Sunny Brook observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sunny Brook observatory clear sky chart from 2005-11-06 to 2024-11-12.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	13% 9% 3 8% 5% 4 4 4 5% 7% 38%	101655
	Night	13% 9% 4 8% 5% 4 4 3 5% 6% 39%	97629
Transparency	Day	45% 5% 13% 25% 12% 1	105237
	Night	44% 5% 12% 24% 13% 1	102186
Seeing	Day	17% 10% 30% 26% 13% 4	16029
	Night	17% 9% 30% 32% 11% 1	25892

By Month

Percentage Cloud Cover SE (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	11% 18% 8% 15% 5% 4 4 2 4 4 25%	2527
	11th to 20th	Day	6% 14% 4 13% 8% 7% 9% 8% 6% 4 20%	2530
	21st to end	Day	11% 20% 7% 11% 6% 3 4 3 5% 6% 24%	3074
February	1st to 10th	Day	8% 12% 5% 10% 7% 5% 4 4 6% 7% 33%	1710
	11th to 20th	Day	9% 11% 6% 9% 4 4 4 3 5% 7% 36%	1664
	21st to end	Day	13% 12% 4 9% 5% 4 4 3 5% 7% 32%	1527
March	1st to 10th	Day	13% 8% 3 6% 4 4 3 3 4 6% 46%	3266
	11th to 20th	Day	10% 10% 3 8% 5% 4 4 3 5% 7% 40%	3480
	21st to end	Day	24% 13% 4 10% 5% 4 4 3 4 5% 25%	3931
April	1st to 10th	Day	18% 12% 3 8% 5% 3 4 3 4 6% 34%	2280
	11th to 20th	Day	21% 12% 3 7% 5% 3 4 3 4 6% 32%	2254
	21st to end	Day	20% 11% 3 8% 5% 5% 4 3 5% 6% 29%	2402
May	1st to 10th	Day	18% 6% 2 7% 4 4 4 4 5% 7% 39%	4336
	11th to 20th	Day	13% 7% 3 6% 5% 4 4 4 6% 8% 41%	4399
	21st to end	Day	18% 7% 3 8% 5% 4 4 4 5% 6% 37%	4824
June	1st to 10th	Day	12% 5% 2 5% 4 4 4 4 5% 9% 45%	2660
	11th to 20th	Day	13% 8% 2 6% 5% 5% 4 4 6% 9% 38%	2660
	21st to end	Day	11% 5% 2 7% 5% 5% 5% 5% 7% 8% 40%	2660
July	1st to 10th	Day	11% 6% 2 6% 6% 5% 5% 5% 7% 10% 37%	4440
	11th to 20th	Day	6% 3 1 4 3 3 5% 4 6% 8% 58%	4440
	21st to end	Day	7% 5% 2 6% 5% 5% 6% 4 7% 9% 44%	4813
August	1st to 10th	Day	12% 5% 2 6% 4 5% 5% 4 7% 7% 42%	4148
	11th to 20th	Day	12% 6% 2 6% 5% 5% 4 4 6% 7% 44%	4041
	21st to end	Day	9% 6% 2 7% 5% 5% 5% 4 6% 8% 44%	4229
September	1st to 10th	Day	12% 6% 2 5% 4 3 4 3 5% 8% 48%	2280
	11th to 20th	Day	12% 6% 1 7% 4 4 4 3 7% 7% 45%	2280
	21st to end	Day	14% 7% 3 6% 4 3 5% 4 6% 7% 43%	1996
October	1st to 10th	Day	16% 5% 3 6% 4 3 4 3 5% 6% 45%	1900
	11th to 20th	Day	14% 10% 3 7% 4 5% 4 3 5% 6% 38%	1900
	21st to end	Day	18% 12% 4 7% 3 3 3 3 4 6% 36%	2017
November	1st to 10th	Day	13% 10% 3 8% 6% 4 4 4 5% 7% 37%	1718
	11th to 20th	Day	14% 14% 5% 9% 6% 4 4 4 5% 6% 29%	1528
	21st to end	Day	13% 11% 4 8% 4 4 3 3 6% 6% 36%	1520
December	1st to 10th	Day	11% 14% 4 13% 7% 6% 5% 4 4 5% 27%	1520
	11th to 20th	Day	11% 13% 5% 11% 6% 5% 5% 4 5% 7% 28%	1918
	21st to end	Day	20% 16% 7% 16% 5% 4 4 2 2 4 19%	2783
January	1st to 10th	Night	9% 17% 9% 14% 5% 4 3 2 4 4 28%	4428
	11th to 20th	Night	9% 11% 5% 15% 7% 7% 7% 7% 6% 4 22%	4440
	21st to end	Night	13% 20% 6% 11% 5% 4 4 3 4 4 25%	4592
February	1st to 10th	Night	6% 12% 6% 12% 6% 6% 5% 3 5% 6% 34%	2470
	11th to 20th	Night	8% 9% 4 9% 6% 5% 5% 4 5% 7% 39%	2403
