Mt Bachelor Star Party
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mt Bachelor Star Party clear sky chart from 2005-11-06 to 2026-10-29.

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	4 8% 4 9% 5% 4 4 3 5% 6% 48%	158924
	Night	3 8% 4 10% 7% 5% 4 4 5% 6% 45%	150524
Transparency	Day	31% 9% 9% 20% 20% 11%	153742
	Night	33% 11% 10% 18% 18% 10%	146715
Seeing	Day	14% 20% 28% 23% 12% 3	17228
	Night	10% 15% 25% 31% 17% 2	26199

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	5% 18% 7% 18% 10% 6% 5% 3 5% 5% 17%	4722
	11th to 20th	Day	4 9% 3 6% 7% 4 3 3 3 5% 54%	4740
	21st to end	Day	2 13% 6% 12% 6% 5% 5% 3 5% 6% 37%	5681
February	1st to 10th	Day	5% 13% 6% 14% 8% 6% 7% 5% 5% 6% 25%	1890
	11th to 20th	Day	4 14% 6% 13% 9% 6% 6% 4 5% 5% 27%	1845
	21st to end	Day	3 14% 7% 16% 10% 7% 6% 4 5% 5% 24%	1720
March	1st to 10th	Day	3 12% 7% 14% 9% 6% 5% 4 6% 7% 28%	4738
	11th to 20th	Day	3 15% 7% 16% 7% 5% 4 2 3 5% 32%	5110
	21st to end	Day	3 15% 8% 21% 10% 6% 5% 4 5% 6% 17%	5820
April	1st to 10th	Day	6% 14% 8% 13% 8% 6% 6% 5% 5% 6% 24%	2520
	11th to 20th	Day	6% 14% 7% 11% 6% 5% 5% 4 6% 6% 31%	2489
	21st to end	Day	3 14% 4 10% 7% 5% 5% 4 6% 7% 34%	2604
May	1st to 10th	Day	5% 8% 3 7% 5% 4 4 4 6% 6% 49%	8111
	11th to 20th	Day	3 8% 3 9% 6% 4 4 3 6% 7% 46%	8160
	21st to end	Day	5% 8% 2 6% 5% 4 4 4 8% 9% 44%	8992
June	1st to 10th	Day	9% 11% 4 8% 4 5% 4 4 5% 7% 41%	2940
	11th to 20th	Day	5% 8% 3 7% 5% 4 5% 4 5% 7% 47%	2940
	21st to end	Day	5% 4 2 6% 4 3 3 4 5% 6% 59%	2940
July	1st to 10th	Day	1 2 1 2 2 2 2 2 3 5% 78%	8219
	11th to 20th	Day	3 2 1 2 2 2 2 2 3 4 76%	8220
	21st to end	Day	3 2 1 2 2 2 2 2 3 5% 76%	8922
August	1st to 10th	Day	2 2 1 3 2 2 3 2 4 6% 73%	7629
	11th to 20th	Day	2 2 1 4 3 3 4 3 5% 6% 69%	7563
	21st to end	Day	6% 4 1 4 2 3 3 3 4 6% 64%	7750
September	1st to 10th	Day	2 3 1 4 3 3 3 3 4 5% 69%	2520
	11th to 20th	Day	4 6% 2 7% 5% 4 5% 3 5% 6% 53%	2520
	21st to end	Day	5% 7% 2 6% 4 4 4 3 5% 6% 54%	2237
October	1st to 10th	Day	4 6% 2 5% 3 4 3 2 4 6% 61%	3380
	11th to 20th	Day	3 7% 3 9% 7% 5% 5% 4 6% 8% 43%	3361
	21st to end	Day	4 9% 6% 15% 7% 5% 5% 4 5% 7% 33%	3522
November	1st to 10th	Day	5% 11% 5% 13% 9% 6% 6% 4 6% 6% 28%	1854
	11th to 20th	Day	3 11% 5% 15% 8% 7% 6% 6% 6% 7% 25%	1685
	21st to end	Day	2 12% 5% 13% 9% 7% 6% 4 6% 6% 29%	1680
December	1st to 10th	Day	3 6% 3 10% 7% 5% 5% 4 5% 7% 45%	2700
	11th to 20th	Day	5% 16% 8% 17% 8% 6% 6% 4 6% 6% 18%	3108
	21st to end	Day	3 15% 8% 21% 11% 6% 5% 4 5% 5% 18%	4092
January	1st to 10th	Night	4 15% 6% 17% 12% 7% 5% 5% 6% 6% 17%	8172
	11th to 20th	Night	2 8% 3 8% 7% 6% 3 3 4 5% 51%	8220
	21st to end	Night	3 13% 6% 13% 8% 5% 5% 3 4 5% 36%	8507
February	1st to 10th	Night	4 11% 5% 14% 10% 7% 6% 5% 5% 7% 26%	2730
	11th to 20th	Night	3 11% 5% 13% 9% 7% 7% 5% 6% 6% 29%	2662
	21st to end	Night	3 9% 6% 15% 11% 7% 6% 5% 6% 6% 26%	2086
