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 2024-01-14.

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% 9% 4 7% 7% 4 5% 5% 5% 7% 33%	74882
	Night	15% 10% 4 7% 6% 3 5% 4 5% 7% 34%	74892
Transparency	Day	49% 6% 11% 20% 12% 1	74589
	Night	50% 6% 11% 20% 12% 1	74706
Seeing	Day	18% 12% 28% 23% 14% 6%	14543
	Night	19% 10% 29% 29% 12% 1	24511

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	15% 14% 7% 10% 9% 5% 6% 4 5% 7% 17%	1517
	11th to 20th	Day	16% 15% 9% 10% 11% 4 5% 5% 4 5% 16%	1464
	21st to end	Day	15% 18% 9% 12% 8% 4 5% 3 3 5% 17%	1676
February	1st to 10th	Day	14% 14% 7% 10% 11% 4 7% 5% 4 5% 19%	1629
	11th to 20th	Day	15% 10% 7% 11% 9% 5% 5% 5% 4 5% 22%	1748
	21st to end	Day	17% 15% 6% 11% 6% 4 5% 4 4 6% 22%	1480
March	1st to 10th	Day	14% 11% 4 9% 9% 5% 5% 6% 6% 6% 27%	1800
	11th to 20th	Day	13% 11% 4 8% 7% 3 4 4 5% 7% 34%	1976
	21st to end	Day	18% 13% 5% 8% 6% 3 5% 4 5% 7% 28%	2178
April	1st to 10th	Day	17% 12% 5% 7% 6% 3 5% 4 4 7% 29%	2155
	11th to 20th	Day	17% 9% 4 6% 5% 3 4 5% 5% 6% 35%	2230
	21st to end	Day	18% 8% 4 7% 6% 3 5% 4 5% 7% 33%	2340
May	1st to 10th	Day	16% 9% 3 6% 7% 4 6% 5% 5% 8% 32%	2340
	11th to 20th	Day	19% 7% 4 6% 6% 4 5% 4 5% 7% 34%	2301
	21st to end	Day	12% 5% 3 5% 5% 4 4 5% 7% 9% 39%	2592
June	1st to 10th	Day	10% 5% 3 6% 5% 4 5% 5% 6% 9% 42%	2520
	11th to 20th	Day	11% 5% 2 5% 6% 3 6% 6% 7% 10% 40%	2520
	21st to end	Day	9% 6% 3 6% 6% 4 6% 7% 7% 10% 38%	2520
July	1st to 10th	Day	7% 5% 2 5% 5% 3 5% 6% 8% 9% 45%	2520
	11th to 20th	Day	9% 5% 3 5% 5% 4 4 6% 5% 10% 44%	2520
	21st to end	Day	7% 5% 3 4 6% 4 6% 7% 7% 9% 42%	2656
August	1st to 10th	Day	8% 5% 2 5% 6% 4 6% 7% 7% 9% 41%	2327
	11th to 20th	Day	10% 5% 2 6% 7% 5% 6% 6% 6% 8% 38%	2303
	21st to end	Day	10% 6% 3 6% 5% 3 5% 5% 6% 8% 43%	2476
September	1st to 10th	Day	11% 7% 3 6% 6% 4 6% 5% 5% 8% 40%	2075
	11th to 20th	Day	9% 5% 2 5% 5% 3 5% 5% 6% 9% 44%	1980
	21st to end	Day	13% 6% 3 6% 6% 4 5% 5% 5% 8% 39%	1980
October	1st to 10th	Day	13% 6% 3 6% 6% 4 4 5% 6% 7% 40%	1976
	11th to 20th	Day	18% 9% 4 8% 6% 4 5% 4 4 6% 33%	1796
	21st to end	Day	20% 10% 3 8% 6% 3 4 5% 5% 7% 29%	1782
November	1st to 10th	Day	12% 9% 3 8% 7% 3 4 4 4 7% 40%	1672
	11th to 20th	Day	14% 14% 6% 9% 7% 3 5% 4 4 7% 28%	1710
	21st to end	Day	20% 12% 6% 7% 6% 3 5% 3 4 7% 27%	1710
December	1st to 10th	Day	14% 17% 9% 11% 7% 3 5% 4 5% 5% 22%	1710
	11th to 20th	Day	14% 15% 7% 10% 7% 4 6% 5% 6% 6% 19%	1920
	21st to end	Day	21% 22% 7% 11% 9% 4 4 4 3 4 11%	2783
January	1st to 10th	Night	17% 13% 7% 10% 8% 4 5% 4 4 6% 22%	2648
	11th to 20th	Night	18% 15% 7% 11% 8% 4 5% 3 5% 6% 19%	2575
	21st to end	Night	13% 14% 9% 12% 10% 4 5% 5% 5% 6% 17%	2678
