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 2025-06-10.

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	15% 10% 3 8% 5% 4 4 3 5% 6% 36%	123869
	Night	16% 10% 3 9% 5% 4 4 3 4 5% 35%	123187
Transparency	Day	49% 5% 11% 17% 13% 4	123617
	Night	51% 6% 11% 17% 12% 4	123026
Seeing	Day	23% 13% 23% 25% 14% 3	15453
	Night	23% 9% 14% 31% 20% 2	24475

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	31% 18% 5% 14% 7% 4 4 2 3 3 8%	3639
	11th to 20th	Day	23% 9% 3 8% 4 4 4 3 6% 7% 28%	3714
	21st to end	Day	20% 10% 3 10% 5% 5% 5% 4 4 4 29%	4510
February	1st to 10th	Day	25% 16% 6% 12% 7% 5% 5% 4 4 4 13%	1800
	11th to 20th	Day	23% 16% 5% 12% 6% 4 4 4 4 5% 17%	1755
	21st to end	Day	22% 20% 5% 12% 5% 4 4 3 4 4 17%	1540
March	1st to 10th	Day	15% 14% 5% 12% 7% 6% 6% 5% 5% 5% 19%	4863
	11th to 20th	Day	22% 16% 5% 11% 5% 5% 4 2 3 3 25%	5000
	21st to end	Day	19% 15% 5% 14% 9% 7% 5% 4 5% 5% 11%	5519
April	1st to 10th	Day	22% 16% 6% 11% 7% 6% 4 3 4 5% 15%	2400
	11th to 20th	Day	21% 13% 4 10% 6% 5% 5% 3 4 4 25%	2388
	21st to end	Day	19% 11% 4 9% 7% 5% 5% 4 6% 6% 24%	2600
May	1st to 10th	Day	14% 8% 3 8% 5% 4 4 3 5% 6% 39%	6051
	11th to 20th	Day	10% 9% 3 9% 5% 5% 5% 4 6% 7% 37%	6277
	21st to end	Day	11% 7% 3 7% 6% 5% 6% 5% 7% 8% 35%	6902
June	1st to 10th	Day	19% 10% 3 8% 4 3 4 4 5% 6% 34%	2789
	11th to 20th	Day	14% 9% 4 8% 6% 5% 5% 5% 7% 8% 30%	2660
	21st to end	Day	8% 6% 2 5% 4 4 4 3 5% 7% 52%	2660
July	1st to 10th	Day	3 2 1 3 2 2 3 2 3 5% 74%	4420
	11th to 20th	Day	4 3 1 2 2 2 2 2 4 4 74%	4420
	21st to end	Day	3 3 1 2 2 2 2 2 3 6% 75%	4670
August	1st to 10th	Day	2 3 1 4 3 3 3 3 4 7% 68%	4091
	11th to 20th	Day	5% 4 2 5% 3 3 4 4 7% 9% 53%	4026
	21st to end	Day	7% 5% 2 4 3 4 4 4 5% 7% 56%	4335
September	1st to 10th	Day	5% 3 1 4 3 3 3 3 5% 7% 63%	2280
	11th to 20th	Day	10% 6% 4 5% 4 4 4 4 6% 8% 45%	2231
	21st to end	Day	14% 7% 3 6% 3 3 4 3 5% 6% 46%	2028
October	1st to 10th	Day	12% 7% 3 6% 4 3 3 3 5% 4 50%	3180
	11th to 20th	Day	13% 8% 3 9% 6% 6% 6% 5% 6% 7% 30%	3161
	21st to end	Day	17% 11% 4 11% 6% 5% 6% 4 6% 8% 22%	3448
November	1st to 10th	Day	24% 12% 6% 10% 6% 5% 5% 3 5% 6% 18%	1660
	11th to 20th	Day	26% 12% 5% 9% 5% 6% 5% 4 6% 5% 17%	1600
	21st to end	Day	23% 13% 4 10% 8% 5% 5% 3 5% 5% 21%	1600
December	1st to 10th	Day	17% 9% 3 9% 6% 5% 5% 4 5% 6% 30%	2620
	11th to 20th	Day	25% 15% 5% 14% 7% 6% 5% 3 5% 6% 9%	3028
	21st to end	Day	27% 17% 6% 17% 9% 5% 4 2 3 3 6%	4004
January	1st to 10th	Night	30% 18% 6% 13% 6% 5% 4 2 3 3 10%	6306
	11th to 20th	Night	21% 12% 4 10% 5% 4 3 3 4 4 29%	6232
	21st to end	Night	23% 12% 4 9% 4 3 3 2 3 4 33%	6468
February	1st to 10th	Night	19% 17% 5% 11% 7% 5% 4 5% 5% 5% 17%	2600
	11th to 20th	Night	20% 14% 4 10% 6% 5% 4 4 4 4 24%	2532
	21st to end	Night	20% 15% 4 10% 6% 5% 5% 3 5% 5% 21%	2090
