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 2024-11-05.

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% 6% 6% 4 6% 7% 39%	105708
	Night	5% 9% 3 8% 6% 5% 6% 4 6% 7% 41%	101864
Transparency	Day	20% 46% 7% 14% 10% 3	105473
	Night	22% 46% 9% 13% 8% 2	101745
Seeing	Day	14% 18% 32% 25% 9% 2	15010
	Night	13% 8% 31% 32% 14% 1	23580

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% 15% 10% 8% 9% 4 6% 6% 18%	2539
	11th to 20th	Day	3 12% 4 10% 6% 7% 7% 5% 7% 7% 32%	2516
	21st to end	Day	5% 17% 7% 18% 10% 7% 6% 3 4 5% 18%	2794
February	1st to 10th	Day	4 13% 4 10% 8% 7% 7% 5% 6% 8% 27%	1587
	11th to 20th	Day	4 12% 5% 10% 6% 6% 6% 4 8% 9% 29%	1665
	21st to end	Day	3 13% 6% 13% 8% 7% 6% 6% 8% 7% 23%	1556
March	1st to 10th	Day	2 12% 7% 11% 6% 6% 8% 4 7% 8% 29%	3138
	11th to 20th	Day	4 9% 3 7% 5% 5% 5% 4 5% 7% 46%	3335
	21st to end	Day	8% 16% 5% 13% 7% 7% 6% 4 5% 5% 22%	4120
April	1st to 10th	Day	7% 16% 4 9% 8% 7% 5% 5% 6% 7% 25%	2280
	11th to 20th	Day	7% 15% 5% 10% 8% 5% 5% 4 7% 7% 28%	2252
	21st to end	Day	7% 12% 3 9% 6% 7% 6% 5% 6% 7% 32%	2586
May	1st to 10th	Day	6% 9% 3 7% 5% 5% 5% 4 6% 9% 42%	4420
	11th to 20th	Day	7% 8% 3 8% 5% 5% 5% 4 6% 12% 38%	4377
	21st to end	Day	14% 12% 4 11% 6% 6% 6% 4 6% 7% 25%	4813
June	1st to 10th	Day	16% 9% 3 8% 5% 6% 5% 4 5% 6% 32%	2733
	11th to 20th	Day	13% 10% 3 9% 7% 7% 6% 5% 6% 7% 28%	2972
	21st to end	Day	10% 7% 3 8% 6% 5% 5% 5% 5% 7% 39%	2942
July	1st to 10th	Day	3 4 1 4 4 4 4 3 4 5% 64%	4651
	11th to 20th	Day	4 3 1 4 3 3 4 3 4 5% 65%	4420
	21st to end	Day	4 3 2 6% 4 4 4 4 5% 6% 57%	4790
August	1st to 10th	Day	3 2 1 4 4 4 5% 4 7% 7% 59%	4401
	11th to 20th	Day	4 3 2 7% 5% 5% 5% 4 6% 7% 51%	4255
	21st to end	Day	7% 5% 2 6% 4 4 5% 4 6% 7% 49%	4214
September	1st to 10th	Day	7% 4 2 5% 4 3 4 3 4 7% 57%	2280
	11th to 20th	Day	8% 7% 2 8% 5% 4 5% 4 5% 7% 45%	2264
	21st to end	Day	8% 8% 3 7% 4 5% 4 3 5% 7% 47%	2067
October	1st to 10th	Day	7% 4 3 7% 4 5% 4 4 5% 8% 48%	3180
	11th to 20th	Day	8% 9% 5% 10% 6% 6% 5% 4 5% 6% 37%	3084
	21st to end	Day	10% 8% 5% 12% 7% 5% 5% 4 6% 5% 34%	3101
November	1st to 10th	Day	8% 14% 5% 10% 6% 5% 7% 5% 7% 7% 26%	1639
	11th to 20th	Day	4 14% 4 9% 7% 6% 7% 4 6% 7% 31%	1520
	21st to end	Day	4 11% 4 12% 7% 7% 10% 5% 6% 7% 26%	1499
December	1st to 10th	Day	3 12% 5% 10% 6% 6% 6% 6% 8% 8% 31%	1330
	11th to 20th	Day	3 8% 5% 10% 8% 9% 14% 6% 7% 7% 22%	1682
	21st to end	Day	4 13% 5% 13% 8% 9% 10% 5% 7% 7% 20%	2706
January	1st to 10th	Night	5% 12% 6% 16% 10% 10% 9% 4 5% 6% 18%	4406
	11th to 20th	Night	4 13% 5% 10% 6% 5% 5% 4 5% 8% 35%	4382
	21st to end	Night	4 13% 6% 19% 11% 9% 9% 4 4 5% 17%	4862
February	1st to 10th	Night	5% 13% 5% 11% 9% 7% 6% 4 7% 6% 28%	2589
	11th to 20th	Night	3 11% 4 8% 6% 6% 6% 5% 6% 8% 36%	2402
	21st to end	Night	4 10% 5% 13% 6% 6% 7% 6% 9% 7% 28%	1897
