Dobie Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dobie Observatory clear sky chart from 2005-11-06 to 2026-02-01.

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% 10% 4 9% 5% 5% 5% 4 5% 7% 33%	127245
	Night	14% 11% 4 9% 5% 4 4 3 5% 6% 33%	124935
Transparency	Day	48% 6% 11% 21% 12% 1	130800
	Night	49% 5% 11% 21% 13% 1	129438
Seeing	Day	18% 13% 28% 22% 13% 5%	17357
	Night	19% 10% 29% 28% 12% 1	27292

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	12% 16% 8% 17% 7% 5% 5% 3 4 6% 18%	3697
	11th to 20th	Day	14% 15% 6% 17% 11% 7% 8% 5% 5% 3 9%	3700
	21st to end	Day	21% 19% 6% 13% 5% 4 4 3 3 5% 17%	4310
February	1st to 10th	Day	14% 15% 5% 11% 9% 6% 6% 4 5% 6% 20%	1810
	11th to 20th	Day	14% 12% 6% 13% 8% 6% 5% 3 4 5% 23%	1948
	21st to end	Day	15% 15% 5% 12% 6% 5% 5% 3 5% 6% 23%	1650
March	1st to 10th	Day	14% 13% 4 12% 6% 5% 4 3 4 5% 29%	4480
	11th to 20th	Day	11% 12% 4 8% 6% 4 4 3 6% 7% 35%	4976
	21st to end	Day	16% 15% 5% 10% 5% 4 5% 3 5% 5% 26%	5465
April	1st to 10th	Day	17% 14% 4 8% 5% 5% 4 3 4 7% 29%	2395
	11th to 20th	Day	16% 10% 3 7% 4 4 4 4 6% 6% 35%	2482
	21st to end	Day	17% 9% 3 8% 5% 4 4 4 5% 7% 34%	2600
May	1st to 10th	Day	20% 10% 3 7% 4 4 4 4 5% 6% 34%	5862
	11th to 20th	Day	14% 8% 3 7% 5% 5% 5% 4 6% 8% 34%	5861
	21st to end	Day	15% 6% 3 7% 4 4 4 3 6% 7% 40%	6606
June	1st to 10th	Day	10% 5% 3 6% 5% 5% 4 4 6% 9% 42%	2800
	11th to 20th	Day	10% 6% 2 6% 5% 4 6% 5% 7% 9% 40%	2800
	21st to end	Day	8% 6% 2 7% 5% 6% 6% 5% 7% 10% 38%	2800
July	1st to 10th	Day	9% 6% 2 6% 4 5% 6% 5% 8% 11% 37%	6360
	11th to 20th	Day	7% 5% 2 6% 5% 5% 5% 4 6% 10% 45%	6360
	21st to end	Day	7% 6% 2 6% 5% 5% 5% 4 7% 9% 43%	6701
August	1st to 10th	Day	11% 5% 2 6% 4 5% 5% 4 6% 9% 43%	4234
	11th to 20th	Day	10% 6% 2 6% 5% 5% 5% 5% 6% 9% 42%	4174
	21st to end	Day	7% 6% 2 7% 5% 5% 6% 4 7% 9% 42%	4487
September	1st to 10th	Day	10% 7% 2 6% 5% 4 5% 5% 5% 8% 43%	2305
	11th to 20th	Day	9% 5% 2 5% 4 5% 5% 4 7% 9% 48%	2200
	21st to end	Day	14% 7% 3 7% 5% 6% 5% 3 5% 8% 38%	2200
October	1st to 10th	Day	12% 6% 2 7% 5% 5% 4 4 5% 7% 43%	2195
	11th to 20th	Day	17% 9% 4 9% 4 5% 4 3 5% 6% 35%	1995
	21st to end	Day	18% 10% 3 9% 5% 4 5% 4 5% 7% 30%	1980
November	1st to 10th	Day	12% 10% 3 8% 6% 4 4 4 5% 7% 39%	1852
	11th to 20th	Day	14% 15% 5% 10% 6% 5% 4 3 4 6% 28%	1890
	21st to end	Day	19% 14% 5% 9% 6% 5% 4 3 4 6% 25%	1890
December	1st to 10th	Day	11% 16% 9% 15% 7% 6% 5% 4 5% 5% 18%	3020
	11th to 20th	Day	18% 20% 7% 11% 7% 5% 4 3 5% 4 15%	3090
	21st to end	Day	23% 21% 7% 12% 6% 5% 3 3 3 4 12%	4070
January	1st to 10th	Night	14% 15% 7% 16% 6% 5% 4 3 4 6% 20%	6488
	11th to 20th	Night	12% 15% 7% 16% 9% 7% 6% 4 6% 5% 12%	6500
	21st to end	Night	18% 16% 7% 11% 6% 5% 5% 3 4 5% 19%	6896
February	1st to 10th	Night	15% 16% 6% 11% 8% 5% 4 4 4 4 23%	2586
	11th to 20th	Night	13% 14% 5% 11% 7% 5% 5% 4 4 5% 27%	2338
