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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1558Z Apr 14, 2014)
 
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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
1158 AM EDT MON APR 14 2014

VALID 12Z THU APR 17 2014 - 12Z MON APR 21 2014

...MODEL/PATTERN OVERVIEW...

TO BEGIN THE PERIOD ON THURSDAY...APRIL 17...A HIGH-AMPLITUDE FLOW
WILL BE IN PLACE WITH A BROAD UPPER TROF SWINGING THROUGH THE
CENTRAL U.S. THIS FEATURE WILL CONSIST OF A SPLIT STREAM WITH THE
SOUTHERN BRANCH OF THE JET SLIDING THROUGH THE CENTRAL PLAINS
WHILE THE OTHER SYSTEM GRADUALLY SHEARS ALONG THE INTERNATIONAL
BORDER. SOUTHWESTERLY FLOW ALOFT WILL CARRY THIS SYSTEM TOWARD THE
NORTH AND EAST WITH AN AREA OF LOW PRESSURE RISING ACROSS THE
OZARKS AND INTO THE MID MS VALLEY EARLY FRIDAY. THE 06Z GFS/00Z
CMC ARE A TAD STRONGER ALOFT WHICH ALLOWS A DEEPER SOLUTION TO
AFFECT THE MS RIVER VALLEY. THE MODELS BEGIN TO DIVERGE ENTERING
THE WEEKEND WITH A POTENTIAL SPLIT IN THE JETS ACROSS THE EASTERN
THIRD OF THE COUNTRY. THE LAST FEW RUNS OF THE GFS ALONG WITH THE
00Z CMC EMPHASIZE THE NORTHERN STREAM WITH THE LATTER BEING MUCH
MORE DEVELOPED WITH A STRONG NEGATIVE TILT INDICATED.
MEANWHILE...THE 00Z ECMWF/UKMET PUT MORE FOCUS ON THE SOUTHERN
STREAM WHICH INDUCES A SURFACE LOW ACROSS THE NORTHERN GULF OF
MEXICO AND EVENTUALLY ALONG THE SOUTHEASTERN U.S. COAST ON
FRIDAY/SATURDAY. THE GLOBAL ENSEMBLE MEANS DEFINITELY ALL SHOW
HINTS AT MODEST DEVELOPMENT ALONG THE EAST COAST SO LEANED IN THIS
DIRECTION FOR THE WPC MEDIUM RANGE PROGS. OVERALL...A MAJORITY OF
THE MODELS DO SHOW AT THE MINIMUM AN INVERTED TROF AXIS ALONG THE
WESTERN ATLANTIC WITH THE MORE AGGRESSIVE SOLUTIONS DEVELOPING AN
AREA OF LOW PRESSURE. AS THIS SYSTEM EVENTUALLY MOVES SLOWLY
OFFSHORE BY LATER IN THE PERIOD...THE PATTERN CONTINUES TO REMAIN
SPLIT IN NATURE ACROSS THE WESTERN/CENTRAL U.S. THE GUIDANCE
DEPICT AN ELONGATED UPPER TROF IN THE VICINITY OF NORTHWESTERN
MEXICO LATE IN THE WEEKEND WHILE THE NORTHERN STREAM REMAINS MUCH
MORE ACTIVE. HOWEVER...IT APPEARS THERE WILL BE AMPLE SEPARATION
BETWEEN THE STREAMS WITH THE NORTHERN BRANCH MAINTAINING A STEADY
FLOW OF SHORTWAVES STRADDLING THE U.S./CANADIAN BORDER. BY EARLY
NEXT WEEK...THE UPPER PATTERN WILL REMAIN WELL DEFINED WITH A
RIDGE ACROSS THE WESTERN U.S. WHILE A TROF ANCHORS THE EASTERN
STATES.

...WPC PREFERENCES...

THE GUIDANCE AVAILABLE WERE IN CLOSE ENOUGH AGREEMENT WITH THE
EXCEPTION OF THE 00Z CMC TO WARRANT A BLEND OF THE 06Z GFS AND 00Z
ECMWF/UKMET THROUGH DAY 4...FRIDAY WITH A BIT MORE EMPHASIS ON THE
06Z GFS/00Z ECMWF SOLUTIONS. MOVING INTO SATURDAY...DECIDED TO
REMOVE THE 06Z GFS FROM THE MIX GIVEN ITS AFOREMENTIONED LACK OF A
SOUTHERN STREAM SYSTEM AFFECTING THE SOUTHEASTERN U.S.
ADDITIONALLY...THE AGGRESSIVE 00Z CMC SEEMED TO BE AN OUTLIER WITH
LITTLE TO NO SUPPORT FROM THE ENSEMBLE MEANS NOR THE SPAGHETTI
PLOTS. WPC LEANED ON A 00Z ECMWF/UKMET SOLUTION ON DAY
5...SATURDAY GIVEN THE REASONABLE HANDLING OF THE DEVELOPMENT OF
LOW PRESSURE ALONG THE SOUTHEASTERN U.S. COAST.
THEREAFTER...ENOUGH SPREAD WITH THE TRACK OF THIS SYSTEM ALONG
WITH DIFFERENCES NOTED UPSTREAM WITHIN THE AMPLIFIED/SPLIT FLOW
REGIME THAT A COMBINATION OF THE 06Z GEFS/00Z ECMWF ENSEMBLE MEANS
WERE UTILIZED THROUGH APRIL 21.

...SENSIBLE WEATHER HIGHLIGHTS...

THE FIRST COUPLE OF DAYS OF THE PERIOD...THURSDAY/FRIDAY...WILL BE
QUITE CHILLY ACROSS THE CENTER OF THE COUNTRY WITH TEMPERATURES 15
TO 20 DEGREES BELOW NORMAL...PARTICULARLY IN THE CENTRAL PLAINS.
THE ACCOMPANYING AREA OF LOW PRESSURE CROSSING THE CO ROCKIES AND
INTO THE SOUTHERN PLAINS WILL SUPPORT AN AREA OF MODERATE/HEAVY
PRECIPITATION ACROSS THE CENTRAL ROCKIES ON THURSDAY. ENHANCED
UPSLOPE FLOW SHOULD AID IN LOCALLY HEAVIER AMOUNTS ALONG THE
FAVORED TERRAIN. GIVEN THE NEGATIVE HEIGHT ANOMALIES IN
PLACE...WINTRY PRECIPITATION MAY BE POSSIBLE ACROSS THE HIGHER
ELEVATIONS. TEMPERATURES SHOULD GRADUALLY MODERATE BY THE WEEKEND
AS THE FLOW BECOMES MORE ZONAL AND WARMER THICKNESSES PREVAIL. AS
THIS SYSTEM MIGRATES EASTWARD...COOLER AND WETTER CONDITIONS ARE
POSSIBLE ACROSS THE CENTRAL/EASTERN GULF COAST AS WELL AS ALONG
THE EASTERN SEABOARD. DEPENDING UPON THE MODEL...IT MAY BE QUITE
AN UNSETTLED PERIOD FROM FRIDAY AND INTO THE WEEKEND.
ELSEWHERE...BUILDING HEIGHTS ACROSS THE WESTERN U.S. SHOULD BRING
ABOVE NORMAL TEMPERATURES TO THE REGION WHICH HAS BEEN THE COMMON
THEME FOR QUITE SOME TIME.


RUBIN-OSTER