Lawshe Memorial Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lawshe Memorial Observatory clear sky chart from 2005-11-06 to 2025-10-19.

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% 11% 4 10% 5% 4 4 3 5% 6% 33%	126088
	Night	15% 13% 5% 12% 6% 5% 4 3 4 5% 28%	123834
Transparency	Day	52% 6% 11% 21% 10% 1	129581
	Night	58% 6% 10% 17% 9% 1	128428
Seeing	Day	21% 15% 29% 23% 10% 3	16947
	Night	22% 13% 28% 27% 10% 1	26469

By Month

Percentage Cloud Cover NE (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	9% 18% 12% 28% 6% 5% 4 2 3 3 8%	3617
	11th to 20th	Day	11% 18% 8% 25% 13% 8% 4 3 3 2 5%	3589
	21st to end	Day	13% 19% 9% 20% 8% 6% 6% 3 4 3 9%	3982
February	1st to 10th	Day	9% 18% 7% 14% 13% 7% 5% 3 4 4 15%	1723
	11th to 20th	Day	12% 15% 7% 15% 8% 6% 5% 4 4 4 20%	1903
	21st to end	Day	12% 17% 6% 13% 6% 6% 4 4 5% 6% 23%	1650
March	1st to 10th	Day	14% 10% 3 11% 5% 4 4 3 6% 6% 33%	4478
	11th to 20th	Day	12% 13% 5% 12% 6% 5% 5% 4 5% 6% 28%	4888
	21st to end	Day	20% 11% 7% 13% 6% 5% 4 3 4 5% 22%	5600
April	1st to 10th	Day	19% 15% 4 7% 5% 4 5% 3 4 7% 28%	2400
	11th to 20th	Day	20% 11% 4 6% 4 3 4 3 5% 5% 35%	2507
	21st to end	Day	15% 12% 4 8% 5% 4 4 4 5% 6% 33%	2600
May	1st to 10th	Day	16% 9% 2 5% 4 3 4 3 5% 6% 42%	5888
	11th to 20th	Day	13% 8% 2 7% 5% 4 4 3 5% 5% 44%	6057
	21st to end	Day	14% 9% 3 6% 4 4 3 3 5% 8% 42%	7035
June	1st to 10th	Day	14% 6% 2 6% 4 4 4 4 6% 7% 43%	3000
	11th to 20th	Day	13% 5% 2 7% 4 5% 5% 4 6% 8% 40%	3000
	21st to end	Day	17% 6% 2 6% 4 3 4 4 5% 8% 41%	3000
July	1st to 10th	Day	16% 7% 2 5% 3 3 3 3 5% 9% 43%	6414
	11th to 20th	Day	12% 5% 1 4 3 3 4 3 6% 8% 52%	6360
	21st to end	Day	10% 5% 2 5% 3 3 4 3 6% 10% 48%	6926
August	1st to 10th	Day	8% 6% 3 6% 5% 5% 5% 5% 7% 8% 43%	4368
	11th to 20th	Day	13% 6% 2 6% 3 4 4 3 5% 7% 47%	4174
	21st to end	Day	15% 6% 2 6% 4 4 4 3 4 7% 44%	4554
September	1st to 10th	Day	16% 6% 2 5% 4 3 4 3 5% 9% 42%	2355
	11th to 20th	Day	13% 6% 1 6% 4 3 5% 4 5% 8% 45%	2200
	21st to end	Day	18% 7% 2 7% 4 4 4 3 6% 9% 37%	2200
October	1st to 10th	Day	19% 10% 2 7% 4 4 3 3 5% 8% 35%	2186
	11th to 20th	Day	24% 17% 4 8% 6% 4 4 3 4 6% 20%	1882
	21st to end	Day	24% 18% 3 9% 6% 5% 5% 3 5% 5% 17%	1881
November	1st to 10th	Day	19% 20% 4 8% 4 4 4 3 4 6% 23%	1762
	11th to 20th	Day	14% 25% 7% 13% 6% 5% 3 3 5% 5% 15%	1800
