Is This Weather Normal? – February 2019

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February 2019 weather in Terrace, BC was abnormal in two ways – cold and dry. The warmer-and-wetter-than-normal January ended abruptly on January 31st, when a dramatic change in pattern brought in colder and drier conditions that lasted through February and March.

Temperature:

February temperature was the 6th coldest on record, averaging -6.1°C, which is 4.8°C colder than the 1971-2000 baseline climate. Temperatures plunged at the beginning of February to well below normal, then approached and reached average conditions by the end of the month (Fig. 1).

Figure 1: Daily average temperature for February 2019 in Terrace, BC (red line). The black line shows the 1971-2000 average. The two gray lines show plus/minus one standard deviation.

The temperature story in 2019 (so far) is one of a much warmer than average January, followed by a much colder than average February (Fig. 2). This difference from one month to the next isn’t abnormal. It’s related to circulation patterns in the atmosphere, particularly the location and direction of the polar and subtropical jet streams here in the northern hemisphere. The jet streams direct storms and act as a kind of barrier between colder air to the north and warmer air to the south. How the jet streams curve (Rossby waves) determine how far south colder air moves, and how far north warmer air moves, in addition to guiding the direction of storms. What is abnormal, however, is how these waves in the jet streams seem to be getting stuck in place, resulting in persistent weather patterns, a process that is hypothesized as likely being caused by global warming.

Figure 2: 2019 average monthly temperature for Terrace, BC through February. The dotted blue curve is 2019, the 10 red lines are the ten warmest years on record, every other year is in gray. The black line is the long-term average, and the error bars mark plus/minus one standard deviation.

Precipitation:

Precipitation in February (or the lack thereof) led to the 2nd driest on record, totaling 11mm, which is 111mm less than the average February precipitation of 122mm, or 9% of normal. This lack of precipitation can be seen graphically by the flat lining of the curves in the cumulative precipitation graph (Fig. 3). Other than a minor snowfall event later in the month, there was no precipitation in February. This February dry spell has resulted in total yearly precipitation to date moving from above average after the warm/wet January (115% of normal), to below average after February (71% of normal).

Figure 3: Cumulative precipitation – where total precipitation (green), rain (dark blue), and snow (light blue) are added throughout the year. Solid lines show the 1971-2000 average. Dotted lines show the 2019 totals to date.

February is an important month for snowfall in the Coast Mountains, building up a snowpack that is later available as liquid water during the spring/summer melt season. The near record setting dry February of 2019 does bode well for a recovery from the ongoing drought (Fig. 4).

Figure 4: 1913-2019 total precipitation for the month of February. The long-term average is in black and dashed. There are two years of missing data (1919 and 1955).

Links:

The jet stream, explained (National Geographic)

Jet streams (North Carolina Weather Office)

Global Warming Is Messing With The Jet Stream. That Means More Extreme Weather. (Inside Climate News)

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