662  
FXUS02 KWBC 281601  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1200 PM EDT SAT JUL 28 2018  
 
VALID 12Z TUE JUL 31 2018 - 12Z SAT AUG 04 2018  
   
..HEAT WAVE MODERATING OVER THE WEST
 
   
..HEAVY RAINFALL THREAT OVER PORTIONS OF THE EAST
 
 
   
..PATTERN OVERVIEW AND GUIDANCE/UNCERTAINTY ASSESSMENT
 
 
MODEL GUIDANCE THIS MORNING SHOWED DECENT AGREEMENT ON THE  
SYNOPTIC PATTERN EVOLUTION ACROSS THE U.S. THROUGH NEXT SATURDAY.  
KEY FEATURES INCLUDE A BERMUDA HIGH REMAINING FIRMLY ESTABLISHED  
WHILE A POSITIVELY-TILTED TROUGH NUDGING ITS WAY EASTWARD CLOSER  
TO THE APPALACHIANS WITH TIME. MEANWHILE, A COOL CANADIAN HIGH  
PRESSURE SYSTEM IS IN THE OFFING FOR THE NORTHERN PLAINS AND GREAT  
LAKES MIDWEEK NEXT WEEK BEFORE A LOW PRESSURE SYSTEM ATTEMPTING TO  
ORGANIZE ACROSS THE PACIFIC NORTHWEST LATE NEXT WEEK REACHING THE  
NORTHERN PLAINS BY NEXT WEEKEND. A GENERAL COMPROMISE BETWEEN THE  
00Z ECMWF AND THE 06Z GFS IS USED TO DERIVE THE WPC GRID PACKAGE  
TREND CLOSER TO THEIR ENSEMBLE MEANS FOR DAYS 6 AND 7. THE 00Z  
ECMWF HAS SWITCHED TO A WARM SOLUTION OVER THE NORTHERN PLAINS  
MIDWEEK WITH A MUCH WEAKER HIGH PRESSURE SYSTEM COMING DOWN FROM  
CANADA THAN WHAT THE GFS INDICATES, AND IT IS JUDGED TO BE  
ANOMALOUSLY HIGH.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
THROUGH A COMBINATION OF SOME ENERGY EJECTING NORTHEASTWARD AND  
THE REMAINDER WEAKENING IN PLACE, EXPECT THE AMPLIFIED TROUGH  
ALOFT OVER OR JUST EAST OF THE MS VALLEY AS OF TUE-WED TO BECOME  
MORE DIFFUSE THEREAFTER. THE EVENTUAL WEAKENING TREND FOR BOTH  
THIS TROUGH AND THE INITIAL WESTERN U.S. RIDGE WILL LEAD TO A FLOW  
EVOLUTION THAT MORE CLOSELY RESEMBLES A MID-LATE SUMMER PATTERN BY  
FRI-SAT WITH LOW AMPLITUDE WESTERLIES ACROSS THE NORTHERN TIER.  
STRONG RIDGING OVER THE WESTERN ATLANTIC WILL BE A MORE PERSISTENT  
FEATURE.  
 
OVER THE EAST, THE FIRST HALF OF THE PERIOD WILL FEATURE MS VALLEY  
LOW PRESSURE TRACKING NORTHEASTWARD AND ASSOCIATED LEADING  
WARM/TRAILING COLD FRONTS PROVIDING WELL-DEFINED FOCUS FOR  
CONVECTION AND HEAVY RAINFALL POTENTIAL. THE COLD FRONT WILL HAVE  
DIFFICULTY REACHING ANY FARTHER THAN NEAR THE EAST COAST DUE TO  
THE STRONG DEEP-LAYER RIDGE OVER THE WESTERN ATLANTIC. MOIST  
GULF/ATLANTIC FLOW AROUND THE BERMUDA HIGH WILL LIKELY INTERACT  
WITH THE STALLING FRONT AND MAINTAIN THE POSSIBILITY OF  
SIGNIFICANT RAINFALL OVER PARTS OF THE  
APPALACHIANS/SOUTHEAST/MID-ATLANTIC. THE FRONT WILL LIKELY  
DISSIPATE BY FRI-SAT BUT SOME DIURNALLY FAVORED CONVECTION SHOULD  
CONTINUE WITH MORE OF A TERRAIN/LOCALIZED BOUNDARY FOCUS. THE  
BEST SIGNAL FOR HIGHEST 5-DAY TOTALS EXISTS OVER THE SOUTHERN  
APPALACHIANS/SOUTHEAST, WHILE OTHER RELATIVE MAXIMA ARE POSSIBLE  
OVER THE OHIO VALLEY/EASTERN GREAT LAKES AND PARTS OF THE  
MID-ATLANTIC.  
 
