Syzygy Observatory, Alberta
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Syzygy Observatory, Alberta clear sky chart from 2005-11-06 to 2026-03-03.

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% 5% 5% 4 7% 8% 35%	135729
	Night	8% 10% 4 10% 6% 5% 5% 4 6% 8% 33%	134126
Transparency	Day	44% 7% 18% 23% 8%	135425
	Night	47% 7% 16% 21% 9% 1	134011
Seeing	Day	12% 6% 24% 31% 20% 7%	17574
	Night	13% 6% 27% 36% 16% 2	26225

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	8% 15% 6% 10% 8% 5% 5% 5% 8% 7% 23%	4125
	11th to 20th	Day	3 8% 3 10% 8% 5% 5% 6% 7% 10% 35%	4119
	21st to end	Day	6% 11% 3 9% 6% 4 6% 5% 7% 8% 33%	4828
February	1st to 10th	Day	7% 13% 5% 11% 7% 6% 7% 5% 8% 8% 23%	1680
	11th to 20th	Day	5% 13% 5% 12% 6% 5% 8% 5% 8% 6% 28%	1772
	21st to end	Day	4 12% 5% 11% 9% 7% 6% 4 6% 7% 29%	1609
March	1st to 10th	Day	5% 8% 5% 11% 7% 7% 6% 4 7% 11% 28%	4539
	11th to 20th	Day	5% 12% 5% 11% 6% 5% 5% 4 6% 9% 33%	4946
	21st to end	Day	8% 14% 5% 15% 6% 5% 4 4 6% 9% 24%	5573
April	1st to 10th	Day	7% 12% 3 9% 6% 5% 6% 5% 7% 8% 32%	2502
	11th to 20th	Day	8% 11% 3 8% 6% 5% 5% 4 7% 8% 33%	2570
	21st to end	Day	10% 9% 3 8% 6% 5% 7% 5% 6% 8% 33%	2600
May	1st to 10th	Day	12% 7% 3 7% 5% 5% 5% 4 6% 7% 38%	6714
	11th to 20th	Day	13% 11% 3 9% 5% 5% 5% 5% 7% 9% 27%	6734
	21st to end	Day	10% 7% 2 7% 6% 5% 6% 4 6% 8% 39%	7405
June	1st to 10th	Day	14% 8% 3 8% 6% 5% 5% 5% 6% 7% 33%	3000
	11th to 20th	Day	18% 9% 3 8% 6% 6% 5% 5% 6% 7% 25%	3174
	21st to end	Day	9% 6% 2 7% 5% 6% 5% 5% 8% 9% 38%	3200
July	1st to 10th	Day	8% 5% 2 5% 4 5% 5% 5% 7% 10% 44%	7113
	11th to 20th	Day	9% 5% 2 7% 5% 5% 5% 4 7% 9% 43%	6780
	21st to end	Day	11% 5% 2 5% 5% 4 5% 4 7% 9% 43%	7376
August	1st to 10th	Day	11% 7% 2 6% 5% 4 5% 4 7% 9% 41%	4685
	11th to 20th	Day	9% 6% 2 6% 4 5% 5% 4 8% 10% 43%	4313
	21st to end	Day	10% 5% 2 7% 5% 4 5% 4 6% 9% 43%	4664
September	1st to 10th	Day	11% 6% 3 7% 4 4 5% 4 6% 8% 43%	2550
	11th to 20th	Day	13% 6% 1 6% 5% 4 5% 4 6% 9% 41%	2200
	21st to end	Day	9% 7% 2 6% 5% 5% 5% 4 6% 8% 43%	2200
October	1st to 10th	Day	9% 9% 3 8% 5% 5% 5% 4 6% 8% 38%	3402
	11th to 20th	Day	11% 10% 3 8% 5% 5% 4 3 6% 8% 36%	2964
	21st to end	Day	7% 10% 6% 8% 5% 6% 5% 4 5% 7% 36%	3141
November	1st to 10th	Day	10% 14% 4 10% 7% 6% 6% 4 5% 7% 28%	1648
