167  
FXUS02 KWBC 111912  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
312 PM EDT SUN SEP 11 2022  
 
VALID 12Z WED SEP 14 2022 - 12Z SUN SEP 18 2022  
   
..OVERVIEW
 
 
AS THE MEDIUM RANGE PERIOD BEGINS WEDNESDAY, AN UPPER RIDGE WILL  
BE IN PLACE OVER THE CENTRAL U.S. CAUSING WARM TEMPERATURES FOR  
MUCH OF THE PLAINS/MISSISSIPPI VALLEY. AWAY FROM THIS RIDGE,  
TROUGHING WILL PREVAIL OVER THE NORTHEAST AND IN THE WEST. THE  
WARM RIDGE WILL TRACK SLIGHTLY EASTWARD AND LIKELY FLATTEN  
SOMEWHAT THROUGH LATE WEEK, THOUGH SOME RIDGING COULD PERSIST OVER  
PARTS OF THE FAR SOUTHERN PLAINS/ROCKIES THROUGH THE WEEKEND.  
MEANWHILE GUIDANCE CONTINUES TO SUGGEST THAT WEAK UPPER LEVEL  
ENERGY MAY 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. PERSISTENT SOUTHWESTERLY FLOW COMING INTO THE WEST THROUGH  
WEDNESDAY-THURSDAY WILL CONTINUE TO DIRECT 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. THEN  
ROUNDS OF RAIN ARE POSSIBLE LATE WEEK INTO THE WEEKEND FOR THE  
NORTH-CENTRAL U.S. WITH SURFACE WAVES AND FRONTAL SYSTEMS PASSING  
THROUGH. WITH LOW CONFIDENCE IN THE DETAILS, THE MEAN TROUGH NEAR  
THE WEST COAST MAY DEEPEN WITH TIME--POSSIBLY ENOUGH TO INCREASE  
COVERAGE OF PRECIPITATION OVER THE NORTHWEST.  
 
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
ONCE AGAIN, LARGER SCALE DIFFERENCES IN THE FORECAST DEVELOP OVER  
THE NORTHEAST PACIFIC BY EARLY THURSDAY AND PROPAGATE INTO THE  
REST OF THE EASTERN PACIFIC AND NORTH AMERICA THROUGH THE REST OF  
THE WEEK AND WEEKEND. THIS SPREAD ORIGINATES FROM MAJOR  
DIFFERENCES IN THE HANDLING OF A STRONG BERING SEA STORM (RANGING  
FROM THE ECMWF BEING QUITE PROGRESSIVE AND THE GFS KEEPING IT FAR  
WESTWARD), THEN COMPOUNDED BY DIFFERENCES IN THE TRACK OF A  
RECURVING PACIFIC TROPICAL SYSTEM. DIFFERENCES WITH THE BERING SEA  
STORM SHOW UP AS THE ECMWF BEING FLAT AND PROGRESSIVE WITH THE  
LEADING NORTHEAST PACIFIC SHORTWAVE VERSUS OTHER GUIDANCE  
AMPLIFYING MORE INTO THE EASTERN PACIFIC/WEST COAST. WHILE HINTED  
AT BY THE GEFS, THE OPERATIONAL 00Z AND 12Z GFS RUNS ARE THE MOST  
EXTREME IN PULLING OFF AN UPPER LOW WELL OFFSHORE. INTERESTINGLY  
THE 06Z GFS BROUGHT THE UPPER LOW CLOSER TO THE PACIFIC NORTHWEST  
AND WHILE THE 00Z ECMWF BROUGHT AN UPPER LOW TO A SIMILAR LOCATION  
THE LATTER MODEL'S LOW WAS FROM A DIFFERENT TRAILING SOURCE. CMC  
RUNS HIGHLIGHT THE VOLATILITY OF THE FORECAST, WITH SOME PRIOR  
RUNS LOOKING LIKE THE 00Z/12Z GFS, THE 00Z RUN POSSIBLY TOO  
OPEN/PROGRESSIVE WITH THE TROUGH, AND NOW THE 12Z CMC SHOWING A  
CLOSED LOW REACHING THE WEST COAST DURING THE WEEKEND. PERHAPS NOT  
SURPRISINGLY, THE NEW 12Z ECMWF DEVELOPS SOME NOTABLE CHANGES FROM  
THE PREVIOUS RUN LATER IN THE PERIOD. THE HIGH UNCERTAINTY OF THE  
FORECAST FAVORED A BLEND APPROACH THAT INCREASINGLY TRENDS TOWARD  
THE ENSEMBLE MEANS WITH TIME. ISSUES WITH THIS PART OF THE PATTERN  
ULTIMATELY AFFECT THE DETAILS FARTHER EAST ACROSS THE NORTHERN  
U.S. AND SOUTHERN CANADA, AS WELL AS EXACTLY HOW MUCH UPPER  
RIDGING PERSISTS SOUTHERN ROCKIES/PLAINS. PREFER TO STAY AS CLOSE  
TO CONTINUITY AS POSSIBLE WHERE PERMITTED BY THE FAVORED FORECAST  
BLEND.  
 
