Angwin
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Angwin clear sky chart from 2005-11-06 to 2024-04-03.

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	9% 4 2 4 3 2 3 3 4 6% 60%	78975
	Night	11% 5% 2 4 4 2 3 3 4 6% 56%	81169
Transparency	Day	27% 3 9% 20% 24% 17%	78693
	Night	30% 3 10% 19% 22% 16%	80973
Seeing	Day	11% 9% 22% 30% 21% 7%	14467
	Night	11% 5% 14% 33% 31% 6%	23874

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	16% 9% 3 6% 6% 3 4 4 4 5% 40%	2649
	11th to 20th	Day	21% 8% 5% 8% 5% 2 4 4 4 6% 33%	2860
	21st to end	Day	22% 8% 3 7% 6% 2 4 4 5% 7% 33%	3146
February	1st to 10th	Day	15% 5% 2 5% 5% 4 5% 4 4 5% 46%	1710
	11th to 20th	Day	13% 6% 3 5% 4 3 4 4 4 8% 44%	1713
	21st to end	Day	16% 5% 2 5% 5% 2 3 4 3 6% 48%	1570
March	1st to 10th	Day	16% 8% 4 7% 6% 3 4 5% 5% 7% 36%	2058
	11th to 20th	Day	16% 7% 2 5% 5% 3 4 5% 5% 7% 41%	2090
	21st to end	Day	14% 6% 2 5% 5% 3 5% 5% 5% 6% 45%	2323
April	1st to 10th	Day	12% 7% 3 6% 5% 3 5% 5% 5% 7% 42%	2185
	11th to 20th	Day	8% 5% 2 4 3 3 4 5% 5% 7% 55%	2129
	21st to end	Day	4 3 2 3 4 3 4 4 5% 8% 60%	2160
May	1st to 10th	Day	5% 4 1 3 3 2 3 4 4 8% 63%	2286
	11th to 20th	Day	5% 2 1 3 3 2 4 4 4 8% 64%	2370
	21st to end	Day	4 2 1 4 3 2 3 4 6% 7% 63%	2723
June	1st to 10th	Day	5% 3 2 3 2 2 4 4 5% 8% 62%	2520
	11th to 20th	Day	1 1 1 2 2 2 2 3 4 6% 78%	2520
	21st to end	Day	2 1 2 2 1 2 2 3 4 82%	2520
July	1st to 10th	Day	1 1 1 2 1 2 2 3 4 83%	2520
	11th to 20th	Day	1 1 1 1 2 1 2 2 3 5% 84%	2390
	21st to end	Day	1 1 1 1 1 2 2 3 5% 84%	2546
August	1st to 10th	Day	1 1 1 1 2 1 2 3 3 6% 78%	2328
	11th to 20th	Day	1 1 1 1 2 3 2 6% 83%	2224
	21st to end	Day	1 1 1 1 1 2 2 3 5% 82%	2376
September	1st to 10th	Day	1 1 1 1 2 2 2 4 85%	2160
	11th to 20th	Day	3 1 1 3 2 2 2 3 3 7% 73%	2160
	21st to end	Day	2 1 1 2 2 1 2 3 3 5% 77%	1898
October	1st to 10th	Day	4 3 1 3 2 1 2 3 3 6% 72%	1800
	11th to 20th	Day	6% 3 1 3 3 2 3 3 3 5% 69%	1800
	21st to end	Day	8% 4 1 4 3 2 2 3 3 6% 65%	1980
November	1st to 10th	Day	10% 4 2 3 3 2 3 4 4 8% 57%	1812
	11th to 20th	Day	10% 4 3 5% 4 4 5% 3 5% 6% 52%	1687
	21st to end	Day	10% 4 2 4 5% 3 5% 4 5% 5% 54%	1520
December	1st to 10th	Day	15% 7% 3 4 5% 2 4 4 4 6% 47%	1520
	11th to 20th	Day	29% 9% 3 6% 4 2 2 4 4 4 32%	1928
	21st to end	Day	24% 7% 2 5% 5% 3 4 4 4 7% 36%	2794
January	1st to 10th	Night	15% 8% 3 4 4 3 3 4 4 7% 44%	4282
	11th to 20th	Night	22% 8% 3 6% 6% 3 4 4 5% 6% 33%	4110
	21st to end	Night	23% 9% 3 6% 5% 3 4 4 4 6% 34%	4521
February	1st to 10th	Night	16% 6% 2 4 4 2 4 3 4 6% 49%	2470
	11th to 20th	Night	11% 6% 2 5% 5% 3 5% 5% 4 7% 47%	2352
	21st to end	Night	12% 5% 2 3 5% 2 4 3 4 6% 54%	1884
March	1st to 10th	Night	16% 10% 3 5% 5% 4 4 5% 4 6% 40%	2119
	11th to 20th	Night	13% 7% 2 5% 5% 3 4 4 5% 7% 46%	2090
