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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1550Z Oct 26, 2014)
 
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EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1150 AM EDT SUN OCT 26 2014

VALID 12Z WED OCT 29 2014 - 12Z SUN NOV 02 2014

...OVERVIEW AND UNCERTAINTY ASSESSMENT...

UPPER PATTERN WILL TREND TOWARD INCREASED AMPLIFICATION BY LATE
THIS WEEK INTO THE WEEKEND AS THE REMNANTS OF TROPICAL STORM 'ANA'
BECOME EMBEDDED WITHIN THE FLOW OUT OF THE NORTHEAST PACIFIC
MIDWEEK. ADDITIONAL ENERGY WITH ORIGINS IN THE BERING SEA WILL
BRING A MORE SUBSTANTIAL FRONT INTO THE WEST LATE THIS WEEK AS THE
LONGWAVE UPPER TROUGH PUSHES INTO THE INTERIOR WEST. ENSEMBLE
AGREEMENT IS NEAR OR BETTER THAN AVERAGE THOUGH TIMING DIFFERENCES
REMAIN. IN THE EAST... AS THE LEAD/INITIAL TROUGHING GETS
REINFORCED BY TRAILING NORTHERN STREAM ENERGY OUT OF CANADA... A
BAROCLINIC ZONE SHOULD MAINTAIN ITSELF JUST OFF THE EAST COAST.
SHOULD THE PATTERN REMAIN AT LEAST SOMEWHAT PROGRESSIVE... SAID
ENERGY SHOULD PROMOTE CYCLOGENESIS JUST OUTSIDE THE 40N/70W
BENCHMARK. HOWEVER... THE DETERMINISTIC MODELS CONTINUE TO OFFER
MANY SOLUTIONS IN RECENT RUNS WHICH DIMINISHES CONFIDENCE.

...MODEL PREFERENCES...

A BLEND AMONG THE 00Z GFS/GEFS MEAN AND ECMWF/ECENS MEAN OFFERED A
GOOD STARTING POINT TO THE FORECAST FOR THE END OF THE WEEK
/WED-FRI/. 06Z GFS/GEFS NUDGED SLIGHTLY AWAY FROM THE BETTER 00Z
CLUSTERING BUT STILL LIE WITHIN THE TOTAL ENSEMBLE SPREAD. BY NEXT
WEEKEND.. DIFFERENCES AMONG THE MODELS INCREASES SHARPLY IN THE
EAST AS THE ECMWF AND MANY OF ITS ENSEMBLE MEMBERS FORECAST A
SLOWER/SHARPER/DEEPER TROUGH AXIS IN THE EAST. THE ENSEMBLES HAVE
TRENDED A BIT QUICKER TO BRING IN THE TROUGH INTO THE WEST WHILE
MAINTAINING THE RIDGE AMPLITUDE DOWNSTREAM OVER THE CENTRAL
STATES... SO WE ARE STILL RELUCTANT TO BITE ON THE SLOWER
ECMWF-LED SOLUTION IN THE SOUTHEAST. NO CLEAR TREND EXISTS AND
THERE IS A LOT OF 00Z/12Z CYCLE OSCILLATION. RECENT VERIFICATION
HAS SHOWN THE ECMWF AND EVEN THE EC MEAN TO BE TOO SLOW WITH
FEATURES OVER THE CONUS... SO WILL CONTINUE A COMPROMISE BETWEEN
THE QUICKER GEFS MEAN AND THE SLOWER ECENS MEAN IN THE EAST BY
SAT-SUN.

...SENSIBLE WEATHER HIGHLIGHTS...

IN THE WEST... WHAT STARTS OUT AS A WINDY AND WET BUT MILD PACIFIC
FLOW WITH EMBEDDED STRONG SOUTH AND SOUTHEAST WIND BURSTS AT THE
COAST AND WINDWARD COASTAL RANGES IS FOLLOWED BY SIGNIFICANT
HEIGHT FALLS AND THE ARRIVAL OF THE POLAR JET AND MODIFIED
MARITIME POLAR AIRMASS. INITIAL 'ATMOSPHERIC RIVER' SET-UP IN THE
PACIFIC NORTHWEST COAST AND NORTHERN DIVIDE... IN PART THE RESULT
OF REMNANT MOISTURE AND ENERGY FROM 'ANA'... SHOULD SLOWLY SINK
SOUTHEASTWARD AS THE COLD FRONT MOVES EASTWARD FRI-SAT... LOSING
ITS TROPICAL CONNECTION. MODEST QPF AROUND 1 INCH/24 HRS SHOULD
SLIDE FROM N TO S /WA TO OR TO N CA AND THE SIERRAS/ DURING THE
PERIOD.

FOR THE NORTHERN ROCKIES AND ADJACENT HIGH PLAINS... WIDESPREAD
DOWNSLOPE CONDITIONS ARE EXPECTED WITH NOTABLY HIGHER WIND
SPEEDS... PERIODS OF HIGH CLOUDS AND RAPIDLY FLUCTUATING AMBIENT
AIR TEMPERATURES. LITTLE IN THE WAY OF RAINFALL IS EXPECTED ASIDE
FROM THE WESTERN SLOPES OF THE NORTHERN DIVIDE WHERE THE MID-LEVEL
WARM ADVECTION IN ASSOCIATION WITH REMNANT 'ANA' MID-LEVEL
MOISTURE MIGRATES EASTWARD.

POST-FROPA IN THE EAST... A SURGE OF COOLER/DRIER CANADIAN AIR
WILL REACH THE ATLANTIC COAST ON THU-FRI. AN ALBERTA CLIPPER...
REINFORCING THE COOLER/DRIER AIRMASS... SHOULD SPREAD THE DRIER
AIRMASS ACROSS THE GREAT LAKES... NORTHEAST... AND ULTIMATELY THE
EASTERN HALF OF THE CONUS BY DAY 6. ENOUGH MOISTURE IN ADVANCE OF
THE CLIPPER COULD SUPPORT SOME LIGHT RAIN OR SNOW SHOWERS IN THE
NORTHEAST WELL AWAY FROM THE COASTAL PLAIN. THE CANADIAN SURFACE
HIGH BUILDING INTO THE MIDWEST SAT SHOULD PROVIDE A NOTABLE DROP
IN DEW POINTS FOR THE SOUTHEAST AND MOST OF FLORIDA... POSSIBLY
DROPPING TO NEAR 40F ALONG THE I-20 AND I-10 CORRIDORS.


FRACASSO/VOJTESAK