The Rose Dorothea Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Rose Dorothea Observatory clear sky chart from 2005-11-06 to 2024-11-05.

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	17% 9% 3 7% 4 4 4 3 5% 7% 38%	101163
	Night	18% 10% 3 7% 4 4 4 3 5% 6% 35%	97876
Transparency	Day	45% 4 12% 23% 14% 2	104731
	Night	49% 4 11% 21% 14% 2	102397
Seeing	Day	21% 7% 24% 30% 15% 3	15206
	Night	23% 9% 25% 28% 13% 2	24019

By Month

Percentage Cloud Cover NE (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	16% 10% 3 8% 5% 4 3 3 4 5% 39%	2517
	11th to 20th	Day	20% 13% 3 6% 3 3 3 3 5% 5% 37%	2520
	21st to end	Day	23% 13% 3 13% 6% 4 3 3 4 5% 24%	2842
February	1st to 10th	Day	21% 9% 5% 8% 5% 4 4 4 5% 6% 28%	1771
	11th to 20th	Day	15% 9% 4 7% 5% 5% 5% 4 5% 6% 35%	1848
	21st to end	Day	18% 10% 3 10% 5% 4 4 3 6% 6% 32%	1570
March	1st to 10th	Day	24% 15% 4 8% 4 3 3 3 4 5% 28%	3116
	11th to 20th	Day	13% 8% 3 7% 4 4 3 3 5% 7% 44%	3416
	21st to end	Day	25% 10% 2 6% 4 4 3 3 3 4 35%	3896
April	1st to 10th	Day	20% 9% 3 6% 3 2 3 3 5% 6% 41%	2280
	11th to 20th	Day	18% 8% 2 5% 3 3 4 3 5% 7% 42%	2315
	21st to end	Day	18% 7% 1 6% 4 3 5% 3 5% 6% 41%	2470
May	1st to 10th	Day	24% 12% 4 9% 5% 3 4 3 4 6% 27%	4106
	11th to 20th	Day	23% 11% 3 6% 4 3 3 3 4 7% 33%	4081
	21st to end	Day	14% 7% 3 6% 3 3 4 3 5% 7% 45%	4725
June	1st to 10th	Day	18% 7% 2 5% 3 3 5% 4 7% 8% 36%	2660
	11th to 20th	Day	15% 7% 2 6% 4 4 4 3 5% 9% 41%	2660
	21st to end	Day	15% 6% 2 6% 4 4 5% 4 6% 8% 40%	2660
July	1st to 10th	Day	11% 8% 3 7% 5% 5% 4 4 7% 9% 38%	4440
	11th to 20th	Day	10% 6% 2 6% 5% 5% 5% 4 7% 11% 40%	4440
	21st to end	Day	17% 6% 2 7% 4 4 4 3 6% 7% 40%	4701
August	1st to 10th	Day	15% 7% 2 6% 5% 5% 5% 4 6% 7% 37%	4105
	11th to 20th	Day	12% 8% 2 7% 4 5% 5% 4 5% 7% 41%	4045
	21st to end	Day	8% 4 2 4 3 3 4 4 6% 8% 54%	4250
September	1st to 10th	Day	13% 6% 2 5% 3 3 4 4 4 6% 49%	2223
	11th to 20th	Day	14% 6% 2 4 3 4 3 3 4 5% 52%	2090
	21st to end	Day	18% 7% 3 6% 4 3 3 3 5% 7% 41%	2090
October	1st to 10th	Day	20% 6% 2 5% 3 3 3 3 4 6% 44%	2090
	11th to 20th	Day	14% 7% 2 5% 4 3 3 3 5% 7% 47%	1886
	21st to end	Day	18% 8% 2 6% 3 3 3 3 6% 7% 41%	1881
November	1st to 10th	Day	19% 7% 3 5% 4 2 3 3 4 7% 43%	1708
	11th to 20th	Day	18% 11% 2 5% 3 2 4 3 5% 7% 39%	1710
	21st to end	Day	18% 8% 3 6% 4 3 4 3 5% 8% 38%	1710
December	1st to 10th	Day	19% 13% 3 8% 5% 4 3 3 5% 6% 30%	1663
	11th to 20th	Day	20% 12% 5% 8% 4 4 3 3 4 6% 31%	1906
	21st to end	Day	23% 15% 4 8% 5% 4 3 3 5% 6% 25%	2772
January	1st to 10th	Night	20% 9% 4 7% 3 3 3 2 4 4 41%	4429
	11th to 20th	Night	17% 12% 5% 10% 4 3 3 3 4 4 34%	4440
	21st to end	Night	23% 16% 6% 11% 6% 4 3 3 3 4 22%	4811
February	1st to 10th	Night	17% 12% 4 8% 6% 5% 5% 4 6% 5% 29%	2409
	11th to 20th	Night	19% 11% 3 8% 5% 4 4 3 4 6% 33%	2218