February	1st to 10th	Night	17% 15% 6% 10% 9% 4 5% 5% 4 4 21%	2326
	11th to 20th	Night	14% 13% 5% 9% 7% 3 6% 5% 4 5% 27%	2098
	21st to end	Night	18% 12% 5% 10% 6% 3 5% 4 4 6% 28%	1776
March	1st to 10th	Night	15% 10% 4 8% 7% 3 4 4 5% 6% 35%	2160
	11th to 20th	Night	13% 10% 3 5% 4 3 5% 5% 5% 7% 38%	1982
	21st to end	Night	20% 9% 4 7% 6% 3 5% 4 4 6% 32%	2178
April	1st to 10th	Night	14% 10% 4 5% 5% 4 4 4 6% 6% 36%	1819
	11th to 20th	Night	18% 8% 3 6% 5% 2 5% 5% 5% 6% 37%	1679
	21st to end	Night	17% 9% 3 6% 5% 3 4 3 5% 8% 37%	1620
May	1st to 10th	Night	17% 9% 3 7% 7% 4 4 5% 5% 8% 32%	1620
	11th to 20th	Night	20% 6% 2 4 5% 2 5% 3 6% 7% 38%	1592
	21st to end	Night	11% 5% 3 5% 5% 3 5% 5% 6% 10% 43%	1679
June	1st to 10th	Night	10% 4 3 3 5% 3 4 6% 6% 9% 47%	1440
	11th to 20th	Night	10% 5% 3 6% 5% 3 4 5% 6% 10% 44%	1440
	21st to end	Night	8% 5% 3 5% 4 2 5% 4 7% 12% 46%	1440
July	1st to 10th	Night	6% 5% 3 5% 5% 3 4 4 5% 9% 53%	1440
	11th to 20th	Night	8% 4 2 4 5% 2 4 5% 6% 8% 52%	1440
	21st to end	Night	5% 3 2 5% 4 3 4 6% 7% 10% 50%	1660
August	1st to 10th	Night	7% 4 1 4 5% 3 4 4 6% 10% 50%	1611
	11th to 20th	Night	8% 4 2 5% 4 3 5% 6% 6% 9% 48%	1598
	21st to end	Night	9% 5% 2 4 5% 2 5% 5% 5% 7% 50%	1876
September	1st to 10th	Night	9% 6% 3 5% 6% 2 4 4 5% 8% 47%	1866
	11th to 20th	Night	10% 4 3 4 4 3 4 4 5% 6% 53%	1980
	21st to end	Night	13% 6% 3 5% 4 3 4 4 6% 7% 44%	1980
October	1st to 10th	Night	13% 7% 3 5% 5% 3 4 5% 4 6% 45%	1983
	11th to 20th	Night	17% 11% 3 8% 6% 3 3 4 4 6% 34%	2160
	21st to end	Night	21% 10% 3 6% 5% 4 4 4 4 6% 32%	2574
November	1st to 10th	Night	13% 11% 3 5% 6% 3 4 4 4 5% 42%	2406
	11th to 20th	Night	15% 12% 5% 7% 6% 4 5% 5% 5% 6% 30%	2470
	21st to end	Night	17% 14% 5% 8% 6% 4 4 4 5% 7% 27%	2470
December	1st to 10th	Night	17% 14% 6% 12% 8% 4 5% 4 5% 6% 19%	2470
	11th to 20th	Night	15% 13% 6% 12% 8% 4 5% 4 5% 6% 21%	3274
	21st to end	Night	27% 20% 6% 10% 6% 3 4 4 4 5% 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% 10% 14% 4	1518
	11th to 20th	Day	71% 6% 11% 8% 4	1464
	21st to end	Day	71% 3 8% 11% 6% 1	1676
February	1st to 10th	Day	67% 6% 8% 12% 6% 1	1629
	11th to 20th	Day	63% 5% 8% 16% 7% 1	1758
	21st to end	Day	63% 5% 11% 14% 6% 1	1480
March	1st to 10th	Day	56% 7% 11% 18% 8% 1	1800
	11th to 20th	Day	50% 5% 10% 19% 13% 3	1976
	21st to end	Day	56% 6% 9% 19% 9% 1	2178
April	1st to 10th	Day	56% 5% 10% 19% 11%	2155
	11th to 20th	Day	49% 5% 11% 20% 13% 2	2230
	21st to end	Day	50% 5% 12% 16% 14% 2	2340
May	1st to 10th	Day	50% 7% 11% 20% 11% 1	2340
	11th to 20th	Day	50% 6% 9% 19% 15% 2	2305
	21st to end	Day	40% 7% 14% 25% 12% 2	2592
June	1st to 10th	Day	38% 8% 11% 27% 15% 2	2520
