|Mesoscale Discussion 12|
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Mesoscale Discussion 0012
NWS Storm Prediction Center Norman OK
0616 PM CST Sun Jan 07 2018
Areas affected...Portions of eastern IL...IN...and western OH
Valid 080016Z - 080615Z
SUMMARY...Freezing rain rates around 0.05 inch per 3 hours should
occur this evening.
DISCUSSION...A shortwave trough over the central/southern Plains at
00Z will dig southeastward to the lower/mid MS Valley by late this
evening. A low-level warm air advection regime and large-scale
ascent associated with this shortwave trough has encouraged a broad
area of light to moderate precipitation to develop from the Ozarks
northeastward into IL. This precipitation shield is forecast to
shift eastward in tandem with the shortwave trough, and
strengthening of a southwesterly low-level jet appears likely across
eastern IL, IN, and western OH through 06Z.
Surface temperatures across much of IL/IN are above freezing as of
00Z, with the exception of northeastern IL (Chicago metro area),
where light freezing rain is ongoing per multiple surface
observations. A residual dry low-level airmass over IN and western
OH will likely experience substantial wet bulb cooling this evening
as the precipitation shield over MO/IL overspreads this region.
Latest RAP Mesoanalysis suggests the 32F wet bulb temperature is
at/below freezing across nearly all of eastern IL, IN, and western
OH. Warm air advection centered around the 900-850 mb layer will
likely melt frozen hydrometeors aloft, allowing for re-freezing at
the surface through wet bulb cooling processes. Freezing rain rates
around 0.05 inch per 3 hours should occur given the light to locally
moderate radar reflectivities noted thus far. A transition to snow
may occur on the western extent of the precipitation shield as
low/mid-level temperatures cool with the shortwave trough passage.
...Please see www.spc.noaa.gov for graphic product...
LAT...LON 39268814 40428868 41968883 42158864 42178777 41978738
41718690 41748555 41658432 40798421 39408470 38918519
38658657 38778743 39268814
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