Anstruther Lake Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Anstruther Lake Observatory clear sky chart from 2005-11-06 to 2024-11-01.

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% 11% 4 8% 5% 4 4 4 5% 7% 32%	101541
	Night	16% 11% 4 9% 5% 5% 4 3 5% 6% 32%	97409
Transparency	Day	51% 5% 11% 21% 10% 1	101299
	Night	52% 6% 11% 20% 10% 1	97270
Seeing	Day	23% 15% 31% 19% 9% 3	14402
	Night	22% 13% 31% 24% 10% 1	23636

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	15% 20% 6% 13% 5% 4 4 2 3 4 23%	2517
	11th to 20th	Day	12% 17% 9% 16% 7% 7% 5% 4 4 3 16%	2552
	21st to end	Day	18% 21% 7% 13% 6% 4 3 3 3 4 19%	3124
February	1st to 10th	Day	13% 17% 7% 15% 8% 5% 5% 3 4 4 21%	1710
	11th to 20th	Day	13% 15% 6% 13% 7% 5% 4 3 4 4 26%	1663
	21st to end	Day	16% 15% 6% 11% 7% 5% 5% 3 4 5% 24%	1475
March	1st to 10th	Day	20% 14% 4 9% 5% 4 3 3 5% 6% 27%	3359
	11th to 20th	Day	11% 19% 5% 10% 6% 4 4 3 5% 6% 26%	3480
	21st to end	Day	14% 9% 3 7% 4 4 4 3 4 5% 43%	3864
April	1st to 10th	Day	20% 14% 3 8% 5% 5% 4 3 5% 5% 29%	2280
	11th to 20th	Day	23% 10% 2 6% 4 4 3 2 5% 5% 36%	2273
	21st to end	Day	22% 10% 3 8% 5% 4 4 3 4 5% 32%	2470
May	1st to 10th	Day	19% 8% 3 7% 5% 5% 4 3 6% 7% 34%	4284
	11th to 20th	Day	17% 10% 3 8% 5% 4 4 4 5% 9% 32%	4398
	21st to end	Day	14% 7% 2 6% 4 4 4 4 6% 7% 42%	4837
June	1st to 10th	Day	19% 9% 2 7% 5% 5% 4 4 5% 8% 32%	2660
	11th to 20th	Day	14% 7% 3 6% 4 6% 5% 5% 6% 9% 35%	2660
	21st to end	Day	17% 7% 2 6% 5% 5% 5% 4 6% 9% 34%	2660
July	1st to 10th	Day	11% 6% 3 7% 5% 5% 5% 4 8% 10% 36%	4440
	11th to 20th	Day	11% 5% 2 5% 5% 5% 5% 4 6% 8% 43%	4440
	21st to end	Day	8% 5% 2 7% 5% 5% 5% 5% 8% 9% 42%	4754
August	1st to 10th	Day	16% 9% 3 7% 4 4 6% 4 6% 8% 34%	4104
	11th to 20th	Day	15% 8% 3 8% 5% 5% 5% 4 7% 9% 33%	4044
	21st to end	Day	10% 5% 2 6% 5% 5% 5% 4 6% 11% 40%	4286
September	1st to 10th	Day	14% 7% 3 6% 5% 4 4 4 5% 9% 40%	2280
	11th to 20th	Day	12% 5% 2 6% 4 4 4 4 4 7% 46%	2256
	21st to end	Day	17% 7% 2 7% 5% 5% 4 4 6% 6% 37%	1996
October	1st to 10th	Day	20% 10% 3 8% 4 4 5% 3 5% 7% 33%	1900
	11th to 20th	Day	23% 11% 3 8% 5% 5% 5% 3 5% 6% 26%	1900
	21st to end	Day	26% 13% 4 8% 5% 5% 3 3 5% 5% 23%	2069
November	1st to 10th	Day	17% 10% 4 8% 5% 5% 4 4 5% 7% 31%	1568
	11th to 20th	Day	17% 15% 4 9% 4 4 4 4 6% 7% 26%	1520
	21st to end	Day	21% 18% 5% 8% 6% 4 5% 4 4 5% 18%	1520
December	1st to 10th	Day	18% 23% 7% 11% 6% 4 4 2 4 5% 15%	1520
	11th to 20th	Day	18% 19% 5% 11% 4 4 4 3 4 4 25%	1906
	21st to end	Day	26% 21% 5% 12% 4 3 3 2 3 4 17%	2772
January	1st to 10th	Night	18% 20% 7% 13% 5% 5% 4 3 4 4 17%	4429
	11th to 20th	Night	13% 14% 6% 16% 10% 7% 6% 4 4 5% 15%	4405
	21st to end	Night	18% 15% 9% 11% 7% 5% 4 3 4 5% 18%	4532
February	1st to 10th	Night	13% 16% 6% 11% 8% 6% 6% 4 6% 6% 20%	2470
	11th to 20th	Night	12% 14% 6% 11% 6% 6% 4 3 5% 5% 28%	2403
