Swan Hills
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Swan Hills clear sky chart from 2005-11-06 to 2025-03-12.

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% 10% 4 9% 6% 5% 5% 4 6% 8% 33%	111976
	Night	6% 9% 4 10% 6% 6% 6% 5% 7% 8% 34%	115665
Transparency	Day	46% 8% 17% 20% 8% 1	111706
	Night	44% 8% 18% 20% 8% 1	115580
Seeing	Day	18% 17% 31% 22% 10% 3	16623
	Night	14% 16% 31% 27% 12% 2	25184

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% 12% 8% 7% 8% 5% 9% 8% 25%	2719
	11th to 20th	Day	1 9% 4 10% 6% 5% 5% 5% 7% 9% 38%	2913
	21st to end	Day	3 8% 5% 10% 5% 6% 5% 5% 7% 8% 39%	3817
February	1st to 10th	Day	4 9% 3 10% 8% 7% 7% 6% 9% 9% 27%	1600
	11th to 20th	Day	2 10% 4 11% 7% 6% 5% 4 9% 10% 31%	1603
	21st to end	Day	2 11% 5% 12% 9% 5% 5% 5% 8% 11% 27%	1591
March	1st to 10th	Day	2 8% 5% 14% 8% 8% 7% 5% 7% 8% 28%	3238
	11th to 20th	Day	3 12% 4 10% 6% 5% 5% 4 5% 7% 38%	3366
	21st to end	Day	4 15% 6% 21% 10% 5% 5% 4 5% 5% 20%	4023
April	1st to 10th	Day	7% 15% 6% 12% 7% 6% 6% 4 6% 7% 24%	2328
	11th to 20th	Day	8% 14% 5% 9% 6% 5% 5% 5% 7% 8% 28%	2440
	21st to end	Day	12% 15% 4 10% 6% 5% 5% 5% 6% 8% 26%	2560
May	1st to 10th	Day	14% 14% 3 7% 5% 5% 4 4 5% 6% 32%	4630
	11th to 20th	Day	11% 12% 4 9% 6% 6% 5% 5% 6% 7% 27%	4694
	21st to end	Day	13% 10% 4 10% 7% 7% 6% 5% 7% 8% 22%	5182
June	1st to 10th	Day	18% 9% 3 8% 6% 5% 5% 5% 6% 7% 27%	3040
	11th to 20th	Day	21% 11% 4 10% 7% 6% 5% 4 6% 7% 19%	3040
	21st to end	Day	12% 8% 3 9% 7% 6% 6% 5% 6% 8% 31%	3040
July	1st to 10th	Day	9% 6% 2 6% 5% 5% 5% 5% 7% 8% 43%	5060
	11th to 20th	Day	9% 6% 2 6% 5% 4 6% 5% 7% 8% 42%	5010
	21st to end	Day	13% 7% 2 6% 5% 5% 4 4 7% 9% 39%	5138
August	1st to 10th	Day	14% 7% 2 7% 4 4 5% 3 5% 7% 42%	4470
	11th to 20th	Day	13% 6% 2 7% 5% 5% 6% 4 6% 7% 38%	4307
	21st to end	Day	14% 6% 2 7% 5% 5% 6% 4 6% 8% 37%	4521
September	1st to 10th	Day	13% 8% 2 7% 5% 4 5% 4 6% 8% 38%	2361
	11th to 20th	Day	13% 10% 2 6% 4 4 5% 4 6% 7% 37%	2147
	21st to end	Day	10% 8% 4 7% 5% 5% 5% 4 7% 8% 38%	2090
October	1st to 10th	Day	11% 13% 4 9% 5% 5% 5% 3 6% 7% 32%	3263
	11th to 20th	Day	11% 14% 4 9% 5% 4 5% 4 6% 7% 30%	2842
	21st to end	Day	7% 13% 5% 10% 5% 5% 6% 4 6% 8% 30%	3101
November	1st to 10th	Day	7% 14% 4 11% 6% 5% 4 5% 6% 9% 29%	1493
	11th to 20th	Day	5% 9% 5% 11% 6% 5% 5% 5% 7% 10% 33%	1400
	21st to end	Day	3 9% 4 13% 9% 6% 6% 4 6% 8% 33%	1400
December	1st to 10th	Day	5% 12% 5% 13% 7% 6% 6% 4 7% 8% 29%	2290
	11th to 20th	Day	4 11% 5% 9% 6% 7% 7% 5% 8% 8% 29%	2267
	21st to end	Day	2 6% 3 7% 6% 4 5% 4 7% 9% 46%	2992
January	1st to 10th	Night	2 8% 4 13% 8% 7% 7% 5% 7% 8% 30%	7226
	11th to 20th	Night	2 7% 4 10% 6% 6% 6% 5% 7% 8% 39%	6971
	21st to end	Night	3 10% 4 11% 6% 6% 6% 5% 7% 8% 34%	7182
February	1st to 10th	Night	4 10% 4 12% 7% 6% 7% 5% 8% 9% 29%	2800
	11th to 20th	Night	2 8% 4 11% 8% 6% 6% 5% 10% 8% 32%	2683
