Aero Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Aero Observatory clear sky chart from 2005-11-06 to 2024-11-01.

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	12% 7% 3 7% 4 4 4 4 6% 8% 42%	101236
	Night	13% 8% 3 6% 4 4 4 3 5% 7% 43%	97795
Transparency	Day	40% 6% 13% 24% 15% 2	101028
	Night	41% 5% 11% 24% 15% 2	97675
Seeing	Day	15% 10% 27% 26% 16% 5%	15667
	Night	16% 10% 30% 30% 13% 1	25469

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	10% 12% 5% 13% 5% 4 4 3 6% 6% 30%	2527
	11th to 20th	Day	13% 11% 4 8% 7% 8% 4 5% 5% 5% 30%	2697
	21st to end	Day	19% 18% 7% 8% 4 4 3 3 3 4 26%	3135
February	1st to 10th	Day	15% 9% 5% 10% 5% 5% 4 3 5% 7% 33%	1710
	11th to 20th	Day	14% 10% 3 6% 6% 5% 5% 3 5% 8% 35%	1800
	21st to end	Day	15% 11% 3 8% 5% 3 4 3 4 7% 37%	1570
March	1st to 10th	Day	17% 12% 3 7% 4 3 3 2 3 6% 42%	3179
	11th to 20th	Day	11% 8% 3 5% 3 3 4 3 5% 7% 47%	3480
	21st to end	Day	16% 10% 4 8% 6% 5% 5% 3 5% 6% 32%	4005
April	1st to 10th	Day	13% 8% 3 7% 5% 5% 5% 3 5% 7% 41%	2280
	11th to 20th	Day	14% 9% 3 7% 4 4 5% 3 5% 6% 41%	2254
	21st to end	Day	18% 7% 3 7% 5% 4 4 4 6% 8% 36%	2280
May	1st to 10th	Day	13% 8% 3 8% 5% 5% 5% 4 7% 10% 32%	3910
	11th to 20th	Day	17% 8% 2 7% 4 4 4 4 5% 7% 37%	4399
	21st to end	Day	9% 6% 2 6% 5% 4 4 4 6% 7% 47%	4824
June	1st to 10th	Day	7% 4 2 5% 4 4 6% 4 7% 10% 47%	2660
	11th to 20th	Day	8% 4 2 4 4 5% 5% 4 7% 9% 50%	2660
	21st to end	Day	6% 4 2 6% 5% 4 6% 5% 7% 9% 46%	2660
July	1st to 10th	Day	13% 6% 2 5% 4 5% 5% 4 6% 10% 39%	4440
	11th to 20th	Day	5% 4 2 5% 4 5% 5% 4 6% 10% 50%	4440
	21st to end	Day	7% 5% 2 7% 5% 5% 6% 5% 7% 11% 41%	4606
August	1st to 10th	Day	6% 4 2 5% 4 4 5% 4 7% 9% 50%	4104
	11th to 20th	Day	12% 5% 2 6% 4 5% 5% 4 7% 9% 42%	3762
	21st to end	Day	6% 4 1 5% 4 5% 5% 4 7% 11% 50%	4180
September	1st to 10th	Day	13% 4 2 4 3 3 4 4 5% 7% 52%	2280
	11th to 20th	Day	9% 5% 2 5% 3 4 4 4 6% 7% 51%	2265
	21st to end	Day	8% 5% 2 5% 4 3 4 4 6% 8% 51%	2066
October	1st to 10th	Day	11% 4 2 5% 3 4 3 3 4 7% 55%	1900
	11th to 20th	Day	15% 7% 2 6% 2 3 3 3 3 6% 50%	1900
	21st to end	Day	17% 7% 3 6% 4 4 3 2 4 5% 46%	2064
November	1st to 10th	Day	11% 5% 2 5% 3 3 4 3 5% 7% 53%	1672
	11th to 20th	Day	14% 8% 3 7% 3 4 3 3 5% 6% 45%	1710
	21st to end	Day	16% 10% 4 7% 5% 4 3 3 4 6% 39%	1596
December	1st to 10th	Day	12% 12% 3 7% 4 4 3 4 5% 7% 39%	1520
	11th to 20th	Day	14% 9% 4 7% 5% 4 5% 4 5% 5% 38%	1918
	21st to end	Day	19% 15% 4 11% 6% 4 3 3 5% 5% 23%	2783
January	1st to 10th	Night	13% 11% 6% 10% 5% 4 4 3 4 5% 34%	4428
	11th to 20th	Night	13% 14% 5% 10% 5% 6% 7% 5% 4 4 27%	4271
	21st to end	Night	23% 18% 5% 9% 4 3 3 2 4 5% 24%	4532
February	1st to 10th	Night	14% 12% 6% 8% 6% 4 5% 3 5% 6% 33%	2470
	11th to 20th	Night	13% 8% 4 7% 5% 4 4 3 5% 5% 40%	2264
	21st to end	Night	16% 9% 4 7% 4 3 4 3 4 5% 42%	1884
