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Crystal Lake, Illinois 7 Day Weather Forecast
Wx Forecast - Wx Discussion - Wx Aviation
NWS Forecast for Crystal Lake IL
National Weather Service Forecast for: Crystal Lake IL
Issued by: National Weather Service Chicago, IL
Updated: 5:57 pm CDT Jul 26, 2025
 
Tonight

Tonight: A 20 percent chance of showers and thunderstorms before 10pm.  Patchy fog after 1am.  Otherwise, mostly cloudy, with a low around 71. Southwest wind around 5 mph becoming calm  in the evening.
Slight Chance
T-storms then
Patchy Fog
Sunday

Sunday: Patchy fog before 9am.  Otherwise, partly sunny, with a high near 90. Heat index values as high as 96. Calm wind becoming southeast around 5 mph in the afternoon.
Patchy Fog
then Mostly
Sunny
Sunday
Night
Sunday Night: Mostly clear, with a low around 72. South wind around 5 mph becoming calm  in the evening.
Mostly Clear

Monday

Monday: Mostly sunny, with a high near 93. Heat index values as high as 107. South southwest wind 5 to 10 mph, with gusts as high as 15 mph.
Mostly Sunny

Monday
Night
Monday Night: Partly cloudy, with a low around 72. West wind around 5 mph becoming calm  in the evening.
Partly Cloudy

Tuesday

Tuesday: A 20 percent chance of showers and thunderstorms.  Mostly sunny, with a high near 89.
Slight Chance
T-storms
Tuesday
Night
Tuesday Night: A 30 percent chance of showers and thunderstorms.  Mostly cloudy, with a low around 68.
Chance
T-storms
Wednesday

Wednesday: A chance of showers and thunderstorms.  Mostly cloudy, with a high near 78.
Chance
T-storms
Wednesday
Night
Wednesday Night: Mostly cloudy, with a low around 61.
Mostly Cloudy

Lo 71 °F Hi 90 °F Lo 72 °F Hi 93 °F Lo 72 °F Hi 89 °F Lo 68 °F Hi 78 °F Lo 61 °F

Hazardous Weather Outlook
 

Tonight
 
A 20 percent chance of showers and thunderstorms before 10pm. Patchy fog after 1am. Otherwise, mostly cloudy, with a low around 71. Southwest wind around 5 mph becoming calm in the evening.
Sunday
 
Patchy fog before 9am. Otherwise, partly sunny, with a high near 90. Heat index values as high as 96. Calm wind becoming southeast around 5 mph in the afternoon.
Sunday Night
 
Mostly clear, with a low around 72. South wind around 5 mph becoming calm in the evening.
Monday
 
Mostly sunny, with a high near 93. Heat index values as high as 107. South southwest wind 5 to 10 mph, with gusts as high as 15 mph.
Monday Night
 
Partly cloudy, with a low around 72. West wind around 5 mph becoming calm in the evening.
Tuesday
 
A 20 percent chance of showers and thunderstorms. Mostly sunny, with a high near 89.
Tuesday Night
 
A 30 percent chance of showers and thunderstorms. Mostly cloudy, with a low around 68.
Wednesday
 
A chance of showers and thunderstorms. Mostly cloudy, with a high near 78.
Wednesday Night
 
Mostly cloudy, with a low around 61.
Thursday
 
Sunny, with a high near 76.
Thursday Night
 
Mostly clear, with a low around 57.
Friday
 
Mostly sunny, with a high near 76.
Friday Night
 
Partly cloudy, with a low around 56.
Saturday
 
Mostly sunny, with a high near 78.

 

Forecast from NOAA-NWS for Crystal Lake IL.

Weather Forecast Discussion
359
FXUS63 KDVN 262336
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
636 PM CDT Sat Jul 26 2025

.KEY MESSAGES...

- Fog tonight, possibly dense along and north of I-80.

- Heat builds back in Sunday through Tuesday, potentially
  dangerous, but there will also be episodes of storms making
  for a challenging temperature forecast and low confidence on
  the spatial extent and magnitude of the heat (day to day
  evaluation needed).

