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Area forecast discussion 
National Weather Service Spokane Washington
440 PM PDT Monday Aug 31 2015

Synopsis...
light rain in the northern mountains will slowly creep north
tonight. Tuesday will feature dry and breezy conditions. A weak
cold front brings a reinforcing shot of cooler air Wednesday
along with a chance for showers and gusty winds. A cooler and
showery weather pattern will linger over the region late week and
into the weekend.

&&

Discussion...

Tonight through Wednesday night: a broad upper-level trough is
anchored over the pac northwest today and will remain in place through
this period. A corridor of rich mid and upper level moisture
currently coming inland along the base of the trough is sprawled
across the northern mountains. Over the next 12-24 hours, another
shortwave will dig into the backside of the trough and back
midlevel flow to the south. This will nudge the clouds and light
rain northward into southern British Columbia and Tuesday will feature light to
locally breezy winds, warmer temperatures, and dry conditions. By
Tuesday night and Wednesday, the aforementioned shortwave dropping
into the trough will round the base and eject inland. This will
usher the next cold front through the inland northwest. The front will
pick up the lingering moisture over southern British Columbia and bring it back
to the southeast. Some showers will get squeezed out along the
front but precipitation amounts will be rather light. The northern
and eastern mountains carry the highest threat for up to a tenth
of rainfall with most other locations getting between a trace and
few hundredths. The frontal boundary stalls somewhere between northwest
Montana and NE Oregon keeping clouds and threat for showers in the
vicinity of far southeastern Washington and the lower Idaho Panhandle.
Behind the front, the atmosphere will become increasingly unstable
increasing the threat for afternoon mountain showers. A majority
of this activity will be confined to the international border and
Cascade crest.

Temperatures will remain below normal with afternoon highs in the
60s and 70s. Overnight lows will be in the 40s and 50s tonight and
Tuesday night then cool Wednesday night. Isolated pockets in the
northern mountains could dip down in the mid 30s. /Sb

Thursday through Friday night: the area of low pressure in the
northern portion of the Gulf of Alaska and in northern British Columbia will
slowly drift south over the region. This will keep temperatures
below normal and keep the weather unsettled. Friday looks to have
the better chances for showers and thunderstorms across the
region. P-wats off of the models are only up half an inch. These
values are relatively low, which would mean that storms are not
expected to be proficient rain producers. However, the steering
flow will be weak, especially over the northwestern portion of the
forecast area. The atmosphere also does not look like it will be
too unstable, but there is a potential for some storm to achieve
deeper convection with heavy downpours possible. The time of day
for thunderstorm development would be in the afternoon. There is a
small chance that a thunderstorm may drift over a fresh burn scar
or burn scar from recent years; although chances are low, the
heavy rain may trigger some minor mud flows or debris flows or
possibly a flash flood if storms are nearly stationary. The risk
doesn't look great at this point do to the lack of moisture
available, but will be a situation we will need to monitor as we
head through this week. Low temperatures may get a bit chilly
with some colder spots lowering into the mid 30s during the
overnight hours. Confidence is low as far as how cold we may get
since I do expect there will be some cloud cover over the region,
which would limit our radiational cooling potential. /Svh

Saturday through monday: models are agreeing that a low will pass
south the region and bring precip to the region. The models differ
on the amount and location of this rainfall. The bast chances for
rainfall is expected to be in the Blue Mountains and Idaho
Panhandle through the weekend. The Cascades and northern
mountains could see some rain on Saturday. Temperatures are
expected to remain on the cool side of normal for this time of
year. /Jdc

&&

Aviation...
00z tafs: areas of light rain will continue across the Cascade
crest and far northern Washington tonight but will not impact any taf
site. Smoke models still bring some smoke from near Pomeroy
toward the kpuw- klws corridor and if this is the case, nocturnal
inversions could result in some reductions of visible until morning.
Confidence is low due to uncertainty with burning behavior of that
NE Oregon wildfire. Some smoke is expected to settle into the
valleys of northern Washington and northern Panhandle of Idaho. Otherwise...
mid and high clouds will persist. Breezy early evening winds will
diminish overnight but will become breezy again Tuesday afternoon.
/Ek

&&

Preliminary point temps/pops...
Spokane 50 75 52 68 44 66 / 10 10 20 10 10 20
Coeur D'Alene 50 74 52 67 43 65 / 10 10 20 20 10 20
Pullman 47 76 50 68 42 66 / 10 0 20 30 10 20
Lewiston 55 83 58 73 49 71 / 0 0 10 20 10 20
Colville 49 74 50 70 40 68 / 20 10 20 30 10 30
Sandpoint 46 72 48 66 40 64 / 20 10 20 20 10 30
Kellogg 46 73 49 65 41 63 / 10 0 20 40 20 20
Moses Lake 53 77 53 73 47 71 / 10 10 10 10 10 10
Wenatchee 54 75 56 71 50 70 / 10 10 10 10 10 10
Omak 48 75 49 72 43 69 / 10 20 20 20 10 20

&&

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

$$

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