General Nathan Twining Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the General Nathan Twining Observatory clear sky chart from 2005-11-06 to 2024-11-03.

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	3 3 1 3 3 3 4 4 6% 8% 64%	100678
	Night	4 4 2 4 3 4 4 4 5% 7% 59%	98550
Transparency	Day	17% 5% 8% 22% 28% 20%	100441
	Night	22% 5% 8% 20% 27% 19%	98376
Seeing	Day	5% 6% 17% 30% 27% 15%	14807
	Night	5% 3 21% 45% 23% 2	25042

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 9% 3 5% 2 3 3 3 6% 7% 56%	2858
	11th to 20th	Day	2 3 1 3 2 2 3 3 5% 8% 68%	2860
	21st to end	Day	5% 6% 2 6% 4 4 4 5% 6% 7% 53%	3146
February	1st to 10th	Day	2 5% 1 3 2 2 3 3 5% 7% 65%	1710
	11th to 20th	Day	3 3 1 5% 4 3 4 3 4 6% 65%	1844
	21st to end	Day	3 4 2 3 2 2 2 3 5% 6% 69%	1570
March	1st to 10th	Day	2 3 1 3 3 3 4 3 5% 7% 66%	3428
	11th to 20th	Day	7% 5% 2 5% 4 4 4 4 5% 7% 52%	3490
	21st to end	Day	2 3 2 4 3 3 4 3 6% 8% 64%	3877
April	1st to 10th	Day	3 3 1 3 2 3 3 4 5% 6% 68%	2280
	11th to 20th	Day	3 3 1 3 3 2 3 2 4 7% 69%	2251
	21st to end	Day	2 2 1 2 2 3 3 2 5% 6% 72%	2280
May	1st to 10th	Day	1 2 2 2 2 2 3 4 6% 75%	3800
	11th to 20th	Day	2 3 1 3 3 3 4 4 6% 8% 63%	3905
	21st to end	Day	1 1 1 2 1 1 1 2 4 5% 81%	4563
June	1st to 10th	Day	1 2 1 2 2 3 4 4 5% 10% 64%	2660
	11th to 20th	Day	2 2 2 2 2 3 3 5% 5% 74%	2660
	21st to end	Day	4 3 1 5% 3 4 4 4 7% 8% 57%	2587
July	1st to 10th	Day	2 2 1 3 3 4 4 4 8% 8% 61%	4110
	11th to 20th	Day	2 2 1 3 2 4 4 5% 8% 11% 60%	4110
	21st to end	Day	2 2 1 4 4 5% 6% 6% 10% 12% 48%	4454
August	1st to 10th	Day	2 2 1 3 3 4 5% 5% 8% 12% 56%	4014
	11th to 20th	Day	2 2 1 3 3 4 5% 4 6% 9% 62%	3726
	21st to end	Day	3 2 1 4 5% 5% 6% 6% 9% 11% 48%	4180
September	1st to 10th	Day	5% 3 1 5% 4 4 4 4 6% 8% 57%	2280
	11th to 20th	Day	5% 3 1 3 3 3 4 3 6% 7% 62%	2280
	21st to end	Day	2 2 1 3 2 2 3 3 4 6% 72%	2033
October	1st to 10th	Day	3 3 1 4 2 3 4 3 5% 5% 67%	1900
	11th to 20th	Day	3 2 1 2 2 2 2 2 3 5% 77%	1900
	21st to end	Day	3 3 1 2 1 2 2 2 3 4 78%	2090
November	1st to 10th	Day	2 1 1 2 2 3 2 2 4 7% 75%	1879
	11th to 20th	Day	2 2 1 3 2 2 3 2 4 6% 73%	1780
	21st to end	Day	4 4 1 4 3 3 4 3 5% 5% 65%	1710
December	1st to 10th	Day	4 4 1 4 4 2 3 3 5% 6% 64%	1549
	11th to 20th	Day	4 4 1 6% 4 4 4 4 6% 7% 57%	1926
	21st to end	Day	3 4 2 4 3 3 4 3 5% 7% 62%	2988
January	1st to 10th	Night	2 7% 2 5% 4 4 4 4 7% 8% 51%	4097
	11th to 20th	Night	4 3 1 3 2 2 3 3 5% 6% 70%	4110
	21st to end	Night	7% 7% 3 5% 4 4 4 4 6% 7% 49%	4521
February	1st to 10th	Night	2 6% 2 4 3 2 3 2 5% 6% 66%	2470
	11th to 20th	Night	5% 5% 1 4 4 3 4 3 5% 6% 60%	2220
	21st to end	Night	3 4 1 4 2 3 3 2 4 5% 69%	1884
March	1st to 10th	Night	4 4 2 4 3 2 3 2 4 5% 68%	3443
	11th to 20th	Night	13% 6% 2 6% 4 3 3 3 4 5% 52%	3490
