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 2024-11-04.

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	6% 5% 2 5% 3 3 3 3 5% 7% 59%	105045
	Night	8% 6% 2 6% 5% 4 4 3 5% 6% 50%	102711
Transparency	Day	26% 5% 8% 19% 23% 19%	104804
	Night	33% 7% 9% 16% 19% 15%	102542
Seeing	Day	10% 11% 28% 33% 15% 3	15397
	Night	11% 6% 16% 36% 26% 5%	24695

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% 10% 3 6% 4 4 5% 3 5% 6% 38%	2699
	11th to 20th	Day	16% 11% 4 10% 5% 5% 4 3 4 5% 33%	2860
	21st to end	Day	20% 11% 3 8% 5% 5% 4 3 5% 7% 29%	3146
February	1st to 10th	Day	16% 7% 2 5% 4 3 3 4 6% 5% 45%	1710
	11th to 20th	Day	13% 7% 3 7% 5% 4 4 4 5% 8% 41%	1741
	21st to end	Day	13% 7% 2 5% 4 4 3 3 4 6% 48%	1570
March	1st to 10th	Day	11% 12% 4 11% 6% 5% 5% 4 5% 7% 30%	3396
	11th to 20th	Day	9% 5% 2 5% 4 3 3 3 5% 7% 54%	3490
	21st to end	Day	11% 8% 3 7% 5% 5% 5% 5% 8% 7% 36%	3876
April	1st to 10th	Day	12% 8% 2 6% 4 4 3 4 6% 8% 45%	2280
	11th to 20th	Day	8% 5% 2 5% 3 4 3 3 4 8% 56%	2249
	21st to end	Day	4 4 2 3 3 3 4 3 6% 9% 59%	2280
May	1st to 10th	Day	5% 3 1 3 2 2 2 2 3 5% 73%	3947
	11th to 20th	Day	3 2 1 3 2 2 2 2 4 7% 73%	4162
	21st to end	Day	2 3 1 3 3 3 3 2 4 6% 71%	4813
June	1st to 10th	Day	4 4 2 3 4 3 3 4 5% 8% 60%	2660
	11th to 20th	Day	1 2 1 2 2 2 2 3 5% 8% 72%	2660
	21st to end	Day	2 2 1 3 3 2 3 2 4 6% 72%	2660
July	1st to 10th	Day	1 2 2 2 1 2 3 5% 81%	4420
	11th to 20th	Day	1 1 3 2 3 3 2 4 7% 73%	4144
	21st to end	Day	1 1 4 3 2 3 2 4 8% 73%	4455
August	1st to 10th	Day	1 2 1 3 3 3 4 5% 6% 10% 62%	4091
	11th to 20th	Day	1 1 3 2 3 3 2 5% 6% 75%	3846
	21st to end	Day	1 2 1 4 2 2 3 2 4 7% 71%	4180
September	1st to 10th	Day	1 3 2 3 2 2 2 2 3 6% 75%	2280
	11th to 20th	Day	3 5% 2 4 4 3 3 3 5% 8% 62%	2280
	21st to end	Day	2 2 1 2 2 2 2 2 3 6% 74%	2012
October	1st to 10th	Day	2 3 1 3 2 2 3 3 4 6% 71%	3180
	11th to 20th	Day	3 4 2 5% 3 3 3 2 4 6% 65%	3161
	21st to end	Day	4 4 2 5% 2 3 3 3 6% 8% 59%	3448
November	1st to 10th	Day	7% 6% 2 4 3 3 3 4 4 8% 56%	1853
	11th to 20th	Day	9% 7% 3 7% 5% 3 4 3 4 6% 48%	1710
	21st to end	Day	10% 7% 1 4 3 3 3 3 7% 6% 52%	1544
December	1st to 10th	Day	13% 8% 3 5% 4 3 5% 4 4 7% 45%	1520
	11th to 20th	Day	23% 11% 4 7% 3 3 4 3 5% 5% 31%	1928
	21st to end	Day	16% 11% 3 8% 4 4 4 3 5% 7% 34%	2794
January	1st to 10th	Night	13% 8% 3 5% 4 3 4 3 5% 8% 44%	4247
	11th to 20th	Night	16% 10% 4 8% 6% 5% 5% 4 5% 6% 32%	4110
	21st to end	Night	20% 12% 3 8% 5% 4 4 3 4 6% 30%	4521
February	1st to 10th	Night	14% 8% 2 5% 3 3 3 3 4 6% 48%	2470
	11th to 20th	Night	11% 7% 3 7% 4 4 4 3 5% 8% 44%	2326
	21st to end	Night	11% 6% 2 5% 4 4 4 3 5% 6% 51%	1884
March	1st to 10th	Night	13% 12% 4 9% 5% 5% 5% 3 5% 5% 36%	3475
	11th to 20th	Night	11% 6% 2 5% 4 4 3 3 3 5% 53%	3490
	21st to end	Night	11% 12% 4 8% 5% 4 4 3 4 6% 39%	3775
April	1st to 10th	Night	9% 8% 3 5% 4 3 4 4 6% 7% 47%	1900
	11th to 20th	Night	8% 7% 2 4 4 3 3 3 4 7% 56%	1879
	21st to end	Night	4 4 1 4 4 3 4 4 5% 8% 59%	1900
