Squamish
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Squamish clear sky chart from 2005-11-06 to 2025-04-26.

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	23% 14% 3 7% 4 4 4 3 4 5% 30%	117103
	Night	26% 16% 3 7% 4 3 3 3 4 5% 27%	120227
Transparency	Day	59% 6% 10% 15% 8% 2	116850
	Night	61% 5% 10% 14% 8% 2	120126
Seeing	Day	29% 15% 26% 21% 8% 1	15926
	Night	35% 8% 23% 23% 11% 1	24251

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	30% 26% 3 5% 3 3 3 3 3 5% 17%	3179
	11th to 20th	Day	18% 12% 4 7% 3 3 3 3 3 7% 35%	3159
	21st to end	Day	37% 17% 2 4 2 2 2 1 2 2 28%	3890
February	1st to 10th	Day	27% 20% 5% 7% 3 3 3 4 3 6% 18%	1800
	11th to 20th	Day	23% 24% 3 6% 3 3 2 3 4 4 24%	1755
	21st to end	Day	17% 28% 5% 9% 4 5% 3 3 3 4 18%	1490
March	1st to 10th	Day	22% 21% 5% 9% 5% 4 4 3 3 4 20%	4684
	11th to 20th	Day	17% 25% 5% 8% 5% 4 3 3 4 4 23%	5000
	21st to end	Day	23% 24% 5% 10% 5% 5% 4 3 4 4 13%	5616
April	1st to 10th	Day	27% 21% 4 9% 5% 4 4 3 4 5% 14%	2400
	11th to 20th	Day	24% 20% 4 8% 5% 4 3 3 4 4 21%	2489
	21st to end	Day	26% 21% 4 7% 4 4 5% 3 4 4 18%	2600
May	1st to 10th	Day	17% 14% 4 8% 5% 4 4 3 4 5% 31%	4420
	11th to 20th	Day	16% 11% 2 6% 4 4 6% 5% 8% 10% 28%	4377
	21st to end	Day	31% 15% 3 7% 4 4 4 4 5% 6% 17%	4991
June	1st to 10th	Day	32% 11% 3 7% 4 4 4 3 4 6% 20%	2850
	11th to 20th	Day	32% 13% 4 8% 5% 4 3 3 5% 6% 17%	2850
	21st to end	Day	24% 10% 3 7% 5% 4 4 3 4 6% 31%	2850
July	1st to 10th	Day	10% 5% 2 4 3 3 2 2 3 4 62%	4740
	11th to 20th	Day	9% 3 1 3 2 2 3 2 3 6% 66%	4740
	21st to end	Day	13% 5% 2 5% 3 3 3 3 6% 8% 48%	4934
August	1st to 10th	Day	8% 3 1 3 2 2 3 2 4 7% 65%	4379
	11th to 20th	Day	17% 6% 3 6% 4 4 5% 3 5% 7% 40%	4026
	21st to end	Day	20% 7% 2 6% 3 3 4 3 5% 7% 39%	4438
September	1st to 10th	Day	16% 6% 3 6% 4 3 4 3 4 6% 45%	2280
	11th to 20th	Day	23% 9% 3 6% 4 3 3 3 3 5% 38%	2271
	21st to end	Day	28% 9% 3 6% 4 3 3 2 4 6% 33%	2005
October	1st to 10th	Day	28% 9% 3 7% 5% 4 4 3 4 6% 25%	3180
	11th to 20th	Day	37% 10% 2 6% 3 4 4 4 4 4 21%	3161
	21st to end	Day	29% 17% 4 9% 6% 4 4 4 4 4 15%	3144
November	1st to 10th	Day	40% 14% 3 6% 4 3 3 3 4 3 17%	1568
	11th to 20th	Day	37% 20% 3 6% 3 2 2 2 2 4 19%	1600
	21st to end	Day	35% 18% 3 5% 4 4 3 2 3 4 19%	1600
December	1st to 10th	Day	24% 15% 3 7% 3 3 4 3 3 5% 30%	2494
	11th to 20th	Day	38% 23% 4 7% 4 3 3 2 3 3 12%	2645
	21st to end	Day	33% 25% 4 8% 5% 5% 4 2 3 3 10%	3498
January	1st to 10th	Night	30% 22% 4 9% 4 3 2 2 3 3 17%	6766
	11th to 20th	Night	20% 11% 4 6% 3 3 4 3 4 9% 34%	6739
	21st to end	Night	33% 17% 2 5% 3 2 2 2 3 4 28%	7063
February	1st to 10th	Night	27% 19% 4 7% 4 4 4 3 4 6% 18%	2600
	11th to 20th	Night	22% 24% 4 7% 3 3 3 2 3 4 24%	2532
	21st to end	Night	22% 26% 3 8% 4 3 3 2 4 4 21%	2140
