Bay Ridges Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bay Ridges Observatory clear sky chart from 2005-11-06 to 2024-11-05.

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	14% 8% 3 8% 5% 5% 5% 4 6% 8% 35%	101484
	Night	16% 9% 3 7% 5% 5% 5% 4 6% 7% 35%	97562
Transparency	Day	45% 7% 14% 22% 11% 1	105086
	Night	47% 6% 13% 21% 11% 1	102048
Seeing	Day	17% 6% 22% 31% 19% 5%	14452
	Night	19% 7% 26% 31% 15% 3	23803

By Month

Percentage Cloud Cover NE (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	16% 12% 4 9% 5% 5% 5% 3 4 6% 31%	2517
	11th to 20th	Day	11% 17% 6% 16% 8% 5% 5% 4 4 5% 19%	2713
	21st to end	Day	20% 17% 5% 11% 6% 5% 5% 3 4 6% 17%	3124
February	1st to 10th	Day	15% 14% 5% 11% 7% 6% 6% 4 5% 6% 23%	1710
	11th to 20th	Day	12% 13% 5% 11% 7% 5% 5% 3 5% 8% 27%	1663
	21st to end	Day	17% 12% 3 10% 7% 5% 4 4 4 6% 28%	1460
March	1st to 10th	Day	19% 9% 3 8% 5% 5% 5% 4 5% 6% 31%	3432
	11th to 20th	Day	10% 12% 5% 9% 6% 6% 6% 4 6% 7% 30%	3480
	21st to end	Day	15% 8% 3 6% 5% 4 5% 4 5% 7% 38%	3815
April	1st to 10th	Day	17% 10% 4 8% 5% 5% 4 4 6% 6% 30%	2260
	11th to 20th	Day	18% 9% 2 7% 4 4 5% 3 6% 6% 36%	2304
	21st to end	Day	19% 7% 3 8% 5% 4 4 4 5% 6% 34%	2470
May	1st to 10th	Day	16% 8% 3 7% 5% 5% 5% 4 6% 8% 32%	4130
	11th to 20th	Day	14% 9% 3 8% 6% 5% 6% 4 6% 7% 31%	4398
	21st to end	Day	10% 5% 2 6% 4 3 5% 4 6% 8% 47%	4837
June	1st to 10th	Day	13% 7% 3 6% 5% 5% 5% 4 7% 9% 36%	2660
	11th to 20th	Day	10% 5% 2 6% 5% 5% 5% 5% 7% 10% 41%	2660
	21st to end	Day	12% 6% 2 5% 5% 5% 5% 4 7% 9% 41%	2660
July	1st to 10th	Day	9% 4 2 5% 4 5% 5% 4 8% 10% 43%	4440
	11th to 20th	Day	9% 4 2 5% 4 4 5% 4 7% 9% 46%	4440
	21st to end	Day	7% 5% 2 6% 5% 6% 6% 5% 8% 9% 42%	4562
August	1st to 10th	Day	15% 7% 3 6% 4 4 4 5% 5% 8% 39%	4104
	11th to 20th	Day	10% 6% 2 7% 5% 5% 5% 4 7% 10% 39%	4044
	21st to end	Day	7% 6% 2 6% 4 4 5% 4 7% 9% 45%	4324
September	1st to 10th	Day	12% 5% 2 6% 4 5% 5% 4 5% 7% 44%	2280
	11th to 20th	Day	10% 5% 2 5% 4 4 4 4 5% 8% 49%	2193
	21st to end	Day	13% 5% 2 7% 5% 5% 5% 4 6% 9% 39%	2036
October	1st to 10th	Day	16% 7% 2 8% 5% 4 5% 4 5% 7% 37%	1900
	11th to 20th	Day	18% 9% 3 7% 5% 4 5% 4 4 7% 33%	1900
	21st to end	Day	21% 9% 4 9% 6% 5% 4 4 5% 7% 26%	2090
November	1st to 10th	Day	13% 8% 3 8% 6% 5% 5% 3 7% 8% 34%	1640
	11th to 20th	Day	15% 10% 3 9% 7% 6% 6% 5% 7% 7% 26%	1520
	21st to end	Day	19% 10% 3 10% 5% 6% 4 4 6% 9% 23%	1520
December	1st to 10th	Day	16% 14% 5% 10% 7% 6% 6% 4 6% 7% 18%	1520
	11th to 20th	Day	19% 13% 4 8% 5% 5% 6% 4 6% 7% 24%	1906
	21st to end	Day	29% 15% 5% 12% 6% 5% 4 3 4 5% 14%	2772
January	1st to 10th	Night	18% 13% 4 9% 5% 5% 4 4 6% 6% 24%	4429
	11th to 20th	Night	15% 12% 5% 12% 8% 6% 6% 4 6% 7% 20%	4244
	21st to end	Night	21% 13% 5% 10% 6% 6% 5% 4 4 6% 21%	4532
February	1st to 10th	Night	13% 15% 4 9% 6% 6% 5% 4 6% 6% 25%	2470
