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 2024-03-08.

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	18% 10% 4 7% 6% 3 4 4 5% 6% 32%	78542
	Night	18% 10% 4 8% 6% 3 4 4 4 6% 33%	81035
Transparency	Day	53% 5% 11% 17% 11% 3	78249
	Night	54% 6% 10% 16% 10% 3	80849
Seeing	Day	23% 12% 22% 25% 14% 3	13809
	Night	23% 9% 14% 31% 21% 2	22936

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% 13% 9% 4 5% 4 3 2 7%	2539
	11th to 20th	Day	34% 12% 4 9% 6% 3 4 3 4 4 16%	2586
	21st to end	Day	27% 13% 4 11% 8% 4 5% 5% 4 5% 13%	3146
February	1st to 10th	Day	26% 14% 6% 10% 9% 3 5% 5% 4 4 14%	1710
	11th to 20th	Day	24% 14% 5% 10% 7% 3 5% 5% 4 5% 17%	1665
	21st to end	Day	23% 18% 5% 11% 7% 3 4 4 3 4 17%	1465
March	1st to 10th	Day	23% 14% 6% 11% 8% 4 5% 5% 4 5% 15%	2016
	11th to 20th	Day	26% 14% 5% 10% 7% 3 4 4 4 6% 18%	1980
	21st to end	Day	26% 15% 6% 10% 9% 4 5% 4 4 5% 12%	2186
April	1st to 10th	Day	24% 15% 6% 10% 9% 4 5% 4 5% 4 15%	2160
	11th to 20th	Day	23% 13% 4 10% 7% 4 5% 5% 4 4 22%	2146
	21st to end	Day	20% 11% 4 8% 7% 4 5% 5% 6% 7% 24%	2340
May	1st to 10th	Day	16% 9% 4 8% 6% 3 4 5% 5% 7% 32%	2407
	11th to 20th	Day	17% 11% 4 8% 6% 4 5% 6% 6% 8% 27%	2477
	21st to end	Day	19% 9% 3 6% 7% 4 5% 5% 6% 8% 28%	2723
June	1st to 10th	Day	20% 9% 4 7% 5% 2 4 5% 5% 6% 31%	2520
	11th to 20th	Day	15% 8% 5% 7% 7% 4 5% 6% 6% 9% 29%	2520
	21st to end	Day	8% 5% 2 4 4 3 4 3 5% 7% 52%	2520
July	1st to 10th	Day	5% 4 2 4 3 2 4 4 5% 8% 59%	2520
	11th to 20th	Day	8% 3 2 3 3 2 2 3 4 6% 64%	2520
	21st to end	Day	4 2 1 2 2 1 2 2 3 7% 73%	2670
August	1st to 10th	Day	2 3 1 4 4 3 3 3 5% 8% 64%	2328
	11th to 20th	Day	4 3 2 3 3 2 3 3 5% 8% 64%	2298
	21st to end	Day	6% 4 2 4 4 2 4 5% 6% 8% 57%	2466
September	1st to 10th	Day	6% 3 1 3 3 2 3 3 5% 7% 64%	2160
	11th to 20th	Day	10% 6% 4 4 5% 3 4 5% 5% 8% 46%	2114
	21st to end	Day	15% 7% 3 5% 4 3 3 4 5% 5% 45%	1922
October	1st to 10th	Day	16% 7% 4 6% 5% 3 4 4 6% 5% 41%	1800
	11th to 20th	Day	16% 9% 4 7% 7% 5% 5% 4 4 7% 33%	1800
	21st to end	Day	19% 11% 4 9% 6% 3 4 4 5% 7% 28%	1980
November	1st to 10th	Day	25% 12% 6% 8% 7% 5% 5% 5% 4 6% 18%	1576
	11th to 20th	Day	26% 11% 4 8% 6% 4 6% 5% 6% 6% 18%	1520
	21st to end	Day	24% 11% 4 8% 8% 4 5% 4 5% 5% 21%	1520
December	1st to 10th	Day	23% 12% 5% 8% 7% 4 4 3 4 5% 24%	1520
	11th to 20th	Day	22% 12% 5% 11% 8% 4 6% 5% 6% 7% 13%	1928
	21st to end	Day	27% 16% 7% 13% 10% 4 5% 4 4 4 7%	2794
January	1st to 10th	Night	28% 18% 7% 13% 9% 4 4 3 3 3 9%	4406
	11th to 20th	Night	31% 15% 5% 11% 7% 3 3 3 3 3 16%	4358
	21st to end	Night	31% 15% 5% 10% 6% 3 4 3 3 4 15%	4521
February	1st to 10th	Night	20% 16% 6% 10% 8% 4 5% 5% 5% 5% 17%	2470
	11th to 20th	Night	19% 13% 5% 9% 7% 4 5% 5% 4 5% 25%	2402
	21st to end	Night	21% 14% 5% 10% 7% 4 5% 4 4 5% 21%	1989
