Alberta Star Party
Clear Sky Chart
History

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

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	9% 9% 3 8% 5% 5% 5% 4 6% 8% 37%	101911
	Night	7% 9% 4 10% 6% 5% 6% 5% 7% 8% 33%	97145
Transparency	Day	43% 8% 16% 23% 9% 1	101652
	Night	45% 8% 15% 22% 9% 1	97050
Seeing	Day	12% 7% 23% 31% 20% 6%	15442
	Night	12% 5% 25% 38% 17% 2	24474

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	4 12% 5% 14% 7% 6% 7% 5% 7% 8% 25%	2219
	11th to 20th	Day	4 10% 4 11% 5% 7% 6% 9% 10% 7% 27%	2199
	21st to end	Day	5% 9% 4 11% 7% 6% 5% 6% 9% 9% 30%	2707
February	1st to 10th	Day	8% 14% 4 11% 7% 8% 4 4 6% 9% 25%	1539
	11th to 20th	Day	6% 14% 6% 11% 8% 6% 6% 5% 7% 8% 25%	1665
	21st to end	Day	3 13% 5% 14% 9% 8% 6% 5% 6% 7% 24%	1471
March	1st to 10th	Day	4 13% 6% 14% 9% 7% 7% 4 6% 6% 24%	3157
	11th to 20th	Day	7% 10% 3 8% 5% 4 5% 4 7% 9% 38%	3489
	21st to end	Day	9% 19% 7% 16% 6% 4 4 3 5% 6% 21%	3825
April	1st to 10th	Day	9% 12% 4 10% 6% 5% 5% 4 6% 8% 32%	2364
	11th to 20th	Day	12% 11% 4 8% 5% 5% 5% 5% 7% 8% 30%	2440
	21st to end	Day	14% 9% 3 9% 6% 6% 5% 3 6% 8% 31%	2470
May	1st to 10th	Day	19% 12% 4 6% 5% 4 5% 4 5% 7% 28%	4407
	11th to 20th	Day	10% 9% 3 8% 6% 5% 6% 5% 7% 8% 33%	4694
	21st to end	Day	15% 8% 3 9% 6% 6% 6% 5% 6% 7% 29%	5161
June	1st to 10th	Day	15% 6% 2 7% 5% 5% 5% 5% 8% 9% 33%	2850
	11th to 20th	Day	18% 8% 3 7% 5% 6% 6% 4 7% 8% 28%	2850
	21st to end	Day	8% 4 2 5% 5% 5% 5% 5% 7% 10% 43%	2850
July	1st to 10th	Day	7% 4 2 5% 4 4 5% 4 7% 9% 50%	4740
	11th to 20th	Day	7% 4 1 5% 3 4 5% 4 6% 10% 50%	4740
	21st to end	Day	4 4 1 5% 4 4 4 3 6% 9% 57%	5138
August	1st to 10th	Day	7% 6% 2 6% 5% 5% 5% 4 7% 8% 43%	4417
	11th to 20th	Day	7% 4 2 5% 5% 5% 5% 5% 7% 11% 44%	4033
	21st to end	Day	10% 4 2 5% 3 3 3 4 6% 8% 51%	4521
September	1st to 10th	Day	11% 5% 2 6% 4 4 5% 4 5% 7% 47%	2384
	11th to 20th	Day	15% 7% 2 5% 4 4 4 2 6% 7% 43%	2090
	21st to end	Day	8% 8% 2 6% 4 4 4 4 6% 8% 47%	2090
October	1st to 10th	Day	12% 10% 3 7% 4 5% 4 3 5% 7% 40%	1969
	11th to 20th	Day	8% 7% 4 9% 5% 5% 5% 3 6% 8% 40%	1796
	21st to end	Day	7% 12% 4 9% 6% 6% 5% 5% 6% 7% 34%	1881
November	1st to 10th	Day	10% 17% 5% 10% 6% 5% 5% 3 6% 8% 24%	1501
	11th to 20th	Day	7% 12% 5% 10% 7% 6% 5% 4 6% 7% 31%	1470
