Red Door Observatory
Clear Sky Chart
History

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

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% 6% 2 6% 4 4 4 4 6% 8% 44%	127322
	Night	14% 6% 2 6% 4 4 4 3 5% 7% 44%	124055
Transparency	Day	38% 4 12% 22% 18% 6%	130981
	Night	39% 4 10% 19% 21% 7%	128465
Seeing	Day	17% 7% 22% 25% 20% 10%	16807
	Night	16% 6% 22% 32% 20% 3	26899

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% 5% 2 5% 3 3 2 2 3 5% 56%	4065
	11th to 20th	Day	12% 7% 2 4 3 3 3 2 3 4 59%	4060
	21st to end	Day	18% 7% 2 5% 4 3 4 3 4 5% 46%	4466
February	1st to 10th	Day	15% 8% 2 5% 4 4 4 4 7% 7% 42%	1800
	11th to 20th	Day	21% 6% 2 4 3 3 3 3 4 5% 45%	1925
	21st to end	Day	18% 8% 3 7% 4 3 3 3 4 5% 42%	1694
March	1st to 10th	Day	21% 8% 2 6% 4 3 3 3 4 6% 41%	4935
	11th to 20th	Day	10% 4 3 6% 3 3 3 3 4 7% 54%	4980
	21st to end	Day	18% 7% 2 6% 3 3 3 2 3 5% 47%	5465
April	1st to 10th	Day	11% 5% 2 4 3 4 3 4 7% 8% 50%	2200
	11th to 20th	Day	13% 5% 2 5% 3 3 4 3 5% 6% 49%	2364
	21st to end	Day	13% 5% 2 5% 3 3 5% 4 5% 7% 48%	2565
May	1st to 10th	Day	10% 6% 2 7% 5% 5% 5% 5% 8% 11% 36%	5862
	11th to 20th	Day	18% 8% 2 7% 5% 4 5% 4 7% 9% 30%	5861
	21st to end	Day	13% 6% 2 6% 4 4 5% 3 6% 8% 43%	6433
June	1st to 10th	Day	9% 6% 3 6% 4 4 6% 4 7% 11% 39%	2600
	11th to 20th	Day	8% 5% 2 6% 5% 4 5% 6% 7% 10% 43%	2600
	21st to end	Day	6% 4 2 6% 5% 6% 5% 5% 8% 12% 41%	2600
July	1st to 10th	Day	8% 6% 2 7% 5% 6% 5% 5% 8% 11% 38%	5900
	11th to 20th	Day	6% 5% 2 7% 5% 6% 6% 6% 9% 13% 35%	5900
	21st to end	Day	9% 6% 3 8% 6% 6% 6% 6% 8% 10% 32%	6424
August	1st to 10th	Day	20% 7% 2 6% 5% 5% 5% 5% 8% 10% 26%	4234
	11th to 20th	Day	9% 6% 2 6% 5% 5% 6% 4 8% 11% 37%	4174
	21st to end	Day	6% 4 1 5% 4 4 5% 4 6% 9% 52%	4388
September	1st to 10th	Day	9% 4 2 5% 4 5% 6% 5% 6% 9% 45%	2220
	11th to 20th	Day	13% 6% 2 5% 4 4 5% 4 6% 9% 43%	2200
	21st to end	Day	17% 7% 2 7% 4 4 4 4 5% 6% 40%	2200
October	1st to 10th	Day	13% 5% 2 4 3 4 3 3 4 5% 56%	2080
	11th to 20th	Day	13% 5% 1 4 3 3 3 2 3 5% 58%	2000
	21st to end	Day	15% 5% 1 4 2 2 2 2 4 5% 57%	2200
November	1st to 10th	Day	13% 6% 2 5% 3 2 3 2 4 5% 55%	2057
	11th to 20th	Day	12% 6% 2 3 2 3 3 2 5% 7% 55%	1932
	21st to end	Day	15% 6% 2 4 4 3 3 3 5% 6% 50%	1890
December	1st to 10th	Day	16% 6% 2 4 3 3 3 2 4 5% 52%	3020
	11th to 20th	Day	18% 7% 2 6% 4 3 4 3 5% 5% 42%	3463
	21st to end	Day	21% 6% 2 4 3 3 3 3 5% 6% 45%	4565
January	1st to 10th	Night	13% 5% 2 4 3 3 3 2 3 4 58%	5903
	11th to 20th	Night	12% 6% 2 4 3 3 3 3 4 4 56%	5900
	21st to end	Night	18% 7% 2 4 3 3 3 3 4 5% 47%	6490
February	1st to 10th	Night	16% 6% 2 6% 4 4 3 4 5% 6% 46%	2600
	11th to 20th	Night	22% 6% 2 5% 3 4 3 3 5% 4 43%	2358
	21st to end	Night	15% 7% 2 4 4 3 3 4 5% 7% 46%	1935
March	1st to 10th	Night	18% 6% 2 6% 4 3 4 3 4 5% 45%	4918
