Geneva College Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Geneva College Observatory clear sky chart from 2005-11-06 to 2024-11-10.

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% 10% 4 8% 5% 5% 5% 4 5% 7% 31%	101164
	Night	18% 11% 4 8% 5% 4 4 3 5% 6% 32%	97925
Transparency	Day	50% 6% 11% 21% 11% 1	104813
	Night	50% 5% 11% 21% 11% 2	102415
Seeing	Day	22% 15% 27% 21% 11% 4	14694
	Night	21% 12% 26% 27% 12% 1	24393

By Month

Percentage Cloud Cover SE (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	19% 22% 9% 12% 4 3 3 2 3 5% 17%	2836
	11th to 20th	Day	14% 25% 8% 13% 7% 5% 3 2 3 4 17%	2840
	21st to end	Day	27% 20% 7% 14% 5% 4 4 3 4 3 10%	3124
February	1st to 10th	Day	20% 18% 5% 10% 7% 5% 3 2 3 5% 22%	1710
	11th to 20th	Day	17% 14% 6% 13% 5% 5% 5% 3 5% 6% 22%	1663
	21st to end	Day	20% 15% 4 9% 5% 4 4 4 5% 5% 24%	1567
March	1st to 10th	Day	22% 11% 5% 9% 5% 4 3 3 5% 7% 27%	3435
	11th to 20th	Day	14% 10% 4 10% 6% 5% 5% 4 4 6% 33%	3480
	21st to end	Day	21% 10% 3 7% 5% 4 4 4 5% 6% 30%	3815
April	1st to 10th	Day	16% 13% 3 8% 5% 4 4 5% 6% 6% 30%	2180
	11th to 20th	Day	18% 11% 3 7% 5% 4 5% 3 5% 6% 33%	2313
	21st to end	Day	22% 9% 3 6% 5% 4 4 3 5% 6% 32%	2470
May	1st to 10th	Day	23% 9% 3 8% 5% 5% 5% 4 5% 7% 28%	4082
	11th to 20th	Day	20% 8% 3 7% 5% 4 5% 4 6% 7% 31%	4081
	21st to end	Day	13% 6% 2 6% 5% 5% 5% 4 7% 9% 39%	4715
June	1st to 10th	Day	14% 7% 3 7% 5% 5% 5% 5% 6% 9% 33%	2660
	11th to 20th	Day	14% 7% 3 6% 5% 5% 5% 5% 6% 10% 35%	2660
	21st to end	Day	14% 6% 2 6% 5% 4 6% 4 7% 9% 38%	2660
July	1st to 10th	Day	9% 6% 3 8% 5% 5% 5% 4 6% 9% 40%	4286
	11th to 20th	Day	10% 6% 2 6% 5% 4 6% 4 7% 9% 41%	4120
	21st to end	Day	12% 7% 2 7% 6% 5% 6% 5% 7% 8% 36%	4466
August	1st to 10th	Day	14% 8% 3 8% 6% 6% 6% 5% 6% 8% 31%	4104
	11th to 20th	Day	12% 7% 3 7% 5% 5% 6% 5% 7% 9% 34%	4044
	21st to end	Day	8% 5% 2 7% 5% 6% 6% 5% 7% 9% 40%	4346
September	1st to 10th	Day	16% 6% 2 5% 4 4 4 3 5% 7% 44%	2266
	11th to 20th	Day	12% 5% 2 6% 4 5% 4 4 7% 7% 44%	2090
	21st to end	Day	19% 8% 3 7% 5% 4 4 4 4 6% 36%	2090
October	1st to 10th	Day	15% 6% 2 6% 5% 5% 4 4 6% 8% 39%	1910
	11th to 20th	Day	20% 7% 3 8% 6% 5% 4 3 5% 5% 33%	1900
	21st to end	Day	22% 11% 3 7% 4 4 5% 3 4 7% 31%	2090
November	1st to 10th	Day	11% 9% 2 6% 5% 5% 5% 3 5% 6% 42%	1839
	11th to 20th	Day	17% 14% 4 8% 5% 4 4 3 5% 6% 31%	1596
