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 2025-06-10.

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% 4 4 4 5% 7% 36%	119269
	Night	14% 10% 4 8% 5% 4 4 3 5% 6% 37%	119140
Transparency	Day	45% 6% 12% 22% 14% 2	122864
	Night	46% 5% 11% 21% 14% 2	123686
Seeing	Day	17% 10% 28% 25% 15% 6%	16485
	Night	18% 10% 30% 30% 12% 1	26400

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% 13% 9% 14% 6% 5% 5% 3 5% 6% 21%	3617
	11th to 20th	Day	11% 14% 8% 15% 6% 6% 4 6% 5% 3 21%	3620
	21st to end	Day	19% 18% 5% 10% 5% 4 3 3 3 5% 25%	4091
February	1st to 10th	Day	16% 12% 5% 10% 6% 5% 6% 3 5% 5% 26%	1925
	11th to 20th	Day	14% 13% 4 9% 5% 5% 4 4 5% 5% 31%	1948
	21st to end	Day	16% 14% 6% 8% 4 4 4 3 5% 6% 31%	1650
March	1st to 10th	Day	19% 15% 3 7% 4 4 3 3 3 4 36%	4480
	11th to 20th	Day	9% 10% 3 7% 4 4 5% 4 6% 8% 41%	4658
	21st to end	Day	17% 12% 6% 10% 6% 5% 5% 4 5% 7% 24%	5939
April	1st to 10th	Day	17% 12% 3 7% 4 4 4 3 6% 7% 34%	2400
	11th to 20th	Day	16% 9% 3 7% 5% 5% 5% 4 5% 6% 37%	2374
	21st to end	Day	19% 8% 3 8% 5% 5% 4 3 5% 7% 34%	2524
May	1st to 10th	Day	18% 8% 3 7% 5% 5% 5% 4 6% 8% 30%	5862
	11th to 20th	Day	15% 6% 2 7% 5% 5% 5% 4 6% 8% 37%	5925
	21st to end	Day	13% 7% 3 7% 4 4 4 4 6% 9% 40%	6935
June	1st to 10th	Day	10% 6% 2 6% 4 4 6% 4 6% 8% 44%	2787
	11th to 20th	Day	8% 5% 2 6% 5% 5% 5% 4 6% 9% 45%	2660
	21st to end	Day	10% 6% 2 7% 6% 5% 6% 4 7% 8% 39%	2660
July	1st to 10th	Day	13% 6% 3 7% 5% 5% 5% 5% 7% 9% 35%	4440
	11th to 20th	Day	7% 5% 2 5% 4 4 5% 4 7% 12% 44%	4440
	21st to end	Day	9% 6% 3 7% 5% 5% 6% 5% 7% 8% 41%	4813
August	1st to 10th	Day	7% 5% 2 5% 5% 5% 5% 4 6% 9% 48%	4203
	11th to 20th	Day	9% 5% 2 6% 4 4 5% 5% 7% 9% 44%	3768
	21st to end	Day	6% 4 2 5% 4 5% 5% 4 6% 9% 50%	4180
September	1st to 10th	Day	10% 6% 2 5% 4 4 5% 4 6% 7% 47%	2280
	11th to 20th	Day	10% 5% 2 5% 4 4 4 3 6% 8% 50%	2123
	21st to end	Day	11% 6% 2 6% 4 4 4 3 5% 8% 45%	2090
October	1st to 10th	Day	12% 7% 2 6% 3 4 4 4 6% 7% 47%	2090
	11th to 20th	Day	17% 7% 3 6% 3 4 5% 4 5% 6% 39%	1880
	21st to end	Day	18% 10% 3 9% 5% 4 4 3 6% 6% 32%	1881
November	1st to 10th	Day	12% 7% 2 4 5% 4 4 3 5% 7% 48%	1762
	11th to 20th	Day	17% 12% 4 7% 5% 3 3 3 4 6% 36%	1800
	21st to end	Day	17% 12% 3 9% 4 3 3 3 4 6% 35%	1800
December	1st to 10th	Day	10% 12% 4 8% 5% 4 3 3 4 6% 41%	2674
	11th to 20th	Day	14% 15% 5% 13% 5% 5% 4 4 5% 6% 23%	3008
	21st to end	Day	27% 19% 8% 13% 5% 4 4 3 4 4 12%	3982
January	1st to 10th	Night	15% 15% 9% 13% 6% 4 4 3 5% 4 23%	6348
	11th to 20th	Night	13% 17% 7% 14% 7% 6% 5% 3 5% 4 19%	6360
	21st to end	Night	19% 15% 6% 8% 5% 4 4 3 3 3 29%	6886
February	1st to 10th	Night	16% 14% 4 8% 6% 5% 4 3 5% 6% 29%	2475
	11th to 20th	Night	15% 12% 4 9% 5% 4 5% 3 5% 6% 34%	2338
	21st to end	Night	19% 12% 3 8% 5% 3 4 3 5% 5% 33%	1980
