River Flood Warning 8, NWS Northern Indiana

Area Forecast Discussion
National Weather Service Northern Indiana
743 AM EDT Thu Mar 14 2024

.KEY MESSAGES...

- Several rounds of showers and storms today, with potential for
  severe storms. Hail and heavy rain are the most likely
  threats, with potential for damaging winds and an isolated
  tornado also possible.

- The best chance for severe weather will be south of US 30 this
  afternoon and evening.

- Confidence is medium in severe weather occurring today.
  However, there is lower confidence with regards to the extent
  of the coverage and storm mode later into the afternoon.

&&

.DISCUSSION...
Issued at 449 AM EDT Thu Mar 14 2024

Main focus for this discussion will be the potential for severe
weather, with several rounds of showers and storms expected as a low
pressure system moves through the area today into tonight. SPC has
our forecast area in a marginal/slight risk-with the dividing line
at US 30. Confidence in at least some isolated severe storms
occurring today is medium, but confidence as to the coverage (how
widespread) and exact storm mode (especially this afternoon) is
lower. The main limitation is surface instability, with questions as
to how the first two rounds set the stage for later this
afternoon/evening-which is when the greatest conditional threat for
supercells exists.

For the today/tonight forecast, leaned towards the HRRR as it seems
to have the better handle on the overnight storms. This gives us
three potential rounds of severe weather, with the third being the
greatest risk as there is potential for discrete supercells (all
hazards on the table).

Period 1: Ongoing now, will continue through the early morning as
elevated storms continue to overspread the forecast area. A
stationary boundary settled over the central CWA (W-E roughly along
US 30) will lift slightly northward as warm air/moisture advection
ahead of the approaching surface low filters in. Additionally, we're
in the left exit region of an upper level jet, which is providing
extra lift for storms to get going. Naturally all instability is
elevated, with mid level lapse rates of around 6.5 to 7.5 C/km.
Expect coverage to increase and boundary to lift northward somewhat.
As far as threats go, with limited surface instability, expect heavy
rain and hail to be the primary concerns with this first round. As
of 4 am, we've received several reports of smaller hail (peas),
heavy rain, and excessive lightning. If travelling this morning, be
cautious of lower visibility and ponding of water on the roads.

Period 2: Late this morning into mid afternoon. Through this time,
the surface low will be lifting into IA/IL, moving eastward into IN
(models disagree on exact placement) into the overnight. The threat
for severe storms is really conditional at this time, as it will
depend on how much instability we can get ahead of the incoming cold
front in the warm sector-which is dependent upon this mornings
storms and how much of the better dewpoints we can get into the area
south of US 30. From roughly 15-20z most of the guidance has a
prefrontal trough swing through, which looks likely to bring a line
of storms from west to east across the CWA. Instability is really
lacking, generally models suggest 100-500 J/kg through 18z (best
values south of US 30). Expect we could get some severe wind gusts
and hail with this round, given lapse rates of 6.5-7.5 C/KM persist-
and we'll have better mixing into the daytime hours than now.

Period 3: Last but definitely not least of our concerns is the 21z-
03z period, where we could see some discrete supercells develop
along our southern CWA border after the line of storms from period 2
exits the eastern zones. The surface low really consolidates as it
moves eastward, with the triple point potentially moving right
across our far southwest CWA---which gives us supercell potential.
Lapse rates in the mid levels are still around 7.5 C/km at this
time, but the surface instability (how much LL moisture we can get
in here, or perhaps heating/recovering behind the line in round 2).
This is the most conditional of all the rounds, with potential for
greater impact if it does occur. If we get discrete supercells, all
threats will be on the table, including tornadoes given lower LCL's
and longer hodographs. It's also possible the threat stays south of
us and/or doesn't materialize because the environment was wrecked by
this morning/afternoon convection.

For the remainder of the period, left consensus pops given active
short term weather. However, a broad upper low is forecast to sink
southward from northern Ontario into the Great Lakes region, where
it lingers through the weekend and early next week. There will be
chances for rain and snow showers, with highs in the 50s and low 60s
through Saturday, then falling back into the 30s and 40s Sun-Tue.
We'll warm back up into the 50s by the end of the period.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 738 AM EDT Thu Mar 14 2024

Active warm front over northern IN this morning with scattered
to numerous showers and storms. Visby's generally ranging
between MVFR and VFR with this activity, though brief IFR cannot
be ruled out. A more organized convective complex over western
IL will likely survive east through the area late morning into
the early afternoon (15-18z) with additional convection/restrictions
anticipated.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...Small Craft Advisory from 8 PM this evening to 4 PM EDT Friday
     for LMZ043-046.

&&

DISCUSSION...MCD
AVIATION...Steinwedel

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