Sept-Īles
Clear Sky Chart
History

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

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	19% 10% 3 7% 5% 4 4 4 5% 6% 33%	101906
	Night	18% 11% 4 8% 5% 4 4 4 5% 6% 32%	97252
Transparency	Day	52% 5% 12% 21% 9% 1	105319
	Night	53% 4 11% 21% 10% 1	101930
Seeing	Day	26% 15% 29% 20% 8% 2	16270
	Night	25% 12% 25% 27% 10% 1	23834

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	10% 14% 4 10% 6% 4 3 3 4 5% 36%	2207
	11th to 20th	Day	11% 13% 4 13% 5% 4 4 2 4 6% 33%	2210
	21st to end	Day	6% 10% 3 8% 6% 4 6% 4 5% 5% 43%	2680
February	1st to 10th	Day	8% 13% 3 10% 7% 5% 4 3 5% 6% 35%	1652
	11th to 20th	Day	8% 16% 6% 9% 6% 4 5% 4 6% 6% 29%	1663
	21st to end	Day	8% 14% 5% 9% 4 5% 5% 4 6% 7% 34%	1446
March	1st to 10th	Day	9% 15% 5% 9% 6% 6% 4 4 5% 6% 33%	3233
	11th to 20th	Day	18% 20% 4 10% 5% 5% 4 3 4 4 22%	3480
	21st to end	Day	20% 17% 4 9% 4 4 3 2 4 4 29%	3816
April	1st to 10th	Day	20% 13% 3 9% 5% 6% 5% 3 5% 5% 27%	2329
	11th to 20th	Day	14% 12% 3 8% 5% 4 4 3 5% 6% 36%	2442
	21st to end	Day	24% 9% 3 6% 4 4 4 4 4 5% 34%	2470
May	1st to 10th	Day	22% 11% 3 7% 5% 4 4 4 6% 6% 28%	4319
	11th to 20th	Day	21% 9% 3 7% 5% 4 4 3 5% 6% 34%	4610
	21st to end	Day	28% 10% 3 7% 5% 4 4 3 5% 6% 25%	5185
June	1st to 10th	Day	24% 8% 3 6% 4 4 5% 4 5% 5% 32%	2850
	11th to 20th	Day	21% 6% 2 6% 4 5% 5% 5% 7% 7% 33%	2850
	21st to end	Day	27% 7% 2 6% 4 4 4 4 6% 7% 28%	2850
July	1st to 10th	Day	17% 6% 2 6% 5% 4 4 4 6% 7% 38%	4760
	11th to 20th	Day	17% 7% 3 7% 4 5% 5% 4 7% 8% 32%	4760
	21st to end	Day	15% 5% 2 5% 4 5% 5% 4 6% 9% 40%	5162
August	1st to 10th	Day	16% 6% 2 7% 4 5% 6% 5% 7% 8% 34%	4250
	11th to 20th	Day	22% 8% 3 8% 5% 5% 5% 4 6% 7% 26%	4045
	21st to end	Day	15% 5% 2 6% 4 4 4 4 5% 7% 43%	4532
September	1st to 10th	Day	21% 6% 2 7% 4 5% 4 3 5% 6% 36%	2342
	11th to 20th	Day	24% 6% 2 5% 3 3 4 3 4 6% 39%	2112
	21st to end	Day	23% 6% 2 6% 3 3 3 4 4 7% 38%	2090
October	1st to 10th	Day	22% 7% 2 6% 4 3 4 3 5% 6% 37%	1910
	11th to 20th	Day	26% 8% 2 6% 5% 4 5% 4 4 7% 28%	1894
	21st to end	Day	29% 10% 3 7% 4 3 4 3 4 4 29%	1865
November	1st to 10th	Day	23% 9% 2 7% 5% 4 5% 3 5% 5% 31%	1518
	11th to 20th	Day	21% 13% 3 6% 5% 5% 5% 3 4 5% 29%	1520
	21st to end	Day	18% 16% 4 7% 5% 5% 4 3 4 5% 29%	1425
