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 2024-01-16.

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	14% 9% 4 7% 6% 3 5% 5% 5% 7% 37%	74824
	Night	14% 8% 4 6% 5% 3 4 4 5% 7% 39%	74993
Transparency	Day	46% 7% 13% 21% 12% 2	74525
	Night	44% 6% 12% 22% 14% 2	74813
Seeing	Day	16% 12% 29% 25% 13% 5%	14654
	Night	17% 10% 31% 29% 11% 1	24638

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	14% 11% 5% 9% 7% 3 4 5% 5% 6% 30%	1517
	11th to 20th	Day	13% 15% 7% 12% 6% 3 4 5% 5% 7% 25%	1480
	21st to end	Day	15% 15% 7% 10% 7% 3 5% 4 5% 7% 23%	1647
February	1st to 10th	Day	15% 14% 6% 8% 7% 4 6% 5% 5% 6% 25%	1634
	11th to 20th	Day	14% 11% 5% 6% 7% 3 4 5% 5% 6% 34%	1748
	21st to end	Day	16% 12% 5% 9% 6% 3 5% 3 4 6% 31%	1480
March	1st to 10th	Day	15% 12% 6% 7% 7% 2 5% 4 4 7% 30%	1800
	11th to 20th	Day	14% 9% 3 7% 5% 3 4 5% 5% 8% 37%	1861
	21st to end	Day	20% 10% 5% 8% 7% 4 5% 4 5% 5% 25%	2376
April	1st to 10th	Day	17% 11% 5% 8% 5% 3 4 4 5% 7% 31%	2160
	11th to 20th	Day	16% 10% 3 6% 5% 3 5% 5% 5% 7% 34%	2134
	21st to end	Day	20% 9% 3 7% 6% 4 4 5% 5% 6% 33%	2240
May	1st to 10th	Day	17% 8% 3 7% 6% 3 5% 6% 6% 8% 30%	2340
	11th to 20th	Day	19% 8% 3 6% 5% 3 5% 5% 5% 7% 33%	2448
	21st to end	Day	14% 7% 3 7% 5% 4 6% 6% 6% 9% 35%	2725
June	1st to 10th	Day	10% 5% 2 5% 5% 3 5% 5% 6% 8% 46%	2520
	11th to 20th	Day	10% 5% 3 5% 5% 3 4 5% 6% 8% 46%	2520
	21st to end	Day	11% 6% 3 6% 6% 4 6% 6% 7% 8% 38%	2520
July	1st to 10th	Day	9% 4 2 5% 5% 4 5% 6% 7% 9% 46%	2520
	11th to 20th	Day	8% 4 3 5% 4 4 6% 5% 7% 9% 46%	2520
	21st to end	Day	7% 4 2 6% 6% 3 6% 6% 6% 9% 44%	2743
August	1st to 10th	Day	8% 4 2 6% 6% 3 5% 6% 7% 9% 43%	2472
	11th to 20th	Day	9% 5% 2 5% 5% 4 5% 6% 7% 10% 42%	2125
	21st to end	Day	8% 4 2 4 5% 3 5% 6% 6% 9% 48%	2376
September	1st to 10th	Day	13% 6% 2 5% 5% 3 5% 5% 5% 8% 44%	2160
	11th to 20th	Day	13% 3 2 3 3 2 4 4 5% 7% 53%	2062
	21st to end	Day	10% 6% 3 5% 5% 3 5% 5% 5% 7% 45%	1980
October	1st to 10th	Day	12% 6% 2 6% 5% 3 4 4 5% 7% 46%	1908
	11th to 20th	Day	19% 9% 3 6% 6% 3 4 5% 5% 7% 34%	1800
	21st to end	Day	20% 9% 3 5% 4 3 4 4 4 5% 38%	1787
November	1st to 10th	Day	12% 8% 3 6% 4 2 5% 4 5% 6% 45%	1672
	11th to 20th	Day	16% 11% 5% 7% 5% 3 4 5% 4 7% 33%	1710
	21st to end	Day	18% 11% 4 8% 6% 3 4 4 3 5% 35%	1618
December	1st to 10th	Day	15% 11% 6% 8% 6% 3 6% 4 4 5% 32%	1520
	11th to 20th	Day	12% 13% 5% 9% 6% 4 5% 5% 5% 7% 29%	1918
