Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 272240
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
239 PM PST SAT DEC 27 2014

.SYNOPSIS...
A vigorous low pressure system will continue to produce
widespread accumulating snow tonight. The heaviest snow amounts
will likely occur over the Idaho Panhandle where amounts of 6 to
10 inches will occur. Bitterly cold northeast winds will develop
by Monday and continue into Monday night. Temperatures will be
well below average with dry conditions most of next week as arctic
high pressure settles over the Inland Northwest.

&&

.DISCUSSION...

.Tonight...
Radar and Satellite indicate an active weather system moving through
the Inland Northwest which will continue through this weekend
producing snow and Cascade Crest and East of the Okanogan Valley
and Moses Lake have the best chance of accumulating snow. This is
the best Winter snow storm so far especially in the Idaho
Panhandle which could see up to 8 inches in the valleys and 12
inches in the Idaho Panhandle mountains as well as the higher
Cascade mountains. Since the storm is coming from the Nrthwest,
the Lower East Slopes of the Cascades will be shadowed from
precipitation. There is an interesting chance that the Wenatchee
area could see a brief snow shower due to convergence over the
Cascades. Overall, it appears Winter has started across the
region.  TC

Sunday through Monday...Winter will continue through this period.
Satellite indicates a deep and cold trough dropping out of the
Gulf of Alaska and approaching the forecast area from the
northwest. By the time Sunday dawns this trough will have
enveloped the forecast area with very cold air aloft causing some
moderate instability. An open surface low will exist over the
region and mid level winds will be driving into the Panhandle
mountains and the Camas Prairie...prolonging further snow
accumulation in these areas. The current Winter Storm warnings for
the Shoshone County mountains and Camas Prairie/Blue Mountains
run through 4 pm Sunday and this still looks good with a very real
potential of a further 4 to 6 inches in these zones during the day
Sunday. The remainder of the forecast area will probably evolve
into a hit-and-miss snow shower pattern during Sunday morning
with the densest areal coverage over the Idaho Panhandle and far
eastern Washington with isolated snow showers over the Cascades
and deep basin. Thus for most locations Sunday will be
characterized by clouds...seasonably cool temperatures and
occasional snow showers capable of lying down a quick further half
inch to an inch or so before moving on to the next town.

Sunday night and Monday a weak secondary wave will drop out of the
north and bring a round of light snow mainly to the deep basin and
Cascades. At this time expectations are for a general 1 to 2
inches in the basin and valleys west of a line from Republic to
Moses Lake. the Cascades may pick up a few inches but at this time
confidence in these amounts is not high enough to seriously
consider any further winter highlights for this weaker follow-on
wave.

The big story on Monday will likely be the winds barreling down
the Okanogan Valley and Purcell Trench as an Arctic high pressure
plunges southward ramming a slug of dense cold and dry air through
the northern mountain gaps and into the basin. Areas of blowing
snow over the northeastern zones and very raw wind chills will
become concerns Monday afternoon and evening. Wind advisories may
be warranted with this Arctic push particularly in the Okanogan
Valley and the Highway 95 corridor from Porthill to Coeur
D`Alene...and breezy and gusty northeast wind conditions will
develop over the entire Columbia Basin during the day Monday. this
very dry air will probably bring an end to any further snow beyond
some light flurries in the mountains surrounding the basin.
/Fugazzi

Monday night through Saturday...Positively tilted flop-over ridge
aloft with axis placed off the coast continues a northerly flow of
dry cold air through much of this forecast interval. Issues of
note would be the robust and gusty northerly winds brought about
initially that continue into Monday night and may need to be
highlighted with a wind advisory. Other than that it remains
fairly cold and benign through most of the workweek until Friday
and beyond where models hint at numerous weather disturbances,
including a cold arctic front, dropping down from the north to
bring more snow and reinforce the cold air in the area. /Pelatti

&&

.AVIATION...
18Z TAFs: A winter storm will bring a long run period of IFR and
occasional LIFR conditions in accumulating dry snow to the
eastern TAF sites of KGEG...KSFF...KCOE and KPUW through 00Z-02Z
Sunday. At the KPUW TAF site snow may mix with rain for a brief
period this afternoon before turning back to snow overnight with
frequent snow showers continuing through 18Z Sunday. At the KGEG
area TAF sites snow may taper off to occasional snow showers after
02-03Z tonight but conditions will be favorable for further
upslope stratus through the night. KLWS will also experience snow
with a rain/snow mix in the afternoon where low MVFR conditions
are more likely with only a chance of brief IFR conditions. KMWH
and KEAT may be entirely skipped by this storm system benefiting
from a downslope rain shadow off the Cascades and may hold VFR
conditions through the TAF period...although confidence is only
moderate that some low stratus will not develop in these low
laying basin locations by Sunday morning. This storm system is
too complex and organized and slow moving to give any confidence
that significant improvement is likely for the next 24 hours over
the eastern TAF sites. /MJF

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        27  31  18  21   6  14 /  70  30  20  10   0   0
Coeur d`Alene  27  31  17  20   5  14 / 100  50  20  10   0   0
Pullman        29  33  19  23   3  14 / 100  70  30  30  10   0
Lewiston       32  38  24  29   9  19 / 100  60  40  30  10   0
Colville       26  33  20  24   1  18 /  50  30  20  10   0   0
Sandpoint      27  32  18  20   2  15 / 100  50  20  10  10   0
Kellogg        26  30  15  17  -1  11 / 100  70  40  20  10   0
Moses Lake     27  33  23  29  12  22 /  10  10  50  30   0   0
Wenatchee      28  34  25  30  13  23 /  10  10  60  40   0   0
Omak           25  29  21  26   9  17 /  20  10  40  20   0   0

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Winter Storm Warning until 4 PM PST Sunday for Central Panhandle
     Mountains-Lewis and Southern Nez Perce Counties.

     Winter Storm Warning until 4 AM PST Sunday for Coeur d`Alene
     Area-Idaho Palouse-Northern Panhandle.

WA...Winter Storm Warning until 4 PM PST Sunday for Northeast Blue
     Mountains.

     Winter Storm Warning until 4 AM PST Sunday for Northeast
     Mountains-Washington Palouse.

     Winter Weather Advisory until 4 AM PST Sunday for East Slopes
     Northern Cascades-Okanogan Highlands.

     Winter Weather Advisory until 10 PM PST this evening for Spokane
     Area.

&&

$$




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