Afterwood Observatory
Clear Sky Chart
History

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

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	15% 10% 4 8% 5% 5% 5% 4 6% 7% 31%	101361
	Night	15% 10% 4 9% 5% 5% 5% 4 5% 6% 33%	97575
Transparency	Day	48% 9% 13% 19% 10% 1	101116
	Night	48% 9% 14% 19% 10% 1	97439
Seeing	Day	23% 20% 29% 18% 8% 2	14800
	Night	21% 20% 29% 22% 8% 1	23877

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	11% 12% 7% 13% 7% 6% 4 3 5% 6% 26%	2517
	11th to 20th	Day	11% 17% 6% 12% 7% 5% 6% 4 5% 5% 23%	2520
	21st to end	Day	17% 17% 7% 13% 5% 5% 4 3 5% 5% 20%	2914
February	1st to 10th	Day	14% 14% 5% 11% 8% 5% 6% 4 4 7% 22%	1710
	11th to 20th	Day	9% 11% 5% 14% 7% 5% 5% 4 5% 6% 28%	1800
	21st to end	Day	16% 14% 4 10% 6% 4 4 3 5% 6% 28%	1570
March	1st to 10th	Day	22% 15% 4 9% 5% 3 3 2 4 5% 27%	3116
	11th to 20th	Day	10% 15% 6% 11% 5% 5% 5% 3 5% 6% 29%	3347
	21st to end	Day	18% 10% 4 8% 6% 4 4 3 3 5% 34%	4124
April	1st to 10th	Day	15% 13% 4 9% 6% 5% 4 3 5% 5% 32%	2280
	11th to 20th	Day	16% 11% 3 8% 5% 5% 4 3 5% 6% 35%	2254
	21st to end	Day	19% 11% 3 8% 5% 5% 4 4 5% 6% 31%	2337
May	1st to 10th	Day	23% 10% 3 8% 5% 4 4 3 4 6% 29%	4228
	11th to 20th	Day	18% 9% 3 7% 5% 5% 5% 4 5% 8% 31%	4398
	21st to end	Day	11% 6% 2 7% 5% 6% 5% 5% 7% 8% 38%	4837
June	1st to 10th	Day	16% 8% 3 8% 5% 6% 6% 4 7% 8% 30%	2660
	11th to 20th	Day	16% 7% 2 7% 5% 6% 6% 4 6% 9% 31%	2660
	21st to end	Day	14% 8% 3 8% 6% 5% 6% 4 6% 7% 32%	2660
July	1st to 10th	Day	10% 7% 3 7% 5% 6% 6% 6% 7% 10% 33%	4440
	11th to 20th	Day	8% 5% 2 7% 6% 7% 7% 5% 8% 12% 32%	4440
	21st to end	Day	12% 8% 3 9% 6% 6% 6% 4 6% 7% 32%	4814
August	1st to 10th	Day	17% 7% 3 8% 6% 5% 5% 4 6% 8% 31%	4338
	11th to 20th	Day	11% 9% 3 7% 6% 6% 6% 5% 8% 9% 29%	3747
	21st to end	Day	13% 7% 3 7% 4 5% 6% 5% 7% 9% 34%	4180
September	1st to 10th	Day	13% 7% 2 7% 5% 4 4 4 5% 8% 40%	2280
	11th to 20th	Day	12% 7% 2 6% 3 3 5% 3 5% 7% 46%	2214
	21st to end	Day	14% 7% 3 5% 4 5% 5% 4 6% 8% 38%	2090
October	1st to 10th	Day	16% 10% 4 7% 5% 4 4 3 6% 6% 34%	1952
	11th to 20th	Day	14% 9% 3 8% 4 4 4 4 6% 7% 37%	1900
	21st to end	Day	20% 12% 3 8% 5% 4 4 3 6% 6% 30%	1916
November	1st to 10th	Day	14% 12% 3 5% 4 4 3 3 5% 6% 40%	1671
	11th to 20th	Day	15% 11% 5% 9% 6% 5% 5% 3 5% 6% 31%	1710
	21st to end	Day	14% 12% 5% 9% 4 5% 5% 4 5% 6% 30%	1539
December	1st to 10th	Day	14% 16% 5% 12% 7% 6% 5% 4 5% 5% 22%	1520
	11th to 20th	Day	18% 13% 5% 10% 4 4 4 3 4 5% 28%	1906
	21st to end	Day	18% 17% 8% 10% 5% 4 5% 4 5% 6% 19%	2772
January	1st to 10th	Night	14% 12% 4 11% 6% 4 5% 4 6% 6% 29%	4429
	11th to 20th	Night	11% 15% 5% 12% 8% 6% 6% 4 5% 6% 23%	4440
	21st to end	Night	18% 14% 7% 12% 7% 6% 4 3 4 5% 21%	4724
February	1st to 10th	Night	13% 14% 4 10% 7% 5% 5% 4 5% 7% 25%	2470
	11th to 20th	Night	10% 11% 5% 12% 8% 6% 6% 5% 6% 7% 25%	2266
