Mount Kobau Star Party
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mount Kobau Star Party clear sky chart from 2005-11-06 to 2025-10-19.

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% 9% 3 9% 6% 5% 6% 4 6% 7% 39%	130928
	Night	4 8% 3 8% 6% 5% 6% 4 6% 7% 41%	127442
Transparency	Day	22% 39% 10% 16% 10% 3	130651
	Night	25% 39% 11% 16% 8% 2	127296
Seeing	Day	14% 18% 32% 24% 9% 2	16245
	Night	13% 8% 31% 32% 14% 1	24751

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	4 14% 6% 17% 9% 7% 7% 4 6% 6% 19%	3639
	11th to 20th	Day	2 8% 3 8% 5% 5% 6% 5% 8% 8% 41%	3616
	21st to end	Day	4 12% 5% 15% 8% 6% 6% 3 5% 6% 30%	4004
February	1st to 10th	Day	4 12% 4 10% 8% 7% 7% 5% 6% 7% 28%	1671
	11th to 20th	Day	4 12% 5% 10% 7% 6% 6% 4 8% 9% 29%	1755
	21st to end	Day	3 13% 6% 14% 8% 7% 6% 6% 8% 7% 23%	1636
March	1st to 10th	Day	2 9% 5% 10% 6% 6% 8% 5% 8% 9% 33%	4518
	11th to 20th	Day	3 11% 4 12% 8% 6% 5% 3 5% 6% 37%	4780
	21st to end	Day	9% 17% 4 13% 7% 6% 6% 4 5% 6% 22%	5898
April	1st to 10th	Day	7% 16% 4 9% 8% 7% 5% 5% 6% 7% 25%	2400
	11th to 20th	Day	6% 14% 5% 10% 8% 5% 5% 4 7% 7% 29%	2372
	21st to end	Day	7% 12% 3 9% 6% 7% 6% 5% 6% 7% 33%	2722
May	1st to 10th	Day	6% 7% 2 7% 5% 5% 5% 4 5% 7% 46%	6320
	11th to 20th	Day	9% 12% 4 10% 6% 5% 5% 4 6% 10% 30%	6277
	21st to end	Day	11% 9% 3 10% 6% 5% 6% 4 6% 8% 32%	6903
June	1st to 10th	Day	15% 8% 3 8% 5% 6% 5% 4 5% 6% 33%	2877
	11th to 20th	Day	12% 10% 3 9% 7% 7% 6% 5% 6% 7% 28%	3129
	21st to end	Day	10% 7% 3 8% 6% 5% 5% 5% 5% 7% 38%	3097
July	1st to 10th	Day	3 3 2 5% 4 4 4 3 5% 6% 61%	6649
	11th to 20th	Day	4 3 2 4 3 3 3 3 4 6% 66%	6320
	21st to end	Day	4 4 2 7% 4 4 5% 4 5% 6% 54%	6874
August	1st to 10th	Day	3 2 1 4 4 4 5% 4 7% 7% 58%	4541
	11th to 20th	Day	4 3 2 7% 5% 5% 5% 4 6% 7% 51%	4393
	21st to end	Day	7% 5% 2 6% 4 4 5% 4 6% 7% 49%	4347
September	1st to 10th	Day	7% 4 2 5% 4 3 4 3 5% 7% 57%	2400
	11th to 20th	Day	8% 6% 2 7% 5% 4 4 4 5% 7% 47%	2383
	21st to end	Day	8% 8% 4 7% 3 5% 4 3 5% 7% 47%	2176
October	1st to 10th	Day	7% 4 3 7% 5% 5% 4 4 5% 8% 48%	3280
	11th to 20th	Day	8% 9% 4 10% 6% 6% 5% 4 5% 6% 37%	3164
	21st to end	Day	10% 8% 5% 12% 7% 5% 5% 4 6% 5% 34%	3101
November	1st to 10th	Day	8% 14% 5% 11% 6% 6% 7% 5% 7% 7% 26%	1689
	11th to 20th	Day	4 14% 5% 10% 7% 6% 7% 4 6% 7% 30%	1600
	21st to end	Day	4 11% 4 12% 7% 7% 10% 5% 7% 7% 26%	1577
December	1st to 10th	Day	3 10% 3 10% 6% 5% 6% 5% 9% 9% 34%	2290
	11th to 20th	Day	4 12% 6% 11% 8% 8% 11% 6% 7% 6% 21%	2642
	21st to end	Day	4 15% 6% 14% 7% 8% 9% 4 8% 7% 18%	3888
January	1st to 10th	Night	4 13% 6% 18% 10% 8% 7% 4 5% 5% 20%	6306
	11th to 20th	Night	3 9% 4 8% 5% 5% 5% 5% 7% 9% 41%	6282
	21st to end	Night	3 9% 5% 16% 8% 7% 7% 4 5% 7% 29%	6952
February	1st to 10th	Night	4 12% 5% 11% 9% 7% 6% 5% 7% 6% 29%	2725
