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 2024-09-14.

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% 3 8% 5% 5% 5% 4 6% 7% 33%	100881
	Night	16% 11% 4 8% 5% 4 4 4 5% 7% 33%	97005
Transparency	Day	48% 8% 14% 19% 10% 1	100649
	Night	49% 8% 13% 18% 10% 1	96856
Seeing	Day	18% 11% 27% 25% 15% 5%	14297
	Night	19% 10% 28% 28% 13% 2	23725

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% 19% 7% 11% 6% 4 3 3 4 4 22%	2517
	11th to 20th	Day	13% 21% 7% 14% 8% 7% 5% 3 4 5% 12%	2821
	21st to end	Day	23% 19% 7% 12% 7% 6% 5% 3 3 4 13%	3124
February	1st to 10th	Day	17% 17% 5% 15% 7% 6% 4 3 5% 4 17%	1710
	11th to 20th	Day	13% 17% 6% 13% 7% 5% 4 4 5% 4 22%	1663
	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% 8% 46%	2084
	21st to end	Day	14% 7% 2 8% 4 5% 6% 4 6% 8% 36%	1947
October	1st to 10th	Day	19% 8% 3 7% 5% 4 5% 3 5% 6% 35%	1800
	11th to 20th	Day	20% 10% 3 10% 5% 4 4 3 6% 6% 30%	1800
	21st to end	Day	23% 13% 3 8% 6% 4 4 4 5% 6% 24%	1980
November	1st to 10th	Day	14% 8% 3 9% 5% 4 5% 4 6% 7% 34%	1655
	11th to 20th	Day	14% 13% 4 9% 5% 5% 5% 3 6% 7% 30%	1520
	21st to end	Day	21% 15% 3 7% 6% 4 5% 3 5% 7% 26%	1520
December	1st to 10th	Day	18% 16% 6% 11% 6% 6% 4 4 5% 5% 20%	1520
	11th to 20th	Day	19% 15% 6% 10% 6% 5% 5% 4 6% 5% 19%	1906
	21st to end	Day	28% 19% 6% 11% 5% 4 4 3 4 3 12%	2772
January	1st to 10th	Night	18% 19% 5% 9% 5% 4 4 3 4 5% 23%	4429
	11th to 20th	Night	14% 18% 7% 12% 7% 5% 5% 3 5% 5% 19%	4124
	21st to end	Night	25% 17% 6% 10% 5% 4 4 3 4 4 16%	4532
February	1st to 10th	Night	17% 16% 5% 10% 7% 6% 4 4 4 6% 21%	2470
	11th to 20th	Night	15% 13% 5% 11% 5% 6% 5% 4 5% 5% 26%	2403
	21st to end	Night	18% 14% 5% 10% 6% 5% 5% 4 5% 7% 23%	1960
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	11% 5% 2 5% 3 3 3 3 5% 7% 54%	1951
	21st to end	Night	14% 7% 2 8% 5% 5% 4 4 5% 7% 39%	2012
October	1st to 10th	Night	17% 7% 3 7% 5% 4 4 3 5% 6% 40%	2160
	11th to 20th	Night	20% 10% 3 8% 5% 4 4 4 5% 6% 32%	2160
	21st to end	Night	23% 9% 3 7% 5% 5% 4 4 5% 7% 28%	2376
November	1st to 10th	Night	16% 8% 3 6% 4 4 3 3 6% 7% 39%	2418
	11th to 20th	Night	15% 10% 3 8% 5% 5% 4 4 5% 8% 31%	2660
	21st to end	Night	19% 12% 4 8% 5% 4 4 4 6% 7% 27%	2660
December	1st to 10th	Night	21% 15% 5% 8% 5% 4 5% 4 5% 6% 22%	2660
	11th to 20th	Night	15% 19% 6% 10% 5% 5% 4 3 5% 5% 22%	3288
	21st to end	Night	29% 16% 6% 9% 5% 5% 4 3 4 5% 13%	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	63% 12% 12% 8% 5%	2518
	11th to 20th	Day	73% 9% 9% 6% 2	2821
	21st to end	Day	75% 7% 10% 6% 2	3124
February	1st to 10th	Day	69% 6% 10% 10% 3 1	1710
	11th to 20th	Day	63% 8% 11% 13% 4	1672
	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% 8% 15% 28% 15% 1	2084
	21st to end	Day	42% 9% 17% 22% 9% 1	1947
October	1st to 10th	Day	48% 7% 15% 17% 11% 1	1800
