Bowen Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bowen Observatory clear sky chart from 2005-11-06 to 2024-01-17.

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	7% 4 2 3 3 2 3 3 4 7% 63%	74748
	Night	8% 5% 2 4 4 2 3 4 4 7% 58%	75092
Transparency	Day	21% 4 8% 21% 26% 20%	74470
	Night	25% 4 8% 21% 23% 19%	74894
Seeing	Day	7% 7% 22% 35% 23% 5%	14446
	Night	8% 3 14% 32% 34% 9%	24117

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	15% 5% 2 4 6% 2 5% 4 4 6% 47%	1634
	11th to 20th	Day	10% 4 2 3 3 2 3 3 4 6% 59%	1675
	21st to end	Day	12% 5% 2 4 3 3 3 5% 4 8% 51%	1782
February	1st to 10th	Day	14% 3 2 4 3 1 2 4 5% 5% 57%	1677
	11th to 20th	Day	11% 3 2 4 4 3 3 3 5% 7% 54%	1750
	21st to end	Day	14% 4 2 4 4 2 4 4 4 6% 53%	1480
March	1st to 10th	Day	12% 7% 3 5% 6% 2 4 4 5% 9% 44%	1862
	11th to 20th	Day	12% 6% 2 5% 4 3 5% 3 6% 8% 47%	1980
	21st to end	Day	9% 5% 2 3 4 3 3 4 4 8% 55%	2268
April	1st to 10th	Day	10% 5% 2 4 3 2 3 4 4 7% 56%	2160
	11th to 20th	Day	7% 5% 2 3 3 2 3 3 5% 7% 60%	2129
	21st to end	Day	8% 4 1 3 2 2 3 4 4 6% 64%	2160
May	1st to 10th	Day	6% 4 2 3 2 1 3 2 4 7% 66%	2160
	11th to 20th	Day	2 3 1 3 3 2 3 3 5% 8% 67%	2197
	21st to end	Day	5% 5% 2 4 3 2 3 2 4 8% 63%	2723
June	1st to 10th	Day	4 3 1 3 3 2 3 3 5% 8% 64%	2520
	11th to 20th	Day	1 3 1 3 2 1 2 3 3 7% 74%	2520
	21st to end	Day	1 2 1 2 2 1 2 3 3 7% 74%	2520
July	1st to 10th	Day	1 2 1 3 2 1 2 3 5% 10% 70%	2518
	11th to 20th	Day	3 2 1 2 3 2 2 3 4 7% 70%	2340
	21st to end	Day	1 2 1 3 3 2 3 5% 6% 10% 65%	2546
August	1st to 10th	Day	1 3 2 3 2 2 3 4 5% 9% 67%	2235
	11th to 20th	Day	1 2 1 3 2 1 2 3 4 6% 75%	2122
	21st to end	Day	2 3 1 2 3 1 2 3 3 7% 72%	2376
September	1st to 10th	Day	1 2 1 2 2 1 2 2 4 8% 75%	2160
	11th to 20th	Day	3 3 1 2 2 1 2 3 3 8% 74%	2160
	21st to end	Day	3 3 1 2 1 1 2 3 5% 7% 73%	1974
October	1st to 10th	Day	4 2 1 2 1 2 3 3 4 5% 74%	1800
	11th to 20th	Day	4 3 1 3 3 1 2 3 3 5% 70%	1800
	21st to end	Day	5% 3 2 3 3 2 2 3 3 6% 68%	1980
November	1st to 10th	Day	7% 3 1 3 3 2 2 3 4 5% 67%	1798
	11th to 20th	Day	7% 3 1 2 3 2 3 4 5% 5% 66%	1710
	21st to end	Day	8% 3 2 4 4 2 3 3 4 5% 62%	1710
December	1st to 10th	Day	11% 5% 3 3 4 2 3 4 5% 7% 53%	1600
	11th to 20th	Day	25% 6% 2 4 3 2 4 4 4 6% 39%	1928
	21st to end	Day	17% 7% 2 4 4 3 4 4 4 7% 43%	2794
January	1st to 10th	Night	14% 6% 2 4 4 3 4 3 4 6% 51%	2529
	11th to 20th	Night	10% 4 2 3 4 2 4 3 4 7% 57%	2429
	21st to end	Night	13% 4 2 4 3 2 3 4 5% 5% 55%	2574
February	1st to 10th	Night	12% 4 1 4 3 2 3 3 3 5% 59%	2282
	11th to 20th	Night	10% 4 2 4 3 2 3 4 4 7% 58%	2098
	21st to end	Night	13% 5% 2 3 4 2 3 3 3 6% 57%	1776
March	1st to 10th	Night	12% 8% 3 4 5% 1 4 5% 5% 8% 46%	2093
	11th to 20th	Night	12% 5% 2 4 5% 2 4 4 6% 7% 50%	1980
