Southwind Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Southwind Observatory clear sky chart from 2005-11-06 to 2024-04-25.

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	17% 7% 3 5% 5% 3 4 5% 5% 7% 39%	83153
	Night	18% 7% 3 5% 4 3 4 4 5% 6% 41%	85920
Transparency	Day	44% 5% 11% 23% 15% 2	82858
	Night	44% 4 11% 23% 15% 2	85749
Seeing	Day	25% 16% 30% 19% 8% 2	14234
	Night	23% 15% 31% 23% 7% 1	23456

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	14% 8% 3 5% 5% 3 4 4 4 5% 46%	2517
	11th to 20th	Day	17% 8% 4 7% 7% 3 5% 5% 5% 5% 35%	2520
	21st to end	Day	22% 11% 4 7% 5% 2 3 4 4 4 32%	2876
February	1st to 10th	Day	18% 7% 3 6% 5% 3 5% 5% 5% 6% 37%	1753
	11th to 20th	Day	14% 6% 3 5% 5% 4 4 4 6% 7% 41%	1848
	21st to end	Day	21% 8% 2 6% 5% 2 4 4 4 5% 38%	1570
March	1st to 10th	Day	28% 10% 2 5% 5% 3 3 3 3 5% 34%	3116
	11th to 20th	Day	11% 4 2 5% 5% 4 6% 6% 7% 7% 42%	3256
	21st to end	Day	21% 6% 3 5% 5% 3 4 4 5% 6% 38%	4166
April	1st to 10th	Day	19% 8% 3 5% 5% 3 4 4 5% 6% 37%	2280
	11th to 20th	Day	19% 5% 2 5% 5% 3 4 4 4 7% 41%	2254
	21st to end	Day	21% 6% 2 5% 4 3 4 4 5% 5% 41%	2294
May	1st to 10th	Day	24% 8% 3 5% 5% 3 4 4 5% 7% 34%	2340
	11th to 20th	Day	20% 6% 2 4 5% 3 4 4 6% 7% 40%	2425
	21st to end	Day	17% 5% 2 4 4 3 4 5% 5% 7% 43%	2725
June	1st to 10th	Day	18% 6% 2 4 5% 4 5% 5% 7% 9% 35%	2520
	11th to 20th	Day	17% 6% 3 6% 4 3 5% 6% 6% 9% 35%	2520
	21st to end	Day	13% 6% 2 6% 5% 4 5% 5% 6% 9% 38%	2520
July	1st to 10th	Day	13% 6% 2 5% 6% 4 5% 6% 6% 8% 39%	2520
	11th to 20th	Day	13% 5% 3 4 5% 3 5% 6% 6% 10% 40%	2520
	21st to end	Day	13% 6% 3 6% 6% 4 5% 5% 8% 8% 38%	2744
August	1st to 10th	Day	11% 6% 3 6% 6% 4 4 6% 7% 10% 37%	2429
	11th to 20th	Day	12% 6% 2 5% 6% 3 5% 5% 7% 9% 39%	2126
	21st to end	Day	13% 5% 3 6% 5% 3 5% 4 5% 9% 42%	2376
September	1st to 10th	Day	14% 6% 2 5% 6% 3 5% 5% 5% 6% 43%	2160
	11th to 20th	Day	13% 6% 2 4 4 3 4 4 5% 7% 49%	2048
	21st to end	Day	18% 5% 2 5% 5% 2 4 4 4 6% 43%	1980
October	1st to 10th	Day	22% 7% 3 4 5% 2 3 4 5% 4 41%	1931
	11th to 20th	Day	15% 6% 2 5% 4 2 4 5% 5% 7% 45%	1800
	21st to end	Day	23% 6% 2 4 5% 3 4 5% 4 6% 38%	1782
November	1st to 10th	Day	14% 6% 2 4 4 2 3 3 4 7% 49%	1671
	11th to 20th	Day	19% 6% 2 3 3 2 4 4 5% 6% 45%	1710
	21st to end	Day	18% 6% 3 5% 4 2 3 4 6% 6% 43%	1658
December	1st to 10th	Day	20% 7% 3 5% 6% 3 4 4 5% 6% 37%	1520
	11th to 20th	Day	23% 5% 2 4 3 2 4 4 4 6% 43%	1906
	21st to end	Day	19% 11% 3 6% 6% 3 4 4 4 6% 32%	2772
January	1st to 10th	Night	17% 7% 2 5% 4 2 3 4 4 6% 45%	4429
	11th to 20th	Night	17% 8% 3 6% 5% 3 3 4 5% 5% 41%	4440
	21st to end	Night	24% 12% 3 6% 4 2 4 3 3 5% 33%	4778
February	1st to 10th	Night	16% 9% 3 6% 4 3 4 3 4 5% 41%	2425
	11th to 20th	Night	15% 8% 3 5% 5% 3 4 4 5% 7% 41%	2218
	21st to end	Night	20% 8% 3 5% 4 2 4 4 4 5% 41%	1884
