Monday, November 24, 2014

11 comments:

Red Pill or Blue Pill?
(Sorry Ravens fans, no Purple Pill this time...)

WINTER STORM WATCHES POSTED FOR MID-ATLANTIC & NORTHEAST
(Click on link above to see latest watches and your local NWS office)




MARYLAND: NEAR 70 DEGREES MONDAY, 5 OR MORE INCHES WEDNESDAY?!?

3:55 PM 11/24 UPDATED: Scenario A & B Map Below

  • Special FREE teleconference briefing available Tuesday late AM and early PM to ask our forecasters your questions about the storm. Send us a message to winter(at) footsforecast.org to register for the call. Indicate what weather information about this event would aid your decision-making. 
  • Four (4) time slots will be available, pick any of them at your convenience.
  • For companies or organizations, denote one representative who can report back to your group. A briefing package will be sent Tuesday AM with call-in details.


OVERVIEW (By Forecaster Mike Natoli) Regardless of heavy rain or snow, we all are likely to see a disruptive storm moving up the East coast at the very least. 
  • We have refined our ideas to two scenarios depending on surface temperatures. Temperatures will be marginal, near or slightly above freezing, which will initially make snow accumulation difficult. However, as computer models have been projecting for the past 24 hours, high snow fall rates may overcome warm surfaces and create a surprise situation Wednesday afternoon.
  • We remain cautious on this storm, because a slight shift of precip arrival or type over just 2 hours on Wednesday morning will impact the entire day's forecast. If we decide we need to make a snow accumulation forecast, that will be issued either later tonight or Tuesday morning. Until then we have narrowed the potential outcomes to TWO SCENARIOS, outlined in the next section.


5 comments:
Get Ready For BOOM!

MAJORITY OF COMPUTER MODELS POINTING TO A 
PERIOD OF HIGH IMPACT HEAVY SNOW WEDNESDAY  PM 
ACROSS THE NORTHEAST METROPOLITAN REGION.

10:45 AM EST 11/24 UPDATED: LATEST SNOWFALL PROBABILITIES from the NOAA Weather Prediction Center should give ANYONE pause if you plan to travel Wednesday, or are in essential services. Teachers, this is a great opportunity to show your students why understanding the legend on a map is critical to good decision-making.
  • INCREASING PROBABILITY OF AT LEAST 8"  NORTH AND WEST OF THE I-95 CORRIDOR. As noted below in the green banding. Source: NOAA WPC Winter Suite
  • CURRENT DATA PROJECTIONS SHOW AT LEAST 0.50" LIQUID FALLING AS SNOW 12-6 PM WEDNESDAY IN METROPOLITAN MID-ATLANTIC. Source: GFS for BWI


THE TAKEAWAY? We don't care that it's going to be 70 F today in some places. That's the ruse. Don't fall for it. How many thousands of travelers on Wednesday will allow today's aberrant warm weather to fool them into false security that "roads will be just fine, sheesh. Not like it's January, right?" 

WRONG: The issue WILL NOT be snow covered roads, it will be VISIBILITY due to heavy wet snow combined with high volume traffic. One person decides to slow to a crawl on 95 at 3 PM in the snow, and BOOM. There goes your holiday weekend. Think about it. Plan ahead. Consider how you can adjust your plans now before reality hits and its too late.

OUR FEAR: Unless something changes drastically in the storm track trends, this series of unfortunate events on the Wednesday before Thanksgiving could become the worst day of mass travel in modern times, if we have a repeat of January 26, 2011.


3:20 AM EST 11/24  Overnight, a trend among most computer models began to take shape, and is centering on what could be considered the "worst case scenario." For those following our Options A, B and C -- it suggests one outcome: Our Goose Is Cooked.
  • Despite today's summer-like feel of temperatures spiking to the 60s in many locations, an equally fast crash back to the 40s comes on Tuesday;
  • Sun angle is now comparable to mid-January, so daytime heating will be a non-issue;
  • By Wednesday Noon, cold rain from the Blue Ridge to the Mid-Atlantic should begin mixing with and rapidly changing to snow. 
  • In just a 6-hour period, precip charts shown below for both BWI and PHL airports depict that over 0.50" of liquid is expected to fall AS SNOW. Need a visual? The "snow monsoon" of January 26, 2011 is our closest example of what to expect. 
SOURCES: GFS LIQUID PROJECTIONS FOR BWI and PHL on coolwx.com

REMEMBERING THE SNOW MONSOON: On that day, in the Baltimore-Washington area, a quick early hit of snow closed many schools, then a changeover to rain washed away most of the snow. Around 4 PM, cold air swept back in turning the rain to snow again. You'll recall fond memories of 7 inches falling in just 3 hours - stranding thousands in their cars. 

