The Looking Glass Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Looking Glass Observatory clear sky chart from 2005-11-06 to 2026-07-31.

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% 8% 3 8% 5% 5% 5% 4 6% 7% 36%	137946
	Night	12% 8% 3 8% 5% 4 4 4 5% 7% 40%	135077
Transparency	Day	43% 8% 12% 20% 14% 3	141672
	Night	41% 7% 12% 21% 16% 3	139422
Seeing	Day	18% 14% 25% 22% 15% 7%	17006
	Night	16% 12% 23% 28% 18% 3	27009

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% 12% 5% 10% 4 4 4 3 4 5% 31%	5258
	11th to 20th	Day	12% 7% 5% 13% 4 3 3 2 3 4 43%	5280
	21st to end	Day	18% 11% 5% 7% 5% 4 4 2 4 5% 34%	5898
February	1st to 10th	Day	16% 11% 4 8% 5% 5% 3 3 5% 5% 34%	2100
	11th to 20th	Day	21% 10% 5% 8% 5% 4 4 3 5% 5% 31%	2048
	21st to end	Day	18% 9% 3 10% 4 4 4 3 5% 5% 35%	1730
March	1st to 10th	Day	17% 11% 4 8% 5% 4 5% 3 5% 6% 32%	4619
	11th to 20th	Day	11% 8% 3 7% 4 4 4 3 5% 5% 45%	5090
	21st to end	Day	13% 8% 3 6% 4 4 5% 4 5% 6% 42%	5586
April	1st to 10th	Day	12% 8% 2 6% 5% 5% 5% 4 5% 7% 41%	2463
	11th to 20th	Day	12% 8% 3 6% 4 4 4 3 4 7% 44%	2494
	21st to end	Day	13% 7% 2 7% 5% 4 5% 5% 6% 7% 39%	2701
May	1st to 10th	Day	16% 9% 3 9% 5% 5% 4 4 6% 8% 30%	7616
	11th to 20th	Day	11% 8% 3 9% 6% 6% 5% 4 6% 7% 35%	7626
	21st to end	Day	15% 11% 4 10% 6% 6% 5% 4 5% 7% 28%	8391
June	1st to 10th	Day	9% 7% 3 7% 5% 6% 6% 5% 8% 9% 36%	2730
	11th to 20th	Day	5% 5% 2 7% 6% 6% 7% 5% 7% 10% 40%	2730
	21st to end	Day	7% 5% 2 6% 6% 6% 5% 5% 9% 12% 37%	2730
July	1st to 10th	Day	5% 5% 2 7% 6% 7% 7% 6% 8% 10% 37%	6030
	11th to 20th	Day	8% 6% 3 9% 8% 7% 7% 7% 8% 10% 27%	6030
	21st to end	Day	11% 9% 4 10% 7% 7% 7% 6% 8% 10% 22%	6554
August	1st to 10th	Day	7% 5% 2 7% 5% 6% 6% 5% 8% 10% 39%	4234
	11th to 20th	Day	7% 5% 2 6% 6% 6% 6% 6% 10% 11% 35%	3959
	21st to end	Day	6% 4 2 6% 5% 5% 5% 5% 7% 8% 47%	4312
September	1st to 10th	Day	14% 6% 2 6% 5% 5% 5% 4 6% 8% 38%	2262
	11th to 20th	Day	12% 7% 3 7% 4 5% 5% 4 6% 7% 40%	2200
	21st to end	Day	14% 6% 2 6% 4 5% 4 4 6% 7% 43%	2200
October	1st to 10th	Day	10% 5% 2 6% 4 4 4 3 5% 7% 51%	2200
	11th to 20th	Day	11% 6% 2 5% 3 3 3 3 5% 7% 52%	2090
	21st to end	Day	14% 8% 2 4 3 3 4 4 5% 7% 46%	2105
November	1st to 10th	Day	10% 6% 2 5% 4 3 4 3 6% 6% 52%	1852
	11th to 20th	Day	12% 6% 3 6% 4 3 4 3 5% 6% 46%	1890
	21st to end	Day	14% 9% 3 6% 5% 4 4 3 4 6% 42%	1890
December	1st to 10th	Day	12% 10% 4 9% 5% 4 4 3 3 4 41%	3020
	11th to 20th	Day	17% 14% 6% 9% 5% 3 5% 3 5% 5% 28%	3463
	21st to end	Day	15% 13% 5% 9% 5% 4 4 4 5% 8% 29%	4565
January	1st to 10th	Night	14% 11% 4 10% 4 3 3 3 4 6% 38%	7635
	11th to 20th	Night	15% 9% 4 8% 5% 5% 3 2 4 4 42%	7680
	21st to end	Night	17% 12% 4 8% 5% 4 4 2 4 5% 37%	8281
February	1st to 10th	Night	15% 9% 3 8% 6% 5% 4 4 6% 6% 34%	2520
	11th to 20th	Night	22% 9% 4 9% 5% 3 4 2 4 5% 32%	2458
	21st to end	Night	19% 9% 4 9% 4 5% 4 4 4 7% 32%	2076
