Swan River
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Swan River clear sky chart from 2005-11-06 to 2024-02-10.

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	12% 9% 4 7% 6% 4 5% 5% 6% 7% 35%	78231
	Night	10% 10% 5% 9% 7% 4 5% 5% 5% 7% 34%	80723
Transparency	Day	46% 9% 15% 22% 8% 1	77937
	Night	49% 8% 14% 21% 8% 1	80599
Seeing	Day	15% 11% 30% 28% 13% 3	15208
	Night	14% 7% 31% 33% 13% 2	24882

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	5% 15% 8% 13% 9% 5% 7% 7% 6% 6% 20%	2219
	11th to 20th	Day	4 10% 4 14% 15% 6% 9% 7% 5% 6% 20%	2330
	21st to end	Day	7% 13% 6% 8% 7% 4 7% 5% 6% 7% 30%	2794
February	1st to 10th	Day	7% 10% 6% 9% 7% 5% 8% 6% 6% 7% 28%	1512
	11th to 20th	Day	5% 9% 4 8% 8% 4 8% 7% 5% 9% 32%	1508
	21st to end	Day	6% 6% 6% 11% 9% 5% 7% 7% 6% 7% 30%	1480
March	1st to 10th	Day	10% 10% 5% 9% 9% 5% 5% 5% 7% 8% 28%	1800
	11th to 20th	Day	9% 9% 4 8% 7% 4 6% 6% 6% 8% 32%	1876
	21st to end	Day	10% 10% 5% 9% 7% 3 4 4 6% 8% 34%	2311
April	1st to 10th	Day	9% 9% 5% 7% 7% 4 5% 6% 6% 7% 37%	2160
	11th to 20th	Day	13% 10% 4 10% 7% 3 5% 5% 5% 7% 30%	2298
	21st to end	Day	11% 8% 3 6% 6% 4 5% 6% 5% 7% 38%	2380
May	1st to 10th	Day	15% 10% 3 6% 5% 3 5% 4 6% 7% 35%	2520
	11th to 20th	Day	13% 7% 2 5% 5% 3 4 5% 5% 7% 43%	2632
	21st to end	Day	21% 7% 3 6% 6% 3 4 5% 6% 7% 33%	2918
June	1st to 10th	Day	18% 7% 3 5% 6% 3 5% 5% 5% 8% 35%	2700
	11th to 20th	Day	21% 5% 2 6% 6% 3 5% 6% 5% 7% 32%	2852
	21st to end	Day	15% 5% 3 5% 6% 4 7% 5% 7% 8% 35%	2880
July	1st to 10th	Day	9% 4 2 5% 5% 3 5% 5% 7% 9% 45%	2849
	11th to 20th	Day	13% 6% 2 5% 4 3 5% 5% 6% 8% 42%	2700
	21st to end	Day	10% 5% 2 4 4 3 4 6% 6% 8% 47%	2813
August	1st to 10th	Day	10% 4 2 5% 4 3 5% 7% 6% 8% 46%	2507
	11th to 20th	Day	13% 5% 2 4 4 3 5% 5% 6% 10% 44%	2437
	21st to end	Day	15% 7% 2 5% 5% 3 4 4 5% 8% 43%	2574
September	1st to 10th	Day	13% 6% 2 5% 5% 3 5% 5% 6% 8% 43%	2160
	11th to 20th	Day	14% 8% 3 5% 5% 3 4 4 5% 8% 41%	2045
	21st to end	Day	12% 8% 2 5% 5% 3 4 4 5% 8% 43%	1980
October	1st to 10th	Day	19% 11% 3 6% 5% 3 4 4 4 6% 36%	1887
	11th to 20th	Day	13% 13% 4 7% 6% 3 6% 4 4 6% 36%	1620
	21st to end	Day	14% 15% 7% 9% 7% 3 4 4 5% 5% 27%	1782
November	1st to 10th	Day	17% 19% 6% 8% 6% 3 3 4 4 5% 25%	1596
	11th to 20th	Day	8% 15% 6% 11% 8% 4 6% 4 4 6% 26%	1330
	21st to end	Day	9% 13% 9% 10% 8% 4 5% 5% 5% 6% 27%	1330
December	1st to 10th	Day	6% 10% 5% 10% 11% 6% 7% 7% 6% 7% 25%	1330
	11th to 20th	Day	10% 15% 6% 14% 9% 5% 4 6% 5% 5% 21%	1679
	21st to end	Day	4 7% 4 8% 7% 3 4 3 5% 6% 49%	2442
January	1st to 10th	Night	5% 13% 8% 14% 11% 5% 7% 7% 7% 5% 18%	4737
	11th to 20th	Night	4 9% 5% 17% 14% 7% 9% 8% 4 5% 17%	4574
	21st to end	Night	5% 13% 8% 11% 8% 5% 6% 5% 5% 6% 27%	4873
February	1st to 10th	Night	9% 11% 4 10% 7% 5% 9% 7% 6% 6% 27%	2653
	11th to 20th	Night	5% 9% 4 10% 9% 5% 8% 6% 6% 7% 32%	2354
