Stars Fell Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stars Fell Observatory clear sky chart from 2005-11-06 to 2024-11-12.

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	13% 7% 2 6% 5% 4 5% 4 6% 8% 40%	100949
	Night	13% 7% 2 6% 4 4 4 4 5% 7% 44%	98214
Transparency	Day	41% 3 11% 22% 19% 5%	104753
	Night	39% 3 9% 22% 21% 6%	102548
Seeing	Day	18% 9% 22% 24% 18% 9%	14634
	Night	16% 8% 22% 29% 21% 4	24620

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% 12% 3 6% 5% 4 3 3 6% 5% 35%	2836
	11th to 20th	Day	17% 8% 3 8% 3 3 3 2 4 4 45%	2840
	21st to end	Day	24% 10% 2 4 3 3 3 2 3 5% 40%	3476
February	1st to 10th	Day	19% 10% 3 6% 4 3 3 3 5% 5% 38%	1900
	11th to 20th	Day	21% 9% 2 6% 5% 4 3 3 4 4 38%	1848
	21st to end	Day	20% 10% 3 7% 4 4 3 3 4 4 37%	1570
March	1st to 10th	Day	23% 12% 2 6% 4 4 5% 3 4 6% 32%	3120
	11th to 20th	Day	15% 8% 2 6% 5% 4 3 3 5% 6% 43%	3402
	21st to end	Day	16% 8% 2 7% 4 5% 5% 4 6% 6% 38%	3903
April	1st to 10th	Day	13% 6% 2 5% 4 4 4 3 7% 8% 45%	2280
	11th to 20th	Day	13% 8% 2 6% 4 3 4 3 6% 6% 45%	2254
	21st to end	Day	10% 5% 2 5% 4 4 5% 5% 6% 7% 47%	2308
May	1st to 10th	Day	12% 6% 2 6% 5% 4 5% 4 6% 9% 42%	4082
	11th to 20th	Day	16% 8% 3 6% 4 4 5% 4 6% 8% 37%	4081
	21st to end	Day	11% 5% 2 6% 5% 4 5% 4 7% 9% 42%	4476
June	1st to 10th	Day	9% 7% 3 7% 6% 6% 6% 5% 8% 9% 34%	2470
	11th to 20th	Day	5% 4 2 6% 4 4 7% 5% 8% 11% 44%	2470
	21st to end	Day	7% 6% 2 6% 6% 6% 6% 6% 7% 9% 39%	2470
July	1st to 10th	Day	6% 6% 2 9% 7% 8% 7% 7% 8% 11% 29%	4120
	11th to 20th	Day	8% 5% 3 8% 7% 6% 7% 6% 9% 12% 31%	4120
	21st to end	Day	13% 9% 4 11% 8% 7% 7% 6% 8% 8% 20%	4466
August	1st to 10th	Day	4 4 1 4 4 4 5% 5% 8% 12% 49%	3856
	11th to 20th	Day	6% 5% 2 6% 4 5% 6% 5% 7% 11% 43%	3729
	21st to end	Day	7% 4 2 5% 5% 5% 5% 4 6% 8% 51%	4180
September	1st to 10th	Day	10% 5% 2 7% 5% 5% 6% 4 7% 8% 40%	2201
	11th to 20th	Day	14% 6% 2 5% 5% 4 6% 4 6% 8% 42%	2090
	21st to end	Day	13% 5% 2 6% 3 4 4 4 5% 6% 48%	2090
October	1st to 10th	Day	10% 5% 2 5% 4 3 4 3 4 5% 55%	2090
	11th to 20th	Day	10% 4 2 5% 3 3 3 3 5% 7% 55%	2090
	21st to end	Day	13% 6% 2 4 3 4 3 3 3 5% 54%	1953
November	1st to 10th	Day	14% 5% 2 5% 3 4 3 3 4 4 53%	1762
	11th to 20th	Day	12% 5% 2 6% 3 3 4 3 5% 7% 49%	1719
	21st to end	Day	16% 6% 2 5% 4 4 4 4 4 6% 45%	1710
December	1st to 10th	Day	21% 9% 2 7% 4 3 4 3 4 6% 37%	1710
	11th to 20th	Day	17% 8% 3 7% 5% 4 4 3 4 4 41%	2153
	21st to end	Day	19% 9% 4 7% 5% 4 4 3 5% 6% 34%	3124
January	1st to 10th	Night	17% 11% 3 6% 3 4 4 3 5% 5% 39%	4109
	11th to 20th	Night	18% 9% 4 6% 3 3 3 3 4 5% 42%	4116
	21st to end	Night	22% 13% 3 5% 3 3 3 2 4 3 38%	4180
February	1st to 10th	Night	18% 8% 2 6% 4 3 3 3 4 6% 42%	2280
	11th to 20th	Night	21% 8% 3 6% 4 3 3 3 4 4 42%	2218
	21st to end	Night	21% 7% 3 6% 4 4 5% 3 5% 6% 37%	1884
