Heavy Rain in Oregon, May 4 to 5, 2024

Area Forecast Discussion
National Weather Service Boise ID
431 AM MDT Sat May 4 2024

.SHORT TERM...Today through Monday night...A deep closed low
positioned off the Oregon coast will come onshore near the
OR/CA border this evening. Showers will break out today in the
increasingly unstable airmass ahead of the low center. A
minimal threat for thunderstorms exists over s-central Idaho
where instability and surface heating overlap with a strong
shear environment. Gusty easterly winds will strengthen through
the morning, channeling through the Snake Plain and Baker
Valley while a strong southerly flow aloft (30-40kt at ~5kft
MSL) mixes to the surface across higher terrain of SE Oregon.
The focus of strongest winds will be across Malheur County in
Oregon and portions of the Treasure Valley where sustained winds
of 25-35 mph and gusts of 40-50 mph are expected. These areas
remain covered by a Wind Advisory.

A band of heavier, steady precipitation will develop along a
cold front which will track into SE Oregon early this afternoon
and SW Idaho by this evening. Precipitation rates of
0.10-0.20"/hr are expected along this line which will be
accompanied by a wind shift to the W-NW. Snow levels of 7-9kft
MSL ahead of the front today will drop to 3-4kft across SE
Oregon and 4-6kft over SW Idaho by Sunday morning. Areas of
Harney county and the western Magic Valley could see
precipitation mix with or change to snow, though surface
temperatures will likely be too warm for any accumulation.
Widespread showers continue in the mountains through Monday
night as the main upper low is followed by a weaker trailing
trough. Lower valleys catch a brief break Sunday night into
early Monday, before the trailing wave brings another round of
rain/snow.

The axis of heavier precipitation totals through Sunday night
arcs from Baker County into the w-central ID mtns south into
lower Snake Plain. These areas will see totals of 0.5-1.0" in
the valleys and 0.75-1.5" in the mountains. Otherwise a
widespread 0.2-0.5" of liquid is expected through Sunday night.
The heaviest snow will be above 5500 feet where total
accumulation of 4-8 inches with locally higher amounts is
possible.

.LONG TERM...Tuesday through Saturday...Showers continue Tuesday
as the low gradually shifts eastward. An upper ridge builds
along the West Coast on Wednesday while the recently departed
low will circle over the upper Great Plains through the
remainder of the week. Models show some variability in how far
west the low will retrograde and introduce the possibility of a
piece splitting off and resettling over the eastern Great
Basin late in the week. While much of the area dries out
starting Wednesday, a slight chance of showers (~20%) remains
over w-central Idaho through Thursday. Temperatures will slowly
warm through the end of the week.

&&

.AVIATION...VFR today. Rain and high mtn snow moving into SE OR
by late morning and into SW ID late afternoon. Isolated
thunderstorms across SW ID Saturday afternoon. Local MVFR/IFR
conditions limited to mountains through this afternoon,
increasing across lower elevations overnight. Mountain
obscuration in precipitation becoming widespread tonight. Snow
levels 7-9kft MSL, lowering to 3-4kft SE OR and 4-6kft SW ID by
Sunday morning. Areas of LLWS this morning, mostly in corridor
from KBKE-KBOI with winds S-SE 35-45 kt at 2000 ft AGL. Surface
winds: S-SE 10-25 kt, with gusts 25-40 kt becoming W-NW 10-20
kt this evening. Winds aloft at 10kft MSL: S 20-40 kt.

KBOI...VFR today with gusty SE surface winds. Rain this evening
will bring wind shift to NW and periods of MVFR conditions.
After 03Z probability of ceilings below 2kft increases to
30-50% with a 20-30% chance of IFR conditions developing.

Sunday Outlook...Change to snow in the mountains will produce
widespread IFR and obscure terrain across w-central Idaho and
e-central Oregon. Snow levels 3500-5500 feet, lowest in SE
Oregon Sunday morning. Elsewhere low VFR-MVFR with showers
continuing through the day. Surface winds: W 10-20 kt with gusts
20-30 kt.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...Wind Advisory from 9 AM this morning to 6 PM MDT this evening
     IDZ014-016.
OR...Wind Advisory from 8 AM to 5 PM PDT Saturday ORZ061.

&&

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SHORT TERM...DG
LONG TERM....DG
AVIATION.....DG