Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 211206
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
406 AM PST Tue Feb 21 2017

.SYNOPSIS...The last in a series of wet weather systems will
impact the Inland Northwest today leading to a mix of rain and
snow. Cooler and showery weather is forecast for Wednesday and
continuing for the rest of the work. Drier but cooler weather is
forecast for the upcoming weekend.

DISCUSSION...
A dynamic and very moist system is approaching the Oregon coast
early this morning. The associated warm front moving north out
ahead of the system is leading to a broad area of overrunning
moisture. As indicated in the evening update, radar returns are a
bit quicker than models had predicted. Areas of dense fog have
developed just ahead of the band of precipitation. This dense fog
should be shortlived as precipitation should be beginning soon.

The biggest challenge this morning is the precip type as the
moisture arrives. Temperatures are near or just below freezing
across the I-90 corridor. The temperature profile may support a
period of freezing rain briefly early this morning in the upper
Columbia Basin. Rain will be the main precip type south of
I-90...but snow will mix in or be the predominant precip type I90
north. High res models vary on the precip type right along that
I90 corridor. Thinking this morning that Spokane to Coeur d`Alene
will see snow initially before transitioning over to rain later
this morning. Models also continue to shift the axis of heavier
precip south and east...so feeling better about leaving out any
snow highlights. The exception that we`ll be watching very closely
this morning is the higher elevations of Kootenai and Shoshone
counties...where brief periods of snow could overcome the warm
pavement temperature and accumulate rapidly. At this time, we
won`t issue an advisory but plan to hit this area with social
media and weather stories to address the potential hazard.

As the shortwave moves across the region through the day and
evening, winds will shift to the west and increase (similar to
what happened Monday afternoon/evening). Freezing levels will drop
again so lingering moisture will fall in the form of snow during
the evening and overnight hours. This time has the best potential
for accumulating snow in the Idaho panhandle. The impacts should
be limited to just the highest mountain passes.

Flood Watch Update: Models continue to trend wetter in the
southern and eastern portion of the CWA and backing off on precip
to the north and west. I`m reluctant to drop Grant, Pend Oreille,
and Stevens counties from the flood watch at this time.
Complicating matters is the relatively low snow levels in the
Idaho panhandle through this last event. Given the very saturated
ground and .5 to 1.00+ inch of potential rain in the valleys,
will keep the watch as is for now and let the day shift call
around and re-evaluate the situation. /AB

Wednesday through Monday: The Inland NW transitions to a colder,
showery pattern. A long-wave trough carves itself out over the
western U.S. and the primary jet stream and storm track largely
steers the more robust/wetter systems away from the region. This
isn`t to say the region will be precipitation-free. Smaller scale
features and west-northwest flow will provide some risk for
snow showers perhaps mixed with some rain through the end of the
week, particularly near and immediately downstream of the
mountains and over the eastern Columbia Basin. Precipitation looks
more hit-and-miss, especially outside of the mountains, and
amounts look light compared to more recent systems. Much of the
area dries out going into Saturday night and Sunday. Sunday night
into Monday the jet stream nudges back north and a slightly wetter
system slides up from the south, renewing precipitation chances
from the lower Columbia Basin to the central Panhandle. That is
several days out so the details are apt to change, including the
threat shifting north or south. Yet at this time if any area has a
better chance of more moderate precipitation it could be toward
the Palouse southward but the deeper moisture still remains south.
Overall colder than normal temperatures and limited precipitation
amounts should mean less snowmelt and/or rain-swollen waterways,
so the risk for flooding should abate for most of this period.
Confidence in precise temperature going into the latter periods
degrades and model agreement is poor (with as much as 10 degrees
difference in values), but colder than normal is projected. /J. Cote`

AVIATION...
12Z TAFs: Moisture is filling in over the Columbia Basin as the
last in a series of systems impacts the Inland Northwest. TAFs are
quite challenging with multiple hazards expected over the next 24
hours and especially the first 12 hours or so. Areas of dense fog
should be lifting soon as snow and rain begin to fall. Visibility
will improve from LIFR to MVFR once precipitation begins. I held
on to the potential for light freezing rain during the onset of
the precipitation early this morning, otherwise all TAF locations
will transition from -SNRA to -RA...before changing back to -SN
this afternoon and evening. Outside of KLWS and KEAT, I`m
reluctant to clear things out and go VFR through early Wednesday
morning. That may come in the 18Z or 00Z TAF packages later today.


&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        38  25  36  21  35  19 /  90  70  30  10  10  10
Coeur d`Alene  39  27  36  19  35  18 /  90  90  40  20  20  10
Pullman        41  29  38  21  36  21 / 100  90  30  10  30  20
Lewiston       48  33  43  27  41  26 / 100  80  30  10  20  20
Colville       41  23  38  21  37  19 /  30  20  30  20  20  10
Sandpoint      39  28  36  21  35  18 /  60  60  40  20  20  20
Kellogg        38  27  36  22  34  20 / 100 100  70  30  40  20
Moses Lake     39  23  37  20  36  20 /  50  20  10  10  10  10
Wenatchee      38  25  37  21  34  20 /  30  10  20  10  10  10
Omak           38  22  36  20  34  19 /  20  10  20  10  10  10

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Flood Watch through Wednesday afternoon for Central Panhandle
     Mountains-Coeur d`Alene Area-Idaho Palouse-Northern
     Panhandle.

WA...Flood Watch through Wednesday afternoon for Moses Lake Area-
     Northeast Mountains-Spokane Area-Upper Columbia Basin-
     Waterville Plateau.

&&

$$



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