Fort Saint John
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fort Saint John clear sky chart from 2005-11-06 to 2025-10-19.

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	8% 9% 3 9% 6% 6% 6% 5% 7% 8% 33%	131151
	Night	7% 11% 4 10% 6% 6% 6% 5% 7% 8% 31%	127227
Transparency	Day	44% 9% 17% 21% 8% 1	130827
	Night	47% 9% 15% 20% 8% 1	127128
Seeing	Day	14% 11% 26% 27% 17% 4	18104
	Night	13% 9% 25% 34% 17% 2	25766

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	6% 13% 6% 15% 7% 9% 8% 4 7% 7% 19%	2719
	11th to 20th	Day	5% 14% 5% 11% 7% 7% 6% 6% 9% 9% 22%	2822
	21st to end	Day	6% 11% 5% 11% 7% 7% 6% 6% 6% 8% 27%	3498
February	1st to 10th	Day	5% 13% 4 12% 9% 8% 6% 5% 5% 9% 26%	1550
	11th to 20th	Day	5% 14% 5% 10% 9% 6% 6% 5% 7% 8% 27%	1664
	21st to end	Day	3 13% 5% 14% 7% 7% 5% 5% 6% 8% 28%	1485
March	1st to 10th	Day	3 10% 4 12% 8% 8% 7% 5% 8% 9% 27%	4518
	11th to 20th	Day	7% 14% 6% 12% 7% 5% 5% 5% 7% 8% 25%	4822
	21st to end	Day	5% 11% 4 11% 6% 5% 5% 4 6% 7% 35%	5851
April	1st to 10th	Day	5% 10% 3 9% 6% 6% 6% 6% 7% 9% 32%	2400
	11th to 20th	Day	8% 13% 4 10% 6% 6% 5% 5% 6% 8% 30%	2624
	21st to end	Day	11% 11% 4 7% 7% 6% 6% 5% 6% 8% 30%	2800
May	1st to 10th	Day	7% 7% 2 6% 5% 5% 6% 6% 8% 9% 40%	6320
	11th to 20th	Day	6% 7% 3 9% 6% 7% 7% 6% 8% 9% 31%	7050
	21st to end	Day	9% 7% 3 9% 6% 7% 7% 6% 9% 9% 28%	7907
June	1st to 10th	Day	12% 7% 3 7% 5% 5% 5% 5% 7% 9% 36%	3200
	11th to 20th	Day	17% 8% 3 8% 6% 6% 5% 5% 7% 8% 27%	3200
	21st to end	Day	9% 5% 2 7% 6% 5% 6% 5% 7% 8% 40%	3200
July	1st to 10th	Day	9% 6% 2 6% 5% 5% 5% 4 7% 9% 40%	7240
	11th to 20th	Day	8% 5% 2 7% 5% 5% 5% 5% 7% 9% 43%	7240
	21st to end	Day	8% 6% 2 6% 4 5% 5% 5% 8% 10% 40%	7606
August	1st to 10th	Day	8% 5% 2 6% 4 5% 4 3 6% 8% 48%	4683
	11th to 20th	Day	11% 7% 2 7% 5% 5% 5% 4 6% 8% 40%	4470
	21st to end	Day	11% 6% 2 5% 5% 5% 5% 5% 8% 10% 39%	4786
September	1st to 10th	Day	12% 5% 2 6% 4 4 5% 4 6% 8% 43%	2400
	11th to 20th	Day	10% 6% 2 7% 6% 5% 5% 4 7% 7% 40%	2400
	21st to end	Day	11% 7% 4 7% 6% 5% 5% 5% 8% 8% 35%	2129
October	1st to 10th	Day	10% 12% 4 8% 5% 6% 6% 5% 7% 7% 31%	3280
	11th to 20th	Day	9% 10% 3 9% 6% 6% 6% 5% 7% 7% 32%	3053
	21st to end	Day	11% 11% 3 7% 5% 5% 4 4 7% 9% 34%	2867
November	1st to 10th	Day	14% 13% 4 11% 6% 4 6% 4 5% 6% 28%	1534
