Sulphur Mountain Cosmic Ray Station
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sulphur Mountain Cosmic Ray Station clear sky chart from 2005-11-06 to 2026-02-16.

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	5% 9% 4 11% 7% 6% 6% 5% 7% 8% 31%	134785
	Night	3 7% 4 10% 7% 6% 7% 5% 8% 10% 33%	134753
Transparency	Day	44% 10% 19% 18% 8% 1	134498
	Night	39% 12% 22% 19% 7% 1	134620
Seeing	Day	17% 21% 33% 20% 8% 1	16787
	Night	10% 19% 39% 24% 8% 1	25998

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	2 3 14% 12% 11% 10% 7% 9% 10% 22%	4125
	11th to 20th	Day	4 3 10% 8% 6% 7% 4 6% 8% 44%	4435
	21st to end	Day	5% 3 8% 6% 7% 7% 6% 9% 12% 38%	5186
February	1st to 10th	Day	1 8% 5% 12% 10% 9% 9% 8% 8% 9% 22%	1680
	11th to 20th	Day	1 8% 4 16% 9% 8% 7% 5% 7% 9% 25%	1743
	21st to end	Day	1 9% 5% 17% 12% 9% 7% 5% 8% 8% 20%	1650
March	1st to 10th	Day	1 6% 5% 18% 9% 7% 5% 4 6% 8% 31%	4518
	11th to 20th	Day	1 9% 5% 12% 9% 9% 8% 5% 7% 8% 27%	4818
	21st to end	Day	2 17% 8% 19% 9% 7% 6% 4 6% 6% 16%	5741
April	1st to 10th	Day	4 17% 7% 19% 9% 8% 5% 4 5% 5% 17%	2400
	11th to 20th	Day	3 19% 8% 16% 8% 5% 5% 4 6% 6% 19%	2567
	21st to end	Day	6% 20% 8% 13% 6% 6% 5% 4 5% 7% 20%	2600
May	1st to 10th	Day	8% 17% 4 8% 4 4 4 4 5% 8% 33%	6274
	11th to 20th	Day	9% 16% 5% 12% 7% 8% 6% 5% 7% 6% 18%	6660
	21st to end	Day	10% 15% 5% 11% 6% 5% 5% 4 5% 7% 27%	7405
June	1st to 10th	Day	16% 15% 4 10% 7% 5% 5% 4 6% 6% 22%	3000
	11th to 20th	Day	19% 14% 5% 11% 7% 6% 6% 4 6% 6% 16%	3000
	21st to end	Day	11% 10% 5% 11% 7% 6% 6% 5% 6% 7% 26%	3000
July	1st to 10th	Day	6% 5% 2 7% 5% 5% 5% 4 6% 7% 47%	6780
	11th to 20th	Day	9% 5% 2 7% 5% 6% 6% 5% 7% 8% 40%	6780
	21st to end	Day	7% 4 2 6% 5% 6% 7% 6% 8% 10% 39%	6997
August	1st to 10th	Day	6% 6% 3 9% 6% 7% 6% 5% 7% 8% 38%	4541
	11th to 20th	Day	7% 5% 2 7% 5% 6% 6% 5% 8% 10% 39%	4311
	21st to end	Day	8% 6% 2 6% 4 6% 6% 4 7% 9% 42%	4664
September	1st to 10th	Day	9% 9% 3 8% 5% 5% 5% 3 6% 7% 41%	2414
	11th to 20th	Day	9% 10% 3 10% 5% 5% 5% 3 6% 7% 38%	2241
	21st to end	Day	6% 9% 3 10% 6% 5% 6% 4 6% 8% 37%	2200
October	1st to 10th	Day	7% 8% 4 9% 6% 5% 5% 4 7% 8% 39%	3492
	11th to 20th	Day	3 7% 4 9% 5% 6% 6% 4 9% 12% 35%	2932
	21st to end	Day	3 9% 3 9% 6% 8% 6% 5% 7% 7% 37%	3200
November	1st to 10th	Day	3 11% 5% 11% 9% 7% 6% 6% 6% 10% 26%	1797
	11th to 20th	Day	1 7% 4 9% 7% 7% 7% 7% 11% 11% 29%	1517
	21st to end	Day	1 9% 4 10% 8% 7% 7% 5% 9% 12% 29%	1470
December	1st to 10th	Day	1 5% 4 9% 7% 5% 6% 7% 10% 12% 34%	2360
	11th to 20th	Day	5% 4 11% 9% 8% 9% 7% 8% 11% 28%	2712
	21st to end	Day	6% 3 9% 7% 8% 9% 6% 9% 12% 32%	3575
January	1st to 10th	Night	4 4 18% 11% 10% 8% 6% 8% 9% 22%	8768
	11th to 20th	Night	3 3 11% 8% 6% 6% 7% 8% 9% 39%	8505
	21st to end	Night	6% 5% 9% 6% 6% 7% 6% 9% 11% 34%	8994
February	1st to 10th	Night	2 8% 4 14% 10% 9% 7% 8% 10% 9% 19%	2940