	21st to end	Night	18% 10% 3 6% 5% 4 4 3 5% 7% 35%	1884
March	1st to 10th	Night	32% 11% 3 5% 3 3 3 3 4 5% 28%	3724
	11th to 20th	Night	12% 10% 3 7% 5% 5% 5% 4 6% 6% 37%	3527
	21st to end	Night	27% 10% 3 7% 5% 4 4 3 3 4 31%	3732
April	1st to 10th	Night	19% 10% 3 7% 5% 4 4 3 6% 5% 35%	1900
	11th to 20th	Night	18% 9% 2 7% 3 4 4 3 5% 7% 37%	1812
	21st to end	Night	18% 9% 2 6% 5% 5% 5% 3 5% 5% 36%	1710
May	1st to 10th	Night	24% 11% 3 10% 4 4 3 3 4 6% 27%	2834
	11th to 20th	Night	23% 11% 3 8% 4 5% 4 4 5% 7% 24%	2813
	21st to end	Night	17% 8% 3 7% 4 4 5% 4 5% 8% 35%	2878
June	1st to 10th	Night	18% 8% 2 6% 4 4 6% 4 6% 6% 34%	1520
	11th to 20th	Night	18% 9% 2 6% 4 4 4 4 6% 8% 37%	1520
	21st to end	Night	17% 8% 3 6% 4 4 4 3 5% 10% 34%	1520
July	1st to 10th	Night	12% 9% 4 9% 5% 5% 5% 5% 7% 8% 31%	2520
	11th to 20th	Night	11% 8% 3 6% 6% 4 5% 4 7% 10% 36%	2520
	21st to end	Night	17% 9% 3 8% 5% 5% 4 4 6% 7% 33%	2819
August	1st to 10th	Night	16% 8% 3 7% 5% 5% 6% 5% 7% 8% 30%	2825
	11th to 20th	Night	11% 9% 2 7% 4 5% 5% 5% 7% 7% 37%	2782
	21st to end	Night	8% 4 2 4 3 3 3 3 5% 9% 54%	3402
September	1st to 10th	Night	11% 6% 2 6% 5% 4 4 4 4 6% 46%	1957
	11th to 20th	Night	14% 6% 2 5% 3 3 3 3 5% 6% 51%	2090
	21st to end	Night	17% 6% 2 7% 4 4 4 4 6% 5% 41%	2090
October	1st to 10th	Night	21% 8% 3 5% 4 4 3 3 5% 5% 39%	2090
	11th to 20th	Night	16% 5% 2 5% 4 4 4 4 5% 5% 45%	2289
	21st to end	Night	21% 9% 3 7% 4 3 3 3 5% 6% 35%	2717
November	1st to 10th	Night	17% 7% 3 6% 4 3 4 3 4 6% 42%	2470
	11th to 20th	Night	17% 10% 3 6% 4 4 4 3 5% 7% 38%	2470
	21st to end	Night	16% 9% 3 7% 4 4 4 3 4 7% 38%	2470
December	1st to 10th	Night	21% 12% 4 8% 4 4 4 3 5% 6% 29%	2512
	11th to 20th	Night	19% 12% 4 7% 4 3 3 3 5% 7% 32%	3288
	21st to end	Night	20% 14% 4 9% 5% 4 4 3 4 5% 29%	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	48% 4 10% 29% 9% 1	2518
	11th to 20th	Day	50% 4 10% 25% 10% 2	2520
	21st to end	Day	63% 5% 8% 16% 7%	2842
February	1st to 10th	Day	57% 4 11% 16% 11% 1	1771
	11th to 20th	Day	50% 5% 11% 22% 11% 1	1857
	21st to end	Day	53% 4 11% 18% 12% 2	1570
March	1st to 10th	Day	62% 3 9% 15% 10% 1	3119
	11th to 20th	Day	41% 3 14% 25% 14% 3	3416
	21st to end	Day	55% 2 6% 17% 15% 6%	3896
April	1st to 10th	Day	45% 3 8% 20% 20% 3	2280
	11th to 20th	Day	43% 3 11% 24% 17% 3	2315
	21st to end	Day	43% 4 9% 23% 18% 3	2470
May	1st to 10th	Day	61% 3 10% 16% 10% 1	4120
	11th to 20th	Day	53% 2 15% 18% 11% 2	4085
	21st to end	Day	40% 3 12% 24% 20% 1	4725
June	1st to 10th	Day	45% 5% 14% 24% 13%	2660
	11th to 20th	Day	41% 4 14% 24% 15% 1	2660
	21st to end	Day	41% 6% 16% 23% 13% 1	2660
July	1st to 10th	Day	43% 7% 14% 21% 15% 1	4370
	11th to 20th	Day	38% 6% 18% 24% 13% 1	4365
	21st to end	Day	43% 5% 14% 24% 12% 2	4551
August	1st to 10th	Day	45% 5% 18% 23% 8%	4092
	11th to 20th	Day	42% 5% 14% 29% 9%	4084
