Rosetown
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rosetown clear sky chart from 2005-11-06 to 2026-01-17.

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	8% 8% 3 9% 5% 5% 5% 4 6% 8% 38%	131054
	Night	7% 9% 3 9% 6% 6% 5% 4 6% 8% 37%	129315
Transparency	Day	43% 7% 16% 25% 9% 1	130755
	Night	44% 6% 15% 23% 10% 1	129195
Seeing	Day	12% 8% 27% 30% 18% 5%	17258
	Night	12% 6% 29% 36% 15% 2	26633

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	6% 11% 5% 13% 8% 6% 5% 5% 7% 6% 26%	3249
	11th to 20th	Day	3 6% 4 13% 8% 6% 8% 5% 7% 10% 30%	3201
	21st to end	Day	6% 13% 4 9% 5% 5% 5% 4 7% 8% 33%	3653
February	1st to 10th	Day	8% 13% 5% 14% 7% 8% 6% 4 5% 7% 23%	1757
	11th to 20th	Day	7% 12% 4 11% 7% 7% 6% 4 7% 7% 29%	1755
	21st to end	Day	5% 11% 4 10% 9% 8% 7% 5% 7% 8% 25%	1485
March	1st to 10th	Day	5% 9% 4 11% 8% 7% 6% 4 7% 9% 29%	4592
	11th to 20th	Day	3 13% 7% 18% 8% 5% 4 3 5% 8% 27%	4999
	21st to end	Day	6% 14% 7% 16% 7% 5% 5% 4 5% 7% 24%	5654
April	1st to 10th	Day	8% 10% 3 9% 6% 6% 5% 4 7% 7% 35%	2400
	11th to 20th	Day	9% 13% 4 10% 6% 5% 5% 6% 6% 7% 29%	2521
	21st to end	Day	13% 10% 3 8% 5% 4 5% 3 6% 8% 35%	2720
May	1st to 10th	Day	15% 8% 2 6% 4 5% 4 4 5% 6% 42%	6340
	11th to 20th	Day	12% 9% 3 9% 7% 7% 7% 6% 8% 7% 26%	6298
	21st to end	Day	10% 7% 3 8% 5% 5% 6% 5% 6% 8% 39%	7402
June	1st to 10th	Day	12% 8% 2 6% 5% 5% 5% 4 6% 7% 39%	3020
	11th to 20th	Day	19% 7% 3 7% 6% 5% 5% 4 7% 8% 30%	3200
	21st to end	Day	10% 5% 2 7% 5% 5% 6% 5% 8% 9% 39%	3062
July	1st to 10th	Day	6% 4 2 6% 5% 5% 5% 5% 7% 10% 46%	6780
	11th to 20th	Day	10% 5% 2 6% 5% 4 5% 4 6% 9% 43%	6780
	21st to end	Day	6% 3 1 4 3 3 4 4 6% 9% 57%	7300
August	1st to 10th	Day	9% 6% 2 5% 4 5% 4 4 6% 8% 48%	4552
	11th to 20th	Day	7% 4 2 5% 4 4 4 4 6% 10% 51%	4261
	21st to end	Day	10% 4 2 4 3 3 4 3 5% 8% 55%	4615
September	1st to 10th	Day	9% 6% 2 6% 4 4 4 3 6% 8% 49%	2400
	11th to 20th	Day	13% 7% 2 6% 4 4 4 4 6% 7% 43%	2400
	21st to end	Day	9% 5% 2 5% 2 4 3 3 5% 7% 55%	2106
October	1st to 10th	Day	7% 6% 2 6% 4 4 4 4 6% 9% 48%	3270
	11th to 20th	Day	5% 5% 3 5% 4 5% 4 4 8% 12% 44%	3250
	21st to end	Day	6% 8% 4 9% 5% 4 5% 5% 6% 8% 40%	3054
November	1st to 10th	Day	11% 15% 4 10% 6% 4 4 4 5% 5% 31%	1648
	11th to 20th	Day	6% 13% 7% 13% 7% 6% 5% 5% 6% 6% 27%	1680
	21st to end	Day	8% 13% 6% 11% 7% 5% 5% 4 6% 7% 27%	1680
December	1st to 10th	Day	6% 10% 3 12% 9% 8% 7% 6% 7% 7% 25%	2106
	11th to 20th	Day	8% 13% 5% 13% 9% 10% 7% 4 6% 5% 20%	2319
	21st to end	Day	3 7% 3 10% 8% 6% 6% 4 6% 7% 39%	3545
January	1st to 10th	Night	3 10% 5% 13% 9% 8% 7% 6% 7% 8% 24%	6916
	11th to 20th	Night	3 9% 4 13% 9% 9% 8% 5% 6% 8% 26%	6830
	21st to end	Night	6% 11% 4 10% 6% 5% 6% 4 7% 9% 32%	7309
February	1st to 10th	Night	7% 13% 5% 12% 7% 6% 6% 5% 7% 8% 25%	2660
	11th to 20th	Night	5% 11% 5% 11% 7% 6% 7% 5% 6% 7% 30%	2532
