Leach Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Leach Observatory clear sky chart from 2005-11-06 to 2024-11-08.

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	9% 5% 2 5% 3 3 4 3 5% 7% 53%	105290
	Night	8% 5% 2 5% 3 3 3 3 5% 7% 55%	102401
Transparency	Day	31% 5% 12% 26% 21% 5%	105057
	Night	29% 5% 12% 26% 23% 5%	102224
Seeing	Day	11% 8% 30% 32% 17% 3	15659
	Night	11% 8% 34% 36% 11% 1	25532

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	9% 8% 3 8% 3 5% 5% 3 6% 7% 43%	2847
	11th to 20th	Day	7% 11% 3 9% 6% 4 4 3 5% 6% 43%	2850
	21st to end	Day	8% 10% 3 9% 4 4 3 3 4 5% 46%	3135
February	1st to 10th	Day	9% 10% 3 7% 5% 3 4 4 4 6% 44%	1753
	11th to 20th	Day	6% 6% 2 6% 5% 4 5% 4 6% 7% 48%	1849
	21st to end	Day	7% 7% 2 5% 4 4 3 4 6% 6% 52%	1570
March	1st to 10th	Day	11% 5% 2 4 2 3 3 2 5% 6% 57%	3240
	11th to 20th	Day	10% 6% 2 4 3 2 3 2 4 5% 59%	3480
	21st to end	Day	12% 8% 3 6% 3 3 4 3 5% 7% 47%	3814
April	1st to 10th	Day	10% 4 2 5% 3 3 3 4 5% 6% 54%	2145
	11th to 20th	Day	10% 7% 2 7% 4 4 4 4 5% 5% 46%	2350
	21st to end	Day	16% 6% 2 5% 3 3 4 3 5% 7% 45%	2470
May	1st to 10th	Day	14% 6% 2 6% 4 4 4 4 6% 6% 45%	4120
	11th to 20th	Day	13% 5% 2 6% 4 4 4 3 5% 7% 47%	4082
	21st to end	Day	12% 5% 2 6% 4 4 5% 4 6% 7% 44%	4489
June	1st to 10th	Day	5% 3 1 4 3 3 5% 4 6% 8% 59%	2470
	11th to 20th	Day	6% 4 2 5% 4 3 4 3 6% 7% 55%	2470
	21st to end	Day	5% 4 1 4 3 3 4 4 7% 8% 58%	2569
July	1st to 10th	Day	9% 5% 2 6% 4 4 4 4 6% 9% 49%	4156
	11th to 20th	Day	4 3 2 5% 3 4 5% 5% 7% 11% 52%	4120
	21st to end	Day	6% 3 1 4 4 4 4 3 6% 9% 56%	4466
August	1st to 10th	Day	9% 6% 2 6% 4 3 3 3 5% 8% 51%	4103
	11th to 20th	Day	10% 4 1 5% 4 3 4 3 6% 9% 50%	4041
	21st to end	Day	4 3 1 4 3 3 4 4 6% 7% 60%	4325
September	1st to 10th	Day	11% 4 2 4 3 3 3 2 4 5% 59%	2133
	11th to 20th	Day	9% 4 2 4 2 3 3 4 4 7% 58%	2090
	21st to end	Day	8% 3 1 5% 3 3 4 3 5% 5% 60%	2090
October	1st to 10th	Day	9% 3 1 2 1 2 2 2 4 6% 69%	3449
	11th to 20th	Day	6% 2 1 3 2 3 3 2 4 7% 68%	3140
	21st to end	Day	9% 4 1 3 2 3 3 3 4 6% 62%	3312
November	1st to 10th	Day	8% 4 1 4 3 2 4 3 5% 6% 61%	1736
	11th to 20th	Day	8% 6% 1 3 3 3 3 2 5% 5% 62%	1710
	21st to end	Day	10% 6% 2 3 2 3 3 2 4 6% 59%	1710
December	1st to 10th	Day	7% 8% 2 6% 3 3 4 3 5% 7% 52%	1710
	11th to 20th	Day	7% 7% 3 6% 4 4 3 3 4 6% 54%	2161
	21st to end	Day	11% 11% 4 10% 4 4 4 3 4 6% 38%	3135
January	1st to 10th	Night	7% 9% 5% 13% 4 3 3 2 4 6% 43%	4108
	11th to 20th	Night	6% 7% 3 7% 4 3 3 3 4 6% 54%	4120
	21st to end	Night	11% 10% 4 7% 4 3 4 3 3 5% 47%	4532
February	1st to 10th	Night	9% 9% 3 6% 5% 4 4 3 5% 6% 46%	2442
	11th to 20th	Night	8% 6% 2 6% 5% 4 5% 4 5% 7% 49%	2218
	21st to end	Night	6% 7% 3 6% 4 3 2 3 3 5% 58%	1884
March	1st to 10th	Night	9% 4 1 4 2 3 3 3 4 6% 62%	3619
