Swain Hill
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Swain Hill 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	17% 11% 4 9% 5% 5% 4 4 5% 6% 29%	101323
	Night	18% 13% 4 10% 5% 4 4 3 5% 5% 27%	97626
Transparency	Day	51% 9% 12% 18% 9% 1	101081
	Night	53% 9% 12% 17% 8% 1	97488
Seeing	Day	26% 19% 28% 17% 7% 2	14823
	Night	25% 16% 26% 24% 8% 1	23700

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% 14% 6% 15% 7% 6% 6% 4 4 4 21%	2517
	11th to 20th	Day	13% 12% 7% 15% 13% 6% 5% 3 3 4 20%	2520
	21st to end	Day	16% 16% 9% 14% 6% 4 4 4 4 5% 20%	2772
February	1st to 10th	Day	15% 16% 4 11% 7% 6% 4 4 5% 5% 23%	1666
	11th to 20th	Day	12% 14% 6% 14% 8% 4 5% 4 5% 6% 22%	1848
	21st to end	Day	14% 14% 5% 12% 7% 4 4 3 6% 5% 26%	1570
March	1st to 10th	Day	19% 16% 5% 13% 6% 5% 4 3 4 4 21%	3116
	11th to 20th	Day	14% 17% 9% 12% 5% 4 3 3 4 5% 25%	3285
	21st to end	Day	18% 12% 5% 12% 5% 5% 4 3 4 6% 27%	4097
April	1st to 10th	Day	20% 15% 4 9% 5% 4 3 3 3 5% 29%	2280
	11th to 20th	Day	17% 14% 4 7% 5% 5% 4 3 5% 5% 32%	2270
	21st to end	Day	21% 13% 4 9% 5% 4 4 3 5% 5% 27%	2470
May	1st to 10th	Day	25% 13% 3 8% 5% 4 4 3 4 5% 24%	4106
	11th to 20th	Day	17% 10% 4 10% 6% 6% 5% 4 6% 7% 26%	4353
	21st to end	Day	12% 8% 3 8% 5% 5% 5% 4 7% 8% 35%	4837
June	1st to 10th	Day	21% 9% 3 8% 5% 5% 4 5% 7% 7% 25%	2660
	11th to 20th	Day	18% 9% 2 6% 6% 4 4 4 6% 8% 32%	2660
	21st to end	Day	20% 10% 3 10% 5% 4 5% 4 6% 6% 27%	2660
July	1st to 10th	Day	15% 7% 2 7% 5% 5% 5% 4 7% 10% 32%	4440
	11th to 20th	Day	13% 6% 2 8% 5% 5% 6% 5% 7% 9% 32%	4440
	21st to end	Day	20% 8% 3 7% 4 4 5% 5% 6% 7% 33%	4814
August	1st to 10th	Day	18% 8% 3 8% 5% 5% 5% 5% 6% 7% 30%	4303
	11th to 20th	Day	19% 8% 3 7% 5% 6% 5% 5% 7% 8% 26%	3998
	21st to end	Day	14% 7% 3 6% 4 4 5% 4 6% 9% 38%	4180
September	1st to 10th	Day	14% 6% 2 6% 4 4 4 4 6% 7% 42%	2280
	11th to 20th	Day	15% 6% 2 6% 3 3 3 3 5% 6% 47%	2119
	21st to end	Day	16% 9% 2 6% 4 5% 4 3 6% 6% 39%	2090
October	1st to 10th	Day	22% 11% 3 7% 5% 3 4 3 4 6% 31%	2090
	11th to 20th	Day	16% 12% 4 7% 5% 3 4 3 5% 6% 35%	1800
	21st to end	Day	25% 16% 4 7% 3 4 4 3 4 4 27%	1881
November	1st to 10th	Day	15% 13% 3 8% 4 4 4 3 5% 7% 34%	1671
	11th to 20th	Day	17% 13% 5% 9% 5% 5% 4 4 5% 5% 26%	1710
	21st to end	Day	19% 14% 4 11% 6% 5% 4 4 4 5% 24%	1622
December	1st to 10th	Day	20% 18% 7% 12% 7% 5% 3 2 3 4 19%	1520
	11th to 20th	Day	21% 18% 4 8% 5% 4 3 3 3 5% 26%	1906
	21st to end	Day	23% 14% 6% 14% 6% 4 3 3 4 4 19%	2772
January	1st to 10th	Night	13% 14% 6% 15% 7% 5% 6% 3 4 5% 21%	4429
	11th to 20th	Night	12% 17% 7% 17% 9% 5% 4 3 5% 4 16%	4440
	21st to end	Night	18% 17% 6% 13% 7% 7% 4 3 4 3 18%	4884
February	1st to 10th	Night	15% 13% 6% 12% 8% 6% 5% 3 5% 6% 22%	2509
	11th to 20th	Night	11% 13% 7% 13% 8% 6% 5% 4 5% 5% 22%	2218
