307  
FXUS02 KWBC 280700  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
159 AM EST THU FEB 28 2019  
 
VALID 12Z SUN MAR 03 2019 - 12Z THU MAR 07 2019  
   
..PATTERN OVERVIEW
 
 
THE FORECAST OF LARGE SCALE FLOW HAS MAINTAINED GOOD CONTINUITY  
OVER THE PAST DAY. DOWNSTREAM FROM PERSISTENT MEAN  
RIDGING/POSITIVE HEIGHT ANOMALIES OVER NORTHWESTERN NORTH AMERICA,  
A TROUGH WILL AMPLIFY INTO THE EASTERN U.S. WITH GREATEST DEPTH  
AROUND MIDWEEK BEFORE THE TROUGH AXIS CONTINUES INTO THE WESTERN  
ATLANTIC. AT THE SAME TIME A MEAN RIDGE WILL BUILD INTO THE  
WEST-CENTRAL U.S. AS A MEAN TROUGH SETTLES NEAR THE WEST COAST.  
THERE ARE EMBEDDED DETAILS THAT WILL TAKE TIME TO RESOLVE THOUGH,  
ESPECIALLY OVER THE EAST EARLY IN THE WEEK AND NEAR THE WEST COAST  
FROM TUE ONWARD. ACCOMPANYING THIS EVOLUTION WILL BE AN EPISODE  
OF EXTREMELY COLD TEMPERATURES FOR EARLY MARCH OVER THE CENTRAL  
U.S. WITH SOME OF THIS COLD EXTENDING THROUGH ALMOST ALL OF THE  
EASTERN STATES AS WELL AS BACK INTO THE INTERIOR NORTHWEST. A  
FAST MOVING WAVE WILL SPREAD A BROAD AREA OF VARIOUS PRECIPITATION  
TYPES ACROSS THE EAST EARLY IN THE WEEK AND ANOTHER WET SOUTHERN  
STREAM PACIFIC SYSTEM WILL BRING MORE MOISTURE INTO THE WEST  
STARTING TUE-TUE NIGHT.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
OVER THE PAST COUPLE DAYS THERE HAS BEEN A PRONOUNCED  
NORTHWESTWARD TREND FOR A WAVE EXPECTED TO TRACK FROM THE LOWER  
HALF OF THE MISSISSIPPI VALLEY INTO THE CANADIAN MARITIMES DURING  
SUN-MON. THIS TREND IS DUE TO A COMBINATION OF FASTER ADJUSTMENTS  
FOR SHORTWAVE ENERGY STREAMING INTO CALIFORNIA ON SAT AND CHANGES  
TOWARD SLOWER PROGRESSION OF NORTHERN TIER U.S. HEIGHT FALLS INTO  
THE NORTHEAST--ALLOWING FOR MORE INTERACTION. THE ECMWF HAS BEEN  
LEADING THIS TREND OVER THE PAST COUPLE DAYS WHILE THE GFS HAS  
BEEN SLOWEST TO TREND TO THIS SCENARIO. THE 12Z ECMWF WAS IN THE  
NORTHERN MINORITY AMONG ALL ENSEMBLE MEMBERS BY LATE SUN-MON SO  
PREFERENCE WAS TO FOLLOW A TRACK SLIGHTLY TO ITS SOUTH (COMPROMISE  
WITH LATEST UKMET/CMC RUNS), BUT TRENDS DO PROVIDE MORE CONFIDENCE  
IN THE NORTHWEST HALF OF THE SPREAD VERSUS THE SOUTHEASTERN HALF.  
NEW 00Z RUNS OFFER HOPE THAT THE FORECAST COULD BECOME A LITTLE  
MORE STABLE SOON.  
 
THE EASTERN PACIFIC/WEST COAST REGION WILL BE A FOCUS FOR  
SIGNIFICANT DETAIL UNCERTAINTY BY MID-LATE PERIOD. THE FULL ARRAY  
OF MODEL/ENSEMBLE GUIDANCE SHOWS A VARIETY OF POSSIBLE EVOLUTIONS  
INVOLVING THREE SEPARATE FEATURES: 1. SHEARED SOUTHWEST BRITISH  
COLUMBIA ENERGY THAT WILL LIKELY FORM A CLOSED LOW SOMEWHERE  
BETWEEN THE PACIFIC NORTHWEST AND OFFSHORE VANCOUVER ISLAND, 2.  
ALASKA/NORTHEASTERN PACIFIC SHORTWAVE ENERGY DROPPING PRACTICALLY  
DUE SOUTHWARD FROM SUN ONWARD, AND 3. A CLOSED SOUTHERN STREAM  
SYSTEM REACHING NEAR 135W BY TUE. THUS FAR RECENT CMC RUNS HAVE  
BEEN FARTHEST SOUTH/SOUTHEAST WITH THE NORTHERN UPPER LOW THUS  
SUPPRESSING SURFACE LOW PRESSURE NEARING THE WEST COAST BY  
MIDWEEK--A SEEMINGLY LOW PROBABILITY SOLUTION AT THIS TIME. IN  
SPITE OF THE POTENTIAL COMPLEXITY OF EVOLUTION, THE ENSEMBLE MEANS  
HAVE BEEN REMARKABLY STABLE/AGREEABLE THUS FAR WITH LOW PRESSURE  
NEARING EXTREME NORTHERN CALIFORNIA BY EARLY WED. THE 12-18Z  
GFS/12Z ECMWF RUNS WERE VERY CLOSE TO THEIR RESPECTIVE MEANS SO  
THOSE SOLUTIONS PROVIDED THE BASIS FOR THE UPDATED FORECAST WITH  
GOOD CONTINUITY. 12-HOURLY GFS RUNS HAVE BEEN FAIRLY STABLE FOR  
THE PAST DAY OR SO WHILE ECMWF RUNS HAVE BEEN OSCILLATING BETWEEN  
12Z RUNS NEAR THE ENSEMBLE MEAN CONSENSUS AND 00Z RUNS THAT WERE  
12-24 HOURS SLOWER.  
 