	21st to end	Night	12% 6% 2 4 3 1 3 3 4 6% 57%	2088
April	1st to 10th	Night	9% 4 2 5% 4 1 3 4 4 7% 57%	1800
	11th to 20th	Night	6% 5% 2 4 3 2 2 3 3 7% 64%	1779
	21st to end	Night	6% 7% 2 3 3 1 2 3 3 8% 62%	1800
May	1st to 10th	Night	4 7% 2 3 4 2 3 3 4 9% 60%	1800
	11th to 20th	Night	4 5% 3 4 4 2 3 3 4 9% 58%	1691
	21st to end	Night	4 9% 3 5% 3 2 3 3 5% 7% 55%	1552
June	1st to 10th	Night	3 6% 2 4 4 2 5% 4 5% 9% 58%	1440
	11th to 20th	Night	2 5% 1 4 3 2 2 3 4 6% 66%	1440
	21st to end	Night	1 4 3 3 2 2 2 3 4 10% 67%	1440
July	1st to 10th	Night	1 3 4 4 3 2 3 5% 5% 9% 61%	1440
	11th to 20th	Night	1 3 1 4 3 2 3 4 5% 10% 64%	1616
	21st to end	Night	1 2 1 5% 6% 3 5% 6% 6% 14% 51%	1773
August	1st to 10th	Night	1 4 1 5% 4 3 3 5% 6% 12% 56%	1702
	11th to 20th	Night	1 3 3 2 2 2 5% 5% 12% 66%	1780
	21st to end	Night	2 2 4 4 2 3 4 5% 9% 65%	1980
September	1st to 10th	Night	3 2 2 3 2 1 2 3 3 7% 73%	1800
	11th to 20th	Night	3 3 1 3 3 2 3 2 3 9% 69%	1800
	21st to end	Night	1 4 1 2 2 1 2 3 3 5% 76%	1980
October	1st to 10th	Night	4 4 1 3 3 2 2 4 3 6% 69%	2160
	11th to 20th	Night	4 3 2 4 4 2 3 4 3 7% 64%	2160
	21st to end	Night	5% 5% 2 4 3 1 2 3 3 5% 67%	2376
November	1st to 10th	Night	5% 3 2 3 3 1 3 2 4 7% 64%	2280
	11th to 20th	Night	4 4 2 3 3 2 3 4 5% 7% 64%	2470
	21st to end	Night	5% 5% 2 3 3 2 4 4 5% 6% 61%	2470
December	1st to 10th	Night	12% 5% 2 4 3 2 3 3 5% 7% 56%	2576
	11th to 20th	Night	23% 7% 2 4 5% 3 3 4 5% 5% 39%	3276
	21st to end	Night	16% 8% 3 5% 5% 3 5% 4 5% 7% 41%	4862

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	37% 5% 7% 23% 20% 7%	1634
	11th to 20th	Day	28% 4 9% 20% 20% 18%	1675
	21st to end	Day	33% 6% 12% 16% 18% 15%	1782
February	1st to 10th	Day	30% 3 6% 20% 22% 19%	1677
	11th to 20th	Day	30% 5% 8% 23% 23% 11%	1760
	21st to end	Day	33% 5% 10% 20% 24% 8%	1480
March	1st to 10th	Day	38% 6% 11% 17% 19% 9%	1862
	11th to 20th	Day	36% 5% 11% 20% 19% 9%	1980
	21st to end	Day	28% 6% 13% 26% 19% 7%	2268
April	1st to 10th	Day	30% 5% 11% 26% 19% 9%	2160
	11th to 20th	Day	25% 4 12% 26% 24% 8%	2132
	21st to end	Day	22% 5% 12% 26% 28% 8%	2160
May	1st to 10th	Day	19% 3 11% 25% 31% 11%	2160
	11th to 20th	Day	17% 3 10% 29% 30% 11%	2200
	21st to end	Day	19% 4 14% 30% 27% 6%	2724
June	1st to 10th	Day	17% 6% 8% 27% 29% 13%	2520
	11th to 20th	Day	11% 2 9% 20% 34% 25%	2520
	21st to end	Day	10% 2 5% 21% 29% 33%	2520
July	1st to 10th	Day	9% 1 3 22% 27% 38%	2449
	11th to 20th	Day	13% 3 5% 18% 28% 32%	2271
	21st to end	Day	12% 3 7% 21% 29% 27%	2405
August	1st to 10th	Day	14% 2 5% 20% 24% 35%	2219
	11th to 20th	Day	9% 1 4 21% 33% 32%	2122
	21st to end	Day	11% 1 4 19% 32% 32%	2376
September	1st to 10th	Day	9% 1 5% 17% 27% 41%	2160
	11th to 20th	Day	11% 2 5% 23% 35% 24%	2160
	21st to end	Day	11% 2 7% 19% 35% 26%	1974
