Cardston
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cardston clear sky chart from 2005-11-06 to 2026-01-17.

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	7% 7% 3 7% 4 4 5% 4 6% 8% 45%	131389
	Night	5% 8% 3 7% 5% 4 5% 4 6% 8% 45%	129035
Transparency	Day	36% 6% 14% 27% 15% 3	131097
	Night	36% 6% 16% 26% 13% 3	128905
Seeing	Day	15% 13% 27% 26% 14% 5%	16839
	Night	12% 12% 31% 32% 11% 1	26148

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	2 10% 5% 11% 7% 6% 5% 3 6% 8% 36%	3249
	11th to 20th	Day	2 9% 4 12% 8% 6% 7% 5% 6% 7% 35%	3411
	21st to end	Day	1 6% 3 7% 5% 4 5% 4 6% 9% 50%	4004
February	1st to 10th	Day	3 11% 3 13% 7% 6% 5% 5% 8% 8% 31%	1680
	11th to 20th	Day	3 13% 4 10% 5% 5% 6% 4 6% 8% 36%	1755
	21st to end	Day	3 9% 4 11% 7% 5% 5% 4 5% 9% 38%	1614
March	1st to 10th	Day	2 8% 3 7% 5% 4 4 4 7% 10% 46%	4550
	11th to 20th	Day	2 8% 3 8% 5% 5% 5% 5% 7% 9% 44%	4999
	21st to end	Day	6% 16% 6% 12% 5% 5% 5% 4 7% 8% 26%	5486
April	1st to 10th	Day	6% 12% 4 8% 6% 5% 5% 4 7% 9% 33%	2441
	11th to 20th	Day	9% 13% 4 8% 6% 4 5% 3 6% 7% 35%	2570
	21st to end	Day	11% 11% 3 9% 5% 4 5% 3 7% 7% 36%	2600
May	1st to 10th	Day	13% 13% 3 6% 3 2 3 3 5% 6% 42%	5880
	11th to 20th	Day	12% 8% 3 9% 5% 6% 6% 5% 7% 8% 32%	6679
	21st to end	Day	11% 6% 2 6% 4 4 5% 4 6% 8% 43%	7405
June	1st to 10th	Day	12% 7% 2 6% 5% 6% 5% 5% 6% 9% 37%	3000
	11th to 20th	Day	15% 7% 2 7% 5% 6% 5% 5% 7% 8% 34%	3000
	21st to end	Day	7% 4 2 5% 4 4 5% 4 6% 9% 50%	3000
July	1st to 10th	Day	7% 4 1 4 4 4 4 4 6% 7% 55%	6780
	11th to 20th	Day	6% 3 1 4 3 3 4 4 5% 8% 58%	6780
	21st to end	Day	6% 3 1 3 2 3 3 3 5% 7% 63%	7057
August	1st to 10th	Day	10% 5% 2 5% 3 4 5% 5% 6% 9% 45%	4432
	11th to 20th	Day	4 3 1 4 4 4 5% 4 6% 8% 56%	4158
	21st to end	Day	7% 3 1 4 3 3 4 4 5% 7% 60%	4664
September	1st to 10th	Day	11% 4 1 4 3 3 3 3 5% 7% 55%	2445
	11th to 20th	Day	10% 6% 2 5% 3 5% 5% 3 5% 7% 50%	2200
	21st to end	Day	11% 5% 2 4 4 3 3 3 5% 7% 53%	2200
October	1st to 10th	Day	7% 6% 2 5% 3 3 3 3 6% 11% 51%	3440
	11th to 20th	Day	4 8% 3 6% 4 3 5% 3 6% 10% 49%	3107
	21st to end	Day	6% 7% 3 7% 4 4 4 4 7% 8% 48%	3200
November	1st to 10th	Day	7% 11% 3 9% 5% 3 4 3 6% 8% 40%	1756
	11th to 20th	Day	3 10% 3 7% 4 4 4 5% 6% 9% 45%	1680
	21st to end	Day	3 9% 5% 9% 6% 5% 4 3 6% 10% 41%	1520
December	1st to 10th	Day	1 6% 3 6% 5% 5% 4 4 6% 10% 50%	2360
	11th to 20th	Day	2 7% 4 9% 7% 6% 6% 5% 7% 8% 39%	2712
	21st to end	Day	3 9% 4 9% 6% 5% 6% 5% 6% 7% 41%	3575
January	1st to 10th	Night	3 10% 4 12% 7% 5% 5% 4 6% 8% 35%	6916
	11th to 20th	Night	2 8% 4 12% 7% 7% 7% 4 5% 8% 36%	6664
	21st to end	Night	2 6% 3 8% 5% 5% 5% 5% 7% 8% 46%	6952
February	1st to 10th	Night	3 13% 5% 11% 6% 4 5% 4 6% 8% 36%	2720
	11th to 20th	Night	3 12% 5% 11% 5% 6% 6% 5% 6% 7% 34%	2532
	21st to end	Night	2 9% 4 10% 7% 6% 5% 5% 6% 7% 38%	2015
