Gas Line Road
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Gas Line Road clear sky chart from 2005-11-06 to 2024-02-20.

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	3 4 2 4 4 3 4 4 5% 7% 61%	78437
	Night	3 4 2 4 4 3 4 4 5% 7% 59%	80775
Transparency	Day	22% 6% 10% 21% 22% 19%	78141
	Night	24% 6% 12% 23% 21% 15%	80592
Seeing	Day	5% 11% 21% 30% 26% 8%	13960
	Night	5% 4 20% 41% 26% 4	23478

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	2 6% 3 6% 7% 4 5% 7% 7% 10% 43%	2539
	11th to 20th	Day	3 7% 4 9% 7% 5% 5% 6% 6% 8% 40%	2540
	21st to end	Day	5% 7% 4 8% 8% 5% 7% 6% 6% 8% 36%	3114
February	1st to 10th	Day	3 5% 3 4 5% 3 5% 5% 7% 9% 52%	1752
	11th to 20th	Day	3 5% 2 5% 5% 3 5% 5% 6% 9% 51%	1841
	21st to end	Day	2 5% 3 4 4 3 4 6% 6% 8% 56%	1480
March	1st to 10th	Day	3 5% 3 5% 6% 3 6% 5% 5% 9% 50%	1800
	11th to 20th	Day	2 6% 2 6% 5% 4 5% 5% 6% 9% 49%	1894
	21st to end	Day	4 4 2 5% 5% 3 4 5% 6% 8% 55%	2351
April	1st to 10th	Day	3 5% 3 4 5% 3 5% 4 6% 9% 53%	2160
	11th to 20th	Day	4 3 2 5% 4 3 4 5% 5% 6% 59%	2129
	21st to end	Day	4 4 1 3 4 2 3 4 4 7% 64%	2160
May	1st to 10th	Day	3 3 2 3 3 2 3 4 5% 8% 64%	2318
	11th to 20th	Day	5% 3 2 4 4 2 3 4 5% 8% 59%	2391
	21st to end	Day	4 5% 2 5% 6% 3 5% 5% 5% 6% 53%	2723
June	1st to 10th	Day	3 2 2 3 4 2 4 4 5% 7% 64%	2520
	11th to 20th	Day	2 2 1 2 3 1 3 3 4 6% 73%	2520
	21st to end	Day	2 2 1 2 2 1 3 3 3 4 76%	2520
July	1st to 10th	Day	1 1 1 2 2 1 3 3 3 5% 79%	2520
	11th to 20th	Day	2 1 1 2 2 2 3 3 5% 4 75%	2520
	21st to end	Day	2 2 1 3 4 2 4 4 4 5% 69%	2741
August	1st to 10th	Day	3 2 1 3 3 2 4 3 4 5% 70%	2284
	11th to 20th	Day	1 1 1 1 2 2 2 3 3 4 80%	2122
	21st to end	Day	2 1 1 1 2 1 1 2 2 3 84%	2376
September	1st to 10th	Day	2 1 1 1 1 1 2 2 2 4 84%	2160
	11th to 20th	Day	2 2 1 2 3 1 2 3 3 5% 77%	2101
	21st to end	Day	2 2 1 2 2 1 2 3 3 5% 77%	1980
October	1st to 10th	Day	4 3 1 3 3 2 3 3 3 5% 70%	1882
	11th to 20th	Day	2 2 1 3 3 2 2 2 4 6% 73%	1800
	21st to end	Day	2 1 1 3 3 2 3 3 4 7% 70%	1886
November	1st to 10th	Day	3 4 2 4 4 3 3 4 6% 9% 59%	1674
	11th to 20th	Day	2 3 2 3 4 2 4 4 6% 9% 62%	1710
	21st to end	Day	3 4 2 5% 5% 3 4 5% 6% 8% 57%	1687
December	1st to 10th	Day	3 7% 2 6% 5% 4 4 4 5% 10% 51%	1520
	11th to 20th	Day	4 7% 3 8% 7% 6% 7% 7% 8% 9% 34%	1928
	21st to end	Day	4 7% 3 7% 6% 4 7% 6% 7% 10% 37%	2794
January	1st to 10th	Night	3 5% 2 6% 6% 3 5% 4 7% 9% 52%	4406
	11th to 20th	Night	2 8% 5% 9% 7% 3 5% 6% 6% 8% 41%	4420
	21st to end	Night	5% 8% 4 7% 7% 4 5% 6% 7% 8% 40%	4549
February	1st to 10th	Night	3 6% 3 4 3 3 5% 5% 6% 9% 53%	2428
	11th to 20th	Night	2 5% 2 4 4 4 4 5% 6% 8% 55%	2211
	21st to end	Night	3 5% 3 5% 6% 3 4 5% 5% 8% 54%	1776
March	1st to 10th	Night	4 6% 4 6% 5% 2 5% 4 5% 7% 51%	2160
