760  
FXUS02 KWBC 210640  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
239 AM EDT WED SEP 21 2022  
 
VALID 12Z SAT SEP 24 2022 - 12Z WED SEP 28 2022  
 
...DANGEROUS FIONA FORECAST TO SLAM TOWARD THE CANADIAN MARITIMES  
SATURDAY WITH TRANSITION FROM HURRICANE TO A DEEP EXTRATROPICAL  
STORM...  
   
..PATTERN OVERVIEW
 
 
GUIDANCE AGREES TO BUILD AN AMPLIFIED/WARMING WESTERN NORTH  
AMERICAN UPPER RIDGE THIS WEEKEND INTO NEXT WEEK WITH DEMISE OF A  
HOT RIDGE OVER THE U.S. SOUTHERN TIER. THIS TRANSITION WOULD ALLOW  
ENERGETIC MID-LATITUDE AND NORTHERN STREAM SHORTWAVE TROUGHS TO  
MORE ROBUSTLY DIG DOWNSTREAM TO CARVE OUT AN AMPLIFIED  
EAST-CENTRAL NORTH AMERICAN UPPER TROUGH TO FOCUS COOLER/UNSETTLED  
WEATHER AND POSSIBLY OFFER SOME CONNECTION TO TROPICAL LATTUDES TO  
MONITOR BY MID-LATER NEXT WEEK.  
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
MODEL GUIDANCE REMAINS AGREEABLE WITH THE TRACK OF HURRICANE FIONA  
TOWARD THE CANADIAN MARITIMES EVEN AS IT TRANSITIONS TO A VERY  
DEEP EXTRATROPICAL LOW DURING THE MEDIUM RANGE PERIOD. WPC AND THE  
NATIONAL HURRICANE CENTER WILL ALSO CONTINUE TO MONITOR THE  
TROPICS REGARDING INVEST 98L, WHICH IS LIKELY TO FORM INTO A  
TROPICAL CYCLONE IN THE CARIBBEAN PER THE NHC TROPICAL WEATHER  
OUTLOOK. RECENT GFS/ECMWF RUNS AGRESSIVELY DEVELOP THE TROPICAL  
SYSTEM INTO NEXT MIDWEEK WITH A MORE NORTHWARD TRACK INTO THE GULF  
OF MEXICO COMPARED BOTH CMC RUNS AND THE CENTROID OF GEFS/ECMWF  
ENSEMBLE MEMBERS. AS PER COLLABORATION WITH NHC, LEANED AWAY FROM  
THE PLAUSIBLE GFS/ECMWF AT THIS POINT, BUT LATEST 00 UTC GFS RUN  
HAVE NOT BACKED OFF. EVEN SO, THERE IS AMPLE UNCERTAINTY AS THE  
TRACK WILL DEPEND ON MULTIPLE FACTORS INCLUDING THE EXACT UPPER  
TROUGH POSITION AND AMPLITUDE TO THE NORTH THAT MAY PROVIDE A  
CONDUIT TO LIFT ANY SYSTEM TOWARD THE U.S.. STAY TUNED FOR  
FORECAST UPDATES OVER THE NEXT FEW DAYS AS THIS SYSTEM COULD  
EVENTUALLY BE IMPACTFUL.  
 
MODEL AND ENSEMBLE SOLUTIONS ARE WELL CLUSTERED THIS WEEKEND INTO  
MONDAY AND A COMPOSITE OF THE BEST CLUSTERED GFS/ECMWF/CANADIAN  
ALONG WITH THE NATIONAL BLEND OF MODELS (NBM) PROVIDES A GOOD  
BASIS FOR THE FORECAST DURING THAT PERIOD, WITH ENHANCED DETAIL  
CONSISTENT WITH A PATTERN WITH ABOVE NORMAL FORECAST  
PREDICTABILITY. FORECAST SPREAD AND UNCERTAINTY ONLY SLOWLY GROWS  
INTO LONGER TIME FRAMES, BUT AFOREMENTIONED TROPICAL SYSTEM  
DIFFERENCES PROMPTED A SWITCH TO FORECAST USAGE OF THE MORE  
COMPATIBLE GEFS/ECMWF ENSEMBLE MEANS AND THE NBM TO MAINTAIN WPC  
MAX PRODUCT CONTINUITY INTO EARLY-MID NEXT WEEK.  
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
A SHORTWAVE TROUGH TRACKING ACROSS THE NORTH-CENTRAL U.S. WILL  
COMBINE WITH ENERGY FROM NORTHERN CANADA TO DEEPEN A TROUGH WITH  
ITS AXIS IN THE EAST-CENTRAL U.S. FOR THE EARLY PART OF NEXT WEEK.  
THIS TROUGH AND A COUPLE OF FRONTAL SYSTEMS AT THE SURFACE SHOULD  
HELP PRODUCE SOME INCREASING RAINFALL CHANCES FROM THE GREAT LAKES  
TO THE OHIO VALLEY INTO THE WEEKEND, SHIFTING INTO THE EASTERN  
SEABOARD BY LATER SUNDAY INTO MONDAY NEAR THE FRONTAL SYSTEM, WITH  
SOME LAKE ENHANCED RAINFALL BEHIND IT. THE WESTERN U.S. SHOULD SEE  
GENERALLY DRY CONDITIONS DURING THE MEDIUM RANGE PERIOD. SHOWERS  
AND STORMS ARE POSSIBLE ACROSS THE FLORIDA PENINSULA AND MAY  
INCREASE IN COVERAGE BY AROUND TUESDAY AND BEYOND AS THERE IS  
POTENTIAL FOR TROPICAL MOISTURE STREAMING IN. HOWEVER, OPTED TO  
TARGET A DECENT DECREASE IN FLORIDA RAINFALL AMOUNTS COMPARED TO  
THE NBM IN THIS TIME WINDOW FOR NOW GIVEN THE UNCERTAINTY WITH  
FUELING TROPICAL INFLUENCES.  
 
A LINGERING UPPER RIDGE WILL FAVOR CONTINUED WARMTH FOR THE  
SOUTHERN PLAINS AND LOWER MISSISSIPPI VALLEY THROUGH THE WEEKEND  
PRIOR TO MODERATING FRONTAL PASSAGES DOWN ACROSS MUCH OF THE  
CENTRAL AND EASTERN U.S., WITH HIGHS IN THE 90S AND PERHAPS  
ISOLATED 100S, WHICH ARE 10-15F ABOVE AVERAGE. AS UPPER RIDGING  
DEVELOPS IN THE WEST, WARMER THAN AVERAGE TEMPERATURES BY AROUND  
5-10F ARE FORECAST FOR THE FIRST PART OF NEXT WEEK, BRINGING THE  
DESERT SOUTHWEST TEMPERATURES WELL INTO THE 100S.  
 
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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