SPC MD 1660


MD 1660 Image

Mesoscale Discussion 1660
NWS Storm Prediction Center Norman OK
1154 AM CST Sun Nov 25 2018

Areas affected...Portions of eastern Iowa...northern Illinois

Concerning...Heavy snow 

Valid 251754Z - 260000Z

SUMMARY...A mix of sleet and snow falling across parts of eastern
Iowa into northern Illinois, is expected to transition to mainly
snow over the next several hours. Very heavy snow, with accumulation
rates of at least 1-2 inches/hour, is likely.

DISCUSSION...A narrow, west-to-east oriented band of mixed wintry
precipitation is ongoing from an area along a Keokuk County IA to
Cook County IL axis. Current KDVN and KLOT dual-polarimetric radar
data suggest that mainly sleet is falling within this band of
heavier precipitation.

The aforementioned band of precipitation has been sustained
predominantly by 700 mb WAA/frontogenetic forcing, which should
continue for several more hours. As a deepening surface low
approaches the area later this afternoon/evening, large scale lift
should only increase with time. Meanwhile, mesoanalysis indicates
relatively strong 925 mb CAA impinging on the horizontal
precipitation band to the north. Latest RAP point forecast soundings
also suggest that cooling of the low-level troposphere will
transpire during the early afternoon hours. As such, a change over
of sleet/mixed wintry precipitation to snow is expected. With very
strong lift expected within a saturating/deepening dendritic growth
zone, very heavy snowfall, with rates of at least 1-2 inches/hour
should prevail through the afternoon hours.

..Squitieri.. 11/25/2018

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


LAT...LON   41189086 41039166 41509232 41919194 42309031 42408784
            41768757 41598764 41209089 41189086 

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