Preliminary Forecasts
Issued by NWS

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FXUS02 KWNH 240557
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
157 AM EDT SUN SEP 24 2017

VALID 12Z WED SEP 27 2017 - 12Z SUN OCT 01 2017

...HEAVY RAIN FOR PORTIONS OF TEXAS, NEW MEXICO, AND OKLAHOMA THIS
WEEK...


...OVERVIEW...

UPPER PATTERN WILL TREND TOWARD INCREASED EASTERN TROUGHING AS A
LEAD COLD FRONT PUSHES ACROSS THE EAST WED-THU AND A REINFORCING
COLD FRONT DIVES THROUGH THE UPPER MIDWEST AND OHIO VALLEY
THU-FRI. THIS SHOULD HELP STEER HURRICANE MARIA OUT TO SEA BUT NOT
BEFORE IT DRAWS CLOSER TO THE OUTER BANKS OF NORTH CAROLINA. HEAVY
RAIN REMAINS IN THE FORECAST FROM THE SHORT RANGE INTO THE MEDIUM
RANGE ACROSS WESTERN/CENTRAL TEXAS AND BACK INTO EASTERN NEW
MEXICO AS WELL AS NORTH INTO OKLAHOMA. FINALLY, A PACIFIC COLD
FRONT WILL PUSH INTO WA/OR ON SATURDAY.


...GUIDANCE EVALUATION/PREFERENCES...

IN THE WEST, THE MODELS/ENSEMBLES HAVE LARGELY SETTLED ON
SPLITTING THE UPPER TROUGH SW TO NE AND LEAVING THE SOUTHWESTERN
UPPER LOW IN PLACE OVER AZ/UT WED-SAT BEFORE DISSIPATING AND/OR
BEING DRAWN BACK NORTHWARD AHEAD OF THE NEXT TROUGH. IN THE EAST,
GFS/ECMWF HAVE LED THE WAY OF THE ENSEMBLES WITH HOW THE UPPER
TROUGH EVOLVES INTO THE EAST -- MAINTAINING A SECONDARY COLD FRONT
THAT WILL USHER IN MUCH COOLER AIR. 12Z GFS/ECMWF WERE USED AS THE
BASIS TO THE FIRST FEW DAYS WITH A SLIGHT ENSEMBLE WEIGHTING TO
SMOOTH OUT SOME DIFFERENCES. 18Z GFS/GEFS WERE DIFFERENT OVERALL
FROM BETTER 12Z AGREEMENT SO DID NOT INCORPORATE ANY "NEW"
GUIDANCE FROM THE GFS. BY NEXT SAT/SUN, DIFFERENCES GREW ACROSS
THE CONUS AND A TREND TOWARD THE FAIRLY AGREEABLE 12Z GEFS/ECENS
MEAN SMOOTHED OUT THE PICTURE. LOTS OF SPREAD IN THE ENSEMBLES WAS
SEEN UPSTREAM IN THE PACIFIC WHICH TRANSLATED WESTWARD INTO THE
PAC NW BY THE WEEKEND SO CONFIDENCE IS LOW IN DETAILS BUT AT LEAST
ONE LOW-AMPLITUDE SHORT WAVE SHOULD PUSH INTO BC AROUND NEXT
SUNDAY. BACK TO THE EAST, ENSEMBLES NICELY SPLIT THE DIFFERENCE
BETWEEN THE QUICKER 12Z GFS AND SLOWER 12Z ECMWF AS THE TROUGH
AXIS REACHES THE APPALACHIANS.


...WEATHER HIGHLIGHTS...

LEAD COLD FRONT MOVES WILL DROPS TEMPERATURES BY ABOUT 20 DEGREES
BUT ONLY TO NEAR AVERAGE VALUES LATER THIS WEEK WHILE THE
SECONDARY FRONT WILL BRING IN COOLER THAN AVERAGE TEMPERATURES
FROM THE HIGH PLAINS AND MIDWEST LATER THIS WEEK INTO THE
NORTHEAST AND MID-ATLANTIC NEXT WEEKEND. OTHER AREA OF COOLER THAN
AVERAGE TEMPERATURES WILL BE OVER THE SOUTHERN PLAINS INTO TEXAS
AND NEW MEXICO DUE TO CLOUDS/RAIN. SOUTHEAST FLOW AT LOW LEVELS
WILL DRAW IN GULF MOISTURE FOR SEVERAL MORE DAYS THIS WEEK,
SETTING UP A MULTI-DAY RAINFALL EVENT FROM THE SHORT RANGE INTO
THE MEDIUM RANGE. TO THE EAST, IT IS BECOMING INCREASINGLY LIKELY
THAT SOME DIRECT IMPACTS FROM MARIA, INCLUDING RAIN, GUSTY WINDS,
HIGH SURF, AND DANGEROUS RIP CURRENTS, WILL OCCUR ALONG PORTIONS
OF THE OUTER BANKS WED-THU BEFORE IT PULLS AWAY TO THE EAST.


FRACASSO


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