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 2024-03-01.

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	17% 11% 4 8% 7% 3 5% 5% 5% 6% 29%	78318
	Night	18% 12% 5% 9% 7% 3 5% 4 5% 6% 28%	81080
Transparency	Day	52% 8% 11% 18% 9% 1	78023
	Night	53% 9% 12% 18% 8% 1	80909
Seeing	Day	26% 19% 28% 17% 7% 2	13860
	Night	25% 16% 26% 24% 8% 1	22929

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% 13% 7% 13% 8% 4 6% 5% 4 4 21%	2517
	11th to 20th	Day	13% 11% 7% 13% 14% 5% 5% 4 3 4 20%	2520
	21st to end	Day	16% 15% 9% 13% 7% 3 5% 5% 4 5% 20%	2772
February	1st to 10th	Day	15% 14% 5% 9% 8% 4 6% 5% 5% 5% 23%	1666
	11th to 20th	Day	12% 13% 7% 12% 10% 3 5% 5% 5% 6% 23%	1848
	21st to end	Day	14% 12% 6% 11% 8% 4 5% 3 5% 6% 27%	1570
March	1st to 10th	Day	14% 12% 7% 11% 7% 4 6% 4 5% 6% 26%	1797
	11th to 20th	Day	16% 13% 7% 9% 6% 3 4 3 5% 5% 29%	1869
	21st to end	Day	17% 14% 6% 8% 7% 4 4 4 4 4 29%	2335
April	1st to 10th	Day	20% 12% 5% 9% 6% 3 3 3 3 5% 30%	2160
	11th to 20th	Day	17% 13% 4 6% 6% 3 5% 4 4 5% 33%	2149
	21st to end	Day	21% 13% 4 8% 7% 3 4 4 5% 5% 26%	2340
May	1st to 10th	Day	23% 13% 3 6% 5% 3 4 4 4 6% 29%	2340
	11th to 20th	Day	20% 9% 3 7% 5% 4 4 4 4 7% 34%	2447
	21st to end	Day	16% 9% 3 6% 6% 4 5% 4 6% 7% 34%	2725
June	1st to 10th	Day	22% 9% 3 7% 7% 3 5% 5% 6% 7% 25%	2520
	11th to 20th	Day	19% 9% 3 5% 6% 4 4 5% 6% 9% 33%	2520
	21st to end	Day	19% 9% 3 8% 7% 3 5% 5% 5% 7% 27%	2520
July	1st to 10th	Day	17% 8% 3 6% 5% 3 5% 5% 5% 9% 35%	2520
	11th to 20th	Day	15% 6% 3 7% 7% 4 6% 6% 6% 9% 33%	2520
	21st to end	Day	16% 6% 3 6% 5% 4 5% 7% 7% 9% 31%	2744
August	1st to 10th	Day	15% 7% 3 7% 7% 3 6% 6% 6% 8% 33%	2441
	11th to 20th	Day	16% 7% 3 6% 7% 4 6% 7% 6% 9% 29%	2285
	21st to end	Day	13% 6% 3 6% 5% 4 6% 6% 7% 8% 37%	2376
September	1st to 10th	Day	14% 6% 2 5% 5% 4 4 6% 5% 8% 41%	2160
	11th to 20th	Day	16% 5% 3 5% 4 2 3 4 4 6% 47%	2008
	21st to end	Day	15% 8% 3 5% 5% 3 5% 4 6% 6% 40%	1980
October	1st to 10th	Day	23% 11% 3 6% 5% 2 4 5% 4 6% 31%	1980
	11th to 20th	Day	17% 11% 4 6% 6% 3 4 4 5% 6% 34%	1706
	21st to end	Day	26% 15% 4 6% 4 3 4 4 3 4 25%	1782
November	1st to 10th	Day	15% 12% 4 7% 4 3 5% 4 5% 7% 34%	1671
	11th to 20th	Day	18% 11% 6% 8% 7% 4 4 5% 5% 5% 26%	1710
	21st to end	Day	19% 13% 5% 9% 8% 3 4 5% 4 5% 25%	1622
December	1st to 10th	Day	20% 16% 7% 11% 8% 4 4 3 3 5% 19%	1520