	21st to end	Night	17% 12% 4 11% 5% 4 5% 3 5% 7% 27%	1980
March	1st to 10th	Night	14% 12% 4 8% 4 3 4 3 4 7% 35%	5373
	11th to 20th	Night	10% 9% 2 6% 4 4 4 4 6% 7% 44%	4982
	21st to end	Night	17% 11% 3 8% 5% 4 4 3 4 6% 35%	5467
April	1st to 10th	Night	16% 11% 3 6% 5% 5% 4 3 5% 6% 36%	2021
	11th to 20th	Night	18% 9% 2 7% 4 4 5% 3 5% 6% 37%	1867
	21st to end	Night	15% 9% 2 7% 5% 4 4 3 5% 7% 37%	1800
May	1st to 10th	Night	19% 12% 3 8% 5% 4 4 3 5% 7% 30%	4033
	11th to 20th	Night	17% 9% 3 7% 4 3 3 3 5% 6% 40%	4032
	21st to end	Night	15% 6% 2 6% 4 5% 4 3 5% 8% 43%	4252
June	1st to 10th	Night	10% 5% 2 4 4 4 3 5% 7% 9% 46%	1600
	11th to 20th	Night	10% 6% 3 6% 4 4 4 4 6% 10% 42%	1600
	21st to end	Night	8% 6% 2 5% 3 3 5% 4 8% 12% 45%	1600
July	1st to 10th	Night	7% 5% 2 6% 4 4 5% 4 6% 10% 48%	3618
	11th to 20th	Night	8% 5% 2 5% 4 3 4 4 6% 8% 51%	3617
	21st to end	Night	9% 6% 2 6% 4 4 5% 4 6% 8% 47%	4160
August	1st to 10th	Night	9% 6% 2 6% 4 4 4 3 6% 8% 48%	2915
	11th to 20th	Night	10% 6% 2 6% 3 4 4 4 6% 8% 47%	2875
	21st to end	Night	9% 7% 2 6% 5% 4 5% 4 5% 7% 46%	3407
September	1st to 10th	Night	9% 7% 3 6% 5% 3 4 3 5% 7% 49%	2074
	11th to 20th	Night	9% 4 2 4 3 3 4 3 4 6% 56%	2200
	21st to end	Night	14% 7% 2 6% 4 4 4 3 5% 7% 43%	2200
October	1st to 10th	Night	11% 7% 2 6% 4 4 4 3 4 6% 47%	2204
	11th to 20th	Night	16% 11% 3 9% 4 5% 3 3 4 6% 36%	2400
	21st to end	Night	19% 9% 3 7% 4 5% 4 3 5% 6% 34%	2860
November	1st to 10th	Night	13% 11% 3 7% 5% 4 4 3 4 5% 42%	2666
	11th to 20th	Night	15% 13% 4 8% 5% 5% 5% 4 5% 6% 30%	2730
	21st to end	Night	17% 16% 4 10% 5% 4 4 3 5% 6% 26%	2730
December	1st to 10th	Night	12% 14% 6% 16% 7% 5% 5% 3 5% 6% 21%	4380
	11th to 20th	Night	15% 19% 6% 14% 8% 5% 4 3 4 5% 16%	5334
	21st to end	Night	25% 21% 6% 11% 5% 4 4 3 4 5% 13%	7150

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	66% 5% 11% 15% 4	3698
	11th to 20th	Day	76% 5% 9% 7% 3	3700
	21st to end	Day	71% 4 10% 10% 6%	4310
February	1st to 10th	Day	64% 6% 9% 14% 7% 1	1810
	11th to 20th	Day	63% 5% 8% 15% 8% 1	1958
	21st to end	Day	62% 5% 11% 14% 7% 1	1650
March	1st to 10th	Day	56% 5% 11% 17% 9% 1	4480
	11th to 20th	Day	47% 5% 15% 23% 9% 2	4976
	21st to end	Day	59% 5% 9% 15% 11% 1	5465
April	1st to 10th	Day	56% 4 9% 19% 11%	2395
	11th to 20th	Day	48% 5% 11% 21% 12% 2	2482
	21st to end	Day	49% 5% 12% 18% 14% 2	2600
May	1st to 10th	Day	50% 6% 10% 19% 15% 1	5897
	11th to 20th	Day	46% 7% 13% 21% 12% 1	5865
	21st to end	Day	41% 5% 10% 23% 18% 3	6620
June	1st to 10th	Day	38% 7% 11% 26% 15% 2	2800
	11th to 20th	Day	38% 7% 13% 23% 17% 2	2800
	21st to end	Day	38% 9% 13% 22% 16% 2	2800
July	1st to 10th	Day	37% 7% 14% 25% 15% 2	6291
	11th to 20th	Day	33% 6% 14% 28% 18% 1	6285
	21st to end	Day	34% 7% 15% 23% 20% 1	6509
August	1st to 10th	Day	36% 7% 14% 26% 17% 1	4221