	21st to end	Night	13% 9% 3 8% 5% 5% 5% 3 5% 5% 37%	1927
March	1st to 10th	Night	10% 8% 3 6% 4 4 4 3 6% 7% 46%	3615
	11th to 20th	Night	9% 8% 3 9% 5% 5% 5% 4 6% 7% 40%	3480
	21st to end	Night	25% 12% 3 12% 5% 3 3 2 3 5% 27%	3699
April	1st to 10th	Night	16% 11% 4 6% 4 4 4 4 5% 7% 37%	1900
	11th to 20th	Night	23% 10% 3 6% 3 3 5% 4 5% 5% 35%	1875
	21st to end	Night	19% 8% 3 6% 5% 4 3 3 5% 7% 38%	1776
May	1st to 10th	Night	16% 7% 3 6% 5% 4 4 3 5% 7% 41%	2556
	11th to 20th	Night	14% 4 2 5% 3 3 3 3 4 7% 51%	2506
	21st to end	Night	12% 8% 3 7% 5% 4 5% 3 5% 7% 41%	2743
June	1st to 10th	Night	10% 5% 2 5% 5% 4 4 5% 6% 8% 46%	1520
	11th to 20th	Night	12% 6% 3 6% 5% 4 4 3 6% 7% 45%	1520
	21st to end	Night	8% 4 2 5% 5% 4 4 4 6% 8% 50%	1520
July	1st to 10th	Night	11% 3 2 5% 3 4 4 4 7% 9% 48%	2530
	11th to 20th	Night	4 2 1 4 3 3 4 4 6% 9% 59%	2530
	21st to end	Night	4 4 2 5% 4 3 4 4 6% 9% 55%	2750
August	1st to 10th	Night	12% 5% 2 6% 4 5% 4 3 5% 7% 47%	2789
	11th to 20th	Night	12% 5% 2 5% 3 3 3 3 5% 7% 51%	2798
	21st to end	Night	10% 6% 3 7% 5% 5% 4 3 5% 7% 46%	3427
September	1st to 10th	Night	9% 5% 2 4 5% 4 4 3 4 6% 54%	1900
	11th to 20th	Night	11% 5% 2 6% 3 3 3 3 5% 8% 52%	1900
	21st to end	Night	13% 5% 2 5% 4 3 3 3 6% 6% 50%	2161
October	1st to 10th	Night	13% 6% 2 5% 3 4 3 4 4 7% 50%	2280
	11th to 20th	Night	15% 8% 3 6% 3 4 3 3 5% 7% 43%	2280
	21st to end	Night	18% 9% 4 6% 5% 4 4 3 4 6% 37%	2580
November	1st to 10th	Night	12% 10% 4 7% 4 4 3 3 4 7% 42%	2576
	11th to 20th	Night	13% 12% 4 9% 6% 5% 5% 3 4 6% 33%	2675
	21st to end	Night	15% 9% 3 10% 4 4 4 3 5% 6% 37%	2660
December	1st to 10th	Night	12% 12% 4 9% 7% 5% 4 4 6% 7% 29%	2660
	11th to 20th	Night	12% 13% 5% 11% 7% 6% 5% 3 5% 6% 28%	3279
	21st to end	Night	23% 16% 6% 11% 5% 4 3 3 4 5% 21%	4884

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	64% 4 12% 16% 4	2528
	11th to 20th	Day	62% 7% 10% 15% 6%	2530
	21st to end	Day	61% 6% 14% 15% 4	3074
February	1st to 10th	Day	50% 5% 15% 19% 10% 1	1710
	11th to 20th	Day	47% 6% 13% 25% 8% 1	1673
	21st to end	Day	51% 5% 11% 20% 11% 1	1527
March	1st to 10th	Day	40% 4 15% 24% 15% 1	3266
	11th to 20th	Day	42% 5% 11% 31% 10% 1	3480
	21st to end	Day	62% 5% 9% 16% 7% 1	3931
April	1st to 10th	Day	51% 6% 10% 21% 11% 1	2280
	11th to 20th	Day	53% 4 9% 20% 12% 2	2254
	21st to end	Day	56% 6% 12% 17% 9% 1	2402
May	1st to 10th	Day	43% 6% 12% 25% 13% 1	4376
	11th to 20th	Day	38% 7% 12% 27% 14% 1	4403
	21st to end	Day	46% 7% 10% 24% 12% 1	4837
June	1st to 10th	Day	35% 7% 14% 29% 15% 2	2660
	11th to 20th	Day	42% 8% 13% 23% 13% 1	2660
	21st to end	Day	39% 8% 15% 25% 11% 2	2660
July	1st to 10th	Day	42% 4 19% 23% 10% 1	4371
	11th to 20th	Day	25% 5% 15% 35% 20% 1	4365
	21st to end	Day	36% 6% 14% 27% 17% 1	4662
August	1st to 10th	Day	39% 5% 12% 28% 14% 1	4133
	11th to 20th	Day	39% 5% 11% 34% 11%	4080
