Arnes
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Arnes clear sky chart from 2005-11-06 to 2024-02-05.

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	11% 8% 4 8% 7% 4 6% 5% 6% 8% 34%	77687
	Night	10% 10% 4 8% 7% 4 6% 5% 6% 7% 32%	81212
Transparency	Day	47% 9% 15% 21% 8% 1	77369
	Night	49% 8% 14% 20% 8% 1	81063
Seeing	Day	14% 5% 25% 32% 19% 5%	15155
	Night	15% 5% 28% 35% 16% 2	25279

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	7% 15% 7% 9% 8% 7% 9% 7% 7% 6% 18%	2218
	11th to 20th	Day	5% 10% 5% 18% 16% 6% 7% 6% 8% 7% 13%	2220
	21st to end	Day	7% 15% 8% 13% 9% 5% 7% 6% 6% 6% 18%	2703
February	1st to 10th	Day	9% 11% 5% 9% 10% 5% 9% 6% 8% 8% 21%	1551
	11th to 20th	Day	8% 10% 4 8% 7% 5% 8% 6% 7% 9% 28%	1574
	21st to end	Day	6% 11% 6% 8% 9% 4 6% 8% 7% 7% 27%	1381
March	1st to 10th	Day	11% 10% 5% 10% 9% 4 7% 6% 5% 7% 24%	1838
	11th to 20th	Day	8% 9% 4 8% 9% 5% 6% 5% 7% 7% 32%	1980
	21st to end	Day	10% 10% 4 7% 7% 4 6% 5% 6% 7% 34%	2178
April	1st to 10th	Day	9% 9% 3 8% 5% 4 5% 4 6% 6% 39%	2210
	11th to 20th	Day	11% 8% 3 6% 5% 3 6% 5% 7% 7% 39%	2312
	21st to end	Day	13% 6% 2 7% 6% 3 6% 6% 6% 8% 37%	2340
May	1st to 10th	Day	13% 7% 4 7% 6% 3 4 4 6% 7% 40%	2452
	11th to 20th	Day	15% 7% 2 6% 5% 3 5% 4 5% 7% 40%	2633
	21st to end	Day	19% 7% 3 6% 5% 3 4 5% 5% 7% 36%	2918
June	1st to 10th	Day	16% 6% 3 5% 6% 3 4 5% 6% 8% 38%	2700
	11th to 20th	Day	14% 6% 3 6% 6% 3 5% 6% 6% 8% 37%	2700
	21st to end	Day	13% 6% 3 5% 5% 3 5% 5% 6% 9% 38%	2700
July	1st to 10th	Day	8% 4 2 4 5% 3 5% 6% 6% 9% 47%	2700
	11th to 20th	Day	10% 5% 2 5% 5% 3 5% 6% 6% 10% 44%	2700
	21st to end	Day	7% 4 2 5% 5% 3 5% 6% 6% 9% 48%	2939
August	1st to 10th	Day	7% 4 2 6% 5% 4 5% 6% 7% 10% 44%	2473
	11th to 20th	Day	11% 4 3 5% 4 3 5% 5% 6% 8% 46%	2301
	21st to end	Day	13% 5% 2 5% 4 3 4 5% 6% 8% 43%	2574
September	1st to 10th	Day	12% 5% 2 4 4 3 5% 6% 5% 8% 47%	2256
	11th to 20th	Day	14% 7% 3 7% 6% 4 5% 4 5% 9% 36%	1980
	21st to end	Day	16% 7% 3 6% 5% 3 5% 5% 6% 8% 38%	1980
October	1st to 10th	Day	19% 11% 4 5% 6% 3 5% 4 5% 8% 29%	1824
	11th to 20th	Day	14% 11% 5% 8% 7% 4 5% 5% 6% 6% 29%	1756
	21st to end	Day	15% 14% 4 9% 8% 6% 6% 6% 4 6% 22%	1774
November	1st to 10th	Day	17% 13% 6% 12% 6% 4 4 4 4 6% 24%	1487
	11th to 20th	Day	10% 15% 5% 12% 10% 4 4 4 4 6% 24%	1520
	21st to end	Day	15% 13% 5% 10% 9% 4 5% 5% 6% 6% 22%	1364
December	1st to 10th	Day	9% 11% 6% 13% 11% 8% 7% 6% 5% 6% 17%	1330
	11th to 20th	Day	9% 13% 7% 12% 9% 3 6% 6% 5% 7% 21%	1679
	21st to end	Day	8% 11% 5% 11% 8% 4 5% 7% 6% 7% 28%	2442
January	1st to 10th	Night	6% 11% 6% 11% 9% 7% 9% 6% 6% 8% 20%	4737
	11th to 20th	Night	6% 11% 7% 14% 15% 8% 8% 7% 5% 5% 15%	4750
	21st to end	Night	8% 16% 7% 12% 9% 4 6% 6% 6% 7% 20%	4960
February	1st to 10th	Night	7% 12% 5% 9% 8% 5% 8% 7% 6% 7% 28%	2503
	11th to 20th	Night	7% 9% 4 9% 6% 3 6% 6% 7% 8% 33%	2273
