NAA Caton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the NAA Caton 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	13% 9% 3 8% 5% 4 5% 4 6% 7% 37%	126808
	Night	14% 9% 4 7% 5% 4 4 3 5% 6% 39%	123478
Transparency	Day	45% 3 11% 24% 14% 2	130329
	Night	46% 3 11% 23% 15% 2	128031
Seeing	Day	17% 8% 27% 26% 16% 6%	17178
	Night	18% 8% 28% 32% 13% 1	26971

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	12% 11% 6% 13% 7% 6% 5% 4 5% 6% 25%	3617
	11th to 20th	Day	10% 11% 6% 12% 6% 6% 5% 5% 6% 4 29%	3620
	21st to end	Day	15% 16% 6% 10% 5% 3 3 3 4 6% 28%	4184
February	1st to 10th	Day	16% 14% 4 9% 5% 6% 5% 3 5% 5% 26%	1827
	11th to 20th	Day	14% 11% 5% 9% 5% 5% 4 4 4 6% 34%	1948
	21st to end	Day	16% 12% 5% 10% 5% 3 3 3 5% 6% 31%	1650
March	1st to 10th	Day	17% 12% 3 6% 4 3 3 3 3 5% 40%	4480
	11th to 20th	Day	9% 6% 3 7% 5% 4 4 4 6% 8% 43%	4708
	21st to end	Day	19% 12% 6% 12% 5% 5% 4 4 5% 5% 21%	5967
April	1st to 10th	Day	17% 13% 3 9% 4 4 4 3 6% 7% 31%	2400
	11th to 20th	Day	16% 9% 3 7% 5% 4 5% 4 5% 6% 36%	2374
	21st to end	Day	20% 8% 3 7% 5% 5% 5% 3 4 7% 34%	2480
May	1st to 10th	Day	18% 7% 2 6% 5% 5% 5% 4 7% 8% 33%	5862
	11th to 20th	Day	15% 6% 2 6% 4 5% 4 4 6% 8% 41%	6214
	21st to end	Day	14% 6% 3 6% 4 4 5% 4 7% 9% 37%	6935
June	1st to 10th	Day	10% 6% 2 5% 5% 4 4 4 6% 7% 47%	2800
	11th to 20th	Day	9% 6% 2 6% 5% 5% 5% 4 6% 8% 45%	2800
	21st to end	Day	10% 7% 2 6% 5% 6% 5% 5% 7% 8% 39%	2800
July	1st to 10th	Day	9% 6% 2 7% 5% 5% 6% 5% 7% 10% 37%	6360
	11th to 20th	Day	8% 5% 2 6% 5% 4 5% 4 7% 11% 41%	6360
	21st to end	Day	11% 6% 3 7% 6% 5% 5% 5% 7% 8% 38%	6924
August	1st to 10th	Day	7% 5% 2 6% 5% 5% 4 4 7% 11% 44%	4428
	11th to 20th	Day	10% 4 2 6% 4 5% 5% 5% 7% 10% 43%	3849
	21st to end	Day	7% 5% 2 6% 4 4 4 4 6% 10% 48%	4312
September	1st to 10th	Day	10% 6% 2 4 4 4 4 3 5% 7% 50%	2400
	11th to 20th	Day	10% 4 2 4 4 3 4 3 5% 8% 53%	2288
	21st to end	Day	9% 7% 2 7% 4 4 4 4 6% 8% 46%	2200
October	1st to 10th	Day	11% 5% 3 7% 4 4 4 3 4 6% 48%	2125
	11th to 20th	Day	16% 8% 3 7% 4 4 4 3 6% 7% 38%	2000
	21st to end	Day	18% 8% 3 7% 4 3 4 3 5% 7% 37%	1992
November	1st to 10th	Day	12% 9% 2 6% 4 3 4 3 5% 7% 45%	1780
	11th to 20th	Day	16% 11% 4 8% 5% 5% 4 3 5% 6% 33%	1800
	21st to end	Day	19% 11% 3 9% 5% 4 3 3 4 5% 34%	1724
December	1st to 10th	Day	9% 10% 3 8% 5% 4 4 3 5% 6% 44%	2610
	11th to 20th	Day	13% 14% 5% 11% 6% 6% 6% 5% 5% 6% 24%	3008
	21st to end	Day	26% 22% 7% 12% 5% 4 4 2 3 4 11%	3982
January	1st to 10th	Night	13% 13% 6% 12% 5% 4 4 3 4 4 31%	6348
	11th to 20th	Night	12% 15% 6% 12% 7% 6% 5% 4 6% 4 23%	6360
	21st to end	Night	17% 14% 6% 8% 5% 4 3 3 3 4 32%	6790
February	1st to 10th	Night	15% 15% 5% 8% 5% 4 4 3 4 6% 32%	2570
	11th to 20th	Night	14% 11% 4 7% 6% 4 5% 3 4 5% 37%	2338
	21st to end	Night	17% 10% 3 9% 4 3 4 2 5% 5% 37%	1980
