Lake Ariel
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lake Ariel clear sky chart from 2005-11-06 to 2024-12-02.

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	16% 9% 3 7% 5% 5% 5% 4 6% 7% 33%	101627
	Night	16% 9% 3 7% 5% 4 4 4 6% 7% 35%	97991
Transparency	Day	47% 6% 12% 21% 12% 1	105161
	Night	45% 7% 13% 21% 12% 1	102546
Seeing	Day	24% 18% 28% 19% 9% 3	14920
	Night	21% 18% 28% 24% 8% 1	24161

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	13% 14% 9% 9% 5% 4 4 3 4 5% 31%	2517
	11th to 20th	Day	12% 14% 7% 13% 6% 6% 5% 3 4 5% 24%	2520
	21st to end	Day	19% 15% 7% 9% 6% 4 4 3 5% 5% 23%	3101
February	1st to 10th	Day	15% 12% 4 9% 6% 5% 6% 5% 5% 5% 28%	1710
	11th to 20th	Day	12% 10% 5% 9% 6% 5% 5% 4 6% 7% 32%	1765
	21st to end	Day	19% 12% 3 8% 6% 4 4 4 5% 5% 30%	1570
March	1st to 10th	Day	24% 12% 4 8% 5% 4 3 3 4 5% 29%	3116
	11th to 20th	Day	10% 11% 4 8% 6% 5% 5% 4 6% 6% 35%	3479
	21st to end	Day	20% 10% 2 6% 4 5% 4 3 4 5% 36%	4034
April	1st to 10th	Day	16% 12% 3 7% 5% 5% 4 4 5% 5% 34%	2280
	11th to 20th	Day	16% 10% 3 7% 5% 4 4 4 5% 6% 37%	2254
	21st to end	Day	17% 8% 3 7% 5% 4 5% 4 6% 6% 35%	2280
May	1st to 10th	Day	27% 8% 2 6% 4 4 4 3 4 6% 31%	4224
	11th to 20th	Day	23% 8% 3 7% 5% 5% 5% 5% 5% 6% 27%	4398
	21st to end	Day	13% 6% 2 6% 4 4 5% 4 7% 9% 40%	4837
June	1st to 10th	Day	15% 7% 2 7% 5% 5% 6% 4 6% 9% 33%	2660
	11th to 20th	Day	14% 8% 3 7% 5% 5% 6% 5% 6% 9% 33%	2660
	21st to end	Day	12% 7% 3 7% 5% 5% 6% 5% 7% 9% 35%	2660
July	1st to 10th	Day	9% 5% 2 7% 7% 6% 6% 5% 8% 10% 35%	4440
	11th to 20th	Day	9% 5% 2 7% 6% 5% 5% 5% 8% 11% 37%	4440
	21st to end	Day	13% 8% 3 8% 5% 5% 5% 5% 6% 8% 33%	4814
August	1st to 10th	Day	22% 6% 2 8% 5% 5% 5% 3 7% 7% 29%	4116
	11th to 20th	Day	15% 6% 2 7% 4 5% 6% 5% 6% 8% 36%	3801
	21st to end	Day	16% 5% 2 5% 4 4 4 4 6% 8% 42%	4180
September	1st to 10th	Day	16% 6% 2 7% 4 5% 5% 4 6% 6% 39%	2280
	11th to 20th	Day	14% 6% 2 5% 4 4 4 3 5% 8% 45%	2257
	21st to end	Day	18% 8% 2 6% 4 4 4 4 6% 7% 36%	2073
October	1st to 10th	Day	17% 8% 3 6% 4 4 4 3 5% 8% 37%	1900
	11th to 20th	Day	13% 9% 3 6% 5% 4 6% 4 6% 7% 38%	1900
	21st to end	Day	19% 11% 2 7% 4 4 5% 4 4 6% 33%	1999
November	1st to 10th	Day	12% 9% 3 7% 4 3 4 4 5% 6% 44%	1761
	11th to 20th	Day	14% 11% 4 7% 5% 5% 4 4 6% 5% 36%	1795
	21st to end	Day	17% 10% 3 7% 6% 5% 5% 4 6% 7% 31%	1600
December	1st to 10th	Day	16% 14% 5% 9% 5% 5% 5% 4 5% 6% 27%	1528
	11th to 20th	Day	21% 11% 5% 8% 4 4 3 3 5% 6% 30%	1906
	21st to end	Day	18% 15% 7% 11% 6% 5% 5% 4 4 5% 20%	2772
January	1st to 10th	Night	14% 9% 7% 8% 5% 4 4 4 6% 7% 30%	4429
	11th to 20th	Night	13% 13% 5% 12% 6% 5% 5% 4 5% 7% 26%	4440
	21st to end	Night	21% 12% 5% 9% 7% 4 4 4 6% 5% 23%	4550
February	1st to 10th	Night	15% 10% 4 7% 5% 5% 6% 4 6% 6% 33%	2470
	11th to 20th	Night	12% 9% 4 9% 6% 5% 5% 5% 7% 6% 29%	2300
