689  
FXUS02 KWBC 161923  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
323 PM EDT FRI SEP 16 2022  
 
VALID 12Z MON SEP 19 2022 - 12Z FRI SEP 23 2022  
 
...MODERATE TO LOCALLY HEAVY RAINFALL THREAT LIKELY FOR PARTS OF  
THE FOUR CORNERS INTO THE CENTRAL 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, THEN SLOWLY EJECT EASTWARD INTO THE NORTH-CENTRAL GREAT  
BASIN/ROCKIES BY THE MIDDLE TO LATTER PART OF NEXT WEEK.  
DOWNSTREAM, SUMMERTIME RIDGING WILL BUILD OVER THE CENTRAL-EASTERN  
U.S. WITH NORTHERN STREAM CANADIAN SHORTWAVE ENERGY DIPPING ACROSS  
THE NORTHERN TIER AND POSSIBLY AMPLIFYING INTO THE NORTHEAST  
AROUND THURSDAY-FRIDAY NEXT WEEK. IT IS THE STRENGTH, TIMING, AND  
EVOLUTION OF THIS TROUGH WHICH HAS STRONG IMPLICATIONS FOR  
STEERING FLOW OF TROPICAL STORM FIONA BEYOND DAY 5, FORECAST TO BE  
NEAR/NORTH OF THE BAHAMAS BY THURSDAY.  
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
GUIDANCE OVERALL WAS IN GOOD ENOUGH AGREEMENT FOR A MULTI-MODEL  
BLEND THE FIRST HALF OF THE PERIOD. AFTER ABOUT WEDNESDAY, TIMING  
DIFFERENCES BECOME MORE APPARENT AS THE UPPER LOW OVER CALIFORNIA  
EJECTS INTO THE GREAT BASIN. 06Z AND 12Z RUNS TODAY OF THE  
GFS/GEFS REMAIN ON THE FASTER SIDE OF THE GUIDANCE, WHILE THE LAST  
COUPLE OF RUNS OF THE ECMWF TENDS TO HANG THE LOW BACK OVER  
CALIFORNIA LONGER. THE ECENS MEAN IS A HAIR FASTER THAN ITS  
DETERMINISTIC COUNTERPART, BUT STILL SLOWER THAN THE GEFS. OPTED  
TO LEAN MORE ON THE ENSEMBLE MEANS HERE, WHICH RESULTED IN A  
SOLUTION VERY CLOSE TO THE PREVIOUS WPC FORECAST. 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, WITH THE LATEST 12Z GUIDANCE FROM TODAY, THERE IS  
INCREASING CONFIDENCE THAT THIS UPPER TROUGH SHOULD HELP STEER  
FIONA SUFFICIENTLY OUT TO SEE WITH ONLY MINIMAL IMPACTS TO THE  
U.S. EAST COAST. 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 SLOW 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 AREA ON THE DAY 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.  
 
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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