	11th to 20th	Day	9% 16% 6% 9% 7% 5% 5% 5% 5% 6% 28%	1400
	21st to end	Day	8% 14% 4 13% 8% 6% 6% 3 5% 6% 26%	1219
December	1st to 10th	Day	12% 18% 4 12% 7% 6% 6% 4 5% 5% 19%	1960
	11th to 20th	Day	7% 15% 5% 11% 8% 10% 8% 6% 6% 8% 16%	2262
	21st to end	Day	3 7% 3 10% 8% 7% 8% 6% 8% 10% 31%	2992
January	1st to 10th	Night	4 13% 5% 15% 9% 8% 5% 6% 7% 7% 20%	7226
	11th to 20th	Night	5% 12% 5% 12% 8% 8% 7% 6% 8% 8% 22%	7107
	21st to end	Night	7% 15% 5% 10% 6% 6% 5% 4 6% 8% 29%	7458
February	1st to 10th	Night	5% 14% 6% 12% 8% 7% 5% 4 7% 7% 25%	2849
	11th to 20th	Night	7% 12% 4 12% 8% 6% 5% 5% 7% 8% 26%	2619
	21st to end	Night	3 12% 5% 13% 8% 6% 6% 6% 7% 8% 28%	2145
March	1st to 10th	Night	2 8% 3 12% 7% 7% 8% 5% 7% 10% 30%	5376
	11th to 20th	Night	5% 15% 6% 12% 7% 5% 6% 4 7% 9% 25%	5175
	21st to end	Night	7% 11% 4 9% 4 4 4 3 5% 8% 40%	5123
April	1st to 10th	Night	4 9% 2 11% 8% 6% 6% 5% 7% 6% 35%	2000
	11th to 20th	Night	9% 12% 2 9% 4 5% 5% 5% 6% 8% 34%	1722
	21st to end	Night	11% 10% 3 10% 6% 5% 6% 4 6% 8% 32%	1600
May	1st to 10th	Night	5% 7% 3 9% 5% 6% 6% 6% 8% 9% 38%	3640
	11th to 20th	Night	7% 7% 4 10% 6% 6% 7% 5% 7% 9% 34%	2831
	21st to end	Night	10% 6% 3 8% 6% 6% 6% 5% 8% 8% 31%	2968
June	1st to 10th	Night	11% 9% 4 10% 6% 5% 7% 5% 5% 7% 34%	1200
	11th to 20th	Night	16% 9% 3 7% 6% 5% 6% 5% 7% 9% 28%	1200
	21st to end	Night	11% 6% 2 6% 4 5% 6% 4 7% 10% 38%	1200
July	1st to 10th	Night	8% 7% 3 10% 7% 6% 5% 4 6% 8% 35%	2720
	11th to 20th	Night	9% 5% 2 6% 5% 5% 6% 4 7% 8% 41%	2720
	21st to end	Night	10% 6% 2 7% 5% 5% 5% 4 6% 9% 41%	3234
August	1st to 10th	Night	6% 3 2 5% 4 4 6% 4 7% 8% 51%	2466
	11th to 20th	Night	10% 4 2 5% 5% 5% 5% 4 7% 8% 46%	2577
	21st to end	Night	8% 5% 2 7% 4 5% 6% 5% 9% 9% 40%	3119
September	1st to 10th	Night	12% 7% 2 7% 3 5% 5% 5% 6% 8% 41%	2000
	11th to 20th	Night	10% 7% 2 6% 5% 5% 4 4 6% 8% 42%	2000
	21st to end	Night	10% 7% 4 8% 4 5% 5% 4 6% 7% 40%	2270
October	1st to 10th	Night	11% 11% 4 8% 6% 6% 5% 4 6% 8% 31%	3920
	11th to 20th	Night	8% 9% 3 7% 5% 5% 6% 4 6% 8% 39%	4054
	21st to end	Night	9% 12% 4 10% 7% 6% 5% 4 6% 7% 32%	4671
November	1st to 10th	Night	13% 14% 3 9% 6% 5% 5% 4 5% 7% 29%	2743
	11th to 20th	Night	7% 17% 6% 10% 7% 5% 6% 4 5% 7% 26%	3000
	21st to end	Night	6% 13% 5% 12% 8% 6% 7% 4 6% 7% 25%	3180
