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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1551Z Jan 24, 2015)
 
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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
1051 AM EST SAT JAN 24 2015

VALID 12Z TUE JAN 27 2015 - 12Z SAT JAN 31 2015

...OVERVIEW...
THE PERSISTENCE OF AN EASTERN NORTH AMERICAN TROUGH---SETS UP A
MUCH COLDER AND LIGHT WINTRY PRECIPITATION SCENARIO BY PERIOD'S
END FOR THE MIDWEST AND NORTHEAST. IN THE WEST...A MILD
UPPER-LEVEL RIDGE WILL BE ACCENTED BY A PERSISTENT AREA OF LOW
PRESSURE OFF THE COAST OF SOUTHERN CALIFORNIA AND BAJA
CALIFORNIA---WHICH CREATES A SPLIT-FLOW PATTERN ALOFT---ALONG AND
EAST OF THE CONTINENTAL DIVIDE. SUBTLE SENSIBLE WEATHER CHANGES
WILL FOLLOW THE MIGRATORY SHORTWAVE ENERGY EXITING THE AREA OF LOW
PRESSURE EMBEDDED IN THIS SOUTHERN STREAM.

...UNCERTAINTY ASSESSMENT...
THERE IS NOT MUCH MODEL DISAGREEMENT WITH THE KEY SYNOPTIC-SCALE
FEATURES. AT DAY 7...THE 24/00Z ECENS...GEFS AND NAEFS SUPPORT A
DEEP AND STATIONARY UPPER-LEVEL LOW INVOF 60N 80W (CENTRAL HUDSON
BAY) AND BROAD UPPER-LEVEL RIDGE AXIS ALONG THE WEST COAST OF THE
CONTINENT ALONG 130W FROM THE YUKON SOUTHWARD TO NORTHERN
CALIFORNIA.

A 24/00Z FORECAST CYCLE 'PERFECT PROG' AT THE SURFACE WOULD CARRY
A SUB 984MB  SURFACE LOW (DAY 3_27/12Z) THAT MAKES LANDFALL OVER
EASTERN NOVA SCOTIA ON/AFTER 28/12Z (DAY 4). THE TREND FOR THE LOW
TRACK IS TO SWING/ARC IT JUST SOUTHEAST AND NORTHEAST OF THE 40N
70W BENCHMARK BETWEEN DAY 3-4. THE DEFORMATION PRECIPITATION
SHIELD---ACCOMPANYING THIS SURFACE CYCLONE---PRODUCES THE FORECAST
UNCERTAINTY WITH RESPECT TO THE AREAL COVERAGE AND INTENSITY OF
COLD-SECTOR PRECIPITATION.

THE NEXT SENSIBLE 'WEATHER-MAKER'---FOR THE LOWER 48---ORIGINATES
IN THE LOWER COLORADO RIVER BASIN AND TAKES A MIGRATORY PATH
ACROSS UTAH AND WYOMING---IN THE FORM OF A MID-LEVEL WAVE---DAYS
3-4. THE SYSTEM EMERGES OVER THE MIDWEST ON DAY 5 (29/12Z) LOW
INVOF NORTHEAST ILLINOIS. AT THIS TIME SCALE...THE 24/00Z
CANADIAN/ECMWF DETERMINISTIC GUIDANCE AND 24/06Z GFS ARE A
WELL-CLUSTERED CONSENSUS SOLUTION (FOR LOCATION AND DEPTH)---WITH
THE 24/00Z GFS...A WEAKER/SLOWER SOLUTION INVOF THE QUAD CITIES.

ALONG THE WEST COAST...THE SYNOPTIC PATTERN IS A RESIDUAL
'GRAVEYARD' OF DYING MID-LATITUDE NORTH PACIFIC FRONTS ALONG
130W---THE RESULT OF A VERY STABLE...DRY AND MILD...MID-TO
UPPER-LEVEL RIDGE. THE DAY 6-7 'REPLACEMENT' SYSTEM IN THE UPPER
LEVELS---OFF THE COAST OF NORTHERN BAJA---IS A SPLITTING SHORTWAVE
THAT ORIGINATES IN THE NORTH CENTRAL PACIFIC AND SUPER-IMPOSES
ATOP THE 'GRAVEYARD' OF LOWER-LEVEL BAROCLINICITY AND CONVERGENT
AIRFLOW.

...MODEL PREFERENCES...
THOUGHT A BLEND OF THE 24/00Z ENSEMBLE GUIDANCE AND THE 24/00Z
DETERMINISTIC ECMWF...CANADIAN AND 24/06Z GFS WILL WORK FOR THIS
MEDIUM RANGE FORECAST PERIOD.  

...SENSIBLE WEATHER HIGHLIGHTS...
THE DAY 3-5 MID-LEVEL WAVE AND SURFACE CYCLONE MOVING ACROSS THE
INTERMOUNTAIN WEST...MISSOURI VALLEY AND REACHING THE CENTRAL
MIDWEST WILL LIKELY BE THE PRIMARY WEATHER FEATURE IN THE LOWER 48
THIS MEDIUM RANGE PERIOD. ITS EFFECTS...TEMPERING THE WARMTH
BENEATH THE SOUTHERN FLANKS OF THE WESTERN NOAM RIDGE---WITH
CLOUDS AND PERIODS OF SCATTERED PRECIPITATION. THE DEPTH OF THE
SURFACE LOW IN THE MIDWEST MAY PRODUCE A NOTABLE SWATH OF
LIGHT/MODERATE SNOWFALL INTENSITY ALONG THE NORTHERN PERIPHERY OF
ITS LOW TRACK.

THE DAY 3-4 EAST COAST SYSTEM STILL HAS A DEPTH AND TRACK THAT
WILL PRODUCE SOME WRAP-AROUND PRECIPITATION POTENTIAL FOR NEW
ENGLAND---INCLUDING MAINE AND THE MOUNTAINS OF FAR NORTHERN NEW
ENGLAND. THE PRIMARY SENSIBLE WEATHER CHANGE IN THE
NORTHEAST...APPEARS TO BE THE INFLUX OF A COLDER NORTHERLY FLOW.

VOJTESAK