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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1529Z Apr 21, 2018)
 
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Abbreviations and acronyms used in this product
 
Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1129 AM EDT SAT APR 21 2018

VALID 12Z TUE APR 24 2018 - 12Z SAT APR 28 2018

...OVERVIEW AND GUIDANCE PREFERENCES...

TROUGHING WILL BE REINFORCED IN THE EASTERN THIRD/HALF OF THE
CONUS NEXT WEEK WHILE RIDGING OVER THE WEST HOLDS AN UPPER LOW OFF
THE COAST. THE MODELS HAVE STRUGGLED WITH THE TRACK OF THE UPPER
LOW AND NORTHERN STREAM FLOW OUT OF CANADA BUT SEEM TO BE HONING
IN ON A BETTER CONSENSUS COMPARED TO 24 HRS AGO. A TREND TOWARD
STRONGER RIDGING ACROSS THE WEST WAS ALSO NOTED AMONG A LARGE
NUMBER OF ENSEMBLE MEMBERS FROM OVERNIGHT. THIS WOULD KEEP THE
UPPER LOW OFF THE CALIFORNIA COAST THROUGH THE WEEK UNTIL NEXT
WEEKEND WHEN IT MAY LIFT NORTHEASTWARD TOWARD THE CA/OR BORDER. A
BLEND OF RECENT DETERMINISTIC GUIDANCE, INCLUDING THE 00Z
ECMWF/UKMET/GFS OFFERED A GOOD STARTING POINT DESPITE SOME
DIFFERENCES IN STRENGTH/TIMING OF A FEW OF THE EASTERN SYSTEMS IN
THE LONGWAVE TROUGH PATTERN. WEIGHTING OF ENSEMBLE MEANS (00Z
ECENS/06Z GEFS) WAS BOOSTED LATER IN THE FORECAST PERIOD TO
ACCOUNT FOR INCREASING UNCERTAINTY SURROUNDING THE UPPER LOW OFF
THE WEST COAST, AND WITH THE AMPLITUDE OF EASTERN U.S. TROUGHING.
COULD NOT NECESSARILY RULE ANY ONE RUN OUT GIVEN THE MULTI-DAY
SHUFFLINGS.


...WEATHER/THREATS HIGHLIGHTS...

EXITING LEAD UPPER/SFC LOW WILL SPREAD RAINS THROUGH THE
MID-ATLANTIC EARLY IN THE PERIOD. MODELS SHOW A FAIR AMOUNT OF
SPREAD AS TO HOW HEAVY RAINS WILL BE, WITH SOME GUIDANCE (00Z
ECMWF/ECENS ALONG WITH A NUMBER OF GEFS MEMBERS) SUGGESTING AT
LEAST SOME POTENTIAL FOR A BAND OF HEAVIER RAINS ACROSS PORTIONS
OF THE CENTRAL OR NORTHERN MID-ATLANTIC, LIKELY THE RESULT OF A
DEFORMATION BAND NORTHWEST OF THE LOW. GENERALLY LIGHTER AMOUNTS
ARE EXPECTED INTO NEW ENGLAND AS THE LOW RIDES UP THE COAST ON
THURSDAY. TRAILING SYSTEMS WILL SPREAD LIGHT RAIN OR MAYBE SOME
WET SNOW THROUGH THE GREAT LAKES AS WEAKER SHORTWAVES SLIP
SOUTHEASTWARD IN THE BROAD CYCLONIC FLOW. TEMPERATURES WILL 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.
PRECIPITATION MAY HOLD OFFSHORE UNTIL NEXT WEEKEND (OR AT LEAST
LATE FRIDAY) WITH THE ENSEMBLE CONSENSUS MOSTLY INTO COASTAL
OREGON BUT ALSO INTO THE SIERRAS AS THE COLD FRONT SHOULD FINALLY
COME ASHORE.

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/RYAN