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 2026-07-16.

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% 6% 5% 5% 6% 8% 32%	142376
	Night	6% 9% 4 10% 6% 6% 6% 5% 7% 8% 34%	138982
Transparency	Day	46% 8% 17% 20% 8% 1	142062
	Night	44% 8% 18% 20% 9% 1	138878
Seeing	Day	18% 17% 31% 22% 10% 3	18599
	Night	14% 16% 31% 27% 11% 1	26821

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% 13% 8% 6% 7% 4 8% 8% 27%	3527
	11th to 20th	Day	1 7% 4 9% 5% 5% 4 4 6% 9% 45%	3803
	21st to end	Day	3 8% 5% 10% 6% 6% 6% 5% 6% 8% 37%	4944
February	1st to 10th	Day	4 9% 3 10% 7% 7% 7% 6% 9% 10% 28%	1680
	11th to 20th	Day	2 10% 4 11% 7% 6% 5% 4 9% 10% 31%	1685
	21st to end	Day	2 11% 5% 13% 9% 5% 5% 5% 8% 10% 26%	1668
March	1st to 10th	Day	3 8% 5% 13% 8% 8% 7% 6% 7% 8% 28%	4618
	11th to 20th	Day	4 15% 5% 13% 8% 5% 4 3 5% 6% 32%	4918
	21st to end	Day	6% 14% 5% 19% 10% 5% 5% 4 6% 6% 20%	5889
April	1st to 10th	Day	7% 15% 6% 12% 7% 6% 5% 4 6% 6% 26%	2574
	11th to 20th	Day	8% 14% 5% 9% 7% 5% 5% 5% 7% 8% 28%	2700
	21st to end	Day	11% 14% 4 10% 6% 5% 5% 5% 6% 8% 26%	2830
May	1st to 10th	Day	9% 10% 3 8% 5% 5% 5% 4 6% 8% 39%	8571
	11th to 20th	Day	13% 15% 4 10% 7% 7% 6% 5% 6% 7% 21%	8755
	21st to end	Day	12% 8% 3 9% 6% 6% 6% 5% 7% 8% 29%	9684
June	1st to 10th	Day	18% 10% 3 8% 6% 5% 6% 5% 6% 7% 27%	3360
	11th to 20th	Day	21% 11% 4 10% 7% 6% 5% 4 5% 7% 19%	3360
	21st to end	Day	12% 8% 3 9% 6% 5% 6% 5% 6% 8% 31%	3360
July	1st to 10th	Day	8% 6% 2 7% 5% 6% 6% 5% 8% 9% 38%	7400
	11th to 20th	Day	9% 6% 2 7% 6% 6% 6% 5% 7% 7% 39%	7257
	21st to end	Day	12% 7% 2 6% 5% 5% 5% 4 7% 9% 36%	7376
August	1st to 10th	Day	14% 7% 2 7% 4 4 5% 3 5% 7% 41%	4612
	11th to 20th	Day	14% 6% 2 7% 5% 5% 6% 4 6% 7% 38%	4446
	21st to end	Day	14% 6% 2 7% 5% 4 6% 5% 6% 8% 38%	4664
September	1st to 10th	Day	12% 8% 2 7% 5% 4 5% 4 6% 8% 39%	2485
	11th to 20th	Day	12% 10% 2 6% 4 4 5% 4 6% 7% 40%	2260
	21st to end	Day	10% 8% 4 7% 5% 5% 5% 4 7% 8% 37%	2200
October	1st to 10th	Day	10% 13% 4 9% 5% 5% 5% 3 6% 7% 32%	3365
	11th to 20th	Day	11% 14% 4 9% 5% 4 5% 4 6% 7% 30%	2932
	21st to end	Day	7% 13% 5% 10% 5% 5% 6% 4 6% 8% 31%	3200
November	1st to 10th	Day	7% 13% 4 10% 6% 5% 4 5% 6% 9% 29%	1568
	11th to 20th	Day	5% 9% 4 11% 6% 5% 5% 5% 7% 9% 33%	1470
	21st to end	Day	3 9% 4 12% 9% 6% 6% 4 6% 8% 33%	1470
December	1st to 10th	Day	5% 12% 5% 13% 7% 6% 6% 4 6% 8% 28%	2360
	11th to 20th	Day	4 11% 5% 10% 6% 7% 7% 5% 8% 8% 28%	2327
	21st to end	Day	2 6% 3 7% 6% 4 5% 4 7% 9% 46%	3058
January	1st to 10th	Night	3 11% 5% 13% 8% 6% 7% 5% 7% 7% 28%	9366
	11th to 20th	Night	1 6% 4 8% 5% 6% 6% 5% 7% 8% 43%	9081
	21st to end	Night	3 9% 4 10% 6% 7% 7% 6% 7% 8% 32%	9293
February	1st to 10th	Night	4 10% 4 12% 7% 6% 7% 5% 8% 9% 30%	2940
	11th to 20th	Night	2 9% 4 11% 7% 6% 6% 5% 9% 8% 32%	2821
	21st to end	Night	2 10% 5% 10% 7% 7% 6% 6% 8% 7% 31%	2134
