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 2026-09-14.

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	11% 9% 4 9% 5% 5% 5% 4 5% 7% 36%	149974
	Night	12% 11% 4 11% 6% 6% 5% 4 5% 6% 31%	141510
Transparency	Day	45% 7% 14% 23% 9% 1	153438
	Night	51% 7% 12% 20% 9% 1	146132
Seeing	Day	16% 6% 23% 34% 18% 4	18750
	Night	18% 7% 25% 32% 16% 2	28530

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	6% 12% 7% 21% 9% 9% 6% 3 4 5% 16%	4691
	11th to 20th	Day	6% 15% 7% 16% 9% 12% 11% 8% 4 3 9%	4679
	21st to end	Day	4 14% 7% 13% 7% 8% 10% 5% 7% 5% 20%	5313
February	1st to 10th	Day	8% 14% 4 12% 7% 8% 6% 6% 6% 7% 23%	1890
	11th to 20th	Day	7% 12% 6% 10% 6% 5% 7% 5% 5% 7% 30%	1844
	21st to end	Day	9% 12% 4 11% 7% 5% 5% 5% 6% 7% 29%	1683
March	1st to 10th	Day	10% 10% 3 7% 5% 4 5% 4 5% 8% 38%	4625
	11th to 20th	Day	8% 11% 5% 12% 7% 5% 5% 4 5% 7% 31%	5090
	21st to end	Day	20% 11% 4 9% 4 3 4 3 5% 5% 33%	5859
April	1st to 10th	Day	15% 11% 4 9% 5% 5% 5% 4 5% 6% 31%	2520
	11th to 20th	Day	18% 12% 3 8% 5% 4 4 3 5% 6% 31%	2494
	21st to end	Day	21% 11% 3 7% 4 3 5% 3 4 6% 34%	2742
May	1st to 10th	Day	11% 6% 2 5% 4 3 4 4 5% 7% 50%	8241
	11th to 20th	Day	13% 8% 3 7% 5% 4 5% 3 5% 6% 42%	8222
	21st to end	Day	12% 7% 3 6% 4 4 4 3 5% 8% 45%	9061
June	1st to 10th	Day	10% 6% 2 6% 4 4 5% 4 6% 9% 44%	2940
	11th to 20th	Day	13% 6% 3 7% 5% 5% 5% 4 6% 8% 38%	2940
	21st to end	Day	13% 6% 2 6% 4 5% 5% 4 6% 9% 39%	2940
July	1st to 10th	Day	9% 6% 2 5% 3 4 4 4 6% 11% 46%	8279
	11th to 20th	Day	8% 5% 2 5% 3 4 4 4 7% 10% 48%	8280
	21st to end	Day	8% 5% 2 5% 4 3 4 4 6% 9% 49%	8992
August	1st to 10th	Day	9% 6% 2 6% 4 4 5% 4 6% 8% 46%	6439
	11th to 20th	Day	12% 6% 2 5% 3 3 4 3 6% 8% 49%	5948
	21st to end	Day	11% 8% 3 7% 4 4 5% 3 6% 8% 41%	6177
September	1st to 10th	Day	12% 7% 2 6% 4 4 5% 3 6% 8% 45%	2520
	11th to 20th	Day	11% 7% 3 7% 5% 5% 5% 3 6% 8% 42%	2436
	21st to end	Day	16% 8% 3 8% 4 4 4 2 4 6% 40%	2119
October	1st to 10th	Day	17% 9% 2 7% 5% 4 4 4 5% 7% 36%	2000
	11th to 20th	Day	18% 14% 4 8% 5% 4 5% 4 5% 6% 28%	2000
	21st to end	Day	21% 15% 4 8% 5% 4 4 3 3 5% 27%	2033
November	1st to 10th	Day	13% 17% 6% 10% 4 5% 4 3 4 6% 28%	1773
	11th to 20th	Day	14% 17% 7% 14% 7% 5% 4 3 4 4 21%	1680
	21st to end	Day	15% 15% 6% 14% 7% 5% 5% 4 5% 5% 20%	1680
December	1st to 10th	Day	8% 18% 8% 26% 10% 6% 4 2 3 3 11%	2690
	11th to 20th	Day	9% 17% 7% 16% 11% 7% 9% 3 3 3 14%	3084
	21st to end	Day	17% 18% 6% 19% 7% 6% 4 3 3 3 14%	4070
January	1st to 10th	Night	7% 14% 8% 20% 9% 8% 5% 3 4 4 18%	8233
	11th to 20th	Night	6% 16% 7% 16% 11% 14% 10% 7% 3 3 7%	8236
	21st to end	Night	5% 15% 5% 14% 9% 9% 8% 7% 7% 4 16%	8896
February	1st to 10th	Night	7% 14% 5% 12% 8% 8% 7% 4 6% 5% 24%	2730
	11th to 20th	Night	8% 11% 4 11% 7% 7% 7% 5% 7% 6% 28%	2663
	21st to end	Night	10% 14% 5% 10% 7% 6% 5% 3 5% 7% 30%	2123
