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Area forecast discussion 
National Weather Service Spokane Washington
427 PM PDT Sat Jul 12 2014

Synopsis...

A prolonged heat wave will continue across the inland northwest
through this weekend and may linger well into next week. Mid to
upper 90s will be common, with triple digit heat in the Lewiston
area and portions of the Columbia Basin. Increased moisture will
enter the area Sunday night into Monday leading to an increased
chance for showers and thunderstorms. Fire weather concerns are
possible with lightning expected and some storms lacking
significant rainfall.



&&

Discussion...

Tonight: strong upper level high pressure will remain anchored
over the inland northwest tonight bringing another unseasonably
warm night. The NAM and GFS continue to advertise a bit of surface
based instability over the Cascade crest this evening. A small
chance of early evening thunderstorms have been retained over the
high terrain of the Cascades through 8 PM. A thick cirrus deck has
limited heating over the last few hours over the Lake Chelan and
Methow Valley, so evening thunder may be a stretch.

Sunday and Sunday night: an upper level disturbance currently off
the north California coast will lift to the northeast Sunday and
Sunday night. An influx of mid-level moisture combined with
increasing upper diffluence will likely trigger clusters of
surface based thunderstorms over central and west central Oregon
Sunday afternoon. The NAM, GFS, and European model (ecmwf) perpetuate thunderstorms
through the night as the upper disturbance translates
northeastward. A Fire Weather Watch (sun evening through Mon
morning) has been issued for the Wenatchee and Lake Chelan areas
for the potential for abundant lightning and dry fuels. Model
soundings suggest cloud bases of 10 thousand feet (or higher), a
very dry sub-cloud layer, and storm motion of 30-35kts. All of
these forecast elements point toward very little precipitation
accompanying any thunderstorms that develop. /Gkoch

Monday through Wednesday evening: the early work week will feature
showers and thunderstorms early with improving conditions midweek.
The shower and thunderstorm threat will continue from Sunday
night and spread east throughout early Monday. The set up for
storms look supportive with an area of low pressure shifting east
over the region throughout Monday. With the low over the western
portion of the state early Monday, increased moisture will advect
into the inland northwest leading to increased instability. Early in the
morning, elevated convection is expected as high level instability
will be the driver coupled with the approaching low. Models
differ on the amount of instability present with the NAM being the
most robust whereas the GFS and Euro are not as aggressive.
Favored the GFS/Euro combo as the NAM has a tendency to overdo
instability, but this will have to be further evaluated with new
model runs. With lower quantitative precipitation forecast values expected for the morning storms,
stray lightning strikes away from rain cores could lead to new
fire starts.

Moving later into the day on Monday the convection will likely
shift to surface based as the lower levels become unstable with
daytime heating and increased moisture. By midday into the late
afternoon the focus will shift to the northern and eastern
portions of the forecast area with only low end chances for other
areas. A shift to surface based convection will also allow for
more quantitative precipitation forecast to fall from the storms as they will have a deeper column
of moisture to work with. For impacted areas, afternoon storms
will have the potential to bring heavy rain and frequent
lightning especially for NE Washington and the Panhandle. The
limiting factor for stronger storms would be the overall lack of
bulk shear as decent cape and negatives Lis will likely be
present. Temperatures for Monday are expected be slightly lower as
cloud cover and precip will help to keep things a bit cooler, but
still above normal.

Monday night and into Tuesday the storm intensity and coverage is
expected to move east as the main area of low pressure also pushes
to the east. Some remnant showers and weak T-storms are all that
is expected for NE Washington and portions of the Panhandle. Tuesday into
Wednesday will be when the ridge of high pressure re-asserts
itself over the inland northwest. This will help to clear the skies and
minimize the shower potential midweek. Temperatures will also
rebound back into the upper 90s to mid 100s with the abundant
sunshine. /Fliehman

Wednesday night through saturday: there are some slight model
differences in the extended forecast. The GFS has been showing a
trough of some kind moving through the inland northwest through
the end of the work week. The 12z GFS has trended slightly weaker
with this system. When doing a dprog/dt between the GFS and the
European model (ecmwf)...it seems the ec has been more consistent in showing a
weaker feature moving through Thursday...and keeping most of the
energy with that feature further north into British Columbia. Have
therefore decided to trend the forecast more towards the European model (ecmwf) Wed
night through Thursday. The 12z ec is showing something new on
Friday with a possible trough moving through...similar to what the
06z GFS was showing. Right now will ignore this solution as this
is the first time the ec has caught on to this and will wait to
see if the GFS and ec can come into better agreement. Models do
agree on temperatures finally cooling on Thursday and even
further on Friday. This could end our consecutive 90 degree streak
for Spokane on Friday with 12 days. Unfortunately, locations such
as Lewiston, Moses Lake and Wenatchee will not be so lucky as they
will still see lower 90s on Friday. Saturday models are not in
good agreement and therefore did not make significant changes to
current forecast. /Nisbet

&&

Aviation...
00z tafs: mainly VFR conditions over the next 24 hours. Wildfires
near the Cascades may contribute to reductions in visibility at
keat, down to around 3 to 5 miles, for late overnight/Sunday
morning with drainage winds and inversions setting up. This threat
should wane after 17-19z. Otherwise some higher clouds will be
found across the region. Just beyond 24 hours (after 00z monday) a
threat of thunderstorms, with little precipitation, encroaches on
the Cascades and lower Columbia Basin. /J. Cote'



&&

Preliminary point temps/pops...
Spokane 67 98 70 91 67 95 / 0 0 10 30 40 10
Coeur D'Alene 61 97 65 90 63 93 / 0 0 10 50 40 10
Pullman 53 97 57 93 60 95 / 0 0 20 20 20 10
Lewiston 68 103 71 100 69 102 / 0 0 20 20 20 10
Colville 57 100 61 90 61 97 / 0 0 10 50 40 10
Sandpoint 54 94 58 89 58 91 / 0 0 10 60 50 10
Kellogg 58 95 62 88 61 90 / 0 0 10 40 50 20
Moses Lake 66 103 70 100 70 104 / 0 0 20 20 10 0
Wenatchee 72 102 73 100 74 102 / 0 0 20 20 10 0
Omak 70 103 70 98 67 103 / 0 0 20 30 20 0

&&

Otx watches/warnings/advisories...
Idaho...none.
Washington...Fire Weather Watch from Sunday evening through Monday morning
for East Washington central Cascade mountains (zone 682)-
East Washington central Cascade valleys (zone 677)-East
Washington south central Cascade mountains (zone 680)-East
Washington south central Cascade valleys (zone 676).

&&

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