Ellicottville Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ellicottville Observatory clear sky chart from 2005-11-06 to 2026-05-17.

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	16% 13% 5% 11% 6% 5% 4 3 5% 6% 26%	132168
	Night	15% 15% 6% 13% 6% 5% 4 3 4 5% 24%	130635
Transparency	Day	58% 5% 10% 17% 9% 1	135763
	Night	61% 4 10% 16% 8% 1	135127
Seeing	Day	27% 18% 28% 16% 8% 3	16482
	Night	26% 16% 26% 22% 9% 1	26015

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% 21% 10% 25% 10% 3 3 2 2 3 8%	4661
	11th to 20th	Day	9% 22% 11% 24% 10% 7% 3 2 2 2 8%	5168
	21st to end	Day	14% 14% 6% 17% 11% 10% 7% 3 4 3 9%	5780
February	1st to 10th	Day	14% 21% 7% 18% 9% 5% 4 2 3 3 15%	1890
	11th to 20th	Day	13% 17% 9% 19% 9% 4 4 3 4 4 15%	1843
	21st to end	Day	17% 18% 6% 13% 7% 4 4 3 4 5% 19%	1654
March	1st to 10th	Day	16% 13% 9% 12% 6% 4 3 2 4 4 27%	5042
	11th to 20th	Day	12% 18% 7% 10% 3 3 4 3 4 6% 30%	5090
	21st to end	Day	19% 15% 7% 12% 4 4 4 3 3 4 25%	5586
April	1st to 10th	Day	17% 18% 5% 9% 5% 4 4 3 4 6% 26%	2506
	11th to 20th	Day	18% 15% 3 7% 4 3 4 4 5% 6% 31%	2494
	21st to end	Day	20% 13% 3 8% 5% 3 4 3 4 5% 33%	2712
May	1st to 10th	Day	25% 12% 3 7% 5% 4 4 3 5% 5% 26%	6018
	11th to 20th	Day	19% 13% 4 8% 5% 4 5% 4 5% 6% 27%	6344
	21st to end	Day	20% 10% 3 7% 5% 5% 5% 4 5% 7% 31%	6949
June	1st to 10th	Day	18% 9% 2 7% 5% 4 4 4 6% 8% 34%	2800
	11th to 20th	Day	16% 8% 2 8% 5% 4 5% 5% 6% 8% 31%	2800
	21st to end	Day	16% 6% 3 6% 4 6% 6% 5% 6% 9% 35%	2800
July	1st to 10th	Day	11% 6% 2 7% 6% 5% 6% 5% 7% 9% 37%	6360
	11th to 20th	Day	13% 8% 3 7% 5% 5% 5% 4 7% 9% 34%	6360
	21st to end	Day	11% 7% 2 7% 5% 5% 5% 4 6% 7% 41%	6424
August	1st to 10th	Day	17% 7% 3 7% 4 5% 5% 4 7% 8% 33%	4234
	11th to 20th	Day	15% 8% 3 9% 6% 6% 7% 5% 7% 9% 25%	4174
	21st to end	Day	14% 7% 2 6% 4 5% 6% 5% 6% 9% 36%	4387
September	1st to 10th	Day	17% 8% 3 7% 4 3 5% 3 6% 8% 36%	2400
	11th to 20th	Day	15% 6% 2 5% 5% 4 5% 4 6% 8% 41%	2330
	21st to end	Day	19% 10% 4 9% 5% 4 5% 4 5% 7% 29%	2128
October	1st to 10th	Day	21% 8% 3 7% 5% 4 4 3 5% 7% 34%	2000
	11th to 20th	Day	22% 15% 4 8% 5% 4 4 3 3 5% 28%	2000
	21st to end	Day	24% 18% 4 8% 3 4 4 3 5% 5% 23%	2200
November	1st to 10th	Day	15% 19% 4 7% 5% 5% 3 3 5% 6% 28%	1880
	11th to 20th	Day	14% 26% 6% 9% 4 3 3 4 4 6% 20%	1680
	21st to end	Day	17% 28% 8% 11% 4 3 4 2 5% 5% 15%	1680
December	1st to 10th	Day	16% 28% 14% 21% 3 2 3 2 2 2 7%	2680
	11th to 20th	Day	17% 21% 8% 18% 8% 5% 3 2 3 4 12%	3066
	21st to end	Day	18% 26% 8% 13% 8% 3 3 2 3 4 12%	4048
January	1st to 10th	Night	12% 21% 10% 29% 12% 3 2 1 2 2 6%	8234
	11th to 20th	Night	8% 19% 12% 25% 11% 6% 4 2 3 3 7%	7700
	21st to end	Night	12% 16% 8% 16% 11% 10% 7% 2 3 3 11%	8401
February	1st to 10th	Night	15% 20% 6% 16% 10% 6% 4 2 3 3 15%	2730
