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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1526Z Apr 16, 2015)
 
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Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1126 AM EDT THU APR 16 2015

VALID 12Z SUN APR 19 2015 - 12Z THU APR 23 2015

...OVERVIEW AND GUIDANCE EVALUATION...

ATMOSPHERIC SHUFFLING IN THE MEDIUM RANGE WILL TREND TOWARD A
CUTOFF/CLOSED LOW IN THE GREAT LAKES REGION ALONG WITH A MORE
PROGRESSIVE UPPER LOW DIVING INTO THE CENTRAL WEST COAST. THE
MODELS/ENSEMBLES HAVE BEEN MUCH MORE STABLE OVER THE PAST SEVERAL
RUNS THAN IN PREVIOUS DAYS... WITH ONLY THE SMALLER DETAIL
DIFFERENCES REMAINING. RECENT GFS/ECMWF AND GEFS/ECENS MEANS RUNS
OFFER GOOD CLUSTERING THROUGH ABOUT NEXT TUE/WED WITH A SOMEWHAT
COMPLICATED FRONTAL STRUCTURE PROGRESSING EASTWARD. BY THEN...
STRENGTHENING UPPER RIDGING IN NW CANADA WILL FORCE A SPLIT FLOW
IN THE NORTHEAST PACIFIC/GULF OF ALASKA. THIS WILL SEND AN UPPER
LOW SOUTHEASTWARD TOWARD CALIFORNIA TOWARD THE END OF THE
PERIOD/THURSDAY. ENSEMBLES ARE IN GOOD AGREEMENT ON THIS
SCENARIO... BUT NOT ON THE QPF. GFS/GEFS MEMBERS MOSTLY HEAVIER
THAN THE ECMWF/EC MEMBERS. TRAJECTORY--FROM THE NW--LIMITS THE
PRECIP POTENTIAL TO BEGIN WITH BUT STRENGTH OF THE UPPER LOW
ITSELF SHOULD COMPENSATE. EITHER WAY... RAIN WILL BE WELCOME IN
SOUTHERN CALIFORNIA AS IT HAS NOT RAINED IN MUCH OF THAT AREA IN
ABOUT 6 WEEKS. BACK EAST... UPPER LOW SHOULD BE IN NO HURRY TO
EXIT EASTWARD LATE NEXT WEEK WITH THE FLOW BEING SO BLOCKY.


...SENSIBLE WEATHER HIGHLIGHTS...

WET PATTERN IN THE CENTRAL/SOUTHERN/EASTERN STATES LATE THIS
WEEKEND INTO EARLY NEXT WEEK AHEAD OF THE MULTI-FRONTAL SYSTEM
THAT SHOULD COALESCE NEAR THE CENTRAL LAKES AND WRAP UP AS THE
UPPER LOW DEEPENS NEAR LAKE SUPERIOR. MILD AIR SHOULD PUSH NORTH
AND EASTWARD BUT MAY TAKE ITS TIME EAST OF THE APPALACHIANS.
TRIPLE POINT LOW IS STILL FORECAST TO DEVELOP OFF THE MID-ATLANTIC
COAST AND SPLIT OFF FROM THE MAIN FRONT AROUND TUESDAY... FOCUSING
MORE PRECIP INTO EASTERN NEW ENGLAND BEFORE THE WHOLE SYSTEM MOVES
OUT TO SEA. GREAT LAKES REGION SHOULD REMAIN RATHER COOL AND
CLOUDY/SHOWERY AS THE UPPER LOW SITS AND SPINS BETWEEN HUDSON BAY
AND MICHIGAN. TEMPERATURES MAY SUPPORT SNOW SHOWERS ESPECIALLY AT
NIGHT. TEMPS WILL RUN ABOUT 10-15F BELOW CLIMO.

WESTERN AREAS WILL MODERATE IN TIME ESPECIALLY WEST OF THE DIVIDE
AS HEIGHTS RISE AND RIDGING BUILDS EASTWARD. SFC HIGH IN THE
PLAINS WILL KEEP TEMPS NEAR OR JUST BELOW CLIMO. ALONG THE WEST
COAST... FRONT SHOULD APPROACH THE REGION LATE TUE INTO WED WITH
THE ENSEMBLES STILL FOCUSING PRECIP ON COASTAL OREGON INITIALLY
AND THEN FARTHER SOUTH INTO CALIFORNIA ON THURSDAY. FARTHER
EAST... FRONT WILL HANG UP THROUGH FLORIDA AND THE GULF WHICH WILL
KEEP WET WEATHER AROUND FOR MIDWEEK AND RETURN FLOW WILL
EVENTUALLY INCREASE PRECIP THROUGH TEXAS WED-THU.


FRACASSO