March	1st to 10th	Night	3 8% 4 7% 5% 5% 6% 6% 9% 10% 36%	3736
	11th to 20th	Night	3 8% 2 6% 5% 4 5% 4 5% 7% 51%	3630
	21st to end	Night	6% 12% 5% 10% 8% 7% 6% 5% 6% 7% 28%	3533
April	1st to 10th	Night	5% 11% 3 7% 6% 7% 6% 5% 6% 7% 36%	1900
	11th to 20th	Night	4 11% 4 8% 5% 6% 6% 5% 6% 6% 40%	1879
	21st to end	Night	6% 8% 3 7% 5% 5% 5% 4 7% 8% 40%	1590
May	1st to 10th	Night	5% 7% 3 6% 4 4 4 3 5% 8% 49%	2540
	11th to 20th	Night	4 3 1 4 5% 4 4 4 7% 10% 53%	2516
	21st to end	Night	9% 7% 2 5% 4 5% 5% 5% 7% 11% 41%	2762
June	1st to 10th	Night	10% 8% 2 7% 5% 5% 5% 5% 7% 8% 40%	1439
	11th to 20th	Night	8% 7% 2 6% 3 4 6% 5% 6% 8% 44%	1202
	21st to end	Night	5% 4 1 4 3 4 6% 4 7% 9% 53%	1229
July	1st to 10th	Night	2 2 1 2 2 2 3 2 4 4 75%	2305
	11th to 20th	Night	2 2 1 3 2 2 2 3 4 5% 75%	2540
	21st to end	Night	3 3 1 3 3 3 3 3 4 6% 69%	2762
August	1st to 10th	Night	2 2 1 4 4 3 5% 3 5% 6% 65%	2529
	11th to 20th	Night	2 3 1 5% 3 3 4 4 7% 9% 60%	2559
	21st to end	Night	6% 3 1 3 3 4 5% 4 6% 8% 57%	3462
September	1st to 10th	Night	5% 4 1 4 3 3 4 3 4 7% 61%	1900
	11th to 20th	Night	6% 5% 1 5% 4 4 3 3 5% 8% 57%	1915
	21st to end	Night	6% 6% 2 5% 4 4 5% 4 6% 8% 50%	2109
October	1st to 10th	Night	5% 5% 2 6% 5% 4 5% 4 6% 7% 52%	3800
	11th to 20th	Night	9% 8% 4 8% 5% 4 5% 4 5% 7% 41%	3838
	21st to end	Night	8% 7% 3 7% 5% 5% 5% 5% 7% 7% 41%	4457
November	1st to 10th	Night	7% 13% 4 8% 6% 6% 6% 4 6% 7% 33%	2539
	11th to 20th	Night	5% 12% 3 8% 7% 7% 6% 5% 7% 8% 33%	2660
	21st to end	Night	3 12% 4 13% 8% 7% 8% 5% 6% 6% 27%	2660
December	1st to 10th	Night	3 12% 5% 11% 7% 6% 7% 5% 6% 6% 32%	2849
	11th to 20th	Night	4 14% 6% 13% 7% 7% 12% 5% 6% 6% 21%	3510
	21st to end	Night	4 14% 6% 14% 8% 7% 8% 4 5% 6% 24%	4976

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	45% 37% 5% 8% 5%	2539
	11th to 20th	Day	34% 36% 14% 9% 2 5%	2540
	21st to end	Day	54% 38% 3 4 1	2794
February	1st to 10th	Day	20% 65% 4 7% 4	1587
	11th to 20th	Day	19% 64% 5% 8% 3	1674
	21st to end	Day	14% 65% 6% 9% 6%	1556
March	1st to 10th	Day	27% 42% 8% 15% 8%	3138
	11th to 20th	Day	14% 39% 13% 29% 5%	3335
	21st to end	Day	33% 40% 10% 9% 8%	4120
April	1st to 10th	Day	16% 64% 7% 9% 4	2280
	11th to 20th	Day	14% 65% 3 12% 5% 1	2252
	21st to end	Day	15% 65% 3 9% 7% 1	2586
May	1st to 10th	Day	18% 40% 5% 20% 17% 1	4420
	11th to 20th	Day	18% 40% 9% 24% 9% 1	4380
	21st to end	Day	28% 41% 12% 13% 5% 1	4814
June	1st to 10th	Day	14% 64% 5% 11% 5% 1	2733
	11th to 20th	Day	13% 64% 4 12% 6% 1	2972
	21st to end	Day	11% 64% 4 13% 7%	2942
July	1st to 10th	Day	6% 35% 3 10% 27% 19%	4579
	11th to 20th	Day	7% 35% 2 8% 25% 23%	4345
	21st to end	Day	10% 37% 7% 17% 19% 10%	4639
August	1st to 10th	Day	7% 38% 5% 18% 26% 6%	4384
	11th to 20th	Day	12% 41% 15% 23% 8% 2	4297
