659
FXUS65 KPIH 220345
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
945 PM MDT Fri Aug 21 2026

.KEY MESSAGES...

- Heat Advisories Active Today: Heat Advisories remain in
  effect through this evening across lower elevations, where
  peak afternoon temperatures will reach the mid-90s to lower
  100s.

- Severe Microburst Risk Tonight (4565 mph Gusts): Monsoonal
  moisture surging into deeply dry lower atmospheric layers
  (inverted-V profiles) will support evening and overnight
  thunderstorms capable of producing localized severe dry
  microburst wind gusts of 45 to 65 mph, especially across the
  lower Snake Plain, Magic Valley, and South Hills.

- Widespread Saturday Storms & Fire Concerns: Convective
  coverage increases markedly on Saturday, introducing
  heightened fire weather concerns from lightning and erratic
  outflow winds before the main trough exits into Western Canada
  on Sunday.

- Seasonable Late-August Trend Next Week: A modest ridge
  rebuilds next week, maintaining isolated afternoon monsoonal
  storm chances and near-normal temperatures in the mid-to-upper
  80s.

&&

.DISCUSSION...
Issued at 134 PM MDT Fri Aug 21 2026

Unseasonably hot conditions continue across eastern Idaho this
afternoon, with widespread lower-elevation Heat Advisories
remaining active through this evening. Temperatures have climbed
rapidly into the lower 90s and are on track to top out in the
mid-90s, with localized readings exceeding 100F across the
lower Snake Plain and Magic Valley prior to peak heating. Mostly
sunny skies will give way to increasing cloudiness late this
afternoon and evening as a plume of monsoonal moisture surges
northward through the Great Basin ahead of an upper-level trough
entering the Pacific Northwest.

High-resolution convective-allowing models (CAMs) continue to
advertise elevated shower and thunderstorm development beginning
this evening and lingering into the early overnight hours.
Forecast soundings reveal deeply inverted-V thermal profiles
across the lower boundary layer, creating an environment highly
efficient at generating strong convective downdrafts. Stronger
storms tonight will be capable of producing localized microburst
wind gusts of 45 to 65 mph, with the highest threat centered
across the lower Snake Plain, Magic Valley, and South Hills.
Nocturnal showers and embedded storms will persist through the
first half of the overnight period.

Following a brief early-morning lull, a more widespread wave of
showers and thunderstorms will overspread eastern Idaho on
Saturday. The combination of widespread lightning strikes and
gusty, erratic outflow winds will introduce elevated fire
weather concerns across dry fuel beds. As the primary upper-
level trough pushes northeastward into Western Canada on Sunday,
large-scale forcing will wane, restricting lingering shower and
thunderstorm chances primarily to the higher terrain.

Subtropical high pressure over the Four Corners will slowly
attempt to rebuild toward the Great Basin early next week.
However, the ambient upper-level flow pattern will remain
favorable for sending weak, periodic pushes of monsoonal
moisture into the Intermountain West. This will maintain at
least isolated afternoon and evening thunderstorm chances
through mid-week. Because 500mb heights are forecast to remain
modest, extreme heat is not expected to return next week.
Daytime maximum temperatures will hold right around seasonal
climatological norms for late August, topping out in the mid-to-
upper 80s across lower elevations with only isolated spots
briefly reaching 90F.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 945 PM MDT Fri Aug 21 2026

Quite a bit of mostly showers with isolated thunderstorms
working up from the south. A rogue gust to 30kts is possible
overnight, but probably not very likely. Convection should clear
around 12z with next round of storms expected during the
afternoon.

&&

.FIRE WEATHER...
Issued at 134 PM MDT Fri Aug 21 2026

Monsoon moisture is beginning to work its way back into Eastern
Idaho today and will continue through this weekend. Isolated storms
will begin to pop up across the area this afternoon and activity
becomes a bit more widespread overnight, though how much lightning
will continue into tonight is a bit more uncertain. Strong wind
gusts to 60 mph will be the main concern with storms today and again
tomorrow with portions of the area under a Marginal Risk for severe
storms both days. As thunderstorms begin to fire on Saturday
afternoon, coverage will also increase, so a RED FLAG WARNING has
been issued for Fire Weather Zones 410, 422, 425, 427, 475, and 476
due to the scattered coverage. These will be a mix of wet and dry
storms with some of the drier storms more likely up in the Central
Mountains and storms becoming wetter farther east. This is also part
of the reason for leaving FWZ 411 and 413 out of the RFW. Coverage
in those two zones will be isolated to nearly scattered at times.
Heading into Sunday, it will be breezy with wind gusts of 25 to 35
mph and min RHs still in the 15 to 20 percent range in the Central
Mountains, so near-critical fire weather conditions will exist there
again, but min RHs elsewhere will range from 20 to 30 percent. We
will still see some isolated to nearly scattered thunderstorms on
Sunday, too. In fact, this monsoon moisture will continue each
afternoon through at least the first half of next week.

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 10 PM MDT this evening for IDZ051>059-061-
062-064-065-067-075.
Red Flag Warning from noon to 9 PM MDT Saturday for IDZ410-422-
425-427-475-476.

&&

$$

DISCUSSION...McKaughan
AVIATION...13
FIRE WEATHER...Messick