Calgary
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Calgary clear sky chart from 2005-11-06 to 2024-12-02.

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 8% 5% 5% 5% 4 7% 8% 38%	105798
	Night	6% 9% 3 9% 5% 5% 5% 4 6% 8% 38%	102378
Transparency	Day	41% 8% 16% 24% 10% 2	105543
	Night	41% 8% 15% 23% 11% 2	102279
Seeing	Day	13% 9% 29% 30% 15% 4	15429
	Night	11% 7% 32% 35% 14% 2	24526

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	3 9% 6% 13% 5% 5% 4 4 8% 8% 36%	2219
	11th to 20th	Day	3 10% 3 10% 7% 5% 6% 6% 9% 7% 34%	2245
	21st to end	Day	5% 7% 3 9% 6% 6% 6% 4 6% 10% 39%	2794
February	1st to 10th	Day	4 10% 5% 13% 7% 6% 7% 5% 7% 8% 29%	1520
	11th to 20th	Day	5% 10% 4 11% 8% 6% 7% 5% 8% 7% 29%	1650
	21st to end	Day	4 12% 5% 11% 6% 5% 6% 5% 6% 9% 30%	1532
March	1st to 10th	Day	2 10% 5% 12% 7% 6% 8% 5% 6% 8% 30%	3138
	11th to 20th	Day	6% 10% 3 6% 4 4 5% 4 6% 9% 44%	3447
	21st to end	Day	8% 21% 7% 13% 7% 4 5% 3 5% 6% 22%	3886
April	1st to 10th	Day	8% 15% 4 10% 7% 5% 6% 5% 6% 9% 26%	2327
	11th to 20th	Day	10% 14% 5% 9% 6% 5% 5% 4 6% 7% 29%	2440
	21st to end	Day	11% 13% 4 8% 6% 6% 6% 4 6% 8% 29%	2470
May	1st to 10th	Day	17% 16% 3 7% 5% 4 4 4 6% 6% 28%	4326
	11th to 20th	Day	10% 9% 4 9% 6% 6% 7% 5% 9% 8% 28%	4694
	21st to end	Day	16% 10% 4 10% 8% 6% 6% 4 6% 7% 23%	5161
June	1st to 10th	Day	16% 7% 3 8% 6% 6% 7% 5% 6% 8% 28%	2850
	11th to 20th	Day	19% 9% 3 8% 7% 6% 6% 4 7% 7% 25%	2850
	21st to end	Day	9% 5% 2 6% 4 6% 6% 5% 8% 9% 41%	2850
July	1st to 10th	Day	7% 4 2 6% 4 5% 6% 5% 6% 9% 47%	4740
	11th to 20th	Day	7% 3 1 4 3 4 5% 5% 7% 10% 50%	4740
	21st to end	Day	3 3 1 4 4 3 4 4 6% 10% 56%	5015
August	1st to 10th	Day	9% 6% 2 6% 4 4 6% 5% 8% 8% 42%	4401
	11th to 20th	Day	6% 5% 2 5% 4 4 5% 5% 8% 11% 44%	4070
	21st to end	Day	9% 4 1 4 3 3 4 3 6% 8% 52%	4521
September	1st to 10th	Day	10% 6% 2 6% 4 3 3 4 4 8% 49%	2356
	11th to 20th	Day	14% 8% 2 5% 4 3 4 3 5% 8% 43%	2090
	21st to end	Day	8% 8% 3 7% 5% 4 5% 3 6% 8% 43%	2090
October	1st to 10th	Day	7% 7% 3 7% 4 4 5% 4 7% 9% 43%	3348
	11th to 20th	Day	5% 7% 3 7% 4 4 5% 5% 8% 10% 42%	2908
	21st to end	Day	7% 7% 3 7% 5% 5% 5% 4 6% 7% 45%	3101
November	1st to 10th	Day	8% 14% 5% 9% 7% 3 5% 4 5% 8% 33%	1639
	11th to 20th	Day	5% 12% 3 8% 5% 6% 5% 4 6% 8% 38%	1519
