Bays Mountain Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bays Mountain Park clear sky chart from 2005-11-06 to 2024-11-06.

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	14% 8% 3 7% 5% 5% 5% 4 6% 8% 37%	101154
	Night	15% 8% 3 7% 5% 4 4 4 6% 7% 39%	97869
Transparency	Day	42% 7% 12% 22% 14% 3	104909
	Night	42% 7% 11% 22% 15% 3	102253
Seeing	Day	17% 9% 19% 23% 21% 10%	15010
	Night	17% 6% 20% 35% 19% 2	25058

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% 14% 4 8% 4 3 5% 4 5% 6% 30%	2836
	11th to 20th	Day	18% 12% 7% 10% 8% 5% 3 2 3 4 26%	2840
	21st to end	Day	19% 15% 3 7% 5% 4 4 3 4 5% 30%	3124
February	1st to 10th	Day	19% 11% 4 7% 4 4 4 3 5% 6% 33%	1767
	11th to 20th	Day	21% 10% 4 9% 5% 5% 4 3 4 6% 31%	1848
	21st to end	Day	22% 9% 3 7% 4 5% 4 3 4 6% 32%	1570
March	1st to 10th	Day	22% 10% 3 8% 4 4 3 3 4 6% 34%	3339
	11th to 20th	Day	14% 7% 2 6% 4 4 3 4 5% 6% 47%	3480
	21st to end	Day	16% 9% 3 7% 4 4 4 3 5% 6% 39%	3815
April	1st to 10th	Day	12% 8% 2 6% 5% 3 4 4 7% 7% 40%	2090
	11th to 20th	Day	15% 7% 2 5% 5% 4 4 3 5% 7% 43%	2311
	21st to end	Day	15% 7% 2 7% 5% 5% 4 4 4 8% 40%	2470
May	1st to 10th	Day	19% 8% 3 8% 6% 5% 6% 3 6% 7% 30%	4082
	11th to 20th	Day	18% 9% 3 8% 5% 5% 6% 4 5% 7% 31%	4081
	21st to end	Day	11% 5% 2 6% 5% 5% 5% 5% 7% 9% 38%	4476
June	1st to 10th	Day	10% 7% 2 7% 5% 6% 6% 4 7% 8% 38%	2470
	11th to 20th	Day	7% 4 2 7% 6% 7% 6% 5% 8% 9% 37%	2470
	21st to end	Day	9% 7% 2 6% 5% 5% 6% 5% 8% 10% 36%	2470
July	1st to 10th	Day	7% 5% 2 6% 4 6% 7% 6% 9% 12% 37%	4120
	11th to 20th	Day	10% 5% 3 6% 6% 6% 5% 5% 7% 10% 38%	4120
	21st to end	Day	17% 10% 4 11% 6% 7% 6% 4 6% 8% 19%	4466
August	1st to 10th	Day	10% 6% 3 8% 5% 6% 7% 5% 8% 11% 30%	4104
	11th to 20th	Day	9% 5% 2 7% 5% 5% 5% 5% 9% 11% 36%	4044
	21st to end	Day	6% 3 1 5% 4 4 4 4 6% 11% 53%	4258
September	1st to 10th	Day	10% 6% 3 6% 5% 4 5% 4 7% 8% 43%	2090
	11th to 20th	Day	12% 6% 2 6% 5% 5% 4 3 5% 8% 43%	2090
	21st to end	Day	16% 6% 2 5% 5% 4 4 3 5% 7% 43%	2090
October	1st to 10th	Day	12% 6% 1 5% 4 4 4 3 3 7% 50%	2052
	11th to 20th	Day	14% 6% 1 5% 3 4 3 3 4 6% 51%	1900
	21st to end	Day	15% 8% 2 5% 4 3 3 3 4 5% 47%	2090
November	1st to 10th	Day	11% 5% 2 5% 4 3 3 4 5% 5% 53%	1784
	11th to 20th	Day	11% 8% 2 5% 5% 4 4 3 5% 7% 46%	1710
	21st to end	Day	15% 7% 3 6% 4 3 3 3 5% 6% 44%	1710
December	1st to 10th	Day	20% 12% 3 6% 4 5% 4 4 4 6% 32%	1710
	11th to 20th	Day	16% 11% 3 7% 3 3 4 4 5% 8% 34%	2153
	21st to end	Day	16% 15% 4 7% 5% 5% 5% 4 5% 6% 27%	3124
January	1st to 10th	Night	17% 14% 5% 8% 5% 5% 4 4 4 5% 29%	4109
	11th to 20th	Night	22% 9% 3 8% 5% 3 3 3 3 4 37%	4120
	21st to end	Night	19% 12% 3 7% 5% 5% 4 3 5% 6% 31%	4532
February	1st to 10th	Night	18% 9% 3 7% 5% 4 5% 4 5% 6% 36%	2409
	11th to 20th	Night	21% 9% 3 7% 4 4 4 3 5% 5% 34%	2218
	21st to end	Night	22% 9% 3 7% 4 4 4 4 6% 5% 32%	1884
