Manastash Ridge Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Manastash Ridge Observatory clear sky chart from 2005-11-06 to 2025-12-03.

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	6% 8% 3 6% 4 4 4 4 5% 7% 50%	131137
	Night	7% 8% 3 6% 4 4 4 4 5% 7% 48%	128272
Transparency	Day	31% 7% 12% 24% 19% 7%	130862
	Night	33% 8% 14% 25% 16% 4	128124
Seeing	Day	12% 19% 31% 25% 11% 2	15724
	Night	10% 13% 33% 29% 13% 2	24710

By Month

Percentage Cloud Cover NW (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	11% 13% 6% 11% 6% 5% 5% 5% 6% 7% 25%	3639
	11th to 20th	Day	8% 12% 3 6% 4 3 4 4 6% 7% 44%	3616
	21st to end	Day	14% 14% 4 7% 4 4 4 4 5% 6% 35%	4004
February	1st to 10th	Day	8% 12% 5% 10% 6% 5% 5% 5% 5% 8% 31%	1795
	11th to 20th	Day	7% 12% 4 9% 5% 5% 4 4 8% 7% 36%	1755
	21st to end	Day	6% 13% 4 9% 6% 5% 6% 5% 6% 8% 33%	1633
March	1st to 10th	Day	3 9% 4 9% 6% 6% 7% 6% 8% 8% 34%	4518
	11th to 20th	Day	5% 12% 4 9% 6% 4 4 4 5% 6% 42%	4929
	21st to end	Day	8% 13% 4 11% 7% 6% 6% 5% 7% 8% 25%	5793
April	1st to 10th	Day	7% 12% 3 9% 6% 6% 6% 5% 7% 8% 30%	2400
	11th to 20th	Day	6% 11% 4 9% 5% 4 5% 4 5% 7% 40%	2372
	21st to end	Day	6% 8% 3 6% 5% 4 5% 4 7% 8% 43%	2616
May	1st to 10th	Day	6% 6% 2 5% 4 4 4 4 5% 6% 55%	6320
	11th to 20th	Day	6% 7% 2 6% 4 3 4 3 5% 7% 52%	6277
	21st to end	Day	9% 7% 2 6% 5% 4 4 4 5% 8% 46%	6903
June	1st to 10th	Day	8% 6% 2 6% 5% 5% 5% 5% 6% 7% 44%	2800
	11th to 20th	Day	5% 4 2 5% 4 4 5% 4 6% 8% 52%	2800
	21st to end	Day	4 4 1 4 3 4 3 3 6% 7% 61%	2800
July	1st to 10th	Day	1 2 1 2 1 2 2 2 3 4 80%	6320
	11th to 20th	Day	2 2 1 2 1 2 2 2 3 3 82%	6320
	21st to end	Day	2 3 1 3 2 3 3 2 3 5% 73%	6874
August	1st to 10th	Day	1 2 1 3 2 3 2 2 5% 6% 73%	4541
	11th to 20th	Day	2 2 1 3 3 3 3 3 6% 8% 66%	4191
	21st to end	Day	5% 6% 2 5% 3 3 3 2 4 5% 61%	4344
September	1st to 10th	Day	3 3 2 4 2 3 3 3 4 7% 67%	2400
	11th to 20th	Day	4 5% 2 5% 4 4 5% 4 5% 7% 55%	2400
	21st to end	Day	6% 5% 2 5% 4 4 4 3 5% 7% 55%	2146
October	1st to 10th	Day	6% 5% 1 5% 3 3 4 3 5% 8% 58%	3280
	11th to 20th	Day	6% 6% 2 6% 5% 5% 5% 5% 6% 8% 46%	3261
	21st to end	Day	9% 9% 3 7% 5% 5% 6% 4 5% 7% 41%	3264
November	1st to 10th	Day	8% 13% 4 7% 6% 5% 6% 5% 6% 7% 32%	1801
	11th to 20th	Day	8% 16% 3 9% 6% 6% 5% 4 6% 8% 30%	1680
	21st to end	Day	8% 14% 4 8% 5% 4 5% 4 7% 7% 33%	1680
December	1st to 10th	Day	8% 10% 3 5% 4 4 5% 4 5% 8% 44%	2636
	11th to 20th	Day	11% 16% 7% 13% 7% 6% 5% 4 4 6% 20%	3025
	21st to end	Day	11% 17% 6% 15% 5% 5% 4 3 5% 6% 23%	4004
January	1st to 10th	Night	12% 15% 6% 11% 7% 5% 5% 4 5% 6% 25%	6306
	11th to 20th	Night	8% 9% 3 5% 3 3 4 3 5% 9% 46%	6282
	21st to end	Night	11% 15% 4 8% 4 4 4 3 5% 6% 36%	6952
February	1st to 10th	Night	8% 12% 4 8% 5% 5% 4 5% 6% 8% 35%	2603
	11th to 20th	Night	7% 11% 3 8% 4 4 4 4 6% 7% 41%	2532