	21st to end	Night	2 10% 5% 10% 8% 7% 6% 6% 8% 8% 32%	2035
March	1st to 10th	Night	2 7% 5% 14% 8% 6% 7% 5% 8% 9% 28%	3856
	11th to 20th	Night	4 11% 3 7% 5% 5% 5% 5% 7% 8% 39%	3641
	21st to end	Night	5% 14% 7% 20% 9% 6% 5% 3 5% 6% 22%	3626
April	1st to 10th	Night	7% 10% 4 8% 7% 6% 6% 5% 7% 8% 32%	1851
	11th to 20th	Night	10% 13% 4 8% 5% 6% 6% 4 6% 6% 32%	1691
	21st to end	Night	11% 12% 5% 8% 5% 4 6% 5% 6% 8% 30%	1619
May	1st to 10th	Night	12% 14% 4 8% 5% 4 6% 3 5% 7% 33%	2330
	11th to 20th	Night	8% 11% 4 10% 5% 5% 5% 6% 7% 8% 30%	2199
	21st to end	Night	14% 9% 3 8% 5% 5% 6% 4 7% 10% 28%	2392
June	1st to 10th	Night	14% 8% 3 9% 6% 5% 6% 5% 7% 6% 31%	1140
	11th to 20th	Night	17% 11% 3 9% 5% 6% 6% 5% 6% 9% 23%	1140
	21st to end	Night	11% 7% 3 7% 6% 5% 6% 5% 9% 7% 34%	1140
July	1st to 10th	Night	8% 6% 2 5% 4 4 4 3 6% 8% 50%	1900
	11th to 20th	Night	10% 7% 2 6% 6% 4 5% 4 6% 8% 41%	1950
	21st to end	Night	12% 6% 2 6% 4 4 4 5% 7% 9% 40%	2414
August	1st to 10th	Night	13% 6% 2 6% 4 4 4 3 5% 7% 44%	2458
	11th to 20th	Night	16% 8% 3 5% 3 3 4 3 6% 7% 41%	2520
	21st to end	Night	10% 7% 2 7% 5% 5% 5% 4 7% 8% 39%	3146
September	1st to 10th	Night	10% 6% 2 5% 5% 5% 6% 4 6% 7% 43%	1815
	11th to 20th	Night	11% 9% 2 6% 4 4 4 4 5% 7% 43%	2033
	21st to end	Night	8% 9% 3 6% 5% 4 6% 4 6% 8% 41%	2090
October	1st to 10th	Night	6% 11% 4 10% 5% 6% 6% 5% 7% 7% 34%	3711
	11th to 20th	Night	6% 9% 4 8% 5% 5% 5% 5% 7% 9% 37%	4086
	21st to end	Night	7% 8% 4 10% 6% 6% 6% 4 7% 10% 32%	4457
November	1st to 10th	Night	9% 14% 4 11% 5% 5% 5% 4 6% 7% 30%	2786
	11th to 20th	Night	4 12% 5% 11% 8% 6% 6% 5% 7% 7% 28%	3000
	21st to end	Night	5% 12% 5% 10% 6% 7% 6% 5% 6% 7% 31%	3000
December	1st to 10th	Night	5% 12% 4 10% 6% 6% 6% 5% 7% 8% 32%	4890
	11th to 20th	Night	6% 13% 4 12% 7% 7% 7% 4 7% 8% 24%	5923
	21st to end	Night	2 5% 3 8% 6% 5% 6% 5% 7% 9% 46%	7964

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% 8% 14% 14% 12% 1	2719
	11th to 20th	Day	39% 9% 15% 11% 20% 5%	2932
	21st to end	Day	37% 11% 29% 16% 6% 1	3817
February	1st to 10th	Day	48% 10% 17% 13% 12% 1	1600
	11th to 20th	Day	46% 9% 17% 18% 10%	1611
	21st to end	Day	49% 7% 16% 18% 9% 1	1591
March	1st to 10th	Day	50% 7% 16% 20% 7%	3238
	11th to 20th	Day	43% 7% 19% 22% 10%	3367
	21st to end	Day	62% 9% 14% 11% 5%	4023
April	1st to 10th	Day	56% 8% 14% 14% 7%	2328
	11th to 20th	Day	51% 7% 16% 17% 9%	2440
	21st to end	Day	53% 8% 13% 19% 6% 1	2560
May	1st to 10th	Day	50% 7% 11% 20% 11% 1	4630
	11th to 20th	Day	51% 8% 11% 21% 9%	4698
	21st to end	Day	53% 10% 15% 13% 8% 1	5183
June	1st to 10th	Day	53% 8% 15% 17% 6% 1	3040
	11th to 20th	Day	62% 8% 11% 15% 4	3040
	21st to end	Day	48% 9% 18% 18% 7%	3040
July	1st to 10th	Day	35% 8% 17% 27% 12% 1	4981
	11th to 20th	Day	36% 9% 15% 31% 10%	4923
	21st to end	Day	39% 8% 23% 23% 6%	4976
August	1st to 10th	Day	41% 8% 18% 31% 2	4452
