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 2024-11-12.

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% 7% 3 6% 4 4 4 4 5% 7% 44%	101080
	Night	11% 8% 3 6% 4 3 4 3 5% 7% 47%	98175
Transparency	Day	38% 5% 11% 25% 17% 4	104730
	Night	36% 5% 11% 25% 19% 4	102665
Seeing	Day	16% 11% 27% 27% 16% 4	15580
	Night	16% 11% 32% 28% 12% 1	25383

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% 12% 4 5% 4 3 3 3 4 4 43%	2847
	11th to 20th	Day	10% 12% 4 7% 5% 4 4 3 4 6% 41%	2850
	21st to end	Day	21% 10% 4 8% 3 2 3 3 3 5% 38%	3135
February	1st to 10th	Day	13% 13% 4 7% 6% 5% 4 4 5% 5% 35%	1710
	11th to 20th	Day	13% 10% 3 8% 4 4 4 4 4 5% 41%	1698
	21st to end	Day	15% 12% 3 5% 4 4 4 4 6% 6% 38%	1618
March	1st to 10th	Day	15% 9% 3 6% 3 3 3 2 4 5% 46%	3436
	11th to 20th	Day	13% 8% 2 4 3 3 3 3 4 7% 50%	3480
	21st to end	Day	15% 10% 3 7% 5% 5% 5% 4 5% 5% 35%	3814
April	1st to 10th	Day	11% 8% 2 7% 4 4 3 3 5% 7% 45%	2265
	11th to 20th	Day	15% 10% 3 7% 4 4 3 4 5% 6% 40%	2254
	21st to end	Day	18% 9% 3 7% 4 4 4 4 5% 6% 36%	2280
May	1st to 10th	Day	17% 8% 2 7% 5% 5% 5% 4 5% 7% 35%	4002
	11th to 20th	Day	14% 6% 3 6% 5% 4 4 4 5% 7% 42%	4082
	21st to end	Day	13% 6% 2 6% 5% 5% 5% 4 7% 8% 41%	4720
June	1st to 10th	Day	8% 5% 2 6% 4 4 5% 3 7% 10% 46%	2660
	11th to 20th	Day	7% 4 2 4 4 4 4 4 8% 10% 48%	2660
	21st to end	Day	5% 4 2 4 4 4 5% 5% 5% 10% 53%	2660
July	1st to 10th	Day	11% 5% 2 6% 4 5% 5% 4 7% 10% 41%	4227
	11th to 20th	Day	5% 4 2 5% 5% 5% 5% 4 7% 11% 47%	4120
	21st to end	Day	7% 5% 2 6% 5% 5% 6% 6% 9% 10% 38%	4465
August	1st to 10th	Day	5% 4 2 5% 4 4 4 3 6% 9% 56%	4104
	11th to 20th	Day	9% 6% 2 7% 5% 4 4 3 7% 8% 45%	3918
	21st to end	Day	6% 4 2 5% 4 4 4 4 6% 8% 53%	4180
September	1st to 10th	Day	11% 5% 2 5% 3 4 3 3 6% 7% 51%	2280
	11th to 20th	Day	9% 7% 3 7% 5% 5% 4 4 4 6% 46%	2240
	21st to end	Day	7% 5% 1 5% 4 4 5% 4 5% 7% 51%	2001
October	1st to 10th	Day	10% 5% 2 5% 3 3 3 3 4 5% 56%	1900
	11th to 20th	Day	12% 6% 3 5% 3 3 2 3 4 5% 54%	1900
	21st to end	Day	16% 7% 2 5% 3 3 3 3 4 6% 47%	2090
November	1st to 10th	Day	11% 6% 2 6% 4 2 4 2 3 5% 56%	1958
	11th to 20th	Day	12% 8% 3 5% 4 3 3 2 5% 7% 48%	1744
	21st to end	Day	14% 9% 3 6% 3 3 3 3 4 5% 48%	1520
December	1st to 10th	Day	12% 10% 3 6% 5% 3 4 4 5% 6% 42%	1520
	11th to 20th	Day	12% 11% 4 8% 4 4 4 3 3 5% 42%	1918
	21st to end	Day	13% 17% 6% 10% 5% 4 4 3 4 5% 28%	2824
January	1st to 10th	Night	11% 10% 5% 10% 5% 4 4 2 4 6% 39%	4108
	11th to 20th	Night	10% 8% 3 9% 7% 4 5% 4 5% 5% 39%	4120
	21st to end	Night	20% 13% 5% 7% 3 3 3 2 4 4 36%	4532
February	1st to 10th	Night	14% 11% 3 7% 4 3 3 3 5% 7% 41%	2470
	11th to 20th	Night	14% 9% 3 7% 4 3 3 3 4 6% 44%	2367
	21st to end	Night	15% 8% 3 6% 5% 4 4 3 5% 6% 42%	1851
March	1st to 10th	Night	16% 10% 2 6% 3 3 3 2 4 5% 45%	3419
