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 2026-07-01.

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% 8% 2 5% 3 3 3 3 5% 6% 53%	146672
	Night	9% 9% 3 6% 4 3 4 3 5% 7% 49%	143210
Transparency	Day	20% 35% 6% 14% 15% 10%	141408
	Night	23% 35% 8% 14% 13% 8%	139481
Seeing	Day	11% 8% 25% 34% 20% 3	17304
	Night	13% 5% 22% 40% 19% 2	27427

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	14% 20% 5% 8% 4 4 3 3 5% 5% 30%	5318
	11th to 20th	Day	7% 13% 4 10% 5% 3 4 3 4 7% 40%	5340
	21st to end	Day	7% 12% 4 8% 3 3 3 3 4 6% 45%	5844
February	1st to 10th	Day	15% 15% 4 8% 4 4 4 4 5% 6% 32%	1890
	11th to 20th	Day	12% 15% 4 9% 5% 4 4 3 6% 7% 31%	1919
	21st to end	Day	10% 15% 6% 9% 5% 4 3 4 5% 6% 32%	1730
March	1st to 10th	Day	7% 20% 5% 9% 4 4 3 3 4 6% 35%	4920
	11th to 20th	Day	7% 13% 3 7% 4 4 4 3 5% 7% 43%	5110
	21st to end	Day	12% 17% 5% 9% 4 4 4 4 5% 6% 30%	5607
April	1st to 10th	Day	12% 9% 3 6% 4 4 4 4 7% 6% 40%	2328
	11th to 20th	Day	11% 10% 3 7% 4 4 5% 4 5% 7% 42%	2672
	21st to end	Day	10% 8% 2 7% 4 4 4 3 6% 8% 45%	2730
May	1st to 10th	Day	7% 6% 2 5% 3 4 4 4 5% 7% 54%	7626
	11th to 20th	Day	9% 8% 2 5% 3 3 3 3 5% 7% 52%	7596
	21st to end	Day	6% 4 2 5% 3 3 4 3 5% 8% 58%	8370
June	1st to 10th	Day	4 4 1 4 4 3 4 3 7% 8% 58%	2851
	11th to 20th	Day	5% 4 2 4 3 2 3 3 5% 7% 63%	2940
	21st to end	Day	3 2 2 3 2 2 3 2 4 5% 72%	2966
July	1st to 10th	Day	2 2 1 2 3 2 3 2 4 4 75%	6017
	11th to 20th	Day	2 3 1 2 2 3 3 3 5% 6% 71%	5880
	21st to end	Day	2 2 1 2 2 2 3 3 4 6% 73%	6401
August	1st to 10th	Day	3 3 1 3 2 2 3 2 4 5% 72%	5779
	11th to 20th	Day	2 2 1 3 2 3 3 3 4 5% 71%	5798
	21st to end	Day	4 3 1 4 3 4 4 3 6% 5% 64%	6435
September	1st to 10th	Day	3 3 1 2 2 2 3 3 4 5% 71%	2254
	11th to 20th	Day	4 3 1 3 3 3 3 3 4 6% 67%	2200
	21st to end	Day	7% 2 1 3 3 2 3 3 3 5% 69%	2200
October	1st to 10th	Day	7% 3 1 3 3 2 3 2 3 5% 67%	3441
	11th to 20th	Day	9% 5% 1 4 3 3 3 3 4 7% 58%	3250
	21st to end	Day	7% 7% 2 6% 3 3 3 2 4 5% 58%	3496
November	1st to 10th	Day	11% 8% 3 6% 4 3 3 3 5% 7% 46%	1854
	11th to 20th	Day	14% 10% 2 5% 3 3 3 3 5% 8% 44%	1890
	21st to end	Day	11% 11% 2 5% 4 4 4 3 4 6% 45%	1722
December	1st to 10th	Day	8% 7% 2 5% 3 3 3 2 4 11% 51%	2700
	11th to 20th	Day	11% 15% 4 7% 5% 4 4 4 6% 8% 32%	3106
	21st to end	Day	16% 15% 4 8% 5% 4 5% 4 5% 6% 27%	4492
January	1st to 10th	Night	14% 17% 4 8% 4 3 3 3 5% 6% 33%	7605
	11th to 20th	Night	10% 12% 5% 6% 3 3 3 3 3 9% 43%	7650
	21st to end	Night	7% 11% 3 7% 3 3 4 3 5% 6% 47%	8370
February	1st to 10th	Night	14% 14% 3 6% 4 5% 4 4 6% 6% 33%	2730
	11th to 20th	Night	14% 13% 4 7% 4 4 3 3 4 6% 38%	2584
	21st to end	Night	9% 15% 5% 7% 5% 4 4 4 5% 6% 37%	2076
March	1st to 10th	Night	13% 16% 3 6% 5% 4 4 4 4 8% 33%	5193
	11th to 20th	Night	8% 12% 3 7% 4 4 4 4 6% 8% 40%	5110
