SOLO Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the SOLO 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	12% 10% 4 9% 5% 5% 5% 4 5% 7% 35%	101642
	Night	13% 12% 4 10% 6% 5% 5% 4 5% 6% 31%	97460
Transparency	Day	47% 8% 14% 21% 9% 1	101398
	Night	51% 8% 13% 19% 8% 1	97322
Seeing	Day	16% 6% 23% 34% 18% 4	16106
	Night	18% 7% 25% 32% 16% 2	25972

By Month

Percentage Cloud Cover NE (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	8% 17% 9% 19% 8% 7% 6% 3 4 4 15%	2527
	11th to 20th	Day	6% 15% 5% 17% 13% 12% 11% 5% 5% 3 8%	2530
	21st to end	Day	6% 18% 8% 18% 8% 7% 6% 4 5% 5% 15%	2856
February	1st to 10th	Day	8% 13% 4 11% 7% 8% 6% 6% 6% 7% 24%	1710
	11th to 20th	Day	8% 12% 6% 10% 6% 5% 6% 5% 5% 7% 30%	1664
	21st to end	Day	9% 12% 4 11% 7% 5% 5% 4 6% 7% 29%	1527
March	1st to 10th	Day	8% 11% 4 8% 5% 5% 5% 5% 5% 6% 38%	3150
	11th to 20th	Day	7% 11% 5% 13% 7% 4 4 4 4 6% 34%	3480
	21st to end	Day	18% 11% 4 12% 4 3 4 3 5% 6% 30%	3998
April	1st to 10th	Day	14% 11% 4 9% 5% 5% 5% 4 4 6% 31%	2280
	11th to 20th	Day	19% 12% 3 7% 4 4 5% 4 5% 6% 31%	2254
	21st to end	Day	21% 11% 3 7% 5% 3 5% 3 4 6% 34%	2481
May	1st to 10th	Day	17% 8% 3 6% 4 4 4 3 5% 6% 40%	4428
	11th to 20th	Day	13% 7% 2 6% 5% 5% 5% 3 6% 7% 41%	4399
	21st to end	Day	17% 8% 3 7% 5% 5% 4 4 5% 7% 35%	4837
June	1st to 10th	Day	10% 6% 2 6% 4 4 5% 4 6% 9% 45%	2660
	11th to 20th	Day	13% 6% 3 7% 5% 5% 5% 4 6% 8% 40%	2660
	21st to end	Day	13% 6% 2 6% 4 5% 5% 4 7% 9% 39%	2660
July	1st to 10th	Day	9% 6% 2 5% 3 4 4 4 6% 10% 48%	4440
	11th to 20th	Day	6% 4 2 5% 4 4 4 4 7% 9% 51%	4440
	21st to end	Day	7% 5% 2 4 4 3 4 4 6% 9% 54%	4814
August	1st to 10th	Day	12% 7% 3 6% 4 5% 5% 4 6% 8% 41%	4394
	11th to 20th	Day	13% 5% 2 4 3 3 3 3 5% 7% 52%	4041
	21st to end	Day	11% 8% 2 7% 4 4 5% 4 6% 8% 42%	4249
September	1st to 10th	Day	11% 6% 2 6% 4 4 5% 3 6% 9% 46%	2280
	11th to 20th	Day	11% 7% 3 7% 5% 5% 5% 3 6% 8% 42%	2280
	21st to end	Day	17% 8% 3 8% 4 4 4 2 4 6% 40%	2013
October	1st to 10th	Day	18% 10% 3 7% 5% 4 4 4 5% 7% 35%	1900
	11th to 20th	Day	18% 14% 4 8% 5% 4 5% 4 4 6% 28%	1900
	21st to end	Day	21% 15% 4 7% 5% 4 4 3 4 5% 27%	1932
November	1st to 10th	Day	12% 17% 5% 10% 4 5% 4 3 5% 6% 29%	1601
	11th to 20th	Day	15% 18% 8% 15% 7% 5% 4 3 4 4 18%	1520
	21st to end	Day	15% 13% 6% 12% 8% 5% 5% 4 6% 5% 20%	1520
December	1st to 10th	Day	10% 18% 6% 16% 12% 8% 6% 2 4 5% 13%	1520
	11th to 20th	Day	12% 18% 7% 18% 9% 7% 7% 3 4 3 12%	1914
	21st to end	Day	21% 20% 6% 18% 6% 5% 4 3 3 2 13%	2783
January	1st to 10th	Night	10% 17% 8% 15% 7% 7% 6% 3 4 5% 18%	4428
	11th to 20th	Night	7% 13% 7% 16% 11% 18% 9% 5% 3 3 8%	4440
	21st to end	Night	8% 20% 8% 17% 7% 5% 5% 3 4 4 18%	4806
February	1st to 10th	Night	7% 13% 5% 13% 8% 7% 7% 4 6% 5% 25%	2470
	11th to 20th	Night	8% 11% 4 10% 7% 7% 6% 5% 7% 6% 29%	2403
