JACKSON, Wyo. — Weather conditions are going to be just about perfect in the Tetons and Jackson Hole this week, save for some strong winds over the high elevations. The smoke is gone and temperatures will be cooler with highs will be in the 70’s in the valley each day from Monday through Saturday.
As we head into mid-September, the weather pattern across Western North America is undergoing a transition phase from a summer pattern to a fall pattern. We’ve already seen hints of fall since late August with chilly morning low temperatures. In fact, temperatures have regularly been dipping below freezing in the valley on clear and calm nights.
Jackson’s average high and low temperature in August are 81ºF and 40ºF, but fall about 10 degrees to 72ºF and 32º in September. This is arguably the best weather month of the year in Jackson Hole with temperatures that are not-too-hot and not-too-cold, and usually just enough precipitation along with higher humidity to reduce fire danger.
Last week, we experienced what was almost certainly our last extended stretch of 80-degree weather. In fact, we were close to record levels late last week when the Town of Jackson hit 89ºF on Thursday.
On Friday night, a storm system and cold front moved through, producing light to moderate rain for Jackson Hole, but ultimately signaling the start to a more fall-like pattern. Ever since then, highs in the 80’s have been replaced with highs in the 70’s.
The decrease in smoke since the middle of last week has also been noteworthy, and most of the Western U.S. has enjoyed cleaner air and crisper skies other than localized areas in proximity to active fires. Cooler temperatures, a more stable atmosphere, higher humidity and rain in some areas have all contributed to the decrease in smoke.
It looks as if the mostly smoke-free conditions will continue throughout this week and into next week. As the seasons change, let’s hope that smoke is something we won’t have to talk about much more this year.
The one slightly inconvenient weather feature we will have to deal with this week is wind. A strong jet stream will be in place over the Northern Rockies during the second half of the week from Wednesday through Saturday, and this will support strong southwest winds across the higher elevations and to a lesser extent the lower elevations.
In fact, over the higher peaks of the Tetons (Grand, Middle, Lower Saddle, etc.), we could see afternoon wind gusts in the 60-70+ mph range from Wednesday through Saturday. Something to keep in mind if you have climbing plans. Morning wind gusts will be lighter but still brisk in the 35-50 mph range (remember, these are gusts, not sustained winds).
The Jackson Hole Valley will see breezy afternoon winds as well in the 30-40 mph range at times. More manageable compared to the higher peaks, but certainly strong enough to impact your plans if you’re going to be out on the water. Fire danger could increase somewhat during this time as well (mainly in grassy/brushy areas), but should quickly decrease again next week.
Aside from the afternoon winds, conditions will be ideal this week for hiking, mountain biking and outdoor activities.
Also, the fall colors have started a bit earlier than usual this year and are already putting on a good show in parts of Teton County. Check out some of the color near String Lake from last Saturday.
The next few weeks should be outstanding if you’re looking to catch the colors.
Over the second half of the weekend and early next week, a stronger storm system is likely to influence our weather, leading to cooler temperatures, increasing rain chances and a strong possibility of high elevation snow that could impact backpackers.
This system will initially hit the Pacific Northwest with heavy precipitation on Friday and Saturday. After that, confidence decreases on the timing and southern extent of the system as it moves inland. For now, it looks like our best chance of precipitation will be between Saturday night and Tuesday (September 19-21).
Stay tuned as the week progresses as we get a better handle on this approaching system and the possible impacts for Jackson Hole. For now, I would count on a transition to colder temperatures and a good chance of rain and high elevation snow if you have backcountry plans around this time.
Alan Smith, Meteorologist