March	1st to 10th	Night	16% 12% 5% 6% 4 4 3 3 4 5% 39%	5373
	11th to 20th	Night	12% 7% 3 6% 4 4 4 4 5% 6% 45%	5302
	21st to end	Night	18% 10% 5% 8% 5% 5% 5% 4 5% 6% 29%	5019
April	1st to 10th	Night	14% 9% 3 8% 5% 4 4 3 5% 7% 38%	2000
	11th to 20th	Night	18% 9% 3 6% 5% 4 4 3 4 6% 38%	1975
	21st to end	Night	17% 8% 2 7% 5% 5% 4 4 5% 7% 35%	1875
May	1st to 10th	Night	19% 10% 3 8% 5% 4 4 3 5% 7% 33%	4033
	11th to 20th	Night	16% 7% 2 6% 3 4 4 3 5% 9% 41%	3955
	21st to end	Night	14% 8% 3 8% 5% 5% 4 4 5% 7% 39%	3942
June	1st to 10th	Night	10% 6% 2 6% 4 3 4 2 6% 9% 49%	1597
	11th to 20th	Night	8% 6% 2 6% 4 4 3 3 6% 9% 49%	1520
	21st to end	Night	9% 7% 2 6% 6% 5% 6% 4 6% 9% 43%	1520
July	1st to 10th	Night	10% 4 2 6% 5% 5% 5% 5% 7% 10% 42%	2530
	11th to 20th	Night	5% 4 2 6% 3 4 4 4 5% 9% 55%	2530
	21st to end	Night	5% 6% 2 8% 5% 5% 5% 5% 6% 7% 45%	2750
August	1st to 10th	Night	8% 5% 2 5% 4 4 4 4 6% 9% 48%	2728
	11th to 20th	Night	7% 5% 2 5% 4 4 5% 4 6% 8% 50%	3058
	21st to end	Night	9% 4 2 5% 4 3 4 4 5% 8% 53%	3476
September	1st to 10th	Night	10% 5% 1 5% 3 3 4 2 5% 8% 53%	1900
	11th to 20th	Night	8% 5% 1 4 3 3 4 3 6% 8% 55%	2038
	21st to end	Night	10% 7% 2 7% 4 4 4 4 5% 7% 47%	2090
October	1st to 10th	Night	11% 6% 2 5% 4 3 3 3 4 6% 53%	2090
	11th to 20th	Night	15% 7% 2 6% 3 4 3 3 4 6% 47%	2295
	21st to end	Night	19% 8% 3 7% 4 3 4 3 5% 6% 38%	2717
November	1st to 10th	Night	12% 8% 3 6% 4 3 4 3 5% 7% 46%	2536
	11th to 20th	Night	14% 9% 3 7% 5% 4 5% 4 6% 6% 37%	2600
	21st to end	Night	17% 12% 3 8% 5% 4 4 3 4 6% 34%	2600
December	1st to 10th	Night	11% 9% 3 7% 4 4 4 3 4 6% 44%	4509
	11th to 20th	Night	17% 14% 4 9% 5% 5% 5% 3 4 4 30%	5199
	21st to end	Night	25% 19% 6% 11% 6% 4 4 3 4 5% 15%	6996

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	63% 5% 10% 14% 7% 1	3618
	11th to 20th	Day	65% 4 9% 8% 11% 3	3620
	21st to end	Day	64% 3 10% 16% 7%	4091
February	1st to 10th	Day	60% 4 12% 15% 7% 2	1925
	11th to 20th	Day	54% 5% 10% 22% 9% 1	1958
	21st to end	Day	53% 6% 11% 20% 8% 2	1650
March	1st to 10th	Day	53% 4 6% 22% 12% 3	4480
	11th to 20th	Day	39% 6% 10% 34% 10% 1	4658
	21st to end	Day	57% 8% 12% 15% 7% 1	5941
April	1st to 10th	Day	49% 6% 11% 20% 13%	2400
	11th to 20th	Day	47% 6% 10% 22% 12% 3	2374
	21st to end	Day	50% 6% 12% 19% 11% 2	2524
May	1st to 10th	Day	48% 8% 12% 20% 11%	5897
	11th to 20th	Day	44% 7% 12% 23% 13% 1	5929
	21st to end	Day	40% 7% 11% 23% 16% 2	6949
June	1st to 10th	Day	37% 7% 12% 25% 16% 3	2787
	11th to 20th	Day	33% 8% 11% 23% 21% 4	2660
	21st to end	Day	40% 9% 13% 20% 16% 3	2660
July	1st to 10th	Day	44% 6% 12% 22% 13% 2	4371
	11th to 20th	Day	31% 8% 16% 28% 16% 1	4365
	21st to end	Day	38% 8% 16% 17% 18% 3	4662
August	1st to 10th	Day	31% 7% 17% 29% 15% 1	4188
	11th to 20th	Day	33% 8% 13% 29% 16% 1	3805
	21st to end	Day	29% 7% 14% 28% 18% 4	4179
