ZCZC SPCSWOMCD ALL
ACUS11 KWNS 090908 
SPC MCD 090908 
MIZ000-OHZ000-INZ000-ILZ000-WIZ000-IAZ000-091515-

Mesoscale Discussion 0062
NWS Storm Prediction Center Norman OK
0308 AM CST Fri Feb 09 2018

Areas affected...Portions of far eastern Iowa to southern Michigan

Concerning...Heavy snow 

Valid 090908Z - 091515Z

SUMMARY...Moderate to locally heavy snow, with rates up to one inch
per hour, will continue expanding eastward this morning.

DISCUSSION...On the nose of stronger 850-700mb warm advection and
related isentropic ascent, moderate snowfall has advanced eastward
into portions of northern Indiana and southern Michigan early this
morning. Forecast soundings depict ascent through a dendritic-growth
layer several thousand feet deep. Therefore, while upward vertical
motion is not particularly robust, relatively efficient crystal
growth should compensate somewhat, yielding rates around 0.5-1 inch
per hour this morning.

Farther west into northern Illinois, the strongest upward motion
related to warm advection has generally remained at temperature
levels too warm for dendritic growth, limiting snowfall rates.
However, likely related to increasing 700-mb confluence and
associated frontogenetic circulations, a narrow band of higher
reflectivity (suggesting an increase in snow aggregation) has
organized over northern Illinois. Ascent associated with this band
exists at colder temperatures, in turn favoring more efficient
crystal production. Supporting this notion, KDVN/Quad Cities 88D
data highlight subtle enhancements in KDP (0.2-0.4 deg/km) around
11-13K ft AGL, which is consistent with an increase in
planar/dendritic crystal growth. This narrow band will slowly shift
east this morning, but will likely be positioned over northern
Illinois over the next several hours, potentially impacting the
morning rush hour with localized snowfall rates up to one inch per
hour.

..Picca.. 02/09/2018

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...DTX...IWX...GRR...LOT...MKX...DVN...

LAT...LON   41619151 42249045 42618839 42838563 42768449 42678370
            42238329 41918348 41728408 41398589 41428878 41459061
            41389115 41399149 41619151 

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