March	1st to 10th	Night	2 6% 4 13% 7% 6% 7% 5% 7% 9% 33%	5496
	11th to 20th	Night	4 10% 3 10% 8% 8% 7% 5% 7% 8% 31%	5301
	21st to end	Night	8% 15% 6% 19% 9% 5% 4 3 4 5% 22%	5324
April	1st to 10th	Night	7% 10% 4 9% 7% 6% 6% 5% 7% 7% 32%	2045
	11th to 20th	Night	9% 13% 4 8% 5% 6% 6% 4 6% 7% 31%	1871
	21st to end	Night	10% 12% 5% 9% 5% 4 5% 5% 6% 8% 31%	1789
May	1st to 10th	Night	9% 9% 3 7% 4 4 5% 3 7% 9% 40%	4334
	11th to 20th	Night	11% 13% 4 10% 6% 6% 6% 5% 7% 7% 24%	4105
	21st to end	Night	11% 8% 3 7% 4 4 5% 4 7% 10% 37%	4472
June	1st to 10th	Night	15% 9% 3 9% 6% 5% 6% 5% 7% 6% 31%	1260
	11th to 20th	Night	17% 10% 3 9% 6% 6% 6% 5% 6% 9% 22%	1260
	21st to end	Night	12% 7% 3 7% 5% 5% 6% 5% 9% 8% 34%	1260
July	1st to 10th	Night	8% 6% 2 6% 4 5% 5% 4 8% 9% 44%	2780
	11th to 20th	Night	9% 8% 3 7% 6% 5% 5% 4 6% 7% 40%	2814
	21st to end	Night	10% 6% 2 6% 4 4 5% 5% 7% 9% 43%	3467
August	1st to 10th	Night	13% 6% 2 6% 4 4 5% 3 5% 8% 43%	2536
	11th to 20th	Night	16% 8% 3 6% 3 3 4 3 6% 7% 40%	2601
	21st to end	Night	10% 7% 2 7% 5% 5% 5% 4 7% 8% 40%	3245
September	1st to 10th	Night	10% 6% 2 5% 5% 5% 6% 4 6% 8% 44%	1911
	11th to 20th	Night	11% 9% 2 6% 4 4 4 4 5% 7% 45%	2140
	21st to end	Night	8% 9% 3 7% 5% 5% 6% 4 6% 8% 41%	2200
October	1st to 10th	Night	6% 11% 4 10% 5% 6% 6% 5% 7% 7% 34%	3828
	11th to 20th	Night	6% 9% 4 8% 5% 5% 5% 4 7% 9% 37%	4216
	21st to end	Night	7% 8% 4 10% 6% 6% 6% 4 7% 10% 32%	4600
November	1st to 10th	Night	9% 14% 4 11% 5% 5% 5% 4 6% 6% 30%	2929
	11th to 20th	Night	4 11% 4 11% 8% 6% 6% 5% 7% 8% 29%	3150
	21st to end	Night	4 12% 5% 10% 6% 7% 5% 4 6% 7% 32%	3150
December	1st to 10th	Night	5% 12% 4 10% 6% 6% 6% 5% 7% 8% 31%	5040
	11th to 20th	Night	6% 13% 4 12% 7% 7% 7% 4 7% 8% 24%	6083
	21st to end	Night	2 5% 3 8% 6% 5% 6% 5% 7% 9% 45%	8140

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	52% 7% 12% 14% 15% 1	3527
	11th to 20th	Day	34% 9% 21% 14% 19% 4	3822
	21st to end	Day	40% 11% 27% 17% 5%	4945
February	1st to 10th	Day	47% 10% 17% 14% 12% 1	1680
	11th to 20th	Day	46% 9% 17% 18% 11%	1693
	21st to end	Day	50% 7% 16% 18% 9% 1	1668
March	1st to 10th	Day	48% 7% 16% 15% 13%	4618
	11th to 20th	Day	51% 6% 14% 21% 8%	4919
	21st to end	Day	61% 7% 12% 13% 7%	5889
April	1st to 10th	Day	55% 8% 14% 15% 7%	2574
	11th to 20th	Day	50% 7% 16% 17% 10%	2700
	21st to end	Day	52% 8% 12% 20% 7% 1	2830
May	1st to 10th	Day	41% 6% 15% 25% 12% 1	8571
	11th to 20th	Day	57% 8% 11% 19% 5%	8759
	21st to end	Day	47% 9% 20% 16% 7% 1	9685
June	1st to 10th	Day	53% 8% 14% 18% 7% 1	3360
	11th to 20th	Day	62% 7% 11% 15% 4	3360
	21st to end	Day	47% 9% 18% 19% 7%	3360
July	1st to 10th	Day	36% 9% 21% 22% 10% 2	7321
	11th to 20th	Day	40% 8% 14% 30% 8%	7170
	21st to end	Day	40% 9% 24% 22% 5%	7169
August	1st to 10th	Day	41% 8% 18% 31% 2	4594
	11th to 20th	Day	41% 9% 17% 23% 10%	4488
