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Area forecast discussion 
National Weather Service Spokane Washington
454 am PDT Sat Aug 23 2014

Synopsis...
a few showers will form over the mountains today...but the weather
will not be as active as the last few days. Another disturbance
will bring a better chance of showers and thunderstorms on Sunday.
A drier and warmer weather pattern is expected for the new work
week with the next storm system arriving next weekend.

&&

Discussion...

Slow moving thunderstorms capable of heavy rain possible Sunday
afternoon near the Cascade burn scars

Saturday: the low pressure system responsible for the unsettled
weather over the last few days ejects into the northern plains
and much quieter weather will settle into the region today. As of
2am...the low was centered over McCall, Idaho and is modeled to cross
the Montana/ND border by this afternoon. Moisture wrapping around the
backside of the low will bring some light showers to portions of
southeast Washington and the Idaho Panhandle mainly south of a line from Lookout
Pass to the blue mtns. This activity will mainly be in the form of
light showers with little to no threat for thunder and heavy rain.
Afternoon cumulus buildups are expected across the mountains
surrounding the Basin. A few of these will be capable of putting
down a brief shower with rainfall amounts ranging between a trace
and few hundredths but the instability is rather shallow in
response to 2 celsius 500mb warming. Afternoon highs will be a few
degrees warmer but still on the cool side of normal. Gusty winds
will occur in the morning and early afternoon...focusing down the
Purcell Trench. Locations like Sandpoint and Coeur D Alene will
experience winds 10 to 20 mph gusting to 25 mph through 11am then
see winds decrease near 10 mph for the remainder of the afternoon.
The remainder of the region will experience winds generally 10 mph
or less.

Saturday night and sunday: the next upper-level low, currently
passing through the Gulf of AK, will drop into the region. This
low looks to take a similar track to the previous low but the main
differences look to be weaker synoptic forcing and less
atmospheric instability in place ahead of it. Remember
temperatures were in the 80's and 90's ahead of the last storm
system but conditions will be unseasonably cool Saturday.
Atmospheric moisture is generally on par with the last system. The
upper-level front crosses through the Cascades around midnight
then into Idaho by 5am. Tapping into a decent Reservoir of
moisture over the Pacific, models do suggest a cluster of showers
developing over Okanogan County... possibly expanding into
Ferry/Stevens/Chelan/Douglas between 2am - 11 am. The hi-res model
simulated reflectivity shows some cores to 40 dbz but fcst
sounding only indicate mu cape extending to -15c until Sunday
afternoon. This does not favor lightning or heavy rains for the
morning hours. By Sunday afternoon, conditions will change as the
surface heats up and surface based cape increases between 500-1000
j/kg. Once again, the 500mb cold pool will be directly overhead
and steering flow will be less than 10 mph. Unfortunately,
conditions will become favorable for slow moving thunderstorms
capable of heavy rainfall. Just about every location is
susceptible to isolated showers or storms given the pattern but
once again, the mountains north and west of the basin will carry
the highest probabilities. /Sb



Sunday night through Thursday...a warming and drying trend is
depicted by the medium range models during this period. Model
continuity over previous runs and agreement between the GFS and
latest European model (ecmwf) is good leading to growing confidence that the
recent stretch of below normal and unsettled conditions will come
to an end with another stretch of Summer weather first perceptible
on Monday but more noticeable on Tuesday and through much of the
upcoming work week. A strengthening ridge aloft will replace the
mean trough starting Monday...with some residual showers over the
Idaho Panhandle. After Monday the ridge becomes dominant with a
new surface thermal trough becoming established over the basin.
Thus a dry forecast from Tuesday through Thursday is eminently
plausible with a warm up to well above normal temperatures as the
week wears on. /Fugazzi

Thursday night through saturday: models start out in general
agreement with an exiting ridge to the east and an approaching
low sliding down the British Columbia coastline. This allows for southwesterly
flow ahead of the system promoting continued above normal temps
for Friday. Where models start to diverge is how the trough
passes with the GFS being much more aggressive in passing the low
directly through the pac northwest as a closed upper low. The Euro was in
agreement with this scenario until the 00z run where it backed off
passing it as an open wave with most impacts to our north. The
verifying model will have major ramifications as to the sensible
weather for Labor Day weekend with the GFS providing a cool and
wet pattern whereas the Euro would be more mild and drier.
Moisture will likely not be a deciding factor as both extended
models show the convergence of mid latitude Pacific moisture with
remnant moisture from decaying Tropical Storm Lowell currently off
the western Baja Coast. What this means is at least increased
cloud cover next weekend.

For this forecast the pops were increased some due to ME favoring
the GFS model mainly based on recent run to run consistency.
Temperatures were also cooled in the far extended as the passing
system should allow cooler Pacific air to infiltrate into our
area. Finally winds will be on the increase as cold air advection
coupled with a tightened pressure gradient allows for breezy to
windy conditions. Ridgetops will likely see the brunt of the
winds with The Lowlands not quite as windy. /Fliehman

&&

Aviation...
12z tafs: area of low pressure continues slowly exit to the
southeast away from the aviation area during the next 12 hours.
Some lingering moisture and a few light showers will skirt
southeastern Washington and the Idaho Panhandle but any pcpn will be light.
The next disturbance drops into central Washington from the northwest overnight.
Look for incr clouds and developing showers mainly north of keat-
kmwh btwn 10-12z. Gusty NE winds channeling through kcoe will decr
near 10 mph or less after 18z. /Sb



&&

Preliminary point temps/pops...
Spokane 77 53 77 56 80 56 / 10 0 40 40 10 10
Coeur D'Alene 73 52 76 53 79 53 / 10 10 40 40 20 20
Pullman 75 48 77 51 81 48 / 10 10 40 40 20 10
Lewiston 80 56 83 59 86 56 / 20 10 20 30 10 10
Colville 79 52 78 52 83 50 / 10 10 60 60 10 10
Sandpoint 70 49 72 49 76 46 / 20 10 50 50 20 20
Kellogg 67 47 72 53 75 56 / 20 10 50 50 30 30
Moses Lake 84 54 83 56 87 56 / 0 0 20 20 0 0
Wenatchee 83 60 81 61 86 62 / 0 10 30 20 10 0
Omak 82 58 80 55 87 55 / 0 10 40 30 10 0

&&

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

$$

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