Prognostic Meteorological Discussion
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000 FXUS02 KWBC 050442 PMDEPD 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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