ES Fox Observatory (BAS/BOEC)
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the ES Fox Observatory (BAS/BOEC) clear sky chart from 2005-11-06 to 2025-04-26.

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	15% 12% 4 9% 5% 4 4 3 5% 6% 31%	113445
	Night	16% 15% 5% 12% 6% 5% 4 3 4 5% 25%	115216
Transparency	Day	52% 7% 12% 18% 10% 1	117022
	Night	59% 7% 11% 15% 8% 1	119803
Seeing	Day	19% 11% 27% 27% 13% 3	15703
	Night	22% 11% 27% 26% 12% 2	25097

By Month

Percentage Cloud Cover NE (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% 20% 12% 18% 13% 5% 5% 3 2 3 8%	3186
	11th to 20th	Day	9% 21% 11% 29% 10% 5% 3 3 3 2 4	3654
	21st to end	Day	14% 18% 11% 21% 8% 7% 4 3 3 3 8%	4466
February	1st to 10th	Day	13% 21% 7% 19% 9% 5% 3 3 3 4 11%	1800
	11th to 20th	Day	12% 16% 7% 14% 8% 6% 6% 4 4 6% 16%	1753
	21st to end	Day	15% 17% 6% 13% 6% 6% 5% 4 5% 5% 20%	1610
March	1st to 10th	Day	16% 12% 4 10% 6% 5% 4 4 4 5% 28%	4785
	11th to 20th	Day	13% 15% 6% 10% 6% 5% 6% 4 6% 6% 24%	4980
	21st to end	Day	18% 14% 5% 9% 5% 4 4 4 5% 6% 27%	5465
April	1st to 10th	Day	18% 12% 4 8% 5% 4 4 3 5% 7% 30%	2307
	11th to 20th	Day	19% 10% 3 6% 4 3 3 3 4 6% 39%	2572
	21st to end	Day	20% 9% 3 7% 4 4 4 3 5% 7% 35%	2535
May	1st to 10th	Day	16% 8% 2 7% 4 4 4 3 5% 7% 40%	4108
	11th to 20th	Day	14% 7% 2 6% 3 4 5% 4 6% 8% 41%	4256
	21st to end	Day	14% 6% 2 5% 4 4 4 3 5% 7% 46%	4837
June	1st to 10th	Day	13% 8% 2 6% 4 4 4 5% 7% 7% 39%	2812
	11th to 20th	Day	11% 5% 2 6% 5% 5% 5% 4 6% 8% 43%	2850
	21st to end	Day	15% 7% 2 5% 4 4 4 4 6% 8% 42%	2850
July	1st to 10th	Day	14% 7% 2 6% 4 5% 5% 4 6% 8% 39%	4760
	11th to 20th	Day	11% 5% 2 5% 3 3 3 3 6% 8% 50%	4670
	21st to end	Day	9% 5% 2 5% 4 3 3 4 6% 9% 50%	4471
August	1st to 10th	Day	11% 6% 2 5% 4 4 4 4 6% 10% 43%	4104
	11th to 20th	Day	15% 6% 2 5% 4 4 4 3 6% 8% 43%	4044
	21st to end	Day	10% 6% 2 6% 3 5% 4 4 6% 9% 46%	4510
September	1st to 10th	Day	13% 6% 3 7% 4 4 4 4 5% 8% 41%	2252
	11th to 20th	Day	12% 6% 2 6% 3 4 4 4 5% 8% 44%	2090
	21st to end	Day	18% 7% 3 8% 4 4 5% 3 6% 6% 36%	2090
October	1st to 10th	Day	20% 9% 3 8% 5% 4 4 3 5% 6% 34%	1929
	11th to 20th	Day	24% 13% 4 9% 5% 4 5% 3 5% 5% 21%	1900
	21st to end	Day	29% 13% 4 11% 5% 5% 3 3 4 5% 18%	2009
November	1st to 10th	Day	20% 19% 4 8% 6% 5% 4 4 5% 6% 20%	1722
	11th to 20th	Day	17% 21% 7% 10% 5% 4 5% 4 4 7% 17%	1600
