Matilda's observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Matilda's observatory clear sky chart from 2005-11-06 to 2025-02-06.

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 5% 4 4 4 4 6% 8% 56%	112405
	Night	2 5% 2 5% 3 3 4 3 5% 7% 59%	114718
Transparency	Day	13% 46% 7% 14% 15% 5%	112158
	Night	14% 44% 7% 15% 16% 5%	114555
Seeing	Day	9% 23% 29% 24% 12% 2	15621
	Night	6% 18% 32% 29% 14% 2	25810

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	4 3 9% 5% 4 4 3 5% 6% 58%	3661
	11th to 20th	Day	3 2 8% 4 3 3 3 4 7% 61%	4100
	21st to end	Day	1 4 3 6% 3 4 4 3 5% 6% 61%	4510
February	1st to 10th	Day	6% 2 7% 3 3 3 3 5% 6% 61%	1778
	11th to 20th	Day	1 4 2 5% 4 3 3 3 6% 8% 61%	1849
	21st to end	Day	1 9% 4 6% 3 3 4 3 4 7% 56%	1570
March	1st to 10th	Day	1 5% 3 6% 3 3 3 3 5% 7% 62%	3180
	11th to 20th	Day	1 7% 3 8% 5% 5% 5% 4 6% 8% 46%	3490
	21st to end	Day	1 8% 4 7% 4 4 3 3 5% 6% 53%	4023
April	1st to 10th	Day	2 6% 3 6% 4 4 4 3 6% 9% 54%	2280
	11th to 20th	Day	3 8% 3 5% 3 4 4 4 6% 7% 53%	2251
	21st to end	Day	4 8% 2 5% 4 4 4 4 6% 8% 51%	2280
May	1st to 10th	Day	2 6% 2 5% 3 3 4 3 4 7% 60%	3800
	11th to 20th	Day	3 6% 2 5% 5% 5% 5% 4 7% 8% 49%	4214
	21st to end	Day	2 3 2 4 3 3 4 3 6% 7% 63%	4825
June	1st to 10th	Day	3 3 2 3 3 3 5% 4 8% 10% 57%	2660
	11th to 20th	Day	3 2 1 3 3 4 4 4 6% 7% 64%	2660
	21st to end	Day	3 3 2 5% 5% 4 6% 5% 8% 10% 50%	2660
July	1st to 10th	Day	2 3 1 5% 4 4 5% 4 7% 8% 57%	4430
	11th to 20th	Day	2 2 1 5% 5% 6% 7% 7% 10% 13% 43%	4377
	21st to end	Day	3 4 2 5% 5% 6% 8% 7% 10% 10% 40%	4454
August	1st to 10th	Day	5% 4 2 6% 6% 7% 8% 7% 10% 11% 35%	4000
	11th to 20th	Day	3 3 1 4 3 4 6% 5% 8% 10% 52%	3726
	21st to end	Day	3 4 1 5% 5% 6% 8% 7% 10% 12% 38%	4180
September	1st to 10th	Day	5% 4 1 5% 5% 4 6% 4 6% 8% 51%	2280
	11th to 20th	Day	5% 3 2 4 4 3 5% 3 5% 6% 59%	2271
	21st to end	Day	3 3 1 4 3 3 3 3 5% 7% 65%	2090
October	1st to 10th	Day	3 3 1 3 2 2 2 2 4 5% 73%	3175
	11th to 20th	Day	3 3 2 3 3 5% 4 4 6% 7% 62%	3150
	21st to end	Day	2 3 1 3 2 2 2 2 4 4 74%	3438
November	1st to 10th	Day	1 3 1 4 3 2 2 3 4 8% 69%	1788
	11th to 20th	Day	1 4 2 3 2 2 2 2 3 7% 71%	1800
	21st to end	Day	2 5% 2 5% 3 2 3 3 4 6% 64%	1800
December	1st to 10th	Day	1 3 1 4 2 2 2 2 3 7% 75%	2625
	11th to 20th	Day	3 1 3 3 3 3 3 7% 10% 63%	3026
	21st to end	Day	4 2 5% 4 3 3 3 6% 8% 62%	4004
January	1st to 10th	Night	5% 3 9% 4 3 3 3 4 7% 57%	6327
	11th to 20th	Night	1 3 2 7% 4 3 3 3 4 7% 62%	5898
	21st to end	Night	1 5% 3 6% 4 3 3 3 5% 7% 61%	6468
February	1st to 10th	Night	1 6% 3 7% 4 3 2 2 3 7% 61%	2509
	11th to 20th	Night	1 7% 3 6% 3 3 3 3 5% 7% 59%	2218
	21st to end	Night	1 9% 4 6% 4 3 2 3 4 6% 58%	1884
March	1st to 10th	Night	2 6% 3 6% 3 3 3 3 4 6% 62%	3683