	11th to 20th	Night	1 8% 6% 15% 8% 7% 7% 5% 8% 9% 26%	2649
	21st to end	Night	7% 4 15% 11% 7% 8% 7% 8% 7% 25%	1980
March	1st to 10th	Night	6% 6% 13% 8% 7% 7% 6% 8% 10% 28%	5376
	11th to 20th	Night	1 7% 5% 9% 6% 7% 7% 5% 9% 13% 31%	5181
	21st to end	Night	2 14% 8% 17% 8% 7% 7% 5% 7% 7% 18%	5231
April	1st to 10th	Night	3 13% 5% 11% 9% 7% 5% 5% 8% 9% 25%	2000
	11th to 20th	Night	2 11% 6% 11% 7% 5% 6% 5% 8% 10% 28%	1784
	21st to end	Night	4 16% 6% 10% 6% 6% 6% 5% 6% 7% 29%	1800
May	1st to 10th	Night	8% 16% 4 7% 4 4 3 3 4 6% 41%	3686
	11th to 20th	Night	6% 12% 4 10% 6% 5% 7% 5% 8% 10% 27%	3233
	21st to end	Night	8% 11% 3 8% 5% 4 5% 3 6% 7% 39%	3470
June	1st to 10th	Night	12% 11% 3 9% 5% 4 5% 4 6% 7% 34%	1400
	11th to 20th	Night	15% 13% 2 8% 5% 6% 5% 4 6% 9% 28%	1400
	21st to end	Night	7% 6% 2 5% 6% 4 5% 5% 9% 9% 41%	1400
July	1st to 10th	Night	5% 4 2 5% 4 4 4 4 5% 8% 54%	3180
	11th to 20th	Night	7% 4 2 4 4 4 4 4 7% 8% 52%	3180
	21st to end	Night	6% 5% 2 6% 4 3 5% 4 6% 8% 52%	3830
August	1st to 10th	Night	8% 7% 3 7% 6% 5% 5% 4 6% 9% 41%	2609
	11th to 20th	Night	6% 4 1 4 4 4 5% 5% 7% 11% 50%	2741
	21st to end	Night	8% 5% 2 5% 3 4 3 4 6% 9% 50%	3245
September	1st to 10th	Night	7% 6% 2 5% 3 4 3 3 7% 9% 50%	1983
	11th to 20th	Night	8% 7% 3 7% 4 4 6% 4 6% 8% 43%	2158
	21st to end	Night	6% 7% 3 6% 3 4 4 5% 7% 9% 45%	2200
October	1st to 10th	Night	4 8% 2 9% 5% 5% 5% 5% 7% 9% 43%	3702
	11th to 20th	Night	2 7% 3 8% 5% 5% 5% 5% 7% 10% 43%	4216
	21st to end	Night	2 9% 4 9% 6% 7% 6% 5% 7% 9% 37%	4600
November	1st to 10th	Night	2 12% 5% 12% 8% 8% 8% 7% 9% 10% 21%	2699
	11th to 20th	Night	1 6% 5% 11% 9% 9% 9% 7% 9% 11% 25%	3100
	21st to end	Night	8% 5% 11% 8% 8% 9% 7% 9% 10% 24%	3150
December	1st to 10th	Night	1 5% 3 9% 7% 6% 7% 6% 11% 13% 32%	5040
	11th to 20th	Night	4 3 12% 10% 10% 11% 8% 10% 12% 20%	5700
	21st to end	Night	1 7% 3 10% 9% 9% 11% 7% 10% 12% 23%	7623

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	40% 14% 25% 16% 5% 1	4125
	11th to 20th	Day	36% 10% 21% 18% 12% 3	4458
	21st to end	Day	29% 18% 27% 18% 7%	5187
February	1st to 10th	Day	47% 14% 18% 11% 7% 3	1680
	11th to 20th	Day	49% 13% 17% 14% 7% 1	1751
	21st to end	Day	55% 12% 16% 10% 6% 1	1650
March	1st to 10th	Day	46% 11% 16% 14% 13%	4518
	11th to 20th	Day	43% 10% 20% 21% 5%	4819
	21st to end	Day	60% 11% 14% 9% 5%	5741
April	1st to 10th	Day	64% 10% 15% 8% 2	2400
	11th to 20th	Day	61% 9% 15% 11% 4	2567
	21st to end	Day	61% 10% 13% 13% 2	2600
May	1st to 10th	Day	47% 7% 17% 21% 8%	6274
	11th to 20th	Day	56% 10% 16% 14% 3	6664
	21st to end	Day	50% 10% 20% 18% 3	7406
June	1st to 10th	Day	58% 9% 11% 15% 5% 1	3000
	11th to 20th	Day	64% 10% 11% 11% 4	3000
	21st to end	Day	51% 10% 15% 15% 7% 1	3000
July	1st to 10th	Day	33% 6% 12% 23% 21% 4	6706
	11th to 20th	Day	37% 7% 16% 25% 12% 3	6699
	21st to end	Day	34% 6% 18% 24% 15% 2	6801
August	1st to 10th	Day	38% 9% 14% 26% 12% 1	4524
