Saint Peters Bay
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Saint Peters Bay clear sky chart from 2005-11-06 to 2026-03-18.

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	18% 13% 5% 10% 5% 4 4 3 5% 6% 27%	132287
	Night	18% 14% 5% 11% 5% 5% 4 3 4 5% 24%	129413
Transparency	Day	38% 38% 8% 11% 4	135806
	Night	42% 37% 7% 10% 4	133986
Seeing	Day	24% 13% 28% 25% 9% 1	19381
	Night	27% 13% 27% 24% 8% 1	26635

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	14% 24% 8% 21% 6% 4 4 2 4 4 10%	4690
	11th to 20th	Day	17% 17% 11% 17% 7% 5% 3 3 3 4 13%	4681
	21st to end	Day	10% 11% 5% 16% 8% 8% 9% 3 4 4 21%	5531
February	1st to 10th	Day	17% 16% 5% 13% 7% 7% 5% 3 4 5% 19%	1890
	11th to 20th	Day	16% 17% 5% 12% 6% 6% 5% 3 4 4 22%	1843
	21st to end	Day	10% 15% 4 11% 7% 6% 5% 4 4 6% 29%	1630
March	1st to 10th	Day	18% 15% 5% 12% 8% 5% 4 3 4 4 23%	4798
	11th to 20th	Day	13% 18% 6% 12% 6% 5% 4 3 5% 6% 22%	5057
	21st to end	Day	23% 19% 7% 15% 4 3 3 3 4 4 16%	5603
April	1st to 10th	Day	20% 14% 5% 9% 5% 4 4 3 4 5% 28%	2400
	11th to 20th	Day	20% 13% 3 6% 5% 3 3 2 5% 7% 32%	2400
	21st to end	Day	20% 14% 5% 7% 3 4 3 4 4 6% 31%	2600
May	1st to 10th	Day	26% 16% 3 6% 4 3 3 2 4 5% 28%	6336
	11th to 20th	Day	19% 11% 3 7% 4 4 4 4 5% 6% 34%	6318
	21st to end	Day	18% 12% 3 7% 4 4 4 3 5% 7% 33%	6948
June	1st to 10th	Day	24% 12% 3 7% 5% 5% 5% 4 6% 6% 24%	2800
	11th to 20th	Day	20% 8% 3 6% 4 5% 5% 4 5% 7% 35%	2927
	21st to end	Day	23% 11% 3 7% 5% 4 3 3 6% 7% 29%	3000
July	1st to 10th	Day	18% 9% 3 8% 5% 5% 5% 5% 6% 8% 29%	6664
	11th to 20th	Day	15% 6% 3 6% 4 3 4 4 6% 8% 41%	6360
	21st to end	Day	13% 8% 3 6% 5% 4 5% 4 7% 9% 37%	6927
August	1st to 10th	Day	18% 9% 3 8% 5% 5% 5% 4 6% 7% 30%	4374
	11th to 20th	Day	16% 7% 2 6% 4 4 5% 4 7% 8% 37%	4175
	21st to end	Day	13% 7% 2 7% 5% 5% 5% 4 6% 7% 40%	4426
September	1st to 10th	Day	18% 6% 3 6% 3 4 4 3 6% 8% 40%	2400
	11th to 20th	Day	19% 10% 3 6% 5% 3 4 4 5% 6% 36%	2400
	21st to end	Day	19% 9% 3 6% 4 4 4 3 4 7% 37%	2095
October	1st to 10th	Day	19% 10% 3 8% 5% 4 4 3 5% 8% 31%	2000
	11th to 20th	Day	20% 14% 3 8% 6% 5% 4 4 6% 6% 22%	2000
	21st to end	Day	21% 18% 4 9% 5% 5% 4 3 4 6% 21%	2103
November	1st to 10th	Day	21% 21% 5% 9% 6% 4 3 3 4 4 20%	1715
	11th to 20th	Day	23% 25% 7% 8% 5% 4 4 3 4 5% 14%	1680
	21st to end	Day	19% 21% 8% 13% 6% 5% 4 3 5% 6% 11%	1680
December	1st to 10th	Day	16% 19% 9% 17% 6% 4 3 2 4 5% 15%	2690
	11th to 20th	Day	22% 17% 7% 18% 5% 4 3 2 3 3 14%	3076
	21st to end	Day	17% 17% 10% 21% 6% 4 4 3 3 3 13%	4070
January	1st to 10th	Night	16% 20% 8% 20% 5% 4 4 3 3 4 13%	8234
	11th to 20th	Night	19% 18% 8% 18% 6% 4 3 3 3 4 14%	8234
	21st to end	Night	8% 12% 6% 17% 8% 9% 7% 3 5% 5% 19%	8657
February	1st to 10th	Night	18% 15% 4 13% 7% 6% 4 3 4 5% 23%	2730
