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 2026-06-16.

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 9% 5% 5% 5% 4 5% 7% 33%	137879
	Night	15% 11% 4 8% 5% 4 4 4 5% 6% 33%	134121
Transparency	Day	49% 7% 13% 19% 10% 1	141475
	Night	50% 7% 12% 18% 11% 1	138612
Seeing	Day	18% 12% 27% 24% 14% 5%	16493
	Night	19% 10% 28% 28% 12% 1	25993

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% 18% 6% 12% 5% 4 4 3 4 5% 24%	4661
	11th to 20th	Day	11% 23% 9% 18% 8% 7% 4 3 4 4 10%	5227
	21st to end	Day	16% 15% 7% 17% 9% 8% 5% 3 3 4 15%	5780
February	1st to 10th	Day	17% 17% 5% 15% 7% 6% 4 3 5% 4 18%	1890
	11th to 20th	Day	14% 16% 6% 14% 7% 5% 4 3 5% 5% 22%	1843
	21st to end	Day	19% 14% 4 12% 6% 5% 4 3 5% 6% 21%	1643
March	1st to 10th	Day	18% 11% 5% 10% 5% 4 4 3 4 5% 30%	5042
	11th to 20th	Day	11% 16% 4 8% 6% 5% 4 4 5% 7% 31%	5090
	21st to end	Day	19% 13% 4 9% 5% 4 4 3 4 5% 32%	5586
April	1st to 10th	Day	19% 14% 4 8% 5% 4 5% 3 4 5% 31%	2473
	11th to 20th	Day	18% 10% 3 7% 5% 4 4 3 5% 6% 34%	2555
	21st to end	Day	19% 9% 3 8% 5% 4 4 4 5% 6% 33%	2730
May	1st to 10th	Day	20% 9% 2 8% 5% 5% 5% 3 5% 7% 32%	7642
	11th to 20th	Day	15% 10% 3 8% 5% 5% 5% 3 5% 7% 34%	8059
	21st to end	Day	17% 6% 2 6% 4 4 4 3 5% 7% 42%	9060
June	1st to 10th	Day	13% 7% 2 6% 5% 4 4 4 6% 8% 42%	2940
	11th to 20th	Day	10% 6% 2 7% 5% 5% 5% 4 7% 9% 39%	2870
	21st to end	Day	13% 6% 2 5% 4 4 5% 4 7% 9% 42%	2800
July	1st to 10th	Day	8% 4 2 6% 4 5% 5% 5% 6% 11% 43%	6360
	11th to 20th	Day	10% 5% 3 6% 4 4 5% 4 7% 9% 42%	6296
	21st to end	Day	8% 5% 2 6% 4 4 5% 4 6% 8% 47%	6424
August	1st to 10th	Day	16% 6% 2 6% 4 4 5% 4 6% 9% 38%	4234
	11th to 20th	Day	12% 6% 3 7% 5% 5% 6% 5% 8% 10% 34%	4174
	21st to end	Day	9% 5% 2 6% 4 5% 4 4 6% 9% 45%	4479
September	1st to 10th	Day	12% 7% 2 5% 4 4 4 4 7% 8% 42%	2400
	11th to 20th	Day	9% 5% 2 5% 5% 4 5% 3 7% 7% 47%	2273
	21st to end	Day	15% 7% 2 8% 4 5% 6% 4 6% 8% 34%	2163
October	1st to 10th	Day	18% 7% 3 6% 5% 4 5% 3 5% 7% 38%	2000
	11th to 20th	Day	19% 9% 3 9% 5% 4 4 3 6% 7% 31%	2000
	21st to end	Day	22% 12% 3 8% 6% 5% 4 4 5% 6% 25%	2200
November	1st to 10th	Day	15% 8% 3 9% 5% 5% 5% 4 6% 7% 33%	1831
	11th to 20th	Day	14% 13% 4 9% 5% 5% 5% 4 5% 7% 30%	1680
	21st to end	Day	20% 15% 3 8% 6% 4 5% 3 5% 7% 25%	1680
December	1st to 10th	Day	20% 15% 5% 11% 6% 6% 5% 4 6% 5% 16%	2680
	11th to 20th	Day	20% 16% 5% 8% 5% 5% 4 3 5% 5% 24%	3066
	21st to end	Day	27% 17% 6% 11% 5% 5% 4 3 5% 4 13%	4048
January	1st to 10th	Night	15% 17% 5% 10% 6% 4 4 3 5% 5% 25%	8234
	11th to 20th	Night	11% 19% 7% 14% 7% 5% 4 3 5% 6% 19%	7643
	21st to end	Night	17% 14% 6% 13% 7% 5% 4 3 4 5% 21%	8401
February	1st to 10th	Night	16% 16% 5% 10% 7% 6% 4 4 5% 6% 23%	2730
	11th to 20th	Night	15% 13% 5% 11% 6% 5% 5% 4 5% 5% 26%	2663
	21st to end	Night	17% 14% 5% 11% 6% 5% 5% 4 5% 7% 22%	2159
