Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 232309
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
609 PM CDT Sat Mar 23 2024

.KEY MESSAGES...

- There is a 40-50% chance that strong southerly winds on Monday gust
  to 45 mph or higher, making travel difficult for high profile
  vehicles on east-west oriented roadways.

- Periods of moderate to heavy rain will accompany a cold front
  Monday into Tuesday. Rainfall totals will be highly variable,
  ranging between 0.25 and 1.75 inches most locations (80% chance).
  Though localized higher amounts could lead to ponding of water
  in urban areas with poor drainage, widespread flooding is not a
  concern.

- Isolated thunderstorms may pose a severe weather risk on Monday
  in areas northwest of the Illinois River Valley, though the
  probability remains low at around 5%.

- There is a moderate (40-70%) chance for a hard freeze both
  Tuesday and Wednesday nights, mainly north of I-70. Those with
  newly emerged sensitive vegetation may need to once again take
  protective precautions.


&&

.DISCUSSION...
Issued at 151 PM CDT Sat Mar 23 2024

After a rather cool day featuring highs in the 40s - about 10
degrees cooler than normal for late March in central and southeast
IL - clouds evident on visible satellite to our west will drift into
the area over the next several hours. With them, highres guidance
continues to suggest overrunning precip will overcome dry low levels
and reach the sfc for a couple hundredths of QPF across some portion
of the area, with the highest chances west of I-55 tonight where
PoPs were increased to 20-35% for rain, likely mixed with sleet
and/or snow. Northeast winds this evening will veer to southeast by
sunrise tomorrow morning, simultaneously increasing and working
together with cloud cover to suppress radiational cooling -
preventing lows from falling below 30 degF in most places.

Tomorrow, better mixing should allow warm advection winds to
increase a bit for a seasonably breezy afternoon with southeasterly
gusts approaching/reaching 30 mph mainly northwest of I-55. These
increased low level winds will usher in a warmer and eventually less
dry airmass, resulting in Sunday afternoon highs in the 50s...to
perhaps 60 in Lawrenceville. Increasingly dense cloud cover during
the afternoon and evening will be followed by perhaps some light
precip overnight Sunday night into Monday morning mainly west of I-
55, though forecast soundings again suggest low levels on the dry
side should limit the probability (and amount) that anything reaches
the sfc.

Deterministic models agree the deep sfc low across the Central
Plains Sunday will lift into western Iowa Monday, perhaps leading to
some severe weather near the triple point and downstream along the
warm front, but guidance continues to suggest optimal kinematics for
severe storms will miss us to the northwest. In addition, NBM
continues to advertise lackluster instability with probabilities for
SBCAPE > 200 J/kg less than 20% CWA-wide. The best chance for a
(likely elevated) storm capable of severe hail would be along/west
of I-55, but even there CSU machine learning continues to
advertise only about a 5% risk. Localized hydrological issues are
not out of the question given cloud bearing flow nearly parallel
to the slow- advancing cold/occluded front conducive to training
convection Monday night, when NBM continues to advertise only a
10-20% chance for more than 2 inches of QPF - just under the
minimum amount that`d be required to cause flooding based on 6h
FFG. The greatest concern with this system is going to be
southerly winds Monday mid morning through afternoon, when EPS
mean for max 6h gusts approaches 45 mph. NBM continues to bring
these strong gusts in overnight Sunday night into Monday, but
thinking is this is due to contamination by overzealous CAMs that
are too deeply mixing a decoupled nocturnal boundary layer; hence,
winds and especially gusts were brought down in the forecast
during that time period but hardly touched late morning into early
Monday afternoon when mixing should be a little deeper (though
still mitigated by cloud cover and showers) and BUFKIT mixing
algorithm suggests gusts to 39-42 kt are possible. All these
things taken into consideration, there`s around a 40-50% chance a
Wind Advisory will be needed for south wind gusts to 45 mph or
higher on Monday, which would lead to difficult driving conditions
for high profile vehicles and could blow around unsecured, light-
weight outdoor objects.

We`ll need to watch for severe weather in our southeast Tuesday
afternoon, depending on the timing of the cold/occluded front which
has trended a little slower in models` forecast over the past 24
hours. Forcing doesn`t look overly impressive, but NBM brings a 50%+
chance for > 200 J/kg of SBCAPE to Lawrence County during that time
frame. Once the front clears the area, however, we`ll be safe and
sound in a stable, though much cooler and blustery, airmass with
westerly wind gusts to 30mph expected to bring wind chills into
the 20s Tuesday evening. Despite winds being slow to ease and
possibly lingering cloud cover, cold advection should be strong
enough to bring a freeze to much of the region Tuesday night and
possibly again Wednesday night when winds are lighter and fewer
clouds are around. NBM suggests there is a 50-70% chance for a
hard freeze (i.e., temps < 28 degF) northwest of I-55 Tuesday
night and 40-60% chance north of I-70 Wednesday night; this has
trended down a bit since this time yesterday, which seems
promising, though the upper feature associated with the yet-to-
develop system responsible is still off the coast of California,
so there`s still time for things to change in the forecast.

While temps late Tuesday into early Thursday are trending cooler
than normal, middle of the road guidance from the LREF suggests
upper ridging will build into the Midwest sometime next weekend into
early the following week. While there are signs it could be a damp
Easter weekend, temps are trending above normal with NBM giving a 40-
60% chance for highs exceeding 70 degF area-wide both Saturday and
Sunday.

Bumgardner

&&

.AVIATION...  (For the 00z TAFs through 00z Sunday Evening)
Issued at 608 PM CDT Sat Mar 23 2024

A few -SHRA are possible overnight (20% chance). Kept mention at
VCSH across all central IL terminals. These would be falling from
a mid level cloud deck, so VFR conditions are forecast. Otherwise
east winds to veer southeast overnight near 10 kt. Pressure
gradient tightens by late morning, so SE gusts near 25 kt are
expected into Sunday afternoon, along with BKN mid/high level
clouds.

25

&&

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

$$


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