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 2025-02-21.

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% 5% 4 4 5% 7% 31%	108663
	Night	18% 12% 4 9% 5% 4 4 3 5% 6% 29%	109897
Transparency	Day	51% 6% 12% 21% 9% 1	112163
	Night	55% 6% 12% 18% 9% 1	114561
Seeing	Day	22% 16% 30% 21% 9% 3	14788
	Night	23% 12% 30% 26% 9% 1	24014

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	16% 19% 7% 14% 5% 6% 4 3 4 4 19%	3597
	11th to 20th	Day	12% 16% 8% 15% 6% 5% 4 4 5% 5% 20%	3570
	21st to end	Day	13% 19% 7% 12% 7% 6% 5% 3 4 5% 19%	4080
February	1st to 10th	Day	17% 16% 4 11% 8% 5% 4 3 5% 5% 23%	1800
	11th to 20th	Day	15% 15% 6% 10% 7% 5% 4 3 4 5% 25%	1794
	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	14% 5% 1 5% 4 4 5% 3 5% 7% 46%	2256
	21st to end	Day	18% 6% 2 6% 4 3 5% 4 6% 7% 39%	2065
October	1st to 10th	Day	20% 7% 3 7% 4 4 5% 3 6% 6% 35%	1900
	11th to 20th	Day	20% 9% 4 9% 6% 5% 5% 3 5% 6% 28%	1900
	21st to end	Day	26% 11% 3 8% 5% 4 4 3 4 6% 27%	1914
November	1st to 10th	Day	16% 11% 3 8% 5% 5% 5% 4 6% 7% 31%	1761
	11th to 20th	Day	17% 13% 3 8% 6% 4 4 4 5% 7% 29%	1655
	21st to end	Day	21% 14% 4 10% 6% 6% 4 4 5% 5% 21%	1600
December	1st to 10th	Day	22% 21% 5% 10% 5% 5% 4 4 5% 5% 14%	2600
	11th to 20th	Day	19% 16% 5% 12% 6% 4 4 4 5% 4 22%	2986
	21st to end	Day	22% 14% 5% 12% 6% 5% 5% 3 3 4 20%	3960
January	1st to 10th	Night	15% 22% 7% 13% 6% 4 3 3 3 5% 19%	6349
	11th to 20th	Night	11% 17% 8% 16% 8% 6% 5% 4 4 4 16%	6315
	21st to end	Night	16% 18% 7% 12% 7% 5% 4 3 4 5% 20%	6858
February	1st to 10th	Night	16% 16% 5% 13% 6% 5% 5% 3 5% 5% 21%	2600
	11th to 20th	Night	14% 14% 5% 12% 7% 4 4 3 4 5% 26%	2491
	21st to end	Night	17% 15% 4 11% 6% 4 4 3 4 5% 28%	1885
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% 50%	1923
	21st to end	Night	15% 6% 3 6% 4 4 4 4 5% 7% 43%	2113
October	1st to 10th	Night	18% 8% 3 7% 4 5% 4 4 5% 7% 36%	2280
	11th to 20th	Night	20% 9% 3 8% 4 4 4 4 5% 6% 34%	2280
	21st to end	Night	24% 10% 3 8% 4 5% 4 3 5% 6% 28%	2682
November	1st to 10th	Night	19% 10% 3 7% 5% 4 3 3 4 5% 35%	2537
	11th to 20th	Night	18% 12% 4 8% 6% 4 5% 3 4 6% 32%	2743
	21st to end	Night	22% 14% 4 9% 5% 5% 4 3 4 6% 24%	2800
December	1st to 10th	Night	20% 17% 7% 12% 6% 5% 5% 4 4 5% 16%	4580
	11th to 20th	Night	23% 16% 4 9% 5% 4 4 3 3 4 25%	5208
	21st to end	Night	26% 16% 4 11% 5% 3 3 3 5% 4 19%	6996

