Area Forecast Discussion
Issued by NWS Indianapolis, IN

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000
FXUS63 KIND 171641
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1241 PM EDT Sun Mar 17 2024

.KEY MESSAGES...

- Breezy again today and colder

- Hard freeze likely Sunday Night and Monday night

- Warming trend mid-week and low rain chance by the end of the
  week

&&

.FORECAST UPDATE...
Issued at 916 AM EDT Sun Mar 17 2024

- Becoming Partly Cloudy this afternoon; Cool

Surface analysis late this morning shows a ridge axis across MO,
extending east to Western KY and then northeast along the Ohio
River. This ridge axis was associated with a much larger area of
high pressure that was centered over Saskatchewan, influencing
weather across the plains and into the Ohio valley. Deep low
pressure was found over Quebec. These two systems were providing a
cold northwesterly flow across Central Indiana.  Aloft, water vapor
imagery showed a deep area of low pressure over Ontario and Quebec.
This was resulting in a broad area of cyclonic flow aloft, with a
trough within the northern upper flow dipping across the northern
plains to the Ohio Valley and the middle Atlantic states. GOES16
shows clear skies across the forecast area, but more widespread
cloud cover was found upstream over the upper Midwest. Dew points
across the area were mainly in the lower to middle 20s.

This afternoon the strong high to the northwest is expected to begin
to dive southeast into the northern plains states. This will begin a
strengthening hold on our weather for the next few days. Little
overall change is expected within the upper flow, and subsidence was
in place. Forecast soundings show a dry column, but do suggest that
convective temperatures will be reached and CU development will
occur this afternoon. Thus we will look for skies to become partly
cloudy this afternoon as temps approach the middle 40s.

Strong cold air advection remains in play this afternoon. 850MB
temps are expected to fall to near -9C by the end of the day. Thus
highs in the middle 40s will be expected. A moderate pressure
gradient across the area along with good mixing today will result in
some wind gusts around 25 mph through the afternoon, resulting in
chilly conditions.

&&

.SHORT TERM (Today and tonight)...
Issued at 207 AM EDT Sun Mar 17 2024

Occluded low over Ontario will move east into Quebec today. A low
amplitude shortwave trough embedded within this low has sent a cold
front through central Indiana. Post frontal cold advection will
result in nearly 20 degree temperature change from 24-hours previous
today. Temperature maximums will be in the mid 40s. Although
stronger flow aloft will move east, remaining peripheral enhanced
flow coupled with diurnal mixing and momentum transfer will result
in breezy conditions again today, albeit less than yesterday. Mixing
depth and momentum transfer in short term models suggest 25-30 mph
peak gusts this afternoon.

Modest PBL moisture may result in some diurnal flat cumulus at the
top of the mixed layer beneath subsident capping inversion. Also,
some cirrus may be present from moisture within the subtropical jet
just to our south.

Minimum temperatures late tonight in the mid-upper 20s are expected.
There should be enough MSLP gradient for light wind and mechanical
mixing to keep radiative processes from significantly enhancing the
cold. Thus a blended approach of raw model guidance should suffice
and forecast confidence is high.

&&

.LONG TERM (Monday through Saturday)...
Issued at 207 AM EDT Sun Mar 17 2024

As aforementioned eastward-moving occluded low continues to fill and
weaken, a lagging embedded shortwave trough will amplify and become
dominant. This, along with amplified high-latitude ridging and
blocking to the west will be favorable for an even more dramatic
push of polar air into Indiana by Monday. This will modify some
given the time of year and sun angle, but it should restrict
afternoon temperatures on Monday from rising out of the 30s at most
locations (-15 degree 2-m temperature anomalies).

Steep low level lapse rates and cyclonic low level flow could result
in some flurries or weak convective snow showers especially across
northeast portions of the area Monday. Moisture is quite limited and
measurable amounts are unlikely.

MSLP gradient should still be enough for light winds and mechanical
mixing limiting the radiative cooling process some Monday night.
Nevertheless, the magnitude of the cold advection and standard
radiative component will bring many locations into the mid-20s and
result in a hard freeze. Another negative factor for even colder
temperatures is that a midlevel stratus deck may peak at the minimum
of the diurnal cycle. Frost doesn`t seem likely either night given
less than optimal radiative conditions and magnitude of dry air.

Tuesday through mid-week, northwesterly flow within the active polar
branch is indicated in models, with one perturbation effectively
veering low-level flow and shifting near normal temperatures into
central Indiana. Near normal temperatures will continue into late
week.

A low-amplitude shortwave trough could bring light precipitation
amounts late Thursday into Friday. Ensemble cluster analysis shows
fairly even distribution among model camps within individual
clusters. Some show less QPF than the multi-model mean, and some
show more. Even though richer moisture will be confined to lower
latitudes and the strongest QPF signal is within the subtropical jet
to our south, we feel modest moisture and ascent with the low
amplitude wave will be enough to justify at least climo PoP, which
is about 30 percent for a 12-hour period this time of year.

Day 8-14: EOF within the ensemble cluster analysis still indicates
timing differences, but there is increasing signal in EPS and GEFS
of phasing and a stronger mid-latitude system toward the beginning
of the week of the 25th. This would potentially lead to warm
advection and above normal temperatures followed by a noteworthy
precipitation event early the week of the 25th.

&&

.AVIATION (18Z TAF Issuance)...
Issued at 1241 PM EDT Sun Mar 17 2024

Impacts:

- Wind gusts around 25 knots this afternoon and again on Monday
afternoon.
- VFR conditions are expected

Discussion:

High pressure over the plains is expected to build across Indiana
through this TAF period. This will allow for continued VFR
conditions. GOES16 shoes diurnal CU across the area, and this is
expected to diminish as heating is lost this evening. Forecast
soundings show a dry column persisting overnight, leading to mostly
clear skies.

On Monday, again forecast soundings show convective temperatures
being reached, leading to diurnal CU development. An upper level
trough axis is expected to pass during the afternoon hours, but
limited moisture within the lower levels will result in only
sprinkles/flurries/virga.

Once again on Monday, a moderate pressure gradient across the area
will lead to wind gusts around 25 knots.

&&

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

$$

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


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