946  
FXUS02 KWBC 211934  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
334 PM EDT THU MAR 21 2019  
 
VALID 12Z SUN MAR 24 2019 - 12Z THU MAR 28 2019  
   
..OVERVIEW AND GUIDANCE ASSESSMENT/PREFERENCES
 
 
TODAY'S GUIDANCE CONTINUES THE RECENT GENERAL THEME ALOFT OF  
STRONG MEAN RIDGING OVER WESTERN CANADA AND/OR ALASKA, PERIODIC  
DOWNSTREAM TROUGHING, AND FEATURES PROGRESSING FROM THE EASTERN  
PACIFIC INTO/ACROSS THE LOWER 48. RECENT MODEL/ENSEMBLE RUNS HAVE  
DISPLAYED SOME SIGNIFICANT DIFFERENCES/TRENDING WITH INDIVIDUAL  
WESTERN-CENTRAL U.S. FEATURES THAT CONTINUE EASTWARD AND AFFECT  
THE FORECAST OVER THE EASTERN HALF OF THE COUNTRY. GUIDANCE HAS  
BEEN A LITTLE BETTER BEHAVED FOR A FAIRLY DEEP EASTERN PACIFIC  
TROUGH/EMBEDDED UPPER LOW THAT SHOULD REACH THE WEST BY WED-THU  
BUT TYPICAL AMPLITUDE/TIMING DIFFERENCES STILL EXIST.  
 
THE FORECAST OVER THE EASTERN HALF OF THE LOWER 48 DEPENDS ON  
SPECIFICS OF A COMPACT UPPER LOW OVER THE NORTH-CENTRAL PLAINS AND  
INTERIOR WEST ENERGY AS OF EARLY DAY 3 SUN, AND PERHAPS TO SOME  
DEGREE CANADIAN TROUGHING THAT DIPS INTO THE GREAT  
LAKES/NORTHEAST. OVER THE PAST DAY THERE HAVE BEEN SOME TRENDS  
TOWARD MORE EMPHASIS ON THE PLAINS FEATURE AND LESS ON THE WESTERN  
ENERGY. THIS HAS LED THE ECMWF/CMC AND THEIR MEANS IN PARTICULAR  
TO TREND FASTER WITH ASSOCIATED LOW PRESSURE CROSSING THE  
MID-LOWER LATITUDES OF THE CENTRAL/EASTERN STATES DURING SUN-TUE.  
THE ADJUSTMENT BRINGS THE GUIDANCE CLUSTER CLOSER TO THE PRIOR  
GFS/GEFS SCENARIO THAT WAS FAIRLY PROGRESSIVE. HOWEVER BY EARLY  
TUE THE 00Z ECMWF/ECMWF MEAN MAY HAVE OVERSHOT THE TREND JUST A  
BIT, FAVORING PARTIAL INCLUSION OF THE 12Z/20 RUN AS PART OF A  
CONSENSUS BLEND THAT INCLUDES THE 06Z GFS AND 00Z UKMET/CMC INTO  
TUE. THE 00Z GFS WAS SLIGHTLY FASTER. IT REMAINS A CLOSE CALL AS  
TO WHETHER THE CANADIAN/NORTHEAST U.S. TROUGH MAY INFLUENCE THE  
SOUTHERN STREAM SYSTEM. RECENT TRENDS FOR THE AMPLITUDE OF THIS  
TROUGH ARE MIXED.  
 
A BLEND/CONSENSUS APPROACH LOOKS REASONABLE FOR DEPICTING THE  
EVOLUTION OF THE AMPLIFIED TROUGH/EMBEDDED UPPER LOW SETTLING OVER  
THE EASTERN PACIFIC DURING THE FIRST HALF OF NEXT WEEK AND THEN  
OPENING UP WITH PROGRESSION INLAND. THE OVERALL UPPER LOW  
CONTAINS MULTIPLE SMALL SHORTWAVES WHOSE SCALE RESULTS IN LOW  
PREDICTABILITY FOR THOSE DETAILS. BY WED-THU THE MODELS AND  
ENSEMBLES HAVE VARIED SOMEWHAT WITH AMPLITUDE/TIMING AS TROUGH  
ENERGY PROGRESSES INTO THE WEST. RECENT ECMWF RUNS AND THEIR  
ENSEMBLES HAVE TENDED TO BE ON THE FASTER SIDE OF THE OVERALL  
SPREAD IN THE PAST DAY AND THE 00Z ECMWF LOOKS PARTICULARLY FAST  
IN BRINGING HEIGHT FALLS INTO THE NORTHERN PLAINS BY THU. THE  
ECMWF MEAN HAS TRENDED SLOWER OVER THE PAST 24 HOURS AND THE 06Z  
GFS IS A BIT SLOWER THAN THE 00Z RUN SO PREFERENCES FOR THIS  
FEATURE LATE IN THE PERIOD TILT MORE TOWARD THE LATEST ECMWF  
MEAN/06Z GEFS MEAN/06Z GFS AND 12Z/20 ECMWF.  
 
DOWNSTREAM FROM AN UPPER HIGH EXPECTED TO CLOSE OFF OVER EASTERN  
ALASKA AND THE YUKON, THERE IS DECENT AGREEMENT THAT AN AMPLIFYING  
TROUGH OVER CENTRAL CANADA WILL PUSH A COLD FRONT INTO THE  
NORTHERN PLAINS AROUND DAY 7 THU. THERE HAVE BEEN ENOUGH SPREAD  
AND VARIABILITY FOR THE CHARACTER OF THE UPPER RIDGE TO SUGGEST  
SOME FUTURE GUIDANCE ADJUSTMENTS ARE POSSIBLE OVER THE NORTHERN  
U.S. AND SOUTHERN CANADA DURING THE LATTER HALF OF THE WEEK.  
 
