Ariel
Clear Sky Chart
History

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

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	23% 9% 2 6% 4 4 4 3 4 5% 35%	101810
	Night	26% 10% 2 6% 4 3 3 2 4 5% 35%	97216
Transparency	Day	51% 7% 11% 15% 12% 4	101576
	Night	53% 7% 11% 15% 10% 4	97096
Seeing	Day	28% 13% 25% 24% 9% 2	14816
	Night	32% 7% 18% 29% 13% 1	23480

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	46% 18% 3 6% 4 3 3 3 3 3 8%	2539
	11th to 20th	Day	42% 11% 3 5% 4 3 2 2 3 3 20%	2516
	21st to end	Day	47% 13% 3 6% 4 3 3 2 3 3 13%	2998
February	1st to 10th	Day	39% 12% 3 7% 4 3 3 3 4 6% 17%	1710
	11th to 20th	Day	37% 13% 4 8% 5% 3 3 2 4 4 18%	1665
	21st to end	Day	36% 17% 3 8% 4 3 3 2 3 4 17%	1489
March	1st to 10th	Day	27% 20% 3 9% 5% 3 3 2 4 5% 18%	3261
	11th to 20th	Day	26% 12% 3 6% 3 3 3 2 3 4 36%	3490
	21st to end	Day	31% 16% 3 9% 5% 4 4 3 4 4 15%	3917
April	1st to 10th	Day	33% 14% 4 9% 5% 3 3 3 4 5% 16%	2280
	11th to 20th	Day	29% 14% 3 7% 5% 4 4 3 4 4 23%	2252
	21st to end	Day	27% 12% 4 7% 5% 5% 4 4 4 5% 22%	2466
May	1st to 10th	Day	23% 10% 2 7% 4 4 4 3 4 5% 33%	4402
	11th to 20th	Day	13% 7% 2 6% 4 4 5% 5% 7% 8% 37%	4377
	21st to end	Day	26% 9% 3 8% 6% 6% 6% 4 5% 5% 22%	4813
June	1st to 10th	Day	25% 7% 3 7% 5% 4 3 3 5% 6% 30%	2660
	11th to 20th	Day	22% 9% 3 7% 6% 6% 5% 4 6% 8% 25%	2661
	21st to end	Day	12% 5% 3 5% 4 5% 4 3 5% 6% 48%	2850
July	1st to 10th	Day	5% 3 1 4 3 3 3 2 4 6% 67%	4494
	11th to 20th	Day	5% 3 1 3 2 2 2 2 3 5% 71%	4420
	21st to end	Day	8% 3 1 3 2 3 3 2 4 6% 64%	4790
August	1st to 10th	Day	4 4 2 4 3 3 3 3 4 6% 65%	4189
	11th to 20th	Day	7% 5% 2 6% 4 5% 4 4 7% 8% 47%	4026
	21st to end	Day	13% 6% 2 6% 3 3 4 3 4 6% 50%	4306
September	1st to 10th	Day	10% 4 2 4 3 3 3 4 4 6% 58%	2280
	11th to 20th	Day	15% 7% 2 7% 5% 4 4 4 4 8% 42%	2280
	21st to end	Day	20% 6% 2 6% 3 3 3 3 4 6% 45%	2002
October	1st to 10th	Day	24% 7% 2 6% 4 3 4 3 4 5% 38%	1900
	11th to 20th	Day	28% 6% 2 6% 4 4 3 3 5% 7% 33%	1900
	21st to end	Day	36% 9% 2 4 4 3 3 3 3 4 30%	2024
November	1st to 10th	Day	39% 12% 4 7% 4 3 4 4 5% 4 16%	1574
	11th to 20th	Day	42% 9% 3 5% 4 3 3 3 4 5% 19%	1520
	21st to end	Day	39% 10% 3 6% 3 3 3 2 4 3 23%	1520
