Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 251755 AAB

Area Forecast Discussion...UPDATED
National Weather Service Quad Cities IA IL
1255 PM CDT Tue Oct 25 2016


Issued at 344 AM CDT Tue Oct 25 2016

Surface ridge axis extends from the Upper Midwest through the
Ohio Valley early this morning. Low level easterly flow continues
ushering in dry air, and with some thinning of high cloudiness at
times seeing several ob sites periodically dipping down into the
30s from roughly the Wapsipinicon and Rock River Valleys into the
Sauk Valley and other portions of northern Illinois, with Freeport
as cold as 32 degrees. Otherwise, temperatures were mainly in the
lower to mid 40s. Water vapor imagery shows broad central conus
ridging ahead of several low amplitude impulses lifting through
the Rockies. 00Z DVN sounding showed a continued large dry wedge
between 900 and 700 mb, which will certainly take some time to
moisten. Low level moist axis resides well to our southwest across
the southern Plains with surface dew points in the upper 50s and
lower 60s. A strengthening low level jet will rapidly advect this
moisture northward over time into a developing warm front, and
the attendant isentropic ascent coupled with strengthening mid
level frontogenetical forcing ahead of approaching shortwave
energy will eventually lead to rain/showers becoming likely across
the area with a few thunderstorms possible over the next 24-30+ hrs.


.SHORT TERM...(Today through Wednesday)
ISSUED AT 344 AM CDT Tue Oct 25 2016

Central conus mid to upper level ridge is forecast to deamplify as
as several shortwave energy packets are ejected from the Rockies
ahead of a Pacific northwest trough. Models remain in decent agreement
on developing a weak surface low over eastern Nebraska by this
evening attendant to approaching shortwave. This low will then track
east across the Mid-Mississippi Valley on Wednesday, with the general
model consensus showing the low passing between U.S. Highway 30 and
I-80. Developing warm front and strong moisture advection along with
the approaching low and mid level shortwave will lead to rain/showers
with a few thunderstorms possible over the next 24-30+ hours.

Precipitation timing/trends...

The dry air above surface to near 700 mb will take time to saturate.
Elevated isentropic ascent and Fgen banding will continue to generate
radar returns this morning into afternoon especially across north
1/3-1/2, but likely only able to saturate down to around 5kft agl
thus dry although a stray sprinkle not entirely out of realm.
Anticipate the main window and area for shower development will be
by mid to late PM back across the west/southwest cwa on nose of 850 mb
moisture transport. Expect this area to expand while lifting
northeastward this evening. As the isentropic ascent migrates
north late evening into early overnight could present a small drier
window especially for areas south of Highway 30. During the early morning
though anticipate a band of showers and few storms shifting from central
Iowa and across the cwa through mid morning Wednesday. Additional
showers and few storms possible Wed PM near I-80 on south ahead of
cold front/low level convergent boundary, while persistent light rain
or drizzle likely to the north with all precipitation tapering off from
west to east by mid to late Wednesday PM. Can`t rule out a short-lived
window for a strong storm across far southeast Iowa, northeast Missouri
and west central Illinois Wed PM as wedge of marginal instability with
MUCAPE of 500+ j/kg works northward ahead of the front. 0-6km shear has
trended weaker at around 20 kts 0-6km and weak winds aloft for venting
would make this potential low.

Rain amounts...

Precipitable water values look to surge to near 1.3 inches by Wednesday
morning, which is above the 90th percentile for late October supporting
moderate to heavy rain potential. Heaviest rainfall is likely to
occur overnight through Wednesday morning, with the areas near Highway
30 northward through Highway 20 especially on the Iowa side favored
for the highest amounts with swaths over 1 inch to upwards of 2 inches
possible the further north you go even into far northeast Iowa and
southwest Wisconsin. Elsewhere, rain amounts generally expected in the
range of around 0.25 to 0.50+ inches.


Highs today will be modulated by the clouds. Coolest readings in
the lower 50s likely northeast Iowa and far northwest Illinois where
potential for evaporative cooling with virga to limit rise. Elsewhere,
expect mid to upper 50s with possibly a few sites around 60 central
and east with any length of thinning clouds and solar insolation.

Lows tonight coolest northeast and far east with drier low level air
aiding lows in the lower 40s. Meanwhile, warmer lows of around
50 or lower 50s anticipated southwest cwa within increasing moisture

Highs Wednesday will be quite challenging due to clouds/rain and
proximity of warm front and low to make for potentially large gradient.
Coolest readings in the 40s anticipated far northeast Iowa into
northwest Illinois north of the low and warm front, with persistent
clouds/rain. Warmest readings far south where pre-frontal surge could
boost highs into the upper 60s.

.LONG TERM...(Wednesday night through Monday)
ISSUED AT 344 AM CDT Tue Oct 25 2016

Wednesday Night and Thursday: Lingering showers in the eastern
forecast area will end early as the sfc low slides into Indiana.
After morning lows in the 40s, temps are forecast to rebound to
seasonal levels into the mid 50s north to lower 60s far south. A
~1025mb sfc high over the Upper Mississippi River Valley will bring
dry weather and light winds.

Friday: Next clipper system slides through the Great Lakes. Brunt of
forcing/mid-level height falls stay well N/NE and for those reasons
this should be a dry system locally. As for temperatures, the very
warm fall continues with forecast highs about 10 F degrees above
normal. Models are streaming up a +16 C 850mb thermal ridge into E
Iowa/NW Illinois and developing breezy SW sfc winds - a favorable
setup for the above average temps.

Saturday through Tuesday Afternoon: Although weak upper disturbances
may work through the WNW mid-level flow, ridging will dominate the
pattern translating to above normal temperatures and mainly dry
weather. The coolest day is likely going to be Sunday when highs are
forecast closer to seasonal normals. The mid-level ridge then
amplifies into early next week in response to a digging trough in
the Western U.S. Both the GFS/ECMWF have 1000-500mb thicknesses
eclipsing 570 dam by Monday. Uttech


.AVIATION...(For the 18Z TAFS through 18Z Wednesday Afternoon)
ISSUED AT 1242 PM CDT Tue Oct 25 2016

Mainly VFR conditions are forecast before a cold front approaches
the area late in the period. CIGS should turn to MVFR and possibly
IFR late in the period. Have held off on the IFR for late in the
period as confidence is low in seeing that. Rain and rain showers
will be possible across the area tonight and into the morning.
Some rumbles of thunder will be possible. At this time, have not
included a LLWS threat. While this looks possible, will hold off
until it becomes more certain in later shifts. VSBYs should be
impacted tonight and into tomorrow with this rain.




LONG TERM...Uttech
AVIATION...Gibbs is the U.S. government's official web portal to all federal, state and local government web resources and services.