Angels Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Angels Observatory clear sky chart from 2005-11-06 to 2024-03-18.

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	16% 6% 3 5% 5% 3 5% 5% 6% 7% 38%	78594
	Night	17% 7% 3 5% 5% 3 4 4 5% 7% 41%	81181
Transparency	Day	30% 36% 8% 15% 9% 1	78300
	Night	30% 35% 8% 16% 10% 1	81009
Seeing	Day	20% 8% 24% 26% 15% 6%	14005
	Night	20% 5% 26% 36% 13% 1	23405

By Month

Percentage Cloud Cover NE (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	15% 8% 2 5% 5% 3 4 4 4 5% 44%	2517
	11th to 20th	Day	15% 11% 5% 7% 6% 4 5% 5% 5% 6% 30%	2529
	21st to end	Day	21% 10% 4 6% 5% 3 4 5% 5% 6% 33%	3124
February	1st to 10th	Day	17% 6% 3 7% 6% 3 5% 5% 6% 7% 36%	1710
	11th to 20th	Day	15% 7% 3 5% 6% 3 5% 5% 5% 7% 39%	1787
	21st to end	Day	19% 8% 4 7% 5% 3 5% 4 6% 4 36%	1570
March	1st to 10th	Day	15% 7% 3 5% 5% 4 5% 4 5% 7% 40%	1897
	11th to 20th	Day	14% 7% 2 5% 6% 4 5% 5% 6% 7% 38%	2053
	21st to end	Day	20% 8% 2 5% 4 3 5% 4 5% 7% 38%	2304
April	1st to 10th	Day	17% 7% 3 6% 5% 3 5% 5% 5% 7% 38%	2160
	11th to 20th	Day	17% 6% 2 6% 6% 3 4 4 5% 7% 39%	2134
	21st to end	Day	18% 5% 2 5% 6% 4 4 5% 6% 7% 38%	2160
May	1st to 10th	Day	22% 6% 3 5% 5% 3 5% 5% 6% 7% 34%	2355
	11th to 20th	Day	20% 7% 2 4 5% 3 6% 5% 5% 7% 36%	2478
	21st to end	Day	16% 6% 2 4 5% 3 4 5% 7% 9% 39%	2725
June	1st to 10th	Day	15% 5% 2 6% 5% 3 6% 6% 6% 9% 37%	2520
	11th to 20th	Day	15% 6% 2 5% 5% 4 6% 5% 7% 9% 35%	2520
	21st to end	Day	13% 5% 2 5% 5% 3 5% 5% 5% 9% 42%	2520
July	1st to 10th	Day	10% 6% 2 5% 6% 4 6% 5% 7% 10% 38%	2520
	11th to 20th	Day	11% 4 2 4 6% 4 6% 5% 8% 10% 41%	2520
	21st to end	Day	12% 6% 3 6% 6% 4 5% 6% 7% 9% 36%	2736
August	1st to 10th	Day	13% 6% 2 5% 6% 4 6% 7% 7% 8% 36%	2327
	11th to 20th	Day	12% 6% 3 7% 6% 4 5% 5% 6% 8% 39%	2148
	21st to end	Day	15% 6% 2 4 4 3 5% 5% 5% 8% 42%	2376
September	1st to 10th	Day	17% 5% 2 5% 5% 4 4 5% 4 8% 40%	2160
	11th to 20th	Day	14% 5% 2 4 4 2 4 5% 4 7% 50%	2134
	21st to end	Day	18% 6% 2 6% 4 3 4 5% 5% 6% 41%	1977
October	1st to 10th	Day	21% 6% 2 5% 4 2 4 4 6% 7% 40%	1800
	11th to 20th	Day	17% 5% 1 5% 4 3 4 4 5% 7% 44%	1800
	21st to end	Day	22% 6% 2 5% 4 3 5% 4 4 6% 38%	1900
November	1st to 10th	Day	15% 7% 2 4 4 2 3 2 4 5% 52%	1671
	11th to 20th	Day	19% 5% 1 4 4 3 5% 5% 5% 6% 44%	1710
	21st to end	Day	18% 6% 2 4 4 3 5% 4 5% 7% 42%	1554
December	1st to 10th	Day	20% 7% 3 7% 5% 3 5% 4 5% 7% 34%	1520
	11th to 20th	Day	21% 7% 2 4 4 3 4 5% 6% 6% 38%	1906
	21st to end	Day	20% 9% 4 8% 7% 4 5% 5% 5% 6% 27%	2772
January	1st to 10th	Night	16% 7% 2 5% 5% 3 4 4 5% 7% 42%	4429
	11th to 20th	Night	17% 9% 3 7% 5% 3 4 5% 6% 6% 36%	4426
	21st to end	Night	24% 10% 3 5% 4 2 4 4 4 5% 35%	4532
February	1st to 10th	Night	16% 8% 3 6% 4 3 4 4 5% 7% 40%	2470
	11th to 20th	Night	16% 7% 4 6% 5% 3 5% 5% 4 5% 39%	2278
