527  
FXUS02 KWBC 081600  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1100 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 OF DAYS DURING THE MEDIUM RANGE PERIOD. A  
STRENGTHENING UPPER RIDGE ACROSS THE NORTHERN ROCKIES/GREAT BASIN  
WILL RESULT IN SPLIT FLOW AS THESE PACIFIC SYSTEMS MOVE EASTWARD,  
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 CLOSED UPPER HIGH THIS  
WEEKEND ACROSS THE MIDWEST/GREAT LAKES/NORTHEAST. THIS SETUP MAY  
RESULT IN SOME PHASING OF NORTHERN/SOUTHERN STREAM WAVES  
ALONG/NEAR THE EAST COAST AS LOW PRESSURE EXITS OFF THE SOUTHERN  
MID-ATLANTIC SUNDAY. 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 THE  
TRANSPORT OF COLD POLAR AIR SOUTHWARD INTO THE EASTERN U.S.,  
SETTING THE STAGE FOR AT LEAST SOME WINTER WEATHER POTENTIAL ON  
THE NORTHERN SIDE OF THE LOW PRESSURE SYSTEM THIS WEEKEND. BY NEXT  
WEEK, ANOTHER SYSTEM IN THE PACIFIC MAY PUSH INTO CENTRAL/SOUTHERN  
CALIFORNIA AND THE DESERT SOUTHWEST.  
 
   
..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) AND ITS SURFACE FRONT EXPECTED TO  
MOVE INTO SOUTHERN CALIFORNIA. FARTHER EAST, NORTHERN AND SOUTHERN  
STREAM SHORTWAVE ENERGY WILL ATTEMPT TO INTERACT/PHASE ACROSS THE  
CENTRAL U.S. DURING THE SAME TIME PERIOD AND CARRY A SURFACE LOW  
EASTWARD THROUGH THE LOWER MISSISSIPPI VALLEY/NORTHERN GULF COAST.  
AS IS OFTEN THE CASE IN THESE SITUATIONS, MODELS SHOW A BIT MORE  
SPREAD WITH THE NORTHERN STREAM WAVE, WITH THE 00Z GFS AMONG THE  
MOST AMPLIFIED SOLUTIONS WHILE THE 00Z CANADIAN WAS MOST AMPLIFIED  
WITH THE SOUTHERN PORTION. ENSEMBLE TRENDS AND SURFACE SETUP  
(1040MB HIGH TO THE NORTH) SEEM TO SUPPORT A LESS PHASED (MORE  
SHEARED) AND WEAKER SOLUTION (LIKE THE 06Z GFS AND 00Z ECMWF)  
RATHER THAN A DEEPER SURFACE LOW (LIKE THE 00Z GFS/CANADIAN). QPF  
WAS MORE UNCERTAIN GIVEN THE BLOCKING COLD AIR TO THE NORTH, BUT A  
STRIPE OF APPRECIABLE SNOW IS LIKELY EVEN GIVEN A SHEARED SYSTEM  
WITH MORE "CONVERSATIONAL SNOW" (LESS THAN A INCH) ON THE NORTHERN  
FRINGE WITH MORE SNOW OVER HIGHER ELEVATION ENHANCED BY UPSLOPE  
FLOW.  
 
BACK TO THE WEST EARLY NEXT WEEK, ADDITIONAL AMPLIFIED ENERGY WILL  
APPROACH THE WEST COAST LATE SUN INTO MON, WITH A TREND A  
SLOWER/DEEPER TROUGH AND LIKELY A CLOSED OFF UPPER LOW NEARING  
SOUTHERN CALIFORNIA. MOST RECENT DETERMINISTIC RUNS SHOW A CLOSED  
LOW AND THE ENSEMBLE TREND HAS SLOWED DOWN QUITE NOTICEABLY IN THE  
ECMWF ENSEMBLES WHILE THE GEFS MEMBERS HAVE BEEN SLOWER FOR  
SEVERAL RUNS. ELONGATION OF THE UPPER RIDGE INTO WESTERN CANADA  
WOULD SUPPORT THE CONTINUED SPLIT FLOW AND RATHER REPETITIVE  
PATTERN IN THE SOUTHWEST THAT IS FORECAST FOR THIS WEEKEND.  
 
   
..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 EASTWARD  
INTO THE SOUTHEAST/SOUTHERN MID-ATLANTIC BY SAT NIGHT/SUN. COLD  
AIR TO THE NORTH OF THE SYSTEM WOULD RESULT IN AREAS OF WINTRY  
PRECIPITATION ACROSS PORTIONS OF THE MID-MISSISSIPPI VALLEY  
(OZARKS NORTHWARD INTO SOUTHERN MISSOURI) ON FRI AND ACROSS AREAS  
FROM THE OHIO VALLEY TO THE SOUTHERN/CENTRAL APPALACHIANS AND  
MID-ATLANTIC BY SAT-SUN. THE NORTHERN EXTENT/AMOUNT OF SNOW  
SAT-SUN ACROSS THE MID-ATLANTIC REGION REMAINS HIGHLY UNCERTAIN  
GIVEN THE DEGREE OF (OR LACK THEREOF) PHASING/AMPLIFICATION.  
 
GENERALLY 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 GIVEN PREDOMINATELY NORTHWEST FLOW OUT OF  
CENTRAL CANADA WHERE TEMPERATURES AS COLD AS 10 TO 20 DEG F BELOW  
AVERAGE WILL BE POSSIBLE FROM FRI THROUGH EARLY NEXT WEEK. SOME  
MODERATION IS LIKELY BY NEXT WEEK AS THE TROUGH MOVES OFF THE  
COAST IN THE WAKE OF THE WEEKEND SYSTEM.  
 
FRACASSO/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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