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 2025-01-07.

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% 4 9% 5% 4 4 3 5% 6% 30%	104989
	Night	18% 16% 5% 9% 5% 4 4 3 4 5% 26%	104049
Transparency	Day	55% 4 11% 20% 9% 1	108595
	Night	60% 3 10% 17% 8% 1	108531
Seeing	Day	27% 16% 29% 18% 7% 2	14687
	Night	27% 16% 26% 20% 8% 1	24261

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	18% 28% 13% 17% 5% 3 3 2 2 3 8%	2577
	11th to 20th	Day	12% 25% 10% 20% 7% 4 4 2 3 3 10%	2840
	21st to end	Day	21% 21% 10% 18% 6% 5% 4 2 3 2 7%	3124
February	1st to 10th	Day	16% 21% 8% 15% 9% 5% 4 3 3 3 13%	1710
	11th to 20th	Day	13% 20% 9% 18% 8% 4 3 3 3 3 16%	1663
	21st to end	Day	19% 17% 5% 12% 7% 5% 4 3 3 5% 20%	1504
March	1st to 10th	Day	19% 15% 6% 9% 4 3 3 3 4 5% 30%	3432
	11th to 20th	Day	12% 21% 7% 9% 4 4 3 3 4 6% 28%	3480
	21st to end	Day	19% 14% 4 12% 4 4 3 3 4 4 29%	3815
April	1st to 10th	Day	17% 16% 3 7% 4 4 4 3 4 6% 31%	2239
	11th to 20th	Day	19% 12% 3 6% 4 4 4 3 5% 7% 34%	2286
	21st to end	Day	21% 12% 3 6% 4 4 4 3 5% 4 34%	2470
May	1st to 10th	Day	21% 9% 3 6% 5% 3 5% 3 5% 7% 32%	4108
	11th to 20th	Day	18% 11% 3 7% 5% 4 4 3 5% 6% 33%	4290
	21st to end	Day	14% 6% 2 6% 4 3 5% 4 6% 8% 45%	4837
June	1st to 10th	Day	17% 6% 2 6% 4 4 5% 3 6% 7% 39%	2660
	11th to 20th	Day	14% 5% 2 6% 5% 4 5% 4 7% 9% 39%	2660
	21st to end	Day	16% 4 2 5% 4 4 4 4 6% 9% 42%	2660
July	1st to 10th	Day	10% 4 2 6% 5% 4 5% 4 6% 11% 44%	4440
	11th to 20th	Day	14% 5% 2 5% 4 4 4 4 6% 9% 43%	4356
	21st to end	Day	10% 6% 2 6% 5% 5% 5% 4 5% 9% 42%	4466
August	1st to 10th	Day	18% 5% 2 6% 4 4 4 4 6% 8% 39%	4104
	11th to 20th	Day	17% 6% 3 7% 4 5% 5% 4 6% 9% 34%	4044
	21st to end	Day	14% 5% 2 5% 4 4 5% 3 6% 9% 44%	4313
September	1st to 10th	Day	17% 7% 2 6% 4 4 5% 4 5% 8% 39%	2280
	11th to 20th	Day	15% 4 2 5% 5% 4 5% 4 6% 7% 44%	2167
	21st to end	Day	19% 7% 3 8% 5% 6% 5% 3 5% 7% 32%	2049
October	1st to 10th	Day	23% 9% 3 6% 4 4 3 3 5% 7% 32%	1900
	11th to 20th	Day	25% 10% 3 7% 5% 3 4 4 4 6% 28%	1900
	21st to end	Day	29% 15% 4 7% 5% 4 4 4 4 5% 21%	2090
November	1st to 10th	Day	18% 18% 4 7% 4 4 4 4 5% 6% 27%	1779
	11th to 20th	Day	17% 26% 4 8% 4 3 4 3 4 6% 20%	1600
	21st to end	Day	22% 28% 6% 8% 5% 3 3 3 4 5% 14%	1600
December	1st to 10th	Day	21% 36% 13% 10% 4 2 3 2 2 2 7%	2600
	11th to 20th	Day	20% 24% 8% 16% 4 3 3 3 3 4 12%	2986
	21st to end	Day	21% 26% 8% 12% 6% 3 3 2 3 4 12%	3960
January	1st to 10th	Night	17% 30% 10% 16% 5% 4 3 2 3 3 7%	4500
	11th to 20th	Night	13% 25% 9% 15% 8% 5% 4 4 4 4 9%	4120
	21st to end	Night	22% 24% 9% 17% 7% 3 3 2 2 2 9%	4532
February	1st to 10th	Night	18% 22% 6% 16% 9% 4 3 2 3 3 15%	2470
	11th to 20th	Night	15% 19% 8% 16% 7% 5% 4 3 4 4 16%	2403
	21st to end	Night	17% 18% 6% 15% 5% 5% 4 3 4 5% 18%	1947
