770  
FXUS02 KWBC 220659  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
158 AM EST TUE JAN 22 2019  
 
VALID 12Z FRI JAN 25 2019 - 12Z TUE JAN 29 2019  
   
..OVERVIEW
 
 
LATEST MODELS AND ENSEMBLES MAINTAIN THE THEME OF AN AMPLIFIED  
WEST COAST/EASTERN PACIFIC RIDGE AND EXPANSIVE CENTRAL-EASTERN  
U.S. MEAN TROUGH. LATER IN THE PERIOD THE D+8 MULTI-DAY MEANS  
STILL SUGGEST THE RIDGE COULD RETROGRADE JUST ENOUGH TO ALLOW FOR  
A LITTLE MORE SOUTHWESTWARD ELONGATION OF SHORTWAVE ENERGY OVER  
THE WEST, PER TELECONNECTIONS RELATIVE TO THE RIDGE'S  
CORRESPONDING POSITIVE HEIGHT ANOMALY CENTER. ANOTHER ASPECT THAT  
PERSISTS IS SPREAD/VARIABILITY FOR SOME IMPORTANT EMBEDDED  
DETAILS--THUS TEMPERING CONFIDENCE IN THE SENSIBLE WEATHER  
FORECAST OVER SOME AREAS IN SPITE OF AN OVERALL MEAN PATTERN THAT  
HAS MUCH HIGHER PREDICTABILITY.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
BASED ON THE ARRAY OF 12Z/18Z GUIDANCE THE PREFERRED BLEND STARTED  
WITH AN AVERAGE OF OPERATIONAL MODEL SOLUTIONS DAYS 3-4 FRI-SAT  
FOLLOWED BY A TRANSITION TO MOSTLY 18Z GEFS/12Z ECMWF MEANS LATE  
IN THE PERIOD AS MODEL DETAILS DIVERGED FROM EACH OTHER AND THE  
LESS VOLATILE ENSEMBLE MEANS.  
 
FORECAST SPECIFICS STILL APPEAR TO BE IN FLUX TO SOME DEGREE WITH  
VARIOUS DIFFERENCES/TRENDS OF NOTE. WAVINESS EXPECTED TO TRACK  
ACROSS THE NORTHERN PLAINS/MIDWEST EARLY IN THE PERIOD HAS TRENDED  
WEAKER OVER THE PAST DAY IN RESPONSE TO A SLIGHTLY MORE SHEARED  
APPEARANCE OF SHORTWAVE ENERGY, WITH A GENERAL TREND TOWARD THE  
FASTER SIDE OF PRIOR SPREAD WHICH WAS REPRESENTED BY THE ECMWF.  
ON THE OTHER HAND THE UPPER LOW INITIALLY OVER HUDSON BAY HAS  
TRENDED FARTHER SOUTH IN LATEST MODEL RUNS. THIS BRINGS A  
STRONGER SURFACE REFLECTION/FRONTAL SYSTEM INTO THE GREAT LAKES  
DURING THE WEEKEND. NOTE THAT THE NEW 00Z CMC HAS CORRECTED FROM  
ITS 12Z RUN THAT HAD BROUGHT THE UPPER LOW AS FAR SOUTH AS THE  
OHIO VALLEY.  
 
FARTHER WEST AND SOUTH THERE IS LOOSE AGREEMENT THAT SHORTWAVE  
ENERGY SHOULD DROP SOUTHWARD ACROSS THE WEST-CENTRAL U.S. INTO THE  
SOUTHERN PLAINS/MEXICO BY AROUND SAT AND THEN CONTINUE AROUND THE  
SOUTHERN/EASTERN PERIPHERY OF THE MEAN TROUGH. DIFFERENCES IN  
SHORTWAVE DETAIL AS WELL AS HOW FLOW TO THE NORTH MAY INTERACT  
WITH THIS ENERGY LEAD TO A VARIETY OF POSSIBLE OUTCOMES FOR  
POTENTIAL GULF/WESTERN ATLANTIC LOW PRESSURE DURING DAYS 5-7  
SUN-TUE. FOR TIMING AND TRACK THE GEFS/ECMWF ENSEMBLE MEANS HAVE  
PROVIDED THE MOST CONSISTENT STARTING POINT FOR THIS POSSIBLE  
DEVELOPMENT. BETTER GUIDANCE AGREEMENT IN FUTURE RUNS MAY HELP TO  
GUIDE DEEPER ADJUSTMENTS IF NEEDED.  
 