	21st to end	Night	16% 9% 4 9% 5% 5% 5% 4 5% 5% 33%	1884
March	1st to 10th	Night	21% 13% 4 8% 5% 4 4 3 5% 5% 30%	3709
	11th to 20th	Night	10% 11% 5% 8% 5% 4 5% 5% 6% 7% 35%	3479
	21st to end	Night	14% 11% 4 8% 5% 4 5% 3 4 5% 38%	3596
April	1st to 10th	Night	15% 11% 4 9% 6% 5% 5% 4 6% 6% 31%	1900
	11th to 20th	Night	16% 10% 2 6% 4 4 4 3 6% 7% 37%	1875
	21st to end	Night	19% 9% 3 5% 4 4 3 3 5% 6% 40%	1900
May	1st to 10th	Night	28% 9% 3 6% 4 3 4 3 4 6% 31%	2729
	11th to 20th	Night	22% 10% 3 6% 4 4 4 3 5% 7% 32%	2495
	21st to end	Night	12% 8% 3 7% 5% 5% 5% 4 7% 8% 37%	2738
June	1st to 10th	Night	16% 7% 1 5% 6% 4 4 3 6% 8% 40%	1520
	11th to 20th	Night	13% 5% 2 6% 5% 4 5% 4 6% 8% 41%	1520
	21st to end	Night	11% 4 2 5% 3 4 4 5% 8% 9% 44%	1520
July	1st to 10th	Night	9% 6% 2 8% 5% 4 6% 4 7% 8% 41%	2520
	11th to 20th	Night	10% 6% 2 5% 5% 5% 5% 4 7% 11% 39%	2520
	21st to end	Night	13% 8% 2 7% 4 4 5% 4 5% 7% 41%	2739
August	1st to 10th	Night	21% 6% 2 6% 4 5% 6% 4 6% 8% 33%	2810
	11th to 20th	Night	17% 5% 2 6% 4 4 4 3 5% 7% 42%	2994
	21st to end	Night	13% 5% 1 5% 4 3 4 4 5% 7% 48%	3476
September	1st to 10th	Night	14% 6% 2 6% 4 4 5% 4 5% 7% 44%	1900
	11th to 20th	Night	13% 5% 2 4 3 3 4 3 4 6% 52%	1921
	21st to end	Night	17% 7% 3 6% 4 4 4 3 6% 6% 41%	2104
October	1st to 10th	Night	20% 7% 2 6% 4 3 3 3 5% 6% 41%	2280
	11th to 20th	Night	15% 8% 2 6% 4 4 4 3 5% 6% 43%	2280
	21st to end	Night	20% 10% 2 5% 3 4 3 3 6% 7% 36%	2598
November	1st to 10th	Night	11% 8% 3 7% 5% 4 4 3 5% 6% 45%	2537
	11th to 20th	Night	16% 8% 3 6% 4 4 4 4 5% 6% 39%	2600
	21st to end	Night	13% 10% 4 7% 4 5% 5% 4 6% 7% 36%	2800
December	1st to 10th	Night	18% 10% 3 8% 5% 5% 4 5% 7% 7% 28%	2686
	11th to 20th	Night	17% 11% 4 7% 5% 5% 5% 4 6% 7% 30%	3288
	21st to end	Night	21% 13% 6% 9% 5% 4 4 4 5% 6% 25%	4884

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% 5% 13% 23% 7% 1	2518
	11th to 20th	Day	59% 5% 11% 17% 7% 2	2520
	21st to end	Day	60% 6% 11% 16% 7% 1	3101
February	1st to 10th	Day	54% 7% 13% 15% 10% 1	1710
	11th to 20th	Day	49% 6% 11% 22% 11% 1	1774
	21st to end	Day	53% 5% 11% 21% 9% 2	1570
March	1st to 10th	Day	57% 4 11% 18% 8% 2	3119
	11th to 20th	Day	42% 10% 15% 23% 9% 1	3479
	21st to end	Day	48% 6% 8% 15% 20% 3	4034
April	1st to 10th	Day	50% 6% 10% 20% 11% 3	2280
	11th to 20th	Day	45% 6% 12% 21% 13% 2	2254
	21st to end	Day	46% 7% 9% 20% 13% 4	2280
May	1st to 10th	Day	54% 6% 10% 18% 10% 2	4238
	11th to 20th	Day	54% 10% 10% 18% 7% 1	4402
	21st to end	Day	36% 9% 14% 25% 15% 2	4837
June	1st to 10th	Day	45% 9% 13% 20% 13%	2660
	11th to 20th	Day	46% 8% 13% 21% 10% 1	2660
	21st to end	Day	42% 9% 13% 25% 11%	2660
July	1st to 10th	Day	43% 8% 14% 22% 12% 1	4370
	11th to 20th	Day	39% 7% 16% 25% 13%	4365
	21st to end	Day	47% 6% 13% 19% 14% 1	4661
August	1st to 10th	Day	52% 7% 14% 19% 8%	4102
