SAPM Rosette 3.5
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the SAPM Rosette 3.5 clear sky chart from 2005-11-06 to 2026-04-17.

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	17% 11% 4 9% 5% 5% 4 3 5% 6% 30%	131582
	Night	18% 13% 5% 10% 5% 5% 4 3 5% 5% 27%	130586
Transparency	Day	53% 6% 12% 20% 9% 1	135025
	Night	57% 6% 11% 17% 9% 1	135217
Seeing	Day	23% 17% 29% 20% 9% 2	16329
	Night	24% 16% 29% 23% 8% 1	25476

By Month

Percentage Cloud Cover NE (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	15% 21% 6% 15% 8% 6% 4 3 3 4 14%	4661
	11th to 20th	Day	10% 18% 9% 18% 9% 6% 5% 3 4 3 16%	4650
	21st to end	Day	11% 15% 7% 13% 10% 10% 5% 3 5% 5% 17%	5124
February	1st to 10th	Day	15% 17% 5% 13% 7% 5% 5% 3 5% 5% 20%	1890
	11th to 20th	Day	13% 14% 5% 13% 8% 6% 4 4 5% 5% 23%	1939
	21st to end	Day	16% 18% 5% 10% 8% 5% 4 3 5% 5% 21%	1730
March	1st to 10th	Day	19% 13% 5% 11% 5% 5% 6% 3 4 5% 23%	4576
	11th to 20th	Day	13% 16% 4 10% 5% 4 4 3 5% 6% 29%	4870
	21st to end	Day	19% 10% 3 10% 5% 4 3 3 4 4 33%	6050
April	1st to 10th	Day	21% 14% 4 7% 5% 4 3 2 4 5% 31%	2520
	11th to 20th	Day	21% 10% 3 7% 5% 4 3 2 4 5% 35%	2446
	21st to end	Day	24% 10% 3 6% 4 4 4 3 4 6% 32%	2525
May	1st to 10th	Day	29% 10% 3 9% 5% 4 4 3 5% 6% 23%	6291
	11th to 20th	Day	21% 9% 3 8% 4 5% 4 4 5% 7% 30%	6318
	21st to end	Day	22% 9% 3 6% 4 4 4 4 6% 7% 31%	6949
June	1st to 10th	Day	23% 8% 3 7% 4 4 5% 3 6% 7% 30%	2800
	11th to 20th	Day	15% 6% 2 7% 4 5% 5% 4 6% 8% 37%	2800
	21st to end	Day	21% 7% 3 6% 4 5% 5% 4 5% 8% 32%	2800
July	1st to 10th	Day	13% 7% 3 8% 5% 5% 6% 4 7% 8% 35%	6360
	11th to 20th	Day	11% 6% 2 6% 5% 5% 5% 5% 6% 8% 41%	6360
	21st to end	Day	13% 5% 2 5% 4 4 4 4 6% 9% 45%	6926
August	1st to 10th	Day	17% 7% 3 7% 5% 4 5% 4 6% 8% 34%	4563
	11th to 20th	Day	16% 6% 3 7% 4 4 5% 4 6% 7% 39%	4058
	21st to end	Day	17% 5% 2 6% 3 4 4 4 7% 8% 39%	4312
September	1st to 10th	Day	14% 6% 2 5% 4 4 4 4 6% 8% 44%	2400
	11th to 20th	Day	14% 6% 2 5% 3 3 3 3 4 7% 49%	2335
	21st to end	Day	15% 6% 3 7% 5% 4 4 4 6% 7% 40%	2200
October	1st to 10th	Day	21% 7% 3 6% 4 4 4 4 5% 7% 35%	2038
	11th to 20th	Day	18% 11% 3 9% 5% 5% 5% 3 5% 6% 30%	1988
	21st to end	Day	27% 12% 4 7% 4 4 3 3 4 6% 27%	1980
November	1st to 10th	Day	18% 13% 4 8% 4 5% 4 3 4 7% 29%	1851
	11th to 20th	Day	17% 14% 5% 9% 5% 4 4 3 6% 6% 26%	1798
