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Area forecast discussion 
National Weather Service Spokane Washington
504 am PDT Thursday may 28 2015

Synopsis...
scattered afternoon showers and thunderstorms will continue today
and Friday. However they will be more focused around the
mountains. Expect a warming trend into the weekend, with highs in
the 80s, with a lingering threat of mainly mountain showers and
thunderstorms. By next Monday and Tuesday the next best chance of
showers and thunderstorms arrives, with the potential for some
stronger storms and the return of cooler temperatures.



&&

Discussion...
today and friday: another upper level low pressure system will
drop south over British Columbia. This area of low pressure will not push much
further south than central British Columbia though as ridging across California
and Oregon keeps it north of the region. Dew point temperatures
will be in the mid 40s to low 50s today. This will result in
uncapped or weakly capped CAPES of around 200-500 j/kg across the
mountains. This will be enough instability for more isolated to
scattered shower activity with isolated thunderstorms also
possible. The NAM model has had a tendency this season to be too
unstable, so I am leaning toward the GFS depiction of our
potential instability today. This solution gives very little
instability over the basin. This makes sense as showers and
thunderstorm coverage was lacking yesterday with our previous low
pressure system making its exit. Heights aloft will be a bit
higher today compared to the last few days with that low moving
into The Rockies. This should result in little to no convection
over the basin this afternoon. A weak disturbance will push across
the region tonight. This will keep showers going over the northern
mountains. Mid level instability also looks fairly weak, so
thunderstorms are not expected to continue into the overnight
hours.

The better instability on Friday will reside over the northern
mountains. This should result in less of a chance for showers and
thunderstorms over the NE blue mtns over to the central Panhandle
mtns. However, we will see showers increasing through the day on
Friday over the northern mountains with a chance for thunderstorms
again in the afternoon. There will be a bit more shear on Friday,
which may lead to a few stronger cells compared to what we see
this afternoon. Any severe thunderstorms would be unlikely, but
small hail, heavy downpours and gusty outflow winds up to 40 mph
will be possible. Best potential for some stronger storms would
be closer to the Canadian border.

Temperatures will continue their upward trend with highs over much
of the region in the 80s. Some of the warmer locations across the
region such as Omak, Leavenworth, Wenatchee, Moses Lake and
Lewiston will be in the upper 80s and even approach the 90 degree
mark on Friday. /Svh

Friday night through Sunday...not a big change in model guidance
through Sunday. To recap another closed low currently moving into
northern b.C. Will drop south into central b.C. Then take a turn
to the east and weaken somewhat Friday night through Sunday. This
will result in zonal flow through the weekend. Drier air will
finally move into the region. This will result in a warming and
drying trend through late Sunday afternoon. Some late day showers
and thunderstorms will be possible on Saturday along the Montana
border due to some lingering moisture...otherwise expect dry
conditions. Temperatures will be mainly in the 80s and 90s both
days. Temperatures were cooled by a couple of degrees Sunday with
850 temps cooling a few degrees c. Late Sunday afternoon moisture
moving up from the south may result in a chance for
showers/thunderstorms across The Blues, the Camas Prairie, and up
into southern Shoshone County. Timing of the moisture will be
everything and we could easily just see some afternoon cloud
buildups.

Sunday through Thursday...guidance has been showing a closed low,
currently out near 40n/150w finally make it's way to the or/cal
coast by Sunday for several days. Southerly flow ahead of said low
will pump moisture up from the south helping to destabilize the
atmosphere. The models are similar up through Sunday evening, then
start showing major differences in timing the front as it moves
north through the region. As such confidence in this portion of
the forecast is less than average. This pattern is very good for
strong convection across the pac northwest. The challenge is all in the
timing.

At this time we are leaning strongly towards the GFS which brings
a cold front through the region on Monday. Mid and upper level
instability, divq and high level totals will increase through
Sunday evening and forcing due to a vigorous shortwave will
provide ample lift to tap into this instability and result in
nocturnal thunderstorms. Wind shear is between 40-50kts through
about 15z Monday morning. Ample moisture will result in locally
heavy rain, small to moderate sized hail, and gusty outflow winds.
For now the best chance for thunderstorms Sunday night will be
roughly east of a line from about the Tri-Cities to Mullan Pass.

There will likely be a break Monday morning, then surface based
CAPES increase to over 1000 j/kg according to the GFS. The front
will act as a focusing point for an active thunderstorm day
Monday. But there are some problems as well. For one the shear
drops down to around 20kts by mid-day Monday that should keep hail
from gaining any size. And ample cloud cover may inhibit deep
convection, but the front will likely overcome the cloud cover. So
an active day, likely not severe, but with pwat's over .75
localized very heavy rain is likely. Again timing will be
everything. There will also be a significant drop in temperatures
with highs dropping back to near seasonal norms. We expect model
guidance will tighten up over the next few days, and at this time
we feel this is the best solution.

Tuesday through Thursday afternoon and evening showers and
possible thunderstorms will linger across the region and were kept
in the forecast, but confidence in the forecast through this
period is even lower than for Monday. We do expect temperatures to
remain near or just on the warm side of normal through the end of
the week. Tobin

&&

Aviation... 12z tafs: a weak impulse of mid level energy is
producing light showers over the central Panhandle mtns this
morning. Higher heights will stabilize the atmosphere overall behind
this batch of showers. With that said, the boundary layer remains
moist and models show a weak cap over the mountains, so I do expect
increasing showers with isolated thunderstorms over the higher
terrain this afternoon; however, this convection is not expected to
impact the taf locations. There will be a weak impulse that moves
into the region off of the Pacific tonight should keep showers going
over the northern mtns overnight. /Svh



&&

Preliminary point temps/pops...
Spokane 79 57 82 59 82 59 / 10 10 10 10 10 10
Coeur D'Alene 78 54 82 57 82 56 / 20 20 10 20 20 10
Pullman 75 52 82 57 80 56 / 10 10 10 20 20 10
Lewiston 83 58 88 64 87 62 / 10 10 10 20 20 20
Colville 82 54 83 55 85 53 / 30 40 40 30 20 20
Sandpoint 78 51 81 52 80 52 / 30 40 30 20 20 20
Kellogg 76 49 81 54 80 53 / 40 40 20 30 30 20
Moses Lake 86 58 90 59 91 58 / 10 10 0 10 10 10
Wenatchee 86 64 89 63 89 62 / 10 10 10 10 10 10
Omak 86 56 87 54 89 53 / 10 20 20 20 10 10

&&

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

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