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Area forecast discussion 
National Weather Service Spokane Washington
355 PM PST Sat Nov 28 2015

strong high pressure will produce light winds and a strong
temperature inversion over the inland northwest through early next
week. Low clouds and fog will become common by Sunday. Air
stagnation may also lead to areas of decreased air quality. A
frontal system is expected to bring a chance of wintry precipitation
Tuesday night into Wednesday...with more unsettled weather
through the rest of the week.


tonight and sunday: what little wind there is remaining through
the Okanogan Valley and Purcell Trench will weaken further
overnight. This will allow the swath of low clouds and fog over
the southeast portion of Washington and into the l-c valley to expand
north and westward. Visibility has improved slightly in the fog
from around Ritzville to Pullman based off of web cams in these
areas. Confidence is high that these visibilities will degrade
quickly with sunset. Pockets of dense fog with visibility down to
1/4 mile will be possible. Temperatures will also be hovering in
the low 20s over much of the region. This may result in some slick
spots on roadways, which will include much of the region as the
fog expands overnight. We may have to end up issuing a dense fog
advisory at some point from this evening into Sunday morning
depending on how widespread and thick the fog becomes.

Much of the lower elevations will be in soup of fog/stratus by
Sunday morning. Winds will be very weak or calm, so I don't see
much of a potential for these low clouds to clear out Sunday
afternoon. Best chances for a little bit of sun on Sunday will be
along the outer edges of the fog bank in the mountains. The best
place to escape the low clouds will be in the mountains above
elevations of 3-4 kft mean sea level. Temperatures will suffer on Sunday as
well with many valley locations remaining in the mid 20s. Higher
elevations above the low clouds will warm up into the mid to upper
30s. This will keep a strong inversion over the inland northwest
with poor air quality conditions expected to remain in place. /Svh

Sunday night through Tuesday...good agreement among the latest
model runs continued through Tuesday strongly suggests a
continuation of the current and increasingly stagnant
inversion conditions through out the region. Persistent fog and
low clouds already occupy the deeper Columbia Basin today and it
is expected that this coverage will slowly expand over the next
few days to include most elevations below 4000 feet...with plenty
of sunshine on the slopes above. The persistent inversion will
also lead to a general deterioration of air quality with pollution
buildup under the inversion. The current air stagnation advisory
will remaining effect until further notice.

Beyond Tuesday models agree on opening the door for a more
progressive flow featuring periodic waves and relatively weak
storm systems...of near misses by stronger organized systems
depending on which model detail is preferred. The first wave
expected to spend itself on the upper ridge will pass through
Tuesday with little more than increased clouds aloft...only
noticeable from the ski slopes above the inversion.

The real noticeable breakdown process begins on or about
Wednesday when a stronger system with a reasonably coherent feed
of Pacific moisture brings an increasing chance of light snow to
most locations and the potential for freezing rain or mixed
precipitation to the deep Basin. A series of stronger waves
reinforce this deterioration trend Thursday and Friday...with
friday's storm appearing to consist of a more organized and
traditional frontal complex capable of wiping out the inversion
and ventilating the region with a breezy cold front passage.


00z tafs: a strong ridge aloft has promoted a strong inversion
over the Columbia Basin...and this inversion will remain through
early next week. Satellite indicates an area of stratus with tops
around 3kft mean sea level spreading through out the Columbia Basin from
south to north this afternoon. It is likely that all taf sites
will be impacted by this stratus deck by 06z tonight...and remain
through 00z Monday. Most tafs will feature IFR and LIFR conditions
through 00z Monday with IFR possibly improving to MVFR at
klws. /Mjf


Preliminary point temps/pops...
Spokane 15 25 17 28 19 30 / 0 0 0 0 0 10
Coeur D'Alene 17 27 18 31 19 31 / 0 0 0 0 0 0
Pullman 18 27 20 32 21 34 / 0 0 0 0 0 0
Lewiston 21 29 22 34 23 38 / 0 0 0 0 0 0
Colville 13 28 19 31 17 30 / 0 0 0 0 0 10
Sandpoint 17 26 19 31 19 30 / 0 0 0 0 0 10
Kellogg 16 29 18 32 20 33 / 0 0 0 0 0 0
Moses Lake 12 26 16 28 19 29 / 0 0 0 0 0 10
Wenatchee 20 25 18 29 20 30 / 0 0 0 0 10 10
Omak 15 25 18 28 18 28 / 0 0 0 0 0 10


Otx watches/warnings/advisories...
Idaho...air stagnation advisory until noon PST Monday for central
Panhandle mountains-Coeur D'Alene area-Idaho Palouse-Lewis
and southern Nez Perce counties-Lewiston area-northern

Washington...air stagnation advisory until noon PST Monday for east slopes
northern Cascades-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-
Wenatchee area.



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