AstroDNA Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the AstroDNA 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	16% 7% 3 7% 5% 4 5% 4 6% 7% 37%	101375
	Night	16% 8% 3 6% 4 4 4 4 5% 7% 40%	97685
Transparency	Day	45% 3 11% 24% 15% 2	104907
	Night	44% 3 11% 25% 15% 2	102242
Seeing	Day	23% 16% 29% 20% 9% 3	14931
	Night	21% 15% 30% 25% 9% 1	24064

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	14% 9% 2 5% 4 4 5% 3 5% 5% 44%	2517
	11th to 20th	Day	14% 10% 4 8% 6% 5% 5% 4 5% 6% 34%	2520
	21st to end	Day	22% 13% 4 7% 4 4 4 2 4 5% 30%	3007
February	1st to 10th	Day	16% 8% 3 7% 5% 5% 5% 4 6% 6% 35%	1710
	11th to 20th	Day	14% 8% 3 7% 4 4 4 4 4 7% 40%	1824
	21st to end	Day	17% 10% 2 7% 4 4 4 4 5% 6% 37%	1570
March	1st to 10th	Day	25% 9% 3 7% 4 3 3 2 4 5% 33%	3116
	11th to 20th	Day	10% 7% 3 7% 5% 5% 5% 4 6% 8% 40%	3372
	21st to end	Day	20% 7% 2 6% 4 4 3 3 4 6% 40%	4120
April	1st to 10th	Day	18% 9% 2 6% 4 4 4 4 5% 7% 37%	2280
	11th to 20th	Day	17% 7% 2 6% 5% 4 4 3 4 7% 40%	2254
	21st to end	Day	18% 7% 2 7% 5% 4 5% 3 5% 6% 38%	2298
May	1st to 10th	Day	26% 8% 2 6% 5% 3 4 4 4 7% 31%	4156
	11th to 20th	Day	21% 9% 2 7% 5% 5% 5% 4 5% 7% 30%	4398
	21st to end	Day	12% 5% 2 6% 3 4 4 4 7% 10% 42%	4837
June	1st to 10th	Day	15% 6% 2 6% 5% 5% 6% 4 6% 9% 36%	2660
	11th to 20th	Day	15% 6% 2 7% 4 5% 5% 5% 8% 9% 35%	2660
	21st to end	Day	12% 7% 2 7% 5% 5% 5% 4 7% 9% 38%	2660
July	1st to 10th	Day	9% 6% 3 8% 6% 7% 7% 5% 7% 10% 33%	4440
	11th to 20th	Day	9% 6% 3 6% 5% 5% 5% 5% 7% 11% 37%	4440
	21st to end	Day	13% 8% 3 8% 5% 5% 5% 4 6% 7% 34%	4814
August	1st to 10th	Day	19% 6% 3 8% 5% 5% 6% 4 7% 7% 31%	4219
	11th to 20th	Day	10% 7% 3 6% 4 4 5% 4 6% 9% 41%	3730
	21st to end	Day	12% 6% 2 5% 3 3 4 3 5% 10% 46%	4180
September	1st to 10th	Day	14% 6% 2 6% 5% 5% 5% 4 5% 7% 43%	2280
	11th to 20th	Day	13% 5% 2 5% 4 3 4 4 5% 7% 48%	2214
	21st to end	Day	17% 6% 2 6% 4 4 4 4 6% 7% 40%	2090
October	1st to 10th	Day	19% 6% 3 6% 4 4 4 3 4 7% 39%	1957
	11th to 20th	Day	13% 6% 2 6% 4 4 5% 3 5% 7% 45%	1900
	21st to end	Day	20% 6% 2 6% 4 4 4 4 5% 6% 38%	1947
November	1st to 10th	Day	14% 7% 2 5% 4 3 3 2 4 6% 52%	1708
	11th to 20th	Day	17% 6% 2 4 5% 4 4 3 4 7% 43%	1710
	21st to end	Day	16% 8% 2 5% 5% 4 3 4 6% 6% 40%	1589
December	1st to 10th	Day	17% 8% 3 8% 6% 4 5% 3 6% 7% 35%	1520
	11th to 20th	Day	21% 7% 2 5% 3 4 3 3 5% 7% 40%	1906
	21st to end	Day	17% 9% 4 10% 6% 5% 5% 4 5% 6% 27%	2772
January	1st to 10th	Night	16% 8% 3 5% 4 4 4 3 5% 6% 43%	4429
	11th to 20th	Night	14% 9% 3 8% 5% 5% 4 3 5% 6% 38%	4440
	21st to end	Night	21% 12% 3 6% 5% 4 4 3 5% 6% 31%	4646
February	1st to 10th	Night	15% 9% 3 6% 4 4 4 3 5% 7% 40%	2470
	11th to 20th	Night	15% 8% 3 7% 5% 4 4 5% 5% 6% 39%	2240
	21st to end	Night	18% 8% 3 6% 5% 4 3 4 4 5% 41%	1884
