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FXUS63 KIND 030444 AFDIND

Area Forecast Discussion National Weather Service Indianapolis IN 1244 AM EDT Wed Jul 3 2024

KEY MESSAGES

- Fair conditions continue tonight as humidity increases - Marginally hot and humid Wednesday - Rain and thunderstorm chances Wednesday through Friday, A few strong to severe storms are possible on Wednesday and Thursday.

FORECAST UPDATE

Main focus for the evening update has been tracking a broken line of convection and impacts to central Indiana towards daybreak tomorrow.
As this line moves further into Illinois it continues to weaken as was previously expected. Expectations going forward is that without a stronger cold pool, this system will continue to weaken as it exits the better dynamic profile of the Mississippi Valley combined with the poor diurnal timing.

Do think that at a minimum there should be fairly robust high level clouds across far western Indiana towards 7AM with the potential for some very light rain, but otherwise no precipitation is expected.
The increasing clouds combined with increasing southerly flow will allow for dewpoints to continue to rise through the night and mild lows in the low to mid 70s.

.SHORT TERM (This evening through Wednesday)...
Issued at 305 PM EDT Tue Jul 2 2024

Tonight...

Mainly quiet weather to continue tonight as the western portions of a stacked ridge continues to drift east across central Indiana.
Southerly flow sustained up to 10 mph will veer slightly as the surface ridge continues to depart across the eastern CONUS. These modest winds will steadily increase dewpoints into the 60s...while southwesterly flow aloft advects precipitable water values to 1.70- 2.10 inches by dawn. Can not rule out isolated showers or a stray rumble of thunder late tonight across the region's northwestern zones, yet expect to impacts. Low 70s will be the rule tonight, with higher dewpoints likely arriving a tad too late to promote any organized fog for southern counties.

Wednesday and Wednesday night...

Marginally hot and humid mid-summer conditions will be on full display Wednesday ahead of an approaching cool frontal boundary...with the potential for afternoon/evening convection including t-storms with strong to severe straight line winds. South- southwesterly winds will veer to southwest during morning hours while increasing slightly to 10-15 mph...with at times gusts to 20- 25 mph through the afternoon hours. This flow will boost dewpoints from the upper 60s in the morning to low 70s throughout the afternoon/evening, while promoting maximum temps in the upper 80s to low 90s. Decided to go with an SPS for heat indices near to just over 100 degrees across the far southern tier of counties where dewpoints will likely be in the mid-70s during peak heating.

PM-hours convection will likely only include a damaging straight- line wind severe threat, although small hail could possibly reach the ground from highest cells. Recent trends are for less intense storms north of I-70, yet 1500-2000 J/kg of CAPE and 20-30 kts of wind shear should help maintain storms in a west to east motion.
Confidence greatest later in the day and for counties farther south as indicated by some inconsistencies in latest CAM output. A limiting factor could be generally mediocre mid level lapse rates, especially if early morning showers are more impressive than expected which would also delay/limit surface-based instability.
Nonetheless expect at least scattered showers/storms over the region's southern third through late day and early evening hours...with embedded damaging winds possible courtesy in part from adequate downward CAPE. Hopefully storm motion will be slow enough to bring at least 0.25-0.50 inches to much of our southern zones.
Strongest storms could lead to localized flooding with shear vector allowing for training storms, although suspect flooding threat greater towards Ohio Valley.

Unlikely that the boundary's southeastward progression will be great enough to bring a noticeable drop in dewpoints Wednesday night, especially over southern counties where 70F+ values should remain.
Areas of fog amid lighter winds will be a concern following any moderate to heavy rainfall. Expect lows again the low 70s, with perhaps readings able to drop below 70 in far northern areas.

.LONG TERM (Wednesday night through Tuesday)...
Issued at 300 PM EDT Tue Jul 2 2024

The 4th of July forecast remains complicated with some uncertainty regarding coverage or timing of thunderstorms. A frontal boundary should be settled near southern portions of the area Thursday morning. Meanwhile aloft, a low amplitude shortwave is expected to move through providing additional forcing for storms. Showers and thunderstorms are likely during the day given favorable forcing and instability, but when or how widespread the convection will be is the question. The best chance for precipitation looks to be through the early afternoon hours before the upper wave departs.

Additional storms are still possible later in the day as the aforementioned front continues to lift north. Weaker upper level forcing should help to limit coverage. Marginal deep-layer shear combined with moderate instability could support a few strong storms. However, confidence is low in the overall threat as previous day convection may augment the thermodynamic environment or where the front sets up. Severe weather appears unlikely, but there is a non-zero threat for an isolated damaging wind gusts and locally heavy rainfall.

Model guidance continues to signal at the development of a storm complex ahead of an approaching cold front over MO Thursday night.
These storms are expected to propagate eastward towards central IN by daybreak Friday and gradually weaken as the complex outpaces the more favorable deep-layer shear. There is a low chance for damaging wind gusts, but confidence remains limited since convection on Thursday could impact how this forecast scenario plays out.
Localized flooding will continue to be a threat, especially if storms train over the same area. The cold front is expected to move through late Friday with the potential for more showers and storms.

Mostly dry conditions are expected over the weekend once the front finally moves out allowing for weak surface high pressure to settle in. Rain chances then return late Sunday into next week with another upper trough approaching. Temperatures look to be slightly below normal through Saturday before returning to seasonal for the latter half of the extended.

.AVIATION (06Z TAF Issuance)...
Issued at 1242 AM EDT Wed Jul 3 2024

Impacts:

-Potential for MVFR to IFR vsbys/cigs due to TS at IND and BMG mid to late afternoon.
-Southwesterly wind gusts to 22kts 15Z to 01Z.

Discussion:

VFR conditions expected through much of the TAF period outside of a low potential for MVFR vsbys at LAF and HUF towards daybreak and a period mid to late afternoon as thunderstorms move through.
Confidence is higher in the second round of convection with IND and BMG likely to see MVFR to briefly IFR vsbys during convection. Winds will gradually become more southwesterly towards the morning hours with gusts to 22kts from 15Z to 01Z before becoming near calm during the overnight.

IND WATCHES/WARNINGS/ADVISORIES
None.

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