	21st to end	Night	13% 7% 2 6% 4 3 3 3 4 5% 49%	2275
April	1st to 10th	Night	9% 5% 3 6% 5% 2 5% 3 5% 7% 51%	1820
	11th to 20th	Night	8% 4 2 4 3 2 3 4 5% 8% 59%	1779
	21st to end	Night	4 3 1 2 3 2 3 4 5% 8% 64%	1800
May	1st to 10th	Night	5% 3 1 3 3 3 4 3 4 7% 64%	1670
	11th to 20th	Night	3 2 1 2 3 2 3 4 5% 8% 66%	1519
	21st to end	Night	4 1 1 2 2 2 3 4 5% 8% 67%	1552
June	1st to 10th	Night	4 2 2 3 3 2 3 3 4 7% 66%	1440
	11th to 20th	Night	1 1 2 2 1 2 2 4 6% 79%	1440
	21st to end	Night	1 2 1 2 2 1 1 2 3 3 81%	1440
July	1st to 10th	Night	1 1 1 1 2 1 2 3 87%	1440
	11th to 20th	Night	1 1 1 1 1 1 2 3 4 83%	1565
	21st to end	Night	1 1 1 2 1 2 3 4 7% 78%	1773
August	1st to 10th	Night	2 1 2 3 2 3 2 4 6% 77%	1611
	11th to 20th	Night	1 1 1 2 1 2 3 3 6% 80%	1674
	21st to end	Night	1 1 1 1 2 2 2 2 3 5% 80%	1980
September	1st to 10th	Night	1 1 1 1 2 3 5% 85%	1800
	11th to 20th	Night	3 2 1 3 3 2 2 2 3 6% 73%	1800
	21st to end	Night	1 1 1 3 2 2 2 3 5% 78%	2056
October	1st to 10th	Night	3 3 2 3 2 1 3 3 4 4 73%	2160
	11th to 20th	Night	4 2 1 3 3 2 3 4 4 6% 67%	2160
	21st to end	Night	8% 3 1 3 2 2 3 3 5% 6% 64%	2376
November	1st to 10th	Night	8% 5% 2 5% 3 2 3 3 4 7% 57%	2264
	11th to 20th	Night	9% 5% 2 4 4 2 4 4 5% 8% 53%	2489
	21st to end	Night	7% 5% 2 5% 4 3 4 3 4 6% 58%	2660
December	1st to 10th	Night	17% 6% 2 5% 5% 2 3 3 4 6% 47%	2660
	11th to 20th	Night	30% 7% 2 4 4 2 4 4 5% 6% 32%	3276
	21st to end	Night	22% 8% 3 5% 5% 3 3 4 4 6% 37%	4862

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	45% 5% 11% 27% 9% 3	2649
	11th to 20th	Day	54% 4 10% 15% 11% 8%	2860
	21st to end	Day	53% 3 10% 16% 13% 5%	3146
February	1st to 10th	Day	41% 4 7% 19% 20% 9%	1710
	11th to 20th	Day	40% 4 9% 18% 21% 7%	1722
	21st to end	Day	39% 2 10% 24% 18% 7%	1570
March	1st to 10th	Day	48% 4 11% 18% 16% 4	2058
	11th to 20th	Day	42% 4 9% 22% 15% 7%	2090
	21st to end	Day	40% 5% 13% 20% 18% 4	2323
April	1st to 10th	Day	41% 5% 11% 20% 18% 6%	2185
	11th to 20th	Day	30% 3 14% 22% 23% 7%	2132
	21st to end	Day	23% 4 16% 29% 22% 7%	2160
May	1st to 10th	Day	21% 4 10% 27% 30% 9%	2286
	11th to 20th	Day	20% 3 11% 33% 24% 10%	2373
	21st to end	Day	20% 4 18% 32% 21% 6%	2724
June	1st to 10th	Day	22% 3 12% 29% 26% 8%	2520
	11th to 20th	Day	9% 2 12% 22% 35% 20%	2520
	21st to end	Day	9% 1 4 17% 36% 32%	2520
July	1st to 10th	Day	8% 1 4 14% 29% 44%	2451
	11th to 20th	Day	7% 2 6% 13% 31% 41%	2318
	21st to end	Day	7% 1 3 12% 27% 49%	2405
August	1st to 10th	Day	10% 2 4 19% 34% 31%	2312
	11th to 20th	Day	6% 1 3 15% 40% 34%	2224
	21st to end	Day	7% 1 5% 17% 36% 35%	2376
September	1st to 10th	Day	6% 1 3 11% 32% 47%	2160
	11th to 20th	Day	14% 3 7% 25% 36% 15%	2160
	21st to end	Day	13% 2 5% 21% 31% 28%	1898
October	1st to 10th	Day	17% 2 7% 16% 32% 26%	1800
