959  
FXUS02 KWBC 170700  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
200 AM EST SUN FEB 17 2019  
 
VALID 12Z WED FEB 20 2019 - 12Z SUN FEB 24 2019  
 
...MULTI-DAY HEAVY RAIN THREAT FOR LOWER MISSISSIPPI/TENNESSEE  
VALLEYS TO THE SOUTHERN/CENTRAL APPALACHIANS AND SNOW/ICE FOR THE  
MID-MISSISSIPPI/OHIO VALLEYS AND NORTHERN/CENTRAL MID-ATLANTIC TO  
SOUTHERN NEW ENGLAND...  
 
...COLD WEATHER PERSISTS IN THE WESTERN TO CENTRAL U.S., WITH  
UNSETTLED WEATHER FOCUSING INTO THE SOUTHWEST...  
 
   
..OVERVIEW
 
 
PERSISTENT WESTERN U.S. MID-UPPER LEVEL TROUGHING WILL BE  
REINFORCED DURING THE MEDIUM RANGE PERIOD BY SHOTS OF RENEWED  
ENERGY. THIS FEATURE PLUS AN UNYIELDING BAHAMAS UPPER RIDGE  
CREATES A FAVORABLE PATTERN FOR A MULTI-DAY HEAVY RAIN THREAT THIS  
WEEK FROM THE LOWER MS/TN VALLEYS TO THE SRN/CENTRAL APPALACHIANS  
AND A SNOW/ICE THREAT FROM THE MID-MS/OH VALLEYS TO ESPECIALLY FOR  
THE N-CENTRAL MID-ATLANTIC TO SRN NEW ENGLAND WED-THU.  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT AND PREFERENCES
 
 
GUIDANCE SEEMS TO AGREE WELL WITH EJECTION OF A LEAD  
MID/UPPER-LEVEL TROUGH FROM THE PLAINS TO NORTHEAST WED-THU AND AN  
UPSTREAM PATTERN THIS WEEK OF POTENT UPPER TROUGHS/HEIGHT FALLS  
PROGRESSING OVERTOP A NORTHEAST PACIFIC RIDGE THAT THEN DIG  
SHARPLY SOUTHWARD TO REINFORCE A WESTERN U.S. MEAN TROUGH. THIS  
PATTERN OFFERS ABOVE NORMAL PREDICTABILITY INTO FRIDAY, BUT  
CONFIDENCE DECREASES NEXT WEEKEND AS GUIDANCE IS MORE MIXED WITH  
MAIN UPPER TROUGH EJECTION FROM THE SOUTHWEST AND DOWNSTREAM  
PHASING AND SURFACE CYCLOGENESIS POTENTIAL OVER THE EAST-CENTRAL  
U.S. ENSEMBLE MEANS OFFER MORE CONSISTENT GUIDANCE. ACCORDINGLY,  
THE WPC MEDIUM RANGE SUITE WAS DERIVED FROM A MULTI-MODEL BLEND OF  
THE REASONABLY WELL CLUSTERED 18 UTC GFS/GEFS MEAN AND 12 UTC  
ECMWF/ECMWF ENSEMBLE MEAN, BUT SUBSTANTIALLY REDUCED WEIGHTING ON  
DETERMINISTIC MODELS NEXT WEEKEND AMID GRADUALLY GROWING FORECAST  
SPREAD/UNCERTAINTY WITH PATTERN TRANSIITON.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
AN PROLONGED EXCESSIVE RAINFALL THREAT FROM THE LOWER MS/TN  
VALLEYS TO THE SRN/CENTRAL APPALACHIANS WILL BE A MAIN STORY THIS  
WEEK. DEEP LAYERED AND HIGHLY ANOMALOUSLY MOIST SOUTHWEST FLOW  
CHANNELED FROM THE SOUTHERN PLAINS TO THE EAST WILL ACT TO SUSTAIN  
A SOUTHEAST RIDGE AND FUEL MULTI-DAY THREATS OF HEAVY  
RAIN/TRAINING. ON THE NORTHERN EDGE, A COLD SURFACE HIGH AND COLD  
AIR DAMMING IN THE MID-ATLANTIC REGION IS EXPECTED, LEADING TO  
FROZEN PRECIPITATION. POTENTIALLY HEAVY SNOW AND ICE IS A  
POSSIBILITY FROM THE MIDDLE MISSISSIPPI VALLEY TO OHIO VALLEY AND  
ESPECIALLY THE NORTHERN MID-ATLANTIC INTO SOUTHERN NEW ENGLAND  
WED-THU.  
 
WITH ANOMALOUSLY LOW HEIGHTS IN THE WESTERN U.S., MUCH BELOW  
AVERAGE TEMPERATURES WILL PREVAIL FOR THE WESTERN AND CENTRAL U.S.  
A MAIN LOW IS PROGGED TO DIG FROM THE PACIFIC NORTHWEST TO  
CALIFORNIA WED/THU TO THE SOUTHWEST BY FRI ALONG WITH ENHANCED  
PRECIPITATION INCLUDING HIGHER ELEVATION HEAVY SNOW. THE MAIN  
SYSTEM IS EXPECTED TO EJECT NORTHEASTWARD ACROSS THE CENTRAL AND  
EAST-CENTRAL U.S. NEXT WEEKEND.  
 
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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