	11th to 20th	Day	7% 12% 5% 12% 6% 6% 5% 4 6% 8% 30%	1486
	21st to end	Day	4 13% 6% 12% 7% 7% 5% 5% 6% 7% 29%	1470
December	1st to 10th	Day	9% 16% 4 12% 7% 7% 6% 4 7% 7% 22%	2360
	11th to 20th	Day	9% 13% 3 12% 7% 7% 7% 5% 8% 8% 21%	2712
	21st to end	Day	4 7% 3 9% 7% 6% 6% 5% 7% 8% 38%	3575
January	1st to 10th	Night	7% 12% 5% 14% 9% 7% 7% 4 5% 7% 23%	8768
	11th to 20th	Night	3 8% 3 10% 7% 5% 5% 4 6% 8% 41%	8779
	21st to end	Night	7% 12% 4 10% 7% 5% 6% 4 6% 8% 31%	9411
February	1st to 10th	Night	6% 10% 5% 13% 8% 7% 6% 5% 7% 7% 26%	2940
	11th to 20th	Night	5% 12% 4 11% 6% 7% 7% 5% 7% 8% 29%	2735
	21st to end	Night	4 10% 6% 10% 7% 6% 7% 6% 7% 8% 29%	2196
March	1st to 10th	Night	3 8% 4 11% 7% 6% 5% 5% 7% 11% 32%	5400
	11th to 20th	Night	5% 9% 4 12% 7% 6% 6% 4 7% 9% 30%	5053
	21st to end	Night	10% 14% 6% 14% 7% 5% 4 4 5% 6% 25%	5388
April	1st to 10th	Night	7% 10% 4 9% 7% 7% 6% 6% 7% 6% 32%	1897
	11th to 20th	Night	9% 11% 4 10% 7% 5% 5% 4 7% 7% 30%	1781
	21st to end	Night	11% 9% 3 8% 5% 5% 5% 4 6% 9% 35%	1800
May	1st to 10th	Night	15% 7% 3 7% 4 4 5% 3 6% 6% 39%	3245
	11th to 20th	Night	14% 10% 3 10% 6% 7% 6% 5% 6% 6% 27%	3159
	21st to end	Night	11% 8% 3 7% 5% 5% 4 4 7% 9% 36%	3470
June	1st to 10th	Night	15% 8% 3 7% 5% 5% 5% 5% 7% 8% 31%	1400
	11th to 20th	Night	15% 10% 3 8% 6% 5% 7% 7% 9% 8% 21%	1221
	21st to end	Night	8% 7% 3 7% 7% 5% 6% 6% 7% 9% 37%	1200
July	1st to 10th	Night	8% 5% 2 6% 5% 4 5% 4 7% 9% 45%	2830
	11th to 20th	Night	10% 6% 3 7% 5% 5% 5% 5% 6% 10% 38%	3180
	21st to end	Night	12% 7% 2 5% 4 4 5% 4 6% 8% 43%	3467
August	1st to 10th	Night	11% 6% 2 8% 5% 4 4 4 6% 7% 41%	2462
	11th to 20th	Night	11% 7% 3 8% 4 5% 5% 4 6% 9% 37%	2739
	21st to end	Night	12% 5% 2 5% 4 4 4 4 6% 9% 46%	3245
September	1st to 10th	Night	12% 5% 3 6% 4 4 3 4 6% 9% 45%	1847
	11th to 20th	Night	12% 7% 2 5% 4 4 4 3 6% 8% 46%	2200
	21st to end	Night	9% 8% 2 7% 4 5% 4 4 5% 7% 45%	2200
October	1st to 10th	Night	7% 7% 3 9% 5% 6% 6% 4 7% 8% 38%	3792
	11th to 20th	Night	9% 8% 3 7% 5% 4 5% 4 7% 9% 39%	4182
	21st to end	Night	7% 9% 3 8% 5% 5% 6% 5% 7% 9% 35%	4627
November	1st to 10th	Night	13% 15% 5% 10% 6% 5% 5% 3 6% 6% 27%	2870
	11th to 20th	Night	7% 13% 5% 11% 8% 5% 6% 4 6% 7% 28%	3129
	21st to end	Night	5% 12% 6% 13% 8% 5% 6% 5% 6% 7% 28%	3150
