Farpoint Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Farpoint Observatory clear sky chart from 2005-11-06 to 2024-01-13.

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	11% 6% 3 5% 5% 3 4 4 5% 7% 46%	74543
	Night	10% 6% 3 5% 4 2 4 4 5% 7% 51%	75192
Transparency	Day	36% 7% 12% 25% 17% 3	74267
	Night	34% 6% 12% 26% 19% 4	74988
Seeing	Day	13% 10% 30% 29% 15% 3	14487
	Night	13% 10% 34% 32% 11% 1	24481

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	10% 7% 3 6% 5% 2 4 4 5% 6% 47%	1707
	11th to 20th	Day	11% 8% 4 7% 5% 4 3 3 5% 6% 45%	1638
	21st to end	Day	8% 7% 4 9% 5% 3 3 4 5% 7% 43%	1782
February	1st to 10th	Day	12% 9% 5% 7% 6% 3 4 3 4 6% 41%	1620
	11th to 20th	Day	10% 7% 3 9% 5% 3 5% 4 6% 6% 42%	1642
	21st to end	Day	10% 10% 3 5% 5% 3 4 5% 4 7% 45%	1480
March	1st to 10th	Day	10% 7% 3 6% 5% 3 4 4 6% 7% 45%	1980
	11th to 20th	Day	18% 10% 3 5% 4 2 3 3 4 6% 42%	1980
	21st to end	Day	16% 11% 3 6% 6% 3 5% 4 5% 6% 34%	2178
April	1st to 10th	Day	14% 5% 3 5% 4 2 3 5% 6% 6% 48%	2016
	11th to 20th	Day	13% 7% 3 6% 5% 3 4 5% 5% 7% 41%	2174
	21st to end	Day	17% 6% 3 6% 6% 4 4 4 5% 6% 39%	2340
May	1st to 10th	Day	17% 8% 3 6% 5% 3 4 4 5% 6% 39%	2340
	11th to 20th	Day	15% 6% 2 5% 5% 3 5% 5% 6% 7% 42%	2302
	21st to end	Day	14% 7% 4 6% 5% 4 6% 5% 6% 8% 35%	2531
June	1st to 10th	Day	6% 4 2 3 4 3 5% 4 7% 10% 52%	2340
	11th to 20th	Day	7% 4 3 4 5% 3 5% 5% 5% 7% 51%	2340
	21st to end	Day	7% 3 2 4 4 3 5% 5% 6% 8% 54%	2340
July	1st to 10th	Day	10% 4 2 4 5% 3 5% 6% 7% 9% 44%	2340
	11th to 20th	Day	4 3 1 4 5% 2 4 6% 7% 8% 56%	2340
	21st to end	Day	8% 5% 2 4 5% 3 5% 5% 6% 9% 47%	2546
August	1st to 10th	Day	8% 5% 2 5% 5% 3 5% 6% 6% 9% 46%	2328
	11th to 20th	Day	7% 4 2 4 5% 3 5% 6% 6% 7% 52%	2301
	21st to end	Day	8% 4 2 4 4 3 4 5% 5% 8% 55%	2494
September	1st to 10th	Day	13% 4 2 4 4 2 4 4 4 7% 52%	2069
	11th to 20th	Day	10% 4 2 5% 5% 3 5% 5% 4 7% 50%	1980
	21st to end	Day	8% 4 1 5% 4 3 4 5% 5% 6% 55%	1980
October	1st to 10th	Day	10% 5% 2 5% 4 3 3 4 5% 7% 52%	1849
	11th to 20th	Day	10% 6% 2 4 4 2 3 3 3 5% 59%	1800
	21st to end	Day	14% 6% 2 4 4 2 3 4 5% 5% 51%	1980
November	1st to 10th	Day	7% 4 2 3 3 3 4 4 5% 8% 56%	1773
	11th to 20th	Day	10% 5% 2 4 3 3 3 4 5% 5% 57%	1710
	21st to end	Day	14% 6% 3 4 3 2 3 3 4 6% 53%	1641
December	1st to 10th	Day	10% 6% 3 4 5% 3 4 4 6% 8% 48%	1520
	11th to 20th	Day	10% 7% 4 7% 6% 4 6% 4 4 6% 44%	2027
	21st to end	Day	12% 11% 7% 15% 7% 3 4 3 4 7% 26%	3135
January	1st to 10th	Night	7% 7% 3 6% 5% 3 4 4 5% 6% 50%	2458
	11th to 20th	Night	9% 8% 4 6% 4 2 4 4 4 7% 46%	2367
	21st to end	Night	8% 7% 4 6% 5% 3 4 4 4 5% 49%	2574
February	1st to 10th	Night	9% 11% 4 6% 5% 3 4 4 5% 6% 42%	2340
	11th to 20th	Night	12% 7% 3 6% 5% 3 5% 4 5% 6% 45%	2219
	21st to end	Night	10% 7% 3 4 5% 3 5% 4 4 5% 49%	1774