	11th to 20th	Night	3 12% 4 8% 6% 6% 6% 5% 6% 8% 36%	2532
	21st to end	Night	3 10% 5% 13% 7% 6% 6% 6% 9% 7% 28%	1993
March	1st to 10th	Night	2 7% 4 7% 5% 5% 6% 5% 9% 10% 40%	5376
	11th to 20th	Night	2 9% 3 8% 6% 4 5% 4 6% 8% 44%	5205
	21st to end	Night	7% 13% 5% 11% 7% 7% 6% 4 6% 7% 26%	5077
April	1st to 10th	Night	5% 11% 3 7% 6% 7% 6% 5% 6% 8% 36%	2000
	11th to 20th	Night	4 10% 3 7% 5% 6% 6% 5% 6% 6% 41%	1979
	21st to end	Night	6% 8% 3 7% 5% 5% 5% 4 6% 8% 42%	1673
May	1st to 10th	Night	4 6% 2 5% 4 4 4 3 5% 8% 53%	3640
	11th to 20th	Night	6% 7% 2 6% 5% 5% 4 4 6% 9% 45%	3616
	21st to end	Night	8% 5% 2 4 3 4 5% 5% 7% 11% 46%	3972
June	1st to 10th	Night	9% 7% 2 6% 5% 5% 4 5% 7% 8% 41%	1515
	11th to 20th	Night	8% 7% 2 5% 4 5% 6% 5% 6% 8% 44%	1265
	21st to end	Night	6% 4 1 4 3 4 6% 4 7% 9% 52%	1294
July	1st to 10th	Night	2 2 1 4 2 2 3 2 4 5% 73%	3307
	11th to 20th	Night	3 2 1 3 2 1 2 3 4 6% 73%	3640
	21st to end	Night	4 3 1 4 3 3 3 3 5% 6% 66%	3969
August	1st to 10th	Night	2 2 1 4 4 3 5% 3 5% 6% 64%	2609
	11th to 20th	Night	3 3 1 5% 3 3 4 4 7% 9% 59%	2641
	21st to end	Night	6% 3 1 3 3 4 5% 4 6% 8% 57%	3571
September	1st to 10th	Night	4 4 1 4 3 3 4 3 5% 7% 61%	2000
	11th to 20th	Night	6% 5% 1 5% 4 4 3 3 5% 7% 57%	2016
	21st to end	Night	6% 6% 2 5% 4 4 5% 4 6% 8% 51%	2220
October	1st to 10th	Night	5% 4 2 6% 4 4 5% 4 6% 7% 52%	3920
	11th to 20th	Night	8% 8% 4 8% 5% 4 5% 4 5% 7% 42%	3934
	21st to end	Night	8% 7% 3 7% 5% 5% 5% 5% 7% 7% 41%	4457
November	1st to 10th	Night	6% 13% 4 8% 6% 6% 6% 4 7% 7% 32%	2609
	11th to 20th	Night	5% 12% 4 9% 7% 7% 6% 5% 7% 7% 33%	2800
	21st to end	Night	3 13% 4 13% 8% 7% 8% 5% 7% 6% 26%	2800
December	1st to 10th	Night	2 8% 4 9% 6% 5% 5% 5% 9% 7% 40%	4889
	11th to 20th	Night	4 14% 6% 13% 8% 8% 10% 5% 7% 6% 19%	5550
	21st to end	Night	4 16% 6% 13% 8% 6% 7% 4 6% 6% 23%	7108

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	49% 31% 7% 10% 4	3639
	11th to 20th	Day	26% 30% 23% 13% 4 4	3640
	21st to end	Day	42% 31% 13% 10% 3	4004
February	1st to 10th	Day	20% 62% 4 8% 5% 1	1671
	11th to 20th	Day	21% 61% 6% 9% 3	1764
	21st to end	Day	16% 62% 7% 9% 6%	1636
March	1st to 10th	Day	24% 33% 15% 17% 11%	4518
	11th to 20th	Day	24% 31% 14% 27% 4	4780
	21st to end	Day	37% 33% 12% 12% 7%	5898
April	1st to 10th	Day	16% 62% 9% 10% 4	2400
	11th to 20th	Day	14% 62% 5% 13% 5% 2	2372
	21st to end	Day	15% 62% 4 11% 7% 1	2722
May	1st to 10th	Day	17% 30% 6% 26% 20% 1	6320
	11th to 20th	Day	28% 32% 13% 20% 7%	6280
	21st to end	Day	24% 31% 16% 22% 6% 1	6904
June	1st to 10th	Day	13% 61% 5% 12% 7% 1	2877
	11th to 20th	Day	14% 61% 4 13% 7% 1	3129
	21st to end	Day	13% 61% 5% 14% 7%	3097
July	1st to 10th	Day	8% 27% 7% 18% 25% 15%	6577
	11th to 20th	Day	7% 26% 7% 23% 21% 16%	6245
	21st to end	Day	13% 28% 11% 24% 16% 8%	6681
August	1st to 10th	Day	8% 37% 6% 19% 25% 6%	4524
