Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Spokane Washington
450 PM PDT Sat Oct 22 2016
drier weather is expected through Sunday. The main exception will
be near the Cascades. A weak system may bring a little rain here
late tonight and early Sunday. Rain and High Mountain snow
chances return Monday and especially Monday night. The next wet
system arrives Wednesday, with the potential for moderate to
locally heavy rainfall across the east slopes of the northern
Cascades. Additional opportunities for precipitation continue into
the end of next week, but it does not appear to be a wash out.
tonight and sunday: a widespread lower cloud deck will continue
to hang around this evening with light boundary layer winds not
able to sufficiently scour resident moisture over the region.
Isolated showers will be possible near the Canadian border near
Ione and Porthill but end by sunset. A weather pattern shift will
put a Dent in the low cloud cover this evening and overnight but
shift and form clouds in other places.
Easterly surface winds will increase tonight ahead of a Pacific
trough becoming parked off the West Coast. This will down slope
off the bitteroot mountains and sufficiently dry parts of the Idaho
Panhandle and eastern Washington to prevent fog formation tonight.
However, the northeast Washington valleys where the drying winds won't
quite reach may see some patchy valley fog tonight. While the low
clouds get mixed out in many areas higher clouds will fill in the
sky tonight ahead of the cold front approaching the West Coast.
This front will increase chances of precipitation over the
Cascades with only light precipitation expected going into Sunday
morning. Even a few sprinkles could fall as far east as Wenatchee,
Omak and the Okanogan Highlands Sunday morning. The front stalls
and weakens on the west side of the Cascades with minimal
additional showers possible on the Cascade crest Sunday afternoon.
The remaining areas east toward the Idaho Panhandle will be mainly
dry with broken to overcast cloud cover Sunday with temperatures
warmer by 2 to 5 degrees. Tc
Sunday night through tuesday: low pressure off of Vancouver Island
and the Washington coast will send across an occluded front Monday night
into Tuesday morning. There will be increasing mid to high level
clouds on Monday with sprinkles possible at times; however, much
of the precipitation is expected to arrive with the front itself.
Although most areas will see the possibility for a light amount of
measurable precipitation Monday night, best chances will be
reserved over the northern mountains where orographics will result
in some additional enhancement. The mountains from the Cascades
over the northern Panhandle will see up to around a quarter of an
inch of precipitation. Much of the basin will see up to around a
tenth of an inch of precipitaiton with the central Panhandle mtns
receiving up to two tenths of an inch or so.
..wet and mild storm system on Wednesday...
Tuesday night through thursday: the storm system that arrives on
Wednesday will be much wetter, at least for the northern and
western portion of the forecast area. The shortwave disturbance
will pack more dynamics and tap into a sub-tropical moisture plume
with an inch plus p-wat plume. The surface low will track offshore
with easterly flow across the region. The combination of strong
isentropic ascent and good upslope flow will focus precipitation
across the Cascade mtns. Temperatures will remain mild with snow
levels climbing above 7,000 feet.
* Rainfall amounts: the Cascade mtns will see between an inch and
an inch and a half. Rainfall amounts will decrease further east,
but still expecting a wet day for the Wenatchee area and
Okanogan Valley. These areas will see between a half an inch and
three-quarters of an inch of rainfall. Downsloping winds off of
the higher terrain in the Panhandle will limit rainfall amounts
to under a quarter of an inch this far east.
* Impacts: much of the region has already seen a very wet October
to date. We will have had a pretty good break since our last
good soaker, so it is difficult to say what another inch plus of
rain will do across the Cascades. Since soils are on the wetter
side, we will see an increased risk for minor mud flows and
debris slides. Highest risk areas will be in and around recent
burn scars. Low lying areas may see some minor flooding as well,
especially if any culverts become plugged up with debris. /Svh
Friday through sunday: this period is expected to be continue the
wet October for the inland northwest. The models are showing a
widespread precip event as a low positioned off the California coast
pushes moisture into the region. Models do not have good agreement
on the timing of this push. The window for precip will be around
the Friday afternoon to evening. With this being a southern push,
this event is expected to be mainly rain with a very limited
amount of snow for the extreme elevations of the Cascades. A brief
break is from the rain is expected for Saturday afternoon before
the models begin to bring in another wave of moisture for Sunday
afternoon to evening. Again the timing of this wave is not in good
agreement. Temperatures will be in the range of upper 40s to 50s
for highs and upper 30s to mid 40s for lows. /Jdc
00z tafs: weak high pressure shifts toward toward western Montana and
a developing southwest flow will allow shortwave disturbances to
enter. Expect increasing middle to high clouds. A threat of
showers comes to the Cascades later tonight into Sunday morning.
The main area that may be impacted will be eat as some moisture
banked up near the Cascades. MVFR conditions are possible but
confidence is low. Elsewhere some guidance suggest lower level
moisture creeping up through the Columbia Basin early Sunday.
This may lead to some MVFR stratus near puw/geg/sff 12z-19z.
Confidence in actual impacts is similarly low but it will be
monitored. /J. Cote'
Preliminary point temps/pops...
Spokane 39 54 45 58 45 53 / 0 10 10 20 90 30
Coeur D'Alene 40 56 44 58 45 52 / 0 10 10 20 80 40
Pullman 42 58 46 62 46 54 / 0 10 10 10 80 40
Lewiston 45 61 48 65 49 59 / 0 10 10 10 40 30
Colville 36 54 41 56 43 52 / 0 10 10 20 90 30
Sandpoint 35 52 40 55 42 48 / 10 10 10 20 80 40
Kellogg 39 56 42 57 44 49 / 0 10 10 20 80 80
Moses Lake 41 58 43 58 42 58 / 0 10 10 20 60 10
Wenatchee 44 55 43 55 43 57 / 10 10 10 40 80 10
Omak 41 55 42 55 43 55 / 10 20 10 40 90 20