March	1st to 10th	Night	21% 12% 2 5% 3 3 3 3 3 4 41%	3702
	11th to 20th	Night	14% 6% 2 5% 3 3 3 2 4 6% 51%	3480
	21st to end	Night	19% 11% 4 8% 4 4 4 3 5% 6% 32%	3626
April	1st to 10th	Night	12% 7% 2 7% 5% 3 4 2 6% 7% 44%	1900
	11th to 20th	Night	13% 6% 2 5% 3 4 5% 3 5% 8% 45%	1875
	21st to end	Night	19% 7% 3 6% 4 4 4 3 4 6% 41%	1900
May	1st to 10th	Night	16% 9% 2 7% 4 4 4 4 6% 8% 37%	2982
	11th to 20th	Night	15% 6% 3 6% 4 4 4 4 5% 7% 42%	2506
	21st to end	Night	8% 6% 2 6% 5% 4 5% 4 6% 9% 46%	2743
June	1st to 10th	Night	7% 4 2 5% 4 4 4 5% 6% 10% 51%	1520
	11th to 20th	Night	6% 5% 2 5% 5% 4 4 4 5% 9% 51%	1520
	21st to end	Night	5% 5% 2 5% 4 5% 4 5% 7% 10% 50%	1520
July	1st to 10th	Night	12% 5% 2 7% 4 4 4 4 6% 9% 43%	2530
	11th to 20th	Night	5% 2 1 4 3 4 3 3 6% 9% 60%	2530
	21st to end	Night	9% 6% 2 7% 5% 5% 5% 4 7% 9% 42%	2953
August	1st to 10th	Night	5% 3 2 4 4 3 3 3 5% 8% 59%	2836
	11th to 20th	Night	10% 5% 2 5% 4 4 4 3 6% 7% 50%	3066
	21st to end	Night	5% 3 1 4 3 4 4 4 6% 10% 56%	3476
September	1st to 10th	Night	11% 4 2 5% 3 3 3 3 4 7% 56%	1900
	11th to 20th	Night	8% 5% 2 6% 3 4 4 4 5% 7% 52%	1900
	21st to end	Night	9% 5% 1 5% 4 4 4 3 5% 7% 55%	2104
October	1st to 10th	Night	9% 4 2 4 3 3 3 3 4 6% 58%	2280
	11th to 20th	Night	13% 5% 2 5% 3 3 3 2 4 7% 52%	2280
	21st to end	Night	17% 8% 2 5% 4 4 3 3 5% 4 46%	2532
November	1st to 10th	Night	9% 5% 2 5% 3 4 3 4 4 6% 55%	2413
	11th to 20th	Night	12% 6% 3 5% 4 3 3 3 5% 6% 49%	2470
	21st to end	Night	17% 9% 3 5% 4 3 3 3 4 5% 43%	2579
December	1st to 10th	Night	15% 11% 4 7% 6% 5% 5% 4 5% 6% 34%	2660
	11th to 20th	Night	16% 10% 3 6% 3 4 3 3 4 6% 41%	3279
	21st to end	Night	19% 21% 6% 10% 6% 5% 4 3 3 4 21%	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	52% 7% 11% 21% 8% 1	2528
	11th to 20th	Day	53% 5% 16% 16% 9%	2697
	21st to end	Day	62% 4 9% 15% 9% 1	3135
February	1st to 10th	Day	51% 5% 12% 21% 10% 1	1710
	11th to 20th	Day	48% 5% 12% 19% 14% 1	1810
	21st to end	Day	47% 4 11% 22% 13% 3	1570
March	1st to 10th	Day	46% 4 8% 21% 18% 2	3179
	11th to 20th	Day	35% 6% 14% 25% 17% 3	3480
	21st to end	Day	48% 9% 16% 20% 6% 1	4005
April	1st to 10th	Day	42% 6% 11% 24% 16% 1	2280
	11th to 20th	Day	44% 5% 10% 25% 13% 3	2254
	21st to end	Day	46% 6% 13% 20% 13% 1	2280
May	1st to 10th	Day	43% 10% 15% 23% 9%	3945
	11th to 20th	Day	45% 8% 10% 25% 11% 1	4403
	21st to end	Day	34% 8% 10% 24% 22% 1	4837
June	1st to 10th	Day	31% 7% 15% 28% 16% 3	2660
	11th to 20th	Day	30% 7% 13% 25% 22% 3	2660
	21st to end	Day	31% 9% 16% 23% 17% 3	2660
July	1st to 10th	Day	39% 7% 12% 28% 13% 2	4371
	11th to 20th	Day	29% 6% 15% 29% 19% 2	4365
	21st to end	Day	35% 7% 19% 27% 11% 1	4461
August	1st to 10th	Day	28% 7% 16% 35% 14% 1	4090
	11th to 20th	Day	38% 7% 13% 26% 15% 1	3798
	21st to end	Day	28% 6% 17% 32% 14% 3	4179
