Prognostic Meteorological Discussion
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000 FXUS02 KWBC 281600 PMDEPD EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1059 AM EST SAT FEB 28 2015 VALID 12Z TUE MAR 03 2015 - 12Z SAT MAR 07 2015 THE 28/00Z ECENS...NAEFS AND/OR GEFS MEAN CONTINUE TO DEPICT A SUBTLE `PROGRESSIVENESS` TO THE FLOW---FOCUSING ON AN ACTIVE LONG-WAVE TROUGH MIGRATION ACROSS THE LOWER 48 AND A PATTERN SHIFT IN THE EASTERN PACIFIC THIS FORECAST PERIOD. THE DETERMINISTIC GUIDANCE DEPICTIONS OF THE FLOW ALOFT---THROUGH FRIDAY EVENING...SUPPORT THE MEANS AND WOULD BE ACCEPTABLE---ALTHOUGH THEIR SURFACE REFLECTIONS NEAREST THE ARCTIC `PORTION` OF THE FRONTAL BOUNDARY IN THE EAST AND OFF THE WEST COAST INVOF 135w LONGITUDE--- LEAVE OUT SOME POTENTIAL DETAIL THAT THE MEANS MAY OVERLY `BROAD BRUSH. ESPECIALLY... ALONG THE WEST COAST...WHERE A POSSIBLE CUTOFF 500MB CIRCULATION IS CURRENTLY DEPICTED IN THE WPC 500MB GRAPHIC---DAY 6-7 TIME FRAME. THE 28/00Z DETERMINISTIC GUIDANCE GENERALLY DEPICTS A LEAD MID-LEVEL WAVE (TUESDAY MORNING) EJECTING OUT OF THE COLORADO FRONT RANGE AND TRACK THIS WAVE NORTHEASTWARD AT 4/00Z TO WEST CENTRAL WISCONSIN IN A RATHER RAPID FASHION (12 HOURS +/- 3HRS). ITS ATTENDANT SURFACE CYCLONE PASSING INVOF SOUTHERN LAKE MICHIGAN---GENERATES A BROAD AREA OF WARM ADVECTION FOR THE LOWER- AND MID-MISSISSIPPI VALLEY---WITH WINTER WEATHER CONDITIONS ACROSS THE CENTRAL PLAINS AND UPPER MISSISSIPPI AND UPPER GREAT LAKES. THE BREATH AND DEPTH OF THE 850MB WINDS IS IMPRESSIVE---AND WITH THIS BEING AN EARLY MARCH FORECAST...THE BAROCLINICITY AND LOW-LEVEL LIFT SUGGESTS `SPRING` CONDITIONS. WHERE MODEL DIFFERENCES REMAIN---CONCERN THE DEPTH OF THE CYCLONE AS IT RACES NORTHEASTWARD THROUGH THE ST LAWRENCE VALLEY ON WEDNESDAY AND THE TRAJECTORIES OF THE ARCTIC AIRMASS---THE REAL DEEP COLD AIR VERSUS THE SHALLOW LEADING EDGE. THE DETERMINISTIC 28/00Z ECMWF WOULD BE THE WEAKER SURFACE SOLUTION WITH THIS LEAD SHORTWAVE`S SURFACE REFLECTION AND LIKELY BE A MORE-SEPARATED SOLUTION BETWEEN `FRONTAL` DEPICTION---WEST AND EAST OF THE APPALACHIANS AROUND THE 5/12Z TIME FRAME. NOT SURE THE MEANS WOULD BE MUCH MORE THAN A WASHED OUT TEMPERATURE `WINDOW` 200 MILES EITHER SIDE OF THE FRONT. APPRECIABLE WARM ADVECTION IS EXPECTED TO MIGRATE EAST AND NORTHEASTWARD ACROSS THE OHIO VALLEY...NEW ENGLAND TO THE ATLANTIC COAST---IE JUST ABOUT EVERYWHERE EAST OF 90W LONGITUDE ON WEDNESDAY. NOT ONLY BECAUSE OF THE DEEP SURGE OF FAST-MOVING LOW-LEVEL SOUTH-SOUTHWESTERLIES AHEAD OF THE FRONT---BUT ALSO WITH THE OPERATIONAL GUIDANCE AND ITS GOOD AGREEMENT AT 250 MILLIBARS. THE UPPER-LEVEL SUPPORT SETTING UP BEHIND THE LEAD WAVE (PER THE 28/00Z CANADIAN-GFS-ECMWF) IS QUITE IMPRESSIVE---WITH 110+ KNOTS OF SOUTHWEST FLOW EXTENDING FROM NORTHEAST TEXAS TO MAINE (AT/AROUND 5/18Z). WITH THIS UPPER SUPPORT PARALLEL TO THE COLD FRONT AND ITS LOW-LEVEL COLD ADVECTION---THE INTERACTION APPEARS TO "SLOW DOWN" THE COLD FRONT. TO ME ANYWAY...THE 250MB JET AXIS SERVES AS THE BROAD BAROCLINIC ZONE BELOW 700 MILLIBARS WHERE A BROAD REGION OF MESOSCALE INTERACTIONS HAVE ROOM TO DEVELOP. WHAT BECOMES OF THE LOW-LEVEL PATTERN ACROSS THE SOUTH APPEARS TO BE THE MOST INTRIGUING---WITH AN `UNDER-GLIDE` SITUATION SETTING UP--- WITH A COLD AND DRY SHALLOW LEADING EDGE OF THE AIRMASS SEEPING SOUTHWARD WITH STRONG UPPER-LEVEL JET TRACKING NORTHEASTWARD ABOVE IT. NORTH OF ABOUT 40 NORTH LATITUDE FROM THE UPPER OHIO VALLEY/DELMARVA NORTHWARD...THE UPPER-LEVEL JET WILL BE MOVING OVER A DEEP LAYER OF COLD BUT DRY AIR ON FRIDAY. THE BRIEF SEQUENCE OF WHAT SPRING OFFERS ALONG AND AHEAD OF THE UPPER-LEVEL JET AXIS---WILL BE ABRUPTLY REPLACED WITH THE `NEW` CANADIAN AIRMASS THAT SPREADS TO THE GULF OF MEXICO---DEEP INTO THE SUBTROPICS BY EARLY DAY 6. THE DETERMINISTIC RUNS DO CARRY A PARENT SURFACE REFLECTION---BY THEN LOCATED INVOF LABRADOR. THIS `NEW` AIRMASS AND ITS 1036-MB+ SURFACE HIGH SURGES SOUTHWARD---WELL SOUTH OF THE RIO GRANDE AND NORTHERN GULF OF MEXICO. BY SOME ACCOUNTS---BY FRIDAY MORNING (DAY 5). VOJTESAK $$

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