Multiple slow-moving areas of low pressure will spin around the Northern/Central Rockies with high moisture levels expected through the weekend. Lightning activity will be more limited but still possible. Fri will be the wettest day in the near term with off-and-on rain throughout the day. Sat also looks showery but not quite as wet as Fri. Sun looks slightly drier but showers are still expected.
Short Term Forecast
Forecast for Friday:
Cloudy skies and periods of rain can be expected throughout the day and also during the overnight hours. Areas of low pressure will be located over Wyoming and Idaho, and this will result in erratic and generally weak winds in the mid-levels of the atmosphere.
As a result, showers will be fairly slow-moving while winds in the upper atmosphere will generally keep the overall movement going in an east-to-west direction (reverse of normal).
Heavy cloud cover and cooler temperatures will limit the strength of updrafts (i.e. rising air currents), resulting in limited lightning activity though occasional strikes couldn't be ruled out.
High levels of water vapor in the atmosphere could result in heavy rain at times. The greatest threat for heavy rainfall and flash flooding will exist along the eastern slopes of the Continental Divide in the Absaroka and Wind River Ranges, where Flash Flood Watches are currently in effect.
A more significant threat for flooding will exist in Southwest Montana, especially in the Beartooth Range and surrounding environs.
Yellowstone will see a threat for heavy rainfall/flash flooding as well (but nothing like they saw last summer – more of an isolated threat), while the localized flooding threat will be lower but not impossible in the Tetons.
Rainfall amounts look fairly impressive over the next 24 hours across Teton County, but more in a beneficial/soaking rain kind of way with less of a flooding threat. Generally speaking, we should see rain amounts of 0.5 to 1.0" in the Tetons and 0.25 to 0.75" in the valleys from Friday AM through Saturday AM.
Isolated higher amounts are also possible in any of these areas if (and where) heavy slow-moving showers or thunderstorms manage to develop.
Snow levels on Friday (and in the days to follow) will generally range from 11,000-12,000 feet with the tops of the highest peaks getting hit with wet snow.
Forecast for Saturday:
Wet conditions will continue heading into the weekend with off-and-on showers during both the morning and the afternoon. Rainfall should be lighter on Saturday compared to Friday, however.
Winds aloft will remain weak and erratic, resulting in slow-moving showers. But we should see shower/storm motions transition back to more of a west-to-east movement.
Lightning activity will also be limited with heavy cloud cover in place resulting in limited heating/instability, though occasional lightning strikes are possible. If we happen to see any breaks in the cloud cover in the afternoon and the sun comes out (unlikely but possible), then the thunderstorm threat would increase.
Shower activity may be lighter and less widespread on Saturday night compared to Friday night, but we will still see a chance of showers throughout the night.
Forecast for Sunday:
We may see some slight improvement on Sunday compared to Friday and Saturday with more breaks in the clouds possible along with slightly warmer temperatures and less widespread showers. That being said, I still expect a fairly active day with showers possible at any time, especially during the afternoon.
Thunderstorms are also possible, though likelihood and coverage will depend on cloud cover and how much sunshine we see during peak heating hours.
Shower/storm motions will transition from a south/southeast to north/northwest direction in response to an area of low pressure moving into Eastern Idaho.
Three-day rain totals through the weekend will generally range from 0.75 to 1.50" in the Tetons and Yellowstone, and 0.40 to 1.00" in the valleys, but fluctuations and isolated higher totals will also be possible in this type of pattern. Significant rain totals are likely north of the Montana border, especially in the Beartooth Range.
Outlook for Next Week (June 5th-11th):
Monday is looking a bit warmer and drier compared to prior days with more sunshine also expected, at least during the first half of the day. This will be in response to an area of low pressure moving east of our area.
However, lingering moisture along with increased sunshine and solar heating will support a good chance of afternoon thunderstorms. In other words, rainfall and cloud cover will be less compared to prior days, but the threat of lightning will be higher during the afternoon hours compared to prior days.
As the week progresses, a larger area of low pressure will work its way into Southern California and the Southwest U.S. with southerly winds and increased "energy" downstream of this system transporting subtropical moisture back into our region.
The result will be another uptick in shower and thunderstorm chances, starting Tuesday and likely continuing through the end of the week. In other words, the active pattern will continue with uncertainty in the day-to-day details this far out.
Temperatures will be warmest early in the week then will gradually trend cooler with increased cloud cover. However, similar to recent weeks, no real cold fronts are expected in this pattern, and snow levels will remain high as a result.
Thanks so much for reading! Next update on Monday (June 5).