Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 240536
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1136 PM CST Wed Jan 23 2019

.SHORT TERM.../Tonight through Thursday/
Issued at 347 PM CST Wed Jan 23 2019

...Strong, Gusty Winds Creating Blowing Snow Later Tonight Through
Late Thursday with Hazardous to Dangerously Cold Wind Chills by
Later Thursday into Friday Morning...

.Overview: Strong, gusty winds from the northwest will develop
behind an Arctic cold front with blowing snow significantly
impacting visibility, especially in rural areas, across much of
central Iowa. This will have an impact on the Thursday morning
commute, particularly over central and northern Iowa. In addition,
falling temperatures and the winds will create hazardous to
dangerous wind chills later Thursday into Friday morning.

The sky is mainly clear over much of central Iowa at mid-afternoon,
but there remains a patch of low clouds over north central Iowa.
This shows up nicely on the GOES-East Day Snow Fog RGB imagery. Main
concern is the short wave trough that is pushing down through the
southern portion of the Alberta, Saskatchewan, and Manitoba
provinces with a good PV anomaly as seen on GOES-East Clean IR
imagery. The Arctic cold front has crossed into the north parts of
North Dakota and Montana and observations show light snow near and
behind the front with blowing snow farther back as the winds are
gusting into the upper 20 knots at 2pm.

This Arctic front will continue to surge southeastward the remainder
of the afternoon into the evening reaching northern Iowa around or
shortly after midnight. As the front drops into the state and
through much of the forecast area by sunrise Thursday, strong, gusty
winds from the northwest will develop. NAM, GFS, and RAP soundings
become saturated in the dendritic layer near and just behind the
front for a few hours before much drier air dries this layer out.
Therefore, have added flurries or slight chance of snow for a
general 4 to 6 hour window based off these soundings and the front`s
arrival. In addition, there is a bit of elevated instability in the
NAM and GFS that could make some of these a bit more vigorous snow
showers.

BUFKIT soundings from the same models show winds at the top of the
mixed layer in the upper 30s to occasionally low to near middle 40
knots. This will allow for sustained winds of 20 to 30 mph spreading
southeastward through the predawn into the morning hours. Wind gusts
over northern Iowa will approach 45 mph and elsewhere exceed 35 mph.
The falling light snow or flurries alone with these winds will
significantly reduce visibilities. Add in the recent snowfall on the
ground, which should be capable of being lofted and blown, expect a
significant reduction in visibility -- especially in rural areas --
that will impact the morning commute over northern and a good
portion of central Iowa. At this time, have issued a Winter Weather
Advisory and will highlight the strong winds and blowing snow
concerns. The only counties left out of the advisory are near and
west of Fort Dodge where this morning`s snow depths were zero to
just a few inches. This should mitigate widespread blowing snow
concerns in those areas. There is still a concern that this could be
a ground blizzard, especially initially with the falling snow that
may create brief periods of whiteout conditions. As the falling snow
ends, more general blowing snow is expected with visibility
reductions more focused in rural areas. So, will be monitoring
trends upstream tonight for the ground blizzard potential and will
upgrade to Blizzard Warning if needed.

Not to be left out are the temperatures, which will be falling
through the day Thursday in the wake of the front. By 3pm Thursday
afternoon, temperatures will be below zero over northern Iowa and
mainly in the single digits above zero elsewhere. Wind chill values
of 20 to 30 below will spread from northern into central Iowa
through the day as well. Have also grouped the hazardous wind chills
into the Winter Weather Advisory until 0z/6pm, when this advisory
drops and a Wind Chill Advisory/Watch will be raised.

.LONG TERM.../Thursday night through Wednesday/
Issued at 347 PM CST Wed Jan 23 2019

Start of the forecast period will see the combination of winds and
bitter cold temperatures producing widespread dangerous wind chills,
especially the northeast half of the forecast area. Have already
issued a wind chill watch for northeast half of the forecast area
where warning values (-30 or below) seem likely. The remainder of
the area will have a wind chill advisory with all headlines valid
through 15Z Friday although the west will likely rise above
criteria prior to that. Next system arrives quickly on Friday with
increasing isentropic lift. Overall lift remains relatively weak
but given the depth of the sounding in the dendritic growth zone,
some light snow seems quite certain in a strip from northwest to
southeast across the forecast area. Amounts should remain under an
inch.

Deep northwest flow will persist across the upper Midwest and much
of the eastern CONUS into the middle of next week.  Iowa will be
near the path of several weak waves over the weekend with chances
for flurries or very light snow during this time.  Temperatures will
remain relatively cold with some moderation into Sunday ahead of a
more significant system approaching Sunday night into Monday.  This
system is deeper with stronger flow and forcing as it moves
southeast.  Impressive isentropic lift is expected by late Sunday
into early Monday across the state with deep saturation occurring
across northeast half of the state.  Snow will develop and spread
southeast during the night before diminishing by midday Monday.
Moderate and even locally heavy accumulations are looking more
likely in the far northeast forecast area with lighter accumulations
to the south and west.  Will continue to watch this system closely
for the potential of additional heavy snow in the state.  This
system will be followed closely by arctic air.  In fact by next
Wednesday, 850mb temperatures are approaching -36 to -37C across
northern Iowa with 1000-500MB thicknesses of under 4800m which is
quite rare.  Looking to be a brutal week temperature-wise as cold
air floods into the upper Midwest from the Arctic.

&&

.AVIATION.../For the 06Z TAFS through 06Z Thursday night/
Issued at 1133 PM CST Wed Jan 23 2019

Little change from the previous forecast as a cold front remains
on track to arrive late tonight into Thursday morning and bring
strong northwest winds and a few areas of light snow and blowing
snow. MVFR cigs will be arriving over northern Iowa and will
impact the KFOD/KMCW/KALO vicinities through 10z. Localized vsbys
in snow and blowing snow may drop to IFR at times at KMCW/KALO. A
few wind gusts may exceed 40 kts. Conditions are expected to
improve late afternoon and into the evening.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 5 AM to 6 PM CST Thursday for
IAZ024>028-036>039-046>050-057>062-070>075.

Wind Chill Advisory from 6 PM Thursday to 9 AM CST Friday for
IAZ046-047-057>060-070>074-081>086-092>097.

Wind Chill Watch from Thursday evening through Friday morning
for IAZ004>007-015>017-024>028-036>039-048>050-061-062-075.

Winter Weather Advisory until 6 PM CST Thursday for IAZ004>007-
015>017.

Winter Weather Advisory from 8 AM to 6 PM CST Thursday for
IAZ081>086-092>097.

Wind Chill Advisory from 8 AM Thursday to 9 AM CST Friday for
IAZ023-033>035-044-045.

&&

$$

SHORT TERM...Ansorge
LONG TERM...Cogil
AVIATION...Donavon



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