Dr. T. K. Lawless Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dr. T. K. Lawless Park clear sky chart from 2005-11-06 to 2025-12-18.

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% 10% 4 9% 5% 4 4 4 5% 7% 33%	126885
	Night	15% 11% 4 10% 5% 4 4 3 5% 6% 32%	124367
Transparency	Day	49% 6% 11% 21% 12% 1	130439
	Night	51% 5% 11% 20% 12% 1	128887
Seeing	Day	17% 11% 28% 24% 14% 5%	17258
	Night	19% 9% 29% 30% 12% 1	27116

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	12% 18% 10% 21% 6% 4 4 3 3 4 14%	3617
	11th to 20th	Day	12% 15% 8% 17% 12% 7% 10% 4 4 3 8%	3620
	21st to end	Day	20% 19% 7% 15% 5% 4 3 3 3 5% 16%	3995
February	1st to 10th	Day	15% 15% 6% 13% 10% 6% 5% 3 4 5% 18%	1910
	11th to 20th	Day	15% 13% 6% 16% 8% 5% 4 3 4 5% 21%	1948
	21st to end	Day	16% 16% 6% 13% 4 5% 5% 4 5% 6% 21%	1650
March	1st to 10th	Day	16% 12% 6% 13% 5% 4 3 3 4 5% 29%	4480
	11th to 20th	Day	11% 9% 7% 7% 5% 4 5% 4 6% 8% 35%	4832
	21st to end	Day	19% 15% 7% 11% 5% 5% 4 3 4 5% 21%	5686
April	1st to 10th	Day	18% 14% 3 8% 5% 5% 4 2 5% 6% 30%	2400
	11th to 20th	Day	16% 11% 3 6% 4 4 4 3 5% 7% 36%	2404
	21st to end	Day	18% 9% 2 7% 5% 4 4 3 5% 7% 36%	2600
May	1st to 10th	Day	20% 9% 3 7% 4 4 4 4 6% 6% 33%	5862
	11th to 20th	Day	15% 7% 2 6% 4 4 4 4 6% 8% 39%	5861
	21st to end	Day	15% 6% 2 6% 4 4 4 3 5% 8% 42%	6836
June	1st to 10th	Day	10% 6% 2 6% 5% 4 4 4 7% 8% 44%	2800
	11th to 20th	Day	10% 6% 2 6% 5% 5% 5% 5% 7% 8% 42%	2800
	21st to end	Day	10% 6% 2 6% 5% 5% 4 5% 7% 8% 42%	2800
July	1st to 10th	Day	10% 6% 3 7% 4 5% 5% 5% 7% 9% 40%	6360
	11th to 20th	Day	9% 5% 2 6% 4 5% 4 4 7% 10% 44%	6360
	21st to end	Day	9% 6% 2 6% 4 5% 5% 4 7% 9% 42%	6907
August	1st to 10th	Day	11% 4 2 6% 4 4 4 4 6% 8% 48%	4234
	11th to 20th	Day	10% 5% 2 6% 4 4 5% 4 6% 8% 46%	4150
	21st to end	Day	8% 5% 2 5% 4 4 5% 4 6% 10% 47%	4312
September	1st to 10th	Day	10% 5% 3 6% 4 4 3 4 5% 9% 47%	2370
	11th to 20th	Day	11% 5% 2 5% 3 4 5% 4 6% 7% 49%	2200
	21st to end	Day	14% 7% 3 6% 5% 4 4 3 6% 8% 40%	2200
October	1st to 10th	Day	13% 6% 2 7% 5% 4 4 3 5% 6% 44%	2200
	11th to 20th	Day	18% 8% 3 8% 4 5% 5% 3 5% 7% 33%	1975
	21st to end	Day	20% 11% 4 8% 6% 4 5% 4 5% 6% 27%	1980
November	1st to 10th	Day	12% 12% 4 7% 4 4 4 3 6% 7% 38%	1852
	11th to 20th	Day	16% 17% 5% 9% 5% 5% 4 3 5% 6% 25%	1890
	21st to end	Day	20% 17% 7% 10% 5% 3 4 3 4 5% 22%	1890
December	1st to 10th	Day	10% 19% 8% 16% 5% 4 4 3 5% 6% 20%	2858
	11th to 20th	Day	16% 21% 11% 14% 7% 4 3 3 3 4 14%	3064
	21st to end	Day	26% 21% 7% 14% 6% 4 3 2 3 4 10%	3982
January	1st to 10th	Night	13% 18% 9% 21% 6% 4 3 3 4 4 14%	6348
	11th to 20th	Night	13% 17% 9% 19% 9% 6% 7% 4 4 4 9%	6360
	21st to end	Night	20% 15% 8% 12% 6% 5% 5% 3 4 5% 19%	6980
February	1st to 10th	Night	17% 15% 5% 12% 8% 5% 4 2 5% 5% 22%	2485
	11th to 20th	Night	14% 13% 5% 12% 7% 6% 5% 3 5% 6% 24%	2338
