Clyde Sachtleben Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Clyde Sachtleben Observatory clear sky chart from 2005-11-06 to 2024-01-13.

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	10% 6% 2 5% 4 3 4 4 5% 7% 49%	75236
	Night	9% 6% 2 4 4 2 4 4 5% 7% 52%	74486
Transparency	Day	33% 6% 14% 26% 17% 3	74955
	Night	31% 6% 13% 27% 19% 4	74291
Seeing	Day	12% 9% 31% 31% 14% 2	14575
	Night	11% 9% 36% 34% 10% 1	24608

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	8% 10% 2 4 5% 3 4 4 5% 7% 49%	1524
	11th to 20th	Day	9% 7% 3 6% 5% 3 4 4 5% 8% 46%	1638
	21st to end	Day	8% 9% 4 7% 6% 4 4 4 5% 6% 44%	1782
February	1st to 10th	Day	9% 9% 5% 7% 6% 3 5% 5% 4 7% 41%	1620
	11th to 20th	Day	6% 7% 4 6% 5% 3 4 4 4 8% 48%	1745
	21st to end	Day	9% 7% 2 6% 5% 3 3 5% 4 7% 49%	1480
March	1st to 10th	Day	7% 7% 2 4 4 3 4 4 5% 7% 53%	1854
	11th to 20th	Day	15% 9% 3 5% 3 2 4 3 6% 6% 45%	1980
	21st to end	Day	14% 10% 4 7% 5% 3 4 4 4 7% 38%	2178
April	1st to 10th	Day	12% 6% 3 5% 4 2 3 5% 5% 6% 48%	2047
	11th to 20th	Day	14% 7% 2 6% 4 3 4 4 5% 7% 43%	2251
	21st to end	Day	18% 6% 2 5% 4 3 4 4 5% 7% 43%	2340
May	1st to 10th	Day	14% 6% 3 5% 5% 3 5% 4 6% 7% 42%	2340
	11th to 20th	Day	16% 6% 3 5% 5% 3 4 4 5% 7% 43%	2302
	21st to end	Day	14% 6% 3 5% 5% 4 5% 5% 7% 8% 39%	2531
June	1st to 10th	Day	5% 4 1 4 4 3 4 6% 6% 8% 55%	2340
	11th to 20th	Day	8% 4 2 4 4 3 4 5% 7% 8% 51%	2507
	21st to end	Day	6% 4 2 4 4 2 4 5% 7% 9% 54%	2520
July	1st to 10th	Day	7% 4 2 4 4 3 5% 5% 6% 9% 52%	2520
	11th to 20th	Day	4 3 1 3 4 3 4 5% 5% 9% 57%	2412
	21st to end	Day	7% 3 1 3 4 3 5% 6% 7% 10% 51%	2546
August	1st to 10th	Day	7% 4 2 5% 6% 3 5% 5% 8% 10% 45%	2328
	11th to 20th	Day	6% 3 2 4 4 2 3 5% 6% 8% 56%	2301
	21st to end	Day	8% 4 2 4 4 2 4 4 4 8% 56%	2510
September	1st to 10th	Day	12% 4 2 4 5% 3 3 3 4 5% 55%	2030
	11th to 20th	Day	9% 4 1 4 4 2 3 4 5% 6% 56%	1980
	21st to end	Day	9% 4 1 3 4 2 3 3 5% 7% 60%	1980
October	1st to 10th	Day	15% 6% 2 3 3 2 3 3 4 5% 54%	1945
	11th to 20th	Day	10% 5% 2 3 3 1 3 3 4 6% 60%	1800
	21st to end	Day	13% 6% 3 5% 3 2 3 3 3 5% 55%	1882
November	1st to 10th	Day	8% 4 1 4 3 2 3 4 5% 7% 58%	1673
	11th to 20th	Day	7% 6% 3 5% 4 2 3 3 4 5% 57%	1710
	21st to end	Day	10% 9% 3 5% 3 2 4 4 4 7% 51%	1710
December	1st to 10th	Day	7% 7% 3 5% 5% 2 3 5% 5% 7% 51%	1710
	11th to 20th	Day	7% 8% 3 6% 6% 3 4 4 5% 6% 49%	2161
	21st to end	Day	12% 10% 4 10% 6% 4 4 4 4 5% 36%	3059
January	1st to 10th	Night	6% 9% 3 5% 4 3 4 5% 6% 8% 47%	2629
	11th to 20th	Night	6% 10% 3 7% 5% 3 4 4 4 6% 49%	2367
	21st to end	Night	7% 7% 3 5% 5% 3 3 5% 6% 7% 48%	2574
February	1st to 10th	Night	9% 10% 4 6% 5% 3 5% 5% 5% 6% 43%	2340
	11th to 20th	Night	6% 7% 3 6% 5% 4 4 5% 6% 8% 46%	2116
	21st to end	Night	7% 7% 3 6% 5% 2 4 4 5% 5% 53%	1776
