Niagara Centre Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Niagara Centre Observatory clear sky chart from 2005-11-06 to 2025-02-21.

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	15% 10% 4 8% 5% 5% 5% 4 5% 7% 32%	108759
	Night	16% 11% 4 8% 5% 4 4 4 5% 6% 32%	109797
Transparency	Day	48% 8% 14% 19% 10% 1	112399
	Night	50% 8% 13% 19% 11% 1	114320
Seeing	Day	18% 11% 27% 25% 15% 5%	14761
	Night	19% 10% 28% 28% 13% 1	24362

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	13% 18% 7% 12% 5% 4 4 3 4 5% 25%	3597
	11th to 20th	Day	12% 21% 8% 15% 8% 6% 5% 3 4 5% 11%	4007
	21st to end	Day	19% 16% 7% 16% 7% 6% 5% 3 3 4 15%	4466
February	1st to 10th	Day	17% 17% 5% 15% 7% 6% 4 3 5% 4 18%	1800
	11th to 20th	Day	13% 16% 6% 13% 8% 5% 4 3 5% 4 21%	1753
	21st to end	Day	19% 14% 4 12% 6% 5% 4 3 5% 6% 21%	1490
March	1st to 10th	Day	20% 11% 4 8% 6% 4 4 3 4 5% 29%	3432
	11th to 20th	Day	10% 19% 4 8% 6% 4 4 4 5% 6% 29%	3480
	21st to end	Day	18% 11% 3 8% 5% 4 4 3 5% 6% 33%	3815
April	1st to 10th	Day	18% 14% 4 8% 5% 4 5% 3 4 5% 31%	2237
	11th to 20th	Day	18% 9% 3 7% 5% 4 4 3 5% 6% 35%	2309
	21st to end	Day	19% 9% 3 8% 5% 4 4 4 5% 5% 33%	2470
May	1st to 10th	Day	18% 9% 2 7% 5% 5% 5% 3 5% 8% 33%	4108
	11th to 20th	Day	14% 10% 4 9% 5% 5% 5% 4 6% 7% 32%	4318
	21st to end	Day	11% 6% 2 5% 4 4 4 3 5% 8% 47%	4837
June	1st to 10th	Day	14% 7% 2 6% 5% 4 4 4 6% 8% 40%	2660
	11th to 20th	Day	10% 6% 2 7% 5% 5% 5% 4 7% 9% 40%	2660
	21st to end	Day	13% 6% 2 5% 4 4 5% 4 7% 8% 42%	2660
July	1st to 10th	Day	8% 4 2 5% 4 5% 5% 4 6% 11% 45%	4440
	11th to 20th	Day	11% 5% 3 5% 4 4 5% 5% 7% 10% 41%	4390
	21st to end	Day	7% 5% 2 6% 5% 5% 6% 5% 7% 9% 43%	4466
August	1st to 10th	Day	16% 6% 2 6% 4 4 5% 4 6% 9% 38%	4104
	11th to 20th	Day	12% 6% 3 7% 5% 5% 6% 5% 8% 10% 34%	4044
	21st to end	Day	9% 5% 2 6% 4 5% 4 4 6% 9% 45%	4342
September	1st to 10th	Day	12% 8% 2 6% 4 4 4 4 6% 8% 42%	2280
	11th to 20th	Day	10% 5% 2 5% 5% 5% 5% 3 7% 7% 47%	2160
	21st to end	Day	15% 7% 3 8% 4 5% 6% 4 6% 8% 34%	2055
October	1st to 10th	Day	18% 8% 3 6% 5% 4 5% 3 5% 7% 36%	1900
	11th to 20th	Day	20% 9% 3 9% 5% 4 4 3 6% 6% 31%	1900
	21st to end	Day	22% 12% 3 8% 6% 5% 4 4 5% 6% 24%	2090
November	1st to 10th	Day	14% 8% 3 9% 5% 5% 5% 4 6% 7% 34%	1743
	11th to 20th	Day	14% 13% 4 9% 5% 5% 5% 3 6% 7% 30%	1600
	21st to end	Day	20% 15% 3 7% 6% 4 5% 3 4 7% 25%	1600
December	1st to 10th	Day	20% 15% 5% 11% 6% 6% 5% 4 6% 5% 16%	2600
	11th to 20th	Day	21% 16% 5% 8% 5% 4 4 3 5% 4 24%	2986
	21st to end	Day	27% 18% 6% 11% 5% 5% 4 3 5% 4 13%	3960
January	1st to 10th	Night	15% 15% 5% 10% 7% 5% 5% 4 5% 5% 26%	6349
	11th to 20th	Night	11% 17% 6% 14% 8% 6% 5% 4 5% 6% 19%	5863
	21st to end	Night	21% 15% 6% 12% 5% 4 4 3 4 5% 20%	6490
February	1st to 10th	Night	17% 16% 5% 10% 7% 6% 4 4 4 6% 21%	2600
	11th to 20th	Night	15% 13% 5% 11% 6% 5% 5% 4 5% 5% 26%	2533
