Crystal Lake, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

607
FXUS63 KDVN 071909
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
209 PM CDT Sun Jun 7 2026

.KEY MESSAGES...

- This morning`s round of heavy rain producing storms has seen
  prolific heavy rain rates, mesoscale storm interactions, and
  nearly continuous redevelopment, resulting in a Flash Flood
  Threat Developing!

- Rounds of nocturnal and diurnal convection through Monday
  night will bring a risk of locally heavy rainfall due to weak
  winds aloft. If the heavy rain is persistent more than 1 hour,
  flash flooding is possible.

- Heat and humidity will return around mid-week with
  temperatures in the 90s and heat indices pushing 100 or
  higher. The probability of heat headlines around mid-week is
  33-40 percent.

&&

.SHORT TERM /THROUGH MONDAY NIGHT/...
Issued at 208 PM CDT Sun Jun 7 2026

Our area has been the focal point of weak synoptic lift from the
approaching upper low, exceptionally high PWAT air mass around 2
inches, and a mesoscale boundary from Lake Michigan which is all
creating a nearly continuous convective activity over the I-80 and
and north this morning.   Day time temperatures and east winds under
these storms have held the boundary in place, while predominantly
dry conditions south have allowed for heating. This will set the
stage for additional torrential rain producing storms over the area,
especially the northeast 1/2. Given this scenario, I`ve opted to
issue a Flood Watch for this scenario where repeated torrential rain
is expected on and off through Monday.

Models are not handling this well, but with the upper low lifting up
over the area, this focusing mechanism is unlikely to stop until the
upper low`s passage.  We have had seen flash flooding already take
place in Bureau County in our east, and additional flooding appears
likely, despite starting the day with dry soil conditions in many
areas.  Several reports through Noon are 2 to 5 inches of rain this
morning.

Rainfall tonight in general may average 0.5 to 1.0 inches, but in
areas that see the repeated storms, tonight may see more areas of 2
to 5 inches.  That certainly won`t be everywhere, but in the
northeast 1/2 were especially prone to this, with advection over the
boundary.

Late this morning, along the boundary in the east, NSP values grew
to around 2-3, and a small tornado was reported by an IL police
deputy, relayed by emergency management. The latest
mesoanalysis from SPC is showing that area lifting northeast of
Bureau Co, and with ongoing rains we may be done with that
threat.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
Issued at 207 AM CDT Sun Jun 7 2026

Tuesday through Sunday
Assessment...high (>80%) confidence of temperatures well above
normal. Low (20-25%) confidence for rain.

Trends with the models continue to show temperatures well above
normal for much of the week.

However, the highest heat indices now look to occur in the
Tuesday/Wednesday time frame. A seasonably strong front arriving
Wednesday night will bring cooler temperatures on Thursday with
temperatures moving to near normal for next weekend.

Heat indices Tuesday continue to indicate 95 to 100 but areas south
of I-80 have a 30-40% probability of exceeding 100. On Wednesday the
probability of seeing heat indices of 100+ is now at 50-60%.
Depending upon how rain chances play out, heat headlines may be
needed in the Tuesday/Wednesday time frame.

The model consensus indicates the daylight hours of Tuesday are dry.
Tuesday night into Wednesday is a question. A weak signal has
started to develop suggesting a nocturnal storm complex running
around the edge of the heat dome. If this occurs it would play
significantly into the need for potential heat headlines Wednesday.

Albeit a weak signal, some of the ensemble members of the various
models are pointing to rain and have a 20-30 percent chance for rain
Tuesday night into Wednesday.

Wednesday night into Thursday looks interesting.

A much stronger front is progged to move through the area that will
be associated with a strong upper level disturbance. Winds in the
mid-levels of the atmosphere are progged to be around 50 knots
indicating organized storms with the potential for severe storms.
CSU ML progs and other ML analog sites from the June 6th model runs
have a 15-30% probability of severe storms occurring. Thus the
transition from hot and humid conditions may have severe storms.

Thus Wednesday night has the best chances for rain. The current
model consensus has 50-70 percent chances for rain. Outside of
Wednesday night, the model consensus has daily 20-35 percent chances
for rain Thursday through Sunday.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1223 PM CDT Sun Jun 7 2026

An upper low with copious moisture is combining with east winds
over northern Illinois to bring widespread shower and
thunderstorms to eastern Iowa and northwest Illinois. This
nearly continuous process will lead to scattered storms with low
visibility, heavy rain, and lower MVFR cigs / brief IFR cigs to
all sites this afternoon and evening, and potentially into
Monday afternoon at times. Expect heavy downpours with all
storms, and possibly localized gusty winds, but otherwise, light
wind flow from the southeast to east southeast.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Flood Watch through Monday evening for IAZ040>042-051>054-
     064>068.
IL...Flood Watch through Monday evening for ILZ001-007-009-015>018-
     024.
MO...None.

&&

$$

SHORT TERM...Ervin
LONG TERM...08
AVIATION...Ervin