March	1st to 10th	Night	23% 11% 3 7% 4 3 3 3 4 6% 33%	3724
	11th to 20th	Night	11% 9% 3 6% 4 4 5% 4 6% 7% 41%	3585
	21st to end	Night	16% 10% 3 7% 5% 3 4 3 5% 6% 38%	3512
April	1st to 10th	Night	18% 7% 3 7% 5% 4 5% 4 6% 7% 35%	1900
	11th to 20th	Night	17% 8% 3 6% 4 4 4 4 5% 7% 39%	1875
	21st to end	Night	19% 7% 2 6% 4 3 3 4 5% 6% 40%	1881
May	1st to 10th	Night	26% 8% 3 7% 3 3 4 3 5% 8% 31%	2812
	11th to 20th	Night	22% 9% 3 7% 4 4 3 4 5% 6% 33%	2495
	21st to end	Night	12% 7% 2 6% 4 4 4 4 7% 8% 41%	2738
June	1st to 10th	Night	15% 5% 2 5% 5% 4 4 3 6% 9% 42%	1520
	11th to 20th	Night	13% 6% 2 5% 4 5% 4 4 7% 9% 42%	1520
	21st to end	Night	11% 4 2 5% 4 4 5% 4 5% 10% 45%	1520
July	1st to 10th	Night	9% 6% 2 7% 5% 5% 5% 5% 7% 9% 39%	2520
	11th to 20th	Night	10% 5% 2 6% 5% 5% 6% 4 6% 10% 39%	2520
	21st to end	Night	14% 7% 2 6% 5% 4 5% 4 6% 8% 37%	2739
August	1st to 10th	Night	19% 7% 2 7% 5% 5% 5% 4 6% 8% 33%	2686
	11th to 20th	Night	13% 7% 3 8% 5% 4 5% 3 5% 6% 41%	3088
	21st to end	Night	10% 5% 2 5% 4 4 4 3 5% 7% 50%	3476
September	1st to 10th	Night	14% 6% 2 6% 3 4 3 3 5% 7% 47%	1900
	11th to 20th	Night	13% 6% 2 4 3 3 3 3 4 6% 53%	1966
	21st to end	Night	16% 6% 3 6% 4 4 4 3 4 7% 45%	2090
October	1st to 10th	Night	20% 6% 2 6% 3 4 3 3 5% 6% 42%	2219
	11th to 20th	Night	14% 6% 1 6% 4 3 4 3 4 7% 48%	2280
	21st to end	Night	21% 6% 2 4 3 3 3 4 5% 7% 42%	2650
November	1st to 10th	Night	11% 6% 3 7% 4 3 4 3 6% 6% 48%	2470
	11th to 20th	Night	18% 7% 2 6% 4 3 3 3 4 6% 44%	2470
	21st to end	Night	14% 7% 2 5% 4 4 5% 3 5% 7% 43%	2588
December	1st to 10th	Night	18% 8% 3 6% 3 4 4 4 5% 7% 37%	2660
	11th to 20th	Night	18% 9% 3 6% 4 4 4 4 5% 6% 37%	3288
	21st to end	Night	20% 10% 3 8% 5% 4 5% 3 5% 6% 32%	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	42% 2 9% 35% 9% 3	2518
	11th to 20th	Day	53% 2 9% 23% 10% 2	2520
	21st to end	Day	57% 2 9% 21% 9% 1	3007
February	1st to 10th	Day	50% 3 11% 22% 13% 1	1710
	11th to 20th	Day	46% 3 8% 24% 17% 3	1833
	21st to end	Day	49% 2 9% 24% 14% 2	1570
March	1st to 10th	Day	55% 1 9% 22% 10% 2	3119
	11th to 20th	Day	43% 2 10% 32% 12% 1	3372
	21st to end	Day	46% 2 6% 17% 24% 4	4120
April	1st to 10th	Day	48% 3 8% 22% 15% 4	2280
	11th to 20th	Day	45% 3 10% 22% 17% 3	2254
	21st to end	Day	47% 3 8% 23% 15% 4	2298
May	1st to 10th	Day	55% 2 12% 17% 13% 2	4170
	11th to 20th	Day	56% 2 11% 20% 9% 2	4402
	21st to end	Day	38% 3 12% 29% 17% 2	4837
June	1st to 10th	Day	45% 4 12% 23% 15% 1	2660
	11th to 20th	Day	44% 5% 12% 27% 11% 2	2660
	21st to end	Day	42% 4 12% 25% 15% 1	2660
July	1st to 10th	Day	45% 6% 11% 22% 14% 1	4370
	11th to 20th	Day	40% 6% 16% 24% 14% 1	4365
	21st to end	Day	49% 4 11% 20% 15% 2	4661
August	1st to 10th	Day	51% 4 13% 21% 10%	4205
	11th to 20th	Day	40% 4 16% 29% 11% 1	3766
	21st to end	Day	36% 4 10% 33% 16% 2	4180