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% 6% 10% 11% 4	3598
	11th to 20th	Day	66% 5% 11% 10% 8%	3600
	21st to end	Day	67% 6% 10% 10% 6%	4080
February	1st to 10th	Day	63% 4 9% 18% 4 1	1800
	11th to 20th	Day	61% 5% 11% 15% 7% 1	1803
	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% 32% 13%	2256
	21st to end	Day	43% 7% 15% 26% 10%	2065
October	1st to 10th	Day	46% 5% 12% 28% 9%	3160
	11th to 20th	Day	48% 5% 16% 24% 6%	3140
	21st to end	Day	49% 4 17% 23% 7%	3126
November	1st to 10th	Day	51% 6% 15% 21% 6% 1	1761
	11th to 20th	Day	54% 6% 13% 16% 10% 1	1655
	21st to end	Day	64% 7% 14% 12% 4	1600
December	1st to 10th	Day	71% 7% 11% 10% 1	2600
	11th to 20th	Day	65% 6% 10% 14% 6%	2986
	21st to end	Day	68% 4 7% 16% 4	3960
January	1st to 10th	Night	69% 5% 11% 11% 3	6349
	11th to 20th	Night	70% 7% 10% 9% 4	6360
	21st to end	Night	66% 5% 9% 9% 10% 1	6858
February	1st to 10th	Night	64% 5% 10% 14% 5% 1	2600
	11th to 20th	Night	59% 6% 10% 18% 6%	2493
	21st to end	Night	58% 5% 9% 17% 10% 1	1885
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% 13% 1	1923
	21st to end	Night	41% 7% 12% 27% 12%	2113
October	1st to 10th	Night	43% 6% 14% 28% 9%	3800
	11th to 20th	Night	45% 5% 15% 26% 9%	3779
	21st to end	Night	50% 5% 17% 20% 8%	4420
November	1st to 10th	Night	51% 6% 14% 20% 9% 1	2537
	11th to 20th	Night	53% 6% 13% 17% 10% 1	2743
	21st to end	Night	62% 6% 12% 15% 5%	2800
December	1st to 10th	Night	71% 5% 12% 10% 2	4580
	11th to 20th	Night	65% 4 8% 14% 8% 1	5208
	21st to end	Night	68% 4 7% 12% 9%	6996

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% 20% 31% 18% 6%	200
	11th to 20th	Day	28% 19% 34% 14% 5% 1	200
	21st to end	Day	21% 19% 34% 19% 5%	247
February	1st to 10th	Day	29% 26% 30% 11% 3	300
	11th to 20th	Day	25% 24% 38% 12% 1	341
	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	12% 8% 24% 24% 21% 12%	490
	21st to end	Day	18% 11% 31% 19% 17% 5%	490
October	1st to 10th	Day	21% 14% 29% 18% 13% 5%	490
	11th to 20th	Day	24% 19% 28% 20% 7% 1	490
	21st to end	Day	31% 16% 26% 21% 6%	446
November	1st to 10th	Day	25% 20% 28% 19% 6% 1	395
	11th to 20th	Day	25% 20% 33% 14% 7%	255
	21st to end	Day	26% 26% 30% 14% 5% 1	200
December	1st to 10th	Day	31% 19% 29% 19% 4	200
	11th to 20th	Day	29% 30% 28% 10% 4 1	200
	21st to end	Day	30% 24% 26% 15% 5% 1	220
January	1st to 10th	Night	28% 15% 33% 21% 3	800
	11th to 20th	Night	29% 16% 29% 22% 4 1	800
	21st to end	Night	21% 13% 35% 27% 4	880
February	1st to 10th	Night	22% 19% 34% 22% 3	800
	11th to 20th	Night	22% 18% 36% 21% 3	783
	21st to end	Night	24% 17% 31% 25% 3	629
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% 20% 32% 22% 4	760
	21st to end	Night	16% 9% 26% 27% 20% 2	760
October	1st to 10th	Night	21% 9% 29% 24% 14% 1	760
	11th to 20th	Night	25% 12% 30% 24% 8%	760
	21st to end	Night	30% 13% 27% 24% 5%	836
November	1st to 10th	Night	26% 15% 28% 23% 8% 1	780
	11th to 20th	Night	25% 16% 32% 19% 8%	800
	21st to end	Night	29% 17% 28% 20% 6%	800
December	1st to 10th	Night	31% 17% 28% 21% 3	800
	11th to 20th	Night	28% 17% 31% 19% 4 1	800
	21st to end	Night	33% 15% 29% 20% 4	880

Page generated at 2025-02-18 03:26:28. Version ac07

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