647
FXUS63 KLOT 121113
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
613 AM CDT Thu Sep 12 2024

.KEY MESSAGES...

- Summer-like daytime warmth continues.

- Persistent dry weather will maintain a heightened threat for
  grass and brush fire starts, particularly today.

- Scattered showers possible at times mainly well inland through
  the weekend, though chances of widespread beneficial rain will
  remain low.

&&

.DISCUSSION...
Issued at 238 AM CDT Thu Sep 12 2024

Through Friday:

Easterly winds will increase today as the surface pressure
gradient starts to tighten between Francine`s remnants well to
the south and expansive high pressure just to our north and east.
Otherwise, expect similar if not slightly warmer high temperatures
inland to those of Wednesday (mid to locally upper 80s) as
850/925 mb temps come up a bit. Lakeshore locales will reach the
upper 70s to around 80F. Dew points will again mix out some
(low-mid 50s) and keep humidity levels low. Cirrus well in
advance of Francine will stream northward this afternoon and
especially tonight, which will prop up overnight lows vs. recent
nights in this dry pattern.

The moisture surge from Francine`s remnants will hit the
proverbial "brick wall" as blocking 500 mb ridging amplifies
(590 DaM over the northern Great Lakes) on Friday. Very dry air
at the lower and mid levels will eat away at the northern
fringes of the showery precip shield. Shower chances of generally
20-30% will remain confined to primarily near and south of US-24
in the morning. Even as a bit better mid-level moisture works
northward in the afternoon, dry easterly trajectories below it
will yield primarily thickening mid clouds and perhaps some
virga. Locations in our far south that observe any light rain in
the morning should be dry in the afternoon. High temperatures
on Friday will range from the upper 70s to lower 80s, coolest
near the Illinois shore, and across the far southern CWA. East-
southeasterly winds will gust up to 20-25 mph.

Castro


Friday Night through Wednesday:

Guidance continues to suggest that Francine`s remnant circulation
will become cut off from the mean flow and will begin to meander
across the Tennessee Valley this weekend. While several peripheral
vorticity spokes around the northern fringes of the circulation
will translate across the region, overall large scale forcing for
ascent is expected to remain only modest on Saturday and Sunday.
The deepest tropospheric moisture is also forecast to slosh mainly
to our west and south over the weekend. As a result of all of
this, while there will be some chances for showers over the
weekend, the highest coverage is expected focus the farther south
and west across the CWA you go. Many locales across our northeast
Illinois and northwest Indiana counties will probably remain
dry this weekend and into Monday.

Through the middle of next week, global guidance shows another
very dry airmass pushing westward across the Ohio River Valley and
into the Lower Great Lakes region. Both the GFS and ECMWF
advertise near -20 to -30 C dewpoints at 700 mb with this airmass.
At this point, the combination of the parched atmospheric column
and most disturbances suppressed to our south and west suggest
mainly precipitation-free conditions will continue.

Carlaw

&&

.AVIATION /12Z TAFS THROUGH 18Z FRIDAY/...
Issued at 613 AM CDT Thu Sep 12 2024

VFR with no significant concerns.

Initially light easterly winds will increase to around 10 kt
toward mid day, with occasional 15-20 kt gusts possible this
afternoon. The direction will trend to about 040-070 deg near
the lake in the late afternoon and early evening. Easterly
speeds will decrease some tonight and then increase after
sunrise on Friday, with 15-20 gusts again possible by the late
morning.

Castro

&&

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

&&

$$

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