573  
FXUS02 KWBC 090700  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
300 AM EDT FRI SEP 09 2022  
 
VALID 12Z MON SEP 12 2022 - 12Z FRI SEP 16 2022  
   
..OVERVIEW
 
 
AS THE MEDIUM RANGE PERIOD BEGINS MONDAY, A CLOSED UPPER LOW AND  
AN OCCLUDED SURFACE LOW AND FRONTAL SYSTEM WILL BE PRESENT ACROSS  
THE UPPER MIDWEST AND MOVE INTO THE GREAT LAKES REGION TUESDAY,  
BEFORE SWEEPING ITS COLD FRONT OFF THE EAST COAST BY MIDWEEK.  
FARTHER WEST, WARM RIDGING IS FORECAST TO SHIFT FROM THE FOUR  
CORNERS REGION INTO THE SOUTH-CENTRAL PLAINS AS NEXT WEEK  
PROGRESSES, WHILE PERIODS OF TROUGHING ALONG THE WEST COAST WILL  
PROMOTE COOLER WEATHER IN THE WEST. THIS FLOW PATTERN SHOULD ALSO  
DIRECT MOISTURE (RELATED TO KAY) INTO THE INTERMOUNTAIN WEST AND  
CAUSE SHOWERS AND THUNDERSTORMS THERE.  
 
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
MODEL GUIDANCE HAS BEEN CONSISTENT WITH SHOWING A CLOSED UPPER LOW  
AND SURFACE SLOWLY MOVING EASTWARD ACROSS THE MIDWEST/GREAT LAKES  
MONDAY-TUESDAY. THE MAIN CHANGE IN THE MODELS OVER THE PAST DAY OR  
SO HAS BEEN TO ACCELERATE THESE FEATURES MORE QUICKLY  
NORTHEASTWARD OUT OF THE CONUS BY LATE WEDNESDAY INTO THURSDAY,  
WHILE OLDER MODEL RUNS HAD THEM FARTHER SOUTH AND LINGERING  
LONGER. THE 12Z (YESTERDAY) GFS WAS STILL ON THE SLOWER SIDE, BUT  
THE 18Z GFS PICKED UP ON THIS TREND THAT THE OTHER 12Z GUIDANCE  
SHOWED. INCOMING 00Z MODELS ARE CONSISTENT WITH THE FASTER  
MOVEMENT OF THESE FEATURES.  
 
MODELS ARE IN GOOD AGREEMENT INITIALLY FOR UPPER RIDGING ACROSS  
THE FOUR CORNERS AND A SHORTWAVE NEAR THE PACIFIC NORTHWEST  
MONDAY. THE DETAILS BECOME MORE NEBULOUS AS THAT SHORTWAVE TRAVELS  
EAST, POSSIBLY DISRUPTING THE NORTHERN EDGE OF THE RIDGE (AS GFS  
RUNS SHOW MOST AGGRESSIVELY) AROUND WEDNESDAY-THURSDAY, AND ROUNDS  
OF UNCERTAIN ADDITIONAL ENERGY ENTER THE LOWER 48 FROM UPSTREAM.  
CLEAR TRENDS OR OUTLIERS WERE NOT REALLY EVIDENT HERE BUT THE  
DIFFERENCES DO MAKE THE DETAILS SOMEWHAT UNCERTAIN.  
 
THE WPC FRONTS/PRESSURES FORECAST WAS BASED ON A BLEND OF THE 18Z  
GFS AND 12Z ECMWF, CMC, AND UKMET EARLY IN THE PERIOD, WITH  
INCREASING WEIGHTING OF THE ECMWF AND GEFS ENSEMBLE MEANS TO ABOUT  
HALF BY THE END OF THE PERIOD. THIS LED TO A FASTER EASTERN  
TROUGH/LOW AND FRONT COMPARED TO THE PREVIOUS FORECAST, WITH SOME  
CHANGES IN THE ASSOCIATED QPF MOVING MORE QUICKLY ACROSS THE  
NORTHEAST TUESDAY-WEDNESDAY.  
 
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
WHILE KAY IS CURRENTLY A TROPICAL STORM IN THE EASTERN PACIFIC OFF  
THE COAST OF BAJA CALIFORNIA, THE NATIONAL HURRICANE CENTER  
FORECASTS KAY TO BECOME A POST-TROPICAL CYCLONE AND THEN DISSIPATE  
THROUGH THE MEDIUM RANGE PERIOD. REGARDLESS OF KAY'S STATUS,  
INCREASED TROPICAL MOISTURE LOOKS TO FLOW INTO MUCH OF THE WEST  
WITH DEEP LAYER FLOW FROM THE SOUTHWEST. RAIN AND SOME  
THUNDERSTORMS ARE POSSIBLE IN THE DESERT SOUTHWEST MONDAY, WITH A  
NORTHWARD TREND TO THE FORECAST RAINFALL INTO THE CENTRAL/NORTHERN  
GREAT BASIN AND ROCKIES AS NEXT WEEK PROGRESSES. THEN FARTHER  
EAST, THE CYCLONE MOVING ACROSS THE UPPER MIDWEST/GREAT LAKES AND  
ITS ATTENDANT FRONTS WILL PRODUCE RAIN AND THUNDERSTORMS ACROSS  
THE NORTHEASTERN QUADRANT OF THE U.S. AND ACROSS THE EASTERN  
SEABOARD MONDAY-TUESDAY BEFORE THE COLD FRONT CLEARS PRECIPITATION  
CHANCES OUT ON WEDNESDAY. ISOLATED FLASH FLOODS ARE POSSIBLE IN  
BOTH THE WEST AND EAST IN AREAS WHERE RAIN IS PARTICULARLY HEAVY.  
THE SOUTHERN END OF THE EASTERN FRONT IS FORECAST TO LINGER NEAR  
THE GULF COAST FOR THE LATTER HALF OF THE WEEK AND COULD CAUSE  
SCATTERED SHOWERS AND STORMS, BUT MOST RAINFALL MAY STAY OFFSHORE  
EXCEPT ACROSS FLORIDA WHERE THE FRONT STALLS.  
 
THE WESTERN U.S. IS FORECAST TO SEE HIGHS AROUND 5-10F BELOW  
NORMAL IN A LIKELY WELCOME CHANGE FROM THE RECENT HEAT.  
OVERNIGHT/MORNING LOWS ARE LIKELY TO REMAIN AROUND AVERAGE TO  
ABOVE AVERAGE THERE. ABOVE NORMAL TEMPERATURES BY AROUND 5-15F ARE  
EXPECTED FOR THE NORTHERN HIGH PLAINS MONDAY AND SPREADING ACROSS  
MUCH OF THE PLAINS TUESDAY AND LASTING INTO LATE WEEK AS THE UPPER  
RIDGE SETTLES THERE. MEANWHILE THE EAST-CENTRAL U.S. SHOULD BE  
COOLER THAN NORMAL BEHIND THE COLD FRONT MONDAY-TUESDAY BUT  
MODERATE TO NEAR NORMAL FOR THE LATTER HALF OF THE WEEK.  
 
TATE  
 
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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