Shank Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Shank Observatory clear sky chart from 2005-11-06 to 2024-11-05.

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	13% 6% 2 6% 5% 5% 5% 4 6% 8% 40%	100981
	Night	14% 6% 2 5% 4 4 4 4 6% 7% 44%	97989
Transparency	Day	41% 4 11% 24% 16% 4	104631
	Night	39% 4 12% 24% 18% 4	102478
Seeing	Day	18% 9% 23% 26% 17% 7%	14970
	Night	17% 6% 23% 36% 16% 2	24746

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% 7% 2 7% 5% 5% 4 4 4 5% 44%	2836
	11th to 20th	Day	12% 10% 3 10% 5% 5% 4 4 4 5% 39%	2840
	21st to end	Day	15% 9% 3 8% 4 5% 4 3 5% 5% 40%	3124
February	1st to 10th	Day	11% 9% 2 8% 5% 4 4 4 5% 7% 41%	1710
	11th to 20th	Day	13% 8% 2 6% 5% 5% 4 3 5% 7% 41%	1663
	21st to end	Day	15% 7% 3 5% 4 5% 5% 3 5% 7% 41%	1628
March	1st to 10th	Day	18% 9% 3 6% 4 4 4 4 5% 7% 36%	3435
	11th to 20th	Day	9% 6% 2 5% 4 4 4 4 5% 6% 52%	3480
	21st to end	Day	15% 9% 3 7% 5% 4 4 4 5% 6% 39%	3815
April	1st to 10th	Day	10% 6% 2 6% 5% 5% 5% 3 6% 7% 45%	2220
	11th to 20th	Day	13% 5% 2 6% 4 4 4 3 5% 7% 46%	2254
	21st to end	Day	17% 6% 3 6% 4 4 4 3 5% 6% 42%	2365
May	1st to 10th	Day	18% 6% 2 7% 6% 6% 6% 5% 6% 8% 30%	4082
	11th to 20th	Day	22% 7% 2 7% 4 4 4 4 5% 6% 34%	4081
	21st to end	Day	10% 5% 2 6% 5% 5% 5% 5% 7% 9% 40%	4653
June	1st to 10th	Day	12% 5% 2 5% 5% 5% 5% 5% 6% 9% 41%	2660
	11th to 20th	Day	9% 6% 2 6% 6% 6% 6% 5% 7% 10% 37%	2660
	21st to end	Day	8% 5% 2 6% 5% 5% 6% 5% 8% 11% 41%	2660
July	1st to 10th	Day	7% 4 2 7% 6% 6% 6% 6% 7% 11% 40%	4165
	11th to 20th	Day	9% 4 2 6% 6% 7% 6% 6% 8% 12% 33%	4120
	21st to end	Day	12% 7% 3 9% 7% 6% 6% 5% 7% 9% 29%	4466
August	1st to 10th	Day	13% 5% 2 8% 6% 6% 7% 5% 8% 10% 31%	4104
	11th to 20th	Day	10% 4 2 6% 6% 6% 7% 5% 8% 10% 37%	4026
	21st to end	Day	8% 4 2 5% 5% 5% 5% 4 7% 9% 46%	4180
September	1st to 10th	Day	14% 5% 2 6% 4 4 5% 3 5% 6% 45%	2280
	11th to 20th	Day	14% 7% 2 5% 3 4 4 4 5% 6% 46%	2157
	21st to end	Day	23% 5% 2 5% 5% 3 4 3 6% 7% 36%	2049
October	1st to 10th	Day	16% 5% 2 6% 3 4 4 3 5% 6% 46%	1900
	11th to 20th	Day	15% 4 1 5% 4 4 4 3 4 5% 50%	1900
	21st to end	Day	14% 5% 1 4 4 3 4 3 5% 6% 51%	2090
November	1st to 10th	Day	10% 5% 2 5% 3 3 4 3 4 6% 55%	1898
	11th to 20th	Day	14% 5% 2 5% 4 3 4 4 5% 5% 50%	1666
	21st to end	Day	14% 5% 1 4 4 4 4 3 5% 7% 49%	1520
December	1st to 10th	Day	14% 9% 2 6% 4 4 6% 4 6% 8% 39%	1520
	11th to 20th	Day	15% 4 1 4 3 4 3 2 4 6% 52%	1910
	21st to end	Day	17% 6% 2 6% 5% 4 5% 4 7% 8% 35%	2864
January	1st to 10th	Night	10% 9% 2 5% 5% 4 4 4 5% 6% 46%	4109
	11th to 20th	Night	14% 9% 3 6% 4 3 4 3 5% 5% 46%	4120
	21st to end	Night	19% 8% 2 5% 3 3 4 3 5% 5% 42%	4532
February	1st to 10th	Night	11% 7% 3 6% 4 4 5% 4 6% 6% 44%	2470
	11th to 20th	Night	16% 8% 2 6% 4 3 4 4 5% 6% 42%	2403
	21st to end	Night	13% 8% 3 6% 5% 4 4 4 6% 8% 41%	1822
