Layton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Layton clear sky chart from 2005-11-06 to 2025-02-25.

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	8% 8% 2 5% 3 3 3 3 5% 6% 52%	113006
	Night	9% 9% 3 6% 4 3 4 3 5% 7% 48%	114519
Transparency	Day	18% 44% 6% 12% 12% 8%	112771
	Night	21% 42% 7% 13% 10% 6%	114343
Seeing	Day	11% 8% 24% 34% 20% 3	15436
	Night	13% 4 21% 40% 20% 2	25686

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	12% 21% 4 7% 4 4 3 4 5% 5% 30%	4098
	11th to 20th	Day	9% 17% 5% 13% 6% 4 4 3 4 5% 29%	4100
	21st to end	Day	9% 14% 4 8% 4 3 3 3 4 6% 42%	4510
February	1st to 10th	Day	16% 15% 4 8% 5% 4 4 4 5% 6% 30%	1800
	11th to 20th	Day	13% 15% 4 9% 5% 3 4 3 5% 6% 32%	1825
	21st to end	Day	10% 16% 6% 9% 5% 4 3 4 5% 6% 30%	1611
March	1st to 10th	Day	8% 20% 5% 9% 4 4 4 3 5% 6% 32%	3343
	11th to 20th	Day	7% 9% 2 6% 5% 4 4 3 6% 7% 48%	3490
	21st to end	Day	14% 18% 5% 9% 5% 5% 4 4 5% 7% 24%	3825
April	1st to 10th	Day	13% 9% 3 6% 4 4 4 4 7% 6% 39%	2106
	11th to 20th	Day	12% 10% 3 7% 4 4 5% 4 5% 6% 41%	2414
	21st to end	Day	10% 8% 2 7% 4 4 3 3 6% 8% 45%	2470
May	1st to 10th	Day	9% 10% 3 6% 4 4 5% 4 6% 8% 41%	4110
	11th to 20th	Day	7% 4 1 4 3 3 3 3 5% 8% 58%	4071
	21st to end	Day	8% 5% 1 5% 3 3 4 3 6% 8% 54%	4477
June	1st to 10th	Day	4 4 1 4 4 4 4 3 7% 9% 57%	2579
	11th to 20th	Day	5% 4 2 4 3 3 3 3 6% 7% 60%	2660
	21st to end	Day	3 2 1 3 2 2 3 2 4 5% 73%	2683
July	1st to 10th	Day	2 2 1 2 2 2 2 2 3 4 78%	4208
	11th to 20th	Day	2 2 1 2 2 3 3 3 6% 7% 69%	4110
	21st to end	Day	3 2 1 3 2 3 3 3 5% 6% 70%	4454
August	1st to 10th	Day	4 3 1 3 3 3 3 3 4 6% 68%	4092
	11th to 20th	Day	2 2 1 4 3 3 4 4 5% 6% 67%	4028
	21st to end	Day	3 2 1 2 2 2 2 2 5% 5% 74%	4501
September	1st to 10th	Day	3 3 1 2 2 2 3 3 4 5% 72%	2142
	11th to 20th	Day	4 2 1 3 3 3 3 4 4 5% 67%	2090
	21st to end	Day	7% 2 1 3 3 2 3 3 4 5% 69%	2090
October	1st to 10th	Day	6% 3 1 4 3 2 3 2 3 5% 67%	3336
	11th to 20th	Day	9% 5% 1 4 3 3 3 3 4 7% 58%	3150
	21st to end	Day	7% 7% 2 6% 3 3 3 2 4 5% 57%	3388
November	1st to 10th	Day	12% 8% 3 6% 4 3 4 4 5% 7% 45%	1764
	11th to 20th	Day	15% 10% 2 5% 3 3 3 3 5% 8% 45%	1800
	21st to end	Day	11% 11% 2 5% 4 4 4 3 5% 5% 44%	1640
December	1st to 10th	Day	8% 7% 2 5% 3 3 2 2 4 11% 51%	2620
	11th to 20th	Day	11% 16% 4 7% 4 4 4 4 6% 8% 31%	3026
	21st to end	Day	16% 15% 4 8% 5% 4 5% 4 5% 6% 27%	4395
January	1st to 10th	Night	12% 17% 4 8% 4 3 3 3 5% 6% 34%	5867
	11th to 20th	Night	14% 16% 6% 8% 4 4 4 3 4 8% 29%	5880
	21st to end	Night	10% 14% 3 7% 3 3 3 3 4 5% 45%	6468
February	1st to 10th	Night	15% 15% 3 6% 4 4 4 4 6% 6% 32%	2600
	11th to 20th	Night	14% 13% 4 6% 4 3 3 3 4 6% 39%	2458
	21st to end	Night	9% 15% 5% 7% 6% 4 4 4 6% 6% 35%	1937
March	1st to 10th	Night	14% 14% 4 8% 6% 5% 4 4 5% 6% 31%	3530
