SIGNIFICANT BC STORM: March 9th-10th

It’s happening.

Intense pressure drops are already being recorded west of Oregon Wednesday morning. A classic wind storm is on the way for parts of British Columbia.

Take a look:

The purples off the western fringes of North America signify pressure drops in excess of 1mb/hr. This will continue to intensify throughout the afternoon.

Before I go any further, let’s briefly analyze the past before diving into the future.

The upper air pattern over the past 48 hours represents a major meridional pattern. A meridional jet stream often means active weather for the British Columbia coast.

The map below is very bizarre in terms of having such an anomalous  powerful upper low over Mexico. The NWS for Portland has recently confirmed that the jet streak (region of fast moving air) over parts of Portland was likely the strongest recorded for that particular station.

 


The calm region above the jet stream above is a NE Pacific trough which has been hampering the region over the past several days and will suppress the storm track towards Vancouver Island and Haida Gwaii as it slowly digs SE over the next 36 hours

How can a system go from a weak open wave of low pressure to a damaging low pressure system?

Picture this: an innocuous trough and bundle of upper level vorticity (lift and instability) is harmlessly drifting west.

This is the barrel of gas.

A super-charged jet stream can be described as a lit match just waiting to fuel any disturbance that interacts with the powerful upper level winds; consequently, providing the divergence aloft and necessary ingredients  to create a powerful low pressure system.

Boom. Explosive cyclogenesis is likely.

Below, a map early Wednesday morning showing the main parent low in the Gulf of Alaska and our benign open wave of low pressure  

To this roughly 24 hours later:

 

A formidable low west of Solander Island off the NW tip of Vancouver Island early Thursday AM—perhaps approaching 960 mb of atmospheric pressure by early tomorrow AM. Climatology says lows really can’t get fall below 960 mb in this part of the world:

Map above shows the approximate return interval for a storm of this magnitude for Southern B.C with about a 1 in 10 year occurrence for NW tip of the Island, but more frequent lower pressures for the Lower Mainland.

TIMING: Use The Weather Network app to look at hourly forecasts in terms of precipitation intensity and wind gusts but a general foreseeable weather threats go something like this:

WINDS

Strong SE winds pick up this afternoon and persist into the evening. Highlighted regions (with the exclamation mark) below where gusts 70-90 km/h may be possible.

A wider crop encompassing all of Vancouver Island lies below.

Comox & Campbell River, this particular model showing SUSTAINED winds of 45 knots, so local gusts to hurricane force through Thursday AM cannot be ruled out especially for this region, but models have some disagreement here.

Notice the storm force region NW of Johnstone Strait?

It’s the only red on the map below. I’ll give a friendly heads up to Port Hardy and Port McNeill to prepare for outages. Tofino has a high confidence to see very strong winds, but Port Alberni is a little more complex and complicated.

By 6-8 am local time the strong associated cold/occluded front races ashore—this puts the Lower Mainland at greatest risk for power outages early tomorrow morning. The part of the storm we have to pay particular close attention to houses the highest pressure gradients—or the back-bent occlusion/ trough that wraps itself around the low pressure system. In rare cases, this can form the ‘poisonous tail of the back-bent occlusion,’ or also simply referred to as a sting jet.

Exposed coastal sections look for winds 60-80 km/h through early tomorrow morning, with some gusts locally higher. Gusts inland may exceed 70+ km/h even into parts of the Fraser Valley such as Abbotsford and Metro Vancouver as well. Our Canadian model below highlights strong southerly winds sustained at 40+ km/h for much of the Lower Mainland:

RAIN

·        Heaviest rain includes the mountainous regions of Vancouver Island and Coastal Mountains including North Shore and Squamish—watch the Comox Valley for localized flooding with high tide tomorrow AM. A boil water advisory is in effect for this region due to recent heavy rainfall and increased levels of turbidity (cloudiness of water).

·        24 hour rain totals for some parts of Vancouver Island will approach 100 mm (see below)

 

·        Yes, this is an atmospheric river stemming from Hawaii, so a Pineapple Express term could be used without hesitation. The yellow area below signals where the moisture river is originating from.

 

COASTAL FLOODING/HIGH SURF

·        BC Storm Surge Forecast Centre shows potential for localized flooding in the yellow regions as the vigorous low pressure system is coinciding with an early Thursday AM high tide at roughly 6am local time. The expected surge plus high tide to be about 50 cm below some extremes recorded, but high enough to toss driftwood into local parks and highways immediately adjacent to Georgia Strait. With that said, drive with caution early tomorrow morning.


MOUNTAIN SNOW

·        Fresh pow alert. We’ll see a spike in freezing levels late this afternoon through pre-dawn Thursday, but primarily a snow event for most ski hills.

·        Look, you won’t believe these 24 snow totals:

 

 

Mt. Washington: 50-80 cm above 1200 metres. Offchance, some highest slopes record 100 cm with this single event on Vancouver Island

Whister: 30-50 cm above 1600 metres

Grouse/Cypress/Seymour: lower snow totals with rain mixing in Thursday: Locally, up to 10-20 cm possible at highest elevations, but rain will hamper totals

Live Blog will be active through tomorrow for BC as this is anticipated to be one of the more impactful winter storms this season.

Stay safe and send photos, videos and tag @weathernetwork and #BCstorm in your tweets.