151  
FXUS02 KWBC 170701  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
300 AM EDT TUE MAY 17 2022  
 
VALID 12Z FRI MAY 20 2022 - 12Z TUE MAY 24 2022  
 
...PERSISTENT RECORD-BREAKING HEAT IS LIKELY IN THE SOUTH-CENTRAL  
U.S. THROUGH THIS WEEK WITH ANOMALOUS HEAT EXPANDING INTO THE EAST  
THIS WEEKEND...  
 
...HEAVY RAINFALL AND FLASH FLOODING POSSIBLE NEAR A STRONG  
NORTHERN TIER SYSTEM ON THURSDAY...  
 
   
..OVERVIEW
 
 
THE PATTERN ACROSS THE LOWER 48 WILL AMPLIFY AGAIN BY THE START OF  
THE MEDIUM RANGE PERIOD ON FRIDAY WITH A DIGGING TROUGH OVER THE  
WEST/NORTH-CENTRAL U.S. AND RISING HEIGHTS IN THE EAST. THIS  
YIELDS COOLER TEMPERATURES AND LOWERING SNOW LEVELS IN THE WEST  
AND A CONTINUED HOT REGIME FOR THE SOUTH AND EAST LATE THIS WEEK.  
A DEEPENING LOW PRESSURE SYSTEM TRACKING FROM THE NORTHERN  
TIER/UPPER GREAT LAKES INTO CANADA WILL PUSH A STRONG COLD FRONT  
EASTWARD, WITH INCREASING CHANCES FOR HEAVY RAINFALL AND SEVERE  
WEATHER ALONG AND AHEAD OF IT. THE FRONT/TROUGH WILL EVENTUALLY  
REACH THE EAST THIS WEEKEND AS THE GUIDANCE CONTINUES TO BE VERY  
UNCERTAIN WITH DETAILS UPSTREAM ACROSS THE NORTHWEST INTO EARLY  
NEXT WEEK. A NORTHWARD SURGE OF TROPICAL MOISTURE WILL ALSO  
INCREASE RAIN/THUNDERSTORM CHANCES ACROSS FLORIDA LATE THIS WEEK  
AND INTO THE WEEKEND.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
OVERALL, GUIDANCE CONTINUES TO SHOW A MORE OPEN SHORTWAVE ACROSS  
THE NORTHERN PLAINS/UPPER MISSISSIPPI VALLEY ON FRIDAY, ALTHOUGH  
THE 00Z UKMET CAME IN SHOWING A COMPACT CLOSED LOW AGAIN, SO SOME  
UNCERTAINTY REMAINS WITH THAT PARTICULAR FEATURE. REGARDLESS, THE  
MODELS SHOW GOOD AGREEMENT (WITH SOME MINOR TIMING DIFFERENCES) ON  
AMPLIFIED TROUGHING SLIDING INTO THE EAST BY THE WEEKEND. AFTER  
SATURDAY/DAY 4, THE MOST PROMINENT SOURCE OF UNCERTAINTY CONTINUES  
TO BE FLOW EVOLUTION ACROSS THE WEST. THE GFS AND MANY GEFS  
MEMBERS CONTINUE TO BE MUCH STRONGER/MORE PRONOUNCED WITH ENERGY  
ON THE BACKSIDE OF THE TRAILING TROUGH INTO THE NORTHWEST THIS  
WEEKEND, WHICH EVENTUALLY RESULTS IN ANOTHER FAIRLY AMPLIFIED  
SHORTWAVE INTO THE INTERMOUNTAIN WEST/ROCKIES BY EARLY NEXT WEEK.  
ON THE OTHER EXTREME, RECENT RUNS OF THE ECMWF ARE RATHER  
FLAT/MORE RIDGY WITH THE FLOW OVER THE WEST LATE PERIOD. THIS ALL  
SEEMS TO STEM FROM DIFFERENCES IN HOW QUICKLY ENERGY FROM THE  
NORTH PACIFIC MOVES INTO WESTERN NORTH AMERICA. THE ECMWF IS MUCH  
FASTER TO BREAK DOWN THE EAST PACIFIC RIDGE WHICH ALLOWS THE  
ENERGY TO SLIDE INLAND, WHILE THE GFS TENDS TO MAINTAIN A MORE  
BLOCKY RIDGE ALLOWING FOR MORE AMPLIFICATION DOWNSTREAM ACROSS THE  
WEST. YESTERDAY 12Z CMC WAS MORE LIKE THE ECMWF, ALTHOUGH TODAYS  
00Z RUN IS MORE AMPLIFIED LIKE THE 18Z/00Z GFS. THE ENSEMBLE MEANS  
THEMSELVES SEEM TO AGREE WITH THEIR DETERMINISTIC COUNTERPARTS,  
ALTHOUGH THERE ARE A FAIR NUMBER OF MEMBERS SHOWING BOTH  
POSSIBILITIES. IN OTHER WORDS, THIS ASPECT OF THE FORECAST REMAINS  
VERY UNCERTAIN.  
 
