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 2024-11-05.

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	9% 9% 3 8% 6% 6% 6% 5% 7% 8% 34%	105927
	Night	8% 11% 4 10% 6% 6% 6% 5% 7% 8% 31%	101652
Transparency	Day	44% 10% 16% 21% 8% 1	105649
	Night	47% 9% 15% 20% 8% 1	101576
Seeing	Day	14% 11% 26% 27% 17% 4	16775
	Night	14% 9% 25% 33% 17% 2	24507

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% 12% 6% 16% 8% 11% 10% 4 5% 5% 17%	1899
	11th to 20th	Day	5% 14% 5% 12% 7% 7% 6% 6% 9% 8% 19%	1960
	21st to end	Day	7% 11% 4 9% 8% 8% 7% 6% 7% 8% 25%	2442
February	1st to 10th	Day	6% 13% 4 12% 9% 8% 6% 4 5% 8% 26%	1472
	11th to 20th	Day	5% 14% 5% 10% 8% 6% 6% 5% 6% 8% 27%	1578
	21st to end	Day	3 13% 5% 14% 7% 7% 5% 4 6% 8% 28%	1413
March	1st to 10th	Day	3 10% 4 13% 8% 8% 6% 4 7% 9% 28%	3138
	11th to 20th	Day	9% 12% 4 9% 6% 5% 4 4 7% 9% 31%	3364
	21st to end	Day	5% 11% 4 12% 6% 5% 5% 5% 5% 7% 34%	4086
April	1st to 10th	Day	6% 11% 4 10% 6% 6% 7% 6% 7% 8% 31%	2280
	11th to 20th	Day	9% 13% 4 10% 6% 6% 5% 5% 6% 8% 30%	2491
	21st to end	Day	12% 11% 3 7% 7% 6% 6% 5% 6% 8% 30%	2660
May	1st to 10th	Day	8% 8% 3 6% 5% 5% 6% 6% 8% 9% 37%	4420
	11th to 20th	Day	8% 7% 3 8% 6% 6% 6% 5% 7% 8% 35%	4912
	21st to end	Day	12% 8% 3 9% 7% 6% 7% 6% 7% 8% 26%	5509
June	1st to 10th	Day	13% 7% 3 8% 5% 5% 5% 5% 7% 9% 35%	3040
	11th to 20th	Day	16% 8% 3 8% 6% 6% 5% 5% 7% 8% 27%	3040
	21st to end	Day	10% 5% 2 7% 6% 5% 6% 5% 7% 8% 40%	3040
July	1st to 10th	Day	10% 5% 1 4 4 4 4 4 7% 9% 47%	5060
	11th to 20th	Day	8% 4 2 5% 5% 5% 5% 4 7% 8% 48%	5060
	21st to end	Day	8% 6% 2 6% 4 5% 5% 5% 8% 11% 40%	5299
August	1st to 10th	Day	8% 5% 2 6% 4 5% 4 3 6% 7% 49%	4539
	11th to 20th	Day	11% 7% 2 7% 5% 5% 5% 4 6% 8% 41%	4330
	21st to end	Day	11% 6% 2 6% 5% 5% 5% 5% 8% 10% 38%	4639
September	1st to 10th	Day	13% 5% 2 6% 4 5% 5% 4 6% 8% 41%	2280
	11th to 20th	Day	10% 6% 2 7% 6% 5% 5% 4 7% 7% 39%	2280
	21st to end	Day	11% 7% 4 7% 6% 4 5% 5% 8% 8% 36%	2023
October	1st to 10th	Day	10% 12% 4 8% 5% 6% 6% 5% 7% 7% 30%	3180
	11th to 20th	Day	9% 10% 3 9% 6% 6% 6% 5% 7% 7% 32%	2977
	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 5% 4 5% 6% 28%	1488
	11th to 20th	Day	9% 15% 5% 9% 7% 5% 5% 5% 5% 6% 29%	1330
	21st to end	Day	8% 14% 4 12% 8% 6% 7% 3 5% 6% 27%	1159
December	1st to 10th	Day	9% 15% 3 11% 7% 5% 6% 5% 5% 7% 27%	1140
	11th to 20th	Day	8% 14% 5% 10% 7% 8% 6% 6% 6% 9% 20%	1442
	21st to end	Day	5% 9% 3 8% 6% 6% 7% 6% 8% 10% 32%	2090
January	1st to 10th	Night	6% 16% 6% 16% 9% 8% 6% 5% 6% 6% 19%	5046
	11th to 20th	Night	5% 11% 4 10% 9% 9% 7% 7% 10% 7% 20%	4955
	21st to end	Night	9% 16% 5% 10% 6% 6% 5% 4 7% 8% 23%	5214
February	1st to 10th	Night	6% 14% 6% 12% 8% 7% 5% 4 7% 7% 25%	2707
	11th to 20th	Night	7% 12% 4 11% 7% 6% 6% 5% 7% 8% 27%	2485
	21st to end	Night	3 12% 4 13% 8% 6% 6% 6% 7% 8% 28%	2041
March	1st to 10th	Night	3 9% 4 13% 9% 7% 8% 4 7% 9% 28%	3736
	11th to 20th	Night	6% 13% 4 9% 7% 6% 6% 5% 7% 10% 28%	3613
