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Area forecast discussion 
National Weather Service Spokane Washington
309 am PDT Friday Jul 31 2015

Synopsis....
dry and hot weather will persist for the next several days. High
temperatures in the 90s to near 105 will be common through the
beginning of next week. A gradual cooling trend will take place by
mid week. A more dramatic change to the hot pattern is possible by
the middle of next week with an increasing threat of thunderstorms
each day from Monday through Thursday.

&&

Discussion...
today through Saturday night: expect more hot and dry weather! In
fact today should be the hottest day of the week as temperatures
rise another 3 to 5 degrees over yesterday, putting daytime highs
in the mid 90s to near 105! Hot! - Yes! But recording breaking? -
Not really for late July. Meanwhile dewpoints will remain low in
the 30s, translating to rather low relative humidity values. Winds will be light
through much of the day. Although the thermally induced surface
pressure trough will nudge into eastern Washington by afternoon
and begin to tighten the surface pressure gradient across the
Cascades. This gradient is expected to be weak of about 4 to 5 mb
due to lack of any upper level support or any marine push on the
west side. It will increase The Gap winds in the east slopes of
the Cascades and parts of the western Columbia Basin late today
with speeds of 10 to 15 mph. The NAM winds seem to be slightly
higher and gustier for this afternoon but sounding profiles in the
Cascades reflecting mixing levels up to 30k ft or above 300 mb!
This maybe a bit far fetched and would lean more toward the GFS
solutions which had mixing levels of 10-15k ft this afternoon. The
wind and low relative humidity will raise fire weather concerns, in addition to
hot and unstable conditions this afternoon. Little relief is
expected tonight into Saturday. After another mild night tonight,
saturday's daytime temperatures will soar into the 90s with a few
readings near 100. Temperatures in the lc valley and surrounding
spots will see daytime highs above 100 today and Saturday which
prompts the issuance of a heat advisory for this area. The cross
Cascade surface pressure gradient will squeeze again leading to
more gap winds late in the day. Saturday's winds may be slightly
higher, but not by much. Meanwhile humidity values stay in the
teens to single digits and low level instability increases across
the Columbia Basin. Skies should remain mostly clear with the
exception of high clouds spreading across southeast Washington and
southern Idaho Panhandle. /Rfox.

Sunday: little change to our hot weather pattern is expected on
Sunday. High temperatures will once again be in the mid 90s to low
100s from central Washington through the Idaho Panhandle. We will
be watching a surge of mid and high level moisture tied to the
desert monsoon. Scattered to broken high clouds on Sunday could
shave a couple degrees off our forecast, but a sustained cloud
shield to significantly cool temperatures on Sunday looks unlikely
at this time. The NAM and GFS move moisture in the 500-300mb
layer northward through Oregon early Sunday morning. At this
time, model forecast soundings keep cloud bases above 15 thousand
feet which seems too high for showers. Models can have difficulty
with moisture flux, so elevated showers or thunderstorms cannot be
completely ruled out at this time, but chances appear slim.
Showers in this type of pattern would probably not produce enough
rain to be of any benefit and the threat of lightning is something
we certainly do not need.

Monday through thursday: the evening model runs of the European model (ecmwf) and
GFS have come into decent agreement with the breakdown of our hot
high pressure ridge. Temperatures for most of the work week have
been lowered. This trend downward may not be enough in some
instances with our forecast still on the warm side of guidance.
Locally breezy winds and widely scattered thunderstorms will
likely accompany the transition from our hot weekend to cooler
weather early in the week. Our air mass this weekend will be so
unusually dry that it is hard to get too excited about
thunderstorms. The models sure don't generate much surface based
instability through Monday. We will need to keep an eye on
thunderstorms that form over Oregon on Monday. If they can become
an organized MCS, cells could move onto the Palouse and Columbia
Basin. However, at this time, the models are not forecasting
enough deep layer shear to sustain organized multi-cell
thunderstorms. Our best shot for scattered showers and
thunderstorms could be Tuesday or Wednesday as the 500mb low
digs southward along the coast of b.C. And Washington. By mid
week, there is enough model uncertainty that we are carrying a
generic low chance of showers and thunderstorms over our
mountainous zones. /Gkoch

&&

Aviation... 06z tafs: high pressure will continue to bring VFR
conditions including clear skies and relatively light winds the taf
sites through Friday evening. The only possible issue could be smoke
from Wolverine fire reaching Wenatchee or maybe Moses Lake later
tonight. Model runs keep most of the smoke confined to Lake Chelan
and points north of Wenatchee however without visible satellite to
see the smoke and confirm the forecast, our confidence is rather
low. Fx

&&

Preliminary point temps/pops...
Spokane 99 64 97 65 97 67 / 0 0 0 0 0 10
Coeur D'Alene 97 59 96 59 97 60 / 0 0 0 0 0 10
Pullman 98 57 97 56 95 59 / 0 0 0 0 0 10
Lewiston 105 68 104 66 103 70 / 0 0 0 0 0 20
Colville 100 57 98 59 100 58 / 0 0 0 0 0 0
Sandpoint 95 51 93 53 93 55 / 0 0 0 0 0 10
Kellogg 96 59 95 58 97 57 / 0 0 0 0 0 10
Moses Lake 103 60 101 62 100 66 / 0 0 0 0 0 10
Wenatchee 101 69 99 70 99 72 / 0 0 0 0 10 0
Omak 103 61 101 63 100 64 / 0 0 0 0 0 0

&&

Otx watches/warnings/advisories...
Idaho...heat advisory from noon today to 8 PM PDT Saturday for Lewiston
area.

Washington...heat advisory from noon today to 8 PM PDT Saturday for lower
Garfield and Asotin counties.

Fire Weather Watch from 2 PM PDT this afternoon through this
evening for East Washington central Cascade valleys (zone
677)-East Washington northern Columbia Basin (zone 673)-
East Washington south central Cascade valleys (zone 676).

&&

$$

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