598
FXUS63 KIWX 180903
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
503 AM EDT Tue Jun 18 2024

.KEY MESSAGES...

- There are nearly daily low chances for showers and
  thunderstorms this week, especially in the afternoon and
  evening hours. Expect coverage to be widely scattered.

- The storm prediction center has portions of Northwest Ohio in
  a marginal risk for severe storms today, particularly this
  afternoon. Gusty winds and heavy rain are the primary threats
  in any stronger storms. Hail is also possible. Isolated
  stronger storms are possible outside of the risk area as well.

- Excessive Heat warnings and advisories are in effect due to an
  extended period of hot and humid conditions. Max heat indices
  this week will range from around 95 to 105, with the highest
  values in the warning area and in urban locations. Overnight
  lows in the 70s will provide little relief from the heat. High
  temperatures will be in the upper 80s and 90s.

&&

.DISCUSSION...
Issued at 454 AM EDT Tue Jun 18 2024

Bottom line up front: Dangerous heat and humidity is expected.
Excessive Heat warnings and advisories are in effect. Heat indices
through at least Friday look to be in the 95 to 100 degree range for
most, with values as high as 105 looking likely in the warning area.
Both headlines continue through Friday at 8 pm EDT.

Will likely need to extend the advisory/warning into Saturday
given the current forecasted heat indices will be around 100
once again, but there are more significant chances for
precipitation so held off for now.

Today will be the coolest of the week thanks to more expansive
cloud cover and the showers and thunderstorms expected through
the early evening, however models are indicating a westward
shift of the ridge axis from yesterday---meaning we`ll see
better potential Wed/Thu/Fri for those higher heat indices (and
potentially Saturday).

As a reminder in the event there are any questions regarding
headlines, our local criteria is:

-Heat Advisory: "A heat index (HI) around 100 degrees or
 higher. Consider a warning if the maximum HI is going to be
 between 95 to 100 degrees for more than 4 consecutive days."

-Warning criteria: HI >105 and a minimum HI >75F for a 48 hour
 period (or if the advisory criteria continues for more than 4
 consecutive days). This is because heat impacts are cumulative-
 particularly for more vulnerable urban populations.

Otherwise, the main change to the forecast today was to narrow down
chances for showers and thunderstorms, which appears futile given
the plethora of conflicting model guidance. Kept it broad and
general for now. However, suspect the morning shower and
thunderstorm activity we`re seeing at the nose of a LLJ/increased
moisture transport into our area (that none of the models had that
far east ha!) will increase in coverage through the afternoon as we
gain instability from daytime heating. Similar to the past few days,
we`ve had a few isolated severe storms and today is no exception.

The storm prediction center has portions of NW OH in a marginal risk
for severe storms, focused in the afternoon, thanks to a potent
shortwave currently over IL rounding the ridge-which will lift north
and then start heading eastward through the late afternoon/early
evening. I think this is reasonable, with damaging winds being the
main threat with the strongest storms. Outside of that we could see
an isolated strong to severe storm, but the best chance will be in
NW OH. DCAPE values look to end up around 1000 J/Kg in that area, so
we may see more of the downburst/microburst situations. Hail is
possible but less likely given the higher freezing level (14Kft) and
-20C (26kft). It`s more likely to be heavy rain given the humid air
mass. Two cells in the huntington area this morning produced about
0.25" in 10 minutes and gusted to around 30-40 mph.



&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 114 AM EDT Tue Jun 18 2024

Hot and humid flow will continue through the TAF period. Daytime
wind gusts at SBN may exceed 20 kts with a little tighter
gradient there. Kept showers/storms out for now due to
uncertainty but can not rule out a TEMPO or VCNTY shower/storm
at some point today.

&&

.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.
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.
MARINE...None.

&&

$$

DISCUSSION...MCD
AVIATION...Skipper