232  
FXUS02 KWBC 201558  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1057 AM EST SUN JAN 20 2019  
 
VALID 12Z WED JAN 23 2019 - 12Z SUN JAN 27 2019  
   
..OVERVIEW
 
 
GUIDANCE CONTINUES TO AGREE WITH THE OVERALL AMPLIFIED PATTERN  
WITH A RIDGE ACROSS THE EASTERN PACIFIC/WEST COAST AND TROUGH OVER  
THE CENTRAL-EASTERN PORTIONS OF CONUS ALOFT. THIS WILL GIVE WAY TO  
A WET PATTERN FOR THE EASTERN HALF OF THE U.S. ESPECIALLY IN THE  
BEGINNING OF THE MEDIUM RANGE PERIOD WITH SOME PRECIPITATION IN  
PORTIONS OF THE PACIFIC NORTHWEST AND INTERMOUNTAIN WEST. HOWEVER,  
THE DETAILS REGARDING THE SHORTWAVES MOVING OVER THE TOP OF THE  
RIDGE AND DOWNSTREAM ACROSS THE MEAN TROUGH STILL REMAIN HIGHLY  
UNCERTAIN.  
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
DURING THE FIRST PORTION OF THE MEDIUM RANGE PERIOD, MODELS ARE  
AGREEABLE WITH THE FEATURES ALOFT AND AT THE SURFACE. THE UPPER  
TROUGH WILL BEGIN TO PUSH FROM THE PLAINS EASTWARD INTO THE  
MISSISSIPPI VALLEY WHILE THE UPPER RIDGE BUILDS ACROSS THE WEST  
COAST. A SHORTWAVE WILL SLIDE OVER THE RIDGE INTO THE PACIFIC  
NORTHWEST/INTERMOUNTAIN WEST DURING THIS TIME. ON DAY 3/WEDNESDAY,  
THE 06Z GFS/00Z ECMWF AND THE 00Z CMC/UKMET WERE IN GOOD AGREEMENT  
WITH THE TIMING OF THE FRONT SWEEPING ACROSS THE EASTERN U.S.  
THUS, DAY 3 HAD A BLEND OF THESE WITH MOST WEIGHT GIVEN TO THE GFS  
AND ECMWF. HOWEVER, BY DAY 4, SLIGHT DIFFERENCES IN THE DETAILS  
ALOFT GIVE WAY TO BIG DIFFERENCES AT THE SURFACE. THE 00Z CMC  
BECOMES TOO DEEP WITH THE SURFACE LOW IN THE MID-ATLANTIC, AND THE  
UKMET IS TOO SLOW WITH THE FRONT. THE GFS/ECMWF WERE STILL  
COMPARABLE--BUT ALREADY BEGUN TO INTRODUCE THEIR ENSEMBLE MEANS BY  
THIS TIME. BY DAY 5, DIFFERENCES IN THE ECMWF AND GFS START TO  
INCREASE BUT STILL WERE REASONABLE ENOUGH TO USE IN THE BLEND. THE  
06Z AND 00Z GFS WERE FASTER AND MORE INTENSE WITH THE SURFACE HIGH  
PRESSURE DROPPING ACROSS THE CENTRAL U.S. THAN THE 00Z ECMWF.  
HOWEVER, THE PREVIOUS RUN OF THE ECMWF WAS MORE ALIGNED WITH THE  
GFS. BECAUSE OF RUN-TO-RUN VARIABILITY WITH THE OPERATIONAL  
MODELS, INCREASED THE MEANS BY THIS TIME. HOWEVER, THE DAYS 6-7  
TIME PERIOD (SAT-SUN) BECOMES EVEN MORE VARIED WITH THE SURFACE  
PATTERN. BECAUSE OF THE LOW CONFIDENCE IN THIS TIME  
PERIOD--FOLLOWED SUIT FROM THE PREVIOUS SHIFT BY DECREASING THE  
USE OF OPERATIONAL MODELS TO 20 PERCENT ON DAY 6, AND WENT 100  
PERCENT WITH THE 06Z GEFS/12Z ECMWF MEAN BY DAY 7.  
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
MOST OF THE PRECIPITATION OCCURRING DURING THE MEDIUM RANGE IS  
EXPECTED ON DAYS 3-4 (WED-THU). HEAVY PRECIPITATION WILL FOLLOW  
ALONG THE COLD FRONT ADVANCING FROM THE MISSISSIPPI VALLEY TO THE  
EAST COAST. EXPECT THE HIGHEST TOTALS ALONG PORTIONS OF THE  
SOUTHERN APPALACHIANS AND SOUTHERN NEW ENGLAND. THERE IS STILL  
UNCERTAINTY IN STRENGTH/TIMING/TRACK OF THE FRONTAL WAVE BUT  
CURRENTLY THE BEST POTENTIAL FOR AT LEAST SOME WINTRY WEATHER  
EXTENDS FROM WEST OF THE APPALACHIANS NORTHEASTWARD INTO NEW  
ENGLAND. THIS SYSTEM WILL EXIT THE EAST COAST BY FRIDAY, WITH SOME  
LINGERING LAKE EFFECT SNOW ACROSS THE GREAT LAKES. LOW PRESSURE  
AND A STRONG COLD FRONT PASSING THROUGH THE REGION MAY BRING A  
PERIOD OF SYNOPTIC SCALE SNOW DURING THE LATTER HALF OF THE WEEK.  
ANOTHER FEATURE COULD ENHANCE SNOWFALL FOR A TIME DURING THE  
WEEKEND.  
 
