Lily Lake Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lily Lake Observatory clear sky chart from 2005-11-06 to 2024-05-13.

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	13% 9% 4 8% 5% 4 5% 4 5% 7% 36%	83469
	Night	14% 10% 4 8% 4 4 4 3 5% 6% 38%	86102
Transparency	Day	47% 7% 13% 21% 11% 2	83170
	Night	46% 6% 12% 21% 13% 2	85922
Seeing	Day	16% 12% 29% 25% 13% 5%	15065
	Night	17% 10% 32% 29% 11% 1	25081

By Month

Percentage Cloud Cover SE (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% 13% 8% 13% 6% 4 4 3 4 4 28%	2527
	11th to 20th	Day	11% 14% 6% 15% 5% 5% 4 7% 8% 5% 20%	2530
	21st to end	Day	17% 19% 8% 11% 5% 4 4 2 4 6% 19%	2888
February	1st to 10th	Day	14% 14% 4 9% 7% 5% 5% 3 5% 6% 27%	1724
	11th to 20th	Day	13% 11% 4 7% 6% 5% 4 4 5% 6% 36%	1848
	21st to end	Day	15% 12% 5% 10% 5% 4 5% 3 5% 6% 31%	1570
March	1st to 10th	Day	13% 12% 5% 8% 5% 4 4 3 4 6% 35%	3120
	11th to 20th	Day	11% 6% 3 7% 5% 5% 4 4 6% 8% 41%	3291
	21st to end	Day	19% 13% 6% 13% 6% 5% 5% 3 5% 5% 19%	4165
April	1st to 10th	Day	17% 14% 4 8% 5% 4 4 3 5% 6% 31%	2280
	11th to 20th	Day	16% 10% 3 7% 4 5% 5% 4 5% 6% 34%	2254
	21st to end	Day	19% 9% 2 8% 5% 5% 4 3 5% 6% 33%	2365
May	1st to 10th	Day	17% 8% 3 8% 6% 4 5% 4 6% 8% 31%	2470
	11th to 20th	Day	18% 8% 3 7% 4 5% 5% 4 6% 7% 33%	2478
	21st to end	Day	13% 8% 2 7% 5% 5% 6% 5% 6% 8% 35%	2725
June	1st to 10th	Day	9% 6% 2 6% 4 4 5% 4 6% 7% 46%	2520
	11th to 20th	Day	9% 6% 2 5% 5% 4 5% 4 6% 9% 45%	2520
	21st to end	Day	11% 7% 2 6% 6% 5% 6% 5% 7% 8% 38%	2520
July	1st to 10th	Day	9% 4 2 6% 4 5% 5% 4 7% 9% 46%	2520
	11th to 20th	Day	8% 5% 2 5% 4 5% 5% 4 7% 9% 46%	2520
	21st to end	Day	7% 4 2 7% 5% 5% 6% 5% 7% 9% 44%	2743
August	1st to 10th	Day	8% 5% 2 7% 5% 5% 5% 5% 8% 9% 43%	2472
	11th to 20th	Day	9% 5% 2 6% 4 5% 5% 5% 7% 10% 42%	2125
	21st to end	Day	8% 5% 2 5% 4 5% 5% 4 6% 9% 48%	2376
September	1st to 10th	Day	12% 6% 2 5% 4 5% 4 4 5% 8% 44%	2160
	11th to 20th	Day	13% 4 2 4 3 3 4 3 5% 7% 53%	2062
	21st to end	Day	10% 7% 2 6% 4 4 5% 4 5% 7% 45%	1980
October	1st to 10th	Day	12% 6% 2 6% 5% 4 4 3 5% 7% 46%	1908
	11th to 20th	Day	19% 9% 3 7% 5% 4 4 4 5% 7% 34%	1800
	21st to end	Day	20% 10% 3 6% 3 4 4 4 4 5% 37%	1787
November	1st to 10th	Day	11% 9% 3 7% 3 3 5% 3 5% 6% 45%	1672
	11th to 20th	Day	15% 13% 4 8% 5% 4 4 4 5% 7% 33%	1710
	21st to end	Day	18% 11% 3 8% 5% 4 4 2 4 5% 35%	1618
December	1st to 10th	Day	15% 12% 6% 9% 5% 3 5% 3 4 5% 32%	1520
	11th to 20th	Day	12% 14% 4 9% 6% 5% 5% 4 6% 6% 29%	1918
	21st to end	Day	20% 22% 9% 13% 5% 4 3 2 3 4 15%	2783
January	1st to 10th	Night	13% 13% 6% 13% 6% 4 3 2 4 4 31%	4428
	11th to 20th	Night	14% 17% 6% 14% 5% 4 4 6% 7% 4 20%	4440
	21st to end	Night	21% 17% 8% 10% 5% 4 3 3 4 5% 21%	4774
February	1st to 10th	Night	14% 14% 5% 9% 5% 5% 4 3 4 6% 32%	2454
	11th to 20th	Night	13% 11% 4 7% 5% 4 4 3 5% 6% 38%	2218
