Stock Dr/Savery
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stock Dr/Savery clear sky chart from 2005-11-06 to 2026-01-02.

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	5% 10% 4 7% 4 4 4 3 5% 7% 47%	136327
	Night	5% 12% 4 8% 4 4 4 3 5% 6% 45%	132525
Transparency	Day	22% 39% 6% 14% 13% 6%	131192
	Night	25% 39% 6% 15% 11% 4	128664
Seeing	Day	14% 18% 31% 24% 11% 2	17168
	Night	13% 11% 30% 32% 13% 2	27321

By Month

Percentage Cloud Cover SW (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	4 18% 9% 15% 4 3 3 2 4 5% 32%	3646
	11th to 20th	Day	6% 18% 7% 17% 8% 4 3 2 3 3 26%	3962
	21st to end	Day	2 21% 7% 11% 5% 3 3 2 3 4 38%	4510
February	1st to 10th	Day	8% 22% 7% 13% 4 3 4 3 3 5% 28%	1800
	11th to 20th	Day	7% 23% 8% 12% 4 3 3 2 3 4 30%	1765
	21st to end	Day	5% 19% 6% 14% 5% 3 4 3 5% 5% 31%	1650
March	1st to 10th	Day	3 16% 8% 11% 5% 4 4 3 3 5% 37%	4773
	11th to 20th	Day	3 18% 6% 9% 4 4 4 3 4 5% 41%	5000
	21st to end	Day	6% 24% 7% 10% 5% 4 4 3 5% 6% 26%	5604
April	1st to 10th	Day	7% 17% 4 8% 5% 4 4 3 6% 7% 36%	2400
	11th to 20th	Day	8% 17% 4 9% 5% 4 4 4 5% 4 35%	2371
	21st to end	Day	7% 14% 4 7% 5% 5% 5% 4 5% 6% 39%	2423
May	1st to 10th	Day	7% 13% 4 8% 5% 4 5% 4 5% 7% 37%	5926
	11th to 20th	Day	5% 9% 2 6% 5% 5% 6% 4 7% 8% 43%	6298
	21st to end	Day	5% 6% 2 6% 5% 5% 5% 4 7% 8% 46%	6925
June	1st to 10th	Day	5% 5% 2 5% 4 5% 4 4 7% 8% 52%	2800
	11th to 20th	Day	4 3 2 5% 3 4 5% 4 6% 7% 58%	2800
	21st to end	Day	3 2 1 4 3 4 4 4 6% 7% 63%	2800
July	1st to 10th	Day	2 2 1 3 3 3 5% 4 6% 8% 63%	6339
	11th to 20th	Day	1 2 1 4 4 4 5% 4 7% 9% 58%	6340
	21st to end	Day	2 3 1 4 3 4 5% 4 6% 9% 58%	6502
August	1st to 10th	Day	2 3 1 5% 4 4 5% 4 7% 9% 56%	5779
	11th to 20th	Day	4 3 1 4 3 4 5% 4 6% 8% 59%	5720
	21st to end	Day	7% 5% 2 6% 5% 4 5% 4 6% 7% 50%	5984
September	1st to 10th	Day	4 3 1 3 4 3 4 4 5% 6% 63%	2400
	11th to 20th	Day	5% 5% 1 5% 3 3 4 3 6% 6% 58%	2400
	21st to end	Day	7% 5% 2 4 3 2 4 3 5% 5% 61%	2117
October	1st to 10th	Day	5% 5% 1 3 2 2 2 2 3 4 69%	3270
	11th to 20th	Day	8% 8% 3 4 3 3 3 3 5% 7% 53%	3250
	21st to end	Day	8% 12% 3 6% 3 2 3 3 4 6% 51%	3548
November	1st to 10th	Day	8% 10% 3 6% 2 3 3 3 5% 8% 47%	1883
	11th to 20th	Day	9% 12% 5% 7% 4 3 3 3 5% 5% 43%	1764
