Lake Hamilton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lake Hamilton clear sky chart from 2005-11-06 to 2026-06-16.

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% 7% 2 6% 4 4 4 4 5% 7% 44%	136847
	Night	14% 6% 2 5% 4 3 3 3 5% 6% 49%	135462
Transparency	Day	38% 6% 10% 22% 19% 6%	140454
	Night	35% 5% 9% 22% 21% 8%	139935
Seeing	Day	17% 9% 24% 26% 19% 6%	17457
	Night	16% 8% 24% 31% 18% 2	27282

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	16% 9% 3 6% 3 3 3 3 4 5% 45%	5289
	11th to 20th	Day	10% 8% 2 5% 3 4 3 2 4 4 55%	5310
	21st to end	Day	22% 7% 2 5% 2 2 2 2 3 5% 48%	5812
February	1st to 10th	Day	22% 9% 3 5% 3 4 5% 2 4 4 40%	1890
	11th to 20th	Day	19% 9% 2 5% 4 3 3 3 4 5% 41%	1948
	21st to end	Day	22% 8% 3 7% 4 3 3 2 4 4 39%	1851
March	1st to 10th	Day	23% 9% 3 6% 3 3 3 2 4 5% 38%	5046
	11th to 20th	Day	11% 6% 2 4 3 3 4 4 5% 7% 50%	5090
	21st to end	Day	14% 9% 3 7% 4 3 3 3 5% 6% 42%	5583
April	1st to 10th	Day	16% 7% 2 6% 3 3 3 3 5% 6% 45%	2475
	11th to 20th	Day	17% 5% 3 7% 4 4 3 3 4 6% 44%	2494
	21st to end	Day	15% 8% 4 7% 5% 5% 4 3 5% 6% 39%	2520
May	1st to 10th	Day	19% 9% 3 7% 4 4 3 3 5% 6% 37%	7072
	11th to 20th	Day	13% 7% 3 8% 5% 5% 5% 4 6% 6% 37%	7627
	21st to end	Day	17% 8% 3 8% 6% 6% 6% 5% 6% 7% 28%	8392
June	1st to 10th	Day	8% 5% 2 7% 5% 5% 6% 4 7% 8% 41%	2730
	11th to 20th	Day	7% 5% 2 7% 5% 6% 6% 5% 7% 8% 42%	2666
	21st to end	Day	4 4 2 5% 4 5% 5% 5% 8% 10% 46%	2600
July	1st to 10th	Day	7% 5% 2 7% 6% 6% 6% 5% 8% 12% 35%	5900
	11th to 20th	Day	5% 4 1 4 4 4 4 4 6% 10% 56%	5900
	21st to end	Day	8% 6% 3 7% 5% 6% 6% 5% 7% 9% 39%	6422
August	1st to 10th	Day	3 2 1 3 3 4 4 4 6% 9% 60%	4234
	11th to 20th	Day	8% 5% 2 6% 4 4 5% 4 6% 10% 45%	3920
	21st to end	Day	5% 3 2 6% 4 4 5% 5% 8% 8% 49%	4312
September	1st to 10th	Day	11% 6% 2 5% 4 5% 5% 3 5% 8% 47%	2400
	11th to 20th	Day	15% 5% 2 4 4 4 5% 4 6% 7% 45%	2336
	21st to end	Day	10% 4 2 4 4 4 4 3 5% 7% 52%	2115
October	1st to 10th	Day	8% 4 2 5% 3 4 3 3 6% 5% 58%	2000
	11th to 20th	Day	15% 4 1 4 2 2 3 2 4 4 58%	2000
	21st to end	Day	19% 4 2 5% 3 3 2 3 3 5% 51%	2200
November	1st to 10th	Day	13% 7% 3 4 3 2 3 2 4 6% 54%	2058
	11th to 20th	Day	12% 5% 1 5% 3 3 3 2 4 7% 54%	2100
	21st to end	Day	20% 7% 3 4 3 3 3 3 4 5% 46%	1909
December	1st to 10th	Day	19% 8% 2 5% 4 2 3 3 3 4 48%	2690
	11th to 20th	Day	19% 9% 3 6% 4 4 3 3 4 5% 42%	3369
	21st to end	Day	21% 8% 2 6% 4 4 3 3 3 5% 41%	4587
January	1st to 10th	Night	17% 8% 2 6% 4 3 3 3 4 5% 45%	7634
	11th to 20th	Night	11% 4 1 3 3 2 2 2 3 4 66%	7680
	21st to end	Night	24% 8% 2 5% 3 3 3 2 3 4 43%	8402