March	1st to 10th	Night	20% 13% 5% 8% 8% 4 5% 5% 5% 6% 22%	2102
	11th to 20th	Night	21% 11% 4 9% 6% 5% 6% 5% 5% 6% 23%	1980
	21st to end	Night	24% 13% 4 9% 8% 4 5% 5% 4 5% 19%	2170
April	1st to 10th	Night	22% 13% 3 9% 9% 3 5% 4 4 6% 22%	1800
	11th to 20th	Night	17% 11% 5% 8% 6% 3 5% 5% 6% 5% 30%	1759
	21st to end	Night	16% 8% 4 8% 7% 4 5% 4 5% 7% 32%	1620
May	1st to 10th	Night	10% 8% 3 7% 8% 4 4 4 5% 6% 41%	1553
	11th to 20th	Night	13% 9% 3 8% 8% 3 4 5% 5% 7% 35%	1416
	21st to end	Night	13% 7% 3 6% 6% 3 4 5% 7% 9% 37%	1552
June	1st to 10th	Night	14% 7% 3 5% 5% 3 6% 5% 5% 6% 42%	1440
	11th to 20th	Night	10% 6% 3 5% 5% 3 4 5% 6% 9% 45%	1440
	21st to end	Night	7% 4 2 3 3 1 3 4 5% 5% 61%	1440
July	1st to 10th	Night	3 3 1 3 3 2 2 3 4 6% 71%	1440
	11th to 20th	Night	4 2 1 2 2 2 3 4 4 7% 69%	1440
	21st to end	Night	2 2 1 1 2 1 2 2 3 6% 79%	1643
August	1st to 10th	Night	2 2 2 2 2 2 4 5% 9% 69%	1611
	11th to 20th	Night	3 2 1 2 3 2 2 3 4 7% 72%	1602
	21st to end	Night	4 2 1 3 3 2 3 3 4 8% 64%	1889
September	1st to 10th	Night	5% 3 1 3 3 2 3 3 4 6% 69%	1800
	11th to 20th	Night	8% 4 2 5% 4 3 4 5% 5% 6% 55%	1844
	21st to end	Night	10% 5% 2 5% 5% 3 4 3 5% 7% 51%	2038
October	1st to 10th	Night	12% 6% 3 4 5% 3 4 4 5% 7% 48%	2160
	11th to 20th	Night	16% 6% 3 5% 7% 3 4 4 5% 8% 41%	2160
	21st to end	Night	18% 8% 4 7% 6% 3 4 4 4 5% 37%	2376
November	1st to 10th	Night	24% 10% 4 7% 6% 3 5% 5% 4 6% 25%	2496
	11th to 20th	Night	25% 11% 5% 8% 7% 4 6% 4 4 4 21%	2660
	21st to end	Night	19% 8% 4 8% 7% 4 5% 5% 6% 6% 28%	2660
December	1st to 10th	Night	22% 11% 5% 7% 7% 3 5% 5% 5% 5% 26%	2660
	11th to 20th	Night	23% 13% 5% 10% 7% 4 5% 4 5% 5% 18%	3276
	21st to end	Night	22% 13% 6% 13% 11% 5% 5% 4 3 4 14%	4862

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 7% 4 1 1	2539
	11th to 20th	Day	74% 2 9% 8% 5% 2	2586
	21st to end	Day	75% 4 8% 7% 5% 1	3146
February	1st to 10th	Day	73% 5% 9% 8% 4 1	1710
	11th to 20th	Day	69% 7% 10% 8% 5% 2	1674
	21st to end	Day	73% 4 8% 8% 5% 2	1465
March	1st to 10th	Day	71% 6% 9% 10% 4	2016
	11th to 20th	Day	69% 5% 9% 12% 5% 1	1980
	21st to end	Day	77% 5% 7% 10% 2	2186
April	1st to 10th	Day	73% 6% 8% 10% 4	2160
	11th to 20th	Day	65% 7% 8% 12% 6% 2	2149
	21st to end	Day	60% 7% 12% 14% 6% 1	2340
May	1st to 10th	Day	52% 7% 13% 20% 9%	2407
	11th to 20th	Day	55% 6% 13% 18% 7% 1	2480
	21st to end	Day	53% 8% 16% 18% 3	2724
June	1st to 10th	Day	54% 5% 15% 20% 5% 1	2520
	11th to 20th	Day	52% 7% 19% 17% 5%	2520
	21st to end	Day	32% 5% 18% 28% 13% 4	2520
July	1st to 10th	Day	25% 7% 13% 25% 24% 6%	2451
	11th to 20th	Day	23% 3 7% 28% 30% 9%	2445
	21st to end	Day	13% 4 6% 33% 36% 8%	2521
August	1st to 10th	Day	18% 6% 15% 33% 22% 6%	2312
	11th to 20th	Day	19% 5% 13% 32% 25% 6%	2298
	21st to end	Day	24% 6% 11% 31% 24% 4	2466
