Astro Acres
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Astro Acres clear sky chart from 2005-11-06 to 2026-10-14.

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% 9% 3 8% 5% 5% 5% 4 6% 8% 36%	149105
	Night	14% 10% 4 8% 5% 4 4 3 5% 6% 37%	142906
Transparency	Day	45% 6% 12% 22% 14% 2	152655
	Night	46% 6% 11% 22% 14% 2	147433
Seeing	Day	16% 10% 28% 25% 15% 6%	18419
	Night	17% 10% 30% 30% 12% 1	28155

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	13% 14% 8% 14% 6% 5% 5% 4 5% 7% 21%	4691
	11th to 20th	Day	9% 12% 7% 16% 7% 7% 6% 5% 5% 4 23%	4710
	21st to end	Day	16% 16% 5% 11% 6% 4 4 4 5% 5% 24%	5293
February	1st to 10th	Day	16% 12% 5% 11% 6% 5% 6% 3 5% 6% 26%	2021
	11th to 20th	Day	13% 13% 4 9% 5% 5% 4 4 5% 5% 31%	2048
	21st to end	Day	15% 14% 5% 9% 4 4 4 3 5% 6% 31%	1730
March	1st to 10th	Day	19% 15% 3 7% 4 3 3 2 3 4 37%	4580
	11th to 20th	Day	9% 10% 3 7% 4 4 5% 4 6% 8% 40%	4761
	21st to end	Day	16% 12% 6% 10% 6% 5% 5% 4 5% 7% 24%	6070
April	1st to 10th	Day	17% 12% 3 7% 4 4 4 3 6% 6% 34%	2520
	11th to 20th	Day	15% 9% 3 7% 5% 5% 5% 4 5% 6% 36%	2494
	21st to end	Day	19% 8% 3 8% 5% 4 4 3 4 7% 34%	2650
May	1st to 10th	Day	17% 8% 3 7% 5% 5% 5% 4 6% 8% 31%	7616
	11th to 20th	Day	14% 7% 3 8% 5% 5% 5% 4 6% 7% 37%	7704
	21st to end	Day	13% 7% 3 7% 5% 5% 4 4 6% 8% 38%	9047
June	1st to 10th	Day	10% 6% 2 7% 5% 4 6% 4 6% 8% 43%	2940
	11th to 20th	Day	9% 5% 2 5% 5% 5% 5% 4 6% 9% 45%	2940
	21st to end	Day	10% 6% 2 7% 6% 5% 6% 4 7% 8% 39%	2940
July	1st to 10th	Day	9% 5% 2 6% 5% 6% 6% 5% 8% 10% 38%	8280
	11th to 20th	Day	8% 5% 3 6% 5% 4 6% 5% 7% 11% 42%	8280
	21st to end	Day	10% 6% 2 7% 5% 5% 6% 5% 7% 8% 38%	8990
August	1st to 10th	Day	11% 5% 2 6% 5% 5% 4 4 6% 9% 44%	6158
	11th to 20th	Day	12% 7% 3 7% 5% 5% 5% 5% 7% 9% 36%	5540
	21st to end	Day	5% 4 2 5% 4 4 5% 4 7% 10% 51%	6080
September	1st to 10th	Day	10% 5% 2 5% 4 4 5% 4 6% 7% 49%	2520
	11th to 20th	Day	11% 5% 2 5% 4 4 4 3 5% 8% 49%	2347
	21st to end	Day	11% 6% 2 7% 4 4 4 4 5% 8% 45%	2310
October	1st to 10th	Day	11% 7% 2 6% 3 4 4 4 6% 6% 48%	2310
	11th to 20th	Day	17% 7% 3 7% 3 4 5% 4 5% 6% 40%	2009
	21st to end	Day	18% 10% 3 9% 5% 4 4 3 6% 6% 33%	1980
November	1st to 10th	Day	12% 7% 2 4 5% 4 4 3 5% 7% 48%	1852
	11th to 20th	Day	17% 12% 4 7% 5% 3 3 3 4 6% 37%	1890
	21st to end	Day	17% 12% 3 10% 4 3 3 3 4 5% 35%	1890
December	1st to 10th	Day	10% 12% 4 9% 6% 4 3 3 4 6% 41%	2756
	11th to 20th	Day	14% 15% 5% 13% 6% 5% 4 4 5% 6% 23%	3088
	21st to end	Day	26% 19% 8% 13% 5% 4 4 3 4 4 12%	4070
January	1st to 10th	Night	13% 14% 8% 12% 6% 4 4 3 5% 5% 25%	8232
	11th to 20th	Night	10% 15% 6% 15% 8% 6% 5% 3 5% 5% 22%	8280
	21st to end	Night	17% 14% 5% 8% 5% 4 5% 3 4 5% 30%	8906
February	1st to 10th	Night	16% 14% 4 9% 6% 5% 4 3 5% 6% 29%	2598
	11th to 20th	Night	15% 11% 4 9% 5% 4 5% 3 5% 6% 34%	2458