	21st to end	Night	16% 14% 3 8% 4 3 4 3 4 6% 36%	1884
March	1st to 10th	Night	18% 9% 3 6% 4 3 3 2 4 5% 41%	3733
	11th to 20th	Night	10% 7% 2 6% 4 4 3 4 5% 7% 48%	3696
	21st to end	Night	22% 10% 5% 11% 4 4 4 3 4 5% 27%	3466
April	1st to 10th	Night	16% 9% 3 7% 5% 3 4 3 5% 6% 39%	1900
	11th to 20th	Night	18% 9% 3 6% 5% 4 4 3 4 6% 39%	1875
	21st to end	Night	17% 8% 3 7% 4 4 4 4 5% 7% 37%	1815
May	1st to 10th	Night	14% 7% 3 7% 5% 5% 5% 5% 7% 7% 36%	1710
	11th to 20th	Night	17% 7% 2 6% 4 4 3 3 5% 9% 40%	1469
	21st to end	Night	13% 6% 2 7% 4 5% 4 3 6% 9% 41%	1551
June	1st to 10th	Night	9% 5% 1 6% 5% 4 3 5% 6% 7% 49%	1440
	11th to 20th	Night	9% 4 2 6% 4 5% 4 4 7% 7% 48%	1440
	21st to end	Night	9% 5% 2 6% 5% 5% 5% 5% 6% 8% 44%	1440
July	1st to 10th	Night	6% 4 1 4 4 5% 4 6% 6% 11% 50%	1440
	11th to 20th	Night	7% 4 1 5% 4 3 5% 4 7% 8% 52%	1440
	21st to end	Night	6% 4 1 5% 4 5% 5% 4 7% 9% 52%	1575
August	1st to 10th	Night	4 4 2 5% 5% 4 6% 4 7% 10% 49%	1462
	11th to 20th	Night	7% 4 1 6% 3 3 4 3 6% 9% 53%	1776
	21st to end	Night	8% 5% 2 5% 3 3 3 3 6% 9% 54%	1980
September	1st to 10th	Night	11% 5% 2 5% 3 4 3 3 4 7% 53%	1800
	11th to 20th	Night	10% 4 2 6% 4 3 3 3 5% 6% 55%	1880
	21st to end	Night	10% 6% 2 5% 4 4 4 4 5% 8% 48%	1980
October	1st to 10th	Night	11% 5% 3 4 4 4 3 4 5% 6% 50%	2049
	11th to 20th	Night	18% 7% 2 5% 3 4 3 3 4 6% 44%	2160
	21st to end	Night	20% 10% 3 6% 4 3 4 3 4 6% 38%	2568
November	1st to 10th	Night	12% 8% 2 5% 4 3 3 3 4 6% 49%	2406
	11th to 20th	Night	14% 11% 3 8% 5% 4 3 3 6% 6% 37%	2470
	21st to end	Night	16% 9% 4 8% 4 4 4 4 4 6% 37%	2560
December	1st to 10th	Night	16% 11% 3 9% 5% 5% 4 3 4 7% 32%	2660
	11th to 20th	Night	15% 13% 4 9% 5% 4 4 4 5% 6% 32%	3279
	21st to end	Night	22% 18% 6% 10% 5% 5% 5% 4 5% 5% 16%	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	59% 6% 11% 16% 7%	2528
	11th to 20th	Day	60% 6% 13% 13% 8%	2530
	21st to end	Day	67% 5% 9% 13% 6%	2888
February	1st to 10th	Day	57% 6% 13% 14% 9% 2	1724
	11th to 20th	Day	48% 6% 12% 23% 9% 2	1858
	21st to end	Day	54% 7% 11% 18% 9% 2	1570
March	1st to 10th	Day	48% 8% 11% 21% 11% 2	3120
	11th to 20th	Day	39% 7% 13% 29% 10% 1	3291
	21st to end	Day	65% 8% 12% 12% 3	4165
April	1st to 10th	Day	54% 6% 10% 20% 10%	2280
	11th to 20th	Day	48% 7% 10% 21% 12% 3	2254
	21st to end	Day	51% 7% 12% 17% 12% 1	2365
May	1st to 10th	Day	48% 9% 13% 21% 8%	2470
	11th to 20th	Day	48% 7% 12% 23% 10%	2482
	21st to end	Day	44% 9% 13% 18% 14% 2	2725
June	1st to 10th	Day	35% 7% 13% 27% 17% 2	2520
	11th to 20th	Day	35% 8% 12% 23% 19% 3	2520
	21st to end	Day	41% 9% 14% 21% 13% 2	2520
July	1st to 10th	Day	33% 8% 15% 27% 14% 3	2451
	11th to 20th	Day	33% 8% 16% 25% 16% 2	2445
	21st to end	Day	33% 9% 18% 23% 14% 3	2591
August	1st to 10th	Day	34% 9% 18% 26% 11% 2	2457
	11th to 20th	Day	35% 9% 16% 25% 14% 1	2125
