365
FXUS63 KIND 211623
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1223 PM EDT Sat Sep 21 2024

.KEY MESSAGES...

- Hot and dry Today

- Thunderstorms moving in overnight

- Turning cooler and more active with greater rain chances Sunday
through early next week

&&

.FORECAST UPDATE...
Issued at 944 AM EDT Sat Sep 21 2024

Fog from earlier this morning continues to diminish across the
northwest half of central Indiana. Still some pockets with
visibilities under a mile and have an SPS to cover that over the
next 60-90 minutes as that dissipates. Elsewhere...skies are mainly
clear. 13Z temperatures were generally in the upper 60s and lower
70s.

Weak surface high pressure with ridging aloft will reestablish
across the region today bringing one more hot afternoon with dry
conditions. Model soundings show increasing subsidence north of the
remnant boundary which has settled near the Ohio River. That in
addition to the redevelopment of a strong capping inversion will
pull drier air back to the surface as mixing increases into the
afternoon. Have pulled dewpoints back into the 50s by later today
over the northern half of the forecast area with slightly higher
dewpoints further south.

Highs will make a push for 90 degrees again but this will be the
last hot day before the pattern shifts to cooler with a greater risk
for rain beginning Sunday. Zone and grid updates out.

&&

.SHORT TERM (Today and tonight)...
Issued at 301 AM EDT Sat Sep 21 2024

Overnight fog and timing and coverage of additional convection
later today and tonight will be the main concerns for the short term.

Early morning radar was showing the convection was shrinking in
coverage and diminishing. This trend should continue with little or
no lingering activity by 09z as the atmosphere stabilizes.

Fog will be the next issue as clearing, residual boundary layer
moisture and very light to calm winds were shaping for an ideal
radiational fog setup especially over northern sections and the
Wabash Valley where temperatures were closing in on their dew
points. Hi-Res soundings and the Hi-Res models in general are all
supporting this with the best timing in the 09z-13z time frame.
After, getting a recent report of quarter mile or less visibility in
Tipton and Hamilton counties and talking with adjacent offices, will
post a dense fog advisory through 13z for our northern third and the
Wabash Valley and mention patchy sense fog elsewhere.

By morning, the front will be stalling near the Ohio River and then
return north as a warm front during the day. Ridging from the Great
Lakes to Texas should keep it dry at least most of the day, although
some of the CAMs attempt to trigger afternoon convection over
southwest parts of central Indiana, where mixed CAPEs will rebound
to as high as 2000 J/kg per DESI. The big limiting factor will be
lack of synoptic forcing, but left over boundaries and or weak
impulses moving through the ridge could be enough. For now, will
leave PoPs out. Otherwise, the fog should burn off by 13z or so as
mainly solar heating should allow temperatures to recover back into
the upper 80s to lower 90s during the afternoon. This will be the
last of the well above normal temperatures through at least next
week.

The ridge will move east of the area tonight as an upper wave moves
into northern Ontario as a center of surface low pressure moves to
Lake Michigan and associated cold front stretches from the low
center to northern Missouri by 12z Sunday. Hi-Res soundings are
indicating a deep moist profile overnight tonight with near max
moving average PWATs and at least some weak instability. This
supports 60% PoPs toward 12z Sunday over the Wabash Valley tapering
off to 20% PoPs over the I-65 corridor.

&&

.LONG TERM (Sunday through Friday)...
Issued at 301 AM EDT Sat Sep 21 2024

Longer term guidance continues to show a fairly abrupt shift back to
much more seasonably mild conditions and potential for scattered to
numerous showers and a few thunderstorms, particularly late in the
weekend into the early portion of the work week.

Uncertainty increases greatly from mid week and beyond as guidance
begins to diverge significantly in its handling of the large scale
pattern and how quickly the upper troughing will depart the region,
along with the potential for tropical remnant influence.

Nonetheless, there appears to be solid potential for the first
appreciable rainfall in many parts of central Indiana in two to
three plus weeks, which may arrest further deterioration in the
local hydrologic situation - though the ongoing drought conditions
are unlikely to be significantly alleviated without multiple
episodes of soaking rainfalls totaling several inches. The couple of
inches that appear possible throughout the coming week will not be
enough to offer dramatic improvement.

With the shifting and weakening of the upper level ridge,
temperatures will moderate significantly, with highs likely to be in
the 70s much of the coming week, much closer to seasonal norms.

&&

.AVIATION (18Z TAF Issuance)...
Issued at 1223 PM EDT Sat Sep 21 2024

Impacts:

- Rain and thunderstorms are possible by Sunday morning

Discussion:

All fog has burned off from earlier this morning leaving mostly
sunny conditions with light and variable winds as high pressure
reestablishes over the region. Expect a gradual increase in mid and
high level clouds by late day into tonight as a frontal boundary
moves into the mid Mississippi Valley. The front will approach the
region Sunday morning with chances for rain and embedded
thunderstorms spreading into central Indiana from the west after
daybreak. Likely to see brief restrictions within storms on Sunday.

Winds will remain light and variable throughout the forecast period.

&&

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

&&

$$

UPDATE...Ryan
SHORT TERM...MK
LONG TERM...Nield
AVIATION...Ryan