Area Forecast Discussion
Issued by NWS Boise, ID
FXUS65 KBOI 240313
Area Forecast Discussion
National Weather Service Boise ID
913 PM MDT Thu Mar 23 2017
.DISCUSSION...Clear, calm and cool tonight ahead of an incoming
Pacific system. Will see precipitation spread across southeast
Oregon during the early morning hours and push into southwest
Idaho as early as 6 AM MDT. Not expecting thunderstorms with this
system as instability is weak to non-existent. However, with a
good bout of moisture off the coast, this system is set to bring
in widespread rain with 0.25 to 0.50 inches expected in Baker
County, in northern portions of Malheur and Harney Counties, and
in Idaho north of the Snake River Plain. Amounts taper off towards
the Nevada border. Snow levels will be around 4500-5500 ft MSL.
Updated the forecast for higher QPF amounts, with slight
adjustments made to chance of precipitation. For hydro details,
see the hydrology section below.
.AVIATION...VFR through tonight. Clouds increasing and lowering,
with rain and higher elevation snow spreading into SE Oregon between
06Z and 12Z. The clouds and precipitation will spread into SW Idaho
after 12Z. MVFR and local IFR conditions will accompany the precip,
along with mountain obscurations. Snow levels around 5000 ft MSL.
Surface winds: Variable 10 kts or less, becoming Southeast to
Southwest 5-15 kts with gusts to 20 kts after 12Z. Winds aloft
near 10k ft MSL: West 10-20 kts becoming Southwest 20-40 kts by 12Z.
.HYDROLOGY...Rivers and streams will generally lower through
Friday then rise slightly again Saturday in response to Friday`s
rain. Rivers should then resume a downward trend into next week.
However, the Snake River at Weiser is forecast to continue a few
inches above flood stage through next week, as will the Boise
River at Glenwood Bridge. An areal flood warning continues for
northern Harney County, OR as does a flood advisory across the
Camas Prairie. See flood products for more details.
SHORT TERM...Tonight through Saturday...Dry conditions noted across
the area this afternoon, which will persist into the overnight hours
for much of the area. Gusty post-frontal wind remains across the
Treasure Valley and Western Magic Valley, which may also persist
into the evening hours. The next Pacific moisture push is on time
with activity arriving across eastern Oregon late this evening, or
during the early morning hours of Friday. As the trough associated
with this moisture progresses eastward, shower activity will become
more widespread, impacting the majority of the area by Friday
afternoon. Precipitation amounts may be significant with this
system, with portions of Harney and Malheur counties seeing between
0.25 and 0.7 inches of moisture. Portions of southwestern Idaho,
especially over the West-Central and Boise Mountains may see up to
an inch of additional liquid by the time this storm weakens Saturday
evening. Some of this moisture will fall as snow to keep hydrology
concerns tempered for areas not already experiencing minor flooding,
or near bankfull conditions.
LONG TERM...Saturday night through Thursday...The unsettled pattern
will continue as Pacific weather systems cross the Intermountain
Region. A brief break in the showers Saturday night and Sunday
morning will be followed Sunday afternoon by more showers spreading
across eastern Oregon into the central Idaho mountains. Showers will
become widespread Sunday night and continue on Monday as a deepening
upper level trough moves inland. Snow levels will be near 5000 feet.
Precipitation will taper off Monday night and Tuesday as the trough
closes off over the southwest states and a weak upper level ridge
builds over our area. Temperatures will be close to normal.
Tuesday night through Thursday...A deep upper Low progresses through
the SW United States Tuesday night into Wednesday bringing in
northwest flow aloft for our CWA. The next upper low begins to push
into our northwest corner by Wednesday morning. Some differences in
timing for this system with the ECMWF being faster than the GFS.
Early Thursday morning looks to be the wettest period thus far. Snow
levels begin above 5500 feet MSL but start to drop by Thursday
morning as the frontal boundary pushes through. By the end of the
period snow levels range from 4500 to 5500 feet MSL meaning
increased chances of snow for the higher elevations. Temperatures
are above normal Thursday then drop to near normal by Friday.
PREV SHORT TERM...KB
PREV LONG TERM....JT/JC