	11th to 20th	Day	13% 40% 15% 22% 8% 2	4435
	21st to end	Day	17% 37% 11% 18% 14% 3	4346
September	1st to 10th	Day	10% 57% 6% 15% 10% 1	2400
	11th to 20th	Day	14% 57% 7% 12% 10% 1	2383
	21st to end	Day	14% 57% 8% 14% 6% 1	2176
October	1st to 10th	Day	16% 37% 15% 25% 7%	3280
	11th to 20th	Day	27% 39% 8% 20% 6%	3164
	21st to end	Day	27% 39% 13% 14% 6%	3101
November	1st to 10th	Day	21% 57% 9% 10% 3	1689
	11th to 20th	Day	24% 57% 8% 6% 3 1	1600
	21st to end	Day	25% 57% 7% 6% 4 1	1577
December	1st to 10th	Day	31% 41% 20% 7% 1	2290
	11th to 20th	Day	50% 34% 7% 7% 2	2644
	21st to end	Day	52% 32% 6% 7% 2	3888
January	1st to 10th	Night	53% 26% 9% 10% 2	6306
	11th to 20th	Night	26% 30% 16% 18% 7% 3	6320
	21st to end	Night	44% 32% 12% 10% 2	6952
February	1st to 10th	Night	23% 62% 4 6% 4 1	2725
	11th to 20th	Night	22% 61% 5% 8% 4	2534
	21st to end	Night	15% 62% 7% 10% 6% 1	1993
March	1st to 10th	Night	22% 31% 16% 22% 9%	5376
	11th to 20th	Night	22% 30% 14% 24% 10%	5206
	21st to end	Night	40% 33% 11% 12% 4	5077
April	1st to 10th	Night	14% 62% 9% 10% 4 1	2000
	11th to 20th	Night	13% 62% 6% 12% 6% 1	1979
	21st to end	Night	13% 61% 4 13% 8%	1673
May	1st to 10th	Night	16% 30% 7% 25% 22% 1	3637
	11th to 20th	Night	23% 30% 12% 23% 9% 2	3616
	21st to end	Night	17% 29% 18% 28% 7% 1	3972
June	1st to 10th	Night	11% 61% 6% 15% 7% 1	1515
	11th to 20th	Night	12% 62% 5% 11% 9% 2	1265
	21st to end	Night	9% 60% 5% 17% 8% 1	1294
July	1st to 10th	Night	7% 25% 7% 18% 28% 13%	3270
	11th to 20th	Night	7% 25% 9% 22% 21% 17%	3592
	21st to end	Night	13% 27% 8% 29% 17% 7%	3857
August	1st to 10th	Night	9% 37% 5% 18% 28% 3	2601
	11th to 20th	Night	9% 40% 19% 21% 9% 1	2665
	21st to end	Night	16% 38% 13% 20% 12% 2	3571
September	1st to 10th	Night	10% 57% 7% 16% 10% 2	2000
	11th to 20th	Night	12% 57% 6% 15% 10%	2016
	21st to end	Night	14% 56% 8% 16% 6%	2220
October	1st to 10th	Night	14% 37% 19% 20% 9% 1	3920
	11th to 20th	Night	25% 38% 11% 19% 7%	3934
	21st to end	Night	22% 39% 13% 21% 4	4457
November	1st to 10th	Night	22% 57% 9% 9% 3	2609
	11th to 20th	Night	22% 58% 8% 7% 4 2	2800
	21st to end	Night	26% 57% 7% 6% 4	2800
December	1st to 10th	Night	27% 41% 19% 12% 1	4889
	11th to 20th	Night	49% 35% 9% 6% 1	5547
	21st to end	Night	49% 31% 8% 8% 3	7108

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	16% 14% 34% 24% 11% 3	200
	11th to 20th	Day	21% 14% 30% 23% 12% 1	200
	21st to end	Day	25% 16% 28% 26% 5% 1	220
February	1st to 10th	Day	13% 20% 44% 19% 3	271
	11th to 20th	Day	15% 18% 41% 20% 5%	395
	21st to end	Day	12% 22% 39% 21% 7% 1	408
March	1st to 10th	Day	18% 23% 32% 21% 5% 1	500
	11th to 20th	Day	16% 21% 32% 20% 10% 2	500
	21st to end	Day	20% 24% 31% 17% 6% 1	550
April	1st to 10th	Day	22% 23% 29% 18% 6% 2	500
	11th to 20th	Day	19% 26% 27% 18% 8% 2	492
