JACKSON, Wyo. — Last week started out unseasonably cool and wet as we closed out the month of June. However, the moisture we received last week is turning out to be a good thing, as we are heading into a very dry pattern for the foreseeable future.
Jackson Hole’s “dry season” is now underway, which typically runs from mid to late June through early October on average, with year to year variations. Clearly, our dry season started a bit on the later side this year given the cool and wet conditions during the final days of June.
Dry Season and the North America Monsoon
July and August are the two driest months of the year on average in Jackson Hole, but we still rely on intermittent rains from afternoon thunderstorms to keep us from drying out too much.
Often, the moisture we receive at this time of year is subtropical in nature and comes from the North American Monsoon circulation that develops over the Four Corners region. Essentially, moisture rotates in a clockwise (“anti-cyclonic”) direction around an area of high pressure that sets up over the Southern Rockies or Southern Plains.
The areas that see the heaviest rains and most frequent thunderstorm activity as a result of the monsoon are Arizona, New Mexico, Colorado and portions of Utah, while in the Northern Rockies we are often on the fringe of this moisture and see lesser impacts.
Still, occasionally the circulation sets up just right to bring more significant monsoon moisture to Northwest Wyoming. In these types of patterns, thunderstorms become a near-daily occurrence and rainfall from these storms tends to be higher compared to ordinary “airmass” thunderstorms with limited moisture, which can produce more lightning than rain and start fires.
Typically, monsoon season lasts from about the Fourth of July through Labor Day, but this varies from year to year. So far in 2020, we are not seeing any signs of the monsoon in the near-term, so this pattern will be developing later than normal.
The latest long range models indicate that a monsoon pattern is about 10-15 days away from developing over the Four Corners region. It then remains to be seen if and when we see any of this moisture reach Jackson Hole. For now, rain chances are looking minimal at best over the next couple of weeks.
Fire Danger
While the weather pattern looks dry over the next couple of weeks, fortunately, recent moisture and cooler than average temperatures in June have kept the vegetation from drying out too quickly.
Soil moisture is above average across Northwest Wyoming and the Northern Rockies, whereas areas to our south in Utah and Colorado are much drier.
The National Interagency Fire Center released its monthly fire outlook, and Jackson Hole and most of Northwest Wyoming is not expected to see significant fire potential this month thanks to the recent moisture. Of course, that could all change by late July and August if we don’t manage to see any decent rainfall during the next several weeks.
Areas to our south in Utah and Colorado may not fare as well in terms of wildfire activity over the upcoming weeks, thanks to a warm and dry spring in these areas and now a delayed start to the monsoon.
Weekly Weather Outlook – July 6-12
As discussed, rain chances will be at a minimum over the next seven days and beyond. A cold front will arrive on Tuesday, and an afternoon thunderstorm can’t be ruled out as a result, but moisture will be limited so the chances are very low.
Otherwise, it will be an outstanding week to get outdoors. Tuesday and Wednesday will be a little bit cooler behind the cold front, then we will warm up into the low 80s by the end of the week and possibly into the mid 80s by this weekend as high pressure strengthens over the Rockies.
Alan Smith, Meteorologist
