Big Bay Point
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Big Bay Point clear sky chart from 2005-11-06 to 2025-12-03.

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% 10% 4 10% 6% 5% 5% 4 5% 6% 32%	126762
	Night	13% 12% 5% 12% 7% 5% 5% 3 5% 6% 27%	124118
Transparency	Day	50% 7% 12% 21% 9% 1	130191
	Night	58% 6% 11% 17% 7% 1	128775
Seeing	Day	17% 8% 24% 30% 16% 3	17390
	Night	20% 10% 27% 28% 13% 2	27348

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	7% 15% 10% 28% 12% 6% 4 2 3 4 7%	3617
	11th to 20th	Day	7% 16% 8% 22% 15% 7% 6% 5% 4 3 7%	3589
	21st to end	Day	8% 15% 7% 16% 12% 6% 5% 4 5% 5% 16%	3982
February	1st to 10th	Day	8% 13% 6% 15% 13% 9% 7% 5% 5% 4 17%	1660
	11th to 20th	Day	7% 12% 5% 16% 11% 9% 7% 5% 4 5% 19%	1878
	21st to end	Day	10% 13% 6% 14% 10% 6% 7% 5% 6% 6% 18%	1650
March	1st to 10th	Day	10% 10% 5% 10% 8% 6% 5% 3 5% 6% 31%	4478
	11th to 20th	Day	10% 12% 6% 16% 9% 6% 4 4 4 5% 24%	4662
	21st to end	Day	20% 14% 6% 14% 7% 5% 4 3 4 4 18%	5969
April	1st to 10th	Day	14% 14% 4 8% 5% 5% 6% 4 6% 7% 28%	2400
	11th to 20th	Day	18% 12% 4 9% 5% 4 4 4 5% 6% 29%	2411
	21st to end	Day	15% 10% 3 8% 5% 4 4 4 5% 7% 34%	2600
May	1st to 10th	Day	13% 7% 2 5% 4 4 4 3 4 6% 49%	6197
	11th to 20th	Day	11% 8% 2 6% 4 4 4 4 6% 8% 42%	6319
	21st to end	Day	10% 8% 3 8% 5% 5% 5% 5% 5% 7% 40%	6949
June	1st to 10th	Day	11% 6% 2 6% 5% 4 5% 3 6% 8% 42%	2800
	11th to 20th	Day	13% 6% 2 6% 5% 5% 5% 4 7% 8% 39%	2857
	21st to end	Day	15% 6% 3 6% 4 5% 4 4 6% 7% 40%	2800
July	1st to 10th	Day	11% 5% 2 6% 4 4 5% 4 5% 9% 45%	6359
	11th to 20th	Day	11% 4 2 5% 3 3 4 3 6% 9% 49%	6360
	21st to end	Day	10% 4 2 4 3 4 4 4 7% 8% 51%	6926
August	1st to 10th	Day	8% 5% 2 7% 5% 5% 5% 4 6% 9% 44%	4563
	11th to 20th	Day	14% 5% 2 4 3 4 3 3 5% 6% 50%	4283
	21st to end	Day	14% 6% 2 5% 3 3 4 3 5% 7% 47%	4325
September	1st to 10th	Day	16% 7% 2 6% 4 4 4 3 6% 7% 41%	2400
	11th to 20th	Day	14% 6% 2 7% 4 5% 5% 4 6% 8% 38%	2277
	21st to end	Day	18% 8% 3 7% 5% 4 5% 4 6% 6% 34%	2200
October	1st to 10th	Day	18% 10% 3 7% 5% 4 4 4 6% 8% 32%	2114
	11th to 20th	Day	21% 14% 4 11% 7% 4 5% 4 6% 6% 19%	1889
	21st to end	Day	21% 21% 5% 10% 6% 4 4 3 4 4 18%	1980
November	1st to 10th	Day	17% 19% 5% 10% 4 4 4 4 6% 5% 21%	1852
	11th to 20th	Day	17% 18% 7% 14% 6% 5% 5% 3 4 5% 16%	1808
	21st to end	Day	16% 22% 9% 17% 6% 5% 4 3 4 3 12%	1680
December	1st to 10th	Day	8% 23% 13% 22% 7% 5% 4 2 4 4 8%	2301
	11th to 20th	Day	10% 21% 10% 22% 9% 5% 5% 3 4 4 7%	2645
	21st to end	Day	17% 23% 12% 18% 7% 4 4 2 3 3 7%	3982
January	1st to 10th	Night	8% 18% 11% 26% 12% 5% 3 2 3 3 11%	6348
	11th to 20th	Night	7% 17% 7% 24% 13% 9% 7% 4 2 3 6%	6316
	21st to end	Night	7% 14% 8% 16% 10% 8% 7% 5% 5% 6% 14%	6996
February	1st to 10th	Night	8% 15% 6% 14% 11% 8% 8% 4 4 5% 16%	2738
	11th to 20th	Night	10% 11% 5% 14% 12% 8% 6% 4 5% 6% 19%	2408
