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 2024-06-30.

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	14% 10% 4 8% 6% 5% 5% 4 5% 7% 32%	89265
	Night	15% 11% 4 8% 5% 4 4 3 5% 6% 33%	89862
Transparency	Day	50% 6% 11% 20% 12% 1	89023
	Night	51% 6% 11% 20% 12% 1	89710
Seeing	Day	18% 12% 28% 23% 13% 5%	15192
	Night	19% 10% 29% 29% 12% 1	25102

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	17% 18% 7% 10% 7% 5% 5% 3 4 6% 19%	2527
	11th to 20th	Day	16% 17% 7% 13% 8% 7% 8% 5% 5% 4 11%	2530
	21st to end	Day	27% 22% 6% 12% 5% 4 3 1 3 4 14%	2940
February	1st to 10th	Day	13% 15% 5% 11% 10% 6% 6% 4 5% 6% 20%	1719
	11th to 20th	Day	14% 12% 6% 13% 8% 6% 5% 3 4 5% 24%	1848
	21st to end	Day	15% 16% 5% 12% 6% 5% 5% 3 5% 6% 23%	1570
March	1st to 10th	Day	16% 16% 4 9% 6% 4 4 3 4 5% 27%	3120
	11th to 20th	Day	12% 11% 4 10% 7% 5% 5% 3 6% 7% 31%	3476
	21st to end	Day	18% 14% 5% 11% 5% 4 5% 3 5% 6% 26%	3815
April	1st to 10th	Day	17% 14% 4 8% 5% 5% 4 3 4 7% 30%	2275
	11th to 20th	Day	17% 10% 3 7% 4 4 4 4 6% 6% 35%	2356
	21st to end	Day	17% 9% 3 8% 5% 5% 4 3 5% 7% 34%	2470
May	1st to 10th	Day	17% 9% 3 7% 5% 4 4 4 5% 7% 35%	4082
	11th to 20th	Day	15% 7% 2 7% 5% 5% 5% 4 6% 9% 35%	4081
	21st to end	Day	10% 6% 3 7% 4 4 4 4 6% 8% 44%	4593
June	1st to 10th	Day	10% 6% 3 6% 5% 5% 5% 4 6% 9% 42%	2660
	11th to 20th	Day	10% 5% 2 6% 5% 4 6% 5% 7% 9% 40%	2660
	21st to end	Day	9% 6% 2 7% 5% 6% 6% 5% 7% 10% 37%	2647
July	1st to 10th	Day	7% 5% 2 6% 4 4 5% 5% 8% 9% 45%	2520
	11th to 20th	Day	9% 5% 2 6% 5% 5% 5% 5% 5% 10% 43%	2520
	21st to end	Day	7% 6% 2 5% 5% 5% 6% 5% 7% 9% 41%	2656
August	1st to 10th	Day	8% 5% 2 6% 5% 6% 6% 5% 7% 9% 40%	2327
	11th to 20th	Day	10% 5% 2 7% 6% 6% 6% 5% 6% 9% 38%	2303
	21st to end	Day	10% 6% 2 6% 5% 5% 5% 3 6% 8% 43%	2476
September	1st to 10th	Day	11% 7% 2 6% 5% 5% 6% 5% 5% 8% 40%	2075
	11th to 20th	Day	9% 5% 2 5% 4 5% 5% 4 7% 9% 44%	1980
	21st to end	Day	13% 6% 2 7% 5% 5% 6% 3 5% 8% 39%	1980
October	1st to 10th	Day	13% 6% 3 7% 5% 5% 4 4 5% 7% 40%	1976
	11th to 20th	Day	18% 9% 4 9% 4 5% 4 3 4 6% 33%	1796
	21st to end	Day	20% 11% 3 9% 5% 4 5% 4 5% 7% 28%	1782
November	1st to 10th	Day	11% 10% 3 9% 6% 4 4 4 4 7% 39%	1672
	11th to 20th	Day	14% 15% 5% 10% 6% 4 4 3 4 6% 28%	1710
	21st to end	Day	20% 13% 5% 8% 6% 5% 4 3 4 6% 27%	1710
December	1st to 10th	Day	13% 18% 8% 11% 6% 5% 4 3 5% 4 22%	1710
	11th to 20th	Day	14% 17% 6% 12% 6% 5% 5% 4 6% 6% 19%	1920
	21st to end	Day	21% 23% 7% 12% 7% 5% 4 3 3 4 11%	2783
January	1st to 10th	Night	16% 16% 8% 11% 6% 5% 4 3 4 5% 21%	4428
	11th to 20th	Night	15% 17% 7% 15% 7% 5% 6% 4 6% 5% 12%	4440
	21st to end	Night	24% 18% 8% 11% 6% 4 4 3 4 4 14%	4720
February	1st to 10th	Night	16% 16% 5% 11% 8% 5% 4 4 4 4 23%	2456
	11th to 20th	Night	13% 14% 5% 10% 6% 5% 5% 4 4 5% 28%	2218
