Fanthorp Inn State Historic Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fanthorp Inn State Historic Site clear sky chart from 2005-11-06 to 2025-12-18.

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	12% 6% 2 6% 4 4 5% 4 6% 8% 43%	127090
	Night	12% 6% 2 5% 4 4 4 3 5% 7% 48%	124192
Transparency	Day	37% 7% 12% 19% 17% 8%	130767
	Night	34% 6% 11% 20% 19% 10%	128578
Seeing	Day	13% 9% 22% 27% 23% 7%	16368
	Night	14% 8% 27% 33% 16% 2	26250

By Month

Percentage Cloud Cover SE (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	17% 9% 3 6% 3 4 3 3 4 5% 43%	4077
	11th to 20th	Day	15% 5% 3 5% 3 3 4 3 4 6% 49%	4080
	21st to end	Day	28% 10% 3 6% 2 2 2 2 3 6% 36%	4488
February	1st to 10th	Day	22% 8% 3 6% 3 3 3 3 4 6% 38%	1929
	11th to 20th	Day	21% 7% 3 7% 5% 3 3 2 3 5% 41%	1949
	21st to end	Day	18% 8% 3 6% 4 3 3 2 4 6% 42%	1777
March	1st to 10th	Day	14% 9% 3 7% 5% 4 4 3 5% 7% 39%	4936
	11th to 20th	Day	12% 7% 3 5% 4 4 4 3 4 7% 47%	4980
	21st to end	Day	16% 7% 3 7% 4 4 5% 3 5% 6% 40%	5462
April	1st to 10th	Day	14% 9% 3 7% 5% 4 5% 3 4 6% 40%	2200
	11th to 20th	Day	13% 9% 3 7% 5% 4 4 4 5% 7% 40%	2298
	21st to end	Day	10% 8% 2 7% 5% 4 4 3 6% 7% 44%	2400
May	1st to 10th	Day	16% 8% 3 8% 5% 5% 5% 4 6% 7% 33%	5743
	11th to 20th	Day	10% 5% 2 7% 5% 5% 5% 4 6% 8% 44%	5862
	21st to end	Day	9% 7% 2 7% 6% 6% 6% 5% 8% 10% 34%	6434
June	1st to 10th	Day	5% 4 2 6% 5% 6% 5% 5% 8% 9% 44%	2600
	11th to 20th	Day	5% 4 1 5% 5% 5% 5% 5% 8% 10% 47%	2600
	21st to end	Day	5% 5% 2 7% 7% 7% 7% 6% 8% 10% 35%	2600
July	1st to 10th	Day	9% 5% 2 7% 5% 5% 6% 5% 7% 12% 36%	5900
	11th to 20th	Day	5% 5% 2 6% 5% 6% 6% 5% 9% 13% 38%	5900
	21st to end	Day	10% 6% 2 6% 5% 5% 6% 5% 7% 10% 38%	6422
August	1st to 10th	Day	1 1 1 3 3 3 3 3 5% 9% 66%	4234
	11th to 20th	Day	3 2 1 4 4 4 5% 5% 8% 13% 51%	4105
	21st to end	Day	5% 4 2 7% 6% 5% 7% 5% 7% 10% 42%	4124
September	1st to 10th	Day	6% 5% 2 6% 5% 6% 5% 5% 7% 8% 44%	2200
	11th to 20th	Day	11% 6% 2 7% 6% 5% 5% 5% 6% 7% 41%	2200
	21st to end	Day	6% 4 2 7% 5% 4 5% 5% 6% 7% 50%	2200
October	1st to 10th	Day	5% 4 1 4 4 4 4 4 4 5% 61%	2112
	11th to 20th	Day	12% 4 2 4 4 4 4 3 3 5% 55%	2000
	21st to end	Day	13% 6% 2 4 3 3 3 3 3 5% 56%	2200
November	1st to 10th	Day	10% 6% 2 5% 5% 4 4 4 5% 6% 49%	2058
