081  
FXUS02 KWBC 080656  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
156 AM EST TUE JAN 08 2019  
 
VALID 12Z FRI JAN 11 2019 - 12Z TUE JAN 15 2019  
   
..OVERVIEW
 
 
PROGRESSIVE AND AMPLIFIED FLOW ACROSS THE NORTH PACIFIC WILL  
CONTINUE TO BRING SIGNIFICANT STORM SYSTEMS TO THE WEST COAST  
EVERY COUPLE DAYS DURING THE MEDIUM RANGE. A STRENGTHENING UPPER  
RIDGE ACROSS THE NORTHERN ROCKIES/GREAT BASIN WILL RESULT IN SPLIT  
FLOW AS THESE PACIFIC SYSTEMS MOVE EAST, WITH ENERGY SEPARATING  
INTO NORTHERN AND SOUTHERN STREAM COMPONENTS. NORTHERN STREAM  
ENERGY WILL AMPLIFY AS IT ENTERS BROAD CYCLONIC UPPER-LEVEL FLOW  
EAST OF THE RIDGE, ACROSS THE MIDWEST/GREAT LAKES/NORTHEAST. THIS  
SETUP ALSO RESULTS IN POTENTIAL PHASING OF NORTHERN/SOUTHERN  
STREAM WAVES AND AN ELEVATED RISK FOR COASTAL LOW DEVELOPMENT OFF  
THE EASTERN SEABOARD. WHILE THIS PATTERN DOES NOT FAVOR A  
WIDESPREAD OUTBREAK OF COLD AIR, PERSISTENT TROUGHING ACROSS THE  
EAST ALONG WITH THE AMPLIFIED WESTERN U.S. RIDGE WILL SUPPORT  
TRANSPORT OF COLD POLAR AIR SOUTH INTO EASTERN U.S., SETTING THE  
STAGE FOR AT LEAST SOME WINTER WEATHER POTENTIAL ON THE NORTHERN  
SIDE A LOW PRESSURE SYSTEM EXPECTED TO TRACK FROM THE GULF COAST  
TO OFF THE EASTERN SEABOARD BY THE WEEKEND.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
MODELS HAVE GENERALLY TRENDED TOWARD A SOMEWHAT SLOWER AND MORE  
AMPLIFIED SOLUTION WITH AN UPPER TROUGH EXPECTED TO APPROACH  
CALIFORNIA FRI-SAT (DAYS 3-4). MEANWHILE, FARTHER EAST, NORTHERN  
AND SOUTHERN STREAM SHORTWAVE ENERGY WILL BEGIN TO INTERACT/PHASE  
ACROSS THE CENTRAL U.S. DURING THE SAME TIME PERIOD. AS IS OFTEN  
THE CASE IN THESE SITUATIONS, MODELS SHOW A BIT MORE SPREAD WITH  
THE NORTHERN STREAM WAVE, WITH THE GFS THE MOST AMPLIFIED SOLUTION  
AND THE UKMET AMONG THE LEAST AMPLIFIED. ENSEMBLE MEANS SEEM TO  
SUPPORT A BLENDED/CONSENSUS SOLUTION HERE. AS A RESULT, A  
MULTI-MODEL DETERMINISTIC BLEND (ECMWF/GFS/UKMET) WAS USED AS A  
FORECAST STARTING POINT FOR DAYS 3-4.  
 
