371  
FXUS02 KWBC 250701  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
200 AM EST MON FEB 25 2019  
 
VALID 12Z THU FEB 28 2019 - 12Z MON MAR 04 2019  
   
..PATTERN OVERVIEW
 
 
FOR THE PERIOD AS A WHOLE EXPECT PROGRESSIVE AND BROADLY CYCLONIC  
MEAN FLOW ALOFT OVER THE LOWER 48. AS AN UPPER RIDGE INITIALLY  
EXTENDING FROM THE GULF OF ALASKA INTO THE ARCTIC DRIFTS INTO  
NORTHWESTERN CANADA, A DEEP SOUTH-CENTRAL CANADA UPPER LOW WILL  
DESCEND CLOSE TO OR ACROSS THE UPPER GREAT LAKES REGION DURING THE  
WEEKEND AND THEN CONTINUE RAPIDLY EASTWARD. FLOW AROUND THIS LOW  
WILL LIKELY INTERACT WITH ENERGY FROM A PACIFIC NORTHWEST COAST  
UPPER LOW THAT OPENS UP AS IT EJECTS INLAND. THE COMBINATION OF  
THESE FEATURES SHOULD PRODUCE AN OHIO VALLEY/GREAT LAKES INTO  
NORTHEAST STORM SYSTEM BY LATE FRI OR FRI NIGHT INTO THE WEEKEND.  
MEANWHILE ANOTHER PACIFIC SYSTEM WILL LIKELY REACH THE WEST COAST  
BY THE WEEKEND. ANTICIPATE HIGHEST PRECIPITATION TOTALS OVER  
FAVORED TERRAIN FROM CALIFORNIA INTO THE CENTRAL ROCKIES AND FROM  
THE GULF COAST REGION INTO THE NORTHEAST, WHILE MUCH BELOW NORMAL  
TEMPERATURES PERSIST OVER PORTIONS OF THE CENTRAL U.S.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
THERE ARE STILL SOME DETAILS THAT REMAIN TO BE RESOLVED BUT IN  
PRINCIPLE THE GUIDANCE IS GRADUALLY IMPROVING IN ITS CLUSTERING  
COMPARED TO SOME PREVIOUS DAYS. THERE IS GOOD AGREEMENT ON THE  
OVERALL EVOLUTION OF EJECTING PACIFIC NORTHWEST UPPER LOW ENERGY,  
THE SOUTHERN CANADA UPPER LOW THAT MAY BRUSH THE UPPER GREAT  
LAKES, AND THEIR INTERACTION THAT SHOULD PRODUCE A STORM SYSTEM  
OVER THE NORTHEASTERN QUADRANT OF THE COUNTRY BY LATE FRI INTO THE  
WEEKEND. HOWEVER MEDIUM-SMALLER SCALE DETAIL AND TRACK/TIMING  
ISSUES (WHICH HAVE LOWER PREDICTABILITY) LEAD TO ONGOING  
UNCERTAINTY FOR THE PRECISE CHARACTER OF THE STORM SYSTEM. GFS  
AND SOME GEFS RUNS HAVE BEEN A BIT ON THE FASTER AND AMPLIFIED  
SIDE OF THE ENVELOPE WITH THE EJECTING WESTERN ENERGY, TENDING TO  
RESULT IN SOME OF THE STRONGER SOLUTIONS FOR THE DOWNSTREAM  
SURFACE LOW. ECMWF RUNS HAVE BEEN INCONSISTENT WHILE THE PAST  
COUPLE CMC RUNS HAVE BEEN FAIRLY WEAK. THE 00Z UKMET IS MUCH  
WEAKER THAN ITS PRIOR RUN. CONTINUITY PROVIDES FAIRLY HIGH  
CONFIDENCE IN THE STORM'S EXISTENCE AND TO SOME DEGREE THE TRACK.  
HOWEVER DEPENDENCE OF THE STORM'S EVOLUTION ON LOWER  
PREDICTABILITY SUBTLE DETAILS AS WELL AS THE OBSERVED  
INCONSISTENCY/SPREAD OF OPERATIONAL MODEL RUNS FOR DEPTH FAVOR AN  
INTERMEDIATE SOLUTION FOR A SINGLE DETERMINISTIC FORECAST.  
 
FOR THE SYSTEM FORECAST TO APPROACH CALIFORNIA BY THE START OF THE  
WEEKEND, SOLUTIONS HAVE MAINTAINED MODERATE SPREAD FOR STRENGTH  
AND TRACK--NORTHERN SOLUTIONS TENDING TO ADJUST BACK DOWN TOWARD  
MAJORITY CLUSTERING OVER SUBSEQUENT RUNS. ON THE OTHER HAND THERE  
HAS BEEN A PERSISTENT SPREAD FOR TIMING. THE CMC HAS BACKED OFF A  
BIT FROM ITS 12Z RUN BUT REMAINS IN THE FASTER PORTION OF THE  
SPREAD (ALONG WITH RECENT UKMET RUNS) WHILE THE PAST COUPLE OF  
ECMWF RUNS ARE SLOWER THAN EARLIER RUNS AND NOW CLUSTER MORE WITH  
GFS/GEFS RUNS THAT HAVE GENERALLY BEEN IN THE SLOWER HALF OF THE  
SPECTRUM. BEHAVIOR OF GUIDANCE OVER RECENT DAYS FAVORS  
MAINTAINING A COMPROMISE APPROACH AS THE BEST STARTING POINT.  
GUIDANCE AGREES THAT SUPPORTING ENERGY ALOFT WILL RAPIDLY SHEAR  
OUT TO THE EAST AS IT BECOMES EMBEDDED WITHIN THE PROGRESSIVE MEAN  
FLOW.  
 
