Paul Plishner Radio Astronomy and Science Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Paul Plishner Radio Astronomy and Science Center 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	4 4 1 4 3 3 3 3 5% 8% 61%	157286
	Night	5% 5% 2 5% 4 4 4 4 6% 7% 55%	151334
Transparency	Day	21% 4 11% 25% 27% 12%	152323
	Night	27% 5% 10% 23% 24% 10%	147322
Seeing	Day	7% 6% 23% 33% 23% 7%	18118
	Night	7% 7% 31% 41% 14% 1	27986

By Month

Percentage Cloud Cover SW (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	2 7% 3 6% 4 4 4 3 5% 6% 55%	4720
	11th to 20th	Day	2 4 2 6% 3 3 4 3 4 6% 63%	4740
	21st to end	Day	3 7% 2 5% 3 3 3 3 5% 7% 60%	5766
February	1st to 10th	Day	4 6% 2 5% 4 5% 4 3 5% 7% 55%	2065
	11th to 20th	Day	2 6% 2 7% 4 4 4 4 5% 6% 55%	2049
	21st to end	Day	3 4 2 6% 5% 3 3 3 4 5% 61%	1730
March	1st to 10th	Day	2 3 2 4 3 4 4 3 4 6% 65%	4600
	11th to 20th	Day	5% 5% 1 5% 3 3 3 3 5% 8% 58%	4765
	21st to end	Day	4 3 1 4 3 3 4 4 6% 9% 59%	6101
April	1st to 10th	Day	5% 5% 1 4 3 3 4 3 6% 7% 60%	2520
	11th to 20th	Day	7% 4 2 5% 4 4 3 3 6% 8% 54%	2491
	21st to end	Day	7% 5% 2 5% 4 4 4 4 6% 7% 53%	2530
May	1st to 10th	Day	11% 5% 2 4 3 3 3 3 4 6% 55%	7655
	11th to 20th	Day	4 3 1 4 3 3 3 3 5% 6% 65%	7627
	21st to end	Day	8% 5% 2 4 3 3 3 3 5% 8% 56%	8872
June	1st to 10th	Day	4 3 1 3 3 3 3 4 8% 11% 57%	2940
	11th to 20th	Day	4 2 1 3 3 3 3 3 5% 7% 64%	2940
	21st to end	Day	3 3 1 4 3 3 4 4 7% 9% 58%	2940
July	1st to 10th	Day	2 2 1 3 3 3 4 4 6% 8% 64%	8249
	11th to 20th	Day	2 1 1 2 2 3 3 3 5% 8% 70%	8250
	21st to end	Day	3 2 1 3 3 3 4 4 8% 11% 57%	8957
August	1st to 10th	Day	4 3 1 4 3 3 4 4 6% 10% 58%	7158
	11th to 20th	Day	3 2 1 3 3 3 4 4 6% 11% 61%	7003
	21st to end	Day	4 3 1 4 3 4 4 4 7% 12% 54%	7751
September	1st to 10th	Day	4 3 1 3 2 3 4 3 6% 7% 63%	2520
	11th to 20th	Day	5% 2 1 3 2 3 3 3 5% 6% 67%	2313
	21st to end	Day	5% 3 2 3 2 2 3 3 4 6% 67%	2200
October	1st to 10th	Day	4 2 1 2 1 2 1 2 4 4 77%	3570
	11th to 20th	Day	5% 2 1 3 3 2 4 2 5% 7% 67%	3250
	21st to end	Day	5% 4 1 4 2 2 1 2 3 4 73%	3271
November	1st to 10th	Day	4 4 2 3 2 2 2 2 5% 6% 69%	1853
	11th to 20th	Day	3 4 2 4 2 3 2 3 4 6% 68%	1890
	21st to end	Day	5% 5% 2 4 3 3 2 2 4 6% 63%	1890
December	1st to 10th	Day	2 6% 2 3 2 2 2 2 3 4 70%	2912
	11th to 20th	Day	3 4 2 3 2 2 3 3 6% 8% 65%	3106
	21st to end	Day	4 7% 2 6% 3 4 4 3 5% 6% 57%	4092
January	1st to 10th	Night	4 8% 2 7% 4 4 4 3 5% 7% 53%	8201
	11th to 20th	Night	2 5% 2 6% 3 3 3 3 5% 6% 62%	8250
	21st to end	Night	3 7% 3 6% 4 3 3 2 4 5% 60%	8493
February	1st to 10th	Night	5% 5% 3 6% 4 4 3 2 4 6% 59%	2552
	11th to 20th	Night	5% 7% 3 7% 4 3 4 3 6% 8% 50%	2458
	21st to end	Night	3 5% 2 5% 3 3 3 3 5% 7% 61%	2076
March	1st to 10th	Night	3 4 2 4 3 3 4 3 4 6% 64%	5494
	11th to 20th	Night	6% 6% 2 5% 3 3 4 3 5% 7% 56%	5420
