920  
FXUS02 KWBC 201600  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1059 AM EST MON NOV 20 2017  
 
VALID 12Z THU NOV 23 2017 - 12Z MON NOV 27 2017  
 
...RECORDS HIGHS ACROSS THE SW/WRN US AND PROLONGED HEAVY  
RAIN/SNOW OVER THE NWRN US...  
 
   
..OVERVIEW
 
 
THE GENERAL PATTERN SETUP FOR THE NEXT WEEK ENTAILS A TROUGH OVER  
THE GULF OF ALASKA/PACIFIC OCEAN... A RIDGE OVER THE WEST AND A  
TROUGH OVER THE EAST. MUCH OF THE PACIFIC NORTHWEST WILL REMAIN IN  
AN ACTIVE, PROLONGED WET PERIOD WITH COOLER TEMPERATURES... AS  
WILL THE GREAT LAKES REGION AND THE NORTHEAST. A VAST MAJORITY OF  
SOUTHERN CALIFORNIA, THE DESERT SOUTHWEST, SOUTHERN ROCKIES AND  
SOUTHERN PLAINS WILL BE DRY WITH ABOVE NORMAL TEMPERATURES. SOME  
LOCATIONS ARE PROGGED TO REACH OR EXCEED PRIOR TEMPERATURE  
RECORDS, PRIMARILY FOR LOCATIONS IN THE SOUTHWEST. THE CENTRAL  
U.S. WILL BEGIN WITH ABOVE AVERAGE TEMPERATURES BUT WILL HAVE A  
COOLING TREND THROUGH THE WEEKEND. ADDITIONAL WET WEATHER IS  
LIKELY OVER FLORIDA ASTRIDE A SLOWLY MOVING AND WAVY FRONTAL  
BOUNDARY.  
 
   
..GUIDANCE/UNCERTAINTY PREFERENCES...
 
 
OVERALL THE DETERMINISTIC MODELS/ENSEMBLE MEANS ARE IN AGREEMENT  
WITH THE LARGE-SCALE SETUP; HOWEVER, WITH PERSISTENT DIFFERENCES  
IN TIMING AND AMPLITUDE. THE INITIAL CONSENSUS WAS BASED ON THE  
00Z ECWMF/CMC/CONTINUITY AND 06Z GFS... WITH INCREASED WEIGHTING  
OF THE ENSEMBLE MEANS TOWARD THE END OF THE FORECAST PERIOD.  
CONFIDENCE OF PREDICTABILITY IS ON THE LOW END OF AVERAGE.  
 
   
..WEATHER HIGHLIGHTS
 
 
HEAVY DAILY RAINS AND LOCALLY HEAVY ELEVATION SNOWS WILL PERSIST  
OVER THE NORTHWESTERN STATES THIS WEEK. UPPER RIDGING WILL SUPPORT  
WELL-ABOVE AVERAGE TEMPERATURES IN THE SOUTHWEST AND SOUTHERN  
CALIFORNIA TO THE INTERMOUNTAIN WEST/ROCKY STATES. SOME RECORD  
HIGHS/LOWS ARE LIKELY. MILD TEMPERATURES WILL EXTEND EASTWARD  
THROUGH THE PLAINS AHEAD OF A COLD FRONT THURSDAY AND FRIDAY.  
COOLER TEMPERATURES WILL FILTER IN THIS WEEKEND AFTER THE FRONTAL  
PASSAGE. THERE IS A GOOD CHANCE FOR APPRECIABLE PRECIPITATION  
ALONG THE GULF/SOUTHEAST US COAST... ESPECIALLY FL... AS LOW  
PRESSURE CENTERS MEANDER ALONG A SLOW MOVING FRONT. RAIN AND SNOW  
WILL IS EXPECTED FOR THE GREAT LAKES REGION WITH POTENT NORTHERN  
STREAM CLIPPER PASSAGES AND POST-SYSTEM LAKE EFFECT.  
 
   
..THANKSGIVING FORECAST
 
 
PRECIPITATION WILL CONCENTRATE FROM THE PACIFIC NORTHWEST SOUTH TO  
NORTHERN CALIFORNIA... AND EASTWARD INTO NORTHERN  
ROCKIES...INCLUDING HIGHER ELEVATION SNOWS. MODEST PRECIPITATION  
IS ALSO POSSIBLE ACROSS THE GREAT LAKES WITH LEAD CLIPPER PASSAGE.  
ORGANIZED RAIN IS POSSIBLE OVER CENTRAL AND SOUTHERN FLORIDA AND  
THE COASTAL SOUTHEAST DEPENDING ON HOW THE SURFACE SYSTEMS EVOLVE.  
HIGHEST RECORD HIGH TEMPERATURES ARE LIKELY IN THE SOUTHWEST WITH  
80S AND SOME 90S. PHOENIX HAS THE CHANCE OF RECORDING THEIR LATEST  
90 DEGREE DAY SO LATE IN THE YEAR (RECORD IS NOV 15 1999)  
INCLUDING THEIR WARMEST THANKSGIVING DAY (RECORD IS 87 ON NOV 23  
1950 AND NOV 27 2014 - THANKS TO THE PHOENIX NWS OFFICE FOR THE  
CLIMATE/RECORD INFORMATION). COOLER 30S/40S IN THE UPPER  
MIDWEST/GREAT LAKES/NORTHEAST/MID-ATLANTIC ARE LIKELY BY NEXT  
WEEKEND BEHIND THE FRONT.  
 
CAMPBELL  
 

 
 
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