281  
FXUS02 KWBC 220700  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
259 AM EDT MON AUG 22 2022  
 
VALID 12Z THU AUG 25 2022 - 12Z MON AUG 29 2022  
 
...SOUTHERN TIER HEAVY RAINFALL THREAT TO BECOME LESS PRONOUNCED  
AFTER MIDWEEK...  
 
...HEAT OVER THE NORTHWEST MAY CHALLENGE SOME DAILY RECORDS ON  
THURSDAY...  
 
   
..OVERVIEW
 
 
LATEST MODELS AND MEANS STILL ADVERTISE A PATTERN TRANSITION  
DURING THE PERIOD, WITH THE EASTERN NORTH AMERICA UPPER TROUGH  
LIFTING OUT AFTER FRIDAY AND A MEAN TROUGH REACHING THE CENTRAL  
U.S./SOUTHERN CANADA BY SATURDAY-MONDAY. THE LATTER TROUGH SHOULD  
BE COMPOSED OF A LEADING TROUGH/COMPACT UPPER LOW EMERGING FROM  
THE NORTHWEST FOLLOWED BY UPSTREAM NORTHEASTERN PACIFIC TROUGH  
ENERGY. INITIAL UPPER RIDGING COVERING THE SOUTHERN HALF OF THE  
WEST WILL TREND WEAKER AND MORE SUPPRESSED AS PACIFIC FLOW  
ARRIVES. MEANWHILE THE WESTERN PERIPHERY OF ATLANTIC UPPER  
RIDGING SHOULD BUILD WESTWARD TO COVER AN INCREASING PORTION OF  
THE EAST/SOUTH DURING THE WEEKEND AND EARLY NEXT WEEK. EXPECT  
SOME AREAS OF RAINFALL TO PERSIST OVER THE SOUTH AND NEARBY AREAS  
DURING THE PERIOD BUT WITH ANY HEAVY TOTALS TENDING TO BE MORE  
LOCALIZED. RAINFALL FOCUSED OVER THE NORTHERN HIGH PLAINS ON  
THURSDAY SHOULD EXPAND AND PUSH EASTWARD WITH TIME AS THE CENTRAL  
U.S. UPPER TROUGH TAKES SHAPE WHILE WESTERN U.S. MONSOONAL  
RAINFALL SHOULD BECOME LIGHTER AND MORE SCATTERED BY THE WEEKEND  
AS UPPER FLOW GAINS A MORE WESTERLY COMPONENT. ABOVE NORMAL  
TEMPERATURES WILL TEND TO BE CONFINED TO THE NORTHWEST, ESPECIALLY  
THURSDAY AND NEXT MONDAY, AS WELL AS THE NORTHEAST. BELOW NORMAL  
HIGHS OVER THE SOUTHERN TIER WILL MODERATE CLOSER TO NORMAL.  
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
THE MOST CONTENTIOUS PART OF THE FORECAST CONTINUES TO INVOLVE THE  
DETAILS OF NORTHEASTERN PACIFIC INTO NORTH AMERICAN FLOW FROM  
ABOUT DAY 4 FRIDAY ONWARD. HIGHLIGHTING THE UNCERTAINTY, THE FULL  
SUITE OF 12Z ENSEMBLE MEMBERS SHOWED ANYTHING FROM A TROUGH TO A  
RIDGE AS POSSIBILITIES OVER THE WEST COAST STATES AND SOUTHWESTERN  
CANADA AS OF EARLY DAY 5 SATURDAY. MEMBERS REMAIN DIVERGENT  
THROUGH THE REST OF THE PERIOD BUT DO EVENTUALLY SHOW A MAJORITY  
SETTLING INTO A PACIFIC TROUGH/WEST COAST-WESTERN CANADA RIDGE AND  
CENTRAL NORTH AMERICA TROUGH BY DAY 7 MONDAY. OPERATIONAL MODELS  
LEANED MORE TO A SHORTWAVE REACHING THE NORTHWEST ON SATURDAY BUT  
WITH THE 12Z/18Z GFS AND 12Z UKMET FLATTER THAN THE 12Z CMC AND  
ESPECIALLY 12Z ECMWF. THE NEW 00Z GFS HAS TRENDED MUCH DEEPER  
WITH THIS SHORTWAVE BUT OTHER MODELS REMAIN MORE MODERATE. BY  
LATE IN THE PERIOD THE 18Z GFS CONFLICTED WITH OTHER GUIDANCE,  
DEVELOPING AN EASTERN PACIFIC RIDGE WHERE CONSENSUS HAD A TROUGH.  
THE NEW 00Z GFS BRINGS A BROAD SHORTWAVE THROUGH THE CONSENSUS  
RIDGE BUILDING INTO BRITISH COLUMBIA SUNDAY-MONDAY BUT AT LEAST IT  
BETTER FITS THE TROUGH TO THE WEST. THE ONE OTHER ITEM OF NOTE IS  
THAT RECENT TRENDS HAVE BECOME MORE SUBDUED WITH ANY POSSIBLE WEAK  
FEATURE OVER THE GULF OF MEXICO. THE 12Z CMC HAD A WEAK SURFACE  
WAVE LIFTING THROUGH THE WESTERN GULF BUT THE 00Z RUN HAS ADJUSTED  
WEAKER/SOUTHWESTWARD.  
 