	11th to 20th	Night	3 5% 3 5% 5% 2 5% 6% 6% 9% 52%	2063
	21st to end	Night	4 4 2 4 3 3 5% 4 5% 7% 58%	2004
April	1st to 10th	Night	3 5% 2 4 5% 3 5% 4 6% 7% 56%	1800
	11th to 20th	Night	3 4 1 3 4 3 3 3 5% 8% 63%	1779
	21st to end	Night	6% 5% 2 4 4 2 3 3 4 7% 62%	1800
May	1st to 10th	Night	6% 3 2 3 3 2 3 4 4 6% 62%	1639
	11th to 20th	Night	6% 3 2 3 3 2 4 4 5% 6% 62%	1498
	21st to end	Night	6% 6% 2 5% 5% 3 4 4 4 6% 54%	1552
June	1st to 10th	Night	4 3 1 4 5% 3 3 4 4 6% 63%	1440
	11th to 20th	Night	3 1 1 2 2 2 3 3 3 5% 74%	1440
	21st to end	Night	2 2 1 2 2 2 2 2 3 5% 77%	1440
July	1st to 10th	Night	1 1 1 2 2 1 3 3 4 4 79%	1440
	11th to 20th	Night	2 1 1 3 2 2 3 3 3 6% 75%	1440
	21st to end	Night	3 3 1 4 3 2 3 3 5% 7% 67%	1576
August	1st to 10th	Night	3 3 1 3 2 3 3 4 4 5% 68%	1651
	11th to 20th	Night	2 1 1 2 2 1 2 3 4 4 78%	1780
	21st to end	Night	2 1 1 1 2 1 2 2 3 4 81%	1980
September	1st to 10th	Night	1 1 1 2 1 1 2 2 3 4 82%	1800
	11th to 20th	Night	2 1 1 2 3 2 3 3 5% 5% 74%	1858
	21st to end	Night	3 1 1 2 2 1 2 3 4 5% 76%	1980
October	1st to 10th	Night	5% 3 1 3 3 2 3 3 3 4 69%	2074
	11th to 20th	Night	3 2 1 2 3 1 2 3 4 6% 75%	2160
	21st to end	Night	3 3 1 2 2 2 2 2 4 6% 73%	2469
November	1st to 10th	Night	4 4 2 4 4 2 3 4 4 7% 63%	2405
	11th to 20th	Night	3 4 2 3 3 2 3 4 4 7% 64%	2470
	21st to end	Night	4 5% 2 4 4 2 4 4 5% 7% 59%	2489
December	1st to 10th	Night	4 7% 3 5% 5% 2 3 4 5% 8% 54%	2660
	11th to 20th	Night	4 7% 3 6% 7% 3 6% 7% 7% 10% 40%	3276
	21st to end	Night	4 7% 3 7% 7% 4 7% 7% 7% 9% 38%	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	29% 11% 21% 31% 8%	2539
	11th to 20th	Day	36% 10% 17% 26% 9% 1	2540
	21st to end	Day	40% 12% 16% 24% 8%	3114
February	1st to 10th	Day	27% 8% 16% 30% 15% 5%	1752
	11th to 20th	Day	27% 6% 14% 32% 18% 3	1851
	21st to end	Day	24% 6% 18% 28% 18% 5%	1480
March	1st to 10th	Day	30% 8% 14% 28% 17% 2	1800
	11th to 20th	Day	30% 8% 14% 23% 20% 5%	1894
	21st to end	Day	26% 8% 18% 30% 15% 4	2351
April	1st to 10th	Day	27% 6% 13% 24% 22% 8%	2160
	11th to 20th	Day	24% 7% 9% 25% 26% 9%	2132
	21st to end	Day	21% 5% 9% 29% 29% 7%	2160
May	1st to 10th	Day	18% 5% 10% 24% 34% 9%	2318
	11th to 20th	Day	23% 5% 8% 23% 30% 11%	2394
	21st to end	Day	30% 6% 10% 21% 24% 9%	2724
June	1st to 10th	Day	19% 6% 8% 18% 32% 17%	2520
	11th to 20th	Day	13% 4 6% 17% 30% 31%	2520
	21st to end	Day	12% 3 3 8% 26% 47%	2520
July	1st to 10th	Day	10% 2 3 8% 20% 56%	2451
	11th to 20th	Day	11% 2 4 8% 21% 53%	2445
	21st to end	Day	17% 3 4 8% 20% 49%	2589
August	1st to 10th	Day	17% 3 4 10% 18% 47%	2267
	11th to 20th	Day	8% 3 4 7% 24% 55%	2122
	21st to end	Day	9% 2 2 7% 25% 56%	2376
September	1st to 10th	Day	8% 2 2 7% 26% 56%	2160
	11th to 20th	Day	12% 4 5% 14% 32% 33%	2101
	21st to end	Day	11% 3 4 17% 34% 30%	1980
