Far Away Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Far Away Observatory clear sky chart from 2005-11-06 to 2024-04-10.

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	7% 4 1 3 3 2 3 4 4 6% 63%	83720
	Night	7% 6% 2 3 4 2 3 4 5% 6% 58%	85212
Transparency	Day	23% 3 6% 17% 25% 26%	83453
	Night	27% 3 7% 15% 22% 26%	85001
Seeing	Day	9% 8% 27% 37% 15% 5%	14910
	Night	8% 3 11% 35% 34% 9%	25333

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	9% 4 1 3 3 2 2 3 3 5% 64%	2858
	11th to 20th	Day	8% 5% 2 3 3 2 4 4 4 8% 56%	3020
	21st to end	Day	14% 6% 2 4 4 3 4 4 5% 8% 47%	3498
February	1st to 10th	Day	12% 5% 1 4 3 2 3 3 3 5% 58%	1900
	11th to 20th	Day	11% 6% 2 3 3 2 4 4 5% 7% 54%	1850
	21st to end	Day	13% 9% 2 5% 4 3 4 4 4 6% 47%	1570
March	1st to 10th	Day	13% 6% 2 4 5% 3 5% 6% 8% 9% 39%	3138
	11th to 20th	Day	6% 5% 2 4 4 2 4 4 5% 7% 56%	3330
	21st to end	Day	13% 7% 1 3 3 2 3 4 5% 6% 51%	4027
April	1st to 10th	Day	9% 5% 2 4 3 2 4 4 5% 7% 55%	2270
	11th to 20th	Day	5% 4 2 3 3 2 4 5% 4 6% 63%	2129
	21st to end	Day	7% 4 1 3 3 1 2 3 4 7% 65%	2160
May	1st to 10th	Day	7% 6% 2 4 4 2 3 4 4 6% 58%	2276
	11th to 20th	Day	4 3 1 3 3 2 4 4 4 7% 66%	2301
	21st to end	Day	5% 5% 2 3 4 2 3 4 5% 7% 61%	2530
June	1st to 10th	Day	4 3 1 2 3 2 3 3 4 6% 70%	2340
	11th to 20th	Day	2 3 1 2 2 1 2 2 2 5% 78%	2340
	21st to end	Day	1 2 1 1 2 1 2 3 3 3 80%	2340
July	1st to 10th	Day	1 2 1 2 3 2 2 3 4 5% 75%	2340
	11th to 20th	Day	1 1 1 2 2 2 2 4 5% 7% 72%	2340
	21st to end	Day	2 2 1 3 3 2 4 4 6% 8% 67%	2448
August	1st to 10th	Day	2 1 1 1 2 2 2 3 4 5% 78%	2149
	11th to 20th	Day	1 1 2 2 1 1 2 3 5% 81%	2122
	21st to end	Day	1 1 1 1 2 2 3 3 4 5% 77%	2376
September	1st to 10th	Day	2 1 1 1 3 2 2 3 4 5% 76%	2142
	11th to 20th	Day	2 2 1 2 1 1 2 2 3 83%	1980
	21st to end	Day	3 1 1 2 3 1 2 3 3 4 77%	1980
October	1st to 10th	Day	5% 4 2 3 3 2 3 4 4 5% 67%	1980
	11th to 20th	Day	6% 3 1 2 3 2 2 2 3 4 71%	1980
	21st to end	Day	4 3 1 3 3 1 2 3 3 5% 73%	1887
November	1st to 10th	Day	6% 3 1 2 2 2 2 3 5% 6% 68%	1674
	11th to 20th	Day	5% 3 1 3 3 2 2 3 3 5% 68%	1710
	21st to end	Day	7% 5% 2 4 3 2 4 3 5% 7% 57%	1710
December	1st to 10th	Day	8% 5% 2 3 3 3 3 4 5% 7% 57%	1710
	11th to 20th	Day	15% 5% 3 5% 4 3 4 4 6% 7% 43%	2169
	21st to end	Day	13% 8% 2 5% 6% 4 6% 4 5% 5% 42%	3146
January	1st to 10th	Night	8% 6% 2 3 3 2 3 3 4 5% 62%	4097
	11th to 20th	Night	8% 6% 2 4 5% 3 3 4 5% 8% 52%	3952
	21st to end	Night	16% 8% 2 4 4 2 3 4 5% 5% 47%	4180
February	1st to 10th	Night	10% 6% 2 3 3 2 3 4 4 5% 58%	2280
	11th to 20th	Night	10% 7% 2 5% 4 3 3 3 3 5% 56%	2218
	21st to end	Night	13% 8% 3 4 3 2 5% 4 4 5% 49%	1884
March	1st to 10th	Night	14% 15% 3 5% 4 2 3 3 5% 7% 37%	3736
	11th to 20th	Night	7% 8% 1 4 4 3 4 4 6% 7% 53%	3649