	21st to end	Day	14% 25% 29% 20% 9% 3	500
May	1st to 10th	Day	12% 24% 31% 24% 7% 2	503
	11th to 20th	Day	17% 16% 30% 23% 11% 3	528
	21st to end	Day	16% 16% 30% 25% 10% 3	573
June	1st to 10th	Day	17% 20% 33% 23% 6% 1	607
	11th to 20th	Day	14% 20% 30% 27% 8% 1	859
	21st to end	Day	8% 15% 36% 28% 12% 1	827
July	1st to 10th	Day	7% 16% 35% 32% 9% 1	670
	11th to 20th	Day	7% 17% 35% 30% 10% 1	524
	21st to end	Day	4 14% 35% 32% 12% 3	575
August	1st to 10th	Day	4 10% 33% 34% 14% 5%	527
	11th to 20th	Day	6% 14% 29% 33% 16% 3	517
	21st to end	Day	8% 17% 31% 28% 10% 6%	583
September	1st to 10th	Day	8% 15% 31% 26% 13% 5%	530
	11th to 20th	Day	12% 16% 32% 25% 12% 3	530
	21st to end	Day	15% 21% 34% 20% 8% 3	530
October	1st to 10th	Day	14% 19% 34% 20% 11% 2	530
	11th to 20th	Day	18% 19% 26% 24% 10% 3	483
	21st to end	Day	21% 18% 32% 22% 6% 2	330
November	1st to 10th	Day	24% 16% 31% 24% 5%	263
	11th to 20th	Day	23% 18% 33% 19% 6% 2	200
	21st to end	Day	17% 18% 35% 20% 10% 2	200
December	1st to 10th	Day	20% 12% 24% 29% 13% 4	200
	11th to 20th	Day	21% 15% 36% 19% 9% 2	200
	21st to end	Day	17% 12% 36% 26% 8% 1	220
January	1st to 10th	Night	19% 11% 32% 28% 9% 2	800
	11th to 20th	Night	18% 9% 34% 29% 9% 2	800
	21st to end	Night	16% 7% 32% 31% 12% 1	880
February	1st to 10th	Night	17% 8% 36% 30% 9% 1	800
	11th to 20th	Night	12% 8% 36% 31% 12% 1	784
	21st to end	Night	13% 9% 32% 32% 13% 1	660
March	1st to 10th	Night	13% 9% 32% 32% 14% 1	800
	11th to 20th	Night	11% 11% 35% 29% 14% 1	800
	21st to end	Night	11% 12% 35% 31% 10% 1	880
April	1st to 10th	Night	13% 10% 31% 32% 13% 1	800
	11th to 20th	Night	9% 10% 39% 28% 12% 2	791
	21st to end	Night	8% 13% 37% 31% 9% 1	473
May	1st to 10th	Night	8% 9% 40% 33% 10% 1	400
	11th to 20th	Night	8% 7% 30% 33% 20% 2	394
	21st to end	Night	11% 7% 28% 39% 14%	433
June	1st to 10th	Night	11% 10% 36% 30% 13%	400
	11th to 20th	Night	11% 9% 34% 36% 10%	400
	21st to end	Night	6% 7% 34% 37% 17%	400
July	1st to 10th	Night	5% 6% 29% 43% 16% 1	390
	11th to 20th	Night	3 6% 37% 37% 16%	388
	21st to end	Night	3 5% 29% 43% 19% 1	438
August	1st to 10th	Night	4 4 22% 45% 24% 1	398
	11th to 20th	Night	3 3 26% 42% 24% 2	434
	21st to end	Night	6% 6% 27% 39% 21% 2	856
September	1st to 10th	Night	5% 7% 25% 37% 24% 2	800
	11th to 20th	Night	8% 5% 21% 34% 29% 3	800
	21st to end	Night	11% 7% 28% 35% 16% 3	800
October	1st to 10th	Night	13% 9% 27% 32% 17% 2	800
	11th to 20th	Night	14% 9% 26% 34% 13% 3	792
	21st to end	Night	19% 8% 29% 31% 11% 2	836
November	1st to 10th	Night	21% 9% 31% 32% 7%	780
	11th to 20th	Night	21% 10% 32% 23% 12% 2	800
	21st to end	Night	19% 10% 30% 27% 12% 3	800
December	1st to 10th	Night	16% 6% 33% 32% 11% 1	999
	11th to 20th	Night	21% 10% 33% 28% 6% 1	1000
	21st to end	Night	19% 11% 34% 28% 7%	945

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