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 2024-01-12.

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 4 4 2 4 4 5% 7% 53%	75010
	Night	9% 5% 2 4 4 2 4 4 5% 7% 55%	74698
Transparency	Day	31% 6% 13% 27% 19% 4	74738
	Night	30% 5% 12% 26% 21% 5%	74493
Seeing	Day	11% 8% 30% 32% 17% 3	14478
	Night	11% 8% 34% 36% 11% 1	24508

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	7% 6% 2 4 4 4 4 3 6% 8% 53%	1707
	11th to 20th	Day	7% 9% 3 6% 5% 2 3 3 5% 7% 50%	1634
	21st to end	Day	7% 7% 3 6% 6% 3 4 4 5% 6% 50%	1782
February	1st to 10th	Day	8% 9% 3 7% 6% 3 4 4 4 6% 46%	1661
	11th to 20th	Day	7% 5% 3 6% 6% 3 5% 5% 6% 7% 47%	1749
	21st to end	Day	7% 7% 2 5% 5% 3 3 5% 6% 6% 51%	1480
March	1st to 10th	Day	7% 6% 2 5% 3 3 3 5% 6% 8% 52%	1858
	11th to 20th	Day	15% 7% 3 4 3 2 3 3 4 5% 50%	1980
	21st to end	Day	14% 8% 3 4 5% 2 5% 4 4 6% 44%	2178
April	1st to 10th	Day	11% 4 2 4 4 2 3 4 5% 6% 54%	2032
	11th to 20th	Day	10% 7% 3 6% 5% 3 5% 5% 5% 5% 46%	2224
	21st to end	Day	16% 6% 2 5% 4 3 4 5% 5% 7% 45%	2340
May	1st to 10th	Day	13% 6% 3 5% 4 2 4 4 6% 6% 47%	2340
	11th to 20th	Day	13% 5% 2 5% 4 3 3 4 4 8% 50%	2302
	21st to end	Day	12% 5% 2 5% 5% 3 5% 6% 6% 9% 42%	2531
June	1st to 10th	Day	4 2 1 3 4 2 5% 5% 5% 8% 59%	2340
	11th to 20th	Day	6% 3 2 4 5% 3 4 4 6% 8% 56%	2340
	21st to end	Day	5% 3 2 3 3 2 4 4 6% 8% 59%	2433
July	1st to 10th	Day	7% 3 2 4 4 3 4 5% 6% 10% 53%	2363
	11th to 20th	Day	4 2 1 3 4 3 4 5% 6% 11% 58%	2340
	21st to end	Day	7% 4 1 3 5% 3 5% 5% 6% 10% 51%	2546
August	1st to 10th	Day	8% 4 2 4 5% 3 4 6% 7% 10% 48%	2328
	11th to 20th	Day	6% 4 1 4 5% 3 4 5% 6% 9% 52%	2301
	21st to end	Day	6% 3 1 3 4 2 4 3 5% 6% 61%	2465
September	1st to 10th	Day	11% 4 2 4 4 2 3 3 4 5% 58%	2021
	11th to 20th	Day	9% 4 2 4 3 2 3 5% 5% 6% 58%	1980
	21st to end	Day	8% 3 1 3 5% 2 4 4 5% 5% 59%	1980
October	1st to 10th	Day	15% 5% 2 3 3 2 2 2 4 7% 55%	1963
	11th to 20th	Day	10% 3 1 3 3 2 3 3 3 5% 64%	1800
	21st to end	Day	12% 5% 2 3 3 2 3 3 3 5% 59%	1913
November	1st to 10th	Day	7% 4 1 3 3 1 4 3 5% 6% 63%	1673
	11th to 20th	Day	8% 5% 2 3 3 2 3 3 4 5% 62%	1710
	21st to end	Day	11% 6% 2 3 2 2 3 3 4 5% 59%	1710
December	1st to 10th	Day	7% 7% 2 5% 3 3 3 5% 5% 7% 52%	1710
	11th to 20th	Day	7% 6% 3 6% 5% 3 3 3 4 6% 54%	2161
	21st to end	Day	11% 11% 4 10% 5% 3 4 4 4 6% 38%	3135
January	1st to 10th	Night	7% 7% 3 7% 4 2 3 3 4 6% 55%	2458
	11th to 20th	Night	7% 6% 2 5% 4 2 3 4 4 6% 55%	2366
	21st to end	Night	6% 6% 3 5% 4 2 4 4 4 7% 54%	2574
February	1st to 10th	Night	8% 8% 4 6% 5% 3 5% 4 4 6% 47%	2313
