Smithers
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Smithers clear sky chart from 2005-11-06 to 2025-07-06.

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	10% 13% 5% 11% 7% 6% 6% 5% 6% 7% 24%	124015
	Night	9% 14% 5% 12% 7% 6% 6% 5% 6% 6% 22%	123402
Transparency	Day	53% 10% 14% 16% 6%	123754
	Night	54% 11% 14% 15% 5%	123306
Seeing	Day	18% 13% 25% 26% 14% 4	17320
	Night	16% 9% 23% 34% 17% 2	24823

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	7% 15% 6% 22% 13% 9% 6% 5% 5% 4 8%	3179
	11th to 20th	Day	8% 15% 5% 12% 8% 7% 6% 5% 7% 8% 20%	3159
	21st to end	Day	11% 21% 8% 14% 5% 5% 4 4 5% 5% 17%	3498
February	1st to 10th	Day	9% 14% 7% 15% 9% 6% 6% 5% 5% 5% 20%	1590
	11th to 20th	Day	5% 16% 6% 9% 7% 7% 7% 5% 7% 6% 26%	1715
	21st to end	Day	4 15% 6% 12% 10% 8% 6% 4 5% 6% 24%	1485
March	1st to 10th	Day	4 15% 6% 17% 10% 7% 7% 4 6% 6% 18%	4495
	11th to 20th	Day	7% 15% 7% 14% 7% 7% 7% 5% 8% 8% 15%	5000
	21st to end	Day	6% 14% 5% 10% 7% 6% 6% 5% 7% 7% 28%	5486
April	1st to 10th	Day	8% 18% 5% 14% 8% 6% 7% 4 6% 6% 18%	2546
	11th to 20th	Day	7% 19% 5% 12% 8% 7% 6% 4 6% 6% 21%	2568
	21st to end	Day	11% 15% 4 10% 8% 8% 6% 5% 6% 6% 21%	2650
May	1st to 10th	Day	10% 12% 4 10% 7% 6% 6% 5% 7% 10% 24%	6688
	11th to 20th	Day	11% 13% 5% 11% 7% 6% 6% 5% 7% 8% 22%	6736
	21st to end	Day	15% 13% 5% 11% 7% 7% 6% 5% 6% 6% 18%	7405
June	1st to 10th	Day	14% 11% 4 12% 7% 7% 5% 5% 6% 6% 23%	3093
	11th to 20th	Day	12% 11% 4 10% 6% 6% 5% 5% 6% 8% 27%	3361
	21st to end	Day	13% 10% 4 11% 7% 6% 6% 4 6% 7% 26%	3363
July	1st to 10th	Day	6% 4 2 6% 5% 6% 6% 5% 8% 7% 46%	5024
	11th to 20th	Day	6% 6% 3 7% 6% 5% 7% 5% 8% 11% 36%	4740
	21st to end	Day	7% 8% 3 9% 7% 6% 7% 6% 8% 9% 29%	5138
August	1st to 10th	Day	4 4 1 5% 4 4 5% 4 6% 9% 53%	4699
	11th to 20th	Day	8% 8% 3 8% 5% 5% 5% 4 7% 8% 40%	4130
	21st to end	Day	13% 11% 4 10% 6% 5% 5% 4 6% 7% 28%	4521
September	1st to 10th	Day	14% 10% 4 10% 8% 5% 5% 4 6% 8% 26%	2427
	11th to 20th	Day	13% 10% 5% 10% 7% 6% 5% 5% 7% 6% 26%	2116
	21st to end	Day	18% 13% 4 12% 6% 7% 7% 4 6% 7% 17%	2090
October	1st to 10th	Day	15% 15% 5% 14% 9% 7% 6% 4 5% 5% 14%	3220
	11th to 20th	Day	17% 13% 4 12% 7% 8% 7% 5% 6% 6% 14%	2944
	21st to end	Day	12% 13% 5% 13% 7% 6% 8% 4 6% 7% 19%	2953
November	1st to 10th	Day	15% 16% 5% 13% 8% 7% 6% 4 6% 5% 16%	1568
	11th to 20th	Day	10% 18% 7% 14% 10% 8% 6% 5% 5% 5% 12%	1440
	21st to end	Day	9% 17% 6% 15% 9% 8% 7% 6% 5% 6% 12%	1400
December	1st to 10th	Day	15% 16% 5% 12% 8% 8% 7% 6% 6% 5% 11%	2012
	11th to 20th	Day	10% 22% 6% 15% 9% 7% 7% 5% 5% 6% 9%	2262
	21st to end	Day	10% 17% 6% 17% 10% 8% 7% 5% 5% 5% 8%	3314
January	1st to 10th	Night	7% 20% 7% 21% 11% 8% 6% 4 4 4 9%	6766
	11th to 20th	Night	8% 14% 5% 10% 7% 7% 7% 4 6% 7% 25%	6739
	21st to end	Night	12% 20% 7% 14% 8% 5% 6% 3 4 5% 16%	7458
February	1st to 10th	Night	9% 17% 6% 14% 8% 6% 5% 4 5% 5% 20%	2809
