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 2024-04-10.

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% 9% 4 7% 7% 4 6% 6% 6% 8% 33%	82061
	Night	8% 10% 4 9% 8% 4 6% 6% 7% 8% 30%	86727
Transparency	Day	46% 10% 16% 20% 7%	81741
	Night	49% 10% 15% 19% 8% 1	86627
Seeing	Day	14% 11% 26% 27% 17% 4	15814
	Night	14% 9% 25% 33% 17% 2	23943

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% 12% 7% 14% 10% 8% 10% 6% 5% 5% 17%	1899
	11th to 20th	Day	5% 14% 6% 11% 9% 5% 7% 8% 8% 8% 19%	1960
	21st to end	Day	7% 10% 4 8% 9% 5% 9% 7% 7% 9% 26%	2442
February	1st to 10th	Day	6% 11% 4 11% 10% 6% 7% 5% 5% 8% 26%	1472
	11th to 20th	Day	6% 13% 5% 8% 9% 5% 6% 6% 6% 8% 28%	1578
	21st to end	Day	4 11% 7% 12% 8% 5% 5% 6% 6% 8% 28%	1413
March	1st to 10th	Day	4 9% 5% 11% 9% 6% 6% 6% 7% 9% 28%	3138
	11th to 20th	Day	9% 11% 4 7% 7% 4 5% 6% 7% 9% 31%	3364
	21st to end	Day	5% 11% 5% 11% 6% 4 6% 6% 5% 7% 34%	4086
April	1st to 10th	Day	6% 10% 4 8% 8% 4 7% 7% 7% 8% 31%	2270
	11th to 20th	Day	9% 12% 4 9% 7% 4 6% 6% 5% 8% 29%	2357
	21st to end	Day	12% 10% 4 7% 7% 4 7% 6% 6% 8% 30%	2520
May	1st to 10th	Day	11% 8% 4 5% 7% 4 7% 6% 6% 9% 33%	2520
	11th to 20th	Day	11% 7% 3 5% 5% 4 6% 5% 6% 7% 39%	2774
	21st to end	Day	16% 6% 3 5% 6% 4 6% 7% 7% 9% 31%	3111
June	1st to 10th	Day	13% 6% 3 6% 5% 3 6% 6% 7% 9% 35%	2880
	11th to 20th	Day	16% 7% 4 8% 7% 4 6% 6% 7% 8% 28%	2880
	21st to end	Day	9% 5% 2 6% 6% 3 6% 6% 7% 8% 41%	2880
July	1st to 10th	Day	11% 6% 2 5% 5% 4 5% 6% 8% 10% 38%	2880
	11th to 20th	Day	13% 5% 3 6% 6% 4 5% 6% 7% 9% 36%	2880
	21st to end	Day	10% 5% 2 5% 5% 4 5% 6% 8% 9% 42%	3029
August	1st to 10th	Day	10% 7% 3 6% 6% 4 5% 6% 6% 9% 38%	2590
	11th to 20th	Day	9% 5% 2 4 5% 4 5% 6% 6% 9% 44%	2475
	21st to end	Day	11% 5% 2 5% 7% 4 5% 6% 7% 9% 38%	2653
September	1st to 10th	Day	14% 5% 2 5% 5% 3 5% 5% 6% 8% 42%	2160
	11th to 20th	Day	11% 6% 2 5% 7% 4 5% 5% 7% 7% 40%	2160
	21st to end	Day	10% 6% 4 7% 7% 3 5% 5% 7% 8% 36%	1918
October	1st to 10th	Day	11% 11% 4 7% 7% 3 6% 6% 5% 7% 34%	1800
	11th to 20th	Day	10% 10% 4 8% 8% 4 5% 4 6% 7% 33%	1699
	21st to end	Day	12% 13% 4 7% 7% 3 4 5% 6% 7% 31%	1656
November	1st to 10th	Day	15% 11% 4 10% 7% 3 5% 5% 5% 7% 28%	1456
	11th to 20th	Day	10% 13% 6% 9% 8% 4 5% 6% 5% 6% 29%	1330
	21st to end	Day	9% 13% 4 11% 9% 5% 7% 4 5% 6% 27%	1159