March	1st to 10th	Night	23% 22% 5% 8% 4 4 4 3 4 4 20%	5210
	11th to 20th	Night	17% 27% 4 8% 4 4 4 2 3 4 23%	4999
	21st to end	Night	27% 23% 5% 8% 4 4 3 2 3 4 16%	5359
April	1st to 10th	Night	26% 22% 4 7% 5% 5% 4 3 4 3 18%	2000
	11th to 20th	Night	22% 19% 3 7% 4 4 3 3 3 6% 26%	1857
	21st to end	Night	26% 17% 3 7% 4 4 3 2 4 6% 24%	1696
May	1st to 10th	Night	17% 14% 3 6% 3 3 3 3 3 5% 41%	2540
	11th to 20th	Night	16% 9% 2 7% 4 4 4 4 6% 10% 34%	2516
	21st to end	Night	29% 17% 3 7% 4 3 4 3 3 5% 22%	2582
June	1st to 10th	Night	28% 10% 3 7% 6% 3 4 3 5% 6% 27%	1330
	11th to 20th	Night	27% 13% 3 8% 6% 3 4 3 5% 6% 23%	1330
	21st to end	Night	21% 9% 3 6% 5% 4 4 3 5% 6% 35%	1330
July	1st to 10th	Night	8% 5% 2 3 2 3 3 2 3 5% 65%	2220
	11th to 20th	Night	7% 3 1 2 2 1 2 2 4 5% 71%	2220
	21st to end	Night	14% 6% 2 4 2 3 4 3 5% 5% 52%	2603
August	1st to 10th	Night	7% 3 1 2 1 2 2 2 3 6% 71%	2551
	11th to 20th	Night	18% 6% 2 5% 4 4 4 3 5% 6% 42%	2812
	21st to end	Night	18% 8% 2 6% 3 4 3 3 5% 6% 41%	3231
September	1st to 10th	Night	14% 6% 2 5% 3 2 3 3 5% 7% 50%	1900
	11th to 20th	Night	24% 8% 2 5% 4 3 4 3 3 5% 39%	1906
	21st to end	Night	27% 10% 3 6% 3 3 3 3 4 6% 33%	2175
October	1st to 10th	Night	24% 14% 4 8% 4 5% 4 3 4 5% 26%	3800
	11th to 20th	Night	33% 12% 2 6% 4 4 3 3 3 5% 25%	3777
	21st to end	Night	31% 17% 4 8% 4 3 4 3 4 4 19%	4413
November	1st to 10th	Night	41% 15% 3 6% 4 3 3 2 3 5% 15%	2730
	11th to 20th	Night	38% 19% 3 5% 3 2 3 2 2 3 19%	2800
	21st to end	Night	33% 19% 4 6% 3 4 3 2 3 3 20%	2800
December	1st to 10th	Night	25% 14% 4 7% 4 3 3 3 4 6% 27%	4682
	11th to 20th	Night	37% 21% 4 7% 3 3 3 2 3 3 12%	5560
	21st to end	Night	36% 25% 4 8% 4 3 3 2 2 3 11%	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	72% 7% 7% 11% 3 1	3179
	11th to 20th	Day	53% 5% 13% 16% 10% 4	3180
	21st to end	Day	68% 2 4 17% 8% 1	3890
February	1st to 10th	Day	69% 5% 8% 8% 8% 2	1800
	11th to 20th	Day	65% 5% 7% 13% 7% 2	1764
	21st to end	Day	72% 6% 7% 9% 4 2	1490
March	1st to 10th	Day	70% 6% 6% 11% 6%	4684
	11th to 20th	Day	68% 4 6% 15% 6%	5000
	21st to end	Day	77% 5% 7% 7% 2 1	5616
April	1st to 10th	Day	75% 7% 10% 7% 1	2400
	11th to 20th	Day	70% 5% 7% 10% 8% 1	2489
	21st to end	Day	73% 6% 7% 9% 5%	2600
May	1st to 10th	Day	57% 7% 12% 17% 7%	4420
	11th to 20th	Day	50% 11% 20% 15% 4	4380
	21st to end	Day	70% 9% 10% 8% 3	4992
June	1st to 10th	Day	67% 8% 10% 9% 4 2	2850
	11th to 20th	Day	73% 6% 11% 8% 3	2850
	21st to end	Day	58% 5% 13% 16% 7% 2	2850
July	1st to 10th	Day	29% 4 9% 26% 21% 12%	4666
	11th to 20th	Day	23% 5% 10% 36% 23% 3	4659
	21st to end	Day	34% 7% 19% 22% 15% 3	4778
August	1st to 10th	Day	22% 6% 10% 37% 24% 1	4362
	11th to 20th	Day	45% 7% 20% 18% 9% 2	4065
	21st to end	Day	46% 7% 17% 20% 10% 1	4437
