Nanaimo
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Nanaimo clear sky chart from 2005-11-06 to 2026-10-29.

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	13% 9% 3 7% 5% 5% 5% 4 6% 7% 37%	154122
	Night	16% 10% 3 7% 5% 4 4 4 5% 6% 35%	146695
Transparency	Day	45% 8% 19% 19% 8% 1	153825
	Night	49% 7% 16% 19% 8% 1	146574
Seeing	Day	18% 10% 24% 28% 16% 3	18139
	Night	22% 9% 18% 27% 19% 4	26113

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	25% 17% 4 10% 6% 6% 4 4 6% 5% 13%	4125
	11th to 20th	Day	16% 11% 3 7% 5% 4 4 5% 7% 8% 31%	4119
	21st to end	Day	26% 14% 4 10% 6% 5% 5% 3 5% 4 19%	5159
February	1st to 10th	Day	20% 17% 5% 10% 7% 4 5% 4 6% 6% 17%	1890
	11th to 20th	Day	18% 14% 4 8% 6% 5% 5% 4 6% 6% 23%	1845
	21st to end	Day	18% 15% 3 10% 7% 6% 5% 4 7% 7% 19%	1557
March	1st to 10th	Day	17% 14% 5% 11% 7% 7% 6% 5% 5% 6% 17%	4838
	11th to 20th	Day	15% 14% 4 9% 6% 6% 5% 4 5% 6% 25%	5110
	21st to end	Day	21% 14% 4 11% 6% 6% 6% 4 5% 6% 17%	5668
April	1st to 10th	Day	18% 13% 4 8% 7% 6% 5% 5% 7% 6% 21%	2520
	11th to 20th	Day	16% 10% 3 9% 7% 6% 6% 5% 6% 6% 27%	2647
	21st to end	Day	15% 11% 3 9% 5% 5% 5% 4 6% 7% 30%	2745
May	1st to 10th	Day	8% 6% 2 6% 4 5% 6% 4 6% 7% 45%	8195
	11th to 20th	Day	9% 8% 3 8% 5% 5% 5% 5% 7% 11% 33%	8160
	21st to end	Day	12% 7% 3 7% 5% 6% 6% 5% 7% 8% 35%	9352
June	1st to 10th	Day	15% 8% 3 8% 5% 5% 6% 5% 5% 8% 31%	3150
	11th to 20th	Day	12% 8% 4 9% 6% 6% 6% 4 6% 8% 31%	3150
	21st to end	Day	11% 7% 2 7% 5% 5% 5% 4 6% 8% 39%	3150
July	1st to 10th	Day	6% 5% 2 5% 4 4 4 4 5% 7% 56%	8820
	11th to 20th	Day	4 3 1 4 2 3 3 3 4 6% 68%	8820
	21st to end	Day	5% 4 1 4 3 4 4 4 6% 8% 57%	9253
August	1st to 10th	Day	3 2 1 3 2 2 3 3 4 5% 72%	6263
	11th to 20th	Day	8% 5% 2 5% 3 4 4 3 7% 9% 50%	5923
	21st to end	Day	8% 6% 2 7% 4 4 4 4 6% 8% 46%	6506
September	1st to 10th	Day	8% 5% 2 5% 3 4 4 4 5% 7% 52%	2520
	11th to 20th	Day	14% 6% 3 7% 4 5% 4 3 5% 6% 43%	2462
	21st to end	Day	16% 7% 2 7% 5% 4 4 4 6% 7% 38%	2247
October	1st to 10th	Day	16% 8% 3 8% 6% 5% 6% 5% 7% 7% 30%	3380
	11th to 20th	Day	22% 9% 3 8% 5% 5% 5% 4 5% 6% 29%	3361
	21st to end	Day	20% 11% 4 10% 7% 5% 5% 4 5% 7% 21%	3345
November	1st to 10th	Day	25% 12% 4 9% 8% 6% 6% 3 4 5% 20%	1648
	11th to 20th	Day	21% 12% 4 9% 6% 6% 5% 5% 5% 6% 22%	1680
	21st to end	Day	23% 14% 4 10% 5% 5% 5% 4 5% 5% 19%	1680
December	1st to 10th	Day	16% 13% 4 10% 5% 5% 4 4 5% 6% 28%	2544
	11th to 20th	Day	29% 16% 3 9% 5% 5% 5% 4 4 5% 14%	2715
	21st to end	Day	27% 17% 5% 12% 6% 6% 5% 4 4 4 10%	3575
January	1st to 10th	Night	25% 17% 5% 11% 6% 6% 5% 4 4 5% 14%	8770
	11th to 20th	Night	16% 9% 2 7% 4 4 4 4 6% 8% 36%	8779
	21st to end	Night	23% 12% 4 9% 5% 4 5% 4 5% 5% 25%	9026
February	1st to 10th	Night	21% 13% 4 11% 6% 5% 5% 3 5% 5% 22%	2730
	11th to 20th	Night	19% 13% 3 7% 5% 5% 5% 3 5% 7% 28%	2662