	21st to end	Night	17% 12% 4 11% 5% 4 5% 3 5% 6% 27%	1884
March	1st to 10th	Night	16% 13% 4 8% 5% 4 3 3 4 6% 35%	3733
	11th to 20th	Night	9% 9% 2 5% 4 4 4 4 6% 7% 45%	3482
	21st to end	Night	17% 10% 4 9% 6% 4 5% 3 5% 6% 33%	3817
April	1st to 10th	Night	15% 11% 3 6% 5% 5% 4 4 6% 6% 36%	1920
	11th to 20th	Night	19% 9% 2 7% 4 4 5% 3 5% 6% 37%	1773
	21st to end	Night	16% 10% 2 7% 5% 4 4 3 5% 7% 37%	1710
May	1st to 10th	Night	15% 10% 3 7% 5% 5% 4 4 6% 8% 33%	2813
	11th to 20th	Night	17% 7% 3 7% 4 3 4 2 5% 6% 41%	2812
	21st to end	Night	11% 5% 2 6% 4 4 4 3 5% 9% 46%	2962
June	1st to 10th	Night	10% 5% 2 4 4 4 3 5% 7% 9% 47%	1520
	11th to 20th	Night	10% 6% 3 7% 4 4 4 4 6% 10% 43%	1520
	21st to end	Night	8% 5% 2 5% 3 3 5% 4 8% 11% 45%	1512
July	1st to 10th	Night	6% 5% 3 5% 4 3 4 3 5% 9% 52%	1440
	11th to 20th	Night	8% 5% 2 4 5% 3 4 5% 7% 8% 52%	1440
	21st to end	Night	5% 4 2 6% 4 4 4 5% 8% 10% 49%	1660
August	1st to 10th	Night	7% 5% 1 5% 5% 4 4 3 6% 9% 50%	1611
	11th to 20th	Night	8% 5% 2 6% 3 5% 4 5% 6% 9% 48%	1598
	21st to end	Night	9% 5% 2 5% 4 4 4 4 5% 7% 50%	1876
September	1st to 10th	Night	9% 7% 3 6% 6% 3 4 3 5% 8% 47%	1866
	11th to 20th	Night	10% 5% 2 5% 3 3 4 3 4 6% 53%	1980
	21st to end	Night	13% 6% 2 6% 4 4 4 4 6% 7% 44%	1980
October	1st to 10th	Night	13% 8% 3 6% 4 4 4 4 4 6% 45%	1983
	11th to 20th	Night	17% 12% 3 9% 5% 4 3 3 5% 6% 34%	2160
	21st to end	Night	21% 10% 3 7% 5% 5% 4 3 4 6% 32%	2574
November	1st to 10th	Night	13% 11% 3 6% 5% 4 4 3 4 5% 42%	2406
	11th to 20th	Night	15% 13% 4 8% 5% 5% 5% 4 5% 6% 30%	2470
	21st to end	Night	17% 15% 4 9% 5% 4 4 3 5% 6% 27%	2470
December	1st to 10th	Night	17% 16% 6% 13% 7% 5% 5% 3 5% 6% 19%	2470
	11th to 20th	Night	15% 14% 6% 14% 7% 5% 5% 3 5% 6% 21%	3274
	21st to end	Night	26% 21% 6% 11% 5% 4 4 3 4 4 12%	4884

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	67% 5% 11% 14% 4	2528
	11th to 20th	Day	73% 5% 11% 8% 3	2530
	21st to end	Day	77% 3 9% 7% 3	2940
February	1st to 10th	Day	64% 6% 9% 14% 7% 1	1719
	11th to 20th	Day	62% 5% 8% 16% 9% 1	1858
	21st to end	Day	62% 5% 11% 14% 6% 1	1570
March	1st to 10th	Day	58% 6% 10% 18% 7% 1	3120
	11th to 20th	Day	51% 6% 12% 21% 8% 2	3476
	21st to end	Day	59% 6% 10% 15% 9% 1	3815
April	1st to 10th	Day	55% 4 10% 19% 11%	2275
	11th to 20th	Day	48% 6% 11% 21% 13% 2	2356
	21st to end	Day	50% 5% 12% 17% 15% 2	2470
May	1st to 10th	Day	47% 7% 11% 22% 13% 1	4120
	11th to 20th	Day	44% 8% 13% 24% 10% 1	4085
	21st to end	Day	36% 6% 11% 20% 23% 3	4606
June	1st to 10th	Day	38% 7% 11% 26% 15% 2	2660
	11th to 20th	Day	37% 7% 12% 23% 18% 2	2660
	21st to end	Day	39% 10% 13% 21% 15% 2	2647
July	1st to 10th	Day	32% 9% 12% 25% 19% 4	2451
	11th to 20th	Day	35% 8% 12% 25% 19% 2	2445
	21st to end	Day	34% 8% 13% 24% 18% 2	2508
August	1st to 10th	Day	35% 9% 14% 27% 13% 1	2314
