Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 272327

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

...00z 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 00Z TAFS through 00Z Thursday evening/
Issued at 622 PM CDT Wed Jul 27 2016

Somewhat tough TAF period for a couple of reasons. First, ongoing
showers/storms in northern Iowa are expected to wane overnight,
leaving KDSM and KOTM alone though KFOD, KMCW, and KALO will see
VCTS/VCSH through the evening and periods of MVFR. Overnight,
stratus deck is expected to build across the state, with
indications that MVFR CIGs may prevail. Have held off on the MVFR
cigs, instead low VFR, overnight and into tomorrow while waiting
for it to show its hand.




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