Astro-Physics
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Astro-Physics 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	14% 9% 4 7% 6% 3 5% 5% 5% 7% 36%	78410
	Night	14% 10% 4 7% 5% 3 4 4 5% 6% 37%	81060
Transparency	Day	47% 6% 13% 21% 11% 1	78111
	Night	47% 6% 12% 21% 13% 2	80880
Seeing	Day	17% 11% 29% 25% 14% 5%	14826
	Night	18% 9% 31% 30% 11% 1	24890

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	12% 14% 10% 12% 7% 3 5% 4 4 4 25%	2527
	11th to 20th	Day	12% 11% 7% 15% 5% 3 4 10% 7% 5% 19%	2530
	21st to end	Day	17% 18% 11% 10% 5% 2 4 3 4 5% 19%	2918
February	1st to 10th	Day	12% 14% 6% 7% 7% 4 6% 5% 5% 7% 27%	1710
	11th to 20th	Day	14% 10% 3 7% 7% 5% 5% 3 5% 6% 37%	1818
	21st to end	Day	14% 14% 4 9% 6% 3 5% 3 4 6% 32%	1570
March	1st to 10th	Day	14% 11% 5% 8% 7% 3 5% 5% 4 6% 33%	1800
	11th to 20th	Day	13% 9% 4 8% 5% 4 3 3 5% 8% 38%	1890
	21st to end	Day	21% 11% 4 7% 7% 3 5% 5% 5% 6% 26%	2361
April	1st to 10th	Day	18% 10% 5% 8% 5% 4 4 5% 4 6% 31%	2160
	11th to 20th	Day	18% 9% 4 6% 5% 3 4 5% 6% 6% 34%	2134
	21st to end	Day	21% 9% 3 7% 6% 3 4 3 5% 6% 32%	2222
May	1st to 10th	Day	18% 9% 4 7% 6% 4 5% 5% 5% 7% 30%	2366
	11th to 20th	Day	19% 8% 3 5% 5% 3 5% 5% 4 6% 35%	2479
	21st to end	Day	14% 7% 3 6% 6% 3 5% 6% 6% 8% 37%	2725
June	1st to 10th	Day	10% 5% 3 5% 6% 3 5% 5% 6% 9% 44%	2520
	11th to 20th	Day	11% 5% 2 4 5% 3 5% 5% 7% 8% 45%	2520
	21st to end	Day	12% 6% 3 5% 6% 3 5% 5% 7% 11% 36%	2520
July	1st to 10th	Day	7% 5% 2 5% 5% 3 5% 6% 7% 10% 46%	2520
	11th to 20th	Day	8% 4 2 5% 5% 3 5% 6% 7% 10% 44%	2520
	21st to end	Day	7% 5% 3 5% 5% 3 6% 6% 6% 10% 44%	2743
August	1st to 10th	Day	8% 4 2 5% 5% 4 6% 5% 8% 11% 42%	2475
	11th to 20th	Day	10% 5% 2 6% 6% 3 5% 5% 6% 8% 44%	2142
	21st to end	Day	10% 5% 3 5% 5% 3 5% 5% 6% 7% 49%	2376
September	1st to 10th	Day	13% 6% 2 5% 5% 3 4 3 5% 8% 46%	2160
	11th to 20th	Day	14% 3 1 4 4 2 4 4 5% 8% 51%	2084
	21st to end	Day	12% 6% 3 7% 5% 3 4 5% 5% 7% 44%	1980
October	1st to 10th	Day	14% 7% 2 6% 4 2 3 4 4 6% 46%	1868
	11th to 20th	Day	21% 10% 3 5% 5% 3 3 4 5% 6% 34%	1800
	21st to end	Day	20% 10% 3 6% 5% 3 3 3 4 5% 37%	1806
November	1st to 10th	Day	13% 8% 4 5% 4 2 4 5% 4 7% 45%	1672
	11th to 20th	Day	15% 11% 4 9% 6% 3 5% 5% 5% 6% 32%	1710
	21st to end	Day	17% 12% 4 7% 6% 2 3 2 4 6% 36%	1563
December	1st to 10th	Day	14% 13% 4 9% 7% 4 5% 5% 4 6% 30%	1520
	11th to 20th	Day	13% 13% 5% 9% 7% 3 6% 4 5% 6% 28%	1918
	21st to end	Day	20% 20% 10% 12% 7% 3 4 3 3 3 15%	2783
January	1st to 10th	Night	13% 13% 9% 11% 7% 3 3 3 3 4 31%	4428
	11th to 20th	Night	14% 16% 7% 12% 7% 3 3 8% 6% 4 20%	4440
	21st to end	Night	18% 18% 8% 10% 6% 3 4 4 3 6% 20%	4747
February	1st to 10th	Night	14% 14% 5% 8% 6% 4 4 3 4 5% 33%	2470
	11th to 20th	Night	13% 10% 4 6% 6% 4 4 4 4 6% 39%	2247
	21st to end	Night	17% 13% 4 7% 4 2 3 4 5% 5% 36%	1884
