Rosthern
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rosthern clear sky chart from 2005-11-06 to 2026-07-01.

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% 8% 3 8% 6% 5% 5% 4 6% 8% 37%	141602
	Night	7% 9% 4 10% 6% 6% 5% 4 6% 8% 35%	139439
Transparency	Day	43% 7% 17% 24% 9%	141297
	Night	45% 6% 16% 23% 9% 1	139329
Seeing	Day	13% 7% 26% 30% 18% 5%	18017
	Night	12% 5% 28% 36% 16% 2	27274

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% 14% 6% 16% 8% 8% 7% 5% 5% 5% 20%	3905
	11th to 20th	Day	4 6% 3 11% 9% 9% 6% 6% 8% 8% 30%	4119
	21st to end	Day	6% 11% 4 13% 7% 6% 5% 4 7% 8% 29%	4826
February	1st to 10th	Day	8% 10% 4 11% 9% 7% 6% 6% 8% 8% 24%	1733
	11th to 20th	Day	7% 11% 4 11% 6% 6% 6% 4 7% 9% 30%	1845
	21st to end	Day	4 9% 4 13% 8% 8% 7% 6% 7% 8% 25%	1591
March	1st to 10th	Day	6% 11% 4 14% 9% 7% 7% 5% 7% 7% 24%	4600
	11th to 20th	Day	6% 12% 5% 12% 8% 6% 5% 4 6% 7% 29%	5012
	21st to end	Day	10% 11% 3 8% 5% 5% 6% 4 6% 7% 35%	5916
April	1st to 10th	Day	6% 10% 4 8% 6% 5% 4 5% 7% 8% 36%	2520
	11th to 20th	Day	11% 12% 3 9% 6% 5% 5% 4 6% 8% 32%	2603
	21st to end	Day	12% 9% 3 8% 6% 5% 5% 4 6% 8% 33%	2940
May	1st to 10th	Day	10% 7% 3 6% 4 4 4 4 5% 8% 46%	8224
	11th to 20th	Day	13% 9% 4 9% 6% 6% 6% 4 6% 8% 30%	8191
	21st to end	Day	10% 7% 2 6% 4 4 5% 4 6% 8% 43%	10006
June	1st to 10th	Day	13% 7% 3 8% 6% 5% 6% 5% 7% 8% 33%	3360
	11th to 20th	Day	21% 8% 3 8% 5% 6% 4 4 6% 7% 27%	3360
	21st to end	Day	15% 6% 2 6% 5% 5% 6% 4 7% 9% 35%	3360
July	1st to 10th	Day	8% 4 2 5% 3 4 4 4 7% 10% 50%	7241
	11th to 20th	Day	10% 4 1 6% 4 5% 5% 5% 6% 10% 44%	6784
	21st to end	Day	7% 3 1 4 4 4 5% 4 7% 11% 51%	7251
August	1st to 10th	Day	12% 4 2 6% 4 5% 5% 4 6% 8% 45%	4552
	11th to 20th	Day	8% 4 2 6% 4 4 4 4 6% 10% 47%	4457
	21st to end	Day	11% 6% 2 5% 3 4 3 3 6% 8% 49%	4550
September	1st to 10th	Day	10% 5% 2 7% 5% 4 4 3 6% 8% 48%	2400
	11th to 20th	Day	12% 7% 3 8% 6% 4 5% 5% 6% 8% 38%	2400
	21st to end	Day	9% 6% 1 5% 4 4 4 4 6% 8% 50%	2130
October	1st to 10th	Day	9% 6% 2 6% 5% 4 4 3 6% 8% 47%	3270
	11th to 20th	Day	6% 7% 2 6% 5% 5% 5% 5% 8% 12% 38%	3155
	21st to end	Day	7% 8% 4 9% 6% 6% 7% 5% 6% 6% 36%	3084
November	1st to 10th	Day	15% 15% 4 9% 7% 5% 5% 3 5% 6% 27%	1648
	11th to 20th	Day	9% 14% 6% 12% 7% 6% 5% 5% 5% 6% 25%	1668
	21st to end	Day	7% 15% 6% 12% 7% 7% 5% 4 6% 8% 23%	1470
December	1st to 10th	Day	6% 14% 4 12% 9% 7% 8% 4 7% 8% 24%	2054
	11th to 20th	Day	5% 13% 7% 16% 10% 8% 5% 3 5% 6% 22%	2319
	21st to end	Day	3 10% 4 14% 7% 5% 5% 4 5% 6% 37%	3058
January	1st to 10th	Night	5% 12% 6% 15% 9% 7% 6% 4 8% 8% 22%	8972
	11th to 20th	Night	3 8% 4 13% 9% 9% 7% 4 6% 8% 30%	8779
	21st to end	Night	5% 10% 3 11% 7% 6% 6% 4 7% 9% 32%	9369
February	1st to 10th	Night	6% 11% 5% 13% 8% 7% 6% 5% 7% 7% 26%	2906
	11th to 20th	Night	4 11% 4 10% 6% 6% 6% 5% 7% 6% 33%	2662
