Crystal Lake, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

869
FXUS63 KDVN 150816
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
316 AM CDT Tue Jul 15 2025

.KEY MESSAGES...

- Dangerous heat Wednesday, with afternoon heat indices near or just
  above 100 degrees along and south of I-80.

- There is a Slight (level 2 out of 5) Risk for severe storms
  and excessive rainfall Wednesday afternoon and evening.
  Damaging winds, heavy rain, and a low risk for tornadoes are
  the primary threats.

- Active weather pattern expected late week and into the weekend
  with periodic chances of showers and storms.

- Extreme heat possible next week, with heat indices over 100
  degrees at times.


&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 308 AM CDT Tue Jul 15 2025

Clear skies and mild conditions were seen early this morning, as the
region sits in-between systems and weak high pressure remains
centered over northern MO. Temperatures and dewpoints at 2am were
mainly in the upper 60s.

Southwesterly flow aloft will be in place today with a compact
shortwave passing to our south this afternoon. Some diurnal Cu to
develop along and east of the MS RVR. Otherwise, dry conditions and
afternoon temperatures topping out a few degrees warmer than
yesterday in the upper 80s/low 90s. Dewpoints in the low 70s (thanks
in part to mature crops) will keep it muggy outside with heat index
values in the mid to upper 90s. In fact, if you haven`t noticed
it has already been quite humid this summer. An interesting
climate fact that I came across this morning is at MLI/Quad
City Airport there has been at least 1 hour each day of a
dewpoint of 65 degrees or greater since June 12th! This is the
2nd most consecutive days (33 total days) in a row dating back
to 2000, with only July 4th through August 10th in 2010 having a
longer stretch (43 days).

Going back to the forecast today, latest CAMs have a few scattered
showers/isolated storms forming after 22z primarily in central
IL, but could see some activity developing across are far
eastern CWA prior to sunset. Deep layer shear will be the
limiting factor and am not anticipating any severe weather.
Brief downpours and gusty winds will be the main hazards.

Tonight...a stronger upstream shortwave will track across the
Dakotas and western IA supporting strong to severe storms in this
region. Instability will wane through the overnight period, thus
this activity should diminish as it moves east over IA. Lows to drop
into the upper 60s/low 70s.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Issued at 308 AM CDT Tue Jul 15 2025

Wednesday...an active period of weather is expected with
dangerous heat and severe potential the main concerns. Decaying
storms are forecast to start the period with an increase in
cloud cover. The amount of clouds during the day will play a key
role in how warm we get and how much instability will be
available for afternoon and evening storms. Will address each
hazard below separately.

Heat Potential

A very warm and humid airmass will be in place characterized by
mid-70 dewpoints. These values combined with forecast ambient temps
in the upper 80s/low 90s to yield heat indices in the upper 90s
and perhaps a few 100+ degree values during the afternoon. At
this time, the probabilities for 100+ degree heat indices is
highest (20-30%) along and south of Hwy 34. A heat headline may
eventually be needed or at the very least an SPS on Wednesday.

Severe Potential

Latest CAMs and RAP model trends continue to suggest the
potential for an MCV to track across the CWA resulting in strong
to severe storms Wednesday afternoon and evening. In addition, a
cold front is progged to move through after 23z providing
another focus for thunderstorm development. A favorable
thermodynamic environment (1500-2500 J/Kg ML CAPE and very high
PWs over 2") will be in place ahead of these features. The
limiting factor will once again be shear with 0-6km values
under 30 kts. That all being said, if an MCV develops and
maintains across eastern IA then shear can be locally enhanced
in close proximity to it thereby increasing the severe
potential. As a result, SPC has introduced a Slight (level 2 out
of 5) risks for severe weather Wednesday. A few organized
multi-cell clusters with damaging winds and a tornado or two
will be possible. Very weak mid-level lapse rates under 5.5 C/Km
to preclude any hail threat. In addition, WPC has added an Day
2 Slight risk for excessive rainfall with rain rates over 1"/hr
possible on top of saturated ground leading to localized flash
flooding. This risk is highest along and north of Hwy 30 as
depicted by the 00z HREF. The one thing that is different of
this event than compared to last Friday is the storms are
expected to be progressive and have storm motions over 20 kts
leading to less residence time at any given location and may
limit any flash flooding.

Thursday-Monday...an active pattern remains likely with a
strong upper level ridge setting up shop across the southeastern
CONUS. This will put the local area on the edge of the main
storm track with several shortwaves rounding the ridge every
36-48 hrs. Not every day will see rainfall, but warm and humid
conditions will bring a continued risk for afternoon storms. The
next best chance (40-55%) of storms appears to occur this
Saturday and Sunday.

Tuesday Onward...some longer range guidance and the latest CPC
8-14 Hazards Outlook shows a building strong upper ridge
developing across the central CONUS pushing the storm track
further north, but unfortunately bringing even warmer air into
the region. Extreme heat may be a growing concern as we enter
next week.


&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1140 PM CDT Mon Jul 14 2025

Model guidance continues to suggest some brief MVFR fog will be
possible prior to sunrise and have included TEMPO groups with
the TAFs. Otherwise, VFR conditions to prevail at all terminals
with the region remaining between systems. Some fair wx Cu
should develop along and east of MS RVR this afternoon. A few
shallow storms may also occur but all new guidance keeps this
activity east of the terminals late afternoon/evening.

&&

.HYDROLOGY...
Issued at 1226 PM CDT Mon Jul 14 2025

The flood warning for the Skunk River at Sigourney has been
canceled as the river has crested near action stage and has
started to slowly fall. There have been no other forecast
changes with flood warnings remaining in effect for the Iowa
River at Marengo as well as the Mississippi River at Gladstone
and Burlington. A flood watch remains in effect for the
Wapsipinicon River at DeWitt. Within bank rises continue on
several area rivers.

&&

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

&&

$$

SHORT TERM...Gross
LONG TERM...Gross
AVIATION...Gross
HYDROLOGY...Cousins