065  
FXUS02 KWBC 191600  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1200 PM EDT TUE MAR 19 2019  
 
VALID 12Z FRI MAR 22 2019 - 12Z TUE MAR 26 2019  
   
..16Z UPDATE
 
 
THE 00Z AND 06Z SUITE OF MODELS MAINTAINED A SIGNAL FOR A  
REASONABLY STRONG LOW PRESSURE SYSTEM CENTERED NEAR CAPE COD ON  
DAY 3 (FRI). THE GFS AND ECMWF AND THEIR ENSEMBLES ARE IN GOOD  
AGREEMENT ON THE PLACEMENT OF THE LOW, WHILE THE 00Z CMC AND UKMET  
MAINTAINED A MORE SOUTHERN SOLUTION LIKE THEIR PREVIOUS RUNS.  
LEANED AWAY FROM THOSE MODELS SINCE THEY WERE NOT SUPPORTED WELL  
BY THE CLUSTERING OF THE LOWS IN THE ENSEMBLES. THE CENTRAL  
PRESSURE OF THE LOW HAS COME INTO BETTER ALIGNMENT AT LEAST WITH  
THE GFS/ECMWF, WITH THE 00Z ECMWF WEAKER COMPARED TO THE PREVIOUS  
RUN, CLOSER TO THE GFS, BUT UNCERTAINTY REMAINS AS AGREEMENT DOES  
NOT NECESSARILY EQUAL CORRECTNESS.  
 
ANOTHER SURFACE LOW IS EXPECTED TO BE SLOW-MOVING ACROSS THE  
SOUTHERN/CENTRAL ROCKIES TO PLAINS ON DAY 3-5, BEFORE MOVING  
EASTWARD MORE QUICKLY ON DAY 6-7 AS UPPER-LEVEL ENERGY SOLIDIFIES  
TO INTENSIFY A TROUGH IN THE EASTERN U.S. IT SEEMS THAT MODELS ARE  
IN BETTER AGREEMENT ON THE EASTWARD PROGRESSION OF THE LOW THAN  
THE LAST CYCLE, WITH THE 00Z AND 06Z GFS TAKING A MORE SOUTHERN  
TRACK ACROSS THE MIDDLE/LOWER MISSISSIPPI VALLEY ON DAY 6 AND THE  
SOUTHEAST ON DAY 7 THAN BEFORE. THIS IS LIKELY DUE TO BETTER  
CONSENSUS ON A STRONGER SURFACE HIGH COMING INTO THE UPPER  
MIDWEST. DETAILS REMAIN ELUSIVE, HOWEVER, WITH THE STRENGTH AND  
POSITION OF THIS LOW. THE MEDIUM RANGE SUITE OF PRODUCTS LEANED  
TOWARD THE 00Z ECMWF MEAN AND OPERATIONAL RUN, WITH COMPONENTS OF  
THE 00Z/06Z GFS AND GEFS MEAN.  
 
SEE PREVIOUS DISCUSSION FOR MORE DETAILS, INCLUDING SENSIBLE  
WEATHER INFORMATION.  
 
TATE  
   
..PREVIOUS DISCUSSION
 
 
   
..OVERVIEW AND GUIDANCE ASSESSMENT/PREFERENCES
 
 
SPLIT FLOW PATTERN IS EXPECTED TO PERSIST ACROSS NORTH AMERICA  
DURING THE EXTENDED PERIOD. ENSEMBLE GUIDANCE SHOWS GOOD CONSENSUS  
THAT A STRONG AND BLOCKING UPPER-LEVEL RIDGE AXIS INITIALLY ACROSS  
THE HIGH PLAINS OF THE U.S. INTO ALBERTA/SASKATCHEWAN WILL MEANDER  
IN PLACE OVER THE NEXT WEEK. THIS WILL CONTINUE TO SPLIT INCOMING  
ENERGY FROM THE PACIFIC INTO NORTHERN STREAM COMPONENTS DIRECTED  
NORTHWARD TOWARD ALASKA, AND SOUTHERN STREAM COMPONENTS THAT  
TRAVERSE THE SOUTHERN/CENTRAL U.S., UNDERCUTTING THE RIDGE.  
DOWNSTREAM OF THE RIDGE, THE NORTHEAST WILL BE SUBJECT TO  
CONTINUED MEAN TROUGHING, REINFORCED BY A SERIES OF ENERGETIC  
SHORTWAVES. SOME GUIDANCE SUGGESTS THAT PERHAPS THIS NORTHERN  
STREAM AMPLIFIED RIDGE/TROUGH PATTERN MAY BEGIN TO WEAKEN BY EARLY  
NEXT WEEK, BUT CONFIDENCE IN THAT IS RELATIVELY LOW AT THIS TIME  
GIVEN INCREASED SPREAD AMONG THE ENSEMBLE GUIDANCE AS TO THE  
INTENSITY AND DURATION OF THE UPPER RIDGE.  
 
