MD 1813 CONCERNING HEAVY SNOW FOR PORTIONS OF NORTHWEST PA AND WESTERN NY
Mesoscale Discussion 1813 NWS Storm Prediction Center Norman OK 0701 PM CST Mon Dec 25 2017 Areas affected...Portions of northwest PA and western NY Concerning...Heavy snow Valid 260101Z - 260500Z SUMMARY...Heavy lake-effect snowfall with rates in excess of 2 in/hr will continue downwind of Lake Ontario through the overnight. Heavy lake-effect snowfall with rates of 1-2 in/hr (locally greater) will continue for a few hours downwind of Lake Erie before intensities decrease after 3Z. DISCUSSION...Latest radar/satellite observations and ground-truth via reports indicate snowfall rates in excess of 1 in/hr occurring downwind of Lake Ontario and Lake Erie. These heavy intensities are a result of favorable low-level westerly/southwesterly trajectories as well as cold advection over the warm waters of the lakes, which is promoting steep low-level lapse rates in excess of 7 C/km near Lake Erie and 8 C/km near Lake Ontario (per objective analysis and the 00Z BUF radiosonde). While the KTYX radar remains inoperable due to motor failure -- with regional radar likely overshooting the heart of the lake-effect band downwind of Lake Ontario -- recent GOES-16 satellite data suggests a stout band of relatively cold cloud top temperatures (e.g., less than -35C) setting up over Lake Ontario. Snowfall rates are expected to exceed 2 in/hr over the next several hours and through the overnight as this narrow band moves onshore over portions of Oswego, Lewis, and Jefferson Counties. The continuation of heavy snow is also supported by CAM solutions, which have consistently indicated heavy snowfall through tonight (despite limited assimilation of radar data over the area). Snowfall rates are expected to decrease after 3Z downwind of Lake Erie as steep low-level lapse rates shift away from the area, low-level trajectories become less favorable, and low-level flow weakens. A few isolated lightning strikes remain possible, as the heavy convective snow bands interact with wind farms and communication towers. The greatest potential will exist near the shorelines, where low-level flow is strongest. ..Elliott.. 12/26/2017 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...ALY...BGM...BUF...CTP...CLE... LAT...LON 42098066 42417993 42687921 43577661 43787620 43747550 43557503 43437503 43257518 42317815 41917938 41867997 41868062 42098066
from SPC Mesoscale Discussions http://bit.ly/1QKryCA
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