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 2024-03-01.

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	15% 10% 4 7% 6% 4 5% 5% 5% 7% 32%	78344
	Night	15% 10% 4 8% 6% 3 5% 5% 5% 7% 33%	81041
Transparency	Day	49% 8% 13% 18% 10% 1	78049
	Night	48% 9% 14% 18% 10% 1	80870
Seeing	Day	23% 20% 29% 18% 8% 2	13830
	Night	21% 20% 29% 22% 7% 1	23096

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% 11% 7% 12% 8% 4 5% 4 5% 6% 26%	2517
	11th to 20th	Day	11% 17% 6% 10% 9% 4 6% 5% 4 5% 23%	2520
	21st to end	Day	17% 16% 8% 11% 6% 4 5% 4 5% 5% 20%	2914
February	1st to 10th	Day	14% 12% 6% 9% 10% 4 6% 5% 4 7% 22%	1710
	11th to 20th	Day	9% 10% 6% 12% 8% 4 6% 6% 6% 6% 28%	1800
	21st to end	Day	17% 13% 4 8% 8% 3 4 4 5% 6% 28%	1570
March	1st to 10th	Day	12% 11% 5% 9% 8% 4 4 4 5% 8% 30%	1797
	11th to 20th	Day	15% 13% 5% 8% 6% 4 5% 4 5% 5% 30%	1903
	21st to end	Day	18% 11% 5% 7% 6% 3 4 4 3 5% 35%	2348
April	1st to 10th	Day	14% 11% 5% 8% 6% 4 5% 4 4 5% 33%	2160
	11th to 20th	Day	15% 9% 3 7% 6% 4 4 4 4 6% 36%	2134
	21st to end	Day	19% 11% 3 7% 5% 3 4 4 5% 6% 31%	2214
May	1st to 10th	Day	20% 10% 4 8% 7% 3 4 5% 4 6% 29%	2406
	11th to 20th	Day	19% 7% 3 5% 5% 3 5% 5% 5% 7% 36%	2478
	21st to end	Day	13% 6% 3 6% 6% 4 6% 6% 5% 8% 37%	2725
June	1st to 10th	Day	16% 7% 3 7% 6% 5% 6% 5% 6% 9% 30%	2520
	11th to 20th	Day	16% 7% 3 6% 6% 4 6% 6% 6% 9% 32%	2520
	21st to end	Day	15% 7% 3 7% 7% 4 6% 6% 5% 8% 32%	2520
July	1st to 10th	Day	11% 7% 3 6% 6% 4 6% 6% 7% 9% 35%	2520
	11th to 20th	Day	10% 5% 3 6% 7% 4 6% 6% 7% 11% 36%	2520
	21st to end	Day	12% 7% 3 7% 7% 4 7% 6% 6% 9% 33%	2744
August	1st to 10th	Day	9% 6% 3 6% 7% 4 7% 5% 7% 10% 35%	2463
	11th to 20th	Day	12% 8% 3 5% 7% 4 6% 7% 8% 9% 30%	2143
	21st to end	Day	14% 6% 3 5% 5% 4 6% 6% 7% 9% 35%	2376
September	1st to 10th	Day	14% 7% 3 6% 6% 3 5% 5% 5% 8% 39%	2160
	11th to 20th	Day	13% 7% 2 5% 4 3 5% 4 5% 7% 45%	2098
	21st to end	Day	14% 6% 3 4 4 3 5% 6% 6% 9% 39%	1980
October	1st to 10th	Day	17% 10% 4 7% 6% 3 4 4 6% 6% 34%	1850
	11th to 20th	Day	14% 9% 3 7% 5% 4 4 5% 6% 8% 36%	1800
	21st to end	Day	21% 12% 3 7% 6% 3 5% 5% 5% 5% 28%	1816
November	1st to 10th	Day	14% 11% 3 4 5% 3 4 3 4 7% 40%	1671
	11th to 20th	Day	15% 10% 5% 8% 7% 4 5% 4 4 6% 31%	1710
	21st to end	Day	15% 11% 5% 7% 6% 4 5% 5% 5% 6% 30%	1539
December	1st to 10th	Day	14% 14% 7% 10% 8% 4 6% 5% 5% 5% 22%	1520
