Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000
FXUS63 KDVN 140902
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
402 AM CDT Sat Oct 14 2017

.SYNOPSIS...
Issued at 330 AM CDT Sat Oct 14 2017

Looming strong upper trof out acrs the central and northern Rockies,
and water vapor imagery indicating unseasonable/high moisture feed
streaming up into the midwest out of west central Mexico, to combine
for a stormy day today into tonight with multiple hazards. Cooler
and windy for the second half of the weekend with some frost
posssible early Monday morning. Then mainly dry/nil weather on tap
for next week.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 330 AM CDT Sat Oct 14 2017

Ongoing elevated showers and thunderstorms along and north of I80 to
decrease by sunrise fro much of the area a temporary lull through
mid morning. But then the first short wave ejecting out in pre-trof
southwesterlies to combine with moisture laden 40 KT southwesterly
H85 MB flow to produce another round of showers and storms funneling
up along and north of the llvl boundary now draped from northeastern
MO, to the southern Chicagoland area from mid morning to the midday
period. the boundary will retreat a bit further north by early
afternoon, and as the midday precip cluster exits off to
northeastern IL, this may allow the south to southeastern half of the
DVN CWA to recharge and heat up some. At least mid sfc 60 DPTS
combined with ambient temps in the mid to upper 70s to make for
CAPES of 1000 to 1500+ by late afternoon in these areas. Further
north of the main warm front and I80, elevated showers and some
thunder may keep going into the afternoon.

As the strong upper trof crosses the central/northern plains by late
afternoon, deep synoptic lift, strong shear profiles and
unseasonable moisture levels all point to a autumn severe weather
event across portions of the area this afternoon and into the
evening. If the airmass can recover like projected in these southern
and eastern areas, bulk shear of 40-60+ KTS, 0-1km of 20-30KTs, and
0-3km SRH profiles of 300-400+ m2/s2 all suggest sctrd pre-frontal
supercells this afternoon and early evening especially south of I80.
These shear profiles, some sfc southeast wind component and low
LCL`s of 2000 FT AGL or less suggest a tornado threat. Then the
second punch of more linear segments or squall line type systems
with 60-70 MPH damaging wind threat to sweep in acrs at least the
southeastern half to third of the CWA this evening through 8 PM to
10 PM or so tonight. A spin up meso-tornado possible as well with
these evening line segments looking at 30 KT 0-3km shear vectors.
All in all, slight to enhanced severe weather outlook look on target
if we get the thermodynamics to go with the high shear. How far
north the main sfc low and triple point makes it still uncertain and
will be a player on how far north the main severe threat extends,
but most latest run models have trended north and west through this
evening.

With the Mexico fetch atmospheric river and very high PWAT feed of
1.6 to near 2 inches possible today ahead of the convective
episodes, the potentail for locally heavy rain of 1-3 inches appears
very possible in swaths where the storms occur. Higher amounts
possible in areas that get repeated storms moving along the same
areas. High shear profiles will also wring out high rainfall rates
with the stronger storms and line segments, up to 2 inches an hour.
With portions of the area getting heavy rain overnight and Friday
afternoon, as well as taking into account the widespread rains a few
days ago, have issued a Flash Flood Watch starting mid morning and
ongoing into late tonight for areas generally along and north of a
line from Sigourney IA, to Aledo IL and to Princeton/Putnam IL for
now. The entire CWA may be at risk for flash flooding, and later
assessment by the day crew may warrant an expansion further south.

Th heavy rain and severe threat to largely sweep east of the CWA
after midnight tonight, with lingering post-frontal precip shield in
the eats and southeast through 3 AM CDT. Tight pressure gradient
southwest of deepening sfc low over central LK MI will make for late
night gusty northwest winds, ranging sustained from 20 to near 30
MPH and higher gusts. Will have to watch for gravity wave
enhancement as well behind the main line of exiting showers late
tonight.    ..12..

.LONG TERM...(Sunday through next Friday)
ISSUED AT 330 AM CDT Sat Oct 14 2017

Sunday, expect strong cold air advection, with a northwest wind and
highs only in the mid to upper 50s. A surface high pressure ridge
will traverse the forecast area Sunday night with a clear sky and
light wind. Ideal radiational cooling conditions should drop lows
into the mid/upper 30s. Expect some patchy frost, mainly along and
north of Interstate 80.

Looking ahead, the rest of the long term period still looks dry with
favorable synoptic model agreement. Upper flow will transition from
northwesterly to zonal, and eventually southwest. Expect a gradual
warming trend through the period with highs back above normal late
in the week.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday Night)
ISSUED AT 1140 PM CDT Fri Oct 13 2017

Unsettled conditions with periods of MVFR and possibly IFR conditions
with mostly areas of passing copious showers and storms to occur the
next 24 hours. A stalled boundary will interact with a surface low
that passes across the region Saturday PM. The best chance of storms
will be late PM Saturday and evening when the cold front passes with
gusty winds possible. Winds will be light east to northeast overnight
becoming south by afternoon with a shift to the northwest and gusty
by midnight behind the cold front with likely MVFR/IFR cloud bases.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Flash Flood Watch from 10 AM CDT this morning through late
     tonight for Benton-Buchanan-Cedar-Clinton-Delaware-Dubuque-
     Iowa-Jackson-Johnson-Jones-Keokuk-Linn-Louisa-Muscatine-
     Scott-Washington.

IL...Flash Flood Watch from 10 AM CDT this morning through late
     tonight for Bureau-Carroll-Henry IL-Jo Daviess-Mercer-
     Putnam-Rock Island-Stephenson-Whiteside.

MO...NONE.
&&

$$

SYNOPSIS...12
SHORT TERM...12
LONG TERM...RP Kinney
AVIATION...Nichols


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