040  
FXUS02 KWBC 210700  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
159 AM EST MON JAN 21 2019  
 
VALID 12Z THU JAN 24 2019 - 12Z MON JAN 28 2019  
   
..OVERVIEW
 
 
FROM LATE THIS WEEK THROUGH MOST OF THE WEEKEND THE FORECAST IS  
CONSISTENT IN SHOWING A HIGHLY AMPLIFIED UPPER PATTERN FEATURING  
AN EASTERN PACIFIC/WEST COAST RIDGE AND EASTERN NORTH AMERICA  
TROUGH. AS IN PREVIOUS DAYS THE OVERALL MEAN PATTERN APPEARS TO  
HAVE FAIRLY HIGH PREDICTABILITY BUT EMBEDDED SHORTWAVES THAT ARE  
SMALLER IN SCALE WILL BE MORE DIFFICULT TO RESOLVE SEVERAL DAYS  
OUT IN TIME. D+8 MEAN CHARTS SUGGEST THAT THE RIDGE MAY  
RETROGRADE A BIT LATE IN THE MEDIUM RANGE PERIOD AND BEYOND.  
TELECONNECTIONS RELATIVE TO THE ASSOCIATED POSITIVE HEIGHT ANOMALY  
CENTER FAVOR INCREASED POTENTIAL FOR POSITIVELY TILTED TROUGHING  
TO DEVELOP OVER THE WEST--WHICH SOME GUIDANCE APPEARS TO BE  
HEADING TOWARD BY EARLY NEXT WEEK. AT THE SAME TIME ANOTHER  
STRONG POSITIVE HEIGHT ANOMALY CENTER EAST OF THE CANADIAN  
MARITIMES WOULD FAVOR MAINTAINING THE MEAN TROUGH OVER EASTERN  
PART OF THE CONTINENT.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
THE TWO FEATURES THAT SHOW REASONABLE AGREEMENT ARE EARLY IN THE  
PERIOD DURING THU-FRI. THESE ARE THE WAVY FRONT WHOSE EMBEDDED  
LOW PRESSURE CONSOLIDATES/DEEPENS AS IT LIFTS NORTHWARD NEAR THE  
EAST COAST INTO THE CANADIAN MARITIMES, AND GREAT LAKES LOW  
PRESSURE WITH TRAILING STRONG COLD FRONT THAT PUSHES QUICKLY  
SOUTH/EAST ACROSS THE CENTRAL/EASTERN STATES THU INTO FRI. FOR  
THE EASTERN SYSTEM THE LATEST GFS/ECMWF RUNS AND THEIR MEANS  
PROVIDE THE BEST CONSENSUS WHILE THE 12Z CMC IS A BIT WEST AND THE  
12Z UKMET SLOW. IN THE NEW 00Z CYCLE THE CMC ALIGNS BETTER WITH  
THE MAJORITY SCENARIO WHILE THE UKMET REMAINS SLOW. RECENT TRENDS  
HAVE GENERALLY BEEN NUDGING THE SYSTEM ALONG A LITTLE FASTER,  
SUGGESTING EVEN LOWER PROBABILITY FOR THE SLOW UKMET. A CONSENSUS  
APPROACH ALSO LOOKS GOOD FOR THE TRAILING LOW PRESSURE/STRONG COLD  
FRONT.  
 
UPSTREAM FEATURES SHOW MORE DIVERGENCE. THERE IS A GOOD SIGNAL  
FOR A CLIPPER TYPE SYSTEM TO TRACK INTO THE NORTHERN STATES IN  
RESPONSE TO SOME COMBINATION OF SHORTWAVE ENERGY ROUNDING THE MEAN  
RIDGE AND CANADIAN FLOW. HOWEVER TIMING DIFFERENCES ARE  
CONSIDERABLE. THE PAST TWO ECMWF RUNS ARE ON THE OPPOSITE SIDES  
OF THE SPECTRUM (12Z RUN FAST, 00Z/20 RUN SLOW). THE FAST 12Z  
ECMWF HAS COMPANY IN THE PAST COUPLE CMC RUNS BUT MOST OTHER  
MODELS/MEANS ARE CLOSER TO THE MIDDLE. MEANWHILE THERE ARE  
INDICATIONS THAT THE SOUTHWESTERN PART OF THE OVERALL SHORTWAVE  
COMPLEX MAY SHARPEN AS IT DROPS THROUGH THE WEST-CENTRAL U.S. AND  
THEN REACHES THE MEAN TROUGH AXIS NEAR 90W LONGITUDE DURING THE  
WEEKEND. THERE IS A GENERAL THEME OF A LOWER SURFACE PRESSURES  
OVER THE EAST-CENTRAL U.S. DURING THE UPCOMING WEEKEND BUT  
CONSIDERABLE SPREAD/RUN-RUN VARIABILITY FOR THE SPECIFICS. THEN  
BY DAY 7 MON THERE IS FAIRLY HIGH POTENTIAL FOR LOW PRESSURE TO  
DEVELOP OFF THE EAST COAST AS THE UPPER ENERGY CONTINUES TO THE  
EAST/NORTHEAST. THE 12Z GEFS/ECMWF MEANS PROVIDE THE BEST  
INTERMEDIATE STARTING POINT GIVEN THE UNCERTAINTY LEADING UP TO  
THIS SYSTEM'S DEVELOPMENT. THE 18Z GEFS MEAN HAD A WEAKER SURFACE  
REFLECTION THUS FAVORING THE 12Z RUN. THUS FAR OPERATIONAL MODELS  
HAVE BEEN INCONSISTENT FOR STRENGTH/TRACK OF THIS SYSTEM, RANGING  
FROM THE VERY STRONG/IMPACTFUL 12Z ECMWF AND 00Z CMC TO WELL  
OFFSHORE 18Z/00Z GFS AND 12Z CMC RUNS.  
 