	11th to 20th	Night	13% 7% 2 4 3 3 4 3 5% 5% 51%	3480
	21st to end	Night	13% 8% 3 8% 6% 5% 5% 4 5% 5% 38%	3817
April	1st to 10th	Night	9% 6% 2 4 3 4 4 3 5% 8% 52%	1914
	11th to 20th	Night	13% 9% 2 4 3 3 4 3 5% 8% 46%	1875
	21st to end	Night	17% 8% 3 6% 5% 4 4 3 5% 6% 40%	1900
May	1st to 10th	Night	13% 7% 2 6% 4 4 4 4 5% 7% 44%	2898
	11th to 20th	Night	13% 9% 3 7% 4 4 4 3 6% 8% 40%	2823
	21st to end	Night	11% 7% 2 5% 5% 4 5% 3 7% 8% 42%	2842
June	1st to 10th	Night	8% 5% 2 4 3 3 4 3 5% 10% 53%	1520
	11th to 20th	Night	4 3 1 4 4 3 4 4 7% 11% 54%	1520
	21st to end	Night	3 2 1 3 3 3 3 3 5% 9% 64%	1520
July	1st to 10th	Night	11% 5% 2 5% 4 4 4 4 6% 7% 48%	2738
	11th to 20th	Night	3 3 1 4 3 4 3 4 6% 8% 60%	2850
	21st to end	Night	5% 5% 2 5% 3 3 4 4 7% 10% 50%	3098
August	1st to 10th	Night	4 2 1 4 3 3 4 3 6% 8% 62%	2836
	11th to 20th	Night	8% 4 2 7% 4 4 5% 3 6% 6% 51%	2914
	21st to end	Night	4 3 1 4 2 3 3 3 6% 8% 61%	3476
September	1st to 10th	Night	8% 5% 2 5% 4 3 3 2 4 7% 57%	1900
	11th to 20th	Night	10% 4 1 5% 4 4 4 3 5% 7% 54%	1935
	21st to end	Night	9% 4 1 5% 3 4 3 3 4 6% 58%	2158
October	1st to 10th	Night	7% 3 1 3 3 3 3 3 4 7% 62%	2280
	11th to 20th	Night	13% 5% 1 4 3 2 3 2 4 5% 56%	2280
	21st to end	Night	16% 7% 2 4 2 3 3 2 5% 6% 50%	2508
November	1st to 10th	Night	12% 6% 1 4 3 2 3 3 4 5% 58%	2340
	11th to 20th	Night	13% 7% 2 5% 3 3 3 2 4 7% 51%	2449
	21st to end	Night	13% 9% 2 6% 4 3 3 3 4 5% 48%	2660
December	1st to 10th	Night	14% 9% 3 7% 4 3 3 3 4 8% 41%	2660
	11th to 20th	Night	13% 10% 4 7% 4 4 3 3 4 6% 42%	3279
	21st to end	Night	14% 18% 6% 9% 4 4 4 3 4 5% 29%	4838

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	45% 3 7% 26% 18% 1	2848
	11th to 20th	Day	45% 4 8% 26% 12% 4	2850
	21st to end	Day	51% 3 9% 17% 16% 5%	3135
February	1st to 10th	Day	51% 4 10% 21% 12% 2	1710
	11th to 20th	Day	46% 4 10% 20% 16% 4	1707
	21st to end	Day	47% 4 7% 21% 15% 6%	1618
March	1st to 10th	Day	41% 4 8% 20% 19% 8%	3436
	11th to 20th	Day	35% 5% 10% 29% 15% 7%	3480
	21st to end	Day	51% 6% 13% 20% 9% 1	3814
April	1st to 10th	Day	40% 4 12% 22% 19% 2	2265
	11th to 20th	Day	44% 6% 12% 20% 15% 3	2254
	21st to end	Day	49% 6% 9% 23% 11% 1	2280
May	1st to 10th	Day	48% 7% 11% 20% 13% 1	4039
	11th to 20th	Day	41% 8% 13% 24% 13%	4086
	21st to end	Day	39% 9% 12% 25% 14% 1	4733
June	1st to 10th	Day	33% 7% 16% 27% 16% 1	2660
	11th to 20th	Day	30% 7% 14% 32% 15% 2	2660
	21st to end	Day	26% 7% 15% 31% 17% 4	2660
July	1st to 10th	Day	38% 7% 15% 25% 13% 2	4163
	11th to 20th	Day	29% 7% 14% 32% 17% 2	4051
	21st to end	Day	35% 9% 21% 25% 9% 1	4325
August	1st to 10th	Day	26% 6% 18% 28% 22% 1	4090
	11th to 20th	Day	37% 7% 13% 29% 14% 1	3957
	21st to end	Day	28% 6% 13% 34% 16% 4	4179
September	1st to 10th	Day	33% 6% 12% 26% 15% 8%	2280
