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 2024-03-01.

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	13% 7% 3 6% 5% 3 5% 5% 5% 7% 41%	78528
	Night	13% 8% 3 6% 5% 3 4 4 5% 6% 42%	80929
Transparency	Day	41% 7% 12% 23% 14% 2	78236
	Night	43% 6% 11% 23% 15% 3	80742
Seeing	Day	15% 10% 27% 26% 17% 5%	14651
	Night	16% 10% 30% 30% 13% 1	24684

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% 6% 12% 6% 3 5% 4 6% 6% 30%	2527
	11th to 20th	Day	13% 10% 5% 7% 8% 5% 6% 6% 5% 5% 31%	2697
	21st to end	Day	19% 17% 8% 7% 5% 3 3 4 3 4 26%	3135
February	1st to 10th	Day	16% 8% 6% 9% 5% 4 4 3 5% 7% 33%	1710
	11th to 20th	Day	14% 9% 4 5% 7% 4 5% 4 5% 8% 35%	1800
	21st to end	Day	15% 11% 3 7% 6% 3 3 4 4 7% 37%	1570
March	1st to 10th	Day	15% 9% 4 6% 6% 3 4 3 4 7% 38%	1831
	11th to 20th	Day	17% 10% 4 6% 5% 2 4 4 5% 6% 36%	1980
	21st to end	Day	20% 11% 5% 7% 6% 4 5% 4 5% 6% 28%	2286
April	1st to 10th	Day	13% 7% 3 6% 6% 3 5% 4 4 7% 42%	2160
	11th to 20th	Day	15% 9% 4 5% 5% 3 4 4 5% 6% 40%	2134
	21st to end	Day	19% 7% 3 6% 6% 3 4 4 6% 8% 36%	2160
May	1st to 10th	Day	16% 7% 3 6% 6% 3 5% 5% 6% 8% 36%	2235
	11th to 20th	Day	17% 6% 2 6% 5% 4 5% 6% 5% 7% 39%	2479
	21st to end	Day	11% 6% 3 7% 6% 4 5% 7% 6% 8% 38%	2725
June	1st to 10th	Day	7% 4 2 4 5% 3 6% 5% 7% 10% 47%	2520
	11th to 20th	Day	8% 4 2 4 5% 4 5% 5% 7% 8% 48%	2520
	21st to end	Day	6% 4 2 5% 5% 3 6% 7% 7% 10% 45%	2520
July	1st to 10th	Day	9% 4 2 4 5% 4 5% 5% 6% 11% 44%	2520
	11th to 20th	Day	5% 3 2 4 4 3 5% 5% 6% 10% 51%	2520
	21st to end	Day	8% 4 2 5% 4 3 5% 5% 6% 9% 49%	2631
August	1st to 10th	Day	8% 5% 2 5% 6% 4 6% 6% 7% 10% 43%	2328
	11th to 20th	Day	7% 5% 2 7% 6% 3 6% 6% 7% 10% 42%	2145
	21st to end	Day	8% 4 2 4 4 3 5% 5% 6% 9% 50%	2376
September	1st to 10th	Day	14% 4 2 3 3 2 4 5% 4 7% 50%	2160
	11th to 20th	Day	9% 4 2 5% 4 3 4 5% 6% 7% 52%	2146
	21st to end	Day	7% 4 2 5% 4 2 4 5% 6% 8% 53%	1958
October	1st to 10th	Day	11% 5% 2 5% 4 3 3 4 4 7% 53%	1800
	11th to 20th	Day	16% 7% 2 5% 4 3 3 3 3 6% 48%	1800
	21st to end	Day	18% 7% 3 5% 5% 3 3 3 4 5% 45%	1956
November	1st to 10th	Day	11% 4 2 4 4 2 5% 3 4 7% 53%	1672
	11th to 20th	Day	14% 7% 3 6% 4 3 4 4 5% 6% 45%	1710
	21st to end	Day	16% 9% 5% 6% 6% 3 3 4 3 6% 40%	1596
December	1st to 10th	Day	12% 11% 4 6% 5% 3 4 4 4 7% 39%	1520
	11th to 20th	Day	14% 8% 5% 6% 6% 3 5% 5% 5% 6% 38%	1918