	11th to 20th	Day	19% 12% 6% 9% 6% 3 4 4 4 5% 28%	1906
	21st to end	Day	18% 16% 9% 9% 5% 3 5% 5% 5% 6% 19%	2772
January	1st to 10th	Night	14% 11% 5% 9% 7% 3 5% 5% 6% 6% 29%	4429
	11th to 20th	Night	11% 14% 5% 10% 9% 5% 6% 5% 5% 6% 23%	4440
	21st to end	Night	18% 14% 7% 11% 8% 5% 4 3 4 5% 21%	4724
February	1st to 10th	Night	13% 12% 5% 9% 8% 4 6% 5% 6% 7% 26%	2470
	11th to 20th	Night	10% 10% 6% 11% 8% 5% 5% 7% 6% 6% 25%	2266
	21st to end	Night	15% 11% 5% 8% 6% 4 6% 5% 6% 7% 27%	1884
March	1st to 10th	Night	14% 11% 4 8% 8% 4 5% 4 5% 7% 30%	2157
	11th to 20th	Night	14% 9% 5% 10% 8% 4 6% 5% 5% 7% 29%	2053
	21st to end	Night	16% 12% 4 6% 6% 3 4 5% 5% 5% 35%	2007
April	1st to 10th	Night	14% 11% 4 9% 6% 3 6% 5% 6% 7% 29%	1800
	11th to 20th	Night	19% 9% 4 5% 5% 3 4 4 4 8% 36%	1775
	21st to end	Night	20% 10% 4 6% 4 3 4 4 5% 6% 35%	1746
May	1st to 10th	Night	20% 14% 4 7% 5% 3 4 3 4 6% 31%	1569
	11th to 20th	Night	16% 8% 3 6% 5% 4 4 5% 5% 8% 36%	1415
	21st to end	Night	10% 6% 3 6% 5% 4 5% 5% 6% 8% 40%	1550
June	1st to 10th	Night	16% 6% 4 6% 5% 3 4 5% 5% 7% 41%	1440
	11th to 20th	Night	15% 7% 2 6% 4 2 5% 5% 6% 9% 40%	1440
	21st to end	Night	10% 4 1 5% 5% 4 6% 5% 6% 10% 44%	1440
July	1st to 10th	Night	9% 6% 2 4 5% 3 5% 5% 6% 8% 45%	1440
	11th to 20th	Night	11% 5% 2 5% 5% 4 4 5% 7% 10% 43%	1440
	21st to end	Night	11% 6% 3 4 5% 4 4 5% 6% 7% 46%	1574
August	1st to 10th	Night	8% 4 2 4 5% 3 6% 6% 7% 9% 45%	1471
	11th to 20th	Night	11% 8% 3 6% 5% 3 5% 5% 6% 8% 40%	1740
	21st to end	Night	14% 5% 2 5% 5% 3 4 5% 6% 9% 44%	1980
September	1st to 10th	Night	13% 7% 2 4 5% 3 4 5% 6% 7% 44%	1800
	11th to 20th	Night	14% 6% 2 4 3 2 3 4 4 6% 52%	1862
	21st to end	Night	12% 5% 3 6% 5% 3 5% 5% 5% 7% 45%	1980
October	1st to 10th	Night	19% 8% 3 6% 5% 2 4 4 5% 6% 37%	2106
	11th to 20th	Night	16% 8% 3 6% 5% 3 4 4 5% 6% 39%	2160
	21st to end	Night	21% 12% 4 5% 5% 2 4 4 5% 7% 30%	2538
November	1st to 10th	Night	14% 10% 4 6% 5% 3 4 4 5% 6% 39%	2407
	11th to 20th	Night	16% 10% 4 7% 6% 4 5% 5% 5% 6% 31%	2470
	21st to end	Night	13% 10% 6% 8% 7% 3 5% 5% 5% 7% 33%	2636
December	1st to 10th	Night	14% 13% 6% 10% 7% 4 5% 6% 6% 7% 24%	2660
	11th to 20th	Night	18% 10% 6% 10% 6% 4 6% 4 5% 6% 26%	3288
	21st to end	Night	22% 12% 7% 10% 5% 3 4 5% 4 6% 22%	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% 8% 12% 16% 10%	1570
March	1st to 10th	Day	51% 7% 14% 17% 9% 2	1800