	21st to end	Night	10% 12% 3 5% 4 2 3 4 6% 8% 42%	3622
April	1st to 10th	Night	9% 9% 2 4 3 2 4 4 5% 8% 51%	1900
	11th to 20th	Night	7% 9% 2 5% 4 2 2 3 4 5% 57%	1779
	21st to end	Night	7% 6% 2 3 4 3 4 3 4 6% 57%	1800
May	1st to 10th	Night	5% 8% 2 4 5% 3 4 4 5% 8% 53%	1683
	11th to 20th	Night	5% 7% 3 4 5% 4 4 5% 5% 6% 53%	1594
	21st to end	Night	6% 10% 2 4 4 2 3 4 4 6% 54%	1746
June	1st to 10th	Night	2 5% 2 3 4 2 5% 4 4 7% 61%	1620
	11th to 20th	Night	1 4 1 2 4 2 2 3 4 6% 70%	1620
	21st to end	Night	2 2 1 3 1 3 3 4 5% 75%	1620
July	1st to 10th	Night	1 1 2 3 2 3 3 3 6% 76%	1620
	11th to 20th	Night	1 1 1 2 2 3 4 5% 8% 72%	1620
	21st to end	Night	2 1 1 3 3 3 3 5% 5% 8% 66%	1867
August	1st to 10th	Night	1 1 1 1 2 2 2 3 6% 7% 74%	1790
	11th to 20th	Night	1 1 1 1 1 1 2 3 4 7% 78%	1780
	21st to end	Night	1 1 1 1 2 1 3 4 5% 5% 76%	1980
September	1st to 10th	Night	2 2 1 2 3 2 4 3 5% 6% 71%	1816
	11th to 20th	Night	2 2 1 2 3 1 2 2 3 3 79%	1980
	21st to end	Night	3 2 1 1 3 2 2 2 3 4 77%	1980
October	1st to 10th	Night	5% 3 2 3 3 2 3 3 3 7% 66%	1980
	11th to 20th	Night	6% 3 1 3 4 2 2 3 3 4 69%	1980
	21st to end	Night	5% 4 1 3 3 2 2 3 4 5% 68%	2462
November	1st to 10th	Night	5% 3 1 2 3 2 3 4 3 6% 67%	2405
	11th to 20th	Night	4 4 2 3 3 2 2 4 3 5% 67%	2470
	21st to end	Night	7% 5% 2 4 4 3 4 5% 6% 7% 54%	2470
December	1st to 10th	Night	9% 5% 2 4 4 2 4 4 6% 7% 54%	2470
	11th to 20th	Night	13% 8% 2 5% 3 2 4 4 5% 7% 45%	3041
	21st to end	Night	11% 8% 3 6% 6% 3 5% 5% 5% 5% 43%	4521

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	24% 3 6% 18% 30% 20%	2859
	11th to 20th	Day	27% 4 10% 25% 19% 15%	3020
	21st to end	Day	35% 4 7% 12% 24% 17%	3498
February	1st to 10th	Day	31% 3 4 12% 21% 29%	1900
	11th to 20th	Day	30% 4 5% 13% 27% 21%	1860
	21st to end	Day	39% 3 6% 14% 19% 19%	1570
March	1st to 10th	Day	36% 4 8% 21% 18% 13%	3138
	11th to 20th	Day	24% 6% 11% 26% 20% 13%	3330
	21st to end	Day	33% 4 9% 31% 16% 8%	4027
April	1st to 10th	Day	29% 4 8% 23% 24% 13%	2270
	11th to 20th	Day	22% 4 7% 20% 28% 20%	2132
	21st to end	Day	21% 3 7% 22% 34% 13%	2160
May	1st to 10th	Day	27% 4 7% 17% 28% 17%	2276
	11th to 20th	Day	19% 4 7% 23% 32% 15%	2304
	21st to end	Day	24% 3 7% 24% 32% 10%	2530
June	1st to 10th	Day	18% 3 5% 22% 32% 21%	2340
	11th to 20th	Day	13% 2 4 11% 29% 42%	2340
	21st to end	Day	11% 2 3 6% 23% 55%	2340
July	1st to 10th	Day	11% 3 3 10% 23% 50%	2276
	11th to 20th	Day	11% 4 7% 23% 27% 29%	2271
	21st to end	Day	15% 5% 11% 24% 29% 17%	2312
August	1st to 10th	Day	10% 2 5% 14% 30% 40%	2135
	11th to 20th	Day	8% 1 5% 16% 30% 40%	2122
	21st to end	Day	11% 3 3 11% 33% 39%	2376
September	1st to 10th	Day	12% 3 4 9% 33% 39%	2142
	11th to 20th	Day	9% 1 2 8% 35% 45%	1980
	21st to end	Day	12% 2 3 11% 31% 40%	1980