	21st to end	Night	12% 14% 3 7% 4 4 4 3 5% 6% 37%	5610
April	1st to 10th	Night	12% 11% 3 5% 3 3 3 3 4 6% 45%	2291
	11th to 20th	Night	10% 10% 2 6% 4 4 4 3 5% 4 47%	1892
	21st to end	Night	11% 8% 3 6% 4 4 4 3 4 7% 46%	1890
May	1st to 10th	Night	7% 8% 2 5% 4 4 4 3 6% 7% 51%	5321
	11th to 20th	Night	8% 5% 2 5% 3 3 3 3 5% 6% 57%	5296
	21st to end	Night	7% 5% 2 5% 4 4 5% 4 6% 8% 52%	5837
June	1st to 10th	Night	5% 5% 2 4 3 3 5% 4 6% 8% 55%	1759
	11th to 20th	Night	6% 3 1 3 3 2 3 3 5% 6% 64%	1680
	21st to end	Night	4 3 1 4 2 2 4 3 4 6% 68%	1627
July	1st to 10th	Night	2 3 1 4 3 3 3 3 4 5% 70%	3934
	11th to 20th	Night	2 4 2 5% 4 4 4 3 5% 7% 59%	4100
	21st to end	Night	3 3 1 4 4 4 4 4 5% 6% 63%	4472
August	1st to 10th	Night	2 2 1 4 3 3 4 3 5% 7% 65%	4033
	11th to 20th	Night	2 3 1 4 3 4 4 4 4 6% 62%	4051
	21st to end	Night	4 4 2 6% 4 4 4 4 4 5% 59%	4540
September	1st to 10th	Night	4 3 1 5% 3 2 3 3 5% 5% 67%	2142
	11th to 20th	Night	6% 3 1 4 3 3 3 3 5% 5% 64%	2200
	21st to end	Night	6% 3 2 3 2 2 2 2 3 5% 70%	2200
October	1st to 10th	Night	7% 3 1 3 3 2 3 2 4 5% 69%	3752
	11th to 20th	Night	10% 6% 2 4 2 3 3 3 4 5% 58%	3898
	21st to end	Night	8% 6% 2 5% 3 3 3 3 5% 7% 55%	4299
November	1st to 10th	Night	11% 9% 2 5% 4 3 3 3 5% 6% 49%	2665
	11th to 20th	Night	12% 8% 2 6% 4 3 3 3 5% 8% 45%	2730
	21st to end	Night	10% 10% 2 5% 4 5% 4 3 5% 6% 47%	2872
December	1st to 10th	Night	8% 8% 2 6% 3 3 3 2 4 13% 47%	4710
	11th to 20th	Night	14% 12% 3 5% 4 3 4 3 5% 7% 39%	5321
	21st to end	Night	16% 13% 4 8% 4 4 4 3 5% 7% 32%	6770

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	47% 23% 17% 8% 4 1	5321
	11th to 20th	Day	32% 22% 13% 23% 8% 2	5340
	21st to end	Day	29% 25% 14% 20% 11%	5844
February	1st to 10th	Day	26% 60% 6% 4 4	1890
	11th to 20th	Day	24% 59% 6% 6% 4	1928
	21st to end	Day	21% 59% 5% 9% 6% 1	1730
March	1st to 10th	Day	37% 31% 5% 18% 7% 3	4920
	11th to 20th	Day	27% 28% 7% 28% 9% 1	5110
	21st to end	Day	39% 33% 10% 13% 4 1	5607
April	1st to 10th	Day	16% 61% 5% 12% 5% 1	2328
	11th to 20th	Day	16% 61% 4 9% 10% 1	2675
	21st to end	Day	17% 59% 5% 11% 7%	2730
May	1st to 10th	Day	20% 24% 8% 20% 24% 4	7626
	11th to 20th	Day	25% 23% 5% 18% 24% 5%	7599
	21st to end	Day	17% 22% 5% 20% 32% 4	8371
June	1st to 10th	Day	6% 59% 2 10% 16% 6%	2851
	11th to 20th	Day	7% 58% 2 8% 15% 9%	2940
	21st to end	Day	7% 57% 2 5% 16% 14%	2966
July	1st to 10th	Day	9% 25% 2 5% 12% 46%	5954
	11th to 20th	Day	10% 25% 3 6% 21% 36%	5811
	21st to end	Day	8% 24% 3 4 21% 40%	6217
August	1st to 10th	Day	12% 35% 3 10% 21% 19%	4208
	11th to 20th	Day	12% 36% 3 10% 24% 16%	4197
	21st to end	Day	8% 36% 3 10% 21% 21%	4642
September	1st to 10th	Day	6% 57% 3 8% 18% 9%	2254
	11th to 20th	Day	8% 57% 3 8% 18% 6%	2200