	11th to 20th	Day	41% 9% 17% 23% 10%	4349
	21st to end	Day	42% 8% 26% 20% 4	4520
September	1st to 10th	Day	42% 8% 19% 24% 6% 1	2361
	11th to 20th	Day	43% 8% 22% 21% 6%	2147
	21st to end	Day	42% 9% 17% 22% 9% 1	2090
October	1st to 10th	Day	47% 9% 21% 18% 5%	3263
	11th to 20th	Day	49% 8% 17% 22% 4	2842
	21st to end	Day	47% 8% 19% 22% 4	3101
November	1st to 10th	Day	51% 8% 16% 18% 6% 1	1493
	11th to 20th	Day	44% 9% 23% 17% 7%	1400
	21st to end	Day	48% 11% 17% 17% 6% 1	1400
December	1st to 10th	Day	51% 11% 20% 12% 5% 1	2290
	11th to 20th	Day	50% 9% 19% 18% 4	2269
	21st to end	Day	32% 7% 16% 29% 15% 1	2992
January	1st to 10th	Night	48% 9% 13% 19% 10% 2	7226
	11th to 20th	Night	40% 9% 15% 15% 17% 5%	7013
	21st to end	Night	42% 10% 26% 16% 7%	7182
February	1st to 10th	Night	49% 9% 15% 14% 11% 2	2800
	11th to 20th	Night	44% 10% 17% 17% 10% 1	2685
	21st to end	Night	47% 7% 14% 22% 9% 1	2035
March	1st to 10th	Night	47% 7% 18% 20% 7%	3856
	11th to 20th	Night	38% 9% 20% 21% 11%	3641
	21st to end	Night	60% 8% 10% 15% 6%	3626
April	1st to 10th	Night	46% 7% 15% 20% 11% 1	1851
	11th to 20th	Night	49% 7% 11% 20% 11% 2	1691
	21st to end	Night	50% 8% 12% 19% 10% 1	1619
May	1st to 10th	Night	48% 8% 14% 18% 12%	2330
	11th to 20th	Night	45% 10% 14% 22% 8% 1	2199
	21st to end	Night	46% 10% 21% 13% 10%	2392
June	1st to 10th	Night	50% 8% 15% 18% 9%	1140
	11th to 20th	Night	55% 8% 14% 21% 2	1140
	21st to end	Night	43% 10% 21% 18% 7%	1140
July	1st to 10th	Night	32% 8% 15% 31% 13%	1870
	11th to 20th	Night	39% 7% 15% 28% 10%	1914
	21st to end	Night	36% 9% 24% 26% 4	2337
August	1st to 10th	Night	38% 9% 20% 30% 2	2451
	11th to 20th	Night	40% 8% 17% 24% 11%	2544
	21st to end	Night	39% 10% 29% 20% 3	3146
September	1st to 10th	Night	37% 8% 21% 26% 6% 2	1815
	11th to 20th	Night	38% 7% 21% 27% 6%	2033
	21st to end	Night	39% 9% 18% 24% 10% 1	2090
October	1st to 10th	Night	44% 9% 22% 18% 7% 1	3711
	11th to 20th	Night	40% 7% 19% 29% 6%	4086
	21st to end	Night	44% 8% 23% 21% 4	4457
November	1st to 10th	Night	53% 7% 15% 20% 5%	2786
	11th to 20th	Night	52% 9% 15% 16% 7% 1	3000
	21st to end	Night	50% 9% 18% 17% 5% 1	3000
December	1st to 10th	Night	48% 10% 19% 17% 6% 1	4890
	11th to 20th	Night	56% 8% 17% 14% 5%	5920
	21st to end	Night	32% 7% 16% 33% 11% 1	7964

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	10% 19% 36% 21% 11% 5%	200
	11th to 20th	Day	19% 20% 32% 16% 12% 3	200
	21st to end	Day	20% 25% 27% 18% 8% 2	220
February	1st to 10th	Day	16% 23% 36% 19% 5% 3	200
	11th to 20th	Day	13% 23% 36% 15% 9% 2	223
	21st to end	Day	12% 23% 35% 22% 6% 2	355
March	1st to 10th	Day	14% 22% 32% 24% 8%	500
	11th to 20th	Day	10% 22% 37% 21% 6% 4	465
	21st to end	Day	14% 19% 36% 23% 8%	506
April	1st to 10th	Day	18% 24% 34% 17% 4 2	460
	11th to 20th	Day	18% 21% 29% 20% 9% 3	452
	21st to end	Day	20% 20% 35% 20% 4 1	460
May	1st to 10th	Day	21% 19% 31% 20% 8% 2	582