	11th to 20th	Day	54% 6% 10% 16% 11% 2	1903
	21st to end	Day	52% 6% 9% 15% 15% 4	2348
April	1st to 10th	Day	52% 7% 9% 21% 10% 2	2160
	11th to 20th	Day	48% 7% 12% 19% 13% 2	2134
	21st to end	Day	52% 7% 11% 16% 11% 3	2214
May	1st to 10th	Day	56% 6% 8% 18% 10% 2	2406
	11th to 20th	Day	46% 7% 11% 21% 13% 2	2482
	21st to end	Day	43% 11% 15% 21% 9% 1	2725
June	1st to 10th	Day	49% 9% 13% 18% 10% 1	2520
	11th to 20th	Day	46% 10% 14% 19% 10% 1	2520
	21st to end	Day	48% 8% 15% 19% 9% 1	2520
July	1st to 10th	Day	44% 10% 13% 20% 12% 1	2450
	11th to 20th	Day	39% 11% 18% 22% 10%	2445
	21st to end	Day	45% 8% 15% 20% 11% 1	2591
August	1st to 10th	Day	41% 12% 14% 21% 11% 1	2449
	11th to 20th	Day	46% 10% 16% 22% 5%	2143
	21st to end	Day	40% 10% 14% 23% 12% 1	2376
September	1st to 10th	Day	43% 8% 13% 23% 12% 1	2160
	11th to 20th	Day	38% 7% 12% 23% 19% 1	2098
	21st to end	Day	39% 9% 13% 24% 13% 2	1980
October	1st to 10th	Day	50% 7% 10% 18% 13% 1	1850
	11th to 20th	Day	44% 9% 15% 22% 10% 1	1800
	21st to end	Day	55% 9% 13% 13% 9% 2	1816
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	50% 8% 13% 18% 9% 1	2167
	11th to 20th	Night	51% 9% 13% 17% 9% 1	2054
	21st to end	Night	48% 7% 11% 17% 14% 3	2007
April	1st to 10th	Night	52% 8% 12% 17% 8% 1	1800
	11th to 20th	Night	47% 7% 13% 19% 14% 1	1775
	21st to end	Night	50% 7% 11% 17% 12% 3	1746
May	1st to 10th	Night	55% 7% 9% 14% 14% 2	1569
	11th to 20th	Night	45% 8% 10% 22% 13% 2	1416
	21st to end	Night	40% 11% 15% 22% 11% 2	1551
June	1st to 10th	Night	43% 8% 12% 24% 12% 2	1440
	11th to 20th	Night	39% 10% 16% 25% 10%	1440
	21st to end	Night	33% 12% 17% 25% 12%	1440
July	1st to 10th	Night	34% 10% 17% 23% 14% 2	1400
	11th to 20th	Night	35% 9% 19% 27% 10%	1392
	21st to end	Night	36% 9% 16% 23% 14% 2	1486
August	1st to 10th	Night	32% 12% 17% 27% 11% 1	1461
	11th to 20th	Night	40% 10% 17% 24% 9%	1740
	21st to end	Night	37% 9% 14% 26% 13% 1	1980
September	1st to 10th	Night	38% 9% 13% 27% 12% 1	1800
	11th to 20th	Night	33% 8% 12% 23% 23% 1	1862
	21st to end	Night	38% 9% 11% 24% 16% 1	1980
October	1st to 10th	Night	46% 8% 14% 19% 12% 1	2106
	11th to 20th	Night	43% 9% 16% 20% 11% 1	2160
	21st to end	Night	52% 8% 14% 17% 9% 1	2538
November	1st to 10th	Night	43% 8% 13% 19% 15% 3	2407
	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% 28% 30% 10% 2	382
March	1st to 10th	Day	29% 29% 30% 11% 2	420
