758  
FXUS02 KWBC 170701  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
300 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 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  
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  
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 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.  
 
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. A SECOND AND STRONGER 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. 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 FOR THIS TIME OF THE  
YEAR. WARMER THAN NORMAL TEMPERATURES WILL EXTEND TO THE EAST  
COAST INTO LATER NEXT WEEK, THOUGH WITH SLIGHTLY LESSER ANOMALIES.  
 
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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