	21st to end	Night	18% 13% 3 8% 5% 3 4 3 5% 5% 33%	2076
March	1st to 10th	Night	16% 13% 5% 6% 4 4 3 3 4 5% 38%	5493
	11th to 20th	Night	12% 7% 3 6% 4 4 4 4 5% 6% 44%	5419
	21st to end	Night	18% 10% 5% 8% 5% 5% 5% 4 5% 6% 29%	5131
April	1st to 10th	Night	14% 9% 3 8% 5% 4 5% 3 6% 7% 37%	2100
	11th to 20th	Night	18% 9% 3 6% 5% 4 4 3 4 7% 38%	2075
	21st to end	Night	17% 8% 2 7% 5% 4 4 4 6% 7% 36%	1969
May	1st to 10th	Night	18% 9% 3 8% 5% 4 4 3 5% 6% 35%	5237
	11th to 20th	Night	14% 6% 2 6% 3 4 4 4 6% 9% 43%	5144
	21st to end	Night	13% 7% 3 8% 5% 5% 4 4 6% 8% 37%	5139
June	1st to 10th	Night	10% 6% 1 7% 4 3 4 2 5% 8% 49%	1680
	11th to 20th	Night	8% 6% 2 6% 4 4 4 3 6% 9% 47%	1680
	21st to end	Night	9% 6% 2 6% 5% 5% 6% 4 6% 9% 43%	1680
July	1st to 10th	Night	9% 5% 2 6% 5% 5% 5% 4 6% 9% 43%	4708
	11th to 20th	Night	6% 5% 2 6% 4 5% 5% 4 6% 9% 49%	4707
	21st to end	Night	8% 6% 2 7% 5% 5% 5% 4 6% 7% 43%	5117
August	1st to 10th	Night	13% 5% 2 6% 4 4 4 4 6% 8% 46%	3996
	11th to 20th	Night	11% 6% 3 7% 4 5% 5% 4 7% 8% 41%	4489
	21st to end	Night	7% 4 2 5% 4 3 4 4 5% 8% 53%	5046
September	1st to 10th	Night	9% 5% 1 6% 3 3 3 2 5% 8% 54%	2100
	11th to 20th	Night	8% 5% 1 4 3 3 4 3 6% 8% 55%	2252
	21st to end	Night	10% 7% 2 6% 4 4 4 4 5% 7% 46%	2310
October	1st to 10th	Night	11% 5% 2 5% 3 3 3 3 4 5% 55%	2310
	11th to 20th	Night	15% 7% 2 6% 4 4 3 3 4 6% 47%	2452
	21st to end	Night	18% 8% 3 7% 4 4 4 3 5% 6% 38%	2860
November	1st to 10th	Night	12% 8% 2 6% 4 4 4 3 5% 7% 45%	2666
	11th to 20th	Night	14% 9% 3 7% 5% 4 5% 4 5% 6% 38%	2730
	21st to end	Night	18% 12% 3 8% 5% 4 3 3 4 5% 34%	2730
December	1st to 10th	Night	12% 10% 3 7% 4 4 4 3 4 6% 43%	4647
	11th to 20th	Night	17% 14% 4 9% 5% 5% 5% 3 4 4 30%	5339
	21st to end	Night	25% 19% 5% 11% 6% 4 4 3 4 5% 15%	7150

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	62% 4 14% 13% 6% 1	4692
	11th to 20th	Day	64% 4 8% 11% 11% 2	4710
	21st to end	Day	62% 4 11% 17% 6%	5293
February	1st to 10th	Day	59% 4 13% 16% 7% 2	2021
	11th to 20th	Day	53% 5% 10% 22% 9% 1	2058
	21st to end	Day	53% 6% 11% 21% 8% 2	1730
March	1st to 10th	Day	53% 4 7% 22% 12% 2	4580
	11th to 20th	Day	39% 6% 10% 34% 10% 1	4761
	21st to end	Day	57% 8% 12% 15% 7% 1	6072
April	1st to 10th	Day	49% 6% 11% 20% 13%	2520
	11th to 20th	Day	47% 6% 11% 22% 12% 3	2494
	21st to end	Day	49% 6% 12% 20% 11% 2	2650
May	1st to 10th	Day	47% 8% 13% 21% 12%	7651
	11th to 20th	Day	45% 7% 12% 20% 15% 1	7708
	21st to end	Day	42% 7% 11% 20% 16% 4	9061
June	1st to 10th	Day	38% 7% 12% 24% 17% 3	2940
	11th to 20th	Day	34% 8% 11% 23% 20% 4	2940
	21st to end	Day	39% 9% 13% 20% 16% 2	2940
July	1st to 10th	Day	37% 7% 14% 25% 15% 1	8211
	11th to 20th	Day	35% 7% 14% 29% 14% 1	8205
	21st to end	Day	40% 7% 14% 23% 14% 2	8794
August	1st to 10th	Day	36% 7% 16% 24% 18%	6143
	11th to 20th	Day	42% 8% 14% 25% 12% 1	5577
