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 2026-05-17.

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 7% 5% 5% 5% 4 5% 7% 37%	135735
	Night	16% 10% 3 8% 5% 4 4 4 5% 6% 35%	135777
Transparency	Day	28% 39% 12% 14% 6% 1	135444
	Night	32% 38% 10% 14% 5% 1	135646
Seeing	Day	15% 6% 18% 28% 25% 9%	17287
	Night	20% 6% 19% 27% 21% 6%	25614

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% 5% 3 5% 5% 14%	4125
	11th to 20th	Day	15% 10% 3 8% 4 4 5% 4 6% 7% 34%	4151
	21st to end	Day	22% 14% 4 9% 6% 5% 5% 3 4 5% 22%	5407
February	1st to 10th	Day	22% 15% 4 10% 7% 6% 5% 4 5% 7% 14%	1890
	11th to 20th	Day	20% 15% 5% 10% 5% 5% 5% 3 4 5% 22%	1845
	21st to end	Day	18% 13% 4 10% 8% 6% 6% 5% 5% 6% 18%	1567
March	1st to 10th	Day	15% 15% 4 10% 7% 7% 6% 4 6% 8% 18%	4838
	11th to 20th	Day	16% 12% 4 10% 5% 5% 5% 4 5% 7% 28%	5110
	21st to end	Day	18% 13% 4 11% 6% 6% 6% 5% 7% 6% 17%	5696
April	1st to 10th	Day	16% 11% 4 8% 7% 7% 6% 4 7% 8% 20%	2520
	11th to 20th	Day	14% 10% 3 8% 8% 6% 6% 4 7% 7% 26%	2601
	21st to end	Day	15% 9% 3 8% 6% 6% 5% 4 6% 8% 30%	2746
May	1st to 10th	Day	11% 6% 2 7% 5% 5% 4 3 5% 7% 44%	6460
	11th to 20th	Day	10% 7% 2 7% 5% 5% 6% 5% 6% 10% 37%	6362
	21st to end	Day	13% 7% 3 8% 4 5% 5% 4 7% 8% 35%	6981
June	1st to 10th	Day	13% 8% 3 8% 5% 4 5% 5% 7% 8% 35%	3000
	11th to 20th	Day	9% 7% 3 8% 7% 6% 6% 5% 6% 9% 35%	3000
	21st to end	Day	9% 6% 2 5% 5% 5% 6% 5% 7% 7% 44%	3000
July	1st to 10th	Day	4 3 1 3 2 2 3 2 4 5% 69%	6780
	11th to 20th	Day	3 2 1 3 2 2 2 2 3 5% 74%	6780
	21st to end	Day	6% 2 1 3 2 2 3 3 5% 7% 67%	6947
August	1st to 10th	Day	3 2 1 3 2 2 3 3 4 6% 71%	4414
	11th to 20th	Day	8% 7% 3 7% 5% 4 5% 4 6% 8% 43%	4156
	21st to end	Day	10% 5% 2 6% 4 4 4 3 5% 8% 47%	4568
September	1st to 10th	Day	7% 5% 2 5% 4 4 5% 3 5% 9% 51%	2400
	11th to 20th	Day	11% 7% 3 6% 4 4 5% 3 5% 7% 44%	2371
	21st to end	Day	15% 7% 2 8% 4 4 4 3 5% 8% 40%	2120
October	1st to 10th	Day	15% 6% 2 7% 6% 6% 6% 5% 8% 9% 31%	3280
	11th to 20th	Day	24% 10% 4 9% 5% 5% 4 3 5% 6% 25%	3261
	21st to end	Day	17% 11% 4 10% 6% 5% 5% 4 6% 9% 23%	3345
November	1st to 10th	Day	25% 13% 4 9% 6% 6% 6% 4 5% 6% 16%	1648
	11th to 20th	Day	24% 12% 4 10% 6% 4 5% 3 4 5% 21%	1680
	21st to end	Day	24% 13% 5% 9% 6% 5% 6% 3 4 5% 19%	1680
December	1st to 10th	Day	15% 15% 4 11% 7% 5% 4 3 4 6% 25%	2700
	11th to 20th	Day	29% 14% 4 9% 6% 5% 5% 4 5% 7% 13%	2731
	21st to end	Day	24% 20% 6% 11% 6% 5% 4 3 5% 6% 10%	3575
January	1st to 10th	Night	26% 16% 4 12% 6% 6% 5% 4 5% 5% 13%	8770
	11th to 20th	Night	16% 10% 3 7% 3 3 4 3 5% 6% 40%	8744
	21st to end	Night	21% 12% 4 8% 5% 4 4 3 4 5% 29%	8769
February	1st to 10th	Night	21% 13% 4 10% 6% 5% 5% 3 5% 7% 22%	2730
	11th to 20th	Night	17% 13% 3 9% 6% 4 5% 4 5% 6% 29%	2662
	21st to end	Night	20% 13% 4 8% 6% 5% 5% 5% 5% 6% 24%	2239
