Aquarius Ranger Station
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Aquarius Ranger Station clear sky chart from 2005-11-06 to 2024-03-18.

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 6% 3 6% 6% 4 5% 5% 6% 7% 49%	79140
	Night	1 4 2 5% 5% 3 5% 5% 6% 8% 55%	80720
Transparency	Day	30% 6% 10% 20% 21% 12%	78867
	Night	23% 6% 12% 23% 24% 13%	80515
Seeing	Day	6% 17% 30% 27% 15% 4	13882
	Night	3 12% 26% 33% 21% 5%	24138

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 4 11% 9% 4 5% 6% 6% 9% 44%	2858
	11th to 20th	Day	3 3 6% 7% 4 8% 7% 9% 8% 46%	2860
	21st to end	Day	1 7% 4 7% 5% 3 4 5% 5% 7% 52%	3146
February	1st to 10th	Day	1 4 3 7% 7% 4 5% 7% 8% 9% 47%	1710
	11th to 20th	Day	1 4 3 7% 7% 4 5% 5% 6% 9% 49%	1771
	21st to end	Day	4 3 7% 7% 4 6% 6% 6% 7% 48%	1570
March	1st to 10th	Day	1 6% 3 7% 6% 4 5% 6% 5% 7% 51%	2069
	11th to 20th	Day	1 7% 5% 8% 5% 3 6% 6% 7% 9% 44%	2058
	21st to end	Day	1 6% 4 8% 6% 4 6% 6% 9% 8% 42%	2178
April	1st to 10th	Day	2 6% 4 5% 5% 4 4 5% 6% 9% 50%	1980
	11th to 20th	Day	1 7% 3 7% 6% 3 5% 5% 5% 8% 49%	2199
	21st to end	Day	4 8% 3 6% 5% 3 5% 5% 5% 7% 49%	2340
May	1st to 10th	Day	4 9% 4 6% 6% 3 5% 5% 6% 7% 45%	2340
	11th to 20th	Day	3 9% 2 7% 6% 4 5% 6% 7% 8% 43%	2301
	21st to end	Day	5% 8% 3 6% 6% 4 4 6% 6% 7% 45%	2530
June	1st to 10th	Day	3 5% 2 5% 4 3 5% 5% 6% 8% 54%	2340
	11th to 20th	Day	5% 5% 2 4 4 3 4 4 3 5% 62%	2340
	21st to end	Day	4 4 2 5% 5% 3 5% 5% 5% 6% 56%	2340
July	1st to 10th	Day	9% 7% 2 7% 6% 3 5% 4 5% 6% 44%	2340
	11th to 20th	Day	8% 8% 4 8% 8% 6% 7% 6% 6% 7% 33%	2340
	21st to end	Day	9% 8% 4 8% 9% 6% 7% 7% 8% 7% 27%	2545
August	1st to 10th	Day	9% 6% 4 7% 8% 4 7% 5% 5% 6% 38%	2328
	11th to 20th	Day	7% 6% 3 7% 8% 4 6% 6% 6% 7% 39%	2299
	21st to end	Day	6% 7% 4 8% 6% 4 5% 5% 6% 6% 43%	2512
September	1st to 10th	Day	8% 7% 3 7% 7% 4 4 5% 4 4 48%	2008
	11th to 20th	Day	7% 6% 2 5% 4 3 5% 4 4 5% 56%	1980
	21st to end	Day	5% 4 1 4 3 3 3 3 5% 5% 63%	1980
October	1st to 10th	Day	6% 7% 3 5% 4 2 3 3 5% 5% 56%	1897
	11th to 20th	Day	3 4 2 3 3 2 4 3 4 7% 67%	1800
	21st to end	Day	3 3 1 4 5% 2 3 3 4 5% 66%	1980
November	1st to 10th	Day	3 2 4 4 1 4 4 6% 9% 63%	1756
	11th to 20th	Day	1 4 2 3 4 2 4 4 5% 8% 65%	1710
	21st to end	Day	1 2 3 6% 5% 3 4 5% 5% 9% 56%	1710
December	1st to 10th	Day	1 3 3 5% 6% 4 5% 5% 6% 8% 54%	1710
	11th to 20th	Day	6% 3 7% 6% 4 5% 5% 7% 12% 45%	2169
	21st to end	Day	1 4 3 8% 8% 4 6% 6% 7% 8% 43%	3146
January	1st to 10th	Night	2 2 7% 6% 5% 6% 7% 8% 12% 44%	4097
	11th to 20th	Night	2 1 5% 6% 4 5% 7% 9% 11% 50%	4110
	21st to end	Night	1 5% 4 7% 8% 4 5% 5% 6% 9% 47%	4521
February	1st to 10th	Night	3 3 6% 6% 4 6% 6% 7% 9% 50%	2470
	11th to 20th	Night	1 4 2 5% 5% 4 7% 6% 6% 8% 52%	2292
	21st to end	Night	3 2 6% 8% 4 6% 8% 6% 8% 49%	1884
March	1st to 10th	Night	4 2 5% 6% 3 6% 7% 8% 11% 47%	2109
