FXUS65 KBOI 202034

Area Forecast Discussion
National Weather Service Boise ID
234 PM MDT Fri Oct 20 2017

.SHORT TERM...Tonight through Sunday...Rain and snow associated
with the frontal passage this morning continues to weaken across
the area. Lingering shower activity mainly noted across
southwestern Idaho. Much cooler temperatures observed across the
area today, resulting in some periods of snowfall for McCall and
Twin Falls. Brief improvement expected this evening, with a
potential for pockets of fog on Saturday morning. Another moisture
push expected Saturday, continuing the cooler temperatures and
the presence of rain and mountain snow across the area. Activity
looks most favorable Saturday afternoon and evening for
southwestern Idaho. Moisture will begin to lift more north Sunday
morning with improving conditions noted for the southern two
thirds of the area. All areas anticipated to see warming
temperatures, with the southern two thirds seeing values return to
around normal.

.LONG TERM...Sunday night through Wednesday night...Moist
westerly flow aloft will continue Sunday night, with a chance of
showers over Baker County Oregon and the west central Idaho and
Boise Mountains. Models have been consistently showing a high
amplitude upper level ridge building over the west coast on
Monday, providing clear skies and slightly above-normal
temperatures for our area through Tuesday night. On Wednesday an
upper level trough from the Gulf of Alaska will weaken as it moves
into British Columbia and encounters the ridge. The trough will
slide southeast across northern Idaho and western Montana
Wednesday afternoon and evening as the ridge rebuilds offshore.
Precipitation with this system is expected to stay mainly north
and east of our area, but there will be a chance of showers over
the west central Idaho mountains Wednesday night.

Thursday and Friday...An upper level trough dips down through
northern Idaho and Montana early Thursday morning. The associated
precipitation with this trough just clips our northern zones
bringing chances of precipitation for the West Central Mountains.
Cooler temperatures aloft will drop snow levels Thursday to around
5000 feet for northern zones, but these levels will climb back
above 9000 feet by the weekend.


.AVIATION...Widespread precipitation in the mountains, with MVFR and
local IFR conditions in the mountain valleys, continuing overnight.
Mainly VFR at lower elevations, with scattered showers becoming
isolated this evening. Snow levels 4k-5k ft MSL. Patchy valley fog
after 06z. Surface winds west 15-25 kts, locally gusting to around
35 kts, decreasing to around 10 kts after 00z. Winds aloft at 10k ft
msl west 20-35 kts.

Weekend Outlook...Precipitation becoming widespread across southeast
Oregon Saturday morning and southwest Idaho Saturday afternoon as a
warm front moves across the area from the west. Snow levels 3500-
4000 ft MSL Saturday morning, rising to 6000-8000 ft MSL by Saturday
night, and 8000-10000 ft MSL by Sunday afternoon. Precipitation
continuing in the mountains through Sunday, but ending at lower
elevations Sunday morning. Patchy night and morning valley fog.
Surface winds southeast to southwest 5-15 kts.






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