March	1st to 10th	Night	12% 10% 3 8% 6% 7% 6% 5% 7% 8% 28%	5271
	11th to 20th	Night	13% 10% 3 8% 5% 5% 6% 4 7% 8% 31%	5109
	21st to end	Night	20% 14% 4 11% 6% 5% 5% 4 5% 6% 20%	5508
April	1st to 10th	Night	17% 9% 3 8% 6% 5% 5% 5% 6% 7% 29%	2100
	11th to 20th	Night	13% 9% 3 7% 6% 4 5% 5% 7% 8% 33%	1966
	21st to end	Night	16% 8% 3 7% 4 4 4 4 6% 7% 36%	1873
May	1st to 10th	Night	11% 7% 2 6% 4 3 3 3 3 5% 53%	3720
	11th to 20th	Night	10% 6% 2 6% 4 4 4 4 6% 9% 45%	3664
	21st to end	Night	11% 6% 3 8% 6% 6% 6% 5% 7% 8% 34%	3890
June	1st to 10th	Night	12% 8% 2 7% 5% 4 5% 4 5% 6% 42%	1400
	11th to 20th	Night	10% 6% 2 5% 5% 4 4 5% 8% 10% 41%	1400
	21st to end	Night	8% 4 2 4 4 4 4 4 6% 9% 51%	1400
July	1st to 10th	Night	4 3 1 3 2 2 2 2 3 5% 71%	3180
	11th to 20th	Night	2 2 1 2 2 2 2 2 3 4 80%	3180
	21st to end	Night	5% 2 1 3 2 2 2 2 3 6% 71%	3895
August	1st to 10th	Night	2 2 1 2 2 2 2 2 4 6% 75%	2736
	11th to 20th	Night	8% 5% 2 6% 4 3 4 4 5% 7% 52%	2902
	21st to end	Night	11% 3 1 4 3 3 3 3 5% 9% 55%	3343
September	1st to 10th	Night	5% 3 1 5% 2 3 4 3 5% 6% 63%	2000
	11th to 20th	Night	12% 6% 3 5% 4 3 4 3 5% 6% 50%	2025
	21st to end	Night	13% 6% 2 6% 4 4 5% 3 5% 6% 45%	2279
October	1st to 10th	Night	12% 6% 2 7% 4 4 4 4 5% 7% 44%	3920
	11th to 20th	Night	21% 8% 3 7% 5% 5% 4 4 5% 7% 31%	3897
	21st to end	Night	19% 9% 3 8% 5% 4 5% 3 5% 6% 31%	4456
November	1st to 10th	Night	24% 11% 4 8% 5% 5% 6% 4 5% 5% 22%	2870
	11th to 20th	Night	23% 11% 3 8% 6% 5% 5% 4 5% 6% 24%	2940
	21st to end	Night	21% 12% 4 10% 6% 5% 5% 3 5% 5% 22%	2940
December	1st to 10th	Night	16% 11% 4 10% 5% 6% 6% 5% 6% 7% 26%	4700
	11th to 20th	Night	29% 16% 5% 11% 6% 5% 5% 3 4 4 13%	5676
	21st to end	Night	22% 14% 5% 11% 7% 5% 5% 4 5% 5% 18%	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	58% 25% 6% 8% 2	4125
	11th to 20th	Day	37% 26% 13% 19% 5%	4172
	21st to end	Day	50% 25% 9% 12% 4	5408
February	1st to 10th	Day	28% 61% 4 4 2 1	1890
	11th to 20th	Day	27% 61% 4 6% 2	1854
	21st to end	Day	25% 60% 7% 4 2 1	1567
March	1st to 10th	Day	41% 33% 12% 11% 4	4838
	11th to 20th	Day	37% 30% 11% 18% 4	5110
	21st to end	Day	45% 33% 12% 9% 2	5696
April	1st to 10th	Day	22% 62% 8% 8% 1	2520
	11th to 20th	Day	20% 62% 7% 7% 3 1	2601
	21st to end	Day	17% 62% 9% 9% 3	2746
May	1st to 10th	Day	25% 29% 14% 22% 8% 1	6460
	11th to 20th	Day	25% 34% 20% 19% 2	6365
	21st to end	Day	29% 32% 21% 14% 3 1	6982
June	1st to 10th	Day	14% 64% 10% 8% 3	3000
	11th to 20th	Day	14% 63% 9% 10% 3	3000
	21st to end	Day	14% 63% 11% 10% 2	3000
July	1st to 10th	Day	11% 26% 17% 18% 18% 8%	6706
	11th to 20th	Day	7% 26% 15% 27% 23% 2	6699
	21st to end	Day	13% 26% 28% 25% 8% 1	6752
August	1st to 10th	Day	7% 36% 9% 33% 13% 2	4397
	11th to 20th	Day	27% 40% 18% 11% 4	4195
	21st to end	Day	26% 38% 11% 18% 8%	4567