	21st to end	Day	19% 21% 6% 10% 5% 4 4 4 4 4 19%	1680
December	1st to 10th	Day	20% 19% 7% 16% 7% 5% 4 3 4 4 12%	2680
	11th to 20th	Day	18% 15% 6% 13% 6% 4 5% 3 5% 4 21%	3066
	21st to end	Day	21% 18% 4 12% 6% 4 4 3 5% 4 21%	4048
January	1st to 10th	Night	14% 22% 9% 17% 6% 4 3 2 3 4 16%	8234
	11th to 20th	Night	12% 20% 9% 20% 7% 5% 5% 3 4 3 12%	8235
	21st to end	Night	12% 17% 6% 14% 9% 7% 5% 3 4 4 19%	9040
February	1st to 10th	Night	14% 16% 6% 15% 8% 6% 4 3 4 5% 19%	2730
	11th to 20th	Night	13% 15% 5% 13% 7% 5% 5% 3 4 5% 24%	2565
	21st to end	Night	14% 17% 5% 11% 7% 5% 4 3 4 5% 26%	2076
March	1st to 10th	Night	21% 13% 4 10% 6% 5% 3 2 3 4 29%	5484
	11th to 20th	Night	15% 16% 4 8% 5% 4 4 3 4 6% 29%	5306
	21st to end	Night	17% 14% 4 11% 5% 4 4 3 4 4 29%	5122
April	1st to 10th	Night	23% 13% 4 8% 5% 4 3 3 4 4 28%	2100
	11th to 20th	Night	23% 11% 2 8% 5% 4 4 3 4 5% 30%	2036
	21st to end	Night	21% 10% 4 8% 4 4 4 2 5% 5% 34%	1874
May	1st to 10th	Night	29% 11% 4 7% 4 4 4 3 5% 6% 23%	3691
	11th to 20th	Night	24% 8% 3 8% 4 4 4 3 5% 6% 31%	3575
	21st to end	Night	18% 10% 3 8% 5% 4 5% 3 5% 7% 30%	3926
June	1st to 10th	Night	21% 8% 3 8% 4 4 4 4 6% 8% 29%	1600
	11th to 20th	Night	18% 6% 3 5% 5% 5% 4 4 5% 7% 39%	1600
	21st to end	Night	18% 8% 3 7% 4 5% 4 4 6% 7% 35%	1600
July	1st to 10th	Night	15% 6% 3 7% 5% 5% 5% 4 7% 8% 35%	3600
	11th to 20th	Night	17% 5% 2 6% 4 3 4 4 6% 7% 42%	3600
	21st to end	Night	13% 6% 2 7% 4 5% 4 4 6% 7% 41%	3926
August	1st to 10th	Night	17% 8% 2 7% 4 4 3 3 5% 7% 39%	2586
	11th to 20th	Night	17% 7% 3 7% 4 4 5% 3 5% 7% 37%	2955
	21st to end	Night	15% 6% 2 6% 3 4 5% 3 7% 7% 42%	3586
September	1st to 10th	Night	14% 6% 2 7% 4 4 4 3 5% 7% 43%	2000
	11th to 20th	Night	15% 5% 2 6% 3 3 2 4 5% 6% 48%	2065
	21st to end	Night	19% 6% 2 5% 4 4 4 3 6% 6% 41%	2200
October	1st to 10th	Night	20% 8% 3 6% 5% 4 4 4 5% 6% 37%	2360
	11th to 20th	Night	19% 10% 3 8% 4 5% 5% 4 5% 5% 33%	2410
	21st to end	Night	24% 12% 3 8% 5% 4 4 3 4 6% 27%	2860
November	1st to 10th	Night	22% 13% 3 7% 4 5% 3 4 5% 6% 29%	2667
	11th to 20th	Night	19% 13% 4 8% 5% 5% 4 3 4 5% 29%	2819
	21st to end	Night	21% 16% 6% 10% 5% 5% 4 3 4 5% 22%	2940
December	1st to 10th	Night	18% 24% 7% 12% 6% 5% 4 3 4 4 13%	4720
	11th to 20th	Night	23% 16% 6% 12% 5% 4 4 3 3 3 21%	5348
	21st to end	Night	23% 17% 5% 12% 5% 4 4 3 3 6% 19%	7150

