052  
FXUS02 KWBC 150646  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
145 AM EST FRI FEB 15 2019  
 
VALID 12Z MON FEB 18 2019 - 12Z FRI FEB 22 2019  
 
...MULTI-DAY HEAVY RAIN THREAT FOR THE TENNESSEE VALLEY AND  
SOUTH-CENTRAL APPALACHIANS/MID-ATLANTIC AND HEAVY SNOW/ICE THREATS  
OVERTOP INTO THE OHIO VALLEY, CENTRAL APPALACHIANS, NORTH-CENTRAL  
MID-ATLANTIC AND SOUTHERN NEW ENGLAND...  
...WINTRY WESTERN-CENTRAL U.S WEATHER FOCUSES OVER  
SOUTHWEST/SOUTHERN ROCKIES...  
 
   
..OVERVIEW
 
 
IT REMAINS THE CASE THAT UPPER-LEVEL RIDGING ACROSS THE NORTH  
PACIFIC AND NEAR THE BAHAMAS SHOWS MINIMAL SIGNS IN GUIDANCE OF  
BREAKING DOWN DURING THE MEDIUM RANGE, AND THUS WILL CONTINUE TO  
INFLUENCE THE LARGE SCALE FLOW ACROSS THE CONUS. THIS REINFORCES A  
PATTERN WITH A COLD/UNSETTLING TROUGH IN THE WEST/SOUTHWEST,  
ARCTIC AIR INTRUSIONS INTO THE N-CENTRAL U.S. AND WAVY SOUTHWEST  
FLOW OVER THE EASTERN HALF OF THE CONUS THROUGH THE NEXT WEEK. A  
RAPID SUCCESSION OF PACIFIC SHORTWAVE ENERGIES WILL TRAVERSE THE  
FLOW, AMPLIFYING THE MEAN TROUGH OVER THE WEST BEFORE EJECTING AND  
INTERACTING WITH A LINGERING POLAR FRONT ALONG THE GULF COAST TO  
GENERATE FREQUENT FRONTAL WAVES WHICH AFFECT THE EAST-CENTRAL AND  
EASTERN U.S.  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT AND PREFERENCES
 
 
A COMPOSITE OF DECENTLY CLUSTERED GUIDANCE OF THE 12 UTC  
ECMWF/ECMWF ENSEMBLES AND FAVORABLY TRENDING OF THE 18 UTC  
GFS/GEFS SEEMS REASONABLE AS A BASIS FOR THE FORECAST MON-WED.  
MODELS SHOW 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 CONSENSUS WAS PREFERRED. THERE IS ALSO RELATIVELY  
GOOD CONSENSUS WITH AMPLIFIED SHORTWAVE ENERGY DIGGING INTO THE  
SOUTHWEST MON-WED.  
 
STRATING DAY 6/THU AND ESPECIALLY BY DAY 7/NEXT FRI, GUIDANCE  
CONTINUES TO SHOW RELATIVELY GOOD AGREEMENT WITH THE BIG PICTURE,  
BUT LARGER DIFFERENCES BEGIN TO EMERGE ON THE SPECIFICS. OPTED TO  
DERIVE THIS FORECAST PERIOD PRIMARILY FROM THE 12 UTC ECMWF  
ENSEMBLE MEAN AND TO A LESSER EXTENT THE 18 UTC GEFS MEAN TO  
ADDRESS GROWING UNCERTAINTY AND MAINTAIN AS MUCH WPC CONTINUITY AS  
FEASIBLE. THE ECMWF ENSEMBLE MEAN OFFERS MORE AMPLIFIED/LESS  
PROGRESSIVE FLOW THAN THE GEFS MEAN.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
A POLAR FRONT LINGERS OVER 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 OVER THE  
TENNESSEE VALLEY AND SOUTH-CENTRAL APPALACHIANS/MID-ATLANTIC.  
THERE IS A THREAT OF MULTI-INCH RAINFALL TOTALS 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 SETTLED IN PLACE  
ON THE NORTHERN PERIPHERY OF THESE LOW PRESSURE SYSTEMS OFFERS  
THREATS OF HEAVY SNOW/ICE FOR THE OHIO VALLEY, CENTRAL  
APPALACHIANS AND FROM THE NORTH-CENTRAL MID-ATLANTIC INTO SOUTHERN  
NEW ENGLAND.  
 
MEANWHILE, CONDITIONS NEXT WEEK ALONG THE WEST COAST WILL BE  
QUIETER THAN SEEN RECENTLY AS THE MAIN UPPER TROUGH AXIS MOVES  
INLAND. THIS WILL SPREAD SNOWS INTO SOUTHWEST/SOUTHERN ROCKIES  
TERRAIN. SOME WIDESPREAD RAIN/SNOW MAY RETURN TO THE PACIFIC  
NORTHWEST BY MIDWEEK AS A MORE SIGNIFICANT SHORTWAVE APPROACHES  
AND DIVES SOUTH ALONG THE COAST INTO THE WINTRY GREAT BASIN THEN  
ROCKIES/N-CENTRAL U.S.  
 
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.  
 
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  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page