037  
FXUS02 KWBC 152036  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
435 PM EDT THU SEP 15 2022  
 
VALID 12Z SUN SEP 18 2022 - 12Z THU SEP 22 2022  
   
..OVERVIEW
 
 
THE OVERALL LARGE-SCALE PATTERN THROUGH THE MEDIUM RANGE PERIOD  
WILL FEATURE A TROUGH AND CLOSED LOW OVER THE EASTERN  
PACIFIC/WESTERN U.S. THAT WILL SLOWLY PROGRESS EASTWARD, RIDGING  
THAT BUILDS IN OVER THE CENTRAL-EASTERN U.S. WITH SHORTWAVE ENERGY  
TRACKING ALONG THE NORTHERN PERIPHERY OVER THE RIDGE TOP. COOLER  
TEMPERATURES AND SOME PRECIPITATION IS IN STORE FOR CALIFORNIA AND  
THE NORTHWEST BEGINNING THIS WEEKEND. MOISTURE INCREASING AHEAD OF  
A POSSIBLY FORMING TROPICAL SYSTEM IN THE EASTERN PACIFIC COULD  
LEAD TO SHOWERS AND THUNDERSTORMS OVER THE FOUR CORNERS REGION BY  
EARLY NEXT WEEK PRIOR TO NORTHERN STREAM TROUGH EDGES A COLD FRONT  
EAST AND CONSIDERABLY COOLS THE NORTH-CENTRAL CONUS. MULTIPLE  
ROUNDS OF RAIN ALONG AND AHEAD OF THIS FRONT WILL SPREAD FROM THE  
PLAINS TO THE GREAT LAKES AND NORTHEAST PROGRESSIVE SHORTWAVES AND  
FRONTAL BOUNDARIES PASSING THROUGH. FURTHER SOUTH, SCATTERED  
THUNDERSTORMS WILL REMAIN POSSIBLE FOR FLORIDA NEAR A LINGERING  
QUASI-STATIONARY FRONTAL BOUNDARY.  
 
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
ANOTHER CYCLE OF GUIDANCE THAT FAVORS HAVING A CLOSED LOW CENTERED  
NEAR THE CALIFORNIA COASTLINE BY SUNDAY THAT MOVES SLOWLY INLAND  
AS THE WEEK PROGRESSES. MOST OF THE MODELS ARE DEPICTING SOME  
SEPARATION FROM THE TROUGH/CLOSED LOW WITHIN THE SOUTHERN STREAM  
FROM THE NORTHERN STREAM; WHICH MOVES MORE QUICKLY TOWARD THE  
EAST. THERE IS SOME DIFFERENCES ON THE STRENGTHEN AND TIMING OF  
THE SHORTWAVE IN THE NORTHERN STREAM WHICH REDUCES CONFIDENCE OF  
WHERE QPF IS EXPECTED TO FALL, THE INTENSITY AND THE AMOUNTS. THE  
ECWMF HAS BEEN PERSISTENTLY GETTING SLOWER IT SEEMS THAT PAST FEW  
DAYS AND QUICKLY LAGS WHILE THE CLUSTER MOVES INLAND AND EAST. THE  
06Z AND 00Z GFS MAINTAIN SEPARATION OF THE STREAMS AND IS THE  
CONTINUES TO BE THE CLOSEST "MIDDLE GROUND" SOLUTION FOR THE  
EXTENDED FORECAST. AS SUCH, THE WPC BLEND USED A MULTI-MODEL  
DETERMINISTIC BLEND THAT FAVORED THE 06/00Z GFS BUT ALSO UTILIZED  
THE UKMET, CMC, ECWMF SPARINGLY EARLY ON AND THEN ELIMINATED ECWMF  
AND CMC WHILE INCREASING THE WEIGHTING OF THE ENSEMBLE MEANS. THIS  
COMBINATION MAINTAINED THE RIDGING FARTHER EAST AND WAS REASONABLE  
FOR AN INITIAL SHORTWAVE TROUGH MOVING FROM THE NORTH-CENTRAL TO  
NORTHEASTERN U.S. SUNDAY-TUESDAY, AND WITH NORTHERN STREAM ENERGY  
PROGRESSING EASTWARD MIDWEEK ATOP THE RIDGE.  
 
