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 2024-11-28.

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 8% 5% 5% 5% 4 6% 7% 33%	101398
	Night	14% 11% 4 8% 5% 4 4 3 5% 7% 34%	98165
Transparency	Day	47% 6% 11% 21% 13% 1	104999
	Night	48% 6% 11% 21% 13% 1	102692
Seeing	Day	18% 12% 28% 23% 13% 5%	15783
	Night	19% 10% 29% 29% 12% 1	25638

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%	2660
July	1st to 10th	Day	10% 7% 2 7% 5% 5% 6% 5% 7% 9% 36%	4440
	11th to 20th	Day	7% 4 2 5% 4 4 5% 4 6% 11% 48%	4440
	21st to end	Day	6% 6% 2 6% 6% 6% 6% 5% 8% 9% 41%	4659
August	1st to 10th	Day	11% 6% 2 6% 4 5% 5% 5% 6% 9% 42%	4104
	11th to 20th	Day	10% 6% 3 6% 5% 5% 5% 4 6% 9% 42%	4044
	21st to end	Day	8% 6% 3 7% 5% 5% 6% 4 7% 9% 42%	4350
September	1st to 10th	Day	11% 7% 2 6% 5% 5% 5% 5% 5% 8% 42%	2190
	11th to 20th	Day	9% 5% 2 5% 4 5% 5% 4 7% 9% 46%	2090
	21st to end	Day	14% 7% 3 7% 5% 6% 5% 3 5% 8% 38%	2090
October	1st to 10th	Day	12% 6% 3 7% 5% 5% 4 4 5% 7% 42%	2085
	11th to 20th	Day	17% 9% 4 9% 4 5% 4 3 4 6% 34%	1895
	21st to end	Day	19% 10% 2 9% 5% 4 5% 4 5% 7% 29%	1881
November	1st to 10th	Day	11% 10% 3 9% 6% 4 4 3 4 7% 39%	1762
	11th to 20th	Day	14% 15% 5% 10% 6% 5% 4 3 4 6% 27%	1800
	21st to end	Day	20% 14% 5% 8% 6% 5% 4 3 4 6% 26%	1773
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% 6% 2 5% 3 3 5% 4 8% 11% 45%	1520
July	1st to 10th	Night	8% 5% 2 6% 4 4 4 4 6% 10% 47%	2530
	11th to 20th	Night	8% 4 2 4 4 3 3 4 6% 7% 56%	2530
	21st to end	Night	6% 5% 2 6% 4 4 5% 4 7% 9% 46%	2898
August	1st to 10th	Night	10% 6% 2 6% 4 4 4 3 6% 8% 47%	2825
	11th to 20th	Night	10% 6% 2 6% 3 4 4 4 6% 8% 47%	2785
	21st to end	Night	9% 7% 2 7% 5% 4 5% 4 5% 7% 45%	3302
September	1st to 10th	Night	9% 7% 3 6% 5% 3 4 3 5% 7% 49%	1970
	11th to 20th	Night	10% 4 2 4 3 3 4 3 4 6% 55%	2090
	21st to end	Night	14% 7% 2 6% 4 4 4 3 6% 7% 43%	2090
October	1st to 10th	Night	12% 7% 3 6% 4 4 4 3 4 6% 46%	2094
	11th to 20th	Night	16% 11% 3 9% 4 5% 3 3 5% 6% 35%	2280
	21st to end	Night	20% 10% 3 7% 4 5% 4 3 5% 6% 33%	2717
November	1st to 10th	Night	13% 11% 3 6% 5% 4 4 3 4 5% 42%	2536
	11th to 20th	Night	15% 13% 4 8% 5% 5% 5% 4 5% 6% 30%	2600
	21st to end	Night	17% 15% 4 9% 5% 4 4 3 5% 6% 27%	2562
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% 9% 13% 21% 16% 2	2660
July	1st to 10th	Day	41% 7% 14% 20% 15% 3	4371
	11th to 20th	Day	29% 7% 14% 32% 18% 1	4365
	21st to end	Day	36% 8% 14% 19% 21% 1	4511
August	1st to 10th	Day	36% 7% 13% 25% 17% 1	4091
	11th to 20th	Day	37% 7% 11% 31% 13% 1	4083
	21st to end	Day	37% 6% 12% 31% 13% 2	4349
September	1st to 10th	Day	38% 8% 13% 23% 15% 2	2190
	11th to 20th	Day	33% 7% 10% 31% 18% 1	2090
	21st to end	Day	44% 6% 12% 22% 16%	2090
