Twin Sugars Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Twin Sugars Observatory clear sky chart from 2005-11-06 to 2024-05-13.

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	15% 8% 3 8% 5% 5% 5% 4 6% 7% 34%	83626
	Night	14% 7% 3 7% 5% 5% 5% 4 6% 7% 37%	85868
Transparency	Day	47% 10% 11% 18% 12% 2	83348
	Night	45% 10% 12% 18% 12% 2	85665
Seeing	Day	24% 16% 25% 20% 11% 5%	14341
	Night	21% 15% 22% 26% 14% 2	24689

By Month

Percentage Cloud Cover SE (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	15% 13% 4 9% 6% 5% 4 4 5% 7% 30%	2836
	11th to 20th	Day	13% 12% 7% 16% 6% 5% 4 3 4 4 26%	2840
	21st to end	Day	19% 13% 5% 7% 4 3 4 3 5% 5% 31%	3124
February	1st to 10th	Day	13% 9% 3 9% 5% 5% 5% 3 6% 7% 33%	1710
	11th to 20th	Day	16% 8% 3 10% 6% 5% 5% 3 5% 7% 31%	1717
	21st to end	Day	19% 11% 3 9% 4 4 4 3 5% 5% 32%	1611
March	1st to 10th	Day	22% 8% 4 7% 4 4 4 4 6% 7% 31%	3435
	11th to 20th	Day	11% 7% 3 7% 4 4 4 3 5% 7% 45%	3480
	21st to end	Day	15% 10% 3 8% 5% 4 5% 4 5% 7% 34%	3815
April	1st to 10th	Day	11% 8% 4 8% 5% 5% 5% 4 4 7% 39%	2146
	11th to 20th	Day	15% 6% 3 7% 5% 6% 4 4 5% 6% 40%	2254
	21st to end	Day	18% 7% 3 7% 5% 5% 4 4 6% 5% 36%	2465
May	1st to 10th	Day	16% 9% 2 8% 6% 5% 6% 5% 6% 7% 31%	2470
	11th to 20th	Day	20% 8% 3 7% 5% 5% 5% 4 6% 8% 29%	2329
	21st to end	Day	13% 6% 2 8% 7% 6% 6% 6% 6% 9% 32%	2531
June	1st to 10th	Day	14% 6% 2 6% 6% 6% 6% 4 6% 8% 36%	2340
	11th to 20th	Day	11% 6% 3 8% 6% 7% 7% 4 7% 9% 33%	2340
	21st to end	Day	10% 6% 3 7% 7% 6% 6% 5% 7% 9% 35%	2340
July	1st to 10th	Day	12% 7% 3 7% 7% 5% 6% 5% 7% 9% 32%	2340
	11th to 20th	Day	8% 5% 2 7% 7% 5% 7% 6% 8% 10% 35%	2340
	21st to end	Day	11% 7% 3 8% 7% 6% 6% 5% 8% 9% 29%	2547
August	1st to 10th	Day	15% 7% 3 7% 6% 7% 6% 5% 7% 11% 27%	2327
	11th to 20th	Day	14% 6% 3 7% 7% 6% 7% 5% 8% 9% 28%	2303
	21st to end	Day	11% 6% 2 8% 5% 6% 6% 5% 7% 10% 33%	2435
September	1st to 10th	Day	15% 6% 2 6% 4 4 5% 5% 5% 8% 40%	2102
	11th to 20th	Day	14% 7% 2 7% 5% 5% 5% 4 5% 7% 39%	1980
	21st to end	Day	23% 7% 2 6% 4 4 5% 4 5% 6% 34%	1980
October	1st to 10th	Day	17% 7% 2 6% 5% 4 4 3 5% 7% 42%	1828
	11th to 20th	Day	16% 9% 2 6% 3 4 4 3 4 7% 43%	1800
	21st to end	Day	16% 9% 2 6% 4 3 4 3 5% 6% 41%	1980
November	1st to 10th	Day	10% 8% 2 5% 5% 4 3 4 4 7% 47%	1838
	11th to 20th	Day	14% 8% 2 7% 6% 4 4 4 4 7% 40%	1710
