Fickle Hill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fickle Hill Observatory clear sky chart from 2005-11-06 to 2025-08-05.

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	14% 7% 2 5% 4 4 4 3 4 6% 47%	129713
	Night	17% 9% 3 6% 4 4 4 3 4 6% 40%	127277
Transparency	Day	34% 6% 11% 22% 17% 9%	129427
	Night	39% 8% 11% 17% 15% 9%	127078
Seeing	Day	20% 11% 25% 27% 13% 4	16131
	Night	20% 6% 13% 29% 26% 6%	25190

By Month

Percentage Cloud Cover SW (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	32% 13% 3 8% 4 3 4 3 4 5% 22%	3796
	11th to 20th	Day	25% 8% 2 4 3 2 3 2 3 3 45%	4100
	21st to end	Day	25% 7% 1 5% 3 3 3 2 4 5% 42%	4510
February	1st to 10th	Day	23% 10% 2 5% 4 4 4 3 5% 7% 33%	1800
	11th to 20th	Day	23% 11% 3 6% 3 4 4 3 4 7% 30%	1755
	21st to end	Day	24% 14% 3 6% 3 3 3 2 4 5% 33%	1613
March	1st to 10th	Day	26% 19% 3 6% 3 4 3 2 4 4 27%	4952
	11th to 20th	Day	26% 13% 2 5% 4 3 3 3 4 5% 33%	5000
	21st to end	Day	30% 13% 3 7% 4 3 4 3 5% 6% 22%	5486
April	1st to 10th	Day	22% 13% 2 7% 5% 5% 5% 4 5% 6% 26%	2363
	11th to 20th	Day	21% 12% 2 6% 4 4 3 3 4 7% 33%	2369
	21st to end	Day	17% 11% 3 5% 4 3 4 3 6% 8% 36%	2545
May	1st to 10th	Day	13% 8% 1 4 2 3 3 3 5% 5% 52%	5880
	11th to 20th	Day	11% 8% 2 5% 3 3 4 3 4 6% 51%	6005
	21st to end	Day	7% 6% 2 5% 4 4 5% 4 5% 8% 50%	6902
June	1st to 10th	Day	14% 9% 2 5% 4 3 5% 3 5% 7% 42%	2800
	11th to 20th	Day	7% 4 1 5% 4 4 4 3 6% 8% 54%	2800
	21st to end	Day	5% 4 1 3 3 3 3 3 4 7% 65%	2800
July	1st to 10th	Day	2 2 1 2 2 4 3 2 4 5% 73%	6319
	11th to 20th	Day	2 2 1 2 2 4 4 2 3 5% 75%	6015
	21st to end	Day	3 1 4 7% 7% 5% 3 4 9% 56%	6402
August	1st to 10th	Day	1 3 1 4 5% 8% 6% 4 6% 9% 52%	4144
	11th to 20th	Day	2 4 2 5% 3 4 4 3 6% 7% 60%	4026
	21st to end	Day	5% 3 1 3 2 2 2 2 4 6% 69%	4256
September	1st to 10th	Day	4 3 1 3 2 2 2 2 4 7% 70%	2280
	11th to 20th	Day	6% 5% 2 5% 4 4 3 3 6% 7% 56%	2180
	21st to end	Day	7% 4 2 3 2 2 2 2 5% 7% 64%	2056
October	1st to 10th	Day	5% 3 2 3 2 2 3 2 3 5% 71%	3180
	11th to 20th	Day	10% 4 2 6% 4 5% 5% 4 6% 7% 47%	3161
	21st to end	Day	17% 7% 2 6% 4 4 4 4 6% 6% 40%	3448
November	1st to 10th	Day	21% 8% 2 6% 4 3 4 3 6% 9% 35%	1918
	11th to 20th	Day	24% 9% 2 5% 5% 3 5% 4 5% 8% 30%	1600