MODEL GUIDANCE HAS MADE A DRAMATIC SHIFT OVER THE PAST 24 HOURS  
WITH RESPECT TO A LOW PRESSURE SYSTEM ALONG/OFF THE EASTERN  
SEABOARD. AT THIS TIME LAST NIGHT, THE CONSENSUS AMONG THE  
MAJORITY OF GUIDANCE WAS FOR A TRACK FARTHER EAST, WITH  
SIGNIFICANT DEEPENING DELAYED UNTIL THE SYSTEM REACHED THE  
CANADIAN MARITIMES. EACH CONSECUTIVE RUN OF THE GUIDANCE, THIS  
MORNING AND THIS EVENING HAS GENERALLY SHIFTED THE TRACK WEST,  
WITH THE ECMWF AND GFS NOW SHOWING A SIGNIFICANT SURFACE LOW JUST  
EAST OF CAPE COD FRI MORNING (AND THE CMC/UKMET MUCH FARTHER  
SOUTHEAST). CLUSTERING OF ENSEMBLE MEMBERS AROUND THIS IDEA IS  
QUITE GOOD AMONG ECENS AND GEFS MEMBERS, WITH A SECONDARY CLUSTER  
FARTHER SOUTHEAST/OFFSHORE COMPRISED PRIMARILY OF CANADIAN  
ENSEMBLE MEMBERS. CLUSTERING AROUND THESE SOLUTIONS REMAINS  
GENERALLY GOOD INTO FRI NIGHT-SAT AS THE SURFACE LOW MOVES  
NORTHEASTWARD, WITH SOME MODEST INCREASE IN SPREAD. FARTHER WEST,  
A MORE STABLE CONSENSUS CONTINUES WITH RESPECT TO A  
SHORTWAVE/UPPER LOW MOVING FROM THE FOUR CORNERS REGION TO THE  
PLAINS FRI-SAT. SOLUTIONS WERE GENERALLY WELL-CLUSTERED WITH  
RESPECT TO THE TIMING AND INTENSITY OF THIS FEATURE DURING DAYS  
3-4. BY DAY 5 (SUN), AS THE SHORTWAVE MOVES INTO THE MIDWEST,  
SOLUTIONS DIFFER AS TO HOW QUICKLY IT WILL WEAKEN, BUT THERE IS  
GENERAL CONSENSUS THAT THE FEATURE SHOULD GRADUALLY SHEAR OUT AS  
IT ENCOUNTERS A COL BETWEEN THE NORTHERN/SOUTHERN STREAM FLOW AND  
THE UPPER RIDGE. FARTHER WEST, ADDITIONAL PACIFIC SHORTWAVE ENERGY  
IS FORECAST TO REACH THE WEST COAST SAT, AND THEN SPLIT, WITH A  
MORE SIGNIFICANT SOUTHERN COMPONENT ALSO MOVING EAST ACROSS THE  
FOUR CORNERS REGION SUN. MODELS DIFFER ON THEIR HANDLING OF THIS  
SPLITTING AS WELL, WITH THE ECMWF PERSISTENT IN SHOWING THE  
STRONGEST SOUTHERN COMPONENT. THE COMPLEX NATURE OF THIS PROCESS  
LENDS TO LOW PREDICTABILITY AND CONFIDENCE IN THIS ASPECT OF THE  
FORECAST. BASED ON THESE CONSIDERATIONS, THE FORECAST DURING DAYS  
3-5 WAS BASED PRIMARILY ON A BLEND OF THE ECMWF AND GFS, WITH SOME  
INFLUENCE FROM THEIR RESPECTIVE ENSEMBLE MEANS AS WELL.  
 
