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Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
1153 PM CDT Thursday Jul 30 2015

issued at 324 PM CDT Thursday Jul 30 2015

The latest surface analysis was indicating high pressure center sagging
south across east central Kansas into MO...while a weak trough was noted
sliding across ND. Surface winds and mixing extent not quite as robust as
earlier well as somewhat higher westerly winds
upstream producing some moisture convergence across the local area
keeping surface dewpoints up more in the low to middle 60s over most of the
County Warning Area/although some 50 dewpoints still occurring in northwestern IL/.
Crop evapotranspiration also a factor. Aloft...12z upper air
analysis as well as middle/upper level moisture flow patterns seen on
the current water vapor loop indicating some large scale
amplification taking place to upstream ridge over The Rockies.
This will effectively steepen the northwesterlies dumping down
across the upper MS River Valley through tomorrow.


Short term...(this evening through friday)
issued at 324 PM CDT Thursday Jul 30 2015 ridge slides south...light west to southwest winds
overnight and mainly clear skies allowing for surface temperatures to cool
toward the ambient dewpoints for overnight lows. A few models in varying
degrees skit a weak vorticity into the western County Warning Area late tonight in
northwesterly steering flow...but main effect should only be to
induce some patchy ac/middle clouds if even that.

Friday...upstream surface trough progresses across the County Warning Area from northwest to
southeast during the morning. A few hires models even generate a few
spotty to isolated showers across southeastern Iowa into west central Illinois
at this time/middle Friday morning...but forcing...moisture convergence
and any instability weak at that time and will keep the forecast dry
through early afternoon. Deep uniform northwest flow continues into the
afternoon...and adequate heating and mixing will make for widespread
middle to upper 80s across the County Warning Area with a few sites around 90. As for
afternoon convection taking off...deep convective index Max/S...
return flow convergent zones and other convective inducing parameters
in a moderate cape but weak shear regime are all pointing at the
active zone for sctrd to isolated storms tomorrow afternoon from
across south central into southeastern Nebraska...into northwestern and
north central MO. Bulk of the latest model runs are also picking
up on this trend...suggesting the County Warning Area will probably remain dry
through 00z Sat while storm clusters Blossom west-southwest of
Omaha and isolated activity tails off toward the northwestern stl
area. For now will trim back slight chance probability of precipitation to the far
southwestern County Warning Area from middle to late afternoon...but if trends
continue the next forecast shift may be able to remove them all
together. ..12..

Long term...(friday night through next thursday)
issued at 324 PM CDT Thursday Jul 30 2015

Have maintained low probability of precipitation across the far south into Friday evening...
although if recent trends continue later shifts may be able to go
dry altogether. The initial main chance for showers and
thunderstorms still looks to be Saturday night into Sunday. Model
inconsistency lingers regarding timing of the main upper forcing
and favored areas for storms. WRF mesoscale convective system diagnostics do indicate some
potential for a complex clipping portions of the forecast area
Saturday night...but confidence in any particular scenario remains
low. Storm Prediction Center has the entire forecast area in the marginal risk area.
General shear/instability parameters do support some potential for
isolated severe storms.

For Sunday afternoon through least slight chance probability of precipitation
continue every period due to typical issues with subtle short wave
timing and location. Monday night...and again Tuesday
night/Wednesday look a bit more favorable at this point.

Turning to temperatures through the period...Saturday through Monday
should be seasonably warm with afternoon highs from the low 80s
north to upper 80s south. Consensus blended temperature guidance continues
to support a cooling trend into the 70s Tuesday through Thursday.
Sunday and Monday will likely be the most humid period...with
dewpoints forecast in the low 70s south...good for afternoon heat
index values in the low to middle 90s.


Aviation...(for the 06z tafs through 06z Friday night)
issued at 1133 PM CDT Thursday Jul 30 2015

VFR conditions will prevail through this taf period. A high
pressure system is forecast to slide to the southwest of the upper
Midwest tonight and Friday. A wave of middle-level instability may
produce an isolated shower or storm through Friday morning but
did not mention in tafs due to expected isolated nature/low
coverage. Daytime mixing into steady winds aloft will create
breezy conditions Friday afternoon with west-northwest gusts between 20-25 kts.


Dvn watches/warnings/advisories...


short term...12
long term...rp Kinney

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