	11th to 20th	Day	10% 6% 2 6% 3 3 4 3 5% 7% 51%	2100
	21st to end	Day	16% 7% 2 6% 5% 4 4 4 5% 5% 43%	1948
December	1st to 10th	Day	21% 8% 2 6% 4 3 3 3 4 5% 41%	3030
	11th to 20th	Day	18% 7% 2 6% 4 4 4 2 4 7% 42%	3454
	21st to end	Day	15% 7% 2 7% 4 3 3 3 3 6% 47%	4488
January	1st to 10th	Night	17% 7% 2 5% 3 3 3 2 4 6% 48%	5888
	11th to 20th	Night	14% 6% 2 4 2 3 3 2 3 5% 56%	5900
	21st to end	Night	27% 9% 3 5% 3 3 3 2 3 5% 38%	6490
February	1st to 10th	Night	18% 8% 3 7% 3 3 3 2 4 5% 42%	2488
	11th to 20th	Night	20% 8% 2 5% 3 3 3 3 3 4 45%	2338
	21st to end	Night	20% 7% 3 6% 4 3 3 3 4 6% 41%	1851
March	1st to 10th	Night	17% 10% 3 6% 3 4 4 2 5% 7% 40%	4919
	11th to 20th	Night	15% 6% 2 7% 4 3 4 3 4 5% 47%	4980
	21st to end	Night	18% 9% 3 6% 4 4 3 3 4 5% 41%	5467
April	1st to 10th	Night	12% 7% 3 5% 4 4 4 4 5% 7% 45%	2200
	11th to 20th	Night	11% 6% 2 7% 4 4 4 3 5% 8% 46%	2050
	21st to end	Night	13% 7% 2 5% 3 4 4 3 5% 7% 46%	2000
May	1st to 10th	Night	16% 9% 3 8% 5% 4 5% 4 6% 8% 31%	4150
	11th to 20th	Night	10% 6% 3 7% 5% 5% 5% 4 6% 7% 43%	4053
	21st to end	Night	9% 6% 2 7% 5% 5% 6% 5% 7% 10% 37%	4443
June	1st to 10th	Night	5% 4 1 5% 3 4 4 4 7% 11% 53%	1800
	11th to 20th	Night	2 3 1 4 3 3 3 4 7% 12% 58%	1800
	21st to end	Night	3 3 2 5% 5% 5% 5% 5% 8% 11% 49%	1800
July	1st to 10th	Night	6% 5% 2 6% 4 5% 6% 6% 9% 13% 39%	4078
	11th to 20th	Night	4 3 1 4 4 3 4 4 7% 13% 53%	4077
	21st to end	Night	8% 6% 2 6% 4 4 4 5% 6% 9% 46%	4449
August	1st to 10th	Night	1 1 1 2 2 2 2 2 5% 10% 73%	2926
	11th to 20th	Night	2 2 1 3 2 3 4 3 7% 13% 60%	2948
	21st to end	Night	3 3 1 5% 3 4 5% 4 8% 11% 50%	3767
September	1st to 10th	Night	4 5% 3 6% 4 3 4 4 6% 10% 50%	2200
	11th to 20th	Night	8% 5% 3 6% 5% 6% 4 4 6% 9% 44%	2200
	21st to end	Night	7% 4 1 4 3 3 4 3 5% 8% 57%	2200
October	1st to 10th	Night	4 3 2 4 3 3 3 3 5% 8% 64%	2265
	11th to 20th	Night	9% 3 1 4 2 3 3 3 5% 6% 62%	2400
	21st to end	Night	11% 5% 2 5% 3 3 3 2 3 4 61%	2640
November	1st to 10th	Night	10% 5% 2 4 3 3 4 3 5% 6% 56%	2460
	11th to 20th	Night	10% 6% 2 5% 4 4 4 3 5% 5% 53%	2520
	21st to end	Night	15% 7% 2 6% 4 3 3 3 4 7% 46%	2667
December	1st to 10th	Night	20% 10% 3 7% 4 3 3 2 4 5% 39%	4380
	11th to 20th	Night	16% 9% 3 6% 4 3 4 2 4 5% 44%	4908
	21st to end	Night	14% 7% 2 5% 3 3 3 2 3 4 53%	6490

