Elliott Island road
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Elliott Island road clear sky chart from 2005-11-06 to 2025-05-11.

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	13% 6% 2 6% 4 4 4 4 6% 8% 45%	113745
	Night	14% 7% 2 6% 4 4 4 3 5% 7% 44%	115208
Transparency	Day	36% 6% 13% 24% 17% 4	117377
	Night	38% 5% 12% 23% 18% 4	119715
Seeing	Day	16% 11% 28% 25% 14% 5%	15741
	Night	17% 10% 28% 30% 13% 2	25302

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	14% 5% 2 4 3 2 3 3 5% 7% 51%	3597
	11th to 20th	Day	14% 7% 3 7% 4 3 3 2 4 5% 48%	4014
	21st to end	Day	14% 7% 3 6% 4 4 5% 3 5% 7% 43%	4466
February	1st to 10th	Day	14% 7% 3 7% 3 5% 5% 4 7% 7% 39%	1800
	11th to 20th	Day	19% 6% 2 5% 4 3 4 3 5% 7% 42%	1901
	21st to end	Day	19% 8% 2 5% 4 4 4 3 5% 6% 40%	1650
March	1st to 10th	Day	17% 5% 2 5% 3 4 4 4 6% 8% 43%	4653
	11th to 20th	Day	10% 5% 2 5% 3 3 4 3 4 7% 54%	4980
	21st to end	Day	16% 7% 2 6% 5% 3 3 3 4 7% 44%	5694
April	1st to 10th	Day	11% 6% 2 6% 3 3 4 4 5% 8% 47%	2400
	11th to 20th	Day	11% 5% 1 5% 4 4 4 4 5% 7% 50%	2374
	21st to end	Day	13% 6% 2 5% 3 3 4 3 6% 8% 47%	2400
May	1st to 10th	Day	20% 7% 2 6% 4 4 4 4 6% 9% 33%	3930
	11th to 20th	Day	17% 8% 2 7% 5% 4 5% 4 6% 8% 35%	4398
	21st to end	Day	9% 4 2 5% 4 3 4 4 6% 11% 49%	4823
June	1st to 10th	Day	9% 4 1 5% 4 5% 5% 4 8% 10% 46%	2660
	11th to 20th	Day	9% 4 1 5% 4 4 4 4 6% 10% 49%	2660
	21st to end	Day	7% 4 2 4 4 4 4 4 8% 11% 48%	2660
July	1st to 10th	Day	6% 4 2 5% 3 4 5% 5% 9% 14% 44%	4440
	11th to 20th	Day	10% 5% 2 6% 4 5% 5% 5% 8% 11% 39%	4440
	21st to end	Day	10% 5% 2 7% 6% 5% 6% 5% 8% 9% 37%	4471
August	1st to 10th	Day	14% 6% 2 7% 4 4 5% 4 8% 10% 35%	4087
	11th to 20th	Day	9% 5% 3 7% 5% 5% 6% 4 7% 9% 41%	3730
	21st to end	Day	8% 3 2 5% 4 4 4 3 6% 9% 52%	4180
September	1st to 10th	Day	12% 5% 1 5% 4 4 4 3 7% 8% 46%	2280
	11th to 20th	Day	10% 6% 3 6% 4 3 3 4 6% 7% 49%	2280
	21st to end	Day	18% 8% 3 6% 4 4 4 3 5% 5% 40%	2047
October	1st to 10th	Day	13% 6% 2 7% 4 4 3 3 5% 6% 47%	1900
	11th to 20th	Day	15% 5% 2 5% 3 3 3 2 4 6% 53%	1900
	21st to end	Day	13% 5% 2 5% 4 3 3 3 4 8% 49%	2090
November	1st to 10th	Day	12% 5% 1 4 5% 2 3 4 5% 7% 52%	1785
	11th to 20th	Day	13% 5% 2 5% 5% 4 4 3 6% 6% 49%	1800
	21st to end	Day	15% 6% 2 5% 4 3 3 3 5% 6% 50%	1705
December	1st to 10th	Day	11% 5% 2 6% 4 4 4 3 5% 6% 51%	2600
	11th to 20th	Day	18% 9% 3 5% 4 3 2 2 4 5% 46%	2990
	21st to end	Day	12% 6% 2 5% 4 4 4 4 5% 7% 46%	3960
January	1st to 10th	Night	13% 7% 3 5% 3 3 4 3 4 6% 49%	6349
	11th to 20th	Night	13% 7% 2 6% 4 3 3 2 3 4 52%	5928
	21st to end	Night	15% 8% 3 6% 3 3 4 3 4 6% 45%	6490
February	1st to 10th	Night	17% 7% 3 5% 4 3 4 3 6% 6% 43%	2600
	11th to 20th	Night	20% 7% 2 5% 3 4 3 3 5% 7% 41%	2383
	21st to end	Night	17% 8% 2 5% 3 2 4 3 5% 7% 44%	1980
March	1st to 10th	Night	16% 7% 2 6% 3 3 3 3 4 5% 46%	5197
