Area Forecast Discussion
Issued by NWS Boise, ID

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000
FXUS65 KBOI 190319
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
819 PM MST Sat Nov 18 2017

.DISCUSSION...Cool and dry this evening, with thin high-level
clouds over the area. East to southeast winds are expected to
continue over most of the area tonight, inhibiting fog formation.
no updates are expected at this time.

&&

.AVIATION...VFR. SCT high level clouds. Surface winds generally
southeasterly 5-10kt. Winds aloft at 10 KFT MSL: Southwest 15-20
kts.

&&

.PREV DISCUSSION...
SHORT TERM...Tonight through Monday...Just high clouds tonight as
ridge aloft moves overhead. By Sunday afternoon clouds increase
and thicken as an upper-level wave in the Gulf of Alaska
approaches. Models have this storm weakening dramatically as a
deeper trough develops in the Eastern Pacific, and the associated
tendency for ridging downstream eats away at this storm.
Nevertheless, there is ample moisture when it moves across the
forecast area on Monday, and it has a favorable flow direction
from the west and northwest aloft, especially for the West Central
Idaho Mountains. Models have been trending lower with precip
totals, so we also trended the forecast that direction - but it is
still a significant system. Snow levels rise steadily as this
system moves through, from about 4000 ft in the north on Monday
morning, to nearly 6000 ft by afternoon. Thus, believe that the
mountain valleys of the West Central mountains, such as McCall
and Cascade will see a couple of inches of snow Sunday Night into
early Monday morning, but will mix with rain during the morning,
and will be all rain by Monday afternoon. The result is probably
not enough snow to support any advisories - but it is worth
watching closely for Monday morning in those areas. Elsewhere,
rain seems likely on Monday, especially north and east of the
Snake River plain. Temperatures actually stay relatively
constant, and near normal, as the storm moves through. Some breezy
southeast winds in the Snake River plain on Sunday ahead of the
system, and breezy southwest winds in Oregon on Monday with the
system - but neither look strong enough to cause many problems.

LONG TERM...Monday night through Saturday...A strong ridge over
southern CA and a storm off the West Coast will provide mild and
moist southwest flow aloft over the area through Thursday. A warm
front will move across the region on Tuesday morning, bringing rain
to most locations, as snow levels rise over 10,000ft MSL.
Temperatures will warm to around 10-15 degrees above normal.
Southwest flow aloft will enhance rain shadowing and warming across
the Snake Plain and SE Oregon. The bulk of the precipitation will be
to our northwest in Western/Central OR and WA and northern ID. On
Thursday, temperatures expected to reach the low 60s in the Snake
Plain, or around 15-20 degrees above normal. The record at BOI is
64F set in 1897. The ridge weakens on Friday, allowing the system
off the West Coast to move inland, which will cool temperatures off
a few degrees, and lower snow levels to 4,500-6,000ft MSL by
Saturday.
&&

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

&&

$$

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DISCUSSION...SP
AVIATION.....EP
PREV SHORT TERM...TB
PREV LONG TERM....KA/WH



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