Batsto
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Batsto clear sky chart from 2005-11-06 to 2025-11-03.

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% 7% 2 6% 4 4 4 4 6% 8% 41%	126759
	Night	15% 7% 2 6% 4 4 4 3 5% 7% 43%	123293
Transparency	Day	40% 6% 11% 23% 17% 3	130300
	Night	40% 5% 11% 23% 18% 4	127839
Seeing	Day	19% 12% 29% 24% 12% 4	16379
	Night	18% 10% 30% 30% 11% 1	25591

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% 8% 2 5% 3 3 4 4 4 5% 51%	3597
	11th to 20th	Day	14% 7% 3 7% 5% 4 4 2 3 5% 46%	3631
	21st to end	Day	19% 9% 3 5% 4 3 4 2 4 5% 42%	4466
February	1st to 10th	Day	14% 9% 2 7% 4 3 4 4 5% 7% 41%	1805
	11th to 20th	Day	17% 9% 2 5% 3 3 4 3 5% 6% 41%	1948
	21st to end	Day	16% 10% 2 6% 4 4 4 3 4 6% 41%	1650
March	1st to 10th	Day	21% 6% 1 3 3 3 3 3 4 5% 48%	4476
	11th to 20th	Day	11% 8% 2 6% 4 4 4 4 5% 6% 46%	4883
	21st to end	Day	17% 6% 2 6% 4 4 4 3 4 6% 44%	5867
April	1st to 10th	Day	17% 8% 2 6% 4 4 4 4 5% 6% 41%	2400
	11th to 20th	Day	14% 6% 2 6% 4 4 4 4 6% 8% 43%	2374
	21st to end	Day	15% 7% 2 6% 4 4 4 4 6% 7% 41%	2400
May	1st to 10th	Day	23% 8% 3 7% 4 4 4 4 5% 8% 30%	5784
	11th to 20th	Day	26% 8% 3 6% 3 4 3 3 4 7% 33%	6261
	21st to end	Day	19% 6% 2 6% 4 4 5% 4 6% 8% 37%	6949
June	1st to 10th	Day	12% 7% 2 7% 4 4 5% 4 6% 8% 39%	2800
	11th to 20th	Day	12% 6% 2 6% 4 6% 5% 5% 6% 8% 40%	2800
	21st to end	Day	10% 5% 1 6% 5% 5% 5% 5% 7% 9% 41%	2800
July	1st to 10th	Day	8% 5% 2 6% 6% 5% 6% 5% 9% 11% 37%	6360
	11th to 20th	Day	10% 7% 3 8% 6% 6% 6% 5% 9% 11% 30%	6360
	21st to end	Day	9% 6% 3 7% 5% 5% 6% 5% 7% 10% 37%	6884
August	1st to 10th	Day	17% 6% 2 6% 5% 5% 6% 5% 6% 10% 31%	4147
	11th to 20th	Day	12% 7% 3 5% 4 5% 6% 5% 7% 9% 37%	3850
	21st to end	Day	9% 5% 2 5% 4 4 5% 4 7% 10% 44%	4312
September	1st to 10th	Day	13% 7% 3 5% 5% 4 5% 3 6% 8% 43%	2400
	11th to 20th	Day	12% 5% 2 6% 4 4 4 3 5% 7% 48%	2338
	21st to end	Day	18% 8% 3 7% 5% 4 4 3 4 7% 37%	2200
October	1st to 10th	Day	18% 6% 2 5% 3 3 3 3 6% 6% 44%	2055
	11th to 20th	Day	16% 6% 2 4 3 2 3 2 5% 6% 50%	2000
	21st to end	Day	16% 6% 2 5% 3 4 4 3 4 6% 47%	2102
November	1st to 10th	Day	13% 5% 2 4 4 4 3 3 3 6% 53%	1779
	11th to 20th	Day	15% 5% 2 5% 4 2 3 3 6% 7% 48%	1800
	21st to end	Day	15% 6% 2 4 3 5% 4 3 5% 7% 47%	1735
December	1st to 10th	Day	12% 5% 2 4 3 3 5% 4 7% 8% 47%	2600
	11th to 20th	Day	20% 9% 2 5% 3 3 3 3 3 4 46%	2986
	21st to end	Day	14% 6% 2 5% 3 4 5% 4 6% 8% 42%	3960
January	1st to 10th	Night	13% 6% 2 5% 3 3 3 3 4 6% 52%	6349
	11th to 20th	Night	15% 8% 2 5% 4 3 3 2 3 4 50%	6251
	21st to end	Night	16% 8% 2 5% 4 4 4 3 5% 6% 44%	6490
February	1st to 10th	Night	17% 9% 2 5% 4 3 4 4 5% 7% 41%	2593
	11th to 20th	Night	18% 9% 3 5% 4 3 4 3 5% 5% 42%	2338
	21st to end	Night	18% 7% 2 6% 4 4 3 3 4 6% 43%	1980
March	1st to 10th	Night	18% 9% 2 5% 3 3 2 3 4 5% 46%	5364