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	43% 4 5% 22% 19% 7%	4078
	11th to 20th	Day	37% 3 5% 18% 27% 11%	4080
	21st to end	Day	51% 3 4 11% 16% 15%	4488
February	1st to 10th	Day	47% 6% 5% 13% 18% 12%	1929
	11th to 20th	Day	47% 4 7% 15% 17% 9%	1959
	21st to end	Day	44% 5% 8% 15% 16% 12%	1777
March	1st to 10th	Day	43% 8% 7% 13% 19% 10%	4936
	11th to 20th	Day	36% 7% 7% 10% 19% 21%	4980
	21st to end	Day	43% 6% 9% 20% 16% 6%	5464
April	1st to 10th	Day	45% 7% 7% 16% 15% 10%	2200
	11th to 20th	Day	43% 6% 10% 14% 17% 9%	2298
	21st to end	Day	38% 7% 9% 19% 21% 6%	2400
May	1st to 10th	Day	46% 9% 10% 20% 11% 3	5780
	11th to 20th	Day	37% 7% 15% 17% 22% 2	5866
	21st to end	Day	39% 11% 13% 24% 12% 1	6447
June	1st to 10th	Day	32% 10% 16% 26% 14% 2	2600
	11th to 20th	Day	30% 10% 16% 25% 16% 4	2600
	21st to end	Day	40% 11% 16% 22% 11% 1	2600
July	1st to 10th	Day	38% 8% 29% 22% 3	5836
	11th to 20th	Day	34% 9% 23% 25% 9%	5831
	21st to end	Day	38% 9% 18% 25% 10% 1	6240
August	1st to 10th	Day	15% 7% 15% 37% 26%	4220
	11th to 20th	Day	21% 8% 31% 32% 7% 1	4144
	21st to end	Day	34% 11% 18% 22% 13% 1	4123
September	1st to 10th	Day	35% 10% 13% 20% 16% 7%	2200
	11th to 20th	Day	40% 9% 13% 17% 16% 5%	2200
	21st to end	Day	31% 9% 11% 20% 17% 13%	2200
October	1st to 10th	Day	15% 4 6% 12% 23% 39%	3437
	11th to 20th	Day	21% 3 7% 16% 33% 20%	3240
	21st to end	Day	25% 4 5% 18% 34% 14%	3538
November	1st to 10th	Day	35% 6% 9% 16% 23% 11%	2058
	11th to 20th	Day	32% 6% 9% 17% 22% 13%	2100
	21st to end	Day	42% 6% 8% 15% 19% 10%	1948
December	1st to 10th	Day	45% 5% 6% 16% 22% 6%	3030
	11th to 20th	Day	43% 4 8% 12% 22% 11%	3452
	21st to end	Day	40% 4 5% 14% 28% 9%	4488
January	1st to 10th	Night	37% 5% 6% 22% 21% 9%	5888
	11th to 20th	Night	32% 3 4 19% 28% 13%	5900
	21st to end	Night	51% 3 4 12% 17% 13%	6490
February	1st to 10th	Night	45% 4 5% 12% 18% 15%	2488
	11th to 20th	Night	44% 4 6% 15% 17% 12%	2338
	21st to end	Night	45% 5% 8% 12% 16% 14%	1851
March	1st to 10th	Night	44% 6% 7% 14% 20% 10%	4919
	11th to 20th	Night	39% 6% 6% 14% 14% 21%	4980
	21st to end	Night	45% 6% 7% 15% 19% 9%	5467
April	1st to 10th	Night	38% 7% 10% 17% 16% 12%	2200
	11th to 20th	Night	36% 6% 11% 18% 16% 13%	2050
	21st to end	Night	36% 7% 11% 19% 21% 7%	2000
May	1st to 10th	Night	49% 8% 10% 21% 10% 3	4178
	11th to 20th	Night	37% 7% 13% 19% 20% 3	4054
	21st to end	Night	38% 10% 16% 25% 11% 1	4452
June	1st to 10th	Night	23% 9% 19% 29% 20% 1	1800
	11th to 20th	Night	19% 8% 20% 30% 19% 4	1800
	21st to end	Night	26% 11% 21% 27% 14% 1	1800
July	1st to 10th	Night	34% 10% 31% 22% 3	4035
	11th to 20th	Night	24% 6% 26% 35% 9%	4026
	21st to end	Night	34% 9% 20% 27% 11% 1	4320
August	1st to 10th	Night	9% 5% 16% 42% 26% 1	2916
	11th to 20th	Night	16% 7% 33% 33% 10% 1	2975
	21st to end	Night	26% 13% 22% 27% 11% 1	3767
September	1st to 10th	Night	28% 10% 20% 21% 14% 8%	2200
	11th to 20th	Night	35% 8% 15% 20% 15% 6%	2200
	21st to end	Night	24% 8% 15% 21% 20% 13%	2200
October	1st to 10th	Night	14% 4 7% 16% 18% 41%	3707
	11th to 20th	Night	15% 3 5% 21% 32% 24%	3899
	21st to end	Night	21% 3 5% 19% 35% 17%	4252
November	1st to 10th	Night	29% 6% 11% 20% 23% 12%	2460
	11th to 20th	Night	32% 6% 9% 18% 20% 14%	2520
	21st to end	Night	39% 5% 9% 16% 19% 12%	2667
December	1st to 10th	Night	49% 4 5% 15% 21% 7%	4380
	11th to 20th	Night	43% 4 9% 8% 21% 14%	4909
	21st to end	Night	36% 4 5% 15% 29% 11%	6490

