Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 311146

Area Forecast Discussion
National Weather Service Spokane WA
446 AM PDT FRI OCT 31 2014

A slow moving frontal system will pass through the region over
the next 24 hours. Rain against the Cascades this morning will
expand east through the day and into tonight. Rain in the Idaho
Panhandle will likely linger into Sunday morning. Mild and
unsettled weather is expected to continue into next week.



Today and tonight: No big changes to the fcst as the slow-moving
north-south frontal boundary currently along the Cascades moves
east the next 24 hours. Hourly pcpn rates have been around 3-6
hundredths most sites as a long rich fetch of moisture accompanies
the front. Of immediate concern is the embedded short-wave now
over W/Cntrl Oregon that will track quickly NE along the frontal/baroclinic
zone as it crosses into the Upper Columbia Basin this morning. It
will be this wave, along with the speed max digging south along
the back side of the trough, that will define the splitting nature
of the frontal boundary and upper trough by late Fri/early Sat. As
a result of these two features, we`ll see two rounds of pcpn...
the first today with the short- wave trough lifting NE across Ern
Wa, and the second tonight over SE Wa and the cntrl Id Panhandle
as what`s left of the front stalls. Halloween pcpn amnts will be
tricky, especially for Spokane which will be close to the point at
which the front splits... between the heaviest rains over Nrn Wa
today, and the heaviest pcpn threat for tonight over SE Wa. Right
now, we`re certain that pcpn will fall late afternoon into early
evening, but it doesn`t look like amnts will be more than a tenth
for Spokane. Stay

Saturday through Sunday: The Idaho Panhandle and extreme eastern fringes
of Washington can expect wet weather to continue on Saturday as a
trowal airstream interacts with a departing moist frontal boundary
along the ID/MT border. Models have been consistent with the idea
of a deepening low to our southeast and band of moderate to heavy
precipitation on its western flank but there remains some
uncertainty how far west this southwest to northeast band of pcpn
will expand into into Ern WA and far northern reaches of the ID
Panhandle. We are not looking at a huge difference in area,
roughly a county or two but this will mean a difference in dry or
wet conditions for locations like Pomeroy...Spokane...Newport...toward
Bonners Ferry. By far, the wettest conditions will be found in the
Idaho Panhandle from the I-90 corridor southward and into the Blue
Mtns with northwest flow enhancing rainfall amounts in the Blue
Mtns and Camas Prairie. Snow levels will range from 6500-7000 feet
during periods of heaviest precipitation then lower near 4500 feet
early Sunday morning as precipitation begins to taper off.
Consequently, we are not anticipated any major travel impacts from
snow on Lookout Pass. Away from the wet weather over Idaho, dry
conditions will be common in the Cascades and most of Central and
Eastern WA for much of the weekend. The next storm system will
spread high clouds late Sunday with rain returning into the
Cascades by Sunday night.

Sunday night through Friday: An atmospheric river becomes aimed
at the Northwestern US bringing several rounds of precipitation,
gusty winds, and mild temperatures. Shortwaves tracking along a
150kt jet oriented roughly from 40N/150W to SW British Columbia
will waver the fire hose north and south at times but overall, its
gonna be another wet period. The initial onslaught of
precipitation will arrive starting Sunday night and continue
through through Tuesday night. Warm moist isentropic ascent
spreads into the Cascades Sunday night then east across much of
Ern WA and Nrn ID through the day on Monday. A cool front presses
through Tuesday but has no dynamic support aloft and will mainly
act to temporarily shut off rain in the lee of the Cascades as
midlevel flow becomes more westerly but will have opposite results
in in the ID Panhandle and far eastern reaches of WA where
precipitation will likely increase.

The front and accompanying westerly flow will shove the tongue
of moisture into northern Oregon Tuesday night with drier
conditions continue to expand east across the Columbia Basin. The
Cascade Crest and ID Panhandle Mtns will not see much of this
break in shower activity as southwest winds keep the orographic
shower machine in full effect. A deeper trof will swing east of
the dateline and buckle the baroclinic region back toward the
north ahead of a developing warm front. Look for stable rains to
spread back into much of WA/ID with the heaviest amounts
continuing to focus along the northern and eastern mountains. The
trof swings inland Thursday and looks to finally bring an end to
the fire hose. Models are in decent agreement with the overall
picture but illustrate vast differences with the strength of the
trof, degree of splitting, and resultant strength/timing of a cold
front Thursday afternoon. The GFS is amongst the most compact,
least splitting models and not only ushers a strong very windy
cold front through Thursday but the trof also takes on a strong
negative tilt and could bring some thunder. The ECMWF splits the
energy before reaching the coast and although the reflection of
the surface low in Alberta is similar, height rises along the
coast are not to the same degree (due to a secondary low off the
Oregon/CA Coast) which supports an increase in winds but near the
windy scenario depicted on the GFS. We anticipate several more
variations in the models before we get to the event but it is
something worth keeping an eye on; especially if wind is of any
concern. As for snow levels, the lowest levels of this period will
be Monday morning with the onset of precipitation. Snow will be
possible down to 3900 feet across mountains WA/ID but these levels
will rise through the day and climb above most peaks and all
mountain passes by afternoon. Snow levels waver some but generally
remain near 6000 feet or higher until the trof passage late
Thursday/Friday. /sb


12Z TAFS: Light rain will continue at KEAT through this morning
with IFR conditions. Precipitation and a lower deck will make it
to KMWH by 17z but conditions are expected to remain VFR. Further
to the east the remainder of the TAF sites will not see
precipitation begin until aft 20z Friday...again with lowering
decks with ocnl MVFR.


Spokane        56  42  48  34  48  35 /  50  60  20  10  10  10
Coeur d`Alene  58  43  46  34  47  34 /  50  70  70  40  10  10
Pullman        59  42  46  36  48  37 /  30  80  70  30  10  10
Lewiston       65  46  48  39  53  38 /  20  80  80  40  10  10
Colville       55  41  50  32  48  35 /  90  60  10  10   0  10
Sandpoint      57  41  47  35  46  32 /  50  70  70  40  10  10
Kellogg        59  41  45  35  44  32 /  20  70 100  60  30  10
Moses Lake     55  41  54  34  53  38 /  90  20  10   0   0  10
Wenatchee      55  39  55  37  54  40 / 100  10   0   0  10  20
Omak           52  37  51  33  51  38 /  90  20  10  10  10  10



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