March	1st to 10th	Night	14% 12% 5% 11% 8% 8% 7% 5% 6% 5% 21%	5029
	11th to 20th	Night	17% 13% 5% 12% 5% 6% 4 3 4 4 29%	5000
	21st to end	Night	19% 17% 5% 12% 7% 6% 5% 3 5% 6% 15%	5456
April	1st to 10th	Night	20% 14% 3 10% 7% 5% 5% 4 4 6% 22%	2000
	11th to 20th	Night	15% 12% 4 8% 5% 4 5% 4 6% 6% 32%	1956
	21st to end	Night	15% 9% 4 9% 6% 5% 5% 4 5% 7% 32%	1800
May	1st to 10th	Night	15% 7% 2 6% 4 4 3 2 4 5% 48%	3921
	11th to 20th	Night	8% 8% 3 9% 7% 6% 4 3 5% 5% 42%	3616
	21st to end	Night	8% 8% 2 7% 5% 5% 4 4 6% 9% 42%	3972
June	1st to 10th	Night	14% 8% 2 5% 5% 5% 5% 4 5% 5% 43%	1595
	11th to 20th	Night	9% 6% 2 6% 4 4 4 4 6% 8% 46%	1520
	21st to end	Night	6% 5% 2 4 3 2 4 3 6% 5% 60%	1520
July	1st to 10th	Night	2 2 2 1 1 2 1 3 4 82%	2540
	11th to 20th	Night	3 2 1 2 2 2 2 2 3 5% 77%	2540
	21st to end	Night	2 2 1 2 2 1 2 2 3 6% 77%	2881
August	1st to 10th	Night	1 2 2 2 3 2 3 4 7% 73%	2848
	11th to 20th	Night	3 2 1 4 3 4 5% 4 6% 8% 60%	2812
	21st to end	Night	5% 3 2 5% 3 3 3 3 4 6% 63%	3337
September	1st to 10th	Night	4 3 1 3 3 3 2 3 5% 6% 68%	1900
	11th to 20th	Night	8% 5% 2 5% 4 4 4 4 5% 6% 54%	1947
	21st to end	Night	9% 5% 2 6% 4 3 4 3 5% 7% 52%	2152
October	1st to 10th	Night	7% 4 2 5% 4 4 4 3 5% 7% 54%	3800
	11th to 20th	Night	13% 6% 3 7% 6% 4 6% 4 6% 9% 36%	3777
	21st to end	Night	17% 11% 4 10% 6% 5% 5% 3 5% 5% 28%	4121
November	1st to 10th	Night	23% 11% 3 9% 5% 5% 5% 4 4 6% 25%	2631
	11th to 20th	Night	25% 12% 4 10% 6% 5% 5% 3 4 4 20%	2800
	21st to end	Night	19% 9% 3 9% 6% 6% 5% 4 6% 6% 27%	2800
December	1st to 10th	Night	14% 9% 3 8% 6% 4 5% 4 5% 6% 36%	4560
	11th to 20th	Night	27% 15% 6% 12% 7% 5% 4 3 4 4 12%	5176
	21st to end	Night	25% 14% 5% 15% 8% 6% 5% 3 4 3 12%	6952

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% 3 6% 5% 3 1	3639
	11th to 20th	Day	55% 3 8% 17% 15% 2	3714
	21st to end	Day	59% 3 7% 10% 15% 6%	4510
February	1st to 10th	Day	73% 5% 9% 8% 4 1	1800
	11th to 20th	Day	69% 6% 9% 8% 5% 2	1764
	21st to end	Day	72% 4 8% 8% 6% 2	1540
March	1st to 10th	Day	63% 7% 13% 12% 4	4863
	11th to 20th	Day	66% 4 6% 16% 8% 1	5000
	21st to end	Day	75% 6% 9% 7% 3	5519
April	1st to 10th	Day	72% 6% 8% 11% 4	2400
	11th to 20th	Day	62% 6% 9% 14% 7% 2	2391
	21st to end	Day	59% 7% 12% 15% 6% 1	2600
May	1st to 10th	Day	46% 6% 9% 25% 14%	6051
	11th to 20th	Day	44% 8% 15% 22% 10% 1	6280
	21st to end	Day	44% 8% 27% 18% 3	6904
June	1st to 10th	Day	51% 5% 15% 21% 7% 1	2789
	11th to 20th	Day	51% 7% 18% 18% 5%	2660
	21st to end	Day	32% 5% 18% 28% 13% 4	2660
July	1st to 10th	Day	15% 4 8% 15% 26% 32%	4351
	11th to 20th	Day	16% 3 5% 19% 35% 22%	4345
	21st to end	Day	13% 4 9% 28% 39% 8%	4522
August	1st to 10th	Day	16% 4 10% 27% 30% 12%	4076
	11th to 20th	Day	26% 8% 16% 31% 16% 3	4065
	21st to end	Day	27% 6% 12% 25% 22% 8%	4334
September	1st to 10th	Day	21% 4 11% 31% 21% 12%	2280
