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 2024-11-10.

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	11% 7% 2 6% 4 4 4 3 5% 7% 46%	100975
	Night	11% 7% 2 6% 4 4 4 3 5% 6% 49%	98249
Transparency	Day	37% 5% 12% 26% 17% 3	104625
	Night	35% 4 11% 26% 20% 4	102739
Seeing	Day	15% 11% 28% 27% 16% 4	15641
	Night	14% 9% 31% 32% 12% 1	25458

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	15% 9% 3 8% 5% 4 4 3 5% 5% 39%	2847
	11th to 20th	Day	11% 10% 4 8% 6% 6% 4 3 4 4 39%	2850
	21st to end	Day	16% 16% 4 6% 4 3 3 2 4 5% 37%	3135
February	1st to 10th	Day	14% 11% 4 7% 5% 3 3 2 4 6% 40%	1710
	11th to 20th	Day	13% 9% 3 7% 5% 4 4 3 4 6% 42%	1664
	21st to end	Day	12% 9% 3 6% 4 4 4 4 6% 7% 41%	1646
March	1st to 10th	Day	14% 9% 3 5% 4 3 3 3 3 5% 48%	3436
	11th to 20th	Day	12% 6% 2 5% 3 3 3 3 5% 6% 53%	3480
	21st to end	Day	15% 12% 3 7% 5% 4 4 4 5% 6% 37%	3814
April	1st to 10th	Day	13% 7% 2 6% 4 4 3 3 5% 6% 45%	2185
	11th to 20th	Day	15% 7% 3 7% 4 4 4 4 5% 7% 41%	2254
	21st to end	Day	20% 8% 3 7% 5% 3 4 3 4 6% 37%	2399
May	1st to 10th	Day	17% 9% 3 7% 4 5% 4 3 5% 6% 37%	4082
	11th to 20th	Day	14% 8% 2 6% 4 4 4 4 6% 8% 40%	4082
	21st to end	Day	12% 6% 3 6% 5% 4 4 4 6% 9% 41%	4477
June	1st to 10th	Day	7% 4 2 5% 4 5% 5% 4 7% 10% 47%	2612
	11th to 20th	Day	7% 5% 2 5% 4 4 5% 4 6% 9% 48%	2660
	21st to end	Day	6% 3 1 4 4 3 4 5% 7% 9% 54%	2532
July	1st to 10th	Day	10% 6% 3 7% 5% 5% 4 4 6% 7% 43%	4120
	11th to 20th	Day	5% 3 2 5% 5% 4 4 4 6% 10% 52%	4120
	21st to end	Day	7% 5% 2 5% 4 5% 6% 5% 8% 9% 44%	4465
August	1st to 10th	Day	5% 3 1 5% 5% 4 5% 4 7% 9% 53%	4104
	11th to 20th	Day	10% 5% 2 6% 4 5% 4 4 6% 8% 46%	4041
	21st to end	Day	5% 3 1 5% 4 4 4 3 6% 8% 57%	4254
September	1st to 10th	Day	12% 5% 2 5% 3 4 2 3 5% 6% 55%	2280
	11th to 20th	Day	9% 4 2 4 4 4 4 4 5% 7% 51%	2094
	21st to end	Day	9% 4 1 6% 3 4 4 3 5% 6% 55%	2083
October	1st to 10th	Day	11% 5% 1 6% 3 3 4 3 5% 6% 54%	1900
	11th to 20th	Day	12% 6% 2 3 3 3 3 3 4 4 58%	1900
	21st to end	Day	16% 7% 2 5% 3 3 3 3 4 4 49%	2090
November	1st to 10th	Day	10% 6% 2 6% 3 3 2 3 5% 6% 55%	1948
	11th to 20th	Day	14% 6% 2 6% 3 2 3 2 5% 6% 51%	1714
	21st to end	Day	15% 8% 2 5% 4 3 2 2 4 5% 49%	1520
December	1st to 10th	Day	10% 8% 3 6% 4 3 4 3 5% 7% 47%	1520
	11th to 20th	Day	14% 8% 4 8% 4 4 3 3 3 4 45%	1918
	21st to end	Day	18% 15% 6% 8% 4 4 4 3 4 5% 28%	3039
January	1st to 10th	Night	10% 9% 4 11% 5% 4 4 3 4 5% 42%	4108
	11th to 20th	Night	10% 7% 4 9% 6% 8% 6% 3 4 5% 38%	4120
	21st to end	Night	19% 11% 4 8% 3 3 4 2 3 6% 37%	4532
February	1st to 10th	Night	12% 11% 3 6% 4 4 4 4 5% 6% 40%	2470
	11th to 20th	Night	12% 9% 2 7% 5% 3 3 4 5% 5% 44%	2403
	21st to end	Night	14% 8% 2 6% 4 3 4 3 4 5% 47%	1821
March	1st to 10th	Night	15% 7% 2 5% 3 3 3 3 4 6% 49%	3419
