Bateson Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bateson Observatory clear sky chart from 2005-11-06 to 2026-01-02.

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	2 4 2 4 3 3 4 3 5% 6% 63%	136086
	Night	2 4 2 5% 4 4 4 4 5% 7% 59%	132665
Transparency	Day	21% 6% 10% 20% 25% 19%	131001
	Night	22% 8% 12% 22% 22% 14%	128735
Seeing	Day	11% 16% 27% 27% 16% 4	16418
	Night	7% 10% 20% 38% 22% 3	25725

By Month

Percentage Cloud Cover SW (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	2 6% 2 7% 5% 6% 7% 7% 9% 9% 40%	3647
	11th to 20th	Day	2 5% 3 7% 6% 5% 5% 4 6% 6% 50%	3750
	21st to end	Day	4 10% 3 8% 5% 5% 5% 4 5% 6% 45%	4510
February	1st to 10th	Day	4 6% 2 7% 4 5% 6% 6% 9% 8% 43%	1800
	11th to 20th	Day	2 7% 3 8% 5% 5% 5% 4 7% 9% 46%	1874
	21st to end	Day	2 6% 2 7% 6% 5% 6% 5% 7% 8% 45%	1650
March	1st to 10th	Day	3 11% 4 9% 6% 6% 7% 5% 6% 7% 35%	4553
	11th to 20th	Day	1 5% 2 4 4 4 5% 5% 8% 9% 52%	5000
	21st to end	Day	2 8% 3 8% 6% 6% 7% 5% 7% 8% 40%	5763
April	1st to 10th	Day	3 8% 3 7% 5% 4 6% 5% 7% 7% 44%	2400
	11th to 20th	Day	3 7% 2 5% 4 4 4 4 6% 8% 52%	2369
	21st to end	Day	4 6% 2 5% 4 5% 5% 3 5% 7% 54%	2400
May	1st to 10th	Day	2 3 2 4 3 2 3 2 3 6% 69%	5843
	11th to 20th	Day	2 3 2 5% 3 3 3 3 4 6% 67%	6277
	21st to end	Day	2 3 1 3 3 2 3 2 4 6% 71%	6902
June	1st to 10th	Day	3 3 2 6% 4 4 4 4 6% 8% 57%	2800
	11th to 20th	Day	1 2 1 3 3 3 3 2 4 5% 71%	2800
	21st to end	Day	1 2 1 2 2 2 2 3 3 4 78%	2800
July	1st to 10th	Day	1 1 1 1 2 1 2 3 87%	6319
	11th to 20th	Day	1 1 1 1 1 1 2 1 3 3 84%	6320
	21st to end	Day	1 2 1 3 2 3 3 3 4 6% 73%	6715
August	1st to 10th	Day	1 1 1 2 2 2 2 2 3 5% 79%	5777
	11th to 20th	Day	1 1 1 1 1 1 2 3 89%	5475
	21st to end	Day	1 2 1 2 2 2 2 2 3 4 80%	5984
September	1st to 10th	Day	1 1 1 1 2 2 2 2 2 4 82%	2400
	11th to 20th	Day	2 2 1 4 3 3 3 2 4 5% 72%	2400
	21st to end	Day	2 2 1 3 2 2 2 2 3 7% 74%	2169
October	1st to 10th	Day	2 2 1 3 2 2 3 2 4 5% 74%	3280
	11th to 20th	Day	2 3 1 4 2 2 3 2 5% 6% 68%	3261
	21st to end	Day	2 2 1 4 4 4 5% 4 6% 7% 62%	3500
November	1st to 10th	Day	4 4 2 5% 5% 4 5% 4 7% 8% 53%	1854
	11th to 20th	Day	2 4 2 5% 5% 6% 7% 6% 7% 11% 45%	1890
	21st to end	Day	1 4 2 5% 4 5% 6% 5% 7% 8% 52%	1704
December	1st to 10th	Day	2 4 1 4 4 3 4 4 7% 9% 56%	2700
	11th to 20th	Day	6% 10% 3 8% 7% 7% 7% 7% 9% 10% 26%	3108
	21st to end	Day	2 6% 3 9% 7% 6% 9% 6% 9% 11% 32%	4092
January	1st to 10th	Night	2 5% 2 7% 5% 6% 7% 5% 10% 11% 40%	6320
	11th to 20th	Night	2 5% 2 8% 6% 6% 5% 4 6% 7% 50%	6215
	21st to end	Night	5% 10% 3 9% 5% 5% 5% 4 4 6% 45%	6468
February	1st to 10th	Night	3 6% 2 6% 4 5% 7% 5% 7% 10% 47%	2600
	11th to 20th	Night	2 5% 2 5% 5% 5% 6% 5% 8% 9% 49%	2412
	21st to end	Night	2 6% 2 4 4 4 5% 6% 7% 9% 49%	1980
March	1st to 10th	Night	1 8% 3 8% 6% 6% 7% 5% 8% 10% 38%	5337
