Geoscience Reference
In-Depth Information
Weather Centre
Warning Criteria
Newfoundland
50 mm in 24 hrs
Maritimes
50 mm in 24 hrs
Quebec
50 mm in 24 hrs or 30 mm in 12 hrs during a spring thaw
50 mm in 12 hrs; sodden ground/bare frozen ground: 25 mm in 24
hrs; spring: 25 mm in 24 hrs; slow moving thunderstorms: 50 mm/3
hrs or 25 mm/3 hrs if ground is sodden.
Ontario
Prairie
80 mm in 24 hrs or 50 mm in 12 hrs
Alberta
50 mm in 24 hrs
Arctic
50 mm in 24 hr
Yukon
40 mm in 24 hr
50 mm in 24 hr except in west Vancouver Island and northern
coastal regions 100 mm in 24 hr and interior of B.C. 25 mm in 24 hr
Pacific
Table 3. Severe Weather Criteria in Canada: Heavy Rainfall Warning
Weather Centre
Warning Criteria
Newfoundland
75 km/h and/or gusts of 100 km/h
Maritimes
65 km/h and/or gusts to 90 km/h
Quebec
50 km/h with gusts to 90 km/h or with only gust to 90 km/h
Ontario
60 km/h for 3 hours, or gusts of 90 km/h for 3 hrs
Prairie
60 km/h and/or gusts to 90 km/h for 1 hr
60 km/h or gusts to 100 km/h except in Lethbridge Region: 70
km/h or gusts to 120 km/h.
Alberta
Arctic
60 km/h or gusts of 90 km/h
Yukon
60 km/h for 3 hr or gusts to 90 km/h
Mandatory 90 km/h expected over adjacent marine areas;
discretionary if gale force winds (63 to 89 km/h) expected over
marine areas; discretionary for interior B.C. 65 km/h or gusts of 90
km/h
Pacific
Table 4. Severe Weather Criteria in Canada: Strong Wind Warning
Warnings for summer severe weather are for extreme or rare events - events that are at the
high end of the spectrum of weather. In terms of statistics, rare events do not occur very
often (by definition) and so statistical analyses are always suspect due to low numbers. It is
difficult to easily demonstrate (using statistics) the efficacy of a warning program (Doswell
et al, 1990; Ebert et al 2004). Qualitative analyses or case studies are required to understand
the relationship between the provision of warnings and the saving of lives (Sills et al, 2004;
Fox et al, 2004). The same applies to determining the efficacy of radar algorithms to the
provision of weather warnings (Joe et al, 2004).
This has a significant impact on statistics but also on the "cry wolf" syndrome (AMS, 2001;
Barnes et al, 2007; Schumacher et al, 2010; Westefeld et al, 2006). An accurate but useless
tornado forecast could be by stating that "next year there will be a tornado in the U.S." This
statement is a climatological or statistical forecast. It has a very high probability of being
true. However, the phenomenon is very small, perhaps 10-20 km in length and 500 m in
width and so this particular prediction is not very useful. The information is highly accurate