March	1st to 10th	Night	15% 13% 4 7% 5% 4 4 4 5% 6% 33%	5452
	11th to 20th	Night	10% 7% 2 6% 4 3 4 4 5% 7% 49%	5090
	21st to end	Night	13% 7% 3 7% 5% 5% 5% 3 5% 6% 40%	5588
April	1st to 10th	Night	11% 6% 2 5% 4 4 4 5% 6% 8% 45%	2174
	11th to 20th	Night	11% 6% 2 6% 3 4 4 3 5% 7% 48%	2075
	21st to end	Night	11% 6% 3 7% 4 5% 5% 3 5% 8% 44%	1916
May	1st to 10th	Night	12% 9% 3 8% 5% 5% 5% 4 7% 10% 33%	5237
	11th to 20th	Night	12% 8% 3 9% 6% 5% 5% 4 6% 7% 36%	5234
	21st to end	Night	14% 9% 4 9% 6% 5% 5% 4 7% 7% 30%	5761
June	1st to 10th	Night	5% 6% 2 7% 5% 6% 5% 5% 7% 8% 43%	1890
	11th to 20th	Night	3 3 2 6% 4 5% 5% 4 7% 12% 50%	1890
	21st to end	Night	6% 4 3 6% 5% 5% 5% 6% 7% 12% 43%	1890
July	1st to 10th	Night	6% 5% 2 6% 5% 5% 6% 5% 8% 10% 42%	4148
	11th to 20th	Night	7% 5% 2 6% 5% 5% 6% 5% 7% 12% 39%	4147
	21st to end	Night	9% 8% 4 10% 6% 6% 6% 5% 7% 11% 28%	4517
August	1st to 10th	Night	5% 4 2 6% 5% 5% 5% 4 7% 10% 48%	2915
	11th to 20th	Night	5% 5% 2 7% 4 5% 4 4 7% 10% 46%	3072
	21st to end	Night	5% 3 1 4 3 4 3 3 6% 9% 59%	3586
September	1st to 10th	Night	10% 6% 3 7% 4 5% 5% 3 5% 8% 44%	2116
	11th to 20th	Night	10% 5% 2 7% 4 3 4 4 5% 8% 46%	2200
	21st to end	Night	11% 6% 3 6% 4 4 4 3 4 6% 51%	2200
October	1st to 10th	Night	9% 5% 2 5% 3 2 3 3 4 6% 58%	2200
	11th to 20th	Night	12% 6% 2 5% 4 3 4 3 4 6% 53%	2308
	21st to end	Night	12% 8% 2 6% 3 3 3 3 4 6% 50%	2730
November	1st to 10th	Night	11% 6% 2 5% 4 4 3 3 5% 5% 51%	2666
	11th to 20th	Night	11% 7% 2 6% 4 4 4 4 5% 6% 47%	2730
	21st to end	Night	12% 10% 3 7% 4 3 3 3 5% 6% 42%	2730
December	1st to 10th	Night	14% 11% 4 9% 5% 4 4 3 4 4 37%	4380
	11th to 20th	Night	17% 14% 6% 10% 4 3 3 3 4 4 33%	4952
	21st to end	Night	13% 10% 6% 10% 5% 6% 5% 4 6% 7% 28%	6633

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	53% 5% 10% 19% 11% 1	5259
	11th to 20th	Day	45% 5% 5% 18% 25% 3	5280
	21st to end	Day	51% 5% 8% 22% 13% 2	5898
February	1st to 10th	Day	52% 5% 9% 16% 16% 2	2100
	11th to 20th	Day	55% 5% 7% 18% 12% 3	2058
	21st to end	Day	51% 5% 8% 16% 16% 5%	1730
March	1st to 10th	Day	50% 6% 8% 12% 14% 9%	4619
	11th to 20th	Day	39% 5% 8% 21% 18% 8%	5090
	21st to end	Day	42% 6% 9% 27% 15% 1	5586
April	1st to 10th	Day	41% 7% 12% 22% 15% 2	2463
	11th to 20th	Day	39% 6% 10% 19% 23% 3	2494
	21st to end	Day	42% 8% 12% 24% 13% 1	2701
May	1st to 10th	Day	47% 10% 12% 20% 10% 1	7651
	11th to 20th	Day	45% 10% 14% 20% 10% 1	7630
	21st to end	Day	54% 9% 10% 15% 10% 2	8405
June	1st to 10th	Day	41% 11% 14% 19% 12% 2	2730
	11th to 20th	Day	36% 11% 17% 20% 14% 2	2730
	21st to end	Day	35% 13% 18% 19% 13% 3	2730
July	1st to 10th	Day	36% 14% 17% 20% 13% 1	5965
	11th to 20th	Day	45% 14% 18% 18% 4 1	5961
	21st to end	Day	52% 12% 15% 16% 4	6370
August	1st to 10th	Day	35% 12% 17% 27% 9%	4221
	11th to 20th	Day	34% 12% 19% 22% 13% 1	3998