	11th to 20th	Day	21% 16% 5% 7% 6% 3 4 3 3 5% 26%	1906
	21st to end	Day	24% 13% 6% 12% 8% 3 4 4 4 4 19%	2772
January	1st to 10th	Night	14% 13% 7% 13% 9% 4 6% 5% 4 6% 21%	4429
	11th to 20th	Night	12% 16% 8% 15% 11% 4 5% 4 5% 4 16%	4440
	21st to end	Night	18% 16% 7% 12% 8% 5% 5% 4 4 3 18%	4884
February	1st to 10th	Night	16% 12% 6% 11% 9% 4 6% 4 5% 6% 22%	2509
	11th to 20th	Night	12% 12% 7% 12% 10% 5% 6% 5% 5% 5% 22%	2218
	21st to end	Night	12% 13% 6% 11% 9% 4 5% 5% 5% 5% 27%	1884
March	1st to 10th	Night	14% 14% 6% 9% 8% 4 6% 4 4 5% 25%	2157
	11th to 20th	Night	16% 13% 5% 11% 7% 3 5% 4 5% 5% 27%	2089
	21st to end	Night	17% 13% 4 8% 5% 2 5% 4 4 5% 32%	2018
April	1st to 10th	Night	21% 13% 5% 6% 5% 3 4 4 5% 5% 29%	1800
	11th to 20th	Night	19% 11% 4 7% 7% 3 4 4 5% 6% 32%	1758
	21st to end	Night	20% 12% 5% 7% 5% 3 4 4 4 6% 31%	1620
May	1st to 10th	Night	22% 12% 4 6% 5% 3 5% 4 5% 6% 28%	1620
	11th to 20th	Night	19% 8% 3 5% 6% 4 4 6% 5% 7% 33%	1461
	21st to end	Night	18% 7% 2 4 5% 4 5% 6% 6% 9% 34%	1550
June	1st to 10th	Night	25% 8% 4 6% 5% 3 5% 4 5% 8% 28%	1440
	11th to 20th	Night	20% 7% 3 5% 5% 4 5% 5% 4 8% 35%	1440
	21st to end	Night	18% 7% 3 6% 5% 4 4 5% 6% 7% 33%	1440
July	1st to 10th	Night	16% 6% 3 4 5% 3 6% 5% 6% 8% 37%	1440
	11th to 20th	Night	15% 7% 4 6% 5% 3 3 4 6% 9% 39%	1440
	21st to end	Night	15% 6% 2 5% 5% 2 4 6% 7% 8% 39%	1574
August	1st to 10th	Night	16% 5% 2 4 5% 4 4 5% 7% 8% 40%	1478
	11th to 20th	Night	14% 7% 4 6% 6% 4 5% 4 6% 7% 38%	1612
	21st to end	Night	16% 7% 3 5% 5% 3 4 4 5% 8% 41%	1980
September	1st to 10th	Night	15% 7% 2 5% 5% 2 3 5% 4 6% 45%	1800
	11th to 20th	Night	17% 7% 2 5% 4 2 2 4 4 7% 45%	1952
	21st to end	Night	18% 8% 2 4 4 3 4 4 5% 7% 42%	1980
October	1st to 10th	Night	23% 9% 2 5% 5% 4 5% 4 5% 6% 33%	1980
	11th to 20th	Night	18% 13% 4 7% 5% 3 4 4 5% 6% 31%	2249
	21st to end	Night	23% 15% 5% 7% 5% 4 4 4 4 5% 24%	2574
November	1st to 10th	Night	17% 12% 4 9% 5% 3 4 4 5% 5% 32%	2407
	11th to 20th	Night	17% 13% 6% 8% 6% 2 4 4 5% 6% 29%	2470
	21st to end	Night	17% 14% 7% 10% 7% 4 4 4 4 5% 25%	2555
December	1st to 10th	Night	20% 17% 8% 12% 7% 4 4 4 4 3 16%	2660
	11th to 20th	Night	21% 15% 6% 12% 6% 2 4 3 5% 6% 19%	3288
	21st to end	Night	23% 15% 6% 13% 6% 4 5% 4 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% 11% 15% 10% 1	1570
March	1st to 10th	Day	55% 8% 10% 16% 8% 3	1800
