Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 221213
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
513 AM PDT Fri Mar 22 2019

.SYNOPSIS...
Friday will be a few degrees cooler as clouds increase ahead of a
weak cold front. The weekend will feature temperatures near
average with rain and mountain snow showers over the Idaho
Panhandle and portions of eastern Washington. Typical cool and
showery weather is expected much of next week with high
temperatures mainly in the 50s.

&&

.DISCUSSION...
Today through Saturday night...
Starting with the big picture, an upper ridge of high pressure is
centered over the Great Plains and arches back toward the west
over central and western Canada. Below this ridge is an upper
level low that is pinching off from a larger upper trof. The upper
low is currently situated over central Utah. An area of
deformation extends north and northwest from that low which is
bringing the Inland Northwest increased upper level moisture. That
increased moisture will be the most notable difference in the
weather Friday as our sunny and dry streak comes to an end.

Mid and high level clouds will increase through the morning which
will help moderate temperatures. The big question is just how much
the high temperatures will decrease today and Saturday. The NAM is
an outlier but worth mentioning that it is aggressively bringing
in more low level moisture to the central basin and thus max temps
only reaching the mid to upper 40s today. This is 10+ degrees
different from our ongoing forecast and what the majority of the
models are suggesting for high temperatures today. As it is, we
are leaning heavily toward the more optimistic models that agree
on a mid to high cloud deck and daytime max temperatures 3-6
degrees cooler than Thursday.

Looking again at the satellite imagery, the other large feature is
a front off of the PacNW coast. It has been well advertised that this
front will fall apart as it moves inland Friday night. Surface
winds will increase from the southwest as the remnants of the
boundary move across the region while temperatures drop down
another notch Saturday.

The last feature in these first few days of note is the next upper
wave that will move across the region Saturday evening. The Euro
and many of the ensemble members keep the Inland Northwest dry but
the recent deterministic models including the GFS and NAM are
indicating a band of rain is likely with this feature. I will be
tweaking the forecast slightly to add the possibility of light
rain Saturday night. Even if these deterministic models prove to
be correct, this should be a very low impact event with overnight
precip amounts less than a tenth of an inch. /AB

Sunday through Tuesday: Low pressure residing off the WA Coast will
send a series of shortwaves into the Pac NW bringing several
rounds of showers and transition toward cooler, near normal
temperatures. Our first shortwave will be quite weak and pass
through the area Sunday. Overcast skies and scattered light
showers will plague much of Idaho and eastern third of WA
throughout the day with clearing expected to reach the Cascades
and eastern Basin before sunset. Precipitation amounts will range
from a few hundredths to up to two tenths. The GFS has pockets of
higher amounts in the Idaho Panhandle but is an outlier and
generally not utilized. A few showers will linger over extreme
Northeastern WA and N ID Sunday night but by large, we should see
this first system exit north into Canada with break in the
precipitation Sunday night and into midday Monday.

The second shortwave will arrive Monday evening and depart to the north
Tuesday afternoon. There are some subtle timing differences with
how fast the shield of precipitation spreads east of the Cascades
but confidence is increasing that this will be a wetter system
compared to Sunday with this system featuring a more dynamic jet
streak and midlevel circulation. QPF between 0.10-0.20" will be
common across the region. Heavier amounts on the order of half
inch or more will be possible in the Cascades and into the
northern mountain valleys of Central WA including the Okanogan
Valley and Republic Area. This moisture will fall as snow for
elevations of 4500 feet and higher and may even have wet snow down
to 3000 feet under some of the more intense precipitation areas.
As such, expect snowy travel across Sherman Pass Monday
night/Tuesday AM and potential for wet slushy accumulations at
Stevens/Loup Loup passes. Any saturated fields experiencing some
degree of minor flooding could worsen. This is also the time of
year when precipitation events of this nature tend to create rock
slides in areas of steep terrain. These are nearly impossible to
predict where they will occur but as the ground continues to
undergo a freeze/thaw cycle and then we add a few tenths of rain,
the threat will become elevated. A few showers linger over the
far northern mountains and along the WA/OR border Tuesday,
otherwise most of the Inland NW will dry out.

Wednesday through Friday: The offshore low tracks inland Wednesday and
Thursday but looks to pass south of the area through Oregon and
southern ID. This is where the focus for light to moderate
precipitation will be which is good news as we continue to deal
with spring melt and runoff. The region will remain under the
influence of a cooler trough which will spark a few mountain
showers at times but any additional precipitation looks to be very
light at this time. By Friday...high pressure begins to
restrengthen over the Ern Pac and Gulf of AK placing the area
under northerly flow. Some models indicate another weather system
dropping in from the north renewing organized precipitation but
there is not a whole lot of of agreement...thus confidence is low.
The air mass however looks to remain seasonably cool keeping
additional contributions of snow melt in check. /sb


&&

.AVIATION...
12Z TAFS: Not many significant changes for this 12Z TAF package.
High clouds will generally increase over the next 12-18 hours
resulting in OVC100 by Friday evening for most locations across
the Inland Northwest. Also made some minor adjustments to the
wind forecast accounting for the increased southwest flow expected
this afternoon. There is a very slight possibility of some
sprinkles at LWS later tonight...kept it out of the TAF for now.
/AB

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        57  37  53  34  48  32 /   0  10  10  10  20  20
Coeur d`Alene  55  36  49  34  46  32 /   0  10  10  20  30  20
Pullman        55  36  49  33  47  32 /   0  10  10  20  20  10
Lewiston       59  43  53  39  51  34 /   0  30  20  20  20  10
Colville       60  35  59  34  53  35 /   0  10  30  20  30  30
Sandpoint      53  37  48  36  46  33 /   0  10  30  20  40  30
Kellogg        56  37  49  36  45  32 /   0  10  20  20  50  20
Moses Lake     63  39  59  35  55  35 /   0  10   0  10  10   0
Wenatchee      57  38  53  35  53  35 /   0  20   0   0  10   0
Omak           61  40  54  37  50  36 /   0  30  10  10  20  10

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...None.
WA...None.

&&

$$


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