	21st to end	Night	3 4 1 4 4 3 4 4 5% 7% 62%	3772
April	1st to 10th	Night	3 2 1 3 3 3 3 3 6% 7% 67%	1900
	11th to 20th	Night	4 5% 1 3 2 2 3 2 4 5% 68%	1877
	21st to end	Night	3 3 1 5% 3 3 3 3 5% 6% 66%	1900
May	1st to 10th	Night	3 3 2 3 2 2 3 2 3 5% 71%	3170
	11th to 20th	Night	4 3 2 4 4 4 4 3 6% 7% 60%	2996
	21st to end	Night	1 2 1 2 2 2 2 2 3 4 79%	3019
June	1st to 10th	Night	3 4 2 4 4 4 4 5% 7% 9% 56%	1520
	11th to 20th	Night	2 2 1 3 3 3 3 4 5% 7% 66%	1520
	21st to end	Night	3 4 2 5% 4 4 5% 6% 8% 10% 48%	1584
July	1st to 10th	Night	3 3 2 5% 5% 5% 6% 5% 6% 8% 53%	2860
	11th to 20th	Night	2 4 2 6% 5% 5% 6% 5% 8% 11% 45%	2860
	21st to end	Night	4 4 2 6% 6% 7% 7% 7% 10% 12% 36%	3109
August	1st to 10th	Night	2 3 2 8% 7% 7% 7% 6% 9% 13% 37%	2922
	11th to 20th	Night	3 4 2 6% 5% 6% 7% 6% 8% 10% 42%	3113
	21st to end	Night	3 4 2 7% 6% 7% 8% 7% 11% 11% 34%	3487
September	1st to 10th	Night	5% 3 2 5% 4 4 5% 5% 7% 9% 49%	1900
	11th to 20th	Night	6% 4 2 5% 3 3 4 4 6% 7% 56%	1900
	21st to end	Night	4 3 1 4 3 3 3 2 4 6% 66%	2142
October	1st to 10th	Night	4 4 1 4 3 3 4 3 5% 7% 63%	2280
	11th to 20th	Night	3 2 1 3 1 3 2 3 4 4 74%	2280
	21st to end	Night	3 3 1 3 2 2 2 2 3 5% 74%	2508
November	1st to 10th	Night	2 2 1 2 1 1 3 2 4 6% 77%	2244
	11th to 20th	Night	1 2 1 3 2 2 3 2 3 5% 75%	2379
	21st to end	Night	6% 5% 1 3 2 2 3 2 4 6% 66%	2470
December	1st to 10th	Night	4 4 1 3 3 2 3 2 4 7% 67%	2627
	11th to 20th	Night	5% 4 2 4 3 4 4 4 6% 10% 56%	3271
	21st to end	Night	5% 5% 1 4 3 4 4 3 4 6% 61%	4705

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	25% 4 4 36% 26% 4	2859
	11th to 20th	Day	14% 3 12% 37% 30% 3	2860
	21st to end	Day	28% 5% 9% 30% 23% 6%	3146
February	1st to 10th	Day	19% 4 7% 25% 30% 16%	1710
	11th to 20th	Day	22% 3 5% 22% 33% 15%	1854
	21st to end	Day	16% 2 4 18% 36% 24%	1570
March	1st to 10th	Day	16% 4 3 19% 33% 25%	3428
	11th to 20th	Day	26% 8% 6% 24% 24% 13%	3490
	21st to end	Day	17% 4 3 21% 39% 16%	3877
April	1st to 10th	Day	16% 4 3 15% 36% 25%	2280
	11th to 20th	Day	16% 3 2 15% 30% 33%	2254
	21st to end	Day	13% 3 3 18% 37% 25%	2280
May	1st to 10th	Day	9% 5% 4 11% 35% 37%	3800
	11th to 20th	Day	16% 6% 7% 18% 32% 22%	3908
	21st to end	Day	6% 3 4 10% 20% 56%	4563
June	1st to 10th	Day	15% 4 7% 19% 25% 31%	2660
	11th to 20th	Day	11% 3 3 11% 21% 51%	2660
	21st to end	Day	22% 5% 8% 18% 20% 28%	2587
July	1st to 10th	Day	18% 6% 10% 14% 22% 30%	4046
	11th to 20th	Day	16% 6% 14% 30% 26% 8%	4041
	21st to end	Day	21% 8% 17% 35% 16% 2	4314
August	1st to 10th	Day	17% 7% 18% 29% 20% 10%	4000
	11th to 20th	Day	17% 6% 12% 22% 27% 17%	3762
	21st to end	Day	25% 9% 17% 23% 19% 6%	4179
September	1st to 10th	Day	24% 6% 9% 21% 25% 16%	2280
	11th to 20th	Day	19% 6% 10% 18% 24% 23%	2280
