498
FXUS63 KIWX 191127
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
727 AM EDT Wed Jun 19 2024

.KEY MESSAGES...

* There is a Marginal Risk for isolated severe storms mainly
  along and east of Interstate 69 this afternoon. The main
  threat is isolated strong to damaging wind gusts.

* Hot and humid conditions expected through Saturday with just
  slight chances of storms. Peak afternoon heat indices will
  approach 100 degrees, hazardous to sensitive and vulnerable
  groups.

&&

.DISCUSSION...
Issued at 350 AM EDT Wed Jun 19 2024

Persistent heat/humidity will continue to be the primary forecast
concern this period. A Marginal Risk of severe storms has been
introduced for this afternoon/early evening, mainly along and east
of Interstate 69 for isolated damaging thunderstorm wind gusts.

For today, portions of northeast Indiana/northwest Ohio should be in
favorable position for some influence from sheared upper level short
waves lifting northeast out of the Lower MS Valley. 00Z RAOB last
evening from Nashville does indicate some slightly stronger
35-45 knot flow in upper levels associated with this forcing.
Weakly confluent low level flow across NE Indiana/NW Ohio today
may provide some focus for isolated afternoon/early evening
convection, which also should be a zone of best low level
moisture quality given some modest low level moisture transport
working in from the Ohio Valley. Surface based CAPES along and
east of I-69 should increase into the 1000-1500 J/kg range this
afternoon. Overall weakly sheared environment and modest
instability would suggest minimal severe risk, but shallow
warm/moist profiles beneath drier mid level air should support
some moderate downdraft CAPES on the order of 1000-1200 J/kg
that could support some isolated strong/severe downdrafts. Areas
east of Interstate 69 have been placed in Day 1 Marginal
outlook, with isolated damaging winds as the main threat this
afternoon. Otherwise in the meantime, difficult to discount
isolated showers and storms developing this morning given the
approach of the sheared upper level forcing and gradually
moistening low levels that could allow some weak elevated
instability to be realized.

Not much change made to maximum temperature forecast today, but
extent of cloud cover and isolated convection will complicate hourly
temperature trends. Extensive mid and high clouds blanket the area
this morning, but these clouds should tend to erode from west to
east this afternoon. Some concern this could be a limiting
factor from realizing full low to mid 90s max temperature
potential today, but areas across the east should see slightly
higher dew points in comparison to yesterday. Peak afternoon
heat indices should be in the mid to possibly upper 90s.

For Thursday and Friday, guidance continues to suggest some slight
retrogression of pattern and subtle mid/upper level height rises
across the Great Lakes/Ohio Valley. Best chances of diurnally
enhanced isolated/scattered showers and thunderstorms should be
across the north given potential of weak short wave to eject out of
Central Plains into the Lower Michigan Thursday afternoon. Peak
afternoon heat indices should once again top out from the mid
90s to around 100 (warmest for southern half of the area).
Persistence forecast continues for Friday, although precip
chances may be more muted for most of the area given mid/upper
level ridging more firmly entrenched. A very shallow cool
frontal feature across the southern Great Lakes could provide
some focus for isolated afternoon convection across far NE
Indiana/SC Lower Michigan Friday afternoon, but low level
moisture quality may be a bit less impressive by this time.

For Saturday, little change in large scale pattern expected with a
more substantial upper level short wave trough still displaced to
the west across central CONUS. Confidence continues to creep upward
that heat indices near 100 will persist into Saturday, with current
expectation that scattered convection will hold off until Saturday
night. Will not extend heat headlines into Saturday yet, but this
will be something to examine over next few shifts.

The best chance of showers and thunderstorms still looks to be in
the Saturday night into early Sunday timeframe as this upstream
trough and associated cool front push across the region. This should
push highs back down into the 80s for Sunday and Monday, but heat
may build once again Tuesday-Wednesday. Confidence is low on heat
index magnitudes toward end of this forecast period however, as
chances of showers and thunderstorms and increased cloud cover may
characterize this period with a series of northern stream short
waves skirting across Northern Plains into the Great Lakes.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 719 AM EDT Wed Jun 19 2024

VFR conditions are expected to dominate KSBN through the period
with maybe a few, low confidence challenges at KFWA with regards
to isolated shower/thunderstorm chances. Some models suggest a
few showers or storms may develop southwest of the airport and
work slowly north east between 12 and 16Z. A shower has
developed in the past hour SW of KMIE with another newly
developed shower well NE of KMZZ. For the moment, have
introduced just a VCSH for a few hours, but if the threat for
thunder becomes more prevalent, an amendment may be needed.
After 16Z the threat for additional showers or storms will be
dictated to some extent by both the impacts of any earlier
convection as well as an approaching wave from the south.
Will leave any mention out for now of any impacts and reassess
through the morning and with the 18Z TAFs.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Heat Advisory until 8 PM EDT /7 PM CDT/ Friday for INZ005>008-
     012>015-020-022-023-103-104-116-203-204-216.
     Excessive Heat Warning until 8 PM EDT Friday for INZ009-017-
     018-024>027-032>034.
     Air Quality Alert from midnight tonight to midnight EDT
     Thursday night for INZ020.
     Air Quality Alert until 11 PM CDT this evening for INZ103-203.
OH...Excessive Heat Warning until 8 PM EDT Friday for OHZ001-002-
     004-005-015-016-024-025.
MI...Heat Advisory until 8 PM EDT Friday for MIZ078>081-177-277.
     Air Quality Alert until midnight EDT tonight for MIZ177-277.
MARINE...None.

&&

$$

DISCUSSION...Marsili
AVIATION...Fisher