Land of Oz Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Land of Oz Observatory clear sky chart from 2005-11-06 to 2025-12-03.

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	12% 7% 2 6% 4 4 4 3 5% 7% 46%	126506
	Night	12% 7% 2 6% 3 3 4 3 5% 6% 49%	124435
Transparency	Day	37% 5% 12% 26% 17% 3	130117
	Night	35% 4 11% 26% 19% 4	128900
Seeing	Day	15% 11% 28% 27% 15% 3	17083
	Night	15% 9% 31% 32% 12% 1	26912

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	18% 9% 3 8% 5% 4 4 3 4 5% 38%	4077
	11th to 20th	Day	8% 9% 4 9% 6% 6% 5% 3 5% 5% 41%	4080
	21st to end	Day	14% 13% 3 6% 4 4 4 3 4 6% 41%	4488
February	1st to 10th	Day	15% 11% 4 7% 5% 3 3 2 5% 7% 39%	1800
	11th to 20th	Day	14% 9% 3 8% 5% 4 4 3 4 6% 42%	1754
	21st to end	Day	12% 9% 3 6% 4 4 4 4 6% 7% 42%	1730
March	1st to 10th	Day	12% 8% 3 5% 4 3 3 3 4 5% 51%	4936
	11th to 20th	Day	10% 6% 2 4 3 3 3 3 5% 6% 56%	4980
	21st to end	Day	13% 10% 3 8% 5% 5% 4 4 5% 7% 36%	5462
April	1st to 10th	Day	14% 7% 3 6% 4 4 3 3 5% 6% 45%	2300
	11th to 20th	Day	15% 7% 3 7% 4 4 4 4 5% 7% 41%	2374
	21st to end	Day	20% 8% 3 7% 5% 4 4 3 4 6% 37%	2525
May	1st to 10th	Day	17% 7% 3 6% 4 4 4 3 5% 6% 41%	5862
	11th to 20th	Day	13% 7% 2 5% 4 4 4 4 6% 7% 44%	5862
	21st to end	Day	19% 5% 2 5% 4 4 4 4 6% 8% 39%	6434
June	1st to 10th	Day	7% 4 2 5% 4 5% 5% 4 7% 10% 47%	2750
	11th to 20th	Day	7% 6% 1 5% 4 4 5% 4 6% 9% 48%	2800
	21st to end	Day	6% 3 1 4 4 3 4 5% 7% 9% 54%	2665
July	1st to 10th	Day	8% 5% 2 6% 4 5% 4 4 6% 8% 46%	5900
	11th to 20th	Day	8% 4 2 5% 4 4 5% 4 6% 11% 47%	5900
	21st to end	Day	7% 5% 2 6% 5% 5% 6% 5% 8% 10% 43%	6422
August	1st to 10th	Day	5% 3 1 5% 5% 4 4 4 7% 9% 53%	4234
	11th to 20th	Day	9% 5% 2 6% 4 5% 4 4 6% 8% 47%	4171
	21st to end	Day	5% 4 1 5% 4 4 4 3 6% 8% 56%	4388
September	1st to 10th	Day	12% 5% 2 5% 3 4 2 3 5% 6% 54%	2400
	11th to 20th	Day	9% 4 2 5% 4 4 4 4 6% 8% 50%	2204
	21st to end	Day	9% 5% 1 6% 3 4 4 3 5% 6% 55%	2192
October	1st to 10th	Day	11% 5% 1 6% 3 3 4 3 5% 6% 54%	2000
	11th to 20th	Day	12% 6% 2 3 3 3 3 3 4 5% 57%	2000
	21st to end	Day	18% 7% 2 5% 3 3 3 3 4 4 49%	2200
November	1st to 10th	Day	10% 6% 2 6% 3 3 2 3 5% 6% 56%	2058
	11th to 20th	Day	14% 6% 2 6% 3 2 3 2 5% 6% 51%	1894
	21st to end	Day	15% 8% 2 6% 3 3 2 2 4 5% 48%	1680
December	1st to 10th	Day	7% 7% 3 5% 3 3 4 3 5% 5% 55%	2626
	11th to 20th	Day	12% 6% 3 6% 4 4 3 2 3 5% 52%	3008
	21st to end	Day	21% 18% 6% 8% 4 4 4 2 3 4 26%	4350
January	1st to 10th	Night	14% 9% 4 11% 5% 4 4 3 4 5% 38%	5888
	11th to 20th	Night	10% 7% 3 9% 5% 7% 4 2 4 4 43%	5900
	21st to end	Night	16% 8% 3 7% 3 3 4 3 4 5% 44%	6490
February	1st to 10th	Night	12% 11% 3 6% 4 4 4 4 6% 6% 40%	2600
	11th to 20th	Night	13% 9% 2 7% 5% 3 3 4 5% 5% 43%	2533
	21st to end	Night	13% 8% 2 6% 4 3 4 3 4 5% 48%	1913