	21st to end	Day	17% 38% 11% 18% 13% 3	4213
September	1st to 10th	Day	10% 60% 6% 13% 10% 1	2280
	11th to 20th	Day	14% 60% 6% 11% 9% 1	2264
	21st to end	Day	13% 60% 8% 13% 6% 1	2067
October	1st to 10th	Day	16% 38% 14% 25% 7%	3180
	11th to 20th	Day	27% 39% 8% 20% 5%	3084
	21st to end	Day	27% 39% 13% 14% 6%	3101
November	1st to 10th	Day	21% 59% 9% 9% 3	1639
	11th to 20th	Day	22% 59% 8% 6% 4 1	1520
	21st to end	Day	23% 59% 6% 6% 4 1	1499
December	1st to 10th	Day	27% 59% 5% 7% 2	1330
	11th to 20th	Day	38% 48% 7% 6% 2	1684
	21st to end	Day	43% 39% 6% 9% 3	2706
January	1st to 10th	Night	47% 35% 8% 8% 2	4406
	11th to 20th	Night	30% 36% 12% 14% 5% 4	4420
	21st to end	Night	54% 38% 4 2 1	4862
February	1st to 10th	Night	23% 65% 4 5% 3 1	2589
	11th to 20th	Night	20% 63% 5% 8% 4	2404
	21st to end	Night	14% 64% 5% 10% 6% 1	1897
March	1st to 10th	Night	23% 40% 12% 16% 9%	3736
	11th to 20th	Night	14% 39% 13% 26% 8%	3631
	21st to end	Night	33% 40% 11% 12% 4	3533
April	1st to 10th	Night	13% 64% 8% 9% 4 1	1900
	11th to 20th	Night	13% 65% 5% 11% 5% 1	1879
	21st to end	Night	13% 64% 3 11% 8%	1590
May	1st to 10th	Night	18% 40% 5% 17% 19% 1	2540
	11th to 20th	Night	13% 39% 10% 23% 12% 3	2516
	21st to end	Night	19% 38% 16% 20% 7%	2762
June	1st to 10th	Night	11% 64% 5% 14% 6% 1	1439
	11th to 20th	Night	11% 65% 5% 11% 7% 2	1202
	21st to end	Night	8% 63% 4 17% 8% 1	1229
July	1st to 10th	Night	5% 34% 1 12% 31% 16%	2268
	11th to 20th	Night	5% 35% 4 8% 24% 24%	2492
	21st to end	Night	10% 36% 6% 19% 20% 10%	2674
August	1st to 10th	Night	8% 38% 4 17% 29% 4	2521
	11th to 20th	Night	8% 42% 19% 21% 9% 1	2583
	21st to end	Night	16% 39% 13% 20% 12% 1	3462
September	1st to 10th	Night	9% 59% 6% 16% 9% 1	1900
	11th to 20th	Night	11% 59% 6% 14% 9%	1915
	21st to end	Night	13% 59% 8% 14% 5%	2109
October	1st to 10th	Night	14% 38% 18% 20% 10% 1	3800
	11th to 20th	Night	25% 39% 11% 19% 6%	3838
	21st to end	Night	22% 39% 13% 21% 4	4457
November	1st to 10th	Night	22% 58% 8% 9% 3	2539
	11th to 20th	Night	20% 60% 8% 7% 4 2	2660
	21st to end	Night	23% 59% 7% 6% 5%	2660
December	1st to 10th	Night	26% 59% 5% 8% 1	2849
	11th to 20th	Night	38% 49% 6% 5% 2	3507
	21st to end	Night	41% 37% 8% 8% 4 1	4976

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	17% 13% 33% 23% 12% 3	180
	11th to 20th	Day	22% 12% 29% 22% 13% 1	180
	21st to end	Day	27% 17% 26% 25% 5% 1	198
February	1st to 10th	Day	13% 21% 45% 19% 2	247
	11th to 20th	Day	16% 19% 40% 20% 5%	365
	21st to end	Day	11% 20% 40% 22% 7% 1	376
March	1st to 10th	Day	19% 23% 32% 20% 5% 1	460
	11th to 20th	Day	15% 22% 31% 20% 11% 2	460
	21st to end	Day	20% 24% 30% 18% 6% 1	506
April	1st to 10th	Day	23% 23% 30% 17% 5% 2	460
	11th to 20th	Day	19% 27% 27% 18% 7% 2	452
	21st to end	Day	14% 27% 29% 19% 8% 3	460
