Thursday, February 16, 2012

Joining forces 
Atmospheric pattern and model projections pointing 
to a Mid-Atlantic Winter Storm Sunday into Monday


5:10 PM EST 2/16/12  We offer this composite overview map of snowfall potential for the #PDIII snow event this weekend in the Mid-Atlantic. Note that we have not established snowfall amounts, but for now are focusing on liquid equivalents until the event gets closer.


ABOUT THE SNOWFALL PROJECTION MAP
  • Preliminary: This is a preliminary estimate of areas where we believe snowfall may accumulate in the late Saturday to early Monday period (2/18-20/2012). 
  • Map Colors: Bright white on this map represents where we believe the best chance for "plowable snowfall" may occur. The grey color on this map indicates more of "nuisance" snowfall which may still require removal.
  • Amounts: Snowfall ranges and specific amounts are generated once onset of snow in the region is within 48 hours. 
  • Timing: We will issue an updated version with a timeline this evening.
Credit for this map goes to Forecaster Jason Warren of our Ohio Valley Winter Stormcast page, which you can view on Facebook. Additional details will be posted in the main site Winter Stormcast tab as we approach the evening.

12:30 PM EST 2/16/12 Latest model runs have indicated more consensus is developing in the project data for a potential President's Day weekend storm. The GFS model (mid-range model) and the NAM (short range model) have both painted a very similar solution which is an increasing wintry scenario for the Mid-Atlantic states. 


NOAA model projection for 8 AM Sunday morning shows low pressure moving through the Carolinas, with the  5,000 foot freezing line parallel with I-68. Liquid amounts from GFS suggest about an inch of liquid could fall, but the big question is how much of that liquid falls as rain and how much falls as frozen precipitation.

Additional details on this developing situation for the region are posted in the Winter Stormcast Zone.   (Forecaster Greg J. and the Foot's Forecast Winter Storm Team)

9 comments:

Andy, Southern York County, PA said...

With a system like this it is never a good idea to post snow totals 3 days out because things will change.  The feb 2010 blizzards were modeled to be a big hit north of Philly in one storm, and a big hit near Richmond for the other.  Final result we were hit.  As the storm gets closer expect model shifts.  I never want to be in the Bullseye 3 days out becasue it will change.  Sometimes for the worse, but also for the much better.

Andy, Southern York County, PA said...

PLENTY OF UNCERTAINTY AND MODEL MAYHEM TO CONTINUE.  THAT"S WHAT MAKES TRACKING A STORM FUN! :)

<pre><span>MODEL DIAGNOSTIC DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
219 PM EST THU FEB 16 2012

VALID FEB 16/1200 UTC THRU FEB 20/0000 UTC


...SEE NOUS42 KWNO ADMNFD FOR THE STATUS OF THE UPPER AIR INGEST...

12Z NAM/GFS EVALUATION INCLUDING THE ECMWF AND PREFERENCES

...SHORTWAVE TROUGH OVER THE OHIO VALLEY...

LARGE-SCALE MODEL FORECASTS ARE SIMILAR.

...UPPER LOW NEAR SOUTHERN CALIFORNIA...