	21st to end	Day	30% 10% 14% 33% 11% 1	4311
September	1st to 10th	Day	42% 9% 12% 17% 16% 4	2262
	11th to 20th	Day	40% 8% 13% 21% 16% 2	2200
	21st to end	Day	39% 7% 11% 21% 18% 4	2200
October	1st to 10th	Day	24% 6% 9% 19% 32% 10%	3590
	11th to 20th	Day	22% 4 8% 24% 30% 11%	3382
	21st to end	Day	28% 6% 11% 25% 21% 10%	3381
November	1st to 10th	Day	32% 5% 9% 22% 26% 4	1852
	11th to 20th	Day	38% 5% 7% 23% 22% 5%	1890
	21st to end	Day	42% 6% 8% 21% 20% 3	1890
December	1st to 10th	Day	46% 6% 5% 20% 22% 2	3020
	11th to 20th	Day	57% 5% 8% 16% 12% 2	3460
	21st to end	Day	51% 6% 14% 19% 9% 1	4565
January	1st to 10th	Night	45% 6% 15% 21% 12% 1	7636
	11th to 20th	Night	45% 5% 6% 18% 22% 4	7680
	21st to end	Night	50% 4 8% 16% 16% 5%	8281
February	1st to 10th	Night	49% 7% 10% 18% 14% 2	2520
	11th to 20th	Night	55% 5% 7% 18% 12% 4	2459
	21st to end	Night	53% 6% 7% 16% 15% 4	2076
March	1st to 10th	Night	49% 7% 10% 14% 16% 4	5452
	11th to 20th	Night	34% 5% 7% 23% 20% 10%	5090
	21st to end	Night	43% 6% 11% 26% 12% 1	5588
April	1st to 10th	Night	36% 8% 12% 24% 18% 3	2174
	11th to 20th	Night	35% 5% 11% 21% 22% 5%	2075
	21st to end	Night	38% 8% 13% 27% 14% 1	1916
May	1st to 10th	Night	45% 9% 14% 23% 9% 1	5264
	11th to 20th	Night	45% 9% 15% 17% 13% 1	5235
	21st to end	Night	49% 11% 12% 18% 10%	5771
June	1st to 10th	Night	35% 11% 15% 24% 13% 2	1890
	11th to 20th	Night	26% 10% 21% 27% 15% 2	1890
	21st to end	Night	32% 12% 15% 24% 13% 3	1890
July	1st to 10th	Night	32% 12% 21% 22% 11% 1	4105
	11th to 20th	Night	35% 12% 24% 23% 6% 2	4096
	21st to end	Night	45% 14% 19% 16% 4 1	4387
August	1st to 10th	Night	29% 10% 16% 32% 12% 1	2904
	11th to 20th	Night	30% 10% 22% 26% 12% 1	3099
	21st to end	Night	22% 7% 14% 41% 14% 1	3586
September	1st to 10th	Night	37% 8% 14% 18% 17% 5%	2116
	11th to 20th	Night	35% 8% 13% 22% 20% 2	2200
	21st to end	Night	35% 7% 10% 22% 22% 4	2200
October	1st to 10th	Night	22% 8% 10% 20% 30% 10%	3590
	11th to 20th	Night	22% 4 7% 25% 27% 15%	3755
	21st to end	Night	25% 4 8% 24% 27% 11%	4404
November	1st to 10th	Night	34% 5% 8% 22% 23% 7%	2666
	11th to 20th	Night	36% 5% 7% 21% 23% 7%	2730
	21st to end	Night	43% 4 7% 23% 18% 4	2730
December	1st to 10th	Night	50% 6% 6% 16% 20% 1	4380
	11th to 20th	Night	54% 5% 7% 19% 14% 2	4954
	21st to end	Night	50% 9% 15% 17% 9%	6633

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	28% 28% 29% 13% 1	330
	11th to 20th	Day	33% 29% 24% 11% 2 1	330
	21st to end	Day	26% 29% 33% 9% 2	363
February	1st to 10th	Day	29% 27% 31% 11% 1	330
	11th to 20th	Day	42% 26% 26% 4 1 1	330
	21st to end	Day	38% 24% 29% 8% 1	273
March	1st to 10th	Day	29% 24% 34% 12% 1	343
	11th to 20th	Day	27% 27% 27% 15% 4	540
	21st to end	Day	24% 23% 34% 15% 5%	594
April	1st to 10th	Day	25% 20% 26% 20% 8% 1	540
	11th to 20th	Day	19% 20% 32% 19% 9% 1	532
	21st to end	Day	20% 15% 32% 20% 11% 1	540
