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000
FXUS63 KILX 160217
AFDILX

Area Forecast Discussion...Updated
National Weather Service Lincoln IL
917 PM CDT Mon Apr 15 2024

.KEY MESSAGES...

- There is a low (20-30%) chance for a thunderstorm with
  damaging hail tonight.

- Tomorrow will be a warm and breezy day with south to
  southeasterly wind gusts of 30-35 mph.

- Showers and thunderstorms are expected (>80% chance) to
  develop from mid-afternoon and last through the early evening
  hours.

- A threat for severe weather exists from 5 to 10 PM tomorrow mainly
  west of I-39 and northwest of I-55 with a threat for all
  hazards (damaging winds, damaging hail, tornadoes).

- After another round of showers and thunderstorms Thursday
  afternoon into early Friday morning, a cooler and drier
  pattern will arrive this weekend.

&&

.UPDATE...
Issued at 917 PM CDT Mon Apr 15 2024

Current forecast looks in good shape, however, lowered overnight
lows by 1 degree across the area, given the lower dewpoints and
lighter winds. Isolated to scattered convection still looks
possible overnight but have reduced pops a bit as HiRes models
only showing isolated showers and storms during the overnight
hours. Update will be out shortly.

Auten

&&

.DISCUSSION...
Issued at 157 PM CDT Mon Apr 15 2024

Tonight through Wednesday Morning:

A recent hand surface analysis revealed an elongated warm front and
associated pressure trough stretching from southern Ohio through far
southern Illinois and into the central Plains. The warm front is
located well ahead of a developing low pressure system currently
centered in far eastern Colorado, downstream of an approaching upper-
level trough traversing the Four Corners region at press time.
Closer to home and north of the warm front, the combination of
surface dew points in the mid 40s to lower 50s, temperatures in the
mid 70s to lower 80s, and plentiful sunshine is affording a
beautiful mid-April day.

Over the next 12 hours, the aforementioned upper-level trough will
eject into the southern Plains and cause the surface low to begin
deepening while moving into northwestern Nebraska. Subtle pressure
falls along the eastern periphery of the expanding cyclonic
circulation in the Midwest will hence encourage the warm front to
lift northward through central Illinois overnight. Even with large-
scale forcing remaining well to our west and across the Plains,
somewhat unfocused but persistent 925- to 850mb low-level flow atop
the warm frontal zone may activate a layer of steep mid-level lapse
rates of 7.5 to 8 K/km. As a result, a few thunderstorms may develop
along the northward-moving frontal zone overnight (currently a 20-
30% chance as the front lifts over any point in time). With 40-45kt
of effective shear within the convective layer largely focused above
the elevated convective inflow layer (e.g. weak storm-relative
flow), and the majority of the CAPE profile remaining above the
freezing level, any storm may produce hail larger than 1" in
diameter with efficiency.

By daybreak Tuesday, the warm front (and any thunderstorm activity)
is expected to move into northern Illinois giving way to a warm and
breezy day. Depending on the amount of cloud cover, deep mixing into
an intensifying low-level wind field may support south to
southeasterly wind gusts of 30 to 35 mph from mid-morning onward.

From Tuesday evening onward, attention will turn completely toward
the threat for severe thunderstorms as an upper-level shortwave
embedded in the approaching trough aloft reaches a northeast-racing
tongue of low-level moisture across west-central Illinois. Showers
and thunderstorms may develop as early as 2-3 pm across central
Illinois, but the severe weather threat will be tied to anything
that develops within (or becomes anchored to the eastern fringe of)
the tongue of low-level moisture more likely between 5 and 10 PM
west of I-39 and northwest of I-55. During this time, the
overlapping kinematic and thermal profiles will be highly supportive
of supercellular structures with a threat for all hazards (damaging
winds, damaging hail, and tornadoes). In fact, low-level hodographs
featuring 0-500m shear of 25-30kt with a high degree of
"streamwiseness" raise the concern for particularly damaging
tornadoes (EF-2+) with any discrete, sustained supercell. Such
a threat is, again, mainly west of I-39 and northwest of I-55,
between 5 and 10 PM. Even with the primary threat for severe
weather across west-central and northern Illinois, a storm or
two may nevertheless produce isolated instances of damaging
winds or hail elsewhere across the area Tuesday evening.

Now, it is worth noting that NAM-based guidance continues to
depict a forecast scenario where the system arrives much later
than as depicted in other model guidance, which would keep the
threat for severe weather tomorrow evening mainly near and west
of the Mississippi River. However, the threat for severe weather
in our area would return Wednesday morning as the cold front of
the system sweeps across the state mainly east of I-39. For
now, we`ll continue assessing model trends and elaborate on such
a scenario in later forecasts if other guidance trends in that
direction. For now, the main message is to stay weather aware
tomorrow afternoon through Wednesday morning.

Borchardt

Wednesday afternoon onward:

Behind the large early-mid week weather system, weak high pressure
will bring a short break in the active weather, as a deep upper
level low meanders through the northern Plains and upper Midwest.
Our region will remain in a zonal flow pattern ahead of this system
with a few disturbances embedded in the flow. The main trigger for
increased chances for showers and isolated thunderstorms will come
with a cold front late Thursday and Thursday night.

The national blend of models does still offer some very low end
chances (~20%) for showers beyond Friday morning pattern,
however in spite of remaining in an active west-northwest flow
pattern aloft, high pressure at the surface and a much drier
airmass should largely bring a much quieter weather period later
Friday and continue through the weekend. Temperatures though
will be on the colder side, with most locations holding below 60
degrees.

KMD

&&

.AVIATION...  (For the 00z TAFs through 00z Tuesday Evening)
Issued at 652 PM CDT Mon Apr 15 2024

VFR conditions will prevail through most of the TAF period with
high cirrus expected this evening. HiRes models show a small band
of scattered showers developing south of the area and moving
through the sites during the overnight hours. Dry weather will
then be expected during the morning into the afternoon hours, but
strong convection is expected to develop out west and then move
into the sites during the late afternoon and continue into the
evening hours. Will keep cigs at VFR but will drop vis to 5sm as
light showers will move across the sites with VCTS. Winds will be
easterly to start with winds around 12kts. The winds will increase
in speed with gusts of 20-21kts during the overnight hours but
then get stronger tomorrow morning and into the afternoon, with
gusts around 30kts. Southeast winds will dominate during the
daytime hours.


Auten

&&

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

$$