	21st to end	Day	27% 7% 15% 32% 17% 3	6079
September	1st to 10th	Day	33% 7% 11% 26% 18% 4	2520
	11th to 20th	Day	33% 6% 11% 24% 23% 4	2347
	21st to end	Day	37% 6% 10% 24% 21% 2	2310
October	1st to 10th	Day	25% 5% 8% 30% 31% 2	3700
	11th to 20th	Day	33% 5% 11% 23% 27% 1	3225
	21st to end	Day	43% 4 9% 25% 17% 2	3180
November	1st to 10th	Day	36% 5% 14% 26% 17% 3	1852
	11th to 20th	Day	50% 4 11% 21% 13% 2	1890
	21st to end	Day	52% 4 10% 22% 10% 1	1890
December	1st to 10th	Day	47% 3 12% 28% 10%	2756
	11th to 20th	Day	62% 4 11% 17% 5%	3085
	21st to end	Day	77% 5% 8% 8% 3	4070
January	1st to 10th	Night	60% 5% 12% 15% 7%	8233
	11th to 20th	Night	64% 4 9% 12% 10% 2	8280
	21st to end	Night	58% 4 10% 20% 8% 1	8906
February	1st to 10th	Night	56% 5% 12% 17% 8% 2	2598
	11th to 20th	Night	51% 4 11% 21% 11% 1	2459
	21st to end	Night	52% 5% 12% 18% 10% 3	2076
March	1st to 10th	Night	48% 5% 8% 25% 10% 3	5493
	11th to 20th	Night	39% 6% 12% 26% 15% 2	5419
	21st to end	Night	53% 7% 10% 21% 8% 1	5131
April	1st to 10th	Night	45% 6% 11% 22% 14% 2	2100
	11th to 20th	Night	46% 5% 9% 21% 15% 4	2075
	21st to end	Night	46% 6% 11% 22% 11% 3	1969
May	1st to 10th	Night	50% 6% 9% 19% 14% 2	5264
	11th to 20th	Night	37% 7% 13% 24% 18% 2	5145
	21st to end	Night	43% 8% 11% 17% 17% 5%	5149
June	1st to 10th	Night	34% 5% 11% 25% 22% 3	1680
	11th to 20th	Night	32% 6% 12% 26% 21% 3	1680
	21st to end	Night	36% 8% 14% 22% 16% 3	1680
July	1st to 10th	Night	35% 7% 13% 27% 15% 3	4670
	11th to 20th	Night	31% 8% 12% 26% 22% 1	4662
	21st to end	Night	37% 7% 14% 22% 16% 4	5002
August	1st to 10th	Night	35% 7% 15% 25% 17% 1	3987
	11th to 20th	Night	38% 9% 16% 22% 14% 1	4518
	21st to end	Night	28% 6% 13% 33% 18% 2	5046
September	1st to 10th	Night	29% 6% 12% 27% 20% 6%	2100
	11th to 20th	Night	26% 6% 9% 28% 27% 4	2252
	21st to end	Night	36% 7% 8% 24% 22% 3	2310
October	1st to 10th	Night	21% 4 6% 31% 36% 2	3700
	11th to 20th	Night	32% 4 9% 23% 30% 2	3975
	21st to end	Night	38% 4 9% 23% 23% 4	4610
November	1st to 10th	Night	38% 5% 10% 26% 18% 3	2666
	11th to 20th	Night	45% 5% 12% 21% 14% 2	2730
	21st to end	Night	53% 4 9% 23% 10%	2730
December	1st to 10th	Night	43% 4 13% 27% 12% 1	4647
	11th to 20th	Night	57% 4 12% 15% 11% 1	5341
	21st to end	Night	72% 5% 8% 10% 4	7150

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	23% 14% 35% 20% 6% 1	330
	11th to 20th	Day	22% 20% 38% 14% 4 1	330
	21st to end	Day	24% 18% 33% 20% 5% 1	363
February	1st to 10th	Day	21% 19% 35% 19% 4 1	330
	11th to 20th	Day	25% 16% 37% 18% 3	330
	21st to end	Day	26% 16% 45% 10% 3	273
March	1st to 10th	Day	24% 18% 38% 18% 2	330
	11th to 20th	Day	28% 15% 33% 19% 5%	393
	21st to end	Day	29% 15% 31% 19% 6% 1	594
April	1st to 10th	Day	26% 14% 29% 23% 6% 1	540
	11th to 20th	Day	20% 16% 33% 17% 11% 3	532
	21st to end	Day	23% 15% 31% 21% 8% 2	540
