237  
FXUS02 KWBC 270658  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
158 AM EST SUN JAN 27 2019  
 
VALID 12Z WED JAN 30 2019 - 12Z SUN FEB 3 2019  
 
***IMPRESSIVE ARCTIC AIRMASS TO AFFECT THE NORTH-CENTRAL U.S. WITH  
RECORD BREAKING TEMPERATURES EXPECTED***  
 
   
..OVERVIEW
 
 
AN AMPLIFIED FLOW PATTERN WILL EXIST ACROSS THE CONTINENTAL U.S.  
AT THE BEGINNING OF THE FORECAST PERIOD ON WEDNESDAY WITH A LOBE  
OF THE POLAR VORTEX CROSSING LAKE SUPERIOR AND SOUTHERN ONTARIO,  
AND A BROAD UPPER RIDGE NEAR THE WEST COAST. WITH THE VORTEX  
LIFTING OUT ACROSS EASTERN CANADA BY THE END OF THE WEEK, THE  
PATTERN IS NOT QUITE AS AMPLIFIED WITH A BROAD RIDGE OVER THE  
INTERMOUNTAIN WEST AND A BROAD TROUGH OVER THE EASTERN HALF OF THE  
NATION. BY NEXT WEEKEND, THERE WILL LIKELY BE A DEVELOPING LOW  
PRESSURE SYSTEM ACROSS THE NORTHERN PLAINS ALONG WITH A TRAILING  
COLD FRONT.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
DETERMINISTIC MODELS ARE IN DECENT OVERALL AGREEMENT REGARDING THE  
DEEP UPPER LOW (LOBE OF POLAR VORTEX) TRACKING ACROSS SOUTHERN  
ONTARIO AND QUEBEC EARLY IN THE FORECAST PERIOD. THE EVENTUAL  
DECAY OF THE WEST COAST UPPER LEVEL RIDGE IS WHERE GREATER MODEL  
DIFFERENCES EMERGE AS A COMPACT UPPER LOW TRIES TO UNDERCUT THE  
RIDGE AS SUGGESTED BY THE ECMWF AND GFS, BUT NOT APPARENT WITH THE  
CMC. THE ECMWF BECOMES STRONGER WITH A SOUTHERN STREAM SHORTWAVE  
CROSSING THE DESERT SOUTHWEST COMPARED TO THE OTHER OPERATIONAL  
GUIDANCE. BY THE END OF THE FORECAST PERIOD ON SUNDAY, THERE IS A  
STRONG MODEL SIGNAL FOR A DEVELOPING SURFACE LOW ACROSS THE  
NORTHERN PLAINS AND UPPER MIDWEST, BUT VARIES SUBSTANTIALLY  
REGARDING THE LOCATION OF THE LOW. THE GEFS/EC MEANS PROVIDED A  
GOOD STARTING POINT FOR THIS AND THE SURFACE HIGH NEAR THE EAST  
COAST. THE FORECAST WAS BASED MAINLY ON THE GFS/ECMWF/CMC EARLY  
ON, AND THEN TRANSITIONING TO INCREASING USE OF THE EC MEAN FOR  
PLACEMENT PURPOSES LATER IN THE FORECAST PERIOD ALONG WITH SOME  
PREVIOUS WPC CONTINUITY.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
THE MAIN THING MAKING WEATHER HEADLINES WILL BE THE IMPRESSIVE  
SURGE OF ARCTIC AIR SINKING SOUTHWARD ACROSS THE NORTH-CENTRAL  
U.S. BY MID-WEEK AS A LOBE OF THE POLAR VORTEX TRACKS ACROSS THE  
NORTHERN GREAT LAKES AND ONTARIO. 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 EXPECTED FOR THESE REGIONS, AND SOME AREAS COULD BE 40 DEGREES  
OR MORE BELOW AVERAGE FOR WEDNESDAY! WIND CHILL VALUES COULD  
REACH 50 BELOW AT TIMES FROM NORTHERN ILLINOIS TO MINNESOTA!  
NUMEROUS RECORD LOW TEMPERATURES ARE EXPECTED, ALONG WITH RECORD  
LOW MAXIMUM TEMPERATURES. SOME PLACES MAY COME WITHIN A FEW  
DEGREES OF ALL-TIME RECORDS. 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 BELOW FREEZING FOR MOST AREAS.  
 
RAIN AND MOUNTAIN SNOW IS EXPECTED TO RETURN TO THE WEST COAST BY  
NEXT WEEKEND AS A LOW PRESSURE SYSTEM WORKS ITS WAY TOWARDS THE  
PACIFIC NORTHWEST. HEAVY RAIN AND MOUNTAIN SNOW ARE EXPECTED FROM  
NORTHERN CALIFORNIA TO WESTERN WASHINGTON, AND SOME OF THIS  
MOISTURE WILL MAKE ITS WAY INLAND ACROSS THE INTERMOUNTAIN WEST.  
THERE WILL LIKELY BE SOME RAIN FOR THE GULF COAST REGION AS RETURN  
FLOW FROM THE GULF ADVECTS MOISTURE INLAND ACROSS TEXAS AND  
LOUISIANA.  
 
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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