Its coming boys!
Mesoscale Discussion 110
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Mesoscale Discussion 0110
NWS Storm Prediction Center Norman OK
0747 AM CST Wed Mar 07 2018
Areas affected...eastern PA...central and northern NJ
Concerning...Heavy snow
Valid 071347Z - 071745Z
SUMMARY...Heavy hourly snowfall rates of 1-2 inches per hour are
likely to develop later this morning. Locally higher rates (2+
inches/hour) are possible primarily after noon local time within the
frontal snow band and/or convectively augmented bursts.
DISCUSSION...13Z surface analysis places a sub 1000mb developing low
60 mi ESE of WAL. Temperatures are in the 32-34 degrees F range
from the northern part of Chesapeake Bay to NYC.
The 12Z IAD RAOB from Dulles, VA showed a temperature profile
subfreezing except immediately near the surface. The 500mb
temperature was -25.5 C. Looping water-vapor imagery indicates the
mid-level trough was located over the central Appalachians as of
13-14Z. As this disturbance approaches the region, strong mid-level
ascent associated with the trough (leading to significant columnar
cooling in the mid-levels) coupled with the northern periphery of a
plume of steep 700-500mb lapse rates (7-8 degrees C per km) will
combine and result in pockets of weak buoyancy and upright
convection. Convection will increase in coverage from northern DE
northeast towards the NYC area during the late morning into the
early afternoon. Models indicate the development of strong
frontogenetic forcing will begin primarily around or after 17Z. As
the deep-layer large-scale ascent strengthens and becomes vertically
juxtaposed with the intensifying frontogenesis, hourly precipitation
rates will markedly increase from around 0.10 inch to 0.10-0.25
inch.
Marginal surface temperatures will effectively result in a
significant concern/limiting factor for the spatial coverage of 1+
inch/hour rates farther southeast across portions of NJ as a sharp
rain/snow precipitation-type gradient becomes established. Eastern
PA into northern NJ will likely maintain snow as the precipitation
type and heavy snowfall rates will focus in a narrow corridor from
the north part of PHL north-northeast into northern NJ. Higher
elevations will likely attain the coldest temperatures (due to the
low-level thermal profile cooling as elevation increases from sea
level to 1-2 kft) and the most intense accumulation/hourly rates.
..Smith.. 03/07/2018
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...OKX...PHI...BGM...
LAT...LON 40197573 41297505 41527459 41407422 41187402 40637420
40077524 40047555 40197573