March	1st to 10th	Night	22% 10% 3 8% 4 5% 4 3 4 6% 31%	3513
	11th to 20th	Night	13% 6% 3 4 4 3 4 3 4 7% 48%	3480
	21st to end	Night	14% 6% 2 5% 5% 5% 5% 4 5% 7% 43%	3817
April	1st to 10th	Night	12% 7% 2 6% 4 5% 4 4 6% 7% 42%	2090
	11th to 20th	Night	13% 6% 2 7% 4 5% 4 3 6% 7% 43%	1833
	21st to end	Night	12% 7% 3 7% 5% 5% 4 4 5% 6% 42%	1710
May	1st to 10th	Night	19% 9% 2 8% 5% 4 4 3 5% 7% 32%	2813
	11th to 20th	Night	18% 7% 3 7% 5% 4 4 4 6% 7% 34%	2812
	21st to end	Night	10% 5% 2 7% 6% 5% 5% 4 7% 8% 40%	3079
June	1st to 10th	Night	10% 6% 3 7% 5% 5% 4 5% 8% 10% 38%	1710
	11th to 20th	Night	5% 5% 2 7% 5% 5% 6% 5% 7% 11% 42%	1710
	21st to end	Night	10% 6% 2 7% 5% 5% 5% 4 8% 10% 38%	1710
July	1st to 10th	Night	9% 6% 2 7% 5% 6% 6% 6% 9% 11% 35%	2840
	11th to 20th	Night	9% 6% 3 6% 4 4 5% 5% 7% 10% 42%	2840
	21st to end	Night	13% 10% 4 11% 6% 7% 7% 4 7% 8% 22%	3087
August	1st to 10th	Night	10% 5% 3 8% 5% 5% 6% 5% 8% 10% 33%	2825
	11th to 20th	Night	10% 5% 2 8% 5% 5% 6% 5% 6% 8% 41%	2785
	21st to end	Night	6% 3 2 4 3 4 4 3 7% 10% 53%	3361
September	1st to 10th	Night	12% 7% 3 7% 5% 4 3 4 5% 6% 43%	2090
	11th to 20th	Night	15% 6% 2 6% 5% 4 3 4 6% 7% 41%	2090
	21st to end	Night	13% 6% 3 5% 5% 4 3 3 5% 7% 47%	2090
October	1st to 10th	Night	13% 6% 2 6% 3 3 4 3 4 6% 50%	2128
	11th to 20th	Night	16% 5% 2 5% 3 3 3 2 5% 5% 51%	2280
	21st to end	Night	15% 5% 1 5% 4 3 4 3 4 7% 50%	2508
November	1st to 10th	Night	13% 6% 2 4 3 3 3 4 5% 5% 52%	2412
	11th to 20th	Night	13% 10% 2 5% 3 3 3 3 4 7% 46%	2470
	21st to end	Night	15% 8% 1 5% 4 3 3 3 6% 6% 45%	2470
December	1st to 10th	Night	21% 11% 3 7% 5% 4 4 4 5% 6% 31%	2470
	11th to 20th	Night	17% 10% 3 8% 4 4 4 3 5% 5% 36%	3042
	21st to end	Night	17% 14% 3 7% 5% 5% 5% 4 6% 7% 26%	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	54% 5% 8% 20% 12% 2	2837
	11th to 20th	Day	61% 7% 6% 16% 10% 1	2840
	21st to end	Day	56% 6% 6% 17% 14% 1	3124
February	1st to 10th	Day	52% 5% 8% 19% 15% 1	1767
	11th to 20th	Day	56% 4 8% 17% 13% 2	1858
	21st to end	Day	53% 4 9% 15% 15% 4	1570
March	1st to 10th	Day	49% 5% 8% 19% 14% 4	3339
	11th to 20th	Day	38% 5% 8% 25% 20% 4	3480
	21st to end	Day	45% 5% 8% 27% 13% 2	3815
April	1st to 10th	Day	39% 7% 12% 23% 16% 3	2090
	11th to 20th	Day	40% 5% 9% 21% 20% 5%	2311
	21st to end	Day	43% 7% 12% 24% 12% 2	2470
May	1st to 10th	Day	50% 9% 12% 19% 9% 1	4120
	11th to 20th	Day	49% 10% 10% 22% 8% 1	4085
	21st to end	Day	36% 11% 16% 22% 12% 3	4489
June	1st to 10th	Day	40% 9% 16% 21% 13% 1	2470
	11th to 20th	Day	38% 11% 17% 18% 14% 2	2470
	21st to end	Day	39% 10% 14% 20% 15% 2	2470
July	1st to 10th	Day	34% 13% 23% 19% 11% 1	4055
	11th to 20th	Day	39% 9% 16% 26% 8% 2	4051
	21st to end	Day	59% 9% 11% 14% 6%	4324
August	1st to 10th	Day	43% 10% 18% 22% 8%	4091
	11th to 20th	Day	36% 9% 18% 23% 11% 1	4083
