185
FXUS63 KIND 130428
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1228 AM EDT Mon May 13 2024

.KEY MESSAGES...

- Showers and a few thunderstorms expected Monday and Tuesday

- Up to around one inch of rain expected

- Rain chances return Thursday into Friday

&&

.FORECAST UPDATE...
Issued at 1029 PM EDT Sun May 12 2024

The forecast is on track for this evening for Central Indiana.

While mainly clear skies are being observed at this hour, expect
high level clouds to increase into the overnight hours ahead an
approaching trough and associated surface low in Kansas. Clouds will
be on the increase and continue to thicken Monday morning; however
guidance has continued the trend of slowing down the arrival time of
precipitation until around or after the 18-21z timeframe, giving
more time for surface heating. Current thoughts are that Monday will
be mainly dry for most of Central Indiana, with Western Indiana
being the first area to see scattered showers and thunderstorms
later afternoon and evening. Very dry conditions in the lowest 3km
of the boundary layer likely will limit overall coverage of
convective activity, especially if daytime heating leads to deep
mixing, further drying out the lower levels. With this in mind, going
a little above guidance for highs tomorrow in the upper 70s and
lower 80s. Steep low level lapse rates and deeper mixing may also
result in gusts of 15-20 mph during the late morning to afternoon
hours tomorrow as well. Any convective activity tomorrow evening and
into tomorrow night is expected to remain sub-severe due to low
instability values and weak shear.

&&

.SHORT TERM (This evening through Monday)...
Issued at 216 PM EDT Sun May 12 2024

Rest of This Afternoon...

Plentiful sunshine will continue through much of the afternoon with
upper ridging across central Indiana. Some high clouds will arrive
later, and a few mid clouds will accompany them.

Tonight...

The upper ridge will slide across the area tonight. An upper level
system will move into the Plains by late tonight.

Clouds will increase during the night from the system to the west. A
few showers may try to sneak into the far western forecast area very
late tonight ahead of the system, but lingering dry air along with
subsidence from the upper ridge should keep central Indiana dry.

Southwest winds and the increasing cloud cover will keep
temperatures warmer than Saturday night, with lows in the middle 50s
common.

Monday...

The upper system will continue its approach from the west, but the
best forcing and moisture will remain west of the area. Even the
limited moisture will take a while to arrive.

Still, there will be some isentropic lift moving in, mainly during
the afternoon hours. This will be enough to go with mainly chance
PoPs, especially late in the day. Moisture might be deep enough for
some likely category PoPs in the southwest near the end of the
period (after 22Z or so). Rainfall amounts will be light.

Temperatures could get near 80 degrees if thicker clouds hold off
for long enough.

&&

.LONG TERM (Monday night through Sunday)...
Issued at 216 PM EDT Sun May 12 2024

The subtropical jet is modeled to amplify over our region Monday
night into Tuesday preceding and eastward-moving shortwave trough.
IVT and PWAT anomalies show broad but modest northward moisture
surge with this system. Timing of initial richer moisture and warm
advection ascent peaking will be Monday early-mid evening. This will
be followed by a period of ascent with the main trough/vorticity
maxima that will be positioned and paced in such a way that it
should force additional precipitation through Tuesday and into
Tuesday night.

Multi-model ensemble model data has around 0.75-1.00 inch storm
total QPF with few members at or above 1.5 and some under 0.50. The
upper end seems to be conditional on convective elements which will
more than likely be limited given weak midlevel lapse rates. If the
dry conveyor belt is optimally positioned over the area and/or the
deformation precipitation band under-achieves as it departs, the
lower end (i.e., 10-25th percentile) precipitation amounts may be
more favored.

There may be opportunities in subsequent forecast updates to add
more precision for possible dry periods early Tuesday after the
initial warm advection precipitation band.

On Wednesday, there should be enough of a push of drier continental
air to decrease clouds and hold temperatures near mid-May climo.

Ridge position and increased warm advection preceding the next
system should push us to around +5 temperature anomalies Thursday,
with increasing clouds.

Thursday through the weekend, the synoptic pattern still features
split progressive flow. These are notoriously lower predictability
patterns and spaghetti plots do show increasing chaos. Models seem
to vary with magnitude of lead wave and initial precipitation
Thursday night, and how quickly precipitation departs Saturday. At
this time, models indicate a CAPE/shear parameter space that isn`t
favorable for organized severe, and a precipitation
duration/magnitude signal that isn`t supportive of flooding.

This isn`t a pattern that`s effective at dislodging higher latitude
continental/colder air, so near or just above climo temperatures are
anticipated this weekend.

A low amplitude northern stream wave is shown in models with some
timing variance possibly bringing some precipitation late Sunday or
early Monday.

Day 8-14: The subtropical jet is shown to be weaker in medium range
model guidance during this period, with more phased and stronger mid-
latitude westerlies. There could be one or more organized synoptic-
scale systems during this period with attendant precipitation and
convective severe potnetial, but details are fuzzy. The pattern
indicates perhaps some opportunities for greater day-to-day
temperature variances than will be seen this week given the more
phased flow, though still probably averaging near or above normal
during the period.

&&

.AVIATION (06Z TAF Issuance)...
Issued at 1228 AM EDT Mon May 13 2024

Impacts:

- Showers and embedded storms arrive late this afternoon into tonight
- IFR conditions developing late tonight

Discussion:

Skies remain mostly clear early this morning as the Ohio Valley
continues under the influence of departing high pressure. High
clouds are slowly expanding towards the region and that will
continue through daybreak. Ceilings will gradually lower during the
afternoon with scattered convection expanding into the Wabash Valley
late day. S/SW winds are expected through late today peaking at 10-
15kts this afternoon with sporadic higher gusts.

Showers will become widespread this evening across central Indiana
with the approach of low pressure from the west. Weak elevated
instability supports embedded thunder tonight but coverage alone
will not warrant introducing a VCTS at the terminals at this time.
LOwer ceilings will arrive through the evening...dropping to MVFR
and eventually IFR overnight with lower visibilities in rain.

&&

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

&&

$$

UPDATE...CM
SHORT TERM...50
LONG TERM...BRB
AVIATION...Ryan