Logan
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Logan clear sky chart from 2005-11-06 to 2024-11-04.

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% 10% 3 6% 3 3 4 3 5% 6% 51%	105525
	Night	8% 10% 3 6% 4 3 4 3 5% 6% 48%	102211
Transparency	Day	35% 4 8% 20% 20% 13%	105286
	Night	37% 4 9% 21% 19% 10%	102039
Seeing	Day	12% 12% 30% 30% 13% 3	15311
	Night	13% 5% 21% 38% 20% 3	25116

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% 21% 5% 11% 4 3 4 3 4 5% 30%	2858
	11th to 20th	Day	10% 23% 7% 12% 4 4 3 2 3 4 28%	2860
	21st to end	Day	10% 21% 6% 10% 5% 4 3 2 3 5% 31%	3146
February	1st to 10th	Day	14% 18% 6% 9% 4 3 3 4 4 6% 29%	1710
	11th to 20th	Day	11% 22% 5% 9% 4 3 4 3 4 4 31%	1707
	21st to end	Day	7% 19% 6% 13% 6% 4 4 3 4 4 29%	1570
March	1st to 10th	Day	8% 22% 6% 9% 5% 3 3 2 4 5% 32%	3343
	11th to 20th	Day	5% 13% 3 6% 4 3 4 3 4 6% 48%	3490
	21st to end	Day	12% 23% 5% 10% 5% 5% 4 3 5% 6% 21%	3825
April	1st to 10th	Day	13% 13% 4 7% 5% 4 3 3 5% 6% 36%	2120
	11th to 20th	Day	10% 12% 4 8% 5% 4 5% 3 6% 6% 38%	2418
	21st to end	Day	9% 12% 3 6% 4 4 4 4 5% 8% 41%	2470
May	1st to 10th	Day	9% 15% 3 7% 4 5% 5% 4 5% 7% 36%	4110
	11th to 20th	Day	6% 5% 2 5% 3 3 4 4 5% 8% 55%	4071
	21st to end	Day	7% 7% 2 6% 4 4 5% 4 7% 7% 46%	4558
June	1st to 10th	Day	5% 5% 2 5% 3 4 5% 4 6% 8% 54%	2660
	11th to 20th	Day	7% 4 2 5% 3 4 4 4 6% 6% 56%	2743
	21st to end	Day	2 3 1 3 3 3 3 3 5% 6% 70%	2850
July	1st to 10th	Day	2 1 1 2 2 2 2 2 3 5% 78%	4372
	11th to 20th	Day	2 2 1 2 2 3 4 4 6% 7% 66%	4110
	21st to end	Day	3 2 1 3 2 2 3 3 5% 6% 68%	4454
August	1st to 10th	Day	3 2 1 4 3 3 3 3 4 6% 67%	4092
	11th to 20th	Day	2 2 1 3 3 3 4 3 4 6% 69%	4028
	21st to end	Day	2 2 1 2 2 2 3 2 4 5% 75%	4504
September	1st to 10th	Day	3 3 1 3 2 2 3 3 5% 5% 70%	2163
	11th to 20th	Day	5% 3 1 4 3 3 4 3 4 7% 64%	2090
	21st to end	Day	7% 4 1 3 3 2 3 2 4 5% 67%	2090
October	1st to 10th	Day	6% 4 1 3 3 3 3 3 3 5% 66%	3312
	11th to 20th	Day	8% 5% 2 4 3 3 4 3 5% 7% 57%	3150
	21st to end	Day	7% 9% 2 5% 3 3 3 3 5% 7% 54%	3378
November	1st to 10th	Day	10% 12% 4 8% 5% 4 4 3 4 4 42%	1701
	11th to 20th	Day	14% 10% 2 5% 4 3 4 3 6% 7% 43%	1681
	21st to end	Day	8% 15% 4 6% 4 3 4 3 5% 7% 41%	1520
December	1st to 10th	Day	12% 15% 5% 9% 4 3 4 3 4 6% 36%	1520
	11th to 20th	Day	13% 16% 6% 9% 4 4 4 3 5% 8% 29%	1926
	21st to end	Day	8% 15% 5% 9% 4 5% 5% 4 6% 7% 33%	2925
January	1st to 10th	Night	8% 20% 7% 11% 5% 3 3 3 4 6% 31%	4097
	11th to 20th	Night	13% 22% 6% 13% 4 3 3 2 3 5% 27%	4110
	21st to end	Night	11% 24% 5% 8% 4 3 3 2 4 6% 31%	4521
February	1st to 10th	Night	11% 20% 6% 8% 4 4 4 3 4 5% 30%	2470
	11th to 20th	Night	10% 15% 4 8% 4 3 4 3 4 6% 39%	2357
	21st to end	Night	5% 19% 5% 10% 5% 4 4 3 4 7% 34%	1884
March	1st to 10th	Night	11% 16% 4 7% 4 5% 4 4 5% 6% 35%	3529
