985  
FXUS02 KWBC 271901  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
300 PM EDT TUE SEP 27 2022  
 
VALID 12Z FRI SEP 30 2022 - 12Z TUE OCT 04 2022  
 
...HURRICANE IAN FORECAST TO BRING HEAVY/EXCESSIVE RAIN AND STRONG  
WINDS TO FLORIDA AND THE SOUTHEAST, WITH SIGNIFICANT RAINFALL THEN  
PUSHING NORTHWARD INTO THE APPALACHIANS AND MID-ATLANTIC...  
   
..OVERVIEW
 
 
THE 18Z NATIONAL HURRICANE CENTER ADVISORY HAS HURRICANE IAN  
REACHING NORTHEASTERN FLORIDA BY THE START OF THE MEDIUM RANGE  
FORECAST PERIOD EARLY FRIDAY AND TRACKING GENERALLY NORTHWARD INTO  
SOUTH CAROLINA BY SATURDAY. ALTHOUGH IAN WILL WEAKEN WITH TIME,  
THE SYSTEM WILL STILL SPREAD SIGNIFICANT RAINFALL AND STRONG WINDS  
NORTHWARD OVER THE PORTIONS OF THE EASTERN U.S. INTO THE WEEKEND,  
WITH THE MOISTURE LIKELY TO REACH AS FAR NORTH AS THE CENTRAL  
APPALACHIANS AND MID-ATLANTIC. THE PATTERN FARTHER WEST BECOMES  
SOMEWHAT BLOCKY FOR A TIME, WITH A SLOW MOVING NORTHERN ROCKIES  
INTO HIGH PLAINS UPPER LOW (AND ACCOMPANYING LOCALLY ENHANCED  
PRECIPITATION) BETWEEN RIDGES NEAR THE WEST COAST AND OVER THE  
MIDWEST.  
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
OVERALL THERE IS REASONABLE CONSENSUS THAT IAN SHOULD LIFT  
NORTHWARD OVER THE EASTERN U.S. WITH THE UPPER LEVEL REFLECTION  
POTENTIALLY OPENING UP AROUND SUNDAY-MONDAY AND THE EXTRATROPICAL  
SURFACE SYSTEM REACHING NEAR THE MID-ATLANTIC COAST. A NON-UKMET  
MODEL BLEND WAS REASONABLE AS A STARTING POINT TO REPRESENT THE  
OVERALL PATTERN FOLLOWED BY SOME ADJUSTMENT TO CONFORM TO THE  
OFFICIAL NHC FORECAST. RECENT CYCLES HAVE BEEN COMING TOGETHER  
FOR A STRONG EASTERN CANADA/NEW ENGLAND SURFACE HIGH AROUND  
SUNDAY-MONDAY, LIMITING THE NORTHWARD PROGRESSION OF THE SYSTEM TO  
SOME DEGREE. MEANWHILE, THE MODELS THROUGH 18Z GENERALLY APPEARED  
TO BE STARTING TO SETTLE INTO A CONSENSUS EVOLUTION FOR THE  
PATTERN OVER THE PACIFIC AND WESTERN THREE-FOURTHS OF THE LOWER 48  
AFTER A NUMBER OF DAYS WITH SOME SIGNIFICANT SPREAD AND RUN-TO-RUN  
VARIABILITY. ONE UNCERTAINTY BY THE FIRST PART OF NEXT WEEK WILL  
BE IF/WHEN THE ROCKIES-HIGH PLAINS UPPER LOW OPENS UP. NEW 00Z  
MODEL RUNS HINT THAT THE LOW COULD HANG ON A LITTLE LONGER THAN  
DEPICTED BY THE PREFERRED 18Z/12Z MODEL AND 18Z GEFS/12Z ECENS  
BLEND BY DAY 7 TUESDAY. SHORTWAVE ENERGY ORIGINATING FROM NEAR  
THE GULF OF ALASKA MAY AMPLIFY AS IT CROSSES CANADA AND PUSH A  
COLD FRONT INTO THE NORTHERN TIER STATES EARLY NEXT WEEK. ADDING  
IN THE NEW 00Z GFS/ECMWF RUNS, THERE IS NOTABLE INCONSISTENCY AS  
THOSE SOLUTIONS HAVE ADJUSTED NOTABLY FASTER/FLATTER WITH THE  
UPPER TROUGH THAN PRIOR CLUSTERING. ALSO SPREAD PERSISTS FOR HOW  
NORTHERN STREAM FLOW MAY EVENTUALLY INTERACT WITH THE UPPER LOW  
WELL OFFSHORE THE WEST COAST, EFFECTING HOW QUICKLY HEIGHT FALLS  
BEGIN TO REACH THE WEST COAST DURING THE FIRST PART OF NEXT WEEK.  
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
EXPECT HURRICANE IAN TO PRODUCE NOTABLE RAINFALL AND WIND THREATS  
TO FLORIDA AND THE SOUTHEAST EXTENDING INTO LATE THIS WEEK. A  
FRONT STALLING OVER FLORIDA IN THE SHORT RANGE WILL LIFT NORTH  
WITH THE SYSTEM AND PROVIDE AN ADDED RAINFALL FOCUS. HIGH PRESSURE  
OVER THE NORTHEAST LATE THIS WEEK SHOULD BE REINFORCED BY ANOTHER  
HIGH REACHING SOUTHEASTERN CANADA AND NEW ENGLAND BY  
SUNDAY-MONDAY. THESE HIGHS WILL HELP TO ENHANCE THE WINDS/ONSHORE  
FLOW TO THE NORTH OF IAN. THE HEAVY RAIN THREAT SHOULD PUSH NORTH  
INTO PARTS OF THE APPALACHIANS AND MID-ATLANTIC BY THE WEEKEND,  
WITH SOME RAINFALL POSSIBLY CONTINUING INTO EARLY NEXT WEEK. THE  
DAY 4 EXPERIMENTAL EXCESSIVE RAINFALL OUTLOOK MAINTAINS THE  
MODERATE RISK FROM THE CHARLESTON TO SAVANNAH METRO AREAS WITH THE  
SLIGHT RISK ENCOMPASSING FAR NORTHERN FLORIDA, MUCH OF GEORGIA,  
ALL OF SOUTH CAROLINA, AND SOUTHERN NORTH CAROLINA. THE NEW DAY 5  
OUTLOOK DEPICTS A SLIGHT RISK AREA APPROXIMATELY FROM NORTHERN  
GEORGIA/FAR NORTHEASTERN ALABAMA INTO NORTHERN SOUTH CAROLINA AND  
NORTHWARD THROUGH MUCH OF VIRGINIA.  
 
