022  
FXUS02 KWBC 100705  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
304 AM EDT SAT SEP 10 2022  
 
VALID 12Z TUE SEP 13 2022 - 12Z SAT SEP 17 2022  
   
..OVERVIEW
 
 
THE MEDIUM RANGE PERIOD BEGINS TUESDAY WITH A FAIRLY AMPLIFIED  
UPPER PATTERN WITH GOOD MODEL AGREEMENT FOR AN UPPER LOW CENTERED  
OVER THE GREAT LAKES REGION, A RIDGE ACROSS THE WEST-CENTRAL U.S.  
CAUSING WARM TEMPERATURES, AND TROUGHING OVERALL FOR THE WEST  
COAST. AT THE SURFACE AN OCCLUDED LOW PRESSURE SYSTEM IN THE GREAT  
LAKES WILL SWEEP A COLD FRONT ACROSS THE EASTERN SEABOARD  
TUESDAY-WEDNESDAY, WITH RAIN AND THUNDERSTORMS ALONG AND AHEAD OF  
IT, WHILE THE WESTERN U.S. FLOW PATTERN DIRECTS AMPLE MOISTURE  
ORIGINATING FROM WHAT WAS TROPICAL CYCLONE KAY INTO THE  
INTERMOUNTAIN WEST AND PARTS OF THE ROCKIES, LEADING TO SOME  
LOCALLY ENHANCED RAINFALL FROM SHOWERS AND THUNDERSTORMS. EXPECT  
SOME FLATTENING IN THE LARGE SCALE PATTERN FOR MIDWEEK AND BEYOND,  
THOUGH SOME RIDGING SHOULD PERSIST AND TRACK AT LEAST AS FAR EAST  
AS THE MISSISSIPPI VALLEY AND PERHAPS THE TENNESSEE/OHIO VALLEYS,  
WHILE ROUNDS OF SHORTWAVE TROUGHING COME INTO THE WEST. ENERGY  
PERHAPS CREATING AN UPPER LOW OR AT LEAST A WEAKNESS IN THE FLOW  
COULD LINGER IN THE THE SOUTHEAST WHILE A FRONT MEANDERS NEARBY,  
WHICH COULD PRODUCE SOME HEAVY RAIN BUT WITH UNCERTAINTY REGARDING  
HOW MUCH RAIN FALLS ONSHORE OF THE EXTREME SOUTHEAST.  
 
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
GOOD MODEL AGREEMENT PERSISTED IN THE 12/18Z YESTERDAY MODEL CYCLE  
WITH THE GREAT LAKES UPPER LOW AND OTHER ASPECTS OF THE SYNOPTIC  
SCALE FLOW AT THE BEGINNING OF THE MEDIUM RANGE PERIOD TUESDAY.  
ONE MINOR EXCEPTION WAS THAT THE 12Z UKMET WAS A BIT FASTER THAN  
CONSENSUS WITH THE UPPER LOW LIFTING ACROSS THE NORTHEAST LATE  
TUESDAY INTO WEDNESDAY. WHILE RIDGING INITIALLY CENTERED OVER THE  
ROCKIES TUESDAY SHIFTS EAST WITH TIME TOWARD THE EAST-CENTRAL U.S.  
WITH REASONABLY GOOD AGREEMENT IN THE GUIDANCE, THE DETAILS OF  
ENERGY AND PERHAPS A WEAK CLOSED LOW SETTLING SOMEWHERE IN THE  
SOUTHEAST THURSDAY-SATURDAY ARE STILL UNCERTAIN. THOUGH THIS  
FEATURE IS SMALL SCALE, THE POSITIONING AND STRENGTH OF THE ENERGY  
WOULD AFFECT THE RAINFALL FORECAST, I.E. THE AMOUNT OF RAINFALL  
THAT REACHES AT LEAST COASTAL AREAS OF GEORGIA/THE CAROLINAS AS  
WELL AS PORTIONS OF THE GULF COAST. THIS FORECAST UPDATE ATTEMPTED  
TO STRIKE A MIDDLE GROUND BETWEEN THE MORE SUPPRESSED ECMWF AND  
THE WETTER GFS/CMC RUNS, MUCH LIKE THE LAST FORECAST. THE NEW 00Z  
GFS IS PARTICULARLY AGGRESSIVE IN SPINNING UP A SURFACE LOW NEAR  
THE CAROLINA COAST LATE WEEK.  
 
IN THE WEST, NORTHERN AND SOUTHERN STREAM SHORTWAVE TROUGHS WILL  
PROVIDE A MESSY MEAN TROUGHING PATTERN. MOST MODEL DIFFERENCES ARE  
RELATIVELY MINOR THROUGH THE PERIOD, THOUGH BY LATE WEEK THE CMC  
BECAME A MORE EXTREME OUTLIER IN THE PACIFIC, CUTTING OFF A DEEP  
UPPER LOW AND AFFECTING ITS PATTERN DOWNSTREAM OVER THE CONUS.  
 