	21st to end	Night	7% 6% 2 6% 4 4 4 3 6% 8% 49%	5094
April	1st to 10th	Night	6% 6% 2 5% 3 3 4 3 5% 8% 56%	2100
	11th to 20th	Night	8% 5% 2 5% 3 3 4 3 6% 8% 53%	2077
	21st to end	Night	10% 6% 2 6% 4 3 4 4 6% 7% 49%	2087
May	1st to 10th	Night	14% 7% 2 6% 3 3 4 3 4 6% 48%	5292
	11th to 20th	Night	8% 4 2 5% 3 4 4 4 5% 8% 53%	5265
	21st to end	Night	14% 6% 2 6% 4 4 4 4 5% 6% 44%	5319
June	1st to 10th	Night	4 4 1 4 4 4 5% 5% 8% 9% 53%	1680
	11th to 20th	Night	4 4 2 4 3 4 4 4 7% 8% 56%	1680
	21st to end	Night	5% 6% 2 4 3 4 5% 5% 7% 8% 50%	1680
July	1st to 10th	Night	5% 3 2 5% 5% 5% 6% 5% 8% 10% 46%	4740
	11th to 20th	Night	5% 3 2 5% 4 4 5% 4 6% 8% 55%	4740
	21st to end	Night	5% 4 2 8% 6% 7% 7% 6% 9% 8% 37%	5152
August	1st to 10th	Night	8% 4 2 7% 5% 5% 6% 5% 8% 9% 42%	5644
	11th to 20th	Night	6% 3 2 7% 5% 6% 6% 6% 8% 10% 41%	5853
	21st to end	Night	8% 5% 2 7% 5% 7% 7% 5% 9% 10% 36%	6465
September	1st to 10th	Night	6% 3 1 4 3 4 3 4 6% 9% 56%	2100
	11th to 20th	Night	5% 3 1 3 3 3 4 4 5% 9% 60%	2152
	21st to end	Night	5% 4 2 5% 3 3 4 2 4 5% 63%	2200
October	1st to 10th	Night	5% 2 1 4 3 3 3 3 4 5% 67%	3608
	11th to 20th	Night	7% 3 1 3 2 2 3 3 5% 7% 63%	3898
	21st to end	Night	4 5% 1 4 3 2 2 2 3 4 69%	4495
November	1st to 10th	Night	3 3 1 3 2 3 3 2 4 6% 68%	2665
	11th to 20th	Night	3 4 1 4 2 2 3 2 4 4 71%	2730
	21st to end	Night	4 5% 2 4 2 3 3 3 5% 6% 63%	2730
December	1st to 10th	Night	2 4 1 4 3 2 3 2 4 6% 70%	4495
	11th to 20th	Night	3 4 2 4 3 3 4 3 4 7% 63%	5321
	21st to end	Night	4 6% 2 6% 4 4 4 3 6% 7% 54%	7128

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	29% 4 7% 31% 22% 7%	4723
	11th to 20th	Day	23% 4 8% 23% 30% 12%	4740
	21st to end	Day	25% 3 8% 24% 29% 11%	5766
February	1st to 10th	Day	29% 5% 9% 25% 23% 10%	2065
	11th to 20th	Day	28% 5% 9% 25% 26% 8%	2059
	21st to end	Day	24% 3 7% 19% 29% 18%	1730
March	1st to 10th	Day	21% 3 5% 16% 34% 20%	4600
	11th to 20th	Day	24% 4 6% 20% 36% 10%	4765
	21st to end	Day	20% 5% 10% 38% 22% 5%	6101
April	1st to 10th	Day	23% 5% 9% 24% 26% 14%	2520
	11th to 20th	Day	26% 4 10% 24% 21% 14%	2494
	21st to end	Day	28% 5% 11% 24% 23% 9%	2530
May	1st to 10th	Day	30% 4 9% 25% 24% 9%	7655
	11th to 20th	Day	20% 4 9% 24% 30% 14%	7631
	21st to end	Day	26% 5% 13% 24% 19% 13%	8873
June	1st to 10th	Day	18% 6% 15% 29% 22% 9%	2940
	11th to 20th	Day	18% 4 9% 23% 25% 20%	2940
	21st to end	Day	21% 5% 11% 23% 25% 16%	2940
July	1st to 10th	Day	16% 6% 9% 20% 35% 14%	8181
	11th to 20th	Day	12% 5% 14% 21% 31% 17%	8175
	21st to end	Day	18% 7% 17% 25% 22% 11%	8759
August	1st to 10th	Day	19% 6% 15% 30% 22% 7%	5674
	11th to 20th	Day	18% 8% 20% 24% 22% 7%	5519
	21st to end	Day	17% 5% 22% 32% 16% 8%	6078
September	1st to 10th	Day	19% 5% 9% 25% 26% 16%	2520
	11th to 20th	Day	18% 4 8% 21% 29% 20%	2313
