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 2025-08-05.

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	6% 10% 3 6% 3 3 4 3 5% 6% 51%	129961
	Night	7% 10% 3 6% 4 3 3 3 5% 6% 49%	127061
Transparency	Day	35% 4 8% 21% 20% 13%	129680
	Night	37% 4 9% 21% 19% 10%	126856
Seeing	Day	12% 12% 30% 30% 13% 3	16334
	Night	13% 5% 21% 38% 19% 3	26106

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% 25% 5% 9% 4 3 4 3 5% 5% 30%	4098
	11th to 20th	Day	7% 19% 7% 12% 5% 4 3 2 3 4 32%	4100
	21st to end	Day	7% 16% 5% 8% 4 4 3 2 3 5% 42%	4510
February	1st to 10th	Day	15% 18% 6% 9% 4 3 3 4 4 6% 28%	1800
	11th to 20th	Day	11% 23% 5% 9% 4 4 4 3 4 4 30%	1800
	21st to end	Day	7% 18% 6% 12% 6% 4 3 3 4 4 31%	1650
March	1st to 10th	Day	7% 21% 6% 9% 4 3 3 2 4 4 36%	4814
	11th to 20th	Day	5% 17% 4 7% 4 4 4 3 5% 5% 42%	5000
	21st to end	Day	11% 20% 5% 10% 5% 5% 4 3 5% 5% 26%	5486
April	1st to 10th	Day	12% 12% 4 7% 5% 4 3 3 5% 6% 37%	2232
	11th to 20th	Day	10% 12% 4 8% 5% 4 5% 3 6% 6% 38%	2547
	21st to end	Day	9% 12% 3 6% 4 4 4 4 5% 8% 41%	2600
May	1st to 10th	Day	7% 11% 3 6% 4 4 4 3 5% 7% 47%	5880
	11th to 20th	Day	8% 7% 2 6% 4 4 5% 5% 6% 8% 45%	5841
	21st to end	Day	5% 5% 2 5% 4 4 4 4 7% 8% 53%	6532
June	1st to 10th	Day	5% 5% 2 5% 3 4 4 4 6% 8% 55%	2800
	11th to 20th	Day	6% 4 2 5% 3 3 4 4 6% 7% 57%	2888
	21st to end	Day	2 3 1 3 3 3 3 3 5% 6% 70%	3000
July	1st to 10th	Day	2 2 1 2 2 3 3 2 3 5% 77%	6258
	11th to 20th	Day	2 2 1 2 2 2 4 3 5% 6% 69%	5880
	21st to end	Day	3 2 1 2 2 2 3 2 4 6% 72%	6401
August	1st to 10th	Day	3 2 1 4 3 3 3 3 4 6% 68%	4145
	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	9% 12% 4 7% 4 4 4 3 4 5% 44%	1764
	11th to 20th	Day	14% 10% 2 5% 4 3 4 3 6% 8% 42%	1769
	21st to end	Day	8% 15% 4 6% 4 3 4 3 5% 7% 42%	1600
December	1st to 10th	Day	7% 10% 3 7% 3 3 3 2 3 5% 55%	2620
	11th to 20th	Day	11% 16% 5% 9% 4 4 4 3 6% 8% 30%	3026
	21st to end	Day	14% 16% 5% 8% 4 5% 4 4 6% 7% 26%	4205
January	1st to 10th	Night	7% 21% 6% 9% 4 3 3 3 4 6% 35%	5867
	11th to 20th	Night	11% 18% 6% 13% 4 3 3 2 3 5% 32%	5880
	21st to end	Night	8% 17% 4 7% 3 3 3 2 3 5% 45%	6468
February	1st to 10th	Night	13% 19% 6% 8% 4 4 4 3 4 5% 30%	2600
	11th to 20th	Night	10% 16% 4 8% 4 3 4 3 4 6% 37%	2484
	21st to end	Night	5% 18% 5% 10% 5% 4 3 3 4 7% 36%	1980
March	1st to 10th	Night	9% 19% 4 6% 3 4 4 4 4 5% 37%	5078
	11th to 20th	Night	5% 13% 3 6% 4 4 5% 4 6% 8% 42%	5000
	21st to end	Night	9% 15% 4 8% 5% 5% 4 3 5% 6% 36%	5489
April	1st to 10th	Night	11% 12% 4 6% 5% 4 4 4 5% 6% 41%	2167
	11th to 20th	Night	8% 12% 3 7% 5% 4 4 3 5% 7% 43%	1796
	21st to end	Night	9% 9% 3 6% 4 4 3 4 6% 7% 46%	1800
May	1st to 10th	Night	7% 11% 3 5% 3 3 3 2 4 7% 51%	4100
	11th to 20th	Night	8% 5% 2 5% 4 4 4 3 6% 6% 54%	4074
	21st to end	Night	7% 5% 2 6% 4 4 3 3 6% 7% 54%	4348
June	1st to 10th	Night	5% 3 1 4 4 3 5% 4 5% 9% 55%	1600
	11th to 20th	Night	5% 4 2 2 3 3 3 3 6% 7% 62%	1504
	21st to end	Night	2 3 1 3 2 3 4 2 5% 7% 69%	1400
July	1st to 10th	Night	2 2 1 4 3 3 3 3 4 5% 70%	3679
	11th to 20th	Night	2 3 1 3 3 3 4 4 6% 7% 64%	4100
	21st to end	Night	2 3 1 4 3 3 3 3 5% 7% 66%	4472
August	1st to 10th	Night	2 2 1 4 3 4 4 4 6% 8% 61%	2883
	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 5% 3 4 3 3 5% 6% 47%	2535
	11th to 20th	Night	11% 9% 3 6% 4 3 3 4 5% 6% 46%	2608
	21st to end	Night	9% 12% 3 5% 5% 4 4 4 5% 6% 43%	2800
December	1st to 10th	Night	7% 9% 3 7% 3 2 3 3 3 5% 55%	4570
	11th to 20th	Night	11% 14% 4 7% 5% 4 3 3 5% 6% 38%	5181
	21st to end	Night	13% 16% 6% 9% 5% 5% 4 4 5% 6% 28%	6815

