Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 280449
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1149 PM CDT Wed Jul 27 2016

...06z Aviation Update...

.SHORT TERM.../Tonight/
Issued at 305 PM CDT Wed Jul 27 2016

Main forecast challenge will focus on progression of surface
boundary tonight and potential convection. Currently...weak
surface front passing into northwest Iowa this afternoon with
instability axis ahead of the front. Expect to see scattered
convection develop along this boundary later this
afternoon/evening as it pushes southeast into central Iowa. Of
recent concern...there is good 0-3km cape of 100-200 J/KG in
northwest/north central Iowa this afternoon, decent surface
vorticity and lapse rates have increased to near 8C/KM recently.
This could lead to the development of a couple of landspouts near
the shear axis with the initial updrafts/convection. These type of
circulations are difficult to see on radar although they are often
visually striking. Will continue to monitor closely over the next
few hours.

The scattered convection is expected to move east and south
through central Iowa tonight as the boundary progresses through
the state. Despite the possibility of landspouts, the overall
severe threat will be low given weak shear. Anticipate the storms
to diminish in coverage later tonight toward morning as the
instability decreases. Otherwise, status will settle southward
into the northern half or so of the forecast area in area of weak
cold advection late tonight.

.LONG TERM.../Thursday through Wednesday/
Issued at 305 PM CDT Wed Jul 27 2016

Lingering showers are anticipated in the northeast and east
central portions of the state on Thursday near trof axis. This
activity will likely graze the eastern portions of the forecast
area during the day although most locations will remain dry on
Thursday. Stratus will likely be in place on Thursday morning
across a good portion of the forecast area before breaking up into
a broken field of cumulus by afternoon. Temperatures will remain
quite cool through the day with light north winds. There will be a
threat of isolated convection remaining in and around Iowa through
Friday and into the weekend, however no large/organized areas of
convection are anticipated during this time nor is much in the way
of severe weather expected. This means storms will be somewhat
hap-hazard in nature and difficult to pinpoint, especially at this
point in time. Temperatures are forecast to moderate later in the
weekend a climb above normal into early next week as upper ridging
builds into the central United States. Highs into the 90s are
expected by Monday in southwest Iowa expanding to the north and
east on Tuesday and Wednesday. High humidity levels will likely
contribute to rather sultry conditions by then.

&&

.AVIATION.../For the 06Z TAFS through 06Z Thursday night/
Issued at 1142 PM CDT Wed Jul 27 2016

With showers and storms this evening having generally faded out,
main concern in TAF period becomes timing stratus deck expected
to expand out of MN/WI. Currently CIGs are primarily MVFR with
pockets of IFR there, and have dropped KMCW, KFOD, and KALO into
MVFR for a period overnight. Kept KDSM and KOTM out of MVFR with
some uncertainty on southern spatial coverage and timing. Toward
end of period, scattered storms will be possible, especially
around KMCW, KFOD, KOTM, but again uncertainty in timing and
coverage is low at the time and have kept mentions out.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

SHORT TERM...Cogil
LONG TERM...Cogil
AVIATION...Curtis


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