Fredonia Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fredonia Observatory clear sky chart from 2005-11-06 to 2026-05-02.

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	17% 13% 5% 9% 5% 4 4 3 5% 6% 29%	131926
	Night	17% 16% 5% 11% 5% 4 4 3 4 5% 25%	130546
Transparency	Day	56% 4 11% 19% 9% 1	135521
	Night	61% 4 10% 16% 8% 1	135037
Seeing	Day	28% 17% 29% 17% 7% 2	16376
	Night	28% 17% 26% 20% 8% 1	25974

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	17% 24% 11% 26% 5% 3 2 2 2 2 6%	4701
	11th to 20th	Day	10% 23% 12% 22% 10% 6% 4 2 3 3 7%	5246
	21st to end	Day	15% 16% 9% 19% 10% 8% 5% 3 3 3 9%	5780
February	1st to 10th	Day	16% 20% 8% 15% 8% 5% 4 3 3 3 15%	1890
	11th to 20th	Day	13% 19% 9% 18% 8% 4 3 3 3 4 16%	1843
	21st to end	Day	18% 17% 6% 12% 7% 5% 5% 3 4 5% 19%	1658
March	1st to 10th	Day	16% 15% 7% 12% 5% 4 3 2 3 4 28%	5042
	11th to 20th	Day	13% 17% 7% 8% 4 4 4 3 4 6% 30%	5090
	21st to end	Day	20% 16% 5% 11% 4 3 3 2 3 4 27%	5586
April	1st to 10th	Day	18% 15% 4 8% 4 4 4 3 4 6% 30%	2475
	11th to 20th	Day	19% 12% 3 6% 4 4 4 3 5% 7% 33%	2530
	21st to end	Day	20% 12% 2 7% 4 4 4 3 5% 5% 35%	2730
May	1st to 10th	Day	23% 9% 3 6% 5% 4 5% 3 5% 6% 30%	5901
	11th to 20th	Day	20% 9% 3 7% 5% 4 5% 3 5% 7% 32%	6168
	21st to end	Day	23% 7% 2 6% 4 3 4 3 5% 7% 37%	6949
June	1st to 10th	Day	17% 6% 2 6% 4 4 4 3 6% 7% 40%	2800
	11th to 20th	Day	15% 6% 2 6% 5% 4 6% 4 7% 9% 38%	2800
	21st to end	Day	15% 4 2 5% 4 4 4 4 6% 9% 42%	2800
July	1st to 10th	Day	11% 5% 2 6% 5% 4 5% 4 6% 10% 44%	6360
	11th to 20th	Day	15% 6% 2 6% 4 4 4 4 6% 8% 41%	6234
	21st to end	Day	12% 5% 2 6% 4 4 4 4 5% 7% 46%	6424
August	1st to 10th	Day	18% 5% 2 6% 4 4 5% 4 6% 8% 40%	4234
	11th to 20th	Day	17% 6% 3 7% 4 5% 5% 4 6% 9% 35%	4174
	21st to end	Day	14% 5% 2 5% 4 4 4 3 6% 9% 44%	4449
September	1st to 10th	Day	16% 7% 2 5% 4 4 5% 4 5% 8% 40%	2400
	11th to 20th	Day	14% 4 2 5% 4 4 5% 4 6% 7% 45%	2281
	21st to end	Day	19% 7% 3 8% 5% 6% 5% 4 5% 7% 32%	2157
October	1st to 10th	Day	22% 8% 2 6% 4 4 3 3 5% 7% 35%	2000
	11th to 20th	Day	25% 10% 3 7% 5% 4 4 4 4 6% 28%	2000
	21st to end	Day	28% 15% 4 7% 5% 4 4 4 4 4 21%	2200
November	1st to 10th	Day	18% 18% 4 7% 4 4 4 4 5% 5% 27%	1870
	11th to 20th	Day	18% 27% 4 8% 4 3 4 3 4 6% 20%	1680
	21st to end	Day	22% 28% 6% 8% 5% 3 3 3 4 5% 14%	1680
December	1st to 10th	Day	21% 35% 12% 10% 4 2 3 2 2 2 7%	2680
	11th to 20th	Day	19% 24% 8% 16% 4 3 3 3 3 3 12%	3066
	21st to end	Day	21% 25% 8% 12% 6% 3 3 2 3 4 12%	4048
January	1st to 10th	Night	17% 26% 9% 28% 6% 3 2 2 2 2 5%	8192
	11th to 20th	Night	10% 24% 10% 22% 9% 5% 4 3 3 3 6%	7639
	21st to end	Night	15% 18% 8% 17% 9% 8% 3 2 3 5% 11%	8401
February	1st to 10th	Night	17% 21% 6% 16% 9% 4 3 2 3 3 15%	2730
	11th to 20th	Night	15% 19% 8% 16% 7% 5% 4 3 4 4 16%	2663
