461  
FXUS02 KWBC 171601  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1100 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-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 BEGINNING OF THE MEDIUM RANGE PERIOD BY  
SHOTS OF RENEWED ENERGY. THE TROUGH WILL EVENTUALLY MOVE EASTWARD  
INTO THE CENTRAL U.S. BY NEXT WEEKEND. 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 SOUTHERN/CENTRAL APPALACHIANS AND A SNOW/ICE THREAT FOR  
PARTS OF THE MID-ATLANTIC AND THE NORTHEAST WED-THU.  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT AND PREFERENCES
 
 
GUIDANCE IS IN GENERAL AGREEMENT FOR DAYS 3-4 OF THE MEDIUM RANGE  
PERIOD REGARDING THE PATTERN OF TROUGHING ACROSS THE WESTERN U.S.  
AND A LEADING TROUGH MOVING ACROSS THE NORTH CENTRAL U.S. ON WED  
AND INTO THE NORTHEAST ON THU, OVERTOP THE SOUTHEASTERN RIDGE. A  
MULTI-MODEL BLEND OF DETERMINISTIC MODELS WAS USED FOR THIS TIME  
FRAME. BY DAYS 4-5, WHILE MODEL AGREEMENT ACROSS THE CONUS IS  
REASONABLY GOOD, THE 00Z DETERMINISTIC ECMWF DEVELOPS AN UPPER LOW  
IN THE GULF OF ALASKA/NORTHERN PACIFIC THAT IS MUCH STRONGER THAN  
OTHER MODELS AND ITS MEAN, DUE TO ITS HANDLING OF ENERGY UPSTREAM  
IN THE NORTHERN PACIFIC. THIS CUTOFF LOW (WHERE OTHER MODELS HAVE  
A TROUGH) PROGRESSES SOUTHWARD THROUGH THE REST OF THE PERIOD AND  
AFFECTS THE WESTERN U.S. THUS LEANED AWAY FROM THE 00Z  
DETERMINISTIC ECMWF FOR THIS FEATURE. BY THE END OF THE FORECAST  
PERIOD, A SURFACE LOW IS EXPECTED TO DEVELOP IN THE  
CENTRAL/EASTERN U.S. AS THE MAIN TROUGH IN THE WESTERN U.S. EJECTS  
OUT INTO THE CENTRAL U.S. THE MOST RECENT GFS RUNS SEEMED TOO  
SUPPRESSED WITH THIS SURFACE LOW, CONSIDERING THE STRENGTH OF THE  
UPPER VORT MAX AND THE REASONABLE FORECAST CONFIDENCE. A BLEND OF  
THE MEANS WAS USED BY THE END OF THE PERIOD, ALONG WITH THE  
DETERMINISTIC CMC AND THE PARALLEL FV3 GFS TO MAINTAIN DETAILS IN  
STRENGTH.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
AN PROLONGED EXCESSIVE RAINFALL THREAT FROM THE LOWER MS/TN  
VALLEYS TO THE SRN/CENTRAL APPALACHIANS WILL BE ONE 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 UPPER 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 ESPECIALLY IN 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., WHILE RIDGING IN THE SOUTHEAST WILL LEAD TO ABOVE AVERAGE  
TEMPERATURES. 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.  
 
TATE/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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