Severe weather report
Quebec, March 7-8-9 2008 winter storm
Atmospheric sciences and environmental issues Meteorological Service of Canada, Environment Canada March 2008
Summary The following is a meteorological analysis of the March 7-8-9 2008 winter storm which took place in Quebec. This storm was perceived as the worst to hit the province during the 20072008 winter season, even if other storms had dropped as much snow earlier in the season. The storm was accompanied by heavy snow and strong winds which, together, produced blowing snow reducing visibility and impending on road, rail and airway transportations. The length of the storm was also an important factor, reaching up to twenty-four hours in some cases. Temporal context played a crucial role in the perceived intensity of the storm. Firstly, because it occurred at the end of the season, hence at a time when people and resources have already been experienced by cold and snow. And secondly, because it is part of an exceptionally “snowy” season over southwestern Quebec. Indeed, this storm pushed total snowfall amounts above previous records in Quebec city, Trois-Rivières and Mirabel. The media talked of overloaded snow deposits, out-of-stock road salt and abrasives, and expended snow removal budgets (see media reviews on the subject). Climatologically, this storm is important but not « extreme », the region having already lived through 35 cm of snow and more in less than 24 hours, and also, although less frequently, blizzard conditions (near zero visibility for several hours). But put in its context, it becomes exceptional.
Snowfall : quantities, duration, intensity and historical recurrence
tta w a M on tré al Tr oi sR iv Q ué ièr be es Sh c er br oo M ke on t-J o G as li pé Se pt -îl Ba es go tv il R ob le er va l
O
Sn o
w fa
ll (
cm )
The March 7-8-9 snowstorm dropped 30 to 50 cm of snow between Ottawa and Quebec, 20 to 40 cm over the lower St-Lawrence and 10 to 20 cm in the Saguenay region (see following table). It started in Ottawa in the afternoon of March 7th, in Montreal during the same evening and overnight eastwards. Rate of snowfall was highest in Ottawa and Montreal on March 8th and during the 9th towards the east. The Eastern townships are an exception since half of the precipitation fell as rain (18 mm of rain).
March 7th 15 March 8th 34 March 9th 3 Total 52
2 26 3 31
9 39 48
17 25 42
15 6 21
11 33 44
6 16 22
8 7 15
7 9 16
2 8 10
The following diagram shows the duration and type of precipitation (snow, ice pellets, freezing rain, and rain) and their intensity (light, moderate, and heavy: see explanations below diagram) where the biggest amounts were recorded. We can see that precipitation lasted roughly twenty to twenty-four hours. A first “impulse” started on the 7th in the afternoon, or in the evening according to regions, and ended the 8th in the morning. The second, and strongest, impulse lasted from midday of the 8th into the 9th. In Ottawa and Montreal, distinction between these two impulses is expressed as a change in intensity. Moderate snow was observed everywhere and, in some places, heavy snow. Ice pellets were also present intermittently, or mixed with snow, in the evening of the 8th and overnight. The heavy to moderate snow period is responsible for the most part of the snow amounts.
Timetable of precipitation, March 7-8-9 2008
Ottawa Montréal Québec Sherbrooke Bagotville Mont-Joli light snow moderate snow
Light Moderate Heavy
heavy snow ice pellets
freezing rain light rain
moderate rain heavy rain
Définition of intensities* Snow Reduces visibility to 5/8 MI (1 km) Reduces visibility between 3/8 and ½ MI (0.6 à 0.8 km) Reduces visibility to 1/4 MI (0.4 km)
* Manual of observations (MANOBS). MSC, Environment Canada
Rain Rain rate of 2.5 mm/h Between 2.6 and 7.5 mm/h Rain rate > 7.6 mm/h
18:00
17:00
16:00
15:00
14:00
13:00
12:00
11:00
10:00
09:00
08:00
07:00
06:00
05:00
04:00
03:00
02:00
01:00
00:00
23:00
22:00
21:00
20:00
19:00
18:00
17:00
16:00
15:00
14:00
March 9th
13:00
12:00
11:00
10:00
09:00
08:00
07:00
06:00
05:00
04:00
03:00
02:00
01:00
00:00
23:00
22:00
March 8th 21:00
20:00
19:00
18:00
17:00
16:00
15:00
March 7th
Now, let’s compare snowfall amounts with historical records. In Ottawa, Trois-Rivières and Mont-Joli (following graph), the total snow that fell over March 7, 8 and 9 is above the mean total snowfall for the whole month of March (1971-2000 Normal). In other words, these places received, in almost/or less than a day (20 to 24 hours), what they usually receive over the entire month. In Montreal and Quebec, the snow almost reached the monthly mean. Elsewhere, it is well below the monthly mean. The same thing can be said about the comparison between total snow and the record snowfall for one single day in March (light blue bars).