LATE IN THE PERIOD ANOTHER PUSH OF HEIGHT FALLS SHOULD DROP INTO  
THE CENTRAL AND WESTERN PARTS OF THE NORTHERN U.S., PERHAPS  
LEADING INTO A PATTERN THAT HAS SOMEWHAT MORE WESTERN U.S.  
TROUGHING PER TELECONNECTIONS RELATIVE TO THE UPSTREAM RIDGE  
POSITION. WHILE THE 12Z/18Z GFS RUNS ARE QUITE STRONG (FOLLOWED  
BY A MUCH WEAKER 00Z GFS), THE GFS IS GENERALLY MUCH CLOSER TO THE  
MEANS IN PRINCIPLE FOR LOW PRESSURE THAT MAY HEAD INTO THE GREAT  
LAKES.  
 
THE EARLY PART OF THE FORECAST REPRESENTS THE PREFERRED GUIDANCE  
CONSENSUS (MORE GFS/ECMWF THAN OTHER OPERATIONAL MODELS). THE  
BLEND YIELDS AN INTERMEDIATE TIMING FOR THE CONTENTIOUS NORTHERN  
U.S. WAVE FRI-SAT. THEN THE FORECAST RAPIDLY INCREASES 12Z  
GEFS/ECMWF MEAN INPUT AS OPERATIONAL MODEL DETAILS DIVERGE MORE  
DRAMATICALLY. THE 18Z GFS IS CLOSE ENOUGH TO THE FAVORED PATTERN  
OVER THE WESTERN 2/3 OF THE COUNTRY TO ALLOW FOR A SMALL MINORITY  
TO PERSIST IN THE BLEND THROUGH DAY 7.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
STRENGTHENING LOW PRESSURE TRACKING NORTHEAST FROM NEAR THE  
MID-ATLANTIC WILL BRING A PERIOD OF SIGNIFICANT PRECIPITATION TO  
THE NORTHEAST ON THU. BEST SNOW POTENTIAL WILL BE OVER INTERIOR  
NEW ENGLAND. AT THE SAME TIME THE FRONT TRAILING FROM THIS SYSTEM  
WILL BRING RAIN OF VARYING INTENSITY TO THE FLORIDA PENINSULA.  
THE GREAT LAKES WILL LIKELY SEE EPISODES OF SNOW THROUGH MOST OF  
THE PERIOD WITH A COMBINATION OF PERIODIC SYNOPTIC SYSTEMS (WITH  
LAKE ENHANCEMENT OVER SOME AREAS) AS WELL AS MORE SIMPLE LAKE  
EFFECT ACTIVITY. OTHER AREAS EAST OF THE ROCKIES MAY SEE SOME  
PRECIPITATION WITH LOW PRESSURE/FRONTAL PASSAGES. THERE IS  
POTENTIAL FOR MORE ORGANIZED PRECIPITATION OVER PARTS OF THE  
EASTERN STATES BY THE WEEKEND INTO NEXT MON BUT WITH LOW  
CONFIDENCE IN COVERAGE/INTENSITY. THE RAIN-SNOW LINE SHOULD  
EXTEND FAIRLY FAR SOUTHWARD GIVEN THE COLD PATTERN BECOMING  
ESTABLISHED OVER THE EASTERN HALF OF THE COUNTRY. MEANWHILE AT  
LEAST A COUPLE SHORTWAVES/FRONTS AND TRAILING HIGH PRESSURE SHOULD  
BRING PERIODS OF SNOW TO PARTS OF THE NORTHERN AND CENTRAL ROCKIES  
WITH MOST ACTIVITY LIKELY TO BE IN THE LIGHT-MODERATE RANGE.  
 
EXPECT THE CORE OF COLDEST AIR DURING THE PERIOD TO BE ACROSS THE  
UPPER MISSISSIPPI VALLEY/MIDWEST WITH READINGS OF 15-25F BELOW  
NORMAL LATE THIS WEEK INTO THE WEEKEND. AFTER THE THU SYSTEM  
BRINGS A BRIEF SURGE OF WARMTH TO THE EAST COAST (MORNING LOWS  
15-25F ABOVE NORMAL), MUCH OF THE EASTERN HALF OF THE COUNTRY  
SHOULD SEE BELOW NORMAL TEMPERATURES FRI ONWARD. GREATEST  
COVERAGE OF HIGHS AT LEAST 10F BELOW NORMAL SHOULD EXIST FRI-SUN.  
ON THE OTHER HAND EXPECT ABOVE NORMAL TEMPERATURES TO PERSIST OVER  
THE WEST COAST STATES AND EXTEND INTO THE NORTHERN ROCKIES AND  
PARTS OF THE HIGH PLAINS WITH LOCALIZED ANOMALIES EXCEEDING PLUS  
10F. THE NORTHERN HALF OF THE WEST SHOULD TREND COOLER BY NEXT  
MON.  
 
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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