Area Forecast Discussion
Issued by NWS Boise, ID

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FXUS65 KBOI 211716
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
1016 AM MST Wed Feb 21 2018

.DISCUSSION...Weakening upper wave moving through the region this
morning has brought light snow to southeast Oregon and portions of
southwest Idaho. Most areas that have seen no more than a dusting
of snow. Satellite trends are showing the system is weakening as
it moves into southwest Idaho this morning. Coverage of snow
showers diminishes in the mountains through afternoon while
valleys remain dry. Any additional accumulations across higher
terrain will be less than an inch. Have made a small update to the
QPF/snow amount totals for today, otherwise forecast remains on
track. Another round of light snowfall is expected Thursday
morning that will bring some light snow to the lower Treasure
Valley.

&&

.AVIATION...VFR today south of a KLKV-KONO-Fairfield line. North
of  that line expect MVFR/IFR conditions in snow this morning,
and terrain obscuration. Conditions in the valleys will improve to
mainly VFR this afternoon. Conditions will deteriorate tonight
across most of southeast Oregon and southwest Idaho as the next
weather system approaches from the north. Surface winds will be
mainly southeast 10-15 kts today. Winds aloft at 10k ft MSL will
be northwest 10-20 kts today shifting to west this evening.

&&

.PREV DISCUSSION...
SHORT TERM...Today through Thursday...Area of high clouds in
southeast Oregon and southwest Idaho will shift into Nevada this
morning.  No snow indicated from these clouds.  Another area of
clouds, just now entering Baker County, does have light snow but
should weaken as it moves southeastward into our CWA today. Little
if any snow will get into Idaho from this.  The next short wave
trough, currently in BC, is of greater concern to our CWA as it
moves in from the NNW late tonight and Thursday.  That trough will
bring light snow to most of our zones, and with the ground already
cold, the snow will stick to the roads.  Even a small amount may
affect travel.  Current models begin light snow in Baker County this
evening and spread it southeastward into the rest of southeast
Oregon by midnight PST, and southwest Idaho overnight. Light snow
will continue Thursday, mainly on the Idaho side, as the trough
closes off a low in eastern Oregon. Total snowfall tonight through
Thursday will be around one inch in the valleys and 1-3 inches in
the mountains, and no advisories will be issued with this forecast.
We may revisit the idea of an advisory later today mainly for
southern Malheur and western Owyhee Counties late tonight and
Thursday, where models put a little more snow than elsewhere.  Winds
will be light southeast today, increasing to light to moderate
southeast tonight and Thursday morning, then shifting to northwest
behind a cold front later Thursday.

LONG TERM...Thursday night through Monday...A series of upper level
troughs will result in below-normal temperatures and an above-
average chance of precipitation. With the cool temps, almost all
precipitation anywhere in the area will fall as snow. There are, as
usual, some timing differences in the EC and GFS, and the following
description will seek to compromise the latest solutions. As one
trough axis swings through Thursday night, isolated to scattered
snow showers will favor the southern part of the CWA. Friday will be
mostly dry as brief weak ridging moves through in northwest flow. By
Friday night, and especially into Saturday, moist northwest will
increase and the next upper level short wave trough will approach.
The trough axis will move through Saturday night, and snow showers
will linger into Sunday. Sunday night and Monday yet another short
wave trough will move through, continuing the chance for snow
showers. Timing differences become more important as we get into
Monday night and continuing through Wed. The GFS is slower with a
significant trough than the EC. We have kept slight chance to chance
PoPs going through Wed to account for these differences, but it is
important to note that both models continue the active pattern.

&&

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

&&

$$

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DISCUSSION...DG
AVIATION.....JT
PREV SHORT TERM...LC
PREV LONG TERM....SP



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