	21st to end	Night	15% 12% 5% 10% 6% 5% 5% 3 6% 7% 27%	1884
March	1st to 10th	Night	20% 12% 3 8% 5% 4 4 4 5% 6% 29%	3724
	11th to 20th	Night	10% 12% 6% 10% 6% 5% 5% 4 5% 6% 29%	3609
	21st to end	Night	13% 14% 5% 11% 5% 4 4 3 4 4 32%	3507
April	1st to 10th	Night	15% 12% 4 10% 5% 5% 5% 4 6% 6% 28%	1900
	11th to 20th	Night	19% 10% 3 6% 4 3 4 3 4 7% 35%	1875
	21st to end	Night	19% 10% 4 7% 4 4 4 3 5% 5% 35%	1843
May	1st to 10th	Night	24% 12% 3 7% 4 3 4 3 4 7% 30%	2741
	11th to 20th	Night	16% 11% 4 8% 5% 5% 5% 4 5% 7% 32%	2495
	21st to end	Night	11% 7% 3 9% 5% 5% 5% 4 6% 9% 37%	2738
June	1st to 10th	Night	15% 6% 3 6% 5% 5% 3 5% 5% 7% 40%	1520
	11th to 20th	Night	14% 7% 2 6% 3 4 4 4 6% 9% 40%	1520
	21st to end	Night	10% 4 1 7% 5% 5% 5% 4 6% 10% 42%	1520
July	1st to 10th	Night	8% 7% 2 7% 6% 6% 5% 5% 6% 8% 39%	2520
	11th to 20th	Night	11% 6% 3 7% 4 4 4 4 7% 9% 41%	2520
	21st to end	Night	12% 8% 2 6% 5% 5% 5% 4 5% 6% 41%	2739
August	1st to 10th	Night	19% 7% 3 7% 5% 4 5% 4 5% 7% 36%	2587
	11th to 20th	Night	14% 7% 3 8% 4 4 4 4 5% 7% 41%	3037
	21st to end	Night	11% 7% 2 6% 4 4 4 3 5% 8% 45%	3476
September	1st to 10th	Night	13% 7% 2 5% 5% 4 5% 4 6% 7% 44%	1900
	11th to 20th	Night	13% 6% 2 4 3 3 4 3 4 6% 53%	1966
	21st to end	Night	13% 6% 3 7% 5% 4 5% 3 5% 6% 43%	2090
October	1st to 10th	Night	18% 9% 3 7% 4 4 4 4 5% 6% 37%	2223
	11th to 20th	Night	15% 8% 3 6% 5% 4 4 4 5% 6% 40%	2280
	21st to end	Night	20% 13% 3 6% 5% 3 4 3 5% 6% 32%	2680
November	1st to 10th	Night	13% 10% 3 7% 4 3 4 4 5% 6% 39%	2414
	11th to 20th	Night	15% 11% 4 8% 5% 5% 5% 4 6% 6% 31%	2470
	21st to end	Night	13% 11% 5% 8% 6% 5% 4 4 5% 6% 33%	2636
December	1st to 10th	Night	13% 14% 6% 11% 5% 5% 5% 5% 6% 6% 23%	2660
	11th to 20th	Night	18% 11% 5% 11% 5% 5% 5% 3 5% 5% 26%	3288
	21st to end	Night	22% 13% 7% 11% 4 4 4 4 4 5% 21%	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	50% 12% 14% 17% 5% 1	2518
	11th to 20th	Day	60% 9% 10% 15% 5% 1	2520
	21st to end	Day	63% 8% 11% 13% 5% 1	2914
February	1st to 10th	Day	58% 8% 12% 13% 7% 1	1710
	11th to 20th	Day	52% 7% 13% 17% 9% 2	1809
	21st to end	Day	54% 7% 12% 16% 10%	1570
March	1st to 10th	Day	58% 6% 12% 13% 9% 1	3119
	11th to 20th	Day	49% 12% 14% 16% 8% 2	3347
	21st to end	Day	49% 7% 9% 15% 17% 3	4124
April	1st to 10th	Day	53% 7% 8% 21% 10% 2	2280
	11th to 20th	Day	48% 7% 11% 19% 13% 1	2254
	21st to end	Day	52% 7% 11% 16% 12% 3	2337
May	1st to 10th	Day	55% 7% 10% 17% 10% 1	4242
	11th to 20th	Day	49% 9% 14% 20% 8% 1	4402
	21st to end	Day	37% 12% 15% 24% 12% 1	4837
June	1st to 10th	Day	48% 10% 14% 18% 10% 1	2660
	11th to 20th	Day	46% 10% 15% 19% 10% 1	2660
	21st to end	Day	48% 9% 15% 19% 9% 1	2660
July	1st to 10th	Day	42% 10% 14% 22% 11% 1	4370
	11th to 20th	Day	39% 11% 18% 22% 10% 1	4365
	21st to end	Day	48% 8% 13% 19% 11%	4661
August	1st to 10th	Day	49% 10% 14% 18% 10%	4324