	21st to end	Day	22% 27% 7% 11% 6% 4 3 3 4 4 9%	1600
December	1st to 10th	Day	16% 33% 9% 12% 6% 4 4 3 3 4 7%	2600
	11th to 20th	Day	21% 23% 7% 17% 6% 4 3 2 4 4 9%	2792
	21st to end	Day	28% 22% 6% 14% 5% 5% 3 2 3 3 8%	3476
January	1st to 10th	Night	12% 21% 11% 22% 8% 4 4 2 3 3 10%	6765
	11th to 20th	Night	12% 19% 10% 25% 9% 5% 4 3 3 3 7%	6245
	21st to end	Night	13% 18% 10% 18% 9% 8% 4 2 3 4 11%	6490
February	1st to 10th	Night	13% 20% 7% 17% 10% 6% 5% 4 4 4 13%	2600
	11th to 20th	Night	14% 16% 7% 17% 8% 5% 4 3 4 5% 18%	2533
	21st to end	Night	14% 15% 5% 11% 7% 5% 4 4 5% 6% 22%	2015
March	1st to 10th	Night	15% 12% 5% 10% 6% 4 4 3 5% 7% 29%	5054
	11th to 20th	Night	11% 14% 5% 9% 6% 4 5% 4 5% 7% 31%	4979
	21st to end	Night	20% 12% 4 10% 5% 5% 5% 3 3 4 29%	5467
April	1st to 10th	Night	20% 11% 4 7% 5% 4 4 3 4 6% 31%	2107
	11th to 20th	Night	18% 10% 3 7% 3 3 5% 3 5% 7% 36%	1777
	21st to end	Night	20% 9% 3 8% 5% 4 4 4 5% 5% 32%	1761
May	1st to 10th	Night	15% 6% 3 9% 4 4 4 4 5% 7% 38%	2833
	11th to 20th	Night	13% 8% 3 7% 5% 4 4 4 6% 7% 40%	2637
	21st to end	Night	12% 6% 2 8% 4 4 4 3 6% 7% 46%	2738
June	1st to 10th	Night	13% 8% 2 7% 5% 5% 4 4 6% 6% 39%	1363
	11th to 20th	Night	10% 5% 2 5% 5% 4 4 5% 7% 10% 42%	1330
	21st to end	Night	14% 7% 2 7% 4 3 5% 4 6% 7% 40%	1330
July	1st to 10th	Night	11% 8% 4 7% 4 3 3 3 4 7% 46%	2210
	11th to 20th	Night	12% 4 2 5% 4 4 4 3 6% 6% 50%	2296
	21st to end	Night	7% 7% 2 5% 5% 4 4 4 6% 7% 49%	3077
August	1st to 10th	Night	11% 7% 2 7% 4 4 4 3 6% 7% 43%	2825
	11th to 20th	Night	12% 6% 3 7% 4 4 5% 4 6% 8% 41%	2785
	21st to end	Night	11% 6% 2 6% 4 4 5% 3 5% 9% 45%	3124
September	1st to 10th	Night	11% 5% 2 6% 3 4 5% 5% 7% 8% 45%	1916
	11th to 20th	Night	12% 5% 2 6% 4 4 4 3 5% 7% 47%	2090
	21st to end	Night	16% 8% 3 8% 6% 5% 5% 3 5% 6% 36%	2090
October	1st to 10th	Night	19% 8% 3 7% 5% 4 5% 4 5% 7% 33%	2250
	11th to 20th	Night	25% 12% 3 9% 5% 4 4 4 5% 6% 22%	2280
	21st to end	Night	27% 13% 4 10% 5% 4 4 4 4 6% 19%	2587
November	1st to 10th	Night	20% 17% 4 8% 5% 4 5% 3 5% 6% 24%	2575
	11th to 20th	Night	19% 20% 6% 11% 6% 5% 4 3 4 6% 16%	2800
	21st to end	Night	24% 25% 6% 9% 5% 4 4 3 4 5% 11%	2800
December	1st to 10th	Night	19% 27% 7% 14% 6% 4 4 3 5% 4 7%	4580
	11th to 20th	Night	17% 26% 8% 17% 7% 4 4 3 3 3 8%	5405
	21st to end	Night	23% 23% 8% 15% 6% 5% 4 2 3 4 7%	7502