December	1st to 10th	Day	9% 14% 4 10% 8% 4 6% 7% 5% 7% 27%	1140
	11th to 20th	Day	8% 14% 5% 9% 9% 6% 7% 7% 6% 10% 20%	1442
	21st to end	Day	5% 8% 3 7% 7% 5% 7% 8% 8% 10% 33%	2090
January	1st to 10th	Night	6% 15% 6% 13% 11% 6% 6% 6% 6% 6% 19%	5046
	11th to 20th	Night	5% 10% 5% 9% 11% 6% 8% 9% 10% 8% 20%	4955
	21st to end	Night	9% 15% 5% 8% 8% 5% 6% 5% 7% 8% 24%	5214
February	1st to 10th	Night	6% 13% 6% 10% 10% 5% 5% 4 7% 7% 25%	2707
	11th to 20th	Night	8% 11% 5% 10% 9% 4 6% 6% 6% 9% 27%	2485
	21st to end	Night	3 11% 6% 11% 10% 4 6% 7% 7% 8% 28%	2041
March	1st to 10th	Night	3 8% 4 12% 10% 5% 8% 6% 7% 9% 28%	3736
	11th to 20th	Night	7% 12% 4 8% 8% 4 6% 6% 7% 10% 28%	3613
	21st to end	Night	6% 12% 5% 9% 6% 4 4 4 5% 7% 37%	3566
April	1st to 10th	Night	5% 8% 3 9% 9% 5% 7% 7% 7% 7% 34%	1900
	11th to 20th	Night	10% 12% 3 8% 6% 3 5% 6% 6% 8% 33%	1549
	21st to end	Night	12% 9% 4 9% 6% 4 5% 5% 6% 8% 33%	1440
May	1st to 10th	Night	11% 10% 4 7% 6% 5% 5% 7% 6% 7% 31%	1440
	11th to 20th	Night	10% 7% 2 7% 6% 3 4 5% 6% 10% 40%	1121
	21st to end	Night	15% 6% 3 7% 7% 3 6% 6% 7% 8% 31%	1164
June	1st to 10th	Night	11% 8% 4 7% 7% 4 6% 6% 5% 7% 34%	1080
	11th to 20th	Night	15% 9% 3 7% 6% 3 6% 7% 7% 9% 28%	1080
	21st to end	Night	12% 6% 2 5% 5% 3 7% 5% 6% 10% 39%	1080
July	1st to 10th	Night	9% 6% 4 7% 7% 4 5% 6% 6% 9% 38%	1080
	11th to 20th	Night	12% 5% 2 5% 5% 4 7% 7% 9% 11% 33%	1080
	21st to end	Night	6% 4 2 6% 6% 4 6% 5% 7% 12% 42%	1285
August	1st to 10th	Night	9% 4 3 5% 6% 4 7% 6% 8% 9% 40%	1348
	11th to 20th	Night	8% 4 2 4 6% 5% 5% 6% 6% 8% 45%	1424
	21st to end	Night	10% 5% 2 6% 5% 4 5% 6% 8% 9% 39%	1702
September	1st to 10th	Night	13% 7% 2 5% 4 3 5% 6% 6% 8% 41%	1800
	11th to 20th	Night	11% 7% 2 5% 6% 3 5% 4 5% 9% 44%	1800
	21st to end	Night	10% 6% 4 7% 5% 4 5% 5% 6% 7% 40%	2042
October	1st to 10th	Night	11% 9% 4 7% 6% 4 5% 6% 6% 8% 34%	2160
	11th to 20th	Night	10% 10% 4 7% 6% 4 6% 6% 7% 8% 33%	2260
	21st to end	Night	12% 13% 4 8% 6% 3 4 5% 6% 7% 32%	2700
November	1st to 10th	Night	14% 13% 4 8% 7% 4 5% 5% 5% 7% 29%	2602
	11th to 20th	Night	7% 15% 6% 9% 7% 4 6% 6% 5% 7% 27%	2850
	21st to end	Night	7% 11% 5% 10% 9% 5% 7% 5% 6% 7% 26%	3021
December	1st to 10th	Night	7% 12% 5% 9% 9% 4 6% 6% 7% 7% 28%	3040
