SPC MD 110

By Newsroom America Feeds at 7 Mar 2018

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 Read more



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