September	1st to 10th	Day	41% 4 11% 25% 18% 2	2280
	11th to 20th	Day	36% 3 8% 26% 25% 3	2214
	21st to end	Day	45% 4 9% 22% 18% 3	2090
October	1st to 10th	Day	41% 3 7% 21% 24% 4	3256
	11th to 20th	Day	31% 4 9% 30% 24% 3	3140
	21st to end	Day	30% 2 16% 27% 21% 4	3185
November	1st to 10th	Day	37% 3 12% 26% 19% 3	1708
	11th to 20th	Day	42% 2 10% 25% 19% 3	1710
	21st to end	Day	44% 2 13% 29% 11% 2	1589
December	1st to 10th	Day	49% 3 14% 19% 13% 1	1520
	11th to 20th	Day	46% 2 16% 23% 11% 2	1906
	21st to end	Day	57% 3 10% 22% 7%	2772
January	1st to 10th	Night	43% 1 11% 30% 12% 3	4429
	11th to 20th	Night	48% 2 10% 25% 12% 2	4440
	21st to end	Night	54% 1 9% 23% 11% 1	4646
February	1st to 10th	Night	45% 3 14% 24% 12% 2	2470
	11th to 20th	Night	45% 4 9% 20% 18% 4	2242
	21st to end	Night	46% 2 7% 25% 16% 4	1884
March	1st to 10th	Night	54% 2 9% 21% 12% 2	3734
	11th to 20th	Night	43% 2 13% 27% 13% 2	3586
	21st to end	Night	48% 3 6% 17% 21% 6%	3512
April	1st to 10th	Night	49% 3 9% 22% 15% 3	1900
	11th to 20th	Night	46% 3 9% 21% 20% 1	1875
	21st to end	Night	45% 3 8% 23% 17% 4	1881
May	1st to 10th	Night	54% 3 9% 21% 11% 1	2818
	11th to 20th	Night	54% 2 14% 18% 11% 1	2496
	21st to end	Night	40% 4 15% 27% 12% 2	2739
June	1st to 10th	Night	41% 4 10% 25% 19% 1	1520
	11th to 20th	Night	39% 5% 16% 30% 10% 1	1520
	21st to end	Night	35% 5% 16% 27% 16% 1	1520
July	1st to 10th	Night	39% 7% 16% 21% 14% 2	2480
	11th to 20th	Night	41% 5% 14% 26% 13% 1	2472
	21st to end	Night	44% 5% 14% 18% 18% 2	2651
August	1st to 10th	Night	49% 6% 16% 19% 9% 1	2676
	11th to 20th	Night	45% 4 14% 28% 9%	3118
	21st to end	Night	32% 4 12% 35% 16% 1	3476
September	1st to 10th	Night	39% 4 10% 27% 19% 1	1900
	11th to 20th	Night	33% 2 11% 26% 26% 2	1966
	21st to end	Night	41% 3 8% 24% 22% 1	2090
October	1st to 10th	Night	42% 4 10% 24% 19% 1	3700
	11th to 20th	Night	28% 2 10% 30% 27% 3	3779
	21st to end	Night	32% 3 15% 31% 19% 1	4362
November	1st to 10th	Night	38% 3 11% 23% 21% 2	2470
	11th to 20th	Night	43% 2 9% 24% 18% 4	2470
	21st to end	Night	41% 3 13% 31% 11% 1	2588
December	1st to 10th	Night	47% 3 12% 24% 13% 1	2660
	11th to 20th	Night	48% 2 12% 20% 15% 3	3288
	21st to end	Night	54% 2 11% 22% 10%	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	32% 21% 29% 15% 3	180
	11th to 20th	Day	36% 21% 29% 12% 1	180
	21st to end	Day	25% 27% 31% 12% 2 2	267
February	1st to 10th	Day	33% 26% 31% 9% 1	270
	11th to 20th	Day	31% 29% 31% 8% 2	432
	21st to end	Day	32% 20% 34% 11% 3	382
March	1st to 10th	Day	29% 23% 29% 15% 4	460
	11th to 20th	Day	26% 28% 29% 13% 3 1	460
	21st to end	Day	32% 21% 30% 11% 4 2	506
April	1st to 10th	Day	32% 19% 30% 12% 6% 1	460
	11th to 20th	Day	27% 23% 31% 11% 6% 2	452
	21st to end	Day	29% 18% 31% 13% 8% 1	460
May	1st to 10th	Day	35% 16% 25% 16% 6% 2	463
