475
FXUS63 KIND 300654
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
254 AM EDT Mon Sep 30 2024

.KEY MESSAGES...

- Isolated to scattered showers through late today

- Areas of fog late tonight into Tuesday morning

- Mainly dry conditions with nearly seasonable temperatures to open
  up October

&&

.SHORT TERM (Today and Tonight)...
Issued at 254 AM EDT Mon Sep 30 2024

Isolated light showers and pockets of drizzle continue to drift
southwest across the region early this morning on the northwest
flank of the upper low. with thick stratus once again draped over
most of the forecast area...temperatures remained steady state in
the mid and upper 60s.

This will be the final day with the upper low and remnants of Helene
in the vicinity of the region as an approaching strong upper trough
moving through the Canadian prairies and northern Plains. The upper
trough will help to kick the upper low off to the east and away from
the Ohio Valley as it weakens further.

While clouds and the potential for scattered showers will linger
today...the loosening influence from the upper low should ensure
increased heating and more breaks in the cloud deck by this
afternoon. First off...the boundary layer remains saturated which
the IND ACARS sounding shows nicely. With increasingly drier air
filtering in aloft...ceilings have slipped back into the 1000-2000ft
level currently with a few locations even lower than that. The lower
stratus will linger over much of the region through the morning with
the possibility for patchy fog as well focused over southeast
counties where there has been some scattering of the stratus.
Northeast winds remain around 10mph but should fall back towards
daybreak. Pockets of light showers and drizzle will also remain over
the southeast half of the forecast area over the next several hours.

As mentioned above...the lower stratus will lift and at least
partially mix out this afternoon as the drier mid level air begins
to work down into the boundary layer. Shallow instability this
afternoon may be enough to generate a few showers focused especially
across the southeast half of the forecast area in closest proximity
to the departing upper low. By early evening...expect showers to
diminish as deeper low level moisture shifts east and heating is
lost.

The focus for tonight will transition to fog and perhaps stratus
redevelopment as well. Despite the presence of an overall drier
column of air...near saturated conditions will linger in the near
surface layer as winds go near calm. The setup is supportive of
broader fog development late tonight through daybreak Tuesday. There
remains uncertainty with respect to the degree of clearing of the
stratocu which may serve to limit fog in some areas. For now will
highlight the potential for areas of fog late.

Temps...warmer temperatures are expected this afternoon with
increased breaks in the stratocu. Much of the forecast area should
warm into the mid 70s. Lows tonight will again fall into the low to
mid 60s.

&&

.LONG TERM (Tuesday through Sunday)...
Issued at 254 AM EDT Mon Sep 30 2024

Mainly quiet weather is anticipated through the long range. A
progressive quasi-zonal jet stream is located along the US-Canadian
border, and should remain at that general latitude through the
coming week. The long wave pattern suggest a trough and associated
cold front swinging through roughly every 3-4 days, with the first
arriving on Tuesday. A second cold front looks to arrive Friday or
Saturday, and then potentially a third by Sunday or early next week.

Some showers are possible with each frontal passage, but heavy
amounts of precipitation are not expected. Reason being is that deep
moisture is displaced far to our south, and no strong sub-tropical
connection looks to become established prior to frontal passage.
Each front should bring a reinforcing shot of dry continental polar
air. Good radiational cooling potential is likely as surface high
pressure builds in behind each front. Tuesday and Wednesday night,
for instance, may see temperatures dip well into the 40s. Highs
rebound nicely into the 70s under full sun.

Given the above pattern, drier than normal conditions are favored
through the long range and perhaps beyond. Near average temperatures
are expected. Average highs are in the low 70s with lows in the low
50s.

&&

.AVIATION (06Z TAF Issuance)...
Issued at 1249 AM EDT Mon Sep 30 2024

Impacts:

- MVFR to IFR ceilings through the morning...improving to VFR by mid
to late afternoon

- Patchy fog possible late tonight and toward sunrise

Discussion:

Dreary conditions continue with pockets of drizzle drifting
southwest across central Indiana. Ceilings will slip back through
the overnight to 500-1000ft with patchy fog in light northeast flow.
Expect these ceilings to gradually lift to MVFR by midday then VFR
by mid to late afternoon as drier air aloft finally works its way
down into the boundary layer.

As the remnants of Helene finally move away to the east by this
evening...drier air will advect into the region with some scattering
of the stratocu deck. A strong signal for fog and perhaps widespread
and dense in spots is in place for late tonight and early Tuesday as
a sharp inversion develops in the near surface layer. Will address
this in greater detail for the 12Z TAF issuance.

&&

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

&&

$$

SHORT TERM...Ryan
LONG TERM...Eckhoff
AVIATION...Ryan