March	1st to 10th	Night	24% 10% 3 7% 4 4 4 3 4 5% 33%	3733
	11th to 20th	Night	13% 6% 1 5% 3 4 4 4 6% 8% 47%	3557
	21st to end	Night	16% 9% 3 7% 5% 4 4 3 4 4 41%	3755
April	1st to 10th	Night	12% 5% 2 5% 4 3 4 4 6% 7% 48%	1900
	11th to 20th	Night	14% 7% 3 5% 2 3 4 3 4 6% 49%	1875
	21st to end	Night	10% 5% 2 5% 4 3 4 4 5% 7% 51%	1870
May	1st to 10th	Night	11% 6% 2 7% 5% 5% 5% 4 6% 8% 42%	2813
	11th to 20th	Night	17% 6% 3 6% 4 4 4 4 6% 7% 40%	2812
	21st to end	Night	7% 4 2 6% 4 5% 4 5% 8% 10% 45%	3079
June	1st to 10th	Night	7% 6% 2 7% 6% 6% 6% 4 7% 10% 39%	1710
	11th to 20th	Night	4 4 1 4 4 4 4 5% 7% 12% 51%	1710
	21st to end	Night	5% 4 2 5% 5% 4 6% 5% 7% 11% 46%	1710
July	1st to 10th	Night	7% 5% 3 8% 6% 7% 6% 5% 8% 12% 34%	2840
	11th to 20th	Night	8% 4 2 5% 4 5% 5% 5% 8% 13% 41%	2840
	21st to end	Night	10% 10% 4 11% 7% 7% 7% 5% 7% 8% 24%	3087
August	1st to 10th	Night	2 3 1 5% 3 4 4 4 7% 12% 55%	3069
	11th to 20th	Night	6% 5% 2 5% 4 4 4 3 6% 9% 52%	3100
	21st to end	Night	6% 4 1 5% 3 4 3 3 5% 8% 57%	3476
September	1st to 10th	Night	8% 5% 2 6% 5% 5% 5% 5% 6% 7% 46%	1957
	11th to 20th	Night	12% 6% 2 6% 5% 4 5% 3 5% 8% 43%	2090
	21st to end	Night	9% 5% 3 6% 3 4 3 3 5% 8% 52%	2090
October	1st to 10th	Night	9% 3 2 4 3 3 3 3 4 6% 60%	2090
	11th to 20th	Night	11% 5% 2 5% 3 3 3 3 4 6% 55%	2090
	21st to end	Night	13% 5% 2 5% 4 3 3 3 3 4 54%	2640
November	1st to 10th	Night	12% 5% 2 6% 3 3 3 3 5% 5% 53%	2536
	11th to 20th	Night	12% 7% 2 4 3 3 3 3 4 6% 54%	2484
	21st to end	Night	15% 8% 2 5% 4 3 3 3 5% 6% 46%	2470
December	1st to 10th	Night	19% 9% 3 6% 4 3 4 3 5% 6% 37%	2470
	11th to 20th	Night	16% 8% 3 5% 3 3 3 3 4 5% 47%	3042
	21st to end	Night	18% 8% 4 7% 4 5% 5% 4 6% 8% 31%	4532

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	51% 1 5% 17% 23% 3	2837
	11th to 20th	Day	45% 1 5% 23% 24% 2	2840
	21st to end	Day	49% 1 6% 19% 21% 4	3476
February	1st to 10th	Day	48% 1 6% 19% 21% 4	1900
	11th to 20th	Day	51% 2 4 19% 18% 6%	1858
	21st to end	Day	52% 2 5% 14% 21% 6%	1570
March	1st to 10th	Day	56% 2 7% 12% 14% 9%	3120
	11th to 20th	Day	43% 2 6% 20% 23% 6%	3402
	21st to end	Day	47% 2 10% 19% 18% 4	3903
April	1st to 10th	Day	38% 3 12% 23% 19% 6%	2280
	11th to 20th	Day	40% 3 6% 20% 24% 7%	2254
	21st to end	Day	35% 3 9% 28% 21% 3	2308
May	1st to 10th	Day	41% 2 12% 27% 16% 2	4120
	11th to 20th	Day	46% 2 11% 28% 12%	4085
	21st to end	Day	39% 3 11% 28% 18% 1	4489
June	1st to 10th	Day	44% 5% 15% 21% 14% 1	2470
	11th to 20th	Day	32% 5% 17% 28% 16% 2	2470
	21st to end	Day	39% 6% 16% 24% 13% 3	2470
July	1st to 10th	Day	45% 5% 23% 20% 6% 1	4055
	11th to 20th	Day	43% 6% 21% 22% 7% 1	4051
	21st to end	Day	59% 6% 14% 15% 6%	4324
August	1st to 10th	Day	26% 4 14% 39% 15% 1	3843
	11th to 20th	Day	34% 4 17% 27% 16% 3	3765
	21st to end	Day	31% 3 15% 23% 23% 4	4179
