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000
FXUS63 KIND 181840
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
240 PM EDT Thu Apr 18 2024

.KEY MESSAGES...

- Severe storms and locally heavy rain are possible this evening
  into tonight.
- Colder but dry Friday through Monday. Some frost potential mainly
  north Sunday morning.

&&

.SHORT TERM (Today and tonight)...
Issued at 258 AM EDT Thu Apr 18 2024

Latest surface observations show surface high pressure building
into the region. Winds have decreased dramatically from earlier this
evening, and are now becoming light and variable. Skies have cleared
and temperatures are falling quickly. Ideal radiational cooling
potential will persist through sunrise and a couple more degrees of
cooling are likely. A few locations may see lows in the upper 40s by
dawn.

After sunrise, winds gradually take on a southeasterly component as
surface low pressure develops to our west. Yesterday`s cold front
did not make much progress southward, and rich moisture will advect
back north through the day as the low strengthens. Convergence along
the system`s cold front combined with favorable dynamics aloft will
set the stage for showers and thunderstorms by evening. Some of
these storms may becomes severe, especially from IND southwestward.
More details below.

Regarding severe weather potential, we`ll start with the bigger
picture. Much of the driving energy for today`s system lies in the
mid-levels...namely, a potent mid-level vort max and associated
speed max. Closer to the surface, a modest low-level jet will help
instability and moisture advect back into the region. The primary
axis of instability looks to be quite narrow, given the short amount
of time taken to bring it back north. Still, enough instability is
present to support convective potential into the overnight hours.
Effective shear over 30kt could lead to some convective organization
and thus severe weather.

As for hazards, CAMs are in relatively good agreement on showing
convection organizing into a line/broken line. Given the primary
forcing mechanism being the surface cold front, this makes sense.
The line may race ahead of the front during the course of the
evening and lead to primarily a damaging wind threat. Model
soundings show steep lapse rates (6.5-7.5 C/km) but relatively
skinny CAPE...still, an isolated instance of large hail is possible
especially earlier in the day when storms are still discrete. The
hail threat may be more into Illinois before becoming mainly a wind
threat into Indiana. This depends on how fast the transition to
linear mode occurs. The tornado threat appears to be minimal and far
to the southwest where better low-level instability and shear
exists. As such near our southwestern border the line of storms will
need to be watched mainly for QLCS spin ups...even though the treat
is low. To summarize, the primary convective hazard is strong wind
gusts with lower threats of hail and embedded tornadoes. Best
timing places storms arriving at the Illinois/Indiana state line
after about 6-8pm.

Showers, storms, and the cold front should be mostly through the CWA
by 12z Friday. Strong northwesterly winds are likely behind this
boundary with gusts between 30-35kt at times. Winds diminish quickly
during the day on Friday as the system departs rapidly to the east.
We`ll be left with a much cooler and dry day along with high cirrus
clouds passing through at times.

&&

.LONG TERM (Friday through Wednesday)...
Issued at 258 AM EDT Thu Apr 18 2024

Friday through Monday...

Central Indiana will remain on the southern side of a large upper
trough through much of the period. This will keep most moisture
confined to south of the area. A few smaller troughs will rotate
through the large one.

At the surface, high pressure will remain in control for much of the
period. The surface high plus lack of significant moisture will lead
to dry conditions.

Colder air will remain in place cold advection continues at times.
Highs will be in the 50s to lower 60s, with lows in the 40s Saturday
morning and in the mid to upper 30s Sunday and Monday mornings. The
coldest temperatures are expected Sunday morning and winds will be
light. However, clouds may linger, potentially inhibiting frost
formation. Will have to keep an eye on it.

Tuesday and beyond...

A stronger upper wave will move in around Tuesday, and this one
looks to have more moisture with it. There remains some timing
uncertainties with the system though. Will go no higher than chance
category PoPs due to the uncertainty.

For now, Wednesday looks dry, but that could change if timing of the
aforementioned system changes.

Temperatures will be closer to, but still below, normal.

&&

.AVIATION (18Z TAF Issuance)...
Issued at 240 PM EDT Thu Apr 18 2024

Impacts:

- Thunderstorms moving in 01-02Z and lasting through 06-09Z

- MVFR ceilings to move in after 03z and IFR possible from 05-10Z,
visibilities may drop within storms

- Winds sustained at 10 kts or higher from 00z and on with gusts up
to 25 kts possible at times with storms

Discussion:

VFR conditions expected through early evening.

Light and variable winds will start off the TAF period but are
expected to increase this evening with the approach of a low
pressure system. Winds will be southerly to southwesterly ahead of
the system but will shift northwesterly during the late overnight
hours and through tomorrow.

High-level clouds will continue to increase through the day as the
front approaches. By about 01-02z, showers and thunderstorms will
begin working their way in from the west. Expect MVFR conditions
from around 03 to 13Z with several hours of IFR ceilings possible
with the passage of the storms and cold front. Visibilities may drop
as well with the storms.

The front should be through Indiana by 10z at the latest, and
conditions will improve to VFR by the morning.

&&

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

$$

SHORT TERM...Eckhoff
LONG TERM...50
AVIATION...KF