Okotoks
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Okotoks clear sky chart from 2005-11-06 to 2025-02-25.

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% 8% 3 8% 5% 5% 5% 4 6% 8% 40%	112137
	Night	6% 9% 4 9% 5% 5% 5% 4 6% 8% 39%	115194
Transparency	Day	39% 6% 15% 26% 12% 2	111883
	Night	41% 6% 15% 24% 13% 2	115094
Seeing	Day	13% 10% 29% 29% 15% 4	15615
	Night	11% 7% 31% 35% 14% 2	24928

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% 7% 13% 8% 7% 5% 4 6% 7% 31%	3179
	11th to 20th	Day	3 8% 3 10% 6% 5% 5% 5% 7% 7% 41%	3271
	21st to end	Day	2 6% 3 8% 5% 5% 5% 4 5% 11% 46%	4004
February	1st to 10th	Day	3 10% 5% 14% 7% 5% 6% 5% 7% 8% 31%	1600
	11th to 20th	Day	3 11% 5% 11% 7% 7% 7% 5% 7% 8% 29%	1755
	21st to end	Day	2 11% 5% 12% 7% 7% 5% 4 5% 8% 32%	1574
March	1st to 10th	Day	2 9% 4 13% 8% 7% 5% 4 5% 7% 35%	3138
	11th to 20th	Day	6% 10% 2 6% 4 3 4 4 4 8% 47%	3452
	21st to end	Day	8% 20% 7% 13% 5% 4 4 4 5% 5% 25%	3876
April	1st to 10th	Day	9% 15% 4 10% 6% 5% 6% 4 6% 7% 29%	2327
	11th to 20th	Day	10% 13% 5% 9% 6% 4 5% 4 6% 8% 31%	2440
	21st to end	Day	12% 11% 3 8% 5% 4 5% 4 7% 8% 32%	2470
May	1st to 10th	Day	16% 15% 4 8% 5% 4 5% 4 5% 6% 29%	4285
	11th to 20th	Day	10% 8% 3 9% 6% 6% 6% 5% 8% 9% 32%	4694
	21st to end	Day	16% 8% 3 10% 8% 6% 6% 5% 6% 7% 25%	5161
June	1st to 10th	Day	16% 8% 3 7% 6% 5% 6% 5% 7% 7% 30%	2850
	11th to 20th	Day	20% 8% 3 8% 6% 5% 5% 4 6% 9% 27%	2850
	21st to end	Day	9% 5% 2 5% 5% 5% 5% 5% 8% 9% 43%	2850
July	1st to 10th	Day	7% 4 2 5% 4 4 5% 5% 6% 8% 50%	4740
	11th to 20th	Day	6% 3 1 4 3 3 4 4 7% 10% 54%	4740
	21st to end	Day	3 3 2 3 3 3 4 4 6% 9% 61%	4990
August	1st to 10th	Day	9% 6% 2 5% 4 4 5% 4 8% 9% 43%	4401
	11th to 20th	Day	7% 5% 2 4 3 4 5% 5% 7% 10% 47%	4057
	21st to end	Day	9% 4 1 4 3 3 4 3 6% 8% 54%	4521
September	1st to 10th	Day	10% 5% 1 6% 4 4 4 3 4 7% 51%	2347
	11th to 20th	Day	13% 8% 2 5% 3 4 4 3 5% 7% 45%	2090
	21st to end	Day	8% 8% 2 6% 4 4 4 3 6% 8% 45%	2090
October	1st to 10th	Day	6% 7% 2 7% 5% 4 5% 4 6% 9% 45%	3347
	11th to 20th	Day	5% 7% 2 6% 5% 4 4 4 8% 11% 44%	2918
	21st to end	Day	6% 8% 3 6% 5% 5% 5% 4 6% 7% 45%	3101
November	1st to 10th	Day	8% 15% 4 8% 6% 4 4 5% 5% 8% 33%	1649
	11th to 20th	Day	5% 12% 4 7% 6% 4 4 4 6% 9% 39%	1540
	21st to end	Day	4 12% 5% 9% 5% 4 6% 5% 7% 10% 35%	1400
December	1st to 10th	Day	2 9% 4 11% 7% 5% 5% 5% 7% 7% 37%	2290
	11th to 20th	Day	2 9% 4 11% 6% 6% 6% 5% 6% 9% 35%	2642
	21st to end	Day	4 10% 4 9% 5% 5% 5% 4 5% 7% 42%	3498
January	1st to 10th	Night	3 13% 5% 14% 9% 7% 6% 4 6% 7% 27%	6766
	11th to 20th	Night	2 7% 5% 13% 7% 6% 6% 6% 6% 8% 35%	6670
	21st to end	Night	3 8% 4 9% 5% 5% 4 4 6% 9% 43%	6952
February	1st to 10th	Night	3 11% 5% 11% 7% 6% 6% 5% 7% 8% 32%	2800
	11th to 20th	Night	4 13% 6% 10% 6% 6% 5% 4 6% 9% 31%	2532
	21st to end	Night	2 10% 5% 12% 9% 7% 5% 4 5% 7% 35%	1972