March	1st to 10th	Night	22% 17% 4 8% 4 4 3 3 3 4 30%	3408
	11th to 20th	Night	19% 20% 7% 9% 3 3 3 3 4 5% 25%	3479
	21st to end	Night	16% 13% 5% 9% 4 4 3 3 4 4 34%	3817
April	1st to 10th	Night	19% 16% 5% 7% 4 4 4 3 5% 5% 29%	1940
	11th to 20th	Night	21% 10% 3 6% 5% 4 3 4 5% 6% 33%	1858
	21st to end	Night	18% 11% 3 5% 5% 4 4 4 5% 6% 34%	1710
May	1st to 10th	Night	26% 9% 3 7% 4 4 4 3 4 5% 31%	2833
	11th to 20th	Night	15% 8% 3 6% 4 5% 5% 4 6% 8% 36%	2601
	21st to end	Night	14% 6% 2 6% 3 3 3 3 5% 10% 45%	2738
June	1st to 10th	Night	15% 6% 2 7% 5% 4 5% 5% 6% 8% 36%	1520
	11th to 20th	Night	13% 7% 2 6% 5% 5% 4 4 6% 8% 39%	1520
	21st to end	Night	15% 7% 2 6% 4 5% 5% 3 6% 7% 40%	1520
July	1st to 10th	Night	13% 7% 2 7% 4 4 3 3 6% 9% 42%	2520
	11th to 20th	Night	13% 5% 2 6% 4 5% 4 4 5% 9% 43%	2601
	21st to end	Night	10% 5% 2 6% 5% 5% 5% 4 6% 8% 44%	3087
August	1st to 10th	Night	13% 7% 3 7% 4 4 4 4 6% 8% 39%	2825
	11th to 20th	Night	21% 8% 2 8% 4 4 4 4 5% 7% 33%	2785
	21st to end	Night	11% 6% 2 6% 4 4 5% 4 6% 9% 43%	3311
September	1st to 10th	Night	17% 7% 2 6% 4 4 4 3 5% 6% 42%	1900
	11th to 20th	Night	16% 5% 2 5% 3 3 4 3 5% 6% 49%	2009
	21st to end	Night	22% 7% 2 8% 4 4 5% 4 6% 6% 33%	2130
October	1st to 10th	Night	19% 7% 3 7% 4 4 4 4 5% 6% 37%	2280
	11th to 20th	Night	25% 11% 3 7% 5% 4 3 3 4 7% 27%	2280
	21st to end	Night	33% 11% 3 6% 4 3 3 3 4 6% 24%	2508
November	1st to 10th	Night	20% 16% 3 7% 4 3 3 3 4 5% 31%	2513
	11th to 20th	Night	19% 23% 4 7% 4 5% 4 3 4 5% 21%	2800
	21st to end	Night	21% 26% 7% 7% 5% 3 3 2 3 5% 17%	2800
December	1st to 10th	Night	19% 35% 9% 10% 5% 4 3 2 3 3 8%	4580
	11th to 20th	Night	20% 27% 9% 14% 5% 4 3 3 3 4 10%	5208
	21st to end	Night	20% 24% 7% 12% 6% 4 3 3 3 4 12%	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	84% 2 5% 7% 1	2578
	11th to 20th	Day	80% 2 8% 7% 3	2840
	21st to end	Day	86% 1 6% 4 2	3124
February	1st to 10th	Day	79% 3 7% 7% 3	1710
	11th to 20th	Day	76% 3 5% 11% 5%	1672
	21st to end	Day	69% 3 8% 13% 5% 2	1504
March	1st to 10th	Day	60% 2 9% 23% 6%	3435
	11th to 20th	Day	60% 2 15% 16% 5% 1	3480
	21st to end	Day	60% 3 6% 21% 9% 1	3815
April	1st to 10th	Day	58% 2 10% 19% 11%	2239
	11th to 20th	Day	52% 3 9% 23% 11% 2	2286
	21st to end	Day	54% 3 10% 18% 13% 1	2470
May	1st to 10th	Day	53% 3 10% 24% 9% 2	4120
	11th to 20th	Day	54% 3 12% 22% 8% 1	4294
	21st to end	Day	39% 4 13% 25% 15% 4	4837
June	1st to 10th	Day	44% 4 12% 24% 14% 1	2660
	11th to 20th	Day	42% 5% 15% 24% 13%	2660
	21st to end	Day	40% 5% 13% 27% 13% 1	2660
July	1st to 10th	Day	36% 4 14% 28% 16% 1	4370
	11th to 20th	Day	37% 5% 14% 27% 17%	4281
	21st to end	Day	40% 6% 14% 25% 15% 1	4324
August	1st to 10th	Day	43% 5% 14% 24% 12%	4091
	11th to 20th	Day	47% 6% 16% 24% 7%	4083
