Lawrence Lake Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lawrence Lake Observatory clear sky chart from 2005-11-06 to 2024-03-08.

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	10% 9% 4 8% 7% 4 6% 6% 6% 8% 31%	77799
	Night	8% 10% 4 9% 8% 4 6% 6% 6% 8% 32%	81710
Transparency	Day	49% 8% 17% 20% 6%	77489
	Night	49% 7% 15% 20% 8% 1	81600
Seeing	Day	14% 12% 31% 26% 14% 3	15167
	Night	14% 9% 31% 31% 14% 2	23875

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	4 12% 8% 14% 14% 5% 6% 7% 7% 6% 17%	1910
	11th to 20th	Day	5% 8% 3 9% 9% 5% 7% 9% 10% 10% 26%	2199
	21st to end	Day	5% 11% 5% 12% 9% 4 5% 5% 6% 7% 32%	2535
February	1st to 10th	Day	6% 12% 5% 11% 8% 5% 7% 6% 7% 8% 23%	1520
	11th to 20th	Day	5% 11% 6% 11% 10% 4 6% 5% 6% 8% 28%	1574
	21st to end	Day	4 11% 7% 11% 9% 5% 9% 7% 6% 9% 23%	1444
March	1st to 10th	Day	4 12% 6% 12% 11% 5% 7% 6% 5% 8% 22%	1871
	11th to 20th	Day	8% 11% 5% 8% 8% 4 6% 6% 6% 7% 31%	1947
	21st to end	Day	10% 14% 7% 9% 7% 4 6% 6% 7% 8% 22%	2222
April	1st to 10th	Day	9% 12% 6% 8% 7% 5% 7% 6% 5% 8% 27%	2259
	11th to 20th	Day	10% 13% 4 8% 8% 5% 5% 6% 5% 6% 28%	2310
	21st to end	Day	13% 12% 5% 8% 8% 4 6% 6% 5% 7% 27%	2367
May	1st to 10th	Day	12% 9% 4 8% 9% 4 6% 6% 6% 7% 29%	2700
	11th to 20th	Day	12% 7% 3 5% 6% 4 6% 4 6% 8% 39%	2654
	21st to end	Day	15% 8% 3 5% 6% 4 5% 6% 6% 8% 33%	2917
June	1st to 10th	Day	16% 8% 3 8% 7% 4 5% 5% 6% 8% 29%	2805
	11th to 20th	Day	21% 9% 4 7% 7% 4 7% 6% 6% 8% 21%	2880
	21st to end	Day	12% 6% 3 6% 6% 5% 7% 7% 8% 9% 31%	2880
July	1st to 10th	Day	12% 6% 3 5% 6% 3 6% 7% 7% 9% 36%	2880
	11th to 20th	Day	12% 6% 2 6% 7% 4 7% 7% 8% 9% 32%	2777
	21st to end	Day	10% 5% 2 5% 6% 3 5% 6% 7% 11% 39%	2938
August	1st to 10th	Day	11% 6% 3 6% 6% 4 6% 6% 7% 10% 34%	2629
	11th to 20th	Day	9% 5% 3 6% 6% 3 5% 5% 8% 9% 41%	2415
	21st to end	Day	11% 7% 3 6% 6% 4 6% 6% 7% 9% 35%	2574
September	1st to 10th	Day	16% 6% 3 7% 5% 3 4 5% 6% 7% 39%	2310
	11th to 20th	Day	15% 7% 2 5% 5% 4 5% 5% 6% 8% 37%	1985
	21st to end	Day	8% 7% 3 6% 6% 4 6% 5% 6% 8% 40%	1980
October	1st to 10th	Day	12% 10% 4 8% 7% 4 5% 5% 5% 8% 32%	1868
	11th to 20th	Day	11% 10% 4 7% 6% 4 6% 5% 5% 7% 35%	1622
	21st to end	Day	12% 15% 6% 10% 9% 3 4 4 4 5% 27%	1726
November	1st to 10th	Day	11% 13% 7% 10% 7% 4 6% 5% 6% 7% 25%	1464