	11th to 20th	Night	12% 6% 2 5% 3 3 4 3 6% 7% 49%	4980
	21st to end	Night	14% 7% 2 6% 4 4 4 3 4 6% 45%	5238
April	1st to 10th	Night	16% 6% 2 6% 5% 4 4 4 6% 6% 41%	2000
	11th to 20th	Night	12% 6% 2 6% 4 3 4 3 5% 6% 47%	1975
	21st to end	Night	16% 4 2 5% 5% 4 5% 3 6% 7% 44%	2000
May	1st to 10th	Night	18% 7% 3 8% 4 5% 5% 4 6% 7% 33%	3212
	11th to 20th	Night	21% 8% 2 6% 4 4 5% 4 5% 7% 33%	2501
	21st to end	Night	10% 5% 2 6% 4 4 4 4 7% 10% 42%	2732
June	1st to 10th	Night	11% 6% 1 6% 5% 5% 5% 5% 6% 7% 43%	1520
	11th to 20th	Night	8% 6% 2 7% 5% 5% 4 4 7% 10% 43%	1520
	21st to end	Night	8% 5% 2 5% 5% 5% 5% 5% 8% 10% 42%	1520
July	1st to 10th	Night	8% 5% 2 7% 4 5% 6% 4 8% 10% 39%	2520
	11th to 20th	Night	10% 5% 2 6% 4 4 5% 5% 8% 11% 40%	2520
	21st to end	Night	13% 7% 3 8% 5% 5% 5% 4 7% 8% 35%	3078
August	1st to 10th	Night	17% 8% 2 7% 5% 4 4 3 6% 9% 34%	2825
	11th to 20th	Night	12% 6% 2 7% 5% 4 5% 4 7% 8% 39%	3081
	21st to end	Night	8% 5% 2 5% 4 4 4 4 5% 8% 51%	3476
September	1st to 10th	Night	13% 7% 2 5% 4 4 3 3 5% 7% 48%	1900
	11th to 20th	Night	9% 4 2 5% 3 4 4 4 6% 9% 50%	1900
	21st to end	Night	19% 7% 3 6% 4 5% 4 3 5% 7% 37%	2130
October	1st to 10th	Night	16% 6% 2 6% 4 3 4 4 4 6% 44%	2280
	11th to 20th	Night	16% 6% 2 4 4 4 3 3 4 5% 50%	2280
	21st to end	Night	16% 6% 1 5% 3 3 3 4 5% 6% 48%	2508
November	1st to 10th	Night	13% 5% 3 5% 4 3 3 3 4 5% 52%	2511
	11th to 20th	Night	16% 7% 2 5% 4 3 3 3 5% 7% 46%	2600
	21st to end	Night	12% 6% 2 4 4 3 4 3 5% 8% 49%	2693
December	1st to 10th	Night	11% 6% 2 5% 3 3 3 3 5% 7% 52%	4580
	11th to 20th	Night	21% 7% 2 6% 4 3 4 3 5% 6% 38%	5205
	21st to end	Night	13% 8% 2 6% 4 4 4 4 6% 7% 42%	6996

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	32% 4 7% 26% 26% 4	3598
	11th to 20th	Day	40% 3 8% 22% 22% 6%	4014
	21st to end	Day	41% 5% 11% 27% 13% 2	4466
February	1st to 10th	Day	42% 6% 12% 25% 13% 2	1800
	11th to 20th	Day	42% 4 10% 23% 18% 4	1910
	21st to end	Day	44% 6% 11% 18% 17% 4	1650
March	1st to 10th	Day	39% 5% 9% 20% 19% 7%	4653
	11th to 20th	Day	30% 4 11% 28% 22% 6%	4980
	21st to end	Day	41% 5% 10% 19% 19% 7%	5694
April	1st to 10th	Day	35% 7% 12% 22% 18% 6%	2400
	11th to 20th	Day	34% 6% 12% 23% 20% 5%	2374
	21st to end	Day	35% 6% 12% 24% 19% 5%	2400
May	1st to 10th	Day	47% 10% 13% 20% 10% 2	3965
	11th to 20th	Day	45% 10% 16% 19% 8% 2	4402
	21st to end	Day	28% 9% 16% 27% 17% 2	4837
June	1st to 10th	Day	32% 9% 15% 27% 15% 2	2660
	11th to 20th	Day	30% 9% 16% 25% 17% 3	2660
	21st to end	Day	29% 9% 16% 26% 18% 2	2660
July	1st to 10th	Day	29% 10% 27% 18% 13% 3	4370
	11th to 20th	Day	38% 7% 21% 25% 7% 1	4365
	21st to end	Day	39% 10% 17% 20% 13% 1	4328
August	1st to 10th	Day	41% 8% 18% 25% 7%	4074
	11th to 20th	Day	37% 8% 15% 28% 12% 1	3766
	21st to end	Day	29% 7% 15% 28% 19% 2	4180
