S&Y Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the S&Y Observatory clear sky chart from 2005-11-06 to 2024-11-28.

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	11% 6% 2 6% 4 4 4 4 6% 8% 45%	101258
	Night	12% 6% 2 5% 3 3 4 3 5% 7% 50%	98374
Transparency	Day	36% 4 10% 22% 19% 8%	105027
	Night	34% 4 10% 22% 20% 11%	102732
Seeing	Day	13% 6% 19% 27% 25% 10%	14950
	Night	14% 7% 26% 35% 17% 2	24854

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	14% 9% 2 5% 3 3 3 3 4 7% 47%	2847
	11th to 20th	Day	17% 5% 1 3 2 2 2 2 4 6% 54%	2850
	21st to end	Day	21% 9% 3 7% 3 2 2 2 3 7% 40%	3178
February	1st to 10th	Day	19% 8% 3 7% 4 3 3 3 4 5% 42%	1900
	11th to 20th	Day	19% 9% 2 6% 3 3 3 3 5% 5% 44%	1849
	21st to end	Day	18% 8% 3 6% 4 3 2 3 4 5% 46%	1612
March	1st to 10th	Day	15% 8% 3 7% 5% 4 4 3 5% 7% 39%	3436
	11th to 20th	Day	19% 8% 3 8% 5% 5% 5% 4 5% 6% 31%	3480
	21st to end	Day	14% 9% 3 6% 4 3 3 3 5% 7% 42%	3814
April	1st to 10th	Day	14% 10% 3 6% 4 4 3 3 6% 6% 40%	2090
	11th to 20th	Day	14% 8% 4 6% 6% 4 3 4 5% 6% 41%	2103
	21st to end	Day	13% 6% 2 6% 4 4 4 4 5% 7% 45%	2353
May	1st to 10th	Day	18% 9% 3 8% 5% 5% 5% 4 6% 7% 32%	4082
	11th to 20th	Day	13% 6% 2 7% 4 4 5% 4 5% 7% 42%	4082
	21st to end	Day	10% 6% 3 7% 5% 5% 6% 5% 8% 11% 36%	4477
June	1st to 10th	Day	5% 4 2 5% 3 5% 5% 5% 7% 10% 49%	2470
	11th to 20th	Day	6% 3 1 4 3 5% 5% 5% 7% 10% 48%	2470
	21st to end	Day	5% 6% 2 6% 6% 6% 6% 6% 8% 11% 38%	2470
July	1st to 10th	Day	6% 4 1 5% 4 4 4 4 8% 11% 48%	4120
	11th to 20th	Day	5% 4 2 5% 4 5% 5% 5% 8% 11% 46%	4120
	21st to end	Day	9% 8% 2 7% 5% 5% 6% 5% 7% 11% 34%	4465
August	1st to 10th	Day	1 1 1 2 2 2 3 3 5% 9% 69%	4104
	11th to 20th	Day	3 2 1 3 3 4 4 4 8% 12% 56%	3959
	21st to end	Day	4 3 2 5% 5% 5% 6% 5% 9% 12% 45%	3895
September	1st to 10th	Day	5% 7% 3 8% 5% 5% 5% 4 6% 8% 45%	2090
	11th to 20th	Day	10% 6% 2 7% 5% 5% 5% 4 7% 7% 43%	2090
	21st to end	Day	6% 3 2 5% 4 6% 6% 4 6% 7% 50%	2090
October	1st to 10th	Day	5% 4 1 4 3 4 4 4 5% 8% 59%	2080
	11th to 20th	Day	12% 4 2 5% 4 2 3 3 4 6% 55%	1900
	21st to end	Day	12% 4 2 4 3 3 3 3 4 5% 58%	2090
November	1st to 10th	Day	12% 7% 2 6% 4 3 4 4 5% 7% 46%	1958
	11th to 20th	Day	10% 7% 2 6% 4 3 3 3 5% 5% 52%	1955
	21st to end	Day	16% 8% 3 6% 4 3 4 3 4 6% 45%	1773
December	1st to 10th	Day	15% 6% 3 5% 4 4 4 3 5% 6% 45%	1710
	11th to 20th	Day	18% 6% 2 7% 4 4 3 3 4 5% 44%	2161
	21st to end	Day	15% 8% 2 5% 3 3 3 2 4 5% 50%	3135
January	1st to 10th	Night	18% 8% 2 4 2 2 2 2 4 5% 51%	4108
	11th to 20th	Night	14% 6% 1 3 2 2 2 2 2 4 62%	4120
	21st to end	Night	21% 6% 3 6% 4 3 3 2 4 5% 43%	4518
February	1st to 10th	Night	18% 8% 3 6% 3 3 3 3 4 6% 45%	2280
	11th to 20th	Night	19% 7% 3 5% 3 3 3 2 4 4 49%	2218
	21st to end	Night	19% 8% 2 5% 3 3 3 3 4 5% 45%	1841
