Warmest day in just under two weeks today. Enjoy! High pressure fades, and a storm system to the southwest enters the chat later this evening.
(From the NWS Indianapolis):
.KEY MESSAGES…
– Mild today and Monday
– Rain returns tonight into Monday with highest amounts across the
southeast half of central Indiana
– Additional precipitation chances through mid week and another
cooldown as a large trough sweeps into the area. A few snowflakes
cannot be ruled out late Tuesday
.SHORT TERM (Today and Tonight)…
Issued at 312 AM EST Sun Dec 8 2024
High clouds continue to stream across the region early this morning
within the fast zonal flow regime aloft. Winds have been gusty since
Saturday evening aided in part by a 50+kt low level jet picoting
through the area. Surface gusts have been as high as around 35mph in
some locations but have been tailing off over the last hour or two.
Temperatures have remained up due to the stronger surface flow and
the high clouds. 07Z temps were primarily in the low to mid 40s.
The zonal flow aloft will briefly transition to ridging today
bringing the warmest air to central Indiana in nearly two weeks.
While the day will be pleasant…the approach of a weakening upper
level low from the southwest tonight will mark a quick shift to a
wetter and more unsettled pattern as widespread rain encompasses the
forecast area.
The core of the low level jet is already in the process of shifting
away to the east and as boundary layer winds decrease through the
predawn hours in tandem with a relaxing of the surface pressure
gradient…should see peak wind gusts drop back and perhaps even
diminish entirely for a short period towards daybreak. Current
satellite imagery depicts very nicely the axis of rather dense
cirrus drifting through the region currently. This will press to the
E/SE over the next several hours leaving a thinner cirrus across the
forecast area by or shortly after daybreak. Skies will remain mostly
sunny for much of the day with dry air persisting underneath the
upper level ridging. Southwest winds will be steady at 10-15mph
throughout the day with some potential for periodic higher gusts
this afternoon.
The aforementioned upper low will track quickly out of the southern
Plains by late day with moisture advecting and clouds expanding into
the region from the southwest towards sunset. Isentropic lift
increases by this evening with model soundings showing saturation
within the column by late evening. Rain will expand into the area
from the southwest…and will be initially light and scattered in
coverage as the boundary layer moistens. As the strongest of the
lift arrives by late evening however…anticipate rain will become
widespread and continue for much of the overnight.
The upper low will weaken into an open wave as it moves into the
Ohio Valley overnight…with the trajectories of the deepest
moisture focused for areas near and south of the Ohio River. The
highest rainfall totals will focus across the southeast half of the
forecast area in closer proximity to the deeper moisture plume.
Expect 0.50 to 0.75 inches in these areas by daybreak Monday with
lighter amounts further northwest across the forecast area. Most of
the steadier rain should move east of the forecast area by 12Z
Monday. Lingering moisture within the low levels however will keep a
stout low stratus deck in place with the possibility of some drizzle
as well as drier air advects into the region above the boundary
layer.
Temps…with continued warm advection today and abundant sunshine
for a goo portion of the day…trended temps above guidance with
highs in the low to mid 50s this afternoon. Temperatures will be
kept up by the low clouds and rain tonight…likely dropping no
lower than the mid 40s in most areas.
.LONG TERM (Monday through Saturday)…
Issued at 312 AM EST Sun Dec 8 2024
Central Indiana will be back on the temperature roller coaster a bit
during the long term period. Above normal temperatures will start
off the period but quickly drop back highs near to below freezing
for midweek before returning to near normal by next weekend.
There will be an ongoing short wave system from the start on Monday
as rain is expected to continue for much of the day, with this first
wave of precipitation ending by late evening. Central Indiana will
sit under the larger upper trough through midweek however, leading
to additional precipitation chances during that time. These midweek
precip chances will depend on where the boundary eventually sets up,
which models still lack an agreement on. Still leaning towards it
setting up further SE of the area but due to a lack of confidence,
keeping with PoPs given by guidance. If we see precipitation on
Wednesday, it will likely be as snow, as the cold front is expected
to have passed through by then.
Dry weather and a surface high will move in behind the front. The
cold weather will stick around for a few days while the upper trough
fully exits to the east. Southerly flow will return again by Friday
and a return to more normal temperatures through the weekend. While
there is decent confidence on nearer to normal weekend temps, the
rest of the forecast is unclear at this time due to wide variance in
the models. Keeping PoPs in for now, which come from one global
model being a bit aggressive on weekend precip while the other is
not. Continue to check back to see how the forecast unfolds for
next weekend and beyond.
Discussion:
High clouds have diminished from earlier this morning with skies
mostly clear across the Ohio Valley. The back side of a low level
jet will continue to move away from the region with the ongoing low
level wind shear diminishing over the next few hours. Surface wind
gusts have fallen back from Saturday evening and earlier this
morning as the pressure gradient relaxes.
Ridging aloft and at the surface will keep skies mainly clear for
most of the day with a continue brisk southwest wind at 10-15kts and
sporadic gusts to around 20kts. Moisture will rapidly expand
northeast into the Ohio Valley near sunset with clouds thickening
and lowering through the evening. Rain will develop by mid evening
and persist tonight with ceilings dropping to IFR levels and lower
producing poor conditions for aviators. Winds will back to a more
southerly direction this evening before veering back to southwest
close to daybreak Monday…





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