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 2024-12-06.

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% 4 9% 5% 4 4 3 5% 6% 27%	102414
	Night	19% 13% 5% 11% 5% 4 4 3 4 5% 25%	97387
Transparency	Day	31% 48% 8% 10% 4	105951
	Night	34% 48% 7% 8% 3	101944
Seeing	Day	25% 13% 28% 24% 9% 1	17670
	Night	27% 13% 27% 24% 8% 1	24830

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% 17% 8% 26% 5% 4 4 2 4 5% 9%	2526
	11th to 20th	Day	13% 15% 6% 17% 10% 7% 4 4 4 4 16%	2530
	21st to end	Day	12% 12% 8% 20% 8% 5% 4 3 5% 4 19%	2978
February	1st to 10th	Day	18% 15% 5% 12% 7% 7% 5% 3 4 5% 20%	1710
	11th to 20th	Day	17% 16% 4 11% 7% 6% 5% 3 4 5% 21%	1663
	21st to end	Day	10% 15% 4 11% 7% 6% 5% 4 5% 6% 28%	1479
March	1st to 10th	Day	21% 15% 4 7% 5% 5% 4 3 4 5% 28%	3264
	11th to 20th	Day	12% 23% 7% 12% 6% 5% 3 3 4 4 20%	3480
	21st to end	Day	23% 19% 7% 11% 4 3 3 3 4 4 19%	3911
April	1st to 10th	Day	19% 15% 5% 8% 5% 4 4 3 4 5% 28%	2280
	11th to 20th	Day	20% 13% 3 6% 5% 3 3 3 5% 7% 33%	2278
	21st to end	Day	19% 14% 4 6% 4 4 3 4 4 6% 31%	2470
May	1st to 10th	Day	24% 18% 3 6% 3 3 3 2 4 6% 28%	4416
	11th to 20th	Day	16% 9% 3 7% 4 4 4 4 5% 6% 38%	4398
	21st to end	Day	18% 11% 3 7% 5% 4 5% 4 5% 8% 30%	4836
June	1st to 10th	Day	25% 12% 3 7% 5% 5% 5% 4 5% 6% 23%	2660
	11th to 20th	Day	20% 8% 3 6% 4 5% 4 4 5% 7% 35%	2780
	21st to end	Day	24% 11% 3 7% 5% 4 3 3 6% 7% 28%	2850
July	1st to 10th	Day	18% 8% 3 7% 5% 4 5% 5% 6% 8% 33%	4646
	11th to 20th	Day	17% 7% 3 6% 5% 4 5% 4 6% 8% 35%	4440
	21st to end	Day	13% 8% 3 7% 5% 4 5% 4 7% 9% 36%	4815
August	1st to 10th	Day	19% 9% 3 8% 5% 5% 5% 4 6% 7% 29%	4240
	11th to 20th	Day	16% 7% 2 7% 4 4 5% 4 7% 8% 36%	4045
	21st to end	Day	13% 7% 2 7% 5% 5% 5% 4 6% 7% 40%	4290
September	1st to 10th	Day	18% 6% 3 6% 3 4 4 3 6% 8% 39%	2280
	11th to 20th	Day	20% 10% 3 6% 4 3 4 4 5% 6% 36%	2280
	21st to end	Day	20% 9% 3 6% 4 4 4 3 4 7% 36%	1990
October	1st to 10th	Day	20% 10% 3 8% 5% 4 4 3 5% 7% 31%	1900
	11th to 20th	Day	20% 14% 3 9% 6% 5% 4 4 6% 6% 22%	1900
	21st to end	Day	22% 19% 4 8% 5% 5% 4 3 4 7% 20%	1998
November	1st to 10th	Day	20% 21% 5% 9% 6% 5% 4 3 4 4 20%	1632
	11th to 20th	Day	22% 24% 7% 8% 5% 4 4 3 4 5% 14%	1600
	21st to end	Day	19% 21% 8% 13% 6% 5% 4 3 5% 6% 11%	1600
December	1st to 10th	Day	23% 22% 8% 15% 5% 4 3 2 4 5% 10%	1560
	11th to 20th	Day	25% 21% 9% 16% 5% 5% 4 2 3 3 6%	1906
	21st to end	Day	20% 20% 10% 14% 6% 3 3 3 3 4 14%	2783
January	1st to 10th	Night	14% 15% 8% 26% 6% 4 3 3 4 4 14%	4429
	11th to 20th	Night	16% 15% 6% 20% 7% 5% 4 3 4 4 15%	4440
	21st to end	Night	13% 14% 7% 23% 7% 5% 4 3 4 5% 15%	4678
February	1st to 10th	Night	18% 15% 4 11% 7% 5% 4 3 4 5% 24%	2470
	11th to 20th	Night	18% 16% 5% 12% 7% 5% 4 3 4 5% 20%	2403
