Owl Hollow
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Owl Hollow clear sky chart from 2005-11-06 to 2024-12-02.

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	5% 5% 2 5% 4 4 4 4 6% 8% 53%	105452
	Night	5% 6% 2 6% 4 4 4 4 6% 7% 52%	102889
Transparency	Day	28% 6% 11% 24% 21% 9%	105193
	Night	29% 6% 12% 25% 21% 7%	102738
Seeing	Day	9% 7% 24% 32% 21% 7%	15767
	Night	8% 7% 30% 41% 14% 1	25798

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	2 7% 3 8% 4 3 3 2 4 6% 57%	2538
	11th to 20th	Day	2 6% 3 8% 6% 6% 7% 5% 7% 7% 46%	2540
	21st to end	Day	1 5% 3 5% 3 4 4 4 6% 7% 58%	3082
February	1st to 10th	Day	3 8% 5% 8% 6% 4 5% 5% 6% 6% 45%	1710
	11th to 20th	Day	2 7% 3 8% 4 5% 5% 4 6% 7% 51%	1840
	21st to end	Day	2 9% 4 7% 4 4 4 4 5% 6% 52%	1570
March	1st to 10th	Day	4 8% 3 6% 3 4 4 4 5% 7% 52%	3130
	11th to 20th	Day	5% 7% 3 6% 4 4 4 3 5% 6% 54%	3357
	21st to end	Day	4 7% 3 7% 5% 5% 5% 5% 6% 9% 43%	4119
April	1st to 10th	Day	8% 7% 2 4 4 4 5% 4 6% 7% 50%	2280
	11th to 20th	Day	11% 9% 3 6% 4 4 4 4 6% 8% 41%	2251
	21st to end	Day	10% 7% 2 6% 4 4 5% 4 7% 8% 43%	2280
May	1st to 10th	Day	10% 9% 3 8% 4 5% 5% 4 6% 6% 41%	4120
	11th to 20th	Day	8% 4 2 6% 4 5% 5% 6% 7% 10% 43%	4373
	21st to end	Day	6% 5% 1 5% 4 4 5% 4 7% 9% 48%	4825
June	1st to 10th	Day	6% 3 1 4 3 4 4 4 8% 11% 52%	2660
	11th to 20th	Day	6% 3 1 4 4 4 5% 4 7% 9% 52%	2660
	21st to end	Day	3 3 1 5% 3 4 5% 5% 8% 9% 54%	2660
July	1st to 10th	Day	7% 4 1 4 3 4 4 4 6% 7% 55%	4430
	11th to 20th	Day	2 2 1 4 4 5% 5% 6% 9% 10% 52%	4430
	21st to end	Day	3 3 2 5% 4 5% 5% 4 6% 9% 55%	4802
August	1st to 10th	Day	11% 3 1 4 4 5% 5% 5% 8% 10% 44%	4151
	11th to 20th	Day	3 4 2 5% 4 4 5% 5% 7% 10% 53%	3726
	21st to end	Day	4 3 1 4 3 4 5% 4 7% 8% 57%	4180
September	1st to 10th	Day	5% 4 1 3 2 3 4 3 5% 9% 61%	2280
	11th to 20th	Day	6% 2 1 4 3 3 4 4 5% 7% 61%	2231
	21st to end	Day	7% 4 1 3 2 3 3 2 4 5% 65%	2090
October	1st to 10th	Day	5% 3 1 2 2 1 2 2 3 5% 75%	3263
	11th to 20th	Day	4 5% 2 4 3 3 2 3 5% 7% 63%	3150
	21st to end	Day	7% 6% 2 4 3 3 3 3 5% 7% 59%	3218
November	1st to 10th	Day	3 5% 2 5% 3 4 3 4 6% 7% 57%	1763
	11th to 20th	Day	4 7% 2 3 3 3 4 3 5% 8% 59%	1800
	21st to end	Day	2 7% 3 5% 4 3 4 3 4 7% 58%	1695
December	1st to 10th	Day	3 6% 3 8% 4 4 4 3 5% 8% 52%	1528
	11th to 20th	Day	4 8% 2 6% 4 4 4 3 5% 8% 52%	1926
	21st to end	Day	3 10% 3 8% 5% 5% 4 3 5% 6% 48%	2794
January	1st to 10th	Night	3 7% 3 6% 4 4 4 4 5% 8% 52%	4417
	11th to 20th	Night	2 5% 3 7% 4 4 5% 4 6% 8% 52%	4430
	21st to end	Night	3 7% 3 8% 4 3 4 3 5% 6% 55%	4614
February	1st to 10th	Night	3 8% 4 7% 5% 4 4 4 5% 7% 48%	2470
	11th to 20th	Night	4 7% 3 7% 4 4 5% 4 6% 7% 48%	2225
	21st to end	Night	3 9% 3 7% 5% 3 3 3 4 5% 55%	1884
March	1st to 10th	Night	4 9% 3 8% 4 3 3 3 5% 5% 53%	3734