December	1st to 10th	Day	34% 13% 3 6% 4 4 3 3 3 3 23%	1520
	11th to 20th	Day	39% 14% 3 6% 4 3 3 3 3 4 18%	1925
	21st to end	Day	37% 14% 5% 9% 5% 4 4 2 3 4 14%	2794
January	1st to 10th	Night	43% 15% 3 7% 4 3 3 2 3 3 12%	4406
	11th to 20th	Night	38% 14% 3 7% 3 3 3 2 4 5% 18%	4382
	21st to end	Night	45% 13% 3 6% 3 3 2 2 3 4 14%	4662
February	1st to 10th	Night	36% 12% 3 7% 4 4 4 3 4 4 19%	2470
	11th to 20th	Night	33% 13% 2 7% 4 3 3 2 4 4 25%	2402
	21st to end	Night	34% 15% 3 6% 3 3 4 3 4 5% 20%	1965
March	1st to 10th	Night	26% 20% 3 8% 6% 4 4 3 4 4 20%	3612
	11th to 20th	Night	25% 11% 2 5% 3 3 3 2 3 3 39%	3489
	21st to end	Night	34% 17% 3 7% 4 4 4 3 4 4 16%	3723
April	1st to 10th	Night	29% 15% 4 7% 5% 4 4 2 3 5% 22%	1900
	11th to 20th	Night	25% 13% 3 6% 4 4 4 3 5% 5% 28%	1879
	21st to end	Night	26% 10% 3 6% 4 4 4 3 5% 6% 28%	1710
May	1st to 10th	Night	25% 9% 3 7% 4 3 3 3 3 4 37%	2556
	11th to 20th	Night	12% 4 2 5% 3 3 3 3 5% 7% 52%	2516
	21st to end	Night	15% 9% 2 8% 6% 4 5% 4 5% 8% 34%	2762
June	1st to 10th	Night	20% 10% 3 8% 5% 3 3 2 3 6% 37%	1520
	11th to 20th	Night	17% 8% 3 6% 3 3 3 3 5% 8% 41%	1508
	21st to end	Night	9% 5% 2 4 3 4 3 2 4 5% 61%	1330
July	1st to 10th	Night	3 2 1 1 2 2 2 1 3 4 79%	2444
	11th to 20th	Night	4 2 1 3 2 2 2 2 3 4 76%	2540
	21st to end	Night	5% 1 1 1 1 1 1 2 3 5% 78%	2762
August	1st to 10th	Night	2 2 1 2 2 2 2 2 4 5% 76%	2745
	11th to 20th	Night	7% 4 2 4 3 3 4 3 5% 6% 61%	2812
	21st to end	Night	12% 4 1 3 3 3 3 2 3 5% 59%	3367
September	1st to 10th	Night	8% 3 1 3 3 3 3 3 4 5% 65%	1900
	11th to 20th	Night	13% 6% 3 5% 4 4 4 3 4 5% 48%	1900
	21st to end	Night	14% 6% 3 5% 3 4 4 3 4 6% 49%	2174
October	1st to 10th	Night	21% 5% 2 5% 4 3 4 2 4 5% 46%	2280
	11th to 20th	Night	24% 7% 2 6% 4 3 3 2 5% 6% 38%	2280
	21st to end	Night	32% 7% 2 6% 3 3 3 2 3 5% 35%	2574
November	1st to 10th	Night	39% 10% 3 6% 4 4 4 2 3 4 22%	2524
	11th to 20th	Night	41% 10% 2 5% 4 4 3 2 3 4 22%	2660
	21st to end	Night	34% 10% 3 7% 3 4 3 3 3 4 27%	2660
December	1st to 10th	Night	34% 11% 3 6% 4 3 3 3 5% 5% 23%	2660
	11th to 20th	Night	37% 13% 3 7% 4 4 3 2 4 5% 19%	3280
	21st to end	Night	38% 15% 4 8% 4 4 4 2 3 3 15%	4862