	11th to 20th	Night	6% 9% 2 6% 4 4 4 4 5% 7% 49%	3490
	21st to end	Night	12% 17% 4 8% 4 4 3 3 5% 6% 33%	3828
April	1st to 10th	Night	13% 12% 3 5% 3 3 3 3 4 6% 45%	2073
	11th to 20th	Night	10% 10% 3 7% 4 5% 4 3 5% 4 46%	1710
	21st to end	Night	11% 8% 2 6% 4 3 4 3 4 7% 47%	1710
May	1st to 10th	Night	11% 12% 3 6% 5% 4 4 4 5% 7% 39%	2860
	11th to 20th	Night	8% 3 1 4 2 3 3 3 5% 6% 60%	2834
	21st to end	Night	10% 6% 2 6% 4 3 4 3 5% 7% 49%	3110
June	1st to 10th	Night	5% 5% 2 4 3 3 5% 4 6% 9% 54%	1591
	11th to 20th	Night	6% 3 1 3 3 3 3 3 5% 7% 63%	1520
	21st to end	Night	3 2 1 3 2 2 4 2 4 6% 70%	1471
July	1st to 10th	Night	2 2 1 2 2 2 3 3 4 5% 74%	2750
	11th to 20th	Night	2 3 2 5% 4 4 5% 4 6% 8% 58%	2860
	21st to end	Night	3 4 2 4 4 3 4 4 5% 6% 61%	3109
August	1st to 10th	Night	3 3 1 4 3 4 5% 3 6% 7% 60%	2847
	11th to 20th	Night	2 4 1 5% 3 5% 5% 4 5% 6% 60%	2811
	21st to end	Night	3 2 1 3 2 3 3 3 4 5% 70%	3164
September	1st to 10th	Night	4 3 1 5% 3 2 3 3 4 4 68%	2035
	11th to 20th	Night	6% 3 1 3 3 3 3 2 5% 6% 65%	2090
	21st to end	Night	7% 3 2 3 2 2 2 2 3 4 71%	2090
October	1st to 10th	Night	6% 3 1 3 3 2 3 2 4 5% 69%	3637
	11th to 20th	Night	10% 6% 2 4 2 3 3 3 4 6% 59%	3778
	21st to end	Night	8% 6% 2 5% 3 3 3 3 5% 7% 54%	4166
November	1st to 10th	Night	11% 9% 2 5% 4 3 3 3 5% 6% 49%	2535
	11th to 20th	Night	12% 8% 2 6% 3 3 3 3 5% 8% 46%	2600
	21st to end	Night	10% 10% 2 5% 4 4 4 3 5% 6% 46%	2735
December	1st to 10th	Night	8% 8% 2 6% 3 3 3 2 4 14% 48%	4570
	11th to 20th	Night	14% 12% 3 5% 4 3 4 3 5% 7% 39%	5181
	21st to end	Night	16% 13% 4 8% 4 4 4 3 5% 7% 32%	6624

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	42% 29% 13% 8% 6% 2	4099
	11th to 20th	Day	41% 29% 12% 13% 4 2	4100
	21st to end	Day	29% 32% 11% 16% 11%	4510
February	1st to 10th	Day	26% 63% 5% 2 4	1800
	11th to 20th	Day	23% 62% 5% 6% 4	1834
	21st to end	Day	21% 64% 4 7% 3 1	1611
March	1st to 10th	Day	31% 45% 4 13% 6%	3343
	11th to 20th	Day	16% 40% 7% 28% 8% 1	3490
	21st to end	Day	36% 47% 6% 8% 2 1	3825
April	1st to 10th	Day	15% 67% 4 9% 4 1	2106
	11th to 20th	Day	14% 67% 4 7% 8%	2417
	21st to end	Day	15% 65% 4 9% 6%	2470
May	1st to 10th	Day	23% 41% 8% 15% 9% 3	4110
	11th to 20th	Day	12% 40% 5% 22% 17% 3	4074
	21st to end	Day	13% 40% 6% 16% 22% 2	4477
June	1st to 10th	Day	5% 65% 3 10% 13% 5%	2579
	11th to 20th	Day	7% 64% 2 9% 12% 5%	2660
	21st to end	Day	6% 63% 2 4 13% 13%	2683
July	1st to 10th	Day	6% 35% 2 5% 7% 45%	4144
	11th to 20th	Day	8% 35% 3 6% 16% 32%	4041
	21st to end	Day	8% 35% 3 5% 21% 29%	4314
August	1st to 10th	Day	12% 36% 3 10% 21% 19%	4078
	11th to 20th	Day	12% 37% 3 10% 23% 15%	4067
	21st to end	Day	7% 37% 3 10% 21% 22%	4500
September	1st to 10th	Day	6% 59% 2 7% 17% 9%	2142