   
..WEATHER HIGHLIGHTS AND HAZARDS
 
 
ONE OR MORE WAVES PROGRESSING ACROSS THE EASTERN HALF OF THE  
COUNTRY WILL PRODUCE AREAS OF MOSTLY RAIN SUN-TUE, WITH  
THUNDERSTORMS POSSIBLE FROM THE SOUTHERN HALF OF THE PLAINS INTO  
THE SOUTHEAST. SOME RAINFALL COULD BE LOCALLY MODERATE/HEAVY BUT  
RECENT FASTER TRENDS SUGGEST THAT ANY INTENSE ACTIVITY SHOULD BE  
FAIRLY BRIEF. AT THE SAME TIME THE FASTER PROGRESSION OF MOISTURE  
MAY LIMIT ANY SNOW IN THE NORTHERN PART OF THE MOISTURE SHIELD TO  
FARTHER NORTH LATITUDES THAN PREVIOUSLY ANTICIPATED--DUE TO A  
HIGHER PROPORTION OF MOISTURE CROSSING THE EAST AHEAD OF THE  
COLDER AIR PUSHING SOUTHEAST FROM CANADA.  
 
MOSTLY DURING SUN-SUN NIGHT AN INITIAL WESTERN U.S. SHORTWAVE WILL  
GENERATE MOUNTAIN SNOW/VALLEY RAIN OVER THE GREAT BASIN AND  
NORTHERN-CENTRAL ROCKIES. SOME OF THIS RAIN/SNOW MAY EXTEND INTO  
THE NORTHERN PLAINS. THE SYSTEM SETTLING INTO THE EASTERN PACIFIC  
DURING THE FIRST HALF OF NEXT WEEK WILL LIKELY BRING MULTIPLE  
SURGES OF MOISTURE INTO THE WEST COAST AND EXTENDING INTO FAVORED  
TERRAIN FARTHER INLAND OVER NORTHERN/CENTRAL PARTS OF THE WEST.  
THE FIRST ROUND OF ENHANCED PRECIPITATION SHOULD COMMENCE BY SUN  
NIGHT-MON. BY THU THERE IS SOME UNCERTAINTY OVER THE EXACT  
CHARACTER OF UPPER FLOW ALONG THE WEST COAST, LOWERING CONFIDENCE  
IN HOW MUCH PRECIPITATION MAY PERSIST OVER THE WEST COAST STATES  
AT THAT TIME. GUIDANCE IS PERSISTENT IN SHOWING BEST POTENTIAL  
FOR HIGHEST PRECIP TOTALS FROM NORTHERN CALIFORNIA/EXTREME  
SOUTHWEST OREGON INTO THE SIERRA NEVADA. THE COMBINATION OF  
EVENTS WILL PROVIDE LESS EXTREME BUT STILL SIGNIFICANT TOTALS OVER  
THE NORTHERN/CENTRAL ROCKIES.  
 
SYSTEM PROGRESSION WILL LEAD TO VARIABLE TEMPERATURES OVER MANY  
AREAS DURING THE PERIOD. EXPECT WARMEST ANOMALIES TO BE FOR  
MORNING LOWS FROM THE ROCKIES INTO PLAINS/MISSISSIPPI VALLEY  
SUN-MON AND THEN FOR MAX/MIN READINGS FROM THE INTERIOR  
WEST/ROCKIES INTO THE PLAINS/UPPER MISSISSIPPI VALLEY TUE-THU.  
THERE MAY BE FAIRLY BROAD COVERAGE OF PLUS 10-20F ANOMALIES OVER  
THE CENTRAL U.S. BY NEXT THU. PARTS OF THE EAST SHOULD SEE  
TEMPERATURES AT LEAST 10F BELOW NORMAL FOR A BRIEF TIME AROUND  
TUE-WED.  
 
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  
 
HAZARDS:  
- HEAVY PRECIPITATION ACROSS PORTIONS OF CALIFORNIA, THE CENTRAL  
GREAT BASIN, THE PACIFIC NORTHWEST, AND THE SOUTHWEST, MON-THU,  
MAR 25-MAR 28.  
- FLOODING POSSIBLE ACROSS PORTIONS OF THE NORTHERN/CENTRAL  
PLAINS, THE UPPER/MIDDLE MISSISSIPPI VALLEY, AND THE GREAT LAKES.  
- FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE  
NORTHERN/CENTRAL PLAINS, THE MISSISSIPPI VALLEY, THE TENNESSEE  
VALLEY, THE GREAT LAKES, AND THE OHIO VALLEY.  
- FLOODING LIKELY ACROSS PORTIONS OF THE NORTHERN/CENTRAL PLAINS,  
THE UPPER/MIDDLE MISSISSIPPI VALLEY, AND THE GREAT LAKES.  
- MUCH ABOVE NORMAL TEMPERATURES ACROSS PORTIONS OF THE  
NORTHERN/CENTRAL PLAINS, AND THE UPPER/MIDDLE MISSISSIPPI VALLEY  
WED-THU, MAR 27-MAR 28.  
 
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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