Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000
FXUS63 KDVN 141157
AFDDVN

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

...12z AVIATION UPDATE...

.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 for 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 potential 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 east 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 12Z TAFS through 12Z Sunday Morning)
ISSUED AT 648 AM CDT Sat Oct 14 2017

Potentially turbulent aviation day with strong vertical wind
fields and shear. IFR to LIFR low cloud decks and some fog with
sctrd showers and thunderstorms this morning...an increase in
storm coverage from the southwest after 9 AM CDT. Low decks and
temporary reduced VSBYS to low MVFR and IFR with this mid to late
morning activity. Then possibly an MVFR window and lull in the
showers and storms from early to mid afternoon, before stronger
storms expected to develop and impact/get into the VCNTY of most
of the TAF sites from mid afternoon through mid evening. Variable
high wind gusts possible with this evening line of storms as they
blow through. Then improvement with CIGS to MVFR and VSBYS with
frontal passage, the big thing then a wind switch to the southwest
and west with a large increase to 15 to 25 KTS late tonight into
Sunday morning. ..12..

&&

.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...12



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