	11th to 20th	Day	7% 60% 3 8% 16% 6%	2090
	21st to end	Day	10% 60% 3 11% 12% 4	2090
October	1st to 10th	Day	10% 36% 2 6% 27% 19%	3336
	11th to 20th	Day	17% 37% 3 17% 19% 7%	3150
	21st to end	Day	18% 36% 7% 23% 14% 2	3388
November	1st to 10th	Day	16% 57% 7% 11% 8%	1764
	11th to 20th	Day	15% 57% 6% 16% 5%	1800
	21st to end	Day	20% 59% 8% 9% 5%	1640
December	1st to 10th	Day	15% 37% 13% 30% 5%	2620
	11th to 20th	Day	32% 32% 17% 17% 3	3024
	21st to end	Day	39% 29% 11% 14% 6%	4395
January	1st to 10th	Night	37% 30% 13% 11% 8%	5867
	11th to 20th	Night	40% 30% 9% 17% 3	5880
	21st to end	Night	28% 32% 11% 19% 10%	6468
February	1st to 10th	Night	25% 62% 5% 4 3 1	2600
	11th to 20th	Night	22% 60% 4 8% 6%	2459
	21st to end	Night	18% 63% 5% 10% 4	1937
March	1st to 10th	Night	31% 43% 7% 9% 9% 1	3530
	11th to 20th	Night	16% 42% 6% 24% 10% 1	3490
	21st to end	Night	32% 44% 5% 15% 3 1	3828
April	1st to 10th	Night	12% 65% 6% 11% 3 2	2073
	11th to 20th	Night	13% 66% 4 10% 8%	1710
	21st to end	Night	14% 66% 4 8% 7% 1	1710
May	1st to 10th	Night	27% 40% 7% 13% 11% 2	2860
	11th to 20th	Night	13% 40% 5% 22% 17% 3	2835
	21st to end	Night	18% 40% 6% 14% 21%	3110
June	1st to 10th	Night	7% 65% 4 6% 13% 5%	1591
	11th to 20th	Night	7% 64% 3 9% 11% 4	1520
	21st to end	Night	7% 62% 2 6% 9% 14%	1471
July	1st to 10th	Night	6% 35% 2 4 7% 46%	2705
	11th to 20th	Night	14% 35% 4 5% 17% 27%	2806
	21st to end	Night	15% 35% 3 5% 17% 25%	3011
August	1st to 10th	Night	16% 36% 4 7% 18% 20%	2838
	11th to 20th	Night	16% 38% 5% 9% 17% 16%	2838
	21st to end	Night	9% 36% 3 6% 15% 30%	3164
September	1st to 10th	Night	9% 59% 3 5% 14% 10%	2035
	11th to 20th	Night	10% 60% 2 6% 15% 7%	2090
	21st to end	Night	10% 60% 2 9% 12% 7%	2090
October	1st to 10th	Night	10% 36% 2 5% 25% 22%	3637
	11th to 20th	Night	18% 36% 2 15% 21% 8%	3778
	21st to end	Night	20% 36% 5% 23% 14% 2	4166
November	1st to 10th	Night	15% 56% 4 15% 9% 1	2535
	11th to 20th	Night	14% 56% 4 17% 8% 1	2600
	21st to end	Night	20% 57% 6% 11% 5%	2735
December	1st to 10th	Night	17% 36% 11% 30% 6%	4570
	11th to 20th	Night	28% 33% 19% 16% 4	5182
	21st to end	Night	37% 28% 14% 13% 7%	6624

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	22% 10% 28% 26% 11% 3	300
	11th to 20th	Day	20% 9% 23% 32% 14% 2	300
	21st to end	Day	18% 5% 30% 32% 14% 1	330
February	1st to 10th	Day	25% 10% 30% 26% 9% 1	300
	11th to 20th	Day	19% 12% 34% 26% 9% 1	370
	21st to end	Day	13% 12% 37% 29% 9% 1	399
March	1st to 10th	Day	16% 11% 33% 30% 9% 1	460
	11th to 20th	Day	13% 10% 28% 35% 14%	460
	21st to end	Day	20% 13% 31% 28% 8%	506
April	1st to 10th	Day	14% 15% 29% 26% 15% 1	460
	11th to 20th	Day	16% 18% 27% 27% 11% 1	452
	21st to end	Day	13% 14% 28% 25% 18% 2	460
May	1st to 10th	Day	10% 15% 31% 29% 14% 2	463
