Lockwood Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lockwood Observatory clear sky chart from 2005-11-06 to 2025-09-19.

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	4 4 1 3 2 2 3 2 4 5% 70%	134807
	Night	4 6% 2 4 2 2 3 2 4 5% 66%	131878
Transparency	Day	16% 4 4 12% 27% 37%	129900
	Night	17% 6% 3 10% 23% 40%	127759
Seeing	Day	9% 11% 30% 31% 13% 6%	16902
	Night	8% 5% 12% 32% 33% 9%	27230

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	6% 6% 2 4 2 2 2 2 3 4 68%	4098
	11th to 20th	Day	5% 4 1 3 2 2 3 2 4 5% 67%	4302
	21st to end	Day	10% 10% 2 4 3 3 3 4 5% 8% 48%	5016
February	1st to 10th	Day	10% 7% 1 4 3 3 3 3 4 4 57%	2000
	11th to 20th	Day	9% 9% 2 4 3 3 3 3 5% 6% 52%	1950
	21st to end	Day	10% 12% 2 5% 4 4 3 3 5% 5% 49%	1650
March	1st to 10th	Day	9% 13% 2 5% 3 3 4 4 6% 8% 43%	4518
	11th to 20th	Day	9% 8% 2 5% 3 3 4 3 5% 6% 53%	4824
	21st to end	Day	8% 8% 1 3 2 3 3 4 5% 6% 56%	5661
April	1st to 10th	Day	8% 6% 2 4 3 3 4 3 4 6% 57%	2400
	11th to 20th	Day	4 4 2 4 2 3 3 2 4 5% 67%	2369
	21st to end	Day	6% 5% 1 3 2 2 2 2 5% 7% 65%	2400
May	1st to 10th	Day	4 7% 1 2 1 2 2 2 2 4 74%	5781
	11th to 20th	Day	1 1 1 2 2 2 2 2 3 4 80%	5841
	21st to end	Day	2 2 1 2 1 1 2 2 3 5% 80%	6423
June	1st to 10th	Day	2 2 1 2 2 2 2 2 3 5% 78%	2600
	11th to 20th	Day	1 1 2 1 1 2 2 2 4 85%	2600
	21st to end	Day	1 2 1 1 1 2 1 3 3 84%	2600
July	1st to 10th	Day	1 1 1 1 1 1 1 2 2 90%	5879
	11th to 20th	Day	1 1 2 1 2 3 2 4 6% 79%	5880
	21st to end	Day	1 1 1 1 1 2 2 3 5% 82%	6195
August	1st to 10th	Day	1 1 1 1 1 2 2 2 3 5% 82%	5346
	11th to 20th	Day	1 1 1 1 1 1 1 2 3 87%	5364
	21st to end	Day	3 1 1 2 2 2 2 2 3 5% 77%	5984
September	1st to 10th	Day	2 2 1 3 2 2 3 3 4 4 74%	2355
	11th to 20th	Day	2 1 1 1 1 1 1 2 3 87%	2179
	21st to end	Day	1 2 1 2 2 2 3 1 3 4 79%	2090
October	1st to 10th	Day	3 2 1 2 2 2 2 3 3 4 77%	3490
	11th to 20th	Day	2 2 1 1 2 1 2 1 2 3 83%	3469
	21st to end	Day	2 3 1 2 2 2 3 3 4 5% 72%	3310
November	1st to 10th	Day	6% 4 1 3 2 2 2 2 3 4 70%	1764
	11th to 20th	Day	3 5% 1 4 2 3 2 3 4 4 68%	1800
	21st to end	Day	8% 5% 2 4 3 3 4 3 4 7% 58%	1800
December	1st to 10th	Day	5% 3 1 2 2 3 3 2 5% 6% 68%	2950
	11th to 20th	Day	8% 5% 2 4 4 5% 6% 3 5% 6% 51%	3409
	21st to end	Day	7% 7% 2 6% 6% 6% 5% 4 7% 7% 43%	4510
January	1st to 10th	Night	4 6% 1 4 3 3 3 2 4 5% 65%	5867
	11th to 20th	Night	3 6% 2 4 3 3 3 2 4 6% 64%	5682
	21st to end	Night	12% 10% 2 6% 3 3 3 2 4 5% 48%	5984
February	1st to 10th	Night	9% 9% 2 4 3 3 3 3 4 5% 56%	2400
	11th to 20th	Night	9% 9% 3 5% 4 4 4 2 3 5% 52%	2338
	21st to end	Night	8% 13% 2 5% 3 4 4 3 4 5% 50%	1980
March	1st to 10th	Night	9% 20% 4 7% 3 3 3 3 5% 6% 38%	5376
	11th to 20th	Night	7% 16% 4 6% 3 3 3 3 4 5% 46%	5176