December	1st to 10th	Day	17% 14% 5% 7% 4 5% 4 3 6% 6% 29%	1330
	11th to 20th	Day	18% 14% 4 9% 4 3 3 3 4 4 34%	1668
	21st to end	Day	11% 14% 4 8% 4 4 3 3 5% 6% 37%	2431
January	1st to 10th	Night	10% 15% 5% 10% 6% 5% 5% 4 4 5% 31%	4748
	11th to 20th	Night	14% 16% 4 9% 5% 5% 4 4 6% 5% 27%	4760
	21st to end	Night	5% 10% 4 9% 5% 4 4 3 5% 6% 45%	4976
February	1st to 10th	Night	7% 13% 4 11% 6% 5% 4 3 5% 6% 36%	2527
	11th to 20th	Night	10% 17% 5% 9% 6% 4 4 3 5% 5% 31%	2403
	21st to end	Night	10% 14% 5% 10% 5% 5% 4 4 5% 5% 32%	2006
March	1st to 10th	Night	11% 12% 4 10% 6% 5% 5% 3 5% 6% 33%	3606
	11th to 20th	Night	18% 21% 6% 10% 6% 4 3 3 3 4 22%	3479
	21st to end	Night	22% 16% 4 8% 4 4 4 2 4 4 26%	3816
April	1st to 10th	Night	22% 13% 3 8% 5% 3 4 3 4 4 30%	1848
	11th to 20th	Night	20% 9% 3 5% 4 4 4 3 4 5% 38%	1688
	21st to end	Night	25% 10% 2 5% 4 4 2 3 3 4 37%	1710
May	1st to 10th	Night	26% 13% 3 8% 5% 4 5% 4 6% 5% 21%	2627
	11th to 20th	Night	19% 8% 3 8% 6% 6% 5% 4 6% 6% 31%	2321
	21st to end	Night	27% 13% 4 7% 4 4 4 3 5% 5% 24%	2401
June	1st to 10th	Night	24% 6% 3 5% 4 3 4 5% 6% 6% 35%	1330
	11th to 20th	Night	21% 7% 2 6% 4 4 5% 5% 7% 5% 32%	1330
	21st to end	Night	26% 7% 2 7% 4 4 4 4 6% 5% 30%	1330
July	1st to 10th	Night	19% 7% 2 5% 3 4 4 4 7% 8% 37%	2210
	11th to 20th	Night	18% 8% 3 7% 5% 5% 4 4 6% 7% 33%	2210
	21st to end	Night	13% 5% 3 5% 4 3 4 4 7% 8% 44%	2402
August	1st to 10th	Night	17% 6% 3 7% 5% 5% 5% 4 6% 8% 34%	2648
	11th to 20th	Night	20% 8% 3 8% 6% 4 5% 5% 6% 6% 28%	2782
	21st to end	Night	16% 6% 2 6% 4 4 5% 4 6% 8% 39%	3124
September	1st to 10th	Night	22% 6% 3 5% 3 3 4 4 4 6% 39%	1838
	11th to 20th	Night	22% 6% 2 4 4 4 5% 3 5% 6% 40%	2066
	21st to end	Night	21% 7% 2 5% 3 3 3 3 5% 6% 41%	2090
October	1st to 10th	Night	24% 7% 3 7% 4 3 3 3 5% 6% 36%	2270
	11th to 20th	Night	28% 8% 3 8% 4 4 4 3 5% 5% 30%	2285
	21st to end	Night	27% 10% 3 6% 4 4 4 3 4 6% 30%	2732
November	1st to 10th	Night	24% 10% 2 5% 4 4 4 4 5% 6% 31%	2660
	11th to 20th	Night	22% 14% 4 6% 4 4 4 3 5% 5% 28%	2660
	21st to end	Night	20% 17% 5% 8% 4 4 4 3 4 5% 27%	2752
December	1st to 10th	Night	20% 15% 4 7% 4 3 3 2 5% 5% 31%	2850
	11th to 20th	Night	23% 12% 5% 7% 3 3 3 2 3 5% 34%	3531
	21st to end	Night	12% 12% 4 10% 5% 5% 6% 4 5% 6% 31%	5236