	21st to end	Night	4 9% 6% 11% 9% 4 5% 4 5% 8% 34%	1776
March	1st to 10th	Night	11% 11% 5% 7% 7% 6% 6% 5% 5% 7% 30%	2160
	11th to 20th	Night	7% 9% 4 8% 8% 5% 6% 5% 6% 8% 33%	2082
	21st to end	Night	9% 11% 5% 7% 6% 4 5% 5% 6% 7% 36%	2044
April	1st to 10th	Night	8% 7% 4 8% 7% 3 5% 5% 6% 7% 41%	1800
	11th to 20th	Night	13% 8% 4 8% 7% 4 4 5% 5% 7% 33%	1613
	21st to end	Night	13% 7% 3 7% 5% 3 4 6% 5% 7% 39%	1578
May	1st to 10th	Night	13% 11% 4 6% 5% 3 4 5% 5% 6% 37%	1440
	11th to 20th	Night	13% 8% 3 6% 5% 4 5% 4 6% 6% 41%	1264
	21st to end	Night	20% 6% 2 4 5% 3 4 4 5% 8% 39%	1358
June	1st to 10th	Night	16% 7% 2 5% 4 4 4 5% 5% 7% 41%	1260
	11th to 20th	Night	19% 5% 3 5% 4 3 5% 6% 6% 7% 36%	1102
	21st to end	Night	13% 6% 3 5% 7% 4 7% 5% 5% 6% 39%	1080
July	1st to 10th	Night	9% 4 2 4 3 3 3 4 7% 9% 52%	1106
	11th to 20th	Night	10% 4 2 4 5% 2 5% 5% 6% 8% 49%	1260
	21st to end	Night	9% 3 3 3 4 3 4 3 5% 7% 56%	1503
August	1st to 10th	Night	9% 3 1 3 3 3 4 5% 5% 8% 55%	1432
	11th to 20th	Night	11% 5% 1 3 5% 1 3 3 5% 9% 54%	1464
	21st to end	Night	16% 6% 2 3 4 2 3 4 5% 6% 49%	1782
September	1st to 10th	Night	9% 6% 2 4 6% 3 3 6% 5% 7% 49%	1798
	11th to 20th	Night	15% 7% 2 4 5% 2 4 4 5% 6% 45%	1914
	21st to end	Night	12% 6% 2 5% 4 3 4 5% 5% 8% 45%	1980
October	1st to 10th	Night	17% 11% 3 5% 5% 2 2 4 4 7% 39%	2051
	11th to 20th	Night	13% 12% 4 6% 6% 3 5% 5% 4 5% 37%	2340
	21st to end	Night	14% 15% 5% 8% 6% 3 5% 4 4 6% 32%	2574
November	1st to 10th	Night	14% 15% 7% 10% 8% 4 5% 4 4 5% 24%	2478
	11th to 20th	Night	11% 14% 7% 11% 9% 4 4 4 5% 6% 25%	2850
	21st to end	Night	10% 13% 7% 11% 10% 4 5% 5% 5% 6% 25%	2850
December	1st to 10th	Night	7% 12% 5% 11% 12% 5% 6% 5% 5% 7% 24%	2850
	11th to 20th	Night	8% 13% 6% 13% 10% 4 6% 6% 5% 6% 22%	3518
	21st to end	Night	5% 8% 4 8% 7% 3 4 4 5% 6% 45%	5225

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	60% 10% 13% 15% 3	2219
	11th to 20th	Day	63% 6% 11% 17% 3	2352
	21st to end	Day	50% 10% 14% 21% 4	2794
February	1st to 10th	Day	52% 10% 14% 17% 8%	1512
	11th to 20th	Day	46% 9% 13% 21% 11%	1516
	21st to end	Day	49% 8% 13% 21% 9%	1480
March	1st to 10th	Day	52% 9% 13% 19% 7%	1800
	11th to 20th	Day	49% 9% 14% 21% 6% 1	1878
	21st to end	Day	48% 8% 16% 20% 8% 1	2311
April	1st to 10th	Day	45% 7% 15% 20% 13% 1	2160
	11th to 20th	Day	53% 7% 11% 16% 10% 2	2298
	21st to end	Day	43% 8% 16% 23% 9% 1	2380
May	1st to 10th	Day	47% 6% 12% 23% 12% 1	2520
	11th to 20th	Day	41% 7% 12% 24% 13% 3	2636
	21st to end	Day	49% 8% 10% 23% 9% 1	2918
June	1st to 10th	Day	48% 8% 13% 22% 9% 1	2700
	11th to 20th	Day	51% 8% 14% 17% 9%	2852
	21st to end	Day	45% 11% 17% 22% 5%	2880
July	1st to 10th	Day	32% 10% 19% 29% 9%	2771
	11th to 20th	Day	39% 10% 17% 28% 6%	2619
	21st to end	Day	34% 9% 21% 31% 6%	2657
August	1st to 10th	Day	34% 11% 21% 27% 7%	2491
	11th to 20th	Day	34% 10% 22% 29% 5%	2437
