Esquimalt
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Esquimalt clear sky chart from 2005-11-06 to 2025-01-22.

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	14% 9% 3 8% 5% 5% 5% 4 5% 7% 36%	108983
	Night	17% 10% 3 8% 5% 4 4 4 5% 6% 34%	108944
Transparency	Day	24% 47% 10% 12% 5% 1	108733
	Night	29% 46% 9% 11% 5% 1	108840
Seeing	Day	15% 5% 17% 27% 26% 9%	15570
	Night	21% 6% 19% 27% 21% 6%	23938

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	27% 15% 5% 10% 6% 6% 5% 3 4 5% 14%	2289
	11th to 20th	Day	21% 14% 4 8% 5% 4 4 4 5% 6% 24%	2274
	21st to end	Day	29% 21% 6% 11% 7% 5% 4 2 4 3 9%	2912
February	1st to 10th	Day	23% 15% 4 10% 6% 5% 5% 5% 5% 7% 15%	1710
	11th to 20th	Day	20% 15% 5% 10% 5% 5% 5% 4 4 5% 22%	1665
	21st to end	Day	17% 13% 4 10% 8% 6% 6% 5% 5% 6% 19%	1422
March	1st to 10th	Day	12% 13% 4 11% 7% 7% 7% 5% 7% 8% 18%	3288
	11th to 20th	Day	14% 10% 4 9% 5% 4 5% 3 5% 7% 35%	3490
	21st to end	Day	18% 14% 4 10% 6% 5% 5% 4 6% 6% 22%	3886
April	1st to 10th	Day	17% 11% 4 9% 8% 7% 6% 4 7% 8% 19%	2280
	11th to 20th	Day	15% 11% 3 9% 8% 6% 6% 4 6% 6% 26%	2350
	21st to end	Day	16% 9% 3 8% 6% 6% 5% 5% 6% 8% 27%	2484
May	1st to 10th	Day	13% 7% 2 6% 5% 5% 5% 4 5% 7% 41%	4420
	11th to 20th	Day	8% 5% 2 6% 5% 5% 6% 5% 7% 10% 42%	4377
	21st to end	Day	17% 10% 4 9% 5% 5% 5% 4 6% 7% 30%	4863
June	1st to 10th	Day	14% 8% 3 8% 5% 4 5% 5% 7% 8% 34%	2850
	11th to 20th	Day	9% 6% 3 8% 7% 6% 6% 4 6% 9% 35%	2850
	21st to end	Day	9% 5% 2 5% 5% 5% 6% 5% 7% 7% 44%	2850
July	1st to 10th	Day	4 3 1 3 3 2 3 2 4 4 70%	4740
	11th to 20th	Day	3 2 1 3 2 2 2 2 4 5% 73%	4740
	21st to end	Day	8% 3 1 3 3 2 2 3 5% 7% 63%	4835
August	1st to 10th	Day	3 2 1 3 2 2 3 3 3 5% 72%	4278
	11th to 20th	Day	8% 7% 3 7% 5% 4 5% 4 6% 8% 43%	4026
	21st to end	Day	11% 5% 2 6% 4 4 4 4 5% 8% 47%	4428
September	1st to 10th	Day	7% 5% 2 5% 4 4 5% 3 5% 9% 51%	2280
	11th to 20th	Day	11% 7% 3 6% 5% 4 5% 3 5% 7% 43%	2253
	21st to end	Day	16% 6% 2 8% 4 4 4 3 5% 8% 40%	2014
October	1st to 10th	Day	15% 6% 2 7% 6% 6% 6% 5% 8% 9% 31%	3180
	11th to 20th	Day	24% 10% 4 10% 5% 5% 4 4 4 6% 24%	3161
	21st to end	Day	17% 11% 4 10% 6% 5% 5% 4 6% 9% 24%	3242
November	1st to 10th	Day	26% 13% 4 9% 6% 6% 5% 4 5% 6% 16%	1568
	11th to 20th	Day	23% 12% 4 10% 6% 4 5% 3 5% 5% 22%	1600
	21st to end	Day	24% 14% 5% 9% 6% 5% 6% 3 4 5% 19%	1600
December	1st to 10th	Day	15% 15% 4 11% 7% 5% 4 3 4 6% 26%	2620
	11th to 20th	Day	29% 14% 4 9% 6% 5% 4 4 5% 7% 13%	2660
	21st to end	Day	24% 20% 6% 11% 6% 5% 4 3 5% 5% 10%	3498
January	1st to 10th	Night	23% 15% 5% 12% 7% 6% 5% 4 5% 4 14%	4876
	11th to 20th	Night	22% 13% 4 8% 4 4 4 3 5% 6% 26%	4841
	21st to end	Night	30% 17% 5% 9% 6% 5% 4 3 4 4 14%	4754
February	1st to 10th	Night	23% 12% 4 9% 6% 5% 5% 3 5% 6% 21%	2470
	11th to 20th	Night	17% 13% 3 9% 6% 4 5% 4 4 6% 29%	2402
