061  
FXUS02 KWBC 141559  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1059 AM EST THU FEB 14 2019  
 
VALID 12Z SUN FEB 17 2019 - 12Z THU FEB 21 2019  
 
...MULTI-DAY HEAVY RAIN EVENT QUITE POSSIBLE FOR PORTIONS OF THE  
SOUTHEAST, TENNESSEE VALLEY, AND SOUTHERN APPALACHIANS NEXT WEEK...  
 
   
..OVERVIEW
 
 
UPPER-LEVEL RIDGING ACROSS 1) THE NORTH PACIFIC AND 2) NEAR THE  
BAHAMAS SHOWS NO SIGNS IN THE GUIDANCE OF BREAKING DOWN DURING THE  
MEDIUM RANGE, AND THUS WILL CONTINUE TO INFLUENCE THE LARGE SCALE  
FLOW ACROSS THE CONUS. THIS WILL REINFORCE A PATTERN WITH A TROUGH  
IN THE WEST AND WAVY SOUTHWEST FLOW IN THE EASTERN HALF OF THE  
CONUS THROUGH THE NEXT WEEK. A RAPID SUCCESSION OF PACIFIC  
SHORTWAVE ENERGY WILL TRAVERSE THE FLOW, AMPLIFYING THE MEAN  
TROUGH OVER THE WEST BEFORE EJECTING EAST AND INTERACTING WITH A  
LINGERING POLAR FRONT ALONG THE GULF COAST TO GENERATE FREQUENT  
FRONTAL WAVES WHICH WILL AFFECT THE SOUTHEAST AND MID-ATLANTIC  
REGIONS DURING THE FORECAST PERIOD.  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT AND PREFERENCES
 
 
MODEL CONSENSUS WAS SUFFICIENT DURING DAYS 3-4 (SUN-MON) TO USE A  
MULTI-MODEL DETERMINISTIC BLEND (00Z ECMWF/CMC/GFS) AS A BASIS FOR  
THE FORECAST. MODELS SHOWED SOME VARIABILITY ON THE SPECIFICS OF A  
FRONTAL WAVE CROSSING THE EASTERN U.S. DURING THAT TIME FRAME,  
WITH VARIATIONS AS TO HOW QUICKLY ENERGY TRANSFERS FROM A LOW OVER  
THE SOUTHERN/CENTRAL APPALACHIANS TO A SECOND LOW OFF THE  
MID-ATLANTIC COAST, BUT A MULTI-MODEL CONSENSUS WAS PREFERRED.  
MODELS SHOWED RELATIVELY GOOD CONSENSUS WITH AMPLIFIED SHORTWAVE  
ENERGY DIGGING INTO THE SOUTHWEST SUN-MON AS WELL.  
 
