Fort Lancaster Scenic Overlook
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fort Lancaster Scenic Overlook clear sky chart from 2005-11-06 to 2025-09-19.

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% 4 2 4 3 3 3 3 5% 7% 60%	134611
	Night	7% 4 1 4 3 3 3 3 4 7% 62%	131809
Transparency	Day	25% 4 8% 21% 24% 18%	129713
	Night	23% 4 9% 22% 24% 18%	127711
Seeing	Day	9% 7% 27% 35% 18% 3	16006
	Night	9% 7% 33% 39% 12% 1	25928

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	6% 5% 2 5% 3 2 3 2 4 5% 63%	4123
	11th to 20th	Day	5% 3 1 3 2 2 2 2 3 5% 71%	4540
	21st to end	Day	11% 6% 2 5% 3 3 3 3 3 5% 57%	4994
February	1st to 10th	Day	6% 7% 2 4 3 3 3 2 4 7% 60%	2000
	11th to 20th	Day	8% 5% 2 5% 3 3 3 3 4 5% 58%	1949
	21st to end	Day	8% 5% 1 3 3 3 4 2 5% 5% 60%	1650
March	1st to 10th	Day	5% 5% 2 5% 3 3 3 3 5% 6% 61%	4500
	11th to 20th	Day	12% 5% 2 4 2 3 2 2 4 6% 59%	4820
	21st to end	Day	4 5% 2 5% 4 4 3 3 4 8% 58%	5619
April	1st to 10th	Day	7% 4 2 3 3 2 3 3 4 6% 63%	2400
	11th to 20th	Day	10% 5% 2 5% 3 2 3 3 4 6% 59%	2371
	21st to end	Day	7% 5% 1 4 3 3 3 3 4 6% 60%	2400
May	1st to 10th	Day	9% 5% 2 5% 3 3 4 3 5% 5% 56%	5576
	11th to 20th	Day	8% 4 2 4 3 3 3 3 5% 6% 58%	5862
	21st to end	Day	9% 5% 2 5% 3 3 3 4 6% 9% 52%	6446
June	1st to 10th	Day	4 3 1 2 3 4 4 3 7% 9% 61%	2600
	11th to 20th	Day	5% 3 1 4 3 3 4 4 5% 8% 60%	2600
	21st to end	Day	6% 4 2 4 4 3 4 3 6% 8% 57%	2600
July	1st to 10th	Day	9% 4 2 5% 4 3 4 4 6% 9% 50%	5899
	11th to 20th	Day	3 3 1 4 3 3 3 4 5% 9% 61%	5855
	21st to end	Day	4 2 1 4 3 3 4 3 5% 7% 63%	5922
August	1st to 10th	Day	1 1 1 1 2 3 2 4 7% 78%	5348
	11th to 20th	Day	3 2 1 2 2 3 4 4 5% 10% 65%	5366
	21st to end	Day	4 3 1 5% 4 4 4 4 7% 10% 54%	5984
September	1st to 10th	Day	10% 5% 2 6% 3 5% 5% 4 6% 7% 47%	2339
	11th to 20th	Day	9% 5% 2 6% 4 5% 5% 5% 6% 7% 46%	2178
	21st to end	Day	8% 4 1 5% 3 4 4 3 5% 6% 55%	2090
October	1st to 10th	Day	4 2 1 3 2 2 2 2 3 5% 74%	3480
	11th to 20th	Day	12% 5% 1 4 2 3 2 2 3 4 62%	3458
	21st to end	Day	7% 3 1 2 2 2 2 1 3 4 72%	3460
November	1st to 10th	Day	10% 4 2 4 3 2 3 2 3 6% 61%	1763
	11th to 20th	Day	7% 4 2 4 3 3 3 3 5% 5% 62%	1800
	21st to end	Day	8% 5% 2 6% 3 2 3 3 5% 6% 56%	1800
December	1st to 10th	Day	15% 9% 3 7% 3 3 3 2 3 4 49%	2940
	11th to 20th	Day	7% 5% 2 5% 3 4 4 3 5% 6% 57%	3391
	21st to end	Day	7% 4 1 3 2 2 2 2 2 4 71%	4488
January	1st to 10th	Night	5% 5% 2 4 2 3 3 2 4 6% 64%	5870
	11th to 20th	Night	4 5% 1 2 2 2 2 2 4 5% 72%	5440
	21st to end	Night	12% 7% 1 4 3 2 3 2 3 6% 56%	5984
February	1st to 10th	Night	7% 6% 2 4 2 3 3 2 4 6% 62%	2400
	11th to 20th	Night	11% 6% 2 5% 4 3 2 3 4 5% 56%	2338
	21st to end	Night	8% 4 1 3 3 3 3 3 5% 7% 59%	1980
March	1st to 10th	Night	4 4 1 4 3 3 3 3 4 7% 64%	5374