	21st to end	Day	24% 7% 18% 34% 15% 1	4258
September	1st to 10th	Day	36% 8% 15% 21% 15% 6%	2090
	11th to 20th	Day	38% 8% 11% 23% 18% 2	2090
	21st to end	Day	40% 7% 12% 20% 18% 4	2090
October	1st to 10th	Day	29% 4 8% 20% 33% 7%	3416
	11th to 20th	Day	26% 4 10% 24% 22% 15%	3140
	21st to end	Day	29% 4 7% 30% 19% 10%	3428
November	1st to 10th	Day	32% 4 9% 21% 29% 5%	1784
	11th to 20th	Day	38% 5% 7% 24% 21% 6%	1710
	21st to end	Day	41% 5% 8% 23% 22% 3	1710
December	1st to 10th	Day	54% 4 9% 20% 11% 2	1710
	11th to 20th	Day	47% 5% 11% 19% 16% 2	2150
	21st to end	Day	55% 7% 8% 21% 8%	3124
January	1st to 10th	Night	56% 6% 8% 16% 12% 2	4109
	11th to 20th	Night	51% 6% 7% 17% 17% 3	4120
	21st to end	Night	53% 6% 8% 19% 13% 1	4532
February	1st to 10th	Night	49% 5% 9% 21% 15% 1	2409
	11th to 20th	Night	52% 4 9% 20% 12% 4	2219
	21st to end	Night	53% 5% 8% 18% 12% 4	1884
March	1st to 10th	Night	52% 6% 9% 17% 14% 2	3513
	11th to 20th	Night	36% 5% 10% 26% 16% 8%	3480
	21st to end	Night	39% 6% 11% 25% 16% 2	3817
April	1st to 10th	Night	39% 7% 12% 22% 16% 4	2090
	11th to 20th	Night	40% 6% 9% 20% 18% 6%	1833
	21st to end	Night	42% 7% 10% 26% 13% 2	1710
May	1st to 10th	Night	48% 10% 13% 21% 8% 1	2840
	11th to 20th	Night	46% 10% 13% 24% 6% 1	2813
	21st to end	Night	34% 13% 16% 22% 12% 2	3087
June	1st to 10th	Night	38% 10% 17% 19% 13% 2	1710
	11th to 20th	Night	33% 12% 18% 22% 12% 2	1710
	21st to end	Night	37% 13% 14% 20% 13% 3	1710
July	1st to 10th	Night	39% 11% 21% 19% 9% 1	2795
	11th to 20th	Night	34% 10% 21% 25% 7% 3	2786
	21st to end	Night	56% 10% 12% 16% 6%	2988
August	1st to 10th	Night	42% 10% 19% 23% 6% 1	2814
	11th to 20th	Night	39% 8% 17% 25% 10% 1	2812
	21st to end	Night	24% 8% 18% 37% 12% 2	3361
September	1st to 10th	Night	39% 8% 12% 20% 16% 5%	2090
	11th to 20th	Night	39% 9% 12% 20% 18% 2	2090
	21st to end	Night	38% 7% 11% 23% 18% 3	2090
October	1st to 10th	Night	34% 5% 9% 18% 27% 6%	3544
	11th to 20th	Night	26% 5% 6% 24% 26% 13%	3779
	21st to end	Night	25% 4 6% 29% 27% 9%	4120
November	1st to 10th	Night	34% 5% 9% 22% 25% 6%	2412
	11th to 20th	Night	38% 4 7% 21% 24% 6%	2470
	21st to end	Night	40% 3 8% 26% 20% 3	2470
December	1st to 10th	Night	54% 5% 9% 18% 11% 2	2470
	11th to 20th	Night	50% 4 8% 20% 16% 2	3044
	21st to end	Night	54% 7% 11% 16% 11%	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	23% 20% 31% 20% 5% 1	270
	11th to 20th	Day	30% 20% 25% 19% 6%	270
	21st to end	Day	24% 22% 29% 19% 6%	297
February	1st to 10th	Day	26% 17% 25% 23% 9% 1	270
	11th to 20th	Day	31% 24% 30% 11% 4	270
	21st to end	Day	31% 20% 31% 14% 4	225
March	1st to 10th	Day	22% 13% 29% 25% 9% 2	398
	11th to 20th	Day	23% 16% 27% 27% 6%	460
	21st to end	Day	22% 16% 26% 26% 9% 1	506
April	1st to 10th	Day	20% 16% 22% 25% 14% 3	460
	11th to 20th	Day	16% 16% 23% 25% 17% 3	452
