Avon
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Avon clear sky chart from 2005-11-06 to 2024-11-02.

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	12% 7% 2 7% 4 4 5% 4 6% 8% 41%	100768
	Night	13% 7% 2 7% 4 4 5% 4 6% 8% 40%	98148
Transparency	Day	23% 49% 8% 12% 7% 2	100567
	Night	23% 49% 7% 12% 8% 2	98019
Seeing	Day	15% 5% 19% 28% 25% 8%	15534
	Night	16% 7% 20% 28% 22% 6%	25129

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	11% 8% 3 7% 3 4 4 3 5% 8% 43%	2691
	11th to 20th	Day	10% 7% 2 7% 4 4 5% 4 6% 7% 44%	2840
	21st to end	Day	13% 12% 4 7% 4 4 4 3 5% 8% 36%	3124
February	1st to 10th	Day	15% 6% 2 6% 4 4 4 4 6% 8% 39%	1786
	11th to 20th	Day	19% 9% 3 6% 4 4 4 3 5% 5% 39%	1848
	21st to end	Day	13% 7% 2 6% 5% 4 4 4 6% 8% 40%	1570
March	1st to 10th	Day	21% 10% 3 7% 4 3 4 4 5% 5% 33%	3233
	11th to 20th	Day	10% 5% 2 5% 4 4 3 2 5% 6% 55%	3480
	21st to end	Day	16% 9% 2 4 3 3 3 3 5% 6% 46%	3996
April	1st to 10th	Day	12% 6% 3 4 4 3 3 4 5% 6% 51%	2280
	11th to 20th	Day	10% 5% 1 6% 4 4 4 4 6% 7% 50%	2254
	21st to end	Day	9% 5% 1 5% 4 4 4 3 5% 8% 53%	2280
May	1st to 10th	Day	9% 6% 2 6% 4 5% 5% 5% 7% 10% 41%	3765
	11th to 20th	Day	16% 10% 3 9% 5% 6% 5% 4 5% 7% 31%	3937
	21st to end	Day	8% 6% 2 6% 4 5% 5% 4 7% 9% 44%	4823
June	1st to 10th	Day	9% 6% 2 6% 5% 5% 5% 5% 8% 9% 40%	2660
	11th to 20th	Day	8% 5% 2 5% 5% 4 5% 4 6% 11% 45%	2660
	21st to end	Day	6% 5% 2 5% 5% 5% 6% 5% 9% 12% 39%	2660
July	1st to 10th	Day	10% 6% 2 6% 5% 5% 5% 4 7% 12% 38%	4440
	11th to 20th	Day	7% 6% 3 8% 6% 6% 5% 5% 8% 11% 35%	4165
	21st to end	Day	9% 6% 3 8% 6% 7% 6% 5% 8% 10% 32%	4466
August	1st to 10th	Day	12% 11% 4 10% 5% 5% 5% 5% 7% 10% 26%	3882
	11th to 20th	Day	7% 4 2 7% 4 5% 5% 4 6% 9% 45%	3730
	21st to end	Day	7% 6% 2 7% 5% 5% 5% 4 7% 9% 42%	4180
September	1st to 10th	Day	11% 7% 2 8% 5% 4 5% 4 8% 10% 36%	2280
	11th to 20th	Day	15% 6% 2 7% 6% 5% 6% 4 6% 7% 37%	2253
	21st to end	Day	18% 7% 3 7% 4 5% 5% 3 5% 6% 37%	2090
October	1st to 10th	Day	12% 6% 2 6% 4 3 4 4 4 7% 48%	1914
	11th to 20th	Day	13% 6% 2 6% 4 3 3 2 4 6% 51%	1900
	21st to end	Day	11% 6% 2 6% 3 4 4 4 5% 6% 50%	2090
November	1st to 10th	Day	16% 7% 2 6% 4 3 4 4 5% 7% 42%	1769
	11th to 20th	Day	16% 7% 2 5% 4 4 4 3 5% 7% 45%	1710
	21st to end	Day	13% 6% 2 5% 4 4 4 4 5% 7% 46%	1710
December	1st to 10th	Day	16% 8% 3 7% 4 4 5% 4 5% 7% 37%	1620
	11th to 20th	Day	16% 7% 2 6% 4 4 4 3 5% 6% 42%	1910
	21st to end	Day	13% 7% 3 6% 4 3 4 4 6% 6% 46%	2772
January	1st to 10th	Night	13% 8% 3 6% 4 4 4 3 5% 7% 43%	4237
	11th to 20th	Night	15% 7% 2 6% 4 4 4 5% 6% 7% 40%	4120
	21st to end	Night	13% 8% 2 7% 5% 5% 5% 4 5% 7% 39%	4532
February	1st to 10th	Night	18% 8% 3 5% 4 4 4 4 5% 7% 39%	2392
	11th to 20th	Night	18% 9% 3 8% 3 3 4 4 5% 6% 38%	2218
	21st to end	Night	16% 7% 2 7% 4 4 4 3 5% 7% 40%	1884
