Rang Saint-Arthur
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rang Saint-Arthur clear sky chart from 2005-11-06 to 2024-11-11.

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	16% 13% 4 10% 6% 5% 5% 4 5% 6% 27%	101473
	Night	15% 13% 5% 11% 6% 5% 5% 4 5% 5% 27%	97732
Transparency	Day	56% 6% 12% 17% 8% 1	104944
	Night	56% 6% 12% 18% 8% 1	102351
Seeing	Day	27% 20% 31% 16% 6% 1	15485
	Night	24% 19% 29% 20% 7% 1	23822

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% 16% 8% 16% 7% 7% 7% 6% 5% 4 14%	2495
	11th to 20th	Day	8% 14% 7% 20% 10% 7% 4 2 4 3 20%	2520
	21st to end	Day	8% 10% 6% 20% 9% 6% 5% 4 5% 6% 22%	2772
February	1st to 10th	Day	10% 16% 6% 14% 10% 8% 5% 5% 4 4 17%	1570
	11th to 20th	Day	11% 18% 7% 15% 7% 5% 5% 4 4 4 20%	1795
	21st to end	Day	9% 16% 6% 14% 8% 5% 5% 3 4 6% 24%	1570
March	1st to 10th	Day	15% 18% 5% 11% 6% 5% 4 3 3 5% 24%	3116
	11th to 20th	Day	12% 26% 6% 12% 6% 5% 4 2 3 3 21%	3379
	21st to end	Day	14% 15% 6% 11% 6% 4 3 3 4 5% 30%	3966
April	1st to 10th	Day	20% 18% 5% 10% 6% 4 4 2 3 5% 24%	2280
	11th to 20th	Day	16% 14% 5% 9% 4 4 3 3 4 5% 33%	2380
	21st to end	Day	20% 15% 3 9% 4 3 3 3 4 6% 29%	2470
May	1st to 10th	Day	18% 12% 4 9% 6% 6% 4 3 5% 6% 28%	4106
	11th to 20th	Day	20% 10% 3 9% 6% 5% 5% 4 6% 7% 26%	4390
	21st to end	Day	15% 9% 3 9% 7% 6% 6% 5% 6% 7% 28%	5019
June	1st to 10th	Day	22% 10% 3 8% 6% 5% 5% 4 5% 8% 24%	2850
	11th to 20th	Day	20% 8% 3 6% 5% 4 5% 4 7% 7% 30%	2850
	21st to end	Day	24% 11% 4 9% 6% 5% 4 4 5% 6% 23%	2850
July	1st to 10th	Day	15% 8% 4 10% 6% 6% 6% 5% 7% 7% 26%	4639
	11th to 20th	Day	16% 8% 2 8% 6% 6% 6% 5% 7% 7% 29%	4440
	21st to end	Day	14% 8% 3 7% 5% 4 5% 4 6% 7% 37%	4814
August	1st to 10th	Day	16% 8% 3 7% 6% 6% 6% 5% 7% 9% 27%	4311
	11th to 20th	Day	17% 9% 4 9% 6% 7% 7% 5% 7% 6% 23%	4045
	21st to end	Day	18% 8% 3 7% 5% 4 5% 3 5% 6% 34%	4418
September	1st to 10th	Day	17% 9% 3 7% 4 5% 4 4 6% 7% 35%	2266
	11th to 20th	Day	18% 8% 3 5% 3 4 4 3 4 7% 41%	2090
	21st to end	Day	18% 9% 3 7% 4 4 3 3 6% 6% 36%	2090
October	1st to 10th	Day	18% 12% 3 8% 5% 4 4 4 5% 6% 31%	2082
	11th to 20th	Day	20% 16% 4 10% 5% 5% 4 4 5% 4 24%	1760
	21st to end	Day	21% 19% 5% 10% 5% 4 4 3 3 5% 21%	1881
November	1st to 10th	Day	16% 17% 5% 10% 6% 5% 3 3 4 4 27%	1761
	11th to 20th	Day	16% 16% 6% 12% 7% 6% 4 3 4 4 22%	1677
	21st to end	Day	16% 19% 6% 11% 9% 5% 4 3 4 3 21%	1392
December	1st to 10th	Day	17% 22% 7% 13% 8% 3 4 2 4 4 17%	1330
	11th to 20th	Day	16% 18% 6% 12% 6% 5% 5% 2 4 3 22%	1668
	21st to end	Day	18% 18% 6% 12% 7% 5% 4 4 4 3 19%	2431
January	1st to 10th	Night	10% 15% 8% 17% 10% 6% 6% 4 4 4 16%	4447
	11th to 20th	Night	8% 15% 5% 17% 10% 8% 6% 3 4 4 18%	4440
	21st to end	Night	7% 12% 7% 17% 6% 7% 6% 6% 6% 6% 21%	4884
February	1st to 10th	Night	8% 15% 6% 12% 9% 8% 6% 5% 5% 4 22%	2608