October	1st to 10th	Day	14% 4 7% 21% 23% 31%	1800
	11th to 20th	Day	18% 3 5% 20% 27% 27%	1800
	21st to end	Day	18% 4 6% 15% 28% 29%	1980
November	1st to 10th	Day	21% 4 7% 19% 29% 20%	1798
	11th to 20th	Day	22% 4 9% 19% 26% 21%	1710
	21st to end	Day	26% 4 6% 17% 25% 22%	1710
December	1st to 10th	Day	32% 4 8% 17% 23% 17%	1600
	11th to 20th	Day	47% 6% 7% 16% 16% 9%	1928
	21st to end	Day	39% 7% 8% 24% 16% 6%	2794
January	1st to 10th	Night	35% 4 9% 21% 24% 8%	2529
	11th to 20th	Night	29% 4 9% 20% 19% 19%	2429
	21st to end	Night	32% 4 12% 15% 19% 18%	2574
February	1st to 10th	Night	30% 3 7% 18% 24% 18%	2282
	11th to 20th	Night	27% 4 8% 22% 25% 15%	2099
	21st to end	Night	31% 5% 8% 22% 24% 10%	1776
March	1st to 10th	Night	36% 5% 11% 22% 16% 9%	2093
	11th to 20th	Night	33% 6% 12% 18% 22% 9%	1980
	21st to end	Night	29% 6% 13% 23% 22% 7%	2088
April	1st to 10th	Night	28% 4 13% 25% 18% 11%	1800
	11th to 20th	Night	23% 3 12% 30% 23% 10%	1779
	21st to end	Night	23% 4 10% 27% 28% 8%	1800
May	1st to 10th	Night	21% 4 12% 24% 26% 13%	1800
	11th to 20th	Night	21% 3 13% 25% 25% 12%	1693
	21st to end	Night	26% 3 14% 25% 26% 7%	1552
June	1st to 10th	Night	20% 5% 11% 23% 27% 14%	1440
	11th to 20th	Night	16% 2 6% 22% 30% 23%	1440
	21st to end	Night	13% 1 6% 22% 27% 32%	1440
July	1st to 10th	Night	13% 1 2 24% 22% 37%	1400
	11th to 20th	Night	14% 2 5% 28% 22% 30%	1563
	21st to end	Night	18% 3 5% 26% 25% 24%	1674
August	1st to 10th	Night	16% 2 4 27% 23% 28%	1693
	11th to 20th	Night	10% 2 4 26% 27% 32%	1780
	21st to end	Night	11% 1 4 24% 27% 33%	1980
September	1st to 10th	Night	13% 1 3 17% 22% 44%	1800
	11th to 20th	Night	14% 2 5% 22% 27% 30%	1800
	21st to end	Night	11% 2 6% 19% 35% 28%	1980
October	1st to 10th	Night	16% 3 5% 25% 21% 30%	2160
	11th to 20th	Night	20% 4 8% 16% 26% 27%	2160
	21st to end	Night	21% 2 6% 16% 28% 28%	2376
November	1st to 10th	Night	19% 4 8% 20% 26% 23%	2280
	11th to 20th	Night	21% 3 10% 18% 25% 22%	2470
	21st to end	Night	25% 5% 9% 16% 22% 23%	2470
December	1st to 10th	Night	30% 4 7% 19% 21% 19%	2576
	11th to 20th	Night	47% 5% 7% 15% 17% 9%	3276
	21st to end	Night	41% 8% 9% 19% 17% 6%	4862

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	24% 10% 24% 28% 12% 1	295
	11th to 20th	Day	13% 9% 28% 30% 18% 1	359
	21st to end	Day	10% 11% 26% 33% 17% 2	374
February	1st to 10th	Day	13% 9% 28% 29% 17% 4	366
	11th to 20th	Day	12% 11% 31% 27% 17% 3	415
	21st to end	Day	11% 14% 32% 31% 12% 2	346
March	1st to 10th	Day	15% 15% 33% 30% 7%	420
	11th to 20th	Day	14% 12% 29% 33% 11% 1	420
	21st to end	Day	12% 19% 29% 29% 11% 1	462
April	1st to 10th	Day	14% 11% 31% 28% 13% 3	420
	11th to 20th	Day	11% 14% 30% 31% 11% 2	412
	21st to end	Day	6% 12% 33% 29% 15% 5%	420
May	1st to 10th	Day	9% 9% 31% 34% 14% 3	423