	21st to end	Night	5% 11% 5% 9% 7% 3 7% 7% 5% 7% 34%	1891
March	1st to 10th	Night	9% 10% 5% 7% 8% 4 6% 5% 6% 7% 33%	2109
	11th to 20th	Night	9% 9% 3 6% 6% 3 4 5% 6% 8% 41%	1979
	21st to end	Night	13% 9% 3 8% 6% 3 4 4 4 6% 38%	2178
April	1st to 10th	Night	11% 8% 2 5% 5% 3 6% 5% 6% 8% 41%	1747
	11th to 20th	Night	12% 10% 4 6% 7% 3 5% 5% 5% 7% 37%	1599
	21st to end	Night	9% 7% 3 7% 6% 3 6% 7% 7% 7% 38%	1620
May	1st to 10th	Night	17% 8% 4 6% 5% 3 5% 5% 4 7% 36%	1508
	11th to 20th	Night	13% 6% 3 7% 5% 3 3 4 5% 8% 43%	1258
	21st to end	Night	18% 6% 2 6% 5% 3 4 5% 5% 7% 39%	1358
June	1st to 10th	Night	15% 8% 2 5% 5% 2 5% 5% 6% 7% 38%	1260
	11th to 20th	Night	14% 7% 2 4 6% 3 4 5% 5% 9% 42%	1260
	21st to end	Night	11% 4 3 4 6% 3 6% 6% 8% 10% 40%	1260
July	1st to 10th	Night	7% 2 1 2 3 2 4 4 6% 10% 57%	1260
	11th to 20th	Night	8% 3 2 3 5% 3 6% 4 7% 7% 51%	1260
	21st to end	Night	7% 4 1 3 4 3 4 5% 6% 9% 54%	1379
August	1st to 10th	Night	7% 3 2 4 4 3 4 5% 5% 9% 53%	1462
	11th to 20th	Night	9% 3 1 3 4 3 4 5% 6% 9% 52%	1600
	21st to end	Night	13% 5% 2 4 5% 3 3 4 5% 8% 49%	1782
September	1st to 10th	Night	11% 5% 2 5% 4 2 5% 5% 5% 8% 48%	1700
	11th to 20th	Night	14% 6% 2 5% 4 3 4 4 6% 9% 43%	1980
	21st to end	Night	15% 6% 3 6% 6% 3 5% 4 6% 7% 40%	1980
October	1st to 10th	Night	18% 10% 3 5% 5% 4 5% 5% 5% 6% 35%	2117
	11th to 20th	Night	16% 11% 4 7% 6% 4 4 5% 4 7% 32%	2203
	21st to end	Night	17% 13% 4 7% 7% 4 5% 5% 5% 6% 28%	2581
November	1st to 10th	Night	14% 13% 5% 9% 7% 4 4 5% 5% 7% 25%	2591
	11th to 20th	Night	11% 15% 6% 13% 8% 4 5% 4 5% 7% 24%	2660
	21st to end	Night	14% 13% 7% 12% 8% 4 6% 5% 5% 6% 21%	2814
December	1st to 10th	Night	8% 11% 6% 12% 12% 7% 7% 6% 5% 6% 22%	2850
	11th to 20th	Night	8% 15% 7% 10% 8% 4 5% 5% 6% 7% 25%	3518
	21st to end	Night	8% 10% 4 11% 10% 4 6% 5% 6% 8% 29%	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	62% 10% 12% 13% 2	2219
	11th to 20th	Day	68% 6% 10% 13% 3	2220
	21st to end	Day	64% 8% 10% 12% 5%	2703
February	1st to 10th	Day	57% 8% 13% 14% 8% 1	1551
	11th to 20th	Day	50% 7% 14% 20% 8%	1583
	21st to end	Day	54% 8% 12% 19% 7%	1381
March	1st to 10th	Day	58% 9% 12% 15% 7%	1840
	11th to 20th	Day	50% 9% 14% 20% 7%	1980
	21st to end	Day	48% 8% 15% 19% 8% 1	2178
April	1st to 10th	Day	44% 7% 14% 23% 11% 1	2210
	11th to 20th	Day	43% 8% 11% 22% 14% 2	2312
	21st to end	Day	44% 7% 14% 24% 8% 1	2340
May	1st to 10th	Day	42% 7% 14% 22% 13% 1	2452
	11th to 20th	Day	43% 7% 10% 24% 14% 1	2637
	21st to end	Day	47% 8% 11% 19% 14% 1	2918
June	1st to 10th	Day	44% 9% 14% 23% 10% 1	2700
	11th to 20th	Day	43% 10% 14% 21% 12% 1	2700
	21st to end	Day	41% 10% 19% 22% 8%	2700
July	1st to 10th	Day	30% 11% 18% 29% 12%	2626
	11th to 20th	Day	33% 10% 19% 28% 9% 1	2619
	21st to end	Day	31% 10% 21% 29% 8%	2776
August	1st to 10th	Day	31% 12% 20% 30% 6%	2456