March	1st to 10th	Night	15% 8% 3 4 3 3 3 3 4 5% 50%	4919
	11th to 20th	Night	8% 6% 2 3 3 3 3 3 6% 7% 58%	4980
	21st to end	Night	14% 7% 3 6% 4 4 4 4 5% 7% 42%	5467
April	1st to 10th	Night	11% 7% 3 5% 3 4 4 3 6% 6% 49%	2100
	11th to 20th	Night	14% 8% 2 4 4 3 3 3 4 6% 47%	1975
	21st to end	Night	16% 6% 3 7% 3 3 3 4 5% 7% 42%	1872
May	1st to 10th	Night	17% 7% 2 5% 4 3 3 3 4 6% 45%	4053
	11th to 20th	Night	13% 6% 3 5% 3 3 3 3 5% 8% 48%	4053
	21st to end	Night	18% 6% 2 4 3 2 2 3 4 6% 50%	4443
June	1st to 10th	Night	6% 3 1 4 4 3 4 5% 6% 10% 53%	1640
	11th to 20th	Night	5% 4 2 5% 3 3 5% 5% 7% 9% 52%	1600
	21st to end	Night	4 3 2 4 2 3 3 4 6% 8% 60%	1725
July	1st to 10th	Night	9% 5% 2 5% 4 4 4 4 6% 9% 50%	4078
	11th to 20th	Night	6% 3 1 5% 4 4 4 3 7% 9% 54%	4077
	21st to end	Night	7% 4 1 5% 5% 5% 5% 5% 8% 11% 44%	4449
August	1st to 10th	Night	3 2 1 3 3 3 4 4 6% 10% 62%	2926
	11th to 20th	Night	9% 5% 2 5% 4 4 4 3 5% 7% 52%	2888
	21st to end	Night	4 3 1 4 3 3 4 4 5% 8% 60%	3512
September	1st to 10th	Night	10% 5% 2 5% 2 3 3 3 4 5% 57%	2000
	11th to 20th	Night	8% 5% 1 5% 3 4 4 4 6% 7% 53%	2192
	21st to end	Night	7% 4 2 4 3 4 4 3 5% 6% 58%	2200
October	1st to 10th	Night	8% 4 2 4 3 3 4 3 4 6% 60%	2386
	11th to 20th	Night	12% 6% 2 5% 3 3 2 2 4 5% 56%	2400
	21st to end	Night	17% 6% 3 5% 3 3 2 2 3 5% 52%	2640
November	1st to 10th	Night	11% 5% 2 3 3 2 2 2 4 5% 60%	2460
	11th to 20th	Night	11% 6% 2 5% 3 3 3 3 4 6% 54%	2718
	21st to end	Night	16% 8% 2 5% 3 2 3 2 3 5% 52%	2940
December	1st to 10th	Night	8% 6% 2 4 3 3 3 3 5% 6% 57%	4609
	11th to 20th	Night	14% 7% 3 5% 3 4 3 3 5% 6% 47%	5199
	21st to end	Night	20% 17% 4 8% 4 3 3 2 3 4 31%	6610

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	49% 3 10% 24% 12% 1	4078
	11th to 20th	Day	46% 4 9% 22% 16% 3	4080
	21st to end	Day	46% 3 10% 19% 16% 6%	4488
February	1st to 10th	Day	48% 5% 11% 24% 9% 2	1800
	11th to 20th	Day	45% 4 12% 21% 15% 3	1763
	21st to end	Day	42% 3 9% 25% 16% 5%	1730
March	1st to 10th	Day	38% 3 7% 22% 23% 7%	4936
	11th to 20th	Day	30% 3 9% 22% 26% 9%	4980
	21st to end	Day	47% 6% 15% 25% 6% 1	5464
April	1st to 10th	Day	41% 5% 11% 24% 17% 3	2300
	11th to 20th	Day	43% 5% 11% 24% 16% 1	2374
	21st to end	Day	49% 4 11% 24% 11% 1	2525
May	1st to 10th	Day	44% 6% 11% 22% 17% 1	5900
	11th to 20th	Day	38% 6% 13% 23% 17% 3	5866
	21st to end	Day	43% 6% 11% 26% 13% 1	6447
June	1st to 10th	Day	30% 8% 17% 26% 17% 1	2750
	11th to 20th	Day	32% 7% 14% 30% 16% 2	2800
	21st to end	Day	25% 6% 16% 32% 18% 3	2665
July	1st to 10th	Day	35% 6% 12% 24% 20% 2	5836
	11th to 20th	Day	32% 7% 13% 33% 14% 1	5831
	21st to end	Day	31% 8% 19% 31% 11%	6240
August	1st to 10th	Day	26% 7% 15% 29% 21% 2	4220
	11th to 20th	Day	35% 7% 16% 27% 14% 1	4210
	21st to end	Day	26% 6% 13% 37% 14% 4	4387
