081  
FXUS02 KWBC 172106  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
505 PM EDT TUE MAY 17 2022  
 
VALID 12Z FRI MAY 20 2022 - 12Z TUE MAY 24 2022  
 
...RECORD HEAT FROM THE SOUTH TO THE MID-ATLANTIC/NORTHEAST FRIDAY  
AND SATURDAY...  
 
...HEAVY RAINFALL AND SEVERE WEATHER THREAT TO FOCUS OVER THE  
EAST-CENTRAL U.S. FRIDAY AND SATURDAY...  
   
..HEAVY SNOW THREAT FOR THE CENTRAL ROCKIES/HIGH PLAINS FRIDAY
 
 
   
..OVERVIEW
 
 
THE OVERALL 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. LEAD SOUTHERN STREAM IMPULSES WILL  
ADD TO CONVECTIVE RAINFALL POTENTIAL ACROSS THE SOUTH. THE MAIN  
FRONT/TROUGH WILL 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 WITH THE  
MODELS ALSO SHOWING DECENT AGREEMENT (WITH SOME MINOR TIMING  
DIFFERENCES) ON AMPLIFIED TROUGHING SLIDING INTO THE EAST BY LATE  
WEEKEND. HOWEVER, THE 00 UTC ECMWF IN PARTICULAR ALSO PLACES MORE  
EMPHASIS ON A SOUTHERN STREAM IMPULSES EJECTING UNDERNEATH ACROSS  
THE SOUTH ALONG WITH HEAVIER CONVECTIVE RAINFALL ACROSS THE  
SOUTH/SOUTHEAST THIS WEEKEND INTO MONDAY. THE 12 UTC GFS/ECMWF  
SUPPORT THIS EMPHASIS.  
 
BY SUNDAY, 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 WEST THIS WEEKEND, WHICH  
EVENTUALLY RESULTS IN ANOTHER FAIRLY AMPLIFIED SHORTWAVE INTO THE  
SOUTH-CENTRAL U.S. 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. THE ENSEMBLE MEANS THEMSELVES SEEM TO  
AGREE WITH THEIR DETERMINISTIC COUNTERPARTS, ALTHOUGH THERE ARE A  
FAIR NUMBER OF MEMBERS SHOWING BOTH POSSIBILITIES. THIS ASPECT OF  
THE FORECAST REMAINS VERY UNCERTAIN, WITH WPC PROGS SUGGESTING A  
SOLUTION A BIT CLOSER TO THE GFS/GEFS.  
 
THE WPC MEDIUM RANGE PRODUCT SUITE WAS PRIMARILY DERIVED FROM A  
GENERAL BLEND OF THE DETERMINISTIC MODELS THROUGH DAY 5 ALONG WITH  
THE NBM AND A TRANSITION TOWARDS THE ENSEMBLE MEANS DAYS 6-7 ALONG  
WITH THE GFS/ECMWF FOR A LITTLE MORE DEFINITION TO INDIVIDUAL  
SYSTEMS.  
 
   
..WEATHER/THREAT HIGHLIGHTS
 
 
THE RELENTLESS HEAT ACROSS THE SOUTHERN PLAINS/LOWER MISSISSIPPI  
VALLEY SHOULD FINALLY BREAK INTO THE WEEKEND AS RECORD HEAT  
SPREADS INTO THE EAST. NUMEROUS DAILY RECORDS COULD BE MET OR  
EXCEEDED STILL FRIDAY ACROSS TEXAS/LOUISIANA AND THE SOUTHEAST,  
WITH RECORD VALUES REACHING THE UPPER OHIO  
VALLEY/APPALACHIANS/MID-ATLANTIC/NORTHEAST FRIDAY INTO THE  
WEEKEND. 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. LEAD SOUTHERN STREAM  
IMPULSE ENERGY MAY ALSO FOCUS HEAVY RAINFALL AREAS UNDERNEATH OVER  
THE SOUTH. BEHIND THIS FRONT, UNSEASONABLY COOL TEMPERATURES WILL  
MOVE FROM THE ROCKIES INTO THE NORTH-CENTRAL U.S., LOWERING SNOW  
LEVELS ACROSS THE ROCKIES. THERE IS A THREAT OF HEAVY SNOW OVER  
THE CENTRAL ROCKIES INTO FRIDAY AND EVEN SOME SNOW INTO THE  
ADJACENT HIGH PLAINS. ADDITIONAL SHORTWAVE DIGGING INTO THE  
SOUTH-CENTRAL U.S. INTO NEXT WEEK MAY RE-KINDLE  
CONVECTION/RAINFALL, ALBEIT WITH LESS CERTAINTY AT THESE LONGER  
TIME FRAMES. 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.  
 
SCHICHTEL/SANTORELLI  
 
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  
 
HAZARDS:  
- HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL/SOUTHERN PLAINS, THE  
LOWER MISSISSIPPI VALLEY, THE  
TENNESSEE VALLEY, THE GREAT LAKES, THE MIDDLE MISSISSIPPI VALLEY,  
AND THE OHIO VALLEY, FRI-SAT, MAY  
20-MAY 21.  
- HEAVY RAIN ACROSS PORTIONS OF THE SOUTHEAST AND THE LOWER  
MISSISSIPPI VALLEY, SUN-MON, MAY 22-MAY 23.  
- HEAVY RAIN ACROSS PORTIONS OF THE SOUTHEAST, FRI, MAY 20.  
- HEAVY RAIN ACROSS PORTIONS OF THE MID-ATLANTIC, SUN, MAY 22.  
- HEAVY SNOW ACROSS PORTIONS OF THE CENTRAL ROCKIES AND THE  
CENTRAL PLAINS, FRI, MAY 20.  
- SEVERE WEATHER ACROSS PORTIONS OF THE CENTRAL PLAINS, THE LOWER  
MISSISSIPPI VALLEY, THE SOUTHERN PLAINS, THE MIDDLE MISSISSIPPI  
VALLEY, THE GREAT LAKES, AND THE OHIO VALLEY, FRI, MAY 20.  
- FLOODING POSSIBLE ACROSS PORTIONS OF THE NORTHERN PLAINS.  
- FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE LOWER  
MISSISSIPPI VALLEY, THE UPPER  
MISSISSIPPI VALLEY, AND THE NORTHERN PLAINS.  
- FLOODING LIKELY ACROSS PORTIONS OF THE NORTHERN PLAINS.  
- EXCESSIVE HEAT ACROSS PORTIONS OF THE CENTRAL GULF COAST, THE  
LOWER MISSISSIPPI VALLEY, AND THE SOUTHERN PLAINS, FRI-SAT, MAY  
20-MAY 21.  
- EXCESSIVE HEAT ACROSS PORTIONS OF THE LOWER GREAT LAKES, THE  
NORTHEAST, THE CENTRAL APPALACHIANS,  
AND THE MID-ATLANTIC, FRI-SUN, MAY 20-MAY 22.  
- MUCH BELOW NORMAL TEMPERATURES ACROSS PORTIONS OF THE CENTRAL  
ROCKIES, THE CENTRAL PLAINS, THE CENTRAL GREAT BASIN, THE NORTHERN  
PLAINS, AND THE NORTHERN ROCKIES, FRI-SAT, MAY 20-MAY 21.  
- ENHANCED WILDFIRE RISK ACROSS PORTIONS OF THE SOUTHERN ROCKIES  
AND THE SOUTHWEST, FRI, MAY 20.  
 
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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