March	1st to 10th	Night	17% 10% 4 6% 4 4 3 3 4 5% 41%	5373
	11th to 20th	Night	11% 7% 2 6% 4 4 4 3 5% 6% 47%	5294
	21st to end	Night	18% 10% 5% 10% 5% 5% 4 3 5% 5% 28%	4962
April	1st to 10th	Night	16% 10% 2 7% 5% 4 3 3 5% 6% 39%	2000
	11th to 20th	Night	19% 8% 2 6% 5% 4 3 3 4 6% 40%	1975
	21st to end	Night	17% 7% 3 8% 5% 4 4 4 6% 7% 35%	1920
May	1st to 10th	Night	18% 9% 2 7% 5% 5% 4 3 5% 7% 35%	4033
	11th to 20th	Night	12% 5% 2 6% 4 4 4 4 7% 8% 44%	3694
	21st to end	Night	13% 8% 3 6% 4 5% 4 4 6% 7% 39%	3942
June	1st to 10th	Night	10% 5% 2 5% 4 4 4 3 6% 7% 51%	1600
	11th to 20th	Night	9% 5% 2 6% 4 5% 5% 4 7% 9% 46%	1600
	21st to end	Night	9% 5% 2 7% 6% 5% 4 5% 6% 7% 44%	1600
July	1st to 10th	Night	10% 5% 2 7% 5% 5% 5% 4 7% 9% 40%	3618
	11th to 20th	Night	7% 5% 2 6% 4 4 4 4 6% 8% 50%	3617
	21st to end	Night	8% 6% 2 7% 5% 5% 5% 4 7% 8% 43%	3947
August	1st to 10th	Night	5% 4 2 6% 4 5% 5% 5% 7% 9% 48%	2710
	11th to 20th	Night	8% 4 2 6% 4 3 5% 5% 6% 9% 50%	3200
	21st to end	Night	8% 4 1 5% 3 3 4 3 6% 9% 53%	3586
September	1st to 10th	Night	9% 5% 3 5% 3 2 3 2 4 7% 56%	2000
	11th to 20th	Night	8% 4 1 4 3 3 3 4 6% 7% 56%	2091
	21st to end	Night	9% 4 2 7% 4 5% 4 4 6% 8% 47%	2200
October	1st to 10th	Night	10% 4 2 5% 4 3 3 3 5% 7% 53%	2272
	11th to 20th	Night	17% 6% 2 5% 3 3 3 3 5% 6% 46%	2400
	21st to end	Night	19% 8% 3 6% 4 3 3 3 4 7% 39%	2846
November	1st to 10th	Night	13% 7% 2 6% 4 2 3 3 5% 6% 49%	2563
	11th to 20th	Night	16% 8% 3 8% 5% 4 4 3 6% 6% 37%	2600
	21st to end	Night	17% 10% 3 7% 5% 4 4 2 5% 5% 37%	2674
December	1st to 10th	Night	12% 8% 3 7% 3 4 4 3 4 6% 43%	4580
	11th to 20th	Night	17% 13% 4 9% 6% 4 4 3 4 5% 32%	5199
	21st to end	Night	24% 18% 6% 10% 5% 4 5% 3 4 5% 16%	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	60% 2 12% 18% 7%	3618
	11th to 20th	Day	56% 3 9% 11% 16% 5%	3620
	21st to end	Day	59% 2 12% 19% 8%	4184
February	1st to 10th	Day	60% 3 10% 17% 9% 2	1827
	11th to 20th	Day	52% 3 11% 24% 9% 2	1958
	21st to end	Day	54% 2 11% 22% 9% 2	1650
March	1st to 10th	Day	50% 1 8% 26% 13% 3	4480
	11th to 20th	Day	40% 2 11% 35% 12% 1	4708
	21st to end	Day	64% 3 11% 15% 7% 1	5969
April	1st to 10th	Day	53% 3 10% 22% 11%	2400
	11th to 20th	Day	48% 3 10% 23% 12% 3	2374
	21st to end	Day	52% 3 12% 19% 13% 2	2480
May	1st to 10th	Day	48% 3 10% 23% 14% 1	5897
	11th to 20th	Day	43% 3 10% 27% 15% 2	6218
	21st to end	Day	42% 3 10% 26% 14% 4	6949
June	1st to 10th	Day	37% 3 11% 29% 18% 2	2800
	11th to 20th	Day	36% 4 10% 25% 20% 3	2800
	21st to end	Day	42% 5% 13% 23% 16% 3	2800
July	1st to 10th	Day	39% 5% 13% 26% 15% 1	6291
	11th to 20th	Day	36% 5% 15% 29% 14% 1	6285
	21st to end	Day	41% 5% 17% 21% 14% 2	6728
August	1st to 10th	Day	34% 4 17% 31% 13% 1	4413
	11th to 20th	Day	34% 5% 12% 33% 15%	3885
	21st to end	Day	32% 5% 11% 32% 18% 2	4311