	11th to 20th	Night	10% 5% 1 4 3 3 3 3 5% 7% 55%	3480
	21st to end	Night	14% 8% 2 5% 3 3 3 3 4 6% 50%	3817
April	1st to 10th	Night	9% 6% 1 4 4 3 3 4 5% 7% 53%	2032
	11th to 20th	Night	11% 4 2 5% 4 3 4 3 5% 6% 51%	1776
	21st to end	Night	14% 6% 2 5% 3 3 4 3 5% 6% 48%	1710
May	1st to 10th	Night	18% 6% 1 4 3 3 3 3 5% 5% 48%	2850
	11th to 20th	Night	11% 4 1 5% 3 3 5% 4 6% 9% 49%	2823
	21st to end	Night	10% 4 1 4 3 4 4 4 7% 10% 49%	3098
June	1st to 10th	Night	5% 2 1 4 2 3 3 4 6% 9% 60%	1710
	11th to 20th	Night	4 3 2 4 4 4 5% 3 7% 10% 55%	1710
	21st to end	Night	4 3 1 4 4 3 4 4 7% 11% 55%	1587
July	1st to 10th	Night	8% 4 2 6% 4 5% 4 4 6% 8% 49%	2778
	11th to 20th	Night	4 2 1 4 3 3 5% 5% 8% 11% 55%	2850
	21st to end	Night	5% 3 1 4 3 4 4 4 7% 10% 55%	3097
August	1st to 10th	Night	5% 3 1 4 4 4 5% 4 6% 11% 52%	2836
	11th to 20th	Night	9% 5% 1 6% 4 4 4 3 5% 8% 50%	2798
	21st to end	Night	4 3 2 4 3 3 4 3 5% 8% 62%	3325
September	1st to 10th	Night	8% 2 1 4 3 3 3 2 5% 6% 63%	2047
	11th to 20th	Night	8% 3 1 4 3 3 4 3 5% 6% 58%	2090
	21st to end	Night	7% 4 1 4 3 3 3 3 5% 5% 62%	2090
October	1st to 10th	Night	7% 3 1 2 2 2 2 2 3 4 73%	3480
	11th to 20th	Night	6% 3 1 2 2 2 3 3 3 6% 70%	3776
	21st to end	Night	7% 3 1 3 2 2 3 2 4 7% 67%	4237
November	1st to 10th	Night	7% 4 1 3 2 2 2 2 4 6% 64%	2503
	11th to 20th	Night	8% 4 1 3 3 3 3 2 4 6% 63%	2470
	21st to end	Night	11% 6% 1 4 3 3 3 3 3 5% 58%	2470
December	1st to 10th	Night	6% 7% 2 4 4 3 3 3 5% 6% 56%	2470
	11th to 20th	Night	7% 6% 2 5% 3 3 3 3 6% 6% 55%	3036
	21st to end	Night	13% 12% 4 6% 3 3 3 2 4 6% 43%	4532

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	38% 6% 15% 27% 13% 2	2848
	11th to 20th	Day	44% 5% 13% 23% 12% 3	2850
	21st to end	Day	41% 4 15% 25% 13% 1	3135
February	1st to 10th	Day	40% 6% 15% 21% 12% 5%	1753
	11th to 20th	Day	34% 6% 16% 24% 15% 5%	1859
	21st to end	Day	30% 5% 11% 25% 22% 7%	1570
March	1st to 10th	Day	30% 4 8% 22% 29% 7%	3240
	11th to 20th	Day	29% 4 11% 27% 25% 3	3480
	21st to end	Day	38% 6% 17% 29% 8% 2	3814
April	1st to 10th	Day	31% 5% 13% 24% 22% 5%	2145
	11th to 20th	Day	37% 7% 11% 25% 17% 3	2353
	21st to end	Day	39% 5% 12% 26% 17% 1	2470
May	1st to 10th	Day	38% 6% 12% 23% 13% 7%	4120
	11th to 20th	Day	36% 7% 13% 28% 16%	4086
	21st to end	Day	37% 8% 12% 26% 15% 3	4489
June	1st to 10th	Day	22% 9% 16% 33% 16% 3	2470
	11th to 20th	Day	27% 6% 13% 28% 22% 5%	2470
	21st to end	Day	23% 7% 12% 28% 23% 7%	2569
July	1st to 10th	Day	33% 5% 12% 23% 22% 5%	4092
	11th to 20th	Day	25% 5% 14% 27% 24% 4	4051
	21st to end	Day	24% 5% 13% 23% 28% 6%	4325
August	1st to 10th	Day	32% 5% 13% 25% 23% 3	4090
	11th to 20th	Day	32% 5% 17% 24% 17% 4	4080
	21st to end	Day	24% 4 14% 27% 22% 8%	4324
September	1st to 10th	Day	29% 4 9% 24% 24% 10%	2133
