Logan Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Logan Observatory clear sky chart from 2005-11-06 to 2024-07-16.

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	3 4 2 5% 4 4 4 4 5% 6% 59%	90033
	Night	1 3 1 4 3 3 4 3 5% 7% 66%	89663
Transparency	Day	24% 6% 8% 15% 27% 19%	89759
	Night	17% 6% 9% 18% 30% 19%	89458
Seeing	Day	10% 18% 26% 24% 16% 6%	14210
	Night	4 14% 25% 30% 21% 5%	24299

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 2 8% 4 4 4 3 5% 7% 61%	2858
	11th to 20th	Day	1 3 2 5% 3 2 3 3 5% 9% 64%	2860
	21st to end	Day	2 8% 4 7% 3 4 4 3 6% 6% 53%	3146
February	1st to 10th	Day	1 4 1 5% 4 2 3 3 5% 6% 65%	1710
	11th to 20th	Day	2 3 2 4 3 3 4 4 4 6% 64%	1727
	21st to end	Day	4 2 5% 3 3 3 3 6% 7% 65%	1727
March	1st to 10th	Day	3 2 5% 4 3 3 3 5% 7% 64%	3444
	11th to 20th	Day	1 5% 2 8% 5% 4 4 4 7% 8% 50%	3490
	21st to end	Day	1 4 3 5% 3 4 4 4 5% 8% 62%	3825
April	1st to 10th	Day	1 2 1 3 3 3 3 4 5% 7% 68%	2167
	11th to 20th	Day	1 5% 2 3 3 3 3 3 4 4 69%	2251
	21st to end	Day	2 4 1 4 3 3 3 3 4 6% 67%	2280
May	1st to 10th	Day	1 2 1 3 2 2 3 2 3 5% 76%	4003
	11th to 20th	Day	2 3 1 5% 4 4 4 4 5% 6% 61%	4071
	21st to end	Day	2 2 1 3 2 2 2 2 3 5% 77%	4477
June	1st to 10th	Day	2 3 1 3 3 3 4 3 4 6% 67%	2470
	11th to 20th	Day	3 2 1 3 3 3 3 2 4 4 71%	2470
	21st to end	Day	4 5% 1 6% 6% 5% 5% 5% 6% 7% 50%	2470
July	1st to 10th	Day	6% 6% 2 8% 7% 6% 6% 6% 7% 6% 39%	2470
	11th to 20th	Day	6% 6% 3 10% 8% 8% 8% 7% 8% 7% 29%	2407
	21st to end	Day	10% 7% 3 10% 8% 8% 9% 6% 7% 8% 23%	2545
August	1st to 10th	Day	8% 7% 4 10% 8% 8% 8% 6% 7% 7% 27%	2328
	11th to 20th	Day	8% 6% 3 11% 8% 7% 7% 5% 8% 7% 31%	2235
	21st to end	Day	7% 6% 3 9% 6% 6% 7% 5% 7% 9% 35%	2376
September	1st to 10th	Day	7% 7% 2 9% 5% 5% 5% 5% 6% 7% 42%	2152
	11th to 20th	Day	5% 5% 2 6% 5% 5% 5% 3 4 5% 54%	1980
	21st to end	Day	4 4 1 5% 3 4 4 3 4 6% 63%	1980
October	1st to 10th	Day	3 4 1 4 3 3 3 3 4 6% 65%	1806
	11th to 20th	Day	2 2 2 2 1 2 1 3 5% 79%	1800
	21st to end	Day	1 3 1 2 2 3 2 2 3 5% 76%	1980
November	1st to 10th	Day	1 2 1 2 2 2 3 2 5% 6% 75%	1859
	11th to 20th	Day	1 3 1 3 2 2 3 3 5% 6% 71%	1900
	21st to end	Day	1 5% 1 4 3 2 3 3 4 7% 66%	1744
December	1st to 10th	Day	2 3 1 4 2 3 4 4 5% 7% 67%	1710
	11th to 20th	Day	2 6% 2 6% 4 4 4 4 5% 7% 57%	2169
	21st to end	Day	3 2 6% 4 5% 4 4 5% 7% 60%	3146
January	1st to 10th	Night	3 2 8% 5% 4 5% 5% 6% 7% 55%	4097
	11th to 20th	Night	1 2 1 2 2 2 2 2 4 5% 78%	4110
	21st to end	Night	1 8% 4 6% 4 4 5% 4 6% 6% 52%	4521
February	1st to 10th	Night	1 3 1 3 3 2 4 4 6% 7% 67%	2470
	11th to 20th	Night	1 4 1 5% 3 3 4 3 5% 6% 66%	2334
	21st to end	Night	1 2 1 3 2 3 3 3 6% 9% 68%	1727
March	1st to 10th	Night	2 1 3 2 2 3 2 3 6% 75%	3430
	11th to 20th	Night	1 3 1 4 2 3 3 3 6% 7% 66%	3490