	21st to end	Day	14% 7% 2 6% 6% 4 4 4 6% 6% 40%	1645
December	1st to 10th	Day	17% 13% 5% 8% 5% 5% 4 4 6% 6% 27%	1520
	11th to 20th	Day	16% 9% 3 8% 5% 4 4 3 5% 6% 37%	2044
	21st to end	Day	18% 13% 4 8% 6% 5% 5% 5% 6% 7% 23%	3124
January	1st to 10th	Night	11% 10% 5% 13% 6% 6% 6% 5% 6% 7% 25%	4109
	11th to 20th	Night	15% 11% 4 10% 6% 4 4 3 4 5% 34%	4120
	21st to end	Night	21% 11% 4 6% 5% 6% 4 3 5% 6% 30%	4532
February	1st to 10th	Night	13% 7% 4 9% 6% 5% 5% 5% 6% 8% 33%	2470
	11th to 20th	Night	17% 8% 3 8% 6% 6% 6% 5% 6% 5% 30%	2346
	21st to end	Night	17% 8% 4 9% 5% 5% 5% 4 5% 7% 31%	1841
March	1st to 10th	Night	23% 10% 3 7% 5% 5% 4 4 5% 5% 29%	3418
	11th to 20th	Night	10% 6% 2 8% 5% 5% 5% 4 6% 7% 42%	3480
	21st to end	Night	15% 7% 2 5% 4 3 4 4 7% 7% 41%	3817
April	1st to 10th	Night	12% 8% 4 8% 5% 5% 5% 4 6% 7% 37%	2033
	11th to 20th	Night	12% 7% 2 5% 5% 5% 5% 4 7% 8% 40%	1875
	21st to end	Night	15% 5% 2 5% 4 5% 5% 4 5% 8% 41%	1729
May	1st to 10th	Night	14% 10% 3 6% 5% 4 5% 4 5% 8% 36%	1710
	11th to 20th	Night	17% 9% 3 8% 5% 4 4 4 6% 8% 34%	1619
	21st to end	Night	15% 6% 2 6% 5% 4 5% 4 5% 10% 39%	1744
June	1st to 10th	Night	10% 5% 2 5% 5% 4 4 5% 7% 10% 43%	1620
	11th to 20th	Night	12% 5% 2 5% 4 3 5% 5% 7% 9% 43%	1620
	21st to end	Night	10% 5% 1 4 5% 4 5% 5% 7% 11% 43%	1620
July	1st to 10th	Night	10% 5% 2 6% 6% 4 5% 4 7% 9% 41%	1620
	11th to 20th	Night	7% 4 1 5% 5% 3 4 5% 6% 11% 48%	1620
	21st to end	Night	7% 5% 2 5% 6% 6% 5% 5% 7% 11% 41%	1771
August	1st to 10th	Night	13% 6% 2 6% 5% 6% 6% 4 6% 9% 38%	1611
	11th to 20th	Night	14% 6% 2 6% 4 5% 5% 3 7% 8% 41%	1598
	21st to end	Night	10% 5% 2 6% 4 4 4 4 6% 9% 45%	1903
September	1st to 10th	Night	13% 4 2 6% 4 4 5% 4 6% 8% 45%	1854
	11th to 20th	Night	13% 6% 2 4 4 4 4 4 5% 7% 48%	1980
	21st to end	Night	18% 6% 3 7% 4 4 4 4 5% 6% 40%	1980
October	1st to 10th	Night	14% 8% 2 6% 3 4 4 4 5% 6% 45%	2131
	11th to 20th	Night	13% 7% 3 7% 4 4 4 3 4 6% 44%	2160
	21st to end	Night	15% 7% 2 6% 4 4 4 4 5% 6% 42%	2376
November	1st to 10th	Night	12% 7% 2 6% 4 4 3 4 6% 7% 46%	2235
	11th to 20th	Night	14% 6% 2 7% 4 4 5% 4 6% 7% 40%	2470
	21st to end	Night	13% 7% 3 6% 5% 5% 5% 4 5% 8% 38%	2527
December	1st to 10th	Night	17% 9% 4 10% 6% 5% 5% 4 5% 7% 28%	2660
	11th to 20th	Night	14% 8% 3 10% 6% 5% 5% 4 4 7% 34%	3137
	21st to end	Night	18% 8% 6% 9% 5% 6% 6% 4 6% 7% 26%	4532