March	1st to 10th	Night	2 9% 4 14% 8% 7% 7% 5% 6% 8% 30%	3736
	11th to 20th	Night	4 9% 3 6% 4 5% 4 4 6% 7% 47%	3526
	21st to end	Night	10% 21% 7% 11% 7% 5% 4 3 5% 6% 22%	3773
April	1st to 10th	Night	8% 15% 4 8% 6% 6% 5% 4 6% 7% 32%	1853
	11th to 20th	Night	10% 12% 5% 10% 6% 4 4 4 6% 7% 32%	1691
	21st to end	Night	10% 11% 4 8% 5% 4 5% 4 6% 8% 35%	1710
May	1st to 10th	Night	17% 14% 4 8% 5% 4 4 3 5% 6% 31%	2664
	11th to 20th	Night	10% 7% 3 8% 5% 5% 5% 5% 6% 10% 34%	2199
	21st to end	Night	15% 8% 3 8% 6% 5% 6% 5% 7% 8% 29%	2414
June	1st to 10th	Night	14% 8% 3 7% 5% 5% 4 4 6% 8% 36%	1330
	11th to 20th	Night	17% 9% 3 7% 4 4 5% 5% 6% 8% 31%	1330
	21st to end	Night	7% 5% 2 4 4 4 5% 4 9% 9% 47%	1330
July	1st to 10th	Night	6% 5% 2 7% 5% 5% 4 3 6% 7% 49%	2220
	11th to 20th	Night	4 3 2 4 3 4 6% 4 7% 9% 54%	2220
	21st to end	Night	5% 4 1 5% 3 3 3 3 5% 7% 61%	2561
August	1st to 10th	Night	10% 5% 2 6% 5% 5% 4 4 8% 8% 44%	2529
	11th to 20th	Night	6% 5% 2 6% 5% 5% 5% 5% 7% 10% 44%	2781
	21st to end	Night	7% 4 1 4 3 3 4 3 6% 9% 55%	3146
September	1st to 10th	Night	10% 6% 2 5% 3 3 4 3 5% 7% 51%	1830
	11th to 20th	Night	13% 7% 2 5% 3 3 3 3 5% 6% 51%	2090
	21st to end	Night	9% 7% 2 4 3 3 4 4 6% 8% 48%	2090
October	1st to 10th	Night	7% 6% 2 5% 3 4 4 4 5% 8% 52%	3628
	11th to 20th	Night	6% 6% 2 5% 4 4 4 3 6% 8% 50%	4008
	21st to end	Night	5% 8% 3 7% 5% 5% 5% 4 6% 7% 46%	4457
November	1st to 10th	Night	7% 13% 4 9% 5% 6% 4 4 5% 7% 36%	2630
	11th to 20th	Night	4 10% 4 8% 6% 4 4 4 7% 8% 41%	2858
	21st to end	Night	4 10% 4 9% 5% 5% 5% 5% 6% 9% 38%	3000
December	1st to 10th	Night	2 8% 4 8% 6% 6% 7% 6% 9% 9% 35%	4890
	11th to 20th	Night	2 10% 4 12% 8% 6% 6% 5% 7% 8% 31%	5550
	21st to end	Night	4 11% 4 9% 5% 5% 5% 4 6% 8% 40%	7458

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	49% 6% 12% 21% 10% 3	3179
	11th to 20th	Day	41% 4 13% 20% 19% 3	3292
	21st to end	Day	32% 5% 14% 34% 15% 1	4004
February	1st to 10th	Day	49% 7% 13% 18% 10% 3	1600
	11th to 20th	Day	48% 7% 13% 21% 9% 2	1764
	21st to end	Day	49% 4 13% 19% 14% 1	1574
March	1st to 10th	Day	45% 9% 12% 19% 14% 1	3138
	11th to 20th	Day	35% 5% 16% 29% 15% 1	3453
	21st to end	Day	58% 7% 13% 17% 5% 1	3876
April	1st to 10th	Day	51% 6% 14% 20% 8% 1	2327
	11th to 20th	Day	49% 5% 13% 22% 10% 2	2440
	21st to end	Day	47% 5% 15% 22% 10% 1	2470
May	1st to 10th	Day	55% 3 11% 25% 6%	4285
	11th to 20th	Day	43% 7% 14% 25% 9%	4698
	21st to end	Day	53% 8% 14% 15% 8% 1	5162
June	1st to 10th	Day	48% 6% 16% 18% 9% 2	2850
	11th to 20th	Day	52% 5% 16% 16% 8% 2	2850
	21st to end	Day	34% 7% 20% 25% 12% 2	2850
July	1st to 10th	Day	29% 5% 16% 28% 17% 5%	4666
	11th to 20th	Day	24% 5% 19% 34% 15% 2	4659
	21st to end	Day	19% 4 12% 29% 24% 11%	4832
August	1st to 10th	Day	32% 6% 16% 36% 8% 1	4384
	11th to 20th	Day	29% 7% 25% 29% 7% 1	4096
