070  
FXUS02 KWBC 150655  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
254 AM EDT THU SEP 15 2022  
 
VALID 12Z SUN SEP 18 2022 - 12Z THU SEP 22 2022  
   
..OVERVIEW
 
 
THE UPPER LEVEL FLOW PATTERN DURING THE MEDIUM RANGE PERIOD WILL  
BE CHARACTERIZED BY AN ANOMALOUSLY DEEP TROUGH/LOW FOR THIS TIME  
OF YEAR OVER THE EASTERN PACIFIC/WESTERN U.S. AND EVENTUALLY  
SHIFTING SLIGHTLY EASTWARD NEXT WEEK, WHILE RIDGING AMPLIFIES  
ACROSS MUCH OF THE CENTRAL AND EASTERN U.S. AHEAD OF IT. THIS WILL  
PROMOTE COOL TEMPERATURES AND SOME PRECIPITATION COMING INTO PARTS  
OF CALIFORNIA AND THE NORTHWEST BEGINNING THIS WEEKEND, AND THEN  
MOISTURE INCREASING AHEAD OF A POSSIBLY FORMING TROPICAL SYSTEM IN  
THE EASTERN PACIFIC COULD LEAD TO SHOWERS AND STORMS IN THE FOUR  
CORNERS STATES POSSIBLY BEGINNING MONDAY AND ESPECIALLY  
TUESDAY-WEDNESDAY OF NEXT WEEK. MEANWHILE WARMER THAN AVERAGE  
TEMPERATURES WILL BE THE NORM ACROSS THE CENTRAL AND EASTERN U.S.  
INTO THE EARLY PART OF NEXT WEEK, BEFORE A NORTHERN STREAM TROUGH  
EDGES A COLD FRONT EAST AND CONSIDERABLY COOLS THE NORTH-CENTRAL  
CONUS. 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.  
 
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
MODEL GUIDANCE HAS BEEN PERSISTENT FOR THE LAST FEW MODEL CYCLES  
SHOWING A CLOSED UPPER LOW CENTERED JUST OFF CALIFORNIA AS THE  
MEDIUM RANGE PERIOD BEGINS SUNDAY. THE TREND OVERALL HAS BEEN FOR  
THIS LOW TO MOVE MORE SLOWLY INLAND INTO THE WEST AS THE WEEK  
PROGRESSES, AS MOST MODELS SHOW SOME SEPARATION BETWEEN IT AND THE  
NORTHERN STREAM TRACKING MORE QUICKLY EASTWARD, BUT NOT UNIFORMLY.  
THE 12Z CMC CONTINUED TO HOLD OUT FOR A MORE PHASED SOLUTION AND  
THUS MORE PROGRESSIVE IN THE SOUTH THAN THE OVERALL CONSENSUS, BUT  
THE NEWER 00Z CMC HAS JUMPED ON BOARD FOR STREAM SEPARATION. THE  
12Z GFS WAS MORE PHASED AS WELL COMPARED TO THE 18Z RUN. THE ECMWF  
CONTINUES TO SHOW STREAM SEPARATION BUT JUST SEEMS TO KEEP GETTING  
SLOWER IN TRACKING THE LOW INLAND, WITH THE 12Z RUN SOMEWHAT  
SLOWER THAN OTHER GUIDANCE AND THE 00Z RUN EVEN MORE SO. THE 18Z  
GFS SEEMED LIKE THE BEST MIDDLE GROUND SOLUTION FOR THE 12/18Z  
MODEL CYCLE.  
 
THE WPC FORECAST BLEND USED A MULTI-MODEL DETERMINISTIC BLEND  
FAVORING THE 18Z GFS AND 12Z ECMWF EARLY ON, THEN ELIMINATED THE  
12Z CMC AND LESSENED THE WEIGHTING OF THE EC IN FAVOR OF THE GEFS  
AND EC ENSEMBLE MEANS AS THE FORECAST PERIOD PROGRESSED. THIS  
BLEND ALSO WORKED FOR OVERALL 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
 
 
UPPER TROUGHING ACROSS THE EASTERN PACIFIC AND WESTERN U.S. WILL  
PROMOTE A COOL SEASON TYPE PRECIPITATION PATTERN EARLY NEXT WEEK,  
WITH RAIN AND EVEN SOME SNOW IN THE HIGHEST ELEVATIONS ACROSS  
CALIFORNIA INTO THE NORTHWEST. SOME HEAVY RAIN MAY OCCUR IN  
NORTHERN CALIFORNIA ON SUNDAY IN PARTICULAR, 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.  
 
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. SOME  
RAINFALL COULD BE MODERATE TO HEAVY, AND INCREASING RAIN AMOUNTS  
IN THE FORECAST ESPECIALLY IN THE NORTHEAST MAKE ISOLATED FLASH  
FLOODING A CONCERN, THOUGH THE DETAILS ARE UNCERTAIN AS THEY WILL  
DEPEND ON THE FRONTAL POSITION. A STRONGER FRONT PUSHING ACROSS  
THE NORTH-CENTRAL U.S. BY MIDWEEK COULD LEAD TO ANOTHER ROUND OF  
RAIN IN THAT AREA. MEANWHILE, 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.  
 
THE WEST COAST WILL BE RATHER COOL PARTICULARLY IN TERMS OF HIGH  
TEMPERATURES FOR THE EARLY PART OF THE WEEK, AS HIGHS 10-20F BELOW  
AVERAGE ARE EXPECTED. THESE COOLER TEMPERATURES ARE FORECAST TO  
SPREAD INTO NORTHERN PARTS OF THE ROCKIES/HIGH PLAINS AND  
EVENTUALLY INTO THE UPPER MIDWEST BY NEXT THURSDAY BEHIND A COLD  
FRONT. MEANWHILE 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.  
 
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  
 

 
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page