Arriola Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Arriola Observatory 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 5% 2 4 4 3 4 5% 5% 7% 56%	78842
	Night	5% 6% 2 4 4 3 4 4 5% 6% 57%	80998
Transparency	Day	27% 5% 9% 20% 25% 15%	78567
	Night	28% 5% 8% 21% 25% 14%	80794
Seeing	Day	9% 13% 27% 30% 17% 4	14120
	Night	8% 6% 21% 38% 23% 4	24529

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	4 7% 3 5% 4 2 4 4 6% 6% 56%	2858
	11th to 20th	Day	4 8% 2 6% 6% 3 5% 5% 4 6% 52%	2860
	21st to end	Day	7% 10% 3 4 4 2 3 3 4 6% 54%	3146
February	1st to 10th	Day	4 9% 3 5% 6% 3 4 3 4 7% 53%	1710
	11th to 20th	Day	5% 9% 3 7% 5% 3 4 4 5% 6% 50%	1665
	21st to end	Day	7% 12% 3 5% 5% 3 3 5% 4 5% 49%	1643
March	1st to 10th	Day	7% 8% 3 4 5% 3 4 5% 5% 8% 47%	2090
	11th to 20th	Day	4 7% 3 6% 6% 3 5% 6% 6% 7% 48%	2058
	21st to end	Day	6% 7% 3 6% 5% 3 5% 4 5% 7% 49%	2178
April	1st to 10th	Day	5% 5% 2 5% 4 3 5% 4 5% 6% 55%	2114
	11th to 20th	Day	3 5% 2 5% 5% 3 5% 5% 5% 7% 53%	2131
	21st to end	Day	5% 4 2 4 4 4 5% 5% 6% 8% 54%	2160
May	1st to 10th	Day	4 4 2 5% 4 3 5% 5% 6% 7% 53%	2340
	11th to 20th	Day	4 5% 2 4 4 3 5% 5% 6% 9% 53%	2301
	21st to end	Day	4 3 1 4 4 2 3 4 6% 6% 62%	2579
June	1st to 10th	Day	3 2 1 2 3 2 3 4 5% 8% 66%	2520
	11th to 20th	Day	2 2 1 2 3 2 2 3 3 6% 73%	2520
	21st to end	Day	1 2 1 3 3 2 4 5% 5% 7% 67%	2491
July	1st to 10th	Day	3 2 1 4 5% 3 5% 6% 7% 8% 56%	2340
	11th to 20th	Day	3 2 2 3 5% 4 6% 6% 9% 10% 50%	2340
	21st to end	Day	6% 5% 2 5% 6% 5% 7% 7% 8% 11% 39%	2545
August	1st to 10th	Day	5% 4 2 5% 6% 4 6% 7% 8% 8% 46%	2328
	11th to 20th	Day	3 3 1 4 6% 3 6% 6% 7% 9% 51%	2268
	21st to end	Day	3 3 2 5% 6% 3 5% 6% 8% 9% 51%	2376
September	1st to 10th	Day	6% 3 2 4 5% 3 5% 5% 5% 7% 56%	2160
	11th to 20th	Day	4 3 2 3 5% 3 5% 5% 6% 5% 58%	2068
	21st to end	Day	4 3 2 3 3 2 2 3 4 6% 69%	1943
October	1st to 10th	Day	7% 3 2 3 5% 2 4 3 4 7% 59%	1800
	11th to 20th	Day	4 2 1 2 2 2 2 3 3 4 74%	1800
	21st to end	Day	4 4 1 3 3 2 3 3 3 5% 68%	1980
November	1st to 10th	Day	3 3 1 3 2 2 2 3 4 7% 68%	1859
	11th to 20th	Day	4 3 1 3 3 2 2 3 5% 5% 69%	1751
	21st to end	Day	5% 7% 3 3 4 2 3 3 4 4 62%	1520
December	1st to 10th	Day	8% 7% 3 4 3 3 4 4 5% 6% 55%	1520
	11th to 20th	Day	8% 8% 3 6% 4 3 4 5% 6% 7% 46%	1926
	21st to end	Day	6% 9% 3 5% 4 2 4 4 4 5% 54%	2954
January	1st to 10th	Night	4 7% 3 7% 5% 3 4 5% 5% 5% 52%	4097
	11th to 20th	Night	5% 9% 2 4 4 3 4 4 5% 7% 54%	4110
	21st to end	Night	6% 10% 3 5% 4 3 4 4 4 6% 51%	4521
February	1st to 10th	Night	4 8% 3 4 4 2 3 3 4 5% 60%	2470
	11th to 20th	Night	7% 7% 2 5% 4 2 4 4 4 6% 55%	2402
	21st to end	Night	6% 9% 3 5% 3 3 4 3 4 6% 51%	1804
March	1st to 10th	Night	7% 6% 3 5% 4 3 4 4 5% 6% 53%	2090
	11th to 20th	Night	4 8% 2 5% 5% 3 4 5% 5% 6% 53%	2068
