Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 211426
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1026 AM EDT Mon Sep 21 2020

.UPDATE...
The NEAR TERM and AVIATION sections have been updated below.

&&

.SYNOPSIS...
Issued at 255 AM EDT Mon Sep 21 2020

Dry...seasonable weather will continue through midweek as the region
remains under the influence of a strong surface ridge. The remnants
of Tropical Storm Beta will pass south of the region Wednesday night
and Thursday...but may bring a few light showers to southern
portions of central Indiana. A better chance for rain and storms
comes this weekend as a cold front tracks through the Ohio Valley.

&&

.NEAR TERM (Rest of Today)...
Issued at 1026 AM EDT Mon Sep 21 2020

Forecast is in great shape. Only minor tweaks made to hourly
forecasts.

Previous discussion follows....

A cool early morning in progress with light easterly flow/ 07Z
temperatures ranged widely under the ideal radiational cooling
setup...from the lower 40s in a few of our normal cool spots to
the mid 50s in the urban locales.

The broad surface ridge encompassing much of the eastern part of the
country will again serve as the primary influence in yet another
spectacular September day. The ridge aloft centered over the
Tennessee Valley this morning will gradually sink slightly south
through the day in response to a fast moving upper wave tracking
east across the Canadian prairies.

Model soundings and RH progs again show deep subsidence present over
the Ohio Valley throughout the day courtesy of a persistent E/SE
flow through the boundary layer. This will maintain dry weather and
generally cloudfree skies again today. One change in the sky though
will be a gradual return of the smoke layer aloft being transported
across the country from the ongoing fires in California and Oregon.
A return to a hazier sky will increase over the northern half of
central Indiana this afternoon as a result. The fire weather risk
appears lower today than Sunday as winds will be weaker and subtle
moisture advection should keep RH values higher as well.

Temps...continuing trend of going a few degrees above the model
blend as the dry ground influences warming. Mid to upper 70s appear
quite reasonable for afternoon highs.

&&

.SHORT TERM /Tonight through Wednesday Night/...
Issued at 255 AM EDT Mon Sep 21 2020

Forecast challenges focus on temperatures throughout the short term
and the potential for an increase in clouds by late Wednesday as
moisture from the remnants of Beta are drawn north into the Ohio
Valley.

The strong surface ridge will remain the primary feature dominating
the weather regime through Wednesday across the region. Tropical
Storm Beta is expected to make landfall on the Texas coast Tuesday
morning before drifting northeast into the lower Mississippi Valley
through midweek. While the deeper moisture will remain south of the
area...the remnant upper level circulation will lift into the Ozarks
by Wednesday morning prior to shifting E/NE into the lower Ohio
Valley by early Thursday.

Dry weather and mainly clear skies will continue under the influence
of the surface ridge through Tuesday night. The smoke layer aloft is
likely to become more prevalent across the area Tuesday based on the
plume forecast...lending to a return to the hazy...milky white sky
experienced last week. Mid and high level clouds will increase from
the southwest as the upper wave approaches on Wednesday...but model
soundings show a noticeable lack of moisture through the boundary
layer. A few light showers may slip into the lower Wabash Valley
early Thursday as the wave aloft moves into the region...but
trending drier than model guidance considering the dry antecedent
conditions over central Indiana and that lack of low level moisture.

Temps...seasonable weather is expected through the short term with
highs in the mid and upper 70s both Tuesday and Wednesday.
Persistence is the way to go with low level thermals supporting
highs a couple degrees warmer than the blend. Lows will again be in
the 40s in outlying areas tonight as another solid setup for
radiational cooling exists. Lows primarily in the 50s are expected
Tuesday and Wednesday nights.

&&

.LONG TERM /Thursday through Sunday/...
Issued at 234 AM EDT Mon Sep 21 2020

Ensembles indicate weak upper troughing can be expected over the
Ohio Valley early in the extended, with the flow becoming more
progressive by next weekend. A potentially stronger trough may
develop nearby by the end of the period.

There remains a few ensemble members that suggest a small
precipitation threat over the southern zones Thursday and possibly
into Thursday night, as the remnants of a tropical low drift
through the Tennessee Valley. Will hold onto the current chance
PoPs over the south on Thursday for now, but at this time the
precipitation potential continues to look small.

A large spread among the ensembles exists with respect to the
weekend system, ranging from a more progressive and weaker
trough, to a stronger and more amplified one. Will bring in PoPs
for next Saturday and Sunday to cover the range of solutions with
this next system.

&&

.AVIATION (Discussion for the 211500Z TAF Update)...
Issued at 1026 AM EDT Mon Sep 21 2020

Bumped up winds and added some high clouds.

Previous discussion follows....

No significant cloud cover and unrestricted visibility expected
at the terminals today. Surface winds 100-120 degrees at 4-7 kts
this morning will veer a bit towards 130-150 degrees at 8-11 kts
by midday.

&&

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

$$

SYNOPSIS...Ryan
NEAR TERM...Ryan/50
SHORT TERM...Ryan
LONG TERM....JAS
AVIATION...JAS/50


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