320 FXUS63 KIND 170126 AFDINDArea Forecast Discussion National Weather Service Indianapolis IN 926 PM EDT Tue Sep 16 2025
.KEY MESSAGES...
- Dry and hot conditions persist for the rest of the work week
- Drying fuels and low RH values each afternoon through Friday may lead to elevated fire threat, but light winds should limit overall concerns
- Next chance of rain and slightly cooler temperatures arrives this weekend and early next week
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.FORECAST UPDATE... Issued at 926 PM EDT Tue Sep 16 2025
Temperatures have been dropping rapidly after sunset due to ideal radiative cooling conditions (light winds, clear skies, low humidity). In fact, cooling has been so efficient it is hard to capture it using various model blends. Incorporating NBM 10th percentile still doesn`t fully capture how quickly temperatures have dropped since sunset, especially in rural areas where low 60s are already being reported. With time, the rate of cooling should level off. For now, we used a blend of NBM10, hi-res guidance, and observations to get a representative near term foreast (the next 3 hours or so).
Some patchy ground fog may be possible by morning. Given the dry atmosphere in place, fog should be limited with the best chance being confined to near rivers and in agricultural/rural areas.
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.SHORT TERM (This evening through Wednesday)... Issued at 247 PM EDT Tue Sep 16 2025
Hot and dry weather continues this week the entire region as high pressure remains the dominant weather influence and keeps the dry airmass in place.
Latest satellite imagery shows mainly clear skies over Indiana due to subsidence under the high pressure. Local ACARs soundings verify this well showing the subsidence inversion at 800mb and an environment too dry to support afternoon cumulus for the northern 2/3rd of the state. Upper troughing over the Mid Atlantic states is advecting upper level moisture into the state, but the only result of this will be cirrus clouds through tonight.
Expect another tranquil night across Indiana as clearing skies, light winds, and dry conditions allow for optimal conditions for radiational cooling. Temperatures quickly fall after sunset with lows bottoming out in the mid 50s to near 60 degrees.
Very similar set up for tomorrow with high pressure keeping the same abnormally dry and hot airmass in place. The upper trough from the previous day pushes northward, switching upper level flow to the north and shutting off any moisture advection aloft. Expect sunny skies and highs a few degrees warmer than on Tuesday with highs reaching the upper 80s to near 90 degrees.
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.LONG TERM (Wednesday night through Tuesday)... Issued at 247 PM EDT Tue Sep 16 2025
The persistent Omega blocking pattern over the area keeping us summer-like and dry in recent days will continue to be the dominant force over the area through at least the end of the work week, gradually beginning to shift orientation and then break down later this week and into the weekend. This process will allow for moderation of temperatures back to near seasonal normals this weekend into early next week, as well as at least low chances for some scattered showers and perhaps isolated thunderstorms at times as early as Friday night onward.
Guidance has slowly but steadily trended slower with the demise of the block, which is fairly typical of both blocking patterns and NWP`s handling of them, so uncertainty is a bit higher than desired, even for the long range, with respect to precipitation chances, particularly over the weekend, but at least low PoPs are merited.
As the block erodes, a couple of upper level lows will eventually push eastward and exert influence on the region over the weekend into next week, again allowing for moderation of temperatures and potential for rainfall.
Abnormally dry or moderate drought antecedent conditions over the area, along with surface high pressure at least partially inhibiting moisture return from the Gulf, additionally add uncertainty to the rain potential. The old maxim of "drought begets drought" may be in play. GFS Integrated Water Vapor Transport progs (IVT) are quite poor to non-existent through at least Saturday evening, but gradually improve with time, particularly by late Sunday onward, though moisture transport is maximized just to our west/northwest.
Significant uncertainty will remain through the end of the period and beyond as global models begin to differ significantly toward the end of the forecast period on the strength and persistence of the second upper level low, which will have significant impacts upon both the degree of cooldown and PoPs/persistence of precipitation chances.
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.AVIATION (00Z TAF Issuance)... Issued at 724 PM EDT Tue Sep 16 2025
Impacts:
- Brief patchy ground fog possible at BMG tonight.
Discussion:
VFR conditions expected through the TAF period.
High cirrus from low pressure over the Mid-Atlantic will continue through the night, gradually diminishing in coverage. Some diurnal cumulus is likely Wednesday afternoon as well.
Some patchy ground fog is possible overnight tonight, with the best chance at BMG.
Winds will become light and variable overnight, with perhaps a residual northeasterly component. Speeds will pick up again during the day Wednesday, remaining less than 10kt, but from a more southeasterly direction.
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.IND WATCHES/WARNINGS/ADVISORIES... None. &&
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UPDATE...Eckhoff SHORT TERM...CM LONG TERM...Nield AVIATION...Eckhoff
NWS IND Office Area Forecast Discussion