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	52% 2 6% 25% 14% 1	2208
	11th to 20th	Day	53% 5% 9% 26% 6% 1	2210
	21st to end	Day	44% 3 10% 19% 20% 4	2680
February	1st to 10th	Day	50% 3 10% 21% 13% 3	1652
	11th to 20th	Day	55% 4 10% 20% 11% 1	1671
	21st to end	Day	49% 5% 7% 23% 13% 2	1446
March	1st to 10th	Day	53% 4 8% 22% 11% 2	3237
	11th to 20th	Day	67% 4 6% 14% 8% 2	3480
	21st to end	Day	61% 3 6% 16% 10% 4	3816
April	1st to 10th	Day	59% 5% 7% 15% 12% 2	2329
	11th to 20th	Day	49% 5% 8% 22% 13% 2	2442
	21st to end	Day	53% 4 10% 17% 13% 2	2470
May	1st to 10th	Day	57% 6% 9% 20% 8%	4334
	11th to 20th	Day	53% 4 11% 23% 9% 1	4614
	21st to end	Day	61% 5% 8% 17% 8% 1	5185
June	1st to 10th	Day	54% 5% 8% 21% 10% 2	2850
	11th to 20th	Day	49% 7% 13% 18% 11% 2	2850
	21st to end	Day	55% 7% 10% 19% 8% 1	2850
July	1st to 10th	Day	44% 6% 12% 29% 9%	4685
	11th to 20th	Day	47% 7% 16% 21% 9%	4679
	21st to end	Day	41% 7% 16% 28% 8%	4998
August	1st to 10th	Day	47% 8% 20% 22% 5%	4235
	11th to 20th	Day	57% 8% 16% 15% 4	4084
	21st to end	Day	41% 6% 19% 26% 8%	4532
September	1st to 10th	Day	48% 6% 15% 22% 9%	2342
	11th to 20th	Day	47% 6% 15% 26% 6%	2112
	21st to end	Day	47% 7% 10% 25% 10%	2090
October	1st to 10th	Day	53% 5% 12% 23% 6% 1	3170
	11th to 20th	Day	50% 6% 13% 25% 6%	3122
	21st to end	Day	51% 4 13% 18% 13% 1	3054
November	1st to 10th	Day	54% 6% 13% 17% 9% 1	1518
	11th to 20th	Day	59% 6% 11% 18% 6%	1520
	21st to end	Day	59% 4 10% 18% 10%	1425
December	1st to 10th	Day	56% 5% 13% 22% 4 1	1330
	11th to 20th	Day	54% 4 8% 21% 12% 1	1668
	21st to end	Day	49% 3 13% 19% 11% 5%	2431
January	1st to 10th	Night	56% 3 8% 19% 12% 2	4748
	11th to 20th	Night	58% 4 9% 22% 7% 1	4760
	21st to end	Night	41% 3 13% 22% 20% 2	4976
February	1st to 10th	Night	50% 3 8% 20% 15% 4	2527
	11th to 20th	Night	55% 3 9% 18% 13% 1	2406
	21st to end	Night	54% 3 7% 19% 14% 2	2006
March	1st to 10th	Night	53% 4 9% 18% 16% 1	3615
	11th to 20th	Night	67% 2 5% 16% 8% 1	3480
	21st to end	Night	63% 3 5% 15% 11% 4	3816
April	1st to 10th	Night	57% 3 7% 14% 15% 3	1848
	11th to 20th	Night	49% 4 8% 19% 17% 3	1688
	21st to end	Night	54% 2 8% 17% 18% 2	1710
May	1st to 10th	Night	62% 5% 9% 18% 6% 1	2632
	11th to 20th	Night	54% 5% 9% 22% 10% 1	2322
	21st to end	Night	63% 5% 7% 18% 7% 1	2402
June	1st to 10th	Night	48% 5% 10% 22% 13% 2	1330
	11th to 20th	Night	50% 5% 12% 19% 13% 2	1330
	21st to end	Night	55% 5% 11% 19% 10%	1330
July	1st to 10th	Night	44% 6% 14% 27% 9%	2175
	11th to 20th	Night	49% 6% 14% 20% 11% 1	2168
	21st to end	Night	36% 6% 18% 27% 12% 2	2325
August	1st to 10th	Night	46% 6% 20% 22% 6%	2639
	11th to 20th	Night	54% 7% 18% 17% 3	2809
	21st to end	Night	41% 6% 14% 30% 9% 1	3124
September	1st to 10th	Night	46% 5% 12% 29% 8%	1838
	11th to 20th	Night	45% 4 16% 26% 8% 1	2066
	21st to end	Night	45% 5% 12% 27% 11%	2090
October	1st to 10th	Night	55% 4 9% 26% 6% 1	3790
	11th to 20th	Night	54% 4 14% 20% 7%	3796
	21st to end	Night	56% 5% 8% 24% 6% 1	4494
November	1st to 10th	Night	55% 6% 11% 18% 9% 1	2660
	11th to 20th	Night	59% 3 12% 18% 7%	2660
	21st to end	Night	61% 4 11% 16% 7%	2752
December	1st to 10th	Night	57% 3 13% 20% 8%	2850
	11th to 20th	Night	56% 3 7% 24% 10% 1	3532
	21st to end	Night	54% 4 12% 17% 10% 4	5236