	21st to end	Night	1 3 1 4 3 3 3 3 5% 8% 66%	3828
April	1st to 10th	Night	1 2 1 2 2 3 3 4 6% 6% 70%	2011
	11th to 20th	Night	1 3 1 3 3 3 3 3 4 4 72%	1877
	21st to end	Night	1 2 1 1 1 2 3 3 4 7% 75%	1900
May	1st to 10th	Night	1 1 2 2 1 2 1 3 4 84%	2964
	11th to 20th	Night	1 2 1 3 3 3 3 3 5% 6% 72%	2834
	21st to end	Night	1 1 1 1 1 1 1 2 3 88%	3110
June	1st to 10th	Night	1 3 1 3 2 3 4 3 4 5% 70%	1710
	11th to 20th	Night	2 2 1 2 2 2 2 2 4 4 78%	1710
	21st to end	Night	1 2 2 5% 4 4 5% 5% 6% 7% 58%	1710
July	1st to 10th	Night	3 4 2 5% 6% 5% 5% 6% 8% 9% 47%	1710
	11th to 20th	Night	3 3 1 7% 5% 7% 7% 8% 10% 12% 37%	1674
	21st to end	Night	5% 5% 2 7% 6% 6% 7% 5% 12% 14% 31%	1773
August	1st to 10th	Night	3 3 2 5% 4 5% 6% 6% 8% 11% 46%	1611
	11th to 20th	Night	3 5% 2 7% 6% 5% 7% 5% 8% 10% 41%	1664
	21st to end	Night	4 3 2 5% 4 5% 4 5% 9% 10% 47%	1980
September	1st to 10th	Night	3 5% 2 6% 4 4 5% 5% 6% 8% 50%	1804
	11th to 20th	Night	3 2 1 4 3 3 3 3 5% 5% 67%	1980
	21st to end	Night	2 2 1 3 2 3 3 3 4 6% 71%	1980
October	1st to 10th	Night	2 2 1 3 3 3 3 3 4 6% 70%	2152
	11th to 20th	Night	1 1 1 2 1 1 2 2 3 4 81%	2160
	21st to end	Night	1 2 1 2 1 2 2 2 3 4 79%	2376
November	1st to 10th	Night	2 1 2 2 2 2 2 5% 6% 75%	2220
	11th to 20th	Night	1 3 1 3 1 2 2 3 4 6% 74%	2280
	21st to end	Night	1 3 1 3 3 3 3 3 5% 7% 69%	2434
December	1st to 10th	Night	2 3 2 3 2 3 3 3 5% 7% 67%	2470
	11th to 20th	Night	1 4 3 5% 3 3 4 3 6% 8% 59%	3041
	21st to end	Night	1 3 1 5% 3 4 4 4 6% 6% 62%	4521

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	19% 9% 10% 19% 32% 12%	2859
	11th to 20th	Day	17% 7% 9% 26% 28% 12%	2860
	21st to end	Day	26% 11% 7% 18% 30% 9%	3146
February	1st to 10th	Day	20% 4 8% 19% 25% 23%	1710
	11th to 20th	Day	21% 4 8% 20% 26% 21%	1736
	21st to end	Day	19% 6% 5% 17% 30% 24%	1727
March	1st to 10th	Day	18% 6% 7% 13% 35% 22%	3444
	11th to 20th	Day	25% 8% 12% 17% 27% 11%	3490
	21st to end	Day	19% 7% 8% 18% 39% 9%	3825
April	1st to 10th	Day	16% 4 7% 17% 38% 19%	2167
	11th to 20th	Day	19% 4 4 14% 33% 27%	2254
	21st to end	Day	18% 4 7% 19% 37% 16%	2280
May	1st to 10th	Day	12% 3 6% 11% 39% 29%	4003
	11th to 20th	Day	19% 7% 8% 13% 33% 20%	4074
	21st to end	Day	10% 3 5% 8% 25% 49%	4477
June	1st to 10th	Day	18% 4 6% 13% 29% 29%	2470
	11th to 20th	Day	18% 3 4 8% 24% 44%	2470
	21st to end	Day	31% 6% 9% 12% 23% 20%	2470
July	1st to 10th	Day	40% 9% 11% 12% 12% 16%	2406
	11th to 20th	Day	47% 13% 17% 13% 6% 5%	2338
	21st to end	Day	51% 13% 19% 12% 3 2	2404
August	1st to 10th	Day	51% 11% 13% 11% 11% 4	2313
	11th to 20th	Day	46% 11% 13% 15% 10% 5%	2235
	21st to end	Day	44% 9% 12% 17% 14% 3	2376
September	1st to 10th	Day	39% 7% 9% 15% 19% 11%	2152
	11th to 20th	Day	32% 5% 7% 15% 27% 15%	1980
	21st to end	Day	23% 4 7% 19% 29% 18%	1980