	21st to end	Night	5% 12% 5% 11% 5% 5% 4 3 5% 7% 37%	3566
April	1st to 10th	Night	4 9% 2 11% 8% 6% 6% 5% 7% 6% 34%	1900
	11th to 20th	Night	9% 13% 2 9% 5% 4 5% 5% 6% 9% 34%	1635
	21st to end	Night	12% 10% 3 10% 6% 5% 5% 4 6% 7% 32%	1520
May	1st to 10th	Night	6% 8% 3 9% 5% 7% 7% 6% 8% 8% 32%	2540
	11th to 20th	Night	9% 6% 3 8% 5% 5% 6% 4 6% 8% 38%	1969
	21st to end	Night	13% 7% 4 10% 7% 6% 6% 5% 8% 8% 28%	2066
June	1st to 10th	Night	11% 9% 4 10% 6% 5% 7% 4 5% 7% 33%	1140
	11th to 20th	Night	15% 9% 3 7% 6% 5% 6% 5% 7% 9% 28%	1140
	21st to end	Night	11% 7% 2 6% 4 5% 6% 4 7% 10% 38%	1140
July	1st to 10th	Night	7% 6% 3 8% 6% 5% 4 4 6% 9% 43%	1900
	11th to 20th	Night	8% 4 1 5% 5% 6% 6% 4 8% 9% 43%	1900
	21st to end	Night	7% 5% 2 7% 5% 5% 6% 4 8% 10% 40%	2250
August	1st to 10th	Night	6% 3 2 5% 4 4 5% 4 7% 8% 51%	2390
	11th to 20th	Night	9% 4 2 5% 4 5% 4 4 7% 8% 46%	2497
	21st to end	Night	8% 5% 2 7% 5% 5% 6% 5% 9% 9% 39%	3024
September	1st to 10th	Night	12% 7% 2 7% 3 5% 5% 5% 6% 8% 40%	1900
	11th to 20th	Night	11% 7% 2 6% 5% 5% 4 4 6% 8% 42%	1900
	21st to end	Night	10% 7% 4 7% 4 6% 5% 4 6% 7% 40%	2156
October	1st to 10th	Night	12% 10% 4 8% 6% 6% 5% 4 6% 8% 31%	3800
	11th to 20th	Night	8% 9% 3 7% 5% 5% 6% 4 6% 8% 39%	3954
	21st to end	Night	9% 12% 4 10% 7% 6% 5% 4 6% 7% 32%	4671
November	1st to 10th	Night	13% 15% 3 9% 6% 5% 5% 4 5% 7% 29%	2670
	11th to 20th	Night	7% 16% 6% 10% 7% 5% 6% 4 5% 7% 27%	2850
	21st to end	Night	7% 13% 5% 11% 8% 6% 7% 4 6% 7% 26%	3021
December	1st to 10th	Night	7% 13% 4 10% 8% 5% 5% 5% 7% 7% 28%	3040
	11th to 20th	Night	8% 15% 4 12% 7% 7% 7% 5% 6% 7% 22%	3750
	21st to end	Night	4 9% 3 9% 7% 7% 8% 5% 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	45% 11% 15% 20% 8% 1	2280
	11th to 20th	Day	50% 9% 14% 18% 9%	2491
	21st to end	Day	50% 9% 13% 21% 6% 1	2660
May	1st to 10th	Day	38% 10% 16% 23% 12% 1	4420
	11th to 20th	Day	39% 11% 13% 25% 12% 1	4916
	21st to end	Day	46% 13% 15% 18% 6% 1	5510
June	1st to 10th	Day	43% 10% 15% 20% 9% 2	3040
	11th to 20th	Day	52% 10% 14% 18% 5%	3040
	21st to end	Day	39% 10% 19% 23% 9%	3040
July	1st to 10th	Day	32% 8% 16% 25% 17% 1	4981
	11th to 20th	Day	32% 9% 18% 27% 13% 1	4973
	21st to end	Day	34% 10% 23% 28% 6% 1	5131
August	1st to 10th	Day	32% 8% 17% 33% 9%	4521
	11th to 20th	Day	40% 8% 16% 21% 14% 1	4372
	21st to end	Day	39% 10% 25% 22% 3	4638
September	1st to 10th	Day	38% 10% 24% 23% 5%	2280
	11th to 20th	Day	41% 10% 19% 25% 6%	2280
	21st to end	Day	43% 11% 18% 20% 8%	2023
October	1st to 10th	Day	49% 8% 18% 21% 4	3180
	11th to 20th	Day	47% 8% 17% 24% 3	2977
	21st to end	Day	45% 9% 19% 21% 6%	2867
November	1st to 10th	Day	55% 9% 12% 19% 5%	1488
	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% 11% 12% 20% 12% 1	1900
	11th to 20th	Night	45% 8% 13% 22% 11% 1	1635
	21st to end	Night	48% 9% 11% 22% 8% 2	1520
May	1st to 10th	Night	42% 11% 12% 20% 13% 2	2540
	11th to 20th	Night	36% 11% 12% 27% 12% 1	1969