December	1st to 10th	Night	9% 16% 5% 12% 7% 5% 5% 3 6% 7% 24%	5040
	11th to 20th	Night	9% 15% 5% 12% 6% 7% 6% 5% 7% 7% 20%	5700
	21st to end	Night	3 7% 3 10% 6% 5% 6% 5% 7% 8% 40%	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	57% 6% 10% 15% 12%	4125
	11th to 20th	Day	42% 6% 17% 16% 18% 1	4140
	21st to end	Day	46% 7% 22% 20% 5%	4829
February	1st to 10th	Day	55% 6% 15% 15% 9%	1680
	11th to 20th	Day	50% 9% 16% 16% 9%	1780
	21st to end	Day	51% 8% 13% 21% 7%	1609
March	1st to 10th	Day	48% 6% 16% 21% 9%	4539
	11th to 20th	Day	46% 7% 16% 22% 8%	4947
	21st to end	Day	55% 7% 11% 21% 6%	5573
April	1st to 10th	Day	45% 10% 17% 19% 8% 1	2502
	11th to 20th	Day	45% 7% 15% 23% 9% 1	2570
	21st to end	Day	46% 8% 16% 22% 6% 1	2600
May	1st to 10th	Day	44% 5% 10% 25% 15% 1	6714
	11th to 20th	Day	50% 8% 12% 24% 6%	6738
	21st to end	Day	38% 9% 20% 22% 9% 1	7406
June	1st to 10th	Day	47% 8% 15% 21% 8% 1	3000
	11th to 20th	Day	55% 9% 16% 16% 5%	3174
	21st to end	Day	40% 9% 23% 22% 6% 1	3200
July	1st to 10th	Day	33% 8% 21% 28% 10%	7036
	11th to 20th	Day	37% 7% 16% 29% 10%	6699
	21st to end	Day	36% 7% 23% 27% 7%	7169
August	1st to 10th	Day	37% 9% 22% 30% 2	4667
	11th to 20th	Day	34% 9% 24% 25% 9%	4355
	21st to end	Day	36% 7% 27% 25% 5%	4663
September	1st to 10th	Day	38% 8% 19% 26% 7% 2	2550
	11th to 20th	Day	38% 7% 20% 27% 8%	2200
	21st to end	Day	37% 8% 18% 27% 8% 2	2200
October	1st to 10th	Day	44% 5% 23% 22% 5%	3402
	11th to 20th	Day	46% 5% 15% 26% 8%	2964
	21st to end	Day	46% 6% 17% 27% 3	3141
November	1st to 10th	Day	54% 7% 16% 16% 6% 1	1648
	11th to 20th	Day	50% 7% 17% 20% 6%	1486
	21st to end	Day	53% 8% 15% 18% 6% 1	1470
December	1st to 10th	Day	60% 6% 18% 12% 4 1	2360
	11th to 20th	Day	57% 7% 18% 13% 4	2714
	21st to end	Day	40% 7% 14% 29% 10% 1	3575
January	1st to 10th	Night	60% 5% 10% 13% 11% 1	8769
	11th to 20th	Night	41% 5% 17% 19% 17% 2	8820
	21st to end	Night	50% 6% 21% 17% 6%	9411
February	1st to 10th	Night	54% 7% 13% 16% 9% 1	2940
	11th to 20th	Night	50% 8% 14% 16% 11% 1	2737
	21st to end	Night	49% 8% 13% 20% 9% 1	2196
March	1st to 10th	Night	44% 7% 18% 22% 9%	5400
	11th to 20th	Night	46% 7% 16% 20% 10% 1	5053
	21st to end	Night	58% 7% 9% 16% 9%	5388
April	1st to 10th	Night	46% 10% 13% 18% 12% 1	1897
	11th to 20th	Night	49% 6% 11% 19% 12% 2	1781
