526
FXUS63 KLOT 030835
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
335 AM CDT Fri May 3 2024

.KEY MESSAGES...

- Increasing chances of showers and thunderstorms capable of
  producing gusty winds Saturday afternoon and evening.

- Periodic shower and thunderstorm chances next week, with some
  potential for strong to severe storms Tuesday.

&&

.DISCUSSION...
Issued at 335 AM CDT Fri May 3 2024

Through Saturday:

Ongoing convective activity across portions of northern
Illinois and northwest Indiana continues to wane early this
morning as remaining instability and associated mid-level lapse
rates decrease. In fact, as of 3am CT, very little lightning has
been observed in the forecast area over the past hour. While a
few lightning strikes are still possible through sunrise, a
departing mid-level wave will limit remaining deeper-layer
support. Meanwhile, a cold front roughly parallel to the
Mississippi River will continue to shift a band of shallow
showers across the area into mid-morning.

High pressure will quickly settle across the western Great
Lakes through tonight. The combination of a rather dry airmass
evident by upstream dew points generally in the 30s along with
fairly clear skies today should allow seasonably warm conditions
in the 60s along the shore and lower 70s inland today.

Today`s cold front will stall across the south half of
Illinois, allowing for a return of low-level moisture behind the
surface high on Saturday. A small mid-level wave lifting
northeast across the far Upper Mississippi River Valley Saturday
morning may brush the northwest CWA. Return of sufficient
moisture by this point remains in question, though an isolated
storm cannot be ruled out for areas west of I-39 late morning
into early afternoon. A disjointed trough passage into the
western Great Lakes later Saturday and into Saturday night
should better align with increasing shallow moisture to produce
scattered showers and storms as far east as around I-57 by
sunset. However, fairly shallow low-level moisture return and a
deep reservoir of dry mid-level air may limit storm coverage but
also support gusty winds with any convection.

Kluber

Saturday Night through Thursday:

Showers and thunderstorms should be ongoing along and ahead of
a cold front Saturday evening. Some of these storms could be
strong to severe early in the evening, with mainly localized
gusty winds, though this threat should diminish with eastward
extent due to diurnal loss of low-level instability and
generally weak deep-layer shear. Sunday through Sunday night
looks to be largely dry and cooler, as Saturday night`s cold
front settles toward the Ohio Valley and surface high pressure
builds east across the upper Midwest and western Great Lakes
region. Temperatures will be limited to the lower 70s well
inland Sunday afternoon, while northeast winds off of Lake
Michigan will keep highs only in the upper 50s near the lake.
Lows will dip into the mid-upper 40s in most spots Sunday night.


Ensemble guidance depicts deep upper level trough developing
across the western and central CONUS heading into next week,
with a closed upper low developing across the Northern Plains
Monday. A series of mid-level short waves are progged to rotate
around the south and southeast periphery of the circulation as
it slowly drifts east, eventually lifting the front across the
lower Ohio Valley northward as a warm front later Monday night
into Tuesday. Some spotty elevated showers are possible as early
as Monday afternoon and evening as warm/moist advection
develops atop the warm frontal slope, though really becomes more
focused into the local area Tuesday into Tuesday night. This
appears to be the period with the greatest potential for
thunderstorms, some potentially strong to severe given strong
mid-level wind fields and warm/moist/conditionally unstable low
levels. Temperatures looks to surge back into the upper
70s/around 80 Tuesday afternoon, with surface dew points rising
into the 60s as the warm front lifts across the area.

Periodic shower and thunderstorm chances linger through the
mid-week period, as ensembles continue to indicate the upper
trough drifting east across the upper Midwest/Great Lakes region
through the end of the forecast period. Blended NBM guidance
maintains chance pops both Wednesday and Thursday, especially
during the more diurnally-favored afternoon/evening hours.
Higher low-level Theta-E air mass gradually gets shunted east of
the area during this time, with temperatures gradually settling
into the lower 70s by Thursday.

Ratzer

&&

.AVIATION /06Z TAFS THROUGH 12Z SATURDAY/...
Issued at 1220 AM CDT Fri May 3 2024

Aviation Key Messages:

- SHRA persist through pre-dawn hours. Embedded TSRA threat
  diminishing but non-zero, especially toward KGYY.

- Period of MVFR ceilings develops pre-dawn and lingers until a
  cold front passes after sunrise.

- Winds shift NNW with cold front after sunrise, then turn NNE-
  NE by mid-morning. NE winds persist through remainder of
  period.

Somewhat diffuse area of low pressure was lifting north-
northeast across eastern WI as of midnight, with a cold front
trailing through far western IL into western MO. This low was
associated with a mid-level disturbance over central IL, and
will continue to lift northeast with the cold front moving
across the terminals by sunrise. SHRA and embedded TSRA will
persist ahead of the front, with TSRA growing more isolated with
time, with greatest coverage of TS likely toward KGYY. MVFR
ceilings along the cold frontal zone will spread across the
terminals pre-dawn, eventually scattering out to VFR by mid-
morning.

Winds, while somewhat disorganized by earlier stronger
convection, will be generally light W-SW ahead of the cold
front, then shift NNW behind the front by sunrise. Winds will
then continue to veer northeast by mid morning behind the front,
and will generally remain northeast through the day.

Winds turn light easterly Friday evening, and there is some
model guidance indication that MVFR stratus may form east of the
area across Lake Michigan and IN, which could drift west into
the terminals later in the night. Confidence is low this far
out, but have included a FEW020 mention in TAFs.

Ratzer

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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