Turner Research Station
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Turner Research Station clear sky chart from 2005-11-06 to 2026-06-16.

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	10% 5% 2 5% 4 4 4 3 5% 7% 51%	137689
	Night	10% 5% 2 5% 3 3 3 3 5% 7% 55%	134691
Transparency	Day	33% 4 9% 22% 23% 10%	141432
	Night	30% 3 9% 21% 23% 13%	139015
Seeing	Day	12% 7% 24% 30% 20% 6%	17147
	Night	12% 7% 29% 35% 14% 2	27063

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	10% 6% 3 5% 3 3 3 2 4 5% 55%	5289
	11th to 20th	Day	9% 5% 1 4 2 2 2 2 4 6% 61%	5310
	21st to end	Day	21% 8% 2 5% 4 3 3 3 3 4 43%	5914
February	1st to 10th	Day	15% 6% 2 5% 3 3 3 2 4 5% 50%	2100
	11th to 20th	Day	14% 8% 3 7% 3 3 3 2 4 5% 48%	2049
	21st to end	Day	17% 6% 2 4 3 2 3 2 3 5% 54%	1730
March	1st to 10th	Day	13% 6% 2 5% 4 4 4 3 5% 6% 50%	5018
	11th to 20th	Day	13% 5% 2 4 3 4 4 3 4 6% 54%	5090
	21st to end	Day	10% 5% 2 5% 4 4 4 4 6% 7% 49%	5583
April	1st to 10th	Day	12% 7% 2 6% 4 4 5% 3 5% 6% 46%	2310
	11th to 20th	Day	13% 6% 3 6% 4 4 4 4 4 6% 45%	2312
	21st to end	Day	14% 5% 2 6% 4 4 4 3 5% 6% 48%	2725
May	1st to 10th	Day	17% 7% 2 6% 4 4 4 4 5% 7% 40%	7617
	11th to 20th	Day	11% 7% 3 8% 5% 4 4 3 5% 6% 42%	7627
	21st to end	Day	12% 7% 3 7% 5% 5% 6% 4 7% 9% 37%	8392
June	1st to 10th	Day	5% 4 2 5% 4 4 5% 4 7% 9% 52%	2730
	11th to 20th	Day	5% 3 2 4 4 4 5% 4 7% 9% 53%	2666
	21st to end	Day	5% 4 1 3 4 5% 5% 4 6% 8% 54%	2600
July	1st to 10th	Day	9% 6% 2 6% 5% 5% 5% 4 6% 8% 42%	5900
	11th to 20th	Day	3 3 1 4 3 4 5% 5% 6% 10% 58%	5900
	21st to end	Day	4 5% 2 5% 4 4 5% 4 7% 10% 50%	6422
August	1st to 10th	Day	1 1 1 2 2 3 3 2 5% 7% 73%	4234
	11th to 20th	Day	4 2 1 3 2 3 3 3 5% 8% 65%	4051
	21st to end	Day	3 2 1 4 4 4 5% 4 7% 10% 56%	4124
September	1st to 10th	Day	10% 5% 2 5% 5% 5% 3 3 5% 6% 51%	2200
	11th to 20th	Day	10% 5% 2 5% 4 4 4 4 6% 7% 51%	2200
	21st to end	Day	7% 3 1 4 3 3 4 3 4 8% 59%	2200
October	1st to 10th	Day	5% 2 1 5% 3 3 4 3 5% 6% 63%	2200
	11th to 20th	Day	9% 4 2 3 2 3 3 2 3 5% 63%	2013
	21st to end	Day	12% 4 2 4 3 3 2 2 3 4 63%	2200
November	1st to 10th	Day	12% 6% 2 5% 3 3 3 3 3 5% 55%	2058
	11th to 20th	Day	7% 4 1 4 3 3 3 4 5% 7% 59%	1937
	21st to end	Day	13% 7% 2 5% 3 3 3 2 3 5% 52%	1890
December	1st to 10th	Day	17% 6% 2 5% 4 3 4 2 5% 4 48%	3030
	11th to 20th	Day	12% 7% 3 8% 4 4 4 3 5% 5% 46%	3481
	21st to end	Day	12% 6% 2 5% 3 3 3 2 3 5% 56%	4587
January	1st to 10th	Night	12% 5% 2 5% 3 3 3 2 3 4 58%	7634
	11th to 20th	Night	7% 3 1 3 2 2 2 2 3 5% 70%	7680
	21st to end	Night	23% 7% 2 6% 4 3 4 3 3 4 42%	8342
February	1st to 10th	Night	13% 6% 3 5% 3 4 3 3 3 5% 53%	2520
	11th to 20th	Night	16% 6% 2 5% 3 3 3 2 3 6% 51%	2458
	21st to end	Night	16% 6% 2 4 3 2 2 2 4 5% 54%	2076