DURING THE LATTER HALF OF THE PERIOD THERE IS DECENT AGREEMENT  
THAT THE COMBINATION OF PACIFIC ENERGY ROUNDING THE RIDGE AND SOME  
CANADIAN FLOW WILL SUPPORT NORTHERN U.S. LOW PRESSURE AND A  
TRAILING COLD SURGE THAT WILL AGAIN FOCUS OVER THE CENTRAL AND  
EVENTUALLY EASTERN STATES BUT ALSO BRING SOMEWHAT MORE COOLING TO  
THE ROCKIES/INTERIOR WEST THAN PRECEDING FRONTS. PREFER A  
MODEL/MEAN BLEND THAT TILTS MORE TO THE MEANS LATE IN THE FORECAST.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
LOCATIONS FROM THE NORTHERN PLAINS INTO THE GREAT LAKES MAY SEE A  
SERIES OF SNOW EVENTS ASSOCIATED WITH SURFACE WAVES TRACKING OVER  
OR JUST SOUTH OF THIS AREA. CONFIDENCE IS NOT YET PARTICULARLY  
HIGH FOR PINPOINTING EXACT INTENSITY/COVERAGE OF SNOW DUE TO  
GUIDANCE SPREAD AND RUN-RUN VARIABILITY/TRENDS. OVER THE GREAT  
LAKES THERE WILL LIKELY BE PERIODS OF PURE LAKE EFFECT SNOW AS  
WELL AS SOME LAKE ENHANCEMENT WITH THE AFOREMENTIONED SYSTEMS.  
DIFFICULTIES IN RESOLVING IMPORTANT DETAILS ALOFT COMPLICATE THE  
FORECAST ACROSS THE SOUTH AND EAST FROM THE WEEKEND INTO NEXT  
WEEK. BEST CONSENSUS WOULD HAVE THE GULF COAST REGION RECEIVING  
AT LEAST SOME RAINFALL DURING THE WEEKEND. ANY MOISTURE EXTENDING  
FARTHER NORTH COULD MEET ENOUGH COLD AIR TO PRODUCE SNOW AT TIMES.  
MOISTURE MAY THEN EXTEND ALONG THE EAST COAST DEPENDING ON  
WESTERN ATLANTIC LOW PRESSURE EVOLUTION. BEST POTENTIAL FOR SOME  
SNOWFALL EXISTS OVER THE NORTHEAST. OVER THE ROCKIES EXPECT TWO  
PRIMARY EPISODES OF LOCALLY ENHANCED SNOW PROGRESSING FROM NORTH  
TO SOUTH, ONE LATE THIS WEEK AND ANOTHER FROM LATE WEEKEND INTO  
EARLY NEXT WEEK.  
 
THE MIDWEST/UPPER MISSISSIPPI VALLEY SHOULD CONTINUE TO BE THE  
MOST PROMINENT FOCUS FOR COLDEST TEMPERATURE ANOMALIES DURING THE  
PERIOD WITH SOME READINGS AT LEAST 20F BELOW NORMAL FRI-SAT AND  
THEN AGAIN BY NEXT TUE. THE REST OF THE EASTERN HALF OF THE  
COUNTRY SHOULD SEE NEAR TO BELOW NORMAL TEMPERATURES. ON THE  
OTHER HAND EXPECT THE WEST COAST STATES TO REMAIN WARMER THAN  
AVERAGE WITH PLUS 10-15F ANOMALIES IN SOME CASES. THE NORTHERN  
ROCKIES/HIGH PLAINS WILL LIKELY BE ON THE WARM SIDE AS WELL  
FRI-SUN, INCLUDING MUCH ABOVE NORMAL MORNING LOWS DURING THE  
WEEKEND. THE ROCKIES AND VICINITY SHOULD SEE A PRONOUNCED COOLING  
TREND EARLY NEXT WEEK.  
 
RAUSCH  
 
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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