	11th to 20th	Night	1 5% 4 6% 5% 3 5% 6% 8% 9% 48%	2068
	21st to end	Night	1 3 3 5% 6% 4 6% 7% 8% 10% 48%	2178
April	1st to 10th	Night	1 6% 2 4 5% 4 5% 4 6% 8% 55%	1979
	11th to 20th	Night	2 5% 2 5% 5% 3 6% 4 6% 7% 55%	1706
	21st to end	Night	1 6% 3 5% 4 3 4 5% 7% 9% 53%	1620
May	1st to 10th	Night	3 5% 2 5% 5% 4 5% 6% 5% 8% 51%	1620
	11th to 20th	Night	2 3 2 3 5% 3 5% 5% 6% 8% 58%	1594
	21st to end	Night	3 3 2 3 4 2 4 5% 5% 8% 60%	1746
June	1st to 10th	Night	1 3 2 3 2 2 4 5% 6% 8% 63%	1620
	11th to 20th	Night	3 3 1 2 3 2 4 3 5% 7% 68%	1620
	21st to end	Night	2 2 1 3 3 3 3 5% 5% 6% 67%	1620
July	1st to 10th	Night	4 3 2 4 5% 4 5% 5% 6% 8% 55%	1620
	11th to 20th	Night	3 4 1 4 4 4 5% 6% 9% 10% 49%	1620
	21st to end	Night	3 4 2 6% 7% 5% 6% 8% 7% 12% 39%	1773
August	1st to 10th	Night	3 4 2 6% 5% 3 4 6% 6% 8% 54%	1611
	11th to 20th	Night	2 4 2 4 5% 3 5% 5% 8% 9% 53%	1602
	21st to end	Night	3 3 2 4 5% 2 4 5% 7% 9% 57%	1844
September	1st to 10th	Night	3 3 1 3 3 2 5% 5% 5% 6% 62%	1948
	11th to 20th	Night	2 2 1 3 4 2 3 3 5% 6% 69%	1980
	21st to end	Night	1 2 1 2 3 2 2 3 4 5% 74%	1980
October	1st to 10th	Night	3 3 2 4 3 3 4 4 5% 6% 62%	2061
	11th to 20th	Night	2 2 1 3 4 2 3 4 4 5% 71%	2160
	21st to end	Night	3 3 2 3 4 3 4 3 5% 6% 65%	2376
November	1st to 10th	Night	1 3 2 3 3 3 4 4 6% 8% 63%	2319
	11th to 20th	Night	1 3 2 3 4 2 5% 5% 5% 8% 63%	2470
	21st to end	Night	1 3 3 4 5% 2 4 5% 6% 9% 58%	2470
December	1st to 10th	Night	1 5% 2 5% 4 3 4 6% 5% 9% 56%	2470
	11th to 20th	Night	1 5% 3 5% 6% 5% 7% 6% 8% 11% 44%	3041
	21st to end	Night	1 4 3 7% 7% 4 6% 6% 7% 9% 46%	4521

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	26% 5% 20% 27% 17% 4	2859
	11th to 20th	Day	23% 7% 18% 28% 20% 5%	2860
	21st to end	Day	30% 6% 11% 26% 21% 6%	3146
February	1st to 10th	Day	27% 8% 15% 23% 20% 7%	1710
	11th to 20th	Day	29% 5% 13% 20% 25% 8%	1781
	21st to end	Day	29% 7% 10% 21% 24% 9%	1570
March	1st to 10th	Day	29% 6% 11% 25% 23% 6%	2069
	11th to 20th	Day	32% 8% 12% 27% 16% 6%	2058
	21st to end	Day	31% 10% 11% 27% 16% 5%	2178
April	1st to 10th	Day	28% 7% 11% 25% 21% 8%	1980
	11th to 20th	Day	31% 6% 11% 22% 23% 6%	2202
	21st to end	Day	31% 5% 11% 26% 23% 4	2340
May	1st to 10th	Day	35% 6% 9% 21% 25% 5%	2340
	11th to 20th	Day	36% 8% 9% 21% 22% 5%	2304
	21st to end	Day	34% 8% 9% 18% 25% 5%	2530
June	1st to 10th	Day	25% 5% 8% 17% 31% 14%	2340
	11th to 20th	Day	25% 4 5% 12% 26% 29%	2340
	21st to end	Day	26% 5% 7% 10% 21% 31%	2340
July	1st to 10th	Day	38% 6% 8% 9% 17% 24%	2276
	11th to 20th	Day	45% 9% 10% 12% 11% 14%	2271
	21st to end	Day	49% 11% 12% 12% 7% 9%	2404
August	1st to 10th	Day	43% 8% 9% 10% 13% 16%	2313
	11th to 20th	Day	40% 8% 9% 9% 15% 18%	2299
	21st to end	Day	37% 7% 10% 14% 20% 13%	2512
September	1st to 10th	Day	37% 6% 6% 9% 20% 22%	2008