	21st to end	Night	18% 14% 5% 10% 6% 5% 5% 4 5% 7% 23%	1961
March	1st to 10th	Night	20% 10% 4 8% 6% 4 4 3 4 4 33%	3408
	11th to 20th	Night	17% 12% 3 7% 4 4 4 3 5% 7% 34%	3479
	21st to end	Night	16% 8% 3 6% 4 4 3 3 5% 5% 43%	3817
April	1st to 10th	Night	19% 11% 4 8% 5% 4 4 3 5% 6% 32%	1943
	11th to 20th	Night	18% 8% 3 7% 5% 4 4 3 5% 6% 36%	1834
	21st to end	Night	15% 9% 3 8% 4 5% 5% 4 5% 7% 35%	1710
May	1st to 10th	Night	18% 11% 4 8% 5% 3 3 3 4 6% 35%	2833
	11th to 20th	Night	12% 8% 3 8% 6% 5% 5% 4 7% 8% 34%	2573
	21st to end	Night	11% 5% 2 5% 4 3 4 4 6% 8% 47%	2738
June	1st to 10th	Night	11% 6% 2 7% 6% 6% 5% 5% 8% 7% 37%	1520
	11th to 20th	Night	9% 5% 2 6% 6% 5% 5% 5% 6% 8% 43%	1520
	21st to end	Night	12% 6% 2 6% 6% 4 5% 4 6% 8% 43%	1520
July	1st to 10th	Night	7% 5% 2 6% 4 4 5% 4 6% 9% 47%	2520
	11th to 20th	Night	10% 4 2 6% 3 4 4 4 6% 8% 48%	2566
	21st to end	Night	8% 5% 2 5% 4 4 5% 4 6% 8% 49%	3087
August	1st to 10th	Night	10% 6% 3 6% 4 4 4 3 6% 9% 45%	2825
	11th to 20th	Night	13% 8% 2 7% 4 4 4 4 6% 8% 41%	2785
	21st to end	Night	8% 4 2 5% 4 4 5% 4 6% 9% 49%	3280
September	1st to 10th	Night	13% 7% 2 7% 3 4 5% 3 5% 6% 46%	1900
	11th to 20th	Night	10% 5% 2 5% 4 3 3 3 5% 7% 54%	2017
	21st to end	Night	15% 7% 2 8% 5% 5% 4 4 5% 7% 37%	2124
October	1st to 10th	Night	16% 6% 3 7% 5% 4 4 3 5% 6% 41%	2280
	11th to 20th	Night	19% 9% 3 8% 5% 4 4 4 5% 6% 33%	2280
	21st to end	Night	22% 8% 3 7% 5% 4 5% 4 5% 7% 30%	2508
November	1st to 10th	Night	15% 8% 3 6% 4 4 4 3 6% 7% 39%	2550
	11th to 20th	Night	15% 10% 3 8% 5% 5% 4 4 5% 8% 31%	2800
	21st to end	Night	19% 12% 4 8% 5% 5% 4 4 5% 7% 27%	2800
December	1st to 10th	Night	16% 17% 4 9% 6% 5% 5% 4 6% 7% 21%	4580
	11th to 20th	Night	17% 19% 5% 9% 5% 5% 4 2 4 5% 24%	5208
	21st to end	Night	25% 16% 6% 10% 5% 5% 4 3 4 5% 16%	6996

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	60% 9% 11% 10% 8% 1	3598
	11th to 20th	Day	74% 7% 9% 5% 4 1	4041
	21st to end	Day	73% 6% 11% 6% 5%	4466
February	1st to 10th	Day	69% 6% 10% 11% 3 1	1800
	11th to 20th	Day	63% 8% 11% 13% 4	1762
	21st to end	Day	62% 8% 12% 12% 5% 1	1490
March	1st to 10th	Day	54% 8% 11% 21% 4 1	3435
	11th to 20th	Day	51% 10% 16% 16% 7% 1	3480
	21st to end	Day	48% 8% 11% 22% 10% 1	3815
April	1st to 10th	Day	54% 6% 12% 16% 11% 1	2237
	11th to 20th	Day	47% 6% 12% 20% 13% 2	2309
	21st to end	Day	50% 7% 12% 16% 12% 2	2470
May	1st to 10th	Day	48% 8% 14% 17% 11% 2	4120
	11th to 20th	Day	47% 12% 14% 19% 7% 1	4322
	21st to end	Day	33% 10% 14% 25% 16% 3	4837
June	1st to 10th	Day	40% 9% 14% 22% 14% 2	2660
	11th to 20th	Day	37% 9% 15% 24% 14% 1	2660
	21st to end	Day	36% 9% 16% 24% 14% 1	2660
July	1st to 10th	Day	32% 7% 14% 27% 18% 2	4370
	11th to 20th	Day	34% 8% 16% 29% 12%	4315
	21st to end	Day	34% 9% 17% 21% 17% 1	4324
August	1st to 10th	Day	42% 7% 16% 21% 13% 1	4091
