Genesee Celestial Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Genesee Celestial Observatory clear sky chart from 2005-11-06 to 2026-07-31.

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% 12% 5% 10% 6% 5% 5% 4 5% 6% 28%	138585
	Night	14% 13% 6% 12% 6% 5% 4 3 5% 6% 26%	134385
Transparency	Day	55% 5% 10% 19% 10% 1	142178
	Night	58% 5% 10% 17% 9% 1	138879
Seeing	Day	26% 20% 29% 16% 7% 3	16841
	Night	25% 19% 28% 20% 8% 1	26184

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	12% 19% 8% 24% 9% 3 3 2 3 3 14%	4661
	11th to 20th	Day	7% 19% 9% 24% 10% 7% 4 2 3 3 12%	5048
	21st to end	Day	13% 12% 6% 14% 10% 8% 7% 4 5% 5% 15%	5780
February	1st to 10th	Day	13% 17% 7% 14% 8% 6% 5% 4 3 3 19%	1890
	11th to 20th	Day	11% 16% 8% 17% 8% 5% 5% 2 4 5% 19%	1843
	21st to end	Day	15% 16% 5% 12% 7% 5% 3 3 4 7% 23%	1685
March	1st to 10th	Day	16% 14% 8% 10% 5% 4 3 2 4 5% 30%	4982
	11th to 20th	Day	11% 16% 8% 9% 4 4 3 3 4 6% 33%	5090
	21st to end	Day	14% 14% 5% 13% 6% 5% 5% 3 4 5% 27%	5632
April	1st to 10th	Day	14% 18% 4 10% 5% 4 4 3 4 6% 27%	2520
	11th to 20th	Day	16% 14% 4 7% 5% 5% 5% 5% 6% 5% 29%	2494
	21st to end	Day	19% 12% 4 8% 5% 4 3 3 5% 5% 33%	2646
May	1st to 10th	Day	23% 11% 4 8% 5% 4 5% 4 5% 6% 26%	7696
	11th to 20th	Day	19% 12% 3 8% 5% 5% 4 3 5% 7% 29%	8221
	21st to end	Day	19% 8% 3 7% 5% 5% 5% 4 6% 6% 31%	9060
June	1st to 10th	Day	16% 8% 3 7% 5% 5% 5% 4 5% 8% 35%	2940
	11th to 20th	Day	15% 8% 3 7% 5% 5% 5% 4 6% 8% 32%	2940
	21st to end	Day	14% 7% 2 7% 5% 5% 6% 4 6% 9% 35%	2940
July	1st to 10th	Day	9% 6% 3 7% 6% 5% 6% 5% 7% 8% 37%	6500
	11th to 20th	Day	8% 7% 3 8% 6% 6% 6% 5% 8% 11% 31%	6500
	21st to end	Day	11% 6% 2 7% 5% 5% 6% 4 6% 7% 40%	6660
August	1st to 10th	Day	17% 8% 3 7% 5% 5% 5% 5% 7% 8% 30%	4234
	11th to 20th	Day	15% 8% 3 9% 6% 6% 7% 5% 7% 9% 25%	4174
	21st to end	Day	13% 7% 3 7% 5% 5% 5% 4 6% 8% 36%	4317
September	1st to 10th	Day	17% 7% 2 7% 4 4 4 4 5% 7% 38%	2400
	11th to 20th	Day	14% 7% 2 6% 4 4 4 4 5% 8% 43%	2387
	21st to end	Day	20% 9% 4 6% 6% 4 4 4 6% 7% 31%	2093
October	1st to 10th	Day	17% 8% 3 8% 4 5% 4 5% 5% 7% 35%	2000
	11th to 20th	Day	18% 13% 4 8% 5% 5% 4 4 4 6% 30%	2000
	21st to end	Day	21% 16% 4 8% 5% 4 4 3 4 5% 26%	2200
November	1st to 10th	Day	12% 16% 5% 7% 5% 4 4 3 5% 6% 33%	1893
	11th to 20th	Day	13% 22% 5% 10% 4 4 4 4 6% 6% 23%	1685
	21st to end	Day	15% 21% 7% 11% 6% 4 4 4 5% 5% 18%	1680
December	1st to 10th	Day	14% 22% 12% 20% 6% 4 2 2 3 4 10%	2680
	11th to 20th	Day	16% 18% 7% 13% 8% 4 3 3 4 4 18%	3066
	21st to end	Day	15% 22% 9% 14% 7% 4 3 3 3 5% 15%	4048
January	1st to 10th	Night	10% 17% 9% 24% 12% 4 4 3 3 3 10%	8234
	11th to 20th	Night	8% 17% 10% 23% 10% 6% 5% 3 4 3 11%	7823
	21st to end	Night	11% 14% 8% 15% 10% 9% 9% 3 3 3 15%	8401
February	1st to 10th	Night	12% 16% 6% 15% 11% 7% 5% 3 4 5% 19%	2730
