A Lead Up To February’s Polar Vortex

As we look into February, many of us have probably already heard that a return to winter appears very likely across much of Canada. The purpose of this article is to focus on the driving factors of the weather pattern with an emphasis on the first half of February.

THE GENERAL PATTERN INTO EARLY FEBRUARY

Looking ahead into the first week of February, it appears that an active Pacific jet stream will continue. This will serve to promote a rather accelerated forward flow pattern across the continent whereby low pressure systems from the Pacific track progressively into the Canadian Prairies or the Upper Plains of the U.S., and finally into the Maritimes. This pattern is likely to bring considerable impacts to both the west and east coast. Heavy alpine snows and lower elevation rainfall events will continue to effect British Columbia. As progressive disturbances tap into tropical moisture and are steered into the Maritimes by the western edge of a ridge over the Atlantic this sets up a scenario conducive to potentially significant winter storms. Secondary areas of low pressure are likely to ride the temperature (frontal) boundary up the East Coast and into the Maritimes bringing the potential for heavy snow and/or rain, strong winds, and even freezing rain. These disturbances crossing the continent along the Pacific jet stream will likely bring quite variable weather across the country. Pushes of milder air bringing temperatures above seasonal are likely within the warm sectors of these systems; predominantly for the Southern Prairies, Ontario, Quebec, and the Maritimes. Since these systems will likely come-and-go rather quickly, warm-ups will be brief and followed by shots of below-seasonal temperatures in their wake. The northward extent of the milder air will be dependent on the individual tracks of low pressure, and hence the positioning of their associated warm fronts.

As a strong upper-level ridge continues to dominate over the Bering Sea this week it will work to dislodge a Polar Vortex southward into Western Canada by early next week as cold air builds across the Far North. This means a healthy shot of cold, Arctic air can be expected across the Prairies to close out the month of January. This shot of cold air advances southeastward into Ontario and Quebec during the first full workweek of February in the wake of a low pressure system. It does appear that this may push the storm track a bit further to the south, which could in turn line up the potential for wintry weather for portions of Southern Ontario, Quebec, and of course, Atlantic Canada. This should lead to below-seasonal temperatures spreading southeastward to encompass the majority of Canada as we head into the second week of February.

Global Ensemble Forecast System (GEFS) modelled Mean 2-meter Temperature Anomaly from 12z January 26th, 2018 to 12z January 31st, 2018 (Courtesy: Tropical Tidbits). Temperature departures from seasonal are shown in degrees Celsius.

Global Ensemble Forecast System (GEFS) modelled Mean 2-meter Temperature Anomaly from 12z January 31st, 2018 to 12z February 5th, 2018 (Courtesy: Tropical Tidbits). Temperature departures from seasonal are shown in degrees Celsius.

Global Ensemble Forecast System (GEFS) modelled Mean 2-meter Temperature Anomaly from 12z February 5th, 2018 to 12z February 10th, 2018 (Courtesy: Tropical Tidbits). Temperature departures from seasonal are shown in degrees Celsius.

Global Ensemble Forecast System (GEFS) modelled 500mb Geopotential Height [dam] and Anomalies [dam] valid 12z February 5th, 2018 (Courtesy: Tropical Tidbits). 500mb geopotential height departures from climatology are shown in decameters [dam]. A Polar Vortex is modelled to set up in the vicinity of Hudson Bay during early February as denoted by the lower heights (i.e., the blue shaded area).

MOVING FORWARD INTO THE SECOND HALF OF FEBRUARY

As a blocking pattern essentially locks the Polar Vortex over the Hudson Bay area the cold should latch into place for the second half of February, and potentially even into early March. The return to cold, Arctic air coupled with Great Lakes that lack in ice coverage could spell some lake effect snow or lake enhancement to the lees of the lakes through February.

WEATHER HIGHLIGHTS INTO EARLY FEBRUARY

  • British Columbia: Periodic heavy alpine snow and lower elevation heavy rainfall through early February.
  • Prairies: Disruptive system (January 30th-31st) with a colder and drier pattern in its wake for early February.
  • Ontario & Quebec: A nuisance disturbance (January 27th-January 28th) brings rain showers to Southern and Northeast Ontario as well as to Southern Quebec, but snow is likely on the backside as temperatures fall. A disruptive system (January 30th-February 1st) brings the potential for snow, although rain is likely for Southern Ontario. Colder air follows on the backside of this low with a secondary system to be monitored for February 2nd, but it will likely track to the east. A wintry system is to be monitored for February 4th-5th with mixed precipitation possible for southern areas.
  • Atlantic Canada: Winter storm potential for January 29th-31st with locales along the East Coast seeing the possibility for mixed precipitation and rain. Uncertainty surrounds a second winter storm potential February 1st-5th.

The European Centre for Medium-Range Weather Forecasts (ECMWF) Ensemble Prediction System (EPS) modelled total snowfall through to 12z February 10th, 2018. This is an ensemble mean value and is based on a Snow-to-Liquid Ratio of 10:1 (i.e. 1mm of precipitation is equivalent to 1cm of snow).

 

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