IND issues Area Forecast Discussion (AFD) at Oct 12, 9:44 PM EDT531
FXUS63 KIND 130144
AFDIND
Area Forecast Discussion
National Weather Service Indianapolis IN
944 PM EDT Sat Oct 12 2024
.KEY MESSAGES...
- Partly cloudy overnight.
- Partly cloudy and cooler on Sunday.
- Coldest air of the Fall for early next week with frost expected on
a few mornings
- Other than low chances for showers across the northern counties
Saturday night into Monday night, dry weather will persist
&&
.FORECAST UPDATE...
Issued at 943 PM EDT Sat Oct 12 2024
Hi-Res soundings, obs and GOES-16 IR loop all support scattered
cloud cover overnight as an upper trough moves into the western
Great Lakes and a cold front drops southeast into the upper Wabash
Valley toward daybreak. Winds behind the front will shift to the
northwest. Meanwhile, MRMS radar mosaic and CAMs suggest only
perhaps at worst a few sprinkles or isolated showers are possible
overnight, mainly well north of Indianapolis. We decided to just
pull showers completely with very low PoPs matching up nicely with
adjacent offices.
&&
.SHORT TERM (This evening through Sunday)...
Issued at 157 PM EDT Sat Oct 12 2024
Synopsis:
Surface analysis early this afternoon shows a frontal boundary
stretching from northern PA, across northern OH and northern IN to
western IL. Low pressure has developed along the front over IA.
Strong surface high pressure was found over the deep south. Another
area of high pressure was found over the Great Lakes. GOES16 shows
mid and high clouds along and ahead of the frontal boundary,
including across Central Indiana, progressing southeast. Aloft
Pacific northwest flow remained in place as a weak ridge was found
over the western CONUS, resulting in NW flow from the northern
plains into the Ohio Valley. A weak short wave was found over the
upper Midwest, generating some showers over MN and NW WI. Additional
showers had developed of NE IN and NW OH. Dew points across the area
were surging higher, into the 50s.
Tonight -
Models suggest the short wave across the upper Midwest will continue
to dive southeast toward the eastern Great Lakes through the evening
and overnight. This is expected to drag the newly developed surface
low eastward along the frontal boundary across northern Indiana
tonight, along with an associated cold front. HRRR fails to generate
much in the way of precipitation with these passing features this
evening and overnight, hinting at the best chances across northern
Central Indiana. Forecast soundings do not show strong saturation
within the mid and lower levels, but do suggest steep lapse rates
with conditional instability. Thus will limit pops this evening and
overnight to the northern most parts of Central Indiana, including
Lafayette, Kokomo and Muncie. Any precipitation should be rather
light with low amounts expected. Points farther south, being farther
away from the forcing, should remain dry given the limited deep
moisture available.
Given the expected clouds overnight and also Central Indiana
spending much of the night in the warm sector, along with mixing
expected to continue, warmer lows are expected. Look for lows in the
upper 50s and lower 60s.
Sunday -
An upper trough over the upper Midwest is expected to settle across
Indiana by the late afternoon. Initially the upper flow will remain
northwesterly on Sunday morning, however the trough will dig across
central Indiana as the day progresses. Within the lower levels
cyclonic flow looks to remain in place due to the departing low
along with ongoing cold air advection through the day. Forecast
soundings fail to show much in the way of saturation, thus a dry but
cooler day will be expected. Look for highs in the lower to mid 70s.
&&
.LONG TERM (Sunday night through Saturday)...
Issued at 157 PM EDT Sat Oct 12 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. Strong
WAA within 850-700mb SW flow should allow for height rises and
ridging later next week, with more consistent broad ridging
development in the 8-14 day period as the PNA weakens.
Temperatures:
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. There is still some uncertainty on overnight
lows Monday Night, but for Tuesday, confidence is growing a
widespread frost event. Those with interests/concerns with
vegetation should monitor closely in the coming days.
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 next weekend; Current ECMWF
Ensemble runs continue to show 99th percentile for 700mb
temperatures next week within the ridge.
Precipitation:
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.
Surface high pressure early to mid week, and then upper level
ridging late week should keep conditions dry through at least next
Saturday.
&&
.AVIATION (00Z TAF Issuance)...
Issued at 708 PM EDT Sat Oct 12 2024
Impacts:
- Can not rule out an isolated thunderstorm at KLAF through 03z
- Non-convective LLWS possible between 05-13Z
- Winds will shift from SSW to NW after 11z-14
- Winds 290-320 to near 15 knots and gusts to near 25 knots
Sunday 20z to 01z Monday, mainly at KIND, KHUF and KBMG
Discussion:
A low level jet will bring the threat for non-convective low level
wind shear to mainly KIND, KHUF and KBMG overnight into the early
morning. Otherwise, can not completely rule out a thunderstorm at
KLAF this evening, but chances much too low to put in the TAF.
Should mostly see passing mid and high clouds tonight an d Sunday.
Winds will switch from SSW to NW just before and after daybreak as a
cold front drops down from the northwest with sustained winds to
near 15 knots and gusts to near 25 knots Sunday afternoon.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...MK
SHORT TERM...Puma
LONG TERM...Updike
AVIATION...MK
Source:
IND issues Area Forecast Discussion (AFD) at Oct 12, 9:44 PM EDT---------------
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