Prognostic Meteorological Discussion
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032
FXUS02 KWBC 241615
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1215 PM EDT TUE APR 24 2018

VALID 12Z FRI APR 27 2018 - 12Z TUE MAY 01 2018

...OVERVIEW AND GUIDANCE PREFERENCES...

MODEL GUIDANCE THIS MORNING CONTINUES TO SUPPORT A PATTERN CHANGE
TOWARD TROUGHING IN THE WESTERN U.S. WHILE RIDGING IS INDICATED
FROM THE PLAINS EASTWARD.  HOWEVER...THERE REMAINS NOTABLE
DIFFERENCES REGARDING THE FORMATION/EVOLUTION OF SMALLER SCALE
FEATURES THROUGH THE MEDIUM-RANGE PERIOD.  THE FIRST FEATURE OF
CONCERN IS THE POSSIBILITY OF A LOW PRESSURE WAVE DEVELOPING ALONG
A STALLED FRONT OVER THE SOUTHEAST U.S. DAY 3/FRIDAY.  BOTH THE
GFS AND CANADIAN TAKE THIS LOW JUST OFF THE MID-ATLANTIC AND NEW
ENGLAND ON SATURDAY.  THE ECMWF HAS BEEN THE WEAKEST REGARDING
THIS FEATURE BUT HAS TRENDED TOWARD A MORE DEVELOPED SOLUTION FOR
THE LAST FEW RUNS.  IT APPEARS THAT SOME FORM OF WAVE DEVELOPMENT
IS CALLED FOR OVER THE SOUTHEAST U.S. SINCE THE SYSTEM CURRENTLY
LOCATED IN THE NORTHERN PLAINS APPEARS A BIT ON THE COMPACT SIZE
FOR THE MODELS TO RESOLVE.  THE 06Z GFS SHOWS THE MOST DEVELOPED
SOLUTION BUT ONLY A SMALL PERCENTAGE IS INCORPORATED INTO THE WPC
BLEND...OUT OF RESPECT FOR CONTINUITY.

OVER THE WESTERN U.S...THE GFS CONTINUES TO SHOW THE FORMATION OF
AN UPPER CLOSED LOW NEAR THE CALIFORNIA COAST EARLY NEXT WEEK.  IN
CONTRAST...THE ECMWF REMAINS MUCH FLATTER WITH THIS FEATURE.  THE
06Z GFS AMPLIFIES THIS FEATURE EVEN MORE SO THAN THE 00Z GFS.  THE
GFS SOLUTION IS CONSIDERED AN OUTLIER AT THIS POINT.

THEREFORE...THE WPC MORNING GRID PACKAGE WAS DERIVED MAINLY USING
THE 00Z ECMWF AND EC MEAN WITH ONLY A SMALL PERCENTAGE OF THE 06Z
GFS.

...WEATHER/THREATS HIGHLIGHTS...

MILD TEMPERATURES INITIALLY IN THE WEST LATE THIS WEEK WILL SLIDE
EASTWARD INTO THE PLAINS BY SUNDAY AND INTO THE NORTHEAST NEXT
TUESDAY. 70S WILL BE FAIRLY WIDESPREAD BY NEXT TUESDAY FROM THE
OHIO VALLEY INTO PARTS OF NEW ENGLAND. CONVERSELY, THE WEST WILL
TREND COOLER WITH TIME AS THE UPPER TROUGH SETTLES IN, WITH
WIDESPREAD RAIN AND SOME HIGH MOUNTAIN SNOW TO WA/OR/ID/MT AND
ACROSS NORTHERN CA/NV/UT. FARTHER EAST, RETURN FLOW FROM THE
WESTERN GULF SHOULD BE SUFFICIENT TO SUPPORT MOSTLY
LIGHT/SCATTERED RAIN OVER THE SOUTHERN ROCKIES INTO THE HIGH
PLAINS BY THE WEEKEND/NEXT MONDAY. AREAS THAT STAND TO SEE THE
MOST PRECIPITATION LIE ACROSS SOUTHERN OREGON INTO SOUTHERN
CENTRAL MONTANA JUST TO THE NORTH OF THE UPPER LOW`S TRACK.  OVER
THE SOUTHEAST U.S....THERE IS AN INCREASING CHANCE OF
PRECIPITATION FRIDAY AND SATURDAY AS THE POSSIBILITY OF A FRONTAL
WAVE PASSAGE INCREASES.

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


KONG/FRACASSO


$$





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