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 2025-01-22.

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	16% 12% 5% 9% 5% 5% 4 4 5% 7% 29%	104861
	Night	16% 13% 5% 10% 5% 4 4 3 5% 6% 29%	104436
Transparency	Day	53% 5% 11% 19% 10% 1	108537
	Night	55% 5% 10% 19% 10% 1	108899
Seeing	Day	24% 17% 29% 19% 9% 3	14784
	Night	23% 15% 27% 23% 10% 1	24646

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%	2926
	11th to 20th	Day	13% 23% 8% 15% 7% 7% 4 3 3 4 12%	2930
	21st to end	Day	24% 21% 12% 16% 7% 4 2 2 2 3 7%	3133
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	13% 7% 3 7% 5% 5% 6% 4 7% 9% 33%	4104
	11th to 20th	Day	12% 7% 3 8% 5% 6% 6% 6% 7% 8% 34%	4044
	21st to end	Day	10% 6% 2 6% 5% 5% 6% 4 7% 9% 40%	4438
September	1st to 10th	Day	15% 7% 2 5% 4 5% 4 4 6% 8% 40%	2206
	11th to 20th	Day	11% 6% 2 7% 5% 4 4 4 7% 8% 42%	2090
	21st to end	Day	20% 9% 2 7% 4 4 3 3 5% 7% 36%	2090
October	1st to 10th	Day	15% 7% 3 7% 4 4 5% 4 5% 7% 38%	1948
	11th to 20th	Day	22% 11% 3 8% 6% 4 4 3 4 5% 32%	1900
	21st to end	Day	22% 13% 4 8% 5% 4 4 3 5% 6% 26%	2090
November	1st to 10th	Day	13% 11% 4 8% 6% 4 4 3 5% 7% 35%	1772
	11th to 20th	Day	19% 17% 5% 8% 4 4 4 3 5% 6% 25%	1728
	21st to end	Day	18% 20% 7% 11% 5% 4 4 3 5% 5% 17%	1600
December	1st to 10th	Day	16% 19% 11% 16% 6% 4 4 3 4 3 14%	2600
	11th to 20th	Day	22% 21% 8% 12% 6% 3 3 3 4 4 13%	2990
	21st to end	Day	23% 25% 8% 14% 6% 4 4 2 3 4 8%	4070
January	1st to 10th	Night	14% 23% 11% 18% 5% 4 3 3 3 4 11%	4239
	11th to 20th	Night	14% 18% 11% 20% 7% 4 6% 4 3 3 10%	4250
	21st to end	Night	24% 19% 9% 16% 7% 3 3 2 2 3 12%	4546
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	11% 9% 3 7% 5% 5% 5% 4 6% 8% 39%	2825
	11th to 20th	Night	15% 9% 2 6% 3 4 3 3 4 7% 42%	2785
	21st to end	Night	8% 6% 2 7% 5% 5% 5% 4 7% 8% 43%	3184
September	1st to 10th	Night	12% 6% 2 5% 4 4 5% 3 6% 7% 45%	1971
	11th to 20th	Night	10% 5% 2 5% 4 4 4 3 5% 8% 51%	2090
	21st to end	Night	17% 7% 3 8% 5% 4 4 3 5% 5% 39%	2090
October	1st to 10th	Night	13% 7% 2 6% 4 4 4 3 6% 7% 43%	2232
	11th to 20th	Night	17% 10% 4 8% 4 4 5% 4 5% 6% 33%	2280
	21st to end	Night	24% 10% 2 7% 4 4 3 4 5% 7% 29%	2508
November	1st to 10th	Night	14% 10% 3 8% 5% 3 4 3 5% 7% 37%	2522
	11th to 20th	Night	16% 18% 5% 10% 4 4 3 3 5% 6% 25%	2669
	21st to end	Night	18% 19% 5% 10% 5% 5% 5% 3 5% 5% 20%	2800
December	1st to 10th	Night	14% 19% 9% 16% 6% 5% 4 3 4 4 16%	4580
	11th to 20th	Night	19% 22% 10% 11% 5% 4 3 2 3 4 16%	5205
	21st to end	Night	22% 23% 8% 12% 5% 4 4 3 4 5% 11%	6882

