249  
FXUS02 KWBC 060640  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
139 AM EST SUN JAN 06 2019  
 
VALID 12Z WED JAN 09 2019 - 12Z SUN JAN 13 2019  
   
..OVERVIEW
 
 
MODERATE PROGRESSIVE FLOW PATTERN EXPECTED TO PERSIST ACROSS THE  
CONUS DURING THE MEDIUM RANGE. PERSISTENT POSITIVE HEIGHT  
ANOMALIES NEAR THE NORTH POLE AS WELL AS FROM JAMES BAY EAST INTO  
THE NORTH ATLANTIC (PER LATEST ENSEMBLE D+8 ANOMALIES) WILL  
CONTINUE TO PREVENT ANY SIGNIFICANT OR PROLONGED INCURSIONS OF  
ARCTIC AIR SOUTHWARD INTO THE CONUS. HOWEVER, TELECONNECTIONS  
ASSOCIATED WITH A STRONG 500 HPA HEIGHT ANOMALY DIPOLE EXTENDING  
FROM SOUTH OF ICELAND (POSITIVE) TO NORTHEAST EUROPE (NEGATIVE) DO  
SUPPORT THE TENDENCY FOR PERIODS OF COLD TEMPERATURES ACROSS THE  
EASTERN U.S. THESE SHOULD BE RELATIVELY SHORT-LIVED, HOWEVER,  
WITHOUT A SIGNIFICANT AND PROLONGED MEANS OF SOUTHWARD TRANSPORT  
FOR COLDER AIR FROM HIGH LATITUDES. MEANWHILE, AN ACTIVE POLAR  
STREAM ACROSS THE NORTH PACIFIC WILL BRING ENERGY TO THE U.S. WEST  
COAST AND EASTWARD ACROSS THE COUNTRY EVERY 1-2 DAYS, WITH SOME  
SPLITTING OF ENERGY INTO NORTHERN/SOUTHERN STREAM COMPONENTS AS  
FEATURES MOVE INLAND OVER THE WESTERN STATES.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
A MULTI-MODEL DETERMINISTIC BLEND (INCLUDING THE ECMWF/GFS/CMC)  
SERVED AS A BASIS FOR THE FORECAST ON DAYS 3-5 (WED-FRI). THESE  
SOLUTIONS SHOWED REASONABLY GOOD CONSENSUS AND CLUSTERING WITH  
ENSEMBLE MEANS FOR THE SYSTEM INITIALLY MOVING AWAY FROM THE NEW  
ENGLAND COAST ON WED AND WITH THE STRONG LOW PRESSURE SYSTEM OFF  
THE PACIFIC NORTHWEST AT THE SAME TIME, WITH ASSOCIATED  
UPPER-LEVEL ENERGY CROSSING THE ROCKIES AND NORTH CENTRAL U.S.  
THU-FRI.  
 
