Skyfall Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Skyfall Observatory clear sky chart from 2005-11-06 to 2026-09-29.

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	11% 5% 2 6% 4 5% 5% 4 7% 9% 42%	148696
	Night	11% 6% 2 6% 4 4 5% 4 6% 8% 43%	142707
Transparency	Day	37% 7% 15% 19% 16% 7%	152482
	Night	37% 6% 13% 18% 18% 8%	146992
Seeing	Day	12% 7% 20% 25% 22% 13%	17564
	Night	13% 6% 22% 32% 23% 4	27526

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	12% 6% 3 7% 4 4 4 3 4 7% 48%	5258
	11th to 20th	Day	14% 5% 2 4 2 2 2 3 5% 7% 55%	5280
	21st to end	Day	14% 8% 3 7% 4 4 4 4 5% 7% 41%	6115
February	1st to 10th	Day	14% 7% 3 7% 5% 4 5% 3 6% 6% 42%	2100
	11th to 20th	Day	18% 6% 2 5% 4 4 4 3 5% 6% 44%	2048
	21st to end	Day	15% 7% 2 5% 4 4 3 4 6% 6% 44%	1730
March	1st to 10th	Day	18% 7% 3 6% 4 4 4 4 5% 6% 39%	4833
	11th to 20th	Day	8% 4 2 4 4 4 4 4 6% 7% 54%	5090
	21st to end	Day	15% 6% 3 6% 4 4 4 3 4 7% 46%	5586
April	1st to 10th	Day	11% 6% 2 5% 5% 4 4 3 6% 6% 48%	2310
	11th to 20th	Day	10% 5% 2 5% 4 3 4 3 5% 7% 54%	2451
	21st to end	Day	7% 4 2 4 4 4 4 4 5% 7% 55%	2682
May	1st to 10th	Day	14% 7% 3 7% 4 4 4 4 5% 8% 40%	7616
	11th to 20th	Day	12% 5% 2 6% 4 4 5% 4 7% 11% 39%	7626
	21st to end	Day	8% 6% 2 7% 5% 6% 6% 5% 7% 9% 38%	8391
June	1st to 10th	Day	11% 5% 2 7% 6% 7% 6% 6% 8% 11% 32%	2730
	11th to 20th	Day	6% 5% 2 5% 5% 5% 5% 6% 8% 11% 42%	2730
	21st to end	Day	5% 5% 2 7% 7% 7% 6% 6% 8% 12% 36%	2730
July	1st to 10th	Day	7% 5% 2 6% 6% 6% 7% 7% 10% 13% 30%	7680
	11th to 20th	Day	4 4 2 6% 5% 6% 7% 7% 9% 14% 37%	7680
	21st to end	Day	5% 5% 2 7% 6% 6% 7% 7% 10% 16% 29%	8340
August	1st to 10th	Day	11% 6% 2 8% 6% 6% 6% 6% 9% 13% 28%	6014
	11th to 20th	Day	4 3 1 5% 4 5% 5% 4 8% 12% 49%	5517
	21st to end	Day	7% 5% 2 7% 5% 5% 6% 5% 8% 12% 36%	5963
September	1st to 10th	Day	9% 5% 2 8% 5% 5% 5% 5% 6% 9% 39%	2310
	11th to 20th	Day	11% 6% 2 7% 4 5% 5% 4 6% 9% 41%	2310
	21st to end	Day	11% 6% 1 7% 6% 5% 5% 3 5% 7% 43%	2288
October	1st to 10th	Day	11% 6% 2 6% 3 3 3 3 5% 6% 51%	2200
	11th to 20th	Day	10% 3 1 4 3 2 3 2 5% 7% 59%	2082
	21st to end	Day	10% 4 2 4 4 3 4 3 5% 6% 56%	2200
November	1st to 10th	Day	12% 6% 2 4 4 3 4 3 5% 6% 53%	1978
	11th to 20th	Day	12% 5% 2 4 4 2 3 2 4 5% 56%	1890
	21st to end	Day	13% 6% 2 5% 4 4 3 3 5% 8% 47%	1890
December	1st to 10th	Day	13% 6% 2 6% 4 3 3 2 4 6% 50%	3020
	11th to 20th	Day	14% 6% 2 5% 3 3 4 3 5% 6% 48%	3463
	21st to end	Day	19% 8% 3 6% 3 2 3 3 4 5% 42%	4565
January	1st to 10th	Night	11% 5% 2 6% 4 4 4 4 6% 7% 48%	7635
	11th to 20th	Night	12% 6% 2 7% 4 4 4 3 4 5% 48%	7680
	21st to end	Night	17% 7% 3 7% 4 4 4 3 5% 7% 40%	8062
February	1st to 10th	Night	13% 7% 3 6% 4 3 4 4 4 6% 47%	2520
	11th to 20th	Night	18% 6% 2 6% 4 3 3 3 4 6% 46%	2458
	21st to end	Night	14% 7% 2 5% 3 4 4 3 6% 6% 46%	2076