May	1st to 10th	Day	20% 12% 33% 24% 8% 3	543
	11th to 20th	Day	18% 12% 27% 25% 14% 4	593
	21st to end	Day	14% 7% 32% 25% 15% 7%	844
June	1st to 10th	Day	11% 8% 29% 28% 18% 6%	780
	11th to 20th	Day	11% 6% 30% 31% 17% 5%	780
	21st to end	Day	12% 7% 29% 31% 16% 5%	780
July	1st to 10th	Day	10% 4 17% 29% 23% 17%	771
	11th to 20th	Day	8% 3 21% 31% 23% 13%	768
	21st to end	Day	9% 4 21% 31% 26% 9%	849
August	1st to 10th	Day	7% 3 16% 30% 29% 14%	633
	11th to 20th	Day	9% 6% 18% 30% 22% 15%	559
	21st to end	Day	6% 3 16% 33% 30% 12%	627
September	1st to 10th	Day	11% 5% 19% 29% 28% 9%	570
	11th to 20th	Day	10% 4 15% 28% 30% 14%	570
	21st to end	Day	13% 9% 24% 24% 22% 9%	570
October	1st to 10th	Day	12% 8% 23% 32% 20% 5%	570
	11th to 20th	Day	17% 19% 25% 27% 11% 1	351
	21st to end	Day	27% 14% 36% 17% 6% 1	363
November	1st to 10th	Day	13% 15% 38% 20% 10% 3	330
	11th to 20th	Day	23% 18% 34% 16% 8% 1	330
	21st to end	Day	27% 13% 37% 19% 3	330
December	1st to 10th	Day	16% 18% 42% 17% 7%	330
	11th to 20th	Day	18% 21% 36% 19% 4 1	330
	21st to end	Day	27% 18% 37% 17% 2	363
January	1st to 10th	Night	22% 16% 36% 21% 5%	1050
	11th to 20th	Night	21% 17% 36% 21% 5%	1050
	21st to end	Night	21% 16% 37% 24% 3	1155
February	1st to 10th	Night	23% 13% 38% 23% 3	918
	11th to 20th	Night	20% 16% 37% 23% 4	823
	21st to end	Night	24% 14% 38% 21% 3	692
March	1st to 10th	Night	20% 15% 37% 23% 5%	840
	11th to 20th	Night	17% 13% 39% 25% 5%	840
	21st to end	Night	22% 11% 39% 22% 6%	726
April	1st to 10th	Night	17% 14% 39% 25% 5%	630
	11th to 20th	Night	22% 11% 35% 23% 8%	623
	21st to end	Night	21% 10% 33% 27% 8%	630
May	1st to 10th	Night	19% 8% 35% 31% 7%	630
	11th to 20th	Night	18% 5% 29% 34% 13% 1	621
	21st to end	Night	10% 5% 26% 40% 17% 1	683
June	1st to 10th	Night	12% 5% 23% 44% 16%	630
	11th to 20th	Night	11% 4 27% 43% 14%	630
	21st to end	Night	10% 5% 24% 41% 20%	630
July	1st to 10th	Night	10% 2 15% 40% 28% 5%	615
	11th to 20th	Night	7% 2 18% 40% 30% 4	612
	21st to end	Night	6% 2 15% 47% 29% 2	690
August	1st to 10th	Night	6% 2 13% 44% 31% 4	627
	11th to 20th	Night	7% 3 14% 41% 31% 4	624
	21st to end	Night	7% 2 12% 39% 36% 4	693
September	1st to 10th	Night	11% 2 16% 42% 26% 3	630
	11th to 20th	Night	8% 5% 14% 38% 31% 4	782
	21st to end	Night	12% 6% 22% 33% 24% 2	840
October	1st to 10th	Night	13% 4 23% 39% 19% 2	840
	11th to 20th	Night	18% 12% 29% 30% 11%	813
	21st to end	Night	22% 15% 32% 25% 6%	880
November	1st to 10th	Night	17% 10% 39% 25% 8% 1	820
	11th to 20th	Night	19% 16% 35% 23% 6% 1	840
	21st to end	Night	23% 15% 32% 24% 6%	840
December	1st to 10th	Night	23% 13% 37% 24% 4	1003
	11th to 20th	Night	24% 13% 33% 24% 6%	1050
	21st to end	Night	30% 15% 31% 22% 2	1155

Page generated at 2026-10-11 04:06:27. Version ac07

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