September	1st to 10th	Day	32% 6% 10% 26% 21% 5%	2280
	11th to 20th	Day	30% 5% 11% 28% 22% 4	2265
	21st to end	Day	30% 6% 10% 29% 22% 3	2066
October	1st to 10th	Day	31% 4 10% 25% 26% 4	1900
	11th to 20th	Day	36% 4 9% 23% 24% 4	1900
	21st to end	Day	42% 4 9% 25% 17% 3	2064
November	1st to 10th	Day	32% 4 13% 26% 20% 4	1672
	11th to 20th	Day	40% 4 12% 23% 18% 4	1710
	21st to end	Day	47% 5% 10% 25% 13%	1596
December	1st to 10th	Day	46% 5% 15% 22% 11%	1520
	11th to 20th	Day	46% 6% 12% 24% 10% 2	1915
	21st to end	Day	61% 7% 10% 15% 7% 1	2783
January	1st to 10th	Night	52% 5% 11% 23% 8% 1	4428
	11th to 20th	Night	59% 5% 9% 19% 8%	4271
	21st to end	Night	63% 5% 8% 17% 6% 1	4532
February	1st to 10th	Night	53% 5% 10% 19% 11% 2	2470
	11th to 20th	Night	46% 5% 11% 21% 15% 2	2265
	21st to end	Night	43% 6% 12% 23% 13% 2	1884
March	1st to 10th	Night	47% 5% 8% 24% 15% 1	3702
	11th to 20th	Night	35% 5% 10% 24% 20% 5%	3480
	21st to end	Night	52% 6% 12% 24% 6%	3626
April	1st to 10th	Night	39% 6% 10% 25% 16% 4	1900
	11th to 20th	Night	36% 7% 12% 23% 19% 4	1875
	21st to end	Night	45% 5% 8% 22% 17% 2	1900
May	1st to 10th	Night	43% 9% 16% 19% 12% 1	3012
	11th to 20th	Night	40% 8% 12% 27% 12% 1	2507
	21st to end	Night	32% 8% 15% 22% 21% 3	2751
June	1st to 10th	Night	27% 8% 15% 27% 19% 4	1520
	11th to 20th	Night	28% 7% 11% 23% 26% 4	1520
	21st to end	Night	27% 8% 16% 25% 18% 7%	1520
July	1st to 10th	Night	38% 5% 10% 31% 13% 2	2490
	11th to 20th	Night	21% 4 13% 38% 21% 2	2482
	21st to end	Night	37% 6% 18% 24% 14% 1	2859
August	1st to 10th	Night	24% 5% 16% 36% 17% 1	2826
	11th to 20th	Night	34% 4 12% 27% 22% 1	3096
	21st to end	Night	24% 5% 17% 33% 17% 4	3476
September	1st to 10th	Night	29% 5% 10% 24% 24% 8%	1900
	11th to 20th	Night	30% 6% 9% 25% 24% 6%	1900
	21st to end	Night	29% 6% 9% 26% 26% 4	2104
October	1st to 10th	Night	28% 5% 10% 24% 29% 5%	2280
	11th to 20th	Night	33% 4 9% 27% 22% 5%	2280
	21st to end	Night	41% 5% 9% 21% 21% 3	2532
November	1st to 10th	Night	31% 5% 12% 26% 20% 6%	2413
	11th to 20th	Night	35% 4 10% 28% 19% 4	2470
	21st to end	Night	44% 4 11% 25% 15% 1	2579
December	1st to 10th	Night	50% 6% 12% 22% 10% 1	2660
	11th to 20th	Night	45% 5% 11% 25% 14% 1	3281
	21st to end	Night	67% 5% 8% 12% 7% 1	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% 21% 32% 20% 5% 1	270
	11th to 20th	Day	27% 22% 34% 15% 1	270
	21st to end	Day	15% 23% 40% 17% 4	297
February	1st to 10th	Day	24% 19% 39% 16% 3	270
	11th to 20th	Day	21% 23% 34% 16% 5%	270
	21st to end	Day	24% 16% 44% 15% 2	225
March	1st to 10th	Day	19% 21% 43% 16% 1	270
	11th to 20th	Day	29% 16% 34% 17% 4	270
	21st to end	Day	28% 17% 35% 16% 4	411
April	1st to 10th	Day	19% 13% 38% 22% 7% 1	460
	11th to 20th	Day	20% 16% 33% 19% 12%	452
	21st to end	Day	21% 17% 33% 22% 6% 1	460
