700  
FXUS02 KWBC 250749  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
248 AM EST FRI JAN 25 2019  
 
VALID 12Z MON JAN 28 2019 - 12Z FRI FEB 1 2019  
   
..OVERVIEW
 
 
THE OVERALL FLOW PATTERN ACROSS THE CONTINENTAL U.S. AND CANADA  
WILL REMAIN HIGHLY AMPLIFIED GOING INTO NEXT WEEK WITH A FULL  
LATITUDE RIDGE SITUATED JUST OFF THE WEST COAST AND A PRONOUNCED  
UPPER LEVEL TROUGH ENCOMPASSING MUCH OF THE CENTRAL AND EASTERN  
U.S. A LARGE AND COLD UPPER LOW, WHICH IS BASICALLY A LOBE OF THE  
POLAR VORTEX, WILL REINFORCE THE TROUGH THROUGH THURSDAY BEFORE A  
SLIGHT DEAMPLIFICATION EVOLVES BY NEXT FRIDAY.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
THE MOST SIGNIFICANT ASPECT OF THE FORECAST IS A DEEP UPPER LOW  
WHICH THE OPERATIONAL MODELS AND THE ENSEMBLE MEANS BRING DOWN  
TOWARD LAKE SUPERIOR BY WEDNESDAY, AND THIS HAS ITS ORIGIN OVER  
THE ARCTIC OCEAN. 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 ECMWF/GFS ALONG WITH THEIR RESPECTIVE  
ENSEMBLE MEANS.  
 
AROUND THE SOUTHERN/EASTERN PERIPHERY OF THE OVERALL TROUGH THERE  
CONTINUES TO BE A MORE SUPPRESSED TREND FOR ANY DISTURBANCES  
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. THE FORECAST NATIONWIDE WAS BASED MAINLY ON A  
BLEND OF THE GFS/ECMWF/UKMET EARLIER IN THE FORECAST, AND THEN  
MORE ENSEMBLE MEANS LATER IN THE FORECAST PERIOD.  
 
   
..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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