	21st to end	Night	20% 6% 3 5% 4 3 4 5% 5% 5% 40%	1884
March	1st to 10th	Night	17% 5% 2 5% 4 2 3 5% 5% 6% 44%	2270
	11th to 20th	Night	17% 7% 3 5% 4 4 4 4 3 6% 44%	2071
	21st to end	Night	17% 7% 2 5% 5% 3 5% 4 5% 6% 40%	2050
April	1st to 10th	Night	17% 6% 3 6% 7% 3 5% 5% 5% 7% 38%	1800
	11th to 20th	Night	17% 6% 3 6% 5% 3 5% 4 5% 8% 40%	1775
	21st to end	Night	21% 5% 2 4 4 2 3 4 5% 6% 44%	1800
May	1st to 10th	Night	22% 8% 3 5% 5% 4 5% 5% 4 6% 34%	1617
	11th to 20th	Night	19% 6% 3 5% 4 3 4 5% 6% 7% 40%	1415
	21st to end	Night	16% 5% 2 6% 4 3 4 5% 5% 7% 42%	1550
June	1st to 10th	Night	17% 7% 2 4 5% 2 4 4 6% 7% 43%	1440
	11th to 20th	Night	13% 6% 2 5% 5% 2 4 6% 6% 8% 42%	1440
	21st to end	Night	13% 3 1 3 5% 3 5% 5% 6% 10% 45%	1440
July	1st to 10th	Night	12% 5% 2 5% 6% 3 6% 5% 6% 9% 40%	1440
	11th to 20th	Night	11% 4 2 4 6% 3 5% 5% 7% 9% 43%	1440
	21st to end	Night	11% 5% 2 4 4 2 6% 6% 6% 10% 43%	1578
August	1st to 10th	Night	12% 5% 2 5% 6% 3 5% 6% 6% 9% 41%	1611
	11th to 20th	Night	13% 7% 3 5% 6% 4 5% 5% 6% 8% 37%	1734
	21st to end	Night	14% 6% 2 5% 5% 3 4 5% 6% 9% 41%	1980
September	1st to 10th	Night	16% 6% 2 5% 5% 3 4 4 5% 6% 45%	1800
	11th to 20th	Night	14% 4 2 4 5% 2 4 3 4 7% 51%	1826
	21st to end	Night	18% 6% 2 5% 4 2 3 4 4 7% 46%	1980
October	1st to 10th	Night	23% 5% 3 4 3 2 4 4 4 6% 43%	2160
	11th to 20th	Night	17% 6% 1 4 4 2 3 4 4 6% 47%	2160
	21st to end	Night	22% 6% 2 4 3 2 3 4 5% 5% 44%	2454
November	1st to 10th	Night	13% 5% 2 4 4 2 5% 4 5% 5% 51%	2407
	11th to 20th	Night	18% 6% 3 4 4 2 3 4 4 5% 46%	2470
	21st to end	Night	15% 6% 2 5% 4 3 4 4 5% 7% 45%	2622
December	1st to 10th	Night	20% 7% 3 5% 4 4 5% 5% 5% 6% 36%	2660
	11th to 20th	Night	19% 7% 2 5% 4 3 4 5% 6% 6% 39%	3288
	21st to end	Night	21% 9% 3 6% 5% 3 4 4 4 6% 35%	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	32% 25% 11% 24% 7% 1	2518
	11th to 20th	Day	42% 26% 8% 15% 7% 1	2529
	21st to end	Day	43% 24% 10% 17% 6% 1	3124
February	1st to 10th	Day	30% 34% 9% 16% 10% 1	1710
	11th to 20th	Day	31% 36% 8% 15% 9% 1	1796
	21st to end	Day	35% 34% 6% 16% 8% 2	1570
March	1st to 10th	Day	29% 34% 9% 20% 7% 1	1900
	11th to 20th	Day	31% 35% 7% 15% 10% 2	2053
	21st to end	Day	32% 36% 6% 14% 10% 2	2304
April	1st to 10th	Day	29% 37% 6% 15% 10% 4	2160
	11th to 20th	Day	31% 35% 7% 14% 9% 3	2134
	21st to end	Day	27% 37% 7% 13% 11% 4	2160
May	1st to 10th	Day	31% 37% 6% 12% 11% 3	2355
	11th to 20th	Day	30% 39% 6% 13% 10% 3	2482
	21st to end	Day	26% 38% 9% 15% 11% 2	2725
June	1st to 10th	Day	27% 38% 11% 14% 8% 1	2520
	11th to 20th	Day	30% 39% 9% 15% 5% 2	2520
	21st to end	Day	27% 39% 10% 17% 7%	2520
July	1st to 10th	Day	28% 39% 8% 15% 9% 1	2450
	11th to 20th	Day	23% 38% 10% 18% 9% 1	2445
	21st to end	Day	28% 40% 7% 13% 11% 1	2583
August	1st to 10th	Day	29% 39% 9% 13% 10%	2314
	11th to 20th	Day	28% 36% 9% 14% 11% 1	2148