	21st to end	Night	10% 15% 5% 9% 6% 6% 4 3 5% 7% 31%	1927
March	1st to 10th	Night	8% 9% 3 8% 5% 5% 5% 3 5% 7% 42%	3708
	11th to 20th	Night	9% 12% 5% 14% 6% 4 4 3 5% 6% 32%	3479
	21st to end	Night	21% 13% 5% 11% 5% 4 3 2 3 4 28%	3632
April	1st to 10th	Night	17% 14% 4 8% 5% 4 5% 3 5% 5% 31%	1900
	11th to 20th	Night	19% 11% 3 7% 4 4 4 4 5% 6% 32%	1875
	21st to end	Night	20% 12% 3 6% 5% 4 4 4 5% 5% 34%	1695
May	1st to 10th	Night	16% 7% 4 8% 4 4 4 4 5% 8% 36%	2523
	11th to 20th	Night	13% 7% 3 6% 5% 4 5% 4 5% 6% 44%	2506
	21st to end	Night	14% 8% 4 7% 7% 5% 5% 5% 6% 7% 32%	2750
June	1st to 10th	Night	14% 6% 1 7% 4 5% 5% 4 6% 7% 40%	1520
	11th to 20th	Night	12% 6% 2 7% 4 5% 4 4 8% 8% 39%	1520
	21st to end	Night	12% 6% 2 7% 6% 5% 4 5% 6% 8% 40%	1520
July	1st to 10th	Night	9% 6% 2 5% 4 4 4 4 6% 10% 48%	2530
	11th to 20th	Night	6% 4 2 5% 3 4 4 4 5% 9% 54%	2530
	21st to end	Night	7% 6% 1 4 3 3 4 3 6% 8% 56%	2750
August	1st to 10th	Night	13% 6% 2 5% 3 4 4 4 5% 7% 44%	2543
	11th to 20th	Night	12% 5% 2 5% 3 4 4 3 6% 8% 48%	2798
	21st to end	Night	15% 7% 2 6% 4 4 4 3 5% 6% 43%	3408
September	1st to 10th	Night	11% 5% 2 7% 4 3 4 4 4 8% 49%	1900
	11th to 20th	Night	11% 6% 2 6% 4 3 5% 4 5% 7% 47%	1900
	21st to end	Night	17% 7% 2 6% 4 3 4 3 5% 7% 41%	2144
October	1st to 10th	Night	16% 10% 3 6% 3 3 3 3 5% 6% 41%	2280
	11th to 20th	Night	17% 14% 3 8% 5% 3 4 3 5% 5% 31%	2280
	21st to end	Night	22% 14% 4 8% 5% 4 4 3 5% 6% 26%	2665
November	1st to 10th	Night	14% 16% 5% 9% 5% 4 4 3 5% 6% 28%	2483
	11th to 20th	Night	14% 18% 8% 14% 6% 5% 4 3 4 5% 21%	2660
	21st to end	Night	14% 13% 5% 15% 7% 5% 4 4 5% 5% 23%	2660
December	1st to 10th	Night	11% 18% 8% 16% 10% 6% 4 3 5% 4 15%	2660
	11th to 20th	Night	12% 15% 7% 15% 10% 7% 6% 4 4 4 16%	3283
	21st to end	Night	24% 20% 5% 12% 6% 5% 4 3 3 4 14%	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	69% 7% 9% 12% 2	2528
	11th to 20th	Day	72% 9% 11% 7% 1	2530
	21st to end	Day	67% 10% 11% 10% 2	2856
February	1st to 10th	Day	55% 7% 13% 17% 6%	1710
	11th to 20th	Day	51% 8% 13% 22% 6%	1673
	21st to end	Day	53% 7% 14% 15% 11% 1	1527
March	1st to 10th	Day	44% 10% 13% 23% 10% 1	3152
	11th to 20th	Day	48% 9% 15% 18% 10%	3480
	21st to end	Day	55% 6% 13% 20% 5% 1	3998
April	1st to 10th	Day	53% 7% 11% 17% 11% 1	2280
	11th to 20th	Day	53% 7% 11% 17% 10% 2	2254
	21st to end	Day	52% 5% 11% 21% 10% 1	2481
May	1st to 10th	Day	43% 7% 12% 23% 14% 1	4440
	11th to 20th	Day	40% 10% 15% 25% 9% 1	4403
	21st to end	Day	47% 9% 12% 18% 13% 1	4837
June	1st to 10th	Day	35% 9% 19% 24% 12% 1	2660
	11th to 20th	Day	41% 9% 14% 21% 14% 1	2660
	21st to end	Day	38% 9% 19% 24% 8% 1	2660
July	1st to 10th	Day	32% 8% 22% 24% 14% 1	4371
	11th to 20th	Day	26% 8% 19% 33% 12% 1	4365
	21st to end	Day	27% 7% 16% 33% 16% 1	4662
August	1st to 10th	Day	40% 7% 18% 24% 10% 1	4379