March	1st to 10th	Night	17% 9% 4 5% 5% 3 4 5% 5% 7% 35%	2167
	11th to 20th	Night	11% 8% 3 5% 6% 3 5% 5% 5% 8% 40%	2087
	21st to end	Night	21% 10% 4 7% 6% 4 4 4 4 6% 32%	1994
April	1st to 10th	Night	18% 9% 4 5% 5% 3 4 5% 4 5% 37%	1800
	11th to 20th	Night	19% 9% 3 6% 5% 3 4 3 4 6% 38%	1775
	21st to end	Night	18% 8% 2 5% 5% 3 5% 5% 5% 6% 37%	1738
May	1st to 10th	Night	15% 7% 3 5% 7% 3 6% 5% 5% 8% 36%	1592
	11th to 20th	Night	16% 7% 2 6% 5% 3 5% 5% 6% 7% 38%	1416
	21st to end	Night	12% 6% 2 5% 6% 3 4 5% 7% 9% 40%	1551
June	1st to 10th	Night	8% 4 1 5% 5% 3 6% 7% 6% 9% 47%	1440
	11th to 20th	Night	10% 6% 1 5% 4 2 4 5% 6% 9% 47%	1440
	21st to end	Night	9% 5% 3 5% 6% 3 5% 4 5% 8% 46%	1440
July	1st to 10th	Night	7% 4 2 5% 5% 2 4 5% 6% 10% 52%	1440
	11th to 20th	Night	8% 4 2 4 3 3 4 4 6% 9% 54%	1440
	21st to end	Night	6% 4 3 3 4 3 4 6% 7% 8% 51%	1575
August	1st to 10th	Night	4 3 2 5% 5% 4 5% 5% 6% 9% 53%	1460
	11th to 20th	Night	8% 3 1 4 4 3 4 4 6% 7% 55%	1759
	21st to end	Night	8% 4 2 4 5% 3 4 4 5% 8% 53%	1980
September	1st to 10th	Night	9% 6% 3 6% 4 2 3 3 5% 5% 55%	1800
	11th to 20th	Night	12% 4 2 4 4 3 4 4 5% 6% 54%	1857
	21st to end	Night	12% 6% 2 4 4 3 4 5% 5% 7% 49%	1980
October	1st to 10th	Night	12% 6% 3 5% 4 3 3 4 4 7% 49%	2089
	11th to 20th	Night	18% 7% 2 6% 4 2 3 4 4 6% 43%	2160
	21st to end	Night	20% 8% 3 6% 4 3 4 5% 5% 6% 37%	2549
November	1st to 10th	Night	12% 8% 3 5% 4 3 3 3 5% 5% 49%	2406
	11th to 20th	Night	15% 9% 4 7% 6% 3 4 5% 5% 6% 36%	2470
	21st to end	Night	18% 10% 4 6% 6% 2 4 3 4 6% 38%	2616
December	1st to 10th	Night	15% 12% 4 9% 6% 4 4 5% 4 6% 31%	2660
	11th to 20th	Night	15% 14% 4 8% 6% 3 4 4 5% 5% 31%	3279
	21st to end	Night	22% 16% 7% 9% 6% 3 5% 5% 4 5% 17%	4884

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	62% 5% 12% 15% 5%	2528
	11th to 20th	Day	60% 6% 14% 12% 7%	2530
	21st to end	Day	67% 5% 9% 13% 5%	2918
February	1st to 10th	Day	55% 6% 13% 16% 9% 1	1710
	11th to 20th	Day	49% 4 11% 24% 10% 1	1828
	21st to end	Day	54% 5% 8% 21% 10% 2	1570
March	1st to 10th	Day	52% 6% 14% 20% 8% 1	1800
	11th to 20th	Day	45% 5% 14% 23% 12% 1	1890
	21st to end	Day	58% 6% 11% 17% 7% 1	2361
April	1st to 10th	Day	55% 5% 10% 21% 9%	2160
	11th to 20th	Day	49% 7% 10% 21% 10% 2	2134
	21st to end	Day	52% 6% 12% 17% 12% 1	2222
May	1st to 10th	Day	52% 7% 12% 21% 6%	2366
	11th to 20th	Day	49% 6% 13% 21% 11%	2483
	21st to end	Day	45% 8% 13% 19% 14% 2	2725
June	1st to 10th	Day	37% 8% 14% 25% 16% 1	2520
	11th to 20th	Day	35% 8% 13% 24% 19% 2	2520
	21st to end	Day	40% 8% 16% 22% 13% 2	2520
July	1st to 10th	Day	31% 7% 16% 30% 12% 3	2451
	11th to 20th	Day	32% 9% 17% 24% 16% 2	2445
	21st to end	Day	33% 8% 17% 25% 15% 3	2591
August	1st to 10th	Day	33% 9% 16% 29% 12% 1	2460
	11th to 20th	Day	36% 7% 15% 27% 14% 1	2142
