111  
FXUS02 KWBC 141903  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
303 PM EDT WED SEP 14 2022  
 
VALID 12Z SAT SEP 17 2022 - 12Z WED SEP 21 2022  
   
..OVERVIEW
 
 
THE UPPER LEVEL FLOW PATTERN DURING THE MEDIUM RANGE PERIOD WILL  
BE CHARACTERIZED BY TROUGHING DEEPENING IN THE WEST 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 BY TUESDAY-WEDNESDAY OF NEXT WEEK. MEANWHILE WARMER  
THAN AVERAGE TEMPERATURES WILL BE THE NORM ACROSS THE CENTRAL AND  
EASTERN U.S. INTO THE FIRST HALF OF NEXT WEEK, THOUGH A COOL DOWN  
MAY REACH THE NORTH-CENTRAL U.S. BY AROUND WEDNESDAY AS THE TROUGH  
AND COLD FRONT EDGE 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.  
 
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
THE LATEST RUN OF GUIDANCE SHOWS AN IMPROVEMENT WITH THE OVERALL  
CLUSTERING OF THE UPPER-LEVEL PATTERN THROUGH THE MOST OF THE  
EXTENDED FORECAST PERIOD, AS THEY HAVE CONVERGED WITH THE NOTION  
THAT AN UPPER-LEVEL TROUGH/CLOSED LOW WILL DEVELOP BY THE  
BEGINNING OF THE WEEK AND RESIDE NEAR THE EASTERN PACIFIC  
OCEAN/WEST COAST. THE CMC CONTINUES TO BE MORE OF AN OUTLIER SINCE  
IT QUICKLY LOOSES THE CLOSED LOW FEATURE AND ADVANCES THE TROUGH  
ACROSS THE WEST WHILE THE REST OF THE PACK MAINTAINS THE LOW AND  
IS SLOW TO PROGRESS EASTWARD. THE CMC HAS THE NORTHERN/SOUTHERN  
STREAMS PHASED THUS THE FASTER PROGRESSION. AS PREVIOUSLY NOTED,  
THE TIMING DIFFERENCES INCREASE DURING TUESDAY-WEDNESDAY WITH THE  
TROUGH'S SLOW EASTWARD MOTION, DEPENDING IN PART ON HOW LONG THE  
CLOSED LOW HOLDS ON AND HOW PHASED THE SOUTHERN/NORTHERN STREAMS  
MAY BE. BOTH THE GFS AND ECWMF KEEP THE SOUTHERN STREAM CLOSED LOW  
CUT OFF AND LINGERING IN THE GREAT BASIN WHILE THE NORTHERN STREAM  
FLOW RUSHED A LOW AMPLITUDE TROUGH EASTWARD INTO THE GREAT LAKES  
NEXT WEDNESDAY. THE ECWMF WAS ON THE WESTERN EDGE OF THE GUIDANCE  
LIKE THE PREVIOUS RUN WHICH KEEPS THE PRECIPITATION MORE NEAR THE  
COAST OFFSHORE THAN THE BULLISH GFS MOVING MUCH FURTHER INLAND  
ACROSS CALIFORNIA/GREAT BASIN. THE ENSEMBLE MEANS FAVOR THE SLOWER  
EVOLUTION OF THEIR PARENT GUIDANCE BUT ALSO HAVE SOME SPREAD AS  
WELL. DOWNSTREAM, RIDGING WILL BUILD OVER THE CENTRAL AND EASTERN  
STATES IN RESPONSE TO THE TROUGHING OVER THE WEST. SIMILAR TO THE  
FORECAST CHALLENGE OF WHERE THE TROUGH/LOW SETUPS, THERE IS SOME  
UNCERTAINTY OF WHERE THE WESTERN EDGE OF THE RIDGE WILL BE.  
ADDITIONALLY, SOME SHORTWAVE ENERGY MAY PASS THROUGH THE NORTHERN  
PERIPHERY OF THE RIDGE WHICH MAY SUPPRESS IT AND ALLOW FOR SHOWERS  
TO SPREAD ACROSS THE PLAINS, UPPER MIDWEST, GREAT LAKES AND INTO  
NEW ENGLAND. THE WPC PREFERRED MODEL BLEND USED THE ECWMF, GFS,  
GEFS MEAN, EC ENSEMBLE MEANS THROUGH ALL PERIODS AND VERY LIGHT  
AMOUNTS OF THE CMC AND UKMET EARLY ON.  
 
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
UPPER TROUGHING ACROSS THE EASTERN PACIFIC AND WESTERN U.S. WILL  
PROMOTE A COOL SEASON TYPE PRECIPITATION PATTERN THIS WEEKEND INTO  
EARLY NEXT WEEK, WITH RAIN AND EVEN SOME SNOW IN THE HIGHEST  
ELEVATIONS ACROSS CALIFORNIA INTO THE NORTHWEST. THE BEST  
POTENTIAL FOR SNOW IS THE NORTHERN ROCKIES BUT MAY REACH AS FAR  
SOUTH AS THE SIERRA NEVADA. TROPICAL MOISTURE FROM A DISTURBANCE  
IN THE EASTERN PACIFIC THAT IS LIKELY TO BECOME TROPICAL (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. A FRONTAL SYSTEM OR TWO AND A SHORTWAVE  
TROUGH ROUNDING THE NORTHERN SIDE OF THE RIDGE SHOULD CAUSE A  
ROUND OF RAINFALL TRACKING EAST FROM THE UPPER MIDWEST AND UPPER  
GREAT LAKES REGION THIS WEEKEND INTO THE NORTHEAST MONDAY. THERE  
MAY BE INSTANCES OF MODERATE, POSSIBLY HIGHER INTENSITY RAINS,  
HOWEVER THE CONFIDENCE OF FLASH FLOODING CONDITIONS ARISING AND  
WHERE IS LOW AT THIS TIME. A STALLED FRONT IS EXPECTED TO LINGER  
OVER FLORIDA AND THE GULF OF MEXICO WHICH MAY TRIGGER SHOWERS AND  
THUNDERSTORMS FOR FLORIDA AND PARTS OF THE GULF COAST.  
 
MUCH OF THE WEST WILL HAVE COOLER TEMPERATURES WHILE LOCATIONS  
EAST OF THE ROCKIES WILL REMAIN TOASTY. HIGHS IN PARTICULAR ARE  
FORECAST TO BE 10-20F BELOW NORMAL IN THE WEST THIS WEEKEND, WITH  
BELOW AVERAGE HIGHS GRADUALLY SHIFTING EASTWARD INTO THE NORTHERN  
ROCKIES AND NORTHERN HIGH PLAINS AS NEXT WEEK PROGRESSES, WHILE  
LOWS REMAIN CLOSER TO NORMAL. MEANWHILE THE CENTRAL PLAINS INTO  
THE MIDDLE MISSISSIPPI VALLEY CAN EXPECT HIGH TEMPERATURES 10-20F  
ABOVE AVERAGE THROUGH TUESDAY, WITH ACTUAL TEMPERATURES WELL INTO  
THE 90S. WARMER THAN NORMAL TEMPERATURES WILL EXTEND EASTWARD ALL  
THE WAY TO THE EAST COAST FOR THE FIRST HALF OF NEXT WEEK, THOUGH  
WITH SLIGHTLY LESSER ANOMALIES.  
 
CAMPBELL/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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