Solarity Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Solarity Observatory clear sky chart from 2005-11-06 to 2024-11-01.

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	13% 6% 2 6% 4 4 5% 4 6% 8% 42%	101115
	Night	13% 6% 2 6% 4 4 4 3 5% 7% 45%	97774
Transparency	Day	39% 6% 11% 21% 18% 4	100926
	Night	38% 5% 10% 21% 20% 6%	97633
Seeing	Day	16% 10% 22% 24% 19% 10%	14704
	Night	15% 8% 22% 29% 22% 4	24410

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% 11% 4 6% 4 3 4 3 4 6% 38%	2836
	11th to 20th	Day	18% 7% 3 7% 3 3 3 2 3 4 47%	3004
	21st to end	Day	24% 9% 2 4 3 3 2 2 4 6% 42%	3476
February	1st to 10th	Day	20% 10% 3 6% 3 3 3 3 4 6% 39%	1900
	11th to 20th	Day	22% 7% 3 5% 4 3 3 3 5% 5% 39%	1848
	21st to end	Day	21% 9% 3 5% 4 4 3 3 4 5% 38%	1570
March	1st to 10th	Day	23% 9% 3 6% 4 4 4 4 5% 5% 33%	3120
	11th to 20th	Day	15% 7% 3 6% 5% 3 3 3 5% 7% 42%	3287
	21st to end	Day	14% 7% 3 8% 4 4 5% 4 5% 7% 39%	4091
April	1st to 10th	Day	11% 5% 3 6% 5% 4 4 4 6% 7% 46%	2280
	11th to 20th	Day	13% 6% 2 6% 4 4 4 3 5% 6% 45%	2254
	21st to end	Day	10% 5% 2 6% 4 4 4 3 5% 9% 48%	2280
May	1st to 10th	Day	10% 5% 2 6% 5% 5% 5% 4 7% 8% 42%	3978
	11th to 20th	Day	15% 7% 2 6% 4 5% 4 4 7% 9% 38%	4081
	21st to end	Day	9% 5% 2 6% 6% 5% 5% 4 7% 9% 42%	4476
June	1st to 10th	Day	10% 5% 2 7% 6% 5% 7% 4 8% 10% 36%	2470
	11th to 20th	Day	5% 4 2 5% 5% 5% 6% 5% 8% 10% 45%	2470
	21st to end	Day	7% 5% 2 6% 5% 5% 6% 5% 6% 9% 43%	2610
July	1st to 10th	Day	6% 5% 2 8% 7% 7% 8% 6% 9% 12% 29%	4318
	11th to 20th	Day	8% 5% 2 6% 5% 6% 7% 7% 10% 13% 30%	4120
	21st to end	Day	13% 8% 4 9% 6% 7% 7% 6% 8% 10% 22%	4312
August	1st to 10th	Day	4 3 1 4 4 4 5% 5% 8% 9% 54%	3785
	11th to 20th	Day	5% 4 2 6% 4 5% 5% 5% 7% 10% 47%	3729
	21st to end	Day	7% 4 1 5% 5% 5% 5% 4 6% 8% 50%	4180
September	1st to 10th	Day	10% 5% 2 6% 5% 5% 7% 4 6% 9% 41%	2261
	11th to 20th	Day	12% 7% 2 7% 4 5% 5% 4 6% 7% 42%	2090
	21st to end	Day	11% 5% 2 6% 4 4 3 4 4 6% 51%	2090
October	1st to 10th	Day	9% 4 2 6% 3 4 4 3 4 7% 54%	2090
	11th to 20th	Day	9% 4 1 5% 3 4 3 3 5% 7% 55%	2059
	21st to end	Day	14% 4 1 5% 3 3 3 2 4 6% 54%	1971
November	1st to 10th	Day	12% 5% 1 6% 3 3 4 3 4 5% 55%	1672
	11th to 20th	Day	13% 6% 2 5% 3 3 4 3 4 6% 52%	1710
	21st to end	Day	16% 6% 2 5% 4 3 4 4 4 7% 44%	1710
December	1st to 10th	Day	22% 10% 2 5% 4 3 4 3 5% 5% 37%	1710
	11th to 20th	Day	18% 8% 3 6% 4 4 4 3 3 4 44%	2153
	21st to end	Day	18% 9% 4 7% 5% 4 4 3 4 6% 36%	3124
January	1st to 10th	Night	18% 11% 2 6% 4 4 3 3 4 5% 40%	4109
	11th to 20th	Night	18% 9% 3 6% 4 2 3 3 4 5% 44%	3951
	21st to end	Night	22% 12% 2 5% 3 3 4 2 4 3 40%	4180
February	1st to 10th	Night	19% 8% 3 6% 3 3 3 3 5% 6% 43%	2280
	11th to 20th	Night	22% 7% 3 6% 3 3 3 2 4 4 43%	2218
	21st to end	Night	21% 6% 2 6% 4 4 4 3 5% 5% 39%	1884
