Romeoville, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

536
FXUS63 KDVN 221144
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
544 AM CST Sun Dec 22 2024

.KEY MESSAGES...

- Warmer temperatures today with nighttime drizzle or freezing
  drizzle is possible early Monday morning.

- Temperatures continue to warm through the week with chances
  for rain Christmas Day into next weekend.

- 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 MONDAY/...
Issued at 241 AM CST Sun Dec 22 2024

Northwest flow aloft becomes more zonal through the period as an
upper level wave approaches the area. SW flow will lead to WAA
in the low levels and temperatures in the 30s to 40s today. With
the exception of high clouds today, the weather will be quiet.
This evening the wave approaches the area from the NW as a
surface low tracks into our area.

Tonight, H85 WAA begins in earnest while the wave approaches the
area between 06z and 12z Monday. At the same time, shallow low
level moisture moves into the area. Soundings in both the HREF
and the LREF depict a drizzle like sounding, especially north of
the Highway 30 corridor. Further south, these soundings depict
more dry low levels and may limit overall drizzle occurrence.
As a result of this have decreased the spatial coverage of the
chc pops to be where the better sounding agreement is.

The majority of the guidance keeps our area above freezing.
Areas along and north of Highway 20, where there is still some
snowpack, is forecast to be just below freezing. With the very
light nature of this QPF, it is possible that elevated surfaces
may see a light glaze of ice. Model soundings have saturation
and possible ice introduction above a dry layer that is above
the sfc moisture. Would not be surprised to see some snowflakes
mix in closer the 12z, especially along the highway 20 corridor.

At this time, will message this in the HWO and graphics. Think
the main impacts will be to untreated surfaces and once the sun
comes up we should warm above freezing. Do not expect this to be
too impactful at this time.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Issued at 241 AM CST Sun Dec 22 2024

Active pattern through the long term continues we see
temperatures warm well above average and a chance for rain
starting Christmas Day lasting into next weekend. After the wave
moves out Monday we see either a shortwave or a longwave trof
almost every 24 hours with the next system moving through the
area for Christmas Eve and the one after that moving just to our
south for Christmas Day. After this, Thursday through Sunday we
see near daily SW lows moving towards us. With some of the
guidance having temps well into the 50s late this week into the
weekend.

Christmas Eve and Christmas Day could see rain in the area.
Guidance has light QPF with these systems, with the majority of
it being south and east of the Quad Cities. With temperatures
above freezing this will not be all that impactful. With the
temperatures warming up, the majority if not the entire area
will see a brown Christmas.

Thursday on, the systems look robust. We will have warm draws
into the area more than any CAA, so we should see temperatures
well above normal. In fact, I would not be surprised to see some
highs in the 50s. With the active pattern, this means guidance
is all over the place. That said, lets just look at the 00z GFS.
This is just one of the solutions and could change. That said,
it does show that we could actually see some thunder Thursday
and Friday. In fact, it even has some low SBCAPE. I am hesitant
to even bring this up as we will see things change between now
and then. Though, with the thermal fields it appears we have a
better chance for storms than we do any snow Monday night on.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 541 AM CST Sun Dec 22 2024

VFR conditions are expected until late in the period when MVFR
cigs will move into the area. There is a chance (30%) for fzdz
or dz at DBQ late tonight. Added a prob30 for that. Otherwise,
wind shear could become a problem after 00z, but have left out
of TAF at this time.

&&

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