Sola Virtus Observatory
Clear Sky Chart
History

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

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	15% 7% 2 6% 4 4 5% 4 6% 8% 39%	101278
	Night	15% 7% 2 6% 4 4 4 3 5% 7% 42%	97723
Transparency	Day	23% 47% 7% 13% 9% 2	104913
	Night	23% 47% 6% 14% 9% 2	102228
Seeing	Day	19% 13% 28% 23% 13% 4	14963
	Night	18% 11% 30% 28% 11% 1	24350

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% 6% 2 5% 4 4 4 3 5% 5% 45%	2517
	11th to 20th	Day	14% 10% 3 9% 7% 5% 4 3 4 5% 36%	2758
	21st to end	Day	18% 10% 3 7% 5% 5% 5% 3 5% 5% 35%	3124
February	1st to 10th	Day	13% 9% 3 6% 5% 4 5% 4 6% 7% 38%	1710
	11th to 20th	Day	15% 8% 2 6% 5% 4 4 4 6% 7% 39%	1739
	21st to end	Day	18% 11% 2 8% 5% 3 3 2 4 6% 38%	1570
March	1st to 10th	Day	22% 6% 2 6% 4 4 4 3 4 6% 38%	3279
	11th to 20th	Day	9% 5% 2 6% 5% 4 4 4 6% 7% 46%	3480
	21st to end	Day	20% 8% 2 6% 4 3 3 3 4 5% 42%	3936
April	1st to 10th	Day	14% 8% 2 6% 4 5% 4 5% 6% 7% 38%	2280
	11th to 20th	Day	13% 6% 2 6% 5% 4 4 4 5% 7% 44%	2254
	21st to end	Day	18% 6% 2 6% 4 4 3 4 6% 7% 40%	2280
May	1st to 10th	Day	28% 8% 2 6% 4 4 4 3 6% 7% 29%	4005
	11th to 20th	Day	23% 8% 3 7% 5% 4 4 4 6% 7% 28%	4398
	21st to end	Day	12% 5% 2 5% 4 4 4 4 7% 9% 43%	4823
June	1st to 10th	Day	12% 6% 2 7% 4 5% 5% 5% 7% 10% 37%	2660
	11th to 20th	Day	12% 6% 2 6% 5% 5% 5% 5% 8% 8% 39%	2660
	21st to end	Day	10% 3 2 6% 5% 4 5% 4 7% 10% 42%	2660
July	1st to 10th	Day	6% 5% 2 6% 6% 5% 6% 5% 9% 11% 39%	4440
	11th to 20th	Day	9% 6% 2 6% 5% 5% 6% 6% 8% 10% 37%	4440
	21st to end	Day	10% 8% 3 8% 5% 6% 5% 5% 7% 9% 34%	4509
August	1st to 10th	Day	18% 6% 2 6% 5% 5% 7% 5% 6% 8% 33%	4104
	11th to 20th	Day	11% 5% 2 6% 4 5% 6% 5% 8% 9% 38%	3834
	21st to end	Day	11% 5% 2 6% 4 4 4 4 6% 8% 46%	4180
September	1st to 10th	Day	15% 6% 2 6% 4 4 4 3 5% 7% 45%	2280
	11th to 20th	Day	12% 6% 1 4 4 4 5% 3 5% 8% 48%	2280
	21st to end	Day	20% 8% 2 6% 3 4 4 4 4 8% 36%	2019
October	1st to 10th	Day	17% 7% 2 5% 4 3 4 2 5% 7% 44%	1900
	11th to 20th	Day	16% 6% 2 5% 4 3 3 3 6% 5% 48%	1900
	21st to end	Day	15% 6% 2 6% 3 3 4 4 4 6% 46%	2090
November	1st to 10th	Day	13% 5% 2 4 3 3 3 3 5% 7% 51%	1741
	11th to 20th	Day	16% 6% 2 4 3 4 4 3 5% 6% 48%	1706
	21st to end	Day	15% 7% 2 5% 4 4 4 3 4 7% 45%	1520
