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MESOSCALE DISCUSSION 0200
NWS STORM PREDICTION CENTER NORMAN OK
0508 PM CST THU MAR 18 2004
AREAS AFFECTED...CENTRAL AND ERN PA...FAR NRN DE...AND CENTRAL NJ
CONCERNING...HEAVY SNOW
VALID 182308Z - 190415Z
SNOW WILL OVERSPREAD S-CENTRAL TO SERN PA FROM THE WEST BETWEEN
19/01Z AND 04Z...AND CENTRAL/S-CENTRAL NJ BETWEEN 04-06Z. A PERIOD
OF 1-2"/HR SNOWFALL RATES WILL LIKELY TRANSLATE ACROSS THE AREA LATE
THIS EVENING THROUGH THE OVERNIGHT PERIOD.
CURRENT OBSERVATIONAL TRENDS ARE CONSISTENT WITH MODEL GUIDANCE
SHOWING RAPID INCREASE IN VERTICAL MOTION FIELDS WITH PROGRESSIVE
TROUGH OVER SRN GREAT LAKES REGION. STRONG UPPER TROPOSPHERIC DRYING
EVIDENT ON WV IMAGERY OVER IND/WRN OH AS 90-100KT 500MB JET DIGS
INTO WRN PORTION OF TROUGH. SHARPENING FLOW FIELDS HAVE BEGUN TO
ENHANCE PVA/UPPER DIVERGENCE WITH COOLING IR TOPS ACROSS SERN
OH/SWRN PA. RAPID INCREASE IN CG LIGHTNING STRIKES HAS OCCURRED
ACROSS THE UPPER OH RIVER VALLEY REGION SINCE 22Z.
HEAVY SNOW AXIS SHOULD DEVELOP ACROSS PA SOUTH OF I-80...NEAR TRACK
OF PROGGED 700MB LOW CENTER SHOWN BY 18Z ETA. UPSTREAM RAINFALL
RATES IN CMH AREA OF 0.1-0.2"/HR SHOULD SUPPORT A SEVERAL HOUR
PERIOD OF 1-2"/HR SNOW ACROSS THE DISCUSSION AREA LATER THIS EVENING
THROUGH TONIGHT...PARTICULARLY AS MID-LEVEL LAPSE RATES STEEPEN
RAPIDLY TONIGHT. ALTHOUGH 23Z SFC TEMPERATURES ARE IN THE UPPER 30S
TO LOWER 40S...STRONG DYNAMIC COOLING ALOFT COMBINED WITH DIABATIC
COOLING IN BOUNDARY LAYER WITH PRECIPITATION ONSET SHOULD RAPIDLY
BRING TEMPERATURES DOWN TO NEAR FREEZING. HEAVY...WET NATURE OF
SNOWFALL MAY POSE A HAZARD TO TREES AND POWER LINES WHERE HEAVIER
ACCUMULATIONS TAKE PLACE.
..BANACOS.. 03/18/2004
