Crystal Lake, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

528
FXUS63 KDVN 220536
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1136 PM CST Sat Dec 21 2024

.KEY MESSAGES...

- Confidence is increasing in a light icing event late Sunday
  night into Monday morning with potential impacts to the Monday
  morning commute.

- Warming temperatures will be seen the remainder of next week
  with several chances for rain with a little snow.

- The potential is increasing for an arctic outbreak shortly
  after the start of the New Year followed by colder than normal
  temperatures through mid-January. Refer to the climate
  section for more information.

&&

.SHORT TERM /THROUGH SUNDAY/...
Issued at 255 PM CST Sat Dec 21 2024

Quiet and cold conditions will prevail through sunset Sunday.
Temperatures will be a bit warmer on Sunday. Attention then turns to
the approaching clipper system.

&&

.LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
Issued at 255 PM CST Sat Dec 21 2024

Sunday night into Monday
Assessment...medium to high confidence on a light icing event

The next storm system will move quickly through the area late Sunday
night into Monday morning. Favorable forcing points to a quick shot
of precipitation. Atmospheric profiles show a narrow layer of
moisture with much drier air aloft. With the lowest layer of the
atmosphere at or a bit below freezing the overall scenario looks
ripe for a drizzle/freezing drizzle event mixed with some snow.

The area most favored for freezing drizzle will be over the snow
field, roughly north of a line from Waterloo, IA to Kewanee, IL.
South of that line some freezing drizzle is possible but with
temperatures marginally warmer, it will be spotty in coverage.

The time frame favorable for any freezing drizzle looks to be from
12 AM to 9 AM on Monday. Amounts look to be less than 0.05 inches of
glaze.

As temperatures slowly rise on Monday, any glaze that occurred
overnight will slowly melt.

Monday night through Saturday
Assessment...high confidence on an active weather pattern. Low
confidence on potential impacts.

After a quiet Monday night and Tuesday, an active weather pattern
will continue the remainder of the week with several chances for
precipitation.

The global models vary on timing and track of the systems. However,
the more favored time periods for precipitation look to be Tuesday
night into Wednesday and Thursday night into Friday. In between
these time frames additional upper level disturbances aloft will be
moving through the area that may result in spotty precipitation.
With the warming temperatures, rain is the favored precipitation.

Where the signal is better for precipitation, the model consensus
has a 20-40% chance for rain Tuesday night/Wednesday and Thursday
night into Friday. There is mainly a 15-30% chance for rain
Wednesday night/Thursday and again Friday night into Saturday.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1131 PM CST Sat Dec 21 2024

VFR conditions are expected to last through the area with winds
being main impact to aviation. Expect winds to become east-
southeasterly later with gusts in the low to mid 25 kt range.

&&

.CLIMATE...
Issued at 255 PM CST Sat Dec 21 2024

Overall the MJO has been active since early December. Now
a low frequency base state is constructively interfering that is
affecting the propagation/magnitude of the MJO. This signal is
consistent with La Nina.

The MJO has been in phase 5 for the about a week which is
favorable for warmer than normal temperatures. The MJO is
forecast to potentially amplify as it moves toward the
international date line in the Pacific into early January but
constructive interference from La Nina may slow the eastward
propagation. The MJO is forecast to move into phase 6 and
eventually through phase 7 and into phase 8 by early January
and possibly into phase 1 by mid-January. While the correlation
is not high, phases 6 and 7 correlates to warmer than normal
temperatures while phases 8 and 1 corresponds to colder than
normal temperatures. Precipitation wise, the correlations are
lower than temperatures but point to drier than normal
conditions.

Stratospheric winds have been quite strong around the arctic
circle which is keeping the polar vortex in place. However, the
average of the GEFS/GEPS ensembles along with the deterministic
GFS are indicating the mean zonal wind at 10 hPa in the
stratosphere will significantly weaken late next week which will
continue into early January. At the same time the 10 hPa
temperatures are forecast to warm. However, the amount of
warming is around 5 Kelvin which is not supportive of a sudden
stratospheric warming event.

The weakening of the 10 hPa zonal winds does point to a
potential break down with the polar vortex from the arctic
circle and an intrusion into the lower latitudes.

Output from the GEFS ensembles show the mean turning negative
for the NAO/AO while the PNA remains slightly positive. There
is a large spread in the ensemble members on what the NAO/AO
will do while PNA spread is much tighter.

Taking this all together points to a potential arctic outbreak
associated with a pattern change aloft shortly after New Years.
This pattern change to a northwest flow points to colder than
normal temperatures along with the potential for drier than
normal conditions.

The Climate Prediction Center outlook corresponds well with the
above data, signaling a 60-70% probability of colder than
normal temperatures through the middle of January along with a
55-60% probability of drier than normal conditions across the
Midwest.

&&

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

&&

$$

SHORT TERM...08
LONG TERM...08
AVIATION...Gibbs
CLIMATE...08