	21st to end	Day	4 13% 4 9% 6% 4 4 5% 6% 10% 35%	1400
December	1st to 10th	Day	4 11% 5% 11% 8% 5% 5% 5% 6% 7% 34%	1337
	11th to 20th	Day	3 10% 5% 13% 7% 6% 6% 5% 7% 7% 30%	1682
	21st to end	Day	3 9% 3 9% 5% 4 5% 4 6% 9% 43%	2442
January	1st to 10th	Night	3 12% 5% 12% 7% 7% 6% 5% 7% 9% 26%	4726
	11th to 20th	Night	3 7% 5% 15% 5% 5% 7% 6% 7% 8% 33%	4670
	21st to end	Night	4 10% 4 10% 6% 5% 5% 4 7% 9% 37%	4862
February	1st to 10th	Night	4 11% 4 11% 7% 6% 6% 5% 7% 7% 32%	2660
	11th to 20th	Night	5% 11% 5% 10% 6% 6% 6% 5% 7% 8% 30%	2417
	21st to end	Night	2 10% 5% 13% 7% 6% 6% 4 6% 7% 33%	1919
March	1st to 10th	Night	2 8% 4 15% 8% 8% 7% 6% 7% 8% 28%	3736
	11th to 20th	Night	5% 8% 2 6% 5% 4 5% 4 6% 10% 45%	3531
	21st to end	Night	9% 20% 7% 14% 6% 4 4 4 5% 6% 20%	3753
April	1st to 10th	Night	9% 15% 3 10% 6% 5% 6% 4 6% 8% 29%	1852
	11th to 20th	Night	11% 13% 4 11% 6% 4 5% 5% 6% 7% 30%	1691
	21st to end	Night	10% 11% 3 10% 5% 4 6% 4 6% 7% 32%	1710
May	1st to 10th	Night	18% 12% 3 9% 5% 4 4 4 5% 6% 30%	2622
	11th to 20th	Night	9% 9% 4 8% 5% 4 5% 5% 7% 10% 34%	2199
	21st to end	Night	14% 10% 4 10% 6% 7% 6% 5% 7% 7% 26%	2414
June	1st to 10th	Night	15% 9% 3 8% 5% 4 4 5% 6% 7% 33%	1330
	11th to 20th	Night	18% 8% 3 6% 5% 5% 6% 4 6% 9% 30%	1330
	21st to end	Night	7% 4 2 6% 5% 6% 6% 4 9% 9% 41%	1330
July	1st to 10th	Night	7% 4 2 7% 5% 5% 5% 4 7% 6% 49%	2220
	11th to 20th	Night	6% 4 1 5% 4 4 4 5% 8% 11% 48%	2220
	21st to end	Night	4 4 1 4 3 4 4 3 6% 7% 59%	2534
August	1st to 10th	Night	9% 6% 3 7% 5% 4 4 5% 7% 9% 42%	2529
	11th to 20th	Night	6% 4 2 6% 4 5% 5% 5% 7% 11% 45%	2767
	21st to end	Night	8% 4 2 4 3 4 4 4 5% 9% 53%	3146
September	1st to 10th	Night	10% 6% 2 6% 3 4 3 5% 6% 8% 48%	1821
	11th to 20th	Night	13% 7% 3 4 3 3 4 3 5% 8% 47%	2090
	21st to end	Night	9% 7% 2 6% 3 4 4 4 6% 9% 46%	2090
October	1st to 10th	Night	8% 6% 2 6% 4 4 5% 4 6% 8% 48%	3614
	11th to 20th	Night	5% 7% 2 6% 4 4 5% 4 6% 8% 48%	4019
	21st to end	Night	5% 8% 4 7% 5% 5% 5% 4 6% 7% 44%	4457
November	1st to 10th	Night	7% 14% 4 8% 4 5% 5% 5% 6% 7% 36%	2637
	11th to 20th	Night	3 11% 4 8% 6% 5% 6% 4 7% 7% 38%	2880
	21st to end	Night	4 11% 4 9% 6% 6% 5% 4 6% 9% 36%	3000
December	1st to 10th	Night	4 11% 4 10% 7% 6% 5% 5% 6% 7% 34%	2878
	11th to 20th	Night	2 9% 5% 12% 8% 6% 5% 5% 7% 10% 32%	3510
