954  
FXUS02 KWBC 030648  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
247 AM EDT THU AUG 03 2023  
 
VALID 12Z SUN AUG 06 2023 - 12Z THU AUG 10 2023  
 
...HEATWAVE TO PERSIST OVER THE SOUTH AND WORK BACK INTO THE  
SOUTHWEST...  
...EXCESSIVE RAIN/FLASH FLOOD THREAT FOR THE UPPER MIDWEST/GREAT  
LAKES SUNDAY AND INTO THE NORTHEAST EARLY NEXT WEEK...  
 
   
..OVERVIEW
 
 
A MONSOONAL MOISTURE CONNECTION OUT FROM THE WEST AND A  
SUBSTANTIAL GULF MOISTURE AND INSTABILITY FEED WITH DEEPENED  
LOW/FRONTAL APPROACH WILL FUEL AN EXCESSIVE RAINFALL THREAT WHOSE  
FOCUS IS SLATED TO REACH THE UPPER MIDWEST/GREAT LAKES SUNDAY  
BEFORE EJECTING ACROSS THE NORTHEAST EARLY NEXT WEEK. AN INITIALLY  
CLOSED UPPER SYSTEM ENERGY WILL SLIDE EASTWARD OVERTOP A MAIN  
UPPER RIDGE AS KICKED BY ADDITIONAL NORTHERN STREAM UPPER  
TROUGHING FROM THE CANADIAN PRAIRIES. THIS SCENARIO ALSO ACTS TO  
SUPPRESS A CENTRAL U.S. UPPER RIDGE AXIS TO THE U.S. SOUTHERN TIER  
AS THEIR HEATWAVE PERSISTS AND ALSO SPREADS BACK INTO THE  
SOUTHWEST.  
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
THE WPC MEDIUM RANGE PRODUCT SUITE WAS PRIMARILY DERIVED FROM A  
BLEND OF THE 12 UTC ECMWF/ECMWF ENSEMBLE MEAN AND 01 UTC NATIONAL  
BLEND OF MODELS. THE 12 UTC ECMWF AND TO A LESSER EXTENT THE 12  
UTC ECMWF ENSEMBLE MEAN OFFER A SOLUTION OF THE SLOWER SIDE OF THE  
FULL MODEL AND ENSEMBLE FORECAST ENVELOPE FOR TRANSLATION OF WHAT  
IS PROVING TO BE A SIGNIFICANT/SLOW MOVING AND INITIALLY CLOSED  
SYSTEM OUT FROM THE WEST TO THE NORTHERN PLAINS AND BY THIS PERIOD  
INTO THE MIDWEST/GREAT LAKES ONWARD TO EASTERN CANADA. THE BLEND  
MAINTAINS THAT TREND AND A STRONGER SURFACE SYSTEM AND HEAVY  
RAINFALL THREAT SIGNAL THROUGH THE WEEKEND INTO NEXT WEEK.  
00 UTC MODEL AND ENSEMBLE GUIDANCE HAS OVERALL TRENDED FAVORABLY  
TOWARD THIS PREFERRED SOLUTION, BOLSTERING FORECAST CONFIDENCE.  
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
THE VERY WET PATTERN FOR THE NORTH-CENTRAL U.S. AND MAIN HEAVY  
CONVECTIVE RAIN FOCUS SHOULD SLOWLY SHIFT TO THE UPPER MIDWEST AND  
GREAT LAKES BY SUNDAY AS THE UPPER RIDGE AXIS CENTERED OVER THE  
HIGH PLAINS WEAKENS/SUPPRESSES SOUTH AND NORTHERN TIER FLOW  
FLATTENS. A LINGERING MONSOONAL MOISTURE CONNECTION AND SLOW  
MOVING AND DEEPENED SURFACE LOW/FRONTAL SYSTEM AND UPPER SYSTEM  
ENERGIES COMBINE WITH A CONTINUED AND PRONOUNCED GULF MOISTURE AND  
INTABILITY FEED TO FUEL AN EXCESSIVE RAIN THREAT. AN UPGRADE TO A  
SLIGHT RISK FOR EXCESSIVE RAINFALL HAS BEEN OUTLINED OVER PORTIONS  
OF AN INCREASINGLY WET UPPER MIDWEST FOR SUNDAY, CENTERED ON  
WISCONSIN, ALONG WITH A SURROUNDING MARGINAL RISK AREA ALSO SPREAD  
DOWNSTREAM ACROSS THE GREAT LAKES SUNDAY AND WITH TRANSLATION FOR  
PARTS OF THE NORTHEAST MONDAY WHERE STILL FAVORABLE INGREDIENTS  
COMBINE WITH LOCALLY INCREASED TERRAIN LIFT.  
 
SOUTH OF THE MAIN LOW, A TRAILING FRONT WILL SPREAD DRIER  
AIR/MODERATED TEMPERATURES ACROSS PARTS OF THE CENTRAL TO EASTERN  
U.S. THIS WEEKEND. SHOWERS AND THUNDERSTORMS WILL ALSO TAP POOLED  
MOISTURE NEAR THE ELONGATED FRONT FROM THE WEEKEND INTO NEXT WEEK  
AND AS WITH ADDITIONAL LOW PRESSURE/FRONTAL SYSTEM AND SECONDARY  
SURGES DOWN ACROSS THE EASTERN/SOUTHEASTERN TO THE CENTRAL U.S.,  
WITH SHOWERS/STORMS ALSO TRAILING BACK ACROSS THE ROCKIES TO  
MONITOR GIVEN POTENTIAL MOISTURE FEED AND LOCAL TERRAIN  
ENHANCEMENT.  
 
MEANWHILE, AN ONGOING HEATWAVE SHOULD SETTLE A BIT SOUTH OVER THIS  
WEEKEND TO THE SOUTH OF THE TRAILING FRONT OVER THE SOUTH AS  
UPPER-TROUGHING SHIFTS SOUTHWARD AND THE UPPER-HIGH FLATTENS OUT.  
HIGH TEMPERATURES WILL BE 5 TO 10 DEGREES ABOVE NORMAL WITH HIGH  
HUMIDITY LEADING TO HEAT INDICES IN THE 110-115F RANGE IN SOME  
AREAS, PARTICULARLY THE LOWER MISSISSIPPI RIVER VALLEY. RECORD  
HIGH MAXIMUM AND ESPECIALLY MINIMUM TEMPERATURES ARE WIDELY  
FORECAST IN THESE REGIONS. ADDITIONALLY, AFTER A BRIEF DROP IN  
TEMPERATURES OVER THE DESERT SOUTHWEST, HIGHS WILL ONCE AGAIN WARM  
INTO THE 110S. SOME ABOVE AVERAGE TEMPERATURES WILL ALSO SPREAD UP  
THE WEST COAST FOLLOWING A BIT OF UPPER-RIDGE AMPLIFICATION, WITH  
HIGHS IN THE CENTRAL CALIFORNIA VALLEYS CLIMBING INTO THE MID-100S  
INTO THE WEEKEND AND EARLY NEXT WEEK.  
 
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 FORECAST, EXCESSIVE RAINFALL OUTLOOK,  
WINTER WEATHER OUTLOOK PROBABILITIES, HEAT INDICES AND KEY  
MESSAGES 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  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW  
 

 
 

 
 
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