702  
FXUS02 KWBC 250658  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
157 AM EST FRI JAN 25 2019  
 
VALID 12Z MON JAN 28 2019 - 12Z FRI FEB 01 2019  
   
..OVERVIEW
 
 
DOWNSTREAM FROM A MEAN RIDGE TENDING TO BE ALIGNED JUST OFF THE  
WEST COAST, VERY DEEP AND AMPLIFIED MEAN TROUGHING WILL PERSIST  
OVER THE EASTERN HALF TO TWO-THIRDS OF NORTH AMERICA. THE EXACT  
SHAPE OF THE OVERALL TROUGH WILL VARY FROM DAY TO DAY IN RESPONSE  
TO EMBEDDED SHORTWAVES. THIS PATTERN WILL MAINTAIN COLD WEATHER  
OVER MANY AREAS EAST OF THE ROCKIES, WITH THE WEST-CENTRAL U.S.  
RECEIVING A GLANCING BLOW OF CHILLY AIR FOR A TIME AS WELL. THE  
MOST NOTABLE CHANGE IN THE GUIDANCE OVER THE PAST DAY APPEARS OVER  
AND NORTH OF THE EAST-CENTRAL PACIFIC. LATEST SOLUTIONS ARE  
SHOWING A MORE PRONOUNCED UPPER HIGH BUILDING OVER OR WEST OF THE  
BERING STRAIT WHILE TROUGHING DIGS OVER THE EAST-CENTRAL PACIFIC.  
THIS EVOLUTION ULTIMATELY KEEPS THE MEAN RIDGE IN PLACE CLOSER TO  
THE WEST COAST. AT LEAST FOR THE MOMENT THE GUIDANCE IS SHOWING  
BETTER AGREEMENT WITH THE MOST SIGNIFICANT FEATURES BUT THERE ARE  
STILL STRAY OPERATIONAL SOLUTIONS AND SOME ENSEMBLES THAT TEMPER  
CONFIDENCE TO SOME DEGREE.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
WITHIN AND AROUND THE CORE OF THE MEAN TROUGH, THE LEADING FEATURE  
OF INTEREST WILL BE AN UPPER LOW FORECAST TO BE OVER ONTARIO AT  
THE START OF THE PERIOD EARLY SUN. THIS UPPER LOW WILL SUPPORT  
LOW PRESSURE THAT SHOULD TRACK ACROSS SOUTHEASTERN CANADA WITH  
ASSOCIATED FRONTAL SYSTEM CROSSING THE GREAT LAKES/NORTHEAST.  
OVER THE PAST 24-36 HOURS THE OPERATIONAL GFS/ECMWF HAVE GENERALLY  
LED THE ENSEMBLE MEANS FOR DEPICTING THIS SYSTEM'S DEFINITION  
WHILE RECENT TRENDS HAVE BEEN SOMEWHAT FASTER. BEHIND THIS SYSTEM  
A VIGOROUS SHORTWAVE DROPPING SOUTHEAST FROM WESTERN CANADA WILL  
BRING A RATHER STRONG CLIPPER TYPE SYSTEM ACROSS THE NORTHERN  
PLAINS AND MIDWEST, THEN MOST LIKELY THE LOWER/EASTERN GREAT LAKES  
INTO NEW ENGLAND AND EASTERN CANADA. A STRONG COLD FRONT WILL  
EXTEND SOUTHWEST FROM THE SURFACE LOW. GUIDANCE HAS PROVIDED A  
SIGNAL FOR THIS SYSTEM OVER MULTIPLE DAYS BUT SO FAR THERE HAS  
BEEN A FAIR AMOUNT OF WAFFLING ON THE EXACT LATITUDE OF SURFACE  
LOW TRACK. THUS THE PREFERRED CONSENSUS/AVERAGE APPROACH COULD  
WELL BE EXTENDED TO A MULTI-RUN MEAN.  
 
WHAT APPEARS TO BE THE MOST EXTREME ASPECT OF THE FORECAST IS A  
DEEP UPPER LOW WHICH A NUMBER OF MODELS (MINUS THE 12Z CMC) BRING  
DOWN TOWARD LAKE SUPERIOR BY DAY 6 WED. THIS LOW HAS ITS ORIGIN  
OVER THE ARCTIC BEYOND THE CANADIAN ARCHIPELAGO. INTERESTINGLY  
THE ECWMF MEAN HAS BEEN LEADING THE GEFS MEAN FOR THE SOUTHWARD  
EXTENT OF THIS UPPER LOW--WITH THE 18Z GEFS MEAN FINALLY MATCHING  
THE ECMWF MEAN POSITION OVER LAKE SUPERIOR EARLY WED--BUT GFS RUNS  
HAVE GENERALLY BEEN A LITTLE LESS ERRATIC THAN THE ECMWF WITH  
SPECIFICS OF THE UPPER LOW AND SURROUNDING FLOW. THUS NOT YET  
CONFIDENT IN THE 12Z ECMWF THAT BRINGS THE UPPER LOW FARTHER SOUTH  
THAN THE AFOREMENTIONED MEANS. DEPENDING ON EXACT UPPER LOW  
DEPTH, 500MB HEIGHT ANOMALIES MAY REACH AT LEAST 3-4 STANDARD  
DEVIATIONS BELOW NORMAL ALONG/SOUTH OF THE LOW'S PATH. THIS  
FEATURE MAY PROMOTE FURTHER STRENGTHENING OF THE MIDWEST/GREAT  
LAKES SYSTEM THROUGH NEW ENGLAND AND EASTERN CANADA. DEEPER  
TRENDS IN THE MEANS FOR THE UPPER LOW BUT SOME LINGERING TRACK  
SPREAD IN THE GUIDANCE FAVOR A COMBINATION OF MODEL/MEAN IDEAS.  
 
