656 FXUS63 KIND 080656 AFDINDArea Forecast Discussion National Weather Service Indianapolis IN 256 AM EDT Mon Sep 8 2025
.KEY MESSAGES...
- Dry and cooler through Tuesday with lows in the 40s
- Warming trend back to the 80s by mid to late week and beyond
- Abnormally dry conditions continue into next weekend
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.SHORT TERM (Today and tonight)... Issued at 255 AM EDT Mon Sep 8 2025
Today.
Another cooler than normal day is expected for today with a surface high pressure slowly moving across the southern Great Lakes region. As of early this morning, winds have been near calm with mostly clear skies allowing for ideal radiational cooling. Temperatures have already fallen into the 40s to low 50s with another few degree drop towards daybreak expected. The boundary layer will deepen to around 5000ft again this afternoon but drier air both at the surface and aloft will prevent saturation at the top of the boundary layer which will greatly limit afternoon cu coverage compared to recent days.
Winds at the top of the boundary layer will be 5 mph or less which will also help to limit the mixing compare to recent days and limit the diurnal fall in surface dew points. That being said, the air mass continues to dry with many locations having seen less than a half inch of rain in the last 15-20 days. Expect to see min RH values again fall down into the upper 20 to low 30 percent range again today which will create a slightly elevated fire weather risk. Additional details on the fire concerns below.
Tonight.
Any diurnal cu will dissipate by sunset with clear skies expected outside of some thin passing cirrus. Another night of efficient radiational cooling is expected with the clear skies and light winds with lows likely to fall into the 40s again.
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.LONG TERM (Tuesday through Sunday)... Issued at 255 AM EDT Mon Sep 8 2025
An extended stretch of abnormally dry conditions and above average temperatures persists for the next 8-14 days across Indiana, potentially leading to rapid onset drought and an elevated fire weather risk. The period begins with weak troughing over the Great Lakes region and a building ridge over the center CONUS. The upper ridge axis builds and continues eastward through the week stretching from Lake Superior to Eastern Texas by Sunday. Long range guidance has been consistent in showing this pattern developing for quite some time, with well above average 500mb heights and 850mb temperatures making for a high confidence forecast for hot and dry conditions through at least next weekend.
The warming trend begins on Tuesday as surface high pressure moves off to the northeast, switching low level flow to the southeast and bringing a warmer airmass northward into the state. High pressure will continue to be the dominant weather influence at the surface through the rest of the week, keeping the atmospheric profile too dry to support any precipitation locally. A front does push through late Wednesday, but such dry antecedent conditions will lead to virtually no impacts as high pressure and an even warmer airmass advect into the region in the following days. This dry pattern is supportive of large diurnal ranges, with temperatures quickly heating up after sunrise...and then plummeting after sunset. High temperatures get a little warmer each day this week, starting out in the upper 70s to low 80s Tuesday, then by Friday and Saturday highs approach the 90 degree mark in many spots. Lows on the other hand remain at or below normal for this time of year... in the upper 40s Tuesday morning and moderating into the upper 50s/low 60s by the end of the week.
Forecast confidence somewhat decreases toward the end of the period as longer range guidance and ensembles struggle to resolve how this pattern evolves as weak storm systems ride up and other the ridge. While higher confidence exists in a hot and dry forecast continuing into the following week, it is worth mentioning that some longer range guidance (ECMWF and ECMWF AI) has been consistent in showing the potnetial for a wave and associated convection to ride over the ridge into Indiana Saturday evening through Sunday. Have introduced a slight chance (20%) of storms for this timeframe to account for this threat. Confidence remains low on the exact mesoscale details this far out, but there is enough confidence in a pattern supporting a thunderstorm complex in the region to add PoPs for this weekend. Despite the slight risk of storms, there is moderate to high confidence in highs still reaching the 90 degree mark for several days in a row, especially for Western and Southern Indiana this weekend into the following week. CPC continues to place the entire Ohio Valley and Midwest in a risk for extreme heat in the Sept 15- 18th timeframe...will be watching this timeframe closely and updating the forecast as needed.
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.AVIATION (06Z TAF Issuance)... Issued at 121 AM EDT Mon Sep 8 2025
Impacts:
- None.
Discussion:
VFR conditions are expected through the period as high pressure remains the dominant weather influence over the region. Satellite imagery shows clear skies with high pressure directly overhead. Expect winds to remain at or near calm the rest of the night before turning southeasterly mid morning. Typical diurnal curves expected for the next several days...increasing winds during peak heating of the day along with afternoon cumulus. Winds are still expected to remain light even during the afternoon with such weak pressure gradient and lack of any low level flow. No vis concerns.
Similar conditions expected for at least the next week.
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.FIRE WEATHER... Issued at 255 AM EDT Mon Sep 8 2025
The lack of any significant rainfall over the last several weeks has resulted in abnormally dry and minor drought conditions to develop across Indiana. With little to no rain in the forecast for the next 7 days, confidence is increasing in an elevated fire weather threat each afternoon as daily min RH values fall into the 20% range. Lowered afternoon dew points each day through next Saturday to the NBM10th percentile to account for such dry conditions and afternoon mixing bringing down even drier air to the surface. The one factor keeping the fire weather threat lower is the lack of wind. Despite deep mixing, very weak low level flow should keep winds under 10 kts through the period. It is worth noting that CPC has placed the majority of the Midwest and Mid Mississippi Valley in a slight risk for extreme heat for Sept 15-18th. If no appreciable rainfall is observed this weekend, the fire weather threat may continue to increase and persist into mid month. Will continue to monitor the extended forecast for increasing fire weather concerns.
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.IND WATCHES/WARNINGS/ADVISORIES... None. &&
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SHORT TERM...White LONG TERM...CM AVIATION...CM FIRE WEATHER...CM
NWS IND Office Area Forecast Discussion