Indiana’s Weather For Sunday

HEADLINES
– Rivers are expected have already reached or are expected to reach moderate to major flood stage in Central Indiana.
– Widespread, significant river flooding continuing into the week.
– Frost and freeze conditions likely Monday night and Tuesday night.

TODAY’S MAP

NWS TECHNICAL DISCUSSION

The surface cold front is now well south of central Indiana with
modest N/NE flow across the region. This will keep conditions cool,
but there will still be precipitation chances despite increasing
low level subsidence as WAA continue to occur in the 800-700mb
layer. This will create a strong temperature inversion aloft
leading to widespread cloud cover and scattered showers. Deep
layer moisture will not be present with this round of showers,
leading to much lower QPF values than the days prior. Temperatures
are expected to remain fairly stagnant today with highs in the
mid 40s, however it will feel even colder within an 8-12mph NE
wind with "feels-like" temps in the 30s.

A few models are trying to show some mixed precipitation within
showers this afternoon, but with the strong temperature inversion
near freezing and temperatures in the 40s as precipitation onset,
wetbulbing likely wouldn`t be enough for snow to remain frozen
prior to reaching the surface. For now, all rain will be the
forecast for central Indiana.

The Flood Watch and Flood Warnings continue across most of Central
Indiana early this morning. Currently do not plan on extending the
flood watch as rainfall rates have diminished significantly and
rainfall today is expected to be less than 0.5". Major stem rivers
will remain elevated above flood stage for the next week or two and
will issue river flood products accordingly.

&&

.LONG TERM (Monday through Saturday)...
Issued at 310 AM EDT Sun Apr 6 2025

A large-scale pattern change will occur in the long term as a quick
moving short wave will organized a push of much colder air into the
Ohio Valley late Monday. The slow-moving trough that has been
bringing us round after round of rainfall finally slides eastward
Sunday night. Still the mid level baroclinic zone and corresponding
jet streaks will aid in the creation of a modest shortwave. This
wave would not be impactful typically, but the cold air behind the
system and associated cold front that moves through late Monday will
be rather sharp. High-res models are showing temperatures dropping
20+ degrees Monday evening, with further diurnal cooling Monday
night pushing temperatures likely below freezing. Due to the
abnormal warmth and moisture throughout late March and early April,
growing seasons have already begun. For that reason a Freeze Watch
has been issued for Monday night.

Behind the cold front on Monday, much drier air is anticipated to
push into central Indiana. However, there could be a brief period of
time where moisture decrease lags behind temperature decreases with
scattered light snow showers. If this does occur, accumulation is not
expected, but something to note nonetheless. Winds may be gusty
behind the front as well, perhaps up to 30-35mph.

Surface high pressure quickly builds in Monday evening, with
diminishing winds and clearing skies. The center of the high doesn`t
arrive until Tuesday, however, and there may be enough cyclonic flow
regionally to promote lingering stratocumulus through the night and
into Tuesday morning. Models tends to be a bit too optimistic with
stratocu in these scenarios by clearing things up too quickly. We
will retain some cloud cover in the forecast, especially northeast
of Indianapolis, for now. Questions regarding cloud cover translate
into questions regarding low temperatures, since lows will partly
depend on the radiative component in addition to the advective.
Should skies end up clearer, then we can expect values as low as the
low 20s. Conversely, cloud cover may keep lows closer to 30.
Regardless, sub-freezing temperatures are expected with widespread
frost and hard freeze conditions.

Sub-freezing lows are possible again Tuesday night, but by 00z that
evening the core of the upper trough will be exiting to the east.
Modest warm air advection begins and continues into the night as
winds turn westerly. Lows in the 20s are possible, especially east
of I-65. There remains some differences within guidance with how
fast the surface high departs. Slower departure favors colder temps
as ideal radiative cooling conditions linger into the night.

Our next chance of precipitation arrive on Wednesday evening or
early Thursday as a moisture-starved system zips by to our north.
Guidance shows some weak convective instability, which combined with
frontal forcing could lead to scattered showers and perhaps a
thunderstorm. Additionally, some breezy southwesterly winds are
possible immediately ahead of the system and its attendant cold
front Wednesday afternoon. Cold advection returns after Thursday as
northwesterly flow aloft and east coast troughing take hold.
Additional overnights with frost potential are possible towards the
end of the week and into next weekend.

NWS CHARTS FOR TODAY/TONIGHT