942
FXUS63 KDVN 181107
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
607 AM CDT Mon Aug 18 2025

.KEY MESSAGES...

- One more day of hot and humid conditions today, particularly
  along and south of Interstate 80 where a Heat Advisory has
  been issued.

- Another round of thunderstorms is possible (40-60% chance) for
  this afternoon into the evening hours. Some storms could be
  strong to severe, with damaging winds being the main threat.
  Torrential rainfall leading to flash flooding is also possible.

- Mostly dry and more seasonal conditions are expected Wednesday
  through the upcoming weekend.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 410 AM CDT Mon Aug 18 2025

Our "ring of fire" synoptic pattern continues for one more day
today, thanks to large-scale ridging over the central CONUS,
allowing a very warm air mass to remain entrenched over the region.
As is common with these kinds of scenarios, hot and humid
conditions, strong to severe storms, and torrential rainfall that
could lead to flash flooding all remain possible for today. Let`s
break it all down:

* HOT AND HUMID CONDITIONS: we continue to remain under a strong
  thermal ridge, characterized by 850 mb level temperatures around
  20 to 22 degrees C per the latest GEFS and ECMWF ensembles.
  Humidity levels have been quite impressive lately, given that we
  are still within the time of year of peak evapotranspiration,
  with dew points generally in the mid to upper 70s once again.
  There were actually a few locations yesterday that reached 80
  degrees on the dew point, which is very impressive and just shows
  how humid it`s been over the region. We`re thinking that it will
  become quite hot and muggy once again, although if any storms
  develop this morning into the afternoon, this could result in
  lower temperatures and humidity levels. However, should storms
  hold off until later this afternoon which appears more likely,
  then dangerous heat and humidity would remain possible. We have
  issued a new Heat Advisory for locations generally along and south
  of Interstate 80, which lines up very well with the 18.00z HREF
  ensemble exceedance probabilities of 100 degree F heat indices of
  80% or higher to the south.

* THUNDERSTORM POTENTIAL: we are watching an expansive area of
  thunderstorms ongoing over eastern NE into far northwest IA. This
  is developing ahead of an advancing mid-level shortwave that will
  continue to march eastward this morning. Unlike the last few days
  where we have had a lack of large-scale forcing mechanisms to
  spark off storms, this shortwave will be the primary focus for
  storms today, along with an attendant surface cold front. CAMs
  have struggled a bit on the timing and coverage of convection the
  last few days with nebulous forcing, so we will see how they do
  with a larger scale forcing mechanism approaching. Generally, CAMs
  indicate the western convection to translate northeastward and
  gradually dissipate after sunrise, likely owing to a weakening
  nocturnal LLJ. However, there appears to be another window of
  scattered storms, some of which could be severe, this afternoon
  through the evening (most likely between 3-11 PM today). It should
  be noted that some CAMs are hinting at an earlier onset timing of
  storms prior to this window, especially if the decaying AM
  convection sparks off outflow boundaries that could generate
  convection themselves, so we will need to keep a close eye on
  model trends. The Storm Prediction Center continues to have the
  entire CWA under a Marginal Risk (level 1 of 5) for strong to
  severe storms, with damaging winds being the main threat given
  steep low-level lapse rates around 7 to 8 C/km and Pwat values
  progged around 1.8 to 2.1 inches.

* HEAVY RAINFALL/FLASH FLOODING POTENTIAL: with the aforementioned
  Pwat values as high as they are expected to be, any storms that
  develop will become very efficient rainfall producers that could
  lead to flash flooding. Additionally, storms should be slow-
  moving, assuming they don`t become cold-pool dominant and surge
  ahead. Corfidi forward-propagation vectors are progged only around
  10 to 15 knots, which is quite slow for robust thunderstorms. One
  thing that will help limit the flooding threat is the Corfidi
  vector orientation is actually almost orthogonal to the scattered
  line of convection, so training storms aren`t as likely. Still, at
  least some minor flash flooding is possible that could result in
  rises in local creeks, rivers, and streams. With this said, WPC
  has the northeastern 2/3rds of our CWA under a Slight Risk (level
  2 of 4) for excessive rainfall.

As we head into the overnight hours tonight, any convection in the
late evening hours should be diminishing as the mid-level shortwave
trough dives southward and northwesterly flow builds in behind an
associated cold front. This should help shunt off the higher
Pwat/moisture content to the south, which will mark the start of a
period of much more seasonal temperatures and humidity for mid-week.
More on that in the Long Term section below!

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Issued at 410 AM CDT Mon Aug 18 2025

Tuesday appears to be our last somewhat active day of this stretch
as the cold front dives southward through the CWA, which should help
scour out the hot and humid conditions from the area. There is a low
chance (10-30%) of storms in the morning hours Tuesday ahead of the
front, but these chances look to fade in the PM hours. Temperatures
from Wednesday through the end of the week should be near seasonal
averages, with dew points falling back to the middle 60s.

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

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 607 AM CDT Mon Aug 18 2025

MVFR to isolated LIFR conditions were observed early this
morning as an expansive area of low stratus and fog has
developed under clear skies and a humid atmosphere. These
conditions will eventually dissipate by mid-morning for most
locations.

Attention then turns to this afternoon into the evening hours
as a complex of strong thunderstorms is possible, which would
result in MVFR/IFR conditions with them if they go over the
terminals. Confidence has increased regarding timing and
coverage for CID and DBQ as models are in a bit better consensus,
so have used TEMPO groups for the most likely window, but used
PROB30 groups for MLI and BRL as the models seem to still
diverge a bit for these locations. Southeasterly winds this
morning will turn more southerly by the afternoon, remaining
around 10 knots or so. However, locally stronger winds will be
possible with the strong storms and have included those in the
TEMPO groups.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Heat Advisory from noon today to 7 PM CDT this evening for
     IAZ067-068-076>078-087>089-098-099.
IL...Heat Advisory from noon today to 7 PM CDT this evening for
     ILZ009-015>018-024>026-034-035.
MO...Heat Advisory from noon today to 7 PM CDT this evening for
     MOZ009-010.

&&

$$

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