Smart Thermostat Schedule for the September 2026 Outlook

As of Aug. 25, 2026, the latest national input for a smart thermostat schedule in September is the NOAA Climate Prediction Center’s September 2026 monthly temperature outlook, issued Aug. 20. CPC also says the updated monthly outlook is scheduled for Aug. 31, so any schedule set now should be treated as a one-week working plan, not a permanent fall setting. The Aug. 20 outlook favors above-normal September monthly mean temperatures for the western contiguous U.S. (CONUS), southern Plains, Southeast, and Southeast Alaska, with the highest probabilities in the north-central Rockies and Intermountain West; it leaves the Northern Plains, Midwest, Northeast, and parts of the Ohio Valley and Mid-Atlantic in Equal Chances territory. [1]

That split is the useful scheduling fork. CPC is not telling anyone what number to put on a thermostat. The thermostat translation here is NestGrid’s interpretation of the CPC outlook: keep cooling logic alive where above-normal September temperatures are favored, and use a shoulder-season heat/cool schedule where CPC shows Equal Chances. The Week 3-4 outlook adds a near-term check for Sept. 5-18, 2026: it favors above-average temperatures across most of the CONUS and Alaska, while noting model disagreement for parts of the West Coast and Great Lakes. It was updated Aug. 21, and CPC refreshes Week 3-4 outlooks every Friday. [2]

Find your September regime before changing the schedule

For a homeowner, the important difference is not whether September feels like “fall” on the calendar. It is whether the house is likely to keep needing cooling during occupied hours, sleep hours, and sunny late afternoons. The CPC map separates that decision more cleanly than a national seasonal checklist.

• Cooling-load regions: western CONUS, southern Plains, Southeast, and Southeast Alaska. The strongest above-normal probabilities are in the north-central Rockies and Intermountain West. In these areas, keep a cooling-first schedule in place for September, then adjust after the Aug. 31 monthly update. [1]
• Shoulder-season regions: Northern Plains, Midwest, Northeast, and parts of the Ohio Valley and Mid-Atlantic. CPC marks these as Equal Chances, which means this is a better place for heat/cool auto logic or mild setbacks than for a hard switch from summer cooling to autumn heating. [1]
• Near-term overlay: Sept. 5-18 leans warmer than average across most of the CONUS and Alaska, but the West Coast and Great Lakes deserve extra attention because CPC notes model disagreement there. [2]

Equal Chances is easy to misuse. It does not mean “normal weather is expected,” and it does not mean “turn the air conditioning off.” It means CPC does not show a favored tilt toward above-, near-, or below-normal monthly mean temperatures for that area. For scheduling, that calls for flexibility: keep both comfort guardrails available, and let the thermostat handle the daily swings.

Cooling-load regions: keep summer logic, but make it less frantic

If you are in the western CONUS, southern Plains, Southeast, Southeast Alaska, north-central Rockies, or Intermountain West, do not let the September label convince you to delete your cooling blocks. The CPC monthly outlook favors above-normal September monthly mean temperatures in these regions, and the strongest probabilities sit in the north-central Rockies and Intermountain West. [1]

The practical schedule is still a cooling schedule: occupied hours stay comfortable, away hours drift warmer, and sleep hours get their own limit instead of inheriting the daytime setting. What changes in September is the amount of panic in the schedule. You usually do not need a high-alert heat-wave routine every day of the month; you need cooling available when the house gains heat, especially in late afternoon and early evening.

• Leave cooling enabled during the main occupied period. Do not replace it with a heating-only fall schedule before the Aug. 31 outlook update.
• Keep an away or eco block if the house is empty, but avoid a recovery plan that waits until the hottest indoor hour to start cooling.
• Use a separate sleep schedule. September nights can be easier on the system than August afternoons, but a warm bedroom is still where a bad “fall” schedule gets noticed first.
• If your thermostat has heat/cool auto mode, set the heating side low enough that the system does not add heat on a cool morning and then need cooling later the same day.

For homes that are still dealing with hot afternoons, use the cooling discipline from smart thermostat settings during a heat advisory as the stricter version of this plan. The September outlook does not say every day will behave like a heat advisory, but it does say these regions should not be scheduled as if cooling season has ended.

