Averted Vision Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Averted Vision Observatory 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	16% 8% 3 6% 6% 3 5% 5% 5% 7% 35%	78323
	Night	17% 8% 3 6% 6% 3 5% 4 5% 6% 35%	81076
Transparency	Day	48% 9% 13% 19% 10% 1	78028
	Night	50% 8% 13% 18% 10% 1	80905
Seeing	Day	21% 16% 30% 22% 9% 3	13813
	Night	20% 12% 30% 28% 8% 1	23018

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	13% 11% 5% 9% 7% 4 5% 5% 6% 6% 31%	2517
	11th to 20th	Day	16% 13% 6% 10% 8% 4 5% 5% 5% 5% 23%	2520
	21st to end	Day	16% 12% 5% 9% 8% 4 5% 5% 6% 5% 24%	2833
February	1st to 10th	Day	13% 12% 5% 8% 7% 4 5% 6% 5% 6% 29%	1710
	11th to 20th	Day	12% 12% 5% 10% 7% 4 6% 5% 5% 6% 29%	1816
	21st to end	Day	19% 11% 5% 6% 6% 3 5% 4 4 5% 32%	1570
March	1st to 10th	Day	14% 8% 5% 8% 7% 4 5% 4 4 7% 34%	1797
	11th to 20th	Day	17% 10% 4 7% 5% 4 4 4 5% 6% 34%	1865
	21st to end	Day	18% 10% 3 7% 6% 3 4 4 4 4 37%	2374
April	1st to 10th	Day	18% 8% 3 7% 5% 3 5% 4 4 5% 37%	2160
	11th to 20th	Day	15% 6% 3 7% 6% 4 5% 4 5% 6% 38%	2134
	21st to end	Day	21% 7% 3 6% 6% 4 5% 5% 5% 6% 32%	2256
May	1st to 10th	Day	22% 8% 4 5% 5% 3 4 4 5% 6% 34%	2392
	11th to 20th	Day	17% 6% 3 6% 5% 3 5% 4 5% 7% 39%	2478
	21st to end	Day	14% 5% 3 5% 6% 3 5% 5% 6% 7% 40%	2725
June	1st to 10th	Day	15% 6% 4 6% 7% 4 5% 5% 6% 9% 33%	2520
	11th to 20th	Day	18% 5% 2 5% 5% 3 6% 6% 6% 8% 36%	2520
	21st to end	Day	16% 5% 3 6% 6% 3 6% 6% 6% 8% 34%	2520
July	1st to 10th	Day	12% 6% 3 5% 5% 4 5% 7% 7% 9% 38%	2520
	11th to 20th	Day	11% 5% 2 5% 6% 4 5% 7% 8% 9% 39%	2520
	21st to end	Day	13% 5% 2 5% 6% 4 5% 6% 7% 9% 36%	2744
August	1st to 10th	Day	11% 4 2 6% 6% 4 6% 6% 7% 9% 39%	2506
	11th to 20th	Day	12% 5% 3 5% 6% 3 6% 7% 7% 10% 36%	2147
	21st to end	Day	12% 4 2 5% 6% 3 5% 5% 6% 8% 43%	2376
September	1st to 10th	Day	13% 5% 2 4 5% 4 5% 5% 6% 7% 45%	2160
	11th to 20th	Day	15% 5% 1 4 4 3 4 4 4 7% 49%	2075
	21st to end	Day	16% 5% 2 4 5% 3 4 5% 6% 7% 42%	1980
October	1st to 10th	Day	21% 8% 3 7% 7% 3 5% 4 5% 5% 33%	1882
	11th to 20th	Day	15% 6% 3 6% 7% 3 4 5% 5% 7% 39%	1796
	21st to end	Day	25% 7% 3 7% 5% 3 6% 4 5% 6% 28%	1782
November	1st to 10th	Day	13% 7% 3 6% 6% 3 4 4 5% 7% 41%	1671
	11th to 20th	Day	17% 8% 4 6% 6% 3 5% 4 6% 7% 37%	1710
	21st to end	Day	18% 8% 3 6% 6% 4 5% 5% 6% 7% 33%	1549
December	1st to 10th	Day	20% 12% 6% 8% 6% 4 5% 4 4 6% 26%	1520
	11th to 20th	Day	22% 9% 3 6% 6% 3 4 3 5% 5% 32%	1906
	21st to end	Day	25% 17% 5% 9% 5% 3 3 3 3 5% 22%	2772
January	1st to 10th	Night	16% 11% 4 8% 6% 3 4 4 4 6% 34%	4429
	11th to 20th	Night	13% 10% 5% 10% 9% 5% 6% 5% 5% 6% 25%	4440
	21st to end	Night	22% 12% 4 8% 7% 3 5% 4 4 4 27%	4820
February	1st to 10th	Night	14% 11% 4 8% 8% 4 6% 5% 6% 7% 28%	2470
	11th to 20th	Night	11% 11% 4 9% 6% 4 5% 5% 6% 6% 34%	2248
	21st to end	Night	17% 9% 3 8% 6% 3 5% 6% 5% 6% 32%	1884
