Pinawa
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pinawa 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	11% 9% 4 9% 6% 5% 5% 4 6% 7% 34%	130935
	Night	10% 11% 4 10% 6% 5% 5% 4 6% 7% 31%	127568
Transparency	Day	47% 7% 14% 22% 9% 1	130630
	Night	51% 6% 13% 20% 8% 1	127453
Seeing	Day	15% 10% 31% 27% 13% 3	17626
	Night	16% 8% 31% 32% 12% 1	27469

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	5% 16% 8% 17% 6% 7% 7% 6% 5% 6% 18%	3179
	11th to 20th	Day	4 11% 6% 16% 10% 10% 10% 8% 10% 6% 10%	3159
	21st to end	Day	6% 18% 10% 19% 8% 7% 6% 4 5% 5% 14%	3837
February	1st to 10th	Day	8% 13% 5% 11% 7% 8% 7% 7% 8% 8% 18%	1769
	11th to 20th	Day	8% 10% 4 10% 7% 8% 8% 5% 8% 7% 25%	1754
	21st to end	Day	6% 12% 5% 13% 7% 7% 7% 4 6% 6% 26%	1499
March	1st to 10th	Day	8% 11% 4 10% 8% 4 5% 4 5% 7% 32%	4712
	11th to 20th	Day	9% 10% 6% 14% 9% 5% 6% 4 5% 7% 26%	4978
	21st to end	Day	10% 14% 5% 9% 6% 5% 4 3 5% 7% 34%	5464
April	1st to 10th	Day	11% 12% 4 9% 5% 4 4 4 5% 6% 36%	2428
	11th to 20th	Day	13% 9% 4 7% 5% 5% 5% 3 5% 7% 36%	2572
	21st to end	Day	16% 10% 3 6% 4 4 5% 3 6% 7% 34%	2600
May	1st to 10th	Day	12% 8% 2 6% 4 3 4 3 4 7% 46%	6262
	11th to 20th	Day	18% 9% 2 7% 5% 4 4 4 6% 8% 33%	6505
	21st to end	Day	15% 7% 2 6% 4 3 3 3 5% 6% 46%	7428
June	1st to 10th	Day	15% 7% 2 7% 6% 5% 5% 4 5% 8% 35%	3000
	11th to 20th	Day	16% 7% 2 6% 5% 4 5% 4 6% 8% 34%	3000
	21st to end	Day	14% 6% 2 7% 5% 6% 6% 5% 6% 9% 33%	3000
July	1st to 10th	Day	8% 5% 2 6% 5% 5% 6% 4 7% 10% 42%	6800
	11th to 20th	Day	10% 5% 2 6% 4 5% 5% 4 6% 9% 44%	6800
	21st to end	Day	10% 5% 2 6% 4 4 5% 4 6% 9% 44%	7400
August	1st to 10th	Day	9% 6% 2 6% 5% 5% 5% 4 6% 9% 42%	4394
	11th to 20th	Day	11% 5% 2 6% 5% 5% 5% 4 6% 9% 43%	4171
	21st to end	Day	15% 6% 2 6% 4 4 5% 4 5% 8% 40%	4675
September	1st to 10th	Day	12% 6% 2 5% 5% 5% 4 4 6% 7% 44%	2463
	11th to 20th	Day	16% 7% 3 8% 5% 5% 4 5% 7% 8% 33%	2248
	21st to end	Day	16% 7% 3 6% 3 4 3 3 5% 7% 41%	2190
October	1st to 10th	Day	14% 10% 2 7% 5% 5% 4 4 6% 8% 36%	3260
	11th to 20th	Day	12% 11% 3 8% 4 4 4 3 6% 8% 38%	3220
	21st to end	Day	15% 13% 3 9% 6% 5% 4 4 6% 8% 28%	3044
November	1st to 10th	Day	16% 18% 6% 11% 4 5% 4 3 4 5% 23%	1567
	11th to 20th	Day	12% 18% 5% 14% 7% 5% 4 2 6% 6% 21%	1600
	21st to end	Day	12% 17% 6% 15% 10% 5% 4 3 5% 6% 17%	1530
December	1st to 10th	Day	11% 16% 6% 17% 12% 10% 5% 5% 4 4 10%	2290
	11th to 20th	Day	8% 14% 6% 14% 7% 5% 6% 6% 8% 9% 18%	2639
	21st to end	Day	8% 17% 7% 19% 7% 7% 5% 4 5% 5% 15%	3498
January	1st to 10th	Night	4 14% 7% 17% 8% 9% 7% 6% 8% 6% 15%	6787
	11th to 20th	Night	5% 13% 6% 15% 10% 10% 10% 7% 9% 5% 10%	6759
	21st to end	Night	7% 19% 8% 14% 7% 6% 6% 4 6% 6% 17%	7140
February	1st to 10th	Night	8% 13% 5% 10% 7% 7% 6% 5% 6% 8% 25%	2630
	11th to 20th	Night	5% 11% 5% 8% 5% 6% 7% 6% 8% 8% 31%	2533
