Haines, Oregon Weather Forecast Discussion

055
FXUS65 KBOI 091618
AFDBOI
Area Forecast Discussion
National Weather Service Boise ID
1018 AM MDT Tue Sep 9 2025
.DISCUSSION...Update was made to the forecast this morning to
increase shower and thunderstorm coverage across the Lower
Treasure Valley into Baker County. Isolated showers and
thunderstorms will continue to lift north this morning, mainly
north of an Ontario to Stanley line. Ahead of an upper level
low over southwest Oregon, there will be enough moisture and
instability for scattered showers and thunderstorms to develop this
afternoon over the central Idaho mountains. Brief heavy rain,
small hail, and gusty outflow winds will be the main threat. The
low will gradually move east on Wednesday with embedded
shortwaves rotating around the low. Lift associated with the
shortwaves combined with precipitable water values around the
80th to 90th percentile will allow for more widespread shower
and thunderstorm development, with a threat for heavy rain,
hail, and gusty outflow winds.
&&
.AVIATION...Mainly VFR. Isolated showers and thunderstorms
between KBKE/KONO/KMYL this morning, otherwise partly cloudy.
Showers and thunderstorms redeveloping this afternoon and
evening in the central ID mtns, primarily near and east of KMYL.
Gusty outflow winds with stronger storms up to 40 kts and
mountain obscuration in precipitation, along with small hail
possible. Additional showers and isolated thunderstorms moving
through overnight into Wednesday morning. Surface winds:
SW-NW 5-10 kt. Winds aloft at 10kft MSL: S-SW 5-15 kt.
KBOI...VFR under mid to high clouds. A 10% chance of showers
and thunderstorms this afternoon. Light rain showers moving
through overnight. Winds NW 4-8 kt.
&&
.PREV DISCUSSION...
SHORT TERM...Today through Thursday night...Today through
Thursday night...A well-defined and slow-moving closed low
pressure system to the west will bring periods of precipitation
through Thursday. Showers and thunderstorms have already
developed across south-central Idaho this morning in response to
good diffluence aloft. Satellite imagery shows the low centered
just off the southwest Oregon coast, with the jet maximum and
moisture plume reaching the Sierra Nevada. This jet and moisture
will lift north-northeast through the day, arriving over the
west-central Idaho mountains this afternoon where thunderstorm
development will be focused. With bulk shear near 30 kts and
CAPE values around 500 J/kg, storms are expected to be longer-
lived and capable of producing brief heavy rain, gusty winds,
and small hail. Meanwhile, a dry slot to the west will limit
storm activity across southeast Oregon.
By Wednesday afternoon the mid-level circulation will move into
southeast Oregon. Showers and thunderstorms will continue to
precede the low, developing over south-central Idaho and the
west-central Idaho mountains, while steadier precipitation
organizes beneath the low across Harney and Malheur Counties.
Precipitable water values of 0.75 to 0.85 inches will support
locally heavy rainfall, highlighted in WPCs Marginal Risk for
Excessive Rainfall. In southwest Idaho, heavy rain will be tied
more to thunderstorms, while southeast Oregon will experience a
longer-duration moderate to locally heavy rainfall with embedded
convection.
High-resolution models depict a favorable environment for
thunderstorms across southwest Idaho Wednesday afternoon,
extending from the west-central Idaho mountains through the
Treasure Valley and western Magic Valley to the Idaho-Nevada
border. This area will initially sit within a dry slot ahead of
an embedded shortwave, allowing for partial clearing and surface
CAPE values up to 800 J/kg with bulk shear around 30 kts. If
this trend holds, a few strong to severe storms will be possible
for strong wind gusts in addition to the potential for heavy
rain.
The low center will drift over the forecast area on Thursday,
keeping showers and thunderstorms in place, though driven more
by weak instability and lift. Temperatures will be near normal
today, with valley highs in the low 80s, before cooling to 5 to
10 degrees below normal Wednesday and Thursday.
LONG TERM...Friday through Tuesday...The upper level low
pressure system will move to our east on Friday, taking most of
the moisture with it but keeping us in a cooler regime. Shower
and thunderstorm chances stay elevated (20-30%) across higher
terrain in Central Idaho and near the NV border during the
weekend. High temperatures will stay slightly below normal, with
valley highs in the upper 70s through the weekend.
A negatively tilted longwave trough will deepen over the West
Coast on Sunday, bringing another push of moisture with cooler
air late on Sunday into Monday. Models show substantial
disagreement on positioning of the trough by early next week,
with varying impacts on precipitation totals and high
temperatures. Current forecasts call for about a 20-30% chance
of showers/thunderstorms through Tuesday morning, with a slight
indication that there will be a ridge building back in late
Tuesday. Valleys look to stay mostly clear on Monday and
Tuesday, with only about a 10-20% chance of
showers/thunderstorms.
&&
.BOI WATCHES/WARNINGS/ADVISORIES...
ID...None.
OR...None.
&&
$$
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DISCUSSION...ST
AVIATION.....ST
SHORT TERM...JDS
LONG TERM....SA

NWS BOI Office Area Forecast Discussion