	11th to 20th	Day	15% 13% 32% 25% 12% 2	675
	21st to end	Day	18% 13% 26% 28% 11% 4	742
June	1st to 10th	Day	22% 15% 30% 23% 9% 1	870
	11th to 20th	Day	26% 11% 26% 24% 11% 3	870
	21st to end	Day	16% 11% 27% 26% 16% 4	870
July	1st to 10th	Day	16% 11% 29% 26% 15% 4	856
	11th to 20th	Day	15% 14% 29% 25% 13% 4	828
	21st to end	Day	15% 9% 28% 29% 14% 6%	739
August	1st to 10th	Day	18% 9% 30% 24% 14% 7%	530
	11th to 20th	Day	14% 15% 35% 25% 8% 2	477
	21st to end	Day	18% 15% 31% 26% 8% 2	539
September	1st to 10th	Day	26% 17% 27% 18% 10% 3	490
	11th to 20th	Day	23% 13% 32% 22% 9% 2	490
	21st to end	Day	19% 26% 27% 18% 7% 2	490
October	1st to 10th	Day	23% 19% 29% 18% 10% 1	427
	11th to 20th	Day	21% 20% 30% 21% 7% 1	300
	21st to end	Day	22% 25% 29% 16% 6% 1	330
November	1st to 10th	Day	16% 23% 33% 19% 6% 3	257
	11th to 20th	Day	15% 26% 32% 16% 8% 4	200
	21st to end	Day	13% 26% 34% 18% 8% 3	200
December	1st to 10th	Day	15% 26% 36% 13% 7% 4	200
	11th to 20th	Day	14% 20% 39% 22% 6% 1	200
	21st to end	Day	10% 20% 29% 25% 12% 5%	220
January	1st to 10th	Night	11% 21% 33% 24% 10% 1	1100
	11th to 20th	Night	14% 20% 35% 22% 8% 1	1051
	21st to end	Night	19% 25% 28% 20% 7% 1	980
February	1st to 10th	Night	13% 18% 28% 27% 13% 2	800
	11th to 20th	Night	9% 17% 35% 26% 11% 1	784
	21st to end	Night	9% 16% 32% 31% 9% 3	660
March	1st to 10th	Night	9% 17% 34% 27% 12% 2	800
	11th to 20th	Night	9% 17% 34% 28% 10% 2	766
	21st to end	Night	13% 12% 34% 28% 12% 2	836
April	1st to 10th	Night	11% 12% 34% 28% 13% 1	711
	11th to 20th	Night	16% 13% 31% 27% 12% 2	563
	21st to end	Night	18% 11% 31% 26% 13% 1	479
May	1st to 10th	Night	18% 11% 24% 32% 14% 2	380
	11th to 20th	Night	16% 9% 30% 29% 15% 1	374
	21st to end	Night	17% 9% 28% 29% 15% 1	411
June	1st to 10th	Night	18% 10% 23% 31% 16% 1	380
	11th to 20th	Night	23% 9% 20% 27% 18% 2	380
	21st to end	Night	14% 7% 20% 34% 21% 3	380
July	1st to 10th	Night	14% 7% 23% 34% 22%	370
	11th to 20th	Night	16% 8% 26% 28% 20% 2	368
	21st to end	Night	12% 7% 22% 34% 21% 3	416
August	1st to 10th	Night	11% 6% 21% 36% 21% 4	378
	11th to 20th	Night	12% 9% 24% 34% 20% 1	386
	21st to end	Night	18% 7% 25% 34% 15% 1	627
September	1st to 10th	Night	16% 9% 24% 33% 16% 2	675
	11th to 20th	Night	16% 11% 26% 31% 15% 1	760
	21st to end	Night	14% 16% 28% 29% 12% 1	760
October	1st to 10th	Night	19% 13% 31% 27% 10% 1	760
	11th to 20th	Night	14% 16% 32% 28% 9% 1	760
	21st to end	Night	19% 20% 30% 23% 7%	836
November	1st to 10th	Night	19% 16% 32% 24% 8% 1	946
	11th to 20th	Night	13% 22% 35% 20% 7% 2	1000
	21st to end	Night	14% 22% 36% 20% 8% 1	1000
December	1st to 10th	Night	13% 21% 34% 21% 8% 3	1000
	11th to 20th	Night	13% 20% 34% 24% 8% 1	1097
	21st to end	Night	8% 16% 35% 27% 12% 2	1210

Page generated at 2025-03-09 06:08:42. Version ac07

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