Preliminary Forecasts
Issued by NWS

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FXUS02 KWNH 220540
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
140 AM EDT SUN APR 22 2018

VALID 12Z WED APR 25 2018 - 12Z SUN APR 29 2018

...OVERVIEW AND GUIDANCE PREFERENCES...

MODELS AND ENSEMBLES CONTINUE TO SHOW PERSISTENT TROUGHING IN THE
EAST AND A CLOSED LOW OFF THE CALIFORNIA COAST EVENTUALLY COMING
ASHORE LATE IN THE WEEK INTO NEXT WEEKEND WITH RIDGING IN BETWEEN,
CENTERED OVER THE ROCKIES. A LEAD AND TRAILING SYSTEM WILL PUSH
THROUGH THE EAST WED-THU WITH A THIRD ON ITS HEELS FRI-SAT, THOUGH
THERE WAS INCREASED TIMING SPREAD WITHIN THE GUIDANCE -- GFS
GENERALLY QUICKER THAN THE ECMWF/UKMET WITH THE ENSEMBLE MEANS IN
BETWEEN. OPTED TO RELY MORE ON THE ENSEMBLE GUIDANCE WITH TIME TO
HELP MITIGATE FUTURE CHANGES TO FRONTAL TIMING. TO THE WEST,
CLOSED LOW APPEARS MUCH BETTER HANDLED UNTIL ABOUT FRIDAY WHEN
THERE BECOMES A N-S DIFFERENCE IN TRACK (THROUGH OREGON OR INTO
CALIFORNIA PER THE ECMWF VS CANADIAN VS FARTHER SOUTH GFS).
ENSEMBLES WERE CLUSTERED NEARER TO THEIR DETERMINISTIC PARENT AND
GIVEN THE MULTI-DAY CHANGES A POSITION IN BETWEEN THE ECMWF/GFS
ENSEMBLE MEANS OFFERED A PRUDENT POSITION, TAKING THE UPPER LOW
THROUGH NORTHERN CALIFORNIA INTO SE OREGON NEXT WEEKEND.


...WEATHER/THREATS HIGHLIGHTS...

EXITING LEAD AND TRAILING UPPER/SFC LOWS WILL SPREAD RAINS THROUGH
THE NORTHEAST AND THEN THROUGH THE SOUTHEAST NEXT WED-FRI WITH
ANOTHER ROUND WITH THE THIRD SYSTEM NEXT FRI/SAT BEFORE THE FRONT
EXITS THE NORTHEAST BY SUNDAY. TEMPERATURES WILL GENERALLY BE
BELOW AVERAGE WITH THE EXCEPTION OF MAINE.

IN THE WEST, UPPER RIDGING WILL ENSURE WELL ABOVE AVERAGE
TEMPERATURES (+10 TO +20F ABOVE CLIMO) WITH SOME RECORDS POSSIBLE
UNTIL THE CLOSED LOW FINALLY PUSHES INLAND. PRECIPITATION WILL
GRADUALLY INCREASE ALONG THE COAST OF NORTHERN CALIFORNIA INTO
OREGON LATE IN THE WEEK THEN THROUGH THE NORTHERN SIERRAS INTO THE
GREAT BASIN WITH AMOUNTS DEPENDING ON THE TRACK OF THE UPPER LOW.
FAVOR THE CONSENSUS SLOWER THAN THE GFS BY NEXT SUNDAY WHICH WOULD
KEEP MOST/ALL OF THE PRECIPITATION WEST OF THE DIVIDE THROUGH THE
CENTRAL ROCKIES.

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


FRACASSO


$$




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