March	1st to 10th	Night	9% 7% 3 4 4 2 3 3 5% 5% 54%	2106
	11th to 20th	Night	13% 8% 2 5% 3 2 3 4 4 6% 51%	1980
	21st to end	Night	13% 9% 3 6% 4 3 5% 4 5% 8% 40%	2178
April	1st to 10th	Night	10% 6% 2 4 5% 3 4 4 5% 7% 48%	1910
	11th to 20th	Night	12% 5% 2 5% 4 3 5% 4 6% 8% 46%	1655
	21st to end	Night	12% 5% 4 4 4 2 3 4 5% 9% 49%	1620
May	1st to 10th	Night	16% 6% 2 4 4 2 5% 5% 5% 6% 43%	1620
	11th to 20th	Night	13% 6% 2 5% 5% 3 3 5% 5% 7% 45%	1593
	21st to end	Night	13% 5% 2 4 5% 3 5% 4 7% 10% 42%	1745
June	1st to 10th	Night	5% 2 2 3 4 2 4 5% 7% 10% 56%	1620
	11th to 20th	Night	8% 3 2 4 4 3 3 5% 6% 9% 55%	1447
	21st to end	Night	3 3 2 3 4 3 4 4 5% 9% 59%	1440
July	1st to 10th	Night	6% 3 2 5% 4 3 4 6% 8% 9% 51%	1440
	11th to 20th	Night	2 3 1 3 3 2 4 6% 7% 9% 59%	1543
	21st to end	Night	4 3 2 3 4 2 4 5% 7% 12% 54%	1772
August	1st to 10th	Night	5% 3 2 4 5% 4 5% 6% 7% 10% 50%	1611
	11th to 20th	Night	6% 4 1 4 4 2 4 5% 6% 8% 57%	1600
	21st to end	Night	6% 3 2 3 4 2 3 4 5% 6% 62%	1843
September	1st to 10th	Night	9% 3 1 2 2 2 2 3 4 6% 64%	1928
	11th to 20th	Night	8% 3 2 4 3 3 4 4 5% 6% 59%	1980
	21st to end	Night	7% 3 1 3 4 2 4 3 4 7% 61%	1980
October	1st to 10th	Night	14% 4 1 4 4 2 4 3 5% 6% 55%	1996
	11th to 20th	Night	11% 5% 2 3 3 2 3 2 4 5% 60%	2160
	21st to end	Night	12% 5% 2 3 3 2 3 3 4 5% 58%	2470
November	1st to 10th	Night	4 3 2 4 3 2 3 4 5% 6% 64%	2405
	11th to 20th	Night	7% 5% 1 3 4 2 4 5% 4 6% 58%	2470
	21st to end	Night	9% 6% 2 3 4 2 3 4 5% 7% 57%	2470
December	1st to 10th	Night	6% 5% 3 4 6% 2 4 3 4 7% 55%	2470
	11th to 20th	Night	7% 5% 2 5% 4 2 4 3 4 8% 55%	3036
	21st to end	Night	16% 10% 4 6% 5% 3 3 3 4 6% 40%	4596

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	36% 5% 17% 26% 15% 1	1525
	11th to 20th	Day	36% 6% 18% 23% 14% 3	1638
	21st to end	Day	40% 6% 17% 24% 11% 2	1782
February	1st to 10th	Day	43% 6% 15% 23% 11% 3	1620
	11th to 20th	Day	36% 5% 15% 25% 15% 4	1755
	21st to end	Day	34% 6% 14% 26% 15% 5%	1480
March	1st to 10th	Day	30% 7% 15% 26% 18% 4	1854
	11th to 20th	Day	39% 5% 11% 25% 15% 3	1980
	21st to end	Day	46% 6% 16% 22% 9% 1	2178
April	1st to 10th	Day	35% 5% 16% 25% 16% 2	2047
	11th to 20th	Day	40% 6% 13% 24% 14% 3	2254
	21st to end	Day	41% 7% 12% 26% 14% 1	2340
May	1st to 10th	Day	41% 6% 14% 22% 14% 2	2340
	11th to 20th	Day	41% 7% 16% 23% 12%	2306
	21st to end	Day	40% 11% 17% 21% 10% 2	2531
June	1st to 10th	Day	25% 7% 19% 33% 14% 2	2340
	11th to 20th	Day	28% 7% 16% 28% 17% 3	2507
	21st to end	Day	24% 8% 15% 30% 18% 5%	2520
July	1st to 10th	Day	28% 6% 14% 29% 20% 2	2451
	11th to 20th	Day	22% 7% 14% 30% 22% 4	2339
	21st to end	Day	26% 9% 16% 30% 18% 1	2405
August	1st to 10th	Day	31% 10% 20% 25% 13% 1	2314
	11th to 20th	Day	25% 8% 15% 32% 18% 2	2301
	21st to end	Day	27% 7% 13% 23% 25% 6%	2510
September	1st to 10th	Day	32% 6% 11% 23% 22% 7%	2030
