the next Polar Vortex might not be so nice

Judah Rose has an article which provides a nice summary of issues causing concerns about adequate electricity supply in winter.

Waiting for the Next Polar Vortex | Fortnightly

...the disturbances of the Polar Vortex might become the new normal in coming winters.
What the Polar Vortex brought to light is that we have had a distorted view of system capacity due to market rules and regulatory assumptions from the U.S. Federal Energy Regulatory Commission (FERC) that have failed to properly value (or consider) reliability. In spite of several FERC decisions since the Polar Vortex to correct these problems, five on-going trends belie assumptions that the grid has sufficient capacity to meet winter peak demands without emergency actions. These trends belie the ability of grid operators to respond to severe winter weather events and thereby raise overall market risks and price volatility:

• Coal Plants. Continuing retirements...
• Natural Gas Delivery. Most gas-fired power plants in deregulated markets lack long-term firm gas supplies...
• Back-up Fuel Requirements. Not defined, even for gas-fueled power plants receiving capacity payments...
• Demand Response. Overly optimistic expectations for winter capacity contributions from interruptible load programs, and 
• Renewables. Overly optimistic expectations for winter capacity contributions from renewable generation.

That's a good enough list to tempt me to buy a subscription to read Rose's entire Waiting for the Next Polar Vortex

I assume he will note the natural gas infrastructure can't handle providing more supply in winter in a number of jurisdictions.

Ontario is one of those jurisdictions. I had a concern with this during the past winter - and then I had a larger concern the system operator was blissfully unaware of the issue.

Ontario has shut its coal plants; for all the bad of coal, one big good was that fuel inventory was on site. This may be true of bunker oil at Lennox, but that's really not an improvement over coal at Lambton. If Ontario is to heat buildings and water while using natural gas to generate electricity too, it's not clear Ontario has the storage capacity to sustain those tasks during cold winters.

As for renewables, the expectations can always be too optimistic, at any time of year.
The IESO has a formula for calculating "Forecast Capability at Winter Peak" that produces average production, and not reliable production. Usually 20% of daily winter peak demand periods are far below the IESO's "Forecast Capability", but in 2014 three of the four daily demand peak hours had supply below the IESO's 576MW forecast - 2 of those far below:

• January 22, wind 267MW at peak
• January 21, wind 152MW at peak
• January 23, wind 427MW at peak

Each day the peak was from 6-7pm, when solar production must surely have been 0.

Ontario currently has approximately 4000MW of wind and solar capacity.