March	1st to 10th	Night	25% 9% 3 6% 4 3 3 3 4 5% 35%	3733
	11th to 20th	Night	13% 6% 2 5% 3 3 4 4 6% 7% 48%	3672
	21st to end	Night	17% 8% 3 7% 5% 4 4 3 3 5% 40%	3567
April	1st to 10th	Night	11% 6% 2 5% 3 4 4 4 6% 8% 47%	1900
	11th to 20th	Night	14% 6% 2 5% 3 4 3 3 5% 6% 49%	1875
	21st to end	Night	10% 5% 2 5% 3 3 3 3 5% 7% 52%	1900
May	1st to 10th	Night	10% 5% 3 7% 5% 5% 4 3 5% 9% 44%	2913
	11th to 20th	Night	15% 7% 3 6% 4 4 4 3 6% 7% 40%	2812
	21st to end	Night	6% 4 1 6% 4 4 5% 5% 8% 12% 45%	3079
June	1st to 10th	Night	6% 5% 2 6% 5% 5% 5% 5% 9% 9% 42%	1710
	11th to 20th	Night	4 4 1 4 4 4 4 3 7% 12% 52%	1710
	21st to end	Night	6% 5% 2 7% 5% 5% 5% 4 6% 9% 47%	1554
July	1st to 10th	Night	6% 6% 3 7% 6% 6% 6% 5% 7% 12% 35%	2623
	11th to 20th	Night	8% 6% 2 7% 6% 6% 6% 4 9% 12% 35%	2840
	21st to end	Night	9% 9% 4 10% 8% 6% 7% 5% 8% 9% 25%	3235
August	1st to 10th	Night	2 2 1 3 4 4 5% 4 6% 11% 58%	3144
	11th to 20th	Night	4 3 1 5% 4 4 4 4 7% 10% 54%	3100
	21st to end	Night	5% 4 1 4 3 4 4 3 5% 8% 56%	3476
September	1st to 10th	Night	8% 6% 3 6% 4 4 4 3 5% 8% 48%	1900
	11th to 20th	Night	11% 6% 2 6% 4 4 4 3 6% 8% 45%	2089
	21st to end	Night	7% 5% 2 5% 4 4 3 4 6% 7% 53%	2090
October	1st to 10th	Night	9% 5% 2 3 3 3 3 3 4 4 61%	2090
	11th to 20th	Night	10% 5% 2 5% 3 3 4 3 5% 6% 55%	2118
	21st to end	Night	15% 5% 2 4 3 3 2 2 3 5% 57%	2625
November	1st to 10th	Night	11% 5% 1 5% 4 3 2 3 4 5% 56%	2413
	11th to 20th	Night	13% 6% 1 4 3 3 3 3 4 7% 53%	2470
	21st to end	Night	15% 6% 2 5% 4 4 4 3 5% 6% 47%	2470
December	1st to 10th	Night	20% 6% 2 5% 4 4 5% 3 4 7% 40%	2470
	11th to 20th	Night	18% 6% 2 5% 4 3 3 3 4 5% 48%	3042
	21st to end	Night	18% 8% 3 7% 4 4 5% 4 6% 7% 33%	4532

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 6% 19% 20% 4	2837
	11th to 20th	Day	43% 3 5% 24% 22% 3	3004
	21st to end	Day	47% 2 7% 20% 20% 5%	3476
February	1st to 10th	Day	47% 3 7% 19% 19% 5%	1900
	11th to 20th	Day	48% 3 6% 18% 19% 7%	1858
	21st to end	Day	48% 4 6% 14% 22% 7%	1570
March	1st to 10th	Day	52% 4 9% 10% 15% 9%	3120
	11th to 20th	Day	42% 4 8% 21% 18% 7%	3287
	21st to end	Day	44% 5% 10% 18% 19% 5%	4091
April	1st to 10th	Day	37% 4 11% 22% 18% 8%	2280
	11th to 20th	Day	38% 4 7% 21% 22% 8%	2254
	21st to end	Day	33% 5% 10% 26% 22% 3	2280
May	1st to 10th	Day	37% 6% 13% 27% 15% 2	4014
	11th to 20th	Day	41% 6% 13% 26% 13% 1	4085
	21st to end	Day	36% 8% 12% 27% 15% 1	4489
June	1st to 10th	Day	40% 9% 15% 19% 17% 1	2470
	11th to 20th	Day	31% 8% 15% 26% 17% 2	2470
	21st to end	Day	36% 9% 15% 23% 12% 5%	2610
July	1st to 10th	Day	39% 13% 22% 19% 6% 1	4252
	11th to 20th	Day	38% 13% 23% 20% 5% 1	4051
	21st to end	Day	53% 11% 14% 15% 6%	4174
August	1st to 10th	Day	22% 8% 13% 36% 21% 1	3773
	11th to 20th	Day	30% 8% 16% 28% 16% 3	3765
	21st to end	Day	30% 8% 14% 20% 23% 4	4179
