Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service Spokane Washington
434 PM PDT Thursday Apr 17 2014

Synopsis...
a strong and wet Pacific weather system will result in widespread
rain tonight, with windy conditions late tonight into Friday. A
weaker front will bring mainly windy conditions Saturday afternoon
and night with some showers across the north. Easter Sunday
should be mild and mainly dry. Active and occasionally showery
conditions will continue through the new work week.

&&

Discussion...
tonight and Friday...the forecast area is under the influence of a
moist Pacific feed which is enhancing into rain over much of the
area compliments of a warm front stretching west to east across
eastern Washington. This will continue through much of the
evening...culminating in a round of heavier showers along and
immediately behind a cold occlusion which is clearly visible on
satellite approaching the coast this afternoon. This front will
probably be sufficient to trigger showers even in the Cascades Lee
this evening...an area that has thus far escaped any appreciable
warm frontal precipitation. Model consensus rainfall amounts tonight
will range from 1/4 inch over the eastern basin...to over 1/2 inch
in the Panhandle and northeast mountains and a tenth or so in the
deep basin. Snow levels will remain in the 4000 to 5000 foot
range with minor accumulations on the higher peaks.

After the occluded front passage...this evening in the west and
overnight in the east...precipitation will quickly taper off and
the weather issue will shift to winds. Strong cool and dry air
advection will fill the basin with a new air mass. This air
movement will manifest itself in windy and gusty conditions off
the Cascades and across the basin through Friday...with lingering
orographic showers over the northeast mountains and Idaho
Panhandle. The gradient strength regardless of which model is used
will not support any Wind Advisory criteria...and gust potential
in the well mixed air mass will support gusts to 30 to 40
mph...windy but not bad enough to warrant any highlights. The
winds will promote adiabatic warming on Friday to only a few
degrees below average despite the cold advective scenario.
Convective parameters suggest only a minimal threat of isolated
and brief thunderstorms over the northeast during the afternoon.
/Fugazzi

Friday night through Sunday night: anticipate clearing skies and
decreasing winds Friday night as one storm system departs the
east. Many valley temperatures will dip near the freezing mark and
patchy river fog is a strong possibility throughout the sheltered
northern valleys. Another potent midlevel shortwave will approach
the Washington coast Saturday morning then swing through the inland northwest
late afternoon and into the night. This will usher another strong
cold front through the region. The available moisture with this
system will be nearly half of what is being transported inland
today (pwats of 0.40" vs 0.80"). In addition, the system will pass
through rather quickly. This will mean little no rainfall for the
basin and generally under a tenth for the surrounding
valleys/mountains. The Cascade crest will receive closer to an
quarter of an inch. Snow levels will rise between 4000-5000' with
the main precipitation threat and given the nocturnal passage, a
few light snow showers could impact area mountain passes.

Gusty winds are expected to accompany the system. Cross County warning area pressure
gradients become tightly packed but generally remain around 10mb
or less. This should drive sustained winds of 10 to 20 mph. The
trickier part of the forecast will be gusts. The cold front
presses through ern Washington and nrn Idaho between 00-04z with sharp
cooling at 850mb from around 8c to 0c. Forecast soundings indicate
a well mixed profile from the surface to 750mb between 00-03z. If
this holds true, we should see wind gusts between 20-30 mph ahead
of the cold front and increasing to 35-45 mph along and immediate
behind the cold front. We have began to increase wind gusts with
the afternoon forecast package and will likely continue this trend
with the overnight package if model trends remain consistent.

The storm system will be out of the region early Sunday morning
and high pressure will begin to build in Sunday and Sunday night.
A weak warm front will lift through the area spreading mid and
high level clouds but most locations will be dry with seasonal
temperatures. There is a slim chance for a few light showers
across the northern mountains but the light nature of this
activity will have very little impact on travel or recreation. /Sb

Monday through thursday: throughout this time frame the region
will remain in a pretty active pattern as a well defined trough
influences our weather pattern. Starting Monday we will be on the
backside of a ridge of high pressure giving US one final day of
pleasant warm conditions due to the associated warm SW flow.
Throughout Monday we will notice increasing clouds as moisture
from the incoming system begins to influence our weather pattern.
Increased moisture will enter the region re-saturating the
atmospheric column Monday into Monday night. Given the need to
re-saturate, the best chances initially for precip will be in the
higher elevations.

For Monday night, the precip associated with the trough will make
it to the Cascades before spreading east of the crest early
Tuesday and through the remainder of the day. With the trough axis
being directly off the Washington coast, it will allow for an abundance of
Pacific moisture to advect into our area and with pwats near .7",
this will lead to a good chance of widespread rain. As the trough
center moves overhead, we will then have cooler air aloft
allowing for lower snow levels and a much more destabilized
atmosphere. With associated weak waves within the closed low
trough, this will promote scattered weak convective showers on
Wednesday. The coverage of these showers will have to be better
refined in the future, but is something to note. Snow levels is
also something to watch as the system brings in quite a bit of
cool air aloft.

Thursday will see a brief drying trend before the next system sets
up for the end of the work week. Overall we can expect to see an
abundance of clouds throughout the period as enough moisture will
remain in place for a higher amount of cover. Aside from the 60s
on Monday, the remainder of the work week will feature below
normal temps in the 50s for most valleys. Winds will also remain
breezy throughout the period, but should not warrant any sort of
highlights. /Fliehman
&&

Aviation...
00z tafs: a cold front running along the Pacific coast at 00z will
move through the region and pass through keat around 03z-04z and
the eastern taf sites between 06z and 12z Friday. Ahead of this
front a moist feed off the Pacific will promote widespread -ra
with mostly MVFR ceilings...with some brief periods of IFR
ceilings especially at the kpuw and kgeg taf sites. After the
frontal passage the air mass will dry quickly with VFR conditions at all taf
sites...but gusty west/southwest winds developing Friday morning
and persisting through 00z Saturday./Mjf



&&

Preliminary point temps/pops...
Spokane 38 55 33 64 37 57 / 100 30 0 0 20 10
Coeur D'Alene 38 54 31 63 37 56 / 100 60 0 0 20 10
Pullman 38 52 34 66 38 56 / 100 20 0 0 20 0
Lewiston 43 60 36 72 41 63 / 100 10 0 0 10 0
Colville 38 60 31 67 34 62 / 100 50 0 10 20 10
Sandpoint 39 54 30 62 36 55 / 100 60 0 0 30 20
Kellogg 37 50 30 63 37 55 / 100 60 0 0 20 20
Moses Lake 40 62 33 69 40 65 / 50 10 0 10 10 0
Wenatchee 40 60 38 65 40 64 / 60 0 0 10 10 10
Omak 37 61 31 66 34 64 / 70 10 0 10 20 10

&&

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

$$