March	1st to 10th	Night	17% 8% 3 8% 4 4 4 4 5% 5% 38%	3419
	11th to 20th	Night	21% 9% 3 6% 5% 4 4 3 5% 6% 33%	3480
	21st to end	Night	13% 7% 3 7% 4 4 4 3 5% 6% 44%	3817
April	1st to 10th	Night	12% 7% 2 5% 4 4 4 4 6% 6% 46%	2090
	11th to 20th	Night	15% 6% 2 6% 4 3 4 3 4 7% 45%	2022
	21st to end	Night	14% 7% 2 6% 3 3 3 3 5% 6% 48%	1821
May	1st to 10th	Night	20% 9% 2 7% 4 4 4 4 5% 6% 35%	2823
	11th to 20th	Night	11% 6% 2 6% 4 3 4 3 5% 8% 47%	2823
	21st to end	Night	9% 7% 2 6% 5% 4 4 4 6% 11% 42%	3090
June	1st to 10th	Night	4 4 1 4 2 3 3 3 6% 10% 60%	1710
	11th to 20th	Night	4 3 1 3 3 3 4 4 6% 9% 60%	1710
	21st to end	Night	4 4 1 5% 3 4 5% 4 7% 11% 52%	1710
July	1st to 10th	Night	5% 3 1 3 4 4 4 4 7% 11% 54%	2850
	11th to 20th	Night	3 4 1 4 4 4 6% 4 6% 11% 54%	2850
	21st to end	Night	7% 8% 2 7% 4 4 5% 4 6% 11% 42%	3098
August	1st to 10th	Night	1 2 2 2 2 3 5% 8% 75%	2836
	11th to 20th	Night	2 3 1 4 3 3 4 4 7% 12% 58%	2861
	21st to end	Night	3 2 1 4 3 4 4 4 7% 11% 55%	3761
September	1st to 10th	Night	5% 5% 2 6% 5% 5% 4 4 6% 8% 52%	2090
	11th to 20th	Night	9% 6% 2 5% 4 4 4 4 6% 9% 47%	2090
	21st to end	Night	6% 4 1 4 4 4 4 4 6% 8% 56%	2090
October	1st to 10th	Night	4 4 1 4 3 3 3 2 5% 6% 65%	2090
	11th to 20th	Night	11% 5% 1 3 3 3 4 3 4 6% 57%	2270
	21st to end	Night	13% 4 1 4 3 3 2 2 4 4 60%	2508
November	1st to 10th	Night	13% 5% 2 5% 3 3 4 3 4 6% 52%	2340
	11th to 20th	Night	9% 5% 2 6% 4 3 3 3 4 6% 54%	2440
	21st to end	Night	15% 7% 1 5% 3 4 3 3 4 6% 48%	2562
December	1st to 10th	Night	15% 8% 2 4 4 3 4 3 4 5% 48%	2470
	11th to 20th	Night	16% 10% 3 6% 3 3 3 3 5% 5% 45%	3036
	21st to end	Night	16% 6% 2 5% 3 3 2 2 3 5% 53%	4532

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	40% 1 3 20% 23% 12%	2848
	11th to 20th	Day	34% 2 5% 20% 29% 10%	2850
	21st to end	Day	49% 2 3 11% 25% 12%	3178
February	1st to 10th	Day	46% 2 5% 13% 21% 13%	1900
	11th to 20th	Day	45% 2 7% 17% 19% 10%	1859
	21st to end	Day	43% 3 6% 19% 17% 14%	1612
March	1st to 10th	Day	47% 2 6% 17% 19% 8%	3436
	11th to 20th	Day	54% 2 9% 12% 16% 8%	3480
	21st to end	Day	44% 2 8% 17% 23% 7%	3814
April	1st to 10th	Day	45% 3 8% 18% 15% 12%	2090
	11th to 20th	Day	46% 3 7% 15% 19% 10%	2103
	21st to end	Day	40% 3 6% 22% 22% 7%	2353
May	1st to 10th	Day	53% 3 10% 17% 13% 5%	4120
	11th to 20th	Day	42% 3 9% 19% 22% 4	4086
	21st to end	Day	42% 3 11% 32% 11% 1	4489
June	1st to 10th	Day	29% 5% 14% 29% 19% 3	2470
	11th to 20th	Day	30% 7% 12% 28% 18% 5%	2470
	21st to end	Day	37% 7% 13% 26% 15% 3	2470
July	1st to 10th	Day	29% 7% 21% 36% 6% 1	4056
	11th to 20th	Day	30% 8% 18% 28% 16% 1	4051
	21st to end	Day	41% 8% 18% 26% 7% 1	4325
August	1st to 10th	Day	13% 4 12% 40% 29% 1	4090
	11th to 20th	Day	20% 5% 26% 37% 10% 2	3998
	21st to end	Day	27% 11% 19% 24% 16% 2	3894