October	1st to 10th	Day	18% 3 7% 18% 33% 20%	1882
	11th to 20th	Day	13% 3 7% 25% 35% 17%	1800
	21st to end	Day	15% 4 9% 31% 30% 11%	1886
November	1st to 10th	Day	22% 7% 12% 26% 26% 6%	1674
	11th to 20th	Day	18% 6% 18% 32% 23% 3	1710
	21st to end	Day	24% 5% 12% 32% 23% 3	1687
December	1st to 10th	Day	29% 6% 18% 29% 16% 2	1520
	11th to 20th	Day	41% 13% 14% 22% 9% 1	1928
	21st to end	Day	35% 11% 24% 22% 8% 1	2794
January	1st to 10th	Night	27% 8% 24% 31% 9% 1	4406
	11th to 20th	Night	39% 8% 18% 23% 11% 2	4420
	21st to end	Night	37% 10% 16% 26% 9%	4549
February	1st to 10th	Night	27% 8% 13% 30% 18% 4	2428
	11th to 20th	Night	25% 6% 13% 33% 20% 2	2212
	21st to end	Night	27% 7% 14% 31% 16% 5%	1776
March	1st to 10th	Night	31% 7% 13% 25% 19% 4	2160
	11th to 20th	Night	25% 8% 16% 24% 20% 6%	2063
	21st to end	Night	24% 7% 19% 29% 17% 4	2004
April	1st to 10th	Night	27% 6% 14% 28% 18% 8%	1800
	11th to 20th	Night	21% 6% 12% 28% 23% 10%	1779
	21st to end	Night	23% 4 11% 27% 28% 6%	1800
May	1st to 10th	Night	22% 6% 7% 23% 33% 9%	1639
	11th to 20th	Night	22% 4 9% 25% 29% 11%	1498
	21st to end	Night	30% 5% 13% 21% 23% 8%	1552
June	1st to 10th	Night	21% 5% 7% 20% 27% 20%	1440
	11th to 20th	Night	13% 4 6% 17% 32% 30%	1440
	21st to end	Night	11% 3 4 11% 28% 42%	1440
July	1st to 10th	Night	10% 3 3 8% 25% 51%	1400
	11th to 20th	Night	12% 3 3 10% 19% 54%	1392
	21st to end	Night	16% 3 5% 9% 22% 45%	1488
August	1st to 10th	Night	16% 4 5% 10% 19% 45%	1643
	11th to 20th	Night	10% 3 3 9% 24% 51%	1780
	21st to end	Night	9% 2 3 7% 26% 53%	1980
September	1st to 10th	Night	8% 2 3 7% 27% 53%	1800
	11th to 20th	Night	12% 4 5% 16% 29% 35%	1858
	21st to end	Night	12% 3 5% 14% 32% 35%	1980
October	1st to 10th	Night	20% 4 6% 17% 30% 25%	2074
	11th to 20th	Night	13% 3 6% 21% 33% 23%	2160
	21st to end	Night	13% 3 7% 26% 34% 16%	2469
November	1st to 10th	Night	20% 6% 12% 27% 24% 11%	2405
	11th to 20th	Night	20% 6% 13% 30% 27% 5%	2470
	21st to end	Night	24% 5% 13% 27% 26% 4	2489
December	1st to 10th	Night	28% 6% 15% 28% 20% 3	2660
	11th to 20th	Night	34% 11% 16% 26% 12% 1	3276
	21st to end	Night	37% 10% 18% 23% 12% 1	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	6% 9% 27% 35% 18% 4	180
	11th to 20th	Day	7% 8% 22% 31% 26% 7%	180
	21st to end	Day	7% 5% 19% 36% 25% 8%	388
February	1st to 10th	Day	5% 13% 23% 31% 24% 4	390
	11th to 20th	Day	6% 15% 23% 32% 21% 3	452
	21st to end	Day	5% 18% 27% 32% 17% 1	346
March	1st to 10th	Day	9% 16% 25% 33% 13% 4	420
	11th to 20th	Day	5% 19% 27% 28% 16% 6%	420
	21st to end	Day	8% 19% 25% 28% 17% 1	462
April	1st to 10th	Day	7% 20% 27% 27% 15% 4	420
	11th to 20th	Day	8% 22% 25% 25% 16% 5%	412
	21st to end	Day	6% 19% 26% 22% 20% 7%	420
May	1st to 10th	Day	8% 17% 26% 27% 17% 5%	423
