FXUS63 KDMX 261123

Area Forecast Discussion
National Weather Service Des Moines IA
623 AM CDT Wed Apr 26 2017

...Updated for 12z Aviation Discussion...

.SHORT TERM.../Today through Tonight/
Issued at 424 AM CDT Wed Apr 26 2017

Message of the Day: Cloudy, Windy, and Cooler
Hazards: Slight
Frost/Freeze Potential (West) Confidence: High

08z Wed sfc analysis shows 994mb sfc low centered over eastern
Iowa. Strong frontogenetical forcing shown at 950mb with attendant
boundary dropping south/southwestward from the low has served as
a focusing mechanism for light to moderate rain overnight.
Meanwhile, there was another weak sfc low centered near the TX/OK
border...which is phased with a weak upper low that is visible on
experimental GOES-R bands 8-10. This upper low will swing along
the base of the longwave trough...nearing SE Iowa by 06z Thu.

Ahead of this low, models zoning in on a pocket of weak isentropic
lift passing through the SE portion of the DMX CWA. With the best
theta-e advection, instability, etc. well into Illinois, have left
out mention of thunder for today. The northernmost low looks to have
much more of a northerly than easterly component to its motion,
meaning the boundary draped across Iowa will be very slow to move
across the state today and stratus will win the day. Behind the
boundary, strong CAA ensues, which, coupled with the lack of
insolation, will inhibit temperatures from warming up more than a
few degrees today.

The aforementioned lows and boundaries should be east and north
of the DMX CWA shortly after 06z Thu. However...Strong NW flow
will overrun Iowa. The pressure gradient looks to remain around
3mb/150km and weak large-scale subsidence is present. BUFKIT
soundings do not decouple winds...with 20kts to the mixed layer.
Thus, am expecting winds to stay up in the 10 to 15 kt range
overnight tonight.

The grasses are greener, and should have some moisture to work
with from the recent rains. Though temperatures will be near to
slightly below freezing across the north, current thinking is the
strong winds will inhibit deposition processes for frost to form.
Will need to watch closely as winds may relax slightly in our far
western counties...but as of now, have opted to leave out headline

.LONG TERM.../Thursday through Tuesday/
Issued at 424 AM CDT Wed Apr 26 2017

Overall not much has changed initially in the forecast, with
Thursday expected to be mainly dry until late Thursday night when a
weak boundary shifts northward across the state. Energy ejecting
northeastward from the western US upper trough to move through the
region and could see some showers continue into Friday. Broad area
of sfc low pressure to be situated across the southerly plains, with
a trough axis extending northeastward toward IA/MO with broad upper
troughing across the western/central US.

Stronger wave to dig into the four corners region toward mid-day
Friday and cutting off across the southern Plains into the
Saturday. This will bring chances of precipitation spreading
northward through the day Saturday, especially through the
afternoon/evening hours. Pops probably somewhat overdone Saturday
morning, but left a chance in still for possible timing/placement
differences. Upper low to move slowly from western OK/TX/KS region
late Saturday into central IA my early Monday, with the sfc low
moving from TX into nrn MO and srn WI by early Monday. This will
allow for an initially push of waa/moisture advection
precipitation across the area during the day Saturday into
Saturday night, with deformation zone precip expected Sunday into
Sunday night and lingering into Monday before the upper wave
finally moves out of the region. Soundings indicating some colder
air wrapping into the system on the backside and may see an area
of rain/snow mix or even all snow across the western/northern CWA
by Sunday into Sunday night. Have dropped highs some especially in
the northwest Sunday. Will have to monitor as could see a period
of some accumulating snow in the west central/northwest before the
system exits Monday. Ground/road temps likely to be warmer which
will limit accumulations some, however depending on snow rates and
if they are high enough some accumulations still possible on
roads even with warmer ground/road temps.

Another shortwave trough to drop southeastward in the northwest
upper level flow pattern toward Tuesday into Wednesday of next week
which could bring some additional chances for rain. Overall
temperature trend still cool through the period with highs expected
to be below average with some warm-up toward the middle of next
week toward average.


.AVIATION.../For the 12Z TAFS through 12Z Thursday morning/
Issued at 619 AM CDT Wed Apr 26 2017

Abundant stratus over Iowa and upper Midwest will keep OVC skies
and at least MVFR conditions throughout TAF period. Given slow
nature in movement of Stratus deck, have medium-high confidence in
timing and location of flight category changes from IFR to MVFR
today. Cannot rule out a return of LIFR at KMCW in the 07z Fri-13z
Fri time period, but not confident enough for mention at this
point. Confidence high in no TS during any precip at TAF sites




SHORT TERM...Kotenberg
LONG TERM...Beerends
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