Shelter Cove
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Shelter Cove clear sky chart from 2005-11-06 to 2026-01-02.

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% 5% 1 4 3 3 4 3 6% 7% 53%	135994
	Night	15% 6% 2 5% 3 3 3 3 5% 6% 51%	132826
Transparency	Day	19% 38% 6% 15% 13% 10%	130820
	Night	23% 38% 6% 12% 12% 9%	128995
Seeing	Day	14% 5% 16% 29% 26% 10%	16743
	Night	16% 3 12% 29% 27% 12%	25924

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	27% 8% 3 5% 4 4 5% 4 6% 6% 28%	3941
	11th to 20th	Day	26% 6% 2 4 2 2 2 2 3 4 47%	4100
	21st to end	Day	27% 6% 2 6% 3 3 2 3 3 6% 41%	4510
February	1st to 10th	Day	25% 7% 2 5% 3 4 4 3 4 7% 38%	1800
	11th to 20th	Day	20% 8% 3 7% 4 4 4 4 6% 7% 34%	1755
	21st to end	Day	22% 7% 2 5% 5% 4 4 4 5% 7% 36%	1640
March	1st to 10th	Day	24% 13% 2 5% 4 3 4 3 5% 7% 30%	4952
	11th to 20th	Day	24% 6% 2 6% 4 4 4 4 5% 7% 36%	5000
	21st to end	Day	27% 13% 3 7% 4 4 4 3 6% 5% 24%	5486
April	1st to 10th	Day	18% 7% 3 5% 5% 5% 5% 5% 7% 8% 33%	2352
	11th to 20th	Day	14% 6% 2 5% 4 4 4 4 6% 8% 42%	2369
	21st to end	Day	9% 5% 2 5% 3 3 3 3 8% 10% 48%	2526
May	1st to 10th	Day	6% 3 1 3 2 3 4 4 5% 6% 62%	5880
	11th to 20th	Day	4 2 1 3 2 2 3 3 7% 8% 64%	5874
	21st to end	Day	4 2 1 3 1 2 3 3 5% 7% 70%	6902
June	1st to 10th	Day	10% 4 2 3 3 3 4 4 7% 7% 52%	2800
	11th to 20th	Day	3 2 1 3 2 2 3 3 5% 7% 70%	2800
	21st to end	Day	4 3 1 3 2 2 2 3 5% 5% 71%	2800
July	1st to 10th	Day	1 1 1 2 1 2 2 2 5% 5% 79%	6284
	11th to 20th	Day	1 1 2 4 2 2 5% 4 10% 6% 62%	5880
	21st to end	Day	1 1 2 2 2 3 3 7% 7% 71%	6402
August	1st to 10th	Day	1 1 1 2 2 2 2 2 6% 6% 76%	5777
	11th to 20th	Day	3 2 1 3 2 2 4 4 8% 7% 64%	5796
	21st to end	Day	3 2 1 3 3 3 5% 4 11% 9% 56%	6076
September	1st to 10th	Day	2 3 1 3 2 2 3 3 7% 7% 67%	2400
	11th to 20th	Day	6% 4 1 3 4 3 4 3 5% 8% 59%	2280
	21st to end	Day	5% 2 1 2 2 2 3 2 4 7% 69%	2170
October	1st to 10th	Day	5% 3 1 2 1 2 2 2 3 5% 73%	3280
	11th to 20th	Day	11% 4 1 5% 4 4 4 4 6% 7% 49%	3261
	21st to end	Day	14% 8% 3 6% 3 3 3 4 5% 7% 45%	3558
November	1st to 10th	Day	18% 6% 3 4 3 4 4 3 6% 9% 40%	2059
	11th to 20th	Day	22% 7% 2 6% 4 4 3 4 6% 8% 35%	1704
	21st to end	Day	15% 5% 1 5% 4 4 4 3 5% 7% 46%	1680
December	1st to 10th	Day	12% 6% 2 5% 3 3 4 3 6% 7% 50%	2700
	11th to 20th	Day	35% 8% 2 6% 4 5% 5% 4 6% 7% 19%	3108
	21st to end	Day	33% 9% 3 7% 4 4 4 3 4 6% 22%	4092
January	1st to 10th	Night	28% 9% 3 6% 4 4 4 3 5% 7% 27%	6035
	11th to 20th	Night	21% 7% 2 6% 3 3 3 2 4 5% 43%	5880
	21st to end	Night	28% 7% 2 5% 3 3 3 2 3 4 40%	6468
February	1st to 10th	Night	23% 8% 2 5% 3 3 4 3 4 7% 38%	2600
	11th to 20th	Night	20% 8% 3 7% 5% 4 4 3 5% 5% 35%	2532
	21st to end	Night	19% 8% 2 4 3 3 4 3 6% 8% 41%	1985
March	1st to 10th	Night	22% 15% 3 7% 4 3 3 3 5% 7% 28%	4942
