419  
FXUS02 KWBC 091901  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
300 PM EDT FRI SEP 09 2022  
 
VALID 12Z MON SEP 12 2022 - 12Z FRI SEP 16 2022  
   
..OVERVIEW
 
 
MOST GUIDANCE AGREES FAIRLY WELL WITH THE LARGE SCALE PATTERN  
THROUGH THE PERIOD. EXPECT A CLOSED UPPER LOW AND OCCLUDED SURFACE  
LOW TO TRACK OVER THE GREAT LAKES DURING THE FIRST PART OF THE  
WEEK, SWEEPING A LEADING COLD FRONT OFF THE EAST COAST BY MIDWEEK.  
A TRAILING UPPER RIDGE SHOULD PROGRESS AT LEAST AS FAR EAST AS THE  
MISSISSIPPI VALLEY, BRINGING MULTIPLE DAYS OF VERY WARM  
TEMPERATURES TO THE SOUTHERN TWO-THIRDS OF THE PLAINS. MEAN  
TROUGHING COMPOSED OF MULTIPLE SHORTWAVES WILL LIKELY SET UP NEAR  
THE WEST COAST AND PROMOTE COOLER WEATHER OVER THE WEST. THE  
WESTERN U.S. FLOW PATTERN SHOULD ALSO DIRECT MOISTURE ORIGINATING  
FROM KAY ACROSS THE INTERMOUNTAIN WEST AND PARTS OF THE ROCKIES,  
LEADING TO SOME LOCALLY ENHANCED RAINFALL FROM SHOWERS AND  
THUNDERSTORMS. FINALLY THERE IS SOME SIGNAL FOR AN UPPER  
LOW/WEAKNESS TO DEVELOP OVER THE SOUTHEASTERN U.S. LATE IN THE  
WEEK AND INTERACT WITH A WAVY STALLED SURFACE FRONT. AT THIS TIME  
CONFIDENCE IS LOW REGARDING COVERAGE AND MAGNITUDE OF ASSOCIATED  
RAINFALL THAT MAY AFFECT PARTS OF THE EXTREME SOUTHEAST AT THAT  
TIME.  
 
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
LATEST GUIDANCE APPEARS TO CONFIRM THE RECENT ACCELERATION IN THE  
EJECTION OF THE MIDWEST/GREAT LAKES UPPER LOW EARLY IN THE WEEK,  
IN RESPONSE TO MORE AMPLIFIED SOUTHERN CANADA FLOW. THE 00Z  
CMC/UKMET WERE STILL SLOWER THAN THE LATEST GFS/ECMWF RUNS THROUGH  
06Z BUT THE NEW 12Z CMC HAS JOINED THE GFS/ECMWF CLUSTER AND THE  
12Z UKMET HAS IN FACT TRENDED EVEN FASTER THAN THE CURRENT  
MAJORITY. AFTER THIS UPPER LOW DEPARTS THERE IS A DEVELOPING  
SIGNAL FOR SOME TRAILING ENERGY TO SETTLE SOMEWHERE OVER THE  
SOUTHEAST LATER IN THE WEEK. HOWEVER UP TO THIS POINT THERE HAS  
BEEN SIGNIFICANT SPREAD AND VARIABILITY IN THE SHAPE AND LOCATION  
OF THE ENERGY--ANYWHERE BETWEEN THE LOWER MISSISSIPPI VALLEY AND  
SOUTHEAST COAST. THE BEST AVERAGE OF MODELS AND MEANS (EITHER  
EXPLICITLY OR IMPLIED) WOULD HAVE THIS FEATURE CENTERED OVER OR A  
LITTLE SOUTH OF THE FAR SOUTHERN APPALACHIANS BY EARLY NEXT  
FRIDAY. SOME INDIVIDUAL SOLUTIONS (SUCH AS THE GFS) HAVE THE  
INTERACTION OF THIS FEATURE AND WAVY SURFACE FRONT TO THE SOUTH  
BRINGING HEAVY RAINFALL INTO PARTS OF THE FAR SOUTHEAST/CAROLINAS  
WHILE THE ECMWF AND ENSEMBLE MEANS ARE NOTABLY SUPPRESSED. OVERALL  
PREFER AN INTERMEDIATE SOLUTION GIVEN THE DETAIL UNCERTAINTY,  
LEADING TO INCREASED RAINFALL POTENTIAL BUT FOR NOW NOT TO THE  
EXTENT OF THE HEAVIEST SOLUTIONS. ANY ADJUSTMENTS OVER THE WEST  
FALL MORE INTO THE MINOR DETAIL REALM. LINGERING UPPER ENERGY FROM  
KAY SHOULD LIFT NORTHEASTWARD AHEAD OF A SHORTWAVE PUSHING INTO  
THE NORTHWEST BY TUESDAY, WITH THE COMBINATION OF THESE FEATURES  
REACHING THE HIGH PLAINS/SOUTHERN CANADA BY MIDWEEK. ANOTHER WEAK  
FEATURE SHOULD DRIFT INTO THE WEST MID-LATE WEEK WHILE A NORTHERN  
STREAM TROUGH MAY PUSH INTO BRITISH COLUMBIA AND POSSIBLY THE  
NORTHWEST ON FRIDAY. SOME NEW 12Z GUIDANCE IS ADDING SOME DOUBT IN  
THE CONSENSUS THOUGH, WITH THE 12Z CMC/ECMWF EACH STRAYING  
SIGNIFICANTLY OUT OF SYNC OVER THE PACIFIC AND/OR SOUTHERN CANADA  
IN VERY DIFFERENT WAYS BY FRIDAY.  
 
