769  
FXUS02 KWBC 101859  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
258 PM EDT SAT SEP 10 2022  
 
VALID 12Z TUE SEP 13 2022 - 12Z SAT SEP 17 2022  
   
..OVERVIEW
 
 
THE MEDIUM RANGE PERIOD BEGINS TUESDAY WITH GUIDANCE AGREEING UPON  
A FAIRLY AMPLIFIED UPPER PATTERN FEATURING AN UPPER LOW CENTERED  
OVER THE GREAT LAKES REGION, A RIDGE ACROSS THE WEST-CENTRAL U.S.  
CAUSING WARM TEMPERATURES, AND GENERAL WEAK TROUGHING NEAR 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 MULTIPLE SHORTWAVES REACH THE WEST WITHIN THE OVERALL  
TROUGH. ENERGY THAT MAY CREATE AN UPPER LOW OR AT LEAST A WEAKNESS  
IN THE FLOW COULD LINGER IN THE SOUTHEAST WHILE A FRONT MEANDERS  
NEARBY, POTENTIALLY LEADING TO SOME AREAS OF HEAVY RAIN BUT WITH  
VERY LOW CONFIDENCE REGARDING HOW MUCH RAIN WILL FALL OFFSHORE  
VERSUS OVER LAND.  
 
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
OVERALL THE GUIDANCE REMAINS FAIRLY WELL CLUSTERED FOR THE UPPER  
LOW AND SURFACE SYSTEM TRACKING OUT THE GREAT LAKES  
TUESDAY-WEDNESDAY. IF ANYTHING, THE LATEST ARRAY OF GUIDANCE  
(ADDING IN THE 12Z RUNS) SUGGESTS PERHAPS A MODEST NUDGE FASTER TO  
CONTINUE THE TREND FROM RECENT DAYS. THEN THERE IS STILL A FAIR  
AMOUNT OF SPREAD WITH RESPECT TO WEAK ENERGY THAT MAY SETTLE OVER  
THE SOUTHEAST LATER IN THE WEEK AS WELL AS FOR THE CORRESPONDING  
SURFACE REFLECTION. ON THE POSITIVE SIDE, THERE IS MODERATE  
CLUSTERING IN PRINCIPLE ALOFT (ECMWF/GFS/UKMET RUNS AND 00Z CMC  
ALONG WITH MOST ENSEMBLE MEANS). THE PROMINENT EXCEPTION NOW IS  
THE 12Z CMC THAT WHISKS THE FEATURE QUICKLY INTO THE ATLANTIC.  
WITHIN THE MAJORITY SCENARIO, RECENT GFS RUNS WERE MUCH STRONGER  
TO INCORPORATE SOME ENERGY ON THE EASTERN SIDE OF THE OVERALL  
CIRCULATION WHICH LED TO MUCH DEEPER AND NORTHWARD SURFACE LOW  
PRESSURE BY FRIDAY-SATURDAY. THE 12Z GFS HAS CONTINUED A SOUTHWARD  
TREND STARTED BY THE 06Z RUN, BRINGING IT CLOSER TO OTHER GUIDANCE  
AT LEAST INTO SATURDAY. PREFERENCE CONTINUES TO BE WITH A  
CONSERVATIVE INTERMEDIATE SOLUTION GIVEN THE UNCERTAINTY OF THE  
EVOLUTION.  
 
THE FORECAST OVER THE WEST IS REASONABLY AGREEABLE/CONSISTENT FROM  
TUESDAY INTO EARLY THURSDAY, WITH SHORTWAVE ENERGY ORIGINATING  
FROM KAY EJECTING THROUGH THE WEST THEN FOLLOWED BY ANOTHER  
FEATURE CROSSING THE NORTHWEST AND A FARTHER SOUTH SHORTWAVE THAT  
ARRIVES WEDNESDAY-THURSDAY. THEN MODELS AND ENSEMBLE MEMBERS  
RAPIDLY DIVERGE WITH FLOW DETAILS OVER THE EASTERN PACIFIC INTO  
WESTERN NORTH AMERICA. SOME OF THIS IS LIKELY DUE TO DIFFERENCES  
THAT DEVELOP FOR THE HANDING OF A POTENTIALLY STRONG BERING SEA  
STORM AS WELL AS FOR A RECURVING WEST-CENTRAL PACIFIC TROPICAL  
SYSTEM. BY LATE IN THE PERIOD THE POSSIBILITIES AMONG THE MODELS  
RANGE FROM A PROGRESSIVE AND LOW-AMPLITUDE SHORTWAVE CROSSING  
WESTERN CANADA PER THE 00Z ECMWF (BUT WITH A TRAILING SHORTWAVE  
REACHING THE WEST COAST) TO MULTIPLE CMC RUNS PULLING OFF AN UPPER  
LOW WELL OFFSHORE THE WEST COAST. THE NEW 12Z GFS IS A SLIGHTLY  
FASTER VERSION OF THE ENSEMBLE MEANS WHICH DEPICT A MORE AMPLIFIED  
PHASED TROUGH REACHING THE WEST COAST BY EARLY SATURDAY. THE  
06Z/00Z GFS RUNS WERE SOMEWHAT DEEPER AND HAD AN UPPER LOW CLOSING  
OFF NEAR VANCOUVER ISLAND OR PACIFIC NORTHWEST DURING THE DAY  
SATURDAY. LOW CONFIDENCE IN SPECIFICS RECOMMENDS KEEPING THE  
FORECAST CLOSEST TO THE MEANS FOR NOW.  
 
