BC: The low pressure centre has reformed over the northern Rocky ranges and is beginning to weaken a little. From the low, a cold front extends down towards Vancouver Island.  Behind the cold front the atmosphere is moist and unstable.  Freezing levels have fallen to approximately 300 to 600 metres. Precipitation rates are light to moderate at one to two mm per hour.  Mountain top winds behind the cold front are westerly 30 to 50 km/h.

Along and ahead of the front a dramatic transition is taking place.  Precipitation rates are moderate at 2 to 3 mm per hour.  In favourable, upslope locations the rates approach 4 to 5 mm per hour.  Freezing levels are sitting at approximately 1000 metres and will fall through the morning and into the afternoon as the frontal system passes further towards the Purcells and Lizard ranges.  

White Pass: Light flurry activity. No significant accumulations are expected any longer.  Northeasterly winds 30 gusting to 50 km/h.

AB Rockies: A low pressure system forming this morning in central Alberta is forecast to have a westward trailing cold front and associated snow across Kakwa and Jasper National Park (JNP). The cold front and associated snow will move southward today, reaching the South Rockies region during the late afternoon hours. Generally, 5-10 cm of new snow is forecast for regions north of Lake Louise. This front will also usher in an unstable air mass, meaning an isolated thunderstorm is possible late in the afternoon for the same area. West-facing slopes across JNP and Banff National Park (BNP) may see up to 15 cm of snowfall under localized heavier/slower moving convective bands of snow. 

A strong southwesterly flow at ridgetop will exist ahead of the cold front, with winds to 80-100 km/h between Kananaskis and the American border. Westerly wind gusts in valley passes reaching 80-90 km/h are to be expected during this time as well. For regions north of Kananaskis, southwesterly ridgetop winds to 40-60 km/h are forecast, except for Kakwa, where winds will turn northwesterly and decrease to 30 km/h this afternoon behind the cold front.

Freezing levels will rise to 1400 metres in Kakwa and 1800 metres in JNP before falling back to valley bottom early this evening behind the cold front. South of the cold front, freezing levels will rise to 2000 to 2200 metres between BNP and Kananaskis, and 2300 to 2400 metres between the South Rockies and Waterton Lakes National Park (WLNP).

BC: By this afternoon you can see the low pressure centre has moved past the Rocky Mountains and has reformed near Lloydminster. A cold front continues to trail back towards the Lizard-Flathead ranges.  It's moved rather quickly through the day.  At this point, all of BC is under a very cool and unsettled airmass.  Freezing levels have settled at 800 m along the south coast ranges, and approximately 1300 metres over the Kootenay-Boundary and Columbia ranges. 

Precipitation has eased significantly, and only light snow is expected at this time in the alpine. Mountain top winds maintain their south-southwesterly direction at 40 to 60 km/h. Across the northern ranges mountain top winds are lighter, just 30 km/h from the west.

Behind this frontal system a new ridge of high pressure has built in and through tonight will move into northern BC, clearing and drying conditions out. 

White Pass: Cloudy with no probability of flurries.  Wind continuing out of the northeast, but has eased to 20 km/h.

AB Rockies: The cold front located near the South Rockies region, will continue its march south, reaching the American border late this evening.  Behind the cold front, an unstable air mass will allow periods of snow to continue across all regions of the Rockies, except for Kakwa, where snow will end early this evening. For JNP and regions southward to the American border, 5-10 cm of snow is possible by Thursday morning. However, west-facing slopes under localized heavier/slower moving convective bands of snow may see up to 15 cm of snowfall overnight. Any risk of an isolated thunderstorm across the Rockies ends early this evening. 

Southwesterly ridgetop winds to 40-60 km/h from JNP to Kananaskis will change to the same winds as Kakwa, by decreasing and shifting northwesterly to 20-30 km/h this evening, as the cold front passes. South of Kananaskis, southwesterly ridgetop winds to 90 km/h will decrease and shift westerly to 50-70 km/h overnight behind the cold front. Westerly wind gusts in valley passes to 80-90 km/h for the South Rockies and WLNP regions will become 50-70 km/h overnight.

Freezing levels fall to valley bottom behind the cold front.

BC: Thursday will prove to be a bit of a "transition" day.  We see the remnants of the cold front well out of our region now, draped over Montana and Oregan.  However, over southern ranges there continues to be enough remnant instability to bring light flurry activity to the alpine. Freezing levels are sitting at between 500 to 1000 m. Mountain top winds remain strong out of the west at 40 to 60 km/h.  Those winds will ease by later Thursday morning and into the early afternoon.

Across the northwest ranges we see our default ridge building in.  Conditions are mainly clear and mostly dry.  It's not a true, stable, dominant ridge, merely one that there between systems and will give a brief reprieve from the moisture onslaught. 

Over the Gulf of Alaska we see our next weather system ramping up and strengthening.  Through Thursday morning it will head initially to the Alaskan Panhandle and will gradually slide into the north coastal regions. As the low deepens, the pressure gradient tightens and we'll begin to see mountain top winds increase to southwest 30 to 50 km/h later Thursday morning. 

White Pass: Becoming mostly cloudy leading up to daybreak.  Light snow is beginning to develop as the next system begins exerting its influence on the region.  Through the morning the snow will pick up and approximately 5 cm accumulation can be expected by early Thursday afternoon. Winds relatively light at this time.