	21st to end	Night	4 14% 3 6% 4 4 4 4 5% 6% 46%	5297
April	1st to 10th	Night	6% 9% 2 6% 3 3 4 3 5% 6% 54%	2000
	11th to 20th	Night	5% 7% 1 5% 2 3 3 3 4 6% 61%	1979
	21st to end	Night	5% 7% 2 4 3 3 3 2 5% 7% 59%	2000
May	1st to 10th	Night	3 5% 2 4 2 3 2 1 2 4 70%	4202
	11th to 20th	Night	1 3 2 4 3 3 3 3 5% 6% 68%	4074
	21st to end	Night	1 2 1 3 3 2 3 2 4 5% 72%	4474
June	1st to 10th	Night	1 2 1 3 2 3 2 2 4 8% 73%	1800
	11th to 20th	Night	1 1 2 2 1 2 1 2 5% 83%	1800
	21st to end	Night	1 2 1 1 2 1 2 1 3 3 83%	1800
July	1st to 10th	Night	1 1 1 2 2 92%	4100
	11th to 20th	Night	1 1 1 1 1 2 1 2 3 86%	4100
	21st to end	Night	1 1 1 1 1 1 2 2 4 85%	4670
August	1st to 10th	Night	1 1 1 1 1 2 3 5% 86%	4486
	11th to 20th	Night	1 1 1 1 1 1 2 3 89%	4506
	21st to end	Night	3 1 1 1 1 1 2 2 4 85%	5015
September	1st to 10th	Night	1 1 1 2 2 2 2 2 3 5% 80%	2045
	11th to 20th	Night	2 1 1 2 1 1 2 1 2 3 83%	2178
	21st to end	Night	1 2 2 2 2 2 2 2 4 81%	2090
October	1st to 10th	Night	3 3 1 2 1 2 1 1 2 3 79%	3490
	11th to 20th	Night	2 3 1 3 1 2 2 1 3 5% 78%	3469
	21st to end	Night	2 4 1 5% 3 3 3 2 4 6% 69%	4246
November	1st to 10th	Night	5% 6% 1 3 3 2 3 2 3 5% 68%	2535
	11th to 20th	Night	3 5% 1 4 3 2 3 3 4 5% 67%	2600
	21st to end	Night	7% 7% 2 5% 4 2 4 4 5% 5% 55%	2600
December	1st to 10th	Night	5% 4 1 3 3 3 3 3 3 4 68%	4240
	11th to 20th	Night	7% 8% 2 5% 4 4 5% 4 6% 7% 48%	4811
	21st to end	Night	6% 9% 2 5% 4 3 4 4 6% 10% 47%	6468

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	18% 6% 2 13% 33% 28%	4099
	11th to 20th	Day	19% 4 5% 16% 18% 39%	4302
	21st to end	Day	30% 7% 5% 9% 23% 26%	5016
February	1st to 10th	Day	28% 4 3 11% 23% 30%	2000
	11th to 20th	Day	29% 6% 3 14% 25% 24%	1960
	21st to end	Day	33% 8% 3 13% 21% 23%	1650
March	1st to 10th	Day	23% 14% 5% 16% 21% 21%	4518
	11th to 20th	Day	26% 7% 8% 20% 25% 14%	4824
	21st to end	Day	21% 10% 5% 24% 28% 11%	5661
April	1st to 10th	Day	26% 5% 4 19% 29% 17%	2400
	11th to 20th	Day	17% 5% 2 17% 31% 27%	2372
	21st to end	Day	18% 5% 4 18% 36% 20%	2400
May	1st to 10th	Day	14% 4 3 15% 37% 26%	5781
	11th to 20th	Day	8% 3 2 11% 42% 33%	5844
	21st to end	Day	9% 3 2 9% 39% 38%	6424
June	1st to 10th	Day	11% 3 1 14% 33% 38%	2600
	11th to 20th	Day	5% 3 1 8% 21% 62%	2600
	21st to end	Day	9% 1 1 5% 15% 68%	2600
July	1st to 10th	Day	5% 1 1 6% 13% 73%	5816
	11th to 20th	Day	9% 2 5% 11% 31% 42%	5811
	21st to end	Day	8% 2 6% 17% 18% 49%	6016
August	1st to 10th	Day	10% 4 7% 20% 30% 29%	3890
	11th to 20th	Day	9% 2 4 10% 24% 51%	3880
	21st to end	Day	9% 1 3 7% 21% 60%	4311
September	1st to 10th	Day	14% 3 5% 10% 24% 44%	2355
	11th to 20th	Day	6% 2 1 6% 32% 54%	2179
	21st to end	Day	11% 3 2 8% 28% 48%	2090
October	1st to 10th	Day	12% 3 3 9% 18% 56%	3490