	21st to end	Night	3 9% 3 9% 5% 5% 6% 5% 6% 7% 43%	5214

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	42% 7% 14% 25% 10% 3	2219
	11th to 20th	Day	44% 7% 11% 17% 18% 4	2266
	21st to end	Day	38% 8% 16% 29% 9% 1	2794
February	1st to 10th	Day	50% 7% 16% 15% 9% 2	1520
	11th to 20th	Day	48% 9% 14% 19% 9% 1	1659
	21st to end	Day	48% 7% 14% 18% 11% 1	1532
March	1st to 10th	Day	47% 7% 17% 15% 12% 1	3138
	11th to 20th	Day	34% 7% 18% 27% 12% 1	3448
	21st to end	Day	59% 8% 13% 14% 5%	3886
April	1st to 10th	Day	51% 9% 16% 17% 8%	2327
	11th to 20th	Day	51% 7% 13% 19% 9% 1	2440
	21st to end	Day	50% 8% 15% 19% 8% 1	2470
May	1st to 10th	Day	55% 7% 11% 23% 4	4326
	11th to 20th	Day	43% 10% 16% 22% 9%	4698
	21st to end	Day	55% 9% 14% 15% 6% 1	5162
June	1st to 10th	Day	49% 9% 15% 16% 8% 1	2850
	11th to 20th	Day	53% 9% 14% 16% 6% 2	2850
	21st to end	Day	34% 10% 19% 24% 10% 2	2850
July	1st to 10th	Day	31% 8% 16% 26% 16% 4	4666
	11th to 20th	Day	27% 8% 19% 34% 11% 1	4659
	21st to end	Day	21% 7% 13% 29% 23% 7%	4856
August	1st to 10th	Day	34% 9% 16% 34% 6% 1	4384
	11th to 20th	Day	30% 8% 27% 28% 6% 1	4109
	21st to end	Day	29% 6% 20% 33% 11% 1	4520
September	1st to 10th	Day	33% 7% 16% 26% 14% 5%	2356
	11th to 20th	Day	40% 6% 15% 26% 12% 2	2090
	21st to end	Day	37% 7% 15% 27% 12% 3	2090
October	1st to 10th	Day	36% 6% 18% 33% 6% 1	3348
	11th to 20th	Day	35% 6% 21% 23% 12% 3	2908
	21st to end	Day	38% 5% 12% 33% 12% 1	3101
November	1st to 10th	Day	50% 6% 12% 20% 10% 1	1639
	11th to 20th	Day	43% 6% 15% 24% 10% 2	1519
	21st to end	Day	43% 6% 17% 22% 9% 2	1400
December	1st to 10th	Day	48% 7% 13% 17% 12% 3	1337
	11th to 20th	Day	49% 8% 16% 18% 8% 1	1684
	21st to end	Day	36% 7% 12% 22% 18% 5%	2442
January	1st to 10th	Night	49% 10% 13% 20% 7% 2	4726
	11th to 20th	Night	46% 7% 12% 16% 14% 5%	4711
	21st to end	Night	41% 8% 14% 25% 11% 1	4862
February	1st to 10th	Night	48% 7% 13% 19% 11% 2	2660
	11th to 20th	Night	48% 7% 14% 18% 11% 1	2418
	21st to end	Night	47% 6% 12% 21% 12% 2	1919
March	1st to 10th	Night	48% 9% 13% 21% 8% 1	3736
	11th to 20th	Night	32% 9% 20% 22% 15% 1	3531
	21st to end	Night	63% 7% 12% 13% 4 1	3753
April	1st to 10th	Night	51% 6% 13% 18% 10% 1	1852
	11th to 20th	Night	51% 8% 12% 19% 9% 1	1691
	21st to end	Night	48% 8% 15% 20% 8% 2	1710