September	1st to 10th	Day	39% 4 16% 18% 16% 6%	2201
	11th to 20th	Day	41% 4 11% 21% 19% 3	2090
	21st to end	Day	37% 3 10% 20% 22% 8%	2090
October	1st to 10th	Day	24% 3 4 14% 39% 16%	3480
	11th to 20th	Day	21% 1 4 18% 30% 25%	3458
	21st to end	Day	26% 2 6% 23% 32% 11%	3190
November	1st to 10th	Day	36% 2 5% 18% 28% 10%	1762
	11th to 20th	Day	35% 2 6% 21% 26% 9%	1719
	21st to end	Day	41% 3 5% 19% 26% 6%	1710
December	1st to 10th	Day	49% 3 7% 16% 20% 5%	1710
	11th to 20th	Day	48% 2 5% 19% 21% 6%	2150
	21st to end	Day	53% 1 7% 18% 18% 2	3124
January	1st to 10th	Night	49% 1 4 19% 25% 3	4109
	11th to 20th	Night	45% 2 4 22% 19% 7%	4116
	21st to end	Night	52% 1 3 16% 22% 5%	4180
February	1st to 10th	Night	45% 2 5% 20% 22% 6%	2280
	11th to 20th	Night	48% 2 5% 18% 19% 8%	2219
	21st to end	Night	49% 3 5% 16% 19% 8%	1884
March	1st to 10th	Night	56% 2 6% 14% 16% 7%	3733
	11th to 20th	Night	36% 2 9% 20% 23% 10%	3557
	21st to end	Night	48% 1 5% 22% 19% 4	3755
April	1st to 10th	Night	35% 4 11% 23% 21% 6%	1900
	11th to 20th	Night	38% 2 5% 21% 22% 11%	1875
	21st to end	Night	34% 3 9% 28% 21% 4	1870
May	1st to 10th	Night	41% 3 12% 23% 19% 2	2840
	11th to 20th	Night	44% 3 13% 27% 13% 1	2813
	21st to end	Night	33% 3 14% 28% 19% 2	3087
June	1st to 10th	Night	40% 4 15% 23% 17% 2	1710
	11th to 20th	Night	25% 4 20% 30% 19% 3	1710
	21st to end	Night	30% 6% 20% 22% 17% 5%	1710
July	1st to 10th	Night	40% 7% 24% 20% 7% 2	2795
	11th to 20th	Night	33% 5% 26% 26% 8% 2	2786
	21st to end	Night	57% 7% 14% 16% 5%	2988
August	1st to 10th	Night	22% 4 15% 41% 16% 2	3058
	11th to 20th	Night	30% 4 18% 29% 17% 2	3130
	21st to end	Night	28% 4 15% 20% 29% 5%	3476
September	1st to 10th	Night	36% 5% 18% 20% 16% 6%	1957
	11th to 20th	Night	40% 5% 11% 19% 21% 4	2090
	21st to end	Night	33% 3 9% 23% 24% 8%	2090
October	1st to 10th	Night	21% 3 5% 18% 35% 18%	3480
	11th to 20th	Night	20% 1 3 18% 31% 26%	3461
	21st to end	Night	25% 2 3 26% 30% 14%	4353
November	1st to 10th	Night	34% 3 8% 20% 23% 12%	2536
	11th to 20th	Night	34% 2 4 20% 28% 11%	2484
	21st to end	Night	40% 2 5% 22% 24% 7%	2470
December	1st to 10th	Night	49% 2 7% 19% 20% 3	2470
	11th to 20th	Night	41% 1 6% 18% 28% 5%	3044
	21st to end	Night	52% 1 5% 20% 19% 2	4532

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% 25% 34% 13% 2	270
	11th to 20th	Day	32% 20% 30% 13% 4 1	270
	21st to end	Day	25% 23% 37% 12% 2 1	297
February	1st to 10th	Day	26% 22% 34% 15% 2 1	270
	11th to 20th	Day	40% 18% 29% 11% 1	270
	21st to end	Day	34% 24% 33% 9%	225
March	1st to 10th	Day	30% 18% 33% 14% 3 1	270
	11th to 20th	Day	24% 17% 33% 19% 7% 1	408
	21st to end	Day	23% 18% 32% 22% 5% 1	506
April	1st to 10th	Day	20% 15% 31% 21% 11% 2	460
	11th to 20th	Day	20% 15% 29% 22% 12% 1	452
	21st to end	Day	15% 12% 31% 27% 13% 2	460
May	1st to 10th	Day	16% 10% 27% 27% 14% 6%	463