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	22% 13% 35% 19% 10% 1	180
	11th to 20th	Day	22% 15% 35% 18% 9% 2	180
	21st to end	Day	19% 22% 27% 24% 7% 2	198
February	1st to 10th	Day	17% 16% 36% 21% 10% 1	312
	11th to 20th	Day	14% 21% 37% 21% 5% 1	366
	21st to end	Day	20% 17% 35% 22% 5% 2	323
March	1st to 10th	Day	20% 20% 34% 18% 6% 2	460
	11th to 20th	Day	24% 13% 32% 20% 9% 2	460
	21st to end	Day	28% 23% 26% 16% 6% 2	506
April	1st to 10th	Day	27% 25% 28% 14% 5% 1	460
	11th to 20th	Day	25% 16% 35% 18% 4 1	452
	21st to end	Day	30% 16% 30% 16% 7% 1	460
May	1st to 10th	Day	27% 13% 31% 19% 8% 2	586
	11th to 20th	Day	26% 15% 28% 21% 8% 2	674
	21st to end	Day	32% 16% 27% 18% 7% 1	735
June	1st to 10th	Day	29% 11% 30% 21% 7% 1	680
	11th to 20th	Day	25% 16% 27% 19% 11% 2	680
	21st to end	Day	29% 10% 27% 23% 8% 2	680
July	1st to 10th	Day	24% 12% 31% 22% 9% 2	670
	11th to 20th	Day	23% 10% 28% 26% 11% 1	668
	21st to end	Day	26% 8% 26% 26% 12% 2	740
August	1st to 10th	Day	26% 10% 25% 28% 8% 3	517
	11th to 20th	Day	25% 10% 30% 25% 8% 2	479
	21st to end	Day	24% 10% 31% 23% 9% 3	539
September	1st to 10th	Day	27% 14% 32% 20% 5% 2	490
	11th to 20th	Day	28% 12% 32% 18% 7% 2	490
	21st to end	Day	26% 16% 29% 18% 9% 2	490
October	1st to 10th	Day	27% 20% 26% 19% 8% 1	395
	11th to 20th	Day	33% 14% 26% 16% 8% 3	390
	21st to end	Day	37% 13% 22% 16% 10% 2	429
November	1st to 10th	Day	32% 18% 26% 19% 5% 1	378
	11th to 20th	Day	29% 16% 28% 19% 7% 1	370
	21st to end	Day	29% 18% 28% 17% 8%	275
December	1st to 10th	Day	26% 9% 23% 29% 11% 2	180
	11th to 20th	Day	22% 24% 29% 17% 7%	180
	21st to end	Day	27% 17% 31% 20% 5% 1	198
January	1st to 10th	Night	21% 13% 32% 27% 7% 1	850
	11th to 20th	Night	26% 15% 29% 24% 6%	850
	21st to end	Night	15% 15% 34% 28% 7%	861
February	1st to 10th	Night	14% 16% 35% 25% 9%	760
	11th to 20th	Night	21% 17% 31% 21% 9% 1	743
	21st to end	Night	19% 15% 30% 25% 8% 3	628
March	1st to 10th	Night	18% 16% 31% 25% 8% 2	760
	11th to 20th	Night	23% 13% 28% 26% 9% 1	760
	21st to end	Night	23% 17% 26% 23% 10% 1	836
April	1st to 10th	Night	29% 14% 26% 24% 6% 1	627
	11th to 20th	Night	24% 13% 29% 22% 11% 1	564
	21st to end	Night	31% 10% 25% 25% 7% 2	570
May	1st to 10th	Night	29% 7% 23% 31% 8% 2	570
	11th to 20th	Night	25% 8% 23% 30% 11% 2	455
	21st to end	Night	28% 9% 23% 30% 9% 1	411
June	1st to 10th	Night	28% 6% 21% 34% 10% 1	380
	11th to 20th	Night	25% 8% 16% 33% 16% 2	380
	21st to end	Night	29% 6% 19% 33% 12% 2	380
July	1st to 10th	Night	24% 5% 21% 32% 17% 1	370
	11th to 20th	Night	23% 5% 16% 38% 16% 1	368
	21st to end	Night	21% 6% 14% 40% 18% 1	416
August	1st to 10th	Night	24% 5% 14% 32% 22% 3	487
	11th to 20th	Night	25% 6% 13% 36% 19% 1	562
	21st to end	Night	22% 7% 20% 31% 19% 2	627
September	1st to 10th	Night	25% 8% 23% 33% 10% 1	570
	11th to 20th	Night	25% 8% 19% 33% 14% 2	736
	21st to end	Night	26% 8% 23% 31% 11% 1	760
October	1st to 10th	Night	29% 12% 23% 26% 10% 1	760
	11th to 20th	Night	32% 8% 22% 22% 14% 1	760
	21st to end	Night	35% 9% 22% 24% 9% 1	844
November	1st to 10th	Night	33% 12% 26% 23% 6% 1	854
	11th to 20th	Night	29% 13% 26% 24% 7% 1	850
	21st to end	Night	30% 13% 25% 24% 7% 1	850
December	1st to 10th	Night	27% 14% 26% 22% 10% 1	850
	11th to 20th	Night	25% 18% 33% 18% 6%	850
	21st to end	Night	22% 16% 32% 21% 8% 1	935

Page generated at 2024-11-03 02:11:10. Version ac07

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