471  
FXUS02 KWBC 120705  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
305 AM EDT MON SEP 12 2022  
 
VALID 12Z THU SEP 15 2022 - 12Z MON SEP 19 2022  
   
..OVERVIEW
 
 
A SOMEWHAT MESSY UPPER LEVEL PATTERN IS FORECAST FOR THE LATTER  
PART OF THE WORKWEEK WITH A MYRIAD OF SMALL SCALE SHORTWAVES  
EMBEDDED WITHIN THE FLOW, BUT WITH A GENERAL PATTERN OF TROUGHING  
ACROSS THE WESTERN TO NORTH-CENTRAL U.S. AND WARM RIDGING FROM THE  
SOUTH-CENTRAL INTO EAST-CENTRAL U.S.--WITH THE EXCEPTION OF ENERGY  
ACROSS THE SOUTHEAST. THIS FLOW PATTERN WILL PROMOTE AMPLE  
MOISTURE ORIGINATING FROM WHAT WAS TROPICAL CYCLONE KAY INTO  
NORTHERN PARTS OF THE INTERMOUNTAIN WEST AND ROCKIES, LEADING TO  
SOME LOCALLY ENHANCED RAINFALL FROM SHOWERS AND THUNDERSTORMS  
THURSDAY-FRIDAY. FARTHER EAST, RAIN FOCUSING ALONG A WARM FRONT IN  
THE UPPER MIDWEST COULD ALSO BRING HEAVY RAIN TO THAT REGION  
THURSDAY INTO FRIDAY, WITH PERHAPS ADDITIONAL ROUNDS OF RAIN  
THROUGH EARLY NEXT WEEK. WEAK UPPER ENERGY COULD SETTLE OVER THE  
SOUTHEAST FOR A TIME, WHICH ALONG WITH A MEANDERING FRONTAL  
BOUNDARY WILL CAUSE RAIN AND THUNDERSTORMS AT LEAST FOR FLORIDA  
AND PERHAPS REACHING THE GEORGIA/CAROLINA COASTS. BY THE WEEKEND  
INTO EARLY NEXT WEEK, MODEL GUIDANCE VARIES WITH THE OVERALL  
PATTERN, BUT WITH PERHAPS SOME AGREEMENT FOR THE MEAN TROUGH NEAR  
THE WEST COAST TO DEEPEN WITH TIME, POSSIBLY ENOUGH TO INCREASE  
COVERAGE OF PRECIPITATION OVER THE NORTHWEST.  
 
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
MODEL GUIDANCE SHOWS REASONABLY GOOD CONSENSUS FOR THE BEGINNING  
OF THE MEDIUM RANGE PERIOD THURSDAY ACROSS THE CONUS, BUT MODEL  
AGREEMENT QUICKLY DEVOLVES ESPECIALLY UPSTREAM OVER THE PACIFIC,  
WHERE MODELS ARE HIGHLY SENSITIVE TO DIFFERENCES THAT ARISE FROM  
ARCTIC AND PACIFIC SOURCES INCLUDING THE EVENTUAL TRACK OF  
TROPICAL STORM 15W AND ITS TRANSITION TO EXTRATROPICAL AS IT  
RECURVES. THE GFS SUITE INCLUDING THE 12/18Z DETERMINISTIC RUNS  
AND MOST GEFS MEMBERS HAVE BEEN MOST AGGRESSIVE AT CLOSING OFF AN  
UPPER LOW WELL OFFSHORE. THIS ALLOWS FOR RIDGING EXTENDING AS FAR  
WEST AS THE THE GREAT BASIN BY EARLY NEXT WEEK. MEANWHILE ECMWF  
DETERMINISTIC AND MANY ENSEMBLE MEMBERS ARE CONSIDERABLY MORE  
PROGRESSIVE AND TRACK TROUGHING ACROSS THE NORTH-CENTRAL U.S. FOR  
A PRETTY MUCH COMPLETELY OUT OF PHASE FLOW PATTERN BY  
SUNDAY-MONDAY. THE NEW 00Z GFS IS FARTHER EAST THAN ITS PREVIOUS  
RUNS BUT STILL SHOWS A CLOSED LOW, WHILE THE NEW 00Z ECMWF IS  
SIMILAR TO ITS PREVIOUS RUN. THE 12Z CMC MODEL SUITE ACTUALLY  
SEEMED TO BE A GOOD MIDDLE GROUND IN BETWEEN THE EC AND GFS, WITH  
PERIODS OF A CLOSED LOW IN THE DETERMINISTIC RUN IN THE EASTERN  
PACIFIC FARTHER EAST THAN THE GFS (THUS CLOSER TO THE EC TROUGHING  
POSITION), AND THE CMC ENSEMBLE MEAN ACTUALLY SEEMED TO SERVE AS  
THE BEST PROXY FOR A MIDDLE GROUND FORECAST THAT WAS NOT TOO  
AGGRESSIVE IN ONE DIRECTION OR ANOTHER. THUS THE WPC  
FRONTS/PRESSURES FORECAST (IN A SOMEWHAT UNUSUAL MODEL BLEND)  
FAVORED THE CMC ENSEMBLE MEAN MOST HEAVILY BY THE LATTER PART OF  
THE PERIOD, WITH SOME EC MEAN AS WELL. THE 18Z GEFS MEAN WAS  
FARTHER WEST OF CONSENSUS LIKE THE DETERMINISTIC GFS RUNS AND THUS  
NOT FAVORED.  
 
