Arnold
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Arnold clear sky chart from 2005-11-06 to 2024-03-01.

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% 5% 2 4 4 2 4 4 5% 7% 55%	78920
	Night	7% 5% 2 4 4 2 3 4 5% 7% 56%	80512
Transparency	Day	29% 5% 12% 27% 21% 6%	78637
	Night	29% 5% 12% 25% 22% 7%	80318
Seeing	Day	10% 7% 30% 33% 16% 3	14581
	Night	10% 8% 35% 36% 10% 1	24706

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	6% 9% 4 5% 4 3 4 4 5% 7% 49%	2538
	11th to 20th	Day	6% 8% 3 5% 5% 4 5% 6% 5% 6% 49%	2706
	21st to end	Day	7% 8% 3 6% 4 2 3 3 4 6% 55%	3135
February	1st to 10th	Day	7% 8% 5% 6% 5% 2 4 3 4 7% 50%	1866
	11th to 20th	Day	5% 5% 3 6% 7% 4 4 5% 5% 6% 52%	1849
	21st to end	Day	6% 6% 1 5% 5% 2 4 3 5% 5% 59%	1570
March	1st to 10th	Day	5% 6% 2 4 4 2 3 4 5% 8% 56%	1800
	11th to 20th	Day	11% 7% 3 5% 4 2 3 4 4 5% 53%	1966
	21st to end	Day	11% 7% 3 4 4 3 4 4 4 7% 50%	2178
April	1st to 10th	Day	9% 5% 2 5% 3 2 3 3 5% 6% 57%	2144
	11th to 20th	Day	10% 7% 2 5% 4 3 4 4 5% 7% 50%	2139
	21st to end	Day	12% 6% 2 4 5% 2 4 4 4 6% 50%	2340
May	1st to 10th	Day	11% 5% 2 4 4 3 4 5% 5% 7% 49%	2340
	11th to 20th	Day	11% 5% 2 4 4 2 4 4 6% 9% 49%	2302
	21st to end	Day	10% 4 2 5% 4 3 5% 5% 6% 9% 47%	2531
June	1st to 10th	Day	5% 2 2 3 4 2 4 4 5% 9% 60%	2357
	11th to 20th	Day	6% 3 2 3 4 3 4 4 5% 8% 59%	2520
	21st to end	Day	4 3 1 4 4 2 3 4 6% 8% 61%	2520
July	1st to 10th	Day	5% 3 2 4 4 3 5% 4 6% 9% 55%	2520
	11th to 20th	Day	3 2 1 3 3 2 4 5% 6% 9% 61%	2458
	21st to end	Day	5% 4 1 4 4 2 5% 5% 7% 10% 52%	2546
August	1st to 10th	Day	8% 3 2 4 4 3 5% 5% 6% 9% 51%	2328
	11th to 20th	Day	6% 3 2 4 4 3 4 5% 6% 8% 55%	2254
	21st to end	Day	6% 3 1 3 4 2 4 4 5% 7% 62%	2376
September	1st to 10th	Day	10% 4 1 4 3 2 4 3 4 6% 59%	2088
	11th to 20th	Day	8% 4 2 4 4 2 3 3 4 7% 59%	1980
	21st to end	Day	7% 3 1 3 3 2 3 4 5% 7% 61%	1980
October	1st to 10th	Day	14% 4 2 3 3 2 3 2 4 6% 56%	1980
	11th to 20th	Day	7% 3 1 3 2 2 2 3 4 5% 67%	1864
	21st to end	Day	8% 6% 2 3 3 2 3 3 3 5% 61%	1815
November	1st to 10th	Day	6% 3 1 3 3 2 3 3 4 6% 65%	1673
	11th to 20th	Day	5% 5% 2 3 3 2 3 3 4 5% 65%	1710
	21st to end	Day	10% 4 2 3 4 2 3 3 4 5% 61%	1710
December	1st to 10th	Day	6% 6% 3 3 4 2 5% 4 5% 8% 56%	1710
	11th to 20th	Day	7% 7% 2 5% 3 2 2 3 4 7% 58%	2161
	21st to end	Day	7% 14% 7% 7% 5% 2 4 3 4 5% 42%	2966
January	1st to 10th	Night	5% 8% 3 8% 7% 3 3 3 4 5% 51%	4417
	11th to 20th	Night	4 5% 2 5% 5% 4 4 4 4 6% 57%	4244
	21st to end	Night	8% 9% 3 6% 4 2 3 3 4 5% 54%	4532
February	1st to 10th	Night	8% 8% 4 7% 4 3 3 4 4 6% 50%	2328
	11th to 20th	Night	6% 5% 3 6% 6% 3 4 4 5% 7% 51%	2218
	21st to end	Night	5% 5% 3 5% 5% 2 4 4 3 5% 58%	1884
March	1st to 10th	Night	6% 5% 2 4 3 3 3 4 5% 8% 57%	2166
	11th to 20th	Night	10% 6% 3 3 4 2 4 4 5% 7% 54%	1993
