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470
FXUS63 KILX 272315
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
615 PM CDT Thu Jun 27 2024

.KEY MESSAGES...

- Thunderstorm activity returns Friday into Saturday. A few of
  these storms could be strong to severe on both days, and pose a
  threat for heavy rain.

- Temperatures turn cooler behind a cold front late this weekend
  into early next week before hot and humid conditions return
  midweek onward.

&&

.SHORT TERM...  (Through Late Friday Night)
Issued at 328 PM CDT Thu Jun 27 2024

Surface analysis this afternoon shows high pressure anchored over
the Great Lakes Region with a surface low and antecedent cold front
stretched from eastern Montana into the southern Plains. Diurnal
cumulus this afternoon will be replaced by mid-level stratus this
evening into the overnight hours as a strong shortwave trough sends
the aforementioned system eastward toward the Midwest states.
Temperatures as of 2 pm are seasonably mild with values ranging
from the upper 70s to middle 80s.

A 40-45 kt LLJ will stretch from the southern Plains into the Upper
Mississippi Valley overnight into Friday morning. Moisture transport
paired with the LLJ, and a subtle shortwave trough rippling through
the flow aloft may spark the development of scattered showers and
storms Friday morning. Better chances for precipitation hold off
until Friday night when the LLJ ramps back up and the cold front
slowly approaches from the west. Some of these storms could be
strong to severe during the evening hours west of I-57, posing a
threat for damaging winds and large hail. Climatologically high
PWATs paired with storm motions nearly parallel to the cold front
will also bring the threat for heavy rain and localized flash
flooding due to training of storms.

NMA

.LONG TERM...  (Saturday through Next Thursday)
Issued at 328 PM CDT Thu Jun 27 2024

Saturday will be an active weather day with an upper level shortwave
trough positioned over the Upper Midwest and its attendant cold
front draped just to our NW on Saturday morning. Within this trough,
embedded shortwave energy will swing through our area on Saturday.
This, along with plenty of moisture in place (surface dewpoints in
the upper 60s to lower 70s), will result in decent chances of rain
across the region, especially during the morning hours on Saturday.
The 24hr probability of rain totals greater than 1 inch has come
down considerably and is now around 10-20% along and north of I-72
in Illinois for Friday into Saturday. However, the 12Z GEFS still
has mean PWAT values around 2.15" across a good portion of the CWA
on Saturday, hinting that the potential for heavier rain still
exists.

Currently, the SPC has a majority of the CWA under a marginal risk
for severe weather on Saturday. The greatest threat for severe
weather appears to be Saturday morning into the afternoon along and
ahead of the approaching cold front where the greatest SBCAPE
(>1,500 J/kg) and sfc-500mb of bulk wind shear (>30kts) overlap each
other. The most likely severe threat with these storms would be
large hail and damaging winds with a lesser threat for tornadoes.
Storm coverage and intensity on Saturday will be highly dependent on
the overall coverage of clouds and rain ahead of the cold front. The
cold front will push through from NW to SE on Saturday entering the
NW CWA midday and exiting the SE CWA by late evening.

Behind the passage of the cold front, an upper level ridge will
build off to the west placing our region in deep northwesterly flow
Sunday into Monday. While under the influence of this ridge,
pleasant and quiet weather will be on tap but short lived. As the
ridge pushes off to the east it will continue to build in the
southern stream and could potentially remain stationary in the SE
CONUS during the remainder of next week. This setup would place our
CWA on the northern periphery of the ridge where any ridge riders
would have a chance of impacting the area. Thus, chance PoPs are in
place Wednesday onward next week.

With modest southerly surface flow in place and dewpoints in the
lower 70s ahead of the cold front on Saturday, highs will be near or
exceed 90 in most locations with heat indices approaching 100 in the
far SE CWA. The cold front will bring a nice relief from the heat
with widespread highs in the upper 70s to mid 80s on Sunday and
Monday. The greatest relief from the heat will be Monday morning
when lows are expected to be in the low-mid 50s with no cloud
cover and calm winds, maximizing radiational cooling. As the upper
level ridge to our SE continues to build next Tuesday, things
will begin to heat back up as surface winds turn southerly
advecting warm air into the region once again. The magnitude of
heat during the middle of next week remains in question due to the
uncertainty in the strength of the ridge and our proximity to the
center of the ridge.

Peine

&&

.AVIATION...  
-- Changed Discussion --
(For the 00z TAFs through 00z Friday Evening)
Issued at 615 PM CDT Thu Jun 27 2024

High pressure will gradually shift eastward from the Great Lakes
this evening to New England by Friday evening, allowing increasing
mid and upper level cloud cover to move in overnight, and showers
to gradually shift into the area as well, likely only from around
KSPI-KBMI northwestward. Thunderstorm chances appear low enough
that no mention has been made in TAFs through 00Z. Winds E 5-10
kts overnight, becoming S-SE around 10 kts by 15Z.

37
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&&

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

$$