	11th to 20th	Night	15% 11% 4 10% 6% 5% 5% 5% 5% 7% 27%	2403
	21st to end	Night	15% 11% 4 9% 6% 5% 5% 4 5% 6% 29%	1988
March	1st to 10th	Night	18% 9% 3 8% 6% 5% 5% 3 5% 6% 33%	3408
	11th to 20th	Night	14% 10% 4 8% 6% 5% 5% 4 5% 6% 35%	3479
	21st to end	Night	17% 6% 2 6% 4 4 4 3 5% 6% 43%	3817
April	1st to 10th	Night	18% 10% 3 8% 5% 4 4 3 5% 7% 34%	1919
	11th to 20th	Night	15% 7% 3 6% 6% 5% 5% 3 6% 5% 39%	1840
	21st to end	Night	16% 7% 3 7% 4 5% 4 5% 6% 7% 35%	1710
May	1st to 10th	Night	18% 7% 2 6% 4 5% 5% 3 5% 6% 39%	2811
	11th to 20th	Night	15% 8% 3 7% 5% 5% 6% 6% 5% 7% 34%	2495
	21st to end	Night	9% 4 2 6% 4 3 4 3 6% 8% 51%	2738
June	1st to 10th	Night	12% 5% 3 6% 4 5% 6% 4 6% 8% 42%	1520
	11th to 20th	Night	8% 5% 3 6% 6% 5% 4 5% 6% 8% 44%	1520
	21st to end	Night	13% 5% 2 5% 6% 4 4 4 6% 8% 43%	1520
July	1st to 10th	Night	6% 5% 2 5% 4 4 5% 4 6% 9% 49%	2520
	11th to 20th	Night	11% 4 2 5% 4 4 4 3 5% 8% 50%	2520
	21st to end	Night	8% 4 2 5% 4 4 4 4 6% 9% 51%	2987
August	1st to 10th	Night	10% 5% 3 5% 5% 4 4 4 6% 8% 47%	2825
	11th to 20th	Night	11% 5% 2 6% 3 3 3 3 5% 7% 51%	2785
	21st to end	Night	10% 5% 2 6% 4 5% 4 4 6% 8% 46%	3299
September	1st to 10th	Night	9% 5% 2 7% 4 4 5% 5% 6% 6% 47%	1900
	11th to 20th	Night	10% 4 2 4 3 4 3 3 5% 8% 54%	1984
	21st to end	Night	15% 6% 3 8% 4 4 4 3 5% 7% 42%	2143
October	1st to 10th	Night	15% 6% 3 8% 5% 4 4 4 6% 7% 40%	2280
	11th to 20th	Night	18% 8% 2 7% 5% 4 5% 4 6% 6% 33%	2280
	21st to end	Night	21% 9% 3 7% 4 4 5% 4 5% 7% 31%	2508
November	1st to 10th	Night	16% 7% 2 7% 5% 5% 4 3 6% 7% 38%	2536
	11th to 20th	Night	16% 9% 3 8% 6% 5% 5% 5% 6% 8% 30%	2660
	21st to end	Night	20% 9% 3 8% 5% 5% 6% 4 6% 8% 26%	2660
December	1st to 10th	Night	20% 13% 4 9% 6% 5% 5% 4 5% 5% 23%	2660
	11th to 20th	Night	16% 16% 4 9% 6% 6% 5% 4 6% 6% 22%	3288
	21st to end	Night	31% 13% 4 9% 5% 5% 5% 4 5% 6% 14%	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	53% 9% 20% 11% 7% 1	2518
	11th to 20th	Day	69% 7% 11% 9% 4	2713
	21st to end	Day	68% 7% 11% 9% 4	3124
February	1st to 10th	Day	63% 6% 11% 15% 4 1	1710
	11th to 20th	Day	56% 7% 12% 17% 7% 1	1672
	21st to end	Day	57% 5% 13% 18% 7%	1460
March	1st to 10th	Day	53% 7% 12% 19% 9%	3435
	11th to 20th	Day	51% 6% 14% 19% 9% 1	3480
	21st to end	Day	43% 5% 13% 23% 14% 2	3815
April	1st to 10th	Day	50% 6% 13% 18% 11% 2	2260
	11th to 20th	Day	47% 6% 10% 21% 14% 2	2304
	21st to end	Day	49% 6% 11% 19% 12% 3	2470
May	1st to 10th	Day	46% 7% 14% 18% 14% 2	4142
	11th to 20th	Day	47% 12% 13% 18% 9% 1	4402
	21st to end	Day	34% 6% 15% 26% 16% 3	4837
June	1st to 10th	Day	41% 8% 14% 22% 14% 1	2660
	11th to 20th	Day	36% 7% 14% 25% 16% 2	2660
	21st to end	Day	36% 6% 18% 25% 14% 1	2660
July	1st to 10th	Day	32% 5% 17% 28% 16% 2	4370
	11th to 20th	Day	32% 5% 15% 36% 11% 1	4365
	21st to end	Day	35% 7% 16% 24% 17% 1	4416
August	1st to 10th	Day	42% 5% 15% 23% 14% 1	4091
