Weather Whiplash: Atmospheric Rivers to Arctic Outflow

GEM Global model indicating by the purple shades that in excess of 150 mm of rain is possible for North Shore mountains/eastern Fraser Valley. North Cascades in Washington State are also targeted for the deluge with flood watches issued in their respective jurisdiction 

GEM Global model indicating by the purple shades that in excess of 150 mm of rain is possible for North Shore mountains/eastern Fraser Valley. North Cascades in Washington State are also targeted for the deluge with flood watches issued in their respective jurisdiction 

Who's hurting?

Specifically, who's has a case of weather whiplash? This fall has been anything but ordinary, with long stretches of dreary rains.

Most recently though, we've been under the influence of an anomalously strong high pressure system with offshore flow -- now, just a distant memory. 

Where do we go from here?

Unfortunately, skiers won't like this. The dreaded atmospheric river is forming as we speak.

See the animation below... A modest atmospheric river is developing...

Latest Precipitable Water Satellite Imagery: Courtesy http://tropic.ssec.wisc.edu/real-time/mimic-tpw/epac/main.html

Latest Precipitable Water Satellite Imagery: Courtesy http://tropic.ssec.wisc.edu/real-time/mimic-tpw/epac/main.html

  • At the end of the animation, look at the amount of moisture becoming entrained in the flow as it travels north of the 30th parallel
    • This moisture has its sights set on the South Coast
    • Localized flooding is LIKELY for portions of western Vancouver Island, and the North Shore. Ponding on roads will be likely this week. 

See for yourself as we check out some model guidance to paint a better picture?

PWV - Copy.png

The area highlighted above in orange is definitely an anomaly. More specifically, an area of the atmosphere with high concentrations of water.

This SW flow will greatly reduce the snow pack for portions of the south coast, and will undoubtedly affect early season conditions and openings. 

First, I want to brush on the impending impacts for the ski hills. The next 72-96 hours will not be beneficial to all South Coast mountains including Whistler. Take a look at temperatures at the 850 mb level on the left for Thursday morning (+5C at around 1500 metres)

850 temperatures for Thursday morning

850 temperatures for Thursday morning

850 temperatures for Saturday morning (48 hours later)

850 temperatures for Saturday morning (48 hours later)

Freezing Level

Latest NAM run mirrors many other model runs and shows an unusually high amount of warm air advection for the South Coast (dry bulb, wet Bulb temperatures plotted below). And, just for clarification, the image below is not a heart beat record of a prospecitive skier or mountain resort owner...

Courtesy: Spotwx

Courtesy: Spotwx

 

  • By Tuesday evening, freezing levels will remain above all local ski hills until Friday AM, but after that,for the foreseeable future will fall below them, even locally to the surface. 
  • December temperatures will be below normal, and any precipitation that falls will be in the form of snow, I nearly guarantee it
  • This freezing level fluctuation will also work to destabilize the snow pack so avalanche risk will be going up

Rainfall Totals:

Yes, Squamish, it's quite possible you'll end up with an additional 20 cm of rainfall this week, with portions of the North Shore Mountains receiving over 20 cm.

Graphic indicated the heaviest rain is likely to fall during the day on Wednesday. Localized flooding is possible with such heavy rainfall amounts falling within 48 hours

Graphic indicated the heaviest rain is likely to fall during the day on Wednesday. Localized flooding is possible with such heavy rainfall amounts falling within 48 hours

We have to resort to ensembles to get an idea of the weather for next week, but models are trending cooler... the rest of this blog will be updated once the latest NAEFS have been processed later tonight..

Lowland snow possibility by weekend

Freezing level plummets by friday evening, but tough to say how much lingering precipitation with remain... the airmass will quickly be drying

freezing level.png

Do the ensembles agree?

HIgh confidence on the cool down, low confidence with the snow forecasts especially for the weekend... although some of you are likely to see your first snowflakes over the next 7 days!

2014112500_054@007_E1_yvr_I_NAEFS@EPSGRAMS_tt@surf@nt@pr@ws@surf_360.png

Later next week the snow pack will begin to rebuild in time for skiing by mid-December, or even earlier if some local ski-hills are lucky enough.

#50shadesofVan