	11th to 20th	Night	7% 10% 3 6% 4 3 3 3 4 6% 52%	3617
	21st to end	Night	7% 7% 3 6% 4 5% 5% 3 6% 8% 44%	3523
April	1st to 10th	Night	7% 7% 2 7% 4 4 4 4 5% 7% 50%	1900
	11th to 20th	Night	12% 8% 3 7% 4 3 4 3 4 6% 45%	1877
	21st to end	Night	13% 8% 3 6% 4 4 5% 3 6% 7% 42%	1898
May	1st to 10th	Night	11% 6% 3 7% 5% 5% 6% 5% 6% 8% 38%	2850
	11th to 20th	Night	12% 4 2 5% 3 4 4 4 7% 10% 43%	2529
	21st to end	Night	9% 5% 2 7% 5% 5% 5% 4 6% 8% 43%	2762
June	1st to 10th	Night	6% 4 1 3 3 3 4 5% 8% 10% 52%	1520
	11th to 20th	Night	6% 4 2 3 2 4 4 4 7% 9% 55%	1520
	21st to end	Night	5% 3 2 5% 4 4 5% 5% 8% 8% 52%	1520
July	1st to 10th	Night	5% 4 2 6% 4 4 5% 4 6% 8% 53%	2540
	11th to 20th	Night	3 2 1 5% 4 4 5% 5% 8% 11% 52%	2540
	21st to end	Night	3 4 2 5% 4 4 5% 5% 7% 10% 51%	2761
August	1st to 10th	Night	12% 4 2 5% 5% 5% 6% 5% 9% 9% 38%	2771
	11th to 20th	Night	4 5% 2 6% 6% 5% 5% 4 7% 9% 46%	3113
	21st to end	Night	3 4 1 5% 4 4 6% 5% 9% 10% 49%	3487
September	1st to 10th	Night	5% 5% 2 5% 3 4 4 3 5% 8% 55%	1900
	11th to 20th	Night	6% 4 1 4 4 3 4 3 5% 6% 59%	1947
	21st to end	Night	7% 3 1 3 3 4 3 3 5% 5% 63%	2090
October	1st to 10th	Night	6% 2 1 4 2 2 2 2 3 5% 69%	3699
	11th to 20th	Night	7% 4 2 5% 3 3 4 3 4 7% 57%	3778
	21st to end	Night	7% 5% 2 5% 3 3 3 3 4 6% 59%	4307
November	1st to 10th	Night	4 5% 3 4 4 4 3 4 5% 7% 57%	2535
	11th to 20th	Night	4 6% 2 5% 3 4 4 3 5% 6% 59%	2600
	21st to end	Night	3 7% 3 5% 4 4 3 3 5% 6% 57%	2700
December	1st to 10th	Night	3 7% 3 6% 4 4 4 3 5% 7% 55%	2687
	11th to 20th	Night	3 6% 3 5% 4 4 4 3 5% 7% 55%	3271
	21st to end	Night	4 9% 4 7% 4 4 4 4 5% 7% 48%	4873

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	27% 4 11% 33% 18% 6%	2539
	11th to 20th	Day	33% 8% 15% 24% 16% 4	2540
	21st to end	Day	23% 6% 17% 31% 19% 4	3082
February	1st to 10th	Day	37% 5% 12% 26% 16% 5%	1710
	11th to 20th	Day	31% 5% 11% 28% 21% 5%	1850
	21st to end	Day	32% 4 9% 26% 21% 8%	1570
March	1st to 10th	Day	29% 5% 10% 20% 29% 7%	3130
	11th to 20th	Day	30% 6% 15% 32% 14% 3	3357
	21st to end	Day	33% 8% 14% 33% 10% 2	4119
April	1st to 10th	Day	31% 6% 13% 24% 17% 9%	2280
	11th to 20th	Day	39% 6% 11% 21% 16% 6%	2254
	21st to end	Day	35% 7% 10% 28% 18% 2	2280
May	1st to 10th	Day	40% 8% 9% 25% 14% 5%	4120
	11th to 20th	Day	30% 11% 14% 26% 16% 3	4377
	21st to end	Day	28% 9% 14% 25% 21% 4	4825
June	1st to 10th	Day	24% 8% 19% 25% 17% 7%	2660
	11th to 20th	Day	26% 7% 9% 23% 22% 12%	2660
	21st to end	Day	22% 7% 11% 25% 23% 12%	2660
July	1st to 10th	Day	26% 5% 9% 17% 26% 16%	4361
	11th to 20th	Day	22% 7% 12% 22% 22% 16%	4355
	21st to end	Day	23% 6% 10% 19% 20% 22%	4651
August	1st to 10th	Day	31% 8% 14% 24% 16% 7%	4136
	11th to 20th	Day	26% 6% 11% 19% 23% 14%	3762
	21st to end	Day	23% 4 10% 21% 25% 17%	4179
September	1st to 10th	Day	20% 4 7% 23% 27% 18%	2280
