Prognostic Meteorological Discussion
Issued by NWS

000
FXUS02 KWBC 251601
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1200 PM EDT WED APR 25 2018

VALID 12Z SAT APR 28 2018 - 12Z WED MAY 02 2018

MODELS AND ENSEMBLES THIS MORNING CONTINUE TO AGREE WITH A GENERAL
PATTERN SHIFT TOWARD TROUGHING IN THE WESTERN U.S. AS AN AMPLIFIED
TROUGH LIFTS OUT OF THE EASTERN U.S. DURING THE WEEKEND BEFORE
STRONG RIDGING BECOMES FIRMLY ESTABLISHED ACROSS THE CENTRAL U.S.
EARLY NEXT WEEK.  THE MAIN UNCERTAINTY REMAINS TO BE OVER THE
WESTERN U.S. EARLY NEXT WEEK REGARDING THE DEGREE OF SEPARATION
BETWEEN A DIGGING UPPER-LEVEL TROUGH NEAR CALIFORNIA AND A BROADER
UPPER TROUGH FARTHER TO THE NORTH.  THE GFS HAS BEEN MAINTAINING
MORE OF A CLOSED-OFF UPPER LOW SOLUTION COMPARED WITH THE ECMWF.
YESTERDAY`S 12Z ECMWF SHOWED A SOLUTION COMPARABLE TO THE GFS BUT
THE 00Z ECMWF REVERTED TO A FLAT ZONAL ORIENTED SHEARED TROUGH.
THE 00Z ECMWF HOWEVER...SHOWED AN AMPLIFIED POSITIVELY-TILTED
TROUGH...WHICH IS QUITE DIFFERENT FROM ITS DETERMINISTIC
SOLUTION...AND IS COMPARABLE TO THE GEFS.  A BLEND OF 55% THE 00Z
EC MEAN/ECMWF WITH 45% 06Z GEFS/GFS WAS USED TO HANDLE THE DAYS 6
AND 7 SEA-LEVEL PRESSURE AND WIND FIELDS.

OVER THE NORTHERN HIGH PLAINS...THE GFS CONTINUES TO SHOW A
STRONGER CYCLONE IN THE VICINITY SUNDAY INTO MONDAY COMPARED WITH
THE ECMWF.  OVER THE EASTERN U.S...A STRONGER SURFACE LOW MORE
COMPARABLE TO THE GFS SOLUTIONS IS USED AS THE LOW LIFTS OUT INTO
SE CANADA DURING THE WEEKEND.  MORE ENSEMBLE MEAN SOLUTIONS THAN
NORMAL ARE INCLUDED TO CREATE DAYS 3-5 WPC GRID FIELDS.

IN TERMS SENSIBLE WEATHER...ENSEMBLE AGREEMENT IS STRONG IN A
RATHER AMPLIFIED TROUGH/RIDGE PATTERN THAT WILL BRING MUCH ABOVE
AVERAGE TEMPERATURES TO THE EAST FOR THE FIRST COUPLE DAYS OF MAY.
THE WEST WILL SEE UNSETTLED WEATHER WITH MOSTLY LIGHT TO MODERATE
RAIN AND HIGH ELEVATION SNOW BUT LOWERING SNOW LEVELS WITH TIME AS
HEIGHTS FALL AND COOLER TEMPERATURES FILTER IN. AREAS TO THE NORTH
OF THE UPPER LOW TRACK (OREGON TO IDAHO TO MONTANA) STAND TO SEE
THE MOST PRECIPITATION THIS WEEKEND INTO EARLY NEXT WEEK. HIGH
PRESSURE TO THE EAST WILL ALLOW MOISTURE TO FLOW NORTHWARD FROM
THE WESTERN GULF THROUGH THE SOUTHERN PLAINS WHERE CONVECTION WILL
BE LIKELY ONCE THE FRONT GETS EAST OF THE FOOTHILLS. THE EAST WILL
THEN DRY OUT NEXT WEEK WITH HARDLY ANY PRECIPITATION EAST OF ABOUT
I-65 (INDIANA TO ALABAMA).


KONG/FRACASSO


ASSOCIATED WPC MEDIUM RANGE FORECASTS OF 500 MB HEIGHTS...SURFACE
SYSTEMS...WEATHER GRIDS...QUANTITATIVE PRECIPITATION FORECASTS
(QPF)...AND WINTER WEATHER OUTLOOK SNOW/SLEET PROBABILITIES CAN BE
FOUND AT...

http://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
http://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
http://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
http://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
http://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4


$$