	21st to end	Day	20% 15% 4 10% 7% 3 4 4 5% 5% 24%	2783
January	1st to 10th	Night	14% 11% 6% 9% 6% 3 4 4 4 5% 34%	4428
	11th to 20th	Night	13% 13% 5% 9% 7% 4 8% 6% 4 4 27%	4271
	21st to end	Night	23% 17% 6% 8% 5% 2 3 3 4 5% 24%	4532
February	1st to 10th	Night	15% 11% 6% 7% 6% 3 5% 4 4 6% 33%	2470
	11th to 20th	Night	14% 8% 4 7% 6% 3 5% 4 4 5% 41%	2264
	21st to end	Night	16% 8% 4 6% 4 2 3 4 4 5% 42%	1884
March	1st to 10th	Night	15% 11% 3 6% 5% 3 4 4 4 5% 42%	2150
	11th to 20th	Night	19% 7% 3 6% 5% 3 4 3 5% 7% 37%	1980
	21st to end	Night	20% 11% 4 7% 4 3 5% 4 5% 8% 28%	2070
April	1st to 10th	Night	12% 6% 3 6% 5% 3 4 3 5% 7% 45%	1800
	11th to 20th	Night	13% 6% 3 5% 4 3 5% 4 5% 8% 45%	1775
	21st to end	Night	19% 7% 3 5% 4 3 4 4 4 6% 41%	1800
May	1st to 10th	Night	14% 6% 3 5% 5% 3 4 5% 6% 8% 41%	1721
	11th to 20th	Night	14% 6% 3 6% 5% 3 4 4 4 7% 44%	1416
	21st to end	Night	9% 6% 3 6% 7% 3 4 5% 6% 9% 42%	1551
June	1st to 10th	Night	7% 4 2 4 5% 3 3 5% 5% 9% 52%	1440
	11th to 20th	Night	6% 4 2 4 6% 3 4 5% 5% 9% 50%	1440
	21st to end	Night	5% 4 2 4 4 3 4 6% 7% 10% 51%	1440
July	1st to 10th	Night	9% 4 1 6% 5% 3 4 5% 5% 10% 50%	1440
	11th to 20th	Night	7% 3 2 3 5% 2 4 3 5% 8% 58%	1440
	21st to end	Night	7% 4 2 4 4 4 4 5% 7% 9% 51%	1683
August	1st to 10th	Night	7% 3 2 4 5% 3 4 5% 6% 9% 52%	1611
	11th to 20th	Night	7% 4 2 5% 5% 4 4 5% 5% 8% 50%	1754
	21st to end	Night	5% 3 1 4 4 3 4 5% 5% 8% 57%	1980
September	1st to 10th	Night	12% 5% 2 4 4 2 3 4 4 7% 54%	1800
	11th to 20th	Night	9% 4 2 5% 4 3 4 5% 5% 7% 53%	1800
	21st to end	Night	7% 4 2 4 4 3 4 4 5% 7% 57%	1993
October	1st to 10th	Night	9% 4 2 4 4 3 3 4 4 6% 56%	2160
	11th to 20th	Night	14% 5% 2 4 4 2 4 3 4 7% 50%	2160
	21st to end	Night	18% 8% 2 4 4 3 3 4 5% 4 45%	2398
November	1st to 10th	Night	10% 5% 2 5% 4 3 3 4 4 6% 55%	2406
	11th to 20th	Night	13% 6% 3 5% 4 2 3 4 5% 6% 49%	2470
	21st to end	Night	17% 8% 3 5% 4 2 4 4 4 6% 43%	2579
December	1st to 10th	Night	15% 10% 4 7% 6% 4 5% 5% 5% 6% 34%	2660
	11th to 20th	Night	16% 10% 4 6% 4 3 4 3 4 6% 41%	3279
	21st to end	Night	19% 20% 6% 8% 7% 3 4 4 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% 2	1570
March	1st to 10th	Day	47% 5% 10% 25% 12% 2	1831
	11th to 20th	Day	50% 6% 11% 20% 12% 2	1980
	21st to end	Day	56% 7% 12% 16% 8% 1	2286
