Mc Call, Idaho Weather Forecast Discussion

558
FXUS65 KBOI 090908
AFDBOI
Area Forecast Discussion
National Weather Service Boise ID
308 AM MDT Tue Sep 9 2025
.SHORT TERM...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 susbtantial 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.
&&
.AVIATION...VFR. Isolated showers and thunderstorms over high
terrain in SW ID and near KBKE this morning, otherwise partly
cloudy. Showers and thunderstorms redeveloping this afternoon in SW
ID, primarily near KMYL. Gusty outflow winds with stronger storms up
to 40 kts and mountain obscuration in precipitation. Surface winds:
variable less than 10 kt. Winds aloft at 10kft MSL: SW-S 5-15 kt.
KBOI...VFR with some mid level clouds overnight and a 20% chance of
showers and thunderstorms this afternoon. Winds NW 4-8 kt becoming
SE less than 10 kt.
&&
.BOI WATCHES/WARNINGS/ADVISORIES...
ID...None.
OR...None.
&&
$$
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SHORT TERM...JDS
LONG TERM....SA
AVIATION.....SA

NWS BOI Office Area Forecast Discussion