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Area forecast discussion
National Weather Service Spokane Washington
1051 am PDT Thu Mar 30 2017

Synopsis...
today will be breezy over much of central Washington while the
Idaho Panhandle and portions of eastern Washington will experience
scattered afternoon showers. The weather on Friday will be mild
and dry with light winds. The weekend and early next week will
feature average temperatures and scattered light showers, mainly
over the mountains.

&&

Discussion...

Today and tonight: the weather today will be breezy across central
and north central Washington as a surface low organizes over
southern Idaho and northeast Nevada. The northwest pressure
gradient will favor gusty winds through the Okanogan Valley,
Waterville Plateau, Moses Lake area, and upper Columbia Basin. By
early afternoon, look for sustained winds around 15 mph with gusts
of 20 to 25 mph in these areas. The Idaho Panhandle and eastern
third of Washington can expect scattered showers today as an
elongated upper level trough creeps over the region. Afternoon
destabilization will contribute to small cells capable of brief
heavy rain, graupel, and maybe some small hail. A few lightning
strikes may accompany some of the strongest cells, but the
atmospheric profile may be a bit too cool for more than a strike
or two. A Flood Watch remains in effect for much of the Idaho
Panhandle and portions of northeast Washington following
yesterday's rainfall. Field and small stream flooding continues to
be an issue after weeks of above average precipitation. The day
shift will call various County agencies this morning to check the
status of flooding. Today's showers won't be widespread enough to
worsen flooding, so we may be able to drop some or all of the
counties from the Flood Watch later this morning.

Previous forecast discussions mentioned the possibility of a wrap
around band of rain/snow this morning for the Blue Mountains and
Camas Prairie. The models have trended further south with this
deformation band. Trends on satellite and radar support the
southerly track advertised by the latest model runs. If there is
any accumulation this morning, it appears as if it will be an inch
or less on grassy surfaces above 4000 feet around Anatone and
Winchester. /Gkoch

Friday: a dry day? A day with light winds and a good deal of
sunshine? Afternoon temperatures in the 50s? Will we be able to
handle a truly nice early Spring day? If we had a "nice day
advisory", we'd need to issue one for Friday so people could
prepare for such a rare occurrence in the Spring of 2017. Mid-
level high pressure will build over the region bringing a rare day
of no precipitation across eastern Washington and north Idaho.
Areas of valley fog in northeast Washington and north Idaho should
dissipate by mid to late morning giving way to partly cloudy
skies. Bands of high clouds will be on the increase in the
afternoon as the next frontal system moves into British Columbia.

Saturday through Monday night: a swift westerly aloft
will take over the inland northwest for Saturday guided by a 120kt+ jet
aloft. With a low in the Gulf of Alaska, an elongated cold front
will push through the region. The GFS seems to be the juiciest
with pwats of near a half an inch with the front, while the European model (ecmwf)
and Canadian trend toward drier solutions. Yes, there will be
moisture, although not quite the caliber of wed's system. In
addition, the westerly flow will enhance downsloping in the Lee of
the Cascades into the basin with mostly dry and breezy
conditions. This should also be the mildest day of the week. The
models are trending to a solution that brings showers across the
northern mountains Saturday morning, then pushing across extreme
eastern Washington into Idaho Panhandle for the afternoon and
evening hours. This convection may spark an isolated thunderstorm
but guidance shows low confidence with this. The front looks to be
a fast mover with showers decreasing Saturday night with drier
air moving into the region. Sunday should start off on the dry
side with shortwave ridging, although a weak trough aloft will
approach from the west. Low level moisture in sheltered valleys
and clearing aloft will increase the fog potential especially in
northeast Washington and north Idaho. This upper trough shows
signs of stretching and splitting, directing the main energy south
of the region into Oregon and leaving colder air aloft and
instability over the inland northwest. Anticipate orographic
showers to increase during the afternoon and evening hours under
the westerly flow, daytime heating and the passage of the upper
trough axis. Mid level moisture does increase with trough axis
passage with scattered mountain showers and snow levels 3k to 4k
ft. By Sunday night into Monday, the trough axis slowly exits
north Idaho as an upper low spins up and tracks into Montana and
Wyoming. Instability and orographic showers will return to extreme
eastern Washington and north Idaho especially by the afternoon
and evening hours. Anticipate temperatures to trend slightly
cooler for Sunday into Monday, and remaining below normal for the
start of April. /Rfox.

Tuesday through thursday: Tuesday a shortwave builds in over the
region bringing US a mostly dry Tuesday and even into the first
half of Wednesday. The only exception could be a few hit and miss
mountain showers. Enjoy the dry weather because late Wednesday
into Thursday another moist frontal system is ushered in,
bringing more rain. Southwest winds will tap into a good Pacific
moisture feed, with pwats from 0.75 to 0.90. These winds will also
advect in some warmer air with temps steadily climbing each day.
Widespread highs in the upper 50s won't be out of the question by
Thursday. /Bwilliams

&&

Aviation...
18z tafs: widely scattered showers over eastern Washington and the Idaho
Panhandle will continue through the aftn hours. Airports with a
decent shot of showers this afternoon are Colville, Sandpoint,
Bonners Ferry, Coeur D'Alene and Pullman. The strongest cells
will have the potential to produce brief heavy rain and soft hail
(up to pea size) in the 20z-01z time frame. Showers should
diminish quickly this evening with the loss of afternoon heating
and dry north advection through the evening. There is the
potential of some low clouds or fog early Fri morning, but
confidence isn't high. Put in a scattered low cloud deck for geg-sff-
Coe-lws, and broken for puw where confidence is a bit higher.



&&

Preliminary point temps/pops...
Spokane 52 34 54 37 56 36 / 30 20 0 0 20 10
Coeur D'Alene 50 33 54 36 54 34 / 40 20 0 0 20 20
Pullman 50 32 51 35 55 35 / 50 30 0 0 20 20
Lewiston 56 36 56 37 59 38 / 50 20 0 0 10 20
Colville 52 32 55 34 54 34 / 20 20 0 0 20 10
Sandpoint 48 32 53 33 51 32 / 30 20 0 0 30 20
Kellogg 46 33 50 33 50 33 / 50 40 0 0 20 20
Moses Lake 61 35 60 39 62 37 / 10 10 0 0 10 10
Wenatchee 57 36 57 39 59 37 / 10 0 0 0 20 10
Omak 56 32 57 36 58 33 / 10 10 0 10 20 10

&&

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

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