	11th to 20th	Day	22% 5% 8% 20% 29% 16%	2231
	21st to end	Day	21% 4 6% 22% 36% 10%	2090
October	1st to 10th	Day	16% 3 6% 18% 33% 26%	3263
	11th to 20th	Day	23% 3 9% 28% 28% 9%	3150
	21st to end	Day	26% 3 8% 27% 28% 8%	3218
November	1st to 10th	Day	24% 5% 12% 25% 24% 10%	1763
	11th to 20th	Day	24% 4 8% 27% 29% 8%	1800
	21st to end	Day	27% 3 10% 24% 28% 9%	1695
December	1st to 10th	Day	29% 6% 12% 29% 19% 6%	1528
	11th to 20th	Day	30% 4 9% 26% 28% 3	1924
	21st to end	Day	35% 6% 8% 26% 20% 4	2794
January	1st to 10th	Night	29% 6% 11% 30% 21% 4	4417
	11th to 20th	Night	28% 8% 15% 21% 22% 6%	4430
	21st to end	Night	30% 6% 14% 31% 16% 3	4614
February	1st to 10th	Night	35% 6% 13% 25% 17% 4	2470
	11th to 20th	Night	33% 6% 11% 26% 19% 4	2225
	21st to end	Night	32% 4 7% 24% 23% 9%	1884
March	1st to 10th	Night	31% 5% 9% 20% 29% 7%	3734
	11th to 20th	Night	33% 6% 13% 23% 22% 2	3617
	21st to end	Night	34% 8% 15% 29% 11% 2	3523
April	1st to 10th	Night	34% 5% 10% 25% 19% 7%	1900
	11th to 20th	Night	39% 5% 11% 23% 17% 5%	1877
	21st to end	Night	40% 7% 9% 24% 18% 2	1898
May	1st to 10th	Night	37% 11% 12% 24% 12% 5%	2850
	11th to 20th	Night	32% 10% 19% 26% 10% 3	2530
	21st to end	Night	34% 11% 17% 19% 13% 5%	2762
June	1st to 10th	Night	24% 8% 23% 27% 13% 5%	1520
	11th to 20th	Night	24% 8% 13% 23% 20% 12%	1520
	21st to end	Night	26% 6% 12% 27% 24% 6%	1520
July	1st to 10th	Night	27% 6% 12% 23% 24% 8%	2500
	11th to 20th	Night	22% 7% 17% 24% 23% 7%	2492
	21st to end	Night	25% 7% 15% 25% 18% 10%	2674
August	1st to 10th	Night	37% 9% 17% 20% 14% 3	2763
	11th to 20th	Night	33% 8% 14% 20% 16% 10%	3143
	21st to end	Night	25% 7% 15% 21% 22% 10%	3487
September	1st to 10th	Night	27% 5% 9% 20% 24% 15%	1900
	11th to 20th	Night	23% 5% 9% 25% 24% 13%	1947
	21st to end	Night	22% 4 8% 24% 30% 11%	2090
October	1st to 10th	Night	19% 4 7% 19% 28% 24%	3699
	11th to 20th	Night	27% 4 10% 26% 24% 8%	3778
	21st to end	Night	27% 3 8% 27% 25% 10%	4307
November	1st to 10th	Night	26% 4 11% 24% 26% 10%	2535
	11th to 20th	Night	25% 4 9% 27% 27% 8%	2600
	21st to end	Night	28% 4 9% 25% 28% 6%	2700
December	1st to 10th	Night	28% 6% 12% 28% 18% 7%	2687
	11th to 20th	Night	28% 4 7% 32% 25% 3	3272
	21st to end	Night	33% 6% 9% 27% 20% 4	4873

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	5% 8% 27% 37% 18% 6%	270
	11th to 20th	Day	10% 8% 35% 34% 13% 1	270
	21st to end	Day	4 10% 37% 38% 8% 3	297
February	1st to 10th	Day	8% 11% 38% 36% 6% 1	270
	11th to 20th	Day	6% 9% 36% 39% 8% 2	270
	21st to end	Day	7% 14% 37% 32% 10%	225
March	1st to 10th	Day	6% 11% 31% 32% 16% 4	270
	11th to 20th	Day	11% 13% 28% 31% 15% 3	379
	21st to end	Day	10% 12% 34% 33% 9% 2	506
April	1st to 10th	Day	14% 15% 31% 27% 11% 2	460
	11th to 20th	Day	18% 19% 28% 22% 11% 2	452