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 13% 14% 10% 1	4099
	11th to 20th	Day	58% 4 13% 15% 7% 3	4100
	21st to end	Day	47% 4 12% 19% 17% 1	4510
February	1st to 10th	Day	59% 5% 12% 16% 7% 1	1800
	11th to 20th	Day	60% 3 11% 17% 8% 1	1809
	21st to end	Day	57% 3 12% 17% 9% 2	1650
March	1st to 10th	Day	53% 4 6% 24% 9% 4	4814
	11th to 20th	Day	44% 5% 8% 30% 13%	5000
	21st to end	Day	60% 3 13% 19% 4	5486
April	1st to 10th	Day	48% 4 12% 21% 12% 2	2232
	11th to 20th	Day	46% 4 8% 24% 17% 1	2550
	21st to end	Day	43% 3 10% 27% 17% 1	2600
May	1st to 10th	Day	37% 4 8% 29% 19% 3	5880
	11th to 20th	Day	35% 6% 5% 30% 18% 5%	5844
	21st to end	Day	28% 6% 5% 33% 26% 2	6533
June	1st to 10th	Day	27% 3 10% 27% 28% 4	2800
	11th to 20th	Day	26% 4 6% 19% 29% 16%	2888
	21st to end	Day	16% 3 3 15% 34% 29%	3000
July	1st to 10th	Day	13% 2 2 10% 19% 54%	6191
	11th to 20th	Day	15% 4 2 10% 33% 38%	5811
	21st to end	Day	14% 3 2 8% 34% 38%	6217
August	1st to 10th	Day	19% 3 3 17% 30% 29%	4131
	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	45% 4 11% 24% 15% 2	1764
	11th to 20th	Day	42% 4 16% 25% 13% 1	1769
	21st to end	Day	44% 4 14% 24% 13% 1	1600
December	1st to 10th	Day	34% 4 13% 35% 12% 2	2620
	11th to 20th	Day	54% 4 15% 22% 4	3024
	21st to end	Day	57% 6% 11% 16% 8%	4205
January	1st to 10th	Night	53% 4 10% 20% 13% 1	5867
	11th to 20th	Night	57% 5% 10% 21% 5% 2	5880
	21st to end	Night	44% 3 13% 19% 20% 1	6468
February	1st to 10th	Night	57% 5% 12% 18% 7% 1	2600
	11th to 20th	Night	49% 4 11% 21% 13% 1	2485
	21st to end	Night	49% 4 10% 23% 12% 3	1980
March	1st to 10th	Night	47% 5% 6% 22% 13% 6%	5078
	11th to 20th	Night	40% 5% 12% 27% 15% 1	5000
	21st to end	Night	49% 4 16% 22% 9% 1	5489
April	1st to 10th	Night	44% 4 13% 22% 12% 5%	2167
	11th to 20th	Night	41% 4 9% 24% 20% 1	1796
	21st to end	Night	37% 3 11% 29% 18% 2	1800
May	1st to 10th	Night	33% 4 10% 23% 27% 3	4097
	11th to 20th	Night	29% 5% 6% 29% 26% 4	4075
	21st to end	Night	28% 5% 6% 29% 29% 3	4348
June	1st to 10th	Night	25% 4 13% 25% 28% 5%	1600
	11th to 20th	Night	22% 4 8% 22% 29% 16%	1504
	21st to end	Night	18% 3 2 17% 31% 30%	1400
July	1st to 10th	Night	18% 3 2 9% 18% 51%	3638
	11th to 20th	Night	20% 4 1 8% 29% 39%	4046
	21st to end	Night	18% 4 3 8% 30% 38%	4344
August	1st to 10th	Night	21% 4 4 14% 27% 31%	2874
	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	38% 3 11% 26% 18% 4	2535
	11th to 20th	Night	39% 4 14% 28% 15% 1	2608
	21st to end	Night	42% 4 12% 27% 13% 2	2800
December	1st to 10th	Night	35% 3 12% 36% 12% 2	4570
	11th to 20th	Night	49% 5% 19% 21% 6%	5182
	21st to end	Night	58% 4 12% 17% 9%	6815

