379
FXUS63 KIWX 281728
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
128 PM EDT Fri Jun 28 2024

.KEY MESSAGES...

- Heavy rain and thunderstorms are expected overnight, with the
  best chance for heavy rain and isolated lowland flooding
  between 2 am EDT tonight to around 10 am EDT Saturday. There
  could be gusty winds with some of the stronger storms, but
  severe weather is not expected during this period.

- There is a marginal to slight risk (NW Ohio) across the area
  for potential strong to severe storms on Saturday between 2 pm
  and 10 pm EDT. The primary threats will be heavy rain,
  damaging winds, and localized flooding. Confidence in severe
  storms occurring is low due to uncertainties with the first
  round of storms and cloud cover.

- Hazardous swimming conditions are expected on Lake Michigan Sunday.
  Dangerous currents are likely, in addition to waves of 4 to 7
  feet. Those planning to visit the beaches should stay out of
  the water.

&&

.DISCUSSION...
Issued at 545 AM EDT Fri Jun 28 2024

Largely dry conditions today, though we do see increasing chances
for showers and thunderstorms out west as we get into the mid-late
afternoon time frame (best chances start at 8 pm onward). At the
moment (5:30 am EDT), high pressure is anchored at the surface with
light easterly winds. A mid level ridge is keeping us pretty subdued
in terms of any precipitation chances this morning, despite
increasing moisture advection on the nose of an 850mb LLJ this
morning. Have isolated sprinkles and mostly cloudy skies in the
forecast through much of the day, eventually becoming more focused
out west by the afternoon hours when the ridge begins to really
break down ahead of the approaching system.

Meanwhile, the surface warm front extending from the surface low
centered over far northwestern MN down into IA/MO/Western IL this
morning will lift E-NE through the day, with highs rising into the
low to mid 80s (warmest south where the warm front is). By the
afternoon, the front will be draped from Lake MI down through
Warsaw, IN and into southern Ohio, and it will continue it`s
northeastward progression into central/northern Lower MI and Upper
MI by 00z. This puts our forecast area into the warm sector, with a
weak prefrontal trough developing ahead of the cold front towards
6z. By this time, with the aid of a 35-40 knot LLJ at 850mb
(directed right into our CWA), PWATS upwards of 175% of normal
advect into our CWA--so expect heavy rain with thunderstorms to
materialize. Gusty winds are possible with any storms that are
stronger, but the primary threat will be heavy rain and isolated
lowland flooding between 2 am EDT tonight to around 10 am EDT
Saturday. Thankfully, system is fairly progressive so don`t expect
major problems with flooding.

The cold front, west of Lake MI by 12z Saturday, will shift eastward
through the day, and by around 00z Sun it is draped from Southern
Ontario to near Lima, OH and southwestward into MO/IL. A post
frontal trough behind the main front is also approaching the western
forecast area at this time. Most of the model guidance shows a break
in the precipitation chances between 15z-18z (or maybe until 21z for
some models) before re-developing additional convection both with
the incoming shortwave and the cold front over NW OH near Lima.
There are a ton of uncertainties at this point, and it`s difficult
to narrow down specifics, but it looks like we have a reasonable
chance for severe weather during the 2-10 pm EDT time frame Saturday-
Saturday evening. Confidence is low because models are in
disagreement on timing/location--and we don`t know what impact round
1 of the heavy rain/storms will have on the environment. The
limiting factor has also been the mid level lapse rates (500-700mb),
which until the 6z NAM, was looking like 5-6 C/km. GFS is the lowest
with 5C/km by 00z Sun, the NAM was most aggressive with more like 6-
7 C/Km, and the ECMWF and others are in between with about 6C/Km. We
have plenty of low level moisture, so I`m not too worried about
that. The lingering question is instability, which we have some of
thanks to that higher PWAT air. However, by about 21z the NAM
especially brings in greater surface instability (suggesting we
recover enough to develop additional convection with the incoming
pre frontal trough. The other models are more subdued, but I suspect
we`ll have around 500-1000 J/kg of DCAPE by the 21z-03z time frame.
The question is where will storms fire?

The Nam actually develops a line of storms just east of Lima
around 00z and moves it east with the cold front into the overnight
hours--then brings in another trough behind that which could kick
off some additional strong-severe storms. Other guidance has the
storms further northeast in NE IN/Lower MI/NW OH...but it`s too
early to say for sure. Something to keep an eye on, but low
confidence. Either way, expect variable cloud cover Saturday
afternoon, with highs in the 80s.

Sunday-Monday will be dry and cooler with highs in the 70s as high
pressure builds in at the surface beneath a brief ridge aloft.
Hazardous swimming conditions are expected on Lake Michigan Sunday
thanks to gusty northerly winds behind the exiting system. Waves
will build to 4 to 7 feet and wave periods look to stay in the 6-8
second range (kind of unusual) thanks to a long fetch down Lake MI.
This will increase the probability of dangerous currents, despite
low wave heights. If the thunderstorms cross the lake Saturday night
(like the NAM suggest), we may also be dealing with
seiche/meteotsunamis which promote development of dangerous currents
and increases their intensity. Will likely need a beach hazards
statement for Sunday into early Monday, as longer wave periods and
water level fluctuations may lead to current activity that
persists even once wave heights drop below 3 feet. Those
planning to visit the beaches this weekend should stay out of
the water.

It will be dry again on Monday-most of Tuesday before additional
chances for showers and thunderstorms move in Tuesday night into
Friday.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 121 PM EDT Fri Jun 28 2024

A shortwave moving through Illinois is currently spreading rain
across northern Indiana. CAMs have not handled this well due to
dry air at the low levels, and the arrival is earlier than
expected. Given this, have updated TAFs for both SBN and FWA to
include rain through the afternoon, with a possible break this
evening. Heavier rain and thunderstorms then move in around 05Z
tonight. Cloud bases are initially quite high and so VFR
ceilings are expected to persist for a while, but will then drop
to at least MVFR later tonight. Southwesterly wind shear is
also possible tonight with the low-level jet. South-
southeasterly winds this afternoon will shift to the southwest
on Saturday morning and become gusty.

&&

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

&&

$$

DISCUSSION...MCD
AVIATION...Cobb