450
FXUS63 KIWX 161933
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
333 PM EDT Sun Jun 16 2024

.KEY MESSAGES...

- Areas close to Lake Michigan may see showers and thunderstorms
  between 10 pm and 4 am. Gusty winds and heavy rain will be the
  main concerns.

- An Excessive Heat Watch remains in effect due to an extended
  period of hot and humid conditions.

- Widely scattered afternoon and evening thunderstorms are
  possible Monday and Tuesday.

&&

.DISCUSSION...
Issued at 226 PM EDT Sun Jun 16 2024

The main story of the upcoming forecast period remains with hot
and humid conditions already starting today and expected to
further intensify, especially in the second half of the week
with afternoon/evening heat indices in the 95 to 100 degree
range and limited cooling during the overnight hours. Extensive
coordination with surrounding offices as resulted in a
continuation of the Excessive Heat Watch with the reasoning to
be explained below. Regardless of what headlines may or may not
exist, the extended period of heat and humidity will still pose
an issue to those working or playing outdoors, those without
adequate means to cool off (both day and night) and those with
health problems made worse by the hot and humid conditions.

Afternoon temperatures have climbed into the upper 80s with some
potential for far SW areas to still touch 90. A large gradient
in dewpoints was also in place across the area with upper 40s
far NE to mid 60s SW. Overnight lows for tonight and much of the
upcoming week will end up in the lower to middle 70s, making for
rather unpleasant sleeping. While many areas will remain dry
into at least Monday morning, far NW locations may see a chance
for showers and thunderstorms later this evening into the
overnight hours as a well defined mcv heading towards the Quad
Cities, continues to move ENE and force additional showers and
storms across northern IL. SPC upgraded to a slight risk ahead
of this feature with the marginal risk being expanded slightly
to roughly a DeMotte to South Bend to Kalamazoo line. Models are
varying somewhat on the strength of storms as they pass over
Lake Michigan and enter SW Lower MI/far NW Indiana and move ENE.
Some models also expand the precipitation further south to at
least US-6 and maybe even a bit more. For the moment have
limited pops to slgt chc to chc and will defer any further
increases to the evening shift. Gusty winds and heavy rain will
be the main concerns.

While the hot and muggy conditions are fairly straight forward,
finer details in cloud cover, chances for showers/storms and
mixing out of dewpoints with drying ground conditions lead to
challenges in upgrading the watch to a Heat Advisory or
Excessive Heat Warning. The greatest concerns for the heat still
exist moreso Wednesday and beyond as the cumulative effects of
the heat as well as lack of rain chances all lead to greater
impacts. Weak disturbances and subtle forcing mechanisms could
help spark widely scattered showers and thunderstorms during the
afternoon and evening hours of Monday and Tuesday. One
mechanism could be any boundaries that may be left over from the
convection tonight. While it will be unstable and generally
uncapped, hard to assign more than a slgt chc to maybe chc of
convection at this point. Any storms that manage to form will
not move much and with the moist conditions will produce very
heavy rain and maybe locally gusty winds. Models do key in on a
disturbance working north Monday night that may help increase
chances for showers and storms, but think models may be overdone
somewhat with general consensus of offices being to keep pops
silent or slgt.

Chances for showers and thunderstorms may increase over the
weekend as the ridge axis orients more west to east and sinks
some. Best chances may exist Sunday but if these don`t pan out,
then the potentially dangerous heat will persist.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 132 PM EDT Sun Jun 16 2024

With a southeast CONUS mid level ridge to our southeast, an MCV was
noted on morning satellite images and this is expected to graze our
northwest between the timeframe of 3 to 7z. How far eastward it can
get is still in question and agree with the sentiment of the
previous shift with its prob30 for TSRA. Inside the 9hr window with
this issuance, will look to include a VCSH mention during this time
frame to still keep it on the radar so to speak. Otherwise, VFR
conditions are expected, especially at FWA, where more confidence in
capping/ dry air winning out remains away from the forcing of the
MCV. Winds become increasingly more southwesterly from southerly
behind a warm front passing through tonight. Gusts to 15 to 20 kts
cannot be ruled out during the peak mixing time frame of the
afternoon.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Excessive Heat Watch from Monday morning through Friday
     evening for INZ005>009-014-017-018-024>027-032>034-104-
     116-204-216.
     Air Quality Alert until midnight EDT tonight for INZ020.
OH...Excessive Heat Watch from Monday morning through Friday
     evening for OHZ001-002-004-005-015-016-024-025.
MI...Excessive Heat Watch from Monday morning through Friday
     evening for MIZ078>081-177-277.
     Air Quality Alert from midnight tonight to midnight EDT Monday
     night for MIZ078-177-277.
MARINE...None.

&&

$$

DISCUSSION...Fisher
AVIATION...Roller