December	1st to 10th	Night	8% 15% 5% 11% 7% 7% 6% 5% 6% 7% 23%	5220
	11th to 20th	Night	8% 16% 5% 13% 7% 8% 7% 5% 7% 7% 19%	5930
	21st to end	Night	3 9% 5% 11% 7% 7% 8% 5% 9% 8% 27%	7964

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% 8% 11% 11% 9%	2719
	11th to 20th	Day	53% 8% 14% 16% 9% 1	2840
	21st to end	Day	49% 12% 17% 14% 8%	3498
February	1st to 10th	Day	54% 7% 11% 15% 11% 1	1550
	11th to 20th	Day	53% 10% 13% 17% 6% 1	1672
	21st to end	Day	52% 8% 16% 17% 6% 1	1485
March	1st to 10th	Day	49% 8% 12% 22% 9%	4518
	11th to 20th	Day	52% 9% 14% 19% 6%	4822
	21st to end	Day	44% 9% 13% 23% 11% 1	5851
April	1st to 10th	Day	44% 10% 15% 22% 9% 1	2400
	11th to 20th	Day	50% 8% 14% 18% 9%	2624
	21st to end	Day	49% 9% 14% 22% 6% 1	2800
May	1st to 10th	Day	35% 8% 14% 25% 15% 3	6320
	11th to 20th	Day	41% 10% 15% 23% 11% 1	7054
	21st to end	Day	43% 12% 17% 17% 9% 1	7908
June	1st to 10th	Day	42% 10% 15% 21% 10% 2	3200
	11th to 20th	Day	53% 10% 14% 18% 5%	3200
	21st to end	Day	39% 10% 19% 23% 9%	3200
July	1st to 10th	Day	37% 8% 19% 21% 14% 1	7161
	11th to 20th	Day	36% 8% 20% 26% 9% 1	7153
	21st to end	Day	35% 9% 24% 27% 5%	7392
August	1st to 10th	Day	33% 8% 17% 32% 9%	4665
	11th to 20th	Day	40% 8% 16% 21% 14% 1	4512
	21st to end	Day	38% 10% 25% 22% 5%	4785
September	1st to 10th	Day	37% 10% 25% 24% 4	2400
	11th to 20th	Day	40% 9% 19% 26% 6%	2400
	21st to end	Day	44% 11% 17% 20% 8%	2129
October	1st to 10th	Day	49% 8% 18% 21% 4	3280
	11th to 20th	Day	47% 8% 17% 24% 4	3053
	21st to end	Day	45% 9% 19% 21% 6%	2867
November	1st to 10th	Day	55% 9% 12% 20% 4	1534
	11th to 20th	Day	56% 8% 17% 15% 4	1400
	21st to end	Day	58% 5% 14% 15% 7% 1	1219
December	1st to 10th	Day	65% 8% 13% 8% 6% 1	1960
	11th to 20th	Day	64% 7% 14% 12% 3	2264
	21st to end	Day	41% 11% 19% 20% 9% 1	2992
January	1st to 10th	Night	58% 8% 11% 14% 8%	7226
	11th to 20th	Night	54% 9% 13% 15% 9% 1	7151
	21st to end	Night	52% 9% 17% 15% 8%	7458
February	1st to 10th	Night	56% 6% 14% 14% 10% 1	2849
	11th to 20th	Night	52% 9% 14% 18% 7% 1	2621
	21st to end	Night	50% 9% 13% 20% 7% 1	2145
March	1st to 10th	Night	44% 9% 16% 20% 11% 1	5376
	11th to 20th	Night	51% 9% 15% 18% 7%	5176
	21st to end	Night	39% 8% 12% 24% 16%	5123
April	1st to 10th	Night	43% 11% 12% 21% 13% 1	2000
	11th to 20th	Night	45% 8% 13% 23% 11% 1	1722