	21st to end	Night	12% 16% 5% 14% 8% 6% 5% 3 5% 6% 22%	1980
March	1st to 10th	Night	10% 8% 4 10% 7% 6% 6% 5% 7% 9% 29%	5362
	11th to 20th	Night	10% 13% 6% 12% 5% 5% 5% 4 6% 7% 26%	5332
	21st to end	Night	20% 11% 6% 13% 7% 5% 4 3 4 5% 21%	4970
April	1st to 10th	Night	16% 14% 4 9% 6% 5% 5% 4 6% 6% 26%	2000
	11th to 20th	Night	20% 10% 4 7% 4 3 4 3 5% 8% 32%	1936
	21st to end	Night	16% 11% 3 7% 5% 4 4 3 5% 7% 35%	1800
May	1st to 10th	Night	13% 7% 2 6% 3 4 4 3 4 6% 47%	3755
	11th to 20th	Night	12% 9% 3 6% 4 4 4 4 5% 7% 41%	3596
	21st to end	Night	13% 10% 3 8% 5% 5% 5% 4 5% 6% 36%	3949
June	1st to 10th	Night	13% 6% 2 7% 5% 5% 5% 3 5% 7% 40%	1600
	11th to 20th	Night	12% 6% 3 8% 6% 6% 7% 4 7% 8% 35%	1476
	21st to end	Night	16% 6% 2 6% 4 4 4 4 6% 8% 38%	1600
July	1st to 10th	Night	11% 6% 2 7% 4 4 5% 4 5% 8% 44%	3620
	11th to 20th	Night	12% 5% 2 5% 3 4 4 3 5% 7% 50%	3620
	21st to end	Night	9% 4 1 5% 4 4 3 4 7% 10% 50%	3948
August	1st to 10th	Night	11% 6% 2 7% 4 4 4 4 5% 8% 44%	2597
	11th to 20th	Night	15% 6% 1 5% 3 3 3 3 4 7% 50%	2767
	21st to end	Night	14% 7% 3 6% 3 4 4 2 4 5% 47%	3570
September	1st to 10th	Night	14% 6% 2 7% 4 4 4 4 4 7% 46%	2000
	11th to 20th	Night	14% 7% 2 6% 6% 5% 5% 4 5% 7% 40%	2102
	21st to end	Night	18% 7% 2 7% 6% 5% 4 4 5% 6% 36%	2200
October	1st to 10th	Night	19% 9% 2 7% 5% 4 4 4 6% 6% 35%	2284
	11th to 20th	Night	19% 14% 4 8% 5% 4 5% 3 5% 7% 26%	2510
	21st to end	Night	21% 18% 4 9% 6% 5% 4 4 4 4 21%	2860
November	1st to 10th	Night	17% 19% 4 10% 5% 4 4 3 4 6% 23%	2666
	11th to 20th	Night	15% 21% 7% 13% 6% 5% 3 3 4 4 18%	2809
	21st to end	Night	16% 21% 10% 17% 6% 4 3 3 4 4 13%	2940
December	1st to 10th	Night	13% 19% 11% 21% 8% 6% 4 3 3 4 8%	4927
	11th to 20th	Night	10% 17% 8% 24% 11% 6% 4 2 3 3 12%	5540
	21st to end	Night	17% 19% 11% 17% 7% 5% 4 2 3 3 12%	6996

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	81% 5% 6% 6% 1	3618
	11th to 20th	Day	81% 6% 5% 8%	3620
	21st to end	Day	67% 8% 11% 9% 4	3982
February	1st to 10th	Day	68% 6% 10% 11% 4	1660
	11th to 20th	Day	65% 7% 11% 12% 5%	1887
	21st to end	Day	63% 8% 10% 12% 6% 1	1650
March	1st to 10th	Day	52% 6% 14% 17% 10% 1	4480
	11th to 20th	Day	60% 6% 12% 14% 6% 1	4662
	21st to end	Day	67% 5% 9% 13% 6%	5969
April	1st to 10th	Day	52% 7% 11% 22% 8% 1	2400
	11th to 20th	Day	54% 6% 9% 21% 9% 2	2411
	21st to end	Day	48% 7% 10% 20% 13% 3	2600
May	1st to 10th	Day	36% 5% 10% 29% 18% 2	6206
	11th to 20th	Day	38% 9% 10% 25% 13% 4	6323
	21st to end	Day	40% 7% 13% 22% 16% 1	6949
June	1st to 10th	Day	39% 7% 14% 26% 13% 2	2800
	11th to 20th	Day	40% 8% 14% 24% 13% 1	2857
	21st to end	Day	42% 7% 13% 25% 12% 1	2800
July	1st to 10th	Day	36% 6% 15% 31% 12% 1	6291
	11th to 20th	Day	30% 7% 17% 34% 12% 1	6285
	21st to end	Day	29% 7% 14% 35% 15%	6728