	11th to 20th	Night	8% 15% 5% 11% 8% 5% 8% 6% 6% 7% 22%	3750
	21st to end	Night	4 8% 3 7% 9% 5% 8% 7% 8% 9% 31%	5566

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	66% 9% 11% 12% 2	1899
	11th to 20th	Day	57% 9% 10% 12% 11% 2	1978
	21st to end	Day	49% 14% 17% 14% 5%	2442
February	1st to 10th	Day	55% 8% 12% 15% 10% 1	1472
	11th to 20th	Day	52% 11% 14% 17% 6% 1	1586
	21st to end	Day	52% 8% 16% 18% 6% 1	1413
March	1st to 10th	Day	49% 9% 11% 21% 9%	3138
	11th to 20th	Day	45% 10% 14% 23% 8%	3364
	21st to end	Day	46% 11% 15% 22% 7%	4086
April	1st to 10th	Day	44% 11% 15% 20% 9% 1	2270
	11th to 20th	Day	52% 9% 15% 18% 7%	2357
	21st to end	Day	50% 9% 13% 21% 6%	2520
May	1st to 10th	Day	45% 9% 17% 20% 8% 1	2520
	11th to 20th	Day	43% 8% 13% 21% 14% 1	2778
	21st to end	Day	47% 10% 15% 21% 6% 1	3112
June	1st to 10th	Day	43% 10% 16% 21% 9% 1	2880
	11th to 20th	Day	51% 10% 14% 18% 5%	2880
	21st to end	Day	39% 10% 18% 23% 9%	2880
July	1st to 10th	Day	38% 11% 19% 24% 8%	2801
	11th to 20th	Day	44% 12% 22% 19% 4	2793
	21st to end	Day	34% 12% 23% 27% 4	2860
August	1st to 10th	Day	41% 10% 22% 23% 4	2572
	11th to 20th	Day	34% 10% 23% 27% 6%	2475
	21st to end	Day	41% 11% 19% 24% 6%	2653
September	1st to 10th	Day	38% 10% 24% 23% 4	2160
	11th to 20th	Day	40% 10% 19% 25% 6%	2160
	21st to end	Day	43% 11% 18% 20% 8%	1918
October	1st to 10th	Day	49% 8% 16% 22% 5%	1800
	11th to 20th	Day	49% 9% 16% 22% 4	1699
	21st to end	Day	50% 8% 18% 18% 6%	1656
November	1st to 10th	Day	55% 9% 12% 19% 5%	1456
	11th to 20th	Day	54% 8% 18% 15% 5%	1330
	21st to end	Day	57% 6% 15% 15% 7% 1	1159
December	1st to 10th	Day	54% 9% 13% 13% 10% 1	1140
	11th to 20th	Day	58% 7% 12% 17% 5%	1444
	21st to end	Day	40% 11% 18% 18% 11% 1	2090
January	1st to 10th	Night	62% 9% 10% 13% 5% 1	5046
	11th to 20th	Night	53% 10% 11% 13% 12% 1	4999
	21st to end	Night	55% 11% 16% 14% 4	5214
February	1st to 10th	Night	56% 7% 14% 14% 8% 1	2707
	11th to 20th	Night	52% 9% 14% 18% 7% 1	2487
	21st to end	Night	50% 9% 13% 19% 7% 1	2041
March	1st to 10th	Night	49% 10% 13% 20% 8% 1	3736
	11th to 20th	Night	44% 11% 18% 19% 7%	3614
	21st to end	Night	41% 11% 15% 23% 10%	3566
April	1st to 10th	Night	45% 10% 12% 19% 12% 1	1900
	11th to 20th	Night	46% 8% 13% 22% 9% 1	1549
	21st to end	Night	47% 9% 11% 23% 8% 2	1440