	21st to end	Night	3 9% 4 9% 8% 7% 6% 5% 7% 10% 32%	2145
March	1st to 10th	Night	5% 9% 4 12% 8% 6% 7% 5% 7% 9% 28%	5282
	11th to 20th	Night	5% 10% 5% 12% 7% 6% 6% 5% 7% 9% 29%	5000
	21st to end	Night	9% 12% 5% 13% 7% 6% 5% 4 6% 7% 27%	5312
April	1st to 10th	Night	6% 9% 2 7% 6% 5% 4 4 6% 9% 41%	2000
	11th to 20th	Night	10% 12% 3 9% 6% 5% 6% 5% 7% 7% 31%	1827
	21st to end	Night	13% 9% 3 9% 5% 5% 5% 5% 5% 7% 34%	1680
May	1st to 10th	Night	14% 8% 2 6% 4 3 4 3 5% 5% 44%	3640
	11th to 20th	Night	14% 10% 3 9% 5% 6% 6% 4 7% 8% 29%	3618
	21st to end	Night	11% 7% 2 7% 4 3 4 4 6% 8% 45%	3470
June	1st to 10th	Night	11% 6% 3 5% 4 5% 4 4 8% 11% 40%	1375
	11th to 20th	Night	17% 5% 2 6% 6% 5% 6% 4 7% 7% 34%	1200
	21st to end	Night	8% 5% 2 5% 4 3 6% 5% 8% 9% 46%	1329
July	1st to 10th	Night	6% 4 1 5% 4 4 5% 4 8% 9% 50%	3180
	11th to 20th	Night	5% 5% 2 6% 4 5% 7% 4 7% 9% 45%	3180
	21st to end	Night	6% 3 1 3 3 3 3 4 6% 9% 59%	3547
August	1st to 10th	Night	7% 4 2 5% 3 4 4 3 5% 8% 54%	2608
	11th to 20th	Night	5% 4 2 5% 4 5% 4 5% 7% 9% 51%	2797
	21st to end	Night	7% 4 2 5% 3 4 4 3 6% 9% 54%	3294
September	1st to 10th	Night	8% 4 2 5% 5% 4 4 3 6% 7% 52%	2000
	11th to 20th	Night	11% 5% 3 6% 4 3 4 4 5% 8% 47%	2000
	21st to end	Night	8% 5% 2 4 2 3 3 3 5% 7% 56%	2291
October	1st to 10th	Night	10% 8% 2 6% 4 4 4 3 5% 7% 47%	3920
	11th to 20th	Night	5% 5% 2 5% 4 4 4 3 5% 8% 53%	3898
	21st to end	Night	7% 8% 3 7% 4 4 5% 4 6% 8% 42%	4698
November	1st to 10th	Night	14% 14% 4 9% 5% 4 4 3 5% 6% 32%	2870
	11th to 20th	Night	6% 10% 5% 12% 7% 6% 5% 3 7% 8% 30%	2940
	21st to end	Night	6% 13% 5% 12% 6% 6% 5% 4 6% 7% 30%	2940
December	1st to 10th	Night	8% 14% 5% 14% 9% 7% 5% 4 6% 7% 20%	5288
	11th to 20th	Night	6% 14% 5% 12% 8% 8% 7% 5% 7% 8% 21%	6093
	21st to end	Night	3 6% 3 11% 9% 6% 5% 4 5% 6% 43%	7646

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	56% 6% 12% 19% 6%	3249
	11th to 20th	Day	48% 7% 14% 19% 12% 1	3222
	21st to end	Day	48% 7% 23% 18% 3	3653
February	1st to 10th	Day	60% 6% 9% 16% 8%	1757
	11th to 20th	Day	53% 6% 13% 18% 11% 1	1764
	21st to end	Day	54% 6% 14% 18% 7%	1485
March	1st to 10th	Day	50% 6% 20% 18% 6%	4592
	11th to 20th	Day	56% 7% 14% 17% 5%	5000
	21st to end	Day	57% 7% 13% 19% 4	5654
April	1st to 10th	Day	45% 7% 14% 21% 12% 1	2400
	11th to 20th	Day	52% 6% 14% 19% 8% 1	2521
	21st to end	Day	47% 6% 13% 23% 9% 1	2720
May	1st to 10th	Day	43% 4 12% 26% 13% 2	6340
	11th to 20th	Day	50% 8% 13% 20% 8%	6302
	21st to end	Day	39% 8% 15% 25% 11% 2	7403
June	1st to 10th	Day	42% 7% 13% 24% 13% 1	3020
	11th to 20th	Day	50% 8% 13% 21% 7% 1	3200
	21st to end	Day	38% 9% 19% 24% 9% 1	3062
July	1st to 10th	Day	32% 8% 20% 28% 13%	6706
	11th to 20th	Day	37% 7% 14% 34% 8%	6699
	21st to end	Day	23% 6% 20% 35% 13% 2	7094
August	1st to 10th	Day	33% 7% 20% 30% 9%	4536
	11th to 20th	Day	28% 7% 17% 37% 10%	4303