September	1st to 10th	Day	14% 61% 11% 9% 4	2400
	11th to 20th	Day	18% 59% 8% 9% 5%	2371
	21st to end	Day	18% 59% 10% 9% 4	2120
October	1st to 10th	Day	31% 40% 13% 14% 2	3280
	11th to 20th	Day	40% 37% 7% 13% 4	3261
	21st to end	Day	35% 38% 11% 11% 5%	3345
November	1st to 10th	Day	32% 57% 6% 4 1	1648
	11th to 20th	Day	26% 56% 7% 7% 2 1	1680
	21st to end	Day	28% 56% 5% 7% 3	1680
December	1st to 10th	Day	42% 37% 8% 12% 2	2700
	11th to 20th	Day	51% 35% 7% 6% 1	2734
	21st to end	Day	54% 31% 8% 5% 2	3575
January	1st to 10th	Night	60% 25% 7% 6% 2	8770
	11th to 20th	Night	33% 24% 14% 19% 10%	8785
	21st to end	Night	45% 25% 10% 16% 5%	8769
February	1st to 10th	Night	27% 60% 4 4 5%	2730
	11th to 20th	Night	27% 59% 5% 6% 3 1	2664
	21st to end	Night	24% 60% 6% 6% 3 1	2239
March	1st to 10th	Night	37% 35% 10% 13% 5%	5271
	11th to 20th	Night	32% 32% 11% 22% 3	5110
	21st to end	Night	48% 32% 9% 10% 1	5508
April	1st to 10th	Night	20% 61% 7% 10% 1	2100
	11th to 20th	Night	19% 61% 7% 8% 4 1	1966
	21st to end	Night	17% 59% 9% 9% 5% 1	1873
May	1st to 10th	Night	25% 29% 10% 24% 12%	3717
	11th to 20th	Night	24% 33% 21% 19% 4	3664
	21st to end	Night	32% 34% 16% 16% 2	3890
June	1st to 10th	Night	14% 63% 7% 12% 3 1	1400
	11th to 20th	Night	13% 63% 7% 13% 4	1400
	21st to end	Night	12% 61% 13% 11% 3	1400
July	1st to 10th	Night	12% 25% 14% 26% 13% 9%	3145
	11th to 20th	Night	5% 25% 15% 26% 27% 2	3138
	21st to end	Night	14% 25% 20% 30% 12%	3785
August	1st to 10th	Night	5% 36% 9% 26% 21% 3	2728
	11th to 20th	Night	25% 39% 20% 11% 4 1	2929
	21st to end	Night	20% 39% 10% 21% 9%	3343
September	1st to 10th	Night	12% 60% 11% 11% 6% 1	2000
	11th to 20th	Night	18% 58% 6% 9% 8% 1	2025
	21st to end	Night	18% 59% 6% 12% 6%	2279
October	1st to 10th	Night	25% 37% 16% 18% 3	3920
	11th to 20th	Night	36% 37% 9% 15% 3	3897
	21st to end	Night	34% 38% 9% 12% 6%	4456
November	1st to 10th	Night	30% 55% 8% 7% 1	2870
	11th to 20th	Night	28% 55% 6% 5% 3 2	2940
	21st to end	Night	29% 57% 5% 5% 5%	2940
December	1st to 10th	Night	37% 39% 8% 13% 2	4700
	11th to 20th	Night	53% 34% 6% 5% 2	5672
	21st to end	Night	49% 30% 11% 8% 2	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	29% 13% 29% 18% 10% 1	220
	11th to 20th	Day	23% 10% 23% 27% 17%	220
	21st to end	Day	27% 7% 23% 26% 15% 2	321
February	1st to 10th	Day	28% 8% 22% 28% 12% 2	430
	11th to 20th	Day	23% 11% 18% 32% 15% 1	425
	21st to end	Day	20% 17% 22% 25% 15% 2	361
March	1st to 10th	Day	19% 10% 19% 30% 18% 4	540
	11th to 20th	Day	23% 8% 20% 26% 17% 6%	540
	21st to end	Day	20% 9% 22% 28% 19% 3	594
April	1st to 10th	Day	16% 9% 21% 26% 21% 7%	540
	11th to 20th	Day	16% 5% 20% 30% 21% 8%	532
	21st to end	Day	16% 5% 23% 26% 22% 8%	540
May	1st to 10th	Day	12% 5% 15% 28% 34% 6%	543
	11th to 20th	Day	14% 7% 14% 25% 32% 9%	553