	11th to 20th	Day	6% 10% 29% 36% 16% 4	448
	21st to end	Day	7% 13% 26% 32% 18% 4	485
June	1st to 10th	Day	6% 5% 20% 40% 24% 5%	450
	11th to 20th	Day	2 5% 21% 39% 26% 6%	450
	21st to end	Day	3 2 19% 39% 29% 8%	450
July	1st to 10th	Day	1 1 14% 43% 34% 7%	446
	11th to 20th	Day	3 6% 39% 37% 14%	444
	21st to end	Day	1 7% 45% 35% 12%	487
August	1st to 10th	Day	3 2 16% 42% 31% 6%	447
	11th to 20th	Day	3 1 8% 40% 36% 11%	437
	21st to end	Day	2 1 11% 44% 34% 8%	495
September	1st to 10th	Day	2 2 12% 37% 38% 8%	450
	11th to 20th	Day	4 4 17% 41% 28% 6%	450
	21st to end	Day	2 6% 14% 40% 32% 6%	450
October	1st to 10th	Day	2 7% 24% 39% 23% 5%	450
	11th to 20th	Day	4 7% 22% 38% 26% 4	450
	21st to end	Day	4 5% 23% 38% 26% 4	495
November	1st to 10th	Day	5% 7% 23% 34% 27% 4	394
	11th to 20th	Day	8% 6% 21% 37% 23% 5%	270
	21st to end	Day	7% 6% 24% 32% 27% 4	270
December	1st to 10th	Day	13% 9% 26% 35% 15% 2	218
	11th to 20th	Day	13% 11% 20% 33% 20% 3	180
	21st to end	Day	20% 11% 28% 26% 12% 4	198
January	1st to 10th	Night	17% 4 18% 36% 21% 5%	760
	11th to 20th	Night	12% 2 17% 40% 23% 6%	748
	21st to end	Night	14% 3 15% 42% 22% 4	792
February	1st to 10th	Night	14% 5% 11% 37% 27% 6%	720
	11th to 20th	Night	11% 6% 19% 35% 24% 5%	704
	21st to end	Night	14% 6% 18% 39% 20% 3	592
March	1st to 10th	Night	15% 6% 19% 37% 20% 3	720
	11th to 20th	Night	13% 3 17% 37% 24% 7%	720
	21st to end	Night	13% 4 20% 33% 24% 4	792
April	1st to 10th	Night	11% 3 19% 37% 27% 3	720
	11th to 20th	Night	8% 6% 21% 33% 25% 6%	711
	21st to end	Night	8% 4 23% 30% 26% 10%	720
May	1st to 10th	Night	8% 3 18% 30% 32% 8%	720
	11th to 20th	Night	6% 3 16% 32% 34% 8%	629
	21st to end	Night	6% 4 22% 30% 30% 8%	389
June	1st to 10th	Night	4 2 16% 26% 44% 8%	360
	11th to 20th	Night	4 1 12% 27% 47% 10%	360
	21st to end	Night	3 2 8% 24% 48% 16%	360
July	1st to 10th	Night	2 7% 15% 58% 17%	350
	11th to 20th	Night	2 2 11% 56% 29%	519
	21st to end	Night	2 4 14% 53% 27%	591
August	1st to 10th	Night	3 9% 23% 49% 16%	628
	11th to 20th	Night	2 1 5% 18% 58% 17%	712
	21st to end	Night	1 5% 22% 55% 17%	792
September	1st to 10th	Night	3 5% 21% 55% 16%	720
	11th to 20th	Night	3 1 6% 30% 45% 14%	720
	21st to end	Night	3 1 9% 26% 48% 14%	720
October	1st to 10th	Night	5% 1 9% 33% 42% 9%	720
	11th to 20th	Night	5% 2 11% 33% 39% 10%	720
	21st to end	Night	6% 3 11% 36% 34% 11%	792
November	1st to 10th	Night	6% 3 14% 35% 34% 7%	740
	11th to 20th	Night	6% 2 14% 40% 31% 7%	760
	21st to end	Night	6% 4 16% 40% 30% 4	760
December	1st to 10th	Night	13% 4 14% 39% 26% 4	760
	11th to 20th	Night	16% 3 16% 39% 23% 3	760
	21st to end	Night	13% 7% 21% 38% 19% 3	836

Page generated at 2024-01-14 06:55:05. Version ac07

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