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Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
1047 PM CDT Monday Aug 3 2015

Synopsis...
issued at 330 PM CDT Monday Aug 3 2015

Latest surface analysis was indicating ridge axis maintaining from
Saskatchewan...down across the Dakotas and nosing down into central Illinois.
Main low level boundary oriented from west-to-east and shunted to the
south of this feature...with better return flow convergence noted on
it across western and central Kansas. Aloft...large closed off cyclone
continued across the James Bay region...with broad cyclonic flow
pattern currently engulfing much of the upper MS River Valley and Great
Lakes.

&&

Short term...(this evening through tuesday)
issued at 330 PM CDT Monday Aug 3 2015

Tonight...embedded/largely channeled vorticity and southwest edge of
upper jet streak may combine with some marginal southwesterly low level jet
running up and over the low level boundary to produce a few elevated
showers or a storm that may make it across the far southwestern County Warning Area
overnight. But more optimum support across eastern Nebraska and
southeastward down toward and southeast of the St Louis area...and
could see the scenario where the dvn County Warning Area remains largely dry through
12z Tuesday morning. But will maintain low chance probability of precipitation across these southern
areas. Otherwise mainly clear skies/light winds further to the north
and with dry down-mixed or advected in surface dewpoints...expect a
seasonably cool night with many areas making it down into the 50s.

Tuesday...western wave energy complex trying to undercut upstream
Omega ridge...as well as ongoing lift mechanisms closer to home may
allow for some northward drift/retreat of the boundary to the south
of the region especially across the Central Plains. Thus there may be a
bit more support for some overrunning showers and cloud debris
pushing up across the southwestern County Warning Area on Tuesday...but again could easily
see the scenario where the County Warning Area remains mainly dry through 00z Wednesday.
Areas away from the thicker cloud debris should be able to warm into
the lower 80s again for highs. ..12..

Long term...(tuesday night through next monday)
issued at 330 PM CDT Monday Aug 3 2015

Overview...temperatures will average near to slightly below normal through this
week as a 500mb negative height anomaly slowly shifts from the
Ontario/Hudson Bay region eastward through Quebec...and as high
pressure over the western Great Lakes results in an easterly
component in the low-level flow locally. Forecast highs are in the
upper 70s/lower 80s most days with Lower/Middle 70s possible Friday.

A series of shortwave troughs will bring chances for showers and
thunderstorms...especially Wednesday/Wednesday night and again on
Friday. The extreme heat/humidity and better chances for strong
storms should stay south of the area through the upcoming weekend.

Tuesday night through Wednesday night...rain chances vary between 20-
50 percent...lowest along Highway 20...highest in the southern two
tier of counties in the County Warning Area. Low instability levels will limit
overall thunderstorm strength. Model consensus has the brunt of the
moisture going south of the forecast area with a moderately strong
vorticity. Maximum traversing through central Missouri. Therefore...may have
to lower probability of precipitation across a good portion of the County Warning Area in future forecasts.

GFS is an outlier tracking the surface low across northern Iowa
resulting in strong warm air advection across east Iowa/west Illinois and widespread rain
Wednesday evening/night...this is the least likely of scenarios.

Thursday and Friday...the slow cool down continues with highs
forecast in the middle/upper 70s by Friday. Models project 1000-500mb
thickness values bottoming out near 570 dam and 850mb temperatures down to
14 c. Another shortwave trough may cross the upper Mississippi River
valley Thursday night into Friday per the European model (ecmwf)/Gem but it does not appear
to have much instability to work with. The GFS keeps this secondary
disturbance on a more southerly track so it is again at odds with
model consensus which is likely tied to the interplay of the two
primary shortwaves.

Saturday and Sunday...temperatures may be a little warmer into the lower to
middle 80s...850mb temperatures climb back up into the middle/upper teens
celsius. Southeasterly flow is forecast to develop in response to
Lee-side trough formation over the Western Plains as strong 500mb
winds flow perpendicular to The Rockies. Chances for precipitation are low
at the moment.

&&

Aviation...(for the 06z tafs through 06z Tuesday night)
issued at 1045 PM CDT Monday Aug 3 2015

VFR conds through this taf cycle as weak high pressure builds into
the area. Any showers will remain in MO closer to a stalled frontal
boundary there. Mainly northwest to west winds less than 10 knots
through the period.

&&

Dvn watches/warnings/advisories...
Iowa...none.
Illinois...none.
MO...none.
&&

$$

Synopsis...12
short term...12
long term...uttech
aviation...haase

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