	11th to 20th	Night	10% 6% 2 4 3 3 3 3 6% 6% 55%	3480
	21st to end	Night	15% 9% 3 7% 5% 4 4 4 4 6% 39%	3817
April	1st to 10th	Night	10% 7% 3 5% 4 4 4 3 6% 6% 50%	1995
	11th to 20th	Night	14% 8% 3 4 4 3 3 3 4 7% 47%	1875
	21st to end	Night	16% 6% 3 7% 4 3 3 4 5% 7% 43%	1779
May	1st to 10th	Night	16% 8% 3 6% 4 4 4 3 5% 6% 41%	2823
	11th to 20th	Night	14% 7% 3 6% 3 4 4 3 5% 8% 43%	2823
	21st to end	Night	11% 6% 2 5% 3 3 3 3 5% 7% 53%	3090
June	1st to 10th	Night	6% 3 1 4 4 3 4 5% 6% 10% 53%	1558
	11th to 20th	Night	4 4 2 5% 3 3 6% 5% 7% 9% 53%	1520
	21st to end	Night	5% 3 2 4 3 3 3 4 5% 8% 60%	1638
July	1st to 10th	Night	11% 5% 2 5% 4 4 4 4 6% 7% 48%	2850
	11th to 20th	Night	4 2 1 4 3 4 4 3 6% 9% 59%	2850
	21st to end	Night	6% 4 1 5% 5% 5% 5% 5% 7% 11% 46%	3098
August	1st to 10th	Night	3 2 1 3 3 3 4 4 7% 10% 61%	2836
	11th to 20th	Night	9% 5% 2 5% 4 4 4 3 5% 7% 51%	2798
	21st to end	Night	4 3 1 4 3 3 4 4 5% 8% 60%	3404
September	1st to 10th	Night	10% 4 2 5% 2 3 3 3 4 5% 58%	1900
	11th to 20th	Night	8% 5% 1 5% 3 4 4 4 5% 7% 54%	2082
	21st to end	Night	7% 4 2 4 3 4 3 3 5% 6% 58%	2090
October	1st to 10th	Night	8% 4 2 4 3 3 4 3 4 6% 59%	2266
	11th to 20th	Night	12% 6% 2 5% 3 3 2 2 4 4 57%	2280
	21st to end	Night	15% 6% 3 5% 3 3 3 2 3 5% 52%	2508
November	1st to 10th	Night	11% 5% 2 3 3 2 2 2 4 5% 60%	2335
	11th to 20th	Night	11% 6% 1 5% 3 3 3 3 5% 6% 53%	2458
	21st to end	Night	16% 8% 2 4 3 2 3 2 3 5% 53%	2660
December	1st to 10th	Night	11% 8% 2 5% 3 4 4 3 5% 7% 47%	2660
	11th to 20th	Night	13% 8% 3 6% 3 4 3 3 5% 6% 46%	3279
	21st to end	Night	19% 16% 5% 8% 4 3 3 3 3 4 32%	4624

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	48% 3 9% 26% 13% 1	2848
	11th to 20th	Day	50% 3 11% 23% 12%	2850
	21st to end	Day	52% 3 10% 19% 16% 1	3135
February	1st to 10th	Day	48% 5% 11% 24% 9% 2	1710
	11th to 20th	Day	44% 3 13% 22% 15% 3	1673
	21st to end	Day	43% 4 9% 24% 15% 5%	1646
March	1st to 10th	Day	41% 3 8% 23% 22% 3	3436
	11th to 20th	Day	34% 4 12% 28% 18% 4	3480
	21st to end	Day	48% 5% 17% 22% 7% 1	3814
April	1st to 10th	Day	40% 5% 12% 24% 17% 2	2185
	11th to 20th	Day	42% 5% 11% 24% 16% 1	2254
	21st to end	Day	49% 4 11% 24% 11% 1	2399
May	1st to 10th	Day	48% 6% 10% 20% 15% 1	4120
	11th to 20th	Day	42% 7% 14% 23% 14%	4086
	21st to end	Day	40% 7% 12% 28% 12% 1	4489
June	1st to 10th	Day	30% 8% 17% 27% 17% 1	2612
	11th to 20th	Day	31% 7% 14% 30% 16% 2	2660
	21st to end	Day	25% 6% 16% 32% 17% 3	2532
July	1st to 10th	Day	39% 6% 12% 22% 17% 3	4056
	11th to 20th	Day	27% 7% 13% 36% 16% 2	4051
	21st to end	Day	30% 9% 20% 28% 12%	4325
August	1st to 10th	Day	27% 7% 15% 29% 21% 2	4090
	11th to 20th	Day	35% 7% 16% 26% 14% 1	4080
	21st to end	Day	25% 6% 13% 38% 14% 4	4253
September	1st to 10th	Day	32% 4 11% 27% 19% 7%	2280
