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Area forecast discussion
National Weather Service Spokane Washington
522 am PDT Mon Mar 27 2017

Synopsis...
showers will linger over the region today behind an exiting cold
front. After a short break in the weather tonight another round of
widespread moderate precipitation will arrive Tuesday night and
last until Thursday. Friday will bring a dry break period before
more unsettled weather for next weekend.

&&

Discussion...
today and tonight...an upper level trough will move through the
region this morning. Satellite imagery shows the trough
shearing/splitting early this morning with the cold core and the
best energy looking more and more like it will drop into Oregon.
Behind the cold front the atmosphere over the inland northwest is
still expected to destabilize. 500mb temps drop to around -29c,
lapse rates increase to right around 7c/km with afternoon heating
and Lis drop 0 to -1. Expect the light stratiform precipitation
from early this morning to decrease through the morning hours with
showers developing through the afternoon and evening. Mu cape
increases to 200-400 j/kg around the middle of the afternoon,
throw in a shearing vort lobe and there is a small chance for a
few afternoon lightning strikes across the eastern basin, the
Palouse and across the Blue Mountains. Sref guidance has backed
off on the probability of thunderstorms with the latest run, so
for now will keep any wording for lighting out of the forecast.

Weak high pressure will build in from the west overnight and
usher in a slightly drier air mass. Showers will still be
possible across the crest of the Cascades and for the Panhandle
mountains, otherwise conditions should be dry. Clearing skies and
light winds will result in fog and stratus development along the
rivers and for the northern valleys.

Tuesday and Tuesday night...the ridge of high pressure will
flatten on Tuesday ahead of a weak short wave expected on
Wednesday. This will allow another warm front to track through the
region Tuesday afternoon and Tuesday night. This frontal system
will again tap into deep and long fetch of Pacific moisture. This
atmospheric river will increase moisture across the region to well
over 200 percent of normal. Isentropic up-Glide along to 290-295
surface increases by late Tuesday afternoon and lingers over the
region through Tuesday night. The result will be another period of
light to moderate stratiform precipitation. Precipitation amounts
outside of the deep basin will be between a tenth and two tenths
of an inch. Snow levels will be 4000-5000 feet so the High
Mountain snow will continue to pile up. Tobin

Wednesday through Thursday night: a warm front will spread into
the area Wednesday followed by a cold front Wednesday evening into
Thursday morning. There is a very good precipitable water tap
that looks to peak across the region late Wednesday morning. The
models are still in good agreement of precipitable water values. The precipitable water values for
Wed aftn are a bit lower than yesterday, but think that is
because of the cold front getting ready to push across the
Cascades and quickly lower values. Have kept our chance of
precipitation for Wed near 100%, but have lowered the amount of
precipitation we should expect. Central Washington valleys could see
0.15-0.30 with eastern Washington and north Idaho valleys having a potential
of 0.30-0.50. The mountains could see half to one inch of liquid,
with the Cascade crest expecting more. Snow levels will be fairly
high, about 5000 ft during the day with snow levels falling with
the passage of the cold front. Snow levels could get as low as
3500-4000 ft by Thursday morning, but the heaviest precip will
have ended across the region. So a valley rain and High Mountain
snow event is expected. It will be possible for Spokane to climb
to the 2nd wettest March spot on the climate records. Still do not
think Spokane will make it to the number one spot. Thursday the
upper level trough moves through the region. Expect an increase in
showers, especially in the afternoon across eastern Washington and north
Idaho. Then Thursday night as the trough exits a ridge will start to
push inland. Our chance of precipitation will wane through the
evening and overnight hours.

*Expect area rivers to respond to the moderate rain Wednesday.
Rivers, small streams and creeks will rise once again through
Friday. Ponding of water over roadways and fields is quite
possible as well. Cannot rule out the continued problems of
debris flows, rock slides and wash outs as the ground remains
saturated from all the rain.

Friday through monday: an upper level ridge builds with dry
northerly flow moving into the region on Friday, for finally a dry
day. Then Friday night into Saturday the flow turns more westerly.
Models are differing pretty substantially on timing, strength and
track of a trough Saturday through Monday. Did not make many
changes to the forecast. Kept the best chance of showers across NE
WA, north Idaho and the Cascades. /Nisbet

&&

Aviation...
12z tafs: a cold front will move into the Panhandle early this
morning and east into Montana before mid-day. Showers will linger
through early this morning for the eastern taf sites with VFR/MVFR
conditions...and for most of the day along the Idaho/Montana border.
There will be some localized fog/stratus early reducing cigs/vsby...but
that should dissipate soon after sunrise. The atmosphere will
destabilize with afternoon heating for isolated to scattered
showers across the eastern taf sites through sunset. Conditions
at the taf sites are expected to improve to VFR with widespread
clearing after sunset. Clearing skies will set the stage for
fog/stratus development along rivers and for the northern valleys
through the night...but at this time it should not affect any of
the taf sites. Tobin



&&

Preliminary point temps/pops...
Spokane 50 34 49 39 51 39 / 40 10 40 50 100 60
Coeur D'Alene 47 34 46 37 49 38 / 70 30 50 60 100 70
Pullman 48 35 49 39 51 40 / 50 20 30 40 100 70
Lewiston 54 37 54 42 56 42 / 40 10 20 20 80 70
Colville 48 33 47 36 49 37 / 40 10 50 70 100 50
Sandpoint 45 33 45 34 46 35 / 50 10 60 70 100 80
Kellogg 44 33 44 35 46 36 / 90 40 50 50 100 80
Moses Lake 58 37 57 43 58 41 / 10 0 10 40 100 10
Wenatchee 53 37 53 39 54 38 / 10 10 20 70 100 10
Omak 52 34 51 39 52 37 / 20 10 20 70 100 20

&&

Otx watches/warnings/advisories...

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