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January 22-23 Mid Atlantic Storm Thread #2 - No Banter


stormtracker

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Details for those north of DC.....

Over 2" qpf gets about 20 miles into pa. 2.5 qpf makes it to the pa border west of about Baltimore. There is a very tight northern gradient but not until you get to near the pa turnpike. Sharp cutoff north of there. It's a great run everyone in here though including us northern md
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Over 2" qpf gets about 20 miles into pa. 2.5 qpf makes it to the pa border west of about Baltimore. There is a very tight northern gradient but not until you get to near the pa turnpike. Sharp cutoff north of there. It's a great run everyone in here though including us northern md

Thanks, sir.  Looks like one for the books.

 

MDstorm

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All that being said let's be careful here. The snow amounts on the European model are extreme. It is quite likely that the northern end of the Shenandoah Valley is NOT going to see 45 inches of snow. It is extremely unlikely that Roanoke is going to see 38 inches of snow or Charlottesville 33 inches of snow even though that is what this particular 0z euro model is depicting.

 

There is a very strong case to be made that the European model is overdoing the extreme precipitation amounts but it is possible that the snow amounts could approach 3 feet in some portions of the Shenandoah Valley into the WVA eastern panhandle into central MD . I I am not at this time forecasting these sorts of extreme snowfall amounts but the fact that this sort of extreme snowfall is rare does not mean that it cannot occur.

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EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1232 AM EST TUE JAN 19 2016

VALID 12Z FRI JAN 22 2016 - 12Z TUE JAN 26 2016

HIGHLIGHTS...

THE PRIMARY IMPACTS THIS PERIOD WILL BE FOR HIGH CONFIDENCE IN A
MAJOR WINTER STORM INCLUDING HEAVY SNOWS FOR THE URBAN CORRIDOR
EXTENDING FROM WASHINGTON DC TO NEW YORK AND BOSTON FRIDAY INTO
SUNDAY WITH THE LOW'S ANTICIPATED TRACK AND SWATH OF HIGH LIQUID
EQUIVALENTS SUPPORTING 1 TO 2 FEET NEAR AND NORTHWEST OF I-95.
COASTAL FLOODING AND OTHER SIGNIFICANT IMPACTS TO MARINE INTERESTS
FROM THE MID-ATLANTIC INTO THE NORTHEAST ARE ALSO LIKELY.

IN THE WEST...PRECIPITATION SHOULD WANE ALONG THE COAST DAY 3 INTO
DAY 4...WITH THE NEXT MAJOR PRECIPITATION EVENT EXPECTED ACROSS
THE PACIFIC NORTHWEST BY NEXT MONDAY OR TUESDAY...WITH SEVERAL
INCHES OF LIQUID EQUIVALENT EXPECTED.

MODEL CHOICES AND CONFIDENCE...

THE GROWING AMPLITUDE AND WAVELENGTH OF THE PATTERN IS ACCOMPANIED
BY MUCH LESS SPREAD OF ALL MEMBERS INCLUDING ENSEMBLES...WHICH
SUPPORTS GREATER USE AND RELIANCE UPON THE DETERMINISTIC SOLUTIONS
FOR ABOUT 1 OR 2 DAYS LONGER THAN APPLIED RECENTLY
. THIS ALLOWS
FOR MORE AMPLITUDE OF THE ANTICIPATED HIGHLIGHTS TO BE MAINTAINED
LONGER
. ALTHOUGH A STRAIGHT MODEL BLEND OF ABOUT 50/50 18Z GFS/12Z
ECMWF WAS USED TO BEGIN DAY 3...BEFORE TRANSITIONING TO
40/40/10/10 18Z GFS/12Z ECMWF/18Z GEFS MEAN/12Z ECMWF ENSEMBLE
MEANS FOR DAY 4...WITH ABOUT 1/4 OF EACH MODEL FOR DAYS 5-7...
THE
LOW ENTERING THE TN VALLEY ON DAY 3 IS PLAGUED BY CONCERNS WITH
THE 12Z ECMWF WHICH IS A BIT SLOWER AND ULTIMATELY MORE SOUTHWARD
CROSSING THE APPALACHIANS COMPARED WITH MOST OTHER
SOLUTIONS...WHICH HAS HUGE IMPLICATIONS FOR THE PRECIPITATION
ALONG THE EAST COAST DAYS 4/5
. TRACING THE LOW TO ITS PRESENT
LOCATION OVER THE EASTERN PACIFIC SHOWS THE ECMWF TO BE A BIT SLOW
INITIALLY
WHICH MAY HAVE TO DO WITH ITS OLDER INITIALIZATION AND
GREATER RELIANCE UPON PRIOR FIRST GUESS FIELDS VERSUS THE GFS
WHICH IS MORE RECENT AND OFTEN MORE SENSITIVE TO SUBTLE SHIFTS IN
OBSERVATIONS. THUS...THE SYSTEM IN THE EAST IS NUDGED MOSTLY
TOWARD THE 18Z GFS WITH SOME INCORPORATION OF THE ENSEMBLE MEANS
AND A LITTLE ECMWF TO ACCOUNT FOR THE SPREAD. THE MORE EVENLY
DISTRIBUTED MODEL BLEND SERVES WELL FOR THE REST OF THE CONUS AS
THE SYSTEMS ARE SLIGHTLY SMALLER WITH TYPICAL TIMING DIFFERENCES
BEST ADDRESSED WITH THE BLENDING OF NUMEROUS SOLUTIONS. THE
PREFERENCE FOR THE LARGE TROUGH NEARING THE WEST COAST AROUND DAY
7 IS NEAR THE CONSENSUS WITH ABOUT AVERAGE CONFIDENCE GIVING THE
GROWING SPREAD...WITH ABOUT 60 PERCENT OF THE ENSEMBLES USED BY
THIS TIME.

JAMES

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6z NAM at 84 has 1000mb SLP in north-central TN with small closed 540 DM h5 low right behind it... SLP also is kinking to SE so transfer is either ongoing or starting up...snowing in C VA at 84 as well to near DCA on composite radar on IWM... semblance of CAD is evident as well on the SLP map

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06z GFS SLP placement:

 

75 -- 1004mb in N AL/S TN

78 -- 1004mb in E TN

81 -- 1004mb in E TN (isobars kinking to SE)

84 -- 1002mb in E TN (isobars kinking to SE)

87 -- transfer ongoing

90 -- broad 1000mb SLP over E NC

93 -- 996mb SLP just NE of HSE

96 -- 992mb SLP E of ORF by about 100 miles or so

99 -- 990mb SLP or so SE of SBY

 

No h5 capture this run... but I would def lean toward EURO/EPS runs over GFS runs

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