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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1444Z Apr 17, 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
1044 AM EDT THU APR 17 2014

VALID 12Z SUN APR 20 2014 - 12Z THU APR 24 2014

...OVERVIEW...
NORTH AMERICAN FLOW WILL TRANSITION FROM LOW-AMPLITUDE MULTI-WAVE
PATTERN TO A STABLE MIGRATORY HIGHER-AMPLITUDE LONG WAVE PATTERN
THIS MEDIUM RANGE PERIOD.  

...PREFERENCES/UNCERTAINTY ASSESSMENT...
THE 17/00Z GEFS/ECENS AND THEIR DETERMINISTIC GUIDANCE WERE IN
VERY GOOD AGREEMENT THROUGH DAY 5 FROM THE NORTH CENTRAL PACIFIC
EASTWARD INTO THE NORTH CENTRAL PLAINS. EVEN BEYOND DAY 5...THEIR
AGREEMENT UPON THE WAVELENGTH WITH RESPECT TO LONGITUDE...MADE FOR
VERY MINIMAL DIFFERENCE IN THE MASS FIELDS FROM WEST COAST TO EAST
COAST. BY THURSDAY MORNING (24/12Z_DAY7)...A 50/50 BLEND OF THE
GEFS/ECENS COULD BE USED WITHOUT MUCH REGRET FOR THE NORTHERN HALF
OF THE CONTINENTAL DIVIDE AND DOWNSTREAM OVER THE EASTERN THIRD OF
THE LOWER 48. ABOVE AVERAGE CONFIDENCE IN OTHER WORDS.

THE NORTH PACIFIC OCEAN DETAILS THAT ARE SLOWLY EVOLVING BUT
SHOWING MUCH BETTER RUN-TO-RUN CONTINUITY CONTINUE TO REVOLVE
AROUND THE DAY 4-5 PERIOD (22/00Z-12Z) WITH THE 500MB TROUGH AXIS
SWEEPING INSIDE INVOF 130W. THE DETERMINISTIC GFS/ECMWF AND TO
SOME EXTENT...THE DETERMINISTIC 17/00Z CANADIAN ALLOW FOR A
MODERATE SHORTWAVE TO BREAK OFF THE PARENT CUTOFF CIRCULATION AND
MIGRATE NORTHEASTWARD INTO COASTAL WASHINGTON...BEFORE REROUTING
THE BULK OF THE DYNAMICS AND MID-LEVEL ENERGY
SOUTHWARD...DIRECTING AN INLAND STRIKE ALONG THE NORTH COAST OF
CALIFORNIA INTO THE BAY AREA ON TUESDAY MORNING. ONLY THE 17/00Z
UKMET ALLOWS THE CUTOFF TO REMAIN FAR ENOUGH OFFSHORE TO HAVE THE
OLYMPIC PENINSULA AND PORTIONS OF LOWER COLUMBIA RIVER BASIN
COMPLETELY MISS OUT--WITH RESPECT TO--THE LEADING EDGE OF THIS
DYNAMIC SYSTEM.

OVERALL...THE DOWNSTREAM RESPONSE TO THE EVOLVING/AMPLIFYING
STABLE WAVELENGTH IN THE WESTERN HALF OF THE CONTINENT LEADS TO
MID-LEVEL RIDGE FORMATION AND WESTERN ATLANTIC COASTAL TROUGH. 
THERE IS GOOD AGREEMENT WITH THE TIMING/AMPLITUDE AND EMBEDDED
DETAILS OF THIS EASTERN MULTI-WAVE TROUGH SWEEPING OFFSHORE OF THE
EAST COAST INTO DAY 6. THE EVENTUAL CONSOLIDATION OF A SURFACE
LOW.---TIED TO A MID-LEVEL SHORTWAVE MIGRATING ALONG THE
US/CANADIAN BORDER--INCLUDES THE MIGRATION OF A A COMPACT CLOSED
MID-LEVEL CIRCULATION OFF THE GA/NE FL COAST NORTHEASTWARD ALONG
THE GULF STREAM AND INTO THE WESTERN ATLANTIC. THE MID-LEVEL RIDGE
SWEEPS THE LAST REMNANTS OF THE LOW-AMPLITUDE MULTI-WAVE PATTERN
INTO THE CANADIAN MARITIMES AND NORTHWESTERN ATLANTIC.