March	1st to 10th	Night	25% 12% 3 5% 4 2 3 4 4 5% 34%	3724
	11th to 20th	Night	11% 7% 2 5% 5% 3 5% 5% 5% 7% 43%	3671
	21st to end	Night	21% 8% 3 5% 4 2 3 3 4 6% 40%	3466
April	1st to 10th	Night	19% 7% 2 5% 4 3 5% 5% 6% 6% 37%	1900
	11th to 20th	Night	19% 6% 3 4 5% 3 4 4 5% 7% 39%	1875
	21st to end	Night	21% 6% 4 5% 5% 2 3 3 4 6% 42%	1765
May	1st to 10th	Night	23% 8% 2 6% 6% 3 4 4 5% 7% 33%	1620
	11th to 20th	Night	20% 7% 3 5% 5% 2 3 4 5% 6% 39%	1483
	21st to end	Night	18% 7% 3 4 4 3 4 4 5% 7% 41%	1550
June	1st to 10th	Night	19% 5% 4 5% 5% 4 4 4 4 7% 40%	1440
	11th to 20th	Night	17% 6% 3 5% 4 2 5% 5% 6% 9% 39%	1440
	21st to end	Night	13% 6% 2 4 5% 3 4 6% 5% 10% 43%	1440
July	1st to 10th	Night	14% 5% 2 4 5% 3 5% 5% 6% 8% 42%	1440
	11th to 20th	Night	13% 6% 2 5% 5% 4 5% 5% 6% 10% 39%	1440
	21st to end	Night	11% 6% 2 5% 5% 4 6% 5% 7% 8% 42%	1574
August	1st to 10th	Night	9% 6% 3 5% 6% 3 6% 5% 7% 8% 44%	1488
	11th to 20th	Night	13% 5% 3 6% 7% 4 5% 6% 6% 8% 38%	1774
	21st to end	Night	16% 5% 2 4 4 3 4 4 6% 7% 45%	1980
September	1st to 10th	Night	16% 7% 3 5% 5% 3 4 4 4 7% 45%	1800
	11th to 20th	Night	13% 5% 2 5% 3 2 3 3 4 6% 53%	1912
	21st to end	Night	17% 6% 2 5% 4 2 4 5% 4 6% 45%	1980
October	1st to 10th	Night	21% 6% 3 5% 4 2 3 3 5% 6% 42%	2024
	11th to 20th	Night	15% 6% 2 5% 5% 2 3 4 4 7% 47%	2160
	21st to end	Night	23% 7% 2 5% 4 3 4 3 5% 5% 40%	2574
November	1st to 10th	Night	14% 6% 2 5% 4 2 4 4 5% 6% 48%	2407
	11th to 20th	Night	19% 6% 2 4 4 2 4 3 4 5% 46%	2470
	21st to end	Night	16% 6% 2 4 5% 3 4 4 4 6% 46%	2517
December	1st to 10th	Night	21% 7% 3 5% 4 3 4 4 4 6% 40%	2660
	11th to 20th	Night	20% 7% 2 4 4 3 4 5% 4 6% 40%	3288
	21st to end	Night	22% 10% 4 6% 4 3 3 3 4 5% 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	39% 5% 10% 32% 11% 3	2518
	11th to 20th	Day	51% 4 10% 24% 11% 1	2520
	21st to end	Day	56% 3 8% 20% 11% 2	2876
February	1st to 10th	Day	48% 4 12% 21% 14% 2	1753
	11th to 20th	Day	42% 4 11% 23% 18% 3	1857
	21st to end	Day	49% 4 9% 22% 13% 3	1570
March	1st to 10th	Day	55% 3 10% 18% 12% 2	3119
	11th to 20th	Day	35% 6% 14% 30% 13% 1	3256
	21st to end	Day	47% 3 6% 17% 21% 6%	4166
April	1st to 10th	Day	47% 4 10% 21% 15% 3	2280
	11th to 20th	Day	44% 5% 10% 22% 17% 3	2254
	21st to end	Day	45% 4 9% 21% 16% 4	2294
May	1st to 10th	Day	51% 5% 8% 20% 15% 2	2340
	11th to 20th	Day	43% 6% 10% 21% 18% 3	2429
	21st to end	Day	41% 7% 16% 21% 14% 2	2725
June	1st to 10th	Day	46% 6% 13% 23% 12% 1	2520
	11th to 20th	Day	45% 6% 12% 23% 12% 1	2520
	21st to end	Day	41% 7% 14% 24% 13% 1	2520
July	1st to 10th	Day	43% 7% 11% 22% 16% 2	2450
	11th to 20th	Day	39% 7% 14% 26% 14% 1	2445
	21st to end	Day	41% 7% 14% 19% 17% 2	2591
August	1st to 10th	Day	40% 7% 14% 25% 13% 1	2415
	11th to 20th	Day	40% 6% 16% 24% 13% 1	2126
	21st to end	Day	40% 6% 11% 23% 18% 2	2376
