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 2026-08-30.

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% 11% 4 9% 5% 4 4 3 5% 7% 33%	144132
	Night	15% 14% 5% 12% 6% 5% 4 3 4 6% 26%	138180
Transparency	Day	51% 6% 12% 20% 10% 1	147666
	Night	58% 6% 10% 16% 9% 1	142735
Seeing	Day	20% 12% 27% 26% 13% 3	17573
	Night	22% 11% 27% 26% 12% 2	26697

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	13% 20% 11% 18% 11% 5% 4 3 3 3 10%	4136
	11th to 20th	Day	9% 22% 11% 29% 11% 5% 3 2 2 2 3	4770
	21st to end	Day	11% 16% 9% 21% 11% 8% 5% 3 3 4 8%	5780
February	1st to 10th	Day	13% 20% 7% 19% 9% 5% 4 3 3 4 12%	1890
	11th to 20th	Day	13% 16% 7% 14% 9% 6% 6% 4 4 6% 15%	1843
	21st to end	Day	15% 17% 6% 14% 6% 6% 5% 4 5% 5% 19%	1688
March	1st to 10th	Day	16% 12% 4 11% 6% 5% 4 4 4 5% 29%	4891
	11th to 20th	Day	13% 15% 6% 10% 6% 5% 6% 4 5% 6% 24%	5090
	21st to end	Day	18% 14% 5% 9% 5% 4 4 4 5% 6% 27%	5586
April	1st to 10th	Day	19% 12% 4 8% 5% 4 4 3 5% 7% 30%	2423
	11th to 20th	Day	20% 10% 3 6% 4 3 3 3 4 6% 38%	2702
	21st to end	Day	20% 9% 3 7% 4 4 4 3 5% 7% 35%	2730
May	1st to 10th	Day	14% 7% 2 7% 4 4 4 4 6% 8% 40%	7642
	11th to 20th	Day	14% 9% 3 6% 4 4 4 4 6% 7% 40%	7941
	21st to end	Day	18% 8% 2 6% 3 3 3 3 4 6% 44%	9060
June	1st to 10th	Day	13% 8% 2 6% 4 4 4 5% 7% 7% 40%	3108
	11th to 20th	Day	12% 5% 2 6% 5% 5% 5% 4 6% 9% 42%	3150
	21st to end	Day	15% 7% 2 6% 4 4 4 4 6% 8% 41%	3150
July	1st to 10th	Day	13% 7% 2 6% 4 4 4 4 5% 8% 41%	8879
	11th to 20th	Day	10% 4 2 4 3 3 3 3 5% 9% 52%	8706
	21st to end	Day	8% 5% 2 5% 4 3 3 4 6% 9% 51%	8345
August	1st to 10th	Day	11% 6% 2 5% 4 4 4 4 6% 10% 44%	4364
	11th to 20th	Day	15% 6% 2 5% 4 4 4 3 6% 8% 43%	4304
	21st to end	Day	10% 6% 2 6% 3 5% 4 4 6% 9% 46%	4769
September	1st to 10th	Day	13% 6% 3 7% 4 5% 4 4 5% 8% 41%	2370
	11th to 20th	Day	12% 6% 2 5% 3 4 4 4 5% 8% 46%	2200
	21st to end	Day	18% 8% 3 8% 5% 4 5% 3 6% 6% 36%	2200
October	1st to 10th	Day	19% 8% 2 8% 4 4 4 3 5% 6% 36%	2030
	11th to 20th	Day	24% 13% 4 9% 5% 4 5% 3 5% 5% 22%	2000
	21st to end	Day	28% 13% 4 11% 5% 5% 3 3 4 5% 18%	2115
November	1st to 10th	Day	20% 19% 4 9% 6% 5% 4 4 5% 6% 20%	1810
	11th to 20th	Day	17% 22% 7% 10% 5% 4 5% 4 4 7% 16%	1680
	21st to end	Day	22% 28% 7% 11% 6% 4 3 3 4 4 9%	1680
December	1st to 10th	Day	16% 33% 9% 12% 6% 4 4 3 3 4 7%	2680
	11th to 20th	Day	21% 23% 7% 17% 6% 4 3 2 4 4 9%	2867
	21st to end	Day	27% 22% 6% 14% 5% 5% 3 2 3 3 8%	3553
January	1st to 10th	Night	13% 21% 11% 21% 8% 4 4 2 3 3 10%	8774
	11th to 20th	Night	11% 24% 11% 23% 9% 5% 4 3 2 3 6%	8137
	21st to end	Night	10% 16% 9% 19% 12% 8% 4 2 3 4 12%	8401
February	1st to 10th	Night	13% 20% 6% 16% 9% 6% 5% 3 4 4 14%	2730
	11th to 20th	Night	13% 16% 7% 17% 8% 5% 4 3 4 5% 19%	2663
	21st to end	Night	14% 16% 5% 11% 7% 5% 4 4 5% 5% 21%	2113