	21st to end	Night	18% 13% 5% 11% 5% 4 4 4 5% 5% 26%	1980
March	1st to 10th	Night	15% 11% 5% 10% 4 4 4 3 4 6% 34%	5373
	11th to 20th	Night	12% 8% 3 6% 4 5% 4 4 5% 7% 42%	5127
	21st to end	Night	18% 12% 4 10% 5% 4 4 3 4 5% 31%	5286
April	1st to 10th	Night	16% 10% 3 7% 4 4 5% 4 5% 7% 36%	2000
	11th to 20th	Night	19% 9% 3 6% 5% 4 5% 3 4 5% 38%	1945
	21st to end	Night	18% 8% 3 7% 5% 4 4 4 5% 7% 37%	1800
May	1st to 10th	Night	19% 10% 3 8% 4 4 4 3 5% 6% 33%	4033
	11th to 20th	Night	18% 8% 2 5% 3 3 4 3 4 7% 43%	4032
	21st to end	Night	17% 6% 3 7% 4 4 3 3 5% 7% 41%	4033
June	1st to 10th	Night	10% 5% 2 5% 4 3 4 4 6% 9% 47%	1600
	11th to 20th	Night	10% 6% 2 6% 5% 4 5% 5% 7% 9% 43%	1600
	21st to end	Night	10% 5% 2 5% 4 4 4 4 7% 10% 43%	1600
July	1st to 10th	Night	9% 5% 2 6% 4 4 5% 5% 7% 9% 46%	3618
	11th to 20th	Night	7% 5% 2 6% 4 4 4 4 6% 8% 51%	3617
	21st to end	Night	10% 6% 2 6% 4 4 4 4 6% 9% 45%	3962
August	1st to 10th	Night	10% 5% 2 6% 4 4 4 4 6% 8% 46%	2915
	11th to 20th	Night	10% 5% 1 5% 4 4 4 4 6% 8% 50%	2896
	21st to end	Night	9% 5% 2 6% 3 4 4 4 5% 8% 49%	3586
September	1st to 10th	Night	10% 6% 2 5% 3 4 3 3 5% 7% 50%	2010
	11th to 20th	Night	10% 4 1 5% 4 4 3 3 5% 7% 56%	2200
	21st to end	Night	14% 6% 2 6% 4 4 3 3 5% 8% 44%	2200
October	1st to 10th	Night	14% 7% 2 5% 4 3 4 3 4 6% 48%	2200
	11th to 20th	Night	17% 9% 3 8% 4 4 3 3 5% 6% 37%	2419
	21st to end	Night	21% 11% 3 7% 4 4 4 3 4 5% 34%	2860
November	1st to 10th	Night	14% 10% 3 7% 5% 4 4 3 5% 6% 39%	2666
	11th to 20th	Night	15% 15% 5% 10% 5% 4 5% 3 6% 6% 27%	2730
	21st to end	Night	18% 19% 5% 9% 5% 4 3 2 5% 6% 24%	2730
December	1st to 10th	Night	12% 17% 7% 16% 5% 5% 5% 4 5% 5% 19%	4544
	11th to 20th	Night	17% 20% 9% 14% 8% 4 4 3 4 4 13%	5298
	21st to end	Night	27% 20% 7% 11% 5% 4 4 3 4 4 11%	6996

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	72% 5% 11% 10% 2	3618
	11th to 20th	Day	76% 5% 10% 7% 3	3620
	21st to end	Day	73% 4 8% 11% 4	3995
February	1st to 10th	Day	68% 5% 9% 12% 5% 1	1910
	11th to 20th	Day	66% 4 8% 14% 8%	1958
	21st to end	Day	63% 5% 11% 13% 7% 1	1650
March	1st to 10th	Day	56% 5% 11% 20% 8%	4480
	11th to 20th	Day	46% 5% 15% 26% 7% 1	4832
	21st to end	Day	65% 5% 8% 15% 7%	5688
April	1st to 10th	Day	55% 5% 9% 20% 11%	2400
	11th to 20th	Day	48% 5% 10% 22% 13% 2	2404
	21st to end	Day	48% 5% 11% 21% 13% 2	2600
May	1st to 10th	Day	49% 7% 9% 20% 14% 1	5897
	11th to 20th	Day	42% 7% 13% 24% 13% 1	5865
	21st to end	Day	39% 6% 10% 25% 19% 1	6850
June	1st to 10th	Day	36% 7% 12% 25% 19% 2	2800
	11th to 20th	Day	36% 7% 12% 25% 18% 3	2800
	21st to end	Day	38% 7% 14% 21% 16% 3	2800
July	1st to 10th	Day	38% 6% 12% 24% 17% 2	6291
	11th to 20th	Day	33% 7% 14% 29% 16% 1	6285
	21st to end	Day	36% 8% 14% 24% 18% 2	6711
August	1st to 10th	Day	34% 6% 14% 28% 17% 1	4221
