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Area forecast discussion 
National Weather Service Spokane Washington
521 PM PDT Friday Mar 27 2015

Synopsis...
a fast moving cold front will arrive tonight bringing widespread
showers, gusty winds, and the potential for thunderstorms to
southeast Washington and portions of the Idaho Panhandle. Saturday
will be quite windy with gusts of 40 mph possible over Palouse,
West Plains, and upper Columbia Basin. The weather Sunday and
Monday should be mild and relatively dry. Another fast moving
front on Tuesday will bring more showers and wind.

&&

Discussion...
tonight and Sat...

Thunder and showers: we backed off the pcpn and thunder potential
through late afternoon to early evening as it looks like much of
the surface will remain capped. Showers and thunder will then
rapidly develop and spread NE across much of ern and north Idaho as
the cold front and upper trough (currently just offshore) moves
inland. Convective mode: shear and thermodynamic profiles show the
main threat will be very gusty winds, with any thunderstorm
outflow augmenting the already strong synoptic-scale pressure
gradient dry slot winds overnight. Severe gusts (gust to 58 mph)
is a possibility, but not likely with the strongest embedded
thunderstorms. Steering flow for these cells alone should be at
least 30-35 kts with this embedded thunder. Small hail is
possible. The challenge tonight will be how much thunder is
generated across nrn WA late tonight as the vort Max (and
associated cold pool and steep mid-level lapse rates) translate
east rather quickly. If this was occurring during peak heating,
thunder would be a certainty.

Winds: we'll issue a Wind Advisory with the passage of the cold
front this evening through midday Sat for especially the Palouse
area as a significant mid-level dry slot surges across ern WA.
Initially the heavy showers and thunder will help to mix stronger
winds aloft (35-40 kts) to the sfc, then strengthening pressure
gradients and cold advection overnight following fropa will help
to Transfer 45-50kt winds aloft in a nearly unidirectional
westerly vertical wind profile.Bz

Saturday night through Friday...a Gulf of Alaska area of low
pressure juxtaposed against a weak ridge of high pressure with
axis placement generally to the east of northern Idaho allows for
a persistent flux of moisture through an elongated baroclinic band
located between the low and the ridge. The placement of the
baroclinic band is far enough to the north through Monday so as to
allow for a dry forecast for most locations with the exception of
locations close to the British Columbia border and the north
Cascade crest. Another cold front wipes out the ridge Monday night
into Tuesday. As it does this is will spread precipitation from
west to east and allow for windy conditions during and after its
passage Tuesday. From about Tuesday night on through Thursday the
jet stream straddles the forecast area along the southern border
which allows for a conditionally unstable airmass and associated
cold pool aloft to overhang eastern Washington and northern Idaho
through most if not all of this interval which allows for a cool
forecast with mainly diurnally driven showers and the possibility
of some frost with more widespread temperatures just below
freezing Wednesday night. By Friday the trof aloft exits to the
east and leaves a more flat zonal flow with the jet stream in
closer proximity which would suggest a further decrease in pops
but perhaps a return of breezy conditions as the jet stream gets
positioned closer overhead of eastern Washington and northern
Idaho. /Pelatti

&&

Aviation...
00z tafs: a vigorous cold front will sweep across the region
overnight. The atmosphere will gradually destabilize through this
evening with strong forcing along the front expected to break the
cap holding down convection this afternoon. Best instability will
be located from northeast or, southeast Washington and into the central
Panhandle mtns. Confidence is high that thunderstorms will develop
this evening along this axis and impact the klws taf site. Kpuw
will also see a chance for thunderstorms this evening, but
confidence is slightly lower. Moderate to heavy showers will then
Blossom ahead of the front east of a line from kepi to komk.
These showers may result in brief MVFR cigs/vis into the early
morning hours on Saturday. Gusty westerly winds will also
accompany the front overnight and continue into Saturday
afternoon. /Svh

&&

Preliminary point temps/pops...
Spokane 47 60 39 59 40 62 / 80 40 0 10 10 10
Coeur D'Alene 45 59 38 59 38 63 / 90 70 0 10 10 10
Pullman 46 58 40 58 41 64 / 90 40 0 10 10 10
Lewiston 51 64 41 63 42 68 / 90 20 0 0 10 10
Colville 44 63 39 60 39 63 / 70 60 0 10 10 10
Sandpoint 45 56 38 57 36 62 / 100 90 0 10 10 10
Kellogg 42 53 36 56 38 60 / 100 100 0 10 10 10
Moses Lake 48 65 40 65 39 67 / 10 10 0 0 10 10
Wenatchee 48 65 43 65 44 68 / 10 10 0 10 10 10
Omak 44 65 39 64 39 66 / 40 10 10 10 10 10

&&

Otx watches/warnings/advisories...
Idaho...Wind Advisory from 11 PM this evening to 11 am PDT Saturday for
Idaho Palouse.

Washington...Wind Advisory from 11 PM this evening to 11 am PDT Saturday for
lower Garfield and Asotin counties-Washington Palouse.

&&

$$

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