December	1st to 10th	Day	17% 8% 3 6% 5% 4 4 4 6% 7% 37%	1520
	11th to 20th	Day	18% 7% 2 6% 3 4 4 4 5% 7% 40%	1910
	21st to end	Day	15% 8% 2 7% 6% 4 5% 4 6% 6% 36%	2772
January	1st to 10th	Night	14% 7% 3 6% 4 5% 4 3 5% 7% 41%	4429
	11th to 20th	Night	18% 9% 2 6% 3 3 3 3 4 6% 43%	4184
	21st to end	Night	21% 9% 3 6% 4 3 3 3 5% 5% 39%	4532
February	1st to 10th	Night	16% 9% 3 6% 4 4 3 3 5% 7% 40%	2470
	11th to 20th	Night	17% 8% 3 6% 4 4 4 3 5% 5% 42%	2326
	21st to end	Night	16% 9% 2 7% 4 4 4 4 4 6% 40%	1884
March	1st to 10th	Night	20% 8% 3 6% 4 3 4 3 4 5% 39%	3556
	11th to 20th	Night	10% 6% 2 5% 4 4 4 3 5% 6% 50%	3480
	21st to end	Night	15% 9% 3 6% 4 3 3 2 3 5% 47%	3695
April	1st to 10th	Night	16% 8% 2 6% 5% 5% 4 3 6% 7% 39%	1900
	11th to 20th	Night	14% 6% 2 6% 4 4 4 4 5% 8% 43%	1875
	21st to end	Night	19% 7% 2 5% 3 3 3 4 5% 6% 43%	1900
May	1st to 10th	Night	24% 8% 3 6% 4 3 3 4 5% 8% 31%	2919
	11th to 20th	Night	24% 12% 4 7% 4 3 3 3 5% 6% 28%	2495
	21st to end	Night	12% 6% 2 5% 3 4 4 4 8% 10% 42%	2732
June	1st to 10th	Night	12% 5% 2 5% 5% 4 4 4 5% 9% 45%	1520
	11th to 20th	Night	11% 6% 2 6% 5% 5% 5% 4 8% 9% 40%	1520
	21st to end	Night	10% 4 1 5% 4 5% 6% 5% 6% 10% 43%	1520
July	1st to 10th	Night	6% 5% 3 8% 6% 6% 6% 4 8% 10% 39%	2520
	11th to 20th	Night	8% 6% 2 7% 5% 5% 5% 6% 8% 10% 38%	2520
	21st to end	Night	12% 8% 3 7% 4 5% 4 4 6% 8% 39%	3041
August	1st to 10th	Night	19% 5% 2 6% 5% 4 5% 4 6% 10% 34%	2825
	11th to 20th	Night	12% 8% 2 8% 4 4 5% 3 6% 8% 39%	2962
	21st to end	Night	12% 6% 2 5% 4 3 4 3 5% 8% 48%	3476
September	1st to 10th	Night	13% 7% 2 6% 3 3 4 3 5% 7% 46%	1900
	11th to 20th	Night	12% 6% 2 5% 3 3 3 2 4 7% 53%	1900
	21st to end	Night	20% 7% 2 6% 3 4 3 3 4 6% 41%	2156
October	1st to 10th	Night	19% 6% 3 5% 4 3 3 3 5% 4 44%	2280
	11th to 20th	Night	15% 5% 2 5% 2 3 4 3 5% 6% 51%	2280
	21st to end	Night	17% 6% 1 4 3 4 4 3 5% 7% 48%	2508
November	1st to 10th	Night	11% 6% 2 5% 4 3 4 3 4 5% 53%	2457
	11th to 20th	Night	15% 7% 2 5% 4 3 4 3 4 6% 47%	2472
	21st to end	Night	13% 5% 2 5% 5% 4 4 3 6% 7% 47%	2660
December	1st to 10th	Night	17% 8% 3 6% 4 4 5% 3 5% 7% 38%	2660
	11th to 20th	Night	17% 6% 2 5% 4 4 4 4 5% 7% 42%	3285
	21st to end	Night	16% 7% 3 7% 5% 5% 5% 5% 7% 7% 34%	4884