	21st to end	Day	29% 5% 18% 36% 12%	4614
September	1st to 10th	Day	33% 7% 14% 27% 15% 4	2400
	11th to 20th	Day	39% 6% 16% 27% 10% 2	2400
	21st to end	Day	29% 6% 15% 34% 15% 2	2106
October	1st to 10th	Day	32% 5% 21% 31% 9% 1	3270
	11th to 20th	Day	32% 5% 19% 34% 10%	3250
	21st to end	Day	41% 7% 16% 30% 7%	3054
November	1st to 10th	Day	56% 4 13% 19% 8%	1648
	11th to 20th	Day	57% 7% 14% 17% 5%	1680
	21st to end	Day	57% 7% 15% 17% 4	1680
December	1st to 10th	Day	56% 11% 15% 12% 6%	2106
	11th to 20th	Day	64% 6% 17% 8% 4	2320
	21st to end	Day	43% 5% 12% 22% 15% 4	3545
January	1st to 10th	Night	54% 7% 15% 17% 6%	6916
	11th to 20th	Night	55% 6% 13% 14% 11%	6871
	21st to end	Night	47% 7% 21% 21% 4	7309
February	1st to 10th	Night	54% 7% 13% 18% 8%	2660
	11th to 20th	Night	51% 7% 14% 17% 11%	2533
	21st to end	Night	45% 6% 16% 23% 10%	2145
March	1st to 10th	Night	49% 6% 19% 20% 5%	5282
	11th to 20th	Night	49% 7% 16% 21% 7%	5000
	21st to end	Night	55% 6% 10% 20% 9%	5312
April	1st to 10th	Night	39% 6% 14% 24% 15% 1	2000
	11th to 20th	Night	50% 6% 12% 19% 11% 2	1827
	21st to end	Night	48% 7% 10% 23% 11% 1	1680
May	1st to 10th	Night	40% 6% 9% 24% 17% 3	3640
	11th to 20th	Night	48% 8% 13% 18% 12% 1	3618
	21st to end	Night	37% 6% 15% 26% 15% 1	3470
June	1st to 10th	Night	36% 7% 16% 27% 13% 1	1375
	11th to 20th	Night	45% 10% 12% 20% 12% 1	1200
	21st to end	Night	31% 8% 20% 30% 9% 2	1329
July	1st to 10th	Night	28% 8% 24% 28% 12%	3145
	11th to 20th	Night	33% 6% 15% 38% 9%	3138
	21st to end	Night	22% 6% 18% 36% 16% 2	3448
August	1st to 10th	Night	29% 6% 19% 32% 13% 2	2600
	11th to 20th	Night	28% 6% 17% 34% 13% 1	2821
	21st to end	Night	26% 6% 15% 34% 17% 1	3294
September	1st to 10th	Night	31% 6% 13% 28% 15% 7%	2000
	11th to 20th	Night	36% 6% 15% 29% 12% 3	2000
	21st to end	Night	27% 6% 12% 34% 18% 3	2291
October	1st to 10th	Night	38% 4 17% 29% 11%	3920
	11th to 20th	Night	30% 4 14% 37% 14% 1	3898
	21st to end	Night	39% 5% 13% 35% 7% 1	4698
November	1st to 10th	Night	54% 6% 12% 20% 8% 1	2870
	11th to 20th	Night	51% 8% 17% 17% 6%	2940
	21st to end	Night	53% 7% 16% 20% 4	2940
December	1st to 10th	Night	64% 7% 15% 10% 4 1	5288
	11th to 20th	Night	59% 7% 19% 11% 4	6091
	21st to end	Night	42% 5% 11% 25% 14% 3	7646

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% 6% 26% 31% 18% 6%	220
	11th to 20th	Day	13% 8% 29% 28% 18% 4	212
	21st to end	Day	11% 11% 29% 31% 14% 3	253
February	1st to 10th	Day	14% 10% 36% 29% 10% 2	300
	11th to 20th	Day	10% 4 32% 33% 16% 6%	300
	21st to end	Day	6% 8% 27% 36% 19% 5%	249
March	1st to 10th	Day	10% 6% 33% 31% 16% 4	341
	11th to 20th	Day	10% 9% 31% 32% 13% 5%	500
	21st to end	Day	14% 9% 31% 26% 17% 3	550
April	1st to 10th	Day	10% 11% 36% 29% 11% 3	500
	11th to 20th	Day	13% 15% 32% 29% 9% 2	492
	21st to end	Day	16% 10% 27% 32% 13% 2	620
May	1st to 10th	Day	14% 8% 26% 29% 18% 6%	703