	11th to 20th	Night	8% 5% 4 6% 5% 3 4 5% 5% 8% 48%	2098
	21st to end	Night	6% 7% 3 6% 5% 2 3 4 2 5% 57%	1776
March	1st to 10th	Night	8% 5% 2 4 4 2 3 3 5% 7% 56%	2101
	11th to 20th	Night	14% 6% 2 4 4 2 3 3 4 6% 53%	1980
	21st to end	Night	15% 8% 2 5% 4 2 4 5% 5% 7% 43%	2178
April	1st to 10th	Night	9% 5% 1 4 4 2 3 5% 5% 8% 53%	1926
	11th to 20th	Night	12% 4 2 4 5% 3 3 4 5% 7% 50%	1682
	21st to end	Night	14% 5% 2 4 4 3 4 3 5% 7% 49%	1620
May	1st to 10th	Night	14% 7% 2 6% 5% 3 5% 4 5% 7% 44%	1620
	11th to 20th	Night	12% 5% 1 4 3 2 4 4 5% 8% 51%	1593
	21st to end	Night	10% 5% 1 3 4 3 5% 5% 7% 10% 47%	1745
June	1st to 10th	Night	6% 2 1 3 2 2 4 5% 6% 10% 60%	1620
	11th to 20th	Night	4 3 2 3 4 2 5% 4 6% 11% 56%	1620
	21st to end	Night	4 3 1 3 4 2 4 4 7% 12% 55%	1504
July	1st to 10th	Night	6% 3 2 3 5% 4 4 4 6% 10% 53%	1574
	11th to 20th	Night	4 2 1 2 3 2 4 5% 7% 11% 59%	1620
	21st to end	Night	6% 3 2 4 4 3 4 6% 8% 11% 50%	1772
August	1st to 10th	Night	5% 2 2 4 5% 3 5% 6% 7% 11% 51%	1611
	11th to 20th	Night	7% 4 1 5% 5% 2 4 4 5% 10% 55%	1600
	21st to end	Night	5% 3 1 3 3 2 4 4 5% 7% 64%	1888
September	1st to 10th	Night	9% 2 1 3 3 2 3 3 5% 7% 62%	1939
	11th to 20th	Night	9% 3 1 4 4 3 4 4 5% 6% 58%	1980
	21st to end	Night	7% 4 1 3 3 3 3 4 5% 5% 62%	1980
October	1st to 10th	Night	12% 4 1 3 4 2 3 4 4 6% 57%	1980
	11th to 20th	Night	9% 4 2 3 3 2 3 3 4 5% 62%	2157
	21st to end	Night	10% 4 1 3 3 2 3 3 4 5% 60%	2440
November	1st to 10th	Night	6% 4 1 3 3 1 2 3 4 7% 66%	2405
	11th to 20th	Night	9% 3 1 3 3 2 3 3 4 7% 63%	2470
	21st to end	Night	11% 5% 1 3 3 2 3 3 3 5% 59%	2470
December	1st to 10th	Night	6% 6% 2 4 4 3 3 4 5% 6% 57%	2470
	11th to 20th	Night	8% 5% 2 4 4 2 4 4 5% 7% 56%	3036
	21st to end	Night	13% 12% 4 5% 4 2 3 3 4 6% 44%	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	31% 5% 15% 30% 17% 3	1708
	11th to 20th	Day	34% 4 15% 28% 16% 3	1634
	21st to end	Day	35% 5% 16% 28% 14% 2	1782
February	1st to 10th	Day	39% 6% 15% 22% 13% 5%	1661
	11th to 20th	Day	35% 6% 16% 24% 14% 5%	1759
	21st to end	Day	32% 5% 11% 26% 20% 6%	1480
March	1st to 10th	Day	30% 5% 11% 27% 22% 5%	1858
	11th to 20th	Day	38% 5% 10% 23% 20% 5%	1980
	21st to end	Day	42% 5% 14% 24% 12% 3	2178
April	1st to 10th	Day	32% 5% 12% 25% 21% 5%	2032
	11th to 20th	Day	38% 7% 11% 25% 16% 2	2227
	21st to end	Day	39% 5% 12% 26% 17% 1	2340
May	1st to 10th	Day	38% 7% 13% 23% 16% 3	2340
	11th to 20th	Day	34% 7% 17% 29% 13% 1	2306
	21st to end	Day	39% 9% 15% 25% 9% 3	2531
June	1st to 10th	Day	22% 9% 16% 34% 16% 4	2340
	11th to 20th	Day	26% 6% 13% 28% 22% 5%	2340