	11th to 20th	Day	54% 7% 10% 14% 13% 2	1869
	21st to end	Day	54% 6% 8% 16% 13% 3	2335
April	1st to 10th	Day	56% 5% 8% 18% 10% 3	2160
	11th to 20th	Day	50% 7% 10% 19% 12% 1	2149
	21st to end	Day	58% 7% 8% 16% 10% 2	2340
May	1st to 10th	Day	57% 5% 8% 19% 10% 2	2340
	11th to 20th	Day	50% 6% 9% 19% 14% 2	2451
	21st to end	Day	46% 8% 14% 20% 10% 2	2725
June	1st to 10th	Day	55% 8% 13% 17% 7%	2520
	11th to 20th	Day	47% 7% 12% 20% 13% 2	2520
	21st to end	Day	54% 9% 11% 17% 8% 1	2520
July	1st to 10th	Day	45% 8% 14% 21% 12%	2450
	11th to 20th	Day	46% 9% 15% 22% 8%	2445
	21st to end	Day	44% 9% 15% 21% 10% 1	2591
August	1st to 10th	Day	46% 10% 15% 20% 8%	2427
	11th to 20th	Day	47% 9% 15% 21% 8%	2285
	21st to end	Day	39% 10% 14% 23% 12% 1	2376
September	1st to 10th	Day	39% 7% 13% 26% 13% 1	2160
	11th to 20th	Day	38% 6% 10% 30% 16% 2	2008
	21st to end	Day	41% 6% 14% 25% 12% 1	1980
October	1st to 10th	Day	54% 7% 9% 19% 10% 1	1980
	11th to 20th	Day	49% 6% 14% 24% 6% 1	1706
	21st to end	Day	62% 7% 9% 14% 7% 2	1782
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% 12% 16% 7% 2	1884
March	1st to 10th	Night	55% 10% 9% 16% 9% 2	2167
	11th to 20th	Night	54% 9% 10% 16% 9% 2	2090
	21st to end	Night	50% 7% 9% 17% 13% 3	2018
April	1st to 10th	Night	55% 7% 8% 18% 10% 2	1800
	11th to 20th	Night	50% 6% 9% 23% 11% 1	1758
	21st to end	Night	53% 6% 11% 17% 11% 3	1620
May	1st to 10th	Night	56% 5% 8% 17% 12% 1	1620
	11th to 20th	Night	47% 9% 10% 18% 13% 3	1462
	21st to end	Night	46% 9% 14% 20% 10% 1	1551
June	1st to 10th	Night	52% 8% 13% 17% 9%	1440
	11th to 20th	Night	48% 7% 13% 20% 11% 2	1440
	21st to end	Night	47% 7% 15% 20% 10%	1440
July	1st to 10th	Night	42% 8% 18% 19% 14% 1	1400
	11th to 20th	Night	40% 9% 17% 23% 11%	1392
	21st to end	Night	38% 8% 17% 25% 10% 1	1486
August	1st to 10th	Night	38% 9% 16% 27% 10%	1468
	11th to 20th	Night	43% 8% 16% 22% 11%	1612
	21st to end	Night	40% 7% 14% 25% 13%	1980
September	1st to 10th	Night	37% 9% 14% 27% 12%	1800
	11th to 20th	Night	38% 7% 12% 28% 14% 1	1952
	21st to end	Night	41% 6% 14% 24% 13% 1	1980
October	1st to 10th	Night	51% 7% 11% 19% 11% 1	1980
	11th to 20th	Night	51% 8% 12% 22% 6% 1	2249
	21st to end	Night	59% 7% 9% 15% 8% 1	2574
November	1st to 10th	Night	48% 10% 11% 20% 9% 2	2407
	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% 32% 13% 4	420
	11th to 20th	Day	34% 27% 24% 11% 4 1	420