	11th to 20th	Night	25% 7% 2 6% 3 3 3 3 4 6% 36%	5000
	21st to end	Night	26% 14% 3 6% 4 3 4 3 4 6% 26%	5489
April	1st to 10th	Night	19% 8% 2 5% 4 3 4 4 5% 6% 40%	2046
	11th to 20th	Night	13% 7% 2 5% 4 4 3 3 6% 8% 46%	1979
	21st to end	Night	10% 4 1 4 4 2 4 4 6% 9% 52%	1870
May	1st to 10th	Night	6% 2 1 2 2 2 3 3 5% 6% 69%	4100
	11th to 20th	Night	5% 3 1 3 2 2 2 2 4 5% 70%	4032
	21st to end	Night	3 2 1 2 1 2 2 2 4 6% 74%	3972
June	1st to 10th	Night	7% 6% 2 5% 3 3 4 3 5% 9% 53%	1600
	11th to 20th	Night	3 2 1 1 2 1 2 2 5% 5% 75%	1600
	21st to end	Night	4 2 1 3 2 2 1 2 4 4 76%	1600
July	1st to 10th	Night	1 1 2 2 1 1 1 3 3 84%	3673
	11th to 20th	Night	1 1 3 8% 3 2 3 3 5% 4 67%	4100
	21st to end	Night	1 1 4 2 2 2 2 7% 4 75%	4472
August	1st to 10th	Night	1 1 1 2 1 2 2 2 6% 4 79%	4035
	11th to 20th	Night	2 2 1 3 2 2 3 2 5% 5% 74%	4052
	21st to end	Night	3 2 1 3 2 2 3 3 7% 5% 70%	4918
September	1st to 10th	Night	2 2 1 2 2 1 1 2 5% 5% 77%	2000
	11th to 20th	Night	5% 4 1 4 2 2 2 2 4 7% 65%	2115
	21st to end	Night	6% 4 1 3 2 2 2 2 3 5% 69%	2230
October	1st to 10th	Night	5% 2 1 3 2 2 2 1 2 4 76%	3920
	11th to 20th	Night	9% 7% 3 5% 4 3 3 2 5% 6% 53%	3897
	21st to end	Night	14% 5% 2 6% 3 4 4 3 5% 7% 46%	4253
November	1st to 10th	Night	17% 6% 2 5% 3 4 3 4 5% 9% 41%	2460
	11th to 20th	Night	22% 6% 2 7% 4 4 4 3 6% 8% 34%	2909
	21st to end	Night	18% 6% 2 3 3 3 4 3 5% 8% 45%	2940
December	1st to 10th	Night	14% 4 1 4 3 3 4 3 6% 9% 48%	4700
	11th to 20th	Night	34% 8% 2 6% 4 4 4 3 5% 6% 23%	5316
	21st to end	Night	39% 7% 2 5% 3 3 3 2 3 5% 27%	7106

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	40% 32% 7% 9% 7% 4	3941
	11th to 20th	Day	33% 28% 4 10% 14% 10%	4100
	21st to end	Day	34% 29% 4 6% 11% 16%	4510
February	1st to 10th	Day	24% 63% 3 6% 4 1	1800
	11th to 20th	Day	25% 61% 4 5% 5% 1	1764
	21st to end	Day	18% 63% 7% 6% 4 3	1640
March	1st to 10th	Day	41% 32% 3 18% 6% 1	4952
	11th to 20th	Day	34% 31% 11% 9% 10% 4	5000
	21st to end	Day	44% 34% 8% 11% 2	5486
April	1st to 10th	Day	18% 63% 7% 8% 4	2352
	11th to 20th	Day	13% 64% 7% 11% 5% 1	2372
	21st to end	Day	13% 63% 6% 10% 6% 1	2526
May	1st to 10th	Day	16% 33% 7% 15% 22% 8%	5880
	11th to 20th	Day	12% 28% 8% 24% 24% 4	5877
	21st to end	Day	6% 28% 10% 45% 11%	6904
June	1st to 10th	Day	6% 62% 6% 13% 9% 4	2800
	11th to 20th	Day	5% 62% 5% 10% 15% 4	2800
	21st to end	Day	5% 59% 3 10% 16% 7%	2800
July	1st to 10th	Day	4 25% 3 14% 19% 36%	6216
	11th to 20th	Day	6% 26% 2 7% 21% 37%	5811
	21st to end	Day	4 26% 8% 25% 19% 18%	6217
August	1st to 10th	Day	6% 36% 3 11% 23% 21%	4206
	11th to 20th	Day	9% 35% 6% 25% 16% 9%	4195
	21st to end	Day	12% 36% 6% 19% 15% 13%	4379
September	1st to 10th	Day	6% 58% 5% 10% 15% 7%	2400
	11th to 20th	Day	9% 57% 6% 13% 12% 2	2280