	11th to 20th	Day	45% 10% 17% 25% 4	3783
	21st to end	Day	38% 10% 14% 28% 8% 1	4180
September	1st to 10th	Day	42% 8% 12% 24% 14% 1	2280
	11th to 20th	Day	36% 7% 12% 24% 19% 1	2214
	21st to end	Day	41% 8% 13% 23% 13% 2	2090
October	1st to 10th	Day	49% 7% 10% 18% 14% 1	1952
	11th to 20th	Day	43% 8% 14% 22% 11% 2	1900
	21st to end	Day	52% 9% 13% 14% 9% 2	1916
November	1st to 10th	Day	43% 7% 13% 22% 13% 2	1671
	11th to 20th	Day	50% 9% 12% 16% 11% 2	1710
	21st to end	Day	51% 8% 15% 18% 7% 1	1539
December	1st to 10th	Day	62% 8% 12% 13% 6%	1520
	11th to 20th	Day	54% 8% 15% 16% 5% 1	1906
	21st to end	Day	63% 9% 10% 11% 7%	2772
January	1st to 10th	Night	48% 10% 17% 16% 8% 1	4429
	11th to 20th	Night	55% 11% 13% 14% 6% 1	4440
	21st to end	Night	63% 8% 10% 13% 5% 1	4724
February	1st to 10th	Night	53% 9% 14% 15% 7% 1	2470
	11th to 20th	Night	53% 9% 14% 15% 9% 1	2268
	21st to end	Night	51% 9% 14% 16% 8% 2	1884
March	1st to 10th	Night	53% 9% 11% 17% 9% 1	3734
	11th to 20th	Night	48% 12% 15% 18% 7% 1	3610
	21st to end	Night	49% 9% 9% 16% 15% 2	3507
April	1st to 10th	Night	53% 9% 12% 17% 8% 1	1900
	11th to 20th	Night	47% 8% 13% 18% 14% 1	1875
	21st to end	Night	49% 7% 11% 17% 13% 3	1843
May	1st to 10th	Night	54% 8% 10% 15% 11% 2	2747
	11th to 20th	Night	49% 9% 14% 19% 8% 1	2496
	21st to end	Night	39% 13% 15% 19% 13% 1	2739
June	1st to 10th	Night	42% 8% 12% 24% 12% 2	1520
	11th to 20th	Night	38% 10% 16% 25% 10%	1520
	21st to end	Night	35% 11% 17% 24% 12%	1520
July	1st to 10th	Night	37% 11% 17% 20% 14% 1	2480
	11th to 20th	Night	36% 9% 18% 25% 12%	2472
	21st to end	Night	42% 9% 13% 24% 12% 1	2651
August	1st to 10th	Night	45% 11% 14% 22% 8%	2577
	11th to 20th	Night	41% 9% 17% 25% 8%	3066
	21st to end	Night	32% 10% 13% 33% 10% 1	3476
September	1st to 10th	Night	37% 9% 13% 27% 13% 1	1900
	11th to 20th	Night	32% 8% 12% 25% 22% 1	1966
	21st to end	Night	40% 9% 11% 23% 15% 1	2090
October	1st to 10th	Night	46% 8% 13% 19% 12% 1	2223
	11th to 20th	Night	42% 9% 16% 20% 12% 1	2280
	21st to end	Night	51% 7% 14% 18% 9% 1	2680
November	1st to 10th	Night	43% 8% 13% 19% 15% 3	2414
	11th to 20th	Night	47% 9% 15% 17% 10% 3	2470
	21st to end	Night	48% 9% 17% 19% 6% 1	2636
December	1st to 10th	Night	54% 12% 16% 14% 5%	2660
	11th to 20th	Night	54% 10% 13% 14% 9%	3288
	21st to end	Night	61% 9% 11% 13% 7%	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	31% 26% 30% 9% 3 1	180
	11th to 20th	Day	35% 30% 24% 9% 2 1	180
	21st to end	Day	26% 30% 30% 10% 3	240
February	1st to 10th	Day	33% 35% 27% 4 1	270
	11th to 20th	Day	34% 34% 23% 8% 1	408
	21st to end	Day	31% 27% 31% 10% 2	382
March	1st to 10th	Day	30% 27% 30% 11% 2	460
	11th to 20th	Day	34% 25% 28% 10% 3	460
	21st to end	Day	35% 27% 24% 9% 4 2	506
April	1st to 10th	Day	32% 27% 22% 12% 6% 1	460
	11th to 20th	Day	28% 31% 22% 12% 4 2	452