May	1st to 10th	Night	4 4 2 4 2 2 2 2 3 4 70%	3024
	11th to 20th	Night	2 3 2 5% 7% 6% 4 3 5% 6% 56%	2720
	21st to end	Night	2 3 2 4 4 6% 3 2 3 4 65%	2762
June	1st to 10th	Night	3 5% 2 5% 4 5% 3 4 7% 9% 52%	1520
	11th to 20th	Night	1 2 1 4 4 4 3 3 4 9% 65%	1520
	21st to end	Night	1 4 1 4 4 6% 4 3 4 7% 60%	1520
July	1st to 10th	Night	2 1 4 4 5% 3 2 3 5% 72%	2540
	11th to 20th	Night	1 2 2 6% 6% 5% 5% 3 5% 8% 57%	2819
	21st to end	Night	1 2 3 10% 10% 8% 6% 4 6% 7% 43%	3109
August	1st to 10th	Night	2 4 2 5% 6% 11% 10% 8% 7% 9% 35%	2848
	11th to 20th	Night	2 1 5% 5% 6% 6% 5% 5% 7% 57%	2997
	21st to end	Night	2 3 2 6% 6% 7% 6% 4 4 6% 55%	3498
September	1st to 10th	Night	1 2 1 4 4 4 4 3 5% 8% 64%	1900
	11th to 20th	Night	3 5% 2 7% 6% 6% 3 2 5% 7% 52%	1900
	21st to end	Night	1 3 1 5% 3 3 2 2 4 7% 67%	2163
October	1st to 10th	Night	3 3 1 4 3 3 3 2 4 6% 69%	3800
	11th to 20th	Night	3 7% 2 7% 5% 5% 4 3 4 5% 55%	3777
	21st to end	Night	4 4 2 5% 3 3 4 4 6% 6% 58%	4121
November	1st to 10th	Night	6% 7% 2 5% 4 4 4 3 4 8% 53%	2294
	11th to 20th	Night	10% 7% 2 5% 3 3 3 3 6% 7% 51%	2470
	21st to end	Night	9% 5% 1 4 4 3 3 3 5% 6% 56%	2634
December	1st to 10th	Night	14% 7% 3 6% 4 3 3 3 4 7% 46%	2660
	11th to 20th	Night	23% 12% 4 6% 3 3 3 3 5% 6% 31%	3276
	21st to end	Night	15% 8% 3 8% 5% 5% 5% 3 5% 6% 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	52% 8% 10% 15% 13% 2	3396
	11th to 20th	Day	31% 5% 13% 28% 13% 11%	3490
	21st to end	Day	41% 10% 15% 21% 11% 2	3876
April	1st to 10th	Day	38% 6% 13% 20% 19% 4	2280
	11th to 20th	Day	30% 5% 16% 23% 21% 6%	2252
	21st to end	Day	23% 5% 13% 29% 25% 4	2280
May	1st to 10th	Day	17% 4 10% 30% 23% 16%	3947
	11th to 20th	Day	15% 5% 6% 28% 34% 12%	4165
	21st to end	Day	17% 8% 10% 29% 32% 4	4814
June	1st to 10th	Day	24% 6% 11% 27% 25% 8%	2660
	11th to 20th	Day	13% 4 10% 22% 35% 16%	2660
	21st to end	Day	16% 4 4 14% 32% 30%	2660
July	1st to 10th	Day	9% 3 2 6% 15% 64%	4351
	11th to 20th	Day	13% 4 4 8% 16% 54%	4073
	21st to end	Day	12% 4 3 9% 29% 43%	4315
August	1st to 10th	Day	18% 5% 4 10% 29% 34%	4076
	11th to 20th	Day	11% 4 3 9% 42% 30%	3885
	21st to end	Day	15% 3 3 15% 35% 28%	4179
September	1st to 10th	Day	14% 2 3 11% 30% 40%	2280
	11th to 20th	Day	23% 4 6% 22% 30% 15%	2280
	21st to end	Day	14% 2 6% 21% 33% 23%	2012
October	1st to 10th	Day	16% 3 5% 11% 28% 38%	3180
	11th to 20th	Day	22% 4 6% 23% 28% 18%	3161
	21st to end	Day	25% 4 7% 23% 27% 14%	3448
November	1st to 10th	Day	28% 5% 11% 27% 19% 11%	1853
	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	48% 11% 11% 14% 14% 3	3475
	11th to 20th	Night	32% 8% 9% 23% 18% 11%	3490
	21st to end	Night	44% 9% 14% 20% 11% 3	3775
April	1st to 10th	Night	36% 6% 13% 21% 20% 5%	1900
	11th to 20th	Night	30% 5% 12% 25% 19% 8%	1879
	21st to end	Night	24% 6% 12% 29% 22% 6%	1900
May	1st to 10th	Night	20% 4 10% 27% 26% 13%	3024
	11th to 20th	Night	22% 14% 10% 17% 24% 13%	2721
	21st to end	Night	19% 14% 9% 27% 28% 2	2762
June	1st to 10th	Night	28% 8% 10% 20% 26% 8%	1520
