Enterprise
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Enterprise clear sky chart from 2005-11-06 to 2026-01-17.

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	10% 5% 2 6% 5% 5% 5% 4 6% 9% 42%	127025
	Night	11% 6% 2 6% 4 4 4 4 6% 8% 44%	124661
Transparency	Day	36% 8% 13% 18% 17% 8%	130894
	Night	36% 7% 12% 17% 19% 9%	128862
Seeing	Day	12% 8% 20% 25% 22% 13%	16295
	Night	12% 6% 22% 31% 23% 5%	26291

By Month

Percentage Cloud Cover SE (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% 5% 2 5% 3 4 3 3 5% 6% 51%	4146
	11th to 20th	Day	13% 5% 2 4 3 3 4 3 4 7% 52%	4369
	21st to end	Day	19% 6% 2 6% 4 4 3 3 4 6% 41%	4972
February	1st to 10th	Day	15% 7% 3 7% 5% 5% 3 3 4 7% 41%	2000
	11th to 20th	Day	17% 7% 3 5% 4 3 3 4 5% 7% 43%	1948
	21st to end	Day	16% 7% 2 6% 4 3 4 3 6% 6% 42%	1650
March	1st to 10th	Day	16% 8% 3 6% 3 4 4 4 6% 6% 40%	4480
	11th to 20th	Day	8% 4 2 5% 4 4 4 4 5% 7% 53%	4928
	21st to end	Day	14% 6% 2 6% 4 4 5% 3 6% 6% 45%	5465
April	1st to 10th	Day	12% 7% 2 5% 4 4 4 4 5% 7% 47%	2390
	11th to 20th	Day	11% 5% 2 7% 4 4 4 3 5% 6% 48%	2374
	21st to end	Day	6% 5% 2 5% 4 5% 4 3 5% 7% 53%	2400
May	1st to 10th	Day	12% 7% 3 7% 5% 5% 5% 4 6% 8% 39%	5771
	11th to 20th	Day	12% 6% 2 6% 4 5% 5% 5% 7% 9% 40%	5861
	21st to end	Day	6% 4 2 6% 5% 5% 5% 5% 8% 10% 45%	6433
June	1st to 10th	Day	8% 7% 2 7% 6% 5% 6% 6% 9% 11% 32%	2600
	11th to 20th	Day	5% 5% 3 8% 6% 6% 7% 5% 8% 12% 37%	2600
	21st to end	Day	6% 5% 3 9% 7% 7% 7% 5% 8% 11% 33%	2600
July	1st to 10th	Day	6% 6% 2 9% 7% 7% 8% 7% 10% 13% 24%	5900
	11th to 20th	Day	5% 4 2 7% 6% 7% 7% 5% 8% 13% 36%	5900
	21st to end	Day	5% 5% 2 8% 7% 7% 8% 7% 10% 15% 25%	6210
August	1st to 10th	Day	6% 5% 2 6% 5% 6% 6% 5% 9% 13% 36%	3905
	11th to 20th	Day	7% 4 2 6% 5% 4 6% 4 6% 10% 46%	3849
	21st to end	Day	6% 6% 2 7% 5% 6% 7% 6% 9% 12% 34%	4312
September	1st to 10th	Day	10% 6% 2 7% 5% 6% 7% 5% 8% 9% 35%	2273
	11th to 20th	Day	12% 6% 2 6% 5% 5% 5% 4 5% 7% 42%	2200
	21st to end	Day	10% 4 2 6% 5% 4 4 4 7% 7% 47%	2200
October	1st to 10th	Day	9% 6% 2 6% 3 3 3 3 6% 7% 51%	2200
	11th to 20th	Day	10% 4 1 3 3 3 3 3 5% 6% 60%	2200
	21st to end	Day	10% 4 2 5% 3 3 3 3 4 6% 57%	2209
November	1st to 10th	Day	9% 6% 2 4 3 3 3 3 4 6% 57%	1852
	11th to 20th	Day	10% 6% 2 4 4 2 4 3 4 6% 56%	1890
