Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 260030
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
430 PM PST Sun Feb 25 2018

.SYNOPSIS...
Bands of rain and snow showers will slowly depart to the southeast
tonight with winds slowly decreasing into the evening. Monday will
feature dry and cool conditions. Snow showers return to the
mountains Tuesday then a milder storm looks likely for Wednesday
and Thursday. Expect showery weather for next weekend.


&&

.DISCUSSION...
This evening and tonight: Satellite reveals a cold core trough sagging
into the Northwestern US at this hour with the leading cold front
currently stretching from Astoria, OR to Republic, WA. Ahead of
the cold front, convective bands of precipitation will be
developing bringing a mix of rain, snow, snow pellets, and hail
and perhaps an outside chance for a stray lightning strike. The
main threat for these banded showers will be before 5PM north of
Hwy 2 but look to linger across Southeastern WA and the lower ID
Panhandle into the evening hours, ending around midnight. Little
to no shower activity is expected in the lee of the Cascades but
strong westerly flow and steep lapse rates will allow a few bands
to stretch from the crest across the Hwy 97 corridor at times and
just in the last hour, the Puget Sound Convergence Zone has
stretched all the way to the Wenatchee AP. Additional snowfall
this evening will be heaviest in southern Shoshone County, Camas
Prairie, Blue Mtns, and proximity of Stevens Pass which will range
from 2-5 inches. Under the most persistent convective bands, a
slushy half inch to two inches will be possible and this is due to
most locations starting above freezing when the showers arrive.

Winds will be on a gradual downward trend this evening as well. Per
the latest VAD wind profile on the OTX radar, winds aloft have
decreased from 50kts earlier to 40kts at 2PM. Sustained winds will
remain in the 15-30 mph range with frequent gusts of 35-40 mph
and isolated 45 mph. As convective showers pass overhead, gusts
between 40-50 mph will also be possible. Consequently, we extended
the wind advisory through 6PM.  Winds will slowly weaken this
evening and decrease near to below 15 mph by midnight.

Temperatures tonight will dip back into the 20s allowing any moisture
to re-freeze to roads so keep this in mind when heading out
during the Monday morning commute.

Monday, the region will be in between storm systems and under a
shortwave ridge. Lingering instability will keep a threat for
light snow showers in the Idaho Panhandle, otherwise a dry day is
on tap with the continued trend for below normal temperatures. /sb

Monday night through Wednesday morning...Northwest flow will
remain over the region through this period. The atmosphere dries
out quite a bit Monday night as the storm system from Sunday
moves away from the region. However, there are a few weak waves
that will track through the region and drag additional moisture
with them Tuesday and another Tuesday night. This will keep at
least a chance for precipitation in the Cascades and the
Panhandle mountains. Any precipitation will fall as snow with up
to 5 inches possible for the higher mountains. It will be
possible to see 1-2 inches for a few of the mountain valleys as
well. Temperatures will see a warming trend both Tuesday and
Wednesday, but remain on the cool side of normal.

Wednesday afternoon through Thursday night...Model guidance is
coming together showing a deep upper level low pressure system
closing off over Haida Gwaii Wednesday afternoon, then dropping
south along the coast Wednesday night and Thursday, then beginning
to move inland Thursday night. Southerly flow ahead of the the
low will increase moisture advection into the area during the day
Wednesday. Strong isentropic upglide will begin along the Cascades
Wednesday afternoon and push inland Wednesday night. The
combination of forcing and deeper moisture will result in
widespread moderate precipitation. Southeast low level flow will
overcome any Cascade shadow effect so even the deep basin and
lower east slopes will see an extended period of rain and snow.

Precipitation type will be a little more difficult as temperatures
begin to warm from the south. It looks like precipitation will
start out as mainly snow, but quickly become a snow/rain mix and
finally rain for the basin early Wednesday evening. The challenge
is that area in the northern basin into the southern portions of
the northern mountain valleys where snow may mix with rain at
times. Right now snow may turn over to a snow/rain mix or all rain
below about 2000-2200 feet Wednesday night. The mountains should
see all snow and the potential is there for elevations above 3000
feet to get quite an accumulation. We will have a better idea for
snow amounts over the next day or so. Winter travel conditions
should be planned and winter highlights will probably needed
starting Wednesday afternoon.

Thursday night through Sunday...The low will move inland Thursday
night and remain over the Pacific Northwest through the weekend.
The cold center of the low will be over the area destabilizing the
atmosphere, add in multiple waves that will likely wrap around the
low and the chances for rain and snow showers are very good. The
only wrench in the gears is that we will lose the deep moisture
tap from Wednesday night and Thursday, but the potential for
brief heavy rain/snow/graupel showers will remain quite high.
Tobin

&&

.AVIATION...
0Z TAFS: Bands of heavy snow will remain over the Wenatchee
mountains as a convergence zone sets up. This may bring brief
moderate snow showers to KEAT at times through 003z and also
mountain obscurations. To the east banded snow showers are moving
into the mountains of the north Panhandle and will also result in
mountain obscuration. to the southeast the front looks like it
will pass through KPUW between 01-0130z. Radar shows a band of
heavy snow stretches from about Harrison back to Washtucna and
this band will result in a short period of heavy snow, shifting
winds and possibly a lighting strike or 2 at KPUW with fropa.
Conditions will improve to VFR at all TAF after sunset and remain
VFR through Monday afternoon. Current southwest winds 15-25kts
with gusts to 30 mph will slowly subside through 06z below 10kts.
Tobin





&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        22  31  22  36  27  38 /  10  10   0  20  20  40
Coeur d`Alene  22  31  20  35  26  39 /  40  10  10  40  50  40
Pullman        24  31  18  34  27  38 /  80  10   0  20  20  30
Lewiston       29  38  23  41  30  45 /  70  10   0  20  10  20
Colville       19  37  21  37  24  38 /  10   0  10  30  20  40
Sandpoint      22  31  21  33  27  37 /  30  10  20  50  60  40
Kellogg        22  29  18  31  26  35 /  80  20  10  60  70  50
Moses Lake     26  42  25  45  28  44 /   0   0   0  10  10  50
Wenatchee      27  41  27  46  28  42 /  30  10   0  10  10  60
Omak           22  37  22  40  24  38 /   0   0  10  10  10  60

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Winter Storm Warning until 11 PM PST this evening for Central
     Panhandle Mountains-Idaho Palouse.

     Wind Advisory until 6 PM PST this evening for Lewiston Area.

WA...Wind Advisory until 6 PM PST this evening for Lower Garfield and
     Asotin Counties-Spokane Area-Upper Columbia Basin-
     Washington Palouse.

     Winter Weather Advisory until 11 PM PST this evening for
     Northeast Blue Mountains.


&&

$$



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