	11th to 20th	Night	9% 14% 7% 15% 8% 6% 5% 5% 5% 4 21%	2270
	21st to end	Night	11% 14% 4 12% 8% 6% 4 3 4 5% 28%	1884
March	1st to 10th	Night	16% 18% 5% 9% 5% 4 5% 3 3 6% 26%	3724
	11th to 20th	Night	10% 17% 6% 13% 7% 6% 5% 4 5% 5% 23%	3580
	21st to end	Night	15% 17% 5% 10% 6% 5% 4 3 4 4 28%	3663
April	1st to 10th	Night	17% 17% 5% 9% 5% 4 5% 4 4 5% 27%	1900
	11th to 20th	Night	16% 13% 3 8% 5% 4 5% 3 5% 7% 30%	1748
	21st to end	Night	18% 13% 4 10% 4 4 4 3 4 5% 30%	1710
May	1st to 10th	Night	20% 10% 3 6% 5% 4 4 4 6% 6% 31%	2834
	11th to 20th	Night	18% 10% 3 9% 5% 5% 4 3 5% 5% 33%	2532
	21st to end	Night	16% 7% 2 7% 4 4 5% 5% 6% 9% 36%	2558
June	1st to 10th	Night	20% 11% 3 7% 6% 6% 6% 4 5% 6% 26%	1330
	11th to 20th	Night	15% 9% 3 8% 5% 3 5% 4 5% 6% 37%	1330
	21st to end	Night	19% 10% 3 8% 6% 5% 5% 4 5% 7% 29%	1330
July	1st to 10th	Night	9% 10% 4 10% 6% 5% 6% 4 6% 7% 33%	2323
	11th to 20th	Night	18% 8% 3 7% 6% 5% 5% 4 5% 6% 31%	2520
	21st to end	Night	11% 8% 3 6% 5% 4 4 4 6% 8% 42%	2739
August	1st to 10th	Night	18% 9% 3 7% 4 4 5% 4 6% 7% 32%	2588
	11th to 20th	Night	14% 9% 4 10% 7% 7% 5% 4 6% 6% 27%	2782
	21st to end	Night	17% 8% 3 7% 4 4 4 3 5% 6% 38%	3236
September	1st to 10th	Night	16% 8% 2 7% 5% 5% 4 4 4 6% 39%	1914
	11th to 20th	Night	16% 8% 2 6% 4 3 4 3 5% 6% 42%	2090
	21st to end	Night	16% 9% 3 7% 4 5% 4 3 4 5% 40%	2090
October	1st to 10th	Night	16% 10% 3 7% 4 4 4 4 5% 6% 36%	2096
	11th to 20th	Night	20% 13% 4 9% 5% 5% 5% 3 4 5% 28%	2418
	21st to end	Night	19% 16% 4 10% 5% 5% 4 3 4 4 26%	2717
November	1st to 10th	Night	16% 14% 4 11% 7% 5% 5% 3 5% 6% 25%	2537
	11th to 20th	Night	15% 12% 5% 10% 7% 6% 5% 4 5% 6% 27%	2509
	21st to end	Night	14% 16% 6% 12% 8% 6% 5% 4 5% 4 20%	2784
December	1st to 10th	Night	16% 17% 7% 14% 8% 6% 4 3 4 5% 16%	2850
	11th to 20th	Night	17% 15% 6% 14% 8% 6% 4 3 3 4 19%	3531
	21st to end	Night	17% 19% 5% 12% 6% 4 3 2 4 3 24%	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	73% 3 10% 10% 3	2496
	11th to 20th	Day	71% 2 6% 12% 8% 1	2520
	21st to end	Day	62% 6% 8% 13% 10% 1	2772
February	1st to 10th	Day	69% 5% 6% 11% 8% 2	1570
	11th to 20th	Day	68% 4 7% 12% 8% 1	1804
	21st to end	Day	62% 4 7% 17% 7% 3	1570
March	1st to 10th	Day	64% 4 8% 13% 9% 2	3119
	11th to 20th	Day	69% 4 9% 12% 6% 1	3379
	21st to end	Day	57% 4 7% 17% 12% 3	3966
April	1st to 10th	Day	64% 4 8% 13% 9% 2	2280
	11th to 20th	Day	53% 5% 8% 21% 11% 2	2380
	21st to end	Day	58% 3 8% 17% 11% 2	2470
May	1st to 10th	Day	56% 5% 9% 17% 11% 1	4120
	11th to 20th	Day	54% 7% 16% 17% 6%	4394
	21st to end	Day	51% 9% 11% 19% 10%	5019
June	1st to 10th	Day	57% 6% 11% 19% 6% 1	2850
	11th to 20th	Day	50% 7% 14% 21% 8% 1	2850
	21st to end	Day	61% 6% 10% 16% 7%	2850
July	1st to 10th	Day	52% 8% 15% 18% 7%	4567
	11th to 20th	Day	48% 9% 18% 22% 3	4365
	21st to end	Day	44% 8% 15% 26% 7%	4661
