IND issues Area Forecast Discussion (AFD) at Oct 10, 9:59 PM EDT982
FXUS63 KIND 110159
AFDIND
Area Forecast Discussion
National Weather Service Indianapolis IN
959 PM EDT Thu Oct 10 2024
.KEY MESSAGES...
- Clear and pleasant; Above normal temperatures Friday and Saturday
- Coldest air of the Fall arrives early next week with frost
possible on a couple mornings
- Scattered showers possible Saturday night, otherwise dry
conditions will continue.
&&
.FORECAST UPDATE...
Issued at 958 PM EDT Thu Oct 10 2024
Another nearly calm and clear night across central Indiana is
allowing readings to quickly cool...courtesy of relatively very low
dewpoints in the 40s to upper 30s. As of 935PM current temperatures
ranged from the low 50s in Anderson, Crawfordsville, Mount Comfort
and Zionsville...to the low 60s in Lafayette, Terre Haute and
Indianapolis. Surface high pressure will continue to plunge from
the eastern Great Lakes to the southern Appalachians by dawn Friday.
This shift will veer local surface flow tonight through easterly
directions, while a very modest gradient holds winds under mainly 5
mph. Readings will drop to seasonably cool levels with mid to upper
40s the rule by daybreak...while dewpoint-depression minimums of 5-
10 degrees discourage any organized fog.
&&
.SHORT TERM (This evening through Friday)...
Issued at 236 PM EDT Thu Oct 10 2024
Synopsis:
Surface analysis early this afternoon shows strong high pressure in
place over Michigan. This high was in control of the weather across
Central Indiana, providing dry easterly lower level flow. GOES16
shows clear skies across the state and the region. Aloft, water
vapor imagery shows ridging in place, stretching from eastern CO to
western Ontario. This was resulting in northwest flow aloft with
ongoing subsidence across Indiana. Dew points were in the
comfortable 40s.
Tonight and Friday -
The previously mentioned strong ridging aloft and the associated
ridge axis is expected to push to Indiana overnight. This will
continue to provide subsidence across the area tonight. Meanwhile
within the lower levels the strong surface high will drift
southeastward reaching KY/TN by Friday morning. Forecast soundings
through the night remain unsaturated. Thus a clear and cool night
will be in store with lows in the middle to upper 40s.
The ridging aloft on Friday is expected to flatten, but northwest
flow aloft will reside across Indiana in the wake. No forcing
dynamics are expected within this flow and time heights forecast
soundings continue to show a dry column. At the surface the strong
high pressure system will then drift to the Carolinas. This will
introduce warmer southerly flow to Central Indiana on Friday. With
sunny skies expected along with warm air advection, slightly warmer
high temperatures than persistence will be expected. Look for highs
in the upper 70s to near 80.
&&
.LONG TERM (Friday night through Thursday)...
Issued at 236 PM EDT Thu Oct 10 2024
Synoptic Pattern:
Central Indiana will begin to see its first taste of fall this week
as the portions of the Midwest and Ohio Valley will be beneath a
robust section of the Polar Jet. This is mostly due to a
strengthening PNA, an amplified West Coast ridge and subsequent
meridional activity on the downwind side of a supergeostrophic Polar
Jet. Initially, low level ridging will be the primary influence, but
this will adjust as multiple vorticity lobes develop in the cyclonic
curvature of the jet. The first low passage will be elongated as it
interacts with ridging over the SE (Saturday into Sunday), but the
second low passage will be backed by much cooler Canadian air,
allowing for the emergence of a cP airmass early next week. Ensemble
guidance is varied, but in general broad ridging through the
troposphere will eventually set up later next week as the PNA
weakens.
Temperatures:
The shortwave ridge early in the Long Term will lead to above normal
temperatures on Saturday with highs in the upper 70s to low 80s. An
initial, weak cold front passage late Saturday into Sunday will push
temperatures back towards seasonal for a brief 24hr period.
As mentioned, a more significant disturbance will arrive late on
Sunday attached with a cool Canadian Airmass. Timing on cold air
arrival is still varied amongst ensemble members, but generally the
expectation is for cold air to arrive Sunday night, creating fall
like conditions through Wednesday.
Mid level cloud cover within deep cyclonic flow is likely to keep
Sunday night temperatures from plummeting, but by Monday night,
skies should begin to clear. At this point is when overnight lows in
the mid 30s will be possible leading to some concerns for a
widespread frost event. Low temperature confidence is still too
varied to sound alarms quite yet, but the potential is significant
enough to monitor closely in the coming days for those with
interest/concerns with vegetation.
A warm up back to above seasonal is likely late next week with
tropospheric ridging and strong southerly flow expected. Highs back
into the 80s cannot be ruled out; Current ECMWF Ensemble runs show
99th percentile for 700mb temperatures next week within the ridge.
Precipitation:
Widespread precipitation is unlikely within these wave passages as
high pressure to the south will block any southerly moisture return.
However, there should be scattered showers and even a few
thunderstorms along the frontal boundary Saturday night into Sunday
morning. 850-750mb deformation stretching over the upper Mississippi
Valley will create a frontogenetic region, leading to amplified
convergence Friday through Saturday. By Saturday night, moisture
should be high enough in the 900-800mb layer for elevated convective
cells to form along the boundary. Total rainfall amounts, are not
likely to be greater than 0.25", but minor rain accumulations will
be possible, primarily over N/NE portions of central Indiana.
A secondary front will arrive Sunday, however this will be forced by
strong CAA, and will lack any significant moisture through the low
and mid levels, of which should lead to a dry frontal passage. As
the cold air arrives, steep vertical temperature gradients between
the Lake and low level temperatures could lead to enough low level
instability for lake effect precipitation. Most of this should
remain north of central Indiana, but a few isolated showers cannot
be ruled out over northern portion of the CWA late Sunday through
Monday.
&&
.AVIATION (00Z TAF Issuance)...
Issued at 728 PM EDT Thu Oct 10 2024
Impacts: None
Discussion:
VFR conditions to continue over central Indiana through Friday
evening as surface high pressure dives from the Great Lakes to the
Carolinas. Very light winds tonight will veer from NE to SSE when
not calm. Despite clear skies, very dry lower levels will prevent
fog formation.
A gentle breeze from 210-230 degrees will return Friday...courtesy
of a slight increase in gradient from a trough crossing southern
Ontario. Winds may gust to around 15KT at times in the afternoon
at KIND/KLAF...with sustained winds over 7KT continuing at KIND
through Friday evening.
&&
.IND WATCHES/WARNINGS/ADVISORIES...None.
&&
$$
UPDATE...AGM
SHORT TERM...Puma
LONG TERM...Updike
AVIATION...AGM
Source:
IND issues Area Forecast Discussion (AFD) at Oct 10, 9:59 PM EDT---------------
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