586
FXUS63 KDVN 171051
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
551 AM CDT Sun Aug 17 2025

.KEY MESSAGES...

- Showers and storms will be possible this morning for the northeastern
  portions of the area, which could pose an isolated flash
  flooding threat. A Flood Watch remains in effect for portions
  of northwest Illinois through 15z/10 AM this morning.

- Another hot and humid day is on tap today, particularly for
  areas along and south of Interstate 80. A Heat Advisory has
  been issued for this afternoon and early evening for the
  southwestern 2/3rds of the forecast area.

- Periodic chances (20-50%) of storms will continue through
  Monday night, especially north of Interstate 80. Some strong
  to severe storms are possible this evening and again Monday.

&&

.SHORT TERM /THROUGH MONDAY NIGHT/...
Issued at 320 AM CDT Sun Aug 17 2025

Early this morning, we continue to keep a close eye on ongoing
thunderstorms, extending from the Chicago metro area northwest
towards southwestern MN. This has developed along a stout 925-850 mb
layer moisture gradient along a stationary boundary on the northern
side of persistent thermal ridging, resulting in deep moist
convergence. As of this writing, we`ve remained on the cusp of this
line of storms, and impacts have been very limited. However, current
radar trends show more robust storms approaching the region, albeit
in a decaying fashion. Some heavy rainfall occurred north of the
area, resulting in a Flash Flood Warning just north of Dubuque. With
Pwat values hovering around 1.5 to 2.0" along the nose of a somewhat
weak nocturnal LLJ, efficient rainfall remains possible with these
storms, and thus, we have expanded the Flood Watch to include
Dubuque and Jackson counties in northeast Iowa for the potential of
flash flooding, if these storms can remain organized and shift
slightly to the south. Strong to severe storms appear unlikely with
this convection.

Eventually, this activity should gradually dissipate after sunrise
this morning as the nocturnal LLJ weakens further. CAMs are in pretty
good agreement with keeping conditions dry for most of the daylight
hours today. The main focus after this morning`s convection will be
on another day of hot and humid conditions. Dew points recovering
into the mid to upper 70s should yet again support very muggy
conditions, along with temperatures warming to the upper 80s to
lower 90s for most locations, save for our far northeast where
lingering cloud cover and perhaps some lake-cooled air off Lake
Michigan should keep conditions in the lower 80s. With that said,
heat indices of 100 degrees F or greater appear very likely for
locations along and south of Interstate 80, where the 17.00z HREF
exceedance probabilities of heat index readings greater than 100 are
around 70 to 100%, so another Heat Advisory has been issued for
generally our southwestern 2/3rds of the forecast area. Another
advisory will likely be needed Monday, particularly across our south
where the HREF exceedance probs of 100 degrees are progged around 50
to 80%.

As far as strong to severe storm potential is concerned for today
and Monday, SPC has actually reduced the previous Marginal Risk
(level 1 of 5) to now only include areas west of an Iowa City to
Dubuque line. The most likely timing of this activity looks to be
this evening when the LLJ looks to re-intensify, leading to enhanced
convergence over our northern areas once again. Monday will also
have potential for strong to severe storms, with a Marginal Risk
remaining in effect for nearly our entire CWA. Monday will actually
have more robust forcing as a mid-level shortwave trough is progged
to move through the area during the daylight hours, which the CAMs
are progging convective initiation ahead of the wave. The main
threat for severe storms remain damaging winds due to steep low-
level lapse rates and precipitation-loaded updrafts, but some
torrential downpours are also possible that could lead to localized
flooding.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
Issued at 320 AM CDT Sun Aug 17 2025

Tuesday appears to be our last active day of this stretch as a cold
front dives southward through the CWA, which should help scour out
the hot and humid conditions from the area. Temperatures from
Wednesday through the end of the week should be near seasonal
averages, with dew points falling back to the middle 60s. There
could still be some showers or storms on Tuesday ahead of the front,
especially for areas along and south of Interstate 80, but strong to
severe storms appear unlikely at this time.

Largely dry conditions are expected for Wednesday through Saturday,
with perhaps our next chances of precipitation coming Friday night
as another front approaches the region.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 551 AM CDT Sun Aug 17 2025

VFR conditions are expected for most of the TAF period. Showers
and storms north of the local outlook area will continue to
diminish throughout the morning, keeping conditions dry through
at least the afternoon hours. Additionally, MVFR fog appears
less likely at this time based on latest NBM probabilistic
output, so we have pulled these out of the TAFs. There could
still be MVFR ceilings at DBQ due to nearby rain-cooled air and
higher saturation this morning, given consensus among the
latest models. There is also a low chance for a thunderstorm
this evening for DBQ. Generally east to southeasterly flow will
remain in place, staying around 5 to 10 knots.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Flood Watch until 10 AM CDT this morning for IAZ042-054.
     Heat Advisory from noon today to 8 PM CDT this evening for
     IAZ051-052-063>065-067-068-076>078-087>089-098-099.
IL...Flood Watch until 10 AM CDT this morning for ILZ001-002-007.
     Heat Advisory from noon today to 8 PM CDT this evening for
     ILZ015>018-024>026-034-035.
MO...Heat Advisory from noon today to 8 PM CDT this evening for
     MOZ009-010.

&&

$$

SHORT TERM...Schultz
LONG TERM...Schultz
AVIATION...Schultz