	11th to 20th	Night	17% 16% 5% 13% 7% 5% 4 3 4 5% 21%	2663
	21st to end	Night	13% 14% 6% 9% 6% 5% 5% 4 5% 5% 28%	2176
March	1st to 10th	Night	20% 15% 5% 11% 8% 5% 4 3 3 4 21%	5257
	11th to 20th	Night	18% 17% 6% 11% 6% 4 4 3 4 5% 23%	5057
	21st to end	Night	25% 17% 5% 11% 5% 4 4 3 3 3 19%	5329
April	1st to 10th	Night	22% 12% 5% 10% 5% 4 4 3 5% 5% 26%	2000
	11th to 20th	Night	22% 13% 3 7% 4 4 3 2 5% 5% 32%	1946
	21st to end	Night	24% 14% 4 6% 4 4 3 3 4 5% 30%	1800
May	1st to 10th	Night	28% 17% 3 8% 4 3 4 3 4 5% 21%	3622
	11th to 20th	Night	16% 10% 4 6% 5% 5% 5% 4 5% 7% 32%	3596
	21st to end	Night	15% 11% 3 6% 5% 5% 5% 4 6% 7% 33%	3948
June	1st to 10th	Night	27% 9% 4 7% 6% 3 4 4 5% 6% 27%	1600
	11th to 20th	Night	18% 8% 3 6% 3 3 5% 3 6% 7% 39%	1486
	21st to end	Night	23% 10% 3 7% 6% 5% 4 4 5% 6% 27%	1400
July	1st to 10th	Night	15% 10% 4 9% 6% 7% 6% 4 7% 8% 25%	3252
	11th to 20th	Night	12% 8% 3 7% 5% 4 6% 4 6% 8% 37%	3620
	21st to end	Night	16% 7% 3 6% 5% 4 4 4 6% 8% 38%	3948
August	1st to 10th	Night	18% 9% 3 8% 4 5% 5% 4 6% 8% 30%	2777
	11th to 20th	Night	14% 7% 3 7% 5% 5% 5% 4 5% 7% 39%	2872
	21st to end	Night	12% 7% 3 6% 5% 5% 4 4 6% 7% 43%	3472
September	1st to 10th	Night	16% 7% 2 7% 5% 4 3 3 4 7% 42%	2000
	11th to 20th	Night	19% 7% 2 6% 4 4 3 4 4 6% 41%	2000
	21st to end	Night	19% 7% 2 7% 5% 4 4 2 6% 7% 37%	2301
October	1st to 10th	Night	21% 8% 3 7% 4 4 4 3 5% 6% 36%	2400
	11th to 20th	Night	21% 12% 4 7% 5% 4 4 4 4 7% 30%	2400
	21st to end	Night	25% 15% 3 8% 5% 4 4 3 4 5% 23%	2735
November	1st to 10th	Night	19% 18% 4 10% 7% 4 4 3 4 5% 22%	2798
	11th to 20th	Night	23% 20% 6% 9% 5% 5% 4 3 4 5% 16%	2940
	21st to end	Night	25% 20% 6% 10% 5% 4 4 3 4 5% 14%	2940
December	1st to 10th	Night	16% 16% 7% 14% 6% 6% 5% 4 4 5% 17%	4720
	11th to 20th	Night	23% 16% 7% 17% 6% 4 3 2 3 3 16%	5353
	21st to end	Night	22% 16% 7% 19% 5% 3 3 2 3 3 15%	7150

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	65% 23% 7% 3 2	4691
	11th to 20th	Day	60% 25% 7% 4 3	4710
	21st to end	Day	56% 26% 5% 10% 3	5531
February	1st to 10th	Day	31% 59% 4 5% 2	1890
	11th to 20th	Day	27% 59% 5% 7% 2	1851
	21st to end	Day	21% 59% 4 9% 6% 1	1630
March	1st to 10th	Day	47% 30% 6% 12% 5%	4802
	11th to 20th	Day	46% 32% 12% 7% 3	5057
	21st to end	Day	54% 30% 6% 7% 2	5603
April	1st to 10th	Day	25% 62% 3 5% 4 1	2400
	11th to 20th	Day	21% 63% 4 8% 4	2400
	21st to end	Day	22% 63% 5% 5% 4 1	2600
May	1st to 10th	Day	44% 30% 9% 12% 5%	6348
	11th to 20th	Day	36% 31% 12% 18% 4	6322
	21st to end	Day	36% 32% 9% 17% 6%	6948
June	1st to 10th	Day	21% 63% 4 9% 3	2800
	11th to 20th	Day	18% 62% 6% 10% 4	2927
	21st to end	Day	22% 60% 4 8% 6%	3000
July	1st to 10th	Day	41% 27% 14% 11% 6%	6592
	11th to 20th	Day	31% 27% 14% 24% 4	6284
	21st to end	Day	30% 28% 17% 20% 5%	6730