THE OTHER SIGNIFICANT FORECAST ISSUE CONTINUES TO INVOLVE THE WEAK  
UPPER LEVEL ENERGY THAT MAY DROP INTO THE SOUTHEAST FOR A TIME,  
WITH CONTINUED UNCERTAINTY OVER ITS SHAPE/STRENGTH AND EVENTUAL  
PROGRESSION AS WELL AS HOW IT MAY INTERACT WITH A WAVY SURFACE  
FRONT. THE OPERATIONAL GFS CONTINUES 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. THE GEFS MEAN HAS  
BEEN HINTING AT THE GFS IDEA BUT IN MUCH LESS PRONOUNCED FORM  
WHILE RECENT NBM RUNS HAVE BEEN SHOWING ENOUGH OF A GFS INFLUENCE  
TO FAVOR DAMPENING THE HIGHER AMOUNTS IN THE NORTHERN PERIPHERY OF  
ITS RAINFALL SHIELD IN THE LATTER PART OF THE PERIOD.  
 
THE EARLY PART OF THE UPDATED FORECAST STARTED WITH A BLEND OF  
06Z/00Z OPERATIONAL MODELS (MORE GFS/ECMWF RELATIVE TO THE  
UKMET/CMC). THE RAPIDLY INCREASING GUIDANCE SPREAD FAVORED  
INCORPORATING SOMEWHAT MORE 06Z GEFS/00Z ECMWF MEAN INPUT THAN  
AVERAGE MID-LATE PERIOD, ALREADY 30 PERCENT BY DAY 5 FRIDAY AND 70  
PERCENT BY DAY 7 SUNDAY.  
 
   
..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. EXPECT RAIN AND SOME  
THUNDERSTORMS TO SPREAD ACROSS THE GREAT BASIN AND NORTHERN  
ROCKIES WEDNESDAY-THURSDAY, WITH POTENTIAL FOR 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. AT THIS TIME THERE IS AT LEAST ENOUGH OF A  
SIGNAL TO FAVOR INTRODUCING A SLIGHT RISK AREA IN THE DAY 4  
EXPERIMENTAL EXCESSIVE RAINFALL OUTLOOK (12Z WEDNESDAY-12Z  
THURSDAY) COVERING PARTS OF UTAH AND SOUTHEASTERN IDAHO. THE BEST  
FOCUS FOR ACTIVITY MAY SHIFT A LITTLE NORTHWARD INTO THE ROCKIES  
OVER THE FOLLOWING 24 HOURS BUT CONFIDENCE IS NOT QUITE HIGH  
ENOUGH TO DEPICT A SLIGHT RISK AREA YET. RAINFALL SHOULD SHIFT  
EASTWARD INTO THE NORTHERN PLAINS AND MIDWEST IN THE VICINITY OF A  
COUPLE OF FRONTAL BOUNDARIES AND SOME EMBEDDED WAVES AFTER  
MIDWEEK. THERE IS A DEVELOPING SIGNAL FOR SOME HEAVY RAINFALL  
POTENTIAL WITH A WAVE/WARM FRONT BETWEEN THE NORTHERN PLAINS AND  
UPPER GREAT LAKES DURING THE MID-LATE PART OF THE WEEK. 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  
DIFFERS IN TERMS OF HOW MUCH RAIN COULD SNEAK ONSHORE. KEEP  
WATCHING FOR UPDATES TO THE FORECAST AS SLIGHT ADJUSTMENTS IN  
SPECIFICS COULD SIGNIFICANTLY INFLUENCE RAINFALL COVERAGE AND  
AMOUNTS OVER SOME LOCATIONS. SOUTHERN TEXAS CAN EXPECT SHOWERS AND  
THUNDERSTORMS WITH THE BACK END OF THE FRONT.  
 
THE FORECAST IS CONSISTENT IN SHOWING MULTIPLE DAYS OF ABOVE  
NORMAL TEMPERATURES OVER MOST OF THE PLAINS EXCEPT FOR FAR  
NORTHERN AREAS. MOST DAYS SHOULD FEATURE PLUS 5-15F ANOMALIES FOR  
HIGHS WHICH EQUATES TO 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)  
WEDNESDAY-THURSDAY, LIKELY A WELCOME CHANGE FROM THE RECENT HEAT.  
HIGHS OVER THE INTERIOR WEST MAY RETURN CLOSER TO NORMAL BY FRIDAY  
AND THE WEEKEND WHILE BELOW NORMAL READINGS BECOME MORE CONFINED  
TO THE PACIFIC NORTHWEST COAST WHERE UPPER TROUGHING MAY GRADUALLY  
DEEPEN. OVERNIGHT/MORNING LOWS SHOULD REMAIN NEAR TO ABOVE  
AVERAGE OVER MOST OF THE WEST THROUGH THE PERIOD. OVER THE EAST,  
EXPECT NEAR NORMAL TEMPERATURES ASIDE FROM SOME MODERATELY BELOW  
NORMAL HIGHS IN THE NORTHEAST THURSDAY-FRIDAY BEHIND A REINFORCING  
COLD FRONT.  
 
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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