Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 250029
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
429 PM PST Sat Feb 24 2018

.SYNOPSIS...
A series of storm systems will impact the Inland Northwest this
weekend into early next week, with the potential for more snow,
breezy conditions and continued below normal temperatures for most
locations. A particularity strong yet mild storm looks possible
by the end of next week.


&&

.DISCUSSION...

...Moderate to Heavy Snow and Blowing Snow Central Idaho Panhandle
and Eastern Whitman County Sunday...

Tonight through Sunday: The storm system that brought snow to the region
Friday night and Saturday will depart to the southeast. Snow showers
will linger over extreme southeastern WA and the lower Idaho
Panhandle through the early evening but intensities will be on a
downward trend and the threat for significant accumulations will
be over by the early evening.

The attention will then turn toward the next storm currently digging down
the northern BC Coastline. This will be a windier storm system
with a 10-12mb cross CWA pressure gradients as a 990mb surface low
tracks through Southwestern Canada. The enhanced wind fields will
lead to strong orographic ascent into the rising terrain of
eastern Whitman County and Idaho Panhandle as well as the Cascade
Crest. Not only will this bring the potential for another round of
moderate to heavy snowfall, but a good chance for blowing and
drifting snow. The storm system currently departing the area gave
these locations between 4-8 inches of fluffy snow which will
easily become blown around as winds ramp up early Sunday morning.
Consequently, there is a lot of concern that the combination of
heavy snow and blowing snow will lead to treacherous travel
conditions and we have issued a winter storm warning for this
reason. Please note that the winter storm warning for Whitman
County will only be for the rising terrain along the Highway 195
corridor. Light to moderate snow will also fall across the
Northern Panhandle and this was covered with a new round of winter
weather advisories given the potential for another 2-4 inches.
Lighter amounts are expected for Northeastern WA which will range
from 0.5-2". Thinking the Camas Prairie and Blue Mountains will
also get another 2-5 inches but confidence is not as certain due
to the strong west/southwest flow which is not as favorable.
Stevens Pass will likely be hammered by heavy snow in this flow
pattern and the Seattle office will address winter highlights for
this pass. Slop over snow will extend into Plain and Leavenworth
but amounts should be near five inches or less and and decrease
further farther east down the Wenatchee River Valley. Little to no
snow is expected for the Methow Valley and in the lee of the
Cascades from Oroville to Wenatchee. The main precipitation threat
for these areas will come with convergence bands developing
Sunday afternoon. There are signs of some surface based CAPE,
especially if temperatures warm into the 40s to 50s from Moses
Lake to Wilbur. It carries a very low probability, but cannot rule
out an isolated thunderstorm.

Models have backed off on winds some.  There is still a 45-50kt low-level
jet expected to setup across Southeastern WA into the Spokane
Area early Sunday morning but the data continues to suggest these
winds will not mix down to the surface and mainly pose a threat to
exposed ridgetops. This was supported by bufkit data and hi-res
models from UW and our local 1km model. The gradients do support
sustained winds over southeastern WA on the order of 25-30 mph
with gusts up to 45 mph and have issued a wind advisory for areas
where we feel the strongest speeds are expected. For the remainder
of the Columbia Basin, winds of 15-25 mph are expected with gusts
25-40 mph. /sb

Sunday night through Saturday...No big changes or surprises to
the extended forecast at least through Wednesday. Northwest flow
will continue to dominate the weather through Wednesday with a
couple of waves moving through the region. By Wednesday afternoon a
much deeper upper level low will drop along the OR/WA coast. This
low will move inland on Thursday and linger over the Pac NW
through Saturday. Several reinforcing waves will rotate around
this low keeping the weather unsettled through next weekend.

Sunday night through Monday night...The storm system responsible
for snow and wind on Sunday will move south of the forecast area
Sunday night with northwest-north flow lingering into Monday.
Higher chances for precipitation were kept in the forecast for the
Cascade crest, and areas south and east of about I-90 for Sunday
evening, then slowly decreasing Sunday night and Monday. The
heaviest snow will be for Shoshone county south of I-90, which
could see 5-8 inches of new snow in the mountains above Avery and
Clarkia. The Camas Prairie and the Blue mountains could see
another 2 inches. Gusty winds will linger into Sunday evening and
result in localized blowing snow.

Tuesday through Wednesday...Northwest flow will remain over the
area through Wednesday. A couple of weak disturbances and up-
sloping flow will keep a chance for snow in the forecast for the
Cascades, and the Panhandle mountains. Snow or a snow/rain mix may
be able to build back to the west as far as Spokane and south to
about Pullman. Snow will continue to pile up for the Panhandle
mountains with 3-8 inches possible. For the lower elevations
anywhere form a trace to an inch or 2 will be possible.

Wednesday night through Saturday...We will see a bit of a pattern
change through this period. A deep low pressure system will close
off along the west coast late in the day on Wednesday. This low
will then slowly move inland and linger over the region through
the weekend with a plethora of disturbances wrapping around the
low. Southerly flow ahead of the low will help to warm up
temperatures and also tap into deeper Pacific moisture. As
mentioned earlier this is out in the forecast pretty far but it is
ramping up to be a fairly wet period. Tobin

&&

.AVIATION...
00Z TAFS: A few bands of snow will linger through sunset near the
Wenatchee mountains in the Cascades and the Clearwater mountains
in southern Shoshone county with localized mountain obscurations.
Otherwise there will be a break in the precipitation until after
12z. Current VFR/MVFR conditions will improve to VFR through
08-10z before deteriorating again. As the snow increases in
intensity after 12z cigs/vsby will drop to IFR and locally to LIFR
with the heaviest snow. Winds will be on the increase after 12z
with southwest 20-25 kts with gusts 30-35 kts. This will result in
blowing and drifting snow for the Washington/Idaho Palouse and
mainly affecting KPUW. Tobin




&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        27  38  19  34  22  37 /  10  70  20  10   0  20
Coeur d`Alene  26  36  19  34  20  36 /  30 100  30  10  10  40
Pullman        26  36  23  33  20  35 /  30  90  60  10   0  20
Lewiston       33  43  26  40  22  43 /  20  40  40  10   0  20
Colville       26  39  16  37  20  37 /  20  70  10  10  10  30
Sandpoint      26  35  20  33  21  34 /  50 100  40  10  10  60
Kellogg        23  33  21  31  19  31 /  60 100  80  30  10  60
Moses Lake     32  46  23  43  25  47 /  10  10  10   0   0  10
Wenatchee      31  42  24  43  25  46 /  10  30  20   0  10  10
Omak           27  39  18  38  22  40 /  10  20  10   0  10  10

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Winter Weather Advisory from 4 AM to 5 PM PST Sunday for Coeur
     d`Alene Area-Northern Panhandle.

     Winter Storm Warning from 4 AM to 11 PM PST Sunday for Central
     Panhandle Mountains-Idaho Palouse.

WA...Wind Advisory from 4 AM to 2 PM PST Sunday for Lower Garfield
     and Asotin Counties-Washington Palouse.

     Winter Storm Warning from 4 AM to 11 PM PST Sunday for the
     Washington Palouse along and east of highway 195.


&&

$$


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