	11th to 20th	Night	4 10% 2 5% 4 4 5% 3 5% 7% 50%	3490
	21st to end	Night	9% 19% 4 9% 6% 5% 4 3 4 6% 31%	3828
April	1st to 10th	Night	11% 13% 4 6% 5% 4 4 4 4 6% 41%	2059
	11th to 20th	Night	8% 12% 3 6% 5% 4 4 3 5% 7% 43%	1705
	21st to end	Night	9% 9% 3 6% 4 4 3 3 6% 7% 47%	1710
May	1st to 10th	Night	9% 15% 3 7% 4 4 4 3 5% 6% 40%	2860
	11th to 20th	Night	6% 5% 2 4 3 3 3 3 5% 5% 60%	2834
	21st to end	Night	9% 6% 2 6% 5% 4 4 3 5% 6% 50%	3026
June	1st to 10th	Night	5% 3 1 4 4 3 5% 4 6% 9% 54%	1520
	11th to 20th	Night	5% 4 2 2 3 3 3 3 6% 7% 61%	1429
	21st to end	Night	2 3 1 3 2 2 4 2 5% 7% 69%	1330
July	1st to 10th	Night	2 2 1 2 2 2 2 3 4 5% 75%	2565
	11th to 20th	Night	2 3 1 3 3 3 4 4 6% 7% 62%	2860
	21st to end	Night	2 3 1 4 3 3 3 3 5% 6% 65%	3109
August	1st to 10th	Night	3 2 1 4 3 4 4 4 6% 8% 61%	2847
	11th to 20th	Night	3 3 2 6% 4 4 4 3 5% 6% 61%	2811
	21st to end	Night	2 2 1 2 2 3 3 3 4 6% 72%	3163
September	1st to 10th	Night	3 3 1 3 3 2 3 2 5% 6% 68%	2013
	11th to 20th	Night	5% 3 1 4 4 3 3 3 4 6% 65%	2090
	21st to end	Night	6% 4 1 3 2 2 3 2 3 5% 69%	2090
October	1st to 10th	Night	5% 3 1 3 2 2 2 3 4 5% 71%	3662
	11th to 20th	Night	10% 6% 2 5% 3 3 4 3 4 4 57%	3778
	21st to end	Night	8% 7% 2 4 3 3 3 4 6% 8% 52%	4176
November	1st to 10th	Night	11% 10% 3 6% 3 4 3 3 5% 6% 47%	2450
	11th to 20th	Night	11% 9% 3 6% 4 3 3 4 5% 7% 46%	2477
	21st to end	Night	9% 12% 3 5% 5% 4 4 4 5% 6% 44%	2660
December	1st to 10th	Night	12% 15% 3 8% 5% 3 4 3 4 5% 38%	2660
	11th to 20th	Night	13% 14% 5% 9% 5% 4 4 4 6% 6% 31%	3271
	21st to end	Night	9% 14% 6% 9% 5% 4 4 4 5% 6% 33%	4770

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	59% 3 14% 18% 5% 1	2859
	11th to 20th	Day	63% 3 14% 13% 5% 1	2860
	21st to end	Day	59% 4 15% 15% 7% 1	3146
February	1st to 10th	Day	58% 5% 13% 17% 6% 1	1710
	11th to 20th	Day	58% 3 12% 18% 8% 2	1716
	21st to end	Day	59% 3 12% 17% 8% 1	1570
March	1st to 10th	Day	56% 3 8% 21% 11% 1	3343
	11th to 20th	Day	38% 4 11% 32% 15%	3490
	21st to end	Day	65% 3 11% 16% 5% 1	3825
April	1st to 10th	Day	50% 3 13% 20% 12% 2	2120
	11th to 20th	Day	47% 4 8% 24% 16% 1	2421
	21st to end	Day	43% 3 10% 26% 17% 1	2470
May	1st to 10th	Day	47% 5% 5% 23% 16% 4	4110
	11th to 20th	Day	26% 5% 5% 36% 21% 7%	4074
	21st to end	Day	34% 6% 6% 30% 22% 2	4558
June	1st to 10th	Day	28% 3 11% 27% 27% 4	2660
	11th to 20th	Day	27% 4 6% 19% 28% 16%	2743
	21st to end	Day	16% 3 3 15% 33% 30%	2850
July	1st to 10th	Day	11% 2 2 10% 17% 58%	4304
	11th to 20th	Day	15% 4 2 11% 27% 40%	4041
	21st to end	Day	17% 3 3 11% 32% 34%	4314
August	1st to 10th	Day	19% 3 3 17% 30% 28%	4078
	11th to 20th	Day	18% 4 2 16% 37% 23%	4067
	21st to end	Day	13% 3 4 15% 35% 30%	4503
September	1st to 10th	Day	17% 2 5% 18% 31% 27%	2163
