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000
FXUS63 KDVN 231053
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
553 AM CDT Sat Sep 23 2023

...AVIATION UPDATE...

.SHORT TERM...(Today and tonight)
Issued at 241 AM CDT Sat Sep 23 2023

Key messages:

1. Most of the daylight hours look dry today.
2. Showers and storms move into the area this evening and
overnight.
3. Marginal risk for severe weather this evening mainly across
Iowa.

Discussion:

Main upper level closed low is expected to push into the area this
afternoon and into the evening. Chances are that some nocturnal
convection associated with a weak H85 LLJ will be ongoing at
daybreak across eastern NE and western IA. This stuff should
generally weaken as the H85 LLJ subsides. A cold front is forecast
to push into the western CWA later today as well. Guidance also has
a leading wave this afternoon. Either the cold front or the old
OFB and leading wave could lead to additional storm development
this afternoon west of the area.

Looking at the CAMs for initiation, CAMs aren`t sure what
initiates first, the OFB or the cold front. All CAM guidance have
storms just to the west of the area around 00z Sunday. This
activity weakens as it moves into our area this evening. This
makes sense, the main wave swings negative to our west and pulls
north into MN taking the better shear with it. The better H85 jet
is north of the area and we look to be in the entrance region of
this LLJ. Honestly, I`m not sure which goes first, the OFB or the
cold front. This will require the day shift to keep an eye on
storms this AM to make this call. If the OFB materializes and
fires storms first, we could see some strong/severe storms across
our west prior to 00z. If it doesn`t, expect strong storms later
across the area.

Looking at the parameter space for severe storm development yields
a small area with good shear. With this wave pulling north,
surface winds back enough that dry air from the east moves into
our CWA. Moisture pooling and better CAPE lies with the cold
front. There is a potential for us to have decent deep layer shear
(~35knts) this afternoon with a limited thermodynamic environment.
With the vectors perpendicular to the forcing, wonder if we see
some LP storms before storms grow up scale. The better shear and
CAPE space is west of the area and thus the better severe chance
is there. Unlike yesterday, 0-3km CAPE looks weak, suggesting a
low tornado threat. With the shear and updraft organization,
likely a wind/hail threat with weakening storms late across the
area as the storms quickly move east into drier/lower CAPE air
this evening.

.LONG TERM...(Sunday through Friday)
Issued at 241 AM CDT Sat Sep 23 2023

Key messages:

1. Another potential sneaker funnel/weak tornado event Sunday.
2. Upper level low continues its slow exit of the area bringing
chances of rain to the area.
3. Temperatures gradually warm as ridging builds into the area to
end the week.

Discussion:

Guidance continues to have pretty good agreement on the flow into
next week despite guidance usually struggling with this. The
closed low looks to lumber across the area until weakening and
being reabsorbed into the flow later in the week. After this,
ridging builds into the area. The main question is if the forecast
is too fast with this occurring. Guidance usually does this, but
with very consistent forecasts between runs, I tend to buy into
that idea over a slower one. That said, my confidence in this is
low at the time.

Looking to Sunday, another potential setup for strong/severe
storms and tornadoes. Even though wave is north of the area, the
deep layer shear that does exist is in the lowest 0/3km of
atmosphere. 0/3km CAPE around 175 J/kg is more than enough CAPE in
the llvls to stretch that shear. Hodographs again depict good
curvature in the llvls due to easterly flow. While this isn`t a
robust thermodynamic environment, the thermo that does exist is
collocated with decent shear in the profile. This is enough to
cause updraft rotation. Main question is what left over convection
could be going on. We may be stable enough at the sfc not to have
any issues and I have low confidence on overnight convection.
Later shifts will need to keep an eye on this again. Will leave
out of the HWO at this time due to that uncertainty and will keep
mention to it here in AFD.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 551 AM CDT Sat Sep 23 2023

VFR conditions are expected at all sites except for CID. MVFR
vsbys are possible still at CID this AM so left in the forecast.
Otherwise, winds are increasing to the mid to upper 20 kt range
today and should stay up through the period. Weakening storms will
move into the area after 00z tonight.

&&

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

$$

SHORT TERM...Gibbs
LONG TERM...Gibbs
AVIATION...Gibbs