May	1st to 10th	Night	53% 7% 12% 21% 6%	2622
	11th to 20th	Night	37% 12% 15% 28% 8% 1	2199
	21st to end	Night	51% 11% 14% 17% 6% 1	2414
June	1st to 10th	Night	47% 10% 14% 19% 10% 1	1330
	11th to 20th	Night	48% 9% 17% 16% 7% 3	1330
	21st to end	Night	34% 10% 22% 25% 8% 1	1330
July	1st to 10th	Night	33% 8% 17% 23% 18% 2	2185
	11th to 20th	Night	26% 10% 21% 31% 8% 4	2178
	21st to end	Night	23% 6% 12% 32% 22% 5%	2454
August	1st to 10th	Night	35% 8% 14% 30% 12% 1	2521
	11th to 20th	Night	31% 9% 26% 25% 8% 1	2794
	21st to end	Night	27% 7% 21% 32% 11% 2	3146
September	1st to 10th	Night	32% 8% 16% 24% 15% 5%	1821
	11th to 20th	Night	35% 6% 16% 26% 12% 4	2090
	21st to end	Night	33% 6% 18% 25% 14% 4	2090
October	1st to 10th	Night	33% 6% 17% 25% 18% 1	3614
	11th to 20th	Night	34% 6% 18% 26% 15% 2	4019
	21st to end	Night	37% 6% 12% 32% 13%	4457
November	1st to 10th	Night	46% 8% 12% 20% 11% 2	2637
	11th to 20th	Night	41% 8% 17% 19% 14% 1	2880
	21st to end	Night	42% 7% 17% 21% 10% 3	3000
December	1st to 10th	Night	47% 7% 13% 20% 10% 3	2878
	11th to 20th	Night	44% 9% 18% 21% 7% 1	3507
	21st to end	Night	37% 7% 13% 24% 14% 5%	5214

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	7% 9% 28% 34% 11% 11%	180
	11th to 20th	Day	7% 12% 35% 24% 19% 3	180
	21st to end	Day	7% 7% 29% 38% 15% 4	198
February	1st to 10th	Day	9% 12% 36% 27% 11% 5%	180
	11th to 20th	Day	9% 8% 37% 34% 11% 2	263
	21st to end	Day	8% 8% 33% 35% 15% 2	344
March	1st to 10th	Day	8% 11% 38% 28% 10% 4	460
	11th to 20th	Day	10% 13% 30% 32% 13% 3	460
	21st to end	Day	13% 16% 33% 22% 11% 4	506
April	1st to 10th	Day	14% 15% 37% 23% 9% 1	460
	11th to 20th	Day	16% 11% 30% 29% 12% 3	452
	21st to end	Day	20% 15% 27% 26% 11% 2	460
May	1st to 10th	Day	18% 11% 26% 27% 14% 3	498
	11th to 20th	Day	16% 6% 26% 28% 20% 4	675
	21st to end	Day	19% 6% 21% 29% 20% 5%	734
June	1st to 10th	Day	17% 9% 28% 29% 14% 3	680
	11th to 20th	Day	21% 10% 27% 28% 12% 3	680
	21st to end	Day	10% 6% 26% 32% 20% 5%	680
July	1st to 10th	Day	10% 5% 25% 33% 23% 5%	671
	11th to 20th	Day	11% 4 27% 32% 21% 4	668
	21st to end	Day	5% 5% 28% 36% 20% 7%	665
August	1st to 10th	Day	11% 5% 26% 32% 20% 6%	487
	11th to 20th	Day	9% 4 22% 37% 22% 6%	477
	21st to end	Day	12% 7% 23% 29% 20% 9%	539