September	1st to 10th	Day	21% 4 11% 31% 21% 12%	2160
	11th to 20th	Day	36% 7% 13% 22% 16% 6%	2114
	21st to end	Day	41% 5% 11% 21% 16% 6%	1922
October	1st to 10th	Day	44% 6% 10% 18% 18% 4	1800
	11th to 20th	Day	51% 6% 12% 16% 14% 2	1800
	21st to end	Day	57% 5% 9% 15% 12% 2	1980
November	1st to 10th	Day	67% 6% 10% 12% 4 1	1576
	11th to 20th	Day	67% 6% 9% 9% 5% 3	1520
	21st to end	Day	64% 6% 8% 8% 11% 3	1520
December	1st to 10th	Day	64% 3 10% 12% 10% 2	1520
	11th to 20th	Day	70% 5% 13% 9% 3	1928
	21st to end	Day	77% 4 10% 5% 2 1	2794
January	1st to 10th	Night	80% 6% 7% 4 3 1	4406
	11th to 20th	Night	75% 3 6% 9% 4 3	4358
	21st to end	Night	74% 4 7% 8% 6% 2	4521
February	1st to 10th	Night	69% 7% 9% 11% 4 1	2470
	11th to 20th	Night	64% 6% 10% 12% 6% 2	2404
	21st to end	Night	67% 5% 7% 12% 7% 2	1989
March	1st to 10th	Night	65% 6% 9% 13% 7%	2102
	11th to 20th	Night	62% 7% 9% 13% 7% 1	1980
	21st to end	Night	68% 6% 11% 12% 2	2170
April	1st to 10th	Night	66% 7% 10% 11% 6%	1800
	11th to 20th	Night	56% 7% 13% 15% 5% 4	1759
	21st to end	Night	53% 7% 12% 19% 7% 2	1620
May	1st to 10th	Night	45% 6% 15% 24% 8% 2	1553
	11th to 20th	Night	50% 5% 14% 20% 7% 3	1416
	21st to end	Night	43% 10% 20% 23% 5%	1552
June	1st to 10th	Night	44% 7% 16% 28% 4 1	1440
	11th to 20th	Night	36% 9% 21% 27% 7%	1440
	21st to end	Night	25% 7% 17% 34% 12% 5%	1440
July	1st to 10th	Night	17% 9% 13% 29% 25% 8%	1400
	11th to 20th	Night	18% 7% 10% 24% 31% 11%	1392
	21st to end	Night	8% 5% 7% 32% 37% 12%	1552
August	1st to 10th	Night	14% 7% 13% 39% 20% 7%	1602
	11th to 20th	Night	15% 5% 11% 39% 22% 8%	1602
	21st to end	Night	20% 8% 8% 35% 24% 6%	1889
September	1st to 10th	Night	19% 6% 10% 28% 25% 13%	1800
	11th to 20th	Night	31% 5% 13% 25% 16% 10%	1844
	21st to end	Night	33% 6% 14% 21% 17% 10%	2038
October	1st to 10th	Night	37% 7% 9% 23% 17% 7%	2160
	11th to 20th	Night	43% 6% 12% 18% 16% 4	2160
	21st to end	Night	50% 6% 10% 15% 14% 5%	2376
November	1st to 10th	Night	61% 7% 8% 15% 8% 1	2496
	11th to 20th	Night	67% 5% 9% 9% 7% 3	2660
	21st to end	Night	57% 7% 9% 10% 12% 5%	2660
December	1st to 10th	Night	60% 6% 9% 12% 12% 1	2660
	11th to 20th	Night	69% 4 10% 11% 5% 1	3276
	21st to end	Night	74% 5% 11% 7% 3 1	4862

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	43% 17% 19% 13% 8%	180
	11th to 20th	Day	40% 13% 18% 18% 9% 1	213
	21st to end	Day	36% 14% 15% 21% 12% 2	407
February	1st to 10th	Day	38% 12% 19% 21% 9% 1	370
	11th to 20th	Day	36% 17% 23% 17% 6% 1	365
	21st to end	Day	35% 19% 21% 17% 6% 1	332
March	1st to 10th	Day	36% 18% 22% 18% 7%	449
	11th to 20th	Day	34% 14% 22% 20% 9% 1	420
	21st to end	Day	35% 20% 18% 17% 8% 1	462
April	1st to 10th	Day	35% 21% 15% 19% 8% 2	420
	11th to 20th	Day	34% 17% 21% 17% 7% 3	412
	21st to end	Day	27% 17% 25% 21% 9% 2	420
