Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service Spokane Washington
451 am PDT Sat Apr 19 2014

Synopsis...
following freezing temperatures this morning for most towns, another
storm system will bring windy conditions this afternoon and night
with some showers mainly for the mountain zones. Easter Sunday
should be mild and mainly dry. After a warm and dry Monday, a cool
and unsettled weather pattern will return Tuesday and linger
through much of the week.



&&

Discussion...
today through Sunday night: satellite imagery shows the next
weather system approaching the region early this morning. A low
pressure circulation is at approximately 140w/50n with an
occluded front at around 130w heading toward the West Coast. The
moisture source with this front can be located on water vapor
satellite imagery by the band of elevated moisture content from
160w/30n stretching to northern California. This moisture tap is
shearing out and, as a result, will be a limiting factor for
precip across the region as the front pushes through this
afternoon. The front itself does have good structure to it and
forcing aloft will be decent. Good cold air advection is expected
as well. This will lead to a fairly tight pressure gradient
developing behind the front. Winds will once again pick up this
afternoon and the timing of the front will promote good mixing
during as it will move through during the afternoon. 850 mb winds
are only progged at around 30-35 kts. These magnitudes will be
sufficient for solidly breezy to windy conditions, but advisory
level winds are not expected. Expect sustained wind speeds of
around 20-25 mph with gusts to around 35-40 mp. Strongest wind
speeds will likely be on the Palouse and in the northeast blue
mtns. These locations could see higher winds closer to 25 mph
sustained with gusts to around 45 mph. A lack of moisture with the
front will result in light precip and much of the lower elevations
may only see some sprinkles, especially in the basin. Best chances
for measurable precip will be in the mountains and in the Idaho
Panhandle. The region will dry out on Easter Sunday as we will be
between systems. Temperatures over the weekend will be near
average for mid April. /Svh

Mon through Wed: there are a number of challenges in this three-
day period...leading to a lower than normal confidence level. Even
with only one well-defined cold front and its accompanying upper
trough passage, timing remains uncertain given the north-south
shearing of the trough as it moves into the pac NW. Model guidance
typically brings this type of trough onshore too fast three days
out, so we still favor a slightly slower progression of the wave.
That said, we lowered pcpn amnts into Mon evening with the initial
frontal boundary. One of the biggest uncertainties concerns
thunder chances Mon nt, mainly from elevated, non sfc- based
instability above 700mb tied to a plume of moisture surging north
ahead of the trough. A number of models show a narrow, but heavy
band of pcpn tues morning close to this elevated instability and
mid-level front. We continued with a broad-brush approach to this
pcpn threat and did not add thunder attm. With the upper trough
directly over the pac NW tues through Wed morning, not only will
the pcpn be highly convective, but snow levels will fall
markedly, leading to a significant snow and/or graupel
accumulation threat. This will especially true for the Idaho
Panhandle Wed morning under a developing trowal and Post-frontal
upslope. It's likely that valley locations will see some snow with
this scenario. Gusty Post-frontal winds will also be likely. Well
below normal temps Wed looks certain for the Idaho Panhandle. Bz

Wednesday night through saturday: parts of the inland northwest
will be dealing with the departing trough Wednesday night/Thursday
morning before brief ridging allows for slight lull in the
precipitation. Any remaining precipitation Wednesday night over
northeast Washington into the northern Idaho Panhandle will still
have somewhat colder air to deal with, meaning snow at least in
the mountains, and possibly into the higher valleys. Amounts
during this period look like they'd be on the low side, so impacts
would be minimal.

Ridging shouldn't last as the next large scale trough approaches
the Pacific northwest to close out the work week. This will bring
more chances for precipitation most areas into the weekend.

Temperatures will remain on the cool side of normal each
afternoon, especially with the cloud cover that may never really
clear out. The best chance, as of now, for more sunshine would be
Thursday over the Columbia Basin. However, breezy conditions may
result due to stronger winds aloft mixing to the surface. All-in-
all, lots to look at for the far extended periods. Could be quite
active. TY



&&

Aviation...
12z tafs: a cold front is beginning to push into western Washington this
morning. This front is expected to cross east of the Cascade mtns
after 20z this afternoon and then quickly spread across eastern
Washington and into the Idaho Panhandle. This front will generate mainly mid
level cloud cover over the taf sites with some sprinkles possible,
but will be dry for the most part. The main impact will be winds
shifting from the east and northeast to out of the west and
becoming gusty at the same time. Expect wind gusts up around 30-35
mph with gusts peaking in the late afternoon and evening hours.
/Svh



&&

Preliminary point temps/pops...
Spokane 60 37 57 40 67 45 / 10 20 0 0 10 50
Coeur D'Alene 61 37 57 38 67 45 / 10 40 10 0 10 50
Pullman 62 36 57 40 68 45 / 10 20 0 0 10 50
Lewiston 69 41 63 43 74 50 / 10 10 0 0 10 50
Colville 64 36 65 36 70 41 / 10 20 10 0 10 50
Sandpoint 60 38 57 35 64 43 / 10 50 10 0 10 30
Kellogg 60 37 55 36 66 40 / 10 50 10 0 10 30
Moses Lake 66 40 66 43 72 46 / 10 10 0 0 10 50
Wenatchee 62 41 66 46 68 48 / 10 10 10 0 10 50
Omak 63 35 66 39 67 43 / 10 10 10 0 10 50

&&

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

$$