spokane wa: fxus66 kotx 100033 cca

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fxus66 kotx 100033 cca
afdotx
area forecast discussion...corrected
national weather service spokane wa
434 pm pst tue feb 9 2010
.synopsis...weak high pressure over the northwest will maintain
dry but variably cloudy conditions tonight through wednesday
morning. a storm system will spread a chance of valley rain and
snow mix and mountain snow over the region wednesday afternoon and
wednesday night. a series of storm systems will have the potential
to bring mountain snow and valley rain to the northwest through
early next week.

.discussion...
tonight and wednesday...satellite reveals the forecast area is
under a weak ridge in a split flow regime...with a deeply wrapped
storm system moving into california and a weaker polar storm track
over british columbia. the next pacific storm system is visible
off the coast and will overrun the region tomorrow afternoon and
evening. gfs and nam models are similar in depicting a weak ridge
holding over the region tonight...with a continuation of variably
cloudy conditions and no precipitation threat outside of a slight
flurry threat over the mountains near the canadian border. a high
stratus deck has persisted under the ridge subsidence inversion
over much of the region through the day today...and fields of this
high stratus will likely persist through tonight with nothing to
knock loose the sub-inversion air mass. thus tonight will be at
least partly to mostly cloudy...dry and feature overnight lows
slightly above normal given reduced opportunity for radiational
cooling presented by the cloud cover.
on wednesday the frontal system off the coast will spread
thickening clouds and increasing chances of valley rain and
mountain snow from west to east during the day...with most
locations north of interstate 90 suffering at least a slight
chance of precipitation by late afternoon...with the best chance
over the western and northern zones. /fugazzi
wednesday night through friday...a mild...unsettled pattern is
in store for the pac nw as the longwave pattern undergoes a few
changes including shifting the longwave ridge axis
inland...allowing the gulf of alaska low to reclaim residence
closer to the coast...and re-establishing a dominate mid level
southwesterly flow across the region. this will allow a deep fetch
of moisture to stream toward the region with a series of weak to
moderate frontal systems tracking through every 8 to 15 hours
bringing periods of precipitation. in general...the mild sw flow
will continue to support mainly valley rain and mtn snow.
amsu satellite shows a deep fetch of moisture with pwat well
over one inch stemming from the subtropics northeastward toward
50n 140w wrapping into a deep low pressure system which is being
driven eastward under a 175kt jet along 40n. model initialization
is plausible but it appears the 12z gfs is a bit quick and dry
with this feature so will trend toward the slower ecmwf in regards
to timing of individual shortwave energy throughout the period.
this matches well with the nam. as the pattern shifts eastward
over the next 36 hours...the moist tongue will nose into the pac
nw with pwats across eastern wa increasing from near 0.30"
currently to 0.50"- 0.75". there are two main shortwaves we will
be focusing our attention on...one coming through wednesday night
into thursday...the second on friday. in btwn...sw flow will
persist...keeping the chance for orographic shwrs ongoing
throughout mtns. the first wave will be ride along the northern
periphery of a flat ridge in place and take a track along the
us/canadian border with the best q-vector convergence focusing
along southern british columbia. in the wake of wave one
(thursday)...we will see the gulf of alaska closing in on the
coast and this will allow ridging to briefly re- amplify
downstream over the pac nw. however this ridge axis will quickly
shift inland thursday nt and friday as the next shortwave ejects
across the pac nw. i have to believe this wave will weaken and
slow down while running into the ridge...taking somewhat of a
negative tilt. therefore...as mentioned abv...will follow closer
to the ecmwf/nam which portrays a stronger stretching and slower
passage opposed to the gfs.
all things considered...first round of light pcpn to come
across the region wednesday nt with another thursday into friday.
we do expect some drying btwn systems...roughly thursday morning.
the strongest drying shows up within the 700-300mb layer with the
sfc-850mb layer remaining saturated with 85h flow persisting out
of the sw. with the drying throughout the -10 to -20 celsius
layer...and bl remaining saturated...i anticipate pcpn will change
over to drizzle; especially for much of northern idaho and ne wa
including upper columbia basin...before the next frontal system
arrives thursday afternoon. another dry-slot should work west to
east friday aftn bringing another short-lived break in the weather
before a third system friday nt. the exact timing is subject to
change some regarding the heavier pcpn chances so will leave at
least chc pops in place and fine tune things as each wave becomes
a bit more evident over the next 24 hrs.
the coolest temperatures of the period will likely be wednesday nt
where some clearing and wet bulb cooling is expected prior to the
arrival of the first pcpn bands. thereafter...a steady s/sw flow
regime will keep temperatures above normal. snow levels will
generally reside near 3000' north to 5000' south. /sb
friday night through tuesday...an upper low in the gulf of alaska
will send a series of systems into the area through early next
week. the prevailing flow aloft will be out of the southwest which
will keep snow levels high enough to support rain in the valleys
and snow in the mountains. timing of systems supports the highest
pops friday night and again on sunday...with near climo pops for
the other forecast periods. temperatures will remain above normal
through the extended period. jw

.aviation...
vfr conditions are expected to predominate through wed afternoon.
local mvfr cigs to below 3000 ft agl will be possible this
morning with low confidence that this will occur at any taf site.
patchy fog is not out of the question as well this morning as
winds are expected to remain light...but low confidence in this
scenario as the stratus deck will limit radiational cooling
overnight. the next pacific weather system will move into the
region sometime btwn 21-00z wed afternoon with -ra at keat and
kmwh and upslope flow producing vcsh near spokane/coeur d'alene.
/svh

.preliminary point temps/pops...
spokane 31 42 32 42 36 43 / 10 20 50 60 70 30
coeur d'alene 31 41 31 41 34 43 / 10 20 50 60 70 60
pullman 32 45 33 46 37 46 / 10 10 60 60 50 40
lewiston 34 51 37 49 40 51 / 0 0 50 40 30 20
colville 30 40 31 40 34 43 / 10 50 40 60 70 60
sandpoint 30 39 30 39 34 41 / 10 40 50 60 70 60
kellogg 30 39 31 39 34 42 / 10 20 70 50 70 60
moses lake 32 45 34 43 37 48 / 0 30 20 50 50 20
wenatchee 31 40 31 40 35 46 / 0 40 20 50 50 20
omak 30 39 31 39 33 44 / 0 40 20 50 70 20

.otx watches/warnings/advisories...
id...none.
wa...none.

Top tags: wednesday, flow, friday, next, region, snow, system, ridge, afternoon, thursday