THE WPC FORECAST UTILIZED A MULTI-MODEL DETERMINISTIC BLEND  
FAVORING THE ECMWF AND GFS EARLY IN THE PERIOD, AND INCORPORATED  
THE EC AND GEFS MEANS WITH INCREASING PROPORTIONS TO ABOUT HALF BY  
THE END OF THE PERIOD TO ACCOUNT FOR INCREASING DETAIL  
DIFFERENCES. THIS MAINTAINED REASONABLY GOOD CONTINUITY FROM THE  
PREVIOUS FORECAST.  
 
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
THOUGH KAY IS NOW A POST-TROPICAL CYCLONE PER THE NATIONAL  
HURRICANE CENTER AND THE LOW SHOULD CONTINUE TO DISSIPATE THROUGH  
THE WEEKEND INTO EARLY NEXT WEEK, IT WILL STILL PROVIDE INCREASED  
MOISTURE (WITH PRECIPITABLE WATER VALUES OF AT LEAST 2-3 STANDARD  
DEVIATIONS ABOVE NORMAL) FLOWING INTO THE INTERIOR WEST THROUGH  
MUCH OF NEXT WEEK GIVEN DEEP LAYER FLOW FROM THE SOUTHWEST. RAIN  
AND SOME THUNDERSTORMS ARE FORECAST ACROSS THE CENTRAL GREAT BASIN  
AND THE FOUR CORNERS STATES TUESDAY WITH A GRADUAL TREND FARTHER  
NORTH INTO THE NORTHERN ROCKIES BY THURSDAY. LOCALLY MODERATE TO  
HEAVY RAINFALL IS A POSSIBILITY IN SOME AREAS, BUT WITH REFINEMENT  
IN THE DETAILS LIKELY TO COME IN THE SHORTER RANGE TIME FRAME.  
 
FARTHER EAST, RAIN AND THUNDERSTORMS ARE LIKELY IN CONJUNCTION  
WITH THE GREAT LAKES LOW PRESSURE SYSTEM AND ITS ATTENDANT COLD  
FRONT TRACKING ACROSS THE EAST. THE FRONT IS FORECAST TO BE  
PUSHING OFFSHORE OF THE MID-ATLANTIC BY EARLY TUESDAY AND CLEAR  
OUT RAIN CHANCES THERE, BUT REMAIN ACROSS THE NORTHEAST TUESDAY,  
ENDING SOMETIME WEDNESDAY. THE SOUTHERN END OF THE FRONT SHOULD  
LINGER NEAR THE GULF COAST AND OFF THE SOUTHEAST COAST THROUGH THE  
LATTER HALF OF THE WEEK. THIS FRONT AND ANY EMBEDDED WAVES MAY  
COMBINE WITH A POSSIBLE DEVELOPING UPPER FEATURE OVER THE  
SOUTHEAST TO INCREASE RAINFALL OVER THE FAR SOUTHEASTERN U.S., BUT  
WITH LOW CONFIDENCE IN THE DETAILS OF HOW MUCH RAIN WILL FALL  
ONSHORE VS. REMAINING OFFSHORE. CONTINUE TO MONITOR FORECASTS AS  
SLIGHT ADJUSTMENTS IN SPECIFICS COULD SIGNIFICANTLY INFLUENCE  
RAINFALL COVERAGE AND AMOUNTS OVER SOME LOCATIONS. REGARDLESS,  
SEVERAL ROUNDS OF CONVECTION ARE POSSIBLE ACROSS FLORIDA WITH THE  
FRONT STRETCHING ACROSS THE STATE WITH POSSIBLY A WAVE OF LOW  
PRESSURE AS WELL.  
 
THE MOST NOTABLE TEMPERATURE ANOMALIES NEXT WEEK WILL BE OVER THE  
PLAINS, WITH ABOVE NORMAL TEMPERATURES BY 5-15F LEADING TO HIGHS  
IN THE 90S FOR THE SOUTHERN HALF OF THE PLAINS. SOME ABOVE AVERAGE  
TEMPERATURES COULD ALSO STRETCH INTO THE MIDWEST AT TIMES.  
MEANWHILE THE WESTERN U.S. WILL SEE INCREASING COVERAGE OF HIGHS  
5-10F BELOW NORMAL, LIKELY A WELCOME CHANGE FROM THE RECENT HEAT.  
OVERNIGHT/MORNING LOWS SHOULD REMAIN NEAR TO ABOVE AVERAGE THERE.  
THE EAST-CENTRAL U.S. SHOULD BE COOLER THAN NORMAL BEHIND THE COLD  
FRONT TUESDAY BUT MODERATE TO NEAR NORMAL FOR THE LATTER HALF OF  
THE WEEK.  
 
TATE/RAUSCH  
 
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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