Penticton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Penticton clear sky chart from 2005-11-06 to 2025-08-05.

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% 8% 3 8% 5% 5% 5% 4 6% 8% 41%	130174
	Night	7% 10% 3 8% 5% 5% 5% 4 6% 8% 37%	126585
Transparency	Day	42% 8% 14% 22% 12% 3	129895
	Night	45% 7% 14% 21% 10% 2	126441
Seeing	Day	13% 18% 30% 25% 12% 3	16171
	Night	12% 11% 27% 32% 17% 2	24581

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	8% 16% 6% 14% 8% 5% 7% 5% 7% 7% 17%	3639
	11th to 20th	Day	8% 10% 2 7% 7% 5% 5% 4 9% 13% 30%	3616
	21st to end	Day	9% 18% 5% 9% 5% 5% 6% 5% 7% 6% 27%	4004
February	1st to 10th	Day	5% 15% 4 13% 7% 7% 7% 5% 5% 7% 26%	1653
	11th to 20th	Day	6% 12% 6% 11% 8% 6% 5% 4 7% 7% 27%	1755
	21st to end	Day	5% 14% 4 13% 9% 7% 6% 5% 7% 7% 23%	1635
March	1st to 10th	Day	3 9% 4 9% 6% 6% 7% 5% 8% 10% 34%	4518
	11th to 20th	Day	3 10% 4 9% 6% 6% 5% 4 6% 8% 40%	4770
	21st to end	Day	7% 14% 4 11% 6% 6% 6% 6% 7% 8% 25%	5915
April	1st to 10th	Day	8% 11% 4 9% 8% 7% 6% 5% 7% 8% 28%	2400
	11th to 20th	Day	7% 11% 3 7% 6% 7% 5% 5% 7% 8% 33%	2383
	21st to end	Day	7% 11% 4 9% 6% 5% 6% 4 6% 9% 33%	2729
May	1st to 10th	Day	6% 8% 3 7% 5% 4 5% 4 5% 7% 46%	6320
	11th to 20th	Day	8% 10% 4 9% 6% 6% 7% 5% 7% 9% 30%	6277
	21st to end	Day	10% 8% 3 8% 5% 5% 5% 4 6% 9% 36%	6903
June	1st to 10th	Day	13% 7% 3 7% 6% 5% 6% 4 6% 7% 35%	2965
	11th to 20th	Day	13% 8% 3 8% 6% 5% 6% 5% 6% 8% 32%	3171
	21st to end	Day	8% 5% 2 6% 6% 5% 6% 5% 7% 8% 43%	3192
July	1st to 10th	Day	3 2 1 3 3 3 4 3 5% 7% 66%	6739
	11th to 20th	Day	2 2 1 3 3 3 3 3 4 5% 72%	6320
	21st to end	Day	2 2 1 4 3 3 4 4 6% 8% 62%	6874
August	1st to 10th	Day	2 1 1 3 3 4 5% 5% 6% 8% 63%	4458
	11th to 20th	Day	3 2 1 4 3 4 5% 4 7% 9% 58%	4299
	21st to end	Day	6% 3 1 4 4 5% 5% 4 6% 8% 53%	4216
September	1st to 10th	Day	5% 5% 2 5% 4 3 3 4 5% 6% 58%	2280
	11th to 20th	Day	8% 5% 2 5% 5% 5% 6% 5% 6% 6% 48%	2259
	21st to end	Day	8% 7% 3 7% 3 5% 4 4 6% 7% 46%	2074
October	1st to 10th	Day	6% 5% 2 7% 5% 5% 4 4 6% 7% 49%	3180
	11th to 20th	Day	9% 8% 4 8% 6% 6% 5% 4 5% 6% 38%	3072
	21st to end	Day	8% 10% 3 9% 5% 6% 6% 5% 6% 6% 36%	3101
November	1st to 10th	Day	11% 13% 4 10% 7% 6% 6% 5% 7% 8% 25%	1682
	11th to 20th	Day	9% 13% 5% 12% 8% 8% 7% 5% 5% 6% 24%	1600
	21st to end	Day	8% 14% 5% 11% 8% 7% 7% 6% 7% 6% 22%	1515
December	1st to 10th	Day	4 10% 2 10% 7% 7% 8% 7% 10% 10% 25%	2290
	11th to 20th	Day	8% 16% 5% 14% 7% 7% 7% 6% 8% 8% 14%	2642
	21st to end	Day	8% 16% 6% 14% 7% 8% 6% 5% 7% 8% 15%	3728
January	1st to 10th	Night	8% 18% 9% 16% 8% 6% 6% 4 6% 5% 14%	6306
	11th to 20th	Night	6% 11% 4 8% 6% 5% 5% 6% 9% 14% 26%	6282
	21st to end	Night	10% 18% 4 10% 5% 6% 5% 4 6% 7% 25%	6952
February	1st to 10th	Night	7% 15% 5% 13% 8% 7% 5% 4 5% 7% 24%	2745
	11th to 20th	Night	7% 15% 4 10% 7% 5% 6% 4 6% 6% 31%	2532
