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 2024-10-25.

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	9% 12% 4 9% 6% 5% 5% 4 6% 6% 34%	102050
	Night	9% 13% 5% 10% 6% 5% 4 4 6% 7% 32%	96820
Transparency	Day	48% 7% 12% 19% 11% 3	101815
	Night	49% 6% 14% 19% 9% 2	96702
Seeing	Day	19% 13% 25% 25% 14% 4	15294
	Night	19% 9% 19% 33% 18% 3	23748

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	11% 20% 9% 20% 10% 7% 4 2 4 4 9%	2539
	11th to 20th	Day	8% 17% 6% 11% 7% 5% 5% 4 5% 8% 23%	2516
	21st to end	Day	11% 27% 9% 15% 5% 3 4 3 4 4 14%	2794
February	1st to 10th	Day	11% 21% 5% 12% 7% 4 4 3 6% 4 22%	1539
	11th to 20th	Day	8% 18% 8% 15% 5% 5% 5% 4 5% 5% 22%	1667
	21st to end	Day	7% 21% 7% 17% 8% 7% 5% 3 3 4 16%	1570
March	1st to 10th	Day	8% 16% 7% 16% 8% 7% 6% 4 5% 5% 19%	3138
	11th to 20th	Day	7% 13% 4 9% 5% 4 4 3 5% 5% 41%	3288
	21st to end	Day	7% 22% 6% 13% 7% 7% 5% 4 5% 4 20%	4155
April	1st to 10th	Day	10% 19% 5% 10% 8% 7% 7% 5% 6% 5% 18%	2280
	11th to 20th	Day	9% 17% 5% 10% 7% 6% 5% 5% 6% 5% 24%	2289
	21st to end	Day	10% 16% 5% 11% 6% 5% 6% 4 6% 6% 25%	2574
May	1st to 10th	Day	7% 12% 4 9% 7% 5% 5% 4 6% 8% 33%	4420
	11th to 20th	Day	8% 10% 3 9% 7% 6% 5% 5% 8% 9% 28%	4377
	21st to end	Day	14% 13% 4 10% 7% 7% 6% 4 6% 7% 21%	4909
June	1st to 10th	Day	21% 10% 3 9% 7% 6% 4 3 5% 6% 26%	2850
	11th to 20th	Day	19% 11% 3 10% 6% 6% 7% 4 5% 5% 23%	2989
	21st to end	Day	11% 7% 3 9% 6% 6% 6% 4 6% 7% 35%	3040
July	1st to 10th	Day	5% 3 2 4 3 4 4 3 5% 6% 61%	4816
	11th to 20th	Day	3 3 1 3 3 3 3 3 4 5% 68%	4420
	21st to end	Day	5% 3 1 4 4 4 5% 4 6% 7% 58%	4790
August	1st to 10th	Day	3 3 1 4 3 4 5% 4 7% 8% 58%	4401
	11th to 20th	Day	5% 3 2 5% 4 5% 6% 4 6% 8% 51%	4330
	21st to end	Day	9% 5% 2 6% 5% 5% 6% 5% 7% 8% 43%	4206
September	1st to 10th	Day	8% 6% 2 6% 3 3 4 3 5% 7% 52%	2280
	11th to 20th	Day	10% 7% 2 7% 4 5% 5% 4 6% 6% 43%	2242
	21st to end	Day	13% 10% 2 7% 4 4 4 4 5% 7% 40%	2090
October	1st to 10th	Day	11% 12% 3 8% 5% 4 4 3 5% 6% 38%	1910
	11th to 20th	Day	15% 11% 3 10% 5% 6% 6% 4 6% 5% 30%	1824
	21st to end	Day	17% 16% 5% 8% 5% 4 4 4 5% 6% 26%	1822
November	1st to 10th	Day	17% 21% 4 10% 5% 6% 5% 3 5% 5% 18%	1612
	11th to 20th	Day	12% 19% 6% 11% 5% 6% 6% 4 4 5% 21%	1520
	21st to end	Day	13% 18% 6% 8% 6% 6% 6% 5% 7% 5% 20%	1367
December	1st to 10th	Day	10% 14% 5% 11% 7% 7% 6% 5% 7% 8% 20%	1330
	11th to 20th	Day	9% 17% 9% 16% 8% 6% 6% 4 6% 5% 15%	1682
	21st to end	Day	11% 19% 7% 15% 7% 7% 6% 4 6% 5% 14%	2474
January	1st to 10th	Night	11% 24% 8% 18% 9% 5% 3 3 4 3 10%	4406
	11th to 20th	Night	9% 15% 6% 12% 6% 5% 3 3 7% 9% 24%	4382
	21st to end	Night	14% 26% 9% 15% 7% 4 4 3 3 4 13%	4862
February	1st to 10th	Night	10% 21% 6% 13% 6% 5% 4 3 6% 5% 21%	2641
	11th to 20th	Night	8% 18% 5% 12% 6% 5% 4 4 5% 6% 28%	2399
	21st to end	Night	8% 19% 5% 13% 7% 6% 5% 4 6% 6% 22%	1884
