A new offshore area of low pressure will produce moist, southwesterly flow over the entirety of the Coast Mountains south of Terrace. 

Due to the onslaught of pacific moisture, moderate to heavy flurries will begin this morning and persist over the weekend. Flurries will be distributed over various areas with southwestern-facing slopes closer to the ocean receiving the heavier amounts.  By end of the day, snowfall accumulation will be 5 to 10 cm locally 15 cm. South Coast inland could see trace up to 5 cm by this afternoon as it's furthest away from the low. Freezing levels will remain below elevations of interest. Moderate southerly ridgetop winds up to 40 km/h over the Insular ranges and 30 km/h over the north shore and Sea-to-Sky.

The northern Coast Mountains will only see trace amounts of snow today. Moderate (20 to 40 km/h) easterly alpine winds over NW coastal ranges with outflow through mainland inlets and valleys slightly stronger due to channelling.

This morning, unsettled conditions are expected with a chance of flurries across all interior ranges. Higher probability of flurries near Kootenay Pass and along the Selkirk ranges (2 to 4 cm by end of the day).  Freezing levels near valley bottom this morning. Ridgetop winds are generally light southwesterly except strong and persistent easterly winds continuing to blow through Pine Pass, resulting in light snowfall east of the pass. Alpine temperatures will hover between -15°C to -20°C across the North Rockies and -10°C to -15°C further south.

The ridge of high pressure remains over the Yukon giving northeasterly winds of 30 km/h gusting to 50. The air mass will be drying out but there is still a slight risk of a few flurries lingering Saturday morning near White Pass. Alpine temperatures near -18C.

Mainly cloudy skies with scattered flurries. More widespread flurries are expected in the afternoon with a trace to 2 cm of snowfall accumulation.

Very light westerly ridgetop winds below 15 km/h from Jasper National Park (JNP) through Kananaskis Country (KC) will increase in the afternoon to near 20 km/h from the southwest. From Waterton Lakes National Park (WLNP) to Highwood Pass, west-northwest winds will be 20-25 km/h. In Kakwa, southeast winds near 20 km/h will prevail. Alpine temperatures between -15⁰C and -20⁰C.

Forecast for this afternoon at 4 p.m. PST

Surprise surprise. The offshore low will remain stationary and continue to push onshore moisture to the south coast. The catch is heavier bands of precipitation should push more toward the Sea-to-Sky and Insular ranges as the low becomes more organized. The snowfall accumulation over the Insular ranges will be highly variable and dependent on the precipitation rate due to the unstable atmosphere. Current forecast guidance suggests the potential for 5 to 10 cm locally 15 cm over the Sea-to-Sky with the Insular ranges expecting 5 to 15 cm with up to 20 cm by Sunday morning if there is a prolonged line of flurries occurring over the same area. Freezing levels will hover near 700 to 1000 metres this afternoon but fall overnight. Moderate-strong southerly ridgetop winds over the Insular ranges and moderate southerlies over the north shore mountains for this evening and tonight.

The northern Coast Mountains will only see trace amounts of snow today and tonight. Moderate easterly alpine winds (20 to 40 km/h) over NW coastal ranges with outflow through mainland inlets and valleys slightly stronger due to channelling.

Minimal change from the morning period. Light snow east of Pine Pass due to orographic forcings. Further south, scattered flurries are likely to persist from the Cariboos down to the border. Accumulation will be minimal, with areas of prolonged flurries bringing a few centimetres by Sunday morning. Freezing levels will rise to 800-1000 m for the K-B ranges, southern Columbia, and the southern Purcells. Winds along the North Rockies will slightly ease as winds veer southerly this evening and reach up to 30 km/h tonight. Moderate southerly winds along western-facing slopes of the Cariboos will also develop this evening and continue into the overnight periods. Alpine temperatures will rise to -15°C across the North Rockies and -10°C everywhere south.

Clear skies. Northeasterly winds of 30 km/h gusting to 50. Alpine low near -22C.

Mainly cloudy conditions persist with scattered flurries and a trace to 2 cm of snowfall accumulation. From KC through WLNP, breaks of clear skies are possible overnight.

West-southwest ridgetop winds south of Kakwa near 20 km/h. Areas near Yoho will see winds peak near 30 km/h near midnight. In Kakwa, southeast winds at 15-20 km/h will shift to south-southwest near 20 km/h by midnight. Alpine temperatures between -10⁰C and -15⁰C.

Forecast for Sunday morning at 5 p.m. PDT

On Sunday, an offshore area of low pressure will continue to produce a moist, southwesterly flow for most of the Coast Mountains south of Terrace. The Insular ranges and mountains northwest of Squamish should bear the brunt of the snowfall with freezing levels idling between 500 to 700 metres. Current forecast guidance suggests the potential for 2 to 8 cm locally 10 over the Sea-to-Sky with the Insular ranges expecting 5 to 10 cm with up to 15 cm by Sunday afternoon along northwest sections if a prolonged line of flurries occurs over the same area. Strong southerly ridgetop winds 30 to 50 km/h over the Insular ranges and moderate southerlies over the north shore mountains today. 