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	71% 7% 12% 9% 2	4662
	11th to 20th	Day	69% 4 11% 8% 7% 1	4680
	21st to end	Day	66% 6% 11% 8% 8% 1	5124
February	1st to 10th	Day	64% 5% 10% 15% 4 1	1890
	11th to 20th	Day	61% 5% 12% 14% 7% 1	1948
	21st to end	Day	64% 5% 10% 13% 8% 1	1730
March	1st to 10th	Day	60% 6% 11% 13% 7% 3	4579
	11th to 20th	Day	53% 5% 17% 14% 9% 1	4870
	21st to end	Day	54% 4 8% 17% 16% 1	6050
April	1st to 10th	Day	56% 4 8% 20% 11% 2	2520
	11th to 20th	Day	52% 4 8% 20% 15% 1	2446
	21st to end	Day	53% 5% 10% 16% 12% 3	2525
May	1st to 10th	Day	62% 6% 9% 15% 7% 1	6302
	11th to 20th	Day	53% 8% 12% 17% 9% 1	6322
	21st to end	Day	50% 7% 12% 20% 10% 1	6949
June	1st to 10th	Day	52% 6% 11% 18% 12% 1	2800
	11th to 20th	Day	43% 7% 12% 23% 13% 2	2800
	21st to end	Day	50% 8% 12% 19% 10% 1	2800
July	1st to 10th	Day	44% 7% 13% 26% 9%	6290
	11th to 20th	Day	38% 7% 14% 28% 13%	6285
	21st to end	Day	34% 7% 13% 37% 8%	6728
August	1st to 10th	Day	46% 7% 15% 23% 8%	4549
	11th to 20th	Day	43% 7% 16% 27% 7%	4099
	21st to end	Day	40% 7% 18% 23% 11%	4312
September	1st to 10th	Day	37% 8% 13% 29% 13%	2400
	11th to 20th	Day	36% 5% 12% 33% 14% 1	2335
	21st to end	Day	42% 7% 15% 25% 11% 1	2200
October	1st to 10th	Day	46% 5% 13% 27% 9%	3311
	11th to 20th	Day	47% 6% 16% 24% 7%	3216
	21st to end	Day	49% 5% 18% 22% 6%	3180
November	1st to 10th	Day	54% 6% 13% 19% 7% 1	1851
	11th to 20th	Day	57% 6% 12% 15% 9% 1	1798
	21st to end	Day	68% 7% 11% 11% 3	1680
December	1st to 10th	Day	75% 6% 9% 9% 1	2680
	11th to 20th	Day	64% 7% 9% 14% 5%	3066
	21st to end	Day	65% 7% 9% 14% 5%	4048
January	1st to 10th	Night	71% 5% 11% 9% 3	8234
	11th to 20th	Night	73% 6% 8% 8% 5%	8280
	21st to end	Night	65% 5% 10% 11% 9%	9040
February	1st to 10th	Night	67% 6% 9% 12% 5% 1	2730
	11th to 20th	Night	61% 4 11% 17% 7%	2567
	21st to end	Night	60% 5% 9% 16% 10%	2076
March	1st to 10th	Night	58% 5% 7% 17% 11% 2	5494
	11th to 20th	Night	55% 6% 16% 14% 8% 2	5307
	21st to end	Night	57% 4 7% 20% 10% 2	5122
April	1st to 10th	Night	58% 4 9% 16% 11% 1	2100
	11th to 20th	Night	56% 5% 10% 18% 11% 1	2036
	21st to end	Night	53% 5% 8% 17% 14% 4	1874
May	1st to 10th	Night	61% 7% 9% 15% 7% 2	3697
	11th to 20th	Night	52% 7% 10% 20% 11% 1	3576
	21st to end	Night	51% 7% 11% 18% 12% 1	3927
June	1st to 10th	Night	51% 8% 11% 17% 12% 1	1600
	11th to 20th	Night	44% 6% 13% 19% 16% 2	1600
	21st to end	Night	48% 7% 12% 21% 11% 1	1600
July	1st to 10th	Night	43% 7% 17% 23% 10%	3560
	11th to 20th	Night	39% 7% 14% 28% 12%	3552
	21st to end	Night	41% 6% 13% 29% 11%	3809
August	1st to 10th	Night	44% 7% 13% 27% 8%	2576
	11th to 20th	Night	46% 7% 17% 22% 8%	2980
	21st to end	Night	39% 8% 16% 23% 13% 1	3586
September	1st to 10th	Night	40% 7% 12% 28% 13% 1	2000
	11th to 20th	Night	36% 6% 13% 33% 12%	2065
	21st to end	Night	42% 7% 12% 24% 14% 1	2200
October	1st to 10th	Night	46% 6% 12% 26% 9%	3854
	11th to 20th	Night	48% 5% 13% 24% 10%	3921
	21st to end	Night	51% 6% 15% 19% 9% 1	4610
November	1st to 10th	Night	55% 6% 13% 17% 8% 1	2667
	11th to 20th	Night	56% 5% 13% 16% 8% 2	2819
	21st to end	Night	64% 7% 11% 13% 4	2940
December	1st to 10th	Night	74% 6% 10% 8% 2	4720
	11th to 20th	Night	67% 5% 9% 12% 7%	5348
	21st to end	Night	65% 6% 9% 11% 8%	7150

