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 2026-08-30.

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	21% 13% 3 6% 4 4 4 3 4 6% 32%	148299
	Night	24% 15% 3 6% 4 3 3 3 4 5% 29%	142615
Transparency	Day	56% 6% 12% 16% 9% 1	148004
	Night	60% 5% 11% 14% 8% 1	142492
Seeing	Day	29% 16% 27% 21% 7% 1	17789
	Night	34% 8% 23% 23% 11% 1	25791

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% 27% 4 7% 4 3 3 2 3 4 13%	4125
	11th to 20th	Day	19% 10% 3 6% 3 3 3 3 4 6% 40%	4119
	21st to end	Day	36% 15% 2 5% 3 3 3 2 3 2 27%	5044
February	1st to 10th	Day	27% 20% 5% 7% 3 3 3 4 3 6% 18%	1890
	11th to 20th	Day	22% 24% 4 6% 3 4 2 3 4 4 24%	1845
	21st to end	Day	17% 29% 5% 9% 4 5% 3 3 3 4 18%	1562
March	1st to 10th	Day	22% 21% 5% 9% 5% 4 4 3 3 4 20%	4787
	11th to 20th	Day	18% 25% 5% 8% 5% 4 3 3 4 4 23%	5110
	21st to end	Day	23% 24% 5% 10% 5% 5% 5% 3 4 4 13%	5740
April	1st to 10th	Day	26% 21% 4 8% 5% 4 4 3 4 5% 15%	2520
	11th to 20th	Day	23% 20% 4 7% 5% 4 4 3 4 5% 21%	2615
	21st to end	Day	25% 20% 4 7% 4 4 5% 3 4 4 21%	2798
May	1st to 10th	Day	13% 11% 4 7% 4 4 4 4 5% 6% 39%	8195
	11th to 20th	Day	18% 13% 3 7% 5% 5% 5% 5% 6% 9% 25%	8160
	21st to end	Day	23% 10% 3 6% 4 4 5% 5% 6% 7% 27%	9311
June	1st to 10th	Day	30% 10% 3 7% 5% 4 4 3 5% 6% 23%	3150
	11th to 20th	Day	29% 12% 3 8% 5% 4 4 3 5% 6% 20%	3150
	21st to end	Day	23% 10% 3 8% 5% 4 4 4 4 6% 30%	3150
July	1st to 10th	Day	12% 6% 2 6% 4 4 4 3 5% 6% 50%	8820
	11th to 20th	Day	6% 4 1 4 2 3 3 3 5% 7% 62%	8820
	21st to end	Day	14% 4 1 4 3 3 4 3 5% 8% 50%	9196
August	1st to 10th	Day	9% 3 1 3 2 2 3 2 4 7% 64%	4657
	11th to 20th	Day	17% 6% 2 6% 4 4 5% 3 5% 7% 41%	4286
	21st to end	Day	20% 7% 2 6% 3 3 4 3 5% 7% 40%	4696
September	1st to 10th	Day	15% 6% 2 6% 4 3 4 3 4 6% 46%	2400
	11th to 20th	Day	22% 8% 3 6% 4 4 3 3 3 5% 39%	2390
	21st to end	Day	28% 8% 3 6% 5% 3 3 2 4 5% 33%	2110
October	1st to 10th	Day	28% 9% 3 7% 5% 4 4 3 4 6% 26%	3280
	11th to 20th	Day	37% 10% 2 7% 3 4 4 4 4 4 21%	3261
	21st to end	Day	30% 17% 4 9% 6% 4 4 4 4 4 14%	3244
November	1st to 10th	Day	39% 15% 3 6% 4 3 4 3 4 3 17%	1648
	11th to 20th	Day	37% 20% 3 6% 3 2 2 2 2 4 19%	1680
	21st to end	Day	35% 18% 3 5% 4 4 3 2 3 4 19%	1680
December	1st to 10th	Day	25% 15% 3 7% 3 3 4 2 3 4 30%	2570
	11th to 20th	Day	38% 23% 4 7% 4 3 3 2 3 3 11%	2715
	21st to end	Day	32% 25% 4 8% 5% 5% 4 3 3 3 9%	3575
January	1st to 10th	Night	29% 25% 5% 10% 4 4 3 2 3 3 14%	8770
	11th to 20th	Night	22% 9% 3 5% 2 2 3 3 4 8% 39%	8779
	21st to end	Night	31% 15% 2 5% 3 3 3 2 3 4 29%	9134
February	1st to 10th	Night	27% 19% 4 8% 4 4 3 2 4 6% 18%	2730
	11th to 20th	Night	22% 24% 4 7% 3 3 3 2 3 4 24%	2662
	21st to end	Night	22% 26% 3 8% 4 3 3 2 4 4 21%	2244
March	1st to 10th	Night	23% 22% 5% 8% 4 4 4 3 4 4 20%	5326