March	1st to 10th	Night	1 8% 4 9% 5% 5% 5% 4 6% 9% 44%	5344
	11th to 20th	Night	2 5% 2 7% 5% 5% 6% 5% 7% 9% 47%	5000
	21st to end	Night	7% 19% 6% 10% 4 4 5% 4 6% 8% 28%	5489
April	1st to 10th	Night	7% 11% 2 6% 4 4 4 5% 6% 7% 43%	1956
	11th to 20th	Night	9% 10% 4 8% 5% 4 5% 4 7% 8% 37%	1781
	21st to end	Night	8% 11% 2 7% 5% 5% 6% 4 6% 6% 42%	1800
May	1st to 10th	Night	12% 13% 2 7% 4 4 4 3 5% 7% 39%	4100
	11th to 20th	Night	10% 8% 3 7% 5% 4 5% 4 6% 8% 39%	3214
	21st to end	Night	11% 5% 1 5% 4 4 4 4 6% 7% 48%	3470
June	1st to 10th	Night	11% 7% 2 5% 5% 3 4 4 6% 8% 46%	1400
	11th to 20th	Night	14% 6% 3 6% 5% 4 4 4 7% 7% 40%	1400
	21st to end	Night	5% 4 1 4 3 4 5% 4 7% 7% 55%	1400
July	1st to 10th	Night	5% 2 1 3 2 3 3 3 5% 8% 63%	3180
	11th to 20th	Night	6% 3 1 3 2 3 3 3 5% 6% 64%	3180
	21st to end	Night	7% 5% 2 4 3 3 3 2 4 5% 63%	3783
August	1st to 10th	Night	10% 4 2 4 3 3 4 3 4 8% 56%	2707
	11th to 20th	Night	4 3 1 5% 4 5% 5% 4 7% 9% 49%	2901
	21st to end	Night	5% 3 1 4 3 3 3 3 4 8% 62%	3245
September	1st to 10th	Night	11% 3 1 4 2 3 3 3 6% 7% 56%	1950
	11th to 20th	Night	10% 6% 2 4 3 4 4 4 6% 6% 52%	2200
	21st to end	Night	9% 5% 1 4 3 3 4 4 5% 7% 55%	2200
October	1st to 10th	Night	7% 5% 1 3 3 3 4 3 7% 8% 57%	3755
	11th to 20th	Night	4 5% 2 5% 4 4 4 3 6% 9% 53%	4039
	21st to end	Night	3 6% 4 8% 4 3 4 4 5% 8% 51%	4600
November	1st to 10th	Night	7% 11% 4 6% 6% 4 4 4 6% 7% 42%	2741
	11th to 20th	Night	2 9% 3 6% 5% 3 5% 4 7% 9% 47%	2940
	21st to end	Night	3 10% 4 9% 5% 5% 3 4 6% 9% 42%	3098
December	1st to 10th	Night	1 7% 3 7% 4 4 5% 4 6% 10% 49%	5040
	11th to 20th	Night	2 8% 4 10% 7% 7% 7% 5% 7% 9% 36%	5700
	21st to end	Night	2 10% 4 8% 5% 4 5% 4 7% 9% 41%	7623

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	46% 6% 13% 24% 9% 1	3249
	11th to 20th	Day	47% 6% 14% 16% 12% 4	3433
	21st to end	Day	30% 7% 17% 34% 12%	4004
February	1st to 10th	Day	48% 8% 15% 18% 8% 3	1680
	11th to 20th	Day	45% 6% 19% 20% 8% 1	1764
	21st to end	Day	43% 7% 15% 21% 12% 2	1614
March	1st to 10th	Day	32% 5% 14% 27% 20% 3	4550
	11th to 20th	Day	34% 6% 16% 29% 14% 1	5000
	21st to end	Day	54% 7% 16% 17% 6%	5486
April	1st to 10th	Day	45% 8% 14% 23% 9%	2441
	11th to 20th	Day	45% 7% 12% 23% 10% 2	2570
	21st to end	Day	45% 6% 14% 23% 10% 1	2600
May	1st to 10th	Day	43% 4 8% 25% 16% 4	5880
	11th to 20th	Day	44% 7% 12% 27% 9% 1	6683
	21st to end	Day	36% 7% 14% 27% 15%	7406
June	1st to 10th	Day	42% 8% 15% 23% 11% 1	3000
	11th to 20th	Day	46% 6% 12% 21% 14% 2	3000
	21st to end	Day	29% 6% 16% 31% 14% 3	3000
July	1st to 10th	Day	26% 4 13% 24% 25% 8%	6706
	11th to 20th	Day	26% 4 12% 29% 22% 7%	6699
	21st to end	Day	21% 3 12% 29% 20% 15%	6860
August	1st to 10th	Day	33% 5% 14% 23% 20% 5%	4415
	11th to 20th	Day	25% 5% 14% 36% 17% 3	4197
	21st to end	Day	23% 3 8% 39% 22% 4	4663
September	1st to 10th	Day	30% 3 12% 27% 19% 9%	2445