	11th to 20th	Day	37% 5% 18% 27% 11% 1	4083
	21st to end	Day	33% 5% 15% 36% 10% 1	4324
September	1st to 10th	Day	36% 8% 14% 29% 12% 1	2280
	11th to 20th	Day	32% 7% 16% 30% 15% 1	2193
	21st to end	Day	41% 7% 16% 27% 10%	2036
October	1st to 10th	Day	36% 5% 17% 27% 15% 1	3160
	11th to 20th	Day	37% 5% 18% 25% 14% 1	3140
	21st to end	Day	49% 4 18% 23% 6%	3428
November	1st to 10th	Day	47% 6% 16% 21% 8% 1	1640
	11th to 20th	Day	54% 8% 15% 15% 8% 1	1520
	21st to end	Day	58% 7% 15% 17% 3	1520
December	1st to 10th	Day	66% 6% 14% 12% 3	1520
	11th to 20th	Day	59% 10% 14% 12% 6%	1906
	21st to end	Day	73% 7% 8% 10% 2	2772
January	1st to 10th	Night	60% 7% 16% 12% 4 1	4429
	11th to 20th	Night	65% 12% 10% 9% 3 1	4244
	21st to end	Night	65% 9% 11% 10% 4 1	4532
February	1st to 10th	Night	59% 8% 11% 17% 4 1	2470
	11th to 20th	Night	57% 6% 11% 17% 8% 1	2405
	21st to end	Night	55% 5% 13% 19% 8% 1	1988
March	1st to 10th	Night	53% 5% 11% 23% 7% 1	3418
	11th to 20th	Night	49% 5% 14% 20% 11% 1	3480
	21st to end	Night	40% 6% 9% 25% 18% 2	3817
April	1st to 10th	Night	51% 4 10% 20% 14% 1	1919
	11th to 20th	Night	47% 5% 10% 20% 16% 2	1840
	21st to end	Night	46% 7% 11% 19% 15% 2	1710
May	1st to 10th	Night	46% 6% 12% 18% 16% 2	2818
	11th to 20th	Night	45% 11% 13% 19% 10% 3	2496
	21st to end	Night	31% 6% 13% 26% 21% 3	2739
June	1st to 10th	Night	39% 6% 12% 24% 16% 2	1520
	11th to 20th	Night	37% 5% 12% 23% 21% 2	1520
	21st to end	Night	38% 6% 13% 24% 17% 1	1520
July	1st to 10th	Night	31% 5% 15% 25% 21% 3	2480
	11th to 20th	Night	32% 5% 13% 34% 15% 1	2472
	21st to end	Night	31% 6% 15% 29% 17% 2	2892
August	1st to 10th	Night	35% 5% 14% 29% 15% 2	2814
	11th to 20th	Night	34% 5% 15% 33% 12% 1	2812
	21st to end	Night	35% 6% 12% 32% 15% 1	3299
September	1st to 10th	Night	35% 7% 14% 28% 15% 1	1900
	11th to 20th	Night	29% 6% 12% 34% 18%	1984
	21st to end	Night	42% 6% 13% 27% 12%	2143
October	1st to 10th	Night	35% 5% 10% 26% 24% 1	3800
	11th to 20th	Night	43% 5% 15% 28% 9%	3779
	21st to end	Night	41% 5% 16% 28% 10% 1	4120
November	1st to 10th	Night	44% 6% 13% 23% 12% 1	2536
	11th to 20th	Night	51% 7% 15% 17% 9% 1	2660
	21st to end	Night	56% 8% 17% 15% 4	2660
December	1st to 10th	Night	62% 7% 12% 15% 5%	2660
	11th to 20th	Night	62% 7% 13% 14% 4	3288
	21st to end	Night	71% 8% 12% 8% 2	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	22% 16% 26% 26% 9% 1	180
	11th to 20th	Day	22% 16% 35% 17% 9%	235
	21st to end	Day	24% 10% 32% 27% 6% 1	297
February	1st to 10th	Day	19% 13% 39% 21% 7%	270
	11th to 20th	Day	18% 14% 38% 24% 6%	270
	21st to end	Day	22% 20% 29% 25% 4	258
March	1st to 10th	Day	21% 8% 33% 30% 8%	460
	11th to 20th	Day	17% 13% 30% 29% 9% 1	460
	21st to end	Day	24% 7% 31% 29% 8% 1	506
April	1st to 10th	Day	17% 10% 27% 37% 8% 1	460
	11th to 20th	Day	25% 6% 29% 25% 12% 3	452
	21st to end	Day	21% 6% 27% 32% 12% 2	460
