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fxus66 kotx 220906 
afdotx

Area forecast discussion
National Weather Service Spokane Washington
206 am PDT sun Sep 22 2019

Synopsis...
a fast moving storm system will bring increasing clouds and
rain showers today into tonight. Drier weather returns early next
week, with occasional gusty winds. Much cooler and unsettled
weather is likely late this week and into the weekend.



&&

Discussion...
today through monday: high pressure continues to bring dry
weather across the region early this morning. The upper level
ridge axis has moved east over Montana as an eastern Pacific
frontal system is pushing toward the coast. Skies remain mostly
clear as of this writing, with the exception of low clouds and
patchy fog being detected across the far northern Idaho Panhandle
and NE Washington valleys. Patchy fog should remain primarily
confined to those areas this morning as the rest of the region
had a chance to dry out on Saturday.

The aforementioned frontal system will move inland through the
course of today into tonight. This system will weaken as it moves
inland: the best chance of showers will be along the Cascades,
along the Canadian border, and along and downstream of the Blue
Mountains. Lower precipitation chances are expected across the
Columbia Basin and into the Spokane area. Marginal instability is
expected with the frontal passage, and a few thunderstorms will be
possible mainly along the Cascade crest and Okanogan Highlands.

The frontal system will pass eastward tonight. With clearing
skies and an injection of low-level moisture in some locations,
more extensive fog coverage will be possible late tonight into
Monday morning across eastern Washington and northern Idaho.

Another shortwave trough will pass through the region on Monday.
High resolution models have trended a bit stronger with this
feature than recent runs, and it wouldn't be surprising if
locations along and north of I-90 see a few light rain showers
with this fast-moving system.
Dang

Monday night through Saturday...the forecast for the next week
can be roughly segmented into two regimes. The first part...Monday
through Wednesday...will be characterized by a swift westerly
flow regime with the polar jet just north of the forecast area
through mid week. Occasional feeds of Pacific moisture will
accompany this flow...but the zonal flow regime will promote a
rain shadow in the basin (albeit with plenty of thick mid and high
clouds at times) while showers will be limited mainly to the
higher terrain of the Cascades...northern mountains and the Idaho
Panhandle. The main weather issue will be periods of breezy and
gusty conditions from the Cascade gaps and through out the
Columbia Basin. Tuesday's high temperatures will probably be near
normal for late September but will begin a gradual cooling every
day there after.

By Wednesday evening a second fetch of moisture will intrude off
the Pacific and concurrently the polar storm track will buckle
southward into the region bringing a better chance of rain to a
wider expanse of the region...not just the mountains but also the
eastern basin with only the deepest western reaches of the basin
still expected to remain dry.

For the later part of the work week and into next weekend the
GFS...European model (ecmwf) and Canadian ensemble mean 500 mb fields are in good
agreement and consistent over previous runs in aggressively
digging an anomalously deep trough into the northwestern US out of
Canada. This creates high confidence...probably a near
certainty...of much cooler than average temperatures leading into
the next weekend with snow levels dropping precipitously. As this
trough descends into the area unsettled conditions will develop in
the unstable and dynamic cusp of this feature with the potential
for widespread mountain snow showers and valley/basin rain showers
from Thursday night through Saturday. In fact...and this is not
certain at this time but possible...any precipitation that occurs
overnight or in the early mornings particularly on Saturday may
manifest itself as snow right down to the floors of the valleys
and the eastern Columbia Basin. This is still pretty far out in
the future to engender high confidence at this time...so the
forecast should be monitored closely over the coming week for the
potential for an early taste of winter by next weekend for much of
the region. /Fugazzi

&&

Aviation...
06z tafs: a shortwave ridge of higher pressure will be
over the region tonight. This will promote clear skies and likely
VFR conditions at the taf sites. The one caveat may be at kcoe
depending how aggressively this sites radiates overnight. There is a
small chance for patchy fog by early Sunday morning. A moist frontal
system will spread clouds over eastern Washington and the Idaho
Panhandle on Sunday. Light rain is expected at keat in the morning
and moving into the Panhandle by Sunday evening. /Svh



&&

Preliminary point temps/pops...
Spokane 72 48 65 47 69 42 / 10 30 10 10 0 0
Coeur D'Alene 73 49 64 46 68 41 / 10 40 10 10 10 0
Pullman 73 45 66 46 68 40 / 20 50 0 10 10 0
Lewiston 79 54 73 54 76 50 / 10 60 0 0 10 0
Colville 73 42 70 39 72 36 / 20 40 20 10 0 0
Sandpoint 71 50 63 44 66 40 / 10 50 20 10 10 0
Kellogg 71 50 62 49 64 43 / 10 60 40 10 20 10
Moses Lake 73 45 72 49 76 43 / 30 20 0 10 0 0
Wenatchee 67 51 69 54 70 50 / 60 10 10 10 10 0
Omak 68 47 68 49 71 45 / 60 20 10 10 0 0

&&

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

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