	21st to end	Day	6% 13% 4 10% 8% 5% 5% 4 6% 8% 31%	1330
December	1st to 10th	Day	8% 12% 6% 11% 8% 8% 6% 4 5% 7% 25%	1330
	11th to 20th	Day	3 12% 6% 15% 8% 7% 6% 5% 8% 7% 23%	1682
	21st to end	Day	4 9% 4 9% 5% 4 5% 4 6% 8% 42%	2442
January	1st to 10th	Night	4 13% 5% 12% 7% 6% 7% 6% 8% 10% 21%	4726
	11th to 20th	Night	4 9% 4 13% 8% 7% 6% 6% 7% 8% 28%	4699
	21st to end	Night	4 11% 4 11% 7% 5% 6% 5% 8% 9% 29%	4976
February	1st to 10th	Night	6% 13% 4 13% 7% 6% 6% 4 6% 8% 28%	2641
	11th to 20th	Night	5% 12% 5% 13% 7% 6% 6% 5% 7% 7% 25%	2402
	21st to end	Night	4 10% 5% 11% 7% 6% 6% 5% 6% 10% 31%	1979
March	1st to 10th	Night	3 9% 5% 15% 10% 7% 6% 5% 6% 7% 26%	3717
	11th to 20th	Night	7% 9% 3 8% 6% 5% 7% 5% 8% 7% 35%	3490
	21st to end	Night	7% 17% 7% 18% 7% 5% 6% 4 6% 6% 16%	3828
April	1st to 10th	Night	10% 9% 4 9% 6% 6% 6% 5% 7% 8% 30%	1815
	11th to 20th	Night	9% 11% 5% 11% 7% 6% 6% 4 7% 7% 29%	1691
	21st to end	Night	11% 10% 4 10% 5% 5% 6% 4 7% 8% 31%	1710
May	1st to 10th	Night	21% 12% 3 8% 5% 4 5% 4 5% 5% 27%	2557
	11th to 20th	Night	9% 8% 2 8% 7% 6% 6% 5% 8% 9% 33%	2199
	21st to end	Night	16% 11% 5% 10% 6% 6% 5% 4 6% 6% 23%	2414
June	1st to 10th	Night	14% 9% 4 8% 6% 5% 6% 4 7% 7% 30%	1330
	11th to 20th	Night	16% 9% 3 9% 8% 6% 6% 5% 7% 6% 26%	1330
	21st to end	Night	9% 5% 3 7% 5% 5% 5% 5% 6% 8% 42%	1330
July	1st to 10th	Night	8% 4 3 7% 6% 5% 6% 4 7% 9% 43%	2220
	11th to 20th	Night	6% 3 1 5% 5% 5% 5% 5% 9% 13% 43%	2220
	21st to end	Night	5% 4 1 6% 4 4 4 4 7% 10% 51%	2414
August	1st to 10th	Night	9% 6% 2 7% 4 5% 5% 4 5% 9% 44%	2497
	11th to 20th	Night	6% 5% 2 7% 4 5% 6% 5% 8% 11% 42%	2806
	21st to end	Night	8% 5% 2 5% 4 3 4 4 7% 10% 47%	3146
September	1st to 10th	Night	11% 5% 2 5% 4 4 4 4 6% 8% 48%	1793
	11th to 20th	Night	14% 7% 2 6% 4 4 4 3 5% 8% 44%	2090
	21st to end	Night	7% 7% 2 6% 3 4 4 4 6% 10% 47%	2090
October	1st to 10th	Night	11% 8% 3 7% 4 4 4 4 6% 8% 41%	2210
	11th to 20th	Night	8% 8% 3 8% 5% 4 5% 4 7% 7% 40%	2384
	21st to end	Night	7% 9% 3 9% 5% 6% 5% 4 7% 8% 35%	2717
November	1st to 10th	Night	11% 12% 5% 8% 5% 5% 5% 5% 6% 8% 31%	2593
	11th to 20th	Night	5% 9% 4 11% 7% 6% 7% 5% 7% 9% 30%	2707
	21st to end	Night	6% 10% 4 10% 7% 6% 6% 5% 7% 9% 31%	2850
December	1st to 10th	Night	7% 14% 4 11% 7% 6% 5% 4 6% 9% 28%	2850
