Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 021041
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
241 AM PST Sat Mar 2 2024

.SYNOPSIS...
A disturbance Saturday will bring a round of light snow to the
lowlands. An unsettled weather pattern will remain in place
through next week with several opportunities for snow and some
rain, with the next best potential for snow that may cause impacts
around Monday and Tuesday, including in the lowlands.

&&

.DISCUSSION...
Saturday through Monday: Starting off the month of March with very
Spring-like weather: convective showers. Friday featured a glimpse
of that and we will see similar conditions over the weekend. High
uncertainty in exactly where snow showers will develop or what areas
will see the higher amounts of snow, but high confidence we will see
these conditions across the Inland Northwest.

* Snow Showers: We have very cold temperatures aloft (500mb, -33C)
  with steep lapse rates (8C/km to 9C/km) and a moisture profile
  that is rather weak but enough moisture in the appropriate zone
  for snow growth or graupel/small hail to form. Saturday and Sunday
  will feature additional rounds of snow showers, some becoming
  convective and a small possibility of additional snow squall
  showers (30% chance). CAPE of 120 J/kg across north-central
  Washington Saturday and similar values Sunday across the northern
  Idaho Panhandle.

* Amounts: Given how unstable the environment is and the nature of
  widely scattered showers, amounts will vary by location and
  especially with elevation. That being said, areas that experience
  bursts of snow could see a quick 1 to 3 inches of snow, and with
  the mountainous terrain of 3000 feet and above those areas could
  see up to 4 or 5 inches of snow. Sunday amounts will be more
  confined to North Idaho with around 1-2 inches in the mountains
  and Valleys half an inch or so.

* Timing: Saturday morning snow showers are already getting underway
  as of 2 AM in the Cascade slopes and Waterville Plateau as well as
  the central Basin and moving into the Palouse. This band of snow
  will continue pushing north- northeast through mid day, finally
  reaching northern Idaho (Sandpoint to Bonner`s Ferry) by lunch
  time. Sunday the onset timing looks a bit later in the day, but
  still should

* Impacts: Cold and below freezing road surfaces this morning will
  result in slick conditions for any snow/precip that falls. A big
  concern for rapid accumulations, bursts of snow, before
  temperatures warm by mid day. Sunday, the timing of snowfall
  should coincide more with warmer road temperatures.

Monday: The broad upper level trough drapped over the Northwest will
shift south and bring a shortwave through the Inland Northwest.
Widespread snowfall from the West Plains, Eastern Washington, and
the Idaho Panhandle will be moderate in amounts and depending on the
timing and intensity, could be impactful to the morning commute with
several inches falling before sunrise Monday morning. Right now,
the NBM has just 5-10% chance for 1" in Spokane between 4 AM and
12 PM Monday morning, a 15% chance for 2" in Coeur d`Alene and 2"
in Pullman, and 15% chance for 4" in Sandpoint. /Dewey

Tuesday through Thursday: Following the widespread snow Monday
night, precipitation will turn more showery in nature as the center
of the cold trough aloft moves over the Inland Northwest Tuesday
afternoon and evening. Similar to the weekend, these showers will be
capable of producing quick bursts of heavy snow and/or graupel which
would result in isolated areas of limited visibility and slick
roads. Temperatures dropping below freezing overnight will cause
slippery conditions on any untreated surfaces. By Wednesday,
temperatures will be relatively cooler as the flow briefly turns to
the northwest under a brief transient ridge. Lows in the teens
across the northernmost Washington and Idaho counties and lows in
the low to mid 20s further south. Models are showing a weak wave
approaching from the west on Thursday, bringing snow to the Cascades
and the Idaho Panhandle. Amounts will be light with only a 20%
chance for 1 inch for areas such as Sandpoint, Kellogg, and Saint
Maries. These amounts will result in little to no impacts during the
day on Thursday, but may create slick conditions on untreated
surfaces overnight into Friday.

Friday and Saturday: Models are in great agreement on a ridge to
move over the Pacific Northwest on Friday as an upper level trough
stretches from the Gulf of Alaska to offshore central California.
Examining the WPC ensemble clusters reveals discrepancies in the
overall strength and evolution of the ridge and subsequent trough.
Since all clusters show the presence of this ridge, there is high
confidence there will be a warming trend next weekend. The exact
degree of warming and the chances for precipitation carry much lower
confidence due to the variation in the ensemble clusters.  About 60%
of ensemble members keep a stronger ridge in place through next
weekend, which would keep the region dry. The other 40% show a
quicker arrival of the trough, increasing chances for precipitation
next weekend. /vmt

&&

.AVIATION...
06Z TAFS: One band of snow is departing to the northeast with a
second quickly on its heels. Light snow will spread into Central
WA early this morning and continue to expand north and east. There
is moderate confidence this will be a light snow event with snow
amounts varying from a few tenths to up to 3 inches. Benches
around Wenatchee, Omak, and the northern mountains carry a 40% for
amounts in excess of 3 inches. As this steady band of snow departs
to the north Saturday afternoon, temperatures will warm above
freezing. Afternoon instability will promote hit or miss showers
of rain and snow. The incoming snow will bring a moderate to high
threat for MVFR conditions along the Hwy 97 corridor and would not
rule out a brief period of moderate snow. Given the timing of the
snow, terminals like Wenatchee, Lake Wenatchee, Chelan, and
Winthrop will carry a moderate threat for accumulations. The break
between systems is allowing a ragged fog or stratus deck to
develop within the valleys of NE WA and along the ID/WA border.
This will impact Pullman for the next few hours with low
confidence for the duration.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: Would not rule out
additional patchy fog or low stratus developing next few hours
06-10z around Spokane-Cd`A though this comes with low confidence.
A few models suggest heavier snowfall amounts Wenatchee,
Waterville, and Chelan than forecast. This comes with low
confidence but would not rule out 4-5 inches if moderate
intensities can persist longer. Overall, there is moderate to high
confidence for the timing of the snow to depart south to north
through Saturday morning and afternoon.

------------------

Confidence descriptors:
Low - Less than a 30 percent chance
Moderate - 30 to 70 percent chance
High - Greater than a 70 percent chance

For additional probabilistic information for NWS Spokane airports,
please refer to the Aviation Dashboard on our webpage:
https://www.weather.gov/otx/avndashboard

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        38  23  38  24  38  24 /  90  20  20  30  50  50
Coeur d`Alene  36  21  37  22  35  23 / 100  20  40  30  70  50
Pullman        37  23  38  25  37  26 /  80  10  40  40  60  60
Lewiston       44  28  43  29  43  31 /  70  10  20  20  40  60
Colville       38  20  38  20  37  18 / 100  40  30  20  50  50
Sandpoint      35  23  35  23  34  22 / 100  40  60  50  80  60
Kellogg        35  23  35  23  35  24 / 100  20  50  50  80  60
Moses Lake     43  25  43  26  42  27 /  60   0  10   0  30  40
Wenatchee      40  24  39  25  39  26 /  70   0  10  10  30  40
Omak           41  23  40  24  40  23 /  90  10  10  10  30  40

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Winter Weather Advisory until 3 PM PST this afternoon for
     Central Panhandle Mountains-Northern Panhandle.

WA...Winter Weather Advisory until 3 PM PST this afternoon for
     Northeast Mountains-Okanogan Highlands.

     Winter Weather Advisory until 11 AM PST Sunday for Okanogan
     Valley-Waterville Plateau-Wenatchee Area.

&&

$$


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