Marys Peak
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Marys Peak clear sky chart from 2005-11-06 to 2026-10-14.

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% 8% 3 8% 5% 4 4 3 5% 6% 41%	158797
	Night	14% 9% 3 8% 5% 4 4 3 5% 6% 39%	150371
Transparency	Day	44% 5% 12% 20% 14% 5%	153571
	Night	47% 6% 11% 18% 13% 5%	146597
Seeing	Day	22% 13% 24% 25% 13% 3	17226
	Night	23% 9% 15% 31% 20% 2	26103

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	28% 18% 6% 15% 8% 5% 4 3 3 3 8%	4722
	11th to 20th	Day	18% 7% 2 6% 3 3 4 3 6% 8% 38%	4842
	21st to end	Day	19% 11% 4 10% 6% 5% 5% 4 5% 4 27%	5843
February	1st to 10th	Day	25% 15% 5% 12% 7% 5% 5% 4 5% 4 14%	1890
	11th to 20th	Day	23% 16% 5% 12% 6% 4 4 4 4 5% 17%	1845
	21st to end	Day	23% 20% 5% 11% 5% 4 4 3 4 4 17%	1615
March	1st to 10th	Day	15% 14% 5% 12% 7% 6% 6% 5% 5% 5% 19%	4971
	11th to 20th	Day	22% 16% 5% 11% 5% 5% 4 2 3 3 24%	5110
	21st to end	Day	19% 15% 5% 14% 9% 7% 5% 4 5% 5% 11%	5640
April	1st to 10th	Day	22% 15% 5% 11% 7% 6% 5% 4 5% 5% 15%	2520
	11th to 20th	Day	21% 13% 4 10% 6% 5% 5% 3 4 4 24%	2509
	21st to end	Day	18% 11% 4 8% 6% 5% 5% 4 6% 6% 25%	2730
May	1st to 10th	Day	11% 7% 2 8% 5% 4 4 4 6% 8% 42%	7848
	11th to 20th	Day	8% 8% 3 9% 5% 5% 5% 5% 7% 8% 38%	8160
	21st to end	Day	10% 6% 2 7% 5% 5% 6% 5% 6% 8% 39%	8992
June	1st to 10th	Day	18% 10% 3 8% 5% 3 4 4 5% 6% 34%	2940
	11th to 20th	Day	13% 8% 4 8% 6% 5% 5% 5% 7% 8% 32%	2940
	21st to end	Day	8% 6% 2 5% 4 4 4 3 5% 7% 50%	2940
July	1st to 10th	Day	2 2 1 2 2 2 3 2 4 6% 74%	8219
	11th to 20th	Day	4 2 1 2 2 2 2 2 3 4 76%	8220
	21st to end	Day	3 3 1 3 2 3 3 3 4 6% 70%	8698
August	1st to 10th	Day	1 2 1 3 3 3 3 2 4 7% 71%	7547
	11th to 20th	Day	3 4 2 4 3 3 4 4 7% 9% 57%	7563
	21st to end	Day	5% 4 2 4 3 3 5% 4 6% 8% 55%	8031
September	1st to 10th	Day	6% 3 1 4 3 3 3 3 5% 7% 60%	2520
	11th to 20th	Day	9% 6% 3 5% 4 4 4 4 6% 8% 46%	2465
	21st to end	Day	14% 7% 3 6% 3 3 4 3 6% 6% 46%	2242
October	1st to 10th	Day	12% 7% 3 6% 4 3 3 3 5% 5% 50%	3380
	11th to 20th	Day	13% 8% 3 9% 6% 6% 6% 5% 6% 7% 31%	3292
	21st to end	Day	17% 11% 4 11% 6% 5% 6% 4 7% 8% 22%	3558
November	1st to 10th	Day	25% 12% 6% 10% 6% 5% 5% 3 5% 6% 18%	1745
	11th to 20th	Day	26% 12% 5% 10% 6% 5% 5% 3 6% 5% 16%	1680
	21st to end	Day	22% 13% 4 9% 8% 5% 5% 3 5% 5% 20%	1680
December	1st to 10th	Day	18% 10% 3 9% 6% 5% 5% 4 5% 6% 30%	2700
	11th to 20th	Day	25% 15% 5% 14% 7% 6% 5% 3 5% 6% 9%	3108
	21st to end	Day	27% 17% 6% 16% 8% 5% 4 2 3 3 6%	4092
January	1st to 10th	Night	27% 17% 6% 13% 7% 5% 4 3 3 3 10%	8172
	11th to 20th	Night	16% 10% 3 9% 5% 4 3 3 4 4 39%	8106
	21st to end	Night	21% 13% 4 10% 4 3 3 3 4 4 31%	8371
February	1st to 10th	Night	19% 16% 5% 12% 7% 5% 4 4 5% 5% 18%	2730
	11th to 20th	Night	19% 15% 4 10% 6% 5% 4 4 4 4 24%	2662
	21st to end	Night	21% 15% 4 10% 6% 5% 5% 3 5% 5% 21%	2191
