Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 211316
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
505 AM PST Wed Feb 21 2018

.SYNOPSIS...
Cold and generally dry conditions will persist throughout the
week outside some passing light snow showers at times. A pair of
stronger storm systems will impact the region by this weekend into
early next week with the potential for snow and breezy conditions
for most locations.

&&

.DISCUSSION...
Today through Thursday night...While one weak system departs the
southeast corner of our forecast area early this morning, another
one is lurking over central BC and has its sights set on the PacNW
for later in the period. For today...things will be generally
placid as chilly NW flow continues. Most locations will begin the
day on a sun-filled note but the BC system will begin to deliver a
surge of high and mid level clouds by midday to the northern
Cascades and spill over the remainder of the Inland NW during the
afternoon and evening hours. Despite the increasing cloud trend,
we aren`t too excited about precipitation chances. If any
precipitation were to fall during the day the best chances would
occur over western Okanogan and Chelan Counties where the moisture
is expected to be deepest. Nonetheless the overall synoptic scale
forcing will be weak and it won`t be helped by any orographic
ascent as cold air advection westerly winds continue at crest
level. While we won`t rule out the chance of snow in these
locations, the precipitation amounts should be quite low. The
chances for light snow will increase overnight as a 500 mb
shortwave trough and 700 mb low tracks into the Cascades during
the evening and into SE Washington or NE Oregon by Thursday
morning. Dendritic layer ascent never looks too strong but a brief
period of upslope E-NE low/mid level winds should deliver the best
chance of measurable snow to the Cascades during evening. The best
threat will shift into SE Washington and NC Idaho toward morning
when N-NW winds develop on the backside of the low. Once again the
forcing looks weak. Snowfall amounts for all these locations
should be an inch or less and in most cases considerably less. Not
convinced there will be much of any chance of measurable
precipitation in between these locations. The low is expected to
exit the region during Thursday afternoon with drier air beginning
to work its way in from the northwest. Temperatures through this
period will maintain their much colder than normal status however
highs today won`t be as chilly as yesterday. That still equates to
highs in the 20s to middle 30s or anywhere from 15-20 degrees
colder than normal for this time of year. The low temperatures for
tonight also won`t be as chilly as the current readings due to the
influx of clouds associated with the upper level system. That
still means most valley locations will see lows in the single
digits to mid teens. Thursday nights lows could be slightly colder
due to fewer clouds. fx

Friday through Tuesday: With a ridge of high pressure parked in
the eastern Pacific, the northerly flow aloft will send a series
of clipper systems into the region. Temperatures will gradual
moderate, although still will remain below normal. One feature
arrives Friday afternoon into Saturday as a weak warm front. Snow
levels will remain low with widespread snow Friday into Friday
night. Southwest winds increase Friday night especially across
southeast Washington. The light snow coupled with the breezy winds
may lead to patchy blowing snow. By Saturday afternoon, warming
will increase and a rain/snow mix is possible across the southern
Basin and LC valley. A weak cold front slides in from the
northwest by Saturday night as precipitation decreases
temporarily. The models show the next system arriving quickly on
Sunday with another warm front. Temperatures rise a couple more
degrees as do snow levels, making Sunday possibly the mildest day
of the week with temperatures in the mid 30s to mid 40s. Southwest
winds increase again Sunday afternoon and evening with patchy
blowing snow possible across exposed locations of southeast
Washington. For the weekend into early next week, the best chances
of snow look to be over the Panhandle mountains, southeast
Washington and near the Cascades. An upper trough digs over the
region as a cold front exits Sunday night. There is the potential
for another system for Monday into Tuesday, but models could be
trending toward a more southern track. Temperatures cool slightly
for early next week with a chance of light snow remaining in the
forecast. /rfox.

&&

.AVIATION...
12Z TAFS: VFR conditions are expected at all taf sites this morning
with the exception of COE. COE is seeing a small area of low clouds
and fog right around the airport and points south. Other areas of
fog were found along the Spokane River and near Lake CdA. This area
should expand a bit this morning, and there is a very small chance
it could expand to SFF. We did not put it in the SFF TAF, but will
monitor satellite to see if it needs to be added. Hopefully this fog
and the IFR conditions it brings should break up between 18-20z but
since models are not handling it all that well to begin with,
confidence is not high. For the remainder of the forecast sites, the
main weather will be an increasing cloud trend for EAT/MWH later
this afternoon and the other sites this evening. Cigs will remain at
or above VFR levels. Any threat of precipitation from these clouds
will remain distant from any of the TAF sites. fx

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        24  11  28  11  29  24 /   0   0   0   0  20  50
Coeur d`Alene  26   8  30   8  28  21 /   0   0   0   0  30  70
Pullman        26  13  29  12  29  24 /   0  10  10   0  20  70
Lewiston       32  18  34  16  36  29 /   0  10  10  10  10  40
Colville       26   9  31   8  29  20 /   0  10   0   0  30  30
Sandpoint      24  10  29  11  26  22 /   0   0   0  10  40  60
Kellogg        23   9  27  10  27  20 /   0   0   0  10  20  80
Moses Lake     31  19  36  16  36  28 /   0  10   0   0  10  10
Wenatchee      30  17  35  17  36  25 /   0  10  10   0  10  10
Omak           26  12  32  12  28  20 /   0  20   0   0  20  10

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...None.
WA...None.

&&

$$


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