	21st to end	Day	9% 57% 4 11% 13% 6%	2170
October	1st to 10th	Day	9% 35% 3 11% 10% 33%	3280
	11th to 20th	Day	22% 37% 7% 16% 15% 3	3261
	21st to end	Day	29% 37% 4 13% 12% 5%	3558
November	1st to 10th	Day	16% 54% 8% 11% 9% 2	2059
	11th to 20th	Day	23% 57% 5% 8% 5% 2	1704
	21st to end	Day	19% 55% 4 8% 6% 8%	1680
December	1st to 10th	Day	23% 35% 4 12% 17% 9%	2700
	11th to 20th	Day	49% 31% 7% 5% 5% 3	3108
	21st to end	Day	48% 28% 6% 11% 5% 1	4092
January	1st to 10th	Night	43% 31% 8% 8% 8% 2	6035
	11th to 20th	Night	34% 29% 3 12% 15% 6%	5880
	21st to end	Night	38% 29% 2 5% 7% 19%	6468
February	1st to 10th	Night	24% 62% 3 5% 5% 1	2600
	11th to 20th	Night	24% 62% 3 5% 5% 1	2534
	21st to end	Night	16% 63% 6% 8% 5% 3	1985
March	1st to 10th	Night	42% 32% 5% 14% 5% 2	4942
	11th to 20th	Night	34% 31% 10% 13% 5% 6%	5000
	21st to end	Night	45% 33% 8% 11% 3	5489
April	1st to 10th	Night	17% 63% 6% 9% 4	2046
	11th to 20th	Night	12% 64% 6% 12% 6% 1	1979
	21st to end	Night	12% 64% 6% 11% 6% 1	1870
May	1st to 10th	Night	11% 31% 8% 14% 26% 9%	4097
	11th to 20th	Night	12% 27% 7% 24% 24% 5%	4033
	21st to end	Night	6% 27% 10% 41% 15%	3972
June	1st to 10th	Night	8% 61% 5% 13% 10% 3	1600
	11th to 20th	Night	3 61% 5% 9% 16% 6%	1600
	21st to end	Night	4 59% 2 9% 17% 8%	1600
July	1st to 10th	Night	3 25% 2 15% 18% 37%	3633
	11th to 20th	Night	7% 28% 4 4 22% 35%	4046
	21st to end	Night	4 25% 6% 17% 27% 21%	4345
August	1st to 10th	Night	7% 35% 2 10% 20% 26%	2929
	11th to 20th	Night	7% 35% 4 19% 24% 11%	2929
	21st to end	Night	9% 35% 4 19% 17% 15%	3537
September	1st to 10th	Night	6% 57% 4 11% 13% 8%	2000
	11th to 20th	Night	8% 57% 4 14% 14% 3	2115
	21st to end	Night	10% 57% 5% 11% 11% 6%	2230
October	1st to 10th	Night	8% 34% 3 7% 13% 35%	3920
	11th to 20th	Night	24% 37% 7% 15% 15% 2	3897
	21st to end	Night	30% 36% 4 14% 10% 6%	4253
November	1st to 10th	Night	17% 54% 8% 10% 8% 2	2460
	11th to 20th	Night	25% 56% 5% 8% 5% 1	2909
	21st to end	Night	20% 55% 5% 6% 7% 7%	2940
December	1st to 10th	Night	21% 35% 6% 14% 15% 9%	4700
	11th to 20th	Night	48% 32% 4 10% 5% 2	5316
	21st to end	Night	45% 29% 10% 10% 5% 1	7106

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	35% 9% 20% 22% 13% 2	327
	11th to 20th	Day	30% 4 14% 27% 17% 8%	400
	21st to end	Day	24% 3 15% 28% 23% 7%	440
February	1st to 10th	Day	25% 6% 17% 27% 19% 6%	400
	11th to 20th	Day	24% 9% 24% 20% 18% 4	395
	21st to end	Day	20% 10% 21% 29% 16% 4	379
March	1st to 10th	Day	32% 10% 19% 24% 11% 4	500
	11th to 20th	Day	27% 6% 18% 29% 17% 4	500
	21st to end	Day	20% 9% 23% 28% 16% 4	550
April	1st to 10th	Day	22% 7% 23% 28% 15% 5%	500
	11th to 20th	Day	15% 7% 23% 29% 20% 6%	492
	21st to end	Day	11% 5% 29% 30% 19% 7%	500
May	1st to 10th	Day	8% 7% 22% 35% 22% 6%	503
