Powerful Pacific Gale or Wimpy Winds?

Past, Present, and future track of Ana.

Past, Present, and future track of Ana.

Yesterday, Tropical Storm Ana finally completed a transition to an extra-tropical cyclone and has now reached peak intensity as a low off the coast of British Columbia. For the past two weeks Ana has carved a path through the Central Pacific Basin that few tropical systems have done  truly remarkable.

Current location of the Pacific low (7:30 AM PDT) with the warm front impacting the coast this afternoon/evening

Current location of the Pacific low (7:30 AM PDT) with the warm front impacting the coast this afternoon/evening

Impacts

One of the most prominent features of these Pacific low pressure system is the tight pressure gradient that accompanies them and trademark SE wind. Meteorologists will often look at pressure gradients to gauge the strength of probable wind velocities 

  • Typically along the coast a pressure difference of 4-6 mb/100 km can give solid gale conditions
  • When the pressure difference approaches 6-10 mb/100 km we start to run into problems (widespread power outages, ferry cancellations etc.). 
  • Highest recorded pressure gradient along the coast was a mind-numbing 18.3 mb/100 km, which occurred on March 12, 2012, which paralyzed the coast with sustained winds approaching hurricane strength

So where do we stand? 

Time-height diagram also reveals gale conditions for several hours this evening and through the overnight for eastern Vancouver Island. 

Time-height diagram also reveals gale conditions for several hours this evening and through the overnight for eastern Vancouver Island. 

  • Doing a very rough calculation, it's approximately 200 km from Port Hardy to Comox, BC, and consulting the most recent MM5-NAM model below there's approximately an 8 mb temperature gradient between YQQ and YZT or 4 mb/100 km. The time-height diagram to the right also reaffirms the strong winds tonight
  • Expect peak wind speeds in the 50-70 km/hr range with higher gusts always possible for northern portions of Georgia Strait

Count the Rings

The tightest pressure gradients are where the lines (isobars) are closest together, which is very likely to occur late this evening

The tightest pressure gradients are where the lines (isobars) are closest together, which is very likely to occur late this evening

The National Weather Service also provides a very high resolution cutting edge forecasting model (HRRR) that also supports gales in Georgia Strait this evening as the main precipitation shield pushes through. Victoria is also likely to see gusty SE winds late this evening which may require a wind warning as well, but confidence a little lower.

Wind speed in knots for 10 PM PDT, close to peak wind values for the system

Wind speed in knots for 10 PM PDT, close to peak wind values for the system

Painted in Yellow? Gusty winds are on your horizon:

Yellow shaded areas indicates the areas that will most likely see gale conditions overnight; consequently, they are at the highest risk of seeing isolated power outages out of ex-Ana 

Yellow shaded areas indicates the areas that will most likely see gale conditions overnight; consequently, they are at the highest risk of seeing isolated power outages out of ex-Ana 

GFS freezing level for Whistler, BC for the next 5 days (120 hours)

GFS freezing level for Whistler, BC for the next 5 days (120 hours)

Did I mention the impending snowfall yet?

Snow levels are likely to be abnormally low tonight, but a sharp rise is forecasted for Tuesday that will turn the heavy wet snow to rain showers and a distant memory. Hang on skiers, we're in for a bit of a rough, bumpy ride into Winter, but I have medium confidence ski hills will be able to open on time or even a bit early! 

Historical 850 temps (~1500 metre temperatures), showing that currently temperatures are in the 25th percentile -- Great for snow lovers, but it will be short lived unfortunately

Historical 850 temps (~1500 metre temperatures), showing that currently temperatures are in the 25th percentile -- Great for snow lovers, but it will be short lived unfortunately