175
FXUS63 KIND 052350
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
650 PM EST Wed Feb 5 2025

.KEY MESSAGES...

- Winter Weather Advisory for freezing rain across our north and
  northeastern counties. Up to 0.1" ice accretion possible.

- All precipitation changing to rain by around 4am.

- Thunderstorms expected overnight with small hail possible.

- Next round of rain with a mix of snow/freezing rain Saturday

&&

.MESOSCALE UPDATE...
Issued at 650 PM EST Wed Feb 5 2025

First wave of widespread showers has moved to the far northeast and
eastern portions of central Indiana, but more are developing in
Illinois with the next wave of forcing.

Air temperatures remain near or below freezing near and along the I-
74 corridor. Elevated icing has been reported in the east and
southeast forecast area. Given the reports and current temperatures,
expanded the Advisory to include Hancock, Shelby, and Rush Counties.

Road temperatures remain above freezing which has helped mitigate
impacts. However, this may change in portions of the northern and
eastern forecast area for a bit this evening as heating has been
lost since the sun has set.

Warm advection should improve conditions from the south later this
evening into the overnight.

&&

.SHORT TERM (This evening through Thursday)...
Issued at 300 PM EST Wed Feb 5 2025

Issued a Winter Weather Advisory for freezing rain this evening
across our northern and northeastern counties.

FREEZING RAIN POTENTIAL

Guidance has come into better agreement regarding timing and
placement of freezing rain and associated ice accretions this
evening. Some of the warmer models, namely the RAP/HRRR, have
trended a bit cooler in these areas as well. Confidence has thus
increased enough to issue a Winter Weather Advisory for locations
north and east of Indianapolis. Further south and west, temperatures
may support a brief period of freezing rain at onset, but should
warm up quickly enough to mitigate impacts to below advisory
threshold.

Focusing on our northeastern counties, temperatures are currently in
the low 30s and should remain there for the rest of the day. Dew
points are in the low to mid 20s and are expected to remain there
until precipitation onset. This would lead to evaporational cooling
for the first couple hours of precip allowing temperatures to hold
steady near or just below freezing. Some rain has advanced into
central Indiana as of 18-19z and surface temps have indeed cooled to
around 32 degrees or so. Enough solar insolation is making it
through the clouds to prevent FZRA so far. Ground temperatures are
in the mid 30s, so primary concerns overnight are for hazardous
travel are elevated surfaces such as overpasses. Slick spots on
untreated local roads are still possible, as ground temperatures are
near enough to freezing that a few spots may be supportive of ice.
Ice accretions on trees and powerlines are likely as well.

Some factors that could limit the ice accretion threat are as
follows: surface temperatures are quite marginal. Even the coldest
members of guidance show values between 30 and 32 degrees. Latent
heat of fusion may be enough to overcome this in areas that are
closer to 32. How much wet-bulbing occurs to counteract this is
critical. Second, winds become southeasterly with warm air advection
at the surface. This will act to limit the amount of time freezing
rain occurs and thus total ice accretion. Third, ground temperatures
as mentioned above are quite marginal. This would limit the overall
coverage of advisory-level ice accretions on road surfaces. Fourth,
and this mainly concerns areas further northwest...is just a lack of
total precipitation. Total precipitation may end up being light
enough to prevent advisory-level ice accretions even if optimal
surface temps are achieved.

With that said, any amount of freezing rain is potentially hazardous
and given that up to a tenth of an inch is possible, and guidance is
in better agreement...felt an advisory is justified.

THUNDERSTORM POTENTIAL

Guidance is showing between 500 to 1000 J/Kg CAPE, elevated above a
strong surface inversion. Additionally, strong shear between 50 to
60 knots is present in the layer containing the CAPE. Hodographs are
long and straight, and given strong surface stability, our primary
convective threat is small hail within the strongest cells. Severe
hail is not expected, as the CAPE profile is thin and relatively
shallow. Still, would not be surprised to see some small hail along
with lightning and thunder overnight. Best chance of elevated
thunderstorms is between 00z and 06z.

REMAINDER OF THE FORECAST PERIOD

Aside from  the above, some wind gusts up to 25 knots are possible
early Thursday as the system responsible pulls away. Hi-resolution
guidance may be overdoing gusts a bit given the expected magnitude
of the PBL inversion. Continued warm advection at the surface should
allow highs to bump into the low 40s on Thursday.

&&

.LONG TERM (Thursday night through Wednesday)...
Issued at 300 PM EST Wed Feb 5 2025

Thursday Night Through Saturday.

Precipitation is expected to fully wrap up by Thursday night with
dry and quiet weather through Friday night. Surface winds will
gradually become easterly again ahead of the next impactful weather
system that is expected to impact central Indiana Saturday into
Saturday night. A surface low is expected to move into the Plains
Saturday morning before undergoing cyclogenesis as it tracks
eastward with fairly good model agreement in a track that roughly
follows the Ohio River.

The 850mb low will be displaced a bit further north which will lead
to the bulk of the LLJ moisture advection to occur across the
southern half of the state and allow for periods of moderate rain
with the potential for around a half inch of QPF. Temperatures
towards the northern third of the state will be just cold enough
initially for brief freezing rain or snow, but the general trend has
been to faster WAA which keeps the better chance for freezing rain
to remain north of the forecast area. As the day progresses
temperatures will continue to rise with the highs expected after
sunset.

Sunday Through Wednesday.

Colder air will quickly then move in late Saturday night into Sunday
with northwesterly to northerly flow. Precipitation chances look
minimal Sunday into Monday with near normal temperatures as rain
remains along and south of the Ohio River. A more substantial
upper level system looks like towards the middle of the week but
there remains significant model differences which keeps forecast
confidence low. Models have generally trended warmer over the last
24 hours which lowers the potential for snow, but expect to see
additional changes in the coming days.

&&

.AVIATION (00Z TAF Issuance)...
Issued at 602 PM EST Wed Feb 5 2025

Impacts:

- Poor flying conditions through at least Thu morning
- IFR and worse conditions common through around 15Z Thu
- Periods of -FZRA possible at KLAF and KIND through 03Z
- A few TSRA possible at all but KLAF into the overnight
- Non-convective LLWS 06Z to around 10Z
- Winds veering from E to W by 12Z

Discussion:

Periods of rain will continue through 06Z with some drizzle and fog
afterward into 12Z Thursday. Some light freezing rain will be
possible at KIND/KLAF through about 03Z. Impacts will be mainly on
elevated surfaces.

A few thunderstorms are possible at all but KLAF tonight, with
KHUF/KBMG the most likely to see any.

Rain will diminish overnight but drizzle and fog will keep
conditions poor. Improvement is expected Thursday afternoon.


&&

.IND WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 4 AM EST Thursday for INZ021-
029>031-038>042-048-049-056-057.

&&

$$

MESOSCALE...50
SHORT TERM...Eckhoff
LONG TERM...White
AVIATION...50