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 2024-09-14.

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% 10% 3 8% 5% 4 4 4 5% 7% 32%	101032
	Night	18% 12% 4 8% 5% 4 4 3 5% 6% 31%	96858
Transparency	Day	51% 7% 12% 20% 9% 1	100790
	Night	54% 6% 12% 18% 9% 1	96720
Seeing	Day	21% 16% 30% 21% 9% 3	14345
	Night	23% 12% 30% 26% 9% 1	23377

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	18% 17% 6% 12% 6% 6% 5% 3 4 4 20%	2517
	11th to 20th	Day	14% 14% 7% 13% 7% 6% 5% 4 5% 5% 21%	2520
	21st to end	Day	16% 19% 6% 12% 7% 6% 5% 3 4 5% 16%	2850
February	1st to 10th	Day	17% 16% 4 10% 8% 5% 4 3 5% 5% 23%	1710
	11th to 20th	Day	15% 15% 6% 10% 7% 5% 4 3 4 5% 26%	1701
	21st to end	Day	19% 16% 4 10% 6% 5% 3 4 4 4 24%	1570
March	1st to 10th	Day	20% 13% 5% 9% 5% 4 4 3 4 5% 27%	3116
	11th to 20th	Day	13% 18% 4 10% 6% 5% 5% 3 4 5% 27%	3433
	21st to end	Day	14% 8% 3 8% 5% 3 4 3 4 6% 40%	4064
April	1st to 10th	Day	22% 14% 3 7% 5% 3 4 3 4 6% 31%	2280
	11th to 20th	Day	22% 10% 3 8% 4 3 3 3 4 5% 36%	2254
	21st to end	Day	24% 9% 4 6% 4 4 4 3 5% 6% 31%	2385
May	1st to 10th	Day	21% 8% 3 7% 5% 5% 5% 4 5% 6% 31%	4426
	11th to 20th	Day	18% 9% 3 9% 4 4 4 4 5% 7% 32%	4398
	21st to end	Day	15% 7% 2 6% 4 5% 4 4 6% 8% 38%	4837
June	1st to 10th	Day	23% 8% 2 7% 5% 5% 4 5% 5% 7% 29%	2660
	11th to 20th	Day	15% 7% 2 6% 5% 5% 5% 4 6% 7% 38%	2660
	21st to end	Day	21% 8% 2 6% 5% 5% 5% 4 6% 8% 31%	2660
July	1st to 10th	Day	12% 6% 2 8% 5% 5% 5% 5% 7% 9% 36%	4440
	11th to 20th	Day	13% 6% 2 6% 5% 5% 5% 5% 7% 9% 38%	4440
	21st to end	Day	11% 5% 2 6% 4 4 5% 4 7% 9% 42%	4814
August	1st to 10th	Day	16% 9% 3 7% 5% 4 5% 4 6% 7% 34%	4398
	11th to 20th	Day	16% 6% 3 6% 5% 4 5% 4 6% 8% 39%	3930
	21st to end	Day	16% 5% 2 6% 4 4 5% 4 6% 8% 39%	4180
September	1st to 10th	Day	14% 5% 2 7% 4 4 4 5% 6% 8% 42%	2280
	11th to 20th	Day	15% 5% 2 5% 4 4 5% 2 5% 7% 46%	2176
	21st to end	Day	18% 6% 2 6% 4 3 4 4 6% 7% 39%	1957
October	1st to 10th	Day	21% 7% 4 7% 5% 4 5% 3 6% 6% 34%	1800
	11th to 20th	Day	21% 9% 4 9% 6% 5% 5% 3 5% 6% 27%	1800
	21st to end	Day	27% 10% 3 7% 5% 5% 4 3 4 6% 26%	1814
November	1st to 10th	Day	16% 11% 3 8% 5% 4 5% 4 5% 7% 32%	1671
	11th to 20th	Day	18% 14% 3 8% 6% 4 4 4 5% 7% 28%	1573
	21st to end	Day	21% 14% 4 10% 6% 6% 4 4 5% 5% 21%	1520
December	1st to 10th	Day	24% 18% 5% 10% 6% 5% 4 4 4 5% 16%	1520