October	1st to 10th	Day	20% 2 5% 16% 25% 32%	1980
	11th to 20th	Day	19% 2 4 10% 27% 38%	1980
	21st to end	Day	17% 2 3 12% 22% 44%	1887
November	1st to 10th	Day	19% 3 5% 15% 23% 36%	1674
	11th to 20th	Day	19% 3 5% 12% 22% 40%	1710
	21st to end	Day	26% 3 6% 11% 21% 33%	1710
December	1st to 10th	Day	28% 3 7% 16% 17% 30%	1710
	11th to 20th	Day	38% 5% 9% 11% 19% 18%	2168
	21st to end	Day	42% 5% 6% 18% 17% 13%	3146
January	1st to 10th	Night	25% 3 6% 14% 29% 23%	4097
	11th to 20th	Night	31% 4 8% 24% 17% 16%	3952
	21st to end	Night	39% 3 7% 8% 25% 18%	4180
February	1st to 10th	Night	29% 3 6% 12% 20% 30%	2280
	11th to 20th	Night	33% 3 5% 12% 22% 25%	2219
	21st to end	Night	38% 4 4 14% 20% 19%	1884
March	1st to 10th	Night	46% 5% 7% 13% 17% 12%	3736
	11th to 20th	Night	28% 6% 9% 25% 19% 13%	3649
	21st to end	Night	40% 5% 9% 20% 18% 8%	3622
April	1st to 10th	Night	32% 3 9% 20% 20% 15%	1900
	11th to 20th	Night	31% 2 7% 16% 22% 21%	1779
	21st to end	Night	29% 4 9% 17% 25% 16%	1800
May	1st to 10th	Night	31% 5% 8% 15% 21% 20%	1683
	11th to 20th	Night	31% 4 10% 17% 22% 15%	1595
	21st to end	Night	32% 3 8% 20% 26% 11%	1746
June	1st to 10th	Night	22% 5% 8% 17% 28% 21%	1620
	11th to 20th	Night	16% 2 6% 12% 24% 40%	1620
	21st to end	Night	11% 2 5% 7% 21% 52%	1620
July	1st to 10th	Night	10% 2 3 11% 24% 50%	1575
	11th to 20th	Night	10% 4 8% 23% 27% 29%	1566
	21st to end	Night	16% 4 12% 23% 29% 16%	1763
August	1st to 10th	Night	9% 2 5% 15% 32% 36%	1780
	11th to 20th	Night	7% 2 6% 19% 31% 35%	1780
	21st to end	Night	10% 2 7% 11% 29% 42%	1980
September	1st to 10th	Night	15% 2 6% 12% 24% 41%	1816
	11th to 20th	Night	13% 1 4 9% 29% 45%	1980
	21st to end	Night	14% 2 4 10% 33% 38%	1980
October	1st to 10th	Night	21% 3 6% 17% 22% 31%	1980
	11th to 20th	Night	21% 2 4 12% 23% 38%	1980
	21st to end	Night	21% 2 4 9% 20% 44%	2462
November	1st to 10th	Night	21% 3 4 13% 21% 38%	2405
	11th to 20th	Night	21% 2 4 12% 21% 40%	2470
	21st to end	Night	29% 3 7% 13% 16% 32%	2470
December	1st to 10th	Night	29% 3 6% 14% 17% 30%	2470
	11th to 20th	Night	38% 4 8% 12% 20% 19%	3041
	21st to end	Night	40% 5% 9% 16% 16% 13%	4521

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	19% 4 30% 33% 12% 1	270
	11th to 20th	Day	15% 9% 25% 35% 14% 2	365
	21st to end	Day	14% 11% 32% 31% 11% 1	506
February	1st to 10th	Day	15% 11% 32% 28% 11% 3	460
	11th to 20th	Day	14% 15% 32% 30% 9%	455
	21st to end	Day	18% 16% 37% 23% 6%	382
March	1st to 10th	Day	16% 16% 36% 22% 8% 1	460
	11th to 20th	Day	14% 13% 34% 27% 10% 2	460
	21st to end	Day	13% 17% 37% 24% 8% 1	506
April	1st to 10th	Day	13% 12% 31% 30% 12% 3	457
	11th to 20th	Day	8% 19% 34% 29% 8% 2	412
	21st to end	Day	10% 12% 33% 28% 14% 4	420
May	1st to 10th	Day	14% 11% 32% 27% 13% 3	423