	11th to 20th	Night	20% 4 7% 19% 33% 16%	1520
	21st to end	Night	22% 9% 4 12% 26% 27%	1520
July	1st to 10th	Night	15% 6% 2 3 16% 57%	2500
	11th to 20th	Night	24% 6% 6% 7% 13% 45%	2767
	21st to end	Night	37% 7% 5% 5% 16% 31%	3011
August	1st to 10th	Night	36% 16% 4 7% 21% 16%	2839
	11th to 20th	Night	21% 8% 6% 6% 33% 26%	3024
	21st to end	Night	27% 7% 7% 9% 28% 22%	3498
September	1st to 10th	Night	20% 4 6% 6% 27% 36%	1900
	11th to 20th	Night	31% 8% 6% 18% 24% 15%	1900
	21st to end	Night	19% 4 5% 20% 29% 23%	2163
October	1st to 10th	Night	17% 4 5% 10% 20% 45%	3800
	11th to 20th	Night	29% 8% 5% 18% 18% 22%	3777
	21st to end	Night	26% 5% 5% 21% 24% 19%	4121
November	1st to 10th	Night	30% 5% 10% 25% 16% 13%	2294
	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	15% 19% 32% 25% 8% 1	506
April	1st to 10th	Day	17% 17% 30% 24% 10% 3	460
	11th to 20th	Day	15% 17% 32% 23% 8% 4	452
	21st to end	Day	8% 20% 29% 28% 10% 5%	460
May	1st to 10th	Day	10% 17% 33% 29% 10% 1	463
	11th to 20th	Day	9% 15% 33% 31% 11% 1	488
	21st to end	Day	8% 14% 33% 31% 12% 2	529
June	1st to 10th	Day	8% 10% 33% 32% 13% 3	490
	11th to 20th	Day	4 12% 36% 38% 8% 2	490
	21st to end	Day	2 7% 34% 42% 12% 2	490
July	1st to 10th	Day	3 4 31% 47% 14% 1	486
	11th to 20th	Day	3 24% 54% 17% 2	484
	21st to end	Day	1 2 30% 48% 15% 4	531
August	1st to 10th	Day	3 6% 30% 45% 13% 3	487
	11th to 20th	Day	2 5% 31% 41% 17% 5%	477
	21st to end	Day	2 3 25% 47% 20% 3	539
September	1st to 10th	Day	2 4 22% 44% 21% 7%	490
	11th to 20th	Day	5% 11% 27% 37% 15% 6%	490
	21st to end	Day	3 8% 25% 33% 27% 4	490
October	1st to 10th	Day	4 7% 28% 30% 22% 8%	490
	11th to 20th	Day	7% 10% 21% 31% 25% 6%	490
	21st to end	Day	9% 9% 25% 29% 22% 6%	539
November	1st to 10th	Day	11% 10% 21% 25% 29% 4	431
	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% 10% 23% 33% 17% 2	836
April	1st to 10th	Night	13% 9% 23% 36% 17% 2	760
	11th to 20th	Night	12% 12% 22% 31% 19% 3	751
	21st to end	Night	8% 8% 28% 32% 21% 4	760
May	1st to 10th	Night	8% 5% 24% 39% 21% 3	669
	11th to 20th	Night	6% 4 20% 41% 27% 3	500
	21st to end	Night	6% 10% 24% 38% 19% 3	411
June	1st to 10th	Night	6% 6% 23% 43% 20% 2	380
	11th to 20th	Night	2 4 21% 54% 17% 2	380
	21st to end	Night	4 3 19% 43% 29% 2	380
July	1st to 10th	Night	2 2 14% 49% 31% 1	370
	11th to 20th	Night	4 1 10% 48% 31% 6%	526
	21st to end	Night	3 4 12% 42% 35% 5%	624
August	1st to 10th	Night	8% 2 16% 39% 30% 4	567
	11th to 20th	Night	3 3 16% 43% 29% 5%	671
	21st to end	Night	6% 1 12% 44% 32% 5%	836
September	1st to 10th	Night	3 1 11% 40% 37% 8%	760
	11th to 20th	Night	6% 3 16% 39% 31% 5%	760
	21st to end	Night	4 3 14% 36% 36% 8%	760
October	1st to 10th	Night	7% 3 14% 34% 34% 8%	760
	11th to 20th	Night	9% 5% 12% 32% 35% 7%	760
	21st to end	Night	9% 4 11% 33% 32% 11%	836
November	1st to 10th	Night	9% 6% 13% 31% 32% 8%	754
	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 2024-11-01 19:47:37. Version ac07

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