	21st to end	Night	20% 13% 4 8% 6% 5% 5% 4 5% 6% 24%	2032
March	1st to 10th	Night	13% 11% 4 9% 7% 7% 6% 5% 7% 8% 25%	3581
	11th to 20th	Night	11% 7% 3 6% 5% 5% 5% 5% 7% 8% 40%	3489
	21st to end	Night	19% 13% 4 10% 6% 5% 5% 4 5% 5% 24%	3754
April	1st to 10th	Night	18% 9% 3 8% 6% 5% 4 5% 6% 7% 28%	1900
	11th to 20th	Night	14% 10% 3 7% 6% 4 5% 5% 6% 8% 33%	1777
	21st to end	Night	17% 9% 4 8% 5% 5% 4 4 6% 7% 33%	1695
May	1st to 10th	Night	12% 7% 2 5% 4 3 4 3 4 5% 52%	2540
	11th to 20th	Night	6% 5% 1 5% 4 4 4 3 6% 7% 54%	2516
	21st to end	Night	14% 7% 3 8% 6% 5% 5% 4 6% 8% 35%	2708
June	1st to 10th	Night	13% 8% 3 7% 5% 4 5% 4 5% 6% 40%	1330
	11th to 20th	Night	10% 6% 2 5% 5% 4 4 5% 8% 9% 40%	1330
	21st to end	Night	8% 4 2 4 4 3 4 4 6% 9% 51%	1330
July	1st to 10th	Night	4 3 1 3 2 2 3 2 3 5% 72%	2220
	11th to 20th	Night	3 2 1 2 2 2 2 2 3 4 79%	2220
	21st to end	Night	8% 3 1 3 2 2 3 2 3 5% 67%	2716
August	1st to 10th	Night	2 2 1 2 2 2 2 2 4 6% 75%	2652
	11th to 20th	Night	8% 5% 2 6% 4 3 4 4 5% 7% 52%	2812
	21st to end	Night	11% 3 1 4 3 3 4 3 5% 9% 54%	3241
September	1st to 10th	Night	5% 3 1 5% 2 3 4 3 5% 6% 63%	1900
	11th to 20th	Night	12% 6% 3 5% 5% 3 4 3 5% 6% 49%	1924
	21st to end	Night	13% 6% 2 6% 4 4 5% 3 5% 6% 45%	2165
October	1st to 10th	Night	12% 6% 2 7% 4 4 4 4 5% 8% 44%	3800
	11th to 20th	Night	21% 8% 3 7% 5% 5% 4 4 5% 7% 31%	3777
	21st to end	Night	19% 10% 3 8% 5% 4 4 3 5% 6% 31%	4317
November	1st to 10th	Night	24% 12% 4 8% 5% 5% 6% 4 5% 5% 22%	2730
	11th to 20th	Night	24% 11% 3 8% 6% 5% 5% 4 5% 6% 24%	2800
	21st to end	Night	20% 12% 5% 10% 7% 5% 5% 3 5% 5% 22%	2800
December	1st to 10th	Night	15% 11% 4 10% 5% 6% 6% 5% 6% 7% 27%	4560
	11th to 20th	Night	29% 16% 5% 10% 6% 5% 5% 3 4 4 13%	5527
	21st to end	Night	22% 14% 5% 11% 7% 5% 5% 4 5% 5% 17%	7458

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	45% 41% 6% 7% 2	2289
	11th to 20th	Day	37% 42% 10% 9% 3	2295
	21st to end	Day	50% 43% 5% 2 1	2912
February	1st to 10th	Day	24% 67% 4 4 2	1710
	11th to 20th	Day	24% 66% 4 5% 1	1674
	21st to end	Day	21% 66% 6% 4 2 1	1422
March	1st to 10th	Day	29% 46% 12% 8% 5%	3288
	11th to 20th	Day	22% 42% 12% 21% 2	3490
	21st to end	Day	32% 45% 13% 8% 1	3886
April	1st to 10th	Day	19% 68% 6% 6% 1	2280
	11th to 20th	Day	18% 68% 6% 5% 2 1	2350
	21st to end	Day	17% 68% 6% 6% 2	2484
May	1st to 10th	Day	20% 42% 11% 19% 7%	4420
	11th to 20th	Day	13% 47% 20% 17% 3	4380
	21st to end	Day	29% 45% 15% 9% 2	4864
June	1st to 10th	Day	14% 67% 9% 6% 3	2850
	11th to 20th	Day	12% 66% 9% 9% 3	2850
	21st to end	Day	12% 65% 10% 10% 3	2850
July	1st to 10th	Day	8% 36% 4 19% 21% 11%	4666
	11th to 20th	Day	5% 37% 7% 25% 24% 2	4659
	21st to end	Day	15% 37% 20% 18% 10% 1	4682
August	1st to 10th	Day	6% 37% 9% 33% 14% 2	4261
	11th to 20th	Day	26% 41% 18% 11% 3	4065
