360
FXUS63 KIND 220203
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1003 PM EDT Tue May 21 2024

.KEY MESSAGES...

- Warm and humid through this evening.

- Isolated severe storms possible late tonight and again Wednesday
  afternoon and evening.

- Additional chances for rain and storms through early next week.

&&

.FORECAST UPDATE...
Issued at 1002 PM EDT Tue May 21 2024

Current surface analysis shows a strong low pressure system centered
near eastern Minnesota with thunderstorms ongoing along an attendant
cold front which stretches from the upper midwest to portions of
AR/OK. Most CAMs suggest a weakening line of thunderstorms along the
approaching front will move into central IN after midnight. Modest
instability and deep-layer shear suggest loosely organized storms
are possible, mainly across far western portions of the area.
Isolated damaging wind gusts cannot be ruled out as these storms
move in.

Expect the line of storms to weaken as it progresses eastward and
should move out before daybreak. POPs were slightly delayed since
latest guidance shows precipitation moving in around 1am. Southerly
flow and increased cloud cover will keep temperatures mild overnight
in the upper 60s.

&&

.SHORT TERM (This Evening through Wednesday)...
Issued at 300 PM EDT Tue May 21 2024

This Evening and Tonight...

Another hot and humid day across Central Indiana as the region is
placed firmly within the warm sector of an area of low pressure
moving NE through Iowa. Satellite imagery this afternoon shows a cu
field over the whole state with widely scattered convective showers
popping up in SE Indiana. IND ACARs sounding show deep mixing this
afternoon up to 2km agl bringing gusty winds to 25 mph down to the
surface. Low to mid level moisture advection evident on regional
soundings has inhibited dry air from mixing down to the surface
with observations reporting dew points in the low to mid 60s.

Focus shifts to the storm threat tonight into the early morning
hours Wednesday as a weakening line of storms approaches Indiana
from the north and west in the 03-08z timeframe. The main area of
low pressure is forecast to eject NE into northern Minnesota tonight
while the main upper level jet energy holds back in the Central
Plains. With the best forcing for ascent and dynamics well to the
west, it is likely that this line of storms will be in a weakening
phase as it crosses the state. Despite a strengthening 45-55kt low
level jet over the region, waning low level instability and lack of
upper level support do not make for a favorable set up strong to
severe storms during the overnight hours across the region. In fact,
some hi-res guidance today suggests the line may break apart as it
approaches the I-65 corridor, leaving portions of East Central
Indiana fairly dry.

Highest confidence for storms remains across portions of Western
Indiana where a few storms could be strong. There likely will be
just enough surface based CAPE around 1000 j/kg in Western Indiana
along with 0-3km and 0-6km shear in the 25-40 kt range to support a
marginal damaging wind threat. Low level hodographs appear to be
strongly curved; however with storms weakening, do not think there
will be much of a tornado threat overnight unless a segment of the
line shows deviant motion or a transverse wave spins up something
quick. Confidence on that scenario is very low. Storms weaken as
they march eastward across the state with low confidence in even a
lightning threat for East Central Indiana. QPF will likely be
highest for Western Indiana with upwards of a half inch along the
IL/IN border and under 0.20" in East Central Indiana.

Wednesday...

Into Early Afternoon Wednesday...

Expect low clouds in the wake of the weakening line of storms
Wednesday morning with guidance hinting at lower stratus being
stubborn to mix out into the early afternoon hours near the front.

The actual front is expected to set up south of I-70 across Southern
Indiana by midday Wednesday with convective initiation right along
it. The southward trend in the location of the front is seen on all
short term and hi-res guidance keeping the main storm and severe
threat in South Central Indiana and points south. Clouds along the
front will likely keep instability down, so not expecting much if
any convection into mid-afternoon. Continued the trend of lowering
PoPs for the northern 2/3 of Central Indiana through the day
tomorrow. Much of Central Indiana will likely remain partly to
mostly cloud through the day with temperatures in the 70s.

Will have to watch observations and satellite closely tomorrow
afternoon to determine where the frontal boundary sets up and if
enough clearing takes place south of it to support convective
activity. A SW to NE oriented upper level jet streak approaches from
the west tomorrow afternoon; however low level flow considerably
weakens. While there is the potential for an isolated strong storm
to form with damaging winds and hail in South Central Indiana
tomorrow afternoon and evening, weak low level shear and slower
storm motion may lead to more of a flooding threat if storms train
and backbuild off of each other. The best threat for any severe
weather and flooding does appear to be south of the forecast area,
but as mentioned before, will watch observations closely tomorrow
afternoon to see where exactly the frontal boundary sets up.