WPCS FORECAST FOR TONIGHT USED A GENERAL BLEND OF THE  
DETERMINISTIC MODELS THROUGH DAY 5, WITH A QUICKER THAN USUAL  
TRANSITION TOWARDS THE ENSEMBLE MEANS DAYS 6-7 (WITH SMALLER PARTS  
OF THE BOTH THE ECMWF AND GFS FOR A LITTLE MORE DEFINITION TO  
INDIVIDUAL SYSTEMS). THIS RESULTED IS A GOOD MIDDLE GROUND  
COMPROMISE FOR THE WESTERN U.S. FLOW, WHICH ALSO MAINTAINED GOOD  
CONTINUITY WITH THE PREVIOUS WPC FORECAST THROUGH DAY 6.  
 
   
..WEATHER/THREAT HIGHLIGHTS
 
 
THE RELENTLESS HEAT ACROSS THE SOUTHERN PLAINS/LOWER MISSISSIPPI  
VALLEY SHOULD FINALLY BREAK AFTER FRIDAY, THOUGH MUCH WARMER THAN  
NORMAL TEMPERATURES CONTINUE ACROSS THE EAST INTO SATURDAY.  
NUMEROUS DAILY RECORDS COULD BE MET OR EXCEEDED STILL ON FRIDAY  
ACROSS TEXAS/LOUISIANA AND THE SOUTHEAST ON FRIDAY, WITH A HANDFUL  
OF RECORD VALUES ON SATURDAY IN THE EAST.  
 
A STRONG COLD FRONT WILL SPREAD FOR RAIN AND THUNDERSTORMS TO  
SPREAD THROUGH THE GREAT LAKES/OHIO VALLEY/MISSISSIPPI VALLEY ON  
FRIDAY AND INTO THE EAST ON SATURDAY. HEAVY RAINFALL AS WELL AS  
SEVERE WEATHER IS POSSIBLE ALONG THIS BOUNDARY GIVEN ABOVE NORMAL  
MOISTURE AND INSTABILITY PRESENT. FLOODING AND FLASH FLOODING  
COULD BE AN ISSUE AS WELL, PARTICULARLY IN PLACES THAT MAY BE  
SENSITIVE TO ADDITIONAL RAINFALL GIVEN WET ANTECEDENT CONDITIONS.  
BEHIND THIS FRONT, UNSEASONABLY COOL TEMPERATURES WILL SLIDE INTO  
THE NORTH-CENTRAL U.S. FRIDAY AND SATURDAY, WITH HIGHS GENERALLY  
10-20F BELOW NORMAL. PARTS OF THE NORTHERN-CENTRAL HIGH PLAINS  
COULD BE COLDER THAN THAT ON FRIDAY. THIS COLD SPELL SHOULD LOWER  
SNOW LEVELS AND POSSIBLY ALLOW FOR SOME LIGHT SNOW TO FALL EVEN IN  
NORTHERN PARTS OF THE HIGH PLAINS. THE NORTHWEST WILL BE FAIRLY  
DRY LATE THIS WEEK BUT MAY SEE SOME MOISTURE RETURN DURING THE  
WEEKEND OR EARLY NEXT WEEK, WITH UNCERTAIN FLOW DETAILS KEEPING  
CONFIDENCE LOW FOR SPECIFICS OF TIMING/COVERAGE/AMOUNTS OF ANY  
PRECIPITATION. THE SOUTHERN HALF OF THE WEST SHOULD SEE A WARMING  
TREND EXPAND FROM WEST TO EAST SATURDAY-MONDAY WITH CALIFORNIA  
SEEING THE WARMEST HIGH TEMPERATURE ANOMALIES OF PLUS 10-15F.  
ELSEWHERE, GUIDANCE AGREES THAT TROPICAL MOISTURE SHOULD SURGE  
NORTHWARD ACROSS THE FLORIDA PENINSULA LATE THIS WEEK INTO THE  
WEEKEND, BRINGING A ROUND OF HEAVY RAINFALL TO PORTIONS OF THE  
SUNSHINE STATE.  
 
SANTORELLI/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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