	11th to 20th	Day	6% 13% 5% 11% 10% 6% 6% 5% 5% 7% 26%	1330
	21st to end	Day	4 10% 6% 12% 10% 5% 6% 5% 5% 7% 30%	1330
December	1st to 10th	Day	5% 11% 5% 10% 9% 6% 7% 5% 6% 9% 27%	1330
	11th to 20th	Day	9% 12% 3 9% 8% 6% 8% 7% 6% 7% 24%	1557
	21st to end	Day	3 7% 5% 8% 8% 4 6% 6% 8% 9% 38%	2090
January	1st to 10th	Night	5% 11% 7% 14% 11% 5% 6% 6% 6% 6% 21%	5032
	11th to 20th	Night	4 10% 4 7% 8% 6% 8% 8% 7% 6% 31%	4699
	21st to end	Night	6% 11% 5% 11% 10% 4 6% 6% 6% 7% 29%	5150
February	1st to 10th	Night	7% 11% 5% 11% 9% 5% 7% 7% 7% 7% 24%	2660
	11th to 20th	Night	7% 10% 5% 9% 9% 5% 7% 6% 6% 7% 29%	2492
	21st to end	Night	3 9% 6% 9% 9% 4 7% 7% 7% 8% 30%	2008
March	1st to 10th	Night	6% 10% 5% 9% 10% 5% 6% 6% 6% 7% 30%	2249
	11th to 20th	Night	9% 10% 4 7% 7% 4 6% 6% 6% 8% 32%	2012
	21st to end	Night	8% 15% 5% 10% 6% 4 5% 4 6% 7% 31%	2132
April	1st to 10th	Night	8% 9% 4 7% 7% 4 6% 5% 7% 9% 34%	1701
	11th to 20th	Night	9% 12% 5% 8% 9% 3 7% 6% 6% 7% 28%	1601
	21st to end	Night	13% 12% 4 7% 6% 4 5% 5% 6% 7% 31%	1592
May	1st to 10th	Night	12% 7% 4 6% 5% 4 5% 6% 7% 9% 33%	1260
	11th to 20th	Night	12% 6% 3 6% 5% 3 5% 4 6% 8% 42%	1239
	21st to end	Night	17% 7% 4 6% 6% 3 5% 6% 7% 8% 32%	1358
June	1st to 10th	Night	14% 7% 4 7% 7% 4 7% 6% 7% 8% 29%	1152
	11th to 20th	Night	18% 7% 4 6% 7% 5% 6% 7% 5% 8% 26%	1080
	21st to end	Night	8% 6% 2 6% 6% 4 7% 7% 8% 9% 36%	1080
July	1st to 10th	Night	12% 6% 2 6% 4 4 6% 6% 6% 10% 37%	1080
	11th to 20th	Night	12% 6% 3 4 5% 3 5% 4 6% 12% 40%	1183
	21st to end	Night	9% 4 2 6% 6% 3 5% 5% 6% 10% 44%	1379
August	1st to 10th	Night	9% 5% 3 4 6% 3 5% 5% 7% 10% 42%	1307
	11th to 20th	Night	9% 6% 2 5% 6% 3 6% 5% 6% 10% 44%	1483
	21st to end	Night	14% 5% 3 7% 5% 4 4 5% 6% 7% 39%	1782
September	1st to 10th	Night	13% 7% 2 5% 6% 3 4 5% 6% 9% 40%	1646
	11th to 20th	Night	12% 7% 3 6% 6% 3 5% 5% 5% 8% 41%	1975
	21st to end	Night	10% 6% 3 6% 6% 4 5% 4 6% 7% 44%	1980
October	1st to 10th	Night	11% 10% 3 7% 6% 4 5% 5% 6% 7% 36%	2092
	11th to 20th	Night	9% 9% 4 7% 6% 3 6% 6% 6% 8% 36%	2335
	21st to end	Night	10% 12% 5% 9% 7% 3 6% 6% 6% 6% 30%	2611
November	1st to 10th	Night	12% 13% 6% 10% 8% 4 6% 4 5% 6% 26%	2613
	11th to 20th	Night	8% 14% 6% 12% 8% 5% 6% 5% 5% 7% 24%	2850
	21st to end	Night	7% 10% 6% 12% 10% 5% 5% 5% 6% 7% 26%	2850