	21st to end	Day	39% 8% 19% 27% 7%	2574
September	1st to 10th	Day	38% 9% 17% 25% 9% 1	2160
	11th to 20th	Day	41% 8% 15% 27% 7%	2045
	21st to end	Day	40% 8% 14% 27% 11%	1980
October	1st to 10th	Day	50% 7% 16% 21% 5% 1	1887
	11th to 20th	Day	50% 7% 11% 24% 7%	1620
	21st to end	Day	59% 8% 13% 16% 5%	1782
November	1st to 10th	Day	62% 6% 10% 16% 5%	1596
	11th to 20th	Day	58% 9% 15% 12% 5%	1330
	21st to end	Day	58% 8% 14% 16% 4	1330
December	1st to 10th	Day	54% 11% 14% 16% 5%	1330
	11th to 20th	Day	62% 9% 14% 12% 3	1680
	21st to end	Day	35% 8% 13% 25% 15% 5%	2442
January	1st to 10th	Night	62% 10% 12% 13% 3	4737
	11th to 20th	Night	66% 8% 10% 12% 4	4614
	21st to end	Night	55% 10% 13% 17% 5%	4873
February	1st to 10th	Night	53% 10% 12% 16% 9% 1	2653
	11th to 20th	Night	49% 7% 14% 20% 10% 1	2356
	21st to end	Night	47% 6% 16% 22% 9%	1776
March	1st to 10th	Night	53% 6% 14% 21% 4 1	2160
	11th to 20th	Night	47% 7% 13% 23% 8% 1	2082
	21st to end	Night	46% 7% 12% 25% 10%	2044
April	1st to 10th	Night	42% 7% 12% 21% 16% 2	1800
	11th to 20th	Night	49% 7% 13% 18% 10% 3	1613
	21st to end	Night	42% 8% 15% 22% 10% 2	1578
May	1st to 10th	Night	47% 8% 8% 20% 16% 1	1440
	11th to 20th	Night	43% 6% 12% 22% 15% 3	1264
	21st to end	Night	44% 8% 11% 21% 16% 1	1358
June	1st to 10th	Night	42% 8% 14% 24% 11% 1	1260
	11th to 20th	Night	45% 9% 18% 17% 10% 2	1102
	21st to end	Night	44% 10% 18% 21% 7%	1080
July	1st to 10th	Night	28% 11% 20% 31% 9% 1	1075
	11th to 20th	Night	30% 11% 18% 31% 10% 1	1218
	21st to end	Night	29% 8% 20% 35% 8%	1420
August	1st to 10th	Night	26% 9% 22% 32% 11%	1424
	11th to 20th	Night	29% 7% 24% 33% 7% 1	1464
	21st to end	Night	36% 6% 17% 31% 9%	1782
September	1st to 10th	Night	32% 9% 16% 31% 11% 2	1798
	11th to 20th	Night	39% 8% 14% 31% 8%	1914
	21st to end	Night	37% 7% 14% 30% 10% 1	1980
October	1st to 10th	Night	45% 7% 18% 24% 5% 1	2051
	11th to 20th	Night	48% 7% 9% 27% 8%	2340
	21st to end	Night	54% 6% 14% 21% 5%	2574
November	1st to 10th	Night	61% 9% 11% 14% 5% 1	2478
	11th to 20th	Night	58% 9% 16% 14% 3	2850
	21st to end	Night	59% 8% 14% 14% 4	2850
December	1st to 10th	Night	57% 9% 12% 16% 5%	2850
	11th to 20th	Night	58% 10% 13% 13% 6%	3516
	21st to end	Night	38% 7% 13% 21% 16% 4	5225

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% 13% 33% 30% 13%	270
	11th to 20th	Day	9% 7% 40% 33% 9% 1	270
	21st to end	Day	13% 8% 32% 35% 10% 2	297
February	1st to 10th	Day	12% 10% 34% 30% 14%	267
	11th to 20th	Day	8% 8% 39% 27% 14% 4	240
	21st to end	Day	4 9% 38% 31% 17% 2	198
March	1st to 10th	Day	16% 6% 31% 31% 13% 3	240
	11th to 20th	Day	8% 10% 39% 31% 10% 3	240
	21st to end	Day	15% 14% 31% 28% 10% 2	397
April	1st to 10th	Day	13% 13% 37% 27% 10% 1	420
	11th to 20th	Day	16% 11% 30% 26% 15% 1	576
	21st to end	Day	14% 13% 32% 29% 11% 1	600
May	1st to 10th	Day	18% 12% 28% 30% 11% 1	603