	21st to end	Night	45% 13% 15% 18% 8%	2066
June	1st to 10th	Night	47% 11% 10% 19% 12% 1	1140
	11th to 20th	Night	51% 9% 14% 19% 6% 1	1140
	21st to end	Night	38% 9% 21% 22% 10% 1	1140
July	1st to 10th	Night	36% 8% 13% 27% 15%	1870
	11th to 20th	Night	32% 11% 17% 22% 16% 1	1864
	21st to end	Night	36% 11% 21% 26% 7%	2179
August	1st to 10th	Night	27% 10% 19% 30% 13%	2383
	11th to 20th	Night	33% 8% 17% 25% 16% 1	2521
	21st to end	Night	37% 10% 27% 21% 5%	3024
September	1st to 10th	Night	39% 10% 21% 23% 7% 1	1900
	11th to 20th	Night	39% 9% 18% 29% 6%	1900
	21st to end	Night	42% 10% 16% 22% 10% 1	2156
October	1st to 10th	Night	49% 8% 15% 19% 7%	3800
	11th to 20th	Night	42% 8% 18% 27% 6%	3954
	21st to end	Night	50% 8% 16% 22% 5%	4671
November	1st to 10th	Night	54% 8% 12% 22% 4	2670
	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% 35% 22% 12% 4	460
	11th to 20th	Day	15% 13% 28% 26% 14% 5%	452
	21st to end	Day	20% 13% 29% 23% 12% 3	460
May	1st to 10th	Day	16% 16% 31% 23% 10% 4	463
	11th to 20th	Day	14% 9% 25% 30% 18% 4	800
	21st to end	Day	15% 10% 24% 26% 20% 5%	940
June	1st to 10th	Day	14% 13% 29% 28% 15% 2	870
	11th to 20th	Day	18% 8% 25% 24% 21% 4	870
	21st to end	Day	13% 7% 20% 28% 24% 8%	870
July	1st to 10th	Day	12% 7% 21% 31% 23% 5%	856
	11th to 20th	Day	13% 7% 23% 28% 21% 9%	852
	21st to end	Day	11% 6% 27% 31% 20% 5%	835
August	1st to 10th	Day	13% 10% 18% 29% 22% 7%	574
	11th to 20th	Day	12% 12% 31% 24% 16% 6%	477
	21st to end	Day	16% 14% 25% 26% 15% 5%	539
September	1st to 10th	Day	17% 10% 25% 27% 16% 5%	490
	11th to 20th	Day	16% 11% 24% 30% 14% 5%	490
	21st to end	Day	14% 21% 29% 23% 11% 2	490
October	1st to 10th	Day	21% 16% 25% 23% 11% 3	490
	11th to 20th	Day	16% 15% 29% 26% 12% 2	383
	21st to end	Day	18% 12% 24% 28% 16% 2	259
November	1st to 10th	Day	22% 11% 26% 28% 13% 2	188
	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% 36% 16% 2	507
	21st to end	Night	14% 9% 27% 30% 19% 1	380
May	1st to 10th	Night	14% 9% 28% 31% 16% 2	380
	11th to 20th	Night	12% 8% 26% 30% 23% 1	374
	21st to end	Night	17% 5% 23% 32% 20% 3	411
June	1st to 10th	Night	12% 9% 27% 28% 22% 2	380
	11th to 20th	Night	18% 5% 17% 32% 23% 4	380
	21st to end	Night	13% 3 20% 33% 28% 2	380
July	1st to 10th	Night	11% 6% 21% 32% 30% 1	370
	11th to 20th	Night	12% 6% 17% 36% 23% 6%	368
	21st to end	Night	8% 6% 21% 40% 23% 3	416
August	1st to 10th	Night	10% 4 13% 28% 39% 6%	378
	11th to 20th	Night	9% 6% 25% 32% 26% 2	376
	21st to end	Night	13% 3 24% 35% 22% 3	544
September	1st to 10th	Night	15% 6% 19% 37% 20% 2	760
	11th to 20th	Night	14% 7% 21% 32% 25% 2	760
	21st to end	Night	14% 12% 29% 30% 14% 1	760
October	1st to 10th	Night	17% 11% 25% 32% 15% 1	760
	11th to 20th	Night	16% 10% 29% 31% 11% 2	760
	21st to end	Night	19% 11% 27% 32% 10% 1	836
November	1st to 10th	Night	19% 9% 25% 31% 14% 2	772
	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

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