	11th to 20th	Night	11% 14% 7% 17% 8% 6% 6% 4 4 5% 17%	2663
	21st to end	Night	13% 15% 6% 16% 8% 5% 4 3 4 5% 21%	2120
March	1st to 10th	Night	13% 14% 6% 12% 9% 6% 4 3 4 5% 25%	5074
	11th to 20th	Night	12% 16% 6% 10% 4 3 4 2 5% 6% 32%	5089
	21st to end	Night	12% 15% 5% 12% 5% 4 4 3 4 5% 30%	5528
April	1st to 10th	Night	16% 15% 5% 9% 5% 4 4 3 5% 6% 26%	2100
	11th to 20th	Night	17% 16% 4 7% 3 3 4 3 4 6% 33%	2075
	21st to end	Night	15% 12% 3 8% 5% 4 4 4 5% 6% 34%	1990
May	1st to 10th	Night	24% 12% 4 8% 4 4 4 3 5% 6% 27%	5203
	11th to 20th	Night	19% 13% 3 7% 4 4 4 3 5% 6% 32%	4639
	21st to end	Night	20% 11% 3 7% 4 4 4 3 5% 6% 33%	5114
June	1st to 10th	Night	15% 7% 3 6% 6% 4 4 4 6% 9% 38%	1680
	11th to 20th	Night	12% 8% 3 7% 5% 4 4 4 7% 8% 37%	1680
	21st to end	Night	11% 6% 2 8% 5% 4 5% 4 5% 9% 42%	1680
July	1st to 10th	Night	10% 9% 3 8% 5% 4 4 4 6% 9% 38%	3680
	11th to 20th	Night	10% 7% 3 7% 5% 5% 5% 4 7% 10% 39%	3680
	21st to end	Night	11% 7% 2 6% 4 4 4 3 5% 8% 45%	4395
August	1st to 10th	Night	16% 10% 3 6% 4 5% 5% 4 6% 7% 35%	2915
	11th to 20th	Night	17% 8% 3 7% 4 4 4 4 6% 8% 36%	2875
	21st to end	Night	11% 6% 3 7% 4 4 5% 4 6% 8% 41%	3548
September	1st to 10th	Night	15% 7% 2 6% 3 4 3 3 5% 7% 46%	2000
	11th to 20th	Night	12% 7% 2 6% 3 4 3 3 5% 7% 47%	2010
	21st to end	Night	18% 9% 3 7% 6% 4 4 3 5% 7% 34%	2305
October	1st to 10th	Night	16% 9% 3 7% 3 4 3 3 5% 7% 40%	2400
	11th to 20th	Night	17% 13% 3 7% 5% 4 4 3 5% 6% 33%	2400
	21st to end	Night	22% 15% 3 7% 4 4 3 3 5% 6% 27%	2640
November	1st to 10th	Night	11% 15% 4 7% 5% 4 4 3 5% 5% 37%	2624
	11th to 20th	Night	14% 18% 5% 10% 6% 5% 4 3 5% 6% 25%	2932
	21st to end	Night	14% 19% 7% 12% 7% 4 4 3 5% 6% 19%	2940
December	1st to 10th	Night	11% 18% 11% 20% 8% 5% 5% 3 4 4 10%	4720
	11th to 20th	Night	17% 18% 8% 15% 6% 5% 4 3 4 4 18%	5348
	21st to end	Night	15% 19% 10% 14% 7% 5% 4 3 4 4 15%	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	78% 2 6% 10% 4 1	4662
	11th to 20th	Day	79% 2 6% 8% 5% 1	5082
	21st to end	Day	71% 3 10% 11% 5%	5780
February	1st to 10th	Day	71% 4 9% 11% 5%	1890
	11th to 20th	Day	68% 3 6% 15% 7%	1852
	21st to end	Day	61% 3 10% 18% 6% 2	1685
March	1st to 10th	Day	58% 3 11% 18% 9% 1	4985
	11th to 20th	Day	54% 3 16% 17% 7% 3	5090
	21st to end	Day	60% 4 5% 18% 11% 2	5632
April	1st to 10th	Day	58% 4 9% 16% 11% 1	2520
	11th to 20th	Day	54% 6% 9% 17% 13% 1	2494
	21st to end	Day	53% 4 9% 19% 13% 2	2646
May	1st to 10th	Day	58% 4 9% 18% 9% 2	7705
	11th to 20th	Day	54% 6% 10% 20% 10%	8225
	21st to end	Day	52% 5% 11% 20% 11% 1	9061
June	1st to 10th	Day	46% 6% 10% 21% 15% 1	2940
	11th to 20th	Day	48% 7% 13% 21% 11% 1	2940
	21st to end	Day	45% 7% 12% 23% 12%	2940
July	1st to 10th	Day	42% 6% 13% 26% 12% 1	6430
	11th to 20th	Day	43% 7% 14% 22% 13%	6425
	21st to end	Day	41% 7% 11% 25% 16%	6473