...SENSIBLE WEATHER HIGHLIGHTS...
THE CUTOFF LOW ENTERING THE NORTH COAST OF CALIFORNIA WILL LIKELY
BECOME THE PRIMARY WEATHER HIGHLIGHT THROUGH TIME ACROSS THE
SIERRA...GREAT BASIN AND ROCKIES. AHEAD OF THIS SYSTEM...LEE SIDE
CYCLOGENESIS AND AN AMPLIFYING MID-LEVEL RIDGE...SUGGESTS A VERY
BROAD AND DEEPENING LAYER OF EAST TO SOUTHEAST UPSLOPE FLOW
SURGING INTO THE MT/WYO PORTION OF THE NORTHERN HIGH PLAINS AND
ALONG THE NORTHERN THIRD OF THE CONTINENTAL DIVIDE. THE DEVELOPING
CYCLONE GRADUALLY SPREADS A BROAD OCCLUSION ACROSS MUCH OF THE
MISSOURI VALLEY BASIN BY PERIOD'S END...WITH POCKETS OF DIURNAL
CONVECTION DEVELOPING ACROSS A SHALLOW...HIGHLY-MODIFIED CANADIAN
AIRMASS BOUNDARY AND LEE TROUGH FROM THE BLACK HILLS SOUTHWARD
INTO THE PERMIAN BASIN. WHAT WILL CHARACTERIZE THIS FRONTAL
BOUNDARY...IS THE LACK OF LOW-LEVEL GULF MOISTURE TRANSPORT ALONG
AND AHEAD OF IT.

IN THIS ANTICIPATED PATTERN...A DRY/VERY WARM GREAT BASIN-4
CORNERS AIRMASS WILL PERIODICALLY SPILL DOWNWIND AND DOWNHILL
ACROSS THE CENTRAL AND SOUTHERN HIGH PLAINS...LEADING TO
BREEZY/WINDY CONDITIONS AND ISOLATED DRYLINE-TYPE...BUT
SLOW-MOVING CONVECTIVE ELEMENTS ALONG THE MIDDLE THIRD OF THE RIO
GRANDE VALLEY NORTHWARD INTO THE COLORADO FRONT RANGE.

DOWNSTREAM...   
BY DAY 5-6...VERY WARM TEMPERATURE ARE EXPECTED OVER THE PLAINS
WITH SOME HIGHS APPROACHING LEVELS THAT WILL BE 15F-20F ABOVE
NORMAL.

DAY 4-5...THE MULTI-WAVE PATTERN OVER THE EASTERN THIRD OF THE
NATION...A COMBINATION OF NORTHERN AND SOUTHERN STREAM
ENERGY...FEATURES A BAND OF SIGNIFICANT RAINFALL POTENTIAL FROM
THE SOUTH CENTRAL OK/TX PLAINS NORTHEASTWARD TO THE MIDWEST AND
GREAT LAKES. THE CONSOLIDATION OF THE FRONT WITH THE
AFOREMENTIONED MID-LEVEL DISTURBANCE ALONG THE US/CANADIAN BORDER
AND GA/NE FL COASTAL LOW MAY ALLOW FOR SOME LINGERING LIGHT
PRECIPITATION...AND MID-LEVEL CLOUDINESS OVER NEW ENGLAND...PRIOR
TO THE WARMUP ASSOCIATED WITH THE MID-LEVEL RIDGE MIGRATING IN
FROM THE SOUTHWEST...DAY 6.  

VOJTESAK