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987
FXUS63 KILX 262320
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
620 PM CDT Wed Jun 26 2024

.KEY MESSAGES...

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- After a dry Thursday, storm chances return Friday to Saturday,
  with the highest chances being Friday night (50-80%). Some of
  these storms could be severe and pose a threat of locally heavy
  rainfall.

- Temperatures will generally be near or slightly below normal
  through early next week. The exception is Saturday, when highs
  are expected to be in the upper 80s, and heat indices could climb
  into the upper 90s, mainly south of I-70.
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&&

.SHORT TERM...  (Through Late Thursday Night)
Issued at 315 PM CDT Wed Jun 26 2024

An upper trough positioned across the area continues to gradually
shift SE, with a rain shield extending along the I-70 corridor and
southward as of 2pm/19z. The northern edge of the cloud shield,
currently located roughly from Quincy to Chicago, continues to
steadily push SE. North of the cloud shield, temps have jumped
into the mid/upper 80s - and areas as far south as I-72 will
likely experience a similar quick warmup after the clouds depart.
Further south, the cloud cover and rain will make it a struggle
for temps to rise above 80F.

RAP-based mesoanalysis fields show modest CAPE present (generally
between 500-1500 J/kg), but weak deep layer shear values less than
30 knots. Additionally, hail growth zone CAPE is less than 300
J/kg and DCAPE values are quite low beneath the cloud deck. So
while I can`t rule out an isolated storm developing and pulsing up
in intensity at times, the severe threat appears quite low today.

As the cold front shifts SE of the area this evening, clear skies
will allow lows to drop into the low 60s. Sfc high pressure
positioned over the upper Midwest takes control for what should be
a dry, pleasant Thursday. Light northeasterly winds will persist
through the day, resulting in temps slightly cooler than normal
with highs in the low 80s as opposed to mid-80s. Afternoon
dewpoints are forecast to be in the upper 50s to low 60s, which
will be a nice change of pace from the more humid conditions over
the last week. Cloud cover will increase from west to east during
the late afternoon/evening.

Erwin

.LONG TERM...  (Friday through Next Wednesday)
Issued at 325 PM CDT Wed Jun 26 2024

On Friday, an upper level shortwave will push east along the
Canadian border making it to the Great Lakes region by Saturday
evening. Ahead of this shortwave and its attendant cold front,
surface winds will switch to a southerly component leading to
moisture return resulting in the next chance for some beneficial
rain. The highest PoPs and greatest rainfall amounts currently
look to be along and north of I-72 in Illinois with a 20-40%
chance of greater than 1 inch of rain by Saturday evening. The
latest GEFS indicates a 60%+ chance of PWAT values exceeding 2" in
the warm sector ahead of this front, which would be well above the
90th percentile of the ILX sounding climatology, so localized
rainfall amounts exceeding 2" could occur. We`ll get a better
handle on the max rainfall potential as CAMs start to capture this
event. There is some potential for severe weather with this
system, both Friday night and Saturday, but there is uncertainty
as to where the overlap of greatest instability and shear will
occur ahead of the approaching front. Storms that occur Fri night
would likely be elevated (primarily a hail threat), and on Sat
hodographs look fairly straight, suggesting more of a wind/hail
threat (with less of a tornado threat).

Surface winds out of the south will lead to widespread highs in
the mid 80s on Friday. With the approaching cold front on
Saturday, pre-frontal compressional warming ahead of the front
will likely lead to highs reaching the upper 80s to low 90s. The
overall coverage and extent of any cloud cover and/or rain will
impact where the warmest locations are at on Saturday, but areas
ahead of the cold front could see afternoon heat indices climb
into the upper 90s. With the passage of the cold front by
Saturday night, deep northwesterly flow will lead to pleasant and
dry weather for the end of the weekend and the start of next week.
Below average temperatures will persist during this time with
highs only topping out in the mid 70s to low 80s for Sunday and
Monday. With the upper level ridge axis overhead Monday morning,
clear skies and calm winds will result in lows on Sunday night
dropping into the low to mid 50s across the area, bringing a nice
relief from the recent heat.

The upper level ridge pushes off to our east by Tuesday morning
allowing our next chance of precip to move in with another upper
level shortwave Tuesday into Wednesday. This upper level shortwave
is also expected to traverse along the Canadian border, once
again, positioning our region under southerly flow resulting in
moisture return. Chance PoPs return on Tuesday evening and stick
around until Wednesday. With southerly flow, temperatures will
rebound with mid 80s and lower 90s returning to the area by
Tuesday and Wednesday.

Peine/Erwin

&&

.AVIATION...  
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(For the 00z TAFs through 00z Thursday Evening)
Issued at 620 PM CDT Wed Jun 26 2024

Subsidence behind a shortwave that has departed the area will
bring rapidly clearing skies this evening from some lingering
patches of diurnal cumulus. Diurnal cumulus and increasing high
clouds will take place Friday, however conditions will remain VFR.
Enough pressure gradient tonight should keep light winds going
through the night, helping to prevent any fog formation. Winds N
4-8 kts overnight, becoming E-NE around 10 kts by 18Z.

37
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&&

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

$$