Malahat
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Malahat clear sky chart from 2005-11-06 to 2024-09-14.

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% 35%	101206
	Night	17% 10% 3 7% 5% 4 4 3 5% 6% 35%	96771
Transparency	Day	22% 51% 9% 12% 6% 1	100955
	Night	25% 51% 8% 10% 5% 1	96668
Seeing	Day	16% 8% 20% 28% 23% 6%	15259
	Night	20% 8% 18% 26% 22% 5%	23392

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% 16% 5% 10% 6% 6% 5% 3 4 4 14%	2219
	11th to 20th	Day	23% 13% 5% 8% 5% 4 4 4 5% 7% 23%	2199
	21st to end	Day	30% 20% 6% 12% 5% 4 4 3 4 3 9%	2893
February	1st to 10th	Day	24% 17% 4 9% 6% 6% 5% 4 5% 6% 15%	1710
	11th to 20th	Day	20% 18% 4 10% 6% 4 4 3 5% 5% 21%	1665
	21st to end	Day	19% 14% 4 10% 7% 6% 5% 4 5% 7% 19%	1414
March	1st to 10th	Day	13% 15% 5% 10% 7% 7% 6% 6% 7% 7% 17%	3308
	11th to 20th	Day	15% 11% 4 9% 5% 4 4 3 5% 7% 33%	3490
	21st to end	Day	22% 13% 5% 10% 5% 5% 5% 4 5% 6% 20%	3881
April	1st to 10th	Day	20% 13% 4 10% 7% 6% 6% 4 6% 6% 18%	2280
	11th to 20th	Day	17% 12% 4 9% 7% 6% 6% 4 6% 6% 24%	2361
	21st to end	Day	20% 11% 4 8% 5% 5% 5% 4 5% 7% 25%	2480
May	1st to 10th	Day	14% 9% 2 7% 5% 5% 5% 4 6% 6% 38%	4420
	11th to 20th	Day	9% 6% 2 7% 5% 5% 6% 4 7% 11% 38%	4377
	21st to end	Day	17% 11% 4 9% 5% 5% 5% 4 6% 8% 27%	4896
June	1st to 10th	Day	16% 9% 3 7% 5% 4 6% 5% 9% 7% 30%	2850
	11th to 20th	Day	11% 8% 3 8% 6% 6% 6% 5% 7% 9% 31%	2850
	21st to end	Day	10% 6% 2 6% 5% 5% 5% 4 7% 8% 41%	2850
July	1st to 10th	Day	5% 3 1 4 2 3 3 3 3 6% 67%	4740
	11th to 20th	Day	4 3 1 3 2 2 3 2 4 5% 72%	4740
	21st to end	Day	7% 4 2 4 2 3 4 3 5% 8% 58%	4866
August	1st to 10th	Day	5% 3 1 3 2 2 2 2 4 6% 70%	4262
	11th to 20th	Day	8% 8% 4 10% 5% 4 4 4 6% 8% 40%	4026
	21st to end	Day	11% 6% 2 7% 5% 4 4 4 6% 7% 45%	4438
September	1st to 10th	Day	9% 5% 2 5% 4 3 4 4 5% 8% 50%	2280
	11th to 20th	Day	13% 7% 3 6% 5% 4 4 4 5% 7% 42%	2166
	21st to end	Day	17% 6% 3 6% 4 5% 3 4 5% 7% 39%	1914
October	1st to 10th	Day	18% 8% 2 6% 4 5% 4 4 5% 7% 36%	1800
	11th to 20th	Day	21% 11% 3 9% 5% 6% 5% 4 5% 8% 23%	1800
	21st to end	Day	22% 11% 4 8% 5% 4 5% 4 5% 7% 25%	1861
November	1st to 10th	Day	28% 12% 4 9% 6% 5% 6% 3 4 6% 15%	1488
	11th to 20th	Day	26% 13% 4 9% 5% 5% 4 3 5% 4 22%	1520
	21st to end	Day	27% 13% 4 10% 4 5% 5% 3 3 5% 20%	1520
December	1st to 10th	Day	21% 15% 5% 9% 7% 5% 4 3 4 5% 22%	1515
	11th to 20th	Day	27% 15% 4 10% 6% 4 5% 4 4 6% 16%	1685
	21st to end	Day	24% 18% 6% 12% 6% 5% 5% 3 4 5% 13%	2442
January	1st to 10th	Night	25% 15% 5% 11% 7% 6% 5% 4 4 4 14%	4726
	11th to 20th	Night	23% 12% 4 9% 4 4 4 4 4 7% 24%	4699
	21st to end	Night	30% 17% 5% 10% 5% 5% 4 3 4 4 13%	4765
February	1st to 10th	Night	24% 13% 5% 9% 6% 5% 5% 4 5% 6% 20%	2470
	11th to 20th	Night	18% 13% 4 8% 5% 5% 5% 3 5% 5% 28%	2402