April	1st to 10th	Day	41% 6% 11% 25% 16% 1	2160
	11th to 20th	Day	45% 5% 10% 25% 13% 3	2134
	21st to end	Day	46% 6% 13% 20% 13% 1	2160
May	1st to 10th	Day	45% 8% 14% 23% 9% 1	2235
	11th to 20th	Day	44% 8% 12% 21% 14% 1	2483
	21st to end	Day	42% 9% 13% 20% 14% 2	2725
June	1st to 10th	Day	31% 7% 15% 28% 16% 2	2520
	11th to 20th	Day	31% 7% 14% 23% 21% 3	2520
	21st to end	Day	31% 10% 16% 23% 16% 4	2520
July	1st to 10th	Day	32% 10% 14% 28% 12% 3	2451
	11th to 20th	Day	26% 9% 17% 27% 18% 3	2445
	21st to end	Day	29% 9% 15% 31% 15% 2	2485
August	1st to 10th	Day	35% 9% 15% 26% 13% 1	2314
	11th to 20th	Day	35% 9% 15% 26% 14% 1	2145
	21st to end	Day	29% 7% 14% 26% 18% 5%	2376
September	1st to 10th	Day	33% 6% 11% 27% 18% 5%	2160
	11th to 20th	Day	29% 5% 11% 28% 22% 4	2146
	21st to end	Day	28% 6% 10% 30% 22% 3	1958
October	1st to 10th	Day	33% 5% 10% 26% 23% 3	1800
	11th to 20th	Day	38% 5% 9% 23% 22% 4	1800
	21st to end	Day	43% 4 9% 25% 16% 3	1956
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% 24% 13% 3	1884
March	1st to 10th	Night	45% 5% 8% 24% 15% 2	2150
	11th to 20th	Night	47% 6% 11% 20% 13% 3	1980
	21st to end	Night	55% 5% 13% 18% 8% 1	2070
April	1st to 10th	Night	38% 6% 11% 25% 16% 4	1800
	11th to 20th	Night	37% 7% 12% 23% 18% 4	1775
	21st to end	Night	45% 6% 8% 21% 17% 2	1800
May	1st to 10th	Night	40% 8% 13% 23% 15% 2	1721
	11th to 20th	Night	41% 7% 10% 24% 17% 1	1417
	21st to end	Night	38% 8% 15% 19% 16% 4	1552
June	1st to 10th	Night	27% 7% 15% 28% 19% 4	1440
	11th to 20th	Night	29% 8% 12% 23% 25% 4	1440
	21st to end	Night	26% 8% 17% 25% 17% 6%	1440
July	1st to 10th	Night	31% 7% 14% 31% 14% 4	1400
	11th to 20th	Night	25% 5% 15% 31% 21% 3	1392
	21st to end	Night	27% 7% 14% 30% 19% 2	1589
August	1st to 10th	Night	29% 7% 15% 31% 17% 2	1601
	11th to 20th	Night	31% 7% 11% 29% 21% 1	1754
	21st to end	Night	24% 7% 15% 26% 22% 6%	1980
September	1st to 10th	Night	30% 5% 11% 25% 22% 7%	1800
	11th to 20th	Night	29% 6% 9% 26% 24% 6%	1800
	21st to end	Night	26% 6% 10% 26% 27% 4	1993
October	1st to 10th	Night	30% 5% 11% 24% 26% 5%	2160
	11th to 20th	Night	34% 4 9% 27% 20% 5%	2160
	21st to end	Night	42% 5% 9% 20% 21% 3	2398
November	1st to 10th	Night	31% 5% 12% 26% 20% 6%	2406
	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	25% 15% 43% 16% 2	225
March	1st to 10th	Day	19% 22% 41% 16% 2	240