	21st to end	Night	3 9% 4 10% 6% 5% 6% 5% 7% 8% 35%	2215
March	1st to 10th	Night	6% 11% 5% 11% 7% 6% 8% 5% 7% 9% 25%	5494
	11th to 20th	Night	8% 10% 4 11% 6% 6% 6% 5% 7% 9% 29%	5200
	21st to end	Night	8% 9% 3 8% 6% 5% 6% 4 8% 10% 31%	5287
April	1st to 10th	Night	5% 10% 3 7% 6% 5% 5% 4 7% 8% 39%	2100
	11th to 20th	Night	10% 11% 4 9% 5% 5% 5% 4 8% 7% 32%	1964
	21st to end	Night	13% 8% 3 10% 6% 4 5% 4 5% 7% 36%	1680
May	1st to 10th	Night	10% 7% 2 6% 5% 4 4 3 4 7% 46%	4724
	11th to 20th	Night	14% 9% 4 10% 6% 5% 5% 4 6% 8% 28%	4702
	21st to end	Night	11% 6% 2 5% 5% 4 5% 4 6% 9% 42%	4151
June	1st to 10th	Night	12% 6% 2 6% 5% 5% 5% 4 6% 9% 41%	1260
	11th to 20th	Night	17% 7% 3 7% 5% 5% 5% 3 7% 7% 33%	1260
	21st to end	Night	12% 6% 2 5% 4 5% 5% 5% 7% 7% 43%	1260
July	1st to 10th	Night	10% 4 2 5% 3 4 5% 5% 7% 11% 46%	2720
	11th to 20th	Night	10% 3 1 4 3 4 4 5% 6% 9% 51%	3172
	21st to end	Night	5% 3 2 5% 4 4 5% 4 6% 9% 55%	3597
August	1st to 10th	Night	7% 3 2 5% 4 4 5% 4 6% 7% 53%	2608
	11th to 20th	Night	7% 3 1 5% 4 5% 6% 5% 7% 10% 47%	2599
	21st to end	Night	10% 4 2 5% 3 3 4 3 5% 8% 53%	3358
September	1st to 10th	Night	9% 4 2 6% 4 3 4 4 6% 7% 51%	2000
	11th to 20th	Night	13% 5% 3 6% 4 4 4 3 5% 8% 44%	2000
	21st to end	Night	8% 5% 2 5% 3 4 5% 3 6% 8% 51%	2268
October	1st to 10th	Night	10% 7% 3 6% 3 3 4 3 6% 8% 48%	3920
	11th to 20th	Night	6% 6% 3 7% 5% 5% 5% 3 5% 6% 49%	3960
	21st to end	Night	8% 9% 4 8% 5% 5% 5% 4 5% 8% 40%	4703
November	1st to 10th	Night	15% 14% 4 8% 6% 5% 5% 4 5% 6% 27%	2870
	11th to 20th	Night	8% 12% 6% 13% 6% 6% 5% 4 6% 7% 26%	2951
	21st to end	Night	5% 13% 5% 12% 7% 6% 4 4 6% 8% 28%	3150
December	1st to 10th	Night	7% 14% 6% 13% 9% 7% 6% 4 5% 7% 22%	5345
	11th to 20th	Night	5% 12% 6% 15% 7% 7% 7% 5% 6% 8% 23%	6093
	21st to end	Night	3 8% 4 14% 8% 5% 5% 3 5% 6% 39%	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	63% 7% 7% 15% 9%	3905
	11th to 20th	Day	47% 6% 16% 20% 11%	4140
	21st to end	Day	52% 7% 18% 16% 8%	4826
February	1st to 10th	Day	54% 9% 14% 15% 8%	1733
	11th to 20th	Day	50% 6% 15% 18% 11% 1	1854
	21st to end	Day	52% 10% 12% 19% 7%	1591
March	1st to 10th	Day	57% 7% 17% 13% 7%	4600
	11th to 20th	Day	52% 9% 14% 18% 7%	5013
	21st to end	Day	47% 7% 12% 19% 15%	5916
April	1st to 10th	Day	42% 9% 17% 21% 11%	2520
	11th to 20th	Day	50% 7% 14% 19% 10% 1	2603
	21st to end	Day	47% 8% 16% 21% 7% 1	2940
May	1st to 10th	Day	36% 4 10% 32% 15% 2	8224
	11th to 20th	Day	49% 7% 11% 24% 8%	8195
	21st to end	Day	35% 8% 12% 29% 15% 1	10006
June	1st to 10th	Day	44% 9% 17% 20% 9% 1	3360
	11th to 20th	Day	54% 8% 15% 17% 7% 1	3360
	21st to end	Day	43% 9% 19% 21% 7%	3360
July	1st to 10th	Day	29% 5% 30% 29% 6%	7162
	11th to 20th	Day	34% 7% 17% 38% 4	6702
	21st to end	Day	27% 6% 25% 34% 8%	7046
August	1st to 10th	Day	37% 7% 22% 28% 6%	4536
	11th to 20th	Day	33% 6% 23% 33% 5%	4499