	21st to end	Night	13% 14% 6% 9% 7% 5% 5% 4 5% 5% 28%	1975
March	1st to 10th	Night	20% 14% 5% 9% 5% 4 4 3 4 5% 27%	3572
	11th to 20th	Night	19% 20% 8% 11% 6% 4 4 3 3 4 18%	3479
	21st to end	Night	25% 17% 5% 8% 5% 5% 4 3 4 4 20%	3721
April	1st to 10th	Night	22% 12% 5% 10% 5% 4 4 3 5% 5% 26%	1900
	11th to 20th	Night	21% 13% 3 6% 3 4 3 2 5% 5% 33%	1848
	21st to end	Night	23% 14% 4 6% 4 4 3 3 4 5% 31%	1710
May	1st to 10th	Night	26% 18% 3 8% 4 4 4 3 4 5% 21%	2532
	11th to 20th	Night	15% 9% 3 5% 5% 5% 5% 4 5% 7% 37%	2506
	21st to end	Night	17% 10% 3 7% 6% 6% 5% 5% 6% 8% 27%	2749
June	1st to 10th	Night	27% 9% 4 7% 6% 3 4 4 5% 6% 26%	1520
	11th to 20th	Night	18% 8% 3 6% 3 3 5% 3 6% 7% 39%	1412
	21st to end	Night	23% 10% 3 8% 6% 4 4 4 5% 6% 27%	1330
July	1st to 10th	Night	15% 11% 4 8% 6% 6% 6% 4 6% 8% 27%	2274
	11th to 20th	Night	15% 8% 3 7% 6% 4 6% 5% 7% 8% 32%	2530
	21st to end	Night	14% 7% 2 5% 4 4 4 4 6% 7% 43%	2750
August	1st to 10th	Night	18% 10% 3 8% 4 5% 5% 4 7% 8% 28%	2691
	11th to 20th	Night	14% 7% 3 7% 5% 5% 5% 4 5% 7% 39%	2782
	21st to end	Night	12% 7% 3 6% 5% 5% 4 4 6% 7% 43%	3366
September	1st to 10th	Night	17% 7% 2 7% 5% 4 4 3 4 6% 41%	1900
	11th to 20th	Night	20% 7% 2 6% 4 3 3 4 4 6% 41%	1900
	21st to end	Night	19% 7% 2 7% 4 4 4 2 6% 7% 37%	2186
October	1st to 10th	Night	21% 8% 3 7% 4 4 4 3 5% 6% 35%	2280
	11th to 20th	Night	21% 11% 4 7% 5% 4 4 4 4 7% 30%	2280
	21st to end	Night	26% 15% 3 8% 5% 4 3 3 4 5% 23%	2598
November	1st to 10th	Night	19% 18% 4 10% 7% 4 4 3 4 5% 23%	2662
	11th to 20th	Night	23% 20% 6% 9% 5% 5% 4 3 4 6% 16%	2800
	21st to end	Night	26% 20% 6% 10% 5% 4 4 3 4 5% 14%	2800
December	1st to 10th	Night	23% 21% 7% 12% 5% 4 4 4 4 4 11%	2737
	11th to 20th	Night	27% 20% 8% 15% 6% 4 3 2 2 3 11%	3293
	21st to end	Night	27% 17% 7% 17% 4 3 3 2 3 3 15%	4884

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	52% 39% 6% 2 1	2527
	11th to 20th	Day	41% 45% 7% 4 3	2530
	21st to end	Day	42% 45% 6% 3 3 1	2978
February	1st to 10th	Day	26% 64% 3 5% 2	1710
	11th to 20th	Day	23% 65% 4 6% 2	1671
	21st to end	Day	18% 65% 4 8% 6% 1	1479
March	1st to 10th	Day	35% 42% 6% 13% 4	3268
	11th to 20th	Day	44% 44% 5% 5% 3	3480
	21st to end	Day	45% 41% 5% 6% 2 1	3911
April	1st to 10th	Day	23% 65% 3 5% 3 1	2280
	11th to 20th	Day	19% 66% 3 7% 4	2278
	21st to end	Day	20% 66% 5% 4 4 1	2470
May	1st to 10th	Day	37% 41% 10% 9% 3	4431
	11th to 20th	Day	25% 43% 11% 17% 4	4402
	21st to end	Day	32% 44% 8% 12% 4	4836
June	1st to 10th	Day	20% 66% 4 8% 2	2660
	11th to 20th	Day	17% 65% 5% 9% 3	2780
	21st to end	Day	20% 63% 3 7% 5%	2850
July	1st to 10th	Day	34% 37% 13% 8% 8%	4574
	11th to 20th	Day	31% 38% 11% 16% 4	4364
	21st to end	Day	24% 38% 16% 17% 4	4662
August	1st to 10th	Day	36% 39% 10% 12% 2	4226