September	1st to 10th	Day	35% 7% 12% 24% 17% 5%	2280
	11th to 20th	Day	32% 6% 11% 24% 22% 4	2123
	21st to end	Day	36% 6% 10% 25% 20% 2	2090
October	1st to 10th	Day	25% 5% 8% 30% 31% 2	3480
	11th to 20th	Day	33% 5% 11% 23% 28% 1	3096
	21st to end	Day	43% 4 9% 25% 17% 2	3081
November	1st to 10th	Day	36% 4 15% 25% 17% 3	1762
	11th to 20th	Day	50% 4 11% 21% 13% 2	1800
	21st to end	Day	52% 5% 10% 22% 10% 1	1800
December	1st to 10th	Day	46% 3 12% 29% 9%	2674
	11th to 20th	Day	62% 4 12% 17% 5%	3005
	21st to end	Day	77% 5% 8% 8% 3	3982
January	1st to 10th	Night	63% 5% 9% 14% 9%	6348
	11th to 20th	Night	68% 3 8% 9% 9% 2	6360
	21st to end	Night	61% 3 8% 17% 10% 1	6886
February	1st to 10th	Night	56% 5% 12% 17% 8% 2	2475
	11th to 20th	Night	52% 4 11% 20% 12% 1	2339
	21st to end	Night	52% 5% 12% 18% 10% 3	1980
March	1st to 10th	Night	48% 5% 8% 25% 10% 3	5373
	11th to 20th	Night	38% 6% 12% 26% 15% 2	5302
	21st to end	Night	53% 7% 10% 21% 8% 1	5019
April	1st to 10th	Night	44% 6% 12% 22% 14% 2	2000
	11th to 20th	Night	47% 5% 9% 21% 15% 4	1975
	21st to end	Night	47% 6% 11% 21% 12% 4	1875
May	1st to 10th	Night	51% 7% 10% 16% 14% 3	4060
	11th to 20th	Night	39% 8% 13% 25% 13% 2	3956
	21st to end	Night	43% 8% 11% 19% 15% 4	3950
June	1st to 10th	Night	33% 5% 12% 25% 22% 3	1597
	11th to 20th	Night	30% 6% 12% 26% 21% 4	1520
	21st to end	Night	37% 8% 14% 22% 15% 4	1520
July	1st to 10th	Night	36% 7% 16% 25% 11% 5%	2490
	11th to 20th	Night	25% 7% 12% 28% 26% 2	2482
	21st to end	Night	35% 7% 16% 19% 18% 5%	2662
August	1st to 10th	Night	30% 8% 18% 27% 15% 2	2719
	11th to 20th	Night	29% 7% 15% 28% 19% 1	3087
	21st to end	Night	29% 7% 12% 31% 19% 3	3476
September	1st to 10th	Night	30% 6% 12% 25% 20% 7%	1900
	11th to 20th	Night	26% 6% 9% 28% 27% 5%	2038
	21st to end	Night	36% 7% 9% 25% 21% 3	2090
October	1st to 10th	Night	21% 4 6% 32% 35% 2	3480
	11th to 20th	Night	32% 4 9% 24% 30% 2	3818
	21st to end	Night	38% 4 9% 23% 23% 4	4467
November	1st to 10th	Night	37% 5% 10% 26% 18% 3	2536
	11th to 20th	Night	46% 5% 12% 20% 14% 3	2600
	21st to end	Night	53% 4 9% 23% 10% 1	2600
December	1st to 10th	Night	42% 4 13% 28% 12% 1	4509
	11th to 20th	Night	57% 4 12% 15% 11% 1	5201
	21st to end	Night	72% 5% 8% 10% 4	6996

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% 13% 37% 18% 7% 1	300
	11th to 20th	Day	23% 18% 39% 15% 4 1	300
	21st to end	Day	25% 16% 33% 19% 5% 1	330
February	1st to 10th	Day	23% 20% 35% 19% 4	300
	11th to 20th	Day	25% 15% 38% 18% 4	300
	21st to end	Day	27% 15% 44% 10% 4	249
March	1st to 10th	Day	23% 18% 38% 19% 2	300
	11th to 20th	Day	27% 15% 32% 20% 5%	360
	21st to end	Day	30% 14% 31% 19% 6% 1	550
April	1st to 10th	Day	25% 14% 29% 25% 6% 1	500
	11th to 20th	Day	21% 15% 33% 16% 11% 3	492
	21st to end	Day	23% 15% 32% 20% 8% 2	500
