Okanagan Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Okanagan Observatory clear sky chart from 2005-11-06 to 2026-08-30.

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	8% 11% 4 9% 5% 5% 5% 4 6% 7% 35%	148753
	Night	8% 12% 4 10% 6% 5% 5% 4 6% 7% 34%	142141
Transparency	Day	45% 9% 13% 21% 11% 2	148477
	Night	46% 8% 14% 21% 10% 2	142000
Seeing	Day	19% 14% 26% 25% 13% 4	17680
	Night	18% 9% 20% 32% 18% 3	26028

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	7% 20% 8% 20% 10% 8% 5% 3 5% 5% 10%	4723
	11th to 20th	Day	7% 11% 6% 11% 6% 4 4 3 5% 8% 36%	4716
	21st to end	Day	8% 20% 6% 14% 6% 4 4 4 4 5% 26%	5186
February	1st to 10th	Day	11% 20% 5% 12% 6% 4 4 4 7% 5% 23%	1701
	11th to 20th	Day	7% 17% 8% 15% 5% 5% 6% 4 5% 5% 23%	1848
	21st to end	Day	7% 21% 6% 16% 8% 7% 5% 4 4 5% 17%	1730
March	1st to 10th	Day	5% 13% 6% 14% 7% 8% 7% 5% 7% 6% 21%	4618
	11th to 20th	Day	6% 15% 5% 11% 6% 5% 5% 4 6% 6% 33%	4810
	21st to end	Day	10% 19% 5% 12% 7% 7% 6% 4 6% 5% 20%	6090
April	1st to 10th	Day	9% 17% 5% 10% 8% 7% 7% 6% 6% 5% 20%	2520
	11th to 20th	Day	9% 17% 5% 10% 7% 5% 5% 5% 6% 6% 26%	2533
	21st to end	Day	9% 15% 5% 10% 6% 5% 6% 4 6% 7% 28%	2845
May	1st to 10th	Day	6% 9% 3 8% 6% 5% 5% 3 6% 8% 42%	8195
	11th to 20th	Day	9% 13% 3 9% 7% 6% 7% 6% 9% 8% 23%	8160
	21st to end	Day	12% 10% 4 9% 7% 6% 6% 5% 7% 8% 26%	9173
June	1st to 10th	Day	20% 10% 3 9% 7% 6% 4 4 5% 6% 27%	3150
	11th to 20th	Day	18% 11% 3 9% 6% 6% 6% 4 6% 6% 26%	3304
	21st to end	Day	11% 8% 3 9% 6% 6% 6% 4 6% 7% 35%	3360
July	1st to 10th	Day	4 3 1 4 3 3 4 3 5% 7% 62%	8966
	11th to 20th	Day	4 3 1 4 3 3 4 3 5% 6% 64%	8220
	21st to end	Day	4 4 1 5% 4 4 5% 3 6% 8% 56%	8916
August	1st to 10th	Day	3 3 1 4 3 4 5% 4 7% 9% 58%	4681
	11th to 20th	Day	5% 3 2 6% 4 5% 6% 4 6% 8% 50%	4610
	21st to end	Day	9% 5% 2 6% 4 5% 5% 5% 7% 8% 44%	4450
September	1st to 10th	Day	8% 5% 2 6% 3 4 4 3 5% 7% 53%	2400
	11th to 20th	Day	10% 7% 2 7% 4 5% 5% 4 6% 6% 44%	2360
	21st to end	Day	13% 10% 2 7% 4 4 4 4 5% 6% 41%	2200
October	1st to 10th	Day	10% 9% 3 8% 4 4 5% 4 6% 7% 39%	3290
	11th to 20th	Day	15% 13% 4 9% 4 5% 5% 4 6% 5% 30%	3130
	21st to end	Day	12% 15% 4 8% 6% 5% 5% 4 5% 5% 30%	3200
November	1st to 10th	Day	16% 21% 5% 10% 5% 5% 5% 4 5% 6% 18%	1784
	11th to 20th	Day	11% 20% 5% 12% 5% 6% 6% 4 4 5% 20%	1680
	21st to end	Day	12% 18% 6% 9% 6% 6% 6% 5% 6% 5% 19%	1510
December	1st to 10th	Day	8% 13% 4 9% 6% 6% 5% 5% 7% 8% 29%	2360
	11th to 20th	Day	9% 20% 7% 13% 8% 5% 6% 4 7% 6% 14%	2712
	21st to end	Day	8% 19% 7% 15% 7% 6% 7% 4 7% 6% 13%	3622
January	1st to 10th	Night	7% 22% 8% 18% 9% 7% 6% 4 5% 3 10%	8172
	11th to 20th	Night	7% 11% 4 9% 5% 4 4 3 7% 8% 37%	8182
	21st to end	Night	9% 18% 6% 13% 6% 4 4 3 4 5% 28%	8994
February	1st to 10th	Night	9% 19% 6% 13% 6% 5% 5% 4 6% 5% 21%	2918
	11th to 20th	Night	7% 17% 5% 12% 6% 5% 4 4 5% 6% 28%	2658