	21st to end	Night	20% 14% 4 8% 6% 5% 5% 4 5% 5% 25%	2039
March	1st to 10th	Night	14% 11% 3 8% 7% 6% 6% 5% 6% 7% 26%	3564
	11th to 20th	Night	11% 8% 2 7% 4 6% 6% 5% 7% 7% 38%	3489
	21st to end	Night	19% 13% 5% 10% 5% 6% 5% 3 6% 5% 24%	3771
April	1st to 10th	Night	18% 10% 3 8% 7% 5% 5% 4 5% 7% 27%	1900
	11th to 20th	Night	15% 9% 4 7% 5% 4 5% 4 5% 8% 33%	1767
	21st to end	Night	17% 9% 3 8% 5% 5% 5% 4 5% 8% 31%	1698
May	1st to 10th	Night	12% 7% 3 5% 3 4 4 2 5% 5% 50%	2540
	11th to 20th	Night	7% 4 2 6% 4 4 3 3 6% 8% 53%	2516
	21st to end	Night	14% 8% 3 8% 6% 5% 6% 4 6% 8% 33%	2676
June	1st to 10th	Night	14% 8% 3 7% 5% 4 4 4 5% 6% 40%	1330
	11th to 20th	Night	10% 5% 2 7% 4 5% 4 5% 6% 11% 40%	1330
	21st to end	Night	8% 4 2 4 3 3 4 4 5% 10% 51%	1330
July	1st to 10th	Night	4 2 1 3 3 3 3 2 4 5% 70%	2220
	11th to 20th	Night	3 1 1 2 2 2 2 2 3 4 78%	2220
	21st to end	Night	7% 3 2 3 2 2 3 3 4 6% 66%	2685
August	1st to 10th	Night	2 2 2 2 2 2 2 4 6% 75%	2656
	11th to 20th	Night	7% 6% 2 6% 4 4 4 3 5% 7% 51%	2812
	21st to end	Night	11% 3 1 4 3 3 4 3 6% 10% 53%	3232
September	1st to 10th	Night	5% 3 2 4 3 3 3 3 6% 6% 62%	1900
	11th to 20th	Night	12% 6% 2 5% 4 3 4 3 4 6% 48%	1869
	21st to end	Night	12% 6% 3 6% 4 4 4 3 5% 7% 44%	2045
October	1st to 10th	Night	15% 7% 2 7% 4 4 4 3 4 6% 44%	2160
	11th to 20th	Night	21% 7% 2 8% 5% 5% 4 4 6% 6% 33%	2160
	21st to end	Night	23% 8% 2 6% 5% 4 5% 3 5% 5% 32%	2492
November	1st to 10th	Night	25% 11% 3 8% 6% 5% 6% 3 5% 5% 22%	2590
	11th to 20th	Night	25% 10% 3 7% 6% 5% 5% 4 5% 6% 24%	2660
	21st to end	Night	22% 12% 4 9% 6% 5% 5% 3 5% 5% 23%	2660
December	1st to 10th	Night	21% 13% 4 9% 5% 4 5% 4 4 5% 25%	2664
	11th to 20th	Night	25% 14% 6% 10% 7% 5% 5% 3 4 5% 16%	3520
	21st to end	Night	22% 15% 5% 12% 6% 6% 5% 3 4 5% 18%	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	43% 41% 5% 7% 3	2219
	11th to 20th	Day	37% 39% 11% 9% 4	2220
	21st to end	Day	52% 43% 3 2 1	2893
February	1st to 10th	Day	25% 66% 3 4 2	1710
	11th to 20th	Day	25% 66% 3 5% 1	1674
	21st to end	Day	22% 66% 6% 4 2 1	1414
March	1st to 10th	Day	31% 49% 8% 7% 5%	3308
	11th to 20th	Day	23% 44% 8% 22% 2	3490
	21st to end	Day	34% 45% 11% 8% 2	3881
April	1st to 10th	Day	20% 69% 4 6% 1	2280
	11th to 20th	Day	20% 68% 5% 4 2 1	2361
	21st to end	Day	19% 67% 5% 6% 2 1	2480
May	1st to 10th	Day	21% 44% 12% 16% 7% 1	4420
	11th to 20th	Day	17% 50% 17% 12% 3	4380
	21st to end	Day	31% 47% 10% 10% 2	4897
June	1st to 10th	Day	14% 68% 8% 6% 3	2850
	11th to 20th	Day	14% 67% 7% 8% 4	2850
	21st to end	Day	13% 66% 8% 10% 3	2850
July	1st to 10th	Day	8% 36% 5% 20% 21% 10%	4666
	11th to 20th	Day	6% 37% 5% 28% 23% 2	4659
	21st to end	Day	16% 39% 20% 17% 8%	4712
August	1st to 10th	Day	7% 38% 7% 33% 15% 1	4245
	11th to 20th	Day	23% 45% 18% 10% 3	4065
