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 2024-11-25.

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	11% 6% 2 6% 5% 5% 5% 4 6% 9% 41%	100976
	Night	11% 6% 2 6% 4 4 4 4 6% 8% 43%	98453
Transparency	Day	36% 9% 12% 18% 17% 8%	104886
	Night	36% 8% 12% 16% 19% 9%	102680
Seeing	Day	12% 8% 20% 25% 22% 14%	14809
	Night	12% 6% 22% 31% 24% 5%	24778

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	15% 5% 2 6% 4 4 4 4 6% 7% 43%	2836
	11th to 20th	Day	11% 5% 2 3 3 3 3 3 5% 7% 54%	3009
	21st to end	Day	22% 7% 2 5% 3 4 3 3 4 6% 40%	3476
February	1st to 10th	Day	15% 7% 3 7% 5% 5% 3 3 4 7% 41%	1900
	11th to 20th	Day	17% 7% 3 5% 4 2 3 4 5% 7% 43%	1848
	21st to end	Day	16% 7% 2 6% 5% 4 5% 3 6% 6% 41%	1570
March	1st to 10th	Day	18% 9% 3 7% 4 4 4 3 5% 6% 36%	3120
	11th to 20th	Day	10% 5% 3 6% 5% 5% 5% 4 6% 8% 44%	3442
	21st to end	Day	14% 5% 2 6% 4 4 5% 3 6% 6% 44%	3815
April	1st to 10th	Day	13% 7% 2 5% 4 4 4 4 5% 7% 46%	2270
	11th to 20th	Day	11% 5% 2 7% 4 5% 4 3 5% 6% 46%	2254
	21st to end	Day	6% 5% 2 5% 4 4 4 3 5% 7% 55%	2280
May	1st to 10th	Day	8% 5% 2 5% 5% 4 5% 4 6% 9% 47%	4019
	11th to 20th	Day	13% 7% 2 7% 4 5% 6% 5% 6% 8% 38%	4081
	21st to end	Day	5% 4 2 6% 5% 5% 5% 5% 7% 10% 47%	4476
June	1st to 10th	Day	9% 7% 2 7% 6% 5% 6% 6% 9% 11% 32%	2470
	11th to 20th	Day	5% 5% 3 7% 6% 6% 6% 5% 8% 12% 38%	2470
	21st to end	Day	7% 5% 2 9% 7% 7% 7% 5% 8% 11% 33%	2470
July	1st to 10th	Day	8% 7% 2 9% 8% 8% 8% 7% 10% 12% 21%	4120
	11th to 20th	Day	7% 5% 2 7% 6% 6% 6% 5% 8% 12% 35%	4120
	21st to end	Day	6% 6% 3 8% 8% 7% 9% 7% 11% 14% 22%	4322
August	1st to 10th	Day	6% 5% 2 6% 5% 6% 6% 5% 9% 13% 37%	3785
	11th to 20th	Day	7% 4 2 6% 5% 4 5% 4 6% 10% 47%	3729
	21st to end	Day	6% 6% 2 7% 5% 6% 7% 6% 9% 12% 34%	4180
September	1st to 10th	Day	10% 7% 2 7% 6% 7% 7% 5% 8% 9% 33%	2160
	11th to 20th	Day	13% 6% 2 7% 5% 5% 5% 4 6% 7% 39%	2090
	21st to end	Day	10% 5% 2 6% 5% 4 4 3 6% 7% 48%	2090
October	1st to 10th	Day	9% 5% 2 6% 3 3 3 3 6% 7% 52%	2090
	11th to 20th	Day	10% 4 1 3 3 3 3 3 5% 7% 59%	2090
	21st to end	Day	9% 4 2 5% 3 3 3 3 5% 6% 58%	2099
November	1st to 10th	Day	9% 6% 2 4 3 3 3 3 5% 6% 56%	1762
	11th to 20th	Day	10% 6% 2 4 4 3 4 3 4 6% 54%	1800
	21st to end	Day	12% 6% 2 6% 4 4 3 3 5% 6% 49%	1746
December	1st to 10th	Day	15% 5% 2 6% 4 4 4 4 5% 7% 45%	1710
	11th to 20th	Day	16% 9% 3 6% 4 3 4 4 4 5% 41%	2153
	21st to end	Day	19% 8% 2 6% 4 4 4 2 4 6% 42%	3124
January	1st to 10th	Night	16% 6% 2 6% 4 5% 4 3 5% 6% 44%	4109
	11th to 20th	Night	10% 7% 2 6% 4 4 4 4 5% 6% 49%	3946
	21st to end	Night	21% 10% 2 5% 4 4 3 2 4 6% 39%	4180
February	1st to 10th	Night	14% 8% 2 5% 5% 3 4 4 5% 6% 43%	2280
	11th to 20th	Night	17% 8% 2 5% 3 3 3 3 4 4 47%	2218
	21st to end	Night	14% 7% 2 6% 5% 4 4 3 5% 6% 43%	1884
March	1st to 10th	Night	21% 12% 3 8% 4 3 3 3 4 5% 34%	3733