	21st to end	Night	8% 19% 5% 12% 7% 5% 5% 4 6% 7% 22%	2076
March	1st to 10th	Night	4 12% 6% 11% 6% 6% 6% 5% 7% 8% 29%	5496
	11th to 20th	Night	6% 12% 5% 12% 6% 5% 5% 3 6% 7% 35%	5407
	21st to end	Night	8% 14% 5% 12% 7% 6% 7% 5% 6% 7% 22%	5127
April	1st to 10th	Night	6% 13% 3 9% 7% 5% 6% 5% 8% 8% 30%	2100
	11th to 20th	Night	8% 12% 3 10% 7% 6% 5% 5% 5% 6% 32%	2038
	21st to end	Night	8% 12% 3 7% 6% 5% 5% 5% 6% 7% 35%	1772
May	1st to 10th	Night	4 6% 2 5% 5% 4 5% 5% 6% 8% 49%	4724
	11th to 20th	Night	6% 11% 4 8% 4 6% 6% 6% 8% 10% 32%	4700
	21st to end	Night	10% 6% 2 7% 5% 6% 7% 5% 7% 8% 38%	4998
June	1st to 10th	Night	15% 10% 3 8% 5% 5% 4 3 6% 8% 32%	1470
	11th to 20th	Night	14% 8% 3 8% 5% 4 5% 4 5% 8% 36%	1309
	21st to end	Night	8% 6% 2 6% 5% 5% 6% 5% 7% 8% 43%	1260
July	1st to 10th	Night	3 3 1 4 4 4 4 3 5% 6% 62%	3972
	11th to 20th	Night	3 3 1 3 3 3 3 2 5% 6% 67%	4740
	21st to end	Night	4 3 1 4 3 3 3 3 5% 7% 63%	5152
August	1st to 10th	Night	2 3 1 4 4 4 4 4 6% 8% 60%	2689
	11th to 20th	Night	4 3 2 6% 3 4 4 4 7% 10% 53%	2657
	21st to end	Night	9% 5% 2 5% 4 4 5% 4 7% 7% 48%	3653
September	1st to 10th	Night	5% 4 2 5% 4 4 4 3 5% 6% 57%	2000
	11th to 20th	Night	9% 7% 3 6% 4 3 4 3 5% 8% 49%	2040
	21st to end	Night	12% 9% 2 7% 3 3 4 4 5% 8% 42%	2200
October	1st to 10th	Night	8% 7% 2 7% 5% 6% 5% 4 6% 7% 42%	3909
	11th to 20th	Night	16% 10% 3 7% 4 4 4 3 6% 7% 36%	4023
	21st to end	Night	11% 12% 5% 9% 6% 4 4 4 6% 5% 34%	4600
November	1st to 10th	Night	16% 17% 6% 10% 5% 5% 4 3 6% 5% 22%	2733
	11th to 20th	Night	14% 18% 5% 10% 7% 6% 4 3 6% 6% 21%	2940
	21st to end	Night	11% 20% 6% 12% 8% 6% 5% 4 5% 6% 18%	3087
December	1st to 10th	Night	8% 13% 4 9% 6% 4 5% 5% 6% 8% 33%	5040
	11th to 20th	Night	9% 19% 7% 15% 7% 7% 6% 4 5% 5% 15%	5700
	21st to end	Night	10% 20% 7% 15% 8% 6% 5% 4 6% 6% 15%	7605

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	69% 11% 10% 8% 2	4723
	11th to 20th	Day	43% 8% 19% 21% 6% 3	4740
	21st to end	Day	59% 8% 9% 15% 8%	5187
February	1st to 10th	Day	62% 6% 13% 12% 6% 2	1701
	11th to 20th	Day	60% 8% 12% 13% 7% 1	1857
	21st to end	Day	69% 5% 11% 12% 4	1730
March	1st to 10th	Day	51% 14% 10% 14% 10%	4618
	11th to 20th	Day	48% 8% 15% 24% 5%	4810
	21st to end	Day	62% 9% 11% 11% 7%	6090
April	1st to 10th	Day	61% 9% 12% 13% 4	2520
	11th to 20th	Day	56% 7% 13% 17% 7% 1	2533
	21st to end	Day	54% 7% 13% 18% 7% 1	2845
May	1st to 10th	Day	37% 7% 11% 31% 13% 1	8195
	11th to 20th	Day	49% 11% 14% 21% 5%	8163
	21st to end	Day	51% 10% 17% 20% 2	9174
June	1st to 10th	Day	56% 5% 10% 16% 9% 3	3150
	11th to 20th	Day	57% 7% 10% 17% 8% 1	3304
	21st to end	Day	45% 6% 14% 21% 12% 2	3360
July	1st to 10th	Day	20% 7% 12% 25% 26% 11%	8894
	11th to 20th	Day	19% 7% 10% 24% 27% 13%	8145
	21st to end	Day	22% 9% 13% 29% 21% 6%	8723
August	1st to 10th	Day	21% 8% 10% 30% 26% 5%	4664
	11th to 20th	Day	28% 9% 17% 33% 11% 2	4652
