Drewsey, Oregon Weather Forecast Discussion

370
FXUS65 KBOI 270250
AFDBOI
Area Forecast Discussion
National Weather Service Boise ID
850 PM MDT Fri Sep 26 2025
.DISCUSSION...Clear skies and light winds are expected tonight
as a weaker upper-level ridge develops behind last night`s
exiting trough. This ridge will lead to clear, colder nights and
sunny, warm days through Sunday. Sunrise inversions on Saturday
morning will allow temperatures to dip a few degrees below
normal. Highs on Saturday will climb to about 5 degrees warmer
than today, with several more degrees of warming expected
Saturday night into Sunday. By Sunday, highs will be
approximately 10 degrees above normal.
A large upper-level system is expected to reach the Pacific
Northwest later on Sunday, marking a significant shift to colder
and wetter conditions more in line with climatology. This system
has the potential to produce periods of moderate rainfall and
breezy conditions from Monday through Wednesday. During this
period, 3-day rainfall totals are forecast to be between 0.75
and 1.25 inches in the mountains, and between 0.25 and 0.75
inches across lower elevations. The current forecast handles
this well, so no updates are needed at this time.
&&
.AVIATION...VFR and clear skies. Surface winds: W-NW 5-15 kt,
becoming variable up to 10kt after sunset. Winds aloft at 10kft MSL:
N-W 10-15 becoming variable 5-10 by Sat/06z.
KBOI...VFR. Surface winds: NW 5-10 kt, becoming light and variable
after Sat/04z.
Weekend Outlook...VFR. Slight chance of showers/thunderstorms in S-
central Idaho Sunday afternoon and evening, thunder capable of
localized outflows of 30 kt. Increasing mid/high-level clouds
Sunday. Surface winds: Variable up to 10 kt through saturday,
becoming SE-SW 10-20kt through Sunday. Winds aloft at 10kft MSL: W-
SW 5-15 kt through Saturday, increasing to 15-25 kt through Sunday.
&&
.PREV DISCUSSION...
SHORT TERM...Tonight through Sunday night...Clear nights and
sunny, warm days through Sunday as a flat upper ridge replaces
last night`s trough which has already moved well east of our
area. Colder tonight in the valleys with little wind to disturb
the sunrise inversion, then about 5 degrees warmer highs
Saturday compared to today. Several degrees further warming
Saturday night and Sunday, with highs Sunday about 10 degrees
above normal. Latest models increase clouds from the south in
south-central Idaho on Sunday as a low pressure area that has
been holding in southern California finally moves into Nevada.
We are forecasting a 10-20 percent chance of showers and
thunderstorms in Twin Falls County late Sunday and Sunday
evening. Clouds will also increase in eastern Oregon Sunday
evening well ahead of a strong Pacific cold front moving onto
the WA and OR coast. A 20-30 percent chance of pre-frontal light
rain showers will begin in Harney County OR Sunday evening, and
the rest of eastern OR overnight, with a 15 percent chance of
showers even in the mountains of western ID toward sunrise.
Winds through Sunday morning will be generally light diurnal,
then become SE through SW Sunday afternoon. SE gusts to 20 mph
are forecast in the Snake Basin late Sunday, and SW gusts to 30
mph in Harney County Sunday night. The stronger winds, and
increasing cloud cover, will continue and will moderate low
temps in the valleys of our CWA Sunday night.
LONG TERM...Monday through Friday...A deep, slow moving upper
trough will impact the Pac NW early next week. Monday will see
the first wave of precipitation arrive along the leading edge
of the upper trough and accompanying cold front. While southwest
flow aloft will add a potential for shadowing, the dynamics and
forcing along the front look to be enough for lower elevations
to see a period of rain and possible thunderstorms on Monday.
Models are in agreement on the precipitation developing along
the front as it exits Oregon resulting in higher amounts east
of the ID/OR border. The main trough remains positioned along
the Pac NW coast through Wednesday with upper waves embedded in
the SW flow aloft bringing periods of additional rainfall to
the region. The 3-day totals (Mon-Wed) place 0.75" to 1.25" in
the mountains with 0.25" to 0.75" across lower elevations. While
confidence in the Thur/Fri forecast is low, the ensemble mean
has trended wetter at least on Thursday as models pick up on
the main trough getting kicked inland. Friday is dry but will
depend on the amplitude/timing of the exiting trough.
Temperatures are 5-10 degrees below normal all of next week
with Tue-Thur being the coolest days.
&&
.BOI WATCHES/WARNINGS/ADVISORIES...
ID...None.
OR...None.
&&
$$
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DISCUSSION...JDS
AVIATION.....NF
SHORT TERM...LC
LONG TERM....DG

NWS BOI Office Area Forecast Discussion