	11th to 20th	Day	41% 9% 17% 23% 9% 1	4083
	21st to end	Day	34% 7% 13% 33% 13% 1	4342
September	1st to 10th	Day	38% 8% 16% 24% 12% 1	2280
	11th to 20th	Day	33% 7% 14% 29% 16% 1	2160
	21st to end	Day	44% 9% 17% 21% 9% 1	2055
October	1st to 10th	Day	37% 6% 16% 24% 16% 1	3160
	11th to 20th	Day	43% 6% 15% 22% 14%	3140
	21st to end	Day	50% 7% 16% 20% 6%	3428
November	1st to 10th	Day	47% 9% 16% 19% 8% 2	1743
	11th to 20th	Day	52% 9% 15% 16% 8% 1	1600
	21st to end	Day	58% 8% 16% 13% 4	1600
December	1st to 10th	Day	67% 7% 15% 9% 2	2600
	11th to 20th	Day	62% 8% 11% 10% 8% 1	2986
	21st to end	Day	73% 8% 9% 7% 3	3960
January	1st to 10th	Night	57% 9% 11% 16% 6%	6349
	11th to 20th	Night	64% 10% 13% 9% 4	5904
	21st to end	Night	67% 7% 9% 9% 9% 1	6490
February	1st to 10th	Night	64% 7% 11% 13% 5% 1	2600
	11th to 20th	Night	58% 7% 14% 16% 5%	2535
	21st to end	Night	60% 8% 12% 13% 7%	1961
March	1st to 10th	Night	54% 6% 12% 21% 6% 1	3418
	11th to 20th	Night	47% 8% 17% 17% 9% 2	3480
	21st to end	Night	41% 6% 11% 25% 15% 2	3817
April	1st to 10th	Night	53% 7% 10% 18% 11% 1	1943
	11th to 20th	Night	48% 7% 10% 18% 15% 2	1834
	21st to end	Night	46% 8% 12% 17% 15% 3	1710
May	1st to 10th	Night	49% 8% 10% 18% 12% 3	2840
	11th to 20th	Night	42% 12% 16% 21% 7% 2	2574
	21st to end	Night	32% 8% 12% 24% 21% 2	2739
June	1st to 10th	Night	40% 11% 11% 20% 16% 1	1520
	11th to 20th	Night	37% 7% 14% 23% 17% 2	1520
	21st to end	Night	38% 8% 13% 24% 15% 2	1520
July	1st to 10th	Night	33% 6% 12% 22% 22% 3	2480
	11th to 20th	Night	32% 6% 15% 31% 15% 1	2518
	21st to end	Night	32% 8% 18% 22% 18% 2	2988
August	1st to 10th	Night	36% 7% 15% 26% 14% 2	2814
	11th to 20th	Night	40% 7% 16% 27% 10%	2812
	21st to end	Night	30% 8% 14% 32% 15% 1	3280
September	1st to 10th	Night	37% 7% 15% 23% 16% 2	1900
	11th to 20th	Night	30% 7% 12% 33% 18% 1	2017
	21st to end	Night	45% 8% 12% 22% 12% 1	2124
October	1st to 10th	Night	36% 5% 10% 26% 23% 1	3800
	11th to 20th	Night	46% 5% 14% 22% 13%	3779
	21st to end	Night	40% 5% 18% 25% 11% 1	4120
November	1st to 10th	Night	43% 7% 13% 23% 11% 1	2550
	11th to 20th	Night	51% 7% 15% 18% 9% 1	2800
	21st to end	Night	55% 11% 16% 15% 3	2800
December	1st to 10th	Night	62% 8% 15% 12% 2	4580
	11th to 20th	Night	63% 7% 9% 11% 10% 1	5208
	21st to end	Night	69% 8% 11% 8% 4	6996

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	21% 20% 35% 16% 8% 1	200
	11th to 20th	Day	26% 22% 34% 12% 5% 1	297
	21st to end	Day	20% 21% 33% 20% 5%	330
February	1st to 10th	Day	23% 21% 38% 15% 3	300
	11th to 20th	Day	24% 22% 38% 15% 2	300
	21st to end	Day	28% 24% 32% 15% 1	250
March	1st to 10th	Day	22% 13% 37% 21% 7% 1	460
	11th to 20th	Day	20% 18% 33% 22% 5% 1	460
	21st to end	Day	26% 12% 31% 21% 9% 1	506
April	1st to 10th	Day	20% 13% 33% 25% 8% 1	460
	11th to 20th	Day	25% 14% 27% 19% 11% 4	452
	21st to end	Day	23% 10% 29% 26% 9% 2	460
