424
FXUS63 KIWX 190753
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
353 AM EDT Thu Sep 19 2024

.KEY MESSAGES...

- Remaining unseasonably warm (upper-80s) through at least
  Saturday.

- Much needed rain enters the forecast as early as Friday for
  some (20-30% chance).

- Not as warm next week with highs in the mid-70s.

&&

.DISCUSSION...
Issued at 343 AM EDT Thu Sep 19 2024

The primary forecast challenge is anticipating when the first
raindrops will actually fall as this stagnant weather pattern
comes to an end in the coming days. But first, dry once again
today with any fog mixing out as the morning progresses. Fog is
once again aided by a marine layer pushing in from Lake Erie.
High cirrus this morning has had little impact on fog thus far,
as fog continues to spread west through northwest Ohio.

High pressure will remain in place over the eastern Great Lakes
while a cold front, currently over central Nebraska, approaches
the Mississippi River through the day. High resolution guidance
is raising some concern for isolated severe storms Friday
afternoon, which is somewhat curious but also within the realm
of possibility. The parent low occludes over the Canadian
Prairie which results in sheared-out forcing aloft locally by
Friday. Moisture return is weak and generally shallow on Friday
due to a strong ridge over Mexico extending through Oklahoma,
along with high pressure to our east steering Atlantic moisture
south of the Ohio River valley. Despite this, dew points in the
low-60s are noted early this morning over far western Iowa and
are forecast to advect east to our area by Friday. Forecast
soundings otherwise depict adequate but not- uniform moisture
through the column. No wonder, then, that box and whisker plots
depict paltry rain amounts (if any) in Michiana Friday
afternoon. With these miss-matched ingredients, I am skeptical
of the high resolution guidance which might be over- convecting
(perhaps due to erroneously high dew points impacting CAPE).
Even with a modest adjustments to dew points closer to 60, low-
level lapse rates would be adequate (7c/km) as would shear (30
knots). This is overall something to keep an eye on and I`ve
increased POPs toward 30% as a result.

Remaining warm both Friday and Saturday as 500-mb heights remain
elevated along with continued balmy 850-mb temperatures. This ridge
breaks down and our persistent eastern Great Lakes high gets kicked
east as a trough over the Four Corners and trough over Manitoba
buckles the jet stream. The result is some much needed rain in the
Sunday through Tuesday time frame. Beyond this, scissors were
deployed for POPs Wednesday and Thursday behind a departing low.
Tried for a dry forecast Thursday, but some guidance and neighbors
preferred the slight chance showers (15% chance).

&&

.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 1148 PM EDT Wed Sep 18 2024

The set up tonight is similar to last night with the potential
for dense fog formation late tonight as lower 60 dew points were
over northeast Indiana with slightly higher moisture amounts
upstream in the synoptic east flow from the Atlantic with some
enhancement (extra moisture) from Lake Erie. The hourly HRRR
lagged some with the fog development last night, but appears to
be on track in at least the right area with rapid dense fog
development over northwest Ohio spreading into northeast Indiana
including the FWA terminal. The 24 hour temp/dew pt changes
showed the FWA spread 5 degrees smaller this past hour then last
night at this time. Also, dense fog had already formed in the
marine moisture rich air at the Toledo Suburban Airport (KDUH).
Updated the FWA TAF with categorical dense fog before daybreak.
The fog will mix out mid to late morning rendering light east
winds..

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...None.

&&

$$

DISCUSSION...Brown
AVIATION...Skipper