	21st to end	Day	33% 22% 25% 11% 6% 3	462
April	1st to 10th	Day	38% 20% 22% 13% 5% 1	420
	11th to 20th	Day	31% 26% 20% 14% 7% 2	412
	21st to end	Day	34% 22% 28% 10% 4 2	420
May	1st to 10th	Day	35% 21% 25% 12% 4 2	423
	11th to 20th	Day	23% 24% 31% 14% 5% 2	447
	21st to end	Day	22% 16% 33% 20% 9% 1	485
June	1st to 10th	Day	24% 18% 35% 16% 7%	450
	11th to 20th	Day	22% 18% 31% 20% 8% 2	450
	21st to end	Day	22% 18% 32% 18% 9% 1	450
July	1st to 10th	Day	21% 14% 30% 24% 10% 2	445
	11th to 20th	Day	17% 9% 36% 27% 9% 2	444
	21st to end	Day	16% 13% 37% 24% 9% 2	488
August	1st to 10th	Day	16% 12% 29% 28% 13% 2	446
	11th to 20th	Day	17% 13% 27% 25% 13% 6%	439
	21st to end	Day	14% 14% 30% 25% 12% 5%	495
September	1st to 10th	Day	18% 13% 26% 24% 14% 5%	450
	11th to 20th	Day	19% 16% 26% 18% 14% 7%	450
	21st to end	Day	20% 17% 27% 21% 11% 5%	450
October	1st to 10th	Day	29% 15% 23% 21% 10% 3	450
	11th to 20th	Day	27% 17% 25% 19% 9% 2	403
	21st to end	Day	37% 18% 23% 17% 6%	396
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% 21% 31% 20% 3	628
March	1st to 10th	Night	28% 18% 31% 20% 3	723
	11th to 20th	Night	30% 19% 25% 20% 5%	720
	21st to end	Night	29% 18% 27% 19% 7% 1	792
April	1st to 10th	Night	32% 19% 24% 21% 4	720
	11th to 20th	Night	26% 19% 26% 22% 7%	694
	21st to end	Night	28% 19% 28% 20% 4	540
May	1st to 10th	Night	30% 14% 25% 23% 8%	540
	11th to 20th	Night	22% 12% 33% 26% 7%	400
	21st to end	Night	22% 7% 27% 33% 10% 1	389
June	1st to 10th	Night	24% 9% 24% 33% 9% 1	360
	11th to 20th	Night	22% 10% 23% 32% 13%	360
	21st to end	Night	19% 9% 22% 41% 9%	360
July	1st to 10th	Night	17% 6% 23% 41% 13%	350
	11th to 20th	Night	17% 3 24% 35% 19% 2	348
	21st to end	Night	15% 5% 21% 42% 16% 1	394
August	1st to 10th	Night	17% 4 17% 42% 20%	404
	11th to 20th	Night	18% 6% 25% 32% 17% 2	548
	21st to end	Night	19% 7% 18% 33% 20% 3	792
September	1st to 10th	Night	17% 8% 24% 32% 18% 2	720
	11th to 20th	Night	20% 10% 20% 26% 20% 3	720
	21st to end	Night	21% 13% 20% 28% 15% 2	720
October	1st to 10th	Night	28% 12% 19% 25% 14% 2	720
	11th to 20th	Night	24% 17% 22% 25% 11% 1	720
	21st to end	Night	33% 16% 25% 20% 6%	792
November	1st to 10th	Night	23% 17% 25% 25% 9% 1	740
	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 2024-02-27 06:30:16. Version ac07

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