531 
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