	11th to 20th	Day	31% 13% 34% 17% 4	240
	21st to end	Day	30% 16% 34% 15% 4 1	372
April	1st to 10th	Day	18% 12% 38% 24% 7% 1	420
	11th to 20th	Day	20% 16% 32% 20% 12%	412
	21st to end	Day	22% 16% 32% 24% 6% 1	420
May	1st to 10th	Day	17% 13% 36% 25% 7% 2	436
	11th to 20th	Day	18% 10% 31% 24% 14% 3	625
	21st to end	Day	15% 6% 31% 27% 13% 8%	679
June	1st to 10th	Day	7% 5% 24% 31% 26% 7%	630
	11th to 20th	Day	9% 3 25% 34% 23% 6%	630
	21st to end	Day	7% 7% 26% 35% 20% 5%	630
July	1st to 10th	Day	10% 2 15% 29% 29% 14%	621
	11th to 20th	Day	6% 4 19% 36% 28% 8%	618
	21st to end	Day	10% 2 16% 34% 31% 7%	684
August	1st to 10th	Day	8% 2 14% 38% 28% 10%	626
	11th to 20th	Day	10% 3 15% 30% 32% 10%	459
	21st to end	Day	9% 2 15% 30% 33% 11%	495
September	1st to 10th	Day	13% 5% 15% 29% 28% 10%	450
	11th to 20th	Day	9% 2 14% 33% 31% 11%	450
	21st to end	Day	7% 10% 21% 30% 25% 7%	428
October	1st to 10th	Day	12% 9% 25% 34% 16% 4	270
	11th to 20th	Day	18% 20% 31% 22% 7% 1	270
	21st to end	Day	26% 20% 30% 18% 6%	297
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% 37% 23% 4	706
	11th to 20th	Night	22% 11% 34% 26% 6%	540
	21st to end	Night	24% 11% 34% 25% 5%	594
April	1st to 10th	Night	16% 16% 36% 28% 5%	540
	11th to 20th	Night	14% 14% 35% 27% 10% 1	533
	21st to end	Night	23% 9% 36% 26% 6%	540
May	1st to 10th	Night	17% 7% 34% 33% 10% 1	540
	11th to 20th	Night	17% 5% 27% 37% 13% 1	531
	21st to end	Night	11% 5% 26% 35% 21% 3	584
June	1st to 10th	Night	9% 3 22% 40% 26% 1	540
	11th to 20th	Night	9% 2 22% 45% 20% 2	540
	21st to end	Night	5% 3 25% 43% 24% 1	540
July	1st to 10th	Night	11% 2 10% 34% 37% 6%	525
	11th to 20th	Night	6% 3 14% 45% 30% 3	522
	21st to end	Night	6% 2 15% 41% 34% 2	591
August	1st to 10th	Night	8% 1 10% 45% 33% 3	537
	11th to 20th	Night	10% 2 13% 39% 32% 5%	534
	21st to end	Night	5% 1 12% 40% 40% 3	594
September	1st to 10th	Night	13% 3 16% 37% 27% 5%	540
	11th to 20th	Night	10% 3 14% 39% 30% 5%	540
	21st to end	Night	9% 6% 24% 32% 25% 4	715
October	1st to 10th	Night	10% 6% 26% 32% 23% 3	720
	11th to 20th	Night	17% 9% 34% 29% 10% 1	720
	21st to end	Night	23% 12% 32% 26% 7%	792
November	1st to 10th	Night	12% 9% 38% 29% 11%	740
	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 2024-02-27 05:30:18. Version ac07

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