	21st to end	Day	13% 4 18% 30% 26% 10%	599
June	1st to 10th	Day	12% 5% 21% 30% 27% 6%	730
	11th to 20th	Day	9% 5% 24% 34% 22% 6%	730
	21st to end	Day	8% 2 18% 32% 28% 12%	730
July	1st to 10th	Day	8% 1 15% 30% 34% 12%	721
	11th to 20th	Day	4 2 16% 31% 35% 13%	718
	21st to end	Day	3 1 11% 29% 35% 20%	609
August	1st to 10th	Day	6% 1 11% 22% 37% 24%	527
	11th to 20th	Day	4 1 7% 22% 44% 21%	517
	21st to end	Day	8% 2 12% 25% 37% 16%	583
September	1st to 10th	Day	10% 2 7% 30% 39% 13%	530
	11th to 20th	Day	13% 2 11% 26% 34% 14%	530
	21st to end	Day	14% 5% 15% 26% 32% 8%	530
October	1st to 10th	Day	17% 4 15% 27% 26% 11%	530
	11th to 20th	Day	24% 7% 15% 25% 23% 5%	530
	21st to end	Day	24% 12% 22% 25% 15% 3	472
November	1st to 10th	Day	25% 7% 26% 25% 15%	220
	11th to 20th	Day	24% 8% 24% 25% 17% 2	220
	21st to end	Day	26% 10% 21% 27% 12% 3	220
December	1st to 10th	Day	29% 7% 20% 24% 18% 2	220
	11th to 20th	Day	33% 14% 21% 20% 11%	220
	21st to end	Day	32% 14% 21% 27% 6%	242
January	1st to 10th	Night	32% 12% 21% 22% 12% 2	950
	11th to 20th	Night	30% 6% 17% 26% 20% 2	944
	21st to end	Night	26% 5% 19% 25% 20% 4	924
February	1st to 10th	Night	28% 10% 18% 26% 14% 3	840
	11th to 20th	Night	23% 8% 21% 27% 18% 3	824
	21st to end	Night	27% 10% 23% 21% 13% 5%	692
March	1st to 10th	Night	21% 9% 19% 27% 20% 4	840
	11th to 20th	Night	22% 7% 23% 24% 18% 5%	840
	21st to end	Night	21% 8% 22% 28% 16% 4	924
April	1st to 10th	Night	19% 8% 20% 25% 23% 4	840
	11th to 20th	Night	17% 5% 25% 28% 19% 5%	718
	21st to end	Night	17% 5% 26% 31% 16% 5%	613
May	1st to 10th	Night	11% 4 23% 33% 25% 4	420
	11th to 20th	Night	12% 7% 20% 29% 26% 6%	406
	21st to end	Night	12% 5% 22% 32% 25% 3	433
June	1st to 10th	Night	15% 6% 22% 33% 24% 2	400
	11th to 20th	Night	12% 4 27% 37% 17% 4	400
	21st to end	Night	9% 3 25% 29% 27% 8%	400
July	1st to 10th	Night	9% 1 19% 35% 33% 4	390
	11th to 20th	Night	7% 2 20% 37% 30% 5%	388
	21st to end	Night	5% 3 18% 34% 32% 8%	438
August	1st to 10th	Night	5% 2 11% 33% 41% 9%	473
	11th to 20th	Night	6% 2 8% 29% 42% 14%	594
	21st to end	Night	8% 2 15% 31% 36% 8%	719
September	1st to 10th	Night	7% 2 11% 33% 34% 14%	800
	11th to 20th	Night	14% 2 10% 26% 31% 17%	800
	21st to end	Night	16% 2 15% 29% 28% 10%	800
October	1st to 10th	Night	16% 4 12% 27% 28% 13%	800
	11th to 20th	Night	22% 4 14% 26% 23% 10%	800
	21st to end	Night	26% 5% 18% 27% 20% 5%	880
November	1st to 10th	Night	30% 7% 19% 26% 16% 2	820
	11th to 20th	Night	27% 10% 21% 24% 14% 3	840
	21st to end	Night	28% 8% 21% 23% 16% 5%	840
December	1st to 10th	Night	26% 7% 20% 24% 20% 3	840
	11th to 20th	Night	30% 11% 22% 26% 10% 1	939
	21st to end	Night	29% 12% 27% 22% 9% 1	1045

Page generated at 2026-05-13 22:58:56. Version ac07

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