933
FXUS65 KPIH 271108
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
508 AM MDT Thu Aug 27 2026

.KEY MESSAGES...

- Marginal risk of severe thunderstorms in the southeast
  highlands today. Isolated thunderstorms forecast this afernoon and
  evening, and again Friday.

- Rainfall amounts from showers and thunderstorms way up on
  Saturday, with some areas having scattered thunderstorms.

- Today is the last hot day for a while. Strong cooling from
  today to Friday. Humidity trends higher.

&&

.DISCUSSION...
Issued at 144 AM MDT Thu Aug 27 2026

Today through Sat night...A trough will enter the Canadian west
coast tonight, shifting airflow to more southwest and
increasing its strength. This will still allow some isolated
showers and thunderstorms for the afternoon and evening tonight.
Wind will also be much stronger than the barely there wind of
the previous 6 days--not that it is approaching Wind Advisory.
The airflow is also bringing in slightly warmer air, and this
will be the warmest day of the next seven. SPC analysis is that
there is a marginal risk of severe thunderstorms in the
southeast highlands for today and tonight.

The model run tonight is doing things a little different. In the
past few days, this trough was staying in southern Canada.
However, tonight the trough turns into a closed low and digs
southward into the American Pacific Northwest, and is still
there on Sat afternoon. Strong upper level wind continues, and
quite a bit more moisture is flowing into southern Idaho.
Precipitable water over all but the central Idaho mountains
exceeds or hovers around 1 inch, which indicates heavy rains. On
the more positive side, extensive cloud cover could reduce the
coverage of thunderstorms, and right now it appears as though
scattered thunderstorms will be limited both Fri and Sat to the
east and southeast highlands, mostly.

Extensive cloud cover, the troughing getting closer than
previous model runs, and evaporative cooling is now generating a
tremendous cool-down from today to Fri. 8 to 12 deg F from one
day to the next, then another 1 to 5 deg F cooling from Fri to
Sat. Overnight lows will cool substantially from tonight to Fri
night, and then small drop Fri to Sat night, just not of the
same magnitude as the high temperatures.

The closer proximity of the low now means overall stronger
surface wind is likely. Sat and Sat night look particularly
moderate at least for the Snake River plain, while today and Fri
will only be that way in the afternoon.

Sun through Wed...On Sun night the closed low will eventually
move to the east of Idaho. In its wake is a dry westerly flow.
Temperatures continue in the cooling trend until Sun afternoon.
Then clearer skies and strong sunshine will bring back a warming
trend; by Mon, temperatures are back to near normal for the time
of year. Wind will still be moderate to strong each afternoon
and evening during this period. However, the thunderstorm and
precipitation risk drops, well, precipitously, from Mon onward.
The upper level ridge axis stays farther east that it has been
lately, and this puts the monsoonal remnants moving into eastern
Utah and Wyoming rather than southern Idaho--for most of the
time.

A key thing, though, is that this change in the forecast is new.
Will guidance keep this new closed low scenario, or dump it
during the days model runs today. Stay tuned.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 501 AM MDT Thu Aug 27 2026

High pressure is starting to give way to a low that will
eventually move into Washington state from the Pacific. Wind
will be the main difference compared to previous days: expect
some G25KT outside of the TSRA expected. TSRA only expected only
at KDIJ, KIDA, and KPIH. Threat at KSUN is extremely low, and
KBYI very low. SHRA should develop with these TS. The moisture
coming in today remains mainly at or above 9000ft AGL, and by
afternoon there should start being CIGs, but nothing impactful.
VSBY not expected to be affected at this time. G45KT to be
expected from TSRA outflow.

&&

.FIRE WEATHER...
Issued at 144 AM MDT Thu Aug 27 2026

The weather forecast is trending wetter and significantly cooler
for a few days starting Fri and continuing into Mon afternoon. A
trough has been expected to cross through southern Canada,
moving a a moderate pace for the summertime and bringing a
moderate cool-down over a couple of days, then a gradual warming
trend. This is changed in the overnight model runs.

A closed low now develops instead of a trough. Closed lows move
rather slow. And even as of Sat this low is still west of Idaho.
This pattern will allow abundant moisture now to flow into
southern Idaho, upping cloud cover, precipitation amounts, and
humidity. It will decrease temperatures more substantially;
instead of a 8 to 12 deg F drop to the high over two days, the
same period will experience a 11 to 16 degree drop now. With
this closed low farther south than previous thinking, wind will
be stronger as well. The unknown is what will happen to
thunderstorm activity. If the cloud cover lingers and is
extensive enough, not enough daytime heating will occur to
trigger thunderstorms, except where breaks in the clouds occur.

Thus, all of these changes are favorable to wildland fire-
fighting efforts, as long as this change is not a blip in the
continuity of automated guidance.

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION...Messick
AVIATION...Messick
FIRE WEATHER...Messick