Jonathan, Idaho Weather Forecast Discussion

375
FXUS65 KBOI 101524
AFDBOI
Area Forecast Discussion
National Weather Service Boise ID
924 AM MDT Wed Sep 10 2025
.DISCUSSION...
A closed low over northern California this morning is
approaching the region today and will bring widespread showers
and scattered thunderstorms. This morning`s sounding had 0.73
inches of precipitable water, around the 80th percentile. While
not astounding, the airmass being as cold as it is means this
amount of PW actually represents a fairly moist sounding. Thus,
while convection is a concern later today, the possibility for
cloud cover throughout the day may limit CAPE buildup, with HREF
ensemble minimums close to 50-100 J/kg while the mean/max is
closer to 400/800 respectively. This could inhibit thunderstorm
formation later today, but the moist atmosphere will mean heavy
to moderate rainfall is a possibility even in showers. This
morning we`ve already had a few strong storms form around Boise,
which none of the guidance indicated. Given this and rainfall
amounts out of "weaker looking" showers yesterday, we`ve put out
a Flash Flood Watch for Eastern Oregon especially across the
Falls, Cow Valley, and Durkee burn scars for debris flows and
excessive rainfall. Precipitation chances peak for much of the
area this afternoon, with light showers continuing overnight
before scattered convection develops again Thursday afternoon
and evening. On both days, thunderstorms could produce outflows
up to 50 mph and small hail.
&&
.AVIATION...VFR. Scattered showers and isolated thunderstorms
this morning. Otherwise mostly cloudy. Showers and
thunderstorms area- wide after 20Z Wednesday. Some storms could
contain wind gusts greater than 40 kt. Surface winds: variable
5-15 kt. Winds aloft at 10kft MSL: E-S 10-20 kt.
KBOI...VFR. Partly cloudy this morning. Morning storms are
moving out of the area quick. Chance for showers and
thunderstorms returns between 23Z Wednesday and 06Z Thursday.
Gusty outflow winds (40% of 35 kts or greater), small hail and
heavy rain could bring brief MVFR conditions. Winds are already
turning northwesterly 5-10 kt and should hold through the day.
&&
.PREV DISCUSSION...
SHORT TERM...Today through Friday night...A well-defined
closed low over northern California this morning will approach
the region today, bringing widespread showers and thunderstorms.
Conditions are favorable for heavy rainfall with stronger
embedded storms, especially across southeast Oregon, where flash
flooding and debris flows are possible on burn scars.
Satellite and radar show a large area of steady precipitation
over northwest Nevada early this morning ahead of the low
circulation. As the low shifts north-northeast, this area of
rain will move into 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. By afternoon, precipitation will lift north and west,
allowing for partial clearing and renewed thunderstorm
development aided by upper-level dynamics and modest surface
instability (CAPE 200 to 500 J/kg).
High-resolution guidance shows storms initiating along the
NevadaIdaho border around 2 PM MDT, then tracking north-
northwest through the Treasure Valley, western Magic Valley,
west-central Idaho mountains, and into Baker County, as well as
northern Malheur and Harney Counties. This second round of
precipitation could bring additional heavy rainfall to southeast
Oregon, further elevating the risk of flash flooding across
burn scars, especially the Durkee/Cow Valley and Falls scars. A
Flash Flood Watch is in effect for this area. Although locally
heavy rain is also possible across the west-central Idaho
mountains, conditions appear less favorable as the strongest
storms are more likely for southeast Oregon this evening. In
addition to heavy rain, small hail and outflow winds up to 50
mph are possible with bulk shear across the southern forecast
area approaching 50 kts.
The low center will drift across the region on Thursday,
maintaining showers and thunderstorms with the greatest focus
near the low center in southeast Oregon and over the mountains
of southwest Idaho. Precipitation chances will decrease Thursday
night with the loss of daytime heating. By Friday, scattered
showers will linger over higher terrain, mainly Baker County and
the west-central Idaho mountains, as the low exits the area.
Temperatures will be near normal today, with valley highs in the
low 80s, then cool to 5 to 10 degrees below normal Thursday and
Friday.
LONG TERM...Saturday through Wednesday...An upper-level ridge
will briefly build over the area Saturday, bringing a break from
precipitation and allowing temperatures to rebound to near
normal by Sunday. Another upper-level low will move into the
Pacific Northwest late Sunday into Monday, resulting in a 30 to
50 percent chance of showers and a slight chance of
thunderstorms during that period. Precipitation chances will
decrease Tuesday as the low shifts east. Overall, this pattern
will keep temperatures near to slightly below normal through the
extended period.
&&
.BOI WATCHES/WARNINGS/ADVISORIES...
ID...None.
OR...Flash Flood Watch from noon MDT /11 AM PDT/ today through this
     evening ORZ061>064.
&&
$$
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DISCUSSION...JM
AVIATION.....JM
SHORT TERM...JDS
LONG TERM....JDS

NWS BOI Office Area Forecast Discussion