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
WITH MULTIPLE DAYS WITH UPPER-LEVEL TROUGHING IN PLACE, COOLER  
TEMPERATURES THAT MAY LEAD TO SOME MIXED PRECIPITATION, OR SNOW  
FOR THE HIGHEST PEAKS ACROSS THE NORTHWEST AND CALIFORNIA. THE  
DAILY TEMPERATURES ARE FORECAST TO BE 10 TO 15 DEGREES F BELOW  
SEASONAL AVERAGE FOR MID SEPTEMBER FOR THE WEST WITH THE COOL  
AIRMASS SPREAD TO THE ROCKIES/HIGH PLAINS EARLY IN THE WEEK AND  
THEN TO THE UPPER MISSISSIPPI VALLEY BY THE MIDDLE/END OF THE WEEK  
AS THE COLD FRONT MAKES ITS WAY EAST. THE ONSHORE RAIN MAY BE  
HEAVY AT TIMES ACROSS PORTIONS OF NORTHERN CALIFORNIA SUNDAY, AND  
BURN SCARS WOULD BE PARTICULARLY VULNERABLE TO FLOODING CONCERNS  
AND DEBRIS FLOWS. THE SIERRA NEVADA COULD SEE SNOW EARLY NEXT  
WEEK, THOUGH THE BEST CHANCES FOR SNOW WITH THIS ACTIVITY ARE IN  
THE NORTHERN ROCKIES BY TUESDAY-WEDNESDAY. TROPICAL MOISTURE FROM  
A DISTURBANCE IN THE EASTERN PACIFIC THAT IS LIKELY TO BECOME A  
TROPICAL CYCLONE (PER THE NATIONAL HURRICANE CENTER) IS FORECAST  
TO STREAM INTO THE FOUR CORNERS STATES AS EARLY AS MONDAY, BUT  
ESPECIALLY BY TUESDAY-WEDNESDAY, INCREASING CHANCES FOR SHOWERS  
AND THUNDERSTORMS THERE WHILE PROVIDING ADDITIONAL MOISTURE FOR  
THE PRECIPITATION ACTIVITY IN THE NORTHWEST. SOME OF THIS DEEP  
MOISTURE WILL ADVECT FURTHER NORTH INTO THE ROCKIES AND ADJACENT  
HIGH PLAINS.  
 
A FRONTAL SYSTEM AND A SHORTWAVE TROUGH ROUNDING THE NORTHERN SIDE  
OF THE UPPER RIDGE SHOULD CAUSE A ROUND OF RAINFALL TRACKING EAST  
FROM THE UPPER GREAT LAKES REGION SPREADING INTO THE NORTHEAST  
SUNDAY AND CONTINUING ACROSS THE INTERIOR NORTHEAST MONDAY. THE  
MODELS SUGGEST THERE COULD BE INSTANCES WHERE MODERATE TO HEAVY  
RAINFALL WILL FALL, PARTICULARLY OVER NEW YORK AND PARTS OF NEW  
ENGLAND WHERE HIGHER AMOUNTS MAY LEAD TO ISOLATED FLASH FLOODING.  
HOWEVER AT THIS TIME THE EXACT LOCATION OF WHERE THERE CONCERNS  
MAY BE IS UNCERTAIN. A SECOND AND STRONG COLD FRONT IS FORECAST TO  
ADVANCE ACROSS THE NORTHERN TIER WHICH WOULD BRING ANOTHER ROUND  
OF SHOWERS. A STALLED FRONT IS FORECAST TO LINGER ACROSS CENTRAL  
TO SOUTHERN FLORIDA AND COULD TRIGGER SHOWERS AND THUNDERSTORMS  
THERE. THE WESTERN END OF THIS FRONT PUSHING SOUTH AND DISSIPATING  
ACROSS THE GULF SHOULD LEAD TO DRIER CONDITIONS FOR THE GULF COAST  
AFTER THE WEEKEND. WITH THE RIDGING BUILDING INTO THE CENTRAL  
U.S., WARMER THAN AVERAGE TEMPERATURES BY 10-20F ARE FORECAST FOR  
THE CENTRAL PLAINS AND MIDDLE MISSISSIPPI VALLEY THROUGH WEDNESDAY  
BEFORE GETTING SUPPRESSED BY THE FRONT, WITH ACTUAL TEMPERATURES  
WELL INTO THE 90S. WARMER THAN NORMAL TEMPERATURES WILL EXTEND  
EASTWARD ALL THE WAY TO THE EAST COAST FOR MUCH OF NEXT WEEK,  
THOUGH WITH SLIGHTLY LESSER ANOMALIES.  
 
CAMPBELL  
 
HAZARDS:  
- HEAVY RAIN ACROSS PORTIONS OF NEW ENGLAND AND NORTHERN  
CALIFORNIA, SUN-MON, SEP 18-SEP 19.  
- HEAVY RAIN ACROSS PORTIONS OF THE FOUR-CORNERS REGION, AS WELL  
AS THE NORTHERN ROCKIES AND NEARBY FOOTHILLS, TUE-WED, SEP 20-SEP  
21.  
- EXCESSIVE HEAT ACROSS PORTIONS OF THE CENTRAL PLAINS, SUN-WED,  
SEP 18-SEP 21.  
 
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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