	11th to 20th	Night	7% 15% 5% 13% 7% 6% 5% 4 7% 7% 25%	2572
	21st to end	Night	4 13% 6% 11% 8% 6% 7% 5% 7% 7% 27%	2145
March	1st to 10th	Night	3 12% 7% 15% 8% 7% 6% 5% 6% 7% 24%	5369
	11th to 20th	Night	8% 13% 5% 13% 8% 7% 8% 6% 7% 7% 18%	4999
	21st to end	Night	6% 15% 4 9% 5% 5% 5% 5% 6% 7% 33%	5489
April	1st to 10th	Night	7% 11% 4 12% 8% 7% 6% 6% 7% 7% 26%	1852
	11th to 20th	Night	5% 15% 5% 11% 7% 6% 5% 4 7% 7% 26%	1781
	21st to end	Night	9% 15% 4 10% 7% 7% 6% 4 5% 7% 25%	1749
May	1st to 10th	Night	6% 9% 4 11% 8% 7% 7% 6% 7% 9% 26%	3257
	11th to 20th	Night	9% 11% 5% 11% 7% 7% 7% 6% 8% 9% 21%	3159
	21st to end	Night	14% 14% 4 10% 6% 6% 5% 5% 7% 6% 22%	3470
June	1st to 10th	Night	10% 11% 4 8% 6% 6% 6% 6% 6% 8% 29%	1305
	11th to 20th	Night	8% 8% 4 9% 5% 4 6% 5% 9% 10% 33%	1034
	21st to end	Night	10% 7% 3 8% 6% 5% 6% 6% 7% 10% 30%	1032
July	1st to 10th	Night	6% 3 1 5% 4 4 5% 4 6% 8% 54%	2044
	11th to 20th	Night	6% 5% 2 6% 5% 5% 5% 5% 7% 10% 43%	2220
	21st to end	Night	6% 5% 3 7% 4 6% 6% 5% 7% 10% 41%	2414
August	1st to 10th	Night	4 2 2 3 3 3 4 4 5% 7% 63%	2229
	11th to 20th	Night	7% 7% 2 8% 4 3 5% 3 5% 7% 48%	2707
	21st to end	Night	13% 10% 4 10% 7% 6% 6% 5% 6% 6% 28%	3146
September	1st to 10th	Night	13% 8% 4 9% 6% 5% 5% 4 5% 7% 35%	1752
	11th to 20th	Night	9% 9% 3 10% 5% 6% 6% 5% 7% 6% 35%	2061
	21st to end	Night	16% 10% 4 11% 6% 6% 6% 6% 7% 7% 22%	2090
October	1st to 10th	Night	19% 14% 4 10% 6% 6% 6% 4 5% 6% 21%	3759
	11th to 20th	Night	16% 14% 5% 12% 7% 7% 6% 5% 7% 6% 15%	3985
	21st to end	Night	14% 14% 4 9% 6% 6% 7% 5% 7% 8% 20%	4600
November	1st to 10th	Night	15% 15% 5% 12% 8% 8% 6% 5% 6% 6% 15%	2730
	11th to 20th	Night	9% 20% 6% 14% 8% 7% 6% 5% 6% 6% 13%	2960
	21st to end	Night	7% 19% 7% 15% 9% 8% 6% 4 6% 6% 13%	3000
December	1st to 10th	Night	14% 19% 6% 12% 8% 6% 5% 5% 6% 6% 12%	5120
	11th to 20th	Night	10% 20% 8% 17% 8% 6% 6% 5% 6% 5% 9%	5930
	21st to end	Night	6% 17% 8% 19% 10% 8% 6% 5% 6% 5% 9%	7670

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	61% 19% 12% 6% 3	3179
	11th to 20th	Day	57% 9% 17% 8% 6% 4	3180
	21st to end	Day	62% 11% 14% 9% 3	3498
February	1st to 10th	Day	62% 9% 7% 10% 11% 2	1590
	11th to 20th	Day	52% 12% 15% 15% 5%	1724
	21st to end	Day	56% 8% 12% 16% 6% 2	1485
March	1st to 10th	Day	60% 8% 10% 14% 8%	4495
	11th to 20th	Day	57% 10% 10% 15% 8%	5000
	21st to end	Day	49% 10% 14% 22% 5%	5486
April	1st to 10th	Day	60% 10% 11% 15% 3	2546
	11th to 20th	Day	61% 7% 11% 14% 6%	2568
	21st to end	Day	59% 9% 13% 14% 6%	2650
May	1st to 10th	Day	49% 11% 16% 15% 9%	6688
	11th to 20th	Day	54% 9% 12% 19% 6%	6739
	21st to end	Day	59% 9% 13% 13% 6%	7406
June	1st to 10th	Day	57% 8% 13% 15% 6%	3093
	11th to 20th	Day	52% 8% 16% 19% 4 1	3361
	21st to end	Day	54% 10% 16% 17% 3	3363
July	1st to 10th	Day	31% 7% 14% 28% 18% 2	4948
	11th to 20th	Day	35% 10% 28% 24% 3	4659
	21st to end	Day	42% 11% 19% 22% 5%	4976