August	1st to 10th	Day	49% 7% 13% 21% 10%	4221
	11th to 20th	Day	52% 8% 14% 20% 6%	4213
	21st to end	Day	45% 6% 10% 30% 8% 1	4317
September	1st to 10th	Day	44% 8% 9% 26% 12% 2	2400
	11th to 20th	Day	40% 5% 11% 27% 16% 1	2387
	21st to end	Day	52% 5% 10% 20% 12% 1	2093
October	1st to 10th	Day	45% 4 11% 22% 16% 1	3260
	11th to 20th	Day	49% 3 13% 16% 15% 4	3240
	21st to end	Day	47% 4 14% 24% 10% 1	3538
November	1st to 10th	Day	52% 5% 10% 18% 12% 2	1893
	11th to 20th	Day	61% 4 9% 18% 6% 2	1685
	21st to end	Day	66% 6% 9% 13% 5% 1	1680
December	1st to 10th	Day	79% 3 7% 8% 3	2680
	11th to 20th	Day	69% 3 10% 12% 5%	3066
	21st to end	Day	74% 3 9% 9% 5%	4048
January	1st to 10th	Night	79% 3 7% 8% 4	8234
	11th to 20th	Night	76% 3 9% 7% 5%	7864
	21st to end	Night	75% 2 7% 9% 6%	8401
February	1st to 10th	Night	69% 4 10% 11% 6%	2730
	11th to 20th	Night	68% 5% 10% 12% 5% 1	2665
	21st to end	Night	65% 4 9% 13% 7% 1	2120
March	1st to 10th	Night	61% 5% 13% 14% 6% 1	5084
	11th to 20th	Night	54% 5% 14% 18% 5% 4	5090
	21st to end	Night	56% 5% 7% 16% 15% 2	5528
April	1st to 10th	Night	58% 5% 9% 17% 10% 1	2100
	11th to 20th	Night	54% 4 11% 18% 12% 1	2075
	21st to end	Night	50% 6% 11% 20% 13% 2	1990
May	1st to 10th	Night	59% 5% 8% 17% 9% 2	5210
	11th to 20th	Night	52% 6% 12% 20% 10%	4640
	21st to end	Night	51% 6% 10% 19% 12% 2	5115
June	1st to 10th	Night	43% 6% 11% 25% 15% 1	1680
	11th to 20th	Night	43% 6% 13% 23% 12% 1	1680
	21st to end	Night	40% 7% 14% 25% 13% 1	1680
July	1st to 10th	Night	44% 6% 13% 24% 13% 1	3640
	11th to 20th	Night	40% 8% 14% 26% 11% 1	3632
	21st to end	Night	38% 6% 11% 26% 19% 1	4267
August	1st to 10th	Night	47% 8% 14% 23% 8% 1	2904
	11th to 20th	Night	45% 7% 14% 26% 8%	2902
	21st to end	Night	40% 7% 12% 32% 9% 1	3548
September	1st to 10th	Night	38% 6% 13% 28% 13% 3	2000
	11th to 20th	Night	37% 5% 12% 28% 17% 1	2010
	21st to end	Night	49% 5% 13% 19% 12% 1	2305
October	1st to 10th	Night	48% 4 10% 23% 15% 1	3920
	11th to 20th	Night	47% 4 11% 18% 14% 6%	3899
	21st to end	Night	46% 4 15% 24% 10% 1	4252
November	1st to 10th	Night	50% 5% 11% 19% 12% 2	2624
	11th to 20th	Night	60% 4 11% 15% 8% 2	2932
	21st to end	Night	64% 5% 11% 15% 4	2940
December	1st to 10th	Night	78% 5% 8% 7% 2	4720
	11th to 20th	Night	70% 3 8% 12% 6%	5348
	21st to end	Night	73% 4 7% 9% 6%	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	34% 30% 24% 9% 2	220
	11th to 20th	Day	37% 34% 22% 5% 1	294
	21st to end	Day	34% 30% 28% 6% 2	363
February	1st to 10th	Day	40% 28% 25% 5% 1	330
	11th to 20th	Day	36% 34% 29% 1 1	330
	21st to end	Day	39% 31% 25% 5%	401
March	1st to 10th	Day	34% 27% 27% 10% 2	540
	11th to 20th	Day	34% 27% 27% 9% 2	540
	21st to end	Day	37% 24% 25% 9% 3 1	594
April	1st to 10th	Day	36% 24% 26% 11% 3 1	540
	11th to 20th	Day	31% 26% 27% 10% 4 2	532
