JACKSON, Wyo. – A heat wave is underway with highs forecast to reach the low to mid 90s in the valley each day through Sunday. Low relative humidity, occasional gusty winds, and a chance of dry thunderstorms this weekend will contribute to increasing fire danger.
Recent Weather
While the heat has officially arrived as of Wednesday afternoon, we actually had a relatively cool start to July. As of July 10, temperatures are running 2.7 degrees below normal so far this month in Jackson.
Last week, a strong ridge of high pressure set up over the West Coast, resulting in excessive heat across the far western states. Jackson Hole and the state of Wyoming were located far enough east of this ridge to see a cooler north/northwest flow instead.
This resulted in refreshing temperatures from July 1-4 with highs only in the low 70s, with highs in the upper 70s from July 5-7. Mornings were quite chilly during this stretch as well, with the low temperature dipping to 33ºF in Jackson on the mornings of July 3 and July 4.
To the west, temperatures were exceptionally hot last week with some locations breaking daily, monthly, and even all-time record high temperatures. Las Vegas, for instance, recorded its hottest temperature on record this past Sunday with a high of 120ºF, breaking its old record of 117ºF.
The ridge of high pressure responsible for this heat is now working its way eastward into Wyoming and the Central Rockies as of Wednesday, July 10.
Hot Temperatures Ahead
The heat wave is now underway across Idaho and Wyoming. On Tuesday, the high temperature hit 89ºF in Jackson and so far on Wednesday the high temperature has reached 91ºF.
High temperatures are projected to reach the 90s each day from Wednesday through Sunday, which would qualify as a significant heat wave for our region as the town of Jackson only averages four 90-degree days per year. Average highs in July are in the low 80s for perspective.
The last time we had a five-day streak of 90+ temperatures in Jackson was in early September of 2022. Before that, you have to go all the way back to 2007 to find the last time we had five consecutive days of 90+ degree heat.
The hottest days during this upcoming stretch are expected to be Thursday, Friday, and Saturday with models projecting highs to reach the 92 to 95ºF range each day.
If we were to hit 95ºF at any point during this heat wave, it would mark our hottest day in Jackson in over 20 years. The last time the temperature was 95ºF or higher in Jackson was in 2003, when it got as high as 97ºF.
Early next week, a slight cooling trend is expected as the high pressure ridge weakens slightly. However, temperatures will still be above average with highs in the mid to upper 80s most days through the first half of next week, while 90+ degree heat is not out of the question toward the end of next week.
Fire Danger on the Rise as Conditions Quickly Dry Out
June was much drier than average in the Jackson Hole-Yellowstone region, and so far, July is also off to a very dry start. We saw some thunderstorm activity on July 1, but the town of Jackson only received 0.08 inches of rain, which is also the only rain that has been recorded in town so far this month.
June was also warmer than average across the region, and the hot temperatures this week will only exacerbate the drying out of vegetation as evaporation rates will be high. Also, the lack of moisture in the atmosphere will result in relative humidity values dropping to 10-15% each afternoon through Saturday.
Teton Interagency Fire (which covers Grand Teton National Park and Bridger-Teton National Forest) and Yellowstone National Park just raised their fire danger to high this week as vegetation is quickly drying out.
In addition to hot temperatures and low relative humidity, we have a couple of other weather factors to consider this week, too.
A disturbance passing north of our area will result in gusty winds during the afternoon hours on Thursday and Friday, which will lead to elevated fire danger.
Also, a little bit of monsoonal moisture will arrive from the south on Sunday and Monday, resulting in a chance of thunderstorms on both days.
Unfortunately, the amount of moisture arriving does not look all that impressive and the airmass will already be very dry ahead of this weak moisture surge. As a result, we could be looking at a potential setup for dry thunderstorms – meaning storms that produce cloud-to-ground lightning but very little rainfall.
The 7-day precipitation projection representing the average of 50 simulations of the European weather model only shows light amounts for Jackson Hole with slightly higher amounts along and east of the Continental Divide.
What About Wildfire Smoke?
You may have noticed that our skies are a bit hazier than usual on Wednesday afternoon. This is due to light smoke aloft drifting into our area from wildfires that are burning in the Pacific Northwest.
We may hang onto this occasional haziness over the next few days, though no air quality concerns are noted just yet (barring any new fire starts or significant fire growth upwind of our area).
On Sunday, winds aloft will shift from northwest to south/southwest (blowing from the south/southwest). This could potentially transport some smoke from Central Utah wildfires into our region – not a sure thing yet this will happen, but it will be something to keep an eye on.
We were lucky enough to have minimal smoke issues during the previous two summers, but we may not be as lucky this summer given the prolonged excessive heat (and subsequent rise in fire danger) that the Western U.S. is currently experiencing.
Extended Weather Outlook
Looking further out (beyond July 16), the pattern continues to favor above-average temperatures in Jackson Hole with limited moisture, at least initially.
The North American Monsoon will continue to strengthen over the Southwest U.S. and Colorado where more numerous thunderstorms and heavier rainfall will occur. This will be something to monitor as we head further out into the future.
We are only expected to see fringe-level moisture from this pattern initially through about July 20 if not later. But we’ll be keeping an eye out in hopes that more significant moisture (that could bring meaningful rainfall rather than dry thunderstorms) may eventually arrive from the south later this month or in early August.
Alan Smith, Meteorologist