	11th to 20th	Day	35% 7% 11% 30% 16% 1	4189
	21st to end	Day	32% 7% 13% 28% 18% 3	4311
September	1st to 10th	Day	34% 6% 15% 25% 17% 3	2370
	11th to 20th	Day	32% 5% 11% 29% 21% 2	2200
	21st to end	Day	42% 5% 10% 25% 18% 1	2200
October	1st to 10th	Day	30% 4 9% 37% 19% 1	3590
	11th to 20th	Day	41% 4 9% 22% 23%	3191
	21st to end	Day	49% 3 10% 25% 12% 2	3180
November	1st to 10th	Day	45% 4 13% 23% 14% 1	1852
	11th to 20th	Day	60% 4 10% 18% 7% 1	1890
	21st to end	Day	65% 5% 11% 15% 4	1890
December	1st to 10th	Day	64% 5% 16% 12% 2	2858
	11th to 20th	Day	75% 4 9% 10% 1	3061
	21st to end	Day	80% 4 6% 8% 2	3982
January	1st to 10th	Night	73% 4 7% 12% 3	6348
	11th to 20th	Night	78% 5% 8% 6% 2	6360
	21st to end	Night	68% 4 12% 10% 5%	6980
February	1st to 10th	Night	65% 4 10% 13% 7% 1	2485
	11th to 20th	Night	61% 3 10% 17% 7%	2339
	21st to end	Night	59% 5% 12% 16% 6% 2	1980
March	1st to 10th	Night	51% 5% 11% 25% 7% 1	5373
	11th to 20th	Night	42% 5% 11% 29% 11% 2	5127
	21st to end	Night	55% 5% 10% 18% 11% 1	5286
April	1st to 10th	Night	48% 5% 12% 21% 13% 1	2000
	11th to 20th	Night	48% 4 8% 19% 18% 2	1945
	21st to end	Night	46% 6% 10% 22% 14% 2	1800
May	1st to 10th	Night	51% 6% 9% 19% 13% 2	4060
	11th to 20th	Night	42% 6% 10% 24% 16% 1	4033
	21st to end	Night	42% 7% 9% 21% 19% 2	4041
June	1st to 10th	Night	32% 6% 11% 30% 18% 3	1600
	11th to 20th	Night	35% 7% 13% 24% 19% 2	1600
	21st to end	Night	34% 7% 17% 24% 16% 3	1600
July	1st to 10th	Night	33% 6% 13% 27% 16% 5%	3580
	11th to 20th	Night	30% 6% 15% 25% 22% 2	3572
	21st to end	Night	36% 6% 13% 21% 22% 2	3847
August	1st to 10th	Night	33% 8% 13% 29% 16% 1	2904
	11th to 20th	Night	31% 7% 12% 30% 18% 1	2923
	21st to end	Night	34% 6% 10% 29% 19% 2	3586
September	1st to 10th	Night	33% 5% 11% 25% 21% 4	2010
	11th to 20th	Night	30% 3 8% 33% 25% 2	2200
	21st to end	Night	40% 5% 10% 26% 18% 1	2200
October	1st to 10th	Night	27% 4 9% 33% 26% 1	3590
	11th to 20th	Night	39% 4 9% 25% 23%	3942
	21st to end	Night	41% 4 8% 29% 17% 1	4610
November	1st to 10th	Night	46% 5% 10% 23% 15% 1	2666
	11th to 20th	Night	56% 5% 13% 18% 8% 2	2730
	21st to end	Night	62% 4 12% 17% 5%	2730
December	1st to 10th	Night	65% 5% 15% 12% 3	4544
	11th to 20th	Night	76% 4 9% 9% 2	5300
	21st to end	Night	77% 5% 9% 8% 2	6996

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	21% 18% 33% 19% 8% 1	300
	11th to 20th	Day	22% 17% 39% 16% 6% 1	300
	21st to end	Day	25% 16% 33% 22% 4	330
February	1st to 10th	Day	24% 22% 29% 19% 6% 1	300
	11th to 20th	Day	26% 19% 33% 19% 4	300
	21st to end	Day	25% 20% 41% 10% 3	249
March	1st to 10th	Day	21% 22% 39% 13% 5%	300
	11th to 20th	Day	23% 18% 29% 22% 7% 1	430
	21st to end	Day	29% 15% 29% 19% 6% 1	550
April	1st to 10th	Day	26% 12% 32% 21% 7% 1	500
	11th to 20th	Day	22% 19% 28% 19% 9% 2	492
	21st to end	Day	24% 12% 33% 20% 9% 2	500
