Area Forecast Discussion
Issued by NWS Des Moines, IA

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658
FXUS63 KDMX 291735
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1235 PM CDT Fri Jul 29 2016

.SHORT TERM.../Today/
Issued at 339 AM CDT Fri Jul 29 2016

The primary concerns today will be precipitation trends and temps.
Water vapor imagery notes SD/NE and WI/MI short waves with very
light precip associated with the two systems currently just beyond
the forecast area to the southwest and northeast. Any forcing
associated with the western wave is expected to remain to the south
and west of IA today with our effects, including the broader low
level cyclonic flow, driven by the Great Lakes wave. Any large scale
forcing will be more kinematic in nature due to DPVA and upper level
divergence as thermodynamic support is nil with weak cold advection
behind the H85/H7 IL low. Models do suggest deeper moisture trying
to develop but forecast soundings show the column never really tries
to saturate. Soundings also suggest shallow instability may
contribute to weak convection with peak MLCapes to around 500 j/kg,
but low level convergence will be weak. With these marginal
mechanisms have only mentioned isolated wording throughout the day,
and what occurs will likely be more due to convection as shown by
cellular high res model reflectivity.

Have been a bit more aggressive with temps based on what occurred
yesterday staying toward the warmer end of the guidance envelope.
Stratus is fairly widespread across northeast IA at the moment and
should advance farther into the state this morning. However high res
model ceiling progs suggest they will lift into cumulus with July
heat allowing for some rebound.

.LONG TERM.../Tonight through Thursday/
Issued at 339 AM CDT Fri Jul 29 2016

We will be going back to a more active pattern again.  Tonight a
shortwave will be exiting to the East and as such any shower
activity should be relegated to the East before exiting the state
later in the evening.

From late tonight through much of Sunday upper level ridging will be
developing over the Rockies and into the plains sharpening a trough
over the Eastern half of Iowa keeping temps still on the cooler side
through Saturday and Sunday will only be a few degrees warmer. Any
precip should stay to the South and West of Iowa.  Sunday into
Monday the upper ridge moves overhead while at the surface we will
be in between a high over the Great Lakes and a low developing over
the plains.  Sunday into Sunday evening warm advection sets up
mainly across Southern/Southwest Iowa bringing back the threat for
storms.  Then late Sunday night and Monday a surface low develops to
our West with a frontal boundary extending into the state.  Models
differ on placement of the low and as a result...the boundary but
we have instability in place...decent low level shear at a minimum
along with a wave of theta-e advection pushing across central Iowa.
Storms should readily develop in this environment and should be
ongoing into Monday morning.  A shortwave then rides atop a building
ridge Monday evening for a chance of storms again late day into the
overnight.  A few storms during this period may become severe.

Attention then turns to heat as a ridge builds into the Upper
Midwest.  Temperatures Tuesday into Thursday will climb into the mid
90s with heat indices around 100 once again.  Headlines may be
needed for a portion of the area but at this point it isn`t looking
like it`s a sure thing and it will not be as hot as the previous
episode...at least at this point.  Both the Euro and GFS drive a
strong shortwave across later Wednesday/Thursday time frame along
with a cold front.  Clouds/storms will likely hamper temps during
this time.

&&

.AVIATION.../For the 18Z TAFS through 18Z Saturday afternoon/
Issued at 1234 PM CDT Fri Jul 29 2016

MVFR ceilings will affect most of Iowa this afternoon. Satellite
imagery indicates that the cloud shield has been slightly
expanding today, but ceiling heights have also been slowly
rising. It is likely that the clouds will persist through tonight
and into Saturday morning, but it remains uncertain whether
ceiling heights will rise to VFR by sunset or not, and either way,
how much they may lower again overnight. For now have advertised
VFR ceilings after this evening but uncertainty is high and this
will be reevaluated for subsequent TAF issuances. A few showers
will also affect the area this afternoon, but any impacts will be
too minimal and brief to include in the TAFs other than at ALO
where they may be a bit more frequent.

&&

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

&&

$$

SHORT TERM...Small
LONG TERM...FAB
AVIATION...Lee



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