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 2024-02-05.

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	17% 9% 4 7% 6% 4 5% 5% 5% 7% 32%	77844
	Night	19% 10% 4 7% 6% 3 5% 4 5% 6% 32%	80971
Transparency	Day	50% 11% 14% 17% 7% 1	77554
	Night	51% 9% 14% 17% 8% 1	80841
Seeing	Day	16% 7% 20% 27% 23% 6%	14340
	Night	20% 8% 18% 26% 22% 5%	22737

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% 9% 7% 4 6% 4 4 4 14%	2219
	11th to 20th	Day	23% 12% 5% 7% 6% 3 4 5% 5% 7% 23%	2199
	21st to end	Day	30% 19% 6% 11% 6% 3 4 4 4 3 9%	2893
February	1st to 10th	Day	25% 16% 4 8% 7% 4 6% 5% 5% 6% 15%	1657
	11th to 20th	Day	21% 16% 4 8% 7% 3 4 4 5% 5% 22%	1575
	21st to end	Day	20% 13% 5% 9% 8% 4 6% 5% 5% 7% 19%	1332
March	1st to 10th	Day	20% 12% 5% 8% 7% 5% 5% 6% 6% 7% 19%	1892
	11th to 20th	Day	24% 14% 5% 9% 7% 3 5% 4 4 5% 19%	1980
	21st to end	Day	22% 13% 5% 9% 7% 5% 7% 5% 5% 5% 15%	2209
April	1st to 10th	Day	20% 12% 5% 8% 8% 4 7% 5% 6% 6% 18%	2160
	11th to 20th	Day	19% 11% 4 8% 9% 4 6% 6% 6% 6% 22%	2235
	21st to end	Day	20% 10% 4 7% 7% 4 6% 5% 5% 7% 26%	2349
May	1st to 10th	Day	14% 8% 3 8% 8% 5% 6% 6% 6% 7% 30%	2520
	11th to 20th	Day	14% 8% 3 6% 7% 5% 6% 6% 6% 8% 31%	2477
	21st to end	Day	16% 8% 4 6% 6% 4 6% 4 5% 8% 33%	2764
June	1st to 10th	Day	16% 8% 3 6% 5% 3 6% 6% 8% 7% 31%	2700
	11th to 20th	Day	11% 7% 4 7% 7% 5% 6% 6% 7% 9% 30%	2700
	21st to end	Day	10% 5% 2 5% 6% 4 5% 5% 7% 8% 42%	2700
July	1st to 10th	Day	9% 5% 2 5% 4 3 5% 5% 4 7% 52%	2700
	11th to 20th	Day	8% 4 2 4 3 3 4 4 6% 8% 56%	2700
	21st to end	Day	5% 2 1 2 2 2 3 3 4 7% 68%	2789
August	1st to 10th	Day	8% 4 2 4 3 2 3 4 5% 7% 59%	2433
	11th to 20th	Day	7% 3 1 4 4 3 3 4 5% 8% 56%	2298
	21st to end	Day	8% 4 2 5% 5% 3 5% 5% 7% 9% 47%	2530
September	1st to 10th	Day	9% 6% 2 4 5% 2 4 5% 5% 8% 50%	2160
	11th to 20th	Day	13% 6% 3 5% 5% 3 4 5% 5% 7% 43%	2128
	21st to end	Day	17% 6% 3 6% 5% 4 4 4 5% 7% 40%	1914
October	1st to 10th	Day	18% 8% 3 6% 5% 4 5% 4 6% 7% 36%	1800
	11th to 20th	Day	21% 10% 4 8% 7% 4 6% 5% 5% 8% 23%	1800
	21st to end	Day	23% 10% 5% 7% 6% 3 5% 5% 5% 7% 25%	1861
November	1st to 10th	Day	29% 12% 4 7% 8% 4 7% 4 4 6% 15%	1488
	11th to 20th	Day	26% 12% 4 9% 5% 3 5% 3 5% 4 23%	1520
	21st to end	Day	27% 11% 5% 9% 6% 4 5% 5% 4 6% 20%	1520
December	1st to 10th	Day	21% 13% 5% 8% 8% 4 4 4 5% 5% 23%	1515
	11th to 20th	Day	28% 15% 4 9% 7% 2 5% 5% 4 6% 16%	1685
	21st to end	Day	25% 17% 6% 10% 8% 4 5% 4 4 5% 13%	2442
January	1st to 10th	Night	25% 15% 5% 10% 8% 5% 5% 5% 4 4 14%	4726
