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Area forecast discussion 
National Weather Service Des Moines Iowa
645 am 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 South Dakota/NE and WI/Michigan 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 Iowa 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 850 mb/700 mb Illinois 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 Iowa 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 12z tafs through 12z Saturday morning/
issued at 645 am CDT Fri Jul 29 2016

An axis of LIFR/IFR stratus stretches from northeast Iowa into Illinois
this morning with surrounding MVFR ceilings. These low clouds are
expected to continue drifting southward this morning but lift
through MVFR to VFR heading into the afternoon. Isolated
showers/storms may also develop during peak heating of the day but
timing and location confidence is not there to include yet, even
to the level of vcsh. Additional MVFR or less ceilings and
visibilities may develop east early Saturday morning as well.

&&

Dmx watches/warnings/advisories...none.

&&

$$

Short term...small
long term...fab
aviation...small

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