Equal Chances zones: let the thermostat manage the shoulder season

The Northern Plains, Midwest, Northeast, and parts of the Ohio Valley and Mid-Atlantic are the places where a September schedule can stop acting like August without pretending winter is here. CPC places these areas in Equal Chances for the September monthly temperature outlook, so the better schedule is one that tolerates variability. [1]

A good shoulder-season setup keeps the cooling ceiling active for warm afternoons and adds a heating floor for cool mornings. The deadband between them matters. If the heat and cool setpoints are too close, the system can chase its own work: heat in the morning, cool by dinner, and leave the homeowner wondering why a “mild” day used so much equipment time.

This is also where setbacks become useful again, as long as the equipment can recover comfortably. If the house is empty during the day, a mild daytime setback makes sense. If the home has a heat pump, avoid aggressive heating recovery on chilly mornings unless the system is configured to avoid unnecessary auxiliary heat. For a fuller setback pattern, use the smart thermostat temperature-drop schedule as the shoulder-season companion to this forecast.

• Use heat/cool auto if your thermostat and HVAC setup handle it reliably.
• Keep cooling available through the afternoon and early evening, especially during the Sept. 5-18 window when CPC favors above-average temperatures across most of the country. [2]
• Set the heating floor for comfort, not for a symbolic start of heating season.
• Review alerts and runtime after the first few mornings. Short, alternating heat and cool calls are a sign the schedule is too tight for shoulder weather.

Use Week 3-4 as a schedule check, not a replacement for the monthly map

The monthly outlook is the anchor for September. The Week 3-4 outlook is the nearer-term pressure test. For Sept. 5-18, CPC favors above-average temperatures across most of the CONUS and Alaska, which argues against shutting down cooling logic too early even in some Equal Chances monthly regions. The same discussion notes model disagreement for parts of the West Coast and Great Lakes, so those areas should be checked again instead of scheduled with false confidence. [2]

That Friday refresh rhythm is useful because thermostat schedules drift out of date quietly. A household can set a reasonable plan on Aug. 25, get the Aug. 31 monthly update, and still need another adjustment after the next Week 3-4 map. The maintenance job is small: check whether your region still leans warm, check whether the disagreement zone moved, and then decide whether to keep, loosen, or tighten the cooling blocks.

The seasonal Sep-Oct-Nov outlook gives the broader backdrop: warmer-than-average fall conditions are favored for most states, with the strongest probabilities in the Pacific Northwest, while Illinois, Indiana, Kentucky, Missouri, Ohio, Tennessee, and West Virginia are shown as Equal Chances. [3] That is helpful context for not tearing out cooling logic too soon, but it is too broad to run the whole September schedule by itself.

CPC’s Week 3-4 material also points to a greater than 90% chance of a very strong El Niño event in fall and winter 2026-27, presented as part of the driver context for the warm tilt. [2] For a thermostat owner, that is background, not a setpoint. The equipment still needs a schedule tied to the September regional outlook and the next forecast refresh.

Put the re-checks on the calendar

A September thermostat schedule should have review dates attached to it. Without them, the schedule becomes stale exactly when the weather gets irregular.

The later fall check is less about September temperatures and more about schedule hygiene. If your thermostat routines have been copied, edited, or tied to smart-home scenes, the daylight saving time change is a good moment to use a DST smart-home schedule fix before small timing errors become comfort problems.

For September 2026, the clean action is regional. If CPC favors above-normal temperatures where you live, keep a cooling-first smart thermostat schedule and soften it only where your house actually stays comfortable. If you are in an Equal Chances zone, move to heat/cool shoulder-season logic and watch for daily swings. Then re-check after the Aug. 31 monthly update and keep using the Friday Week 3-4 refreshes. This is a provisional schedule, not a national seasonal switch.

References

1. 30-Day Outlook Discussion, NOAA Climate Prediction Center, Aug. 20, 2026
2. Week 3-4 Outlook, NOAA Climate Prediction Center, Aug. 21, 2026
3. Seasonal Outlook, NOAA Climate Prediction Center, Aug. 20, 2026