387  
FXUS02 KWBC 130659  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
258 AM EDT TUE SEP 13 2022  
 
VALID 12Z FRI SEP 16 2022 - 12Z TUE SEP 20 2022  
   
..OVERVIEW
 
 
THE MEDIUM RANGE PERIOD BEGINS FRIDAY WITH BROAD UPPER TROUGHING  
WITH EMBEDDED SHORTWAVES ACROSS MUCH OF THE WESTERN TO  
NORTH-CENTRAL U.S., WHILE WARM RIDGING IS IN PLACE OVER THE  
EAST-CENTRAL CONUS. TROUGHING IS FORECAST TO SHARPEN UP AND DEEPEN  
OVER THE WEST BY THE WEEKEND INTO EARLY NEXT WEEK, THOUGH WITH  
SOME LINGERING MODEL DIFFERENCES IN THE PLACEMENT/TIMING. THIS  
WILL LEAD TO COOLER TEMPERATURES AND SOME PRECIPITATION COMING  
INTO THE WEST. FARTHER EAST, ROUNDS OF RAIN ARE POSSIBLE ALONG THE  
NORTHERN TIER WITH PROGRESSIVE SHORTWAVES AND FRONTAL BOUNDARIES  
PASSING THROUGH, WHILE A MEANDERING FRONT SHOULD CONTINUE TO ALLOW  
FOR SCATTERED THUNDERSTORMS ACROSS FLORIDA AND THE GULF COAST.  
TEMPERATURES SHOULD BE ABOVE NORMAL UNDERNEATH RIDGING IN THE  
CENTRAL U.S. AND EVENTUALLY INTO THE EAST.  
 
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
MODEL GUIDANCE HAS FORTUNATELY COME TO MUCH BETTER CONSENSUS  
COMPARED TO A DAY OR SO AGO WITH THE OVERALL PATTERN AND  
PARTICULARLY THE EVOLUTION OF THE PACIFIC TO WEST COAST TROUGHING.  
HOWEVER SOME MODEL DIFFERENCES REMAIN WITH TIMING OF THE TROUGH'S  
MOVEMENT EASTWARD AS WELL AS THE POTENTIAL FOR A CLOSED LOW WITHIN  
THE TROUGH. GIVEN THAT SOME RELATED ENERGY STEMS UPSTREAM FROM THE  
UNCERTAIN ALASKA/NORTHERN PACIFIC REGION AND SOME FROM THE  
RECURVATURE OF TYPHOON MERBOK IN THE CENTRAL PACIFIC, THE DETAILS  
MAY TAKE MORE TIME TO RESOLVE. FOR THE 12/18Z MODEL CYCLE, THE  
ECMWF REMAINED A SOMEWHAT FASTER SOLUTION WITH LESS POTENTIAL FOR  
A ROUNDED AND PERSISTENT CLOSED LOW COMPARED TO OTHER GUIDANCE.  
GFS RUNS WERE FARTHEST WEST AND SLOWER AS THEY CLOSED OFF A LOW,  
WHILE THE UKMET AND CMC WERE SOMEWHAT IN BETWEEN WITH THE  
POSITION. BY MONDAY AND ESPECIALLY TUESDAY, GFS RUNS KEPT AN UPPER  
LOW CLOSED OFF IN THE PACIFIC WITH EVEN A BIT OF A RETROGRADE, AND  
THIS SOLUTION WAS NOT FAVORED AS IT DID NOT HAVE MUCH ENSEMBLE  
MEMBER SUPPORT. ANY SIGNIFICANT MODEL DIFFERENCES DOWNSTREAM WERE  
MAINLY RELATED TO WHERE RIDGING SETS UP DEPENDENT ON HOW FAR EAST  
THE TROUGH PUSHES INLAND. THUS THE WPC FORECAST USED A BLEND OF  
THE DETERMINISTIC 12Z ECMWF, CMC, AND UKMET AND 18Z GFS EARLY ON,  
LESSENING THE WEIGHTINGS ESPECIALLY OF THE FASTER EC AND SLOWER  
GFS IN FAVOR OF THE GEFS AND EC ENSEMBLE MEANS, WHICH SHOWED  
FAIRLY SIMILAR SOLUTIONS TO EACH OTHER, AND AGREED FAIRLY WELL  
WITH CONTINUITY. THE INCOMING 00Z GFS ESPECIALLY AND TO SOME  
EXTENT THE 00Z CMC HAVE TRENDED A LITTLE FASTER TOWARD THE 12Z AND  
NOW 00Z ECMWF SOLUTIONS.  
 