	21st to end	Day	19% 7% 3 7% 5% 4 3 3 5% 8% 37%	1600
December	1st to 10th	Day	14% 6% 2 5% 3 3 4 3 5% 8% 47%	2620
	11th to 20th	Day	33% 10% 4 8% 5% 4 5% 3 5% 6% 17%	3028
	21st to end	Day	36% 12% 4 8% 5% 5% 4 3 3 3 17%	4004
January	1st to 10th	Night	33% 13% 3 7% 4 4 4 3 4 5% 21%	6152
	11th to 20th	Night	21% 9% 3 6% 4 3 3 2 3 4 42%	5880
	21st to end	Night	30% 9% 2 4 2 2 2 2 2 4 39%	6468
February	1st to 10th	Night	21% 11% 3 7% 4 4 4 3 4 6% 33%	2600
	11th to 20th	Night	23% 11% 3 8% 5% 4 4 2 4 5% 31%	2532
	21st to end	Night	21% 13% 2 5% 4 3 4 3 4 7% 33%	2011
March	1st to 10th	Night	26% 20% 2 6% 2 3 3 3 5% 6% 24%	4942
	11th to 20th	Night	21% 14% 3 6% 4 4 3 3 4 6% 33%	5000
	21st to end	Night	29% 17% 3 7% 4 3 4 3 3 5% 20%	5489
April	1st to 10th	Night	20% 14% 4 6% 5% 5% 4 3 5% 8% 27%	2035
	11th to 20th	Night	17% 13% 3 6% 4 4 4 3 6% 6% 34%	1979
	21st to end	Night	17% 10% 3 6% 4 4 3 3 7% 7% 35%	1852
May	1st to 10th	Night	11% 7% 2 6% 3 4 4 3 5% 6% 49%	4100
	11th to 20th	Night	9% 13% 4 8% 4 4 3 2 3 5% 45%	3900
	21st to end	Night	5% 8% 3 9% 6% 6% 6% 4 5% 5% 44%	3972
June	1st to 10th	Night	12% 10% 3 7% 3 4 4 4 7% 7% 38%	1600
	11th to 20th	Night	5% 6% 2 6% 4 4 5% 3 4 8% 51%	1600
	21st to end	Night	5% 5% 1 5% 3 5% 5% 3 5% 7% 57%	1600
July	1st to 10th	Night	1 3 3 6% 4 7% 5% 2 3 5% 60%	3640
	11th to 20th	Night	1 1 1 3 3 7% 7% 4 3 5% 64%	3954
	21st to end	Night	7% 5% 11% 7% 10% 8% 3 3 5% 41%	4472
August	1st to 10th	Night	3 2 10% 7% 12% 9% 4 4 6% 42%	2884
	11th to 20th	Night	2 5% 3 7% 4 7% 4 2 4 6% 55%	2812
	21st to end	Night	5% 2 1 4 2 3 4 3 3 7% 66%	3420
September	1st to 10th	Night	3 3 1 3 2 2 3 2 4 8% 71%	1900
	11th to 20th	Night	5% 5% 2 4 3 4 4 2 5% 8% 58%	1998
	21st to end	Night	7% 5% 2 4 3 3 3 3 5% 6% 60%	2123
October	1st to 10th	Night	5% 4 2 4 2 2 4 2 3 4 68%	3800
	11th to 20th	Night	12% 8% 3 7% 4 3 3 3 5% 7% 46%	3777
	21st to end	Night	15% 7% 2 7% 4 5% 5% 4 6% 8% 38%	4121
November	1st to 10th	Night	19% 9% 2 7% 4 4 4 4 5% 6% 36%	2376
	11th to 20th	Night	22% 10% 3 8% 5% 5% 4 3 5% 7% 28%	2800
	21st to end	Night	20% 8% 2 6% 4 3 4 4 5% 7% 38%	2800
December	1st to 10th	Night	15% 6% 2 5% 4 3 4 3 6% 7% 46%	4560
	11th to 20th	Night	30% 11% 4 8% 5% 4 5% 3 4 5% 20%	5176
	21st to end	Night	33% 10% 2 7% 4 5% 4 3 4 5% 23%	6952

