Lawrence Hall of Science
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lawrence Hall of Science clear sky chart from 2005-11-06 to 2024-03-23.

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	8% 5% 2 4 4 2 3 4 5% 7% 55%	78876
	Night	9% 6% 3 5% 5% 3 4 4 5% 7% 48%	81043
Transparency	Day	30% 5% 9% 20% 22% 14%	78595
	Night	36% 6% 10% 17% 18% 12%	80846
Seeing	Day	10% 11% 28% 33% 15% 3	14493
	Night	11% 6% 16% 36% 26% 5%	23946

By Month

Percentage Cloud Cover SW (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% 9% 3 6% 5% 3 5% 4 5% 6% 38%	2699
	11th to 20th	Day	16% 11% 4 9% 6% 3 4 4 4 6% 33%	2860
	21st to end	Day	20% 10% 3 7% 6% 3 5% 4 5% 7% 30%	3146
February	1st to 10th	Day	16% 6% 3 5% 5% 2 3 4 6% 5% 45%	1710
	11th to 20th	Day	13% 7% 3 6% 5% 3 5% 5% 6% 8% 42%	1741
	21st to end	Day	13% 6% 3 4 5% 3 4 4 4 6% 48%	1570
March	1st to 10th	Day	14% 9% 3 6% 6% 3 4 4 6% 8% 36%	2054
	11th to 20th	Day	13% 7% 3 6% 5% 3 4 4 6% 7% 40%	2090
	21st to end	Day	11% 6% 2 6% 5% 3 5% 5% 6% 7% 44%	2227
April	1st to 10th	Day	13% 7% 3 5% 5% 3 4 4 5% 8% 44%	2160
	11th to 20th	Day	8% 5% 2 4 3 3 3 3 4 7% 57%	2129
	21st to end	Day	5% 4 2 3 4 2 4 4 6% 9% 59%	2160
May	1st to 10th	Day	5% 5% 1 4 3 2 3 3 5% 7% 62%	2242
	11th to 20th	Day	5% 3 2 3 3 3 3 3 5% 8% 62%	2353
	21st to end	Day	4 4 2 4 4 3 3 3 5% 8% 58%	2723
June	1st to 10th	Day	4 4 2 3 3 2 3 4 5% 8% 60%	2520
	11th to 20th	Day	1 2 1 2 3 1 2 4 4 8% 72%	2520
	21st to end	Day	2 2 1 3 3 2 3 3 3 6% 72%	2520
July	1st to 10th	Day	1 2 1 3 3 2 2 3 5% 7% 71%	2520
	11th to 20th	Day	1 2 1 2 3 2 3 3 5% 9% 68%	2361
	21st to end	Day	1 2 1 3 3 1 3 3 4 8% 72%	2546
August	1st to 10th	Day	2 2 2 4 5% 2 3 4 4 8% 65%	2328
	11th to 20th	Day	1 2 1 3 3 2 3 3 4 7% 71%	2196
	21st to end	Day	1 2 2 4 3 1 3 3 4 7% 70%	2376
September	1st to 10th	Day	1 2 2 2 2 2 2 3 3 6% 75%	2160
	11th to 20th	Day	3 4 2 3 5% 2 3 3 4 8% 63%	2160
	21st to end	Day	2 2 1 2 3 1 2 3 3 6% 74%	1907
October	1st to 10th	Day	3 3 2 3 3 2 3 4 3 5% 69%	1800
	11th to 20th	Day	5% 4 2 4 3 2 4 3 5% 6% 63%	1800
	21st to end	Day	7% 4 2 3 3 2 3 3 4 7% 61%	1980
November	1st to 10th	Day	8% 5% 2 4 3 3 3 4 4 8% 56%	1822
	11th to 20th	Day	9% 6% 3 6% 6% 2 4 4 4 7% 48%	1710
	21st to end	Day	10% 6% 2 4 4 2 3 3 6% 7% 53%	1544
