The Top Of The Sky Mini Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Top Of The Sky Mini Observatory clear sky chart from 2005-11-06 to 2024-08-30.

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	15% 12% 5% 9% 5% 5% 4 4 5% 7% 30%	95322
	Night	16% 13% 5% 10% 5% 4 4 3 5% 6% 30%	93654
Transparency	Day	53% 6% 11% 18% 10% 1	95095
	Night	55% 6% 10% 18% 10% 1	93485
Seeing	Day	23% 17% 29% 19% 9% 3	14329
	Night	23% 15% 27% 23% 10% 1	24069

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	16% 22% 11% 15% 5% 3 4 2 3 4 14%	2836
	11th to 20th	Day	13% 24% 8% 14% 7% 7% 4 3 3 5% 12%	2840
	21st to end	Day	24% 21% 12% 16% 7% 4 2 2 2 3 7%	3124
February	1st to 10th	Day	16% 21% 7% 11% 8% 5% 3 2 4 5% 19%	1710
	11th to 20th	Day	14% 15% 7% 16% 7% 5% 4 3 4 4 19%	1691
	21st to end	Day	17% 18% 4 13% 6% 4 5% 3 4 4 22%	1570
March	1st to 10th	Day	21% 12% 7% 10% 5% 4 3 4 4 6% 25%	3375
	11th to 20th	Day	12% 15% 6% 11% 6% 4 4 3 3 5% 31%	3480
	21st to end	Day	20% 13% 5% 10% 5% 4 3 3 4 5% 28%	3815
April	1st to 10th	Day	14% 15% 4 9% 5% 4 4 3 5% 6% 31%	2143
	11th to 20th	Day	18% 12% 3 7% 5% 4 4 3 5% 5% 33%	2392
	21st to end	Day	20% 12% 3 7% 4 4 3 3 4 5% 33%	2470
May	1st to 10th	Day	19% 10% 3 8% 5% 5% 4 4 5% 7% 29%	4082
	11th to 20th	Day	20% 10% 3 7% 5% 4 4 4 5% 7% 32%	4081
	21st to end	Day	10% 7% 2 7% 5% 5% 5% 4 6% 7% 39%	4629
June	1st to 10th	Day	14% 6% 3 7% 5% 5% 4 4 6% 8% 36%	2660
	11th to 20th	Day	13% 7% 2 7% 4 4 4 4 6% 9% 38%	2660
	21st to end	Day	12% 6% 3 5% 4 4 5% 5% 6% 10% 39%	2660
July	1st to 10th	Day	9% 6% 3 7% 5% 5% 6% 5% 7% 10% 38%	4198
	11th to 20th	Day	9% 5% 2 6% 4 5% 5% 5% 7% 10% 42%	4120
	21st to end	Day	11% 6% 3 7% 5% 5% 5% 4 6% 9% 39%	4466
August	1st to 10th	Day	9% 7% 3 6% 5% 5% 6% 4 7% 9% 38%	2457
	11th to 20th	Day	11% 6% 2 8% 6% 6% 6% 6% 8% 8% 34%	2433
	21st to end	Day	11% 6% 2 6% 5% 5% 6% 4 7% 9% 38%	2640
September	1st to 10th	Day	15% 7% 2 6% 4 5% 4 4 6% 8% 39%	2090
	11th to 20th	Day	12% 6% 2 6% 5% 4 5% 4 7% 8% 41%	1980
	21st to end	Day	19% 9% 2 7% 4 4 3 3 5% 7% 37%	1980
October	1st to 10th	Day	16% 7% 4 7% 4 4 5% 4 5% 7% 36%	1846
	11th to 20th	Day	22% 11% 3 8% 6% 4 4 3 4 5% 31%	1800
	21st to end	Day	23% 13% 4 8% 5% 4 4 3 5% 6% 24%	1980
November	1st to 10th	Day	12% 12% 5% 7% 6% 4 4 3 5% 6% 35%	1682
	11th to 20th	Day	19% 17% 5% 8% 4 4 4 3 5% 6% 25%	1642
	21st to end	Day	18% 20% 7% 10% 6% 4 4 4 5% 5% 18%	1520
December	1st to 10th	Day	16% 24% 9% 13% 6% 5% 4 2 4 3 14%	1520
	11th to 20th	Day	17% 18% 8% 17% 5% 4 4 4 4 5% 14%	1910
	21st to end	Day	23% 26% 8% 13% 5% 4 3 2 3 4 9%	2840
January	1st to 10th	Night	14% 24% 11% 17% 5% 4 3 3 3 4 11%	4109
	11th to 20th	Night	15% 18% 11% 20% 6% 4 6% 4 3 3 10%	4120
	21st to end	Night	24% 20% 9% 16% 7% 4 2 2 2 3 12%	4532
February	1st to 10th	Night	18% 17% 5% 14% 7% 4 3 3 4 4 18%	2470