	21st to end	Day	27% 4 16% 31% 20% 1	4250
September	1st to 10th	Day	36% 4 10% 27% 21% 1	2223
	11th to 20th	Day	35% 3 9% 29% 21% 3	2090
	21st to end	Day	43% 4 8% 24% 19% 2	2090
October	1st to 10th	Day	41% 3 13% 25% 17% 2	3480
	11th to 20th	Day	33% 2 8% 31% 23% 3	3102
	21st to end	Day	32% 3 13% 34% 16% 2	3081
November	1st to 10th	Day	44% 4 13% 23% 15% 2	1708
	11th to 20th	Day	45% 4 11% 22% 17% 1	1710
	21st to end	Day	45% 6% 14% 25% 10% 1	1710
December	1st to 10th	Day	54% 4 13% 15% 13% 1	1663
	11th to 20th	Day	56% 4 13% 15% 10% 2	1906
	21st to end	Day	60% 5% 12% 15% 7% 1	2772
January	1st to 10th	Night	49% 3 10% 28% 8% 2	4429
	11th to 20th	Night	54% 4 9% 22% 10% 1	4440
	21st to end	Night	68% 2 7% 15% 7%	4811
February	1st to 10th	Night	57% 3 11% 18% 9% 1	2409
	11th to 20th	Night	55% 3 8% 21% 12% 1	2220
	21st to end	Night	49% 3 9% 24% 12% 3	1884
March	1st to 10th	Night	61% 2 9% 17% 10% 2	3734
	11th to 20th	Night	48% 3 12% 18% 18% 2	3528
	21st to end	Night	60% 2 5% 12% 15% 6%	3732
April	1st to 10th	Night	51% 3 8% 19% 16% 3	1900
	11th to 20th	Night	48% 3 7% 21% 18% 2	1812
	21st to end	Night	50% 3 8% 20% 17% 3	1710
May	1st to 10th	Night	60% 2 12% 17% 7% 2	2840
	11th to 20th	Night	59% 3 14% 14% 7% 2	2814
	21st to end	Night	48% 3 12% 21% 15% 1	2879
June	1st to 10th	Night	49% 5% 13% 21% 11% 1	1520
	11th to 20th	Night	46% 3 10% 24% 16% 1	1520
	21st to end	Night	46% 5% 13% 23% 13% 1	1520
July	1st to 10th	Night	50% 6% 10% 18% 16%	2480
	11th to 20th	Night	42% 6% 15% 24% 11% 1	2472
	21st to end	Night	50% 5% 11% 20% 12% 1	2729
August	1st to 10th	Night	51% 6% 14% 19% 9% 1	2813
	11th to 20th	Night	43% 7% 15% 26% 9%	2809
	21st to end	Night	27% 4 16% 29% 23% 1	3402
September	1st to 10th	Night	39% 4 10% 25% 20% 2	1957
	11th to 20th	Night	35% 4 9% 26% 24% 2	2090
	21st to end	Night	44% 4 7% 23% 20% 2	2090
October	1st to 10th	Night	44% 4 11% 27% 13% 1	3480
	11th to 20th	Night	31% 2 9% 25% 31% 2	3812
	21st to end	Night	37% 2 10% 29% 20% 1	4467
November	1st to 10th	Night	44% 3 11% 23% 15% 3	2470
	11th to 20th	Night	47% 3 10% 21% 16% 3	2470
	21st to end	Night	46% 4 13% 26% 10% 2	2470
December	1st to 10th	Night	58% 4 11% 17% 10%	2512
	11th to 20th	Night	52% 4 12% 17% 14% 1	3288
	21st to end	Night	58% 4 11% 18% 9%	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	29% 14% 30% 21% 6%	180
	11th to 20th	Day	27% 16% 30% 22% 6%	180
	21st to end	Day	22% 12% 37% 21% 6% 1	242
February	1st to 10th	Day	27% 14% 34% 21% 3	399
	11th to 20th	Day	23% 18% 38% 18% 2	456
	21st to end	Day	22% 14% 35% 23% 5% 1	382
March	1st to 10th	Day	25% 12% 35% 22% 6%	460
	11th to 20th	Day	19% 14% 36% 25% 6%	460
	21st to end	Day	25% 10% 34% 20% 8% 3	506
April	1st to 10th	Day	25% 10% 31% 26% 7% 2	460
	11th to 20th	Day	23% 6% 32% 31% 8% 1	452
	21st to end	Day	23% 5% 26% 33% 11% 2	460
