634  
FXUS02 KWBC 240628  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
226 AM EDT WED AUG 24 2022  
 
VALID 12Z SAT AUG 27 2022 - 12Z WED AUG 31 2022  
   
..OVERVIEW
 
 
A RATHER NONDISCRIPT AND SLOWLY PROGRESSIVE MULTI-STREAM UPPER  
FLOW PATTERN LADEN WITH NUMEROUS EMBEDDED IMPULSES OVER THE LOWER  
48 IS EXPECTED TO CONSOLIDATE AND SIGNIFICANTLY AMPLIFY AFTER THE  
WEEKEND IN RESPONSE TO THE SHARP DIGGING OF AN AMPLIFIED GULF OF  
ALASKA UPPER TROUGH. THE AMPLIFIED FLOW WILL THEN HIGHLIGHT A  
RIDGE OVER WESTERN NORTH AMERICA AND A TROUGH OVER EASTERN  
PORTIONS OF THE CONTINENT.  
 
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
THE GFS/ECMWF/UKMET/CANADIAN MODELS OFFER ONLY BROADLY SIMILAR  
MID-LARGER SCALE PATTERN EVOLUTION OVER MUCH OF THE MEDIUM RANGE  
FORECAST PERIOD AS GREATER THAN NORMAL SYSTEM DIFFERENCES AND RUN  
TO RUN CONTINUITY ISSUES REMAIN PREVALENT. THESE ARE MAINLY  
ASSOCIATED WITH THE DEPICTION OF A SLEW OF UPPER FLOW EMBEDDED  
SHORTWAVE IMPULSES AND ASSOCIATED SURFACE SYSTEM REFLECTIONS.  
ACCORDINGLY, THE WPC PRODUCT SUITE WAS PRIMARILY DERIVED FROM A  
COMPOSITE BLEND OF THE MORE STEADY AND COMPATIBLE 18 UTC GEFS/12  
UTC ECMWF ENSEMBLE MEANS ALONG WITH THE 01 UTC NATIONAL BLEND OF  
MODELS (NBM). WPC CONTINUITY IS WELL MAINTAINED IN THE MANNER.  
MODEL AND ENSEMBLE MAIN QPF PATTERNS SEEM FAIRLY ORGANIZED FOR  
AUGUST AND IN SYNC, SO MANUALLY TARGETED CHANGES TO NBM QPF WAS  
CONFINED TO THE EXPANSION OF LIGHT MONSOONAL RAINFALL COVERAGE  
FROM THE SOUTHWEST INTO THE ROCKIES GIVEN LINGERING MOISTURE FROM  
THE RECENT WET PATTERN AND SECONDLY TO ACCELERATE FRONTAL  
CONVECTION OVER THE CENTRAL U.S. NEXT WEEK MORE IN LINE WITH THE  
SLIGHTLY MORE PROGRESSIVE 12 UTC ECMWF/ECMWF ENSEMBLES GIVEN  
RECENT TRENDS, DRIVING HEIGHT FALLS/DENSITY CURRENT POTENTIAL AND  
OVERALL GUIDANCE CONVECTIVE PROPAGATION BIAS.  
 
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
THE BRIEF TRANSITION TO MORE PROGRESSIVE FLOW ALOFT OVER THE WEST  
DURING THE WEEKEND SHOULD PROMOTE A LIGHTER AND MORE SCATTERED  
TREND FOR MONSOON RAINFALL OVER THE SOUTHWEST/FOUR CORNERS STATES.  
SOME OF THE WESTERN U.S. DEEP MOISTURE THAT IS PUSHED EASTWARD MAY  
CONTRIBUTE TO THE EXPANDING AREA OF RAINFALL FORECAST TO SPREAD  
ACROSS THE PLAINS AND EVENTUALLY INTO THE MISSISSIPPI VALLEY/GREAT  
LAKES. A LEADING WARM FRONT FOLLOWED BY A SURFACE TROUGH AND COLD  
FRONT, AS WELL AS NORTHERN TIER UPPER DYNAMICS, WILL ALL PROVIDE  
VARYING DEGREES OF FOCUS FOR WHAT COULD BE MULTIPLE AREAS OF  
LOCALLY MODERATE TO HEAVY RAINFALL WITHIN THE BROAD MOISTURE  
SHIELD. CURRENT FORECASTS SHOW ONE AREA OF RAINFALL FOCUS AROUND  
OKLAHOMA/MISSOURI/ARKANSAS WHERE THE FRONT MAY BE LESS PROGRESSIVE  
THAN THE NORTHERN PART OF THE FRONT AND AS ENHANCED GULF MOISTURE  
RETURNS INLAND ACROSS THE LOWER MISSISSIPPI VALLEY.  
 
SHOWERS/THUNDERSTORMS WILL LIKELY CONTINUE OVER THE SOUTH AND  
FLORIDA PENINSULA THROUGH THE PERIOD BUT WITH ANY AREAS OF  
ENHANCED TOTALS LIKELY TO BE MORE LOCALIZED AND UNCERTAIN ON A  
DAY-TO-DAY BASIS, INCLUDING SOME MODEL VARIABILITY WITH WHETHER  
THE BULK OF RAINFALL WILL BE OFFSHORE OR ONSHORE IN ANY GIVEN  
PERIOD. A WEAKENING FRONT REACHING THE GULF/SOUTHEAST COASTS MAY  
STILL PROVIDE SOME FOCUS LATE THIS WEEK INTO THE WEEKEND. A FRONT  
OVER THE EAST THIS WEEKEND MAY PRODUCE AREAS OF RAINFALL WITH  
VARYING INTENSITY.  
 
WHILE SEASONAL OR EVEN MODERATED LATE SUMMER TEMPERATURES WILL  
STILL FEEL WARM FOR MANY, THE GREATEST THREAT OF ANOMALOUS HEAT IN  
THIS PATTERN MAY EMERGE EARLY-MID NEXT WEEK OVER THE INTERIOR  
NORTHWEST WITH EXPECTED FLOW PATTERN AMPLIFICATION SET TO BUILD AN  
UPPER RIDGE OVER THE REGION LEADING TO MAXIMUM TEMPERATURES  
UPWARDS TO 10-15 DEGREES ABOVE NORMAL VALUES POSSIBLE.  
 
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  
 

 
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page