FROM DAY 5 (TUE) ONWARD, MODELS CONTINUE TO SHOW RELATIVELY GOOD  
AGREEMENT WHEN IT COMES TO THE BIG PICTURE, BUT LARGER DIFFERENCES  
BEGIN TO EMERGE ON THE SPECIFICS. CONFIDENCE IS RELATIVELY HIGH  
THAT ENERGETIC SHORTWAVE ENERGY SHOULD MOVE FROM THE FOUR CORNERS  
REGION TUE MORNING INTO THE CENTRAL U.S., WEAKENING TO SOME DEGREE  
AS IT BEGINS TO ENCOUNTER ANTICYCLONIC FLOW ON THE WESTERN  
PERIPHERY OF THE SUBTROPICAL RIDGE. DIFFERENCES AMONG THE GUIDANCE  
AS TO HOW QUICKLY THIS WAVE LIFTS OUT AND THE DEGREE OF  
INTERACTION WITH THE NORTHERN STREAM RESULT IN VARYING SURFACE  
EVOLUTIONS. THERE IS AT LEAST GENERAL CONSENSUS THAT ANOTHER  
FRONTAL WAVE SHOULD DEVELOP IN THE NORTHWESTERN GULF OF MEXICO TUE  
AND THEN LIFT NORTHEASTWARD ACROSS THE TN VALLEY/SOUTHEAST TUE  
NIGHT/WED. RUN-TO-RUN VARIABILITY AMONG DETERMINISTIC SOLUTIONS  
REMAINS BUT A MODERATE DEGREE OF ENSEMBLE CLUSTERING LENT TO  
GRADUALLY HEAVIER USE OF ESPECIALLY THE 00Z ECMWF ENSEMBLE MEAN  
(AND SOME OF THE 00Z GEFS MEAN) SOLUTIONS. MEANWHILE, AS  
ADDITIONAL SHORTWAVE ENERGY DIVES SOUTH ALONG THE WEST COAST AND  
REINFORCES THE MEAN TROUGH, SOLUTIONS VARY AS TO THE SPECIFIC  
NATURE OF THE NEXT WAVE AND ITS AFFECT ON THE LARGER MEAN TROUGH.  
TELECONNECTIONS RELATIVE TO THE STRONG NORTH PACIFIC RIDGE SUPPORT  
THE IDEA OF KEEPING THE WESTERN U.S. MEAN TROUGH FROM PROGRESSING  
EASTWARD TOO QUICKLY, AND THE RECENT ECENS MEAN RUNS HAVE MORE  
CONSISTENTLY HELD THIS FEATURE FARTHER WEST RELATIVE TO THE RECENT  
GEFS MEAN RUNS BY THE MIDDLE OF NEXT WEEK, WHICH HAVE BEEN SLOWLY  
TRENDING WESTWARD. THUS, THE FORECAST DURING DAYS 5-7 WAS BASED  
MORE HEAVILY ON THE ENSEMBLE MEANS WITH MORE WEIGHT PLACED ON THE  
00Z ECMWF ENSEMBLE MEAN RELATIVE TO THE 06Z GEFS.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
THE POLAR FRONT WILL LINGER ACROSS THE SOUTHEAST/GULF COAST  
THROUGH THE FORECAST PERIOD, WITH MULTIPLE WAVES/SURFACE LOWS  
TRAVERSING THE FRONT BRINGING SEVERAL ROUNDS OF WIDESPREAD AND  
POTENTIALLY HEAVY RAIN. MODEL/ENSEMBLE GUIDANCE SHOW THE STRONGEST  
SIGNAL FOR HEAVY RAINS ON THE NORTHWEST SIDE OF THE UPPER HIGH  
CIRCULATION ACROSS PORTIONS OF CENTRAL/NORTHERN MISSISSIPPI,  
ALABAMA, AND GEORGIA, AS WELL AS TENNESSEE AND WESTERN PORTIONS OF  
THE CAROLINAS. MULTI-INCH RAINFALL TOTALS ARE POSSIBLE ACROSS  
THESE AREAS FROM SUN ONWARD INTO THE MIDDLE OF NEXT WEEK AS THE  
BLOCKING RIDGING CHANNELS MOISTURE ALONG THE SAME AXIS. ENSEMBLE  
SITUATIONAL AWARENESS TABLE HIGHLIGHTED THIS AREA WITH "MAX"  
VALUES PER THE GEFS QPF RELATIVE TO THE REFORECAST DATABASE --  
SIGNALING THE RARITY OF THE GEFS ENSEMBLES TO BE THIS WET THIS FAR  
OUT THIS TIME OF YEAR (JAN/FEB/MAR). COLDER AIR IN PLACE ON THE  
NORTHERN PERIPHERY OF THESE LOW PRESSURE SYSTEMS MAY RESULT IN  
AREAS OF WINTRY PRECIPITATION FOR PORTIONS OF THE CENTRAL  
APPALACHIANS AND MID-ATLANTIC.  
 
MEANWHILE, CONDITIONS ALONG THE WEST COAST WILL BE AT LEAST A BIT  
QUIETER THAN SEEN RECENTLY, AS THE MAIN UPPER TROUGH AXIS MOVES  
INLAND BY TUE. THIS WILL SPREAD SNOWS INTO THE SOUTHERN ROCKIES  
SUN-MON. MORE WIDESPREAD RAIN/SNOW MAY RETURN TO THE PACIFIC  
NORTHWEST BY NEXT TUE-WED AS A MORE SIGNIFICANT SHORTWAVE  
APPROACHES AND DIVES SOUTH ALONG THE COAST INTO THE GREAT BASIN.  
 
WELL-BELOW AVERAGE TEMPERATURES WILL PERSIST ACROSS MUCH OF THE  
WESTERN/CENTRAL U.S. DURING THE NEXT WEEK AS THE UPPER TROUGH AXIS  
MOVES INLAND. TEMPERATURES AS COLD AS 15 TO 40 DEG F BELOW AVERAGE  
WILL INITIALLY BE CONCENTRATED ACROSS THE NORTHERN/CENTRAL HIGH  
PLAINS SUN, BUT WILL BECOME MORE WIDESPREAD FROM MON ONWARD, WITH  
MUCH OF THE WESTERN AND CENTRAL U.S. EXPECTED TO SEE TEMPERATURES  
RANGING FROM 10 TO AS MUCH AS 30 DEG BELOW AVERAGE. RECORD COLD  
MAXIMUM TEMPERATURE ARE QUITE POSSIBLE OVER PORTIONS OF THE WEST  
INCLUDING SOUTHERN CALIFORNIA THROUGH THE PERIOD. FARTHER EAST  
NEAR THE UPPER RIDGE, RECORD HIGH TEMPERATURES WILL BE POSSIBLE  
ALONG THE GULF COAST INTO FLORIDA.  
 
FRACASSO/RYAN  
 
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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