	11th to 20th	Day	38% 8% 12% 23% 17% 2	2520
	21st to end	Day	39% 10% 13% 21% 16% 2	2520
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	63% 5% 10% 16% 6%	2648
	11th to 20th	Night	67% 5% 12% 10% 5%	2575
	21st to end	Night	67% 5% 12% 11% 5% 1	2678
February	1st to 10th	Night	66% 6% 9% 12% 5% 1	2326
	11th to 20th	Night	58% 5% 10% 17% 9% 1	2099
	21st to end	Night	57% 3 13% 17% 8% 2	1776
March	1st to 10th	Night	51% 4 11% 22% 10% 1	2160
	11th to 20th	Night	45% 7% 11% 19% 15% 2	1982
	21st to end	Night	53% 5% 8% 21% 11% 2	2178
April	1st to 10th	Night	47% 6% 10% 22% 14% 1	1819
	11th to 20th	Night	48% 4 11% 17% 17% 2	1679
	21st to end	Night	47% 4 12% 20% 14% 3	1620
May	1st to 10th	Night	52% 5% 10% 21% 10% 2	1620
	11th to 20th	Night	44% 7% 10% 18% 20% 2	1593
	21st to end	Night	36% 7% 15% 25% 15% 3	1680
June	1st to 10th	Night	33% 7% 12% 29% 18% 3	1440
	11th to 20th	Night	36% 7% 13% 25% 17% 3	1440
	21st to end	Night	31% 8% 14% 27% 19% 1	1440
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	22% 18% 41% 14% 3 1	249
	21st to end	Day	30% 16% 32% 17% 5%	264
February	1st to 10th	Day	29% 22% 35% 12% 2	240
	11th to 20th	Day	30% 18% 38% 12% 2	240
	21st to end	Day	30% 27% 31% 11% 1	198
March	1st to 10th	Day	23% 25% 38% 10% 3	240
	11th to 20th	Day	25% 11% 33% 24% 6% 1	416
	21st to end	Day	28% 16% 29% 19% 6% 2	462
April	1st to 10th	Day	24% 13% 32% 22% 8% 1	420
	11th to 20th	Day	25% 17% 32% 15% 8% 3	412
	21st to end	Day	22% 15% 32% 19% 10% 2	420
May	1st to 10th	Day	24% 14% 29% 20% 9% 4	423
	11th to 20th	Day	21% 10% 28% 23% 13% 6%	447
	21st to end	Day	14% 10% 21% 27% 20% 8%	546
June	1st to 10th	Day	12% 6% 31% 30% 15% 5%	630
	11th to 20th	Day	13% 7% 26% 30% 19% 5%	630
	21st to end	Day	10% 9% 30% 30% 17% 5%	630
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% 14% 35% 21% 5% 1	920
	21st to end	Night	19% 12% 37% 27% 5%	896
February	1st to 10th	Night	26% 15% 36% 20% 3	720
	11th to 20th	Night	23% 15% 36% 24% 3	703
	21st to end	Night	27% 13% 39% 18% 3	592
March	1st to 10th	Night	22% 13% 34% 23% 7% 1	720
	11th to 20th	Night	19% 13% 37% 23% 7% 1	720
	21st to end	Night	24% 12% 31% 24% 8%	792
April	1st to 10th	Night	18% 14% 37% 25% 4 1	559
	11th to 20th	Night	20% 10% 36% 24% 9% 1	533
	21st to end	Night	21% 7% 35% 29% 8% 1	540
May	1st to 10th	Night	21% 7% 29% 34% 8% 1	540
	11th to 20th	Night	24% 4 28% 32% 12% 1	531
	21st to end	Night	13% 4 24% 38% 20% 2	584
June	1st to 10th	Night	13% 3 24% 44% 16% 1	540
	11th to 20th	Night	14% 3 24% 39% 19% 1	540
	21st to end	Night	9% 4 22% 41% 21% 3	540
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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