	21st to end	Night	47% 9% 11% 23% 8% 1	1600
May	1st to 10th	Night	38% 8% 13% 25% 13% 3	3637
	11th to 20th	Night	39% 10% 14% 25% 10% 1	2831
	21st to end	Night	41% 11% 17% 18% 10% 3	2968
June	1st to 10th	Night	46% 11% 11% 20% 12% 1	1200
	11th to 20th	Night	51% 9% 14% 19% 6% 1	1200
	21st to end	Night	38% 9% 22% 22% 10% 1	1200
July	1st to 10th	Night	45% 8% 14% 20% 13%	2690
	11th to 20th	Night	36% 10% 17% 25% 12%	2684
	21st to end	Night	38% 8% 19% 28% 7%	3143
August	1st to 10th	Night	28% 11% 19% 30% 13%	2459
	11th to 20th	Night	34% 8% 18% 24% 16% 1	2601
	21st to end	Night	36% 9% 27% 21% 7%	3119
September	1st to 10th	Night	38% 9% 22% 24% 7% 1	2000
	11th to 20th	Night	38% 9% 18% 29% 6%	2000
	21st to end	Night	42% 10% 15% 22% 10% 1	2270
October	1st to 10th	Night	49% 8% 15% 20% 7%	3920
	11th to 20th	Night	41% 7% 18% 28% 6%	4054
	21st to end	Night	50% 8% 16% 22% 5%	4671
November	1st to 10th	Night	53% 8% 12% 22% 4	2743
	11th to 20th	Night	56% 9% 14% 17% 5%	3000
	21st to end	Night	57% 8% 13% 17% 5% 1	3180
December	1st to 10th	Night	57% 9% 13% 15% 6%	5220
	11th to 20th	Night	60% 8% 16% 11% 5%	5927
	21st to end	Night	48% 9% 17% 20% 5% 1	7964

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	10% 10% 32% 34% 10% 6%	200
	11th to 20th	Day	18% 11% 30% 32% 8% 3	200
	21st to end	Day	14% 14% 30% 30% 9% 3	220
February	1st to 10th	Day	12% 13% 28% 31% 11% 7%	200
	11th to 20th	Day	12% 11% 28% 31% 15% 3	304
	21st to end	Day	11% 13% 33% 26% 13% 5%	331
March	1st to 10th	Day	12% 14% 25% 27% 17% 6%	500
	11th to 20th	Day	10% 14% 31% 28% 15% 3	500
	21st to end	Day	15% 15% 27% 24% 17% 2	550
April	1st to 10th	Day	11% 17% 35% 22% 12% 4	500
	11th to 20th	Day	15% 14% 29% 24% 13% 5%	492
	21st to end	Day	19% 13% 29% 23% 12% 3	500
May	1st to 10th	Day	17% 16% 32% 23% 10% 3	503
	11th to 20th	Day	13% 9% 25% 30% 19% 4	857
	21st to end	Day	15% 11% 24% 26% 19% 5%	1006
June	1st to 10th	Day	14% 13% 29% 28% 14% 2	930
	11th to 20th	Day	19% 8% 24% 24% 21% 4	930
	21st to end	Day	12% 7% 20% 29% 24% 8%	930
July	1st to 10th	Day	13% 8% 22% 31% 22% 5%	916
	11th to 20th	Day	13% 7% 22% 28% 21% 9%	912
	21st to end	Day	11% 6% 26% 30% 21% 5%	895
August	1st to 10th	Day	13% 10% 18% 30% 21% 7%	618
	11th to 20th	Day	13% 11% 32% 24% 16% 5%	517
	21st to end	Day	14% 13% 23% 25% 17% 7%	583