	21st to end	Night	45% 7% 11% 24% 13% 1	1800
May	1st to 10th	Night	44% 5% 10% 21% 17% 3	3244
	11th to 20th	Night	52% 10% 12% 19% 7%	3159
	21st to end	Night	41% 8% 19% 23% 8% 1	3470
June	1st to 10th	Night	48% 8% 13% 20% 10% 1	1400
	11th to 20th	Night	54% 10% 15% 16% 4	1221
	21st to end	Night	40% 10% 21% 23% 6% 1	1200
July	1st to 10th	Night	35% 7% 21% 21% 15% 1	2798
	11th to 20th	Night	41% 7% 14% 31% 7%	3138
	21st to end	Night	38% 7% 22% 27% 6%	3369
August	1st to 10th	Night	40% 8% 20% 31% 1	2455
	11th to 20th	Night	42% 8% 19% 22% 9%	2763
	21st to end	Night	34% 6% 25% 29% 6%	3245
September	1st to 10th	Night	36% 6% 18% 29% 9% 2	1847
	11th to 20th	Night	36% 6% 17% 30% 11% 1	2200
	21st to end	Night	37% 7% 15% 27% 12% 2	2200
October	1st to 10th	Night	41% 7% 21% 25% 7%	3792
	11th to 20th	Night	40% 5% 14% 33% 7%	4182
	21st to end	Night	42% 8% 22% 23% 5%	4627
November	1st to 10th	Night	58% 5% 11% 19% 6%	2870
	11th to 20th	Night	54% 7% 14% 18% 7%	3129
	21st to end	Night	53% 8% 15% 17% 5% 1	3150
December	1st to 10th	Night	60% 6% 15% 13% 5% 1	5040
	11th to 20th	Night	61% 6% 16% 12% 5%	5697
	21st to end	Night	39% 6% 15% 25% 12% 2	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	11% 9% 24% 34% 18% 5%	220
	11th to 20th	Day	9% 10% 28% 35% 14% 5%	220
	21st to end	Day	12% 9% 30% 30% 13% 5%	242
February	1st to 10th	Day	10% 7% 29% 33% 13% 7%	220
	11th to 20th	Day	11% 5% 31% 31% 16% 6%	292
	21st to end	Day	6% 6% 32% 32% 17% 7%	325
March	1st to 10th	Day	11% 5% 25% 37% 18% 4	509
	11th to 20th	Day	10% 4 21% 37% 21% 7%	500
	21st to end	Day	14% 4 23% 31% 23% 5%	550
April	1st to 10th	Day	8% 6% 27% 35% 20% 4	500
	11th to 20th	Day	12% 8% 23% 32% 18% 8%	492
	21st to end	Day	12% 8% 25% 30% 18% 7%	500
May	1st to 10th	Day	13% 8% 23% 31% 20% 5%	673
	11th to 20th	Day	11% 6% 24% 33% 20% 7%	725
	21st to end	Day	15% 6% 18% 31% 20% 10%	789
June	1st to 10th	Day	16% 8% 26% 29% 18% 3	730
	11th to 20th	Day	20% 5% 21% 27% 21% 7%	904
	21st to end	Day	12% 4 18% 30% 25% 11%	930
July	1st to 10th	Day	11% 4 17% 33% 26% 9%	869
	11th to 20th	Day	12% 5% 20% 28% 26% 9%	718
	21st to end	Day	11% 4 18% 30% 28% 10%	794
August	1st to 10th	Day	12% 5% 18% 27% 25% 14%	619
	11th to 20th	Day	10% 5% 22% 34% 21% 7%	517
	21st to end	Day	9% 8% 21% 28% 23% 11%	583
September	1st to 10th	Day	14% 7% 25% 27% 17% 9%	530
