640
FXUS65 KBOI 060307
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
907 PM MDT Sun May 5 2024

.DISCUSSION...An upper level low is progressing eastward across
northern Nevada this evening, positioning the surface somewhere
between Featherville and Ketchum by 8 PM. This system will
sustain the potential for precipitation until at least mid-
Monday morning. Convective showers are observed near the surface
low center, with additional wrap-around showers moving south
into southeast Oregon and the West Central Mountains tonight.
These showers are anticipated to reach southeast Oregon by 10 PM
and extend into southwest Idaho around 1 AM MDT, exiting
southeast Oregon by 3 AM MDT Monday and south-central Idaho by 8
AM MDT. Snow levels are expected to drop to around 4000 feet by
5 AM, leading to rain mixing with wet snow, primarily in the
Western Magic Valley, though minimal snow accumulation is
anticipated. Light snow is forecasted above 4500 feet with 1-3
inches possible tonight through Monday morning.

Following the departure of the low, a strengthening pressure
gradient will result in gusty winds, particularly early Monday,
especially in the Western Magic Valley and southern Twin Falls
County. Based on the model forecasts of the past five weeks,
there is a high likelihood (0.95) of advisory level winds
through much of Monday according to EC EFI. The latest guidance
indicates no deviation from this trend, thus the advisory
remains intact for tomorrow.

High- resolution models indicate a weak shortwave and cold
frontal passage late Monday from the northwest to southwest,
fostering scattered thunderstorm development. Thunderstorms are
expected to initiate across southeast Oregon around 1 PM MDT,
shifting southeastward and traversing the Treasure Valley around
5 PM MDT, then reaching the Western Magic Valley around 9 PM
MDT. Although instability is limited to around 200 J/KG, a 40-50
kt 700 MB jet is forecasted which is enough to support surface
wind gusts up to 45 KTS, especially with stronger storms along
the front. Additionally, storms could generate graupel or small
hail and cause blowing dust.

The wind forecast for tonight into Monday has been updated with
the latest guidance, but no changes are required to the wind
advisory at this time. An updated forecast will be released
shortly.

&&

.AVIATION...Numerous showers overnight with MVFR to IFR conditions.
Mountains obscured. Snow levels 4000-5000 ft MSL. Break in precip
Monday morning, then numerous afternoon showers with an up to 30%
chance for thunderstorms in most areas through Tue/06z. Potential
for small hail and outflow gusts to 30-45 kt. Surface winds: NW-SW
10-20 kt, except 15-25 kt with gusts 30-35 kt for MUO to JER/TWF
beginning early Monday. Winds aloft at 10kft MSL: W-NW 20-30 kt by
00z/Mon.

KBOI...VFR, then periods of MVFR in rain, mainly after Mon/06z.
A break in rain Mon/12z-23z, with a return to VFR. Showers and a 30%
chance of thunderstorms Monday afternoon/eve. Small hail and outflow
gusts to 35-45 kt possible, especially between Tue/00z and Tue/03z.
Surface winds: W-NW 10-15 kt, with gusts up to 25 kt a possibility
tonight.

&&

.PREV DISCUSSION...
SHORT TERM...Tonight through Tuesday night...At 2 PM MDT our
upper low was still centered in eastern OR with showers
extending from eastern NV through south-central ID, across the
Boise Mountains and Upper Weiser River area into Baker County
and western Harney County, but relatively dry closer to the low
center. The low is forecast to move eastward along the ID/NV
border tonight and the showers to the north and west of the
low center will move back over our CWA. As the low exits east
overnight, westerly winds will increase significantly in south-
central ID. A Wind Advisory has been issued for the Magic
Valley and southern Twin Falls County from 3 AM MDT to 6 PM MDT
Monday. After brief ridging and drying in western Idaho and
eastern Oregon Monday morning, another Pacific trough will move
inland later Monday and Monday night with more rain and mountain
snow. Monday night. That trough will exit east early Tuesday,
and again west winds will increase in south-central Idaho,
possibly even stronger than on Monday. Instability will allow a
slight chance of thunderstorms in all zones Monday afternoon,
and in southwest Idaho Monday evening, and again in eastern-most
Idaho zones Tuesday afternoon. Temperatures will change little
(i.e., stay cold) through Wednesday, with snow level generally
4000-5000 feet MSL.

LONG TERM...Wednesday through Sunday...An upper low will remain
over the western US through Thursday. This will keep temperatures
around 10 degrees below normal on Wednesday before warming to
near normal by Thursday as the trough exits the area. Thereafter,
an upper ridge is forecast to build over the Pacific NW and
southwest Canada on Friday into the weekend. Temperatures are
expected to rapidly rise to around 5-10 degrees above normal
during this time, with mostly dry conditions expected through
the weekend. Temperatures in the low elevations have a 50-70%
chance of hitting 80 degrees Saturday, with higher chances on
Sunday.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...Wind Advisory from 3 AM to 6 PM MDT Monday IDZ016-030.
OR...None.

&&

$$

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DISCUSSION...JDS
AVIATION.....JM
SHORT TERM...LC
LONG TERM....SH