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Area forecast discussion 
National Weather Service Spokane Washington
435 am PDT Wednesday Apr 1 2015

Synopsis...
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.

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Discussion...
today and tonight: a trough of cold air is squarely over the pac
northwest today. This creates a very unstable atmosphere with steep lapse
rates. Surface afternoon heating is all we'll need to realize this
instability into showers. The limiting factor will be moisture;
there's not a lot of it. Surface dew points are generally in the
20s. Showers will develop by midday and gradually die off after
sunset. The northeast mountains and the central Panhandle will be
favored in this pattern, with the lowest chance of showers in the
Columbia Basin. The northwest flow means that showers that develop
over the selkirks could move into the Spokane/cda Metro area in
the late afternoon.

The cold dry air means that some of the precipitation could be in
the form of snow or graupel. This also isn't good for the
thunderstorm potential, as lifted condensation levels (lcls) will
have temperatures of -5c or colder, which is often too cold for
much lightning.

Freezing temperatures are expected in many areas tonight. Much of
our area still hasn't started its growing season. But the Moses
Lake area has, so a freeze warning will be issued for there.
Lewiston and Wenatchee will likely be in the mid 30s tonight.

Thursday and Thursday night: the cold air aloft moves to the east
into Montana. As such, the atmosphere in the inland northwest will
stablize somewhat. So shower activity should be less on Thursday.
The favored location for showers will be in the Panhandle
mountains. Rj

Friday through Saturday night: a cold upper level low pressure
system will dig off of the West Coast. Models are in good
agreement that a shortwave swinging around this upper level low
will push across a cold front around the Friday afternoon into
Friday night time frame. The upper level dynamics with this system
looks to weaken as it pushes further inland away from its parent
upper low. This should translate into more of a weak to moderately
strong cold front passage. Best forcing would be across the
northern portion of the forecast area where precip chances will be
highest. Precip type is expected to be in the form of valley rain
and mountain snow showers. Snow levels will drop behind the front
with diurnally driven rain/graupel showers possible for the
afternoon on Saturday.

..valley snow possible in the Panhandle Sunday night...

Sunday through wednesday: the cold upper level trough of low
pressure in the eastern Pacific will dig further down the coast
through the weekend. A second shortwave disturbance will rotate
around the upper trough and push across or, the Idaho Panhandle and
into western Montana. There is general agreement amongst the mid range
model guidance that this piece of energy will maintain its
strength as it moves inland. The second piece of energy will be
working with stronger jet dynamics that will help to fuel
cyclogenesis at lower levels in the atmosphere. The track of the
surface low and its intensity is still a matter of great
uncertainty at this time. The European model (ecmwf) and Canadian solutions show
more of a westerly track to the surface low across the Idaho
Panhandle. This would lend to a better chance for drawing down
colder air from the north with a deformation band developing
across western Montana and across the Idaho Panhandle. If this solution
verifies, then there is a chance for snow down to valley floors.
A couple of inches of snow or more in the valleys would not be out
of the question; however, there is too much uncertainty amongst
the model guidance to put much confidence in this scenario, but it
will be a situation Worth monitoring as the weekend approaches.

The upper level low in the eastern Pacific is progged to open up
and push into the western U.S. For early next week with the
weather over the inland northwest remaining unsettled. Showers
are more likely to be diurnal in nature. Temperatures are
expected to be below normal through the weekend into early next
week. /Svh

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Aviation...
12z tafs: numerous showers and a few thunderstorms will form over
the mountains this afternoon. A few showers will also form over
the basin. These showers will be brief and will contain light rain
or graupel and possible gusty winds. This shower activity will die
off quickly after sunset. Rj



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Preliminary point temps/pops...
Spokane 50 30 53 33 54 29 / 50 30 10 10 10 30
Coeur D'Alene 49 28 52 30 54 27 / 70 40 30 20 20 40
Pullman 48 31 49 33 54 33 / 50 30 20 10 10 30
Lewiston 53 33 54 33 59 34 / 40 20 20 10 10 40
Colville 53 30 57 32 55 28 / 60 30 20 10 20 40
Sandpoint 50 28 52 28 52 28 / 70 40 30 30 20 50
Kellogg 44 29 47 31 50 30 / 70 60 30 40 20 40
Moses Lake 58 30 59 33 59 31 / 20 0 0 0 10 20
Wenatchee 58 37 60 38 58 33 / 20 0 0 10 20 40
Omak 57 32 60 33 58 28 / 40 10 10 10 30 40

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Otx watches/warnings/advisories...
Idaho...none.
Washington...freeze warning from 3 am to 9 am PDT Thursday for Moses Lake
area.

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