JACKSON, Wyo. – Heavy smoke from the Pack Trail Fire has impacted the Jackson Hole Valley this week, as we have been in an extended dry and warm spell dating back to mid-September. The next opportunity for precipitation is about 7-10 days away.
An Unusually Long Stretch of Dry Weather
We are currently in the midst of what is likely to end up being the longest dry spell in the past 15 years. After picking up some respectable moisture in mid-September, we have gone 21 days without measurable precipitation in the Jackson Hole Valley.
The longest dry spell during the past 15 years was 25 days in September 2018. This current dry spell is tied for 5th place on the list of longest dry spells in the past 15 years, and with another week of dry weather expected, this is likely to surpass the September 2018 dry spell.
Jackson’s Longest Dry Spells in the Past 15 Years:
- 25 Days – September 2018
- 24 Days – August 2020
- 23 Days – October 2022
- 22 Days – August 2013
- 21 Days – September-October 2024* (ongoing as of October 9th)
- 21 Days – August 2019
- 20 Days – July 2020
- 20 Days – August 2012
- 19 Days – June-July 2016
- 19 Days – September-October 2012
Temperatures have been above-average in this pattern, but we’ve also been experiencing huge temperature swings between morning lows and afternoon highs. The nights are getting longer at this time of year, and with clear skies and light winds most nights, morning lows have been quite cold.
Through the first 9 days of October, the average high is 73ºF and the average low is 25ºF. On some days, we have seen temperature swings of more than 50 degrees. Last Friday, the high temperature reached 79ºF in Jackson, which was our warmest October day since 2011, but did not set a record.
Smoke from the Pack Trail Fire and Weather Influences
The Fish Creek Fire and Pack Trail Fire, near and south of Togwotee Pass, merged over the weekend and the entire fire complex is now being referred to as the Pack Trail Fire. The total acreage burned is now over 66,000 acres.
Windy conditions last Friday-Saturday combined with consistent warmth and low relative humidity have contributed to the fire spread.
Smoke has also been impacting the Jackson Hole Valley on a near daily basis. Smoke levels have varied from day to day and hour to hour, but generally speaking, smoke has been most impactful during the morning and early afternoon hours, before dispersing mid to late afternoon.
Nighttime and morning temperature inversions are typical in our region during clear weather, with cold/dense air sinking into the Jackson Hole Valley.
During the early morning hours when temperatures are coldest, the smoke column over the fire collapses, and smoke spreads out across the valleys, filtering into the Jackson Hole Valley from north to south.
Here is a view of the smoke in the Jackson Hole Valley on Wednesday morning from the top of Snow King.
Since the days are getting shorter and the nights are getting colder at this time of year, it takes longer for the morning inversions to erode (when the valleys heat up and are warmer compared to surrounding higher terrain).
Once the valleys eventually heat up, the atmosphere becomes well-mixed and air near the surface is able to rise. Smoke eventually lifts out of the valleys when this happen, but often not until early to mid-afternoon as there is a lag time for the smoke to disperse after the inversion erodes.
The extent of the smoke, wind, and temperature also play a role on when the smoke disperses. If a morning is particularly cold, winds stay light, and air quality/smoke thickness is really bad, then it may be late in the day before the smoke clears. This was the case on Tuesday when the smoke did not clear out of Jackson until about 6 p.m.
Stronger winds can help to clear the smoke out earlier in the day, however, as wind helps the atmosphere become better mixed, and can erode inversions more quickly.
The air quality has been particularly bad this week. On Tuesday, air quality reached “Hazardous” levels, with Air Quality Index (AQI) values peaking at 300 to 400. If you were in town and walked outside, you probably noticed it smelled like a campfire and you may have quickly felt the effects in your eyes, nose, and lungs.
On Wednesday, the peak AQI values were bad but not quite as bad as Tuesday, peaking around 250 in town. This is still right around the lower end of “Hazardous”. Fortunately, the smoke dispersed earlier in the afternoon, and the mid to late afternoon was very pleasant with sunny skies, good air quality, and highs in the 70s.
During the smoky period on Wednesday morning, the Dornan’s webcam provided an oddly scenic view of the fall colors with a hazy look at the Tetons in the background.
The depth of the smoke has been very shallow overall in this pattern, similar to what you would see with a winter temperature inversion when valleys are very cold and sometimes have low cloud layers, whereas you can go skiing in comparatively balmy conditions above the inversion layer.
The same has been true with the smoke this week, with generally better air quality across the higher elevations.
Also, the Tetons have prevented this shallow smoke layer from penetrating west of the range, and Driggs and Victor have enjoyed much better air quality than Jackson.
The only exception was on Monday afternoon and to a lesser extent on Tuesday, when smoke from the Commissary Fire west of Palisades Reservoir reached Teton Valley.
The Commissary Fire has generally been burning at low to moderate intensity, but occasionally has produced enough smoke to reach portions of Teton Valley and the Jackson Hole Valley during the late afternoon hours.
How Long Will This Dry and Smoky Pattern Continue?
Unfortunately, no significant changes to the weather pattern are expected over the next 7 days. As a result, the Pack Trail Fire will remain active and we can anticipate the general pattern to repeat itself with smoky conditions taking hold in the Jackson Hole Valley each morning.
Fire danger will also remain “very high” due to dry fuels. Moderately gusty winds will develop most afternoons, but no major wind events are anticipated during the next week.
Highs will reach the 70s in the valleys each day, and no precipitation is expected. It would be a perfect late fall weather pattern if not for the fires and smoke.
Some Hope for Moisture Beyond 7 Days
We are starting to see some signs that the persistent high pressure ridge may finally start to weaken enough for Pacific storm systems to approach our area, possibly as early as October 17-18 (next Thursday-Friday).
This is more than a week away so confidence is low in the details, and there are certainly no guarantees. But hopefully, we can start to pick up some moisture to help squash these wildfires.
Temperatures are also projected to cool to more seasonal levels after the 17th-18th. While we have been routinely seeing highs in the 70s lately, for perspective, average highs at this time of year are in the low 60s in early October and mid 50s in mid-October.
Alan Smith, Meteorologist