	11th to 20th	Night	12% 11% 3 6% 3 3 3 3 4 5% 48%	5071
	21st to end	Night	16% 8% 2 6% 4 4 4 3 4 5% 44%	5064
April	1st to 10th	Night	17% 8% 2 7% 4 4 4 3 5% 6% 40%	2000
	11th to 20th	Night	15% 7% 3 7% 5% 4 4 3 5% 6% 43%	1975
	21st to end	Night	17% 5% 2 5% 4 4 4 3 6% 7% 43%	2000
May	1st to 10th	Night	19% 10% 3 8% 4 4 4 4 6% 9% 29%	4156
	11th to 20th	Night	22% 9% 2 7% 4 3 4 3 6% 7% 32%	3675
	21st to end	Night	21% 7% 2 7% 4 3 3 3 5% 8% 37%	3926
June	1st to 10th	Night	14% 7% 2 5% 5% 4 4 3 6% 9% 41%	1600
	11th to 20th	Night	10% 6% 4 6% 5% 5% 5% 4 6% 9% 41%	1600
	21st to end	Night	9% 6% 2 6% 4 4 5% 5% 8% 10% 41%	1600
July	1st to 10th	Night	8% 7% 3 9% 6% 6% 6% 5% 6% 10% 34%	3600
	11th to 20th	Night	10% 9% 3 8% 5% 6% 6% 5% 7% 10% 31%	3600
	21st to end	Night	10% 7% 2 7% 5% 4 5% 4 6% 10% 39%	3964
August	1st to 10th	Night	20% 7% 3 7% 4 4 5% 4 6% 8% 32%	2968
	11th to 20th	Night	12% 6% 2 7% 4 4 5% 3 6% 8% 43%	3197
	21st to end	Night	9% 5% 2 5% 4 3 4 3 5% 8% 51%	3586
September	1st to 10th	Night	14% 7% 2 6% 3 4 4 4 4 7% 47%	2000
	11th to 20th	Night	11% 5% 2 4 4 3 4 3 5% 8% 52%	2061
	21st to end	Night	19% 8% 2 5% 4 4 4 3 6% 7% 39%	2200
October	1st to 10th	Night	17% 5% 2 6% 4 3 4 3 5% 6% 45%	2342
	11th to 20th	Night	17% 4 1 5% 3 2 3 2 4 6% 52%	2400
	21st to end	Night	16% 7% 2 5% 3 3 3 3 5% 6% 48%	2735
November	1st to 10th	Night	11% 5% 2 5% 3 4 3 3 5% 6% 53%	2564
	11th to 20th	Night	15% 7% 2 5% 3 4 4 3 4 5% 48%	2600
	21st to end	Night	13% 6% 2 5% 4 3 4 4 5% 7% 47%	2660
December	1st to 10th	Night	13% 6% 2 4 4 3 3 3 5% 6% 50%	4580
	11th to 20th	Night	21% 7% 2 5% 3 3 3 3 5% 7% 41%	5208
	21st to end	Night	16% 8% 3 6% 4 4 4 4 5% 6% 41%	6996

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	35% 3 8% 26% 25% 3	3598
	11th to 20th	Day	42% 3 8% 23% 17% 7%	3661
	21st to end	Day	46% 4 9% 25% 13% 3	4466
February	1st to 10th	Day	43% 4 13% 25% 13% 1	1805
	11th to 20th	Day	44% 5% 8% 24% 16% 3	1957
	21st to end	Day	45% 5% 8% 22% 14% 5%	1650
March	1st to 10th	Day	40% 4 8% 25% 17% 7%	4479
	11th to 20th	Day	37% 4 8% 28% 17% 5%	4883
	21st to end	Day	42% 4 8% 16% 23% 7%	5867
April	1st to 10th	Day	43% 6% 10% 20% 16% 6%	2400
	11th to 20th	Day	39% 6% 12% 24% 17% 4	2374
	21st to end	Day	40% 5% 11% 20% 19% 5%	2400
May	1st to 10th	Day	52% 6% 14% 18% 9% 1	5795
	11th to 20th	Day	51% 5% 10% 21% 12% 1	6265
	21st to end	Day	43% 7% 10% 23% 15% 1	6949
June	1st to 10th	Day	40% 9% 12% 21% 16% 2	2800
	11th to 20th	Day	40% 8% 12% 25% 12% 3	2800
	21st to end	Day	37% 9% 13% 22% 17% 2	2800
July	1st to 10th	Day	38% 11% 16% 21% 13% 1	6290
	11th to 20th	Day	44% 9% 18% 20% 8% 1	6285
	21st to end	Day	39% 8% 10% 22% 20% 1	6686
August	1st to 10th	Day	45% 9% 16% 21% 9% 1	4134
	11th to 20th	Day	40% 7% 13% 26% 12% 1	3886
	21st to end	Day	32% 7% 12% 29% 18% 2	4312