	11th to 20th	Night	1 5% 2 6% 5% 5% 6% 6% 8% 9% 50%	5000
	21st to end	Night	2 7% 3 8% 6% 6% 7% 6% 7% 9% 39%	5211
April	1st to 10th	Night	1 5% 3 5% 5% 6% 5% 4 8% 11% 47%	2000
	11th to 20th	Night	4 5% 2 4 4 4 4 5% 6% 9% 53%	1979
	21st to end	Night	3 4 2 4 4 3 3 5% 6% 7% 59%	2000
May	1st to 10th	Night	2 4 1 4 3 3 3 3 4 6% 68%	4118
	11th to 20th	Night	2 4 2 3 2 2 2 2 4 5% 71%	3616
	21st to end	Night	2 3 1 4 2 2 2 2 4 4 73%	3972
June	1st to 10th	Night	3 4 2 5% 4 3 3 4 5% 8% 58%	1600
	11th to 20th	Night	1 2 1 2 3 3 3 2 3 7% 73%	1600
	21st to end	Night	2 2 1 3 3 3 2 2 3 4 77%	1600
July	1st to 10th	Night	1 1 1 1 1 2 3 89%	3640
	11th to 20th	Night	1 1 1 2 1 1 1 1 2 2 87%	3640
	21st to end	Night	1 2 1 3 2 2 3 3 4 5% 73%	4139
August	1st to 10th	Night	2 2 1 2 1 1 2 2 4 5% 80%	4035
	11th to 20th	Night	1 1 1 1 1 1 1 2 3 89%	4387
	21st to end	Night	2 2 1 3 2 2 3 2 3 4 76%	5015
September	1st to 10th	Night	2 1 1 2 1 2 1 2 2 5% 82%	2000
	11th to 20th	Night	3 2 1 2 2 2 2 2 4 5% 74%	2000
	21st to end	Night	2 2 1 2 1 2 2 2 4 5% 76%	2226
October	1st to 10th	Night	2 2 1 2 2 3 3 2 2 3 78%	3920
	11th to 20th	Night	1 2 1 2 2 2 3 2 4 5% 75%	3897
	21st to end	Night	2 2 1 3 3 3 5% 4 6% 7% 63%	4307
November	1st to 10th	Night	4 4 1 5% 4 4 5% 4 7% 9% 53%	2665
	11th to 20th	Night	3 4 2 5% 4 4 5% 5% 8% 10% 51%	2730
	21st to end	Night	2 3 1 4 4 5% 4 5% 7% 10% 55%	2914
December	1st to 10th	Night	2 4 1 4 3 3 3 3 5% 7% 64%	4700
	11th to 20th	Night	6% 7% 3 7% 7% 7% 7% 7% 9% 12% 30%	5316
	21st to end	Night	4 7% 3 9% 7% 7% 7% 6% 8% 9% 34%	7106

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	31% 14% 21% 26% 7%	3647
	11th to 20th	Day	30% 9% 13% 26% 19% 3	3750
	21st to end	Day	38% 8% 10% 16% 23% 5%	4510
February	1st to 10th	Day	32% 11% 16% 25% 14% 3	1800
	11th to 20th	Day	32% 7% 16% 26% 17% 2	1883
	21st to end	Day	33% 10% 15% 23% 14% 5%	1650
March	1st to 10th	Day	41% 9% 12% 19% 15% 4	4553
	11th to 20th	Day	21% 7% 19% 33% 19% 1	5000
	21st to end	Day	32% 9% 21% 22% 14% 2	5763
April	1st to 10th	Day	34% 9% 14% 25% 15% 3	2400
	11th to 20th	Day	27% 7% 16% 25% 21% 5%	2372
	21st to end	Day	28% 5% 15% 27% 21% 3	2400
May	1st to 10th	Day	16% 4 8% 27% 39% 6%	5843
	11th to 20th	Day	16% 5% 10% 22% 39% 8%	6280
	21st to end	Day	15% 4 7% 27% 40% 7%	6904
June	1st to 10th	Day	23% 6% 12% 22% 31% 7%	2800
	11th to 20th	Day	15% 3 8% 21% 35% 19%	2800
	21st to end	Day	11% 3 4 14% 33% 34%	2800
July	1st to 10th	Day	5% 1 3 8% 19% 65%	6251
	11th to 20th	Day	7% 1 2 5% 14% 71%	6245
	21st to end	Day	12% 4 4 14% 26% 40%	6519
August	1st to 10th	Day	13% 2 4 8% 21% 52%	4206
	11th to 20th	Day	5% 1 2 7% 35% 49%	3956
	21st to end	Day	7% 1 3 11% 41% 37%	4311
September	1st to 10th	Day	9% 1 3 11% 30% 47%	2400
	11th to 20th	Day	14% 3 8% 18% 33% 23%	2400