	21st to end	Day	6% 12% 5% 10% 4 3 2 2 4 6% 45%	1680
December	1st to 10th	Day	5% 13% 4 13% 4 2 2 2 2 3 48%	2700
	11th to 20th	Day	5% 20% 4 8% 3 2 3 3 5% 6% 40%	3106
	21st to end	Day	8% 20% 6% 12% 5% 4 3 3 4 6% 30%	4092
January	1st to 10th	Night	4 16% 7% 16% 7% 5% 3 3 4 5% 30%	6342
	11th to 20th	Night	5% 20% 6% 17% 8% 5% 3 2 3 4 28%	6048
	21st to end	Night	4 20% 6% 10% 5% 3 3 2 4 4 40%	6468
February	1st to 10th	Night	8% 19% 7% 14% 5% 4 3 3 4 5% 28%	2600
	11th to 20th	Night	6% 20% 7% 11% 4 4 3 3 4 5% 32%	2521
	21st to end	Night	5% 18% 7% 11% 5% 4 3 3 4 6% 34%	1980
March	1st to 10th	Night	4 14% 6% 11% 4 4 4 3 4 5% 42%	5110
	11th to 20th	Night	3 10% 5% 8% 4 4 4 3 5% 6% 48%	5000
	21st to end	Night	7% 23% 6% 10% 4 4 4 3 5% 5% 30%	5364
April	1st to 10th	Night	7% 16% 3 6% 4 4 3 4 5% 6% 42%	2000
	11th to 20th	Night	9% 13% 3 8% 5% 4 5% 4 5% 6% 39%	1977
	21st to end	Night	9% 12% 2 7% 4 4 4 4 6% 6% 42%	1973
May	1st to 10th	Night	7% 12% 3 7% 4 3 4 3 4 7% 45%	4037
	11th to 20th	Night	9% 10% 2 7% 5% 5% 5% 4 7% 8% 39%	3617
	21st to end	Night	9% 8% 2 6% 4 4 4 3 6% 7% 47%	3972
June	1st to 10th	Night	5% 5% 1 4 3 4 4 5% 6% 9% 55%	1600
	11th to 20th	Night	4 4 2 5% 4 4 4 4 6% 6% 56%	1600
	21st to end	Night	2 3 1 4 3 3 3 3 4 6% 68%	1600
July	1st to 10th	Night	5% 5% 2 5% 3 5% 6% 4 6% 7% 53%	3640
	11th to 20th	Night	2 3 2 6% 5% 4 5% 4 7% 9% 53%	3640
	21st to end	Night	1 3 2 4 4 5% 5% 5% 7% 8% 56%	4368
August	1st to 10th	Night	2 4 2 4 3 4 5% 5% 7% 9% 57%	4033
	11th to 20th	Night	3 3 2 6% 4 4 5% 4 6% 7% 56%	4129
	21st to end	Night	5% 4 2 4 4 5% 5% 5% 7% 9% 51%	4993
September	1st to 10th	Night	5% 4 1 3 3 3 3 3 5% 7% 64%	2000
	11th to 20th	Night	5% 5% 1 4 3 3 5% 3 5% 6% 59%	2000
	21st to end	Night	6% 3 1 2 2 2 3 3 4 5% 67%	2278
October	1st to 10th	Night	5% 5% 1 3 2 2 2 2 3 5% 71%	3920
	11th to 20th	Night	7% 6% 1 4 3 3 4 3 5% 7% 55%	3898
	21st to end	Night	6% 11% 3 6% 3 2 3 3 3 6% 52%	4252
November	1st to 10th	Night	9% 12% 3 5% 2 2 3 3 5% 5% 50%	2615
	11th to 20th	Night	9% 14% 3 7% 3 3 3 3 5% 6% 44%	2851
	21st to end	Night	6% 14% 4 8% 4 3 3 3 4 7% 45%	2940
December	1st to 10th	Night	6% 12% 4 8% 3 3 2 2 4 5% 52%	4710
	11th to 20th	Night	6% 15% 5% 8% 4 3 4 3 6% 7% 39%	5321
	21st to end	Night	8% 21% 6% 10% 5% 3 4 3 4 5% 30%	7128