	21st to end	Night	11% 6% 3 5% 4 3 5% 4 4 8% 47%	2178
April	1st to 10th	Night	9% 5% 2 4 4 2 3 5% 5% 8% 55%	1814
	11th to 20th	Night	11% 5% 2 6% 4 2 4 4 4 7% 50%	1767
	21st to end	Night	12% 4 2 3 4 2 4 4 5% 6% 54%	1620
May	1st to 10th	Night	11% 5% 3 5% 5% 3 5% 5% 5% 7% 47%	1620
	11th to 20th	Night	11% 4 1 3 3 2 3 4 5% 10% 53%	1593
	21st to end	Night	9% 4 2 4 5% 3 5% 6% 6% 9% 46%	1745
June	1st to 10th	Night	5% 2 1 4 4 2 3 5% 6% 13% 57%	1598
	11th to 20th	Night	6% 3 2 4 4 3 3 4 7% 8% 55%	1440
	21st to end	Night	4 3 2 3 4 2 5% 5% 6% 12% 55%	1440
July	1st to 10th	Night	7% 3 2 4 6% 3 5% 5% 7% 11% 49%	1440
	11th to 20th	Night	3 2 1 2 3 2 4 5% 6% 12% 59%	1500
	21st to end	Night	6% 3 2 4 4 3 5% 6% 6% 10% 50%	1772
August	1st to 10th	Night	5% 3 2 4 5% 3 5% 5% 7% 11% 48%	1611
	11th to 20th	Night	6% 4 1 4 4 3 4 5% 7% 8% 54%	1644
	21st to end	Night	4 3 1 4 4 2 4 4 6% 7% 62%	1980
September	1st to 10th	Night	7% 3 1 4 3 2 4 4 4 6% 62%	1871
	11th to 20th	Night	7% 4 1 4 2 2 3 3 4 6% 62%	1980
	21st to end	Night	7% 3 2 4 3 2 3 3 5% 6% 62%	1980
October	1st to 10th	Night	11% 4 2 3 3 1 2 3 4 7% 57%	1980
	11th to 20th	Night	7% 3 1 2 2 1 2 3 3 6% 68%	2077
	21st to end	Night	9% 4 1 3 3 2 2 3 3 4 65%	2538
November	1st to 10th	Night	4 3 1 3 2 2 3 3 4 6% 69%	2405
	11th to 20th	Night	6% 3 2 3 3 2 3 4 4 5% 67%	2470
	21st to end	Night	8% 5% 2 4 3 2 3 4 4 6% 59%	2470
December	1st to 10th	Night	6% 4 2 4 4 3 3 4 5% 7% 58%	2470
	11th to 20th	Night	7% 4 2 3 4 3 3 4 4 7% 60%	3036
	21st to end	Night	8% 12% 4 6% 4 3 3 4 4 6% 47%	4691

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	34% 5% 13% 27% 20% 2	2539
	11th to 20th	Day	35% 7% 14% 21% 17% 5%	2706
	21st to end	Day	32% 5% 14% 30% 16% 3	3135
February	1st to 10th	Day	36% 4 13% 25% 16% 6%	1866
	11th to 20th	Day	32% 5% 13% 24% 19% 7%	1859
	21st to end	Day	28% 3 10% 24% 24% 10%	1570
March	1st to 10th	Day	27% 4 11% 24% 25% 8%	1800
	11th to 20th	Day	34% 4 10% 21% 23% 7%	1966
	21st to end	Day	35% 7% 13% 25% 15% 4	2178
April	1st to 10th	Day	28% 5% 12% 24% 23% 9%	2144
	11th to 20th	Day	35% 5% 12% 26% 18% 5%	2142
	21st to end	Day	37% 4 10% 27% 19% 3	2340
May	1st to 10th	Day	36% 5% 11% 28% 16% 4	2340
	11th to 20th	Day	31% 7% 17% 29% 14% 1	2306
	21st to end	Day	34% 9% 17% 24% 13% 4	2531
June	1st to 10th	Day	22% 6% 18% 34% 16% 4	2357
	11th to 20th	Day	24% 6% 12% 28% 23% 8%	2520
	21st to end	Day	21% 6% 10% 29% 26% 8%	2520
July	1st to 10th	Day	26% 6% 12% 27% 24% 4	2451
	11th to 20th	Day	18% 6% 13% 28% 27% 7%	2383
	21st to end	Day	25% 7% 16% 33% 17% 1	2405
August	1st to 10th	Day	28% 9% 17% 28% 16% 3	2314
	11th to 20th	Day	26% 7% 13% 28% 20% 6%	2254
	21st to end	Day	22% 5% 11% 24% 28% 9%	2376
September	1st to 10th	Day	28% 4 9% 25% 23% 11%	2088
	11th to 20th	Day	26% 4 8% 26% 28% 8%	1980
