163  
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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