BASED ON SYSTEM CONSIDERATIONS THE UPDATED FORECAST STARTED WITH  
AN OPERATIONAL MODEL BLEND FOR DAYS 3-4 THU-FRI AND THEN ADJUSTED  
TOWARD A BLEND OF 18Z GFS/12Z ECMWF RUNS AND THEIR ENSEMBLE MEANS.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
DURING THU-FRI THE INITIAL FLOW OF MOISTURE OVER THE WEST WILL  
BRING AREAS OF RAIN AND HIGHER ELEVATION SNOW TO ABOUT THE  
NORTHERN 2/3 OF THE REGION WITH A BRIEF DRYING TREND PROGRESSING  
FROM WEST TO EAST. THE NEXT PACIFIC SYSTEM SHOULD START TO BRING  
MOISTURE INTO CALIFORNIA BY THE START OF THE WEEKEND WITH  
RAIN/MOUNTAIN SNOW THEN SPREADING EASTWARD INTO THE ROCKIES. FOR  
THE 5-DAY PERIOD EXPECT AN AREA OF ENHANCED PRECIPITATION FROM  
NORTHERN-CENTRAL CALIFORNIA/SOUTHWEST OREGON INTO THE  
NORTH-CENTRAL/CENTRAL ROCKIES WITH HIGHEST TOTALS LIKELY OVER  
WINDWARD TERRAIN OF THE SIERRA NEVADA RANGE.  
 
LATE THIS WEEK DIFFUSE SHORTWAVE ENERGY MAY ASSIST IN PRODUCING  
RAINFALL OF VARYING INTENSITY OVER THE SOUTHERN HALF OF THE EAST  
WHILE THE NORTHERN FRINGE OF THE MOISTURE SHIELD COULD CONTAIN A  
LITTLE LIGHT SNOW FROM THE MID MISSISSIPPI VALLEY INTO THE  
NORTHERN MID-ATLANTIC. THE DEVELOPING STORM SYSTEM EXPECTED TO  
REACH THE NORTHEAST DURING THE WEEKEND SHOULD INITIALLY SPREAD  
SNOW ACROSS PARTS OF THE NORTHERN PLAINS LATE THIS WEEK WITH  
PRECIPITATION COVERAGE THEN EXPANDING OVER THE EASTERN STATES.  
BEST SNOWFALL POTENTIAL WILL EXTEND FROM THE MIDWEST THROUGH THE  
GREAT LAKES INTO NEW ENGLAND. POCKETS OF LOCALLY MODERATE-HEAVY  
RAINFALL MAY BE POSSIBLE OVER THE SOUTH BUT THUS FAR WITH NO  
COHERENT SIGNAL IN THE GUIDANCE FOR PRECISE LOCATION/MAGNITUDE.  
THIS SYSTEM MAY PRODUCE STRONG WINDS OVER SOME AREAS EVEN IF NOT  
TO THE MAGNITUDE OF THE SYSTEM CURRENTLY AFFECTING THE GREAT  
LAKES/NORTHEAST. EXPECT A PERIOD OF LAKE EFFECT SNOW IN THE WAKE  
OF THIS SYSTEM WHILE LINGERING MOISTURE ALONG SOUTHERN LATITUDES  
MAY PRODUCE SOME RAIN NEAR THE GULF COAST INTO EARLY NEXT WEEK.  
 
BEHIND THE AFOREMENTIONED DEVELOPING STORM, A STRONG SURGE OF VERY  
COLD AIR WILL SPREAD SOUTH AND EAST ACROSS THE CENTRAL/EASTERN  
U.S. FROM LATE WEEK ONWARD. THE FORECAST HAS BEEN CONSISTENT IN  
FOCUSING COLDEST ANOMALIES (AT LEAST 30-40F BELOW NORMAL) OVER THE  
NORTHERN PLAINS WHILE HIGH TEMPERATURES OF AT LEAST 10F BELOW  
NORMAL MAY REACH THE GULF/EAST COASTS BY NEXT MON. EXPECT THE  
BEST POTENTIAL FOR DAILY RECORDS TO BE FOR COLD DAYTIME HIGHS OVER  
THE NORTHERN-CENTRAL PLAINS AND MIDWEST DURING THE WEEKEND. THE  
MEAN PATTERN WILL TEND TO KEEP THE SOUTHERN 2/3 OF THE WEST WARMER  
THAN AVERAGE FOR MORNING LOWS BUT NEAR TO SLIGHTLY BELOW NORMAL  
FOR HIGHS. NORTHERN AREAS SHOULD REMAIN BELOW NORMAL. THE SOUTH  
AND PARTS OF THE EAST WILL SEE ABOVE NORMAL TEMPERATURES LATE  
WEEK/EARLY WEEKEND AHEAD OF THE DEVELOPING STORM SYSTEM BEFORE THE  
TREND TOWARD COLDER READINGS.  
 
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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