BY DAY 5 (SUN), MODELS HAVE TRENDED A BIT TOWARD A MORE PHASED  
SOLUTION WITH A MORE AMPLIFIED TROUGH ACROSS THE OHIO  
VALLEY/APPALACHIANS AND A SOMEWHAT LESS SUPPRESSED LOW TRACK ALONG  
THE EASTERN SEABOARD RELATIVE TO THIS TIME LAST NIGHT. AT THIS  
TIME THE GFS ALONG WITH THE CMC CONTINUE TO SHOW THE FARTHEST WEST  
LOW TRACK ALONG THE SOUTHEAST/MID-ATLANTIC COAST ON SUN, WITH THE  
ECMWF AND UKMET APPROXIMATELY 100 MILES FARTHER SOUTH/EAST. THE  
GFS REMAINS ON THE WESTERN FRINGE OF THE ENSEMBLE DISTRIBUTION,  
WHILE THE ECENS/GEFS/NAEFS ENSEMBLE MEANS ARE MUCH CLOSER TO  
SOMETHING ALONG THE LINES OF THE ECMWF/UKMET. FARTHER WEST,  
ADDITIONAL AMPLIFIED ENERGY APPROACHES THE WEST COAST BY SUN, WITH  
A TREND A SLOWER/DEEPER SOLUTION WITH THIS FEATURE, OR PERHAPS  
EVEN CUTTING THE SYSTEM OFF WEST OF CALIFORNIA THROUGH EARLY NEXT  
WEEK. CONTINUED VARIABILITY AMONG SOLUTIONS AND THE COMPLEX NATURE  
OF THE PHASING PROCESS WITH THE EASTERN SYSTEM REDUCES CONFIDENCE  
IN ANY PARTICULAR DETERMINISTIC SOLUTION. THUS, FROM DAY 5 ONWARD  
SUBSTANTIALLY INCREASED WEIGHT WAS PLACED TOWARD THE ECENS AND  
GEFS ENSEMBLE MEANS.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
EXPECT THE POTENTIAL FOR MULTIPLE ROUNDS OF HEAVY PRECIPITATION  
(LOW ELEVATION RAIN AND MOUNTAIN SNOWS) ACROSS THE WEST COAST  
DURING THE FORECAST PERIOD AS A RAPID SUCCESSION OF PACIFIC  
SYSTEMS IMPACTS THE REGION. AS SHORTWAVE ENERGY REACHES THE  
SOUTHERN PLAINS/LOWER MISSISSIPPI VALLEY BY FRI-SAT, AREAS OF  
HEAVY RAIN WILL BE POSSIBLE, WITH PRECIPITATION SPREADING EAST  
INTO THE SOUTHEAST/SOUTHERN MID-ATLANTIC BY SAT NIGHT/SUN. COLD  
AIR TO THE NORTH OF THE SYSTEM COULD RESULT IN AREAS IF WINTRY  
PRECIPITATION ACROSS PORTIONS OF THE MID-MISSISSIPPI VALLEY ON FRI  
AND ACROSS AREAS FROM THE OHIO VALLEY TO THE SOUTHERN/CENTRAL  
APPALACHIANS AND MID-ATLANTIC BY SAT-SUN. THE NORTHERN EXTENT OF  
WINTER WEATHER POTENTIAL SAT-SUN ACROSS THE MID-ATLANTIC REGION  
REMAINS HIGHLY UNCERTAIN GIVEN THE FACTORS DESCRIBED ABOVE. AS THE  
SYSTEM TRACKS NORTHEASTWARD IN THE ATLANTIC OCEAN SUN-MON, NEW  
ENGLAND MAY FACE A THREAT FOR WINTER WEATHER BUT THIS WILL AGAIN  
HINGE LARGELY ON THE EVENTUAL TRACK OF THE SYSTEM AND HOW CLOSE IT  
REMAINS TO THE COASTLINE.  
 
ABOVE AVERAGE TEMPERATURES WILL PERSIST THROUGH THE FORECAST  
PERIOD ACROSS THE NORTH CENTRAL U.S., WITH MAX TEMP ANOMALIES IN  
THE +10 TO +15 DEG F RANGE (EVEN WARMER FOR SOME AREAS) THROUGH  
MUCH OF THE PERIOD. THE COLDEST TEMPERATURES WILL BE ACROSS THE  
NORTHEAST, WHERE TEMPERATURES AS COLD AS 10 TO 20 DEG BELOW  
AVERAGE WILL BE POSSIBLE FROM FRI THROUGH EARLY NEXT WEEK.  
 
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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