May	1st to 10th	Day	20% 18% 33% 17% 8% 3	543
	11th to 20th	Day	15% 12% 28% 26% 12% 6%	567
	21st to end	Day	17% 11% 22% 26% 15% 9%	617
June	1st to 10th	Day	11% 9% 24% 28% 18% 11%	570
	11th to 20th	Day	5% 7% 18% 31% 26% 12%	570
	21st to end	Day	8% 5% 23% 28% 24% 14%	570
July	1st to 10th	Day	9% 4 15% 27% 25% 19%	565
	11th to 20th	Day	9% 6% 16% 26% 25% 18%	564
	21st to end	Day	11% 7% 14% 25% 29% 13%	616
August	1st to 10th	Day	13% 5% 18% 27% 23% 14%	526
	11th to 20th	Day	10% 4 18% 30% 26% 11%	519
	21st to end	Day	10% 5% 11% 27% 30% 17%	583
September	1st to 10th	Day	10% 5% 15% 28% 29% 12%	530
	11th to 20th	Day	13% 4 13% 29% 29% 12%	530
	21st to end	Day	17% 5% 19% 28% 23% 7%	530
October	1st to 10th	Day	11% 10% 21% 26% 23% 8%	530
	11th to 20th	Day	15% 13% 28% 25% 17% 3	530
	21st to end	Day	21% 14% 30% 23% 12% 1	488
November	1st to 10th	Day	17% 14% 37% 24% 7% 2	330
	11th to 20th	Day	18% 19% 39% 21% 3	330
	21st to end	Day	20% 21% 37% 16% 5% 1	330
December	1st to 10th	Day	29% 23% 34% 11% 3	330
	11th to 20th	Day	27% 23% 30% 15% 5%	330
	21st to end	Day	31% 23% 31% 12% 2 1	363
January	1st to 10th	Night	22% 23% 31% 20% 4	840
	11th to 20th	Night	26% 23% 28% 19% 4	840
	21st to end	Night	21% 18% 37% 21% 2	924
February	1st to 10th	Night	22% 17% 34% 24% 3	840
	11th to 20th	Night	29% 20% 32% 17% 1	823
	21st to end	Night	27% 23% 30% 18% 1	692
March	1st to 10th	Night	20% 17% 34% 25% 3	840
	11th to 20th	Night	20% 20% 31% 23% 5% 1	840
	21st to end	Night	22% 15% 31% 25% 7%	924
April	1st to 10th	Night	16% 18% 27% 28% 10%	704
	11th to 20th	Night	16% 11% 30% 30% 11%	623
	21st to end	Night	13% 11% 31% 34% 10% 1	630
May	1st to 10th	Night	13% 11% 28% 32% 14% 2	630
	11th to 20th	Night	11% 9% 22% 35% 20% 4	621
	21st to end	Night	9% 5% 19% 33% 29% 5%	683
June	1st to 10th	Night	7% 7% 14% 39% 29% 5%	630
	11th to 20th	Night	4 3 14% 36% 36% 6%	630
	21st to end	Night	7% 3 11% 38% 33% 8%	630
July	1st to 10th	Night	10% 3 6% 30% 41% 10%	615
	11th to 20th	Night	8% 4 8% 25% 45% 10%	612
	21st to end	Night	8% 3 9% 30% 40% 10%	687
August	1st to 10th	Night	8% 3 9% 29% 44% 8%	597
	11th to 20th	Night	7% 4 11% 33% 41% 5%	594
	21st to end	Night	10% 2 7% 30% 40% 11%	660
September	1st to 10th	Night	9% 3 12% 33% 36% 8%	716
	11th to 20th	Night	12% 3 11% 31% 35% 8%	800
	21st to end	Night	14% 4 17% 30% 31% 4	800
October	1st to 10th	Night	12% 7% 17% 27% 30% 7%	800
	11th to 20th	Night	15% 9% 24% 32% 19% 2	800
	21st to end	Night	15% 12% 27% 30% 14% 2	880
November	1st to 10th	Night	13% 12% 21% 36% 16% 2	820
	11th to 20th	Night	14% 18% 29% 28% 10% 1	840
	21st to end	Night	19% 18% 26% 27% 10%	840
December	1st to 10th	Night	24% 19% 28% 24% 5%	840
	11th to 20th	Night	21% 17% 28% 27% 6%	840
	21st to end	Night	26% 17% 27% 25% 5%	924

Page generated at 2026-07-28 03:25:23. Version ac07

Copyright © 2026 Attilla Danko.