March 7-9 snowfall versus monthly normal snowfall and record snow for one day in March March 7-8-9 snowfall
Record for one day in March
Normal snow for the whole month
Ottawa Montréal Trois-Rivières Québec Sherbrooke Mont-Joli Gaspé Sept-îles Bagotville Roberval 0
10
20
30
40 Snowfall (cm)
50
60
70
80
In addition, in Ottawa, Montreal and Trois-Rivières the maximum snowfall for a single day during the storm was greater than the maximum record snowfalls for March 7, 8 and 9th. In Quebec and Mont-Joli this value was just below, but elsewhere it is considerably lower. This result suggests that the intensity of the snow (rate of fall) was quite high at some places, and exceptional in Ottawa, Montreal and Trois-Rivières for this time of the year (March). This type of comparison with record values for specific dates is important in the case of snow occurring in March since the probability of getting snow decreases rapidly between the beginning and the end of the month. Such a comparison is meaningful during transitional seasons (spring and autumn) when the mean values of weather change rapidly, and even more still in the case of intense events. Maximum daily snowfall between March 7th and 9th versus highest daily record between March 7th and 9th max daily snowfall for March 7-8-9
Highest daily record between March 7th and 9th
Ottawa Montréal Trois-Rivières Québec Sherbrooke Mont-Joli Gaspé Sept-îles Bagotville Roberval 0
5
10
15
20
25
30
35
40
45
Snowfall (cm)
Following these analyses, we can state that snowfall during the March 7 to 9th 2008 storm was: -
exceptional (record breaking) in Ottawa, Trois-Rivières and Mont-Joli (40 to 50 cm) abnormally high (non record breaking) in Montreal and Quebec (30 to 40 cm).
Wind speed Wind was an important factor during this storm since gusty strong winds combined with falling snow to create widespread blowing snow, which resulted in decreased visibility, which in turn delayed transportations and caused some accidents. Analyzed here is hourly wind speed (average over two minutes before the hour) and maximum daily gust (lasting five seconds). For hourly wind, amongst the ten places monitored for snow, the ones showing the highest hourly winds are Montreal, Quebec, Trois-Rivières and Mont-Joli (peak wind speeds between 60 and 75 km/h). The graph below shows the hourly wind values between the 8th at noon and the 9th at midnight. In southwestern Quebec, winds increased from 30 to 70 km/h in the afternoon/evening of the 8th, and came back down overnight. In the east, they stayed around 50 km/h until the 9th in the afternoon. Winds were particularly strong late in the evening of the 8th. Finally, winds picked up a bit in Montreal near midday, and diminished afterwards.