September	1st to 10th	Day	38% 6% 13% 19% 21% 3	2400
	11th to 20th	Day	35% 5% 9% 25% 23% 3	2338
	21st to end	Day	47% 5% 9% 18% 18% 3	2200
October	1st to 10th	Day	36% 3 9% 19% 28% 5%	3341
	11th to 20th	Day	26% 3 8% 24% 30% 9%	3240
	21st to end	Day	26% 3 12% 27% 26% 6%	3379
November	1st to 10th	Day	34% 3 13% 27% 19% 4	1779
	11th to 20th	Day	36% 4 10% 23% 24% 3	1800
	21st to end	Day	38% 4 11% 30% 14% 3	1735
December	1st to 10th	Day	34% 5% 17% 25% 16% 3	2600
	11th to 20th	Day	44% 3 10% 29% 12% 3	2986
	21st to end	Day	38% 6% 12% 23% 18% 2	3960
January	1st to 10th	Night	35% 3 7% 24% 23% 7%	6349
	11th to 20th	Night	39% 3 8% 24% 19% 7%	6296
	21st to end	Night	42% 4 9% 24% 18% 3	6490
February	1st to 10th	Night	43% 4 13% 23% 14% 2	2593
	11th to 20th	Night	44% 4 8% 20% 17% 6%	2340
	21st to end	Night	43% 3 9% 22% 17% 6%	1980
March	1st to 10th	Night	42% 4 8% 23% 13% 10%	5374
	11th to 20th	Night	39% 5% 12% 24% 15% 5%	5072
	21st to end	Night	43% 5% 8% 16% 24% 5%	5064
April	1st to 10th	Night	45% 4 9% 20% 18% 5%	2000
	11th to 20th	Night	42% 5% 10% 19% 20% 4	1975
	21st to end	Night	39% 7% 9% 20% 21% 5%	2000
May	1st to 10th	Night	51% 7% 12% 17% 10% 2	4162
	11th to 20th	Night	51% 6% 10% 19% 13% 1	3676
	21st to end	Night	46% 6% 11% 21% 14% 2	3927
June	1st to 10th	Night	40% 7% 11% 21% 20% 2	1600
	11th to 20th	Night	39% 9% 12% 25% 13% 2	1600
	21st to end	Night	35% 8% 16% 23% 17% 2	1600
July	1st to 10th	Night	45% 8% 14% 20% 12% 1	3560
	11th to 20th	Night	46% 8% 18% 19% 7% 1	3552
	21st to end	Night	39% 7% 13% 23% 18%	3847
August	1st to 10th	Night	49% 7% 18% 18% 9%	2957
	11th to 20th	Night	38% 5% 13% 31% 12% 1	3227
	21st to end	Night	31% 5% 11% 30% 21% 2	3586
September	1st to 10th	Night	38% 6% 13% 20% 20% 4	2000
	11th to 20th	Night	32% 5% 11% 25% 24% 4	2061
	21st to end	Night	44% 5% 9% 21% 18% 2	2200
October	1st to 10th	Night	37% 4 10% 24% 22% 3	3836
	11th to 20th	Night	24% 3 10% 25% 30% 7%	3899
	21st to end	Night	26% 4 10% 31% 25% 5%	4408
November	1st to 10th	Night	32% 4 11% 25% 21% 6%	2564
	11th to 20th	Night	40% 4 8% 21% 22% 5%	2600
	21st to end	Night	36% 4 12% 26% 19% 2	2660
December	1st to 10th	Night	36% 4 12% 29% 17% 3	4580
	11th to 20th	Night	44% 3 11% 23% 15% 4	5208
	21st to end	Night	43% 5% 11% 20% 18% 3	6996

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% 22% 33% 16% 4 2	200
	11th to 20th	Day	25% 28% 29% 15% 2	212
	21st to end	Day	26% 20% 35% 14% 4 2	330
February	1st to 10th	Day	22% 24% 36% 14% 3 1	305
	11th to 20th	Day	27% 22% 36% 13% 2	496
	21st to end	Day	25% 20% 34% 17% 4	414
March	1st to 10th	Day	23% 20% 32% 21% 3	500
	11th to 20th	Day	20% 22% 37% 14% 6% 2	500
	21st to end	Day	23% 18% 35% 19% 4 1	550
April	1st to 10th	Day	26% 18% 33% 17% 5% 1	500
	11th to 20th	Day	19% 17% 35% 20% 6% 2	492
	21st to end	Day	24% 13% 34% 20% 7% 2	500