September	1st to 10th	Day	37% 8% 14% 18% 17% 5%	2261
	11th to 20th	Day	39% 8% 11% 17% 20% 4	2090
	21st to end	Day	34% 6% 10% 21% 22% 8%	2090
October	1st to 10th	Day	30% 5% 8% 21% 27% 10%	2090
	11th to 20th	Day	29% 4 7% 22% 27% 11%	2059
	21st to end	Day	33% 4 5% 18% 31% 9%	1971
November	1st to 10th	Day	33% 3 7% 19% 29% 9%	1672
	11th to 20th	Day	34% 4 6% 19% 26% 10%	1710
	21st to end	Day	39% 5% 6% 18% 24% 7%	1710
December	1st to 10th	Day	49% 4 7% 15% 20% 5%	1710
	11th to 20th	Day	46% 3 6% 19% 22% 5%	2150
	21st to end	Day	49% 3 8% 21% 18% 2	3124
January	1st to 10th	Night	48% 3 5% 16% 25% 3	4109
	11th to 20th	Night	44% 3 5% 22% 18% 7%	3951
	21st to end	Night	50% 3 3 19% 19% 5%	4180
February	1st to 10th	Night	44% 3 6% 20% 21% 6%	2280
	11th to 20th	Night	47% 3 5% 18% 19% 8%	2219
	21st to end	Night	46% 5% 6% 15% 19% 9%	1884
March	1st to 10th	Night	52% 4 7% 14% 15% 8%	3733
	11th to 20th	Night	34% 5% 9% 21% 21% 10%	3672
	21st to end	Night	48% 3 6% 20% 20% 3	3567
April	1st to 10th	Night	36% 4 12% 22% 20% 6%	1900
	11th to 20th	Night	36% 3 7% 21% 21% 12%	1875
	21st to end	Night	31% 5% 10% 26% 23% 5%	1900
May	1st to 10th	Night	37% 7% 12% 22% 20% 2	2942
	11th to 20th	Night	41% 7% 14% 24% 12% 2	2813
	21st to end	Night	29% 8% 14% 28% 17% 2	3087
June	1st to 10th	Night	34% 10% 14% 21% 18% 2	1710
	11th to 20th	Night	25% 7% 17% 28% 20% 4	1710
	21st to end	Night	32% 8% 14% 23% 20% 4	1554
July	1st to 10th	Night	39% 10% 24% 19% 6% 2	2580
	11th to 20th	Night	34% 12% 25% 21% 7% 1	2786
	21st to end	Night	51% 12% 16% 14% 6% 1	3132
August	1st to 10th	Night	18% 7% 15% 37% 21% 2	3132
	11th to 20th	Night	23% 9% 18% 30% 17% 3	3130
	21st to end	Night	25% 7% 15% 22% 24% 6%	3476
September	1st to 10th	Night	34% 7% 16% 20% 17% 6%	1900
	11th to 20th	Night	36% 7% 12% 18% 21% 6%	2089
	21st to end	Night	28% 7% 9% 24% 23% 9%	2090
October	1st to 10th	Night	27% 4 6% 22% 26% 14%	2090
	11th to 20th	Night	31% 3 7% 19% 27% 13%	2118
	21st to end	Night	33% 3 5% 18% 31% 11%	2625
November	1st to 10th	Night	31% 3 7% 18% 27% 14%	2413
	11th to 20th	Night	32% 3 7% 18% 28% 12%	2470
	21st to end	Night	38% 4 7% 20% 23% 8%	2470
December	1st to 10th	Night	44% 4 8% 18% 21% 4	2470
	11th to 20th	Night	40% 3 7% 18% 26% 6%	3044
	21st to end	Night	47% 4 7% 20% 19% 3	4532

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	29% 22% 31% 13% 4	270
	11th to 20th	Day	30% 20% 30% 14% 6%	270
	21st to end	Day	25% 24% 38% 10% 3 1	297
February	1st to 10th	Day	29% 19% 34% 14% 5%	270
	11th to 20th	Day	36% 19% 29% 14% 2 1	270
	21st to end	Day	34% 24% 34% 8%	225
March	1st to 10th	Day	26% 21% 35% 12% 5% 1	270
	11th to 20th	Day	24% 21% 32% 16% 6% 1	345
	21st to end	Day	21% 16% 35% 19% 8%	506
April	1st to 10th	Day	19% 18% 27% 24% 10% 2	460
	11th to 20th	Day	19% 15% 27% 24% 13% 2	452
	21st to end	Day	14% 13% 30% 28% 14% 2	460
