Spirit Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Spirit Lake clear sky chart from 2005-11-06 to 2026-02-01.

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	10% 10% 3 7% 5% 4 5% 4 5% 6% 42%	131134
	Night	11% 10% 3 8% 5% 5% 5% 4 5% 6% 38%	129594
Transparency	Day	42% 5% 12% 22% 14% 4	130860
	Night	46% 6% 12% 20% 12% 4	129445
Seeing	Day	16% 12% 24% 26% 17% 5%	16395
	Night	19% 7% 17% 33% 21% 3	25684

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	16% 26% 10% 14% 6% 5% 4 3 4 3 9%	3719
	11th to 20th	Day	13% 12% 3 10% 7% 6% 6% 4 5% 6% 27%	3696
	21st to end	Day	16% 16% 5% 9% 5% 4 5% 4 7% 5% 23%	4092
February	1st to 10th	Day	17% 23% 6% 10% 5% 3 5% 4 4 4 19%	1600
	11th to 20th	Day	14% 19% 5% 11% 5% 4 5% 4 5% 4 23%	1857
	21st to end	Day	15% 21% 5% 10% 6% 4 5% 4 3 6% 23%	1650
March	1st to 10th	Day	8% 13% 4 8% 5% 6% 7% 4 7% 7% 32%	4518
	11th to 20th	Day	10% 12% 3 7% 5% 5% 5% 4 5% 6% 38%	4729
	21st to end	Day	13% 16% 4 11% 7% 6% 6% 5% 6% 7% 19%	5868
April	1st to 10th	Day	14% 15% 4 8% 6% 6% 6% 5% 7% 6% 23%	2400
	11th to 20th	Day	12% 12% 3 8% 6% 5% 6% 4 5% 7% 32%	2465
	21st to end	Day	12% 10% 3 8% 7% 6% 6% 4 6% 6% 33%	2600
May	1st to 10th	Day	7% 7% 3 7% 5% 4 5% 5% 6% 8% 43%	6161
	11th to 20th	Day	8% 8% 3 9% 5% 5% 5% 4 8% 11% 34%	6277
	21st to end	Day	7% 6% 3 7% 6% 6% 5% 4 6% 8% 41%	7121
June	1st to 10th	Day	16% 7% 3 6% 6% 4 4 4 5% 7% 38%	3000
	11th to 20th	Day	15% 6% 2 7% 5% 5% 6% 5% 7% 7% 36%	3000
	21st to end	Day	7% 4 1 5% 4 4 5% 4 6% 7% 53%	3000
July	1st to 10th	Day	4 3 1 3 2 3 3 3 4 5% 69%	6558
	11th to 20th	Day	2 1 1 2 2 2 2 3 3 4 78%	6320
	21st to end	Day	3 2 1 3 2 2 2 2 3 5% 74%	6874
August	1st to 10th	Day	3 3 1 3 2 3 4 3 5% 7% 67%	4541
	11th to 20th	Day	3 3 1 3 2 3 3 3 5% 7% 66%	4257
	21st to end	Day	3 2 1 4 3 4 4 4 6% 8% 61%	4451
September	1st to 10th	Day	4 4 2 3 3 3 4 3 5% 7% 63%	2400
	11th to 20th	Day	8% 6% 2 5% 4 4 4 4 6% 7% 50%	2270
	21st to end	Day	8% 6% 2 6% 5% 4 5% 4 7% 8% 46%	2200
October	1st to 10th	Day	8% 5% 1 5% 4 3 4 2 4 7% 56%	3509
	11th to 20th	Day	8% 7% 3 7% 5% 6% 5% 4 6% 7% 42%	3015
	21st to end	Day	16% 9% 4 8% 5% 6% 6% 5% 6% 6% 29%	3200
November	1st to 10th	Day	21% 18% 4 7% 5% 5% 4 3 4 6% 22%	1854
	11th to 20th	Day	21% 17% 6% 9% 5% 4 5% 4 4 4 20%	1796
	21st to end	Day	14% 21% 6% 14% 6% 5% 5% 3 4 4 18%	1470
December	1st to 10th	Day	12% 14% 5% 15% 7% 5% 5% 5% 4 6% 21%	2360
	11th to 20th	Day	16% 26% 8% 13% 7% 5% 5% 3 4 3 10%	2712
	21st to end	Day	16% 24% 9% 14% 6% 5% 4 3 4 4 11%	3594
January	1st to 10th	Night	17% 22% 7% 14% 6% 5% 5% 3 4 4 12%	6469
	11th to 20th	Night	11% 11% 4 10% 6% 6% 6% 4 7% 6% 28%	6422
	21st to end	Night	15% 18% 4 8% 5% 4 5% 4 10% 6% 21%	7106
February	1st to 10th	Night	18% 20% 4 8% 5% 4 4 3 5% 5% 24%	2800
	11th to 20th	Night	13% 16% 5% 9% 5% 5% 4 3 5% 5% 29%	2426
	21st to end	Night	12% 16% 4 9% 5% 5% 5% 4 6% 7% 28%	1980