	21st to end	Day	13% 2 6% 23% 32% 24%	2169
October	1st to 10th	Day	14% 3 5% 15% 34% 30%	3280
	11th to 20th	Day	16% 5% 7% 29% 35% 9%	3261
	21st to end	Day	18% 5% 12% 32% 27% 7%	3500
November	1st to 10th	Day	26% 7% 16% 23% 23% 5%	1854
	11th to 20th	Day	27% 10% 18% 26% 17% 1	1890
	21st to end	Day	26% 9% 14% 25% 22% 3	1704
December	1st to 10th	Day	23% 7% 12% 30% 26% 2	2700
	11th to 20th	Day	44% 14% 16% 17% 8% 1	3108
	21st to end	Day	35% 15% 23% 20% 6% 1	4092
January	1st to 10th	Night	30% 13% 21% 25% 10%	6320
	11th to 20th	Night	29% 10% 15% 22% 19% 5%	6215
	21st to end	Night	39% 7% 9% 15% 25% 5%	6468
February	1st to 10th	Night	28% 11% 13% 27% 16% 4	2600
	11th to 20th	Night	29% 8% 18% 28% 16% 1	2414
	21st to end	Night	28% 10% 18% 23% 15% 5%	1980
March	1st to 10th	Night	33% 12% 15% 23% 12% 4	5337
	11th to 20th	Night	22% 12% 16% 31% 18% 1	5000
	21st to end	Night	31% 15% 21% 23% 10% 1	5211
April	1st to 10th	Night	27% 11% 18% 27% 13% 3	2000
	11th to 20th	Night	25% 9% 18% 25% 19% 5%	1979
	21st to end	Night	21% 8% 18% 32% 17% 3	2000
May	1st to 10th	Night	17% 5% 10% 27% 33% 7%	4115
	11th to 20th	Night	17% 4 8% 27% 34% 9%	3616
	21st to end	Night	14% 5% 9% 27% 41% 5%	3972
June	1st to 10th	Night	23% 7% 13% 25% 26% 6%	1600
	11th to 20th	Night	13% 3 10% 22% 39% 13%	1600
	21st to end	Night	13% 3 5% 17% 32% 31%	1600
July	1st to 10th	Night	4 1 2 9% 23% 61%	3600
	11th to 20th	Night	7% 1 2 5% 15% 70%	3592
	21st to end	Night	13% 3 4 17% 28% 35%	4023
August	1st to 10th	Night	12% 2 3 9% 22% 52%	2929
	11th to 20th	Night	7% 1 2 9% 37% 45%	3175
	21st to end	Night	9% 2 2 13% 40% 34%	3608
September	1st to 10th	Night	9% 2 2 10% 29% 47%	2000
	11th to 20th	Night	14% 3 7% 19% 30% 27%	2000
	21st to end	Night	11% 3 6% 21% 32% 26%	2226
October	1st to 10th	Night	14% 2 5% 13% 32% 34%	3920
	11th to 20th	Night	12% 4 7% 32% 35% 10%	3897
	21st to end	Night	15% 7% 11% 31% 26% 10%	4307
November	1st to 10th	Night	25% 10% 16% 23% 20% 7%	2665
	11th to 20th	Night	25% 10% 17% 26% 20% 1	2730
	21st to end	Night	20% 10% 17% 29% 19% 5%	2914
December	1st to 10th	Night	19% 8% 11% 30% 26% 7%	4700
	11th to 20th	Night	37% 15% 15% 21% 10% 1	5316
	21st to end	Night	38% 15% 18% 19% 9% 1	7106

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% 15% 30% 21% 8% 1	202
	11th to 20th	Day	18% 18% 25% 27% 12% 1	245
	21st to end	Day	13% 17% 29% 28% 12% 2	440
February	1st to 10th	Day	18% 20% 27% 26% 7% 1	400
	11th to 20th	Day	18% 25% 26% 24% 7%	456
	21st to end	Day	17% 19% 27% 30% 7%	414
March	1st to 10th	Day	21% 25% 31% 16% 5% 1	500
	11th to 20th	Day	23% 20% 26% 21% 10%	500
	21st to end	Day	21% 26% 26% 20% 7% 1	550
April	1st to 10th	Day	15% 25% 30% 21% 8% 1	500
	11th to 20th	Day	19% 24% 25% 21% 8% 3	492
	21st to end	Day	12% 22% 27% 23% 13% 2	500
May	1st to 10th	Day	14% 20% 33% 21% 9% 2	503
