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000
FXUS63 KIND 210522
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
122 AM EDT Sun Apr 21 2024

.KEY MESSAGES...

- Mostly Cloudy tonight; Cold with Frost possible

- Partly Cloudy and warmer on Sunday

- Widespread frost possible Monday morning.

- Increasing rain chances Tuesday, low chance for thunderstorms

- Temperatures generally near seasonal next week, but brief cooldown
  is possible Wednesday into Thursday

&&

.FORECAST UPDATE...
Issued at 918 PM EDT Sat Apr 20 2024

GOES-16 IR satellite imagery, obs and Hi-Res soundings support
raising cloud cover the rest of the evening especially. The increase
in cloud cover along with winds expected to stay up to 5 knots or so
should keep frost from being a big issue overnight. Raised overnight
lows a degree or two based on the more pessimistic cloud cover.

&&

.SHORT TERM (This evening through Sunday)...
Issued at 243 PM EDT Sat Apr 20 2024

Synopsis:

Surface analysis early this afternoon shows strong high pressure in
place over eastern Montana, Western SD and western NB. A surface
ridge extended southeast from the high, stretching across northern
MO to SW Indiana and Central KY. Cool northwest surface flow was in
place across Central Indiana, along with a moderate pressure
gradient. Dew points were in the dry mid 20s. GOES16 shows clear
skies in place across most of the forecast area. Some CU had
developed across northern Indiana, and some high cloud was blowing
off some convection over the southern plains, spilling into the Ohio
Valley. Aloft, a deep area of low pressure was found east of Hudson
Bay. This feature was providing a nearly zonal westerly flow in
place aloft across Indiana and water vapor imagery showed only
Pacific moisture aloft within that flow.

Tonight...

The mostly clear skies in place across Central Indiana today are
expected to be lost to cloudiness this evening and overnight. Models
suggest the upper flow becomes a bit southwesterly tonight. This
will allow for the advection of mid and high cloud from the Central
and southern plains to arrive across Central Indiana through the
overnight hours. Furthermore, a weak upper trough rotating around
the low is expected to push toward central Indiana providing some
lift well aloft. HRRR suggests the arrival of high clouds in this
manner, arriving this evening before exiting shortly after daybreak
on Sunday. Forecast soundings also trend toward high cloud
saturation with subsidence in place in the lower and middle levels.
Meanwhile at the surface the strong ridging is expected to remain in
place with cool air in place at the surface. Given our cool, dry air
mass, lows in the middle 30s will be expected overnight with light
winds.

This would be an ideal setup fro frost, but with the expected cloud
cover, frost may not form. Confidence on clouds is high, thus
confidence for frost is low. Hence will issue an SPS for isolated
frost overnight. Should the evening shift determine that the cloud
cover will not come to pass, a frost advisory will likely be needed.

Sunday...

The weak upper trough axis is suggested to arrive and pass across
Central Indiana on Sunday. This will quickly usher the mid and high
cloud out of central Indiana by late morning and early afternoon as
subsidence becomes predominate through the entire column. Again
forecast soundings show drying within the column, with some late
afternoon flat topped CU possible due to a mid level inversion when
convective temperatures are reached. The lower levels will remain
under the influence of the strong high pressure system over the
southern plains, along with an associated ridge axis stretching
across the Ohio Valley.

There is some slight warm air advection in place on Sunday
afternoon, thus slightly warmer highs in the middle 50s will be
expected.

&&

.LONG TERM (Sunday night through Saturday)...
Issued at 243 PM EDT Sat Apr 20 2024

Sunday night through Monday...

Quiet weather conditions will persist as surface high pressure and
upper ridging is centered near the central CONUS. Expect one more
cool night before warm air advection from the building ridge leads
to a warm up early next week. Lows dropping into the 30s Monday
morning combined with clear skies and light winds will likely lead
to widespread frost development. Expect surface high pressure to
then shift east on Monday allowing for return flow to warm
temperatures into the 60s.

Monday night onward...

Rain chances return Tuesday as a shortwave trough and associated low
pressure system move across the Great Lakes Region. Subsidence
induced dry air still present across the Mid-South may lend to limit
overall moisture return further north. Guidance shows a narrow
corridor of sufficient moisture return and increasing dynamics from
the approaching system to support rainfall. QPF amounts should
remain light due to a lack of deeper moisture, likely under half an
inch. Weak destabilization could also support a few PM
thunderstorms.

Expect the progressive pattern aloft to help push this system
further east by Tuesday night resulting in drier conditions
returning late. Cold air advection and surface high pressure
building in behind the departing low will allow for quiet weather
conditions to persist through much of Thursday before another
system approaches late next week. Temperatures falling into the
30s Thursday morning leads to some frost concern, though at this
time it appears winds may remain elevated enough to limit this
potential.

Models begin to diverge by late next week which limits forecast
confidence, but there is a general signal for an active pattern to
return. One thing to note, Indianapolis is already in the top 13
for wettest April`s on record. Numerous chances for rainfall
Tuesday, and then again late next week into the weekend will
likely push Indianapolis at least into the top 10 for wettest
April`s on record.

&&

.AVIATION (06Z TAF Issuance)...
Issued at 122 AM EDT Sun Apr 21 2024

Impacts:

- None

Discussion:

~5,000 ft stratus should gradually clear during the pradawn hours.
Cirrus will be periodically observed otherwise. VFR conditions will
prevail. Winds will be steady from the west-northwest generally
below 10 knots.

&&

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

$$

UPDATE...MK
SHORT TERM...Puma
LONG TERM...Melo
AVIATION...BRB