May	1st to 10th	Day	27% 15% 31% 17% 8% 2	503
	11th to 20th	Day	25% 10% 31% 24% 8% 2	527
	21st to end	Day	19% 9% 20% 31% 18% 4	573
June	1st to 10th	Day	15% 11% 28% 28% 14% 4	530
	11th to 20th	Day	16% 9% 29% 29% 12% 5%	530
	21st to end	Day	12% 6% 25% 34% 17% 6%	530
July	1st to 10th	Day	14% 2 20% 32% 24% 8%	525
	11th to 20th	Day	7% 3 22% 34% 26% 9%	524
	21st to end	Day	11% 4 23% 34% 20% 8%	576
August	1st to 10th	Day	13% 4 24% 30% 21% 8%	526
	11th to 20th	Day	14% 3 16% 34% 23% 9%	519
	21st to end	Day	12% 4 24% 30% 20% 10%	583
September	1st to 10th	Day	18% 5% 24% 25% 17% 10%	530
	11th to 20th	Day	14% 4 22% 32% 19% 9%	530
	21st to end	Day	24% 8% 27% 25% 11% 5%	530
October	1st to 10th	Day	22% 5% 22% 27% 13% 10%	530
	11th to 20th	Day	18% 11% 26% 26% 14% 4	530
	21st to end	Day	20% 10% 33% 21% 14% 2	528
November	1st to 10th	Day	15% 10% 33% 26% 13% 2	401
	11th to 20th	Day	18% 18% 31% 25% 9%	400
	21st to end	Day	19% 16% 32% 22% 9% 2	335
December	1st to 10th	Day	25% 15% 40% 14% 6% 1	200
	11th to 20th	Day	29% 17% 33% 18% 4 1	200
	21st to end	Day	25% 14% 30% 21% 8% 2	220
January	1st to 10th	Night	20% 18% 36% 23% 4 1	800
	11th to 20th	Night	23% 16% 33% 24% 4	800
	21st to end	Night	19% 14% 39% 25% 2	880
February	1st to 10th	Night	23% 13% 38% 25% 2	800
	11th to 20th	Night	23% 20% 40% 15% 1	783
	21st to end	Night	23% 17% 35% 22% 3	660
March	1st to 10th	Night	21% 15% 36% 24% 4	800
	11th to 20th	Night	22% 14% 36% 23% 5% 1	800
	21st to end	Night	21% 11% 40% 22% 6%	880
April	1st to 10th	Night	21% 16% 37% 21% 5%	800
	11th to 20th	Night	18% 14% 36% 27% 6%	791
	21st to end	Night	19% 10% 36% 29% 6%	800
May	1st to 10th	Night	21% 10% 34% 28% 8%	650
	11th to 20th	Night	22% 7% 32% 31% 7%	442
	21st to end	Night	21% 3 18% 41% 16% 1	433
June	1st to 10th	Night	17% 4 24% 41% 13% 1	400
	11th to 20th	Night	11% 3 25% 46% 16%	400
	21st to end	Night	10% 2 23% 48% 17% 1	400
July	1st to 10th	Night	11% 3 17% 48% 18% 2	390
	11th to 20th	Night	9% 4 15% 45% 24% 3	388
	21st to end	Night	9% 2 18% 47% 23% 1	451
August	1st to 10th	Night	13% 2 12% 46% 26% 2	624
	11th to 20th	Night	13% 3 15% 40% 26% 2	790
	21st to end	Night	14% 2 15% 41% 25% 4	880
September	1st to 10th	Night	16% 3 20% 38% 18% 4	800
	11th to 20th	Night	14% 4 16% 37% 26% 4	800
	21st to end	Night	24% 5% 21% 33% 17% 1	800
October	1st to 10th	Night	20% 5% 23% 29% 19% 4	800
	11th to 20th	Night	20% 8% 25% 33% 14% 1	800
	21st to end	Night	19% 7% 34% 28% 10% 1	880
November	1st to 10th	Night	14% 8% 34% 30% 12% 1	789
	11th to 20th	Night	19% 11% 33% 29% 7% 1	800
	21st to end	Night	15% 13% 36% 27% 8% 1	800
December	1st to 10th	Night	23% 13% 34% 22% 7% 1	800
	11th to 20th	Night	20% 12% 37% 26% 6%	800
	21st to end	Night	19% 12% 37% 28% 3	880

Page generated at 2025-10-31 02:02:36. Version ac07

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