	21st to end	Day	27% 5% 17% 36% 14% 1	4520
September	1st to 10th	Day	33% 4 15% 26% 17% 5%	2347
	11th to 20th	Day	37% 5% 16% 27% 14% 2	2090
	21st to end	Day	36% 4 15% 29% 13% 3	2090
October	1st to 10th	Day	34% 5% 17% 35% 9% 1	3347
	11th to 20th	Day	32% 4 21% 27% 14% 3	2918
	21st to end	Day	36% 6% 11% 33% 12% 2	3101
November	1st to 10th	Day	48% 7% 12% 20% 11% 2	1649
	11th to 20th	Day	42% 5% 17% 24% 11% 2	1540
	21st to end	Day	41% 7% 18% 22% 10% 3	1400
December	1st to 10th	Day	44% 6% 14% 26% 8% 2	2290
	11th to 20th	Day	43% 7% 21% 21% 7% 1	2644
	21st to end	Day	40% 4 10% 24% 18% 4	3498
January	1st to 10th	Night	55% 6% 11% 21% 6% 2	6766
	11th to 20th	Night	45% 5% 13% 19% 13% 5%	6711
	21st to end	Night	37% 4 15% 26% 17% 1	6952
February	1st to 10th	Night	47% 6% 12% 20% 12% 3	2800
	11th to 20th	Night	49% 6% 13% 19% 12% 2	2533
	21st to end	Night	48% 5% 11% 22% 12% 3	1972
March	1st to 10th	Night	48% 8% 10% 22% 11% 1	3736
	11th to 20th	Night	33% 8% 19% 24% 15% 1	3526
	21st to end	Night	60% 7% 12% 15% 5% 1	3773
April	1st to 10th	Night	48% 7% 11% 22% 11% 1	1853
	11th to 20th	Night	50% 5% 13% 22% 9% 1	1691
	21st to end	Night	46% 6% 14% 23% 9% 2	1710
May	1st to 10th	Night	54% 4 11% 23% 7%	2664
	11th to 20th	Night	41% 7% 14% 30% 8% 1	2199
	21st to end	Night	49% 6% 17% 18% 8% 1	2414
June	1st to 10th	Night	44% 5% 16% 23% 11% 1	1330
	11th to 20th	Night	47% 6% 17% 18% 10% 3	1330
	21st to end	Night	30% 5% 23% 27% 13% 2	1330
July	1st to 10th	Night	32% 6% 16% 23% 19% 3	2185
	11th to 20th	Night	23% 7% 21% 35% 10% 4	2178
	21st to end	Night	22% 5% 10% 31% 23% 10%	2480
August	1st to 10th	Night	35% 6% 15% 28% 14% 2	2521
	11th to 20th	Night	32% 7% 23% 27% 10% 1	2808
	21st to end	Night	25% 5% 18% 35% 14% 3	3146
September	1st to 10th	Night	30% 5% 16% 27% 17% 5%	1830
	11th to 20th	Night	33% 4 15% 30% 14% 4	2090
	21st to end	Night	33% 4 17% 27% 14% 4	2090
October	1st to 10th	Night	29% 5% 15% 29% 20% 2	3628
	11th to 20th	Night	30% 5% 19% 25% 18% 2	4008
	21st to end	Night	35% 5% 12% 33% 15% 1	4457
November	1st to 10th	Night	46% 6% 13% 21% 12% 2	2630
	11th to 20th	Night	39% 6% 16% 22% 16% 1	2858
	21st to end	Night	40% 6% 17% 22% 11% 4	3000
December	1st to 10th	Night	40% 9% 20% 20% 9% 2	4890
	11th to 20th	Night	47% 7% 22% 17% 8%	5547
	21st to end	Night	40% 4 11% 25% 16% 3	7458

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	3 10% 28% 36% 15% 10%	200
	11th to 20th	Day	9% 8% 36% 32% 13% 4	200
	21st to end	Day	7% 10% 24% 45% 10% 3	220
February	1st to 10th	Day	8% 13% 37% 29% 11% 3	200
	11th to 20th	Day	6% 8% 37% 35% 13% 2	300
	21st to end	Day	6% 13% 34% 31% 14% 1	362
March	1st to 10th	Day	8% 16% 40% 23% 10% 3	460
	11th to 20th	Day	9% 14% 33% 29% 13% 2	460
	21st to end	Day	13% 19% 32% 22% 10% 3	506
April	1st to 10th	Day	13% 19% 36% 24% 7% 1	460
	11th to 20th	Day	17% 14% 29% 26% 11% 3	452