	21st to end	Night	6% 16% 5% 11% 6% 5% 5% 4 6% 7% 27%	1994
March	1st to 10th	Night	3 8% 3 9% 6% 7% 6% 5% 9% 10% 36%	5376
	11th to 20th	Night	3 10% 3 8% 6% 5% 6% 4 6% 8% 41%	5226
	21st to end	Night	7% 12% 4 11% 7% 8% 7% 5% 7% 8% 24%	5060
April	1st to 10th	Night	7% 10% 3 7% 5% 6% 5% 5% 6% 10% 35%	2000
	11th to 20th	Night	6% 8% 3 7% 6% 5% 6% 5% 7% 8% 38%	1967
	21st to end	Night	7% 9% 2 8% 6% 6% 5% 5% 6% 8% 38%	1670
May	1st to 10th	Night	6% 6% 2 5% 4 5% 5% 4 6% 8% 51%	3640
	11th to 20th	Night	7% 8% 2 7% 5% 5% 5% 5% 7% 10% 39%	3616
	21st to end	Night	8% 5% 2 5% 4 4 5% 4 6% 9% 47%	3972
June	1st to 10th	Night	10% 8% 2 7% 5% 4 5% 4 6% 9% 40%	1430
	11th to 20th	Night	10% 7% 2 7% 5% 5% 4 4 7% 8% 42%	1224
	21st to end	Night	6% 4 1 5% 5% 4 4 4 6% 7% 52%	1202
July	1st to 10th	Night	3 2 1 3 2 2 3 3 4 5% 72%	3216
	11th to 20th	Night	2 1 1 3 2 3 3 2 5% 5% 74%	3640
	21st to end	Night	3 2 1 3 3 3 3 3 5% 7% 67%	3969
August	1st to 10th	Night	2 2 1 4 3 4 4 4 5% 6% 64%	2561
	11th to 20th	Night	2 2 1 3 3 4 4 4 7% 11% 59%	2527
	21st to end	Night	6% 4 2 5% 4 4 5% 5% 6% 7% 53%	3461
September	1st to 10th	Night	5% 3 1 4 3 3 4 4 5% 7% 61%	1900
	11th to 20th	Night	6% 5% 2 5% 3 4 3 3 5% 8% 54%	1920
	21st to end	Night	7% 6% 3 7% 4 4 4 4 6% 8% 48%	2104
October	1st to 10th	Night	7% 5% 2 6% 4 5% 5% 4 6% 7% 50%	3800
	11th to 20th	Night	13% 8% 3 7% 4 4 4 4 6% 7% 40%	3862
	21st to end	Night	9% 10% 3 9% 5% 5% 5% 4 5% 6% 39%	4457
November	1st to 10th	Night	12% 14% 4 8% 6% 6% 6% 4 7% 7% 25%	2615
	11th to 20th	Night	8% 14% 5% 11% 7% 7% 5% 5% 6% 7% 25%	2800
	21st to end	Night	7% 16% 5% 11% 8% 7% 7% 5% 7% 7% 20%	2863
December	1st to 10th	Night	5% 10% 4 9% 6% 5% 6% 5% 9% 11% 31%	4890
	11th to 20th	Night	8% 17% 7% 14% 8% 6% 8% 5% 7% 6% 14%	5550
	21st to end	Night	10% 19% 6% 12% 8% 6% 6% 5% 8% 6% 15%	7256

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	64% 8% 10% 15% 2	3639
	11th to 20th	Day	41% 7% 22% 21% 5% 4	3640
	21st to end	Day	59% 7% 13% 13% 8%	4004
February	1st to 10th	Day	58% 10% 12% 12% 8% 2	1653
	11th to 20th	Day	58% 10% 13% 13% 6% 1	1764
	21st to end	Day	61% 10% 12% 12% 5%	1635
March	1st to 10th	Day	48% 9% 12% 15% 15% 1	4518
	11th to 20th	Day	44% 6% 15% 28% 6%	4770
	21st to end	Day	57% 11% 12% 13% 8%	5915
April	1st to 10th	Day	56% 12% 14% 14% 4 1	2400
	11th to 20th	Day	52% 11% 10% 18% 8% 1	2383
	21st to end	Day	49% 11% 12% 19% 9% 1	2729
May	1st to 10th	Day	38% 9% 8% 28% 17% 1	6320
	11th to 20th	Day	49% 10% 15% 20% 6%	6280
	21st to end	Day	44% 9% 15% 26% 6%	6904
June	1st to 10th	Day	49% 9% 10% 16% 11% 4	2965
	11th to 20th	Day	51% 11% 11% 19% 8%	3171
	21st to end	Day	40% 11% 15% 21% 13% 1	3192
July	1st to 10th	Day	20% 4 11% 26% 26% 13%	6665
	11th to 20th	Day	16% 3 12% 29% 26% 14%	6245
	21st to end	Day	21% 4 15% 31% 21% 7%	6681
August	1st to 10th	Day	20% 6% 10% 29% 29% 6%	4441
	11th to 20th	Day	24% 6% 20% 34% 13% 3	4341