	11th to 20th	Day	23% 2 6% 20% 31% 17%	2090
	21st to end	Day	21% 2 5% 24% 37% 11%	2090
October	1st to 10th	Day	24% 3 4 20% 31% 19%	3312
	11th to 20th	Day	29% 4 7% 27% 26% 7%	3150
	21st to end	Day	32% 4 12% 33% 18% 1	3378
November	1st to 10th	Day	46% 4 11% 23% 14% 2	1701
	11th to 20th	Day	42% 3 16% 26% 13% 1	1681
	21st to end	Day	44% 4 15% 24% 13% 1	1520
December	1st to 10th	Day	51% 6% 16% 16% 8% 3	1520
	11th to 20th	Day	55% 3 17% 20% 5%	1924
	21st to end	Day	50% 4 14% 19% 12% 1	2925
January	1st to 10th	Night	56% 4 11% 20% 8% 1	4097
	11th to 20th	Night	63% 4 13% 14% 5% 1	4110
	21st to end	Night	56% 3 16% 16% 7% 1	4521
February	1st to 10th	Night	56% 5% 13% 19% 7%	2470
	11th to 20th	Night	48% 4 12% 22% 13% 1	2358
	21st to end	Night	51% 4 10% 23% 11% 2	1884
March	1st to 10th	Night	49% 6% 7% 21% 16% 1	3529
	11th to 20th	Night	33% 3 16% 33% 14% 1	3490
	21st to end	Night	55% 4 11% 25% 5% 1	3828
April	1st to 10th	Night	45% 4 13% 22% 11% 6%	2059
	11th to 20th	Night	41% 4 9% 25% 20% 1	1705
	21st to end	Night	37% 3 11% 29% 19% 2	1710
May	1st to 10th	Night	43% 5% 7% 21% 20% 4	2860
	11th to 20th	Night	24% 4 8% 32% 26% 6%	2835
	21st to end	Night	33% 5% 7% 29% 24% 1	3026
June	1st to 10th	Night	26% 4 13% 25% 27% 5%	1520
	11th to 20th	Night	22% 3 8% 22% 28% 16%	1429
	21st to end	Night	17% 3 2 16% 31% 31%	1330
July	1st to 10th	Night	13% 2 3 9% 17% 56%	2524
	11th to 20th	Night	20% 4 1 9% 28% 38%	2806
	21st to end	Night	20% 3 3 10% 31% 33%	3011
August	1st to 10th	Night	21% 4 4 14% 27% 30%	2838
	11th to 20th	Night	26% 3 3 13% 30% 26%	2838
	21st to end	Night	15% 3 4 10% 32% 36%	3163
September	1st to 10th	Night	18% 3 4 18% 25% 33%	2013
	11th to 20th	Night	21% 3 6% 16% 33% 21%	2090
	21st to end	Night	20% 2 4 23% 35% 16%	2090
October	1st to 10th	Night	18% 3 5% 18% 40% 17%	3662
	11th to 20th	Night	32% 3 5% 27% 26% 8%	3778
	21st to end	Night	31% 4 7% 34% 20% 3	4176
November	1st to 10th	Night	39% 3 11% 25% 17% 4	2450
	11th to 20th	Night	39% 3 14% 27% 15% 1	2477
	21st to end	Night	42% 4 12% 26% 13% 3	2660
December	1st to 10th	Night	49% 4 17% 19% 7% 4	2660
	11th to 20th	Night	53% 4 14% 21% 8%	3272
	21st to end	Night	52% 4 14% 17% 12%	4770

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	23% 8% 27% 28% 11% 1	270
	11th to 20th	Day	23% 10% 28% 27% 10% 1	270
	21st to end	Day	20% 9% 27% 31% 12% 1	297
February	1st to 10th	Day	26% 16% 31% 20% 7% 1	270
	11th to 20th	Day	21% 14% 37% 19% 8% 2	312
	21st to end	Day	19% 20% 36% 19% 5% 1	382
March	1st to 10th	Day	20% 19% 32% 23% 5% 1	460
	11th to 20th	Day	16% 19% 32% 28% 5%	460
	21st to end	Day	23% 20% 34% 19% 4	506
April	1st to 10th	Day	20% 18% 32% 23% 6% 1	460
	11th to 20th	Day	22% 20% 33% 18% 6% 1	452
	21st to end	Day	17% 19% 30% 24% 8% 2	460
May	1st to 10th	Day	15% 20% 30% 27% 7% 1	463
