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 2024-11-05.

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% 2 6% 4 4 4 4 5% 7% 38%	101269
	Night	18% 8% 2 6% 4 4 4 3 5% 6% 40%	97759
Transparency	Day	44% 5% 11% 22% 15% 2	104803
	Night	44% 4 11% 23% 15% 2	102302
Seeing	Day	24% 16% 30% 19% 8% 2	14994
	Night	23% 15% 31% 24% 8% 1	24040

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 6% 4 4 4 3 4 5% 46%	2517
	11th to 20th	Day	17% 9% 3 8% 5% 4 5% 4 5% 5% 35%	2520
	21st to end	Day	22% 12% 4 9% 4 3 3 3 4 4 32%	2876
February	1st to 10th	Day	18% 8% 2 7% 5% 4 5% 4 5% 6% 37%	1753
	11th to 20th	Day	14% 7% 2 6% 4 5% 4 4 6% 7% 41%	1848
	21st to end	Day	21% 9% 2 7% 4 3 4 3 4 6% 38%	1570
March	1st to 10th	Day	27% 11% 2 6% 4 3 3 2 3 5% 33%	3116
	11th to 20th	Day	11% 5% 2 6% 4 5% 6% 5% 7% 7% 42%	3256
	21st to end	Day	21% 7% 2 6% 4 4 4 3 5% 6% 37%	4166
April	1st to 10th	Day	19% 9% 2 6% 5% 4 4 4 5% 6% 37%	2280
	11th to 20th	Day	19% 6% 2 5% 4 4 4 4 4 7% 40%	2254
	21st to end	Day	21% 6% 2 6% 4 4 4 3 4 6% 40%	2369
May	1st to 10th	Day	28% 8% 3 6% 3 3 4 3 6% 7% 30%	4106
	11th to 20th	Day	22% 8% 2 7% 5% 4 4 4 5% 7% 32%	4317
	21st to end	Day	16% 5% 2 4 4 4 4 4 6% 8% 45%	4837
June	1st to 10th	Day	18% 6% 2 5% 5% 5% 5% 4 7% 9% 35%	2660
	11th to 20th	Day	16% 7% 3 5% 4 5% 4 5% 7% 9% 36%	2660
	21st to end	Day	13% 6% 2 7% 4 5% 5% 4 6% 9% 37%	2660
July	1st to 10th	Day	12% 7% 2 7% 5% 6% 5% 5% 6% 9% 35%	4440
	11th to 20th	Day	13% 6% 3 6% 4 4 5% 5% 6% 9% 39%	4440
	21st to end	Day	17% 8% 3 7% 5% 5% 5% 4 7% 7% 32%	4814
August	1st to 10th	Day	20% 7% 3 7% 5% 5% 4 4 6% 8% 31%	4277
	11th to 20th	Day	12% 6% 3 6% 5% 4 4 4 7% 9% 40%	3730
	21st to end	Day	10% 5% 2 6% 4 4 5% 4 5% 9% 45%	4180
September	1st to 10th	Day	14% 6% 2 6% 5% 4 4 4 5% 6% 44%	2280
	11th to 20th	Day	13% 6% 2 4 3 4 4 3 5% 7% 49%	2161
	21st to end	Day	19% 6% 2 6% 4 4 4 3 4 6% 41%	2090
October	1st to 10th	Day	21% 7% 2 5% 4 3 4 3 5% 5% 41%	2038
	11th to 20th	Day	14% 6% 2 6% 3 3 4 4 5% 7% 46%	1899
	21st to end	Day	22% 6% 2 5% 4 4 4 4 4 6% 40%	1881
November	1st to 10th	Day	14% 7% 2 4 4 3 3 3 4 7% 49%	1708
	11th to 20th	Day	19% 6% 2 4 3 4 3 3 5% 6% 45%	1710
	21st to end	Day	17% 7% 3 5% 4 3 3 3 6% 6% 43%	1658
December	1st to 10th	Day	20% 8% 2 6% 5% 4 4 3 5% 6% 37%	1520
	11th to 20th	Day	23% 6% 2 4 2 3 4 3 4 6% 43%	1906
	21st to end	Day	19% 12% 3 7% 6% 4 4 3 4 6% 32%	2772
January	1st to 10th	Night	17% 7% 2 5% 3 3 3 4 4 6% 45%	4429
	11th to 20th	Night	17% 9% 3 7% 4 3 4 3 5% 5% 41%	4440
	21st to end	Night	24% 12% 3 7% 4 3 3 2 4 5% 33%	4778
February	1st to 10th	Night	16% 10% 3 6% 4 4 4 3 5% 5% 41%	2425
	11th to 20th	Night	15% 8% 3 6% 4 4 4 3 5% 6% 41%	2218
	21st to end	Night	19% 9% 2 6% 4 4 4 3 5% 5% 41%	1884
March	1st to 10th	Night	25% 12% 3 6% 3 3 3 3 4 5% 34%	3724