	21st to end	Day	18% 15% 6% 8% 6% 3 4 4 5% 6% 25%	1520
December	1st to 10th	Day	21% 19% 6% 11% 7% 5% 3 3 5% 5% 17%	1520
	11th to 20th	Day	19% 17% 8% 11% 4 4 4 3 5% 6% 19%	1910
	21st to end	Day	27% 23% 7% 9% 5% 4 3 2 3 5% 12%	2776
January	1st to 10th	Night	17% 22% 8% 12% 5% 4 4 3 3 4 18%	4109
	11th to 20th	Night	17% 19% 7% 14% 7% 6% 4 3 4 4 15%	4120
	21st to end	Night	29% 17% 7% 11% 5% 4 3 2 3 3 15%	4532
February	1st to 10th	Night	21% 13% 5% 11% 6% 4 4 4 4 5% 24%	2470
	11th to 20th	Night	19% 14% 5% 12% 5% 5% 4 3 5% 4 25%	2403
	21st to end	Night	21% 13% 5% 11% 6% 4 4 3 4 4 25%	1880
March	1st to 10th	Night	24% 12% 3 6% 4 4 2 3 4 6% 32%	3418
	11th to 20th	Night	19% 12% 5% 8% 4 3 3 3 4 6% 33%	3480
	21st to end	Night	18% 10% 3 7% 4 4 3 3 4 5% 39%	3817
April	1st to 10th	Night	18% 11% 4 6% 5% 4 3 3 5% 7% 34%	2000
	11th to 20th	Night	17% 10% 3 6% 5% 5% 4 4 5% 6% 35%	1833
	21st to end	Night	15% 9% 3 7% 5% 4 3 4 6% 8% 35%	1710
May	1st to 10th	Night	28% 9% 2 6% 4 4 4 4 5% 7% 28%	2813
	11th to 20th	Night	18% 9% 3 7% 4 3 4 4 5% 7% 36%	2812
	21st to end	Night	11% 6% 2 5% 4 3 5% 5% 7% 11% 42%	2836
June	1st to 10th	Night	9% 5% 3 6% 5% 5% 4 5% 7% 8% 43%	1520
	11th to 20th	Night	12% 4 2 7% 5% 4 4 3 7% 10% 42%	1520
	21st to end	Night	10% 5% 2 6% 5% 5% 5% 4 7% 8% 43%	1520
July	1st to 10th	Night	10% 8% 3 8% 5% 5% 4 4 5% 8% 41%	2669
	11th to 20th	Night	11% 5% 2 5% 4 4 5% 4 7% 9% 44%	2840
	21st to end	Night	10% 6% 3 7% 5% 5% 5% 4 6% 8% 41%	3087
August	1st to 10th	Night	12% 9% 3 8% 5% 4 5% 4 6% 7% 37%	2825
	11th to 20th	Night	13% 7% 2 7% 5% 4 4 3 5% 8% 42%	2785
	21st to end	Night	9% 5% 2 6% 4 5% 6% 5% 7% 8% 44%	3277
September	1st to 10th	Night	14% 5% 2 5% 3 4 4 4 6% 6% 48%	1909
	11th to 20th	Night	10% 5% 1 4 3 3 4 4 6% 8% 52%	2090
	21st to end	Night	17% 8% 3 6% 4 4 4 3 5% 7% 40%	2090
October	1st to 10th	Night	15% 6% 2 6% 4 3 4 3 5% 6% 45%	2270
	11th to 20th	Night	18% 7% 3 7% 4 4 5% 3 5% 6% 38%	2280
	21st to end	Night	24% 9% 2 5% 3 3 4 3 5% 6% 36%	2508
November	1st to 10th	Night	14% 8% 2 5% 5% 4 3 4 5% 5% 44%	2440
	11th to 20th	Night	19% 11% 4 8% 5% 4 4 4 5% 6% 31%	2582
	21st to end	Night	19% 15% 4 8% 5% 4 3 3 5% 5% 29%	2660
December	1st to 10th	Night	23% 18% 7% 9% 5% 4 4 3 4 5% 20%	2660
	11th to 20th	Night	19% 19% 5% 9% 5% 4 3 3 5% 5% 22%	3285
	21st to end	Night	26% 19% 6% 10% 5% 4 4 3 4 5% 13%	4875