	21st to end	Day	39% 5% 13% 31% 12% 1	4313
September	1st to 10th	Day	44% 4 13% 26% 12% 1	2280
	11th to 20th	Day	40% 5% 12% 28% 15% 1	2167
	21st to end	Day	52% 4 11% 23% 10% 1	2049
October	1st to 10th	Day	45% 5% 13% 23% 12% 1	3160
	11th to 20th	Day	51% 3 14% 17% 12% 3	3140
	21st to end	Day	52% 4 14% 22% 7%	3428
November	1st to 10th	Day	60% 3 9% 17% 9% 2	1779
	11th to 20th	Day	66% 3 9% 14% 7% 2	1600
	21st to end	Day	74% 2 9% 10% 4 1	1600
December	1st to 10th	Day	87% 2 5% 6% 1	2600
	11th to 20th	Day	79% 2 9% 8% 1	2986
	21st to end	Day	78% 3 10% 7% 2	3960
January	1st to 10th	Night	85% 1 7% 5% 2	4500
	11th to 20th	Night	80% 2 10% 6% 2	4120
	21st to end	Night	85% 1 6% 6% 2	4532
February	1st to 10th	Night	76% 2 8% 10% 3	2470
	11th to 20th	Night	73% 3 6% 13% 5%	2405
	21st to end	Night	71% 2 8% 12% 6% 1	1947
March	1st to 10th	Night	61% 2 9% 21% 6%	3418
	11th to 20th	Night	64% 3 10% 17% 6% 1	3480
	21st to end	Night	54% 3 8% 20% 13% 2	3817
April	1st to 10th	Night	59% 3 9% 18% 10% 1	1940
	11th to 20th	Night	53% 3 10% 19% 12% 2	1858
	21st to end	Night	51% 4 10% 20% 13% 3	1710
May	1st to 10th	Night	56% 2 8% 20% 10% 4	2840
	11th to 20th	Night	47% 3 15% 25% 7% 2	2602
	21st to end	Night	36% 3 11% 29% 16% 4	2739
June	1st to 10th	Night	44% 5% 10% 25% 14% 2	1520
	11th to 20th	Night	42% 4 12% 24% 16% 2	1520
	21st to end	Night	44% 5% 12% 25% 13% 1	1520
July	1st to 10th	Night	40% 5% 12% 23% 16% 3	2480
	11th to 20th	Night	37% 6% 13% 27% 15% 1	2553
	21st to end	Night	38% 6% 15% 24% 16% 1	2988
August	1st to 10th	Night	42% 5% 11% 31% 9% 2	2814
	11th to 20th	Night	49% 5% 16% 22% 8%	2812
	21st to end	Night	37% 5% 14% 31% 11% 1	3311
September	1st to 10th	Night	43% 4 12% 26% 13% 2	1900
	11th to 20th	Night	38% 3 12% 28% 18% 1	2009
	21st to end	Night	51% 4 11% 22% 11% 1	2130
October	1st to 10th	Night	45% 6% 9% 22% 18% 1	3800
	11th to 20th	Night	52% 3 12% 18% 13% 2	3779
	21st to end	Night	48% 3 15% 21% 12% 1	4120
November	1st to 10th	Night	56% 3 9% 20% 10% 2	2513
	11th to 20th	Night	66% 3 9% 13% 6% 3	2800
	21st to end	Night	73% 2 11% 11% 3	2800
December	1st to 10th	Night	84% 3 7% 5% 1	4580
	11th to 20th	Night	80% 3 8% 8% 2	5208
	21st to end	Night	77% 3 9% 9% 2	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	32% 32% 27% 6% 3 1	198
	11th to 20th	Day	39% 32% 20% 6% 2 1	270
	21st to end	Day	28% 34% 29% 7% 2	297
February	1st to 10th	Day	33% 31% 30% 6%	270
	11th to 20th	Day	32% 37% 26% 4 1	270
	21st to end	Day	40% 24% 30% 5%	266
March	1st to 10th	Day	32% 24% 31% 9% 4	460
	11th to 20th	Day	31% 22% 35% 9% 2 1	460
	21st to end	Day	37% 20% 27% 11% 4	506
April	1st to 10th	Day	31% 23% 30% 12% 4	460
	11th to 20th	Day	35% 21% 24% 13% 6% 2	452
	21st to end	Day	31% 18% 32% 14% 3 1	460
May	1st to 10th	Day	33% 14% 30% 16% 6% 1	463