	11th to 20th	Night	10% 4 1 4 3 3 4 3 5% 8% 54%	4980
	21st to end	Night	16% 4 2 5% 4 4 4 3 5% 6% 48%	5467
April	1st to 10th	Night	13% 6% 1 5% 4 4 4 3 5% 8% 48%	2200
	11th to 20th	Night	12% 5% 2 5% 4 3 3 4 5% 7% 51%	1985
	21st to end	Night	11% 5% 2 5% 5% 5% 4 3 5% 7% 48%	1851
May	1st to 10th	Night	13% 7% 3 8% 4 4 5% 3 6% 9% 39%	4033
	11th to 20th	Night	19% 7% 2 6% 4 5% 4 4 6% 9% 32%	4032
	21st to end	Night	15% 5% 2 6% 4 4 4 4 6% 9% 41%	4421
June	1st to 10th	Night	9% 6% 2 8% 5% 5% 7% 6% 6% 12% 35%	1800
	11th to 20th	Night	10% 6% 2 6% 6% 6% 6% 5% 6% 11% 37%	1800
	21st to end	Night	7% 5% 2 7% 5% 6% 6% 6% 9% 12% 36%	1800
July	1st to 10th	Night	9% 8% 2 9% 7% 6% 6% 5% 8% 10% 29%	4058
	11th to 20th	Night	7% 6% 3 9% 6% 6% 6% 6% 10% 12% 28%	4057
	21st to end	Night	11% 9% 3 9% 7% 6% 7% 5% 8% 11% 23%	4427
August	1st to 10th	Night	21% 10% 3 7% 5% 5% 5% 5% 6% 10% 23%	2915
	11th to 20th	Night	10% 7% 3 8% 5% 6% 6% 6% 7% 10% 32%	2875
	21st to end	Night	5% 5% 2 7% 5% 5% 4 4 7% 9% 48%	3476
September	1st to 10th	Night	8% 6% 2 6% 4 5% 5% 4 6% 9% 44%	2175
	11th to 20th	Night	15% 7% 2 6% 4 4 6% 4 6% 7% 39%	2200
	21st to end	Night	18% 6% 2 7% 4 5% 5% 3 5% 6% 39%	2200
October	1st to 10th	Night	13% 6% 2 6% 3 3 3 3 4 6% 51%	2318
	11th to 20th	Night	14% 5% 2 4 3 2 3 3 5% 5% 55%	2400
	21st to end	Night	13% 4 2 5% 3 3 2 3 3 4 58%	2640
November	1st to 10th	Night	13% 6% 2 5% 3 4 2 2 4 6% 53%	2461
	11th to 20th	Night	13% 5% 2 4 3 3 4 3 4 5% 53%	2685
	21st to end	Night	13% 5% 1 4 4 3 5% 3 5% 6% 51%	2730
December	1st to 10th	Night	17% 6% 2 5% 3 3 3 2 4 5% 51%	4380
	11th to 20th	Night	19% 8% 3 6% 3 3 3 3 4 5% 43%	4952
	21st to end	Night	21% 4 2 4 3 3 4 3 4 6% 47%	6633

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	35% 2 4 20% 32% 8%	4066
	11th to 20th	Day	32% 2 4 16% 37% 9%	4060
	21st to end	Day	43% 2 3 19% 24% 9%	4466
February	1st to 10th	Day	39% 4 10% 23% 20% 5%	1800
	11th to 20th	Day	43% 3 6% 20% 21% 6%	1935
	21st to end	Day	45% 2 6% 17% 22% 8%	1694
March	1st to 10th	Day	46% 2 5% 16% 19% 12%	4935
	11th to 20th	Day	32% 2 7% 15% 26% 18%	4980
	21st to end	Day	42% 3 5% 24% 21% 5%	5465
April	1st to 10th	Day	32% 3 11% 23% 25% 6%	2200
	11th to 20th	Day	36% 3 9% 22% 22% 9%	2364
	21st to end	Day	36% 3 11% 26% 19% 4	2565
May	1st to 10th	Day	42% 5% 19% 21% 12% 1	5897
	11th to 20th	Day	51% 4 14% 19% 11% 1	5865
	21st to end	Day	39% 4 14% 22% 18% 4	6447
June	1st to 10th	Day	38% 6% 16% 27% 13% 1	2600
	11th to 20th	Day	34% 7% 20% 23% 15% 1	2600
	21st to end	Day	33% 8% 18% 25% 15% 2	2600
July	1st to 10th	Day	39% 7% 18% 24% 11% 1	5835
	11th to 20th	Day	37% 10% 33% 17% 4	5831
	21st to end	Day	44% 8% 18% 22% 7% 1	6240
August	1st to 10th	Day	50% 6% 19% 20% 5%	4221
	11th to 20th	Day	39% 6% 21% 21% 11% 2	4213
	21st to end	Day	27% 6% 16% 35% 15% 2	4388