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	70% 4 9% 12% 4	2837
	11th to 20th	Day	72% 3 7% 14% 3 1	2840
	21st to end	Day	78% 4 8% 7% 2	3124
February	1st to 10th	Day	67% 3 9% 14% 7%	1710
	11th to 20th	Day	64% 5% 9% 14% 7%	1672
	21st to end	Day	61% 4 12% 15% 7% 1	1567
March	1st to 10th	Day	57% 5% 10% 22% 6%	3435
	11th to 20th	Day	51% 6% 13% 22% 8% 1	3480
	21st to end	Day	52% 5% 11% 20% 11% 1	3815
April	1st to 10th	Day	53% 5% 11% 19% 11% 2	2180
	11th to 20th	Day	51% 6% 10% 17% 14% 2	2313
	21st to end	Day	52% 5% 10% 22% 10% 2	2470
May	1st to 10th	Day	55% 6% 10% 20% 8% 1	4120
	11th to 20th	Day	51% 7% 12% 21% 8% 1	4085
	21st to end	Day	39% 8% 15% 23% 12% 3	4729
June	1st to 10th	Day	45% 7% 13% 22% 11% 1	2660
	11th to 20th	Day	44% 7% 14% 22% 12% 1	2660
	21st to end	Day	41% 8% 12% 26% 12% 1	2660
July	1st to 10th	Day	41% 6% 12% 23% 15% 3	4220
	11th to 20th	Day	38% 6% 12% 28% 16% 1	4051
	21st to end	Day	42% 8% 12% 21% 16% 1	4324
August	1st to 10th	Day	49% 8% 12% 22% 9%	4091
	11th to 20th	Day	43% 6% 12% 28% 10% 1	4083
	21st to end	Day	38% 8% 12% 27% 13% 2	4346
September	1st to 10th	Day	39% 6% 10% 22% 19% 3	2266
	11th to 20th	Day	37% 6% 14% 27% 16% 1	2090
	21st to end	Day	49% 5% 11% 22% 13% 1	2090
October	1st to 10th	Day	32% 5% 10% 32% 19% 1	3170
	11th to 20th	Day	46% 5% 10% 22% 14% 4	3140
	21st to end	Day	39% 4 13% 28% 16% 1	3428
November	1st to 10th	Day	42% 5% 12% 22% 17% 2	1839
	11th to 20th	Day	54% 4 11% 18% 10% 2	1596
	21st to end	Day	59% 5% 12% 16% 6% 1	1520
December	1st to 10th	Day	70% 5% 10% 11% 3	1520
	11th to 20th	Day	67% 4 10% 16% 3	1906
	21st to end	Day	77% 3 10% 9% 2	2776
January	1st to 10th	Night	69% 5% 10% 13% 3	4109
	11th to 20th	Night	73% 5% 9% 11% 2	4120
	21st to end	Night	76% 3 7% 12% 3	4532
February	1st to 10th	Night	63% 4 10% 17% 6%	2470
	11th to 20th	Night	62% 4 10% 17% 7%	2405
	21st to end	Night	62% 5% 9% 14% 9% 1	1880
March	1st to 10th	Night	55% 4 10% 22% 8%	3418
	11th to 20th	Night	52% 5% 13% 23% 6% 1	3480
	21st to end	Night	47% 6% 11% 23% 13% 2	3817
April	1st to 10th	Night	51% 5% 10% 18% 13% 2	2000
	11th to 20th	Night	48% 5% 12% 17% 15% 3	1833
	21st to end	Night	45% 6% 12% 22% 13% 2	1710
May	1st to 10th	Night	55% 7% 8% 19% 10% 2	2840
	11th to 20th	Night	47% 7% 11% 24% 10% 2	2813
	21st to end	Night	33% 10% 14% 25% 14% 4	2843
June	1st to 10th	Night	36% 8% 14% 24% 17% 2	1520
	11th to 20th	Night	36% 8% 16% 23% 15% 2	1520
	21st to end	Night	37% 8% 13% 24% 16% 2	1520
July	1st to 10th	Night	41% 7% 10% 23% 17% 2	2625
	11th to 20th	Night	34% 7% 13% 28% 16% 1	2786
	21st to end	Night	40% 7% 11% 17% 22% 3	2988
August	1st to 10th	Night	45% 8% 12% 22% 12% 1	2814
	11th to 20th	Night	40% 6% 10% 28% 14% 1	2812
	21st to end	Night	34% 8% 13% 30% 13% 2	3277
September	1st to 10th	Night	34% 7% 11% 23% 20% 5%	1909
	11th to 20th	Night	29% 8% 14% 26% 23% 1	2090
	21st to end	Night	43% 5% 12% 21% 17% 1	2090
October	1st to 10th	Night	35% 5% 8% 27% 23% 2	3790
	11th to 20th	Night	39% 5% 12% 24% 14% 7%	3779
	21st to end	Night	36% 3 10% 30% 19% 2	4120
November	1st to 10th	Night	41% 4 12% 24% 16% 3	2440
	11th to 20th	Night	53% 4 11% 20% 10% 2	2582
	21st to end	Night	57% 4 12% 21% 6% 1	2660
December	1st to 10th	Night	67% 5% 11% 13% 4	2660
	11th to 20th	Night	64% 5% 12% 16% 3	3288
	21st to end	Night	74% 5% 10% 10% 2	4875