September	1st to 10th	Day	41% 8% 11% 24% 11% 4	2280
	11th to 20th	Day	51% 4 9% 17% 16% 3	2271
	21st to end	Day	56% 6% 11% 16% 9% 2	2005
October	1st to 10th	Day	61% 7% 10% 16% 7%	3180
	11th to 20th	Day	68% 5% 8% 13% 6%	3161
	21st to end	Day	73% 5% 7% 9% 4 1	3144
November	1st to 10th	Day	73% 7% 6% 8% 5% 1	1568
	11th to 20th	Day	73% 4 7% 7% 6% 3	1600
	21st to end	Day	71% 5% 5% 10% 7% 2	1600
December	1st to 10th	Day	60% 4 11% 14% 10% 1	2494
	11th to 20th	Day	82% 3 6% 5% 2 1	2648
	21st to end	Day	81% 5% 4 7% 3 1	3498
January	1st to 10th	Night	75% 4 5% 9% 7% 1	6766
	11th to 20th	Night	49% 7% 12% 20% 9% 3	6780
	21st to end	Night	63% 4 8% 15% 9% 1	7063
February	1st to 10th	Night	69% 6% 7% 8% 8% 2	2600
	11th to 20th	Night	66% 5% 8% 10% 7% 3	2534
	21st to end	Night	68% 4 9% 10% 6% 2	2140
March	1st to 10th	Night	68% 5% 8% 11% 7% 1	5210
	11th to 20th	Night	67% 6% 7% 13% 8%	5000
	21st to end	Night	73% 7% 9% 7% 2 1	5359
April	1st to 10th	Night	71% 7% 11% 10% 1	2000
	11th to 20th	Night	61% 7% 10% 13% 7% 1	1857
	21st to end	Night	64% 6% 12% 11% 6%	1696
May	1st to 10th	Night	48% 6% 15% 23% 8%	2540
	11th to 20th	Night	45% 9% 25% 17% 4	2516
	21st to end	Night	66% 9% 12% 10% 3	2582
June	1st to 10th	Night	62% 6% 17% 9% 4 3	1330
	11th to 20th	Night	65% 7% 14% 10% 4	1330
	21st to end	Night	52% 9% 14% 16% 6% 2	1330
July	1st to 10th	Night	26% 5% 11% 26% 24% 9%	2185
	11th to 20th	Night	19% 5% 12% 35% 27% 2	2178
	21st to end	Night	35% 6% 14% 25% 13% 6%	2520
August	1st to 10th	Night	18% 4 12% 36% 29% 2	2543
	11th to 20th	Night	44% 7% 21% 16% 9% 3	2839
	21st to end	Night	46% 6% 18% 21% 8% 1	3231
September	1st to 10th	Night	35% 9% 15% 24% 13% 4	1900
	11th to 20th	Night	48% 6% 11% 16% 14% 5%	1906
	21st to end	Night	55% 5% 13% 16% 8% 3	2175
October	1st to 10th	Night	62% 6% 12% 12% 7%	3800
	11th to 20th	Night	65% 5% 6% 16% 8%	3777
	21st to end	Night	69% 5% 6% 13% 5% 1	4413
November	1st to 10th	Night	75% 4 7% 7% 4 2	2730
	11th to 20th	Night	73% 4 7% 7% 6% 3	2800
	21st to end	Night	71% 4 6% 9% 9% 2	2800
December	1st to 10th	Night	60% 5% 11% 15% 7% 2	4682
	11th to 20th	Night	79% 5% 6% 7% 3 1	5556
	21st to end	Night	81% 4 4 6% 4 1	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	43% 13% 23% 14% 6% 2	200
	11th to 20th	Day	38% 9% 26% 22% 6%	200
	21st to end	Day	45% 9% 23% 15% 8%	233
February	1st to 10th	Day	38% 17% 28% 13% 5%	400
	11th to 20th	Day	35% 14% 29% 18% 3 1	395
	21st to end	Day	32% 22% 26% 16% 4	334
March	1st to 10th	Day	34% 17% 25% 18% 5%	500
	11th to 20th	Day	38% 16% 19% 18% 8% 1	500
	21st to end	Day	38% 18% 24% 13% 6% 1	550
April	1st to 10th	Day	39% 17% 23% 15% 5% 1	500
	11th to 20th	Day	33% 18% 25% 16% 6% 1	492
	21st to end	Day	32% 21% 22% 16% 7% 1	481
May	1st to 10th	Day	24% 19% 27% 24% 6%	463