	21st to end	Night	7% 12% 5% 9% 5% 4 5% 5% 6% 6% 37%	1996
March	1st to 10th	Night	4 7% 2 7% 5% 6% 7% 5% 7% 9% 40%	5376
	11th to 20th	Night	4 9% 3 7% 5% 4 5% 4 5% 7% 46%	5056
	21st to end	Night	7% 8% 3 9% 7% 6% 6% 5% 7% 9% 32%	5169
April	1st to 10th	Night	8% 6% 2 7% 5% 5% 6% 7% 8% 9% 39%	2000
	11th to 20th	Night	5% 7% 3 6% 4 4 4 4 6% 7% 50%	1979
	21st to end	Night	5% 6% 2 5% 5% 5% 5% 4 7% 9% 47%	1779
May	1st to 10th	Night	5% 3 2 6% 4 3 3 3 4 6% 61%	3640
	11th to 20th	Night	4 5% 2 5% 3 3 3 4 5% 6% 60%	3616
	21st to end	Night	5% 4 1 4 3 3 4 4 8% 9% 53%	3972
June	1st to 10th	Night	7% 4 1 5% 5% 4 5% 4 7% 7% 52%	1600
	11th to 20th	Night	5% 4 2 5% 4 3 4 4 6% 7% 57%	1600
	21st to end	Night	2 3 1 4 3 4 4 3 5% 6% 64%	1600
July	1st to 10th	Night	1 1 2 1 1 2 2 3 4 83%	3640
	11th to 20th	Night	1 1 1 1 1 2 2 3 4 84%	3640
	21st to end	Night	1 1 1 1 1 1 2 2 3 5% 82%	3969
August	1st to 10th	Night	2 2 1 2 1 2 2 2 4 5% 78%	2609
	11th to 20th	Night	2 2 1 3 2 2 3 3 4 6% 73%	2863
	21st to end	Night	5% 3 1 4 2 3 3 3 4 6% 68%	3575
September	1st to 10th	Night	3 2 1 3 2 2 2 3 4 6% 71%	2000
	11th to 20th	Night	4 2 1 5% 3 4 4 4 5% 6% 61%	2000
	21st to end	Night	5% 4 1 4 3 3 4 3 5% 7% 61%	2250
October	1st to 10th	Night	3 3 1 4 3 3 4 3 6% 8% 61%	3920
	11th to 20th	Night	5% 4 2 5% 4 4 5% 4 7% 9% 50%	3897
	21st to end	Night	9% 6% 2 7% 5% 4 4 4 6% 7% 46%	4538
November	1st to 10th	Night	13% 9% 3 7% 4 5% 5% 4 6% 8% 36%	2713
	11th to 20th	Night	8% 10% 4 9% 5% 5% 5% 5% 6% 7% 36%	2940
	21st to end	Night	8% 12% 4 8% 6% 5% 5% 4 6% 7% 36%	2940
December	1st to 10th	Night	6% 8% 3 6% 4 4 4 4 5% 6% 50%	4588
	11th to 20th	Night	13% 17% 5% 11% 8% 6% 6% 4 5% 6% 19%	5180
	21st to end	Night	15% 16% 6% 12% 5% 4 4 3 4 5% 26%	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	55% 12% 12% 16% 5%	3639
	11th to 20th	Day	39% 7% 16% 29% 8%	3640
	21st to end	Day	49% 9% 10% 20% 12%	4004
February	1st to 10th	Day	49% 10% 17% 18% 5% 2	1795
	11th to 20th	Day	43% 10% 17% 21% 9% 1	1764
	21st to end	Day	42% 12% 16% 18% 10% 1	1633
March	1st to 10th	Day	38% 8% 15% 19% 19% 1	4518
	11th to 20th	Day	38% 7% 10% 32% 12% 1	4929
	21st to end	Day	48% 12% 18% 16% 7%	5793
April	1st to 10th	Day	45% 9% 16% 19% 9% 1	2400
	11th to 20th	Day	39% 6% 16% 23% 14% 2	2372
	21st to end	Day	34% 8% 15% 26% 16% 2	2616
May	1st to 10th	Day	24% 6% 11% 25% 27% 7%	6320
	11th to 20th	Day	27% 7% 14% 29% 21% 2	6280
	21st to end	Day	30% 9% 19% 30% 11% 1	6904
June	1st to 10th	Day	33% 8% 13% 25% 17% 4	2800
	11th to 20th	Day	26% 7% 13% 30% 21% 2	2800
	21st to end	Day	20% 6% 13% 33% 21% 7%	2800
July	1st to 10th	Day	9% 3 6% 23% 27% 32%	6251
	11th to 20th	Day	9% 2 4 17% 33% 35%	6245
	21st to end	Day	12% 4 7% 26% 34% 17%	6681
August	1st to 10th	Day	13% 3 7% 18% 38% 21%	4524
	11th to 20th	Day	13% 5% 11% 39% 26% 6%	4231
	21st to end	Day	24% 4 10% 24% 33% 5%	4343