	11th to 20th	Day	40% 9% 12% 24% 13% 2	2303
	21st to end	Day	37% 6% 10% 25% 18% 2	2476
September	1st to 10th	Day	40% 9% 13% 22% 14% 2	2075
	11th to 20th	Day	34% 7% 11% 32% 16% 1	1980
	21st to end	Day	42% 6% 12% 23% 17%	1980
October	1st to 10th	Day	43% 6% 10% 25% 14% 2	1976
	11th to 20th	Day	53% 5% 11% 20% 11%	1796
	21st to end	Day	55% 5% 13% 18% 9% 1	1782
November	1st to 10th	Day	45% 5% 10% 24% 15% 1	1672
	11th to 20th	Day	57% 5% 10% 19% 8% 2	1710
	21st to end	Day	59% 4 13% 16% 7% 1	1710
December	1st to 10th	Day	65% 6% 10% 14% 4	1710
	11th to 20th	Day	63% 6% 13% 15% 4	1917
	21st to end	Day	78% 4 8% 6% 4	2783
January	1st to 10th	Night	64% 5% 10% 15% 6% 1	4428
	11th to 20th	Night	72% 4 11% 8% 5%	4440
	21st to end	Night	74% 4 9% 10% 3	4720
February	1st to 10th	Night	64% 6% 10% 13% 6% 1	2456
	11th to 20th	Night	57% 5% 10% 18% 9% 1	2219
	21st to end	Night	57% 4 12% 17% 8% 2	1884
March	1st to 10th	Night	51% 5% 12% 25% 7% 1	3733
	11th to 20th	Night	37% 7% 13% 21% 21% 2	3482
	21st to end	Night	52% 5% 12% 21% 10% 1	3817
April	1st to 10th	Night	48% 6% 10% 22% 14% 1	1920
	11th to 20th	Night	48% 5% 11% 18% 17% 2	1773
	21st to end	Night	46% 5% 12% 19% 15% 3	1710
May	1st to 10th	Night	47% 7% 9% 21% 13% 2	2840
	11th to 20th	Night	41% 8% 9% 26% 14% 1	2813
	21st to end	Night	34% 8% 12% 22% 21% 3	2970
June	1st to 10th	Night	32% 7% 12% 29% 18% 2	1520
	11th to 20th	Night	36% 7% 12% 26% 17% 2	1520
	21st to end	Night	31% 8% 14% 26% 19% 1	1512
July	1st to 10th	Night	29% 8% 10% 28% 21% 4	1400
	11th to 20th	Night	29% 7% 12% 28% 21% 3	1392
	21st to end	Night	27% 8% 16% 25% 21% 3	1568
August	1st to 10th	Night	30% 7% 13% 33% 15% 2	1600
	11th to 20th	Night	31% 9% 14% 29% 15% 3	1598
	21st to end	Night	33% 6% 12% 26% 22% 2	1876
September	1st to 10th	Night	36% 6% 10% 26% 18% 3	1866
	11th to 20th	Night	31% 6% 9% 31% 21% 2	1980
	21st to end	Night	38% 6% 12% 27% 15% 1	1980
October	1st to 10th	Night	40% 6% 10% 23% 19% 1	1983
	11th to 20th	Night	50% 5% 10% 20% 14% 1	2160
	21st to end	Night	53% 5% 10% 21% 9% 1	2574
November	1st to 10th	Night	45% 5% 11% 23% 16% 1	2406
	11th to 20th	Night	53% 4 14% 19% 9% 1	2470
	21st to end	Night	57% 5% 12% 19% 7%	2470
December	1st to 10th	Night	65% 6% 10% 12% 6%	2470
	11th to 20th	Night	63% 5% 12% 14% 5%	3276
	21st to end	Night	75% 5% 10% 7% 3	4884

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% 20% 35% 16% 7% 1	270
	11th to 20th	Day	24% 19% 40% 14% 3 1	270
	21st to end	Day	32% 16% 31% 17% 4	297
February	1st to 10th	Day	27% 21% 36% 13% 3 1	270
	11th to 20th	Day	28% 18% 37% 16% 1	270
	21st to end	Day	29% 25% 32% 12% 1	225
March	1st to 10th	Day	23% 25% 38% 11% 3	270
	11th to 20th	Day	25% 12% 34% 22% 6% 1	456
	21st to end	Day	27% 18% 29% 19% 6% 1	506
April	1st to 10th	Day	23% 15% 32% 22% 7% 1	460
	11th to 20th	Day	26% 17% 32% 15% 7% 3	452