	11th to 20th	Day	31% 7% 21% 32% 8%	4080
	21st to end	Day	37% 10% 18% 24% 10%	4248
September	1st to 10th	Day	35% 7% 18% 30% 10%	2280
	11th to 20th	Day	40% 9% 18% 27% 6%	2280
	21st to end	Day	46% 7% 14% 26% 8%	2013
October	1st to 10th	Day	48% 7% 15% 24% 6%	1900
	11th to 20th	Day	56% 7% 12% 17% 7%	1900
	21st to end	Day	59% 8% 11% 17% 6%	1932
November	1st to 10th	Day	56% 6% 11% 18% 8% 1	1601
	11th to 20th	Day	70% 6% 10% 10% 4	1520
	21st to end	Day	62% 9% 12% 13% 4 1	1520
December	1st to 10th	Day	72% 8% 11% 8% 1	1520
	11th to 20th	Day	72% 9% 9% 8% 2	1915
	21st to end	Day	77% 5% 6% 9% 2	2783
January	1st to 10th	Night	65% 8% 12% 11% 3	4428
	11th to 20th	Night	69% 13% 11% 5% 1	4440
	21st to end	Night	66% 8% 11% 13% 2	4806
February	1st to 10th	Night	57% 7% 12% 17% 6% 1	2470
	11th to 20th	Night	50% 7% 15% 19% 8%	2404
	21st to end	Night	52% 6% 12% 20% 8% 2	1927
March	1st to 10th	Night	39% 8% 16% 20% 15% 2	3719
	11th to 20th	Night	51% 7% 12% 23% 7% 1	3480
	21st to end	Night	60% 5% 8% 15% 10% 1	3632
April	1st to 10th	Night	54% 6% 9% 16% 14% 1	1900
	11th to 20th	Night	51% 7% 10% 19% 11% 2	1875
	21st to end	Night	51% 5% 8% 24% 11% 1	1695
May	1st to 10th	Night	44% 9% 14% 23% 10% 1	2530
	11th to 20th	Night	38% 8% 10% 26% 14% 3	2507
	21st to end	Night	46% 11% 13% 18% 10% 2	2751
June	1st to 10th	Night	40% 8% 15% 23% 12% 2	1520
	11th to 20th	Night	38% 9% 15% 19% 17% 2	1520
	21st to end	Night	40% 9% 12% 28% 11% 1	1520
July	1st to 10th	Night	31% 9% 21% 25% 12% 3	2490
	11th to 20th	Night	24% 8% 17% 37% 13% 1	2482
	21st to end	Night	24% 7% 14% 34% 18% 2	2662
August	1st to 10th	Night	37% 7% 13% 25% 15% 2	2534
	11th to 20th	Night	33% 8% 17% 33% 9% 1	2825
	21st to end	Night	38% 9% 18% 24% 10% 1	3408
September	1st to 10th	Night	33% 7% 15% 32% 12% 1	1900
	11th to 20th	Night	33% 7% 19% 32% 8%	1900
	21st to end	Night	42% 7% 15% 27% 9%	2144
October	1st to 10th	Night	43% 6% 13% 26% 11% 1	2280
	11th to 20th	Night	53% 7% 13% 19% 8% 1	2280
	21st to end	Night	58% 7% 10% 19% 6%	2665
November	1st to 10th	Night	55% 8% 12% 18% 7%	2483
	11th to 20th	Night	66% 6% 11% 10% 6%	2660
	21st to end	Night	61% 8% 15% 11% 4	2660
December	1st to 10th	Night	69% 8% 11% 10% 2	2660
	11th to 20th	Night	66% 10% 11% 11% 2	3281
	21st to end	Night	73% 7% 7% 10% 3	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	13% 11% 35% 25% 14% 1	270
	11th to 20th	Day	18% 9% 30% 31% 11%	270
	21st to end	Day	15% 9% 28% 34% 12% 1	297
February	1st to 10th	Day	11% 11% 35% 34% 8% 1	270
	11th to 20th	Day	12% 13% 43% 20% 11% 1	270
	21st to end	Day	14% 9% 39% 34% 4	225
March	1st to 10th	Day	14% 9% 28% 37% 13%	270
	11th to 20th	Day	15% 6% 31% 35% 11% 2	270
	21st to end	Day	23% 7% 28% 28% 12% 2	404
April	1st to 10th	Day	16% 9% 31% 33% 8% 2	460
	11th to 20th	Day	23% 8% 22% 33% 11% 2	452
