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 2024-10-25.

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 6% 4 3 3 3 4 5% 31%	101662
	Night	27% 16% 3 6% 3 3 3 2 4 5% 28%	97217
Transparency	Day	57% 6% 10% 16% 9% 2	101409
	Night	60% 6% 10% 14% 8% 2	97116
Seeing	Day	29% 15% 26% 21% 8% 1	15416
	Night	35% 8% 23% 23% 11% 1	23485

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	33% 27% 3 5% 3 3 2 2 2 4 16%	2219
	11th to 20th	Day	26% 17% 4 9% 4 3 2 2 2 5% 27%	2199
	21st to end	Day	48% 21% 3 5% 3 2 2 1 2 2 12%	2708
February	1st to 10th	Day	28% 21% 5% 7% 3 3 3 3 3 5% 18%	1710
	11th to 20th	Day	23% 23% 3 6% 3 3 2 3 4 4 24%	1665
	21st to end	Day	17% 28% 5% 9% 4 5% 3 3 3 4 19%	1418
March	1st to 10th	Day	20% 26% 5% 9% 4 3 3 2 3 4 20%	3252
	11th to 20th	Day	20% 22% 4 6% 4 3 2 2 3 4 30%	3490
	21st to end	Day	23% 24% 5% 8% 5% 4 4 3 4 4 17%	3916
April	1st to 10th	Day	27% 22% 4 8% 5% 4 3 3 4 5% 14%	2280
	11th to 20th	Day	25% 21% 4 8% 5% 4 3 3 4 4 19%	2363
	21st to end	Day	26% 21% 5% 7% 4 4 5% 3 4 4 17%	2532
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 5% 4 3 4 3 4 4 34%	1900
	11th to 20th	Day	37% 9% 2 6% 3 3 4 4 4 5% 24%	1900
	21st to end	Day	38% 11% 3 6% 4 3 2 2 3 5% 23%	1854
November	1st to 10th	Day	40% 14% 3 6% 3 3 3 3 3 3 18%	1488
	11th to 20th	Day	37% 20% 3 6% 3 2 2 2 2 3 20%	1520
	21st to end	Day	37% 18% 3 5% 4 4 3 2 2 3 20%	1520
December	1st to 10th	Day	30% 20% 3 6% 3 2 2 2 2 3 27%	1450
	11th to 20th	Day	37% 20% 3 7% 4 3 2 2 2 3 16%	1685
	21st to end	Day	35% 23% 4 8% 4 4 4 2 2 3 12%	2442
January	1st to 10th	Night	33% 25% 3 8% 3 3 2 2 2 3 15%	4726
	11th to 20th	Night	29% 14% 3 6% 3 2 3 3 4 8% 24%	4699
	21st to end	Night	45% 22% 3 6% 2 2 2 1 2 3 12%	4944
February	1st to 10th	Night	29% 20% 4 7% 4 4 3 2 4 6% 17%	2470
	11th to 20th	Night	23% 24% 4 7% 3 3 3 2 4 4 23%	2402
	21st to end	Night	21% 26% 3 8% 4 3 3 2 4 4 22%	2036
March	1st to 10th	Night	23% 25% 4 7% 4 3 4 3 4 4 20%	3622
	11th to 20th	Night	20% 22% 3 6% 3 3 4 2 3 4 30%	3489
	21st to end	Night	25% 23% 4 8% 4 3 3 2 3 4 21%	3737
April	1st to 10th	Night	26% 22% 4 7% 5% 5% 3 3 4 3 18%	1900
	11th to 20th	Night	23% 19% 3 7% 4 4 3 3 3 6% 25%	1763
	21st to end	Night	27% 17% 3 7% 5% 4 3 2 4 6% 23%	1648
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	26% 11% 2 5% 3 4 4 3 4 4 34%	2280
	11th to 20th	Night	34% 11% 2 5% 4 4 3 2 4 4 27%	2280
	21st to end	Night	35% 12% 3 6% 3 3 4 3 3 4 23%	2605
November	1st to 10th	Night	42% 15% 3 6% 4 3 3 2 3 4 15%	2590
	11th to 20th	Night	38% 19% 3 5% 3 2 3 2 3 3 20%	2660
	21st to end	Night	35% 18% 3 6% 3 4 3 2 2 3 21%	2660
December	1st to 10th	Night	29% 16% 4 7% 4 3 3 2 4 4 25%	2726
	11th to 20th	Night	38% 21% 5% 7% 3 3 2 2 3 3 13%	3520
	21st to end	Night	38% 23% 4 7% 3 3 2 2 2 3 14%	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	73% 8% 6% 9% 3 1	2219
	11th to 20th	Day	63% 3 9% 12% 7% 6%	2220
	21st to end	Day	82% 3 4 7% 3 1	2708
February	1st to 10th	Day	70% 5% 8% 8% 7% 2	1710
	11th to 20th	Day	66% 5% 7% 12% 7% 2	1674
	21st to end	Day	71% 6% 7% 9% 4 2	1418
March	1st to 10th	Day	71% 6% 8% 9% 6%	3252
	11th to 20th	Day	61% 3 8% 19% 8%	3490
	21st to end	Day	72% 6% 9% 8% 3 1	3916
April	1st to 10th	Day	75% 7% 10% 7% 1	2280
	11th to 20th	Day	71% 5% 7% 8% 8% 1	2363
	21st to end	Day	75% 6% 6% 9% 5%	2532
