Baker Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Baker Observatory 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	11% 8% 3 6% 4 4 4 4 5% 7% 44%	126870
	Night	11% 8% 3 6% 4 3 4 3 5% 7% 47%	124710
Transparency	Day	38% 5% 11% 25% 17% 4	130481
	Night	37% 5% 10% 25% 19% 4	129175
Seeing	Day	16% 11% 27% 26% 15% 4	17103
	Night	16% 11% 32% 28% 12% 1	26969

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	16% 11% 4 6% 5% 4 4 3 4 4 40%	4086
	11th to 20th	Day	7% 12% 4 7% 5% 4 4 3 4 6% 44%	4080
	21st to end	Day	18% 9% 3 8% 3 3 4 3 3 5% 41%	4488
February	1st to 10th	Day	14% 13% 3 7% 6% 5% 4 4 5% 5% 34%	1800
	11th to 20th	Day	13% 10% 3 8% 4 4 4 4 4 5% 40%	1790
	21st to end	Day	14% 11% 3 5% 4 4 4 4 6% 6% 39%	1701
March	1st to 10th	Day	12% 10% 3 5% 3 3 4 3 4 6% 47%	4936
	11th to 20th	Day	9% 7% 2 4 3 3 4 3 5% 7% 53%	4980
	21st to end	Day	12% 9% 3 8% 5% 6% 5% 4 6% 7% 34%	5462
April	1st to 10th	Day	12% 8% 2 7% 4 4 3 3 5% 7% 44%	2384
	11th to 20th	Day	15% 9% 3 6% 4 4 3 4 5% 6% 41%	2374
	21st to end	Day	18% 10% 3 7% 4 4 4 4 5% 7% 35%	2400
May	1st to 10th	Day	17% 8% 2 7% 4 5% 5% 4 6% 7% 34%	5740
	11th to 20th	Day	11% 6% 3 7% 5% 5% 5% 4 6% 8% 41%	5862
	21st to end	Day	20% 6% 2 6% 4 4 4 4 6% 7% 39%	6789
June	1st to 10th	Day	9% 5% 2 6% 4 4 5% 3 7% 10% 46%	2800
	11th to 20th	Day	8% 5% 2 5% 4 4 4 4 8% 9% 47%	2800
	21st to end	Day	5% 4 2 4 4 4 5% 5% 5% 10% 53%	2800
July	1st to 10th	Day	9% 5% 2 6% 4 5% 5% 4 6% 9% 45%	6049
	11th to 20th	Day	6% 5% 2 6% 5% 5% 6% 5% 7% 11% 42%	5900
	21st to end	Day	6% 4 2 5% 4 4 5% 5% 8% 11% 45%	6422
August	1st to 10th	Day	5% 4 2 4 3 4 4 3 6% 9% 56%	4234
	11th to 20th	Day	9% 6% 2 6% 5% 4 4 4 7% 8% 45%	4044
	21st to end	Day	6% 4 2 5% 4 4 4 4 6% 8% 52%	4312
September	1st to 10th	Day	11% 5% 2 5% 3 4 3 3 6% 7% 51%	2400
	11th to 20th	Day	9% 7% 3 7% 5% 5% 4 4 4 7% 45%	2358
	21st to end	Day	8% 6% 2 5% 4 4 5% 4 5% 7% 51%	2106
October	1st to 10th	Day	10% 5% 2 5% 3 4 4 3 4 5% 56%	2000
	11th to 20th	Day	12% 6% 3 5% 3 3 2 3 4 5% 54%	2000
	21st to end	Day	17% 7% 3 5% 3 3 3 3 4 6% 46%	2200
November	1st to 10th	Day	10% 6% 2 6% 4 2 4 2 3 5% 56%	2058
	11th to 20th	Day	12% 8% 3 6% 4 3 2 2 5% 7% 49%	1916
	21st to end	Day	14% 9% 4 6% 3 3 3 2 4 6% 47%	1680
December	1st to 10th	Day	10% 9% 2 6% 3 2 3 3 4 5% 52%	2690
	11th to 20th	Day	10% 10% 4 7% 4 3 3 2 3 5% 48%	3088
	21st to end	Day	16% 20% 6% 10% 4 4 3 2 3 5% 27%	4141
January	1st to 10th	Night	13% 10% 5% 12% 6% 4 4 3 4 5% 34%	5902
	11th to 20th	Night	9% 8% 3 11% 6% 4 4 3 4 5% 43%	5900
	21st to end	Night	16% 11% 4 8% 3 3 3 2 4 4 42%	6490
February	1st to 10th	Night	15% 11% 3 7% 4 3 3 3 5% 7% 40%	2600
	11th to 20th	Night	15% 10% 3 7% 4 3 3 3 4 6% 43%	2495
	21st to end	Night	14% 8% 2 6% 5% 4 4 3 5% 6% 43%	1945
March	1st to 10th	Night	14% 12% 3 7% 4 3 3 2 3 4 44%	4919
