609  
FXUS02 KWBC 170734  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
334 AM EDT SAT SEP 17 2022  
 
VALID 12Z TUE SEP 20 2022 - 12Z SAT SEP 24 2022  
 
..TROPICAL STORM FIONA FORECAST TO SLOWLY GAIN STRENGTH WHILE  
LIFTING FROM THE CARIBBEAN TOWARD/EAST OF THE BAHAMAS INTO  
MIDWEEK...  
 
...MODERATE TO LOCALLY HEAVY RAINFALL THREAT FROM THE FOUR CORNERS  
REGION INTO THE ROCKIES TUESDAY-THURSDAY...  
 
   
..PATTERN OVERVIEW
 
 
THE UPPER PATTERN DURING THE MEDIUM RANGE PERIOD WILL FEATURE A  
VERY AMPLIFIED TROUGH/CLOSED LOW SLATED TO FORM OFF THE CALIFORNIA  
COAST THAT MAY SLOWLY EJECT NORTHEASTWARD OVER THE NORTH-CENTRAL  
GREAT BASIN/ROCKIES BY THE LATTER PART OF NEXT WEEK. DOWNSTREAM,  
HOT SUMMERTIME RIDGING WILL BUILD OVER THE CENTRAL-EASTERN U.S.  
AND AMPLE NORTHERN STREAM CANADIAN SHORTWAVE ENERGY SEEMS SLATED  
TO DIG SOUTHEASTWARD ACROSS THE NORTHERN TIER TO AMPLIFY OVER THE  
GREAT LAKES NORTHEAST AROUND THURSDAY-SATURDAY OF NEXT WEEK. THIS  
SYSTEM HAS SOME ENERGY CONNECTION OF THE CURRENT EXTREMELY DEEP  
BERING SEA LOW ASSOCIATED WITH THE EXTRATROPICAL REMNANTS OF  
TYPHOON MERBOK. THE EVOLUTION OF THIS TROUGH HAS STRONG  
IMPLICATIONS FOR EVENTUAL STEERING FLOW OF TROPICAL STORM FIONA  
BEYOND DAY 5, FORECAST TO REACH HURRICANE STRENGTH WITH A TRACK  
NEAR/EAST OF THE BAHAMAS WEDNESDAY INTO THURSDAY.  
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
GUIDANCE OVERALL REMAINS IN GOOD ENOUGH AGREEMENT FOR A  
MULTI-MODEL BLEND MIDWEEK. AFTER ABOUT WEDNESDAY, TIMING  
DIFFERENCES REMAIN MORE APPARENT THURSDAY INTO NEXT WEEKEND AS THE  
UPPER LOW OVER CALIFORNIA UNCERTAINLY EJECTS INLAND ACROSS THE  
NORTH-CENTRAL GREAT BASIN/ROCKIES. RECENT RUNS OF THE GFS/GEFS AND  
TO A LESSER EXTENT THE CANADIAN REMAIN ON THE FASTER SIDE OF THE  
GUIDANCE, WHILE RECENT RUNS OF THE ECMWF/ECMWF ENSEMBLES AND UKMET  
HANG THE LOW BACK OVER CALIFORNIA LONGER. PREFER MORE INTO THE  
SLOWER SIDE OF THE ENVELOPE OF SOLUTIONS CLOSEST TO THE ECMWF  
ENSEMBLE MEAN GIVEN THE NATURE OF CLOSED SYSTEMS IN SEPARATED FLOW  
AND AS PER FAVORABLE LATEST RUN TO RUN GUIDANCE TRENDS.  
 
