353
FXUS63 KIWX 040711
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
311 AM EDT Thu Jul 4 2024

.KEY MESSAGES...

- Chances for showers and thunderstorms will be possible today
  with the greatest chances mainly south of US-30. Additional
  chances for showers and storms occur on Friday with strong to
  perhaps severe weather possible.

- The best day of this weekend looks to be Sunday with
  seasonable high temperatures in the low to mid 80s and a mix
  of sun and clouds. Some rain is possible on Saturday,
  especially the first half of the day, and temperatures look to
  be below normal.

- Our next round of showers and storms looks to occur between
  Monday and Tuesday.

&&

.DISCUSSION...
Issued at 304 AM EDT Thu Jul 4 2024

Much of this period`s pattern will be shaped by a subtropical high
in the Western CONUS and another in the Gulf States as well as a
trough in the middle CONUS States. A Pacific upper jet within the
mid to northern tier of the United States contains a deepening upper
low that enters the northwestern Great Lakes tonight into Friday.

Closer to the surface, a cold front pushed through the forecast area
yesterday evening and now straddles the southern portion to just
slightly south of the forecast area this morning and appears to wash
out as the day goes on. As we head into the afternoon and evening
hours, a low level jet encroaches on our southwestern areas, this
brings additional moisture and better forcing to the area. Models
indicate the better instability will be south of the front, but also
that initial dry air may cut into the intensity of showers that try
to approach from the southwest in the midday to early afternoon time
frame. As a result, they would just be light showers or virga at the
onset. One component of this setup that`s still without a lot of
confidence is the placement of the warm front through the day today.
Some models are still stalling it out in the same spot through the
day today while others are allowing it push farther north. As a
result, am more confident in chance PoPs south of US-30, but slight
chance PoPs north. As these showers move in, models also are gutting
instability until at least after midnight tonight. Sub 30 kt
effective shear during this time frame will likely keep severe
weather at bay, but given the moisture available, there could be
ponding with training of storms over the same area, especially if
that warm front stays stalled over the area today.

At the very least, we can expect a cold front to push through, from
west to east, from sunrise Friday morning through Friday afternoon.
The greatest residence time of instability appears to reside east of
I-69 and perhaps south of US-24. With some stronger shear in this
bounded area, perhaps a few stronger to severe storms could form. At
least by this point, models are bringing that potentially stalled
warm front northward. Even still, model reflectivities are not
forming strong storms. This will need to be watched going forward
and wouldn`t be surprised to see a marginal risk of severe weather
hoisted by SPC for Friday.

Friday`s cold front looks to gut the humidity by Saturday. However,
enough mid level moisture, cooled mid level temperatures, and
forcing may still be around to provide some showers as vorticity
wraps around the departing upper low. There`s little if any
instability though so this would have limited convective
enhancement, but it does look to have some large scale ascent to aid
its QPF output. As a result, also expect below average temperatures
for this time of year with highs in the mid to upper 70s.

Sunday looks to be the better of the two weekend days with surface
high pressure skating by in the early portion of the day and mid
level ridging moving through providing dry weather and a return to
more seasonable temperatures with highs in the low to mid 80s.

Our next trough, which is slowly deepening, enters the Northern
Plains on Monday and models indicate there will be an instability
axis oriented such that Lake MI-adjacent counties are in around 1000
J/kg of MUCAPE as waves of vorticity on the weaker side of the scale
move northeast into the Northern Great Lakes Monday morning. The
base of the trough continues traversing eastward through the day so
that a stronger area of vorticity reaches the area Monday
night. While instability appears to wane at night without the
diurnal influence, can`t totally rule out a convective influence
and rain chances continuing into the night. Monday looks like
the warmest day of the long term with highs in the mid to upper
80s and heat indices around 90 degrees.

Additional afternoon chances for showers/storms will be possible
Wednesday and Thursday as an upper low sets up to our north and
spokes of vorticity pass through in the flow.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 150 AM EDT Thu Jul 4 2024

VFR Conditions are expected at the TAF sites for a majority of
the period, with the exception of brief dips to MVFR this
morning with any BR that develops. Calm winds, low level
moisture, and a mix of clearing/clouds led to areas of BR and
patchy FG. Most of the visibilities at the moment are in the
2-6SM range where BR has developed, with isolated spots less
than 2 miles. Most of the guidance keeps both KFWA/KSBN VFR, but
there are a few suggesting around 4-5SM for KFWA later this
morning. Held of for KSBN at the moment given no drops in
visibility yet and the guidance all showing VFR/P6SM tonight-but
wouldn`t be surprised if I had to add in later. Have a tempo in
at KFWA from 10-13z. Otherwise, variable winds will shift
south-southwest and increase slightly through the afternoon.
There are chances for showers at both terminals in the
afternoon, but the better confidence is at KFWA so have a prob30
in there from 19-23z, then becoming a prevailing group after
00z. KSBN is dry for now.

&&

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

&&

$$

DISCUSSION...Roller
AVIATION...MCD