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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