	21st to end	Day	31% 38% 6% 12% 11% 2	2376
September	1st to 10th	Day	29% 37% 6% 13% 13% 2	2160
	11th to 20th	Day	21% 36% 7% 17% 17% 2	2134
	21st to end	Day	31% 36% 5% 12% 14% 2	1977
October	1st to 10th	Day	28% 37% 8% 16% 11%	1800
	11th to 20th	Day	27% 37% 9% 18% 9% 1	1800
	21st to end	Day	32% 38% 6% 15% 8% 1	1900
November	1st to 10th	Day	21% 39% 8% 16% 14% 2	1671
	11th to 20th	Day	28% 40% 6% 17% 8% 1	1710
	21st to end	Day	27% 39% 10% 16% 7% 1	1554
December	1st to 10th	Day	31% 40% 10% 13% 5%	1520
	11th to 20th	Day	33% 32% 13% 16% 6%	1906
	21st to end	Day	45% 27% 11% 13% 4	2772
January	1st to 10th	Night	33% 26% 12% 23% 6% 1	4429
	11th to 20th	Night	37% 26% 10% 18% 7% 2	4426
	21st to end	Night	43% 23% 8% 18% 7%	4532
February	1st to 10th	Night	31% 35% 8% 16% 9% 1	2470
	11th to 20th	Night	31% 36% 7% 14% 9% 2	2280
	21st to end	Night	31% 34% 6% 17% 10% 2	1884
March	1st to 10th	Night	26% 35% 10% 18% 8% 1	2280
	11th to 20th	Night	32% 35% 7% 15% 9% 2	2072
	21st to end	Night	29% 37% 6% 13% 12% 3	2050
April	1st to 10th	Night	31% 37% 7% 12% 10% 3	1800
	11th to 20th	Night	31% 37% 6% 12% 13% 1	1775
	21st to end	Night	26% 37% 7% 14% 12% 3	1800
May	1st to 10th	Night	32% 38% 6% 11% 11% 2	1617
	11th to 20th	Night	28% 38% 7% 12% 13% 2	1416
	21st to end	Night	24% 40% 11% 13% 10% 3	1551
June	1st to 10th	Night	27% 38% 8% 14% 11% 1	1440
	11th to 20th	Night	25% 39% 11% 16% 7% 1	1440
	21st to end	Night	23% 39% 10% 20% 8%	1440
July	1st to 10th	Night	29% 41% 10% 12% 8% 1	1400
	11th to 20th	Night	24% 40% 10% 16% 9% 1	1392
	21st to end	Night	20% 41% 12% 14% 12% 1	1490
August	1st to 10th	Night	23% 40% 10% 15% 11% 1	1600
	11th to 20th	Night	29% 38% 9% 12% 11% 1	1734
	21st to end	Night	29% 39% 7% 12% 11% 1	1980
September	1st to 10th	Night	27% 36% 7% 15% 12% 2	1800
	11th to 20th	Night	23% 37% 6% 16% 17% 2	1826
	21st to end	Night	26% 37% 5% 16% 14% 1	1980
October	1st to 10th	Night	28% 37% 7% 17% 10% 1	2160
	11th to 20th	Night	28% 37% 8% 18% 8% 1	2160
	21st to end	Night	29% 37% 8% 16% 10% 1	2454
November	1st to 10th	Night	20% 41% 8% 14% 15% 2	2407
	11th to 20th	Night	26% 39% 7% 16% 10% 2	2470
	21st to end	Night	26% 39% 8% 18% 9%	2622
December	1st to 10th	Night	29% 40% 9% 15% 6% 1	2660
	11th to 20th	Night	31% 33% 9% 15% 11% 1	3288
	21st to end	Night	41% 26% 11% 17% 5%	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	25% 12% 31% 23% 7% 2	180
	11th to 20th	Day	23% 21% 33% 18% 4 1	184
	21st to end	Day	20% 11% 34% 24% 8% 3	297
February	1st to 10th	Day	23% 16% 33% 23% 4 1	270
	11th to 20th	Day	24% 10% 35% 27% 4 1	395
	21st to end	Day	27% 9% 29% 30% 5%	382
March	1st to 10th	Day	20% 16% 28% 28% 8% 1	460
	11th to 20th	Day	20% 13% 31% 27% 6% 2	449
	21st to end	Day	26% 13% 26% 23% 9% 3	462
April	1st to 10th	Day	21% 12% 32% 25% 9% 1	420
	11th to 20th	Day	20% 12% 29% 23% 11% 5%	412