	21st to end	Night	16% 19% 6% 16% 6% 5% 4 3 4 5% 17%	2145
March	1st to 10th	Night	19% 17% 5% 9% 6% 4 3 3 3 4 27%	5018
	11th to 20th	Night	16% 16% 6% 8% 3 3 3 3 4 6% 33%	5089
	21st to end	Night	16% 15% 5% 10% 5% 4 4 3 4 4 30%	5588
April	1st to 10th	Night	19% 17% 5% 8% 4 4 3 3 4 5% 27%	2144
	11th to 20th	Night	21% 10% 3 6% 5% 4 4 4 5% 5% 32%	2056
	21st to end	Night	19% 11% 3 6% 5% 4 4 4 5% 6% 34%	1890
May	1st to 10th	Night	25% 10% 3 7% 5% 4 4 3 4 5% 29%	4062
	11th to 20th	Night	18% 7% 2 6% 5% 5% 5% 4 5% 7% 36%	3723
	21st to end	Night	21% 8% 2 6% 3 3 3 3 5% 8% 39%	3926
June	1st to 10th	Night	15% 6% 2 7% 5% 4 5% 5% 6% 8% 36%	1600
	11th to 20th	Night	14% 7% 2 7% 5% 6% 4 4 6% 8% 38%	1600
	21st to end	Night	15% 7% 2 6% 5% 5% 5% 3 6% 7% 40%	1600
July	1st to 10th	Night	12% 6% 3 7% 4 4 4 3 6% 10% 41%	3600
	11th to 20th	Night	14% 5% 2 6% 4 5% 4 4 6% 8% 42%	3709
	21st to end	Night	10% 6% 2 6% 4 4 4 4 6% 7% 47%	4428
August	1st to 10th	Night	13% 7% 3 7% 4 4 4 4 6% 9% 39%	2915
	11th to 20th	Night	21% 8% 2 8% 4 4 4 4 5% 7% 34%	2875
	21st to end	Night	11% 6% 2 6% 4 4 5% 4 6% 9% 43%	3416
September	1st to 10th	Night	17% 7% 2 6% 4 4 4 3 5% 6% 43%	2000
	11th to 20th	Night	15% 5% 2 5% 3 3 4 3 5% 6% 51%	2115
	21st to end	Night	21% 7% 2 8% 4 4 5% 4 6% 6% 33%	2242
October	1st to 10th	Night	19% 7% 3 6% 4 4 4 4 5% 6% 38%	2400
	11th to 20th	Night	24% 11% 3 7% 5% 4 3 4 4 7% 28%	2400
	21st to end	Night	33% 11% 3 6% 4 3 3 3 4 5% 25%	2640
November	1st to 10th	Night	20% 17% 3 7% 4 3 3 3 4 5% 31%	2642
	11th to 20th	Night	19% 23% 5% 7% 4 5% 4 3 4 5% 21%	2940
	21st to end	Night	21% 26% 7% 8% 4 3 3 3 3 4 16%	2940
December	1st to 10th	Night	18% 35% 9% 10% 5% 4 3 2 3 3 8%	4720
	11th to 20th	Night	19% 27% 9% 14% 5% 4 3 3 3 4 10%	5348
	21st to end	Night	20% 24% 7% 12% 6% 4 3 3 3 4 12%	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	87% 2 4 6% 1	4702
	11th to 20th	Day	84% 2 6% 5% 3	5280
	21st to end	Day	81% 3 7% 7% 2	5780
February	1st to 10th	Day	77% 3 7% 9% 4	1890
	11th to 20th	Day	75% 3 6% 11% 5%	1852
	21st to end	Day	70% 3 8% 13% 5% 1	1658
March	1st to 10th	Day	61% 2 12% 19% 5%	5045
	11th to 20th	Day	57% 3 15% 18% 5% 1	5090
	21st to end	Day	62% 3 5% 20% 9% 1	5586
April	1st to 10th	Day	58% 3 10% 18% 10%	2475
	11th to 20th	Day	53% 3 9% 23% 11% 2	2530
	21st to end	Day	53% 3 10% 20% 13% 2	2730
May	1st to 10th	Day	55% 4 9% 20% 8% 4	5910
	11th to 20th	Day	52% 5% 10% 22% 10% 1	6172
	21st to end	Day	49% 4 12% 22% 11% 3	6949
June	1st to 10th	Day	44% 4 12% 24% 15% 1	2800
	11th to 20th	Day	43% 5% 15% 24% 13%	2800
	21st to end	Day	40% 5% 13% 27% 14% 1	2800
July	1st to 10th	Day	36% 5% 13% 27% 17% 1	6290
	11th to 20th	Day	40% 5% 13% 24% 16%	6159
	21st to end	Day	37% 5% 12% 27% 18%	6240
August	1st to 10th	Day	43% 5% 14% 25% 13%	4221