	21st to end	Day	18% 4 7% 19% 35% 17%	2200
October	1st to 10th	Day	13% 2 6% 16% 37% 25%	3570
	11th to 20th	Day	18% 3 10% 24% 34% 12%	3250
	21st to end	Day	18% 2 5% 23% 36% 17%	3271
November	1st to 10th	Day	18% 3 9% 26% 29% 16%	1853
	11th to 20th	Day	18% 3 6% 28% 33% 12%	1890
	21st to end	Day	24% 3 7% 20% 31% 15%	1890
December	1st to 10th	Day	19% 2 7% 26% 37% 9%	2912
	11th to 20th	Day	17% 3 7% 29% 37% 7%	3104
	21st to end	Day	28% 3 7% 26% 27% 8%	4092
January	1st to 10th	Night	31% 5% 7% 28% 24% 6%	8202
	11th to 20th	Night	23% 4 10% 24% 27% 12%	8250
	21st to end	Night	27% 3 8% 22% 29% 10%	8493
February	1st to 10th	Night	27% 3 9% 24% 27% 9%	2552
	11th to 20th	Night	30% 5% 10% 24% 23% 8%	2458
	21st to end	Night	23% 3 7% 21% 30% 16%	2076
March	1st to 10th	Night	21% 4 5% 17% 33% 20%	5494
	11th to 20th	Night	27% 4 9% 16% 26% 17%	5420
	21st to end	Night	30% 6% 11% 30% 19% 4	5094
April	1st to 10th	Night	26% 5% 8% 23% 25% 12%	2100
	11th to 20th	Night	28% 6% 11% 24% 21% 11%	2077
	21st to end	Night	32% 5% 13% 24% 20% 6%	2087
May	1st to 10th	Night	36% 6% 13% 22% 16% 7%	5293
	11th to 20th	Night	28% 6% 11% 25% 19% 11%	5266
	21st to end	Night	38% 7% 14% 18% 13% 9%	5321
June	1st to 10th	Night	23% 8% 21% 26% 15% 7%	1680
	11th to 20th	Night	24% 5% 14% 22% 20% 15%	1680
	21st to end	Night	28% 7% 11% 20% 22% 12%	1680
July	1st to 10th	Night	29% 7% 12% 25% 21% 6%	4700
	11th to 20th	Night	26% 6% 14% 18% 27% 9%	4692
	21st to end	Night	40% 8% 11% 17% 18% 6%	5038
August	1st to 10th	Night	36% 7% 14% 22% 15% 6%	4464
	11th to 20th	Night	39% 10% 15% 21% 12% 3	4613
	21st to end	Night	34% 9% 18% 22% 12% 5%	5069
September	1st to 10th	Night	24% 5% 13% 22% 22% 14%	2100
	11th to 20th	Night	21% 5% 11% 22% 24% 17%	2152
	21st to end	Night	23% 4 6% 19% 33% 15%	2200
October	1st to 10th	Night	19% 4 7% 17% 30% 22%	3608
	11th to 20th	Night	20% 4 7% 26% 27% 16%	3898
	21st to end	Night	21% 3 6% 21% 35% 14%	4495
November	1st to 10th	Night	18% 2 8% 25% 29% 18%	2665
	11th to 20th	Night	18% 3 5% 25% 35% 15%	2730
	21st to end	Night	23% 3 9% 21% 29% 15%	2730
December	1st to 10th	Night	17% 2 7% 34% 30% 9%	4495
	11th to 20th	Night	22% 3 5% 28% 34% 9%	5322
	21st to end	Night	29% 4 8% 24% 28% 7%	7128

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	6% 6% 24% 44% 16% 3	330
	11th to 20th	Day	10% 8% 27% 35% 17% 3	330
	21st to end	Day	7% 6% 25% 40% 18% 3	363
February	1st to 10th	Day	6% 8% 37% 36% 12% 1	330
	11th to 20th	Day	5% 6% 38% 38% 12% 1	330
	21st to end	Day	3 10% 35% 40% 11% 1	273
March	1st to 10th	Day	4 10% 28% 38% 16% 4	330
	11th to 20th	Day	10% 8% 32% 26% 18% 5%	354
	21st to end	Day	11% 13% 31% 32% 11% 2	594
April	1st to 10th	Day	9% 12% 34% 28% 14% 4	540
	11th to 20th	Day	10% 16% 33% 27% 12% 2	532
	21st to end	Day	11% 15% 31% 28% 12% 3	550
