Area Forecast Discussion
Issued by NWS Des Moines, IA

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955
FXUS63 KDMX 170919
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
419 AM CDT Thu Aug 17 2017

.SHORT TERM.../Today through Tonight/
Issued at 419 AM CDT Thu Aug 17 2017

The main forecast concern was focused on winds today with a
tightly wound surface low pressure traveling across southern
Minnesota/far northern Iowa this morning. Sharp pressure gradient
and trop fold with the low this morning. Winds already gusting
over 20 knots in portions of southwest Minnesota. Plus, with a
rapid 3-hour surface pressure rise across the north and west
through 12-15z this morning, confident winds should gust over 20
to 25 knots today. Mixing will deepen later this morning into the
afternoon and with winds atop the mixed layer range around 30
knots and much of these winds should reach the surface. Stratus
across the north will hinder the very deep mixing, but with the
pressure gradient and mixing to around 900mb, increased winds and
wind gusts today. Some shower activity is possible this morning
across the far north with the surface low passing through. Winds
decouple and subside b/t 00-03z Friday.

.LONG TERM.../Friday through Wednesday/
Issued at 419 AM CDT Thu Aug 17 2017

Shortwave will drop through the northern Plains on Friday with a
weak surface reflection and front passing through the Missouri
River Valley into Iowa during the day. A narrow ribbon of warm
advection and moisture transport will move into the state during
the day as mid level kinematics produce lift across the state.
Scattered showers and storms will pass through Iowa during the
day as the forcing crosses east over the state. These will linger
mainly in the east on Friday evening before ending altogether
overnight. Decent mid level lapse rates and bulk shear values over
30kts may lead to some organization with some of the storms.
Therefore, a few of the storms may approach severe limits with
main concern from large hail and gusty winds.

Quiet weather is expected on Saturday in the wake of the system
with general subsidence across the state. However, warm advection
will begin again by late Saturday and persist into Sunday with
temperatures approaching 90 by Sunday afternoon in southern Iowa.
The return of moisture and frontal convergence should lead to
convection developing along a surface front across South Dakota
into Minnesota on Sunday night as good forcing slides just north
of Iowa overnight. These storms may enter northern Iowa on Sunday
night and linger into Monday. However, central and southern Iowa
will likely be in the warm sector for much of Monday with partly
cloudy conditions. These areas appear to have at least a decent
chances to view the eclipse as the bulk of the precipitation
should be farther north. Both models indicate the best threat of
storms will come Monday night into Tuesday morning as the boundary
settles across the state. It appears relatively dry into the
middle of next week with temperatures seasonable.

&&

.AVIATION.../For the 06Z TAFS through 06Z Thursday night/
Issued at 1142 PM CDT Wed Aug 16 2017

Low clouds have begun to wrap low pressure over south central
Minnesota into northwest Iowa with MVFR ceilings moving over the
northern terminals tonight. Ceilings are expected to drop into IFR
at KMCW toward daybreak and this is also the terminal with the
best chance of spotty showers tomorrow morning. IFR conditions are
possible at KFOD and KALO, but still uncertain if those low of
ceilings will be that far south. Ceilings will improve into VFR
toward midday Thursday and into the afternoon hours. For the
southern terminals, expect VFR ceilings. Otherwise, winds from
the west will become from the northwest and turn gusty tomorrow
morning, especially over northern Iowa. Winds will decrease
around sunset Thursday.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

SHORT TERM...Podrazik
LONG TERM...Cogil
AVIATION...Ansorge



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