Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 230903
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
403 AM CDT Mon Oct 23 2017

.SHORT TERM.../Today through Tonight/
Issued at 403 AM CDT Mon Oct 23 2017

A couple strong upper level short waves and associated surface
boundaries will impact the area today into tonight. The initial
boundary is no moving into far northwest Iowa. Temperatures behind
this boundary are warmer than pre-frontal due to mixing and some
downslope component. This boundary will sweep across Iowa this
morning and will bring breezy west to northwest winds to the
state. A few light showers may also accompany this boundary
passage this morning.

Water vapor imagery is currently showing drying and thus subsidence
increasing over northern South Dakota. This will reach Iowa later
this afternoon along with a stronger push of cold advection.
Portions of northwest Iowa will have falling temperatures by mid
afternoon. In addition, the cold advection will enhance mixing and
in combination with the aforementioned subsidence and cold
advection, should push wind into wind advisory criteria for western
portions of the area. Have maintained the currently headline as is
for now however may need to expand to cover northern portions of the
forecast area east to Mason City for strong winds developing by mid
to late afternoon. The mixing should diminish early this evening for
a 4-6 hour period before another surge of cold advection arrives
after 06z. Strong mixing and good momentum transport of mixed layer
winds to the surface likely will bring wind advisory conditions to
an large portion of central Iowa. Mixed layer winds in excess of 50
kts are possible. The pressure gradient will increase overnight as
well as a strong area of low pressure rapidly deepens over Michigan.
The combination of the mixed layer winds and the increasing pressure
gradient do pose concern of wind gusts of 50 mph or greater by late
tonight. Further, wrap around showers over the far northeast area
possible. Higher gusts could develop in vicinity of these showers.
In collaboration with surrounding forecast offices, have not issued
an advisory for tonight and to keep it separated from this
afternoon`s headline.


.LONG TERM.../Tuesday through Sunday/
Issued at 403 AM CDT Mon Oct 23 2017

A series of system will affect Iowa this week with the main issue
being very strong winds on Tuesday and again by later Thursday
into Thursday night. Winds will already be quite strong tonight
and these winds should strengthen into Tuesday morning as surface
low bombs across the northern Michigan. Tight pressure gradient
along with clearing skies allowing insolation to aid in mixing.
Both GFS and NAM Bufr soundings indicate 40-50kts at top of mixed
layer during the morning into early afternoon and would expect
surface gusts of 50 mph quite possible, especially in the north
and west with sustained winds of 30 mph. Headlines for winds
appear likely for Tuesday with the possibility of high wind
warning should indications of strong mixing persist. A few
lingering showers will be possible on Tuesday morning in far
eastern areas as well associated with the backside of the
deformation zone.

Wind fields begin to gradually relax on Tuesday night into
Wednesday with strong warm advection by Wednesday morning. Thermal
ridging in the Plains will race eastward with readings climbing
above normal. However, this will be the last day of warmth for the
week as a strong cold front is expected to pass through the state
on Thursday as another robust upper system moves into the Midwest.
The track of the system keep the surface low north and east of the
state with bulk of forcing/lift to the north along with the deeper
saturation, therefore little in the way of precipitation is
expected with this system. However, strong pressure rises, cold
advection and strong wind fields should produce another round of
near advisory to advisory criteria winds later Thursday into
Thursday night. The coldest air of the season will drop into the
state with the winds as 850mb temps plummet. Whatever is left of
the growing season will effectively end on Friday night as
readings drop below freezing across the forecast area. Little
additional sensible weather is expected at this point for next
weekend as temperatures slowly moderate into Sunday.

&&

.AVIATION.../For the 06Z TAFS through 06Z Monday night/
Issued at 1149 PM CDT Sun Oct 22 2017

Main concerns remain wind with some concern for MVFR cigs north
sites at KMCW/KALO toward 00z Tuesday. Cold front expected to move
south during the day with first burst of wind/gusts...followed by
second front by 00z and another significant increase in wind/gusts.
During both periods LLWS is possible and have added as needed.
Following the second front HIRES models now suggesting that
potential for some MVFR cigs at two most northern sites aft 22z
and have adjusted for potential lower cloud deck. /rev

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Wind Advisory from 1 PM this afternoon to 7 PM CDT this evening
for IAZ004-015-023-033-034-044-045-057-070.

&&

$$

SHORT TERM...Donavon
LONG TERM...Cogil
AVIATION...REV



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