September	1st to 10th	Day	36% 8% 15% 19% 18% 4	2280
	11th to 20th	Day	34% 8% 10% 25% 21% 3	2280
	21st to end	Day	46% 5% 10% 19% 17% 3	2047
October	1st to 10th	Day	34% 5% 9% 22% 25% 6%	3160
	11th to 20th	Day	26% 3 6% 27% 28% 10%	3140
	21st to end	Day	23% 4 9% 30% 26% 9%	3428
November	1st to 10th	Day	32% 4 11% 28% 20% 4	1785
	11th to 20th	Day	37% 5% 12% 21% 21% 4	1800
	21st to end	Day	37% 3 10% 29% 17% 3	1705
December	1st to 10th	Day	35% 4 15% 27% 16% 3	2600
	11th to 20th	Day	43% 2 13% 25% 14% 3	2986
	21st to end	Day	36% 6% 15% 26% 16% 1	3960
January	1st to 10th	Night	36% 3 8% 23% 25% 5%	6349
	11th to 20th	Night	37% 4 7% 26% 21% 5%	5928
	21st to end	Night	41% 3 9% 28% 17% 2	6490
February	1st to 10th	Night	41% 5% 13% 24% 16% 2	2600
	11th to 20th	Night	44% 5% 8% 20% 19% 4	2385
	21st to end	Night	41% 4 9% 22% 18% 5%	1980
March	1st to 10th	Night	39% 5% 8% 22% 17% 8%	5197
	11th to 20th	Night	34% 5% 11% 24% 20% 6%	4980
	21st to end	Night	41% 4 9% 21% 18% 6%	5238
April	1st to 10th	Night	42% 6% 11% 17% 19% 5%	2000
	11th to 20th	Night	36% 5% 13% 20% 20% 6%	1975
	21st to end	Night	39% 6% 11% 23% 17% 4	2000
May	1st to 10th	Night	48% 9% 12% 21% 8% 2	3242
	11th to 20th	Night	48% 9% 13% 19% 9% 1	2502
	21st to end	Night	35% 8% 17% 23% 15% 2	2739
June	1st to 10th	Night	37% 9% 13% 23% 16% 2	1520
	11th to 20th	Night	35% 9% 14% 25% 14% 2	1520
	21st to end	Night	34% 9% 16% 23% 16% 3	1520
July	1st to 10th	Night	38% 11% 20% 19% 10% 2	2480
	11th to 20th	Night	35% 8% 24% 24% 7% 1	2472
	21st to end	Night	45% 8% 16% 19% 13%	2980
August	1st to 10th	Night	47% 7% 17% 21% 8%	2814
	11th to 20th	Night	40% 8% 15% 27% 9%	3111
	21st to end	Night	30% 6% 12% 26% 24% 2	3476
September	1st to 10th	Night	36% 6% 16% 20% 17% 5%	1900
	11th to 20th	Night	31% 6% 11% 28% 21% 3	1900
	21st to end	Night	46% 7% 9% 18% 16% 3	2130
October	1st to 10th	Night	36% 6% 11% 23% 21% 4	3800
	11th to 20th	Night	26% 3 10% 22% 29% 10%	3779
	21st to end	Night	23% 2 10% 30% 26% 8%	4120
November	1st to 10th	Night	35% 4 10% 26% 20% 5%	2511
	11th to 20th	Night	39% 4 10% 22% 19% 6%	2600
	21st to end	Night	34% 5% 11% 27% 20% 3	2693
December	1st to 10th	Night	33% 4 13% 26% 21% 3	4580
	11th to 20th	Night	47% 3 12% 21% 12% 4	5208
	21st to end	Night	39% 6% 14% 24% 16% 1	6996

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	27% 23% 31% 14% 6%	200
	11th to 20th	Day	23% 29% 31% 15% 2	290
	21st to end	Day	19% 22% 41% 15% 4	330
February	1st to 10th	Day	22% 21% 40% 12% 4	300
	11th to 20th	Day	29% 21% 35% 12% 3	449
	21st to end	Day	23% 21% 33% 18% 4	414
March	1st to 10th	Day	21% 20% 33% 21% 4 1	500
	11th to 20th	Day	22% 19% 34% 19% 4 2	500
	21st to end	Day	21% 15% 40% 18% 5% 1	550
April	1st to 10th	Day	18% 18% 40% 17% 6% 1	500
	11th to 20th	Day	14% 17% 35% 24% 9% 2	492
	21st to end	Day	18% 14% 32% 24% 11% 1	500