	11th to 20th	Day	34% 10% 22% 29% 5%	2301
	21st to end	Day	36% 10% 18% 29% 7%	2574
September	1st to 10th	Day	33% 9% 19% 30% 8%	2256
	11th to 20th	Day	45% 8% 18% 25% 4	1980
	21st to end	Day	43% 8% 17% 25% 6%	1980
October	1st to 10th	Day	52% 8% 17% 18% 5%	1824
	11th to 20th	Day	52% 11% 13% 19% 3 1	1756
	21st to end	Day	61% 9% 16% 11% 3	1774
November	1st to 10th	Day	60% 7% 13% 15% 4 1	1487
	11th to 20th	Day	60% 9% 15% 13% 3	1520
	21st to end	Day	60% 9% 16% 12% 2	1364
December	1st to 10th	Day	65% 11% 11% 10% 3	1330
	11th to 20th	Day	59% 8% 17% 11% 4	1680
	21st to end	Day	50% 11% 15% 16% 9%	2442
January	1st to 10th	Night	59% 10% 13% 14% 4	4737
	11th to 20th	Night	69% 7% 9% 12% 3	4750
	21st to end	Night	61% 8% 12% 14% 4	4960
February	1st to 10th	Night	53% 7% 13% 17% 9% 1	2503
	11th to 20th	Night	44% 8% 17% 21% 10%	2274
	21st to end	Night	47% 8% 10% 23% 10%	1891
March	1st to 10th	Night	50% 6% 13% 20% 10% 1	2120
	11th to 20th	Night	40% 6% 15% 27% 11% 2	1980
	21st to end	Night	46% 7% 13% 20% 12% 2	2178
April	1st to 10th	Night	40% 5% 11% 23% 17% 3	1747
	11th to 20th	Night	46% 5% 10% 20% 16% 3	1599
	21st to end	Night	42% 8% 11% 24% 13% 2	1620
May	1st to 10th	Night	47% 7% 9% 24% 13%	1508
	11th to 20th	Night	40% 5% 11% 26% 15% 3	1259
	21st to end	Night	44% 8% 11% 19% 16% 2	1358
June	1st to 10th	Night	43% 9% 14% 24% 9% 1	1260
	11th to 20th	Night	38% 7% 17% 22% 13% 2	1260
	21st to end	Night	33% 12% 21% 25% 8% 1	1260
July	1st to 10th	Night	22% 6% 20% 36% 15% 1	1225
	11th to 20th	Night	28% 9% 20% 30% 11% 2	1218
	21st to end	Night	26% 7% 18% 36% 12%	1302
August	1st to 10th	Night	28% 8% 18% 35% 10% 1	1455
	11th to 20th	Night	26% 9% 24% 30% 10%	1600
	21st to end	Night	33% 6% 17% 33% 10% 1	1782
September	1st to 10th	Night	32% 7% 19% 31% 11%	1700
	11th to 20th	Night	37% 9% 19% 25% 9% 1	1980
	21st to end	Night	42% 7% 16% 26% 8%	1980
October	1st to 10th	Night	48% 7% 16% 21% 8%	2117
	11th to 20th	Night	52% 7% 14% 23% 5%	2203
	21st to end	Night	54% 9% 17% 16% 3	2581
November	1st to 10th	Night	58% 9% 15% 13% 5% 1	2591
	11th to 20th	Night	60% 10% 14% 10% 5%	2660
	21st to end	Night	63% 8% 15% 11% 3	2814
December	1st to 10th	Night	61% 8% 17% 10% 4	2850
	11th to 20th	Night	56% 8% 17% 13% 6%	3516
	21st to end	Night	51% 10% 12% 16% 11% 1	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% 4 32% 33% 16% 4	270
	11th to 20th	Day	9% 4 29% 37% 17% 4	270
	21st to end	Day	16% 4 24% 36% 15% 4	297
February	1st to 10th	Day	12% 5% 29% 37% 14% 3	252
	11th to 20th	Day	13% 7% 29% 31% 15% 6%	240
	21st to end	Day	6% 4 37% 28% 25% 1	198
March	1st to 10th	Day	11% 4 29% 30% 24% 2	240
	11th to 20th	Day	11% 5% 29% 36% 16% 4	240
	21st to end	Day	13% 6% 27% 31% 19% 5%	264
April	1st to 10th	Day	13% 4 26% 39% 14% 3	470
	11th to 20th	Day	14% 7% 25% 33% 19% 3	590
	21st to end	Day	14% 7% 27% 33% 18% 3	600