GUIDANCE COMPARISONS LED TO STARTING WITH A 12Z/18Z OPERATIONAL  
MODEL COMPOSITE DURING THE FIRST HALF OF THE PERIOD, YIELDING AN  
INTERMEDIATE DEPICTION FOR THE SHORTWAVE EXPECTED TO REACH THE  
NORTHWEST BY EARLY SATURDAY (AND NOW SUPPORTED BY THE NEW 00Z  
ECMWF). INCREASING DETAIL UNCERTAINTIES THEREAFTER, ALONG WITH  
INCREASINGLY SUSPECT 18Z GFS HANDLING OF THE EASTERN PACIFIC  
PATTERN, LED TO A RAPID INCREASE OF 18Z GEFS/00Z ECMWF MEAN WEIGHT  
AND EVENTUAL REPLACEMENT OF THE 18Z GFS COMPONENT WITH THE 12Z  
RUN. TOTAL ENSEMBLE WEIGHT REACHED 60 PERCENT BY DAY 7 MONDAY.  
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
EXPECT SOME EPISODES OF SHOWERS AND THUNDERSTORMS TO CONTINUE  
ACROSS THE SOUTH AND FLORIDA PENINSULA THROUGH THE PERIOD, BUT  
WITH ANY AREAS OF ENHANCED TOTALS LIKELY TO BE MORE LOCALIZED AND  
MORE UNCERTAIN IN LOCATION/MAGNITUDE THAN IN THE SHORTER TERM. A  
WEAKENING FRONT REACHING THE GULF/SOUTHEAST COASTS MAY STILL  
PROVIDE SOME FOCUS LATE THIS WEEK INTO THE FIRST PART OF THE  
WEEKEND. LOCATIONS OVER THE NORTHERN HIGH PLAINS MAY SEE SOME  
ENHANCED RAINFALL THURSDAY AND POSSIBLY INTO FRIDAY WITH A COUPLE  
FRONTS OVER THE AREA AND THE UPPER TROUGH/LOW APPROACHING FROM THE  
NORTHWEST. THIS MOISTURE SHOULD THEN PROGRESS EASTWARD AND EXPAND  
WITH TIME AS THE CENTRAL U.S. MEAN TROUGH DEVELOPS. MEANWHILE  
MONSOONAL RAIN AND THUNDERSTORMS SHOULD CONTINE OVER AND NEAR THE  
FOUR CORNERS STATES THROUGH LATE THIS WEEK FOLLOWED BY A DRIER  
TREND FROM WEST TO EAST AS THE UPPER RIDGE INITIALLY OVER THE  
REGION COLLAPSES. SOME OF THE DEEP MOISTURE MAY REACH EASTWARD  
AND CONTRIBUTE TO THE EXPANDING AREA OF CENTRAL U.S. RAINFALL  
DURING THE WEEKEND. A COLD FRONT DROPPING SOUTHWARD THROUGH THE  
EAST DURING THE PERIOD MAY PRODUCE AREAS OF RAINFALL WITH VARYING  
INTENSITY, THOUGH CURRENTLY WITH NO COHERENT SIGNAL FOR ORGANIZED  
AREAS OF SIGNIFICANT TOTALS.  
 
WARMEST TEMPERATURE ANOMALIES SHOULD BE OVER THE NORTHWEST ON  
THURSDAY WITH SOME LOCATIONS SEEING HIGHS 10-15F ABOVE NORMAL AND  
A FEW LOCATIONS POSSIBLY CHALLENGING RECORD HIGHS. MORNING LOWS  
WILL ALSO BE QUITE WARM THURSDAY-FRIDAY WITH SOME DAILY RECORDS  
POSSIBLE. THE NORTHWEST SHOULD RETURN TO NEAR NORMAL FOR THE  
WEEKEND AND THEN REBOUND TO 5-10F ABOVE NORMAL NEXT MONDAY AS AN  
UPPER RIDGE BUILDS IN. MEANWHILE PARTS OF THE NORTHEAST SHOULD  
SEE HIGHS UP TO 5-10F ABOVE NORMAL LATE THIS WEEK WITH THE GREAT  
LAKES/NORTHEAST SEEING SIMILAR ANOMALIES SUNDAY-MONDAY. COOL HIGH  
TEMPERATURES ACROSS THE SOUTHERN TIER, UP TO 5-10F BELOW NORMAL ON  
THURSDAY, WILL LIKELY MODERATE GRADUALLY TO YIELD NEAR TO ONLY  
SLIGHTLY BELOW NORMAL READINGS BY THE WEEKEND AND EARLY NEXT WEEK.  
NORTHERN PLAINS AREAS SHOULD SEE A COUPLE EPISODES OF SLIGHTLY  
BELOW NORMAL HIGHS, ONE LATE THIS WEEK AND ANOTHER SUNDAY-MONDAY.  
 
RAUSCH  
 
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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