	11th to 20th	Night	3 11% 4 13% 7% 6% 7% 5% 7% 9% 28%	3510
	21st to end	Night	4 8% 3 9% 6% 5% 5% 4 6% 10% 41%	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	51% 9% 11% 20% 8% 1	2219
	11th to 20th	Day	48% 7% 15% 12% 16% 2	2220
	21st to end	Day	44% 8% 17% 25% 6%	2707
February	1st to 10th	Day	56% 5% 14% 15% 9% 1	1539
	11th to 20th	Day	55% 8% 13% 16% 8% 1	1674
	21st to end	Day	57% 6% 11% 17% 9%	1471
March	1st to 10th	Day	57% 7% 15% 13% 9%	3157
	11th to 20th	Day	40% 8% 18% 22% 12%	3490
	21st to end	Day	61% 8% 11% 16% 4	3825
April	1st to 10th	Day	48% 8% 18% 18% 8% 1	2364
	11th to 20th	Day	49% 8% 14% 21% 8% 1	2440
	21st to end	Day	49% 8% 13% 21% 7% 1	2470
May	1st to 10th	Day	53% 8% 13% 21% 4	4407
	11th to 20th	Day	44% 9% 14% 25% 9%	4698
	21st to end	Day	49% 10% 15% 19% 6% 1	5162
June	1st to 10th	Day	44% 9% 16% 21% 8% 1	2850
	11th to 20th	Day	51% 9% 15% 19% 6% 1	2850
	21st to end	Day	33% 11% 20% 27% 7% 1	2850
July	1st to 10th	Day	29% 8% 17% 28% 16% 2	4666
	11th to 20th	Day	27% 9% 17% 35% 12%	4659
	21st to end	Day	24% 7% 15% 30% 20% 4	4976
August	1st to 10th	Day	35% 9% 17% 30% 8% 1	4399
	11th to 20th	Day	31% 9% 26% 28% 7% 1	4072
	21st to end	Day	30% 7% 23% 30% 9% 1	4520
September	1st to 10th	Day	34% 9% 16% 26% 12% 4	2384
	11th to 20th	Day	41% 5% 15% 29% 9% 1	2090
	21st to end	Day	34% 8% 17% 27% 10% 4	2090
October	1st to 10th	Day	44% 6% 16% 24% 9% 1	1969
	11th to 20th	Day	40% 8% 17% 24% 10% 1	1796
	21st to end	Day	45% 9% 13% 22% 10% 1	1881
November	1st to 10th	Day	57% 6% 13% 17% 6% 1	1501
	11th to 20th	Day	51% 6% 14% 21% 8% 1	1470
	21st to end	Day	50% 7% 16% 19% 8% 1	1330
December	1st to 10th	Day	58% 6% 12% 16% 6% 2	1330
	11th to 20th	Day	54% 10% 14% 19% 3 1	1684
	21st to end	Day	37% 6% 12% 26% 16% 3	2442
January	1st to 10th	Night	52% 10% 12% 19% 5% 1	4726
	11th to 20th	Night	50% 6% 12% 15% 14% 2	4740
	21st to end	Night	45% 9% 15% 23% 8% 1	4976
February	1st to 10th	Night	52% 6% 12% 19% 10%	2641
	11th to 20th	Night	53% 7% 13% 16% 10% 1	2403
	21st to end	Night	47% 6% 14% 21% 11% 1	1979
March	1st to 10th	Night	52% 8% 14% 20% 6%	3717
	11th to 20th	Night	41% 9% 20% 21% 8% 1	3490
	21st to end	Night	64% 9% 11% 11% 4	3828
April	1st to 10th	Night	50% 7% 16% 16% 11% 1	1815
	11th to 20th	Night	51% 7% 12% 21% 8% 1	1691
	21st to end	Night	46% 8% 14% 22% 8% 2	1710