	11th to 20th	Day	33% 26% 27% 11% 3	420
	21st to end	Day	34% 27% 24% 10% 4 2	462
April	1st to 10th	Day	31% 28% 22% 13% 6% 1	420
	11th to 20th	Day	25% 31% 24% 12% 5% 3	412
	21st to end	Day	34% 20% 28% 12% 4 2	420
May	1st to 10th	Day	32% 22% 28% 10% 6% 3	423
	11th to 20th	Day	20% 21% 34% 17% 7% 1	447
	21st to end	Day	19% 11% 33% 21% 12% 3	485
June	1st to 10th	Day	18% 18% 34% 21% 8% 1	450
	11th to 20th	Day	17% 17% 32% 23% 9% 2	450
	21st to end	Day	17% 17% 32% 22% 10% 1	450
July	1st to 10th	Day	11% 12% 34% 26% 14% 3	445
	11th to 20th	Day	9% 10% 36% 31% 11% 3	444
	21st to end	Day	12% 11% 39% 25% 10% 3	488
August	1st to 10th	Day	8% 10% 34% 27% 16% 4	446
	11th to 20th	Day	13% 10% 29% 28% 12% 7%	439
	21st to end	Day	12% 15% 27% 25% 14% 6%	495
September	1st to 10th	Day	17% 11% 29% 22% 16% 6%	450
	11th to 20th	Day	15% 14% 27% 20% 16% 9%	450
	21st to end	Day	18% 13% 29% 22% 12% 6%	450
October	1st to 10th	Day	23% 16% 26% 17% 14% 3	450
	11th to 20th	Day	22% 21% 26% 24% 6% 1	450
	21st to end	Day	26% 23% 29% 17% 4	412
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% 26% 29% 14% 2	628
March	1st to 10th	Night	27% 28% 30% 13% 2	723
	11th to 20th	Night	24% 29% 28% 15% 3	720
	21st to end	Night	27% 23% 30% 16% 5% 1	792
April	1st to 10th	Night	24% 26% 29% 17% 3	720
	11th to 20th	Night	24% 23% 30% 17% 6%	711
	21st to end	Night	27% 19% 28% 18% 7%	666
May	1st to 10th	Night	28% 18% 27% 20% 6% 1	489
	11th to 20th	Night	21% 16% 30% 27% 4 1	354
	21st to end	Night	15% 8% 31% 32% 12% 1	389
June	1st to 10th	Night	17% 12% 29% 28% 12% 1	360
	11th to 20th	Night	16% 14% 26% 32% 13%	360
	21st to end	Night	11% 7% 34% 36% 12% 1	360
July	1st to 10th	Night	11% 7% 26% 40% 15% 1	350
	11th to 20th	Night	12% 6% 26% 36% 18% 1	348
	21st to end	Night	12% 5% 26% 44% 12% 1	394
August	1st to 10th	Night	8% 5% 31% 35% 20% 1	397
	11th to 20th	Night	13% 7% 23% 36% 18% 3	676
	21st to end	Night	15% 7% 24% 33% 20% 2	792
September	1st to 10th	Night	14% 9% 28% 32% 16% 2	720
	11th to 20th	Night	16% 11% 25% 26% 17% 5%	720
	21st to end	Night	16% 11% 26% 31% 13% 3	720
October	1st to 10th	Night	22% 15% 23% 23% 14% 2	720
	11th to 20th	Night	20% 17% 30% 25% 8%	720
	21st to end	Night	26% 21% 28% 20% 4	792
November	1st to 10th	Night	21% 21% 26% 25% 7%	740
	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 2024-02-27 06:30:18. Version ac07

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