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	24% 38% 8% 19% 8% 3	2518
	11th to 20th	Day	34% 38% 5% 12% 9% 3	2758
	21st to end	Day	32% 42% 6% 14% 5% 1	3124
February	1st to 10th	Day	17% 66% 6% 7% 3 1	1710
	11th to 20th	Day	15% 65% 3 9% 6% 2	1748
	21st to end	Day	17% 66% 4 8% 5% 1	1570
March	1st to 10th	Day	32% 42% 6% 14% 5% 2	3279
	11th to 20th	Day	19% 42% 6% 20% 12% 2	3480
	21st to end	Day	27% 41% 6% 12% 12% 2	3936
April	1st to 10th	Day	17% 66% 3 6% 6% 1	2280
	11th to 20th	Day	14% 67% 5% 8% 5% 1	2254
	21st to end	Day	16% 65% 4 7% 7% 1	2280
May	1st to 10th	Day	36% 42% 6% 11% 4	4041
	11th to 20th	Day	35% 44% 9% 11% 2	4402
	21st to end	Day	19% 43% 10% 16% 12% 1	4837
June	1st to 10th	Day	15% 66% 3 9% 5%	2660
	11th to 20th	Day	14% 66% 4 9% 6% 1	2660
	21st to end	Day	13% 65% 6% 9% 7%	2660
July	1st to 10th	Day	25% 39% 13% 13% 8% 3	4370
	11th to 20th	Day	27% 38% 12% 17% 7%	4365
	21st to end	Day	32% 36% 8% 12% 12% 1	4365
August	1st to 10th	Day	33% 38% 8% 16% 4	4091
	11th to 20th	Day	23% 38% 8% 21% 9%	3873
	21st to end	Day	20% 37% 7% 21% 14% 1	4180
September	1st to 10th	Day	15% 61% 5% 9% 8% 2	2280
	11th to 20th	Day	15% 59% 4 11% 8% 2	2280
	21st to end	Day	22% 60% 3 9% 6%	2019
October	1st to 10th	Day	24% 37% 3 10% 22% 4	3160
	11th to 20th	Day	13% 37% 6% 19% 17% 8%	3140
	21st to end	Day	10% 36% 8% 21% 22% 4	3428
November	1st to 10th	Day	17% 58% 6% 9% 7% 3	1741
	11th to 20th	Day	13% 60% 4 11% 12% 1	1706
	21st to end	Day	14% 60% 6% 14% 5% 2	1520
December	1st to 10th	Day	22% 60% 6% 7% 5% 1	1520
	11th to 20th	Day	23% 48% 4 18% 6% 1	1906
	21st to end	Day	32% 40% 10% 12% 6%	2772
January	1st to 10th	Night	27% 38% 7% 17% 8% 3	4429
	11th to 20th	Night	27% 37% 7% 17% 10% 2	4184
	21st to end	Night	32% 40% 4 16% 6% 1	4532
February	1st to 10th	Night	16% 66% 5% 10% 3 1	2470
	11th to 20th	Night	16% 64% 2 7% 9% 1	2328
	21st to end	Night	15% 65% 4 8% 5% 2	1884
March	1st to 10th	Night	34% 42% 4 14% 5% 1	3556
	11th to 20th	Night	16% 41% 7% 24% 10% 1	3480
	21st to end	Night	24% 40% 4 12% 16% 3	3695
April	1st to 10th	Night	17% 65% 3 9% 6% 1	1900
	11th to 20th	Night	13% 67% 5% 8% 6% 1	1875
	21st to end	Night	15% 65% 3 8% 7% 1	1900
May	1st to 10th	Night	36% 42% 5% 11% 6% 1	2949
	11th to 20th	Night	39% 42% 7% 9% 3	2496
	21st to end	Night	21% 44% 9% 15% 8% 2	2739
June	1st to 10th	Night	14% 66% 3 10% 7%	1520
	11th to 20th	Night	13% 66% 5% 9% 7%	1520
	21st to end	Night	12% 65% 5% 11% 5% 1	1520
July	1st to 10th	Night	25% 39% 14% 10% 8% 3	2480
	11th to 20th	Night	28% 38% 11% 16% 6%	2472
	21st to end	Night	32% 37% 8% 13% 10% 1	2944
August	1st to 10th	Night	34% 38% 12% 12% 4 1	2814
	11th to 20th	Night	25% 38% 6% 21% 9%	2989
	21st to end	Night	20% 37% 5% 25% 12% 1	3476
September	1st to 10th	Night	15% 61% 6% 10% 7% 2	1900
	11th to 20th	Night	15% 60% 4 10% 10% 2	1900
	21st to end	Night	21% 60% 4 8% 7%	2156
October	1st to 10th	Night	29% 37% 7% 11% 16% 1	3800
	11th to 20th	Night	12% 36% 7% 18% 22% 5%	3779
	21st to end	Night	12% 36% 8% 23% 18% 4	4120
November	1st to 10th	Night	15% 58% 6% 12% 7% 3	2457
	11th to 20th	Night	14% 59% 3 9% 11% 2	2472
	21st to end	Night	13% 60% 5% 14% 7% 1	2660
December	1st to 10th	Night	20% 61% 6% 8% 6%	2660
	11th to 20th	Night	21% 49% 6% 11% 11% 3	3288
	21st to end	Night	30% 41% 10% 12% 7% 1	4884

