963  
FXUS02 KWBC 160757  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
357 AM EDT FRI SEP 16 2022  
 
VALID 12Z MON SEP 19 2022 - 12Z FRI SEP 23 2022  
   
..PATTERN OVERVIEW
 
 
TROPICAL STORM FIONA IS FORECAST BY THE NATIONAL HURRICANE CENTER  
(NHC) TO GRADUALLY REACH HURRICANE STRENGTH ON A TRACK FROM THE  
GREATER ANTILLES TO THE SOUTHERN BAHAMAS OVER THE NEXT 5 DAYS. THE  
SYSTEM WILL THEN CONTEND WITH A LARGE-SCALE UPPER LEVEL PATTERN  
OVER THE LOWER 48 TO FEATURE A TROUGH/CLOSED LOW SLATED TO FORM  
OFF THE CALIFORNIA COAST THEN SLOWLY EJECT OVER CALIFORNIA AND THE  
NORTH-CENTRAL GREAT BASIN/ROCKIES, SUMMERTIME RIDGING BUILDING  
OVER THE CENTRAL-EASTERN U.S. AND LESS CERTAIN NORTHERN STREAM  
CANADIAN SHORTWAVE TROUGH ENERGIES DIPPING ACROSS THE U.S.  
NORTHERN TIER OVERTOP THE RIDGE.  
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
THE WPC MEDIUM RANGE PRODUCT SUITE WAS PRIMARILY DERIVED FROM A  
COMPOSITE BLEND OF REASONABLY WELL CLUSTERED GUIDANCE FROM THE  
LATEST GFS/ECMWF/UKMET/CANADIAN ALONG WITH COMPATIBLE GUIDANCE  
FROM THE 01 UTC NATIONAL BLEND OF MODELS (NBM) FOR MONDAY/TUESDAY.  
SUPPORTIVE GEFS/ECMWF ENSEMBLE MEANS AND THE NBM WERE MAINLY USED  
FOR MID-LATER NEXT WEEK IN A PERIOD OF GRADUALLY GROWING FORECAST  
SPREAD LEADING INTO ANY LATE PERIOD U.S. THREAT FROM FIONA.  
 
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
THE EXPECTED SLOW INLAND EJECTION OF AN INITIALLY QUITE AMPLIFIED  
UPPER LEVEL TROUGH FROM CALIFORNIA THROUGH THE NORTH-CENTRAL GREAT  
BASIN/ROCKIES NEXT WEEK WILL SUPPORT COOLER TEMPERATURES THAT MAY  
LEAD TO SOME MIXED PRECIPITATION, OR SNOW FOR THE HIGHEST PEAKS  
ACROSS CALIFORNIA AND THE NORTH-CENTRAL GREAT BASIN/ROCKIES. THE  
DAILY TEMPERATURES ARE FORECAST TO BE 10 TO 15 DEGREES F BELOW  
SEASONAL AVERAGE FOR MID SEPTEMBER FOR THE WEST WITH THE COOL  
AIRMASS SPREAD TO THE ROCKIES/HIGH PLAINS EARLY IN THE WEEK AND  
THEN TO THE UPPER MISSISSIPPI VALLEY BY THE MIDDLE/END OF THE WEEK  
AS THE COLD FRONT MAKES ITS WAY EAST. THE ONSHORE RAIN MAY BE  
HEAVY AT TIMES ACROSS PORTIONS OF NORTHERN CALIFORNIA SUNDAY, AND  
BURN SCARS WOULD BE PARTICULARLY VULNERABLE TO FLOODING CONCERNS  
AND DEBRIS FLOWS. THE SIERRA NEVADA COULD SEE SNOW EARLY NEXT  
WEEK, THOUGH THE BEST CHANCES FOR SNOW WITH THIS ACTIVITY ARE IN  
THE NORTHERN ROCKIES TUESDAY-THURSDAY. MOISTURE WITH SOME  
CONNECTION FROM THE TROPICAL EASTERN PACIFIC IS FORECAST TO LIFT  
ACROSS THE FOUR CORNERS STATES AND NORTHWARD EARLY-MID NEXT WEEK  
AHEAD OF THE EJECTING WESTERN U.S. UPPER TROUGH, THAT WITH UPPER  
SUPPORT MAY INCREASE CHANCES FOR SHOWERS AND THUNDERSTORMS.  
 
A FRONTAL SYSTEM AND A SHORTWAVE TROUGH ROUNDING/DIGGING ON THE  
NORTHERN SIDE OF THE UPPER RIDGE SHOULD CAUSE A ROUND OF RAINFALL  
WITH MAIN FOCUS FROM THE MID-UPPER OHIO VALLEY THROUGH THE  
NORTHEAST MONDAY. THE MODELS SUGGEST THERE COULD BE INSTANCES  
WHERE MODERATE TO HEAVY RAINFALL WILL FALL, PARTICULARLY OVER NEW  
YORK AND PARTS OF NEW ENGLAND WHERE HIGHER AMOUNTS MAY LEAD TO  
ISOLATED FLASH FLOODING. HOWEVER AT THIS TIME THE EXACT LOCATION  
OF WHERE THERE CONCERNS MAY BE IS UNCERTAIN. A SECOND AND STRONG  
COLD FRONT IS FORECAST TO ADVANCE ACROSS THE NORTHERN TIER WHICH  
WOULD BRING ANOTHER ROUND OF SHOWERS. A STALLED FRONT IS FORECAST  
TO LINGER ACROSS CENTRAL TO SOUTHERN FLORIDA AND COULD TRIGGER  
SHOWERS AND THUNDERSTORMS THERE. THE WESTERN END OF THIS FRONT  
PUSHING SOUTH AND DISSIPATING ACROSS THE GULF SHOULD LEAD TO DRIER  
CONDITIONS FOR THE GULF COAST AFTER THE WEEKEND. WITH THE RIDGING  
BUILDING INTO THE CENTRAL U.S., WARMER THAN AVERAGE TEMPERATURES  
BY 10-20F ARE FORECAST FOR THE CENTRAL PLAINS AND MIDDLE  
MISSISSIPPI VALLEY THROUGH WEDNESDAY BEFORE GETTING SUPPRESSED BY  
THE FRONT, WITH ACTUAL TEMPERATURES WELL INTO THE 90S THREATENING  
RECORD VALUES. WARMER THAN NORMAL TEMPERATURES WILL EXTEND TO THE  
EAST COAST INTO LATER NEXT WEEK, THOUGH WITH SLIGHTLY LESSER  
ANOMALIES.  
 
MEANWHILE, A LOOMING QUESTION FOR LATER NEXT WEEK CONCERNS A  
POTENTIAL THREAT FOR THE BAHAMAS THEN POSSIBLY FLORIDA/SOUTHEAST  
DEPENDENT ON THE FUTURE STRENGTH AND TRACK OF CURRENT TROPICAL  
STORM FIONA THAT IS NOW APPROACHING THE ANTILLES. PLEASE REFER TO  
THE LATEST NHC FORECAST FOR UPDATED INFO.  
 
SCHICHTEL  
 
ADDITIONAL 3-7 DAY HAZARD INFORMATION CAN BE FOUND ON THE WPC  
MEDIUM RANGE HAZARDS OUTLOOK CHART AT:  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP  
 
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION, EXPERIMENTAL EXCESSIVE RAINFALL  
OUTLOOK, WINTER WEATHER OUTLOOK PROBABILITIES AND HEAT INDICES ARE  
AT:  
 
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=ERO  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML  
 

 
 

 
 
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