May	1st to 10th	Night	49% 10% 12% 20% 9%	1440
	11th to 20th	Night	39% 7% 12% 25% 15% 1	1121
	21st to end	Night	48% 9% 13% 19% 10% 1	1164
June	1st to 10th	Night	46% 11% 11% 20% 12% 1	1080
	11th to 20th	Night	51% 10% 14% 19% 5% 1	1080
	21st to end	Night	37% 9% 21% 22% 10% 1	1080
July	1st to 10th	Night	40% 10% 16% 24% 8%	1050
	11th to 20th	Night	41% 14% 20% 20% 5%	1044
	21st to end	Night	32% 14% 22% 28% 4	1214
August	1st to 10th	Night	35% 13% 19% 25% 7%	1341
	11th to 20th	Night	34% 10% 20% 28% 7% 1	1424
	21st to end	Night	38% 11% 21% 22% 8%	1702
September	1st to 10th	Night	38% 10% 22% 23% 7% 1	1800
	11th to 20th	Night	38% 9% 17% 30% 6%	1800
	21st to end	Night	42% 10% 15% 22% 9% 1	2042
October	1st to 10th	Night	45% 10% 18% 20% 7% 1	2160
	11th to 20th	Night	47% 9% 16% 22% 5%	2260
	21st to end	Night	50% 9% 15% 18% 7%	2700
November	1st to 10th	Night	54% 8% 12% 22% 4	2602
	11th to 20th	Night	55% 9% 14% 17% 5%	2850
	21st to end	Night	55% 8% 14% 17% 5% 1	3021
December	1st to 10th	Night	53% 8% 12% 17% 9% 1	3040
	11th to 20th	Night	56% 10% 13% 14% 6%	3747
	21st to end	Night	44% 10% 17% 20% 8% 1	5566

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% 9% 31% 35% 9% 6%	180
	11th to 20th	Day	17% 8% 31% 32% 9% 3	180
	21st to end	Day	15% 12% 28% 33% 10% 3	198
February	1st to 10th	Day	13% 13% 28% 31% 9% 5%	180
	11th to 20th	Day	13% 12% 27% 28% 16% 4	278
	21st to end	Day	11% 12% 31% 28% 14% 5%	307
March	1st to 10th	Day	12% 15% 24% 27% 17% 5%	460
	11th to 20th	Day	10% 14% 30% 28% 15% 2	460
	21st to end	Day	15% 15% 26% 25% 17% 1	506
April	1st to 10th	Day	12% 16% 34% 22% 12% 4	457
	11th to 20th	Day	16% 13% 27% 25% 14% 5%	412
	21st to end	Day	21% 13% 30% 23% 11% 2	420
May	1st to 10th	Day	16% 16% 31% 23% 9% 4	423
	11th to 20th	Day	14% 8% 25% 31% 18% 4	743
	21st to end	Day	16% 9% 23% 26% 20% 5%	874
June	1st to 10th	Day	14% 12% 28% 28% 16% 2	810
	11th to 20th	Day	18% 8% 26% 25% 21% 3	810
	21st to end	Day	12% 7% 21% 27% 24% 8%	810
July	1st to 10th	Day	12% 8% 22% 31% 22% 6%	796
	11th to 20th	Day	13% 7% 23% 27% 20% 9%	792
	21st to end	Day	10% 6% 26% 31% 21% 5%	775
August	1st to 10th	Day	13% 11% 18% 30% 22% 7%	530
	11th to 20th	Day	12% 12% 32% 23% 15% 6%	437
	21st to end	Day	16% 13% 25% 25% 16% 6%	495
September	1st to 10th	Day	18% 10% 24% 27% 16% 5%	450