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	42% 27% 10% 11% 10% 1	3647
	11th to 20th	Day	50% 27% 7% 8% 5% 3	3962
	21st to end	Day	34% 31% 7% 13% 12% 3	4510
February	1st to 10th	Day	26% 63% 3 5% 3	1800
	11th to 20th	Day	23% 61% 5% 7% 3 1	1774
	21st to end	Day	21% 61% 4 8% 5% 1	1650
March	1st to 10th	Day	32% 31% 8% 15% 9% 6%	4773
	11th to 20th	Day	33% 30% 6% 22% 8%	5000
	21st to end	Day	40% 34% 8% 12% 6% 1	5604
April	1st to 10th	Day	18% 62% 5% 8% 6% 1	2400
	11th to 20th	Day	19% 63% 3 8% 6% 1	2374
	21st to end	Day	18% 63% 4 10% 5%	2423
May	1st to 10th	Day	29% 32% 8% 14% 16% 1	5926
	11th to 20th	Day	24% 32% 8% 20% 15% 1	6302
	21st to end	Day	20% 32% 6% 22% 19% 1	6926
June	1st to 10th	Day	8% 62% 4 11% 13% 3	2800
	11th to 20th	Day	7% 62% 5% 9% 11% 6%	2800
	21st to end	Day	9% 61% 2 8% 13% 6%	2800
July	1st to 10th	Day	12% 27% 4 9% 20% 28%	6271
	11th to 20th	Day	14% 28% 4 16% 22% 16%	6265
	21st to end	Day	13% 27% 5% 13% 25% 18%	6315
August	1st to 10th	Day	15% 38% 5% 18% 13% 11%	4208
	11th to 20th	Day	17% 38% 6% 13% 19% 6%	4143
	21st to end	Day	16% 37% 5% 12% 15% 14%	4311
September	1st to 10th	Day	9% 58% 4 10% 13% 6%	2400
	11th to 20th	Day	10% 56% 3 12% 14% 4	2400
	21st to end	Day	12% 57% 3 11% 14% 4	2117
October	1st to 10th	Day	8% 35% 3 12% 31% 11%	3270
	11th to 20th	Day	18% 36% 3 23% 16% 3	3250
	21st to end	Day	22% 36% 6% 24% 10% 1	3548
November	1st to 10th	Day	17% 54% 6% 15% 6% 1	1883
	11th to 20th	Day	17% 54% 7% 14% 7% 1	1764
	21st to end	Day	23% 54% 5% 12% 6%	1680
December	1st to 10th	Day	27% 34% 7% 26% 6%	2700
	11th to 20th	Day	26% 33% 15% 21% 4	3104
	21st to end	Day	38% 27% 9% 18% 7% 1	4092
January	1st to 10th	Night	43% 28% 8% 11% 7% 4	6342
	11th to 20th	Night	49% 29% 7% 7% 7% 1	6048
	21st to end	Night	32% 31% 9% 9% 14% 4	6468
February	1st to 10th	Night	28% 62% 3 4 3	2600
	11th to 20th	Night	21% 61% 4 8% 4 1	2522
	21st to end	Night	18% 62% 5% 8% 7% 1	1980
March	1st to 10th	Night	29% 31% 6% 16% 11% 6%	5110
	11th to 20th	Night	25% 31% 8% 24% 11% 1	5000
	21st to end	Night	39% 34% 7% 15% 4	5364
April	1st to 10th	Night	15% 62% 6% 10% 6% 1	2000
	11th to 20th	Night	16% 64% 4 9% 6% 2	1977
	21st to end	Night	14% 64% 6% 11% 6% 1	1973
May	1st to 10th	Night	26% 30% 7% 21% 15% 1	4034
	11th to 20th	Night	29% 34% 7% 19% 9% 3	3618
	21st to end	Night	23% 31% 6% 25% 14% 1	3972
June	1st to 10th	Night	6% 62% 4 13% 11% 5%	1600
	11th to 20th	Night	9% 63% 5% 8% 10% 6%	1600
	21st to end	Night	8% 60% 2 9% 14% 7%	1600
July	1st to 10th	Night	21% 29% 3 9% 18% 21%	3600
	11th to 20th	Night	20% 27% 5% 18% 19% 11%	3592
	21st to end	Night	15% 27% 5% 14% 24% 15%	4243
August	1st to 10th	Night	14% 38% 6% 17% 12% 14%	2928
	11th to 20th	Night	23% 39% 7% 12% 13% 6%	2982
	21st to end	Night	15% 39% 7% 10% 16% 12%	3597
September	1st to 10th	Night	8% 57% 4 10% 15% 6%	2000
	11th to 20th	Night	10% 58% 3 12% 14% 4	2000
	21st to end	Night	10% 57% 2 11% 14% 6%	2278
October	1st to 10th	Night	9% 35% 2 10% 31% 13%	3920
	11th to 20th	Night	18% 37% 3 22% 18% 3	3898
	21st to end	Night	22% 37% 7% 21% 11% 2	4252
November	1st to 10th	Night	17% 54% 5% 13% 10% 1	2615
	11th to 20th	Night	17% 55% 4 14% 8% 1	2851
	21st to end	Night	22% 55% 5% 12% 6%	2940
December	1st to 10th	Night	22% 36% 6% 26% 10%	4710
	11th to 20th	Night	25% 35% 12% 22% 6%	5322
	21st to end	Night	41% 27% 8% 16% 7% 1	7128