	11th to 20th	Day	31% 5% 10% 26% 25% 2	2094
	21st to end	Day	30% 5% 9% 27% 26% 4	2083
October	1st to 10th	Day	19% 3 6% 22% 41% 9%	3160
	11th to 20th	Day	19% 2 4 27% 39% 9%	3140
	21st to end	Day	32% 4 9% 27% 25% 4	3428
November	1st to 10th	Day	32% 4 11% 29% 20% 4	1948
	11th to 20th	Day	36% 3 9% 26% 22% 4	1714
	21st to end	Day	39% 3 9% 28% 19% 2	1520
December	1st to 10th	Day	38% 4 11% 33% 13% 1	1520
	11th to 20th	Day	45% 3 10% 26% 14% 2	1915
	21st to end	Day	58% 4 11% 19% 7% 2	3039
January	1st to 10th	Night	44% 3 14% 24% 13% 1	4108
	11th to 20th	Night	49% 4 10% 23% 12% 1	4120
	21st to end	Night	50% 4 11% 21% 12% 2	4532
February	1st to 10th	Night	45% 5% 11% 23% 15% 2	2470
	11th to 20th	Night	41% 4 11% 25% 16% 3	2404
	21st to end	Night	41% 3 7% 23% 19% 7%	1821
March	1st to 10th	Night	38% 4 9% 23% 22% 5%	3419
	11th to 20th	Night	31% 4 9% 26% 27% 3	3480
	21st to end	Night	45% 5% 15% 23% 10% 1	3817
April	1st to 10th	Night	35% 5% 10% 22% 24% 5%	1995
	11th to 20th	Night	38% 4 8% 26% 20% 4	1875
	21st to end	Night	43% 4 10% 26% 15% 1	1779
May	1st to 10th	Night	44% 6% 14% 20% 14% 2	2850
	11th to 20th	Night	39% 6% 13% 28% 13% 1	2824
	21st to end	Night	31% 5% 12% 29% 21% 1	3099
June	1st to 10th	Night	25% 6% 18% 31% 17% 4	1558
	11th to 20th	Night	25% 8% 16% 30% 19% 2	1520
	21st to end	Night	22% 4 14% 33% 22% 5%	1638
July	1st to 10th	Night	35% 6% 12% 25% 19% 3	2805
	11th to 20th	Night	20% 7% 13% 37% 22% 3	2796
	21st to end	Night	27% 7% 20% 31% 14% 1	2999
August	1st to 10th	Night	18% 5% 19% 31% 20% 7%	2826
	11th to 20th	Night	32% 6% 12% 28% 20% 1	2825
	21st to end	Night	21% 5% 13% 39% 18% 4	3404
September	1st to 10th	Night	28% 5% 10% 27% 22% 8%	1900
	11th to 20th	Night	29% 5% 10% 25% 26% 5%	2082
	21st to end	Night	26% 4 9% 27% 29% 5%	2090
October	1st to 10th	Night	17% 2 5% 20% 43% 12%	3786
	11th to 20th	Night	22% 3 5% 24% 31% 15%	3779
	21st to end	Night	31% 3 7% 30% 25% 4	4120
November	1st to 10th	Night	28% 4 11% 27% 24% 6%	2335
	11th to 20th	Night	33% 4 8% 25% 26% 4	2458
	21st to end	Night	37% 3 8% 27% 21% 3	2660
December	1st to 10th	Night	38% 5% 12% 27% 17% 1	2660
	11th to 20th	Night	40% 4 8% 29% 17% 2	3281
	21st to end	Night	58% 4 8% 19% 10% 2	4624

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	24% 17% 32% 22% 5%	270
	11th to 20th	Day	30% 18% 35% 15% 1	270
	21st to end	Day	16% 19% 44% 18% 2	297
February	1st to 10th	Day	26% 23% 34% 14% 2 1	270
	11th to 20th	Day	18% 25% 40% 13% 4	270
	21st to end	Day	25% 27% 34% 12% 1	225
March	1st to 10th	Day	23% 18% 41% 15% 2	270
	11th to 20th	Day	25% 20% 32% 19% 4	270
	21st to end	Day	30% 26% 30% 11% 2 1	297
April	1st to 10th	Day	20% 19% 41% 13% 6% 1	365
	11th to 20th	Day	22% 19% 35% 19% 6%	452
	21st to end	Day	22% 16% 33% 22% 5% 1	579
May	1st to 10th	Day	20% 17% 34% 21% 8% 1	653