	11th to 20th	Night	11% 7% 2 6% 4 5% 5% 4 6% 6% 43%	3671
	21st to end	Night	21% 9% 3 5% 3 3 3 2 4 6% 40%	3466
April	1st to 10th	Night	19% 8% 2 6% 4 5% 5% 4 6% 6% 36%	1900
	11th to 20th	Night	19% 6% 2 5% 4 4 4 3 5% 6% 39%	1875
	21st to end	Night	20% 6% 3 6% 4 3 3 3 4 6% 42%	1810
May	1st to 10th	Night	25% 10% 2 8% 5% 4 4 3 4 7% 28%	2834
	11th to 20th	Night	22% 9% 3 7% 5% 4 4 4 5% 6% 32%	2605
	21st to end	Night	17% 8% 2 5% 3 3 4 3 5% 7% 42%	2738
June	1st to 10th	Night	18% 6% 3 5% 5% 5% 3 4 4 7% 40%	1520
	11th to 20th	Night	16% 7% 2 5% 4 3 4 4 6% 9% 40%	1520
	21st to end	Night	13% 7% 1 5% 5% 4 4 5% 5% 10% 41%	1520
July	1st to 10th	Night	13% 6% 2 6% 4 4 6% 4 7% 8% 38%	2520
	11th to 20th	Night	17% 6% 2 6% 4 4 5% 4 6% 9% 37%	2520
	21st to end	Night	19% 9% 2 6% 4 5% 4 4 6% 6% 34%	2739
August	1st to 10th	Night	23% 7% 3 7% 5% 4 5% 3 6% 6% 30%	2618
	11th to 20th	Night	16% 7% 3 6% 5% 4 4 4 5% 7% 41%	3097
	21st to end	Night	11% 4 2 4 3 3 4 3 5% 8% 53%	3476
September	1st to 10th	Night	15% 7% 2 6% 4 3 4 3 4 6% 46%	1900
	11th to 20th	Night	13% 5% 2 5% 3 3 3 3 4 7% 53%	2019
	21st to end	Night	18% 7% 2 5% 3 3 5% 3 4 6% 44%	2090
October	1st to 10th	Night	20% 7% 3 6% 4 3 3 3 5% 6% 42%	2137
	11th to 20th	Night	14% 6% 2 5% 4 3 3 3 4 7% 48%	2280
	21st to end	Night	22% 7% 2 5% 3 4 3 3 5% 5% 41%	2717
November	1st to 10th	Night	13% 6% 2 6% 4 3 4 3 5% 6% 48%	2470
	11th to 20th	Night	19% 7% 2 5% 4 3 3 3 4 5% 46%	2470
	21st to end	Night	16% 7% 2 5% 4 4 4 3 5% 6% 45%	2517
December	1st to 10th	Night	20% 7% 3 6% 4 4 4 3 5% 6% 39%	2660
	11th to 20th	Night	20% 7% 2 5% 3 4 4 4 5% 6% 39%	3288
	21st to end	Night	22% 11% 4 7% 4 4 3 3 5% 5% 34%	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% 5% 10% 21% 16% 4	2369
May	1st to 10th	Day	54% 5% 13% 15% 12% 1	4120
	11th to 20th	Day	51% 6% 13% 19% 10% 1	4321
	21st to end	Day	37% 6% 12% 26% 18% 2	4837
June	1st to 10th	Day	44% 6% 13% 23% 13% 1	2660
	11th to 20th	Day	44% 6% 13% 24% 12% 2	2660
	21st to end	Day	41% 7% 14% 23% 14% 1	2660
July	1st to 10th	Day	45% 8% 10% 20% 16% 1	4370
	11th to 20th	Day	41% 7% 15% 23% 13% 1	4365
	21st to end	Day	50% 6% 11% 17% 14% 1	4661
August	1st to 10th	Day	50% 6% 14% 21% 8%	4263
	11th to 20th	Day	39% 6% 14% 30% 11% 1	3766
	21st to end	Day	35% 6% 11% 29% 17% 2	4180
September	1st to 10th	Day	41% 6% 10% 23% 19% 2	2280
	11th to 20th	Day	35% 5% 9% 24% 25% 2	2161
	21st to end	Day	45% 5% 8% 21% 17% 3	2090
October	1st to 10th	Day	40% 5% 7% 19% 24% 5%	3389
	11th to 20th	Day	29% 4 8% 25% 30% 4	3127
	21st to end	Day	32% 3 13% 24% 24% 4	3081
November	1st to 10th	Day	37% 3 12% 25% 20% 3	1708
	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% 23% 16% 4	1810
May	1st to 10th	Night	57% 5% 11% 16% 10% 1	2840
	11th to 20th	Night	54% 6% 13% 16% 10% 1	2606
	21st to end	Night	42% 4 13% 25% 13% 2	2739