AROUND THE SOUTHERN/EASTERN PERIPHERY OF THE OVERALL TROUGH THERE  
CONTINUES TO BE A MORE SUPPRESSED TREND FOR ANY WAVINESS ACROSS  
THE GULF OF MEXICO AND INTO THE WESTERN ATLANTIC. MODEL  
INCONSISTENCY AND SPREAD KEEP CONFIDENCE BELOW AVERAGE FOR  
SPECIFICS THAT AFFECT INTENSITY OF RAINFALL OVER THE FLORIDA  
PENINSULA. GUIDANCE AS A WHOLE IS MAINTAINING RECENT TRENDS  
TOWARD LOWER POTENTIAL FOR ANY WAVES TO HAVE A SIGNIFICANT EFFECT  
ON THE EAST COAST.  
 
ALONG THE WEST COAST THE AFOREMENTIONED ADJUSTMENTS WITH THE  
UPSTREAM PATTERN LEAD TO FAIRLY GOOD AGREEMENT IN THE MODELS/MEANS  
TOWARD A MORE PERSISTENT RIDGE ALOFT WITH GFS/ECMWF RUNS GENERALLY  
A LITTLE STRONGER THAN THEIR MEANS. THE 00Z CMC HAS STRENGTHENED  
ITS RIDGE COMPARED TO THE 12Z RUN THAT WAS MORE ROUNDED SO THERE  
IS SUPPORT FOR OPERATIONAL MODEL INPUT TO ENHANCE THE MEANS LATE  
IN THE PERIOD.  
 
BASED ON THE ABOVE ASSESSMENT THE UPDATED FORECAST USED MOSTLY  
OPERATIONAL GUIDANCE DURING THE FIRST HALF OF THE PERIOD AND THEN  
TRENDED TOWARD AN EVEN MODEL/ENSEMBLE MEAN BLEND EMPLOYING THE  
12Z-18Z GFS/12Z ECMWF AND THE 18Z GEFS/12Z ECMWF MEANS.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
THE MAIN STORM SYSTEM OF INTEREST DURING THIS FORECAST PERIOD WILL  
BE A CLIPPER TYPE SYSTEM DROPPING SOUTHEAST FROM CENTRAL CANADA  
ALONG WITH AN ARCTIC FRONT. THIS WILL BRING A BAND OF LIGHT TO  
MODERATE SNOW ACROSS THE SOUTHERN GREAT LAKES AND EXTENDING ACROSS  
THE NORTHERN OHIO VALLEY ON MONDAY, AND THEN REACHING THE  
NORTHEAST U.S. AND MID-ATLANTIC REGION BY LATE TUESDAY. THIS IS  
STILL SUBJECT TO SOME CHANGE DUE TO TRACK VARIABILITY IN THE  
OPERATIONAL GUIDANCE. ONCE THE FRONT TRAILING FROM THE LOW  
REACHES THE MISSISSIPPI VALLEY AND POINTS EAST, SOME RAIN MAY  
DEVELOP IN THE WARM SECTOR AND THEN POSSIBLY END AS A PERIOD OF  
SNOW WITH THE FRONTAL PASSAGE. AFTER THIS SYSTEM DEPARTS, MORE  
LAKE EFFECT SNOW IS LIKELY DOWNWIND OF THE GREAT LAKES.  
 
ANOTHER THING THAT WILL BE MAKING WEATHER HEADLINES BY THE MIDDLE  
OF THE UPCOMING WEEK WILL BE AN IMPRESSIVE ROUND OF FRIGID  
TEMPERATURES AS A LOBE OF THE POLAR VORTEX SINKS SOUTHEASTWARD  
ACROSS CANADA AND THEN REACHES THE NORTHERN GREAT LAKES.  
TEMPERATURES ARE EXPECTED TO PLUMMET WELL BELOW ZERO ACROSS THE  
UPPER MIDWEST, MOST OF THE GREAT LAKES REGION, AND THE NORTHERN  
OHIO VALLEY BY WEDNESDAY AND THURSDAY. ANOMALIES ON THE ORDER OF  
25 TO 35 DEGREES BELOW NORMAL ARE A GOOD POSSIBILITY FOR THESE  
REGIONS, AND IT IS QUITE LIKELY THAT THIS WOULD WARRANT WIND CHILL  
WARNINGS FOR MANY OF THESE AREAS. ALTHOUGH THE AIRMASS WILL  
MODIFY SOME BY THE TIME IT REACHES THE EAST COAST, IT SHOULD STILL  
BE QUITE COLD FOR THE MID-ATLANTIC AND NORTHEAST U.S. ON THURSDAY  
WITH HIGHS WELL BELOW FREEZING.  
 
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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