Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 120450
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1150 PM CDT Wed Oct 11 2017

...AVIATION UPDATE...

.SYNOPSIS...
Issued at 240 PM CDT Wed Oct 11 2017

Storm system that brought widespread soaking rain to much of the
cwa yesterday was in the Ohio Valley region. Cyclonic flow as far
west as central IA/eastern MN, combined with the moist ground, has
kept low stratus in place all day. As a result, temperatures were
on the cool side with afternoon readings only in the 50s to around 60.

&&

.SHORT TERM...(This Evening through Thursday)
ISSUED AT 240 PM CDT Wed Oct 11 2017

Forecast focus on clouds and possible drizzle.

Tonight: Weak surface ridge comes across the cwa providing very
light winds. This will be tough to scour out the clouds considering
forecast soundings indicate a strengthening inversion at 850 mb.
This will keep the low level moisture from the recent rainfall
trapped below the inversion. Therefore, the widespread low stratus
is expected to remain in place. Also, soundings indicate a
classic drizzle scenario with very dry air above the inversion,
and weak omega in the stratus layer, which the HRRR picks up on.
For now will keep the mention of patchy drizzle and patchy fog in
the grids. Later shifts can monitor for the possibility of more
widespread drizzle if the forcing is a bit stronger in the sub-
inversion layer. Due to the low stratus, there won`t be much of a
diurnal spread in temperatures, with lows in the lower 50s.

Thursday: Low stratus to remain in place for much of the morning,
then skies should clear from west to east during the afternoon.
High pressure ridge will shift to our east with warm air advection
kicking in (southerly winds), which should allow for the stratus
to gradually erode. Maximum temperatures will push into the 60s,
which is normal for mid October.

.LONG TERM...(Thursday Night through Wednesday)
ISSUED AT 240 PM CDT Wed Oct 11 2017

Main forecast concern for the long term forecast are the chances for
thunderstorms this weekend and with it the chance for heavy rain and
severe weather.  After this front this weekend, the rest of the long
term looks dry and more seasonal as far as sensible weather goes.

Friday...the return of warmer temperatures and boundary layer
moisture is expected as the mean flow turns southwest.  H85 flow
will advect in warmer more moist air.  H85 convergence is expected
to be just north of the CWA as a weak wave ripples through the flow.
This will be enough to initiate showers and some thunderstorms across
the northern CWA Friday evening.  As this convection continues
through the overnight, the effective warm front will be pushed south
into our CWA.  Rain from Friday night across the area, may set the
stage for hydro concerns on Saturday.  Friday night, instability
will be low, however deep layer shear is conducive for midlevel
storm rotation.  Any midlevel rotation would lead to increased
rainfall across the area along with possibly the isolated elevated
hail storm.  The threat for severe weather is low on Friday evening.

Saturday, major questions remain as to where the effective warm
front is.  A strong short wave is expected to approach the area
later in the day into the evening.  At the same time a low is
expected to move across the boundary. Short of a negatively tilted
trof, wherever the warm front is Saturday morning is probably where
it will stay. Shear is quite strong along this boundary and would
lend itself well to low level storm rotation. Any storm near this
boundary will likely have a threat to become severe.  The next
question is whether or not we will have a lull in the precip and
cloud cover on Saturday.  If we dont have a lull, convection will
likely increase with the sfc low.  If there is a lull, the threat
for severe weather will increase.

Another concern is the stalled boundary with PWATs near 2 inches.
Near continuous H85 flow will feed convection plenty of moisture.
Areas near and north of the warm front could see heavy rain on
Saturday.  With the rain we had yesterday along with the forecast
rain for Friday, hydro issues could become an issue with possible
rises on area rivers along with potential flash flooding.

There are a lot of possibilities with the forecast for this weekend.
Regardless, now is the time to start paying attention to this
forecast.  Additional model runs will lead to more confidence in a
forecast solution.

Past Saturday, cooler and drier air is expected without a good
chance of precip through mid next week.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday Night)
ISSUED AT 1146 PM CDT Wed Oct 11 2017

Cloudy skies with mostly IFR/LIFR conditions with isolated very
light drizzle are possible until mid morning with light east to
southeast winds. The patchy light nature of the drizzle have left
out of the TAF attm. Light fog for with low ceilings to prevail
with mainly visibilities of 1 to 4 miles. VFR conditions to
develop with clearing by mid to late day with winds becoming
southerly through Thursday evening.

&&

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

&&

$$

SYNOPSIS...Haase
SHORT TERM...Haase
LONG TERM...Gibbs
AVIATION...Nichols



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