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 2024-11-03.

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	15% 9% 3 8% 5% 5% 5% 4 5% 7% 36%	101732
	Night	17% 10% 3 7% 5% 5% 4 4 5% 6% 34%	97323
Transparency	Day	47% 7% 17% 18% 8% 1	101478
	Night	51% 7% 15% 18% 8% 1	97223
Seeing	Day	19% 9% 24% 28% 16% 4	15539
	Night	23% 8% 18% 27% 20% 4	23592

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	24% 18% 4 10% 6% 5% 4 4 6% 5% 13%	2219
	11th to 20th	Day	21% 14% 3 8% 6% 5% 5% 5% 8% 8% 16%	2199
	21st to end	Day	31% 20% 5% 10% 6% 5% 4 3 5% 3 7%	2768
February	1st to 10th	Day	21% 17% 4 10% 6% 4 5% 4 6% 6% 17%	1710
	11th to 20th	Day	19% 14% 5% 8% 6% 5% 5% 4 6% 6% 23%	1665
	21st to end	Day	18% 15% 3 9% 7% 6% 5% 4 7% 7% 20%	1413
March	1st to 10th	Day	13% 15% 5% 12% 8% 8% 7% 5% 5% 6% 16%	3289
	11th to 20th	Day	13% 10% 3 9% 6% 6% 5% 4 5% 7% 33%	3490
	21st to end	Day	20% 13% 4 9% 6% 5% 6% 4 5% 6% 22%	3872
April	1st to 10th	Day	19% 13% 4 9% 7% 6% 5% 4 7% 6% 20%	2280
	11th to 20th	Day	17% 10% 4 9% 7% 6% 6% 5% 5% 6% 26%	2391
	21st to end	Day	17% 12% 3 9% 5% 5% 5% 4 6% 7% 26%	2483
May	1st to 10th	Day	12% 8% 3 7% 4 5% 5% 4 5% 6% 41%	4420
	11th to 20th	Day	8% 6% 2 7% 5% 5% 4 4 6% 11% 41%	4377
	21st to end	Day	19% 10% 4 10% 6% 5% 5% 4 7% 6% 24%	5004
June	1st to 10th	Day	16% 9% 4 9% 5% 5% 6% 5% 6% 8% 29%	2850
	11th to 20th	Day	13% 8% 4 9% 6% 7% 6% 4 6% 8% 29%	2850
	21st to end	Day	11% 7% 3 7% 5% 5% 5% 4 6% 8% 39%	2850
July	1st to 10th	Day	5% 3 1 4 3 2 3 3 4 5% 67%	4740
	11th to 20th	Day	4 3 1 3 2 2 3 2 4 5% 71%	4740
	21st to end	Day	6% 4 1 4 3 3 4 4 6% 8% 56%	4963
August	1st to 10th	Day	4 3 1 3 3 2 3 2 4 6% 69%	4279
	11th to 20th	Day	11% 7% 3 6% 3 4 4 3 6% 8% 44%	4026
	21st to end	Day	10% 6% 2 7% 4 4 4 4 5% 7% 47%	4473
September	1st to 10th	Day	8% 5% 2 5% 3 4 4 4 5% 8% 53%	2280
	11th to 20th	Day	15% 7% 3 8% 4 5% 4 3 5% 6% 42%	2228
	21st to end	Day	16% 7% 2 7% 5% 4 4 4 6% 6% 39%	2033
October	1st to 10th	Day	18% 7% 3 6% 4 3 5% 4 6% 7% 36%	1900
	11th to 20th	Day	21% 10% 3 8% 5% 5% 5% 5% 5% 7% 26%	1900
	21st to end	Day	21% 11% 3 8% 5% 4 5% 4 5% 7% 26%	1930
November	1st to 10th	Day	25% 11% 4 8% 8% 5% 6% 3 4 5% 20%	1504
	11th to 20th	Day	21% 12% 4 9% 7% 5% 4 4 5% 5% 23%	1520
	21st to end	Day	23% 13% 4 9% 6% 5% 5% 4 5% 5% 21%	1520
December	1st to 10th	Day	17% 17% 4 9% 6% 5% 4 4 4 5% 25%	1439
	11th to 20th	Day	25% 16% 4 11% 5% 6% 5% 4 4 6% 14%	1685
	21st to end	Day	26% 17% 5% 12% 6% 6% 5% 4 5% 4 11%	2442
January	1st to 10th	Night	23% 15% 5% 11% 7% 6% 5% 4 5% 4 15%	4726
	11th to 20th	Night	21% 13% 3 9% 6% 5% 4 4 7% 8% 21%	4699
	21st to end	Night	30% 15% 5% 10% 6% 5% 4 4 5% 4 13%	4885
February	1st to 10th	Night	21% 13% 4 10% 6% 5% 5% 4 5% 5% 21%	2470
	11th to 20th	Night	19% 13% 3 7% 5% 5% 5% 4 5% 7% 28%	2402
	21st to end	Night	18% 15% 4 9% 5% 3 5% 4 4 6% 27%	2041