	11th to 20th	Night	15% 16% 6% 14% 7% 5% 4 3 4 5% 19%	2370
	21st to end	Night	20% 13% 5% 13% 6% 5% 4 3 4 4 23%	1884
March	1st to 10th	Night	21% 15% 4 8% 4 3 3 3 4 4 32%	3478
	11th to 20th	Night	15% 11% 6% 11% 5% 4 4 3 4 5% 31%	3480
	21st to end	Night	18% 13% 4 9% 5% 4 4 3 4 5% 32%	3817
April	1st to 10th	Night	17% 14% 5% 8% 5% 3 4 4 5% 6% 30%	2036
	11th to 20th	Night	16% 10% 3 7% 5% 5% 4 4 6% 6% 33%	1754
	21st to end	Night	15% 10% 4 7% 4 4 5% 4 5% 7% 35%	1710
May	1st to 10th	Night	23% 11% 2 7% 5% 4 4 3 6% 6% 29%	2813
	11th to 20th	Night	15% 10% 3 6% 4 4 4 3 6% 8% 36%	2812
	21st to end	Night	11% 5% 2 5% 4 4 5% 3 7% 11% 44%	2924
June	1st to 10th	Night	11% 7% 2 6% 5% 5% 6% 4 6% 7% 41%	1520
	11th to 20th	Night	9% 5% 2 8% 4 6% 5% 4 6% 8% 42%	1520
	21st to end	Night	11% 5% 2 6% 4 4 5% 5% 7% 9% 41%	1520
July	1st to 10th	Night	10% 7% 2 6% 4 4 3 3 6% 9% 45%	2743
	11th to 20th	Night	10% 5% 2 6% 4 4 4 3 6% 8% 48%	2840
	21st to end	Night	7% 6% 2 7% 5% 5% 5% 4 6% 8% 45%	3087
August	1st to 10th	Night	7% 5% 2 7% 4 4 5% 3 7% 8% 47%	1701
	11th to 20th	Night	10% 7% 2 7% 4 5% 4 4 5% 8% 44%	1688
	21st to end	Night	9% 6% 2 5% 5% 4 5% 4 5% 9% 46%	1905
September	1st to 10th	Night	12% 6% 2 5% 4 4 5% 3 6% 7% 44%	1867
	11th to 20th	Night	10% 5% 2 5% 4 3 4 3 5% 8% 50%	1980
	21st to end	Night	15% 7% 3 8% 5% 4 4 4 5% 5% 41%	1980
October	1st to 10th	Night	13% 7% 2 6% 4 4 4 3 6% 7% 42%	2114
	11th to 20th	Night	18% 10% 4 8% 4 5% 5% 4 5% 6% 32%	2160
	21st to end	Night	25% 11% 2 7% 5% 4 3 4 5% 7% 28%	2376
November	1st to 10th	Night	14% 10% 3 8% 5% 4 4 3 5% 7% 37%	2392
	11th to 20th	Night	16% 18% 5% 10% 4 4 3 3 5% 6% 25%	2535
	21st to end	Night	18% 19% 5% 10% 5% 5% 5% 3 5% 5% 21%	2660
December	1st to 10th	Night	19% 21% 8% 11% 5% 4 4 3 4 5% 17%	2660
	11th to 20th	Night	16% 20% 8% 12% 5% 4 4 3 4 4 19%	3285
	21st to end	Night	23% 24% 9% 11% 6% 4 4 3 3 4 10%	4812

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	75% 4 10% 9% 2	2837
	11th to 20th	Day	77% 5% 8% 9% 2	2840
	21st to end	Day	84% 4 4 5% 2	3124
February	1st to 10th	Day	70% 4 8% 12% 5%	1710
	11th to 20th	Day	69% 5% 7% 13% 6%	1700
	21st to end	Day	64% 6% 10% 12% 6% 2	1570
March	1st to 10th	Day	59% 6% 10% 21% 4	3375
	11th to 20th	Day	55% 6% 14% 18% 6% 1	3480
	21st to end	Day	57% 7% 7% 17% 11% 1	3815
April	1st to 10th	Day	53% 6% 11% 17% 13% 1	2143
	11th to 20th	Day	52% 6% 10% 17% 13% 2	2392
	21st to end	Day	53% 4 10% 20% 10% 2	2470
May	1st to 10th	Day	53% 6% 9% 22% 8% 1	4120
	11th to 20th	Day	49% 7% 11% 22% 9% 1	4085
	21st to end	Day	40% 9% 12% 19% 15% 5%	4643
June	1st to 10th	Day	45% 7% 10% 25% 12% 1	2660
	11th to 20th	Day	41% 8% 14% 21% 15% 1	2660
	21st to end	Day	39% 7% 13% 25% 15% 2	2660
July	1st to 10th	Day	42% 4 12% 24% 15% 3	4133
	11th to 20th	Day	37% 5% 12% 28% 18% 1	4051
	21st to end	Day	42% 5% 14% 19% 19% 2	4324
August	1st to 10th	Day	40% 7% 13% 26% 13%	2444