	21st to end	Day	23% 5% 9% 29% 26% 8%	1980
October	1st to 10th	Day	30% 4 9% 24% 26% 6%	1980
	11th to 20th	Day	21% 3 8% 24% 30% 13%	1864
	21st to end	Day	27% 3 9% 25% 27% 9%	1815
November	1st to 10th	Day	22% 3 9% 27% 29% 10%	1673
	11th to 20th	Day	23% 3 8% 29% 30% 7%	1710
	21st to end	Day	28% 2 7% 25% 29% 9%	1710
December	1st to 10th	Day	28% 4 12% 28% 23% 4	1710
	11th to 20th	Day	28% 3 9% 36% 21% 3	2159
	21st to end	Day	46% 4 9% 21% 17% 3	2966
January	1st to 10th	Night	37% 4 11% 27% 18% 3	4417
	11th to 20th	Night	29% 4 15% 25% 21% 6%	4244
	21st to end	Night	34% 5% 12% 25% 21% 3	4532
February	1st to 10th	Night	37% 4 13% 22% 17% 7%	2328
	11th to 20th	Night	33% 6% 11% 25% 21% 5%	2218
	21st to end	Night	29% 4 7% 22% 25% 13%	1884
March	1st to 10th	Night	27% 3 11% 21% 27% 11%	2166
	11th to 20th	Night	31% 4 12% 21% 24% 8%	1993
	21st to end	Night	37% 6% 12% 25% 15% 4	2178
April	1st to 10th	Night	28% 5% 11% 22% 26% 7%	1814
	11th to 20th	Night	33% 5% 14% 25% 17% 6%	1767
	21st to end	Night	31% 6% 12% 25% 23% 4	1620
May	1st to 10th	Night	37% 7% 12% 21% 17% 6%	1620
	11th to 20th	Night	28% 6% 19% 27% 17% 3	1594
	21st to end	Night	34% 9% 20% 22% 12% 4	1746
June	1st to 10th	Night	20% 6% 19% 33% 17% 4	1598
	11th to 20th	Night	26% 6% 13% 25% 24% 5%	1440
	21st to end	Night	24% 7% 12% 27% 23% 8%	1440
July	1st to 10th	Night	28% 8% 11% 25% 23% 5%	1400
	11th to 20th	Night	17% 7% 16% 27% 25% 8%	1452
	21st to end	Night	29% 8% 12% 30% 18% 4	1673
August	1st to 10th	Night	29% 8% 16% 30% 14% 3	1601
	11th to 20th	Night	27% 6% 16% 27% 18% 5%	1644
	21st to end	Night	21% 6% 14% 25% 26% 9%	1980
September	1st to 10th	Night	24% 5% 10% 23% 27% 11%	1871
	11th to 20th	Night	24% 5% 8% 23% 30% 9%	1980
	21st to end	Night	24% 5% 8% 23% 30% 10%	1980
October	1st to 10th	Night	29% 3 10% 20% 29% 9%	1980
	11th to 20th	Night	20% 3 9% 22% 31% 15%	2077
	21st to end	Night	24% 3 8% 23% 28% 13%	2538
November	1st to 10th	Night	19% 3 9% 27% 28% 14%	2405
	11th to 20th	Night	21% 3 8% 29% 30% 10%	2470
	21st to end	Night	28% 3 8% 23% 25% 12%	2470
December	1st to 10th	Night	26% 4 12% 29% 22% 7%	2470
	11th to 20th	Night	26% 3 9% 35% 23% 4	3037
	21st to end	Night	39% 4 11% 27% 16% 3	4691

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	9% 8% 38% 33% 10% 3	270
	11th to 20th	Day	17% 8% 36% 32% 7% 1	270
	21st to end	Day	10% 8% 42% 30% 9%	297
February	1st to 10th	Day	15% 11% 42% 23% 9%	270
	11th to 20th	Day	10% 10% 43% 24% 10% 3	270
	21st to end	Day	7% 17% 48% 24% 4	225
March	1st to 10th	Day	10% 11% 43% 29% 6%	240
	11th to 20th	Day	18% 12% 30% 30% 8% 2	240
	21st to end	Day	17% 10% 45% 21% 6% 1	264
April	1st to 10th	Day	11% 16% 45% 22% 5% 1	404
	11th to 20th	Day	15% 16% 40% 22% 5% 1	420
	21st to end	Day	17% 12% 36% 25% 8% 1	600