	11th to 20th	Night	11% 17% 9% 20% 9% 5% 5% 2 4 4 13%	2663
	21st to end	Night	15% 17% 7% 17% 9% 4 4 2 4 3 18%	2149
March	1st to 10th	Night	16% 16% 6% 12% 8% 6% 3 2 4 5% 23%	5018
	11th to 20th	Night	14% 16% 7% 9% 4 3 3 2 4 6% 31%	5089
	21st to end	Night	14% 14% 7% 13% 5% 4 4 3 4 5% 28%	5588
April	1st to 10th	Night	18% 17% 6% 9% 5% 4 4 3 4 5% 26%	2113
	11th to 20th	Night	19% 15% 3 6% 4 4 4 3 4 6% 33%	2075
	21st to end	Night	15% 14% 3 6% 5% 5% 4 4 5% 7% 31%	1926
May	1st to 10th	Night	26% 14% 3 7% 4 4 3 3 4 5% 27%	4143
	11th to 20th	Night	17% 12% 4 7% 5% 4 4 3 4 6% 34%	3680
	21st to end	Night	19% 12% 3 6% 3 3 3 3 5% 8% 34%	3926
June	1st to 10th	Night	14% 9% 3 8% 5% 5% 6% 4 6% 8% 34%	1600
	11th to 20th	Night	13% 7% 3 6% 4 5% 5% 4 7% 8% 38%	1600
	21st to end	Night	14% 6% 3 6% 5% 5% 5% 2 6% 9% 40%	1600
July	1st to 10th	Night	13% 9% 2 7% 5% 4 4 4 6% 9% 39%	3600
	11th to 20th	Night	12% 7% 2 7% 4 4 5% 4 6% 9% 40%	3600
	21st to end	Night	11% 6% 3 6% 4 4 4 4 6% 8% 44%	4423
August	1st to 10th	Night	13% 10% 3 7% 4 4 5% 4 6% 7% 37%	2915
	11th to 20th	Night	17% 10% 3 7% 4 5% 4 3 6% 7% 33%	2875
	21st to end	Night	9% 7% 2 7% 4 5% 5% 4 6% 8% 42%	3477
September	1st to 10th	Night	15% 8% 2 5% 3 4 3 4 5% 7% 43%	2000
	11th to 20th	Night	13% 7% 2 6% 4 4 4 3 5% 6% 47%	2066
	21st to end	Night	20% 8% 3 8% 5% 5% 4 4 6% 7% 31%	2271
October	1st to 10th	Night	18% 8% 3 7% 4 4 4 3 5% 6% 38%	2400
	11th to 20th	Night	21% 11% 3 8% 5% 4 5% 3 4 6% 29%	2400
	21st to end	Night	26% 15% 3 7% 4 3 4 3 4 5% 26%	2640
November	1st to 10th	Night	16% 17% 4 8% 4 3 3 3 4 6% 32%	2635
	11th to 20th	Night	16% 22% 5% 9% 5% 4 4 4 4 6% 20%	2940
	21st to end	Night	16% 24% 8% 13% 5% 4 3 3 4 4 17%	2940
December	1st to 10th	Night	14% 25% 13% 19% 6% 4 4 2 3 3 8%	4720
	11th to 20th	Night	17% 22% 11% 16% 6% 4 3 2 3 3 12%	5348
	21st to end	Night	17% 23% 9% 15% 7% 4 3 3 3 4 11%	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	83% 2 6% 6% 3	4662
	11th to 20th	Day	84% 2 5% 7% 3	5202
	21st to end	Day	79% 3 8% 7% 3	5780
February	1st to 10th	Day	75% 4 8% 9% 4	1890
	11th to 20th	Day	73% 4 6% 12% 5%	1852
	21st to end	Day	68% 4 9% 14% 5% 1	1654
March	1st to 10th	Day	61% 3 11% 19% 6%	5045
	11th to 20th	Day	56% 4 16% 17% 6% 2	5090
	21st to end	Day	62% 3 6% 18% 10% 1	5586
April	1st to 10th	Day	59% 5% 10% 15% 11%	2506
	11th to 20th	Day	53% 5% 10% 19% 11% 1	2494
	21st to end	Day	54% 5% 10% 18% 13% 1	2712
May	1st to 10th	Day	59% 4 8% 18% 8% 3	6027
	11th to 20th	Day	55% 7% 8% 19% 9% 1	6348
	21st to end	Day	52% 6% 11% 19% 11% 1	6949
June	1st to 10th	Day	48% 6% 12% 20% 14% 2	2800
	11th to 20th	Day	48% 7% 13% 20% 11%	2800
	21st to end	Day	45% 7% 13% 22% 13%	2800
July	1st to 10th	Day	42% 5% 13% 24% 15% 1	6290
	11th to 20th	Day	45% 6% 13% 20% 15%	6285
	21st to end	Day	41% 5% 11% 26% 16%	6240
August	1st to 10th	Day	48% 7% 13% 21% 11%	4221