August	1st to 10th	Day	35% 38% 10% 13% 3	4360
	11th to 20th	Day	27% 38% 10% 17% 7%	4214
	21st to end	Day	28% 37% 9% 18% 7%	4426
September	1st to 10th	Day	16% 58% 7% 14% 5%	2400
	11th to 20th	Day	24% 57% 7% 9% 3	2400
	21st to end	Day	17% 58% 6% 12% 6%	2095
October	1st to 10th	Day	34% 38% 10% 14% 4	3260
	11th to 20th	Day	37% 37% 7% 15% 4	3240
	21st to end	Day	35% 37% 13% 15% 1	3385
November	1st to 10th	Day	35% 54% 5% 4 1	1715
	11th to 20th	Day	39% 55% 3 2 1	1680
	21st to end	Day	37% 55% 5% 3 1	1680
December	1st to 10th	Day	49% 38% 4 9% 1	2690
	11th to 20th	Day	53% 31% 6% 5% 5%	3075
	21st to end	Day	57% 29% 6% 5% 2	4070
January	1st to 10th	Night	63% 24% 6% 6% 1	8234
	11th to 20th	Night	63% 26% 5% 4 2	8280
	21st to end	Night	58% 26% 6% 7% 3	8657
February	1st to 10th	Night	29% 59% 3 6% 4 1	2730
	11th to 20th	Night	27% 58% 5% 7% 3	2666
	21st to end	Night	23% 59% 3 9% 5% 1	2176
March	1st to 10th	Night	49% 29% 6% 10% 6%	5266
	11th to 20th	Night	48% 30% 9% 8% 4 1	5058
	21st to end	Night	55% 31% 4 7% 3	5329
April	1st to 10th	Night	23% 62% 4 7% 4 1	2000
	11th to 20th	Night	22% 62% 4 7% 3 1	1946
	21st to end	Night	25% 62% 3 6% 4 1	1800
May	1st to 10th	Night	50% 30% 5% 8% 7%	3627
	11th to 20th	Night	36% 32% 12% 14% 6%	3597
	21st to end	Night	33% 32% 13% 17% 4	3949
June	1st to 10th	Night	20% 62% 5% 10% 3	1600
	11th to 20th	Night	16% 62% 5% 10% 6%	1486
	21st to end	Night	21% 61% 5% 8% 5% 1	1400
July	1st to 10th	Night	46% 28% 10% 10% 5% 1	3215
	11th to 20th	Night	32% 28% 13% 19% 8%	3572
	21st to end	Night	31% 28% 16% 18% 6%	3831
August	1st to 10th	Night	35% 38% 12% 12% 3	2766
	11th to 20th	Night	27% 39% 12% 17% 5%	2899
	21st to end	Night	26% 37% 10% 19% 7%	3471
September	1st to 10th	Night	16% 58% 6% 16% 4	2000
	11th to 20th	Night	21% 58% 6% 12% 3	2000
	21st to end	Night	20% 58% 5% 12% 4	2301
October	1st to 10th	Night	36% 37% 9% 14% 4	3920
	11th to 20th	Night	37% 38% 6% 14% 5%	3899
	21st to end	Night	36% 38% 10% 12% 4	4408
November	1st to 10th	Night	32% 55% 6% 5% 2	2798
	11th to 20th	Night	36% 55% 5% 3	2940
	21st to end	Night	36% 56% 4 3 1	2940
December	1st to 10th	Night	49% 37% 5% 8% 1	4720
	11th to 20th	Night	52% 31% 6% 9% 2	5355
	21st to end	Night	57% 27% 7% 8% 2	7150

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% 22% 34% 14% 4	430
	11th to 20th	Day	29% 20% 26% 18% 6%	430
	21st to end	Day	17% 22% 39% 19% 3	473
February	1st to 10th	Day	25% 22% 30% 16% 5% 1	430
	11th to 20th	Day	22% 27% 30% 17% 4 1	426
	21st to end	Day	17% 19% 32% 25% 6% 1	355
March	1st to 10th	Day	21% 19% 34% 21% 4 1	480
	11th to 20th	Day	20% 19% 33% 23% 4 1	528
	21st to end	Day	28% 18% 29% 19% 5% 1	550
April	1st to 10th	Day	27% 20% 35% 13% 4	500
	11th to 20th	Day	25% 18% 33% 18% 6% 1	492
	21st to end	Day	23% 14% 30% 25% 7% 1	500
May	1st to 10th	Day	32% 10% 27% 20% 7% 3	694