August	1st to 10th	Day	50% 9% 19% 18% 5%	4297
	11th to 20th	Day	54% 9% 19% 13% 4	4084
	21st to end	Day	48% 7% 15% 18% 11% 1	4418
September	1st to 10th	Day	46% 7% 15% 22% 10%	2266
	11th to 20th	Day	43% 5% 13% 27% 11%	2090
	21st to end	Day	48% 5% 13% 24% 10% 1	2090
October	1st to 10th	Day	54% 6% 11% 22% 6%	3459
	11th to 20th	Day	52% 9% 14% 20% 5%	2898
	21st to end	Day	52% 6% 15% 18% 8%	3081
November	1st to 10th	Day	60% 6% 11% 17% 6%	1761
	11th to 20th	Day	65% 6% 8% 14% 6% 1	1677
	21st to end	Day	68% 5% 8% 14% 4	1392
December	1st to 10th	Day	73% 3 8% 11% 5%	1330
	11th to 20th	Day	67% 4 6% 16% 7% 1	1668
	21st to end	Day	69% 4 8% 10% 7% 2	2431
January	1st to 10th	Night	71% 4 9% 12% 4	4447
	11th to 20th	Night	69% 5% 9% 13% 5%	4440
	21st to end	Night	60% 6% 9% 13% 10% 2	4884
February	1st to 10th	Night	61% 7% 8% 14% 9% 1	2608
	11th to 20th	Night	64% 5% 8% 15% 7% 1	2272
	21st to end	Night	58% 4 7% 17% 12% 2	1884
March	1st to 10th	Night	61% 4 9% 16% 9% 1	3734
	11th to 20th	Night	61% 6% 13% 11% 6% 1	3581
	21st to end	Night	59% 4 7% 19% 10% 2	3663
April	1st to 10th	Night	58% 5% 6% 14% 13% 3	1900
	11th to 20th	Night	51% 6% 8% 22% 12% 1	1748
	21st to end	Night	57% 4 8% 18% 11% 2	1710
May	1st to 10th	Night	51% 6% 13% 19% 10% 1	2840
	11th to 20th	Night	51% 7% 13% 19% 9%	2533
	21st to end	Night	43% 8% 16% 20% 13%	2559
June	1st to 10th	Night	56% 7% 13% 19% 6%	1330
	11th to 20th	Night	46% 6% 13% 22% 11% 2	1330
	21st to end	Night	54% 6% 16% 16% 8% 1	1330
July	1st to 10th	Night	45% 9% 20% 20% 5%	2285
	11th to 20th	Night	47% 9% 21% 19% 4	2472
	21st to end	Night	38% 9% 24% 22% 7%	2651
August	1st to 10th	Night	49% 7% 18% 23% 3	2578
	11th to 20th	Night	50% 11% 18% 16% 4	2809
	21st to end	Night	44% 7% 15% 20% 11% 2	3236
September	1st to 10th	Night	43% 7% 13% 25% 10% 1	1914
	11th to 20th	Night	42% 6% 17% 26% 8% 1	2090
	21st to end	Night	46% 6% 11% 24% 12% 1	2090
October	1st to 10th	Night	46% 6% 12% 27% 9%	3499
	11th to 20th	Night	50% 10% 10% 23% 6%	4019
	21st to end	Night	49% 6% 19% 17% 8% 1	4467
November	1st to 10th	Night	57% 7% 13% 18% 5%	2537
	11th to 20th	Night	57% 6% 12% 15% 9% 1	2509
	21st to end	Night	64% 6% 10% 14% 5%	2784
December	1st to 10th	Night	70% 4 10% 12% 4	2850
	11th to 20th	Night	68% 5% 6% 15% 7%	3532
	21st to end	Night	66% 4 7% 14% 8% 1	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	26% 29% 35% 8% 1 1	180
	11th to 20th	Day	32% 27% 32% 6% 3 1	180
	21st to end	Day	18% 32% 33% 13% 3 1	198
February	1st to 10th	Day	38% 23% 26% 10% 2	230
	11th to 20th	Day	30% 26% 32% 9% 2	431
	21st to end	Day	27% 29% 29% 13% 2	382
March	1st to 10th	Day	28% 25% 32% 12% 3	460
	11th to 20th	Day	29% 25% 29% 11% 6%	460
	21st to end	Day	30% 24% 25% 13% 6% 1	506
April	1st to 10th	Day	37% 23% 21% 14% 5% 1	460
	11th to 20th	Day	31% 24% 27% 15% 3 1	452
	21st to end	Day	34% 18% 31% 10% 4 2	460