	11th to 20th	Day	43% 6% 15% 27% 9%	3839
	21st to end	Day	39% 5% 11% 33% 12% 1	4180
September	1st to 10th	Day	43% 7% 12% 21% 16% 1	2280
	11th to 20th	Day	36% 6% 11% 23% 22% 2	2257
	21st to end	Day	46% 6% 11% 20% 16% 1	2073
October	1st to 10th	Day	47% 3 7% 21% 20% 2	3160
	11th to 20th	Day	38% 4 9% 26% 18% 6%	3140
	21st to end	Day	33% 4 17% 27% 15% 3	3276
November	1st to 10th	Day	39% 5% 14% 23% 16% 2	1761
	11th to 20th	Day	45% 6% 12% 21% 13% 2	1795
	21st to end	Day	49% 7% 15% 22% 7% 1	1600
December	1st to 10th	Day	55% 6% 17% 13% 8% 1	1528
	11th to 20th	Day	53% 6% 16% 19% 6%	1906
	21st to end	Day	64% 6% 10% 14% 6%	2772
January	1st to 10th	Night	48% 6% 14% 23% 8% 2	4429
	11th to 20th	Night	53% 7% 15% 17% 7% 1	4440
	21st to end	Night	59% 6% 11% 16% 7% 1	4550
February	1st to 10th	Night	48% 6% 15% 20% 10% 1	2470
	11th to 20th	Night	49% 7% 13% 18% 12% 2	2302
	21st to end	Night	49% 5% 11% 20% 11% 3	1884
March	1st to 10th	Night	54% 5% 11% 17% 10% 1	3719
	11th to 20th	Night	40% 9% 18% 23% 9% 1	3480
	21st to end	Night	45% 7% 9% 18% 19% 4	3596
April	1st to 10th	Night	51% 7% 11% 18% 12% 2	1900
	11th to 20th	Night	44% 8% 11% 21% 15% 1	1875
	21st to end	Night	45% 7% 10% 20% 15% 3	1900
May	1st to 10th	Night	54% 7% 9% 21% 8% 1	2735
	11th to 20th	Night	51% 10% 13% 16% 9% 1	2496
	21st to end	Night	39% 10% 15% 22% 13% 1	2739
June	1st to 10th	Night	40% 7% 12% 25% 16% 1	1520
	11th to 20th	Night	39% 8% 16% 26% 10% 1	1520
	21st to end	Night	32% 9% 19% 27% 13%	1520
July	1st to 10th	Night	39% 8% 18% 19% 16% 1	2480
	11th to 20th	Night	38% 8% 17% 25% 12% 1	2472
	21st to end	Night	41% 6% 15% 21% 16% 1	2651
August	1st to 10th	Night	47% 7% 18% 21% 7%	2800
	11th to 20th	Night	41% 6% 16% 27% 10%	3022
	21st to end	Night	35% 5% 12% 33% 15% 1	3476
September	1st to 10th	Night	38% 7% 13% 25% 16% 1	1900
	11th to 20th	Night	33% 6% 12% 24% 23% 2	1921
	21st to end	Night	42% 7% 9% 23% 18% 1	2104
October	1st to 10th	Night	47% 4 10% 22% 17% 1	3800
	11th to 20th	Night	34% 4 11% 25% 21% 5%	3779
	21st to end	Night	33% 4 17% 28% 17% 1	4271
November	1st to 10th	Night	39% 5% 12% 22% 19% 2	2537
	11th to 20th	Night	44% 5% 12% 22% 15% 2	2600
	21st to end	Night	44% 7% 16% 23% 10% 1	2800
December	1st to 10th	Night	51% 7% 15% 20% 7%	2686
	11th to 20th	Night	50% 7% 14% 17% 10% 1	3288
	21st to end	Night	57% 8% 13% 17% 5%	4884

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	34% 27% 25% 13% 1 1	180
	11th to 20th	Day	39% 28% 22% 9% 1	180
	21st to end	Day	27% 33% 27% 9% 4	292
February	1st to 10th	Day	34% 32% 27% 7% 1	270
	11th to 20th	Day	35% 29% 30% 5% 1	373
	21st to end	Day	34% 29% 26% 9% 2	382
March	1st to 10th	Day	32% 22% 30% 14% 2	460
	11th to 20th	Day	32% 26% 27% 12% 3	460
	21st to end	Day	32% 28% 25% 10% 4 1	506
April	1st to 10th	Day	34% 24% 25% 12% 5%	460
	11th to 20th	Day	28% 26% 26% 12% 6% 2	452
	21st to end	Day	30% 20% 31% 14% 3 2	460