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	24% 18% 36% 16% 5% 1	300
	11th to 20th	Day	26% 15% 33% 20% 3 2	300
	21st to end	Day	25% 19% 35% 16% 5%	330
February	1st to 10th	Day	28% 16% 34% 18% 4	300
	11th to 20th	Day	34% 17% 30% 17% 2	300
	21st to end	Day	27% 26% 33% 11% 3	249
March	1st to 10th	Day	22% 25% 33% 16% 4	300
	11th to 20th	Day	16% 27% 39% 14% 4	300
	21st to end	Day	21% 18% 40% 16% 6%	330
April	1st to 10th	Day	19% 20% 38% 19% 4	300
	11th to 20th	Day	20% 20% 30% 20% 8% 1	416
	21st to end	Day	16% 15% 36% 24% 7% 1	500
May	1st to 10th	Day	14% 11% 41% 27% 7%	648
	11th to 20th	Day	13% 8% 32% 31% 13% 2	725
	21st to end	Day	9% 8% 30% 34% 16% 3	789
June	1st to 10th	Day	5% 3 20% 36% 29% 7%	730
	11th to 20th	Day	7% 2 17% 39% 28% 7%	730
	21st to end	Day	6% 2 13% 31% 35% 12%	730
July	1st to 10th	Day	7% 2 10% 31% 36% 14%	721
	11th to 20th	Day	4 2 5% 38% 38% 14%	718
	21st to end	Day	6% 1 5% 30% 45% 14%	794
August	1st to 10th	Day	4 1 4 26% 50% 16%	726
	11th to 20th	Day	5% 1 4 22% 52% 16%	675
	21st to end	Day	7% 1 6% 18% 45% 23%	473
September	1st to 10th	Day	6% 2 8% 30% 38% 15%	330
	11th to 20th	Day	8% 2 8% 26% 37% 18%	330
	21st to end	Day	7% 3 8% 34% 34% 13%	330
October	1st to 10th	Day	5% 2 16% 38% 29% 10%	330
	11th to 20th	Day	11% 6% 22% 34% 22% 6%	330
	21st to end	Day	23% 9% 24% 24% 15% 5%	363
November	1st to 10th	Day	15% 8% 22% 33% 19% 2	330
	11th to 20th	Day	15% 10% 26% 38% 10% 2	330
	21st to end	Day	22% 17% 32% 19% 8% 2	330
December	1st to 10th	Day	22% 8% 39% 20% 7% 4	330
	11th to 20th	Day	22% 17% 31% 22% 4 3	321
	21st to end	Day	20% 18% 36% 18% 7% 1	330
January	1st to 10th	Night	22% 12% 33% 28% 6%	1000
	11th to 20th	Night	21% 14% 34% 25% 7%	1000
	21st to end	Night	22% 13% 33% 27% 5%	1100
February	1st to 10th	Night	23% 14% 36% 23% 3	888
	11th to 20th	Night	27% 12% 34% 23% 4	784
	21st to end	Night	24% 16% 40% 17% 2	531
March	1st to 10th	Night	20% 16% 40% 21% 4	600
	11th to 20th	Night	18% 13% 38% 26% 5%	600
	21st to end	Night	15% 12% 44% 24% 5%	660
April	1st to 10th	Night	15% 14% 41% 27% 4	600
	11th to 20th	Night	15% 12% 35% 31% 6%	593
	21st to end	Night	17% 10% 40% 25% 9%	600
May	1st to 10th	Night	13% 12% 41% 27% 6% 1	600
	11th to 20th	Night	12% 7% 34% 33% 13% 1	591
	21st to end	Night	8% 5% 33% 38% 15% 1	650
June	1st to 10th	Night	7% 2 18% 46% 25% 3	600
	11th to 20th	Night	3 2 22% 52% 21% 1	600
	21st to end	Night	4 1 14% 45% 32% 5%	600
July	1st to 10th	Night	5% 2 9% 47% 33% 5%	585
	11th to 20th	Night	3 1 9% 52% 32% 4	582
	21st to end	Night	4 1 7% 52% 32% 4	657
August	1st to 10th	Night	2 5% 54% 36% 3	597
	11th to 20th	Night	5% 5% 48% 37% 4	594
	21st to end	Night	4 2 9% 36% 44% 7%	660
September	1st to 10th	Night	5% 2 9% 38% 40% 7%	600
	11th to 20th	Night	11% 1 8% 35% 39% 7%	600
	21st to end	Night	11% 1 12% 35% 36% 5%	600
October	1st to 10th	Night	4 2 14% 43% 31% 5%	665
	11th to 20th	Night	10% 3 25% 39% 21% 2	800
	21st to end	Night	14% 8% 28% 30% 18% 2	880
November	1st to 10th	Night	11% 5% 26% 39% 18% 1	820
	11th to 20th	Night	12% 10% 29% 36% 14%	840
	21st to end	Night	18% 10% 32% 27% 12% 1	987
December	1st to 10th	Night	22% 10% 31% 27% 10%	1050
	11th to 20th	Night	24% 12% 28% 30% 6%	1036
	21st to end	Night	21% 11% 33% 29% 7%	1100

Page generated at 2025-12-15 00:13:49. Version ac07

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