	11th to 20th	Day	39% 5% 7% 22% 25% 2	2240
	21st to end	Day	33% 6% 8% 27% 24% 3	2001
October	1st to 10th	Day	18% 3 5% 19% 36% 19%	3160
	11th to 20th	Day	22% 2 5% 23% 33% 15%	3140
	21st to end	Day	29% 3 7% 31% 25% 5%	3428
November	1st to 10th	Day	34% 3 8% 27% 23% 5%	1958
	11th to 20th	Day	37% 3 7% 22% 25% 6%	1744
	21st to end	Day	40% 4 9% 24% 21% 3	1520
December	1st to 10th	Day	43% 4 9% 29% 13% 2	1520
	11th to 20th	Day	47% 3 6% 19% 22% 2	1915
	21st to end	Day	58% 5% 8% 16% 12% 2	2824
January	1st to 10th	Night	48% 3 9% 24% 15% 1	4108
	11th to 20th	Night	46% 4 11% 24% 13% 2	4120
	21st to end	Night	52% 3 9% 20% 14% 2	4532
February	1st to 10th	Night	44% 4 11% 23% 15% 3	2470
	11th to 20th	Night	43% 4 10% 22% 18% 4	2368
	21st to end	Night	44% 4 7% 22% 17% 6%	1851
March	1st to 10th	Night	42% 5% 9% 19% 19% 6%	3419
	11th to 20th	Night	35% 6% 10% 25% 21% 3	3480
	21st to end	Night	46% 7% 13% 23% 10% 1	3817
April	1st to 10th	Night	32% 5% 12% 24% 22% 5%	1914
	11th to 20th	Night	37% 5% 11% 23% 19% 6%	1875
	21st to end	Night	45% 5% 10% 24% 15% 1	1900
May	1st to 10th	Night	40% 6% 12% 24% 15% 3	2926
	11th to 20th	Night	41% 7% 12% 25% 13% 1	2824
	21st to end	Night	39% 8% 14% 27% 12% 1	2850
June	1st to 10th	Night	28% 6% 15% 29% 18% 3	1520
	11th to 20th	Night	23% 6% 15% 32% 21% 3	1520
	21st to end	Night	17% 5% 19% 32% 21% 6%	1520
July	1st to 10th	Night	35% 7% 14% 25% 16% 4	2693
	11th to 20th	Night	20% 6% 12% 39% 22% 2	2796
	21st to end	Night	26% 8% 21% 33% 12%	2999
August	1st to 10th	Night	20% 5% 15% 35% 24% 2	2826
	11th to 20th	Night	33% 7% 13% 28% 17% 1	2941
	21st to end	Night	20% 5% 15% 37% 18% 4	3476
September	1st to 10th	Night	29% 5% 11% 27% 20% 7%	1900
	11th to 20th	Night	30% 5% 9% 25% 27% 4	1935
	21st to end	Night	29% 4 8% 25% 30% 4	2158
October	1st to 10th	Night	14% 3 6% 18% 43% 17%	3800
	11th to 20th	Night	22% 2 6% 21% 29% 20%	3779
	21st to end	Night	30% 3 6% 31% 25% 5%	4120
November	1st to 10th	Night	30% 4 9% 27% 23% 7%	2340
	11th to 20th	Night	35% 3 6% 24% 26% 5%	2449
	21st to end	Night	40% 4 7% 23% 22% 3	2660
December	1st to 10th	Night	43% 5% 11% 22% 18% 2	2660
	11th to 20th	Night	47% 3 7% 21% 20% 2	3281
	21st to end	Night	58% 4 10% 16% 9% 2	4838

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% 23% 37% 17% 1	270
	11th to 20th	Day	29% 24% 35% 11%	270
	21st to end	Day	19% 24% 42% 14% 1	297
February	1st to 10th	Day	22% 21% 43% 11% 2	270
	11th to 20th	Day	28% 24% 31% 16% 1	270
	21st to end	Day	30% 24% 36% 9% 1	225
March	1st to 10th	Day	21% 26% 38% 14% 1	270
	11th to 20th	Day	27% 22% 32% 16% 2	270
	21st to end	Day	30% 22% 36% 9% 2	297
April	1st to 10th	Day	20% 20% 36% 18% 5% 1	445
	11th to 20th	Day	23% 21% 34% 17% 5%	452
	21st to end	Day	26% 17% 34% 18% 5% 1	460
