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 2024-01-16.

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% 7% 3 7% 6% 4 5% 5% 6% 8% 34%	74590
	Night	14% 7% 3 6% 6% 3 5% 5% 6% 8% 38%	75192
Transparency	Day	47% 10% 12% 18% 12% 2	74312
	Night	45% 10% 12% 19% 12% 2	74989
Seeing	Day	23% 16% 25% 20% 11% 5%	13910
	Night	21% 15% 22% 26% 15% 2	24236

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	13% 8% 6% 9% 9% 5% 5% 4 5% 6% 30%	1706
	11th to 20th	Day	17% 11% 6% 10% 7% 3 5% 4 4 5% 28%	1665
	21st to end	Day	15% 11% 6% 8% 6% 3 4 4 5% 5% 34%	1782
February	1st to 10th	Day	14% 9% 4 8% 7% 4 6% 5% 5% 8% 31%	1620
	11th to 20th	Day	16% 8% 3 10% 7% 4 5% 5% 5% 7% 31%	1624
	21st to end	Day	19% 10% 4 8% 6% 3 5% 4 5% 6% 31%	1518
March	1st to 10th	Day	14% 6% 3 7% 5% 3 3 4 6% 7% 41%	1980
	11th to 20th	Day	17% 9% 5% 7% 6% 3 4 5% 5% 7% 33%	1980
	21st to end	Day	18% 8% 4 8% 6% 4 4 4 5% 7% 33%	2178
April	1st to 10th	Day	11% 7% 5% 6% 6% 4 5% 4 4 7% 40%	2033
	11th to 20th	Day	15% 5% 4 6% 6% 4 5% 5% 5% 6% 40%	2134
	21st to end	Day	19% 7% 3 6% 6% 3 5% 5% 6% 6% 35%	2335
May	1st to 10th	Day	16% 8% 3 7% 7% 4 5% 6% 5% 7% 32%	2340
	11th to 20th	Day	20% 7% 4 7% 6% 4 5% 5% 6% 8% 29%	2301
	21st to end	Day	13% 5% 3 6% 8% 4 7% 6% 6% 9% 32%	2531
June	1st to 10th	Day	14% 5% 3 6% 6% 4 6% 6% 6% 8% 37%	2340
	11th to 20th	Day	11% 5% 3 7% 6% 5% 8% 6% 7% 10% 34%	2340
	21st to end	Day	10% 5% 3 6% 7% 5% 7% 6% 7% 9% 35%	2340
July	1st to 10th	Day	12% 7% 3 6% 7% 4 6% 7% 7% 9% 33%	2340
	11th to 20th	Day	8% 4 3 6% 7% 4 7% 8% 8% 10% 35%	2340
	21st to end	Day	12% 6% 3 7% 8% 4 6% 7% 8% 9% 29%	2547
August	1st to 10th	Day	15% 6% 3 7% 6% 5% 6% 7% 7% 11% 27%	2327
	11th to 20th	Day	15% 6% 3 6% 8% 4 7% 6% 8% 9% 28%	2303
	21st to end	Day	11% 6% 2 6% 7% 4 7% 7% 7% 10% 33%	2435
September	1st to 10th	Day	15% 6% 2 4 5% 3 5% 6% 5% 8% 40%	2102
	11th to 20th	Day	14% 6% 2 6% 7% 4 5% 5% 5% 7% 40%	1980
	21st to end	Day	23% 6% 3 5% 5% 3 4 5% 5% 6% 34%	1980
October	1st to 10th	Day	17% 6% 2 5% 5% 3 4 4 6% 7% 42%	1828
	11th to 20th	Day	16% 9% 2 5% 4 2 4 4 4 7% 43%	1800
	21st to end	Day	16% 8% 3 5% 4 3 4 4 5% 6% 41%	1980
November	1st to 10th	Day	10% 7% 2 5% 5% 2 4 5% 4 8% 47%	1838
	11th to 20th	Day	14% 7% 3 6% 6% 4 4 5% 4 7% 41%	1710
	21st to end	Day	14% 7% 3 5% 6% 3 4 5% 5% 7% 40%	1645
December	1st to 10th	Day	17% 13% 5% 7% 6% 4 4 5% 6% 7% 27%	1520
	11th to 20th	Day	16% 9% 3 7% 5% 3 4 4 5% 6% 37%	2044
	21st to end	Day	18% 13% 4 7% 7% 4 5% 6% 6% 7% 23%	3124