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	55% 6% 12% 16% 11%	1900
	11th to 20th	Day	64% 5% 9% 15% 6% 1	1900
	21st to end	Day	67% 4 9% 12% 7% 1	1854
November	1st to 10th	Day	72% 7% 6% 8% 6% 1	1488
	11th to 20th	Day	73% 4 7% 7% 7% 3	1520
	21st to end	Day	71% 5% 5% 10% 8% 2	1520
December	1st to 10th	Day	65% 5% 8% 11% 10% 2	1450
	11th to 20th	Day	76% 4 6% 8% 3 2	1688
	21st to end	Day	78% 6% 4 8% 3 1	2442
January	1st to 10th	Night	77% 4 4 8% 5% 1	4726
	11th to 20th	Night	59% 6% 10% 13% 8% 4	4740
	21st to end	Night	80% 4 4 6% 4 1	4944
February	1st to 10th	Night	70% 5% 7% 8% 7% 2	2470
	11th to 20th	Night	66% 5% 9% 10% 7% 3	2404
	21st to end	Night	67% 4 9% 11% 6% 2	2036
March	1st to 10th	Night	68% 5% 9% 11% 7% 1	3622
	11th to 20th	Night	59% 6% 9% 16% 10%	3490
	21st to end	Night	68% 8% 11% 8% 3 2	3737
April	1st to 10th	Night	70% 7% 10% 10% 1	1900
	11th to 20th	Night	62% 7% 9% 12% 8% 1	1763
	21st to end	Night	65% 6% 12% 11% 6%	1648
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	55% 6% 12% 15% 11% 1	2280
	11th to 20th	Night	63% 5% 9% 15% 8%	2280
	21st to end	Night	66% 5% 7% 12% 8% 1	2605
November	1st to 10th	Night	75% 4 7% 8% 5% 2	2590
	11th to 20th	Night	72% 5% 7% 7% 6% 3	2660
	21st to end	Night	70% 4 6% 8% 9% 2	2660
December	1st to 10th	Night	64% 6% 9% 11% 9% 2	2726
	11th to 20th	Night	78% 6% 5% 5% 4 2	3516
	21st to end	Night	79% 3 3 8% 5% 1	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	46% 12% 19% 14% 6% 2	180
	11th to 20th	Day	42% 10% 22% 19% 7%	180
	21st to end	Day	48% 8% 21% 16% 7%	210
February	1st to 10th	Day	39% 17% 27% 12% 4	370
	11th to 20th	Day	36% 14% 29% 17% 3 1	365
	21st to end	Day	31% 22% 26% 17% 4	310
March	1st to 10th	Day	35% 17% 25% 18% 5%	460
	11th to 20th	Day	38% 16% 18% 19% 9% 1	460
	21st to end	Day	39% 17% 24% 13% 6% 1	506
April	1st to 10th	Day	40% 17% 23% 14% 5% 1	460
	11th to 20th	Day	35% 18% 24% 15% 6% 1	452
	21st to end	Day	34% 22% 21% 15% 7% 1	460
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% 13% 22% 14% 7% 1	370
November	1st to 10th	Day	39% 16% 23% 17% 6%	180
	11th to 20th	Day	46% 11% 14% 14% 12% 2	180
	21st to end	Day	46% 16% 17% 8% 10% 3	180
December	1st to 10th	Day	45% 8% 18% 16% 11% 2	180
	11th to 20th	Day	46% 10% 21% 16% 7% 1	180
	21st to end	Day	40% 9% 33% 14% 4	198
January	1st to 10th	Night	49% 11% 21% 15% 4 1	850
	11th to 20th	Night	42% 10% 24% 20% 4	850
	21st to end	Night	43% 10% 25% 18% 4	863
February	1st to 10th	Night	38% 10% 31% 17% 3	760
	11th to 20th	Night	34% 11% 31% 21% 3	744
	21st to end	Night	35% 12% 25% 20% 7%	628
March	1st to 10th	Night	37% 11% 23% 18% 10% 1	760
	11th to 20th	Night	42% 10% 21% 22% 6%	760
	21st to end	Night	40% 9% 24% 17% 10% 1	836
April	1st to 10th	Night	37% 9% 21% 24% 8% 1	760
	11th to 20th	Night	32% 7% 27% 26% 7% 1	635
	21st to end	Night	33% 8% 28% 22% 9%	508
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% 8% 26% 17% 4 1	812
November	1st to 10th	Night	50% 11% 21% 16% 1	740
	11th to 20th	Night	48% 9% 25% 15% 4	760
	21st to end	Night	43% 13% 22% 17% 5% 1	760
December	1st to 10th	Night	37% 10% 30% 18% 6%	791
	11th to 20th	Night	49% 9% 29% 12% 2	850
	21st to end	Night	47% 11% 28% 13% 1	935

Page generated at 2024-10-22 17:21:02. Version ac07

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