December	1st to 10th	Day	13% 7% 3 5% 4 2 4 5% 4 7% 45%	1520
	11th to 20th	Day	23% 10% 4 7% 4 2 4 5% 5% 6% 31%	1928
	21st to end	Day	16% 11% 4 7% 5% 3 4 4 5% 7% 34%	2794
January	1st to 10th	Night	13% 7% 3 5% 4 2 4 4 5% 8% 44%	4247
	11th to 20th	Night	16% 10% 4 6% 7% 4 6% 4 5% 6% 32%	4110
	21st to end	Night	20% 12% 4 8% 6% 3 4 4 4 6% 30%	4521
February	1st to 10th	Night	14% 7% 3 5% 4 2 4 4 4 6% 48%	2470
	11th to 20th	Night	11% 7% 3 6% 5% 3 5% 4 5% 8% 44%	2326
	21st to end	Night	11% 6% 3 4 4 3 4 3 5% 6% 51%	1884
March	1st to 10th	Night	15% 10% 3 6% 4 3 5% 4 4 5% 40%	2123
	11th to 20th	Night	14% 7% 3 5% 5% 3 4 4 5% 8% 42%	2090
	21st to end	Night	12% 8% 3 5% 5% 2 3 3 3 6% 50%	2172
April	1st to 10th	Night	9% 7% 3 5% 5% 2 4 4 6% 7% 47%	1800
	11th to 20th	Night	8% 7% 2 4 4 2 3 3 4 7% 56%	1779
	21st to end	Night	4 3 2 3 4 2 4 5% 5% 8% 60%	1800
May	1st to 10th	Night	4 5% 3 5% 5% 2 3 5% 4 7% 57%	1714
	11th to 20th	Night	3 4 3 5% 6% 4 5% 5% 5% 7% 53%	1536
	21st to end	Night	4 4 4 6% 6% 4 4 4 5% 6% 53%	1552
June	1st to 10th	Night	4 5% 2 5% 5% 3 4 5% 7% 9% 52%	1440
	11th to 20th	Night	1 2 1 4 5% 2 3 4 4 9% 64%	1440
	21st to end	Night	1 4 2 3 5% 5% 5% 4 4 7% 59%	1440
July	1st to 10th	Night	1 3 1 5% 6% 5% 5% 4 4 8% 59%	1440
	11th to 20th	Night	2 3 2 4 6% 4 5% 5% 7% 11% 52%	1593
	21st to end	Night	1 3 3 8% 11% 5% 7% 6% 8% 8% 41%	1773
August	1st to 10th	Night	2 6% 3 7% 9% 6% 5% 5% 6% 10% 41%	1611
	11th to 20th	Night	2 2 6% 8% 6% 6% 6% 7% 10% 47%	1703
	21st to end	Night	4 3 7% 9% 4 5% 4 5% 8% 51%	1980
September	1st to 10th	Night	1 2 2 4 5% 4 4 3 5% 8% 64%	1800
	11th to 20th	Night	3 5% 2 6% 7% 4 4 3 6% 7% 52%	1800
	21st to end	Night	2 3 2 4 4 2 3 3 4 7% 67%	2048
October	1st to 10th	Night	5% 5% 1 3 4 2 4 4 4 5% 63%	2160
	11th to 20th	Night	5% 5% 2 5% 5% 3 4 4 4 6% 57%	2160
	21st to end	Night	6% 4 2 4 4 2 4 5% 6% 6% 57%	2376
November	1st to 10th	Night	7% 6% 3 4 4 3 4 4 4 8% 54%	2253
	11th to 20th	Night	10% 6% 2 4 4 2 4 4 5% 7% 51%	2470
	21st to end	Night	9% 5% 2 4 5% 2 3 4 5% 6% 57%	2634
December	1st to 10th	Night	14% 7% 3 5% 5% 3 4 4 4 7% 46%	2660
	11th to 20th	Night	24% 11% 4 5% 4 2 3 4 5% 7% 31%	3276
	21st to end	Night	16% 8% 3 7% 6% 3 6% 4 5% 7% 35%	4862