May	1st to 10th	Day	21% 16% 26% 22% 13% 3	423
	11th to 20th	Day	29% 14% 19% 23% 13% 3	448
	21st to end	Day	21% 13% 21% 25% 17% 4	485
June	1st to 10th	Day	23% 10% 25% 23% 16% 3	450
	11th to 20th	Day	18% 17% 27% 25% 12% 1	450
	21st to end	Day	8% 8% 25% 38% 19% 3	450
July	1st to 10th	Day	7% 7% 26% 37% 18% 5%	446
	11th to 20th	Day	6% 7% 29% 34% 19% 5%	444
	21st to end	Day	3 5% 24% 40% 25% 5%	487
August	1st to 10th	Day	3 5% 22% 40% 22% 8%	447
	11th to 20th	Day	4 4 18% 38% 29% 8%	437
	21st to end	Day	7% 6% 28% 32% 22% 4	495
September	1st to 10th	Day	8% 6% 28% 30% 23% 5%	450
	11th to 20th	Day	15% 8% 21% 32% 18% 6%	450
	21st to end	Day	19% 10% 22% 32% 13% 4	450
October	1st to 10th	Day	19% 11% 25% 25% 16% 4	450
	11th to 20th	Day	22% 12% 18% 24% 18% 5%	450
	21st to end	Day	30% 13% 22% 20% 10% 5%	495
November	1st to 10th	Day	29% 16% 23% 18% 12% 1	234
	11th to 20th	Day	31% 13% 23% 21% 11% 2	180
	21st to end	Day	35% 16% 18% 18% 13% 1	180
December	1st to 10th	Day	38% 12% 15% 21% 7% 7%	180
	11th to 20th	Day	37% 14% 23% 19% 7% 1	180
	21st to end	Day	37% 15% 18% 20% 10%	198
January	1st to 10th	Night	41% 11% 14% 19% 12% 1	760
	11th to 20th	Night	36% 11% 14% 21% 15% 3	760
	21st to end	Night	32% 8% 11% 31% 15% 3	836
February	1st to 10th	Night	31% 12% 14% 28% 14% 2	760
	11th to 20th	Night	29% 11% 15% 28% 15% 1	744
	21st to end	Night	33% 15% 12% 26% 13%	628
March	1st to 10th	Night	29% 13% 17% 28% 12% 1	750
	11th to 20th	Night	30% 10% 14% 29% 15% 2	720
	21st to end	Night	33% 12% 15% 24% 14% 1	792
April	1st to 10th	Night	31% 13% 12% 26% 16% 2	720
	11th to 20th	Night	25% 12% 17% 27% 16% 3	691
	21st to end	Night	20% 9% 17% 33% 19% 1	540
May	1st to 10th	Night	14% 10% 19% 34% 22% 1	473
	11th to 20th	Night	18% 6% 13% 37% 24% 3	354
	21st to end	Night	16% 7% 14% 35% 25% 2	389
June	1st to 10th	Night	18% 6% 14% 33% 28% 1	360
	11th to 20th	Night	15% 4 15% 46% 19% 1	360
	21st to end	Night	10% 4 12% 45% 28%	360
July	1st to 10th	Night	4 3 8% 47% 39%	350
	11th to 20th	Night	5% 4 11% 53% 26% 1	348
	21st to end	Night	3 2 8% 46% 39% 3	461
August	1st to 10th	Night	3 2 7% 41% 42% 5%	537
	11th to 20th	Night	4 1 7% 36% 48% 4	534
	21st to end	Night	6% 3 14% 41% 33% 3	701
September	1st to 10th	Night	7% 4 13% 40% 33% 3	720
	11th to 20th	Night	10% 6% 12% 32% 35% 6%	720
	21st to end	Night	13% 6% 11% 40% 27% 4	720
October	1st to 10th	Night	17% 6% 15% 32% 26% 4	720
	11th to 20th	Night	20% 6% 10% 34% 24% 6%	720
	21st to end	Night	25% 11% 16% 26% 18% 4	792
November	1st to 10th	Night	31% 10% 13% 31% 14% 1	740
	11th to 20th	Night	34% 12% 15% 23% 14% 1	760
	21st to end	Night	22% 12% 17% 29% 17% 3	760
December	1st to 10th	Night	30% 8% 15% 27% 18% 3	760
	11th to 20th	Night	37% 10% 15% 24% 14% 1	760
	21st to end	Night	39% 12% 14% 24% 9% 1	836

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