	21st to end	Day	12% 6% 2 6% 4 4 3 3 5% 7% 48%	1890
December	1st to 10th	Day	18% 5% 2 4 3 3 3 3 4 6% 50%	3020
	11th to 20th	Day	12% 7% 2 5% 3 3 3 3 4 6% 49%	3463
	21st to end	Day	18% 7% 2 6% 3 3 4 3 4 6% 45%	4565
January	1st to 10th	Night	14% 5% 2 5% 3 4 4 3 4 5% 49%	6019
	11th to 20th	Night	14% 8% 2 7% 4 4 4 3 5% 6% 44%	5719
	21st to end	Night	17% 8% 2 5% 4 4 4 3 5% 8% 39%	5984
February	1st to 10th	Night	14% 8% 2 5% 5% 3 4 4 6% 7% 42%	2400
	11th to 20th	Night	18% 8% 3 5% 3 3 3 3 4 4 46%	2338
	21st to end	Night	14% 7% 2 6% 5% 4 4 3 5% 5% 44%	1980
March	1st to 10th	Night	20% 10% 3 7% 4 3 3 3 5% 6% 36%	5373
	11th to 20th	Night	11% 6% 2 6% 3 4 4 4 5% 7% 49%	5031
	21st to end	Night	11% 7% 2 6% 4 4 4 3 4 6% 49%	5467
April	1st to 10th	Night	11% 6% 2 5% 4 4 3 4 7% 7% 47%	2025
	11th to 20th	Night	10% 6% 3 6% 4 4 3 4 6% 6% 49%	1975
	21st to end	Night	6% 5% 2 5% 4 3 4 3 6% 7% 56%	2000
May	1st to 10th	Night	10% 6% 3 7% 4 4 4 4 6% 9% 43%	4109
	11th to 20th	Night	13% 7% 3 6% 4 4 4 4 6% 8% 41%	4032
	21st to end	Night	5% 5% 2 5% 5% 4 5% 5% 8% 14% 42%	4421
June	1st to 10th	Night	8% 6% 3 8% 5% 5% 6% 5% 9% 11% 35%	1800
	11th to 20th	Night	4 5% 2 4 6% 5% 6% 5% 8% 12% 44%	1800
	21st to end	Night	5% 5% 2 8% 5% 5% 6% 5% 8% 12% 39%	1800
July	1st to 10th	Night	7% 6% 3 9% 7% 7% 8% 7% 11% 13% 23%	4058
	11th to 20th	Night	3 4 2 7% 5% 6% 7% 7% 10% 15% 33%	4057
	21st to end	Night	4 6% 3 8% 6% 7% 8% 6% 10% 13% 28%	4622
August	1st to 10th	Night	6% 4 3 7% 6% 7% 7% 5% 9% 13% 35%	3244
	11th to 20th	Night	5% 3 2 6% 5% 4 5% 5% 8% 11% 45%	3200
	21st to end	Night	6% 6% 2 7% 5% 6% 6% 5% 9% 11% 35%	3586
September	1st to 10th	Night	10% 7% 3 7% 5% 6% 6% 6% 7% 9% 35%	2105
	11th to 20th	Night	13% 6% 2 5% 4 4 5% 4 7% 8% 41%	2200
	21st to end	Night	10% 5% 3 6% 4 5% 3 3 4 7% 49%	2200
October	1st to 10th	Night	8% 5% 2 5% 4 3 4 3 6% 7% 53%	2200
	11th to 20th	Night	8% 4 1 3 3 3 3 3 5% 6% 61%	2200
	21st to end	Night	9% 6% 2 5% 3 3 3 3 5% 6% 55%	2625
November	1st to 10th	Night	8% 4 2 5% 3 3 4 4 4 6% 57%	2666
	11th to 20th	Night	11% 5% 2 4 3 3 3 3 4 6% 55%	2730
	21st to end	Night	12% 5% 2 5% 3 4 4 3 6% 6% 50%	2730
December	1st to 10th	Night	14% 6% 2 4 3 2 3 3 5% 6% 53%	4380
	11th to 20th	Night	14% 5% 2 5% 3 3 3 3 4 5% 53%	4952
	21st to end	Night	17% 7% 3 6% 4 3 3 2 4 5% 45%	6633

