681
FXUS65 KBOI 150235
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
835 PM MDT Sat Sep 14 2024

.DISCUSSION...Clouds continue to increase this evening in
advance of our approaching storm system. Showers and isolated
thunderstorms will move into eastern Oregon tomorrow and into
southwest Idaho tomorrow night. Models are trending slower with
the eastward progression of the system, and our afternoon
forecast team anticipated this development. Therefore, no update
is needed at this time.

&&

.AVIATION...VFR. Increasing mid-high level cloud cover into
Sunday. Local MVFR in scattered showers and isolated
thunderstorms Sunday afternoon/evening, and a slight chance of
thunder mainly in SE Oregon and S-Central Idaho. Surface winds:
variable 5-10 kt. Winds at 10kft: SW 10-20 kt.

KBOI...VFR. A less than 30% chance of showers Sunday evening.
While thunder isn`t impossible, chances are far too low to
include in the TAF. Surface winds: variable less than 6 kt
through 05Z, then SE 5-10 kt.

&&

.PREV DISCUSSION...
SHORT TERM...Tonight through Monday night...Increasing cloud
cover tonight as a very wet upper low approaches the coast.
Precipitation chances are 40% in SE Oregon Sunday afternoon and
increase to 60% Sunday evening with coverage expanding into
S-Central Idaho. The rest of the area has only a slight chance
of precipitation, near 20%. On Monday the low moves directly
south, and begins to move northeastward. As it pivots around our
area moisture flow will persist through the rest of the short
term. Much of the area has a 60% chance of precipitation Monday
evening, while Idaho stays about an 80% chance. While models
generally indicate an even higher chance of precipitation (up to
90%), we are skeptical about chances being that high while
showers remain the primary precipitation mode. PW`s are near the
95th percentile, so while it is a particularly moist system the
local nature of showery precip and possible deviations from the
forecast movement could be factors that burn the forecast. WPC
QPFs for Idaho Monday night through Tuesday are just under an
inch, while 24-hour ensemble QPFs for the same period are
0.4-0.6". While an indication of the uncertainty in the
precipitation forecast with this system, even 0.4" will some provide
relief to fires. Monday evening will be unstable, with some
decent dynamics present, so a chance of thunder exists. Heavy
rainfall underneath storms poses a flash flood risk on recent
burn scars.

LONG TERM...Tuesday through Saturday...Widespread showers set
to continue through Tuesday, so the concern of excessive
rainfall and flash flooding over burn scars continues. Another
upper low develops over the PacNW late Tuesday that tracks
further west and south than the previous one. Models currently
only show precipitation along our western and southern borders
with this system, so unless it gets a little closer it may just
miss us. Models diverge significantly after this system, with
the GFS and Canadian completely missing a trough that the ECMWF
has to our northeast. Temperatures remain 10-20 degrees below
normal for the whole period, with Boise hovering around 70
degree highs each day.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...None.
OR...None.

&&

$$

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DISCUSSION...SP
AVIATION.....SP
SHORT TERM...JM
LONG TERM....JM