	21st to end	Night	15% 15% 4 9% 5% 5% 5% 4 6% 6% 26%	1978
March	1st to 10th	Night	18% 12% 4 8% 6% 5% 4 3 5% 5% 30%	3479
	11th to 20th	Night	13% 17% 7% 10% 5% 5% 4 3 5% 5% 27%	3479
	21st to end	Night	15% 7% 3 7% 4 5% 4 4 6% 7% 38%	3768
April	1st to 10th	Night	20% 11% 4 7% 5% 4 4 4 5% 6% 31%	1900
	11th to 20th	Night	17% 10% 3 8% 4 4 3 3 5% 6% 36%	1871
	21st to end	Night	18% 10% 2 7% 6% 5% 4 5% 6% 5% 33%	1710
May	1st to 10th	Night	19% 8% 3 7% 5% 4 4 3 5% 5% 37%	2655
	11th to 20th	Night	16% 7% 2 7% 5% 5% 4 4 6% 6% 36%	2495
	21st to end	Night	11% 7% 2 6% 4 4 5% 4 4 8% 45%	2738
June	1st to 10th	Night	15% 8% 2 6% 4 4 5% 3 6% 9% 37%	1520
	11th to 20th	Night	12% 6% 1 6% 5% 5% 5% 4 6% 8% 43%	1520
	21st to end	Night	13% 8% 3 7% 5% 5% 4 4 6% 7% 39%	1520
July	1st to 10th	Night	8% 5% 2 8% 5% 5% 4 4 6% 8% 44%	2520
	11th to 20th	Night	14% 6% 2 5% 3 4 4 3 5% 7% 48%	2520
	21st to end	Night	9% 6% 2 5% 4 4 4 4 6% 8% 48%	2795
August	1st to 10th	Night	12% 5% 2 6% 4 4 5% 4 5% 8% 47%	2825
	11th to 20th	Night	14% 6% 2 6% 4 4 4 3 6% 7% 43%	2785
	21st to end	Night	11% 5% 2 5% 4 4 4 4 5% 8% 48%	3337
September	1st to 10th	Night	11% 6% 3 6% 4 4 3 4 7% 9% 43%	1900
	11th to 20th	Night	12% 5% 1 5% 4 3 4 3 6% 6% 51%	1920
	21st to end	Night	19% 6% 2 6% 4 4 5% 3 5% 5% 42%	2183
October	1st to 10th	Night	17% 7% 3 8% 5% 4 5% 3 5% 6% 38%	2280
	11th to 20th	Night	21% 10% 4 8% 5% 4 4 4 5% 6% 30%	2280
	21st to end	Night	22% 13% 3 8% 5% 5% 4 4 4 6% 26%	2527
November	1st to 10th	Night	18% 10% 3 6% 5% 3 4 4 5% 6% 35%	2513
	11th to 20th	Night	18% 13% 3 7% 5% 4 5% 3 5% 6% 29%	2660
	21st to end	Night	20% 13% 4 10% 6% 5% 5% 4 6% 6% 22%	2660
December	1st to 10th	Night	21% 18% 7% 12% 6% 4 4 4 4 5% 17%	2660
	11th to 20th	Night	16% 20% 5% 12% 5% 4 3 3 4 5% 23%	3288
	21st to end	Night	27% 20% 5% 12% 4 4 4 2 3 4 13%	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	66% 5% 11% 11% 7% 1	2518
	11th to 20th	Day	71% 5% 9% 8% 6% 1	2552
	21st to end	Day	72% 4 7% 10% 6% 1	3124
February	1st to 10th	Day	67% 4 8% 14% 4 1	1710
	11th to 20th	Day	61% 5% 8% 13% 11% 2	1672
	21st to end	Day	62% 4 9% 14% 9% 1	1475
March	1st to 10th	Day	58% 4 13% 14% 10% 1	3362
	11th to 20th	Day	57% 5% 12% 16% 8% 2	3480
	21st to end	Day	43% 4 9% 24% 17% 3	3864
April	1st to 10th	Day	57% 4 7% 19% 11% 3	2280
	11th to 20th	Day	52% 4 8% 21% 15% 1	2273
	21st to end	Day	55% 4 8% 19% 12% 3	2470
May	1st to 10th	Day	49% 4 9% 24% 11% 2	4296
	11th to 20th	Day	48% 7% 12% 22% 11% 1	4402
	21st to end	Day	41% 6% 13% 22% 15% 3	4837
June	1st to 10th	Day	51% 6% 11% 18% 13% 1	2660
	11th to 20th	Day	44% 6% 11% 24% 13% 2	2660
	21st to end	Day	47% 6% 12% 22% 11% 1	2660
July	1st to 10th	Day	40% 7% 16% 24% 13% 1	4370
	11th to 20th	Day	36% 7% 15% 31% 10%	4365
	21st to end	Day	35% 8% 11% 33% 12%	4602
August	1st to 10th	Day	47% 7% 13% 23% 10% 1	4091
