JACKSON, Wyo. – A prolonged stretch of cool and wet weather took hold across Jackson Hole in early August. Rainfall totals so far this month have ranged from 2-3 inches in the Jackson Hole Valley and the higher peaks of the Tetons have been dusted with snow on multiple occasions.
Significant Rainfall In Early August
For the 24-hour period ending at 9 a.m. each morning, weather stations across Teton County have recorded measurable rainfall on nine consecutive days since August 1. This would be an impressive streak at any time of year, but is especially impressive during mid-summer!
Rainfall totals so far in August include 2.86 inches in Moose, 2.76 inches in Wilson, 2.51 inches at Jackson Lake/Moran, 2.21 inches in Jackson (downtown), and 2.10 inches at the Jackson Hole Visitor Center.
Rainfall amounts have been even higher in Teton Valley, including 3.05 inches in Driggs and 3.04 inches in Alta.
There are no rain gauges in operation in the Teton Range itself, but rainfall amounts have almost certainly been even heavier there moving up in elevation.
For perspective, the Town of Jackson and other climate sites across the Jackson Hole Valley average about 1.25 inches of rain during the month of August. So we are already well above average and are not even halfway through the month.
This will also be the third consecutive August with above-average rainfall.
Why have we had so much rainfall lately?
The main culprit is a surge of significant monsoonal moisture that arrived from the south last week. A slow-moving area of low pressure moving from south to north across the Great Basin helped to transport this moisture into our area, and it stuck around for an extended period of time, becoming displaced from its usual home in the Southwest U.S.
Moisture lingered through last weekend and into the early part of this week as several low pressure systems moved across the Northwest and Northern Rockies. These systems interacted with moisture in place to result in frequent showers and thunderstorms along with significant lightning activity.
Here is a look at rainfall compared to average through the first eight days of August across the Western U.S.
Snow Makes An Appearance On The Higher Peaks
In addition to abundant precipitation, temperatures have also been well below average over the past week. As a result, snow levels and freezing levels began to drop late last week and the upper slopes of the Grand Teton and surrounding peaks have been blasted with snow on several occasions.
A webcam image from the top of Grand Targhee revealed snow cover down to about 11,000 feet on the Grand, Middle and South Tetons on Tuesday morning, including the Lower Saddle between the Grand and Middle.
While not exactly typical, mid-summer snow on the Teton summits is not as unusual as you might expect. Snow can fall across the higher elevations at any time of year. Nevertheless, the persistence of this pattern has resulted in challenging conditions for Grand Teton climbers, as both snow and lightning have been frequent hazards.
Chilly Temperatures in Early August
The Jackson Hole Valley saw highs in the mid 80s on the first day of August, but temperatures have been well below average since then.
From August 2-8, highs only reached the 60s in the Town of Jackson on four out of these seven days. Average highs in early August are in the low 80s.
So far this month, temperatures are running 2.6ºF below normal in the Town of Jackson when factoring in both high and low temperatures.
More impressively, high temperatures are running 11.0ºF below normal so far during August. Low temperatures have been warmer than average, however, due to the abundance of moisture and cloud cover.
Jackson actually set two new daily records for low maximum temperatures over the past week with a high of only 62ºF on August 2 and a high of only 61ºF on August 4.
Temperatures have been cooler than average through the first eight days of August across a large portion of the West Central U.S. which is a big change from July!
Warmer and Drier Pattern Ahead
The early August cool and wet period is now coming to an end with more seasonal summer conditions ahead. However, this upcoming stretch of weather will still be cooler than what we experienced during July.
Following a dry day with partly cloudy skies on Wednesday, a low pressure system will pass north of our area on Wednesday night and Thursday.
It is possible we could see some isolated showers or thunderstorms develop on Thursday morning and Thursday afternoon, but the odds are lower compared to recent days. Any showers or storms that develop will be fast-moving and will only produce brief, light rain.
High temperatures will reach the mid to upper 70s on Wednesday and Thursday with gusty winds expected at times, especially on Thursday.
A further drying trend can be expected from Friday through Sunday with highs topping out in the upper 70s to low 80s in the valley each day along with breezy afternoon winds. This is right around average for this time of year.
Thunderstorms are not expected from Friday through Sunday as monsoon moisture will be suppressed further to the south. It’s possible some isolated storms could sneak into the Salt River, Wyoming, and Wind River Ranges on Saturday, though.
Early next week, a weaker and shorter-lived surge of monsoonal moisture is expected to arrive from the south, resulting in a chance of thunderstorms on Monday and Tuesday. Temperatures will remain seasonally warm, however, with highs in the low 80s.
Pictured below is the rainfall projection over the next seven days. Monsoonal moisture will largely remain south of our area, except for a little bit of moisture reaching our area on Monday-Tuesday.
Extended Outlook
During the second half of next week, an overall nice weather pattern is expected with seasonally warm and dry conditions.
A trough of low pressure is expected to set up over Montana, which should keep high pressure and warmer temperatures suppressed to our south. As a result, temperatures should be around average for mid to late August (near 80ºF most days, give or take a few degrees).
Also, any shower/thunderstorm chances are expected to be irregular occurrences during the second half of next week with not much in the way of rainfall expected.
Alan Smith, Meteorologist