September	1st to 10th	Day	34% 3 11% 28% 19% 5%	2400
	11th to 20th	Day	30% 2 11% 31% 23% 3	2288
	21st to end	Day	36% 3 9% 28% 22% 2	2200
October	1st to 10th	Day	27% 2 7% 29% 33% 2	3463
	11th to 20th	Day	31% 2 12% 26% 27% 1	3240
	21st to end	Day	41% 3 9% 28% 16% 3	3192
November	1st to 10th	Day	41% 2 14% 26% 16% 2	1780
	11th to 20th	Day	53% 2 10% 23% 11% 1	1800
	21st to end	Day	54% 2 10% 23% 10%	1724
December	1st to 10th	Day	42% 2 15% 31% 9%	2610
	11th to 20th	Day	61% 3 12% 17% 6% 1	3005
	21st to end	Day	80% 2 6% 8% 4	3982
January	1st to 10th	Night	58% 2 9% 20% 11%	6348
	11th to 20th	Night	64% 2 10% 10% 13% 1	6360
	21st to end	Night	58% 2 11% 18% 11% 1	6790
February	1st to 10th	Night	56% 2 10% 19% 11% 2	2570
	11th to 20th	Night	50% 3 9% 24% 13% 1	2339
	21st to end	Night	51% 2 11% 20% 13% 3	1980
March	1st to 10th	Night	47% 2 10% 25% 11% 5%	5373
	11th to 20th	Night	39% 3 10% 30% 15% 3	5294
	21st to end	Night	59% 2 9% 21% 8% 1	4962
April	1st to 10th	Night	46% 3 10% 25% 14% 2	2000
	11th to 20th	Night	46% 2 8% 22% 17% 4	1975
	21st to end	Night	48% 4 10% 23% 13% 3	1920
May	1st to 10th	Night	50% 2 11% 19% 15% 4	4060
	11th to 20th	Night	38% 4 13% 28% 13% 4	3695
	21st to end	Night	44% 3 10% 24% 16% 3	3950
June	1st to 10th	Night	33% 3 13% 28% 20% 4	1600
	11th to 20th	Night	35% 3 11% 26% 22% 3	1600
	21st to end	Night	38% 5% 15% 22% 17% 3	1600
July	1st to 10th	Night	40% 4 14% 24% 16% 3	3580
	11th to 20th	Night	31% 5% 14% 28% 20% 1	3572
	21st to end	Night	37% 6% 15% 22% 17% 3	3832
August	1st to 10th	Night	30% 6% 17% 28% 18% 1	2701
	11th to 20th	Night	29% 5% 16% 30% 19% 1	3230
	21st to end	Night	28% 4 12% 34% 19% 3	3586
September	1st to 10th	Night	30% 3 10% 29% 24% 4	2000
	11th to 20th	Night	28% 2 7% 33% 26% 3	2091
	21st to end	Night	36% 4 10% 28% 19% 3	2200
October	1st to 10th	Night	22% 2 7% 36% 30% 3	3714
	11th to 20th	Night	34% 2 7% 25% 31% 2	3899
	21st to end	Night	40% 2 9% 26% 20% 3	4596
November	1st to 10th	Night	38% 3 9% 28% 19% 4	2563
	11th to 20th	Night	47% 2 12% 23% 14% 2	2600
	21st to end	Night	50% 2 11% 25% 12% 1	2674
December	1st to 10th	Night	43% 2 14% 29% 11% 1	4580
	11th to 20th	Night	56% 2 12% 18% 11% 1	5201
	21st to end	Night	73% 2 8% 12% 6%	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	21% 8% 34% 27% 9% 1	300
	11th to 20th	Day	21% 13% 37% 22% 6% 1	300
	21st to end	Day	25% 14% 27% 27% 6% 1	330
February	1st to 10th	Day	20% 18% 35% 22% 5%	300
	11th to 20th	Day	22% 16% 36% 20% 6%	300
	21st to end	Day	23% 11% 44% 16% 5%	249
March	1st to 10th	Day	25% 17% 34% 21% 3	300
	11th to 20th	Day	24% 17% 33% 18% 7% 1	309
	21st to end	Day	28% 12% 32% 20% 7% 2	550
April	1st to 10th	Day	25% 11% 31% 24% 7% 1	500
	11th to 20th	Day	22% 17% 28% 21% 10% 3	492
	21st to end	Day	24% 11% 30% 24% 9% 2	500
May	1st to 10th	Day	21% 10% 28% 28% 11% 3	503