	11th to 20th	Day	22% 17% 4 10% 5% 3 4 4 5% 4 23%	1906
	21st to end	Day	27% 16% 5% 11% 5% 4 4 2 3 3 20%	2772
January	1st to 10th	Night	18% 18% 6% 11% 6% 5% 4 3 4 5% 21%	4429
	11th to 20th	Night	13% 17% 6% 15% 8% 6% 6% 4 5% 4 17%	4440
	21st to end	Night	19% 20% 7% 11% 6% 4 3 3 4 4 20%	4788
February	1st to 10th	Night	16% 16% 5% 13% 6% 5% 5% 3 5% 5% 21%	2470
	11th to 20th	Night	14% 15% 5% 12% 6% 4 4 3 4 5% 27%	2364
	21st to end	Night	17% 15% 4 11% 6% 4 4 3 4 5% 28%	1884
March	1st to 10th	Night	21% 11% 4 7% 5% 4 3 3 4 4 33%	3724
	11th to 20th	Night	20% 18% 4 8% 5% 3 3 2 4 5% 27%	3524
	21st to end	Night	16% 11% 3 6% 4 4 4 3 4 5% 40%	3567
April	1st to 10th	Night	22% 10% 3 8% 5% 3 4 3 4 5% 32%	1900
	11th to 20th	Night	20% 10% 3 7% 5% 4 4 3 5% 6% 34%	1875
	21st to end	Night	22% 8% 3 7% 5% 4 3 2 4 6% 35%	1810
May	1st to 10th	Night	22% 9% 2 7% 6% 4 4 4 6% 7% 28%	2514
	11th to 20th	Night	20% 9% 3 8% 4 3 4 3 5% 6% 35%	2495
	21st to end	Night	14% 7% 2 6% 4 5% 4 4 6% 8% 39%	2738
June	1st to 10th	Night	17% 7% 3 8% 5% 5% 6% 5% 6% 9% 29%	1520
	11th to 20th	Night	15% 6% 2 6% 4 4 5% 4 6% 8% 39%	1520
	21st to end	Night	21% 8% 3 6% 4 3 4 4 5% 8% 34%	1520
July	1st to 10th	Night	13% 8% 3 8% 5% 5% 5% 4 6% 9% 35%	2520
	11th to 20th	Night	14% 7% 2 6% 4 4 4 4 6% 9% 41%	2520
	21st to end	Night	11% 7% 3 6% 4 5% 5% 4 7% 8% 40%	2739
August	1st to 10th	Night	15% 8% 3 7% 4 4 4 4 5% 8% 39%	2528
	11th to 20th	Night	15% 7% 3 7% 4 5% 5% 4 5% 7% 39%	2867
	21st to end	Night	12% 6% 2 6% 5% 5% 6% 4 6% 8% 41%	3476
September	1st to 10th	Night	14% 7% 2 6% 4 4 5% 4 5% 6% 45%	1900
	11th to 20th	Night	14% 6% 2 5% 3 3 3 3 5% 6% 49%	1861
	21st to end	Night	15% 6% 3 6% 4 4 4 4 5% 6% 42%	2001
October	1st to 10th	Night	19% 8% 3 7% 3 5% 4 4 5% 7% 35%	2160
	11th to 20th	Night	20% 9% 3 8% 4 5% 4 4 5% 6% 32%	2160
	21st to end	Night	25% 10% 3 8% 4 5% 4 3 5% 5% 27%	2540
November	1st to 10th	Night	20% 10% 3 7% 5% 4 3 3 4 5% 36%	2407
	11th to 20th	Night	18% 12% 4 8% 5% 4 4 3 4 6% 32%	2605
	21st to end	Night	22% 14% 4 9% 4 5% 4 3 4 6% 24%	2660
December	1st to 10th	Night	22% 18% 6% 10% 5% 5% 5% 4 4 5% 17%	2660
	11th to 20th	Night	22% 17% 4 9% 5% 4 4 2 3 4 26%	3288
	21st to end	Night	32% 15% 4 11% 5% 3 3 3 3 4 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	66% 7% 13% 9% 5%	2518
	11th to 20th	Day	64% 6% 13% 10% 6%	2520
