Triplet Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Triplet Observatory clear sky chart from 2005-11-06 to 2024-01-17.

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% 6% 3 5% 5% 3 5% 5% 6% 8% 39%	74750
	Night	16% 6% 2 5% 5% 3 4 5% 5% 7% 41%	75066
Transparency	Day	43% 6% 12% 22% 14% 2	74460
	Night	41% 6% 12% 23% 15% 2	74890
Seeing	Day	20% 12% 27% 23% 13% 4	13781
	Night	20% 10% 27% 31% 12% 1	23228

By Month

Percentage Cloud Cover NE (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	12% 7% 3 5% 6% 4 5% 5% 6% 8% 39%	1517
	11th to 20th	Day	16% 8% 4 6% 6% 4 6% 5% 6% 6% 33%	1560
	21st to end	Day	14% 8% 4 7% 6% 3 5% 5% 5% 7% 36%	1782
February	1st to 10th	Day	16% 7% 3 6% 7% 3 5% 6% 5% 7% 34%	1620
	11th to 20th	Day	15% 7% 3 7% 5% 3 4 4 6% 9% 37%	1660
	21st to end	Day	20% 8% 4 6% 6% 3 4 4 4 6% 35%	1480
March	1st to 10th	Day	13% 6% 2 5% 5% 4 5% 5% 5% 7% 44%	1844
	11th to 20th	Day	16% 6% 3 6% 6% 3 6% 4 6% 8% 36%	1980
	21st to end	Day	21% 6% 3 5% 5% 3 4 4 4 6% 39%	2271
April	1st to 10th	Day	16% 7% 3 6% 6% 3 4 4 5% 8% 38%	2160
	11th to 20th	Day	16% 6% 2 6% 4 3 4 4 5% 7% 42%	2134
	21st to end	Day	17% 4 3 5% 5% 3 5% 5% 7% 8% 39%	2160
May	1st to 10th	Day	17% 7% 2 5% 5% 3 5% 7% 5% 8% 35%	2337
	11th to 20th	Day	21% 6% 3 5% 5% 3 5% 5% 6% 8% 34%	2478
	21st to end	Day	14% 6% 2 6% 5% 3 5% 6% 6% 8% 39%	2725
June	1st to 10th	Day	12% 6% 2 5% 6% 3 5% 6% 6% 10% 37%	2520
	11th to 20th	Day	14% 5% 2 5% 5% 4 5% 7% 6% 9% 37%	2520
	21st to end	Day	11% 4 2 5% 5% 4 5% 6% 6% 11% 41%	2520
July	1st to 10th	Day	10% 5% 2 5% 7% 4 7% 6% 7% 10% 37%	2520
	11th to 20th	Day	8% 4 2 5% 6% 4 6% 7% 8% 9% 43%	2520
	21st to end	Day	9% 5% 3 7% 6% 4 7% 6% 7% 8% 38%	2658
August	1st to 10th	Day	11% 5% 3 6% 6% 4 7% 6% 8% 8% 37%	2327
	11th to 20th	Day	12% 5% 2 5% 6% 3 5% 5% 7% 8% 40%	2178
	21st to end	Day	14% 5% 2 5% 5% 3 4 5% 8% 9% 40%	2376
September	1st to 10th	Day	17% 5% 2 5% 5% 3 4 5% 5% 6% 43%	2160
	11th to 20th	Day	13% 5% 2 4 4 3 4 4 5% 8% 50%	2160
	21st to end	Day	18% 7% 2 6% 5% 3 4 3 4 6% 41%	1931
October	1st to 10th	Day	19% 6% 3 4 3 2 5% 4 6% 8% 42%	1800
	11th to 20th	Day	17% 4 3 5% 6% 3 4 4 4 8% 43%	1800
	21st to end	Day	20% 6% 2 4 4 3 3 4 5% 7% 41%	1953
November	1st to 10th	Day	13% 7% 3 4 4 2 3 3 4 7% 50%	1671
	11th to 20th	Day	17% 5% 2 4 4 2 4 4 6% 8% 44%	1710