September	1st to 10th	Day	33% 4 12% 27% 18% 7%	2400
	11th to 20th	Day	32% 5% 11% 26% 24% 2	2204
	21st to end	Day	30% 5% 9% 27% 26% 4	2192
October	1st to 10th	Day	19% 2 6% 22% 41% 9%	3260
	11th to 20th	Day	20% 2 4 27% 38% 8%	3240
	21st to end	Day	33% 4 8% 26% 25% 4	3538
November	1st to 10th	Day	31% 4 11% 30% 20% 4	2058
	11th to 20th	Day	36% 3 8% 27% 21% 5%	1894
	21st to end	Day	40% 3 9% 28% 18% 1	1680
December	1st to 10th	Day	31% 3 10% 38% 17% 1	2626
	11th to 20th	Day	38% 3 9% 32% 17% 2	3005
	21st to end	Day	62% 3 10% 18% 6% 1	4350
January	1st to 10th	Night	49% 3 12% 22% 12% 1	5888
	11th to 20th	Night	45% 4 8% 23% 16% 4	5900
	21st to end	Night	43% 4 9% 20% 17% 6%	6490
February	1st to 10th	Night	45% 5% 11% 23% 15% 2	2600
	11th to 20th	Night	43% 4 11% 24% 16% 3	2534
	21st to end	Night	40% 3 7% 24% 19% 7%	1913
March	1st to 10th	Night	39% 3 7% 21% 24% 5%	4919
	11th to 20th	Night	28% 3 7% 22% 33% 7%	4980
	21st to end	Night	41% 6% 15% 25% 12% 2	5467
April	1st to 10th	Night	35% 5% 10% 22% 23% 4	2100
	11th to 20th	Night	38% 4 8% 26% 20% 5%	1975
	21st to end	Night	43% 5% 11% 26% 15% 1	1872
May	1st to 10th	Night	41% 5% 13% 24% 14% 2	4080
	11th to 20th	Night	36% 5% 12% 24% 16% 6%	4054
	21st to end	Night	36% 5% 10% 27% 20% 2	4452
June	1st to 10th	Night	26% 6% 17% 30% 18% 3	1640
	11th to 20th	Night	26% 8% 15% 29% 20% 2	1600
	21st to end	Night	22% 4 15% 32% 22% 5%	1725
July	1st to 10th	Night	31% 6% 13% 25% 22% 3	4035
	11th to 20th	Night	25% 7% 13% 36% 17% 2	4026
	21st to end	Night	28% 7% 17% 35% 12% 1	4320
August	1st to 10th	Night	17% 5% 19% 32% 20% 7%	2916
	11th to 20th	Night	32% 6% 12% 29% 20% 1	2915
	21st to end	Night	21% 6% 13% 39% 18% 4	3512
September	1st to 10th	Night	29% 5% 10% 27% 21% 8%	2000
	11th to 20th	Night	30% 5% 11% 25% 24% 5%	2192
	21st to end	Night	26% 4 9% 26% 29% 5%	2200
October	1st to 10th	Night	17% 3 5% 20% 43% 12%	3906
	11th to 20th	Night	23% 3 5% 24% 31% 14%	3899
	21st to end	Night	32% 3 7% 30% 25% 4	4252
November	1st to 10th	Night	28% 4 11% 28% 24% 6%	2460
	11th to 20th	Night	32% 3 8% 26% 26% 4	2718
	21st to end	Night	38% 3 8% 28% 20% 3	2940
December	1st to 10th	Night	29% 4 13% 36% 17% 1	4609
	11th to 20th	Night	39% 4 9% 28% 18% 2	5201
	21st to end	Night	60% 3 9% 20% 7% 1	6610

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% 16% 33% 22% 4	300
	11th to 20th	Day	28% 19% 37% 14% 2	300
	21st to end	Day	17% 18% 44% 18% 2	330
February	1st to 10th	Day	25% 24% 34% 14% 2 1	300
	11th to 20th	Day	20% 26% 38% 13% 4	300
	21st to end	Day	23% 26% 38% 11% 2	249
March	1st to 10th	Day	23% 18% 40% 16% 3	300
	11th to 20th	Day	26% 19% 32% 18% 4 1	300
	21st to end	Day	28% 26% 33% 10% 2 1	330
April	1st to 10th	Day	23% 19% 39% 14% 5% 1	400
	11th to 20th	Day	23% 20% 34% 18% 5%	492
	21st to end	Day	23% 16% 33% 22% 5% 1	625