	21st to end	Day	20% 21% 10% 12% 6% 3 3 3 3 4 15%	2783
January	1st to 10th	Night	14% 11% 5% 9% 6% 3 4 4 4 5% 35%	2648
	11th to 20th	Night	15% 13% 5% 10% 6% 3 4 4 5% 5% 28%	2591
	21st to end	Night	15% 11% 8% 10% 6% 3 4 5% 5% 6% 27%	2704
February	1st to 10th	Night	15% 13% 6% 8% 6% 3 4 4 3 6% 31%	2325
	11th to 20th	Night	14% 11% 4 6% 5% 3 4 4 5% 6% 37%	2098
	21st to end	Night	17% 13% 3 7% 5% 2 4 3 3 6% 35%	1776
March	1st to 10th	Night	17% 9% 4 7% 6% 3 4 4 5% 5% 36%	2160
	11th to 20th	Night	13% 7% 4 5% 5% 3 4 5% 6% 6% 42%	2112
	21st to end	Night	20% 9% 4 8% 6% 3 5% 4 4 6% 32%	1980
April	1st to 10th	Night	16% 8% 3 6% 6% 2 5% 4 5% 6% 39%	1800
	11th to 20th	Night	18% 8% 3 6% 5% 3 4 4 4 6% 38%	1775
	21st to end	Night	18% 7% 4 6% 5% 3 4 5% 4 8% 37%	1720
May	1st to 10th	Night	14% 6% 4 6% 5% 4 5% 6% 6% 8% 36%	1620
	11th to 20th	Night	17% 6% 3 5% 5% 3 3 4 5% 10% 40%	1444
	21st to end	Night	13% 5% 3 6% 5% 4 4 4 5% 10% 41%	1551
June	1st to 10th	Night	9% 5% 2 5% 6% 2 4 5% 6% 7% 49%	1440
	11th to 20th	Night	10% 4 2 5% 5% 4 4 5% 6% 8% 48%	1440
	21st to end	Night	9% 5% 2 5% 5% 4 6% 5% 6% 8% 44%	1440
July	1st to 10th	Night	6% 4 1 4 4 3 4 7% 7% 10% 50%	1440
	11th to 20th	Night	7% 4 2 5% 4 3 4 5% 6% 9% 53%	1440
	21st to end	Night	6% 3 1 4 4 3 5% 6% 6% 9% 52%	1575
August	1st to 10th	Night	5% 4 2 4 5% 3 5% 5% 7% 10% 49%	1462
	11th to 20th	Night	7% 4 2 5% 4 2 4 5% 6% 9% 53%	1776
	21st to end	Night	8% 4 2 4 4 3 4 3 5% 9% 55%	1980
September	1st to 10th	Night	11% 5% 2 4 4 3 3 4 4 7% 53%	1800
	11th to 20th	Night	10% 4 2 5% 4 2 3 3 5% 6% 55%	1880
	21st to end	Night	10% 6% 2 4 5% 3 3 5% 5% 8% 49%	1980
October	1st to 10th	Night	11% 5% 3 4 5% 3 4 4 5% 6% 50%	2049
	11th to 20th	Night	18% 7% 2 5% 4 3 3 4 4 6% 44%	2160
	21st to end	Night	20% 10% 3 5% 5% 2 4 4 4 6% 38%	2568
November	1st to 10th	Night	12% 7% 2 5% 4 2 3 4 4 6% 49%	2406
	11th to 20th	Night	15% 10% 3 7% 5% 3 4 4 6% 6% 37%	2470
	21st to end	Night	16% 9% 4 7% 4 3 4 4 4 6% 38%	2560
December	1st to 10th	Night	16% 10% 4 7% 6% 3 4 5% 4 7% 33%	2660
	11th to 20th	Night	15% 12% 4 8% 6% 3 4 4 4 7% 32%	3279
	21st to end	Night	23% 17% 7% 9% 6% 4 5% 5% 5% 5% 17%	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	54% 6% 12% 16% 11%	1518
	11th to 20th	Day	59% 6% 14% 15% 5% 1	1480
	21st to end	Day	62% 5% 10% 13% 10%	1647
February	1st to 10th	Day	59% 6% 12% 13% 8% 1	1634
	11th to 20th	Day	50% 6% 12% 21% 9% 2	1758
	21st to end	Day	55% 7% 10% 17% 9% 1	1480