	21st to end	Day	22% 7% 13% 29% 22% 7%	2433
July	1st to 10th	Day	27% 7% 14% 28% 21% 3	2299
	11th to 20th	Day	21% 7% 15% 26% 25% 6%	2271
	21st to end	Day	27% 7% 14% 30% 19% 2	2405
August	1st to 10th	Day	30% 8% 17% 28% 14% 3	2314
	11th to 20th	Day	27% 6% 13% 30% 18% 5%	2301
	21st to end	Day	24% 6% 12% 25% 26% 8%	2465
September	1st to 10th	Day	30% 4 10% 23% 23% 10%	2021
	11th to 20th	Day	27% 6% 10% 26% 27% 5%	1980
	21st to end	Day	26% 5% 10% 27% 27% 5%	1980
October	1st to 10th	Day	32% 3 8% 27% 26% 4	1963
	11th to 20th	Day	25% 4 7% 26% 29% 10%	1800
	21st to end	Day	30% 3 9% 26% 24% 8%	1913
November	1st to 10th	Day	23% 4 12% 29% 27% 5%	1673
	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	33% 3 13% 29% 19% 3	2458
	11th to 20th	Night	31% 5% 11% 29% 22% 3	2366
	21st to end	Night	32% 5% 14% 28% 17% 4	2574
February	1st to 10th	Night	39% 6% 11% 23% 15% 6%	2313
	11th to 20th	Night	35% 6% 11% 27% 17% 4	2098
	21st to end	Night	33% 3 9% 22% 24% 10%	1776
March	1st to 10th	Night	29% 4 10% 25% 24% 8%	2101
	11th to 20th	Night	34% 4 10% 25% 20% 7%	1980
	21st to end	Night	42% 5% 12% 23% 14% 3	2178
April	1st to 10th	Night	30% 6% 14% 23% 24% 4	1926
	11th to 20th	Night	33% 6% 15% 24% 19% 2	1682
	21st to end	Night	35% 6% 11% 25% 19% 3	1620
May	1st to 10th	Night	41% 6% 14% 19% 16% 4	1620
	11th to 20th	Night	32% 6% 18% 27% 16% 1	1594
	21st to end	Night	31% 9% 23% 25% 10% 2	1746
June	1st to 10th	Night	18% 8% 18% 33% 18% 4	1620
	11th to 20th	Night	23% 8% 14% 28% 22% 6%	1620
	21st to end	Night	22% 6% 16% 26% 25% 5%	1504
July	1st to 10th	Night	27% 7% 15% 25% 22% 5%	1529
	11th to 20th	Night	18% 7% 16% 29% 25% 6%	1566
	21st to end	Night	26% 7% 15% 30% 19% 3	1673
August	1st to 10th	Night	25% 9% 18% 30% 14% 4	1601
	11th to 20th	Night	27% 6% 15% 30% 18% 4	1600
	21st to end	Night	21% 5% 12% 26% 27% 9%	1888
September	1st to 10th	Night	24% 6% 10% 25% 26% 10%	1939
	11th to 20th	Night	26% 6% 10% 23% 26% 8%	1980
	21st to end	Night	24% 5% 11% 22% 31% 7%	1980
October	1st to 10th	Night	29% 6% 9% 24% 26% 7%	1980
	11th to 20th	Night	26% 3 8% 23% 31% 10%	2157
	21st to end	Night	26% 5% 10% 23% 26% 10%	2440
November	1st to 10th	Night	21% 3 9% 28% 30% 9%	2405
	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% 40% 26% 14% 1	270
	11th to 20th	Day	19% 11% 36% 24% 9% 1	245
	21st to end	Day	10% 8% 44% 32% 6%	264
February	1st to 10th	Day	13% 12% 46% 25% 5%	240
	11th to 20th	Day	13% 10% 45% 23% 7% 2	240
	21st to end	Day	8% 18% 49% 19% 6%	198
March	1st to 10th	Day	10% 12% 48% 23% 6% 1	240
	11th to 20th	Day	20% 11% 38% 21% 7% 3	240