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	82% 5% 6% 4 2 1	2539
	11th to 20th	Day	70% 5% 7% 10% 5% 2	2540
	21st to end	Day	77% 6% 6% 6% 5% 1	2998
February	1st to 10th	Day	71% 7% 8% 9% 5%	1710
	11th to 20th	Day	72% 6% 7% 10% 4 2	1674
	21st to end	Day	73% 6% 7% 7% 6% 1	1489
March	1st to 10th	Day	67% 10% 12% 8% 4	3261
	11th to 20th	Day	55% 5% 7% 25% 7%	3490
	21st to end	Day	73% 9% 9% 7% 3	3917
April	1st to 10th	Day	71% 7% 10% 9% 2	2280
	11th to 20th	Day	65% 7% 10% 9% 7% 2	2252
	21st to end	Day	66% 9% 8% 11% 6% 1	2466
May	1st to 10th	Day	52% 10% 12% 14% 12%	4402
	11th to 20th	Day	39% 16% 20% 16% 7% 1	4380
	21st to end	Day	63% 12% 14% 10% 1	4814
June	1st to 10th	Day	56% 8% 15% 14% 7%	2660
	11th to 20th	Day	58% 10% 16% 11% 5%	2661
	21st to end	Day	37% 8% 16% 25% 10% 4	2850
July	1st to 10th	Day	20% 5% 8% 17% 20% 29%	4425
	11th to 20th	Day	17% 4 6% 19% 38% 15%	4345
	21st to end	Day	21% 4 12% 27% 32% 4	4639
August	1st to 10th	Day	21% 4 10% 25% 29% 11%	4172
	11th to 20th	Day	33% 6% 18% 27% 11% 5%	4065
	21st to end	Day	36% 5% 11% 22% 17% 8%	4305
September	1st to 10th	Day	28% 6% 13% 23% 19% 11%	2280
	11th to 20th	Day	43% 8% 12% 15% 14% 7%	2280
	21st to end	Day	43% 6% 13% 19% 14% 5%	2002
October	1st to 10th	Day	49% 6% 8% 19% 15% 3	1900
	11th to 20th	Day	53% 6% 12% 15% 13% 2	1900
	21st to end	Day	60% 5% 7% 14% 13% 1	2024
November	1st to 10th	Day	71% 8% 6% 10% 4	1574
	11th to 20th	Day	68% 7% 9% 8% 6% 2	1520
	21st to end	Day	67% 6% 4 9% 13% 1	1520
December	1st to 10th	Day	66% 6% 6% 11% 8% 2	1520
	11th to 20th	Day	69% 8% 10% 10% 3	1928
	21st to end	Day	74% 8% 10% 6% 3	2794
January	1st to 10th	Night	79% 6% 6% 5% 3 1	4406
	11th to 20th	Night	69% 7% 7% 11% 4 2	4420
	21st to end	Night	75% 5% 6% 7% 5% 1	4662
February	1st to 10th	Night	69% 8% 8% 10% 4 1	2470
	11th to 20th	Night	66% 6% 8% 11% 6% 2	2404
	21st to end	Night	68% 7% 9% 9% 6% 1	1965
March	1st to 10th	Night	66% 8% 10% 12% 3	3612
	11th to 20th	Night	50% 7% 12% 22% 9% 1	3490
	21st to end	Night	74% 8% 8% 8% 2	3723
April	1st to 10th	Night	68% 7% 10% 11% 4	1900
	11th to 20th	Night	58% 8% 11% 12% 8% 2	1879
	21st to end	Night	58% 10% 12% 13% 5% 2	1710
May	1st to 10th	Night	49% 10% 11% 18% 10% 1	2556
	11th to 20th	Night	32% 12% 21% 26% 8% 2	2516
	21st to end	Night	49% 17% 21% 11% 3	2762
June	1st to 10th	Night	50% 6% 16% 20% 6% 1	1520
	11th to 20th	Night	45% 9% 19% 20% 7%	1508
	21st to end	Night	30% 5% 19% 32% 10% 5%	1330
July	1st to 10th	Night	12% 5% 9% 23% 21% 30%	2404
	11th to 20th	Night	15% 3 7% 20% 35% 19%	2492
	21st to end	Night	12% 4 13% 29% 35% 7%	2674
August	1st to 10th	Night	12% 4 11% 32% 32% 8%	2737
	11th to 20th	Night	26% 5% 26% 27% 11% 5%	2839
	21st to end	Night	29% 5% 15% 24% 19% 8%	3367
September	1st to 10th	Night	23% 6% 14% 27% 20% 11%	1900
	11th to 20th	Night	39% 7% 13% 21% 11% 10%	1900
	21st to end	Night	37% 8% 16% 18% 16% 7%	2174
October	1st to 10th	Night	42% 5% 9% 22% 18% 3	2280
	11th to 20th	Night	49% 7% 10% 16% 17% 2	2280
	21st to end	Night	54% 6% 8% 15% 14% 3	2574
November	1st to 10th	Night	68% 6% 8% 12% 6% 1	2524
	11th to 20th	Night	68% 6% 9% 9% 7% 2	2660
	21st to end	Night	64% 5% 7% 8% 14% 2	2660
December	1st to 10th	Night	63% 7% 10% 10% 10% 1	2660
	11th to 20th	Night	69% 7% 8% 9% 6%	3276
	21st to end	Night	74% 9% 7% 7% 3	4862