	21st to end	Night	7% 8% 3 6% 4 3 4 5% 5% 6% 48%	2178
April	1st to 10th	Night	7% 6% 2 4 4 3 5% 6% 5% 6% 52%	1845
	11th to 20th	Night	6% 5% 2 5% 5% 3 4 4 5% 6% 56%	1777
	21st to end	Night	4 4 2 4 5% 3 4 5% 4 6% 60%	1797
May	1st to 10th	Night	5% 4 3 5% 4 3 3 4 5% 8% 57%	1620
	11th to 20th	Night	6% 6% 3 5% 4 2 4 3 5% 7% 58%	1594
	21st to end	Night	6% 4 1 4 5% 2 3 5% 4 6% 60%	1692
June	1st to 10th	Night	2 2 1 3 3 2 3 3 5% 7% 68%	1440
	11th to 20th	Night	3 3 1 3 3 2 3 3 4 6% 71%	1440
	21st to end	Night	1 2 1 3 3 2 5% 5% 6% 7% 65%	1462
July	1st to 10th	Night	3 3 2 5% 5% 4 6% 6% 7% 9% 51%	1620
	11th to 20th	Night	2 3 3 6% 7% 5% 6% 8% 8% 8% 46%	1620
	21st to end	Night	4 4 3 6% 7% 5% 7% 8% 9% 12% 35%	1773
August	1st to 10th	Night	2 3 2 5% 5% 3 6% 7% 8% 9% 49%	1611
	11th to 20th	Night	4 4 2 3 5% 3 5% 5% 8% 10% 51%	1632
	21st to end	Night	3 3 2 4 5% 4 5% 6% 7% 11% 51%	1980
September	1st to 10th	Night	5% 2 2 5% 6% 3 6% 5% 7% 7% 52%	1800
	11th to 20th	Night	3 3 3 4 4 2 4 5% 4 6% 62%	1888
	21st to end	Night	6% 3 1 3 3 2 3 3 3 5% 69%	2016
October	1st to 10th	Night	8% 3 2 3 3 2 4 4 5% 6% 60%	2160
	11th to 20th	Night	2 3 1 3 3 1 3 3 3 4 74%	2160
	21st to end	Night	4 3 1 4 3 2 2 3 3 5% 69%	2376
November	1st to 10th	Night	5% 4 1 2 2 1 3 4 4 6% 68%	2220
	11th to 20th	Night	4 3 1 3 2 1 3 3 4 5% 70%	2403
	21st to end	Night	5% 7% 2 3 3 2 3 3 5% 5% 62%	2660
December	1st to 10th	Night	7% 7% 2 4 4 2 3 3 3 6% 59%	2660
	11th to 20th	Night	7% 9% 3 5% 5% 3 4 3 5% 8% 47%	3271
	21st to end	Night	7% 10% 3 4 3 2 3 3 4 5% 56%	4741

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% 5% 14% 30% 19% 3	2859
	11th to 20th	Day	34% 4 17% 29% 14% 3	2860
	21st to end	Day	34% 5% 8% 28% 21% 4	3146
February	1st to 10th	Day	33% 4 13% 22% 22% 7%	1710
	11th to 20th	Day	37% 3 8% 23% 23% 6%	1674
	21st to end	Day	38% 3 7% 16% 30% 6%	1643
March	1st to 10th	Day	35% 4 6% 22% 27% 6%	2090
	11th to 20th	Day	32% 5% 8% 25% 24% 6%	2058
	21st to end	Day	34% 5% 8% 21% 27% 5%	2178
April	1st to 10th	Day	30% 4 6% 19% 27% 14%	2114
	11th to 20th	Day	30% 4 6% 18% 28% 13%	2134
	21st to end	Day	26% 4 7% 22% 30% 12%	2160
May	1st to 10th	Day	28% 5% 7% 17% 30% 12%	2340
	11th to 20th	Day	27% 6% 9% 18% 29% 11%	2304
	21st to end	Day	22% 4 6% 16% 29% 22%	2579
June	1st to 10th	Day	16% 3 6% 16% 31% 28%	2520
	11th to 20th	Day	15% 3 4 9% 23% 46%	2520
	21st to end	Day	14% 4 6% 13% 25% 39%	2491
July	1st to 10th	Day	21% 7% 11% 14% 18% 29%	2276
	11th to 20th	Day	24% 8% 14% 19% 18% 17%	2271
	21st to end	Day	33% 11% 17% 18% 14% 7%	2404
August	1st to 10th	Day	32% 9% 12% 15% 14% 18%	2313
	11th to 20th	Day	25% 7% 11% 17% 20% 20%	2268
	21st to end	Day	25% 7% 10% 19% 25% 14%	2376
September	1st to 10th	Day	27% 5% 8% 14% 23% 23%	2160
	11th to 20th	Day	23% 6% 9% 15% 21% 26%	2068
	21st to end	Day	18% 3 4 14% 37% 22%	1943