	21st to end	Day	29% 21% 33% 13% 4 1	540
May	1st to 10th	Day	31% 23% 28% 10% 6% 2	543
	11th to 20th	Day	26% 19% 31% 16% 5% 3	567
	21st to end	Day	21% 18% 29% 21% 7% 4	617
June	1st to 10th	Day	20% 19% 31% 20% 8% 1	570
	11th to 20th	Day	22% 16% 29% 21% 10% 2	570
	21st to end	Day	17% 15% 37% 21% 6% 2	570
July	1st to 10th	Day	14% 11% 31% 27% 13% 4	565
	11th to 20th	Day	12% 10% 32% 28% 12% 5%	564
	21st to end	Day	14% 11% 36% 27% 10% 3	616
August	1st to 10th	Day	13% 8% 29% 28% 16% 6%	526
	11th to 20th	Day	18% 9% 29% 26% 12% 6%	519
	21st to end	Day	15% 11% 31% 23% 13% 7%	583
September	1st to 10th	Day	20% 13% 24% 22% 13% 7%	530
	11th to 20th	Day	13% 8% 26% 21% 22% 9%	530
	21st to end	Day	25% 15% 29% 17% 10% 4	530
October	1st to 10th	Day	20% 16% 28% 20% 13% 3	530
	11th to 20th	Day	30% 21% 29% 12% 6% 2	530
	21st to end	Day	34% 21% 27% 16% 2	583
November	1st to 10th	Day	28% 23% 28% 13% 6% 2	447
	11th to 20th	Day	38% 22% 28% 11% 1	225
	21st to end	Day	38% 25% 31% 5%	220
December	1st to 10th	Day	41% 26% 26% 4 3	220
	11th to 20th	Day	41% 26% 27% 5%	220
	21st to end	Day	35% 32% 27% 5% 1	242
January	1st to 10th	Night	28% 30% 29% 11% 2	840
	11th to 20th	Night	29% 30% 27% 12% 2	840
	21st to end	Night	27% 32% 28% 12% 1	924
February	1st to 10th	Night	28% 29% 30% 13% 1	840
	11th to 20th	Night	31% 30% 27% 11% 1	823
	21st to end	Night	33% 27% 28% 11% 2	692
March	1st to 10th	Night	27% 29% 30% 12% 2	840
	11th to 20th	Night	30% 26% 26% 14% 3	840
	21st to end	Night	28% 24% 30% 12% 4 1	924
April	1st to 10th	Night	30% 20% 30% 17% 2	840
	11th to 20th	Night	29% 19% 29% 16% 6% 1	831
	21st to end	Night	23% 14% 32% 26% 4	730
May	1st to 10th	Night	25% 14% 26% 26% 9%	614
	11th to 20th	Night	22% 12% 29% 29% 8%	414
	21st to end	Night	18% 11% 27% 30% 13% 1	455
June	1st to 10th	Night	17% 11% 31% 30% 10% 1	420
	11th to 20th	Night	17% 10% 27% 35% 11%	420
	21st to end	Night	14% 7% 31% 36% 11% 1	420
July	1st to 10th	Night	9% 7% 25% 40% 16% 2	410
	11th to 20th	Night	9% 7% 28% 36% 19% 2	408
	21st to end	Night	14% 4 27% 35% 18% 1	629
August	1st to 10th	Night	13% 5% 24% 37% 19% 2	597
	11th to 20th	Night	15% 6% 21% 31% 25% 2	594
	21st to end	Night	16% 7% 23% 31% 21% 3	855
September	1st to 10th	Night	19% 7% 25% 30% 16% 3	800
	11th to 20th	Night	17% 6% 19% 26% 27% 4	800
	21st to end	Night	24% 12% 22% 23% 15% 3	800
October	1st to 10th	Night	21% 13% 28% 21% 16% 2	800
	11th to 20th	Night	25% 19% 31% 19% 6% 1	800
	21st to end	Night	34% 18% 30% 15% 4	880
November	1st to 10th	Night	22% 20% 32% 19% 6%	820
	11th to 20th	Night	29% 23% 28% 14% 4 1	840
	21st to end	Night	29% 26% 29% 12% 4	840
December	1st to 10th	Night	33% 26% 28% 10% 3	840
	11th to 20th	Night	30% 29% 29% 11% 2	840
	21st to end	Night	31% 27% 29% 11% 2	924

Page generated at 2026-07-28 03:25:24. Version ac07

Copyright © 2026 Attilla Danko.