September	1st to 10th	Day	16% 10% 24% 27% 19% 5%	530
	11th to 20th	Day	15% 11% 25% 30% 15% 5%	530
	21st to end	Day	16% 22% 28% 22% 10% 2	530
October	1st to 10th	Day	20% 16% 26% 23% 12% 3	530
	11th to 20th	Day	17% 16% 29% 25% 11% 2	411
	21st to end	Day	18% 12% 24% 28% 16% 2	259
November	1st to 10th	Day	21% 11% 27% 28% 12% 2	200
	11th to 20th	Day	19% 11% 30% 29% 11% 2	200
	21st to end	Day	15% 14% 27% 29% 14% 2	200
December	1st to 10th	Day	14% 12% 32% 26% 14% 4	200
	11th to 20th	Day	16% 11% 24% 31% 19% 1	200
	21st to end	Day	9% 7% 20% 40% 21% 4	220
January	1st to 10th	Night	13% 8% 24% 38% 15% 2	1100
	11th to 20th	Night	13% 13% 28% 35% 11% 1	1063
	21st to end	Night	18% 13% 30% 28% 10% 1	990
February	1st to 10th	Night	13% 10% 22% 32% 18% 4	824
	11th to 20th	Night	12% 7% 26% 36% 16% 2	784
	21st to end	Night	7% 8% 29% 33% 20% 3	660
March	1st to 10th	Night	8% 11% 26% 34% 18% 4	800
	11th to 20th	Night	11% 8% 29% 33% 18% 2	800
	21st to end	Night	14% 7% 21% 34% 22% 2	880
April	1st to 10th	Night	9% 9% 27% 35% 19% 2	800
	11th to 20th	Night	15% 8% 24% 35% 16% 2	534
	21st to end	Night	14% 9% 27% 30% 19% 1	400
May	1st to 10th	Night	13% 10% 29% 31% 15% 2	400
	11th to 20th	Night	11% 8% 27% 30% 23% 1	394
	21st to end	Night	16% 6% 24% 32% 20% 3	433
June	1st to 10th	Night	12% 9% 28% 29% 21% 2	400
	11th to 20th	Night	18% 5% 17% 33% 23% 4	400
	21st to end	Night	13% 3 20% 34% 28% 2	400
July	1st to 10th	Night	12% 6% 22% 32% 28% 1	390
	11th to 20th	Night	12% 7% 17% 34% 24% 6%	388
	21st to end	Night	8% 6% 20% 39% 24% 3	438
August	1st to 10th	Night	10% 4 14% 29% 38% 5%	398
	11th to 20th	Night	10% 7% 25% 32% 25% 2	396
	21st to end	Night	12% 3 23% 35% 24% 3	573
September	1st to 10th	Night	15% 6% 19% 38% 21% 2	800
	11th to 20th	Night	13% 7% 21% 33% 24% 2	800
	21st to end	Night	15% 13% 29% 29% 13% 1	800
October	1st to 10th	Night	16% 10% 26% 32% 15% 1	800
	11th to 20th	Night	16% 10% 29% 32% 11% 2	792
	21st to end	Night	19% 11% 27% 32% 10% 1	836
November	1st to 10th	Night	19% 9% 25% 32% 14% 2	793
	11th to 20th	Night	14% 11% 31% 34% 9%	1000
	21st to end	Night	13% 11% 28% 34% 13% 1	1090
December	1st to 10th	Night	14% 10% 29% 34% 11% 1	1100
	11th to 20th	Night	14% 11% 25% 36% 13% 1	1100
	21st to end	Night	12% 6% 25% 36% 18% 2	1210

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