	21st to end	Day	31% 6% 18% 28% 16% 1	4215
September	1st to 10th	Day	28% 7% 16% 28% 17% 4	2280
	11th to 20th	Day	36% 9% 11% 24% 17% 3	2259
	21st to end	Day	38% 8% 19% 21% 12% 2	2074
October	1st to 10th	Day	39% 6% 17% 32% 6%	3180
	11th to 20th	Day	49% 6% 11% 27% 7%	3072
	21st to end	Day	50% 7% 16% 20% 6%	3101
November	1st to 10th	Day	60% 11% 11% 13% 6%	1682
	11th to 20th	Day	60% 11% 11% 13% 5% 1	1600
	21st to end	Day	59% 10% 14% 11% 5% 1	1515
December	1st to 10th	Day	47% 9% 26% 16% 2	2290
	11th to 20th	Day	64% 10% 12% 10% 5%	2644
	21st to end	Day	65% 9% 13% 10% 3	3728
January	1st to 10th	Night	70% 6% 10% 13% 2	6306
	11th to 20th	Night	43% 9% 18% 18% 9% 4	6320
	21st to end	Night	58% 6% 13% 15% 8%	6952
February	1st to 10th	Night	59% 8% 12% 12% 7% 1	2745
	11th to 20th	Night	54% 7% 14% 17% 7% 1	2534
	21st to end	Night	57% 9% 14% 14% 6%	1994
March	1st to 10th	Night	44% 9% 12% 22% 13%	5376
	11th to 20th	Night	43% 6% 16% 25% 10%	5227
	21st to end	Night	58% 9% 11% 15% 6%	5060
April	1st to 10th	Night	46% 13% 18% 18% 5%	2000
	11th to 20th	Night	44% 9% 14% 20% 11%	1967
	21st to end	Night	43% 9% 13% 24% 10%	1670
May	1st to 10th	Night	32% 6% 10% 33% 18% 1	3637
	11th to 20th	Night	38% 9% 19% 28% 6% 1	3616
	21st to end	Night	33% 10% 18% 33% 5% 1	3972
June	1st to 10th	Night	43% 8% 12% 21% 13% 3	1430
	11th to 20th	Night	41% 9% 15% 24% 12%	1224
	21st to end	Night	29% 11% 17% 27% 13% 2	1202
July	1st to 10th	Night	17% 4 13% 26% 27% 13%	3181
	11th to 20th	Night	15% 4 16% 24% 28% 14%	3592
	21st to end	Night	19% 3 12% 37% 21% 8%	3857
August	1st to 10th	Night	23% 4 8% 28% 33% 4	2553
	11th to 20th	Night	19% 5% 23% 35% 16% 2	2551
	21st to end	Night	30% 6% 18% 30% 15% 2	3461
September	1st to 10th	Night	23% 8% 14% 31% 20% 4	1900
	11th to 20th	Night	28% 9% 12% 27% 20% 4	1920
	21st to end	Night	34% 9% 17% 26% 11% 2	2104
October	1st to 10th	Night	38% 5% 18% 29% 10%	3800
	11th to 20th	Night	46% 5% 11% 26% 11%	3862
	21st to end	Night	48% 6% 15% 25% 7%	4457
November	1st to 10th	Night	58% 9% 13% 14% 5% 1	2615
	11th to 20th	Night	59% 9% 14% 13% 5% 1	2800
	21st to end	Night	61% 10% 12% 12% 5% 1	2863
December	1st to 10th	Night	43% 9% 20% 24% 4	4890
	11th to 20th	Night	67% 8% 13% 10% 3	5547
	21st to end	Night	63% 9% 12% 12% 4	7256

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	15% 23% 30% 19% 11% 3	200
	11th to 20th	Day	14% 16% 32% 24% 12% 3	200
	21st to end	Day	17% 18% 36% 22% 7%	220
February	1st to 10th	Day	14% 21% 40% 19% 5%	253
	11th to 20th	Day	12% 22% 39% 22% 5% 1	395
	21st to end	Day	14% 22% 36% 18% 9% 1	407
March	1st to 10th	Day	15% 25% 30% 21% 8% 1	500
	11th to 20th	Day	12% 25% 27% 23% 11% 2	500
	21st to end	Day	17% 24% 31% 18% 8% 2	550
April	1st to 10th	Day	24% 23% 27% 16% 7% 2	500
	11th to 20th	Day	17% 25% 28% 18% 9% 3	492
	21st to end	Day	15% 21% 31% 21% 9% 3	500
May	1st to 10th	Day	13% 21% 32% 23% 9% 2	503
