403  
FXUS02 KWBC 251557  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1056 AM EST FRI JAN 25 2019  
 
VALID 12Z MON JAN 28 2019 - 12Z FRI FEB 01 2019  
 
...SIGNIFICANT COLD AIR OUTBREAK EXPECTED NEXT WEEK FROM THE  
MIDWEST TO THE MID-ATLANTIC/NORTHEAST...  
 
   
..OVERVIEW
 
 
BREAKDOWN OF THE POLAR VORTEX ONGOING DURING THE SHORT RANGE WILL  
ALLOW A LOBE OF STRONGLY NEGATIVE HEIGHT ANOMALIES/COLD  
TEMPERATURES TO SPREAD SOUTHWARD INTO THE NORTH  
CENTRAL/NORTHEASTERN CONUS DURING THE MEDIUM RANGE. PERSISTENT  
UPPER RIDGING OFF THE WEST COAST EXPANDING NORTH INTO THE ARCTIC  
DURING THE MEDIUM RANGE WILL ENSURE THAT THIS HIGHLY AMPLIFIED  
LONG WAVE PATTERN WILL PERSIST FOR A WHILE, AS NUMEROUS ARCTIC  
SHORTWAVES DIVE SOUTHEAST ACROSS CENTRAL CANADA AND REINFORCE THE  
BROAD TROUGH ACROSS CENTRAL/EASTERN NORTH AMERICA.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
A CLIPPER SYSTEM CROSSING THE NORTH CENTRAL/NORTHEASTERN U.S. WILL  
BE MOST SIGNIFICANT LOW PRESSURE SYSTEM DURING THE MEDIUM RANGE,  
WITH MODELS SUGGESTING THE POTENTIAL FOR DEVELOPMENT OF A LOW  
ALONG THE MID-ATLANTIC COAST TUE/TUE NIGHT. MODELS SHOWED  
RELATIVELY GOOD CONSENSUS DURING DAYS 3-5 (MON-WED), AND A GENERAL  
BLEND OF RECENT DETERMINISTIC SOLUTIONS SERVED AS A GOOD FORECAST  
STARTING POINT. FROM LATE WED ONWARD MODELS CONTINUE TO STRUGGLE  
WITH THE EXACT STRUCTURE OF THE DEEP VORTEX DIVING SOUTHWARD  
ACROSS CANADA INTO THE GREAT LAKES, AS WELL AS WITH PACIFIC  
SHORTWAVE ENERGY ATTEMPTING TO ERODE THE RIDGE, HAVING SOME  
POTENTIAL IMPACT ON THE UPPER FLOW ACROSS WESTERN PORTIONS OF  
CANADA AND THE CONUS. THE 00Z ECMWF WAS THE MOST AGGRESSIVE WITH  
UNDERCUTTING THE RIDGE, AND WAS NOT NECESSARILY THE PREFERRED  
SOLUTION AT THIS TIME. RATHER, AN INCREASE IN ENSEMBLE MEAN  
WEIGHTING AFTER DAY 5 SHOULD ALLOW FOR SOME REFLECTION OF  
WEAKENING SHORTWAVE ENERGY TO APPROACH THE U.S. WEST COAST, BUT  
NOT TO THE DEGREE SHOWN BY THE ECMWF. A MORE ENSEMBLE-BASED  
APPROACH WAS ALSO PREFERABLE FARTHER EAST IN THE VICINITY OF THE  
DEEP UPPER VORTEX, AS MODELS SHOW FAIRLY LARGE VARIABILITY WITH  
ARCTIC SHORTWAVE ENERGY ROTATING AROUND THE LOW. SOME DEGREE OF  
MODEST CONSENSUS WAS NOTED AMONG MODELS/ENSEMBLES THAT PACIFIC  
SHORTWAVE ENERGY COULD RESULT IN A SURFACE FRONTAL WAVE DEVELOPING  
ACROSS THE SOUTHERN PLAINS BY NEXT FRI, ALTHOUGH CONFIDENCE IN THE  
SPECIFICS IS VERY LOW AT THIS TIME.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
CLIPPER LOW PRESSURE SYSTEM IS EXPECTED TO BRING A PERIOD OF  
MODERATE TO PERHAPS HEAVY SNOW TO PORTIONS OF THE MIDWEST/GREAT  
LAKES MON-TUE. DEVELOPMENT OF A LOW ALONG THE MID-ATLANTIC COAST  
LATE TUE COULD BRING A PERIOD OF ENHANCED SNOWFALL POTENTIAL TO  
THE MID-ATLANTIC AND ESPECIALLY THE NORTHEAST TUE NIGHT INTO WED.  
IN THE WAKE OF THIS SYSTEM, DEEP UPPER LOW DIGGING SOUTH  
TOWARD/INTO THE MIDWEST/GREAT LAKES WILL SERVE AS THE EPICENTER OF  
A FORMIDABLE COLD AIR OUTBREAK. TEMPERATURES 20-30 DEG F BELOW  
AVERAGE (FOR BOTH MAX AND MIN TEMPS) ARE FORECAST TO SPREAD INTO  
THE MIDWEST (WHERE MAX TEMPS MAY REMAIN IN THE DOUBLE DIGITS BELOW  
0) BY TUE AND INTO THE OHIO VALLEY/LOWER GREAT LAKES WED. THE AIR  
MASS MAY MODERATE SLIGHTLY BY THU-FRI AS IT REACHES THE  
MID-ATLANTIC/NORTHEAST WITH WIDESPREAD TEMPERATURES 15-20 DEG  
BELOW AVERAGE. WIND CHILL VALUES IN THE WAKE OF THE DEEPENING LOW  
PRESSURE SYSTEM ACROSS THE ALONG THE EASTERN SEABOARD BY TUE-WED  
COULD RESULT IN EXTREMELY COLD WIND CHILL VALUES WELL BELOW ZERO  
ACROSS PORTIONS OF THE MIDWEST AND GREAT LAKES. FARTHER WEST,  
PRECIPITATION MAY SPREAD INTO AREAS ALONG THE WEST COAST BY  
THU-FRI AS AN UPPER TROUGH APPROACHES.  
 
RYAN  
 
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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