May	1st to 10th	Day	14% 10% 28% 27% 14% 6%	463
	11th to 20th	Day	9% 8% 27% 28% 18% 10%	487
	21st to end	Day	10% 6% 22% 29% 19% 15%	529
June	1st to 10th	Day	13% 3 19% 27% 26% 12%	490
	11th to 20th	Day	8% 3 16% 28% 26% 21%	490
	21st to end	Day	9% 3 16% 27% 29% 15%	630
July	1st to 10th	Day	7% 1 10% 28% 31% 22%	604
	11th to 20th	Day	8% 1 9% 22% 29% 31%	484
	21st to end	Day	8% 3 10% 20% 36% 24%	532
August	1st to 10th	Day	9% 3 11% 23% 29% 25%	486
	11th to 20th	Day	9% 1 11% 30% 32% 17%	479
	21st to end	Day	12% 2 9% 22% 33% 21%	539
September	1st to 10th	Day	9% 4 12% 30% 33% 13%	490
	11th to 20th	Day	12% 4 12% 25% 31% 15%	490
	21st to end	Day	14% 4 15% 24% 32% 10%	490
October	1st to 10th	Day	12% 3 22% 30% 25% 7%	490
	11th to 20th	Day	10% 10% 27% 36% 16% 1	459
	21st to end	Day	18% 12% 23% 29% 16% 2	330
November	1st to 10th	Day	21% 7% 30% 26% 11% 4	270
	11th to 20th	Day	15% 17% 40% 21% 7%	270
	21st to end	Day	16% 18% 34% 24% 7% 1	270
December	1st to 10th	Day	30% 17% 30% 18% 4 1	270
	11th to 20th	Day	24% 19% 33% 16% 7% 1	270
	21st to end	Day	31% 15% 31% 18% 4 1	297
January	1st to 10th	Night	23% 14% 33% 24% 5%	760
	11th to 20th	Night	25% 15% 28% 26% 7%	760
	21st to end	Night	22% 15% 33% 27% 3	836
February	1st to 10th	Night	23% 13% 30% 30% 5%	760
	11th to 20th	Night	27% 13% 30% 26% 3	743
	21st to end	Night	26% 16% 33% 23% 2	628
March	1st to 10th	Night	20% 16% 29% 30% 5%	760
	11th to 20th	Night	18% 14% 32% 27% 9% 1	760
	21st to end	Night	19% 12% 31% 27% 11%	689
April	1st to 10th	Night	14% 14% 31% 28% 13% 1	570
	11th to 20th	Night	16% 10% 32% 26% 14% 2	563
	21st to end	Night	13% 9% 28% 33% 15% 1	570
May	1st to 10th	Night	11% 5% 27% 32% 22% 3	570
	11th to 20th	Night	12% 4 23% 31% 26% 4	561
	21st to end	Night	8% 2 14% 35% 35% 7%	617
June	1st to 10th	Night	9% 2 11% 35% 36% 7%	570
	11th to 20th	Night	5% 1 11% 26% 44% 13%	570
	21st to end	Night	8% 1 8% 28% 44% 11%	570
July	1st to 10th	Night	6% 1 6% 26% 46% 14%	555
	11th to 20th	Night	7% 1 5% 24% 43% 21%	552
	21st to end	Night	8% 1 8% 25% 43% 16%	624
August	1st to 10th	Night	5% 1 3 27% 49% 16%	567
	11th to 20th	Night	7% 1 7% 31% 44% 10%	564
	21st to end	Night	13% 2 6% 26% 43% 11%	627
September	1st to 10th	Night	8% 2 13% 30% 39% 8%	570
	11th to 20th	Night	13% 3 12% 28% 38% 6%	759
	21st to end	Night	9% 2 15% 31% 37% 5%	760
October	1st to 10th	Night	10% 4 18% 33% 29% 6%	760
	11th to 20th	Night	13% 7% 23% 35% 21% 2	760
	21st to end	Night	17% 6% 19% 35% 21% 2	836
November	1st to 10th	Night	13% 7% 21% 34% 21% 3	743
	11th to 20th	Night	14% 10% 29% 33% 13% 2	760
	21st to end	Night	19% 8% 28% 31% 13% 1	760
December	1st to 10th	Night	22% 12% 25% 30% 10%	760
	11th to 20th	Night	24% 11% 28% 27% 10%	760
	21st to end	Night	25% 12% 29% 27% 6%	836

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