March	1st to 10th	Night	9% 8% 3 7% 4 4 4 4 5% 6% 44%	5468
	11th to 20th	Night	11% 13% 5% 13% 6% 4 5% 3 5% 5% 28%	5089
	21st to end	Night	21% 13% 5% 10% 4 3 3 2 4 5% 30%	5313
April	1st to 10th	Night	18% 15% 4 7% 5% 4 4 3 5% 5% 30%	2100
	11th to 20th	Night	19% 11% 3 7% 4 4 4 4 5% 6% 33%	2075
	21st to end	Night	21% 12% 3 6% 4 4 3 3 5% 5% 34%	1873
May	1st to 10th	Night	12% 6% 3 7% 4 4 4 4 6% 8% 43%	4688
	11th to 20th	Night	18% 7% 3 5% 4 4 4 3 4 5% 44%	4670
	21st to end	Night	11% 7% 3 6% 5% 4 4 4 6% 8% 42%	5148
June	1st to 10th	Night	14% 6% 1 7% 5% 5% 5% 3 6% 7% 40%	1680
	11th to 20th	Night	13% 7% 2 7% 4 5% 4 4 8% 8% 39%	1680
	21st to end	Night	12% 7% 2 7% 5% 5% 4 4 6% 8% 39%	1680
July	1st to 10th	Night	7% 6% 2 5% 4 4 5% 4 7% 11% 45%	4710
	11th to 20th	Night	9% 4 2 4 3 4 4 4 6% 9% 52%	4710
	21st to end	Night	10% 6% 2 7% 4 4 4 4 6% 8% 46%	5118
August	1st to 10th	Night	10% 6% 2 5% 4 5% 4 4 6% 8% 46%	3728
	11th to 20th	Night	11% 7% 2 6% 4 4 4 3 6% 8% 43%	4118
	21st to end	Night	14% 8% 2 7% 5% 5% 4 4 5% 7% 40%	4952
September	1st to 10th	Night	12% 5% 2 7% 4 3 4 4 5% 7% 48%	2100
	11th to 20th	Night	11% 6% 2 5% 4 3 4 4 6% 7% 46%	2030
	21st to end	Night	17% 7% 2 6% 4 3 4 3 5% 7% 42%	2257
October	1st to 10th	Night	16% 10% 3 6% 3 3 3 3 5% 6% 41%	2400
	11th to 20th	Night	17% 14% 3 8% 5% 4 4 3 5% 5% 32%	2400
	21st to end	Night	21% 14% 4 9% 5% 4 4 3 5% 6% 27%	2805
November	1st to 10th	Night	15% 15% 5% 9% 5% 4 4 3 6% 6% 28%	2744
	11th to 20th	Night	14% 18% 7% 13% 6% 5% 3 3 4 5% 23%	2940
	21st to end	Night	13% 13% 5% 17% 7% 5% 4 4 5% 5% 22%	2940
December	1st to 10th	Night	10% 17% 9% 24% 9% 6% 4 3 3 3 11%	4720
	11th to 20th	Night	11% 16% 8% 16% 8% 8% 10% 3 3 3 12%	5343
	21st to end	Night	20% 18% 5% 13% 7% 6% 5% 3 4 4 15%	7150

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	68% 6% 10% 12% 4	4692
	11th to 20th	Day	72% 7% 11% 7% 3	4710
	21st to end	Day	61% 8% 10% 18% 3	5313
February	1st to 10th	Day	57% 7% 13% 17% 7%	1890
	11th to 20th	Day	51% 7% 13% 22% 7%	1853
	21st to end	Day	53% 7% 14% 15% 10% 1	1683
March	1st to 10th	Day	43% 8% 14% 22% 11% 2	4627
	11th to 20th	Day	49% 8% 14% 17% 11% 1	5090
	21st to end	Day	53% 5% 12% 18% 11%	5859
April	1st to 10th	Day	54% 7% 10% 17% 11% 1	2520
	11th to 20th	Day	53% 7% 11% 17% 10% 2	2494
	21st to end	Day	52% 5% 10% 20% 11% 1	2742
May	1st to 10th	Day	32% 6% 13% 30% 18% 1	8250
	11th to 20th	Day	41% 8% 11% 23% 12% 5%	8226
	21st to end	Day	37% 7% 10% 29% 16% 1	9061
June	1st to 10th	Day	35% 9% 18% 24% 12% 1	2940
	11th to 20th	Day	41% 9% 14% 21% 13% 1	2940
	21st to end	Day	39% 9% 19% 24% 9% 1	2940
July	1st to 10th	Day	31% 9% 22% 29% 9%	8211
	11th to 20th	Day	29% 8% 18% 34% 11% 1	8205
	21st to end	Day	30% 8% 18% 31% 14%	8794
August	1st to 10th	Day	34% 7% 20% 28% 10% 1	6424
	11th to 20th	Day	32% 7% 25% 30% 6%	5987