	21st to end	Day	33% 10% 17% 27% 12% 1	4449
September	1st to 10th	Day	31% 5% 16% 29% 15% 4	2400
	11th to 20th	Day	38% 6% 13% 24% 17% 2	2360
	21st to end	Day	43% 6% 20% 20% 10% 2	2200
October	1st to 10th	Day	40% 9% 21% 24% 7%	3290
	11th to 20th	Day	52% 7% 11% 25% 5%	3130
	21st to end	Day	52% 10% 15% 18% 5%	3200
November	1st to 10th	Day	64% 9% 11% 13% 4	1784
	11th to 20th	Day	64% 8% 13% 11% 3 1	1680
	21st to end	Day	62% 8% 13% 11% 5% 1	1510
December	1st to 10th	Day	51% 9% 22% 15% 3	2360
	11th to 20th	Day	65% 12% 11% 9% 3	2714
	21st to end	Day	66% 13% 11% 8% 3	3622
January	1st to 10th	Night	69% 13% 8% 8% 2	8172
	11th to 20th	Night	41% 7% 15% 24% 9% 3	8220
	21st to end	Night	57% 7% 10% 16% 10%	8994
February	1st to 10th	Night	61% 7% 11% 14% 5% 2	2918
	11th to 20th	Night	55% 6% 13% 16% 8% 1	2660
	21st to end	Night	59% 4 13% 16% 7%	2076
March	1st to 10th	Night	46% 12% 11% 20% 11%	5496
	11th to 20th	Night	44% 8% 16% 24% 8%	5408
	21st to end	Night	57% 9% 13% 15% 7%	5127
April	1st to 10th	Night	48% 7% 20% 19% 6%	2100
	11th to 20th	Night	49% 7% 15% 19% 8% 1	2038
	21st to end	Night	44% 8% 13% 24% 10% 1	1772
May	1st to 10th	Night	29% 7% 12% 38% 14%	4721
	11th to 20th	Night	37% 11% 21% 26% 5%	4700
	21st to end	Night	40% 9% 20% 26% 4	5002
June	1st to 10th	Night	48% 6% 13% 19% 12% 2	1470
	11th to 20th	Night	44% 6% 14% 24% 11% 1	1309
	21st to end	Night	35% 7% 18% 28% 10% 2	1260
July	1st to 10th	Night	20% 7% 13% 28% 22% 10%	3936
	11th to 20th	Night	17% 5% 15% 19% 29% 14%	4692
	21st to end	Night	20% 6% 11% 36% 20% 6%	5040
August	1st to 10th	Night	20% 7% 9% 32% 28% 4	2681
	11th to 20th	Night	21% 10% 22% 29% 15% 2	2681
	21st to end	Night	31% 8% 17% 28% 14% 2	3653
September	1st to 10th	Night	27% 5% 15% 31% 19% 4	2000
	11th to 20th	Night	35% 4 13% 26% 18% 4	2040
	21st to end	Night	39% 6% 20% 24% 11% 1	2200
October	1st to 10th	Night	37% 9% 18% 27% 8%	3909
	11th to 20th	Night	45% 6% 13% 25% 10%	4023
	21st to end	Night	47% 9% 17% 21% 5%	4600
November	1st to 10th	Night	60% 9% 11% 14% 5%	2733
	11th to 20th	Night	63% 8% 12% 11% 5% 1	2940
	21st to end	Night	65% 6% 13% 9% 5% 1	3087
December	1st to 10th	Night	47% 10% 20% 19% 4	5040
	11th to 20th	Night	69% 9% 11% 8% 2	5697
	21st to end	Night	64% 11% 11% 11% 3	7605

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	24% 15% 25% 20% 10% 5%	220
	11th to 20th	Day	20% 12% 25% 26% 14% 4	220
	21st to end	Day	23% 13% 26% 26% 11% 1	242
February	1st to 10th	Day	24% 12% 32% 23% 6% 3	241
	11th to 20th	Day	19% 18% 31% 20% 10% 3	428
	21st to end	Day	23% 15% 29% 23% 10%	446
March	1st to 10th	Day	23% 19% 30% 19% 7% 2	540
	11th to 20th	Day	21% 22% 24% 19% 11% 3	540
	21st to end	Day	25% 21% 22% 18% 10% 3	594
April	1st to 10th	Day	25% 16% 29% 21% 8% 1	540
	11th to 20th	Day	20% 21% 27% 19% 9% 5%	532
	21st to end	Day	21% 14% 26% 24% 10% 5%	540
May	1st to 10th	Day	17% 16% 29% 25% 10% 3	543