	21st to end	Day	11% 57% 3 12% 13% 5%	2200
October	1st to 10th	Day	10% 35% 2 6% 27% 18%	3441
	11th to 20th	Day	17% 36% 3 18% 19% 7%	3250
	21st to end	Day	18% 35% 7% 24% 14% 2	3496
November	1st to 10th	Day	16% 54% 7% 13% 9%	1854
	11th to 20th	Day	18% 54% 7% 16% 5%	1890
	21st to end	Day	21% 56% 8% 10% 4	1722
December	1st to 10th	Day	16% 36% 14% 30% 5%	2700
	11th to 20th	Day	32% 31% 16% 17% 3	3104
	21st to end	Day	40% 28% 11% 14% 6%	4492
January	1st to 10th	Night	42% 24% 17% 11% 6%	7605
	11th to 20th	Night	31% 23% 13% 26% 7%	7650
	21st to end	Night	27% 25% 13% 22% 13%	8370
February	1st to 10th	Night	25% 59% 6% 5% 3 1	2730
	11th to 20th	Night	24% 58% 4 8% 6%	2585
	21st to end	Night	18% 59% 4 12% 5% 1	2076
March	1st to 10th	Night	36% 30% 5% 14% 12% 3	5193
	11th to 20th	Night	29% 30% 7% 21% 13% 1	5110
	21st to end	Night	33% 31% 11% 17% 7% 1	5610
April	1st to 10th	Night	14% 59% 6% 13% 6% 2	2291
	11th to 20th	Night	14% 60% 4 11% 10% 1	1892
	21st to end	Night	17% 60% 4 9% 9% 1	1890
May	1st to 10th	Night	22% 23% 8% 16% 25% 6%	5319
	11th to 20th	Night	21% 23% 5% 17% 25% 10%	5297
	21st to end	Night	21% 22% 6% 16% 32% 3	5838
June	1st to 10th	Night	8% 59% 3 6% 15% 8%	1759
	11th to 20th	Night	8% 58% 3 9% 13% 9%	1680
	21st to end	Night	9% 57% 2 6% 11% 15%	1627
July	1st to 10th	Night	13% 25% 3 4 8% 47%	3889
	11th to 20th	Night	17% 24% 3 4 15% 36%	4046
	21st to end	Night	16% 24% 3 4 17% 36%	4344
August	1st to 10th	Night	15% 35% 4 7% 18% 21%	2928
	11th to 20th	Night	16% 37% 4 9% 17% 17%	2928
	21st to end	Night	10% 35% 3 7% 15% 30%	3264
September	1st to 10th	Night	9% 56% 3 6% 15% 10%	2142
	11th to 20th	Night	12% 57% 2 6% 16% 7%	2200
	21st to end	Night	11% 57% 2 9% 13% 8%	2200
October	1st to 10th	Night	10% 35% 3 5% 26% 21%	3752
	11th to 20th	Night	19% 35% 2 15% 20% 8%	3898
	21st to end	Night	20% 35% 5% 23% 15% 2	4299
November	1st to 10th	Night	16% 53% 5% 16% 10% 1	2665
	11th to 20th	Night	16% 54% 4 17% 8% 1	2730
	21st to end	Night	21% 55% 7% 12% 5%	2872
December	1st to 10th	Night	18% 35% 12% 30% 5%	4710
	11th to 20th	Night	28% 33% 18% 17% 4	5322
	21st to end	Night	38% 28% 14% 13% 7%	6770

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% 10% 28% 25% 11% 3	330
	11th to 20th	Day	18% 8% 23% 34% 15% 2	330
	21st to end	Day	17% 5% 29% 35% 13% 1	363
February	1st to 10th	Day	23% 9% 30% 26% 10% 2	330
	11th to 20th	Day	20% 12% 33% 25% 8% 1	404
	21st to end	Day	13% 12% 37% 29% 9% 1	446
March	1st to 10th	Day	15% 12% 34% 29% 9% 1	540
	11th to 20th	Day	14% 12% 29% 33% 12%	540
	21st to end	Day	18% 13% 32% 29% 8%	594
April	1st to 10th	Day	14% 14% 29% 26% 16% 1	540
	11th to 20th	Day	15% 17% 29% 26% 11% 1	532
	21st to end	Day	13% 15% 29% 26% 16% 2	540
May	1st to 10th	Day	9% 13% 31% 30% 14% 2	543
