IWX issues Area Forecast Discussion (AFD) at Aug 14, 3:17 AM EDT847
FXUS63 KIWX 140717
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
317 AM EDT Thu Aug 14 2025
.KEY MESSAGES...
- Lower humidity today with seasonable temperatures.
- Heat and humidity creep up through the weekend with heat
indices well into the 90s and possibly reaching 100 for some
locations Saturday and Sunday.
- Periodic chances of storms return for Sunday through Tuesday.
&&
.DISCUSSION...
Issued at 315 AM EDT Thu Aug 14 2025
In the near term, patchy fog is developing across portions of
the area. Slightly higher crossover temps across the far
east/southeast have been more favorable for fog formation early
this morning across northwest Ohio. A second area of potential
patchy dense fog is across northwest Indiana into southern Lower
Michigan where marine modified air from yesterday may be
hastening fog development. Expecting any patchy fog to mix out
shortly after 13Z this morning.
Otherwise for today weak mid subsidence will persist with just some
potential of some flat afternoon cu. Have utilized a persistence
forecast in terms of temperatures for today. Low level thermals
are starting out a bit cooler than yesterday, but this low level
airmass should continue to modify through the day. With good
insolation, this should support highs fairly close to that of
yesterday into the mid 80s most locations. Another weak lake
breeze is expected to form today, but really no sensible weather
impacts with this feature other than just providing a few
degrees of cooling near the lakeshore once again.
For tonight low level ridge axis is expected to drift east across
the eastern Great Lakes with some light return southerly flow
developing into Friday. Some patchy fog is possible again Friday
morning and may be preferred in similar locations as this morning.
Some weak low level return theta-e advection is expected on Friday
as a weak/broad mid level trough approaches from the Corn Belt.
Moisture transport will be limited by the weak nature to the
low level flow. Some guidance does indicate a weak to modest
instability axis nosing into east central IN/portions of
northeast IN Friday afternoon, but will maintain a dry forecast
given weak nature of mid/upper level forcing and still some
questions as to instability magnitudes (or if any low level CIN
persists).
The main weather story for the weekend will center on increasing
heat and humidity along with greater storm chances, especially
headed toward latter portions of the weekend into early next week. A
longwave upper level ridge will make limited eastward progress to
the western Great Lakes this weekend. This should promote a bit more
of a veered westerly low level component and the ability to
advect much richer low level theta-e air eastward from the Mid
MS Rvr Valley. However, best low level moisture convergence
through the weekend may end up being tied to locations northwest
of the local area at the nose of 30 knot southwesterly low
level jet across Iowa/southern Minnesota. This ridge appears to
be remain anchored through Monday with increasing chance of
better ridge suppression Monday and Tuesday. As has been
discussed past few forecast cycles, convective modification of
these upstream disturbances will play a large part in
determining the southward extent of these greater storm
chances/convective complexes. Unfortunately, this remains a low
predictability item at this forecast distance. However, given
that the local area should be in favorable strong instability
gradient regime and on the downstream side of a thickness ridge,
it is conceivable that some convective organization could
impact southern Great Lakes Monday-Tuesday.
Not much change has been made to the max temp/heat index forecast
this weekend, with potential complications from upstream convective
debris cloud moving into the area. Confidence remains high in heat
indices well into the 90s, with at least a potential of reaching 100
for some locations Saturday/Sunday.
Reamplification of western CONUS longwave ridge by the middle of
next week still looks to support better chances of frontal passage
by the Wednesday timeframe, with another period of cooler/less humid
and dry conditions toward the end of this forecast valid
period.
&&
.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 107 AM EDT Thu Aug 14 2025
Light and variable winds and clear skies are on tap for much of
the day today. With leftover ground moisture from Tuesday's
rain and storms, some patchy fog development is possible this
morning between 09-13Z. Otherwise, a very tranquil and pleasant
Thursday is ahead.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...None.
&&
$$
DISCUSSION...Marsili
AVIATION...Johnson
Source:
IWX issues Area Forecast Discussion (AFD) at Aug 14, 3:17 AM EDT---------------
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