March	1st to 10th	Night	19% 7% 2 5% 4 3 4 4 5% 6% 40%	5240
	11th to 20th	Night	9% 4 2 4 3 4 4 4 6% 8% 51%	5090
	21st to end	Night	13% 5% 2 6% 4 4 4 4 5% 6% 48%	5588
April	1st to 10th	Night	11% 5% 2 5% 4 4 4 3 6% 7% 48%	2310
	11th to 20th	Night	10% 4 2 5% 3 4 4 4 5% 9% 51%	2134
	21st to end	Night	6% 4 1 5% 3 4 4 4 6% 7% 55%	1937
May	1st to 10th	Night	13% 7% 3 7% 4 4 5% 4 6% 9% 39%	5237
	11th to 20th	Night	13% 5% 2 6% 4 4 5% 5% 7% 9% 41%	5234
	21st to end	Night	9% 6% 3 8% 5% 5% 5% 5% 7% 11% 36%	5761
June	1st to 10th	Night	9% 6% 2 8% 6% 5% 6% 6% 8% 10% 33%	1890
	11th to 20th	Night	5% 4 2 6% 6% 6% 6% 6% 8% 10% 41%	1890
	21st to end	Night	5% 5% 2 6% 5% 6% 8% 5% 9% 11% 37%	1890
July	1st to 10th	Night	8% 6% 3 8% 6% 7% 6% 5% 9% 13% 28%	5278
	11th to 20th	Night	5% 5% 3 7% 7% 6% 7% 6% 10% 13% 30%	5277
	21st to end	Night	7% 6% 2 8% 6% 6% 7% 6% 9% 15% 28%	5736
August	1st to 10th	Night	11% 7% 3 8% 6% 6% 7% 5% 8% 12% 26%	4135
	11th to 20th	Night	4 3 1 5% 4 5% 5% 5% 9% 14% 44%	4511
	21st to end	Night	7% 5% 2 6% 5% 5% 5% 5% 7% 11% 41%	5114
September	1st to 10th	Night	10% 6% 2 6% 5% 6% 5% 5% 8% 10% 37%	2310
	11th to 20th	Night	11% 6% 3 7% 5% 4 5% 4 5% 7% 42%	2310
	21st to end	Night	9% 6% 3 7% 5% 4 4 5% 7% 8% 44%	2289
October	1st to 10th	Night	10% 6% 2 6% 4 3 4 3 5% 6% 52%	2200
	11th to 20th	Night	11% 4 1 4 3 3 3 3 3 5% 61%	2315
	21st to end	Night	10% 5% 1 4 3 3 4 3 3 5% 57%	2640
November	1st to 10th	Night	11% 4 2 5% 4 4 3 3 4 5% 55%	2535
	11th to 20th	Night	13% 5% 2 4 3 2 3 3 4 6% 56%	2730
	21st to end	Night	12% 6% 2 5% 4 3 4 3 5% 6% 50%	2730
December	1st to 10th	Night	13% 5% 2 5% 3 3 3 2 4 5% 55%	4380
	11th to 20th	Night	14% 5% 2 5% 4 4 3 3 4 5% 51%	4952
	21st to end	Night	17% 8% 3 6% 4 4 3 3 4 5% 43%	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	37% 4 6% 19% 27% 7%	5259
	11th to 20th	Day	30% 2 5% 15% 31% 17%	5280
	21st to end	Day	43% 4 7% 16% 19% 12%	6115
February	1st to 10th	Day	43% 5% 7% 16% 21% 9%	2100
	11th to 20th	Day	41% 4 6% 17% 24% 8%	2058
	21st to end	Day	40% 5% 7% 16% 20% 12%	1730
March	1st to 10th	Day	44% 5% 8% 14% 19% 9%	4833
	11th to 20th	Day	28% 5% 10% 15% 21% 22%	5090
	21st to end	Day	39% 4 9% 19% 18% 11%	5586
April	1st to 10th	Day	37% 6% 8% 21% 18% 10%	2310
	11th to 20th	Day	31% 4 7% 21% 24% 12%	2451
	21st to end	Day	28% 5% 11% 25% 24% 6%	2682
May	1st to 10th	Day	43% 5% 14% 19% 17% 3	7651
	11th to 20th	Day	38% 6% 18% 24% 11% 2	7630
	21st to end	Day	40% 9% 16% 18% 15% 1	8405
June	1st to 10th	Day	42% 10% 16% 18% 12% 2	2730
	11th to 20th	Day	31% 11% 19% 22% 15% 1	2730
	21st to end	Day	37% 13% 18% 19% 11% 2	2730
July	1st to 10th	Day	40% 11% 29% 18% 2	7615
	11th to 20th	Day	34% 13% 33% 19% 2	7611
	21st to end	Day	39% 12% 27% 18% 4	8156
August	1st to 10th	Day	44% 10% 26% 18% 3	6001
	11th to 20th	Day	25% 8% 23% 33% 10%	5553
	21st to end	Day	38% 8% 20% 25% 8% 1	5963