THE PACIFIC NORTHWEST/INTERMOUNTAIN WEST WILL EXPERIENCE RAIN AND  
HIGHER ELEVATION SNOW ON WED-THU. LOCATIONS ALONG THE EASTERN  
SLOPES OF THE NORTHERN HALF OF THE ROCKIES MAY SEE ADDITIONAL  
PERIODS OF LIGHT SNOW DEPENDING ON HOW SHORTWAVES EVOLVE  
DOWNSTREAM FROM THE WEST COAST RIDGE ALOFT. AS THE SHORTWAVE  
ENERGY AND SURFACE REFLECTION MOVES SOUTH AND EAST, PRECIPITATION  
WILL ALSO FOLLOW AND COULD EXTEND INTO THE CENTRAL  
PLAINS/MISSISSIPPI VALLEY BY THE WEEKEND. CONFIDENCE REMAINS LOW  
IN COVERAGE/INTENSITY OF PRECIP IS VERY LOW. WITHIN THE MOISTURE  
SHIELD THE RAIN-SNOW LINE MAY REACH FAIRLY FAR SOUTH GIVEN THE  
COLD PATTERN.  
 
A WARM UP ACROSS THE EASTERN U.S. IS EXPECTED ON WED-THU AHEAD OF  
THE INCOMING WAVY COLD FRONT--WITH HIGH TEMPERATURES NEARING  
10-15F ABOVE NORMAL. HOWEVER, COLD, ARCTIC AIR WILL QUICKLY SPREAD  
ACROSS THE NORTHERN TIER STATES, UPPER MIDWEST AND INTO THE  
EASTERN U.S. BY FRI-SAT. ON FRIDAY, HIGH TEMPERATURES IN THE UPPER  
MIDWEST WILL BE 15-25F BELOW NORMAL--WITH SOME TEMPERATURE  
READINGS NOT GETTING ABOVE ZERO. BY SATURDAY, THE MID-ATLANTIC AND  
NORTHEAST WILL HAVE HIGH TEMPERATURES 10-15F BELOW NORMAL. THE  
WEST COAST WILL STAY 5-10F ABOVE NORMAL THROUGH THE MEDIUM RANGE  
DUE TO THE UPPER RIDGE.  
 
REINHART/RAUSCH  
 
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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