	11th to 20th	Day	26% 14% 30% 22% 6% 1	487
	21st to end	Day	18% 10% 36% 23% 9% 4	529
June	1st to 10th	Day	21% 15% 34% 21% 7% 2	490
	11th to 20th	Day	20% 12% 31% 25% 10% 3	490
	21st to end	Day	20% 11% 34% 25% 9% 1	490
July	1st to 10th	Day	15% 7% 29% 29% 15% 5%	485
	11th to 20th	Day	19% 8% 30% 27% 11% 5%	484
	21st to end	Day	14% 6% 38% 26% 12% 3	532
August	1st to 10th	Day	16% 7% 28% 31% 13% 6%	486
	11th to 20th	Day	19% 6% 28% 26% 16% 5%	479
	21st to end	Day	18% 7% 31% 27% 12% 5%	539
September	1st to 10th	Day	21% 11% 25% 24% 14% 6%	490
	11th to 20th	Day	15% 6% 24% 31% 17% 8%	490
	21st to end	Day	24% 16% 24% 21% 10% 4	490
October	1st to 10th	Day	28% 11% 26% 21% 11% 3	490
	11th to 20th	Day	33% 17% 30% 14% 6% 1	490
	21st to end	Day	40% 18% 25% 14% 2	539
November	1st to 10th	Day	30% 23% 31% 12% 4 1	355
	11th to 20th	Day	43% 17% 30% 9% 3	200
	21st to end	Day	44% 24% 27% 5% 2	200
December	1st to 10th	Day	43% 23% 26% 7% 2	200
	11th to 20th	Day	38% 28% 26% 9%	200
	21st to end	Day	38% 29% 27% 5% 2	220
January	1st to 10th	Night	35% 26% 26% 9% 3	785
	11th to 20th	Night	33% 28% 26% 12% 1	760
	21st to end	Night	25% 28% 30% 14% 3	836
February	1st to 10th	Night	32% 27% 26% 14% 1	760
	11th to 20th	Night	28% 29% 29% 12% 2	743
	21st to end	Night	31% 27% 28% 13% 1	628
March	1st to 10th	Night	29% 21% 30% 16% 4	760
	11th to 20th	Night	30% 22% 28% 16% 4 1	760
	21st to end	Night	28% 15% 32% 17% 6% 1	836
April	1st to 10th	Night	29% 19% 29% 19% 4	760
	11th to 20th	Night	28% 15% 30% 20% 6% 1	734
	21st to end	Night	26% 11% 32% 23% 6% 1	570
May	1st to 10th	Night	27% 8% 26% 28% 10% 1	570
	11th to 20th	Night	19% 7% 32% 33% 9%	441
	21st to end	Night	15% 9% 28% 30% 15% 2	411
June	1st to 10th	Night	16% 8% 34% 29% 12% 1	380
	11th to 20th	Night	19% 8% 26% 36% 11% 1	380
	21st to end	Night	18% 7% 31% 32% 13% 1	380
July	1st to 10th	Night	12% 5% 24% 38% 18% 3	370
	11th to 20th	Night	13% 5% 27% 34% 19% 3	410
	21st to end	Night	12% 4 25% 38% 19% 1	624
August	1st to 10th	Night	13% 3 23% 37% 21% 3	567
	11th to 20th	Night	15% 4 20% 33% 24% 3	564
	21st to end	Night	17% 4 24% 31% 21% 4	736
September	1st to 10th	Night	21% 7% 21% 29% 19% 4	760
	11th to 20th	Night	19% 4 20% 30% 23% 4	760
	21st to end	Night	26% 11% 19% 26% 14% 4	760
October	1st to 10th	Night	24% 10% 27% 23% 14% 2	760
	11th to 20th	Night	34% 14% 27% 18% 6% 1	760
	21st to end	Night	41% 16% 25% 16% 2	836
November	1st to 10th	Night	33% 16% 25% 20% 5%	780
	11th to 20th	Night	37% 20% 26% 11% 5% 1	800
	21st to end	Night	38% 23% 25% 10% 4	800
December	1st to 10th	Night	41% 25% 23% 9% 3	800
	11th to 20th	Night	35% 29% 23% 12% 2	800
	21st to end	Night	34% 27% 27% 10% 1	880

Page generated at 2025-01-04 03:24:01. Version ac07

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