Preliminary Forecasts
Issued by NWS

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FXUS02 KWNH 280553
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
152 AM EDT THU MAY 28 2015

VALID 12Z SUN MAY 31 2015 - 12Z THU JUN 04 2015

THE WPC MEDIUM RANGE FORECAST CONTINUED TO FEATURE A SERIES OF
PACIFIC SYSTEMS THAT MIGRATE EASTWARD THROUGH THE NORTHERN US ---
AND FOLLOW A RATHER ZONAL WESTERLY FLOW ALOFT AND STORM TRACK
THROUGH CENTRAL CANADA. THE DE-AMPLIFIED FLOW OVER NORTH AMERICA
REMAINS A KEY COMPONENT OF THE MEDIUM RANGE FORECAST ACROSS THE
LOWER 48 AND SHOULD LIMIT THE EQUATORWARD (SOUTHWARD) MOVEMENT OF
COOLER CANADIAN AIR INTO THE UNITED STATES --- IE VERSUS A
HIGHLY-AMPLIFIED PATTERN.

IN A VERY BROAD DESCRIPTIVE MANNER FOR THIS MEDIUM RANGE PERIOD
--- THE PRECIPITATION AND PRIMARY SENSIBLE WEATHER CHANGES
ASSOCIATED WITH THESE PACIFIC SYSTEMS SHOULD STAY ALONG AND NORTH
OF THE I-80/I-70 CORRIDOR --- ASIDE FROM A LOCALLY ACTIVE DRY-LINE
SCENARIO IN THE SOUTHERN HIGH PLAINS.

THE MEDIUM RANGE FORECAST UNCERTAINTY REMAINS ALONG THE SOUTHERN
END OF THE COLD FRONT THAT MIGRATES THROUGH THE NORTHEAST QUARTER
OF THE NATION ON SUNDAY AND MONDAY---  AND TO WHAT EXTENT --- A
SURFACE WAVE AND MID-LEVEL CIRCULATION CAN HOLD TOGETHER ACROSS
THE LOWER MISSISSIPPI VALLEY DAYS 3-5 --- COMPLETELY DETACHED FROM
THE WESTERLIES RACING ACROSS SOUTHERN CANADA AND THE PACIFIC
TROUGH MIGRATING ACROSS THE NORTHERN ROCKIES.

THE 27/12Z DETERMINISTIC GFS/ECMWF WERE IN BETTER AGREEMENT WITH
THIS MEANDERING SUB-SYNOPTIC SCALE FEATURE AND WERE IMPLEMENTED
---ALONG WITH THEIR ENSEMBLE MEANS ---THROUGH THE ENTIRETY OF THE
WPC MEDIUM RANGE PACKAGE. TO A LESSER EXTENT---THE DETERMINISTIC
GFS WAS UTILIZED BEYOND DAY 5 --- BUT ONLY BECAUSE OF ITS
`INTENSE` SOLUTION IN THE SOUTHEAST WITH THE AFOREMENTIONED
MID-LEVEL DISTURBANCE`S INCORPORATION OF SUBTROPICAL MOISTURE THAT
ORIGINATES IN THE BAHAMAS AND EAST CENTRAL FLORIDA. THE LIFE-CYCLE
OF THIS MID-LATITUDE FEATURE  IS NOT NECESSARILY IN QUESTION (OR
DOUBT) --- FOR THE 27/12Z DETERMINISTIC GUIDANCE (INCLUDING THE
UKMET...CANADIAN...ECMWF...GFS AND EVEN THE DGEX) CARRY THIS
FEATURE. BUT WHAT IS STILL UNCLEAR --- IS THE CIRCULATION`S
MEANDERING NATURE --- AND THE WIDE DISPARITY IN QPF SOLUTIONS FOR
THE SOUTHEASTERN QUADRANT OF THE UNITED STATES. IT`S CERTAINLY A
FEATURE THAT WORTH WATCHING --- AND THOUGHT FOR NOW --- THE MEANS
WERE THE BEST WAY TO HANDLE IT FOR THE DAY 5-7 PERIOD.

VOJTESAK



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