	11th to 20th	Day	47% 6% 16% 24% 7%	4213
	21st to end	Day	39% 5% 13% 31% 12% 1	4449
September	1st to 10th	Day	43% 4 13% 27% 12% 1	2400
	11th to 20th	Day	39% 4 12% 29% 15% 1	2281
	21st to end	Day	52% 4 11% 23% 10% 1	2157
October	1st to 10th	Day	44% 5% 13% 24% 13% 1	3260
	11th to 20th	Day	51% 3 14% 17% 12% 3	3240
	21st to end	Day	52% 4 14% 22% 7% 1	3538
November	1st to 10th	Day	60% 3 9% 17% 9% 2	1870
	11th to 20th	Day	66% 3 9% 14% 6% 2	1680
	21st to end	Day	74% 3 9% 10% 4 1	1680
December	1st to 10th	Day	86% 2 5% 6% 1	2680
	11th to 20th	Day	79% 2 9% 8% 1	3066
	21st to end	Day	78% 3 10% 7% 2	4048
January	1st to 10th	Night	89% 2 5% 3 1	8192
	11th to 20th	Night	83% 3 7% 5% 2	7680
	21st to end	Night	77% 3 7% 8% 4	8401
February	1st to 10th	Night	76% 2 8% 10% 3	2730
	11th to 20th	Night	73% 3 7% 12% 4	2665
	21st to end	Night	72% 2 8% 11% 6% 1	2145
March	1st to 10th	Night	62% 3 10% 17% 7% 1	5028
	11th to 20th	Night	55% 3 11% 22% 8% 2	5090
	21st to end	Night	57% 4 7% 17% 13% 2	5588
April	1st to 10th	Night	61% 3 9% 17% 10% 1	2144
	11th to 20th	Night	54% 3 10% 19% 12% 2	2056
	21st to end	Night	51% 4 9% 21% 12% 2	1890
May	1st to 10th	Night	59% 3 7% 15% 10% 6%	4069
	11th to 20th	Night	48% 5% 13% 23% 9% 1	3724
	21st to end	Night	45% 4 10% 25% 12% 3	3927
June	1st to 10th	Night	44% 5% 10% 25% 14% 3	1600
	11th to 20th	Night	43% 4 12% 23% 16% 1	1600
	21st to end	Night	43% 5% 13% 24% 14% 1	1600
July	1st to 10th	Night	39% 5% 13% 26% 15% 2	3560
	11th to 20th	Night	38% 6% 12% 26% 16% 1	3661
	21st to end	Night	36% 5% 13% 23% 21% 2	4297
August	1st to 10th	Night	42% 5% 11% 31% 10% 2	2904
	11th to 20th	Night	48% 5% 15% 23% 8%	2902
	21st to end	Night	37% 5% 14% 31% 11% 1	3416
September	1st to 10th	Night	42% 4 12% 27% 13% 2	2000
	11th to 20th	Night	36% 3 12% 30% 18% 1	2115
	21st to end	Night	51% 4 11% 22% 11% 1	2242
October	1st to 10th	Night	44% 6% 9% 23% 18% 1	3920
	11th to 20th	Night	52% 3 12% 18% 14% 2	3899
	21st to end	Night	48% 4 14% 21% 12% 1	4252
November	1st to 10th	Night	57% 3 9% 20% 9% 2	2642
	11th to 20th	Night	66% 3 9% 14% 6% 2	2940
	21st to end	Night	73% 2 10% 11% 3	2940
December	1st to 10th	Night	84% 3 7% 5% 1	4720
	11th to 20th	Night	79% 3 8% 8% 2	5348
	21st to end	Night	77% 3 9% 9% 2	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	35% 32% 25% 5% 2 1	228
	11th to 20th	Day	41% 32% 20% 5% 2 1	330
	21st to end	Day	34% 31% 28% 6% 2	363
February	1st to 10th	Day	33% 29% 31% 7%	330
	11th to 20th	Day	34% 34% 28% 3 1	330
	21st to end	Day	39% 26% 29% 5%	318
March	1st to 10th	Day	33% 24% 30% 9% 4	540
	11th to 20th	Day	34% 23% 32% 9% 2 1	540
	21st to end	Day	39% 21% 26% 10% 4	594
April	1st to 10th	Day	34% 22% 29% 11% 3	540
	11th to 20th	Day	36% 21% 24% 13% 5% 2	532
	21st to end	Day	31% 19% 32% 14% 3 1	540