May	1st to 10th	Day	34% 20% 26% 12% 6% 2	463
	11th to 20th	Day	24% 17% 31% 20% 6% 2	487
	21st to end	Day	18% 13% 30% 24% 12% 4	529
June	1st to 10th	Day	20% 16% 31% 22% 9% 2	490
	11th to 20th	Day	18% 17% 26% 24% 13% 1	490
	21st to end	Day	15% 15% 34% 26% 9% 2	490
July	1st to 10th	Day	14% 8% 30% 27% 16% 5%	485
	11th to 20th	Day	9% 9% 32% 31% 16% 3	484
	21st to end	Day	13% 10% 37% 27% 10% 3	532
August	1st to 10th	Day	13% 9% 27% 26% 18% 6%	486
	11th to 20th	Day	15% 9% 25% 30% 16% 5%	479
	21st to end	Day	14% 11% 28% 25% 15% 7%	539
September	1st to 10th	Day	19% 13% 22% 22% 17% 7%	490
	11th to 20th	Day	13% 8% 27% 24% 17% 10%	490
	21st to end	Day	26% 12% 26% 21% 11% 3	490
October	1st to 10th	Day	25% 15% 23% 21% 11% 5%	490
	11th to 20th	Day	21% 21% 29% 20% 8% 1	490
	21st to end	Day	26% 20% 29% 17% 7% 1	491
November	1st to 10th	Day	23% 21% 25% 20% 9% 2	395
	11th to 20th	Day	28% 24% 29% 15% 4 1	395
	21st to end	Day	36% 20% 34% 9% 2	200
December	1st to 10th	Day	34% 30% 22% 9% 4 1	182
	11th to 20th	Day	41% 24% 24% 8% 3	180
	21st to end	Day	30% 27% 28% 13% 2	198
January	1st to 10th	Night	23% 29% 32% 13% 2	760
	11th to 20th	Night	26% 25% 29% 18% 2	760
	21st to end	Night	20% 29% 34% 15% 2	836
February	1st to 10th	Night	28% 21% 35% 15% 1	760
	11th to 20th	Night	26% 30% 33% 11% 1	743
	21st to end	Night	29% 26% 30% 14% 2	628
March	1st to 10th	Night	27% 24% 32% 14% 2	760
	11th to 20th	Night	26% 25% 29% 16% 4	760
	21st to end	Night	22% 26% 31% 17% 4	836
April	1st to 10th	Night	22% 24% 31% 20% 2	760
	11th to 20th	Night	25% 20% 30% 19% 6%	751
	21st to end	Night	24% 18% 30% 22% 5%	760
May	1st to 10th	Night	28% 15% 28% 22% 7%	517
	11th to 20th	Night	20% 13% 33% 28% 6% 1	374
	21st to end	Night	14% 10% 26% 36% 13%	411
June	1st to 10th	Night	16% 9% 23% 38% 13% 1	380
	11th to 20th	Night	14% 7% 29% 39% 11% 1	380
	21st to end	Night	11% 6% 27% 45% 10% 1	380
July	1st to 10th	Night	14% 5% 21% 39% 19% 2	370
	11th to 20th	Night	11% 5% 22% 44% 17% 1	368
	21st to end	Night	12% 7% 22% 43% 16%	416
August	1st to 10th	Night	14% 2 21% 41% 18% 3	552
	11th to 20th	Night	14% 6% 15% 39% 24% 2	683
	21st to end	Night	15% 7% 19% 36% 22% 2	836
September	1st to 10th	Night	16% 8% 24% 32% 18% 3	760
	11th to 20th	Night	13% 8% 24% 28% 21% 6%	760
	21st to end	Night	21% 10% 23% 29% 16% 3	760
October	1st to 10th	Night	24% 14% 21% 23% 17% 2	760
	11th to 20th	Night	20% 14% 27% 30% 8% 1	760
	21st to end	Night	27% 17% 29% 22% 5%	836
November	1st to 10th	Night	17% 19% 31% 24% 8%	780
	11th to 20th	Night	24% 23% 27% 19% 6% 1	800
	21st to end	Night	22% 23% 33% 18% 5% 1	800
December	1st to 10th	Night	27% 23% 32% 14% 4	768
	11th to 20th	Night	25% 23% 31% 18% 3	760
	21st to end	Night	26% 25% 31% 16% 2	836

Page generated at 2024-11-29 10:43:04. Version ac07

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