864  
FXUS02 KWBC 281600  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1100 AM EST MON JAN 28 2019  
 
VALID 12Z THU JAN 31 2019 - 12Z MON FEB 04 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 DEPARTURE OF A DEEP UPPER LEVEL VORTEX OVER QUEBEC AT THE  
BEGINNING OF THE FORECAST PERIOD THURSDAY AND GRADUAL WEAKENING OF  
MEAN TROUGHING ALOFT OVER THE EASTERN U.S. LATE THIS WEEK AND THE  
WEEKEND WILL PROMOTE A SIGNIFICANT WARMING TREND OVER THE EASTERN  
U.S. AT THE SAME TIME THE SHORT-RANGE WEST COAST MEAN RIDGE ALOFT  
WILL GIVE WAY TO A SERIES OF PACIFIC SYSTEMS THAT WILL BRING A  
RETURN OF SIGNIFICANT PRECIPITATION TO PARTS OF THE WEST WITH  
MOISTURE THEN SPREADING FARTHER EASTWARD. BY THE LATTER HALF OF  
THE PERIOD THE MEAN PATTERN SHOULD EVOLVE TOWARD A POSITIVELY  
TILTED MEAN TROUGH OVER THE WEST AND POSITIVE HEIGHT  
ANOMALIES/SOME DEGREE OF RIDGING OVER THE EAST. THIS  
CONFIGURATION IS CONSISTENT WITH WHAT TELECONNECTIONS SUGGEST  
BASED ON THE CORE OF POSITIVE HEIGHT ANOMALIES WHICH D+8 MULTI-DAY  
MEANS SHOW OVER EAST-CENTRAL PACIFIC.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
DECENT CLUSTERING EXISTS FOR THE LEADING COMPACT PACIFIC SYSTEM  
REACHING CALIFORNIA BY DAY 3 THU. THE 00Z UKMET IS THE ONE  
EXTREME WITH SLOWER TIMING THAN MOST OTHER SOLUTIONS. GUIDANCE IS  
STILL IN THE PROCESS OF CONSOLIDATING FOR THE NEXT SOMEWHAT LARGER  
SCALE SYSTEM EXPECTED TO REACH THE WEST COAST IN THE FRI-SAT TIME  
FRAME. MUCH OF THIS NARROWING OF THE SPREAD HAS BEEN BY WAY OF  
GFS/GEFS MEAN RUNS TRENDING SIGNIFICANTLY SLOWER AND MORE  
AMPLIFIED TOWARD THE ECMWF/ECMWF MEAN WHICH HAVE BEEN FAIRLY  
STEADY OVER THE PAST COUPLE DAYS. AS OF DAY 5 SAT THE 00Z  
UKMET/CMC ARE CLOSE TO THE ECMWF SCENARIO. THE 06Z GFS/GEFS MEAN  
ARE FAVORABLY SLOWER THAN THEIR RESPECTIVE 00Z RUNS BUT STILL NOT  
QUITE AS SLOW AS THE ECMWF CLUSTER. THE 00Z FV3 GFS BETTER  
REFLECTS THE SLOWER TIMING BUT THE OPERATIONAL 06Z GFS RUN  
COMPARES CLOSER TO CONSENSUS DEPTH. SO OVERALL PREFERENCES REMAIN  
CLOSER TO THE ECMWF CLUSTER WITH MINORITY INPUT FROM THE 06Z  
GFS/00Z FV3 GFS TO BALANCE TIMING/DEPTH CONSIDERATIONS. AS THE  
UPPER LEVEL ENERGY PROGRESSES NORTHEASTWARD EXPECT A SIGNIFICANT  
LOW PRESSURE SYSTEM TO TRACK ACROSS THE PLAINS INTO THE GREAT  
LAKES REGION BY SUN-MON. TRACK WILL DEPEND ON THE  
TIMING/EVOLUTION OF EJECTING WESTERN ENERGY AS WELL AS POSSIBLE  
INTERACTION WITH NORTHERN STREAM FLOW. TIMING CONSIDERATIONS  
UPSTREAM FAVOR LEANING SOMEWHAT MORE TOWARD THE ECMWF/ECMWF  
THROUGH DAY 7 MON ALTHOUGH THE CMC DOES EVENTUALLY GRAVITATE  
TOWARD THE FASTER AND NORTHWARD GFS/GEFS MEAN. AHEAD OF THIS  
SYSTEM THERE WILL LIKELY BE A WAVE TRACKING ALONG THE  
U.S.-CANADIAN BORDER WITH SOME NOTABLE TIMING/TRACK DIFFERENCES.  
THE FAVORED BLEND MAINTAINS A FORECAST CLOSE TO CONTINUITY.  
FINALLY, THE NEXT SYSTEM TO REACH THE WEST BY SUN-MON BECOMES A  
LITTLE FASTER IN GFS/FV3 GFS RUNS WHILE THE GEFS MEAN IS SLOWER TO  
ALIGN BETTER WITH THE ECMWF/ECMWF MEAN--ALSO FAVORING A BLEND THAT  
TILTS MORE THAN 2/3 TO THE SLOWER HALF OF THE ENVELOPE.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
EXPECT THE EXTREME ARCTIC AIR INTRUSION AFFECTING AREAS FROM THE  
UPPER MIDWEST THROUGH THE GREAT LAKES/OHIO VALLEY INTO NORTHEAST  
TO CONTINUE INTO THURSDAY. THE COLDEST TEMPERATURES OF THIS EVENT  
ARE LIKELY ON WEDNESDAY (NOW IN THE SHORT RANGE TIME FRAME) OVER  
THE UPPER MIDWEST AND NORTHERN GREAT LAKES BUT FRIGID TEMPERATURES  
WILL CONTINUE INTO THE NEXT DAY WITH HIGHS RUNNING 20-30F BELOW  
NORMAL OVER THE UPPER MIDWEST/GREAT LAKES-OHIO VALLEY/NORTHEAST.  
ALSO EXPECT SOME READINGS TO APPROACH OR FALL BELOW RECORD  
LOW/RECORD COLD HIGH VALUES. DANGEROUSLY LOW WIND CHILL VALUES  
WILL BE POSSIBLE AS WELL. A PRONOUNCED WARMING TREND WILL MOVE  
INTO THE CENTRAL AND THEN EASTERN STATES DURING THE WEEKEND AND  
EARLY NEXT WEEK, WITH LOW TEMPERATURES IN PARTICULAR POSSIBLY  
REACHING 10-25F ABOVE NORMAL.  
 
