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 2024-03-23.

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	16% 10% 4 7% 6% 4 5% 5% 5% 7% 32%	78231
	Night	18% 10% 4 7% 6% 4 5% 5% 5% 6% 31%	81606
Transparency	Day	52% 7% 17% 16% 6% 1	77938
	Night	54% 7% 15% 17% 7% 1	81479
Seeing	Day	19% 9% 23% 28% 17% 4	14593
	Night	23% 8% 18% 27% 20% 4	22930

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 9% 7% 4 5% 4 6% 5% 13%	2219
	11th to 20th	Day	22% 14% 4 7% 7% 4 5% 6% 8% 8% 16%	2199
	21st to end	Day	31% 19% 5% 9% 7% 4 5% 4 5% 3 8%	2768
February	1st to 10th	Day	21% 16% 5% 8% 7% 4 4 5% 6% 6% 17%	1710
	11th to 20th	Day	19% 14% 5% 7% 7% 4 5% 5% 6% 6% 23%	1665
	21st to end	Day	18% 14% 4 8% 8% 4 6% 5% 7% 7% 20%	1413
March	1st to 10th	Day	17% 13% 5% 9% 7% 5% 7% 6% 5% 7% 20%	1990
	11th to 20th	Day	19% 12% 3 8% 8% 5% 5% 5% 5% 7% 24%	2090
	21st to end	Day	21% 11% 5% 9% 7% 4 6% 5% 4 6% 23%	2223
April	1st to 10th	Day	20% 12% 4 8% 7% 5% 6% 6% 6% 6% 21%	2160
	11th to 20th	Day	18% 10% 4 8% 7% 5% 6% 6% 5% 6% 24%	2263
	21st to end	Day	17% 11% 3 8% 7% 4 6% 5% 6% 7% 27%	2352
May	1st to 10th	Day	11% 7% 3 7% 6% 5% 7% 6% 7% 8% 34%	2520
	11th to 20th	Day	14% 8% 3 7% 7% 4 5% 5% 6% 9% 33%	2477
	21st to end	Day	15% 9% 4 7% 5% 4 5% 5% 7% 7% 32%	2830
June	1st to 10th	Day	17% 8% 4 8% 6% 4 6% 6% 5% 8% 29%	2700
	11th to 20th	Day	13% 8% 4 9% 7% 5% 7% 6% 6% 8% 28%	2700
	21st to end	Day	11% 6% 3 6% 5% 4 5% 5% 6% 8% 41%	2700
July	1st to 10th	Day	9% 6% 2 6% 5% 3 5% 4 5% 6% 48%	2700
	11th to 20th	Day	6% 4 3 4 4 2 5% 5% 6% 7% 54%	2700
	21st to end	Day	5% 3 2 3 4 2 3 4 5% 7% 63%	2844
August	1st to 10th	Day	7% 4 2 5% 4 3 4 4 5% 7% 55%	2437
	11th to 20th	Day	6% 4 3 4 4 2 5% 4 6% 7% 56%	2298
	21st to end	Day	7% 5% 2 6% 5% 3 4 5% 6% 10% 48%	2552
September	1st to 10th	Day	9% 5% 2 4 4 3 4 5% 5% 7% 52%	2160
	11th to 20th	Day	15% 6% 3 7% 4 3 4 4 5% 6% 42%	2111
	21st to end	Day	16% 7% 2 5% 6% 3 4 5% 6% 6% 40%	1926
October	1st to 10th	Day	18% 7% 3 5% 5% 2 4 5% 6% 8% 37%	1800
	11th to 20th	Day	20% 10% 3 7% 6% 4 5% 6% 5% 7% 27%	1800
	21st to end	Day	21% 10% 3 7% 6% 3 4 6% 5% 7% 27%	1830
November	1st to 10th	Day	25% 11% 5% 8% 8% 4 6% 4 4 5% 20%	1488
	11th to 20th	Day	22% 10% 5% 8% 6% 4 5% 5% 5% 5% 23%	1520
	21st to end	Day	23% 12% 5% 8% 6% 4 5% 5% 5% 6% 21%	1520
December	1st to 10th	Day	18% 15% 6% 8% 7% 4 4 5% 4 5% 25%	1439
