427
FXUS63 KILX 070346
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1046 PM CDT Sat Jul 6 2024

.KEY MESSAGES...

- Scattered thunderstorms are possible west of the Illinois River
  on Sunday (20-30% chance). Severe weather is not expected.

- Precip chances persist across much of the area Monday-Tuesday
  (20-50% chance), then shift to southeastern Illinois on
  Wednesday as the remnants of TS Beryl approach the Ohio Valley.

&&

.UPDATE...
Issued at 814 PM CDT Sat Jul 6 2024

00z surface map indicated broad high pressure stretched from the
mid Mississippi Valley northeast into the eastern Great Lakes.
This will provide light winds and mostly clear skies overnight. A
convective complex over the eastern Plains will spread some high
clouds in from the northwest after midnight. Some decaying showers
associated with the shortwave could reach our far northwest
counties after daybreak, and will keep slight chance (20%) PoPs
after 12z. Low temperatures to be seasonable, primarily in the mid
60s.

25

&&

.DISCUSSION...
Issued at 212 PM CDT Sat Jul 6 2024

Weak, broad sfc high pressure, with MSLP values around
1016-1018mb, continues to slowly shift east across the mid-
Mississippi Valley, and should shift east of Illinois tonight.
Diurnal Cu will fade this evening, resulting in mostly clear skies
through the evening. A shortwave over the northern Plains has led
to storms forming across the Plains, and these are expected to
track towards the Upper Midwest. CAMs depict most, if not all, of
this activity staying north/west of the ILX CWA as it passes by
during the pre-dawn hours of Sunday, but the far northwest
portions of the CWA could be clipped by this precip activity. This
disturbance will also result in mid/high cloud cover increasing
west of I-55 after midnight.

A trough over the central Plains will gradually shift east through
early next week, resulting in occasional scattered precip chances
through Wed. The most favored area for precip will shift east each
day, beginning with areas west of the IL River on Sunday, peaking
area-wide on Monday (30-50%), shifting east on Tues (20-40% east
of I-55), and lingering but diminishing on Wed (20% chance
near/east of I-57). While it`s difficult to completely rule out an
isolated strong storm or locally heavy rainfall this time of
year, overall the probability of such hazards is quite low. That`s
in large part due to tropical system Beryl, which will prevent
gulf moisture from advecting into the Midwest, as well as prevent
EML advection out of the SW US. Ensemble mean PWAT values across
central IL with this wave are in the 1.50-1.75" range, which is
above normal but not excessive, with such values being below the
90th percentile of the ILX sounding climatology. The lack of an
EML really limits the instability values, with MUCAPE values
generally below 1000 J/kg each day Mon-Wed. Additionally, upper
level heights gradually start to rise on Tues-Wed as the main
upper trough starts to lift northeast.

The one exception is Sunday, with modest instability (around 1500
J/kg) developing west of the IL River, although shear values are
marginal (less than 30 knots). Most CAMs do show some storm
development across west-central IL, aided either by previous
t-storm outflows or an MCV lifting out of MO. Unfortunately
pinpointing the specific placement of either of these mesoscale
features is a low confidence venture. The 06.12z run of the HRRR
indicates some spotty higher wind gusts out of the Sun PM storms,
however it`s forecast soundings appear significantly overmixed,
and thus have disregarded this signal for now. Perhaps the
presence of an MCV can locally enhance shear values across west-
central IL tomorrow afternoon and allow for better storm
organization, but otherwise the prospects of severe weather are
looking quite slim.

Late Wed into Thurs, the remnants of Beryl are progged to curve
northeast towards the Ohio River Valley. Most guidance still keeps
the system and the bulk of its associated rainfall south of the
ILX CWA. The "cone of uncertainty" does extend as far north as the
I-72 corridor, illustrating the typical track error of such
systems at this range. Adding to the difficulty is the fact that
there could be a tight northern gradient to the precip with this
system. The NBM PoPs did seem too low compared to other ensemble
guidance, so in coordination with neighboring offices to the
south/east, PoPs were raised. Significant temperature swings are
not expected over the next week, with highs generally in the
mid/upper 80s and lows in the mid/upper 60s.

Erwin

&&

.AVIATION...  (For the 06z TAFs through 06z Sunday Night)
Issued at 1046 PM CDT Sat Jul 6 2024

VFR conditions through much of the forecast with scattered
diurnal cu redeveloping Sunday morning. High pressure will shift
over the area tonight, resulting in light to calm winds. After
the high pushes off to our east Sunday morning, winds will set up
from the south/southwest around 10 kt. A slow moving front will
bring scattered showers and a few storms to northwest IL late
tonight and Sunday morning, with a low chance of storms reaching
KPIA by late afternoon to evening where a PROB30 group will be
added.

25

&&

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

$$