	11th to 20th	Day	36% 7% 14% 21% 16% 6%	2231
	21st to end	Day	40% 5% 11% 23% 16% 6%	2028
October	1st to 10th	Day	36% 5% 6% 19% 26% 7%	3180
	11th to 20th	Day	51% 7% 16% 15% 11% 1	3161
	21st to end	Day	57% 6% 9% 16% 10% 1	3448
November	1st to 10th	Day	67% 6% 11% 12% 4 1	1660
	11th to 20th	Day	68% 6% 9% 9% 5% 3	1600
	21st to end	Day	64% 6% 8% 9% 11% 3	1600
December	1st to 10th	Day	51% 4 8% 13% 20% 4	2620
	11th to 20th	Day	76% 5% 10% 7% 2	3028
	21st to end	Day	82% 4 8% 4 2	4004
January	1st to 10th	Night	79% 5% 6% 5% 4 1	6306
	11th to 20th	Night	57% 5% 7% 16% 13% 2	6232
	21st to end	Night	57% 3 5% 10% 17% 7%	6468
February	1st to 10th	Night	69% 7% 8% 11% 4 1	2600
	11th to 20th	Night	65% 6% 9% 11% 6% 2	2534
	21st to end	Night	66% 5% 8% 12% 7% 2	2090
March	1st to 10th	Night	62% 7% 11% 13% 5% 2	5029
	11th to 20th	Night	62% 6% 8% 16% 8% 1	5000
	21st to end	Night	70% 6% 12% 10% 1	5456
April	1st to 10th	Night	65% 7% 11% 12% 5%	2000
	11th to 20th	Night	53% 7% 13% 17% 6% 3	1956
	21st to end	Night	53% 8% 12% 19% 7% 2	1800
May	1st to 10th	Night	39% 5% 11% 29% 16% 1	3918
	11th to 20th	Night	42% 11% 12% 24% 9% 3	3616
	21st to end	Night	38% 8% 31% 19% 3	3972
June	1st to 10th	Night	43% 6% 16% 29% 5% 1	1595
	11th to 20th	Night	35% 9% 21% 27% 8% 1	1520
	21st to end	Night	25% 8% 17% 34% 12% 5%	1520
July	1st to 10th	Night	10% 6% 8% 18% 24% 35%	2500
	11th to 20th	Night	13% 4 7% 18% 26% 32%	2492
	21st to end	Night	10% 6% 10% 27% 37% 10%	2791
August	1st to 10th	Night	11% 5% 10% 30% 30% 14%	2839
	11th to 20th	Night	19% 10% 17% 35% 14% 5%	2839
	21st to end	Night	21% 7% 9% 31% 24% 8%	3337
September	1st to 10th	Night	19% 6% 10% 28% 25% 13%	1900
	11th to 20th	Night	32% 5% 13% 25% 15% 9%	1947
	21st to end	Night	32% 6% 14% 23% 16% 9%	2152
October	1st to 10th	Night	28% 7% 8% 26% 25% 6%	3800
	11th to 20th	Night	44% 7% 17% 19% 10% 2	3777
	21st to end	Night	57% 7% 9% 17% 8% 3	4121
November	1st to 10th	Night	60% 8% 8% 14% 8% 1	2631
	11th to 20th	Night	68% 5% 9% 9% 7% 3	2800
	21st to end	Night	57% 7% 9% 11% 11% 5%	2800
December	1st to 10th	Night	46% 7% 9% 15% 21% 4	4560
	11th to 20th	Night	77% 5% 7% 8% 3	5176
	21st to end	Night	77% 5% 10% 6% 2 1	6952

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% 18% 19% 13% 8%	200
	11th to 20th	Day	36% 14% 21% 18% 10% 1	235
	21st to end	Day	35% 14% 16% 21% 13% 2	440
February	1st to 10th	Day	38% 14% 19% 20% 9% 1	400
	11th to 20th	Day	37% 18% 22% 16% 6% 1	395
	21st to end	Day	36% 18% 22% 17% 6% 1	359
March	1st to 10th	Day	36% 17% 24% 18% 6%	500
	11th to 20th	Day	35% 13% 22% 19% 9% 2	500
	21st to end	Day	35% 19% 21% 17% 7% 1	550
April	1st to 10th	Day	34% 20% 18% 19% 8% 2	500
	11th to 20th	Day	31% 18% 24% 18% 7% 3	492
	21st to end	Day	26% 18% 25% 22% 7% 2	500
May	1st to 10th	Day	21% 16% 27% 20% 13% 2	503