	21st to end	Night	6% 12% 4 13% 7% 6% 6% 5% 5% 6% 29%	2145
March	1st to 10th	Night	7% 13% 5% 11% 8% 5% 5% 4 5% 6% 30%	5156
	11th to 20th	Night	7% 10% 4 9% 6% 6% 5% 4 6% 7% 36%	4980
	21st to end	Night	12% 13% 5% 10% 5% 5% 4 3 5% 5% 33%	5467
April	1st to 10th	Night	11% 10% 3 6% 5% 5% 5% 4 6% 6% 40%	1970
	11th to 20th	Night	14% 11% 3 8% 4 4 4 4 6% 6% 36%	1779
	21st to end	Night	11% 10% 3 8% 5% 5% 6% 3 5% 7% 36%	1800
May	1st to 10th	Night	13% 7% 3 6% 4 3 3 3 5% 6% 47%	3717
	11th to 20th	Night	17% 6% 2 5% 4 4 5% 4 6% 8% 38%	3407
	21st to end	Night	13% 8% 2 5% 3 3 3 3 6% 6% 49%	3470
June	1st to 10th	Night	13% 7% 2 6% 4 4 5% 4 6% 9% 39%	1400
	11th to 20th	Night	14% 7% 2 7% 4 3 4 3 6% 8% 42%	1400
	21st to end	Night	12% 6% 2 5% 5% 5% 5% 4 6% 8% 42%	1400
July	1st to 10th	Night	8% 4 2 5% 4 4 4 4 5% 8% 51%	3180
	11th to 20th	Night	9% 4 2 5% 4 4 5% 5% 7% 9% 47%	3180
	21st to end	Night	7% 4 2 5% 4 4 5% 4 7% 10% 48%	3466
August	1st to 10th	Night	8% 4 2 7% 4 4 5% 4 7% 10% 46%	2763
	11th to 20th	Night	10% 4 2 5% 3 4 5% 4 6% 9% 50%	2888
	21st to end	Night	11% 6% 2 6% 4 4 4 3 6% 9% 44%	3234
September	1st to 10th	Night	12% 4 2 5% 4 3 4 3 5% 7% 49%	1936
	11th to 20th	Night	17% 7% 3 6% 4 4 4 4 5% 7% 40%	2150
	21st to end	Night	17% 8% 2 5% 4 3 4 3 5% 7% 42%	2200
October	1st to 10th	Night	16% 7% 2 6% 4 4 4 3 5% 8% 41%	3910
	11th to 20th	Night	12% 12% 3 7% 4 4 4 4 5% 8% 37%	3876
	21st to end	Night	12% 13% 4 8% 5% 5% 5% 4 5% 6% 33%	4498
November	1st to 10th	Night	14% 17% 4 11% 6% 5% 5% 4 4 5% 26%	2731
	11th to 20th	Night	13% 17% 6% 15% 8% 5% 4 3 4 5% 22%	2800
	21st to end	Night	12% 17% 7% 16% 8% 6% 4 4 4 4 17%	2868
December	1st to 10th	Night	9% 19% 7% 18% 11% 7% 5% 3 4 4 12%	4900
	11th to 20th	Night	8% 13% 6% 15% 8% 5% 6% 7% 7% 7% 19%	5568
	21st to end	Night	8% 13% 8% 20% 8% 6% 5% 4 5% 5% 18%	7480

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	67% 5% 8% 12% 7%	3179
	11th to 20th	Day	68% 5% 9% 15% 3	3180
	21st to end	Day	72% 5% 8% 12% 3	3837
February	1st to 10th	Day	60% 6% 12% 13% 8% 1	1769
	11th to 20th	Day	53% 5% 14% 20% 8%	1763
	21st to end	Day	56% 7% 12% 14% 9% 1	1499
March	1st to 10th	Day	50% 6% 15% 16% 10% 3	4712
	11th to 20th	Day	55% 8% 12% 17% 8%	4980
	21st to end	Day	50% 6% 10% 23% 11% 1	5464
April	1st to 10th	Day	47% 6% 11% 22% 12% 1	2428
	11th to 20th	Day	47% 5% 11% 22% 13% 2	2572
	21st to end	Day	48% 6% 13% 22% 10% 1	2600
May	1st to 10th	Day	36% 7% 11% 26% 19% 1	6261
	11th to 20th	Day	46% 7% 10% 22% 13% 1	6509
	21st to end	Day	38% 6% 8% 24% 21% 4	7428
June	1st to 10th	Day	46% 7% 12% 22% 11% 1	3000
	11th to 20th	Day	45% 8% 15% 21% 10% 1	3000
	21st to end	Day	44% 9% 19% 21% 7%	3000
July	1st to 10th	Day	35% 8% 20% 28% 8% 1	6726
	11th to 20th	Day	35% 7% 19% 34% 5%	6719
	21st to end	Day	35% 7% 19% 32% 7%	7193
August	1st to 10th	Day	37% 7% 17% 29% 10%	4377
