Prognostic Meteorological Discussion
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000
FXUS02 KWBC 231516
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1116 AM EDT SAT MAY 23 2015

VALID 12Z TUE MAY 26 2015 - 12Z SAT MAY 30 2015

...OVERVIEW...

ONE AREA OF UPPER RIDGING IS FORECAST TO RETROGRADE WESTWARD
THROUGH NORTHERN ALASKA WHILE ANOTHER SHOULD DRIFT FROM THE SE
CONUS TOWARD NEW ENGLAND AND THE NW ATLANTIC. THIS WILL KEEP
SHORTWAVE FEATURES IN THE WESTERN/CENTRAL STATES WHICH WILL ACT TO
KEEP A RATHER WET PATTERN FOR THE NORTHERN/CENTRAL ROCKIES INTO
THE PLAINS... AND ALSO ALONG AND JUST WEST OF THE APPALACHIANS.


...MODEL PREFERENCES/UNCERTAINTY ASSESSMENT...

THE AMPLIFYING RIDGE IN THE EAST BETWEEN TUE-FRI SHOULD CHALLENGE
THE EASTWARD ADVANCE OF A MID-CONTINENTAL FRONTAL PROGRESSION.
UPPER-LEVEL RIDGE OVER NW CANADA CONTINUES TO BE `UNDERCUT` BY
PACIFIC FLOW ORIGINATING AT HIGH AND LOW LATITUDES. THIS MAKES
TIMING THESE FAIRLY WEAK SYSTEMS CHALLENGING... BUT PREFERRED TO
LIMIT THE SOUTHEASTWARD PUSH OF ANY CANADIAN AIRMASS TOO FAR INTO
THE GREAT LAKES AND NORTHEAST AS THE UPPER LOW IN FAR NE CANADA
SHOULD PULL A BIT NORTHWARD AND ELONGATE W-E OVER THE PERIOD. 00Z
GFS/GEFS SEEMED TO LIE ON THE SE SIDE OF THE ENSEMBLE SPREAD WHILE
THE 06Z RUNS OFFERED A SEEMINGLY `BETTER` SOLUTION -- SOMETHING
LIKE THE 00Z ECMWF AND ITS MEAN. UPSTREAM FLOW OVER ALASKA GETS TO
BE COMPLICATED VIA A `LOST` UPPER LOW NEAR THE PANHANDLE AND ALSO
WITH INCOMING PACIFIC ENERGY THAT MAY INFLUENCE HOW QUICKLY
TROUGHING HEADS TOWARD THE PAC NW EARLY NEXT WEEKEND. ENSEMBLE
MEAN COMPROMISE SEEMED TO BE THE BEST SOLUTION FOR NOW.

IN THE CENTRAL/EASTERN STATES... A BLEND OF THE 06Z GFS/GEFS AND
00Z ECMWF/ECENS MEAN OFFERED A DECENT STARTING POINT... WITH ONE
WEAK FRONTAL BOUNDARY LIMPING EASTWARD TUE-THU WHILE A STRONGER
BOUNDARY TO THE NORTH DIPS THROUGH SOUTHERN CANADA. WESTERN
MID-LEVEL ENERGY MAY MANIFEST ITSELF AS A SFC FRONT THU-SAT IN THE
CENTRAL PLAINS WHICH SHOULD -- AT THE LEAST -- ACT TO ENHANCE
SHOWERS/CONVECTION. ENSEMBLE COMPROMISE BETWEEN THE 06Z GEFS AND
00Z ECENS KEPT LOWER PRESSURES NEAR NE/IA BY NEXT SAT -- NOT
UNLIKE THE 00Z ECMWF BUT ALSO A COMPROMISE BETWEEN THE 00Z AND 06Z
GFS RUNS.

...SENSIBLE WEATHER HIGHLIGHTS...

SUMMER-LIKE PATTERN FOR THE EAST... WIDESPREAD MID 80S TO MID 90S
AND HIT-N-MISS AFTERNOON AND EVENING AIRMASS
SHOWERS/THUNDERSTORMS. MORE FOCUSED ACTIVITY WILL BE ALONG AND
AHEAD OF THE SFC BOUNDARY TUE-THU FROM THE MIDWEST TO THE CENTRAL
APPALACHIANS AND NORTHEAST.

SLOW-MOVING FRONTAL BOUNDARY WILL BE THE FOCUS FOR MORE-ORGANIZED
PRECIPITATION AND PERIODS OF LOCALLY HEAVY RAINFALL ACROSS THE
SOUTHERN PLAINS... UPPER-MISSISSIPPI VALLEY/MIDWEST... AND WESTERN
GREAT LAKES LATE IN THE PERIOD... ADDING TO THE IMPRESSIVE MONTHLY
RAINFALL TOTALS IN SOME AREAS.


FRACASSO/VOJTESAK

$$





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