March	1st to 10th	Day	54% 7% 12% 19% 8% 1	1800
	11th to 20th	Day	46% 7% 13% 22% 10% 1	1861
	21st to end	Day	61% 7% 10% 16% 5% 1	2376
April	1st to 10th	Day	54% 6% 11% 20% 9%	2160
	11th to 20th	Day	48% 7% 10% 20% 11% 3	2134
	21st to end	Day	51% 7% 12% 17% 11% 2	2240
May	1st to 10th	Day	50% 9% 13% 21% 7%	2340
	11th to 20th	Day	49% 7% 12% 22% 10%	2452
	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	52% 6% 11% 19% 12% 1	2648
	11th to 20th	Night	58% 6% 13% 13% 10%	2591
	21st to end	Night	57% 6% 12% 15% 9% 1	2704
February	1st to 10th	Night	56% 5% 11% 16% 11% 1	2325
	11th to 20th	Night	47% 6% 12% 21% 13% 1	2099
	21st to end	Night	51% 5% 11% 18% 10% 4	1776
March	1st to 10th	Night	50% 5% 14% 20% 10% 1	2160
	11th to 20th	Night	41% 7% 12% 20% 17% 3	2112
	21st to end	Night	55% 6% 9% 19% 10% 1	1980
April	1st to 10th	Night	45% 6% 13% 22% 13% 2	1800
	11th to 20th	Night	47% 5% 6% 21% 16% 4	1775
	21st to end	Night	46% 7% 11% 22% 11% 3	1720
May	1st to 10th	Night	44% 8% 13% 24% 11%	1620
	11th to 20th	Night	41% 8% 14% 23% 14% 1	1445
	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	22% 18% 37% 20% 4	255
	21st to end	Day	20% 20% 35% 18% 5% 1	264
February	1st to 10th	Day	21% 20% 41% 14% 3	240
	11th to 20th	Day	25% 20% 34% 17% 3	240
	21st to end	Day	25% 20% 40% 13% 3 1	198
March	1st to 10th	Day	24% 23% 34% 17% 2	240
	11th to 20th	Day	27% 18% 31% 18% 5% 1	247
	21st to end	Day	27% 16% 32% 17% 6% 2	462
April	1st to 10th	Day	23% 14% 34% 23% 5%	420
	11th to 20th	Day	21% 20% 28% 19% 10% 2	412
	21st to end	Day	21% 16% 29% 24% 8% 1	420
May	1st to 10th	Day	21% 13% 32% 24% 8% 2	423
	11th to 20th	Day	21% 12% 29% 25% 10% 2	594
	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% 22% 5% 1	926
	21st to end	Night	20% 13% 37% 26% 4	990
February	1st to 10th	Night	23% 13% 38% 22% 4	885
	11th to 20th	Night	20% 15% 38% 22% 5%	703
	21st to end	Night	23% 17% 36% 20% 4	592
March	1st to 10th	Night	21% 14% 36% 22% 6%	720
	11th to 20th	Night	16% 10% 39% 27% 8%	680
	21st to end	Night	22% 13% 31% 27% 6% 1	594
April	1st to 10th	Night	19% 15% 34% 26% 6%	540
	11th to 20th	Night	23% 13% 31% 27% 7%	533
	21st to end	Night	20% 10% 35% 27% 8%	540
May	1st to 10th	Night	18% 9% 36% 29% 8% 1	540
	11th to 20th	Night	20% 7% 31% 30% 13%	531
	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 2024-01-13 00:38:12. Version ac07

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