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fxus63 kdmx 110602 

Area forecast discussion
National Weather Service Des Moines Iowa
1202 am CST Wed Dec 11 2019

Discussion.../tonight through Tuesday/
issued at 331 PM CST Tue Dec 10 2019

Impressive short burst of snow today due to thin stratus situated
within the dendritic growth zone. This light snow and flurries is
moving off to the southeast with drying occurring into central
and northwest Iowa. The next system will quickly sweep into the
state tonight. A weak area of low pressure will move southeast
ahead of high pressure overnight with a band snow developing
mainly just north/northeast of the surface reflection. This band
will be mainly thermally driven with vigorous forcing within a
relatively deep dendritic layer of around 5 kft. Supersaturation
within this layer looks supportive of larger dendrites which would
further support the potential for a short period of intense
snowfall rates > 1 inch per hour. As of now, these higher snowfall
rates look to be aligned from near Fort Dodge to Marshalltown and
Montezuma with a band of snowfall of 1 to 2 inches possible. Much
of this snow would fall between midnight and 6 am across the area
with the more intense rates lasting an hour or less. Again, the
greatest threat will be the snow accumulating quickly on roadways.
While the wind is not expected to be a factor, the fluffy nature
of the snow with snow ratios near 20:1 would be supportive of snow
fog created by vehicles lofting the snow and further reducing
visibilities. No headlines at this time but will continue to
monitor and adjust the forecast as needed.

The snow will end quickly from west to east late tonight into early
Wednesday morning as high pressure arrives from the north. The
system will help drive another round of cold advection into the
state. High temperatures over northern Iowa will again be in the
single digits above zero while highs over the south will be in the
low 30s. The combination of the cold temperatures and increasing
wind Wednesday morning will drop wind chills over far northern
Iowa into the 10 below to 15 below range. Another chance for light
snow will pass across northern Iowa Wednesday night as warm
advection lifts through the state. Drier mid level air should
limit precipitation chances into central Iowa though some
discrepancies on the amount of low level saturation which could
impact drizzle chances. Temperatures Thursday will be warmer over
the central and south with highs in the mid to upper 40s, assuming
the stratus breaks. The mild conditions will persist into Friday
before the next short wave passes by Friday night into Saturday.
This system will lead to a transition to a thermal trough dipping
into the Midwest and colder temperatures. Some light snow is
possible over the weekend but no significant impacts are
anticipated. Lower confidence into early next week due to
uncertainty in the overall evolution of the Hudson Bay low.


Aviation.../for the 06z tafs through 06z Wednesday night/
issued at 1202 am CST Wed Dec 11 2019

The next round of snow was just reaching kfod and should continue
moving northwest-southeast across central Iowa. Conditions may dip to IFR at
kfod with VFR/MVFR at sites either side of the snow axis at other
sites. Conditions should improve quickly after the precip ends
10-12z with mostly clear/VFR expected for the remainder of the


Dmx watches/warnings/advisories...none.


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