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	54% 14% 16% 11% 5%	180
	11th to 20th	Day	52% 12% 20% 8% 7%	180
	21st to end	Day	48% 10% 17% 18% 6%	324
February	1st to 10th	Day	48% 12% 19% 15% 6% 1	370
	11th to 20th	Day	46% 14% 22% 15% 2 1	365
	21st to end	Day	47% 16% 19% 17% 2	343
March	1st to 10th	Day	41% 17% 25% 13% 3	460
	11th to 20th	Day	36% 14% 25% 17% 6% 2	460
	21st to end	Day	42% 19% 19% 15% 4 1	506
April	1st to 10th	Day	42% 15% 22% 13% 6% 1	460
	11th to 20th	Day	34% 19% 25% 15% 5% 1	452
	21st to end	Day	32% 20% 28% 15% 5%	460
May	1st to 10th	Day	22% 20% 28% 21% 8% 2	463
	11th to 20th	Day	30% 16% 21% 22% 8% 3	488
	21st to end	Day	27% 13% 25% 23% 10% 2	529
June	1st to 10th	Day	27% 13% 23% 24% 10% 1	490
	11th to 20th	Day	25% 17% 30% 20% 6% 1	491
	21st to end	Day	12% 13% 33% 30% 11% 2	680
July	1st to 10th	Day	11% 10% 32% 35% 11% 1	534
	11th to 20th	Day	8% 9% 32% 34% 14% 3	484
	21st to end	Day	6% 7% 31% 35% 17% 4	531
August	1st to 10th	Day	9% 6% 25% 39% 16% 5%	487
	11th to 20th	Day	5% 5% 26% 39% 20% 4	477
	21st to end	Day	12% 11% 29% 33% 13% 2	539
September	1st to 10th	Day	10% 8% 31% 39% 10% 2	490
	11th to 20th	Day	19% 9% 24% 32% 14% 1	490
	21st to end	Day	22% 11% 27% 28% 11% 1	490
October	1st to 10th	Day	26% 9% 26% 24% 14% 1	490
	11th to 20th	Day	30% 11% 22% 22% 14% 1	490
	21st to end	Day	38% 14% 19% 19% 8% 2	473
November	1st to 10th	Day	43% 14% 21% 15% 6%	222
	11th to 20th	Day	44% 11% 22% 15% 7% 2	180
	21st to end	Day	44% 11% 19% 22% 4	180
December	1st to 10th	Day	47% 10% 19% 15% 7% 1	180
	11th to 20th	Day	52% 12% 21% 13% 3	180
	21st to end	Day	51% 11% 21% 14% 4	198
January	1st to 10th	Night	50% 10% 16% 18% 6%	760
	11th to 20th	Night	45% 8% 19% 20% 8%	760
	21st to end	Night	41% 6% 22% 21% 8% 1	836
February	1st to 10th	Night	41% 9% 19% 24% 6% 1	760
	11th to 20th	Night	41% 10% 18% 23% 8%	744
	21st to end	Night	43% 10% 18% 22% 6%	628
March	1st to 10th	Night	39% 12% 16% 23% 10% 1	760
	11th to 20th	Night	39% 9% 20% 24% 8%	760
	21st to end	Night	43% 11% 16% 21% 9%	836
April	1st to 10th	Night	37% 11% 20% 21% 11% 1	760
	11th to 20th	Night	30% 10% 23% 25% 11% 1	751
	21st to end	Night	33% 7% 16% 32% 12%	570
May	1st to 10th	Night	22% 9% 24% 30% 14% 1	396
	11th to 20th	Night	23% 4 17% 36% 19% 1	374
	21st to end	Night	18% 8% 20% 35% 19% 1	411
June	1st to 10th	Night	24% 5% 18% 36% 16%	380
	11th to 20th	Night	22% 9% 19% 36% 14%	380
	21st to end	Night	12% 5% 21% 41% 21%	380
July	1st to 10th	Night	7% 2 17% 50% 24%	370
	11th to 20th	Night	7% 3 17% 49% 24% 1	368
	21st to end	Night	4 3 16% 51% 25% 2	416
August	1st to 10th	Night	5% 2 12% 42% 35% 4	503
	11th to 20th	Night	7% 2 8% 43% 38% 3	564
	21st to end	Night	10% 5% 17% 43% 23% 1	757
September	1st to 10th	Night	11% 4 16% 44% 23% 2	760
	11th to 20th	Night	17% 4 14% 34% 29% 2	760
	21st to end	Night	18% 5% 19% 38% 20% 1	760
October	1st to 10th	Night	22% 6% 18% 36% 16% 2	760
	11th to 20th	Night	28% 6% 14% 32% 17% 2	760
	21st to end	Night	37% 7% 19% 25% 11% 1	836
November	1st to 10th	Night	44% 8% 17% 25% 6%	744
	11th to 20th	Night	48% 9% 18% 19% 6% 1	760
	21st to end	Night	39% 8% 22% 24% 7%	760
December	1st to 10th	Night	39% 8% 23% 21% 7% 1	760
	11th to 20th	Night	48% 8% 18% 21% 4	760
	21st to end	Night	54% 10% 17% 14% 5%	836

Page generated at 2024-10-29 22:22:57. Version ac07

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