	11th to 20th	Day	8% 18% 22% 24% 19% 8%	448
	21st to end	Day	6% 13% 19% 25% 25% 12%	485
June	1st to 10th	Day	3 15% 21% 23% 29% 9%	450
	11th to 20th	Day	6% 11% 24% 28% 21% 9%	450
	21st to end	Day	3 8% 18% 32% 30% 9%	450
July	1st to 10th	Day	1 4 19% 33% 33% 10%	446
	11th to 20th	Day	2 5% 11% 30% 39% 13%	444
	21st to end	Day	2 2 13% 32% 39% 11%	487
August	1st to 10th	Day	4 5% 16% 27% 34% 13%	447
	11th to 20th	Day	2 5% 15% 30% 32% 16%	437
	21st to end	Day	2 3 17% 31% 38% 10%	495
September	1st to 10th	Day	2 5% 15% 29% 37% 12%	450
	11th to 20th	Day	3 8% 17% 34% 30% 8%	450
	21st to end	Day	2 7% 20% 30% 35% 6%	450
October	1st to 10th	Day	4 8% 20% 29% 32% 8%	450
	11th to 20th	Day	4 8% 18% 27% 36% 7%	450
	21st to end	Day	4 7% 18% 32% 28% 10%	401
November	1st to 10th	Day	5% 6% 21% 31% 24% 11%	270
	11th to 20th	Day	1 5% 18% 39% 24% 12%	270
	21st to end	Day	3 8% 20% 33% 29% 7%	259
December	1st to 10th	Day	5% 7% 21% 31% 26% 11%	180
	11th to 20th	Day	4 8% 21% 35% 24% 7%	180
	21st to end	Day	9% 7% 23% 34% 22% 5%	198
January	1st to 10th	Night	7% 3 23% 37% 23% 7%	760
	11th to 20th	Night	4 4 20% 44% 25% 5%	760
	21st to end	Night	8% 3 17% 43% 23% 5%	836
February	1st to 10th	Night	4 4 22% 43% 23% 4	760
	11th to 20th	Night	3 5% 22% 44% 22% 4	742
	21st to end	Night	4 5% 30% 40% 18% 3	592
March	1st to 10th	Night	6% 6% 27% 40% 18% 3	720
	11th to 20th	Night	5% 7% 24% 37% 23% 4	720
	21st to end	Night	6% 8% 29% 39% 16% 2	792
April	1st to 10th	Night	4 9% 27% 36% 22% 2	720
	11th to 20th	Night	5% 10% 27% 36% 18% 5%	711
	21st to end	Night	7% 10% 26% 32% 22% 3	720
May	1st to 10th	Night	7% 9% 27% 36% 18% 3	559
	11th to 20th	Night	7% 6% 24% 39% 23% 2	436
	21st to end	Night	7% 5% 21% 41% 24% 3	389
June	1st to 10th	Night	6% 6% 21% 41% 24% 2	360
	11th to 20th	Night	3 5% 24% 42% 25% 1	360
	21st to end	Night	1 2 24% 49% 23% 1	360
July	1st to 10th	Night	2 2 20% 49% 26% 1	350
	11th to 20th	Night	2 1 20% 54% 22%	348
	21st to end	Night	2 2 15% 46% 34% 1	394
August	1st to 10th	Night	4 2 18% 43% 31% 2	577
	11th to 20th	Night	2 3 15% 46% 32% 2	712
	21st to end	Night	2 1 17% 46% 31% 2	792
September	1st to 10th	Night	2 2 13% 38% 39% 5%	720
	11th to 20th	Night	3 2 16% 36% 37% 7%	720
	21st to end	Night	3 3 15% 36% 34% 9%	720
October	1st to 10th	Night	6% 3 16% 42% 27% 7%	720
	11th to 20th	Night	4 3 15% 37% 35% 6%	720
	21st to end	Night	4 3 14% 36% 32% 11%	792
November	1st to 10th	Night	5% 3 16% 37% 32% 8%	740
	11th to 20th	Night	5% 4 13% 46% 27% 5%	760
	21st to end	Night	5% 3 19% 39% 28% 6%	760
December	1st to 10th	Night	6% 3 21% 41% 24% 4	760
	11th to 20th	Night	6% 4 21% 43% 23% 3	760
	21st to end	Night	6% 7% 25% 44% 17% 1	836

Page generated at 2024-02-17 03:28:42. Version ac07

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