Horseappleacres Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Horseappleacres Observatory clear sky chart from 2005-11-06 to 2025-01-07.

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	3 5% 2 5% 4 4 5% 4 6% 8% 53%	108844
	Night	3 5% 2 5% 4 4 4 4 6% 8% 57%	108943
Transparency	Day	25% 6% 11% 23% 24% 11%	108589
	Night	23% 6% 12% 25% 24% 9%	108789
Seeing	Day	7% 11% 31% 29% 17% 5%	15734
	Night	6% 6% 34% 38% 14% 2	25856

By Month

Percentage Cloud Cover SW (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	1 4 2 4 3 4 5% 4 6% 8% 60%	2586
	11th to 20th	Day	1 3 2 5% 4 4 6% 5% 6% 9% 55%	2636
	21st to end	Day	1 5% 2 8% 4 3 4 3 5% 6% 58%	3146
February	1st to 10th	Day	1 7% 3 6% 3 4 4 3 5% 7% 56%	1723
	11th to 20th	Day	1 3 2 5% 4 5% 5% 4 7% 7% 57%	1849
	21st to end	Day	1 6% 3 7% 3 4 4 3 5% 5% 58%	1570
March	1st to 10th	Day	2 6% 3 6% 3 4 4 3 5% 6% 58%	3130
	11th to 20th	Day	3 11% 4 7% 4 5% 4 3 5% 8% 46%	3417
	21st to end	Day	2 7% 3 6% 4 4 4 4 7% 8% 51%	4086
April	1st to 10th	Day	4 8% 2 5% 4 4 4 5% 6% 8% 51%	2280
	11th to 20th	Day	5% 8% 3 7% 4 5% 5% 4 6% 6% 46%	2251
	21st to end	Day	6% 8% 2 5% 4 4 5% 5% 6% 8% 45%	2280
May	1st to 10th	Day	7% 8% 3 6% 5% 5% 5% 5% 7% 8% 43%	4006
	11th to 20th	Day	7% 6% 2 7% 5% 5% 5% 5% 6% 9% 42%	4289
	21st to end	Day	3 5% 2 5% 4 5% 6% 6% 8% 9% 48%	4825
June	1st to 10th	Day	4 4 2 5% 5% 5% 6% 7% 8% 9% 47%	2660
	11th to 20th	Day	4 3 1 5% 4 5% 5% 5% 8% 9% 50%	2660
	21st to end	Day	3 3 2 5% 6% 6% 6% 5% 9% 10% 46%	2660
July	1st to 10th	Day	4 3 1 5% 4 4 6% 4 7% 10% 51%	4430
	11th to 20th	Day	3 4 2 6% 5% 6% 6% 5% 9% 11% 44%	4430
	21st to end	Day	5% 4 2 6% 4 5% 5% 5% 6% 8% 50%	4709
August	1st to 10th	Day	7% 6% 2 7% 5% 6% 7% 6% 9% 9% 36%	4031
	11th to 20th	Day	4 4 2 5% 5% 5% 6% 6% 8% 10% 46%	3726
	21st to end	Day	4 4 2 5% 4 6% 5% 5% 8% 10% 47%	4180
September	1st to 10th	Day	5% 4 2 4 4 4 4 4 6% 7% 56%	2280
	11th to 20th	Day	5% 3 2 4 4 4 4 4 5% 8% 58%	2242
	21st to end	Day	5% 3 1 4 4 4 4 3 4 5% 64%	2090
October	1st to 10th	Day	3 2 1 3 3 2 3 2 3 4 73%	3238
	11th to 20th	Day	4 4 2 5% 4 3 4 3 5% 7% 59%	3150
	21st to end	Day	3 4 1 3 2 2 2 3 4 6% 70%	3317
November	1st to 10th	Day	2 3 2 3 2 3 3 3 7% 8% 64%	1763
	11th to 20th	Day	1 5% 2 3 3 3 3 3 5% 8% 64%	1800
