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Area forecast discussion 
National Weather Service Spokane Washington
253 PM PDT Friday Aug 28 2015

Synopsis...
a cold front will push through the inland northwest on Saturday
and bring high winds to the region. This will create a situation
for blowing dust with reduced visibility. There is the potential
for toppled trees and downed power lines as well. A cooler and
occasionally breezy regime with some shower activity will persist
through the next week.

&&

Discussion...

..strong low pressure system to deliver very strong winds and
areas of blowing dust on Saturday...

Tonight through saturday: the highly advertised low pressure
system is beginning to take shape out at 130w/40n off of the
northern California coast. The surface low will continue to deep
ahead of a dynamic upper level shortwave trough of lower pressure.
The track will take the low up the coast line tonight. Additional
cyclogenesis will take place in the Lee of the Cascades over
south-central Washington early Saturday morning and track northward into
southern British Columbia through the late morning hours. The associated cold
front will result in strong cold air advection that is expected to
result in good momentum mixing with much strong winds a loft
mixing down to the surface. The track of the low across the basin
and across the northern mountains of eastern Washington will place the
strongest winds across this part of the region. With that said,
all areas will likely experience windy conditions. Most of the
rainfall with the front will occur across the east slopes of the
northern Cascade mtns with only a chance expected in the Post
frontal air mass across much of the rest of the region.

* Winds: sustained winds of 25 to 35 mph with gusts to between 50
to 60 mph will be possible with frontal passage from the late
morning hours into the early afternoon. Gusts more into the 40
to 50 mph range will be more likely later in the afternoon as
the surface low pushes further away from the region. High
profile vehicles will likely have a difficult time due to strong
cross winds. Southerly winds will result in the strongest cross
winds occurring along I-90 and Highway 2 across the basin.
Strong cross winds can also be expected along Highway 95 and 195
across the Palouse.

* Blowing dust: the basin is not expected to receive much precip
between now through Saturday afternoon. The strong winds through
the day on Saturday is expected to present a potential dangerous
blowing dust concern. The basin will be the greatest concern for
blowing dust. Visibility may drop down to a 1/4 mile very
quickly making for dangerous travel conditions. The blowing dust
may stretch as far east as the Spokane/Coeur D'Alene areas,
Palouse and as far north as over the Waterville Plateau and
Okanogan Valley.

* Precipitation: around a quarter of inch to three-quarters of
rain can be expected across the east slopes of the northern
Cascades mtns. Higher accumulations are expected closer to the
crest with localized amounts of near an inch possible tonight
into Saturday. Much of this rainfall will occur in low to
moderate rainfall intensities. There will be a slight chance of
convection behind the cold front late in the morning into the
early afternoon. This may result in some higher rainfall
intensities near the burn scars in the Cascades. Minor mud or
debris flows will be possible in and around recent burn scars,
but flash flooding is not expected.

Sunday: a second cold front will swing through the region. This
front will be wetter east of the Cascade mountains. Rainfall
amounts of near a tenth of an inch with localized amounts near one
quarter of an inch will be possible across the eastern half of Washington.
Thunderstorms will also be possible in the afternoon behind the
cold front. Some of these storms may pulse up quickly with near
500-800 j/kg of cape exhibited off of the NAM model. Upper level
winds will still be very strong and any convection May Draw down
these stronger winds toward the surface. Best chances for
thunderstorms are expected across the northern mountains of Washington and
ID, but a chance of thunderstorms will be possible across the
basin as well that push east through the afternoon.

Monday and Monday night: a cool and showery pattern will continue
into early next week. Best chance for showers are expected across
the northern half of the forecast area. Temperatures will be
below normal with highs both Sunday and Monday in the 60s and 70s.
/Svh

Tuesday through friday: cooler and more unsettled weather can be
expected for next week as an upper level trough remains over the
region. The center of the upper low pivots across northwest
Washington through Wednesday but the speed it takes to push across
inland northwest is not clear. The GFS wants to hold a highly
amplitude trough over the Pacific northwest through the week, meanwhile
the European model (ecmwf) shows the low kicking out quicker and leaving a baggy
trough behind. The difference in the sensible weather will be
coverage of showers. Initally, a frontal band will push across the
Cascades Tuesday afternoon ahead of the upper trough and then
stall over southeast Washington into north Idaho by Wednesday and
even into Thursday. Anticipate the best chance of Post fronal
showers to be with the low center across the northern zones. West
to southwest winds will become gusty at times especially over the
afternoon and evening hours. Will continue to keep patchy smoke in
forecast through the week mainly near the source regions, although
anticipate more smoke dispersion with the winds and precipitation.
Expect daytime temperatures in the 70s, running below normal for
early September. /Rfox.

&&

Aviation...
18z tafs: clouds have thickened across the region and radar shows
a band of very light showers moving east of the Cascades and
across eastern Washington. So far, only the higher terrain is
measuring the precipitation, and believe the taf sites will just
see virga or vcsh through the afternoon. Cloud decks will be above
10k ft. Some smoke will be an issue in the kgeg-kcoe corridor
through midday, but as winds increase this should lift. Likewise
kpuw and klws will see some improvements this afternoon. Overnight
winds turn to the east and this should bring the smoke back into
these eastern taf sites overnight with MVFR vsbys possible.
Gusty prefrontal winds will increase by 15z which should help
lift vsbys and dissperse the smoke. Light showers will move over
the Cascades before 18z. /Rfox

&&

Preliminary point temps/pops...
Spokane 66 81 53 67 52 68 / 10 30 20 70 10 20
Coeur D'Alene 62 82 52 63 49 69 / 10 40 20 70 10 20
Pullman 65 82 52 67 50 73 / 10 30 20 50 10 10
Lewiston 67 88 58 72 55 79 / 10 20 20 40 10 10
Colville 60 82 51 68 50 68 / 20 40 30 80 20 30
Sandpoint 57 82 50 62 48 66 / 20 40 20 80 20 30
Kellogg 59 82 49 61 47 69 / 10 30 30 70 20 20
Moses Lake 65 79 55 73 54 75 / 10 20 40 40 10 10
Wenatchee 65 76 56 70 55 72 / 30 30 50 30 20 20
Omak 60 77 52 68 51 72 / 30 40 70 50 20 20

&&

Otx watches/warnings/advisories...
Idaho...red flag warning from 11 am to 7 PM PDT Saturday for northern
and central Idaho Panhandle (zone 101).

High wind watch from Saturday morning through Saturday evening
for central Panhandle mountains-Coeur D'Alene area-Idaho
Palouse-Lewis and southern Nez Perce counties-Lewiston area-
northern Panhandle.

Washington...red flag warning from 11 am to 7 PM PDT Saturday for East
Washington northeast (zone 686)-East Washington northern
Columbia Basin (zone 673)-East Washington Okanogan
Highlands (zone 687)-East Washington Okanogan/Methow
valleys (zone 684)-East Washington Palouse and Spokane area
(zone 674).

High wind watch from Saturday morning through Saturday evening
for lower Garfield and Asotin counties-Moses Lake area-
northeast Blue Mountains-northeast mountains-Okanogan
Highlands-Okanogan Valley-Spokane area-upper Columbia Basin-
Washington Palouse-Waterville Plateau.

Red flag warning from 11 am to 8 PM PDT Saturday for East
Washington central Cascade valleys (zone 677).

&&

$$

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