May	1st to 10th	Day	22% 9% 27% 27% 12% 4	463
	11th to 20th	Day	16% 8% 21% 30% 21% 4	487
	21st to end	Day	11% 7% 22% 32% 22% 6%	529
June	1st to 10th	Day	14% 7% 27% 33% 15% 3	490
	11th to 20th	Day	11% 8% 24% 31% 22% 4	490
	21st to end	Day	16% 5% 27% 32% 16% 4	490
July	1st to 10th	Day	9% 4 16% 31% 30% 10%	485
	11th to 20th	Day	15% 5% 19% 27% 25% 10%	484
	21st to end	Day	8% 4 23% 36% 21% 7%	532
August	1st to 10th	Day	10% 4 19% 30% 24% 13%	486
	11th to 20th	Day	10% 6% 20% 30% 22% 12%	479
	21st to end	Day	12% 4 20% 32% 23% 10%	539
September	1st to 10th	Day	13% 6% 21% 27% 22% 11%	490
	11th to 20th	Day	9% 5% 17% 24% 28% 18%	490
	21st to end	Day	16% 10% 24% 25% 18% 7%	490
October	1st to 10th	Day	20% 10% 25% 20% 19% 6%	490
	11th to 20th	Day	19% 15% 32% 21% 10% 3	490
	21st to end	Day	30% 15% 27% 19% 9%	539
November	1st to 10th	Day	18% 19% 32% 21% 8% 2	323
	11th to 20th	Day	25% 21% 24% 23% 6% 2	200
	21st to end	Day	26% 19% 37% 15% 4	200
December	1st to 10th	Day	25% 21% 32% 19% 4 1	200
	11th to 20th	Day	29% 22% 31% 17% 3	200
	21st to end	Day	24% 22% 35% 15% 4 1	220
January	1st to 10th	Night	26% 18% 33% 18% 6%	800
	11th to 20th	Night	26% 17% 35% 18% 4	800
	21st to end	Night	21% 14% 36% 23% 5%	880
February	1st to 10th	Night	25% 16% 35% 21% 2	800
	11th to 20th	Night	20% 17% 35% 25% 3	783
	21st to end	Night	24% 14% 35% 24% 3	629
March	1st to 10th	Night	20% 11% 35% 27% 7%	760
	11th to 20th	Night	23% 13% 32% 23% 9%	760
	21st to end	Night	20% 8% 33% 28% 10% 1	836
April	1st to 10th	Night	22% 11% 30% 31% 5%	760
	11th to 20th	Night	20% 10% 33% 26% 9% 1	710
	21st to end	Night	18% 7% 30% 34% 11%	570
May	1st to 10th	Night	18% 7% 24% 32% 17% 2	570
	11th to 20th	Night	14% 3 26% 43% 15%	426
	21st to end	Night	13% 4 24% 32% 24% 3	411
June	1st to 10th	Night	13% 2 30% 37% 18%	380
	11th to 20th	Night	12% 3 25% 39% 20% 1	380
	21st to end	Night	12% 4 22% 44% 18%	380
July	1st to 10th	Night	7% 3 18% 44% 26% 2	370
	11th to 20th	Night	10% 4 20% 40% 23% 4	388
	21st to end	Night	9% 2 17% 44% 24% 2	624
August	1st to 10th	Night	9% 4 14% 40% 30% 4	567
	11th to 20th	Night	10% 3 17% 31% 36% 4	564
	21st to end	Night	11% 1 19% 38% 28% 4	718
September	1st to 10th	Night	14% 6% 18% 33% 24% 6%	760
	11th to 20th	Night	12% 4 18% 29% 31% 7%	760
	21st to end	Night	17% 6% 21% 30% 21% 5%	760
October	1st to 10th	Night	18% 7% 26% 27% 19% 3	760
	11th to 20th	Night	23% 12% 28% 26% 10% 1	760
	21st to end	Night	26% 12% 29% 27% 6%	836
November	1st to 10th	Night	19% 11% 33% 25% 10% 2	780
	11th to 20th	Night	21% 15% 33% 21% 9% 2	800
	21st to end	Night	25% 13% 36% 20% 6%	800
December	1st to 10th	Night	29% 17% 31% 19% 5%	800
	11th to 20th	Night	25% 19% 33% 18% 5%	800
	21st to end	Night	29% 14% 32% 23% 2	880

Page generated at 2025-02-18 03:26:30. Version ac07

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