	11th to 20th	Day	42% 9% 14% 23% 10% 2	2433
	21st to end	Day	39% 8% 14% 23% 13% 3	2640
September	1st to 10th	Day	42% 7% 14% 20% 14% 3	2090
	11th to 20th	Day	39% 7% 14% 24% 15% 1	1980
	21st to end	Day	47% 5% 10% 24% 14% 1	1980
October	1st to 10th	Day	45% 7% 13% 21% 13% 1	1846
	11th to 20th	Day	55% 4 11% 20% 8% 1	1800
	21st to end	Day	61% 5% 12% 13% 8% 1	1980
November	1st to 10th	Day	49% 6% 11% 19% 14% 1	1682
	11th to 20th	Day	60% 4 11% 15% 7% 3	1642
	21st to end	Day	67% 7% 8% 13% 6%	1520
December	1st to 10th	Day	75% 5% 8% 10% 3	1520
	11th to 20th	Day	72% 6% 7% 12% 3	1906
	21st to end	Day	82% 4 7% 6% 1	2840
January	1st to 10th	Night	77% 5% 6% 10% 3	4109
	11th to 20th	Night	80% 5% 6% 7% 2	4120
	21st to end	Night	80% 3 6% 9% 2	4532
February	1st to 10th	Night	69% 5% 8% 13% 5%	2470
	11th to 20th	Night	68% 4 8% 15% 5%	2372
	21st to end	Night	65% 5% 7% 14% 7% 1	1884
March	1st to 10th	Night	56% 4 12% 20% 8%	3478
	11th to 20th	Night	53% 7% 14% 17% 8% 1	3480
	21st to end	Night	54% 6% 7% 21% 10% 1	3817
April	1st to 10th	Night	54% 6% 10% 16% 12% 2	2036
	11th to 20th	Night	50% 5% 10% 19% 14% 2	1754
	21st to end	Night	47% 6% 10% 20% 14% 3	1710
May	1st to 10th	Night	55% 5% 9% 19% 10% 2	2840
	11th to 20th	Night	44% 9% 10% 22% 12% 2	2813
	21st to end	Night	31% 8% 15% 26% 18% 3	2931
June	1st to 10th	Night	40% 8% 10% 25% 15% 2	1520
	11th to 20th	Night	39% 6% 13% 22% 18% 2	1520
	21st to end	Night	37% 9% 12% 24% 17% 1	1520
July	1st to 10th	Night	38% 4 11% 25% 18% 4	2698
	11th to 20th	Night	33% 5% 11% 29% 19% 2	2786
	21st to end	Night	37% 5% 13% 19% 23% 2	2988
August	1st to 10th	Night	33% 8% 13% 28% 16% 1	1690
	11th to 20th	Night	37% 8% 14% 27% 12% 2	1688
	21st to end	Night	34% 7% 11% 27% 16% 3	1905
September	1st to 10th	Night	38% 7% 12% 25% 16% 3	1867
	11th to 20th	Night	32% 6% 13% 27% 20% 1	1980
	21st to end	Night	44% 6% 10% 22% 17% 1	1980
October	1st to 10th	Night	40% 6% 13% 22% 18% 1	2114
	11th to 20th	Night	51% 6% 9% 22% 11% 1	2160
	21st to end	Night	56% 6% 10% 17% 9% 1	2376
November	1st to 10th	Night	46% 6% 11% 22% 12% 3	2392
	11th to 20th	Night	60% 4 10% 16% 7% 3	2535
	21st to end	Night	65% 5% 10% 15% 5%	2660
December	1st to 10th	Night	72% 4 10% 10% 4	2660
	11th to 20th	Night	69% 5% 10% 13% 2	3288
	21st to end	Night	78% 6% 8% 7% 1	4812

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	34% 26% 29% 9% 3	270
	11th to 20th	Day	33% 32% 28% 5% 1 1	270
	21st to end	Day	31% 32% 29% 7% 2	297
February	1st to 10th	Day	37% 22% 35% 5%	270
	11th to 20th	Day	34% 33% 27% 5%	270
	21st to end	Day	40% 31% 26% 4	225
March	1st to 10th	Day	30% 24% 30% 14% 3	422
	11th to 20th	Day	31% 23% 31% 11% 3 1	460
	21st to end	Day	35% 24% 24% 14% 3	506
April	1st to 10th	Day	26% 27% 28% 14% 5%	460
	11th to 20th	Day	33% 19% 27% 13% 7% 1	452
	21st to end	Day	31% 19% 31% 14% 5% 1	460