October	1st to 10th	Day	31% 5% 10% 34% 20% 1	3462
	11th to 20th	Day	42% 4 10% 25% 19%	3123
	21st to end	Day	46% 5% 13% 24% 11% 2	3081
November	1st to 10th	Day	45% 5% 10% 24% 14% 1	1762
	11th to 20th	Day	58% 5% 9% 18% 8% 2	1800
	21st to end	Day	60% 4 13% 16% 7% 1	1773
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	1520
July	1st to 10th	Night	31% 7% 12% 28% 15% 6%	2490
	11th to 20th	Night	26% 5% 13% 32% 22% 2	2482
	21st to end	Night	31% 8% 18% 17% 24% 2	2806
August	1st to 10th	Night	34% 6% 13% 30% 15% 1	2814
	11th to 20th	Night	32% 7% 11% 34% 14% 2	2812
	21st to end	Night	37% 6% 11% 29% 16% 1	3302
September	1st to 10th	Night	34% 6% 10% 27% 20% 3	1970
	11th to 20th	Night	30% 6% 8% 31% 22% 2	2090
	21st to end	Night	40% 6% 11% 27% 15% 1	2090
October	1st to 10th	Night	26% 4 10% 34% 26% 1	3497
	11th to 20th	Night	43% 4 10% 22% 20%	3779
	21st to end	Night	39% 4 9% 32% 15% 1	4467
November	1st to 10th	Night	45% 5% 10% 23% 16% 1	2536
	11th to 20th	Night	53% 4 14% 18% 9% 2	2600
	21st to end	Night	57% 5% 11% 19% 7%	2562
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	11% 10% 30% 29% 16% 5%	680
July	1st to 10th	Day	9% 5% 21% 30% 23% 12%	671
	11th to 20th	Day	11% 6% 25% 28% 21% 10%	668
	21st to end	Day	9% 6% 23% 32% 22% 9%	647
August	1st to 10th	Day	10% 5% 20% 27% 21% 18%	486
	11th to 20th	Day	13% 4 19% 27% 28% 10%	479
	21st to end	Day	10% 3 22% 30% 23% 12%	539
September	1st to 10th	Day	15% 6% 22% 23% 22% 12%	490
	11th to 20th	Day	8% 3 21% 24% 29% 14%	490
	21st to end	Day	18% 11% 22% 22% 17% 9%	490
October	1st to 10th	Day	16% 8% 28% 26% 16% 7%	490
	11th to 20th	Day	19% 20% 26% 24% 9% 2	485
	21st to end	Day	29% 16% 35% 15% 4 1	330
November	1st to 10th	Day	16% 19% 35% 22% 7% 1	300
	11th to 20th	Day	24% 24% 32% 15% 6%	300
	21st to end	Day	29% 17% 38% 11% 4	291
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 23% 40% 20% 3	570
July	1st to 10th	Night	8% 3 17% 40% 28% 4	555
	11th to 20th	Night	9% 3 17% 44% 25% 3	552
	21st to end	Night	7% 2 19% 46% 26% 1	624
August	1st to 10th	Night	10% 1 14% 44% 27% 3	567
	11th to 20th	Night	9% 1 16% 40% 27% 6%	564
	21st to end	Night	13% 2 15% 37% 30% 4	627
September	1st to 10th	Night	12% 4 17% 37% 25% 5%	640
	11th to 20th	Night	12% 5% 14% 34% 31% 3	760
	21st to end	Night	17% 7% 21% 31% 20% 4	760
October	1st to 10th	Night	16% 7% 26% 32% 18% 1	760
	11th to 20th	Night	21% 14% 28% 27% 9% 1	760
	21st to end	Night	25% 13% 32% 24% 7%	836
November	1st to 10th	Night	20% 12% 30% 28% 10% 1	780
	11th to 20th	Night	22% 14% 35% 22% 6%	800
	21st to end	Night	26% 13% 33% 24% 3	789
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

Page generated at 2024-11-25 00:22:18. Version ac07

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