March	1st to 10th	Night	16% 9% 4 7% 7% 3 6% 5% 5% 5% 34%	2157
	11th to 20th	Night	17% 9% 4 6% 5% 3 5% 5% 5% 5% 35%	2092
	21st to end	Night	17% 9% 3 7% 5% 3 4 3 5% 6% 39%	1980
April	1st to 10th	Night	20% 7% 3 6% 5% 3 5% 4 5% 6% 37%	1800
	11th to 20th	Night	18% 7% 4 6% 5% 3 4 4 5% 6% 37%	1775
	21st to end	Night	21% 7% 2 6% 4 3 4 4 5% 5% 38%	1702
May	1st to 10th	Night	22% 8% 3 8% 6% 2 4 4 4 6% 33%	1584
	11th to 20th	Night	17% 7% 4 5% 4 3 5% 3 5% 6% 40%	1415
	21st to end	Night	14% 4 3 6% 5% 4 5% 5% 5% 7% 41%	1550
June	1st to 10th	Night	19% 4 2 5% 5% 4 5% 6% 7% 7% 37%	1440
	11th to 20th	Night	19% 5% 2 4 4 3 5% 4 5% 8% 41%	1440
	21st to end	Night	14% 5% 2 5% 5% 3 5% 6% 5% 8% 41%	1440
July	1st to 10th	Night	13% 5% 2 5% 6% 3 6% 4 6% 9% 41%	1440
	11th to 20th	Night	14% 4 2 4 5% 3 5% 5% 6% 9% 43%	1440
	21st to end	Night	11% 5% 2 5% 5% 3 4 6% 6% 8% 45%	1574
August	1st to 10th	Night	10% 5% 2 5% 5% 3 4 4 6% 10% 46%	1432
	11th to 20th	Night	13% 6% 2 5% 5% 4 5% 5% 7% 8% 39%	1730
	21st to end	Night	15% 5% 2 4 4 3 4 4 5% 9% 45%	1980
September	1st to 10th	Night	13% 6% 2 5% 5% 3 3 5% 6% 7% 45%	1800
	11th to 20th	Night	14% 5% 2 4 4 2 4 3 5% 6% 51%	1885
	21st to end	Night	15% 5% 2 4 6% 3 5% 4 5% 6% 45%	1980
October	1st to 10th	Night	21% 6% 3 7% 7% 4 4 4 5% 5% 35%	2074
	11th to 20th	Night	16% 6% 2 6% 7% 3 5% 6% 5% 6% 39%	2164
	21st to end	Night	24% 7% 3 6% 5% 3 4 5% 5% 6% 31%	2574
November	1st to 10th	Night	14% 9% 3 6% 6% 3 4 4 5% 5% 41%	2407
	11th to 20th	Night	19% 6% 3 6% 5% 3 4 4 5% 6% 39%	2470
	21st to end	Night	16% 8% 3 6% 6% 3 5% 5% 4 7% 37%	2628
December	1st to 10th	Night	20% 11% 4 7% 6% 4 4 4 5% 5% 29%	2660
	11th to 20th	Night	23% 9% 3 6% 6% 3 6% 4 5% 6% 30%	3288
	21st to end	Night	26% 14% 5% 7% 6% 3 3 4 4 5% 23%	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	51% 12% 14% 18% 5%	2518
	11th to 20th	Day	60% 10% 12% 12% 5% 1	2520
	21st to end	Day	61% 10% 11% 12% 5% 1	2833
February	1st to 10th	Day	57% 9% 12% 15% 6% 1	1710
	11th to 20th	Day	58% 7% 11% 15% 9% 1	1825
	21st to end	Day	55% 7% 11% 14% 11% 2	1570
March	1st to 10th	Day	51% 7% 13% 17% 10% 2	1800
	11th to 20th	Day	52% 7% 11% 13% 14% 3	1865
	21st to end	Day	51% 5% 8% 17% 15% 4	2374
April	1st to 10th	Day	50% 7% 8% 20% 11% 3	2160
	11th to 20th	Day	46% 7% 11% 19% 15% 2	2134
	21st to end	Day	52% 8% 9% 16% 12% 4	2256
May	1st to 10th	Day	52% 7% 9% 18% 13% 2	2392
	11th to 20th	Day	44% 8% 12% 19% 16% 2	2482
	21st to end	Day	42% 9% 16% 21% 11% 1	2725
June	1st to 10th	Day	47% 10% 15% 17% 9% 1	2520
	11th to 20th	Day	45% 9% 13% 19% 13% 1	2520
	21st to end	Day	48% 9% 14% 19% 10%	2520
July	1st to 10th	Day	39% 10% 14% 22% 14% 1	2450
	11th to 20th	Day	37% 10% 17% 27% 8%	2445
	21st to end	Day	41% 10% 15% 22% 10% 1	2591
August	1st to 10th	Day	38% 11% 19% 22% 10% 1	2492
	11th to 20th	Day	41% 11% 17% 22% 9%	2147