March	1st to 10th	Night	20% 10% 4 9% 5% 4 4 3 5% 5% 30%	3616
	11th to 20th	Night	13% 6% 2 6% 4 3 4 3 5% 5% 50%	3480
	21st to end	Night	16% 9% 3 6% 4 2 3 2 4 4 47%	3635
April	1st to 10th	Night	12% 6% 2 6% 3 3 4 3 5% 8% 47%	1900
	11th to 20th	Night	8% 7% 2 5% 5% 5% 6% 4 6% 8% 44%	1875
	21st to end	Night	11% 5% 2 5% 4 4 3 3 6% 7% 49%	1900
May	1st to 10th	Night	9% 5% 2 7% 5% 6% 6% 6% 8% 9% 37%	3130
	11th to 20th	Night	19% 8% 2 7% 5% 5% 4 3 6% 8% 34%	2980
	21st to end	Night	8% 8% 2 7% 4 4 5% 4 7% 10% 41%	2733
June	1st to 10th	Night	11% 6% 2 6% 5% 5% 4 4 7% 10% 40%	1520
	11th to 20th	Night	7% 3 1 5% 4 4 5% 6% 8% 12% 45%	1520
	21st to end	Night	8% 5% 2 7% 5% 5% 5% 5% 9% 13% 36%	1520
July	1st to 10th	Night	7% 5% 2 6% 4 4 6% 5% 8% 12% 40%	2520
	11th to 20th	Night	9% 6% 2 7% 6% 6% 5% 7% 9% 12% 31%	2791
	21st to end	Night	10% 6% 2 7% 6% 5% 6% 6% 9% 12% 31%	3087
August	1st to 10th	Night	12% 11% 4 10% 5% 5% 6% 4 8% 11% 25%	3017
	11th to 20th	Night	6% 4 2 7% 6% 6% 6% 6% 8% 9% 40%	3097
	21st to end	Night	8% 6% 2 8% 5% 5% 6% 5% 8% 10% 39%	3476
September	1st to 10th	Night	12% 6% 2 7% 5% 5% 6% 5% 9% 9% 33%	1900
	11th to 20th	Night	14% 7% 3 9% 4 5% 6% 4 6% 8% 34%	1925
	21st to end	Night	18% 6% 3 7% 6% 6% 4 4 6% 7% 34%	2090
October	1st to 10th	Night	12% 7% 2 6% 4 4 4 3 5% 7% 45%	2261
	11th to 20th	Night	15% 6% 2 4 3 3 4 3 4 6% 48%	2280
	21st to end	Night	11% 6% 2 5% 4 4 4 3 5% 7% 49%	2508
November	1st to 10th	Night	15% 7% 2 6% 4 5% 4 3 5% 6% 41%	2340
	11th to 20th	Night	15% 7% 3 7% 4 4 4 4 5% 7% 40%	2470
	21st to end	Night	13% 6% 2 5% 4 3 4 3 6% 7% 46%	2470
December	1st to 10th	Night	16% 9% 2 8% 5% 4 4 3 5% 6% 37%	2555
	11th to 20th	Night	14% 8% 3 6% 5% 4 4 3 5% 7% 43%	3285
	21st to end	Night	13% 8% 2 5% 4 4 4 4 5% 7% 45%	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	26% 36% 3 22% 11% 1	2692
	11th to 20th	Day	25% 36% 4 15% 15% 5%	2840
	21st to end	Day	30% 41% 6% 11% 10% 3	3124
February	1st to 10th	Day	16% 65% 5% 8% 5%	1786
	11th to 20th	Day	18% 64% 3 7% 6% 2	1857
	21st to end	Day	15% 66% 3 7% 7% 3	1570
March	1st to 10th	Day	40% 40% 6% 7% 3 4	3233
	11th to 20th	Day	16% 39% 5% 14% 16% 12%	3480
	21st to end	Day	24% 39% 6% 17% 11% 4	3996
April	1st to 10th	Day	14% 65% 5% 7% 8% 1	2280
	11th to 20th	Day	12% 66% 5% 10% 5% 2	2254
	21st to end	Day	10% 65% 5% 12% 6%	2280
May	1st to 10th	Day	26% 42% 15% 12% 4 1	3800
	11th to 20th	Day	37% 39% 6% 16% 2	3941
	21st to end	Day	21% 40% 10% 22% 6%	4837
June	1st to 10th	Day	14% 66% 6% 8% 5%	2660
	11th to 20th	Day	9% 66% 9% 11% 4	2660
	21st to end	Day	12% 66% 9% 10% 3	2660
July	1st to 10th	Day	26% 37% 19% 13% 4	4370
	11th to 20th	Day	30% 40% 22% 7% 1	4094
	21st to end	Day	32% 41% 11% 10% 7%	4324
August	1st to 10th	Day	40% 39% 14% 5% 1	3869
	11th to 20th	Day	22% 40% 10% 21% 8%	3766
	21st to end	Day	21% 38% 15% 19% 7%	4180