September	1st to 10th	Day	10% 8% 30% 29% 17% 6%	490
	11th to 20th	Day	20% 6% 25% 29% 15% 5%	490
	21st to end	Day	13% 15% 28% 30% 11% 3	490
October	1st to 10th	Day	15% 8% 29% 29% 15% 4	413
	11th to 20th	Day	11% 11% 34% 28% 13% 3	300
	21st to end	Day	16% 13% 35% 23% 10% 3	330
November	1st to 10th	Day	16% 12% 31% 30% 8% 3	300
	11th to 20th	Day	14% 13% 38% 25% 9% 2	259
	21st to end	Day	9% 8% 37% 25% 15% 7%	200
December	1st to 10th	Day	7% 5% 40% 32% 13% 3	182
	11th to 20th	Day	7% 9% 41% 27% 13% 3	180
	21st to end	Day	10% 6% 28% 35% 18% 4	198
January	1st to 10th	Night	8% 10% 36% 34% 10% 2	950
	11th to 20th	Night	7% 8% 39% 35% 9% 1	934
	21st to end	Night	10% 11% 36% 34% 9% 1	836
February	1st to 10th	Night	8% 10% 33% 32% 14% 4	760
	11th to 20th	Night	9% 7% 34% 37% 11% 1	744
	21st to end	Night	6% 8% 33% 32% 18% 4	628
March	1st to 10th	Night	8% 5% 37% 34% 13% 3	760
	11th to 20th	Night	8% 7% 36% 35% 11% 2	760
	21st to end	Night	13% 6% 31% 34% 13% 3	836
April	1st to 10th	Night	13% 9% 31% 31% 15% 1	712
	11th to 20th	Night	17% 5% 35% 32% 10%	563
	21st to end	Night	15% 9% 31% 34% 11%	570
May	1st to 10th	Night	17% 8% 28% 30% 16%	473
	11th to 20th	Night	13% 8% 24% 39% 16%	374
	21st to end	Night	19% 5% 23% 33% 18% 1	411
June	1st to 10th	Night	18% 8% 28% 31% 14% 1	380
	11th to 20th	Night	20% 4 28% 33% 15% 1	380
	21st to end	Night	9% 4 20% 46% 19% 2	380
July	1st to 10th	Night	8% 2 20% 44% 25% 1	370
	11th to 20th	Night	10% 2 23% 43% 19% 2	368
	21st to end	Night	6% 2 21% 46% 22% 2	416
August	1st to 10th	Night	13% 2 13% 41% 28% 3	378
	11th to 20th	Night	9% 2 19% 45% 24% 2	532
	21st to end	Night	10% 4 22% 41% 23%	627
September	1st to 10th	Night	13% 3 26% 36% 20% 2	671
	11th to 20th	Night	17% 4 20% 38% 18% 3	760
	21st to end	Night	12% 6% 32% 33% 14% 2	760
October	1st to 10th	Night	15% 4 29% 35% 15% 2	760
	11th to 20th	Night	12% 5% 34% 33% 14% 2	760
	21st to end	Night	11% 7% 34% 36% 11% 1	836
November	1st to 10th	Night	15% 8% 39% 29% 9% 1	882
	11th to 20th	Night	8% 11% 43% 29% 8% 1	1000
	21st to end	Night	8% 8% 41% 33% 9% 2	1000
December	1st to 10th	Night	10% 7% 38% 31% 13% 2	960
	11th to 20th	Night	5% 7% 40% 38% 8% 2	950
	21st to end	Night	8% 6% 38% 35% 11% 2	1045

Page generated at 2024-11-29 08:43:09. Version ac07

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