	21st to end	Day	14% 3 5% 20% 31% 26%	2033
October	1st to 10th	Day	18% 5% 8% 19% 26% 24%	1900
	11th to 20th	Day	13% 3 3 13% 36% 33%	1900
	21st to end	Day	12% 2 4 22% 40% 19%	2090
November	1st to 10th	Day	11% 2 3 24% 40% 20%	1879
	11th to 20th	Day	13% 2 5% 25% 41% 13%	1780
	21st to end	Day	22% 3 4 22% 34% 14%	1710
December	1st to 10th	Day	21% 3 8% 34% 26% 9%	1549
	11th to 20th	Day	26% 5% 9% 29% 26% 6%	1924
	21st to end	Day	21% 5% 8% 22% 32% 13%	2988
January	1st to 10th	Night	26% 5% 7% 29% 27% 5%	4097
	11th to 20th	Night	16% 2 9% 32% 34% 6%	4110
	21st to end	Night	31% 5% 8% 26% 25% 6%	4521
February	1st to 10th	Night	19% 3 7% 23% 31% 16%	2470
	11th to 20th	Night	24% 4 4 21% 29% 17%	2220
	21st to end	Night	18% 2 3 18% 34% 24%	1884
March	1st to 10th	Night	18% 4 2 16% 37% 23%	3443
	11th to 20th	Night	30% 8% 4 19% 26% 13%	3490
	21st to end	Night	18% 6% 3 22% 35% 16%	3772
April	1st to 10th	Night	15% 4 4 13% 35% 29%	1900
	11th to 20th	Night	19% 4 3 13% 25% 35%	1877
	21st to end	Night	19% 4 4 14% 34% 26%	1900
May	1st to 10th	Night	14% 4 3 10% 30% 39%	3170
	11th to 20th	Night	19% 6% 9% 15% 26% 24%	2997
	21st to end	Night	8% 4 5% 8% 16% 60%	3019
June	1st to 10th	Night	21% 6% 8% 17% 20% 28%	1520
	11th to 20th	Night	15% 4 4 11% 18% 47%	1520
	21st to end	Night	27% 5% 11% 16% 15% 25%	1584
July	1st to 10th	Night	27% 7% 12% 14% 15% 25%	2815
	11th to 20th	Night	28% 7% 14% 27% 18% 4	2806
	21st to end	Night	32% 10% 18% 28% 9% 2	3011
August	1st to 10th	Night	32% 9% 17% 21% 15% 7%	2913
	11th to 20th	Night	30% 9% 14% 17% 17% 13%	3143
	21st to end	Night	36% 9% 17% 20% 12% 5%	3487
September	1st to 10th	Night	27% 7% 13% 19% 20% 15%	1900
	11th to 20th	Night	25% 6% 10% 15% 20% 24%	1900
	21st to end	Night	18% 4 5% 15% 30% 28%	2142
October	1st to 10th	Night	20% 5% 8% 16% 24% 27%	2280
	11th to 20th	Night	14% 3 4 12% 29% 38%	2280
	21st to end	Night	15% 2 4 17% 38% 25%	2508
November	1st to 10th	Night	10% 3 2 23% 40% 22%	2244
	11th to 20th	Night	13% 3 3 21% 38% 22%	2379
	21st to end	Night	22% 2 5% 17% 37% 16%	2470
December	1st to 10th	Night	20% 2 7% 27% 33% 11%	2627
	11th to 20th	Night	23% 3 9% 29% 29% 7%	3272
	21st to end	Night	22% 4 6% 26% 31% 10%	4705

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	10% 3 16% 48% 20% 3	270
	11th to 20th	Day	9% 6% 19% 38% 22% 6%	270
	21st to end	Day	3 6% 20% 39% 25% 7%	297
February	1st to 10th	Day	7% 6% 21% 37% 23% 5%	270
	11th to 20th	Day	7% 7% 22% 46% 17% 1	270
	21st to end	Day	12% 12% 26% 39% 8% 4	225
March	1st to 10th	Day	6% 16% 30% 31% 14% 3	444
	11th to 20th	Day	10% 13% 26% 27% 18% 4	460
	21st to end	Day	8% 22% 28% 26% 13% 3	506
April	1st to 10th	Day	8% 13% 27% 29% 15% 8%	460
	11th to 20th	Day	6% 16% 33% 27% 14% 4	452
	21st to end	Day	7% 12% 29% 33% 17% 3	460