September	1st to 10th	Day	38% 6% 10% 22% 17% 8%	2090
	11th to 20th	Day	38% 6% 13% 19% 20% 5%	2090
	21st to end	Day	31% 6% 9% 23% 17% 15%	2090
October	1st to 10th	Day	16% 3 6% 13% 22% 39%	3457
	11th to 20th	Day	20% 2 6% 18% 34% 19%	3140
	21st to end	Day	25% 4 5% 20% 31% 15%	3428
November	1st to 10th	Day	38% 4 9% 18% 21% 11%	1958
	11th to 20th	Day	34% 3 8% 18% 22% 15%	1955
	21st to end	Day	42% 3 7% 17% 20% 12%	1773
December	1st to 10th	Day	41% 2 9% 19% 21% 8%	1710
	11th to 20th	Day	45% 1 6% 13% 23% 12%	2159
	21st to end	Day	39% 2 4 15% 27% 13%	3135
January	1st to 10th	Night	39% 1 4 17% 23% 16%	4108
	11th to 20th	Night	31% 1 4 17% 31% 15%	4120
	21st to end	Night	46% 1 3 14% 25% 11%	4518
February	1st to 10th	Night	43% 3 6% 13% 20% 16%	2280
	11th to 20th	Night	42% 3 6% 16% 20% 14%	2218
	21st to end	Night	43% 3 5% 17% 17% 15%	1841
March	1st to 10th	Night	50% 2 7% 16% 16% 9%	3419
	11th to 20th	Night	55% 2 9% 14% 13% 7%	3480
	21st to end	Night	44% 3 8% 14% 22% 9%	3817
April	1st to 10th	Night	39% 3 8% 19% 18% 13%	2090
	11th to 20th	Night	40% 3 10% 16% 17% 14%	2022
	21st to end	Night	39% 3 7% 22% 20% 8%	1821
May	1st to 10th	Night	51% 3 8% 21% 13% 5%	2850
	11th to 20th	Night	38% 3 10% 23% 19% 8%	2824
	21st to end	Night	38% 3 14% 32% 12% 1	3099
June	1st to 10th	Night	22% 4 18% 32% 22% 3	1710
	11th to 20th	Night	21% 5% 15% 33% 20% 6%	1710
	21st to end	Night	26% 7% 16% 31% 17% 3	1710
July	1st to 10th	Night	24% 6% 28% 35% 6%	2805
	11th to 20th	Night	23% 7% 20% 34% 14% 1	2796
	21st to end	Night	36% 7% 23% 26% 7%	2999
August	1st to 10th	Night	9% 4 15% 42% 29% 1	2826
	11th to 20th	Night	19% 6% 30% 32% 12% 2	2888
	21st to end	Night	21% 11% 22% 30% 14% 2	3761
September	1st to 10th	Night	29% 6% 16% 24% 16% 8%	2090
	11th to 20th	Night	35% 6% 14% 22% 16% 6%	2090
	21st to end	Night	26% 5% 15% 21% 18% 14%	2090
October	1st to 10th	Night	14% 3 6% 17% 19% 41%	3480
	11th to 20th	Night	18% 2 7% 18% 33% 23%	3769
	21st to end	Night	22% 3 4 24% 30% 17%	4120
November	1st to 10th	Night	34% 4 8% 20% 21% 13%	2340
	11th to 20th	Night	33% 3 8% 19% 22% 16%	2440
	21st to end	Night	39% 2 7% 18% 18% 15%	2562
December	1st to 10th	Night	40% 3 6% 22% 18% 11%	2470
	11th to 20th	Night	44% 2 5% 12% 22% 15%	3037
	21st to end	Night	37% 2 4 15% 29% 12%	4532

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	22% 8% 38% 23% 8% 1	270
	11th to 20th	Day	23% 11% 30% 27% 7% 1	270
	21st to end	Day	20% 13% 37% 23% 6%	297
February	1st to 10th	Day	28% 16% 26% 22% 8% 1	270
	11th to 20th	Day	27% 16% 32% 19% 5%	270
	21st to end	Day	25% 13% 41% 18% 2	225
March	1st to 10th	Day	20% 13% 37% 22% 7%	270
	11th to 20th	Day	18% 17% 36% 23% 6% 1	270
	21st to end	Day	19% 12% 38% 22% 7% 1	297
April	1st to 10th	Day	20% 15% 39% 20% 5% 1	270
	11th to 20th	Day	16% 14% 38% 25% 7% 1	301