AB Rockies: An upper trough will pass through the Alberta Rockies Thursday producing periods of snow during the day between Banff National Park (BNP) and Waterton Lakes National Park (WLNP). Trace accumulations of snow is forecast from BNP to Kananaskis, with 5-10 cm possible in the South Rockies and WLNP regions. Elsewhere, Kakwa and Jasper National Park (JNP) will see a mix of sun and cloud on Thursday.

Westerly ridgetop winds to 20-40 km/h across the Alberta Rockies are forecast, except for the South Rockies and WLNP regions, where southwesterly ridgetop winds to 50-70 km/h will decrease to westerly 20-40 km/h during the morning hours. Wind gusts through valley gap to 50-70 km/h will diminish to light Thursday morning in the South Rockies and WLNP regions.

Freezing levels will rise Thursday afternoon across the Alberta Rockies to 1400 to 1600 metres.

BC: The ridge of high pressure that had been over the northwest ranges has moved south to sit over Vancouver Island and stretch to the south Columbia range. This has brought a brief respite from moisture for the time, although the ridge is being aggressively pushed into Washington State by Thursday evening. 

A deepening low pressure centre remains near the Alaskan Panhandle.  The main frontal wave is rapidly moving down the BC coast with a trowel extending north towards the parent low. Along this trough one can expect moderate snowfall of 3 to 4 mm moisture equivalent per hour. The mountain top winds are quite strong, clocking in at 60 to 80 km/h from the southwest. Freezing levels are at approximately 800 metres.

By Thursday night and into Friday morning, the frontal system will have made its way into the south coast ranges, spreading moderate rates of precipitation with mountain top winds picking up to moderate strength from the southwest as well.

White Pass: Moderate to heavy snowfall now occurring. Winds at this time remain relatively light, now out of the northeast. From 5pm Thursday through to early Friday morning, snowfall accumulations of 10 to 15 cm are expected.

AB Rockies: As the upper trough supporting the snow departs the Rockies Thursday evening, snow will end from north to south. As such, skies will turn partly cloudy early in the evening for BNP and late in the evening for WLNP. Any respite is brief however, as the frontal system located in northern British Columbia will begin to approach Alberta, bringing increasing cloudiness overnight across the range and snow to Kakwa before morning. 

Thursday evening, southwesterly ridgetop winds to 40 km/h across the entire range will increase to 60-80 km/h overnight as the next frontal system approaches. 

Freezing levels fall quickly to valley bottom during the evening. 

BC: On Friday our next frontal system is primed and sitting along the coast, spreading moderate amounts of precipitation to northwest ranges.  Precipitation rates of 2 to 3 mm per hour can be expected early on and those heavier rates will spread down into southern coastal ranges later in the day as the system moves south. Strong southwesterly winds expected at mountain top. 

Overnight Friday and into early Saturday all BC ranges are left under a troughy weather pattern.  What this means is generally a northwesterly flow brining cooler and unsettled conditions with below average freezing levels for this time of year. 

On Saturday finally a reprieve in the cool, wet weather. We have offshore a ridge of high pressure beginning to build and poking into BC. This is acting to clear out the weather in BC and bring back drier conditions. 

White Pass: Period of snow on Friday as the frontal system comes onshore and passes through to the southeast.  Total snowfall accumulations for Friday range from 5 to 10 cm. Strong northerly winds expected. As we transition into Saturday, the frontal system is well out of the area, but unsettled northerly flow contributes for a few more centimetres of snow through the day and moderate northerly winds continue.

AB: A warm southwest flow returns to the Rockies on Friday morning with increasing ridgetop winds and bringing a brief rise in freezing levels. Freezing levels are expected to reach 1500-1700 m from Banff to Jasper and 2000 m from Kananaskis south on Friday. Cloudy conditions are expected with this flow along with light snow generally north and west of Kananaskis. Winds are expected to be strong through the day on Friday with extreme winds sustaining through the day in regions south of Kananaskis.

 As a lee low moves east in Alberta, a cold front will slide south along the Rockies, turning down the feed of moisture and the strong to extreme wind by Saturday morning. An unstable air mass sits over the area on Saturday again giving mainly cloudy conditions with light snow generally south of Jasper. Winds by end of day Saturday will fall for all regions to 20-30 km/h at ridgetop. Under a cool air mass, freezing levels Saturday will rebound slightly above valley bottom, but lower than on Friday. 

Just A Blip...

Dave Wray

Let's call today's weather system "just a blip".  Well, actually, it's a bit more than just that!  The frontal system currently traversing through the south coast has become a slight hiccup in the dry, warmer weather we've been enjoying for much of the past month.  A wet day today, will be followed by a mostly dry day on Thursday.  

By all reckoning this system today will give approximately 12 hours of moderate precipitation to the south coast area.  Nowhere near warning criteria is expected, however, alpine locations in favourable upslope areas could see upwards to 30 to 40 cm of snowfall accumulation before all is said and done.

A default ridge sets up for Thursday.  Let's call this a short-lived break, because right on its heels another frontal system affects coastal ranges once again on Friday.

A strong upper trough is digging in along the BC coast.  Through the day the trough will move over inland BC ranges. As the upper trough moves towards the Rocky Mountain ranges a weak upper ridge will begin to build in behind over the north coastal ranges. Through Thursday that upper ridge transits through BC very quickly, so that by later afternoon it is almost completely through. 

Right on the ridge's heels a new upper trough is building and gaining strength in the Gulf of Alaska.  This next trough will be the weather maker over northern ranges overnight Thursday and into Friday.