Area Forecast Discussion
Issued by NWS Spokane, WA

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS66 KOTX 261058
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
258 AM PST Sun Feb 26 2017

.SYNOPSIS...
The Inland Northwest will have several opportunities for snow
today through Wednesday. The most significant accumulations will
likely occur over the Idaho Panhandle the next several 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...

Today: As of 230 AM, snow has been gradually increasing over the
Idaho Panhandle and eastern Washington. Radar and web cameras
suggest that the most persistent snow has been falling over the
central Idaho Panhandle. So far, it looks like around an inch has
fallen in places like Deary, Clarkia, Kellogg, and Wallace. Across
the border in Washington, accumulating snow has been slow to
develop and spotty. The 06z runs of the GFS and NAM are doing a
decent job depicting the areas where the accumulations are
occurring, but they may be overdoing amounts so far.

The 6 AM to 2 PM time frame will make or break our snow forecast.
As a compact 500mb low slides down the Washington coast, we should
see bands of convective snow increase over southeast Washington
and the central and southern Idaho Panhandle. This region will be
under an increasingly difluent flow as mid-level lapse rates
become more favorable for upward motion. This area will also
undergo several hours of modest moist isentropic ascent.
Accumulation on road surfaces will be favored prior to 10 AM
before road surfaces warm during through the afternoon. Given the
convective environment, we may see quite a bit of variability with
snow amounts today. A blend of GFS and ECMWF qpf yields around 2
to 4 inches over the Palouse, Camas Prairie, St Joe/St Maries
Valleys and the Silver Valley today with the potential for another
inch or two overnight. Spokane, Coeur d`Alene, Deer Park, and
Sandpoint have a shot of 1 to 3 today and an additional inch
overnight.

Monday and Tuesday: Our 500mb low will move into central and
southern Oregon during the early morning hours on Monday. It looks
like there will be a bit of a lull in our snow showers prior to
sunrise, however the presence of a weak surface trough over
southeast Washington and the southern Idaho Panhandle may be
sufficient to produce scattered snow showers through the night in
places like Pullman, Lewiston, St Maries, Craigmont, and Kellogg.
We should see increasing coverage of snow showers during the day
Monday and into Monday night as a broad upper trough sets up over
the region. The west to northwest flow will favor snow showers
over the Cascade Crest, the Blue Mountains, and the
central/southern Idaho Panhandle. While the most concentrated snow
showers will be over orographically favored areas, the presence
of any small scale shortwave will have the potential to produce
brief snow showers. Given the cold mid-level temps, these snow
showers will have the potential to put down an inch of snow
quickly. /GKoch

Tuesday night through Friday...Flow across the region is much
near zonal with the jet stream in very close proximity to the
northern border through this time interval. This jet placement will
allow for windy conditions Wednesday and again Friday (expected to
be the windiest day) and the resulting mixing allowing for warmer
than average temperatures both those days as well. On Thursday brief
shortwave ridging pushes the jet stream a bit away to the north and
allows for a day with lesser wind compared to those forecast for
Wednesday and Friday. The general zonal pattern allows for
disturbances to pass with a general rain/snow shadow (in the form of
considerably lower pops and qpf in the forecast) off the Cascade
crest extending over the Columbia Basin and into some of the close
by lowlands with higher pops lingering in the close proximity of the
Cascade Crest, Southeast Washington, and the North Idaho Panhandle.
/Pelatti

Friday night thru Sunday...Models still show westerly flow aloft
and a strong jet overhead in the far extended. Additionally, a
couple of upper level waves with associated surface lows will pass
to our north...one around Friday night and another around
Saturday night. Both of which will drag a frontal boundary through
the region that may get hung up across our area or perhaps just
to our south depending on which model you believe. In either case,
precipitation chances will continue into the weekend with the
westerly flow favoring the Idaho Panhandle and the Cascade crest.
Snow levels will be fluctuating based on the progression and
eventual placement of previously mentioned fronts leading to, in
general, snow north and rain south. The other issue to mention is
wind potential Friday evening and perhaps into Saturday. While the
GFS has backed off its windier solution from last night,
ensembles show winds throughout various levels of the atmosphere
in the 90-99th percentile. How much momentum is able to mix down
to the surface is yet to be seen with area mountains seeing the
highest gust potential. /Kalin

&&

.AVIATION...
06Z TAFs: Snow is filling in across the region and will impact all
terminals through the taf period. Periods of moderate snow will be
possible at Spokane, Coeur D Alene, and Pullman which could
deliver visibilities near 1/2sm at times. 1 to 3 inches will be
possible at these terminals. For KEAT/KMWH up to an inch is
expected through 18z Sunday...while at KLWS marginal temperatures
for accumulating snow may result in only a dusting. Impacts at the
terminals may be low late morning through afternoon given the late
Feb sun angle and potential for effective melting on blacktop but
refreezing is expected once again after dark with snow continuing
at the eastern terminals and winding down in the lee of the
Cascades. /sb


&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        33  23  33  16  33  22 / 100  60  70  50  10  30
Coeur d`Alene  33  23  33  17  34  22 / 100  80  80  70  20  30
Pullman        33  24  33  20  35  25 / 100  70  90  80  60  50
Lewiston       38  28  38  26  41  29 /  90  70  60  80  60  40
Colville       35  19  34  16  35  19 /  70  50  30  30  10  20
Sandpoint      32  23  33  18  33  21 /  90  60  70  50  20  40
Kellogg        33  22  32  20  33  23 / 100  90  90  90  60  60
Moses Lake     38  24  38  17  40  26 /  90  50  30  30  10  10
Wenatchee      36  25  36  19  38  25 /  90  50  30  20  10  30
Omak           36  20  35  15  35  22 /  60  20  20  20  10  30

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Winter Weather Advisory until 3 PM PST Monday for Coeur d`Alene
     Area-Northern Panhandle.

     Winter Weather Advisory until 10 AM PST Tuesday for Central
     Panhandle Mountains-Idaho Palouse.

     Winter Weather Advisory until 10 AM PST Tuesday for Lewis and
     Southern Nez Perce Counties.

     Winter Weather Advisory until 3 PM PST this afternoon for
     Lewiston Area.

WA...Winter Weather Advisory until 3 PM PST Monday for Northeast
     Mountains-Spokane Area.

     Winter Weather Advisory until 10 AM PST Tuesday for Washington
     Palouse.

     Winter Weather Advisory until 10 AM PST Tuesday for Northeast
     Blue Mountains.

     Winter Weather Advisory until 3 PM PST this afternoon for Lower
     Garfield and Asotin Counties.

     Winter Weather Advisory until 3 PM PST this afternoon for
     Okanogan Highlands-Upper Columbia Basin.

&&

$$


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.