	11th to 20th	Day	36% 8% 22% 26% 7% 1	4353
	21st to end	Day	34% 8% 24% 25% 9% 1	4663
September	1st to 10th	Day	40% 8% 17% 22% 11% 2	2414
	11th to 20th	Day	42% 9% 14% 23% 10% 1	2241
	21st to end	Day	42% 11% 19% 20% 8% 1	2200
October	1st to 10th	Day	41% 8% 19% 26% 6%	3492
	11th to 20th	Day	34% 10% 28% 20% 7% 1	2932
	21st to end	Day	37% 9% 26% 23% 5%	3200
November	1st to 10th	Day	48% 16% 20% 10% 5%	1797
	11th to 20th	Day	37% 20% 24% 13% 6%	1517
	21st to end	Day	41% 16% 22% 14% 6% 1	1470
December	1st to 10th	Day	35% 20% 29% 13% 4	2360
	11th to 20th	Day	38% 17% 28% 13% 4	2714
	21st to end	Day	33% 13% 23% 20% 10% 1	3575
January	1st to 10th	Night	45% 12% 23% 14% 5% 1	8769
	11th to 20th	Night	36% 11% 21% 15% 12% 5%	8544
	21st to end	Night	33% 18% 23% 19% 6% 1	8994
February	1st to 10th	Night	50% 16% 13% 12% 7% 2	2940
	11th to 20th	Night	47% 14% 20% 12% 8% 1	2651
	21st to end	Night	49% 11% 16% 15% 8% 1	1980
March	1st to 10th	Night	41% 15% 21% 13% 9%	5376
	11th to 20th	Night	34% 11% 21% 24% 9%	5181
	21st to end	Night	54% 12% 16% 12% 6%	5231
April	1st to 10th	Night	49% 13% 20% 14% 5%	2000
	11th to 20th	Night	46% 13% 21% 13% 6%	1784
	21st to end	Night	50% 10% 17% 17% 5% 1	1800
May	1st to 10th	Night	44% 7% 14% 29% 5% 1	3683
	11th to 20th	Night	44% 12% 19% 21% 3	3233
	21st to end	Night	37% 11% 23% 24% 5%	3470
June	1st to 10th	Night	47% 12% 14% 21% 7% 1	1400
	11th to 20th	Night	52% 11% 15% 16% 7%	1400
	21st to end	Night	33% 12% 22% 24% 8% 1	1400
July	1st to 10th	Night	26% 6% 17% 30% 17% 4	3145
	11th to 20th	Night	27% 7% 24% 27% 13% 3	3138
	21st to end	Night	29% 6% 22% 25% 15% 3	3722
August	1st to 10th	Night	37% 8% 16% 29% 9% 1	2601
	11th to 20th	Night	25% 8% 33% 28% 6%	2765
	21st to end	Night	28% 8% 32% 26% 7%	3245
September	1st to 10th	Night	29% 10% 22% 27% 11% 1	1983
	11th to 20th	Night	34% 12% 19% 23% 10% 1	2158
	21st to end	Night	32% 12% 23% 24% 9%	2200
October	1st to 10th	Night	34% 8% 24% 25% 9%	3702
	11th to 20th	Night	31% 11% 26% 25% 7%	4216
	21st to end	Night	35% 10% 26% 25% 4	4600
November	1st to 10th	Night	48% 18% 17% 11% 5% 1	2699
	11th to 20th	Night	44% 18% 20% 11% 6% 1	3100
	21st to end	Night	43% 17% 20% 13% 5% 2	3150
December	1st to 10th	Night	34% 17% 33% 11% 4	5040
	11th to 20th	Night	43% 20% 23% 10% 4	5697
	21st to end	Night	38% 15% 23% 16% 6% 1	7623

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	13% 21% 37% 21% 5% 2	220
	11th to 20th	Day	10% 23% 47% 14% 6%	220
	21st to end	Day	10% 29% 41% 14% 5% 2	242
February	1st to 10th	Day	22% 24% 34% 14% 5% 1	220
	11th to 20th	Day	10% 18% 44% 22% 5% 1	296
	21st to end	Day	19% 26% 32% 18% 4 1	414
March	1st to 10th	Day	16% 29% 31% 16% 5% 2	500
	11th to 20th	Day	13% 29% 35% 17% 4 2	500
	21st to end	Day	17% 25% 33% 17% 5% 2	550
April	1st to 10th	Day	18% 27% 35% 15% 5%	500
	11th to 20th	Day	15% 27% 31% 19% 7% 1	492