	11th to 20th	Day	9% 2 1 7% 31% 50%	3469
	21st to end	Day	13% 2 3 6% 30% 45%	3310
November	1st to 10th	Day	17% 5% 2 11% 25% 40%	1764
	11th to 20th	Day	19% 4 3 9% 25% 40%	1800
	21st to end	Day	27% 4 3 11% 22% 33%	1800
December	1st to 10th	Day	19% 2 3 9% 26% 41%	2950
	11th to 20th	Day	28% 6% 6% 12% 28% 20%	3408
	21st to end	Day	30% 10% 5% 15% 22% 17%	4510
January	1st to 10th	Night	18% 6% 2 13% 28% 32%	5867
	11th to 20th	Night	17% 9% 3 14% 19% 39%	5682
	21st to end	Night	32% 7% 4 8% 21% 28%	5984
February	1st to 10th	Night	28% 5% 2 11% 20% 33%	2400
	11th to 20th	Night	33% 5% 2 10% 22% 27%	2339
	21st to end	Night	31% 8% 2 11% 21% 27%	1980
March	1st to 10th	Night	25% 21% 5% 9% 19% 21%	5376
	11th to 20th	Night	29% 10% 5% 16% 29% 11%	5176
	21st to end	Night	21% 17% 5% 14% 23% 20%	5297
April	1st to 10th	Night	27% 6% 3 13% 28% 22%	2000
	11th to 20th	Night	20% 7% 2 12% 26% 33%	1979
	21st to end	Night	20% 8% 2 12% 30% 28%	2000
May	1st to 10th	Night	14% 6% 4 6% 38% 32%	4199
	11th to 20th	Night	9% 4 7% 8% 31% 42%	4075
	21st to end	Night	10% 8% 3 7% 23% 50%	4474
June	1st to 10th	Night	10% 4 2 9% 27% 48%	1800
	11th to 20th	Night	5% 4 1 6% 14% 70%	1800
	21st to end	Night	9% 2 1 4 13% 71%	1800
July	1st to 10th	Night	3 1 5% 11% 80%	4055
	11th to 20th	Night	6% 2 3 11% 25% 54%	4046
	21st to end	Night	7% 1 3 16% 19% 54%	4538
August	1st to 10th	Night	6% 2 4 21% 31% 35%	3256
	11th to 20th	Night	5% 2 5% 11% 20% 56%	3256
	21st to end	Night	5% 1 1 5% 16% 72%	3608
September	1st to 10th	Night	9% 3 2 10% 24% 51%	2045
	11th to 20th	Night	7% 4 1 5% 24% 60%	2178
	21st to end	Night	9% 3 2 8% 29% 50%	2090
October	1st to 10th	Night	12% 2 2 6% 17% 61%	3490
	11th to 20th	Night	8% 3 3 5% 22% 59%	3469
	21st to end	Night	14% 4 3 6% 25% 48%	4246
November	1st to 10th	Night	18% 5% 2 8% 25% 41%	2535
	11th to 20th	Night	19% 4 2 9% 23% 43%	2600
	21st to end	Night	28% 6% 4 11% 20% 31%	2600
December	1st to 10th	Night	20% 3 2 8% 23% 43%	4240
	11th to 20th	Night	28% 6% 5% 12% 24% 25%	4811
	21st to end	Night	24% 10% 6% 18% 23% 20%	6468

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	23% 10% 26% 30% 10% 1	300
	11th to 20th	Day	18% 12% 28% 32% 9% 1	385
	21st to end	Day	18% 20% 30% 25% 6% 2	550
February	1st to 10th	Day	17% 16% 37% 20% 8% 3	500
	11th to 20th	Day	17% 19% 33% 23% 7%	495
	21st to end	Day	20% 22% 32% 18% 7%	414
March	1st to 10th	Day	20% 21% 36% 17% 5% 1	500
	11th to 20th	Day	19% 16% 35% 20% 8% 2	500
	21st to end	Day	18% 23% 34% 18% 7% 1	550
April	1st to 10th	Day	15% 17% 33% 21% 12% 3	500
	11th to 20th	Day	8% 23% 39% 18% 9% 3	492
	21st to end	Day	10% 18% 32% 22% 12% 6%	500
May	1st to 10th	Day	14% 16% 31% 23% 12% 4	503
	11th to 20th	Day	8% 13% 38% 26% 11% 5%	528