	21st to end	Day	16% 20% 32% 21% 10% 2	460
May	1st to 10th	Day	19% 10% 28% 25% 13% 4	489
	11th to 20th	Day	18% 8% 24% 28% 18% 4	675
	21st to end	Day	19% 7% 23% 26% 20% 4	734
June	1st to 10th	Day	17% 10% 28% 30% 12% 3	680
	11th to 20th	Day	21% 10% 28% 26% 12% 2	680
	21st to end	Day	12% 8% 27% 31% 18% 5%	680
July	1st to 10th	Day	10% 6% 25% 34% 22% 4	671
	11th to 20th	Day	11% 7% 26% 34% 20% 3	668
	21st to end	Day	6% 6% 30% 31% 21% 5%	653
August	1st to 10th	Day	9% 7% 28% 34% 17% 4	487
	11th to 20th	Day	9% 6% 27% 34% 18% 7%	477
	21st to end	Day	12% 7% 28% 30% 16% 7%	539
September	1st to 10th	Day	13% 9% 30% 28% 14% 6%	490
	11th to 20th	Day	18% 8% 26% 28% 15% 4	490
	21st to end	Day	14% 18% 25% 30% 10% 3	490
October	1st to 10th	Day	14% 11% 25% 30% 17% 4	412
	11th to 20th	Day	14% 11% 30% 25% 14% 5%	300
	21st to end	Day	14% 12% 38% 23% 10% 3	330
November	1st to 10th	Day	19% 10% 28% 31% 9% 3	300
	11th to 20th	Day	12% 16% 33% 30% 8% 2	270
	21st to end	Day	9% 13% 29% 31% 11% 9%	200
December	1st to 10th	Day	8% 8% 35% 30% 18% 4	200
	11th to 20th	Day	5% 11% 40% 29% 12% 5%	200
	21st to end	Day	9% 5% 28% 32% 23% 3	220
January	1st to 10th	Night	9% 11% 36% 33% 10% 1	1000
	11th to 20th	Night	8% 8% 37% 35% 11% 1	970
	21st to end	Night	9% 10% 34% 36% 9% 1	880
February	1st to 10th	Night	8% 11% 32% 33% 13% 4	800
	11th to 20th	Night	10% 7% 33% 37% 12% 1	784
	21st to end	Night	7% 6% 30% 37% 17% 3	646
March	1st to 10th	Night	8% 7% 35% 34% 13% 3	760
	11th to 20th	Night	9% 10% 35% 34% 11% 2	760
	21st to end	Night	12% 8% 31% 36% 11% 3	836
April	1st to 10th	Night	13% 11% 32% 31% 12% 1	713
	11th to 20th	Night	16% 9% 35% 31% 9%	563
	21st to end	Night	17% 9% 31% 31% 11%	570
May	1st to 10th	Night	16% 10% 24% 31% 18%	493
	11th to 20th	Night	13% 8% 23% 34% 20% 1	374
	21st to end	Night	21% 7% 23% 33% 16% 1	411
June	1st to 10th	Night	16% 9% 26% 35% 13% 2	380
	11th to 20th	Night	21% 6% 28% 31% 13% 1	380
	21st to end	Night	10% 4 20% 40% 24% 2	380
July	1st to 10th	Night	10% 3 18% 44% 24% 1	370
	11th to 20th	Night	10% 3 20% 43% 23% 2	368
	21st to end	Night	6% 3 21% 44% 23% 2	416
August	1st to 10th	Night	12% 3 14% 39% 30% 2	378
	11th to 20th	Night	9% 3 18% 45% 23% 2	546
	21st to end	Night	9% 5% 23% 40% 22% 1	627
September	1st to 10th	Night	13% 3 27% 36% 19% 3	672
	11th to 20th	Night	19% 4 20% 35% 20% 2	760
	21st to end	Night	12% 6% 33% 35% 11% 3	760
October	1st to 10th	Night	15% 4 27% 37% 14% 3	760
	11th to 20th	Night	12% 6% 32% 33% 14% 3	760
	21st to end	Night	11% 7% 33% 37% 11% 1	836
November	1st to 10th	Night	13% 10% 38% 29% 9% 1	875
	11th to 20th	Night	10% 13% 39% 30% 7% 2	1000
	21st to end	Night	9% 7% 40% 33% 9% 2	1000
December	1st to 10th	Night	8% 8% 35% 34% 12% 3	1000
	11th to 20th	Night	6% 8% 40% 36% 9% 1	1000
	21st to end	Night	9% 7% 35% 34% 12% 2	1100

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