River Flood Warning 6, NWS Boise, ID

Area Forecast Discussion
National Weather Service Boise ID
955 AM MST Mon Mar 6 2017

.DISCUSSION...Upper level jet moves over the region this
afternoon and evening which will provide support for showers in
the valley and orographically enhance snowfall in the mountains.
Look for a mix of rain, snow and sleet in the lower valleys with
the stronger showers producing dusting of sleet and snow. The West
Central and Boise Mountains could see 3 to 6 inches of snow in
the mountain valleys and up to a foot of snow in the higher peaks
tonight through Tuesday. A significantly moist warm pattern will
begin Tuesday with passage of a warm front. This will bring
significant precipitation to the mountains Tuesday night through
Wednesday. Snow level rise quickly from the valley floors Tuesday
morning to around 5000 feet Wednesday morning. A winter weather
advisory may be needed for the mountain zones tonight through
Tuesday and will be evaluated with the afternoon package. Have
updated pops today and tonight and added a mention of sleet.
Update will be out shortly.

&&

.AVIATION...VFR, with scattered valley and numerous mountain snow
showers, mainly after 18Z. Mountains obscured. MVFR and isolated IFR
conditions will accompany the showers. Surface winds: Southwest 5-15
kts north of a KBNO-KJER line, and Southwest 10-20 kts with gusts to
30 kts south of a KBNO-KJER line. Winds aloft at 10k ft MSL: West 20-
35 kts.

&&

.HYDROLOGY...Additional water will be released on the Boise River
from Lucky Peak which will bring the river to flood stage (7000
CFS) by Tuesday Evening. A flood warning will be issued as minor
flooding is expected along the Boise River. Significant rainfall
of 0.75 to 1.5 inches over the Central Idaho mountains below about
5000-6000 feet during the Tuesday through Friday period will
likely cause significant low- elevation snowmelt and rises on area
streams and rivers. The Weiser and Payette Rivers, as well as
numerous smaller creeks and streams north of the Snake River
Valley will need be monitored closely this week for potential
flooding issues.

&&

.PREV DISCUSSION...
SHORT TERM...Today through Thursday...Cold trough overhead will
support scattered snow showers today, down to the valley floors at
times. This afternoon a jet max aloft moves overhead providing a
bit more support for showers, especially over the mountains, and
could see a lightning strike or two. Tuesday a warm front pushes
in from the Pacific. Snow levels rise to 4500 ft near McCall, and
6000 ft near the Nevada border by Wednesday morning. Then
moderate to strong westerly flow continues through Thursday.
Pretty significant band of Pacific moisture lingers overhead from
Tuesday through Thursday in this strong flow - mainly north of the
Snake River. This is a good setup for significant precip in the
Central Idaho mountains over a long period, and models are in
fairly good agreement that snow levels will remain near 5000 ft,
and even increase to 6000 ft by Thursday. Significant snow in the
high mountains above this are not likely to cause too many
issues, but low-level snowmelt is likely to cause rises on area
rivers. See hydrology section below.

LONG TERM...Thursday night through Monday...The moist zonal flow
continues Thursday night into Friday with widespread precipitation
going through Friday night. Snow levels begin around 7000 feet MSL
before slowly dropping again. Rain showers will be the dominant
precipitation type through Friday night for most of the CWA. A
brief break in precipitation Saturday morning before more moisture
pours into the area. Models are still in disagreement for the
weekend forecast. GFS remains the faster and wetter model with
cooler temperatures, but the temperature forecast has been
trending upwards closer to the ECMWF. Left the mention of
precipitation through the end of the period, but raised
temperatures during the weekend per the model trends. Snow levels
stay close to 3000 feet MSL or higher for the extended period
meaning snow will remain in the higher elevations.
&&

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

&&

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DISCUSSION...JDS
AVIATION.....BW
HYDROLOGY...JDS/TB
PREV SHORT TERM...TB
PREV LONG TERM....JC