838  
FXUS02 KWBC 251926  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
325 PM EDT THU APR 25 2019  
 
VALID 12Z SUN APR 28 2019 - 12Z THU MAY 02 2019  
   
..OVERVIEW AND GUIDANCE PREFERENCES
 
 
AN EXPANSIVE REX BLOCK ACROSS THE NORTH/CENTRAL PACIFIC, EXTENDING  
FROM HAWAII TO ALASKA, WILL SUPPORT A DOWNSTREAM MEAN UPPER TROUGH  
CENTERED ACROSS THE NORTHERN ROCKIES THROUGH THE EXTENDED FORECAST  
PERIOD. A PERSISTENT UPPER LOW CENTERED WEST OF HUDSON BAY, AND  
SLOWLY RETROGRADING THROUGH THE PERIOD, WILL SUPPORT SOUTHWARD  
TRANSPORT OF CHILLY POLAR AIR INTO THE NORTH CENTRAL U.S. FARTHER  
EAST, THE SUBTROPICAL RIDGE IS EXPECTED TO GRADUALLY EXERT ITS  
INFLUENCE NORTHWARD INTO THE SOUTHEAST AND SOUTHERN MID-ATLANTIC  
EARLY NEXT WEEK.  
 
PREFERRED A MULTI-MODEL BLEND APPROACH INITIALLY DURING DAYS 3-5  
(SUN-TUE), INCORPORATING THE 00Z ECMWF/GFS/UKMET/CANADIAN. THIS  
BLEND LEANED TOWARD THE SLOWER SOLUTIONS WITH THE SOUTHERN STREAM  
UPPER LOW APPROACHING SOUTHERN CALIFORNIA LATE SUN-MON THAT  
CONTINUED TO SHOW SOME TIMING DIFFERENCES. WAS NOT AS SLOW AS THE  
ECMWF/CANADIAN BUT NOT AS FAST AS THE GFS WHICH ENDED UP NEAR THE  
00Z UKMET. AS IT MOVED THROUGH AZ EARLY TUESDAY, REMOVED THE GFS  
FROM THE BLEND AS BOTH 00Z/06Z RUNS BECAME QUICKER THAN THE REST.  
IN TURN, FAVORED THE SLOWER 06Z FV3-GFS WHICH CLUSTERED NEAR THE  
UKMET. EXITING LOW THROUGH THE NORTHEAST AND INCOMING WEAKENING  
UPPER LOW OVER MONTANA WERE HANDLED WELL BY THE CONSENSUS BLEND TO  
START.  
 
DURING DAYS 6-7 (WED-THU) MODEL CONSENSUS HAS IMPROVED A BIT THAT  
THE ARRIVAL OF ADDITIONAL SHORTWAVE ENERGY INTO THE PACIFIC  
NORTHWEST EARLY-MID NEXT WEEK SHOULD SERVE TO FURTHER AMPLIFY A  
BROAD UPPER TROUGH AXIS CENTERED OVER THE NORTHERN GREAT  
BASIN/NORTHERN ROCKIES, WITH A CONSOLIDATED AREA OF SHORTWAVE  
ENERGY PERHAPS LIFTING OUT INTO THE NORTHERN PLAINS BY THU. GEFS  
AND ECMWF ENSEMBLE MEANS SHOWED GENERAL AGREEMENT ON THIS IDEA  
DESPITE INCREASING SPREAD, BUT THE SHAPE OF THE WESTERN TROUGH AND  
UPSTREAM RIDGE/TROUGH COUPLET OUT OF THE NORTHEASTERN PACIFIC INTO  
THE PAC NW DIFFERED BETWEEN THOSE MEANS, AS WELL AS THE NORTHERN  
EXTENT OF THE UPPER HIGH ALONG THE SOUTHEAST COAST. PREFERRED TO  
SIDE MORE WITH THE ECMWF ENSEMBLE MEAN BY NEXT THU AS IT HAD A  
MORE COHERENT SURFACE LOW LIFTING TOWARD THE GREAT LAKES WHICH WAS  
THE BROAD IDEA OF THE DETERMINISTIC MODELS (THE GEFS MEAN HAD TOO  
MUCH HIGH PRESSURE). KEPT THE 00Z ECMWF IN FOR SOME ADDED DETAILS  
AS IT FIT THIS IDEA BEST.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
SHOWERS AND PERHAPS A FEW THUNDERSTORMS ARE EXPECTED TO ACCOMPANY  
THE LOW PRESSURE SYSTEM MOVING FROM THE OHIO VALLEY/LOWER GREAT  
LAKES TO THE NORTHEAST ON SUN. AFTER THAT, THE FOCUS SHIFTS TO THE  
CENTRAL U.S., WHERE A PERSISTENT STALLED FRONTAL BOUNDARY ALONG  
WITH A FEW PASSING UPPER SHORTWAVES WILL FOCUS MULTIPLE ROUNDS OF  
SHOWERS AND THUNDERSTORMS, WITH THE POTENTIAL FOR AREAS OF HEAVY  
RAINFALL. THE STRONGEST SIGNAL IN THE GUIDANCE FOR HEAVY RAIN WAS  
SEEN FROM PORTIONS OF THE SOUTHERN/CENTRAL PLAINS TO THE  
MID-MISSISSIPPI VALLEY FROM MON THROUGH THE MIDDLE OF NEXT WEEK,  
WITH QPF GUIDANCE SUGGESTING THE POTENTIAL FOR MULTI-INCH RAINFALL  
TOTALS OVER THE COURSE OF A FEW DAYS. ON THE NORTHERN FRINGE OF  
THIS AREA OF PRECIPITATION IN THE CENTRAL U.S. SUFFICIENT COLD AIR  
MAY BE IN PLACE TO SUPPORT SOME SNOW ON SUN ACROSS PORTIONS OF THE  
NORTHERN PLAINS. A SECOND ROUND OF POTENTIAL SNOW OR RAIN/SNOW MIX  
WILL BE POSSIBLE ACROSS PORTIONS OF THE NORTHERN HIGH PLAINS  
TUE-WED. FARTHER WEST, LOWERING HEIGHTS AND THE PASSAGE OF  
MULTIPLE SHORTWAVES WILL GENERATE RAIN AND MOUNTAIN SNOW FOR  
PORTIONS OF THE GREAT BASIN AND CENTRAL/NORTHERN ROCKIES THROUGH  
THE PERIOD. SEVERE WEATHER WILL BE AN ALMOST DAILY POSSIBILITY IN  
THE WARM SECTOR OF THE SOUTHERN PLAINS FROM MON-THU, BUT THE FOCUS  
FOR NOW IS AROUND TUESDAY WHERE THE STORM PREDICTION CENTER HAS  
OUTLINED A 15% AREA ACROSS MUCH OF OKLAHOMA INTO NORTH CENTRAL  
TEXAS.  
 