May	1st to 10th	Day	19% 17% 32% 21% 10% 2	503
	11th to 20th	Day	16% 10% 32% 30% 11% 3	487
	21st to end	Day	16% 5% 25% 29% 19% 6%	529
June	1st to 10th	Day	11% 7% 27% 31% 18% 6%	490
	11th to 20th	Day	10% 6% 24% 32% 20% 8%	490
	21st to end	Day	9% 3 25% 40% 19% 4	490
July	1st to 10th	Day	9% 4 19% 36% 22% 9%	485
	11th to 20th	Day	6% 1 14% 38% 31% 10%	484
	21st to end	Day	11% 2 19% 36% 23% 8%	532
August	1st to 10th	Day	12% 3 17% 33% 27% 8%	486
	11th to 20th	Day	11% 2 17% 32% 31% 8%	479
	21st to end	Day	8% 4 16% 31% 28% 13%	539
September	1st to 10th	Day	13% 4 20% 28% 20% 14%	490
	11th to 20th	Day	11% 4 23% 28% 23% 10%	490
	21st to end	Day	24% 11% 23% 26% 13% 4	490
October	1st to 10th	Day	16% 7% 23% 29% 16% 8%	490
	11th to 20th	Day	17% 11% 26% 26% 16% 4	490
	21st to end	Day	15% 11% 33% 23% 13% 4	539
November	1st to 10th	Day	16% 11% 30% 24% 15% 4	408
	11th to 20th	Day	18% 13% 36% 23% 10% 1	400
	21st to end	Day	19% 20% 27% 22% 8% 4	305
December	1st to 10th	Day	20% 22% 38% 15% 7% 1	200
	11th to 20th	Day	26% 20% 30% 19% 6% 1	200
	21st to end	Day	21% 16% 30% 23% 10%	220
January	1st to 10th	Night	19% 20% 35% 22% 4	800
	11th to 20th	Night	22% 14% 33% 26% 5%	800
	21st to end	Night	19% 16% 38% 25% 2	880
February	1st to 10th	Night	20% 12% 38% 26% 4	800
	11th to 20th	Night	23% 21% 35% 20% 2	783
	21st to end	Night	22% 14% 39% 21% 3	660
March	1st to 10th	Night	21% 17% 34% 24% 6%	800
	11th to 20th	Night	22% 14% 33% 23% 6% 1	800
	21st to end	Night	20% 11% 35% 28% 5%	880
April	1st to 10th	Night	18% 14% 40% 23% 5%	800
	11th to 20th	Night	15% 12% 35% 31% 7%	791
	21st to end	Night	18% 9% 33% 31% 9% 1	800
May	1st to 10th	Night	16% 11% 33% 31% 9% 1	795
	11th to 20th	Night	15% 6% 28% 40% 11%	376
	21st to end	Night	12% 4 21% 40% 20% 3	411
June	1st to 10th	Night	10% 6% 23% 44% 17% 1	380
	11th to 20th	Night	9% 4 21% 45% 20% 2	380
	21st to end	Night	10% 2 19% 46% 23% 1	380
July	1st to 10th	Night	11% 2 14% 42% 29% 2	370
	11th to 20th	Night	5% 1 11% 47% 32% 4	368
	21st to end	Night	8% 2 17% 40% 32% 2	615
August	1st to 10th	Night	11% 3 11% 41% 32% 3	567
	11th to 20th	Night	12% 3 13% 40% 29% 3	734
	21st to end	Night	10% 3 13% 38% 31% 6%	836
September	1st to 10th	Night	15% 3 14% 36% 28% 4	760
	11th to 20th	Night	11% 2 16% 36% 29% 5%	760
	21st to end	Night	23% 5% 18% 31% 21% 2	760
October	1st to 10th	Night	18% 5% 20% 31% 21% 5%	760
	11th to 20th	Night	17% 10% 26% 30% 17% 1	760
	21st to end	Night	18% 10% 28% 27% 15% 2	836
November	1st to 10th	Night	15% 8% 31% 29% 14% 3	780
	11th to 20th	Night	18% 12% 30% 29% 9% 1	800
	21st to end	Night	17% 16% 28% 29% 10% 1	800
December	1st to 10th	Night	22% 14% 32% 22% 9% 1	800
	11th to 20th	Night	21% 13% 36% 24% 6%	800
	21st to end	Night	18% 12% 33% 32% 5%	880

Page generated at 2025-05-08 09:33:56. Version ac07

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