	11th to 20th	Day	12% 9% 22% 32% 19% 6%	725
	21st to end	Day	13% 9% 20% 28% 22% 7%	789
June	1st to 10th	Day	13% 11% 27% 26% 18% 5%	730
	11th to 20th	Day	18% 11% 27% 26% 13% 5%	730
	21st to end	Day	12% 8% 21% 31% 22% 7%	730
July	1st to 10th	Day	8% 4 23% 33% 24% 7%	721
	11th to 20th	Day	11% 6% 24% 28% 23% 8%	718
	21st to end	Day	8% 4 23% 28% 27% 10%	794
August	1st to 10th	Day	10% 5% 20% 31% 23% 10%	726
	11th to 20th	Day	9% 7% 19% 31% 26% 7%	584
	21st to end	Day	11% 6% 20% 34% 21% 8%	583
September	1st to 10th	Day	13% 7% 26% 28% 21% 6%	530
	11th to 20th	Day	18% 6% 25% 29% 18% 4	530
	21st to end	Day	15% 7% 29% 33% 11% 5%	431
October	1st to 10th	Day	17% 5% 27% 26% 19% 5%	330
	11th to 20th	Day	9% 9% 31% 31% 15% 5%	330
	21st to end	Day	11% 12% 40% 24% 10% 3	363
November	1st to 10th	Day	18% 9% 32% 30% 10% 1	330
	11th to 20th	Day	11% 12% 36% 30% 9% 2	330
	21st to end	Day	9% 8% 35% 32% 12% 5%	330
December	1st to 10th	Day	10% 5% 35% 34% 11% 5%	222
	11th to 20th	Day	11% 13% 33% 32% 10% 1	220
	21st to end	Day	12% 4 31% 32% 19% 2	242
January	1st to 10th	Night	9% 7% 34% 37% 12% 2	1050
	11th to 20th	Night	10% 9% 35% 33% 11% 1	1031
	21st to end	Night	12% 8% 37% 32% 10% 1	1100
February	1st to 10th	Night	11% 6% 29% 35% 16% 2	860
	11th to 20th	Night	10% 6% 29% 38% 15% 2	784
	21st to end	Night	6% 5% 26% 35% 24% 5%	660
March	1st to 10th	Night	10% 6% 30% 38% 14% 2	800
	11th to 20th	Night	8% 6% 31% 38% 15% 2	800
	21st to end	Night	12% 7% 28% 36% 14% 2	806
April	1st to 10th	Night	10% 9% 30% 39% 12% 1	600
	11th to 20th	Night	16% 10% 32% 30% 11% 1	593
	21st to end	Night	17% 7% 27% 34% 14%	600
May	1st to 10th	Night	14% 4 25% 38% 17% 2	600
	11th to 20th	Night	12% 7% 26% 34% 19% 2	591
	21st to end	Night	18% 8% 19% 33% 19% 3	433
June	1st to 10th	Night	13% 6% 28% 35% 16% 2	400
	11th to 20th	Night	19% 8% 20% 35% 17% 1	400
	21st to end	Night	10% 7% 20% 39% 23% 3	400
July	1st to 10th	Night	7% 4 21% 45% 23% 1	390
	11th to 20th	Night	9% 3 25% 43% 18% 2	388
	21st to end	Night	4 3 24% 44% 24% 2	468
August	1st to 10th	Night	6% 4 19% 42% 27% 3	597
	11th to 20th	Night	7% 4 20% 41% 26% 2	594
	21st to end	Night	10% 3 25% 37% 24%	660
September	1st to 10th	Night	11% 4 24% 42% 18% 2	600
	11th to 20th	Night	14% 4 22% 39% 20% 1	600
	21st to end	Night	11% 4 32% 37% 14% 2	793
October	1st to 10th	Night	16% 6% 26% 36% 15%	800
	11th to 20th	Night	10% 6% 32% 36% 14% 2	800
	21st to end	Night	15% 8% 34% 32% 10% 1	1055
November	1st to 10th	Night	20% 8% 29% 33% 8% 1	1025
	11th to 20th	Night	10% 9% 34% 33% 12% 2	1050
	21st to end	Night	12% 7% 36% 35% 10% 1	1050
December	1st to 10th	Night	14% 7% 33% 30% 14% 3	1050
	11th to 20th	Night	12% 9% 36% 31% 11% 1	1050
	21st to end	Night	11% 5% 30% 35% 15% 4	1155

Page generated at 2026-01-14 00:14:29. Version ac07

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