May	1st to 10th	Day	12% 23% 32% 24% 7% 2	463
	11th to 20th	Day	17% 15% 30% 23% 11% 3	488
	21st to end	Day	17% 14% 30% 25% 10% 3	529
June	1st to 10th	Day	18% 20% 33% 24% 6% 1	563
	11th to 20th	Day	14% 21% 30% 26% 9% 1	802
	21st to end	Day	7% 15% 36% 28% 12% 1	772
July	1st to 10th	Day	7% 16% 34% 33% 9% 1	623
	11th to 20th	Day	7% 17% 34% 31% 10% 1	484
	21st to end	Day	4 14% 35% 33% 11% 3	531
August	1st to 10th	Day	4 11% 33% 34% 14% 5%	487
	11th to 20th	Day	5% 12% 29% 34% 16% 3	477
	21st to end	Day	8% 18% 31% 29% 8% 6%	539
September	1st to 10th	Day	9% 17% 33% 26% 11% 5%	490
	11th to 20th	Day	12% 17% 31% 24% 12% 3	490
	21st to end	Day	15% 20% 33% 20% 8% 3	490
October	1st to 10th	Day	14% 18% 33% 21% 11% 2	490
	11th to 20th	Day	16% 19% 26% 24% 11% 3	451
	21st to end	Day	21% 18% 32% 22% 6% 2	330
November	1st to 10th	Day	24% 15% 31% 24% 5%	249
	11th to 20th	Day	21% 17% 34% 20% 6% 2	180
	21st to end	Day	16% 18% 34% 20% 10% 2	180
December	1st to 10th	Day	21% 13% 24% 26% 12% 4	180
	11th to 20th	Day	19% 14% 36% 19% 9% 2	180
	21st to end	Day	17% 10% 36% 27% 8% 2	198
January	1st to 10th	Night	19% 10% 32% 28% 10% 2	760
	11th to 20th	Night	18% 8% 34% 29% 9% 2	760
	21st to end	Night	17% 7% 32% 31% 12% 1	836
February	1st to 10th	Night	17% 7% 35% 31% 9% 1	760
	11th to 20th	Night	12% 7% 35% 32% 13% 1	744
	21st to end	Night	13% 8% 32% 32% 14% 1	628
March	1st to 10th	Night	13% 9% 31% 32% 14% 1	760
	11th to 20th	Night	10% 11% 34% 29% 14% 1	760
	21st to end	Night	11% 11% 35% 32% 10% 1	836
April	1st to 10th	Night	13% 10% 30% 33% 13% 1	760
	11th to 20th	Night	10% 9% 39% 29% 12% 2	751
	21st to end	Night	9% 14% 37% 31% 9% 1	450
May	1st to 10th	Night	8% 9% 40% 32% 11% 1	380
	11th to 20th	Night	8% 7% 29% 34% 20% 2	374
	21st to end	Night	11% 7% 29% 38% 15%	411
June	1st to 10th	Night	11% 10% 37% 29% 14%	380
	11th to 20th	Night	11% 9% 33% 37% 10%	380
	21st to end	Night	6% 6% 34% 38% 16%	380
July	1st to 10th	Night	5% 5% 29% 44% 16% 1	370
	11th to 20th	Night	3 5% 38% 38% 17%	368
	21st to end	Night	3 6% 28% 44% 19% 1	416
August	1st to 10th	Night	4 3 21% 45% 25% 1	378
	11th to 20th	Night	3 3 25% 42% 25% 2	412
	21st to end	Night	6% 6% 28% 37% 22% 2	813
September	1st to 10th	Night	5% 8% 26% 36% 23% 2	760
	11th to 20th	Night	8% 6% 21% 33% 29% 3	760
	21st to end	Night	11% 7% 28% 35% 17% 3	760
October	1st to 10th	Night	13% 9% 26% 33% 18% 2	760
	11th to 20th	Night	15% 9% 25% 35% 14% 3	760
	21st to end	Night	19% 8% 29% 31% 11% 2	836
November	1st to 10th	Night	21% 9% 31% 31% 7%	760
	11th to 20th	Night	21% 10% 32% 23% 12% 2	760
	21st to end	Night	19% 9% 31% 26% 12% 3	760
December	1st to 10th	Night	17% 6% 33% 32% 11% 1	949
	11th to 20th	Night	21% 10% 34% 28% 6% 1	950
	21st to end	Night	19% 11% 35% 29% 7%	898

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