	11th to 20th	Night	10% 6% 1 3 3 2 2 2 3 6% 61%	5146
	21st to end	Night	4 4 2 4 3 3 3 3 5% 7% 63%	5302
April	1st to 10th	Night	7% 5% 1 3 3 3 4 4 5% 7% 60%	2000
	11th to 20th	Night	9% 5% 1 3 3 3 3 3 5% 6% 59%	1977
	21st to end	Night	8% 6% 1 3 3 2 2 3 4 5% 62%	2000
May	1st to 10th	Night	13% 6% 2 5% 3 3 3 3 4 6% 54%	4402
	11th to 20th	Night	6% 4 1 3 3 3 4 4 4 7% 61%	4053
	21st to end	Night	8% 4 1 4 3 3 4 4 7% 8% 54%	4451
June	1st to 10th	Night	3 1 1 3 3 3 4 3 6% 9% 63%	1800
	11th to 20th	Night	2 2 1 3 3 3 4 4 6% 11% 61%	1800
	21st to end	Night	4 3 1 4 3 3 3 3 7% 8% 62%	1800
July	1st to 10th	Night	7% 4 2 5% 3 4 3 3 5% 11% 55%	4080
	11th to 20th	Night	2 1 1 2 2 2 2 3 5% 9% 70%	4119
	21st to end	Night	3 2 1 3 3 3 3 4 6% 8% 64%	4951
August	1st to 10th	Night	1 1 1 1 2 2 2 5% 9% 75%	4464
	11th to 20th	Night	2 1 1 2 2 2 3 4 6% 12% 65%	4483
	21st to end	Night	4 3 1 5% 3 4 4 4 6% 11% 55%	4993
September	1st to 10th	Night	8% 5% 1 4 4 4 3 3 5% 8% 53%	2060
	11th to 20th	Night	6% 4 2 5% 4 4 5% 3 7% 9% 51%	2178
	21st to end	Night	8% 3 2 3 3 3 3 3 7% 8% 57%	2090
October	1st to 10th	Night	3 2 1 2 2 2 2 2 3 5% 77%	3480
	11th to 20th	Night	11% 4 1 4 2 2 2 2 3 3 66%	3460
	21st to end	Night	6% 2 1 2 1 2 2 2 3 4 75%	4043
November	1st to 10th	Night	9% 5% 1 3 3 3 3 2 3 5% 63%	2535
	11th to 20th	Night	5% 4 1 4 3 3 3 2 4 6% 64%	2600
	21st to end	Night	8% 6% 2 4 2 3 3 3 4 6% 59%	2600
December	1st to 10th	Night	18% 8% 2 4 2 2 3 2 4 5% 49%	4250
	11th to 20th	Night	7% 5% 2 5% 3 3 3 3 4 5% 61%	4816
	21st to end	Night	6% 6% 1 3 2 2 2 2 3 5% 66%	6490

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	24% 3 4 20% 27% 23%	4124
	11th to 20th	Day	18% 2 5% 22% 30% 22%	4540
	21st to end	Day	31% 3 5% 16% 27% 19%	4994
February	1st to 10th	Day	27% 3 5% 15% 24% 27%	2000
	11th to 20th	Day	29% 4 5% 21% 22% 19%	1959
	21st to end	Day	26% 4 3 12% 30% 25%	1650
March	1st to 10th	Day	26% 3 4 12% 22% 34%	4500
	11th to 20th	Day	29% 3 4 9% 17% 37%	4820
	21st to end	Day	26% 4 5% 14% 24% 27%	5619
April	1st to 10th	Day	24% 3 6% 18% 22% 26%	2400
	11th to 20th	Day	28% 4 5% 17% 22% 23%	2374
	21st to end	Day	27% 4 6% 20% 24% 19%	2400
May	1st to 10th	Day	30% 5% 6% 14% 20% 26%	5576
	11th to 20th	Day	27% 4 6% 13% 28% 21%	5866
	21st to end	Day	29% 6% 9% 23% 16% 16%	6447
June	1st to 10th	Day	19% 6% 11% 33% 24% 7%	2600
	11th to 20th	Day	22% 5% 11% 22% 28% 12%	2600
	21st to end	Day	25% 7% 12% 25% 23% 8%	2600
July	1st to 10th	Day	31% 6% 14% 33% 15% 1	5836
	11th to 20th	Day	21% 5% 18% 35% 19% 3	5786
	21st to end	Day	20% 5% 15% 29% 25% 5%	5752
August	1st to 10th	Day	10% 4 11% 34% 35% 5%	3892
	11th to 20th	Day	17% 5% 14% 39% 24% 2	3882
	21st to end	Day	26% 7% 16% 24% 22% 4	4311
September	1st to 10th	Day	35% 6% 10% 20% 19% 9%	2339
	11th to 20th	Day	36% 7% 10% 21% 20% 6%	2178