	11th to 20th	Night	18% 27% 4 8% 4 3 4 2 3 4 23%	5109
	21st to end	Night	27% 23% 5% 8% 5% 4 3 2 3 4 16%	5477
April	1st to 10th	Night	25% 22% 4 7% 5% 5% 4 3 5% 4 18%	2100
	11th to 20th	Night	22% 19% 3 7% 4 4 3 3 3 6% 26%	1951
	21st to end	Night	25% 16% 3 8% 4 4 3 2 4 6% 25%	1822
May	1st to 10th	Night	14% 11% 2 5% 3 4 4 3 3 5% 46%	4724
	11th to 20th	Night	18% 13% 3 7% 5% 4 4 4 5% 8% 28%	4700
	21st to end	Night	20% 12% 3 7% 4 4 4 3 5% 7% 31%	4844
June	1st to 10th	Night	27% 9% 3 6% 6% 3 4 3 5% 6% 29%	1470
	11th to 20th	Night	25% 12% 3 7% 6% 3 4 3 5% 6% 26%	1470
	21st to end	Night	21% 9% 3 7% 4 4 4 3 4 6% 35%	1470
July	1st to 10th	Night	12% 5% 2 4 3 3 4 3 5% 6% 54%	4140
	11th to 20th	Night	6% 3 1 3 2 2 2 2 4 5% 69%	4140
	21st to end	Night	14% 5% 2 4 2 3 4 3 5% 7% 52%	4857
August	1st to 10th	Night	7% 3 1 2 1 2 2 2 3 6% 70%	2712
	11th to 20th	Night	18% 6% 2 5% 4 4 4 3 5% 6% 42%	2992
	21st to end	Night	17% 8% 2 6% 3 4 3 3 5% 6% 42%	3414
September	1st to 10th	Night	13% 6% 2 5% 3 2 3 3 5% 7% 50%	2000
	11th to 20th	Night	23% 8% 2 5% 4 3 3 3 4 5% 40%	2007
	21st to end	Night	28% 10% 3 6% 3 3 3 3 4 5% 33%	2290
October	1st to 10th	Night	24% 14% 4 8% 4 5% 4 3 4 5% 26%	3920
	11th to 20th	Night	33% 11% 2 6% 4 4 3 2 3 5% 26%	3897
	21st to end	Night	31% 17% 4 9% 4 3 4 3 4 4 19%	4555
November	1st to 10th	Night	41% 15% 3 6% 4 3 3 2 3 5% 15%	2870
	11th to 20th	Night	37% 19% 3 5% 4 2 3 2 3 3 19%	2940
	21st to end	Night	33% 19% 4 7% 3 4 3 2 2 3 20%	2940
December	1st to 10th	Night	25% 15% 4 7% 4 3 3 3 4 6% 26%	4826
	11th to 20th	Night	37% 22% 5% 7% 4 3 3 2 3 3 12%	5710
	21st to end	Night	35% 25% 4 8% 4 3 3 2 2 3 12%	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	76% 6% 6% 8% 2 1	4125
	11th to 20th	Day	49% 5% 11% 18% 15% 3	4140
	21st to end	Day	68% 2 3 15% 10% 1	5045
February	1st to 10th	Day	69% 5% 7% 8% 8% 2	1890
	11th to 20th	Day	65% 5% 7% 14% 7% 2	1854
	21st to end	Day	72% 6% 7% 9% 4 2	1562
March	1st to 10th	Day	70% 6% 7% 11% 6%	4787
	11th to 20th	Day	68% 4 6% 15% 6%	5110
	21st to end	Day	77% 5% 7% 7% 2 1	5740
April	1st to 10th	Day	74% 7% 11% 8% 1	2520
	11th to 20th	Day	69% 5% 8% 10% 8% 1	2615
	21st to end	Day	70% 6% 7% 11% 6%	2798
May	1st to 10th	Day	49% 5% 14% 23% 8% 1	8195
	11th to 20th	Day	58% 9% 20% 12% 2	8163
	21st to end	Day	57% 8% 15% 15% 4	9312
June	1st to 10th	Day	65% 8% 11% 9% 5% 2	3150
	11th to 20th	Day	69% 6% 11% 11% 4	3150
	21st to end	Day	58% 5% 13% 16% 7% 1	3150
July	1st to 10th	Day	37% 6% 15% 22% 14% 6%	8746
	11th to 20th	Day	24% 6% 14% 33% 20% 2	8739
	21st to end	Day	33% 5% 24% 20% 16% 2	8997
August	1st to 10th	Day	23% 6% 10% 36% 23% 1	4640
	11th to 20th	Day	44% 7% 20% 18% 9% 2	4325
	21st to end	Day	45% 7% 17% 20% 10% 1	4695
