Monday, 1 September 2014

August Ends Historical 10-Month Cold Streak in Winnipeg



     It's official, the cold streak has finally ended (for now)! At 0.5°C above the previous 30-year (1984-2013) average mean temperature of 18.7°C, August was the first month since September last year to finish warmer than the previous 30-year average. This 10-month cold streak from October 2013 to July 2014 was the 4th longest on record and the longest streak of its kind since an 11-month streak in 1887-1888. The following table summarizes the cold streak by showing how much each month deviated from the previous 30-year average. A list of notable events and stats are also included.

Month
Deviation from previous 30-year average mean temperature
Notable events
September 2013
+2.5
October 2013
-0.6

November 2013
-1.1
December 2013
-7.4
January 2014
-3.8
February 2014
-6.4
March 2014
-6.8
April 2014
-4.1
May 2014
-0.1

June 2014
-0.1

July 2014
-1.0
August 2014
+0.5


     Despite being slightly above normal, only 2 days reached 30°C in August, below the normal of 5 days. So far this year, we have seen 7 days over 30°C, below the normal of 13 days up to now.

Moist, stormy August


     With an average dew point temperature of 14.4°C, August 2014 had the 4th highest average dew point in August on record since 1953 and the highest since 2010 when the average dewpoint temperature was 14.9°C. 24 days saw dew point temperatures over 15°C, well above the normal of 18 days.

Thunderstorm near Warren, Mb, August 24
     Rainfall during the second half of the month was the biggest story of August. During the last 2 weeks of the month, generally 85 to 150 mm of rain fell over the Winnipeg area. The biggest rainfall events occurred on the 21st and 29th, associated with thunderstorm activity. On the 21st, a stationary storm over the city in the evening dumped 50-100 mm of rain from downtown to Whyte Ridge causing significant street and overland flooding. On the 29th, training thunderstorms in the morning south of the city dumped 50-100 mm of rain again, this time in the Niverville to Steinbach regions. Remarkably, much of this rain fell in just half an hour.

     In total, 104.4 mm of rain fell at the airport in August, the first wetter than normal August since 2010 and the 23rd wettest August since 1873. Higher totals fell in other areas, including: 110.7 mm in south St Vital, 137.2 mm in Charleswood, ~142 mm at The Forks and locally over 160 mm in the Lindenwoods area. There were also 6 thunderstorm days, bang on normal.

Wednesday, 27 August 2014

Warmer; Some Storm Chances

     Nothing but sun in the RRV today. I'm expecting a high around 23-24°C in Winnipeg. Warmer night tonight with lows in the low teens. Much better than the 7.9°C low this morning at the airport.

     The sun continues tomorrow as temperatures reach high 20's. Highs around 27-28°C look likely for Winnipeg. There will be a risk for thunderstorms in southwestern Manitoba in the evening as a cold front approaches. An isolated severe storm cannot be ruled out there.

     A cloudy start to Friday with a chance of showers and thunderstorms associated with the cold front. Skies should clear for the afternoon, but it will be cooler behind the front with highs only in the low 20's.

     Looks like we will warmup already for Saturday with highs in the mid 20's. Another cold front moves into southwestern Manitoba late in the day which could bring some more thunderstorm activity to the area. Again, isolated severe storms cannot be ruled out closer to the Saskatchewan border. That front will pass through the RRV on Sunday bringing a chance for showers and thunderstorms again.

Tuesday, 26 August 2014

March to August Temperature Forecast Evaluation

     It is time to look back and see how my Winnipeg forecast, issued daily in the 'Winnipeg Forecast' tab, has faired. I have only evaluated the temperature forecast due to the fact that precipitation and wind forecasts are a little trickier to compare with other forecasts. Different weather agencies have different methods of giving out precipitation and wind forecasts. Some will give you a range, others will give more precise values. This makes it difficult to compare their forecasts with mine. Temperatures are not a problem because all forecasts will give just one specific value as their forecast.

     The evaluation period goes from March 1, 2014 to August 23, 2014. To evaluate how my temperature forecasts have faired, I have compared them to forecasts by various sources: Environment Canada, The Weather Network, Intellicast, Accuweather, A Weather Moment and CBC Manitoba. I will not give the specific results of these sources, because I feel I should not do so if I do not have their permission. Instead, I will compare the results of my forecast with the average result across all sources.

     First, the following table shows what percentage of temperature forecasts were PERFECT. For example, a forecast high of 33°C would be considered a perfect forecast if the actual high was between 32.5°C and 33.9°C.

Table 1: Percentage of temperature forecasts that were perfect (from March 1, 2014 to August 23, 2014)


My forecasts
Average of all sources
Range of all sources
Day 1 high
51%
41%
31-51%
Day 2 AM low
36%
34%
27-42%
Day 2 high
41%
35%
29-41%
Day 3 AM low
32%
28%
22-36%
Day 3 high
20%
23%
11-35%




Overall
36%
32%
26-36%

     I am happy with the results. My forecasts had the highest percentage of perfect forecasts for both the day 1 and day 2 highs. May and July were the best months for the day 1 forecast with percentages of 58% ad 62% respectively. May was an exceptional month considering the average across all sources was just 32%. Interestingly, day 2 forecasts in July faired better than the day 1 forecasts. 66% of day 2 forecasts were perfect that month. Day 3 high forecasts continue to be my downfall, averaging slightly below average.

    Overall, considering all the temperature forecasts from day 1 to day 3, July was the best month (47%) and March the worst (27%). This is to be expected because temperatures tend to be less predictable in the colder months versus the warmer months.

     The last table below shows the percentage of forecasts that were WITHIN 1°C of the actual value. For example, a forecast high of 33°C would be considered within 1°C of actual if the actual high was between 31.5°C and 34.9°C.

Table 2: Percentage of temperature forecasts that were within 1°C of actual (from March 1, 2014 to August 23, 2014)


My forecasts
Average of all sources
Range of all sources
Day 1 high
81%
75%
64-81%
Day 2 AM low
66%
63%
56-67%
Day 2 high
67%
66%
57-70%
Day 3 AM low
59%
57%
49-62%
Day 3 high
55%
54%
40-69%




Overall
66%
63%
54-67%

     Again, day 1 high forecasts continue to be my strength. July was the best month with 97% of day 1 forecasts being within 1°C of actual. March was the worst at 68%. Overall, all forecasts from day 1 day 3 were within 1°C of actual 66% of the time, above the average of 63% across all sources. July was my best month at 83% and May the worst at 53%.

     I will continue to compare my forecasts with other forecasts for the foreseeable future. It has become a goal of mine to continue to remain above average and provide the best day 1 to day 3 temperature forecasts for Winnipeg. Unless interest is high, I don't plan to give another evaluation post like this one until next spring. Thanks for reading :)