	11th to 20th	Day	13% 22% 28% 22% 11% 5%	528
	21st to end	Day	11% 15% 27% 26% 17% 4	573
June	1st to 10th	Day	9% 15% 27% 25% 17% 6%	530
	11th to 20th	Day	9% 20% 32% 22% 13% 3	530
	21st to end	Day	3 13% 28% 31% 19% 6%	530
July	1st to 10th	Day	1 9% 31% 32% 21% 6%	526
	11th to 20th	Day	1 6% 29% 33% 23% 7%	524
	21st to end	Day	2 6% 28% 35% 22% 7%	575
August	1st to 10th	Day	3 7% 28% 29% 24% 8%	527
	11th to 20th	Day	2 10% 25% 29% 25% 10%	517
	21st to end	Day	2 8% 27% 34% 23% 6%	583
September	1st to 10th	Day	3 9% 29% 33% 22% 5%	530
	11th to 20th	Day	4 12% 26% 33% 21% 3	530
	21st to end	Day	6% 12% 25% 34% 20% 3	530
October	1st to 10th	Day	6% 16% 26% 26% 23% 3	530
	11th to 20th	Day	10% 13% 19% 32% 24% 2	530
	21st to end	Day	13% 13% 24% 28% 19% 2	549
November	1st to 10th	Day	12% 13% 22% 30% 20% 2	330
	11th to 20th	Day	10% 12% 29% 26% 19% 4	330
	21st to end	Day	10% 15% 22% 31% 18% 3	232
December	1st to 10th	Day	16% 12% 20% 26% 19% 5%	220
	11th to 20th	Day	15% 14% 29% 20% 17% 5%	220
	21st to end	Day	22% 11% 27% 24% 14% 2	242
January	1st to 10th	Night	10% 13% 24% 32% 16% 4	804
	11th to 20th	Night	8% 13% 22% 37% 18% 2	800
	21st to end	Night	10% 7% 26% 35% 19% 3	880
February	1st to 10th	Night	10% 13% 25% 35% 16% 2	800
	11th to 20th	Night	8% 14% 23% 35% 17% 3	784
	21st to end	Night	10% 16% 22% 38% 13% 1	660
March	1st to 10th	Night	11% 17% 26% 31% 13% 3	800
	11th to 20th	Night	11% 16% 22% 29% 20% 2	800
	21st to end	Night	10% 21% 25% 29% 13% 1	880
April	1st to 10th	Night	6% 16% 26% 36% 14% 1	800
	11th to 20th	Night	12% 14% 23% 30% 17% 3	791
	21st to end	Night	6% 14% 24% 34% 19% 2	800
May	1st to 10th	Night	7% 15% 29% 31% 16% 2	618
	11th to 20th	Night	7% 7% 25% 36% 22% 3	394
	21st to end	Night	6% 8% 21% 38% 24% 2	433
June	1st to 10th	Night	4 8% 18% 43% 25% 2	400
	11th to 20th	Night	3 7% 24% 44% 22% 1	400
	21st to end	Night	2 3 17% 49% 28% 1	400
July	1st to 10th	Night	1 1 14% 53% 31% 1	390
	11th to 20th	Night	2 2 12% 59% 25% 1	388
	21st to end	Night	1 1 8% 51% 37% 2	506
August	1st to 10th	Night	3 10% 50% 34% 4	597
	11th to 20th	Night	2 3 17% 44% 32% 3	736
	21st to end	Night	1 2 16% 47% 31% 3	880
September	1st to 10th	Night	3 2 15% 44% 32% 4	800
	11th to 20th	Night	5% 4 16% 36% 34% 6%	800
	21st to end	Night	3 5% 18% 38% 30% 8%	800
October	1st to 10th	Night	5% 6% 19% 39% 27% 5%	800
	11th to 20th	Night	5% 7% 17% 37% 30% 5%	800
	21st to end	Night	7% 8% 17% 36% 24% 8%	880
November	1st to 10th	Night	8% 11% 20% 34% 23% 5%	820
	11th to 20th	Night	7% 9% 24% 40% 17% 3	840
	21st to end	Night	5% 12% 19% 39% 22% 3	840
December	1st to 10th	Night	10% 11% 20% 36% 20% 3	840
	11th to 20th	Night	12% 11% 19% 37% 17% 3	840
	21st to end	Night	13% 15% 23% 35% 13% 1	924

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