March	1st to 10th	Night	21% 8% 2 7% 4 3 5% 3 5% 5% 37%	3418
	11th to 20th	Night	9% 5% 2 5% 3 4 4 4 6% 8% 52%	3480
	21st to end	Night	14% 7% 2 5% 3 4 3 3 4 7% 48%	3817
April	1st to 10th	Night	14% 7% 2 4 4 4 4 4 5% 5% 45%	1959
	11th to 20th	Night	12% 4 2 5% 4 4 5% 3 6% 8% 47%	1875
	21st to end	Night	16% 4 2 5% 4 4 4 3 5% 8% 45%	1829
May	1st to 10th	Night	20% 7% 2 6% 5% 5% 5% 4 6% 7% 34%	2813
	11th to 20th	Night	23% 7% 2 6% 4 4 3 4 4 5% 37%	2812
	21st to end	Night	12% 3 2 5% 4 4 4 4 7% 9% 45%	2900
June	1st to 10th	Night	10% 5% 2 5% 4 4 3 5% 7% 12% 44%	1520
	11th to 20th	Night	11% 5% 1 5% 4 5% 5% 4 7% 8% 44%	1520
	21st to end	Night	9% 4 1 5% 4 4 5% 5% 8% 10% 45%	1520
July	1st to 10th	Night	6% 4 2 6% 5% 5% 5% 5% 7% 11% 44%	2775
	11th to 20th	Night	8% 6% 3 7% 6% 5% 5% 5% 7% 11% 39%	2840
	21st to end	Night	8% 7% 3 9% 7% 6% 6% 4 7% 10% 34%	3087
August	1st to 10th	Night	14% 5% 2 7% 5% 5% 5% 5% 6% 9% 37%	2825
	11th to 20th	Night	11% 5% 2 6% 5% 6% 6% 5% 8% 7% 40%	2785
	21st to end	Night	10% 5% 2 5% 4 4 4 4 6% 8% 48%	3462
September	1st to 10th	Night	13% 4 1 5% 4 4 4 4 5% 6% 49%	1900
	11th to 20th	Night	14% 5% 2 6% 3 4 4 3 5% 7% 46%	2019
	21st to end	Night	23% 7% 2 5% 4 3 3 3 4 5% 41%	2130
October	1st to 10th	Night	17% 5% 2 5% 3 4 4 3 5% 7% 45%	2280
	11th to 20th	Night	14% 5% 1 4 3 3 4 3 5% 5% 53%	2280
	21st to end	Night	14% 3 2 4 4 3 3 3 5% 7% 51%	2508
November	1st to 10th	Night	11% 6% 2 5% 3 3 4 3 4 6% 53%	2280
	11th to 20th	Night	13% 5% 2 4 4 3 4 3 5% 6% 51%	2506
	21st to end	Night	14% 5% 2 3 4 4 4 4 5% 6% 49%	2660
December	1st to 10th	Night	15% 7% 2 6% 5% 5% 4 4 5% 5% 43%	2660
	11th to 20th	Night	13% 6% 3 5% 4 4 4 3 5% 6% 47%	3285
	21st to end	Night	16% 5% 2 6% 4 4 5% 4 7% 8% 39%	4788

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	44% 2 5% 24% 19% 6%	2837
	11th to 20th	Day	49% 1 6% 17% 19% 8%	2840
	21st to end	Day	48% 1 7% 23% 18% 3	3124
February	1st to 10th	Day	43% 3 10% 22% 18% 4	1710
	11th to 20th	Day	44% 3 8% 22% 19% 5%	1672
	21st to end	Day	43% 3 11% 18% 19% 6%	1628
March	1st to 10th	Day	50% 2 8% 21% 14% 6%	3435
	11th to 20th	Day	34% 2 7% 27% 23% 7%	3480
	21st to end	Day	48% 2 10% 21% 15% 4	3815
April	1st to 10th	Day	39% 3 10% 21% 19% 8%	2220
	11th to 20th	Day	39% 2 11% 22% 21% 6%	2254
	21st to end	Day	44% 2 11% 23% 15% 4	2365
May	1st to 10th	Day	53% 3 10% 22% 11% 2	4120
	11th to 20th	Day	52% 3 9% 23% 10% 2	4085
	21st to end	Day	39% 3 16% 22% 15% 4	4667
June	1st to 10th	Day	39% 5% 14% 25% 16% 1	2660
	11th to 20th	Day	41% 6% 16% 22% 13% 2	2660
	21st to end	Day	35% 6% 15% 28% 14% 2	2660
July	1st to 10th	Day	37% 9% 17% 21% 10% 6%	4100
	11th to 20th	Day	38% 9% 17% 27% 8% 1	4051
	21st to end	Day	50% 6% 10% 23% 11% 1	4324
August	1st to 10th	Day	45% 7% 16% 23% 8%	4091
	11th to 20th	Day	38% 8% 14% 28% 12% 1	4065
	21st to end	Day	34% 6% 17% 29% 13% 1	4180