	11th to 20th	Day	37% 8% 12% 30% 13% 1	4213
	21st to end	Day	36% 6% 12% 31% 12% 2	4486
September	1st to 10th	Day	37% 8% 13% 25% 15% 2	2305
	11th to 20th	Day	32% 6% 11% 31% 18% 1	2200
	21st to end	Day	44% 6% 11% 22% 17%	2200
October	1st to 10th	Day	31% 5% 10% 34% 20% 1	3572
	11th to 20th	Day	42% 4 10% 25% 19%	3223
	21st to end	Day	46% 5% 12% 24% 11% 2	3180
November	1st to 10th	Day	45% 5% 10% 25% 14% 1	1852
	11th to 20th	Day	57% 5% 10% 19% 8% 2	1890
	21st to end	Day	61% 4 12% 16% 6%	1890
December	1st to 10th	Day	67% 7% 13% 9% 3	3020
	11th to 20th	Day	71% 4 9% 13% 3	3087
	21st to end	Day	76% 4 8% 8% 4	4070
January	1st to 10th	Night	64% 5% 8% 15% 6% 1	6488
	11th to 20th	Night	71% 5% 10% 9% 5%	6500
	21st to end	Night	66% 5% 11% 12% 6%	6896
February	1st to 10th	Night	64% 6% 9% 13% 6% 1	2586
	11th to 20th	Night	58% 5% 10% 17% 8% 1	2339
	21st to end	Night	56% 4 13% 17% 8% 2	1980
March	1st to 10th	Night	49% 5% 12% 24% 9% 1	5373
	11th to 20th	Night	38% 6% 12% 26% 16% 1	4982
	21st to end	Night	51% 4 11% 19% 14% 1	5467
April	1st to 10th	Night	48% 6% 9% 21% 14% 1	2021
	11th to 20th	Night	47% 4 11% 18% 17% 2	1867
	21st to end	Night	46% 5% 12% 20% 15% 3	1800
May	1st to 10th	Night	54% 6% 8% 16% 14% 3	4060
	11th to 20th	Night	44% 7% 9% 25% 13% 2	4033
	21st to end	Night	38% 6% 11% 23% 19% 3	4260
June	1st to 10th	Night	32% 7% 12% 28% 19% 2	1600
	11th to 20th	Night	37% 6% 12% 26% 16% 2	1600
	21st to end	Night	31% 8% 14% 26% 19% 1	1600
July	1st to 10th	Night	31% 7% 13% 27% 16% 5%	3580
	11th to 20th	Night	30% 5% 15% 29% 20% 2	3572
	21st to end	Night	33% 6% 14% 21% 24% 2	4039
August	1st to 10th	Night	34% 6% 13% 30% 16% 1	2904
	11th to 20th	Night	32% 7% 11% 34% 14% 2	2902
	21st to end	Night	36% 6% 12% 30% 15% 1	3407
September	1st to 10th	Night	34% 6% 10% 28% 19% 3	2074
	11th to 20th	Night	29% 5% 9% 32% 23% 2	2200
	21st to end	Night	40% 6% 11% 26% 16% 1	2200
October	1st to 10th	Night	26% 4 10% 34% 26% 1	3607
	11th to 20th	Night	42% 4 10% 22% 20%	3899
	21st to end	Night	39% 4 9% 32% 15% 1	4610
November	1st to 10th	Night	45% 5% 10% 23% 16% 1	2666
	11th to 20th	Night	52% 4 13% 19% 9% 2	2730
	21st to end	Night	59% 5% 11% 19% 7%	2730
December	1st to 10th	Night	64% 5% 13% 14% 4	4380
	11th to 20th	Night	69% 5% 10% 12% 4	5336
	21st to end	Night	74% 4 8% 8% 5%	7150

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	22% 19% 37% 16% 6% 1	330
	11th to 20th	Day	24% 24% 38% 12% 2 1	330
	21st to end	Day	31% 18% 32% 16% 4	363
February	1st to 10th	Day	28% 22% 34% 12% 3 1	300
	11th to 20th	Day	29% 19% 36% 14% 1	300
	21st to end	Day	30% 25% 32% 12% 1	249
March	1st to 10th	Day	23% 26% 38% 10% 3	300
	11th to 20th	Day	26% 13% 34% 21% 6% 1	496
	21st to end	Day	27% 19% 30% 18% 5% 1	550
April	1st to 10th	Day	25% 15% 32% 21% 7% 1	500
	11th to 20th	Day	26% 17% 33% 15% 7% 3	492
	21st to end	Day	21% 16% 31% 20% 10% 2	500