January	1st to 10th	Night	13% 7% 3 8% 8% 5% 7% 5% 6% 7% 29%	2459
	11th to 20th	Night	17% 9% 5% 9% 6% 3 5% 5% 5% 7% 27%	2406
	21st to end	Night	14% 8% 6% 7% 7% 4 6% 4 5% 6% 33%	2574
February	1st to 10th	Night	13% 6% 4 8% 6% 4 5% 6% 6% 8% 32%	2340
	11th to 20th	Night	17% 7% 4 7% 7% 4 6% 6% 6% 5% 29%	2219
	21st to end	Night	17% 8% 5% 8% 6% 3 5% 5% 5% 7% 31%	1736
March	1st to 10th	Night	13% 6% 3 6% 7% 4 4 6% 5% 5% 41%	1980
	11th to 20th	Night	17% 7% 3 6% 7% 4 5% 6% 5% 7% 33%	1980
	21st to end	Night	15% 7% 3 6% 6% 3 5% 6% 7% 7% 34%	2178
April	1st to 10th	Night	13% 7% 3 7% 6% 4 5% 4 5% 7% 38%	1926
	11th to 20th	Night	12% 7% 3 5% 5% 4 5% 5% 7% 8% 40%	1775
	21st to end	Night	16% 5% 3 5% 5% 3 6% 4 6% 8% 41%	1638
May	1st to 10th	Night	13% 9% 3 6% 5% 3 5% 5% 5% 8% 37%	1620
	11th to 20th	Night	17% 8% 3 7% 6% 3 4 5% 5% 8% 34%	1592
	21st to end	Night	15% 5% 2 5% 6% 3 5% 5% 5% 10% 39%	1744
June	1st to 10th	Night	10% 5% 2 4 5% 3 5% 6% 7% 10% 43%	1620
	11th to 20th	Night	12% 5% 2 4 5% 2 4 6% 7% 9% 43%	1620
	21st to end	Night	10% 4 2 3 5% 3 5% 6% 7% 11% 43%	1620
July	1st to 10th	Night	10% 5% 3 5% 6% 3 5% 5% 6% 9% 42%	1620
	11th to 20th	Night	7% 4 2 4 6% 2 5% 6% 6% 11% 48%	1620
	21st to end	Night	7% 5% 2 5% 6% 4 5% 6% 7% 11% 42%	1771
August	1st to 10th	Night	13% 6% 2 5% 6% 5% 6% 5% 6% 9% 38%	1611
	11th to 20th	Night	14% 6% 2 5% 5% 3 5% 5% 6% 8% 41%	1598
	21st to end	Night	10% 5% 2 5% 5% 3 4 6% 6% 9% 45%	1903
September	1st to 10th	Night	13% 4 1 5% 5% 3 5% 5% 6% 8% 45%	1854
	11th to 20th	Night	13% 6% 2 3 4 3 3 5% 5% 7% 48%	1980
	21st to end	Night	18% 6% 3 6% 5% 3 4 4 5% 6% 40%	1980
October	1st to 10th	Night	14% 7% 2 5% 4 3 4 4 5% 6% 46%	2131
	11th to 20th	Night	13% 7% 3 6% 5% 3 4 5% 4 6% 44%	2160
	21st to end	Night	15% 7% 2 5% 5% 3 5% 4 5% 7% 43%	2376
November	1st to 10th	Night	12% 7% 3 5% 4 2 4 4 6% 7% 46%	2235
	11th to 20th	Night	14% 5% 3 6% 5% 3 5% 6% 6% 8% 40%	2470
	21st to end	Night	13% 6% 3 5% 5% 4 5% 5% 5% 8% 39%	2527
December	1st to 10th	Night	18% 9% 4 8% 7% 3 6% 5% 5% 7% 28%	2660
	11th to 20th	Night	14% 7% 3 9% 6% 4 5% 5% 4 7% 34%	3137
	21st to end	Night	18% 7% 6% 8% 6% 4 6% 5% 6% 7% 27%	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	56% 8% 9% 16% 10% 1	1707
	11th to 20th	Day	59% 10% 8% 13% 9% 1	1665
	21st to end	Day	53% 8% 10% 15% 13% 2	1782
February	1st to 10th	Day	52% 8% 10% 20% 9% 2	1620
	11th to 20th	Day	54% 7% 10% 17% 11% 1	1633