	21st to end	Night	12% 14% 4 12% 8% 5% 4 4 4 6% 27%	1884
March	1st to 10th	Night	21% 16% 4 9% 7% 5% 4 3 4 5% 23%	3724
	11th to 20th	Night	13% 20% 6% 11% 5% 4 5% 3 4 4 26%	3673
	21st to end	Night	20% 17% 5% 11% 4 3 4 2 4 5% 27%	3532
April	1st to 10th	Night	21% 14% 4 7% 5% 4 3 3 5% 5% 28%	1900
	11th to 20th	Night	19% 12% 3 9% 5% 4 3 4 5% 5% 31%	1857
	21st to end	Night	19% 13% 4 8% 5% 4 3 3 4 6% 32%	1710
May	1st to 10th	Night	26% 12% 3 8% 4 5% 4 3 6% 6% 23%	2834
	11th to 20th	Night	19% 11% 4 8% 6% 5% 6% 4 6% 6% 26%	2569
	21st to end	Night	15% 8% 2 5% 4 4 5% 4 6% 9% 37%	2738
June	1st to 10th	Night	24% 9% 4 7% 4 4 4 4 5% 8% 27%	1520
	11th to 20th	Night	19% 8% 3 6% 5% 5% 5% 4 4 8% 35%	1520
	21st to end	Night	20% 7% 3 7% 5% 5% 4 4 6% 7% 32%	1520
July	1st to 10th	Night	14% 9% 3 6% 5% 6% 6% 4 7% 8% 33%	2520
	11th to 20th	Night	20% 8% 3 7% 3 3 3 3 5% 7% 37%	2520
	21st to end	Night	20% 8% 2 6% 4 4 4 5% 6% 6% 37%	2739
August	1st to 10th	Night	26% 8% 2 6% 4 4 3 3 5% 6% 32%	2594
	11th to 20th	Night	19% 9% 4 8% 5% 4 5% 3 6% 7% 32%	2812
	21st to end	Night	12% 11% 2 6% 4 4 4 3 7% 7% 39%	3476
September	1st to 10th	Night	15% 8% 2 5% 4 3 3 4 4 6% 45%	1900
	11th to 20th	Night	16% 7% 2 5% 4 3 3 3 5% 6% 46%	2061
	21st to end	Night	18% 8% 2 5% 4 4 4 3 5% 6% 41%	2090
October	1st to 10th	Night	22% 9% 2 6% 5% 5% 4 3 5% 6% 33%	2090
	11th to 20th	Night	17% 14% 3 8% 4 4 4 3 5% 6% 32%	2375
	21st to end	Night	22% 16% 4 8% 5% 4 4 3 4 5% 25%	2717
November	1st to 10th	Night	16% 12% 4 10% 5% 4 4 3 5% 5% 32%	2414
	11th to 20th	Night	17% 15% 5% 9% 5% 3 4 3 5% 6% 28%	2470
	21st to end	Night	17% 15% 6% 11% 6% 5% 4 3 4 5% 25%	2555
December	1st to 10th	Night	20% 18% 6% 13% 6% 4 4 3 4 3 16%	2660
	11th to 20th	Night	21% 17% 5% 13% 5% 4 4 3 5% 5% 19%	3288
	21st to end	Night	23% 16% 6% 14% 5% 5% 4 3 4 3 17%	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	54% 15% 9% 18% 4	2518
	11th to 20th	Day	63% 9% 9% 13% 4 1	2520
	21st to end	Day	61% 10% 9% 13% 6% 1	2772
February	1st to 10th	Day	59% 7% 10% 16% 6% 2	1666
	11th to 20th	Day	56% 9% 12% 14% 8% 1	1857
	21st to end	Day	56% 7% 10% 15% 10% 1	1570
March	1st to 10th	Day	63% 7% 8% 11% 9% 1	3119
	11th to 20th	Day	55% 10% 10% 14% 9% 2	3285
	21st to end	Day	55% 6% 7% 14% 16% 2	4097
April	1st to 10th	Day	57% 5% 8% 18% 10% 3	2280
	11th to 20th	Day	51% 7% 10% 19% 12% 1	2270
	21st to end	Day	57% 7% 7% 16% 10% 2	2470
May	1st to 10th	Day	59% 7% 9% 17% 6% 1	4120
	11th to 20th	Day	52% 9% 15% 14% 8% 1	4357
	21st to end	Day	39% 11% 14% 25% 11% 1	4837
June	1st to 10th	Day	54% 8% 13% 18% 7%	2660
	11th to 20th	Day	46% 7% 12% 20% 12% 2	2660
	21st to end	Day	54% 9% 11% 17% 8% 1	2660
July	1st to 10th	Day	42% 9% 16% 21% 11%	4370
	11th to 20th	Day	42% 10% 17% 24% 7%	4365
	21st to end	Day	46% 8% 12% 22% 11%	4661
August	1st to 10th	Day	48% 9% 16% 19% 8%	4289