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 9% 9% 2	2927
	11th to 20th	Day	77% 5% 8% 9% 2	2930
	21st to end	Day	84% 4 4 5% 2	3133
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	46% 5% 13% 24% 11%	4091
	11th to 20th	Day	45% 6% 10% 29% 9% 1	4083
	21st to end	Day	40% 5% 14% 29% 11% 2	4438
September	1st to 10th	Day	41% 7% 14% 21% 16% 3	2206
	11th to 20th	Day	38% 6% 13% 24% 17% 1	2090
	21st to end	Day	48% 5% 10% 23% 13% 1	2090
October	1st to 10th	Day	36% 4 13% 27% 19% 1	3234
	11th to 20th	Day	50% 2 10% 20% 15% 3	3140
	21st to end	Day	46% 3 13% 24% 14% 1	3428
November	1st to 10th	Day	49% 6% 11% 20% 14% 1	1772
	11th to 20th	Day	61% 4 11% 14% 8% 2	1728
	21st to end	Day	68% 6% 8% 12% 5%	1600
December	1st to 10th	Day	76% 3 9% 10% 2	2600
	11th to 20th	Day	76% 4 6% 12% 2	2986
	21st to end	Day	83% 3 6% 7% 1	4070
January	1st to 10th	Night	77% 4 6% 10% 3	4239
	11th to 20th	Night	81% 5% 6% 7% 2	4250
	21st to end	Night	80% 3 6% 9% 2	4546
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	43% 6% 11% 26% 13% 1	2814
	11th to 20th	Night	43% 5% 9% 30% 12% 1	2812
	21st to end	Night	38% 5% 11% 30% 15% 2	3184
September	1st to 10th	Night	37% 7% 11% 26% 16% 3	1971
	11th to 20th	Night	32% 6% 13% 27% 20% 2	2090
	21st to end	Night	46% 6% 9% 21% 16% 1	2090
October	1st to 10th	Night	36% 4 9% 29% 22% 1	3726
	11th to 20th	Night	46% 3 10% 21% 17% 3	3779
	21st to end	Night	44% 3 12% 25% 15% 1	4120
November	1st to 10th	Night	46% 6% 11% 22% 13% 2	2522
	11th to 20th	Night	61% 4 9% 16% 7% 3	2669
	21st to end	Night	66% 5% 10% 15% 4	2800
December	1st to 10th	Night	73% 3 11% 10% 3	4580
	11th to 20th	Night	74% 3 8% 13% 2	5208
	21st to end	Night	77% 4 8% 10% 1	6882

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	35% 26% 29% 8% 2	300
	11th to 20th	Day	34% 32% 28% 5% 1 1	300
	21st to end	Day	31% 32% 28% 7% 2	300
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	12% 7% 27% 28% 18% 8%	539
September	1st to 10th	Day	16% 9% 25% 26% 19% 6%	490
	11th to 20th	Day	11% 6% 23% 29% 22% 9%	490
	21st to end	Day	25% 12% 25% 22% 12% 4	490
October	1st to 10th	Day	15% 15% 29% 21% 17% 3	490
	11th to 20th	Day	26% 19% 31% 16% 6% 2	490
	21st to end	Day	35% 18% 29% 14% 4	539
November	1st to 10th	Day	26% 21% 31% 14% 7% 1	310
	11th to 20th	Day	35% 20% 28% 13% 4	263
	21st to end	Day	35% 22% 38% 6% 1	200
December	1st to 10th	Day	33% 27% 27% 12% 1 2	200
	11th to 20th	Day	37% 27% 28% 8% 2	200
	21st to end	Day	34% 29% 29% 8%	243
January	1st to 10th	Night	30% 26% 30% 11% 3	800
	11th to 20th	Night	31% 27% 28% 12% 2	800
	21st to end	Night	27% 25% 29% 16% 2	841
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	661
September	1st to 10th	Night	15% 7% 19% 31% 24% 3	760
	11th to 20th	Night	13% 4 19% 34% 26% 4	760
	21st to end	Night	20% 9% 25% 27% 16% 4	760
October	1st to 10th	Night	19% 9% 28% 26% 16% 2	760
	11th to 20th	Night	25% 16% 27% 23% 8% 1	760
	21st to end	Night	32% 15% 30% 19% 4	836
November	1st to 10th	Night	22% 17% 28% 23% 9% 1	780
	11th to 20th	Night	29% 23% 28% 14% 5% 1	800
	21st to end	Night	33% 20% 30% 13% 4	800
December	1st to 10th	Night	33% 23% 28% 12% 4	800
	11th to 20th	Night	30% 26% 28% 14% 2	800
	21st to end	Night	34% 20% 31% 13% 1	880

Page generated at 2025-01-19 03:06:48. Version ac07

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