	21st to end	Night	19% 15% 4 9% 5% 4 5% 4 4 6% 26%	2249
March	1st to 10th	Night	16% 14% 4 8% 6% 5% 4 4 5% 7% 27%	5273
	11th to 20th	Night	13% 10% 3 8% 5% 5% 5% 4 7% 7% 31%	5109
	21st to end	Night	23% 13% 3 9% 5% 5% 5% 4 6% 6% 21%	5549
April	1st to 10th	Night	16% 11% 3 8% 6% 5% 6% 5% 5% 7% 27%	2100
	11th to 20th	Night	13% 9% 3 8% 5% 6% 5% 4 6% 8% 33%	1919
	21st to end	Night	14% 9% 3 8% 5% 5% 5% 4 7% 8% 34%	1874
May	1st to 10th	Night	8% 5% 2 5% 4 4 5% 3 5% 7% 53%	4724
	11th to 20th	Night	8% 5% 3 7% 5% 5% 5% 5% 6% 10% 42%	4700
	21st to end	Night	11% 7% 3 8% 6% 6% 5% 4 6% 8% 37%	4802
June	1st to 10th	Night	12% 8% 2 8% 6% 5% 5% 4 6% 6% 38%	1470
	11th to 20th	Night	10% 7% 2 7% 5% 5% 6% 5% 6% 8% 39%	1470
	21st to end	Night	7% 5% 2 6% 4 4 5% 5% 7% 9% 47%	1470
July	1st to 10th	Night	5% 3 1 4 4 4 4 4 5% 7% 59%	4140
	11th to 20th	Night	2 2 1 3 2 2 2 2 3 6% 75%	4140
	21st to end	Night	5% 4 2 4 3 3 4 4 5% 7% 58%	4812
August	1st to 10th	Night	3 2 1 2 2 1 1 2 3 5% 77%	3891
	11th to 20th	Night	10% 5% 1 4 3 3 4 3 5% 7% 54%	4142
	21st to end	Night	10% 4 1 5% 4 4 5% 4 5% 8% 48%	4644
September	1st to 10th	Night	6% 2 1 4 3 3 3 3 5% 7% 60%	2100
	11th to 20th	Night	12% 7% 2 5% 4 4 5% 3 6% 6% 46%	2154
	21st to end	Night	15% 7% 3 7% 4 4 4 3 5% 7% 41%	2373
October	1st to 10th	Night	13% 7% 3 9% 5% 4 5% 4 6% 7% 38%	4040
	11th to 20th	Night	20% 9% 3 7% 5% 5% 5% 3 5% 7% 31%	4017
	21st to end	Night	21% 10% 3 8% 5% 4 4 3 5% 6% 32%	4629
November	1st to 10th	Night	25% 13% 3 7% 6% 5% 5% 4 5% 5% 21%	2870
	11th to 20th	Night	20% 13% 4 8% 5% 5% 5% 4 5% 6% 24%	2940
	21st to end	Night	22% 11% 3 9% 7% 6% 5% 4 5% 5% 23%	2940
December	1st to 10th	Night	17% 13% 4 9% 6% 5% 4 4 5% 7% 26%	4854
	11th to 20th	Night	29% 18% 4 9% 6% 5% 4 4 4 5% 13%	5710
	21st to end	Night	24% 15% 4 11% 6% 5% 5% 4 5% 5% 16%	7623

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	72% 6% 9% 11% 2	4125
	11th to 20th	Day	48% 13% 13% 20% 6% 1	4140
	21st to end	Day	69% 5% 9% 14% 3	5160
February	1st to 10th	Day	68% 7% 10% 10% 4 1	1890
	11th to 20th	Day	61% 7% 13% 13% 5%	1854
	21st to end	Day	61% 7% 15% 10% 4 1	1557
March	1st to 10th	Day	63% 9% 11% 13% 4	4838
	11th to 20th	Day	57% 7% 13% 19% 4	5110
	21st to end	Day	65% 8% 16% 8% 2	5668
April	1st to 10th	Day	60% 8% 17% 13% 3	2520
	11th to 20th	Day	56% 7% 14% 12% 9% 2	2647
	21st to end	Day	51% 8% 15% 17% 7% 1	2745
May	1st to 10th	Day	36% 6% 21% 24% 12% 1	8195
	11th to 20th	Day	41% 9% 27% 18% 4	8163
	21st to end	Day	42% 11% 22% 17% 7% 1	9353
June	1st to 10th	Day	49% 8% 20% 15% 6% 2	3150
	11th to 20th	Day	47% 9% 22% 16% 5%	3150
	21st to end	Day	42% 8% 21% 20% 8% 2	3150
July	1st to 10th	Day	27% 8% 22% 23% 16% 5%	8746
	11th to 20th	Day	17% 6% 20% 35% 20% 2	8739
	21st to end	Day	23% 8% 32% 25% 11% 1	9052
August	1st to 10th	Day	16% 4 16% 42% 19% 2	6246
	11th to 20th	Day	29% 9% 33% 22% 6% 1	5962
