Sunrise 6:11 AM   Sunset 9:11 PM Moonrise 6:41 PM   Moonset 3:58 AM

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FXUS65 KBOI 210920 AFDBOI

Area Forecast Discussion National Weather Service Boise ID 320 AM MDT Tue May 21 2024

SHORT TERM
Today through Thursday night...Dry and cool north flow aloft this morning will transition to warmer west- northwest as weak ridging builds over the Pacific Northwest today. While temperatures will remain slightly below normal, today will be the warmest day in the short term period. A cold, vigorous trough will approach from western Canada late tonight, spreading moisture southeastward overnight through early Thursday. Precipitation is likely (70-100% chance) for the majority of the forecast area Wednesday morning and/or afternoon ahead and along the accompanying cold front.
Afternoon instability will ramp up as the relatively cold air mass moves overhead and enough lift is generated with the front.
This will promote convective activity with a slight chance (15%) of thunderstorms for late Wednesday morning/afternoon, as the center of the low continues to track into northeast Oregon and w-central Idaho.

In addition to shower activity, west and northwest winds will become breezy to windy along and behind the cold front, with gusts reaching 30-40 mph in east Oregon and far southwest/south- central Idaho. Temperatures will cool to 10-15 degrees below normal for Wednesday and Thursday from the colder air influence and wet weather. In correlation, snow levels will rapidly lower throughout the day Wednesday, allowing the potential for light snow accumulations as low as 4500 ft MSL by Wednesday night.
There is a 60% chance or greater that elevations above 7000 ft will receive at least 6 inches of total snow accumulation in the central Idaho mountains Wednesday through Thursday afternoon.
While shower coverage will begin to decrease by Wednesday evening, wrap-around moisture behind the low will maintain a chance of showers (30-50%) over the southwest Idaho mountains through Thursday afternoon. Breezy west-northwest winds will continue Thursday afternoon/eve in south-central Idaho while drier north-northwest flow aloft establishes over the forecast area.

LONG TERM
Friday through Tuesday...Fair and mostly sunny skies will start off the period and dominate throughout most of the five day extended forecast. The exception, starting late Friday through all of Saturday, will be a change to showery conditions as a rapid influx of moist, unsettled atmospheric determinants associated with a closed low pressure system speeds through the region. The track of this system will direct most of the activity across the northern thru northeastern portions of the forecast area with the lion's share dropping out across Adams and Valley counties Saturday afternoon. Model probabilities show 30 to 40 percent chances for precipitation, with isolated areas in and near Valley county experiencing chances between 55 to 75 percent. With the drop in snow levels in the north (to between 5500 and 6500 ft) during this onslaught, the higher elevations could see a dusting of snow. Breezy winds are also expected on Saturday throughout the major valleys and higher elevations in the south, especially around showers. By Monday a relatively drier, more stable ridge will build into the region allowing for sunnier skies and temperatures to warm up once again to normals and slightly above.

AVIATION
VFR. Increasing and lowering clouds today. Numerous showers after Wed/03Z in E Oregon, and after Wed/06Z in SW Idaho. Showers creating periods of MVFR in valleys, IFR/LIFR in mountains. Mountains becoming obscured. Snow levels 6500-7500 ft MSL tonight, lowering Wed. Surface winds: variable less than 10 kt, then SW to NW 5-15 kt by late morning. Winds aloft at 10k ft MSL: NW 5-15 kt, then W-SW 10-20 kt after Tue/18Z.

KBOI...VFR. Increasing and lowering clouds beginning this afternoon/eve. Rain beginning around Wed/09-11Z, with a 20% chance of brief MVFR ceilings. Winds: light/variable becoming NW 5-10 kt after Tue/16Z, then SE around sunset. Brief switch to NW winds 10-20 kt with the cold front/rain early Wed morning.

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

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