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Currently windloaded aspects have slabs built up in upper ridgetop areas. Once you get off the ridgetops the snow becomes soft and loose where it is protected on the NE aspects. With the arctic front coming through the winds will be out of the NE and will slab up these aspects and add more snow with the winds. Watch for more slabbing to continue with the storm that is expected to bring 2-4 and 5-9 tonight.
National Weather Service Spokane WA 510 AM PDT Fri Mar 13 2020 .SYNOPSIS... Big weather changes arrive later today and last through the weekend with blustery north winds, snow, and very cold temperatures as an arctic front moves into the region. Poor travel conditons expected Friday evening into Saturday. The work week will start off dry and cold, but temperatures return to normal by mid week. && .DISCUSSION... ...MODERATE TO HEAVY SNOWFALL AND BLOWING SNOW EXPECTED ACROSS THE INLAND NORTHWEST Friday INTO SATURDAY WITH FRIDAY EVENING COMMUTE TO BE IMPACTED... Today through Saturday night: This morning, a deepening low pressure system dropping south from southern BC and then southeast across the Gulf of Alaska and further deepen as it pushes closer towards the Pacific Northwest. IR satellite imagery shows a deep moisture field ahead of the upper trough that is advancing southeast then extends east into the Inland Northwest. This system will exert its influence across the region into the weekend.
The most favorable dynamics aloft will advance in force with a deepening upper level low that will begin to exert its greatest influence by this evening and continue to provide the necessary combination of forcing and moisture flux across the region through Saturday morning. That said, we will see continued low and mid- level moistening across much of the northern half of the CWA with an accompanying increase in isentropic ascent across northeast Washington and the Northern Idaho Panhandle. As this plays out, a tightening of temperature and pressure gradients will signal the entrance of a strong arctic frontal boundary that increases a low- level easterly downslope flow off of the higher terrain across the northern zones. As the northeast winds ramp up across the basin, orographics will then play an increasing role with regards to snow production along the east slopes of the northern Cascades which will continue through overnight hours. These favorable dynamics aloft have the potential to overcome the drying affect of the downslope flow off of the Panhandle Mountains and further bring the best chances for snow further east across the basin tonight into Saturday morning. The Northerly winds will also increase today and peak overnight into Saturday morning. The combination of strong winds and fresh, relatively dry snow, will create the potential for patchy blowing snow especially in the northern Idaho. A transient low pressure circulation appearing as far down as 850 mbs in HIRes model guidance will linger over the basin Saturday morning but quickly fill during the subsequent afternoon. Snow will then decrease with time with less accumulations by the afternoon hours and surface convergence slows as well. Winds will continue to be breezy adding to the threat of blowing snow into the afternoon as cold Arctic air continues to filter down across the region. Temperatures will be much colder than average with highs only expected to top out in the mid 20s to lower 30s for many locations on Saturday. * Snow Amounts: Storm total of 3 to 5 inches of snow accumulation across the northern rim of the basin and into the mountains from the Cascades to the Northern Panhandle. Snow amounts will decrease further south across the basin into the Spokane/Coeur d`Alene corridor, Palouse and Central Panhandle Mountains with 1 to 3 inches expected. * Winds: Strongest wind gusts of 40 to 45 mph will be possible down the Purcell Trench with peak gusts occurring tonight into Saturday morning. The Okanogan Valley, Waterville Plateau and the basin will see wind gusts in the range of 35 to 45 mph. * Impacts: A wide variety of impacts are possible with this late winter storm with possible impacts to this evening commute. Snow amounts alone will not be as large a concern than the increasing winds ablating fresh dry snow over parts of the CWA. The basin should see at least a couple of inches of snow, and that Coupled with the increasing winds could raise concerns for reduced visibility due to patchy blowing snow. The areas at most risk will still be down the Purcell Trench and down the Okanogan Valley and onto the Waterville Plateau. The potential for near . Blizzard like conditions are possible for those areas. Moderate to heavy snow is still expected across the Okanogan Highlands and Northeast Mountains as well. A winter storm warning has been Issued for these areas as well. Much of the rest of the Inland Northwest is covered with a winter weather advisory. A wind advisory has also been issued to address the windy conditions over northern Idaho Panhandle that continues west and southwest into the Columbia Basin. * Wind Chills: Winds will be blustery with wind chills still expected To drop below zero across the Northern Panhandle both Saturday morning and again Sunday morning even though winds start winding down but ambient temperatures will remain mostly in the single digits. Single digit wind chills are possible down the Okanogan Valley and out across the basin through the weekend as well. /ayoung Saturday night through Sunday: With the passage of the arctic front, brisk northeast to north winds continue, especially from the Purcell Trench of north Idaho and across the Columbia Basin. Patchy blowing and drifting snow will be a concern mainly through Saturday evening. While the gustiness decreases late Saturday night into Sunday morning, daytime mixing will bring a return of the gusts for Sunday afternoon. Skies gradually clear Saturday night from the north as snow showers chances remain on the upslope side of the northern Blue mountains. Strong cold air advection and radiational cooling will lead to one of the coldest nights of the season, even more so where the winds are able to decouple. Many record low temperatures may be broken by Sunday morning. The track of the cutoff low looks slow to depart the region, and theres the potential of wrap around moisture with an embedded shortwave to brush southeast Washington Sunday. This would elevate the snow shower chances into the lower Columbia Basin and Palouse. Any additional snow amounts will be light given the drier air mass. Daytime temperatures are expected to rise above freezing in most areas. Monday through Thursday: The cutoff low continues to sink further south from Oregon into California, allowing a drier northerly flow to invade the region. Winds aloft become light as a col sets up over the region, while surface winds become light as well. Temperatures profiles gradually moderate and should experience warming each day. While daytime high return to normal by mid week, the dry airmass will yield to sub freezing overnight lows for much of the week. The low elevation snow pack will slowly erode. It will remain dry for Monday and Tuesday, although could see a return of patchy fog in the northern valleys. By mid week, the models show the cutoff low opening into an upper trough as it swings inland. Moisture creeps northward into southern Idaho and Oregon and could see the potential of afternoon convection developing as close as southeast Washington into the southern ID panhandle on Wednesday and Thursday. /rfox. &&
On Snowy Top in the Selkirks yesterday, Kevin and I found a mix of surface snow conditions ranging from crust at lower elevations, powder in the trees, sun affected snow on the solar aspects, soft snow on the flats and North aspects, and wind affected surfaces on exposed upper elevation terrain. You pretty much have to be on a hard North aspect to get some fresh snow conditions. There were some small failures in the storm snow from last weekend and earlier this week and then about 1.5 feet down there is a 1 inch thick subtle ice crust with facets on top where we had a clean shear with moderate results. This layer could wake up with any significant snow accumulation and could be triggered by new wind slabs forming on top and releasing, therefore causing enough disturbance to step down to this weaker faceted layer.
|0600 temperature:||22 deg. F.|
|Max. temperature in the last 24 hours:||30 deg. F.|
|Average wind direction during the last 24 hours:||SW|
|Average wind speed during the last 24 hours:||mph|
|Maximum wind gust in the last 24 hours:||mph|
|New snowfall in the last 24 hours:||0 inches|
|Total snow depth:||137 inches|
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