	21st to end	Day	18% 25% 10% 13% 6% 4 3 3 3 4 11%	1576
December	1st to 10th	Day	11% 34% 12% 17% 5% 3 4 3 3 2 6%	2280
	11th to 20th	Day	14% 26% 8% 20% 10% 5% 4 2 3 3 6%	2621
	21st to end	Day	22% 24% 8% 15% 6% 4 3 2 3 4 10%	3632
January	1st to 10th	Night	10% 17% 8% 31% 7% 4 3 2 3 3 11%	6348
	11th to 20th	Night	11% 15% 8% 23% 16% 8% 4 3 2 3 7%	6316
	21st to end	Night	11% 19% 9% 19% 8% 8% 4 3 4 4 10%	6996
February	1st to 10th	Night	10% 18% 7% 16% 10% 7% 4 4 4 4 16%	2675
	11th to 20th	Night	11% 15% 7% 13% 9% 6% 5% 3 4 5% 21%	2381
	21st to end	Night	14% 16% 5% 12% 7% 5% 4 3 6% 6% 22%	1980
March	1st to 10th	Night	17% 10% 3 8% 6% 4 3 3 4 7% 36%	5362
	11th to 20th	Night	11% 13% 4 9% 5% 5% 5% 4 5% 8% 31%	5071
	21st to end	Night	22% 12% 5% 9% 4 4 4 3 4 5% 28%	5362
April	1st to 10th	Night	20% 11% 3 8% 5% 5% 4 4 6% 6% 28%	2000
	11th to 20th	Night	19% 10% 4 7% 4 4 4 2 5% 5% 35%	1841
	21st to end	Night	17% 11% 3 8% 5% 3 4 3 5% 6% 35%	1800
May	1st to 10th	Night	15% 7% 3 6% 4 5% 4 3 5% 5% 42%	4053
	11th to 20th	Night	15% 9% 2 7% 5% 3 4 3 5% 6% 40%	3842
	21st to end	Night	17% 9% 3 6% 4 3 3 3 4 6% 42%	3861
June	1st to 10th	Night	15% 6% 3 6% 5% 5% 4 4 5% 7% 40%	1400
	11th to 20th	Night	12% 6% 3 7% 5% 4 5% 4 7% 9% 40%	1400
	21st to end	Night	14% 7% 2 6% 6% 4 4 4 5% 6% 43%	1400
July	1st to 10th	Night	13% 7% 3 7% 4 4 4 4 6% 7% 41%	3560
	11th to 20th	Night	10% 6% 2 5% 4 4 4 3 5% 6% 51%	3620
	21st to end	Night	8% 5% 2 5% 4 4 4 4 6% 8% 51%	3948
August	1st to 10th	Night	13% 6% 3 7% 5% 4 5% 4 5% 7% 42%	2783
	11th to 20th	Night	14% 5% 2 5% 3 4 3 3 5% 7% 49%	2875
	21st to end	Night	12% 5% 2 5% 4 4 4 3 4 6% 50%	3340
September	1st to 10th	Night	13% 6% 2 6% 4 3 4 4 5% 7% 46%	2025
	11th to 20th	Night	14% 6% 2 6% 5% 4 4 3 5% 8% 45%	2200
	21st to end	Night	18% 8% 2 5% 4 5% 4 3 5% 7% 39%	2200
October	1st to 10th	Night	17% 9% 3 7% 4 3 4 3 4 6% 39%	2213
	11th to 20th	Night	23% 14% 3 9% 4 4 4 3 4 6% 24%	2473
	21st to end	Night	26% 16% 3 8% 5% 4 4 3 4 5% 21%	2717
November	1st to 10th	Night	18% 17% 4 9% 5% 4 3 3 4 6% 27%	2536
	11th to 20th	Night	16% 23% 6% 12% 6% 5% 4 3 4 4 17%	2600
	21st to end	Night	18% 24% 9% 14% 5% 4 4 3 4 3 12%	2819
December	1st to 10th	Night	11% 26% 11% 19% 7% 5% 4 3 3 3 8%	4910
	11th to 20th	Night	14% 24% 8% 22% 7% 5% 4 2 3 3 9%	5586
	21st to end	Night	23% 20% 10% 14% 6% 5% 4 3 4 4 9%	7341

