505
FXUS63 KIND 201621
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1221 PM EDT Fri Sep 20 2024

.KEY MESSAGES...

- Above normal temperatures continue into the weekend

- Isolated to scattered thunderstorms this afternoon and
  evening

- Cooler temperatures early next week with increasing rain chances

&&

.FORECAST UPDATE...
Issued at 928 AM EDT Fri Sep 20 2024

An area of convection is moving into the northern Wabash Valley this
morning but is showing signs of weakening. Skies were mainly sunny
elsewhere across central Indiana. At 13Z...temperatures ranged from
the mid 60s to the lower 70s.

The initial focus for the update is on the ongoing convection just
to our northwest. Cloud tops continue to warm and have seen a
gradual weakening trend as showers move into northwest portions of
central Indiana. Dewpoints are noticeably higher across central
Illinois and have aided in feeding the convection over the last few
hours. Drier air remains however across much of the forecast area
and expect that to keep the showers from making much headway into
the area over the next hour or so. Will hold onto low pops in the
northern Wabash Valley through about 15Z otherwise expect showers
will diminish with leftover cloud debris lingering through midday.

The focus then shifts to convective potential for later this
afternoon into the evening as a weak frontal boundary moves into the
region from the northwest. Decent BL shear exists for convective
maintenance late today but as has been mentioned...a lack of deeper
moisture and overall poor lapse rates will likely keep convection in
a scattered...disorganized multicellular mode. Cannot entirely rule
out a stronger gust from any collapsing cell but that will be the
exception rather than the norm. The best news is that some will get
much needed rainfall into the evening and it appears increasingly
likely that this will serve as an appetizer for more widespread
rainfall potential Sunday through Tuesday.

Have left highs for this afternoon as is in the upper 80s and lower
90s. May need to make adjustments by midday if cloud debris from
morning convection lingers longer than anticipated and curtails
diurnal heating. Zone and grid updates out.

&&

.SHORT TERM (Today and tonight)...
Issued at 302 AM EDT Fri Sep 20 2024

An upper trough will pivot from the upper Midwest to northern
Ontario through tonight as a dome of high pressure remains parked
over Texas. Meanwhile, a weak cold front will move into the Wabash
Valley this evening spread into southern Indiana by Saturday
morning. MRMS reflectivity was showing widespread convection across
Wisconsin with more scattered activity southwest into Iowa along and
ahead of this front.

As the front reaches central Indiana, it will have limited low level
moisture and weak to moderate instability to work with after
examining Hi-Resolution soundings. In addition, lapse rates will be
weak. So confidence in anything other than isolated late day and
evening convection is low. That said, with marginal 30-35 knot deep
shear to go with the weak to moderate instability and a curved
hodograph, would not rule out marginally severe hail and or
thunderstorm gusts per the SPC Day1 Severe Weather Outlook. Best
timing and highest chances will be after 19z and over the upper
Wabash Valley.

Once again, deep mixing, diurnal heating and light breezy southwest
winds should result in well above normal temperatures in the upper
80s and lower 90s today. Meanwhile, the frontal passage should have
little effect on temperatures tonight with lows in the 60s. Normal
high temperatures for this time of year are in the upper 70s and
lower 80s and normal lows are in the 50s.

&&

.LONG TERM (Saturday through Thursday)...
Would not rule out some late afternoon and evening thunderstorms as
a cold front moves in. However, chances are too low to put in the
TAFs. Otherwise, good confidence in VFR flying conditions through
the TAF period.
Issued at 302 AM EDT Fri Sep 20 2024

Some relief from the recent hot and dry conditions appears to be on
the way for next week, with growing chances for enough of a soaking
rain to at least prevent worsening of ongoing drought conditions,
and perhaps offer some improvement.

Guidance is generally in agreement on a weakening of the persistent
subtropical ridge that has kept us dry and hot in recent days and
weeks, allowing for multiple upper level disturbances to impinge
upon the area late in the weekend into early next week. Model
precipitable water values are anomalously high well into next week,
which should allow for rainfall as modest forcing moves through the
region.

Model spread increases from mid week onward with respect to
evolution of the synoptic pattern, which will significantly impact
resultant conditions, but broadly speaking, expect the first
significant rainfall chances in quite some time Sunday into Tuesday,
along with a fairly substantial cooldown to much nearer
climatological normals, followed by continued milder conditions and
perhaps some low rain chances late in the week into next weekend,
depending upon the degree to which the upper level ridge reasserts
influence near the region.

Model QPF is likely a bit overdone given the relatively modest
forcing, but WPC 7 day QPF of an inch or two total is certainly
reasonable and would put a substantial dent in the monthly deficit,
were it widespread enough.

&&

.AVIATION (18Z TAF Issuance)...
Issued at 1221 PM EDT Fri Sep 20 2024

Impacts:

- Isolated to scattered convection late afternoon and evening
possibly impacting KIND and KLAF

- Fog developing late tonight through daybreak Saturday...especially
at KLAF

Discussion:

Axis of mid and high level clouds diminishing as it drifts across
central Indiana early this afternoon. Skies will quickly shift back
to mostly clear for the afternoon before an increase in clouds
coinciding with scattered convective development expands in from the
northwest by late afternoon. Trends continue to support potential
for convection to potentially impact KIND and KLAF in the 21Z to 01Z
timeframe ahead of a weak frontal boundary. Confidence remains lower
in any convection at KBMG and KHUF and will keep any precip mention
out at those sites at this time. W/SW winds will generally be around
10kts through early evening but could see briefly gustier winds
within any convection that passes over or near a terminal.

High pressure and dry air will reestablish overnight with light and
variable flow likely to go near calm in the predawn hours. There is
support for fog development at the outlying terminals and especially
at KLAF that will likely last through daybreak. Expect mostly sunny
skies Saturday with light southeast flow developing.

&&

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

&&

$$

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