405  
FXUS02 KWBC 181842  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
241 PM EDT SUN SEP 18 2022  
 
VALID 12Z WED SEP 21 2022 - 12Z SUN SEP 25 2022  
 
...FIONA TO GAIN HURRICANE STRENGTH LIFTING FROM THE CARIBBEAN TO  
JUST EAST OF THE BAHAMAS TOWARD BERMUDA...  
 
...HEAVY RAINFALL THREAT FOR THE FOUR CORNERS REGION INTO  
WEDNESDAY-THURSDAY...  
 
   
..PATTERN OVERVIEW
 
 
THE OVERALL UPPER PATTERN MID-LATER THIS WEEK WILL FEATURE A  
STEADY EJECTION OF AN AMPLIFIED TROUGH/CLOSED LOW FROM CALIFORNIA  
TO OVER THE NORTH-CENTRAL GREAT BASIN/ROCKIES TO THE NORTH-CENTRAL  
U.S. AS A HOT SUMMERTIME RIDGING BECOMES SUPPRESSED FROM THE  
CENTRAL U.S. TO THE SOUTH. MEANWHILE, AMPLE NORTHERN STREAM TROUGH  
ENERGIES WILL DIG SOUTHEASTWARD FROM CANADA THROUGH THE UPPER  
MIDWEST TO THE EAST. THIS SCENARIO SHOULD ACT TO STEER HURRICANE  
FIONA WELL AWAY FROM THE U.S. EAST COAST WITH A FORECAST TRACK  
FROM EAST OF THE BAHAMAS TOWARDS/JUST WEST OF BERMUDA.  
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
MOST RECENT MODELS AND ENSEMBLES CONTINUE TO OFFER A MORE CLOSELY  
ALIGNED PATTERN EVOLUTION AT MEDIUM RANGE TIME SCALE OVER THE  
LOWER 48, BOLSTERING FORECAST CONFIDENCE DESPITE SOME LINGERING  
LOCAL EMBEDDED SYSTEM TIMING/STRENGTH DIFFERENCES. THE MOST  
NOTABLE DIFFERENCES ARISE AFTER DAY 5 WITH AMPLITUDE/SPEED OF THE  
DEPARTING TROUGH OUT OF THE NORTHEAST (LIKELY INFLUENCED BY  
INTERACTION WITH/ABSORBTION OF FIONA) AND ALSO THE NEXT SHORTWAVE  
INTO THE PACIFIC NORTHWEST. FOR THE LATTER, THE 00Z ECMWF WAS THE  
QUICKEST WITH THIS WAVE, BUT THE LATEST SUITE OF 12Z MODELS APPEAR  
TO HAVE TRENDED TOWARDS THAT MORE FAST SOLUTION (WITH THE  
EXCEPTION OF THE GFS). THE WPC MEDIUM RANGE PRODUCT SUITE WAS  
PRIMARILY DERIVED FROM A BLEND OF THE LATEST 00Z/06Z DETERMINISTIC  
GUIDANCE THROUGH DAY 5, WITH MUCH MORE INCLUSION OF THE ENSEMBLE  
MEANS FOR THE LATE PERIODS WHICH HELPS MITIGATE SOME DIFFERENCES  
NOTED ABOVE. THIS ALSO MAINTAINS GOOD WPC PRODUCT CONTINUITY.  
   
..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 MID-LATE WEEK WILL SUPPORT  
COOLER TEMPERATURES THAT MAY LEAD TO SOME SNOW FOR HIGHER  
ELEVATIONS OF 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/PLAINS EARLY IN THE WEEK AND THEN TO THE  
UPPER MISSISSIPPI VALLEY/MIDWEST BY THE LATER WEEK/WEEKEND AS THE  
COLD FRONT WORKS DOWNSTREAM. ANOMALOUS MOISTURE WITH SOME EAST  
PACIFIC SUBTROPICAL/TROPICAL CONNECTION IS FORECAST TO LIFT ACROSS  
THE FOUR CORNERS REGION AND NORTHWARD INTO MID-LATE WEEK AHEAD OF  
THE EJECTING UPPER TROUGH, THAT WITH UPPER SUPPORT MAY INCREASE  
CHANCES FOR MODERATE TO LOCALLY HEAVY OR EXCESSIVE RAINFALL AND  
THUNDERSTORMS. THERE REMAINS SUPPORT IN THE LATEST GUIDANCE TO  
CONTINUE SLIGHT RISK AREAS ON THE DAY 4 AND 5 EXPERIMENTAL WPC  
EXCESSIVE RAINFALL OUTLOOK ACROSS PARTS OF SOUTHWEST COLORADO INTO  
NORTHERN NEW MEXICO. FARTHER TO THE NORTH, ADDITIONAL ORGANIZED  
ACTIVITY INCLUDING SOME POTENTIAL FOR LOCAL CONVECTIVE  
DOWNPOURS/RUNOFF ISSUES ARE EXPECTED TO DEVELOP WITH SYSTEM  
APPROACH FROM NORTHERN CALIFORNIA/OREGON MIDWEEK THROUGH THE NORTH  
GREAT BASIN/ROCKIES THEN NORTH-CENTRAL U.S. LATER WEEK INTO THE  
WEEKEND GIVEN FAVORABLE SYSTEM FOCUS.  
 
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. WARMER THAN NORMAL TEMPERATURES WILL LINGER  
INTO THE SOUTHEAST ON 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 THROUGH  
THE GREAT LAKES TO THE NORTHEAST WEDNESDAY INTO THURSDAY. LEADING  
HEAT WILL QUICKLY GET SUPPRESSED WITH THIS FRONTAL SURGE/PASSAGE  
AS QUITE COOLED CANADIAN POST-FRONTAL HIGH PRESSURE SETTLES IN.  
MEANWHILE, A STALLED FRONT IS FORECAST TO LINGER ACROSS FLORIDA  
AND COULD TRIGGER SHOWERS AND THUNDERSTORMS THERE AS FIONA LIFTS  
WELL OFFSHORE THE U.S. MAINLAND FROM NEAR/EAST OF THE BAHAMAS  
TOWARD BERMUDA WEDNESDAY/THURSDAY AS PER THE LATEST NHC TRACK.  
 
SANTORELLI/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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