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	26% 27% 29% 14% 3 1	180
	11th to 20th	Day	33% 24% 28% 14% 1	249
	21st to end	Day	20% 30% 33% 10% 6%	297
February	1st to 10th	Day	24% 23% 38% 11% 4	270
	11th to 20th	Day	27% 27% 38% 6% 2	346
	21st to end	Day	31% 19% 32% 16% 2	382
March	1st to 10th	Day	22% 24% 31% 19% 3	460
	11th to 20th	Day	22% 25% 32% 16% 4 2	460
	21st to end	Day	25% 19% 33% 17% 5% 1	506
April	1st to 10th	Day	22% 21% 34% 17% 5% 1	460
	11th to 20th	Day	18% 21% 29% 19% 9% 4	452
	21st to end	Day	25% 15% 33% 19% 6% 2	460
May	1st to 10th	Day	25% 18% 26% 19% 10% 2	463
	11th to 20th	Day	21% 14% 28% 23% 11% 3	487
	21st to end	Day	18% 6% 24% 26% 20% 5%	529
June	1st to 10th	Day	14% 10% 31% 24% 16% 5%	490
	11th to 20th	Day	16% 7% 26% 30% 15% 5%	490
	21st to end	Day	13% 7% 27% 33% 14% 6%	490
July	1st to 10th	Day	13% 3 20% 30% 25% 11%	485
	11th to 20th	Day	6% 3 21% 36% 27% 8%	484
	21st to end	Day	12% 5% 24% 33% 20% 6%	532
August	1st to 10th	Day	12% 4 21% 31% 23% 8%	486
	11th to 20th	Day	12% 3 18% 35% 21% 10%	479
	21st to end	Day	10% 5% 21% 31% 22% 11%	539
September	1st to 10th	Day	19% 7% 19% 22% 21% 11%	490
	11th to 20th	Day	15% 4 20% 29% 22% 9%	490
	21st to end	Day	28% 10% 21% 24% 13% 4	490
October	1st to 10th	Day	23% 7% 24% 24% 15% 6%	490
	11th to 20th	Day	18% 14% 26% 25% 13% 3	490
	21st to end	Day	17% 13% 37% 23% 9% 2	539
November	1st to 10th	Day	16% 12% 30% 27% 12% 2	394
	11th to 20th	Day	19% 17% 33% 20% 10%	366
	21st to end	Day	23% 19% 33% 18% 6% 1	180
December	1st to 10th	Day	25% 22% 35% 13% 3 2	180
	11th to 20th	Day	29% 22% 30% 13% 6%	180
	21st to end	Day	23% 20% 32% 17% 8%	198
January	1st to 10th	Night	18% 17% 43% 19% 3	760
	11th to 20th	Night	23% 17% 33% 24% 3	760
	21st to end	Night	18% 18% 43% 20% 1	836
February	1st to 10th	Night	20% 18% 37% 23% 2	760
	11th to 20th	Night	23% 22% 38% 16% 1	743
	21st to end	Night	22% 22% 37% 17% 3	628
March	1st to 10th	Night	19% 18% 38% 21% 4	760
	11th to 20th	Night	21% 19% 35% 19% 5% 1	760
	21st to end	Night	20% 15% 39% 20% 5%	836
April	1st to 10th	Night	21% 19% 38% 19% 4	760
	11th to 20th	Night	17% 13% 34% 28% 7%	751
	21st to end	Night	22% 12% 33% 25% 7%	760
May	1st to 10th	Night	21% 10% 28% 31% 9% 1	640
	11th to 20th	Night	20% 7% 32% 31% 9%	374
	21st to end	Night	16% 4 21% 42% 17% 1	411
June	1st to 10th	Night	12% 4 25% 39% 19% 1	380
	11th to 20th	Night	12% 4 24% 44% 15% 1	380
	21st to end	Night	11% 3 23% 46% 16%	380
July	1st to 10th	Night	10% 1 18% 40% 27% 2	370
	11th to 20th	Night	7% 2 15% 45% 28% 3	368
	21st to end	Night	10% 2 17% 45% 25% 2	591
August	1st to 10th	Night	12% 2 13% 44% 26% 2	567
	11th to 20th	Night	13% 2 18% 37% 28% 2	663
	21st to end	Night	14% 2 15% 40% 26% 3	836
September	1st to 10th	Night	16% 3 21% 33% 23% 4	760
	11th to 20th	Night	13% 3 17% 36% 26% 4	760
	21st to end	Night	23% 4 21% 31% 19% 2	760
October	1st to 10th	Night	21% 6% 23% 27% 18% 4	760
	11th to 20th	Night	18% 9% 29% 31% 12% 1	760
	21st to end	Night	19% 11% 32% 25% 13%	836
November	1st to 10th	Night	14% 9% 34% 32% 10% 1	764
	11th to 20th	Night	19% 15% 31% 27% 7% 1	760
	21st to end	Night	15% 16% 35% 26% 7%	760
December	1st to 10th	Night	22% 16% 36% 20% 6%	760
	11th to 20th	Night	18% 15% 40% 22% 5%	760
	21st to end	Night	19% 16% 36% 27% 2	836

Page generated at 2024-11-03 13:19:01. Version ac07

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