September	1st to 10th	Day	40% 4 13% 18% 20% 5%	2280
	11th to 20th	Day	40% 3 7% 27% 20% 4	2157
	21st to end	Day	48% 3 8% 21% 18% 3	2049
October	1st to 10th	Day	32% 5% 6% 21% 28% 7%	3160
	11th to 20th	Day	25% 2 8% 29% 23% 13%	3140
	21st to end	Day	23% 2 9% 31% 24% 12%	3428
November	1st to 10th	Day	32% 2 8% 26% 27% 5%	1898
	11th to 20th	Day	36% 3 9% 21% 23% 9%	1666
	21st to end	Day	36% 2 9% 27% 23% 3	1520
December	1st to 10th	Day	44% 3 10% 24% 15% 4	1520
	11th to 20th	Day	35% 2 8% 29% 20% 7%	1906
	21st to end	Day	48% 2 11% 24% 13% 2	2864
January	1st to 10th	Night	41% 2 7% 23% 23% 4	4109
	11th to 20th	Night	43% 2 7% 23% 19% 7%	4120
	21st to end	Night	46% 2 7% 25% 19% 3	4532
February	1st to 10th	Night	39% 4 12% 27% 16% 3	2470
	11th to 20th	Night	44% 3 8% 21% 18% 6%	2405
	21st to end	Night	42% 3 12% 23% 15% 6%	1822
March	1st to 10th	Night	50% 2 7% 23% 14% 4	3418
	11th to 20th	Night	32% 2 8% 25% 27% 6%	3480
	21st to end	Night	39% 2 12% 24% 19% 5%	3817
April	1st to 10th	Night	41% 3 10% 22% 20% 5%	1959
	11th to 20th	Night	34% 3 15% 22% 21% 5%	1875
	21st to end	Night	39% 2 12% 27% 16% 3	1829
May	1st to 10th	Night	50% 4 13% 20% 10% 2	2840
	11th to 20th	Night	51% 3 10% 26% 10% 1	2813
	21st to end	Night	36% 4 19% 27% 10% 4	2907
June	1st to 10th	Night	33% 7% 16% 29% 14% 1	1520
	11th to 20th	Night	36% 6% 16% 26% 13% 2	1520
	21st to end	Night	31% 7% 19% 23% 18% 2	1520
July	1st to 10th	Night	33% 9% 23% 19% 13% 3	2730
	11th to 20th	Night	38% 8% 19% 24% 10% 1	2786
	21st to end	Night	43% 9% 17% 21% 10%	2988
August	1st to 10th	Night	43% 7% 18% 25% 7% 1	2814
	11th to 20th	Night	38% 7% 16% 24% 14%	2812
	21st to end	Night	33% 5% 17% 32% 11% 2	3462
September	1st to 10th	Night	36% 6% 15% 20% 19% 5%	1900
	11th to 20th	Night	38% 3 8% 29% 19% 3	2019
	21st to end	Night	46% 4 8% 22% 18% 2	2130
October	1st to 10th	Night	40% 4 8% 20% 23% 4	3800
	11th to 20th	Night	24% 3 10% 23% 30% 10%	3779
	21st to end	Night	21% 2 10% 30% 28% 8%	4120
November	1st to 10th	Night	34% 2 8% 24% 24% 7%	2280
	11th to 20th	Night	35% 2 8% 25% 24% 6%	2506
	21st to end	Night	36% 3 10% 25% 22% 5%	2660
December	1st to 10th	Night	44% 3 9% 26% 15% 4	2660
	11th to 20th	Night	40% 2 9% 24% 19% 7%	3288
	21st to end	Night	44% 2 11% 23% 18% 2	4788

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	21% 21% 32% 20% 5% 1	270
	11th to 20th	Day	26% 19% 33% 18% 4	270
	21st to end	Day	24% 19% 34% 19% 3 1	297
February	1st to 10th	Day	22% 20% 34% 18% 6%	270
	11th to 20th	Day	30% 21% 39% 9% 1	270
	21st to end	Day	27% 14% 36% 19% 4	336
March	1st to 10th	Day	19% 19% 30% 25% 6%	460
	11th to 20th	Day	18% 19% 33% 21% 7% 2	460
	21st to end	Day	20% 15% 32% 25% 8% 1	506
April	1st to 10th	Day	21% 17% 28% 23% 10% 2	460
	11th to 20th	Day	18% 12% 27% 24% 15% 4	452
	21st to end	Day	25% 9% 29% 22% 12% 3	460
