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afddmx

Area forecast discussion
National Weather Service Des Moines Iowa
358 am CST sun Dec 8 2019

Discussion.../today through Saturday/
issued at 358 am CST sun Dec 8 2019

Overview...wintry precipitation - mainly rain or snow - is expected
as a strong front passes through the state on Monday. Accompanied by
gusty winds, colder air will surge into the state Monday into Monday
night with the coldest conditions Tuesday into Thursday morning.

Details...high clouds were passing over the state this morning with
additional high clouds off to the west streaming onto the Central
Plains. Low clouds and a sign of low level moisture that will be
moving into the state later today into tonight is seen over the
Ozarks and points south in GOES-east nighttime microphysics rgb.
Today will feature increasing and thickening clouds as a shortwave
trough that is currently over the Canadian rockies per GOES-east mid-
level water vapor imagery approaches from the northwest. As the low
stratus moves into eastern Iowa, NAM, GFS, and rap soundings show a
1 to perhaps near 2km depth of saturation. This should equate to
some drizzle over eastern portions of Iowa this evening. Over
northern Iowa, saturation takes longer to reach and occur there. NAM
temperatures and soundings are much colder and have stayed away from
the colder solutions. While GFS soundings are milder and overall
temperature guidance is warmer, temperatures over northern Iowa will
be near or just shy of freezing. Therefore, there could be a short
window of freezing drizzle, but this is highly dependent on two
things -- drizzle occurring and temperatures at or below freezing.

As the front enters the state, this will spread generally light
precipitation southeastward. Much of the qg convergence will remain
north of the state with weaker passing through Iowa. Any light
freezing precipitation will change over to snow as soundings
saturate and thermal profiles lower below freezing. Over southeast
Iowa before the colder air arrives, just rain may occur before
precipitation changes over to snow. Snow amounts continue to be on
the light side with perhaps near an inch near the Iowa Minnesota
border. As previously mentioned and added in this forecast, there
could be a dusting to perhaps a half an inch of snow over the
southwestern quadrant toward south central Iowa. This would be tied
to the the 850mb front with strong cold air advection noted in the
850-700mb layer as well. As the front passes through, gusty winds
from the northwest will develop with colder air following as well.
Precipitation will end in the afternoon as subsidence spreads from
west to east across the state.

The colder air will be the main story from Monday night through
Thursday morning. Brisk winds will continue on Tuesday, which will
accentuate the chill. There could be some scattered flurries over
northern Iowa as well as profiles near saturation up to a depth of
1.5km in the dendritic growth zone. There could be another shot of
light snow on Wednesday, but models disagree placement and less so
on timing of where this may end up occurring. Temperatures will
begin to make strides back towards normal on Thursday and be close
by Friday. Another chance of precipitation takes shape by late this
week or early next weekend.

&&

Aviation.../for the 06z tafs through 06z Sunday night/
issued at 1125 PM CST Sat Dec 7 2019

Breezy southerly winds will continue for the next few hours,
before subsiding as the gradient relaxes. Low level wind shear conditions will
also continue over the next few hours at all sites, relaxing from
west to east by the morning hours. MVFR and IFR conditions will
begin to slide in around 00z from both the north/northwest and the
south/southeast as two areas of stratus affect the state. Have
generally kept from going prevailing IFR, but will be possible,
especially beyond the current taf period.

&&

Dmx watches/warnings/advisories...
none.
&&

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