March	1st to 10th	Night	15% 12% 5% 10% 5% 4 4 3 5% 7% 29%	5168
	11th to 20th	Night	11% 14% 5% 9% 6% 4 5% 4 5% 7% 30%	5089
	21st to end	Night	20% 12% 4 10% 5% 5% 5% 3 4 4 28%	5588
April	1st to 10th	Night	20% 11% 3 8% 5% 4 4 3 5% 6% 31%	2212
	11th to 20th	Night	18% 10% 3 7% 4 4 4 3 5% 7% 36%	1867
	21st to end	Night	20% 9% 3 8% 5% 4 4 3 5% 5% 33%	1890
May	1st to 10th	Night	15% 7% 3 9% 4 4 4 4 5% 7% 37%	5257
	11th to 20th	Night	16% 8% 3 7% 4 3 4 3 5% 6% 41%	4905
	21st to end	Night	18% 6% 2 7% 4 3 3 3 5% 6% 43%	5114
June	1st to 10th	Night	13% 7% 2 7% 5% 5% 3 4 5% 7% 41%	1507
	11th to 20th	Night	11% 5% 2 5% 5% 4 5% 5% 7% 9% 41%	1470
	21st to end	Night	14% 7% 2 7% 4 3 5% 4 6% 8% 40%	1470
July	1st to 10th	Night	12% 8% 3 7% 4 4 3 4 5% 8% 42%	4110
	11th to 20th	Night	10% 4 2 5% 4 4 4 3 6% 8% 49%	4280
	21st to end	Night	10% 6% 2 6% 4 4 4 4 6% 8% 47%	5727
August	1st to 10th	Night	11% 7% 2 7% 4 4 4 3 6% 7% 44%	3005
	11th to 20th	Night	12% 6% 3 7% 4 4 5% 4 6% 8% 41%	2965
	21st to end	Night	11% 6% 2 6% 4 4 4 3 5% 8% 45%	3304
September	1st to 10th	Night	11% 5% 2 6% 3 4 5% 5% 7% 8% 44%	2018
	11th to 20th	Night	11% 5% 2 6% 4 4 4 3 5% 7% 48%	2200
	21st to end	Night	17% 8% 3 8% 5% 5% 5% 3 5% 6% 37%	2200
October	1st to 10th	Night	18% 8% 3 7% 5% 4 5% 4 5% 7% 34%	2369
	11th to 20th	Night	25% 12% 3 9% 5% 4 4 4 5% 6% 23%	2400
	21st to end	Night	26% 13% 4 10% 5% 4 4 4 4 6% 20%	2723
November	1st to 10th	Night	19% 18% 4 8% 5% 4 5% 3 4 6% 24%	2707
	11th to 20th	Night	18% 20% 6% 11% 6% 5% 4 3 4 6% 16%	2940
	21st to end	Night	24% 26% 6% 9% 5% 4 4 3 4 5% 11%	2940
December	1st to 10th	Night	18% 27% 8% 14% 6% 4 3 3 5% 4 7%	4720
	11th to 20th	Night	16% 26% 8% 18% 7% 4 4 3 3 3 8%	5550
	21st to end	Night	23% 23% 8% 14% 6% 5% 4 3 3 4 7%	7667

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	78% 6% 7% 5% 3	4137
	11th to 20th	Day	90% 4 3 2 1	4801
	21st to end	Day	79% 8% 6% 5% 2	5780
February	1st to 10th	Day	76% 7% 7% 8% 2	1890
	11th to 20th	Day	69% 10% 10% 8% 3	1852
	21st to end	Day	66% 7% 10% 12% 4	1688
March	1st to 10th	Day	56% 7% 14% 12% 10% 1	4894
	11th to 20th	Day	58% 7% 12% 16% 6% 1	5090
	21st to end	Day	56% 7% 13% 16% 7% 1	5586
April	1st to 10th	Day	55% 6% 11% 18% 10%	2423
	11th to 20th	Day	48% 4 9% 22% 15% 1	2702
	21st to end	Day	47% 7% 13% 20% 11% 2	2730
May	1st to 10th	Day	41% 7% 13% 23% 14% 3	7651
	11th to 20th	Day	42% 8% 11% 22% 17% 1	7945
	21st to end	Day	41% 5% 10% 25% 15% 3	9061
June	1st to 10th	Day	39% 8% 11% 23% 16% 1	3108
	11th to 20th	Day	38% 6% 13% 25% 17% 1	3150
	21st to end	Day	40% 8% 13% 24% 14% 2	3150
July	1st to 10th	Day	40% 7% 16% 23% 14% 1	8806
	11th to 20th	Day	29% 5% 14% 38% 14% 1	8625
	21st to end	Day	30% 6% 14% 34% 15% 1	8161
August	1st to 10th	Day	35% 7% 15% 28% 14% 1	4351
	11th to 20th	Day	39% 6% 18% 26% 11%	4343