March	1st to 10th	Night	6% 9% 3 9% 5% 5% 6% 5% 6% 6% 40%	5376
	11th to 20th	Night	10% 12% 4 8% 5% 4 3 3 4 5% 42%	5269
	21st to end	Night	13% 11% 3 9% 7% 7% 8% 6% 8% 8% 21%	5104
April	1st to 10th	Night	10% 10% 3 8% 6% 5% 6% 5% 7% 7% 33%	2000
	11th to 20th	Night	11% 9% 3 8% 6% 5% 5% 3 4 6% 40%	1885
	21st to end	Night	9% 8% 3 8% 5% 5% 6% 6% 5% 7% 39%	1800
May	1st to 10th	Night	9% 5% 2 6% 5% 5% 5% 4 6% 7% 45%	3790
	11th to 20th	Night	10% 8% 3 7% 5% 5% 5% 5% 6% 8% 39%	3616
	21st to end	Night	8% 6% 2 6% 4 4 5% 4 7% 8% 45%	3752
June	1st to 10th	Night	14% 6% 2 6% 4 4 4 5% 5% 8% 42%	1400
	11th to 20th	Night	10% 5% 1 8% 4 6% 5% 5% 7% 9% 41%	1400
	21st to end	Night	6% 4 2 5% 4 4 5% 4 6% 8% 53%	1400
July	1st to 10th	Night	4 1 1 2 2 2 2 2 4 5% 75%	3398
	11th to 20th	Night	2 2 1 2 2 2 2 2 3 4 80%	3640
	21st to end	Night	2 2 1 3 2 2 3 2 3 5% 74%	3969
August	1st to 10th	Night	3 2 1 3 2 2 2 3 4 7% 71%	2609
	11th to 20th	Night	3 3 2 5% 2 4 4 4 6% 7% 61%	2797
	21st to end	Night	3 3 1 4 3 5% 4 4 4 6% 63%	3461
September	1st to 10th	Night	3 2 1 4 3 3 3 3 6% 7% 65%	2000
	11th to 20th	Night	5% 5% 2 7% 5% 5% 4 3 5% 8% 51%	2130
	21st to end	Night	10% 4 2 5% 3 4 4 4 6% 8% 51%	2200
October	1st to 10th	Night	6% 4 2 4 4 3 3 3 5% 7% 60%	3688
	11th to 20th	Night	9% 5% 2 6% 4 4 4 4 5% 7% 49%	4134
	21st to end	Night	11% 6% 2 6% 4 4 5% 5% 7% 7% 42%	4600
November	1st to 10th	Night	21% 13% 3 7% 5% 4 6% 4 5% 7% 25%	2665
	11th to 20th	Night	19% 15% 4 8% 6% 5% 5% 4 5% 5% 23%	2815
	21st to end	Night	20% 14% 4 10% 6% 5% 4 3 5% 5% 24%	3130
December	1st to 10th	Night	10% 10% 5% 10% 7% 6% 6% 7% 5% 6% 27%	5040
	11th to 20th	Night	16% 22% 6% 13% 7% 6% 5% 3 5% 4 13%	5700
	21st to end	Night	16% 18% 9% 15% 8% 6% 5% 4 4 4 11%	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	81% 5% 7% 6% 1	3719
	11th to 20th	Day	58% 7% 15% 14% 4 2	3720
	21st to end	Day	62% 6% 13% 15% 4	4092
February	1st to 10th	Day	68% 6% 12% 8% 5% 1	1600
	11th to 20th	Day	63% 8% 11% 11% 6%	1867
	21st to end	Day	63% 8% 9% 14% 6%	1650
March	1st to 10th	Day	48% 6% 13% 19% 13%	4518
	11th to 20th	Day	46% 5% 17% 27% 5%	4730
	21st to end	Day	64% 6% 14% 12% 4	5868
April	1st to 10th	Day	57% 8% 15% 15% 4	2400
	11th to 20th	Day	50% 7% 14% 20% 9% 1	2465
	21st to end	Day	50% 7% 14% 20% 8% 1	2600
May	1st to 10th	Day	37% 6% 12% 27% 18%	6161
	11th to 20th	Day	41% 6% 18% 27% 8%	6280
	21st to end	Day	40% 6% 19% 27% 8%	7122
June	1st to 10th	Day	45% 6% 13% 22% 12% 1	3000
	11th to 20th	Day	44% 7% 14% 22% 11% 2	3000
	21st to end	Day	28% 6% 15% 30% 17% 3	3000
July	1st to 10th	Day	18% 3 8% 23% 31% 18%	6488
	11th to 20th	Day	12% 3 5% 26% 28% 26%	6245
	21st to end	Day	15% 2 6% 33% 30% 15%	6681
August	1st to 10th	Day	18% 3 6% 28% 33% 12%	4524
	11th to 20th	Day	18% 4 9% 43% 24% 3	4298
	21st to end	Day	22% 4 11% 36% 24% 3	4450
