Get to know the Colorado Low.

Wednesday November 30, 2022

Forecast wind gusts at 3 am Thursday. The blocking high south of the Avalon is expected to steer the Colorado Low up to James Bay.

 

In Canada, our winter storm systems don’t carry “given” names, but systems that are commonly found in certain regions are often named for their area of origin.

The wind and rain that might keep you awake tonight are compliments of a Colorado Low; an area of lower pressure that develops in the vicinity of Colorado on the eastern side of the Rocky Mountains. This type of storm system keeps forecasters on their toes from the Southern Plains, across the Upper Midwest, the New England States and right here in Atlantic Canada. From heavy snow and torrential rains to supercell family outbreaks and strong winds, this type of storm system has it all.

Typically, an extensive band of moisture tracks well in advance of the low’s centre.  It stretches north-eastward toward the Great Lakes. 

Rain or snow?

The track of the storm will dictate the type of precipitation. Depending on the location of the Bermuda High or other blocking areas of high pressure to the east, a Colorado low can be steered northward towards James Bay or track right across the Maritimes then on to Newfoundland.  If upper-level conditions are right, the jet stream can push the low farther south, bringing wintry precipitation as far south as Texas.

Right now:

There is a large area of high pressure off the Nova Scotia coast. That means this approaching Colorado Low won’t be able to track from west to east. Instead, it will pull northward extending a warm front and then a cold front across our region.  

Temperature profile

Today’s strengthening south wind will bring warm air into the region well into the night.  Temperatures are expected to climb from 10° to 12° overnight to Thursday morning.; they will fall back in the cooler west wind in the wake of the system on Thursday.

Rain:

Rainfall totals are not expected to be excessive this time, anywhere from 30 to 40 mm. However, the rain will fall in a relatively short period of time so watch for water pooling on the roads.

Snow?

Temperatures will tumble in the wake of the system, but I don’t think there will be much moisture around by the time it’s cold enough for snow.  Having said that, the cooler, drier west winds will trigger onshore snow along west-facing coastlines on Thursday.  Watch for those if you’re travelling.

Winds:

During the intensification stage also known as cyclogenesis, a pressure difference between highs and lows creates a difference in air density. In an attempt for the atmosphere to attain equilibrium, an increase in pressure gradient force is achieved. Strong southerly winds ahead of Colorado Lows often gust to 80 and even 100 km/h. The winds behind the low drop off quickly with a shift to the west.

The strongest winds will be overnight tonight- midnight or so over western regions and sunrise to late morning in the east on Thursday.  They’ll blow from the SE to the S at 60 km/h with gusts to 80 or 90 km/h, especially along south-facing coastlines.  A Suêtes wind warning is in effect for Thursday morning with gusts as high as 130 km/h.

Plan for possible power outages but hope for the best and be safe!