textproduct: Boise

DISCUSSION

Scattered rain and snow showers continue across the region this evening. A brief drying trend is expected later tonight, with the exception of south central Idaho where a passing shortwave will support additional showers late tonight. Snow levels generally remain between 5000 and 6500 feet. High clouds should limit widespread fog development across the area, though a few sheltered valleys could see patchy fog early Monday morning.

Another round of precipitation is expected Monday afternoon into Tuesday morning. Snow levels will range between 4000 feet in the north to 5500 feet in the south. This system is expected to produce 2 to 4 inches of new wet snow for the Long Valley and 4 to 6 inches above 7000 feet. The current forecast remains on track and no updates are needed at this time.

AVIATION

Periods of rain and snow will continue overnight into Monday, especially over the mountains. Generally LIFR/IFR in snow and MVFR/VFR in rain. Mountains obscured. Snow levels 4000-5500 feet MSL. MVFR and possibly IFR in low stratus/patchy fog developing overnight into Monday morning in the Snake Plain east of KBOI and lower elevations across SE Oregon. Surface winds: SE-SW 5-15 kt, gusts to 25 kt across the higher terrain and SE Oregon. Winds aloft at 10kft MSL: SW 20-30 kt.

KBOI...Generally VFR with scattered rain showers. A 30% chance of MVFR ceilings developing during light precipitation. Light surface winds (mostly from the SE) through Monday morning.

PREV DISCUSSION

SHORT TERM...Tonight through Tuesday night...Current radar (as of typing this) shows showers increasing over the SW-Idaho and E-Oregon as a shortwave makes it's way over the area. With steepening lapse rates, and some instability building in (although lack of clearing has limited the amount), some showers may take on a more convective nature this afternoon. Have kept thunder chances below 15 percent, although a lightning flash is not out of the picture for the strongest showers. High temperatures this afternoon will be cooler than yesterday, although still 10-15 degrees above normal.

The active pattern will continue come Monday. The trough currently sitting off of the west coast will close off into a low and dig down off of the California Coast. As that is taking a place, a then out of phase shortwave (and associated cold front) will progress across our area through the day Monday bringing precipitation with it. Over the course of today and Monday, Precipitation totals within the Snake River Plain will generally be under 0.10 inches (between 0.10 and 0.20 inches near the western Magic Valley. Locations within the West Central and Boise Mountain zones will see between 0.25-0.75 inches of liquid precip, with locally higher amounts across higher ridges. Snow levels will range from 3-5 kft MSL by Monday morning. Mountain valleys will generally see 2 to 4 inches of snow fall from Monday morning through Tuesday morning.

After Monday, some may assume the attention would then be towards Tuesday... they would have assumed correctly in this case. Tuesday afternoon, yet another trough will begin to dig down across our area. With increasing wind speeds in the mid- levels, and those becoming oriented to the west-southwest as the trough digs, we will have good orographic enhancement of precip in our mountain zones. Snow levels will continue to range from 3-5kft MSL at this point (lowest to the northwest), so in general elevations below 4kft MSL will just see precip in the form of rain. As alluded to above, our mountain zones will likely see a good amount of snowfall beginning Tuesday afternoon. Stepping on the long term forecasters period a little bit here, but from Tuesday 5p MST to Wednesday 5p MST the NBM shows a 50+% chance of mountain valleys seeing greater than 4 inches of snow fall. With this, an advisory may be warranted for our mountain zones, but will defer to later shifts for the time being. Our current forecast carries 4-8 inches of snowfall over that period for mountain valleys, with 12-16 inches across the highest peaks. In regard to QPF for lower elevations, E-Oregon will be on the drier side (generally less that 0.05 inches); the Snake River Plain in Idaho will range from 0.05-0.25 inches of rain.

LONG TERM...Wednesday through Sunday...The region remains under an active NW flow with mtns keeping a 60-80% chance of snow through Thursday night while valleys carry a 20-40% chance of rain and snow. The heaviest precipitation is on the back end of an exiting trough on Wednesday which will bring an additional 1 to 3 inches of snow to the mtns (see short term disc. for storm totals/NBM probabilities). Valleys are rain or rain/snow mix (no accumulation) with snow levels 2.5-4.5 kft MSL. Snow levels will drop to valley floors behind this system which could make Wednesday night and Thursday night a bit more interesting in the valleys. Current ensemble mean keeps valley snow amounts less than an inch Wednesday night with little if any precipitation Thursday night. Mountains are inline for another 1 to 3 inches through Thursday night, though the 12Z models have trended wetter for this period, especially in the e-central Oregon and w- central Idaho mtns.

Dry weather returns for Friday into the weekend as an upper ridge builds over the western US. The warming aloft will result in the development of a temperature inversion which would open up the possibility for fog or low cloud development. Temperatures in the mtns will see the most fluctuation in the extended going from several degrees below normal Wed/Thur to above normal over the weekend. Valleys will hold slightly above normal with a slight cooling trend possible under the inversion.

AVIATION...Areas of IFR in e-central Oregon and w-central ID mtns with ceilings and snow obscuring terrain. Snow levels 5-6kft MSL. VFR in valleys with scattered showers. Some heavier showers and lightning possible through 02Z. MVFR developing in the Snake Plain east of KBOI after 06Z tonight and across SE Oregon after 15Z Monday morning. Rain/snow on Monday will keep low flight conditions in the mtns. Surface winds: SE-SW 5-15 kt with local 10-20 kt gusting 20-30 kt through 00Z this evening. Winds aloft at 10kft MSL: SW 20-30 kt.

KBOI...VFR with scattered showers bringing variable ceiling heights. A 30% chance of MVFR ceilings with light precipitation developing after 12Z Monday. Light surface winds (mostly from the SE) through Monday morning.

BOI WATCHES/WARNINGS/ADVISORIES

ID...None. OR...None.