	21st to end	Day	25% 5% 21% 32% 14% 3	598
May	1st to 10th	Day	21% 5% 25% 36% 11% 3	653
	11th to 20th	Day	18% 4 21% 35% 18% 4	675
	21st to end	Day	17% 7% 16% 34% 22% 4	734
June	1st to 10th	Day	11% 4 22% 39% 20% 4	680
	11th to 20th	Day	14% 4 21% 42% 17% 2	680
	21st to end	Day	15% 4 18% 37% 21% 5%	680
July	1st to 10th	Day	10% 1 11% 40% 30% 9%	671
	11th to 20th	Day	9% 3 16% 37% 24% 10%	668
	21st to end	Day	8% 2 12% 41% 27% 9%	739
August	1st to 10th	Day	13% 3 15% 35% 28% 7%	676
	11th to 20th	Day	12% 5% 11% 32% 34% 6%	665
	21st to end	Day	15% 5% 15% 33% 25% 6%	582
September	1st to 10th	Day	12% 3 17% 40% 25% 4	490
	11th to 20th	Day	13% 7% 17% 35% 24% 4	490
	21st to end	Day	21% 7% 23% 26% 18% 5%	390
October	1st to 10th	Day	20% 5% 26% 31% 14% 4	300
	11th to 20th	Day	20% 11% 30% 30% 8% 1	300
	21st to end	Day	27% 9% 32% 26% 7%	330
November	1st to 10th	Day	19% 8% 34% 29% 10%	270
	11th to 20th	Day	20% 14% 33% 24% 8% 1	270
	21st to end	Day	20% 10% 33% 31% 6% 1	270
December	1st to 10th	Day	17% 13% 36% 26% 8% 2	270
	11th to 20th	Day	20% 17% 30% 25% 7%	270
	21st to end	Day	24% 14% 33% 24% 4 1	297
January	1st to 10th	Night	15% 11% 35% 28% 10% 1	950
	11th to 20th	Night	16% 9% 36% 28% 9% 1	950
	21st to end	Night	17% 8% 35% 30% 8% 1	1045
February	1st to 10th	Night	14% 10% 32% 33% 9% 1	950
	11th to 20th	Night	13% 8% 35% 31% 12% 1	929
	21st to end	Night	17% 6% 30% 37% 10%	671
March	1st to 10th	Night	16% 7% 27% 38% 11% 1	759
	11th to 20th	Night	18% 5% 32% 34% 11% 1	570
	21st to end	Night	21% 4 26% 32% 14% 4	627
April	1st to 10th	Night	22% 8% 26% 34% 8% 2	570
	11th to 20th	Night	25% 5% 20% 36% 12% 2	563
	21st to end	Night	27% 3 19% 32% 15% 4	570
May	1st to 10th	Night	19% 5% 23% 36% 14% 2	570
	11th to 20th	Night	17% 3 19% 39% 18% 4	561
	21st to end	Night	17% 6% 14% 36% 27% 1	617
June	1st to 10th	Night	15% 4 17% 37% 24% 2	570
	11th to 20th	Night	17% 3 13% 44% 22% 1	570
	21st to end	Night	14% 4 14% 40% 24% 4	570
July	1st to 10th	Night	7% 3 10% 37% 36% 6%	555
	11th to 20th	Night	10% 2 16% 37% 29% 5%	552
	21st to end	Night	9% 2 11% 41% 30% 6%	624
August	1st to 10th	Night	11% 3 10% 41% 32% 3	567
	11th to 20th	Night	13% 4 13% 32% 34% 5%	564
	21st to end	Night	15% 3 14% 34% 30% 4	627
September	1st to 10th	Night	13% 3 18% 34% 27% 5%	570
	11th to 20th	Night	14% 4 17% 38% 25% 4	570
	21st to end	Night	19% 5% 24% 26% 22% 3	717
October	1st to 10th	Night	22% 5% 24% 29% 17% 3	760
	11th to 20th	Night	23% 9% 29% 28% 11% 1	760
	21st to end	Night	30% 7% 25% 29% 9%	836
November	1st to 10th	Night	21% 10% 28% 32% 8% 1	813
	11th to 20th	Night	22% 13% 32% 22% 10% 1	950
	21st to end	Night	21% 13% 33% 26% 7%	950
December	1st to 10th	Night	20% 13% 35% 24% 8%	950
	11th to 20th	Night	22% 14% 31% 24% 8% 1	950
	21st to end	Night	28% 10% 34% 22% 6%	1045

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