	11th to 20th	Day	25% 15% 4 9% 7% 5% 5% 6% 4 6% 14%	1685
	21st to end	Day	26% 16% 5% 11% 8% 4 5% 5% 5% 4 11%	2442
January	1st to 10th	Night	23% 15% 5% 10% 8% 5% 6% 5% 5% 4 15%	4726
	11th to 20th	Night	21% 12% 4 7% 7% 4 5% 5% 6% 8% 21%	4699
	21st to end	Night	30% 14% 5% 9% 7% 4 4 5% 5% 5% 13%	4885
February	1st to 10th	Night	22% 12% 4 9% 8% 4 5% 5% 5% 5% 21%	2470
	11th to 20th	Night	19% 12% 4 6% 5% 4 5% 4 5% 7% 28%	2402
	21st to end	Night	19% 13% 5% 8% 7% 2 4 5% 4 6% 27%	2041
March	1st to 10th	Night	17% 11% 4 6% 7% 4 5% 5% 6% 7% 27%	2189
	11th to 20th	Night	17% 10% 3 6% 7% 4 6% 6% 7% 8% 27%	2089
	21st to end	Night	16% 12% 4 9% 7% 5% 6% 5% 6% 6% 24%	2178
April	1st to 10th	Night	17% 10% 4 7% 7% 4 6% 7% 5% 8% 27%	1800
	11th to 20th	Night	15% 9% 4 7% 5% 4 6% 5% 6% 7% 31%	1643
	21st to end	Night	15% 9% 4 7% 6% 4 6% 5% 6% 8% 31%	1607
May	1st to 10th	Night	11% 5% 3 5% 6% 4 7% 6% 5% 8% 41%	1440
	11th to 20th	Night	10% 6% 3 6% 7% 3 6% 7% 7% 10% 36%	1416
	21st to end	Night	12% 8% 4 6% 5% 4 5% 5% 6% 7% 38%	1442
June	1st to 10th	Night	12% 7% 2 8% 8% 4 5% 5% 5% 6% 37%	1260
	11th to 20th	Night	11% 7% 3 6% 5% 4 6% 8% 6% 7% 38%	1260
	21st to end	Night	8% 4 2 4 4 3 5% 5% 6% 10% 48%	1260
July	1st to 10th	Night	7% 5% 2 4 5% 3 5% 5% 5% 6% 54%	1260
	11th to 20th	Night	4 3 2 3 4 2 3 3 5% 7% 64%	1260
	21st to end	Night	4 2 1 2 3 1 3 4 4 6% 69%	1470
August	1st to 10th	Night	6% 4 2 4 4 2 3 3 4 6% 63%	1498
	11th to 20th	Night	4 3 1 2 4 2 3 4 5% 7% 64%	1602
	21st to end	Night	8% 4 2 3 4 2 4 6% 6% 10% 51%	1804
September	1st to 10th	Night	6% 2 1 4 4 2 4 4 5% 7% 62%	1800
	11th to 20th	Night	13% 7% 2 4 5% 3 5% 5% 6% 6% 44%	1845
	21st to end	Night	14% 7% 3 6% 6% 3 4 4 4 7% 43%	2034
October	1st to 10th	Night	13% 6% 2 6% 6% 3 4 5% 5% 5% 45%	2160
	11th to 20th	Night	20% 9% 3 5% 5% 3 5% 4 5% 7% 33%	2160
	21st to end	Night	24% 8% 3 5% 6% 4 4 4 5% 6% 32%	2522
November	1st to 10th	Night	26% 12% 4 6% 7% 4 6% 5% 5% 5% 22%	2590
	11th to 20th	Night	20% 11% 5% 7% 6% 4 5% 5% 5% 6% 25%	2660
	21st to end	Night	23% 9% 3 8% 7% 4 6% 6% 5% 5% 24%	2660
December	1st to 10th	Night	18% 13% 5% 9% 7% 3 5% 5% 5% 5% 24%	2740
	11th to 20th	Night	26% 16% 5% 8% 7% 4 5% 5% 5% 5% 14%	3520
	21st to end	Night	24% 15% 5% 10% 7% 3 5% 4 5% 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% 7% 14% 11% 4 1	1990