	21st to end	Day	26% 39% 10% 18% 7%	4427
September	1st to 10th	Day	14% 64% 9% 9% 5%	2280
	11th to 20th	Day	17% 62% 7% 7% 5%	2253
	21st to end	Day	17% 62% 9% 8% 4	2014
October	1st to 10th	Day	31% 41% 12% 14% 2	3180
	11th to 20th	Day	40% 38% 7% 12% 4	3161
	21st to end	Day	34% 40% 11% 11% 5%	3242
November	1st to 10th	Day	31% 59% 6% 3 1	1568
	11th to 20th	Day	24% 59% 7% 7% 2 1	1600
	21st to end	Day	26% 59% 5% 7% 3	1600
December	1st to 10th	Day	40% 38% 8% 12% 2	2620
	11th to 20th	Day	50% 36% 7% 6% 1	2663
	21st to end	Day	53% 31% 8% 5% 2	3498
January	1st to 10th	Night	46% 42% 6% 4 2	4876
	11th to 20th	Night	35% 39% 11% 12% 2	4882
	21st to end	Night	50% 44% 3 3	4754
February	1st to 10th	Night	24% 66% 3 3 3	2470
	11th to 20th	Night	24% 66% 4 4 2	2404
	21st to end	Night	20% 66% 5% 5% 3 1	2032
March	1st to 10th	Night	31% 48% 8% 10% 4	3581
	11th to 20th	Night	17% 44% 14% 23% 1 1	3490
	21st to end	Night	37% 44% 9% 9% 1	3754
April	1st to 10th	Night	18% 68% 6% 7% 1	1900
	11th to 20th	Night	18% 67% 4 7% 3 1	1777
	21st to end	Night	17% 65% 6% 6% 4 1	1695
May	1st to 10th	Night	20% 41% 9% 21% 8% 1	2540
	11th to 20th	Night	12% 45% 20% 18% 5%	2516
	21st to end	Night	26% 46% 13% 12% 3	2708
June	1st to 10th	Night	15% 66% 5% 11% 2 1	1330
	11th to 20th	Night	12% 66% 7% 11% 4	1330
	21st to end	Night	11% 64% 11% 10% 3	1330
July	1st to 10th	Night	9% 36% 4 21% 17% 13%	2185
	11th to 20th	Night	5% 35% 7% 23% 29% 1	2178
	21st to end	Night	17% 35% 11% 22% 14%	2630
August	1st to 10th	Night	5% 36% 8% 26% 21% 3	2644
	11th to 20th	Night	24% 40% 20% 11% 4 1	2839
	21st to end	Night	21% 40% 10% 21% 8%	3241
September	1st to 10th	Night	11% 62% 10% 10% 6% 1	1900
	11th to 20th	Night	18% 61% 6% 8% 7% 1	1924
	21st to end	Night	16% 61% 6% 11% 5%	2165
October	1st to 10th	Night	25% 38% 16% 18% 3	3800
	11th to 20th	Night	36% 38% 9% 14% 2	3777
	21st to end	Night	34% 39% 9% 12% 6%	4317
November	1st to 10th	Night	28% 58% 7% 6% 1	2730
	11th to 20th	Night	25% 58% 6% 5% 4 2	2800
	21st to end	Night	27% 59% 4 4 5%	2800
December	1st to 10th	Night	36% 40% 8% 13% 2	4560
	11th to 20th	Night	52% 35% 6% 4 2	5523
	21st to end	Night	49% 31% 11% 7% 2	7458

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	29% 13% 29% 18% 11% 2	200
	11th to 20th	Day	23% 11% 24% 27% 16%	200
	21st to end	Day	29% 7% 24% 25% 14% 1	271
February	1st to 10th	Day	30% 8% 22% 27% 12% 2	370
	11th to 20th	Day	24% 10% 19% 32% 14% 1	365
	21st to end	Day	18% 17% 22% 25% 16% 3	312
March	1st to 10th	Day	19% 8% 20% 30% 19% 4	460
	11th to 20th	Day	21% 7% 20% 26% 20% 7%	460
	21st to end	Day	20% 8% 21% 28% 20% 3	506
April	1st to 10th	Day	17% 10% 22% 25% 19% 6%	460
	11th to 20th	Day	17% 5% 18% 31% 20% 8%	452
	21st to end	Day	18% 6% 24% 24% 21% 7%	460
May	1st to 10th	Day	13% 5% 14% 29% 33% 6%	463
	11th to 20th	Day	14% 5% 12% 26% 35% 9%	488
