Prognostic Meteorological Discussion
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000
FXUS02 KWBC 240413
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1112 PM EST THU FEB 23 2017

VALID 12Z MON FEB 27 2017 - 12Z FRI MAR 03 2017

...OVERVIEW...

A WESTERN US SYSTEM IS POISED TO SWING OUT OF THE CENTRAL PLAINS
ON TUESDAY AND INTO THE GREAT LAKES ON WEDNESDAY BEFORE PUSHING
OFF THE EAST COAST ON THURSDAY. HIGH PRESSURE IS FORECAST TO BUILD
THROUGH THE WEST AND CENTRAL STATES NEXT WED-FRI.


...MODEL EVALUATION/PREFERENCES...

AFTER RATHER SIGNIFICANT DIFFERENCES AMONG THE GUIDANCE IN THE
SHORT TERM THIS WEEKEND (SEE THE PMDHMD FOR AN UPDATE WITH THE
LATEST 00Z GUIDANCE), THE ENSEMBLES SHOW RATHER GOOD AGREEMENT IN
THE MEDIUM RANGE NEXT MON-FRI. THIS INCLUDES A WESTERN TROUGH
LIFTING NORTHEASTWARD AS UPPER RIDGING OVER THE BAHAMAS REASSERTS
ITSELF OVER THE FLORIDA STRAITS BY MIDWEEK. BY THE END OF THE
PERIOD, TROUGHING WILL MOVE INTO THE EASTERN HALF OF THE CONUS.
THE RECENT GFS RUNS (18Z/12Z) WERE MOSTLY AWAY FROM THE BETTER
ECMWF-LED ENSEMBLE CONSENSUS IN THE WEST AT THE START OF THE
PERIOD THOUGH THAT PRONOUNCED DIFFERENCE DAMPENED WITH TIME.
HOWEVER, AS THE MAIN SYSTEM LIFTS INTO THE GREAT LAKES NEXT
WEDNESDAY, THE GFS WAS ON THE SOUTHEAST SIDE OF THE MULTI-CENTER
ENSEMBLE SPREAD AND NOT PREFERRED (THOUGH NOT TOTALLY DISCOUNTED).
A BLEND OF CONTINUITY WITH THE 12Z CANADIAN/ECMWF/ECENS MEAN AND
18Z GEFS MEAN FORMED A REASONABLE STARTING POINT. BY THE END OF
THE PERIOD, ENSEMBLE SHOW A RELATIVE MAX AREA OF SPREAD OFF THE
WA/OR COAST BUT SEEM TO INDICATE THAT TROUGHING OR AN UPPER LOW
WILL TRY TO MAINTAIN ITSELF IN THE GULF OF ALASKA, FIGHTING THE
RIDGING TO ITS SOUTH. FAST FLOW IN BETWEEN YIELDS LOW
PREDICTABILITY FOR TIMING EMBEDDED SYSTEMS.


...WEATHER HIGHLIGHTS/THREATS...

AS THE FRONT LIFTS NORTHEASTWARD, MODERATE TO LOCALLY HEAVIER RAIN
WILL OVERSPREAD THE LOWER MISSISSIPPI VALLEY AND INTO THE
SOUTHEAST BUT ALSO NORTHWARD THROUGH THE MIDWEST AND UPPER MIDWEST
AS THE SURFACE LOW DEEPENS. SNOW IS LIKELY ON THE NORTHWEST SIDE
OF THE LOW FROM THE HIGH PLAINS INTO MINNESOTA. ANOTHER SURGE OF
MILD AIR, ALBEIT BRIEF, SHOULD PUSH NORTHEASTWARD AHEAD OF THE
COLD FRONT (+10 TO +15F ABOVE AVERAGE), BUT TEMPERATURES WILL FALL
BACK TO NEAR CLIMATOLOGICAL VALUES LATER IN THE WEEK AFTER THE
FRONT EXITS OFF THE EASTERN SEABOARD. BY LATE NEXT WEEK, THE
WESTERN HALF OF THE COUNTRY (EXCEPT WASHINGTON AND PORTIONS OF
ID/MT) SHOULD BE LARGELY DRY THANKS TO UPPER RIDGING AND SURFACE
HIGH PRESSURE.


FRACASSO


$$





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