	11th to 20th	Day	27% 5% 12% 30% 23% 3	1980
	21st to end	Day	25% 4 11% 33% 25% 2	1980
October	1st to 10th	Day	33% 4 9% 26% 25% 2	1945
	11th to 20th	Day	27% 4 9% 29% 23% 8%	1800
	21st to end	Day	33% 4 11% 24% 23% 5%	1882
November	1st to 10th	Day	26% 5% 13% 31% 22% 4	1673
	11th to 20th	Day	29% 5% 11% 26% 26% 4	1710
	21st to end	Day	34% 5% 11% 26% 21% 4	1710
December	1st to 10th	Day	33% 4 16% 29% 16% 2	1710
	11th to 20th	Day	36% 5% 15% 31% 13%	2159
	21st to end	Day	49% 6% 11% 20% 13% 1	3059
January	1st to 10th	Night	35% 5% 13% 29% 17% 2	2629
	11th to 20th	Night	38% 4 12% 28% 17% 1	2367
	21st to end	Night	35% 6% 16% 27% 13% 2	2574
February	1st to 10th	Night	41% 7% 13% 21% 14% 4	2340
	11th to 20th	Night	35% 6% 14% 28% 15% 3	2116
	21st to end	Night	33% 4 13% 21% 22% 7%	1776
March	1st to 10th	Night	32% 4 13% 26% 20% 5%	2106
	11th to 20th	Night	35% 5% 10% 25% 21% 4	1980
	21st to end	Night	43% 7% 16% 22% 11% 2	2178
April	1st to 10th	Night	34% 6% 15% 22% 20% 2	1910
	11th to 20th	Night	36% 6% 16% 26% 15% 2	1655
	21st to end	Night	33% 7% 13% 27% 18% 2	1620
May	1st to 10th	Night	40% 8% 13% 23% 14% 2	1620
	11th to 20th	Night	38% 7% 17% 24% 14% 1	1594
	21st to end	Night	38% 8% 18% 23% 11% 2	1746
June	1st to 10th	Night	21% 9% 19% 31% 17% 2	1620
	11th to 20th	Night	26% 8% 14% 27% 18% 6%	1447
	21st to end	Night	21% 6% 17% 31% 20% 4	1440
July	1st to 10th	Night	26% 8% 16% 26% 18% 5%	1400
	11th to 20th	Night	20% 8% 16% 28% 22% 6%	1494
	21st to end	Night	20% 8% 18% 34% 17% 3	1673
August	1st to 10th	Night	26% 10% 20% 27% 14% 3	1601
	11th to 20th	Night	24% 6% 17% 33% 18% 3	1600
	21st to end	Night	22% 7% 13% 24% 26% 8%	1843
September	1st to 10th	Night	22% 5% 11% 27% 26% 10%	1928
	11th to 20th	Night	26% 5% 10% 29% 25% 5%	1980
	21st to end	Night	24% 5% 10% 28% 29% 4	1980
October	1st to 10th	Night	32% 5% 10% 26% 23% 4	1996
	11th to 20th	Night	28% 4 8% 26% 26% 8%	2160
	21st to end	Night	29% 4 12% 25% 23% 8%	2470
November	1st to 10th	Night	21% 4 12% 30% 27% 7%	2405
	11th to 20th	Night	26% 5% 10% 28% 26% 5%	2470
	21st to end	Night	28% 4 12% 27% 24% 4	2470
December	1st to 10th	Night	30% 5% 14% 30% 19% 2	2470
	11th to 20th	Night	29% 5% 12% 35% 18% 1	3037
	21st to end	Night	44% 6% 11% 26% 11% 2	4596

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	14% 13% 39% 27% 7% 1	270
	11th to 20th	Day	18% 14% 33% 27% 9%	246
	21st to end	Day	14% 9% 47% 25% 5% 1	264
February	1st to 10th	Day	11% 15% 46% 25% 4	240
	11th to 20th	Day	12% 13% 42% 26% 6% 1	240
	21st to end	Day	12% 18% 47% 19% 4 1	198
March	1st to 10th	Day	13% 12% 48% 21% 5% 1	240
	11th to 20th	Day	24% 10% 35% 21% 9%	240
	21st to end	Day	23% 16% 38% 18% 5%	264
April	1st to 10th	Day	15% 18% 44% 19% 4	307
	11th to 20th	Day	17% 14% 39% 25% 4	532
	21st to end	Day	20% 14% 36% 19% 9% 2	600
