084
FXUS63 KIND 021713
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
113 PM EDT Sun Jun 2 2024

.KEY MESSAGES...

- Potential for patchy fog overnight

- Warmer next week with periodic thunderstorm chances.
  The best chances will be Wednesday.

&&

.MESOSCALE UPDATE...
Issued at 111 PM EDT Sun Jun 2 2024

Latest LAPS data and SPC mesoscale data was indicating the
atmosphere has become unstable over the southeastern two thirds of
central Indiana with SB CAPES 500-1000 J/kg and radar was showing
some modestly building echoes. So, added 20% PoPs for the next
few hours. With forcing and shear weak, not expecting either
significant coverage or long lasting convection but with a few
spots reporting light rain showers and instability increasing,
felt the need to put these low PoPs in. Will re-exam the need
ahead of the mid afternoon forecast package.

&&

.FORECAST UPDATE...
Issued at 944 AM EDT Sun Jun 2 2024

Hi-Res soundings are showing a saturated or near rated layer from
the surface up to near 10K feet. Winds were less than 10 knots
through this layer, so despite a very dry layer above, mixing out of
the boundary layer will be a slow process at best. So, expect little
improvement through early afternoon with perhaps some improvement
late in the day. This will have a big impact on temperatures. May
need to lower temperatures a few degrees this afternoon. Will see
how things play out and do just that for the next update if needed.
Meanwhile, the weak surface system moving through has aided in
generating a few very light showers over southeastern sections and
they may continue for a few more hours but then ridge induced
subsidence should put an end to it.

&&

.SHORT TERM (Today and tonight)...
Issued at 257 AM EDT Sun Jun 2 2024

Early this morning mid-lvl water vapor was still at a maximum over
Central Indiana, with some drying noted upstream across
Illinois/Missouri. The lack of a pressure field coupled with the
moist boundary layer is allowing some lingering drizzle or mist to
continue; however, this should become more widespread during the pre-
dawn hours. This opens the door to potentially seeing fog
development. The moist/damp surface from earlier showers will couple
with the shallow stratus deck loosing the upward energy and sinking,
then the lack of a pressure gradient to encourage mixing of
saturated parcels or at least causing any additional vertical motion
sets the stage for early morning fog to develop. VWP from KIND
already indicating most targets under 5kts, with the only lingering
wind above 3kft agl but this area is also decreasing. Some
encouraging guidance is that many hi-res members displayed within
DESI suggests only patchy dense fog developing and only the HRRR has
been more suggestive of greater coverage. This helps with confidence
to lean towards only patchy fog developing from the sinking stratus
deck. But once any fog does develop, due to a lack of
mixing/isallobaric field would suggest it will linger through mid-
morning before burning off.

Today... Boundary layer will continue to be moist through midday,
perhaps into the afternoon hours. Lack of a gradient from a weak
anti-cyclonic feature arriving should delay the erosion of any
shallow stratus/fog from early in the morning. Which could cause a
slower response for temperatures due to the shielding lingering
longer. The mid-lvl flow does flatten out, with indications that
perhaps an increase to the forward propagation will occur and help
to push the departing moist layer east. But the caveat is that the
surface remains disjointed and will not realize this upper level
flow through much of the day. So temps will likely remain in the 60s
perhaps around 70 by the afternoon hours, then once the stratus deck
erodes enough the surface parcels should quickly respond and push
temps into the mid/upr 70s quickly.

Given the quasi-sinking air overhead this afternoon, not expecting
development to a cumulus field. Which should inhibit our potential
for seeing any convection let alone see rain become organized. So
will maintain the dry forecast.

Tonight... Could see a repeat setup for fog late tonight. With a
lack of diurnally induced mixing scouring any moisture from the
surface/boundary layer in the afternoon/evening hours, expect more
optimal conditions for fog to develop. Again the wild card will
be winds aloft. While the boundary layer appears to be lacking any
substantial pressure gradient with guidance suggestive of minimal
isallobaric pressure change in place, this should lay the
foundation for fog development after sunset. But flow in the mid-
lvls and aloft do appear to be more zonal and could be just enough
to limit the fog growth tonight if perhaps only allowing patchy
fog to occur.

&&

.LONG TERM (Monday through Saturday)...
Issued at 257 AM EDT Sun Jun 2 2024

The long term period will be warm, with highs in the 80s, for much
of the week before temperatures drop back into the 70s for the
weekend. There will be periodic chances for showers and
thunderstorms through the week as multiple shortwaves and then a
larger trough moves through into the Great Lakes region while an
upper high settles into the southern plains and SW states.

South to southwest flow at the surface for most of the week will
advect warm and moist air into the region. Models still don`t have
great agreement with precipitation through the period but generally
expecting to see chances for rain Monday night into Tuesday followed
by another wave Late Tuesday into Wednesday. A break between waves
may be possible. As the high over Mexico moves into the south-
central to southwest portion of the CONUS, the large upper low near
the Dakotas will progress towards the Great Lakes. The associated
cold front looks to advance through central Indiana sometime
Thursday night into Friday and lower temperatures for the weekend.
Additional precipitation may form along the front and another
rain chance possible over the weekend. Severe weather is not
expected at this time but can`t rule out a few storms producing
some gusts midweek.

&&

.AVIATION (18Z TAF Issuance)...
Issued at 103 PM EDT Sun Jun 2 2024

Impacts:

- MVFR and possibly brief VFR conditions to start off

- Would not rule out thunder at all but KLAF

- Would not rule out more IFR conditions after 06z-09z in stratus
  or fog

Discussion:

The deep boundary layer is showing signs of some dry air entrainment
with ceilings mostly improved to MVFR late this morning. This trend
should continue this afternoon with dry air and a high sun angle.
That said, winds were less than 10 knots through and adjacent to the
boundary layer, so mixing will be limited.

Would not completely rule out an isolated thunderstorm over any TAF
site except KLAF as the atmosphere has become unstable. However,
with the cold front east of the terminals and ridging building in,
chances too low to put in any form in the TAFs.

Low stratus or fog will be possible overnight as winds go very light
to calm. Winds will shift to the south and increase to closer to 10
knots towards Monday afternoon.


&&

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

$$

MESOSCALE...MK
UPDATE...MK
SHORT TERM...Beach
LONG TERM...KF
AVIATION...MK