September	1st to 10th	Day	40% 8% 12% 25% 12% 4	2400
	11th to 20th	Day	50% 5% 9% 18% 16% 3	2390
	21st to end	Day	56% 6% 12% 15% 9% 2	2110
October	1st to 10th	Day	61% 6% 11% 16% 7%	3280
	11th to 20th	Day	68% 5% 8% 13% 6%	3261
	21st to end	Day	74% 5% 7% 9% 4 1	3244
November	1st to 10th	Day	73% 6% 6% 8% 5% 1	1648
	11th to 20th	Day	74% 4 6% 7% 6% 3	1680
	21st to end	Day	72% 5% 5% 9% 7% 2	1680
December	1st to 10th	Day	61% 4 10% 14% 9% 1	2570
	11th to 20th	Day	83% 3 5% 5% 2 1	2718
	21st to end	Day	81% 6% 4 7% 3 1	3575
January	1st to 10th	Night	79% 3 5% 7% 5% 1	8770
	11th to 20th	Night	46% 6% 9% 19% 17% 3	8820
	21st to end	Night	62% 3 7% 15% 12% 1	9134
February	1st to 10th	Night	69% 5% 7% 9% 7% 2	2730
	11th to 20th	Night	65% 5% 8% 11% 8% 3	2664
	21st to end	Night	69% 4 9% 10% 6% 2	2244
March	1st to 10th	Night	68% 5% 9% 11% 7% 1	5326
	11th to 20th	Night	67% 6% 7% 13% 8%	5110
	21st to end	Night	73% 7% 9% 7% 2 1	5477
April	1st to 10th	Night	70% 7% 11% 11% 1	2100
	11th to 20th	Night	62% 7% 10% 13% 8% 1	1951
	21st to end	Night	62% 6% 12% 13% 6%	1822
May	1st to 10th	Night	43% 4 17% 27% 8%	4721
	11th to 20th	Night	56% 8% 20% 14% 2	4700
	21st to end	Night	55% 7% 18% 16% 4	4848
June	1st to 10th	Night	60% 6% 17% 9% 5% 3	1470
	11th to 20th	Night	62% 7% 13% 13% 5%	1470
	21st to end	Night	53% 8% 14% 17% 6% 2	1470
July	1st to 10th	Night	33% 6% 18% 24% 14% 5%	4105
	11th to 20th	Night	21% 6% 16% 32% 24% 2	4098
	21st to end	Night	34% 5% 23% 21% 14% 4	4751
August	1st to 10th	Night	19% 4 12% 35% 28% 2	2704
	11th to 20th	Night	44% 7% 22% 16% 9% 3	3019
	21st to end	Night	45% 6% 18% 21% 9% 2	3414
September	1st to 10th	Night	35% 9% 16% 24% 13% 4	2000
	11th to 20th	Night	48% 6% 11% 17% 14% 5%	2007
	21st to end	Night	55% 5% 14% 16% 8% 2	2290
October	1st to 10th	Night	62% 6% 13% 13% 6%	3920
	11th to 20th	Night	65% 5% 7% 16% 8%	3897
	21st to end	Night	70% 5% 6% 13% 5% 1	4555
November	1st to 10th	Night	75% 4 7% 7% 4 1	2870
	11th to 20th	Night	73% 4 7% 7% 5% 3	2940
	21st to end	Night	71% 4 6% 9% 9% 2	2940
December	1st to 10th	Night	61% 5% 10% 15% 7% 2	4826
	11th to 20th	Night	80% 5% 6% 6% 3 1	5706
	21st to end	Night	81% 4 4 7% 4 1	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	44% 14% 22% 13% 5% 2	220
	11th to 20th	Day	36% 9% 27% 22% 6%	220
	21st to end	Day	44% 9% 23% 17% 8%	256
February	1st to 10th	Day	37% 16% 28% 13% 4	430
	11th to 20th	Day	35% 15% 28% 19% 3 1	425
	21st to end	Day	33% 23% 25% 16% 3	358
March	1st to 10th	Day	34% 17% 25% 18% 5%	540
	11th to 20th	Day	39% 17% 19% 17% 8% 1	540
	21st to end	Day	38% 19% 24% 13% 5% 1	594
April	1st to 10th	Day	37% 17% 23% 16% 6% 1	540
	11th to 20th	Day	32% 18% 26% 17% 7% 1	532
	21st to end	Day	31% 23% 24% 15% 7% 1	540
May	1st to 10th	Day	23% 20% 28% 23% 5%	543