May	1st to 10th	Day	16% 13% 36% 26% 7% 2	477
	11th to 20th	Day	17% 10% 30% 25% 15% 3	675
	21st to end	Day	14% 7% 31% 27% 13% 7%	734
June	1st to 10th	Day	7% 6% 26% 31% 24% 7%	680
	11th to 20th	Day	9% 3 25% 35% 22% 5%	680
	21st to end	Day	6% 7% 29% 34% 19% 4	680
July	1st to 10th	Day	11% 3 16% 29% 28% 13%	671
	11th to 20th	Day	6% 3 19% 36% 28% 7%	668
	21st to end	Day	10% 2 17% 34% 31% 7%	739
August	1st to 10th	Day	8% 2 16% 38% 26% 9%	676
	11th to 20th	Day	11% 4 17% 29% 29% 10%	500
	21st to end	Day	9% 2 14% 32% 32% 10%	539
September	1st to 10th	Day	12% 5% 16% 29% 28% 10%	490
	11th to 20th	Day	9% 2 13% 33% 31% 11%	490
	21st to end	Day	9% 10% 22% 29% 23% 7%	466
October	1st to 10th	Day	11% 8% 26% 33% 17% 5%	300
	11th to 20th	Day	17% 19% 31% 24% 8% 2	300
	21st to end	Day	25% 20% 30% 19% 6%	330
November	1st to 10th	Day	10% 12% 39% 25% 10% 4	270
	11th to 20th	Day	18% 19% 31% 21% 10% 1	270
	21st to end	Day	23% 15% 33% 23% 4 1	270
December	1st to 10th	Day	13% 20% 38% 19% 7% 3	270
	11th to 20th	Day	21% 16% 36% 22% 4	270
	21st to end	Day	24% 24% 36% 15% 2	297
January	1st to 10th	Night	17% 15% 39% 23% 6%	950
	11th to 20th	Night	20% 17% 37% 21% 5%	950
	21st to end	Night	20% 15% 38% 25% 2	1045
February	1st to 10th	Night	21% 13% 38% 25% 3	950
	11th to 20th	Night	20% 14% 39% 24% 3	789
	21st to end	Night	22% 17% 37% 21% 3	628
March	1st to 10th	Night	20% 16% 38% 23% 4	742
	11th to 20th	Night	21% 12% 35% 26% 6%	570
	21st to end	Night	24% 12% 33% 26% 5%	627
April	1st to 10th	Night	16% 16% 36% 27% 5%	570
	11th to 20th	Night	14% 14% 35% 27% 9% 1	563
	21st to end	Night	22% 10% 36% 26% 6%	570
May	1st to 10th	Night	17% 8% 33% 32% 9% 1	570
	11th to 20th	Night	16% 5% 27% 37% 13% 1	561
	21st to end	Night	11% 5% 27% 34% 20% 3	617
June	1st to 10th	Night	9% 3 24% 39% 25% 1	570
	11th to 20th	Night	9% 2 23% 46% 19% 2	570
	21st to end	Night	5% 3 26% 42% 23% 1	570
July	1st to 10th	Night	12% 2 11% 34% 35% 5%	555
	11th to 20th	Night	6% 3 14% 45% 29% 3	552
	21st to end	Night	7% 2 14% 42% 34% 2	624
August	1st to 10th	Night	8% 2 11% 44% 33% 2	567
	11th to 20th	Night	9% 2 14% 39% 31% 5%	564
	21st to end	Night	5% 1 12% 40% 40% 2	627
September	1st to 10th	Night	12% 3 16% 37% 28% 5%	570
	11th to 20th	Night	9% 2 13% 39% 31% 5%	570
	21st to end	Night	10% 6% 24% 32% 24% 3	755
October	1st to 10th	Night	10% 5% 26% 32% 23% 3	760
	11th to 20th	Night	16% 9% 34% 29% 11% 1	760
	21st to end	Night	22% 12% 32% 27% 7%	836
November	1st to 10th	Night	12% 9% 38% 30% 11%	743
	11th to 20th	Night	15% 15% 36% 29% 6%	760
	21st to end	Night	22% 13% 34% 25% 7%	869
December	1st to 10th	Night	20% 13% 37% 24% 5% 1	950
	11th to 20th	Night	22% 11% 32% 30% 5%	950
	21st to end	Night	26% 16% 33% 22% 3	1045

Page generated at 2024-10-29 10:20:44. Version ac07

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