PREFERENCE: GFS OR 00Z ECMWF

THE SOLUTION SPREAD IS QUITE SUBSTANTIAL FROM SATURDAY
ONWARD...WITH THE LOW'S TRACK POSSIBLY DEPENDENT UPON THE
EVOLUTION AND INTERACTIONS OF 3 SEPARATE SHORTWAVE TROUGHS MOVING
TO ITS NORTH. MODEL INITIALIZATION OF THESE SYSTEMS IS A
CONCERN...PARTICULARLY THE SHORTWAVE TROUGH ENTERING BRITISH
COLUMBIA...WITH MID-LEVEL DIAGNOSTICS FIELDS FROM THE GFS ALIGNING
BEST WITH THE STRUCTURE SEEN ON WATER VAPOR IMAGERY COMPARED TO
THE NAM AND ECMWF...WHICH APPEAR WORST. AMONG THE REMAINING
SOLUTIONS...THE CANADIAN PRODUCES AN OUTLIER SOLUTION CROSSING THE
GULF COAST AND THUS IS DISCARDED...WHILE THE UKMET IS VERY MUCH
LIKE THE NAM/ECMWF BUT HAS A TENDENCY TO OVER-DEVELOP OR DEEPEN
CYCLONES. THUS...CONFIDENCE IN THE UKMET IS LOW. FINALLY...THE
GLOBAL ENSEMBLE MEANS...INCLUDING THE GFS/ECMWF ENSEMBLE MEANS ARE
SLIGHTLY SLOWER AND FASTER THAN THE GFS RESPECTIVELY BUT WHEN
AVERAGED RESULT IN A GFS-LIKE SOLUTION. THUS...ENSEMBLE MEMBER
SUPPORT FOR THE GFS IS QUITE GOOD...AND GIVEN THE EXISTING SPREAD
AND UNCERTAINTY INVOLVING MULTIPLE SMALL-SCALE SYSTEMS...THE
ENSEMBLE MEANS MAY OFFER THE MOST MEANINGFUL AND CONSISTENT
DAY-TO-DAY FORECAST CHANGES THAT ADEQUATELY ACCOUNT FOR THE
POTENTIAL SOLUTION ENVELOPE. ANOTHER ALTERNATIVE WOULD BE TO USE A
POOR-MANS ENSEMBLE THAT AVERAGES ALL OF THE DETERMINISTIC
SOLUTIONS...EXCEPT FOR PERHAPS THE CANADIAN WHICH IS AN OUTLIER.
HOWEVER...THIS APPROACH MAY NOT PROPERLY ACCOUNT FOR THE
DISPERSION OF SOLUTIONS. THUS...UNTIL THESE MULTIPLE SYSTEMS CAN
BE BETTER SAMPLED...THE PREFERENCE IS BETWEEN THE GFS/ECMWF
ENSEMBLE MEANS...WHICH IS BEST APPROXIMATED BY THE 12Z OPERATIONAL
GFS WITH THE 00Z ECMWF A CLOSE SECOND.

CONFIDENCE: LOW</span></pre>

Andy, Southern York County, PA said...

NWS/BALT WASH

<pre>Coastal system Saturday night through Sunday...decent consistency in
the last few global model runs of a southern stream dominant system
moving northeast from the western Gulf Coast...across the deep south
and across the Carolinas. Phasing with northern stream energy does
look to take place across the middle MS valley which will aid
cyclogenesis...particularly as the system reaches the Carolinas. The
12z European model (ecmwf) has come in slower and farther south...so run-to-run
fluctuations can be expected over the next few days. Confidence is
greater with the track being south of lwx...and with high pressure
over the Great Lakes bringing cold air south...<span>snow is looking more
likely for lwx
</span>
. Left broad swaths of rain/snow from the balt-wash
metros and northwest to the Blue Ridge on Sunday. <span>One thing is for
sure...guidance will fluctuate and the forecast will change over the
next couple days. Stay tuned. </span>
</pre>

Andy, Southern York County, PA said...

If trends continue to hold there is little chance that the Baltimore area will see any type of a plowable snow.  The system continues to trend south and weaker.  I want to see the overnight models before putting a fork in this one, especially in light of the HPC analysis.  Things look bad for us if you like snow, but it is still something to track at this range  ans I'm not ready to close the books on this yet. :'(

Katherine Engers said...

Hi Andy~ rufus here how have you been? So it is looking bad for snow? Dang it!

ravensbbr said...

Good news. I'm right under the word "significant"in "significant snowfall" on the graphic.
Bad news. That word will dance around, disappear, reappear (elsewhere) during the next few days. I spoke with a NWS precip forecaster from church who confirmed that the models are indeed pretty much everywhere, and only time will tell on this one.

Got the snowthrower all set, fridge stocked, etc.

Should be fun to see what happens ;) .

Andy, Southern York County, PA said...

not looking GREAT but time will tell.

JULIE said...

come on snow! I knew I shouldn't have bought that snowblower 2 yrs ago. SCREWED we are. I am right smack in the snow hole.

FaithInTheflakes~!

JULIE said...

Hi Rufus!