August	1st to 10th	Day	25% 8% 17% 31% 19% 1	4681
	11th to 20th	Day	38% 9% 19% 26% 8%	4171
	21st to end	Day	51% 10% 19% 17% 3	4520
September	1st to 10th	Day	53% 12% 16% 17% 2	2427
	11th to 20th	Day	53% 9% 16% 18% 3 1	2116
	21st to end	Day	62% 10% 13% 11% 3	2090
October	1st to 10th	Day	65% 12% 11% 9% 4	3220
	11th to 20th	Day	61% 14% 16% 7% 3	2944
	21st to end	Day	51% 14% 20% 13% 2	2953
November	1st to 10th	Day	66% 9% 11% 12% 2	1568
	11th to 20th	Day	69% 10% 9% 9% 4	1440
	21st to end	Day	65% 13% 11% 9% 3	1400
December	1st to 10th	Day	64% 16% 10% 8% 2	2012
	11th to 20th	Day	69% 12% 8% 8% 2	2264
	21st to end	Day	66% 15% 9% 6% 4	3314
January	1st to 10th	Night	69% 13% 9% 7% 3	6766
	11th to 20th	Night	52% 9% 16% 12% 7% 4	6780
	21st to end	Night	60% 14% 15% 8% 3	7458
February	1st to 10th	Night	61% 9% 8% 10% 10% 2	2809
	11th to 20th	Night	53% 9% 14% 17% 6%	2574
	21st to end	Night	51% 10% 12% 19% 7% 1	2145
March	1st to 10th	Night	50% 12% 12% 18% 8%	5369
	11th to 20th	Night	53% 13% 11% 15% 7%	5000
	21st to end	Night	45% 9% 13% 27% 6%	5489
April	1st to 10th	Night	50% 11% 14% 17% 7%	1852
	11th to 20th	Night	52% 9% 14% 19% 6%	1781
	21st to end	Night	54% 8% 14% 18% 5%	1749
May	1st to 10th	Night	45% 13% 16% 18% 7%	3254
	11th to 20th	Night	53% 10% 17% 15% 5%	3159
	21st to end	Night	55% 10% 13% 19% 3	3470
June	1st to 10th	Night	48% 9% 16% 21% 5%	1305
	11th to 20th	Night	42% 12% 17% 22% 6%	1034
	21st to end	Night	44% 11% 21% 20% 4	1032
July	1st to 10th	Night	25% 8% 16% 29% 21% 1	2011
	11th to 20th	Night	31% 10% 32% 23% 4	2178
	21st to end	Night	33% 12% 25% 23% 7%	2337
August	1st to 10th	Night	18% 7% 20% 39% 15%	2222
	11th to 20th	Night	34% 9% 20% 30% 7%	2732
	21st to end	Night	53% 10% 22% 14% 2	3146
September	1st to 10th	Night	46% 11% 21% 19% 3	1752
	11th to 20th	Night	44% 10% 19% 22% 4	2061
	21st to end	Night	57% 13% 12% 14% 4	2090
October	1st to 10th	Night	58% 9% 18% 12% 3	3759
	11th to 20th	Night	61% 12% 15% 10% 2	3985
	21st to end	Night	52% 15% 18% 12% 2	4600
November	1st to 10th	Night	64% 11% 10% 12% 3	2730
	11th to 20th	Night	65% 11% 10% 11% 2	2960
	21st to end	Night	66% 12% 9% 10% 3	3000
December	1st to 10th	Night	67% 11% 12% 7% 2	5120
	11th to 20th	Night	70% 11% 9% 7% 2	5927
	21st to end	Night	65% 15% 10% 7% 3	7670

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	16% 11% 23% 32% 17% 2	200
	11th to 20th	Day	21% 11% 22% 29% 13% 6%	200
	21st to end	Day	14% 15% 18% 36% 13% 3	220
February	1st to 10th	Day	16% 15% 26% 27% 13% 4	390
	11th to 20th	Day	15% 12% 26% 32% 11% 3	395
	21st to end	Day	17% 15% 30% 25% 8% 5%	331
March	1st to 10th	Day	13% 19% 25% 22% 15% 5%	408
	11th to 20th	Day	14% 15% 29% 27% 13% 2	500
	21st to end	Day	20% 14% 25% 23% 13% 5%	550
April	1st to 10th	Day	20% 15% 29% 20% 14% 2	500
	11th to 20th	Day	18% 13% 25% 24% 15% 5%	492
	21st to end	Day	19% 19% 26% 20% 11% 4	500
May	1st to 10th	Day	20% 14% 29% 25% 10% 2	663
