Preliminary Forecasts
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FXUS02 KWNH 280622
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
121 AM EST FRI NOV 28 2014

VALID 12Z MON DEC 01 2014 - 12Z FRI DEC 05 2014


...MODEL PREFERENCES...
A BLEND OF THE 27/12Z ECENS AND 27/18Z GEFS LOOKED VERY REASONABLE
THROUGH DAY 7 ACROSS THE LOWER 48---WITH THEIR DETERMINISTIC
GUIDANCE IN RATHER GOOD AGREEMENT UNTIL DAY 6. FOR DAYS 3-5...BOTH
DEVELOP A VERY COLD CORE OF ARCTIC AIR (IN THE M27C-M30C RANGE)
AND MIGRATE THE CORE ACROSS THE UPPER GREAT LAKES REGION AND
ACROSS WESTERN ONTARIO. THE SAME APPEARS TRUE OF THEIR STRONG
SURFACE SURFACE HIGH SOLUTIONS---ALLOWING SOME COLD AIR TO SEEP
WEST OF THE DIVIDE---AND INTO THE PACIFIC
NORTHWEST---PRE-DAY3---THEN ALLOWING SURFACE RIDGING AND ITS
COLD/DRY AIRMASS TO SPREAD THE PREVAILING AIRMASS ACROSS A LARGE
PORTION OF THE LOWER 48.

AT DAY 6...THE 27/18Z AND 28/00Z GFS TAKES THE FAST LEAD IN
LOW-LEVEL WARM ADVECTION AND PRECIPITATION `BREAKOUT` FROM
NORTHEAST TEXAS TO SOUTHERN ILLINOIS. THIS PRECIPITATION---SHOULD
IT DEVELOP---WOULD BE WITHIN THE BROADENING WARM SECTOR---AHEAD OF
A SURFACE CYCLONE EJECTING OUT OF THE UPPER MISSOURI VALLEY. I
CAN`T ARGUE AGAINST THIS SOLUTION...AND WITH THE PACIFIC JET IN A
FAST-WESTERLY MODE---CAN`T DISCOUNT THE GEFS---ONLY BECAUSE (ITS
BIAS) IS TO BE A FASTER SOLUTION VERSUS THE ECENS.

...UNCERTAINTY ASSESSMENT...
IN SIMPLE TERMS...THE DETERMINISTIC ECMWF/GFS DIFFERENCES ALONG
THE WEST COAST STILL SEEM RELATED TO THE SAME ENERGY TRANSFER
ISSUES---THE MODELS HAVE BEEN DEALING WITH ALONG 160W (NEAR THE
ALEUTIANS) AND NORTHEAST OF HAWAI`I FOR MORE THAN A WEEK NOW. SAME
MODEL ISSUES EMERGING NORTHWEST OF HAWAI`I NEAR THE DATELINE.

MUCH OF THE DIFFERENCE CONCERNS AN ACTIVE PACIFIC JET THAT HAS
GENERATED A SERIES OF VERY INTENSE SHORTWAVES OFF THE COAST OF
JAPAN. ANOTHER KEY FEATURE OF THE PATTERN IS THE ANCHORING
UPPER-LEVEL TROUGH IN THE SOUTHERN BERING SEA. ONCE THESE SYSTEMS
APPROACH THE DATELINE---THEY BEGIN TO SHEAR OUT---SENDING SOME
ENERGY INTO THE SOUTHEAST BERING SEA---SENDING A WEAKENING VERSION
OF THE WAVE INTO THE EAST CENTRAL PACIFIC ALONG 45N LATITUDE TO
BECOME PART OF THE BROAD TROUGH ALONG THE WEST COAST. AND LAST BUT
NOT LEAST...DIG SOME OF THE ENERGY INTO THE SUBTROPICS...AND ALLOW
SOME REFLECTION AT THE SURFACE...TO MAKE A GRADUAL APPROACH
TOWARDS HAWAI`I FROM THE NORTHWEST IN THE FORM OF A COLD FRONT
AND/OR ORGANIZED SERIES OF WEAK SHEAR LINES. IF THE ANCHORING LOW
WERE IN ITS `NORMAL` LOCATION---THE GULF OF ALASKA---THEN THERE
WOULD BE A VERY CLEAN SET OF WAVE CYCLONES MIGRATING ACROSS THE
NORTH PACIFIC---AND THE SHEARING WOULD BE OCCURRING A GOOD 15-20
DEGREES EAST OF THE CURRENT LONGITUDE.

...SENSIBLE WEATHER HIGHLIGHTS...
1040MB CANADIAN SURFACE HIGH MIGRATES ACROSS THE UPPER MS VALLEY
DAYS 3-4---RESULTING IN COLD CONDITIONS FOR A LARGE PORTION OF THE
MISSOURI VALLEY AND MISSISSIPPI VALLEY. A FAST-MOVING UPPER-LEVEL
WESTERLY FLOW MAY PROVIDE SOME LOCALIZED LIGHT SNOWFALLS FROM THE
WYOMING/COLORADO BORDER---EASTWARD INTO THE CENTRAL MIDWEST.

UNSETTLED WEATHER ALONG THE WEST COAST...WITH PERIODS OF
PRECIPITATION DIRECTED ACROSS CALIFORNIA AND OREGON.
INITIALLY...PRECIPITATION FOCUS WILL BE ALONG A SLOW-MOVING COLD
FRONT FOR DAY 3---FOLLOWED BY A SURFACE CYCLONE THAT MEANDERS OFF
THE CALIFORNIA COAST DURING DAYS 4-5. THIS CYCLONE EVENTUALLY
MOVES INLAND AROUND DAY 6-7---AHEAD OF A MID-LEVEL TROUGH
MIGRATING ACROSS THE EAST PACIFIC AND INSIDE OF 130W.

VOJTESAK

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