	21st to end	Day	34% 4 22% 34% 7%	4549
September	1st to 10th	Day	34% 7% 18% 27% 12% 2	2400
	11th to 20th	Day	44% 8% 18% 23% 6% 1	2400
	21st to end	Day	31% 6% 17% 32% 11% 2	2130
October	1st to 10th	Day	36% 4 24% 26% 10%	3270
	11th to 20th	Day	38% 4 22% 29% 6% 1	3155
	21st to end	Day	47% 6% 20% 24% 4	3084
November	1st to 10th	Day	58% 7% 13% 16% 7%	1648
	11th to 20th	Day	60% 9% 14% 13% 4	1668
	21st to end	Day	57% 9% 14% 15% 4	1470
December	1st to 10th	Day	58% 5% 17% 13% 6%	2054
	11th to 20th	Day	64% 5% 16% 11% 4	2320
	21st to end	Day	48% 5% 12% 20% 13% 2	3058
January	1st to 10th	Night	58% 6% 12% 17% 7%	8973
	11th to 20th	Night	52% 5% 15% 18% 10%	8820
	21st to end	Night	48% 7% 19% 18% 8%	9369
February	1st to 10th	Night	54% 8% 12% 17% 8%	2906
	11th to 20th	Night	46% 7% 14% 23% 10%	2663
	21st to end	Night	42% 8% 18% 24% 9%	2215
March	1st to 10th	Night	52% 7% 18% 17% 6%	5494
	11th to 20th	Night	49% 7% 16% 19% 8%	5200
	21st to end	Night	45% 6% 12% 25% 12%	5287
April	1st to 10th	Night	39% 8% 17% 23% 13% 1	2100
	11th to 20th	Night	47% 6% 15% 18% 12% 2	1964
	21st to end	Night	46% 7% 13% 23% 11% 1	1680
May	1st to 10th	Night	36% 6% 10% 30% 16% 2	4724
	11th to 20th	Night	52% 7% 10% 21% 9% 1	4702
	21st to end	Night	35% 9% 11% 27% 16% 2	4155
June	1st to 10th	Night	37% 8% 16% 25% 11% 2	1260
	11th to 20th	Night	48% 8% 16% 17% 10% 1	1260
	21st to end	Night	36% 9% 20% 25% 10%	1260
July	1st to 10th	Night	32% 6% 25% 34% 4	2690
	11th to 20th	Night	30% 5% 16% 42% 7%	3131
	21st to end	Night	25% 5% 24% 37% 8% 1	3497
August	1st to 10th	Night	31% 6% 22% 32% 9%	2600
	11th to 20th	Night	31% 6% 24% 30% 9%	2623
	21st to end	Night	30% 4 21% 34% 10%	3358
September	1st to 10th	Night	30% 9% 17% 29% 12% 4	2000
	11th to 20th	Night	37% 8% 16% 30% 9% 1	2000
	21st to end	Night	29% 6% 15% 32% 16% 2	2268
October	1st to 10th	Night	35% 4 20% 34% 7%	3920
	11th to 20th	Night	36% 4 14% 32% 13%	3960
	21st to end	Night	42% 5% 21% 26% 6%	4703
November	1st to 10th	Night	57% 8% 13% 16% 6% 1	2870
	11th to 20th	Night	56% 9% 16% 14% 5%	2951
	21st to end	Night	53% 9% 16% 18% 4	3150
December	1st to 10th	Night	62% 6% 14% 14% 4	5345
	11th to 20th	Night	58% 6% 18% 13% 4	6091
	21st to end	Night	46% 4 11% 24% 12% 2	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	15% 6% 24% 31% 19% 6%	220
	11th to 20th	Day	10% 7% 32% 32% 16% 2	220
	21st to end	Day	14% 8% 29% 30% 17% 2	295
February	1st to 10th	Day	10% 6% 33% 30% 18% 3	330
	11th to 20th	Day	11% 3 24% 35% 21% 6%	330
	21st to end	Day	5% 7% 30% 36% 16% 4	273
March	1st to 10th	Day	13% 8% 26% 35% 15% 2	330
	11th to 20th	Day	13% 7% 28% 33% 16% 2	495
	21st to end	Day	14% 7% 27% 33% 17% 2	594
April	1st to 10th	Day	10% 9% 34% 29% 13% 5%	540
	11th to 20th	Day	13% 12% 28% 30% 13% 3	542
	21st to end	Day	12% 10% 26% 32% 16% 4	750
May	1st to 10th	Day	11% 8% 24% 34% 17% 5%	753