	21st to end	Day	17% 4 2 5% 4 3 5% 6% 5% 7% 42%	1520
December	1st to 10th	Day	18% 8% 2 6% 6% 3 5% 4 6% 7% 34%	1520
	11th to 20th	Day	21% 6% 2 4 5% 3 4 5% 5% 7% 38%	1906
	21st to end	Day	19% 7% 3 7% 6% 3 5% 6% 6% 7% 31%	2772
January	1st to 10th	Night	15% 7% 3 6% 5% 3 4 5% 5% 8% 42%	2649
	11th to 20th	Night	17% 8% 3 5% 5% 3 4 5% 6% 7% 36%	2540
	21st to end	Night	13% 8% 3 5% 5% 3 4 5% 5% 7% 42%	2574
February	1st to 10th	Night	17% 8% 3 5% 4 3 5% 4 5% 7% 37%	2340
	11th to 20th	Night	16% 7% 3 7% 6% 2 5% 5% 5% 6% 38%	2184
	21st to end	Night	19% 7% 3 5% 4 4 5% 4 4 7% 39%	1776
March	1st to 10th	Night	14% 5% 2 4 5% 3 4 4 5% 7% 45%	2100
	11th to 20th	Night	18% 7% 3 5% 4 3 4 3 5% 5% 43%	1979
	21st to end	Night	18% 6% 2 5% 5% 3 4 4 5% 7% 41%	2084
April	1st to 10th	Night	18% 6% 2 4 6% 3 4 5% 6% 7% 38%	1800
	11th to 20th	Night	14% 6% 2 5% 5% 3 4 5% 5% 7% 43%	1775
	21st to end	Night	20% 4 2 4 5% 3 4 4 5% 5% 43%	1800
May	1st to 10th	Night	19% 7% 2 6% 4 3 5% 4 5% 6% 38%	1635
	11th to 20th	Night	18% 6% 3 6% 5% 3 5% 5% 6% 6% 38%	1415
	21st to end	Night	15% 6% 3 6% 3 4 5% 5% 5% 8% 40%	1550
June	1st to 10th	Night	15% 6% 3 5% 5% 2 4 4 6% 8% 43%	1440
	11th to 20th	Night	13% 5% 3 5% 5% 3 5% 5% 6% 9% 41%	1440
	21st to end	Night	11% 4 2 5% 4 3 5% 6% 7% 10% 44%	1440
July	1st to 10th	Night	10% 5% 3 7% 6% 4 5% 6% 7% 9% 39%	1440
	11th to 20th	Night	8% 4 2 4 5% 4 5% 5% 8% 10% 45%	1440
	21st to end	Night	10% 5% 2 4 7% 3 6% 6% 7% 10% 40%	1656
August	1st to 10th	Night	10% 5% 2 5% 6% 2 5% 5% 7% 8% 43%	1611
	11th to 20th	Night	11% 5% 3 8% 6% 4 5% 6% 6% 8% 39%	1705
	21st to end	Night	13% 5% 2 4 4 4 6% 5% 6% 8% 43%	1980
September	1st to 10th	Night	15% 6% 2 6% 4 3 3 3 5% 7% 47%	1800
	11th to 20th	Night	14% 4 2 4 4 3 4 4 5% 6% 51%	1800
	21st to end	Night	17% 5% 2 5% 5% 3 5% 4 6% 6% 43%	2027
October	1st to 10th	Night	20% 6% 2 4 4 2 4 3 5% 6% 43%	2160
	11th to 20th	Night	17% 6% 3 4 4 3 3 4 4 7% 47%	2160
	21st to end	Night	20% 5% 2 3 3 2 4 4 4 7% 45%	2402
November	1st to 10th	Night	12% 5% 2 4 4 3 4 4 5% 6% 51%	2407
	11th to 20th	Night	16% 7% 3 5% 4 2 4 3 4 7% 46%	2470
	21st to end	Night	15% 4 2 5% 4 3 4 5% 5% 8% 44%	2655
December	1st to 10th	Night	19% 7% 3 6% 6% 3 4 6% 5% 7% 35%	2660
	11th to 20th	Night	18% 7% 2 5% 5% 3 4 5% 5% 6% 39%	3288
	21st to end	Night	18% 8% 3 7% 5% 3 5% 5% 6% 7% 34%	4884

