246  
FXUS02 KWBC 191600  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1059 AM EST SAT JAN 19 2019  
 
VALID 12Z TUE JAN 22 2019 - 12Z SAT JAN 26 2019  
   
..OVERVIEW
 
 
LATEST GUIDANCE CONTINUES SO SHOW AGREEMENT IN REGARDS TO THE  
AMPLIFIED PATTERN WITH A RIDGE OVER THE EASTERN PACIFIC/WEST COAST  
AND A TROUGH DOMINANT OVER THE CENTRAL AND EASTERN U.S. THIS  
PATTERN WILL GIVE WAY TO COLD, CANADIAN AIR SPILLING INTO THE  
NORTHERN TIER--MAKING ITS WAY DOWN INTO THE MIDDLE MISSISSIPPI  
VALLEY AND PORTIONS OF THE CENTRAL PLAINS. THIS PATTERN ALSO  
SUGGESTS HIGHER PRECIPITATION CHANCES IN THE EASTERN HALF OF THE  
U.S. WHILE THE WEST COAST SHOULD BE DRY NEAR THE UPPER RIDGE AXIS.  
THOUGH MODELS WERE CONSISTENT WITH THE OVERALL PATTERN ALOFT,  
DIFFERENCES IN THE SMALLER SCALE LEAD TO SIGNIFICANT DIFFERENCES  
AT THE SURFACE. THIS IMPACT WILL AFFECT SENSIBLE WEATHER AND TAKE  
ADDITIONAL TIME TO RESOLVE.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
MODELS/ENSEMBLE MEANS CONTINUE TO SHOW SIGNIFICANT DIFFERENCES AND  
TRENDS FOR VARIOUS ASPECTS OF THE FORECAST--ESPECIALLY WITH  
REGARDS TO SHORTWAVE SPECIFICS AND STREAM INTERACTIONS. INITIALLY,  
ON DAY 3/TUESDAY, MODELS ARE IN LINE AND IN GENERAL HAVE THE  
SURFACE LOW IN THE SAME GENERAL REGION OF THE CENTRAL PLAINS.  
HOWEVER, EVEN BY DAY 4, THE 00Z ECMWF BEGINS TO DIVERGE FROM MOST  
OF THE MODELS AT THE SURFACE WHERE TO PLACE THE MAIN SURFACE LOW  
SINCE THE ECMWF IS SLOW TO LIFT A SHORTWAVE EMBEDDED IN THE  
TROUGH. THE 00Z AND 06Z GFS, 00Z UKMET/CMC ARE ALL IN AGREEMENT TO  
LIFT THIS SHORTWAVE QUICKLY FROM THE GREAT LAKES. ISSUES CONTINUE  
TO DETERIORATE FURTHER GOING OUT IN TIME. THE 00Z ECMWF, BOTH  
06Z/00Z GFS, AND THEIR MEANS STILL HAVE NOT COME TO AN AGREEMENT  
WHERE TO PLACE THE SURFACE LOW IN THE SOUTHEAST/MID-ATLANTIC BY  
DAY 5/THU. UP TO DAY 5, USED A GENERAL BLEND OF THE 06Z GFS/00Z  
ECMWF/00Z UKMET/00Z CMC AND THE 00Z GFS PARALLEL. BY DAY 6, THE  
06Z GFS WAS MUCH STRONGER WITH THE SURFACE LOW LIFTING NORTH OF  
THE CANADIAN MARITIMES--THUS THE WPC BLEND BY DAY 6 AND 7 USED THE  
00Z GFS IN LIEU OF THE 06Z GFS BECAUSE OF THIS WHILE INCREASING  
THE ENSEMBLE MEANS.  
 