	11th to 20th	Day	26% 12% 27% 23% 10% 1	488
	21st to end	Day	29% 15% 27% 20% 7% 1	629
June	1st to 10th	Day	33% 18% 26% 18% 5% 1	680
	11th to 20th	Day	31% 21% 27% 17% 4 1	680
	21st to end	Day	22% 16% 29% 26% 6% 1	680
July	1st to 10th	Day	19% 13% 31% 27% 7% 2	671
	11th to 20th	Day	13% 14% 33% 28% 9% 3	668
	21st to end	Day	11% 11% 31% 31% 12% 3	623
August	1st to 10th	Day	13% 10% 26% 32% 14% 5%	487
	11th to 20th	Day	12% 8% 29% 34% 13% 4	477
	21st to end	Day	17% 15% 31% 24% 10% 2	539
September	1st to 10th	Day	19% 17% 31% 22% 10% 1	490
	11th to 20th	Day	28% 14% 27% 21% 8% 2	490
	21st to end	Day	30% 15% 25% 20% 8% 2	490
October	1st to 10th	Day	31% 14% 25% 19% 9% 2	490
	11th to 20th	Day	40% 11% 21% 17% 8% 2	490
	21st to end	Day	43% 14% 22% 14% 6% 1	386
November	1st to 10th	Day	41% 15% 23% 17% 6%	200
	11th to 20th	Day	46% 13% 15% 15% 11% 2	200
	21st to end	Day	43% 16% 20% 9% 10% 3	200
December	1st to 10th	Day	41% 8% 18% 19% 13% 2	200
	11th to 20th	Day	46% 11% 20% 17% 7% 1	200
	21st to end	Day	41% 8% 32% 15% 4	220
January	1st to 10th	Night	47% 11% 22% 14% 4 1	900
	11th to 20th	Night	40% 10% 26% 20% 4	900
	21st to end	Night	41% 10% 26% 19% 4	910
February	1st to 10th	Night	37% 11% 32% 17% 3	800
	11th to 20th	Night	33% 10% 31% 22% 4	784
	21st to end	Night	36% 12% 25% 20% 7%	660
March	1st to 10th	Night	37% 11% 23% 19% 10% 1	800
	11th to 20th	Night	41% 10% 21% 22% 6%	800
	21st to end	Night	40% 10% 23% 17% 10% 1	880
April	1st to 10th	Night	36% 9% 21% 25% 8% 1	800
	11th to 20th	Night	31% 8% 27% 27% 7% 1	669
	21st to end	Night	32% 8% 27% 23% 9%	524
May	1st to 10th	Night	22% 7% 24% 32% 16% 1	380
	11th to 20th	Night	24% 5% 21% 33% 17% 1	374
	21st to end	Night	26% 5% 26% 30% 13%	411
June	1st to 10th	Night	29% 6% 26% 25% 13% 1	380
	11th to 20th	Night	29% 8% 24% 26% 12% 1	380
	21st to end	Night	24% 5% 22% 30% 19% 1	380
July	1st to 10th	Night	14% 2 21% 36% 26% 1	370
	11th to 20th	Night	13% 4 14% 39% 30% 1	368
	21st to end	Night	11% 2 11% 36% 36% 3	416
August	1st to 10th	Night	13% 2 9% 33% 38% 4	387
	11th to 20th	Night	13% 1 10% 38% 35% 2	564
	21st to end	Night	18% 4 20% 33% 24% 1	673
September	1st to 10th	Night	17% 4 22% 36% 19% 1	760
	11th to 20th	Night	27% 5% 17% 26% 23% 3	760
	21st to end	Night	34% 6% 18% 28% 13% 1	760
October	1st to 10th	Night	30% 7% 21% 27% 14% 1	760
	11th to 20th	Night	40% 5% 22% 22% 10% 1	760
	21st to end	Night	43% 9% 26% 17% 4 1	836
November	1st to 10th	Night	49% 11% 22% 17% 1	780
	11th to 20th	Night	48% 9% 25% 15% 4	800
	21st to end	Night	42% 13% 23% 17% 5% 1	800
December	1st to 10th	Night	35% 10% 30% 19% 6%	835
	11th to 20th	Night	49% 9% 28% 12% 2	900
	21st to end	Night	47% 12% 27% 13% 1	990

Page generated at 2025-04-23 06:25:01. Version ac07

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