	11th to 20th	Day	21% 2 8% 20% 24% 25%	1800
	21st to end	Day	24% 2 8% 20% 27% 19%	1980
November	1st to 10th	Day	28% 4 7% 28% 21% 13%	1812
	11th to 20th	Day	33% 5% 10% 23% 20% 9%	1687
	21st to end	Day	32% 3 10% 19% 22% 14%	1520
December	1st to 10th	Day	41% 3 8% 19% 21% 9%	1520
	11th to 20th	Day	58% 3 6% 12% 17% 5%	1928
	21st to end	Day	48% 5% 12% 17% 13% 4	2794
January	1st to 10th	Night	39% 5% 18% 24% 10% 4	4282
	11th to 20th	Night	52% 5% 12% 12% 11% 8%	4110
	21st to end	Night	53% 3 11% 13% 14% 6%	4521
February	1st to 10th	Night	38% 3 8% 19% 20% 12%	2470
	11th to 20th	Night	38% 3 10% 20% 20% 10%	2354
	21st to end	Night	32% 5% 9% 26% 22% 7%	1884
March	1st to 10th	Night	47% 4 13% 14% 18% 4	2119
	11th to 20th	Night	39% 3 8% 23% 19% 8%	2090
	21st to end	Night	36% 6% 13% 22% 18% 6%	2275
April	1st to 10th	Night	35% 5% 13% 20% 21% 6%	1820
	11th to 20th	Night	26% 4 13% 28% 18% 11%	1779
	21st to end	Night	20% 3 14% 32% 25% 7%	1800
May	1st to 10th	Night	20% 3 9% 24% 31% 12%	1670
	11th to 20th	Night	17% 3 14% 29% 27% 11%	1519
	21st to end	Night	15% 5% 17% 33% 23% 7%	1552
June	1st to 10th	Night	19% 4 11% 25% 32% 9%	1440
	11th to 20th	Night	9% 3 7% 25% 34% 22%	1440
	21st to end	Night	11% 1 3 17% 34% 33%	1440
July	1st to 10th	Night	7% 1 2 15% 31% 46%	1400
	11th to 20th	Night	7% 1 5% 15% 27% 46%	1515
	21st to end	Night	9% 2 4 14% 23% 48%	1674
August	1st to 10th	Night	12% 1 4 18% 31% 35%	1602
	11th to 20th	Night	8% 2 5% 14% 31% 40%	1674
	21st to end	Night	9% 1 5% 17% 32% 37%	1980
September	1st to 10th	Night	5% 2 3 11% 32% 47%	1800
	11th to 20th	Night	16% 1 6% 19% 39% 18%	1800
	21st to end	Night	11% 1 5% 22% 28% 33%	2056
October	1st to 10th	Night	17% 2 7% 18% 28% 28%	2160
	11th to 20th	Night	18% 2 9% 20% 24% 27%	2160
	21st to end	Night	22% 2 8% 20% 24% 24%	2376
November	1st to 10th	Night	28% 4 9% 25% 19% 14%	2264
	11th to 20th	Night	30% 3 12% 25% 19% 10%	2489
	21st to end	Night	29% 3 8% 21% 24% 14%	2660
December	1st to 10th	Night	39% 4 9% 17% 19% 12%	2660
	11th to 20th	Night	54% 4 8% 13% 16% 4	3276
	21st to end	Night	50% 5% 11% 17% 14% 4	4862

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	33% 9% 23% 21% 11% 3	251
	11th to 20th	Day	22% 11% 23% 29% 12% 4	370
	21st to end	Day	17% 13% 22% 27% 17% 5%	407
February	1st to 10th	Day	22% 12% 24% 22% 16% 4	370
	11th to 20th	Day	23% 16% 26% 21% 13% 2	388
	21st to end	Day	19% 13% 28% 27% 10% 3	382
March	1st to 10th	Day	25% 16% 26% 20% 12% 1	460
	11th to 20th	Day	24% 12% 25% 21% 15% 3	460
	21st to end	Day	20% 16% 29% 24% 9% 1	506
April	1st to 10th	Day	17% 17% 25% 25% 12% 4	429
	11th to 20th	Day	16% 17% 29% 19% 13% 5%	412
	21st to end	Day	8% 15% 27% 28% 16% 6%	420
May	1st to 10th	Day	11% 14% 30% 27% 14% 3	423
	11th to 20th	Day	9% 12% 28% 27% 18% 6%	448