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	25% 24% 25% 18% 7% 1	303
	11th to 20th	Day	20% 26% 34% 15% 5%	300
	21st to end	Day	15% 27% 40% 14% 3 1	330
February	1st to 10th	Day	30% 32% 27% 10% 1	300
	11th to 20th	Day	28% 29% 26% 16% 1	300
	21st to end	Day	25% 28% 32% 12% 2	249
March	1st to 10th	Day	20% 31% 30% 14% 4	417
	11th to 20th	Day	14% 30% 34% 17% 4	500
	21st to end	Day	23% 28% 35% 12% 2	550
April	1st to 10th	Day	19% 30% 32% 16% 4	500
	11th to 20th	Day	23% 29% 32% 12% 4	492
	21st to end	Day	20% 21% 29% 22% 7% 1	500
May	1st to 10th	Day	17% 21% 34% 19% 8% 1	523
	11th to 20th	Day	17% 11% 30% 24% 16% 2	725
	21st to end	Day	15% 14% 29% 24% 16% 2	789
June	1st to 10th	Day	7% 11% 28% 30% 19% 5%	730
	11th to 20th	Day	9% 16% 34% 28% 12% 1	730
	21st to end	Day	7% 11% 30% 31% 18% 3	730
July	1st to 10th	Day	4 7% 26% 37% 23% 4	721
	11th to 20th	Day	2 6% 30% 35% 22% 5%	718
	21st to end	Day	4 6% 27% 39% 19% 4	624
August	1st to 10th	Day	6% 8% 39% 32% 13% 2	527
	11th to 20th	Day	4 7% 34% 34% 18% 3	517
	21st to end	Day	6% 10% 33% 30% 17% 3	583
September	1st to 10th	Day	7% 11% 30% 29% 18% 5%	530
	11th to 20th	Day	11% 14% 36% 23% 13% 3	530
	21st to end	Day	11% 17% 27% 28% 12% 5%	414
October	1st to 10th	Day	14% 15% 28% 26% 14% 4	330
	11th to 20th	Day	22% 20% 28% 21% 8% 2	330
	21st to end	Day	21% 22% 33% 19% 4 1	363
November	1st to 10th	Day	21% 28% 29% 15% 6% 1	330
	11th to 20th	Day	22% 24% 35% 16% 2 1	330
	21st to end	Day	15% 24% 39% 17% 4 1	330
December	1st to 10th	Day	24% 26% 27% 18% 5% 1	330
	11th to 20th	Day	19% 27% 37% 15% 2	330
	21st to end	Day	28% 23% 31% 14% 4 1	363
January	1st to 10th	Night	18% 15% 34% 25% 7% 1	1006
	11th to 20th	Night	17% 16% 35% 24% 6% 1	877
	21st to end	Night	13% 15% 39% 26% 6% 1	880
February	1st to 10th	Night	19% 17% 40% 19% 5% 1	800
	11th to 20th	Night	16% 17% 36% 26% 5%	784
	21st to end	Night	15% 18% 39% 23% 4	660
March	1st to 10th	Night	16% 15% 33% 28% 8% 1	800
	11th to 20th	Night	11% 11% 32% 37% 9% 1	800
	21st to end	Night	13% 13% 38% 28% 8% 1	832
April	1st to 10th	Night	15% 16% 32% 32% 6%	600
	11th to 20th	Night	16% 15% 34% 26% 8% 1	593
	21st to end	Night	15% 11% 28% 34% 12% 2	600
May	1st to 10th	Night	15% 10% 29% 31% 14% 1	600
	11th to 20th	Night	13% 4 21% 42% 18% 2	591
	21st to end	Night	13% 8% 22% 38% 18% 2	650
June	1st to 10th	Night	7% 7% 22% 38% 24% 2	600
	11th to 20th	Night	7% 6% 30% 43% 14%	600
	21st to end	Night	5% 4 19% 47% 24% 2	600
July	1st to 10th	Night	6% 3 15% 41% 32% 3	585
	11th to 20th	Night	4 2 14% 48% 30% 2	582
	21st to end	Night	3 2 11% 46% 36% 3	657
August	1st to 10th	Night	6% 1 16% 47% 29% 1	597
	11th to 20th	Night	5% 2 15% 46% 30% 2	594
	21st to end	Night	5% 2 15% 43% 30% 5%	660
September	1st to 10th	Night	6% 2 17% 46% 24% 5%	600
	11th to 20th	Night	8% 4 22% 40% 22% 4	600
	21st to end	Night	8% 5% 21% 36% 23% 7%	763
October	1st to 10th	Night	13% 7% 25% 37% 16% 2	800
	11th to 20th	Night	11% 11% 26% 37% 13% 2	800
	21st to end	Night	14% 11% 32% 32% 9% 2	880
November	1st to 10th	Night	15% 15% 35% 24% 9% 1	975
	11th to 20th	Night	17% 16% 39% 22% 5%	1050
	21st to end	Night	13% 13% 39% 29% 6%	1050
December	1st to 10th	Night	19% 16% 36% 24% 5%	1050
	11th to 20th	Night	17% 18% 40% 20% 5%	1050
	21st to end	Night	21% 20% 36% 18% 5% 1	1155

Page generated at 2025-12-29 23:14:05. Version ac07

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