Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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094
FXUS63 KDVN 140446
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1146 PM CDT Fri Oct 13 2017

...AVIATION UPDATE...

.SYNOPSIS...
Issued at 319 PM CDT Fri Oct 13 2017

18Z surface data has a weak frontal boundary running from eastern
Wisconsin, to just southeast of Dubuque, and to near KLWD. Dew
points were in the 50s ahead of the front with 60s from Missouri
into Oklahoma. Behind the front dew points were in the 30s and
40s.

&&

.SHORT TERM...(This Evening through Saturday)
ISSUED AT 319 PM CDT Fri Oct 13 2017

Through sunset, the best chances for rain looks to be in a narrow
band behind the front roughly along a KEFT, KDBQ, to KMIW line where
rainfall could be locally heavy.  South of this line forcing is weak
with a capped atmosphere so dry conditions are expected.

After sunset forcing will increase across the area as moisture
slowly moves into the area. As the forcing increases, areal coverage
of showers and some thunderstorms will increase across the northwest
half of the area during the evening hours.

Based on what has occurred so far today, the potential exists for
storms to repeatedly move across the same areas creating locally
heavy rainfall.

After midnight, the large scale forcing increases further as more
moisture aloft moves into the area. Areal coverage of showers and
thunderstorms will increase further. However, trends with several
models are suggesting that storms may be concentrated in a diagonal
band from roughly De Kalb, IL back toward Ottumwa, IA or possibly
south of that line.

Given the strong anomaly associated with the moisture moving into
the area, locally heavy rainfall will be possible late tonight. If
storms would move repeatedly over the same areas, localized
excessive rainfall is possible.

On Saturday, areal coverage of the rain will decrease during the
morning as the forcing weakens. However, by late morning and during
the afternoon hours forcing and moisture will again increase as the
storm system moves into the area.

Given the significant moisture anomaly and strong forcing with the
system, the potential is there for heavy rainfall. Additionally, one
cannot rule out the potential for severe storms to develop.

.LONG TERM...(Saturday Night through Friday)
ISSUED AT 319 PM CDT Fri Oct 13 2017

Strong upper, mid level, and low level forcing will be maximized
over the CWA Saturday evening. This will produce a severe weather
threat along and south of the low track, or triple point, as well
as a heavy rain threat.  The exceptional moisture plume remains well
forecast by all guidance, but the placement of the forcing remains
split between individual models. I believe that the triple point and
max forcing are not going to move north as the GFS and NAM have
suggested, but will pass over the southern half of the CWA, similar
to the GEM/ECMWF and convective allowing models/ NMM. Thus, we will
be seeing the convection most widespread over the northern 2/3rds of
the CWA early in the period, mainly due to stratification of storms,
which will occur in all locations as the cold front arrives, and
forcing continues behind the low level front.   In any case, the
tornado threat should be triple point and south as well, and
confined mainly to prior to 8 PM. There will be ample shear along
the boundary for low level rotation on storms crossing the likely
stalled out boundary somewhere between Highway 34 and Interstate 80.
We will need to watch these, but over all, the widespread nature of
storms should reduce the severe weather threat.

Rainfall of 1 to 2 inches should occur during the evening, and
depending on the locations of the higher amounts, a flash flood
watch may exist.   Following the cold fropa, windy northwest winds
will sweep in, sustained around 25 mph at times through Sunday
morning.  Gusts to 35 mph are possible.

Beyond Sunday morning, a patchy frost may occur Sunday night in
lower elevations, but is not expected to be widespread, as
temperature drop to the upper 30s.

Monday through Friday, beautiful Fall weather is anticipated with
dry conditions as high pressure dominates the region.

&&

.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...NONE.
IL...NONE.
MO...NONE.

&&

$$

SYNOPSIS...08
SHORT TERM...08
LONG TERM...Ervin
AVIATION...Nichols



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