March	1st to 10th	Night	11% 7% 2 6% 4 4 4 3 5% 6% 48%	5044
	11th to 20th	Night	11% 6% 1 5% 3 3 3 3 4 7% 54%	5090
	21st to end	Night	10% 7% 2 6% 4 3 3 3 4 6% 52%	5588
April	1st to 10th	Night	9% 5% 2 5% 3 3 3 4 6% 8% 53%	2310
	11th to 20th	Night	11% 6% 2 5% 4 4 4 3 4 7% 49%	2257
	21st to end	Night	11% 6% 2 4 4 3 3 4 7% 7% 49%	1890
May	1st to 10th	Night	17% 7% 3 6% 3 3 4 3 6% 8% 41%	5266
	11th to 20th	Night	9% 7% 3 7% 5% 5% 5% 4 6% 7% 45%	5265
	21st to end	Night	11% 7% 3 6% 4 4 5% 4 7% 9% 41%	5793
June	1st to 10th	Night	4 2 1 4 4 4 3 3 6% 9% 60%	1890
	11th to 20th	Night	3 3 1 3 3 3 3 3 7% 8% 63%	1845
	21st to end	Night	3 4 1 3 3 3 3 4 6% 9% 61%	1800
July	1st to 10th	Night	8% 5% 2 6% 4 3 5% 4 7% 10% 48%	4078
	11th to 20th	Night	2 2 1 3 2 3 3 3 6% 10% 65%	4077
	21st to end	Night	3 3 2 4 3 3 5% 4 7% 10% 56%	4449
August	1st to 10th	Night	1 1 1 1 1 2 2 4 7% 80%	2926
	11th to 20th	Night	3 2 1 3 2 2 3 3 5% 11% 65%	3002
	21st to end	Night	3 2 1 3 3 3 4 3 6% 10% 61%	3779
September	1st to 10th	Night	8% 4 2 4 3 4 4 4 5% 8% 55%	2200
	11th to 20th	Night	10% 5% 2 5% 3 3 3 4 6% 7% 53%	2200
	21st to end	Night	6% 3 1 3 2 3 4 3 4 8% 62%	2200
October	1st to 10th	Night	5% 3 1 3 2 2 3 3 5% 5% 69%	2200
	11th to 20th	Night	10% 3 1 3 2 3 2 2 4 5% 66%	2365
	21st to end	Night	12% 4 1 4 2 2 2 2 3 4 62%	2640
November	1st to 10th	Night	10% 5% 2 3 3 3 3 2 4 3 62%	2460
	11th to 20th	Night	6% 5% 2 4 4 3 3 3 4 6% 60%	2678
	21st to end	Night	14% 5% 2 5% 3 3 3 2 4 6% 53%	2730
December	1st to 10th	Night	17% 6% 3 5% 3 3 2 3 4 5% 50%	4380
	11th to 20th	Night	13% 8% 2 6% 4 3 3 2 4 5% 50%	4946
	21st to end	Night	12% 7% 2 5% 3 3 3 2 3 4 58%	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	33% 2 6% 24% 28% 8%	5290
	11th to 20th	Day	27% 1 4 20% 32% 15%	5310
	21st to end	Day	46% 2 4 14% 22% 12%	5914
February	1st to 10th	Day	38% 4 5% 15% 23% 15%	2100
	11th to 20th	Day	39% 3 7% 18% 21% 11%	2059
	21st to end	Day	35% 3 5% 15% 25% 17%	1730
March	1st to 10th	Day	37% 3 6% 14% 21% 19%	5018
	11th to 20th	Day	32% 5% 8% 11% 16% 28%	5090
	21st to end	Day	33% 4 10% 23% 20% 9%	5585
April	1st to 10th	Day	40% 4 8% 17% 18% 13%	2310
	11th to 20th	Day	40% 5% 8% 16% 20% 11%	2312
	21st to end	Day	39% 4 7% 19% 24% 8%	2725
May	1st to 10th	Day	44% 4 11% 21% 18% 3	7655
	11th to 20th	Day	43% 3 6% 15% 26% 6%	7631
	21st to end	Day	43% 5% 13% 21% 13% 5%	8405
June	1st to 10th	Day	27% 6% 14% 27% 21% 4	2730
	11th to 20th	Day	27% 6% 13% 30% 19% 7%	2666
	21st to end	Day	26% 7% 14% 25% 23% 5%	2600
July	1st to 10th	Day	40% 5% 18% 28% 9% 1	5836
	11th to 20th	Day	22% 3 17% 34% 20% 3	5831
	21st to end	Day	28% 4 15% 31% 21% 2	6240
August	1st to 10th	Day	12% 3 10% 35% 37% 3	4220
	11th to 20th	Day	18% 4 16% 40% 20% 2	4090
	21st to end	Day	24% 6% 19% 30% 19% 2	4123
September	1st to 10th	Day	34% 5% 9% 20% 21% 10%	2200