	21st to end	Day	31% 8% 13% 26% 19% 3	2376
September	1st to 10th	Day	37% 7% 12% 24% 16% 4	2160
	11th to 20th	Day	30% 6% 12% 29% 20% 3	2062
	21st to end	Day	36% 6% 12% 25% 19% 1	1980
October	1st to 10th	Day	38% 6% 13% 24% 17% 1	1908
	11th to 20th	Day	49% 6% 12% 20% 12% 1	1800
	21st to end	Day	49% 6% 11% 22% 10% 2	1787
November	1st to 10th	Day	40% 6% 15% 22% 16% 2	1672
	11th to 20th	Day	51% 5% 13% 21% 10% 1	1710
	21st to end	Day	53% 5% 11% 23% 8%	1618
December	1st to 10th	Day	54% 5% 13% 19% 8% 1	1520
	11th to 20th	Day	53% 6% 16% 17% 7% 1	1915
	21st to end	Day	76% 4 7% 9% 4	2783
January	1st to 10th	Night	56% 7% 10% 18% 9% 1	4428
	11th to 20th	Night	65% 5% 11% 12% 8%	4440
	21st to end	Night	66% 5% 10% 13% 5% 1	4774
February	1st to 10th	Night	53% 5% 11% 17% 13% 2	2454
	11th to 20th	Night	46% 5% 12% 22% 14% 1	2219
	21st to end	Night	51% 5% 11% 19% 10% 4	1884
March	1st to 10th	Night	45% 6% 13% 23% 10% 4	3733
	11th to 20th	Night	36% 6% 11% 28% 18% 2	3696
	21st to end	Night	58% 7% 9% 18% 6% 1	3466
April	1st to 10th	Night	45% 6% 12% 22% 13% 2	1900
	11th to 20th	Night	47% 6% 7% 21% 16% 4	1875
	21st to end	Night	46% 7% 11% 22% 11% 3	1815
May	1st to 10th	Night	44% 8% 14% 23% 11% 1	1710
	11th to 20th	Night	40% 7% 14% 23% 14% 1	1470
	21st to end	Night	40% 8% 13% 21% 17% 2	1552
June	1st to 10th	Night	32% 7% 13% 24% 20% 3	1440
	11th to 20th	Night	34% 6% 11% 25% 22% 3	1440
	21st to end	Night	35% 11% 14% 21% 17% 2	1440
July	1st to 10th	Night	27% 10% 15% 28% 16% 4	1400
	11th to 20th	Night	26% 8% 15% 28% 19% 3	1392
	21st to end	Night	26% 8% 17% 25% 18% 5%	1487
August	1st to 10th	Night	27% 9% 17% 30% 14% 2	1453
	11th to 20th	Night	27% 7% 17% 29% 19% 1	1776
	21st to end	Night	27% 6% 13% 29% 19% 5%	1980
September	1st to 10th	Night	31% 7% 12% 25% 23% 3	1800
	11th to 20th	Night	29% 6% 9% 33% 22% 2	1880
	21st to end	Night	34% 6% 12% 30% 16% 2	1980
October	1st to 10th	Night	34% 6% 10% 26% 21% 2	2049
	11th to 20th	Night	41% 5% 11% 23% 18% 2	2160
	21st to end	Night	48% 5% 10% 23% 12% 1	2568
November	1st to 10th	Night	37% 6% 8% 27% 18% 3	2406
	11th to 20th	Night	47% 5% 13% 21% 12% 2	2470
	21st to end	Night	48% 5% 12% 23% 11%	2560
December	1st to 10th	Night	52% 6% 12% 21% 8% 1	2660
	11th to 20th	Night	53% 5% 13% 20% 9% 1	3281
	21st to end	Night	68% 7% 10% 11% 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% 13% 36% 23% 4 1	270
	11th to 20th	Day	21% 17% 39% 19% 3	270
	21st to end	Day	22% 19% 34% 19% 5% 1	297
February	1st to 10th	Day	19% 20% 40% 17% 4	270
	11th to 20th	Day	23% 20% 34% 19% 3	270
	21st to end	Day	23% 19% 41% 13% 4	225
March	1st to 10th	Day	23% 23% 36% 17% 1	270
	11th to 20th	Day	27% 19% 32% 17% 4 1	278
	21st to end	Day	27% 17% 32% 17% 6% 2	506
April	1st to 10th	Day	24% 15% 34% 22% 5%	460
	11th to 20th	Day	21% 20% 28% 19% 9% 2	452
	21st to end	Day	22% 17% 29% 23% 8% 1	460