September	1st to 10th	Day	21% 4 12% 32% 22% 9%	2400
	11th to 20th	Day	32% 6% 13% 26% 20% 3	2270
	21st to end	Day	35% 6% 20% 25% 11% 3	2200
October	1st to 10th	Day	29% 3 14% 38% 15%	3509
	11th to 20th	Day	41% 4 20% 23% 12%	3015
	21st to end	Day	54% 6% 14% 19% 6%	3200
November	1st to 10th	Day	63% 7% 14% 12% 3 1	1854
	11th to 20th	Day	67% 8% 11% 9% 4 1	1796
	21st to end	Day	68% 5% 12% 11% 4	1470
December	1st to 10th	Day	65% 8% 14% 11% 2	2360
	11th to 20th	Day	80% 5% 7% 6% 2	2714
	21st to end	Day	77% 4 9% 6% 3	3594
January	1st to 10th	Night	77% 5% 9% 8% 1	6469
	11th to 20th	Night	55% 9% 13% 16% 6% 2	6460
	21st to end	Night	62% 8% 12% 13% 4	7106
February	1st to 10th	Night	61% 7% 13% 12% 5% 1	2800
	11th to 20th	Night	57% 7% 15% 13% 7% 1	2427
	21st to end	Night	55% 7% 12% 16% 7% 1	1980
March	1st to 10th	Night	42% 8% 13% 22% 15% 1	5376
	11th to 20th	Night	45% 5% 13% 27% 10%	5269
	21st to end	Night	58% 9% 14% 16% 3	5104
April	1st to 10th	Night	46% 7% 16% 23% 8%	2000
	11th to 20th	Night	46% 5% 12% 23% 14% 1	1885
	21st to end	Night	43% 7% 11% 26% 12% 1	1800
May	1st to 10th	Night	36% 6% 9% 27% 21% 1	3787
	11th to 20th	Night	39% 7% 12% 29% 13%	3616
	21st to end	Night	35% 6% 14% 33% 11% 1	3752
June	1st to 10th	Night	39% 7% 10% 24% 17% 3	1400
	11th to 20th	Night	38% 6% 13% 23% 16% 4	1400
	21st to end	Night	27% 6% 11% 28% 22% 6%	1400
July	1st to 10th	Night	13% 2 6% 20% 35% 24%	3359
	11th to 20th	Night	11% 2 3 21% 28% 36%	3592
	21st to end	Night	15% 2 3 25% 33% 22%	3857
August	1st to 10th	Night	14% 3 5% 23% 37% 18%	2601
	11th to 20th	Night	22% 4 6% 35% 27% 7%	2822
	21st to end	Night	22% 3 10% 29% 28% 8%	3461
September	1st to 10th	Night	18% 5% 9% 28% 28% 12%	2000
	11th to 20th	Night	31% 6% 10% 25% 22% 6%	2130
	21st to end	Night	31% 5% 17% 27% 16% 5%	2200
October	1st to 10th	Night	24% 3 13% 44% 16%	3688
	11th to 20th	Night	35% 4 15% 26% 19% 1	4134
	21st to end	Night	40% 6% 16% 28% 8% 1	4600
November	1st to 10th	Night	58% 7% 16% 14% 4 1	2665
	11th to 20th	Night	61% 7% 14% 11% 5% 1	2815
	21st to end	Night	62% 6% 14% 14% 3	3130
December	1st to 10th	Night	56% 12% 13% 16% 2	5040
	11th to 20th	Night	73% 7% 12% 7% 1	5697
	21st to end	Night	75% 6% 10% 7% 2	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	29% 20% 19% 18% 12% 3	220
	11th to 20th	Day	29% 10% 23% 20% 11% 6%	220
	21st to end	Day	29% 7% 23% 27% 12% 2	242
February	1st to 10th	Day	29% 18% 29% 15% 8% 3	200
	11th to 20th	Day	28% 16% 22% 24% 10% 1	431
	21st to end	Day	29% 17% 20% 22% 11% 1	414
March	1st to 10th	Day	22% 21% 25% 18% 11% 3	500
	11th to 20th	Day	24% 14% 21% 19% 20% 2	500
	21st to end	Day	25% 19% 25% 21% 9% 1	550
April	1st to 10th	Day	23% 16% 28% 19% 11% 3	500
	11th to 20th	Day	17% 22% 25% 19% 13% 3	492
	21st to end	Day	15% 16% 29% 26% 11% 3	500
May	1st to 10th	Day	14% 12% 28% 29% 13% 4	503