	21st to end	Day	25% 41% 12% 16% 6%	4437
September	1st to 10th	Day	14% 65% 8% 9% 5%	2280
	11th to 20th	Day	17% 65% 5% 7% 6%	2166
	21st to end	Day	16% 65% 7% 8% 4	1914
October	1st to 10th	Day	19% 64% 6% 8% 3	1800
	11th to 20th	Day	23% 64% 5% 6% 1	1800
	21st to end	Day	22% 64% 4 7% 4	1861
November	1st to 10th	Day	29% 61% 5% 4 1	1488
	11th to 20th	Day	22% 62% 5% 7% 3 1	1520
	21st to end	Day	24% 61% 6% 5% 4	1520
December	1st to 10th	Day	25% 61% 4 7% 2	1515
	11th to 20th	Day	36% 53% 6% 3 1	1688
	21st to end	Day	47% 41% 6% 3 2	2442
January	1st to 10th	Night	44% 42% 7% 5% 3	4726
	11th to 20th	Night	34% 40% 10% 12% 4	4740
	21st to end	Night	49% 43% 4 3	4765
February	1st to 10th	Night	24% 66% 4 3 3 1	2470
	11th to 20th	Night	24% 66% 4 4 2	2404
	21st to end	Night	20% 66% 4 6% 3 1	2039
March	1st to 10th	Night	30% 45% 10% 10% 4	3564
	11th to 20th	Night	17% 44% 11% 23% 4	3490
	21st to end	Night	36% 45% 8% 10% 1	3771
April	1st to 10th	Night	18% 67% 7% 6% 1	1900
	11th to 20th	Night	17% 67% 4 8% 3 1	1767
	21st to end	Night	17% 65% 6% 6% 4 1	1698
May	1st to 10th	Night	19% 41% 7% 18% 13% 1	2540
	11th to 20th	Night	14% 42% 20% 20% 4	2516
	21st to end	Night	30% 43% 13% 12% 2	2676
June	1st to 10th	Night	14% 66% 6% 11% 4	1330
	11th to 20th	Night	12% 66% 8% 10% 5%	1330
	21st to end	Night	10% 64% 11% 10% 4	1330
July	1st to 10th	Night	9% 36% 5% 20% 19% 12%	2185
	11th to 20th	Night	5% 35% 6% 24% 30% 1	2178
	21st to end	Night	17% 37% 11% 21% 13% 1	2600
August	1st to 10th	Night	5% 37% 8% 27% 23% 1	2648
	11th to 20th	Night	26% 42% 18% 10% 4 1	2839
	21st to end	Night	18% 40% 13% 20% 9%	3232
September	1st to 10th	Night	10% 62% 10% 9% 7% 2	1900
	11th to 20th	Night	17% 62% 6% 7% 7% 1	1869
	21st to end	Night	15% 64% 5% 10% 6%	2045
October	1st to 10th	Night	16% 64% 7% 9% 4	2160
	11th to 20th	Night	21% 64% 5% 6% 4	2160
	21st to end	Night	20% 63% 4 7% 5%	2492
November	1st to 10th	Night	26% 60% 7% 6% 1	2590
	11th to 20th	Night	23% 61% 5% 5% 4 2	2660
	21st to end	Night	23% 61% 5% 5% 5%	2660
December	1st to 10th	Night	26% 62% 3 6% 3	2664
	11th to 20th	Night	36% 53% 7% 3 2	3516
	21st to end	Night	41% 41% 8% 7% 2	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	25% 18% 29% 14% 12% 1	180
	11th to 20th	Day	29% 17% 21% 18% 13% 2	180
	21st to end	Day	30% 14% 22% 23% 10% 1	273
February	1st to 10th	Day	29% 14% 26% 22% 8% 1	370
	11th to 20th	Day	25% 13% 26% 25% 10%	365
	21st to end	Day	22% 19% 22% 25% 9% 2	308
March	1st to 10th	Day	20% 11% 27% 24% 16% 1	460
	11th to 20th	Day	20% 12% 23% 22% 18% 4	460
	21st to end	Day	23% 10% 25% 26% 15% 2	506
April	1st to 10th	Day	20% 15% 23% 25% 14% 3	460
	11th to 20th	Day	18% 10% 25% 28% 14% 6%	452
	21st to end	Day	20% 8% 26% 26% 16% 4	460
May	1st to 10th	Day	10% 7% 19% 35% 24% 4	463
	11th to 20th	Day	13% 6% 15% 30% 28% 8%	488