May	1st to 10th	Day	3 11% 32% 28% 20% 5%	463
	11th to 20th	Day	4 7% 24% 31% 22% 11%	488
	21st to end	Day	3 10% 27% 29% 23% 8%	576
June	1st to 10th	Day	2 4 16% 31% 35% 11%	680
	11th to 20th	Day	3 4 14% 34% 33% 12%	680
	21st to end	Day	6% 1 13% 32% 33% 15%	607
July	1st to 10th	Day	1 1 6% 27% 35% 29%	486
	11th to 20th	Day	3 3 16% 31% 47%	484
	21st to end	Day	2 2 3 15% 35% 44%	531
August	1st to 10th	Day	2 1 5% 18% 38% 36%	487
	11th to 20th	Day	3 2 5% 20% 37% 34%	477
	21st to end	Day	4 1 4 21% 38% 32%	539
September	1st to 10th	Day	4 2 6% 23% 33% 31%	490
	11th to 20th	Day	3 2 12% 24% 40% 17%	490
	21st to end	Day	4 5% 12% 23% 34% 22%	362
October	1st to 10th	Day	3 5% 14% 24% 34% 20%	300
	11th to 20th	Day	8% 4 12% 28% 36% 11%	300
	21st to end	Day	8% 6% 10% 25% 35% 15%	330
November	1st to 10th	Day	4 7% 16% 37% 29% 7%	276
	11th to 20th	Day	3 3 10% 38% 39% 9%	270
	21st to end	Day	8% 7% 19% 38% 21% 7%	270
December	1st to 10th	Day	9% 2 14% 47% 23% 6%	270
	11th to 20th	Day	4 6% 23% 42% 20% 4	270
	21st to end	Day	13% 4 21% 44% 16% 2	297
January	1st to 10th	Night	5% 1 22% 50% 20% 2	760
	11th to 20th	Night	8% 2 25% 47% 17% 1	760
	21st to end	Night	7% 4 25% 46% 18% 1	836
February	1st to 10th	Night	5% 4 28% 49% 13% 1	760
	11th to 20th	Night	7% 4 31% 48% 9%	744
	21st to end	Night	6% 4 39% 47% 4	628
March	1st to 10th	Night	6% 6% 35% 44% 9% 1	760
	11th to 20th	Night	6% 6% 30% 45% 13%	760
	21st to end	Night	7% 7% 31% 46% 9%	805
April	1st to 10th	Night	4 4 39% 44% 8%	570
	11th to 20th	Night	7% 8% 37% 40% 8%	563
	21st to end	Night	4 8% 37% 41% 10%	570
May	1st to 10th	Night	5% 4 34% 48% 9%	570
	11th to 20th	Night	7% 2 21% 50% 19% 1	561
	21st to end	Night	3 3 29% 51% 14%	617
June	1st to 10th	Night	3 3 19% 51% 24% 1	570
	11th to 20th	Night	2 3 22% 52% 20% 1	570
	21st to end	Night	4 2 15% 49% 29% 1	570
July	1st to 10th	Night	5% 2 8% 39% 41% 4	555
	11th to 20th	Night	3 1 4 33% 53% 5%	552
	21st to end	Night	4 2 4 28% 54% 9%	624
August	1st to 10th	Night	3 2 2 26% 56% 10%	567
	11th to 20th	Night	4 2 4 36% 49% 5%	564
	21st to end	Night	2 3 2 33% 53% 7%	627
September	1st to 10th	Night	6% 2 6% 44% 39% 3	570
	11th to 20th	Night	9% 2 8% 46% 33% 2	570
	21st to end	Night	4 2 12% 46% 33% 3	684
October	1st to 10th	Night	5% 2 16% 47% 28% 2	760
	11th to 20th	Night	4 4 16% 52% 22% 2	760
	21st to end	Night	4 2 19% 43% 27% 4	836
November	1st to 10th	Night	4 1 17% 52% 25% 1	748
	11th to 20th	Night	2 2 19% 53% 22% 2	859
	21st to end	Night	8% 5% 21% 42% 24% 1	950
December	1st to 10th	Night	7% 2 21% 52% 17% 1	950
	11th to 20th	Night	7% 4 24% 46% 18%	950
	21st to end	Night	7% 4 24% 51% 13% 1	942

Page generated at 2024-10-31 01:39:28. Version ac07

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