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	80% 6% 5% 4 4	3187
	11th to 20th	Day	88% 5% 4 3 1	3685
	21st to end	Day	80% 8% 6% 4 1	4466
February	1st to 10th	Day	77% 7% 7% 8% 1	1800
	11th to 20th	Day	68% 10% 10% 8% 3	1762
	21st to end	Day	65% 7% 11% 12% 4	1610
March	1st to 10th	Day	56% 7% 14% 12% 10% 1	4788
	11th to 20th	Day	57% 7% 13% 16% 6% 1	4980
	21st to end	Day	55% 7% 13% 17% 7% 1	5465
April	1st to 10th	Day	54% 6% 11% 18% 10%	2307
	11th to 20th	Day	48% 4 9% 23% 15% 1	2572
	21st to end	Day	48% 7% 13% 19% 11% 3	2535
May	1st to 10th	Day	42% 7% 12% 19% 17% 2	4120
	11th to 20th	Day	38% 10% 16% 23% 12% 1	4260
	21st to end	Day	36% 7% 13% 20% 19% 5%	4837
June	1st to 10th	Day	40% 9% 12% 23% 15% 1	2812
	11th to 20th	Day	37% 6% 12% 25% 18% 1	2850
	21st to end	Day	40% 8% 13% 23% 14% 2	2850
July	1st to 10th	Day	41% 7% 16% 20% 14% 1	4686
	11th to 20th	Day	30% 6% 16% 34% 12% 1	4589
	21st to end	Day	31% 7% 13% 31% 18% 1	4329
August	1st to 10th	Day	35% 7% 15% 27% 14% 1	4091
	11th to 20th	Day	40% 6% 17% 25% 12%	4083
	21st to end	Day	34% 7% 15% 33% 11% 1	4510
September	1st to 10th	Day	40% 8% 14% 25% 12% 1	2252
	11th to 20th	Day	36% 8% 15% 28% 13%	2090
	21st to end	Day	48% 9% 12% 22% 8%	2090
October	1st to 10th	Day	42% 7% 13% 25% 12%	3202
	11th to 20th	Day	52% 7% 12% 20% 8%	3140
	21st to end	Day	62% 5% 13% 16% 4	3285
November	1st to 10th	Day	65% 5% 12% 14% 5%	1722
	11th to 20th	Day	68% 9% 10% 8% 5%	1600
	21st to end	Day	78% 7% 9% 6%	1600
December	1st to 10th	Day	81% 8% 8% 3 1	2600
	11th to 20th	Day	79% 5% 10% 5% 1	2791
	21st to end	Day	82% 5% 6% 5% 2	3476
January	1st to 10th	Night	79% 6% 5% 5% 4	6765
	11th to 20th	Night	83% 6% 4 5% 2	6289
	21st to end	Night	76% 8% 8% 4 3	6490
February	1st to 10th	Night	75% 7% 8% 8% 2	2600
	11th to 20th	Night	68% 7% 10% 11% 4	2535
	21st to end	Night	62% 7% 13% 12% 6%	2015
March	1st to 10th	Night	53% 6% 14% 15% 10% 1	5064
	11th to 20th	Night	51% 6% 16% 17% 8% 1	4980
	21st to end	Night	56% 7% 9% 15% 11% 1	5467
April	1st to 10th	Night	54% 5% 10% 19% 11% 1	2107
	11th to 20th	Night	47% 5% 8% 21% 17% 1	1777
	21st to end	Night	53% 6% 9% 15% 15% 2	1761
May	1st to 10th	Night	42% 7% 13% 18% 18% 2	2840
	11th to 20th	Night	41% 7% 11% 22% 17% 2	2638
	21st to end	Night	37% 7% 11% 22% 20% 4	2739
June	1st to 10th	Night	42% 7% 10% 21% 18% 2	1363
	11th to 20th	Night	35% 6% 14% 25% 19% 2	1330
	21st to end	Night	40% 7% 12% 25% 14% 2	1330
July	1st to 10th	Night	39% 5% 12% 22% 16% 5%	2175
	11th to 20th	Night	32% 7% 10% 35% 15% 1	2254
	21st to end	Night	33% 7% 12% 24% 23% 1	2979
August	1st to 10th	Night	39% 6% 15% 25% 14% 1	2814
	11th to 20th	Night	40% 8% 17% 20% 14% 1	2812
	21st to end	Night	35% 6% 14% 31% 13% 1	3124
September	1st to 10th	Night	34% 8% 14% 28% 14% 2	1916
	11th to 20th	Night	35% 8% 15% 28% 14%	2090
	21st to end	Night	47% 8% 13% 22% 10%	2090
October	1st to 10th	Night	39% 7% 11% 26% 17%	3757
	11th to 20th	Night	52% 6% 14% 19% 8%	3779
	21st to end	Night	56% 7% 15% 18% 4	4261
November	1st to 10th	Night	60% 7% 12% 17% 4	2575
	11th to 20th	Night	68% 7% 13% 8% 3 1	2800
	21st to end	Night	74% 9% 11% 6% 1	2800
December	1st to 10th	Night	79% 7% 11% 2 1	4580
	11th to 20th	Night	80% 7% 8% 5% 1	5405
	21st to end	Night	82% 5% 7% 4 1	7502