June	1st to 10th	Night	46% 5% 9% 21% 17% 2	1520
	11th to 20th	Night	39% 7% 15% 26% 11% 1	1520
	21st to end	Night	38% 7% 13% 26% 15% 1	1520
July	1st to 10th	Night	42% 8% 15% 19% 14% 1	2480
	11th to 20th	Night	43% 6% 15% 23% 12%	2472
	21st to end	Night	49% 6% 13% 15% 16% 2	2651
August	1st to 10th	Night	53% 7% 12% 18% 9% 1	2608
	11th to 20th	Night	43% 6% 13% 30% 8% 1	3127
	21st to end	Night	29% 5% 12% 35% 17% 1	3476
September	1st to 10th	Night	41% 4 9% 26% 18% 2	1900
	11th to 20th	Night	33% 4 10% 24% 25% 2	2019
	21st to end	Night	42% 6% 7% 23% 20% 2	2090
October	1st to 10th	Night	39% 4 12% 22% 20% 2	3566
	11th to 20th	Night	27% 4 9% 27% 29% 4	3779
	21st to end	Night	34% 3 13% 29% 19% 2	4467
November	1st to 10th	Night	37% 4 11% 22% 21% 4	2470
	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	31% 18% 31% 13% 5% 1	460
May	1st to 10th	Day	35% 19% 26% 13% 6% 1	463
	11th to 20th	Day	25% 17% 36% 17% 5% 1	487
	21st to end	Day	21% 11% 33% 24% 9% 2	529
June	1st to 10th	Day	22% 12% 31% 22% 10% 2	490
	11th to 20th	Day	18% 14% 34% 23% 11% 1	490
	21st to end	Day	17% 11% 33% 27% 10% 1	490
July	1st to 10th	Day	17% 8% 30% 27% 15% 3	485
	11th to 20th	Day	12% 8% 33% 28% 16% 2	484
	21st to end	Day	14% 10% 35% 28% 12% 1	532
August	1st to 10th	Day	17% 7% 26% 34% 11% 5%	486
	11th to 20th	Day	16% 7% 25% 32% 14% 5%	479
	21st to end	Day	12% 11% 30% 25% 15% 6%	539
September	1st to 10th	Day	19% 11% 27% 23% 16% 5%	490
	11th to 20th	Day	16% 10% 29% 26% 11% 9%	490
	21st to end	Day	22% 12% 32% 20% 9% 4	490
October	1st to 10th	Day	28% 10% 27% 16% 14% 4	490
	11th to 20th	Day	18% 21% 30% 21% 8% 2	489
	21st to end	Day	30% 13% 31% 17% 8% 1	429
November	1st to 10th	Day	21% 15% 29% 23% 10% 2	378
	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% 35% 18% 4 1	670
May	1st to 10th	Night	30% 13% 32% 20% 5%	570
	11th to 20th	Night	23% 18% 32% 22% 5%	445
	21st to end	Night	22% 8% 29% 32% 7% 1	411
June	1st to 10th	Night	20% 8% 32% 31% 9% 1	380
	11th to 20th	Night	18% 7% 29% 35% 11% 1	380
	21st to end	Night	16% 5% 27% 42% 9%	380
July	1st to 10th	Night	15% 4 25% 37% 18% 1	370
	11th to 20th	Night	15% 4 23% 41% 16% 2	368
	21st to end	Night	15% 5% 26% 38% 15% 1	416
August	1st to 10th	Night	12% 5% 28% 38% 16% 1	438
	11th to 20th	Night	16% 5% 20% 37% 19% 2	750
	21st to end	Night	15% 5% 23% 36% 19% 2	836
September	1st to 10th	Night	18% 5% 30% 32% 13% 3	760
	11th to 20th	Night	17% 7% 23% 32% 18% 4	760
	21st to end	Night	22% 9% 26% 27% 15% 1	760
October	1st to 10th	Night	24% 9% 27% 25% 13% 2	760
	11th to 20th	Night	19% 15% 31% 26% 9% 1	760
	21st to end	Night	28% 13% 32% 20% 7%	836
November	1st to 10th	Night	18% 14% 35% 24% 9% 1	760
	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 2024-11-03 02:11:19. Version ac07

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