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Area forecast discussion 
National Weather Service Spokane Washington
400 am PST Friday Feb 27 2015

Synopsis...
a weather system will clip the region today with the best chance
for rain and mountain snow showers in the Cascades. Cooler,
breezy, and dry weather is expected on Saturday. Another weather
system will pass through Monday and Tuesday with wintry weather
possible especially the Idaho Panhandle. Much colder air will move
into the area behind this system with temperatures well below
average for the middle of next week.



&&

Discussion...
for today...the well advertised upper level low is currently
dropping south along the Washington coast maybe a little slower
than model guidance had indicated. It still looks like the low
will continue to drop south along the Washington/or coast this morning and
then move southeast through central and southern Oregon tonight.
Wrap around moisture will result in high pops across the east
slopes of the Cascades and as far east as the deep basin through
mid morning...then begin to pull south as the low continues it's
southward trek. Even though the deeper moisture will move south
there will be enough lingering low level moisture and up-sloping
flow into the north Cascades to hold onto to some precipitation
through the afternoon. The remainder of the forecast area will
remain on the dry side with variable cloudiness through the day.
As the low drops south the surface pressure gradient will
increase from northeast to southwest. This will increase winds
through the afternoon and also allow cooler air to move down the
Purcell Trench and into the forecast area. Winds were increased
accordingly but will remain below the breezy category.

Tonight and Saturday...as the upper low continues to move south
and east the surface gradient will increase to between 12-13mb
through the night and into Saturday. 850 mb winds increase to
between 30-40kts depending on just what guidance one uses. We may
see a weak inversion tonight with clearing skies and that may
inhibit mixing these stronger mid level winds down to the surface
a bit. That may result in slightly less winds overnight but the
forecast will definitely trend windier. The mixing will not be an
issue on Saturday with ample sunshine destabilizing the
atmosphere. As such expect winds to increase later this afternoon
and overnight. Sustained winds of 15-30 mph with gust 30-40 mph
can expected down the Okanogan Valley...the Purcell Trench...the
West Plains...the Palouse and into the Columbia Basin tonight and
Saturday.

In addition cool and very dry air will move into the region as the
low moves out. Relative humidity will drop to 20-30 percent on
Saturday and combined with the gusty winds could create a control
challenge if any grass or brush fires get started. Temperatures
will also cool off by 3-5 degrees from Friday and will be below
seasonal averages. Tobin

Saturday night through sunday: the backedge of the trough
continues to move south out of the area. North to northeasterly
winds will decrease through the evening hours. Mostly clear skies
and light winds expected during the overnight hours will lead to
some very chilly temps come Sunday morning. Widespread min temps
in the teens to mid 20s are expected. Sunday temperatures rebound
a bit, but still remain slightly below average for this time of
the year. Clouds will start to increase late in the afternoon
ahead of the next weather system moving down the British Columbia coast.

Monday and tuesday: there are still some model discrepancies as
to the next weather system moving into the pac northwest. The 00z European model (ecmwf)
has trended a bit sharper with the trough over the area and
extending the energy associated with the trough further south and
not really weakening or shearing it out. Meanwhile the GFS and
Canadian seem to remain fairly consistent. Confidence is still low
on this event, but will be trending forecast towards the drier
GFS/Canadian.

Main forecast change was to decrease chance of precip across
central Washington. GFS is showing quite a bit of dry air moving into the
area late Monday. Also have lowered winds across the area...mainly
referring to northeast Washington and the north Idaho Panhandle. Northerly
winds do look to come down the Okanogan Valley and into the basin,
but have decreased those winds a bit as well. Have northerly winds
sustained 10 to 20 mph with gusts up to 30 mph through Monday
night and into Tuesday morning.

Precipitation that does fall with this system will be fairly
light. Currently models are showing the best area to be northeast
Washington and the Idaho Panhandle. Any valleys that do see some snow, it
will be pretty light, generally an inch or less. Not very
exciting, but at least it may be something... the mountains could
pick up 2-3 inches potentially. Any snow that is sticking to the
ground by Tuesday morning will likely melt during the day.
Temperatures will be right around freezing during the day across
the northeast portion of the forecast area, but mostly sunny skies
will quickly melt any snow.

Wednesday through friday: the forecast remains dry as an upper
level ridge builds across the area. Models disagree on a potential
system for Friday, but that is the European model (ecmwf) with all other models
saying the fairly Flat Ridge will remain.

Temperatures Wednesday morning are the coldest temps in the 7 day
forecast. Even though the colder 850 temps are Tuesday morning
with that system exiting, Wednesday morning we will have less
winds, and mostly clear skies which will provide a great scenario
for cold low temps. By Wednesday our winds will shift to a warmer
southwesterly flow which will help bring our temperatures back up,
with US at or just a few degrees below average by Thursday
afternoon. /Nisbet

&&

Aviation...
12z tafs: a Pacific storm system will drop south along the
Washington coast today and into Oregon tonight and Saturday.
Wraparound moisture will result in precipitation for the Cascades
and east into the deep basin. This will mainly effect keat with
-ra this morning...becoming -shra this afternoon. VFR/MVFR
conditions at keat through 19z then as the precip moves south
conditions will become VFR. Kmwh may see some light -ra/-shra at
times through the morning with prevailing VFR conditions. For the
remainder of the taf sites variable high clouds will be around
before clearing later this afternoon. The surface gradient will
tighten this afternoon and result in NE winds increasing late this
afternoon and overnight. Expect sustained NE winds 15-18kts with
gusts around 25kts after 18-19z then increasing after 00z 18-25kts
with gusts 25-30kts through Saturday afternoon.

&&

Preliminary point temps/pops...
Spokane 43 23 39 20 41 24 / 10 0 0 0 0 0
Coeur D'Alene 44 23 40 19 43 22 / 10 0 0 0 0 0
Pullman 47 26 38 20 41 24 / 10 10 0 0 0 0
Lewiston 49 29 43 22 45 26 / 10 10 0 0 0 0
Colville 46 25 45 22 46 26 / 10 10 0 0 0 0
Sandpoint 41 22 38 18 40 22 / 0 0 0 0 0 0
Kellogg 40 21 34 18 41 25 / 10 10 0 0 0 0
Moses Lake 52 30 48 23 47 27 / 40 10 0 0 0 0
Wenatchee 49 32 49 27 48 31 / 60 20 0 0 0 10
Omak 50 30 48 24 48 28 / 20 30 0 0 0 10

&&

Otx watches/warnings/advisories...
Idaho...none.
Washington...none.
&&

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