	11th to 20th	Day	21% 8% 27% 27% 13% 4	672
	21st to end	Day	15% 5% 32% 23% 17% 8%	789
June	1st to 10th	Day	12% 8% 26% 28% 20% 6%	730
	11th to 20th	Day	12% 5% 27% 31% 20% 5%	730
	21st to end	Day	14% 5% 30% 29% 16% 5%	730
July	1st to 10th	Day	11% 3 16% 30% 24% 16%	721
	11th to 20th	Day	13% 4 20% 31% 22% 11%	718
	21st to end	Day	8% 3 20% 35% 26% 8%	794
August	1st to 10th	Day	7% 2 15% 35% 29% 13%	685
	11th to 20th	Day	13% 3 16% 26% 28% 14%	519
	21st to end	Day	7% 1 16% 32% 29% 14%	583
September	1st to 10th	Day	12% 4 19% 28% 28% 9%	530
	11th to 20th	Day	11% 1 14% 29% 30% 15%	530
	21st to end	Day	15% 5% 24% 25% 22% 9%	530
October	1st to 10th	Day	14% 4 25% 32% 20% 6%	455
	11th to 20th	Day	16% 17% 31% 25% 10% 1	330
	21st to end	Day	27% 11% 34% 20% 7% 1	363
November	1st to 10th	Day	16% 11% 35% 23% 10% 4	306
	11th to 20th	Day	22% 13% 36% 20% 7% 2	300
	21st to end	Day	26% 9% 32% 24% 8%	300
December	1st to 10th	Day	18% 12% 40% 21% 8% 1	300
	11th to 20th	Day	19% 12% 38% 23% 7%	300
	21st to end	Day	32% 14% 33% 18% 3	330
January	1st to 10th	Night	22% 12% 36% 25% 5%	1000
	11th to 20th	Night	22% 12% 36% 24% 5% 1	1000
	21st to end	Night	21% 11% 32% 31% 4	1100
February	1st to 10th	Night	23% 10% 36% 26% 4 1	970
	11th to 20th	Night	21% 11% 35% 28% 5%	783
	21st to end	Night	23% 10% 38% 25% 3	660
March	1st to 10th	Night	21% 13% 35% 26% 6%	800
	11th to 20th	Night	18% 11% 34% 31% 6% 1	755
	21st to end	Night	25% 9% 34% 24% 7% 1	660
April	1st to 10th	Night	20% 10% 36% 27% 7%	600
	11th to 20th	Night	22% 11% 32% 29% 7%	593
	21st to end	Night	22% 8% 32% 30% 8%	600
May	1st to 10th	Night	21% 4 35% 32% 9%	600
	11th to 20th	Night	19% 5% 27% 36% 12% 1	591
	21st to end	Night	14% 5% 24% 40% 16% 1	650
June	1st to 10th	Night	12% 2 25% 45% 15%	600
	11th to 20th	Night	12% 3 25% 47% 13% 1	600
	21st to end	Night	10% 4 26% 40% 19% 2	600
July	1st to 10th	Night	10% 2 13% 42% 29% 4	585
	11th to 20th	Night	8% 2 17% 41% 28% 3	582
	21st to end	Night	6% 2 12% 48% 30% 3	657
August	1st to 10th	Night	5% 1 9% 48% 32% 5%	597
	11th to 20th	Night	8% 2 10% 42% 34% 4	594
	21st to end	Night	8% 1 14% 42% 33% 3	660
September	1st to 10th	Night	11% 2 16% 38% 30% 3	600
	11th to 20th	Night	10% 2 15% 37% 31% 4	691
	21st to end	Night	13% 5% 22% 36% 23% 2	800
October	1st to 10th	Night	13% 5% 24% 38% 20% 1	800
	11th to 20th	Night	21% 10% 27% 31% 11%	800
	21st to end	Night	24% 10% 31% 28% 8%	880
November	1st to 10th	Night	16% 10% 35% 27% 11% 1	789
	11th to 20th	Night	21% 12% 32% 27% 7% 1	800
	21st to end	Night	21% 11% 35% 28% 6%	874
December	1st to 10th	Night	22% 9% 35% 27% 6%	1000
	11th to 20th	Night	23% 10% 32% 28% 7%	1000
	21st to end	Night	29% 12% 31% 25% 3	1100

Page generated at 2025-10-31 01:02:37. Version ac07

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