March	1st to 10th	Night	5% 13% 6% 13% 8% 6% 6% 4 7% 7% 25%	3736
	11th to 20th	Night	7% 12% 4 8% 4 3 4 3 6% 7% 43%	3689
	21st to end	Night	8% 15% 4 11% 7% 6% 6% 4 6% 7% 26%	3498
April	1st to 10th	Night	7% 14% 3 9% 7% 5% 5% 4 7% 8% 30%	1900
	11th to 20th	Night	8% 12% 3 10% 7% 6% 5% 5% 5% 6% 31%	1842
	21st to end	Night	9% 13% 3 8% 6% 5% 5% 5% 5% 7% 33%	1604
May	1st to 10th	Night	6% 10% 4 8% 5% 4 4 5% 6% 8% 40%	2540
	11th to 20th	Night	6% 6% 2 6% 4 6% 6% 6% 9% 12% 36%	2516
	21st to end	Night	12% 8% 3 7% 5% 6% 7% 6% 7% 8% 30%	2666
June	1st to 10th	Night	16% 9% 3 7% 5% 5% 5% 3 7% 8% 31%	1330
	11th to 20th	Night	15% 9% 3 8% 5% 4 5% 4 5% 9% 33%	1185
	21st to end	Night	7% 6% 2 6% 5% 5% 6% 5% 7% 8% 44%	1140
July	1st to 10th	Night	3 3 1 4 3 3 3 3 5% 6% 68%	2136
	11th to 20th	Night	3 3 1 4 3 2 3 2 4 6% 69%	2540
	21st to end	Night	4 3 1 4 3 3 4 3 5% 6% 65%	2762
August	1st to 10th	Night	2 2 1 4 4 4 4 4 6% 8% 61%	2529
	11th to 20th	Night	4 3 2 5% 3 3 4 4 7% 10% 55%	2497
	21st to end	Night	9% 5% 2 5% 4 4 5% 5% 7% 7% 47%	3456
September	1st to 10th	Night	5% 5% 2 5% 5% 4 4 3 5% 6% 56%	1900
	11th to 20th	Night	9% 7% 2 6% 4 3 4 3 5% 9% 48%	1938
	21st to end	Night	12% 9% 2 6% 3 3 4 4 5% 8% 42%	2090
October	1st to 10th	Night	11% 8% 2 8% 5% 5% 5% 4 5% 6% 41%	2269
	11th to 20th	Night	14% 11% 3 8% 6% 4 4 4 5% 6% 35%	2355
	21st to end	Night	15% 12% 4 9% 5% 4 4 3 6% 6% 32%	2639
November	1st to 10th	Night	18% 18% 6% 10% 5% 5% 4 3 6% 5% 22%	2466
	11th to 20th	Night	14% 18% 5% 10% 6% 5% 4 3 5% 6% 23%	2660
	21st to end	Night	11% 20% 6% 11% 8% 6% 4 4 5% 5% 19%	2793
December	1st to 10th	Night	10% 18% 5% 12% 8% 5% 5% 5% 5% 6% 23%	2850
	11th to 20th	Night	10% 23% 8% 13% 6% 7% 6% 4 5% 5% 14%	3510
	21st to end	Night	11% 20% 8% 15% 8% 5% 5% 3 4 6% 13%	5210

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	75% 8% 7% 7% 2	2539
	11th to 20th	Day	59% 5% 15% 13% 3 5%	2540
	21st to end	Day	74% 6% 8% 9% 3	2794
February	1st to 10th	Day	64% 5% 13% 12% 4 2	1539
	11th to 20th	Day	62% 7% 12% 12% 6% 1	1676
	21st to end	Day	70% 4 10% 12% 4	1570
March	1st to 10th	Day	62% 7% 8% 14% 9%	3138
	11th to 20th	Day	42% 6% 19% 29% 4	3288
	21st to end	Day	64% 6% 11% 11% 7%	4155
April	1st to 10th	Day	64% 9% 11% 12% 4	2280
	11th to 20th	Day	58% 6% 11% 17% 7% 1	2289
	21st to end	Day	57% 6% 13% 17% 6% 1	2574
May	1st to 10th	Day	45% 7% 12% 24% 11% 1	4420
	11th to 20th	Day	47% 6% 16% 24% 7%	4380
	21st to end	Day	59% 8% 12% 18% 3	4910
June	1st to 10th	Day	59% 5% 10% 15% 8% 3	2850
	11th to 20th	Day	61% 7% 10% 16% 6% 1	2989
	21st to end	Day	45% 6% 14% 21% 11% 2	3040
July	1st to 10th	Day	23% 6% 8% 20% 26% 16%	4744
	11th to 20th	Day	19% 4 6% 20% 33% 18%	4345
	21st to end	Day	23% 7% 11% 24% 25% 10%	4639
August	1st to 10th	Day	21% 7% 10% 30% 27% 5%	4384
	11th to 20th	Day	28% 9% 17% 33% 11% 2	4372
	21st to end	Day	33% 10% 18% 26% 12% 1	4205