&&

.LONG TERM (Wednesday Night through Tuesday)...
Issued at 300 PM EDT Tue May 21 2024

The frontal boundary will settle over the lower Ohio Valley for late
week as a progressive quasi-zonal flow aloft sets up over the
region. The presence of the front to our south and weak disturbances
tracking through the zonal flow will maintain periodic chances for
scattered convection into the weekend but overall model trends have
shifted drier into Saturday.

More substantial upper level energy will be confined well to our
northwest with the bulk of the unsettled conditions remaining over
western Canada into the northern Plains and upper Midwest through
the end of the week. A more potent upper wave will eject out into
the Plains late Saturday and approach the region Sunday with an
attendant surface wave. This will be the onset of an increasingly
unsettled pattern for the region with additional upper waves
tracking into the region and buckling heights aloft as a ridge
develops over the western states for early next week.

Wednesday Night through Saturday Night

The focus for any ongoing convection Wednesday evening will be
across southern Indiana and more likely in the vicinity of the Ohio
River and points south as the frontal boundary interacts with a
modestly unstable airmass over Kentucky. The front will remain quasi-
stationary through late week somewhere near or just south of the
Ohio River...likely close enough to warrant a continued threat for
scattered convection over southern portions of the forecast area
Thursday and the first part of Friday. Drier air and subsidence
associated with high pressure across the Great Lakes will limit
northward extent of any rain with an increasing likelihood that many
locations north of I-70 see only a few showers or storms through
midday Friday.

A stronger upper low pivoting through the upper Midwest Friday will
aid in drawing deeper moisture back north into the region by Friday
night ahead of another front. A weak wave aloft ahead of this
feature may be enough to generate storms Friday afternoon with
additional convection Friday night as the front swings across the
region. The bulk of the deeper forcing aloft will remain displaced
well to the northwest of central Indiana on Friday night however...
resulting in storms likely to be in a weakening state Friday night.
High pressure will then quickly return for Saturday with a lower
threat for any rain and an overall pleasant day to start the holiday
weekend. Temperatures will remain seasonable through Saturday with
highs ranging from the mid 70s to lower 80s.

Sunday through Tuesday

The last few runs of the extended model suite has place an
increasing focus on an upper wave rounding the western Canadian
upper trough and then kicking east through the central Plains and
into the mid Mississippi Valley over the weekend. In tandem with the
upper wave is the development of a surface low over the High Plains
Saturday evening that will track east and approach the region for
Sunday. While the various models and ensemble members vary in
strength and track of the surface low at this point...there is a
notable signal across the model suite of the feature in the vicinity
of the Ohio and mid Mississippi Valleys by Sunday afternoon with a
warm front in the region as well.

The threat for rain and thunderstorms is growing for Sunday into
Sunday night with the aforementioned system tracking into the region
and considering the potential strength of the surface low...an
increasing threat for severe weather is on the table as well with
ample shear and instability present over parts of the region. Remain
too far out to delve into the specifics yet...but the recent model
trends are not looking conducive at all for outdoor activities on
Sunday with growing potential for higher impact convection in the
region as well. Stay tuned.

An upper level low will follow for early next week as the overall
pattern aloft gradually transitions to a more amplified regime with
a ridge west and a trough east. This will bring additional rounds of
rain and storms through the middle of next week along with a cool
down as highs fall back mainly into the 70s.

&&

.AVIATION (00Z TAF Issuance)...
Issued at 734 PM EDT Tue May 21 2024

Impacts:

- Southerly wind gusts around 18-26 kts through this evening

- Showers and a few storms possible 05z-09z

- MVFR cigs possible at times 09z-16z Wednesday

Discussion:

Mainly VFR conditions will prevail through 04z tonight as central
Indiana sits under the tightening gradient between broad high
pressure well to the east and a deepening surface low centered near
southeast Minnesota.

A weakening line of storms associated with the deepening low will
likely enter Indiana from the west after 05z and track eastward
through the state from around 05-09z. Periods of lightning, heavy
rain, and erratic wind directions and speeds are possible with the
line of storms. Expect MVFR cigs to develop on the backside of the
line through the early morning hours before daytime heating helps
the cloud deck lift towards midday.

Expect gusty SSW winds up to 26 kts to continue through sunset
before diminishing some. Sporadic higher gusts will be possible in
thunderstorms overnight. Sustained winds will likely remain elevated
overnight in the 10-15 kt range.


&&

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

$$

UPDATE...Melo
SHORT TERM...CM
LONG TERM...Ryan
AVIATION...Melo