May	1st to 10th	Day	19% 16% 34% 22% 8% 1	703
	11th to 20th	Day	19% 13% 29% 25% 12% 2	725
	21st to end	Day	17% 9% 31% 25% 14% 4	789
June	1st to 10th	Day	8% 5% 22% 37% 22% 7%	730
	11th to 20th	Day	8% 5% 27% 37% 20% 3	730
	21st to end	Day	6% 7% 33% 34% 18% 2	730
July	1st to 10th	Day	9% 4 15% 35% 28% 9%	721
	11th to 20th	Day	6% 2 21% 36% 28% 7%	718
	21st to end	Day	9% 2 15% 34% 32% 8%	794
August	1st to 10th	Day	6% 3 19% 40% 26% 5%	726
	11th to 20th	Day	7% 3 16% 39% 29% 5%	715
	21st to end	Day	9% 2 14% 33% 34% 8%	633
September	1st to 10th	Day	13% 3 14% 36% 28% 7%	530
	11th to 20th	Day	6% 2 22% 40% 23% 6%	334
	21st to end	Day	14% 7% 23% 35% 16% 6%	330
October	1st to 10th	Day	12% 8% 31% 26% 17% 5%	330
	11th to 20th	Day	15% 15% 38% 25% 7% 1	330
	21st to end	Day	26% 17% 31% 21% 4	363
November	1st to 10th	Day	14% 16% 40% 20% 7% 3	330
	11th to 20th	Day	19% 19% 31% 22% 8% 1	330
	21st to end	Day	24% 16% 31% 22% 5%	330
December	1st to 10th	Day	14% 14% 44% 18% 7% 3	306
	11th to 20th	Day	21% 18% 34% 22% 5%	300
	21st to end	Day	22% 25% 36% 15% 1	330
January	1st to 10th	Night	16% 13% 38% 26% 6%	1000
	11th to 20th	Night	17% 14% 39% 25% 5% 1	1000
	21st to end	Night	14% 14% 41% 28% 3	1100
February	1st to 10th	Night	18% 15% 40% 23% 3	1000
	11th to 20th	Night	20% 15% 38% 26% 2	979
	21st to end	Night	20% 15% 38% 24% 3	593
March	1st to 10th	Night	17% 12% 41% 26% 4	600
	11th to 20th	Night	19% 13% 35% 26% 6% 1	600
	21st to end	Night	23% 13% 37% 24% 3	660
April	1st to 10th	Night	15% 14% 37% 28% 5%	600
	11th to 20th	Night	20% 13% 36% 25% 6%	593
	21st to end	Night	19% 13% 35% 27% 6%	600
May	1st to 10th	Night	18% 8% 35% 31% 9%	600
	11th to 20th	Night	15% 8% 30% 31% 15% 1	591
	21st to end	Night	13% 5% 30% 31% 17% 3	650
June	1st to 10th	Night	6% 3 21% 42% 28% 1	600
	11th to 20th	Night	7% 3 25% 46% 18% 2	600
	21st to end	Night	5% 2 30% 46% 16% 1	600
July	1st to 10th	Night	8% 3 12% 42% 32% 4	585
	11th to 20th	Night	3 2 18% 43% 32% 2	582
	21st to end	Night	7% 2 12% 42% 36% 2	657
August	1st to 10th	Night	4 2 15% 48% 29% 2	597
	11th to 20th	Night	8% 2 12% 47% 28% 3	594
	21st to end	Night	7% 1 12% 42% 36% 3	660
September	1st to 10th	Night	12% 3 17% 42% 23% 4	600
	11th to 20th	Night	10% 2 20% 38% 27% 4	600
	21st to end	Night	9% 5% 22% 40% 22% 3	600
October	1st to 10th	Night	10% 4 28% 36% 20% 2	786
	11th to 20th	Night	16% 9% 38% 29% 9% 1	800
	21st to end	Night	20% 11% 33% 28% 8% 1	880
November	1st to 10th	Night	13% 10% 36% 30% 10% 1	820
	11th to 20th	Night	14% 14% 37% 28% 8%	1024
	21st to end	Night	20% 12% 35% 28% 5%	1050
December	1st to 10th	Night	16% 12% 38% 28% 6% 1	1011
	11th to 20th	Night	21% 11% 36% 27% 5%	1000
	21st to end	Night	22% 15% 33% 27% 4	1100

Page generated at 2025-11-30 00:00:57. Version ac07

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