361
FXUS63 KDVN 170121
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
821 PM CDT Mon Jun 16 2025

.KEY MESSAGES...

- Active weather pattern continues tonight through at least Wednesday
  evening, with some strong to severe storms possible at times

- Confidence remains low on the timing and coverage of this activity,
  given that how showers/storms develop one day will impact the
  convective environment the following day

- Very warm/hot conditions becoming more likely this weekend (highs
  in the 90s; heat indices near 100)

&&

.UPDATE...
Issued at 741 PM CDT Mon Jun 16 2025

We are currently watching a line of strong to severe convection
northwest of the Des Moines metro area, which is generally
moving east-southeast. If these storms are to continue over the
next couple hours, they will be close to our forecast area.
Current trajectory brings the line near our western border
around 9-10 PM local time. The track of this line is difficult,
as the northern portion of the line is moving more easterly,
while the southern half continues east-sutheasterly towards the
Des Moines metro. With that, the northern end of the line has
been the area that has been dying off over the last few hours,
while the strongest cores continue to build south. So, if that
trend continues, areas along or south of Interstate 80 would see
the best chance for any showers or storms if this line makes
it. Confidence is low on it making it, but it will come close
enough that mention is needed. This line has a history of winds
around 60-70 mph and these winds cannot be ruled out as it
continues over the next couple of hours. Although, it has been
on a downward trend over the last hour or so. Thus, confidence
is low overall.

This line of convection may not be the only source of storms
late this evening and into the night. We currently have discrete
storms developing south of the Minneapolis Metro. Guidance hints
that these will continue to move southeast through the night,
with some coming close to our area as well. So, I just wanted to
mention that areas north of Interstate 80 are not completely
out of the threat yet.

For both situations, short term guidance is not capturing these
storms well at all. Thus, we have truly been relying on
observational trends throughout the area, which would favor some
longevity to at least the line of storms out west. Environment
in place would favor the primary hazard in any storm being
winds, but hail has also been seen and cannot be ruled out.

&&

.SHORT TERM /THROUGH TUESDAY NIGHT/...
Issued at 233 PM CDT Mon Jun 16 2025

Periodic chances of showers and storms will remain in the picture
for tonight through late Wednesday as a few mid-level shortwaves
crosses our region. Confidence remains lower as the forcing will be
a bit more nebulous, at least at first, and with how daily showers
and storms impact the convective environment the following day.
Presently this afternoon, a cluster of strong to severe storms
persists over our northwestern CWA from a weak convergence boundary
and mid-level impulse. The convective environment is more driven by
thermodynamic processes given fairly weak deep-layer shear (<30
kts), with SBCAPE values around 2000-3000 J/kg per the RAP/SPC
mesoanalysis fields. Mid- and low-level lapse rates appear to be
fairly modest in scope, but still should be sufficient to support
some locally strong wind gusts and hail to the size of quarters. As
such, SPC has maintained a Marginal Risk (level 1 of 5) for severe
storms tonight along and north of a line from Sigourney, IA to
Clinton, IA to Freeport, IL.

For this entire period, confidence in thunderstorms remains highest
for severe storm potential on Tuesday PM as a more robust mid-level
impulse crosses the region during peak heating. CAMs are actually in
decent agreement on the timing of storms in the afternoon, albeit a
bit more spread out in terms of coverage. Initially, the deep-layer
shear will be pretty meager, but instability will be pretty high,
with SBCAPE values progged around 1500-2500 J/kg per the 16.12z HREF
ensemble, and low-level lapse rates between 7-8 C/km. We will have
to watch for additional convection Tuesday night as a southerly low-
level jet develops, with the nose of the LLJ right over our region
concurrent with large-scale forcing ahead of an upper-level trough.
SPC has also maintained the severe risk for Tuesday, with a Slight
Risk (level 2 of 5) for severe storms over our southwestern CWA,
with a Marginal Risk elsewhere.

The other thing to keep an eye on will be heavy rainfall with this
convection as PWAT values are progged around 1.7 to 2.0+ inches.
Values over 2 inches would be near the daily maximum for PWATs per
the SPC sounding climatology, so very efficient rainfall can be
expected with these storms. While the HREF LPMM QPF shows a pretty
wide range of rainfall amounts due to the more scattered nature of
the convection, the upper bounds of rainfall totals could reach
around 2 to 3 inches, and if this occurs over an urban area, this
could pose a flash flooding threat. WPC continues to have locations
along and north of Interstate 80 in a Slight Risk (level 2 of 4) for
excessive rainfall/flash flooding.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Issued at 233 PM CDT Mon Jun 16 2025

We`re not out of the woods with the severe storm threat Wednesday as
the aforementioned upper-level trough translates through the area.
The convective parameter space continues to indicate hefty amounts
of instability, with perhaps some stronger deep-layer shear thanks
to the nocturnal LLJ persisting into the morning hours. An attendant
850 low does appear to shift to the northeast early in the day
Wednesday, which will likely keep the severe threat later on in the
day to our east. SPC has also maintained the Slight Risk for severe
weather across our southeast areas, with Marginal Risk for locations
southeast of a line from Dubuque, IA to Sigourney, IA. Chances of
showers and storms should remain in the wake of the 850 low as a few
additional PVA impulses move through the area. Overall, the
remainder of the extended period from Thursday through Sunday looks
largely dry, but we can`t rule out a chance of showers and storms on
Friday.

Attention then turns to big-time upper-level ridging for the
upcoming weekend, which will help push the heat dome farther
northward over our area. Both the EC and GEFS ensembles indicate 850
mb temperatures around the 23 to 26 C range, which is near the daily
maximum for the SPC sounding climatology on Saturday. Additionally,
the ECMWF EFI indicates values between 0.7 to 0.9 for high
temperatures, which increases confidence in a hot air mass settling
in. High temperatures likely warming into the 90s both days, with
heat indices possibly reaching 100 degrees F. The LREF exceedance
probability of heat indices of 100 degrees is roughly around 30 to
50%, so we will need to keep an eye on some hot and humid conditions
coming for the weekend.

&&

.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 616 PM CDT Mon Jun 16 2025

VFR conditions will remain through much, if not all of the TAF
period. There will be the chance for brief MVFR conditions
between 02-08z tonight, as a line of thunderstorms may move
through the area. Our confidence remains low on how far this
line would move into our area tonight, as guidance doesn`t have
a good grasp on it. Either way, the environment currently in
place would favor longevity in this line later into the evening.
So, we opted to show this in TAFs right now as a PROB30 group
for all sites but BRL. We will amend accordingly if confidence
increases. With any storms that come through, we can see
reductions in vis/cigs to MVFR conditions. Otherwise, winds will
largely remain southerly at 5-10 KTs tonight, shifting
southeasterly after 12-15z Tuesday.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...None.
IL...None.
MO...None.

&&

$$

UPDATE...Gunkel
SHORT TERM...Schultz
LONG TERM...Schultz
AVIATION...Gunkel