Spring Outlook 2019

February

Winter 2018/19 started out quite mild. In fact, for a while I was beginning to think that we might not even dip to -20C during the cold season for the first time since records began, as we had escaped those values through November, December, and even January - with weak El Nino conditions being forecast to develop. We even saw an explosion in the tick population during mid-winter, which is quite unusual for the area.

However, come February 1st, it was like a switch was flipped, and we went from anomalously mild conditions to anomalous cold. In fact, February 2019 turned out to be the 4th coldest February in Calgary since records began (1885), after 1904, 1887, and the coldest ever, in 1936. The mean temperature for the month was -18.2C, compared with an average monthly mean temperature of -5.4C. This is in stark contrast to the recent and memorable February of 2016, during a strong El Nino, when the monthly average was 1.4C - the second warmest February on record in Calgary!

Highly anomalous cold existed in the western Canadian Prairies and northern US high plains during February. Image courtesy Weatherbell. 

Every day during the month featured below average temperatures.

A sudden stratospheric warming event took place around New Years, which resulted in the Polar Vortex splitting into two daughter vortices - one of which camped out over northern Hudson Bay for several weeks, sending wave after wave of extreme cold across the Canadian Prairies. Edmonton had an extreme cold warning for 11 consecutive days during the first half of February, and one of Calgary's two weather stations at CYYC failed to rise above freezing the entire month.

The ECCC climate station at Calgary International Airport (not the Nav Canada station, whose data is used publicly) reached -0.4C on Feb 22. Image courtesy ECCC's historical climate data site. 

Going Forward

It seems the current cold in early March across the prairies will be the last extended period of extreme cold of the cold season, as a large-scale pattern change is expected mid-month. Current -EPO conditions will abate in the coming days, as a blocking high over the Beaufort Sea breaks down. Moreover, as deep convection continues to move east across the Indian Ocean, we will likely maintain phase 3 of the MJO for several days which generally teleconnects to continued cool conditions across the prairies. By mid-month, we begin to see signs of neutral and even +PNA conditions, yielding much longed-for upper ridging over western North America, at which time we may see a period of above seasonal values across western Canada between the second and fourth weeks of March. This could yield rapid snowmelt and the possibility of at least minor overland flooding across parts of the prairies, in areas where snowpack is more substantial. Meanwhile, a weak El Nino is ongoing, and has a 55% chance of continuing through the rest of spring according to NCEP. This signal should further yield dry conditions with above seasonal temperatures - especially over the western prairies. Ongoing drought conditions in places and the potential for seasonal wildfires in May throughout the boreal forest are likely to be considerations. 

EPS Ensemble forecasts hinting at +PNA conditions developing during mid-month. Image courtesy weathermodels.com

Weak El Nino conditions could persist into early summer. Image courtesy IRI/CPC. 

The Canadian Drought Monitor reveals that local areas of severe drought have developed across parts of the prairies, with local D2 (severe drought) conditions in far NW Alberta and along the southern foothills, in south-central Saskatchewan, and in the extreme southern Red River Valley of Manitoba. Apparently there is even a pocket of D3 conditions near Fort Vermilion. These are likely the cumulative result of the past two relatively hot and dry growing seasons across much of the prairies. A below-normal snowpack also exists across parts of south-central Alberta. However, winter snowpack plays much less of a role in the development of drought than does a lack of growing season precipitation - since drought conditions are particularly sensitive to the amount of rain that falls in the summer. This is both due to the fact that the ground is frozen in winter, preventing absorption of water, and that over two thirds of annual prairie precipitation falls during the spring and summer - with a large proportion of that resulting from thunderstorms. Dry ground also helps with getting crops planted quicker and more efficiently. We just need that June monsoon to come!

Image from the Canadian Drought Monitor.

Image courtesy ACIS, revealing current snowpack relative to the long-term normal over stubble.

The extreme cold across the eastern prairies, combined with recent heavy snows across southern Manitoba and parts of North Dakota have led to an increased flood risk this spring. A deeply frozen ground and potential rapid warming trend later in March could lead to significant runoff and overland flooding - especially along the Red River Valley south of Winnipeg. Ice jams will also pose a somewhat greater threat this spring owing to the thicker ice that has formed in the extreme cold. The area is accustomed to dealing with spring flood risks, with only minor flooding expected over cropland and some roadways near the Red River. However, the degree of severity of potential flooding will depend on how the month of March transpires - both in terms of additional precipitation, and rapid warming trends following extreme cold. Hopefully, flooding turns out more like 2011 than 2009!  

Snow water equivalent, courtesy NOAA, reveals a sizeable snowpack across parts of central AB/SK, and southern MB.

Meanwhile, the Alberta mountain snowpack is generally normal to above normal north of Highway 1, below normal between Highways 1 and 3, and closer to normal south of Highway 3 to the US border. There is still time for snow to be added to mountain snowpacks, but a dry signal overall through spring reduces the likelihood of this scenario. Nonetheless, both an average summer, or one influenced by El Nino conditions, would tend to yield more normal rains in southern Alberta in June and July, which would both curb developing drought conditions, and ensure a lack of water shortages for southern Alberta's irrigation country. 

Mountain snowpack west and southwest of Calgary is generally running below normal. Image courtesy the Government of Alberta Rivers website. 

...and beyond

For what it's worth, my sense is that following a dry spring, this summer's rainfall and convective activity will trend toward more normal conditions than we saw during the past two years. Weak El Nino conditions may or may not persist into summer, but in either case, more normal precipitation patterns would tend to be expected across southern and central Alberta. In terms of the PDO, slightly cool conditions will likely persist into spring, which also tends to favour cooler and wetter conditions across the prairies - at least in years where more significant negative PDO conditions exist. It is unknown to what extent (if any) this will play on prairie weather this coming warm season, or if the combination of -PDO and weak El Nino conditions will work against each other, reducing their effects. This also goes for tornado season in the US Plains. El Nino conditions often translate to quieter US tornado seasons - however, with no significant large-scale climate patterns expected to dominate into the summer, we could easily see more normal tornado numbers there as well - which might seem like a lot, given the past couple of seasons!

To be taken with a grain of salt at this range, but climate models have been fairly consistent with the transition to wetter conditions in the late spring/early summer in parts of the prairies, including southern Alberta. Image courtesy Tropical Tidbits.

Slightly cooler than average SSTs (-PDO) exist along the west coast of North America. Image courtesy NOAA.