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Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
333 PM CDT sun Aug 30 2015

Synopsis...
issued at 314 PM CDT sun Aug 30 2015

Surface ridge axis extends from the Great Lakes through the County Warning Area
and into the south Central Plains at middle afternoon. The fairly
widespread dense fog burned off by middle to late am leaving behind
fairly extensive stratus which has been steadily eroding from the
south and evolving into scattered stratocu deck. The increasing
peaks of sunshine has helped to bump temperatures up to near late
August normals with many areas in the upper 70s to lower 80s.
The exception being mainly portions of northeast Iowa where stratus
sill lingers and aiding in holding temperatures down in the lower 70s
attim... but with more late day sunshine should see temperatures in these
areas surge late. Pattern aloft features an amplified ridge /heat dome/
through the plains in advance of a Pacific northwest trough. The next
24 hours will see this ridge and warmer air build into the middle-
Mississippi Valley as the Pacific northwest trough shifts across the
northern rockies. This will result in continuation of dry conditions
with warmer temperatures on Monday.

&&

Short term...(this evening through monday)
issued at 314 PM CDT sun Aug 30 2015

Main challenge remains low clouds and fog potential with impact on
temperatures.

Following trends per satellite and observation from late afternoon with decreasing stratus
northwest County Warning Area evolving into scattered stratocumulus then mostly
clear for a time this evening. Late evening and overnight with
continued weak winds and abundant low level moisture expect
redevelopment of fog dense in some areas... with also some stratus
possible although uncertain on extent of any stratus formation with
latest rap and NAM models showing around 15+ kts of wind just above
moist layer which may be sufficient mixing to offset widespread stratus
formation and with just diurnal cumulus across MO Don/T expect any
advection of low deck. Min temperatures will be challenging and dependent on
fog and stratus trends. As we saw this am... potential for areas that
stay clear longer to radiate down into the 50s with near calm winds.
Otherwise... with temperatures a bit warmer today for many and with middle afternoon
dewpoints in middle/upper 60s I have kept lows mainly in range of 60-67 degrees.

On Monday...any fog should burn off a bit earlier tomorrow by middle am
with a bit stronger southerly wind developing of 5-10 kts. Any
stratus should lift to fair weather cumulus during afternoon and generally
mostly sunny skies. This will allow temperatures to climb well into the 80s
with widespread middle to a few upper 80s. These temperatures coupled with
dewpoints well in the 60s to near 70 degrees will make for very warm feel
with heat indices around 90/l90s.

Long term...(monday night through sunday)
issued at 314 PM CDT sun Aug 30 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.

Tuesday and Wednesday...1000-500mb thickness values are forecast to
be near 576-579 dam with 850mb temperatures in the upper teens/near 20 c.
Forecast highs are in the upper 80s to near 90 f...with heat indices
in the lower to middle 90s.

A shortwave trough from remnant monsoonal convection may traverse
the Midwest on Wednesday but models track it northwest of east Iowa/west
Illinois. Consequently kept the forecast dry.

Thursday through Saturday...raw models still appear to have a warm
bias and are projecting lower to middle 90s. Humid
conditions...850mb temperatures in the upper teens to possibly lower 20s
celsius...and a lower September sun angle back a temperature forecast
slightly below the higher raw model data.

&&

Aviation...(for the 18z tafs through 18z Monday afternoon)
issued at 116 PM CDT sun Aug 30 2015

Anticipate stratus to continue lifting to scattered-broken stratocu deck with
widespread MVFR bases and ceilings becoming VFR by late PM. Given
continued weak low level flow and abundant moisture expect more fog
to develop by late evening and overnight with potential for some stratus
with conditions lowering into MVFR to IFR... with pockets of LIFR/vlifr.
On Monday expect similar trends to today with fog lifting by around
middle am with any stratus lifting into VFR stratocu deck during afternoon.
Light and variable winds will turn southerly at 5-10 kts on Monday.

&&

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

$$

Synopsis...McClure
short term...McClure
long term...uttech
aviation...McClure

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