May	1st to 10th	Night	57% 5% 10% 21% 7%	2557
	11th to 20th	Night	41% 10% 14% 25% 10%	2199
	21st to end	Night	57% 11% 11% 16% 4 1	2414
June	1st to 10th	Night	48% 9% 13% 20% 9%	1330
	11th to 20th	Night	53% 10% 14% 15% 7% 1	1330
	21st to end	Night	38% 10% 18% 24% 9% 1	1330
July	1st to 10th	Night	35% 9% 19% 21% 15% 1	2185
	11th to 20th	Night	28% 10% 17% 35% 7% 3	2178
	21st to end	Night	26% 7% 16% 29% 18% 4	2337
August	1st to 10th	Night	36% 9% 15% 30% 10% 1	2490
	11th to 20th	Night	32% 10% 21% 30% 6% 1	2833
	21st to end	Night	29% 7% 22% 32% 8% 2	3146
September	1st to 10th	Night	33% 8% 16% 23% 13% 6%	1793
	11th to 20th	Night	39% 6% 14% 26% 11% 4	2090
	21st to end	Night	32% 7% 16% 28% 15% 2	2090
October	1st to 10th	Night	41% 7% 16% 25% 11% 1	2210
	11th to 20th	Night	41% 7% 16% 24% 10% 2	2384
	21st to end	Night	44% 8% 16% 24% 7% 1	2717
November	1st to 10th	Night	50% 6% 14% 21% 8% 1	2593
	11th to 20th	Night	48% 8% 15% 19% 10% 1	2707
	21st to end	Night	47% 10% 17% 19% 6% 2	2850
December	1st to 10th	Night	53% 7% 11% 20% 8% 1	2850
	11th to 20th	Night	49% 10% 18% 17% 6%	3507
	21st to end	Night	38% 6% 14% 24% 15% 4	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% 4 22% 32% 22% 12%	180
	11th to 20th	Day	9% 4 26% 33% 26% 2	180
	21st to end	Day	12% 8% 22% 30% 21% 7%	198
February	1st to 10th	Day	12% 8% 25% 31% 18% 6%	189
	11th to 20th	Day	11% 6% 25% 34% 19% 5%	270
	21st to end	Day	8% 5% 21% 41% 20% 6%	283
March	1st to 10th	Day	11% 4 31% 31% 19% 5%	460
	11th to 20th	Day	8% 4 25% 35% 21% 6%	460
	21st to end	Day	12% 6% 28% 30% 18% 6%	506
April	1st to 10th	Day	11% 13% 27% 33% 12% 4	460
	11th to 20th	Day	13% 9% 31% 26% 17% 4	452
	21st to end	Day	19% 10% 25% 29% 14% 3	460
May	1st to 10th	Day	16% 10% 21% 27% 20% 6%	572
	11th to 20th	Day	12% 9% 21% 35% 20% 4	675
	21st to end	Day	18% 5% 20% 28% 22% 7%	734
June	1st to 10th	Day	15% 8% 24% 33% 17% 3	680
	11th to 20th	Day	18% 8% 23% 31% 15% 4	680
	21st to end	Day	10% 4 23% 31% 25% 8%	680
July	1st to 10th	Day	10% 5% 17% 34% 26% 8%	671
	11th to 20th	Day	11% 5% 18% 33% 26% 7%	668
	21st to end	Day	6% 4 19% 31% 29% 11%	739
August	1st to 10th	Day	10% 4 21% 34% 21% 10%	503
	11th to 20th	Day	9% 4 19% 31% 28% 8%	477
	21st to end	Day	11% 9% 20% 27% 23% 10%	539
September	1st to 10th	Day	14% 6% 26% 27% 21% 6%	490