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
UPPER TROUGHING APPROACHING AND FRONTAL SYSTEMS MAKING THEIR WAY  
ACROSS THE WEST LATE THIS WEEK INTO EARLY NEXT WEEK COULD LEAD TO  
SOME LIGHT TO MODERATE PRECIPITATION ACROSS PARTS OF THE PACIFIC  
NORTHWEST/NORTHERN CALIFORNIA AND INTO PARTS OF THE GREAT BASIN  
AND NORTHERN ROCKIES. WITH THE COLD TROUGHING ALOFT COMING IN  
EARLY NEXT WEEK, THIS COULD PRODUCE SNOW IN THE HIGHEST ELEVATIONS  
OF THE NORTHWEST. FARTHER SOUTH, MOISTURE FROM A TROPICAL SYSTEM  
THAT MAY FORM AND TRACK NEAR BAJA CALIFORNIA COULD LEAD TO SHOWERS  
AND THUNDERSTORMS FOR THE FOUR CORNERS STATES BY AROUND MONDAY.  
INTO THE NORTHERN PLAINS TO MIDWEST, A COUPLE OF FRONTS AND SOME  
SHORTWAVE ENERGY COULD FOCUS MOISTURE AND LEAD TO ROUNDS OF  
RAINFALL THERE DURING THE MEDIUM RANGE PERIOD, PERHAPS REACHING  
THE NORTHEAST EARLY NEXT WEEK. SOME HEAVY RAIN POTENTIAL MAY BE  
POSSIBLE OCCASIONALLY, BUT THERE IS LOW CONFIDENCE FOR PARTICULAR  
AREAS OR TIMES WHEN THIS COULD OCCUR. MEANWHILE, A  
QUASI-STATIONARY FRONT LINGERING FOR SEVERAL DAYS ACROSS THE  
FLORIDA PENINSULA AND BACK ACROSS THE GULF OF MEXICO AND WESTERN  
ATLANTIC SHOULD SUPPORT ROUNDS OF SHOWERS AND THUNDERSTORMS. THE  
HEAVIEST RAIN CONTINUES TO BE FORECAST OFFSHORE OF THE  
GEORGIA/CAROLINA COASTS AND THE GULF COAST, BUT SOME RAINFALL  
COULD SNEAK ONSHORE FROM SOUTHERN TEXAS TO THE NORTH CAROLINA  
OUTER BANKS, BUT WITH THE BEST CHANCE FOR NOTABLE RAIN ONSHORE  
ACROSS FLORIDA.  
 
AS CONFIDENCE IN THE PATTERN OF TROUGHING IN THE WEST AND RIDGING  
DEVELOPING FARTHER EAST GROWS, TEMPERATURE FORECASTS FOR A COOLER  
WEST AND WARMER CENTRAL/EASTERN U.S. ARE BECOMING MORE CLEAR.  
COOLER THAN AVERAGE TEMPERATURES PARTICULARLY IN TERMS OF HIGHS  
ARE EXPECTED TO OVERTAKE THE WESTERN U.S. BY THIS WEEKEND INTO  
EARLY NEXT WEEK. HIGHS OF 10-15F BELOW AVERAGE MAY BE COMMON IN  
THE WEST COAST STATES INTO THE INTERMOUNTAIN WEST, WITH EVEN  
COOLER READINGS CURRENTLY FORECAST CENTERED OVER NORTHERN  
CALIFORNIA ON SUNDAY. MEANWHILE TEMPERATURES ARE FORECAST TO WARM  
TO 10-15F ABOVE AVERAGE (WITH ACTUAL TEMPERATURES WELL INTO THE  
90S) CENTERED IN THE CENTRAL PLAINS/MIDDLE MISSISSIPPI VALLEY FOR  
THIS WEEKEND INTO EARLY NEXT WEEK, AND WARMER THAN NORMAL  
CONDITIONS COULD STRETCH INTO THE MIDWEST/GREAT LAKES TO EASTERN  
U.S. WITH TIME.  
 
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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