May	1st to 10th	Day	14% 12% 32% 31% 10% 1	603
	11th to 20th	Day	18% 9% 33% 24% 13% 2	625
	21st to end	Day	16% 10% 31% 27% 14% 2	679
June	1st to 10th	Day	5% 6% 26% 36% 20% 7%	630
	11th to 20th	Day	8% 6% 36% 33% 16% 1	630
	21st to end	Day	7% 6% 33% 34% 17% 3	630
July	1st to 10th	Day	8% 3 18% 40% 27% 5%	621
	11th to 20th	Day	4 3 19% 45% 23% 6%	618
	21st to end	Day	9% 2 17% 42% 26% 5%	684
August	1st to 10th	Day	9% 3 16% 44% 24% 4	626
	11th to 20th	Day	7% 2 21% 42% 27% 2	615
	21st to end	Day	9% 2 22% 40% 22% 5%	629
September	1st to 10th	Day	14% 4 24% 37% 15% 5%	320
	11th to 20th	Day	6% 5% 28% 40% 16% 6%	270
	21st to end	Day	13% 8% 32% 29% 15% 3	270
October	1st to 10th	Day	23% 6% 23% 29% 14% 4	270
	11th to 20th	Day	9% 13% 43% 23% 11% 1	270
	21st to end	Day	16% 18% 34% 22% 9% 1	297
November	1st to 10th	Day	11% 16% 36% 27% 9% 3	270
	11th to 20th	Day	9% 17% 44% 21% 9%	270
	21st to end	Day	20% 13% 34% 22% 10% 1	270
December	1st to 10th	Day	7% 10% 44% 27% 10% 1	270
	11th to 20th	Day	15% 9% 40% 29% 6%	270
	21st to end	Day	18% 13% 45% 22% 2	297
January	1st to 10th	Night	11% 11% 38% 32% 6% 1	950
	11th to 20th	Night	12% 10% 39% 31% 7% 1	911
	21st to end	Night	11% 10% 43% 30% 7%	990
February	1st to 10th	Night	13% 11% 44% 28% 5%	900
	11th to 20th	Night	10% 10% 45% 31% 4	722
	21st to end	Night	11% 13% 43% 27% 5%	592
March	1st to 10th	Night	12% 14% 43% 28% 3 1	666
	11th to 20th	Night	15% 11% 40% 27% 6% 1	540
	21st to end	Night	16% 13% 43% 22% 6%	594
April	1st to 10th	Night	14% 12% 43% 27% 3	540
	11th to 20th	Night	16% 14% 41% 25% 4	533
	21st to end	Night	14% 12% 35% 31% 6% 1	540
May	1st to 10th	Night	17% 9% 35% 31% 7%	540
	11th to 20th	Night	16% 8% 35% 33% 7% 1	531
	21st to end	Night	15% 9% 31% 33% 12% 1	584
June	1st to 10th	Night	7% 5% 26% 46% 14% 2	540
	11th to 20th	Night	7% 5% 38% 39% 11%	540
	21st to end	Night	4 5% 35% 44% 12%	540
July	1st to 10th	Night	6% 3 20% 44% 26%	525
	11th to 20th	Night	3 2 22% 52% 21% 1	522
	21st to end	Night	3 1 16% 56% 23% 1	591
August	1st to 10th	Night	5% 3 19% 52% 20% 2	537
	11th to 20th	Night	8% 2 23% 49% 17% 1	534
	21st to end	Night	7% 2 23% 45% 22% 1	594
September	1st to 10th	Night	11% 3 26% 43% 16% 1	540
	11th to 20th	Night	10% 2 34% 37% 16% 1	540
	21st to end	Night	7% 6% 36% 36% 14% 1	540
October	1st to 10th	Night	16% 7% 34% 31% 12%	556
	11th to 20th	Night	14% 10% 38% 30% 9%	720
	21st to end	Night	14% 12% 31% 32% 10%	886
November	1st to 10th	Night	7% 10% 37% 39% 7%	925
	11th to 20th	Night	10% 11% 41% 30% 7%	950
	21st to end	Night	11% 11% 34% 32% 11% 1	950
December	1st to 10th	Night	10% 10% 43% 33% 4 1	950
	11th to 20th	Night	13% 10% 39% 30% 7%	950
	21st to end	Night	16% 11% 38% 31% 5%	1045

Page generated at 2024-01-10 00:25:05. Version ac07

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