September	1st to 10th	Day	42% 7% 10% 22% 18% 2	2160
	11th to 20th	Day	35% 5% 10% 24% 24% 2	2048
	21st to end	Day	43% 5% 8% 22% 18% 3	1980
October	1st to 10th	Day	47% 5% 7% 23% 16% 3	1931
	11th to 20th	Day	38% 5% 12% 27% 16% 2	1800
	21st to end	Day	47% 4 9% 21% 16% 3	1782
November	1st to 10th	Day	37% 3 12% 25% 19% 3	1671
	11th to 20th	Day	39% 4 10% 24% 19% 3	1710
	21st to end	Day	41% 4 13% 27% 13% 3	1658
December	1st to 10th	Day	48% 4 14% 18% 15% 1	1520
	11th to 20th	Day	43% 3 16% 19% 17% 2	1906
	21st to end	Day	54% 4 10% 22% 10% 1	2772
January	1st to 10th	Night	40% 3 11% 30% 12% 4	4429
	11th to 20th	Night	45% 4 11% 24% 13% 3	4440
	21st to end	Night	55% 3 8% 20% 11% 2	4778
February	1st to 10th	Night	46% 4 12% 23% 12% 2	2425
	11th to 20th	Night	44% 4 10% 19% 19% 4	2220
	21st to end	Night	46% 3 8% 24% 14% 5%	1884
March	1st to 10th	Night	53% 3 10% 19% 12% 2	3734
	11th to 20th	Night	39% 5% 14% 25% 15% 3	3672
	21st to end	Night	46% 3 7% 14% 24% 6%	3466
April	1st to 10th	Night	46% 5% 10% 21% 16% 3	1900
	11th to 20th	Night	44% 5% 10% 20% 20% 1	1875
	21st to end	Night	45% 4 9% 22% 16% 4	1765
May	1st to 10th	Night	52% 5% 9% 18% 14% 2	1620
	11th to 20th	Night	47% 5% 9% 19% 18% 2	1484
	21st to end	Night	44% 5% 15% 21% 12% 2	1551
June	1st to 10th	Night	46% 5% 10% 21% 17% 2	1440
	11th to 20th	Night	41% 7% 15% 25% 11% 1	1440
	21st to end	Night	37% 7% 14% 27% 15% 1	1440
July	1st to 10th	Night	39% 8% 15% 22% 14% 2	1400
	11th to 20th	Night	41% 7% 15% 27% 10% 1	1392
	21st to end	Night	37% 7% 16% 22% 15% 3	1486
August	1st to 10th	Night	36% 8% 15% 25% 15% 1	1478
	11th to 20th	Night	43% 8% 14% 24% 10% 1	1774
	21st to end	Night	37% 7% 13% 23% 19% 1	1980
September	1st to 10th	Night	42% 4 10% 27% 17% 1	1800
	11th to 20th	Night	34% 4 11% 24% 26% 3	1912
	21st to end	Night	41% 6% 6% 23% 21% 3	1980
October	1st to 10th	Night	45% 5% 11% 23% 14% 3	2024
	11th to 20th	Night	40% 4 12% 29% 15% 1	2160
	21st to end	Night	47% 3 11% 21% 15% 1	2574
November	1st to 10th	Night	37% 4 11% 22% 21% 4	2407
	11th to 20th	Night	42% 3 9% 24% 19% 4	2470
	21st to end	Night	40% 4 12% 30% 12% 2	2517
December	1st to 10th	Night	46% 4 12% 22% 15% 1	2660
	11th to 20th	Night	45% 4 13% 18% 17% 3	3288
	21st to end	Night	52% 4 10% 23% 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	36% 20% 29% 12% 2	180
	11th to 20th	Day	31% 29% 28% 9% 2	180
	21st to end	Day	26% 28% 30% 11% 5%	229
February	1st to 10th	Day	33% 27% 28% 10% 1	313
	11th to 20th	Day	31% 27% 31% 10% 1	456
	21st to end	Day	34% 22% 29% 11% 3	382
March	1st to 10th	Day	30% 20% 34% 13% 2	460
	11th to 20th	Day	30% 25% 32% 11% 3 1	460
	21st to end	Day	31% 23% 31% 10% 3 2	506
April	1st to 10th	Day	33% 24% 26% 10% 6% 1	460
	11th to 20th	Day	33% 18% 31% 13% 4 2	452
	21st to end	Day	32% 19% 31% 12% 5% 1	437