	11th to 20th	Day	12% 17% 28% 29% 11% 3	488
	21st to end	Day	12% 14% 22% 30% 17% 4	571
June	1st to 10th	Day	6% 11% 27% 33% 18% 4	680
	11th to 20th	Day	9% 12% 29% 33% 14% 2	680
	21st to end	Day	3 9% 30% 35% 19% 4	680
July	1st to 10th	Day	2 8% 37% 37% 13% 3	486
	11th to 20th	Day	4 7% 36% 35% 14% 4	484
	21st to end	Day	5% 3 26% 44% 19% 3	531
August	1st to 10th	Day	6% 6% 33% 34% 16% 4	487
	11th to 20th	Day	3 5% 31% 40% 18% 3	477
	21st to end	Day	5% 8% 27% 38% 18% 4	539
September	1st to 10th	Day	3 9% 27% 37% 21% 4	490
	11th to 20th	Day	6% 11% 31% 30% 18% 3	490
	21st to end	Day	7% 11% 27% 31% 20% 4	490
October	1st to 10th	Day	9% 9% 27% 30% 23% 2	390
	11th to 20th	Day	10% 12% 24% 29% 20% 5%	300
	21st to end	Day	12% 14% 32% 28% 15%	330
November	1st to 10th	Day	21% 12% 24% 29% 10% 4	279
	11th to 20th	Day	17% 9% 29% 30% 11% 3	270
	21st to end	Day	17% 7% 28% 30% 13% 4	270
December	1st to 10th	Day	18% 10% 27% 29% 13% 3	270
	11th to 20th	Day	23% 7% 27% 33% 9% 1	270
	21st to end	Day	20% 11% 31% 28% 9% 1	297
January	1st to 10th	Night	20% 4 21% 34% 18% 3	760
	11th to 20th	Night	21% 5% 20% 34% 16% 3	760
	21st to end	Night	22% 4 19% 37% 15% 3	836
February	1st to 10th	Night	21% 7% 24% 36% 10% 2	760
	11th to 20th	Night	17% 5% 26% 35% 15% 2	744
	21st to end	Night	14% 9% 27% 35% 13% 2	628
March	1st to 10th	Night	18% 7% 25% 36% 12% 3	760
	11th to 20th	Night	12% 8% 24% 38% 16% 1	760
	21st to end	Night	17% 8% 24% 37% 13% 1	836
April	1st to 10th	Night	17% 7% 26% 35% 13% 2	729
	11th to 20th	Night	13% 10% 26% 35% 14% 1	563
	21st to end	Night	14% 6% 23% 36% 19% 2	570
May	1st to 10th	Night	13% 8% 24% 36% 18% 2	570
	11th to 20th	Night	9% 6% 19% 35% 27% 3	561
	21st to end	Night	12% 5% 18% 36% 26% 4	617
June	1st to 10th	Night	8% 6% 17% 38% 29% 2	570
	11th to 20th	Night	7% 6% 22% 42% 23% 1	479
	21st to end	Night	3 3 20% 41% 28% 5%	380
July	1st to 10th	Night	4 3 21% 35% 34% 4	388
	11th to 20th	Night	3 3 16% 46% 31% 1	552
	21st to end	Night	3 1 11% 46% 34% 4	624
August	1st to 10th	Night	4 2 12% 48% 32% 2	567
	11th to 20th	Night	3 2 17% 46% 29% 4	564
	21st to end	Night	4 3 16% 42% 31% 4	627
September	1st to 10th	Night	4 4 14% 46% 28% 4	683
	11th to 20th	Night	7% 4 16% 43% 26% 6%	760
	21st to end	Night	8% 3 19% 37% 25% 9%	760
October	1st to 10th	Night	10% 4 16% 46% 20% 4	760
	11th to 20th	Night	13% 3 17% 38% 25% 3	760
	21st to end	Night	10% 4 22% 37% 22% 4	836
November	1st to 10th	Night	14% 7% 20% 38% 18% 3	754
	11th to 20th	Night	15% 5% 22% 38% 16% 4	767
	21st to end	Night	14% 8% 20% 37% 17% 4	950
December	1st to 10th	Night	19% 6% 24% 37% 13% 1	950
	11th to 20th	Night	20% 6% 25% 35% 13% 2	950
	21st to end	Night	24% 6% 24% 34% 11% 1	981

Page generated at 2024-11-01 20:47:41. Version ac07

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