NORTHERN STREAM FLOW ACROSS THE NORTHERN TIER AND EVENTUALLY INTO  
THE NORTHEAST CONTINUES TO PROVIDE PLENTY OF UNCERTAINTIES ON  
TIMING AND AMPLITUDE. THIS WOULD HAVE STRONG IMPLICATIONS ON HOW  
CLOSE TO THE US EAST COAST FIONA EVENTUALLY TRACKS IN THE LATE  
PERIODS. HOWEVER, RECENT GUIDANCE OFFERS INCREASING CONFIDENCE  
THAT THIS UPPER TROUGH SHOULD HELP STEER FIONA SUFFICIENTLY OUT TO  
SEE WITH ONLY MINIMAL IMPACTS TO THE U.S. EAST COAST. A SLOWED  
EJECTION OF THE CALIFORNIAN CLOSED LOW ALSO LEAVES MORE ROOM FOR  
THE NORTHERN STREAM UPPER TROUGH TO AMPLIFY A BIT MORE DOWNSTREAM  
THAN PREVIOUS FORECASTS. IMPORTANT TO NOTE THOUGH THAT WHILE ODDS  
FAVOR A WELL OFFSHORE TRACK, THERE IS STILL SOME LINGERING  
POTENTIAL FIONA COULD COME CLOSE ENOUGH TO THE EAST COAST FOR SOME  
GREATER IMPACTS. PLEASE REFER TO THE LATEST NHC FORECAST FOR THE  
UPDATED INFORMATION REGARDING FIONA.  
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
THE EXPECTED SLOWER INLAND EJECTION OF AN INITIALLY QUITE  
AMPLIFIED UPPER LEVEL TROUGH FROM CALIFORNIA THROUGH THE COOLING  
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 SPREADING 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  
LINGERING ONSHORE RAIN MAY BE HEAVY AT TIMES ACROSS PORTIONS OF  
NORTHERN CALIFORNIA INTO OREGON INTO MONDAY, 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 SUBTROPICAL/TROPICAL  
CONNECTION IS FORECAST TO LIFT ACROSS THE FOUR CORNERS REGION AND  
NORTHWARD EARLY-MID NEXT WEEK AHEAD OF THE EJECTING WESTERN U.S.  
UPPER TROUGH, THAT WITH UPPER SUPPORT MAY INCREASE CHANCES FOR  
MODERATE TO LOCALLY HEAVY OR EXCESSIVE RAINFALL AND THUNDERSTORMS.  
THERE WAS ENOUGH SUPPORT IN THE LATEST GUIDANCE FOR A SMALL SLIGHT  
RISK AREAS ON THE DAY 4 AND 5 EXPERIMENTAL WPC EXCESSIVE RAINFALL  
OUTLOOK ACROSS PARTS OF SOUTHWEST COLORADO AND NORTHERN NEW MEXICO  
IN THE VICINITY OF THE SAN JUAN MOUNTAINS. PRECIPITABLE WATER AND  
ARIS ARE ENHANCED AND THE AREA IS ALSO IN THE ECMWF ENSEMBLES  
MAXIMUM PROBABILITY FOR 1"+ PLUS DAILY RAIN TOTALS.  
 
WITH LEAD RIDGING BUILDING INTO THE CENTRAL U.S. INTO THE START OF  
THIS PERIOD, WARMER THAN AVERAGE TEMPERATURES BY 10-20F+ ARE  
FORECAST FOR THE CENTRAL PLAINS AND MIDDLE MISSISSIPPI VALLEY  
THROUGH WEDNESDAY WITH ACTUAL TEMPERATURES WELL INTO THE 90S INTO  
MIDWEEK THREATENING RECORD VALUES FOR THIS TIME OF THE YEAR.  
WARMER THAN NORMAL TEMPERATURES WILL EXTEND TO THE EAST COAST INTO  
AROUND THURSDAY, THOUGH WITH SLIGHTLY LESSER ANOMALIES. A STRONG  
COLD FRONT IS FORECAST TO THEN ADVANCE ACROSS THE NORTHERN TIER  
FROM CANADA WHICH WOULD BRING SHOWERS/THUNDERSTORMS WITH SOME  
LOCALLY ENHANCED DOWNPOURS INTO THE MIDWEST/GREAT LAKES THEN  
NORTHHEAST WEDNESDAY INTO THURSDAY. SUSPECT THE NBM IS TOO LIGHT  
WITH QPF AND MODESTLY INCREASES AMOUNTS GIVEN POTENTIAL FOR  
AMPLIFICATION. LEAD HEAT WILL THEN GET SUPPRESSED WITH THIS  
CENTRAL TO EASTERN U.S. FRONTAL PASSAGE AND QUITE COOLED CANADIAN  
POST-FRONTAL HIGH PRESSURE.  
 
MEANWHILE, A STALLED FRONT IS FORECAST TO LINGER ACROSS CENTRAL TO  
SOUTHERN FLORIDA AND COULD TRIGGER SHOWERS AND THUNDERSTORMS THERE  
AS FIONA LIFTS WELL OFFSHORE THE U.S. MAINLAND AS PER THE LATEST  
NHC TRACK.  
 
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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