959
FXUS63 KIND 160628
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
228 AM EDT Thu May 16 2024

.KEY MESSAGES...

- Patchy to areas of fog through daybreak again and possibly
  again tonight.

- Rain and storm chances return at times late today through Saturday.

- Above normal temperatures this weekend through the middle of next
  week.

- Increasing threat for strong to severe storms by Tuesday and
  Wednesday next week.

&&

.MESOSCALE UPDATE...
Issued at 228 AM EDT Thu May 16 2024

Latest observations show RH values nearing 100 percent across much
of central Indiana with pockets of non-dense fog forming across the
northeastern portions of the forecast area where clouds cleared
earlier this evening.

Cloud cover over the last hour has cleared further to the southwest
with the expectation that patchy to areas of fog will spread across
much if not all of central Indiana towards daybreak.  The main
question will be whether fog can become dense with only a weak near
surface inversion and lack of subsidence limiting the threat for
widespread dense fog.

Will continue to monitor the observational trends and may need to
introduce a brief Dense Fog Advisory in the coming hours if the
visibility drop becomes more widespread and intense compared to
current expectations.

&&

.SHORT TERM (Today and tonight)...
Issued at 228 AM EDT Thu May 16 2024

Today.

Any morning fog will quickly begin to dissipate as daytime heating
increases the dewpoint depression and erodes the fog.  Conditions
then look dry and quiet through much of the day before the next
broad trough brings a return to rain late this evening into the
early overnight hours. Models are struggling to get a handle on the
mesoscale forcing of the system with a fairly wide spread on areas
of heavier precipitation leading to a lower confidence in location
for showers and a few rumbles of thunder after 22Z.

A front will push towards the area but is expected to become
gradually more diffuse as it pushes through Illinois and races out
ahead of the better forcing associated with the parent low pressure
system in the Dakotas.  This will further help to limit shower
coverage into the evening along with keeping the thunder potential
to a minimum. Temperatures will be a bit warmer today with the
periods of clear skies through the early afternoon which will allow
for highs to climb into the mid to upper 70s.

Tonight.

Clouds and scattered showers will likely stick around for much of the
night tonight with model soundings showing persistent saturation at
the top of the boundary layer, but will have to keep an eye out for
any locations that do begin to clear as the recent rains will help
to supersaturate the low levels and may allow for some fog
formation, especially across northwest Indiana where rain to be less
in coverage. Further to the southeast, clouds and occasional rain
should help to limit the fog formation with less efficient
radiational cooling even as winds drop to near calm.

These thoughts are backed up by the HREF probabilities for MVFR to
IFR fog generally remaining under 10 percent outside of the
Lafayette area and closer to Chicago where probabilities are closer
to 50 percent. Lows tonight will only drop into the low 60s with the
higher expected dewpoints tonight compared to the previous night.

&&

.LONG TERM (Friday through Wednesday)...
Issued at 228 AM EDT Thu May 16 2024

Progressive pattern aloft will continue into the weekend with
the potential for another round of rain and storms Friday into early
Saturday as a weak upper wave passes through the Ohio and Tennessee
Valleys. Ridging develops over the Ohio Valley by Sunday as a split
level upper level flow develops in response to an expanding trough
over the western states. This will transition into a more amplified
regime for next week with multiple waves kicking out of the upper
trough and across the Midwest...increasing the risks for more robust
convection and severe weather by Tuesday and Wednesday next week.

Friday through Sunday Night

The focus will be on the positively tilted upper wave tracking from
the southern Plains Friday morning into the upper Ohio Valley by
late Saturday. Trends have started to shift the focus of the most
widespread rainfall south closer to the Ohio River and points south.
The main reason for this shift is the expected development and track
of a convective cluster through the lower Mississippi Valley late
tonight into Friday which is likely to mitigate some of the deeper
moisture transport as far north as central Indiana. The strong low
level jet dynamics that had been showing up as well the last few
days by late Friday have also been displaced to the south.

The catalyst in the secondary wave of rainfall for late Friday into
Saturday morning is a weak surface wave tracking through the
Tennessee Valley. The greatest coverage to rain and convection will
now focus across the southern half of the forecast area with the
bullseye of deepest forcing aloft and moisture suggesting heaviest
rainfall will set up across Kentucky. Locally heavy rainfall and
higher rates within convective cells remain a possibility but should
be more scattered in nature across southern Indiana. These trends
have lowered the overall flood concerns for Friday afternoon into
Saturday locally at this time...but any fluctuation back north would
bring the swath of heaviest rainfall north of the Ohio River and
could potentially bring concerns back into play for southern
counties.

The remnant upper wave will be drifting across the lower Ohio and
Tennessee Valleys Saturday...with enough moisture and instability
available across the region to produce scattered convection on
Saturday...peaking during peak heating in the afternoon. The upper
wave will move east of the area Saturday night with ridging aloft
quickly expanding into the region. With the addition of surface high
pressure by Sunday...expect warm and dry conditions across central
Indiana to wrap up the weekend.

Temperatures will remain seasonable through Saturday with highs
mainly in the 70s. By Sunday with the influx of warm advection and
ridging aloft...highs into the lower and mid 80s look reasonable.

Monday through Wednesday

With the transition to a more amplified upper level pattern across
the country...ridging will remain the prominent feature over much of
the eastern states to begin next week. An influx of moist...humid
southerly flow on the back side of the surface ridge will maintain
warmer temperatures across the region with mid and possibly upper
80s in play by Tuesday.

The shift in the upper level pattern will also introduce a greater
threat for more significant convection and severe weather across the
region by Tuesday and perhaps extending out further into next week.
As the western trough begins to shift east...waves will eject from
the parent trough and move into the Plains...upper Midwest and
eventually further east into the Great Lakes and Ohio Valley. Those
waves aloft will interact with an increasingly moist and unstable
airmass to generate increasing risks for convective clusters and a
heightened potential for severe weather...with Tuesday highlighted
as a cold front approaches the region. The active and stormy pattern
may extend into Wednesday as the front pushes through the
area...with potential for more storms by later next week as the
front returns north into the region. Highs will dip back into the
mid and upper 70s midweek as the front passes through.

&&

.AVIATION (06Z TAF Issuance)...
Issued at 1254 AM EDT Thu May 16 2024

Impacts:

- IFR vsbys due to FG from 10Z to 13Z.
- RA returns after 20Z, MVFR cigs towards 06Z.

Discussion:

MVFR to IFR vsbys are expected towards daybreak with current
observations showing some lowered vsbys already across outlying
areas. Fog may be brief, but confidence is too low to go lower than
1SM at this time.  Daytime heating will bring a quick end to the fog
with quiet weather and VFR conditions through much of the day.  Rain
is likely to return this evening into tonight with highest coverage
after 06Z so will keep just a VCSH mention for now before that
point. Winds will generally remain less than 10kts with a general
southerly direction through the TAF period.


&&

.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

MESOSCALE...White
SHORT TERM...White
LONG TERM...Ryan
AVIATION...White