	11th to 20th	Night	24% 12% 5% 8% 5% 3 4 4 4 7% 25%	4699
	21st to end	Night	30% 17% 5% 9% 6% 3 5% 4 4 4 14%	4765
February	1st to 10th	Night	24% 11% 5% 8% 7% 4 5% 4 5% 7% 21%	2397
	11th to 20th	Night	18% 12% 4 7% 6% 4 5% 4 5% 6% 29%	2272
	21st to end	Night	20% 13% 4 7% 7% 3 5% 5% 5% 6% 25%	1923
March	1st to 10th	Night	19% 10% 4 7% 6% 4 5% 5% 5% 8% 27%	2066
	11th to 20th	Night	19% 10% 3 8% 7% 5% 6% 6% 6% 6% 23%	1979
	21st to end	Night	19% 12% 5% 7% 6% 5% 6% 4 5% 5% 24%	2146
April	1st to 10th	Night	19% 9% 4 7% 7% 3 5% 5% 5% 7% 28%	1800
	11th to 20th	Night	17% 8% 4 6% 6% 3 5% 6% 5% 8% 31%	1673
	21st to end	Night	17% 8% 3 6% 6% 3 5% 5% 5% 8% 33%	1609
May	1st to 10th	Night	11% 7% 3 5% 5% 3 6% 4 5% 7% 43%	1440
	11th to 20th	Night	11% 6% 2 7% 5% 3 5% 6% 7% 8% 40%	1416
	21st to end	Night	11% 6% 4 5% 6% 3 4 4 6% 10% 40%	1508
June	1st to 10th	Night	14% 7% 3 6% 6% 2 5% 5% 5% 6% 40%	1260
	11th to 20th	Night	11% 5% 3 6% 5% 3 6% 5% 6% 11% 40%	1260
	21st to end	Night	8% 3 2 3 4 2 4 5% 6% 10% 52%	1260
July	1st to 10th	Night	7% 3 2 3 4 2 4 4 5% 7% 58%	1260
	11th to 20th	Night	5% 2 2 3 3 2 3 4 4 6% 65%	1260
	21st to end	Night	3 2 1 2 2 1 2 3 3 6% 75%	1527
August	1st to 10th	Night	4 4 1 3 4 2 3 2 5% 6% 66%	1503
	11th to 20th	Night	4 2 1 2 2 2 2 4 4 7% 68%	1602
	21st to end	Night	7% 3 2 3 4 2 4 4 7% 9% 54%	1826
September	1st to 10th	Night	5% 3 2 4 3 2 3 4 5% 6% 62%	1800
	11th to 20th	Night	12% 5% 2 4 5% 2 4 4 4 7% 49%	1829
	21st to end	Night	12% 6% 3 5% 5% 3 5% 4 5% 7% 44%	2045
October	1st to 10th	Night	15% 7% 2 6% 5% 3 4 4 4 5% 44%	2160
	11th to 20th	Night	21% 7% 2 7% 6% 3 5% 5% 6% 6% 33%	2160
	21st to end	Night	23% 8% 2 5% 6% 3 5% 4 5% 5% 32%	2492
November	1st to 10th	Night	26% 10% 4 7% 7% 4 6% 5% 5% 5% 22%	2590
	11th to 20th	Night	25% 9% 4 6% 6% 4 5% 4 5% 6% 25%	2660
	21st to end	Night	22% 11% 5% 9% 7% 4 5% 5% 5% 5% 23%	2660
December	1st to 10th	Night	22% 12% 5% 8% 6% 3 5% 5% 4 5% 25%	2664
	11th to 20th	Night	26% 14% 6% 9% 8% 4 5% 4 4 5% 16%	3520
	21st to end	Night	23% 14% 5% 10% 7% 4 5% 4 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	70% 9% 7% 9% 4	2219
	11th to 20th	Day	61% 7% 14% 12% 5%	2220
	21st to end	Day	79% 8% 7% 5% 1	2893
February	1st to 10th	Day	67% 10% 9% 9% 5%	1657
	11th to 20th	Day	62% 10% 9% 12% 5% 1	1584
	21st to end	Day	63% 10% 13% 9% 4 2	1332
March	1st to 10th	Day	62% 12% 12% 10% 4 1	1892
	11th to 20th	Day	63% 10% 10% 11% 4 1	1980
	21st to end	Day	64% 12% 11% 10% 2	2209
April	1st to 10th	Day	60% 13% 13% 12% 3	2160
	11th to 20th	Day	56% 13% 11% 12% 8% 1	2235