	11th to 20th	Day	28% 14% 27% 21% 9% 1	568
	21st to end	Day	28% 17% 28% 20% 6% 1	727
June	1st to 10th	Day	31% 19% 27% 18% 4 1	780
	11th to 20th	Day	28% 21% 28% 18% 4 1	780
	21st to end	Day	22% 16% 29% 26% 6% 1	780
July	1st to 10th	Day	19% 14% 31% 26% 7% 2	771
	11th to 20th	Day	13% 15% 35% 26% 8% 2	768
	21st to end	Day	12% 11% 30% 32% 12% 3	721
August	1st to 10th	Day	13% 10% 27% 31% 13% 5%	567
	11th to 20th	Day	12% 9% 29% 33% 13% 4	557
	21st to end	Day	16% 15% 30% 24% 12% 2	620
September	1st to 10th	Day	17% 17% 30% 23% 12% 1	530
	11th to 20th	Day	27% 13% 27% 23% 9% 2	530
	21st to end	Day	31% 15% 26% 19% 7% 2	530
October	1st to 10th	Day	31% 15% 24% 19% 9% 2	530
	11th to 20th	Day	39% 13% 20% 17% 8% 2	530
	21st to end	Day	43% 15% 22% 14% 6% 1	420
November	1st to 10th	Day	42% 15% 24% 15% 5%	220
	11th to 20th	Day	46% 12% 15% 15% 10% 2	220
	21st to end	Day	44% 17% 19% 9% 9% 3	220
December	1st to 10th	Day	44% 8% 18% 17% 11% 2	220
	11th to 20th	Day	49% 10% 19% 15% 6%	220
	21st to end	Day	40% 9% 33% 14% 4	242
January	1st to 10th	Night	47% 12% 22% 14% 4 1	950
	11th to 20th	Night	39% 10% 27% 20% 4	950
	21st to end	Night	40% 10% 26% 19% 4	957
February	1st to 10th	Night	37% 11% 32% 17% 4	840
	11th to 20th	Night	33% 11% 31% 22% 4	824
	21st to end	Night	37% 12% 24% 20% 7%	692
March	1st to 10th	Night	37% 11% 23% 19% 9% 1	840
	11th to 20th	Night	42% 10% 21% 21% 5%	840
	21st to end	Night	39% 10% 24% 17% 9% 1	924
April	1st to 10th	Night	36% 9% 21% 26% 8% 1	840
	11th to 20th	Night	30% 8% 27% 27% 7% 1	703
	21st to end	Night	31% 9% 28% 23% 9%	562
May	1st to 10th	Night	21% 7% 24% 32% 16%	420
	11th to 20th	Night	24% 6% 21% 32% 16% 1	414
	21st to end	Night	24% 5% 26% 33% 12%	455
June	1st to 10th	Night	28% 7% 26% 26% 12%	420
	11th to 20th	Night	27% 7% 26% 27% 12% 1	420
	21st to end	Night	23% 5% 22% 31% 18% 1	420
July	1st to 10th	Night	15% 2 21% 36% 26%	410
	11th to 20th	Night	12% 4 16% 39% 27% 1	408
	21st to end	Night	12% 2 12% 35% 36% 3	460
August	1st to 10th	Night	14% 2 9% 34% 37% 4	428
	11th to 20th	Night	14% 2 10% 37% 36% 2	624
	21st to end	Night	17% 3 19% 35% 24% 1	736
September	1st to 10th	Night	17% 4 22% 36% 21% 1	800
	11th to 20th	Night	27% 5% 17% 27% 22% 3	800
	21st to end	Night	35% 6% 19% 27% 13% 1	800
October	1st to 10th	Night	30% 8% 22% 26% 14% 1	800
	11th to 20th	Night	40% 6% 22% 22% 10% 1	800
	21st to end	Night	43% 9% 26% 16% 4 1	880
November	1st to 10th	Night	49% 11% 22% 17% 1	820
	11th to 20th	Night	47% 9% 25% 14% 4	840
	21st to end	Night	42% 13% 23% 17% 5% 1	840
December	1st to 10th	Night	37% 10% 29% 18% 6%	879
	11th to 20th	Night	49% 10% 27% 11% 2	950
	21st to end	Night	46% 13% 28% 13% 1	1045

Page generated at 2026-08-27 01:07:10. Version ac07

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