	11th to 20th	Day	11% 5% 23% 29% 23% 9%	528
	21st to end	Day	9% 8% 22% 32% 22% 7%	573
June	1st to 10th	Day	10% 5% 18% 35% 25% 6%	530
	11th to 20th	Day	4 8% 23% 38% 22% 5%	530
	21st to end	Day	3 2 13% 39% 33% 10%	530
July	1st to 10th	Day	5% 2 15% 38% 28% 13%	526
	11th to 20th	Day	3 2 12% 37% 35% 11%	524
	21st to end	Day	2 2 7% 26% 40% 23%	575
August	1st to 10th	Day	4 2 6% 35% 39% 15%	527
	11th to 20th	Day	4 1 10% 30% 45% 11%	517
	21st to end	Day	5% 3 8% 26% 38% 20%	583
September	1st to 10th	Day	4 2 12% 28% 39% 15%	530
	11th to 20th	Day	7% 2 12% 25% 39% 16%	530
	21st to end	Day	6% 3 12% 28% 35% 16%	530
October	1st to 10th	Day	9% 3 16% 22% 31% 19%	530
	11th to 20th	Day	12% 4 13% 25% 29% 18%	530
	21st to end	Day	16% 4 13% 26% 29% 12%	583
November	1st to 10th	Day	16% 5% 18% 26% 23% 11%	535
	11th to 20th	Day	18% 7% 11% 28% 27% 9%	244
	21st to end	Day	14% 5% 11% 30% 26% 13%	220
December	1st to 10th	Day	22% 5% 13% 28% 19% 14%	220
	11th to 20th	Day	32% 4 15% 24% 17% 8%	220
	21st to end	Day	29% 7% 16% 29% 15% 5%	242
January	1st to 10th	Night	28% 5% 14% 28% 18% 6%	804
	11th to 20th	Night	25% 4 14% 27% 20% 10%	800
	21st to end	Night	24% 4 12% 27% 24% 9%	880
February	1st to 10th	Night	26% 4 14% 32% 20% 5%	800
	11th to 20th	Night	23% 6% 17% 28% 18% 8%	784
	21st to end	Night	22% 7% 18% 32% 20% 3	660
March	1st to 10th	Night	30% 7% 17% 26% 15% 6%	800
	11th to 20th	Night	25% 5% 13% 28% 24% 5%	800
	21st to end	Night	23% 5% 19% 29% 18% 5%	880
April	1st to 10th	Night	21% 5% 19% 29% 19% 7%	800
	11th to 20th	Night	15% 4 20% 30% 21% 10%	791
	21st to end	Night	11% 3 17% 39% 21% 9%	670
May	1st to 10th	Night	8% 3 19% 35% 27% 8%	600
	11th to 20th	Night	8% 3 13% 36% 26% 15%	576
	21st to end	Night	9% 5% 18% 36% 23% 9%	433
June	1st to 10th	Night	9% 4 16% 35% 31% 6%	400
	11th to 20th	Night	3 2 18% 49% 24% 5%	400
	21st to end	Night	4 1 6% 37% 44% 8%	400
July	1st to 10th	Night	2 2 8% 33% 39% 17%	397
	11th to 20th	Night	2 1 3 38% 37% 20%	582
	21st to end	Night	2 4 23% 42% 29%	657
August	1st to 10th	Night	3 2 1 28% 46% 21%	597
	11th to 20th	Night	3 1 3 26% 45% 22%	594
	21st to end	Night	4 1 5% 20% 46% 23%	835
September	1st to 10th	Night	3 1 6% 22% 48% 21%	800
	11th to 20th	Night	8% 2 8% 26% 35% 21%	800
	21st to end	Night	8% 1 9% 24% 35% 24%	800
October	1st to 10th	Night	8% 2 14% 24% 29% 22%	800
	11th to 20th	Night	12% 3 8% 26% 33% 19%	800
	21st to end	Night	15% 3 10% 28% 29% 15%	880
November	1st to 10th	Night	16% 4 13% 29% 26% 12%	820
	11th to 20th	Night	23% 4 11% 29% 26% 7%	840
	21st to end	Night	19% 3 13% 31% 26% 8%	840
December	1st to 10th	Night	22% 4 13% 32% 20% 9%	840
	11th to 20th	Night	31% 4 14% 27% 19% 6%	840
	21st to end	Night	31% 7% 18% 26% 14% 4	924

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