March	1st to 10th	Night	9% 7% 3 4 5% 2 5% 4 5% 7% 50%	1980
	11th to 20th	Night	14% 7% 2 5% 3 2 4 4 4 6% 46%	1980
	21st to end	Night	19% 9% 3 6% 4 3 4 3 4 7% 37%	2178
April	1st to 10th	Night	10% 4 2 5% 4 2 4 4 4 7% 53%	1944
	11th to 20th	Night	13% 8% 2 5% 5% 2 4 4 4 7% 47%	1733
	21st to end	Night	16% 6% 2 4 4 2 5% 4 5% 6% 46%	1620
May	1st to 10th	Night	15% 7% 2 6% 4 2 5% 4 6% 7% 41%	1620
	11th to 20th	Night	12% 6% 2 4 4 3 4 4 5% 7% 49%	1593
	21st to end	Night	9% 6% 2 5% 5% 2 5% 5% 6% 10% 46%	1745
June	1st to 10th	Night	5% 2 1 3 5% 2 3 4 7% 10% 57%	1620
	11th to 20th	Night	6% 2 2 4 4 3 5% 5% 7% 10% 53%	1620
	21st to end	Night	6% 2 1 3 3 2 4 4 6% 8% 60%	1620
July	1st to 10th	Night	8% 4 2 3 4 3 5% 5% 6% 7% 54%	1620
	11th to 20th	Night	2 2 1 2 2 2 4 5% 6% 10% 61%	1620
	21st to end	Night	7% 3 2 5% 4 3 4 5% 6% 10% 50%	1772
August	1st to 10th	Night	4 2 1 4 4 4 6% 5% 6% 10% 53%	1611
	11th to 20th	Night	6% 4 2 4 5% 3 4 4 5% 8% 56%	1600
	21st to end	Night	5% 3 2 3 4 2 4 3 5% 7% 62%	1862
September	1st to 10th	Night	11% 4 1 4 4 2 2 4 5% 6% 57%	1888
	11th to 20th	Night	8% 5% 1 4 4 2 5% 4 5% 7% 55%	1980
	21st to end	Night	7% 3 2 4 4 2 3 4 5% 6% 60%	1980
October	1st to 10th	Night	11% 5% 2 4 4 2 4 3 4 7% 54%	2092
	11th to 20th	Night	12% 5% 2 3 3 2 3 3 4 5% 59%	2160
	21st to end	Night	13% 7% 2 4 3 3 3 3 3 5% 54%	2376
November	1st to 10th	Night	7% 4 1 4 3 2 3 4 3 5% 62%	2301
	11th to 20th	Night	8% 5% 3 4 4 2 4 4 4 6% 57%	2470
	21st to end	Night	12% 5% 2 4 3 2 3 3 4 5% 55%	2531
December	1st to 10th	Night	8% 7% 3 5% 5% 3 5% 4 6% 6% 49%	2660
	11th to 20th	Night	9% 8% 3 5% 5% 2 4 4 5% 6% 48%	3152
	21st to end	Night	16% 11% 7% 9% 6% 3 3 4 3 5% 34%	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	37% 5% 13% 26% 17% 2	1708
	11th to 20th	Day	41% 5% 13% 24% 14% 1	1638
	21st to end	Day	40% 6% 17% 25% 12% 1	1782
February	1st to 10th	Day	46% 4 13% 23% 10% 3	1620
	11th to 20th	Day	42% 6% 12% 25% 13% 3	1651
	21st to end	Day	38% 6% 10% 25% 17% 4	1480
March	1st to 10th	Day	39% 6% 11% 23% 18% 4	1980
	11th to 20th	Day	46% 4 10% 22% 16% 3	1980
	21st to end	Day	51% 6% 14% 19% 8% 2	2178
April	1st to 10th	Day	36% 6% 13% 24% 19% 3	2016
	11th to 20th	Day	42% 6% 12% 22% 16% 1	2174
	21st to end	Day	45% 7% 10% 26% 12% 1	2340
May	1st to 10th	Day	46% 7% 12% 20% 14% 1	2340
	11th to 20th	Day	40% 8% 14% 25% 13%	2306
	21st to end	Day	45% 9% 15% 20% 9% 2	2531
June	1st to 10th	Day	25% 10% 16% 31% 15% 2	2340
	11th to 20th	Day	31% 8% 12% 28% 19% 2	2340
	21st to end	Day	26% 7% 15% 29% 18% 4	2340
July	1st to 10th	Day	32% 10% 14% 26% 15% 4	2276
	11th to 20th	Day	23% 8% 17% 26% 20% 5%	2271
	21st to end	Day	30% 8% 15% 31% 15% 1	2405
August	1st to 10th	Day	31% 10% 16% 27% 15% 2	2314
	11th to 20th	Day	29% 7% 12% 31% 18% 3	2301
	21st to end	Day	27% 7% 11% 26% 22% 7%	2494