May	1st to 10th	Day	25% 11% 30% 20% 11% 3	503
	11th to 20th	Day	23% 10% 25% 24% 13% 5%	527
	21st to end	Day	13% 8% 28% 26% 18% 7%	742
June	1st to 10th	Day	11% 10% 28% 30% 16% 5%	730
	11th to 20th	Day	13% 6% 29% 29% 17% 6%	730
	21st to end	Day	13% 7% 28% 29% 17% 6%	730
July	1st to 10th	Day	9% 4 22% 28% 23% 14%	721
	11th to 20th	Day	10% 4 26% 29% 20% 11%	718
	21st to end	Day	7% 4 22% 35% 23% 9%	789
August	1st to 10th	Day	8% 3 16% 29% 26% 17%	526
	11th to 20th	Day	10% 5% 19% 30% 25% 11%	519
	21st to end	Day	9% 4 18% 29% 28% 11%	583
September	1st to 10th	Day	12% 7% 21% 24% 24% 11%	530
	11th to 20th	Day	9% 3 18% 24% 30% 17%	530
	21st to end	Day	17% 11% 21% 24% 19% 8%	530
October	1st to 10th	Day	15% 7% 27% 27% 19% 5%	530
	11th to 20th	Day	22% 16% 27% 25% 9% 1	435
	21st to end	Day	28% 14% 37% 17% 4 1	363
November	1st to 10th	Day	18% 17% 33% 21% 8% 3	330
	11th to 20th	Day	27% 19% 31% 17% 6%	330
	21st to end	Day	29% 14% 38% 15% 3	330
December	1st to 10th	Day	22% 23% 33% 15% 7% 1	330
	11th to 20th	Day	21% 21% 37% 17% 3	321
	21st to end	Day	24% 22% 37% 14% 3	330
January	1st to 10th	Night	22% 15% 35% 22% 5%	1000
	11th to 20th	Night	24% 14% 35% 22% 4 1	1000
	21st to end	Night	21% 12% 37% 26% 4	1097
February	1st to 10th	Night	25% 10% 36% 26% 3	800
	11th to 20th	Night	21% 15% 35% 26% 4	783
	21st to end	Night	26% 11% 37% 23% 4	660
March	1st to 10th	Night	22% 11% 35% 24% 7% 1	800
	11th to 20th	Night	19% 12% 37% 25% 7% 1	800
	21st to end	Night	25% 10% 28% 31% 5% 1	802
April	1st to 10th	Night	20% 12% 34% 28% 6% 1	600
	11th to 20th	Night	24% 9% 34% 26% 6% 1	593
	21st to end	Night	22% 7% 34% 28% 9%	600
May	1st to 10th	Night	21% 5% 31% 35% 8% 1	600
	11th to 20th	Night	23% 5% 26% 32% 14% 1	591
	21st to end	Night	14% 4 24% 38% 19% 1	650
June	1st to 10th	Night	11% 4 25% 44% 16% 1	600
	11th to 20th	Night	13% 3 25% 42% 17% 1	600
	21st to end	Night	11% 2 21% 42% 23% 2	600
July	1st to 10th	Night	8% 3 16% 41% 29% 4	585
	11th to 20th	Night	9% 3 16% 41% 27% 4	582
	21st to end	Night	7% 2 15% 42% 32% 2	657
August	1st to 10th	Night	8% 2 10% 46% 30% 3	597
	11th to 20th	Night	9% 2 15% 42% 28% 5%	594
	21st to end	Night	9% 2 15% 37% 34% 3	660
September	1st to 10th	Night	12% 2 16% 38% 29% 4	610
	11th to 20th	Night	10% 3 16% 37% 29% 5%	800
	21st to end	Night	18% 5% 23% 30% 20% 5%	800
October	1st to 10th	Night	15% 6% 24% 35% 19% 2	800
	11th to 20th	Night	22% 11% 27% 29% 10%	800
	21st to end	Night	26% 13% 30% 24% 7%	880
November	1st to 10th	Night	21% 10% 32% 26% 10%	820
	11th to 20th	Night	23% 15% 33% 22% 6% 1	840
	21st to end	Night	26% 11% 33% 25% 4	840
December	1st to 10th	Night	25% 14% 36% 21% 4	939
	11th to 20th	Night	23% 14% 36% 22% 4	1036
	21st to end	Night	32% 14% 31% 21% 3	1100

Page generated at 2025-12-15 01:13:51. Version ac07

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