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Area forecast discussion 
National Weather Service Spokane Washington
432 PM PDT Thursday Aug 21 2014

Synopsis...
thunderstorms are expected this evening over north central and
northeast Washington into the Idaho Panhandle. Friday has the
potential to be even wetter for the inland northwest with good
chances for thunderstorms region-wide, including the Columbia
Basin and Palouse. Locally heavy rain and frequent lightning will
accompany thunderstorms. The threat for widely scattered showers
and thunderstorms will continue into the weekend, followed by a
warmer and drier pattern by the middle of next week.

&&

Discussion...

Tonight through friday: as a trough pattern continues to build into
the region, widespread convection will bring thunderstorms with
brief periods of heavy downpours, small hail, and gusty winds to
the northern portion of Washington and the Idaho Panhandle. A
shortwave embedded in the trough will push into the region in the
early evening and allow for the eastern Cascades and portions of
the central Columbia Basin to begin to have some isolated
convection develop during the overnight hours. With potential
thunderstorms impacting the burn scar areas, flash flooding is
possible during the heavy downpours from these cells.

A low pressure system will begin to move along the
Oregon/Washington border on Friday and bring another wave of
instability to the region and bring the potential for isolated
thunderstorms to the inland northwest. The amount of cloud cover
in the northern portion of the region will keep diminsh the
chances for thunderstorms. But most other locations will the slow
steering flow with the low and the amount of precipitable water value of 0.8"
and decent sb cape in the Cascades area will keep the potential
for flash flooding as the cells will be slow moving and drop a
lot of rain over the burn scars. /Jdc

Saturday through Saturday night: the region will be in between
weather systems as some shortwave ridging builds in. Lingering
showers and an isolated thunderstorm threat is expected in extreme
southeastern Washington and in the Panhandle as low pressure exits the
region. A stiff northerly breeze will continue through the Purcell
Trench into Saturday. Northerly winds down the Okanogan Valley
will usher in some drier air across the basin with dew points
dropping into the low to mid 40s. Temperatures on Saturday will
remain below normal with highs generally in the 70s to low 80s.
/Svh

Sunday through Thursday...there is general model agreement during
the extended period.

Sunday and monday: another upper level wave will track across
northeast Washington into the Idaho Panhandle Sunday night into
Monday. This will bring another round of scattered showers and
isolated thunderstorms to the northern mountains and Idaho
Panhandle, with a few showers also possibly coming off the
mountains into the Spokane/Coeur D'Alene area due to a favorable
northwest steering flow.

Tuesday and wednesday: an upper level ridge will build in
bringing a warmer and drier conditions. 850mb temps of 21-23c on
Wednesday will yield more Summer like conditions with valley highs
in the mid 80s to lower 90s.

Thursday: another upper level trough descending out of British
Columbia will flatten the ridge on Thursday. Increasing
thermal/pressure gradients especially near the Cascades will bring
an increase in winds. Given this is a day 7 forecast confidence
in precise wind values is low...but the potential for breezy to
locally windy conditions exists. Jw

&&

Aviation...
00z tafs: a somewhat moist and unstable airmass associated with an
area of low pressure will continue to influence the aviation area
for the next 24 hours. During the daytime hours surface based
convective showers and thunderstorms will occur, primarily over
and near mountain locations. Additionally there looks to be a few
disturbances moving around in and along the edges of the low to
keep a mention of showers and thunderstorms during the late
evening, overnight, and early morning hours. The expectation is
slow storm motion will allow these storms to produce localized
heavy rainfall amounts at times. /Pelatti

&&

Preliminary point temps/pops...
Spokane 57 76 55 75 54 79 / 50 40 40 10 10 20
Coeur D'Alene 56 74 52 73 51 76 / 70 60 50 10 10 20
Pullman 52 76 51 74 49 79 / 20 50 50 20 20 20
Lewiston 61 81 59 79 56 84 / 20 20 50 30 20 10
Colville 53 79 50 79 49 81 / 60 60 50 10 10 20
Sandpoint 51 71 48 72 46 73 / 60 70 50 10 10 20
Kellogg 54 68 51 68 47 72 / 70 70 60 40 20 30
Moses Lake 58 83 58 83 56 85 / 20 30 50 10 0 10
Wenatchee 63 80 63 83 58 84 / 30 40 50 10 10 10
Omak 60 80 58 82 53 85 / 60 60 40 10 10 20

&&

Otx watches/warnings/advisories...
Idaho...none.
Washington...Flash Flood Watch through Friday evening for east slopes
northern Cascades-Okanogan Valley-Wenatchee area.

&&

$$

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