MULTIPLE PACIFIC SYSTEMS WILL BRING PRECIPITATION (RAIN AND  
MOUNTAIN SNOW) TO A LARGE PORTION OF THE WEST AND THEN TO AREAS  
EAST OF THE ROCKIES. THE FIRST SYSTEM WILL BE COMPACT AND CONFINE  
ITS MOISTURE MOSTLY TO CALIFORNIA AND THE SOUTHWEST ON  
THURSDAY-THURSDAY NIGHT. AS THE SHORTWAVE CONTINUES ONWARD SOME  
LOCALLY ENHANCED RAINFALL MAY BE POSSIBLE OVER PARTS OF THE GULF  
COAST STATES WITH SOME RAINFALL EXTENDING NORTHEASTWARD. THE NEXT  
SYSTEM WILL FIRST SPREAD RAIN/SNOW INTO THE NORTHWEST AND  
GRADUALLY MOVE SOUTH/SOUTHEAST. EXPECT HEAVIEST TOTALS OVER  
FAVORED TERRAIN IN CALIFORNIA AND ARIZONA. DURING THE LATTER HALF  
OF THE PERIOD THE MOISTURE FROM THIS SYSTEM WILL SPREAD ACROSS THE  
ROCKIES AND THEN LOW PRESSURE TRACKING NORTHEAST FROM THE CENTRAL  
PLAINS MAY PRODUCE A SIGNIFICANT SNOW EVENT OVER NORTHERN AREAS  
WITH RAIN IN THE WARM SECTOR. ADDITIONAL RAINFALL MAY DEVELOP  
OVER PORTIONS OF THE SOUTH.  
 
RAUSCH/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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