September	1st to 10th	Day	18% 62% 10% 6% 3 1	2280
	11th to 20th	Day	21% 61% 6% 8% 3 1	2253
	21st to end	Day	22% 60% 7% 6% 4	2090
October	1st to 10th	Day	16% 60% 4 11% 8% 1	1914
	11th to 20th	Day	12% 60% 4 11% 10% 3	1900
	21st to end	Day	11% 59% 3 11% 15% 1	2090
November	1st to 10th	Day	19% 59% 5% 9% 8% 1	1769
	11th to 20th	Day	17% 60% 3 8% 9% 4	1710
	21st to end	Day	15% 60% 4 12% 9% 1	1710
December	1st to 10th	Day	21% 60% 5% 9% 4 1	1620
	11th to 20th	Day	21% 47% 2 13% 13% 4	1906
	21st to end	Day	27% 37% 6% 19% 10% 1	2772
January	1st to 10th	Night	27% 36% 3 16% 15% 2	4237
	11th to 20th	Night	30% 36% 4 14% 13% 4	4120
	21st to end	Night	29% 40% 5% 9% 13% 4	4532
February	1st to 10th	Night	15% 65% 4 11% 5% 1	2392
	11th to 20th	Night	20% 64% 3 6% 7% 1	2220
	21st to end	Night	18% 65% 3 7% 5% 2	1884
March	1st to 10th	Night	44% 40% 5% 7% 4	3616
	11th to 20th	Night	20% 40% 5% 9% 16% 11%	3480
	21st to end	Night	25% 39% 4 18% 9% 4	3635
April	1st to 10th	Night	14% 65% 5% 7% 8% 2	1900
	11th to 20th	Night	14% 67% 5% 10% 3 1	1875
	21st to end	Night	12% 66% 4 12% 6%	1900
May	1st to 10th	Night	27% 42% 14% 12% 4 1	3160
	11th to 20th	Night	33% 41% 7% 13% 5%	2981
	21st to end	Night	25% 40% 12% 17% 7%	2740
June	1st to 10th	Night	15% 66% 6% 8% 5% 1	1520
	11th to 20th	Night	8% 68% 8% 10% 6%	1520
	21st to end	Night	12% 66% 8% 11% 3	1520
July	1st to 10th	Night	23% 39% 21% 14% 3	2480
	11th to 20th	Night	31% 41% 19% 8% 1	2739
	21st to end	Night	30% 43% 11% 7% 9%	2988
August	1st to 10th	Night	38% 38% 15% 7% 1	3006
	11th to 20th	Night	23% 39% 13% 19% 6%	3127
	21st to end	Night	22% 38% 12% 21% 6%	3476
September	1st to 10th	Night	19% 61% 8% 7% 4	1900
	11th to 20th	Night	20% 61% 6% 7% 5% 1	1925
	21st to end	Night	22% 61% 6% 9% 3	2090
October	1st to 10th	Night	16% 60% 4 11% 7% 1	2261
	11th to 20th	Night	13% 60% 4 10% 10% 3	2280
	21st to end	Night	11% 59% 3 13% 12% 2	2508
November	1st to 10th	Night	21% 58% 5% 10% 6% 1	2340
	11th to 20th	Night	19% 60% 3 6% 8% 4	2470
	21st to end	Night	15% 59% 4 12% 9% 1	2470
December	1st to 10th	Night	22% 60% 4 7% 5% 1	2555
	11th to 20th	Night	20% 49% 3 12% 13% 4	3288
	21st to end	Night	26% 37% 8% 17% 12% 1	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	17% 12% 36% 26% 8% 1	231
	11th to 20th	Day	18% 10% 30% 33% 8% 1	270
	21st to end	Day	18% 11% 35% 24% 11% 1	297
February	1st to 10th	Day	17% 9% 33% 32% 8% 1	346
	11th to 20th	Day	26% 12% 32% 25% 5%	456
	21st to end	Day	18% 10% 29% 31% 11% 1	382
March	1st to 10th	Day	18% 12% 31% 26% 12% 2	460
	11th to 20th	Day	18% 10% 33% 27% 12% 1	460
	21st to end	Day	15% 9% 31% 30% 13% 2	506
April	1st to 10th	Day	17% 10% 30% 27% 15% 2	460
	11th to 20th	Day	11% 6% 23% 37% 21% 2	452
	21st to end	Day	9% 5% 23% 39% 19% 5%	460
May	1st to 10th	Day	13% 4 23% 33% 21% 6%	463
