Preliminary Forecasts
Issued by NWS

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FXUS02 KWNH 230540
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
139 AM EDT MON APR 23 2018

VALID 12Z THU APR 26 2018 - 12Z MON APR 30 2018

...OVERVIEW AND GUIDANCE PREFERENCES...

RELOADING TROUGHING IN THE EAST MAY RELENT BY NEXT WEEK AS AN
UPPER LOW OFF THE CALIFORNIA COAST SLOWLY BUT SURELY MEANDERS
INLAND BY THE WEEKEND. THE ENSEMBLES REMAIN RATHER STEADY IN THIS
LONGWAVE EVOLUTION BUT RECENT GFS (12Z/18Z) RUNS WERE STILL
QUICKER THAN MOST OR EVEN ALL OF THE ENSEMBLES THROUGHOUT THE
PERIOD. OPTED TO RELY ON THE SLOWER AND LARGER CONSENSUS OF THE
12Z ECMWF/UKMET/CANADIAN WITH SUPPORT FROM THE 12Z ECMWF ENSEMBLE
MEAN WHILE THE 18Z GEFS MEAN WAS QUICKER BUT NOT AS QUICK AS THE
GFS. BY THE WEEKEND, THE ECMWF/CANADIAN MAY BE TOO DEEP/SLOW WITH
THE EASTERN TROUGH LIFTING OUT AND AS SUCH TRENDED TOWARD THE
ECMWF ENSEMBLE MEAN WHICH WAS JUST A BIT SLOWER THAN THE GEFS
MEAN. IN THE WEST, STILL PREFERRED TO TAKE THE UPPER LOW INTO SE
OREGON THEN EASTWARD INTO ID AND SW MT BY NEXT MONDAY BUT WITH LOW
CONFIDENCE GIVEN THE ENSEMBLE SPREAD. UPSTREAM FLOW OUT OF THE
NORTH EAST PACIFIC BECOMES QUITE UNCERTAIN BY THE WEEKEND AS THE
GFS/GEFS ALLOW NORTHERN STREAM ENERGY TO SLIDE EAST-SOUTHEASTWARD
TOWARD THE PAC NW OR AT LEAST BRITISH COLUMBIA WHILE THE OTHER
ENSEMBLES KEEP IT FARTHER NORTH. PREFER TO LET THE UPPER RIDGE
OVER IDAHO AND BRITISH COLUMBIA STAY DOMINANT ENOUGH (HAND-IN-HAND
WITH A SLOWER UPPER LOW) TO PREVENT SIGNIFICANT HEIGHT FALLS PER
THE GEFS.


...WEATHER/THREATS HIGHLIGHTS...


UNSETTLED WEATHER DUE TO THE EASTERN TROUGH WILL MAINTAIN A
PERSISTENT BUT NON-CONTINUOUS CHANCE OF LIGHT TO MODERATE RAIN IN
THE EAST FROM THURSDAY INTO THE WEEKEND BEFORE THE FRONT EXITS THE
NORTHEAST BY SUNDAY. TEMPERATURES WILL GENERALLY BE BELOW AVERAGE
BUT TRENDING BACK TO MORE SEASONABLE VALUES NEXT WEEK.

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 FRIDAY INTO SATURDAY THEN THROUGH THE REST OF THE PAC
NW INTO THE NORTHERN ROCKIES. SNOW LEVELS WILL BE HIGH TO START
BUT GRADUALLY LOWER AS THE UPPER LOW MOVES THROUGH. RAIN AMOUNTS
SHOULD GENERALLY BE LIGHT TO MODERATE. ENOUGH OF A RETURN FLOW
FROM THE W GULF SHOULD ALLOW FOR GENERALLY LIGHT/SCATTERED RAIN
OVER NEW MEXICO INTO COLORADO AHEAD OF THE WESTERN SYSTEM,
EVENTUALLY EXPANDING INTO THE PLAINS LATE NEXT MONDAY AND BEYOND.

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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