September	1st to 10th	Day	31% 6% 13% 25% 18% 7%	2069
	11th to 20th	Day	33% 7% 11% 25% 21% 3	1980
	21st to end	Day	29% 7% 9% 28% 25% 3	1980
October	1st to 10th	Day	32% 6% 11% 26% 22% 3	1849
	11th to 20th	Day	30% 4 7% 24% 28% 6%	1800
	21st to end	Day	35% 5% 11% 22% 20% 7%	1980
November	1st to 10th	Day	27% 6% 13% 29% 20% 6%	1773
	11th to 20th	Day	30% 5% 10% 27% 24% 4	1710
	21st to end	Day	35% 4 10% 26% 23% 2	1641
December	1st to 10th	Day	34% 6% 14% 30% 15% 1	1520
	11th to 20th	Day	42% 5% 10% 26% 15% 1	2025
	21st to end	Day	58% 6% 9% 18% 8% 1	3135
January	1st to 10th	Night	34% 5% 14% 26% 18% 3	2458
	11th to 20th	Night	39% 5% 13% 25% 17% 1	2367
	21st to end	Night	37% 6% 15% 25% 14% 3	2574
February	1st to 10th	Night	43% 6% 12% 22% 14% 4	2340
	11th to 20th	Night	40% 5% 11% 25% 15% 3	2220
	21st to end	Night	37% 5% 10% 22% 19% 7%	1774
March	1st to 10th	Night	35% 5% 11% 24% 20% 6%	1980
	11th to 20th	Night	39% 5% 12% 23% 16% 5%	1980
	21st to end	Night	48% 6% 12% 19% 13% 2	2178
April	1st to 10th	Night	32% 5% 12% 24% 23% 4	1944
	11th to 20th	Night	37% 5% 11% 26% 18% 3	1733
	21st to end	Night	39% 6% 13% 24% 16% 2	1620
May	1st to 10th	Night	42% 8% 14% 19% 16% 2	1620
	11th to 20th	Night	35% 7% 15% 25% 18% 1	1594
	21st to end	Night	33% 8% 20% 24% 12% 2	1746
June	1st to 10th	Night	22% 8% 19% 33% 16% 3	1620
	11th to 20th	Night	25% 8% 14% 32% 17% 3	1620
	21st to end	Night	20% 6% 14% 35% 20% 4	1620
July	1st to 10th	Night	27% 7% 16% 28% 17% 4	1575
	11th to 20th	Night	16% 8% 16% 32% 23% 5%	1566
	21st to end	Night	28% 7% 14% 31% 19% 1	1673
August	1st to 10th	Night	24% 8% 18% 32% 14% 3	1601
	11th to 20th	Night	26% 7% 11% 31% 23% 2	1600
	21st to end	Night	22% 6% 12% 28% 25% 7%	1862
September	1st to 10th	Night	28% 5% 12% 27% 19% 8%	1888
	11th to 20th	Night	28% 5% 11% 26% 24% 5%	1980
	21st to end	Night	25% 6% 8% 26% 30% 5%	1980
October	1st to 10th	Night	31% 5% 10% 24% 24% 6%	2092
	11th to 20th	Night	29% 4 6% 28% 25% 8%	2160
	21st to end	Night	33% 5% 9% 21% 26% 5%	2376
November	1st to 10th	Night	26% 5% 10% 28% 24% 8%	2301
	11th to 20th	Night	28% 5% 10% 28% 25% 4	2470
	21st to end	Night	32% 4 11% 28% 21% 4	2531
December	1st to 10th	Night	35% 5% 13% 28% 18% 1	2660
	11th to 20th	Night	37% 5% 10% 29% 17% 2	3153
	21st to end	Night	54% 5% 9% 21% 9% 2	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	18% 16% 34% 23% 9%	270
	11th to 20th	Day	23% 17% 41% 17% 2	246
	21st to end	Day	10% 14% 51% 22% 2	264
February	1st to 10th	Day	20% 18% 40% 17% 3	240
	11th to 20th	Day	18% 16% 45% 15% 6%	240
	21st to end	Day	19% 22% 42% 13% 4 1	198
March	1st to 10th	Day	14% 18% 45% 20% 3	240
	11th to 20th	Day	27% 12% 38% 18% 6%	240
	21st to end	Day	26% 19% 41% 12% 2	264
April	1st to 10th	Day	19% 20% 34% 20% 6%	276
	11th to 20th	Day	18% 16% 38% 21% 5% 1	452
	21st to end	Day	21% 17% 35% 18% 9% 1	600
