Five Ferns Observation Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Five Ferns Observation Site clear sky chart from 2005-11-06 to 2024-01-31.

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	18% 9% 4 7% 6% 3 5% 5% 5% 6% 32%	74888
	Night	19% 11% 4 7% 6% 3 4 4 5% 6% 31%	75236
Transparency	Day	51% 6% 12% 19% 10% 1	74593
	Night	53% 6% 12% 18% 10% 1	75065
Seeing	Day	22% 15% 30% 21% 9% 3	13455
	Night	23% 12% 30% 26% 9% 1	22683

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	20% 18% 7% 11% 7% 3 5% 4 4 3 19%	1517
	11th to 20th	Day	19% 16% 7% 10% 6% 4 5% 4 4 4 21%	1520
	21st to end	Day	14% 15% 5% 10% 9% 5% 5% 5% 5% 6% 22%	1715
February	1st to 10th	Day	18% 15% 5% 10% 8% 4 5% 4 5% 5% 22%	1620
	11th to 20th	Day	16% 14% 6% 9% 6% 3 4 4 4 6% 26%	1609
	21st to end	Day	20% 15% 5% 10% 7% 4 4 4 4 4 23%	1480
March	1st to 10th	Day	15% 13% 7% 9% 8% 4 4 4 4 4 29%	1797
	11th to 20th	Day	18% 12% 4 8% 6% 4 5% 4 4 5% 30%	1947
	21st to end	Day	20% 11% 3 6% 5% 2 3 4 4 6% 36%	2316
April	1st to 10th	Day	22% 12% 4 6% 6% 2 4 3 3 6% 32%	2160
	11th to 20th	Day	21% 9% 3 7% 5% 2 3 3 4 5% 36%	2134
	21st to end	Day	24% 9% 4 6% 5% 2 4 4 4 6% 31%	2259
May	1st to 10th	Day	20% 8% 3 6% 5% 3 4 4 4 7% 35%	2520
	11th to 20th	Day	16% 7% 3 7% 5% 3 4 4 5% 7% 39%	2478
	21st to end	Day	16% 6% 3 5% 5% 4 5% 6% 6% 8% 38%	2725
June	1st to 10th	Day	23% 7% 2 6% 6% 3 5% 6% 5% 8% 30%	2520
	11th to 20th	Day	15% 6% 3 5% 6% 4 5% 5% 6% 7% 39%	2520
	21st to end	Day	20% 7% 2 5% 6% 3 6% 5% 6% 8% 32%	2520
July	1st to 10th	Day	12% 5% 2 6% 5% 3 5% 5% 6% 7% 43%	2520
	11th to 20th	Day	13% 6% 3 5% 6% 4 6% 5% 6% 10% 37%	2520
	21st to end	Day	12% 5% 2 6% 5% 3 6% 6% 7% 9% 38%	2744
August	1st to 10th	Day	13% 6% 2 6% 6% 3 5% 6% 7% 7% 38%	2495
	11th to 20th	Day	13% 6% 3 5% 6% 3 5% 6% 6% 8% 40%	2245
	21st to end	Day	14% 6% 2 5% 5% 4 5% 5% 6% 8% 40%	2376
September	1st to 10th	Day	14% 5% 2 6% 4 3 5% 6% 6% 8% 41%	2160
	11th to 20th	Day	15% 5% 2 5% 4 3 5% 4 5% 7% 46%	2138
	21st to end	Day	18% 6% 2 5% 5% 2 5% 5% 6% 7% 39%	1957
October	1st to 10th	Day	21% 7% 4 6% 5% 3 4 4 5% 6% 34%	1800
	11th to 20th	Day	21% 9% 4 8% 7% 4 5% 4 5% 6% 27%	1800
	21st to end	Day	28% 10% 3 7% 5% 4 5% 3 4 6% 26%	1814
November	1st to 10th	Day	17% 10% 4 6% 6% 3 5% 5% 5% 8% 32%	1671
	11th to 20th	Day	19% 12% 3 7% 6% 3 4 5% 5% 7% 28%	1573
	21st to end	Day	21% 13% 5% 9% 7% 4 5% 5% 5% 5% 21%	1520
December	1st to 10th	Day	24% 17% 6% 9% 6% 3 5% 4 4 5% 16%	1520
	11th to 20th	Day	23% 16% 4 9% 6% 3 4 4 5% 4 23%	1906
	21st to end	Day	27% 16% 5% 10% 6% 3 4 3 3 3 20%	2772
January	1st to 10th	Night	19% 17% 7% 10% 8% 4 4 4 4 5% 19%	2649
	11th to 20th	Night	18% 17% 6% 11% 7% 3 5% 4 4 4 19%	2660
	21st to end	Night	14% 15% 6% 10% 7% 4 4 4 4 5% 26%	2863
February	1st to 10th	Night	17% 14% 6% 12% 7% 4 5% 4 5% 5% 20%	2340