	11th to 20th	Night	11% 8% 2 4 3 3 4 3 5% 5% 52%	4980
	21st to end	Night	11% 7% 3 7% 5% 4 5% 4 6% 7% 41%	5467
April	1st to 10th	Night	10% 7% 1 4 3 4 4 3 5% 7% 51%	2015
	11th to 20th	Night	13% 9% 2 4 3 3 4 3 5% 8% 46%	1975
	21st to end	Night	17% 8% 3 7% 4 4 4 3 5% 6% 40%	2000
May	1st to 10th	Night	15% 9% 3 6% 4 3 3 3 5% 7% 42%	4154
	11th to 20th	Night	12% 8% 2 6% 4 4 4 3 6% 9% 41%	4053
	21st to end	Night	18% 9% 2 5% 4 4 4 2 5% 6% 40%	4083
June	1st to 10th	Night	8% 5% 2 4 3 3 4 3 5% 10% 52%	1600
	11th to 20th	Night	5% 3 1 4 4 4 4 4 7% 11% 53%	1600
	21st to end	Night	3 2 1 3 3 3 3 3 5% 9% 65%	1600
July	1st to 10th	Night	9% 5% 2 6% 4 4 5% 4 6% 8% 46%	3910
	11th to 20th	Night	3 4 1 5% 4 4 4 4 6% 9% 55%	4077
	21st to end	Night	4 4 2 4 3 3 4 4 7% 12% 52%	4449
August	1st to 10th	Night	4 2 1 4 3 3 4 3 5% 8% 62%	2926
	11th to 20th	Night	8% 4 2 6% 4 4 4 3 6% 6% 51%	3008
	21st to end	Night	4 3 1 4 2 3 3 3 6% 8% 61%	3586
September	1st to 10th	Night	8% 5% 2 5% 4 3 3 2 5% 7% 55%	2000
	11th to 20th	Night	9% 4 1 5% 4 4 4 3 5% 7% 52%	2037
	21st to end	Night	9% 4 1 5% 3 4 3 3 4 6% 57%	2272
October	1st to 10th	Night	7% 3 1 3 3 3 3 3 5% 7% 62%	2400
	11th to 20th	Night	13% 5% 1 4 3 3 3 2 4 5% 56%	2400
	21st to end	Night	16% 8% 2 4 2 2 3 2 4 5% 50%	2640
November	1st to 10th	Night	11% 6% 1 4 3 2 3 3 3 5% 58%	2460
	11th to 20th	Night	12% 6% 2 4 3 3 3 2 4 7% 52%	2694
	21st to end	Night	14% 9% 3 6% 4 3 3 3 4 5% 48%	2940
December	1st to 10th	Night	10% 9% 3 7% 4 3 3 3 4 7% 48%	4720
	11th to 20th	Night	14% 9% 3 6% 4 4 3 2 4 5% 46%	5339
	21st to end	Night	19% 18% 5% 8% 4 4 4 3 3 5% 28%	7074

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	48% 3 8% 22% 17% 2	4087
	11th to 20th	Day	43% 3 7% 26% 16% 6%	4080
	21st to end	Day	47% 3 8% 17% 15% 10%	4488
February	1st to 10th	Day	52% 4 10% 21% 12% 2	1800
	11th to 20th	Day	48% 4 10% 19% 16% 4	1799
	21st to end	Day	45% 4 7% 22% 16% 6%	1701
March	1st to 10th	Day	39% 3 7% 21% 18% 12%	4936
	11th to 20th	Day	32% 4 7% 23% 23% 11%	4980
	21st to end	Day	48% 7% 12% 24% 9% 1	5464
April	1st to 10th	Day	41% 4 12% 22% 19% 2	2384
	11th to 20th	Day	44% 5% 11% 21% 16% 3	2374
	21st to end	Day	49% 6% 10% 23% 11% 1	2400
May	1st to 10th	Day	47% 6% 12% 19% 14% 1	5777
	11th to 20th	Day	40% 8% 13% 24% 14% 1	5866
	21st to end	Day	44% 7% 11% 24% 13% 1	6803
June	1st to 10th	Day	33% 7% 15% 27% 16% 2	2800
	11th to 20th	Day	31% 7% 13% 32% 15% 2	2800
	21st to end	Day	26% 7% 16% 30% 17% 4	2800
July	1st to 10th	Day	35% 6% 13% 24% 19% 2	5985
	11th to 20th	Day	34% 8% 15% 29% 12% 1	5831
	21st to end	Day	30% 8% 19% 33% 11%	6240
August	1st to 10th	Day	25% 6% 18% 29% 22% 1	4220
	11th to 20th	Day	36% 7% 13% 29% 14% 1	4083
	21st to end	Day	29% 6% 12% 33% 16% 4	4311
September	1st to 10th	Day	32% 6% 12% 26% 15% 8%	2400