September	1st to 10th	Day	16% 5% 10% 30% 31% 10%	2400
	11th to 20th	Day	26% 6% 13% 25% 23% 7%	2400
	21st to end	Day	27% 7% 15% 28% 19% 5%	2146
October	1st to 10th	Day	22% 5% 12% 38% 21% 1	3280
	11th to 20th	Day	31% 9% 17% 24% 18% 1	3261
	21st to end	Day	35% 10% 14% 23% 13% 5%	3264
November	1st to 10th	Day	45% 10% 16% 19% 9% 2	1801
	11th to 20th	Day	49% 11% 15% 17% 6% 1	1680
	21st to end	Day	46% 13% 16% 16% 9% 1	1680
December	1st to 10th	Day	37% 10% 19% 26% 9%	2636
	11th to 20th	Day	61% 14% 10% 10% 4	3028
	21st to end	Day	59% 11% 10% 15% 5%	4004
January	1st to 10th	Night	57% 13% 12% 12% 5%	6306
	11th to 20th	Night	36% 7% 17% 28% 11%	6320
	21st to end	Night	50% 10% 9% 20% 10%	6952
February	1st to 10th	Night	46% 9% 20% 18% 7% 1	2603
	11th to 20th	Night	40% 10% 17% 22% 10% 2	2534
	21st to end	Night	42% 10% 16% 19% 11% 1	1996
March	1st to 10th	Night	33% 9% 14% 24% 18% 2	5376
	11th to 20th	Night	32% 8% 16% 31% 12% 1	5057
	21st to end	Night	40% 14% 17% 22% 6%	5169
April	1st to 10th	Night	35% 11% 18% 23% 11% 2	2000
	11th to 20th	Night	30% 8% 17% 26% 17% 2	1979
	21st to end	Night	30% 9% 17% 30% 13% 1	1779
May	1st to 10th	Night	22% 5% 9% 28% 32% 4	3637
	11th to 20th	Night	22% 5% 14% 35% 21% 3	3616
	21st to end	Night	22% 9% 25% 35% 10% 1	3972
June	1st to 10th	Night	28% 8% 15% 30% 17% 3	1600
	11th to 20th	Night	22% 7% 18% 32% 20% 1	1600
	21st to end	Night	19% 4 14% 36% 21% 5%	1600
July	1st to 10th	Night	8% 2 8% 25% 27% 30%	3600
	11th to 20th	Night	5% 2 5% 20% 33% 35%	3592
	21st to end	Night	8% 2 7% 30% 34% 19%	3857
August	1st to 10th	Night	10% 3 6% 19% 41% 21%	2601
	11th to 20th	Night	12% 5% 16% 38% 22% 7%	2889
	21st to end	Night	17% 6% 13% 25% 32% 7%	3575
September	1st to 10th	Night	14% 4 10% 31% 30% 11%	2000
	11th to 20th	Night	21% 7% 13% 27% 24% 8%	2000
	21st to end	Night	21% 6% 16% 32% 20% 6%	2250
October	1st to 10th	Night	18% 5% 12% 44% 20% 1	3920
	11th to 20th	Night	26% 9% 17% 29% 17% 1	3897
	21st to end	Night	33% 9% 14% 27% 17% 1	4538
November	1st to 10th	Night	43% 10% 15% 19% 12% 1	2713
	11th to 20th	Night	44% 12% 16% 19% 8% 1	2940
	21st to end	Night	45% 12% 15% 18% 10% 1	2940
December	1st to 10th	Night	34% 9% 16% 30% 11%	4588
	11th to 20th	Night	62% 14% 11% 10% 4	5176
	21st to end	Night	58% 10% 12% 14% 6%	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	18% 18% 24% 25% 12% 4	200
	11th to 20th	Day	23% 11% 26% 27% 11% 4	200
	21st to end	Day	15% 14% 28% 25% 15% 3	220
February	1st to 10th	Day	19% 21% 35% 19% 6% 1	395
	11th to 20th	Day	18% 22% 36% 18% 6%	395
	21st to end	Day	15% 22% 37% 20% 6% 1	407
March	1st to 10th	Day	15% 24% 32% 22% 6% 1	500
	11th to 20th	Day	13% 22% 31% 24% 9% 1	500
	21st to end	Day	19% 23% 33% 20% 5%	550
April	1st to 10th	Day	17% 29% 27% 19% 5% 2	500
	11th to 20th	Day	14% 30% 29% 17% 7% 3	492
	21st to end	Day	14% 27% 30% 22% 6% 2	500
May	1st to 10th	Day	14% 23% 32% 24% 7% 1	503
