177
FXUS63 KDVN 111724
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1224 PM CDT Tue Aug 11 2026

.KEY MESSAGES...

-  Strong to severe storms will be possible again on Wednesday.
   The entire area is under a Marginal, level 1 out of 5, Risk
   for severe storms.

- A Heat Advisory remains in effect for areas along/south of an
  Sigourney, IA to Aledo, IL line. Storm clouds and outflow may
  prevent it to be needed further north but it will still be
  very humid north of the advisory.

&&

.UPDATE...
Issued at 1132 AM CDT Tue Aug 11 2026

The morning storms and associated outflow boundaries did not get
into Keokuk county east through Mercer county. As a result, dew
points in those areas remain in the mid and upper 70s. Thus a
tactical extension of the heat advisory has been done to include
these counties for the afternoon.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 245 AM CDT Tue Aug 11 2026

The latest sfc analysis continues to indicate a west-to-east oriented
quasi-stationary frontal boundary acrs central IA into northern IL,
with rather light sfc flow going on around it making for another
morning with patchy to areas of fog. Isolated to sctrd elevated WAA
showers and a few thunderstorms are occurring north of the LLVL
front acrs the north half of IA into WI even with a west-southwest
veering H85 MB jet. Profiler network showing better southwesterly
LLJ of 35-40 KTs converging on the MO RVR Valley, just to the lee of
a seasonably robust short wave upper trof seen on water vapor
imagery digging acrs eastern SD/southwest MN ATTM. This should be
the region for MCS generation this morning, with a few storm
clusters already occurring there.

Tightening CAPE and THTA-E gradient and prime H85 20C thermal ribbon
align from southeast SD/ southwest MN down along to north of the
local I-80 corridor through midday, and that`s the currently
expected path of an eventual MCS or QLCS type convective feature
feeding on the LLJ jet that should be getting shunted this way ahead
of the short wave as well as a mid level jet max. If this convective
system can organize with a cold pool and mix along at least a 3000
J/kg MLCAPE pool at that time of morning, feel the already 70 KT+
wind gust potential could be there. Several of the latest CAM runs
continue to target the highest wind gusts and bow apex along the Hwy
20 corridor and areas along the northern CWA border from around 10
am to noon or so. Some uncertainty on this, as a southwest tailing
bow structure may also bring damaging winds down toward the I-80
corridor.

As this feature exit by early afternoon, it`s cool pool outflow
could very well shunt the main boundary further southward again with
lingering convergence and diurnal heating help produce sctrd showers
and a few thunderstorms in the wake of the main complex until the
short wave can get by. Then would expect little convective activity
by late afternoon and into the evening period as short wave ridging
bulges overhead. Much of tonight may then be quiet until late toward
dawn Wed when heights start to fall again and some LLVL jet
convergence can maybe initiate some isolated showers and storms
along or north of the southward shunted LLVL boundary acrs south
central IA into the southern CWA. These may fester and last well
into Wednesday with some severe risk if even somewhat elevated.
Locally heavy rainfall and flooding may become more of a factor into
Wed as well where the axis of storms can fire...right now it looks
acrs the southern CWA.

As for the Heat Advisory, will let it ride and not expand it north
with worries that this morning storms, debris and outflow will limit
the ambient temps along and north of I-80 enough to fall short of
advisory criteria. But it will still be oppressively humid, and if
the MCS track further to the north than currently expected it may
indeed need to be expanded north.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Issued at 245 AM CDT Tue Aug 11 2026

Wednesday...Talked a little bit about Wed above with some morning
convection possible. But then it currently appears that the local
area will lay in between the more organized forcing again for a
potentially low activity period until maybe toward Thu morning
when the next main short wave may be approaching. Also Wed will
be another hot and humid day especially if convection is more
scarce and can`t rule out the eventual need of a heat headline
for portions of the area.

Thursday through Monday...If the currently extrapolated short wave
train along the edge of the heat dome is in the ballpark, we may
have another MCS moving into the local area Thu morning with severe
weather and heavy rain risks. The temperature battle will continue
as well with LLVL baroclinicity and thermal ribbon wavering acrs the
region for high heat or not so bad depending on the daily flux.
Rainfall amounts may really add up by the weekend and early next
week on the northern fringe of the heat dome from the west central
plains, acrs IA/IL, and curving down acrs the eastern OH RVR Valley.
Will have to watch the Thu through Friday period for heavy rain and
back building MCS potential depending on LLVL boundary and
convergent flow axis`s lay out if long range 2 inch PWAT feed
indicators are accurate.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1220 PM CDT Tue Aug 11 2026

Isolated SHRA/TSRA will fester across eastern Iowa and northern
Illinois through 02z/12. Probability of a TAF site being
impacted is 10 percent or less. After 06z/12 patchy fog is again
expected resulting is areas of MVFR VSBYS. After 12z/12 yet
another storm complex will move through parts of eastern Iowa
and into Illinois bringing SHRA/TSRA with a high probability of
MVFR/IFR conditions.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Heat Advisory until 8 PM CDT this evening for IAZ076>078-
     087>089-098-099.
IL...Heat Advisory until 8 PM CDT this evening for ILZ024>026-034-
     035.
MO...Heat Advisory until 8 PM CDT this evening for MOZ009-010.

&&

$$

UPDATE...08
SHORT TERM...12
LONG TERM...12
AVIATION...08