	11th to 20th	Day	19% 7% 20% 28% 21% 5%	490
	21st to end	Day	11% 13% 25% 32% 15% 5%	490
October	1st to 10th	Day	17% 7% 22% 28% 19% 7%	369
	11th to 20th	Day	10% 11% 29% 30% 14% 6%	300
	21st to end	Day	14% 11% 30% 29% 13% 2	330
November	1st to 10th	Day	20% 7% 22% 32% 14% 4	273
	11th to 20th	Day	15% 4 28% 35% 15% 3	246
	21st to end	Day	8% 4 28% 32% 17% 11%	180
December	1st to 10th	Day	8% 5% 25% 33% 21% 9%	180
	11th to 20th	Day	7% 3 36% 36% 17% 2	180
	21st to end	Day	10% 2 19% 36% 25% 8%	198
January	1st to 10th	Night	10% 6% 27% 38% 16% 2	950
	11th to 20th	Night	12% 5% 27% 39% 15% 2	950
	21st to end	Night	12% 7% 24% 40% 14% 2	898
February	1st to 10th	Night	11% 7% 23% 37% 19% 3	760
	11th to 20th	Night	12% 5% 28% 36% 18% 1	744
	21st to end	Night	8% 3 20% 42% 21% 6%	628
March	1st to 10th	Night	8% 5% 25% 40% 18% 4	760
	11th to 20th	Night	9% 5% 24% 41% 18% 3	760
	21st to end	Night	15% 5% 24% 36% 18% 2	836
April	1st to 10th	Night	13% 6% 28% 33% 17% 3	665
	11th to 20th	Night	13% 8% 30% 36% 12% 1	563
	21st to end	Night	16% 8% 25% 37% 14% 1	570
May	1st to 10th	Night	17% 9% 23% 35% 14% 1	507
	11th to 20th	Night	11% 6% 27% 37% 17% 2	374
	21st to end	Night	22% 5% 23% 31% 18% 2	411
June	1st to 10th	Night	19% 7% 25% 36% 12% 1	380
	11th to 20th	Night	17% 5% 27% 32% 18% 1	380
	21st to end	Night	11% 4 23% 36% 23% 2	380
July	1st to 10th	Night	10% 2 18% 44% 24% 2	370
	11th to 20th	Night	11% 2 20% 45% 21% 2	368
	21st to end	Night	6% 2 22% 40% 27% 3	416
August	1st to 10th	Night	12% 3 19% 38% 26% 2	378
	11th to 20th	Night	8% 5% 16% 45% 25% 1	559
	21st to end	Night	9% 5% 19% 42% 25%	627
September	1st to 10th	Night	13% 3 20% 41% 20% 2	608
	11th to 20th	Night	16% 4 18% 40% 21% 1	760
	21st to end	Night	11% 5% 27% 40% 16% 2	760
October	1st to 10th	Night	13% 5% 24% 37% 18% 2	760
	11th to 20th	Night	13% 5% 27% 38% 14% 2	760
	21st to end	Night	11% 7% 29% 39% 13% 1	836
November	1st to 10th	Night	16% 7% 29% 35% 12% 1	911
	11th to 20th	Night	9% 7% 36% 34% 12% 2	950
	21st to end	Night	10% 5% 28% 41% 14% 1	950
December	1st to 10th	Night	12% 8% 25% 36% 16% 3	950
	11th to 20th	Night	9% 4 31% 39% 13% 2	950
	21st to end	Night	11% 5% 26% 38% 17% 3	1045

Page generated at 2024-10-30 11:19:25. Version ac07

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