The northwest coastal ranges could see a few cm of snowfall today. Moderate (20 to 40 km/h) easterly alpine winds easing in the afternoon with outflow through mainland inlets and valleys slightly stronger due to channelling effects.

"Weak" upper ridging will not hold back isolated flurries from continuing today. Over the North Rockies periods of light snow will continue with alpine winds switching to light southeasterly in the morning. Trace to 2 cm forecasted by end of day. Further south, partly cloudy conditions with isolated flurries today as heavier precipitation from the coast continues its march towards the interior. Flurries from Cariboo range down to the US could spill a trace to 2 cm of snowfall by end of the day, primarily over the Northern Monashees and Selkirks. Light alpine winds except for moderate southerlies up to 30 km/h over the Cariboo Mountains.  Alpine temperatures will hover near -10°C.

Clear skies persist, but the ridge of high pressure over central Yukon weakens. Northeasterly winds of 20 km/h gusting to 40 diminish to light easterlies late in the day. Alpine highs near -17C.

A mix of sun and cloud with scattered flurries. Flurries will be most widespread Yoho and northwards, where a trace to 2 cm of accumulation is expected.

Ridgetop winds will be southwesterly (except southerly in Kakwa) near 20 km/h and strengthen to near 30 km/h by the afternoon. Freezing levels will remain at valley bottom, except south of Crowsnest Pass where levels will rise to near 1500 m. Alpine temperatures between -10⁰C and -15⁰C.

Forecast for Sunday afternoon at 5 p.m. PDT

 A new upper low forming over the Gulf of Alaska will develop Sunday evening and push our aforementioned upper low towards the BC coast. This means the south coast inland ranges will see a ramp up in precipitation Sunday night. Freezing levels will rise slightly above 1000 m on Sunday near the coast. Precipitation will be accompanied with strong southerly or southeasterly winds developing overnight. Subtle hints of extreme alpine winds over the north shore after midnight (confidence low). Regarding precipitation, high levels of water equivalent will be directed toward the north shore and Sea-to-Sky mountains primarily initiating after midnight.

The northwest coastal ranges could see a few cm of snowfall today. Wind light.

On Sunday, bands of precipitation from the coast continue their inland march. Timing and intensity are difficult to forecast at this time. However, the likeliest outcome will be scattered/occasional flurries Sunday day with after midnight looking like the favourable start for higher amounts.  Freezing levels will also rise with the sub-tropical airmass ushering warmer air, with the K-B and southern ranges reaching up to 1500 m by afternoon. Moderate southerly winds along the K-B and Monashee ranges becoming strong Sunday night. Keep an eye out for extreme thresholds developing along the K-B alpine before Monday morning. Alpine temperatures will rise to -5°C to -10°C everywhere south of the North Rockies in the afternoon.

Mainly clear skies with some cloudy periods late overnight. Light northeast winds. Alpine low near -23C.

Mainly cloudy conditions, with flurries north of Crowsnest Pass. South of the Pass, periods of clear skies are likely. Widespread snow will begin late overnight as a low pressure system approaches the British Columbia interior. Upwards of 5 cm of snowfall accumulation, locally, in Yoho and Jasper National Park (JNP). Elsewhere, expect near 2 cm.

South-southwest ridgetop winds near 30 km/h in JNP and Kakwa. Otherwise, southwest winds near 30 km/h will increase to near 40 km/h in Banff National Park and Kananaskis Country by midnight. From Waterton Lakes National Park to Highwood Pass, southwest winds near 30 km/h will increase to near 50 km/h overnight. Freezing levels will fall to valley bottom south of Highwood Pass, and remain at valley bottom elsewhere. Alpine temperatures between -10⁰C and -15⁰C.

On Monday, heavy precipitation over the island will temporarily subside Monday afternoon/evening as the upper trough moves further inland. However, moderate to heavy precipitation will continue over the mainland south coast ranges before temporarily easing Monday night into Tuesday morning. Freezing levels should rise to 1000 - 1500 metres by the afternoon. Strong southwesterly winds funnelling through the Fraser Valley Monday and likely reaching extreme thresholds in the morning for associated ranges. 

On Tuesday, another coastal low will slide towards the island bringing snow at times heavy to the south coast ranges, with freezing levels falling below our lowest elevation of interest Tuesday morning and rising to ~800 m by the afternoon. The onslaught of snow will persist until Wednesday morning. Moderate-strong southwesterly winds associated with this next system should also impact the Insular ranges. 