	21st to end	Day	33% 7% 12% 26% 19% 2	2376
September	1st to 10th	Day	37% 7% 10% 26% 18% 2	2160
	11th to 20th	Day	31% 6% 12% 32% 17% 2	2084
	21st to end	Day	38% 6% 10% 29% 16% 1	1980
October	1st to 10th	Day	39% 5% 12% 28% 15% 1	1868
	11th to 20th	Day	50% 5% 11% 21% 12% 1	1800
	21st to end	Day	50% 4 11% 22% 12% 1	1806
November	1st to 10th	Day	40% 6% 15% 24% 15% 1	1672
	11th to 20th	Day	53% 4 13% 20% 9% 1	1710
	21st to end	Day	51% 5% 13% 23% 8%	1563
December	1st to 10th	Day	56% 5% 14% 17% 8% 1	1520
	11th to 20th	Day	55% 5% 16% 15% 7% 2	1915
	21st to end	Day	75% 4 8% 8% 4	2783
January	1st to 10th	Night	58% 4 10% 18% 8% 1	4428
	11th to 20th	Night	65% 5% 10% 11% 8%	4440
	21st to end	Night	67% 4 10% 13% 5% 1	4747
February	1st to 10th	Night	54% 4 11% 18% 12% 1	2470
	11th to 20th	Night	47% 5% 12% 23% 14% 1	2248
	21st to end	Night	50% 5% 12% 19% 11% 4	1884
March	1st to 10th	Night	49% 6% 15% 20% 10% 1	2167
	11th to 20th	Night	42% 6% 12% 21% 16% 2	2087
	21st to end	Night	54% 5% 10% 19% 10% 1	1994
April	1st to 10th	Night	47% 6% 12% 20% 14% 2	1800
	11th to 20th	Night	48% 4 6% 21% 17% 4	1775
	21st to end	Night	45% 7% 12% 22% 11% 2	1738
May	1st to 10th	Night	45% 8% 13% 22% 12%	1592
	11th to 20th	Night	43% 8% 12% 22% 14% 2	1417
	21st to end	Night	39% 8% 14% 20% 17% 2	1552
June	1st to 10th	Night	30% 8% 16% 25% 19% 2	1440
	11th to 20th	Night	33% 7% 11% 23% 24% 3	1440
	21st to end	Night	36% 6% 15% 23% 18% 2	1440
July	1st to 10th	Night	27% 8% 16% 29% 17% 4	1400
	11th to 20th	Night	27% 6% 14% 30% 20% 2	1392
	21st to end	Night	26% 8% 16% 26% 18% 5%	1487
August	1st to 10th	Night	27% 7% 18% 30% 14% 3	1451
	11th to 20th	Night	27% 7% 15% 30% 20% 1	1759
	21st to end	Night	28% 7% 12% 27% 21% 4	1980
September	1st to 10th	Night	32% 6% 11% 25% 23% 3	1800
	11th to 20th	Night	31% 6% 10% 32% 19% 2	1857
	21st to end	Night	35% 6% 11% 30% 17% 2	1980
October	1st to 10th	Night	36% 6% 9% 28% 20% 2	2089
	11th to 20th	Night	42% 5% 11% 23% 17% 1	2160
	21st to end	Night	47% 5% 11% 23% 11% 1	2549
November	1st to 10th	Night	37% 5% 10% 27% 18% 3	2406
	11th to 20th	Night	48% 5% 14% 20% 12% 1	2470
	21st to end	Night	49% 5% 12% 23% 11% 1	2616
December	1st to 10th	Night	55% 6% 11% 19% 8% 1	2660
	11th to 20th	Night	54% 6% 13% 19% 8% 1	3281
	21st to end	Night	68% 6% 10% 12% 4	4884

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% 15% 31% 25% 9%	270
	11th to 20th	Day	21% 14% 38% 23% 3 1	270
	21st to end	Day	23% 11% 36% 26% 4 1	297
February	1st to 10th	Day	17% 20% 40% 18% 6%	270
	11th to 20th	Day	20% 20% 34% 21% 5%	270
	21st to end	Day	23% 20% 38% 17% 2	225
March	1st to 10th	Day	18% 22% 39% 15% 6%	240
	11th to 20th	Day	24% 17% 34% 16% 8% 2	240
	21st to end	Day	30% 15% 28% 19% 7% 2	447
April	1st to 10th	Day	25% 12% 35% 22% 5%	420
	11th to 20th	Day	21% 20% 27% 20% 9% 3	412
	21st to end	Day	25% 13% 29% 22% 10% 2	420
