Crystal Lake, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

474
FXUS63 KDVN 171740
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1140 AM CST Wed Dec 17 2025

.KEY MESSAGES...

- Wednesday will be another day of at or above normal
  temperatures for the area.

- A strong storm system will bring very windy conditions to the
  area Thursday. There is a 20-50% probability that wind gusts
  may exceed 40 mph Thursday afternoon and evening.

- Mainly dry conditions over the weekend with large swings in
  temperatures. A persistent trend of above normal temperatures
  will be seen next week.

&&

.SHORT TERM /THROUGH THURSDAY/...
Issued at 229 AM CST Wed Dec 17 2025

The cold front will clear the area by sunrise. Post-frontal
temperatures are still in the 30s so we will see a continued melt of
the snow pack.

The question then becomes how warm will it get today. Satellite
trends suggest a period of partly cloudy or clear skies but high
level clouds in the Plains are racing east. Thus cloud cover should
be on the increase late morning/afternoon which may hold down
temperatures somewhat.

Wednesday evening will be dry across the area as the storm system
approaches the area. Winds, however, will be on the increase and
should be in the 15-25 mph range for much of the night with gusts
approaching 35 mph at times.

Moisture racing north from the Gulf will interact with the cold
front and allow rain to develop across the area. The better signal
for rain is along/east of the Mississippi with rain being more
scattered across eastern Iowa.

While it cannot be ruled out, the signal for thunder is very weak.
Right now no thunder is being forecast but I cannot rule out a
couple of rogue cells developing.

Attention then turns to Thursday.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Issued at 229 AM CST Wed Dec 17 2025

Thursday/Thursday night
Assessment...a certainty (>99%) of very windy conditions and
temperatures turning sharply colder

The strong cold front looks to clear the area around mid-day
Thursday as the upper level dry punch arrives. This will allow
several hours of dry conditions before wrap around precipitation
develops in the afternoon. Ahead of the front windy conditions will
be seen with gusts up to 35 mph.

The passage of the front should be marked by a 5-10 degree
temperature drop and a decrease in winds for a few hours.

Strong cold advection takes hold Thursday afternoon resulting in
steadily falling temperatures. At the same time, winds will increase
significantly. Winds atop of the mixed layer continue to be at least
40 knots which should easily mix down in the cold advection during
the afternoon and evening. The probability of wind gusts exceeding
40 mph ranges from 20 to 50 percent with the higher probabilities
west of the Mississippi.

Thus the potential is there for wind headlines Thursday afternoon
and evening.

The wrap around moisture arrives mid-afternoon with temperatures
aloft dropping below freezing followed by near surface temperatures.
Thus the stage is set for snow showers from mid-afternoon Thursday
that will continue into Thursday evening before ending. Internal
signals from the models are suggesting the potential for some fairly
robust snow showers in the 3-9 PM time frame Thursday
afternoon/evening which may impact the evening commute.

Lingering snow showers will dissipate by midnight but windy
conditions will continue through sunrise. While I cannot fully rule
it out, isolated to scattered flurries are possible late Thursday
night.

Friday through Sunday night
Assessment...medium (40-60%) confidence on mainly dry conditions

Modified arctic air associated with a fast moving high will pour
into the Midwest Friday behind the departing storm system.
Temperatures look to be around or slightly below normal. Return flow
developing Friday night signals a return to above normal
temperatures for Saturday.

While the model consensus is dry for Friday night, the strength of
the warm advection aloft raises the prospects of some sprinkles or
very isolated showers. Right now the signal is weak but it is there
is some of the model solutions.

On Saturday another Canadian front will sweep through the area in
the late morning or afternoon. Atmospheric profiles are quite dry so
the frontal passage looks to be marked with an increase in clouds.

Saturday night and Sunday will be dry as another fast moving high
moves through the Midwest. Temperatures look to average below
normal.

Sunday night return flow develops again across the area. Overnight
low will likely occur during the evening with steady or slowly
rising temperatures the remainder of the night. Atmospheric profiles
are even drier than Friday night so dry conditions should be seen.

Monday through Tuesday
Assessment...medium (40-60%) confidence on dry conditions

Most models have a passing upper level disturbance and associated
weak cold front moving through the area Monday afternoon/night. The
model consensus has dry conditions so this front should only be
marked with an increase in clouds.

As the storm track continues to shift further north, the intrusions
of colder air will be come less intense which will allow
temperatures to average above normal.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1132 AM CST Wed Dec 17 2025

VFR conditions are expected until late evening/overnight. A
strong LLJ will bring a risk of LLWS between 1-2kft overnight
ahead of a strong cold front. Strong forcing and moisture return
will result in scattered rain showers Thursday morning, with
rapidly deteriorating MVFR/IFR conditions developing. Winds to
increase and switch out of the west behind fropa, gusting over
30kts at times late morning and just beyond the TAF period.


&&

.CLIMATE...
Issued at 1204 PM CST Tue Dec 16 2025

A broad and anomalous 500mb ridge (588 dm or 99th percentile
per climatology for late December) will be across the central
CONUS next week. The 8-14 day temperature outlook from the
Climate Prediction Center shows 85-90% combined probabilities of
near/above normal temperatures for the December 23rd-29th time
frame. Normal highs for this period are in the lower 30s and
normal lows are in the middle teens. Should see some substantial
melting take place before and during Christmas across the
forecast area.

&&

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

&&

$$

SHORT TERM...08
LONG TERM...08
AVIATION...Gross
CLIMATE...Gross