October	1st to 10th	Day	27% 4 8% 19% 27% 16%	1800
	11th to 20th	Day	15% 2 4 17% 39% 22%	1800
	21st to end	Day	20% 3 6% 23% 37% 10%	1980
November	1st to 10th	Day	18% 2 7% 26% 37% 10%	1859
	11th to 20th	Day	18% 3 7% 29% 36% 7%	1751
	21st to end	Day	27% 4 7% 25% 27% 10%	1520
December	1st to 10th	Day	31% 4 12% 26% 19% 7%	1520
	11th to 20th	Day	37% 6% 10% 25% 20% 1	1924
	21st to end	Day	33% 5% 11% 16% 25% 10%	2954
January	1st to 10th	Night	33% 4 9% 32% 19% 3	4097
	11th to 20th	Night	30% 4 16% 31% 17% 3	4110
	21st to end	Night	35% 4 7% 28% 21% 3	4521
February	1st to 10th	Night	28% 4 11% 25% 24% 8%	2470
	11th to 20th	Night	31% 3 8% 23% 27% 7%	2403
	21st to end	Night	34% 3 6% 19% 29% 9%	1804
March	1st to 10th	Night	31% 5% 5% 22% 28% 8%	2090
	11th to 20th	Night	31% 5% 6% 24% 26% 8%	2068
	21st to end	Night	35% 5% 7% 21% 25% 7%	2178
April	1st to 10th	Night	31% 4 6% 19% 26% 13%	1845
	11th to 20th	Night	30% 4 5% 16% 29% 16%	1777
	21st to end	Night	27% 4 4 20% 32% 14%	1797
May	1st to 10th	Night	27% 4 6% 15% 35% 12%	1620
	11th to 20th	Night	28% 5% 7% 20% 26% 14%	1595
	21st to end	Night	26% 4 7% 15% 24% 24%	1692
June	1st to 10th	Night	16% 4 5% 14% 29% 32%	1440
	11th to 20th	Night	16% 3 5% 10% 20% 47%	1440
	21st to end	Night	16% 5% 5% 11% 22% 40%	1462
July	1st to 10th	Night	27% 8% 11% 12% 13% 29%	1575
	11th to 20th	Night	32% 9% 11% 13% 16% 19%	1566
	21st to end	Night	37% 11% 16% 17% 10% 9%	1674
August	1st to 10th	Night	29% 10% 13% 15% 14% 20%	1602
	11th to 20th	Night	28% 8% 11% 14% 15% 24%	1632
	21st to end	Night	25% 7% 12% 17% 21% 17%	1980
September	1st to 10th	Night	29% 6% 8% 13% 18% 25%	1800
	11th to 20th	Night	24% 5% 7% 17% 20% 28%	1888
	21st to end	Night	20% 4 5% 12% 32% 28%	2016
October	1st to 10th	Night	25% 5% 8% 17% 21% 24%	2160
	11th to 20th	Night	16% 3 5% 13% 37% 26%	2160
	21st to end	Night	19% 4 4 23% 35% 16%	2376
November	1st to 10th	Night	20% 3 5% 21% 36% 15%	2220
	11th to 20th	Night	18% 3 7% 25% 38% 9%	2403
	21st to end	Night	25% 3 7% 21% 32% 13%	2660
December	1st to 10th	Night	29% 3 10% 27% 21% 10%	2660
	11th to 20th	Night	36% 5% 8% 24% 24% 3	3272
	21st to end	Night	33% 3 9% 18% 25% 12%	4741

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% 12% 30% 27% 11% 2	270
	11th to 20th	Day	14% 14% 32% 27% 11% 1	270
	21st to end	Day	10% 12% 30% 31% 13% 3	297
February	1st to 10th	Day	11% 18% 31% 29% 10%	270
	11th to 20th	Day	13% 18% 35% 26% 9%	270
	21st to end	Day	14% 22% 38% 19% 7%	301
March	1st to 10th	Day	15% 22% 32% 23% 8%	460
	11th to 20th	Day	12% 22% 33% 23% 10% 1	449
	21st to end	Day	15% 29% 35% 14% 6% 1	462
April	1st to 10th	Day	11% 23% 35% 21% 9% 1	420
	11th to 20th	Day	17% 25% 33% 17% 6% 2	412
	21st to end	Day	13% 27% 33% 20% 7%	420
May	1st to 10th	Day	11% 20% 37% 24% 7% 1	423
