Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Spokane Washington
225 am PDT Thursday Apr 2 2015
a cool and showery Spring weather pattern will continue through
the week and into the weekend. Nighttime freezing temperatures
will be common over the next 7 days with daytime temperatures in
the 50s. There will be the potential for a wetter system by Sunday
and Monday, which will bring a chance for some snow down as low as
some higher valley locations.
today and tonight: the cold pool of air aloft has moved into
Montana, but the back edge of it will still be over the eastern
portion of the forecast area today. As such, our atmosphere is
still quite unstable. I expect another round of afternoon/evening
showers, similar to Wednesday, but not quite as much coverage.
Best chance will be in the Panhandle mountains, with less in
northeast Washington. Didn't put any mention of thunder in the
forecast, but wouldn't be surprised if there's a clap or two in
the central Panhandle.
Friday: the next in the series of Pacific fronts will move through
the area. This will be a cold front, which will reach the Cascades
by Friday afternoon, fall apart over them, and reform from
northeast Oregon into the Panhandle. Thus the basin and Palouse
won't see much from this front. The pressure gradients and winds
aloft aren't very impressive, so I don't see much Post-frontal
wind with this system. Snow levels will be 3-4000 feet so the
passes should pick up a few inches of snow. Rj
Saturday and Saturday night: Post frontal showers will be possible
Saturday afternoon into Saturday evening. I do not expect these
showers to be widespread and will be more likely over the higher
terrain in the Cascades and mtns of northeast Washington. Best instability
behind the front will be in British Columbia as 500 mb heights look to increase
in response to another approaching shortwave trough of lower
pressure pivoting around the upper level trough in the eastern
Pacific. Chances for showers should be on the decrease through
Saturday night and set up another potential for freezing or near
freezing temperatures across much of the region.
..light to moderate snow possible across northeast Washington
and in the Idaho Panhandle Sunday night into Monday morning...
Sunday through thursday: the next shortwave disturbance to impact
the region is expected to push south to north across the region
Sunday afternoon into Sunday night. By Sunday morning, the closed
upper level low will dig further south offshore at around 130w
45n. A negatively tilted shortwave disturbance will rotate around
this upper level low into or and then push into eastern Washington and the
Idaho Panhandle through Sunday night. The combination of positive vorticity advection and
upper level diffluence is expected to spin up an area of lower
pressure at lower levels from eastern Washington into the southern Idaho
Panhandle that pivots northward into the northeast mtns and the
northern Panhandle. This would be a focus for low level
convergence and an area of enhanced lift. Finally, there will also
be a trough of warm air aloft (trowal) that sets up over this
portion of the region that will contain some additional lift and
deeper layer of moisture. Confidence is growing that a band of
stratiform precip will develop along this aforementioned axis of
enhanced lift out ahead of this next shortwave. The Idaho Panhandle
and extreme eastern portions of Washington will see the best chances for
precip and then gradually lessen further west toward the Cascades.
Precip type is still some matter of question for the valleys.
Temperatures should be at their coolest with the precip moving in
at night. It is looking more likely that valley locations in the
central to northern Panhandle will be cold enough for at least
some wet snow accumulations. Thermal profiles look to be a bit
warmer out into eastern Washington. Models are trending colder and is
looking more likely that the precip type for locations such as
Pullman, Spokane and Deer Park will be as snow. Warmer ground
temperatures should limit snow ratios in the valleys, but there is
the potential for light to moderate accumulations from Sunday
night into Monday morning.
The upper level low in the eastern Pacific will then open up and
push across the region for Tuesday and then begin to exit on
Wednesday. This will result in diurnally driven showers through
the middle portion of next week. Graupel showers and maybe a clap
of thunder will be a possibility for the afternoons. A ridge will
then begin to build across the region on Thursday. This will
result in a decreasing trend for precip. Temperatures will be
below normal through the weekend into next week under the trough.
We should then see a rebound in temperatures late in the work week
as the ridge builds in. /Svh
06z tafs: showers that occurred over eastern Washington and north
Idaho have moistened the air mass more than previously thought.
With clearing skies tonight and looking at latest boundary layer
moisture progs off the GFS and NAM, kpuw looks most favored for
stratus development...followed by kcoe. Ksff will also be prone
due to heavy showers from the early evening and close proximity to
water. Mostly IFR/MVFR stratus is expected although patches of fog
will likely form as well...with 12-17z the main threat window. On
Thursday high pressure will begin nosing into the region and thus
the atmosphere will not be as unstable. However enough instability
will be present for isolated/scattered shower development mainly
over the eastern third of Washington/north Idaho. Jw
Preliminary point temps/pops...
Spokane 52 32 55 32 51 31 / 30 10 20 20 10 10
Coeur D'Alene 51 30 55 30 51 29 / 30 10 20 30 10 10
Pullman 49 31 55 33 50 32 / 20 0 20 30 10 10
Lewiston 54 33 60 36 54 34 / 20 0 20 50 10 20
Colville 55 32 57 31 54 28 / 30 10 30 30 20 10
Sandpoint 52 29 54 30 51 26 / 30 10 30 40 20 10
Kellogg 46 30 51 32 48 28 / 40 20 20 50 20 10
Moses Lake 59 33 60 30 57 31 / 0 0 10 10 0 0
Wenatchee 60 37 59 36 57 36 / 0 10 10 10 10 10
Omak 59 32 58 31 56 30 / 10 10 30 40 10 10
Idaho...freeze warning until 9 am PDT this morning for Lewiston area.
Washington...freeze warning until 9 am PDT this morning for lower Garfield
and Asotin counties-Moses Lake area.