	11th to 20th	Day	34% 6% 12% 27% 17% 4	2200
	21st to end	Day	32% 5% 13% 32% 14% 4	2200
October	1st to 10th	Day	27% 4 12% 37% 17% 2	3440
	11th to 20th	Day	31% 3 17% 28% 19% 1	3107
	21st to end	Day	35% 5% 12% 30% 15% 3	3200
November	1st to 10th	Day	43% 8% 13% 24% 10% 2	1756
	11th to 20th	Day	35% 8% 20% 25% 11% 1	1680
	21st to end	Day	40% 6% 21% 20% 10% 2	1520
December	1st to 10th	Day	31% 7% 25% 28% 7% 3	2360
	11th to 20th	Day	41% 6% 23% 24% 5% 1	2714
	21st to end	Day	41% 7% 11% 24% 16% 3	3575
January	1st to 10th	Night	46% 7% 15% 24% 7% 1	6916
	11th to 20th	Night	47% 6% 15% 18% 11% 3	6704
	21st to end	Night	34% 8% 17% 29% 12% 1	6952
February	1st to 10th	Night	45% 8% 15% 18% 12% 2	2720
	11th to 20th	Night	48% 6% 15% 20% 10% 2	2533
	21st to end	Night	45% 5% 15% 23% 10% 2	2015
March	1st to 10th	Night	36% 6% 15% 25% 14% 4	5344
	11th to 20th	Night	30% 9% 18% 28% 15%	5000
	21st to end	Night	55% 5% 15% 18% 7%	5489
April	1st to 10th	Night	39% 6% 17% 29% 9%	1956
	11th to 20th	Night	43% 7% 14% 26% 10% 1	1781
	21st to end	Night	42% 6% 16% 26% 9% 1	1800
May	1st to 10th	Night	44% 5% 10% 25% 14% 2	4097
	11th to 20th	Night	41% 6% 12% 28% 12% 1	3214
	21st to end	Night	32% 7% 15% 30% 14% 1	3470
June	1st to 10th	Night	37% 6% 17% 29% 10% 1	1400
	11th to 20th	Night	41% 5% 15% 22% 14% 2	1400
	21st to end	Night	26% 6% 18% 30% 17% 2	1400
July	1st to 10th	Night	21% 4 15% 26% 23% 12%	3145
	11th to 20th	Night	20% 4 15% 33% 19% 9%	3138
	21st to end	Night	25% 3 14% 26% 19% 14%	3676
August	1st to 10th	Night	28% 4 13% 26% 20% 9%	2699
	11th to 20th	Night	29% 4 17% 30% 17% 3	2928
	21st to end	Night	22% 4 10% 37% 23% 5%	3245
September	1st to 10th	Night	28% 4 12% 30% 17% 9%	1950
	11th to 20th	Night	31% 5% 15% 28% 17% 5%	2200
	21st to end	Night	30% 4 15% 31% 17% 3	2200
October	1st to 10th	Night	26% 4 11% 35% 21% 3	3755
	11th to 20th	Night	30% 3 17% 29% 18% 3	4039
	21st to end	Night	32% 5% 13% 34% 14% 1	4600
November	1st to 10th	Night	42% 6% 18% 22% 11% 2	2741
	11th to 20th	Night	34% 7% 22% 22% 14% 1	2940
	21st to end	Night	38% 6% 23% 20% 10% 3	3098
December	1st to 10th	Night	32% 7% 24% 24% 11% 2	5040
	11th to 20th	Night	42% 8% 24% 20% 6% 1	5697
	21st to end	Night	38% 6% 15% 24% 15% 3	7623

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	15% 17% 28% 22% 10% 7%	220
	11th to 20th	Day	16% 14% 28% 29% 10% 3	212
	21st to end	Day	16% 17% 37% 19% 7% 4	220
February	1st to 10th	Day	19% 15% 27% 27% 10% 3	240
	11th to 20th	Day	14% 11% 37% 28% 8% 2	300
	21st to end	Day	18% 24% 29% 23% 6% 1	378
March	1st to 10th	Day	14% 20% 32% 23% 8% 3	500
	11th to 20th	Day	14% 18% 28% 24% 13% 5%	500
	21st to end	Day	14% 18% 35% 22% 8% 2	550
April	1st to 10th	Day	19% 21% 29% 23% 8%	500
	11th to 20th	Day	19% 19% 29% 22% 8% 3	492
	21st to end	Day	22% 16% 25% 22% 12% 4	500
May	1st to 10th	Day	19% 12% 28% 23% 14% 4	503
