761
FXUS63 KIWX 201820
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
220 PM EDT Thu Jun 20 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 and Friday, mainly
  north of US 30. Locally heavy rainfall, lightning and wind gusts
  in excess of 40 mph are the primary threats.

* Better shower and thunderstorm chances (40-70%) arrive Saturday
  night into early Sunday along a cold front.

&&

.DISCUSSION...
Issued at 220 PM EDT Thu Jun 20 2024

A shallow/weak sfc trough the focus for diurnally driven convection
this afternoon into early this evening, mainly north of US 30. A
slightly drier boundary layer and lacking forcing/flow to once again
limit coverage (isolated to scattered), and the threat for severe
storms, though stronger water loaded pulse cells will carry the
potential for wind gusts in excess of 40 mph in the collapse
phase. 700 mb temps warming to +10C plus should should keep a lid on
convection across southern portions of the area.

Gradual suppression of the OH/TN Valley upper ridge is expected into
Friday and Saturday in advance of an upper trough ejecting from the
Rockies into the Upper Midwest. The associated active/elevated
frontal zone will remain north of the area with mainly dry/hot
conditions anticipated, though still cannot rule isolated convection
again Friday afternoon-evening near any lingering outflow
boundaries in the north. Continued to carry a dry forecast during
the day on Saturday with the area capped in deeper pre-frontal
southwest flow. Long duration heat wave remains the primary wx story
otherwise through Saturday on the northern fringes of the 595-598 dm
500 mb upper ridge.

Round of height falls through the Great Lakes does bring a well
needed cold front through Saturday night into Sunday morning with
chances for showers/storms, followed by a break from headline worthy
heat into early next week. Poor diurnal timing of the frontal
forcing and resulting limited buoyancy suggests a weakening trend
and lesser coverage (40-70%) of convection later Saturday night
into Sunday morning.

Theta-e ridge axis builds in advance of the next approaching
Upper Midwest upper trough Tuesday into Wednesday with chances
for a convective complex to bring needed rain/storms. Confidence
at this range is low however given a notable ensemble and
deterministic model solution spread.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1246 PM EDT Thu Jun 20 2024

Minimal changes needed for the 18Z TAFs...updated wind
directions and speeds for this evening. Otherwise, VFR ceilings
between 5 to 7 kft are expected to persists through the rest of
today and overnight. There is a slight chance (20-30%) for a
stray pop up shower or storm this evening, so have left that in
the KSBN TAF for now. Cumulus clouds are starting to develop
along an axis of convergence in far NW Indian and SW Lower
Michigan, where storms may develop this afternoon/evening.

&&

.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/ Friday night
     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...Steinwedel
AVIATION...Johnson