556  
FXUS02 KWBC 090646  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
145 AM EST WED JAN 09 2019  
 
VALID 12Z SAT JAN 12 2019 - 12Z WED JAN 16 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.,  
LIKELY SETTING THE STAGE FOR 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
 
 
MODEL SOLUTIONS SEEM TO HAVE SETTLED ON AN AMPLIFIED AND  
NEGATIVELY TILTED UPPER TROUGH REACHING CALIFORNIA ON DAY 4 (SAT),  
WITH AN INTENSIFYING RIDGE ACROSS THE NORTHERN GREAT BASIN/ROCKIES  
CAUSING THE TROUGH TO SHEAR AND SEPARATE INTO THE  
NORTHERN/SOUTHERN STREAM COMPONENTS BY SUN. MEANWHILE, PHASING OF  
SOUTHERN/NORTHERN STREAM SHORTWAVE ENERGY WILL BE UNDERWAY ACROSS  
THE PLAINS AND MISSISSIPPI VALLEY. MODELS CONTINUE TO STRUGGLE A  
BIT WITH THE PHASING PROCESS, WITH SOME RUN-TO-RUN VARIABILITY  
STILL DURING THE SAT-SUN TIME FRAME. A SURFACE LOW IS EXPECTED TO  
TRACK ACROSS THE GULF COAST STATES SAT-SUN WITH A SECOND COASTAL  
LOW DEVELOPING ALONG THE NORTH/SOUTH CAROLINA COASTLINE SAT NIGHT  
INTO SUN MORNING. BY DAY 5 (MON) THERE IS SOME DISAGREEMENT AS TO  
HOW QUICKLY THE LOW MOVES OUT TO SEA, ALTHOUGH CONSENSUS HAS  
IMPROVED RELATIVE TO THIS TIME LAST NIGHT TOWARD A TRACK MORE  
EAST-NORTHEASTERLY OUT TO SEA RATHER THAN CLOSER TO THE NORTHEAST  
U.S. COASTLINE. ALSO BY DAY 4-5 ANOTHER AMPLIFIED TROUGH AND  
ASSOCIATED FRONTAL SYSTEM WILL APPROACH THE WEST COAST. MODELS  
CONTINUE TO SHOW SOME VARIABILITY ON THE EXACT STRUCTURE OF THIS  
FEATURE (COMPACT CLOSED LOW OR MORE ELONGATED UPPER TROUGH). GIVEN  
THE VARIABILITY AT SMALLER SCALES AND GENERAL LARGE SCALE  
AGREEMENT, OPTED TO TAKE A MULTI-MODEL DETERMINISTIC BLEND  
APPROACH DURING DAYS 3-5, INCLUDING THE ECMWF/GFS/UKMET.  
 
BY TUE-WED (DAYS 6-7), ADDITIONAL SOUTHERN STREAM SHORTWAVE ENERGY  
SHOULD CROSS THE SOUTHEAST (THE ENERGY WHICH BEGAN NEAR CA ON DAY  
3) WHILE THE NEXT PACIFIC TROUGH MOVES INTO THE FOUR CORNERS  
REGION AND EVENTUALLY THE PLAINS (MODELS HAVE ALMOST UNIVERSALLY  
SPED THIS FEATURE UP COMPARED TO PREVIOUS RUNS WHICH KEPT A CLOSED  
LOW LINGERING OFFSHORE FOR LONGER). MODEL/ENSEMBLE SOLUTIONS HAVE  
SHOWN A LARGE DEGREE OF INCONSISTENCY/VARIABILITY BY THIS TIME  
FRAME SO WAS LEERY OF LEANING TOO HEAVILY TOWARD DETERMINISTIC  
GUIDANCE. THUS, WEIGHT WAS SHIFTED HEAVILY TOWARD THE  
ECENS/GEFS/NAEFS ENSEMBLE MEANS BY DAYS 6-7.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
EXPECT THE POTENTIAL FOR MULTIPLE ROUNDS OF 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 LOWER  
MISSISSIPPI VALLEY/SOUTHEAST BY SAT-SUN, PRECIPITATION WILL  
OVERSPREAD MUCH OF THE REGION, AS FAR NORTH AS THE OHIO VALLEY,  
APPALACHIANS, AND SOUTHERN MID-ATLANTIC. COLD AIR ON THE NORTHERN  
SIDE OF THE SYSTEM WILL RESULT IN A THREAT OF WINTRY PRECIPITATION  
FROM PORTIONS OF THE OHIO VALLEY TO THE SOUTHERN MID-ATLANTIC.  
CONFIDENCE HAS INCREASED COMPARED TO THIS TIME YESTERDAY WITH  
RESPECT TO THE POTENTIAL FOR ACCUMULATING SNOWS FROM PORTIONS OF  
CENTRAL/EASTERN KENTUCKY EAST INTO THE SOUTHERN/CENTRAL  
APPALACHIANS AND SOUTHERN MID-ATLANTIC. THE EXACT AREAS TO RECEIVE  
ANY POTENTIALLY HEAVY SNOW REMAIN MORE UNCERTAIN AT THIS TIME AND  
WILL DEPEND ON THE EXACT TRACK OF THE SURFACE LOW PRESSURE SYSTEM  
OFF THE SOUTHEAST/SOUTHERN MID-ATLANTIC COASTLINE.  
 
GENERALLY ABOVE AVERAGE TEMPERATURES WILL PERSIST THROUGH MUCH OF  
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). 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 THE WEEKEND 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.  
 
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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