Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 220040

Area Forecast Discussion
National Weather Service Des Moines IA
640 PM CST Sun Jan 21 2018

Issued at 627 PM CST Sun Jan 21 2018

Low level moisture pooling along the I-80 corridor ahead of a
stalled boundary is producing a corridor of very low visibilities.
since sundown visibilities have gone to a quarter mile or less and
near zero at times prompting the addition of a dense fog advisory
for the tonight period. Once rain starts it should improve
visibilities to something more than a quarter mile but that may
not be until later tonight. There may also need to be an extension
in area as well which will be monitored.


.SHORT TERM.../Tonight through Tuesday Night/
Issued at 353 PM CST Sun Jan 21 2018

Obvious focus on the blizzard and
wintry mix potential late tonight and throughout the day Monday and
Monday evening. A few changes to the ongoing headlines were added a
sliver of counties to the southeast in a Winter Weather Advisory,
added Crawford County to current the Blizzard Warning, and delayed
the start time to 09z Monday for all headlines. Leaned toward a
blend of the hires models for much of the forecast with HRRR/ARW/NMM
in good agreement.

Tonight...mainly looking at areas of drizzle and fog to persist
across much of the forecast area with the far northwest seeing a
wintry mix late tonight. Confident to delay the onset of all snow
transition to 09z in the Blizzard Warning as soundings indicate the
deep moisture doesn`t move into the warning area until past 06z. The
deformation zone looks to set up from west-central Iowa northeast
into south-central Minnesota late tonight. The pivot point of the
snow band is likely around Sioux City to Cherokee to Spencer area,
close enough to the northwest corner of the CWA to have high
confidence in the heavy snow and blizzard conditions. However, this
is ever so slightly further southeast than previously anticipated
which resulted in adding a few counties to headlines.

Strong omega within the dendritic layer and winds atop the mixed
layer ranging from 40-45 knots per soundings via DNS, SPW, and FRM.
There is also the factor of negative EPV present to release CSI and
thus enhance the snowfall rates in northwest Iowa. Early in the
event Monday morning, the consistency of the snow is likely to be
the wet-heavy type as the sounding profiles are near the 0C line
before the colder air moves into NW later Monday morning. This snow
looks to potentially stick very easily and thus continued the
mention of damage to trees and powerlines with the heavy wet snow
combined with the strong winds.

The surface low looks continue to track across south-central Iowa
during the day Monday and will be in southeast Iowa by 00z Tuesday,
placing much of the forecast area within the CAA regime. At this
time, the deformation zone and heaviest snow band will be ongoing
with significant snowfall rates.  The TROWAL is likely to push in
the northeast portions of the forecast area, providing some wintry
mix to the Mason City to Fort Dodge area until the CAA sets in by
around 14-18z Monday when the predominant precipitation type will be
snow. Bufr soundings do suggest a brief period Monday afternoon in
the aforementioned location to lose ice introduction and thus lead
to the FZRA potential in the advisory location. This also due to the
dry slot punching maybe as far north to Highway 20. The strong winds
are expected across the entire CWA by 00z Tuesday at the latest and
with the falling snow, certainly some visibility restrictions are
possible southeast of the current headline area. Low confidence with
any headline across this location with the lack of heavy snow attm.

.LONG TERM.../Tuesday night through Sunday/
Issued at 353 PM CST Sun Jan 21 2018

Long range will begin with a weak upper level trough digging through
the region in a general northwest flow pattern aloft. Fairly weak
system with little moisture, so have left the forecast dry and
mainly see an increase in cloud cover. NW flow pattern aloft remains
in place into Wednesday and begins to transition into Thursday and
Friday as upper ridging builds into the central US. WAA will occur
with this, with the thermal ridge building into the central US and
IA into Friday. This will bring a return to mild temperatures to end
the week. Warming likely to be limited a bit at first in areas that
are to see heavy snow with the current system to impact the area, so
may have to drop temps some in those areas by mid/late week. A large
upper trough to dig into the western US by late week, and will begin
to shove eastward through the central US this weekend. Main upper
trough to track further to the north of the state, but several
shortwaves rotating through the main trough to allow it to wobble
through the region and scrape Iowa with a lobe of energy on the
backside of the system. This should bring some chances for
precipitation to the state from later Friday into Saturday. See a
push of cold air with this system as well, as H85 temps drop to
around -10C for the weekend.  A large upper trough across the
western US into the latter portion of the weekend to then build
eastward into early next week. This will likely bring a return to
mild and dry conditions for the end of the forecast period and just


.AVIATION.../For the 00Z TAFS through 00Z Monday evening/
Issued at 627 PM CST Sun Jan 21 2018

LIFR conditions will prevail this TAF period. Southern TAF`s will
have vsby restrictions in dense fog along with very low cigs and
KDSM and KOTM may even get a rumble of thunder between 04Z and
08Z. Northern TAF locations will have a wintery mix of precip
beginning late tonight changing over to snow/blowing snow and
reducing vsbys and cigs aft 12z.


Dense Fog Advisory until 4 AM CST Monday for IAZ049-050-058>062-

Winter Weather Advisory from 3 AM Monday to midnight CST Monday
night for IAZ017-025-035-045-046-057.

Winter Storm Warning from 3 AM Monday to midnight CST Monday
night for IAZ007-016-024-034.

Blizzard Warning from 3 AM Monday to midnight CST Monday night
for IAZ004>006-015-023-033-044.



SHORT TERM...Podrazik
LONG TERM...Beerends
AVIATION...FAB is the U.S. government's official web portal to all federal, state and local government web resources and services.