	11th to 20th	Day	14% 10% 21% 30% 18% 6%	775
	21st to end	Day	16% 9% 21% 27% 20% 7%	844
June	1st to 10th	Day	14% 10% 30% 27% 14% 4	780
	11th to 20th	Day	21% 9% 25% 24% 16% 5%	780
	21st to end	Day	15% 7% 22% 25% 21% 10%	780
July	1st to 10th	Day	10% 5% 20% 30% 27% 9%	722
	11th to 20th	Day	11% 6% 19% 30% 25% 9%	718
	21st to end	Day	6% 6% 21% 29% 28% 10%	794
August	1st to 10th	Day	11% 5% 20% 31% 24% 10%	726
	11th to 20th	Day	9% 4 21% 34% 25% 7%	702
	21st to end	Day	14% 7% 22% 31% 19% 7%	583
September	1st to 10th	Day	12% 10% 26% 29% 18% 4	530
	11th to 20th	Day	15% 6% 27% 33% 16% 4	530
	21st to end	Day	13% 8% 28% 30% 19% 2	375
October	1st to 10th	Day	16% 5% 28% 29% 18% 5%	330
	11th to 20th	Day	12% 11% 29% 28% 15% 4	330
	21st to end	Day	13% 10% 36% 24% 13% 4	363
November	1st to 10th	Day	20% 6% 32% 28% 12% 2	330
	11th to 20th	Day	13% 11% 35% 30% 9% 1	330
	21st to end	Day	12% 5% 32% 37% 13% 2	330
December	1st to 10th	Day	8% 6% 30% 34% 17% 6%	231
	11th to 20th	Day	11% 6% 34% 34% 15%	220
	21st to end	Day	12% 3 26% 34% 17% 8%	242
January	1st to 10th	Night	12% 5% 31% 36% 15% 2	1050
	11th to 20th	Night	11% 7% 34% 36% 11% 1	1050
	21st to end	Night	12% 7% 36% 34% 9% 1	1155
February	1st to 10th	Night	10% 5% 27% 37% 18% 2	1016
	11th to 20th	Night	8% 6% 26% 39% 17% 4	824
	21st to end	Night	7% 3 24% 39% 24% 4	692
March	1st to 10th	Night	12% 5% 30% 35% 16% 3	840
	11th to 20th	Night	10% 6% 30% 37% 14% 2	840
	21st to end	Night	14% 3 27% 37% 17% 2	782
April	1st to 10th	Night	8% 7% 30% 36% 17% 3	630
	11th to 20th	Night	14% 9% 29% 34% 12% 1	623
	21st to end	Night	16% 7% 28% 35% 13% 1	630
May	1st to 10th	Night	14% 5% 29% 37% 14% 1	630
	11th to 20th	Night	14% 7% 27% 33% 17% 1	621
	21st to end	Night	16% 6% 23% 34% 19% 3	479
June	1st to 10th	Night	15% 6% 28% 32% 17% 2	420
	11th to 20th	Night	20% 6% 22% 30% 19% 2	420
	21st to end	Night	15% 5% 19% 39% 22% 1	420
July	1st to 10th	Night	8% 4 19% 41% 27% 1	390
	11th to 20th	Night	12% 3 20% 44% 19% 3	388
	21st to end	Night	4 4 23% 36% 30% 3	493
August	1st to 10th	Night	7% 3 21% 39% 27% 4	597
	11th to 20th	Night	8% 3 18% 46% 23% 3	594
	21st to end	Night	11% 4 24% 36% 23% 2	660
September	1st to 10th	Night	11% 4 26% 38% 19% 2	600
	11th to 20th	Night	16% 5% 20% 42% 17% 1	600
	21st to end	Night	9% 5% 33% 40% 12% 1	713
October	1st to 10th	Night	16% 6% 25% 39% 13% 1	800
	11th to 20th	Night	12% 5% 31% 37% 14% 2	837
	21st to end	Night	15% 7% 34% 31% 12% 1	1100
November	1st to 10th	Night	21% 5% 29% 34% 8% 1	1025
	11th to 20th	Night	14% 7% 33% 32% 12% 2	1050
	21st to end	Night	12% 6% 34% 36% 10% 2	1050
December	1st to 10th	Night	10% 5% 31% 37% 16% 3	1050
	11th to 20th	Night	13% 6% 33% 32% 14% 2	1050
	21st to end	Night	11% 2 27% 35% 20% 5%	1155

Page generated at 2026-06-28 00:10:45. Version ac07

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