Mesoscale Discussion 0015
NWS Storm Prediction Center Norman OK
0200 PM CST Fri Jan 11 2019
Areas affected...East-central Missouri...far west-central Illinois
Valid 112000Z - 120200Z
SUMMARY...Heavy snow is expected over the next several hours, with
up to 1 in/hr rates likely in some spots, especially along the I-70
corridor, including the St. Louis metropolitan area.
DISCUSSION...As a mid-level trough continues to progress across the
Central Plains during the afternoon, the northward advection of a
deep, moist airmass will continue across the region along with
increasing large-scale ascent. Recent Mesoanalysis has indicated
700-500 mb frontogenesis is underway across the area, where an
800-1000 m deep, near-saturated to saturated dendritic layer is
present, fostering the potential for efficient snowfall production.
Latest KEAX and KLSX dual-polarimetric data suggest a transition to
all snow north of a west-east oriented line approximately through
Cass County to Jefferson County in Missouri.
While several locations are above freezing at the surface, 10+F T/Td
spreads and a sub-saturated sfc-850 mb layer suggest that
evaporative cooling with the onset of the initial precipitation will
cool and saturate the lower-level troposphere to foster occasionally
heavy snow, with up to 1 in/hr rates possible in some areas. Latest
high resolution ensemble guidance continues to suggest that the
greatest threat for heavy snow will remain confined in a narrow
corridor across portions of central/eastern Missouri through the
...Please see www.spc.noaa.gov for graphic product...
LAT...LON 38608991 38299021 38249085 38789260 39229373 39589353
39549207 39499078 39148997 38868989 38608991