	11th to 20th	Night	10% 6% 2 6% 4 4 5% 4 6% 8% 44%	3517
	21st to end	Night	12% 7% 3 6% 4 4 4 3 4 7% 47%	3817
April	1st to 10th	Night	11% 6% 2 5% 4 4 3 4 7% 7% 47%	1924
	11th to 20th	Night	10% 6% 3 7% 4 4 3 4 6% 6% 47%	1875
	21st to end	Night	6% 5% 1 4 4 3 4 3 6% 7% 58%	1900
May	1st to 10th	Night	7% 6% 2 7% 5% 4 5% 4 6% 8% 47%	2861
	11th to 20th	Night	12% 8% 3 6% 5% 4 4 3 5% 7% 44%	2812
	21st to end	Night	5% 5% 1 5% 4 4 4 4 7% 13% 47%	3079
June	1st to 10th	Night	8% 6% 3 8% 5% 5% 6% 5% 8% 11% 35%	1710
	11th to 20th	Night	4 5% 2 4 6% 5% 5% 5% 8% 12% 44%	1710
	21st to end	Night	5% 5% 2 8% 5% 5% 7% 5% 8% 12% 38%	1710
July	1st to 10th	Night	7% 6% 3 9% 7% 7% 8% 7% 11% 14% 23%	2840
	11th to 20th	Night	4 4 2 6% 5% 6% 7% 6% 9% 13% 37%	2840
	21st to end	Night	4 7% 3 8% 7% 7% 8% 6% 10% 13% 27%	3226
August	1st to 10th	Night	5% 4 3 7% 6% 7% 7% 5% 9% 13% 35%	3144
	11th to 20th	Night	5% 3 2 6% 5% 4 5% 5% 8% 11% 45%	3100
	21st to end	Night	6% 6% 2 7% 5% 6% 6% 5% 9% 12% 36%	3476
September	1st to 10th	Night	10% 7% 3 7% 6% 6% 6% 6% 7% 9% 34%	2000
	11th to 20th	Night	13% 6% 2 5% 5% 4 5% 5% 7% 8% 39%	2090
	21st to end	Night	10% 5% 2 6% 4 5% 3 3 4 7% 49%	2090
October	1st to 10th	Night	8% 5% 2 5% 4 3 3 3 6% 7% 53%	2090
	11th to 20th	Night	8% 4 1 3 3 3 3 3 5% 6% 60%	2090
	21st to end	Night	9% 5% 2 5% 3 3 3 3 5% 6% 56%	2493
November	1st to 10th	Night	8% 5% 2 5% 3 3 4 4 4 6% 56%	2536
	11th to 20th	Night	12% 6% 2 5% 3 3 3 3 4 6% 54%	2600
	21st to end	Night	12% 5% 2 5% 3 4 4 3 5% 6% 51%	2529
December	1st to 10th	Night	13% 6% 2 4 4 3 4 4 6% 6% 47%	2470
	11th to 20th	Night	15% 7% 3 6% 4 3 4 3 5% 5% 46%	3042
	21st to end	Night	17% 9% 3 8% 4 3 3 3 5% 6% 39%	4532

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	38% 5% 6% 18% 23% 10%	2837
	11th to 20th	Day	30% 4 6% 16% 32% 12%	3009
	21st to end	Day	45% 6% 5% 13% 18% 12%	3476
February	1st to 10th	Day	44% 5% 7% 15% 19% 10%	1900
	11th to 20th	Day	41% 5% 6% 14% 23% 12%	1858
	21st to end	Day	42% 6% 7% 17% 17% 11%	1570
March	1st to 10th	Day	46% 7% 8% 17% 15% 7%	3120
	11th to 20th	Day	36% 7% 9% 16% 20% 12%	3442
	21st to end	Day	37% 8% 11% 17% 17% 10%	3815
April	1st to 10th	Day	37% 7% 9% 17% 16% 13%	2270
	11th to 20th	Day	37% 5% 8% 18% 20% 11%	2254
	21st to end	Day	28% 6% 10% 23% 24% 8%	2280
May	1st to 10th	Day	31% 10% 11% 25% 20% 5%	4056
	11th to 20th	Day	42% 9% 10% 22% 15% 2	4085
	21st to end	Day	29% 10% 15% 27% 17% 2	4489
June	1st to 10th	Day	41% 12% 16% 20% 10% 2	2470
	11th to 20th	Day	35% 11% 18% 22% 11% 2	2470
	21st to end	Day	40% 13% 18% 16% 10% 2	2470
July	1st to 10th	Day	47% 17% 24% 8% 3	4055
	11th to 20th	Day	38% 14% 29% 15% 3	4051
	21st to end	Day	44% 19% 23% 11% 3	4184
August	1st to 10th	Day	33% 11% 19% 24% 12% 1	3773
	11th to 20th	Day	31% 9% 15% 26% 18% 2	3765
	21st to end	Day	37% 13% 23% 17% 10% 1	4179