May	1st to 10th	Day	27% 21% 29% 17% 4 2	463
	11th to 20th	Day	25% 11% 32% 21% 7% 3	487
	21st to end	Day	16% 10% 32% 26% 12% 4	529
June	1st to 10th	Day	16% 14% 37% 21% 10% 2	490
	11th to 20th	Day	17% 11% 31% 27% 12% 2	490
	21st to end	Day	16% 14% 32% 24% 10% 3	490
July	1st to 10th	Day	13% 8% 25% 29% 19% 7%	485
	11th to 20th	Day	13% 10% 28% 25% 17% 6%	484
	21st to end	Day	11% 8% 30% 28% 15% 7%	532
August	1st to 10th	Day	11% 9% 24% 30% 19% 6%	486
	11th to 20th	Day	16% 8% 29% 25% 15% 8%	479
	21st to end	Day	11% 7% 26% 29% 18% 8%	532
September	1st to 10th	Day	17% 8% 24% 26% 19% 6%	450
	11th to 20th	Day	12% 6% 23% 28% 21% 9%	450
	21st to end	Day	22% 13% 25% 22% 13% 5%	450
October	1st to 10th	Day	16% 14% 29% 21% 17% 3	450
	11th to 20th	Day	27% 20% 32% 15% 4 1	450
	21st to end	Day	36% 19% 30% 13% 3	495
November	1st to 10th	Day	26% 21% 29% 15% 8% 1	280
	11th to 20th	Day	35% 20% 27% 13% 5%	237
	21st to end	Day	33% 22% 39% 6% 1	180
December	1st to 10th	Day	33% 27% 25% 12% 1 2	180
	11th to 20th	Day	34% 29% 29% 7% 1	180
	21st to end	Day	34% 30% 28% 7%	218
January	1st to 10th	Night	30% 26% 30% 11% 3	760
	11th to 20th	Night	31% 26% 28% 13% 2	760
	21st to end	Night	27% 25% 30% 16% 2	836
February	1st to 10th	Night	32% 22% 28% 17% 1	760
	11th to 20th	Night	29% 23% 31% 15% 1	743
	21st to end	Night	32% 25% 29% 14% 1	628
March	1st to 10th	Night	26% 22% 30% 19% 4	760
	11th to 20th	Night	26% 21% 29% 18% 6% 1	760
	21st to end	Night	27% 18% 30% 20% 5%	836
April	1st to 10th	Night	27% 17% 31% 21% 5%	760
	11th to 20th	Night	23% 18% 33% 18% 7% 1	630
	21st to end	Night	20% 15% 34% 25% 6%	570
May	1st to 10th	Night	24% 11% 29% 27% 9% 1	570
	11th to 20th	Night	20% 10% 28% 32% 9% 2	561
	21st to end	Night	12% 5% 29% 35% 18% 1	526
June	1st to 10th	Night	12% 5% 34% 36% 12% 1	380
	11th to 20th	Night	12% 6% 30% 39% 13% 1	380
	21st to end	Night	12% 7% 29% 36% 15%	380
July	1st to 10th	Night	9% 4 19% 38% 26% 4	497
	11th to 20th	Night	10% 3 24% 35% 24% 3	552
	21st to end	Night	10% 4 19% 42% 23% 2	624
August	1st to 10th	Night	9% 5% 19% 40% 26% 2	567
	11th to 20th	Night	12% 5% 17% 36% 26% 3	564
	21st to end	Night	12% 4 19% 33% 29% 3	657
September	1st to 10th	Night	15% 7% 19% 31% 24% 3	720
	11th to 20th	Night	14% 4 19% 33% 26% 4	720
	21st to end	Night	18% 9% 26% 27% 16% 4	720
October	1st to 10th	Night	19% 9% 28% 26% 16% 2	720
	11th to 20th	Night	25% 17% 28% 23% 7% 1	720
	21st to end	Night	33% 15% 30% 18% 4	792
November	1st to 10th	Night	21% 17% 28% 24% 9% 1	740
	11th to 20th	Night	28% 23% 28% 14% 6% 1	760
	21st to end	Night	32% 20% 30% 13% 4	760
December	1st to 10th	Night	33% 24% 28% 12% 4	760
	11th to 20th	Night	29% 26% 29% 14% 2	760
	21st to end	Night	34% 21% 31% 13% 1	836

Page generated at 2024-08-27 09:49:41. Version ac07

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