The problem today is identical to then: Road crews could NOT pretreat because it was raining all day. When the snow came, plows and salt trucks were as helpless as the rest of of us. We are NOT whistling dixie or playing up for ratings. This is the real deal, again.

LESSONS LEARNED: Forget the 70 degrees today, it's a fluke. We urge school districts, road crews, operations centers and transportation systems to BE PREPARED for a complete repeat of this situation on the WORST possible day travel day of the year. Improved technology has provided a more refined look at the potential, and we feel in the interests of public safety and travelers, we are obliged to convey this information for all.

For the computer model followers: A look at last night's European projection for 7 PM Wednesday shows heavy precipitation plastering the entire Northeast corridor with heavy coastal rain and inland heavy wet snow. 


The Foot's Forecast Winter Stormcast Team

Sunday, November 23, 2014

10 comments:
Turkey in the Snow?
MID-ATLANTIC AND NORTHEAST MAY SEE FIRST 
WIDESPREAD WHITE THANKSGIVING SINCE 1989

7:30 PM EST 11/23 - UPDATED - Discussion of scenarios below. 

NOAA Snow Probabilities: Moderate (40%) chance of 4" for Northeast US


1:05 PM 11/23 (By the Kentucky & Winter Stormcast Teams) Although the Thanksgiving holiday period is finally arriving, Mother Nature shows no signs of taking time off as the potential is increasing for a significant weather event that could snarl one of the busiest travel days of the year.

THE SITUATION: Our team first identified the potential for a "White Thanksgiving" in an October 25 post, due in part to data showing a record high snow-cover for Siberia and the downstream effects that large Arctic highs would have coming across the Pole. Now in present day, numerous medium range model runs support a significant winter storm occurring on Wednesday into Thanksgiving morning near the East coast. 
  • The areas which may see notable to significant impacts from this system extend from South Carolina to the Mid-Atlantic, into the Northeast all the way to Maine. 
  • As with all storm forecasts more than 72 hours out, we expect considerable variance between forecasted data and outcomes, until shortly before the event begins.
  • The timing of this system creates additional concern for the traveling public, hence we are outlining scenarios early to help identify which pattern will prevail.


SCENARIO A: OUR GOOSE IS COOKED. An area of low pressure develops in the northern Gulf and moves along the East coast, bringing Gulf moisture while drawing in Atlantic moisture. The system would tap cold air from a snow-cover influenced surface high in western PA/NY. 

  • This track would hug the shoreline, bringing heavy rain and tidal flooding to coastal communities and heavy snow in the interior. 
  • As temperatures fall into the 30s through the Mid-Atlantic and Northeast, rain would change to snow in the major cities and continue heavy overnight, producing  a major snowfall to a majority of the Northeastern states. 
  • CNN features long lines of weary travelers stuck in airports.
The latest liquid projections by the US Global Forecast System for BWI airport show why there's much concern for Scenario A. Nearly 1.0" of liquid falling as snow would be a major problem.

SCENARIO B: BETTER LEAVE EARLY ANYWAY. The storm develops weaker and further east than in Scenario A. This would produce far less precip for the Carolinas, Mid-Atlantic and Northeast. 

  • However, colder air will be more available, as northwest flow would rush in behind the departing storm. Coastal areas would see a cold rain or wet snow that has trouble sticking until after nightfall Wednesday. 
  • The bulk of energy would affect northern states, especially New England while the Mid-Atlantic is only brushed with light accumulations. 


SCENARIO C: CANCEL THE SNOWSUIT SEARCH! Strength and influence of the Great Lakes system on Tuesday nudges any coastal Low pressure away from the eastern seaboard, in tandem with surface high pressure to the north. 

  • This would bring only brief light precipitation to coastal areas, little or no precipitation to major cities and minimal impacts on Thanksgiving travel.

Our Winter Stormcast Team will be frequently monitoring the latest changes and updating here as data becomes available. Our next update is planned for Monday where we will narrow the scenarios to 2 options and begin discussing precip and snowfall ideas.

(Report by the Kentucky Team: Forecasters Kyle Jackson, Darius Mack, and Lead Forecaster Chris Reece. Additional content by Maryland Team members Mike Natoli, Connor Meehan, Joey Krastel and Rich Foot)