On Monday, expect little change from Sunday night with precipitation crashing over the interior. Strong southerly winds look likely to develop Monday morning from the Monashees east to the Lizard ranges. Early indications suggest freezing levels reaching 1500 - 2000 m Monday afternoon for the Monashee, Selkirk, and Purcell ranges (confidence medium-high). Due to the high precipitable water in the atmosphere, precipitation from this event will be high and should bear monitoring as we progress closer to the event.

On Tuesday, heavy precipitation associated with the back edge of lee cyclogenesis (i.e. fancy way of saying a surface low forming over Alberta) will result in continued heavy precipitation for areas south of the Cariboo Mountains down the US border. By the evening period, the coastal low will push our moisture plume out of the Cariboo Mountains and primarily over the AB-BC border.

On Monday a new low drops out of Alaska and heads for the waters west of Haida Gwaii. The combination of the passing low and an area of high pressure over the Arctic will reinvigorate the pressure gradient over White Pass. Northeasterly winds will once again return with speeds near 30 km/h. Moisture coming from central BC will bring cloudy skies and a chance of light snow but amounts will be negligible. Alpine high near -15C.

On Tuesday, a surface trough lies southwest of the Yukon keeping a surface outflow pressure gradient in place. Expect mainly cloudy but dry conditions. There’s a chance of snow late in the day as the upper flow strengthens from the southwest. Snowfall amounts look light. Alpine winds are light northerlies becoming southerly 30 km/h in the evening. Alpine high near -15C.

On Monday, cloudy and snowy conditions will persist through the day as a low pressure system continues its trek through central British Columbia. The heaviest snow will fall over higher elevations along west-facing slopes from Banff National Park northwards. 10 to 20 cm seems reasonable along west-facing slopes, with upwards of 10 cm elsewhere throughout the Range. Over lower elevations, wet snow or rain is likely with freezing levels set to rise to 2000 m south of JNP, and approaching 1400 m in Jasper National Park itself. Freezing levels in Kakwa look to remain at valley bottom. Overnight into Tuesday, freezing levels will fall to near 1700 m south of Highwood Pass and fall to or remain at valley bottom elsewhere. Southwest winds at ridgetop will be strong to extreme, except moderate south-southeast in Kakwa. Alpine temperatures -5⁰C to -10⁰C, except falling to near -15⁰C overnight in Kakwa.

On Tuesday, a low pressure system will develop in lee of the Rockies with snow continuing under cloudy skies. The heaviest snow looks to end in the morning as the cold front associated with this low pressure system moves south through the Range. As the front and low pressure system move away, a strengthening ridge of high pressure will settle over central Alberta. Flurries are likely to continue behind the main area of snow with residual unstable atmospheric conditions. Upwards of an additional 5 cm of snowfall accumulation is possible. West-southwest ridgetop winds will weaken to moderate to strong in the morning, and weaken further to light or moderate overnight into Wednesday. Freezing levels will remain at valley bottom, except fall from near 1700 m south of Highwood Pass to 1300 m in the afternoon. Freezing levels will fall to or remain at valley bottom by the evening. Alpine temperatures will fall to between -10⁰C and -15⁰C.

There remains considerable uncertainty on the track of these two low pressure systems, especially over Alberta. Snowfall timing and amounts are subject to change.

Atmospheric River En Route

Ken D, Mike G, and Paul S

An offshore low drops down to Haida Gwaii, placing its roots down and becoming stationary for the weekend. Onshore flow will begin this morning resulting in flurries over the south coast ranges. Hot spots will be over western-facing slopes of the Insular ranges and the Sea-To-Sky.

Sunday night into Monday is when the interior gets concerning. The coastal low will steer sub-tropical air towards the BC interior resulting in very high precipitation and strong winds until likely Tuesday afternoon/evening. Along south coast, anticipate little/no breaks between the persistent onshore flow and the sub-tropical push Sunday evening/night. This atmospheric push will bring very high precipitation and rising freezing levels so mixed precipitation in the form of rain or snow can be expected along higher terrain for end of the weekend into early next week.

The 500 mb animation depicted above shows a stagnant upper low southwest of Haida Gwaii. This feature will produce a moist, southwesterly flow over Vancouver Island and the southern Coast Mountains this weekend. Further inland, isolated/scattered flurries for parts of the interior with a weak upper ridge blocking the heavier bands of coastal precipitation from invading. If we progress the animation we notice a trough line to the Pacific lows west develop and begin to dig southwards into Sunday. This will cause the sub-tropical airmass previously invading California with heavy precipitation and convection to reorientate its path. Therefore a moisture plume with higher thicknesses (540 dm on the blue dashed line representing warmer air) will crash into the south coast Sunday afternoon/evening through Washington state, then the interior Sunday night/Monday morning. 

Looking into early next week, as the trough line along the BC coast continues to usher in sub-tropical air, precipitation will stretch from the US border up to the North Rockies before easing Tuesday afternoon/evening over the interior. The south coast however should get hit with another system originating from the Gulf of Alaska Tuesday day.