	11th to 20th	Day	19% 12% 29% 27% 12% 2	675
	21st to end	Day	16% 9% 31% 25% 15% 4	734
June	1st to 10th	Day	7% 5% 21% 38% 23% 7%	680
	11th to 20th	Day	8% 5% 27% 37% 20% 3	680
	21st to end	Day	6% 7% 32% 34% 18% 2	680
July	1st to 10th	Day	9% 4 15% 34% 29% 10%	671
	11th to 20th	Day	5% 2 21% 36% 29% 7%	668
	21st to end	Day	9% 2 15% 33% 33% 8%	739
August	1st to 10th	Day	7% 3 17% 40% 28% 5%	676
	11th to 20th	Day	8% 3 17% 40% 28% 5%	665
	21st to end	Day	8% 2 14% 32% 35% 8%	587
September	1st to 10th	Day	13% 4 14% 33% 29% 7%	490
	11th to 20th	Day	6% 2 23% 40% 24% 6%	304
	21st to end	Day	13% 8% 25% 35% 13% 5%	300
October	1st to 10th	Day	11% 9% 31% 25% 17% 6%	300
	11th to 20th	Day	14% 16% 38% 24% 6% 1	300
	21st to end	Day	23% 18% 32% 22% 5%	330
November	1st to 10th	Day	14% 15% 38% 21% 8% 3	297
	11th to 20th	Day	19% 21% 29% 23% 8% 1	270
	21st to end	Day	24% 16% 32% 22% 6%	270
December	1st to 10th	Day	14% 13% 45% 17% 7% 3	270
	11th to 20th	Day	22% 18% 31% 23% 6%	270
	21st to end	Day	20% 28% 37% 14% 1	297
January	1st to 10th	Night	15% 13% 38% 27% 6%	950
	11th to 20th	Night	17% 14% 39% 24% 5% 1	950
	21st to end	Night	14% 14% 40% 29% 4	1045
February	1st to 10th	Night	18% 15% 40% 23% 3	950
	11th to 20th	Night	19% 14% 39% 26% 2	929
	21st to end	Night	21% 15% 38% 22% 4	565
March	1st to 10th	Night	17% 12% 41% 26% 4	570
	11th to 20th	Night	19% 14% 34% 27% 6% 1	570
	21st to end	Night	23% 13% 35% 25% 3	627
April	1st to 10th	Night	14% 15% 38% 28% 5%	570
	11th to 20th	Night	20% 12% 36% 25% 7%	563
	21st to end	Night	19% 13% 35% 26% 6%	570
May	1st to 10th	Night	18% 8% 36% 30% 8%	570
	11th to 20th	Night	15% 8% 30% 32% 15% 1	561
	21st to end	Night	12% 6% 30% 32% 18% 3	617
June	1st to 10th	Night	5% 4 20% 41% 28% 1	570
	11th to 20th	Night	6% 3 26% 46% 18% 2	570
	21st to end	Night	5% 2 30% 46% 16% 1	570
July	1st to 10th	Night	8% 3 12% 42% 32% 3	555
	11th to 20th	Night	3 2 18% 43% 33% 2	552
	21st to end	Night	7% 2 12% 41% 37% 2	624
August	1st to 10th	Night	5% 2 14% 47% 30% 2	567
	11th to 20th	Night	9% 2 13% 48% 26% 2	564
	21st to end	Night	7% 1 11% 42% 37% 3	627
September	1st to 10th	Night	11% 3 17% 42% 23% 4	570
	11th to 20th	Night	11% 2 20% 37% 26% 4	570
	21st to end	Night	9% 5% 23% 40% 21% 3	570
October	1st to 10th	Night	10% 4 28% 35% 20% 2	746
	11th to 20th	Night	16% 9% 38% 29% 9% 1	760
	21st to end	Night	19% 11% 32% 29% 8% 1	836
November	1st to 10th	Night	13% 10% 35% 30% 11% 1	779
	11th to 20th	Night	14% 14% 36% 27% 9%	926
	21st to end	Night	20% 11% 35% 29% 5%	950
December	1st to 10th	Night	16% 12% 38% 27% 6% 1	950
	11th to 20th	Night	20% 11% 36% 28% 4	950
	21st to end	Night	21% 15% 34% 26% 4	1045

Page generated at 2024-11-07 05:55:44. Version ac07

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