May	1st to 10th	Day	29% 17% 35% 15% 2 1	463
	11th to 20th	Day	26% 17% 31% 19% 7% 1	487
	21st to end	Day	23% 20% 35% 17% 5% 1	633
June	1st to 10th	Day	26% 15% 35% 17% 7%	680
	11th to 20th	Day	23% 17% 28% 23% 8% 1	680
	21st to end	Day	30% 13% 28% 21% 7% 1	680
July	1st to 10th	Day	21% 17% 35% 20% 7% 1	604
	11th to 20th	Day	22% 16% 40% 17% 6%	484
	21st to end	Day	20% 14% 39% 21% 5% 1	532
August	1st to 10th	Day	23% 15% 32% 22% 7% 1	486
	11th to 20th	Day	20% 13% 34% 23% 9% 1	479
	21st to end	Day	22% 16% 29% 21% 9% 4	539
September	1st to 10th	Day	19% 20% 30% 20% 9% 3	490
	11th to 20th	Day	23% 12% 33% 19% 9% 2	490
	21st to end	Day	20% 19% 31% 16% 9% 5%	490
October	1st to 10th	Day	24% 19% 26% 20% 8% 2	485
	11th to 20th	Day	31% 20% 29% 13% 6% 1	390
	21st to end	Day	36% 25% 25% 11% 4	429
November	1st to 10th	Day	37% 19% 29% 13% 3	395
	11th to 20th	Day	26% 27% 23% 16% 6% 1	370
	21st to end	Day	31% 29% 29% 10% 2	242
December	1st to 10th	Day	33% 17% 30% 16% 4 1	180
	11th to 20th	Day	37% 27% 26% 9% 1 1	180
	21st to end	Day	36% 25% 27% 11% 2	198
January	1st to 10th	Night	24% 27% 34% 12% 3	763
	11th to 20th	Night	24% 26% 30% 16% 2	760
	21st to end	Night	16% 25% 36% 19% 4	836
February	1st to 10th	Night	19% 30% 32% 15% 4	760
	11th to 20th	Night	24% 26% 34% 13% 3 1	743
	21st to end	Night	24% 22% 34% 16% 4	628
March	1st to 10th	Night	25% 21% 35% 16% 4	760
	11th to 20th	Night	22% 25% 33% 14% 5% 1	760
	21st to end	Night	24% 21% 28% 22% 6%	836
April	1st to 10th	Night	29% 20% 29% 17% 5%	760
	11th to 20th	Night	25% 17% 30% 21% 5% 1	624
	21st to end	Night	31% 14% 26% 21% 7% 1	570
May	1st to 10th	Night	26% 12% 31% 24% 8%	570
	11th to 20th	Night	22% 11% 28% 27% 11% 1	398
	21st to end	Night	23% 13% 29% 26% 8% 1	411
June	1st to 10th	Night	26% 9% 29% 25% 10% 1	380
	11th to 20th	Night	20% 9% 26% 32% 12% 1	380
	21st to end	Night	25% 10% 25% 31% 9% 1	380
July	1st to 10th	Night	17% 9% 35% 27% 12%	370
	11th to 20th	Night	20% 8% 30% 30% 11% 1	368
	21st to end	Night	17% 7% 26% 37% 12%	416
August	1st to 10th	Night	19% 6% 29% 30% 15% 1	421
	11th to 20th	Night	21% 7% 26% 32% 13% 1	562
	21st to end	Night	17% 10% 29% 29% 12% 2	687
September	1st to 10th	Night	20% 11% 31% 27% 11% 1	760
	11th to 20th	Night	22% 9% 28% 26% 13% 2	760
	21st to end	Night	21% 13% 27% 25% 13% 1	760
October	1st to 10th	Night	21% 17% 27% 25% 9% 1	760
	11th to 20th	Night	28% 19% 26% 19% 7% 1	760
	21st to end	Night	31% 21% 28% 14% 6%	836
November	1st to 10th	Night	28% 22% 29% 15% 4	780
	11th to 20th	Night	27% 22% 25% 19% 6% 1	778
	21st to end	Night	26% 26% 28% 15% 4 1	850
December	1st to 10th	Night	29% 22% 30% 14% 5% 1	850
	11th to 20th	Night	27% 26% 25% 17% 5%	850
	21st to end	Night	30% 25% 25% 16% 3	935

Page generated at 2024-11-08 06:44:48. Version ac07

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