	21st to end	Day	38% 10% 17% 27% 8%	6176
September	1st to 10th	Day	36% 7% 18% 28% 10%	2520
	11th to 20th	Day	40% 9% 18% 27% 6%	2436
	21st to end	Day	45% 7% 14% 26% 8%	2119
October	1st to 10th	Day	38% 5% 17% 30% 9% 1	3260
	11th to 20th	Day	49% 6% 11% 25% 10%	3240
	21st to end	Day	54% 7% 14% 20% 5%	3258
November	1st to 10th	Day	58% 6% 11% 16% 8% 1	1773
	11th to 20th	Day	67% 5% 11% 13% 4	1680
	21st to end	Day	64% 9% 11% 12% 3 1	1680
December	1st to 10th	Day	78% 6% 8% 7% 1	2690
	11th to 20th	Day	71% 8% 8% 8% 4	3085
	21st to end	Day	74% 6% 7% 12% 2	4070
January	1st to 10th	Night	67% 6% 11% 10% 5%	8233
	11th to 20th	Night	75% 9% 9% 5% 2	8280
	21st to end	Night	63% 7% 11% 14% 5%	8896
February	1st to 10th	Night	58% 6% 12% 17% 6% 1	2730
	11th to 20th	Night	52% 7% 14% 19% 8%	2664
	21st to end	Night	53% 6% 12% 20% 8% 1	2123
March	1st to 10th	Night	38% 6% 16% 19% 17% 4	5479
	11th to 20th	Night	55% 7% 11% 20% 7%	5090
	21st to end	Night	58% 5% 9% 15% 12% 1	5313
April	1st to 10th	Night	55% 6% 9% 16% 13% 1	2100
	11th to 20th	Night	51% 6% 10% 20% 11% 2	2075
	21st to end	Night	51% 5% 8% 24% 12% 1	1873
May	1st to 10th	Night	36% 8% 13% 28% 14% 1	4695
	11th to 20th	Night	41% 7% 8% 24% 14% 6%	4671
	21st to end	Night	36% 8% 11% 28% 16% 1	5149
June	1st to 10th	Night	41% 7% 14% 23% 12% 2	1680
	11th to 20th	Night	40% 9% 14% 20% 16% 2	1680
	21st to end	Night	41% 9% 12% 27% 11% 1	1680
July	1st to 10th	Night	31% 9% 19% 29% 10% 2	4670
	11th to 20th	Night	26% 7% 18% 35% 13% 1	4662
	21st to end	Night	34% 7% 14% 30% 15% 1	5002
August	1st to 10th	Night	33% 7% 16% 28% 14% 2	3719
	11th to 20th	Night	37% 8% 19% 28% 7% 1	4145
	21st to end	Night	40% 9% 15% 27% 8% 1	4952
September	1st to 10th	Night	35% 7% 15% 31% 12% 1	2100
	11th to 20th	Night	35% 7% 20% 31% 7%	2030
	21st to end	Night	41% 7% 14% 28% 10%	2257
October	1st to 10th	Night	31% 5% 10% 33% 19% 1	3920
	11th to 20th	Night	48% 6% 12% 21% 13%	3899
	21st to end	Night	56% 5% 11% 21% 7%	4530
November	1st to 10th	Night	55% 8% 12% 18% 7% 1	2744
	11th to 20th	Night	64% 5% 11% 13% 6% 1	2940
	21st to end	Night	63% 8% 14% 10% 4	2940
December	1st to 10th	Night	76% 6% 9% 7% 1	4720
	11th to 20th	Night	73% 8% 8% 9% 2	5341
	21st to end	Night	70% 7% 8% 11% 3	7150

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	12% 10% 34% 30% 14% 1	330
	11th to 20th	Day	16% 9% 31% 31% 12% 1	330
	21st to end	Day	14% 9% 31% 34% 11% 1	363
February	1st to 10th	Day	12% 11% 35% 32% 8% 2	330
	11th to 20th	Day	12% 12% 39% 24% 12% 2	330
	21st to end	Day	13% 9% 39% 34% 5%	273
March	1st to 10th	Day	14% 8% 29% 38% 11% 1	330
	11th to 20th	Day	14% 6% 32% 37% 9% 2	330
	21st to end	Day	23% 7% 29% 29% 10% 2	482
April	1st to 10th	Day	18% 9% 31% 32% 8% 1	540
	11th to 20th	Day	22% 7% 23% 35% 12% 2	532
	21st to end	Day	25% 5% 20% 33% 14% 3	692
May	1st to 10th	Day	18% 5% 24% 35% 15% 3	753
