411
FXUS63 KIWX 041912
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
312 PM EDT Sat May 4 2024

.KEY MESSAGES...

- Light rain and a few embedded thunderstorms are possible at
  times through Monday but no severe weather is expected.

- Additional showers and storms are likely Tuesday and
  Wednesday. Some of those storms may be severe.

- After cooler weather Sunday and Monday, highs climb back to around
  80 for Tuesday and Wednesday.

&&

.DISCUSSION...
Issued at 312 PM EDT Sat May 4 2024

Midlevel shortwave currently seen on water vapor imagery over
northern MN will continue to lift NE and send a decaying cold front
through the region tonight. A line of convection will continue
to develop over IL late this afternoon, capitalizing on 1500
J/kg of MLCAPE ahead of the front. However, all ingredients
point to a quick demise as it enters our CWA late this evening.
Not only do we lose daytime heating but convection will outrun
better forcing and shear as it enters our area, quickly becoming
outflow-dominant and weakening. Low level moisture convergence
and midlevel lapse rates appear insufficient to maintain robust
nocturnal convection in our area, but do anticipate some showers
with a few isolated storms to linger into the night with the
best chances in our far west 01-04Z. The chance of showers will
continue in our eastern zones into Sunday as increasingly
broad/diffuse cold front makes slow eastward progress. A few
models suggest our extreme E/SE zones may have time for some
marginal destabilization by early afternoon yielding the chance
for a few storms. However, most hi-res guidance suggests any
convection will be well outside of our CWA. Maintained a low
chance PoP for late tonight into midday Sun but any rain during
this period will be very light and very isolated. High temps
tomorrow will be much cooler in our NW CWA, especially near the
lake where 50s are likely. SE zones still have a shot at mid 70s
again before the front passes though.

Another weak shortwave ejects out of the Southern Plains and into
the Ohio Valley by Monday. However, the Great Lakes remain firmly
under the influence of AVA/subsidence with sharp midlevel ridge
approaching from the Upper Midwest. Exactly how far north precip
manages to extend remains a bit uncertain but prefer to lean on the
dry side with easterly surface winds and marginal 850mb theta-e
advection just barely touching our border. High-res guidance
available that far out also supports a drier forecast.

Situation changes drastically for Tue and Wed though. Deep upper low
just now coming onshore the West Coast will eventually pinwheel its
way across the northern CONUS as a second Pacific trough follows
quickly behind it. Global models still show some discrepancies in
how exactly this pattern will evolve with smaller details crucial to
determining the severe weather threat. Initial warm front/theta-e
surge occurs Tue AM. A few strong, elevated storms may be possible
during this time but the better severe chances appear to be Tue
evening when initial trough/upper low (potentially) approaches the
Great Lakes with moderate instability in place and (again,
potentially) a highly supportive kinematic environment. A second
round is then possible Wed evening as the second piece of energy
rotates through the region with a similar environment. There is
still alot of uncertainty with important details but definitely need
to keep an eye on these periods.

The rest of the forecast period is relatively quiet. Light rain and
breezy conditions may persist into the late week depending on how
the upper low evolves but the instability should clear out by Thu.
Cooler temps are also expected Thu-Sat.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 133 PM EDT Sat May 4 2024

Two boundaries collocated with mid level vorticity and areas of low
level convergence allow for times of cloud cover and rain between
the start and end of this TAF period. A boundary pushed north
and west this morning allowing cloud cover at FWA. CIGs rising
from MVFR to VFR start this TAF period there as a result. Light
rain and drizzle was observed under that cloud this morning,
but with the raising ceilings expect to see less of that for the
afternoon. Expect VFR conditions to continue into later portion
of the overnight. On the other hand, an area of vorticity and
surface convergence associated with a line of convective showers
moving eastward from IL encroaches on SBN this evening. With
much of the insolation staying west of IN-15 today, low level
lapse rates steepen and instability increases ahead of the line.
Even still models, dissipate it as it moves inland from Lake
MI. Wouldn`t be surprised to see a brief increase of winds from
the outflow boundary as well as some showers or perhaps a
thunderstorm at SBN before it dissipates. Guidance indicates the
cold pool associated with this may leave some MVFR CIGs behind
at SBN for late tonight/early Sunday morning and perhaps FWA for
Sunday morning. IFR CIGs may also be possible at SBN, but
confidence on that is low at this time.

&&

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

&&

$$

DISCUSSION...AGD
AVIATION...Roller