	11th to 20th	Day	17% 11% 24% 30% 14% 5%	450
	21st to end	Day	12% 21% 29% 24% 11% 2	450
October	1st to 10th	Day	21% 15% 24% 24% 12% 4	450
	11th to 20th	Day	16% 14% 28% 27% 13% 2	349
	21st to end	Day	19% 12% 24% 27% 17% 2	234
November	1st to 10th	Day	21% 11% 26% 29% 13% 2	180
	11th to 20th	Day	18% 11% 30% 29% 11% 2	180
	21st to end	Day	17% 15% 26% 27% 13% 2	180
December	1st to 10th	Day	13% 12% 32% 26% 14% 4	180
	11th to 20th	Day	16% 12% 25% 27% 19% 1	180
	21st to end	Day	10% 7% 21% 40% 19% 3	198
January	1st to 10th	Night	14% 8% 23% 38% 14% 2	1040
	11th to 20th	Night	13% 12% 27% 35% 11% 1	1005
	21st to end	Night	18% 12% 29% 29% 10% 1	935
February	1st to 10th	Night	14% 10% 23% 32% 17% 4	782
	11th to 20th	Night	13% 8% 26% 35% 16% 2	744
	21st to end	Night	7% 7% 27% 34% 20% 4	628
March	1st to 10th	Night	8% 10% 26% 34% 19% 4	760
	11th to 20th	Night	11% 8% 29% 33% 18% 1	760
	21st to end	Night	15% 7% 20% 34% 22% 2	836
April	1st to 10th	Night	9% 9% 27% 34% 19% 2	760
	11th to 20th	Night	15% 7% 24% 35% 16% 2	481
	21st to end	Night	14% 9% 27% 29% 19% 1	360
May	1st to 10th	Night	15% 9% 28% 31% 15% 3	360
	11th to 20th	Night	12% 7% 25% 30% 24% 1	354
	21st to end	Night	17% 6% 21% 33% 21% 3	389
June	1st to 10th	Night	13% 9% 25% 29% 23% 2	360
	11th to 20th	Night	18% 5% 17% 32% 24% 4	360
	21st to end	Night	13% 3 21% 33% 28% 2	360
July	1st to 10th	Night	11% 5% 22% 31% 30% 1	350
	11th to 20th	Night	12% 5% 18% 35% 23% 6%	348
	21st to end	Night	7% 5% 21% 40% 24% 3	394
August	1st to 10th	Night	11% 4 13% 27% 39% 6%	358
	11th to 20th	Night	10% 6% 25% 31% 26% 2	356
	21st to end	Night	13% 2 24% 35% 23% 3	514
September	1st to 10th	Night	16% 6% 20% 36% 20% 2	720
	11th to 20th	Night	14% 7% 21% 32% 25% 2	720
	21st to end	Night	14% 12% 28% 30% 14% 1	720
October	1st to 10th	Night	16% 10% 25% 32% 16% 1	720
	11th to 20th	Night	17% 10% 28% 31% 12% 2	720
	21st to end	Night	19% 11% 27% 31% 11% 1	792
November	1st to 10th	Night	19% 8% 25% 32% 14% 2	752
	11th to 20th	Night	14% 11% 31% 34% 10%	950
	21st to end	Night	13% 12% 28% 34% 12% 1	1031
December	1st to 10th	Night	13% 10% 29% 34% 12% 1	1040
	11th to 20th	Night	14% 11% 25% 36% 13% 2	1040
	21st to end	Night	13% 6% 25% 36% 17% 2	1144

Page generated at 2024-04-07 06:28:13. Version ac07

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