Prognostic Meteorological Discussion
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000 FXUS02 KWBC 171445 PMDEPD EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1044 AM EDT THU APR 17 2014 VALID 12Z SUN APR 20 2014 - 12Z THU APR 24 2014 ...OVERVIEW... NORTH AMERICAN FLOW WILL TRANSITION FROM LOW-AMPLITUDE MULTI-WAVE PATTERN TO A STABLE MIGRATORY HIGHER-AMPLITUDE LONG WAVE PATTERN THIS MEDIUM RANGE PERIOD. ...PREFERENCES/UNCERTAINTY ASSESSMENT... THE 17/00Z GEFS/ECENS AND THEIR DETERMINISTIC GUIDANCE WERE IN VERY GOOD AGREEMENT THROUGH DAY 5 FROM THE NORTH CENTRAL PACIFIC EASTWARD INTO THE NORTH CENTRAL PLAINS. EVEN BEYOND DAY 5...THEIR AGREEMENT UPON THE WAVELENGTH WITH RESPECT TO LONGITUDE...MADE FOR VERY MINIMAL DIFFERENCE IN THE MASS FIELDS FROM WEST COAST TO EAST COAST. BY THURSDAY MORNING (24/12Z_DAY7)...A 50/50 BLEND OF THE GEFS/ECENS COULD BE USED WITHOUT MUCH REGRET FOR THE NORTHERN HALF OF THE CONTINENTAL DIVIDE AND DOWNSTREAM OVER THE EASTERN THIRD OF THE LOWER 48. ABOVE AVERAGE CONFIDENCE IN OTHER WORDS. THE NORTH PACIFIC OCEAN DETAILS THAT ARE SLOWLY EVOLVING BUT SHOWING MUCH BETTER RUN-TO-RUN CONTINUITY CONTINUE TO REVOLVE AROUND THE DAY 4-5 PERIOD (22/00Z-12Z) WITH THE 500MB TROUGH AXIS SWEEPING INSIDE INVOF 130W. THE DETERMINISTIC GFS/ECMWF AND TO SOME EXTENT...THE DETERMINISTIC 17/00Z CANADIAN ALLOW FOR A MODERATE SHORTWAVE TO BREAK OFF THE PARENT CUTOFF CIRCULATION AND MIGRATE NORTHEASTWARD INTO COASTAL WASHINGTON...BEFORE REROUTING THE BULK OF THE DYNAMICS AND MID-LEVEL ENERGY SOUTHWARD...DIRECTING AN INLAND STRIKE ALONG THE NORTH COAST OF CALIFORNIA INTO THE BAY AREA ON TUESDAY MORNING. ONLY THE 17/00Z UKMET ALLOWS THE CUTOFF TO REMAIN FAR ENOUGH OFFSHORE TO HAVE THE OLYMPIC PENINSULA AND PORTIONS OF LOWER COLUMBIA RIVER BASIN COMPLETELY MISS OUT--WITH RESPECT TO--THE LEADING EDGE OF THIS DYNAMIC SYSTEM. OVERALL...THE DOWNSTREAM RESPONSE TO THE EVOLVING/AMPLIFYING STABLE WAVELENGTH IN THE WESTERN HALF OF THE CONTINENT LEADS TO MID-LEVEL RIDGE FORMATION AND WESTERN ATLANTIC COASTAL TROUGH. THERE IS GOOD AGREEMENT WITH THE TIMING/AMPLITUDE AND EMBEDDED DETAILS OF THIS EASTERN MULTI-WAVE TROUGH SWEEPING OFFSHORE OF THE EAST COAST INTO DAY 6. THE EVENTUAL CONSOLIDATION OF A SURFACE LOW.---TIED TO A MID-LEVEL SHORTWAVE MIGRATING ALONG THE US/CANADIAN BORDER--INCLUDES THE MIGRATION OF A A COMPACT CLOSED MID-LEVEL CIRCULATION OFF THE GA/NE FL COAST NORTHEASTWARD ALONG THE GULF STREAM AND INTO THE WESTERN ATLANTIC. THE MID-LEVEL RIDGE SWEEPS THE LAST REMNANTS OF THE LOW-AMPLITUDE MULTI-WAVE PATTERN INTO THE CANADIAN MARITIMES AND NORTHWESTERN ATLANTIC. ...SENSIBLE WEATHER HIGHLIGHTS... THE CUTOFF LOW ENTERING THE NORTH COAST OF CALIFORNIA WILL LIKELY BECOME THE PRIMARY WEATHER HIGHLIGHT THROUGH TIME ACROSS THE SIERRA...GREAT BASIN AND ROCKIES. AHEAD OF THIS SYSTEM...LEE SIDE CYCLOGENESIS AND AN AMPLIFYING MID-LEVEL RIDGE...SUGGESTS A VERY BROAD AND DEEPENING LAYER OF EAST TO SOUTHEAST UPSLOPE FLOW SURGING INTO THE MT/WYO PORTION OF THE NORTHERN HIGH PLAINS AND ALONG THE NORTHERN THIRD OF THE CONTINENTAL DIVIDE. THE DEVELOPING CYCLONE GRADUALLY SPREADS A BROAD OCCLUSION ACROSS MUCH OF THE MISSOURI VALLEY BASIN BY PERIOD`S END...WITH POCKETS OF DIURNAL CONVECTION DEVELOPING ACROSS A SHALLOW...HIGHLY-MODIFIED CANADIAN AIRMASS BOUNDARY AND LEE TROUGH FROM THE BLACK HILLS SOUTHWARD INTO THE PERMIAN BASIN. WHAT WILL CHARACTERIZE THIS FRONTAL BOUNDARY...IS THE LACK OF LOW-LEVEL GULF MOISTURE TRANSPORT ALONG AND AHEAD OF IT. IN THIS ANTICIPATED PATTERN...A DRY/VERY WARM GREAT BASIN-4 CORNERS AIRMASS WILL PERIODICALLY SPILL DOWNWIND AND DOWNHILL ACROSS THE CENTRAL AND SOUTHERN HIGH PLAINS...LEADING TO BREEZY/WINDY CONDITIONS AND ISOLATED DRYLINE-TYPE...BUT SLOW-MOVING CONVECTIVE ELEMENTS ALONG THE MIDDLE THIRD OF THE RIO GRANDE VALLEY NORTHWARD INTO THE COLORADO FRONT RANGE. DOWNSTREAM... BY DAY 5-6...VERY WARM TEMPERATURE ARE EXPECTED OVER THE PLAINS WITH SOME HIGHS APPROACHING LEVELS THAT WILL BE 15F-20F ABOVE NORMAL. DAY 4-5...THE MULTI-WAVE PATTERN OVER THE EASTERN THIRD OF THE NATION...A COMBINATION OF NORTHERN AND SOUTHERN STREAM ENERGY...FEATURES A BAND OF SIGNIFICANT RAINFALL POTENTIAL FROM THE SOUTH CENTRAL OK/TX PLAINS NORTHEASTWARD TO THE MIDWEST AND GREAT LAKES. THE CONSOLIDATION OF THE FRONT WITH THE AFOREMENTIONED MID-LEVEL DISTURBANCE ALONG THE US/CANADIAN BORDER AND GA/NE FL COASTAL LOW MAY ALLOW FOR SOME LINGERING LIGHT PRECIPITATION...AND MID-LEVEL CLOUDINESS OVER NEW ENGLAND...PRIOR TO THE WARMUP ASSOCIATED WITH THE MID-LEVEL RIDGE MIGRATING IN FROM THE SOUTHWEST...DAY 6. VOJTESAK $$

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