	21st to end	Day	38% 4 14% 29% 14% 1	4228
September	1st to 10th	Day	35% 6% 14% 30% 15% 1	2280
	11th to 20th	Day	37% 6% 15% 32% 9% 1	2280
	21st to end	Day	40% 5% 12% 31% 11%	1996
October	1st to 10th	Day	28% 3 8% 36% 24%	3160
	11th to 20th	Day	39% 4 12% 25% 19% 2	3140
	21st to end	Day	43% 3 13% 31% 9%	3307
November	1st to 10th	Day	47% 6% 14% 19% 13% 2	1718
	11th to 20th	Day	56% 7% 11% 17% 8% 1	1528
	21st to end	Day	48% 5% 18% 21% 8% 1	1520
December	1st to 10th	Day	59% 7% 13% 15% 6%	1520
	11th to 20th	Day	54% 8% 17% 16% 5%	1915
	21st to end	Day	71% 4 8% 13% 4	2783
January	1st to 10th	Night	61% 4 10% 18% 6%	4428
	11th to 20th	Night	60% 6% 12% 15% 6%	4440
	21st to end	Night	62% 5% 9% 18% 5% 1	4592
February	1st to 10th	Night	51% 5% 12% 22% 9% 1	2470
	11th to 20th	Night	45% 5% 14% 26% 8% 1	2404
	21st to end	Night	48% 5% 12% 23% 10% 2	1927
March	1st to 10th	Night	37% 5% 14% 28% 14% 2	3615
	11th to 20th	Night	41% 5% 11% 27% 15% 1	3480
	21st to end	Night	60% 4 8% 20% 7% 1	3699
April	1st to 10th	Night	47% 5% 10% 21% 15% 2	1900
	11th to 20th	Night	51% 5% 8% 18% 15% 2	1875
	21st to end	Night	46% 6% 11% 20% 15% 2	1776
May	1st to 10th	Night	42% 7% 12% 17% 20% 1	2580
	11th to 20th	Night	32% 5% 9% 30% 20% 4	2507
	21st to end	Night	40% 8% 10% 25% 17% 1	2751
June	1st to 10th	Night	32% 8% 13% 29% 16% 2	1520
	11th to 20th	Night	38% 6% 13% 22% 18% 3	1520
	21st to end	Night	31% 7% 15% 30% 15% 3	1520
July	1st to 10th	Night	33% 4 21% 28% 12% 2	2490
	11th to 20th	Night	22% 4 15% 37% 20% 2	2482
	21st to end	Night	26% 6% 16% 30% 20% 3	2662
August	1st to 10th	Night	38% 4 11% 29% 15% 3	2780
	11th to 20th	Night	34% 5% 13% 30% 16% 2	2825
	21st to end	Night	38% 4 16% 28% 14% 2	3427
September	1st to 10th	Night	31% 5% 11% 35% 18% 1	1900
	11th to 20th	Night	31% 5% 15% 32% 16%	1900
	21st to end	Night	35% 5% 13% 31% 15% 1	2161
October	1st to 10th	Night	26% 3 6% 36% 27% 4	3800
	11th to 20th	Night	33% 3 11% 28% 22% 2	3779
	21st to end	Night	46% 3 11% 25% 14%	4240
November	1st to 10th	Night	43% 5% 12% 24% 14% 1	2576
	11th to 20th	Night	53% 6% 12% 18% 10% 1	2675
	21st to end	Night	49% 5% 15% 23% 7% 1	2660
December	1st to 10th	Night	53% 7% 15% 20% 5%	2660
	11th to 20th	Night	56% 6% 14% 17% 6% 1	3281
	21st to end	Night	66% 5% 10% 14% 5%	4884

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	16% 14% 32% 27% 10% 2	270
	11th to 20th	Day	20% 14% 38% 20% 6% 1	270
	21st to end	Day	19% 12% 34% 24% 10% 1	297
February	1st to 10th	Day	17% 16% 44% 16% 5% 1	270
	11th to 20th	Day	16% 24% 36% 17% 7%	270
	21st to end	Day	20% 15% 42% 22% 1	225
March	1st to 10th	Day	19% 15% 40% 17% 9% 1	270
	11th to 20th	Day	21% 13% 36% 21% 7% 2	270
	21st to end	Day	27% 12% 29% 21% 9% 2	363
April	1st to 10th	Day	27% 13% 34% 20% 5% 1	460
	11th to 20th	Day	30% 14% 26% 21% 8% 1	452
	21st to end	Day	28% 12% 28% 21% 9% 2	582