September	1st to 10th	Day	32% 5% 16% 29% 15% 4	2280
	11th to 20th	Day	39% 6% 13% 23% 16% 2	2242
	21st to end	Day	43% 6% 19% 19% 11% 2	2090
October	1st to 10th	Day	46% 5% 16% 25% 8%	1910
	11th to 20th	Day	52% 6% 14% 23% 5%	1824
	21st to end	Day	57% 7% 14% 17% 5%	1822
November	1st to 10th	Day	65% 8% 11% 12% 4	1612
	11th to 20th	Day	64% 7% 14% 11% 3 1	1520
	21st to end	Day	62% 8% 13% 12% 5% 1	1367
December	1st to 10th	Day	60% 7% 12% 16% 4	1330
	11th to 20th	Day	70% 7% 10% 9% 4	1684
	21st to end	Day	68% 9% 9% 10% 3	2474
January	1st to 10th	Night	75% 8% 8% 7% 2 1	4406
	11th to 20th	Night	56% 4 12% 17% 6% 6%	4420
	21st to end	Night	74% 6% 8% 7% 3 1	4862
February	1st to 10th	Night	63% 5% 12% 14% 5% 1	2641
	11th to 20th	Night	56% 5% 14% 16% 7% 1	2401
	21st to end	Night	60% 4 13% 16% 7% 1	1884
March	1st to 10th	Night	52% 11% 12% 17% 8%	3736
	11th to 20th	Night	38% 6% 20% 29% 6%	3690
	21st to end	Night	55% 7% 15% 16% 7%	3498
April	1st to 10th	Night	49% 7% 20% 18% 6%	1900
	11th to 20th	Night	51% 6% 15% 18% 9% 1	1842
	21st to end	Night	47% 7% 13% 23% 9%	1604
May	1st to 10th	Night	39% 6% 13% 30% 12%	2540
	11th to 20th	Night	34% 5% 25% 28% 8%	2516
	21st to end	Night	46% 8% 19% 24% 3	2666
June	1st to 10th	Night	48% 6% 13% 20% 11% 2	1330
	11th to 20th	Night	47% 6% 15% 23% 9% 1	1185
	21st to end	Night	34% 7% 18% 29% 10% 2	1140
July	1st to 10th	Night	17% 4 10% 30% 24% 16%	2100
	11th to 20th	Night	18% 3 9% 19% 35% 16%	2492
	21st to end	Night	19% 5% 12% 28% 25% 11%	2674
August	1st to 10th	Night	20% 6% 9% 33% 28% 4	2521
	11th to 20th	Night	20% 10% 22% 30% 15% 2	2521
	21st to end	Night	32% 8% 17% 28% 13% 1	3456
September	1st to 10th	Night	28% 5% 14% 31% 18% 4	1900
	11th to 20th	Night	35% 4 13% 25% 18% 4	1938
	21st to end	Night	39% 6% 20% 23% 11% 1	2090
October	1st to 10th	Night	42% 7% 16% 26% 8% 1	2269
	11th to 20th	Night	49% 5% 14% 23% 9%	2355
	21st to end	Night	51% 6% 16% 20% 7%	2639
November	1st to 10th	Night	61% 8% 11% 14% 6%	2466
	11th to 20th	Night	63% 6% 13% 12% 5% 1	2660
	21st to end	Night	65% 5% 13% 10% 5% 1	2793
December	1st to 10th	Night	60% 6% 13% 17% 3 1	2850
	11th to 20th	Night	72% 7% 9% 8% 3	3507
	21st to end	Night	69% 7% 10% 11% 3	5210

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% 22% 22% 11% 6%	180
	11th to 20th	Day	21% 11% 22% 27% 14% 5%	180
	21st to end	Day	25% 15% 23% 24% 12% 2	198
February	1st to 10th	Day	26% 13% 32% 22% 6% 2	199
	11th to 20th	Day	22% 17% 28% 20% 10% 2	367
	21st to end	Day	21% 13% 30% 25% 11% 1	382
March	1st to 10th	Day	23% 18% 31% 17% 8% 3	460
	11th to 20th	Day	20% 18% 25% 20% 13% 4	460
	21st to end	Day	26% 17% 23% 20% 11% 3	506
April	1st to 10th	Day	26% 16% 29% 20% 7% 1	460
	11th to 20th	Day	20% 21% 24% 20% 10% 5%	452
	21st to end	Day	22% 15% 26% 22% 10% 5%	460
May	1st to 10th	Day	18% 15% 28% 25% 10% 4	463
