Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 241120
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
620 AM CDT Thu Aug 24 2017

...AVIATION UPDATE...

.SYNOPSIS...
Issued at 342 AM CDT Thu Aug 24 2017

A cool and dry airmass was in place under Canadian high pressure
reaching from WI to MO. 3 am temperatures were in the 50s with light
and variable winds across the forecast area. Satellite imagery
showed an axis of mid and high clouds in the upper level northwest
flow, across much of northern and central IA reaching into eastern
IA. In this axis of elevated warm advection and weak mid level
forcing, isolated showers and few thunderstorms were occurring
across central and northwest IA. KDVN showed a few very weak
showers, likely just sprinkles reaching into east central and
southwest IA, rapidly weakening as they moved away from the upper
level support and into the drier air under the low level ridge.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 342 AM CDT Thu Aug 24 2017

Main challenges center around temperatures and the potential for
light showers today and tonight. This morning, recent trends with
the showers dissipating as they move away from the upper level
support over western IA should continue through early morning and
will have only isolated light showers mentioned until mid morning.
Weak impulses acting on meager mid and upper level moisture, will
continue to stream clouds over the area, resulting in partly to
mostly cloudy skies. Given the cool start and less sunshine in a
similar airmass, today should be cooler in most areas than the past
couple days and have held highs to the lower 70s north, and mid to
upper 70s from the central to the far south.

Tonight, the surface ridge shifts eastward with developing elevated
warm advection showers returning along the western edge, similar to
tonight`s setup. Most models suggest the focus for dissipating
showers, or sprinkles, will be into east central IA, mainly north of
I-80 and have slight chances there after midnight. Cloud cover in
the west will hold mins in the mid to upper 50s, while the potential
for periods of clear skies will again lead to lows around 50 over
northwest IL.

.LONG TERM...(Friday through Wednesday)
ISSUED AT 342 AM CDT Thu Aug 24 2017

Friday through Wednesday

Expect temps to average in the middle 70s across the north to near
80 F in the south, or about 3-5 F degrees below late August normals.
At night, we will drop into the 50s to lower 60s.

A piece of an upper jet over west-central Canada will break off and
round the northern periphery of the Western ridge. A small jet
streak will then carve out an upper-level low over the Upper Midwest
Saturday night into Sunday. The upper low is progged to linger in
the Western Great Lakes region through Tuesday. Scattered showers
and isolated thunderstorms are expected during this period with the
best chances for rain Sunday afternoon and evening along a cold
front when model blend PoPs are 50-60%. It is too early to assess
the risk for severe weather on Sunday.

Models continue to track the remnants of tropical system Harvey
along the Ohio Valley toward the middle or end of next week, well SE
of E Iowa/NW Illinois. Uttech

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday Morning)
ISSUED AT 620 AM CDT Thu Aug 24 2017

Isolated light rain showers, mostly in the form of sprinkles,
will continue to stream across eastern Iowa through mid morning.
This rain is falling from high cloud bases and not expected to
drop any sites below VFR thresholds for visibility or ceilings.
VCNTY wording has been utilized at CID and BRL early this morning.
Otherwise, high pressure over the area will result in light
surface winds, with VFR conditions through tonight. Another round
of similar very light scattered showers is possible overnight, but
confidence was too low to include a mention of these in the
forecasts.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...NONE.
MO...NONE.
&&

$$

SYNOPSIS...Sheets
SHORT TERM...Sheets
LONG TERM...Uttech
AVIATION...Sheets


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