March	1st to 10th	Night	15% 15% 4 9% 6% 5% 5% 4 6% 7% 25%	3583
	11th to 20th	Night	11% 7% 3 6% 5% 5% 5% 5% 8% 8% 38%	3489
	21st to end	Night	18% 14% 4 10% 6% 6% 5% 4 5% 5% 24%	3781
April	1st to 10th	Night	16% 11% 3 8% 6% 5% 6% 6% 5% 7% 27%	1900
	11th to 20th	Night	14% 10% 3 8% 5% 6% 5% 4 6% 7% 33%	1735
	21st to end	Night	15% 9% 3 8% 5% 5% 5% 4 7% 7% 31%	1696
May	1st to 10th	Night	11% 6% 2 6% 4 4 5% 3 5% 6% 47%	2540
	11th to 20th	Night	7% 5% 2 6% 4 3 4 4 6% 11% 50%	2516
	21st to end	Night	14% 11% 4 9% 6% 6% 5% 3 5% 6% 32%	2554
June	1st to 10th	Night	12% 8% 2 9% 7% 4 5% 4 6% 6% 36%	1330
	11th to 20th	Night	11% 7% 2 7% 5% 5% 6% 6% 6% 8% 37%	1330
	21st to end	Night	7% 5% 2 5% 4 5% 5% 4 6% 9% 47%	1330
July	1st to 10th	Night	4 3 1 3 3 3 4 3 3 4 69%	2220
	11th to 20th	Night	2 2 1 2 2 2 2 2 3 5% 78%	2220
	21st to end	Night	7% 5% 2 3 3 3 4 4 4 6% 59%	2586
August	1st to 10th	Night	3 2 1 3 2 2 2 2 3 5% 76%	2651
	11th to 20th	Night	14% 8% 2 5% 3 3 4 3 5% 6% 48%	2812
	21st to end	Night	11% 4 1 4 4 4 5% 4 5% 8% 49%	3196
September	1st to 10th	Night	6% 2 1 4 3 3 4 3 5% 7% 62%	1900
	11th to 20th	Night	13% 7% 2 5% 4 4 5% 4 6% 6% 45%	1948
	21st to end	Night	14% 7% 3 7% 4 4 4 3 4 7% 42%	2147
October	1st to 10th	Night	14% 7% 2 7% 5% 3 5% 4 5% 5% 44%	2280
	11th to 20th	Night	20% 10% 3 6% 4 4 5% 3 5% 7% 33%	2280
	21st to end	Night	23% 9% 3 7% 5% 5% 4 3 5% 6% 32%	2664
November	1st to 10th	Night	26% 12% 3 7% 6% 5% 5% 4 5% 5% 22%	2618
	11th to 20th	Night	20% 12% 4 8% 5% 5% 5% 5% 5% 6% 25%	2660
	21st to end	Night	22% 10% 3 8% 7% 6% 5% 5% 5% 5% 24%	2660
December	1st to 10th	Night	18% 15% 4 9% 7% 5% 4 4 5% 5% 24%	2740
	11th to 20th	Night	26% 17% 5% 9% 6% 5% 5% 4 5% 5% 14%	3520
	21st to end	Night	24% 16% 4 12% 6% 5% 4 4 4 4 17%	5214

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	73% 6% 7% 11% 3	2219
	11th to 20th	Day	61% 14% 13% 8% 3 1	2220
	21st to end	Day	81% 5% 7% 6% 1	2768
February	1st to 10th	Day	68% 6% 11% 11% 4 1	1710
	11th to 20th	Day	62% 7% 13% 13% 5%	1674
	21st to end	Day	61% 7% 15% 11% 4 1	1413
March	1st to 10th	Day	63% 9% 12% 10% 5%	3289
	11th to 20th	Day	51% 7% 15% 24% 4 1	3490
	21st to end	Day	60% 8% 20% 10% 2	3872
April	1st to 10th	Day	61% 7% 16% 12% 3	2280
	11th to 20th	Day	57% 6% 14% 12% 9% 2	2391
	21st to end	Day	54% 8% 14% 15% 7% 1	2483
May	1st to 10th	Day	42% 6% 21% 20% 10% 1	4420
	11th to 20th	Day	36% 7% 29% 21% 5% 1	4380
	21st to end	Day	56% 10% 18% 12% 4	5005
June	1st to 10th	Day	51% 8% 21% 14% 5% 2	2850
	11th to 20th	Day	50% 9% 22% 15% 4	2850
	21st to end	Day	42% 8% 21% 19% 8% 2	2850
July	1st to 10th	Day	21% 5% 13% 26% 26% 9%	4666
	11th to 20th	Day	15% 5% 16% 38% 24% 2	4659
	21st to end	Day	24% 8% 28% 24% 14% 2	4806
August	1st to 10th	Day	18% 4 16% 45% 16% 1	4262
	11th to 20th	Day	36% 9% 29% 16% 9% 1	4065
	21st to end	Day	36% 8% 23% 23% 9% 1	4472