	21st to end	Day	32% 22% 29% 12% 4 2	460
May	1st to 10th	Day	31% 22% 27% 11% 5% 3	463
	11th to 20th	Day	19% 21% 33% 18% 8% 1	487
	21st to end	Day	19% 12% 34% 22% 11% 3	529
June	1st to 10th	Day	18% 19% 33% 22% 8% 1	490
	11th to 20th	Day	16% 17% 32% 24% 10% 2	490
	21st to end	Day	18% 18% 32% 22% 9% 1	490
July	1st to 10th	Day	11% 12% 37% 25% 13% 3	485
	11th to 20th	Day	9% 10% 36% 31% 11% 2	484
	21st to end	Day	13% 11% 40% 24% 10% 3	532
August	1st to 10th	Day	11% 10% 34% 26% 15% 4	486
	11th to 20th	Day	13% 12% 29% 29% 11% 6%	479
	21st to end	Day	13% 15% 28% 25% 14% 5%	539
September	1st to 10th	Day	17% 11% 29% 22% 15% 6%	490
	11th to 20th	Day	14% 13% 26% 21% 18% 9%	490
	21st to end	Day	19% 12% 30% 22% 12% 5%	490
October	1st to 10th	Day	22% 17% 26% 17% 14% 3	490
	11th to 20th	Day	23% 21% 26% 23% 6% 1	490
	21st to end	Day	25% 22% 30% 18% 4	446
November	1st to 10th	Day	24% 22% 24% 18% 11% 1	365
	11th to 20th	Day	30% 25% 25% 15% 4 1	370
	21st to end	Day	28% 25% 31% 15% 2	199
December	1st to 10th	Day	29% 34% 23% 9% 5%	180
	11th to 20th	Day	37% 26% 28% 8% 2	180
	21st to end	Day	29% 33% 27% 8% 3 1	198
January	1st to 10th	Night	23% 29% 33% 12% 2	760
	11th to 20th	Night	26% 25% 32% 15% 2 1	760
	21st to end	Night	20% 30% 32% 16% 2	836
February	1st to 10th	Night	23% 26% 37% 12% 1	760
	11th to 20th	Night	24% 31% 31% 13% 1	743
	21st to end	Night	29% 25% 29% 14% 2	628
March	1st to 10th	Night	27% 28% 30% 13% 3	760
	11th to 20th	Night	24% 29% 29% 15% 2	760
	21st to end	Night	28% 23% 29% 16% 4	836
April	1st to 10th	Night	24% 26% 30% 17% 3	760
	11th to 20th	Night	25% 23% 30% 17% 6%	751
	21st to end	Night	26% 20% 27% 19% 7%	703
May	1st to 10th	Night	28% 17% 28% 20% 6% 1	516
	11th to 20th	Night	21% 16% 29% 28% 5% 1	374
	21st to end	Night	15% 9% 31% 32% 11% 1	411
June	1st to 10th	Night	16% 12% 31% 28% 12% 1	380
	11th to 20th	Night	15% 14% 26% 33% 13%	380
	21st to end	Night	11% 8% 34% 34% 12% 1	380
July	1st to 10th	Night	11% 7% 26% 40% 15% 1	370
	11th to 20th	Night	13% 8% 25% 37% 17% 1	368
	21st to end	Night	12% 5% 26% 43% 13% 1	416
August	1st to 10th	Night	9% 6% 31% 34% 19% 1	420
	11th to 20th	Night	14% 7% 23% 36% 17% 3	714
	21st to end	Night	14% 8% 24% 32% 20% 1	836
September	1st to 10th	Night	14% 10% 28% 31% 16% 1	760
	11th to 20th	Night	16% 10% 24% 26% 19% 5%	760
	21st to end	Night	17% 11% 26% 31% 13% 3	760
October	1st to 10th	Night	22% 15% 24% 23% 14% 1	760
	11th to 20th	Night	20% 18% 29% 25% 8%	760
	21st to end	Night	25% 21% 29% 21% 4	836
November	1st to 10th	Night	21% 21% 26% 25% 7%	743
	11th to 20th	Night	24% 24% 27% 18% 6% 1	760
	21st to end	Night	22% 26% 27% 20% 4 1	760
December	1st to 10th	Night	23% 30% 29% 14% 4	760
	11th to 20th	Night	26% 25% 30% 16% 3	760
	21st to end	Night	28% 30% 28% 13% 2	836

Page generated at 2024-10-29 11:20:47. Version ac07

Copyright © 2024 Attilla Danko.