	11th to 20th	Day	28% 39% 9% 16% 7%	4084
	21st to end	Day	28% 38% 9% 17% 7%	4290
September	1st to 10th	Day	15% 61% 7% 11% 4	2280
	11th to 20th	Day	23% 60% 6% 8% 3	2280
	21st to end	Day	17% 61% 6% 10% 5%	1990
October	1st to 10th	Day	34% 39% 10% 13% 4	3160
	11th to 20th	Day	37% 38% 7% 15% 3	3140
	21st to end	Day	35% 38% 13% 14% 1	3280
November	1st to 10th	Day	33% 57% 5% 4 1	1632
	11th to 20th	Day	37% 57% 3 2 1	1600
	21st to end	Day	36% 57% 4 2 1	1600
December	1st to 10th	Day	35% 59% 2 3 1	1560
	11th to 20th	Day	46% 49% 2 2 1	1905
	21st to end	Day	47% 40% 8% 3 3	2783
January	1st to 10th	Night	48% 40% 8% 3 1	4429
	11th to 20th	Night	45% 45% 4 4 2	4440
	21st to end	Night	48% 42% 4 4 2	4678
February	1st to 10th	Night	24% 65% 3 5% 3 1	2470
	11th to 20th	Night	24% 64% 4 6% 2	2406
	21st to end	Night	19% 65% 3 8% 5% 1	1975
March	1st to 10th	Night	33% 42% 7% 12% 5%	3581
	11th to 20th	Night	46% 43% 4 4 2	3480
	21st to end	Night	45% 43% 4 5% 3	3721
April	1st to 10th	Night	21% 65% 4 6% 4 1	1900
	11th to 20th	Night	19% 66% 4 7% 3 1	1848
	21st to end	Night	23% 65% 2 5% 4 1	1710
May	1st to 10th	Night	43% 42% 6% 7% 3	2537
	11th to 20th	Night	25% 42% 14% 14% 5%	2507
	21st to end	Night	32% 46% 12% 7% 3	2750
June	1st to 10th	Night	19% 65% 5% 9% 2	1520
	11th to 20th	Night	15% 65% 5% 10% 5%	1412
	21st to end	Night	19% 64% 5% 7% 4	1330
July	1st to 10th	Night	39% 38% 9% 8% 5% 1	2237
	11th to 20th	Night	32% 39% 13% 13% 4	2482
	21st to end	Night	22% 38% 17% 15% 9%	2663
August	1st to 10th	Night	36% 40% 12% 11% 2	2680
	11th to 20th	Night	27% 40% 12% 17% 5%	2809
	21st to end	Night	26% 38% 10% 19% 7%	3365
September	1st to 10th	Night	16% 61% 5% 14% 4	1900
	11th to 20th	Night	20% 60% 6% 11% 3	1900
	21st to end	Night	19% 61% 5% 12% 3	2186
October	1st to 10th	Night	36% 38% 8% 13% 4	3800
	11th to 20th	Night	36% 39% 6% 14% 5%	3779
	21st to end	Night	36% 39% 10% 11% 4	4271
November	1st to 10th	Night	30% 58% 6% 5% 2	2662
	11th to 20th	Night	34% 58% 5% 3 1	2800
	21st to end	Night	35% 58% 4 2 1	2800
December	1st to 10th	Night	35% 58% 3 3 1	2737
	11th to 20th	Night	42% 49% 4 4 1	3295
	21st to end	Night	48% 38% 7% 6% 1	4884

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% 23% 35% 14% 3	370
	11th to 20th	Day	28% 22% 28% 18% 5%	370
	21st to end	Day	18% 21% 39% 19% 3	407
February	1st to 10th	Day	28% 22% 31% 14% 5% 1	370
	11th to 20th	Day	22% 27% 31% 15% 4 1	366
	21st to end	Day	17% 20% 32% 25% 6% 1	307
March	1st to 10th	Day	23% 16% 35% 22% 4 1	411
	11th to 20th	Day	20% 19% 33% 23% 5% 1	460
	21st to end	Day	28% 18% 30% 18% 6% 1	506
April	1st to 10th	Day	27% 20% 35% 14% 4	460
	11th to 20th	Day	24% 19% 32% 18% 5% 1	452
	21st to end	Day	23% 14% 30% 25% 8% 1	460
May	1st to 10th	Day	33% 10% 28% 19% 8% 3	644