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	55% 8% 8% 19% 10% 1	2837
	11th to 20th	Day	62% 10% 6% 12% 9% 1	2840
	21st to end	Day	55% 9% 9% 14% 12% 1	3124
February	1st to 10th	Day	50% 8% 10% 19% 11% 2	1710
	11th to 20th	Day	53% 8% 10% 16% 12% 2	1726
	21st to end	Day	54% 8% 8% 15% 12% 3	1611
March	1st to 10th	Day	49% 11% 11% 19% 8% 1	3435
	11th to 20th	Day	38% 9% 12% 19% 19% 2	3480
	21st to end	Day	49% 10% 9% 18% 12% 3	3815
April	1st to 10th	Day	44% 10% 11% 18% 14% 4	2146
	11th to 20th	Day	44% 8% 10% 20% 15% 3	2254
	21st to end	Day	47% 10% 12% 19% 10% 2	2465
May	1st to 10th	Day	50% 11% 11% 17% 9% 1	2470
	11th to 20th	Day	52% 11% 13% 17% 5% 2	2333
	21st to end	Day	48% 12% 16% 17% 8%	2531
June	1st to 10th	Day	43% 10% 13% 20% 12%	2340
	11th to 20th	Day	44% 12% 14% 16% 13% 1	2340
	21st to end	Day	42% 13% 13% 20% 11% 1	2340
July	1st to 10th	Day	45% 13% 13% 16% 11% 2	2275
	11th to 20th	Day	39% 15% 14% 18% 13% 1	2271
	21st to end	Day	46% 13% 13% 19% 9% 1	2405
August	1st to 10th	Day	48% 13% 17% 16% 7%	2314
	11th to 20th	Day	49% 13% 13% 18% 7%	2303
	21st to end	Day	42% 14% 15% 17% 9% 2	2435
September	1st to 10th	Day	40% 10% 12% 19% 15% 3	2102
	11th to 20th	Day	44% 8% 10% 20% 17% 2	1980
	21st to end	Day	49% 8% 11% 16% 15% 2	1980
October	1st to 10th	Day	40% 8% 13% 20% 15% 4	1828
	11th to 20th	Day	43% 7% 11% 21% 17% 2	1800
	21st to end	Day	44% 7% 9% 23% 14% 4	1980
November	1st to 10th	Day	37% 7% 10% 21% 21% 4	1838
	11th to 20th	Day	44% 8% 9% 18% 18% 4	1710
	21st to end	Day	43% 9% 12% 19% 15% 2	1645
December	1st to 10th	Day	57% 9% 9% 15% 9% 1	1520
	11th to 20th	Day	49% 7% 10% 17% 16% 2	2041
	21st to end	Day	55% 11% 11% 16% 8%	3124
January	1st to 10th	Night	56% 13% 8% 11% 10% 1	4109
	11th to 20th	Night	53% 8% 8% 17% 12% 2	4120
	21st to end	Night	56% 9% 9% 15% 10% 1	4532
February	1st to 10th	Night	48% 10% 12% 16% 13% 1	2470
	11th to 20th	Night	54% 9% 9% 14% 11% 2	2348
	21st to end	Night	52% 9% 11% 16% 8% 4	1841
March	1st to 10th	Night	54% 8% 11% 16% 9% 2	3418
	11th to 20th	Night	41% 9% 10% 23% 15% 1	3480
	21st to end	Night	40% 10% 12% 19% 16% 3	3817
April	1st to 10th	Night	45% 10% 11% 18% 14% 2	2033
	11th to 20th	Night	41% 9% 13% 18% 15% 4	1875
	21st to end	Night	40% 9% 15% 24% 10% 1	1729
May	1st to 10th	Night	47% 10% 14% 16% 11% 1	1710
	11th to 20th	Night	47% 12% 15% 18% 7% 1	1620
	21st to end	Night	41% 12% 18% 22% 6% 1	1745
June	1st to 10th	Night	35% 12% 18% 23% 12%	1620
	11th to 20th	Night	35% 13% 19% 19% 12% 1	1620
	21st to end	Night	33% 14% 17% 25% 11% 1	1620
July	1st to 10th	Night	38% 14% 14% 17% 13% 3	1575
	11th to 20th	Night	30% 13% 19% 23% 13% 2	1566
	21st to end	Night	34% 13% 16% 25% 12%	1672
August	1st to 10th	Night	42% 12% 17% 21% 8%	1600
	11th to 20th	Night	39% 11% 16% 22% 11% 1	1598
	21st to end	Night	34% 11% 18% 25% 11% 2	1903
September	1st to 10th	Night	36% 12% 14% 20% 15% 3	1854
	11th to 20th	Night	35% 9% 13% 23% 18% 2	1980
	21st to end	Night	44% 8% 12% 22% 13% 1	1980
October	1st to 10th	Night	37% 10% 12% 22% 16% 3	2131
	11th to 20th	Night	41% 8% 11% 22% 17% 2	2160
	21st to end	Night	42% 7% 10% 22% 15% 4	2376
November	1st to 10th	Night	38% 8% 12% 19% 20% 5%	2235
	11th to 20th	Night	43% 8% 11% 17% 17% 4	2470
	21st to end	Night	44% 8% 11% 18% 15% 3	2527
December	1st to 10th	Night	55% 10% 9% 16% 8% 2	2660
	11th to 20th	Night	52% 8% 10% 15% 14% 1	3139
	21st to end	Night	55% 12% 10% 14% 9%	4532

