Preliminary Forecasts
Issued by NWS

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FXUS02 KWNH 300522
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
121 AM EDT TUE JUN 30 2015

VALID 12Z FRI JUL 03 2015 - 12Z TUE JUL 07 2015

THE 29/12Z ECENS...NAEFS AND GEFS MEANS SERVED AS THE BASELINE FOR
THIS MORNING`S NATIONAL FORECAST --- AND MAINTAIN A PROGRESSIVE
MID-LEVEL PATTERN ACROSS SOUTHERN CANADA FROM PACIFIC COAST TO
ATLANTIC COAST. THE 29/12Z DETERMINISTIC GFS/ECMWF WERE REASONABLE
SOLUTIONS ALOFT ON SUNDAY (DAY 5) ACROSS SOUTH CENTRAL CANADA WITH
THE NEXT MIGRATORY TROUGH AND FRESH CANADIAN AIRMASS INTRUSION
INTO THE UPPER MISSOURI VALLEY AND UPPER GREAT LAKES (BY DAY 6).
IN THE GREAT LAKES...THE DETERMINISTIC ECMWF IS THE STRONGER
SOLUTION AND ACCEPTABLE --- THOUGH THE NATIONAL FORECAST BLEND
WENT WITH MORE OF A 50/30/20 BLEND RESPECTIVELY OF THE THREE
AFOREMENTIONED MEANS (BY 6/00Z).

A `FLATTER` UPPER-LEVEL RIDGE AXIS WEST OF THE DIVIDE --- DOES NOT
APPRECIABLY CHANGE THE SENSIBLE WEATHER PATTERN --- AS 500MB
HEIGHTS REMAIN AT/ABOVE 582DM FOR NEARLY THE ENTIRE MEDIUM RANGE
PERIOD EXCEPT FOR THE IMMEDIATE PACIFIC COAST LINE BETWEEN 40N AND
48 N LATITUDES. THE NOMINAL HEIGHT FALLS ALONG THE WEST COAST
SERVE TO TEMPER THE DRY HEAT WITH A MARINE LAYER INTRUSION.

DOWNSTREAM...THE CHALLENGES ARE SUBTLE AND CENTER ON THE MEDIUM
RANGE PRECIPITATION DISTRIBUTIONS ACROSS THE PLAINS STATES.

THE 29/12Z DETERMINISTIC GFS/ECMWF FORECAST THE CORE OF THE
ANTICYCLONE TO REMAIN STRONG --- IN THE 594DM RANGE DURING THE
LATTER HALF OF THE FORECAST PERIOD. AND THESE DETERMINISTIC
SOLUTIONS ARE USEFUL --- IN ADDING DETAIL TO THE FORECAST FOR
CONTINUED HEAT TO SPREAD EASTWARD INTO THE COLORADO/NEW MEXICO
PORTION OF THE ROCKY MOUNTAINS. WHAT CONFIDENCE IS ADDED BY THE
ECMWF/GFS WITH RESPECT TO ANTICYCLONIC FLOW AND MID-LEVEL STEERING
CURRENTS--- IS QUICKLY `SUBTRACTED` --- WITH RESPECT TO HEAVY
RAINFALL POTENTIAL. THE CHALLENGE BEING --- PROJECTING THE
TRAJECTORY AND LIFE-CYCLE OF ACTIVE `CONVECTIVE CLUSTERS`
MIGRATING AWAY FROM THE SYNOPTIC-SCALE FLOW ALONG AND WEST OF 100W
LONGITUDE.

VOJTESAK









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