	21st to end	Day	70% 7% 11% 9% 3	2850
February	1st to 10th	Day	63% 5% 10% 18% 3 1	1710
	11th to 20th	Day	60% 5% 12% 15% 7% 1	1710
	21st to end	Day	63% 6% 10% 12% 8% 1	1570
March	1st to 10th	Day	58% 6% 10% 18% 7% 1	3119
	11th to 20th	Day	57% 6% 13% 14% 8% 1	3433
	21st to end	Day	44% 5% 9% 23% 16% 3	4064
April	1st to 10th	Day	55% 4 8% 19% 12% 2	2280
	11th to 20th	Day	52% 4 7% 20% 15% 2	2254
	21st to end	Day	54% 6% 9% 15% 14% 3	2385
May	1st to 10th	Day	51% 7% 11% 20% 10% 2	4440
	11th to 20th	Day	50% 9% 12% 19% 9% 1	4402
	21st to end	Day	41% 8% 12% 24% 14% 1	4837
June	1st to 10th	Day	52% 7% 12% 17% 11% 1	2660
	11th to 20th	Day	43% 7% 12% 24% 12% 2	2660
	21st to end	Day	50% 9% 12% 19% 10% 1	2660
July	1st to 10th	Day	42% 7% 13% 26% 11%	4370
	11th to 20th	Day	40% 7% 14% 31% 8%	4365
	21st to end	Day	37% 8% 14% 32% 10%	4661
August	1st to 10th	Day	47% 7% 15% 23% 9%	4384
	11th to 20th	Day	43% 6% 16% 28% 8%	3969
	21st to end	Day	41% 7% 17% 24% 11%	4180
September	1st to 10th	Day	39% 8% 13% 28% 12%	2280
	11th to 20th	Day	36% 7% 13% 31% 12%	2176
	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	65% 7% 14% 10% 3	4429
	11th to 20th	Night	67% 8% 13% 8% 4	4440
	21st to end	Night	68% 6% 11% 9% 5% 1	4788
February	1st to 10th	Night	65% 5% 11% 13% 5% 1	2470
	11th to 20th	Night	58% 6% 10% 19% 7%	2366
	21st to end	Night	58% 5% 9% 17% 10% 1	1884
March	1st to 10th	Night	54% 6% 9% 21% 9% 1	3734
	11th to 20th	Night	59% 6% 15% 13% 7% 1	3525
	21st to end	Night	47% 4 8% 23% 16% 3	3567
April	1st to 10th	Night	54% 4 9% 18% 13% 2	1900
	11th to 20th	Night	50% 6% 9% 19% 14% 1	1875
	21st to end	Night	51% 5% 10% 16% 15% 3	1810
May	1st to 10th	Night	52% 8% 11% 17% 9% 3	2520
	11th to 20th	Night	48% 9% 12% 19% 11% 2	2496
	21st to end	Night	40% 8% 13% 20% 17% 2	2739
June	1st to 10th	Night	50% 8% 13% 17% 11% 1	1520
	11th to 20th	Night	41% 5% 13% 21% 17% 2	1520
	21st to end	Night	46% 8% 13% 18% 13% 1	1520
July	1st to 10th	Night	44% 7% 14% 20% 14% 1	2480
	11th to 20th	Night	38% 7% 14% 32% 8%	2472
	21st to end	Night	40% 8% 15% 22% 15%	2651
August	1st to 10th	Night	43% 7% 15% 25% 9%	2518
	11th to 20th	Night	44% 6% 15% 27% 8%	2894
	21st to end	Night	40% 6% 15% 25% 12% 1	3476
September	1st to 10th	Night	40% 7% 12% 26% 15% 1	1900
	11th to 20th	Night	34% 5% 15% 33% 11% 1	1861
	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	22% 17% 34% 21% 6%	222
