801
FXUS63 KILX 020502
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1202 AM CDT Thu May 2 2024

.KEY MESSAGES...

- Level 1 risk of severe weather on Thursday has been expanded
  eastward to near I-55, though smaller scale features from
  leftover morning showers/storms may play a role in severe
  weather extent

- Warmest period through this weekend will be on Thursday, with
  widespread highs in the mid 80s

- Numerous chances for showers and thunderstorms over the next
  several days, though a significantly long dry period is hard to
  pin down right now

&&

.UPDATE...
Issued at 822 PM CDT Wed May 1 2024

This evening, a weak shortwave trough is noted over south central
Missouri with scattered thunderstorms ahead of this feature south
of the St Louis area. This wave will move east late this evening
and overnight with some potential for a few showers and storms
mainly near and south of I-70. 00Z ILX sounding indicated very dry
air is in place below 800mb with an overall dry column (PWat 0.60
inches). Given the weak forcing, unfavorable diurnal timing, and
dry antecedent conditions, convection will struggle as it moves
into Illinois. HRRR is now calling for dry conditions through the
night, though the RAP/NAMNest continue to show decaying showers
reaching southern parts of the forecast area late this evening.
Have lowered PoPs some to account for observed conditions and
model trends, but maintain at least a slight chance mention in the
SE this evening. Further NW across the Illinois River Valley,
strengthening WAA will overspread the region late tonight and
could bring another chance of showers and storms. Models have
mostly slowed the arrival of precip until Thursday morning, so
have lower PoPs accordingly.

Deubelbeiss

&&

.DISCUSSION...
Issued at 307 PM CDT Wed May 1 2024

An active weather pattern will remain in place over the next week.
In the shorter range, a broad upper low currently over northern
Montana will gradually wobble eastward the next 36-48 hours,
before finally lifting toward Hudson Bay on Friday. However, a
stronger upper low moves onto the West Coast this weekend, then
moves toward the central Rockies. The longer range synoptic models
are in decent agreement with this feature eventually ending up in
Montana or North Dakota as well. Thus, the overall upper pattern
remains of Pacific origin. A lot of our weather will hinge on
various waves ejecting ahead of, or circulating around, these
features.

Early afternoon surface map shows the wind shift with the front
has settled south of I-70, while the drier air lags behind a bit.
Dew points are down into the 40s west of I-55, but still linger
in the 60s as far north as Mattoon and Paris. Radar mosaics show a
cluster of storms developing over north central Arkansas, with the
morning HiRes-ARW run handling it the best. Its solution shows a
general development of scattered convection over central and
southern Missouri this afternoon, extending eastward along the
boundary toward early evening. Much of this is diurnally driven,
and isolated PoP`s are in the forecast along it. However, more of
a focus is expected after midnight, with elevated convection as
the front lifts northward. The various high-res models have some
disagreements with the eastward extent, and overall PoP`s after
midnight haven`t been changed too much from previous, generally
in the 30-40% range north of I-72. Any lingering showers from this
elevated activity should be north of the forecast area by mid
morning.

Latest SPC Day2 outlook has expanded the level 1 (marginal) risk
eastward to near I-55, though some complications arise if the
overnight activity manages to form an MCS. We`ll fully be in the
warm sector, with over 1,000 J/kg of surface based CAPE, though
overall bulk shear parameters would only be more favorable west of
the Illinois River. However, if the morning activity manages to
get any boundaries in place, an uptick in activity is possible.
For now, most daytime PoP`s will be confined to areas near and
west of I-55, with activity spreading eastward in the evening.
Rain chances linger into Friday, though primarily east of I-55.

Going into the longer range, a shortwave is expected to track out
of the Plains on Saturday. The day may start out dry, but
scattered showers/storms are expected by afternoon as the front
approaches. This front is expected to get hung up near or just
south of the Ohio River later in the weekend, where we again get
to monitor its northward return early next week as the upper low
moves toward the central Rockies. Deterministic models suggest a
period of dry weather Monday night and early Tuesday, though
ensemble probabilities are harder to pin down a definite period.
Earlier CSU machine learning probabilities suggested Tuesday as a
potential day to watch for strong/severe storms, with timing still
looking favorable, but it`s still way out there to get any real
specifics.

Geelhart

&&

.AVIATION...  (For the 06z TAFs through 06z Thursday Night)
Issued at 1202 AM CDT Thu May 2 2024

Low pressure will lift from CO to WI through the period with a
trailing cold front moving across central IL late Thursday evening
and overnight. Light NE winds in place currently will veer to SE
and begin gusting to around 20kt Thursday morning. Winds will
continue to veer to SSE by around midday with gusts continuing in
the 20-25 kt range. As the cold front approaches in the evening,
scattered showers and storms are possible with winds turning NW
behind the front.

Deubelbeiss

&&

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

$$