March	1st to 10th	Night	14% 12% 5% 11% 8% 8% 7% 5% 6% 5% 21%	5141
	11th to 20th	Night	17% 13% 5% 12% 5% 5% 4 3 3 4 28%	5110
	21st to end	Night	19% 17% 5% 12% 7% 6% 5% 3 5% 6% 16%	5576
April	1st to 10th	Night	20% 14% 3 10% 7% 5% 5% 4 4 6% 22%	2100
	11th to 20th	Night	15% 12% 4 8% 5% 5% 4 4 6% 6% 31%	2055
	21st to end	Night	15% 9% 4 9% 6% 5% 5% 4 5% 7% 33%	1890
May	1st to 10th	Night	11% 6% 2 5% 4 4 3 3 5% 7% 49%	5088
	11th to 20th	Night	8% 8% 3 9% 7% 6% 4 3 5% 6% 40%	4700
	21st to end	Night	7% 7% 2 7% 5% 5% 4 4 7% 9% 44%	5181
June	1st to 10th	Night	14% 8% 2 5% 5% 5% 5% 4 5% 5% 43%	1680
	11th to 20th	Night	9% 5% 2 5% 4 4 4 4 6% 8% 48%	1680
	21st to end	Night	7% 5% 2 4 3 3 4 3 6% 5% 58%	1680
July	1st to 10th	Night	1 1 1 1 2 3 3 4 6% 78%	4740
	11th to 20th	Night	2 2 1 2 2 2 2 2 3 5% 78%	4740
	21st to end	Night	2 2 1 3 2 2 3 3 4 6% 71%	5385
August	1st to 10th	Night	2 2 1 3 3 3 3 3 4 6% 71%	5275
	11th to 20th	Night	4 2 1 4 3 4 5% 4 6% 8% 58%	5292
	21st to end	Night	3 3 1 4 3 3 4 3 5% 7% 63%	6202
September	1st to 10th	Night	4 3 1 3 3 3 3 3 5% 6% 65%	2100
	11th to 20th	Night	7% 4 2 5% 4 4 4 4 5% 6% 55%	2152
	21st to end	Night	9% 5% 2 6% 4 3 4 3 6% 7% 52%	2378
October	1st to 10th	Night	7% 4 2 5% 4 4 4 3 5% 7% 54%	4040
	11th to 20th	Night	13% 6% 3 7% 6% 4 5% 4 6% 8% 36%	3933
	21st to end	Night	16% 11% 4 10% 6% 5% 5% 3 5% 5% 28%	4253
November	1st to 10th	Night	23% 11% 3 9% 5% 5% 5% 4 4 6% 24%	2766
	11th to 20th	Night	25% 13% 4 10% 6% 5% 5% 3 4 4 20%	2940
	21st to end	Night	19% 10% 3 9% 6% 5% 5% 5% 6% 6% 27%	2940
December	1st to 10th	Night	14% 9% 3 8% 6% 4 5% 4 5% 6% 35%	4700
	11th to 20th	Night	27% 15% 6% 12% 7% 5% 4 3 4 4 12%	5316
	21st to end	Night	25% 14% 5% 15% 8% 6% 5% 3 4 3 12%	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	82% 4 6% 5% 3 1	4723
	11th to 20th	Day	43% 3 7% 15% 19% 12%	4842
	21st to end	Day	61% 3 6% 10% 14% 6%	5843
February	1st to 10th	Day	72% 5% 9% 8% 4 1	1890
	11th to 20th	Day	70% 6% 9% 8% 5% 2	1854
	21st to end	Day	71% 4 8% 8% 7% 2	1615
March	1st to 10th	Day	63% 7% 13% 12% 4	4971
	11th to 20th	Day	66% 4 6% 16% 8% 1	5110
	21st to end	Day	75% 5% 9% 7% 3	5640
April	1st to 10th	Day	70% 6% 9% 11% 3	2520
	11th to 20th	Day	63% 6% 9% 13% 7% 2	2512
	21st to end	Day	58% 7% 12% 16% 6% 1	2730
May	1st to 10th	Day	40% 6% 10% 32% 12%	7848
	11th to 20th	Day	40% 9% 19% 24% 8% 1	8163
	21st to end	Day	40% 8% 26% 22% 4	8994
June	1st to 10th	Day	51% 5% 14% 21% 7% 1	2940
	11th to 20th	Day	49% 6% 17% 20% 7% 1	2940
	21st to end	Day	33% 6% 17% 27% 14% 3	2940
July	1st to 10th	Day	12% 4 12% 32% 22% 17%	8151
	11th to 20th	Day	14% 2 5% 17% 43% 19%	8145
	21st to end	Day	15% 5% 12% 36% 27% 4	8502
August	1st to 10th	Day	13% 4 8% 23% 34% 19%	5976
	11th to 20th	Day	22% 7% 16% 37% 15% 3	5962
	21st to end	Day	24% 6% 14% 33% 18% 6%	6298
