Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 262237
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
237 PM PST Sun Feb 26 2017

.SYNOPSIS...
Occasional snow will continue through Tuesday. The most
significant accumulations will likely occur over the Palouse and
Idaho Panhandle the next couple of days. A breezy and somewhat
milder weather pattern is expected for Wednesday into the weekend.
Precipitation over the second half of the week will likely
transition to low elevation rain and high elevation snow.

&&

.DISCUSSION...
Tonight: An upper level low will be dropping south along the OR
coast tonight, shifting the main area of diffluence aloft and a
surface boundary southward across southeast Washington and the
central ID panhandle. Radar shows widespread precipitation across
the Columbia Basin, Spokane/Coeur d`Alene and, Palouse and
southeast Washington and into central ID panhandle. It has been a
tricky forecast as most observation sites continue to report snow.
Some of this precipitation is turning more convective with more
intense showers with cooling aloft. Yet web cams show low land
accumulations have been light and roadways wet thanks in part to
warmer road and low level temperatures. More accumulations will be
likely above 3K ft. The mesoscale models show a drying trend
moving from the north this evening, decreasing the precipitation
across the northern Basin and Spokane/Coeur d`Alene area. Drier
northerly winds will spread down the Okanogan valley toward the
western Basin overnight to further the drying. Meanwhile a surface
boundary over the Palouse into the central Panhandle will keep
the focus for precipitation overnight, mostly in the form of light
to moderate snow. As temperatures drop overnight, so will the
accumulations. Anticipate more fog overnight as low level moisture
remains high across the sheltered valleys of northeast
Washington. Overnight temperatures will dip below freezing
overnight, leading to the potential for slick and icy road
surfaces by morning. /rfox.

Monday through Tuesday night...An unstable...moist northwest flow
is expected Monday through Tuesday morning. This will result in
the focus of most persistent and widespread snow shower activity
into the Cascade crest, Palouse, Blue Mountains, Camas Prairie,
and Central Panhandle Mountains. A wave embedded within this
trough will track through the region late Monday afternoon into
Monday night. Bands of heavy snow showers are possible with this
feature given the steep mid level lapse rates and mid level
convergence. A couple model solutions such as the 18z NAM and 12z
GEM have showed the mid level convergence boundary further north
over the Spokane/Coeur D`Alene area Monday night but confidence
at this point is highest for additional accumulations on a larger
scale over SE Washington into the Central Panhandle Mountains
where persistent upslope flow will occur.

Given the instability under this trough...areas not mentioned yet
over much of Central and Eastern Washington will have a chance of
snow showers given the instability in place...with the best
chances in the afternoon and early evening when lapse rates are
steepest. Locally heavy showers Monday afternoon could put down a
quick inch...but the higher late February sun angle should melt
most of this after the shower passes.

The next system arrives Tuesday night but passes mostly north of
the Canadian border where a 100 kt jet lies. Strong northwest flow
into the Cascade crest as well as isentropic ascent into the Idaho
panhandle will produce another round of snow however. This strong
jet will produce an increase in 850mb winds by Wednesday morning
especially in the Cascades with NAM showing 50 kts and GFS 50-60
kts. Soundings show these winds will have a difficult time mixing
down into the Cascade valleys...but the ridges...especially
Mission Ridge will become very windy.  JW

Wed through Sunday: No changes to the fcst. Much of our focus
still remains on Wed and Fri. Expect N Idaho snow, as well as very
gusty winds for much of Ern Wa and higher elevations of the east
slopes of the Cascades Wed and Fri. Under broad ridging with a
prolonged decent moisture fetch over the region south of the jet,
increasingly veered flow and will not only produce moderate snow
accumulations for the N Idaho mtns Wed, but will also produce a
pronounced lee-Cascade pcpn shadow that should keep much of the
Upper Columbia Basin dry, though windy. Elsewhere, mtn wind gusts
could exceed 50 mph for exposed areas. Valley snow accumulations
are possible for the N Id Panhandle Wed morning as well. Very
windy wx is again possible Fri... with snow and rain for all but
the lower Basin zones. High temps closer to normal (40s) by mid
to late week combined with the N Id pcpn could lead to more river
rises for the weekend. bz

&&

.AVIATION...
00z TAFs: There will be a decreasing trend in precipitaiton this
evening from north to south, and affecting the KGEG-KCOE area and
KEAT. Expect MVFR cigs and vsbys with snow and fog slowly
improving this evening, although there is the potential for more
fog reforming especially in the KGEG area toward morning.
Scattered snow showers will increase over the KGEG-KCOE corridor
by midday Monday. Looks like northerly winds will keep KMWH on
the drier side and should see improving conditions. KPUW and KLWS
will be under the area of persistent snow overnight and into
Monday with the surface boundary staying near this area. Expect
mainly IFR conditions. KLWS may see a rain/snow mix early this
evening and again tomorrow afternoon. /rfox.

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        24  31  18  32  26  42 /  20  50  50  10  20  40
Coeur d`Alene  22  32  18  32  25  40 /  20  70  70  20  40  50
Pullman        26  32  22  34  29  44 /  80  80  80  60  50  30
Lewiston       31  38  26  41  33  50 /  70  60  60  60  20  30
Colville       21  33  16  34  23  43 /  20  40  40  10  20  30
Sandpoint      22  32  18  32  23  40 /  20  70  70  20  70  80
Kellogg        24  31  21  31  23  38 /  90  90  90  70  80 100
Moses Lake     24  34  17  36  25  48 /  20  30  30  10   0  10
Wenatchee      25  32  16  35  26  46 /  20  30  30  10  10  20
Omak           22  30  13  32  23  42 /  10  20  20  10  20  30

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Winter Weather Advisory until 10 AM PST Tuesday for Central
     Panhandle Mountains-Idaho Palouse-Lewis and Southern Nez
     Perce Counties.

WA...Winter Weather Advisory until 10 AM PST Tuesday for Northeast
     Blue Mountains-Washington Palouse.

&&

$$



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