September	1st to 10th	Day	31% 8% 21% 25% 13% 2	2280
	11th to 20th	Day	43% 7% 17% 19% 13% 2	2228
	21st to end	Day	45% 7% 17% 19% 10% 1	2033
October	1st to 10th	Day	46% 7% 20% 20% 7%	1900
	11th to 20th	Day	56% 8% 16% 16% 3	1900
	21st to end	Day	58% 7% 14% 14% 7%	1930
November	1st to 10th	Day	69% 6% 11% 10% 4 1	1504
	11th to 20th	Day	64% 7% 10% 13% 5% 1	1520
	21st to end	Day	65% 8% 8% 13% 6%	1520
December	1st to 10th	Day	63% 6% 12% 14% 4	1439
	11th to 20th	Day	73% 6% 12% 6% 2	1688
	21st to end	Day	75% 7% 8% 7% 3	2442
January	1st to 10th	Night	71% 7% 9% 10% 3	4726
	11th to 20th	Night	60% 10% 15% 11% 3 1	4740
	21st to end	Night	76% 5% 8% 9% 2	4885
February	1st to 10th	Night	64% 7% 12% 11% 5% 1	2470
	11th to 20th	Night	57% 7% 14% 14% 7%	2404
	21st to end	Night	59% 7% 10% 16% 7% 1	2041
March	1st to 10th	Night	58% 6% 13% 17% 6%	3583
	11th to 20th	Night	41% 7% 19% 26% 6%	3490
	21st to end	Night	60% 8% 15% 15% 2	3781
April	1st to 10th	Night	55% 8% 16% 17% 5%	1900
	11th to 20th	Night	50% 7% 12% 18% 10% 2	1735
	21st to end	Night	51% 7% 15% 17% 10% 1	1696
May	1st to 10th	Night	36% 6% 16% 29% 13%	2540
	11th to 20th	Night	31% 5% 27% 28% 8% 1	2516
	21st to end	Night	53% 7% 18% 17% 5%	2554
June	1st to 10th	Night	48% 7% 19% 18% 6% 3	1330
	11th to 20th	Night	42% 7% 24% 21% 5% 1	1330
	21st to end	Night	32% 8% 23% 24% 9% 3	1330
July	1st to 10th	Night	20% 4 12% 29% 24% 11%	2185
	11th to 20th	Night	12% 3 16% 39% 27% 3	2178
	21st to end	Night	24% 7% 18% 30% 19% 2	2504
August	1st to 10th	Night	14% 3 14% 38% 29% 2	2643
	11th to 20th	Night	37% 7% 28% 17% 9% 3	2839
	21st to end	Night	32% 8% 22% 28% 10%	3196
September	1st to 10th	Night	23% 7% 19% 32% 15% 4	1900
	11th to 20th	Night	39% 8% 15% 18% 17% 4	1948
	21st to end	Night	43% 6% 17% 22% 8% 3	2147
October	1st to 10th	Night	42% 7% 18% 21% 11% 1	2280
	11th to 20th	Night	52% 6% 16% 19% 7%	2280
	21st to end	Night	55% 7% 12% 18% 8%	2664
November	1st to 10th	Night	65% 6% 11% 12% 4 1	2618
	11th to 20th	Night	61% 7% 13% 11% 6% 1	2660
	21st to end	Night	62% 7% 11% 13% 6% 1	2660
December	1st to 10th	Night	63% 6% 13% 13% 4	2740
	11th to 20th	Night	72% 7% 12% 7% 2	3516
	21st to end	Night	72% 5% 9% 10% 3	5214

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	34% 13% 24% 14% 8% 7%	180
	11th to 20th	Day	36% 14% 18% 19% 8% 4	180
	21st to end	Day	34% 14% 20% 21% 8% 3	265
February	1st to 10th	Day	32% 14% 26% 19% 8% 1	370
	11th to 20th	Day	26% 15% 28% 22% 8% 1	365
	21st to end	Day	24% 16% 29% 21% 9% 1	307
March	1st to 10th	Day	24% 13% 24% 26% 11% 2	451
	11th to 20th	Day	25% 11% 24% 26% 13% 2	460
	21st to end	Day	27% 13% 29% 21% 8% 3	506
April	1st to 10th	Day	25% 11% 30% 22% 9% 2	460
	11th to 20th	Day	21% 12% 31% 21% 14% 1	452
	21st to end	Day	21% 10% 31% 23% 12% 2	460
May	1st to 10th	Day	14% 7% 26% 35% 14% 3	463
