854  
FXUS02 KWBC 201602  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1101 AM EST WED FEB 20 2019  
 
VALID 12Z SAT FEB 23 2019 - 12Z WED FEB 27 2019  
 
...SIGNIFICANT WINTER STORM FROM THE SOUTH-CENTRAL PLAINS TO THE  
UPPER MIDWEST/GREAT LAKES AND INTERIOR NEW ENGLAND THIS WEEKEND...  
 
...HEAVY RAINFALL/FLOODING THREAT IN THE SOUTHEAST SATURDAY AND  
AGAIN NEXT WEEK...  
 
   
..PATTERN OVERVIEW
 
 
THE PACIFIC NORTHWEST WILL SEE ADDITIONAL/RELOADING TROUGHING OUT  
OF WESTERN CANADA DOWNSTREAM OF A VERY STRONG UPPER HIGH OVER  
ALASKA NEXT WEEK. TO THE EAST, A POTENT SHORTWAVE WILL DEEPEN AND  
LIFT NORTHEASTWARD INTO THE GREAT LAKES AS THE UPPER RIDGE OVER  
THE BAHAMAS REMAINS IN PLACE. THIS WILL KEEP THE STORM TRACK  
INLAND WELL WEST OF THE COASTAL PLAIN TO THE SOUTH OF A HUDSON BAY  
UPPER LOW.  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT AND PREFERENCES
 
 
GUIDANCE WAS REASONABLY WELL-CLUSTERED AT MID-LARGER SCALES  
THROUGH THE MEDIUM RANGE PERIOD UNTIL ABOUT MONDAY. A COMPOSITE  
BLEND OF THE LATEST GFS/ECMWF/UKMET/CANADIAN OFFERED A REASONABLE  
STARTING POINT FOR SAT-MON AS A RAPIDLY DEEPENING SYSTEM (CENTRAL  
PRESSURE FALL OF ABOUT 20MB/24 HRS BETWEEN SAT AND SUN MORNING)  
LIFTS INTO THE GREAT LAKES AND THEN EXITS OUT THE ST. LAWRENCE  
VALLEY SUNDAY INTO MONDAY. THIS SYSTEM HAS THE POTENTIAL TO DEEPEN  
INTO THE UPPER 970S MB OR AT LEAST LOW 980S MB WHICH MAY BE CLOSE  
TO MONTHLY RECORD LOW PRESSURE VALUES FOR PORTIONS OF LOWER  
MICHIGAN SUNDAY MORNING.  
 
IN THE WEST, THE MODELS/ENSEMBLES DIVERGE ON HOW TO HANDLE THE  
UPPER HIGH OVER ALASKA AND DOWNSTREAM FLOW OVER SOUTHWESTERN  
CANADA/PACIFIC NORTHWEST -- ECMWF AND MANY OF ITS ENSEMBLES TAKE  
SHORTWAVE VORTICITY BACK WESTWARD UNDERNEATH THE UPPER HIGH WHILE  
THE GFS AND MANY OF ITS ENSEMBLES (AS WELL AS THE CANADIAN/UKMET)  
TOOK IT SOUTHWARD THEN SLOWLY EASTWARD ALONG THE OREGON COAST. THE  
PARALLEL 06Z FV3-GFS WAS LESS AGGRESSIVE THAN THE GFS. PATTERN  
WOULD ALLOW A WESTWARD/RETROGRADING SHORTWAVE SO OPTED TO KEEP  
SOME ECMWF INFLUENCE TO THE FORECAST BUT OTHERWISE TRENDED TOWARD  
THE ENSEMBLES WHICH WOULD GIVE WAY TO AT LEAST FLATTER FLOW BY  
NEXT WED INTO OR/NORCAL. IN THE EAST, SOME SEMBLANCE OF A SYSTEM  
SHOULD LIFT TOWARD THE GREAT LAKES NEXT TUESDAY THEN OFF THE COAST  
NEXT WEDNESDAY BUT HOW IT EVOLVES IS UNCERTAIN.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
WEEKEND SYSTEM WILL BRING A THREAT FOR SIGNIFICANT ACCUMULATING  
SNOW WITH SOME ICING POSSIBLE TO THE NORTHWEST/NORTH/NORTHEAST OF  
THE SURFACE LOW WITH STRONG/GUSTY WINDS AND POTENTIAL BLIZZARD  
CONDITIONS ACROSS THE UPPER MIDWEST AND GREAT LAKES. MILD AIR WILL  
SURGE NORTHWARD EAST OF THE FRONT WITH A BRIEF SPIKE IN  
TEMPERATURES INTO THE 60S AND 70S ACROSS THE MID-ATLANTIC. FARTHER  
SOUTH, HEAVY RAIN FROM THE END OF THE SHORT RANGE WILL BE POSSIBLE  
INTO THE START OF THE MEDIUM RANGE AIDED BY CONVECTION IN THE WARM  
SECTOR AND PLENTY OF GULF MOISTURE. SPC HAS DENOTED A CHANCE OF  
SEVERE WEATHER ON SATURDAY FROM ARKANSAS TO KY/TN AND NORTHERN  
ALABAMA. FLORIDA MAY ESCAPE MOST OF THE RAINFALL BUT RECORD WARM  
TEMPERATURES WILL BE POSSIBLE WITH THE MILD UPPER PATTERN.  
 
A LONG-STANDING AND WINTRY MEAN UPPER TROUGH OVER THE WEST WILL  
AGAIN BE REINFORCED SAT-MON AS ENERGY DIGS TO THE LEE OF A  
BLOCKING ALASKA-CENTERED UPPER HIGH. THESE SYSTEMS WILL BE LESS  
AMPLIFIED THAN PRIOR SYSTEMS IN THIS RECENT PATTERN, BUT WILL  
BRING UNSETTLED WEATHER THROUGH THE NORTHWEST AND NORTH-CENTRAL  
INTERMOUNTAIN WEST AND ROCKIES, WITH THE BEST CHANCE FOR  
ACCUMULATING SNOWFALL OVER THE CASCADES INTO ESPECIALLY NORTHERN  
CALIFORNIA. FOCUS OF THE PRECIPITATION MAY REMAIN CONCENTRATED  
OVER THE SAME AREA DEPENDING ON HOW THE PATTERN EVOLVES OFFSHORE  
INTO THE WEST COAST, WHICH WOULD RESULT IN SEVERAL DAYS OF  
RAIN/MOUNTAIN SNOW.  
 
FRACASSO/SCHICHTEL  
 
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION AND WINTER WEATHER OUTLOOK  
PROBABILITIES 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  
 

 
 
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