	21st to end	Day	13% 3 17% 30% 27% 9%	553
June	1st to 10th	Day	13% 5% 22% 30% 25% 6%	680
	11th to 20th	Day	10% 5% 24% 35% 21% 5%	680
	21st to end	Day	8% 2 19% 32% 28% 12%	680
July	1st to 10th	Day	8% 1 14% 29% 35% 13%	671
	11th to 20th	Day	5% 1 16% 31% 35% 13%	668
	21st to end	Day	3 1 12% 28% 36% 20%	563
August	1st to 10th	Day	5% 1 11% 22% 36% 25%	487
	11th to 20th	Day	4 1 7% 21% 45% 23%	477
	21st to end	Day	9% 2 13% 26% 35% 15%	539
September	1st to 10th	Day	10% 1 8% 31% 38% 12%	490
	11th to 20th	Day	13% 1 11% 27% 34% 13%	490
	21st to end	Day	14% 4 15% 26% 32% 9%	490
October	1st to 10th	Day	17% 5% 15% 26% 26% 11%	490
	11th to 20th	Day	25% 6% 13% 26% 24% 6%	490
	21st to end	Day	23% 11% 22% 25% 16% 3	435
November	1st to 10th	Day	27% 7% 26% 24% 17%	200
	11th to 20th	Day	21% 9% 25% 25% 18% 3	200
	21st to end	Day	26% 10% 21% 27% 14% 4	200
December	1st to 10th	Day	27% 7% 19% 26% 20% 3	200
	11th to 20th	Day	33% 13% 21% 21% 13%	200
	21st to end	Day	34% 14% 21% 25% 6%	220
January	1st to 10th	Night	31% 11% 22% 22% 12% 2	900
	11th to 20th	Night	29% 6% 18% 25% 19% 2	895
	21st to end	Night	27% 5% 19% 25% 19% 4	840
February	1st to 10th	Night	29% 9% 18% 26% 13% 3	760
	11th to 20th	Night	23% 8% 22% 26% 18% 3	744
	21st to end	Night	28% 10% 23% 21% 14% 6%	628
March	1st to 10th	Night	21% 8% 19% 27% 20% 4	760
	11th to 20th	Night	21% 7% 23% 24% 20% 5%	760
	21st to end	Night	21% 7% 22% 28% 17% 5%	836
April	1st to 10th	Night	20% 8% 21% 25% 23% 4	760
	11th to 20th	Night	18% 5% 25% 29% 18% 6%	649
	21st to end	Night	18% 6% 26% 30% 15% 4	555
May	1st to 10th	Night	11% 4 24% 31% 25% 4	380
	11th to 20th	Night	11% 5% 19% 31% 27% 7%	374
	21st to end	Night	13% 5% 22% 32% 25% 3	411
June	1st to 10th	Night	15% 6% 22% 32% 23% 2	380
	11th to 20th	Night	12% 4 27% 36% 17% 4	380
	21st to end	Night	9% 2 25% 29% 26% 8%	380
July	1st to 10th	Night	8% 1 18% 35% 34% 4	370
	11th to 20th	Night	7% 2 19% 37% 29% 5%	368
	21st to end	Night	5% 3 18% 33% 33% 8%	416
August	1st to 10th	Night	5% 2 10% 32% 42% 9%	449
	11th to 20th	Night	5% 1 7% 29% 43% 15%	564
	21st to end	Night	9% 2 15% 32% 34% 8%	683
September	1st to 10th	Night	8% 1 11% 33% 33% 14%	760
	11th to 20th	Night	14% 2 10% 26% 30% 17%	760
	21st to end	Night	16% 2 15% 29% 28% 11%	760
October	1st to 10th	Night	17% 3 12% 26% 28% 14%	760
	11th to 20th	Night	23% 4 13% 26% 24% 11%	760
	21st to end	Night	27% 5% 18% 26% 20% 5%	836
November	1st to 10th	Night	31% 6% 19% 26% 17% 2	780
	11th to 20th	Night	27% 10% 21% 24% 15% 4	800
	21st to end	Night	28% 8% 21% 22% 16% 5%	800
December	1st to 10th	Night	25% 7% 20% 24% 20% 3	800
	11th to 20th	Night	30% 10% 22% 26% 10% 1	890
	21st to end	Night	29% 12% 27% 21% 9% 1	990

Page generated at 2025-01-19 00:06:49. Version ac07

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