May	1st to 10th	Day	12% 6% 25% 36% 18% 2	603
	11th to 20th	Day	17% 5% 22% 31% 20% 5%	625
	21st to end	Day	19% 6% 19% 29% 23% 4	679
June	1st to 10th	Day	16% 4 24% 32% 19% 4	630
	11th to 20th	Day	14% 5% 27% 34% 15% 4	630
	21st to end	Day	13% 5% 20% 30% 25% 7%	630
July	1st to 10th	Day	9% 4 23% 35% 24% 5%	621
	11th to 20th	Day	10% 5% 25% 30% 23% 6%	618
	21st to end	Day	7% 4 21% 32% 25% 10%	684
August	1st to 10th	Day	9% 3 22% 33% 24% 9%	626
	11th to 20th	Day	11% 5% 20% 31% 23% 10%	615
	21st to end	Day	16% 4 19% 31% 24% 5%	693
September	1st to 10th	Day	12% 4 27% 37% 17% 2	546
	11th to 20th	Day	16% 7% 29% 32% 13% 3	270
	21st to end	Day	19% 7% 29% 33% 11% 1	270
October	1st to 10th	Day	22% 9% 23% 28% 13% 5%	270
	11th to 20th	Day	16% 10% 26% 37% 10% 2	270
	21st to end	Day	22% 8% 29% 25% 13% 2	297
November	1st to 10th	Day	22% 9% 23% 32% 12% 1	270
	11th to 20th	Day	17% 7% 37% 24% 13% 1	270
	21st to end	Day	21% 9% 33% 30% 7%	270
December	1st to 10th	Day	14% 6% 31% 31% 13% 6%	270
	11th to 20th	Day	16% 9% 35% 26% 12% 2	270
	21st to end	Day	12% 3 28% 33% 19% 5%	297
January	1st to 10th	Night	13% 4 32% 32% 16% 2	950
	11th to 20th	Night	13% 5% 29% 39% 12% 2	950
	21st to end	Night	15% 5% 28% 37% 14% 2	1045
February	1st to 10th	Night	13% 4 26% 40% 15% 2	923
	11th to 20th	Night	10% 4 28% 35% 18% 4	879
	21st to end	Night	9% 5% 30% 36% 19% 1	707
March	1st to 10th	Night	13% 4 26% 35% 18% 3	680
	11th to 20th	Night	12% 5% 34% 34% 12% 2	540
	21st to end	Night	16% 6% 26% 32% 15% 5%	594
April	1st to 10th	Night	13% 3 29% 39% 13% 2	540
	11th to 20th	Night	16% 5% 25% 36% 17% 1	533
	21st to end	Night	12% 4 28% 42% 14% 1	540
May	1st to 10th	Night	19% 4 28% 35% 13% 1	540
	11th to 20th	Night	15% 5% 25% 33% 20% 2	531
	21st to end	Night	19% 4 25% 36% 15% 1	584
June	1st to 10th	Night	17% 5% 21% 34% 23% 1	540
	11th to 20th	Night	15% 6% 25% 36% 17% 2	540
	21st to end	Night	12% 4 17% 39% 25% 2	540
July	1st to 10th	Night	7% 3 20% 44% 24% 2	525
	11th to 20th	Night	9% 3 24% 39% 22% 3	522
	21st to end	Night	8% 2 19% 38% 29% 5%	591
August	1st to 10th	Night	8% 3 19% 42% 24% 4	537
	11th to 20th	Night	8% 2 19% 40% 26% 5%	534
	21st to end	Night	14% 4 20% 37% 23% 2	594
September	1st to 10th	Night	14% 4 24% 39% 16% 4	540
	11th to 20th	Night	17% 5% 25% 38% 15% 1	540
	21st to end	Night	16% 5% 31% 33% 14% 1	540
October	1st to 10th	Night	22% 5% 31% 32% 9%	677
	11th to 20th	Night	21% 7% 28% 31% 12% 1	763
	21st to end	Night	21% 9% 29% 30% 9% 2	990
November	1st to 10th	Night	20% 8% 34% 25% 12% 1	925
	11th to 20th	Night	16% 9% 35% 28% 9% 3	950
	21st to end	Night	19% 8% 38% 27% 7% 1	950
December	1st to 10th	Night	11% 6% 28% 37% 15% 3	950
	11th to 20th	Night	15% 7% 34% 32% 10% 2	950
	21st to end	Night	16% 5% 31% 29% 17% 2	1045

Page generated at 2024-02-02 04:20:27. Version ac07

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