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% 7% 30% 27% 10% 1	300
	11th to 20th	Day	22% 10% 28% 29% 10% 1	300
	21st to end	Day	19% 8% 29% 31% 12% 2	330
February	1st to 10th	Day	28% 15% 30% 20% 6% 1	300
	11th to 20th	Day	21% 15% 36% 19% 7% 1	345
	21st to end	Day	18% 19% 35% 20% 7% 1	414
March	1st to 10th	Day	19% 18% 31% 24% 6% 1	500
	11th to 20th	Day	17% 19% 31% 28% 5%	500
	21st to end	Day	22% 19% 34% 19% 5% 1	550
April	1st to 10th	Day	19% 18% 31% 24% 7% 1	500
	11th to 20th	Day	21% 20% 33% 18% 7% 1	492
	21st to end	Day	16% 19% 30% 25% 8% 2	500
May	1st to 10th	Day	14% 19% 28% 28% 10% 1	503
	11th to 20th	Day	13% 17% 29% 28% 11% 2	528
	21st to end	Day	11% 14% 22% 30% 19% 4	617
June	1st to 10th	Day	6% 11% 27% 33% 18% 5%	730
	11th to 20th	Day	9% 12% 29% 34% 15% 2	730
	21st to end	Day	3 9% 30% 35% 18% 4	730
July	1st to 10th	Day	2 8% 37% 38% 13% 3	526
	11th to 20th	Day	4 6% 35% 36% 15% 4	524
	21st to end	Day	4 4 27% 43% 18% 3	575
August	1st to 10th	Day	6% 7% 34% 34% 16% 4	504
	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	19% 11% 26% 29% 11% 4	300
	11th to 20th	Day	17% 10% 29% 31% 10% 3	300
	21st to end	Day	17% 7% 28% 31% 13% 4	300
December	1st to 10th	Day	17% 9% 25% 29% 15% 5%	300
	11th to 20th	Day	23% 7% 27% 33% 10% 1	300
	21st to end	Day	21% 12% 31% 26% 8% 1	330
January	1st to 10th	Night	20% 5% 23% 33% 17% 3	800
	11th to 20th	Night	21% 5% 21% 34% 16% 3	800
	21st to end	Night	21% 4 21% 38% 14% 3	880
February	1st to 10th	Night	22% 8% 24% 35% 10% 2	800
	11th to 20th	Night	17% 5% 27% 34% 14% 2	784
	21st to end	Night	14% 9% 28% 35% 13% 2	660
March	1st to 10th	Night	18% 7% 25% 35% 12% 3	800
	11th to 20th	Night	12% 9% 25% 38% 16% 1	800
	21st to end	Night	16% 9% 25% 36% 13% 1	880
April	1st to 10th	Night	17% 7% 26% 35% 13% 2	767
	11th to 20th	Night	13% 10% 27% 34% 14% 1	593
	21st to end	Night	14% 6% 25% 35% 18% 2	600
May	1st to 10th	Night	13% 7% 23% 37% 18% 2	600
	11th to 20th	Night	10% 7% 19% 35% 26% 3	591
	21st to end	Night	11% 5% 18% 37% 25% 3	650
June	1st to 10th	Night	7% 6% 18% 39% 28% 2	600
	11th to 20th	Night	7% 6% 22% 42% 22% 1	504
	21st to end	Night	4 3 20% 42% 27% 5%	400
July	1st to 10th	Night	4 3 22% 35% 32% 4	409
	11th to 20th	Night	3 3 16% 47% 30% 1	582
	21st to end	Night	3 1 13% 46% 33% 4	657
August	1st to 10th	Night	4 2 12% 48% 32% 2	579
	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% 21% 38% 18% 2	780
	11th to 20th	Night	15% 5% 24% 37% 16% 4	808
	21st to end	Night	15% 8% 21% 36% 16% 4	1000
December	1st to 10th	Night	18% 6% 25% 37% 14% 1	1000
	11th to 20th	Night	19% 6% 26% 35% 12% 2	1000
	21st to end	Night	25% 6% 25% 33% 11% 1	1032

Page generated at 2025-08-01 23:32:27. Version ac07

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