	21st to end	Day	28% 6% 11% 18% 22% 14%	2090
October	1st to 10th	Day	15% 3 5% 15% 22% 39%	3480
	11th to 20th	Day	29% 3 6% 14% 17% 31%	3458
	21st to end	Day	19% 2 3 19% 41% 16%	3460
November	1st to 10th	Day	27% 4 7% 20% 24% 18%	1763
	11th to 20th	Day	25% 3 9% 18% 23% 22%	1800
	21st to end	Day	30% 3 6% 16% 27% 18%	1800
December	1st to 10th	Day	42% 3 5% 15% 22% 15%	2940
	11th to 20th	Day	29% 3 6% 19% 26% 17%	3389
	21st to end	Day	20% 2 2 17% 34% 24%	4488
January	1st to 10th	Night	22% 4 4 18% 31% 20%	5870
	11th to 20th	Night	18% 2 3 20% 28% 28%	5440
	21st to end	Night	32% 3 4 17% 25% 19%	5984
February	1st to 10th	Night	25% 3 5% 15% 26% 26%	2400
	11th to 20th	Night	32% 3 5% 17% 22% 20%	2338
	21st to end	Night	25% 3 5% 13% 27% 26%	1980
March	1st to 10th	Night	20% 4 5% 17% 22% 32%	5374
	11th to 20th	Night	27% 4 5% 10% 18% 37%	5146
	21st to end	Night	22% 5% 9% 15% 22% 27%	5302
April	1st to 10th	Night	23% 6% 8% 19% 19% 25%	2000
	11th to 20th	Night	26% 5% 7% 20% 19% 22%	1977
	21st to end	Night	25% 6% 9% 23% 21% 17%	2000
May	1st to 10th	Night	32% 5% 9% 19% 17% 19%	4399
	11th to 20th	Night	22% 4 11% 17% 26% 20%	4054
	21st to end	Night	26% 8% 12% 22% 18% 13%	4452
June	1st to 10th	Night	16% 7% 15% 34% 23% 4	1800
	11th to 20th	Night	17% 7% 14% 27% 27% 9%	1800
	21st to end	Night	20% 6% 14% 28% 24% 9%	1800
July	1st to 10th	Night	27% 5% 17% 37% 13% 1	4035
	11th to 20th	Night	13% 5% 16% 42% 21% 4	4065
	21st to end	Night	18% 6% 17% 31% 23% 5%	4808
August	1st to 10th	Night	10% 4 11% 32% 38% 5%	3244
	11th to 20th	Night	13% 5% 18% 43% 18% 3	3243
	21st to end	Night	24% 7% 17% 26% 22% 4	3597
September	1st to 10th	Night	29% 6% 13% 22% 20% 10%	2060
	11th to 20th	Night	29% 8% 16% 20% 21% 6%	2178
	21st to end	Night	24% 5% 12% 24% 19% 16%	2090
October	1st to 10th	Night	12% 3 8% 15% 22% 40%	3480
	11th to 20th	Night	26% 3 6% 13% 22% 31%	3460
	21st to end	Night	16% 2 5% 26% 34% 16%	4043
November	1st to 10th	Night	26% 4 6% 20% 26% 18%	2535
	11th to 20th	Night	23% 3 8% 21% 23% 22%	2600
	21st to end	Night	27% 4 7% 17% 24% 21%	2600
December	1st to 10th	Night	39% 3 6% 18% 18% 17%	4250
	11th to 20th	Night	27% 3 6% 18% 28% 18%	4817
	21st to end	Night	23% 3 4 19% 30% 21%	6490

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	9% 14% 36% 33% 7% 1	300
	11th to 20th	Day	14% 10% 32% 34% 9% 1	300
	21st to end	Day	14% 9% 40% 27% 8% 1	330
February	1st to 10th	Day	17% 9% 31% 28% 11% 3	300
	11th to 20th	Day	15% 11% 41% 26% 5% 1	300
	21st to end	Day	16% 11% 43% 25% 5%	249
March	1st to 10th	Day	13% 14% 46% 22% 5%	300
	11th to 20th	Day	19% 10% 40% 25% 6%	300
	21st to end	Day	9% 16% 46% 24% 4 1	395
April	1st to 10th	Day	9% 17% 45% 25% 4	500
	11th to 20th	Day	12% 21% 41% 24% 3	492
	21st to end	Day	8% 13% 49% 26% 4 1	500