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	44% 7% 14% 25% 8% 3	2699
	11th to 20th	Day	54% 5% 11% 13% 11% 7%	2860
	21st to end	Day	54% 7% 9% 14% 12% 4	3146
February	1st to 10th	Day	40% 5% 9% 18% 20% 8%	1710
	11th to 20th	Day	39% 6% 10% 18% 21% 6%	1750
	21st to end	Day	37% 5% 9% 25% 18% 7%	1570
March	1st to 10th	Day	44% 7% 11% 19% 15% 3	2054
	11th to 20th	Day	43% 5% 10% 21% 15% 5%	2090
	21st to end	Day	37% 8% 13% 21% 17% 4	2227
April	1st to 10th	Day	39% 6% 13% 19% 19% 4	2160
	11th to 20th	Day	29% 5% 15% 23% 21% 6%	2132
	21st to end	Day	24% 5% 13% 29% 25% 4	2160
May	1st to 10th	Day	23% 5% 10% 27% 28% 7%	2242
	11th to 20th	Day	23% 6% 8% 32% 23% 9%	2356
	21st to end	Day	27% 6% 15% 26% 23% 4	2724
June	1st to 10th	Day	25% 6% 10% 26% 25% 8%	2520
	11th to 20th	Day	13% 4 10% 22% 34% 16%	2520
	21st to end	Day	17% 5% 4 15% 32% 28%	2520
July	1st to 10th	Day	15% 4 4 11% 26% 40%	2451
	11th to 20th	Day	16% 5% 7% 14% 23% 36%	2290
	21st to end	Day	14% 3 4 13% 27% 39%	2405
August	1st to 10th	Day	21% 4 6% 13% 30% 26%	2312
	11th to 20th	Day	16% 3 4 13% 33% 31%	2196
	21st to end	Day	18% 2 4 17% 33% 26%	2376
September	1st to 10th	Day	14% 2 3 11% 30% 39%	2160
	11th to 20th	Day	23% 4 6% 22% 29% 15%	2160
	21st to end	Day	15% 3 6% 22% 32% 23%	1907
October	1st to 10th	Day	20% 3 7% 17% 31% 23%	1800
	11th to 20th	Day	24% 4 9% 19% 22% 22%	1800
	21st to end	Day	25% 4 9% 21% 23% 18%	1980
November	1st to 10th	Day	28% 5% 10% 27% 19% 12%	1822
	11th to 20th	Day	37% 4 10% 22% 20% 6%	1710
	21st to end	Day	30% 4 11% 19% 24% 11%	1544
December	1st to 10th	Day	38% 6% 10% 20% 17% 8%	1520
	11th to 20th	Day	55% 5% 9% 12% 15% 4	1928
	21st to end	Day	48% 6% 13% 20% 10% 3	2794
January	1st to 10th	Night	40% 6% 20% 22% 9% 3	4247
	11th to 20th	Night	53% 6% 12% 12% 9% 8%	4110
	21st to end	Night	55% 6% 10% 12% 11% 6%	4521
February	1st to 10th	Night	38% 4 9% 19% 19% 10%	2470
	11th to 20th	Night	38% 6% 10% 17% 20% 8%	2328
	21st to end	Night	33% 5% 11% 28% 18% 5%	1884
March	1st to 10th	Night	46% 7% 10% 17% 16% 4	2123
	11th to 20th	Night	41% 5% 8% 22% 18% 6%	2090
	21st to end	Night	38% 6% 13% 21% 18% 5%	2172
April	1st to 10th	Night	37% 6% 13% 19% 20% 5%	1800
	11th to 20th	Night	30% 5% 12% 24% 19% 8%	1779
	21st to end	Night	24% 6% 12% 29% 22% 6%	1800
May	1st to 10th	Night	29% 4 8% 25% 24% 11%	1714
	11th to 20th	Night	29% 9% 9% 22% 23% 7%	1537
	21st to end	Night	33% 8% 12% 21% 22% 4	1552
June	1st to 10th	Night	30% 8% 10% 19% 26% 8%	1440
	11th to 20th	Night	21% 4 8% 19% 32% 16%	1440
	21st to end	Night	23% 9% 5% 12% 26% 25%	1440
July	1st to 10th	Night	23% 8% 4 6% 25% 34%	1400
	11th to 20th	Night	25% 6% 9% 11% 18% 30%	1541
	21st to end	Night	39% 5% 7% 7% 15% 27%	1674
August	1st to 10th	Night	39% 5% 7% 9% 20% 19%	1602
	11th to 20th	Night	31% 5% 6% 9% 23% 26%	1703
	21st to end	Night	32% 5% 6% 10% 24% 23%	1980
September	1st to 10th	Night	21% 4 6% 6% 27% 36%	1800
	11th to 20th	Night	30% 8% 6% 18% 23% 15%	1800
	21st to end	Night	19% 4 5% 20% 29% 23%	2048
October	1st to 10th	Night	23% 5% 7% 17% 24% 24%	2160
	11th to 20th	Night	28% 5% 6% 18% 19% 24%	2160
	21st to end	Night	27% 5% 7% 20% 21% 20%	2376
November	1st to 10th	Night	30% 5% 10% 25% 17% 13%	2253
	11th to 20th	Night	33% 5% 11% 25% 19% 8%	2470
	21st to end	Night	29% 5% 10% 21% 23% 13%	2634
December	1st to 10th	Night	39% 5% 10% 17% 17% 11%	2660
	11th to 20th	Night	53% 5% 9% 14% 15% 4	3276
	21st to end	Night	48% 7% 15% 16% 11% 4	4862