October	1st to 10th	Day	22% 5% 8% 17% 24% 24%	1806
	11th to 20th	Day	11% 3 4 12% 35% 35%	1800
	21st to end	Day	14% 2 6% 16% 42% 20%	1980
November	1st to 10th	Day	11% 3 6% 24% 34% 22%	1859
	11th to 20th	Day	16% 3 5% 16% 37% 23%	1900
	21st to end	Day	20% 5% 5% 14% 34% 21%	1744
December	1st to 10th	Day	18% 4 7% 23% 28% 19%	1710
	11th to 20th	Day	27% 5% 10% 19% 22% 17%	2168
	21st to end	Day	21% 7% 8% 16% 27% 20%	3146
January	1st to 10th	Night	19% 13% 10% 19% 25% 14%	4097
	11th to 20th	Night	11% 3 11% 26% 40% 10%	4110
	21st to end	Night	26% 11% 8% 16% 29% 10%	4521
February	1st to 10th	Night	16% 6% 9% 22% 27% 21%	2470
	11th to 20th	Night	19% 5% 8% 21% 27% 20%	2335
	21st to end	Night	14% 4 7% 18% 30% 26%	1727
March	1st to 10th	Night	10% 4 6% 14% 44% 21%	3430
	11th to 20th	Night	13% 8% 13% 22% 33% 11%	3490
	21st to end	Night	13% 8% 8% 29% 34% 8%	3828
April	1st to 10th	Night	13% 5% 7% 23% 37% 16%	2011
	11th to 20th	Night	15% 4 5% 17% 35% 23%	1877
	21st to end	Night	10% 4 7% 22% 41% 16%	1900
May	1st to 10th	Night	7% 2 5% 13% 53% 20%	2964
	11th to 20th	Night	12% 7% 6% 16% 38% 20%	2835
	21st to end	Night	6% 2 3 9% 28% 52%	3110
June	1st to 10th	Night	15% 4 6% 12% 33% 30%	1710
	11th to 20th	Night	11% 3 3 12% 29% 42%	1710
	21st to end	Night	22% 7% 11% 13% 23% 24%	1710
July	1st to 10th	Night	29% 9% 13% 15% 14% 19%	1665
	11th to 20th	Night	32% 15% 23% 18% 7% 5%	1620
	21st to end	Night	35% 16% 31% 11% 4 2	1674
August	1st to 10th	Night	28% 14% 22% 14% 15% 7%	1602
	11th to 20th	Night	33% 13% 19% 16% 12% 6%	1664
	21st to end	Night	28% 11% 18% 21% 18% 4	1980
September	1st to 10th	Night	30% 8% 14% 18% 19% 11%	1804
	11th to 20th	Night	19% 5% 10% 20% 31% 15%	1980
	21st to end	Night	15% 4 7% 21% 32% 21%	1980
October	1st to 10th	Night	16% 5% 10% 21% 26% 23%	2152
	11th to 20th	Night	9% 2 5% 16% 34% 35%	2160
	21st to end	Night	11% 3 5% 19% 42% 20%	2376
November	1st to 10th	Night	11% 4 5% 22% 37% 22%	2220
	11th to 20th	Night	13% 3 7% 18% 33% 27%	2280
	21st to end	Night	16% 3 7% 20% 32% 22%	2434
December	1st to 10th	Night	18% 5% 6% 23% 26% 21%	2470
	11th to 20th	Night	22% 7% 11% 18% 26% 16%	3041
	21st to end	Night	20% 8% 10% 17% 23% 23%	4521

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% 27% 35% 19% 8% 3	270
	11th to 20th	Day	14% 24% 26% 17% 14% 5%	270
	21st to end	Day	7% 23% 28% 25% 14% 3	297
February	1st to 10th	Day	8% 26% 31% 20% 11% 3	270
	11th to 20th	Day	16% 31% 28% 18% 5% 1	316
	21st to end	Day	19% 35% 29% 13% 4	382
March	1st to 10th	Day	17% 34% 29% 15% 5% 1	460
	11th to 20th	Day	18% 26% 26% 20% 8% 2	460
	21st to end	Day	17% 36% 27% 16% 4 1	506
April	1st to 10th	Day	8% 27% 37% 17% 7% 3	460
	11th to 20th	Day	15% 29% 36% 14% 6% 1	452
	21st to end	Day	13% 29% 33% 17% 6% 2	460
May	1st to 10th	Day	7% 25% 39% 21% 7% 2	463
