766
FXUS63 KILX 250508
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1108 PM CST Sun Nov 24 2024

.KEY MESSAGES...

- Light rain/drizzle (30-40% chance) develops tonight into Monday.
  Precipitation amounts will be light, less than 0.10".

- A frontal system looming on the horizon could bring our next
  chance for a wintry rain/snow mix (40-60% chance) Wednesday into
  Thanksgiving morning. Confidence remains low, but probabilities
  for accumulating snow have decreased.

- An arctic blast will bring bitterly cold temperatures late this
  week into the start of December. In the days following
  Thanksgiving, air temperatures will struggle to warm above
  freezing with wind chills in the teens to single digits.

&&

.DISCUSSION...
Issued at 239 PM CST Sun Nov 24 2024

Surface ridging has been pushed east into Ohio early this afternoon
as southerly flow ramps up ahead of a developing low in the central
Plains. Persistent WAA out ahead of the system has filtered warmer
air northward, allowing highs to warm into the middle 50s to low 60s
as of 2 pm. A warm front is in the process of lifting north through
the area, with forecast soundings showing the surface to ~750-800 mb
layer saturating by this evening/overnight, introducing light
precipitation chances as lift increases ahead of the low. Mid-level
air will struggle to moisten even as the surface low lifts
through the area on Monday, which should keep any precipitation
very light or in the form of drizzle. Some reduced visibility may
develop with drizzle, but chances for visibility falling below 1
mile is relatively low.

Temperatures drop quite a bit behind a cold front Monday night with
overnight lows in the 20s. Temperatures will remain below normal
through the midweek period, giving us a taste what`s to come later
in the week.

The forecast becomes a little more tricky by midweek as a frontal
system develops in the southern Plains states and ejects northward
toward the Ohio Valley Wednesday into Thanksgiving morning. The last
several runs of deterministic guidance have done some flip-flopping,
with the ECMWF continuing to show a deeper trough swinging through
the middle Mississippi Valley and hence a stronger/deeper surface
low. Despite this, ECMWF QPF amounts have come down significantly
over central Illinois since yesterday`s 23.12Z run. The GFS and CMC
continue to show a shallower trough, which would keep the surface
low further south and most of the QPF in southeast IL as rain.
Ensemble members show mean snow accumulation from nearly nothing
(GEFS and GEPS) to a couple inches of snow (ENS), which is a
downward trend from previous runs. The NBM`s probabilities for
snow have also decreased with less than a 20% chance of seeing 1
inch north of I-74 where some signal for frontogenetic banding
lies ahead of the main wave. This continues to be a relatively low
confidence forecast, but the probability of seeing impactful
accumulating snow has come down.

There is good agreement that arctic air will intrude most of the
central and eastern US later this week, sending bitterly cold
temperatures southward as a Canadian surface high noses south.
Beginning Thanksgiving night, it appears that there will be an
extended period where air temperatures do not rise above freezing
(32 degrees) for most of our counties. Wind chills late this week
could drop into the teens to single digits. Temperatures should
break above the freezing mark by the middle of next week, but will
remain below normal (60-80% chance) through the first full weekend
of December.

A quick hitting clipper system could bring light accumulating snow
to central Illinois over the weekend, but there remain differences
with timing and placement.

NMA

&&

.AVIATION...  (For the 06z TAFs through 06z Monday Night)
Issued at 1108 PM CST Sun Nov 24 2024

Updated the TAFs this cycle to be less pessimistic on ceilings
overnight as it now appears MVFR ceilings won`t start to develop
over the central IL terminals until closer to daybreak. Also
removed IFR ceilings for the morning hours, with MVFR likely to
continue until clearing from the southwest Monday evening. South
winds tonight to veer northwest behind a cold front after sunrise,
with gusts increasing to 20-25 kt by late morning, then
lowering after skies clear. Any showers tonight/early Mon morning
to be light and brief.

25

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$