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Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
804 PM CDT Friday Aug 28 2015

Update...
issued at 749 PM CDT Friday Aug 28 2015

Evening update to refine probability of precipitation for latest trends...a general
increase especially central and northern counties. Latest model
runs are also indicating potential for shower redevelopment during
the day Saturday along an inverted surface trough...and have
pulled the probability of precipitation a bit farther west. Expecting periods of moderate
to occasionally heavy rain to continue to gradually spread
eastward through late evening and overnight. Some areas could pick
up an additional inch or so...especially north of Highway 30...although
the threat for flash flooding is low.

&&

Synopsis...
issued at 339 PM CDT Friday Aug 28 2015

Approaching upper level disturbance and low to middle level warm
moist advection aiding widespread coverage of showers and
some storms from north central into northeast Iowa at middle afternoon
with more widely scattered activity further south. Slow moving
band of convection nearly anchored west to east immediately
ahead of vorticity maximum within zone of strong moisture transport
(pwats of 1.7-1.8+ inches) which is leading to localized swath
of very heavy rain 3-5+ inches and some flash flooding over north
central now advancing into northeast Iowa. This slow moving system
will look to bring increasing rain chances to much of County Warning Area tonight
(heavy rain portions of northeast ia) with the rain lingering
into Saturday while gradually shifting eastward.

&&

Short term...(this evening through saturday)
issued at 339 PM CDT Friday Aug 28 2015

Rain chances will continue to expand and increase tonight as slow
moving disturbance moves into the region. Greatest rain chances
will be found immediately ahead of middle level wave or roughly
along/north of Highway 30... although do anticipate increase in coverage
tonight further south. Fairly high warm cloud depths and precipitable waters
increasing to over 1.7 to 1.8 inches will bring likelihood of high
rainfall efficiency...with areas near/north of Highway 30 and
especially on Iowa side favored for heaviest rains being immediately
ahead of middle level wave and remaining in veered low level jet and
moisture transport the longest. In some of these areas near/north of
Highway 30 could see locally 2-3+ inches and potential for localized
flash flooding issues with convection and higher rates along with
slow movement. With clouds and southerly winds have stayed near
blend or warm side of guidance for lows... and have range from
around 60 north to middle 60s south.

Saturday...will see gradual ending of rain chances from west to
east during day... with even some decrease in clouds west of the
Mississippi by middle to late PM. Highs will be challenging and
dependent on amount of sunshine... and generally have middle 70s to
around 80 degrees with warmest readings likely being found over
western portions of County Warning Area.

Long term...(saturday night through friday)
issued at 339 PM CDT Friday Aug 28 2015

Overview...building and persistent upper-level ridge over the
central U.S. Will lead to above average temperatures and humid
conditions through the extended period. Overall chances for rain
are very low.

Saturday night through Sunday...have 20 probability of precipitation early Saturday night
along and east of the Mississippi River...nothing widespread is
expected and most areas will stay dry as upper disturbance exits to
the east. On Sunday...lower 80s on average for highs and partly sunny
skies will make for a nice end to the weekend.

Monday and Tuesday...expect warmer temperatures into the middle/upper 80s
as upper-level ridge builds over the Midwest. 1000-500mb thickness
values are forecast to hover near 576 dam and 850mb temperatures near 18 c.

Wednesday...a shortwave trough from remnant monsoonal convection
may traverse the Midwest but plenty of uncertainty as to whether
this feature even develops. Introduced slight chances for showers
and thunderstorms. No significant change in 1000-500mb thicknesses
or 850mb temperatures means highs should still average in the middle/upper 80s.

Thursday and Friday...models indicate a slight uptick in 850mb temperatures
toward 20c. Current forecast has upper 80s on average across the County Warning Area.
Raw models such as the European model (ecmwf)/GFS are in the lower to middle 90s but
feel this is too warm given 850mb temperatures at 20c or lower...humid surface
conditions with dewpoints in the upper 60s...and a lower September
sun angle.

&&

Aviation...(for the 00z tafs through 00z Saturday evening)
issued at 749 PM CDT Friday Aug 28 2015

Little change for the 00z/29 taf issuance. Periods of rain will
continue overnight...especially at kcid/kdbq/kmli. MVFR ceilings
will be common...along with IFR/MVFR fog favored toward daybreak.
There is some potential for showers to redevelop Saturday
afternoon...mainly impacting kbrl/kmli.

&&

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

$$

Update...rp Kinney
synopsis...McClure
short term...McClure
long term...uttech
aviation...rp Kinney

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