630
FXUS63 KIND 072259
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
559 PM EST Fri Feb 7 2025

.KEY MESSAGES...

- Rain returns late tonight and Saturday, with a brief period of
  freezing rain possible mainly northern half of central Indiana
  through Saturday morning

- Active weather pattern with additional chances for wintry
  precipitation next week

&&

.SHORT TERM (This Evening through Saturday)...
Issued at 318 PM EST Fri Feb 7 2025

High pressure over the region this afternoon providing for quiet and
cool conditions. A lingering axis of mid and high level clouds
persist over far northern counties while a broader and thicker cloud
deck approaches from the southwest. Temps have warmed into the 30s
this afternoon.

As high pressure drifts east into the Mid Atlantic region tonight...
low pressure will kick out into the southern Plains with a warm
front extending E/NE into the Ohio Valley. The surface wave will
track across the area Saturday bringing rain to central Indiana...
but lingering subfreezing temps within the near surface layer late
tonight and Saturday morning present the potential for some mischief
in the form of light freezing rain or drizzle in spots.

Will keep some sun over the next couple hours but the approaching
cloud deck from the southwest will gradually encompass the entire
forecast area by this evening. As the warm front lifts to near the
Ohio River...a subtle increase in lift and moisture will lead to
light rain or drizzle developing across the lower Wabash Valley by
mid evening. Expansion to the northeast across central Indiana will
be slowed by the presence of dry air and subsidence lingering even
into the boundary layer and the overall isentropic lift and forcing
associated with the frontal boundary remaining weak. Low level
moisture profiles remain largely unimpressive until the predawn
hours and even then the easterly flow will limit northward moisture
advection until the arrival of the low level jet to our south and a
subsequent increase in isentropic lift until closer to daybreak
increases the chances for light precip. Even with the increase in
areal coverage...overall amounts should remain light with the
deepest moisture and lift remaining shallow.

The surface temperatures will be the critical component with respect
to rain versus freezing rain or a mixture of both after midnight and
continuing into Saturday morning. Expect temperatures will fall
quickly this evening as the airmass remains dry with lows being
reached by midnight or shortly after. As it stands at this
point...expect much of the northern half of the forecast area will
fall to 32F or below by the early overnight with slowly rising
temperatures thereafter. Begin to introduce pockets of light
freezing rain as the precip chances spread north with temperatures
at or below freezing in most locations north of I-74 by daybreak
Saturday. As temperatures rise further...expect precipitation to
transition to all rain across the entire northern part of the
forecast area by late morning. As low pressure moves up into the
region on Saturday...rain will become widespread before diminishing
by early evening as the system moves off to the east.

There will likely be a 3 to 4 hour period across the northern half
of the area where precipitation will fall as strictly light freezing
rain with overall icing amounts of just a couple hundredths at most.
While this will be enough to create ice on elevated surfaces and
slick spots on roadways...a more widespread and higher impact from
ice is not anticipated. Will put out an SPS to highlight the light
icing.

Temps...as mentioned above...lows will be reached by the end of the
evening before a slow climb into Saturday morning. Low level
thermals support a modest temp gradient from north to south across
the forecast area Saturday...ranging from the mid and upper 30s to
the mid and upper 40s over far southern portions of central Indiana.

&&

.LONG TERM (Saturday Night through Friday)...
Issued at 318 PM EST Fri Feb 7 2025

A transition to a colder and more active pattern is expected this
weekend and into next week. On the global scale, guidance is in good
agreement showing the Arctic Oscillation (AO) turning negative.
During negative phase AO, the polar jet typically weakens and
becomes more amplified. Such jet configurations can lead to arctic
air moving more freely southward, as may be the case next week.
Another large-scale teleconnections, the North Atlantic Oscillation
(NAO), is shown by guidance to be generally neutral with perhaps a
slight trends towards negative. Negative NAO tends to bring about a
blocking pattern which can also lead to a more amplified jet pattern
and thus colder temperatures over the Midwest / Eastern US. However,
the AO turns sharply negative well before the NAO reaches neutral so
our long term weather should be more influenced by the AO. We`ll
likely see the trend towards cooler temperatures but with a more
progressive and active pattern. That is, more storm systems moving
quickly eastward within a wavy jet stream.

Downscaling further, we`ll see the first system of the period arrive
late Monday or early Tuesday. A strong zonal baroclinic zone should
be in place by this point, and most guidance depicts it stretching
from near the Oklahoma Panhandle to southern Missouri to eastern
Kentucky. This zone is a great source of instability for developing
mid-latitude cyclones, so it`ll act as a good indicator of the
preferred storm track in the upcoming active pattern. A track
passing just to our south is conducive for wintry weather here in
Indiana. That`ll likely be the case with the first system as model
soundings show a thermal profile supporting primarily snow for our
area. Though its still a bit early to talk about amounts, guidance
generally shows the system being quite weak and suppressed
southward. Ensemble QPF looks low, and if the system ends up too far
south then snow may fail to reach some of our northern locations
entirely.

The next system looks to arrive Wednesday into Thursday, and may be
a bit more robust. Though differences remain, there is relatively
decent agreement within guidance showing this system passing to our
southeast while intensifying. Such a track is also favorable for
snow across Indiana. We will need to monitor model trends carefully,
as storm track and intensity are likely to be critical in
determining who sees what and how much.

Yet another system is shown by multiple models next weekend, but by
this point model agreement is beginning to diverge and lose
coherency. Still, the pattern described above supports continued
activity through the period...but we will take it one storm at a
time for now. Confidence in temperatures towards the end of next
week becomes more uncertain since they are dependent on how the
aforementioned systems evolve. A stronger system tracking closer to
Indiana, for instance, could pull warmer air northward more than
guidance currently indicates.

&&

.AVIATION (00Z TAF Issuance)...
Issued at 558 PM EST Fri Feb 7 2025

Impacts:

- Scattered light precipitation developing overnight
- A low risk for -FZRA at KLAF/KIND into Saturday morning, with
  best chance at KLAF.
- Poor flying conditions developing Saturday morning with IFR and
  worse after 15Z
- Wind shift to northwest Saturday afternoon

Discussion:

Clouds will gradually lower through the VFR category during the
night. A few sprinkles are possible into the early overnight south,
then some light precipitation will spread north later in the night.

Temperatures at KIND will be marginal for some -FZRA late tonight
into the early daylight hours of Saturday morning. Confidence is not
high enough to include at this time for KIND. However, temperatures
will be a bit cooler at KLAF so mentioned -FZRA in the TAF there.

Readings will warm and change all precipitation to rain as it
becomes more widespread into Saturday afternoon. Conditions will
deteriorate to IFR and worse later Saturday morning into the
afternoon.

&&

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

$$

SHORT TERM...Ryan
LONG TERM...Eckhoff
AVIATION...50