	11th to 20th	Day	44% 8% 14% 26% 8%	4083
	21st to end	Day	37% 7% 12% 33% 10% 1	4286
September	1st to 10th	Day	41% 6% 12% 28% 12% 1	2280
	11th to 20th	Day	37% 5% 13% 30% 14% 1	2256
	21st to end	Day	47% 6% 14% 23% 11%	1996
October	1st to 10th	Day	51% 5% 11% 21% 11% 1	1900
	11th to 20th	Day	58% 6% 13% 15% 7% 1	1900
	21st to end	Day	63% 4 11% 15% 6%	2069
November	1st to 10th	Day	52% 5% 15% 20% 8% 1	1568
	11th to 20th	Day	57% 6% 13% 14% 8% 2	1520
	21st to end	Day	67% 6% 11% 10% 5% 1	1520
December	1st to 10th	Day	73% 5% 9% 9% 4	1520
	11th to 20th	Day	64% 7% 8% 12% 9%	1906
	21st to end	Day	73% 3 7% 12% 4	2772
January	1st to 10th	Night	71% 4 9% 12% 4	4429
	11th to 20th	Night	70% 7% 9% 9% 5% 1	4405
	21st to end	Night	69% 5% 9% 10% 6%	4532
February	1st to 10th	Night	63% 6% 10% 15% 6% 1	2470
	11th to 20th	Night	59% 4 9% 19% 9%	2405
	21st to end	Night	57% 5% 11% 19% 9%	1978
March	1st to 10th	Night	56% 5% 9% 19% 10% 1	3489
	11th to 20th	Night	57% 6% 13% 16% 7% 1	3480
	21st to end	Night	43% 5% 9% 25% 16% 2	3768
April	1st to 10th	Night	54% 5% 8% 20% 12% 2	1900
	11th to 20th	Night	49% 4 9% 21% 15% 1	1871
	21st to end	Night	51% 6% 9% 16% 16% 2	1710
May	1st to 10th	Night	48% 5% 10% 19% 15% 2	2662
	11th to 20th	Night	45% 8% 12% 22% 11% 2	2496
	21st to end	Night	38% 5% 13% 23% 19% 2	2739
June	1st to 10th	Night	43% 5% 13% 23% 14% 2	1520
	11th to 20th	Night	37% 7% 12% 24% 18% 2	1520
	21st to end	Night	43% 6% 14% 22% 12% 1	1520
July	1st to 10th	Night	36% 6% 16% 24% 16% 1	2480
	11th to 20th	Night	36% 5% 11% 34% 14%	2472
	21st to end	Night	33% 7% 14% 32% 14%	2706
August	1st to 10th	Night	35% 7% 14% 26% 17% 1	2814
	11th to 20th	Night	38% 7% 18% 24% 12% 1	2812
	21st to end	Night	33% 6% 13% 34% 11% 2	3337
September	1st to 10th	Night	36% 7% 16% 27% 14% 1	1900
	11th to 20th	Night	34% 5% 13% 34% 14% 1	1920
	21st to end	Night	44% 5% 11% 28% 11%	2183
October	1st to 10th	Night	47% 6% 11% 22% 14%	2280
	11th to 20th	Night	55% 6% 12% 21% 6%	2280
	21st to end	Night	60% 6% 11% 14% 10%	2527
November	1st to 10th	Night	49% 6% 13% 23% 9%	2513
	11th to 20th	Night	55% 6% 13% 17% 8% 2	2660
	21st to end	Night	61% 7% 13% 14% 4	2660
December	1st to 10th	Night	68% 6% 10% 11% 5%	2660
	11th to 20th	Night	65% 4 10% 14% 7%	3288
	21st to end	Night	76% 4 6% 10% 4	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	23% 24% 31% 16% 6% 1	180
	11th to 20th	Day	26% 21% 34% 14% 4 1	189
	21st to end	Day	26% 19% 35% 13% 5% 1	297
February	1st to 10th	Day	29% 21% 37% 9% 3	270
	11th to 20th	Day	28% 26% 40% 5% 1	270
	21st to end	Day	34% 18% 36% 11% 1	287
March	1st to 10th	Day	24% 18% 38% 16% 3	460
	11th to 20th	Day	26% 20% 33% 18% 3 1	460
	21st to end	Day	31% 18% 31% 13% 6% 1	506
April	1st to 10th	Day	27% 21% 33% 12% 7%	460
	11th to 20th	Day	35% 20% 20% 15% 8% 3	452
	21st to end	Day	30% 18% 31% 14% 6% 1	460