	11th to 20th	Day	17% 4 22% 35% 18% 4	775
	21st to end	Day	16% 6% 15% 36% 23% 4	844
June	1st to 10th	Day	11% 4 21% 39% 22% 3	780
	11th to 20th	Day	14% 5% 21% 42% 16% 2	780
	21st to end	Day	15% 5% 18% 38% 21% 4	780
July	1st to 10th	Day	10% 2 11% 39% 30% 8%	771
	11th to 20th	Day	9% 3 15% 39% 24% 10%	768
	21st to end	Day	8% 2 12% 42% 27% 8%	849
August	1st to 10th	Day	12% 3 15% 35% 28% 7%	776
	11th to 20th	Day	12% 5% 12% 33% 32% 6%	765
	21st to end	Day	14% 6% 14% 33% 27% 5%	674
September	1st to 10th	Day	14% 3 17% 39% 24% 5%	570
	11th to 20th	Day	14% 6% 17% 35% 24% 4	542
	21st to end	Day	20% 6% 23% 25% 21% 5%	425
October	1st to 10th	Day	18% 5% 25% 31% 16% 5%	330
	11th to 20th	Day	21% 10% 31% 30% 8% 1	330
	21st to end	Day	26% 8% 30% 28% 8% 1	363
November	1st to 10th	Day	21% 8% 33% 28% 10%	330
	11th to 20th	Day	18% 14% 33% 26% 8% 2	330
	21st to end	Day	22% 9% 32% 29% 7% 1	330
December	1st to 10th	Day	15% 12% 37% 27% 8% 2	330
	11th to 20th	Day	17% 16% 34% 26% 7%	330
	21st to end	Day	25% 12% 29% 27% 6% 1	363
January	1st to 10th	Night	14% 11% 35% 29% 11% 1	1050
	11th to 20th	Night	16% 10% 36% 29% 9% 1	1050
	21st to end	Night	16% 9% 36% 30% 8% 1	1155
February	1st to 10th	Night	14% 10% 32% 34% 9% 1	1050
	11th to 20th	Night	13% 7% 35% 31% 12% 1	1029
	21st to end	Night	16% 6% 30% 36% 10%	739
March	1st to 10th	Night	16% 7% 27% 39% 11% 1	839
	11th to 20th	Night	19% 5% 31% 34% 10% 1	630
	21st to end	Night	20% 5% 27% 32% 13% 3	693
April	1st to 10th	Night	23% 9% 25% 33% 9% 2	630
	11th to 20th	Night	25% 5% 19% 36% 12% 1	623
	21st to end	Night	28% 3 18% 32% 15% 3	630
May	1st to 10th	Night	18% 6% 21% 38% 16% 2	630
	11th to 20th	Night	18% 3 19% 38% 18% 4	621
	21st to end	Night	16% 5% 13% 37% 27% 1	683
June	1st to 10th	Night	14% 4 16% 38% 25% 3	630
	11th to 20th	Night	17% 3 14% 44% 21% 1	630
	21st to end	Night	14% 4 14% 40% 23% 4	630
July	1st to 10th	Night	7% 3 10% 39% 35% 7%	615
	11th to 20th	Night	10% 2 16% 38% 30% 5%	612
	21st to end	Night	9% 2 11% 41% 31% 6%	690
August	1st to 10th	Night	11% 3 10% 42% 32% 3	627
	11th to 20th	Night	14% 4 13% 32% 33% 5%	624
	21st to end	Night	14% 2 14% 35% 31% 4	693
September	1st to 10th	Night	14% 3 17% 34% 27% 5%	630
	11th to 20th	Night	14% 4 17% 36% 25% 3	609
	21st to end	Night	18% 5% 23% 26% 24% 3	755
October	1st to 10th	Night	21% 5% 24% 29% 18% 3	800
	11th to 20th	Night	22% 8% 29% 29% 12% 1	800
	21st to end	Night	29% 7% 25% 29% 9% 1	880
November	1st to 10th	Night	21% 10% 28% 32% 8% 1	898
	11th to 20th	Night	22% 12% 32% 22% 11% 1	1050
	21st to end	Night	21% 13% 33% 26% 7%	1050
December	1st to 10th	Night	19% 13% 36% 24% 8%	1050
	11th to 20th	Night	22% 15% 32% 24% 7% 1	1050
	21st to end	Night	27% 10% 33% 23% 6% 1	1155

Page generated at 2026-09-11 03:11:57. Version ac07

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