BASED ON THE ABOVE CONSIDERATIONS, THE LATEST FORECAST UPDATE  
BASED ON DATA THROUGH THE 06Z CYCLE INCORPORATED AN OPERATIONAL  
MODEL COMPOSITE FOR THE FIRST HALF OF THE PERIOD (MORE 06Z GFS AND  
00Z ECMWF THAN 00Z CMC/UKMET) FOLLOWED BY A TRANSITION TOWARD  
ABOUT HALF TOTAL WEIGHT OF THE 06Z GEFS/00Z ECMWF MEANS BY DAY 7  
SATURDAY.  
 
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
THE SURFACE LOW ASSOCIATED WITH FORMER TROPICAL CYCLONE KAY SHOULD  
CONTINUE TO DISSIPATE OVER THE EASTERN PACIFIC IN COMING DAYS,  
PERHAPS LOSING DEFINITION BY NEXT TUESDAY. HOWEVER DEEP LAYER  
SOUTHWESTERLY FLOW WILL LIKELY CARRY THE LINGERING MOISTURE FROM  
KAY INTO THE INTERIOR WEST/ROCKIES NEXT WEEK, LEADING TO  
PRECIPITABLE WATER VALUES OF AT LEAST 2-3 STANDARD DEVIATIONS  
ABOVE NORMAL. EXPECT RAIN AND SOME THUNDERSTORMS TO SPREAD ACROSS  
THE CENTRAL GREAT BASIN AND THE FOUR CORNERS STATES TUESDAY WITH A  
GRADUAL TREND FARTHER NORTH INTO THE NORTHERN ROCKIES BY THURSDAY.  
THE ANOMALOUS MOISTURE MAY INCREASE THE POTENTIAL FOR SOME AREAS  
OF LOCALLY MODERATE TO HEAVY RAINFALL. REFINING THE AREAS OF BEST  
FOCUS FOR THIS POTENTIAL WILL DEPEND ON EXACT SHORTWAVE  
DETAILS/TIMING ALONG WITH OTHER INGREDIENTS, SO CONTINUE TO  
MONITOR FORECASTS OVER THE COMING DAYS. RAINFALL SHOULD TREND  
LIGHTER TOWARD THE END OF THE WEEK.  
 
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 SHOULD PUSH OFFSHORE OF  
THE MID-ATLANTIC BY EARLY TUESDAY AND CLEAR OUT RAIN CHANCES  
THERE, BUT IT WILL TAKE ANOTHER DAY FOR THE RAIN TO CROSS THE  
NORTHEAST, 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 VERSUS REMAINING OFFSHORE. KEEP  
WATCHING FOR UPDATES TO THE FORECAST 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.  
 
ELSEWHERE, LOCATIONS OVER AND NEAR SOUTHERN TEXAS MAY SEE PERIODS  
OF RAIN DUE TO PERSISTENT EASTERLY LOW LEVEL FLOW AND A LINGERING  
FRONT. AT THE SAME TIME A WAVY FRONT WILL SET UP OVER THE NORTHERN  
PLAINS FOR MULTIPLE DAYS, PROVIDING A POTENTIAL FOCUS FOR SOME  
EPISODES OF RAINFALL. THUS FAR THERE IS NOT AN AGREEABLE SIGNAL  
FOR ANY SPECIFIC HEAVY RAIN EPISODES ALONG THIS BOUNDARY BUT THIS  
REGION WILL REQUIRE WATCHING SINCE SOME OF THE MOISTURE OVER THE  
WEST THROUGH MIDWEEK SHOULD EVENTUALLY SPREAD OVER THE NORTHERN  
PLAINS.  
 
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 FAIRLY BROAD COVERAGE OF BELOW  
NORMAL HIGHS (BY UP TO 5-10F) TUESDAY-THURSDAY, LIKELY A WELCOME  
CHANGE FROM THE RECENT HEAT. HIGHS OVER THE WEST MAY RETURN CLOSER  
TO NORMAL FRIDAY-SATURDAY WHILE STAYING A LITTLE ON THE COOL SIDE  
OVER THE PACIFIC NORTHWEST. OVERNIGHT/MORNING LOWS SHOULD REMAIN  
NEAR TO ABOVE AVERAGE OVER THE WEST THROUGH THE PERIOD. OVER THE  
EAST, EAST-CENTRAL LOCATIONS WILL BE COOLER THAN NORMAL BEHIND A  
LEADING COLD FRONT TUESDAY AND NEW ENGLAND SHOULD SEE MODERATELY  
BELOW NORMAL HIGHS BEHIND A REINFORCING FRONT LATER IN THE WEEK.  
OTHERWISE EXPECT NEAR NORMAL TEMPERATURES ON MOST DAYS.  
 
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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