May	1st to 10th	Day	27% 14% 30% 17% 6% 5%	463
	11th to 20th	Day	20% 15% 34% 19% 9% 3	487
	21st to end	Day	20% 12% 36% 19% 10% 4	529
June	1st to 10th	Day	23% 14% 33% 21% 8% 1	490
	11th to 20th	Day	18% 12% 33% 24% 10% 3	490
	21st to end	Day	22% 10% 36% 21% 9% 2	490
July	1st to 10th	Day	13% 8% 32% 31% 13% 4	485
	11th to 20th	Day	14% 10% 31% 25% 14% 5%	484
	21st to end	Day	13% 11% 31% 30% 11% 4	532
August	1st to 10th	Day	15% 8% 29% 29% 13% 6%	486
	11th to 20th	Day	16% 5% 26% 31% 15% 6%	479
	21st to end	Day	15% 8% 32% 24% 14% 7%	539
September	1st to 10th	Day	15% 12% 30% 23% 13% 6%	490
	11th to 20th	Day	11% 10% 25% 22% 20% 11%	490
	21st to end	Day	20% 12% 26% 25% 11% 6%	490
October	1st to 10th	Day	25% 16% 25% 17% 14% 4	490
	11th to 20th	Day	25% 23% 29% 16% 6% 1	490
	21st to end	Day	33% 18% 28% 15% 5%	527
November	1st to 10th	Day	27% 17% 30% 17% 8% 1	262
	11th to 20th	Day	30% 23% 32% 9% 4 2	180
	21st to end	Day	33% 17% 35% 13% 2 1	180
December	1st to 10th	Day	31% 22% 28% 18% 2	180
	11th to 20th	Day	35% 22% 27% 13% 2 1	180
	21st to end	Day	32% 23% 31% 10% 3 1	198
January	1st to 10th	Night	28% 18% 31% 18% 5%	760
	11th to 20th	Night	29% 15% 31% 19% 5%	760
	21st to end	Night	20% 14% 35% 24% 6% 1	836
February	1st to 10th	Night	22% 20% 36% 19% 2	760
	11th to 20th	Night	20% 19% 40% 17% 4	743
	21st to end	Night	23% 21% 32% 20% 4	628
March	1st to 10th	Night	23% 19% 34% 19% 3	760
	11th to 20th	Night	23% 17% 34% 20% 4 1	760
	21st to end	Night	20% 14% 34% 24% 8% 1	836
April	1st to 10th	Night	26% 14% 32% 22% 5%	760
	11th to 20th	Night	23% 18% 31% 19% 8% 1	747
	21st to end	Night	23% 11% 32% 23% 11%	570
May	1st to 10th	Night	24% 7% 29% 26% 12% 2	470
	11th to 20th	Night	17% 10% 34% 30% 9%	374
	21st to end	Night	13% 8% 32% 35% 11% 1	411
June	1st to 10th	Night	17% 7% 34% 31% 12%	380
	11th to 20th	Night	15% 9% 28% 37% 11% 1	380
	21st to end	Night	17% 7% 28% 36% 12%	380
July	1st to 10th	Night	6% 6% 29% 42% 16% 1	370
	11th to 20th	Night	12% 5% 27% 37% 18% 1	368
	21st to end	Night	11% 4 27% 41% 16% 1	448
August	1st to 10th	Night	12% 3 23% 35% 25% 2	567
	11th to 20th	Night	11% 5% 21% 37% 25% 2	564
	21st to end	Night	13% 5% 29% 31% 20% 2	749
September	1st to 10th	Night	12% 7% 32% 29% 18% 3	760
	11th to 20th	Night	13% 4 24% 31% 23% 5%	760
	21st to end	Night	21% 9% 20% 29% 17% 3	760
October	1st to 10th	Night	21% 12% 27% 23% 15% 2	760
	11th to 20th	Night	28% 14% 29% 20% 8% 1	760
	21st to end	Night	29% 15% 31% 20% 5%	836
November	1st to 10th	Night	24% 13% 28% 27% 8%	743
	11th to 20th	Night	27% 14% 34% 17% 6% 2	760
	21st to end	Night	29% 15% 29% 21% 5% 1	760
December	1st to 10th	Night	32% 17% 32% 15% 4	760
	11th to 20th	Night	25% 18% 35% 17% 4 1	760
	21st to end	Night	34% 14% 31% 17% 3	836

Page generated at 2024-10-29 11:20:49. Version ac07

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