	11th to 20th	Night	2 9% 3 7% 4 4 4 3 5% 7% 51%	3490
	21st to end	Night	3 12% 4 6% 3 3 3 2 3 5% 55%	3621
April	1st to 10th	Night	3 7% 2 4 3 3 3 3 5% 7% 60%	1900
	11th to 20th	Night	2 8% 2 5% 3 3 3 4 6% 8% 56%	1877
	21st to end	Night	5% 9% 3 5% 3 3 4 3 5% 7% 54%	1900
May	1st to 10th	Night	4 7% 1 3 3 3 3 2 3 6% 65%	3170
	11th to 20th	Night	4 5% 2 6% 3 5% 5% 4 6% 9% 51%	2686
	21st to end	Night	5% 4 2 4 2 3 3 3 4 6% 65%	2762
June	1st to 10th	Night	1 2 1 3 3 4 5% 5% 7% 9% 60%	1520
	11th to 20th	Night	1 2 1 3 3 2 3 4 5% 7% 68%	1520
	21st to end	Night	3 5% 1 4 4 4 5% 4 9% 9% 52%	1520
July	1st to 10th	Night	2 3 2 6% 6% 6% 6% 5% 7% 8% 48%	2540
	11th to 20th	Night	2 3 1 4 5% 7% 7% 6% 11% 12% 42%	2589
	21st to end	Night	3 4 2 5% 5% 6% 7% 6% 9% 11% 42%	3109
August	1st to 10th	Night	6% 5% 2 7% 6% 7% 7% 6% 9% 10% 35%	2938
	11th to 20th	Night	3 3 2 4 4 5% 7% 7% 9% 13% 43%	3113
	21st to end	Night	3 4 2 5% 6% 6% 8% 6% 11% 13% 37%	3487
September	1st to 10th	Night	4 4 2 4 4 4 5% 6% 6% 9% 52%	1900
	11th to 20th	Night	3 2 1 3 4 3 4 3 5% 8% 64%	1908
	21st to end	Night	4 3 1 3 2 2 3 3 4 6% 68%	2090
October	1st to 10th	Night	3 3 1 3 2 3 3 3 4 6% 70%	3791
	11th to 20th	Night	3 3 1 3 2 3 4 3 6% 7% 65%	3778
	21st to end	Night	3 3 1 3 2 2 3 2 3 4 75%	4120
November	1st to 10th	Night	1 4 1 2 2 2 2 2 4 6% 72%	2487
	11th to 20th	Night	1 4 1 2 2 2 2 2 4 6% 73%	2600
	21st to end	Night	2 6% 2 4 3 3 3 4 5% 7% 62%	2600
December	1st to 10th	Night	1 3 2 5% 2 2 3 2 3 4 73%	4560
	11th to 20th	Night	1 4 1 3 2 2 3 3 4 7% 69%	5181
	21st to end	Night	1 6% 3 7% 4 4 4 3 5% 6% 58%	6974

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	19% 34% 7% 18% 16% 5%	3662
	11th to 20th	Day	18% 32% 8% 14% 21% 7%	4100
	21st to end	Day	18% 32% 5% 12% 25% 8%	4510
February	1st to 10th	Day	7% 64% 6% 12% 6% 4	1778
	11th to 20th	Day	8% 65% 4 11% 9% 3	1859
	21st to end	Day	12% 66% 1 6% 11% 4	1570
March	1st to 10th	Day	7% 46% 6% 10% 25% 5%	3180
	11th to 20th	Day	15% 53% 8% 13% 10% 2	3490
	21st to end	Day	13% 47% 7% 21% 10% 2	4023
April	1st to 10th	Day	9% 67% 3 11% 8% 1	2280
	11th to 20th	Day	10% 68% 3 8% 9% 3	2254
	21st to end	Day	11% 67% 4 9% 8%	2280
May	1st to 10th	Day	13% 44% 5% 10% 18% 10%	3800
	11th to 20th	Day	16% 47% 7% 12% 13% 5%	4218
	21st to end	Day	7% 43% 6% 10% 25% 8%	4825
June	1st to 10th	Day	7% 68% 6% 8% 8% 4	2660
	11th to 20th	Day	7% 66% 3 7% 9% 8%	2660
	21st to end	Day	8% 66% 5% 8% 10% 4	2660
July	1st to 10th	Day	12% 38% 3 11% 17% 18%	4361
	11th to 20th	Day	17% 38% 11% 26% 6% 2	4302
	21st to end	Day	17% 38% 9% 21% 10% 4	4314
August	1st to 10th	Day	25% 40% 19% 11% 3 1	3986
	11th to 20th	Day	13% 40% 14% 13% 13% 7%	3762
	21st to end	Day	23% 40% 15% 13% 9% 1	4179
September	1st to 10th	Day	11% 64% 5% 9% 8% 3	2280
	11th to 20th	Day	9% 61% 4 10% 12% 5%	2271