May	1st to 10th	Day	20% 16% 29% 24% 8% 3	449
	11th to 20th	Day	23% 10% 29% 24% 12% 2	625
	21st to end	Day	16% 10% 28% 23% 16% 7%	679
June	1st to 10th	Day	9% 7% 32% 29% 18% 5%	630
	11th to 20th	Day	13% 6% 31% 29% 16% 5%	630
	21st to end	Day	13% 8% 26% 33% 16% 4	630
July	1st to 10th	Day	10% 2 18% 31% 26% 14%	621
	11th to 20th	Day	10% 4 26% 31% 20% 9%	618
	21st to end	Day	8% 4 23% 37% 21% 7%	684
August	1st to 10th	Day	8% 3 20% 32% 26% 11%	626
	11th to 20th	Day	10% 5% 17% 27% 23% 18%	456
	21st to end	Day	12% 4 18% 32% 24% 11%	495
September	1st to 10th	Day	15% 8% 22% 26% 23% 7%	450
	11th to 20th	Day	12% 3 20% 31% 22% 11%	450
	21st to end	Day	14% 11% 25% 25% 17% 7%	450
October	1st to 10th	Day	16% 11% 28% 25% 17% 3	338
	11th to 20th	Day	24% 22% 29% 19% 6%	270
	21st to end	Day	29% 15% 29% 22% 5% 1	297
November	1st to 10th	Day	16% 16% 36% 20% 10% 3	270
	11th to 20th	Day	20% 17% 39% 16% 8%	270
	21st to end	Day	29% 9% 39% 17% 6%	270
December	1st to 10th	Day	17% 19% 40% 16% 5% 2	270
	11th to 20th	Day	18% 13% 38% 21% 9% 1	270
	21st to end	Day	26% 16% 40% 16% 1	297
January	1st to 10th	Night	19% 13% 36% 26% 5%	950
	11th to 20th	Night	21% 13% 36% 23% 5% 1	950
	21st to end	Night	20% 11% 35% 28% 6%	1045
February	1st to 10th	Night	23% 10% 39% 23% 5%	950
	11th to 20th	Night	19% 14% 36% 26% 5%	772
	21st to end	Night	23% 14% 38% 21% 4	628
March	1st to 10th	Night	21% 11% 36% 25% 6%	723
	11th to 20th	Night	17% 11% 34% 30% 8%	647
	21st to end	Night	24% 12% 29% 28% 6% 1	594
April	1st to 10th	Night	23% 12% 35% 25% 5%	540
	11th to 20th	Night	24% 11% 30% 27% 7%	533
	21st to end	Night	21% 8% 34% 29% 7%	540
May	1st to 10th	Night	17% 10% 34% 30% 8% 1	540
	11th to 20th	Night	18% 6% 32% 32% 11%	531
	21st to end	Night	14% 5% 29% 36% 16%	584
June	1st to 10th	Night	8% 4 28% 44% 15%	540
	11th to 20th	Night	12% 4 30% 40% 13% 1	540
	21st to end	Night	10% 4 28% 40% 17% 1	540
July	1st to 10th	Night	7% 2 16% 42% 30% 3	525
	11th to 20th	Night	8% 3 21% 42% 24% 1	522
	21st to end	Night	7% 2 19% 47% 23% 1	591
August	1st to 10th	Night	4 3 15% 46% 29% 3	537
	11th to 20th	Night	8% 3 13% 40% 31% 5%	534
	21st to end	Night	10% 2 16% 41% 28% 3	594
September	1st to 10th	Night	9% 5% 22% 35% 24% 4	540
	11th to 20th	Night	12% 4 22% 32% 27% 3	597
	21st to end	Night	13% 8% 26% 31% 20% 2	720
October	1st to 10th	Night	14% 6% 31% 32% 16% 2	720
	11th to 20th	Night	22% 12% 30% 27% 9%	720
	21st to end	Night	24% 11% 33% 24% 8%	792
November	1st to 10th	Night	16% 10% 40% 24% 10% 1	740
	11th to 20th	Night	20% 15% 35% 24% 6%	760
	21st to end	Night	22% 12% 34% 25% 7%	906
December	1st to 10th	Night	22% 12% 38% 21% 6%	950
	11th to 20th	Night	22% 11% 34% 26% 5% 1	950
	21st to end	Night	28% 12% 34% 22% 2	1045

Page generated at 2024-02-27 05:30:17. Version ac07

Copyright © 2024 Attilla Danko.