- Pattern change late week to usher in cooler, more seasonable
  and drier conditions.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 212 PM CDT Sat Jul 26 2025

Following early day activity, coverage of showers and storms
has decreased with isolated to widely scattered activity
possible into this evening. No severe weather or new flooding is
expected.

For tonight, a 15-20% chance for showers and non-severe storms
will remain mainly along the Highway 34 corridor. Look for Fog
to develop across much of the area due to surface moisture from
recent rainfall and clearing skies. Models are hitting areas
along and north of I-80 for the greatest coverage and potential
for dense fog. A Dense Fog Advisory may be needed.

&&

.LONG TERM /SUNDAY THROUGH SATURDAY/...
Issued at 212 PM CDT Sat Jul 26 2025

A ridge builds into the central U.S. Sunday into Tuesday, with
the CWA being on the northeastern periphery, which will allow
for potential for excessive heat and MCS activity.

Sunday looks dry for the most part, with 15-20% chances for
convection along and south of the Highway 34 corridor. With
highs around 90 and dew points in the mid 70s to around 80
(highest south), heat index values are expected to be 100-105
south of I-80. A Heat Advisory has been issued for these
southern areas.

Sunday night into Tuesday will see the greatest heat and MCS
potential. These two hazards may counter each other since any
thunderstorm activity may keep daytime temperatures cooler,
depending on track, timing, and coverage of convection which is
highly uncertain at this time. Any MCS activity, which would
most likely fall in the late night into morning hours both
Sunday night and Monday night, would bring potential for severe
thunderstorm winds and flooding. If convective activity does
not interfere with daytime temperatures, look for highs in the
low to mid 90s. Temperatures combined with dewpoints in the mid
70s to around 80, due in part to transpiration, heat index
values may be oppressive in the 105-110+ range both days. Heat
headlines may be needed as factors become more certain. Again,
confidence in these hazards is low a this time, so check back
for updates.

A pattern change then occurs mid to late week with chances for
showers and cooler conditions Wednesday, followed by cooler and
drier conditions late week. Highs in the 70s to around 80 are
currently expected.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 630 PM CDT Sat Jul 26 2025

Main concern tonight into Sunday AM will be areas of dense fog
leading to periods of LIFR to VLIFR (~1/4SM visibilities), most
likely at DBQ and CID. A very humid air mass, clearing skies
and light winds will set the stage for fog development which
will expand in coverage late tonight into early Sunday AM;
confidence on dense fog is a little lower at MLI and BRL.
Another potential impact for tonight is isolated to scattered
storms near MLI, so have mentioned thunder in a PROB30 there.
The fog will gradually dissipate through the mid morning hours
on Sunday, with light winds expected to continue.

&&

.HYDROLOGY...
Issued at 200 PM CDT Sat Jul 26 2025

Some local tributary rivers are experiencing flooding from
rainfall that fell last night and this morning, especially in our
southern forecast area. Specifically, we are expecting rapid rises
along the Fox River in Wayland Missouri, where Moderate Flood
Stage is forecast. Rises into Minor Flood Stage are also being
seen along the Des Moines River in St. Francisville Missouri.
These crests are expected to last about 24 to 36 hours before
going back down below flood stage. Isolated-scattered storms can
be seen this afternoon and evening, but are not expected to have
too much more of an impact on the current forecasts out. If this
is to change, we will update accordingly.

Please see the latest Flood Statements and Flood Warnings for
details.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Heat Advisory from 1 PM to 9 PM CDT Sunday for IAZ076>078-
     087>089-098-099.
IL...Heat Advisory from 1 PM to 9 PM CDT Sunday for ILZ024>026-034-
     035.
MO...Heat Advisory from 1 PM to 9 PM CDT Sunday for MOZ009-010.

&&

$$

SHORT TERM...NWS
LONG TERM...NWS
AVIATION...Uttech
HYDROLOGY...Gunkel
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Forecast Discussion from: NOAA-NWS Script developed by: El Dorado Weather






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