September	1st to 10th	Day	44% 12% 17% 13% 12% 3	2160
	11th to 20th	Day	42% 10% 13% 16% 14% 6%	2090
	21st to end	Day	34% 8% 9% 19% 21% 8%	2090
October	1st to 10th	Day	33% 4 7% 12% 18% 26%	3480
	11th to 20th	Day	17% 3 5% 16% 24% 34%	3458
	21st to end	Day	18% 3 5% 18% 39% 18%	3438
November	1st to 10th	Day	29% 4 9% 19% 23% 15%	1762
	11th to 20th	Day	31% 5% 7% 17% 27% 14%	1800
	21st to end	Day	36% 4 8% 18% 21% 13%	1746
December	1st to 10th	Day	38% 6% 11% 15% 20% 8%	1710
	11th to 20th	Day	44% 6% 5% 16% 22% 8%	2150
	21st to end	Day	45% 4 5% 18% 22% 6%	3124
January	1st to 10th	Night	39% 5% 7% 12% 24% 14%	4109
	11th to 20th	Night	34% 6% 7% 15% 27% 12%	3946
	21st to end	Night	47% 4 5% 14% 23% 6%	4180
February	1st to 10th	Night	40% 5% 7% 16% 20% 12%	2280
	11th to 20th	Night	42% 4 6% 12% 21% 15%	2219
	21st to end	Night	41% 6% 7% 16% 16% 15%	1884
March	1st to 10th	Night	52% 6% 7% 14% 13% 8%	3733
	11th to 20th	Night	34% 7% 11% 17% 20% 11%	3517
	21st to end	Night	38% 6% 9% 18% 19% 10%	3817
April	1st to 10th	Night	35% 6% 11% 15% 20% 14%	1924
	11th to 20th	Night	36% 4 8% 19% 23% 10%	1875
	21st to end	Night	25% 6% 9% 27% 24% 9%	1900
May	1st to 10th	Night	30% 11% 16% 19% 18% 5%	2888
	11th to 20th	Night	38% 8% 13% 22% 15% 3	2813
	21st to end	Night	25% 10% 17% 29% 15% 4	3087
June	1st to 10th	Night	38% 12% 18% 18% 12% 1	1710
	11th to 20th	Night	30% 12% 20% 24% 12% 3	1710
	21st to end	Night	35% 15% 20% 18% 10% 3	1710
July	1st to 10th	Night	45% 17% 26% 9% 2 1	2795
	11th to 20th	Night	33% 15% 32% 16% 3	2786
	21st to end	Night	43% 20% 21% 12% 4	3123
August	1st to 10th	Night	34% 13% 21% 22% 8% 1	3132
	11th to 20th	Night	29% 12% 21% 22% 15% 1	3130
	21st to end	Night	35% 13% 23% 17% 9% 1	3476
September	1st to 10th	Night	43% 13% 17% 13% 9% 6%	2000
	11th to 20th	Night	40% 10% 13% 15% 16% 5%	2090
	21st to end	Night	35% 8% 11% 16% 21% 9%	2090
October	1st to 10th	Night	34% 5% 7% 11% 22% 20%	3480
	11th to 20th	Night	15% 3 5% 15% 29% 33%	3461
	21st to end	Night	20% 4 4 15% 38% 20%	4104
November	1st to 10th	Night	29% 5% 8% 17% 24% 17%	2536
	11th to 20th	Night	32% 4 6% 14% 29% 15%	2600
	21st to end	Night	34% 5% 9% 15% 23% 14%	2529
December	1st to 10th	Night	36% 6% 9% 18% 23% 7%	2470
	11th to 20th	Night	40% 5% 6% 12% 27% 10%	3044
	21st to end	Night	46% 5% 6% 17% 22% 5%	4532

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% 17% 40% 18% 6% 1	270
	11th to 20th	Day	12% 19% 32% 27% 7% 3	270
	21st to end	Day	20% 21% 40% 16% 3 1	297
February	1st to 10th	Day	21% 19% 37% 19% 5%	270
	11th to 20th	Day	27% 16% 36% 19% 4	270
	21st to end	Day	14% 24% 38% 20% 4	225
March	1st to 10th	Day	16% 19% 36% 23% 6% 1	270
	11th to 20th	Day	14% 16% 31% 26% 11% 2	435
	21st to end	Day	13% 14% 33% 28% 11% 1	506
April	1st to 10th	Day	17% 14% 24% 28% 14% 2	460
	11th to 20th	Day	12% 12% 32% 25% 18% 2	452