BASED ON ABOVE CONSIDERATIONS THE UPDATED FORECAST BLEND WENT 70  
PERCENT TOWARD THE 12Z ECMWF/UKMET/CMC CLUSTER FOR DAYS 3-4  
SUN-MON AND THEN REMOVED THE CMC FROM CONSIDERATION DUE TO ITS  
SUSPECT SOLUTION ALONG THE WEST COAST. AT THE SAME TIME THE  
FORECAST STARTED TO INCORPORATE THE 18Z GEFS/12Z ECMWF MEANS ON  
DAY 5 TUE WITH A GRADUAL INCREASE OF THE MEANS TO SLIGHTLY MORE  
WEIGHT THAN THE 18Z GFS/12Z ECMWF BY DAY 7 THU.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
A BROAD AREA OF PRECIPITATION WILL ACCOMPANY A VIGOROUS WAVE  
TRACKING NORTHEAST OVER PARTS OF THE EASTERN STATES AND INTO THE  
CANADIAN MARITIMES SUN-MON. NORTHWEST TRENDS IN THE PAST DAY HAVE  
PUSHED THE MOST LIKELY AREA FOR SIGNIFICANT WINTRY WEATHER TO AN  
AXIS EXTENDING FROM THE MID-MISSISSIPPI VALLEY/OHIO VALLEY INTO  
THE NORTHEAST. A MORE CONSISTENT THEME FROM YESTERDAY IS THE  
POTENTIAL FOR HEAVY RAINFALL OVER PARTS OF THE LOWER MISSISSIPPI  
VALLEY AND TENNESSEE VALLEY/INTERIOR SOUTHEAST. MUCH OF THE EAST  
WILL TREND DRIER AFTER THE WAVE'S PASSAGE THOUGH MOISTURE MAY  
LINGER FOR A TIME OVER THE EXTREME SOUTHEAST/FLORIDA. EXPECT  
PERIODS OF LAKE EFFECT SNOW DOWNWIND FROM ICE-FREE AREAS OF THE  
GREAT LAKES AND ONE OR TWO AREAS OF LIGHT SNOW MAY PASS THROUGH  
THE PLAINS/MIDWEST.  
 
RAIN AND HIGHER ELEVATION SNOW IN PROGRESS OVER THE  
CENTRAL/SOUTH-CENTRAL PARTS OF THE WEST LATE IN THE WEEKEND WILL  
TAPER OFF FROM WEST TO EAST. THEN FROM TUE ONWARD THE NEXT SYSTEM  
IN THE SERIES WILL SPREAD A BROAD AREA OF MOISTURE ACROSS THE  
WEST, WITH GREATER NORTHWARD EXTENT THAN WITH THE PREVIOUS SYSTEM.  
FAVORED TERRAIN OVER NORTHERN AND CENTRAL CALIFORNIA SHOULD ONCE  
AGAIN SEE THE HIGHEST PRECIPITATION TOTALS WITH THIS SYSTEM.  
MOISTURE REACHING NORTHERN PORTIONS OF THE WEST MAY BRING WINTRY  
WEATHER TO LOW ELEVATIONS OVER SOME AREAS GIVEN THE COLD  
TEMPERATURES IN PLACE FROM EARLY IN THE WEEK.  
 
CONTINUE TO EXPECT COLDEST TEMPERATURES RELATIVE TO NORMAL DURING  
SUN-MON WITH SOME CENTRAL U.S. LOCATIONS SEEING ANOMALIES OF  
30-45F BELOW NORMAL AND A WIDESPREAD AREA OVER THE PLAINS/MIDWEST  
WITH READINGS THAT WILL APPROACH OR BREAK DAILY RECORDS--MORE  
LIKELY A GREATER NUMBER FOR COLD HIGHS. INTERIOR NORTHWEST  
LOCATIONS MAY ALSO SEE SOME TEMPERATURES AT LEAST 20F BELOW NORMAL  
WITH LOCAL CHALLENGES TO DAILY RECORDS. THE AREA OF POTENTIAL  
DAILY RECORDS WILL LIKELY SHIFT MORE INTO THE EASTERN HALF OF THE  
COUNTRY (MIDWEST/GREAT LAKES/OHIO VALLEY) BY TUE. AS OF THU  
EXPECT COVERAGE OF MINUS 20F OR GREATER ANOMALIES TO DECREASE  
CONSIDERABLY BUT THE EASTERN HALF OF THE COUNTRY WILL STILL BE  
CHILLY VERSUS NORMAL. THE SOUTHERN 2/3 OF THE WEST CONTINUES TO  
LOOK WARM FOR MORNING LOWS WHILE HIGHS SHOULD BE WITHIN A FEW  
DEGREES OF NORMAL.  
 
RAUSCH  
 
ADDITIONAL 3-7 DAY HAZARDS INFORMATION CAN BE FOUND ON THE WPC  
MEDIUM RANGE HAZARDS CHART AT:  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP  
 
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION, WINTER WEATHER OUTLOOK PROBABILITIES  
AND HEAT INDICES ARE 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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