	21st to end	Day	35% 10% 26% 22% 7% 1	6505
September	1st to 10th	Day	31% 8% 22% 25% 12% 2	2520
	11th to 20th	Day	41% 7% 18% 19% 13% 1	2462
	21st to end	Day	46% 7% 17% 19% 10% 1	2247
October	1st to 10th	Day	50% 9% 19% 18% 4	3380
	11th to 20th	Day	55% 7% 13% 18% 7%	3361
	21st to end	Day	60% 9% 13% 13% 5%	3345
November	1st to 10th	Day	69% 6% 11% 9% 4 1	1648
	11th to 20th	Day	65% 7% 10% 13% 4 1	1680
	21st to end	Day	66% 8% 8% 12% 5%	1680
December	1st to 10th	Day	56% 7% 13% 19% 4	2544
	11th to 20th	Day	72% 7% 12% 7% 2	2718
	21st to end	Day	75% 8% 9% 6% 3	3575
January	1st to 10th	Night	72% 7% 8% 10% 4	8770
	11th to 20th	Night	45% 9% 16% 19% 10% 1	8820
	21st to end	Night	61% 7% 10% 19% 4	9026
February	1st to 10th	Night	63% 7% 11% 12% 6% 1	2730
	11th to 20th	Night	56% 7% 14% 15% 8%	2664
	21st to end	Night	59% 7% 11% 15% 7% 1	2249
March	1st to 10th	Night	56% 6% 13% 17% 8%	5273
	11th to 20th	Night	49% 6% 15% 23% 7%	5110
	21st to end	Night	62% 9% 13% 12% 3	5549
April	1st to 10th	Night	54% 7% 16% 18% 4	2100
	11th to 20th	Night	49% 7% 13% 19% 10% 2	1919
	21st to end	Night	47% 7% 17% 18% 10% 1	1874
May	1st to 10th	Night	31% 5% 16% 34% 14% 1	4721
	11th to 20th	Night	37% 7% 24% 25% 7%	4700
	21st to end	Night	44% 7% 22% 22% 5%	4806
June	1st to 10th	Night	46% 7% 19% 18% 8% 2	1470
	11th to 20th	Night	40% 7% 22% 24% 6%	1470
	21st to end	Night	32% 8% 23% 25% 9% 3	1470
July	1st to 10th	Night	23% 8% 21% 26% 16% 6%	4105
	11th to 20th	Night	13% 4 20% 38% 22% 3	4098
	21st to end	Night	23% 7% 28% 25% 14% 2	4708
August	1st to 10th	Night	12% 3 17% 39% 27% 3	3883
	11th to 20th	Night	29% 7% 32% 23% 7% 2	4169
	21st to end	Night	32% 10% 23% 27% 8% 1	4644
September	1st to 10th	Night	24% 8% 20% 31% 14% 4	2100
	11th to 20th	Night	38% 8% 16% 18% 17% 4	2154
	21st to end	Night	44% 6% 19% 21% 8% 3	2373
October	1st to 10th	Night	45% 8% 21% 18% 8% 1	4040
	11th to 20th	Night	52% 6% 15% 20% 6%	4017
	21st to end	Night	53% 6% 16% 18% 6% 1	4629
November	1st to 10th	Night	66% 7% 11% 11% 4 1	2870
	11th to 20th	Night	62% 7% 13% 11% 6% 1	2940
	21st to end	Night	64% 6% 11% 13% 5% 1	2940
December	1st to 10th	Night	57% 8% 14% 18% 3	4854
	11th to 20th	Night	74% 7% 11% 6% 2	5706
	21st to end	Night	69% 8% 10% 10% 3	7623

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	35% 12% 24% 16% 7% 6%	220
	11th to 20th	Day	32% 15% 20% 19% 10% 5%	220
	21st to end	Day	32% 14% 21% 21% 10% 3	317
February	1st to 10th	Day	30% 14% 26% 21% 8% 1	430
	11th to 20th	Day	25% 14% 28% 23% 9% 1	425
	21st to end	Day	25% 18% 29% 19% 8% 1	355
March	1st to 10th	Day	24% 15% 25% 26% 10% 2	529
	11th to 20th	Day	27% 13% 24% 23% 11% 2	540
	21st to end	Day	26% 14% 29% 20% 8% 3	594
April	1st to 10th	Day	25% 12% 29% 23% 9% 2	540
	11th to 20th	Day	19% 13% 31% 22% 14% 2	532
	21st to end	Day	20% 10% 31% 25% 12% 2	540
May	1st to 10th	Day	13% 9% 27% 35% 14% 2	543