February	1st to 10th	Day	29% 26% 30% 11% 4	270
	11th to 20th	Day	24% 23% 40% 12% 1	308
	21st to end	Day	27% 19% 35% 17% 2	382
March	1st to 10th	Day	24% 17% 35% 18% 5%	460
	11th to 20th	Day	24% 19% 35% 18% 4 1	460
	21st to end	Day	27% 18% 32% 16% 6% 1	506
April	1st to 10th	Day	28% 18% 31% 17% 5% 1	460
	11th to 20th	Day	27% 25% 21% 17% 6% 2	452
	21st to end	Day	28% 19% 31% 12% 8% 1	460
May	1st to 10th	Day	24% 16% 30% 21% 8% 2	463
	11th to 20th	Day	17% 17% 35% 18% 10% 2	487
	21st to end	Day	17% 18% 29% 22% 12% 1	529
June	1st to 10th	Day	26% 12% 28% 25% 7% 2	490
	11th to 20th	Day	14% 16% 32% 25% 10% 3	490
	21st to end	Day	25% 12% 30% 19% 11% 2	490
July	1st to 10th	Day	13% 9% 29% 31% 14% 3	485
	11th to 20th	Day	14% 10% 30% 30% 13% 3	484
	21st to end	Day	14% 9% 30% 32% 14% 2	532
August	1st to 10th	Day	17% 8% 25% 34% 13% 4	486
	11th to 20th	Day	13% 7% 25% 30% 17% 7%	479
	21st to end	Day	14% 10% 30% 24% 14% 7%	539
September	1st to 10th	Day	14% 10% 30% 26% 11% 9%	490
	11th to 20th	Day	13% 8% 25% 24% 19% 11%	463
	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% 28% 5%	836
February	1st to 10th	Night	22% 18% 35% 22% 3	760
	11th to 20th	Night	22% 18% 36% 21% 3	743
	21st to end	Night	25% 17% 32% 25% 3	628
March	1st to 10th	Night	25% 13% 34% 23% 4	760
	11th to 20th	Night	25% 19% 30% 21% 4	760
	21st to end	Night	23% 14% 29% 26% 8%	836
April	1st to 10th	Night	27% 13% 31% 26% 4	760
	11th to 20th	Night	24% 17% 31% 21% 7%	751
	21st to end	Night	27% 12% 29% 23% 8% 1	670
May	1st to 10th	Night	25% 9% 29% 27% 8% 2	380
	11th to 20th	Night	18% 10% 34% 29% 7%	374
	21st to end	Night	14% 8% 40% 25% 12%	411
June	1st to 10th	Night	18% 7% 30% 36% 8% 1	380
	11th to 20th	Night	18% 9% 29% 31% 12% 1	380
	21st to end	Night	19% 7% 31% 31% 12% 1	380
July	1st to 10th	Night	9% 6% 30% 41% 13% 1	370
	11th to 20th	Night	16% 4 25% 38% 17% 1	368
	21st to end	Night	11% 5% 26% 47% 10% 1	416
August	1st to 10th	Night	15% 4 24% 40% 16% 1	387
	11th to 20th	Night	14% 3 21% 38% 23% 1	607
	21st to end	Night	15% 5% 28% 33% 17% 2	836
September	1st to 10th	Night	16% 7% 27% 33% 16%	760
	11th to 20th	Night	17% 6% 21% 32% 20% 4	736
	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

Page generated at 2024-09-11 10:00:02. Version ac07

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