	21st to end	Day	34% 7% 16% 32% 10% 1	4769
September	1st to 10th	Day	40% 8% 14% 25% 12% 1	2370
	11th to 20th	Day	35% 8% 15% 30% 12%	2200
	21st to end	Day	48% 9% 12% 22% 9%	2200
October	1st to 10th	Day	41% 7% 13% 26% 12%	3303
	11th to 20th	Day	52% 7% 12% 21% 8%	3240
	21st to end	Day	61% 5% 13% 16% 5%	3391
November	1st to 10th	Day	64% 5% 12% 14% 5%	1810
	11th to 20th	Day	68% 8% 11% 8% 5%	1680
	21st to end	Day	78% 7% 9% 6%	1680
December	1st to 10th	Day	81% 8% 8% 3 1	2680
	11th to 20th	Day	79% 5% 10% 5% 1	2866
	21st to end	Day	82% 4 6% 5% 2	3553
January	1st to 10th	Night	79% 6% 5% 5% 4	8774
	11th to 20th	Night	85% 5% 4 5% 2	8181
	21st to end	Night	76% 7% 7% 5% 5%	8401
February	1st to 10th	Night	73% 7% 8% 9% 3	2730
	11th to 20th	Night	68% 7% 10% 11% 4	2665
	21st to end	Night	63% 7% 13% 12% 6%	2113
March	1st to 10th	Night	53% 6% 14% 16% 10% 1	5178
	11th to 20th	Night	52% 6% 16% 17% 8% 1	5090
	21st to end	Night	56% 6% 9% 15% 11% 1	5588
April	1st to 10th	Night	54% 5% 10% 19% 10% 1	2212
	11th to 20th	Night	48% 5% 8% 21% 17% 1	1867
	21st to end	Night	52% 6% 9% 17% 15% 2	1890
May	1st to 10th	Night	44% 6% 10% 21% 16% 4	5264
	11th to 20th	Night	43% 6% 9% 23% 18% 1	4906
	21st to end	Night	41% 5% 8% 26% 17% 3	5115
June	1st to 10th	Night	41% 6% 10% 21% 19% 3	1507
	11th to 20th	Night	37% 6% 13% 25% 18% 1	1470
	21st to end	Night	41% 7% 12% 25% 13% 2	1470
July	1st to 10th	Night	40% 5% 15% 22% 15% 3	4075
	11th to 20th	Night	31% 6% 11% 35% 16% 1	4238
	21st to end	Night	33% 5% 11% 30% 19% 1	5597
August	1st to 10th	Night	39% 5% 14% 26% 15% 1	2994
	11th to 20th	Night	40% 8% 17% 21% 14% 1	2992
	21st to end	Night	36% 7% 14% 31% 12% 1	3304
September	1st to 10th	Night	34% 8% 14% 28% 13% 2	2018
	11th to 20th	Night	34% 7% 15% 29% 15%	2200
	21st to end	Night	47% 8% 12% 22% 10% 1	2200
October	1st to 10th	Night	38% 7% 11% 27% 17%	3876
	11th to 20th	Night	52% 6% 14% 19% 9%	3899
	21st to end	Night	56% 7% 15% 18% 4	4397
November	1st to 10th	Night	61% 6% 11% 17% 4	2707
	11th to 20th	Night	68% 7% 13% 8% 4 1	2940
	21st to end	Night	75% 8% 10% 6% 1	2940
December	1st to 10th	Night	79% 7% 11% 3 1	4720
	11th to 20th	Night	80% 6% 8% 5% 1	5550
	21st to end	Night	82% 5% 7% 4 1	7667

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	25% 20% 34% 16% 3 1	228
	11th to 20th	Day	22% 20% 37% 16% 5%	330
	21st to end	Day	27% 18% 29% 20% 6%	363
February	1st to 10th	Day	22% 25% 33% 16% 4	330
	11th to 20th	Day	26% 18% 35% 18% 2	330
	21st to end	Day	23% 26% 35% 15% 1	273
March	1st to 10th	Day	23% 17% 35% 19% 6% 1	462
	11th to 20th	Day	24% 16% 30% 24% 5% 1	540
	21st to end	Day	27% 14% 29% 23% 5% 1	594
April	1st to 10th	Day	24% 15% 31% 22% 9% 1	540
	11th to 20th	Day	28% 13% 28% 16% 11% 5%	532
	21st to end	Day	25% 12% 28% 25% 9% 1	540
May	1st to 10th	Day	19% 11% 31% 26% 11% 2	543
