437  
FXUS02 KWBC 221949  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
349 PM 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 LATEST DETERMINISTIC AND ENSEMBLE GUIDANCE CAPTURE THE GENERAL  
SYNOPTIC PATTERN RELATIVELY WELL. THE MAIN AREA OF UNCERTAINTY IS  
WITH THE ARRIVAL OF AN UPPER-LEVEL TROUGH OVER THE PACIFC  
NORTHWEST/BRITISH COLUMBIA ON DAY 5 CONTINUING INTO DAY 6. A  
GENERAL MODEL BLEND OF 00Z EC/UK/CMC AND THE 06Z GFS WERE USED ON  
DAY 3 WITH THE CMC AND UK FAVORED FOR THEIR HANDLING OF A TROUGH  
IN THE SOUTHEAST. A GMB WAS UTILIZED AGAIN ON DAY 4, EXCEPT THIS  
TIME THE 06Z GFS WAS WEIGHTED LESS THAN THE 00Z SUITE DUE TO SMALL  
SCALE DISCREPANCIES IN THE UPPER TROUGH OVER MONTANA. THE 00Z CMC  
IS AN OUTLIER WITH RESPECT TO A POTENT SHORTWAVE THAT IT HAS  
SPINNING THROUGH THE NORTHERN PLAINS. THE 00Z EC ENSEMBLE MEAN WAS  
INCORPORATED INTO THE GMB ON DAY 5 TO MITIGATE DEEP TROUGHING  
ACROSS THE PLAINS AND COASTAL CALIFORNIA BY THE 00Z UK. 06Z GFS  
INTRODUCES AN ANOMALOUS TROUGH IN THE NORTHWEST AS WELL WHICH IT  
MOVES INTO THE NORTHERN ROCKIES BY DAY 6. THE 00Z GFS ATTEMPTS TO  
SPIN UP A SHORTWAVE ALONG THE NORTHERN CALIFORNIA COAST ON DAY 6  
WHICH WOULD BE MORE IN LINE WITH WHAT THE OTHER DETERMINISTICS AND  
ENSEMBLES ARE SIGNALING WHICH IS WHY IT WAS INCLUDED IN THE BLEND  
FOR THAT DAY. AN ENSEMBLE MEAN BLEND WAS USED ON DAY 7 WITH SOME  
00Z EC.  
   
..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/KEBEDE  
 
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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