	11th to 20th	Day	7% 18% 33% 26% 13% 3	448
	21st to end	Day	10% 17% 31% 25% 14% 4	534
June	1st to 10th	Day	4 9% 23% 37% 22% 4	630
	11th to 20th	Day	4 10% 25% 36% 20% 5%	630
	21st to end	Day	2 7% 26% 40% 19% 5%	601
July	1st to 10th	Day	3 3 16% 45% 28% 5%	446
	11th to 20th	Day	5% 2 12% 39% 32% 10%	444
	21st to end	Day	6% 1 14% 39% 31% 9%	487
August	1st to 10th	Day	6% 3 16% 44% 26% 5%	447
	11th to 20th	Day	4 3 22% 37% 27% 7%	437
	21st to end	Day	4 3 20% 40% 26% 6%	495
September	1st to 10th	Day	7% 2 22% 37% 26% 6%	450
	11th to 20th	Day	4 7% 26% 37% 20% 5%	450
	21st to end	Day	6% 14% 22% 32% 21% 6%	413
October	1st to 10th	Day	11% 15% 23% 20% 21% 10%	270
	11th to 20th	Day	7% 12% 27% 29% 20% 5%	270
	21st to end	Day	11% 15% 24% 30% 18% 3	297
November	1st to 10th	Day	9% 16% 26% 31% 16% 3	270
	11th to 20th	Day	7% 10% 32% 32% 15% 3	270
	21st to end	Day	11% 14% 28% 30% 13% 3	270
December	1st to 10th	Day	11% 11% 29% 31% 14% 3	270
	11th to 20th	Day	11% 14% 30% 24% 18% 3	270
	21st to end	Day	19% 14% 26% 30% 10%	297
January	1st to 10th	Night	10% 4 23% 40% 18% 4	760
	11th to 20th	Night	9% 7% 26% 36% 20% 3	760
	21st to end	Night	11% 6% 27% 36% 16% 4	836
February	1st to 10th	Night	9% 7% 31% 37% 14% 2	760
	11th to 20th	Night	9% 7% 32% 38% 12% 2	744
	21st to end	Night	13% 9% 31% 35% 11% 1	628
March	1st to 10th	Night	11% 8% 29% 35% 15% 2	760
	11th to 20th	Night	9% 8% 24% 38% 19% 2	752
	21st to end	Night	11% 11% 25% 36% 15% 2	792
April	1st to 10th	Night	11% 11% 25% 41% 10% 1	585
	11th to 20th	Night	11% 17% 25% 31% 15% 2	533
	21st to end	Night	8% 13% 28% 37% 12% 1	540
May	1st to 10th	Night	9% 8% 25% 42% 16% 1	540
	11th to 20th	Night	10% 5% 22% 40% 20% 4	531
	21st to end	Night	9% 9% 23% 35% 22% 3	584
June	1st to 10th	Night	2 6% 18% 41% 30% 2	540
	11th to 20th	Night	4 5% 18% 43% 25% 4	540
	21st to end	Night	2 2 18% 41% 34% 3	540
July	1st to 10th	Night	5% 1 12% 38% 41% 4	525
	11th to 20th	Night	3 1 7% 34% 47% 7%	522
	21st to end	Night	5% 2 7% 29% 49% 8%	591
August	1st to 10th	Night	3 7% 33% 46% 10%	537
	11th to 20th	Night	6% 2 8% 38% 40% 7%	534
	21st to end	Night	3 1 9% 37% 42% 8%	594
September	1st to 10th	Night	6% 1 11% 40% 37% 5%	540
	11th to 20th	Night	4 2 14% 41% 32% 6%	628
	21st to end	Night	7% 4 16% 36% 30% 7%	720
October	1st to 10th	Night	9% 6% 22% 38% 23% 2	720
	11th to 20th	Night	4 3 19% 47% 22% 4	720
	21st to end	Night	6% 7% 21% 37% 24% 6%	792
November	1st to 10th	Night	7% 4 19% 43% 22% 5%	740
	11th to 20th	Night	6% 5% 22% 40% 22% 5%	826
	21st to end	Night	10% 9% 21% 35% 20% 5%	950
December	1st to 10th	Night	11% 6% 21% 41% 17% 3	950
	11th to 20th	Night	15% 6% 24% 35% 18% 2	950
	21st to end	Night	13% 10% 22% 39% 14% 2	965

Page generated at 2024-03-15 12:01:43. Version ac07

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