Most of Canada and US under warnings ahead of winter storm

Active winter storm warnings (pink) and winter storm watches (purple) issued by the National Weather Service

A significant amount of people will be impacted or is currently being impacted by the infamous winter storm that is moving northeast. More than 12 US states are under a winter storm warnings as of 8pm eastern time. More than 8 provinces have warnings and statements. Several states such as North Dakota, Minnesota and South Dakota are impacted by this storm in a different way, extreme cold.

Environment Canada watches/warnings as of 8pm eastern time

Most of Canada is also under either extreme cold warnings or under special weather statements. Parts of southern Ontario and Quebec are still under winter storm warnings.

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
256 PM EST Fri Jan 18 2019

Valid 00Z Sat Jan 19 2019 - 00Z Mon Jan 21 2019

...Major winter storm expected to move rapidly across the Midwest into the
Northeast this weekend...

...Severe weather and flash flooding are possible in the Southeast...

...Heavy rain likely for the Pacific Northwest into California this
weekend, with heavy snow in higher elevations of the Northwest...

A surface low pressure system is strengthening across the Plains today,
and is forecast to move eastward across the Mississippi and Tennessee
Valleys on Saturday and northeastward across the Northeast coast on
Sunday. North and west of the low, widespread winter weather is expected,
and a major winter storm is on tap from the Midwest to parts of the Ohio
Valley and the Northeast. 6 to 10 inches of snow is forecast for parts of
the Midwest, but the highest snow totals are expected for the interior
Northeast, where 1 to 2 feet of snow is forecast. Along the transition
zone between rain and snow, sleet and freezing rain are possible for
portions of the Ohio Valley into the Mid-Atlantic region and the Northeast
coast. Strong winds are likely as well, with a tight pressure gradient
between the surface low and an Arctic high pushing into the Plains. The
high will cause very cold temperatures behind the low system. Temperatures
that are 15 to 25 degrees below average are forecast for the Plains into
the Mississippi Valley on Saturday, and these much below normal
temperatures will shift into the Ohio Valley and Lower Great Lakes region
on Sunday.

Farther south, rain and thunderstorms are likely for the Southern Plains
and Lower Mississippi Valley on Friday night, shifting eastward into the
Southeast and Tennessee Valley on Saturday, as Gulf moisture streams into
the warm sector. A Slight Risk of severe weather is forecast for portions
of the Central Gulf Coast states, and a Slight Risk of flash flooding is
in place for parts of the Tennessee Valley and Southern Appalachians on
Saturday.

In the West, a strong surface low pressure system will approach western
Canada Friday night, with another low moving into the Northwest by Sunday
morning. An influx of moisture will focus into Oregon and California,
creating the potential for heavy rain there. A Marginal Risk of excessive
rainfall is in effect through Friday night, increasing to a Slight Risk on
Saturday near the Oregon/California border. In the higher elevations of
the Cascades, snowfall totals of 4 to 8 inches are expected through Sunday
evening, with higher snowfall totals of 8 to 12 inches are possible in the
Northern Rockies region.

This map is the official NWS snowfall forecast in inches during the time period shown on the graphic. This snowfall amount is determined by NWS forecasters to be the most likely outcome based on evaluation of data from computer models, satellite, radar, and other observations

...WINTER STORM WARNING REMAINS IN EFFECT FROM 4 PM SATURDAY TO
6 PM EST SUNDAY...
...WIND CHILL WATCH REMAINS IN EFFECT FROM SUNDAY EVENING THROUGH
MONDAY AFTERNOON...

* WHAT...Heavy snow and blowing snow expected. Dangerously cold
  wind chills possible. Total snow accumulations of 10 to 15
  inches expected. Winds gusting as high as 30 mph will produce
  significant blowing and drifting snow. Wind chills as low as 30
  to 40 below zero possible.

* WHERE...Oswego and Lewis counties.

* WHEN...For the Winter Storm Warning, from 4 PM Saturday to 6 PM
  EST Sunday. For the Wind Chill Watch, from Sunday evening
  through Monday afternoon. The heaviest snow will fall from late
  Saturday evening through midday Sunday.

* ADDITIONAL DETAILS...Travel could be very difficult to
  impossible. If you must travel, be prepared for severe winter
  driving conditions with deep snow cover and very low visibility
  from heavy snow and blowing snow. The dangerously cold wind
  chills could cause frostbite on exposed skin in as little as 10
  minutes.
 

Warnings

3:07 PM EST Friday 18 January 2019 Winter storm warning in effect for (areas in red)

Winter storm conditions expected Saturday. Snow at times heavy and blowing snow is expected to develop early Saturday morning and taper off Saturday night. Although the storm system responsible will track well to the south of the Great Lakes, northeast winds off Lake Ontario will pick up extra moisture resulting in higher snowfall totals. Snowfall accumulations of 15 to 25 cm are expected. Snowfall amounts should be considerably less for areas north of Hamilton and Burlington. In addition, strong northeast winds gusting to 60 km/h will generate widespread blowing snow and cold wind chill values near minus 20. Near zero visibility is likely at times. Consider postponing non-essential travel until conditions improve. Surfaces such as highways, roads, walkways and parking lots may become difficult to navigate due to accumulating snow. Visibility will be suddenly reduced to near zero at times in heavy snow and blowing snow.

Environment Canada warnings for Ontario as of 8pm eastern time

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