May	1st to 10th	Day	11% 11% 29% 30% 17% 2	753
	11th to 20th	Day	9% 8% 29% 30% 18% 6%	775
	21st to end	Day	9% 10% 28% 29% 19% 4	844
June	1st to 10th	Day	5% 5% 22% 31% 27% 10%	780
	11th to 20th	Day	5% 6% 26% 34% 24% 4	780
	21st to end	Day	5% 5% 23% 33% 28% 7%	780
July	1st to 10th	Day	5% 2 18% 33% 32% 10%	771
	11th to 20th	Day	3 1 10% 33% 40% 14%	768
	21st to end	Day	6% 2 9% 29% 39% 16%	849
August	1st to 10th	Day	4 2 12% 34% 35% 13%	623
	11th to 20th	Day	3 3 15% 34% 32% 13%	557
	21st to end	Day	3 1 15% 36% 30% 15%	627
September	1st to 10th	Day	4 1 17% 36% 28% 14%	570
	11th to 20th	Day	3 3 16% 33% 31% 14%	419
	21st to end	Day	8% 4 16% 26% 29% 17%	330
October	1st to 10th	Day	9% 5% 19% 27% 23% 18%	330
	11th to 20th	Day	4 6% 25% 31% 25% 9%	330
	21st to end	Day	10% 7% 23% 30% 23% 7%	363
November	1st to 10th	Day	7% 4 25% 36% 20% 8%	330
	11th to 20th	Day	5% 6% 21% 37% 27% 4	330
	21st to end	Day	10% 9% 22% 34% 20% 5%	330
December	1st to 10th	Day	4 5% 23% 44% 20% 4	330
	11th to 20th	Day	8% 5% 26% 40% 18% 2	330
	21st to end	Day	8% 8% 29% 42% 11% 1	363
January	1st to 10th	Night	6% 5% 29% 45% 13% 2	1050
	11th to 20th	Night	6% 5% 32% 42% 14% 1	1050
	21st to end	Night	6% 6% 30% 47% 10% 1	969
February	1st to 10th	Night	7% 6% 36% 43% 9%	840
	11th to 20th	Night	8% 8% 41% 35% 8%	824
	21st to end	Night	6% 9% 38% 40% 6%	692
March	1st to 10th	Night	7% 8% 38% 37% 9% 1	840
	11th to 20th	Night	9% 8% 35% 36% 10% 1	814
	21st to end	Night	10% 11% 42% 31% 5%	693
April	1st to 10th	Night	10% 13% 43% 30% 5%	630
	11th to 20th	Night	11% 13% 44% 28% 4	623
	21st to end	Night	13% 14% 33% 31% 9%	630
May	1st to 10th	Night	14% 11% 35% 30% 10%	630
	11th to 20th	Night	10% 10% 33% 34% 11% 1	621
	21st to end	Night	12% 11% 39% 31% 7%	683
June	1st to 10th	Night	4 7% 32% 43% 12% 1	630
	11th to 20th	Night	5% 6% 41% 40% 8%	630
	21st to end	Night	7% 5% 34% 43% 11%	630
July	1st to 10th	Night	6% 3 26% 46% 18% 1	615
	11th to 20th	Night	5% 2 17% 53% 23% 1	612
	21st to end	Night	8% 3 16% 44% 27% 1	690
August	1st to 10th	Night	7% 3 22% 39% 28% 1	627
	11th to 20th	Night	6% 3 24% 49% 18%	624
	21st to end	Night	5% 1 21% 48% 24% 2	693
September	1st to 10th	Night	6% 2 25% 47% 19% 1	630
	11th to 20th	Night	6% 3 26% 45% 19% 1	609
	21st to end	Night	6% 5% 27% 42% 19% 1	600
October	1st to 10th	Night	11% 7% 29% 37% 16%	605
	11th to 20th	Night	4 7% 30% 39% 19% 2	800
	21st to end	Night	8% 8% 25% 39% 18% 2	1022
November	1st to 10th	Night	5% 5% 28% 43% 18% 1	1025
	11th to 20th	Night	5% 6% 27% 44% 17% 1	1050
	21st to end	Night	8% 7% 25% 43% 16% 1	1050
December	1st to 10th	Night	5% 6% 30% 45% 14% 1	1050
	11th to 20th	Night	6% 6% 31% 43% 14%	1050
	21st to end	Night	7% 10% 31% 42% 10%	1155

Page generated at 2026-09-11 02:11:56. Version ac07

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