278  
FXUS02 KWBC 140619  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
119 AM EST THU FEB 14 2019  
 
VALID 12Z SUN FEB 17 2019 - 12Z THU FEB 21 2019  
 
...MULTI-DAY HEAVY RAIN EVENT POSSIBLE FOR PORTIONS OF THE  
SOUTHEAST, TENNESSEE VALLEY, AND SOUTHERN APPALACHIANS NEXT WEEK...  
 
   
..OVERVIEW
 
 
UPPER-LEVEL RIDGE ACROSS THE NORTH PACIFIC 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 RIDGING OFF  
THE SOUTHEAST U.S. COAST 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 (12Z ECMWF/UKMET/CMC AND 18Z 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 SOUTHEAST TUE NIGHT/WED.  
RUN-TO-RUN VARIABILITY AMONG DETERMINISTIC SOLUTIONS BUT A  
MODERATE DEGREE OF ENSEMBLE CLUSTERING LENT TO GRADUALLY HEAVIER  
USE OF ECENS/GEFS MEAN SOLUTIONS. MEANWHILE, AS ADDITIONAL  
SHORTWAVE ENERGY DIVES SOUTH ALONG THE WEST COAST AND REINFORCES  
THE MEAN TROUGH, SOLUTIONS VARY WIDELY AS TO THE SPECIFIC NATURE  
OF THE NEXT WAVE, AND ITS EFFECT 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  
EAST TOO QUICKLY, AND THE ECENS MEAN HAS MORE CONSISTENTLY HELD  
THIS FEATURE FARTHER WEST RELATIVE TO THE GEFS MEAN BY THE MIDDLE  
OF NEXT WEEK. THUS, THE FORECAST DURING DAYS 5-7 WAS BASED MORE  
HEAVILY ON THE ENSEMBLE MEANS, WITH MORE WEIGHT PLACED ON THE  
ECENS RELATIVE TO THE 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 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. 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. 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.  
 
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 30 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.  
 
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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