BY FRI-SAT (DAYS 6-7) THE SOUTHERN STREAM COMPONENT OF THE  
PREVIOUS WEST COAST SYSTEM IS EXPECTED TO INTERACT WITH WITH A  
LINGERING FRONTAL BOUNDARY ACROSS THE NORTHERN GULF OF MEXICO,  
RESULTING IN A NEW FRONTAL WAVE, WITH ENERGY EVENTUALLY PERHAPS  
TRANSFERRING TO A NEW LOW OFF THE SOUTHEAST U.S. COAST. AS IS  
TYPICAL OF THESE SYSTEMS INVOLVING SOME DEGREE OF INTERACTION  
BETWEEN NORTHERN/SOUTHERN STREAM ENERGY AND RESULTANT FRONTAL  
WAVES, MODEL/ENSEMBLE SOLUTIONS SHOW A SIGNIFICANT DEGREE OF  
SPREAD AND VARIABILITY, ALTHOUGH THE GENERAL EVOLUTION DESCRIBED  
HAS GOOD CONSENSUS SUPPORT. NONETHELESS, IT IS CERTAINLY TOO EARLY  
TO SPECULATE ON SPECIFICS OF ANY POTENTIAL LOW PRESSURE SYSTEM  
ALONG THE SOUTHEAST/MID-ATLANTIC COAST NEXT WEEKEND. MEANWHILE,  
THE NEXT HIGHLY AMPLIFIED SYSTEM SHOULD REACH THE WEST COAST  
DURING THAT TIME FRAME. MODELS SHOW SOME CONSENSUS THAT AS THIS  
PACIFIC SYSTEM APPROACHES ANOTHER SOUTHERN STREAM COMPONENT SHOULD  
SEPARATE OUT AND MOVE MORE QUICKLY INTO THE SOUTHWEST STATES WHILE  
A BROAD UPPER TROUGH LINGERS OFF THE PACIFIC NORTHWEST COAST.  
MODELS SHOW EXPECTED DIFFERENCES AS THE SPECIFICS OF THIS PROCESS,  
WITH A BIT MORE CONSISTENCY FOUND IN THE ENSEMBLE MEANS. GIVEN  
THESE CONSIDERATIONS DURING THE LATTER PORTION OF THE EXTENDED  
PERIOD, A MAJORITY ENSEMBLE MEAN-BASED APPROACH WAS USED, WITH  
SIGNIFICANT FORECAST WEIGHT PLACED ON THE ECENS AND GEFS MEANS.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
EXPECT MULTIPLE ROUNDS OF POTENTIALLY HEAVY PRECIPITATION (LOW  
ELEVATIONS RAINS AND MOUNTAIN SNOWS) ALONG THE WEST COAST THROUGH  
THE FORECAST PERIOD. THE FOCUS FOR THE GREATEST PRECIP AMOUNTS ON  
WED-THU WILL BE FROM NORTHERN CALIFORNIA NORTH TO THE PACIFIC  
NORTHWEST, SHIFTING SOUTHWARD ACROSS MUCH OF CALIFORNIA BY  
FRI-SAT. FARTHER EAST, THE SYSTEM PULLING AWAY FROM NEW ENGLAND ON  
WED COULD STILL PRODUCE AREAS OF HEAVY SNOW FOR NORTHERN NEW  
ENGLAND THROUGH WED, WITH SOME POTENTIAL FOR LAKE EFFECT ENHANCED  
SNOWS DOWNWIND OF LAKES ERIE AND ONTARIO AS WELL. SOUTHERN STREAM  
ENERGY AN AFOREMENTIONED FRONTAL BOUNDARY INTERACTIONS WILL CAUSE  
PRECIPITATION TO GRADUALLY DEVELOP ACROSS THE SOUTHERN PLAINS BY  
THU, SPREADING EAST TOWARD THE GULF COAST/LOWER MISSISSIPPI VALLEY  
AND SOUTHEAST FRI-SAT. THERE IS SOME POTENTIAL FOR WINTRY WEATHER  
ON THE NORTHERN PERIPHERY OF THIS SYSTEM ACROSS THE  
SOUTHERN/CENTRAL APPALACHIANS BY NEXT WEEKEND, BUT CONFIDENCE IN  
THIS ASPECT OF THE FORECAST IS LOW AT THIS TIME.  
 
THE LARGEST TEMPERATURE ANOMALIES WILL BE FROM THE  
NORTHERN/CENTRAL ROCKIES EAST INTO THE PLAINS THROUGH MUCH OF THE  
FORECAST PERIOD. HIGH TEMPERATURES RANGING FROM 5-15 DEG F ABOVE  
AVERAGE ARE EXPECTED, WITH SOME AREAS APPROACHING +20 DEG  
ANOMALIES ON THU. MEANWHILE, TEMPERATURES FROM THE GREAT LAKES TO  
THE EASTERN SEABOARD WILL BE NEAR TO SEVERAL DEGREES BELOW  
AVERAGE. THE BEST POTENTIAL FOR SIGNIFICANTLY BELOW AVERAGE  
TEMPERATURES APPEARS TO BE ACROSS NEW ENGLAND ON FRI-SAT, WHERE  
HIGHS OF 10-15 DEG F BELOW AVERAGE ARE POSSIBLE - THE RESULT OF  
STRONG COLD AIR ADVECTION IN THE WAKE OF THE MID-WEEK LOW PRESSURE  
SYSTEM.  
 
RYAN  
 
WPC MEDIUM RANGE 500 MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION, WINTER WEATHER OUTLOOK PROBABILITIES  
AND HEAT INDEXES 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  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML  
 

 
 
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