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	33% 4 6% 16% 33% 7%	4147
	11th to 20th	Day	33% 4 4 14% 32% 12%	4369
	21st to end	Day	43% 5% 8% 15% 16% 13%	4972
February	1st to 10th	Day	43% 5% 7% 15% 20% 9%	2000
	11th to 20th	Day	41% 5% 6% 14% 23% 11%	1958
	21st to end	Day	42% 6% 8% 17% 17% 11%	1650
March	1st to 10th	Day	42% 6% 8% 16% 17% 10%	4480
	11th to 20th	Day	29% 6% 8% 14% 21% 22%	4928
	21st to end	Day	38% 6% 9% 18% 17% 11%	5465
April	1st to 10th	Day	37% 7% 9% 18% 16% 13%	2390
	11th to 20th	Day	36% 5% 8% 18% 22% 12%	2374
	21st to end	Day	29% 6% 11% 23% 23% 8%	2400
May	1st to 10th	Day	40% 8% 10% 22% 16% 3	5807
	11th to 20th	Day	37% 9% 16% 25% 11% 1	5865
	21st to end	Day	30% 9% 16% 25% 18% 1	6447
June	1st to 10th	Day	40% 12% 16% 20% 10% 2	2600
	11th to 20th	Day	36% 12% 19% 21% 11% 2	2600
	21st to end	Day	40% 13% 19% 16% 10% 2	2600
July	1st to 10th	Day	43% 17% 25% 12% 3	5835
	11th to 20th	Day	35% 15% 32% 16% 2	5831
	21st to end	Day	41% 17% 25% 14% 2	6031
August	1st to 10th	Day	34% 11% 19% 23% 11% 1	3893
	11th to 20th	Day	31% 9% 15% 26% 17% 2	3885
	21st to end	Day	37% 13% 23% 17% 10% 1	4311
September	1st to 10th	Day	42% 12% 17% 14% 12% 3	2273
	11th to 20th	Day	40% 9% 12% 18% 15% 6%	2200
	21st to end	Day	34% 8% 9% 20% 21% 8%	2200
October	1st to 10th	Day	33% 4 7% 12% 17% 26%	3590
	11th to 20th	Day	17% 2 5% 16% 25% 34%	3568
	21st to end	Day	19% 3 5% 17% 39% 17%	3548
November	1st to 10th	Day	29% 4 9% 19% 24% 16%	1852
	11th to 20th	Day	30% 4 7% 18% 28% 14%	1890
	21st to end	Day	36% 4 8% 18% 21% 12%	1890
December	1st to 10th	Day	37% 4 7% 16% 29% 7%	3020
	11th to 20th	Day	36% 5% 6% 22% 23% 8%	3460
	21st to end	Day	42% 4 5% 18% 27% 4	4565
January	1st to 10th	Night	36% 4 5% 14% 31% 10%	6019
	11th to 20th	Night	40% 5% 5% 13% 27% 10%	5719
	21st to end	Night	43% 4 7% 17% 21% 8%	5984
February	1st to 10th	Night	40% 5% 7% 16% 20% 12%	2400
	11th to 20th	Night	42% 4 6% 12% 21% 14%	2339
	21st to end	Night	40% 6% 7% 16% 16% 15%	1980
March	1st to 10th	Night	48% 5% 6% 13% 20% 8%	5373
	11th to 20th	Night	34% 5% 9% 14% 19% 20%	5031
	21st to end	Night	37% 5% 8% 20% 18% 13%	5467
April	1st to 10th	Night	34% 6% 11% 16% 20% 14%	2025
	11th to 20th	Night	34% 4 8% 18% 25% 11%	1975
	21st to end	Night	26% 7% 10% 26% 22% 8%	2000
May	1st to 10th	Night	35% 9% 19% 19% 13% 4	4136
	11th to 20th	Night	38% 8% 16% 23% 12% 2	4033
	21st to end	Night	28% 10% 19% 27% 13% 3	4429
June	1st to 10th	Night	39% 12% 18% 18% 12% 2	1800
	11th to 20th	Night	30% 12% 22% 23% 11% 3	1800
	21st to end	Night	34% 15% 20% 19% 9% 3	1800
July	1st to 10th	Night	45% 17% 26% 10% 2	4015
	11th to 20th	Night	34% 15% 35% 14% 2	4006
	21st to end	Night	41% 18% 22% 16% 3	4488
August	1st to 10th	Night	35% 13% 21% 22% 8% 1	3232
	11th to 20th	Night	29% 12% 21% 22% 15% 1	3230
	21st to end	Night	36% 13% 23% 17% 9% 1	3586
September	1st to 10th	Night	41% 13% 17% 14% 9% 5%	2105
	11th to 20th	Night	38% 10% 13% 16% 18% 5%	2200
	21st to end	Night	35% 7% 12% 17% 21% 8%	2200
October	1st to 10th	Night	35% 5% 8% 11% 22% 20%	3590
	11th to 20th	Night	14% 3 5% 16% 29% 33%	3571
	21st to end	Night	21% 4 4 15% 37% 20%	4236
November	1st to 10th	Night	28% 5% 8% 17% 25% 18%	2666
	11th to 20th	Night	30% 3 6% 16% 30% 15%	2730
	21st to end	Night	34% 5% 10% 16% 22% 13%	2730
December	1st to 10th	Night	34% 4 6% 19% 28% 10%	4380
	11th to 20th	Night	34% 4 6% 23% 24% 9%	4954
	21st to end	Night	41% 4 5% 19% 27% 4	6633