	21st to end	Day	8% 62% 4 9% 14% 4	2090
October	1st to 10th	Day	6% 37% 2 9% 30% 17%	3175
	11th to 20th	Day	18% 36% 5% 21% 16% 4	3150
	21st to end	Day	10% 36% 2 13% 33% 6%	3438
November	1st to 10th	Day	8% 56% 3 10% 17% 6%	1788
	11th to 20th	Day	8% 58% 3 10% 16% 5%	1800
	21st to end	Day	11% 58% 5% 10% 12% 5%	1800
December	1st to 10th	Day	6% 35% 4 25% 26% 4	2625
	11th to 20th	Day	8% 34% 5% 23% 27% 3	3024
	21st to end	Day	14% 28% 6% 23% 22% 7%	4004
January	1st to 10th	Night	21% 29% 5% 21% 18% 6%	6327
	11th to 20th	Night	17% 35% 7% 15% 16% 10%	5898
	21st to end	Night	19% 31% 5% 14% 23% 9%	6468
February	1st to 10th	Night	9% 64% 6% 9% 9% 3	2509
	11th to 20th	Night	9% 65% 4 11% 9% 2	2218
	21st to end	Night	11% 65% 1 7% 12% 3	1884
March	1st to 10th	Night	12% 45% 3 10% 25% 6%	3683
	11th to 20th	Night	17% 46% 7% 18% 10% 2	3490
	21st to end	Night	17% 44% 10% 20% 8%	3621
April	1st to 10th	Night	9% 65% 5% 11% 8% 1	1900
	11th to 20th	Night	9% 67% 3 10% 8% 2	1877
	21st to end	Night	13% 67% 5% 10% 5%	1900
May	1st to 10th	Night	12% 42% 5% 13% 21% 7%	3170
	11th to 20th	Night	13% 46% 10% 17% 8% 5%	2687
	21st to end	Night	8% 43% 7% 13% 23% 5%	2762
June	1st to 10th	Night	7% 67% 6% 8% 7% 4	1520
	11th to 20th	Night	5% 66% 4 8% 9% 8%	1520
	21st to end	Night	9% 65% 5% 9% 9% 3	1520
July	1st to 10th	Night	19% 37% 6% 13% 10% 15%	2500
	11th to 20th	Night	20% 37% 18% 20% 3 2	2541
	21st to end	Night	18% 39% 13% 16% 12% 3	3011
August	1st to 10th	Night	32% 40% 14% 8% 4 1	2929
	11th to 20th	Night	17% 42% 16% 10% 10% 5%	3143
	21st to end	Night	24% 40% 15% 13% 7%	3487
September	1st to 10th	Night	9% 62% 6% 11% 9% 3	1900
	11th to 20th	Night	7% 61% 5% 9% 14% 4	1908
	21st to end	Night	8% 61% 3 10% 16% 3	2090
October	1st to 10th	Night	10% 37% 2 11% 29% 11%	3791
	11th to 20th	Night	16% 36% 6% 20% 18% 5%	3778
	21st to end	Night	11% 37% 2 16% 28% 6%	4120
November	1st to 10th	Night	8% 56% 3 11% 17% 5%	2487
	11th to 20th	Night	7% 57% 2 12% 17% 5%	2600
	21st to end	Night	11% 58% 4 11% 12% 4	2600
December	1st to 10th	Night	9% 35% 3 27% 22% 4	4560
	11th to 20th	Night	9% 33% 5% 21% 27% 5%	5182
	21st to end	Night	20% 28% 8% 16% 24% 5%	6974

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	11% 27% 33% 21% 7% 1	300
	11th to 20th	Day	10% 29% 39% 19% 3 1	300
	21st to end	Day	4 24% 42% 20% 11%	330
February	1st to 10th	Day	8% 42% 29% 18% 3	285
	11th to 20th	Day	7% 47% 27% 12% 6%	270
	21st to end	Day	21% 39% 27% 12% 1	225
March	1st to 10th	Day	16% 38% 23% 17% 5% 1	294
	11th to 20th	Day	14% 35% 30% 15% 5% 1	460
	21st to end	Day	23% 41% 28% 7% 1	506
April	1st to 10th	Day	15% 42% 27% 13% 2 1	460
	11th to 20th	Day	19% 45% 26% 7% 3	452
	21st to end	Day	17% 40% 30% 10% 2	460
May	1st to 10th	Day	14% 38% 34% 11% 3	463