	11th to 20th	Day	49% 10% 16% 20% 5%	4037
	21st to end	Day	35% 11% 18% 22% 13% 1	4180
September	1st to 10th	Day	38% 7% 13% 28% 13% 1	2280
	11th to 20th	Day	37% 6% 10% 30% 15% 2	2119
	21st to end	Day	42% 6% 13% 25% 12% 1	2090
October	1st to 10th	Day	53% 7% 9% 20% 10% 1	2090
	11th to 20th	Day	48% 6% 14% 23% 7% 1	1800
	21st to end	Day	60% 7% 9% 15% 8% 2	1881
November	1st to 10th	Day	48% 6% 14% 20% 12% 1	1671
	11th to 20th	Day	53% 9% 12% 14% 10% 2	1710
	21st to end	Day	56% 9% 16% 15% 4	1622
December	1st to 10th	Day	67% 6% 11% 12% 4	1520
	11th to 20th	Day	57% 8% 8% 15% 10% 1	1906
	21st to end	Day	64% 9% 8% 11% 7%	2772
January	1st to 10th	Night	54% 12% 15% 16% 4	4429
	11th to 20th	Night	61% 12% 10% 12% 4	4440
	21st to end	Night	62% 12% 9% 12% 5% 1	4884
February	1st to 10th	Night	58% 9% 11% 13% 8% 1	2509
	11th to 20th	Night	55% 11% 9% 15% 9% 1	2220
	21st to end	Night	52% 11% 11% 17% 7% 2	1884
March	1st to 10th	Night	60% 7% 10% 13% 8% 1	3734
	11th to 20th	Night	55% 10% 9% 17% 8% 1	3674
	21st to end	Night	56% 6% 7% 13% 16% 2	3532
April	1st to 10th	Night	55% 7% 9% 18% 11% 2	1900
	11th to 20th	Night	52% 6% 9% 23% 11%	1857
	21st to end	Night	52% 7% 11% 17% 12% 3	1710
May	1st to 10th	Night	60% 8% 10% 15% 7% 1	2840
	11th to 20th	Night	54% 11% 11% 15% 7% 1	2570
	21st to end	Night	39% 11% 17% 19% 12% 2	2739
June	1st to 10th	Night	52% 9% 13% 18% 9%	1520
	11th to 20th	Night	47% 8% 14% 19% 11% 2	1520
	21st to end	Night	49% 7% 15% 19% 9% 1	1520
July	1st to 10th	Night	42% 10% 18% 17% 12%	2480
	11th to 20th	Night	42% 8% 15% 25% 10%	2472
	21st to end	Night	43% 8% 13% 24% 10%	2651
August	1st to 10th	Night	51% 7% 13% 21% 8%	2584
	11th to 20th	Night	47% 9% 16% 18% 9%	2839
	21st to end	Night	33% 13% 21% 21% 12%	3476
September	1st to 10th	Night	37% 9% 14% 28% 13%	1900
	11th to 20th	Night	37% 7% 12% 29% 14% 1	2061
	21st to end	Night	42% 6% 14% 23% 13% 1	2090
October	1st to 10th	Night	50% 7% 12% 19% 10% 1	2090
	11th to 20th	Night	50% 8% 12% 22% 7% 1	2375
	21st to end	Night	58% 7% 10% 16% 8% 1	2717
November	1st to 10th	Night	48% 10% 11% 20% 9% 2	2414
	11th to 20th	Night	52% 8% 12% 18% 9% 2	2470
	21st to end	Night	56% 8% 14% 17% 5%	2555
December	1st to 10th	Night	67% 8% 9% 12% 3	2660
	11th to 20th	Night	58% 12% 10% 12% 7%	3288
	21st to end	Night	66% 9% 8% 14% 3	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	32% 19% 32% 14% 2 1	180
	11th to 20th	Day	38% 25% 25% 9% 2 1	180
	21st to end	Day	22% 31% 29% 13% 4 1	198
February	1st to 10th	Day	38% 28% 25% 8% 2	274
	11th to 20th	Day	33% 27% 28% 10% 2	456
	21st to end	Day	33% 24% 28% 13% 2	382
March	1st to 10th	Day	30% 22% 31% 13% 3	460
	11th to 20th	Day	33% 27% 24% 11% 4 1	460
	21st to end	Day	35% 23% 24% 11% 5% 3	506
April	1st to 10th	Day	38% 22% 22% 12% 5% 1	460
	11th to 20th	Day	33% 27% 20% 12% 6% 2	452
	21st to end	Day	33% 23% 27% 10% 4 2	460