	11th to 20th	Day	9% 9% 27% 31% 20% 3	488
	21st to end	Day	9% 9% 22% 32% 23% 4	529
June	1st to 10th	Day	5% 7% 24% 37% 25% 3	599
	11th to 20th	Day	7% 8% 23% 41% 19% 2	680
	21st to end	Day	4 5% 24% 41% 22% 4	545
July	1st to 10th	Day	1 3 20% 44% 29% 2	486
	11th to 20th	Day	2 2 15% 46% 31% 3	484
	21st to end	Day	4 1 11% 49% 32% 3	531
August	1st to 10th	Day	5% 2 18% 44% 28% 3	487
	11th to 20th	Day	3 3 18% 39% 32% 3	477
	21st to end	Day	4 4 15% 37% 36% 3	539
September	1st to 10th	Day	4 4 17% 33% 34% 7%	490
	11th to 20th	Day	6% 5% 24% 34% 27% 5%	490
	21st to end	Day	6% 5% 20% 32% 32% 4	490
October	1st to 10th	Day	11% 5% 21% 32% 25% 5%	401
	11th to 20th	Day	9% 6% 26% 27% 24% 7%	300
	21st to end	Day	9% 10% 23% 38% 19% 1	330
November	1st to 10th	Day	19% 6% 24% 30% 15% 5%	300
	11th to 20th	Day	14% 8% 24% 34% 16% 3	300
	21st to end	Day	16% 5% 24% 31% 19% 5%	300
December	1st to 10th	Day	14% 7% 23% 35% 15% 7%	300
	11th to 20th	Day	19% 6% 27% 36% 10% 1	300
	21st to end	Day	25% 10% 23% 29% 12% 2	330
January	1st to 10th	Night	21% 4 24% 33% 18% 1	800
	11th to 20th	Night	19% 5% 20% 38% 16% 2	800
	21st to end	Night	20% 3 23% 38% 13% 3	880
February	1st to 10th	Night	22% 5% 25% 37% 11% 1	800
	11th to 20th	Night	18% 4 26% 37% 14% 1	784
	21st to end	Night	14% 7% 30% 37% 11%	646
March	1st to 10th	Night	19% 6% 24% 38% 12% 1	760
	11th to 20th	Night	13% 4 25% 42% 15% 1	760
	21st to end	Night	19% 6% 25% 38% 12% 1	836
April	1st to 10th	Night	18% 7% 24% 39% 11% 1	743
	11th to 20th	Night	13% 8% 30% 34% 14%	563
	21st to end	Night	13% 5% 22% 39% 20% 1	570
May	1st to 10th	Night	11% 6% 28% 37% 17% 1	570
	11th to 20th	Night	11% 3 22% 35% 27% 2	561
	21st to end	Night	12% 6% 17% 37% 27% 2	617
June	1st to 10th	Night	6% 6% 18% 40% 29% 1	570
	11th to 20th	Night	8% 5% 23% 42% 22% 1	570
	21st to end	Night	4 3 19% 44% 27% 3	397
July	1st to 10th	Night	5% 1 18% 43% 31% 2	484
	11th to 20th	Night	5% 2 15% 49% 29% 1	552
	21st to end	Night	4 2 9% 47% 38% 1	624
August	1st to 10th	Night	5% 1 13% 50% 30% 1	567
	11th to 20th	Night	3 1 16% 46% 33% 1	564
	21st to end	Night	4 3 15% 42% 34% 2	627
September	1st to 10th	Night	4 4 15% 43% 31% 3	705
	11th to 20th	Night	7% 3 17% 42% 28% 3	760
	21st to end	Night	7% 3 19% 36% 29% 6%	760
October	1st to 10th	Night	10% 4 18% 43% 23% 1	760
	11th to 20th	Night	13% 3 17% 39% 26% 2	760
	21st to end	Night	11% 3 24% 39% 21% 2	836
November	1st to 10th	Night	15% 4 19% 42% 18% 2	780
	11th to 20th	Night	13% 5% 26% 42% 13% 2	800
	21st to end	Night	15% 5% 24% 36% 18% 3	935
December	1st to 10th	Night	17% 4 24% 39% 15% 1	1000
	11th to 20th	Night	22% 6% 21% 38% 12% 1	1000
	21st to end	Night	26% 6% 24% 35% 9% 1	945

Page generated at 2025-02-22 04:51:37. Version ac07

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