BELOW AVERAGE TEMPERATURES ARE EXPECTED FROM SUN INTO NEXT WEEK  
FROM THE NORTHERN ROCKIES TO THE GREAT LAKES. THE GREATEST  
ANOMALIES ARE EXPECTED SUN-WED FROM THE NORTHERN ROCKIES TO THE  
NORTHERN HIGH PLAINS WHERE HIGH TEMPERATURES MAY BE 10-20 DEG F  
BELOW AVERAGE (MAINLY IN THE 40S). WARMING TEMPERATURES ARE  
EXPECTED ACROSS THE SOUTHEAST AND SOUTHERN MID-ATLANTIC BY EARLY  
NEXT WEEK AS THE SUBTROPICAL RIDGE BUILDS NORTHWARD. HIGHS ACROSS  
THESE AREAS MAY REACH 10 TO 15 DEG ABOVE AVERAGE TUE-THU.  
TEMPERATURE SPREAD IN THE ENSEMBLES REMAINED QUITE LARGE EAST OF  
THE APPALACHIANS AND ALONG THE FRONTAL BOUNDARY TO THE WEST AS THE  
DIFFERENCE BETWEEN COOL NORTHEASTERLY FLOW OFF THE COLD ATLANTIC  
WATERS VS A WARM DOWNSLOPING SOUTHWESTERLY FLOW TRANSLATES INTO  
50S VS 80S FOR HIGH TEMPERATURES IN THE MID-ATLANTIC. HIGHER  
CONFIDENCE EXISTED AT LEAST A COUPLE HUNDRED MILES SOUTH OR NORTH  
OF THE FORECAST FRONTAL POSITION FOR WARMER OR COOLER TEMPERATURES  
COMPARED TO AVERAGE, RESPECTIVELY.  
 
FRACASSO/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  
 
HAZARDS:  
- HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL/SOUTHERN PLAINS, THE  
MIDDLE/LOWER MISSISSIPPI VALLEY, THE GREAT LAKES, AND THE OHIO  
VALLEY, SUN-THU, APR 28-MAY 2.  
- HEAVY SNOW ACROSS PORTIONS OF THE NORTHERN ROCKIES, SUN, APR 28.  
- HEAVY SNOW ACROSS PORTIONS OF THE NORTHERN/CENTRAL ROCKIES  
MON-WED, APR 29-MAY 1.  
- HEAVY SNOW ACROSS PORTIONS OF THE NORTHERN PLAINS (BIGHORN  
MOUNTAINS), TUE-WED, APR 30-MAY 1.  
- SEVERE WEATHER ACROSS PORTIONS OF THE MIDDLE MISSISSIPPI VALLEY,  
THE LOWER MISSISSIPPI VALLEY, AND THE SOUTHERN PLAINS, TUE, APR 30.  
- FLOODING POSSIBLE ACROSS PORTIONS OF THE GREAT LAKES AND THE  
SOUTHERN PLAINS.  
- FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE  
MISSISSIPPI VALLEY, THE NORTHERN AND SOUTHERN PLAINS, THE  
TENNESSEE VALLEY, THE GREAT LAKES, THE NORTHERN ROCKIES, THE  
NORTHERN GREAT BASIN, THE OHIO VALLEY, AND THE NORTHEAST.  
- FLOODING LIKELY ACROSS PORTIONS OF THE NORTHERN GREAT BASIN.  
 
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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