	21st to end	Day	16% 15% 26% 25% 14% 4	460
May	1st to 10th	Day	17% 11% 24% 29% 16% 4	653
	11th to 20th	Day	17% 7% 21% 29% 20% 6%	675
	21st to end	Day	10% 7% 25% 30% 21% 7%	734
June	1st to 10th	Day	6% 5% 18% 34% 25% 12%	680
	11th to 20th	Day	7% 5% 28% 33% 23% 4	680
	21st to end	Day	5% 4 22% 36% 27% 7%	680
July	1st to 10th	Day	9% 1 12% 32% 36% 9%	671
	11th to 20th	Day	3 2 13% 34% 33% 14%	668
	21st to end	Day	5% 1 14% 29% 39% 12%	739
August	1st to 10th	Day	7% 1 13% 33% 35% 10%	541
	11th to 20th	Day	3 4 18% 35% 26% 14%	477
	21st to end	Day	4 2 19% 32% 31% 11%	539
September	1st to 10th	Day	6% 3 17% 36% 27% 11%	490
	11th to 20th	Day	6% 3 20% 27% 31% 13%	441
	21st to end	Day	9% 2 20% 27% 24% 17%	300
October	1st to 10th	Day	10% 5% 21% 23% 24% 16%	300
	11th to 20th	Day	4 8% 28% 34% 15% 11%	300
	21st to end	Day	10% 9% 27% 32% 18% 5%	330
November	1st to 10th	Day	7% 11% 26% 34% 15% 7%	300
	11th to 20th	Day	6% 10% 31% 37% 13% 3	300
	21st to end	Day	8% 8% 28% 40% 14% 3	300
December	1st to 10th	Day	6% 13% 29% 34% 16% 2	273
	11th to 20th	Day	7% 8% 40% 36% 8%	270
	21st to end	Day	9% 14% 31% 33% 11% 2	297
January	1st to 10th	Night	6% 9% 32% 39% 12% 2	950
	11th to 20th	Night	7% 9% 39% 35% 9% 1	950
	21st to end	Night	8% 5% 42% 37% 8% 1	890
February	1st to 10th	Night	7% 8% 43% 34% 8%	760
	11th to 20th	Night	7% 9% 39% 40% 6%	744
	21st to end	Night	6% 11% 43% 37% 4	628
March	1st to 10th	Night	6% 8% 34% 43% 8%	760
	11th to 20th	Night	9% 8% 31% 41% 11%	760
	21st to end	Night	10% 8% 41% 34% 7% 1	660
April	1st to 10th	Night	12% 11% 38% 34% 5%	570
	11th to 20th	Night	16% 10% 34% 33% 6% 1	563
	21st to end	Night	17% 9% 30% 32% 11%	570
May	1st to 10th	Night	15% 11% 25% 35% 13% 1	570
	11th to 20th	Night	19% 4 25% 37% 13% 2	561
	21st to end	Night	11% 4 30% 39% 15% 1	617
June	1st to 10th	Night	7% 4 22% 43% 23% 1	570
	11th to 20th	Night	8% 4 27% 48% 13%	570
	21st to end	Night	5% 4 21% 50% 19%	570
July	1st to 10th	Night	7% 3 15% 46% 28% 1	555
	11th to 20th	Night	3 1 13% 52% 29% 2	552
	21st to end	Night	6% 2 11% 48% 33% 1	624
August	1st to 10th	Night	8% 2 13% 46% 29% 2	567
	11th to 20th	Night	4 2 14% 54% 25% 1	564
	21st to end	Night	4 3 14% 51% 28% 1	627
September	1st to 10th	Night	7% 4 17% 46% 24% 2	570
	11th to 20th	Night	9% 4 19% 44% 22% 3	570
	21st to end	Night	8% 3 25% 43% 20% 2	570
October	1st to 10th	Night	12% 7% 23% 36% 21% 2	698
	11th to 20th	Night	9% 5% 28% 40% 16% 1	760
	21st to end	Night	10% 7% 28% 41% 12% 1	948
November	1st to 10th	Night	7% 6% 32% 43% 12% 1	975
	11th to 20th	Night	8% 9% 31% 44% 7% 1	1000
	21st to end	Night	6% 8% 34% 41% 10% 1	1000
December	1st to 10th	Night	6% 8% 38% 41% 6%	960
	11th to 20th	Night	7% 7% 36% 42% 7% 1	950
	21st to end	Night	8% 11% 34% 40% 8% 1	1045

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