Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 241430
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1030 AM EDT Sat Oct 24 2020

.UPDATE...
The AVIATION section has been updated below.

&&

.SYNOPSIS...
Issued at 318 AM EDT Sat Oct 24 2020

High pressure over the upper Midwest will bring dry and cooler
conditions to central Indiana for most of the weekend. Rain chances
will increase late weekend and especially for the early part of the
upcoming week. Cool temperatures will continue for much of next week
before gradually warming by next weekend.

&&

.NEAR TERM /Rest of Today/...

Issued at 948 AM EDT Sat Oct 24 2020

Conditions have generally evolved as expected thus far. Made minor
adjustments to the sky conditions as this stratus deck persists
across the western counties. The deck has slowly begun to erode,
but portions may persist into the early afternoon while some
diurnal cu forms out east. Tried to account for the increased sky
in the west by lowering temps a couple of degrees this afternoon.
Relevant portions of previous discussion follows...

Brisk...raw and damp morning ongoing as gusty northwest winds
continue. The winds will subside over the next several hours as the
surface pressure gradient relaxes with the expansion and approach of
high pressure over the upper Midwest. The main focus for the morning
will be the gradual thinning of the lower stratus as northerly flow
continues to drive drier air into the forecast area.

Expect increasing sunshine by late morning into the afternoon with
the clouds mixing out into a scattered cu field. Any clearing over
southern counties is likely to be brief as not only will those areas
be the last to mix out from the stratus deck later this morning...
but the approach of an inverted surface trough into the lower Ohio
Valley late day will spread clouds back into the region from the
south. N/NE winds will be a steady 10-15mph much of the day with a
periodic higher gust during the afternoon.

Temps...low level thermals support undercutting general temp
guidance for highs today. Expect low to mid 50s for much of the
forecast area.

&&

.SHORT TERM /Tonight through Monday Night/...
Issued at 318 AM EDT Sat Oct 24 2020

Forecast challenges focus on rain chances returning late weekend
into early next week.

Broad zonal flow aloft across the lower 48 tonight and Sunday will
transition to a more amplified regime as a deepening upper low dives
south from the northern Rockies into the Four Corners region. This
will be accompanied by a strong surface high pressure that will
drive south down the east side of the Rockies before settling into
the central Plains Tuesday morning.

An initial surge of isentropic lift associated with the inverted
surface trough moving through the lower Ohio and Tennessee Valleys
tonight into Sunday will produce a chance for light showers across
southern portions of the forecast area as lower clouds gradually
expand back north through the region. Model soundings show a
developing boundary layer inversion by Sunday afternoon with
increasing moisture advecting across the region late Sunday into
Monday courtesy of a moist southwest flow aloft downstream of the
digging upper low over the Intermountain West.

A lack of deeper isentropic lift Sunday evening will limit any light
rain but as forcing aloft strengthens and the entire column
saturates on Monday...expect rain to become widespread across
central Indiana. The overall setup for embedded thunder does not
look nearly as impressive for Monday with little to no elevated
instability and an overall disorganized setup. Have pulled any
thunder mention with the more likely scenario being another
raw...damp period Monday and Monday night as a stiff E/NE wind
combines with the rain. Colder air will begin to advect into the
region late Monday night as the deeper moisture shifts to the
southeast. The boundary layer cools enough during the predawn hours
Tuesday to become marginally supportive of a few snowflakes mixing
in as precip ends. Confidence is quite low in this solution and have
not introduced any mention of snowflakes at this time...but it is a
possibility as freezing levels tumble into the 2-4kft range.

Temps...cooler conditions will persist through the short term as
E/NE winds and the presence of clouds and at times precip limit any
substantial warming. An overall model blend was supported by low
level thermals throughout with highs in the low to mid 50s and lows
ranging from the mid 30s to low 40s both tonight and Monday
night...with slightly warmer conditions Sunday night.

&&

.LONG TERM /Tuesday through Friday/...
Issued at 318 AM EDT Sat Oct 24 2020

Remnant moisture in the aftermath of Monday`s low pressure system
will create chances for showers early on Tuesday. This should
quickly diminish later in the day as a surface ridge builds over
the Ohio Valley. The source of warm moist air looks to remain well
south of central Indiana for Tuesday, blocked by a stalled
boundary. Even so, cloud cover should still be prominent with
primarily zonal and fairly direct gulf flow aloft. This should
lead to below seasonal temperatures to start the long term; expect
highs on Tuesday and Wednesday in the upper 40s to mid 50s.

The next disturbance of concern will approach Indiana from the south
on Thursday. Model ensembles vary greatly on how far north the low
will track, leading to outcomes that range from no precipitation to a
few inches of rain possible. This low looks to be closed off from
any upper level wave, and there for subtle dynamic forcings will play
a large role in its progression. As this system develops, models
should get a better handle on its movement, increasing confidence.
For now, expectations are for far southern portions of central
Indiana to be within the greatest risk for precipitation with
northern portions on the threshold of no rain.

Initially, cool air should encompass Indiana in the wake of the low,
but a quick resurgence of southerly flow will help build a ridge
over the Ohio Valley, raising temperatures for most of the weekend.
The presence of a low level ridge should help keep central
Indiana dry over the weekend.

&&

.AVIATION (Discussion for the 241500Z TAF Update)...
Issued at 1030 AM EDT Sat Oct 24 2020

Delayed return of VFR based on latest trends seen on satellite.
Will have to watch for additional MVFR conditions from additional
stratocumulus popping up in the cleared area, but for now am not
confident to put into the TAF. Used a scattered low layer instead
for now.

Previous discussion follows....

MVFR ceilings are ongoing over KIND and KBMG. Surface ridging to
the west has helped lift cloud decks slightly over western sites,
to above 3000 feet. As the morning progresses, cloud decks should
begin to break apart and lift. All sites should be in VFR by
1500Z.

KIND still is reporting gusts upwards of 20 knots this morning.
This should diminish quickly, but have included a TEMPO group to
depict the ongoing conditions. Winds are mostly out of the south
between 8 and 12 knots this morning. A subtle shift eastward is
likely throughout the day, although wind speeds should remain
similar. No threat of MVFR conditions are expected this afternoon
through tonight.
&&

.IND WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SYNOPSIS...Ryan
NEAR TERM...Ryan/White
SHORT TERM...Ryan
LONG TERM....Updike
AVIATION...Updike/50



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