	11th to 20th	Day	16% 13% 28% 25% 15% 2	625
	21st to end	Day	19% 11% 27% 26% 14% 3	679
June	1st to 10th	Day	20% 12% 29% 23% 12% 4	630
	11th to 20th	Day	20% 13% 28% 23% 11% 4	630
	21st to end	Day	17% 9% 27% 27% 14% 6%	630
July	1st to 10th	Day	10% 10% 27% 30% 18% 5%	621
	11th to 20th	Day	12% 11% 29% 27% 16% 4	618
	21st to end	Day	10% 9% 24% 28% 21% 8%	684
August	1st to 10th	Day	11% 10% 28% 28% 19% 4	626
	11th to 20th	Day	14% 7% 24% 28% 19% 7%	615
	21st to end	Day	18% 7% 26% 30% 17% 1	693
September	1st to 10th	Day	16% 15% 34% 27% 7% 2	450
	11th to 20th	Day	20% 12% 31% 26% 9% 3	335
	21st to end	Day	17% 10% 33% 26% 13% 1	270
October	1st to 10th	Day	24% 10% 27% 25% 11% 3	270
	11th to 20th	Day	20% 13% 36% 22% 9% 1	270
	21st to end	Day	23% 11% 33% 22% 9% 2	297
November	1st to 10th	Day	27% 10% 30% 26% 6% 1	270
	11th to 20th	Day	16% 11% 37% 26% 8% 1	270
	21st to end	Day	17% 11% 40% 21% 9% 1	270
December	1st to 10th	Day	9% 10% 36% 32% 13% 1	270
	11th to 20th	Day	14% 13% 39% 28% 6%	270
	21st to end	Day	9% 5% 26% 39% 17% 3	297
January	1st to 10th	Night	12% 9% 37% 31% 10% 1	950
	11th to 20th	Night	12% 7% 38% 31% 11% 2	950
	21st to end	Night	14% 9% 35% 32% 9% 1	1045
February	1st to 10th	Night	11% 7% 33% 35% 14% 1	948
	11th to 20th	Night	9% 7% 35% 33% 15% 2	847
	21st to end	Night	7% 6% 29% 39% 18% 1	592
March	1st to 10th	Night	15% 5% 26% 40% 13% 1	720
	11th to 20th	Night	11% 7% 34% 34% 12% 2	642
	21st to end	Night	12% 8% 28% 30% 18% 3	594
April	1st to 10th	Night	11% 5% 31% 34% 18% 2	540
	11th to 20th	Night	17% 6% 32% 30% 14% 1	533
	21st to end	Night	14% 8% 36% 34% 8% 1	540
May	1st to 10th	Night	18% 7% 29% 34% 12%	540
	11th to 20th	Night	16% 9% 31% 30% 13% 1	531
	21st to end	Night	22% 8% 23% 34% 12% 1	584
June	1st to 10th	Night	18% 6% 27% 34% 14% 1	540
	11th to 20th	Night	20% 4 27% 33% 15% 2	382
	21st to end	Night	12% 6% 26% 37% 18% 1	360
July	1st to 10th	Night	9% 6% 26% 41% 17% 1	375
	11th to 20th	Night	10% 6% 29% 36% 18% 2	522
	21st to end	Night	8% 4 24% 39% 21% 4	591
August	1st to 10th	Night	9% 6% 23% 38% 22% 2	537
	11th to 20th	Night	14% 3 20% 35% 25% 3	534
	21st to end	Night	17% 3 25% 39% 14% 1	594
September	1st to 10th	Night	12% 6% 28% 36% 17% 1	540
	11th to 20th	Night	18% 6% 24% 38% 13% 1	540
	21st to end	Night	13% 5% 28% 41% 12% 1	540
October	1st to 10th	Night	21% 7% 27% 33% 10% 1	611
	11th to 20th	Night	20% 9% 27% 32% 11% 1	900
	21st to end	Night	21% 8% 30% 29% 10% 1	990
November	1st to 10th	Night	20% 10% 32% 28% 8% 1	925
	11th to 20th	Night	17% 8% 37% 27% 9% 2	950
	21st to end	Night	16% 13% 35% 27% 8% 1	950
December	1st to 10th	Night	11% 9% 36% 28% 13% 4	950
	11th to 20th	Night	16% 9% 33% 29% 11% 2	950
	21st to end	Night	12% 6% 28% 37% 14% 3	1045

Page generated at 2024-02-07 05:11:52. Version ac07

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