	11th to 20th	Day	23% 9% 21% 25% 17% 6%	720
	21st to end	Day	23% 7% 18% 25% 19% 7%	789
June	1st to 10th	Day	16% 16% 24% 25% 15% 4	730
	11th to 20th	Day	22% 14% 24% 24% 12% 3	730
	21st to end	Day	9% 9% 29% 29% 19% 6%	730
July	1st to 10th	Day	8% 7% 23% 31% 24% 7%	721
	11th to 20th	Day	9% 7% 23% 37% 19% 4	718
	21st to end	Day	7% 6% 26% 36% 18% 8%	654
August	1st to 10th	Day	11% 6% 23% 32% 20% 8%	527
	11th to 20th	Day	6% 7% 23% 30% 25% 8%	517
	21st to end	Day	11% 8% 24% 34% 18% 6%	583
September	1st to 10th	Day	13% 12% 24% 26% 19% 6%	530
	11th to 20th	Day	14% 9% 28% 27% 16% 6%	530
	21st to end	Day	19% 17% 28% 19% 13% 4	530
October	1st to 10th	Day	18% 11% 22% 29% 14% 5%	435
	11th to 20th	Day	15% 14% 30% 22% 13% 6%	330
	21st to end	Day	18% 16% 33% 20% 9% 4	363
November	1st to 10th	Day	25% 18% 28% 22% 5% 1	330
	11th to 20th	Day	18% 18% 36% 21% 5% 1	330
	21st to end	Day	11% 22% 32% 20% 10% 5%	245
December	1st to 10th	Day	12% 22% 33% 22% 7% 4	220
	11th to 20th	Day	18% 20% 31% 22% 8% 2	220
	21st to end	Day	12% 14% 35% 23% 10% 6%	242
January	1st to 10th	Night	14% 21% 32% 24% 8% 1	1050
	11th to 20th	Night	13% 14% 39% 27% 6% 1	955
	21st to end	Night	9% 19% 36% 27% 6% 2	880
February	1st to 10th	Night	13% 14% 31% 29% 10% 3	800
	11th to 20th	Night	14% 13% 33% 30% 10%	784
	21st to end	Night	10% 14% 35% 27% 13% 1	660
March	1st to 10th	Night	8% 13% 35% 31% 10% 3	800
	11th to 20th	Night	10% 13% 33% 34% 9% 2	800
	21st to end	Night	13% 13% 30% 32% 11% 1	880
April	1st to 10th	Night	14% 13% 32% 29% 11% 1	742
	11th to 20th	Night	15% 11% 37% 29% 7%	593
	21st to end	Night	17% 9% 32% 31% 11%	600
May	1st to 10th	Night	17% 11% 26% 30% 16%	600
	11th to 20th	Night	14% 6% 26% 37% 16% 1	418
	21st to end	Night	21% 8% 21% 30% 19% 1	433
June	1st to 10th	Night	16% 7% 29% 35% 11% 2	400
	11th to 20th	Night	19% 9% 31% 31% 10% 1	400
	21st to end	Night	8% 5% 30% 40% 17% 1	400
July	1st to 10th	Night	6% 4 21% 47% 21% 1	390
	11th to 20th	Night	7% 4 27% 45% 16% 1	388
	21st to end	Night	7% 4 18% 53% 17% 1	438
August	1st to 10th	Night	8% 2 18% 48% 23% 1	457
	11th to 20th	Night	8% 2 22% 43% 23% 2	594
	21st to end	Night	9% 5% 24% 45% 16% 2	660
September	1st to 10th	Night	14% 3 22% 39% 19% 3	695
	11th to 20th	Night	14% 4 21% 38% 20% 3	800
	21st to end	Night	12% 10% 28% 35% 12% 2	800
October	1st to 10th	Night	16% 7% 25% 35% 15% 2	800
	11th to 20th	Night	12% 13% 30% 32% 12% 1	800
	21st to end	Night	13% 18% 33% 27% 8% 1	880
November	1st to 10th	Night	17% 14% 37% 27% 5%	896
	11th to 20th	Night	13% 21% 36% 24% 5% 1	1050
	21st to end	Night	11% 17% 37% 25% 8% 1	1050
December	1st to 10th	Night	10% 17% 34% 28% 10% 2	1050
	11th to 20th	Night	10% 17% 37% 29% 8%	1050
	21st to end	Night	12% 16% 37% 25% 9% 2	1155

Page generated at 2026-01-13 23:14:29. Version ac07

Copyright © 2026 Attilla Danko.