited the possibilities down to two scenarios that we believe are most likely. At this point, we think that Scenario A is the more likely of the two, but we cannot eliminate Scenario B just yet. 

CURRENT SNOWFALL PROBABILITIES FOR 4 OR MORE INCHES, SUNDAY NIGHT - MONDAY 

Source: NOAA Weather Prediction Center
  • SCENARIO A Most Probable: "The Warmer Storm" In this scenario, the low pressure center would take a more northerly track, and flood warm air in off the ocean. Since the storm has access to only marginal cold air, it would be forced to create its own, but due to low precipitation rates, more rain would dominate. 
POSSIBLE RESULTS?  Coastal areas of the Mid-Atlantic would be all rain. For those along the I-95 Corridor, this scenario would bring rain, with snow mixed in at times, but little accumulation. In this case most of the snow would be confined well NW of I-95, and at higher elevations. 

  • SCENARIO BLess Probable: "The Colder StormIn this scenario, we would have the storm staying a little further south. Instead of pulling warm air off the ocean, it may have access so some cold air being fed from the north, but the set up is marginal for that as well. 
POSSIBLE RESULTS? With more cold air available for the storm to work with, we would be looking at snow reaching the I-95 corridor and the major cities. Accumulations would NOT be extreme, but given the time of year, even light accumulations are noteworthy. For the coast, this scenario would bring rain with snow mixing in at times. 

Check back later tonight for an update from the weather graphics team that will visually depict these scenarios, and thanks for your interest in our information. (Forecasters Mike N., Connor M., Jason M., Zach F., Meteorologist Alex D., Advisor R. Foot)


17 comments:

BioPat said...

So, Andy what do you think. I know the models are looking good at the moment, but we've been taken too many times this winter. I'd love to see it but experience i a hard teacher.

ravensbbr said...

18Z NAM looks interesting...looks like most of the precip at this point could fall during the rel. colder hours and more critically, w/o the ever-increasing sun angle...

BioPat said...

JB is showing comparative data winter, 1942 and winter, 2013 - could prove to be a very interesting analysis.

Unknown said...

March 29-30, 1942: The Palm Sunday Snowstorm dumped the state's heaviest March snow on record in Maryland. The storm began as rain but changed over to a wet heavy snow. The snow stuck to power lines, trees and shrubs damaging them under its weight. Many of the fruit trees had begun to blossom. Over 20 inches fell over northern Anne Arundel, Howard, Southern and western Baltimore County, Carroll County, eastern and northern Frederick County, and north-central Washington County. Maximum amounts reported were 31 inches at Clear Springs (just 12 days earlier the temperature had reached 79�F here), 32 inches at Westminister, 30 to 36 inches at State Sanatorium (Frederick County) and 36 inches at Edgemont (Washington County). Baltimore City received its greatest snow in 20 years with 22 inches measured. Hagerstown and Westminister reported 22 inches in 24 hours. Frederick had 17 inches in 24 hours. Washington, DC received a total of 11.5 inches of snow.

Unknown said...

http://www.erh.noaa.gov/lwx/Historic_Events/md-winter.html


This is my source.Great site has all the major Snow events recorded thruout the years.If you pull it up,ENJOY!

ravensbbr said...

Good site, Mike, have to check it out further. Looks very informative.

BioPat said...

Thanks Mike for the info, perhaps we'll have a chance to read more as the storm moves in over the weekend.

ravensbbr said...

Anyone see the fireball tonight???

Missed it, re-watching Zero Dark Thirty with the wife, she hadn't seen it yet. Seeing as our first date was the great Leonid meteor shower of 2001, we would have traded the movie for seeing this one in a heartbeat. Anyone get a picture of it?

Andy, Southern York County Pa said...

I am in the wait and see bench warming mode. I would honestly be blowing the horn if this were modeled 4 weeks ago, but the time of year is a big strike against this. Large snowstorms are POSSIBLE even into the first week of April, but again we are talking about climatological anomalies.

For this storm to be one for the books and produce a widespread plowable snow everything has to go right as the set-up is fragile.

1) We need heavy precip rates to overcome the low level warmth generated by the high sun angle. We are HISTORICALLY FRIGID for this time of year despite sun angle so the anomalously historical cold is why we are even talking about snow. (20 degree below normal highs is remarkable)

2) We need the bulk of the precip to fall at night with the heavy rates to pull down the coldest air to the surface to chill the ground levels that have absorbed and reflected solar radiation from the day high sun angle.

3) The transfer of energy from the Ohio Valley Low to the Coast has to happen perfectly assuring the best dynamics to remain over us.

4) Nam has led the way with showing a comma like signature when the transfer first occurs. The Euro picked up on this last night. 6z GFS looks very promising.

5) This is a fragile set-up and everything has to go perfectly to give us a 4-8 inch plowable snow which is the max potential here in my opinion.

6) If we do not get the rates, night time heavy precip, perfect transfer etc then we are only talking about a slushy 1-2 inches on the grass, cars, trash can lids event that wets the sidewalks and roads.

7) We will know better by this evening where we stand, but I EXPECT THE NWS TO ISSUE WINTER STORM WATCHES FOR MOST OF US BY THIS AFTERNOON REGARDLESS. Whether or not they result in WARNINGS or ADVISORIES by Sunday morning for Sunday night into Monday time will tell. This storm looks GREAT on the MODELS but has a LOT of CLIMATOLOGY against it.

ravensbbr said...

Thanks, Andy!

Got an e-mail from my NWS buddy in Sterling, they think similar to you, but having been burned so much this year, they're wait and see as well.

He was optimistic about the majority of the precipitation falling from sundown to sunup...

Unknown said...

J Bastardi posted on his twitter acct the latest projections from the NAM. I am unable to put the screen shot on the blog. I have tried everything I know. It has the east in pink 10-12 inches! He is starting to get on the bandwagon.I am not saying I agree,just informing you of what I am seeing/reading.Let me know if there is a way to post the screen shot I have.

Andy, Southern York County Pa said...

Winter storm watches will likely be posted overnight. All trends have been wetter and colder.

BioPat said...

Saw the models that JB posted a few hour ago, they all seem to be in alignment - that's novel but show a colder wetter scenario than earlier forecasts. So, now we wait. I refuse to jump on this bandwagon until I'm looking for the snow shovel.

Andy, Southern York County Pa said...

I agree with BP. We may get 12 inches of snow but no more than 2 may stick to the ground at any given time. Sun angle is nuclear and if we dont have heavy rates we dont have accumulation

Unknown said...

Andy, that's if this storm falls during the day. If we get heavy snow at night, then it's a whole different story.

ravensbbr said...

Jeremy, you're right. this thing hits at night, well, the nighttime lows up here last night were barely in the upper twenties...

#WINTEROF1942ALLOVERAGAIN:-)

ravensbbr said...
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