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	18% 18% 40% 18% 5% 1	330
	11th to 20th	Day	14% 19% 32% 26% 7% 3	318
	21st to end	Day	20% 20% 40% 17% 3 1	330
February	1st to 10th	Day	20% 17% 37% 20% 6%	300
	11th to 20th	Day	27% 17% 35% 18% 3	300
	21st to end	Day	14% 23% 39% 20% 4	249
March	1st to 10th	Day	17% 20% 37% 21% 5% 1	300
	11th to 20th	Day	15% 17% 30% 26% 10% 1	474
	21st to end	Day	14% 14% 33% 28% 11% 1	550
April	1st to 10th	Day	17% 14% 26% 27% 14% 2	500
	11th to 20th	Day	11% 12% 32% 26% 17% 2	492
	21st to end	Day	8% 10% 25% 31% 20% 6%	500
May	1st to 10th	Day	9% 7% 23% 30% 24% 7%	503
	11th to 20th	Day	8% 5% 17% 33% 23% 13%	527
	21st to end	Day	9% 4 16% 31% 24% 17%	573
June	1st to 10th	Day	11% 3 12% 28% 27% 18%	530
	11th to 20th	Day	7% 2 9% 25% 32% 25%	530
	21st to end	Day	5% 2 10% 24% 33% 26%	530
July	1st to 10th	Day	6% 2 7% 15% 34% 36%	525
	11th to 20th	Day	7% 2 3 14% 34% 40%	524
	21st to end	Day	6% 1 4 19% 36% 34%	576
August	1st to 10th	Day	8% 1 5% 16% 37% 33%	526
	11th to 20th	Day	7% 2 6% 18% 35% 33%	519
	21st to end	Day	9% 3 9% 23% 33% 22%	583
September	1st to 10th	Day	11% 2 10% 23% 32% 22%	530
	11th to 20th	Day	14% 2 9% 26% 32% 15%	530
	21st to end	Day	10% 5% 10% 28% 33% 15%	530
October	1st to 10th	Day	12% 6% 22% 35% 19% 6%	530
	11th to 20th	Day	9% 5% 21% 29% 27% 9%	530
	21st to end	Day	11% 8% 22% 32% 24% 3	543
November	1st to 10th	Day	17% 6% 24% 31% 17% 5%	330
	11th to 20th	Day	12% 8% 36% 30% 12% 2	330
	21st to end	Day	13% 16% 28% 29% 11% 2	330
December	1st to 10th	Day	22% 13% 31% 24% 8% 2	330
	11th to 20th	Day	22% 14% 35% 20% 8% 1	330
	21st to end	Day	19% 12% 31% 26% 11% 1	363
January	1st to 10th	Night	17% 13% 36% 27% 6% 1	840
	11th to 20th	Night	17% 12% 29% 32% 10%	825
	21st to end	Night	20% 11% 37% 28% 5%	880
February	1st to 10th	Night	18% 9% 33% 33% 8%	800
	11th to 20th	Night	22% 10% 33% 28% 8%	783
	21st to end	Night	16% 13% 38% 31% 3	660
March	1st to 10th	Night	16% 11% 32% 34% 8%	800
	11th to 20th	Night	14% 9% 34% 32% 11% 1	800
	21st to end	Night	11% 12% 33% 33% 11%	880
April	1st to 10th	Night	13% 10% 27% 36% 14%	625
	11th to 20th	Night	12% 8% 29% 32% 18% 1	593
	21st to end	Night	8% 4 25% 40% 21% 2	600
May	1st to 10th	Night	7% 5% 26% 38% 23% 2	600
	11th to 20th	Night	8% 4 20% 37% 24% 6%	591
	21st to end	Night	8% 3 12% 35% 38% 5%	650
June	1st to 10th	Night	8% 3 10% 32% 42% 5%	600
	11th to 20th	Night	5% 1 9% 31% 43% 11%	600
	21st to end	Night	6% 1 8% 30% 45% 11%	600
July	1st to 10th	Night	6% 1 4 24% 50% 15%	585
	11th to 20th	Night	7% 2 2 21% 46% 23%	582
	21st to end	Night	4 1 4 21% 53% 17%	657
August	1st to 10th	Night	8% 1 6% 21% 44% 20%	597
	11th to 20th	Night	8% 1 4 20% 52% 16%	594
	21st to end	Night	10% 3 7% 26% 40% 14%	660
September	1st to 10th	Night	11% 3 10% 27% 37% 12%	705
	11th to 20th	Night	13% 2 11% 32% 36% 5%	800
	21st to end	Night	12% 2 13% 31% 37% 5%	800
October	1st to 10th	Night	10% 3 24% 35% 25% 3	800
	11th to 20th	Night	9% 4 21% 36% 27% 3	800
	21st to end	Night	12% 6% 22% 35% 25% 1	880
November	1st to 10th	Night	10% 5% 23% 40% 20% 2	820
	11th to 20th	Night	13% 8% 27% 35% 16% 1	840
	21st to end	Night	14% 8% 30% 31% 15% 1	840
December	1st to 10th	Night	18% 8% 29% 32% 12% 1	840
	11th to 20th	Night	19% 6% 30% 32% 12% 1	840
	21st to end	Night	23% 10% 27% 29% 11%	924

Page generated at 2026-01-14 00:14:31. Version ac07

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