Area Forecast Discussion
Issued by NWS Boise, ID

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FXUS65 KBOI 290248
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
848 PM MDT Tue Mar 28 2017

.DISCUSSION...High pressure remains over the region through early
Wednesday for dry conditions. High clouds ahead of the next system
will continue to stream in overnight. Next storm system for
Wednesday night into Thursday remains on track and will bring
significant rainfall Wednesday night followed by strong
northwesterly winds Thursday afternoon. Satellite showing the
upper level low pressure system near 150W and 50N at 02z moving
quickly eastward. The surface low reaches the Washington Coast by
12z Wednesday bring a weak warm frontal passage across our
northern zones Wednesday morning between 09z and 15z. Expect rain
showers with the frontal passage. Precipitation coverage increases
Wednesday night with the cold frontal passage expected Thursday
morning. Could see brief heavy rain and lightning strikes with the
frontal passage early Thursday morning. Strong northwesterly
winds follow the frontal passage Thursday afternoon. Current wind
headlines for Thursday cover this well. No updates needed at this
time.

&&

.AVIATION...VFR with increasing cloud cover. Showers moving into
areas near KBNO, KBKE and KMYL early Wednesday morning, then slowing
spreading east through the evening hours. Snow levels 7500-8500 ft
then rapidly lowering to 3500-4500 ft behind a cold front on
Thursday afternoon. Surface winds: 10-15 kts with occasional gusts
to 20 kts, then increasing Thursday afternoon. Winds aloft near 10
KFT MSL: northwest 20-30 kts.

&&

.HYDROLOGY...Hydrologic outlook has been issued for the entire
area Wednesday night through the end of the week for increasing
river and stream levels.  A strong north Pacific storm will
bring significant rain Wednesday night and Thursday, but continued
snowmelt will also contribute to the increased flow.  Meanwhile,
the Boise River at Glenwood Bridge continues in minor flood for
at least several more days, and the small stream flood advisory for
central Elmore and southern Camas Counties has been extended
until 1 am MDT Friday.

&&

.PREV DISCUSSION...
SHORT TERM...High clouds are beginning to stream in from the
northwest this afternoon.  Clouds will increase and lower
tonight with light rain starting in Baker County toward
morning.  Rain will spread southeast over our CWA Wednesday
a little faster than forecast earlier.  Rain will increase
significantly Wednesday night and Thursday as a strong upper
trough speeds across the north Pacific and then turns
southeast right through our CWA Thursday.  Upper trough will
close off a low as it moves into Nevada Thursday.  Surface
low will also intensify as it moves away from us, and the
tightening surface pressure gradient will develop strong
west or northwest winds in southeast Oregon and southwest
Idaho Thursday, possibly reaching high wind criteria.
Surface cold front will pass through southern Idaho Thursday
morning and may develop thunderstorms in south-central Idaho
midday Thursday.  Snow level will lower sharply Thursday
afternoon from the north and west, but by then the heaviest
precipitation will be ending.  Even so, several inches of
snow may accumulate above 5000 feet MSL late Thursday.

LONG TERM...Thursday night through Tuesday...Upper low begins to
press southeastward Thursday night into Friday morning. Moisture
that is wrapping around this low will continue to impact areas in
Southern Twin Falls County and the Southwest Highlands. Snow levels
sit right around 4000 feet MSL Friday morning. Highest snow
accumulations expected close to the Nevada border in SE portions of
the Southwest Highlands and SW portions of Southern Twin Falls
County. Snow levels quickly rise again Friday night into Saturday
as an upper level ridge begins to build in from the west. Things
remain dry for the CWA through Saturday night. After this, models
are not in agreement on placement or timing of the next disturbance
to pass through. The GFS is a little more excited and faster to
bring in another wave of precipitation while the ECMWF places much
of the precipitation with this disturbance outside of our CWA.
Chances of precipitation were left in the forecast to show this
uncertainty. Models continue to disagree through the remainder of
the period making forecast confidence in timing and location
difficult. Temperatures sit above normal through Sunday then drop to
right around or just below normal through the rest of the period.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...Wind Advisory from 10 AM to 6 PM MDT Thursday IDZ012-016-029-030.
     High Wind Watch from Thursday morning through Thursday afternoon
     IDZ014-015.
OR...Wind Advisory from 10 AM MDT /9 AM PDT/ to 6 PM MDT /5 PM PDT/
     Thursday ORZ061>064.

&&

$$

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DISCUSSION...JDS
AVIATION.....EP
HYDROLOGY...LC
PREV SHORT TERM...LC
PREV LONG TERM....JC/WH


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