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FXUS63 KIND 081727 AFDIND

Area Forecast Discussion National Weather Service Indianapolis IN 1227 PM EST Fri Dec 8 2023

Key Messages

- Mild and breezy through Saturday.

- Gusts generally 20-25+ MPH through Friday, increasing to 30-35 MPH Friday night and Saturday.

- Rain at times Friday night through Saturday night.

- Drizzle or flurries possible on Sunday, highs in the 30s

- Quiet weather conditions expected next week. Below normal temperatures early next week warm back up to near seasonal by mid- week.

Forecast Update
Issued at 1035 AM EST Fri Dec 8 2023

Going forecast is in good shape on most variables. Did make significant increases to cloud cover, as low level theta e axis has surged into the area this morning on southwest flow, producing widespread clouds between about 4-6kft as the column rapidly moistens in a shallow layer below a midlevel inversion.

Warm advection should drive temperatures well into the 50s and perhaps even 60s in spots today, though the cloud cover will be limiting insolation and counteracting that a bit. For now, high temperatures look good but overperforming is certainly possible this afternoon.

Short Term
(Today and tonight)
Issued at 305 AM EST Fri Dec 8 2023

Surface analysis early this morning shows deep low pressure in place over eastern North Dakota. A secondary low was found over the TX/OK panhandle and a weak trough connected these two systems. Strong High pressure was found along the GA/FL coastline. This was resulting in a moderate pressure gradient across MO/IL and Indiana.
GOES16 shows high cirrus exiting Indiana this morning, but some low cloud was found ahead of the trough over IA/IL and MO. Water vapor imagery showed an active flow aloft. Strong ridging was in place over Indiana, Ohio and the Great Lakes. Upstream, a moderate trough was found over the Dakotas, associated with the deep surface low. A quick flow aloft was found across the southwestern states. Dry air and subsidence was shown over MO and IA. Winds across Central Indiana this morning were from the south at about 10-20 mph, resulting in good mixing and preventing sharp temperature falls.

Today...

Models today show the ridging aloft over Indiana will push to the east coast today, while the trough over the Dakotas and Rockies will become deeper, producing a more amplified pattern. This results in a strong southwest flow aloft over Indiana today, but little in the way of forcing dynamics appears present. BUFKIT soundings show dry air aloft along with subsidence as this was being depicted upstream within the water vapor imagery. Meanwhile within the lower levels, warm air advection was in play on southerly winds. Here BUFKIT soundings show saturation arriving within the lower levels this afternoon. Thus we will trend toward increasing clouds today.
Meanwhile the story today will be gusty winds. The strong pressure gradient in place today should allow for wind gusts, particularly this morning to reach 25 to 35 mph per BUFKIT momentum transfer.
These winds will be notable today.

Regarding temperatures, winds overnight have not allowed temperatures to fall too much as we are in the upper 40s to near 50 at many locations. Thus with the warmer than expected start along with the dry southwest wind expected through the day, high temperatures should overperform. Look for highs in the upper 50s.
Lower 60s will be possible at locations in southwest Central Indiana. This is about 15-20 degrees above our seasonal normals.

Tonight...

The southwest flow is expected to persist aloft overnight. Meanwhile upstream the deepening trough over the plains is expected to begin to advance eastward. Models suggest some upper forcing begging to push toward Indiana, although the best forcing remains well to the west with the main trough. The GFS 295K isentropic surface shows moderate lift arriving overnight, and persisting through 12Z.
Specific humidities look quite high, around 7 g/kg. Meanwhile forecast soundings suggest deepening saturation within the lower levels, but dry air remains aloft. HRRR shows scattered to isolated showers across Indiana ahead of the main forcing after 06Z. Thus there is high confidence for some spotty light showers tonight, mainly late, but low confidence on any given location. Best forcing appears to be pulled north from northern IL toward Michigan and the Great Lakes. Nonetheless, pops will be needed tonight for light rain as all the discussed dynamics pass. Will use highest pops across the NW parts of Central Indiana, including locations like LAF, trending to lesser pops across the south.

It should be a warm night for December. Winds will remain southerly all night and the moderate pressure gradient looks to remain in play. This will keep mixing in place, and along with cloud cover temperatures should not fall much. Look for lows in the lower 50s.

Long Term
(Saturday through Thursday)
Issued at 305 AM EST Fri Dec 8 2023

Expect a large upper trough with embedded waves to track through the region over the weekend with a few chances for precipitation. Strong SSW flow ahead of the main trough will advect anomalous moisture into the region with dewpoints in the 50s. This combined with a cold front moving in at the start of the period should support widespread showers saturday morning. Rainfall amounts during the first half of the day should be light as the embedded upper shortwave and stronger forcing associated with the front remain displaced northwest of central Indiana. SSW Wind gusts up to 30-35 mph will be possible early in the day due to a strong pressure gradient. These winds should then diminish rather quickly later in the day once the gradient relaxes. The strong warm-moist flow will lead to well-above average temperatures in the low 60s for portions of the area. Highs across northwest portions of the area will likely not reach the 60s as the cold front should pass through early Saturday morning.

By Saturday evening, guidance shows strong PVA overruning the aforementioned front likely still lingering over parts of the area with the main upper trough axis still near the Iowa/Illinois border.
This will likely support additional rain chances during the evening and overnight hours, mainly across southeastern counties. It is worth noting, some guidance is slower with the front lingering across far southeast portions of central Indiana late in the day while others push the boundary further east and out of the forecast area. If the slower solutions were to verify, stronger overall forcing would support heavier storm total rainfall amounts around half an inch to one inch. Further north and west, total QPF amounts should be around 0.25 inches or less.

As the system moves out on Sunday, lingering low-level moisture may support light drizzle or possibly flurries at times during the day.
Clouds and cold air advection will keep highs in the 30s.
Thereafter, quiet weather conditions are expected for the remainder of the period as strong high pressure builds across the region. Look for temperatures to warm up through the week and possibly return to the 50s by late next week.

Aviation
(18Z TAF Issuance)
Issued at 1227 PM EST Fri Dec 8 2023

Impacts:

- Winds gusting 20-25KT throughout the period with isolated higher gusts.

- MVFR ceilings possible at some sites late this afternoon/early evening, with widespread MVFR developing overnight.

- Scattered showers late tonight through Saturday morning.

Discussion:

Ahead of an approaching cold front, strong southerly winds will continue through today and into tonight, with sustained winds 10- 15KT with gusts 20-25KT, and a few isolated higher gusts possible.
Wind directions ahead of the front will generally be 180-200 degrees, quickly shifting to 240-250 very late in the period/during the morning hours Saturday. Winds aloft will be strong, and transient LLWS conditions cannot be ruled out, but low level lapse rates suggest gustiness is likely to predominate throughout the period (and gustiness implies the presence of low level shear).

Scattered showers will be possible, mainly late tonight into Saturday morning. Will handle with VCSH as impact at any one site is fairly uncertain still.

Some areas of MVFR will be possible late this afternoon into the early evening, but more widespread MVFR appears likely later tonight into Saturday. IFR conditions are unlikely and not expected at this time.

IND WATCHES/WARNINGS/ADVISORIES
None.

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