SMALLER SCALE ENERGY IN THE SOUTHEAST AND HOW IT INTERACTS WITH A  
WAVY FRONT IS ALSO A FORECAST CONSIDERATION THROUGH THE PERIOD AS  
IT AFFECTS THE RAINFALL FORECAST ACROSS THAT REGION. OPERATIONAL  
GFS RUNS CONTINUE TO BE ON THE STRONG SIDE OF THE SPREAD FOR THE  
UPPER ENERGY AND THE STRENGTH/NORTHWARD EXTENT OF SURFACE LOW  
PRESSURE ALONG THE EAST COAST, LEADING TO MORE QPF ONSHORE OF THE  
CAROLINAS AND GEORGIA COAST, WHILE OTHER GUIDANCE HAS LITTLE TO NO  
QPF THERE. THE FORECAST PREFERENCE REMAINS DRIER THAN SOME GFS  
RUNS GIVEN BETTER MODEL AGREEMENT FOR DRIER CONDITIONS.  
 
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
WHILE THE SURFACE LOW ASSOCIATED WITH FORMER TROPICAL CYCLONE KAY  
SHOULD CONTINUE TO DISSIPATE OVER THE EASTERN PACIFIC DURING THE  
SHORT RANGE PERIOD, DEEP LAYER SOUTHWESTERLY FLOW WILL LIKELY  
CARRY THE LINGERING MOISTURE FROM KAY INTO THE INTERIOR  
WEST/ROCKIES THIS WEEK, LEADING TO PRECIPITABLE WATER VALUES OF AT  
LEAST 2-3 STANDARD DEVIATIONS ABOVE NORMAL. BY THE MEDIUM RANGE  
TIMEFRAME, THIS ANOMALOUS MOISTURE SHOULD BE IN PLACE ACROSS  
NORTHERN PARTS OF THE GREAT BASIN AND ROCKIES, LEADING TO RAIN AND  
SOME THUNDERSTORMS WITH POTENTIAL FOR LOCALLY MODERATE TO HEAVY  
RAINFALL. FLOODING/FLASH FLOODING IMPACTS OF THIS RAIN ARE  
UNCERTAIN SO THIS PRECLUDES A SLIGHT RISK IN THE EXPERIMENTAL DAY  
4 EXCESSIVE RAINFALL OUTLOOK AT THIS TIME. ANOTHER AREA OF FOCUS  
FOR HEAVY RAIN WILL BE PARTS OF THE UPPER MIDWEST, WHERE GOOD  
MOISTURE TRANSPORT WILL BE PRESENT IN THE VICINITY OF A WARM FRONT  
THURSDAY AND PERHAPS INTO FRIDAY. BEHIND THIS AREA OF RAINFALL,  
CONFIDENCE IN DETAILS ACROSS THE NORTHERN HALF OF THE PLAINS AND  
VICINITY DECREASES CONSIDERABLY. THE PACIFIC NORTHWEST MAY START  
TO SEE AN INCREASE IN PRECIPITATION TOWARD THE END OF THE WEEK OR  
WEEKEND BUT AGAIN CONFIDENCE IS VERY LOW IN THE SPECIFICS AT THIS  
TIME.  
 
A QUASI-STATIONARY FRONT AND PERHAPS A WAVE OR TWO ALONG IT WILL  
BE STALLED ACROSS THE FLORIDA PENINSULA AND BACK ACROSS THE GULF  
OF MEXICO AND WESTERN ATLANTIC THROUGH THE LATTER HALF OF THE WEEK  
INTO THE WEEKEND. THIS WAVY FRONT AND A POSSIBLE DEVELOPING UPPER  
FEATURE OVER THE SOUTHEAST COULD FOCUS RAIN CHANCES ACROSS THESE  
AREAS. FLORIDA IS MOST LIKELY TO SEE ROUNDS OF CONVECTION WITH  
POSSIBLY HEAVY RAINFALL TOTALS. RAIN AMOUNTS ACROSS AREAS LIKE  
COASTAL GEORGIA AND THE CAROLINAS ARE MUCH LESS CERTAIN. MODEL  
GUIDANCE AGREES THAT THE HEAVIEST QPF SHOULD BE OFFSHORE, BUT A  
FEW MODEL RUNS STILL SNEAK SOME RAINFALL ONSHORE NEAR THE ATLANTIC  
COAST. SOUTHERN TEXAS CAN EXPECT SHOWERS AND THUNDERSTORMS WITH  
THE BACK END OF THE FRONT.  
 
THE CENTRAL U.S. IS EXPECTED TO BE QUITE WARM DURING THE MEDIUM  
RANGE TIMEFRAME WITH PERIODS OF RIDGING ALOFT. HIGHS OF 5-15F  
ABOVE AVERAGE WILL BE WIDESPREAD ACROSS MUCH OF THE PLAINS AND  
MISSISSIPPI VALLEY, WITH THE CENTRAL PLAINS PERHAPS SEEING THE  
GREATEST ANOMALIES NEARING 20F ABOVE NORMAL WITH ACTUAL  
TEMPERATURES WELL INTO THE 90S. THE WEST MEANWHILE MAY SEE COOLER  
THAN NORMAL HIGHS BY 5-10F THOUGH LOWS COULD BE AROUND AVERAGE,  
BUT DETAILS DEPEND ON UNCERTAIN TROUGHING ALOFT. OVER THE EAST,  
EXPECT NEAR NORMAL TEMPERATURES ASIDE FROM SOME MODERATELY BELOW  
NORMAL HIGHS IN THE NORTHEAST THURSDAY-FRIDAY BEHIND A REINFORCING  
COLD FRONT.  
 
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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