	11th to 20th	Day	16% 13% 28% 25% 13% 5%	528
	21st to end	Day	13% 12% 20% 28% 21% 7%	661
June	1st to 10th	Day	16% 10% 24% 25% 19% 5%	730
	11th to 20th	Day	15% 15% 29% 23% 14% 4	730
	21st to end	Day	7% 9% 25% 28% 25% 7%	730
July	1st to 10th	Day	6% 7% 25% 33% 25% 4	633
	11th to 20th	Day	5% 8% 28% 33% 19% 6%	524
	21st to end	Day	4 7% 25% 37% 19% 9%	575
August	1st to 10th	Day	7% 5% 23% 34% 24% 8%	527
	11th to 20th	Day	4 4 22% 36% 24% 10%	517
	21st to end	Day	7% 9% 24% 28% 21% 11%	583
September	1st to 10th	Day	7% 7% 25% 26% 24% 11%	530
	11th to 20th	Day	12% 9% 22% 26% 21% 10%	530
	21st to end	Day	12% 13% 25% 24% 21% 6%	530
October	1st to 10th	Day	13% 9% 27% 26% 19% 6%	530
	11th to 20th	Day	18% 14% 22% 25% 13% 7%	387
	21st to end	Day	26% 11% 21% 26% 11% 3	363
November	1st to 10th	Day	32% 13% 19% 24% 12% 1	330
	11th to 20th	Day	30% 13% 21% 21% 14% 1	283
	21st to end	Day	23% 11% 26% 24% 15% 1	220
December	1st to 10th	Day	30% 13% 20% 18% 15% 5%	220
	11th to 20th	Day	33% 15% 22% 18% 10% 2	220
	21st to end	Day	36% 11% 19% 21% 11% 2	242
January	1st to 10th	Night	37% 8% 17% 25% 11% 1	850
	11th to 20th	Night	28% 8% 17% 31% 14% 2	840
	21st to end	Night	24% 7% 18% 33% 16% 2	924
February	1st to 10th	Night	30% 9% 21% 28% 10% 2	800
	11th to 20th	Night	24% 9% 18% 32% 15% 1	784
	21st to end	Night	22% 11% 19% 29% 16% 3	660
March	1st to 10th	Night	19% 9% 20% 34% 17% 2	800
	11th to 20th	Night	20% 9% 17% 33% 20% 1	800
	21st to end	Night	20% 9% 21% 34% 14% 2	880
April	1st to 10th	Night	17% 7% 18% 38% 20% 1	800
	11th to 20th	Night	15% 8% 26% 34% 16% 1	697
	21st to end	Night	13% 9% 23% 33% 21% 2	600
May	1st to 10th	Night	10% 6% 19% 35% 28% 2	472
	11th to 20th	Night	13% 5% 16% 27% 31% 7%	394
	21st to end	Night	13% 6% 14% 32% 31% 5%	433
June	1st to 10th	Night	16% 5% 13% 38% 25% 4	400
	11th to 20th	Night	12% 5% 23% 36% 22% 3	400
	21st to end	Night	7% 2 13% 40% 35% 3	400
July	1st to 10th	Night	3 2 11% 41% 41% 3	390
	11th to 20th	Night	3 2 12% 45% 35% 3	388
	21st to end	Night	1 2 10% 40% 44% 3	438
August	1st to 10th	Night	4 2 9% 39% 41% 6%	398
	11th to 20th	Night	5% 3 6% 35% 43% 9%	526
	21st to end	Night	5% 3 13% 38% 38% 3	785
September	1st to 10th	Night	5% 2 12% 39% 35% 7%	800
	11th to 20th	Night	7% 4 13% 33% 36% 7%	800
	21st to end	Night	12% 5% 17% 34% 28% 5%	800
October	1st to 10th	Night	13% 6% 13% 40% 26% 3	800
	11th to 20th	Night	17% 6% 17% 31% 26% 3	800
	21st to end	Night	20% 5% 21% 33% 18% 2	880
November	1st to 10th	Night	30% 8% 16% 34% 13%	820
	11th to 20th	Night	30% 9% 18% 28% 14% 1	840
	21st to end	Night	30% 9% 15% 29% 16% 2	1030
December	1st to 10th	Night	26% 9% 17% 32% 15% 1	1050
	11th to 20th	Night	34% 7% 20% 29% 10%	1050
	21st to end	Night	34% 10% 20% 27% 9%	1155

Page generated at 2026-01-28 22:21:43. Version ac07

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