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	81% 5% 5% 6% 2 1	3618
	11th to 20th	Day	88% 4 3 3 1	3620
	21st to end	Day	78% 8% 8% 4 2	3982
February	1st to 10th	Day	72% 6% 9% 10% 3	1723
	11th to 20th	Day	68% 7% 8% 10% 6%	1913
	21st to end	Day	63% 6% 9% 16% 4	1650
March	1st to 10th	Day	51% 5% 16% 15% 11% 2	4480
	11th to 20th	Day	56% 5% 14% 18% 7% 1	4888
	21st to end	Day	64% 6% 8% 14% 7% 1	5600
April	1st to 10th	Day	57% 5% 9% 18% 10% 1	2400
	11th to 20th	Day	51% 5% 10% 20% 13% 1	2507
	21st to end	Day	51% 6% 11% 15% 14% 3	2600
May	1st to 10th	Day	42% 5% 10% 21% 19% 3	5897
	11th to 20th	Day	42% 5% 8% 25% 19% 2	6061
	21st to end	Day	40% 6% 11% 21% 18% 4	7035
June	1st to 10th	Day	39% 7% 11% 28% 14% 2	3000
	11th to 20th	Day	40% 8% 12% 22% 16% 1	3000
	21st to end	Day	42% 7% 13% 24% 13% 2	3000
July	1st to 10th	Day	39% 5% 15% 28% 13% 1	6346
	11th to 20th	Day	31% 6% 14% 38% 12% 1	6285
	21st to end	Day	32% 5% 12% 34% 15% 1	6728
August	1st to 10th	Day	37% 7% 13% 30% 13%	4353
	11th to 20th	Day	38% 6% 12% 32% 11% 1	4213
	21st to end	Day	40% 6% 14% 30% 9% 1	4553
September	1st to 10th	Day	41% 7% 13% 25% 14% 1	2355
	11th to 20th	Day	37% 8% 14% 29% 11% 1	2200
	21st to end	Day	45% 7% 14% 25% 10%	2200
October	1st to 10th	Day	38% 4 10% 32% 16%	3563
	11th to 20th	Day	57% 5% 9% 20% 9%	3059
	21st to end	Day	65% 6% 12% 15% 3	3081
November	1st to 10th	Day	62% 6% 10% 17% 5%	1762
	11th to 20th	Day	72% 6% 9% 9% 4	1800
	21st to end	Day	78% 5% 9% 6% 1	1576
December	1st to 10th	Day	85% 5% 6% 3 1	2280
	11th to 20th	Day	85% 6% 5% 4 1	2621
	21st to end	Day	80% 5% 6% 5% 3	3632
January	1st to 10th	Night	79% 5% 7% 6% 3	6348
	11th to 20th	Night	83% 6% 6% 4 2	6360
	21st to end	Night	77% 6% 7% 8% 3	6996
February	1st to 10th	Night	72% 5% 8% 9% 4 1	2675
	11th to 20th	Night	67% 5% 9% 15% 3	2382
	21st to end	Night	63% 7% 11% 13% 6%	1980
March	1st to 10th	Night	50% 4 17% 18% 10% 1	5373
	11th to 20th	Night	52% 5% 17% 19% 7% 1	5072
	21st to end	Night	57% 6% 10% 16% 10% 1	5362
April	1st to 10th	Night	55% 6% 9% 17% 11% 1	2000
	11th to 20th	Night	51% 4 9% 22% 12% 2	1841
	21st to end	Night	51% 6% 8% 18% 15% 3	1800
May	1st to 10th	Night	43% 6% 11% 20% 17% 3	4060
	11th to 20th	Night	44% 6% 7% 24% 17% 1	3843
	21st to end	Night	44% 6% 11% 22% 12% 5%	3862
June	1st to 10th	Night	41% 5% 11% 26% 15% 1	1400
	11th to 20th	Night	40% 7% 13% 24% 14% 3	1400
	21st to end	Night	41% 7% 12% 24% 15% 2	1400
July	1st to 10th	Night	40% 5% 14% 24% 15% 2	3520
	11th to 20th	Night	33% 5% 12% 31% 18% 1	3572
	21st to end	Night	31% 6% 15% 30% 18% 1	3832
August	1st to 10th	Night	41% 6% 14% 27% 12% 1	2774
	11th to 20th	Night	34% 6% 15% 32% 13% 1	2902
	21st to end	Night	35% 6% 14% 29% 15% 1	3340
September	1st to 10th	Night	37% 7% 14% 24% 16% 1	2025
	11th to 20th	Night	37% 7% 16% 27% 12% 1	2200
	21st to end	Night	44% 7% 15% 23% 10%	2200
October	1st to 10th	Night	41% 6% 10% 31% 12%	3616
	11th to 20th	Night	52% 6% 11% 19% 12%	4035
	21st to end	Night	60% 6% 13% 17% 4	4467
November	1st to 10th	Night	59% 6% 12% 17% 5% 1	2536
	11th to 20th	Night	70% 5% 10% 9% 5%	2600
	21st to end	Night	76% 6% 10% 6% 1	2819
December	1st to 10th	Night	81% 7% 7% 5% 1	4910
	11th to 20th	Night	81% 5% 7% 5% 2	5585
	21st to end	Night	79% 7% 6% 6% 2	7341