	21st to end	Day	41% 8% 25% 21% 4	4663
September	1st to 10th	Day	41% 8% 20% 24% 6% 1	2485
	11th to 20th	Day	41% 7% 22% 23% 7%	2260
	21st to end	Day	42% 9% 17% 22% 9% 1	2200
October	1st to 10th	Day	47% 8% 21% 19% 5%	3365
	11th to 20th	Day	48% 8% 17% 22% 5%	2932
	21st to end	Day	47% 8% 20% 22% 4	3200
November	1st to 10th	Day	50% 8% 16% 18% 6% 1	1568
	11th to 20th	Day	44% 9% 22% 17% 8%	1470
	21st to end	Day	47% 11% 16% 18% 6% 2	1470
December	1st to 10th	Day	52% 11% 19% 12% 5% 1	2360
	11th to 20th	Day	51% 9% 19% 17% 4	2329
	21st to end	Day	32% 7% 16% 29% 15% 1	3058
January	1st to 10th	Night	51% 8% 11% 17% 12% 1	9367
	11th to 20th	Night	34% 8% 18% 19% 16% 4	9123
	21st to end	Night	43% 10% 25% 15% 6%	9293
February	1st to 10th	Night	48% 9% 15% 15% 11% 2	2940
	11th to 20th	Night	44% 10% 17% 17% 10% 1	2823
	21st to end	Night	48% 7% 14% 22% 8% 1	2134
March	1st to 10th	Night	43% 6% 19% 17% 14%	5496
	11th to 20th	Night	46% 9% 16% 19% 10%	5301
	21st to end	Night	61% 7% 8% 13% 10%	5324
April	1st to 10th	Night	47% 7% 14% 20% 10% 1	2045
	11th to 20th	Night	49% 7% 13% 20% 11% 1	1871
	21st to end	Night	48% 8% 12% 20% 11% 1	1789
May	1st to 10th	Night	38% 6% 16% 25% 12% 1	4331
	11th to 20th	Night	54% 9% 11% 20% 6%	4105
	21st to end	Night	38% 9% 26% 21% 6%	4476
June	1st to 10th	Night	50% 7% 15% 18% 10%	1260
	11th to 20th	Night	56% 7% 14% 21% 2	1260
	21st to end	Night	43% 10% 21% 19% 7%	1260
July	1st to 10th	Night	34% 9% 21% 24% 12%	2750
	11th to 20th	Night	42% 7% 14% 30% 7%	2778
	21st to end	Night	35% 9% 28% 25% 3	3369
August	1st to 10th	Night	39% 9% 20% 30% 2	2529
	11th to 20th	Night	41% 8% 17% 23% 11%	2625
	21st to end	Night	37% 9% 28% 21% 4	3245
September	1st to 10th	Night	36% 9% 22% 26% 6% 2	1911
	11th to 20th	Night	37% 7% 20% 28% 7%	2140
	21st to end	Night	39% 8% 18% 24% 9% 1	2200
October	1st to 10th	Night	43% 9% 22% 18% 8% 1	3828
	11th to 20th	Night	39% 7% 19% 29% 6%	4216
	21st to end	Night	44% 8% 23% 21% 4	4600
November	1st to 10th	Night	53% 7% 15% 19% 6%	2929
	11th to 20th	Night	51% 9% 15% 16% 8% 1	3150
	21st to end	Night	49% 9% 17% 17% 6% 2	3150
December	1st to 10th	Night	49% 10% 18% 17% 6% 1	5040
	11th to 20th	Night	56% 8% 17% 14% 5%	6080
	21st to end	Night	32% 7% 16% 32% 11% 1	8140

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	12% 19% 35% 19% 10% 4	220
	11th to 20th	Day	22% 20% 30% 15% 11% 3	220
	21st to end	Day	20% 24% 27% 18% 8% 2	242
February	1st to 10th	Day	17% 23% 35% 18% 5% 2	220
	11th to 20th	Day	13% 25% 36% 15% 9% 2	245
	21st to end	Day	13% 22% 36% 21% 6% 2	384
March	1st to 10th	Day	16% 22% 31% 22% 8%	540
	11th to 20th	Day	12% 22% 37% 19% 5% 4	540
	21st to end	Day	14% 21% 35% 22% 7% 1	594
April	1st to 10th	Day	19% 23% 34% 19% 4 2	540
	11th to 20th	Day	18% 23% 29% 19% 8% 3	532
	21st to end	Day	18% 19% 36% 21% 5% 1	540
May	1st to 10th	Day	21% 18% 32% 19% 7% 2	674