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	44% 5% 13% 23% 13% 3	1518
	11th to 20th	Day	50% 6% 13% 19% 10% 2	1560
	21st to end	Day	47% 5% 11% 22% 12% 2	1782
February	1st to 10th	Day	47% 7% 13% 20% 11% 1	1620
	11th to 20th	Day	46% 5% 11% 24% 12% 2	1669
	21st to end	Day	52% 4 9% 21% 10% 3	1480
March	1st to 10th	Day	40% 6% 12% 27% 13% 2	1847
	11th to 20th	Day	46% 6% 11% 20% 14% 4	1980
	21st to end	Day	48% 5% 9% 19% 17% 3	2271
April	1st to 10th	Day	44% 5% 10% 21% 15% 5%	2160
	11th to 20th	Day	41% 6% 11% 22% 16% 5%	2134
	21st to end	Day	42% 6% 11% 21% 15% 5%	2160
May	1st to 10th	Day	46% 7% 10% 19% 15% 3	2337
	11th to 20th	Day	48% 7% 10% 19% 13% 2	2482
	21st to end	Day	41% 8% 14% 22% 13% 2	2725
June	1st to 10th	Day	40% 9% 13% 23% 13% 2	2520
	11th to 20th	Day	42% 9% 13% 23% 10% 3	2520
	21st to end	Day	37% 8% 14% 26% 14% 1	2520
July	1st to 10th	Day	40% 8% 13% 22% 15% 2	2450
	11th to 20th	Day	34% 8% 14% 26% 15% 2	2445
	21st to end	Day	41% 8% 11% 22% 15% 3	2509
August	1st to 10th	Day	41% 8% 13% 22% 15% 1	2314
	11th to 20th	Day	39% 7% 15% 23% 14% 1	2178
	21st to end	Day	38% 8% 12% 22% 17% 3	2376
September	1st to 10th	Day	41% 6% 11% 21% 18% 3	2160
	11th to 20th	Day	34% 5% 10% 25% 22% 4	2160
	21st to end	Day	45% 4 9% 19% 21% 2	1931
October	1st to 10th	Day	41% 5% 13% 24% 16% 1	1800
	11th to 20th	Day	40% 5% 12% 24% 18% 1	1800
	21st to end	Day	43% 5% 10% 24% 16% 2	1953
November	1st to 10th	Day	35% 4 14% 25% 19% 3	1671
	11th to 20th	Day	38% 6% 11% 24% 18% 2	1710
	21st to end	Day	39% 6% 13% 30% 9% 2	1520
December	1st to 10th	Day	50% 6% 14% 19% 10% 1	1520
	11th to 20th	Day	46% 5% 15% 25% 8% 1	1906
	21st to end	Day	51% 8% 13% 21% 8% 1	2772
January	1st to 10th	Night	42% 5% 12% 24% 14% 3	2649
	11th to 20th	Night	47% 5% 14% 22% 10% 2	2540
	21st to end	Night	41% 5% 11% 26% 15% 2	2574
February	1st to 10th	Night	46% 4 14% 24% 9% 2	2340
	11th to 20th	Night	47% 5% 10% 20% 16% 3	2186
	21st to end	Night	46% 4 9% 21% 16% 3	1776
March	1st to 10th	Night	38% 5% 12% 26% 16% 3	2110
	11th to 20th	Night	43% 5% 9% 24% 16% 3	1980
	21st to end	Night	43% 5% 10% 19% 19% 4	2084
April	1st to 10th	Night	44% 4 11% 21% 15% 4	1800
	11th to 20th	Night	39% 6% 11% 21% 20% 3	1775
	21st to end	Night	41% 6% 10% 21% 17% 5%	1800
May	1st to 10th	Night	46% 6% 10% 20% 14% 3	1635
	11th to 20th	Night	45% 7% 13% 15% 18% 3	1416
	21st to end	Night	42% 8% 15% 18% 15% 3	1551
June	1st to 10th	Night	40% 8% 10% 22% 19% 2	1440
	11th to 20th	Night	39% 8% 13% 24% 14% 1	1440
	21st to end	Night	33% 8% 14% 29% 13% 2	1440
July	1st to 10th	Night	41% 9% 14% 20% 14% 3	1400
	11th to 20th	Night	33% 8% 16% 26% 14% 2	1392
	21st to end	Night	35% 10% 16% 22% 15% 2	1564
August	1st to 10th	Night	37% 8% 15% 23% 16% 1	1600
	11th to 20th	Night	42% 8% 14% 18% 16% 2	1705
	21st to end	Night	37% 8% 13% 20% 19% 2	1980
September	1st to 10th	Night	39% 5% 11% 24% 18% 4	1800
	11th to 20th	Night	33% 6% 9% 24% 25% 3	1800
	21st to end	Night	41% 5% 9% 21% 22% 2	2027
October	1st to 10th	Night	42% 5% 12% 24% 16% 2	2160
	11th to 20th	Night	38% 5% 11% 29% 15% 2	2160
	21st to end	Night	40% 4 10% 27% 17% 2	2402
November	1st to 10th	Night	33% 5% 13% 25% 19% 4	2407
	11th to 20th	Night	41% 4 9% 25% 17% 4	2470
	21st to end	Night	38% 5% 13% 29% 14% 1	2655
December	1st to 10th	Night	48% 5% 12% 21% 13% 1	2660
	11th to 20th	Night	44% 6% 13% 21% 14% 2	3288
	21st to end	Night	47% 7% 15% 23% 9%	4884