	11th to 20th	Day	16% 9% 26% 30% 16% 3	567
	21st to end	Day	15% 8% 26% 27% 19% 4	617
June	1st to 10th	Day	13% 7% 28% 34% 15% 2	738
	11th to 20th	Day	14% 9% 27% 32% 15% 3	780
	21st to end	Day	17% 6% 28% 32% 14% 3	780
July	1st to 10th	Day	10% 5% 25% 33% 24% 4	771
	11th to 20th	Day	11% 7% 25% 34% 18% 6%	768
	21st to end	Day	11% 6% 23% 37% 17% 6%	625
August	1st to 10th	Day	13% 6% 23% 31% 20% 8%	566
	11th to 20th	Day	14% 6% 18% 35% 21% 7%	559
	21st to end	Day	15% 7% 23% 29% 19% 6%	619
September	1st to 10th	Day	16% 7% 21% 33% 17% 6%	530
	11th to 20th	Day	10% 5% 20% 27% 26% 12%	530
	21st to end	Day	18% 11% 23% 25% 19% 5%	530
October	1st to 10th	Day	20% 12% 25% 24% 15% 4	530
	11th to 20th	Day	23% 18% 32% 22% 4 1	530
	21st to end	Day	31% 17% 29% 18% 4	498
November	1st to 10th	Day	34% 16% 27% 18% 6%	308
	11th to 20th	Day	29% 21% 30% 15% 3 1	220
	21st to end	Day	30% 24% 33% 12% 2	220
December	1st to 10th	Day	33% 19% 30% 15% 4	220
	11th to 20th	Day	32% 22% 29% 14% 4	220
	21st to end	Day	37% 18% 33% 10% 2	242
January	1st to 10th	Night	24% 18% 32% 20% 5% 1	1050
	11th to 20th	Night	29% 16% 30% 19% 5%	1016
	21st to end	Night	21% 12% 33% 25% 7% 1	924
February	1st to 10th	Night	21% 17% 36% 22% 5%	840
	11th to 20th	Night	19% 13% 35% 26% 6%	823
	21st to end	Night	22% 16% 35% 23% 4	692
March	1st to 10th	Night	20% 12% 37% 25% 7%	840
	11th to 20th	Night	20% 14% 34% 24% 7% 1	840
	21st to end	Night	22% 10% 30% 27% 10% 1	924
April	1st to 10th	Night	24% 13% 30% 27% 6% 1	840
	11th to 20th	Night	22% 10% 26% 27% 12% 2	623
	21st to end	Night	24% 8% 26% 28% 13% 1	630
May	1st to 10th	Night	16% 6% 23% 38% 15% 2	630
	11th to 20th	Night	19% 4 20% 38% 19% 1	513
	21st to end	Night	14% 3 23% 37% 20% 3	455
June	1st to 10th	Night	15% 7% 22% 37% 17% 2	420
	11th to 20th	Night	11% 6% 25% 38% 20%	420
	21st to end	Night	16% 4 21% 36% 23% 1	420
July	1st to 10th	Night	10% 4 16% 47% 22% 2	410
	11th to 20th	Night	10% 3 19% 35% 29% 3	461
	21st to end	Night	9% 4 17% 42% 27% 1	690
August	1st to 10th	Night	12% 3 17% 36% 30% 2	627
	11th to 20th	Night	10% 4 16% 35% 29% 6%	624
	21st to end	Night	14% 5% 21% 30% 27% 3	687
September	1st to 10th	Night	11% 7% 20% 34% 21% 6%	790
	11th to 20th	Night	12% 5% 18% 33% 26% 6%	800
	21st to end	Night	18% 8% 21% 28% 20% 6%	800
October	1st to 10th	Night	20% 9% 25% 29% 15% 2	800
	11th to 20th	Night	29% 15% 23% 25% 7% 2	800
	21st to end	Night	31% 14% 28% 22% 5% 1	880
November	1st to 10th	Night	31% 14% 27% 21% 8% 1	820
	11th to 20th	Night	28% 19% 28% 18% 8%	840
	21st to end	Night	37% 16% 28% 17% 3	840
December	1st to 10th	Night	32% 21% 30% 13% 4	840
	11th to 20th	Night	26% 20% 35% 15% 3	933
	21st to end	Night	34% 15% 33% 15% 3	1155

Page generated at 2026-08-27 04:07:16. Version ac07

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