Crystal Lake, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

892
FXUS63 KDVN 200648
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
148 AM CDT Thu Aug 20 2026

.KEY MESSAGES...

- There will be the chance for fog through the remainder of
  tonight into Thursday morning, especially for areas south of
  Interstate 80. Elsewhere, patchy dense fog is possible,
  especially in river valleys.

- Another system will pass through the area Friday, bringing the
  chance for afternoon showers/storms along a passing cold
  front. A few stronger storms are possible.

- A stretch of quiet and mostly dry weather will be seen this
  weekend and into next week, with seasonal temperatures.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 135 AM CDT Thu Aug 20 2026

Once again, we will see the potential for fog through the remainder
of tonight into Thursday morning. Short term guidance has not been
picking up on this too much, so there remains some uncertainty. We
will continue to see clouds clear out from northwest to southeast
through tonight, with light winds and a boundary draped just south
of the area. Recent rainfall in our south will also allow for
readily available moisture near the surface as well. Thus, these
conditions would be favorable for fog development, especially with
surface high pressure over our north. There remains uncertainty on
how dense and widespread the fog will be, but river valleys and
areas with recent rainfall will be first in line, especially south
of Interstate 80.

Surface high pressure will pass overhead through the day today,
bringing along quite a pleasant day. Temperatures will remain
seasonal, with lower humidity and a light breeze making it feel
quite comfortable. Mostly clear skies will remain through the day,
with increasing cloud cover this evening and through tonight. These
increasing clouds will be in response to increasing moisture ahead
of an approaching shortwave. Overall, this will be a weak wave, with
little forcing and limited moisture. Much uncertainty exists on us
seeing much precipitation overnight, as the surface front is not
forecast to come through until Friday. Thus, lacking surface forcing
will make it difficult to get much precipitation. If we do see
anything, they should largely be light showers and confined to
our northwest where the better moisture and forcing will reside.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Issued at 135 AM CDT Thu Aug 20 2026

Friday, we will see the chance for showers/storms increase through
the day. Much of the aforementioned wave will have moved off, with
the low-end risk (20-30% chance) for residual showers into mid
morning. From there, the next bout of energy is forecast to pass
through the area midday. This will be a compact and low amplitude
shortwave trof, dragging a cold front through the area Friday
afternoon/evening. With little convective debris expected that
morning, we should see a mix of clouds and sun, allowing us to build
instability through the day. Guidance favors anywhere between 2000-
3000 J/kg of CAPE to develop through the afternoon, with sufficient
lapse rates and forcing to favor the development of afternoon storms
along the cold front. The deep layer shear is forecast to be
relatively meager, roughly ranging between 25-30 KTs. Thus, storm
organization will be difficult, but not impossible. If we manage to
get storms to organize, there will be the chance for a few stronger
storms in the afternoon. A look at model soundings would largely
favor wind gusts being the main threat, but confidence is low on
this currently. Overall, forcing and moisture content are not the
best. Thus, the threat would be isolated-scattered and focused along
the passing cold front through the afternoon and early evening.
Another limiting factor would be any AM convective debris that could
limit destabilization. Thus, plenty of uncertainty and will be
something to keep an eye on for future forecast updates.

Through the remainder of the forecast period, we will remain
dominated by upper level northwest flow. This will continue to usher
shortwaves through the area, but this pattern is not favorable for
much moisture return. Thus, precipitation chances will remain
limited through this timeframe, with passing clouds and shifting
winds being the main signs of the passing waves. After Friday night,
precipitation chances are limited until the middle of next
week. Thus, enjoy this stretch of seasonal temperatures and dry
weather!

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1236 AM CDT Thu Aug 20 2026

VFR conditions will prevail through much of the TAF period, with
light and variable winds. Between 09-15z, we will see the
potential for fog development. Best chances will be in our
south, where a slow moving boundary remains. Although, northern
areas have also cleared out and patchy dense fog cannot be ruled
out there either as high pressure approaches, especially in
river valleys. Opted to largely message fog potential with
TEMPO groups at this time. Otherwise, light/variable winds and a
mix of clouds/sun will remain after 15z today.

&&

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

&&

$$

SHORT TERM...Gunkel
LONG TERM...Gunkel
AVIATION...Gunkel