Mesoscale Discussion 1813

Issued

Dec 25, 2017, 8:01 PM EST (01:01 UTC)

Expired

Dec 26, 2017, 12:00 AM EST

In force

4 hr

Issued by

the Storm Prediction Center

Counties Cattaraugus County, NY, Cayuga County, NY, Chautauqua County, NY, Erie County, NY, Genesee County, NY, Livingston County, NY, Oneida County, NY, Onondaga County, NY, Ontario County, NY, Oswego County, NY, Seneca County, NY, Wayne County, NY, Wyoming County, NY, Erie County, PA

The Buffalo radar (KBUF), 63 km from the middle of the area, began a volume at 01:02 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

842 
ACUS11 KWNS 260101
SWOMCD
SPC MCD 260101 
NYZ000-PAZ000-OHZ000-260500-

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

Mesoscale Discussions in New York, 2017Mesoscale Discussions in Pennsylvania, 2017Every mesoscale discussion in 2017

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.