March	1st to 10th	Night	17% 10% 5% 8% 7% 4 5% 3 5% 5% 33%	5018
	11th to 20th	Night	14% 10% 3 7% 4 4 4 3 5% 8% 37%	5089
	21st to end	Night	19% 10% 3 7% 4 4 3 3 5% 5% 38%	5588
April	1st to 10th	Night	19% 11% 4 8% 6% 4 4 3 5% 6% 31%	2147
	11th to 20th	Night	18% 8% 3 7% 5% 4 4 3 5% 6% 36%	2030
	21st to end	Night	15% 9% 3 8% 4 5% 4 4 5% 7% 36%	1890
May	1st to 10th	Night	21% 10% 4 8% 5% 4 4 3 4 6% 31%	5257
	11th to 20th	Night	13% 9% 3 8% 5% 5% 5% 4 6% 7% 35%	4799
	21st to end	Night	19% 6% 2 5% 3 3 4 4 5% 7% 41%	5114
June	1st to 10th	Night	11% 6% 2 7% 6% 6% 5% 5% 7% 7% 39%	1680
	11th to 20th	Night	9% 5% 2 6% 6% 5% 5% 5% 6% 9% 42%	1640
	21st to end	Night	12% 6% 2 6% 6% 4 4 3 6% 8% 44%	1600
July	1st to 10th	Night	8% 5% 2 7% 4 4 5% 4 6% 9% 46%	3600
	11th to 20th	Night	9% 5% 2 7% 4 5% 5% 4 6% 8% 47%	3660
	21st to end	Night	9% 5% 2 6% 4 4 4 4 5% 8% 51%	4428
August	1st to 10th	Night	10% 6% 3 6% 4 4 4 3 6% 9% 45%	2915
	11th to 20th	Night	13% 7% 2 7% 4 4 4 4 6% 8% 42%	2875
	21st to end	Night	7% 4 2 5% 4 4 5% 4 6% 9% 49%	3384
September	1st to 10th	Night	12% 6% 2 6% 3 4 5% 3 5% 6% 47%	2000
	11th to 20th	Night	10% 4 2 4 3 3 3 3 5% 7% 55%	2123
	21st to end	Night	15% 7% 2 8% 5% 5% 4 3 5% 7% 38%	2236
October	1st to 10th	Night	16% 6% 3 7% 4 4 4 3 5% 6% 43%	2400
	11th to 20th	Night	19% 9% 3 8% 5% 4 4 4 5% 6% 34%	2400
	21st to end	Night	21% 8% 3 7% 5% 4 5% 4 5% 6% 31%	2640
November	1st to 10th	Night	15% 9% 3 6% 4 4 4 3 6% 7% 39%	2680
	11th to 20th	Night	15% 10% 3 8% 5% 5% 4 4 5% 8% 31%	2940
	21st to end	Night	19% 12% 4 8% 5% 5% 4 4 5% 7% 26%	2940
December	1st to 10th	Night	16% 18% 4 9% 5% 5% 5% 4 6% 7% 21%	4720
	11th to 20th	Night	17% 19% 5% 9% 5% 5% 4 2 4 5% 25%	5348
	21st to end	Night	25% 16% 6% 11% 5% 5% 4 3 4 5% 16%	7150

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	62% 8% 12% 10% 8% 1	4662
	11th to 20th	Day	78% 5% 7% 4 4 1	5261
	21st to end	Day	73% 5% 10% 6% 5%	5780
February	1st to 10th	Day	68% 6% 10% 12% 4 1	1890
	11th to 20th	Day	63% 7% 11% 14% 4	1852
	21st to end	Day	62% 7% 12% 13% 5% 1	1643
March	1st to 10th	Day	55% 6% 14% 17% 8%	5045
	11th to 20th	Day	50% 8% 17% 17% 7% 2	5090
	21st to end	Day	53% 6% 9% 21% 10% 1	5586
April	1st to 10th	Day	55% 5% 12% 16% 11% 1	2473
	11th to 20th	Day	49% 6% 12% 20% 12% 1	2555
	21st to end	Day	50% 7% 12% 17% 12% 2	2730
May	1st to 10th	Day	51% 6% 13% 17% 9% 4	7651
	11th to 20th	Day	47% 8% 12% 21% 10% 1	8063
	21st to end	Day	41% 7% 11% 25% 14% 2	9061
June	1st to 10th	Day	39% 8% 13% 22% 15% 2	2940
	11th to 20th	Day	38% 9% 15% 24% 13% 1	2870
	21st to end	Day	35% 9% 16% 24% 14% 1	2800
July	1st to 10th	Day	34% 7% 14% 27% 17% 1	6290
	11th to 20th	Day	35% 7% 15% 27% 14% 1	6221
	21st to end	Day	33% 7% 15% 26% 18% 1	6240
August	1st to 10th	Day	41% 7% 16% 21% 13% 1	4221
	11th to 20th	Day	41% 9% 17% 23% 9% 1	4213