	21st to end	Day	37% 9% 15% 25% 13% 1	2376
September	1st to 10th	Day	37% 8% 14% 28% 13% 1	2160
	11th to 20th	Day	35% 7% 12% 26% 19% 1	2075
	21st to end	Day	38% 8% 14% 25% 13% 1	1980
October	1st to 10th	Day	52% 8% 9% 17% 12% 1	1882
	11th to 20th	Day	43% 9% 16% 23% 7% 1	1796
	21st to end	Day	56% 8% 12% 14% 9% 1	1782
November	1st to 10th	Day	41% 8% 16% 23% 11% 1	1671
	11th to 20th	Day	48% 8% 13% 16% 13% 1	1710
	21st to end	Day	51% 8% 17% 17% 6% 1	1549
December	1st to 10th	Day	61% 8% 12% 13% 6% 1	1520
	11th to 20th	Day	56% 7% 14% 17% 5% 1	1906
	21st to end	Day	66% 7% 9% 13% 6%	2772
January	1st to 10th	Night	51% 11% 16% 14% 8% 1	4429
	11th to 20th	Night	59% 10% 12% 13% 6% 1	4440
	21st to end	Night	61% 8% 11% 13% 6% 1	4820
February	1st to 10th	Night	58% 8% 12% 15% 6% 1	2470
	11th to 20th	Night	53% 9% 10% 17% 9% 1	2250
	21st to end	Night	52% 8% 13% 18% 8% 2	1884
March	1st to 10th	Night	51% 9% 10% 19% 10% 1	2167
	11th to 20th	Night	51% 8% 10% 19% 10% 2	2093
	21st to end	Night	48% 7% 9% 17% 16% 4	1980
April	1st to 10th	Night	50% 6% 12% 20% 11% 2	1800
	11th to 20th	Night	49% 7% 9% 21% 12% 1	1775
	21st to end	Night	49% 7% 10% 18% 13% 4	1702
May	1st to 10th	Night	53% 6% 9% 15% 14% 2	1584
	11th to 20th	Night	47% 6% 12% 19% 14% 3	1416
	21st to end	Night	43% 9% 14% 21% 12% 2	1551
June	1st to 10th	Night	45% 8% 15% 21% 11% 1	1440
	11th to 20th	Night	41% 9% 16% 22% 12% 1	1440
	21st to end	Night	40% 10% 15% 23% 12% 1	1440
July	1st to 10th	Night	38% 11% 14% 22% 14% 1	1400
	11th to 20th	Night	37% 10% 16% 26% 10%	1392
	21st to end	Night	35% 11% 14% 26% 12% 2	1486
August	1st to 10th	Night	33% 11% 19% 26% 11%	1422
	11th to 20th	Night	40% 11% 16% 22% 11%	1730
	21st to end	Night	38% 7% 14% 26% 14% 1	1980
September	1st to 10th	Night	38% 8% 13% 27% 13% 1	1800
	11th to 20th	Night	34% 7% 13% 27% 18% 1	1885
	21st to end	Night	38% 9% 12% 23% 17% 2	1980
October	1st to 10th	Night	50% 7% 10% 20% 11% 2	2074
	11th to 20th	Night	45% 9% 16% 21% 8% 1	2164
	21st to end	Night	55% 8% 13% 15% 9% 1	2574
November	1st to 10th	Night	45% 8% 11% 20% 13% 2	2407
	11th to 20th	Night	47% 7% 13% 20% 11% 2	2470
	21st to end	Night	49% 8% 17% 19% 7%	2628
December	1st to 10th	Night	58% 9% 13% 15% 5%	2660
	11th to 20th	Night	56% 9% 14% 13% 8% 1	3288
	21st to end	Night	64% 7% 11% 15% 3	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	26% 19% 29% 17% 8% 1	180
	11th to 20th	Day	29% 27% 29% 12% 2 1	180
	21st to end	Day	20% 21% 35% 18% 6% 1	215
February	1st to 10th	Day	27% 30% 32% 10%	270
	11th to 20th	Day	26% 26% 34% 12% 2	424
	21st to end	Day	28% 19% 34% 16% 3	382
March	1st to 10th	Day	25% 17% 35% 20% 3	420
	11th to 20th	Day	25% 23% 33% 15% 4 1	420
	21st to end	Day	29% 21% 26% 13% 9% 1	462
April	1st to 10th	Day	29% 20% 27% 17% 7% 1	420
	11th to 20th	Day	26% 24% 25% 15% 8% 2	412
	21st to end	Day	29% 17% 31% 16% 5% 2	420