March	1st to 10th	Night	3 8% 4 12% 9% 8% 7% 6% 7% 8% 28%	5372
	11th to 20th	Night	1 9% 5% 16% 13% 6% 5% 3 4 5% 32%	5110
	21st to end	Night	2 11% 6% 21% 11% 7% 6% 5% 6% 7% 18%	5397
April	1st to 10th	Night	4 11% 5% 13% 8% 6% 7% 5% 6% 7% 27%	2100
	11th to 20th	Night	3 9% 4 11% 9% 7% 6% 5% 6% 7% 34%	2079
	21st to end	Night	4 10% 5% 10% 7% 5% 6% 4 6% 7% 37%	2012
May	1st to 10th	Night	5% 7% 3 6% 3 4 3 3 4 5% 56%	4808
	11th to 20th	Night	3 7% 3 7% 5% 5% 4 4 6% 7% 50%	4700
	21st to end	Night	4 6% 3 7% 5% 3 4 3 5% 9% 52%	5181
June	1st to 10th	Night	9% 11% 4 7% 4 4 3 3 5% 8% 42%	1680
	11th to 20th	Night	4 6% 3 6% 4 4 5% 5% 6% 8% 50%	1680
	21st to end	Night	5% 5% 2 4 3 3 3 3 5% 5% 63%	1680
July	1st to 10th	Night	1 2 1 3 2 2 2 2 3 4 78%	4740
	11th to 20th	Night	3 4 1 2 1 1 1 2 2 3 79%	4740
	21st to end	Night	2 3 1 2 2 2 2 2 3 4 78%	5153
August	1st to 10th	Night	1 2 1 3 2 2 3 3 4 6% 73%	5172
	11th to 20th	Night	1 3 1 4 2 2 3 2 4 5% 72%	5292
	21st to end	Night	4 3 1 4 2 2 2 2 4 5% 69%	6498
September	1st to 10th	Night	2 2 1 3 2 2 3 2 4 6% 72%	2100
	11th to 20th	Night	3 4 2 7% 5% 4 4 3 5% 6% 58%	2100
	21st to end	Night	4 5% 2 5% 4 4 4 4 5% 6% 57%	2379
October	1st to 10th	Night	2 5% 2 5% 4 3 3 2 3 5% 65%	4040
	11th to 20th	Night	4 6% 2 8% 6% 5% 5% 4 6% 8% 47%	4017
	21st to end	Night	4 8% 4 15% 9% 6% 5% 4 6% 6% 33%	4460
November	1st to 10th	Night	4 10% 5% 14% 9% 6% 6% 5% 5% 7% 29%	2665
	11th to 20th	Night	3 11% 5% 12% 10% 8% 7% 6% 6% 7% 25%	2930
	21st to end	Night	2 7% 5% 12% 10% 7% 6% 5% 7% 7% 32%	2940
December	1st to 10th	Night	3 6% 3 9% 6% 5% 5% 4 5% 7% 48%	4700
	11th to 20th	Night	5% 18% 7% 17% 10% 6% 6% 4 5% 7% 17%	5316
	21st to end	Night	5% 16% 7% 16% 10% 6% 5% 4 5% 5% 22%	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	55% 18% 10% 10% 5% 2	4723
	11th to 20th	Day	31% 8% 7% 13% 21% 20%	4740
	21st to end	Day	40% 11% 8% 12% 17% 12%	5681
February	1st to 10th	Day	51% 12% 13% 15% 8% 1	1890
	11th to 20th	Day	50% 13% 11% 14% 9% 3	1854
	21st to end	Day	53% 13% 12% 12% 7% 3	1720
March	1st to 10th	Day	39% 16% 11% 20% 11% 3	4738
	11th to 20th	Day	46% 12% 8% 22% 10% 1	5110
	21st to end	Day	48% 21% 13% 14% 4	5820
April	1st to 10th	Day	53% 11% 12% 15% 7% 1	2520
	11th to 20th	Day	47% 10% 13% 15% 12% 2	2492
	21st to end	Day	41% 10% 15% 22% 10% 2	2604
May	1st to 10th	Day	29% 9% 9% 28% 21% 4	8111
	11th to 20th	Day	29% 11% 10% 24% 24% 2	8163
	21st to end	Day	29% 9% 18% 32% 11% 2	8994
June	1st to 10th	Day	39% 8% 13% 26% 12% 2	2940
	11th to 20th	Day	32% 7% 13% 26% 16% 4	2940
	21st to end	Day	22% 6% 12% 28% 23% 8%	2940
July	1st to 10th	Day	11% 3 4 19% 31% 32%	8151
	11th to 20th	Day	13% 3 4 10% 23% 48%	8145
	21st to end	Day	12% 3 4 22% 38% 21%	8723
August	1st to 10th	Day	12% 3 4 14% 33% 35%	6045
	11th to 20th	Day	17% 4 7% 27% 37% 9%	5962
	21st to end	Day	17% 3 4 28% 32% 16%	6077