	11th to 20th	Day	29% 5% 8% 14% 23% 21%	1980
	21st to end	Day	21% 4 6% 17% 34% 17%	1980
October	1st to 10th	Day	30% 5% 7% 18% 25% 15%	1897
	11th to 20th	Day	18% 3 6% 21% 35% 17%	1800
	21st to end	Day	20% 4 7% 29% 31% 10%	1980
November	1st to 10th	Day	18% 3 12% 26% 28% 12%	1756
	11th to 20th	Day	16% 5% 10% 30% 29% 10%	1710
	21st to end	Day	23% 5% 9% 25% 26% 13%	1710
December	1st to 10th	Day	23% 8% 16% 25% 19% 10%	1710
	11th to 20th	Day	29% 7% 13% 24% 19% 8%	2168
	21st to end	Day	33% 6% 11% 17% 16% 16%	3146
January	1st to 10th	Night	22% 4 22% 27% 20% 5%	4097
	11th to 20th	Night	19% 7% 20% 31% 16% 6%	4110
	21st to end	Night	30% 5% 13% 24% 22% 6%	4521
February	1st to 10th	Night	23% 8% 16% 23% 21% 10%	2470
	11th to 20th	Night	24% 5% 11% 19% 28% 13%	2293
	21st to end	Night	26% 8% 11% 23% 23% 9%	1884
March	1st to 10th	Night	25% 7% 13% 25% 22% 9%	2109
	11th to 20th	Night	29% 5% 10% 28% 22% 6%	2068
	21st to end	Night	24% 9% 14% 32% 17% 4	2178
April	1st to 10th	Night	25% 5% 12% 26% 22% 10%	1979
	11th to 20th	Night	24% 6% 11% 23% 29% 8%	1706
	21st to end	Night	22% 7% 11% 32% 24% 4	1620
May	1st to 10th	Night	28% 5% 8% 25% 28% 5%	1620
	11th to 20th	Night	21% 6% 9% 30% 27% 7%	1595
	21st to end	Night	20% 5% 12% 25% 33% 5%	1746
June	1st to 10th	Night	18% 3 7% 21% 38% 13%	1620
	11th to 20th	Night	18% 3 6% 13% 29% 31%	1620
	21st to end	Night	16% 4 6% 12% 24% 38%	1620
July	1st to 10th	Night	25% 7% 8% 12% 19% 29%	1575
	11th to 20th	Night	25% 8% 12% 20% 16% 18%	1566
	21st to end	Night	33% 9% 20% 18% 9% 11%	1674
August	1st to 10th	Night	25% 8% 12% 17% 18% 20%	1602
	11th to 20th	Night	25% 6% 12% 14% 20% 23%	1602
	21st to end	Night	21% 7% 10% 17% 27% 17%	1844
September	1st to 10th	Night	21% 5% 10% 16% 22% 26%	1948
	11th to 20th	Night	16% 4 11% 17% 27% 24%	1980
	21st to end	Night	13% 4 6% 21% 34% 22%	1980
October	1st to 10th	Night	24% 4 6% 23% 29% 15%	2061
	11th to 20th	Night	15% 3 8% 18% 40% 16%	2160
	21st to end	Night	19% 3 9% 26% 33% 11%	2376
November	1st to 10th	Night	19% 4 11% 24% 30% 13%	2319
	11th to 20th	Night	16% 5% 10% 23% 35% 11%	2470
	21st to end	Night	21% 5% 9% 22% 29% 15%	2470
December	1st to 10th	Night	22% 6% 15% 26% 21% 10%	2470
	11th to 20th	Night	27% 8% 13% 22% 21% 9%	3041
	21st to end	Night	30% 5% 12% 19% 16% 18%	4521

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	3 23% 35% 26% 10% 4	270
	11th to 20th	Day	2 24% 33% 26% 10% 4	270
	21st to end	Day	1 17% 35% 30% 13% 3	297
February	1st to 10th	Day	1 28% 40% 19% 11% 1	270
	11th to 20th	Day	2 24% 44% 23% 7% 1	377
	21st to end	Day	3 28% 38% 25% 5% 1	382
March	1st to 10th	Day	5% 26% 35% 22% 11% 1	460
	11th to 20th	Day	5% 17% 37% 27% 11% 2	449
	21st to end	Day	6% 31% 39% 20% 4	462
April	1st to 10th	Day	5% 24% 36% 20% 13% 1	420
	11th to 20th	Day	8% 26% 40% 17% 7% 1	412