December	1st to 10th	Night	7% 11% 5% 9% 8% 5% 6% 7% 6% 7% 29%	2850
	11th to 20th	Night	7% 14% 5% 12% 10% 5% 7% 6% 6% 6% 22%	3631
	21st to end	Night	3 7% 3 7% 7% 4 6% 5% 6% 10% 40%	5566

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	62% 7% 12% 14% 4	1910
	11th to 20th	Day	49% 6% 11% 19% 13% 2	2220
	21st to end	Day	50% 6% 21% 15% 7%	2535
February	1st to 10th	Day	55% 7% 13% 17% 8%	1520
	11th to 20th	Day	52% 8% 17% 17% 7%	1582
	21st to end	Day	54% 8% 16% 15% 7%	1444
March	1st to 10th	Day	59% 7% 15% 15% 4	1871
	11th to 20th	Day	50% 7% 14% 20% 8%	1948
	21st to end	Day	58% 8% 14% 16% 4	2222
April	1st to 10th	Day	53% 8% 15% 17% 7%	2259
	11th to 20th	Day	53% 7% 11% 21% 7% 1	2310
	21st to end	Day	55% 7% 11% 18% 7% 1	2367
May	1st to 10th	Day	52% 7% 12% 20% 9%	2700
	11th to 20th	Day	42% 6% 11% 26% 13%	2658
	21st to end	Day	47% 8% 11% 24% 10% 1	2918
June	1st to 10th	Day	51% 8% 14% 20% 7%	2805
	11th to 20th	Day	59% 9% 13% 14% 4	2880
	21st to end	Day	45% 11% 19% 19% 5%	2880
July	1st to 10th	Day	41% 10% 20% 23% 5% 1	2801
	11th to 20th	Day	44% 12% 25% 17% 2	2691
	21st to end	Day	37% 10% 25% 25% 3	2775
August	1st to 10th	Day	42% 12% 25% 19% 2	2611
	11th to 20th	Day	37% 10% 26% 22% 5%	2415
	21st to end	Day	43% 9% 24% 21% 4	2574
September	1st to 10th	Day	44% 8% 21% 22% 5% 1	2310
	11th to 20th	Day	42% 9% 23% 21% 5%	1985
	21st to end	Day	39% 9% 18% 24% 8% 1	1980
October	1st to 10th	Day	50% 6% 20% 18% 5%	1868
	11th to 20th	Day	47% 8% 16% 23% 6%	1622
	21st to end	Day	59% 6% 12% 18% 5%	1726
November	1st to 10th	Day	56% 7% 16% 16% 5%	1464
	11th to 20th	Day	56% 7% 19% 12% 5%	1330
	21st to end	Day	54% 8% 16% 17% 4 1	1330
December	1st to 10th	Day	54% 7% 14% 17% 7% 1	1330
	11th to 20th	Day	55% 8% 16% 16% 4	1558
	21st to end	Day	39% 7% 12% 30% 11% 2	2090
January	1st to 10th	Night	60% 7% 13% 14% 6% 1	5032
	11th to 20th	Night	49% 6% 12% 19% 13% 1	4740
	21st to end	Night	53% 7% 21% 13% 5%	5150
February	1st to 10th	Night	55% 8% 13% 17% 7%	2660
	11th to 20th	Night	53% 7% 13% 18% 9%	2494
	21st to end	Night	49% 7% 15% 21% 8%	2008
March	1st to 10th	Night	51% 7% 14% 21% 7%	2249
	11th to 20th	Night	48% 7% 13% 22% 10% 1	2012
	21st to end	Night	52% 7% 13% 20% 7%	2132
April	1st to 10th	Night	44% 6% 13% 22% 13% 1	1701
	11th to 20th	Night	53% 7% 10% 18% 11% 3	1601