May	1st to 10th	Day	7% 12% 42% 32% 5%	561
	11th to 20th	Day	12% 10% 36% 32% 9% 1	725
	21st to end	Day	13% 9% 38% 32% 7% 1	789
June	1st to 10th	Day	6% 4 25% 50% 14% 2	730
	11th to 20th	Day	7% 2 30% 45% 16% 1	730
	21st to end	Day	5% 3 17% 48% 23% 3	730
July	1st to 10th	Day	10% 1 7% 42% 32% 6%	721
	11th to 20th	Day	4 1 8% 45% 37% 5%	699
	21st to end	Day	1 7% 49% 36% 6%	575
August	1st to 10th	Day	2 1 7% 42% 43% 5%	527
	11th to 20th	Day	7% 1 9% 38% 35% 10%	517
	21st to end	Day	4 1 6% 39% 41% 8%	583
September	1st to 10th	Day	10% 2 8% 40% 33% 8%	469
	11th to 20th	Day	6% 1 8% 40% 37% 9%	324
	21st to end	Day	9% 2 12% 34% 32% 11%	300
October	1st to 10th	Day	5% 3 19% 42% 25% 5%	300
	11th to 20th	Day	13% 5% 22% 38% 22% 1	300
	21st to end	Day	13% 8% 30% 28% 18% 3	330
November	1st to 10th	Day	17% 8% 30% 30% 14% 2	300
	11th to 20th	Day	15% 10% 27% 25% 17% 6%	300
	21st to end	Day	13% 14% 36% 25% 10% 2	300
December	1st to 10th	Day	14% 9% 28% 34% 13% 2	300
	11th to 20th	Day	9% 13% 38% 25% 13% 2	300
	21st to end	Day	12% 9% 37% 32% 9%	330
January	1st to 10th	Night	9% 6% 36% 40% 8%	995
	11th to 20th	Night	14% 8% 31% 39% 8%	800
	21st to end	Night	14% 8% 37% 35% 6%	880
February	1st to 10th	Night	11% 9% 39% 34% 8%	800
	11th to 20th	Night	14% 11% 42% 27% 6%	784
	21st to end	Night	11% 13% 48% 27% 1	660
March	1st to 10th	Night	13% 13% 44% 27% 3	800
	11th to 20th	Night	11% 14% 46% 26% 4	675
	21st to end	Night	8% 16% 50% 24% 2	660
April	1st to 10th	Night	9% 11% 56% 22% 3	600
	11th to 20th	Night	11% 14% 53% 20% 2	593
	21st to end	Night	10% 14% 51% 22% 3	600
May	1st to 10th	Night	9% 9% 53% 26% 3	600
	11th to 20th	Night	8% 10% 45% 31% 5%	591
	21st to end	Night	8% 7% 53% 27% 6%	650
June	1st to 10th	Night	3 6% 37% 49% 5%	600
	11th to 20th	Night	3 3 48% 40% 6%	600
	21st to end	Night	5% 3 31% 46% 15% 1	600
July	1st to 10th	Night	9% 2 15% 52% 21% 2	585
	11th to 20th	Night	3 1 15% 59% 22% 1	582
	21st to end	Night	2 2 11% 64% 22%	657
August	1st to 10th	Night	2 10% 59% 28% 1	597
	11th to 20th	Night	5% 1 9% 55% 28% 3	594
	21st to end	Night	4 2 8% 50% 34% 2	660
September	1st to 10th	Night	9% 2 9% 48% 31% 2	600
	11th to 20th	Night	8% 1 12% 51% 27% 1	594
	21st to end	Night	9% 1 16% 48% 24% 2	570
October	1st to 10th	Night	5% 2 26% 49% 18%	570
	11th to 20th	Night	13% 6% 23% 49% 8%	570
	21st to end	Night	11% 7% 28% 37% 16% 1	786
November	1st to 10th	Night	13% 6% 28% 40% 13% 1	975
	11th to 20th	Night	8% 6% 31% 40% 14% 1	1000
	21st to end	Night	10% 8% 35% 36% 11% 1	1000
December	1st to 10th	Night	13% 7% 27% 42% 10% 1	1000
	11th to 20th	Night	13% 8% 35% 36% 8%	1000
	21st to end	Night	10% 6% 35% 39% 9%	1100

Page generated at 2025-09-16 00:49:14. Version ac07

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