709
FXUS65 KBOI 030918
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
318 AM MDT Mon Jun 3 2024

.SHORT TERM...Today through Wednesday night...The atmospheric
river has moved into the region tonight, bringing widespread
rainfall to the region. As of 2:30 am MDT, the McCall airport
has seen almost a third of an inch of rain, with hi-res models
indicating the stratiform rainfall to continue through about 8
am. Current forecasts show around 2 inches of rain falling over
ridgetops and 1 inch of rain falling in central ID mountain
valleys, with locally higher amounts depicted on a few
ridgetops west of the Long Valley. The Snake River Valley can
still expect to see about half of an inch of rain, while areas
in the rain shadow (eastern side) of the Owyhee Mountains/Blue
Mountains will likely see much less precipitation from the
stratiform event. A cold frontal passage later this morning
will bring a push of convective showers, with a potential for
training thunderstorms, mainly over high terrain in the West
Central Mountains. However, higher wind speeds aloft (30-40 kt
at 700 mb) look to slightly limit the potential for training
shower and thunderstorms. This combination of heavy rain during
the night with the potential for heavy rain from convective
showers in addition to the snowmelt could lead to rapid stream
and creek rises and minor flooding. Therefore, the flood watch
will remain in effect through Monday evening.

The cold frontal passage later this morning will also bring
breezy winds across the region, with gusts near ridgetops
reaching 40-50 mph, and sustained westerly winds near 20 mph
everywhere except the Snake River Valley. This will help with
some initial drying, although patchy valley fog and low stratus
has a potential (~40% chance) to form in sheltered high terrain
valleys that see a combination of overnight clearing with high
rainfall totals from Monday. Another push of moisture across the
Northern Panhandle will allow for some slight precipitation
chances over the northern portions of the West Central Mountains
on Tuesday evening. However, confidence is low due to weak
upper level dynamics. Temperatures will remain near normal as
zonal flow persists through Tuesday. However, much hotter
temperatures are expected to begin on Wednesday with the advent
of an upper level ridge building into the region.

.LONG TERM...Thursday through Monday...No significant changes in the
latest deterministic models and ensembles regarding the dominance of
an upper ridge across the region for the remainder of the week and
into the weekend. The summer-like pattern results in temperatures 15-
20 degrees above normal with highs in the 90s across the lower
valleys each day. There remains uncertainty in the amount of
moisture available to support convection. Probabilities of
afternoon/evening showers and thunderstorms remain low (15-30
percent chance). Models somewhat agree that a Pacific trough moves
through early next week for 5-10 degrees of cooling and drier/stable
conditions behind the exiting trough on Monday.

&&

.AVIATION...Rain through morning at all sites, decreasing from west
to east after 03/15Z. High confidence (90 percent chance) of
MVFR/IFR conditions at KMYL, low to moderate confidence (30-60
percent chance) elsewhere. Low confidence (less than 30 percent
chance) of thunderstorms (mainly SW Idaho) after 03/18Z. Mountains
obscured in rain and clouds. Areas of LLWS through 03/18Z. Surface
winds: SW-NW 10-20 kt, except SE 5-15 kt becoming W-NW after 03/16Z
in the Treasure Valley. Gusts to 35 kt mainly higher elevations. 10k
ft MSL winds: W 30-50 kt.

KBOI...VFR with low confidence (less than 30 percent chance) of MVFR
conditions. Rain persisting through late morning. Southeast winds 5-
15 kt with gusts to around 20 kt shifting to the northwest after
03/18Z.

&&

.HYDROLOGY...Current hydrologic forecasts indicate that, of the main
stem rivers, only the Middle Fork of the Payette in Crouch will
see a rise to action stage from this rainfall. However,
localized flooding from heavier convective showers are very
difficult to model with great precision, so there could be
impacts like rock slides in steep and mountainous terrain near
the heaviest rainfall totals. Near-surface soil is slightly
drier than is normal for this time of year, so there is some
room for at least initial rainfall to be absorbed by the soil.
Some smaller tributary creeks and streams could reach or exceed
bankfull resulting in minor flooding. Use caution if traveling
in the mountains on Monday and Tuesday, and avoid recreation
near rivers and creeks in mountainous and steep terrain.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...Flood Watch through this evening IDZ011-013.
OR...None.

&&

$$

www.weather.gov/Boise

Interact with us via social media:
www.facebook.com/NWSBoise
www.twitter.com/NWSBoise

SHORT TERM...SA
LONG TERM....BW
AVIATION.....BW
HYDROLOGY...SA