	21st to end	Day	21% 16% 32% 19% 9% 2	460
May	1st to 10th	Day	24% 15% 29% 20% 9% 3	463
	11th to 20th	Day	20% 10% 27% 23% 13% 7%	487
	21st to end	Day	14% 10% 22% 27% 20% 7%	594
June	1st to 10th	Day	13% 8% 30% 30% 15% 4	680
	11th to 20th	Day	12% 8% 27% 31% 18% 5%	680
	21st to end	Day	10% 9% 30% 29% 16% 5%	676
July	1st to 10th	Day	8% 5% 20% 30% 24% 13%	621
	11th to 20th	Day	12% 5% 25% 28% 20% 9%	618
	21st to end	Day	9% 6% 23% 30% 22% 10%	597
August	1st to 10th	Day	9% 4 18% 28% 22% 19%	446
	11th to 20th	Day	13% 4 18% 26% 28% 10%	439
	21st to end	Day	11% 3 23% 28% 23% 12%	495
September	1st to 10th	Day	16% 6% 21% 23% 23% 11%	450
	11th to 20th	Day	9% 4 22% 25% 28% 13%	450
	21st to end	Day	16% 12% 22% 23% 17% 10%	450
October	1st to 10th	Day	17% 7% 28% 25% 16% 7%	450
	11th to 20th	Day	20% 21% 26% 24% 8% 1	446
	21st to end	Day	31% 16% 33% 15% 4 1	297
November	1st to 10th	Day	16% 19% 34% 23% 7% 1	270
	11th to 20th	Day	24% 23% 31% 15% 6%	270
	21st to end	Day	29% 17% 38% 12% 4	270
December	1st to 10th	Day	26% 26% 30% 12% 6%	270
	11th to 20th	Day	25% 26% 35% 11% 3	270
	21st to end	Day	24% 27% 31% 17% 1	297
January	1st to 10th	Night	23% 15% 37% 20% 5%	950
	11th to 20th	Night	24% 15% 35% 21% 5% 1	950
	21st to end	Night	20% 12% 37% 26% 5%	946
February	1st to 10th	Night	25% 15% 35% 21% 3	760
	11th to 20th	Night	22% 15% 37% 24% 3	743
	21st to end	Night	25% 14% 39% 18% 3	628
March	1st to 10th	Night	21% 13% 35% 23% 7% 1	760
	11th to 20th	Night	18% 14% 38% 22% 6% 1	760
	21st to end	Night	24% 12% 32% 24% 8%	836
April	1st to 10th	Night	19% 14% 37% 25% 4 1	590
	11th to 20th	Night	21% 12% 35% 23% 8% 1	563
	21st to end	Night	20% 8% 35% 28% 8% 1	570
May	1st to 10th	Night	21% 8% 28% 35% 8% 1	570
	11th to 20th	Night	23% 4 28% 33% 11% 1	561
	21st to end	Night	13% 5% 24% 38% 19% 2	617
June	1st to 10th	Night	13% 3 25% 44% 15% 1	570
	11th to 20th	Night	14% 3 25% 40% 18% 1	570
	21st to end	Night	9% 4 22% 41% 20% 3	567
July	1st to 10th	Night	8% 3 15% 40% 30% 4	525
	11th to 20th	Night	9% 3 17% 44% 25% 2	522
	21st to end	Night	7% 2 20% 46% 25% 1	591
August	1st to 10th	Night	10% 1 14% 45% 27% 3	537
	11th to 20th	Night	8% 1 16% 40% 29% 6%	534
	21st to end	Night	13% 2 15% 37% 30% 4	594
September	1st to 10th	Night	13% 4 16% 38% 24% 5%	606
	11th to 20th	Night	12% 5% 15% 34% 30% 3	720
	21st to end	Night	16% 7% 21% 31% 21% 5%	720
October	1st to 10th	Night	17% 7% 26% 32% 18% 1	720
	11th to 20th	Night	22% 14% 28% 26% 8% 1	720
	21st to end	Night	26% 12% 32% 23% 6%	792
November	1st to 10th	Night	19% 12% 30% 28% 11% 1	740
	11th to 20th	Night	22% 14% 35% 22% 6%	760
	21st to end	Night	26% 13% 33% 25% 4	760
December	1st to 10th	Night	24% 14% 37% 19% 6%	760
	11th to 20th	Night	23% 14% 39% 20% 3	945
	21st to end	Night	32% 13% 33% 19% 2	1045

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