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	22% 19% 38% 17% 4	300
	11th to 20th	Day	23% 20% 39% 14% 3 1	300
	21st to end	Day	27% 16% 33% 18% 5%	330
February	1st to 10th	Day	22% 31% 30% 10% 6%	300
	11th to 20th	Day	20% 30% 34% 14% 2	300
	21st to end	Day	29% 26% 36% 6% 2	249
March	1st to 10th	Day	23% 28% 32% 14% 4	300
	11th to 20th	Day	23% 20% 31% 20% 5% 1	460
	21st to end	Day	29% 18% 27% 20% 6% 1	550
April	1st to 10th	Day	27% 21% 29% 16% 6% 1	500
	11th to 20th	Day	30% 20% 24% 15% 9% 2	492
	21st to end	Day	22% 16% 33% 20% 8% 2	500
May	1st to 10th	Day	25% 18% 27% 17% 10% 2	503
	11th to 20th	Day	17% 14% 35% 23% 7% 4	606
	21st to end	Day	18% 12% 28% 27% 13% 2	789
June	1st to 10th	Day	17% 14% 31% 28% 9% 2	730
	11th to 20th	Day	17% 11% 33% 28% 9% 3	730
	21st to end	Day	19% 10% 30% 28% 11% 2	730
July	1st to 10th	Day	11% 8% 31% 32% 15% 3	721
	11th to 20th	Day	13% 9% 30% 30% 14% 5%	718
	21st to end	Day	12% 7% 30% 34% 14% 4	794
August	1st to 10th	Day	9% 7% 23% 33% 22% 5%	609
	11th to 20th	Day	14% 6% 22% 30% 19% 8%	519
	21st to end	Day	20% 9% 24% 25% 17% 5%	583
September	1st to 10th	Day	20% 10% 25% 23% 16% 6%	530
	11th to 20th	Day	13% 11% 20% 28% 20% 8%	530
	21st to end	Day	19% 11% 22% 28% 16% 3	530
October	1st to 10th	Day	23% 17% 25% 21% 12% 2	530
	11th to 20th	Day	31% 18% 29% 19% 3	424
	21st to end	Day	32% 19% 33% 12% 3 1	330
November	1st to 10th	Day	36% 16% 30% 12% 5%	300
	11th to 20th	Day	27% 22% 30% 16% 4	300
	21st to end	Day	29% 30% 29% 11% 1	207
December	1st to 10th	Day	34% 23% 29% 9% 5% 2	200
	11th to 20th	Day	26% 27% 36% 10% 2 1	200
	21st to end	Day	35% 26% 27% 8% 3 1	253
January	1st to 10th	Night	21% 20% 32% 22% 5% 1	1000
	11th to 20th	Night	24% 18% 32% 20% 6%	1000
	21st to end	Night	21% 15% 33% 26% 5% 1	1100
February	1st to 10th	Night	19% 19% 34% 23% 5%	875
	11th to 20th	Night	20% 20% 30% 23% 6%	783
	21st to end	Night	24% 16% 32% 23% 4	660
March	1st to 10th	Night	19% 14% 33% 25% 8% 1	800
	11th to 20th	Night	20% 14% 36% 23% 7% 1	800
	21st to end	Night	22% 11% 28% 30% 8% 1	839
April	1st to 10th	Night	26% 12% 31% 26% 5% 1	600
	11th to 20th	Night	25% 11% 28% 27% 8% 1	593
	21st to end	Night	22% 10% 30% 29% 8% 1	600
May	1st to 10th	Night	15% 9% 28% 38% 9% 1	600
	11th to 20th	Night	18% 6% 31% 34% 10% 1	591
	21st to end	Night	16% 7% 22% 38% 17%	614
June	1st to 10th	Night	18% 7% 26% 37% 12% 1	400
	11th to 20th	Night	12% 6% 24% 41% 16%	400
	21st to end	Night	16% 5% 26% 37% 15% 1	400
July	1st to 10th	Night	12% 3 19% 47% 17% 2	551
	11th to 20th	Night	10% 5% 20% 36% 25% 3	582
	21st to end	Night	9% 4 23% 39% 23% 2	657
August	1st to 10th	Night	12% 3 20% 39% 25% 1	597
	11th to 20th	Night	13% 5% 14% 38% 27% 3	594
	21st to end	Night	18% 4 19% 36% 20% 2	660
September	1st to 10th	Night	16% 6% 21% 33% 20% 4	625
	11th to 20th	Night	17% 5% 21% 32% 22% 3	800
	21st to end	Night	22% 6% 21% 32% 15% 4	800
October	1st to 10th	Night	23% 12% 25% 28% 12% 1	800
	11th to 20th	Night	32% 13% 27% 22% 6% 1	793
	21st to end	Night	37% 14% 25% 19% 5% 1	836
November	1st to 10th	Night	28% 16% 28% 21% 6% 1	780
	11th to 20th	Night	29% 19% 29% 18% 5%	800
	21st to end	Night	31% 19% 31% 15% 3	839
December	1st to 10th	Night	26% 21% 32% 16% 5%	1000
	11th to 20th	Night	25% 23% 33% 15% 3 1	1000
	21st to end	Night	31% 16% 31% 18% 3	1100

Page generated at 2025-10-16 01:50:24. Version ac07

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