September	1st to 10th	Day	16% 4 7% 24% 31% 18%	2520
	11th to 20th	Day	28% 7% 10% 22% 24% 9%	2520
	21st to end	Day	28% 6% 11% 24% 21% 10%	2237
October	1st to 10th	Day	24% 5% 7% 19% 34% 11%	3380
	11th to 20th	Day	32% 10% 13% 23% 18% 3	3361
	21st to end	Day	39% 15% 9% 18% 17% 2	3522
November	1st to 10th	Day	47% 11% 13% 15% 12% 1	1854
	11th to 20th	Day	51% 14% 12% 13% 8% 2	1685
	21st to end	Day	47% 11% 13% 11% 16% 2	1680
December	1st to 10th	Day	32% 11% 8% 18% 22% 10%	2700
	11th to 20th	Day	58% 14% 10% 13% 5% 1	3108
	21st to end	Day	53% 21% 9% 13% 4 1	4092
January	1st to 10th	Night	47% 23% 11% 12% 5% 2	8172
	11th to 20th	Night	31% 9% 7% 13% 18% 22%	8220
	21st to end	Night	44% 11% 8% 7% 13% 18%	8507
February	1st to 10th	Night	49% 14% 12% 14% 9% 2	2730
	11th to 20th	Night	46% 15% 15% 14% 7% 4	2664
	21st to end	Night	49% 15% 12% 13% 10% 2	2086
March	1st to 10th	Night	38% 15% 13% 20% 10% 4	5372
	11th to 20th	Night	36% 20% 12% 22% 9% 1	5110
	21st to end	Night	46% 22% 12% 15% 3	5397
April	1st to 10th	Night	46% 14% 16% 15% 7% 1	2100
	11th to 20th	Night	41% 13% 15% 19% 10% 2	2079
	21st to end	Night	41% 12% 15% 19% 11% 2	2012
May	1st to 10th	Night	26% 9% 9% 29% 24% 3	4806
	11th to 20th	Night	27% 10% 13% 27% 22% 1	4700
	21st to end	Night	25% 11% 19% 32% 11% 2	5182
June	1st to 10th	Night	37% 10% 11% 29% 11% 1	1680
	11th to 20th	Night	26% 8% 16% 29% 17% 3	1680
	21st to end	Night	20% 6% 12% 32% 24% 7%	1680
July	1st to 10th	Night	12% 3 4 21% 30% 30%	4700
	11th to 20th	Night	14% 1 4 12% 23% 46%	4692
	21st to end	Night	13% 2 3 26% 37% 19%	5040
August	1st to 10th	Night	11% 2 4 14% 34% 35%	4093
	11th to 20th	Night	15% 3 7% 25% 42% 8%	4169
	21st to end	Night	15% 2 5% 27% 36% 14%	5091
September	1st to 10th	Night	13% 4 7% 25% 35% 16%	2100
	11th to 20th	Night	23% 8% 10% 22% 27% 10%	2100
	21st to end	Night	24% 7% 11% 24% 23% 12%	2379
October	1st to 10th	Night	22% 5% 7% 20% 35% 11%	4040
	11th to 20th	Night	30% 9% 16% 24% 16% 4	4017
	21st to end	Night	36% 20% 8% 16% 17% 3	4460
November	1st to 10th	Night	45% 14% 14% 13% 12% 2	2665
	11th to 20th	Night	49% 15% 13% 13% 9% 2	2930
	21st to end	Night	42% 13% 12% 13% 15% 5%	2940
December	1st to 10th	Night	29% 11% 8% 15% 26% 11%	4700
	11th to 20th	Night	57% 16% 11% 10% 6% 1	5316
	21st to end	Night	48% 20% 12% 14% 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	28% 29% 22% 14% 6% 1	220
	11th to 20th	Day	25% 13% 23% 24% 11% 3	220
	21st to end	Day	15% 27% 24% 20% 11% 2	415
February	1st to 10th	Day	21% 26% 26% 18% 9%	430
	11th to 20th	Day	20% 35% 24% 16% 5% 1	425
	21st to end	Day	23% 28% 25% 18% 6%	441
March	1st to 10th	Day	19% 30% 29% 18% 4	540
	11th to 20th	Day	23% 25% 25% 19% 7% 1	540
	21st to end	Day	23% 29% 29% 14% 5%	594
April	1st to 10th	Day	22% 23% 28% 15% 9% 2	540
	11th to 20th	Day	19% 30% 27% 17% 5% 2	532
	21st to end	Day	13% 29% 30% 19% 8% 2	540