September	1st to 10th	Day	23% 5% 11% 30% 19% 11%	2520
	11th to 20th	Day	35% 7% 14% 22% 16% 5%	2465
	21st to end	Day	39% 5% 11% 22% 17% 5%	2242
October	1st to 10th	Day	36% 5% 6% 19% 26% 7%	3380
	11th to 20th	Day	50% 7% 16% 16% 11% 1	3292
	21st to end	Day	58% 6% 9% 16% 10% 1	3558
November	1st to 10th	Day	67% 5% 11% 12% 4 1	1745
	11th to 20th	Day	69% 6% 9% 9% 5% 3	1680
	21st to end	Day	64% 6% 9% 9% 10% 3	1680
December	1st to 10th	Day	52% 5% 8% 12% 19% 4	2700
	11th to 20th	Day	76% 5% 10% 7% 2	3108
	21st to end	Day	81% 4 8% 5% 2	4092
January	1st to 10th	Night	78% 5% 6% 6% 3 1	8172
	11th to 20th	Night	47% 4 6% 13% 16% 13%	8106
	21st to end	Night	58% 3 5% 9% 18% 8%	8371
February	1st to 10th	Night	68% 6% 9% 11% 4 1	2730
	11th to 20th	Night	65% 6% 9% 12% 6% 2	2664
	21st to end	Night	66% 5% 8% 11% 8% 2	2191
March	1st to 10th	Night	62% 7% 11% 13% 5% 2	5141
	11th to 20th	Night	62% 6% 8% 15% 8% 1	5110
	21st to end	Night	70% 6% 12% 10% 2	5576
April	1st to 10th	Night	64% 7% 11% 13% 5%	2100
	11th to 20th	Night	54% 7% 14% 17% 6% 3	2055
	21st to end	Night	51% 8% 12% 20% 7% 2	1890
May	1st to 10th	Night	35% 6% 15% 30% 14% 1	5086
	11th to 20th	Night	42% 11% 14% 25% 7% 2	4700
	21st to end	Night	36% 8% 30% 22% 4	5182
June	1st to 10th	Night	43% 7% 15% 28% 6% 1	1680
	11th to 20th	Night	33% 8% 20% 28% 10% 1	1680
	21st to end	Night	26% 8% 16% 32% 13% 4	1680
July	1st to 10th	Night	8% 7% 12% 32% 23% 19%	4700
	11th to 20th	Night	12% 4 8% 16% 34% 26%	4692
	21st to end	Night	14% 6% 14% 33% 27% 6%	5269
August	1st to 10th	Night	9% 5% 8% 22% 36% 21%	4169
	11th to 20th	Night	18% 10% 18% 37% 14% 3	4169
	21st to end	Night	18% 8% 12% 36% 20% 5%	4860
September	1st to 10th	Night	21% 6% 11% 27% 23% 12%	2100
	11th to 20th	Night	31% 5% 14% 25% 17% 8%	2152
	21st to end	Night	31% 6% 14% 24% 16% 8%	2378
October	1st to 10th	Night	28% 7% 8% 26% 25% 6%	4040
	11th to 20th	Night	44% 7% 17% 19% 11% 2	3933
	21st to end	Night	57% 6% 8% 17% 8% 3	4253
November	1st to 10th	Night	61% 7% 8% 14% 8% 1	2766
	11th to 20th	Night	68% 5% 9% 9% 7% 3	2940
	21st to end	Night	57% 7% 9% 11% 11% 5%	2940
December	1st to 10th	Night	47% 6% 9% 14% 20% 3	4700
	11th to 20th	Night	77% 5% 7% 8% 3	5316
	21st to end	Night	77% 5% 10% 6% 2	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	44% 17% 20% 12% 7%	220
	11th to 20th	Day	33% 12% 22% 21% 11% 1	257
	21st to end	Day	35% 14% 18% 20% 12% 2	473
February	1st to 10th	Day	37% 14% 19% 21% 8% 1	430
	11th to 20th	Day	36% 18% 24% 16% 5% 1	425
	21st to end	Day	36% 18% 22% 17% 6% 1	386
March	1st to 10th	Day	36% 18% 24% 17% 6%	540
	11th to 20th	Day	36% 14% 22% 18% 9% 2	540
	21st to end	Day	34% 20% 22% 16% 7% 1	594
April	1st to 10th	Day	32% 19% 18% 19% 9% 2	540
	11th to 20th	Day	31% 19% 23% 17% 7% 3	532
	21st to end	Day	25% 18% 26% 21% 8% 2	540
May	1st to 10th	Day	20% 15% 28% 21% 13% 2	543
