Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service Spokane Washington
444 PM PDT Friday Apr 18 2014

Synopsis...
clearing skies, lighter winds, and cool temperatures will be the
trend tonight. Another storm system will bring windy conditions
Saturday afternoon and night with some showers across the north.
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...
tonight into Saturday morning: a pool of instability remains
across far northeastern Washington and the northern Idaho Panhandle this
afternoon. Radar and satellite trends indicate at least one last
cluster of showers crossing through boundary and Bonner counties
then most shower activity will wane. This will lead to clearing
skies through much of the night. As for winds, pressure gradients
peaked around 12z and are slowly coming down. Afternoon mixing and
cold air advection has led to breezy to gusty winds through much
of the day but all trends will support the idea of decreasing
winds through the evening hours...becoming around 10 mph or less
overnight. Meanwhile, much drier air has settled into the region
behind this morning's cold front. The combination of these
ingredients will lead to another chilly night across the region
with most sheltered northern valleys experiences well below freezing
temperatures.

The potential for near freezing temperatures will likely extend
into the basin and toward the Moses Lake area. There is not
enough confidence nor model support to issue freeze warnings based
on the coverage being more localized and a deep freeze just
experienced on the 14th. We also looked back into that event from
the 14th and dewpoints were significantly drier than today.
Nonetheless, we do anticipate temperatures to dip between 34 and
31f within the Moses Lake, Royal City, George, Ephrata, and
Beverly areas and those with sensitive plants within these
locations should prepare for near freezing temperatures but
not panic of a hard freeze.

A few clouds will begin crossing the Cascades before
sunrise...associated with the next frontal system but overall,
dry conditions will prevail through Saturday morning. Any fog that
develops in the northern valleys will burn off my late morning.
/Sb

Saturday afternoon through Monday...a cold front will move
through the region Saturday, bringing scattered showers to the
inland northwest. There is decent upper level forcing but moisture
will be the limiting factor. Showers will mainly affect the higher
elevations as there will be some dry air in the lower levels.
There may be some occasional sprinkles for the basin into the
Spokane area but the more favored areas will be the rising terrain
north and east of the basin. Strong southwest flow aloft will add
orographic ascent to the mix. Southerly flow will also bring
warmer air into the forecast area. Daytime temperatures will warm
into the 60s with low 70s for the warmer valleys. Gusty winds will
accompany the front, increasing the mixing potential for the late
afternoon/early evening period. Wind gusts of 25 to 35 mph will be
common across the basin and Waterville Plateau, spreading into the
Palouse and Spokane area. Considering the timing of the front
during the most unstable time of day, there is the possibility of
even higher wind gusts. For now, it looks like winds will remain
below advisory criteria but it will be watched closely for the
next forecast package. Diminishing winds overnight along with
clearing skies will allow for good radiational cooling. The more
sheltered northern valleys will likely dip below freezing but
areas south of I-90 will probably stay above freezing as winds
will remain elevated for much of the overnight period.

A building ridge of high pressure will keep Sunday dry except for
some lingering showers over the Idaho Panhandle early in the day.
Temperatures will be near seasonal normals but not quite as warm
as saturday's readings. Sunshine will be filtered by high clouds
moving in from the west ahead of the next Pacific system that will
start to affect the area Monday. Expect showers to spread to the
Cascade crest late Monday morning. Easterly upslope flow will
enhance lift into the east slopes for a greater chance of precip.
As winds shift to the south during the day, warm frontal precip
will spread across the western half of the forecast area Monday
afternoon and evening. Strong warm air advection will bring
temperatures above normal with most valley locations in the upper
60s to low 70s. The Lewis-Clark Valley could see upper 70s and
even 80 degrees in some locations. /Kelch

Monday night through saturday: all eyes for the beginning of this
period will be on the system moving from west to east across the
region. The frontal system associated with the incoming trough
looks to be a rather slow mover leading to an increased time frame of
widespread precipitation. Throughout Monday night and into Tuesday
will be the best shot of precip with wetting rains expected for
most. As the trough continues to push inland on Tuesday, we expect
the associated precip to move east as well with much of the basin
expected to dry out by late Tuesday. Rain is still expected for
far eastern Washington and the Panhandle through Tuesday night as the
system slowly pushes into western Montana. The main question with
this system and also where models tend to disagree is the amount
of wrap around moisture. The GFS wraps moisture back into the
northern Panhandle and far NE Washington whereas the Euro keeps it further
north late Tuesday and into Wednesday. Current trend is to follow
the GFS more as it has been more consistent over the past few runs
but this may have to be better refined as models come into better
agreement.

The next factor to monitor will be the snow levels. As the trough
center moves overhead, an abundance of associated cold air will
enter brining 850 temps down below zero for portions of our
forecast area Tuesday night into Wednesday morning. What this
means is a chance for both high and Lower Mountain snow with some
higher valleys even having a shot for some snowfall. Any valley
snow will likely be in the Cascades and northern Washington. Impacts for
the lower areas will be minimal as none of the snow is anticipated
to stick. Higher areas will see a good shot of accumulating snow.
Snow levels rise back to more seasonal levels come daytime
Wednesday leading to valley rain and higher mountain snow.

Winds in the Tuesday and Wednesday time frame look to remain
breezy due to a tightened surface pressure gradient. Currently no
major impacts are expected, but with the cooler daytime temps, the
breeze will make it feel quite cool. Temperatures for the middle
part of the week will remain well below normal with daytime highs
staying in the 50s for most valley locations. Also the sun will
likely be hard to come by as clouds will be prominent with the
system.

Wednesday night and early Thursday looks to feature a brief break
period from the widespread rain as weak ridging builds between
the exiting and next incoming system. The mentioned next system
looks to reach the Cascades Thursday evening before spilling over
on Friday and into the weekend. Detail will have to wait for this
system as models need to come into better agreement. Overall the
period looks to be rather active with widespread rain expected.
/Fliehman

&&

Aviation...
00z tafs: winds will weaken this evening and the cloud cover
will decrease as well over the aviation area. A second robust cold
front will move through the aviation area Saturday allowing
clouds to invade the sky from the south and west which will
thicken and lower with time along with some shower activity.
The most significant impact of this front passage will be another
windy interval, primarily Saturday afternoon and evening. /Pelatti

&&

Preliminary point temps/pops...
Spokane 33 63 35 59 40 67 / 0 10 10 0 10 10
Coeur D'Alene 31 62 36 58 39 67 / 10 10 30 10 10 10
Pullman 33 65 35 58 41 68 / 0 10 20 0 0 10
Lewiston 36 71 41 65 45 74 / 0 10 10 0 0 10
Colville 31 66 32 65 36 70 / 10 20 20 10 10 10
Sandpoint 28 61 36 58 36 64 / 10 10 30 10 10 10
Kellogg 31 62 35 57 37 66 / 10 10 30 10 10 10
Moses Lake 32 68 38 66 43 72 / 0 10 10 0 0 10
Wenatchee 37 64 42 66 47 68 / 0 20 10 10 10 10
Omak 29 63 35 65 40 67 / 0 20 10 10 10 10

&&

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

$$