	21st to end	Day	8% 10% 25% 31% 20% 5%	460
May	1st to 10th	Day	8% 7% 22% 30% 26% 7%	463
	11th to 20th	Day	8% 4 15% 33% 24% 15%	487
	21st to end	Day	9% 4 14% 30% 24% 19%	529
June	1st to 10th	Day	12% 3 10% 27% 28% 20%	490
	11th to 20th	Day	7% 2 10% 25% 31% 25%	490
	21st to end	Day	6% 2 10% 23% 34% 25%	490
July	1st to 10th	Day	6% 2 7% 15% 34% 35%	485
	11th to 20th	Day	7% 2 2 14% 33% 41%	484
	21st to end	Day	6% 1 4 19% 35% 35%	532
August	1st to 10th	Day	8% 1 4 15% 37% 34%	486
	11th to 20th	Day	8% 2 5% 18% 35% 32%	479
	21st to end	Day	10% 3 6% 23% 35% 23%	539
September	1st to 10th	Day	12% 2 9% 21% 33% 23%	490
	11th to 20th	Day	15% 3 9% 27% 31% 15%	490
	21st to end	Day	10% 5% 10% 27% 33% 15%	490
October	1st to 10th	Day	13% 6% 20% 35% 20% 6%	490
	11th to 20th	Day	9% 5% 21% 30% 27% 9%	490
	21st to end	Day	11% 8% 21% 33% 25% 3	501
November	1st to 10th	Day	17% 6% 25% 31% 16% 5%	300
	11th to 20th	Day	13% 9% 38% 28% 10% 2	300
	21st to end	Day	13% 14% 28% 32% 11% 2	282
December	1st to 10th	Day	19% 13% 30% 26% 10% 2	270
	11th to 20th	Day	24% 14% 34% 20% 7%	270
	21st to end	Day	21% 12% 31% 24% 11% 1	297
January	1st to 10th	Night	17% 12% 36% 27% 7% 1	760
	11th to 20th	Night	16% 12% 29% 32% 10%	760
	21st to end	Night	20% 11% 37% 27% 5%	836
February	1st to 10th	Night	18% 10% 33% 33% 7%	760
	11th to 20th	Night	21% 9% 34% 28% 8%	743
	21st to end	Night	16% 13% 38% 31% 3	628
March	1st to 10th	Night	15% 11% 32% 34% 8%	760
	11th to 20th	Night	14% 8% 34% 32% 11% 1	760
	21st to end	Night	11% 12% 32% 33% 11%	836
April	1st to 10th	Night	13% 10% 26% 37% 14%	594
	11th to 20th	Night	12% 8% 29% 31% 18% 1	563
	21st to end	Night	8% 4 25% 40% 21% 1	570
May	1st to 10th	Night	6% 5% 26% 37% 24% 2	570
	11th to 20th	Night	8% 4 19% 37% 25% 6%	561
	21st to end	Night	8% 3 12% 34% 39% 5%	617
June	1st to 10th	Night	8% 2 9% 33% 42% 5%	570
	11th to 20th	Night	5% 1 9% 31% 42% 11%	570
	21st to end	Night	6% 1 9% 31% 43% 11%	570
July	1st to 10th	Night	6% 1 4 24% 50% 15%	555
	11th to 20th	Night	7% 2 2 21% 45% 24%	552
	21st to end	Night	4 1 3 22% 53% 16%	624
August	1st to 10th	Night	7% 6% 20% 45% 21%	567
	11th to 20th	Night	8% 1 4 21% 51% 16%	564
	21st to end	Night	10% 3 6% 25% 41% 15%	627
September	1st to 10th	Night	11% 2 10% 25% 38% 13%	670
	11th to 20th	Night	14% 2 12% 31% 36% 6%	760
	21st to end	Night	12% 2 13% 30% 38% 5%	760
October	1st to 10th	Night	10% 3 24% 35% 25% 4	760
	11th to 20th	Night	9% 4 21% 36% 26% 3	760
	21st to end	Night	11% 6% 22% 35% 26% 1	836
November	1st to 10th	Night	10% 5% 24% 39% 20% 2	780
	11th to 20th	Night	13% 9% 27% 34% 16% 1	800
	21st to end	Night	15% 8% 30% 31% 16% 1	779
December	1st to 10th	Night	16% 8% 28% 33% 14% 2	760
	11th to 20th	Night	20% 6% 31% 31% 12% 1	760
	21st to end	Night	24% 10% 28% 28% 10%	836

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