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FXUS65 KBOI 041528

AFDBOI



Area Forecast Discussion

National Weather Service Boise ID

928 AM MDT Sat May 4 2024



.DISCUSSION...Major north Pacific storm now moving onshore 

in Oregon. Ahead of it, warm, dry air in our CWA with gusty 

southeast to south winds today. Wind Advisory remains in 

effect for the Upper Treasure Valley, Western Magic Valley,

and Harney County. Winds will decrease before the rain moves 

in. Rainfall will be substantial as the storm's cold front

moves through: .15 to .50 inch in the Oregon valleys, .50 to 

1.00 inch in the Oregon mountains, .40 to 1.00 inch in the

Idaho valleys, and .80 to 1.75 inch in the Idaho mountains. 

That is, wetter in Idaho than in Oregon. Forecast also has

a 20 percent chance of thunderstorms in south-central Idaho 

this afternoon. Much colder behind the cold front overnight 

and Sunday, with a little wet snow down to the valley floors

in eastern Oregon early Sunday morning, and as low as 4000

feet MSL in western Idaho. Current forecast is on track. 

No updates at this time.



&&



.AVIATION...VFR today. Rain and high mtn snow moving into 

SE OR this morning and into SW ID this afternoon. Isolated 

thunderstorms across SW ID this 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 Sunday morning. Areas of LLWS this morning near KONO 

with winds S-SE 35-45 kt at 2000 ft AGL and light winds at

the surface. 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...Rain changing 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.



&&



.PREV DISCUSSION...

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 strongly 

sheared 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 will 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 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

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.



&&



.BOI WATCHES/WARNINGS/ADVISORIES...

ID...Wind Advisory until 6 PM MDT this evening IDZ014-016.

OR...Wind Advisory until 5 PM PDT this afternoon ORZ061.



&&



$$



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DISCUSSION...LC

AVIATION.....SP

SHORT TERM...DG

LONG TERM....DG