May	1st to 10th	Day	25% 14% 29% 20% 9% 3	503
	11th to 20th	Day	20% 11% 28% 23% 12% 6%	527
	21st to end	Day	15% 12% 22% 26% 18% 7%	642
June	1st to 10th	Day	13% 8% 30% 30% 15% 4	730
	11th to 20th	Day	12% 7% 28% 32% 17% 4	730
	21st to end	Day	10% 9% 30% 30% 16% 5%	730
July	1st to 10th	Day	9% 5% 21% 30% 22% 12%	721
	11th to 20th	Day	11% 6% 26% 27% 21% 9%	718
	21st to end	Day	8% 6% 23% 32% 22% 10%	697
August	1st to 10th	Day	9% 5% 19% 27% 23% 17%	526
	11th to 20th	Day	13% 4 19% 27% 27% 10%	519
	21st to end	Day	10% 4 22% 30% 23% 12%	583
September	1st to 10th	Day	15% 6% 22% 22% 22% 13%	530
	11th to 20th	Day	8% 3 20% 24% 30% 16%	530
	21st to end	Day	18% 11% 21% 23% 17% 10%	530
October	1st to 10th	Day	16% 7% 27% 26% 18% 6%	530
	11th to 20th	Day	19% 18% 27% 25% 9% 2	525
	21st to end	Day	28% 17% 35% 17% 4 1	363
November	1st to 10th	Day	19% 18% 35% 21% 6% 1	330
	11th to 20th	Day	26% 24% 30% 15% 5%	330
	21st to end	Day	28% 19% 37% 12% 4	330
December	1st to 10th	Day	25% 25% 29% 12% 7%	330
	11th to 20th	Day	27% 26% 32% 12% 3	330
	21st to end	Day	27% 26% 31% 15% 1	363
January	1st to 10th	Night	23% 16% 36% 20% 5%	1050
	11th to 20th	Night	23% 16% 36% 19% 5%	1050
	21st to end	Night	20% 14% 36% 25% 5%	1044
February	1st to 10th	Night	25% 16% 35% 21% 3	801
	11th to 20th	Night	23% 15% 36% 23% 3	783
	21st to end	Night	25% 14% 40% 17% 3	660
March	1st to 10th	Night	22% 13% 36% 23% 6% 1	800
	11th to 20th	Night	18% 15% 37% 22% 6% 1	800
	21st to end	Night	24% 13% 31% 24% 8%	880
April	1st to 10th	Night	20% 14% 37% 24% 4 1	621
	11th to 20th	Night	20% 12% 35% 23% 9% 1	593
	21st to end	Night	20% 9% 35% 29% 7% 1	600
May	1st to 10th	Night	22% 8% 28% 34% 8% 1	600
	11th to 20th	Night	23% 5% 29% 32% 11% 1	591
	21st to end	Night	13% 5% 25% 38% 18% 2	650
June	1st to 10th	Night	13% 3 25% 43% 15% 1	600
	11th to 20th	Night	14% 3 25% 40% 18% 1	600
	21st to end	Night	9% 4 23% 40% 21% 3	600
July	1st to 10th	Night	8% 3 16% 41% 28% 3	585
	11th to 20th	Night	9% 3 17% 44% 25% 2	582
	21st to end	Night	8% 2 19% 46% 26% 1	657
August	1st to 10th	Night	9% 1 14% 44% 28% 3	597
	11th to 20th	Night	9% 2 16% 40% 27% 6%	594
	21st to end	Night	12% 2 15% 38% 29% 4	660
September	1st to 10th	Night	12% 4 17% 37% 25% 5%	674
	11th to 20th	Night	11% 5% 14% 34% 33% 4	800
	21st to end	Night	17% 6% 21% 31% 21% 5%	800
October	1st to 10th	Night	15% 7% 25% 33% 18% 1	800
	11th to 20th	Night	21% 13% 28% 27% 9% 1	800
	21st to end	Night	24% 12% 33% 24% 7%	880
November	1st to 10th	Night	19% 12% 31% 27% 10% 1	820
	11th to 20th	Night	21% 15% 35% 23% 6%	840
	21st to end	Night	27% 13% 33% 23% 3	840
December	1st to 10th	Night	23% 15% 37% 20% 6%	840
	11th to 20th	Night	23% 15% 39% 19% 3	1045
	21st to end	Night	32% 13% 34% 18% 2	1155

Page generated at 2026-01-29 01:21:43. Version ac07

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