	11th to 20th	Day	32% 7% 11% 22% 21% 7%	2200
	21st to end	Day	24% 6% 9% 23% 24% 14%	2200
October	1st to 10th	Day	14% 3 6% 13% 31% 34%	3590
	11th to 20th	Day	18% 3 6% 18% 34% 21%	3253
	21st to end	Day	22% 2 4 22% 37% 13%	3538
November	1st to 10th	Day	34% 3 7% 19% 26% 11%	2058
	11th to 20th	Day	25% 4 9% 20% 26% 15%	1937
	21st to end	Day	37% 3 4 19% 23% 13%	1890
December	1st to 10th	Day	40% 3 5% 20% 23% 9%	3030
	11th to 20th	Day	41% 3 6% 11% 26% 13%	3479
	21st to end	Day	33% 2 5% 17% 29% 14%	4587
January	1st to 10th	Night	32% 2 5% 19% 30% 12%	7635
	11th to 20th	Night	21% 1 3 18% 34% 22%	7680
	21st to end	Night	48% 2 3 12% 21% 13%	8342
February	1st to 10th	Night	36% 4 6% 13% 24% 17%	2520
	11th to 20th	Night	37% 2 7% 17% 24% 13%	2458
	21st to end	Night	34% 3 6% 15% 23% 19%	2076
March	1st to 10th	Night	38% 3 8% 13% 22% 17%	5044
	11th to 20th	Night	32% 4 8% 15% 17% 25%	5090
	21st to end	Night	34% 4 8% 18% 25% 11%	5588
April	1st to 10th	Night	30% 5% 10% 21% 18% 15%	2310
	11th to 20th	Night	37% 5% 10% 16% 19% 14%	2257
	21st to end	Night	34% 5% 12% 17% 23% 8%	1890
May	1st to 10th	Night	43% 3 10% 24% 15% 5%	5293
	11th to 20th	Night	39% 5% 10% 16% 20% 10%	5266
	21st to end	Night	39% 5% 15% 27% 9% 5%	5805
June	1st to 10th	Night	21% 6% 16% 31% 21% 4	1890
	11th to 20th	Night	19% 5% 15% 32% 22% 7%	1845
	21st to end	Night	21% 8% 13% 28% 25% 6%	1800
July	1st to 10th	Night	33% 4 19% 34% 8% 1	4035
	11th to 20th	Night	16% 3 18% 40% 20% 2	4026
	21st to end	Night	23% 5% 19% 32% 19% 3	4320
August	1st to 10th	Night	6% 3 10% 37% 39% 5%	2916
	11th to 20th	Night	16% 3 19% 39% 19% 3	3029
	21st to end	Night	20% 7% 21% 32% 18% 3	3779
September	1st to 10th	Night	28% 6% 11% 23% 21% 11%	2200
	11th to 20th	Night	31% 5% 13% 22% 21% 8%	2200
	21st to end	Night	22% 5% 9% 26% 22% 17%	2200
October	1st to 10th	Night	12% 2 6% 15% 24% 40%	3590
	11th to 20th	Night	15% 2 7% 18% 33% 25%	3851
	21st to end	Night	22% 2 3 20% 36% 16%	4252
November	1st to 10th	Night	28% 3 7% 19% 27% 15%	2460
	11th to 20th	Night	26% 4 8% 21% 24% 18%	2678
	21st to end	Night	36% 3 7% 17% 25% 14%	2730
December	1st to 10th	Night	38% 3 6% 19% 24% 11%	4380
	11th to 20th	Night	40% 2 6% 10% 26% 16%	4947
	21st to end	Night	33% 2 4 17% 25% 18%	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	17% 16% 41% 20% 5% 1	330
	11th to 20th	Day	21% 13% 38% 20% 6% 2	330
	21st to end	Day	22% 13% 39% 20% 6%	363
February	1st to 10th	Day	23% 16% 35% 22% 4	330
	11th to 20th	Day	21% 17% 43% 16% 3	330
	21st to end	Day	26% 18% 37% 15% 4	273
March	1st to 10th	Day	23% 17% 37% 19% 4	330
	11th to 20th	Day	22% 18% 38% 18% 3 1	330
	21st to end	Day	14% 14% 42% 24% 5%	363
April	1st to 10th	Day	22% 17% 37% 21% 4	330
	11th to 20th	Day	20% 16% 35% 25% 4	350
	21st to end	Day	19% 13% 40% 21% 6% 1	745
