108
FXUS63 KDVN 182346
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
646 PM CDT Fri Jul 18 2025

...06z Aviation Update...

.KEY MESSAGES...

- Active pattern returns to the area tonight as warmer and more
  moist air moves into the area.

- Ring of fire moves over the area bringing daily chances for
  thunderstorms. Some of which could be strong to severe with
  heavy rain and flash flooding.

- The heat returns in earnest by the middle of next week.

&&

.SHORT TERM /THROUGH SATURDAY/...
Issued at 146 PM CDT Fri Jul 18 2025

Impactful weather begins tonight across the area as returning
low level moisture advects into the area ahead of a weak wave
moving through the flow. Where the edge of this dewpoint axis
sets up will see the potential for repeated rounds of
thunderstorms overnight. CAMs are in good agreement on a MCS
tracking SE into the area near daybreak. Consensus has this
precip west of a line from Cambridge IL to DBQ, IA. Some shift
east or west is possible. CAMs also have a wing of WAA
convection setting up a potential flash flood scenario for
Saturday morning, especially in urban areas. As such, a flood
watch for flash flooding has been issued from tonight into
Sunday morning when another round of storms are possible. PWATs
through the period exceed 2 inches as well.

Also, this MCS looks to have winds mixing to the ground based on
the CAMs. The environment is supportive of strong to severe
storms during the morning. This is not the typical time for
severe weather across the area, but it looks like on top of the
flash flooding risk, we could have a severe wind risk as well.
SPC has the area in a slight risk tomorrow, while most of that
is in the evening, there is still a threat in the AM. After
this, a relatively quiet rest of the period as the sfc
boundary, likely reinforced by any outflow from the earlier
storms. Storms will try to form later in the period, especially
NW of the CWA on this boundary and march east along the boundary
into Sunday morning.

&&

.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
Issued at 146 PM CDT Fri Jul 18 2025

Impactful weather is expected through the entire long term
period as the ring of fire MCS track continues across our area.
We will be dealing with severe weather, flash flooding, likely
river flooding and dangerous heat through this period. Saturday
evening looks be rather potent with large instability, deep
layer shear, PWATs over 2 inches, a strong wave for the summer
and a stalled out boundary. This wave, or rather a series of
successive waves will move through the area during the day on
Sunday into Monday morning. The GFS has the sfc boundary
retreating north bringing the main ring of fire north. The ECM
keeps the boundary near us. I think the ECM has the right idea
as the waves will struggle to mix the boundary north with
convective debris, this means more showers and storms Sunday
night into Monday. Towards the middle of the week the heat
should build into the area.

Focusing on Saturday evening into Sunday morning. This setup has
me the most concerned for the area and really the impetus for
the flood watch. As the better wave moves into the area, the
stalled out boundary will retreat some to the north. Deep layer
shear suggests splitting supercells will develop along the
boundary. 12z HRRR had those supercells near us, the 18z has
them further west. Regardless, these supercells, wherever they
form, will have the potential for all modes of severe weather.
They will likely become outflow driven as a series of MCSs run
down the boundary and into our area overnight. Deep layer shear
will support balanced cold pool/shear processes and severe wind
producing storms. Also, storms near the boundary may pose a
tornado threat as they move across the area into the overnight.
Coincident with the severe risk, heavy rain and flooding are
likely to begin quickly as warm rain processes and high PWATs
rapidly stack up the rain. The flood watch may need to be
adjusted, but wanted to get it out to cover tonight`s lower end
risk and tomorrows enhanced risk. Areas that saw flash flooding
last week are especially susceptible and those living along
creeks and rivers that flooded should remain abreast of the
weather and have multiple ways to receive weather warnings
overnight.

The pattern looks to be very favorable late in the weekend
through early next week for several storm complexes to
traverse in/near the area, as we`ll reside just north of
the upper ridge/heat dome within the `ring of fire` and
barrage of ridge riders on the southern periphery of the
stronger mid level flow traversing the International border.
This will bring about perhaps greater concerns for a more
widespread severe weather threat due to the likelihood of
MCS`s, along with torrential rain and flooding particularly
as soils are likely to be quite saturated and rivers running
high in those areas that receive noteworthy rainfall in the
days prior.

