294
FXUS63 KILX 072331
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
631 PM CDT Sun Jul 7 2024

.KEY MESSAGES...

- Scattered thunderstorms are expected west of the Illinois River
  this evening into tonight. There is a low chance (level 1 of 5)
  of severe wind gusts or hail from these storms.

- The remnants of Tropical Storm Beryl are expected to bring
  widespread rainfall, including a corridor of 2"+ totals (30-60%
  chance) to the area Tuesday into Wednesday. The exact placement
  of the axis of heaviest rainfall totals remains uncertain.

&&

.SHORT TERM...  (Through Late Monday Night)
Issued at 238 PM CDT Sun Jul 7 2024

Sunday afternoon, a long wave trough was present over the central
Plains/upper Midwest, while Tropical Storm Beryl continued it`s
approach towards the TX Coast. Closer to home, thunderstorms have
blossomed along a weak convergence boundary that extends from the
northern Chicago suburbs to the far NE corner of MO. The storm
coverage is already surpassing that shown in any of the available
CAMs, and RAP-based mesoanalysis fields show weak near-sfc fgen
and moisture convergence all along this corridor, suggesting
continued support for the ongoing t-storm activity into the
evening. While this weak boundary is expected to be slow-moving,
the storm evolution may become dependent on specific storm outflow
interactions. Between this and the poor CAM depiction, there is
some uncertainty as to how quickly storms will progress SE
(meaning there is some potential for storms to push SE faster than
what is currently forecast). At any rate, the expectation is that
scattered to widespread thunderstorms are likely to continue
along this zone, shifting E/SE in time. These storms could
occasional pulse to near severe limits, as there is modest
instability of 1000-1500 J/kg of SBCAPE present, but deep layer
shear values below 30 knots will limit organization.

Tonight into Monday, as perturbations continue to progress through
the upper trough, additional scattered storm development will be
possible (20-50% chance), with the precip chances gradually shifting
east in time. Severe storms are unlikely during this time frame.
Skies will stay mostly cloudy tonight, keeping lows in the upper
60s.

Erwin

.LONG TERM...  (Tuesday through Next Sunday)
Issued at 238 PM CDT Sun Jul 7 2024

The forecast for the remnants of Beryl remains fluid, with
ensemble guidance trending towards a considerably faster system
and greater impacts across central IL compared to just 24 hours
ago. The center line of the latest NHC forecast track (issued 1 PM
Sun) now has the remnants of Beryl reaching the Great Lakes by
Thurs morning, as opposed to yesterday`s forecast which had it
reaching the Ohio Valley Thurs morning. This means the associated
rains will arrive in central IL on Tues-Wed, rather than late Wed
into Thurs. Additionally, ensemble mean precipitable water (PWAT)
values now depict values over 2" (rather than the 1.5-1.75" shown
yesterday).

The latest ECMWF shift of tails (based on the 00z run of the
ECMWF) highlights the potential for an outlier heavy rain event
(focused mainly east of I-55). All three of the GEFS, EC Ens, and
GEPS have a swath where the probability of 2"+ of rainfall is
30-60%, although there is still spread in the placement of this
swath, with the GEFS being further north (near the IL River) than
the other two ensembles. Run-to-run consistency of the models
remains poor, for example, the deterministic GFS has oscillated
the rainfall axis from near the I-70 corridor, to near the IL
River, then back south to the I-70 corridor over its last several
iterations. Wherever that rainfall swath does occur, higher
amounts aren`t out of the question given the tropical moisture
combined with broad forcing from both the remnant circulation of
Beryl and the synoptic trough over the Midwest. The Grand Ensemble
shows 90th to 95th percentile precip amounts (5-10% chance of
exceedance) in the 3-4" range, which if realized would likely
lead to some hydrologic issues given 6-hour flash flood guidance
in the 2.5-4" range. There are still some factors that give me
pause regarding the rainfall totals, such as the fact that Beryl
continues to struggle to organize prior to landfall (although
conditions are expected to be more favorable over the next 24
hours and Beryl`s vis satellite appearance has recently improved)
and the antecedent dry conditions (much of the area was
classified as abnormally dry or moderate drought in the last
Drought Monitor).

The remnants of Beryl could also bring some blustery winds to the
region. The exact speeds will depend on how well an organized sfc
low is able to maintain its structure as the remnants lift
northeast, but current guidance suggests gusts of 20-30 mph are
most likely east of I-55 on Wed., and a few outlier members of the
EC Ens have gusts over 40 mph. With increased cloud cover and
rainfall, temperature forecasts for Tues-Wed have lowered, with
highs now forecast to be in the upper 70s/low 80s.

The rains associated with Beryl are expected to depart the ILX CWA
before Wed night. Into the latter half of the work week, guidance
has a shortwave digging into WI, keeping upper level troughing in
place over the Midwest despite the remnants of Beryl lifting to
the northeast, and the presence of that upper wave could result in
some light, scattered precip on Thurs. Upper ridging will persist
over the intermountain west into the weekend, and while PoPs are
below mentionable thresholds after Friday we`ll need to keep an
eye on the potential for MCS activity as disturbances round the
upper ridge. For now, the favored track of any such systems
appears to be north of the ILX CWA. Persistent southerly flow Fri
into the weekend will result in increasing temps and moisture
content, with highs forecast to climb into the mid 90s by next
Sun, and heat indices approaching the triple digits.

Erwin

&&

.AVIATION...  (For the 00z TAFs through 00z Monday Evening)
Issued at 631 PM CDT Sun Jul 7 2024

A frontal boundary was pushing into western IL this evening,
bringing scattered TSRA west of KPIA. These could affect KPIA over
the next couple hours with brief reductions to IFR. With the loss
of diurnal heating the storms are expected to dissipate and
currently not expecting them to impact other terminals this
evening, though scattered showers could. The front will be slow to
move across the region Monday with a few showers and storms
around, but confidence in coverage and timing is too low to
include in TAFs. Besides an isolated storm, conditions should be
VFR through 00z with south to southwest winds at 5-10 kt.

25

&&

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

$$