	11th to 20th	Day	16% 8% 20% 30% 21% 6%	530
	21st to end	Day	11% 12% 31% 28% 14% 3	530
October	1st to 10th	Day	13% 10% 27% 27% 19% 4	410
	11th to 20th	Day	13% 8% 29% 31% 16% 2	330
	21st to end	Day	15% 13% 34% 24% 11% 3	363
November	1st to 10th	Day	18% 5% 33% 27% 15% 2	330
	11th to 20th	Day	10% 6% 34% 35% 13% 4	228
	21st to end	Day	7% 9% 33% 30% 13% 7%	220
December	1st to 10th	Day	11% 6% 33% 36% 8% 5%	220
	11th to 20th	Day	10% 7% 27% 37% 15% 3	220
	21st to end	Day	12% 5% 23% 32% 21% 7%	242
January	1st to 10th	Night	11% 6% 32% 35% 14% 2	1050
	11th to 20th	Night	10% 10% 31% 35% 13% 1	1050
	21st to end	Night	14% 11% 33% 29% 12% 2	1071
February	1st to 10th	Night	10% 7% 26% 37% 17% 4	840
	11th to 20th	Night	11% 4 32% 36% 16% 1	824
	21st to end	Night	7% 6% 28% 35% 19% 5%	692
March	1st to 10th	Night	9% 5% 27% 40% 15% 3	808
	11th to 20th	Night	11% 5% 29% 35% 16% 3	800
	21st to end	Night	14% 6% 23% 37% 19% 2	880
April	1st to 10th	Night	11% 5% 24% 38% 18% 3	697
	11th to 20th	Night	14% 5% 27% 38% 15% 2	593
	21st to end	Night	15% 6% 24% 37% 17% 1	600
May	1st to 10th	Night	14% 5% 25% 34% 19% 2	409
	11th to 20th	Night	12% 5% 22% 39% 19% 2	394
	21st to end	Night	19% 6% 20% 34% 20% 2	433
June	1st to 10th	Night	18% 8% 19% 40% 13% 2	400
	11th to 20th	Night	20% 5% 19% 30% 24% 2	400
	21st to end	Night	11% 4 19% 36% 27% 4	400
July	1st to 10th	Night	12% 5% 15% 41% 26% 1	390
	11th to 20th	Night	13% 3 19% 39% 23% 3	388
	21st to end	Night	11% 5% 14% 40% 27% 4	438
August	1st to 10th	Night	9% 5% 15% 34% 32% 5%	398
	11th to 20th	Night	12% 4 18% 38% 26% 3	493
	21st to end	Night	12% 3 20% 39% 24% 2	660
September	1st to 10th	Night	14% 4 19% 38% 23% 2	642
	11th to 20th	Night	14% 4 18% 43% 19% 2	800
	21st to end	Night	14% 6% 29% 38% 12% 2	800
October	1st to 10th	Night	15% 6% 26% 39% 13% 1	800
	11th to 20th	Night	12% 7% 30% 37% 12% 2	800
	21st to end	Night	13% 8% 34% 32% 13%	895
November	1st to 10th	Night	20% 6% 31% 31% 10% 2	1025
	11th to 20th	Night	12% 7% 34% 32% 12% 3	1050
	21st to end	Night	10% 6% 36% 35% 12% 2	1050
December	1st to 10th	Night	13% 9% 33% 30% 13% 3	1050
	11th to 20th	Night	12% 6% 33% 34% 13% 2	1050
	21st to end	Night	11% 5% 27% 37% 17% 4	1155

Page generated at 2026-02-27 23:40:24. Version ac07

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