	11th to 20th	Day	29% 14% 20% 23% 11% 3	568
	21st to end	Day	19% 13% 25% 24% 16% 4	617
June	1st to 10th	Day	23% 10% 26% 23% 14% 3	570
	11th to 20th	Day	15% 18% 29% 26% 11% 1	570
	21st to end	Day	9% 9% 26% 38% 16% 2	570
July	1st to 10th	Day	6% 6% 27% 38% 19% 4	566
	11th to 20th	Day	5% 8% 31% 34% 18% 4	564
	21st to end	Day	3 6% 26% 37% 23% 5%	619
August	1st to 10th	Day	3 5% 25% 38% 21% 8%	567
	11th to 20th	Day	4 5% 21% 36% 27% 7%	557
	21st to end	Day	8% 7% 28% 31% 21% 5%	627
September	1st to 10th	Day	8% 6% 28% 31% 22% 5%	570
	11th to 20th	Day	14% 9% 24% 31% 17% 6%	570
	21st to end	Day	18% 10% 24% 32% 12% 3	570
October	1st to 10th	Day	17% 11% 26% 24% 18% 3	570
	11th to 20th	Day	22% 13% 20% 24% 16% 4	543
	21st to end	Day	30% 15% 23% 19% 9% 4	583
November	1st to 10th	Day	33% 16% 22% 18% 11% 1	283
	11th to 20th	Day	34% 14% 22% 19% 9% 2	220
	21st to end	Day	34% 15% 18% 20% 13%	220
December	1st to 10th	Day	40% 10% 15% 21% 8% 6%	220
	11th to 20th	Day	40% 15% 21% 16% 6%	220
	21st to end	Day	39% 16% 19% 17% 9%	242
January	1st to 10th	Night	42% 11% 15% 19% 11% 1	840
	11th to 20th	Night	32% 11% 15% 22% 16% 3	840
	21st to end	Night	31% 9% 11% 31% 15% 3	924
February	1st to 10th	Night	29% 13% 15% 28% 13% 2	840
	11th to 20th	Night	30% 12% 17% 27% 14% 1	824
	21st to end	Night	35% 14% 13% 26% 12%	692
March	1st to 10th	Night	30% 13% 18% 28% 10% 1	840
	11th to 20th	Night	31% 10% 16% 26% 14% 2	840
	21st to end	Night	33% 13% 16% 23% 13% 1	924
April	1st to 10th	Night	30% 13% 13% 27% 16% 2	840
	11th to 20th	Night	23% 13% 19% 29% 15% 2	807
	21st to end	Night	19% 10% 19% 33% 17% 1	630
May	1st to 10th	Night	14% 9% 20% 35% 21% 1	551
	11th to 20th	Night	17% 8% 15% 36% 21% 2	414
	21st to end	Night	16% 8% 16% 35% 24% 2	455
June	1st to 10th	Night	18% 6% 16% 33% 25% 1	420
	11th to 20th	Night	13% 5% 18% 46% 16% 1	420
	21st to end	Night	10% 6% 13% 45% 25%	420
July	1st to 10th	Night	4 2 11% 46% 36%	410
	11th to 20th	Night	4 3 14% 54% 23% 1	408
	21st to end	Night	2 2 11% 46% 36% 3	539
August	1st to 10th	Night	3 2 11% 41% 38% 5%	627
	11th to 20th	Night	5% 1 8% 38% 45% 3	624
	21st to end	Night	5% 4 17% 42% 30% 3	818
September	1st to 10th	Night	7% 5% 15% 41% 30% 3	840
	11th to 20th	Night	9% 7% 14% 34% 32% 5%	840
	21st to end	Night	13% 6% 13% 40% 24% 3	840
October	1st to 10th	Night	16% 6% 17% 32% 26% 3	840
	11th to 20th	Night	19% 8% 12% 33% 22% 5%	812
	21st to end	Night	25% 11% 17% 26% 17% 4	880
November	1st to 10th	Night	31% 10% 13% 30% 14% 1	820
	11th to 20th	Night	35% 13% 16% 22% 13% 1	840
	21st to end	Night	23% 12% 17% 29% 16% 3	840
December	1st to 10th	Night	30% 8% 14% 28% 18% 2	840
	11th to 20th	Night	38% 11% 15% 22% 13% 1	840
	21st to end	Night	39% 13% 15% 23% 9% 1	924

Page generated at 2026-10-11 02:06:28. Version ac07

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