	11th to 20th	Day	15% 3 17% 31% 27% 7%	487
	21st to end	Day	14% 2 9% 29% 28% 18%	529
June	1st to 10th	Day	12% 3 12% 30% 33% 10%	490
	11th to 20th	Day	10% 2 10% 28% 35% 14%	490
	21st to end	Day	8% 1 9% 22% 48% 11%	490
July	1st to 10th	Day	12% 2 6% 20% 44% 17%	485
	11th to 20th	Day	9% 2 4 22% 46% 18%	484
	21st to end	Day	9% 2 7% 27% 45% 10%	532
August	1st to 10th	Day	12% 2 8% 26% 37% 15%	486
	11th to 20th	Day	10% 1 6% 21% 37% 24%	479
	21st to end	Day	14% 1 6% 24% 40% 16%	539
September	1st to 10th	Day	13% 1 10% 24% 30% 21%	490
	11th to 20th	Day	18% 3 9% 28% 32% 10%	490
	21st to end	Day	20% 4 12% 25% 30% 9%	490
October	1st to 10th	Day	17% 3 14% 23% 32% 11%	490
	11th to 20th	Day	15% 4 19% 31% 23% 7%	490
	21st to end	Day	12% 6% 19% 29% 26% 9%	539
November	1st to 10th	Day	19% 8% 16% 30% 21% 6%	413
	11th to 20th	Day	20% 7% 26% 30% 15% 2	370
	21st to end	Day	14% 8% 25% 31% 21% 1	370
December	1st to 10th	Day	18% 10% 34% 28% 10% 1	280
	11th to 20th	Day	18% 12% 29% 26% 11% 3	180
	21st to end	Day	18% 8% 30% 29% 15% 1	198
January	1st to 10th	Night	17% 17% 33% 23% 10% 1	760
	11th to 20th	Night	18% 14% 28% 29% 10% 1	760
	21st to end	Night	20% 14% 32% 26% 7%	836
February	1st to 10th	Night	21% 10% 32% 28% 9% 1	760
	11th to 20th	Night	25% 13% 31% 25% 6%	743
	21st to end	Night	19% 13% 29% 29% 10% 1	628
March	1st to 10th	Night	15% 12% 33% 28% 11% 1	760
	11th to 20th	Night	17% 10% 29% 31% 10% 4	760
	21st to end	Night	18% 10% 27% 30% 13% 2	836
April	1st to 10th	Night	14% 8% 33% 30% 13% 2	760
	11th to 20th	Night	11% 8% 25% 35% 18% 4	751
	21st to end	Night	13% 6% 24% 35% 20% 2	760
May	1st to 10th	Night	15% 6% 18% 38% 19% 4	760
	11th to 20th	Night	15% 3 19% 36% 21% 6%	664
	21st to end	Night	14% 2 8% 29% 33% 15%	412
June	1st to 10th	Night	12% 3 12% 31% 34% 8%	380
	11th to 20th	Night	9% 1 8% 33% 39% 11%	380
	21st to end	Night	10% 4 7% 34% 36% 10%	380
July	1st to 10th	Night	9% 1 6% 29% 43% 12%	370
	11th to 20th	Night	11% 2 3 24% 44% 15%	518
	21st to end	Night	11% 2 6% 30% 41% 9%	624
August	1st to 10th	Night	14% 1 8% 26% 41% 9%	681
	11th to 20th	Night	10% 2 5% 25% 38% 19%	750
	21st to end	Night	15% 2 5% 22% 41% 15%	836
September	1st to 10th	Night	14% 3 9% 23% 34% 18%	760
	11th to 20th	Night	18% 3 10% 22% 38% 9%	760
	21st to end	Night	22% 3 11% 22% 34% 8%	760
October	1st to 10th	Night	14% 4 14% 26% 31% 11%	760
	11th to 20th	Night	18% 6% 18% 29% 24% 4	760
	21st to end	Night	15% 6% 22% 25% 24% 8%	836
November	1st to 10th	Night	18% 7% 18% 30% 21% 5%	748
	11th to 20th	Night	19% 10% 20% 32% 17% 3	760
	21st to end	Night	16% 11% 23% 29% 19% 2	760
December	1st to 10th	Night	19% 10% 31% 25% 13% 1	760
	11th to 20th	Night	17% 11% 30% 28% 12% 2	760
	21st to end	Night	16% 12% 28% 31% 12% 1	836

Page generated at 2024-10-30 13:19:22. Version ac07

Copyright © 2024 Attilla Danko.