	21st to end	Night	51% 6% 10% 21% 11% 1	1592
May	1st to 10th	Night	44% 7% 15% 21% 12% 2	1260
	11th to 20th	Night	39% 6% 9% 29% 15% 2	1239
	21st to end	Night	46% 8% 12% 22% 10% 2	1358
June	1st to 10th	Night	49% 8% 16% 17% 9% 1	1152
	11th to 20th	Night	55% 8% 13% 20% 5%	1080
	21st to end	Night	40% 10% 20% 24% 6% 1	1080
July	1st to 10th	Night	40% 8% 20% 23% 7% 2	1050
	11th to 20th	Night	38% 9% 26% 26% 1	1146
	21st to end	Night	34% 9% 25% 27% 5%	1302
August	1st to 10th	Night	35% 11% 26% 26% 2	1300
	11th to 20th	Night	34% 10% 23% 26% 7% 1	1483
	21st to end	Night	43% 7% 19% 25% 6%	1782
September	1st to 10th	Night	39% 8% 20% 25% 7% 2	1646
	11th to 20th	Night	40% 6% 21% 25% 8%	1975
	21st to end	Night	37% 7% 17% 27% 11% 1	1980
October	1st to 10th	Night	45% 6% 15% 26% 8%	2092
	11th to 20th	Night	44% 8% 16% 25% 6%	2335
	21st to end	Night	52% 7% 14% 20% 6%	2611
November	1st to 10th	Night	59% 6% 10% 21% 4	2613
	11th to 20th	Night	58% 8% 14% 16% 4	2850
	21st to end	Night	56% 7% 17% 15% 4 1	2850
December	1st to 10th	Night	52% 7% 13% 19% 9% 1	2850
	11th to 20th	Night	61% 7% 14% 14% 5%	3629
	21st to end	Night	39% 6% 16% 26% 12% 1	5566

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	8% 9% 39% 29% 12% 3	180
	11th to 20th	Day	13% 13% 31% 28% 13% 2	180
	21st to end	Day	14% 11% 43% 21% 9% 2	198
February	1st to 10th	Day	13% 17% 43% 22% 3 2	180
	11th to 20th	Day	10% 15% 36% 25% 12% 1	225
	21st to end	Day	8% 18% 36% 26% 9% 3	256
March	1st to 10th	Day	7% 18% 37% 28% 9% 2	449
	11th to 20th	Day	9% 18% 37% 24% 10% 2	420
	21st to end	Day	18% 14% 34% 24% 8% 1	462
April	1st to 10th	Day	11% 18% 39% 22% 8% 3	420
	11th to 20th	Day	15% 16% 29% 25% 11% 4	412
	21st to end	Day	18% 18% 37% 18% 8% 1	421
May	1st to 10th	Day	13% 16% 29% 27% 12% 3	603
	11th to 20th	Day	14% 10% 28% 26% 18% 4	625
	21st to end	Day	18% 8% 24% 30% 14% 6%	679
June	1st to 10th	Day	18% 11% 32% 26% 11% 2	735
	11th to 20th	Day	23% 8% 25% 25% 16% 4	810
	21st to end	Day	13% 7% 23% 31% 20% 6%	810
July	1st to 10th	Day	12% 7% 26% 32% 20% 4	796
	11th to 20th	Day	14% 7% 27% 29% 20% 3	690
	21st to end	Day	10% 7% 27% 29% 19% 9%	684
August	1st to 10th	Day	12% 7% 22% 29% 21% 9%	569
	11th to 20th	Day	11% 12% 30% 31% 13% 3	437
	21st to end	Day	14% 10% 26% 32% 15% 3	495
September	1st to 10th	Day	21% 15% 28% 22% 10% 4	450