September	1st to 10th	Day	39% 9% 19% 16% 15% 3	2310
	11th to 20th	Day	39% 8% 11% 20% 18% 4	2310
	21st to end	Day	40% 7% 10% 18% 19% 6%	2288
October	1st to 10th	Day	35% 3 6% 13% 26% 16%	3590
	11th to 20th	Day	16% 2 5% 17% 26% 34%	3374
	21st to end	Day	20% 4 5% 18% 38% 16%	3538
November	1st to 10th	Day	33% 4 8% 14% 25% 15%	1978
	11th to 20th	Day	31% 4 7% 16% 28% 15%	1890
	21st to end	Day	36% 5% 8% 18% 23% 10%	1890
December	1st to 10th	Day	37% 4 7% 15% 28% 10%	3020
	11th to 20th	Day	37% 4 7% 22% 22% 8%	3460
	21st to end	Day	44% 4 5% 20% 23% 4	4565
January	1st to 10th	Night	34% 4 9% 18% 27% 8%	7636
	11th to 20th	Night	38% 3 4 16% 26% 13%	7680
	21st to end	Night	45% 4 6% 16% 21% 9%	8062
February	1st to 10th	Night	39% 4 8% 16% 23% 11%	2520
	11th to 20th	Night	40% 4 7% 15% 22% 12%	2459
	21st to end	Night	38% 4 8% 16% 18% 15%	2076
March	1st to 10th	Night	43% 5% 8% 15% 17% 11%	5240
	11th to 20th	Night	30% 5% 9% 14% 24% 19%	5090
	21st to end	Night	36% 4 8% 17% 20% 13%	5588
April	1st to 10th	Night	35% 6% 10% 18% 19% 13%	2310
	11th to 20th	Night	30% 6% 6% 21% 25% 12%	2134
	21st to end	Night	26% 6% 11% 25% 23% 8%	1937
May	1st to 10th	Night	41% 7% 15% 17% 15% 5%	5264
	11th to 20th	Night	36% 7% 18% 24% 12% 2	5235
	21st to end	Night	41% 8% 15% 20% 14% 2	5771
June	1st to 10th	Night	41% 11% 16% 18% 13% 2	1890
	11th to 20th	Night	33% 10% 20% 23% 12% 2	1890
	21st to end	Night	36% 13% 19% 18% 12% 3	1890
July	1st to 10th	Night	44% 12% 26% 14% 4	5235
	11th to 20th	Night	41% 13% 29% 14% 2	5226
	21st to end	Night	42% 12% 26% 15% 4 1	5606
August	1st to 10th	Night	48% 11% 22% 17% 2	4124
	11th to 20th	Night	25% 9% 26% 30% 8% 1	4540
	21st to end	Night	36% 8% 21% 26% 8% 1	5114
September	1st to 10th	Night	39% 10% 18% 17% 13% 3	2310
	11th to 20th	Night	39% 9% 13% 16% 18% 4	2310
	21st to end	Night	36% 8% 14% 17% 20% 5%	2289
October	1st to 10th	Night	35% 4 8% 13% 22% 18%	3590
	11th to 20th	Night	17% 3 5% 13% 28% 35%	3762
	21st to end	Night	19% 3 4 18% 33% 21%	4252
November	1st to 10th	Night	32% 4 7% 14% 27% 15%	2535
	11th to 20th	Night	31% 3 6% 16% 28% 16%	2730
	21st to end	Night	36% 5% 7% 19% 22% 12%	2730
December	1st to 10th	Night	33% 3 6% 19% 28% 10%	4380
	11th to 20th	Night	36% 4 9% 19% 23% 9%	4954
	21st to end	Night	44% 4 5% 20% 24% 3	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	14% 18% 46% 18% 4	330
	11th to 20th	Day	14% 19% 36% 21% 8% 2	330
	21st to end	Day	22% 20% 40% 13% 4	363
February	1st to 10th	Day	15% 19% 38% 23% 5%	330
	11th to 20th	Day	26% 16% 34% 22% 2	330
	21st to end	Day	17% 20% 40% 19% 4	273
March	1st to 10th	Day	15% 17% 28% 29% 10% 2	440
	11th to 20th	Day	14% 12% 33% 29% 11% 2	540
	21st to end	Day	15% 12% 33% 29% 10% 1	594
April	1st to 10th	Day	16% 14% 26% 27% 15% 3	540
	11th to 20th	Day	11% 10% 29% 26% 20% 5%	532
	21st to end	Day	7% 8% 23% 31% 24% 7%	540