	21st to end	Day	8% 15% 33% 28% 10% 7%	573
June	1st to 10th	Day	3 10% 30% 35% 15% 9%	530
	11th to 20th	Day	1 7% 35% 33% 15% 10%	530
	21st to end	Day	2 4 32% 34% 17% 11%	530
July	1st to 10th	Day	1 2 20% 46% 18% 13%	526
	11th to 20th	Day	2 17% 47% 18% 16%	524
	21st to end	Day	2 1 17% 46% 20% 15%	575
August	1st to 10th	Day	2 2 25% 39% 20% 14%	527
	11th to 20th	Day	2 2 21% 41% 18% 16%	517
	21st to end	Day	1 2 20% 48% 17% 11%	583
September	1st to 10th	Day	4 3 27% 41% 19% 7%	530
	11th to 20th	Day	3 6% 35% 34% 16% 5%	523
	21st to end	Day	3 11% 27% 38% 16% 6%	490
October	1st to 10th	Day	6% 9% 34% 33% 14% 3	490
	11th to 20th	Day	4 10% 37% 33% 13% 2	490
	21st to end	Day	7% 9% 29% 33% 17% 4	417
November	1st to 10th	Day	13% 9% 26% 34% 16% 2	300
	11th to 20th	Day	8% 12% 29% 34% 16% 2	300
	21st to end	Day	15% 14% 31% 26% 11% 2	300
December	1st to 10th	Day	9% 11% 33% 32% 13% 1	300
	11th to 20th	Day	8% 12% 30% 32% 16% 2	300
	21st to end	Day	19% 17% 31% 20% 12% 2	330
January	1st to 10th	Night	12% 8% 21% 33% 20% 7%	800
	11th to 20th	Night	10% 9% 22% 34% 21% 5%	800
	21st to end	Night	18% 10% 19% 32% 18% 3	880
February	1st to 10th	Night	14% 8% 21% 31% 20% 5%	800
	11th to 20th	Night	15% 9% 20% 35% 16% 5%	784
	21st to end	Night	18% 11% 18% 33% 17% 3	660
March	1st to 10th	Night	16% 11% 20% 36% 15% 3	800
	11th to 20th	Night	16% 6% 14% 36% 20% 8%	800
	21st to end	Night	12% 7% 16% 38% 23% 4	880
April	1st to 10th	Night	13% 7% 15% 38% 23% 5%	800
	11th to 20th	Night	9% 7% 15% 40% 23% 5%	791
	21st to end	Night	10% 7% 12% 33% 31% 7%	800
May	1st to 10th	Night	8% 6% 12% 36% 34% 4	650
	11th to 20th	Night	4 5% 12% 36% 36% 7%	591
	21st to end	Night	5% 5% 13% 37% 36% 4	650
June	1st to 10th	Night	2 3 7% 39% 42% 8%	600
	11th to 20th	Night	2 1 6% 40% 46% 5%	600
	21st to end	Night	2 1 4 33% 51% 9%	600
July	1st to 10th	Night	1 25% 61% 13%	585
	11th to 20th	Night	1 1 17% 68% 14%	582
	21st to end	Night	3 1 1 16% 61% 19%	741
August	1st to 10th	Night	1 1 20% 58% 19%	796
	11th to 20th	Night	2 1 12% 61% 24%	792
	21st to end	Night	2 1 14% 59% 23%	880
September	1st to 10th	Night	1 1 3 22% 56% 17%	800
	11th to 20th	Night	2 1 4 36% 45% 12%	792
	21st to end	Night	2 1 8% 36% 39% 13%	760
October	1st to 10th	Night	7% 4 8% 41% 34% 6%	760
	11th to 20th	Night	5% 5% 13% 38% 29% 10%	760
	21st to end	Night	5% 3 16% 36% 28% 13%	836
November	1st to 10th	Night	10% 4 15% 41% 23% 8%	780
	11th to 20th	Night	7% 4 20% 34% 24% 11%	800
	21st to end	Night	12% 8% 18% 33% 23% 6%	800
December	1st to 10th	Night	13% 7% 19% 33% 22% 6%	800
	11th to 20th	Night	16% 7% 22% 33% 17% 4	800
	21st to end	Night	15% 9% 19% 33% 18% 6%	880

Page generated at 2025-09-15 22:49:15. Version ac07

Copyright © 2025 Attilla Danko.