Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 012324

Area Forecast Discussion
National Weather Service Spokane WA
324 PM PST SUN MAR 1 2015

A weak weather system will pass through the region tonight and
Monday with the potential for light snow mainly for the Idaho
Panhandle, along with breezy conditions across much of the region
Monday night. Much colder air moves in behind this system, with
temperatures well below average for the middle of the week. A dry
period, with moderating temperature will follow for the end of
the week.


Tonight through Monday Night...Satellite imagery reveals a
northwest trajectory upper level short wave descending down the
Canadian Pacific coast this afternoon. Latest models initialize
this feature plausibly and are in agreement in tracking the
dynamic base of this wave to the west of the forecast area over
the next 24 hours. There is a weaker secondary wave embedded in
the main frontal band over northern British Columbia. While the
main wave will pass harmlessly to the west other than a few snow
showers in the Cascades tonight...the secondary wave will
sideswipe the region and provide some lift and frontal focus over
the Idaho Panhandle during the day on Monday...with some snow
shower activity slopping into far eastern Washington. The deep
basin and Cascades will be too far west to be impacted beyond
increased clouds and stray flurries in the mountains.

In the wake of this wave passage another shot of cold Canadian air
will invade the region Monday night...squeezing through the
northern gaps of the Okanogan Valley and Purcell trench for
blustery...windy and raw conditions overnight and into Tuesday

* Snow amounts: Scattered to numerous snow showers will arrive early
  Monday over north Idaho and the northeast Washington
  mountains...and spread over the entire Idaho Panhandle during
  the day (with fringing hit- and-miss snow showers over far
  eastern Washington) and linger over the Shoshone County High
  terrain and Camas Prairie Monday night. Snow amounts will range
  from less than an inch in the north Idaho Valleys to two to 4
  inches over the mountains above 4000 feet. Afternoon instability
  promoted by mild upper 30s to low 40s surface temperatures will
  combine with cold temperatures aloft in the cusp of this wave to
  promote instability showers over the threat area. Some of these
  snow showers could be briefly intense but will be mainly focused
  over high terrain. By afternoon road surface temperatures will
  be well above freezing so no significant impacts are expected
  unless an unusually burly shower dumps an inch or so in a short
  time thus overwhelming the specific heat capacity of the road
  surface. This possibility cannot be pinned down with any
  certainty at this time.

* Wind: Monday evening the next dry and cool Canadian air mass
  invasion will commence through the northern mountain gaps.
  Expected gradient orientation suggest the Okanogan Valley will
  be the favored channel for this dense dry air with the Purcell
  trench also receiving a windy push. At this time gradient
  strength does not look sufficient for any wind highlights but a
  solid 20 to 30 mph through the Okanogan and 15 to 25 mph through
  the Purcell trench looks quite plausible. This dense air will
  follow gravity into the deep basin with breezy conditions also
  expected over the Waterville Plateau and into the Moses Lake
  region. Ramifications of this push besides the normal wind
  hazards will be very cool wind chill temperatures Tuesday
  morning across much of the region.

Tuesday through Wednesday...Dry and mostly clear conditions will
return for this period with the next strong upper level ridge
building aloft with continued but diminishing dry northerly flow
at the surface. The main issue will be cold morning low
temperatures particularly on Wednesday morning as winds die out
and radiational cooling becomes dominant.
significant weather is expected. /Fugazzi

Thursday through Sunday. Very few changes were made to the
extended forecast because very little weather is expected during
this time. The beginning of this time frame will feature an area
of high pressure centered just off shore from San Francisco Bay.
An upper level ridge will extend north and west. The upper level
ridge axis to our west and a broad trough over the eastern half of
the US places the Inland Northwest under northwesterly flow aloft.
The northwesterly flow aloft will usher in the occasional
disturbance bringing increased cloud coverage and enhancing the
chance for precipitation. At this time, a slight chance of
rain/snow was added to the forecast for one of these waves
embedded in the northwest flow. The best chance of precipitation
will occur over far northeastern Washington and the northern Idaho
counties. Otherwise, dry conditions are expected with near to
slightly above average temperatures.

Looking at the weekend and beyond, a very large low will deepen
over the eastern Pacific (near 40N 150W). The extended models are
in great agreement of this feature developing which by the end of
the weekend will displace the upper level ridge directly over the
Pacific Northwest. Then by early next week, the open trough over
the Pacific begins to eject moisture in the form of southwesterly
flow aloft toward our region. While this is typically a warm
pattern, it does introduce the possibility for rain and mountain
snow mid next week. That is well beyond what I feel comfortable
forecasting for but given our warm and dry weather, it`s worth
pointing out any potential changes to this stubborn pattern.


00Z TAFS: VFR conditions can be expected at all TAF sites through
Monday 00z. High clouds will thicken tonight. Some light snow is
possible over the north Cascades tonight but should not effect any
of the TAF sites. On Monday a weak weather disturbance will cross
the area from north to south. scattered -SHSN will develop over
the eastern third of WA and all of north ID. There is a chance of
brief MVFR visibilities in -SN at the KCOE TAF site during the
afternoon and some showers will exist in the vicinity of
KGEG...KSFF...KPUW and KLWS...but the densest concentration of
showers will lay to the east of the TAF sites with isolated _SHSN
over the Cascades. /MJF


Spokane        29  42  20  35  17  41 /  10  30  10  10   0   0
Coeur d`Alene  27  42  18  36  14  44 /  10  50  30  10   0   0
Pullman        29  41  21  35  17  44 /   0  40  20  10   0   0
Lewiston       30  46  25  40  20  47 /   0  20  20  10   0   0
Colville       28  44  22  40  16  46 /  10  50  10  10   0   0
Sandpoint      26  39  16  33  12  40 /  10  60  50  10   0   0
Kellogg        26  38  16  31  13  40 /   0  70  70  10   0   0
Moses Lake     32  49  25  44  20  48 /  10  10   0   0   0   0
Wenatchee      32  50  25  44  21  49 /  10  10   0   0   0   0
Omak           29  45  22  45  19  49 /  10  10   0   0   0   0



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