	11th to 20th	Day	16% 14% 32% 25% 12% 2	775
	21st to end	Day	19% 14% 26% 27% 11% 4	853
June	1st to 10th	Day	24% 16% 29% 21% 8% 1	990
	11th to 20th	Day	26% 12% 26% 24% 10% 3	990
	21st to end	Day	17% 10% 28% 25% 16% 5%	990
July	1st to 10th	Day	16% 11% 30% 26% 14% 3	976
	11th to 20th	Day	16% 15% 29% 24% 13% 4	918
	21st to end	Day	14% 10% 27% 29% 14% 6%	794
August	1st to 10th	Day	17% 9% 30% 24% 14% 7%	572
	11th to 20th	Day	15% 16% 35% 24% 8% 2	517
	21st to end	Day	16% 14% 31% 26% 10% 3	583
September	1st to 10th	Day	24% 16% 27% 19% 11% 3	530
	11th to 20th	Day	22% 12% 33% 23% 9% 2	530
	21st to end	Day	20% 28% 27% 17% 7% 2	530
October	1st to 10th	Day	23% 20% 29% 17% 10% 1	463
	11th to 20th	Day	22% 20% 30% 20% 7% 1	330
	21st to end	Day	24% 26% 28% 15% 6% 1	363
November	1st to 10th	Day	18% 24% 32% 17% 6% 3	282
	11th to 20th	Day	16% 25% 34% 15% 7% 3	220
	21st to end	Day	14% 25% 33% 17% 8% 3	220
December	1st to 10th	Day	16% 26% 36% 12% 6% 3	220
	11th to 20th	Day	14% 23% 38% 20% 5%	220
	21st to end	Day	12% 21% 28% 24% 11% 5%	242
January	1st to 10th	Night	11% 22% 33% 24% 9% 1	1160
	11th to 20th	Night	15% 20% 34% 21% 8% 1	1106
	21st to end	Night	19% 25% 28% 20% 6% 1	1029
February	1st to 10th	Night	13% 18% 29% 26% 12% 2	840
	11th to 20th	Night	10% 18% 36% 26% 10% 1	824
	21st to end	Night	10% 16% 32% 29% 9% 3	692
March	1st to 10th	Night	9% 17% 34% 26% 11% 2	840
	11th to 20th	Night	10% 18% 33% 28% 10% 2	840
	21st to end	Night	13% 13% 34% 28% 11% 1	924
April	1st to 10th	Night	10% 12% 35% 28% 13% 1	785
	11th to 20th	Night	16% 13% 32% 26% 11% 1	623
	21st to end	Night	17% 12% 31% 27% 13% 1	529
May	1st to 10th	Night	17% 11% 25% 32% 13% 2	420
	11th to 20th	Night	16% 9% 30% 29% 15% 1	414
	21st to end	Night	17% 9% 28% 30% 15% 1	455
June	1st to 10th	Night	20% 12% 23% 30% 15% 1	420
	11th to 20th	Night	23% 10% 19% 28% 18% 2	420
	21st to end	Night	15% 8% 21% 33% 21% 3	420
July	1st to 10th	Night	14% 7% 23% 34% 21%	410
	11th to 20th	Night	16% 8% 26% 29% 19% 2	398
	21st to end	Night	12% 7% 22% 35% 21% 3	438
August	1st to 10th	Night	11% 6% 21% 36% 22% 4	398
	11th to 20th	Night	12% 10% 24% 33% 20% 1	407
	21st to end	Night	17% 7% 24% 34% 17% 1	660
September	1st to 10th	Night	16% 9% 24% 33% 17% 2	711
	11th to 20th	Night	15% 10% 25% 33% 16% 1	800
	21st to end	Night	15% 17% 28% 28% 11% 1	800
October	1st to 10th	Night	18% 13% 31% 27% 10% 1	800
	11th to 20th	Night	14% 17% 32% 28% 9% 1	800
	21st to end	Night	19% 21% 30% 22% 7%	880
November	1st to 10th	Night	20% 17% 32% 23% 7% 1	995
	11th to 20th	Night	13% 23% 35% 20% 7% 2	1050
	21st to end	Night	13% 22% 36% 20% 8% 1	1050
December	1st to 10th	Night	14% 22% 33% 20% 8% 2	1050
	11th to 20th	Night	13% 21% 34% 23% 7% 1	1157
	21st to end	Night	9% 16% 34% 26% 11% 2	1276

Page generated at 2026-07-13 01:14:53. Version ac07

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