	21st to end	Day	12% 5% 22% 30% 26% 5%	573
June	1st to 10th	Day	14% 6% 23% 32% 22% 4	680
	11th to 20th	Day	10% 8% 27% 34% 18% 3	680
	21st to end	Day	8% 4 18% 33% 31% 6%	680
July	1st to 10th	Day	8% 2 15% 32% 35% 9%	671
	11th to 20th	Day	5% 2 15% 33% 35% 10%	668
	21st to end	Day	4 3 13% 27% 40% 13%	581
August	1st to 10th	Day	6% 2 10% 26% 39% 17%	487
	11th to 20th	Day	4 1 10% 29% 41% 14%	477
	21st to end	Day	9% 4 17% 31% 31% 9%	539
September	1st to 10th	Day	10% 2 15% 35% 31% 7%	490
	11th to 20th	Day	13% 5% 17% 27% 30% 8%	463
	21st to end	Day	15% 5% 22% 27% 27% 4	450
October	1st to 10th	Day	19% 7% 17% 26% 25% 6%	450
	11th to 20th	Day	24% 8% 20% 24% 19% 5%	450
	21st to end	Day	23% 14% 27% 22% 10% 4	397
November	1st to 10th	Day	25% 12% 30% 22% 11% 1	180
	11th to 20th	Day	28% 9% 22% 22% 15% 4	180
	21st to end	Day	29% 8% 28% 17% 11% 7%	180
December	1st to 10th	Day	31% 11% 22% 18% 17% 2	180
	11th to 20th	Day	31% 13% 25% 19% 12% 1	180
	21st to end	Day	30% 17% 24% 22% 6% 1	198
January	1st to 10th	Night	30% 14% 24% 19% 11% 2	850
	11th to 20th	Night	28% 12% 17% 24% 17% 2	850
	21st to end	Night	28% 10% 19% 25% 17% 2	842
February	1st to 10th	Night	28% 13% 21% 21% 13% 3	760
	11th to 20th	Night	23% 13% 20% 27% 16% 2	744
	21st to end	Night	24% 16% 21% 21% 14% 4	628
March	1st to 10th	Night	21% 12% 21% 25% 18% 4	760
	11th to 20th	Night	21% 10% 22% 25% 17% 4	760
	21st to end	Night	22% 11% 20% 27% 17% 3	836
April	1st to 10th	Night	22% 9% 19% 27% 18% 4	760
	11th to 20th	Night	17% 8% 22% 31% 18% 4	639
	21st to end	Night	20% 6% 20% 33% 17% 3	558
May	1st to 10th	Night	11% 6% 18% 34% 27% 4	380
	11th to 20th	Night	12% 3 16% 29% 31% 8%	374
	21st to end	Night	12% 4 18% 34% 28% 4	411
June	1st to 10th	Night	15% 6% 19% 29% 28% 3	380
	11th to 20th	Night	13% 5% 24% 33% 22% 4	380
	21st to end	Night	9% 4 18% 30% 32% 7%	380
July	1st to 10th	Night	8% 1 12% 33% 38% 7%	370
	11th to 20th	Night	6% 1 12% 37% 38% 6%	368
	21st to end	Night	5% 2 9% 31% 43% 10%	416
August	1st to 10th	Night	5% 1 7% 26% 45% 16%	453
	11th to 20th	Night	5% 2 4 26% 49% 14%	564
	21st to end	Night	9% 2 13% 31% 38% 7%	674
September	1st to 10th	Night	7% 1 10% 34% 37% 11%	760
	11th to 20th	Night	13% 3 12% 23% 32% 16%	736
	21st to end	Night	14% 4 14% 29% 31% 7%	720
October	1st to 10th	Night	18% 4 13% 26% 28% 10%	720
	11th to 20th	Night	22% 6% 14% 27% 22% 9%	720
	21st to end	Night	26% 9% 18% 26% 17% 4	792
November	1st to 10th	Night	29% 10% 20% 27% 13% 1	740
	11th to 20th	Night	27% 13% 22% 21% 14% 2	760
	21st to end	Night	25% 11% 22% 23% 14% 4	760
December	1st to 10th	Night	26% 10% 18% 26% 17% 2	762
	11th to 20th	Night	27% 14% 25% 22% 10% 1	850
	21st to end	Night	32% 13% 26% 20% 8% 1	935

Page generated at 2024-09-11 07:00:08. Version ac07

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