	11th to 20th	Night	15% 13% 5% 11% 7% 3 5% 4 4 6% 27%	2236
	21st to end	Night	17% 14% 4 9% 7% 2 5% 3 4 5% 28%	1776
March	1st to 10th	Night	18% 14% 5% 9% 6% 3 5% 3 4 4 29%	2150
	11th to 20th	Night	19% 12% 4 6% 6% 2 4 4 4 5% 33%	2010
	21st to end	Night	19% 10% 3 6% 6% 3 4 3 4 4 39%	2039
April	1st to 10th	Night	22% 9% 4 7% 6% 3 4 3 4 6% 33%	1800
	11th to 20th	Night	20% 9% 3 6% 5% 2 5% 4 6% 6% 35%	1775
	21st to end	Night	22% 8% 3 6% 5% 3 4 3 4 7% 34%	1715
May	1st to 10th	Night	22% 7% 3 5% 5% 3 4 4 5% 7% 35%	1440
	11th to 20th	Night	17% 8% 2 7% 5% 3 4 5% 5% 6% 39%	1415
	21st to end	Night	14% 4 2 4 5% 4 5% 5% 6% 8% 43%	1550
June	1st to 10th	Night	18% 6% 3 7% 5% 4 6% 6% 6% 9% 30%	1440
	11th to 20th	Night	16% 5% 3 5% 5% 3 4 5% 6% 8% 40%	1440
	21st to end	Night	19% 7% 2 5% 5% 2 5% 5% 5% 9% 36%	1440
July	1st to 10th	Night	10% 4 3 5% 5% 3 6% 5% 6% 10% 43%	1440
	11th to 20th	Night	12% 6% 2 5% 4 3 4 6% 7% 10% 42%	1440
	21st to end	Night	10% 6% 3 4 3 3 6% 6% 7% 10% 42%	1574
August	1st to 10th	Night	12% 6% 2 5% 5% 3 4 5% 6% 9% 43%	1440
	11th to 20th	Night	12% 5% 4 6% 5% 3 5% 5% 5% 7% 42%	1638
	21st to end	Night	13% 5% 3 5% 4 3 5% 4 5% 7% 45%	1980
September	1st to 10th	Night	14% 6% 2 5% 5% 3 5% 5% 5% 6% 44%	1800
	11th to 20th	Night	15% 5% 2 4 4 2 4 4 5% 7% 49%	1821
	21st to end	Night	15% 6% 3 5% 5% 3 4 4 5% 6% 43%	2001
October	1st to 10th	Night	19% 7% 3 6% 4 4 4 5% 5% 7% 35%	2160
	11th to 20th	Night	21% 9% 3 7% 5% 3 5% 4 5% 6% 32%	2160
	21st to end	Night	25% 10% 3 7% 5% 4 4 4 5% 6% 27%	2540
November	1st to 10th	Night	20% 9% 3 6% 6% 3 4 3 4 5% 36%	2407
	11th to 20th	Night	19% 11% 4 7% 6% 3 5% 3 4 6% 32%	2605
	21st to end	Night	23% 13% 5% 9% 5% 4 5% 4 4 6% 24%	2660
December	1st to 10th	Night	22% 17% 6% 9% 7% 3 5% 5% 4 5% 17%	2660
	11th to 20th	Night	23% 16% 5% 8% 6% 3 4 3 3 4 26%	3288
	21st to end	Night	32% 15% 5% 10% 6% 3 3 3 3 3 18%	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	69% 5% 11% 10% 5%	1518
	11th to 20th	Day	67% 4 9% 10% 9% 1	1520
	21st to end	Day	63% 6% 12% 13% 6% 1	1715
February	1st to 10th	Day	65% 4 10% 17% 3 1	1620
	11th to 20th	Day	60% 5% 11% 16% 7% 1	1618
	21st to end	Day	64% 5% 10% 12% 8% 1	1480
March	1st to 10th	Day	59% 4 11% 16% 9% 1	1800
	11th to 20th	Day	56% 5% 12% 14% 11% 3	1947
	21st to end	Day	51% 4 8% 19% 14% 5%	2316
April	1st to 10th	Day	55% 4 7% 19% 12% 2	2160
	11th to 20th	Day	51% 4 7% 20% 15% 2	2134
	21st to end	Day	54% 6% 9% 15% 14% 3	2259
May	1st to 10th	Day	50% 5% 8% 19% 15% 3	2520
	11th to 20th	Day	45% 6% 10% 21% 16% 2	2482
	21st to end	Day	44% 8% 13% 20% 13% 2	2725
June	1st to 10th	Day	52% 7% 12% 17% 11% 1	2520
	11th to 20th	Day	43% 7% 12% 24% 12% 2	2520
	21st to end	Day	50% 9% 12% 19% 10% 1	2520
July	1st to 10th	Day	38% 8% 12% 27% 15% 1	2450
	11th to 20th	Day	39% 9% 16% 27% 9%	2445
	21st to end	Day	40% 9% 17% 23% 10%	2591