	11th to 20th	Day	11% 12% 28% 29% 19% 2	568
	21st to end	Day	8% 10% 24% 31% 22% 4	617
June	1st to 10th	Day	4 7% 25% 36% 24% 4	691
	11th to 20th	Day	7% 8% 24% 41% 18% 2	780
	21st to end	Day	5% 7% 24% 40% 20% 4	631
July	1st to 10th	Day	1 3 22% 45% 27% 2	527
	11th to 20th	Day	3 2 15% 47% 29% 3	524
	21st to end	Day	4 1 14% 47% 30% 3	575
August	1st to 10th	Day	4 2 20% 44% 27% 3	527
	11th to 20th	Day	3 3 19% 40% 31% 3	517
	21st to end	Day	5% 4 16% 37% 34% 4	583
September	1st to 10th	Day	4 5% 17% 35% 34% 7%	530
	11th to 20th	Day	5% 6% 24% 33% 26% 5%	530
	21st to end	Day	6% 5% 20% 33% 32% 5%	530
October	1st to 10th	Day	11% 6% 22% 32% 24% 5%	436
	11th to 20th	Day	10% 6% 28% 27% 22% 7%	330
	21st to end	Day	9% 10% 22% 38% 20% 1	363
November	1st to 10th	Day	18% 7% 23% 30% 15% 6%	330
	11th to 20th	Day	15% 9% 23% 33% 17% 3	330
	21st to end	Day	16% 5% 24% 32% 19% 5%	330
December	1st to 10th	Day	15% 8% 25% 34% 13% 6%	330
	11th to 20th	Day	20% 6% 26% 35% 11% 2	330
	21st to end	Day	26% 11% 21% 28% 12% 2	363
January	1st to 10th	Night	21% 4 24% 33% 17% 1	840
	11th to 20th	Night	18% 5% 21% 38% 16% 2	840
	21st to end	Night	19% 3 24% 39% 12% 3	924
February	1st to 10th	Night	21% 5% 24% 38% 11% 1	840
	11th to 20th	Night	18% 5% 26% 37% 13% 1	824
	21st to end	Night	14% 6% 31% 37% 11%	692
March	1st to 10th	Night	20% 7% 24% 37% 12% 1	840
	11th to 20th	Night	13% 5% 27% 41% 13% 1	840
	21st to end	Night	18% 6% 26% 38% 11% 1	924
April	1st to 10th	Night	18% 7% 24% 39% 11%	821
	11th to 20th	Night	13% 8% 31% 34% 13%	623
	21st to end	Night	13% 6% 23% 39% 18% 1	630
May	1st to 10th	Night	10% 5% 27% 38% 18% 1	630
	11th to 20th	Night	12% 4 23% 35% 25% 2	621
	21st to end	Night	11% 6% 18% 38% 25% 2	683
June	1st to 10th	Night	6% 6% 20% 39% 27% 1	630
	11th to 20th	Night	8% 5% 23% 43% 20%	630
	21st to end	Night	5% 4 20% 43% 26% 2	439
July	1st to 10th	Night	5% 2 17% 45% 30% 2	510
	11th to 20th	Night	4 2 15% 50% 28% 1	582
	21st to end	Night	4 2 10% 48% 36% 1	657
August	1st to 10th	Night	5% 2 14% 50% 28% 1	597
	11th to 20th	Night	3 1 15% 47% 32% 1	594
	21st to end	Night	5% 3 15% 43% 33% 2	660
September	1st to 10th	Night	4 4 15% 43% 31% 3	742
	11th to 20th	Night	7% 3 17% 42% 28% 3	800
	21st to end	Night	7% 3 19% 36% 29% 6%	800
October	1st to 10th	Night	10% 4 19% 43% 23% 1	800
	11th to 20th	Night	13% 4 18% 38% 25% 2	800
	21st to end	Night	11% 3 24% 40% 21% 2	880
November	1st to 10th	Night	14% 4 19% 43% 17% 2	820
	11th to 20th	Night	13% 5% 26% 42% 12% 2	840
	21st to end	Night	14% 4 24% 37% 18% 3	982
December	1st to 10th	Night	17% 4 24% 38% 15% 1	1050
	11th to 20th	Night	21% 6% 21% 38% 12% 1	1050
	21st to end	Night	26% 7% 24% 34% 9% 1	992

Page generated at 2026-06-28 00:10:49. Version ac07

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