May	1st to 10th	Day	21% 13% 32% 25% 9% 1	653
	11th to 20th	Day	20% 13% 26% 25% 14% 3	675
	21st to end	Day	18% 10% 27% 25% 15% 4	734
June	1st to 10th	Day	12% 8% 28% 32% 17% 4	680
	11th to 20th	Day	17% 8% 34% 29% 11% 2	680
	21st to end	Day	12% 6% 33% 27% 16% 5%	680
July	1st to 10th	Day	9% 3 22% 30% 26% 11%	671
	11th to 20th	Day	9% 6% 25% 31% 19% 9%	668
	21st to end	Day	6% 4 27% 37% 18% 8%	739
August	1st to 10th	Day	12% 4 22% 32% 24% 6%	676
	11th to 20th	Day	14% 4 21% 31% 24% 6%	665
	21st to end	Day	12% 6% 25% 29% 21% 6%	575
September	1st to 10th	Day	13% 7% 28% 31% 15% 5%	490
	11th to 20th	Day	11% 6% 28% 32% 19% 4	490
	21st to end	Day	18% 11% 29% 26% 12% 4	344
October	1st to 10th	Day	18% 13% 29% 24% 13% 2	300
	11th to 20th	Day	21% 14% 38% 20% 6% 1	300
	21st to end	Day	28% 16% 33% 17% 5% 2	330
November	1st to 10th	Day	21% 12% 35% 23% 9% 1	300
	11th to 20th	Day	19% 17% 42% 16% 5%	273
	21st to end	Day	22% 13% 42% 16% 6%	270
December	1st to 10th	Day	18% 11% 40% 26% 5% 1	270
	11th to 20th	Day	19% 17% 39% 19% 6% 1	270
	21st to end	Day	26% 15% 40% 17% 2	297
January	1st to 10th	Night	15% 13% 35% 29% 8% 1	950
	11th to 20th	Night	17% 11% 36% 28% 7% 1	950
	21st to end	Night	19% 11% 34% 29% 7%	1045
February	1st to 10th	Night	12% 13% 37% 30% 7% 1	950
	11th to 20th	Night	12% 14% 40% 25% 8%	929
	21st to end	Night	18% 15% 32% 28% 7%	671
March	1st to 10th	Night	17% 11% 36% 27% 7% 1	694
	11th to 20th	Night	20% 9% 34% 29% 6%	570
	21st to end	Night	23% 9% 31% 27% 9% 2	627
April	1st to 10th	Night	22% 12% 35% 26% 6%	570
	11th to 20th	Night	28% 9% 28% 28% 7%	563
	21st to end	Night	24% 8% 30% 29% 8% 1	570
May	1st to 10th	Night	21% 8% 32% 31% 6% 1	570
	11th to 20th	Night	20% 6% 29% 34% 10% 1	561
	21st to end	Night	17% 5% 25% 39% 13% 1	617
June	1st to 10th	Night	13% 4 25% 43% 14%	570
	11th to 20th	Night	15% 3 30% 40% 11%	570
	21st to end	Night	10% 4 21% 47% 17% 1	570
July	1st to 10th	Night	6% 2 21% 41% 27% 2	555
	11th to 20th	Night	6% 4 21% 45% 20% 3	552
	21st to end	Night	6% 2 18% 49% 22% 2	624
August	1st to 10th	Night	8% 3 15% 48% 25% 2	567
	11th to 20th	Night	13% 2 16% 39% 27% 4	564
	21st to end	Night	10% 3 22% 38% 26% 2	627
September	1st to 10th	Night	12% 4 23% 38% 18% 5%	570
	11th to 20th	Night	11% 3 28% 36% 19% 3	570
	21st to end	Night	15% 10% 27% 31% 16% 1	689
October	1st to 10th	Night	17% 8% 27% 32% 14% 2	760
	11th to 20th	Night	19% 12% 31% 30% 7%	760
	21st to end	Night	23% 10% 28% 32% 7%	836
November	1st to 10th	Night	18% 10% 34% 30% 8% 1	820
	11th to 20th	Night	19% 13% 36% 25% 7%	956
	21st to end	Night	20% 14% 33% 27% 6%	950
December	1st to 10th	Night	18% 10% 36% 28% 7% 1	950
	11th to 20th	Night	22% 10% 34% 26% 7% 1	950
	21st to end	Night	27% 12% 31% 25% 5%	1045

Page generated at 2024-11-08 21:45:37. Version ac07

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