THE UPDATE TO THE WPC FRONTS/PRESSURES FORECAST EMPHASIZED THE 06Z  
GFS/00Z ECMWF WITH LESSER INPUT OF THE CMC/UKMET EARLY IN THE  
PERIOD. DETAIL UNCERTAINTIES LED TO INCREASING GEFS/ECMWF ENSEMBLE  
MEAN WEIGHTS TO ABOUT HALF TOTAL BY THE END OF THE PERIOD. THIS  
APPROACH LED TO FAIRLY GOOD CONTINUITY WITH MOST ASPECTS OF THE  
FORECAST. THE MAIN CHANGE REFLECTS THE DEVELOPING SIGNAL FOR A  
BETTER DEFINED LATE-WEEK UPPER FEATURE OVER THE SOUTHEAST AND  
ASSOCIATED QPF INCREASE. STILL, PREFERENCE WAS TO TEMPER THE  
HEAVIEST NBM TOTALS A BIT WITH ALONG THE GULF/SOUTHEAST COASTS TO  
ALLOW FOR A SMOOTHER CONTINUITY TRANSITION.  
 
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
WHILE KAY IS CURRENTLY A TROPICAL STORM IN THE EASTERN PACIFIC OFF  
THE COAST OF NORTHERN BAJA CALIFORNIA PER THE 1500Z NATIONAL  
HURRICANE CENTER ADVISORY, NHC FORECASTS SHOW KAY BECOMING A  
POST-TROPICAL CYCLONE AND THEN DISSIPATING DURING 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. MOST GUIDANCE SHOWS PRECIPITABLE WATER VALUES OF AT  
LEAST 2-3 STANDARD DEVIATIONS ABOVE NORMAL WITHIN THIS MOISTURE  
SHIELD. THUS EXPECT SOME LOCALLY MODERATE TO HEAVY RAINFALL WITH  
REFINEMENT IN THE DETAILS LIKELY TO COME IN THE SHORTER RANGE TIME  
FRAME. 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. AT THE MOMENT, THE BEST CONFIDENCE IN A  
CONCENTRATED AREA OF HEAVY RAINFALL IS WITH A BAND NORTH OF THE  
GREAT LAKES UPPER LOW. THE EXPERIMENTAL DAY 4 EXCESSIVE RAINFALL  
OUTLOOK HAS INTRODUCED A SLIGHT RISK AREA FOR THAT ACTIVITY. THE  
SOUTHERN END OF THE EASTERN 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. CONFIDENCE IS LOW IN  
DETAILS AS THIS EVOLUTION HAS REALLY JUST STARTED TO BECOME MORE  
APPARENT IN THE GUIDANCE OVER THE PAST DAY. CONTINUE TO MONITOR  
FORECASTS AS SLIGHT ADJUSTMENTS IN SPECIFICS COULD SIGNIFICANTLY  
INFLUENCE RAINFALL COVERAGE AND AMOUNTS OVER SOME LOCATIONS.  
 
THE MOST NOTABLE TEMPERATURE ANOMALIES NEXT WEEK WILL BE OVER THE  
PLAINS. NORTHERN AREAS WILL SEE HIGHS 10-15F ABOVE NORMAL ON  
MONDAY FOLLOWED BY A COOLER TREND CLOSER TO NORMAL. THEN ABOVE  
NORMAL READINGS WILL SETTLE OVER THE CENTRAL-SOUTHERN PLAINS FOR  
THE REST OF THE WEEK WITH SOME PLUS 10-15F ANOMALIES FOR HIGHS  
AND/OR MORNING LOWS. 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. 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.  
 
RAUSCH/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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