August	1st to 10th	Day	41% 10% 16% 25% 9%	2481
	11th to 20th	Day	40% 7% 17% 26% 10%	2245
	21st to end	Day	40% 8% 14% 26% 11% 1	2376
September	1st to 10th	Day	39% 8% 13% 27% 12%	2160
	11th to 20th	Day	37% 7% 12% 31% 13%	2138
	21st to end	Day	43% 7% 15% 26% 9%	1957
October	1st to 10th	Day	49% 7% 12% 21% 11%	1800
	11th to 20th	Day	56% 8% 14% 15% 6% 1	1800
	21st to end	Day	61% 5% 11% 15% 7% 1	1814
November	1st to 10th	Day	51% 6% 15% 21% 7% 1	1671
	11th to 20th	Day	55% 6% 13% 16% 9% 1	1573
	21st to end	Day	63% 8% 14% 11% 4	1520
December	1st to 10th	Day	69% 8% 11% 10% 2	1520
	11th to 20th	Day	64% 7% 12% 13% 3	1906
	21st to end	Day	72% 4 7% 14% 3	2772
January	1st to 10th	Night	68% 5% 11% 11% 4	2649
	11th to 20th	Night	68% 6% 10% 9% 7% 1	2660
	21st to end	Night	60% 5% 11% 15% 8% 1	2863
February	1st to 10th	Night	66% 5% 10% 13% 5% 1	2340
	11th to 20th	Night	58% 6% 10% 19% 7%	2238
	21st to end	Night	59% 5% 9% 17% 10% 1	1776
March	1st to 10th	Night	59% 4 10% 15% 10% 1	2160
	11th to 20th	Night	54% 5% 10% 19% 9% 2	2011
	21st to end	Night	51% 5% 8% 18% 14% 4	2039
April	1st to 10th	Night	54% 4 9% 19% 13% 1	1800
	11th to 20th	Night	49% 6% 9% 19% 15% 2	1775
	21st to end	Night	52% 5% 9% 16% 15% 4	1715
May	1st to 10th	Night	48% 5% 9% 18% 15% 5%	1440
	11th to 20th	Night	45% 5% 9% 21% 17% 3	1416
	21st to end	Night	38% 8% 16% 19% 16% 3	1551
June	1st to 10th	Night	49% 8% 14% 17% 11% 1	1440
	11th to 20th	Night	42% 6% 13% 20% 17% 2	1440
	21st to end	Night	45% 9% 14% 19% 13% 1	1440
July	1st to 10th	Night	34% 9% 13% 26% 17% 2	1400
	11th to 20th	Night	35% 9% 14% 30% 12%	1392
	21st to end	Night	36% 10% 16% 24% 14% 1	1486
August	1st to 10th	Night	37% 9% 18% 22% 12% 1	1430
	11th to 20th	Night	40% 7% 15% 24% 13% 1	1638
	21st to end	Night	37% 8% 15% 27% 12% 1	1980
September	1st to 10th	Night	40% 7% 12% 25% 14% 1	1800
	11th to 20th	Night	35% 6% 15% 33% 11% 1	1821
	21st to end	Night	41% 7% 12% 28% 11%	2001
October	1st to 10th	Night	47% 7% 12% 22% 12% 1	2160
	11th to 20th	Night	52% 6% 13% 21% 8%	2160
	21st to end	Night	58% 6% 13% 14% 8% 1	2540
November	1st to 10th	Night	51% 6% 14% 20% 9% 1	2407
	11th to 20th	Night	53% 6% 14% 17% 9% 2	2605
	21st to end	Night	62% 6% 13% 15% 5%	2660
December	1st to 10th	Night	69% 6% 11% 11% 3	2660
	11th to 20th	Night	63% 5% 11% 15% 6% 1	3288
	21st to end	Night	72% 5% 8% 12% 2	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	26% 21% 27% 19% 7%	180
	11th to 20th	Day	29% 20% 31% 14% 5% 1	180
	21st to end	Day	23% 17% 33% 21% 6%	219
February	1st to 10th	Day	31% 27% 32% 9% 1	240
	11th to 20th	Day	25% 22% 40% 11% 1	276
	21st to end	Day	28% 19% 34% 17% 2	346
March	1st to 10th	Day	24% 17% 36% 19% 5%	420
	11th to 20th	Day	25% 18% 35% 17% 4 1	420
	21st to end	Day	29% 17% 30% 17% 6% 1	462
April	1st to 10th	Day	27% 18% 32% 17% 5% 1	420
	11th to 20th	Day	26% 24% 21% 19% 7% 2	412