May	1st to 10th	Day	14% 8% 34% 31% 12% 1	603
	11th to 20th	Day	16% 8% 30% 28% 14% 3	625
	21st to end	Day	12% 8% 34% 33% 12% 1	679
June	1st to 10th	Day	5% 5% 27% 37% 18% 8%	630
	11th to 20th	Day	7% 6% 31% 37% 18% 2	630
	21st to end	Day	7% 4 28% 40% 20% 2	630
July	1st to 10th	Day	6% 2 18% 41% 25% 7%	621
	11th to 20th	Day	4 1 17% 44% 28% 6%	618
	21st to end	Day	6% 1 11% 42% 33% 7%	684
August	1st to 10th	Day	8% 1 13% 40% 33% 5%	626
	11th to 20th	Day	7% 1 17% 45% 27% 3	568
	21st to end	Day	6% 2 19% 41% 25% 6%	495
September	1st to 10th	Day	10% 2 19% 41% 23% 4	378
	11th to 20th	Day	5% 4 24% 38% 21% 8%	270
	21st to end	Day	12% 7% 24% 34% 20% 4	270
October	1st to 10th	Day	20% 5% 24% 33% 13% 5%	270
	11th to 20th	Day	4 7% 43% 27% 14% 4	270
	21st to end	Day	16% 11% 30% 30% 11% 2	297
November	1st to 10th	Day	9% 11% 33% 32% 12% 4	270
	11th to 20th	Day	11% 9% 39% 26% 13% 2	270
	21st to end	Day	17% 10% 31% 29% 12% 1	270
December	1st to 10th	Day	9% 4 39% 31% 15% 2	270
	11th to 20th	Day	16% 11% 35% 28% 9% 1	270
	21st to end	Day	17% 13% 40% 24% 6%	297
January	1st to 10th	Night	8% 8% 38% 38% 7% 1	950
	11th to 20th	Night	10% 9% 38% 33% 9% 1	950
	21st to end	Night	8% 8% 41% 36% 7%	1045
February	1st to 10th	Night	12% 9% 41% 31% 7%	808
	11th to 20th	Night	9% 10% 45% 31% 6%	744
	21st to end	Night	8% 13% 44% 28% 6%	628
March	1st to 10th	Night	9% 14% 38% 33% 6%	722
	11th to 20th	Night	14% 10% 35% 32% 7% 1	553
	21st to end	Night	17% 12% 41% 26% 4	594
April	1st to 10th	Night	11% 13% 46% 27% 3	540
	11th to 20th	Night	16% 15% 40% 26% 4	533
	21st to end	Night	16% 13% 34% 30% 7% 1	540
May	1st to 10th	Night	13% 11% 39% 31% 6%	540
	11th to 20th	Night	14% 10% 35% 30% 10% 1	531
	21st to end	Night	10% 11% 40% 30% 9%	584
June	1st to 10th	Night	6% 7% 34% 36% 15% 1	540
	11th to 20th	Night	8% 5% 44% 34% 9%	540
	21st to end	Night	6% 4 34% 45% 11% 1	540
July	1st to 10th	Night	6% 1 29% 46% 17% 1	525
	11th to 20th	Night	4 25% 51% 19% 1	522
	21st to end	Night	7% 1 17% 51% 23% 1	591
August	1st to 10th	Night	7% 2 18% 50% 22% 1	537
	11th to 20th	Night	8% 1 23% 50% 18%	534
	21st to end	Night	4 1 26% 46% 21% 2	594
September	1st to 10th	Night	9% 2 26% 47% 14% 1	540
	11th to 20th	Night	10% 3 34% 38% 13% 2	540
	21st to end	Night	9% 5% 29% 42% 14% 1	540
October	1st to 10th	Night	14% 6% 32% 35% 13%	540
	11th to 20th	Night	9% 8% 37% 35% 10% 1	637
	21st to end	Night	12% 9% 32% 33% 13% 1	954
November	1st to 10th	Night	7% 8% 33% 43% 9% 1	925
	11th to 20th	Night	8% 9% 38% 36% 8% 1	950
	21st to end	Night	12% 8% 31% 37% 11% 2	950
December	1st to 10th	Night	10% 8% 37% 38% 7%	950
	11th to 20th	Night	11% 11% 37% 33% 8%	950
	21st to end	Night	13% 10% 36% 34% 7%	1045

Page generated at 2024-02-27 05:30:18. Version ac07

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