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	25% 24% 28% 17% 5% 1	180
	11th to 20th	Day	28% 24% 31% 13% 3	204
	21st to end	Day	21% 22% 35% 15% 4 2	264
February	1st to 10th	Day	28% 21% 33% 16% 2 1	240
	11th to 20th	Day	28% 18% 38% 14% 1	327
	21st to end	Day	32% 14% 32% 20% 1	346
March	1st to 10th	Day	22% 20% 32% 22% 3	420
	11th to 20th	Day	23% 23% 32% 16% 4 1	420
	21st to end	Day	29% 18% 29% 17% 6% 1	462
April	1st to 10th	Day	23% 18% 33% 17% 7% 2	420
	11th to 20th	Day	21% 20% 28% 19% 9% 3	412
	21st to end	Day	28% 14% 33% 18% 5% 3	420
May	1st to 10th	Day	29% 12% 28% 18% 10% 3	423
	11th to 20th	Day	24% 11% 32% 21% 10% 2	447
	21st to end	Day	19% 6% 24% 27% 16% 7%	485
June	1st to 10th	Day	16% 10% 31% 25% 14% 4	450
	11th to 20th	Day	19% 9% 28% 25% 16% 3	450
	21st to end	Day	14% 11% 28% 28% 15% 5%	450
July	1st to 10th	Day	13% 4 20% 28% 24% 11%	445
	11th to 20th	Day	6% 6% 21% 33% 26% 8%	444
	21st to end	Day	11% 4 28% 33% 20% 5%	488
August	1st to 10th	Day	11% 4 21% 30% 23% 11%	446
	11th to 20th	Day	15% 3 18% 32% 23% 9%	439
	21st to end	Day	14% 4 22% 29% 18% 12%	495
September	1st to 10th	Day	19% 7% 19% 24% 22% 9%	450
	11th to 20th	Day	14% 5% 21% 28% 21% 12%	450
	21st to end	Day	23% 12% 21% 22% 18% 5%	450
October	1st to 10th	Day	24% 6% 22% 24% 18% 6%	450
	11th to 20th	Day	19% 11% 28% 25% 15% 2	450
	21st to end	Day	22% 11% 31% 23% 11% 2	481
November	1st to 10th	Day	18% 12% 26% 26% 14% 3	365
	11th to 20th	Day	20% 15% 31% 26% 8% 1	370
	21st to end	Day	21% 18% 34% 20% 6% 1	180
December	1st to 10th	Day	28% 19% 32% 14% 6% 1	180
	11th to 20th	Day	26% 23% 29% 16% 6% 1	180
	21st to end	Day	28% 18% 27% 19% 6% 2	198
January	1st to 10th	Night	20% 15% 38% 24% 3	760
	11th to 20th	Night	24% 14% 30% 27% 4	748
	21st to end	Night	17% 16% 36% 29% 2	792
February	1st to 10th	Night	24% 15% 32% 27% 2	720
	11th to 20th	Night	23% 18% 37% 19% 2	703
	21st to end	Night	26% 16% 34% 21% 2	592
March	1st to 10th	Night	21% 16% 33% 25% 5%	720
	11th to 20th	Night	25% 16% 32% 22% 6% 1	720
	21st to end	Night	21% 13% 36% 25% 5% 1	792
April	1st to 10th	Night	24% 17% 32% 22% 5%	720
	11th to 20th	Night	18% 12% 35% 26% 8%	711
	21st to end	Night	24% 12% 28% 29% 7%	720
May	1st to 10th	Night	25% 8% 27% 30% 8%	555
	11th to 20th	Night	19% 9% 28% 34% 10% 1	354
	21st to end	Night	17% 6% 19% 40% 17% 1	389
June	1st to 10th	Night	16% 6% 22% 36% 19%	360
	11th to 20th	Night	14% 5% 24% 42% 15% 1	360
	21st to end	Night	12% 2 20% 49% 17% 1	360
July	1st to 10th	Night	12% 3 17% 43% 23% 3	350
	11th to 20th	Night	9% 3 17% 42% 28% 1	348
	21st to end	Night	10% 4 14% 45% 25% 1	476
August	1st to 10th	Night	12% 4 9% 43% 29% 2	537
	11th to 20th	Night	15% 3 11% 37% 31% 2	641
	21st to end	Night	15% 5% 14% 36% 27% 3	792
September	1st to 10th	Night	16% 3 21% 34% 23% 3	720
	11th to 20th	Night	14% 5% 14% 37% 26% 5%	720
	21st to end	Night	19% 4 18% 36% 21% 2	720
October	1st to 10th	Night	23% 6% 20% 29% 18% 4	720
	11th to 20th	Night	21% 9% 22% 34% 14% 1	720
	21st to end	Night	24% 10% 27% 30% 9%	792
November	1st to 10th	Night	15% 8% 30% 32% 13% 1	740
	11th to 20th	Night	20% 13% 28% 30% 8% 1	760
	21st to end	Night	18% 13% 29% 33% 7%	760
December	1st to 10th	Night	26% 12% 31% 24% 6% 1	760
	11th to 20th	Night	21% 12% 32% 30% 5%	760
	21st to end	Night	23% 10% 33% 30% 3	836

Page generated at 2024-01-14 09:54:59. Version ac07

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