	21st to end	Day	18% 12% 45% 20% 4 1	264
April	1st to 10th	Day	12% 13% 42% 26% 6% 1	292
	11th to 20th	Day	14% 14% 43% 24% 5%	505
	21st to end	Day	19% 14% 37% 20% 7% 2	600
May	1st to 10th	Day	15% 10% 31% 30% 12% 1	603
	11th to 20th	Day	16% 9% 30% 25% 15% 4	625
	21st to end	Day	15% 8% 31% 30% 14% 2	679
June	1st to 10th	Day	4 4 25% 35% 23% 8%	630
	11th to 20th	Day	4 4 32% 38% 18% 3	630
	21st to end	Day	6% 4 31% 39% 18% 2	630
July	1st to 10th	Day	6% 4 19% 35% 30% 7%	621
	11th to 20th	Day	4 1 16% 43% 30% 6%	618
	21st to end	Day	7% 2 10% 44% 31% 5%	684
August	1st to 10th	Day	8% 3 12% 42% 29% 5%	626
	11th to 20th	Day	7% 2 16% 41% 30% 4	615
	21st to end	Day	6% 3 18% 38% 29% 6%	584
September	1st to 10th	Day	11% 5% 19% 36% 26% 3	311
	11th to 20th	Day	4 4 21% 41% 21% 7%	270
	21st to end	Day	11% 6% 27% 31% 21% 3	270
October	1st to 10th	Day	21% 9% 22% 23% 21% 4	270
	11th to 20th	Day	6% 11% 40% 27% 14% 2	270
	21st to end	Day	15% 14% 33% 25% 10% 3	297
November	1st to 10th	Day	13% 13% 32% 30% 10% 3	270
	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% 36% 38% 7%	950
	11th to 20th	Night	10% 9% 37% 35% 8% 1	910
	21st to end	Night	10% 9% 42% 34% 5%	990
February	1st to 10th	Night	12% 8% 39% 35% 5%	873
	11th to 20th	Night	10% 11% 41% 33% 5%	704
	21st to end	Night	9% 13% 43% 29% 6% 1	592
March	1st to 10th	Night	12% 13% 39% 31% 5%	661
	11th to 20th	Night	18% 7% 35% 30% 9%	540
	21st to end	Night	20% 13% 39% 22% 6% 1	594
April	1st to 10th	Night	12% 11% 44% 28% 5%	540
	11th to 20th	Night	14% 14% 39% 28% 5%	533
	21st to end	Night	16% 11% 35% 30% 8% 1	540
May	1st to 10th	Night	16% 9% 35% 32% 7%	540
	11th to 20th	Night	13% 10% 31% 36% 9% 1	531
	21st to end	Night	11% 9% 32% 34% 12% 2	584
June	1st to 10th	Night	6% 4 29% 41% 19% 1	540
	11th to 20th	Night	5% 5% 37% 37% 15%	540
	21st to end	Night	3 4 40% 39% 12% 1	540
July	1st to 10th	Night	6% 4 22% 43% 24% 1	525
	11th to 20th	Night	4 1 25% 48% 20% 1	522
	21st to end	Night	6% 3 17% 48% 25% 1	591
August	1st to 10th	Night	5% 2 18% 53% 22%	537
	11th to 20th	Night	9% 1 17% 53% 19% 1	534
	21st to end	Night	5% 2 21% 47% 24% 2	594
September	1st to 10th	Night	8% 3 25% 45% 17% 2	540
	11th to 20th	Night	9% 4 32% 36% 18% 1	540
	21st to end	Night	9% 4 32% 40% 14% 1	540
October	1st to 10th	Night	14% 7% 29% 36% 14% 1	540
	11th to 20th	Night	12% 9% 36% 33% 9%	717
	21st to end	Night	13% 9% 35% 30% 12% 1	856
November	1st to 10th	Night	8% 9% 33% 39% 11%	925
	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 2024-01-09 15:24:26. Version ac07

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