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	31% 28% 27% 10% 4 1	270
	11th to 20th	Day	33% 27% 30% 8% 1	270
	21st to end	Day	29% 29% 31% 8% 2 1	297
February	1st to 10th	Day	34% 20% 36% 9% 1	270
	11th to 20th	Day	35% 29% 29% 7%	270
	21st to end	Day	37% 26% 29% 8%	237
March	1st to 10th	Day	31% 20% 30% 16% 3	460
	11th to 20th	Day	32% 20% 30% 13% 5% 1	460
	21st to end	Day	33% 18% 28% 15% 4 1	506
April	1st to 10th	Day	29% 21% 26% 15% 8% 1	460
	11th to 20th	Day	26% 20% 27% 15% 8% 3	452
	21st to end	Day	29% 17% 31% 17% 6% 2	460
May	1st to 10th	Day	27% 19% 25% 18% 7% 3	463
	11th to 20th	Day	22% 15% 30% 20% 9% 4	487
	21st to end	Day	15% 8% 28% 26% 18% 6%	529
June	1st to 10th	Day	14% 14% 30% 25% 13% 4	490
	11th to 20th	Day	17% 12% 24% 29% 14% 4	490
	21st to end	Day	14% 10% 34% 27% 12% 3	490
July	1st to 10th	Day	13% 6% 22% 27% 21% 10%	485
	11th to 20th	Day	13% 7% 26% 28% 19% 8%	484
	21st to end	Day	13% 7% 24% 29% 19% 8%	532
August	1st to 10th	Day	11% 7% 23% 30% 19% 10%	486
	11th to 20th	Day	15% 6% 23% 29% 18% 9%	479
	21st to end	Day	11% 5% 24% 27% 22% 12%	539
September	1st to 10th	Day	17% 8% 21% 27% 19% 8%	490
	11th to 20th	Day	12% 5% 19% 31% 22% 11%	490
	21st to end	Day	22% 13% 24% 23% 15% 4	490
October	1st to 10th	Day	16% 10% 28% 25% 17% 5%	490
	11th to 20th	Day	22% 17% 29% 22% 8% 2	490
	21st to end	Day	28% 16% 31% 18% 7%	539
November	1st to 10th	Day	18% 19% 34% 16% 9% 3	383
	11th to 20th	Day	31% 19% 30% 13% 7% 1	216
	21st to end	Day	24% 23% 40% 12% 1	180
December	1st to 10th	Day	31% 27% 27% 9% 3 2	180
	11th to 20th	Day	29% 23% 33% 12% 2	180
	21st to end	Day	36% 24% 28% 12% 2	200
January	1st to 10th	Night	29% 21% 33% 14% 3	760
	11th to 20th	Night	30% 19% 32% 17% 2	760
	21st to end	Night	27% 22% 28% 20% 3	836
February	1st to 10th	Night	29% 18% 28% 23% 3	760
	11th to 20th	Night	30% 19% 34% 16% 1	743
	21st to end	Night	29% 19% 31% 19% 3	628
March	1st to 10th	Night	25% 18% 31% 23% 3	760
	11th to 20th	Night	26% 18% 27% 23% 5% 1	760
	21st to end	Night	24% 16% 32% 21% 6% 1	836
April	1st to 10th	Night	25% 16% 29% 24% 6%	760
	11th to 20th	Night	21% 13% 32% 24% 9% 1	709
	21st to end	Night	21% 9% 35% 29% 6%	570
May	1st to 10th	Night	21% 11% 25% 33% 8% 2	570
	11th to 20th	Night	20% 7% 27% 32% 13% 1	561
	21st to end	Night	11% 3 25% 36% 22% 3	477
June	1st to 10th	Night	11% 5% 25% 40% 19%	380
	11th to 20th	Night	13% 4 24% 39% 19% 1	380
	21st to end	Night	8% 5% 28% 36% 23% 1	380
July	1st to 10th	Night	7% 2 18% 41% 25% 6%	450
	11th to 20th	Night	8% 2 19% 37% 28% 5%	552
	21st to end	Night	11% 4 14% 43% 27% 2	624
August	1st to 10th	Night	10% 2 17% 39% 29% 3	567
	11th to 20th	Night	11% 4 13% 40% 27% 4	564
	21st to end	Night	12% 3 20% 31% 27% 6%	715
September	1st to 10th	Night	15% 4 18% 34% 25% 4	760
	11th to 20th	Night	11% 3 16% 35% 31% 3	760
	21st to end	Night	18% 9% 24% 27% 19% 4	760
October	1st to 10th	Night	17% 7% 24% 29% 21% 2	760
	11th to 20th	Night	21% 12% 30% 24% 11% 1	760
	21st to end	Night	28% 12% 26% 26% 8%	836
November	1st to 10th	Night	19% 11% 26% 31% 13%	779
	11th to 20th	Night	27% 16% 27% 21% 8% 1	760
	21st to end	Night	27% 17% 27% 22% 6%	760
December	1st to 10th	Night	33% 17% 27% 18% 5%	760
	11th to 20th	Night	29% 18% 28% 21% 4	760
	21st to end	Night	30% 18% 29% 21% 2	836

Page generated at 2024-11-07 06:55:43. Version ac07

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