May	1st to 10th	Day	19% 14% 36% 21% 9% 1	603
	11th to 20th	Day	20% 11% 28% 27% 12% 2	625
	21st to end	Day	17% 9% 31% 25% 15% 3	679
June	1st to 10th	Day	5% 4 24% 36% 24% 6%	630
	11th to 20th	Day	8% 4 29% 38% 16% 4	630
	21st to end	Day	7% 8% 35% 36% 13% 1	630
July	1st to 10th	Day	10% 3 16% 34% 28% 9%	621
	11th to 20th	Day	3 2 19% 45% 24% 8%	618
	21st to end	Day	8% 2 18% 39% 29% 4	684
August	1st to 10th	Day	9% 2 19% 37% 29% 3	626
	11th to 20th	Day	8% 2 17% 44% 24% 4	615
	21st to end	Day	10% 3 14% 35% 32% 7%	613
September	1st to 10th	Day	14% 1 19% 38% 23% 4	359
	11th to 20th	Day	7% 2 26% 36% 26% 3	270
	21st to end	Day	11% 7% 31% 34% 14% 2	270
October	1st to 10th	Day	14% 7% 32% 26% 14% 7%	270
	11th to 20th	Day	9% 20% 42% 21% 8%	270
	21st to end	Day	22% 17% 32% 22% 6% 1	297
November	1st to 10th	Day	13% 13% 37% 29% 7% 2	270
	11th to 20th	Day	15% 16% 37% 23% 7% 2	270
	21st to end	Day	20% 13% 39% 19% 10%	270
December	1st to 10th	Day	10% 13% 41% 26% 7% 2	270
	11th to 20th	Day	15% 17% 40% 21% 7% 1	270
	21st to end	Day	19% 19% 41% 20% 1	297
January	1st to 10th	Night	11% 14% 39% 29% 7%	950
	11th to 20th	Night	15% 13% 39% 27% 6% 1	911
	21st to end	Night	12% 13% 42% 28% 5%	990
February	1st to 10th	Night	16% 13% 43% 25% 3	900
	11th to 20th	Night	16% 13% 40% 28% 3	825
	21st to end	Night	13% 16% 43% 22% 5%	590
March	1st to 10th	Night	12% 14% 44% 25% 5%	540
	11th to 20th	Night	18% 12% 38% 27% 5% 1	540
	21st to end	Night	25% 13% 36% 22% 4	594
April	1st to 10th	Night	12% 16% 42% 24% 6%	540
	11th to 20th	Night	18% 14% 36% 27% 4	533
	21st to end	Night	19% 12% 39% 24% 6% 1	540
May	1st to 10th	Night	18% 9% 34% 33% 6% 1	540
	11th to 20th	Night	15% 10% 31% 33% 10%	531
	21st to end	Night	11% 9% 30% 32% 16% 2	584
June	1st to 10th	Night	5% 3 26% 42% 23% 2	540
	11th to 20th	Night	6% 3 30% 44% 17%	540
	21st to end	Night	5% 5% 34% 44% 11% 1	540
July	1st to 10th	Night	8% 2 15% 46% 28% 1	525
	11th to 20th	Night	3 2 18% 49% 25% 2	522
	21st to end	Night	8% 2 16% 47% 27% 1	591
August	1st to 10th	Night	5% 1 19% 47% 26% 2	537
	11th to 20th	Night	6% 3 15% 48% 27% 1	534
	21st to end	Night	6% 1 16% 43% 31% 2	594
September	1st to 10th	Night	13% 3 22% 40% 18% 3	540
	11th to 20th	Night	10% 2 26% 38% 22% 2	540
	21st to end	Night	9% 4 27% 41% 19% 1	540
October	1st to 10th	Night	14% 5% 28% 36% 16% 1	652
	11th to 20th	Night	15% 9% 41% 26% 8%	720
	21st to end	Night	18% 11% 35% 26% 9% 1	792
November	1st to 10th	Night	9% 10% 36% 32% 11% 1	821
	11th to 20th	Night	11% 14% 39% 29% 7%	950
	21st to end	Night	15% 10% 37% 31% 7%	950
December	1st to 10th	Night	13% 13% 38% 29% 6% 1	950
	11th to 20th	Night	16% 11% 40% 29% 4	950
	21st to end	Night	17% 15% 37% 27% 3	1045

Page generated at 2024-01-10 00:25:02. Version ac07

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