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000
FXUS65 KBOI 131532
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
932 AM MDT Sat Apr 13 2024

.DISCUSSION...Areas of patchy fog that formed in mountain
valleys should mix out by later this morning, with above normal
temperatures and dry conditions anticipated for most of the
area. Showers southwest of Harney County in California are
moving northward as the upper level low moves inland. This low
still looks to bring showers and thunderstorms into Oregon
later this afternoon, however, hi-res models have delayed the
onset in Malheur-Harney County to later this evening around
7-8pm. Precipitation still looks to stay to the southwest of the
Snake River Valley, but there is a slight chance for weak
afternoon thunderstorms (20% chance) east of McCall early this
afternoon over the Central ID mountains with lingering
instability and moisture from the southerly flow. No forecast
updates necessary.

&&

.AVIATION...Patchy MVFR fog in northern valleys ending by Sat/17Z.
Scattered showers and isolated thunderstorms developing in central
Oregon this afternoon. This activity will eventually impact KBNO,
bringing bursts of rain, isolated lightning, and outflow wind gusts
up to 40 kt between Sun/00-06Z. Periods of MVFR in precipitation.
Surface winds: variable 5-10 kt, becoming E to SE 5-15 kt with gusts
to around 20 kt after Sat/18Z. Winds aloft at 10kft MSL: SE to S 15-
25 kt.

KBOI...VFR and mostly clear. Light southeast surface winds to 10 kt,
increasing to 10-20 kt after Sat/18Z.

Sunday Outlook...Mountain obscuration with MVFR to IFR in scattered
showers and thunderstorms in E Oregon and mountains of SW Idaho.
Isolated coverage in the Snake River Plain. Surface winds SW-SE 10-
25 kt, decreasing by sunset. Snow levels lowering to 6000-7500 ft
MSL Sunday.

&&

.HYDROLOGY...The Owyhee River below Owyhee Dam is expected to
remain above flood stage through early next week, then lowering
below flood stage on Wednesday. It is expected to lower from
moderate to minor flood stage by this afternoon.

&&

.PREV DISCUSSION...
SHORT TERM...Today through Monday night...Anticipate another
warm day ahead, albeit with increased cloud cover, courtesy of
a substantial low-pressure system lingering off the California
coast. This setup will maintain a southerly flow, pushing
temperatures above 80 degrees in many lower valley areas.
However, the influx of mid-level moisture shifting westward will
somewhat inhibit shower and thunderstorm activity today.

Satellite imagery shows the moisture axis stretching across
central Oregon which is expected to persist into late evening as
the low center gradually edges toward San Francisco. The
scarcity of moisture will hinder thunderstorm development,
despite favorable atmospheric conditions such as significant
wind shear and surface-based CAPEs ranging from 400-800 J/KG
across southeast Oregon later today. As the low and associated
moisture gradually progress eastward, isolated thunderstorms
will develop across Harney county this evening, possibly
extending into Malheur County after sunset. While high-
resolution models offer mixed signals regarding convective
development, inverted-V profiles suggest the potential for gusty
winds and hail within stronger storms, though the likelihood of
severe thunderstorms remains low, below 3%.

With the low center positioned to the southwest, expect
continued warm southeasterly flow across much of our forecast
area, resulting in temperatures approximately 15 degrees above
average. Several areas in the western Snake River Plain have a
85-95% chance of surpassing 80 degrees. Southeast Oregon may
experience slightly cooler temperatures and a slight chance of
precipitation, owing to its proximity to the northeast flank of
the upper low.

Guidance indicates the low center expanding across Nevada by
Sunday, with its northern edge extending northward across the
forecast area. This shift will bring cooler temperatures along
with showers and thunderstorms, particularly across southeast
Oregon and the West Central Mountains. While precipitation
patterns remain consistent in most guidance, the overall
instability and moisture levels suggest that most areas will
have at least a slight chance of showers and thunderstorms on
Sunday.

By Monday, the low center moves further east into Utah,
establishing a tight pressure gradient across the forecast area,
resulting in gusty winds. The lower valleys, stretching from
Baker City through the Western Magic Valley, are expected to
experience the strongest winds. Probabilistic data indicates a
50% chance of wind gusts exceeding 48 knots in the Western Magic
Valley Monday. Continued trends in guidance may necessitate
wind headlines for Monday afternoon.

LONG TERM...Tuesday through Saturday...A large upper level
trough over western Canada will move southeastward and clip the
forecast area Tuesday and Wednesday. Northwest flow will
increase and surface winds are expected to become breezy both
days. Models have backed off on the amount of cold air and
precipitation expected with this trough, resulting in
precipitation chances (15-30%) remaining limited to central
Idaho. Temperatures will lower to near/slightly below normal as
a result of the trough influence. Thereafter, models diverge on
how quickly the trough will exit and be replaced by a building
ridge. This progression will determine how fast temperatures are
able to rebound above normal toward the end of the week,
resulting in a lower confidence temperature forecast Thursday
and Friday. Overall, conditions are expected to trend warmer and
dry for the end of the week and into the early weekend
associated with increasing high pressure.

&&

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

&&

$$

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DISCUSSION...SA
AVIATION.....BW
HYDROLOGY...SA
SHORT TERM...JDS
LONG TERM....SH