	11th to 20th	Day	18% 16% 22% 27% 14% 5%	725
	21st to end	Day	21% 15% 27% 25% 9% 3	790
June	1st to 10th	Day	20% 17% 25% 24% 13% 1	823
	11th to 20th	Day	14% 12% 30% 27% 14% 3	930
	21st to end	Day	14% 9% 25% 29% 19% 4	893
July	1st to 10th	Day	13% 12% 26% 30% 15% 6%	697
	11th to 20th	Day	13% 12% 27% 27% 17% 5%	668
	21st to end	Day	13% 9% 31% 29% 15% 4	739
August	1st to 10th	Day	10% 10% 23% 31% 16% 9%	676
	11th to 20th	Day	16% 11% 28% 24% 17% 4	545
	21st to end	Day	21% 14% 26% 21% 14% 4	539
September	1st to 10th	Day	23% 13% 24% 22% 14% 4	490
	11th to 20th	Day	18% 13% 19% 24% 18% 7%	490
	21st to end	Day	27% 13% 27% 19% 11% 2	490
October	1st to 10th	Day	26% 14% 21% 20% 16% 4	490
	11th to 20th	Day	24% 15% 26% 21% 11% 3	423
	21st to end	Day	23% 13% 23% 25% 12% 3	343
November	1st to 10th	Day	28% 14% 16% 30% 9% 6%	200
	11th to 20th	Day	23% 8% 16% 27% 23% 4	200
	21st to end	Day	22% 13% 19% 24% 17% 7%	200
December	1st to 10th	Day	15% 8% 14% 37% 22% 6%	200
	11th to 20th	Day	15% 8% 18% 39% 18% 4	200
	21st to end	Day	16% 5% 15% 37% 20% 7%	220
January	1st to 10th	Night	16% 11% 27% 34% 12% 1	900
	11th to 20th	Night	17% 12% 26% 34% 11% 1	900
	21st to end	Night	19% 12% 24% 30% 13% 2	990
February	1st to 10th	Night	15% 12% 27% 30% 14% 1	900
	11th to 20th	Night	14% 7% 23% 40% 14% 2	804
	21st to end	Night	11% 10% 25% 37% 14% 2	660
March	1st to 10th	Night	10% 13% 26% 30% 20% 2	800
	11th to 20th	Night	10% 13% 24% 36% 16% 2	800
	21st to end	Night	16% 10% 21% 28% 22% 4	880
April	1st to 10th	Night	12% 9% 23% 32% 21% 4	610
	11th to 20th	Night	13% 10% 23% 30% 22% 3	593
	21st to end	Night	16% 9% 25% 30% 19% 1	549
May	1st to 10th	Night	12% 8% 22% 40% 18% 1	400
	11th to 20th	Night	14% 6% 20% 36% 22% 2	394
	21st to end	Night	18% 8% 21% 34% 19%	433
June	1st to 10th	Night	15% 6% 19% 39% 19% 1	400
	11th to 20th	Night	11% 6% 28% 39% 17% 1	400
	21st to end	Night	12% 6% 19% 43% 20% 1	400
July	1st to 10th	Night	10% 6% 22% 39% 22% 1	380
	11th to 20th	Night	13% 4 20% 40% 21% 2	368
	21st to end	Night	6% 4 20% 49% 20% 2	416
August	1st to 10th	Night	9% 5% 14% 34% 37% 1	383
	11th to 20th	Night	11% 4 22% 35% 25% 2	564
	21st to end	Night	17% 5% 19% 37% 21% 1	627
September	1st to 10th	Night	17% 8% 19% 34% 20% 2	612
	11th to 20th	Night	13% 7% 20% 32% 24% 4	760
	21st to end	Night	21% 9% 23% 30% 14% 2	760
October	1st to 10th	Night	23% 10% 18% 30% 17% 2	760
	11th to 20th	Night	24% 10% 19% 31% 14% 2	760
	21st to end	Night	23% 9% 22% 32% 13% 1	836
November	1st to 10th	Night	23% 12% 26% 24% 12% 2	780
	11th to 20th	Night	19% 12% 26% 30% 12% 2	880
	21st to end	Night	18% 9% 28% 29% 14% 1	900
December	1st to 10th	Night	13% 10% 22% 36% 16% 3	1039
	11th to 20th	Night	14% 9% 24% 36% 15% 2	1100
	21st to end	Night	14% 8% 26% 35% 14% 2	1085

Page generated at 2025-07-02 22:30:14. Version ac07

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