BY DAYS 6-7 (MON-TUE) THE SECOND PACIFIC SHORTWAVE SHOULD REACH  
THE SOUTHERN/CENTRAL PLAINS IN SOME FORM (SOLUTIONS ARE SIMILAR IN  
TIMING EVEN IF THEY DIFFER ON THE AMPLITUDE), LIKELY PROMOTING  
DEVELOPMENT OF A SURFACE LOW. ENSEMBLE MEMBERS SHOW SOME DEGREE OF  
CLUSTERING EVEN THROUGH DAY 7 WITH RESPECT TO THIS SYSTEM, AND THE  
ECMWF WAS GENERALLY WELL-CENTERED IN THE SPREAD. THE GFS, ON THE  
OTHER HAND, SEEMS TO SUFFER ITS PREVALENT BIAS AND ACCELERATE THE  
SYSTEM EASTWARD FAR MORE QUICKLY THAN CONSENSUS. DIFFERENCES ALSO  
EMERGE IN THE NORTHERN STREAM BY EARLY NEXT WEEK, WITH DIFFERENT  
DEGREES OF TROUGHING ACROSS NEW ENGLAND. GIVEN SOME DEGREE OF  
PERSISTENT RIDGING UPSTREAM, WOULD LIKELY LEAN TOWARD A SOMEWHAT  
MORE AMPLIFIED TROUGH FOR NEW ENGLAND AS SHOWN BY THE ECMWF AND  
18Z/00Z GFS RUNS. THE GFS HAS COME MORE IN LINE WITH CONSENSUS  
WITH ANOTHER SYSTEM OFF THE WEST COAST EARLY NEXT WEEK, NOW  
SHOWING A CLOSED UPPER LOW LINGER OFFSHORE RATHER THAN AN OPEN  
WAVE RUSHING INLAND AS IT SHOWED LAST NIGHT. BASED ON THESE  
FACTORS, THE FORECAST DURING DAYS 6-7 WAS BASED PRIMARILY ON A  
BLEND OF THE ECMWF AND THE ECENS/GEFS ENSEMBLE MEANS.  
 
   
..WEATHER HIGHLIGHTS AND HAZARDS
 
 
THE LOW PRESSURE SYSTEM OFF THE NORTHEAST COAST EARLY FRI IS  
EXPECTED TO PRODUCE WIDESPREAD PRECIPITATION FOR NEW ENGLAND. RAIN  
WILL BE LIKELY CLOSE TO THE COAST, WITH SNOW POSSIBLE FOR THE  
INTERIOR. MARGINAL THERMAL PROFILES WILL MAKE THE PRECIPITATION  
TYPE ACROSS NEW ENGLAND HIGHLY SENSITIVE TO THE EVENTUAL TRACK OF  
THE SURFACE LOW. SHOWERS AND THUNDERSTORMS SHOULD INCREASE IN  
COVERAGE ACROSS PORTIONS OF THE SOUTHERN AND CENTRAL PLAINS  
FRI-SAT AHEAD OF THE LEADING PACIFIC SYSTEM. BY SUN-MON, AS THE  
SECOND PACIFIC SHORTWAVE REACHES THE CENTRAL U.S., RAIN AND  
THUNDERSTORMS SHOULD SPREAD EAST INTO THE MISSISSIPPI/OHIO  
VALLEYS, GULF COAST, AND PORTIONS OF THE SOUTHEAST. CONFIDENCE IS  
LOW AS TO THE DEGREE OF MOISTURE RETURN AND THE STRENGTH OF THE  
SURFACE LOW, BUT AT LEAST LOCALLY HEAVY RAIN APPEARS POSSIBLE.  
ACROSS THE WEST, THE PASSAGE OF THESE SYSTEMS WILL BRING A COUPLE  
ROUNDS OF ELEVATION-BASED RAIN/SNOW FROM THE WEST COAST THE GREAT  
BASIN AND ROCKIES. PRECIPITATION MAY INCREASE ONCE AGAIN FOR  
NORTHERN CALIFORNIA EARLY NEXT WEEK AHEAD OF THE NEXT PACIFIC LOW  
PRESSURE SYSTEM.  
 
MEANWHILE, THE MIDWEST WILL SEE THE GREATEST POTENTIAL FOR ABOVE  
AVERAGE TEMPERATURES THROUGH THE MEDIUM RANGE. HIGH TEMPERATURES  
OF 5-15 DEG F ABOVE AVERAGE ARE EXPECTED FRI-SAT, WITH ABOVE  
AVERAGE TEMPERATURES EXPANDING EASTWARD BY SUN-MON.  
 
RYAN  
 
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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