	21st to end	Day	7% 10% 24% 33% 20% 7%	485
June	1st to 10th	Day	8% 10% 23% 34% 17% 7%	450
	11th to 20th	Day	4 10% 27% 38% 18% 4	450
	21st to end	Day	1 4 23% 38% 26% 8%	450
July	1st to 10th	Day	1 2 18% 44% 29% 6%	446
	11th to 20th	Day	1 1 15% 39% 34% 10%	444
	21st to end	Day	1 1 13% 41% 33% 11%	487
August	1st to 10th	Day	2 2 17% 39% 30% 10%	447
	11th to 20th	Day	1 2 18% 36% 28% 14%	437
	21st to end	Day	1 1 14% 38% 35% 11%	495
September	1st to 10th	Day	2 14% 38% 34% 12%	450
	11th to 20th	Day	4 4 18% 33% 30% 10%	450
	21st to end	Day	3 6% 22% 35% 25% 9%	450
October	1st to 10th	Day	5% 10% 23% 27% 24% 11%	450
	11th to 20th	Day	7% 8% 20% 27% 28% 11%	450
	21st to end	Day	12% 6% 20% 30% 24% 7%	495
November	1st to 10th	Day	14% 7% 18% 22% 30% 8%	408
	11th to 20th	Day	9% 7% 19% 26% 27% 11%	259
	21st to end	Day	13% 9% 21% 32% 18% 7%	180
December	1st to 10th	Day	24% 13% 18% 21% 14% 11%	180
	11th to 20th	Day	24% 12% 21% 21% 16% 6%	180
	21st to end	Day	21% 10% 24% 24% 15% 6%	198
January	1st to 10th	Night	21% 4 16% 31% 23% 5%	760
	11th to 20th	Night	20% 6% 15% 36% 18% 5%	760
	21st to end	Night	19% 6% 15% 31% 24% 4	836
February	1st to 10th	Night	19% 7% 14% 36% 20% 3	760
	11th to 20th	Night	15% 10% 16% 33% 22% 4	744
	21st to end	Night	15% 9% 21% 32% 20% 3	628
March	1st to 10th	Night	20% 8% 19% 29% 20% 4	760
	11th to 20th	Night	18% 7% 17% 30% 25% 3	760
	21st to end	Night	17% 9% 24% 31% 18% 2	836
April	1st to 10th	Night	12% 8% 21% 36% 20% 3	728
	11th to 20th	Night	11% 11% 20% 30% 23% 5%	711
	21st to end	Night	6% 10% 21% 32% 25% 6%	720
May	1st to 10th	Night	6% 7% 23% 30% 29% 5%	590
	11th to 20th	Night	4 4 17% 32% 37% 6%	457
	21st to end	Night	5% 6% 16% 34% 35% 4	389
June	1st to 10th	Night	6% 6% 16% 35% 34% 3	360
	11th to 20th	Night	2 4 15% 43% 36% 1	360
	21st to end	Night	1 1 13% 42% 39% 3	360
July	1st to 10th	Night	1 8% 35% 52% 4	350
	11th to 20th	Night	1 4 31% 55% 9%	471
	21st to end	Night	1 3 32% 54% 9%	591
August	1st to 10th	Night	2 1 6% 30% 52% 9%	537
	11th to 20th	Night	1 6% 36% 47% 10%	606
	21st to end	Night	1 1 5% 33% 53% 8%	792
September	1st to 10th	Night	1 2 7% 33% 50% 8%	720
	11th to 20th	Night	4 2 7% 35% 44% 8%	720
	21st to end	Night	2 3 11% 36% 37% 11%	720
October	1st to 10th	Night	4 5% 13% 32% 36% 9%	720
	11th to 20th	Night	5% 4 11% 35% 37% 7%	720
	21st to end	Night	9% 3 14% 30% 33% 11%	792
November	1st to 10th	Night	9% 4 16% 30% 31% 9%	740
	11th to 20th	Night	11% 4 14% 36% 30% 5%	760
	21st to end	Night	11% 7% 14% 37% 25% 6%	760
December	1st to 10th	Night	19% 5% 14% 34% 22% 5%	760
	11th to 20th	Night	24% 5% 14% 31% 22% 3	760
	21st to end	Night	22% 7% 17% 34% 19% 2	836

Page generated at 2024-03-31 03:08:53. Version ac07

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