	11th to 20th	Day	26% 6% 10% 26% 27% 5%	2090
	21st to end	Day	26% 5% 9% 27% 26% 6%	2090
October	1st to 10th	Day	20% 2 5% 21% 41% 11%	3449
	11th to 20th	Day	19% 2 9% 34% 26% 10%	3140
	21st to end	Day	25% 2 9% 25% 32% 6%	3312
November	1st to 10th	Day	24% 4 12% 29% 26% 5%	1736
	11th to 20th	Day	25% 4 9% 28% 29% 5%	1710
	21st to end	Day	29% 3 10% 28% 25% 5%	1710
December	1st to 10th	Day	32% 5% 13% 28% 20% 2	1710
	11th to 20th	Day	33% 4 12% 34% 16% 1	2159
	21st to end	Day	47% 5% 11% 23% 12% 2	3135
January	1st to 10th	Night	44% 4 12% 24% 14% 2	4108
	11th to 20th	Night	32% 5% 14% 27% 21% 2	4120
	21st to end	Night	40% 5% 13% 24% 16% 2	4532
February	1st to 10th	Night	40% 6% 11% 22% 15% 6%	2442
	11th to 20th	Night	34% 6% 11% 27% 18% 4	2218
	21st to end	Night	32% 3 8% 21% 25% 10%	1884
March	1st to 10th	Night	25% 4 8% 26% 29% 8%	3619
	11th to 20th	Night	27% 5% 11% 23% 29% 4	3480
	21st to end	Night	36% 5% 17% 31% 9% 2	3817
April	1st to 10th	Night	29% 5% 14% 23% 24% 5%	2032
	11th to 20th	Night	32% 6% 14% 24% 21% 3	1776
	21st to end	Night	36% 6% 11% 25% 19% 3	1710
May	1st to 10th	Night	38% 6% 13% 22% 13% 9%	2850
	11th to 20th	Night	31% 8% 16% 26% 19% 1	2824
	21st to end	Night	28% 9% 18% 28% 15% 2	3099
June	1st to 10th	Night	19% 8% 18% 33% 19% 4	1710
	11th to 20th	Night	23% 7% 14% 29% 21% 5%	1710
	21st to end	Night	22% 6% 15% 26% 25% 6%	1587
July	1st to 10th	Night	33% 5% 13% 20% 23% 6%	2733
	11th to 20th	Night	23% 5% 13% 30% 26% 5%	2796
	21st to end	Night	24% 5% 14% 26% 25% 6%	2999
August	1st to 10th	Night	26% 6% 14% 27% 21% 5%	2826
	11th to 20th	Night	33% 5% 16% 25% 18% 3	2825
	21st to end	Night	22% 4 15% 29% 23% 7%	3325
September	1st to 10th	Night	23% 6% 10% 24% 26% 10%	2047
	11th to 20th	Night	25% 6% 10% 23% 27% 8%	2090
	21st to end	Night	24% 5% 10% 21% 32% 7%	2090
October	1st to 10th	Night	17% 4 5% 18% 47% 10%	3480
	11th to 20th	Night	18% 2 8% 28% 31% 13%	3776
	21st to end	Night	19% 3 8% 27% 36% 6%	4237
November	1st to 10th	Night	22% 3 9% 28% 29% 9%	2503
	11th to 20th	Night	23% 3 10% 29% 28% 6%	2470
	21st to end	Night	30% 3 10% 25% 25% 6%	2470
December	1st to 10th	Night	28% 4 14% 28% 23% 3	2470
	11th to 20th	Night	29% 4 9% 36% 19% 2	3037
	21st to end	Night	43% 5% 11% 27% 13% 2	4532

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	8% 11% 39% 26% 14% 1	270
	11th to 20th	Day	17% 13% 36% 24% 9% 1	270
	21st to end	Day	10% 9% 40% 32% 8%	297
February	1st to 10th	Day	14% 11% 45% 24% 6%	270
	11th to 20th	Day	12% 9% 45% 24% 8% 2	270
	21st to end	Day	8% 16% 52% 19% 5%	225
March	1st to 10th	Day	11% 11% 46% 24% 7% 1	270
	11th to 20th	Day	19% 11% 39% 23% 7% 2	270
	21st to end	Day	19% 11% 44% 20% 5% 1	297
April	1st to 10th	Day	12% 14% 41% 25% 6% 1	325
	11th to 20th	Day	13% 15% 42% 24% 5%	551
	21st to end	Day	19% 15% 37% 20% 8% 2	650