	21st to end	Day	34% 7% 13% 33% 12% 1	4479
September	1st to 10th	Day	37% 8% 16% 25% 12% 1	2400
	11th to 20th	Day	33% 7% 14% 30% 15% 1	2273
	21st to end	Day	44% 9% 17% 21% 9% 1	2163
October	1st to 10th	Day	36% 6% 16% 25% 16% 1	3260
	11th to 20th	Day	42% 6% 15% 22% 14%	3240
	21st to end	Day	50% 7% 16% 20% 7%	3538
November	1st to 10th	Day	48% 8% 16% 19% 8% 2	1831
	11th to 20th	Day	52% 8% 15% 16% 8% 1	1680
	21st to end	Day	59% 8% 15% 14% 4	1680
December	1st to 10th	Day	67% 7% 15% 9% 2	2680
	11th to 20th	Day	63% 8% 11% 10% 8% 1	3066
	21st to end	Day	73% 7% 9% 7% 3	4048
January	1st to 10th	Night	60% 8% 11% 15% 5%	8234
	11th to 20th	Night	65% 8% 11% 8% 8%	7684
	21st to end	Night	66% 6% 8% 10% 9% 1	8401
February	1st to 10th	Night	63% 6% 11% 14% 5%	2730
	11th to 20th	Night	58% 7% 14% 16% 5%	2665
	21st to end	Night	61% 7% 12% 13% 7%	2159
March	1st to 10th	Night	53% 5% 13% 17% 10% 2	5028
	11th to 20th	Night	43% 7% 18% 20% 10% 2	5090
	21st to end	Night	47% 5% 10% 21% 15% 2	5588
April	1st to 10th	Night	54% 6% 10% 17% 11% 1	2147
	11th to 20th	Night	49% 6% 10% 18% 14% 2	2030
	21st to end	Night	46% 8% 11% 18% 14% 2	1890
May	1st to 10th	Night	53% 6% 9% 14% 13% 4	5264
	11th to 20th	Night	45% 8% 13% 20% 12% 1	4800
	21st to end	Night	42% 6% 9% 24% 17% 2	5115
June	1st to 10th	Night	39% 10% 11% 20% 17% 2	1680
	11th to 20th	Night	37% 7% 14% 23% 17% 2	1640
	21st to end	Night	38% 8% 13% 23% 17% 2	1600
July	1st to 10th	Night	34% 6% 13% 22% 22% 2	3560
	11th to 20th	Night	33% 6% 14% 29% 16% 1	3612
	21st to end	Night	32% 6% 14% 23% 23% 2	4297
August	1st to 10th	Night	35% 7% 15% 25% 14% 3	2904
	11th to 20th	Night	40% 7% 16% 27% 10% 1	2902
	21st to end	Night	30% 8% 15% 32% 14% 1	3384
September	1st to 10th	Night	36% 7% 14% 25% 16% 2	2000
	11th to 20th	Night	29% 7% 12% 34% 18% 1	2123
	21st to end	Night	45% 8% 12% 22% 13% 2	2236
October	1st to 10th	Night	35% 5% 10% 27% 23% 1	3920
	11th to 20th	Night	46% 5% 14% 21% 13%	3899
	21st to end	Night	40% 5% 18% 25% 12% 1	4252
November	1st to 10th	Night	44% 7% 13% 24% 11% 1	2680
	11th to 20th	Night	51% 7% 15% 17% 9% 1	2940
	21st to end	Night	55% 10% 16% 15% 3	2940
December	1st to 10th	Night	62% 8% 15% 12% 3	4720
	11th to 20th	Night	63% 7% 9% 11% 10% 1	5348
	21st to end	Night	69% 8% 11% 8% 4	7150

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% 36% 15% 7%	220
	11th to 20th	Day	28% 23% 32% 11% 5% 1	327
	21st to end	Day	21% 21% 33% 19% 5%	363
February	1st to 10th	Day	22% 20% 38% 15% 5%	330
	11th to 20th	Day	24% 21% 38% 15% 2	330
	21st to end	Day	29% 23% 33% 15% 1	301
March	1st to 10th	Day	23% 14% 37% 19% 6% 1	540
	11th to 20th	Day	21% 21% 31% 21% 5% 1	540
	21st to end	Day	27% 13% 32% 20% 8% 1	594
April	1st to 10th	Day	23% 14% 32% 23% 8% 1	540
	11th to 20th	Day	25% 14% 27% 19% 11% 3	532
	21st to end	Day	24% 10% 29% 25% 10% 2	540