	21st to end	Day	10% 26% 31% 21% 9% 3	420
May	1st to 10th	Day	10% 20% 38% 22% 8% 2	423
	11th to 20th	Day	8% 19% 32% 22% 12% 6%	448
	21st to end	Day	10% 21% 29% 23% 13% 4	485
June	1st to 10th	Day	4 15% 28% 33% 16% 4	450
	11th to 20th	Day	8% 15% 33% 28% 13% 4	450
	21st to end	Day	6% 11% 32% 36% 11% 4	450
July	1st to 10th	Day	9% 5% 23% 37% 20% 6%	446
	11th to 20th	Day	7% 4 18% 35% 26% 10%	444
	21st to end	Day	8% 3 13% 33% 31% 11%	487
August	1st to 10th	Day	9% 5% 25% 34% 22% 6%	447
	11th to 20th	Day	8% 4 23% 34% 24% 7%	437
	21st to end	Day	7% 3 25% 35% 22% 7%	495
September	1st to 10th	Day	7% 7% 22% 32% 21% 10%	450
	11th to 20th	Day	5% 17% 26% 29% 18% 5%	450
	21st to end	Day	7% 13% 23% 31% 19% 6%	450
October	1st to 10th	Day	9% 18% 29% 22% 15% 8%	367
	11th to 20th	Day	4 17% 22% 27% 23% 7%	270
	21st to end	Day	5% 18% 31% 29% 14% 3	297
November	1st to 10th	Day	7% 23% 22% 26% 19% 3	270
	11th to 20th	Day	3 13% 37% 27% 14% 6%	270
	21st to end	Day	3 18% 27% 28% 21% 3	270
December	1st to 10th	Day	3 15% 36% 28% 13% 5%	270
	11th to 20th	Day	3 19% 32% 26% 18% 2	270
	21st to end	Day	5% 21% 38% 24% 10% 2	297
January	1st to 10th	Night	3 16% 28% 31% 16% 6%	760
	11th to 20th	Night	3 14% 34% 29% 18% 3	760
	21st to end	Night	3 15% 32% 30% 16% 4	836
February	1st to 10th	Night	1 19% 36% 27% 11% 4	760
	11th to 20th	Night	2 16% 39% 30% 11% 2	744
	21st to end	Night	4 17% 39% 29% 10% 2	628
March	1st to 10th	Night	4 18% 32% 31% 14% 1	760
	11th to 20th	Night	3 12% 31% 32% 18% 3	752
	21st to end	Night	2 20% 35% 29% 11% 3	792
April	1st to 10th	Night	5% 20% 33% 26% 14% 2	719
	11th to 20th	Night	5% 19% 34% 27% 13% 2	533
	21st to end	Night	5% 22% 26% 29% 14% 4	540
May	1st to 10th	Night	4 12% 34% 34% 14% 2	540
	11th to 20th	Night	2 10% 27% 32% 23% 5%	531
	21st to end	Night	4 14% 25% 33% 19% 4	584
June	1st to 10th	Night	3 9% 23% 43% 20% 2	540
	11th to 20th	Night	4 10% 26% 40% 19% 2	540
	21st to end	Night	2 3 26% 42% 25% 3	540
July	1st to 10th	Night	4 1 13% 36% 39% 7%	525
	11th to 20th	Night	4 1 8% 38% 40% 8%	522
	21st to end	Night	4 1 5% 34% 49% 8%	591
August	1st to 10th	Night	4 1 9% 43% 39% 5%	537
	11th to 20th	Night	3 1 13% 37% 40% 5%	534
	21st to end	Night	3 2 12% 39% 34% 9%	594
September	1st to 10th	Night	4 4 13% 33% 35% 12%	688
	11th to 20th	Night	2 6% 16% 36% 30% 10%	720
	21st to end	Night	3 8% 18% 30% 32% 9%	720
October	1st to 10th	Night	5% 11% 25% 33% 21% 5%	720
	11th to 20th	Night	3 9% 23% 37% 22% 7%	720
	21st to end	Night	4 13% 25% 29% 20% 8%	792
November	1st to 10th	Night	3 15% 22% 32% 23% 6%	740
	11th to 20th	Night	3 11% 31% 33% 17% 6%	760
	21st to end	Night	3 16% 25% 30% 21% 6%	760
December	1st to 10th	Night	4 11% 32% 31% 17% 4	760
	11th to 20th	Night	5% 14% 31% 31% 18% 2	760
	21st to end	Night	3 16% 37% 32% 10% 2	836

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