Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus66 kotx 180023 
afdotx

Area forecast discussion
National Weather Service Spokane Washington
423 PM PST Wed Jan 17 2018

Synopsis...
a moist frontal system will bring widespread rain to the inland
northwest tonight into Thursday. The Methow Valley in north
central Washington will have the opportunity for accumulating snow
tonight, but most lowland communities will experience rain tonight
into Thursday. More rain and snow is expected this weekend with
the potential for some lowland snow accumulations on Sunday.

&&

Discussion...

Tonight: a moist frontal system will move across the inland
northwest tonight. As of 230 am, a band of moderate rain was
entering the Seattle Metro, and by early evening we should see
rain and snow spread across the Cascade crest. With afternoon
temperatures in the 30s, precipitation type will be a tough
forecast for the valleys of the east slopes of the Cascades. At
this time, it looks like much of the Wenatchee River Valley will
be a bit too warm for snow to accumulate in places like
Leavenworth and Cashmere. Plain and Lake Wenatchee may experience
a mix of rain and snow will minor accumulations. Further north,
mid afternoon temperatures and dewpoints in the Methow Valley
suggest the potential for wet snow accumulations of 2 to 5 inches
for Winthrop, Twisp, and Mazama. The majority of this accumulation
is expected this evening with snow rates decreasing after
midnight. A Winter Weather Advisory is in effect for portions of
the east slopes of the northern Cascades through Thursday morning.

The remainder of The Lowlands across the inland northwest will
experience a cold rain tonight. By sunrise, the band of
precipitation should be well into the Idaho Panhandle. Overnight
snow levels in the Panhandle are expected to be in the 5500 to
6500ft range...well above Lookout Pass (elevation 4700 feet).

Thursday: periods of light to moderate rain will effect the Idaho
Panhandle, the Palouse, l-c valley and the Spokane Metro for a
good portion of the day on Thursday. The majority of precipitation
will occur along and just ahead of the slowly moving cold front.
Panhandle snow levels will slowly fall into the 3000-4000ft range
in the afternoon and evening bringing about a change from rain to
snow for Lookout Pass. Elevations above 4000 feet in Shoshone,
boundary, and Bonner counties will have a shot of 3 to 6 inches of
snow accumulation by late Thursday night. Elsewhere, rain amounts
of a half to three quarters of an inch will be possible over The
Lowlands of the northern and central Idaho Panhandle as well
portions of northeast Washington down to the Palouse. Places like
Sandpoint, Bonners Ferry, Kettle Falls, and Metaline Falls have
the potential to become a slushy/sloppy mess with 10 to 20 inches
of snow on the ground. The snowpack is deep enough in many places
that the snow will absorb much of the runoff, but some ponding
will be possible in areas with poor drainage. There is less low
level snowpack in the southern and central Idaho Panhandle. Areas
with steep terrain may be prone to rock and mud slides.

Friday and saturday: a cooler air mass will spread over the region
Fri and Sat. The majority of the inland northwest will experience
afternoon highs in the 30s and overnight lows in the mid to upper
20s. Westerly upslope flow into the Cascade crest and over the
Idaho Panhandle mountains will produce periods of accumulating
snow in the mountains Fri and Sat. The NAM, GFS and European model (ecmwf) are
hinting at a subtle shortwave Sat morning which may even produce a
bit of light accumulation around Colville, Spokane, and Pullman
before temperatures rise into the mid to upper 30s in the
afternoon. /Gkoch

Saturday night through wednesday: models more or less suggest two
additional storm systems moving through eastern Washington and
northern Idaho Sunday and Tuesday night/Wednesday. Intervals of less
intense and generally showery precipitation in between these two
storm systems are brought about by orographics and/or minor small
scale disturbance passing through either a conditionally unstable
airmass or dropping down the east edge of low amplitude ridging. The
somewhat warm moisture taps extending south to north feeding into
both sunday's and Tuesday night/wednesday's passing weather systems
should allow snow levels to rise some to allow a changeover to rain
for lowland locations in and along the outer edge of the Columbia
Basin. High temperatures should show peaks on those two days as well
over the seven day forecast (but not as high as those expected this
thursday). /Pelatti

&&

Aviation...
00z tafs: a band of light to moderate rain will move west to east
across eastern Washington this evening and into northern Idaho by
early morning. A belt of strong low level winds along and ahead of
the front will produce low level wind shear at Spokane, Pullman,
and Coeur D'Alene tonight. Ceilings will be tough. There will be
plenty of low level moisture for low stratus, but frontal mixing
may inhibit low cloud development. For this round of tafs, we
brought cigs below 1000 feet for several hours behind cold frontal
passage at keat, kmwh, kgeg, ksff, and kpuw with improving
conditions by late morning or afternoon. /Gkoch

&&

Preliminary point temps/pops...
Spokane 38 43 30 37 29 37 / 100 100 20 10 20 50
Coeur D'Alene 37 42 30 36 29 37 / 100 100 20 30 40 60
Pullman 40 45 32 39 30 38 / 90 100 20 20 30 50
Lewiston 42 48 34 43 32 43 / 40 100 30 20 20 30
Colville 36 43 30 36 28 37 / 90 50 30 20 30 40
Sandpoint 36 40 30 35 29 36 / 100 100 30 30 40 50
Kellogg 35 40 29 34 28 35 / 100 100 30 50 50 70
Moses Lake 37 48 30 41 29 42 / 100 20 0 10 10 10
Wenatchee 34 44 29 37 28 39 / 50 10 10 10 20 10
Omak 35 40 27 34 26 37 / 100 20 20 10 20 10

&&

Otx watches/warnings/advisories...
Idaho...none.
Washington...Winter Weather Advisory until 7 am PST Thursday for east slopes
northern Cascades.

National Weather Service Glossary of Abbreviations