	21st to end	Day	53% 15% 12% 14% 6% 1	2349
May	1st to 10th	Day	46% 15% 16% 17% 6% 1	2520
	11th to 20th	Day	46% 12% 17% 18% 6%	2480
	21st to end	Day	47% 13% 17% 20% 3	2765
June	1st to 10th	Day	46% 15% 17% 15% 5% 2	2700
	11th to 20th	Day	46% 16% 20% 14% 4	2700
	21st to end	Day	37% 13% 20% 20% 9% 1	2700
July	1st to 10th	Day	31% 12% 15% 27% 12% 3	2626
	11th to 20th	Day	25% 11% 20% 30% 13% 1	2619
	21st to end	Day	16% 10% 17% 39% 15% 3	2634
August	1st to 10th	Day	24% 11% 18% 30% 14% 2	2416
	11th to 20th	Day	25% 11% 20% 27% 15% 2	2298
	21st to end	Day	29% 13% 20% 30% 7% 1	2530
September	1st to 10th	Day	29% 12% 19% 25% 12% 3	2160
	11th to 20th	Day	40% 9% 14% 20% 15% 2	2128
	21st to end	Day	43% 11% 16% 19% 10% 1	1914
October	1st to 10th	Day	46% 11% 15% 19% 9% 1	1800
	11th to 20th	Day	58% 11% 14% 13% 4	1800
	21st to end	Day	58% 8% 13% 13% 8%	1861
November	1st to 10th	Day	67% 10% 11% 8% 4 1	1488
	11th to 20th	Day	63% 8% 10% 12% 6% 2	1520
	21st to end	Day	66% 7% 11% 10% 5%	1520
December	1st to 10th	Day	63% 10% 9% 12% 5% 1	1515
	11th to 20th	Day	68% 12% 11% 6% 2 1	1688
	21st to end	Day	71% 9% 10% 7% 3	2442
January	1st to 10th	Night	69% 10% 9% 8% 3	4726
	11th to 20th	Night	58% 8% 13% 16% 5% 1	4740
	21st to end	Night	73% 8% 7% 9% 3	4765
February	1st to 10th	Night	63% 9% 13% 10% 5% 1	2397
	11th to 20th	Night	56% 9% 12% 14% 8% 1	2274
	21st to end	Night	59% 7% 11% 16% 7% 1	1923
March	1st to 10th	Night	53% 10% 13% 16% 7%	2066
	11th to 20th	Night	56% 11% 11% 16% 5% 1	1980
	21st to end	Night	60% 9% 13% 15% 2	2146
April	1st to 10th	Night	53% 8% 18% 16% 5%	1800
	11th to 20th	Night	48% 11% 13% 19% 8% 2	1673
	21st to end	Night	49% 9% 14% 18% 10% 1	1609
May	1st to 10th	Night	38% 10% 19% 22% 11% 1	1440
	11th to 20th	Night	38% 10% 18% 25% 8% 1	1416
	21st to end	Night	40% 9% 22% 23% 6%	1508
June	1st to 10th	Night	42% 8% 18% 22% 6% 3	1260
	11th to 20th	Night	36% 11% 26% 21% 5%	1260
	21st to end	Night	27% 10% 26% 23% 10% 4	1260
July	1st to 10th	Night	26% 7% 20% 29% 13% 5%	1225
	11th to 20th	Night	20% 7% 21% 32% 17% 3	1218
	21st to end	Night	10% 7% 16% 37% 26% 4	1442
August	1st to 10th	Night	20% 7% 19% 32% 19% 3	1495
	11th to 20th	Night	16% 8% 23% 31% 15% 7%	1602
	21st to end	Night	25% 9% 19% 35% 12% 1	1826
September	1st to 10th	Night	22% 7% 20% 29% 18% 5%	1800
	11th to 20th	Night	35% 7% 15% 20% 18% 5%	1829
	21st to end	Night	38% 9% 16% 23% 12% 2	2045
October	1st to 10th	Night	42% 7% 17% 22% 12% 1	2160
	11th to 20th	Night	48% 8% 17% 18% 9%	2160
	21st to end	Night	50% 9% 13% 17% 10%	2492
November	1st to 10th	Night	62% 9% 12% 13% 5% 1	2590