	11th to 20th	Day	36% 7% 23% 28% 5%	4210
	21st to end	Day	41% 7% 21% 27% 4	4674
September	1st to 10th	Day	38% 7% 17% 29% 8% 1	2463
	11th to 20th	Day	47% 8% 19% 21% 4	2248
	21st to end	Day	43% 5% 15% 31% 6%	2190
October	1st to 10th	Day	45% 6% 16% 27% 6%	3260
	11th to 20th	Day	44% 5% 15% 22% 13%	3220
	21st to end	Day	53% 6% 19% 19% 3	3044
November	1st to 10th	Day	63% 7% 12% 13% 4 1	1567
	11th to 20th	Day	65% 7% 13% 12% 3	1600
	21st to end	Day	68% 6% 16% 9% 2	1530
December	1st to 10th	Day	76% 7% 10% 5% 2	2290
	11th to 20th	Day	59% 6% 15% 14% 7%	2640
	21st to end	Day	67% 7% 10% 14% 3	3498
January	1st to 10th	Night	66% 6% 10% 11% 8%	6787
	11th to 20th	Night	68% 6% 8% 14% 4	6800
	21st to end	Night	66% 6% 11% 12% 5%	7140
February	1st to 10th	Night	55% 6% 13% 17% 8% 1	2630
	11th to 20th	Night	45% 7% 17% 22% 8%	2534
	21st to end	Night	53% 6% 12% 18% 10%	2145
March	1st to 10th	Night	53% 6% 12% 14% 10% 4	5156
	11th to 20th	Night	43% 8% 16% 20% 12% 1	4980
	21st to end	Night	51% 6% 9% 22% 12% 1	5467
April	1st to 10th	Night	43% 5% 10% 23% 15% 3	1970
	11th to 20th	Night	47% 5% 9% 22% 15% 2	1779
	21st to end	Night	47% 5% 9% 24% 13% 1	1800
May	1st to 10th	Night	37% 6% 9% 28% 19% 1	3717
	11th to 20th	Night	42% 6% 12% 27% 12% 2	3407
	21st to end	Night	34% 6% 9% 24% 23% 3	3470
June	1st to 10th	Night	39% 9% 18% 21% 12% 1	1400
	11th to 20th	Night	39% 7% 15% 23% 14% 2	1400
	21st to end	Night	39% 8% 18% 27% 8% 1	1400
July	1st to 10th	Night	32% 6% 18% 35% 9% 1	3145
	11th to 20th	Night	30% 8% 21% 36% 5% 1	3138
	21st to end	Night	30% 8% 24% 31% 7%	3368
August	1st to 10th	Night	31% 7% 17% 35% 10%	2756
	11th to 20th	Night	30% 7% 25% 32% 6%	2915
	21st to end	Night	35% 6% 21% 30% 7%	3234
September	1st to 10th	Night	33% 7% 17% 32% 11%	1936
	11th to 20th	Night	43% 8% 17% 24% 8% 1	2150
	21st to end	Night	41% 6% 14% 29% 9% 1	2200
October	1st to 10th	Night	41% 5% 13% 31% 9%	3910
	11th to 20th	Night	46% 6% 16% 25% 8%	3876
	21st to end	Night	51% 6% 15% 23% 4	4498
November	1st to 10th	Night	61% 6% 15% 13% 5% 1	2731
	11th to 20th	Night	66% 6% 13% 11% 4	2800
	21st to end	Night	71% 6% 12% 9% 2	2868
December	1st to 10th	Night	76% 5% 11% 7% 2	4900
	11th to 20th	Night	60% 7% 12% 11% 9%	5566
	21st to end	Night	67% 6% 9% 14% 4	7480

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	10% 8% 36% 29% 15% 2	300
	11th to 20th	Day	10% 10% 29% 35% 14% 1	300
	21st to end	Day	15% 10% 33% 28% 12% 2	330
February	1st to 10th	Day	14% 14% 29% 33% 9% 2	300
	11th to 20th	Day	11% 15% 30% 29% 13% 3	300
	21st to end	Day	10% 11% 40% 27% 11% 1	249
March	1st to 10th	Day	11% 11% 34% 30% 13% 1	300
	11th to 20th	Day	10% 17% 28% 31% 12% 3	300
	21st to end	Day	14% 10% 34% 28% 12% 2	330
April	1st to 10th	Day	16% 10% 32% 31% 9% 3	528
	11th to 20th	Day	19% 13% 30% 27% 10% 1	690
	21st to end	Day	19% 11% 32% 26% 10% 2	700