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	28% 18% 31% 17% 5%	220
	11th to 20th	Day	30% 27% 30% 10% 3	220
	21st to end	Day	22% 23% 33% 18% 3	242
February	1st to 10th	Day	27% 26% 32% 12% 2	330
	11th to 20th	Day	24% 27% 35% 12% 1	426
	21st to end	Day	29% 21% 32% 17% 2	446
March	1st to 10th	Day	27% 23% 29% 16% 5%	540
	11th to 20th	Day	24% 24% 32% 16% 4 1	540
	21st to end	Day	29% 23% 26% 13% 9%	594
April	1st to 10th	Day	29% 21% 29% 15% 5%	540
	11th to 20th	Day	30% 22% 24% 16% 8% 1	516
	21st to end	Day	29% 18% 29% 16% 7% 1	500
May	1st to 10th	Day	26% 15% 33% 17% 8% 1	503
	11th to 20th	Day	19% 15% 32% 20% 12% 2	527
	21st to end	Day	20% 18% 27% 24% 8% 2	573
June	1st to 10th	Day	25% 15% 28% 23% 7% 2	530
	11th to 20th	Day	15% 14% 34% 26% 8% 2	530
	21st to end	Day	24% 14% 34% 18% 9% 2	530
July	1st to 10th	Day	14% 12% 33% 24% 14% 3	525
	11th to 20th	Day	15% 11% 31% 30% 10% 3	524
	21st to end	Day	14% 10% 32% 30% 12% 2	576
August	1st to 10th	Day	15% 8% 30% 29% 15% 4	526
	11th to 20th	Day	14% 9% 27% 30% 15% 5%	519
	21st to end	Day	17% 12% 29% 22% 14% 6%	583
September	1st to 10th	Day	15% 10% 29% 24% 16% 6%	530
	11th to 20th	Day	15% 10% 20% 28% 19% 8%	530
	21st to end	Day	16% 13% 27% 25% 15% 4	530
October	1st to 10th	Day	22% 15% 26% 19% 13% 4	530
	11th to 20th	Day	24% 21% 27% 16% 10% 1	522
	21st to end	Day	34% 15% 27% 18% 6%	462
November	1st to 10th	Day	32% 20% 24% 15% 8%	425
	11th to 20th	Day	30% 24% 25% 14% 7% 1	338
	21st to end	Day	31% 26% 24% 15% 5%	220
December	1st to 10th	Day	31% 19% 28% 16% 6%	220
	11th to 20th	Day	29% 29% 28% 12% 2	220
	21st to end	Day	31% 24% 26% 15% 3 1	242
January	1st to 10th	Night	25% 23% 33% 17% 2	840
	11th to 20th	Night	29% 21% 30% 16% 4	840
	21st to end	Night	20% 19% 35% 21% 4	924
February	1st to 10th	Night	21% 23% 32% 21% 4	840
	11th to 20th	Night	22% 22% 36% 18% 2	823
	21st to end	Night	24% 18% 34% 22% 2	692
March	1st to 10th	Night	27% 20% 30% 20% 4	840
	11th to 20th	Night	25% 21% 31% 18% 4	840
	21st to end	Night	27% 16% 28% 24% 5%	924
April	1st to 10th	Night	29% 18% 30% 20% 4	840
	11th to 20th	Night	28% 17% 29% 20% 5%	816
	21st to end	Night	27% 15% 29% 22% 7%	674
May	1st to 10th	Night	29% 11% 27% 24% 8%	445
	11th to 20th	Night	21% 11% 31% 28% 9% 1	394
	21st to end	Night	17% 11% 33% 28% 10%	433
June	1st to 10th	Night	23% 9% 33% 27% 7% 1	400
	11th to 20th	Night	19% 11% 28% 31% 11% 1	400
	21st to end	Night	19% 9% 31% 28% 13% 1	400
July	1st to 10th	Night	12% 8% 33% 34% 13% 1	390
	11th to 20th	Night	11% 7% 30% 37% 14% 1	388
	21st to end	Night	15% 5% 31% 38% 10% 1	438
August	1st to 10th	Night	14% 5% 24% 39% 17% 1	398
	11th to 20th	Night	15% 6% 23% 35% 19% 2	633
	21st to end	Night	16% 7% 29% 32% 16% 1	880
September	1st to 10th	Night	15% 9% 28% 34% 14% 1	800
	11th to 20th	Night	15% 8% 23% 33% 18% 3	800
	21st to end	Night	20% 10% 26% 25% 18% 2	800
October	1st to 10th	Night	23% 12% 28% 21% 14% 1	800
	11th to 20th	Night	25% 15% 26% 25% 8% 1	800
	21st to end	Night	29% 17% 29% 21% 4	880
November	1st to 10th	Night	29% 19% 25% 21% 6%	820
	11th to 20th	Night	25% 20% 30% 16% 9%	840
	21st to end	Night	29% 22% 24% 19% 6%	840
December	1st to 10th	Night	30% 21% 29% 17% 3	840
	11th to 20th	Night	29% 23% 28% 16% 4 1	840
	21st to end	Night	33% 21% 28% 15% 3	924

Page generated at 2026-04-14 02:44:26. Version ac07

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