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	36% 29% 23% 9% 3 1	270
	11th to 20th	Day	44% 24% 26% 6%	270
	21st to end	Day	40% 24% 24% 8% 3	297
February	1st to 10th	Day	36% 25% 26% 11% 2	270
	11th to 20th	Day	49% 24% 21% 5% 1	270
	21st to end	Day	44% 23% 25% 7% 1	266
March	1st to 10th	Day	33% 26% 22% 15% 4	460
	11th to 20th	Day	34% 27% 22% 12% 5% 1	460
	21st to end	Day	29% 27% 25% 15% 4	506
April	1st to 10th	Day	28% 27% 25% 13% 7% 1	460
	11th to 20th	Day	25% 19% 30% 14% 8% 3	452
	21st to end	Day	30% 21% 24% 14% 9% 2	460
May	1st to 10th	Day	26% 21% 28% 13% 9% 3	463
	11th to 20th	Day	21% 16% 31% 17% 11% 4	456
	21st to end	Day	18% 11% 25% 24% 14% 8%	485
June	1st to 10th	Day	15% 12% 27% 25% 13% 8%	450
	11th to 20th	Day	12% 12% 30% 25% 13% 8%	450
	21st to end	Day	11% 11% 33% 26% 13% 6%	450
July	1st to 10th	Day	15% 7% 22% 26% 18% 13%	445
	11th to 20th	Day	5% 7% 26% 34% 17% 11%	444
	21st to end	Day	11% 8% 26% 28% 17% 10%	488
August	1st to 10th	Day	18% 7% 20% 26% 18% 11%	446
	11th to 20th	Day	13% 8% 19% 27% 22% 12%	439
	21st to end	Day	11% 6% 23% 26% 22% 13%	495
September	1st to 10th	Day	16% 6% 21% 25% 20% 12%	450
	11th to 20th	Day	15% 5% 17% 30% 26% 7%	450
	21st to end	Day	24% 12% 21% 25% 13% 4	450
October	1st to 10th	Day	21% 10% 23% 24% 18% 4	450
	11th to 20th	Day	22% 15% 26% 23% 12% 1	450
	21st to end	Day	27% 18% 24% 19% 10% 2	495
November	1st to 10th	Day	19% 18% 26% 24% 9% 3	436
	11th to 20th	Day	34% 16% 26% 19% 4	270
	21st to end	Day	26% 23% 30% 16% 4	239
December	1st to 10th	Day	39% 24% 20% 11% 4 1	180
	11th to 20th	Day	36% 24% 20% 18% 2	222
	21st to end	Day	35% 24% 23% 14% 4	297
January	1st to 10th	Night	32% 26% 24% 16% 3	760
	11th to 20th	Night	32% 22% 26% 17% 2	760
	21st to end	Night	31% 23% 26% 18% 1	836
February	1st to 10th	Night	25% 22% 29% 20% 3	760
	11th to 20th	Night	34% 27% 25% 14% 1	743
	21st to end	Night	28% 27% 28% 16% 1	628
March	1st to 10th	Night	26% 20% 30% 21% 3	760
	11th to 20th	Night	28% 22% 25% 18% 6%	760
	21st to end	Night	23% 23% 29% 20% 6%	836
April	1st to 10th	Night	21% 23% 28% 23% 4	760
	11th to 20th	Night	21% 15% 26% 25% 12%	751
	21st to end	Night	18% 16% 26% 31% 8% 1	589
May	1st to 10th	Night	20% 15% 23% 28% 12% 1	570
	11th to 20th	Night	19% 12% 24% 29% 15%	540
	21st to end	Night	15% 6% 17% 32% 26% 4	584
June	1st to 10th	Night	11% 6% 19% 35% 26% 3	540
	11th to 20th	Night	12% 6% 17% 34% 28% 2	540
	21st to end	Night	11% 4 17% 40% 24% 3	540
July	1st to 10th	Night	13% 3 13% 34% 32% 6%	525
	11th to 20th	Night	8% 3 11% 34% 38% 7%	522
	21st to end	Night	8% 5% 12% 35% 37% 4	591
August	1st to 10th	Night	16% 3 11% 34% 34% 3	537
	11th to 20th	Night	15% 3 12% 32% 35% 4	534
	21st to end	Night	13% 4 11% 34% 32% 6%	715
September	1st to 10th	Night	15% 4 13% 34% 29% 6%	720
	11th to 20th	Night	14% 6% 13% 32% 30% 4	720
	21st to end	Night	22% 9% 17% 27% 24% 2	720
October	1st to 10th	Night	15% 11% 19% 31% 22% 2	720
	11th to 20th	Night	19% 17% 22% 25% 16% 1	720
	21st to end	Night	21% 16% 23% 27% 12% 1	792
November	1st to 10th	Night	18% 12% 26% 30% 12% 2	740
	11th to 20th	Night	25% 16% 22% 28% 9% 1	760
	21st to end	Night	22% 20% 24% 28% 6% 1	760
December	1st to 10th	Night	29% 23% 24% 19% 5%	760
	11th to 20th	Night	23% 24% 25% 24% 4	760
	21st to end	Night	29% 17% 27% 23% 4	836

Page generated at 2024-05-10 12:38:57. Version ac07

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