	11th to 20th	Day	61% 7% 14% 13% 4 1	2090
	21st to end	Day	63% 6% 17% 12% 2	2223
April	1st to 10th	Day	62% 6% 17% 12% 3	2160
	11th to 20th	Day	59% 6% 14% 12% 8% 1	2263
	21st to end	Day	54% 8% 14% 15% 7% 1	2352
May	1st to 10th	Day	46% 8% 22% 17% 6% 1	2520
	11th to 20th	Day	48% 8% 19% 19% 5% 1	2480
	21st to end	Day	48% 8% 22% 17% 3	2831
June	1st to 10th	Day	51% 8% 21% 14% 4 2	2700
	11th to 20th	Day	51% 9% 23% 14% 4	2700
	21st to end	Day	41% 8% 22% 20% 8% 2	2700
July	1st to 10th	Day	36% 6% 21% 24% 10% 3	2626
	11th to 20th	Day	26% 8% 25% 30% 9% 1	2619
	21st to end	Day	20% 6% 26% 30% 15% 3	2686
August	1st to 10th	Day	29% 6% 24% 27% 12% 2	2420
	11th to 20th	Day	27% 8% 24% 24% 15% 2	2298
	21st to end	Day	32% 8% 27% 25% 7% 1	2552
September	1st to 10th	Day	32% 8% 20% 26% 12% 2	2160
	11th to 20th	Day	43% 7% 15% 19% 14% 2	2111
	21st to end	Day	44% 7% 17% 20% 10% 1	1926
October	1st to 10th	Day	46% 7% 20% 20% 7%	1800
	11th to 20th	Day	56% 8% 16% 16% 3	1800
	21st to end	Day	58% 7% 14% 14% 7%	1830
November	1st to 10th	Day	69% 6% 11% 10% 4 1	1488
	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	56% 7% 13% 18% 6%	2189
	11th to 20th	Night	54% 6% 15% 17% 7% 1	2090
	21st to end	Night	61% 6% 14% 16% 3	2178
April	1st to 10th	Night	55% 7% 16% 17% 5%	1800
	11th to 20th	Night	51% 7% 12% 19% 9% 1	1643
	21st to end	Night	50% 7% 16% 17% 10% 1	1607
May	1st to 10th	Night	40% 7% 19% 23% 10% 1	1440
	11th to 20th	Night	43% 7% 20% 22% 7% 1	1416
	21st to end	Night	44% 7% 22% 21% 5%	1442
June	1st to 10th	Night	48% 7% 18% 18% 5% 3	1260
	11th to 20th	Night	43% 7% 25% 20% 5% 1	1260
	21st to end	Night	32% 8% 23% 25% 9% 3	1260
July	1st to 10th	Night	31% 7% 20% 26% 14% 3	1225
	11th to 20th	Night	21% 6% 27% 29% 15% 2	1218
	21st to end	Night	15% 6% 19% 35% 21% 4	1388
August	1st to 10th	Night	25% 4 20% 30% 18% 3	1490
	11th to 20th	Night	20% 6% 26% 27% 16% 5%	1602
	21st to end	Night	28% 8% 24% 32% 8% 1	1804
September	1st to 10th	Night	24% 7% 19% 31% 15% 3	1800
	11th to 20th	Night	39% 8% 14% 17% 18% 4	1845
	21st to end	Night	43% 6% 17% 23% 9% 3	2034
October	1st to 10th	Night	42% 6% 18% 21% 11% 1	2160
	11th to 20th	Night	51% 6% 17% 19% 7%	2160
	21st to end	Night	55% 7% 12% 18% 8%	2522
November	1st to 10th	Night	65% 6% 12% 12% 4 1	2590
	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% 23% 25% 13% 2	460