	11th to 20th	Day	23% 8% 22% 25% 16% 6%	488
	21st to end	Day	20% 11% 22% 24% 18% 5%	586
June	1st to 10th	Day	22% 12% 25% 25% 13% 3	680
	11th to 20th	Day	24% 13% 23% 23% 14% 3	819
	21st to end	Day	14% 10% 24% 27% 20% 5%	870
July	1st to 10th	Day	13% 10% 25% 32% 17% 4	723
	11th to 20th	Day	8% 13% 27% 32% 15% 5%	484
	21st to end	Day	4 10% 27% 36% 18% 5%	531
August	1st to 10th	Day	7% 8% 27% 31% 17% 9%	487
	11th to 20th	Day	6% 8% 27% 33% 18% 8%	477
	21st to end	Day	11% 14% 25% 28% 14% 7%	539
September	1st to 10th	Day	13% 11% 29% 25% 16% 5%	490
	11th to 20th	Day	16% 12% 25% 27% 17% 4	490
	21st to end	Day	23% 13% 27% 19% 14% 4	490
October	1st to 10th	Day	20% 12% 27% 24% 13% 5%	490
	11th to 20th	Day	23% 16% 21% 23% 14% 4	414
	21st to end	Day	28% 9% 27% 23% 9% 3	311
November	1st to 10th	Day	30% 14% 20% 25% 10% 1	240
	11th to 20th	Day	23% 14% 23% 21% 14% 4	180
	21st to end	Day	22% 9% 23% 21% 16% 8%	180
December	1st to 10th	Day	22% 7% 18% 22% 22% 9%	180
	11th to 20th	Day	21% 13% 26% 21% 14% 5%	180
	21st to end	Day	25% 6% 18% 35% 12% 4	198
January	1st to 10th	Night	32% 10% 20% 26% 10% 2	760
	11th to 20th	Night	22% 8% 24% 32% 11% 2	760
	21st to end	Night	22% 9% 22% 31% 13% 2	836
February	1st to 10th	Night	24% 9% 22% 31% 11% 3	760
	11th to 20th	Night	20% 10% 21% 35% 13% 1	744
	21st to end	Night	16% 11% 21% 29% 20% 3	628
March	1st to 10th	Night	19% 9% 23% 28% 18% 2	760
	11th to 20th	Night	19% 13% 19% 30% 16% 2	760
	21st to end	Night	19% 10% 20% 30% 18% 3	836
April	1st to 10th	Night	16% 8% 20% 36% 18% 3	760
	11th to 20th	Night	15% 10% 20% 35% 18% 2	714
	21st to end	Night	13% 11% 24% 35% 15% 2	464
May	1st to 10th	Night	13% 7% 17% 36% 24% 2	380
	11th to 20th	Night	14% 5% 14% 38% 25% 4	374
	21st to end	Night	16% 6% 13% 30% 29% 5%	411
June	1st to 10th	Night	20% 8% 16% 34% 19% 2	380
	11th to 20th	Night	19% 7% 16% 37% 17% 3	380
	21st to end	Night	11% 7% 13% 39% 27% 3	380
July	1st to 10th	Night	5% 4 12% 36% 40% 2	370
	11th to 20th	Night	8% 5% 15% 41% 27% 4	368
	21st to end	Night	4 3 13% 40% 35% 5%	416
August	1st to 10th	Night	5% 2 11% 33% 41% 8%	378
	11th to 20th	Night	7% 2 8% 38% 38% 7%	376
	21st to end	Night	8% 6% 14% 38% 30% 3	807
September	1st to 10th	Night	8% 6% 14% 39% 26% 6%	760
	11th to 20th	Night	14% 6% 12% 28% 30% 10%	760
	21st to end	Night	19% 7% 16% 32% 21% 5%	760
October	1st to 10th	Night	16% 8% 16% 33% 24% 3	760
	11th to 20th	Night	22% 8% 18% 31% 19% 2	760
	21st to end	Night	22% 6% 27% 30% 12% 4	812
November	1st to 10th	Night	28% 11% 21% 31% 9% 1	740
	11th to 20th	Night	26% 13% 21% 26% 13% 2	760
	21st to end	Night	25% 11% 19% 30% 12% 3	893
December	1st to 10th	Night	21% 9% 20% 35% 14% 2	950
	11th to 20th	Night	25% 11% 23% 31% 9% 1	950
	21st to end	Night	27% 11% 23% 30% 9% 1	1041

Page generated at 2024-10-22 17:21:03. Version ac07

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