May	1st to 10th	Day	20% 13% 33% 24% 9% 2	463
	11th to 20th	Day	21% 13% 29% 25% 10% 2	605
	21st to end	Day	17% 9% 29% 24% 16% 5%	679
June	1st to 10th	Day	9% 8% 31% 30% 16% 5%	630
	11th to 20th	Day	11% 8% 31% 30% 16% 4	630
	21st to end	Day	12% 10% 30% 31% 12% 5%	630
July	1st to 10th	Day	9% 4 20% 33% 20% 15%	621
	11th to 20th	Day	10% 5% 26% 33% 17% 8%	618
	21st to end	Day	7% 4 26% 37% 18% 7%	684
August	1st to 10th	Day	8% 4 19% 36% 22% 11%	601
	11th to 20th	Day	9% 5% 18% 29% 24% 15%	439
	21st to end	Day	7% 4 22% 32% 25% 11%	495
September	1st to 10th	Day	17% 6% 19% 29% 23% 6%	450
	11th to 20th	Day	10% 5% 19% 30% 25% 10%	450
	21st to end	Day	10% 15% 24% 25% 19% 7%	450
October	1st to 10th	Day	16% 8% 28% 28% 15% 4	378
	11th to 20th	Day	22% 21% 32% 18% 6%	270
	21st to end	Day	31% 16% 31% 16% 5% 1	297
November	1st to 10th	Day	16% 14% 38% 20% 9% 3	270
	11th to 20th	Day	24% 18% 33% 17% 6% 1	270
	21st to end	Day	25% 13% 37% 22% 4	270
December	1st to 10th	Day	16% 23% 39% 17% 6%	270
	11th to 20th	Day	18% 18% 37% 21% 5% 1	270
	21st to end	Day	24% 22% 38% 13% 2	297
January	1st to 10th	Night	18% 14% 42% 21% 4	950
	11th to 20th	Night	20% 17% 36% 21% 5% 1	950
	21st to end	Night	20% 13% 37% 26% 4	1045
February	1st to 10th	Night	22% 13% 37% 23% 4	934
	11th to 20th	Night	19% 15% 38% 23% 5%	743
	21st to end	Night	22% 17% 38% 20% 3	628
March	1st to 10th	Night	21% 14% 36% 22% 6%	760
	11th to 20th	Night	16% 11% 40% 26% 7%	717
	21st to end	Night	22% 13% 32% 26% 6% 1	627
April	1st to 10th	Night	19% 15% 35% 25% 5%	570
	11th to 20th	Night	22% 14% 31% 26% 6%	563
	21st to end	Night	19% 11% 35% 27% 8%	570
May	1st to 10th	Night	18% 10% 35% 29% 7% 1	570
	11th to 20th	Night	20% 7% 31% 30% 13%	540
	21st to end	Night	15% 5% 26% 36% 18%	584
June	1st to 10th	Night	11% 4 29% 40% 16% 1	540
	11th to 20th	Night	10% 4 31% 43% 12% 1	540
	21st to end	Night	10% 5% 30% 38% 17% 1	540
July	1st to 10th	Night	7% 2 18% 42% 28% 3	525
	11th to 20th	Night	8% 2 23% 40% 24% 2	522
	21st to end	Night	5% 2 22% 45% 25% 2	591
August	1st to 10th	Night	5% 2 14% 46% 29% 4	537
	11th to 20th	Night	6% 3 15% 40% 32% 4	534
	21st to end	Night	9% 1 19% 40% 29% 2	594
September	1st to 10th	Night	12% 3 21% 36% 24% 4	540
	11th to 20th	Night	11% 4 21% 34% 27% 4	620
	21st to end	Night	11% 8% 25% 32% 21% 3	720
October	1st to 10th	Night	13% 7% 26% 34% 17% 2	720
	11th to 20th	Night	21% 13% 31% 25% 9%	720
	21st to end	Night	26% 12% 32% 22% 8%	792
November	1st to 10th	Night	17% 11% 37% 25% 10% 1	740
	11th to 20th	Night	20% 17% 32% 25% 6%	760
	21st to end	Night	19% 14% 38% 23% 6%	850
December	1st to 10th	Night	21% 14% 38% 22% 5%	950
	11th to 20th	Night	22% 12% 35% 26% 4	950
	21st to end	Night	28% 15% 35% 20% 2	1045

Page generated at 2024-05-10 11:39:07. Version ac07

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