May	1st to 10th	Day	37% 18% 26% 13% 6% 1	423
	11th to 20th	Day	25% 18% 36% 16% 4 1	447
	21st to end	Day	21% 11% 31% 25% 9% 3	485
June	1st to 10th	Day	22% 13% 30% 22% 10% 2	450
	11th to 20th	Day	19% 14% 34% 22% 9% 1	450
	21st to end	Day	16% 11% 32% 29% 11% 1	450
July	1st to 10th	Day	17% 8% 29% 27% 15% 4	445
	11th to 20th	Day	13% 8% 31% 28% 18% 3	444
	21st to end	Day	13% 10% 35% 29% 12% 1	488
August	1st to 10th	Day	15% 7% 26% 35% 11% 5%	446
	11th to 20th	Day	16% 7% 24% 33% 14% 6%	439
	21st to end	Day	13% 11% 30% 24% 15% 7%	495
September	1st to 10th	Day	19% 11% 26% 22% 16% 5%	450
	11th to 20th	Day	17% 10% 30% 24% 9% 8%	450
	21st to end	Day	21% 13% 32% 20% 10% 5%	450
October	1st to 10th	Day	30% 10% 27% 16% 14% 4	450
	11th to 20th	Day	18% 22% 29% 21% 8% 2	450
	21st to end	Day	31% 14% 32% 16% 7%	396
November	1st to 10th	Day	21% 16% 28% 23% 10% 2	365
	11th to 20th	Day	29% 21% 26% 19% 4 1	370
	21st to end	Day	27% 20% 31% 17% 4 1	318
December	1st to 10th	Day	31% 19% 31% 15% 4 1	180
	11th to 20th	Day	39% 22% 26% 10% 2	180
	21st to end	Day	29% 24% 27% 14% 4 2	198
January	1st to 10th	Night	25% 19% 36% 17% 3	760
	11th to 20th	Night	29% 21% 30% 18% 3	760
	21st to end	Night	25% 22% 33% 18% 2	836
February	1st to 10th	Night	25% 19% 34% 19% 2	760
	11th to 20th	Night	27% 23% 36% 13% 1	743
	21st to end	Night	30% 20% 31% 16% 3	628
March	1st to 10th	Night	27% 21% 33% 17% 3	760
	11th to 20th	Night	23% 24% 34% 16% 2 1	760
	21st to end	Night	26% 20% 33% 17% 4	836
April	1st to 10th	Night	27% 19% 33% 18% 3	760
	11th to 20th	Night	24% 19% 35% 19% 3	751
	21st to end	Night	24% 19% 34% 18% 4 1	655
May	1st to 10th	Night	30% 13% 33% 19% 5%	540
	11th to 20th	Night	23% 18% 33% 22% 5%	422
	21st to end	Night	22% 8% 29% 32% 8% 2	389
June	1st to 10th	Night	20% 7% 32% 30% 10% 1	360
	11th to 20th	Night	19% 7% 28% 34% 11%	360
	21st to end	Night	16% 4 27% 44% 9%	360
July	1st to 10th	Night	15% 3 25% 36% 19% 1	350
	11th to 20th	Night	14% 3 24% 41% 16% 2	348
	21st to end	Night	13% 5% 27% 39% 15% 1	394
August	1st to 10th	Night	11% 5% 29% 39% 16% 1	414
	11th to 20th	Night	16% 5% 20% 37% 19% 2	710
	21st to end	Night	16% 5% 22% 37% 18% 2	792
September	1st to 10th	Night	18% 5% 30% 33% 12% 3	720
	11th to 20th	Night	18% 8% 24% 31% 16% 3	720
	21st to end	Night	21% 8% 26% 28% 16% 1	720
October	1st to 10th	Night	25% 9% 27% 24% 13% 2	720
	11th to 20th	Night	20% 15% 30% 26% 9%	720
	21st to end	Night	29% 13% 33% 18% 7%	792
November	1st to 10th	Night	18% 14% 34% 24% 9% 1	740
	11th to 20th	Night	25% 16% 33% 19% 7% 1	760
	21st to end	Night	24% 17% 30% 22% 5% 1	760
December	1st to 10th	Night	28% 17% 31% 19% 4 1	760
	11th to 20th	Night	25% 22% 29% 21% 3	760
	21st to end	Night	30% 17% 34% 17% 2	836

Page generated at 2024-04-22 09:25:47. Version ac07

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