	21st to end	Day	26% 10% 30% 20% 12% 2	420
May	1st to 10th	Day	31% 11% 24% 18% 11% 5%	423
	11th to 20th	Day	21% 7% 29% 26% 13% 4	447
	21st to end	Day	20% 4 18% 26% 23% 9%	485
June	1st to 10th	Day	17% 7% 23% 26% 20% 7%	450
	11th to 20th	Day	18% 6% 22% 26% 20% 7%	450
	21st to end	Day	17% 4 20% 29% 23% 6%	450
July	1st to 10th	Day	15% 2 15% 27% 26% 16%	445
	11th to 20th	Day	13% 2 13% 30% 28% 13%	444
	21st to end	Day	16% 2 20% 30% 24% 8%	488
August	1st to 10th	Day	14% 2 16% 29% 27% 12%	446
	11th to 20th	Day	15% 3 13% 34% 23% 12%	439
	21st to end	Day	15% 2 17% 29% 23% 14%	495
September	1st to 10th	Day	20% 4 18% 23% 23% 13%	450
	11th to 20th	Day	14% 3 18% 27% 21% 17%	450
	21st to end	Day	21% 6% 20% 28% 18% 8%	450
October	1st to 10th	Day	26% 5% 17% 23% 21% 8%	450
	11th to 20th	Day	17% 8% 30% 27% 15% 4	450
	21st to end	Day	25% 6% 32% 25% 11% 2	455
November	1st to 10th	Day	18% 8% 25% 29% 17% 4	365
	11th to 20th	Day	21% 13% 27% 29% 9% 1	370
	21st to end	Day	20% 10% 35% 26% 8% 1	214
December	1st to 10th	Day	24% 17% 32% 18% 8% 2	180
	11th to 20th	Day	24% 15% 28% 25% 7% 1	180
	21st to end	Day	27% 9% 30% 23% 8% 2	198
January	1st to 10th	Night	19% 7% 38% 31% 5%	760
	11th to 20th	Night	24% 7% 31% 32% 5%	760
	21st to end	Night	19% 5% 38% 35% 3	836
February	1st to 10th	Night	20% 5% 35% 37% 3	760
	11th to 20th	Night	20% 8% 43% 27% 2	743
	21st to end	Night	22% 8% 35% 31% 3	628
March	1st to 10th	Night	21% 6% 36% 32% 5%	760
	11th to 20th	Night	20% 7% 35% 32% 6%	752
	21st to end	Night	20% 5% 33% 33% 8% 1	792
April	1st to 10th	Night	20% 9% 37% 28% 6%	720
	11th to 20th	Night	19% 6% 32% 32% 10%	711
	21st to end	Night	23% 5% 27% 36% 8%	720
May	1st to 10th	Night	26% 6% 25% 34% 9% 1	537
	11th to 20th	Night	20% 3 27% 40% 10%	354
	21st to end	Night	17% 2 13% 46% 20% 1	389
June	1st to 10th	Night	18% 3 15% 42% 21% 1	360
	11th to 20th	Night	15% 2 17% 48% 17% 1	360
	21st to end	Night	13% 1 10% 54% 20%	360
July	1st to 10th	Night	15% 1 12% 44% 26% 3	350
	11th to 20th	Night	13% 2 11% 46% 27% 1	348
	21st to end	Night	13% 2 12% 47% 25% 1	398
August	1st to 10th	Night	13% 1 7% 46% 30% 3	537
	11th to 20th	Night	16% 2 8% 39% 32% 3	670
	21st to end	Night	17% 2 9% 40% 30% 3	792
September	1st to 10th	Night	20% 2 13% 38% 24% 3	720
	11th to 20th	Night	16% 2 10% 40% 27% 5%	720
	21st to end	Night	21% 3 15% 39% 21% 2	720
October	1st to 10th	Night	23% 3 19% 31% 20% 3	720
	11th to 20th	Night	20% 3 23% 40% 13% 1	720
	21st to end	Night	25% 3 27% 34% 10% 1	792
November	1st to 10th	Night	17% 4 27% 38% 14% 1	740
	11th to 20th	Night	20% 6% 30% 33% 11% 1	760
	21st to end	Night	17% 6% 31% 37% 8%	760
December	1st to 10th	Night	24% 5% 31% 33% 6% 1	760
	11th to 20th	Night	22% 5% 31% 36% 7%	760
	21st to end	Night	23% 6% 33% 36% 3	836

Page generated at 2024-03-15 14:01:40. Version ac07

Copyright © 2024 Attilla Danko.