	11th to 20th	Day	21% 11% 30% 25% 11% 2	450
	21st to end	Day	13% 15% 36% 20% 14% 3	450
October	1st to 10th	Day	17% 14% 30% 24% 13% 2	338
	11th to 20th	Day	17% 11% 37% 26% 8% 1	270
	21st to end	Day	21% 16% 32% 20% 10% 1	297
November	1st to 10th	Day	21% 11% 32% 26% 8% 2	258
	11th to 20th	Day	13% 13% 40% 19% 13% 2	180
	21st to end	Day	6% 15% 46% 21% 9% 3	180
December	1st to 10th	Day	9% 11% 43% 21% 14% 3	180
	11th to 20th	Day	14% 16% 36% 26% 8% 1	180
	21st to end	Day	9% 4 31% 38% 14% 5%	198
January	1st to 10th	Night	13% 10% 33% 33% 10% 2	1034
	11th to 20th	Night	11% 11% 37% 31% 9% 1	950
	21st to end	Night	14% 15% 36% 24% 10% 1	1007
February	1st to 10th	Night	12% 11% 31% 32% 13% 1	760
	11th to 20th	Night	12% 9% 35% 30% 13% 1	744
	21st to end	Night	7% 7% 34% 36% 13% 3	628
March	1st to 10th	Night	10% 9% 35% 32% 13% 2	750
	11th to 20th	Night	12% 8% 35% 30% 14% 1	720
	21st to end	Night	14% 9% 30% 31% 14% 2	792
April	1st to 10th	Night	10% 8% 30% 33% 16% 2	621
	11th to 20th	Night	17% 8% 31% 32% 12% 2	533
	21st to end	Night	18% 10% 27% 30% 13% 1	514
May	1st to 10th	Night	16% 7% 24% 33% 18% 2	360
	11th to 20th	Night	16% 6% 27% 31% 18% 2	354
	21st to end	Night	19% 4 25% 33% 17% 2	389
June	1st to 10th	Night	17% 5% 26% 33% 16% 2	360
	11th to 20th	Night	20% 6% 17% 31% 24% 3	360
	21st to end	Night	12% 3 18% 41% 23% 3	360
July	1st to 10th	Night	15% 3 21% 36% 25% 1	350
	11th to 20th	Night	15% 5% 23% 38% 18% 3	348
	21st to end	Night	12% 5% 19% 34% 27% 4	394
August	1st to 10th	Night	13% 2 20% 35% 26% 4	358
	11th to 20th	Night	11% 4 27% 34% 23% 1	415
	21st to end	Night	16% 4 22% 38% 19% 2	594
September	1st to 10th	Night	16% 6% 25% 33% 19% 2	566
	11th to 20th	Night	15% 7% 21% 40% 16% 1	720
	21st to end	Night	12% 7% 31% 34% 14% 1	720
October	1st to 10th	Night	16% 6% 31% 32% 13% 2	720
	11th to 20th	Night	15% 7% 34% 32% 11% 1	720
	21st to end	Night	17% 13% 30% 29% 10% 1	829
November	1st to 10th	Night	18% 9% 34% 29% 9% 2	925
	11th to 20th	Night	15% 13% 36% 25% 10% 2	950
	21st to end	Night	12% 12% 40% 26% 9% 1	950
December	1st to 10th	Night	13% 12% 35% 26% 12% 2	950
	11th to 20th	Night	13% 14% 35% 28% 10% 1	986
	21st to end	Night	11% 6% 33% 33% 14% 3	1144

Page generated at 2024-03-05 05:24:04. Version ac07

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