	11th to 20th	Day	15% 14% 30% 25% 14% 3	528
	21st to end	Day	15% 16% 27% 24% 14% 3	573
June	1st to 10th	Day	15% 16% 28% 28% 11% 2	695
	11th to 20th	Day	15% 17% 30% 24% 11% 2	901
	21st to end	Day	9% 12% 30% 28% 19% 2	922
July	1st to 10th	Day	6% 13% 33% 32% 15% 2	706
	11th to 20th	Day	6% 14% 29% 31% 16% 4	524
	21st to end	Day	5% 10% 29% 35% 15% 6%	575
August	1st to 10th	Day	5% 7% 26% 36% 19% 7%	504
	11th to 20th	Day	5% 9% 29% 31% 19% 7%	477
	21st to end	Day	8% 17% 27% 28% 14% 6%	539
September	1st to 10th	Day	9% 16% 30% 25% 15% 6%	490
	11th to 20th	Day	11% 15% 28% 25% 16% 4	490
	21st to end	Day	15% 20% 32% 19% 10% 3	490
October	1st to 10th	Day	14% 20% 27% 23% 12% 3	490
	11th to 20th	Day	16% 19% 26% 25% 10% 3	439
	21st to end	Day	16% 18% 33% 24% 7% 1	330
November	1st to 10th	Day	19% 22% 29% 24% 5%	258
	11th to 20th	Day	20% 25% 28% 18% 8% 2	200
	21st to end	Day	15% 22% 29% 20% 13% 3	200
December	1st to 10th	Day	15% 16% 24% 24% 18% 5%	200
	11th to 20th	Day	14% 20% 35% 21% 9% 2	200
	21st to end	Day	13% 17% 33% 28% 8% 2	220
January	1st to 10th	Night	17% 16% 32% 26% 9% 1	800
	11th to 20th	Night	13% 12% 33% 31% 10% 2	800
	21st to end	Night	11% 13% 33% 30% 11% 2	880
February	1st to 10th	Night	15% 14% 32% 28% 10% 2	800
	11th to 20th	Night	12% 9% 32% 35% 11% 1	784
	21st to end	Night	12% 15% 28% 28% 16% 1	660
March	1st to 10th	Night	11% 12% 30% 27% 18% 2	800
	11th to 20th	Night	9% 14% 31% 31% 15% 1	800
	21st to end	Night	11% 13% 29% 32% 14% 1	880
April	1st to 10th	Night	11% 13% 25% 34% 15% 3	800
	11th to 20th	Night	10% 11% 33% 29% 17% 1	779
	21st to end	Night	10% 11% 32% 31% 15% 1	470
May	1st to 10th	Night	10% 9% 27% 37% 17% 1	400
	11th to 20th	Night	12% 5% 18% 38% 26% 2	394
	21st to end	Night	12% 6% 21% 32% 26% 2	433
June	1st to 10th	Night	12% 8% 26% 40% 14% 1	400
	11th to 20th	Night	12% 8% 25% 36% 19% 1	400
	21st to end	Night	7% 5% 24% 38% 24% 2	400
July	1st to 10th	Night	6% 4 19% 40% 30% 2	390
	11th to 20th	Night	4 6% 23% 40% 26% 2	388
	21st to end	Night	3 5% 16% 42% 31% 3	438
August	1st to 10th	Night	4 3 14% 37% 38% 3	386
	11th to 20th	Night	5% 1 16% 36% 38% 5%	393
	21st to end	Night	6% 5% 20% 38% 29% 3	812
September	1st to 10th	Night	6% 6% 21% 36% 28% 4	760
	11th to 20th	Night	8% 6% 16% 32% 29% 9%	760
	21st to end	Night	11% 7% 23% 34% 22% 3	760
October	1st to 10th	Night	13% 7% 20% 33% 24% 3	760
	11th to 20th	Night	12% 12% 24% 34% 17% 2	760
	21st to end	Night	17% 11% 29% 29% 12% 3	836
November	1st to 10th	Night	17% 13% 33% 28% 7% 1	780
	11th to 20th	Night	18% 17% 28% 25% 12% 2	800
	21st to end	Night	14% 16% 30% 26% 10% 3	863
December	1st to 10th	Night	13% 14% 29% 31% 12% 2	1000
	11th to 20th	Night	16% 14% 34% 27% 9% 1	1000
	21st to end	Night	19% 14% 34% 26% 7%	1015

Page generated at 2025-08-01 22:32:28. Version ac07

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