	11th to 20th	Day	17% 21% 28% 24% 9% 1	528
	21st to end	Day	13% 18% 32% 23% 13% 1	573
June	1st to 10th	Day	12% 22% 32% 21% 12% 1	530
	11th to 20th	Day	11% 27% 38% 17% 6% 1	530
	21st to end	Day	6% 19% 32% 27% 14% 2	530
July	1st to 10th	Day	4 15% 38% 33% 10% 1	526
	11th to 20th	Day	4 18% 34% 32% 11% 1	524
	21st to end	Day	3 13% 31% 35% 17% 2	575
August	1st to 10th	Day	4 11% 30% 35% 17% 3	527
	11th to 20th	Day	4 9% 29% 36% 18% 4	517
	21st to end	Day	6% 15% 27% 34% 14% 4	583
September	1st to 10th	Day	5% 13% 30% 30% 18% 5%	530
	11th to 20th	Day	6% 14% 30% 31% 17% 2	530
	21st to end	Day	10% 17% 30% 28% 15% 2	530
October	1st to 10th	Day	12% 15% 30% 24% 16% 2	530
	11th to 20th	Day	11% 18% 27% 25% 15% 4	530
	21st to end	Day	15% 18% 29% 25% 10% 3	403
November	1st to 10th	Day	19% 21% 26% 26% 8% 1	302
	11th to 20th	Day	15% 22% 32% 15% 13% 4	220
	21st to end	Day	16% 14% 29% 26% 13% 2	220
December	1st to 10th	Day	17% 14% 24% 21% 15% 10%	204
	11th to 20th	Day	14% 18% 31% 27% 11%	200
	21st to end	Day	15% 15% 31% 26% 12% 1	220
January	1st to 10th	Night	17% 13% 28% 29% 12% 1	800
	11th to 20th	Night	15% 11% 28% 31% 13% 2	800
	21st to end	Night	16% 9% 26% 32% 16% 2	880
February	1st to 10th	Night	13% 14% 32% 29% 11% 1	800
	11th to 20th	Night	13% 14% 31% 29% 11% 1	784
	21st to end	Night	13% 16% 31% 28% 11% 1	660
March	1st to 10th	Night	11% 12% 31% 35% 11% 1	800
	11th to 20th	Night	9% 12% 33% 31% 14% 1	800
	21st to end	Night	10% 18% 34% 29% 8% 1	880
April	1st to 10th	Night	10% 16% 36% 27% 10% 1	800
	11th to 20th	Night	9% 21% 33% 27% 8% 2	791
	21st to end	Night	8% 20% 39% 25% 9%	579
May	1st to 10th	Night	8% 21% 35% 28% 7% 1	400
	11th to 20th	Night	8% 14% 38% 27% 11% 2	394
	21st to end	Night	8% 13% 39% 29% 10% 1	433
June	1st to 10th	Night	9% 15% 43% 25% 9%	400
	11th to 20th	Night	8% 24% 46% 19% 5%	400
	21st to end	Night	4 18% 39% 26% 12% 1	400
July	1st to 10th	Night	3 13% 47% 30% 6%	390
	11th to 20th	Night	1 19% 50% 24% 6% 1	388
	21st to end	Night	2 16% 39% 33% 9% 1	438
August	1st to 10th	Night	2 11% 46% 27% 13% 1	398
	11th to 20th	Night	2 9% 36% 33% 16% 5%	567
	21st to end	Night	3 14% 33% 30% 16% 3	860
September	1st to 10th	Night	3 13% 32% 31% 19% 3	800
	11th to 20th	Night	4 11% 29% 29% 22% 5%	800
	21st to end	Night	5% 12% 30% 30% 20% 4	800
October	1st to 10th	Night	8% 12% 29% 32% 18% 2	800
	11th to 20th	Night	8% 13% 27% 30% 18% 3	800
	21st to end	Night	12% 12% 31% 30% 11% 3	880
November	1st to 10th	Night	15% 10% 33% 31% 10%	820
	11th to 20th	Night	14% 14% 32% 26% 13% 2	840
	21st to end	Night	15% 9% 29% 30% 14% 3	840
December	1st to 10th	Night	14% 10% 30% 28% 15% 2	808
	11th to 20th	Night	17% 9% 32% 31% 11% 1	800
	21st to end	Night	18% 13% 30% 33% 7%	880

Page generated at 2025-11-29 22:00:55. Version ac07

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