901  
FXUS02 KWBC 231552  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1151 AM EDT MON JUL 23 2018  
 
VALID 12Z THU JUL 26 2018 - 12Z MON JUL 30 2018  
   
..SOUTHWEST/WEST HEAT WAVE EASING BY LATE WEEK
 
 
...HEAVY RAINFALL THREAT SHIFTS BACK TO THE CENTRAL ROCKIES/PLAINS  
THEN MID-MS VALLEY/MID-SOUTH...  
   
..GUIDANCE/UNCERTAINTY ASSESSMENT AND WEATHER THREATS
 
 
DEEP TROUGHING ACROSS THE EASTERN U.S. AT THE END OF THE SHORT  
RANGE GETS REPLACED WITH ADDITIONAL AMPLIFIED MID-UPPER LEVEL  
TROUGHING WORKING ITS WAY ACROSS THE GREAT LAKES AND INTO THE  
NORTHEAST DAYS 3-5. PERIODS OF HEAVY CONVECTIVE RAINFALL  
ASSOCIATED WITH POOLING MOISTURE ALONG AND AHEAD OF A SURFACE  
FRONT CAN BE EXPECTED, WITH LOCAL RUNOFF ISSUES POSSIBLE  
(ESPECIALLY GIVEN THE VERY WET ANTECEDENT CONDITIONS). ADDITIONAL  
ACTIVITY WILL TRAIL SOUTHWARD ALONG OR OFF THE EAST COAST AND  
ACROSS FLORIDA. MEANWHILE, A HOT MID-UPPER LEVEL RIDGE AND RECORD  
MAXIMUM TEMPERATURES OVER THE SOUTHWEST AND INTO THE WEST WILL  
EASE BY LATER THIS WEEK, WITH RECORD HIGH MINIMUM TEMPS ALSO  
POSSIBLE GIVEN LINGERING MONSOONAL MOISTURE THROUGH THE WEEK.  
 
A SERIES OF IMPULSES ROTATING WITHIN AND AROUND THE UPPER RIDGE  
DIG SOUTHWARD INTO THE CENTRAL STATES TO INTERACT WITH SURFACE  
BOUNDARIES, INSTABILITY, AND FAVORABLE LOW LEVEL MOISTURE  
INFLOW/CONVERGENCE. FORECAST SPREAD BEGINS TO INCREASE BY DAY 6/7  
WITH ADDITIONAL WAVES ROTATING SOUTHWARD INTO CENTRAL CANADA AND  
UPPER LEVEL TROUGH REDEVELOPMENT FROM THE NORTH-CENTRAL U.S. INTO  
THE MISSISSIPPI VALLEY. RECENT RUNS OF THE DETERMINISTIC GFS/ECMWF  
HAVE SORT OF FLIP-FLOPPED BETWEEN A MORE AMPLIFIED/PROGRESSIVE  
WAVE IN CENTRAL CANADA, OR A MORE SUPPRESSED/SLOWER WAVE. THE  
GEFS/EC ENSEMBLE MEANS ARE FAIRLY CONSISTENT (AT LEAST FOR DAY 7  
STANDARDS) WITH SHOWING A SOLUTION MORE IN THE MIDDLE OR MAYBE  
SLIGHTLY WEIGHTED TOWARDS MORE AMPLIFIED, WHICH IS BETTER  
SUPPORTED BY SOUTHWESTERN U.S. RIDGE POSITION, RECENT EASTERN U.S.  
TROUGH HISTORY, AND PREVIOUS SHIFT CONTINUITY. REGARDLESS, THIS  
PATTERN WOULD SUPPORT MULTIPLE EPISODES OF HEAVY CONVECTION FROM  
THE CENTRAL ROCKIES/PLAINS INTO THE MID-MISSISSIPPI/OHIO/TENNESSEE  
VALLEYS. HEAVY RAINFALL AND REPEAT CELLS MAY LEAD TO A LOCALLY  
EXCESSIVE RAINFALL THREAT.  
 
THIS CYCLE OF THE MEDIUM RANGE FORECAST SUITE USED A BLEND OF THE  
WELL CLUSTERED GFS/ECMWF/UKMET FOR DAYS 3-5, WITH INCREASED  
CONTRIBUTIONS FROM THE GEFS/ECMWF BY DAYS 6-7. DAYS 6-7 WERE ALSO  
SLIGHTLY MORE WEIGHTED WITH THE LATEST DETERMINISTIC GFS RUN IN  
ORDER TO SHOW A SLIGHTLY MORE AMPLIFIED WAVE (AS DISCUSSED ABOVE)  
AND A BETTER MATCH TO PREVIOUS SHIFT CONTINUITY.  
 
SANTORELLI  
 
WPC MEDIUM RANGE 500 MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION, WINTER WEATHER OUTLOOK PROBABILITIES  
AND HEAT INDEXES ARE FOUND 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/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