	11th to 20th	Day	28% 14% 19% 23% 12% 4	528
	21st to end	Day	19% 13% 24% 24% 16% 4	573
June	1st to 10th	Day	23% 10% 25% 24% 15% 3	527
	11th to 20th	Day	18% 18% 27% 26% 11% 1	490
	21st to end	Day	8% 9% 25% 38% 18% 3	490
July	1st to 10th	Day	7% 7% 27% 37% 18% 5%	486
	11th to 20th	Day	5% 7% 29% 35% 19% 5%	484
	21st to end	Day	3 5% 25% 38% 24% 5%	531
August	1st to 10th	Day	3 5% 24% 40% 22% 7%	487
	11th to 20th	Day	4 4 20% 36% 28% 8%	477
	21st to end	Day	8% 7% 27% 31% 22% 5%	539
September	1st to 10th	Day	8% 5% 27% 31% 23% 5%	490
	11th to 20th	Day	14% 8% 23% 32% 17% 5%	490
	21st to end	Day	19% 10% 23% 32% 12% 4	490
October	1st to 10th	Day	18% 12% 26% 24% 17% 4	490
	11th to 20th	Day	21% 12% 20% 24% 17% 4	490
	21st to end	Day	31% 14% 23% 19% 9% 4	539
November	1st to 10th	Day	31% 16% 22% 18% 12% 2	258
	11th to 20th	Day	34% 15% 21% 20% 10% 2	200
	21st to end	Day	34% 16% 17% 19% 14% 1	200
December	1st to 10th	Day	37% 11% 15% 23% 9% 7%	200
	11th to 20th	Day	40% 14% 23% 17% 7% 1	200
	21st to end	Day	40% 15% 17% 18% 9%	220
January	1st to 10th	Night	42% 11% 15% 19% 12% 1	800
	11th to 20th	Night	34% 12% 15% 22% 15% 3	800
	21st to end	Night	32% 8% 11% 31% 15% 3	880
February	1st to 10th	Night	30% 13% 14% 28% 13% 2	800
	11th to 20th	Night	30% 12% 16% 27% 14% 1	784
	21st to end	Night	34% 15% 12% 27% 13%	660
March	1st to 10th	Night	29% 13% 17% 29% 11% 1	800
	11th to 20th	Night	31% 11% 15% 28% 15% 2	800
	21st to end	Night	34% 13% 16% 23% 14% 1	880
April	1st to 10th	Night	30% 13% 13% 26% 16% 2	800
	11th to 20th	Night	23% 13% 19% 28% 15% 2	768
	21st to end	Night	20% 10% 19% 33% 18% 1	600
May	1st to 10th	Night	15% 9% 19% 35% 21% 1	525
	11th to 20th	Night	18% 7% 15% 36% 22% 2	394
	21st to end	Night	16% 8% 15% 35% 24% 2	433
June	1st to 10th	Night	18% 6% 15% 33% 27% 2	399
	11th to 20th	Night	14% 5% 16% 46% 18% 1	380
	21st to end	Night	10% 4 12% 46% 27%	380
July	1st to 10th	Night	4 3 10% 46% 37%	370
	11th to 20th	Night	5% 4 11% 55% 25% 1	368
	21st to end	Night	2 2 9% 46% 38% 3	487
August	1st to 10th	Night	2 2 9% 41% 40% 5%	567
	11th to 20th	Night	4 1 7% 36% 47% 4	564
	21st to end	Night	6% 4 15% 40% 32% 3	740
September	1st to 10th	Night	6% 4 13% 41% 32% 3	760
	11th to 20th	Night	10% 6% 13% 32% 33% 6%	760
	21st to end	Night	13% 6% 12% 40% 26% 4	760
October	1st to 10th	Night	16% 6% 16% 31% 26% 4	760
	11th to 20th	Night	20% 7% 11% 34% 23% 6%	760
	21st to end	Night	25% 11% 17% 26% 17% 4	836
November	1st to 10th	Night	30% 10% 14% 31% 14% 1	780
	11th to 20th	Night	35% 13% 15% 22% 13% 1	800
	21st to end	Night	23% 12% 17% 29% 17% 3	800
December	1st to 10th	Night	29% 8% 15% 28% 19% 3	800
	11th to 20th	Night	38% 11% 15% 23% 13% 1	800
	21st to end	Night	40% 13% 14% 23% 8% 1	880

Page generated at 2025-06-07 07:28:20. Version ac07

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