May	1st to 10th	Day	23% 13% 34% 23% 6% 1	598
	11th to 20th	Day	19% 12% 28% 25% 13% 2	675
	21st to end	Day	14% 8% 33% 26% 13% 6%	734
June	1st to 10th	Day	10% 5% 20% 33% 25% 7%	680
	11th to 20th	Day	8% 3 21% 39% 25% 5%	680
	21st to end	Day	7% 3 29% 37% 19% 5%	680
July	1st to 10th	Day	11% 3 15% 31% 30% 9%	671
	11th to 20th	Day	5% 3 15% 41% 30% 6%	668
	21st to end	Day	10% 1 13% 34% 30% 11%	739
August	1st to 10th	Day	9% 3 14% 41% 28% 5%	676
	11th to 20th	Day	10% 4 19% 35% 27% 6%	594
	21st to end	Day	10% 2 11% 32% 34% 11%	539
September	1st to 10th	Day	10% 3 11% 38% 30% 8%	490
	11th to 20th	Day	11% 2 20% 37% 23% 7%	450
	21st to end	Day	10% 6% 30% 31% 19% 4	300
October	1st to 10th	Day	12% 10% 28% 30% 16% 5%	300
	11th to 20th	Day	16% 16% 35% 23% 9% 1	300
	21st to end	Day	28% 15% 31% 22% 4 1	330
November	1st to 10th	Day	16% 14% 38% 23% 8% 1	300
	11th to 20th	Day	19% 21% 32% 21% 7% 1	273
	21st to end	Day	24% 21% 30% 20% 4 1	270
December	1st to 10th	Day	19% 23% 35% 15% 6% 2	270
	11th to 20th	Day	22% 19% 38% 16% 5%	270
	21st to end	Day	20% 29% 37% 13% 1	297
January	1st to 10th	Night	18% 20% 37% 20% 5%	950
	11th to 20th	Night	21% 19% 40% 16% 4	950
	21st to end	Night	20% 19% 40% 20% 2	1045
February	1st to 10th	Night	20% 17% 43% 17% 2	950
	11th to 20th	Night	20% 18% 42% 18% 2	893
	21st to end	Night	21% 21% 41% 16% 2	595
March	1st to 10th	Night	20% 15% 40% 22% 3	570
	11th to 20th	Night	24% 14% 35% 22% 5%	570
	21st to end	Night	22% 17% 36% 20% 4	627
April	1st to 10th	Night	14% 16% 39% 26% 4	570
	11th to 20th	Night	19% 14% 37% 25% 5%	563
	21st to end	Night	22% 11% 39% 21% 7%	570
May	1st to 10th	Night	16% 7% 37% 33% 7%	570
	11th to 20th	Night	16% 6% 30% 33% 16% 1	561
	21st to end	Night	14% 5% 31% 31% 18% 2	617
June	1st to 10th	Night	10% 3 18% 41% 25% 2	570
	11th to 20th	Night	5% 2 24% 44% 24% 1	570
	21st to end	Night	4 2 24% 48% 22% 1	570
July	1st to 10th	Night	9% 1 12% 43% 30% 5%	555
	11th to 20th	Night	4 1 14% 45% 32% 4	552
	21st to end	Night	5% 1 12% 46% 33% 3	624
August	1st to 10th	Night	7% 2 14% 43% 32% 2	567
	11th to 20th	Night	10% 1 13% 48% 25% 3	564
	21st to end	Night	7% 13% 40% 34% 5%	627
September	1st to 10th	Night	9% 2 15% 38% 33% 3	570
	11th to 20th	Night	13% 1 14% 43% 26% 3	570
	21st to end	Night	11% 4 25% 38% 19% 3	638
October	1st to 10th	Night	8% 5% 30% 34% 21% 3	760
	11th to 20th	Night	18% 10% 35% 29% 7% 1	760
	21st to end	Night	21% 11% 33% 27% 7%	836
November	1st to 10th	Night	15% 10% 41% 26% 8%	780
	11th to 20th	Night	18% 14% 36% 24% 7%	774
	21st to end	Night	20% 14% 37% 22% 7%	950
December	1st to 10th	Night	22% 15% 38% 22% 4	950
	11th to 20th	Night	23% 13% 38% 22% 3	950
	21st to end	Night	21% 18% 40% 19% 2	1045

Page generated at 2024-11-08 21:45:35. Version ac07

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