	11th to 20th	Day	15% 5% 24% 31% 18% 9%	487
	21st to end	Day	14% 5% 17% 30% 22% 13%	529
June	1st to 10th	Day	14% 2 18% 32% 23% 11%	490
	11th to 20th	Day	7% 3 17% 25% 28% 20%	490
	21st to end	Day	12% 2 14% 29% 27% 16%	490
July	1st to 10th	Day	11% 1 7% 27% 31% 24%	485
	11th to 20th	Day	9% 2 7% 24% 31% 27%	484
	21st to end	Day	11% 2 9% 22% 34% 22%	532
August	1st to 10th	Day	11% 1 11% 23% 32% 21%	486
	11th to 20th	Day	11% 2 9% 33% 31% 14%	479
	21st to end	Day	17% 1 8% 25% 33% 16%	539
September	1st to 10th	Day	10% 3 13% 29% 32% 12%	490
	11th to 20th	Day	17% 2 13% 26% 30% 12%	490
	21st to end	Day	16% 4 15% 29% 28% 8%	490
October	1st to 10th	Day	14% 3 22% 32% 19% 9%	490
	11th to 20th	Day	13% 9% 26% 32% 17% 2	490
	21st to end	Day	18% 10% 23% 33% 15% 1	392
November	1st to 10th	Day	22% 8% 32% 26% 10% 3	300
	11th to 20th	Day	17% 19% 37% 23% 5%	273
	21st to end	Day	18% 16% 39% 19% 8% 1	270
December	1st to 10th	Day	31% 17% 30% 16% 5%	270
	11th to 20th	Day	26% 18% 33% 17% 6%	270
	21st to end	Day	32% 15% 33% 16% 3 1	297
January	1st to 10th	Night	23% 17% 33% 23% 4	760
	11th to 20th	Night	23% 16% 30% 24% 6%	760
	21st to end	Night	21% 14% 37% 25% 3	836
February	1st to 10th	Night	23% 12% 32% 28% 5%	760
	11th to 20th	Night	26% 14% 32% 25% 3	743
	21st to end	Night	27% 15% 34% 22% 3	628
March	1st to 10th	Night	20% 15% 31% 29% 5%	760
	11th to 20th	Night	21% 12% 32% 25% 9% 1	760
	21st to end	Night	20% 14% 30% 27% 9% 1	799
April	1st to 10th	Night	15% 11% 32% 29% 13%	570
	11th to 20th	Night	18% 9% 32% 27% 13% 1	563
	21st to end	Night	13% 6% 28% 36% 15% 1	570
May	1st to 10th	Night	12% 5% 24% 33% 23% 3	570
	11th to 20th	Night	14% 2 20% 35% 24% 6%	561
	21st to end	Night	9% 2 12% 37% 34% 6%	617
June	1st to 10th	Night	11% 1 11% 36% 34% 7%	570
	11th to 20th	Night	4 1 11% 31% 41% 12%	570
	21st to end	Night	8% 1 8% 31% 42% 11%	570
July	1st to 10th	Night	8% 1 5% 24% 46% 16%	555
	11th to 20th	Night	8% 1 5% 23% 43% 20%	552
	21st to end	Night	8% 2 7% 25% 46% 13%	624
August	1st to 10th	Night	5% 1 4 30% 46% 14%	567
	11th to 20th	Night	11% 1 9% 27% 43% 10%	564
	21st to end	Night	13% 1 5% 30% 41% 10%	627
September	1st to 10th	Night	11% 1 8% 30% 38% 10%	627
	11th to 20th	Night	15% 2 10% 30% 37% 6%	760
	21st to end	Night	11% 2 15% 31% 37% 4	760
October	1st to 10th	Night	11% 4 19% 34% 26% 6%	760
	11th to 20th	Night	14% 7% 24% 33% 19% 3	760
	21st to end	Night	16% 8% 19% 36% 19% 3	836
November	1st to 10th	Night	15% 7% 24% 33% 19% 3	780
	11th to 20th	Night	16% 8% 30% 32% 11% 1	765
	21st to end	Night	19% 9% 29% 30% 11% 1	760
December	1st to 10th	Night	25% 12% 28% 26% 9%	760
	11th to 20th	Night	22% 11% 31% 27% 9%	760
	21st to end	Night	26% 12% 27% 28% 6%	836

Page generated at 2024-11-08 21:45:34. Version ac07

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