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067
FXUS63 KIWX 061747
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
147 PM EDT Mon May 6 2024

.KEY MESSAGES...

- Severe weather threat for Tuesday afternoon and evening.
  Damaging winds, large hail, and even a few tornadoes are
  possible in any severe storms that develop. Heavy rain and
  minor flooding is possible.

- Severe weather is possible again late Wednesday afternoon into
  the overnight, especially south of US 30. Damaging winds,
  hail, and localized flooding are the primary threats.
  Confidence is low at this time.

- Cooler with chances for showers and thunderstorms later this
  week into the weekend. Highs Friday into Sunday will be in the
  50s and 60s. Otherwise, expect temperatures in the mid to
  upper 60s and 70s.

&&

.DISCUSSION...
Issued at 520 AM EDT Mon May 6 2024

Mostly dry today into tonight with high pressure settled in at the
surface over Lower MI and a ridge aloft. This afternoon a sharp
shortwave attempts to break down the ridge, generating showers and
storms for locations south of US 30 (best chances further south,
around 20% just south of Fort Wayne). The wave eventually washes
out, leaving us zonal flow aloft ahead of the deep, broad upper low
encompassing the west and central CONUS. Beyond that expect partly
to mostly sunny skies north of US 30, with increased cloudiness in
the south.

The ever evolving severe weather threat is still on the table for
Tuesday afternoon and evening, with still low to medium confidence
overall. I think we`ll see severe weather somewhere on Tuesday
afternoon and evening, but the details are still uncertain as models
continue to disagree on how far into the warm sector we get.

The warm front associated with the surface low over the northern
plains will lift northeastward through the morning hours Tuesday,
with a secondary surface low developing over MO/IL in response to
divergence at the nose of a 135 knot jet at 300mb. This low moves
into our CWA (or north of it depending on the model) around 18-00z
as it begins to occlude-which is when our threat is greatest for the
best storms. Most of the models show a swath of showers/decaying
convection in the morning (warm front) quickly followed by another,
more potent line moving in as the cold front enters the western CWA
and begins to occlude. Models vary as to how far into the warm
sector we get, but the general consensus is that we`ll have between
600-2500 J/kg of surface CAPE, greatest values in the 18-21z time,
and depending on the model, 6-7C/km 500-700 mb lapse rates. Being at
the nose of the jet, we`ll have around 50-75 knots of 0-6 km shear,
and plenty of moisture to work with. All hazards would certainly be
on the table for this, with decent 0-1 km shear and LCL`s around 500-
1000 m. For now, SPC has much of our area in a slight risk (further
south and east). The best chance for severe weather will be between
2-10 pm EDT Tuesday. All hazards are on the table, including
possible tornadoes.

Behind the system on Tuesday night, we`ll see a lull in the
precipitation that last through roughly Wednesday afternoon...where
we rinse and repeat Tuesday`s forecast for Wednesday afternoon into
the overnight hours! SPC has our CWA south of US 30 in a slight
risk, with an enhanced risk just shy of Jay County. This second
system is a bit more potent, but the surface low may go further
south than the one forecasted for Tuesday, which makes the better
chance outside our area if that occurs. Low confidence for now given
that much will also depend on how the first system behaves as far as
boundaries, etc. Opted to keep consensus pops for now to focus on
the south.

Otherwise, with the upper low moving overhead on Thursday into the
weekend, we`ll see continued shower activity and maybe even a few
thunderstorms again. Models are conflicted on the larger scale
pattern, especially Sunday and Monday with the ECMWF having us dry
with a surface high in place and an upper level ridge, and the GFS
keeping a broad trough over the Great Lakes and continued rain. Kept
the consensus pops for now, but with the upper low expect it will be
cooler/cloudier than it`s been, with highs in the 50s and 60s.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
-- Changed Discussion --
Issued at 147 PM EDT Mon May 6 2024

A weak area of vorticity moves from the lower Mississippi Valley
into the Mid Atlantic Coast during this TAF period at the same time
that a surface high pressure system moves northeast into eastern
Canada. This sets the area up for winds out of the east ahead of a
warm front that attempts to move through Tuesday morning. A low
level inversion has formed below 850 mb and this allowed for times
of MVFR CIGs this morning as the inversion traps residual moisture
from recent rainfall and moisture from Lake Erie underneath it.
The diurnal trends this morning also helped CIGs rise above MVFR
so will keep that out of the afternoon TAFs. It`ll take until
moisture rises northward with the stronger moisture stream
Tuesday morning just behind the warm front. This also brings
additional opportunities for MVFR CIGs, and perhaps IFR, Tuesday
morning and there could be some showers or perhaps some
thunderstorms with the morning batch, but the instability
appears to be weaker. The NAM and even the ECMWF do show
increasing instability during the midday and afternoon hours
allowing for an opportunity for thunderstorms that could be
strong during the afternoon time, but that`s beyond this TAF
period.
-- End Changed Discussion --

&&

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

&&

$$

DISCUSSION...T
AVIATION...Roller