Preliminary Forecasts
Issued by NWS

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FXUS02 KWNH 050442
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1241 AM EDT WED AUG 05 2015

VALID 12Z SAT AUG 08 2015 - 12Z WED AUG 12 2015

A BLEND OF THE PREVIOUS WPC NATIONAL FORECAST (TEMPS/POPS AND MASS
FIELDS)---ALONG WITH THE 4/12Z ECENS/NAEFS MEANS APPEARS TO VERY
REASONABLY HANDLE THE COMPLEXITY OF THE PATTERN. THE NATIONAL
FORECAST AND PROJECTED FRONTAL PROGRESSIONS LOOK TO BE ON
TRACK---AND RATHER `PROGRESSIVE` FOR A MID-AUGUST AND MID-LATITUDE
NORTH AMERICA.

THE UNUSUAL FLOW PATTERN ALOFT---THE UPPER-LEVEL CYCLONES
ANCHORING EACH COAST---PROVIDE A VERY STEADY STREAM OF NORTHWEST
FLOW OVER THE CENTRAL PORTION OF THE CONTINENT. AND IT`S A LESS
HUMID ONE---THAT DRAPES ACROSS THE MISSOURI/PLATTE VALLEYS AND
DOWNSTREAM TO THE OHIO AND SOUTH CENTRAL APPALACHIANS...THE GREAT
LAKES AND NORTHEAST.

THERE WILL BE NO RELIEF FOR THE SOUTHERN PLAINS WITH THE
UPPER-LEVEL RIDGE MOVING VERY LITTLE DURING THE PERIOD AND THE
WEST COAST SHOULD BE IN AN UNUSUALLY ACTIVE PATTERN ---FOR A
SOUTHWEST FLOW ALOFT IN MID AUGUST. THAT BEING---A HIGHER THAN
NORMAL FREQUENCY OF SHORTWAVE IMPULSES---MIGRATING AHEAD OF THE
PACIFIC FRONTS ROLLING ACROSS THE GULF OF ALASKA AND CANADIAN
ROCKIES THIS FORECAST PERIOD. AND THE WESTERN PERIPHERY OF THE
UPPER-LEVEL ANTICYCLONE---IN MID-AUGUST FORM---WITH AN ACTIVE
MONSOON SWEEPING NORTH-NORTHWESTWARD THROUGH THE UPPER HALF OF THE
RIO GRANDE.

WHAT IS AN IMPRESSIVE OUTCOME OF THE PATTERN---IS HOW NICELY THE
PERSISTENCE AND DURATION OF NORTHWESTERLY MID-LEVEL FLOW OVER THE
MISSOURI VALLEY SPREADS THE MODIFIED CANADIAN AIR SOUTHEASTWARD
THROUGH TIME---AND POOLS THIS AIRMASS INTO THE NORTHEAST QUARTER
OF THE LOWER 48. TEMPERATURES ARE PRACTICALLY A `PERSISTENCE`
FORECAST---AND SEASONAL TO SLIGHTLY BELOW NORMAL.

VOJTESAK













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