Hourly wind speed, from March 8th 12:00 to March 9th 24:00 80 70
Montréal
Trois-Rivières
Québec
Mont-Joli
60 50 km/h 40 30 20 10 0 12:00 14:00 16:00 18:00 20:00 22:00 0:00 2:00 4:00 6:00 8:00 10:00 12:00 14:00 16:00 18:00 20:00 22:00
The following graph shows the number of hours above given thresholds. In Montreal, Quebec and Trois-Rivières, winds stayed above 40 km/h for eight hours consecutively, of which half were above 60 km/h (except for Trois-Rivières). In Mont-Joli, this number is doubled (17 hours above 40 km/h instead of 8 hours), but hours above 60 km/h are the same. Consecutive hours above 40, 50 and 60 km/h, March 7-8-9 2008
Mont-Joli Québec
> 60 km/h > 50 km/h
Trois-Rivières
> 40 km/h
Montréal 0
5
10
15
20
From a historical point of view, winds approached record values for the whole month of March in the case of mean winds but also in the case of gusts. The highest hourly winds approached record values in Montreal and Mont-Joli, whereas peak gusts where just below record values for March (from about 10%) in the case of Quebec and Mont-Joli (record values for Trois-Rivières are not available). Peak wind and gust during March 7-8-9 versus record wind and gust for the whole month peak wind March 7-9
record wind in March
peak gust March 7-9
record gust in March
Mont-Joli Québec Trois-Rivières Montréal 0
20
40
60
80 km/h
100
120
140
160
Combined effects of snow and wind : blowing snow Blowing snow was reported in many places and for several hours. Visibility was reduced to the point of heavily impacting road, railway and air transportation. Visibility will be examined here, but lets firstly examine what values of visibility are critical. The two most impacted domains are aviation and road transportation. Hence, we will examine the visibility thresholds for these two domains. For aviation, visibility starts to be monitored when it falls below 10 km (or 6 miles). Below 1.6 km (1 mile), impacts start to be felt: landing and take-off manoeuvres have to take into account visibility in their flight plan. Below 0.4 km (1/4 mile), smaller airplanes cannot fly and bigger planes necessarily fly by instruments. From an observational standpoint, this “critical” value of 0.4 km corresponds to “heavy” snowfall. Finally, below 0.2 km (1/8 mile) most take-offs and landings are restrained and some airport managers will freeze all operations. In the case of roads, visibility thresholds are much closer and less restrictive. Above 0.5 km, visibility is said to be good. Between 0.5 and 0.1 km it is said to be « reduced ». And below 0.1 km, it is « null » or totally prohibitive. Road transportation then starts to be impacted where aviation is already heavily impacted. This obliges us to consider values of visibilities ranging from at least 2 km down to zero, and to include the threshold of 0.4 km or 0.5 km weather we want to emphasize aviation or roads.
Visibility is hereafter analyzed for places reporting at least five hours below 1 km during the storm. These places are the same as that chosen for the analysis of wind, which comes as no surprise considering the causal link between blowing snow, visibility and wind speed. The figure below computes the number of hours below the following thresholds: 2, 1, 0.5 and 0.25 km. We see that while hours below 2 km are approximately the same between Montreal, Quebec and Mont-Joli, hours below 0.5 and below 0.25 km are quite different; Quebec and Mont-Joli having twice as much hours as Montreal (in Ottawa, the lowest observed visibility during the storm was 0.4 km). Hence, it is Quebec and Mont-Joli that had the greatest potential for road visibility reduction and impacts, even if Ottawa experienced the most hours of reduced visibility regardless of values (18 hours below 2 km versus 12, 13 and 14 hours elsewhere).
Hours below visibility threshold, March 7-9 2008 < 2km
< 1km
< 0.5km
< 0.25km
20 18 16 14 12 10 8 6 4 2 0 Montréal
Ottawa
Québec
Mont-Joli
Time wise (following figure), visibility literally « fell » (plunged) and rose back up, just as quickly, fifteen hours later. Such rapid variations are typically of snowstorms, more so when the wind is strong. In Ottawa, Montreal and Quebec, visibility fell below 1 km during the afternoon of the 8th, and near midnight in Mont-Joli. Visibility drops are in phase with maximum snowfalls and peak winds, which is what we expect. Quebec and Mont-Joli experienced the most hours with visibility below critical value of 0.5 km.