	11th to 20th	Day	53% 7% 13% 21% 6%	4213
	21st to end	Day	42% 6% 11% 31% 10% 1	4387
September	1st to 10th	Day	46% 6% 10% 25% 12% 1	2400
	11th to 20th	Day	41% 6% 12% 26% 15% 1	2330
	21st to end	Day	53% 7% 10% 19% 10% 1	2128
October	1st to 10th	Day	46% 5% 11% 22% 15% 1	3260
	11th to 20th	Day	51% 3 13% 15% 14% 4	3240
	21st to end	Day	52% 3 15% 22% 8% 1	3538
November	1st to 10th	Day	55% 5% 11% 17% 10% 2	1880
	11th to 20th	Day	65% 5% 9% 13% 5% 2	1680
	21st to end	Day	73% 4 9% 10% 4 1	1680
December	1st to 10th	Day	85% 2 5% 6% 2	2680
	11th to 20th	Day	78% 4 7% 9% 2	3066
	21st to end	Day	77% 3 9% 7% 3	4048
January	1st to 10th	Night	87% 2 5% 4 2	8234
	11th to 20th	Night	84% 2 6% 5% 2	7741
	21st to end	Night	79% 3 6% 8% 4	8401
February	1st to 10th	Night	74% 3 9% 10% 4	2730
	11th to 20th	Night	74% 4 7% 10% 4	2665
	21st to end	Night	70% 4 8% 11% 6% 1	2149
March	1st to 10th	Night	64% 4 10% 16% 5%	5028
	11th to 20th	Night	55% 3 13% 19% 6% 3	5090
	21st to end	Night	58% 4 8% 15% 13% 2	5588
April	1st to 10th	Night	61% 4 9% 15% 9% 1	2113
	11th to 20th	Night	53% 5% 11% 17% 13% 2	2075
	21st to end	Night	51% 6% 10% 20% 11% 2	1926
May	1st to 10th	Night	59% 5% 8% 15% 10% 3	4150
	11th to 20th	Night	51% 7% 11% 20% 9% 1	3681
	21st to end	Night	48% 6% 11% 21% 10% 3	3927
June	1st to 10th	Night	46% 6% 11% 23% 13% 1	1600
	11th to 20th	Night	41% 8% 14% 23% 13% 1	1600
	21st to end	Night	41% 7% 13% 26% 12% 1	1600
July	1st to 10th	Night	42% 4 14% 24% 14% 1	3560
	11th to 20th	Night	41% 6% 15% 26% 12% 1	3552
	21st to end	Night	37% 5% 13% 24% 20% 1	4293
August	1st to 10th	Night	44% 7% 13% 26% 8% 1	2904
	11th to 20th	Night	48% 6% 16% 23% 8%	2902
	21st to end	Night	37% 6% 14% 33% 9% 1	3477
September	1st to 10th	Night	39% 7% 13% 26% 13% 2	2000
	11th to 20th	Night	37% 5% 13% 27% 16% 1	2066
	21st to end	Night	51% 7% 12% 18% 11% 1	2271
October	1st to 10th	Night	47% 4 8% 21% 18% 1	3920
	11th to 20th	Night	49% 4 11% 16% 15% 4	3899
	21st to end	Night	46% 4 15% 24% 10% 1	4252
November	1st to 10th	Night	52% 6% 11% 20% 10% 2	2635
	11th to 20th	Night	64% 5% 10% 13% 6% 2	2940
	21st to end	Night	71% 5% 10% 12% 3	2940
December	1st to 10th	Night	83% 3 7% 6% 2	4720
	11th to 20th	Night	78% 3 7% 10% 3	5348
	21st to end	Night	78% 4 7% 8% 3	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	32% 31% 25% 9% 2	220
	11th to 20th	Day	40% 31% 22% 5% 2	316
	21st to end	Day	35% 28% 26% 9% 2	363
February	1st to 10th	Day	38% 25% 30% 5% 2	330
	11th to 20th	Day	37% 30% 30% 3 1	330
	21st to end	Day	43% 25% 27% 5% 1	356
March	1st to 10th	Day	34% 23% 28% 12% 3	540
	11th to 20th	Day	35% 25% 28% 10% 2 1	540
	21st to end	Day	38% 22% 24% 12% 3 1	594
April	1st to 10th	Day	34% 24% 24% 13% 4 1	540
	11th to 20th	Day	35% 23% 23% 11% 6% 2	532
	21st to end	Day	30% 19% 32% 15% 4 1	540