FLATTENING OF THE WESTERN U.S. RIDGE WILL BE AIDED BY THE EASTWARD  
PROGRESSION OF ENERGY WITHIN/AROUND AN UPPER LOW STILL FORECAST TO  
BE NEAR NORTHERN VANCOUVER ISLAND AS OF EARLY WED. THIS UPPER  
SUPPORT WILL BRING A GENERAL AREA OF LOW PRESSURE WITH ONE OR MORE  
CENTERS INTO THE NORTHERN PLAINS/SOUTHERN CANADA BY THE LATTER  
HALF OF THE PERIOD--LED BY A WARM FRONT REPRESENTING THE NORTHWARD  
RETURN OF THE COLD FRONT THAT INITIALLY DROPS INTO THE NORTHERN  
TIER TUE-WED. THE INITIAL COLD FRONT WILL BRING SOME  
PRECIPITATION TO NORTHERN AREAS AND THEN THE LATE-PERIOD SYSTEM  
SHOULD LEAD TO ONE OR MORE AREAS OF CONVECTION--SOME POSSIBLY  
HEAVY--WITHIN AN AREA BETWEEN THE NORTHERN PLAINS AND WESTERN  
GREAT LAKES.  
 
MEANWHILE EXPECT DIURNALLY FAVORED CONVECTION OF VARYING INTENSITY  
TO PERSIST OVER THE FOUR CORNERS STATES, THOUGH WITH UTAH TENDING  
TO SEE LIGHTER/MORE SCATTERED ACTIVITY THAN THE REST OF THE REGION.  
 
THE PATTERN CHANGE ALOFT OVER THE NORTHWEST WILL BRING A  
PRONOUNCED COOLING TREND TO THAT REGION. SOME LOCATIONS IN THE  
INTERIOR MAY SEE HIGHS 10-15F ABOVE NORMAL TUE BUT THEN EXPECT  
MODESTLY BELOW NORMAL HIGHS BY THU-SAT. FROM THE GREAT BASIN  
SOUTHWARD MIN TEMPS WILL LIKELY REMAIN WELL ABOVE NORMAL THROUGH  
THE PERIOD WHILE ANOMALIES FOR HIGHS SHOULD BE LESS EXTREME. MOST  
OF THE CENTRAL U.S. WILL SEE WELL BELOW NORMAL READINGS ESPECIALLY  
TUE-WED WITH LESSER COOL ANOMALIES FOR HIGHS EXTENDING INTO THE  
SOUTHEAST FOR MOST OF THE PERIOD GIVEN PERSISTENT CLOUDS/RAINFALL.  
ON THE OTHER HAND MOIST FLOW WILL KEEP MIN TEMPS WELL ABOVE  
NORMAL OVER THE MID-ATLANTIC/NORTHEAST. AFTER THE COOL START TO  
THE PERIOD, THE NORTHERN TIER WILL SEE TEMPERATURES REBOUND LATE  
IN THE WEEK AS SOUTHERLY FLOW DEVELOPS AHEAD OF NORTHERN PLAINS  
LOW PRESSURE.  
 
RAUSCH  
 
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