	21st to end	Day	19% 11% 33% 26% 9% 2	533
May	1st to 10th	Day	17% 9% 33% 29% 11%	653
	11th to 20th	Day	15% 8% 26% 32% 17% 3	675
	21st to end	Day	13% 5% 25% 33% 21% 3	734
June	1st to 10th	Day	5% 2 12% 39% 31% 11%	680
	11th to 20th	Day	7% 2 11% 43% 31% 7%	680
	21st to end	Day	5% 3 13% 28% 36% 15%	680
July	1st to 10th	Day	8% 2 6% 31% 36% 18%	671
	11th to 20th	Day	3 1 3 26% 47% 19%	668
	21st to end	Day	6% 2 3 27% 46% 17%	739
August	1st to 10th	Day	3 3 22% 52% 19%	676
	11th to 20th	Day	6% 3 22% 50% 19%	622
	21st to end	Day	6% 1 3 19% 36% 35%	371
September	1st to 10th	Day	6% 2 6% 19% 35% 32%	300
	11th to 20th	Day	6% 1 6% 18% 42% 27%	300
	21st to end	Day	10% 3 6% 24% 35% 23%	300
October	1st to 10th	Day	4 2 9% 29% 41% 15%	300
	11th to 20th	Day	11% 2 18% 34% 26% 8%	300
	21st to end	Day	18% 9% 24% 22% 20% 7%	330
November	1st to 10th	Day	18% 8% 20% 29% 19% 6%	300
	11th to 20th	Day	17% 9% 24% 28% 17% 5%	300
	21st to end	Day	19% 16% 31% 19% 11% 4	291
December	1st to 10th	Day	20% 6% 31% 25% 13% 6%	270
	11th to 20th	Day	23% 13% 31% 23% 9% 1	270
	21st to end	Day	21% 11% 35% 23% 8% 2	297
January	1st to 10th	Night	19% 11% 31% 31% 7% 1	950
	11th to 20th	Night	21% 11% 30% 31% 8%	950
	21st to end	Night	20% 10% 32% 31% 7%	1031
February	1st to 10th	Night	23% 11% 34% 27% 4	760
	11th to 20th	Night	23% 11% 37% 25% 4	744
	21st to end	Night	24% 15% 41% 18% 2	585
March	1st to 10th	Night	20% 14% 38% 25% 3	570
	11th to 20th	Night	19% 10% 37% 29% 5%	570
	21st to end	Night	15% 11% 44% 26% 4	627
April	1st to 10th	Night	14% 11% 45% 27% 4	570
	11th to 20th	Night	18% 10% 41% 26% 5%	563
	21st to end	Night	15% 11% 41% 24% 8%	570
May	1st to 10th	Night	12% 11% 43% 28% 5% 1	570
	11th to 20th	Night	14% 6% 32% 35% 12% 1	561
	21st to end	Night	10% 4 31% 41% 14%	617
June	1st to 10th	Night	6% 2 18% 46% 27% 2	570
	11th to 20th	Night	3 2 25% 52% 17% 1	570
	21st to end	Night	4 1 12% 48% 30% 5%	570
July	1st to 10th	Night	6% 1 9% 46% 34% 3	555
	11th to 20th	Night	4 9% 49% 35% 3	552
	21st to end	Night	4 1 7% 49% 36% 3	624
August	1st to 10th	Night	1 1 7% 52% 35% 4	567
	11th to 20th	Night	6% 1 5% 52% 33% 4	564
	21st to end	Night	4 1 5% 38% 46% 7%	627
September	1st to 10th	Night	8% 1 7% 40% 39% 6%	570
	11th to 20th	Night	10% 2 8% 36% 40% 4	570
	21st to end	Night	9% 1 11% 37% 38% 5%	570
October	1st to 10th	Night	5% 1 12% 48% 30% 5%	570
	11th to 20th	Night	12% 3 22% 41% 20% 2	750
	21st to end	Night	13% 7% 27% 32% 19% 2	836
November	1st to 10th	Night	14% 5% 23% 38% 19% 1	780
	11th to 20th	Night	12% 9% 27% 37% 15% 1	840
	21st to end	Night	20% 9% 28% 30% 12% 1	986
December	1st to 10th	Night	19% 9% 27% 33% 11% 1	950
	11th to 20th	Night	24% 12% 26% 32% 7% 1	950
	21st to end	Night	21% 8% 30% 34% 7%	1045

Page generated at 2024-11-24 23:22:19. Version ac07

Copyright © 2024 Attilla Danko.