May	1st to 10th	Day	15% 16% 32% 26% 10% 2	703
	11th to 20th	Day	21% 12% 27% 25% 13% 2	725
	21st to end	Day	19% 10% 25% 28% 15% 3	789
June	1st to 10th	Day	16% 12% 30% 24% 13% 4	730
	11th to 20th	Day	16% 11% 36% 25% 10% 2	730
	21st to end	Day	14% 8% 28% 28% 16% 5%	730
July	1st to 10th	Day	11% 8% 31% 27% 17% 7%	721
	11th to 20th	Day	12% 10% 30% 27% 17% 4	718
	21st to end	Day	8% 7% 30% 29% 18% 8%	794
August	1st to 10th	Day	11% 8% 31% 28% 17% 6%	726
	11th to 20th	Day	11% 7% 27% 31% 16% 8%	715
	21st to end	Day	15% 9% 28% 27% 17% 3	803
September	1st to 10th	Day	12% 9% 31% 32% 12% 3	593
	11th to 20th	Day	19% 9% 36% 26% 9% 2	378
	21st to end	Day	19% 8% 38% 25% 7% 2	330
October	1st to 10th	Day	22% 11% 30% 27% 7% 2	330
	11th to 20th	Day	20% 15% 33% 27% 6% 1	324
	21st to end	Day	28% 12% 29% 24% 6% 1	330
November	1st to 10th	Day	23% 10% 31% 27% 8% 1	300
	11th to 20th	Day	20% 8% 43% 22% 7%	300
	21st to end	Day	19% 13% 39% 23% 5%	300
December	1st to 10th	Day	14% 6% 35% 28% 13% 3	300
	11th to 20th	Day	15% 7% 42% 28% 7%	300
	21st to end	Day	12% 9% 31% 30% 12% 5%	330
January	1st to 10th	Night	12% 10% 34% 30% 13% 2	1000
	11th to 20th	Night	15% 7% 34% 35% 9% 2	1000
	21st to end	Night	14% 8% 35% 32% 10% 1	1100
February	1st to 10th	Night	13% 7% 33% 35% 12% 1	1000
	11th to 20th	Night	10% 6% 33% 35% 14% 2	979
	21st to end	Night	10% 9% 36% 31% 12% 2	825
March	1st to 10th	Night	13% 8% 33% 31% 14% 1	712
	11th to 20th	Night	12% 8% 40% 27% 11% 2	600
	21st to end	Night	18% 10% 26% 28% 14% 3	660
April	1st to 10th	Night	15% 7% 29% 39% 9% 2	600
	11th to 20th	Night	18% 7% 28% 34% 12%	593
	21st to end	Night	14% 8% 31% 37% 11%	600
May	1st to 10th	Night	17% 8% 34% 32% 9% 1	600
	11th to 20th	Night	19% 7% 30% 29% 13% 1	591
	21st to end	Night	19% 8% 30% 29% 14%	650
June	1st to 10th	Night	16% 6% 30% 32% 17% 1	600
	11th to 20th	Night	16% 7% 31% 32% 14%	600
	21st to end	Night	14% 7% 23% 37% 18% 2	600
July	1st to 10th	Night	6% 5% 25% 40% 22% 2	585
	11th to 20th	Night	9% 5% 27% 38% 19% 2	582
	21st to end	Night	8% 3 25% 41% 21% 3	657
August	1st to 10th	Night	9% 4 23% 41% 21% 2	597
	11th to 20th	Night	11% 4 24% 36% 21% 4	594
	21st to end	Night	15% 5% 24% 37% 18% 2	660
September	1st to 10th	Night	14% 4 31% 35% 15% 2	600
	11th to 20th	Night	21% 6% 29% 33% 11%	600
	21st to end	Night	18% 8% 32% 29% 12% 1	600
October	1st to 10th	Night	22% 9% 34% 28% 7%	790
	11th to 20th	Night	23% 9% 31% 28% 8% 1	793
	21st to end	Night	25% 10% 30% 27% 7% 1	1026
November	1st to 10th	Night	21% 10% 35% 24% 9% 1	975
	11th to 20th	Night	20% 11% 35% 25% 8% 2	1000
	21st to end	Night	20% 12% 38% 23% 6% 1	1000
December	1st to 10th	Night	14% 8% 34% 33% 10% 2	1000
	11th to 20th	Night	17% 10% 37% 29% 7% 1	1000
	21st to end	Night	16% 9% 28% 31% 14% 1	1100

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