May	1st to 10th	Day	31% 16% 28% 13% 9% 2	423
	11th to 20th	Day	17% 17% 35% 22% 7% 2	447
	21st to end	Day	15% 14% 32% 25% 11% 3	485
June	1st to 10th	Day	17% 16% 32% 23% 10% 3	450
	11th to 20th	Day	19% 12% 33% 24% 10% 2	450
	21st to end	Day	17% 14% 32% 25% 10% 2	450
July	1st to 10th	Day	13% 9% 27% 31% 16% 4	445
	11th to 20th	Day	11% 9% 30% 31% 17% 3	444
	21st to end	Day	15% 6% 36% 30% 11% 2	488
August	1st to 10th	Day	10% 9% 28% 31% 17% 5%	446
	11th to 20th	Day	15% 6% 28% 27% 18% 5%	439
	21st to end	Day	12% 11% 24% 31% 15% 7%	495
September	1st to 10th	Day	14% 11% 24% 28% 16% 8%	450
	11th to 20th	Day	15% 11% 27% 21% 16% 10%	450
	21st to end	Day	18% 9% 28% 26% 12% 6%	450
October	1st to 10th	Day	26% 13% 24% 19% 12% 6%	450
	11th to 20th	Day	17% 18% 30% 25% 9% 1	448
	21st to end	Day	30% 14% 26% 24% 6%	396
November	1st to 10th	Day	21% 15% 26% 24% 13%	365
	11th to 20th	Day	26% 16% 31% 20% 5% 1	370
	21st to end	Day	25% 21% 32% 19% 4	209
December	1st to 10th	Day	24% 23% 31% 17% 4 1	180
	11th to 20th	Day	33% 19% 33% 13% 2	180
	21st to end	Day	26% 24% 30% 17% 3	198
January	1st to 10th	Night	21% 16% 35% 26% 3	760
	11th to 20th	Night	25% 17% 31% 24% 2	760
	21st to end	Night	18% 15% 38% 26% 3	836
February	1st to 10th	Night	20% 16% 40% 22% 2	760
	11th to 20th	Night	19% 20% 40% 20% 2	743
	21st to end	Night	23% 20% 33% 20% 3	628
March	1st to 10th	Night	22% 16% 37% 22% 3	723
	11th to 20th	Night	25% 15% 33% 22% 4	720
	21st to end	Night	22% 16% 33% 22% 7%	792
April	1st to 10th	Night	25% 16% 33% 23% 3	720
	11th to 20th	Night	22% 18% 31% 22% 7%	711
	21st to end	Night	25% 16% 28% 25% 6%	622
May	1st to 10th	Night	26% 11% 28% 25% 10%	504
	11th to 20th	Night	20% 10% 37% 27% 5% 1	354
	21st to end	Night	14% 11% 25% 37% 13% 1	389
June	1st to 10th	Night	21% 5% 26% 36% 13% 1	360
	11th to 20th	Night	19% 6% 27% 38% 11%	360
	21st to end	Night	12% 4 30% 43% 11%	360
July	1st to 10th	Night	12% 5% 23% 43% 17% 1	350
	11th to 20th	Night	14% 3 20% 44% 17% 1	348
	21st to end	Night	12% 3 24% 44% 15% 1	394
August	1st to 10th	Night	10% 2 22% 47% 18% 1	358
	11th to 20th	Night	14% 4 23% 37% 20% 3	666
	21st to end	Night	14% 7% 20% 39% 20% 1	792
September	1st to 10th	Night	15% 4 23% 37% 18% 2	720
	11th to 20th	Night	16% 7% 24% 29% 18% 5%	720
	21st to end	Night	16% 7% 27% 32% 16% 2	720
October	1st to 10th	Night	24% 11% 23% 27% 14% 1	720
	11th to 20th	Night	18% 11% 27% 34% 9%	720
	21st to end	Night	28% 10% 30% 26% 6%	792
November	1st to 10th	Night	17% 13% 33% 29% 8%	740
	11th to 20th	Night	21% 14% 32% 24% 7% 1	760
	21st to end	Night	20% 14% 35% 25% 6% 1	760
December	1st to 10th	Night	26% 15% 33% 22% 4	760
	11th to 20th	Night	26% 14% 31% 24% 4	760
	21st to end	Night	28% 14% 35% 20% 3	836

Page generated at 2024-02-27 06:30:18. Version ac07

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