Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000
FXUS63 KDVN 281758
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1158 AM CST Mon Nov 28 2016

...18z AVIATION UPDATE...

.SYNOPSIS...
Issued at 324 AM CST Mon Nov 28 2016

06Z surface data has a strong low in eastern South Dakota. A warm
front ran across southern Minnesota into eastern Iowa while the cold
front ran from the low into western Iowa and then into eastern
Kansas. Dew points were in the 30s and 40s across the Midwest with a
tongue of 50s and higher from Texas into central Iowa.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 324 AM CST Mon Nov 28 2016

Through sunrise, patchy drizzle and isolated rain showers will be
possible along with above normal temperatures.

After sunrise, isolated rain showers are expected to continue
through mid-morning as moisture continue to surge into the area. By
late morning forcing will be on the increase as the next upper level
disturbance moves northeast across Missouri. Areal coverage of the
showers will be on the increase with isolated thunderstorms
developing just prior to the noon hour.

During the afternoon hours, areal coverage of the rain will continue
to increase with additional thunderstorm development.

The question during the afternoon is whether or not there will be a
chance of severe storms. The forcing being provided by the upper
level disturbance moving out of Missouri will be quite strong.
However, what is being suggested by the models is that thunderstorms
associated with this feature may not be surface based. If that is
the case then localized downbursts may be possible only if the sub
cloud layer is unstable.

The chances for any surface based storms appear to be central Iowa
that might get into the far west and southwest areas prior to
sunset. The area being suggested is between KGGI and KVTI south to
between KOTM and KFFL and then into far northeast Missouri. This
area is along the interface of the dry slot and frontal boundary.
The forcing is strong and the shear is high but the overall
instability is low.

If storms develop in this area then stretching of the updraft early
in the storm development could produce very brief spin-up tornadoes.
The window of opportunity for this to occur is very brief, generally
between 3 and 5 PM.

Tonight, the rain with embedded thunderstorms will continue east of
the Mississippi during the early evening with more scattered
convection west of the Mississippi. By mid-evening the rain will
begin to rapidly end from west to east with most if not all of the
area dry after midnight.

.LONG TERM...(Tuesday through Sunday)
ISSUED AT 324 AM CST Mon Nov 28 2016

Much of the rest of the week will be characterized by a slowly
filling cut-off low lifting from the Upper Midwest through the
Great Lakes region.

Tuesday, the cwa will reside in the dry slot south of the low.
This will feature sunshine, gusty swly winds and weak warm
advection, which will equate to one last day of above normal
temperatures with highs from near 50 northwest to the upper 50s
southeast. Late in the day and especially Tuesday evening there is
some mixed signals with precipitation ahead of the main cold cold
front. Incoming cold pocket of air aloft results in rather steep
lapse rates of around 8c/km in 850 mb to 500 mb layer by evening.
However, limiting factors are low level moisture lacking and weak
forcing with vorticity more channeled and to our southwest. Better
area for any precipitation would then appear to be eastern and
southern Illinois, but after coordination with ILX and LOT I have
added a buffer of slight chance pops mainly south/east of the Quad
Cities during the evening.   Overnight Tuesday night with the
passage of the cold front will see arrival of colder air and
increasing clouds in cyclonic flow/caa.

Wednesday through Thursday, will feature colder temperatures (near
seasonal norms) along with a prolonged period of cloudiness, and
some rain/snow chances in the wrap-around especially north of I-80,
as the low moves into the Great Lakes ahead of upstream shortwave
over the Pacific Northwest. With surface temperatures above freezing
little if any snow accumulation is expected.

Friday through Saturday, anticipate dry conditions with skies
becoming partly cloudy with general suggestion of broad high pressure
in control. Temperatures look to remain seasonable with highs in the
upper 30s to lower 40s, and lows mainly in the 20s.

Sunday into early next week offers considerable uncertainty, as the
main focus will be with an anomalously potent energy packet digging
into the southwest U.S. Latest GFS depicts a cut-off low near the
Baja of California which doesn`t move much at all, which is a bit
perplexing as it`s much stronger and further south with northern stream
shortwave traversing Alberta. Meanwhile, the ECMWF is much more
progressive as it has the cutoff low eventually phasing with this
northern stream energy and jettisons the low northeast through the
Mid-Mississippi Valley, which is also a bit perplexing given how
potent and anomalously deep (sub 550-DM, roughly 5 sigma below climo)
the energy is and how much weaker and further north it has the Canadian
shortwave. The ECMWF solution would allow for significant moisture
transport northward ahead of deepening cyclone, and signal much greater
precipitation chances late in the weekend into early next week. The
forecast at this time is closer to GFS which leads to some small chances
for rain/snow showers Sunday with weaker wave in northwest flow, but
confidence is extremely low.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday Afternoon)
ISSUED AT 1143 AM CST Mon Nov 28 2016

Solid MVFR deck this afternoon with sctrd fast moving showers and
some thunderstorms streaming up quickly from north-to-south ahead
of an incoming front acrs western IA ATTM. If a TAF site manages
to get hit by one of the passing thunderstorm cells, visibilties
may be reduced temporarily down to 3-4SM by brief downpours and
possibly embedded with small hail. Clearing will try to move in
from the southwest this evening and overnight in the northern MN
cyclone`s dry streak. Brisk southeasterly sfc winds this afternoon
gusting to 25-30 KTS at times, will become more southwesterly
later this evening and diminish to 10-15 KTS into Tue morning.
    ..12..

&&

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

$$

SYNOPSIS...08
SHORT TERM...08
LONG TERM...McClure
AVIATION...12



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