Hourly visibility between March 8th 10:00 and March 9th 18:00 3 Montréal
Ottawa
Québec
Mont-Joli
2,5
1,5
1
0,5
16 :0 0
14 :0 0
12 :0 0
10 :0 0
08 :0 0
06 :0 0
04 :0 0
02 :0 0
00 :0 0
22 :0 0
20 :0 0
18 :0 0
16 :0 0
14 :0 0
12 :0 0
0 10 :0 0
km
2
Let’s analyze now the link between visibility and wind in a timely fashion. The following temporal diagram illustrates the evolution of visibility and wind over the time span of the storm, with the use of color codes. Pale colors indicate light winds and high visibilities, and dark colors, strong winds and low visibilities. Absence of color indicates winds below 40 km/h and visibility above 2 km. Timetable of visibility and wind from March 8th 10:00 to March 9th 13:00
Montreal
vis wind
Ottawa
vis wind
Quebec
vis wind
Mont-Joli
vis wind
Visibility: 1-2 km 0.5-1 km 0.25-0.5 km < 0.25 km
13:00
12:00
11:00
9:00
10:00
8:00
7:00
6:00
5:00
4:00
3:00
2:00
1:00
0:00
23:00
22:00
21:00
20:00
March 9th 19:00
18:00
17:00
16:00
15:00
14:00
13:00
12:00
11:00
10:00
March 8th
Wind: 40-50 km/h 50-60 km/h 60-70 km/h > 70 km/h
From a broad view, the temporal window of the winds seems to match the temporal window of decreased visibility. On an average, this period was fifteen hours long. But, the lowest visibility periods match more or less well the periods of highest winds. This is possibly due to the fact that wind does not act only on falling snow, but also on fallen snow, snow that’s already on the ground. On the other hand, in Quebec and Mont Joli, winds above 60 km/h (two darkest shades of orange) correspond quite well with visibilities below 0.5 km (two darkest shades of blue). In a historical perspective, visibility reductions observed during this storm were not exceptional. Other storms in the past have reduced visibility to near zero for a few hours before, generating at times blizzard-like conditions even though such conditions are generally found in northern Quebec. But the fact that it is the only storm this season to have generated blowing snow gives the impression that it is the most severe storm of the season, doubled by the fact that it took place at the end of a very “snowy” season and, also, that it is the fifth storm to total more than 25 cm in the southwest this season.
Conclusion Main features of the March 7-8-9 2008 storm are the record breaking snow accumulations at a few places over southern Quebec, but mostly it is the seasonal and climatological context in which it took place. The storm occurred after several other ones of similar amplitude: in Montreal it is the fifth storm to leave behind at least 25 cm of snow since November 1st, and in Quebec city it is the seventh one of the same amplitude (over one or two climatological days). Furthermore, it added snow to already very high seasonal totals, of which record breaking amounts on the order of 350, 500 and 400 cm at Mirabel, Quebec and Trois-Rivières (see http://www.criacc.qc.ca/climat/suivi/Evenements/CumulHivernalNeige_e.html ). The fact that the storm took place at the end of the winter season (“extended” winter season: Nov-March) also contributed to increase the impacts and the perception of severity: over-used snow removal resources, strained workers (public security and health), beaten moral of general public, etc. Finally, the fact that this storm was the only one this season to create serious transportation hazards (due blowing snow) amplifies the impression that it is THE storm of the year, and even more: the most severe storm of the “century”, an expression that came about in the media. Snow wise, the December 3-4-5 2007 snowstorm left at least as much as this one did (Dec 3-4-5 storm: 35 cm in Montréal and 40 cm in Quebec). . Other snow indices probably also contributed to the perceived uniqueness of this storm. For instance, permanent snow cover, which started earlier this year than the last years, and also average snow cover (snow on the ground) which was quite high due to abnormally low “snow depletion” events (thaws, long sunshine periods which sublimate snow, strong winds which pack and push around snow, etc.), even considering the “January thaw” this year was very strong (record breaking number of melting degree-days in certain areas). As a matter of fact, the average snow cover in Montreal (based on the last day of each month) was the third highest in the last 30 years (1978-2008), and if it wasn’t for the intense January thaw it would have been in first place. As a concluding remark, we can say that this event illustrates with no doubt the importance of the context of a storm: its context within the season, compared to previous extreme events, human and societal context (preparedness and response), and state of public health, public services, etc. Statistics cannot in themselves describe the severity of a meteorological event whatsoever.