	21st to end	Day	1 5% 2 4 3 3 4 3 5% 6% 63%	1754
December	1st to 10th	Day	1 4 2 5% 3 2 2 2 4 6% 69%	2620
	11th to 20th	Day	1 3 2 4 3 3 3 2 5% 7% 68%	3026
	21st to end	Day	1 4 2 6% 4 4 4 3 5% 7% 60%	4004
January	1st to 10th	Night	5% 3 7% 4 4 4 3 6% 8% 56%	4502
	11th to 20th	Night	1 3 1 3 4 4 4 4 6% 8% 63%	4365
	21st to end	Night	1 5% 2 6% 5% 4 3 4 4 7% 59%	4521
February	1st to 10th	Night	1 5% 3 7% 4 3 5% 3 5% 8% 57%	2456
	11th to 20th	Night	1 6% 3 6% 5% 4 4 5% 6% 7% 54%	2218
	21st to end	Night	1 6% 2 6% 3 4 4 3 4 5% 63%	1884
March	1st to 10th	Night	1 5% 2 6% 4 3 4 4 6% 6% 58%	3734
	11th to 20th	Night	5% 12% 3 5% 4 3 4 3 5% 6% 51%	3557
	21st to end	Night	2 6% 2 6% 4 4 4 4 7% 8% 53%	3557
April	1st to 10th	Night	3 6% 2 5% 4 4 3 3 5% 6% 57%	1900
	11th to 20th	Night	6% 10% 2 6% 4 4 4 3 5% 6% 49%	1877
	21st to end	Night	7% 9% 2 5% 4 5% 4 3 5% 6% 49%	1900
May	1st to 10th	Night	7% 7% 2 5% 4 4 5% 4 6% 7% 48%	2960
	11th to 20th	Night	7% 7% 2 6% 4 4 4 5% 6% 9% 45%	2612
	21st to end	Night	4 4 2 6% 5% 5% 4 4 6% 7% 53%	2762
June	1st to 10th	Night	3 4 1 4 3 4 4 5% 7% 11% 54%	1520
	11th to 20th	Night	3 3 1 4 3 3 4 4 6% 10% 60%	1520
	21st to end	Night	3 4 2 4 4 5% 5% 5% 7% 8% 52%	1520
July	1st to 10th	Night	5% 3 2 5% 5% 4 5% 4 7% 6% 54%	2540
	11th to 20th	Night	2 3 2 5% 4 5% 5% 5% 8% 11% 50%	2540
	21st to end	Night	4 2 1 5% 4 5% 5% 4 7% 11% 52%	2850
August	1st to 10th	Night	7% 5% 2 8% 7% 6% 6% 5% 8% 11% 35%	2906
	11th to 20th	Night	3 3 2 6% 5% 6% 6% 5% 8% 10% 46%	3113
	21st to end	Night	2 3 1 5% 4 5% 6% 5% 9% 12% 47%	3487
September	1st to 10th	Night	4 5% 2 5% 4 4 6% 5% 6% 9% 51%	1900
	11th to 20th	Night	5% 2 1 5% 3 4 4 3 5% 7% 61%	1936
	21st to end	Night	4 3 2 4 3 2 4 3 5% 6% 63%	2090
October	1st to 10th	Night	4 3 1 3 2 2 3 3 4 5% 69%	3726
	11th to 20th	Night	7% 4 1 5% 4 3 4 3 5% 6% 57%	3778
	21st to end	Night	3 3 2 4 3 3 4 3 4 5% 67%	4208
November	1st to 10th	Night	1 4 1 5% 3 3 3 3 5% 7% 65%	2535
	11th to 20th	Night	1 3 2 5% 3 2 3 3 4 6% 68%	2600
	21st to end	Night	2 5% 2 5% 4 4 3 3 5% 6% 61%	2644
December	1st to 10th	Night	1 2 1 4 2 3 2 2 4 6% 73%	4570
	11th to 20th	Night	1 3 2 4 4 3 3 2 5% 8% 65%	5181
	21st to end	Night	2 6% 2 5% 4 4 4 3 5% 8% 57%	6974