May	1st to 10th	Day	33% 16% 30% 15% 5% 1	507
	11th to 20th	Day	28% 14% 30% 22% 6% 1	527
	21st to end	Day	21% 10% 35% 21% 9% 4	573
June	1st to 10th	Day	21% 15% 35% 20% 7% 2	530
	11th to 20th	Day	20% 12% 32% 24% 9% 2	530
	21st to end	Day	19% 12% 35% 25% 8% 1	530
July	1st to 10th	Day	14% 8% 30% 29% 15% 4	525
	11th to 20th	Day	18% 9% 30% 27% 10% 5%	524
	21st to end	Day	14% 6% 38% 27% 12% 3	576
August	1st to 10th	Day	14% 7% 28% 32% 13% 6%	526
	11th to 20th	Day	20% 6% 27% 26% 16% 5%	519
	21st to end	Day	17% 8% 31% 27% 12% 5%	583
September	1st to 10th	Day	20% 12% 24% 24% 14% 6%	530
	11th to 20th	Day	14% 5% 23% 32% 17% 8%	530
	21st to end	Day	23% 16% 25% 22% 10% 4	530
October	1st to 10th	Day	27% 10% 27% 22% 12% 3	530
	11th to 20th	Day	33% 17% 31% 13% 5% 1	530
	21st to end	Day	41% 17% 27% 13% 2	583
November	1st to 10th	Day	32% 23% 30% 11% 3 1	386
	11th to 20th	Day	44% 16% 29% 8% 3	220
	21st to end	Day	45% 23% 25% 5% 1	220
December	1st to 10th	Day	44% 23% 26% 6% 1	220
	11th to 20th	Day	38% 28% 26% 8%	220
	21st to end	Day	39% 29% 26% 4 2	242
January	1st to 10th	Night	35% 27% 26% 9% 3	840
	11th to 20th	Night	35% 28% 25% 11% 1	840
	21st to end	Night	27% 29% 29% 13% 2	924
February	1st to 10th	Night	31% 27% 26% 15% 2	840
	11th to 20th	Night	29% 29% 29% 12% 2	823
	21st to end	Night	32% 27% 28% 12% 1	692
March	1st to 10th	Night	30% 22% 30% 15% 3	840
	11th to 20th	Night	31% 22% 29% 15% 4	840
	21st to end	Night	30% 15% 32% 17% 6% 1	924
April	1st to 10th	Night	30% 19% 29% 18% 4	840
	11th to 20th	Night	29% 15% 30% 19% 5% 1	812
	21st to end	Night	26% 12% 33% 22% 6% 1	630
May	1st to 10th	Night	27% 8% 27% 28% 9% 1	603
	11th to 20th	Night	19% 7% 33% 32% 9%	464
	21st to end	Night	17% 9% 29% 29% 14% 2	433
June	1st to 10th	Night	16% 8% 35% 29% 12% 1	400
	11th to 20th	Night	20% 9% 26% 35% 11% 1	400
	21st to end	Night	17% 7% 30% 33% 13% 1	400
July	1st to 10th	Night	12% 5% 25% 38% 17% 3	390
	11th to 20th	Night	13% 5% 26% 35% 18% 3	432
	21st to end	Night	12% 4 25% 39% 19% 1	657
August	1st to 10th	Night	13% 3 24% 36% 21% 3	597
	11th to 20th	Night	15% 4 20% 33% 24% 3	594
	21st to end	Night	17% 4 24% 31% 21% 3	775
September	1st to 10th	Night	20% 7% 22% 29% 19% 4	800
	11th to 20th	Night	18% 4 19% 31% 25% 4	800
	21st to end	Night	26% 10% 20% 26% 14% 4	800
October	1st to 10th	Night	23% 10% 28% 24% 14% 2	800
	11th to 20th	Night	33% 14% 28% 18% 6% 1	800
	21st to end	Night	40% 16% 25% 17% 2	880
November	1st to 10th	Night	34% 16% 25% 19% 5%	820
	11th to 20th	Night	37% 20% 27% 11% 5% 1	840
	21st to end	Night	39% 23% 25% 9% 4	840
December	1st to 10th	Night	41% 24% 23% 9% 3	840
	11th to 20th	Night	35% 29% 23% 11% 2	840
	21st to end	Night	35% 26% 27% 10% 1	924

Page generated at 2026-04-29 02:21:48. Version ac07

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