May	1st to 10th	Day	34% 21% 25% 13% 4 2	463
	11th to 20th	Day	22% 23% 32% 15% 6% 2	487
	21st to end	Day	21% 17% 33% 20% 8% 1	529
June	1st to 10th	Day	23% 18% 35% 17% 7%	490
	11th to 20th	Day	21% 18% 32% 20% 8% 1	490
	21st to end	Day	24% 19% 31% 17% 8% 1	490
July	1st to 10th	Day	20% 14% 32% 23% 9% 2	485
	11th to 20th	Day	17% 10% 37% 26% 9% 2	484
	21st to end	Day	17% 13% 36% 23% 8% 2	532
August	1st to 10th	Day	16% 14% 29% 27% 13% 2	486
	11th to 20th	Day	18% 14% 27% 23% 12% 5%	479
	21st to end	Day	13% 16% 30% 24% 12% 5%	539
September	1st to 10th	Day	19% 14% 26% 23% 13% 5%	490
	11th to 20th	Day	18% 15% 24% 20% 16% 7%	490
	21st to end	Day	20% 16% 27% 20% 11% 5%	490
October	1st to 10th	Day	28% 15% 24% 20% 9% 3	490
	11th to 20th	Day	28% 17% 24% 19% 9% 2	437
	21st to end	Day	37% 18% 23% 17% 5%	429
November	1st to 10th	Day	27% 19% 22% 23% 9% 1	365
	11th to 20th	Day	32% 22% 24% 16% 5% 1	370
	21st to end	Day	35% 20% 27% 15% 4	282
December	1st to 10th	Day	31% 26% 27% 13% 4	180
	11th to 20th	Day	39% 19% 32% 7% 2	180
	21st to end	Day	35% 19% 32% 13% 1	198
January	1st to 10th	Night	24% 24% 31% 19% 3	760
	11th to 20th	Night	30% 20% 28% 19% 2	760
	21st to end	Night	20% 25% 33% 19% 3	836
February	1st to 10th	Night	24% 21% 35% 18% 2	760
	11th to 20th	Night	25% 25% 32% 16% 2	743
	21st to end	Night	25% 22% 31% 20% 3	628
March	1st to 10th	Night	28% 18% 31% 19% 3	760
	11th to 20th	Night	30% 20% 25% 20% 5%	760
	21st to end	Night	30% 18% 26% 19% 6% 1	836
April	1st to 10th	Night	32% 19% 24% 21% 4	760
	11th to 20th	Night	27% 20% 26% 21% 6%	733
	21st to end	Night	28% 20% 27% 21% 4	570
May	1st to 10th	Night	30% 15% 25% 23% 7%	570
	11th to 20th	Night	22% 12% 32% 27% 7%	422
	21st to end	Night	21% 8% 27% 34% 10%	411
June	1st to 10th	Night	23% 10% 25% 33% 8% 1	380
	11th to 20th	Night	22% 10% 24% 32% 12%	380
	21st to end	Night	21% 9% 22% 39% 8%	380
July	1st to 10th	Night	16% 7% 22% 42% 13%	370
	11th to 20th	Night	18% 4 24% 35% 18% 2	368
	21st to end	Night	16% 5% 20% 41% 16% 1	416
August	1st to 10th	Night	19% 4 16% 42% 19%	427
	11th to 20th	Night	18% 7% 25% 32% 17% 2	579
	21st to end	Night	18% 8% 19% 33% 20% 3	836
September	1st to 10th	Night	18% 8% 24% 31% 18% 1	760
	11th to 20th	Night	19% 10% 20% 25% 22% 4	760
	21st to end	Night	21% 13% 21% 29% 15% 2	760
October	1st to 10th	Night	27% 12% 19% 26% 15% 2	760
	11th to 20th	Night	25% 17% 22% 24% 11% 1	760
	21st to end	Night	33% 16% 25% 21% 6%	836
November	1st to 10th	Night	23% 17% 25% 25% 9% 1	743
	11th to 20th	Night	26% 18% 27% 20% 7% 1	760
	21st to end	Night	28% 19% 28% 18% 6% 1	760
December	1st to 10th	Night	32% 21% 29% 16% 3	760
	11th to 20th	Night	32% 19% 29% 17% 4	760
	21st to end	Night	32% 22% 26% 17% 2	836

Page generated at 2024-10-29 11:20:49. Version ac07

Copyright © 2024 Attilla Danko.