	11th to 20th	Day	39% 5% 8% 22% 24% 2	2358
	21st to end	Day	33% 6% 8% 26% 25% 4	2106
October	1st to 10th	Day	18% 3 5% 19% 36% 18%	3260
	11th to 20th	Day	22% 2 5% 23% 33% 14%	3240
	21st to end	Day	30% 3 7% 31% 24% 5%	3538
November	1st to 10th	Day	33% 3 8% 28% 23% 5%	2058
	11th to 20th	Day	37% 3 7% 22% 24% 7%	1916
	21st to end	Day	41% 4 8% 25% 20% 2	1680
December	1st to 10th	Day	36% 3 8% 35% 17% 1	2690
	11th to 20th	Day	41% 3 6% 27% 21% 2	3085
	21st to end	Day	62% 4 8% 17% 9% 1	4141
January	1st to 10th	Night	54% 3 8% 20% 13% 2	5902
	11th to 20th	Night	44% 3 8% 22% 20% 2	5900
	21st to end	Night	47% 3 7% 20% 18% 5%	6490
February	1st to 10th	Night	45% 4 11% 23% 14% 3	2600
	11th to 20th	Night	45% 3 9% 21% 17% 4	2496
	21st to end	Night	43% 4 8% 22% 19% 6%	1945
March	1st to 10th	Night	45% 4 7% 17% 22% 6%	4919
	11th to 20th	Night	33% 5% 8% 23% 21% 10%	4980
	21st to end	Night	41% 7% 13% 25% 14% 1	5467
April	1st to 10th	Night	33% 4 13% 24% 22% 5%	2015
	11th to 20th	Night	37% 5% 11% 23% 19% 6%	1975
	21st to end	Night	45% 5% 11% 24% 15% 1	2000
May	1st to 10th	Night	43% 6% 13% 24% 13% 2	4182
	11th to 20th	Night	40% 7% 12% 23% 14% 4	4054
	21st to end	Night	44% 6% 11% 25% 11% 3	4091
June	1st to 10th	Night	29% 6% 15% 29% 18% 3	1600
	11th to 20th	Night	24% 6% 14% 31% 21% 3	1600
	21st to end	Night	17% 5% 19% 32% 21% 6%	1600
July	1st to 10th	Night	35% 6% 12% 23% 20% 3	3867
	11th to 20th	Night	24% 8% 12% 38% 16% 1	4026
	21st to end	Night	23% 7% 19% 37% 14%	4320
August	1st to 10th	Night	20% 5% 15% 35% 24% 2	2916
	11th to 20th	Night	32% 7% 14% 29% 17% 1	3035
	21st to end	Night	20% 5% 15% 37% 18% 4	3586
September	1st to 10th	Night	31% 5% 11% 27% 20% 7%	2000
	11th to 20th	Night	31% 5% 10% 25% 25% 4	2037
	21st to end	Night	29% 4 8% 25% 30% 4	2272
October	1st to 10th	Night	14% 3 6% 18% 43% 16%	3920
	11th to 20th	Night	22% 3 6% 21% 29% 19%	3899
	21st to end	Night	30% 3 6% 31% 25% 5%	4252
November	1st to 10th	Night	30% 4 9% 27% 24% 7%	2460
	11th to 20th	Night	34% 3 7% 25% 25% 6%	2694
	21st to end	Night	41% 4 7% 24% 21% 3	2940
December	1st to 10th	Night	38% 4 8% 32% 17% 1	4720
	11th to 20th	Night	43% 3 7% 24% 22% 2	5341
	21st to end	Night	60% 4 9% 18% 7% 2	7074

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% 38% 17% 1	303
	11th to 20th	Day	27% 24% 38% 11%	300
	21st to end	Day	19% 24% 42% 15% 1	330
February	1st to 10th	Day	25% 20% 43% 11% 2	300
	11th to 20th	Day	28% 25% 31% 14% 1	300
	21st to end	Day	28% 23% 37% 10% 2	249
March	1st to 10th	Day	22% 24% 38% 13% 3	300
	11th to 20th	Day	27% 23% 32% 15% 2	300
	21st to end	Day	30% 21% 37% 10% 2	330
April	1st to 10th	Day	23% 20% 34% 17% 5% 1	484
	11th to 20th	Day	23% 22% 34% 17% 5%	492
	21st to end	Day	25% 16% 33% 19% 5% 1	500
May	1st to 10th	Day	22% 14% 34% 24% 6%	645