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	17% 5% 12% 34% 23% 9%	2587
	11th to 20th	Day	21% 5% 15% 29% 22% 8%	2636
	21st to end	Day	24% 5% 10% 28% 26% 6%	3146
February	1st to 10th	Day	25% 5% 12% 27% 21% 10%	1723
	11th to 20th	Day	22% 6% 10% 27% 29% 8%	1859
	21st to end	Day	25% 5% 8% 22% 23% 17%	1570
March	1st to 10th	Day	21% 6% 10% 18% 30% 14%	3130
	11th to 20th	Day	31% 7% 13% 30% 16% 3	3417
	21st to end	Day	24% 8% 11% 30% 23% 4	4086
April	1st to 10th	Day	26% 7% 12% 24% 21% 10%	2280
	11th to 20th	Day	33% 7% 11% 21% 18% 9%	2254
	21st to end	Day	32% 8% 13% 24% 19% 4	2280
May	1st to 10th	Day	31% 9% 12% 24% 13% 11%	4006
	11th to 20th	Day	33% 10% 14% 21% 19% 3	4293
	21st to end	Day	24% 11% 15% 21% 19% 9%	4825
June	1st to 10th	Day	27% 9% 15% 23% 17% 10%	2660
	11th to 20th	Day	24% 7% 12% 18% 23% 16%	2660
	21st to end	Day	27% 8% 12% 20% 22% 11%	2660
July	1st to 10th	Day	26% 7% 9% 16% 28% 13%	4361
	11th to 20th	Day	30% 7% 11% 21% 21% 10%	4355
	21st to end	Day	29% 7% 11% 17% 18% 18%	4561
August	1st to 10th	Day	39% 8% 16% 22% 12% 4	4017
	11th to 20th	Day	30% 8% 13% 17% 18% 14%	3762
	21st to end	Day	28% 6% 14% 20% 26% 7%	4179
September	1st to 10th	Day	25% 5% 10% 22% 24% 14%	2280
	11th to 20th	Day	23% 6% 10% 17% 29% 16%	2242
	21st to end	Day	22% 4 8% 21% 33% 13%	2090
October	1st to 10th	Day	15% 4 7% 15% 39% 20%	3238
	11th to 20th	Day	25% 3 6% 24% 31% 9%	3150
	21st to end	Day	16% 2 5% 24% 37% 15%	3317
November	1st to 10th	Day	15% 4 12% 23% 28% 18%	1763
	11th to 20th	Day	16% 5% 7% 28% 31% 13%	1800
	21st to end	Day	21% 4 9% 22% 30% 15%	1754
December	1st to 10th	Day	18% 3 8% 30% 31% 10%	2620
	11th to 20th	Day	17% 3 7% 30% 31% 11%	3024
	21st to end	Day	22% 5% 8% 28% 25% 11%	4004
January	1st to 10th	Night	23% 4 11% 29% 27% 5%	4502
	11th to 20th	Night	16% 7% 13% 29% 25% 9%	4365
	21st to end	Night	23% 6% 13% 32% 21% 5%	4521
February	1st to 10th	Night	24% 6% 11% 28% 23% 9%	2456
	11th to 20th	Night	27% 5% 10% 28% 21% 8%	2218
	21st to end	Night	21% 4 7% 27% 26% 15%	1884
March	1st to 10th	Night	20% 7% 10% 18% 34% 11%	3734
	11th to 20th	Night	31% 7% 13% 23% 23% 3	3557
	21st to end	Night	23% 8% 13% 28% 24% 4	3557
April	1st to 10th	Night	25% 5% 13% 23% 24% 10%	1900
	11th to 20th	Night	32% 5% 12% 25% 18% 7%	1877
	21st to end	Night	31% 8% 13% 27% 16% 5%	1900
May	1st to 10th	Night	28% 8% 16% 24% 14% 10%	2960
	11th to 20th	Night	31% 10% 19% 24% 9% 7%	2613
	21st to end	Night	22% 12% 15% 24% 19% 7%	2762
June	1st to 10th	Night	23% 8% 21% 25% 14% 9%	1520
	11th to 20th	Night	18% 7% 15% 24% 19% 17%	1520
	21st to end	Night	25% 9% 10% 23% 23% 10%	1520
July	1st to 10th	Night	28% 7% 11% 19% 28% 7%	2500
	11th to 20th	Night	25% 6% 16% 31% 17% 5%	2492
	21st to end	Night	23% 9% 16% 25% 14% 14%	2761
August	1st to 10th	Night	40% 9% 18% 19% 11% 4	2897
	11th to 20th	Night	31% 7% 19% 20% 19% 5%	3143
	21st to end	Night	27% 7% 20% 25% 18% 4	3487
September	1st to 10th	Night	27% 7% 10% 22% 22% 11%	1900
	11th to 20th	Night	21% 4 11% 22% 27% 15%	1936
	21st to end	Night	22% 5% 8% 24% 31% 10%	2090
October	1st to 10th	Night	18% 4 8% 21% 34% 17%	3726
	11th to 20th	Night	26% 4 7% 28% 26% 9%	3778
	21st to end	Night	18% 3 7% 27% 31% 15%	4208
November	1st to 10th	Night	18% 4 11% 23% 28% 16%	2535
	11th to 20th	Night	16% 4 8% 28% 32% 12%	2600
	21st to end	Night	21% 4 10% 22% 31% 12%	2644
December	1st to 10th	Night	14% 3 8% 33% 33% 9%	4570
	11th to 20th	Night	18% 3 7% 29% 35% 9%	5182
	21st to end	Night	24% 5% 10% 22% 26% 12%	6974