August	1st to 10th	Day	35% 8% 17% 29% 10% 1	4548
	11th to 20th	Day	34% 6% 17% 33% 10%	4324
	21st to end	Day	35% 7% 17% 27% 13% 1	4324
September	1st to 10th	Day	42% 7% 12% 30% 10%	2400
	11th to 20th	Day	41% 9% 18% 25% 6%	2277
	21st to end	Day	48% 8% 15% 22% 8%	2200
October	1st to 10th	Day	37% 7% 13% 31% 11%	3439
	11th to 20th	Day	60% 5% 10% 15% 10%	3053
	21st to end	Day	63% 6% 12% 15% 4	3180
November	1st to 10th	Day	63% 6% 10% 15% 6%	1852
	11th to 20th	Day	72% 5% 9% 10% 4	1808
	21st to end	Day	78% 7% 8% 6% 2	1680
December	1st to 10th	Day	82% 5% 6% 6% 1	2301
	11th to 20th	Day	82% 6% 6% 5% 1	2645
	21st to end	Day	82% 6% 5% 7% 1	3982
January	1st to 10th	Night	81% 4 6% 8% 1	6348
	11th to 20th	Night	83% 7% 5% 5%	6360
	21st to end	Night	69% 9% 13% 8% 2	6996
February	1st to 10th	Night	69% 7% 9% 11% 4	2738
	11th to 20th	Night	64% 6% 10% 15% 4	2409
	21st to end	Night	63% 6% 11% 15% 6%	1980
March	1st to 10th	Night	48% 8% 18% 17% 7% 1	5373
	11th to 20th	Night	56% 6% 14% 17% 7%	5333
	21st to end	Night	65% 5% 8% 16% 6% 1	4970
April	1st to 10th	Night	57% 5% 11% 17% 10% 1	2000
	11th to 20th	Night	51% 6% 9% 21% 11% 2	1936
	21st to end	Night	48% 6% 10% 20% 14% 2	1800
May	1st to 10th	Night	38% 5% 11% 28% 14% 4	3762
	11th to 20th	Night	41% 8% 9% 24% 13% 5%	3597
	21st to end	Night	47% 7% 9% 20% 16% 2	3950
June	1st to 10th	Night	42% 6% 11% 26% 14% 1	1600
	11th to 20th	Night	45% 9% 11% 22% 12% 1	1476
	21st to end	Night	42% 8% 14% 22% 13% 1	1600
July	1st to 10th	Night	37% 6% 17% 27% 12% 2	3580
	11th to 20th	Night	33% 6% 15% 35% 10% 1	3572
	21st to end	Night	30% 7% 15% 28% 20% 1	3832
August	1st to 10th	Night	37% 6% 12% 31% 12% 2	2588
	11th to 20th	Night	35% 5% 15% 33% 11% 1	2792
	21st to end	Night	40% 6% 12% 26% 14% 2	3570
September	1st to 10th	Night	39% 6% 14% 28% 13% 1	2000
	11th to 20th	Night	43% 9% 14% 27% 7% 1	2102
	21st to end	Night	48% 7% 14% 23% 8% 1	2200
October	1st to 10th	Night	38% 5% 12% 31% 13% 1	3739
	11th to 20th	Night	50% 5% 12% 21% 12%	4085
	21st to end	Night	60% 7% 13% 17% 4	4610
November	1st to 10th	Night	63% 5% 11% 14% 6%	2666
	11th to 20th	Night	70% 5% 10% 9% 6%	2809
	21st to end	Night	76% 6% 9% 8% 2	2940
December	1st to 10th	Night	81% 6% 6% 5% 1	4927
	11th to 20th	Night	78% 5% 8% 7% 2	5539
	21st to end	Night	78% 6% 5% 8% 4	6996

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	17% 15% 29% 30% 8% 1	300
	11th to 20th	Day	19% 13% 34% 25% 5% 3	300
	21st to end	Day	20% 9% 35% 32% 4 1	330
February	1st to 10th	Day	13% 17% 38% 25% 6% 1	300
	11th to 20th	Day	11% 17% 41% 26% 6%	300
	21st to end	Day	18% 20% 34% 24% 4	249
March	1st to 10th	Day	13% 12% 37% 29% 7% 1	300
	11th to 20th	Day	15% 14% 30% 31% 9% 1	341
	21st to end	Day	21% 11% 34% 23% 10% 1	550
April	1st to 10th	Day	20% 11% 31% 30% 7% 1	500
	11th to 20th	Day	23% 12% 25% 26% 10% 2	492
	21st to end	Day	22% 9% 27% 27% 13% 2	500