May	1st to 10th	Day	15% 11% 32% 30% 11% 1	653
	11th to 20th	Day	15% 9% 30% 26% 16% 4	675
	21st to end	Day	14% 9% 32% 30% 14% 2	734
June	1st to 10th	Day	4 4 25% 35% 24% 8%	680
	11th to 20th	Day	5% 5% 32% 38% 17% 3	680
	21st to end	Day	6% 5% 33% 38% 17% 2	680
July	1st to 10th	Day	6% 4 20% 34% 28% 7%	671
	11th to 20th	Day	4 2 16% 44% 29% 6%	668
	21st to end	Day	6% 2 13% 42% 30% 6%	739
August	1st to 10th	Day	9% 3 12% 43% 28% 5%	676
	11th to 20th	Day	8% 2 17% 41% 28% 4	665
	21st to end	Day	6% 3 19% 39% 28% 6%	632
September	1st to 10th	Day	10% 4 18% 38% 26% 3	343
	11th to 20th	Day	4 4 24% 41% 20% 6%	300
	21st to end	Day	11% 6% 26% 30% 21% 6%	300
October	1st to 10th	Day	19% 9% 21% 24% 23% 4	300
	11th to 20th	Day	6% 10% 41% 27% 15% 2	300
	21st to end	Day	15% 14% 32% 25% 10% 3	330
November	1st to 10th	Day	15% 13% 32% 29% 9% 2	291
	11th to 20th	Day	11% 11% 38% 27% 11% 1	270
	21st to end	Day	19% 10% 33% 27% 10% 2	270
December	1st to 10th	Day	9% 8% 40% 28% 11% 4	270
	11th to 20th	Day	11% 13% 36% 30% 9% 1	270
	21st to end	Day	19% 12% 38% 26% 5%	297
January	1st to 10th	Night	10% 8% 37% 38% 7%	950
	11th to 20th	Night	10% 9% 37% 35% 8% 1	950
	21st to end	Night	9% 9% 40% 35% 6%	1045
February	1st to 10th	Night	13% 8% 38% 35% 5%	922
	11th to 20th	Night	10% 11% 40% 34% 5%	744
	21st to end	Night	8% 13% 44% 29% 5%	628
March	1st to 10th	Night	12% 13% 39% 31% 5%	697
	11th to 20th	Night	17% 8% 35% 31% 9%	570
	21st to end	Night	20% 12% 39% 23% 6% 1	627
April	1st to 10th	Night	12% 12% 43% 28% 5%	570
	11th to 20th	Night	14% 14% 40% 27% 5%	563
	21st to end	Night	16% 11% 36% 29% 7% 1	570
May	1st to 10th	Night	17% 9% 35% 32% 6%	570
	11th to 20th	Night	12% 9% 31% 38% 8% 1	561
	21st to end	Night	11% 9% 33% 34% 12% 2	617
June	1st to 10th	Night	6% 5% 29% 41% 18% 1	570
	11th to 20th	Night	5% 5% 38% 37% 15%	570
	21st to end	Night	4 5% 40% 40% 12% 1	570
July	1st to 10th	Night	6% 4 23% 43% 23% 1	555
	11th to 20th	Night	4 1 26% 48% 20% 1	552
	21st to end	Night	6% 3 18% 46% 25% 1	624
August	1st to 10th	Night	6% 2 17% 53% 21%	567
	11th to 20th	Night	10% 2 18% 52% 18% 1	564
	21st to end	Night	6% 2 21% 47% 23% 2	627
September	1st to 10th	Night	8% 3 24% 46% 18% 2	570
	11th to 20th	Night	9% 3 33% 37% 17% 1	570
	21st to end	Night	9% 4 31% 41% 14% 1	570
October	1st to 10th	Night	13% 7% 29% 35% 16% 1	570
	11th to 20th	Night	11% 9% 36% 35% 9%	757
	21st to end	Night	13% 10% 35% 29% 12% 1	904
November	1st to 10th	Night	9% 9% 32% 39% 10%	963
	11th to 20th	Night	10% 9% 40% 32% 8%	950
	21st to end	Night	13% 10% 30% 35% 11% 1	950
December	1st to 10th	Night	9% 9% 36% 37% 8%	950
	11th to 20th	Night	13% 10% 35% 34% 7%	950
	21st to end	Night	15% 9% 33% 36% 7%	1045

Page generated at 2024-11-05 07:15:51. Version ac07

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