Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service Spokane Washington
256 am PDT Thursday Apr 17 2014

Synopsis...
a strong and wet Pacific weather system will result in widespread
rain Thursday and Thursday night, with windy conditions late
tonight into Friday. A weaker front will bring mainly windy
conditions Saturday afternoon and night. Easter Sunday should be
mild and mainly dry. Showers will be more prevalent for the first
part of next week.

&&

Discussion...

..a strong weather system featuring moderate rainfall today and
gusty winds late tonight into Friday...

Today through friday: satellite imagery shows a very dynamic low
pressure system pushing into western Washington at around 2:30 am. The
cold front with this system is beginning to cross 130w with well
defined darkening behind the front noticeable on the water vapor
imagery. Strong isentropic ascent will develop ahead of the front
across eastern Washington and into the Idaho Panhandle. All areas will see a
good chance for some rain this morning into the afternoon.
Heaviest accumulations will likely be across the eastern two-
thirds of the forecast area as we will see some downsloping taking
place along the Lee side of the Cascades. Strong frontal forcing
is expected to result in a period of moderate to heavy rainfall
along the cold front late this afternoon into this evening. Mid
level laps rates will steepen to 7-9 c/km between 700-500 mbs.
This destabilization will result in roughly 200 j/kg of cape with
cloud tops potentially topping out above 20 kft. The instability
is decent, but I would like to see a bit more to have higher
confidence for thunderstorms. Nevertheless, the dynamics will be
quite strong with this system and could be enough to overcome the
instability deficiencies. Best chances for thunderstorms will be
right along and behind the cold front. This will mainly be for the
late afternoon and evening hours for the western portion of the
forecast area and shifting eastward overnight as the upper level
shortwave trough moves into the region.

Gusty winds can be anticipate with the front overnight. 850 mb
winds will be up around 30-40 kts. There shouldn't be a problem
mixing down these stronger winds with how strong the front will be and
advisory level strength will be possible; however, confidence at
this time is too low for a highlight. Any thunderstorms that do
develop will also be capable of producing even stronger gusts.
Most areas are expected to see sustained winds of 20-30 mph with
gusts up to 40 mph possible for late tonight and continuing into
Friday morning. Winds will remain breezy into Friday afternoon,
but strongest winds will likely occur with and directly behind the
front.

A cold and rainy Spring day is expected today with highs only
getting into the 50s, and some areas may not warm above the 50
degree mark especially in the Panhandle. Temperatures will remain
below normal on Friday, but should be warmer compared to today
with a good chance for sun as much drier air filters in behind
this system. /Svh

Friday night through monday: in the wake of the Thursday/Friday
rain, skies will clear Friday night and winds will subside,
allowing for fog formation in the usual valley locations. There's
a decent amount of dry air that moves in behind the cold front
though, so the fog and low clouds shouldn't be very extensive.
Otherwise Saturday looks to be a warm and sunny day. But this is
short-lived as the next Pacific system will reach the Cascade
crest by the late afternoon. This front is entirely different
beast than our Thursday/Friday system. Instead, moisture is
largely confined in the mid-layers of the atmosphere. This favors
just light precipitation over the mountains and nothing over the
basin.

The more noteworthy part of this system will be the winds. The
cold front will pass through the area Saturday afternoon/evening
bringing gusty winds to the area. At this point I went with gusts
to 30 or 35 mph. We'll need to keep an eye on this forecast as
the winds could be a bit stronger than this.

Easter Sunday looks mostly dry with more sun than clouds. The
exception will be over the Cascades, the northeast mountains, and
the northern Panhandle, where a few showers may develop.

Monday will see yet another weak Pacific front. Similar to its
predecessor, the majority of the moisture will be in the mid and
upper atmosphere. So again, mountains will be favored with little
or nothing in the lower elevations, especially in the basin. Rj

Tuesday through thursday: a more unsettled weather pattern will
overspread the inland northwest for the early/middle portion of
next week. A large scale trough, which is fairly well agreed upon
by the extended models, will begin to move inland by Tuesday, with
another round of precipitation affecting much of the region. How
much is still a little more in question, but the potential exists
for this trough to briefly tap into a better moisture tap in
southwest flow, which could give some heavier rainfall amounts to mainly
eastern Washington and the Idaho Panhandle Tuesday and/or Tuesday
night. Afterwards, the better chances for precipitation would move
to the east. While the more organized precipitation would be east
of the region by Wednesday, the cold pool aloft associated with
the larger trough will still be overhead. This would promote more
scattered afternoon showers during the afternoon hours, with a
drying trend going into Thursday.

With regards to temperatures, readings look to remain on the cool
side with precipitation Tuesday (3 to 5 degrees below normal),
with maybe a slight warming trend Wednesday and Thursday. TY

&&

Aviation... 06z tafs: a wave pressing along the Cascades is
pushing moisture over and increasing cloud Clover for the
taf sites. This moisture is mainly upper level and not creating
any issues or precip for the sites. Cigs in these areas are
hovering around MVFR and will continue to as another more moist
system moves into the region around 18z and bringing rain showers
to the inland northwest. The region can expect to be under the
influence of rain showers through the period. /Jdc



&&

Preliminary point temps/pops...
Spokane 51 38 56 33 63 37 / 100 100 30 0 0 20
Coeur D'Alene 50 38 55 32 63 39 / 100 100 50 10 0 30
Pullman 54 38 53 33 66 38 / 60 100 20 0 0 20
Lewiston 60 43 59 36 72 43 / 30 100 10 0 0 20
Colville 54 36 61 31 68 34 / 100 100 40 10 10 20
Sandpoint 49 38 54 31 62 36 / 100 100 60 20 0 30
Kellogg 50 37 52 32 62 38 / 90 100 60 10 0 50
Moses Lake 58 39 64 35 69 39 / 90 50 10 0 10 10
Wenatchee 60 40 62 41 66 43 / 80 40 0 0 10 10
Omak 56 36 62 33 67 34 / 80 70 10 10 10 20

&&

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

$$