232
FXUS63 KIWX 180515
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
115 AM EDT Sat May 18 2024

.KEY MESSAGES...

- Patchy fog is possible tonight and a few locations could see
  locally dense fog.

- Warm conditions for this weekend into Tuesday. Highs Sunday
  through Tuesday into the lower to middle 80s.

- A potential for more organized storms with some strong/severe
  potential late Tuesday and Tuesday night, but still low
  confidence on timing and extent of severe threat.

&&

.DISCUSSION...
Issued at 225 PM EDT Fri May 17 2024

Still with some moisture around south of US-24 and lingering forcing
around may allow a shower or storm this afternoon before dissipation
occurs with the diurnal curve. With winds dying off, clouds clearing
out, and winds going light to calm, can see another instance of fog
formation taking place tonight into Saturday morning. The moisture
axis pulls farther away from the area for Saturday afternoon causing
dew points to struggle to reach 60F degrees and making shower and
storm chances a little more difficult especially with surface high
pressure and mid level ridging beginning to build into the west.
Some convergence from a slowed up baroclinic boundary to our west or
a lake breeze may make a shower or storm possible there, thinking
the chances will be lesser than today and yesterday. A similar day
to today and Saturday will be in store for Sunday with more pop
showers and possible especially during the afternoon. Minimal
forcing is available aside from any lake breeze that forms, but the
instability is much higher on Sunday than Saturday and today. Shear
is still non-existent through all 3 of these afternoon chances
limiting the extent of severe weather expected. DCAPE is much higher
on Sunday, though, so if a storm can form on Sunday, there is a
potential for downdrafts within those storms. A warming trend is
expected for highs and lows over the next couple of days making
upper 70s possible for today`s highs, low 80s for Saturday, and mid
80s for Sunday.

Surface high pressure shifts eastward, but the mid level ridging
still tries to hang behind overhead. Meanwhile trough builds in to
our west in the Western CONUS allowing waves of vorticity to pass by
to our west and north. Their close enough in proximity to not
completely rule out a shower or storm in our Lake MI-adjacent
counties with the greatest chances occuring Monday night. This is as
the low level jet finally builds into our west. There appears to be
a break in forcing that may keep organized storm activity at bay
Tuesday before a low pressure system sliding through the Western
Great Lakes region pushes its cold front through the area in
conjunction with some mid level vorticity Tuesday night. Some shear
may be available with this so could see some stronger storms around.
DCAPE reaches 900 J/kg during the daytime Tuesday, but may be on the
decline before the shear arrives Tuesday night. So any pop storm
Tuesday could tap into that making a downburst possible then. Mid
level lapse rates around 7 C/km also look to eject towards the area
from the Plains and provided that airmass isn`t modified by the time
it arrives, large hail could be a hazard in addition to damaging
wind gusts as that cold front moves through.

Recent model runs have been slowing down the FROPA for early/mid
next week, but am still holding out some hope of a drier Wednesday
with the ECMWF showing the moisture axis/cold front shifting out of
the area by midday Wednesday. Meanwhile, the GFS holds the
baroclinic boundary/cold front back, allowing a wave of low pressure
to form along it keeping weather active on Wednesday instead. Will
still have chance PoPs for Wednesday to cover the GFS`s solution.

Have more confidence of a dry Thursday with both models bringing the
front through by Thursday morning providing surface high pressure.
This would allow highs to trend back toward the mid to upper 70s for
the mid to late week period.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 111 AM EDT Sat May 18 2024

Steering flow aloft and near the surface is incredibly weak, so
winds will remain light and variable throughout the day at less
than 5 knots. The main concern for this TAF cycle will be fog
this morning between 09-13Z. Uncertainty remains in just how
locally dense this fog becomes, but current thinking is that
visibilities may drop below 1 mile and ceiling could drop as
low as 300 to 500 feet. IFR/LIFR ceilings and/or visibilities
are possible, but it`s likely they won`t persist for the entire
aforementioned 4 hour window. Much like yesterday morning,
visibilities will likely vary across small distances, leading to
fluctating conditions. Fog will lift after 12Z this morning,
with high MVFR/low VFR ceilings for the rest of the day.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Air Quality Alert until midnight EDT /11 PM CDT/ tonight for
     INZ005-012>015-022-023-103-104-116-203-204-216.
OH...None.
MI...Air Quality Alert until midnight EDT tonight for MIZ078-177-
     277.
MARINE...None.

&&

$$

DISCUSSION...Roller
AVIATION...Johnson