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% 20% 34% 18% 3 1	207
	11th to 20th	Day	19% 18% 39% 18% 6%	300
	21st to end	Day	27% 17% 29% 21% 6%	330
February	1st to 10th	Day	24% 24% 33% 16% 3	300
	11th to 20th	Day	25% 18% 36% 18% 2	300
	21st to end	Day	22% 28% 34% 15% 1	249
March	1st to 10th	Day	21% 15% 35% 20% 7% 1	426
	11th to 20th	Day	22% 15% 31% 26% 6% 1	500
	21st to end	Day	25% 13% 30% 25% 6% 1	550
April	1st to 10th	Day	22% 14% 31% 23% 9% 1	500
	11th to 20th	Day	27% 13% 28% 16% 11% 5%	492
	21st to end	Day	25% 11% 28% 25% 10% 1	480
May	1st to 10th	Day	20% 8% 27% 30% 13% 2	463
	11th to 20th	Day	16% 7% 24% 32% 17% 3	487
	21st to end	Day	12% 7% 24% 30% 22% 5%	529
June	1st to 10th	Day	13% 6% 27% 35% 16% 3	642
	11th to 20th	Day	12% 7% 26% 35% 17% 4	680
	21st to end	Day	17% 5% 26% 33% 15% 3	680
July	1st to 10th	Day	10% 4 22% 34% 25% 4	671
	11th to 20th	Day	11% 6% 23% 34% 19% 6%	668
	21st to end	Day	11% 4 20% 39% 19% 7%	537
August	1st to 10th	Day	13% 5% 21% 32% 20% 9%	486
	11th to 20th	Day	14% 4 14% 37% 23% 9%	479
	21st to end	Day	15% 6% 22% 29% 21% 7%	539
September	1st to 10th	Day	15% 7% 21% 33% 18% 6%	490
	11th to 20th	Day	10% 6% 21% 26% 26% 11%	490
	21st to end	Day	18% 11% 22% 25% 19% 5%	490
October	1st to 10th	Day	21% 13% 24% 23% 14% 4	490
	11th to 20th	Day	24% 17% 31% 22% 4 1	490
	21st to end	Day	32% 17% 29% 17% 5%	458
November	1st to 10th	Day	33% 16% 26% 18% 7%	280
	11th to 20th	Day	29% 20% 30% 17% 3 2	200
	21st to end	Day	29% 23% 34% 13% 2	200
December	1st to 10th	Day	31% 19% 30% 16% 5%	200
	11th to 20th	Day	30% 23% 29% 15% 4	200
	21st to end	Day	34% 19% 34% 10% 2	220
January	1st to 10th	Night	23% 18% 33% 21% 5% 1	1000
	11th to 20th	Night	28% 15% 31% 20% 6% 1	968
	21st to end	Night	21% 12% 33% 26% 7% 1	880
February	1st to 10th	Night	21% 16% 36% 22% 4	800
	11th to 20th	Night	19% 14% 35% 26% 6% 1	783
	21st to end	Night	21% 15% 35% 24% 4	660
March	1st to 10th	Night	20% 11% 36% 25% 7%	800
	11th to 20th	Night	19% 14% 34% 25% 7% 1	800
	21st to end	Night	21% 9% 30% 28% 11% 1	880
April	1st to 10th	Night	23% 12% 30% 28% 6% 1	800
	11th to 20th	Night	23% 9% 26% 27% 12% 2	593
	21st to end	Night	25% 7% 26% 28% 14% 1	587
May	1st to 10th	Night	16% 4 23% 39% 16% 2	570
	11th to 20th	Night	18% 3 19% 39% 20% 1	464
	21st to end	Night	12% 3 23% 38% 21% 3	411
June	1st to 10th	Night	14% 7% 22% 38% 17% 2	380
	11th to 20th	Night	10% 5% 23% 38% 22% 1	380
	21st to end	Night	16% 3 20% 35% 24% 1	380
July	1st to 10th	Night	10% 4 14% 46% 24% 2	370
	11th to 20th	Night	10% 3 19% 34% 30% 3	415
	21st to end	Night	9% 3 17% 42% 29% 1	624
August	1st to 10th	Night	12% 4 16% 36% 31% 2	567
	11th to 20th	Night	9% 4 16% 33% 31% 6%	564
	21st to end	Night	13% 5% 21% 30% 28% 4	627
September	1st to 10th	Night	11% 6% 21% 34% 22% 7%	750
	11th to 20th	Night	13% 5% 19% 33% 24% 6%	760
	21st to end	Night	18% 8% 21% 27% 20% 6%	760
October	1st to 10th	Night	21% 10% 24% 27% 16% 2	760
	11th to 20th	Night	29% 15% 22% 24% 8% 2	760
	21st to end	Night	32% 14% 27% 22% 4 1	836
November	1st to 10th	Night	30% 13% 27% 21% 8% 1	780
	11th to 20th	Night	28% 19% 28% 18% 8%	800
	21st to end	Night	36% 15% 28% 18% 3	800
December	1st to 10th	Night	33% 20% 30% 12% 5%	800
	11th to 20th	Night	26% 20% 35% 15% 3	888
	21st to end	Night	33% 14% 34% 16% 3	1100

Page generated at 2025-04-23 09:25:01. Version ac07

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