By Wednesday, there is fairly good agreement that the upper
ridge will build into the region shunting the main storm
track to our north. This will bring about the threat for
dangerous heat Wednesday with highs well into the 90s and
dew points in the mid/upper 70s (possibly 80+F in some areas
due to evapotranspiration from maturing corn crops) owing to
heat index readings of 100-110+. This dangerous heat could
extend into Thursday, particularly across our south/east ahead
of a cold front. This front will also bring a return of storm
chances over the latter portion of next week and possibly through
next weekend.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 642 PM CDT Fri Jul 18 2025

A VFR TAF period into the late night with general light
southerly winds. But then thunderstorms are expected to move in
from the northwest late tonight and into Sat morning. Some of
these storms could be strong with gusty variable winds and
sharply reduced VSBYs from passing bouts of heavy rain. Will
have to watch for isolated to wdly sctrd precursor elevated
showers or even a thunderstorm mainly after midnight ahead of
the main incoming band of storms. After the morning storms
clear, we may have a lull period from the storms with VFR
conditions during the afternoon into early evening.

&&

.HYDROLOGY...
Issued at 1157 AM CDT Fri Jul 18 2025

The atmospheric set up over the weekend and through Tuesday
points to a heat dome over the Plains with Iowa/Illinois in or
near the active organized thunderstorm track. Such a scenario
points to the potential for rounds of heavy rainfall.

Over the previous seven days eastern Iowa and northern Illinois
has received anywhere from 175 to over 500% of the normal
rainfall with a vast majority of that occurring in the 48-hour
time period of July 10-11th. This rainfall has resulted in a
20-40% improvement in soil moisture and has essentially
eliminated the abnormally dry to moderate drought conditions
across eastern Iowa. However, soil anomalies are still -20 to
-40% dry with the worst conditions east of the Mississippi where
abnormally dry to moderate drought persists.

While river levels are falling from the heavy rainfall of July
10-11th, area tributaries across eastern Iowa are running above
to much above normal for mid- summer. Tributaries in Illinois
are near normal with the Mississippi running normal to above
normal.

Weather models this weekend through Tuesday have atmospheric
moisture levels increasing to at least 2 inches which is greater
than the 90th percentile for July. Additionally, weather models
indicate a tropical moisture connection developing by early
next week with the Gulf. With freezing levels in the atmosphere
projected to be very high, warm rain processes have a high
probability of dominating which will lead to very efficient
rainfall production along with a high probability of rainfall
rates of 1 to 2+ inches per hour.

Based on available information, it appears there will be a
daily nocturnal storm complex that arrives in eastern Iowa in
the pre-dawn hours and dissipates over Illinois around mid-day.
Boundaries left over from the nocturnal complex will dictate
where new storms develop during the afternoon/evening. This
scenario looks to play out three to four times through Tuesday.

What is not fully known yet is whether or not storms will repeat
over the same areas. If this occurs (the probability is around
50%), then excessive rainfall rates of 2+ inches per hour would
lead to rapid runoff of water into low lying areas and resultant
flash flooding. Repeated rounds of heavy rainfall would then
result in rising river levels and the potential for river
flooding.

The Weather Prediction Center has a daily slight risk of
excessive rainfall through Tuesday. The time period of Saturday
night into Sunday is the most concerning. The probabilities for
excessive rainfall are at the upper end of the slight risk.

The following tributary rivers will need to be especially
watched through the end of July since they already have above
normal streamflow; Cedar, Iowa, Skunk and Wapsipinicon. General
rises on the Mississippi are also expected.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Flood Watch from 1 AM CDT Saturday through Sunday afternoon
     for IAZ051>053-063>068-076>078-087>089-098-099.
IL...Flood Watch from 1 AM CDT Saturday through Sunday afternoon
     for ILZ015-016-024>026-034-035.
MO...None.

&&

$$

SHORT TERM...Gibbs
LONG TERM...Gibbs
AVIATION...12
HYDROLOGY...08