	21st to end	Day	17% 25% 31% 18% 7% 2	500
May	1st to 10th	Day	19% 19% 28% 22% 10% 1	503
	11th to 20th	Day	18% 12% 30% 27% 12% 2	690
	21st to end	Day	23% 13% 25% 27% 10% 2	789
June	1st to 10th	Day	22% 21% 30% 19% 7% 1	730
	11th to 20th	Day	25% 21% 29% 18% 7% 1	730
	21st to end	Day	16% 17% 32% 23% 10% 2	730
July	1st to 10th	Day	15% 14% 29% 26% 14% 2	721
	11th to 20th	Day	15% 18% 31% 24% 10% 2	718
	21st to end	Day	9% 17% 35% 26% 11% 2	633
August	1st to 10th	Day	13% 16% 35% 25% 9% 2	527
	11th to 20th	Day	11% 19% 38% 22% 8% 2	517
	21st to end	Day	15% 20% 33% 20% 10% 2	583
September	1st to 10th	Day	17% 22% 31% 18% 9% 3	530
	11th to 20th	Day	18% 19% 36% 19% 7% 1	530
	21st to end	Day	27% 28% 26% 16% 2 1	530
October	1st to 10th	Day	23% 20% 31% 17% 9% 1	502
	11th to 20th	Day	19% 26% 28% 22% 5% 1	330
	21st to end	Day	20% 27% 36% 14% 2 1	363
November	1st to 10th	Day	16% 32% 35% 13% 3 1	330
	11th to 20th	Day	16% 26% 47% 8% 3 1	245
	21st to end	Day	15% 25% 32% 15% 10% 3	220
December	1st to 10th	Day	13% 23% 40% 17% 5% 3	220
	11th to 20th	Day	11% 28% 41% 14% 5%	220
	21st to end	Day	8% 25% 42% 21% 3 1	242
January	1st to 10th	Night	10% 26% 47% 15% 2 1	1050
	11th to 20th	Night	7% 26% 46% 17% 3 1	956
	21st to end	Night	7% 28% 46% 16% 4	924
February	1st to 10th	Night	11% 22% 39% 21% 7%	840
	11th to 20th	Night	7% 20% 46% 22% 5%	804
	21st to end	Night	8% 19% 42% 22% 8% 1	660
March	1st to 10th	Night	6% 20% 45% 22% 6% 1	800
	11th to 20th	Night	7% 20% 46% 20% 6% 1	800
	21st to end	Night	8% 18% 39% 24% 10% 1	880
April	1st to 10th	Night	11% 19% 35% 28% 7% 1	800
	11th to 20th	Night	7% 17% 38% 31% 7% 1	596
	21st to end	Night	11% 18% 36% 26% 9% 1	600
May	1st to 10th	Night	13% 10% 31% 35% 10%	420
	11th to 20th	Night	11% 8% 26% 35% 19% 1	394
	21st to end	Night	20% 8% 25% 29% 17% 2	433
June	1st to 10th	Night	18% 13% 32% 24% 12% 1	400
	11th to 20th	Night	22% 11% 30% 27% 11%	400
	21st to end	Night	10% 13% 25% 33% 20%	400
July	1st to 10th	Night	9% 8% 25% 40% 17%	390
	11th to 20th	Night	11% 11% 28% 32% 16% 1	388
	21st to end	Night	7% 6% 20% 48% 18% 1	438
August	1st to 10th	Night	8% 6% 19% 43% 22% 1	398
	11th to 20th	Night	9% 10% 22% 38% 19% 2	495
	21st to end	Night	11% 10% 28% 33% 17% 1	660
September	1st to 10th	Night	13% 13% 27% 30% 15% 2	783
	11th to 20th	Night	13% 13% 28% 29% 15% 3	800
	21st to end	Night	14% 19% 35% 22% 9% 1	800
October	1st to 10th	Night	14% 13% 36% 28% 8% 1	800
	11th to 20th	Night	12% 19% 39% 26% 5% 1	800
	21st to end	Night	11% 22% 42% 21% 4	880
November	1st to 10th	Night	11% 26% 45% 14% 3	854
	11th to 20th	Night	10% 28% 45% 14% 3	1050
	21st to end	Night	8% 25% 44% 19% 4 1	1050
December	1st to 10th	Night	8% 25% 45% 17% 5%	1050
	11th to 20th	Night	7% 26% 48% 14% 4	1050
	21st to end	Night	6% 23% 49% 17% 5% 1	1155

Page generated at 2026-02-12 23:42:11. Version ac07

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