	11th to 20th	Day	16% 6% 25% 31% 18% 4	568
	21st to end	Day	14% 7% 28% 32% 15% 5%	742
June	1st to 10th	Day	17% 8% 26% 32% 14% 2	780
	11th to 20th	Day	13% 11% 28% 31% 14% 2	780
	21st to end	Day	11% 7% 24% 37% 18% 3	780
July	1st to 10th	Day	11% 5% 23% 32% 24% 5%	771
	11th to 20th	Day	5% 5% 22% 41% 22% 5%	768
	21st to end	Day	4 4 15% 39% 31% 5%	739
August	1st to 10th	Day	7% 3 17% 35% 29% 9%	567
	11th to 20th	Day	8% 4 19% 39% 24% 6%	557
	21st to end	Day	10% 7% 23% 37% 20% 4	627
September	1st to 10th	Day	10% 8% 23% 35% 20% 4	570
	11th to 20th	Day	16% 9% 20% 30% 21% 4	570
	21st to end	Day	19% 12% 27% 25% 14% 2	570
October	1st to 10th	Day	21% 11% 23% 26% 17% 2	570
	11th to 20th	Day	26% 11% 25% 21% 13% 4	570
	21st to end	Day	26% 15% 29% 19% 8% 2	483
November	1st to 10th	Day	30% 17% 30% 16% 6%	220
	11th to 20th	Day	28% 12% 23% 18% 15% 5%	220
	21st to end	Day	34% 14% 20% 15% 10% 6%	220
December	1st to 10th	Day	32% 13% 17% 15% 16% 7%	220
	11th to 20th	Day	33% 14% 24% 20% 8% 1	220
	21st to end	Day	38% 14% 21% 20% 6% 1	242
January	1st to 10th	Night	35% 13% 19% 20% 11% 2	950
	11th to 20th	Night	29% 12% 17% 23% 18% 2	950
	21st to end	Night	32% 9% 14% 27% 16% 2	968
February	1st to 10th	Night	29% 11% 20% 26% 12% 2	840
	11th to 20th	Night	27% 9% 20% 25% 17% 1	824
	21st to end	Night	28% 10% 21% 26% 12% 3	692
March	1st to 10th	Night	24% 11% 22% 25% 15% 3	840
	11th to 20th	Night	25% 11% 23% 25% 14% 3	840
	21st to end	Night	24% 10% 21% 24% 17% 4	924
April	1st to 10th	Night	21% 10% 18% 29% 18% 4	840
	11th to 20th	Night	19% 9% 23% 30% 17% 2	671
	21st to end	Night	18% 7% 22% 32% 19% 3	614
May	1st to 10th	Night	13% 3 23% 32% 25% 4	420
	11th to 20th	Night	13% 7% 15% 32% 24% 9%	414
	21st to end	Night	14% 6% 16% 35% 25% 5%	455
June	1st to 10th	Night	16% 6% 20% 37% 17% 4	420
	11th to 20th	Night	13% 6% 21% 33% 23% 4	420
	21st to end	Night	10% 4 17% 39% 25% 5%	420
July	1st to 10th	Night	9% 6% 12% 33% 33% 7%	410
	11th to 20th	Night	3 4 20% 34% 32% 6%	408
	21st to end	Night	6% 3 10% 31% 43% 7%	460
August	1st to 10th	Night	8% 2 13% 31% 36% 11%	496
	11th to 20th	Night	6% 2 13% 31% 38% 9%	624
	21st to end	Night	10% 4 14% 33% 32% 7%	719
September	1st to 10th	Night	8% 3 15% 34% 32% 7%	840
	11th to 20th	Night	15% 7% 14% 22% 31% 10%	840
	21st to end	Night	18% 6% 20% 29% 23% 5%	840
October	1st to 10th	Night	17% 7% 18% 29% 24% 5%	840
	11th to 20th	Night	25% 7% 18% 26% 19% 5%	840
	21st to end	Night	29% 9% 21% 25% 13% 3	912
November	1st to 10th	Night	33% 9% 19% 28% 10% 1	820
	11th to 20th	Night	28% 12% 22% 23% 13% 2	840
	21st to end	Night	29% 13% 17% 25% 13% 3	840
December	1st to 10th	Night	28% 11% 15% 27% 17% 2	887
	11th to 20th	Night	35% 14% 20% 21% 10% 1	950
	21st to end	Night	36% 12% 24% 20% 8% 1	1045

Page generated at 2026-10-26 01:37:47. Version ac07

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