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	6% 9% 36% 34% 13% 3	288
	11th to 20th	Day	7% 13% 33% 34% 11% 1	270
	21st to end	Day	1 12% 41% 31% 12% 3	297
February	1st to 10th	Day	4 14% 49% 24% 7% 2	270
	11th to 20th	Day	3 16% 46% 25% 10% 1	270
	21st to end	Day	2 22% 46% 25% 5%	225
March	1st to 10th	Day	4 15% 40% 28% 10% 2	270
	11th to 20th	Day	10% 17% 37% 23% 10% 2	413
	21st to end	Day	12% 23% 38% 20% 6% 1	506
April	1st to 10th	Day	11% 19% 40% 21% 8% 1	460
	11th to 20th	Day	14% 27% 34% 18% 6% 2	452
	21st to end	Day	14% 18% 34% 25% 7% 1	460
May	1st to 10th	Day	13% 19% 36% 22% 8% 2	578
	11th to 20th	Day	12% 12% 30% 29% 13% 3	675
	21st to end	Day	9% 13% 31% 26% 17% 4	734
June	1st to 10th	Day	6% 11% 24% 31% 22% 6%	680
	11th to 20th	Day	6% 11% 30% 32% 17% 4	680
	21st to end	Day	5% 7% 28% 31% 23% 6%	680
July	1st to 10th	Day	7% 4 20% 29% 31% 8%	671
	11th to 20th	Day	6% 1 16% 34% 34% 9%	668
	21st to end	Day	8% 2 16% 29% 35% 11%	682
August	1st to 10th	Day	10% 3 18% 37% 25% 7%	487
	11th to 20th	Day	7% 4 23% 32% 25% 9%	477
	21st to end	Day	6% 3 26% 38% 20% 7%	539
September	1st to 10th	Day	7% 6% 24% 36% 18% 10%	490
	11th to 20th	Day	5% 7% 30% 28% 23% 7%	452
	21st to end	Day	8% 8% 21% 26% 29% 8%	300
October	1st to 10th	Day	8% 13% 19% 28% 21% 10%	300
	11th to 20th	Day	3 9% 34% 32% 17% 5%	300
	21st to end	Day	7% 13% 36% 25% 17% 2	330
November	1st to 10th	Day	6% 15% 33% 28% 14% 4	300
	11th to 20th	Day	3 10% 37% 36% 11% 3	300
	21st to end	Day	5% 13% 37% 29% 11% 4	300
December	1st to 10th	Day	4 15% 39% 25% 15% 2	300
	11th to 20th	Day	4 10% 43% 30% 12% 1	300
	21st to end	Day	4 14% 45% 27% 9% 2	330
January	1st to 10th	Night	3 6% 39% 36% 12% 3	981
	11th to 20th	Night	4 6% 43% 37% 9% 2	911
	21st to end	Night	2 4 39% 43% 10% 1	836
February	1st to 10th	Night	3 5% 53% 32% 6% 1	760
	11th to 20th	Night	3 6% 51% 33% 7%	744
	21st to end	Night	4 9% 52% 31% 4	628
March	1st to 10th	Night	3 7% 48% 33% 8% 1	760
	11th to 20th	Night	6% 8% 36% 41% 8% 1	760
	21st to end	Night	5% 10% 45% 33% 6%	681
April	1st to 10th	Night	7% 11% 46% 31% 5%	570
	11th to 20th	Night	14% 11% 37% 31% 7% 1	563
	21st to end	Night	13% 11% 36% 32% 8% 1	570
May	1st to 10th	Night	11% 11% 31% 37% 9% 1	570
	11th to 20th	Night	14% 7% 30% 36% 12% 2	561
	21st to end	Night	11% 6% 35% 33% 14% 2	617
June	1st to 10th	Night	5% 6% 24% 43% 19% 3	570
	11th to 20th	Night	4 6% 28% 49% 13%	570
	21st to end	Night	5% 2 21% 48% 21% 1	570
July	1st to 10th	Night	6% 3 16% 45% 27% 3	555
	11th to 20th	Night	5% 1 12% 45% 33% 4	552
	21st to end	Night	8% 2 10% 40% 37% 3	624
August	1st to 10th	Night	8% 2 13% 41% 33% 3	567
	11th to 20th	Night	6% 2 13% 50% 27% 2	564
	21st to end	Night	5% 2 13% 47% 29% 4	627
September	1st to 10th	Night	6% 3 16% 44% 28% 4	570
	11th to 20th	Night	8% 2 19% 48% 21% 4	570
	21st to end	Night	5% 4 26% 43% 19% 4	570
October	1st to 10th	Night	9% 5% 28% 38% 17% 3	712
	11th to 20th	Night	5% 3 35% 38% 16% 3	760
	21st to end	Night	6% 6% 33% 36% 16% 3	888
November	1st to 10th	Night	3 5% 35% 41% 13% 2	975
	11th to 20th	Night	3 6% 39% 41% 9% 2	1000
	21st to end	Night	5% 7% 36% 38% 12% 2	1000
December	1st to 10th	Night	2 6% 43% 38% 10% 1	1000
	11th to 20th	Night	3 6% 45% 34% 11% 1	1000
	21st to end	Night	4 10% 44% 34% 7% 1	1100

Page generated at 2025-01-04 01:23:59. Version ac07

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