	11th to 20th	Day	21% 16% 34% 18% 9% 2	487
	21st to end	Day	18% 11% 27% 30% 12% 2	529
June	1st to 10th	Day	18% 13% 31% 24% 11% 2	490
	11th to 20th	Day	17% 11% 31% 27% 12% 1	490
	21st to end	Day	17% 12% 31% 28% 11% 2	490
July	1st to 10th	Day	15% 7% 29% 28% 16% 5%	485
	11th to 20th	Day	12% 5% 30% 32% 18% 3	484
	21st to end	Day	12% 8% 33% 32% 12% 2	532
August	1st to 10th	Day	13% 7% 30% 29% 15% 7%	486
	11th to 20th	Day	15% 6% 26% 32% 14% 7%	479
	21st to end	Day	15% 9% 25% 28% 16% 7%	539
September	1st to 10th	Day	18% 12% 24% 23% 16% 7%	490
	11th to 20th	Day	15% 7% 29% 23% 14% 12%	490
	21st to end	Day	23% 10% 27% 24% 11% 5%	490
October	1st to 10th	Day	27% 10% 26% 18% 14% 6%	490
	11th to 20th	Day	18% 17% 31% 21% 12% 2	490
	21st to end	Day	25% 14% 32% 17% 10% 1	463
November	1st to 10th	Day	19% 16% 29% 23% 10% 2	378
	11th to 20th	Day	25% 24% 26% 19% 5% 1	370
	21st to end	Day	27% 22% 28% 18% 4 1	249
December	1st to 10th	Day	29% 28% 27% 10% 6%	180
	11th to 20th	Day	37% 22% 29% 10% 2	180
	21st to end	Day	25% 23% 34% 12% 5% 1	198
January	1st to 10th	Night	21% 25% 35% 17% 3	760
	11th to 20th	Night	25% 21% 31% 20% 4	760
	21st to end	Night	20% 23% 35% 19% 2	836
February	1st to 10th	Night	24% 19% 36% 20% 1	760
	11th to 20th	Night	25% 27% 34% 13% 1	743
	21st to end	Night	29% 21% 32% 15% 3	628
March	1st to 10th	Night	26% 22% 31% 18% 4	760
	11th to 20th	Night	24% 24% 31% 18% 3 1	760
	21st to end	Night	23% 22% 33% 17% 5% 1	836
April	1st to 10th	Night	24% 21% 33% 18% 4	760
	11th to 20th	Night	23% 17% 33% 21% 5%	751
	21st to end	Night	23% 17% 30% 24% 5%	741
May	1st to 10th	Night	27% 14% 31% 23% 4	561
	11th to 20th	Night	23% 11% 36% 24% 7% 1	374
	21st to end	Night	16% 7% 26% 39% 11% 2	411
June	1st to 10th	Night	18% 5% 28% 37% 10% 1	380
	11th to 20th	Night	14% 7% 30% 34% 14% 1	380
	21st to end	Night	12% 5% 31% 41% 11%	380
July	1st to 10th	Night	14% 3 21% 42% 19% 2	370
	11th to 20th	Night	13% 2 25% 42% 16% 1	368
	21st to end	Night	12% 4 26% 40% 17% 1	416
August	1st to 10th	Night	12% 1 23% 44% 18% 1	480
	11th to 20th	Night	15% 3 21% 36% 23% 1	741
	21st to end	Night	16% 3 20% 37% 22% 2	836
September	1st to 10th	Night	16% 5% 24% 36% 18% 2	760
	11th to 20th	Night	16% 5% 24% 29% 21% 4	760
	21st to end	Night	19% 6% 25% 31% 17% 2	760
October	1st to 10th	Night	22% 10% 26% 26% 15% 2	760
	11th to 20th	Night	18% 12% 33% 28% 9%	760
	21st to end	Night	25% 12% 33% 22% 7%	836
November	1st to 10th	Night	16% 15% 34% 24% 9% 1	760
	11th to 20th	Night	22% 19% 30% 21% 7% 1	760
	21st to end	Night	20% 20% 33% 20% 6% 1	760
December	1st to 10th	Night	27% 19% 31% 18% 6%	760
	11th to 20th	Night	23% 21% 32% 20% 4	760
	21st to end	Night	27% 20% 35% 16% 3	836

Page generated at 2024-11-03 02:11:18. Version ac07

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