927
FXUS63 KDVN 281945
AFDDVN
Area Forecast Discussion
National Weather Service Quad Cities IA IL
245 PM CDT Sun Jun 28 2026
.KEY MESSAGES...
- Lightning-heavy concentrated area of thunderstorms (70-90%
coverage) will continue along to push along the U.S. Highway
30 corridor into northwest Illinois through mid-late afternoon.
- A prolonged period of hot and very humid conditions will
expand area-wide Monday, highlighted by day-to-day peak heat
index values of 100 to 110 and nighttime low temperatures no
cooler than the mid 70s. Increasing potential to extend the
Extreme Heat Warning through midweek.
- Thunderstorm chances will be limited tonight through midweek,
with increasing chances Wednesday night onward (including the
July 4th weekend), with the resultant cloud cover potentially
having an impact on how high of temperatures but at least
will remain very humid.
&&
.UPDATE...
Issued at 240 PM CDT Sun Jun 28 2026
The concentrated but strong storm cluster heading into northwest
Illinois has had occasional severe wind and hail due to
effective shear of 45-50 kt and MUCAPE of 2000-2500 J/kg. This
is feeding on an instability gradient and has had well-defined
storm structure at times (including mesocyclone presence and
inflow). This has shown its likely closer rooted to the
boundary layer than a couple hours ago. However, there is
capping impinging on this from the southwest, as sampled by our
18Z sounding and continued warming of the 800 mb layer. The
most likely scenario will be 40-50 mph gusts, small hail, and
brief but torrential downpours, with a more persistent severe
threat being the higher end outcome. Departure time in far
eastern CWA in eastern Whiteside County should be near 430 PM,
and if it clips northern/northeast Bureau County would be 530
PM. Some temporary wake low effects of non-thunderstorm wind
gusts of >35 mph from the east will be seen for one to maybe two
hours after the storms along/north of U.S. Highway 30.
&&
.SHORT TERM /THROUGH WEDNESDAY NIGHT/...
Issued at 240 PM CDT Sun Jun 28 2026
After thunderstorms depart the area by sunset, we will settle
into a true midsummer hot and very humid pattern. This is
characterized by an expansive and slightly retrograding 500 mb
high pressure ridge just to our southeast (591+ dm center), and
channeled low-level thermal ridge directly over the area (850
mb temps of 21-24C). Confidence is high in convective cloud
cover being limited over the area, though there is some model
signature for some cirrus Monday afternoon. The setup is also
not supportive of storms in the CWA through Wednesday morning,
and if they were to occur they would likely only be in the
northwest portion of the CWA (near/north and west of Cedar
Rapids) and during nighttime hours. In addition, confidence is
high in very warm nighttime lows, with NBM membership
probabilities over 70 percent of 75+ degree lows for most of
the CWA through Wednesday night. So their seems little that
would work against the going Extreme Heat Warning, issued
especially for persistence, and an increasing likelihood that
some or all of the CWA will see it extended through Wednesday.
The warm nighttime lows start tonight, thanks to 70-75 degree
dew points and a more southerly wind direction. That theme looks
to be consistent during the upcoming nights. For dew point
adjustments, have capped some of the NBM upper 70s to 80 dew
points to more mid 70s, which are more consistent with upstream
trusted observations. Also in line with that is the fact we are
still a little ahead of the peak evapotranspiration season (mid
July into early August). On the note of the winds, these will
be breezy again on Monday, with gusts of 20-25 mph, maybe
slightly higher at times. While that can nudge heat effects a
bit down when near thresholds, we are comfortably into the
multi-day extreme heat values (heat index of 105+). So that
should only offer a slight reprieve.
For Wednesday and even Wednesday night, the chances for
thunderstorms continue to ease, with the convective breeding
ground likely being the western Corn Belt region to Minnesota,
and steering vectors still favoring more of a northeast movement.
&&
.LONG TERM /THURSDAY THROUGH SATURDAY/...
Issued at 240 PM CDT Sun Jun 28 2026
For this time period, confidence is high in continued very humid
air especially through Saturday. However, convective effects may
influence temperatures as the upper pattern flattens a bit over
the Upper Midwest and Corn Belt. Using ensemble means and
deterministic guidance, the current best convective potential
looks to be over the weekend as a short wave trough approaches.
That said, predictability at this distance is low, and some
noteworthy shifting such as MCS effects prior or a change in
trough passage timing certainly can occur. Otherwise,
synoptically the pattern of 850 mb temperatures of 20-22C
support high temperatures at least in the lower 90s, which would
mean heat index values into the 100+ range, and potentially
105-110.
&&
.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1240 PM CDT Sun Jun 28 2026
Primary concerns with the TAFs are MVFR ceilings and nearby
thunderstorms through mid afternoon, gusty southeast winds at
times this afternoon, and potential for LLWS tonight.
Semi-orgnized thunderstorms will continue to move east-southeast
over portions of eastern Iowa and eventually into northwest
Illinois through mid-afternoon. While DBQ will see some
effects, it is less certain at MLI. If they occur at MLI, they
would likely be between 1930-21Z, and probably have some gusts
25-35 kt. Apart from storms, areas of MVFR ceilings are present
and will be slow to depart through mid-afternoon. DBQ could even
hold onto them through the entirety of the daytime hours.
For winds, east to southeast winds will have regular gusts this
afternoon. There are likely to be what we call "wake low"
effects at DBQ and possibly CID, which even gustier east-
southeast non-thunderstorm winds that occur in the wake of a
persistent area of storms. These could result in temporary (~1
hr) gusts to 30-40 kt, but confidence in that is low.
While gusts abate after sunset, sustained winds should hold
around 10 kt, maybe higher at times. The setup also favors a
35-40 kt low-level jet AOA 1.5 kft, and that is borderline for
true LLWS development given those sustained surface winds. If it
occurs atop area airports, 03Z-09Z is the most favored time.
&&
.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Extreme Heat Warning from noon Monday to 9 PM CDT Tuesday for
IAZ040>042-051>054-066.
Extreme Heat Warning until 9 PM CDT Tuesday for IAZ063>065-067-
068-076>078-087>089-098-099.
IL...Extreme Heat Warning from noon Monday to 9 PM CDT Tuesday for
ILZ001-002-007-009-016>018.
Extreme Heat Warning until 9 PM CDT Tuesday for ILZ015-024>026-
034-035.
MO...Extreme Heat Warning until 9 PM CDT Tuesday for MOZ009-010.
&&
$$
UPDATE...Friedlein
SHORT TERM...Friedlein
LONG TERM...Friedlein
AVIATION...Friedlein
View a Different U.S. Forecast Discussion Location
(In alphabetical order by state)
|
|
