Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Spokane Washington
207 PM PDT Tuesday Aug 4 2015
cooler temperatures, continued breezy conditions, with a small
threat of showers and thunderstorms over the northern mountains
are expected through Thursday in the wake of a cold front.
Another threat of showers and thunderstorms arrives this weekend,
as yet another low pressure is expected to move into the region.
tonight through Wednesday evening: satellite indicates a closed
upper low descending into the forecast area from British Columbia.
There seems to be two distinct mid level fronts with this
low...one which also has a surface reflection is passing through
the forecast area this afternoon bringing breezy conditions to
most of the forecast area. Relatively high temperatures this
afternoon will probably allow achievement of red flag wind/rh over
much of the Columbia Basin and Cascade Gap areas late this
afternoon and evening and also trigger isolated showers and
possibly a garden variety brief thunderstorm or two over the
The second mid level front/disturbance is visible on satellite
approaching the northern tip of Vancouver Isle this
afternoon...and will sweep through the forecast area during the
day tomorrow. There may be another surface front embedded in this
wave...and in any event models maintain a tight cross Cascades
pressure gradient through tomorrow. This argues for a continuation
of the red flag warnings fro the Columbia Basin for tomorrow's
afternoon and evening period as well...although with cooler
temperatures minimum relative humidity may have trouble reaching critical values.
It is too close to call at this time and since the product is
already out...it will be allowed to continue. The other
ramification of this second wave will be a continued threat of
isolated showers and thunderstorms across the northern mountains
once again Wednesday afternoon and evening.
Otherwise no significant weather is expected through the next 24
to 36 hours for the lion's share of the forecast area. Partly
cloudy skies with cooler temperatures on Wednesday and much less
smoke given the new air mass exchange and well mixed nature of
this Post frontal air mass. /Fugazzi
Wednesday night through tuesday: a lingering shower threat wanes
early this period, before the next trough advances toward the
Pacific northwest next weekend into early next week. Model agreement
falters, however, going into early next week. Some runs progress
the trough through; others hold it near the coast. So confidence
wanes by this time. The most recent runs lean toward the slower
First Wednesday night and Thursday the current upper trough
shifts out through the northern rockies into the Canadian
prairies. A couple disturbances embedded in the flow around it
will continue to provide a lingering shower/T-storm threat. The
best moisture and instability Wednesday night, a pocket of
unstable high level total totals, migrates through northeast Washington
and north Idaho. Surface-based instability blossoms across the
northern mountains Thursday afternoon too. So these respective
areas will have the primary shower/T-storm threat. However these
are expected to be isolated in nature as the region becomes
removed from the core of the trough and lift. Temperatures will be
the coolest of the next seven days during this time frame, with
values some 5 or so degrees below average.
From Thursday night through Friday a shortwave ridge builds over
the region, even as the next two weather features approach. There
will be a lull in the weather and temperatures will begin to
moderate back to average.
Between Friday night and next Tuesday the next weather features
come in. First, low pressure off the California coast pushes
inland and mainly skims by southeast Washington and the lower Idaho Panhandle
through Saturday. At the same time low pressure (currently
migrating into the Gulf of ak) pushes toward the Pacific northwest
coast. As said, most recent runs keep the trough axis along the
coast through the duration of this period, with the trough simply
content right now to sent weaker impulses inland. This set-up and
our forecast then supports a shower and T-storm threat across the
Cascades and northern mountains, as well as over far southeast Washington
to the lower Idaho Panhandle each day with these impulses sliding in.
Chances will be best between Saturday and Tuesday during the
afternoon and evening hours. Yet it should be stressed that none
of this looks particularly widespread or wet, but mainly isolated.
So even with the shower/T-storm chances there should be a fair
amount of sun, save for perhaps near the Cascade crest. Expect
some breezy conditions, especially Saturday. Temperatures will be
near seasonal values. /J. Cote'
18z tafs: an upper level low pressure will move into
the region today and linger into Wednesday. This system will
result in a chance for showers and thunderstorms near the Canadian
border this afternoon. An associated cold front will result in
breezy conditions this afternoon across the region with gusts up
to 25 mph possible. Otherwise...VFR conditions are expected
through 18z Wednesday. /Mjf
Preliminary point temps/pops...
Spokane 61 80 57 77 56 86 / 10 10 10 10 0 0
Coeur D'Alene 59 80 55 77 53 86 / 10 10 10 10 0 0
Pullman 55 78 52 76 49 85 / 10 10 0 10 0 0
Lewiston 65 87 61 85 59 92 / 10 10 0 10 0 0
Colville 56 83 56 80 53 88 / 20 20 30 10 0 10
Sandpoint 54 80 52 75 46 83 / 10 10 20 20 10 10
Kellogg 59 78 53 75 51 85 / 10 10 10 10 0 10
Moses Lake 61 85 57 83 55 89 / 0 0 10 0 0 0
Wenatchee 66 83 63 84 63 89 / 0 10 10 0 0 0
Omak 60 84 55 84 55 89 / 10 20 20 10 10 0
Washington...red flag warning until 9 PM PDT this evening for East Washington
south central Cascade valleys (zone 676).
Red flag warning until 9 PM PDT Wednesday for East Washington
central Cascade valleys (zone 677)-East Washington northern
Columbia Basin (zone 673)-East Washington Palouse and
Spokane area (zone 674).