	11th to 20th	Day	7% 24% 35% 24% 8% 1	665
	21st to end	Day	10% 25% 29% 25% 9% 1	734
June	1st to 10th	Day	3 16% 32% 29% 18% 2	680
	11th to 20th	Day	4 19% 35% 24% 15% 3	680
	21st to end	Day	5% 15% 28% 30% 18% 4	680
July	1st to 10th	Day	5% 6% 24% 37% 24% 5%	671
	11th to 20th	Day	3 5% 18% 35% 33% 6%	641
	21st to end	Day	5% 4 21% 40% 25% 5%	531
August	1st to 10th	Day	6% 6% 28% 34% 22% 3	487
	11th to 20th	Day	5% 8% 27% 40% 18% 3	477
	21st to end	Day	6% 8% 29% 34% 18% 5%	539
September	1st to 10th	Day	8% 8% 27% 33% 20% 4	490
	11th to 20th	Day	6% 16% 35% 29% 11% 4	481
	21st to end	Day	5% 15% 28% 32% 15% 6%	300
October	1st to 10th	Day	7% 27% 21% 25% 15% 5%	300
	11th to 20th	Day	10% 24% 30% 22% 9% 5%	300
	21st to end	Day	15% 23% 26% 22% 11% 3	330
November	1st to 10th	Day	11% 32% 29% 18% 9% 2	300
	11th to 20th	Day	7% 27% 31% 22% 12% 1	300
	21st to end	Day	11% 27% 28% 23% 9% 1	300
December	1st to 10th	Day	12% 28% 33% 17% 8% 1	300
	11th to 20th	Day	6% 30% 39% 20% 4 1	300
	21st to end	Day	17% 31% 33% 16% 4	330
January	1st to 10th	Night	5% 22% 35% 28% 10% 2	1000
	11th to 20th	Night	6% 21% 35% 27% 10% 1	805
	21st to end	Night	4 19% 38% 29% 10% 1	880
February	1st to 10th	Night	5% 25% 41% 24% 6%	780
	11th to 20th	Night	5% 31% 38% 20% 5%	744
	21st to end	Night	10% 31% 40% 17% 2	628
March	1st to 10th	Night	8% 30% 34% 22% 6% 1	760
	11th to 20th	Night	7% 22% 37% 27% 7% 1	760
	21st to end	Night	7% 32% 37% 19% 5%	719
April	1st to 10th	Night	9% 32% 40% 16% 3	570
	11th to 20th	Night	9% 28% 37% 21% 5%	563
	21st to end	Night	10% 26% 37% 21% 6%	570
May	1st to 10th	Night	10% 18% 37% 26% 8%	570
	11th to 20th	Night	9% 16% 34% 28% 11% 1	561
	21st to end	Night	7% 18% 34% 28% 11% 1	617
June	1st to 10th	Night	2 9% 34% 34% 21% 1	570
	11th to 20th	Night	2 12% 39% 34% 12% 1	570
	21st to end	Night	3 6% 30% 35% 24% 2	570
July	1st to 10th	Night	6% 3 19% 40% 30% 1	555
	11th to 20th	Night	3 2 13% 39% 38% 4	552
	21st to end	Night	4 1 9% 35% 42% 8%	624
August	1st to 10th	Night	5% 3 12% 37% 39% 5%	567
	11th to 20th	Night	6% 3 17% 43% 27% 4	564
	21st to end	Night	4 2 18% 41% 30% 5%	627
September	1st to 10th	Night	5% 5% 20% 41% 24% 4	570
	11th to 20th	Night	3 8% 27% 35% 24% 3	570
	21st to end	Night	4 12% 24% 39% 19% 1	570
October	1st to 10th	Night	6% 17% 29% 33% 14% 2	751
	11th to 20th	Night	4 16% 36% 27% 15% 2	760
	21st to end	Night	7% 20% 28% 28% 15% 3	836
November	1st to 10th	Night	6% 20% 30% 29% 13% 1	927
	11th to 20th	Night	4 22% 37% 25% 11% 2	1000
	21st to end	Night	7% 23% 29% 29% 12% 1	1000
December	1st to 10th	Night	8% 23% 35% 25% 8% 1	1000
	11th to 20th	Night	5% 26% 35% 25% 8%	1000
	21st to end	Night	8% 23% 38% 25% 5% 1	1100

Page generated at 2025-02-03 01:05:51. Version ac07

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