	21st to end	Day	29% 18% 31% 13% 8% 1	420
May	1st to 10th	Day	24% 16% 30% 19% 8% 2	423
	11th to 20th	Day	17% 17% 36% 18% 10% 2	447
	21st to end	Day	17% 17% 30% 22% 12% 1	485
June	1st to 10th	Day	27% 12% 28% 24% 7% 2	450
	11th to 20th	Day	14% 16% 32% 26% 9% 3	450
	21st to end	Day	22% 12% 30% 21% 12% 2	450
July	1st to 10th	Day	13% 9% 28% 32% 15% 3	445
	11th to 20th	Day	13% 9% 29% 31% 14% 3	444
	21st to end	Day	14% 8% 31% 31% 13% 2	488
August	1st to 10th	Day	16% 8% 25% 34% 14% 4	446
	11th to 20th	Day	13% 6% 26% 30% 18% 8%	439
	21st to end	Day	14% 11% 30% 24% 14% 7%	495
September	1st to 10th	Day	13% 10% 29% 26% 12% 10%	450
	11th to 20th	Day	13% 8% 26% 24% 18% 11%	450
	21st to end	Day	18% 11% 31% 19% 17% 5%	450
October	1st to 10th	Day	22% 15% 27% 18% 13% 5%	450
	11th to 20th	Day	25% 19% 27% 20% 7% 2	450
	21st to end	Day	32% 16% 25% 21% 6%	412
November	1st to 10th	Day	24% 20% 28% 20% 7% 1	365
	11th to 20th	Day	26% 19% 32% 15% 8%	233
	21st to end	Day	23% 25% 31% 14% 6% 1	180
December	1st to 10th	Day	31% 18% 29% 17% 4	180
	11th to 20th	Day	28% 29% 29% 10% 3 1	180
	21st to end	Day	32% 24% 25% 14% 3 2	198
January	1st to 10th	Night	28% 15% 32% 21% 4	760
	11th to 20th	Night	29% 16% 29% 22% 4 1	760
	21st to end	Night	22% 12% 34% 27% 5%	835
February	1st to 10th	Night	23% 18% 36% 21% 3	720
	11th to 20th	Night	23% 17% 36% 21% 3	703
	21st to end	Night	25% 16% 32% 25% 3	592
March	1st to 10th	Night	25% 14% 34% 23% 4	720
	11th to 20th	Night	25% 18% 31% 22% 4	720
	21st to end	Night	24% 13% 29% 26% 8%	792
April	1st to 10th	Night	27% 13% 30% 26% 4	720
	11th to 20th	Night	23% 16% 31% 22% 7%	711
	21st to end	Night	27% 12% 29% 23% 8% 1	635
May	1st to 10th	Night	26% 9% 28% 27% 8% 2	360
	11th to 20th	Night	19% 9% 35% 29% 8%	354
	21st to end	Night	15% 7% 40% 25% 13%	389
June	1st to 10th	Night	19% 7% 31% 36% 7% 1	360
	11th to 20th	Night	18% 9% 29% 31% 13% 1	360
	21st to end	Night	18% 7% 31% 31% 13% 1	360
July	1st to 10th	Night	9% 6% 30% 41% 13% 1	350
	11th to 20th	Night	15% 3 25% 38% 18% 1	348
	21st to end	Night	11% 4 27% 47% 10% 1	394
August	1st to 10th	Night	15% 4 24% 40% 17% 1	366
	11th to 20th	Night	14% 3 21% 38% 23% 1	574
	21st to end	Night	15% 5% 28% 32% 17% 2	792
September	1st to 10th	Night	16% 7% 26% 34% 17%	720
	11th to 20th	Night	18% 6% 21% 33% 19% 3	720
	21st to end	Night	16% 10% 26% 27% 20% 2	720
October	1st to 10th	Night	22% 9% 29% 24% 14% 1	720
	11th to 20th	Night	25% 13% 30% 24% 8%	720
	21st to end	Night	30% 13% 27% 25% 5%	792
November	1st to 10th	Night	26% 13% 29% 22% 8% 1	740
	11th to 20th	Night	24% 16% 32% 19% 9%	760
	21st to end	Night	28% 17% 28% 20% 6%	760
December	1st to 10th	Night	31% 17% 27% 21% 3	760
	11th to 20th	Night	28% 16% 32% 19% 4 1	760
	21st to end	Night	33% 15% 29% 20% 3	836

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