May	1st to 10th	Day	16% 11% 38% 27% 7% 1	753
	11th to 20th	Day	16% 8% 33% 28% 12% 2	775
	21st to end	Day	13% 6% 30% 32% 15% 4	844
June	1st to 10th	Day	6% 2 21% 42% 23% 7%	780
	11th to 20th	Day	6% 1 21% 45% 22% 4	756
	21st to end	Day	5% 2 12% 41% 31% 10%	730
July	1st to 10th	Day	9% 2 8% 35% 35% 11%	721
	11th to 20th	Day	2 1 6% 37% 42% 11%	718
	21st to end	Day	4 2 5% 36% 37% 16%	794
August	1st to 10th	Day	2 5% 35% 43% 15%	726
	11th to 20th	Day	7% 1 3 39% 38% 12%	647
	21st to end	Day	6% 2 3 30% 39% 21%	473
September	1st to 10th	Day	9% 2 7% 28% 36% 17%	330
	11th to 20th	Day	5% 1 7% 26% 46% 15%	330
	21st to end	Day	11% 2 8% 35% 32% 13%	330
October	1st to 10th	Day	3 1 17% 37% 35% 8%	330
	11th to 20th	Day	9% 4 27% 34% 22% 4	330
	21st to end	Day	21% 9% 23% 28% 16% 2	363
November	1st to 10th	Day	20% 5% 31% 28% 13% 3	330
	11th to 20th	Day	13% 11% 30% 30% 14% 2	330
	21st to end	Day	18% 15% 34% 22% 10% 1	330
December	1st to 10th	Day	18% 8% 39% 25% 8% 2	330
	11th to 20th	Day	18% 13% 38% 22% 8% 2	330
	21st to end	Day	19% 9% 37% 25% 8% 1	363
January	1st to 10th	Night	16% 9% 38% 30% 7%	1050
	11th to 20th	Night	16% 13% 35% 29% 7%	1050
	21st to end	Night	17% 13% 35% 29% 6%	1134
February	1st to 10th	Night	17% 14% 37% 27% 5%	840
	11th to 20th	Night	19% 15% 39% 24% 3	824
	21st to end	Night	21% 13% 42% 20% 3	692
March	1st to 10th	Night	18% 13% 40% 26% 3	645
	11th to 20th	Night	17% 11% 39% 27% 5%	630
	21st to end	Night	11% 13% 46% 26% 3	693
April	1st to 10th	Night	11% 11% 46% 27% 4	630
	11th to 20th	Night	14% 13% 42% 25% 5%	623
	21st to end	Night	15% 9% 44% 24% 7%	630
May	1st to 10th	Night	13% 8% 43% 30% 5%	630
	11th to 20th	Night	14% 7% 37% 28% 12% 2	621
	21st to end	Night	10% 5% 34% 37% 13% 2	683
June	1st to 10th	Night	5% 2 24% 46% 20% 3	630
	11th to 20th	Night	4 2 30% 48% 14% 1	615
	21st to end	Night	3 2 17% 50% 25% 4	600
July	1st to 10th	Night	8% 1 11% 47% 28% 5%	585
	11th to 20th	Night	3 1 10% 55% 27% 3	582
	21st to end	Night	2 1 9% 50% 35% 3	657
August	1st to 10th	Night	2 5% 53% 37% 4	597
	11th to 20th	Night	7% 1 6% 47% 34% 5%	594
	21st to end	Night	5% 1 5% 44% 39% 7%	660
September	1st to 10th	Night	10% 1 8% 43% 33% 5%	600
	11th to 20th	Night	12% 1 7% 44% 33% 5%	600
	21st to end	Night	9% 1 14% 39% 33% 5%	600
October	1st to 10th	Night	6% 2 15% 45% 28% 4	600
	11th to 20th	Night	11% 4 28% 38% 17% 2	765
	21st to end	Night	15% 7% 30% 32% 15% 1	880
November	1st to 10th	Night	12% 5% 28% 39% 14% 1	820
	11th to 20th	Night	9% 7% 31% 37% 15% 1	998
	21st to end	Night	17% 9% 35% 27% 11% 1	1050
December	1st to 10th	Night	15% 9% 34% 34% 8%	1050
	11th to 20th	Night	20% 8% 33% 32% 7%	1050
	21st to end	Night	18% 8% 36% 30% 7%	1155

Page generated at 2026-06-13 01:31:40. Version ac07

Copyright © 2026 Attilla Danko.