May	1st to 10th	Day	16% 23% 31% 20% 8% 3	543
	11th to 20th	Day	21% 22% 23% 18% 12% 3	568
	21st to end	Day	14% 17% 31% 21% 12% 4	617
June	1st to 10th	Day	12% 22% 26% 24% 12% 4	570
	11th to 20th	Day	12% 23% 32% 22% 9% 2	570
	21st to end	Day	6% 16% 27% 29% 17% 4	570
July	1st to 10th	Day	2 11% 37% 32% 14% 5%	566
	11th to 20th	Day	4 13% 37% 26% 15% 4	564
	21st to end	Day	3 12% 33% 30% 16% 5%	619
August	1st to 10th	Day	3 10% 32% 33% 17% 6%	567
	11th to 20th	Day	2 10% 28% 32% 19% 8%	557
	21st to end	Day	7% 10% 30% 32% 15% 7%	627
September	1st to 10th	Day	5% 10% 30% 33% 17% 5%	570
	11th to 20th	Day	9% 14% 25% 34% 15% 4	570
	21st to end	Day	11% 17% 25% 30% 15% 2	570
October	1st to 10th	Day	13% 18% 26% 22% 19% 2	570
	11th to 20th	Day	15% 21% 23% 23% 17% 2	570
	21st to end	Day	16% 23% 27% 17% 14% 3	548
November	1st to 10th	Day	20% 20% 27% 21% 11% 1	330
	11th to 20th	Day	17% 24% 30% 18% 8% 3	223
	21st to end	Day	15% 25% 23% 24% 10% 2	220
December	1st to 10th	Day	17% 22% 20% 22% 11% 7%	220
	11th to 20th	Day	23% 25% 28% 17% 6%	220
	21st to end	Day	22% 26% 26% 16% 7% 2	242
January	1st to 10th	Night	20% 20% 29% 18% 10% 2	840
	11th to 20th	Night	14% 19% 25% 23% 16% 2	840
	21st to end	Night	12% 17% 27% 28% 12% 3	924
February	1st to 10th	Night	13% 20% 28% 29% 9% 1	840
	11th to 20th	Night	11% 21% 29% 27% 11% 1	824
	21st to end	Night	15% 20% 32% 26% 7%	692
March	1st to 10th	Night	14% 23% 27% 27% 8% 1	840
	11th to 20th	Night	11% 24% 26% 27% 11% 1	840
	21st to end	Night	13% 24% 30% 23% 10%	924
April	1st to 10th	Night	12% 20% 29% 27% 12% 1	840
	11th to 20th	Night	9% 21% 32% 24% 12% 3	831
	21st to end	Night	9% 17% 31% 30% 12% 1	752
May	1st to 10th	Night	9% 15% 26% 30% 19% 1	453
	11th to 20th	Night	10% 14% 21% 34% 21% 1	414
	21st to end	Night	10% 7% 25% 36% 20% 2	455
June	1st to 10th	Night	12% 11% 23% 35% 18% 2	420
	11th to 20th	Night	6% 9% 30% 39% 15% 1	420
	21st to end	Night	6% 4 21% 50% 19%	420
July	1st to 10th	Night	3 2 18% 52% 24% 1	410
	11th to 20th	Night	1 2 21% 55% 20%	408
	21st to end	Night	2 2 13% 54% 28% 1	460
August	1st to 10th	Night	2 1 12% 44% 37% 3	589
	11th to 20th	Night	2 1 13% 44% 36% 5%	624
	21st to end	Night	3 4 23% 42% 27% 1	923
September	1st to 10th	Night	3 4 21% 42% 28% 3	840
	11th to 20th	Night	5% 7% 18% 36% 31% 4	840
	21st to end	Night	7% 8% 23% 34% 25% 3	840
October	1st to 10th	Night	7% 7% 30% 30% 23% 3	840
	11th to 20th	Night	9% 14% 23% 29% 21% 3	840
	21st to end	Night	13% 17% 25% 25% 15% 4	912
November	1st to 10th	Night	12% 19% 29% 27% 11% 1	820
	11th to 20th	Night	16% 22% 25% 25% 12% 1	840
	21st to end	Night	10% 21% 23% 30% 12% 3	840
December	1st to 10th	Night	14% 15% 27% 28% 15% 2	840
	11th to 20th	Night	16% 21% 25% 26% 10% 1	840
	21st to end	Night	15% 29% 26% 21% 8% 1	924

Page generated at 2026-10-26 01:37:49. Version ac07

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