	11th to 20th	Day	24% 10% 23% 23% 14% 5%	568
	21st to end	Day	20% 12% 24% 23% 16% 5%	680
June	1st to 10th	Day	21% 13% 27% 24% 12% 2	780
	11th to 20th	Day	23% 14% 24% 24% 13% 3	934
	21st to end	Day	15% 11% 25% 27% 19% 5%	990
July	1st to 10th	Day	13% 11% 26% 31% 15% 4	828
	11th to 20th	Day	8% 15% 28% 31% 13% 4	564
	21st to end	Day	5% 11% 27% 35% 18% 5%	619
August	1st to 10th	Day	7% 9% 27% 32% 16% 9%	567
	11th to 20th	Day	6% 9% 27% 33% 17% 8%	557
	21st to end	Day	11% 13% 24% 28% 15% 8%	620
September	1st to 10th	Day	12% 11% 27% 25% 17% 7%	530
	11th to 20th	Day	15% 11% 25% 28% 17% 5%	530
	21st to end	Day	23% 14% 28% 18% 13% 3	530
October	1st to 10th	Day	19% 13% 28% 23% 12% 5%	530
	11th to 20th	Day	23% 16% 23% 22% 13% 3	450
	21st to end	Day	28% 12% 27% 23% 8% 3	363
November	1st to 10th	Day	31% 16% 22% 22% 8% 1	292
	11th to 20th	Day	26% 17% 23% 20% 12% 3	220
	21st to end	Day	20% 11% 28% 20% 14% 7%	220
December	1st to 10th	Day	24% 7% 20% 21% 20% 8%	220
	11th to 20th	Day	26% 15% 24% 18% 12% 4	220
	21st to end	Day	26% 8% 20% 32% 11% 3	242
January	1st to 10th	Night	30% 13% 21% 25% 9% 2	840
	11th to 20th	Night	21% 9% 26% 31% 11% 2	840
	21st to end	Night	21% 10% 24% 32% 12% 2	924
February	1st to 10th	Night	23% 10% 24% 31% 10% 3	840
	11th to 20th	Night	19% 10% 21% 36% 13% 1	824
	21st to end	Night	17% 12% 22% 29% 18% 2	692
March	1st to 10th	Night	18% 10% 24% 29% 17% 2	840
	11th to 20th	Night	20% 14% 20% 29% 15% 1	840
	21st to end	Night	19% 12% 22% 28% 16% 3	924
April	1st to 10th	Night	15% 8% 20% 36% 18% 3	840
	11th to 20th	Night	15% 10% 22% 34% 18% 2	790
	21st to end	Night	13% 11% 23% 36% 16% 2	512
May	1st to 10th	Night	12% 8% 19% 36% 24% 2	420
	11th to 20th	Night	15% 7% 15% 37% 23% 4	414
	21st to end	Night	16% 6% 15% 30% 28% 5%	455
June	1st to 10th	Night	20% 9% 16% 35% 18% 2	420
	11th to 20th	Night	17% 8% 18% 39% 15% 3	420
	21st to end	Night	11% 8% 14% 38% 26% 3	420
July	1st to 10th	Night	5% 5% 13% 36% 38% 2	410
	11th to 20th	Night	7% 5% 17% 41% 25% 3	408
	21st to end	Night	3 3 15% 40% 34% 4	460
August	1st to 10th	Night	6% 3 12% 33% 39% 7%	418
	11th to 20th	Night	6% 3 9% 39% 36% 7%	416
	21st to end	Night	8% 6% 14% 38% 31% 3	884
September	1st to 10th	Night	8% 5% 14% 39% 28% 6%	800
	11th to 20th	Night	13% 7% 13% 29% 30% 9%	800
	21st to end	Night	18% 7% 18% 32% 20% 4	800
October	1st to 10th	Night	16% 9% 16% 33% 23% 3	800
	11th to 20th	Night	21% 9% 19% 31% 18% 2	800
	21st to end	Night	22% 7% 27% 29% 11% 3	880
November	1st to 10th	Night	28% 11% 22% 29% 8% 1	820
	11th to 20th	Night	27% 14% 21% 25% 12% 2	840
	21st to end	Night	24% 12% 21% 29% 12% 2	987
December	1st to 10th	Night	21% 10% 20% 34% 13% 2	1050
	11th to 20th	Night	26% 12% 23% 29% 9% 1	1050
	21st to end	Night	27% 12% 23% 29% 8% 1	1150

Page generated at 2026-08-27 01:07:11. Version ac07

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