	21st to end	Day	19% 11% 25% 24% 17% 5%	460
May	1st to 10th	Day	17% 14% 24% 21% 17% 6%	463
	11th to 20th	Day	18% 6% 16% 29% 22% 9%	487
	21st to end	Day	13% 6% 17% 20% 25% 20%	529
June	1st to 10th	Day	13% 4 14% 25% 29% 14%	490
	11th to 20th	Day	9% 3 14% 25% 31% 18%	490
	21st to end	Day	13% 2 20% 24% 27% 14%	490
July	1st to 10th	Day	12% 3 12% 20% 27% 27%	485
	11th to 20th	Day	13% 1 9% 22% 32% 23%	484
	21st to end	Day	16% 2 9% 25% 30% 18%	532
August	1st to 10th	Day	14% 3 13% 22% 28% 19%	486
	11th to 20th	Day	14% 3 10% 25% 30% 18%	479
	21st to end	Day	12% 3 7% 17% 35% 26%	539
September	1st to 10th	Day	10% 3 10% 21% 36% 19%	490
	11th to 20th	Day	13% 3 13% 18% 32% 21%	490
	21st to end	Day	19% 4 17% 22% 28% 9%	490
October	1st to 10th	Day	16% 4 14% 27% 28% 11%	490
	11th to 20th	Day	14% 10% 18% 27% 25% 6%	490
	21st to end	Day	19% 7% 20% 27% 22% 5%	539
November	1st to 10th	Day	14% 8% 24% 28% 21% 5%	352
	11th to 20th	Day	16% 16% 23% 29% 14% 3	270
	21st to end	Day	17% 11% 28% 23% 19% 3	270
December	1st to 10th	Day	26% 16% 26% 24% 7% 1	270
	11th to 20th	Day	22% 16% 22% 27% 11% 2	270
	21st to end	Day	22% 16% 30% 22% 8% 2	297
January	1st to 10th	Night	22% 13% 27% 34% 4	760
	11th to 20th	Night	28% 11% 25% 32% 4	760
	21st to end	Night	19% 10% 35% 33% 3	836
February	1st to 10th	Night	22% 10% 27% 38% 3	760
	11th to 20th	Night	25% 12% 35% 26% 2	743
	21st to end	Night	26% 12% 33% 26% 2	628
March	1st to 10th	Night	19% 10% 29% 37% 5%	760
	11th to 20th	Night	20% 11% 30% 31% 8%	760
	21st to end	Night	17% 8% 30% 36% 9%	836
April	1st to 10th	Night	15% 12% 27% 36% 10%	760
	11th to 20th	Night	15% 8% 27% 37% 13% 1	629
	21st to end	Night	15% 6% 24% 44% 11% 1	570
May	1st to 10th	Night	16% 6% 21% 39% 15% 2	570
	11th to 20th	Night	16% 5% 17% 37% 24% 1	561
	21st to end	Night	9% 2 15% 32% 37% 4	617
June	1st to 10th	Night	10% 2 12% 40% 33% 4	570
	11th to 20th	Night	7% 1 10% 36% 40% 5%	570
	21st to end	Night	12% 1 10% 37% 37% 4	570
July	1st to 10th	Night	12% 2 6% 28% 46% 6%	555
	11th to 20th	Night	12% 1 5% 26% 47% 8%	552
	21st to end	Night	11% 1 7% 34% 40% 7%	624
August	1st to 10th	Night	13% 1 6% 30% 46% 4	567
	11th to 20th	Night	14% 1 7% 34% 38% 6%	564
	21st to end	Night	10% 1 7% 29% 44% 9%	660
September	1st to 10th	Night	14% 2 9% 28% 40% 6%	760
	11th to 20th	Night	17% 3 8% 30% 36% 5%	760
	21st to end	Night	16% 2 15% 37% 28% 2	760
October	1st to 10th	Night	15% 4 13% 33% 31% 4	760
	11th to 20th	Night	16% 5% 20% 39% 19% 1	760
	21st to end	Night	17% 6% 19% 40% 17% 1	836
November	1st to 10th	Night	15% 5% 18% 43% 17% 2	764
	11th to 20th	Night	17% 8% 22% 42% 11% 1	760
	21st to end	Night	19% 7% 22% 41% 10% 1	760
December	1st to 10th	Night	25% 9% 27% 34% 6%	760
	11th to 20th	Night	21% 8% 25% 40% 7%	760
	21st to end	Night	24% 11% 24% 35% 6%	836

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