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	63% 8% 7% 11% 8% 3	3796
	11th to 20th	Day	45% 5% 4 14% 19% 12%	4100
	21st to end	Day	45% 5% 8% 9% 16% 17%	4510
February	1st to 10th	Day	51% 6% 11% 16% 11% 5%	1800
	11th to 20th	Day	52% 7% 10% 17% 12% 1	1764
	21st to end	Day	56% 5% 10% 17% 10% 3	1613
March	1st to 10th	Day	60% 6% 6% 19% 8% 1	4952
	11th to 20th	Day	54% 6% 13% 12% 12% 3	5000
	21st to end	Day	61% 8% 14% 15% 2	5486
April	1st to 10th	Day	56% 9% 14% 14% 7% 1	2363
	11th to 20th	Day	50% 6% 15% 17% 9% 3	2372
	21st to end	Day	44% 8% 15% 20% 11% 1	2545
May	1st to 10th	Day	31% 8% 12% 24% 21% 4	5880
	11th to 20th	Day	30% 7% 15% 21% 24% 2	6008
	21st to end	Day	23% 11% 20% 40% 5%	6904
June	1st to 10th	Day	37% 10% 14% 24% 13% 2	2800
	11th to 20th	Day	24% 8% 16% 31% 18% 3	2800
	21st to end	Day	17% 6% 16% 30% 25% 7%	2800
July	1st to 10th	Day	7% 4 6% 28% 21% 33%	6251
	11th to 20th	Day	8% 2 6% 17% 33% 35%	5942
	21st to end	Day	5% 6% 13% 39% 23% 14%	6217
August	1st to 10th	Day	10% 5% 11% 27% 34% 13%	4129
	11th to 20th	Day	12% 7% 13% 33% 26% 10%	4065
	21st to end	Day	14% 4 11% 29% 32% 9%	4255
September	1st to 10th	Day	13% 4 9% 19% 34% 22%	2280
	11th to 20th	Day	23% 6% 14% 26% 25% 5%	2180
	21st to end	Day	20% 5% 13% 23% 23% 16%	2056
October	1st to 10th	Day	18% 3 9% 18% 18% 33%	3180
	11th to 20th	Day	28% 8% 13% 28% 17% 6%	3161
	21st to end	Day	41% 7% 10% 19% 15% 8%	3448
November	1st to 10th	Day	46% 7% 12% 18% 12% 5%	1918
	11th to 20th	Day	51% 7% 13% 13% 9% 8%	1600
	21st to end	Day	47% 6% 10% 12% 13% 11%	1600
December	1st to 10th	Day	36% 5% 8% 18% 22% 11%	2620
	11th to 20th	Day	67% 8% 7% 9% 7% 2	3028
	21st to end	Day	72% 6% 5% 10% 6% 2	4004
January	1st to 10th	Night	64% 7% 9% 9% 8% 2	6152
	11th to 20th	Night	46% 6% 6% 13% 20% 10%	5880
	21st to end	Night	51% 4 4 8% 11% 21%	6468
February	1st to 10th	Night	52% 7% 11% 15% 11% 5%	2600
	11th to 20th	Night	55% 7% 11% 14% 10% 3	2534
	21st to end	Night	51% 7% 14% 17% 8% 3	2011
March	1st to 10th	Night	59% 7% 9% 18% 6% 2	4942
	11th to 20th	Night	50% 11% 12% 14% 8% 6%	5000
	21st to end	Night	63% 9% 11% 12% 4 1	5489
April	1st to 10th	Night	53% 11% 13% 15% 5% 2	2035
	11th to 20th	Night	47% 10% 16% 15% 8% 3	1979
	21st to end	Night	43% 11% 18% 19% 7% 2	1852
May	1st to 10th	Night	27% 11% 14% 17% 24% 7%	4097
	11th to 20th	Night	35% 8% 16% 18% 20% 3	3901
	21st to end	Night	24% 19% 21% 32% 4	3972
June	1st to 10th	Night	38% 10% 18% 22% 11% 1	1600
	11th to 20th	Night	23% 10% 18% 28% 17% 4	1600
	21st to end	Night	15% 8% 17% 30% 24% 7%	1600
July	1st to 10th	Night	9% 8% 10% 23% 17% 33%	3600
	11th to 20th	Night	7% 3 8% 15% 39% 29%	3904
	21st to end	Night	11% 15% 15% 27% 21% 11%	4345
August	1st to 10th	Night	11% 9% 16% 27% 28% 9%	2875
	11th to 20th	Night	13% 7% 15% 31% 26% 8%	2839
	21st to end	Night	14% 5% 12% 29% 30% 11%	3420
September	1st to 10th	Night	11% 5% 11% 19% 31% 24%	1900
	11th to 20th	Night	19% 8% 18% 29% 21% 6%	1998
	21st to end	Night	23% 5% 14% 21% 19% 17%	2123
October	1st to 10th	Night	18% 4 8% 18% 19% 34%	3800
	11th to 20th	Night	34% 8% 11% 26% 16% 5%	3777
	21st to end	Night	40% 8% 11% 18% 15% 8%	4121
November	1st to 10th	Night	48% 9% 13% 13% 12% 5%	2376
	11th to 20th	Night	55% 9% 12% 12% 8% 5%	2800
	21st to end	Night	45% 6% 10% 15% 13% 10%	2800
December	1st to 10th	Night	36% 6% 8% 17% 20% 12%	4560
	11th to 20th	Night	67% 6% 7% 12% 8% 1	5176
	21st to end	Night	60% 10% 12% 11% 5% 2	6952