May	1st to 10th	Day	23% 10% 29% 25% 10% 3	543
	11th to 20th	Day	17% 9% 23% 28% 19% 3	567
	21st to end	Day	13% 8% 24% 29% 20% 6%	617
June	1st to 10th	Day	14% 8% 29% 32% 14% 3	570
	11th to 20th	Day	12% 8% 26% 30% 20% 4	550
	21st to end	Day	15% 5% 27% 32% 17% 4	530
July	1st to 10th	Day	9% 4 16% 31% 30% 9%	525
	11th to 20th	Day	15% 6% 20% 26% 25% 9%	524
	21st to end	Day	8% 4 24% 36% 21% 7%	576
August	1st to 10th	Day	10% 3 18% 30% 26% 13%	526
	11th to 20th	Day	10% 6% 20% 30% 22% 12%	519
	21st to end	Day	12% 4 21% 32% 22% 10%	583
September	1st to 10th	Day	14% 6% 21% 25% 22% 12%	530
	11th to 20th	Day	8% 5% 16% 24% 28% 19%	530
	21st to end	Day	16% 9% 23% 25% 20% 7%	530
October	1st to 10th	Day	19% 10% 24% 21% 19% 7%	530
	11th to 20th	Day	18% 16% 33% 21% 9% 3	530
	21st to end	Day	29% 14% 27% 20% 9%	583
November	1st to 10th	Day	19% 19% 32% 20% 7% 2	351
	11th to 20th	Day	24% 23% 24% 21% 6% 3	220
	21st to end	Day	27% 20% 35% 15% 4	220
December	1st to 10th	Day	26% 21% 30% 19% 3 1	220
	11th to 20th	Day	28% 23% 30% 17% 3	220
	21st to end	Day	25% 22% 34% 14% 4 1	242
January	1st to 10th	Night	25% 18% 33% 18% 6%	840
	11th to 20th	Night	26% 19% 33% 18% 3	840
	21st to end	Night	20% 15% 36% 23% 5%	924
February	1st to 10th	Night	24% 16% 35% 22% 3	840
	11th to 20th	Night	20% 17% 35% 25% 3	823
	21st to end	Night	24% 15% 34% 24% 3	692
March	1st to 10th	Night	20% 13% 35% 26% 6%	840
	11th to 20th	Night	24% 14% 32% 23% 8%	840
	21st to end	Night	21% 10% 33% 27% 9% 1	924
April	1st to 10th	Night	22% 12% 31% 30% 5%	840
	11th to 20th	Night	20% 11% 32% 26% 9% 1	786
	21st to end	Night	18% 7% 30% 34% 10%	630
May	1st to 10th	Night	19% 7% 25% 31% 16% 2	630
	11th to 20th	Night	14% 3 27% 42% 14%	472
	21st to end	Night	15% 5% 24% 32% 21% 2	455
June	1st to 10th	Night	13% 2 29% 39% 18%	420
	11th to 20th	Night	12% 3 26% 39% 19%	410
	21st to end	Night	12% 4 22% 44% 18%	400
July	1st to 10th	Night	7% 3 18% 44% 26% 2	390
	11th to 20th	Night	9% 4 20% 40% 23% 4	409
	21st to end	Night	9% 2 17% 44% 25% 3	657
August	1st to 10th	Night	8% 4 13% 41% 31% 4	597
	11th to 20th	Night	10% 3 16% 32% 36% 4	594
	21st to end	Night	11% 1 18% 39% 27% 4	756
September	1st to 10th	Night	14% 6% 17% 33% 25% 5%	800
	11th to 20th	Night	11% 4 17% 29% 32% 7%	800
	21st to end	Night	17% 5% 21% 31% 21% 5%	800
October	1st to 10th	Night	18% 7% 25% 28% 20% 3	800
	11th to 20th	Night	23% 12% 28% 26% 9% 1	800
	21st to end	Night	26% 11% 29% 28% 6%	880
November	1st to 10th	Night	19% 12% 33% 25% 10% 2	820
	11th to 20th	Night	21% 16% 33% 21% 8% 1	840
	21st to end	Night	25% 13% 36% 19% 6%	840
December	1st to 10th	Night	28% 17% 30% 19% 5%	840
	11th to 20th	Night	24% 20% 34% 18% 5%	840
	21st to end	Night	29% 14% 33% 22% 2	924

Page generated at 2026-06-13 02:31:44. Version ac07

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