September	1st to 10th	Day	33% 7% 15% 22% 19% 4	2220
	11th to 20th	Day	38% 5% 14% 21% 20% 3	2200
	21st to end	Day	45% 4 11% 20% 17% 4	2200
October	1st to 10th	Day	30% 3 7% 22% 28% 10%	3392
	11th to 20th	Day	21% 2 5% 20% 28% 24%	3240
	21st to end	Day	27% 3 5% 26% 25% 15%	3538
November	1st to 10th	Day	34% 2 6% 21% 28% 8%	2057
	11th to 20th	Day	31% 2 7% 25% 27% 7%	1932
	21st to end	Day	36% 3 7% 23% 24% 7%	1890
December	1st to 10th	Day	36% 2 6% 20% 27% 8%	3020
	11th to 20th	Day	45% 3 8% 16% 21% 6%	3460
	21st to end	Day	41% 2 8% 29% 18% 2	4565
January	1st to 10th	Night	32% 2 5% 17% 35% 9%	5903
	11th to 20th	Night	34% 2 4 16% 37% 8%	5900
	21st to end	Night	40% 2 4 19% 26% 9%	6490
February	1st to 10th	Night	39% 3 9% 22% 21% 6%	2600
	11th to 20th	Night	45% 2 7% 16% 23% 6%	2359
	21st to end	Night	39% 2 10% 19% 23% 7%	1935
March	1st to 10th	Night	43% 2 6% 13% 28% 9%	4918
	11th to 20th	Night	29% 2 6% 15% 28% 18%	4980
	21st to end	Night	39% 3 6% 25% 21% 7%	5467
April	1st to 10th	Night	36% 3 9% 21% 24% 6%	2200
	11th to 20th	Night	33% 3 8% 23% 24% 9%	1985
	21st to end	Night	37% 4 12% 23% 21% 4	1851
May	1st to 10th	Night	43% 4 16% 21% 14% 1	4060
	11th to 20th	Night	50% 5% 14% 19% 11% 1	4033
	21st to end	Night	40% 4 12% 26% 16% 2	4429
June	1st to 10th	Night	42% 7% 15% 22% 12% 2	1800
	11th to 20th	Night	41% 7% 17% 23% 11% 2	1800
	21st to end	Night	37% 9% 16% 21% 13% 4	1800
July	1st to 10th	Night	47% 8% 18% 16% 9% 1	4015
	11th to 20th	Night	44% 12% 26% 14% 3 1	4006
	21st to end	Night	52% 9% 18% 17% 5%	4297
August	1st to 10th	Night	55% 5% 20% 14% 5%	2904
	11th to 20th	Night	45% 7% 23% 15% 9% 1	2902
	21st to end	Night	31% 6% 13% 29% 19% 2	3476
September	1st to 10th	Night	36% 6% 15% 20% 18% 5%	2175
	11th to 20th	Night	43% 6% 11% 17% 21% 2	2200
	21st to end	Night	46% 4 12% 17% 17% 4	2200
October	1st to 10th	Night	36% 4 8% 19% 25% 7%	3786
	11th to 20th	Night	23% 1 6% 20% 28% 21%	3899
	21st to end	Night	29% 2 5% 21% 28% 15%	4252
November	1st to 10th	Night	35% 2 7% 20% 25% 10%	2461
	11th to 20th	Night	34% 2 7% 19% 27% 12%	2685
	21st to end	Night	34% 3 6% 22% 27% 7%	2730
December	1st to 10th	Night	37% 2 6% 20% 26% 8%	4380
	11th to 20th	Night	45% 3 8% 16% 18% 9%	4954
	21st to end	Night	40% 2 11% 23% 22% 2	6633

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	20% 17% 36% 23% 4	303
	11th to 20th	Day	23% 18% 32% 19% 6% 1	300
	21st to end	Day	22% 16% 38% 17% 6%	330
February	1st to 10th	Day	20% 18% 35% 20% 7% 1	300
	11th to 20th	Day	36% 13% 35% 12% 4	300
	21st to end	Day	26% 16% 34% 20% 4	293
March	1st to 10th	Day	24% 12% 30% 25% 7% 1	500
	11th to 20th	Day	20% 12% 39% 22% 7%	500
	21st to end	Day	23% 11% 35% 23% 7% 1	550
April	1st to 10th	Day	19% 13% 33% 20% 12% 2	500
	11th to 20th	Day	16% 12% 31% 24% 15% 3	492
	21st to end	Day	17% 7% 29% 26% 16% 5%	500