May	1st to 10th	Day	20% 12% 32% 25% 9% 3	503
	11th to 20th	Day	19% 10% 26% 26% 15% 5%	552
	21st to end	Day	14% 7% 33% 25% 14% 7%	789
June	1st to 10th	Day	11% 8% 28% 29% 18% 6%	726
	11th to 20th	Day	10% 4 29% 33% 19% 6%	680
	21st to end	Day	12% 7% 29% 31% 16% 5%	680
July	1st to 10th	Day	10% 4 18% 27% 22% 18%	671
	11th to 20th	Day	8% 3 22% 31% 23% 13%	668
	21st to end	Day	9% 4 19% 31% 27% 10%	739
August	1st to 10th	Day	7% 3 16% 30% 30% 15%	547
	11th to 20th	Day	9% 5% 17% 30% 22% 16%	479
	21st to end	Day	7% 2 16% 33% 31% 12%	539
September	1st to 10th	Day	12% 5% 18% 29% 29% 8%	490
	11th to 20th	Day	9% 3 14% 29% 31% 14%	490
	21st to end	Day	13% 9% 24% 24% 22% 8%	490
October	1st to 10th	Day	14% 8% 22% 30% 20% 6%	490
	11th to 20th	Day	18% 20% 26% 24% 10% 2	311
	21st to end	Day	28% 12% 35% 16% 7% 1	330
November	1st to 10th	Day	13% 14% 38% 20% 11% 3	300
	11th to 20th	Day	22% 17% 35% 16% 9% 1	300
	21st to end	Day	26% 13% 38% 20% 3	300
December	1st to 10th	Day	17% 19% 40% 16% 8%	300
	11th to 20th	Day	17% 21% 36% 20% 5% 1	300
	21st to end	Day	27% 17% 35% 18% 2	330
January	1st to 10th	Night	22% 17% 35% 21% 5%	1000
	11th to 20th	Night	22% 17% 35% 22% 5%	1000
	21st to end	Night	21% 15% 36% 24% 4	1100
February	1st to 10th	Night	24% 13% 38% 22% 3	875
	11th to 20th	Night	20% 16% 36% 24% 4	783
	21st to end	Night	25% 13% 38% 21% 3	660
March	1st to 10th	Night	20% 14% 37% 24% 6%	800
	11th to 20th	Night	17% 13% 39% 26% 5%	800
	21st to end	Night	23% 10% 39% 22% 7%	691
April	1st to 10th	Night	17% 12% 39% 26% 5% 1	600
	11th to 20th	Night	21% 11% 35% 24% 8%	593
	21st to end	Night	21% 10% 33% 27% 8%	600
May	1st to 10th	Night	19% 8% 35% 31% 7% 1	600
	11th to 20th	Night	19% 5% 29% 33% 14% 1	591
	21st to end	Night	10% 5% 26% 40% 17% 1	650
June	1st to 10th	Night	12% 5% 23% 44% 16%	599
	11th to 20th	Night	11% 3 27% 44% 15% 1	570
	21st to end	Night	10% 5% 25% 40% 20%	570
July	1st to 10th	Night	9% 1 16% 40% 29% 5%	555
	11th to 20th	Night	7% 2 18% 40% 29% 4	552
	21st to end	Night	5% 2 14% 47% 30% 2	624
August	1st to 10th	Night	6% 2 13% 45% 30% 4	567
	11th to 20th	Night	6% 2 15% 40% 32% 4	564
	21st to end	Night	8% 2 13% 37% 37% 4	627
September	1st to 10th	Night	12% 2 16% 41% 26% 3	570
	11th to 20th	Night	8% 5% 14% 37% 32% 4	708
	21st to end	Night	12% 6% 23% 32% 24% 3	760
October	1st to 10th	Night	14% 4 23% 38% 19% 2	760
	11th to 20th	Night	19% 13% 29% 28% 11%	760
	21st to end	Night	22% 15% 31% 25% 7%	836
November	1st to 10th	Night	17% 10% 38% 25% 8% 2	780
	11th to 20th	Night	19% 16% 34% 24% 7% 1	800
	21st to end	Night	22% 14% 33% 24% 7%	800
December	1st to 10th	Night	23% 12% 37% 24% 4	955
	11th to 20th	Night	24% 13% 33% 24% 6%	1000
	21st to end	Night	30% 15% 30% 23% 2	1100

Page generated at 2025-06-07 09:28:17. Version ac07

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