	11th to 20th	Day	23% 9% 26% 28% 12% 2	724
	21st to end	Day	22% 11% 30% 27% 9% 1	790
June	1st to 10th	Day	30% 7% 27% 24% 11% 1	730
	11th to 20th	Day	19% 7% 25% 37% 10% 1	730
	21st to end	Day	27% 7% 25% 29% 11% 2	730
July	1st to 10th	Day	19% 6% 25% 36% 12% 2	720
	11th to 20th	Day	16% 5% 25% 33% 19% 2	718
	21st to end	Day	21% 5% 22% 34% 17% 2	795
August	1st to 10th	Day	16% 2 22% 39% 18% 3	613
	11th to 20th	Day	17% 4 24% 31% 17% 6%	519
	21st to end	Day	19% 7% 21% 33% 16% 3	583
September	1st to 10th	Day	16% 5% 29% 35% 11% 3	530
	11th to 20th	Day	24% 10% 23% 28% 12% 2	530
	21st to end	Day	23% 9% 30% 23% 14% 2	461
October	1st to 10th	Day	24% 12% 24% 26% 13% 1	420
	11th to 20th	Day	26% 13% 28% 21% 10% 3	420
	21st to end	Day	31% 16% 28% 18% 5% 1	462
November	1st to 10th	Day	36% 18% 27% 15% 4	425
	11th to 20th	Day	40% 15% 27% 13% 4 1	430
	21st to end	Day	34% 20% 28% 16% 2 1	430
December	1st to 10th	Day	34% 19% 27% 17% 3	430
	11th to 20th	Day	33% 24% 30% 12% 1	430
	21st to end	Day	24% 27% 30% 16% 3	473
January	1st to 10th	Night	29% 21% 31% 16% 4	950
	11th to 20th	Night	28% 19% 31% 17% 5%	950
	21st to end	Night	21% 24% 30% 19% 5%	971
February	1st to 10th	Night	27% 17% 30% 21% 5%	840
	11th to 20th	Night	25% 19% 34% 17% 4 1	823
	21st to end	Night	20% 16% 32% 24% 8%	692
March	1st to 10th	Night	24% 16% 35% 23% 3	840
	11th to 20th	Night	22% 14% 30% 24% 9%	829
	21st to end	Night	28% 15% 27% 22% 8% 1	820
April	1st to 10th	Night	27% 15% 28% 25% 6%	600
	11th to 20th	Night	26% 11% 31% 23% 8% 1	594
	21st to end	Night	29% 9% 29% 21% 10% 1	600
May	1st to 10th	Night	31% 8% 23% 24% 11% 3	600
	11th to 20th	Night	24% 5% 23% 32% 14% 2	592
	21st to end	Night	21% 8% 32% 30% 9%	649
June	1st to 10th	Night	30% 8% 25% 28% 9% 1	600
	11th to 20th	Night	20% 6% 24% 38% 10% 1	486
	21st to end	Night	27% 5% 23% 36% 9% 1	400
July	1st to 10th	Night	20% 4 22% 36% 17% 1	428
	11th to 20th	Night	16% 4 22% 42% 15% 1	582
	21st to end	Night	21% 5% 17% 45% 12% 1	656
August	1st to 10th	Night	16% 4 19% 42% 17% 2	598
	11th to 20th	Night	19% 4 19% 37% 19% 2	592
	21st to end	Night	16% 5% 22% 35% 21% 1	660
September	1st to 10th	Night	20% 6% 28% 33% 13% 1	600
	11th to 20th	Night	24% 7% 22% 32% 14% 1	600
	21st to end	Night	24% 8% 28% 28% 10% 2	776
October	1st to 10th	Night	27% 8% 26% 26% 12% 1	800
	11th to 20th	Night	29% 11% 25% 23% 10% 2	800
	21st to end	Night	36% 15% 26% 20% 4	932
November	1st to 10th	Night	34% 18% 28% 16% 4 1	930
	11th to 20th	Night	35% 19% 27% 14% 5% 1	950
	21st to end	Night	36% 18% 26% 16% 3	950
December	1st to 10th	Night	33% 20% 27% 15% 5%	950
	11th to 20th	Night	31% 24% 29% 13% 2	950
	21st to end	Night	34% 20% 26% 16% 3 1	1045

Page generated at 2026-03-15 03:23:51. Version ac07

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