THE COMBINATION OF ANOMALOUS MOISTURE AND THE UPPER LOW TRACKING  
OVER THE NORTHERN ROCKIES/HIGH PLAINS SHOULD PRODUCE SOME AREAS  
AREAS OF LOCALLY HEAVY RAINFALL WITHIN AN AREA FROM MONTANA  
THROUGH WYOMING AND PARTS OF UTAH/COLORADO, ESPECIALLY DURING  
FRIDAY-SATURDAY. RAINFALL SHOULD TREND LIGHTER AND MORE SCATTERED  
THEREAFTER AS THE MOISTURE SHIELD DRIFTS EASTWARD AND THE UPPER  
LOW TRENDS A LITTLE WEAKER. HIGHEST ELEVATIONS UNDER THE UPPER  
LOW COULD SEE SOME SNOW.  
 
CLOUD COVER/RAIN FROM IAN WILL SUPPORT BELOW NORMAL HIGHS OVER THE  
SOUTHERN TWO-THIRDS OF THE EAST FOR MOST OF THE PERIOD, WITH THE  
COOLEST ANOMALIES OF 10-15F BELOW NORMAL MOST LIKELY  
FRIDAY-SATURDAY. THE PLAINS WILL BE ON THE WARM SIDE FRIDAY WITH  
SOME AREAS UP TO 10-15F ABOVE NORMAL. THEREAFTER, NORTHERN AREAS  
SHOULD TREND TOWARD NORMAL BY TUESDAY WHILE PLUS 5-10F ANOMALIES  
FOR HIGHS PERSIST OVER THE SOUTHERN PLAINS. THE UPPER LOW  
DRIFTING OVER THE ROCKIES/HIGH PLAINS WILL BRING COOL TEMPERATURES  
ALONG ITS PATH WITH A FEW LOCATIONS AT LEAST 10F BELOW NORMAL FOR  
HIGHS FRIDAY-SATURDAY. THE UPPER RIDGE NEAR THE WEST COAST WILL  
PROMOTE A GRADUALLY EXPANDING AREA OF MODERATELY ABOVE NORMAL  
TEMPERATURES, WITH SOME LOCALIZED PLUS 10F OR SO ANOMALIES OVER  
THE NORTHWEST FROM SATURDAY ONWARD.  
 
RAUSCH/KEBEDE  
 
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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