	21st to end	Day	27% 12% 29% 21% 9% 3	471
April	1st to 10th	Day	25% 12% 31% 21% 9% 2	420
	11th to 20th	Day	21% 10% 31% 21% 16% 1	412
	21st to end	Day	20% 10% 31% 24% 12% 2	420
May	1st to 10th	Day	14% 8% 26% 36% 15% 2	423
	11th to 20th	Day	18% 4 20% 32% 22% 5%	448
	21st to end	Day	13% 5% 23% 35% 17% 6%	592
June	1st to 10th	Day	18% 6% 25% 32% 16% 3	630
	11th to 20th	Day	14% 8% 28% 32% 15% 2	630
	21st to end	Day	11% 6% 22% 39% 19% 3	630
July	1st to 10th	Day	12% 4 21% 30% 27% 6%	621
	11th to 20th	Day	6% 5% 19% 40% 24% 6%	618
	21st to end	Day	4 3 14% 40% 35% 5%	590
August	1st to 10th	Day	8% 2 17% 32% 32% 10%	447
	11th to 20th	Day	6% 4 16% 42% 25% 7%	437
	21st to end	Day	10% 5% 24% 36% 21% 4	495
September	1st to 10th	Day	12% 8% 24% 35% 19% 3	450
	11th to 20th	Day	18% 8% 19% 29% 22% 4	450
	21st to end	Day	19% 10% 25% 27% 16% 3	450
October	1st to 10th	Day	23% 10% 21% 25% 19% 2	450
	11th to 20th	Day	28% 10% 22% 21% 14% 4	450
	21st to end	Day	25% 14% 30% 19% 9% 3	383
November	1st to 10th	Day	32% 16% 28% 17% 8%	180
	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% 20% 25% 18% 5%	800
April	1st to 10th	Night	22% 10% 18% 27% 18% 4	720
	11th to 20th	Night	20% 7% 22% 31% 18% 3	575
	21st to end	Night	18% 7% 21% 32% 18% 3	527
May	1st to 10th	Night	14% 4 22% 29% 27% 5%	360
	11th to 20th	Night	14% 5% 12% 32% 26% 10%	354
	21st to end	Night	14% 6% 13% 33% 27% 6%	389
June	1st to 10th	Night	16% 5% 17% 38% 18% 4	360
	11th to 20th	Night	14% 4 21% 34% 23% 4	360
	21st to end	Night	10% 4 17% 38% 25% 6%	360
July	1st to 10th	Night	9% 5% 11% 32% 35% 8%	350
	11th to 20th	Night	4 4 18% 33% 34% 7%	348
	21st to end	Night	5% 3 10% 31% 43% 8%	394
August	1st to 10th	Night	8% 2 12% 27% 38% 13%	424
	11th to 20th	Night	4 2 13% 32% 39% 9%	534
	21st to end	Night	10% 4 15% 31% 33% 7%	616
September	1st to 10th	Night	8% 3 16% 34% 32% 7%	720
	11th to 20th	Night	16% 6% 14% 21% 31% 12%	720
	21st to end	Night	18% 6% 18% 29% 24% 5%	720
October	1st to 10th	Night	18% 6% 18% 27% 25% 6%	720
	11th to 20th	Night	27% 6% 17% 25% 20% 6%	720
	21st to end	Night	30% 9% 20% 25% 13% 3	792
November	1st to 10th	Night	34% 9% 18% 28% 11% 1	740
	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 2024-03-19 20:31:09. Version ac07

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