	11th to 20th	Day	17% 4 22% 32% 20% 5%	488
	21st to end	Day	15% 5% 25% 33% 17% 6%	642
June	1st to 10th	Day	18% 6% 26% 33% 15% 3	680
	11th to 20th	Day	13% 9% 28% 32% 15% 2	680
	21st to end	Day	11% 7% 23% 38% 18% 4	680
July	1st to 10th	Day	11% 5% 23% 30% 26% 6%	671
	11th to 20th	Day	5% 4 19% 41% 24% 6%	668
	21st to end	Day	4 4 15% 39% 33% 5%	639
August	1st to 10th	Day	7% 2 16% 33% 31% 10%	487
	11th to 20th	Day	7% 4 17% 41% 24% 7%	477
	21st to end	Day	11% 6% 23% 37% 20% 4	539
September	1st to 10th	Day	11% 7% 23% 35% 21% 3	490
	11th to 20th	Day	18% 9% 20% 29% 21% 4	490
	21st to end	Day	20% 11% 26% 26% 15% 3	490
October	1st to 10th	Day	22% 10% 22% 26% 18% 2	490
	11th to 20th	Day	28% 10% 23% 21% 14% 4	490
	21st to end	Day	25% 14% 31% 18% 9% 3	417
November	1st to 10th	Day	32% 16% 28% 17% 8%	184
	11th to 20th	Day	27% 14% 21% 17% 17% 5%	180
	21st to end	Day	34% 14% 19% 14% 11% 7%	180
December	1st to 10th	Day	33% 13% 17% 16% 16% 7%	180
	11th to 20th	Day	31% 12% 25% 21% 10% 1	180
	21st to end	Day	39% 13% 21% 20% 6% 2	198
January	1st to 10th	Night	36% 13% 18% 19% 12% 2	850
	11th to 20th	Night	31% 12% 15% 22% 18% 2	850
	21st to end	Night	33% 10% 14% 26% 15% 2	872
February	1st to 10th	Night	30% 11% 19% 25% 13% 2	760
	11th to 20th	Night	27% 10% 21% 24% 17% 1	744
	21st to end	Night	28% 9% 20% 26% 13% 4	628
March	1st to 10th	Night	24% 10% 22% 24% 16% 4	760
	11th to 20th	Night	24% 10% 22% 26% 15% 3	760
	21st to end	Night	24% 9% 21% 24% 18% 4	836
April	1st to 10th	Night	21% 10% 19% 28% 18% 4	760
	11th to 20th	Night	20% 7% 23% 30% 17% 3	607
	21st to end	Night	19% 7% 21% 32% 19% 3	556
May	1st to 10th	Night	14% 3 22% 31% 26% 4	380
	11th to 20th	Night	14% 6% 14% 32% 25% 9%	374
	21st to end	Night	15% 6% 14% 34% 26% 6%	411
June	1st to 10th	Night	17% 6% 18% 38% 18% 4	380
	11th to 20th	Night	13% 5% 21% 33% 24% 4	380
	21st to end	Night	10% 4 18% 38% 25% 6%	380
July	1st to 10th	Night	9% 6% 12% 33% 33% 7%	370
	11th to 20th	Night	4 4 18% 33% 35% 7%	368
	21st to end	Night	6% 3 11% 31% 42% 7%	416
August	1st to 10th	Night	8% 2 11% 28% 38% 12%	448
	11th to 20th	Night	5% 2 12% 31% 39% 10%	564
	21st to end	Night	10% 4 15% 31% 32% 7%	651
September	1st to 10th	Night	8% 3 15% 34% 33% 7%	760
	11th to 20th	Night	16% 6% 14% 21% 31% 11%	760
	21st to end	Night	18% 6% 19% 28% 24% 5%	760
October	1st to 10th	Night	18% 6% 18% 27% 25% 6%	760
	11th to 20th	Night	27% 6% 16% 26% 19% 5%	760
	21st to end	Night	29% 9% 20% 26% 13% 3	836
November	1st to 10th	Night	34% 9% 18% 27% 11% 1	748
	11th to 20th	Night	28% 12% 21% 23% 14% 2	760
	21st to end	Night	29% 12% 17% 25% 14% 3	760
December	1st to 10th	Night	27% 12% 15% 27% 16% 3	798
	11th to 20th	Night	35% 13% 19% 22% 10% 1	850
	21st to end	Night	36% 12% 23% 20% 8% 1	935

Page generated at 2024-10-31 00:39:22. Version ac07

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