759
FXUS63 KIWX 210800
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
400 AM EDT Fri Jun 21 2024

.KEY MESSAGES...

* Hot and humid conditions will persist through Saturday. Peak
  afternoon heat indices will approach 100 degrees in many
  locations, hazardous to sensitive and vulnerable groups.

* Isolated to scattered thunderstorms (20-40%) are possible
  during the afternoon and early evening hours today especially
  across far northeast Indiana/northwest Ohio, along with south
  central Lower Michigan. A few storms may produce wind gusts
  to 50 mph.

* Better shower and thunderstorm chances (50-80%) arrive
  Saturday night into early Sunday along a cold front followed
  by additional chances Tuesday and Wednesday.

&&

.DISCUSSION...
Issued at 355 AM EDT Fri Jun 21 2024

Dangerous multi-day heat event will continue into Saturday. Heat
indices this afternoon into Saturday will top out around 100
degrees for many locations. No changes will be made to heat
headlines this morning with both the Heat Advisory and Excessive
Heat Warning in effect through 00Z Saturday evening.

Stagnant upper level pattern will allow for a persistence forecast
to be a good first estimate for today. Old stalled weak surface
boundary currently resides just south of the US 6 corridor this
morning. Some weak overrunning flow atop this boundary has
allowed for continuation of some isolated showers across Lake
Michigan vicinity this morning, but trends should continue to be
downward over the next few hours. This sfc trough will continue
to lose its integrity across northern portions of the forecast
area today, but some weak pooled moisture and dew points around
70 or lower 70s could persist this afternoon. The combination
of remnants of this pooled moisture, favored track of weak short
waves across the southern Great Lakes, and slightly cooler mid
level temps from south central Lower Michigan into far northwest
Ohio, should favor best chances of afternoon/early evening
storms in roughly the Hillsdale MI to Wauseon OH corridor.
Convective temperatures looked to be reached in the 16Z-17Z
timeframe once again. In terms of severe weather potential,
similar ingredients appear to be in place today including low
shear environment, steep low level lapse rates, and dry mid
level air. This could support an isolated gusty wind threat to
50 mph with the strongest cores in the 18Z-23Z timeframe, with a
low end potential of an isolated damaging wind gust. Any
isolated to scattered storms should weaken around 00Z timeframe
similar to last evening.

Heat indices are expected to to range from the mid 90s to around 100
today. Slightly cooler temperatures across northern portions of
the heat headlines should be partially offset by slightly
higher dew points for what should be fairly uniform distribution
of peak heat indices.

For this evening, some subtle increase in low level
southwesterlies should take remnants of the old sfc trough north
of the local area, and any isolated showers should be confined
north of the area after 02Z this evening.

For tonight into Saturday, mid/upper level ridging will finally
experience more suppression, but as this occurs stronger
southwesterly flow downstream of more notable eastern Pacific
short wave troughs will allow an increase in low level warm
advection. Saturday should feature highs in the mid 90s across
much of the area, although some better low level mixing could
temper dew points into the mid-upper 60s for another afternoon
of peak heat indices around 100. Deep dry adiabatic lapse rates
in low levels should promote peak wind gusts to 25 to 30 mph
Saturday afternoon.

For Saturday night into Sunday morning, attention turns to
approach of a couple of low amplitude short waves that will
eventually allow cool frontal progression into the local area
Saturday night into Sunday. Some uptick in deep layer shear to
20 to 30 knots is expected ahead of the cool front Saturday
night, but instability should be a limiting factor for a more
expansive severe weather threat. Best MUCAPE should reside
across the Mid MS Valley with a possibility that more vigorous
convection could tend to propagate upwind to the west of the
local area. Expecting upstream convection to have more of an
outflow dominance as it approaches the local area Saturday night
given lack of instability and marginal shear profiles. SPC has
placed northwest half of the area in Day 2 Marginal Risk,
primary for isolated strong wind gusts late evening/early
overnight Saturday.

During the day Sunday, effective frontal position will likely take
potential for more vigorous convection to the southeast of the local
area with a reduction in PoPs from NW to SE during the day.
Temperatures will trend to more seasonable levels post-frontal
Sunday.

Monday shaping up to be a nice day across the area with low humidity
and seasonable temps as sfc anticyclone drifts across the Ohio
Valley. Rapid departure of this anticyclone will allow for
renewed warm/moist advection into Tuesday, with a potential of 1
day heat indices approaching the 95 to 100 degree range Tuesday
afternoon. Additional storm chances persist Tuesday and
Wednesday although details in timing still murky at this
forecast distance. A more vigorous upper level short wave
tracking across Upper Midwest/northern Great Lakes will dampen
upper ridging once again with another frontal passage midweek.
Some potential of strong storms could accompany this period, but
much of this will depend on timing and southward extent of
better shear profiles. A trend to quieter conditions is
anticipated for Thursday and Friday as mid level heights rise
once again in wake of midweek system.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 125 AM EDT Fri Jun 21 2024

VFR to MVFR conditions expected at the TAF sites. Light and
variable winds with partly to mostly clear skies will lead to
some BR development overnight (KSBN is at 5SM right now, KFWA
may drop to 4-5SM at 9-12z). Otherwise, mid level clouds with
some showers/storms over Lake Michigan and near KBEH (north of
KSBN). Don`t anticipate any reaching the terminal but may be
around for the late evening hours along an upper level front.
Will amend to remove once trends diminish on radar.

&&

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

&&

$$

DISCUSSION...Marsili
AVIATION...MCD