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	27% 12% 29% 15% 15% 1	275
	11th to 20th	Day	21% 11% 22% 33% 12% 2	370
	21st to end	Day	15% 9% 28% 30% 16% 1	407
February	1st to 10th	Day	20% 12% 21% 28% 18% 2	370
	11th to 20th	Day	21% 15% 27% 25% 11% 1	401
	21st to end	Day	14% 16% 27% 27% 14% 1	382
March	1st to 10th	Day	22% 18% 29% 20% 9% 2	460
	11th to 20th	Day	18% 19% 26% 21% 13% 4	460
	21st to end	Day	14% 18% 31% 27% 8% 1	471
April	1st to 10th	Day	18% 17% 30% 24% 9% 2	420
	11th to 20th	Day	15% 18% 34% 22% 7% 4	412
	21st to end	Day	8% 21% 28% 28% 10% 5%	420
May	1st to 10th	Day	10% 17% 33% 29% 10% 1	423
	11th to 20th	Day	10% 16% 33% 29% 11% 1	448
	21st to end	Day	8% 14% 34% 30% 11% 2	485
June	1st to 10th	Day	9% 10% 32% 32% 14% 3	450
	11th to 20th	Day	4 12% 35% 39% 8% 2	450
	21st to end	Day	2 8% 32% 43% 13% 2	450
July	1st to 10th	Day	3 4 33% 46% 13%	446
	11th to 20th	Day	2 23% 54% 18% 2	444
	21st to end	Day	1 1 28% 50% 15% 4	487
August	1st to 10th	Day	3 6% 30% 45% 13% 3	447
	11th to 20th	Day	1 3 28% 44% 18% 5%	437
	21st to end	Day	1 3 24% 48% 20% 3	495
September	1st to 10th	Day	2 4 20% 46% 21% 7%	450
	11th to 20th	Day	4 9% 26% 39% 15% 6%	450
	21st to end	Day	3 8% 25% 33% 26% 5%	450
October	1st to 10th	Day	5% 8% 28% 30% 21% 8%	450
	11th to 20th	Day	7% 10% 21% 30% 26% 6%	450
	21st to end	Day	10% 8% 23% 29% 23% 6%	495
November	1st to 10th	Day	11% 9% 21% 25% 29% 5%	418
	11th to 20th	Day	8% 9% 17% 36% 26% 5%	270
	21st to end	Day	14% 6% 27% 34% 18% 2	192
December	1st to 10th	Day	17% 14% 24% 25% 16% 4	180
	11th to 20th	Day	18% 12% 24% 28% 17% 1	180
	21st to end	Day	20% 11% 31% 25% 12% 1	198
January	1st to 10th	Night	20% 5% 15% 33% 22% 6%	760
	11th to 20th	Night	15% 7% 15% 36% 23% 4	760
	21st to end	Night	19% 5% 14% 35% 23% 3	836
February	1st to 10th	Night	19% 6% 13% 36% 23% 3	760
	11th to 20th	Night	15% 9% 17% 33% 21% 5%	744
	21st to end	Night	15% 9% 19% 34% 21% 2	628
March	1st to 10th	Night	20% 9% 19% 28% 20% 3	760
	11th to 20th	Night	17% 9% 17% 32% 22% 3	760
	21st to end	Night	16% 9% 23% 33% 18% 2	800
April	1st to 10th	Night	13% 9% 22% 36% 17% 2	720
	11th to 20th	Night	13% 12% 23% 30% 19% 3	711
	21st to end	Night	8% 8% 27% 32% 21% 4	720
May	1st to 10th	Night	8% 5% 23% 39% 22% 3	634
	11th to 20th	Night	6% 4 20% 39% 27% 3	474
	21st to end	Night	7% 11% 24% 37% 19% 3	389
June	1st to 10th	Night	6% 6% 23% 44% 20% 2	360
	11th to 20th	Night	2 4 20% 54% 18% 2	360
	21st to end	Night	4 3 18% 42% 31% 2	360
July	1st to 10th	Night	2 2 14% 48% 32% 1	350
	11th to 20th	Night	4 1 9% 47% 33% 6%	497
	21st to end	Night	3 4 10% 41% 37% 5%	591
August	1st to 10th	Night	8% 2 16% 37% 32% 4	537
	11th to 20th	Night	3 2 15% 43% 31% 6%	635
	21st to end	Night	6% 1 11% 43% 33% 5%	792
September	1st to 10th	Night	3 1 11% 39% 37% 8%	720
	11th to 20th	Night	6% 3 14% 39% 33% 5%	720
	21st to end	Night	4 3 13% 35% 36% 9%	720
October	1st to 10th	Night	7% 3 14% 34% 34% 8%	720
	11th to 20th	Night	8% 5% 12% 32% 36% 7%	720
	21st to end	Night	9% 4 11% 32% 33% 11%	792
November	1st to 10th	Night	9% 5% 13% 31% 33% 8%	740
	11th to 20th	Night	13% 3 13% 35% 29% 7%	760
	21st to end	Night	11% 5% 13% 37% 27% 6%	760
December	1st to 10th	Night	17% 6% 14% 35% 23% 5%	760
	11th to 20th	Night	24% 6% 13% 33% 21% 3	760
	21st to end	Night	20% 9% 20% 31% 19% 1	836

Page generated at 2024-03-19 20:31:03. Version ac07

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