747  
FXUS02 KWBC 150656  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
255 AM EDT MON AUG 15 2022  
 
VALID 12Z THU AUG 18 2022 - 12Z MON AUG 22 2022  
 
...EXCESSIVE HEAT THREAT FROM INTERIOR CALIFORNIA THROUGH THE  
NORTHWEST/NORTH-CENTRAL INTERMOUNTAIN WEST THIS WEEK...  
 
...MONSOONAL HEAVY RAIN THREAT CONTINUES FOR THE SOUTHWEST AND  
SOUTH-CENTRAL GREAT BASIN/ROCKIES THIS WEEK.  
   
..NEW ENGLAND COASTAL STORM THREAT INTO THURSDAY
 
 
...SOUTH/SOUTHEAST HEAVY RAIN THREAT THIS WEEK.  
 
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
MODELS AND ENSEMBLES REMAIN QUITE AGREEABLE ON PREDICTING THE  
AMPLIFIED UPPER AIR PATTERN ACROSS THE MAINLAND U.S. OVER THE NEXT  
WEEK. AMPLE SMALLER SCALE DIFFERENCES REMAIN, BUT OVERALL FORECAST  
SPREAD SEEMS TO HAVE DECREASED WITH RECENT GUIDANCE RUNS.  
ACCORDINGLY FELT COMFORTABLE USING A COMPOSITE BLEND OF THE  
GFS/ECMWF/UKMET/CANADIAN AND GEFS/ECMWF ENSEMNBLE MEANS ALONG WITH  
THE NATIONAL BLEND OF MODELS (NBM).  
   
..PATTERN OVERVIEW AND WEATHER/HAZARDS HIGHLIGHTS
 
 
AMPLIFIED UPPER RIDGING OVER THE WEST/NORTHWEST THIS WEEK WILL  
SUPPORT A HEAT WAVE WITH DAYTIME/OVERNIGHT TEMPERATURE 10-20F  
ABOVE NORMAL. THESE TEMPERATURES ARE LIKELY TO PRODUCE SOME RECORD  
DAYTIME AND OVERNIGHT VALUES. MEANWHILE, BELOW NORMAL HIGHS ARE  
EXPECTED IN THE EAST-CENTRAL U.S. BEHIND A MAIN FRONT. GIVEN  
RAINFALL AND CLOUDINESS OVER THE SOUTHWEST AND SOUTH-CENTRAL GREAT  
BASIN/ROCKIES, MAXIMUM TEMPERATURES THERE SHOULD ALSO TEND TO BE  
BELOW NORMAL.  
 
MEANWHILE, A LARGE SWATH OF THE WEST HAVE SEEN PERSISTENT  
MONSOONAL MOISTURE OVER THE PAST COUPLE OF MONTHS, AND THIS WEEK  
WILL CONTINUE THAT PATTERN AS ANOMALOUSLY HIGH MOISTURE FEEDS INTO  
THE SOUTHWEST AND SOUTH-CENTRAL GREAT BASIN/ROCKIES IN CONJUNCTION  
WITH SMALL-SCALE SHORTWAVE ENERGY TO PRODUCE RAIN AND  
THUNDERSTORMS, PARTICULARLY IN THE AFTERNOON AND EVENING HOURS.  
ISSUED A WPC EXPERIMENTAL MEDIUM RANGE SLIGHT RISK OF EXCESSIVE  
RAINFALL FOR SOUTHERN ARIZONA FOR THURSDAY AND FRIDAY GIVEN  
ENHANCED QPF/ARI AND OVERALL PERSISTENT FAVORABLE PATTERN. THE 01  
UTC NBM HAS SIGNIFICANTLY TRENDED RAIN AMOUNTS UPWARD ACROSS THE  
SOUTHWEST, BUT TO MITIGATE SOME OF THE CONTINUITY CHANGE WPC QPF  
ALSO INCLUDED A THIRD OF WPC DAYSHIFT CONTINUITY BASED FROM  
YESTERDAYS 13 UTC NBM.  
 
CONVECTIVE ACTIVITY WILL PERSIST THROUGH LATER WEEK/WEEKEND NEAR A  
SLOW MOVING AND WAVY FRONT ACROSS THE SOUTH/SOUTHEAST WITHIN THE  
DEEPLY MOIST PRECIPITABLE WATER VALUES. THE HIGHEST THREAT OF  
HEAVY RAIN MAY BE OVER THE LOWER MISSISSIPPI VALLEY WHERE WPC HAS  
AN EXPERIMENTAL MEDIUM RANGE SLIGHT RISK OF EXCESSIVE RAINFALL  
THURSDAY INTO FRIDAY. TARGETED AN INCREASE IN NBM QPF THERE FRIDAY  
INTO SATURDAY. ORGANIZED RAINS WILL ALSO SLOWLY LIFT TO THE  
MID-ATLANTIC THIS WEEKEND WITH WAVY FRONT RETURN FLOW.  
 
THERE IS LINGERING THREAT FOR COOLED WRAP-AROUND RAINS/ENHANCED  
WINDS OVER ESPECIALLY NORTHERN NEW ENGLAND THURSDAY WITH COASTAL  
CYCLOGENESIS AHEAD OF A CLOSED UPPER LOW. THE DEEPENED COASTAL LOW  
THEN DEPARTS FOR THE CANADIAN MARITIMES WITH EJECTION OF THE  
CLOSED UPPER SYSTEM.  
 
EXPECT ORGANIZED CONVECTION WILL SPREAD ACROSS THE MIDWEST WITH  
LATE WEEK/WEEKEND DIGGING OF SHORTWAVE ENERGY AND A SLOWLY  
PROGRESSIVE LEAD LOW/FRONTAL PASSAGE. NBM QPF HAS TRENDED UPWARD,  
BUT WAS ONCE AGAIN INCREASED ACROSS THIS BROAD REGION GIVEN UPPER  
SUPPORT AND FRONTAL/LOW PASSAGE.  
 
INCREASINGLY ORGANIZED CONVECTIVE RAINS ARE SLATED TO SPREAD OUT  
ACROSS THE SOUTH-CENTRAL PLAINS TO THE MID-MISSISSIPPI VALLEY OVER  
THE WEEKEND. THIS SEEMS REASONABLE AS MOISTURE AND INSTABILITY  
POOL WITH RETURN FLOW INTO A SLOW MOVING FRONT IN FAVORABLE UPPER  
DIFFLUENT FLOW ALOFT. HOWEVER, GIVEN INCREASED UNCERTAINTIES AT  
THESE LONG FORECAST TIME FRAMES, OPTED TO MITIGATE SOME OF THE  
SIGNIFICANTLY INCREASED 01 UTC NBM QPF AREAL COVERAGE/AMOUNTS.  
 
SCHICHTEL  
 
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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