Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 231749

Area Forecast Discussion
National Weather Service Des Moines IA
1249 PM CDT Sun Jul 23 2017

.SHORT TERM.../Today through Tonight/
Issued at 354 AM CDT Sun Jul 23 2017

The main forecast concern was focused on temperatures and fog
develop tonight into Monday morning. Leaned closer to the NAM for
temperatures today and tonight as the GFS seemed slightly too cool
for max temps today, at least across the southern portions of the
forecast area. Mixing to around 850mb develops later this morning
and persist into the afternoon hours. Increased winds and gusts a
few knots this afternoon with the CAA through much of the day
prior to the surface high settling into the state by tonight. With
the surface high centering over northwest Iowa into southern
Minnesota overnight tonight, have mention of fog past 06z across
the north with good radiational cooling setting up. Also, went a
little cooler across the north to coincide with this radiational

.LONG TERM.../Monday through Saturday/
Issued at 354 AM CDT Sun Jul 23 2017

Residual fog will linger in portions of northern and western Iowa
on Monday morning with surface ridge centered nearby. However,
warm advection is expected to increase by late in the day as
southeast winds strengthen. The warm advection will persist into
Tuesday with 850mb temperatures continuing to climb along with
increasing theta-e advection. Still some uncertainty as to if
there will be any convection Monday night into Tuesday night with
the increasing moisture, however forcing is relatively weak during
this time and there is an overall lack of focus as well.
Temperatures on Tuesday should be quite warm in the western half
with proximity of thermal ridge and have added a couple of degrees
to the highs on that day, especially since mixing looks to be
rather good.

A surface front will settle toward the state on Wednesday as upper
trof passes along the US/Canadian border. This will provide the
focus for convection on Wednesday into Thursday morning as it
drops through the state. Shear will be increasing during this time
as well with the westerlies dipping south toward the state. There
will likely be some organized convection during this time given
the shear and instability profiles but overall extent is still to
be determined. This system will pass by midday Thursday with
relatively quiet weather into next weekend. Temperatures will also
cool by the end of the period as Canadian high pressure builds
into the upper Midwest.


.AVIATION.../For the 18Z TAFS through 18Z Monday afternoon/
Issued at 1249 PM CDT Sun Jul 23 2017

Main concern will be coverage and density of fog tonight through
14z Monday along with potential IFR/MVFR cigs with fog. Hires/guidance
hitting most of northern/northwest hard overnight. Despite
lowering dewpoints...cooler air will filter in behind a secondary
cold front and allow temps to drop through morning hours.
Expecting the most affected areas from KFOD to near KMCW with
lesser impacts for KALO/KDSM/KOTM. Possible 1/4sm at KFOD with
1-3sm KALO/KMCW from 11-13z. Aft 14z...fog should dissipate with
little impacts remainder of period. /rev




SHORT TERM...Podrazik
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