	11th to 20th	Day	22% 8% 27% 28% 12% 2	674
	21st to end	Day	23% 11% 31% 27% 8% 1	735
June	1st to 10th	Day	31% 7% 28% 23% 10% 1	680
	11th to 20th	Day	20% 7% 25% 37% 10% 1	680
	21st to end	Day	27% 7% 24% 29% 11% 2	680
July	1st to 10th	Day	19% 6% 26% 36% 12% 2	670
	11th to 20th	Day	17% 5% 26% 33% 17% 2	668
	21st to end	Day	21% 5% 22% 33% 17% 1	740
August	1st to 10th	Day	17% 2 23% 38% 17% 2	569
	11th to 20th	Day	19% 4 24% 31% 17% 5%	479
	21st to end	Day	20% 7% 20% 32% 17% 4	539
September	1st to 10th	Day	17% 6% 30% 34% 10% 3	490
	11th to 20th	Day	26% 9% 24% 27% 12% 2	490
	21st to end	Day	24% 9% 29% 22% 14% 2	427
October	1st to 10th	Day	24% 12% 24% 25% 14% 2	390
	11th to 20th	Day	27% 13% 28% 21% 9% 2	390
	21st to end	Day	31% 17% 29% 17% 5% 1	429
November	1st to 10th	Day	33% 18% 28% 16% 4 1	395
	11th to 20th	Day	40% 16% 27% 14% 3 1	400
	21st to end	Day	36% 20% 27% 16% 2	400
December	1st to 10th	Day	34% 18% 29% 16% 3	385
	11th to 20th	Day	34% 24% 30% 11% 1	370
	21st to end	Day	26% 29% 29% 14% 2	407
January	1st to 10th	Night	28% 22% 31% 16% 4	850
	11th to 20th	Night	27% 19% 33% 17% 4	850
	21st to end	Night	22% 23% 29% 20% 5%	875
February	1st to 10th	Night	28% 17% 29% 21% 5%	760
	11th to 20th	Night	24% 20% 36% 16% 3 1	743
	21st to end	Night	19% 17% 32% 24% 8%	628
March	1st to 10th	Night	25% 14% 35% 23% 3	760
	11th to 20th	Night	23% 14% 30% 24% 9%	760
	21st to end	Night	28% 15% 26% 22% 8% 1	779
April	1st to 10th	Night	26% 14% 29% 25% 6%	570
	11th to 20th	Night	26% 10% 32% 23% 9% 1	564
	21st to end	Night	29% 9% 30% 21% 10% 1	570
May	1st to 10th	Night	31% 8% 24% 24% 11% 3	570
	11th to 20th	Night	24% 5% 23% 32% 15% 2	562
	21st to end	Night	22% 7% 33% 29% 8%	616
June	1st to 10th	Night	31% 7% 26% 27% 8% 1	570
	11th to 20th	Night	21% 6% 24% 37% 10% 1	462
	21st to end	Night	27% 4 22% 36% 9% 1	380
July	1st to 10th	Night	20% 4 23% 35% 16% 1	406
	11th to 20th	Night	16% 4 22% 41% 15% 1	552
	21st to end	Night	21% 4 17% 45% 12% 1	623
August	1st to 10th	Night	17% 4 20% 41% 17% 1	568
	11th to 20th	Night	20% 4 19% 38% 18% 2	562
	21st to end	Night	16% 5% 21% 35% 22% 1	627
September	1st to 10th	Night	20% 6% 28% 32% 13% 1	570
	11th to 20th	Night	25% 6% 23% 31% 14% 1	570
	21st to end	Night	25% 8% 29% 27% 10% 2	737
October	1st to 10th	Night	28% 8% 26% 26% 12% 1	760
	11th to 20th	Night	29% 11% 25% 23% 10% 1	760
	21st to end	Night	37% 15% 26% 19% 3	883
November	1st to 10th	Night	33% 18% 28% 16% 5% 1	880
	11th to 20th	Night	34% 19% 28% 14% 4 1	900
	21st to end	Night	38% 19% 26% 15% 3	900
December	1st to 10th	Night	34% 19% 28% 14% 5%	878
	11th to 20th	Night	32% 24% 29% 13% 2	850
	21st to end	Night	35% 19% 27% 14% 3 1	935

Page generated at 2024-12-03 07:45:15. Version ac07

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