913  
FXUS02 KWBC 180618  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
118 AM EST SUN NOV 18 2018  
 
VALID 12Z WED NOV 21 2018 - 12Z SUN NOV 25 2018  
 
...RECORD COLD TEMPERATURES ON THANKSGIVING FOR MUCH OF THE  
NORTHEAST...  
 
   
..OVERVIEW
 
 
UPPER TROUGHING IN THE NORTHEAST WED/THU WILL GIVE WAY TO WEAK  
RIDGING AS LEAD AND THEN REINFORCING TROUGHING PUSH THROUGH THE  
WEST. THIS YIELDS A VERY COLD START TO THE PERIOD IN THE NORTHEAST  
AND A DECIDEDLY WET SEVERAL DAYS (AND WHITE AT HIGHER ELEVATIONS)  
WEST OF THE DIVIDE. TO THE SOUTH, A LINGERING STATIONARY BOUNDARY  
MAY TRY TO SPIN UP A SURFACE LOW AND TREK ACROSS FLORIDA THEN OFF  
THE CAROLINAS NEXT WEEKEND.  
 
   
..GUIDANCE/UNCERTAINTY ASSESSMENT
 
 
THE MODELS/ENSEMBLES HAVE MOSTLY CONVERGED ON THE INITIAL FLOW  
EVOLUTION OUT OF THE PACIFIC INTO THE WEST WED-FRI WITH A 1-2  
PUNCH OF SYSTEMS. FOR NEXT WEEKEND, AGAIN SEE A LOT OF SPREAD IN  
THE GUIDANCE WITH THE CENTRAL/EASTERN SYSTEMS OWING TO A LACK OF A  
WELL-DEFINED SINGULAR TROUGH. WEAKER SHORTWAVES WILL BE HARDER TO  
FORECAST FOR A FEW MORE DAYS AT THE LEAST. FOR NOW, TRENDED TOWARD  
THE ENSEMBLE MEANS WHICH FIT IN BETWEEN THE GFS/ECMWF SOLUTIONS  
WITH THE SOUTHERN THEN EASTERN/COASTAL SYSTEM. ECMWF ENSEMBLE MEAN  
WAS MUCH MORE BULLISH ACROSS FLORIDA AND OFF THE SOUTHEAST COAST  
THAN THE GEFS MEAN, BUT IT HAS HAD BETTER CONTINUITY THAN THE GEFS  
RECENTLY.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
THANKSGIVING SUMMARY (THU 11/22) - RECORD COLD IN THE NORTHEAST  
WITH HIGH TEMPERATURES 15 TO NEAR 30 DEG F BELOW AVERAGE AND MANY  
AREAS STAYING WELL BELOW FREEZING. WET ALONG THE WEST COAST INTO  
THE GREAT BASIN AND ROCKIES WITH NEAR AVERAGE TEMPERATURES AND  
HIGHER ELEVATION SNOW. MILDER AND DRY FOR THE HIGH PLAINS WITH  
40S/50S COMMON. RAIN CHANCE FOR THE GULF COAST FROM TEXAS EASTWARD  
THROUGH MUCH OF FLORIDA TO THE NORTH OF A FRONT IN THE FLORIDA  
STRAITS.  
 
THE ENTIRE WEST COAST AND MUCH OF THE INTERIOR WILL SEE WIDESPREAD  
RAIN/ELEVATION SNOW TO START THE PERIOD WEDNESDAY. PRECIPITATION  
FOCUS STILL APPEARS TO BE AROUND NORTHERN CALIFORNIA AND THE  
NORTHERN SIERRAS INTO SOUTHWESTERN OREGON AS THE UPPER TROUGH  
SPLITS N-S. MULTI-DAY RAINFALL AMOUNTS MAY BE IN THE 3-6 INCH  
RANGE OVER FAVORED AREAS AND EVEN ABOUT AN INCH TO AN INCH AND A  
HALF IN THE CENTRAL VALLEY. SNOW LEVELS WILL FALL THROUGH THE  
PERIOD WITH SEVERAL FEET OF SNOW LIKELY AT THE HIGHEST ELEVATIONS.  
 
MUCH BELOW AVERAGE TEMPERATURES IN THE NORTHEAST WILL BE SLOW TO  
EASE BUT WILL TREND BACK TOWARD TYPICAL LATE NOVEMBER VALUES BY  
NEXT WEEKEND. TEMPERATURES IN THE WEST WILL BE NEAR TO ABOVE  
AVERAGE FOR OVERNIGHT LOWS BUT NEAR TO BELOW AVERAGE FOR AFTERNOON  
HIGHS THANKS TO AN ABUNDANCE OF CLOUD COVER. THE PLAINS AND UPPER  
MIDWEST WILL SEE MILDER TEMPERATURES THURSDAY-SATURDAY, GENERALLY  
ABOVE FREEZING FOR AFTERNOON HIGHS. COLDER AIR WILL PROBABLY WORK  
BACK SOUTH ACROSS THE BORDER BY NEXT SUNDAY.  
 
FRACASSO  
 
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  
 

 
 
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