116  
FXUS02 KWBC 300700  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
259 AM EDT FRI SEP 30 2022  
 
VALID 12Z MON OCT 03 2022 - 12Z FRI OCT 07 2022  
 
...IAN FORECAST TO BRING POSSIBLY HEAVY TO EXCESSIVE RAINFALL AND  
BRISK TO STRONG WINDS TO MAINLY COASTAL MID-ATLANTIC EARLY NEXT  
WEEK...  
   
..OVERVIEW
 
 
A SOMEWHAT BLOCKY PATTERN SHOULD BE IN PLACE BY THE START OF THE  
MEDIUM RANGE PERIOD ON MONDAY, WITH A TROUGH/UPPER LOW OVER THE  
EAST (WHICH INCLUDES THE EXTRATROPICAL REFLECTION OF IAN) AND A  
SLOW MOVING NORTHERN ROCKIES INTO HIGH PLAINS UPPER LOW. THE  
LATTER IS SANDWICHED BETWEEN RIDGES OVER THE WEST COAST AND  
CENTRAL-SOUTHERN PLAINS INTO THE MIDWEST. TROUGHING LOOKS TO BE  
MAINTAINED OVER THE EAST EVEN AS THE REMNANTS OF IAN MOVE OFFSHORE  
TUES-WED, BUT UPPER LEVEL RIDGING BUILDING OVER THE WEST WHICH  
SHOULD ACT TO ACCELERATE THE SECOND SHORTWAVE TOWARDS THE UPPER  
MIDWEST AND FURTHER AMPLIFY TROUGHING OVER THE EAST LATE NEXT  
WEEK. SENSIBLE WEATHER THREATS HOWEVER DURING THE MEDIUM RANGE  
PERIOD LOOK TO MAINLY SURROUND THE REMNANTS OF IAN AS THEY MOVE  
THROUGH THE MID-ATLANTIC NEXT MONDAY-TUESDAY WITH SOME LOCALLY  
HEAVY RAINFALL AND GUSTY WINDS LINGERING ALONG MAINLY COASTAL  
REGIONS FROM THE OUTER BANKS, NC TO SOUTHERN NEW ENGLAND.  
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
DIFFERENCES IN THE DETAILS CONTINUE TO SURROUND THE REMNANTS OF  
IAN AND POSSIBLE INTERACTION WITH ADDITIONAL SHORTWAVE ENERGY INTO  
THE EAST MONDAY TO TUESDAY, AND THEN HOW QUICKLY THE SHORTWAVE  
EXITS THE COAST. THE 18Z/SEPT 29 GFS RUN WAS SLOWEST WITH THIS  
ENERGY, WHILE THE UKMET WAS MUCH TOO QUICK. THE ECMWF AND CMC HAVE  
MORE SUPPORT FROM THE ENSEMBLE MEANS ON A MIDDLE GROUND SOLUTION  
AND THUS WPC RELIED MORE CLOSELY ON THESE SOLUTIONS (ALONG WITH  
THE NATIONAL BLEND OF MODELS) FOR QPF CONCERNS EARLY IN THE  
PERIOD. ELSEWHERE, SOME TIMING DIFFERENCES REMAIN WITH THE NEXT  
SHORTWAVE EVENTUALLY PUSHING THROUGH THE NORTHERN PLAINS/UPPER  
MIDWEST MID NEXT WEEK AND EVENTUAL AMPLIFICATION OF LARGER SCALE  
TROUGHING OVER THE EAST, WITH MORE SIGNIFICANT DIFFERENCES OVER  
THE NORTHEAST PACIFIC/WESTERN NORTH AMERICA WHICH SPILL INTO PARTS  
OF THE NORTHWEST U.S. LATER NEXT WEEK. FOR THE LATTER HALF OF NEXT  
WEEK, WPC PREFERRED A BLEND MORE TOWARDS THE ENSEMBLE MEANS WHICH  
HELP TO MITIGATE THESE DIFFERENCES MORE.  
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
THE POTENTIALLY SLOW MOVING EASTERN U.S. UPPER LOW AND ASSOCIATED  
LOW PRESSURE (WHETHER INITIALLY FROM IAN OR EVENTUAL REDEVELOPMENT  
JUST OFF THE EAST COAST) MAY CONTINUE TO PRODUCE LOCALLY HEAVY  
RAINFALL OVER PARTS OF THE MID-ATLANTIC INTO EARLY NEXT WEEK.  
BRISK TO STRONG WINDS, AIDED BY HIGH PRESSURE TO THE NORTH, SHOULD  
BE MOST NOTICEABLE OVER COASTAL AREAS. LINGERING GUIDANCE  
DIFFERENCES FOR SPECIFICS AT THE SURFACE AND ALOFT DIRECTLY  
RELATED TO THE EXTRATROPICAL TRANSITION OF IAN THIS WEEKEND  
CONTINUE TO OFFER A LOWER CONFIDENCE FORECAST IN RAINFALL COVERAGE  
AND AMOUNTS, SO ADJUSTMENTS TO THE CURRENT FORECAST IS LIKELY IN  
THE DAYS TO COME.  
 
THE REMAINDER OF THE CONUS LOOKS TO BE FAIRLY QUIET IN TERMS OF  
ANY LARGER SCALE PRECIPITATION FOCUS AREAS NEXT WEEK. THE UPPER  
LOW EMERGING FROM THE NORTHERN ROCKIES SHOULD PRODUCE AREAS OF  
PRECIPITATION FROM THE SOUTHWEST/FOUR CORNER REGION INTO THE HIGH  
PLAINS AND SUFFICIENT MOISTURE COULD SUPPORT SOME AREAS OF LOCALLY  
MODERATE TO HEAVY RAINFALL EARLY NEXT WEEK. HIGHEST ELEVATIONS  
UNDER THE UPPER LOW MAY SEE SOME SNOW AS WELL. THIS PRECIPITATION  
SHOULD BECOME LIGHTER/MORE SCATTERED BY THE MIDDLE OF NEXT WEEK  
AND ONWARD AS THE UPPER FEATURE OPENS UP AND MOVES EASTWARD.  
 
MUCH OF THE EAST WILL SEE BELOW NORMAL HIGHS DURING THE FIRST HALF  
OF NEXT WEEK. PARTS OF THE MID-ATLANTIC INTO SOUTHEAST MAY BE  
10-15F BELOW NORMAL INTO EARLY NEXT WEEK WITH THE CLOUDS/RAIN  
ORIGINALLY ASSOCIATED WITH IAN, WHILE COOL HIGH PRESSURE PREVAILS  
OVER NEW ENGLAND. OUT WEST, PERSISTENT UPPER RIDGING WILL KEEP  
MUCH OF THE WEST WARMER THAN AVERAGE WITH SOME LOCATIONS IN THE  
NORTHWEST POTENTIALLY SEEING HIGHS 10-15F ABOVE NORMAL FOR MOST OF  
THE PERIOD. MODESTLY ABOVE NORMAL TEMPERATURES OVER THE PLAINS  
WILL EVENTUALLY SHIFT MORE OVER SOUTHERN AREAS WHILE LOCATIONS  
OVER THE NORTHERN TIER AND INTO THE MIDWEST/GREAT LAKES SHOULD  
TREND COLDER AS CANADIAN HIGH PRESSURE SETTLES INTO THE REGION.  
 
SANTORELLI  
 
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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