May	1st to 10th	Day	10% 11% 36% 23% 16% 4	503
	11th to 20th	Day	19% 4 18% 26% 23% 9%	527
	21st to end	Day	16% 4 14% 22% 28% 16%	573
June	1st to 10th	Day	12% 3 13% 32% 29% 11%	530
	11th to 20th	Day	11% 2 15% 27% 26% 19%	530
	21st to end	Day	9% 2 9% 28% 34% 18%	530
July	1st to 10th	Day	10% 2 8% 21% 33% 26%	525
	11th to 20th	Day	7% 1 5% 28% 34% 26%	524
	21st to end	Day	7% 1 7% 25% 39% 21%	576
August	1st to 10th	Day	17% 2 10% 24% 29% 18%	526
	11th to 20th	Day	12% 3 6% 29% 28% 23%	519
	21st to end	Day	12% 2 7% 25% 29% 25%	583
September	1st to 10th	Day	12% 2 10% 24% 30% 22%	530
	11th to 20th	Day	15% 3 12% 20% 31% 20%	530
	21st to end	Day	21% 3 18% 23% 26% 8%	530
October	1st to 10th	Day	16% 4 20% 25% 24% 12%	530
	11th to 20th	Day	13% 5% 22% 29% 23% 7%	530
	21st to end	Day	19% 6% 19% 30% 19% 7%	583
November	1st to 10th	Day	21% 5% 22% 31% 16% 4	535
	11th to 20th	Day	17% 10% 32% 30% 9% 3	372
	21st to end	Day	13% 9% 34% 29% 12% 3	330
December	1st to 10th	Day	28% 7% 35% 22% 8% 1	330
	11th to 20th	Day	21% 11% 32% 25% 10% 2	330
	21st to end	Day	24% 12% 32% 22% 8% 2	363
January	1st to 10th	Night	21% 12% 31% 28% 7%	805
	11th to 20th	Night	20% 11% 32% 31% 5%	800
	21st to end	Night	19% 9% 36% 33% 3	880
February	1st to 10th	Night	19% 9% 33% 35% 4	800
	11th to 20th	Night	25% 10% 40% 23% 2	783
	21st to end	Night	20% 12% 36% 28% 3	660
March	1st to 10th	Night	17% 11% 31% 35% 6%	800
	11th to 20th	Night	17% 11% 34% 30% 8% 1	800
	21st to end	Night	22% 9% 33% 29% 7%	880
April	1st to 10th	Night	17% 11% 33% 30% 9%	800
	11th to 20th	Night	13% 13% 29% 29% 15%	791
	21st to end	Night	14% 6% 25% 37% 17%	651
May	1st to 10th	Night	13% 6% 27% 36% 18% 1	600
	11th to 20th	Night	16% 5% 20% 36% 23% 2	591
	21st to end	Night	17% 3 9% 33% 34% 3	650
June	1st to 10th	Night	12% 2 10% 41% 31% 4	600
	11th to 20th	Night	13% 3 11% 30% 34% 10%	600
	21st to end	Night	9% 2 9% 33% 41% 6%	600
July	1st to 10th	Night	11% 3 5% 28% 44% 9%	585
	11th to 20th	Night	8% 2 5% 29% 46% 10%	582
	21st to end	Night	8% 2 6% 33% 45% 7%	657
August	1st to 10th	Night	15% 3 5% 30% 38% 9%	597
	11th to 20th	Night	13% 3 5% 30% 40% 9%	594
	21st to end	Night	11% 4 6% 24% 47% 7%	809
September	1st to 10th	Night	10% 2 9% 30% 42% 8%	800
	11th to 20th	Night	17% 3 11% 25% 37% 8%	800
	21st to end	Night	20% 4 13% 31% 29% 3	800
October	1st to 10th	Night	16% 4 17% 30% 28% 6%	800
	11th to 20th	Night	16% 5% 21% 35% 21% 3	800
	21st to end	Night	14% 5% 22% 35% 22% 2	880
November	1st to 10th	Night	16% 5% 22% 36% 18% 3	820
	11th to 20th	Night	15% 8% 29% 36% 12% 1	840
	21st to end	Night	15% 7% 29% 36% 13% 1	840
December	1st to 10th	Night	24% 8% 26% 35% 8%	840
	11th to 20th	Night	21% 7% 25% 37% 9%	840
	21st to end	Night	24% 9% 24% 33% 9%	924

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