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Area forecast discussion 
National Weather Service Spokane Washington
353 PM PST Friday Nov 27 2015


Chilly temperatures and clear skies are expected through at least
Friday as strong high pressure builds over the Pacific northwest.
Light winds and a strengthening inversion will increase the
potential for air stagnation this weekend. We will also have the
potential for areas of fog and low clouds over the weekend into
early next week. The next chance of precipitation is expected next
Wednesday with the arrival of a frontal system.


tonight through tues: the biggest challenge will be determining
the areal coverage of stratus (low clouds) fog the next few
nights. We simply tried to re-introduce low clouds in the areas
that had coverage this morning... but modified it to increase
coverage. The most persistent stratus should be along the highways
2 and 95 corridor in boundary and Bonner counties Idaho. The are a
couple models producing light amnts of pcpn mainly Sat nt and
sun nt across the cntrl part of the Columbia Basin. The NAM fcst
soundings also show a sufficiently deep saturated sfc lyr (with a
dry dendritic layer aloft) to produce snow grains for the above-
mentioned nights. We did not put any pcpn in the fcst attm.
However, we did put some snow in the fcst for tues along the east.
Slopes of the Cascades as backing S/southeast flow helps to increase
isentropic ascent over a pool of cold air dammed against the
Cascades. The beginning of this pcpn event may also be the
beginning of an increase in air quality across the region. Bz

Tuesday night through Friday...this interval is supposed to mark
the slow eastward movement away of the Omega block which has kept
the past several days on the dry and stagnant side. Most models
begin Tuesday night with a substantial moisture plume running more
south to north than southwest to northeast which is burrowing into
the west side of the ridge weakens and its axis tilts to the
northeast and over Montana. With the poor mixing and stagnant
conditions preceding the passage of the moisture plume it is
highly likely this moisture plume will have enough cold air at low
levels to overrun and produce snow, without a snow-shadow on the
Lee side of the crest, mostly on Wednesday. The more favored European model (ecmwf)
digs an inflection point into the moisture feed off the California
coast and this stalls the moisture feed in position and allows for
moisture to continue to stream into the not only on Wednesday but
through Thursday as well, finally moving the feed to the east
Friday morning and allowing a cold conditionally unstable air-mass
void of substantial shortwaves passing through it to take its
place over the forecast area Friday. GFS solution moisture plume
placement and passages differs with the European model (ecmwf) with it allowing for
a drier Thursday then passes the moisture plume through late
Thursday night and allows for the cold conditionally unstable air-
mass to move into place Friday...but there appear to be more
smaller scale disturbances moving through and near that cold air-
mass producing more snow showers. Compromise between these
solutions is to keep the moderate pops for Wednesday through
Thursday night that show a decrease for the showers Friday. This
winter precipitation should help clean out the low levels of the
atmosphere some and allow for some improvement in air quality but
the winds don't shift and increase to a more favorable southwest
wind until Thursday night into Friday which means the air is
likely to stagnate until this wind increase Thursday night/Friday.


00z tafs: we're expecting a near repeat of what we had this
morning for fog and/or stratus tonight...but with greater areal
coverage. Fog will be potentially LIFR at times...and stratus
likely IFR/MVFR. The main taf sites that will encounter these
reductions in ceilings and vsbys will be klws...kmwh...and kcoe.
Fog should dissipate by midday giving way to sunny skies.


Preliminary point temps/pops...
Spokane 17 31 19 30 17 30 / 0 0 0 0 0 10
Coeur D'Alene 17 32 21 31 19 31 / 0 0 0 0 0 10
Pullman 18 32 20 33 21 33 / 0 0 0 0 0 10
Lewiston 21 33 22 33 24 36 / 0 0 0 0 0 10
Colville 17 35 19 34 19 34 / 0 0 0 0 0 10
Sandpoint 16 32 17 30 22 33 / 0 0 0 0 0 10
Kellogg 16 35 17 34 22 33 / 0 0 0 0 0 10
Moses Lake 15 33 21 31 19 32 / 0 0 0 0 0 10
Wenatchee 21 33 23 31 21 33 / 0 0 0 0 0 10
Omak 18 35 22 33 21 32 / 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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