May	1st to 10th	Day	22% 11% 26% 25% 12% 5%	463
	11th to 20th	Day	24% 6% 26% 23% 17% 5%	487
	21st to end	Day	18% 4 18% 28% 22% 11%	529
June	1st to 10th	Day	13% 4 24% 27% 24% 9%	490
	11th to 20th	Day	11% 6% 20% 30% 22% 12%	490
	21st to end	Day	9% 3 21% 38% 23% 7%	490
July	1st to 10th	Day	12% 2 14% 27% 30% 15%	485
	11th to 20th	Day	6% 1 12% 34% 31% 16%	484
	21st to end	Day	12% 2 11% 32% 28% 14%	532
August	1st to 10th	Day	15% 3 13% 27% 26% 17%	486
	11th to 20th	Day	15% 1 13% 28% 26% 16%	479
	21st to end	Day	11% 1 9% 28% 30% 20%	539
September	1st to 10th	Day	17% 2 14% 24% 25% 17%	490
	11th to 20th	Day	16% 3 11% 27% 28% 14%	490
	21st to end	Day	29% 6% 16% 24% 20% 6%	490
October	1st to 10th	Day	21% 5% 15% 29% 23% 7%	490
	11th to 20th	Day	14% 11% 25% 28% 18% 4	490
	21st to end	Day	16% 8% 30% 31% 12% 3	539
November	1st to 10th	Day	15% 7% 28% 31% 15% 4	472
	11th to 20th	Day	19% 13% 29% 26% 11% 2	281
	21st to end	Day	20% 11% 33% 24% 10% 1	180
December	1st to 10th	Day	21% 12% 37% 23% 6% 2	180
	11th to 20th	Day	24% 9% 32% 25% 9% 1	180
	21st to end	Day	21% 13% 33% 22% 9% 2	223
January	1st to 10th	Night	18% 12% 37% 29% 4	760
	11th to 20th	Night	20% 10% 31% 34% 5%	760
	21st to end	Night	17% 9% 40% 31% 3	836
February	1st to 10th	Night	16% 10% 35% 35% 3	760
	11th to 20th	Night	24% 12% 37% 26% 1	743
	21st to end	Night	22% 10% 37% 28% 3	628
March	1st to 10th	Night	17% 11% 35% 32% 5%	760
	11th to 20th	Night	20% 12% 32% 27% 8% 1	760
	21st to end	Night	21% 8% 31% 33% 6% 1	836
April	1st to 10th	Night	19% 13% 31% 29% 8%	760
	11th to 20th	Night	15% 9% 30% 33% 13% 1	751
	21st to end	Night	19% 5% 26% 39% 10% 1	689
May	1st to 10th	Night	19% 6% 20% 37% 18% 1	570
	11th to 20th	Night	21% 2 19% 36% 19% 2	561
	21st to end	Night	15% 2 12% 41% 27% 3	515
June	1st to 10th	Night	10% 1 15% 48% 24% 2	380
	11th to 20th	Night	11% 3 11% 46% 27% 3	380
	21st to end	Night	9% 2 12% 49% 27% 2	380
July	1st to 10th	Night	14% 1 6% 35% 38% 6%	516
	11th to 20th	Night	6% 1 6% 39% 43% 6%	552
	21st to end	Night	9% 1 6% 41% 37% 5%	624
August	1st to 10th	Night	12% 1 6% 41% 35% 5%	567
	11th to 20th	Night	15% 1 5% 39% 36% 4	564
	21st to end	Night	14% 2 7% 38% 34% 6%	822
September	1st to 10th	Night	16% 1 9% 34% 33% 7%	760
	11th to 20th	Night	16% 2 7% 38% 31% 6%	760
	21st to end	Night	26% 3 14% 32% 23% 2	760
October	1st to 10th	Night	19% 4 16% 33% 25% 4	760
	11th to 20th	Night	17% 5% 26% 35% 16% 1	760
	21st to end	Night	16% 6% 24% 39% 13% 2	836
November	1st to 10th	Night	16% 5% 21% 41% 14% 2	760
	11th to 20th	Night	16% 9% 26% 36% 12% 1	760
	21st to end	Night	18% 8% 29% 35% 9% 2	760
December	1st to 10th	Night	20% 8% 30% 35% 7% 1	760
	11th to 20th	Night	14% 8% 32% 39% 6%	760
	21st to end	Night	18% 8% 28% 41% 5%	836

Page generated at 2024-11-03 02:11:14. Version ac07

Copyright © 2024 Attilla Danko.