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Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
328 PM CDT Tuesday Sep 23 2014

Synopsis...
issued at 327 PM CDT Tuesday Sep 23 2014

12z upper air analysis had an upper high over the western Great Lakes. A
low level jet ran from West Texas into the Central Plains and a plume of
tropical moisture ran from Mexico into the northern plains.
Satellite trends through middle afternoon show a slow increase in high
and some middle level clouds across Iowa that slowly evaporate as it
hits the dry air over the Great Lakes.

18z surface analysis has weak lows in western South Dakota with high
pressure over the Ohio Valley. Dew points were in the 40s over the
Ohio Valley with 50s over parts of the Great Lakes and plains.

&&

Short term...(this evening through wednesday)
issued at 327 PM CDT Tuesday Sep 23 2014

Dry conditions will be seen from late this afternoon through sunset
with only a slow increase in clouds.

After sunset...very weak forcing begins moving into the far west
associated with an approaching upper level disturbance. This forcing
weakens with time through sunrise. Thus an increase in clouds will
be seen through sunrise Wednesday. At the very worst some isolated
sprinkles may occur across the northwest quarter of the area.

The first round of weak forcing exits the area by middle day Wednesday.
Thus any sprinkles across the northwest third of the area will
slowly end.

Another round of weak forcing arrives middle to late Wednesday afternoon.
The dryness of the air should result in nothing more than isolated
sprinkles over the western third of the area.



Long term...(wednesday night through next tuesday)
issued at 327 PM CDT Tuesday Sep 23 2014

Wednesday night through Friday...weakening upper wave still on track
to drift eastward across the County Warning Area Wednesday night into Thursday. Although this
feature still tries to top-down saturate as it progresses
across...extent of dry low to middle levels just to allow for some
isolated to sctrd high based sprinkles Wednesday night into Thursday morning
across mainly the northern two thirds or half. Main effect of the
upper level wave probably still to be a passing middle deck of clouds
Wednesday night into Thursday morning...before the wave passes and washes out
to allow for even this deck to decay as Thursday progresses. May turn
mostly sunny by Thursday afternoon especially west of the MS river. Cloud
cover may allow for some lows Wednesday night not to dip out of the middle
50s...cooler east of the MS river where there will be some time before
clouds thicken and advect across...if lingering ridge axis off to the
east doesn/T eat at them as they try to move that way. Some sunshine
by Thursday afternoon to allow for advertised warm up to take hold with
values in the middle to upper 70s. Thermal profiles continue to
moderate into Friday with the low to middle level thermal structure
supporting widespread upper 70s to lower 80s...although a
mixing-limiting 850 mb mb inversion and boundary layer southeasterly
flow may inhibit the true warm up potential some. Large diurnal
swings from lows to highs to continue in drying surface layer and when
cloud cover is not a factor.

Saturday through next Tuesday...12z run medium range solutions
generally suggest broad Rex type block to reign across much of the
Continental U.S. Over the weekend. Remnant upper low may gyrate somewhere across
the region rom MO and across Iowa...but dry vertical column and dominant
ridge across the middle Continental U.S. To limit any kind of moisture return flow to
fuel any precipitation. Will keep the forecast dry into Monday with near or
above normal temperatures especially during the day. In-building l/west trough
from the west to eventually translate into the next main precipitation
chances by next Tuesday or Wednesday as it draws Gulf moisture and even a
possible wave up the MS River Valley to the Lee of it. The medium range
model solutions again diverge on timing...phasing and handling of
this process...and probably will continue to through the next 24-48
hours of runs.

&&

Aviation...(for the 18z tafs through 18z Wednesday afternoon)
issued at 1219 PM CDT Tuesday Sep 23 2014

VFR conditions are expected through 00z/25 as high pressure moves
to the East Coast. A passing upper level disturbance will increase
middle and high clouds that may result in some sprinkles across
eastern Iowa after 03z/24.

&&

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

$$

Synopsis...08
short term...08
long term...12
aviation...08

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