	11th to 20th	Day	52% 8% 15% 18% 7% 1	1800
	21st to end	Day	62% 6% 13% 13% 5% 1	1980
November	1st to 10th	Day	47% 9% 16% 19% 8% 2	1655
	11th to 20th	Day	52% 9% 16% 15% 8% 1	1520
	21st to end	Day	57% 9% 16% 14% 4	1520
December	1st to 10th	Day	65% 9% 13% 11% 1	1520
	11th to 20th	Day	64% 11% 13% 9% 3	1906
	21st to end	Day	75% 9% 9% 6% 1	2772
January	1st to 10th	Night	62% 12% 12% 11% 3	4429
	11th to 20th	Night	65% 13% 14% 6% 2	4124
	21st to end	Night	71% 9% 9% 9% 2	4532
February	1st to 10th	Night	64% 7% 11% 13% 4 1	2470
	11th to 20th	Night	58% 7% 14% 16% 5%	2405
	21st to end	Night	60% 8% 12% 13% 7%	1960
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% 17% 1	1951
	21st to end	Night	43% 8% 13% 22% 13% 1	2012
October	1st to 10th	Night	44% 7% 13% 21% 14% 1	2160
	11th to 20th	Night	51% 7% 16% 17% 9%	2160
	21st to end	Night	56% 7% 14% 15% 9% 1	2376
November	1st to 10th	Night	43% 8% 13% 23% 11% 1	2418
	11th to 20th	Night	50% 7% 15% 18% 8% 1	2660
	21st to end	Night	54% 11% 16% 15% 3	2660
December	1st to 10th	Night	63% 10% 13% 11% 3	2660
	11th to 20th	Night	63% 10% 12% 11% 4	3288
	21st to end	Night	72% 10% 11% 6% 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% 19% 33% 17% 9% 1	180
	11th to 20th	Day	27% 20% 34% 12% 6% 1	267
	21st to end	Day	19% 20% 33% 21% 6%	297
February	1st to 10th	Day	21% 20% 39% 15% 4	270
	11th to 20th	Day	23% 20% 40% 16% 2	270
	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% 16%	463
	21st to end	Day	15% 9% 23% 25% 19% 8%	450
October	1st to 10th	Day	21% 11% 24% 19% 20% 6%	450
	11th to 20th	Day	19% 16% 33% 20% 9% 2	450
	21st to end	Day	32% 14% 27% 19% 9%	495
November	1st to 10th	Day	19% 19% 31% 21% 8% 3	295
	11th to 20th	Day	26% 21% 23% 22% 6% 2	180
	21st to end	Day	27% 17% 38% 14% 4	180
December	1st to 10th	Day	23% 22% 32% 18% 4 1	180
	11th to 20th	Day	27% 24% 31% 15% 3	180
	21st to end	Day	23% 23% 37% 15% 3	198
January	1st to 10th	Night	27% 17% 33% 17% 6%	760
	11th to 20th	Night	27% 17% 33% 19% 4	760
	21st to end	Night	21% 14% 36% 24% 6%	836
February	1st to 10th	Night	25% 16% 35% 21% 3	760
	11th to 20th	Night	19% 17% 35% 26% 3	743
	21st to end	Night	24% 14% 35% 25% 3	628
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% 5% 18% 29% 29% 7%	736
	21st to end	Night	16% 6% 22% 30% 21% 5%	720
October	1st to 10th	Night	19% 7% 25% 27% 19% 3	720
	11th to 20th	Night	24% 12% 29% 26% 9% 1	720
	21st to end	Night	28% 12% 28% 26% 6%	792
November	1st to 10th	Night	19% 11% 32% 26% 11% 2	740
	11th to 20th	Night	20% 15% 35% 20% 9% 2	760
	21st to end	Night	25% 13% 35% 20% 6%	760
December	1st to 10th	Night	29% 17% 30% 18% 5%	760
	11th to 20th	Night	24% 19% 34% 18% 5%	760
	21st to end	Night	29% 14% 33% 22% 2	836

Page generated at 2024-09-11 10:00:07. Version ac07

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