May	1st to 10th	Day	17% 6% 28% 31% 15% 3	630
	11th to 20th	Day	16% 4 24% 36% 15% 4	725
	21st to end	Day	14% 5% 21% 35% 21% 3	789
June	1st to 10th	Day	12% 7% 22% 37% 19% 4	730
	11th to 20th	Day	15% 4 17% 42% 19% 3	730
	21st to end	Day	17% 3 17% 38% 20% 4	730
July	1st to 10th	Day	8% 2 15% 39% 29% 6%	721
	11th to 20th	Day	13% 3 16% 36% 27% 5%	718
	21st to end	Day	9% 2 16% 39% 27% 7%	794
August	1st to 10th	Day	11% 4 17% 37% 27% 4	726
	11th to 20th	Day	16% 5% 12% 31% 29% 8%	592
	21st to end	Day	18% 7% 17% 30% 23% 5%	583
September	1st to 10th	Day	21% 6% 22% 25% 19% 7%	530
	11th to 20th	Day	14% 5% 24% 27% 24% 7%	530
	21st to end	Day	20% 7% 22% 24% 24% 4	530
October	1st to 10th	Day	23% 7% 27% 23% 15% 4	444
	11th to 20th	Day	26% 14% 24% 27% 9%	330
	21st to end	Day	33% 15% 25% 20% 7% 1	363
November	1st to 10th	Day	22% 14% 27% 28% 7% 2	330
	11th to 20th	Day	25% 19% 36% 14% 5% 2	330
	21st to end	Day	26% 19% 30% 21% 4	330
December	1st to 10th	Day	22% 13% 35% 19% 10% 1	207
	11th to 20th	Day	25% 23% 36% 10% 4 1	206
	21st to end	Day	26% 19% 29% 18% 7% 1	330
January	1st to 10th	Night	17% 17% 36% 25% 5% 1	1000
	11th to 20th	Night	20% 15% 37% 21% 7%	1000
	21st to end	Night	19% 14% 35% 27% 5% 1	1100
February	1st to 10th	Night	16% 18% 33% 25% 8% 1	1000
	11th to 20th	Night	15% 13% 37% 25% 10% 1	853
	21st to end	Night	19% 9% 34% 30% 7% 1	660
March	1st to 10th	Night	14% 11% 32% 31% 12% 1	800
	11th to 20th	Night	17% 12% 33% 28% 10% 1	800
	21st to end	Night	21% 10% 26% 30% 10% 2	668
April	1st to 10th	Night	22% 6% 28% 35% 8% 2	600
	11th to 20th	Night	24% 7% 24% 31% 11% 2	593
	21st to end	Night	21% 6% 25% 31% 14% 3	600
May	1st to 10th	Night	18% 4 23% 33% 18% 4	600
	11th to 20th	Night	17% 4 23% 36% 16% 4	591
	21st to end	Night	14% 4 18% 37% 24% 3	650
June	1st to 10th	Night	15% 4 16% 39% 23% 3	600
	11th to 20th	Night	15% 3 17% 39% 24% 2	476
	21st to end	Night	20% 4 14% 36% 22% 5%	600
July	1st to 10th	Night	11% 2 13% 38% 31% 4	585
	11th to 20th	Night	15% 2 17% 35% 26% 5%	582
	21st to end	Night	10% 1 16% 39% 28% 5%	657
August	1st to 10th	Night	13% 2 15% 37% 30% 3	597
	11th to 20th	Night	13% 3 16% 29% 32% 8%	594
	21st to end	Night	15% 4 19% 36% 23% 3	660
September	1st to 10th	Night	16% 6% 18% 32% 22% 7%	600
	11th to 20th	Night	18% 5% 21% 32% 21% 3	702
	21st to end	Night	23% 5% 21% 29% 20% 4	800
October	1st to 10th	Night	24% 7% 27% 25% 14% 2	800
	11th to 20th	Night	25% 11% 30% 25% 8%	800
	21st to end	Night	31% 13% 23% 23% 8% 1	880
November	1st to 10th	Night	29% 13% 28% 25% 5%	820
	11th to 20th	Night	26% 17% 34% 16% 7%	919
	21st to end	Night	26% 18% 30% 20% 6%	1050
December	1st to 10th	Night	22% 18% 36% 18% 5% 1	1011
	11th to 20th	Night	21% 18% 34% 20% 5% 2	1000
	21st to end	Night	29% 14% 34% 17% 5%	1100

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