May	1st to 10th	Day	34% 20% 26% 13% 5% 2	543
	11th to 20th	Day	28% 15% 29% 19% 8% 1	551
	21st to end	Day	20% 15% 29% 20% 12% 4	573
June	1st to 10th	Day	22% 18% 30% 19% 8% 2	530
	11th to 20th	Day	21% 13% 28% 23% 13% 2	530
	21st to end	Day	19% 13% 36% 22% 8% 1	530
July	1st to 10th	Day	13% 10% 30% 25% 17% 6%	525
	11th to 20th	Day	14% 10% 28% 27% 15% 5%	524
	21st to end	Day	12% 9% 37% 24% 13% 4	576
August	1st to 10th	Day	13% 9% 29% 26% 15% 8%	526
	11th to 20th	Day	17% 8% 28% 25% 14% 8%	519
	21st to end	Day	17% 10% 28% 23% 14% 8%	583
September	1st to 10th	Day	21% 11% 22% 22% 17% 7%	530
	11th to 20th	Day	14% 8% 23% 23% 23% 10%	530
	21st to end	Day	24% 15% 27% 17% 13% 4	530
October	1st to 10th	Day	23% 13% 26% 20% 14% 5%	530
	11th to 20th	Day	31% 21% 27% 14% 6% 2	530
	21st to end	Day	38% 15% 28% 17% 2	583
November	1st to 10th	Day	31% 19% 27% 15% 5% 2	416
	11th to 20th	Day	40% 20% 27% 8% 2 1	220
	21st to end	Day	39% 23% 31% 6%	220
December	1st to 10th	Day	44% 23% 25% 5% 3 1	220
	11th to 20th	Day	42% 25% 27% 5% 1	220
	21st to end	Day	42% 22% 31% 3 2	242
January	1st to 10th	Night	32% 29% 26% 10% 3	840
	11th to 20th	Night	32% 26% 27% 12% 2	840
	21st to end	Night	27% 29% 29% 13% 2	924
February	1st to 10th	Night	30% 25% 28% 15% 1	840
	11th to 20th	Night	29% 27% 31% 11% 1	823
	21st to end	Night	32% 25% 29% 12% 1	692
March	1st to 10th	Night	29% 21% 33% 14% 2	840
	11th to 20th	Night	35% 19% 24% 17% 4	840
	21st to end	Night	26% 20% 33% 15% 5% 1	924
April	1st to 10th	Night	30% 19% 29% 19% 3	840
	11th to 20th	Night	30% 17% 27% 19% 6% 1	831
	21st to end	Night	23% 12% 30% 28% 6%	666
May	1st to 10th	Night	24% 12% 25% 28% 11%	630
	11th to 20th	Night	18% 10% 29% 35% 8%	437
	21st to end	Night	18% 9% 24% 31% 16% 2	433
June	1st to 10th	Night	17% 6% 28% 37% 12% 1	400
	11th to 20th	Night	19% 9% 23% 38% 11%	400
	21st to end	Night	15% 6% 31% 34% 15%	400
July	1st to 10th	Night	11% 6% 17% 45% 17% 4	390
	11th to 20th	Night	12% 3 23% 39% 23% 1	388
	21st to end	Night	15% 4 20% 37% 24% 1	652
August	1st to 10th	Night	12% 3 19% 36% 28% 2	597
	11th to 20th	Night	16% 5% 18% 30% 30% 2	594
	21st to end	Night	13% 7% 21% 34% 22% 2	810
September	1st to 10th	Night	18% 7% 21% 31% 21% 2	800
	11th to 20th	Night	15% 8% 17% 28% 29% 4	800
	21st to end	Night	23% 11% 21% 26% 16% 3	800
October	1st to 10th	Night	23% 11% 25% 23% 17% 2	800
	11th to 20th	Night	29% 14% 29% 22% 6% 1	800
	21st to end	Night	34% 15% 28% 19% 4	880
November	1st to 10th	Night	28% 15% 28% 23% 6%	820
	11th to 20th	Night	32% 19% 27% 16% 5% 1	840
	21st to end	Night	32% 23% 27% 14% 4	840
December	1st to 10th	Night	36% 25% 25% 11% 3	840
	11th to 20th	Night	34% 25% 27% 12% 2	840
	21st to end	Night	34% 23% 30% 12% 1	924

Page generated at 2026-05-14 01:58:59. Version ac07

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