	11th to 20th	Day	8% 9% 31% 35% 13% 3	448
	21st to end	Day	10% 10% 33% 32% 12% 3	485
June	1st to 10th	Day	4 5% 27% 40% 19% 6%	450
	11th to 20th	Day	3 4 24% 45% 18% 6%	450
	21st to end	Day	2 3 24% 43% 20% 8%	450
July	1st to 10th	Day	2 1 12% 53% 22% 11%	446
	11th to 20th	Day	2 10% 50% 23% 15%	444
	21st to end	Day	2 1 9% 51% 24% 13%	487
August	1st to 10th	Day	2 17% 49% 20% 11%	447
	11th to 20th	Day	2 1 11% 54% 18% 15%	437
	21st to end	Day	1 1 14% 52% 21% 11%	495
September	1st to 10th	Day	3 1 25% 47% 18% 7%	450
	11th to 20th	Day	4 5% 27% 44% 18% 3	450
	21st to end	Day	5% 7% 28% 38% 17% 5%	450
October	1st to 10th	Day	6% 7% 31% 36% 18% 2	450
	11th to 20th	Day	6% 6% 33% 37% 16% 1	450
	21st to end	Day	6% 6% 26% 38% 20% 3	398
November	1st to 10th	Day	9% 6% 21% 39% 23% 3	270
	11th to 20th	Day	6% 7% 22% 42% 20% 4	270
	21st to end	Day	11% 9% 31% 30% 13% 4	270
December	1st to 10th	Day	12% 5% 28% 36% 16% 3	270
	11th to 20th	Day	7% 6% 29% 36% 18% 3	270
	21st to end	Day	22% 10% 25% 28% 12% 2	297
January	1st to 10th	Night	11% 3 22% 37% 21% 6%	760
	11th to 20th	Night	10% 4 18% 41% 21% 6%	760
	21st to end	Night	14% 5% 17% 41% 20% 3	836
February	1st to 10th	Night	14% 3 17% 37% 23% 6%	760
	11th to 20th	Night	13% 4 20% 37% 21% 6%	744
	21st to end	Night	16% 6% 16% 37% 20% 4	628
March	1st to 10th	Night	15% 6% 15% 42% 20% 2	760
	11th to 20th	Night	13% 3 12% 40% 24% 8%	760
	21st to end	Night	11% 5% 16% 38% 26% 5%	836
April	1st to 10th	Night	13% 3 13% 43% 24% 4	760
	11th to 20th	Night	11% 5% 13% 38% 27% 5%	711
	21st to end	Night	10% 3 12% 38% 30% 7%	720
May	1st to 10th	Night	10% 4 11% 38% 32% 6%	603
	11th to 20th	Night	8% 2 12% 32% 38% 8%	531
	21st to end	Night	11% 4 12% 35% 34% 4	584
June	1st to 10th	Night	3 2 12% 39% 38% 7%	540
	11th to 20th	Night	3 1 7% 41% 43% 5%	540
	21st to end	Night	2 1 5% 36% 48% 8%	540
July	1st to 10th	Night	1 26% 60% 12%	525
	11th to 20th	Night	1 1 20% 66% 12%	522
	21st to end	Night	1 2 1 16% 62% 19%	685
August	1st to 10th	Night	2 1 26% 54% 16%	716
	11th to 20th	Night	1 1 15% 62% 21%	712
	21st to end	Night	2 1 15% 59% 23%	792
September	1st to 10th	Night	2 1 3 25% 54% 16%	720
	11th to 20th	Night	4 1 3 33% 49% 11%	720
	21st to end	Night	4 1 7% 34% 41% 13%	720
October	1st to 10th	Night	7% 2 6% 43% 34% 8%	720
	11th to 20th	Night	7% 2 10% 40% 31% 11%	720
	21st to end	Night	8% 1 12% 34% 31% 14%	792
November	1st to 10th	Night	7% 2 11% 42% 28% 10%	740
	11th to 20th	Night	6% 1 13% 42% 28% 11%	760
	21st to end	Night	10% 4 16% 38% 24% 7%	760
December	1st to 10th	Night	12% 2 18% 40% 21% 7%	760
	11th to 20th	Night	16% 3 17% 42% 19% 4	760
	21st to end	Night	14% 4 18% 37% 20% 6%	836

Page generated at 2024-04-07 06:28:13. Version ac07

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