Area Forecast Discussion
Issued by NWS Boise, ID

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FXUS65 KBOI 220955

Area Forecast Discussion
National Weather Service Boise ID
255 AM MST Thu Feb 22 2018

.SHORT TERM...Today through friday...Snow began shortly after
midnight in southwest Idaho, a little earlier than expected.
At 2 AM MST KCBX radar showed a nearly stationary band of snow
over northwestern Ada County, ID, where at least one inch of
snow has fallen already.  NAM depicts this band especially well
and GFS is also quite good.  Both models keep snow going there
through mid morning, but averaging in other models results in
3-4 inches total, locally 5 inches, total accumulation from
about Eagle, ID, through Horseshoe bend, ID, i.e., at the upper
end of advisory amounts.  The rest of the Treasure valley should
get 2-3 inches total snowfall through noon MST.  A winter weather
advisory has therefore been issued for the entire area, including
the Owyhee Nountains.  Lesser amounts of 1-2 inches are expected
over the rest of southwest Idaho, and southern Malheur County, OR,
mainly this morning.  Less than an inch is expected in the rest of
eastern Oregon, and the advisory issued earlier for that area has
been cancelled.  Later today the snow will shift to central Idaho
as a cold front moves across from west to east.  Snow will end
from west to east this afternoon and evening with partial clearing.
Breezy west/northwest winds Thursday night are expected to keep
temperatures from dropping as far as they would with light winds
above fresh snow cover.  However, if the winds die down, Friday
morning will be very cold.  Latest MOS temps are not showing this.
Friday looks mostly sunny in eastern Oregon, partly cloudy in
southwestern Idaho, and mostly cloudy in south-central Idaho.
High temps today and Friday should be in the 20s in the mountains
to mid 30s in the warmest valleys.

.LONG TERM...Friday night through Thursday...Models are in
reasonable agreement until Monday night, showing a series of
shortwave troughs moving over us in northwest flow aloft. The first
will bring snow to the region Saturday, while the next follows
rapidly and brings another round of snow Sunday night into Monday.
The models diverge strongly after that time, with the EC digging a
strong cutoff low south into southern CA before moving it back
toward Utah next Thu. The GFS brings a broader trough into the PacNW
and as a result backs our upper level flow to southwest. Some
members of the GFS ensemble mimic the EC, but the majority back the
operational run. At this time, we will keep a chance of snow over
the region for Monday through Thursday, as either solution could
end up being the most accurate, and the one thing they agree on is
that we will remain in an active pattern with energy moving across
the western US. Temps will remain below normal, both because of the
general northwest flow aloft and also because of snow on the ground
following not only today`s system, but the ones that will follow.


.AVIATION...MVFR/IFR conditions as snow increases through 22/18Z.
Mountains will be obscured. Conditions improve after 22/21Z, with
VFR tonight except some mtns still obscured. Surface winds:
generally 12 kts or less. Winds aloft at 10kft MSL: SW 15-20 kts,
shifting to W 5-15 kts this afternoon.


ID...Winter Weather Advisory until noon MST today IDZ012-014-029-033.
OR...Winter Weather Advisory until noon MST /11 AM PST/ today ORZ063.



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