	11th to 20th	Day	6% 20% 36% 25% 11% 2	488
	21st to end	Day	9% 23% 36% 20% 10% 2	529
June	1st to 10th	Day	4 13% 34% 32% 14% 3	490
	11th to 20th	Day	4 16% 30% 31% 13% 6%	490
	21st to end	Day	6% 8% 26% 38% 18% 4	490
July	1st to 10th	Day	8% 4 19% 30% 29% 9%	486
	11th to 20th	Day	9% 3 9% 28% 32% 19%	465
	21st to end	Day	11% 1 10% 24% 32% 21%	487
August	1st to 10th	Day	9% 3 12% 25% 33% 19%	447
	11th to 20th	Day	11% 2 14% 30% 29% 14%	437
	21st to end	Day	7% 2 13% 30% 31% 15%	495
September	1st to 10th	Day	10% 6% 15% 30% 29% 9%	450
	11th to 20th	Day	6% 7% 27% 33% 21% 6%	450
	21st to end	Day	8% 12% 25% 28% 20% 6%	450
October	1st to 10th	Day	6% 17% 28% 26% 16% 7%	276
	11th to 20th	Day	8% 14% 23% 29% 18% 7%	270
	21st to end	Day	8% 12% 29% 24% 22% 5%	297
November	1st to 10th	Day	7% 25% 27% 26% 12% 3	270
	11th to 20th	Day	3 16% 30% 24% 20% 7%	270
	21st to end	Day	10% 26% 26% 21% 13% 4	270
December	1st to 10th	Day	8% 24% 23% 28% 15% 3	270
	11th to 20th	Day	8% 27% 29% 23% 12% 3	270
	21st to end	Day	13% 28% 29% 20% 8% 1	297
January	1st to 10th	Night	4 18% 22% 34% 16% 7%	760
	11th to 20th	Night	6% 15% 28% 29% 18% 4	760
	21st to end	Night	4 19% 26% 29% 16% 5%	836
February	1st to 10th	Night	4 21% 27% 30% 15% 4	760
	11th to 20th	Night	5% 26% 32% 24% 12% 1	744
	21st to end	Night	10% 25% 32% 23% 8% 2	628
March	1st to 10th	Night	9% 27% 29% 24% 10% 2	760
	11th to 20th	Night	6% 22% 32% 24% 13% 4	760
	21st to end	Night	8% 22% 32% 24% 12% 2	836
April	1st to 10th	Night	4 23% 35% 25% 11% 1	681
	11th to 20th	Night	6% 25% 36% 23% 8% 1	563
	21st to end	Night	2 23% 31% 28% 13% 3	570
May	1st to 10th	Night	2 16% 37% 30% 13% 2	570
	11th to 20th	Night	3 10% 36% 32% 16% 3	561
	21st to end	Night	3 16% 34% 31% 14% 2	617
June	1st to 10th	Night	2 7% 32% 37% 19% 2	570
	11th to 20th	Night	2 8% 32% 40% 16% 2	570
	21st to end	Night	2 2 22% 40% 28% 5%	570
July	1st to 10th	Night	6% 1 14% 35% 37% 8%	555
	11th to 20th	Night	4 8% 29% 45% 13%	540
	21st to end	Night	6% 1 7% 23% 48% 16%	591
August	1st to 10th	Night	4 1 7% 22% 49% 16%	537
	11th to 20th	Night	5% 1 8% 30% 43% 13%	534
	21st to end	Night	5% 8% 27% 47% 13%	594
September	1st to 10th	Night	4 1 16% 31% 41% 8%	544
	11th to 20th	Night	4 2 21% 34% 31% 8%	720
	21st to end	Night	2 11% 17% 34% 28% 8%	720
October	1st to 10th	Night	3 13% 30% 32% 18% 4	720
	11th to 20th	Night	3 9% 24% 37% 21% 6%	720
	21st to end	Night	4 11% 23% 30% 24% 8%	792
November	1st to 10th	Night	2 15% 23% 34% 18% 8%	740
	11th to 20th	Night	2 14% 24% 32% 22% 5%	760
	21st to end	Night	5% 21% 23% 26% 19% 6%	760
December	1st to 10th	Night	6% 18% 19% 32% 20% 4	760
	11th to 20th	Night	4 21% 29% 26% 15% 3	760
	21st to end	Night	6% 22% 27% 30% 11% 4	836

Page generated at 2024-07-13 07:19:48. Version ac07

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