Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 131740
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1240 PM CDT Fri Oct 13 2017

...AVIATION UPDATE...

.SYNOPSIS...
Issued at 330 AM CDT Fri Oct 13 2017

Latest sfc analysis was indicating upstream front laying out from
western KS, up through north central MN with llvl cyclogenesis
ongoing acrs north central KS. Aloft, broad southwesterlies were
streaming from the southwestern CONUS, all the way up toward the
James Bay region of Canada. A lead vort max noted embedded in this
flow on water vapor imagery acrs NE, while much stronger digging
upper Trof noted acrs the Pacific NW, which will eventually be late
Saturday`s prime weather maker/forcing agent. Signs of unseasonable
long fetch moisture feed potentially wrapping up toward the region
by Sat out of western Mexico.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 330 AM CDT Fri Oct 13 2017

Today...The incoming vort out of NE, with a pre-feed SSW H85 MB jet
of 20-30+ KTS increasingly THTA-E laden, will help the developing
precip leaf currently acrs NE into SD, to feed acrs the northern CWA
this afternoon and early evening. Will increase POPS accordingly
north of I80 this afternoon, with saturation profiles and convergent
LLJ zone supporting elevated showers with higher coverage along and
north of Hwy 30 through 00z. MUCAPES in the elevated layer at 200-
400 J/KG supporting at least some isolated thunder in these areas
this afternoon. The northeast-to-southwest sfc front is projected to
make it acrs the CWA and generally bisect it from NE-to-SW by mid
afternoon. Cloud cover and variable sfc flow/winds either side of
this feature to make for challenging high temp fcst and potentially
large range of values from northwest to southeast...low to mid 60s
to mid 70s. Strong deep layer shear values along and north of the
front in storm bearing layer may allow for an isolated storm to
produce hail this afternoon before deeper saturation occurs, but low
confidence on hail size for the afternoon or if it will occur.

Tonight...Ongoing southwesterly 30-40 KT H85 MB jet feeding up and
over the llvl boundary/baroclinicity, and PWAT`s increasing to 1.3 to
near 1.5 overnight should produce an increasing areal coverage of
elevated showers and some thunderstorms overnight. The higher mid
layer MUCAPE pool of 1000 to 1500 J/Kg projected to lay out along
and just south of the I80 corridor by midnight, and could see an
uptick of thunder coverage in these areas as the night progresses.
Strong elevated shear profiles may still support a storm capable of
producing large hail, but increasing saturation depth may also start
to hinder severe size hail production after midnight. But still see
a window where there will have to be a watch out for elevated
hailers. Most areas that manage to get in on the rain to get
anywhere from a quarter inch, up to three quarters of an inch by 12z
Sat. But with those type of unseasonable precipital waters, could
see localized swaths over an inch by sat morning. Where the rain can
wane late tonight, some chance for at least patchy fog but will
leave out mention for now. Overnight lows in the 50s in the
northwest, to the low to mid 60s in the far south/southeast. ..12..

.LONG TERM...(Saturday through next Thursday)
ISSUED AT 330 AM CDT Fri Oct 13 2017

The main focus of the long term period is the first part of the
weekend, with periods of heavy rain and potential for severe storms.

Ingredients still look favorable for widespread heavy rain
continuing Saturday and Saturday night. The latest NAEFS
precipitable water anomalies indicate moisture above 3 standard
deviations for mid October. This abundant moisture, combined with
warm front enhanced shear, and eventually a strong cold front push,
point to all types of severe weather in play, including pockets of
flash flooding and tornadoes.

The southwest quarter of the forecast area remains in the day 2
slight risk area, with the rest in marginal risk. This looks
reasonable, given the more favorable CAPE and expected warm front
position. More discrete cells near the boundary will carry the risk
of a tornado. Very fast storm motion over 40 kts will also heighten
the risk of damaging straight line winds, and reduce the time to
seek safe shelter. Latest CAMS suggest a transition to linear mode
with a wind threat into Saturday evening as the main cold front and
upper low move through.

Recent heavy rain over much of the forecast area does increase the
flash flood threat somewhat. Repeat thunderstorms could produce
pockets of 3+ inches. A flood watch may be necessary as confidence
increases in the favored area for heavy rain. Continued or new rises
on area tribs and the Mississippi are expected, especially on the
faster responding rivers such as the Maquoketa and Wapsi.

Looking ahead, have removed the low pops Sunday morning. Sunday will
be much cooler, with afternoon highs in the 50s. Surface high
pressure will overspread the area Sunday night, with a light wind
and clear sky. Conditions will be ideal for some frost, especially
north of Interstate 80. Have introduced some patchy frost into the
gridded forecast.

For Monday through Thursday, expect a gradual warming trend into the
60s to low 70s with dry conditions as the main storm track remains
well to the north.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday Afternoon)
ISSUED AT 1236 PM CDT Fri Oct 13 2017

Mainly VFR conditions will be seen through 00z/14 as a front
stalls across eastern Iowa and northern Illinois. Brief periods of
MVFR/IFR conditions are possible with TSRA across northeast Iowa.
After 00z/14 nocturnal convection will slowly develop and become
fairly widespread by 12z/14. VFR conditions will deteriorate to
widespread MVFR with areas of IFR conditions.

&&

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

$$

SYNOPSIS...12
SHORT TERM...12
LONG TERM...RP Kinney
AVIATION...08



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