	21st to end	Day	55% 8% 8% 15% 12% 3	1518
March	1st to 10th	Day	42% 8% 11% 23% 13% 2	1980
	11th to 20th	Day	51% 9% 11% 15% 11% 3	1980
	21st to end	Day	52% 9% 8% 18% 10% 3	2178
April	1st to 10th	Day	43% 9% 11% 18% 14% 4	2033
	11th to 20th	Day	44% 8% 10% 20% 16% 3	2134
	21st to end	Day	48% 10% 12% 19% 10% 2	2335
May	1st to 10th	Day	50% 11% 11% 17% 10% 1	2340
	11th to 20th	Day	53% 11% 12% 16% 5% 2	2305
	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	53% 11% 9% 15% 10% 2	2459
	11th to 20th	Night	56% 10% 10% 12% 10% 2	2406
	21st to end	Night	53% 9% 11% 16% 10% 2	2574
February	1st to 10th	Night	49% 11% 13% 16% 10% 1	2340
	11th to 20th	Night	55% 9% 9% 14% 11% 2	2221
	21st to end	Night	53% 9% 10% 16% 8% 4	1736
March	1st to 10th	Night	45% 8% 10% 20% 15% 3	1980
	11th to 20th	Night	49% 10% 11% 19% 10% 1	1980
	21st to end	Night	47% 11% 11% 15% 13% 3	2178
April	1st to 10th	Night	44% 10% 11% 18% 14% 2	1926
	11th to 20th	Night	41% 9% 13% 18% 15% 4	1775
	21st to end	Night	41% 9% 15% 23% 10% 1	1638
May	1st to 10th	Night	46% 10% 14% 16% 12% 1	1620
	11th to 20th	Night	48% 12% 15% 17% 7% 1	1593
	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	42% 24% 27% 6%	255
	21st to end	Day	42% 24% 23% 8% 3	264
February	1st to 10th	Day	38% 26% 26% 8% 1	240
	11th to 20th	Day	49% 25% 21% 5%	240
	21st to end	Day	44% 23% 24% 7% 1	236
March	1st to 10th	Day	32% 27% 23% 15% 3	420
	11th to 20th	Day	34% 26% 22% 12% 5% 1	420
	21st to end	Day	29% 26% 25% 16% 4	462
April	1st to 10th	Day	27% 26% 25% 14% 7% 1	420
	11th to 20th	Day	25% 18% 29% 16% 9% 3	412
	21st to end	Day	31% 21% 24% 14% 9% 2	420
May	1st to 10th	Day	26% 21% 29% 12% 9% 3	423
	11th to 20th	Day	21% 16% 31% 17% 11% 4	447
	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	31% 22% 26% 18% 2	741
	21st to end	Night	31% 24% 26% 18% 1	792
February	1st to 10th	Night	26% 23% 29% 19% 3	720
	11th to 20th	Night	33% 27% 25% 14% 1	703
	21st to end	Night	28% 28% 28% 16% 1	592
March	1st to 10th	Night	25% 20% 31% 21% 3	720
	11th to 20th	Night	28% 22% 25% 19% 7%	720
	21st to end	Night	22% 22% 29% 21% 6% 1	792
April	1st to 10th	Night	21% 23% 28% 23% 5%	720
	11th to 20th	Night	21% 15% 26% 25% 12%	711
	21st to end	Night	19% 16% 25% 32% 8% 1	558
May	1st to 10th	Night	20% 15% 24% 28% 12% 1	540
	11th to 20th	Night	19% 12% 24% 29% 16%	531
	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 2024-01-13 01:38:13. Version ac07

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