May	1st to 10th	Day	29% 3 28% 29% 8% 2	463
	11th to 20th	Day	20% 3 27% 35% 14% 2	487
	21st to end	Day	18% 2 20% 35% 20% 4	529
June	1st to 10th	Day	20% 2 19% 35% 21% 3	490
	11th to 20th	Day	16% 2 20% 40% 18% 4	490
	21st to end	Day	15% 3 19% 39% 21% 4	490
July	1st to 10th	Day	16% 2 12% 36% 27% 7%	485
	11th to 20th	Day	13% 1 12% 37% 32% 5%	484
	21st to end	Day	14% 1 12% 42% 26% 5%	532
August	1st to 10th	Day	13% 1 11% 43% 26% 6%	486
	11th to 20th	Day	16% 2 11% 32% 30% 8%	479
	21st to end	Day	13% 2 13% 36% 25% 11%	539
September	1st to 10th	Day	19% 2 14% 33% 23% 9%	490
	11th to 20th	Day	20% 2 19% 27% 23% 10%	490
	21st to end	Day	22% 3 22% 30% 17% 6%	490
October	1st to 10th	Day	24% 4 19% 29% 20% 4	490
	11th to 20th	Day	17% 7% 29% 27% 18% 3	407
	21st to end	Day	25% 7% 30% 24% 12% 3	429
November	1st to 10th	Day	19% 10% 26% 30% 12% 3	378
	11th to 20th	Day	26% 14% 27% 24% 8% 1	370
	21st to end	Day	20% 15% 28% 27% 8% 1	370
December	1st to 10th	Day	24% 12% 38% 19% 7%	323
	11th to 20th	Day	27% 20% 33% 15% 6%	180
	21st to end	Day	30% 11% 34% 17% 6% 2	198
January	1st to 10th	Night	26% 17% 34% 19% 4	760
	11th to 20th	Night	29% 17% 31% 18% 4	760
	21st to end	Night	25% 17% 33% 20% 4 1	836
February	1st to 10th	Night	26% 16% 32% 24% 3	760
	11th to 20th	Night	26% 18% 37% 16% 3	743
	21st to end	Night	23% 16% 33% 23% 5%	628
March	1st to 10th	Night	25% 14% 31% 23% 6%	760
	11th to 20th	Night	23% 13% 34% 22% 7% 1	760
	21st to end	Night	25% 10% 30% 25% 9% 1	836
April	1st to 10th	Night	25% 9% 31% 28% 7% 1	760
	11th to 20th	Night	22% 7% 32% 31% 8%	688
	21st to end	Night	23% 6% 24% 32% 13% 1	570
May	1st to 10th	Night	29% 2 23% 33% 10% 2	570
	11th to 20th	Night	23% 4 28% 32% 11% 1	562
	21st to end	Night	23% 3 16% 40% 16% 1	499
June	1st to 10th	Night	24% 4 17% 38% 16% 2	380
	11th to 20th	Night	21% 3 13% 43% 17% 3	380
	21st to end	Night	21% 3 14% 42% 19% 1	380
July	1st to 10th	Night	14% 3 11% 42% 29% 2	370
	11th to 20th	Night	15% 2 11% 44% 26% 1	368
	21st to end	Night	17% 1 12% 42% 26% 2	459
August	1st to 10th	Night	11% 2 14% 43% 27% 2	568
	11th to 20th	Night	13% 2 12% 44% 27% 2	562
	21st to end	Night	14% 2 10% 38% 30% 5%	788
September	1st to 10th	Night	15% 2 16% 36% 27% 4	760
	11th to 20th	Night	16% 3 16% 31% 25% 8%	760
	21st to end	Night	21% 3 17% 32% 23% 4	760
October	1st to 10th	Night	25% 5% 19% 27% 20% 4	760
	11th to 20th	Night	20% 7% 28% 28% 15% 3	760
	21st to end	Night	27% 9% 27% 25% 10% 1	836
November	1st to 10th	Night	21% 7% 28% 30% 13% 2	760
	11th to 20th	Night	24% 16% 28% 23% 9% 1	760
	21st to end	Night	21% 21% 27% 23% 7% 1	760
December	1st to 10th	Night	29% 14% 31% 20% 6%	760
	11th to 20th	Night	27% 20% 30% 19% 3	760
	21st to end	Night	26% 16% 34% 19% 4	836

Page generated at 2024-11-03 02:11:16. Version ac07

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