	11th to 20th	Day	18% 13% 29% 25% 13% 2	725
	21st to end	Day	16% 8% 33% 25% 13% 5%	789
June	1st to 10th	Day	11% 5% 21% 32% 24% 7%	730
	11th to 20th	Day	9% 3 20% 38% 25% 4	730
	21st to end	Day	7% 3 28% 38% 20% 5%	730
July	1st to 10th	Day	11% 3 15% 32% 30% 9%	721
	11th to 20th	Day	6% 4 15% 41% 29% 6%	718
	21st to end	Day	10% 2 13% 34% 31% 11%	794
August	1st to 10th	Day	9% 3 14% 42% 27% 5%	726
	11th to 20th	Day	9% 3 17% 34% 29% 7%	640
	21st to end	Day	10% 2 13% 32% 32% 10%	583
September	1st to 10th	Day	10% 3 12% 38% 31% 7%	530
	11th to 20th	Day	11% 2 18% 36% 25% 7%	488
	21st to end	Day	11% 7% 28% 31% 19% 5%	330
October	1st to 10th	Day	11% 10% 28% 32% 16% 5%	330
	11th to 20th	Day	16% 15% 33% 24% 10% 1	330
	21st to end	Day	30% 14% 31% 21% 4 1	363
November	1st to 10th	Day	15% 15% 40% 22% 8% 1	330
	11th to 20th	Day	18% 21% 35% 18% 6% 1	330
	21st to end	Day	25% 20% 31% 18% 5% 1	330
December	1st to 10th	Day	20% 21% 37% 15% 5% 2	330
	11th to 20th	Day	20% 20% 39% 16% 4	330
	21st to end	Day	21% 26% 37% 14% 1	363
January	1st to 10th	Night	18% 20% 37% 20% 4	1006
	11th to 20th	Night	20% 20% 40% 16% 4	1000
	21st to end	Night	19% 19% 40% 20% 2	1100
February	1st to 10th	Night	21% 17% 43% 17% 2	1000
	11th to 20th	Night	22% 18% 41% 17% 2	941
	21st to end	Night	20% 20% 41% 17% 1	625
March	1st to 10th	Night	20% 16% 40% 22% 3	600
	11th to 20th	Night	25% 14% 35% 21% 5%	600
	21st to end	Night	21% 17% 38% 20% 4	660
April	1st to 10th	Night	15% 16% 39% 26% 4	600
	11th to 20th	Night	18% 15% 37% 25% 5%	593
	21st to end	Night	22% 11% 39% 21% 7%	600
May	1st to 10th	Night	16% 7% 36% 34% 7%	600
	11th to 20th	Night	15% 6% 30% 32% 15% 1	591
	21st to end	Night	15% 5% 30% 31% 17% 2	650
June	1st to 10th	Night	11% 3 18% 41% 24% 2	600
	11th to 20th	Night	6% 3 24% 42% 24% 1	600
	21st to end	Night	4 2 23% 48% 23% 1	600
July	1st to 10th	Night	8% 2 12% 42% 31% 5%	585
	11th to 20th	Night	4 1 14% 45% 31% 4	582
	21st to end	Night	5% 1 11% 46% 33% 4	657
August	1st to 10th	Night	7% 2 14% 45% 30% 2	597
	11th to 20th	Night	9% 1 12% 47% 27% 3	594
	21st to end	Night	7% 1 13% 42% 34% 5%	660
September	1st to 10th	Night	9% 3 16% 38% 32% 3	600
	11th to 20th	Night	12% 1 13% 43% 27% 4	600
	21st to end	Night	11% 4 25% 38% 19% 3	672
October	1st to 10th	Night	8% 4 30% 35% 21% 3	800
	11th to 20th	Night	17% 9% 35% 30% 8% 1	800
	21st to end	Night	22% 11% 34% 27% 7%	880
November	1st to 10th	Night	14% 11% 41% 26% 8%	820
	11th to 20th	Night	18% 14% 37% 24% 7%	851
	21st to end	Night	20% 15% 36% 22% 7%	1050
December	1st to 10th	Night	20% 15% 39% 21% 4	1050
	11th to 20th	Night	22% 14% 39% 22% 3	1050
	21st to end	Night	22% 17% 39% 19% 2	1155

Page generated at 2025-12-30 00:14:11. Version ac07

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