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	41% 15% 21% 17% 5% 1	266
	11th to 20th	Day	35% 9% 21% 21% 10% 4	400
	21st to end	Day	29% 10% 21% 24% 12% 3	440
February	1st to 10th	Day	30% 13% 26% 22% 7% 3	400
	11th to 20th	Day	38% 12% 24% 18% 8%	395
	21st to end	Day	34% 16% 25% 17% 7% 1	376
March	1st to 10th	Day	36% 16% 25% 17% 5% 1	500
	11th to 20th	Day	33% 14% 25% 20% 7% 2	500
	21st to end	Day	35% 16% 25% 17% 7% 1	550
April	1st to 10th	Day	32% 18% 26% 17% 6% 2	500
	11th to 20th	Day	30% 15% 22% 23% 7% 3	492
	21st to end	Day	24% 14% 31% 19% 9% 3	500
May	1st to 10th	Day	20% 16% 29% 22% 10% 3	503
	11th to 20th	Day	29% 14% 26% 20% 9% 3	528
	21st to end	Day	19% 16% 28% 24% 11% 3	573
June	1st to 10th	Day	18% 13% 28% 25% 12% 4	530
	11th to 20th	Day	12% 18% 32% 27% 9% 2	530
	21st to end	Day	5% 9% 34% 35% 14% 3	530
July	1st to 10th	Day	6% 6% 31% 38% 14% 4	526
	11th to 20th	Day	2 5% 31% 40% 16% 5%	524
	21st to end	Day	1 5% 23% 43% 21% 7%	575
August	1st to 10th	Day	4 6% 29% 36% 17% 7%	504
	11th to 20th	Day	3 8% 22% 42% 18% 7%	477
	21st to end	Day	5% 5% 24% 41% 17% 8%	539
September	1st to 10th	Day	6% 6% 26% 36% 19% 6%	490
	11th to 20th	Day	9% 11% 21% 38% 16% 4	490
	21st to end	Day	10% 9% 25% 31% 19% 5%	490
October	1st to 10th	Day	10% 11% 23% 31% 19% 6%	490
	11th to 20th	Day	16% 8% 17% 29% 22% 7%	490
	21st to end	Day	18% 11% 25% 26% 17% 3	539
November	1st to 10th	Day	22% 11% 22% 28% 13% 5%	464
	11th to 20th	Day	25% 10% 19% 21% 19% 7%	200
	21st to end	Day	23% 11% 12% 31% 20% 4	200
December	1st to 10th	Day	25% 15% 17% 21% 14% 9%	200
	11th to 20th	Day	39% 8% 18% 21% 12% 4	200
	21st to end	Day	36% 10% 20% 19% 13% 2	220
January	1st to 10th	Night	32% 7% 16% 26% 16% 3	800
	11th to 20th	Night	29% 5% 16% 28% 16% 5%	800
	21st to end	Night	30% 4 12% 29% 21% 4	880
February	1st to 10th	Night	28% 8% 14% 32% 16% 2	800
	11th to 20th	Night	28% 9% 16% 24% 18% 4	784
	21st to end	Night	29% 7% 18% 31% 14%	660
March	1st to 10th	Night	36% 10% 16% 24% 12% 3	800
	11th to 20th	Night	29% 8% 14% 26% 21% 3	800
	21st to end	Night	32% 10% 16% 26% 14% 2	880
April	1st to 10th	Night	28% 8% 18% 27% 16% 3	800
	11th to 20th	Night	23% 9% 19% 26% 19% 4	791
	21st to end	Night	22% 7% 13% 32% 22% 5%	652
May	1st to 10th	Night	16% 8% 17% 30% 25% 4	600
	11th to 20th	Night	17% 7% 11% 30% 27% 7%	522
	21st to end	Night	16% 8% 14% 32% 26% 3	433
June	1st to 10th	Night	16% 6% 13% 33% 28% 4	400
	11th to 20th	Night	8% 5% 18% 46% 22% 2	400
	21st to end	Night	7% 4 8% 39% 40% 3	400
July	1st to 10th	Night	3 3 9% 38% 42% 4	390
	11th to 20th	Night	3 5% 3 33% 46% 10%	518
	21st to end	Night	2 3 6% 25% 49% 16%	657
August	1st to 10th	Night	3 5% 7% 27% 46% 12%	579
	11th to 20th	Night	3 2 7% 24% 52% 12%	564
	21st to end	Night	4 3 8% 31% 43% 12%	784
September	1st to 10th	Night	4 1 9% 30% 44% 12%	760
	11th to 20th	Night	6% 4 10% 31% 38% 11%	760
	21st to end	Night	9% 4 11% 28% 36% 12%	760
October	1st to 10th	Night	9% 4 11% 30% 37% 9%	760
	11th to 20th	Night	15% 4 10% 28% 32% 11%	760
	21st to end	Night	16% 6% 12% 30% 27% 9%	836
November	1st to 10th	Night	22% 6% 17% 29% 20% 7%	780
	11th to 20th	Night	27% 8% 13% 29% 20% 3	800
	21st to end	Night	24% 5% 15% 32% 20% 3	800
December	1st to 10th	Night	25% 8% 15% 29% 21% 3	800
	11th to 20th	Night	33% 9% 18% 25% 14% 2	800
	21st to end	Night	41% 7% 14% 25% 11% 2	880

Page generated at 2025-08-01 22:32:24. Version ac07

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