FOR THE MOST PART SHORTWAVE DETAILS ARE SUFFICIENTLY SMALL IN  
SCALE TO YIELD LOW CONFIDENCE IN SPECIFICS, AND WILL BE PRONE TO  
RUN-RUN/DAY-DAY VARIABILITY. THUS EXPECT WORSE THAN AVERAGE  
CONTINUITY FOR ASSOCIATED WAVES/FRONTAL SYSTEMS.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
DURING TUE-WED PLAINS LOW PRESSURE TRACKING THROUGH THE GREAT  
LAKES AND INTO EASTERN CANADA WILL SPREAD SNOW FROM THE  
NORTH-CENTRAL PLAINS AND UPPER MISSISSIPPI VALLEY THROUGH THE  
CENTRAL-NORTHERN GREAT LAKES INTO NEW ENGLAND. THE TRAILING FRONT  
SHOULD BEGIN TO INTERACT WITH GULF MOISTURE BY TUE NIGHT-WED WITH  
EXPANDING AREAS OF LOCALLY MODERATE/HEAVY WARM SECTOR RAINFALL.  
CONFIDENCE IS INCREASING THAT A SIGNIFICANT WAVE MAY FORM ALONG  
THE TRAILING FRONT AND SPREAD A BROAD SHIELD OF  
PRECIPITATION--SOME HEAVY--ACROSS THE SOUTH AND EASTERN STATES AT  
LEAST THROUGH THU. THE TRACK AND TIMING OF THIS WAVE STILL REMAINS  
UNCERTAIN; THUS, CONFIDENCE IN REMAINS LOW WHERE THE LOCATION OF  
HEAVIEST RAIN/SNOW WILL FALL AS WELL AS PRECIPITATION TYPES. THE  
BEST POTENTIAL FOR HIGHEST TOTAL PRECIPITATION REMAINS WITHIN AN  
AREA FROM THE EAST-CENTRAL GULF COAST/TENNESSEE VALLEY/SOUTHERN  
APPALACHIANS NORTHEASTWARD INTO SOUTHERN NEW ENGLAND. BEST  
SNOW/WINTRY MIX POTENTIAL WILL LIE TO THE NORTHWEST OF THAT AREA.  
AFTER PASSAGE OF THIS SYSTEM, ONE OR MORE WAVES/FRONTS MAY PRODUCE  
AREAS OF LIGHT-MODERATE SNOW OVER SOME AREAS EAST OF THE ROCKIES  
AND COLD FLOW OVER THE MOSTLY ICE-FREE GREAT LAKES SHOULD PROMOTE  
EPISODES OF LAKE EFFECT SNOW.  
 
THE FORECAST LOOKS FAIRLY CONSISTENT FOR THE FOCUSED BAND OF  
SHORTWAVE ENERGY AND MOISTURE THAT WILL BRING A PERIOD OF ENHANCED  
SNOW AND LOW ELEVATION RAIN TO LOCATIONS FROM THE PACIFIC  
NORTHWEST INTO THE NORTHERN/CENTRAL ROCKIES TUE-WED NIGHT. LATE  
WEEK INTO THE WEEKEND ADDITIONAL SHORTWAVE ENERGY WITHIN  
NORTHWESTERLY FLOW ALOFT ALONG WITH A PERSISTENT STATIONARY FRONT  
AT THE SURFACE WILL PROVIDE FOCUS FOR SNOW ALONG THE NORTHERN HALF  
OF THE ROCKIES.  
 
PORTIONS OF THE EAST WILL SEE A VERY COLD START TO THE PERIOD ON  
TUE (SOME LOWS 20F OR MORE BELOW NORMAL OVER THE SOUTHEASTERN  
GREAT LAKES/NORTHERN APPALACHIANS) BEFORE A BRIEF WARM-UP AHEAD OF  
THE APPROACHING FRONT/WAVE, WITH SOME READINGS UP TO 10-20F OR SO  
ABOVE NORMAL. COLD AIR DROPPING INTO THE EAST-CENTRAL U.S. LATER  
IN THE PERIOD MAY BRING TEMPERATURES DOWN TO AT LEAST 15-25F BELOW  
NORMAL ALONG THE UPPER AND PORTIONS OF THE MIDDLE MISSISSIPPI  
VALLEY. CONTINUE TO EXPECT MODERATELY ABOVE NORMAL TEMPERATURES  
OVER THE WEST COAST STATES AFTER MIDWEEK AS THE UPPER RIDGE AXIS  
SETTLES NEARBY.  
 
REINHART/RAUSCH  
 
WPC MEDIUM RANGE 500 MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION, WINTER WEATHER OUTLOOK PROBABILITIES  
AND HEAT INDEXES 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  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML  
 

 
 
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