	11th to 20th	Night	60% 9% 12% 12% 7% 2	2660
	21st to end	Night	60% 8% 12% 12% 7% 1	2660
December	1st to 10th	Night	61% 9% 12% 12% 6% 1	2664
	11th to 20th	Night	68% 12% 11% 6% 3	3516
	21st to end	Night	66% 10% 11% 10% 4	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% 7% 1	353
	11th to 20th	Day	27% 13% 27% 24% 10%	335
	21st to end	Day	23% 18% 23% 25% 10% 2	280
March	1st to 10th	Day	22% 12% 25% 24% 15% 1	420
	11th to 20th	Day	22% 13% 25% 22% 16% 3	420
	21st to end	Day	23% 9% 26% 25% 15% 2	462
April	1st to 10th	Day	21% 15% 21% 25% 14% 3	420
	11th to 20th	Day	19% 8% 24% 27% 15% 6%	412
	21st to end	Day	19% 8% 26% 26% 17% 4	420
May	1st to 10th	Day	10% 7% 19% 35% 24% 4	423
	11th to 20th	Day	15% 5% 14% 28% 29% 9%	448
	21st to end	Day	11% 4 21% 30% 27% 6%	526
June	1st to 10th	Day	14% 6% 24% 32% 21% 4	630
	11th to 20th	Day	10% 7% 27% 35% 18% 3	630
	21st to end	Day	8% 3 18% 33% 32% 6%	630
July	1st to 10th	Day	9% 2 13% 32% 35% 10%	621
	11th to 20th	Day	5% 3 16% 32% 35% 10%	618
	21st to end	Day	3 2 12% 26% 43% 14%	535
August	1st to 10th	Day	6% 2 10% 25% 38% 18%	447
	11th to 20th	Day	4 1 9% 29% 43% 14%	437
	21st to end	Day	8% 3 16% 32% 32% 10%	495
September	1st to 10th	Day	11% 3 15% 36% 29% 6%	450
	11th to 20th	Day	13% 5% 17% 27% 30% 9%	450
	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% 14% 22% 21% 13% 3	738
	11th to 20th	Night	23% 12% 20% 27% 16% 2	704
	21st to end	Night	23% 15% 21% 22% 15% 4	592
March	1st to 10th	Night	21% 11% 22% 25% 17% 4	720
	11th to 20th	Night	23% 10% 22% 26% 16% 3	720
	21st to end	Night	22% 11% 21% 26% 17% 3	792
April	1st to 10th	Night	22% 9% 19% 26% 19% 4	720
	11th to 20th	Night	18% 8% 22% 29% 19% 5%	605
	21st to end	Night	20% 5% 21% 33% 17% 3	529
May	1st to 10th	Night	11% 6% 17% 35% 26% 4	360
	11th to 20th	Night	13% 3 15% 29% 32% 8%	354
	21st to end	Night	11% 3 17% 34% 29% 5%	389
June	1st to 10th	Night	15% 6% 18% 29% 29% 3	360
	11th to 20th	Night	13% 4 23% 34% 22% 4	360
	21st to end	Night	9% 3 18% 30% 33% 8%	360
July	1st to 10th	Night	9% 1 12% 32% 39% 8%	350
	11th to 20th	Night	6% 1 12% 36% 38% 6%	348
	21st to end	Night	4 2 8% 31% 44% 10%	394
August	1st to 10th	Night	5% 1 8% 26% 43% 17%	429
	11th to 20th	Night	4 1 5% 26% 49% 15%	534
	21st to end	Night	8% 2 13% 31% 37% 8%	638
September	1st to 10th	Night	7% 2 11% 35% 35% 11%	720
	11th to 20th	Night	13% 3 12% 23% 33% 17%	720
	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 2024-02-02 02:20:32. Version ac07

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