May	1st to 10th	Day	9% 9% 26% 29% 20% 7%	543
	11th to 20th	Day	10% 3 18% 33% 24% 13%	567
	21st to end	Day	9% 5% 13% 28% 29% 15%	617
June	1st to 10th	Day	11% 2 11% 30% 30% 17%	570
	11th to 20th	Day	9% 3 12% 22% 26% 28%	570
	21st to end	Day	6% 1 10% 24% 32% 27%	570
July	1st to 10th	Day	6% 2 5% 17% 34% 36%	565
	11th to 20th	Day	5% 2 4 15% 33% 41%	564
	21st to end	Day	5% 1 6% 18% 41% 29%	620
August	1st to 10th	Day	13% 2 7% 20% 30% 29%	566
	11th to 20th	Day	6% 1 4 16% 35% 38%	559
	21st to end	Day	12% 2 6% 22% 35% 23%	627
September	1st to 10th	Day	10% 3 8% 26% 32% 20%	570
	11th to 20th	Day	13% 2 11% 26% 34% 15%	570
	21st to end	Day	12% 2 13% 26% 30% 17%	562
October	1st to 10th	Day	15% 3 22% 31% 19% 10%	530
	11th to 20th	Day	9% 5% 19% 31% 28% 8%	530
	21st to end	Day	10% 8% 24% 31% 23% 4	583
November	1st to 10th	Day	18% 4 21% 33% 18% 5%	456
	11th to 20th	Day	12% 10% 36% 27% 12% 2	330
	21st to end	Day	10% 14% 33% 28% 13% 2	330
December	1st to 10th	Day	20% 14% 34% 23% 7% 2	330
	11th to 20th	Day	21% 13% 34% 20% 8% 4	330
	21st to end	Day	23% 13% 26% 26% 11% 1	363
January	1st to 10th	Night	16% 12% 38% 27% 6% 1	840
	11th to 20th	Night	15% 11% 33% 31% 10%	840
	21st to end	Night	20% 11% 37% 29% 3	924
February	1st to 10th	Night	15% 10% 35% 32% 7%	840
	11th to 20th	Night	19% 11% 36% 29% 5%	823
	21st to end	Night	17% 10% 38% 31% 3	692
March	1st to 10th	Night	13% 12% 31% 36% 8%	840
	11th to 20th	Night	12% 11% 34% 32% 11%	840
	21st to end	Night	11% 12% 33% 34% 11%	924
April	1st to 10th	Night	13% 11% 29% 33% 15%	840
	11th to 20th	Night	12% 7% 29% 33% 18% 1	682
	21st to end	Night	7% 5% 25% 41% 21% 1	630
May	1st to 10th	Night	9% 5% 25% 39% 21% 1	630
	11th to 20th	Night	9% 3 21% 38% 25% 4	621
	21st to end	Night	8% 3 14% 35% 35% 5%	683
June	1st to 10th	Night	10% 3 11% 39% 33% 5%	630
	11th to 20th	Night	6% 1 9% 34% 40% 11%	630
	21st to end	Night	6% 1 9% 30% 45% 9%	630
July	1st to 10th	Night	8% 2 6% 27% 41% 17%	615
	11th to 20th	Night	8% 1 3 19% 50% 18%	612
	21st to end	Night	7% 1 5% 27% 49% 10%	690
August	1st to 10th	Night	7% 3 8% 24% 43% 15%	627
	11th to 20th	Night	8% 2 4 20% 54% 11%	624
	21st to end	Night	11% 2 7% 26% 40% 13%	722
September	1st to 10th	Night	10% 2 8% 30% 40% 9%	840
	11th to 20th	Night	13% 1 9% 31% 40% 6%	840
	21st to end	Night	12% 1 12% 32% 39% 3	833
October	1st to 10th	Night	13% 3 18% 36% 27% 5%	800
	11th to 20th	Night	12% 4 19% 34% 27% 3	800
	21st to end	Night	12% 5% 21% 37% 24% 2	880
November	1st to 10th	Night	13% 6% 20% 39% 21% 1	820
	11th to 20th	Night	15% 7% 26% 37% 14% 2	840
	21st to end	Night	15% 8% 31% 30% 15% 1	840
December	1st to 10th	Night	15% 8% 31% 32% 13% 1	840
	11th to 20th	Night	16% 7% 31% 33% 12% 1	840
	21st to end	Night	22% 10% 24% 35% 9% 1	924

Page generated at 2026-09-26 04:18:41. Version ac07

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