675  
FXUS02 KWBC 280658  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
157 AM EST MON JAN 28 2019  
 
VALID 12Z THU JAN 31 2019 - 12Z MON FEB 4 2019  
 
***IMPRESSIVE ARCTIC AIRMASS TO AFFECT THE NORTH-CENTRAL U.S. WITH  
RECORD BREAKING TEMPERATURES AND EXTREME WIND CHILLS EXPECTED ON  
THURSDAY, FOLLOWED BY A MODERATING TREND***  
 
   
..OVERVIEW
 
 
THE DEEP UPPER LEVEL VORTEX SITUATED OVER SOUTHERN QUEBEC AT THE  
BEGINNING OF THE FORECAST PERIOD THURSDAY WILL QUICKLY LIFT OUT,  
AND THE RECENT PERSISTENT UPPER LEVEL TROUGHING THAT WILL BE OVER  
THE EASTERN U.S. THIS WEEK WILL BEGIN UNDERGOING A PATTERN CHANGE  
IN TIME FOR THE WEEKEND. THE FLOW PATTERN ALOFT IS FORECAST TO  
BECOME MORE PROGRESSIVE THROUGH THE MEDIUM RANGE PERIOD, WITH A  
SOUTHERN STREAM SHORTWAVE PERTURBATION OVER THE DESERT SOUTHWEST  
QUICKLY TRACKING EASTWARD TOWARDS THE NORTHERN GULF OF MEXICO.  
HEIGHT RISES IN THE WAKE OF THE DEPARTING POLAR VORTEX LOBE WILL  
GRADUALLY ALLOW BROAD UPPER LEVEL RIDGING TO ENCOMPASS MUCH OF THE  
EASTERN U.S. BY NEXT MONDAY AND A BROAD TROUGH BECOMING  
ESTABLISHED OVER THE WESTERN U.S.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
MODELS AND ENSEMBLE MEANS HAVE IMPROVED OVER THE PAST COUPLE OF  
DAYS REGARDING PLACEMENT AND STRENGTH OF THE DEEP VORTEX CROSSING  
SOUTHERN AND SOUTHEAST CANADA LATE IN THE WEEK. THIS ALSO HOLDS  
TRUE FOR SUPPORTING THE COMPACT UPPER LOW CROSSING CALIFORNIA AND  
THE DESERT SOUTHWEST EARLY IN THE FORECAST PERIOD, WITH THE  
EXCEPTION OF THE 12Z UKMET WHICH IS SLOWER THAN THE ENSEMBLE  
MEANS, AND ALSO SLOWER WITH THE NEXT MAJOR PACIFIC DISTURBANCE  
APPROACHING ON SATURDAY. A BLEND OF THE 12Z ECMWF/18Z GFS  
REPRESENTED THIS CONSENSUS WELL, AND SERVED AS A FORECAST STARTING  
POINT THROUGH FRIDAY.  
 
BY DAY 5 ON SATURDAY, SPEED AND AMPLITUDE DIFFERENCES ARE APPARENT  
WITH THE LARGE SCALE TROUGH NEAR CALIFORNIA. THE 18Z FV3 GFS IS A  
LITTLE SLOWER THAN THE OPERATIONAL GFS AND CLOSER TO THE CMC AND  
ECMWF SOLUTIONS, AND THIS REMAINS THE CASE GOING INTO SUNDAY AS  
THE DISTURBANCE APPROACHES THE PLAINS. WITH THAT CONSIDERATION IN  
MIND, THE WPC FORECAST FAVORED THE SLOWER SET OF SOLUTIONS FOR  
THIS REGION, BUT NOT TO THE DEGREE INDICATED BY THE UKMET GIVEN  
ITS LACK OF ENSEMBLE SUPPORT.  
 
IN THE NORTHERN STREAM, A NUMBER OF SOLUTIONS SUGGEST  
AMPLIFICATION OF A SHORTWAVE ACROSS THE CANADIAN PRAIRIES NEXT  
WEEKEND, WITH AN ASSOCIATED SURFACE LOW PASSING ALONG THE  
U.S./CANADA BORDER TOWARD THE GREAT LAKES. MODEL CONSENSUS WAS A  
BIT BETTER HERE AND ENSEMBLE MEMBERS SHOWED REASONABLE CLUSTERING  
WITH RESPECT TO THE SURFACE LOW TRACK, EVEN WITH SOME  
TIMING/INTENSITY VARIABILITY EVIDENT IN DETERMINISTIC SOLUTIONS.  
GIVEN THESE CONSIDERATIONS, THE FORECAST DURING THE SECOND HALF OF  
THE FORECAST PERIOD CONTINUED TO EMPHASIZE THE ECMWF/FV3 GFS WITH  
INCREASING USE OF THE ENSEMBLE MEANS BY LATE IN THE FORECAST  
PERIOD.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
THE EXTREME ARCTIC AIR INTRUSION IS EXPECTED TO CONTINUE GOING  
INTO THURSDAY FROM THE GREAT LAKES AND OHIO VALLEY TO THE  
NORTHEAST U.S. ALTHOUGH THE COLDEST TEMPERATURES OF THIS EVENT  
ARE EXPECTED ON WEDNESDAY FOR THE UPPER MIDWEST AND NORTHERN GREAT  
LAKES, FRIGID TEMPERATURES ARE STILL FORECAST WITH HIGHS RUNNING  
ABOUT 30 DEGREES BELOW NORMAL FROM MINNESOTA TO NORTHERN OHIO, AND  
ABOUT 20-25 DEGREES BELOW NORMAL FOR THE BIG CITIES OF THE  
NORTHEAST U.S. RECORD LOW TEMPERATURES ARE LIKELY FOR SOME OF  
THESE AREAS THURSDAY MORNING ALONG WITH IMPRESSIVE WIND CHILLS  
COLDER THAN 40 BELOW AT TIMES! TEMPERATURES ARE FORECAST TO  
MODERATE SUBSTANTIALLY GOING INTO FRIDAY AND ESPECIALLY BY THE  
WEEKEND FOR THE ENTIRE EASTERN U.S. AS THE DEEP UPPER LEVEL TROUGH  
LIFTS OUT AND MILDER WESTERLY FLOW FROM THE PACIFIC BRINGS  
CONDITIONS CLOSER TO SEASONAL AVERAGES OR EVEN SLIGHTLY ABOVE.  
 
ALONG THE WEST COAST, THE ARRIVAL OF A COUPLE PACIFIC SYSTEMS WILL  
KEEP PRECIPITATION (RAIN AND MOUNTAIN SNOW) FAIRLY WIDESPREAD,  
STARTING IN THE NORTHWEST AND GRADUALLY MOVING SOUTH ACROSS  
CALIFORNIA. RAIN/SNOW WILL GRADUALLY SPREAD INTO THE GREAT BASIN  
AND THE ROCKIES BY NEXT WEEKEND AS THE SECOND AND LARGER UPPER  
TROUGH MOVES INLAND. RAIN IS ALSO EXPECTED TO INCREASE IN  
COVERAGE OVER THE GULF COAST REGION AND EXTENDING NORTHWARD ACROSS  
THE DEEP SOUTH AND TENNESSEE RIVER VALLEY AS SOUTHERLY FLOW  
ADVECTS MOISTURE NORTHWARD AHEAD OF THE STORM SYSTEM DEVELOPING  
ACROSS THE PLAINS BY SUNDAY AND MONDAY.  
 
D. HAMRICK  
 
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION AND WINTER WEATHER OUTLOOK  
PROBABILITIES 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  
 

 
 
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