May	1st to 10th	Day	20% 4 20% 34% 18% 5%	463
	11th to 20th	Day	15% 2 17% 37% 25% 5%	487
	21st to end	Day	12% 2 15% 36% 29% 7%	529
June	1st to 10th	Day	13% 4 17% 39% 22% 3	490
	11th to 20th	Day	12% 3 14% 36% 31% 4	490
	21st to end	Day	15% 3 12% 41% 25% 4	490
July	1st to 10th	Day	8% 1 10% 34% 38% 9%	485
	11th to 20th	Day	14% 1 9% 32% 34% 10%	484
	21st to end	Day	8% 3 10% 39% 31% 8%	532
August	1st to 10th	Day	12% 2 9% 33% 31% 12%	486
	11th to 20th	Day	9% 1 11% 34% 31% 13%	479
	21st to end	Day	11% 2 14% 31% 32% 11%	539
September	1st to 10th	Day	10% 3 15% 33% 28% 11%	490
	11th to 20th	Day	9% 2 12% 31% 26% 20%	490
	21st to end	Day	14% 4 20% 32% 20% 10%	490
October	1st to 10th	Day	20% 5% 23% 26% 19% 7%	490
	11th to 20th	Day	19% 8% 31% 29% 11% 3	490
	21st to end	Day	26% 8% 26% 27% 12% 1	539
November	1st to 10th	Day	20% 10% 26% 28% 15% 2	283
	11th to 20th	Day	20% 14% 27% 29% 9% 1	180
	21st to end	Day	22% 10% 35% 25% 7% 1	180
December	1st to 10th	Day	22% 10% 34% 25% 8% 2	180
	11th to 20th	Day	23% 16% 37% 18% 6% 1	180
	21st to end	Day	28% 12% 39% 18% 4	198
January	1st to 10th	Night	24% 12% 38% 19% 8%	760
	11th to 20th	Night	28% 12% 31% 24% 5%	760
	21st to end	Night	19% 10% 36% 27% 7% 1	836
February	1st to 10th	Night	21% 13% 39% 23% 4	760
	11th to 20th	Night	21% 12% 35% 26% 6%	743
	21st to end	Night	20% 10% 41% 24% 5%	628
March	1st to 10th	Night	19% 8% 34% 33% 7% 1	760
	11th to 20th	Night	20% 9% 36% 26% 8% 1	760
	21st to end	Night	19% 7% 29% 32% 12% 1	836
April	1st to 10th	Night	23% 6% 28% 34% 8% 1	760
	11th to 20th	Night	18% 6% 28% 34% 12% 2	716
	21st to end	Night	21% 5% 22% 37% 13% 1	570
May	1st to 10th	Night	18% 3 18% 38% 21% 2	561
	11th to 20th	Night	17% 1 19% 39% 23% 2	374
	21st to end	Night	9% 3 13% 40% 30% 4	411
June	1st to 10th	Night	13% 2 15% 42% 24% 3	380
	11th to 20th	Night	10% 3 15% 41% 28% 3	380
	21st to end	Night	12% 2 14% 41% 28% 3	380
July	1st to 10th	Night	6% 2 8% 44% 33% 6%	370
	11th to 20th	Night	13% 3 10% 37% 33% 5%	368
	21st to end	Night	9% 3 8% 43% 34% 4	563
August	1st to 10th	Night	11% 2 10% 35% 36% 7%	567
	11th to 20th	Night	8% 2 10% 36% 35% 8%	564
	21st to end	Night	11% 3 15% 35% 31% 5%	724
September	1st to 10th	Night	11% 3 16% 35% 27% 8%	760
	11th to 20th	Night	13% 3 14% 29% 30% 11%	760
	21st to end	Night	17% 5% 17% 30% 25% 6%	760
October	1st to 10th	Night	19% 4 25% 28% 20% 5%	760
	11th to 20th	Night	23% 7% 26% 31% 12% 2	760
	21st to end	Night	26% 7% 26% 31% 9% 1	836
November	1st to 10th	Night	22% 7% 24% 34% 12% 2	760
	11th to 20th	Night	21% 10% 32% 26% 9% 2	760
	21st to end	Night	24% 9% 30% 29% 7% 1	760
December	1st to 10th	Night	28% 11% 34% 23% 5%	760
	11th to 20th	Night	21% 11% 39% 23% 5% 1	760
	21st to end	Night	31% 10% 34% 22% 4	836

Page generated at 2024-11-03 02:11:21. Version ac07

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