February	1st to 10th	Night	21% 8% 3 6% 3 3 4 2 4 4 43%	2730
	11th to 20th	Night	19% 8% 3 5% 4 3 3 2 4 5% 44%	2558
	21st to end	Night	20% 7% 2 4 3 3 3 2 4 5% 47%	1971
March	1st to 10th	Night	19% 8% 3 5% 4 4 3 3 5% 5% 42%	5029
	11th to 20th	Night	11% 6% 2 5% 4 3 3 3 5% 6% 52%	5090
	21st to end	Night	13% 7% 3 7% 4 4 3 3 5% 7% 45%	5588
April	1st to 10th	Night	13% 6% 3 4 3 3 3 3 5% 7% 49%	2143
	11th to 20th	Night	14% 4 2 5% 4 3 4 3 6% 7% 50%	2075
	21st to end	Night	13% 7% 2 5% 3 3 3 4 5% 7% 47%	2100
May	1st to 10th	Night	20% 8% 3 6% 4 4 4 4 5% 7% 35%	5779
	11th to 20th	Night	16% 8% 3 8% 5% 4 4 3 5% 6% 38%	5265
	21st to end	Night	18% 9% 3 7% 5% 4 4 4 5% 7% 34%	5793
June	1st to 10th	Night	7% 4 2 4 3 4 4 4 7% 10% 52%	1890
	11th to 20th	Night	5% 5% 1 5% 4 3 4 3 5% 9% 57%	1845
	21st to end	Night	4 3 1 3 4 3 4 4 6% 10% 59%	1800
July	1st to 10th	Night	7% 4 2 7% 5% 6% 6% 5% 8% 10% 41%	4078
	11th to 20th	Night	4 3 1 4 3 3 4 3 6% 12% 57%	4077
	21st to end	Night	6% 4 2 6% 5% 5% 4 4 7% 10% 47%	4449
August	1st to 10th	Night	2 2 1 3 2 2 2 2 4 7% 72%	2926
	11th to 20th	Night	5% 3 1 4 3 4 5% 4 7% 10% 54%	3131
	21st to end	Night	4 3 1 4 3 4 5% 4 7% 9% 55%	3586
September	1st to 10th	Night	6% 4 2 5% 4 4 4 4 6% 7% 55%	2000
	11th to 20th	Night	9% 6% 2 5% 4 4 5% 3 5% 7% 50%	2059
	21st to end	Night	8% 4 1 4 3 3 3 3 5% 5% 59%	2264
October	1st to 10th	Night	8% 3 1 4 3 3 3 3 4 6% 62%	2400
	11th to 20th	Night	10% 5% 2 4 3 2 3 2 3 5% 62%	2400
	21st to end	Night	16% 6% 2 5% 3 3 2 2 3 4 55%	2640
November	1st to 10th	Night	12% 5% 2 4 2 3 3 3 4 4 57%	2460
	11th to 20th	Night	10% 5% 2 5% 4 3 3 3 4 5% 57%	2520
	21st to end	Night	16% 7% 2 5% 3 2 3 3 3 5% 52%	2699
December	1st to 10th	Night	15% 7% 2 5% 3 3 3 3 4 4 50%	4720
	11th to 20th	Night	18% 9% 3 7% 4 3 3 2 3 4 44%	5048
	21st to end	Night	19% 9% 3 6% 3 3 3 2 4 5% 44%	6633

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	43% 3 9% 27% 16% 2	5290
	11th to 20th	Day	34% 3 7% 19% 30% 6%	5310
	21st to end	Day	42% 2 4 17% 24% 11%	5812
February	1st to 10th	Day	49% 3 8% 19% 17% 4	1890
	11th to 20th	Day	45% 5% 7% 20% 18% 5%	1957
	21st to end	Day	49% 3 6% 12% 20% 9%	1851
March	1st to 10th	Day	49% 4 5% 15% 15% 12%	5046
	11th to 20th	Day	33% 5% 7% 18% 23% 15%	5090
	21st to end	Day	43% 4 9% 23% 19% 2	5585
April	1st to 10th	Day	40% 5% 8% 22% 19% 6%	2475
	11th to 20th	Day	42% 4 8% 20% 20% 6%	2494
	21st to end	Day	44% 6% 10% 18% 18% 3	2520
May	1st to 10th	Day	47% 6% 8% 23% 14% 2	7107
	11th to 20th	Day	43% 8% 11% 20% 16% 2	7631
	21st to end	Day	51% 9% 12% 15% 10% 3	8405
June	1st to 10th	Day	37% 8% 14% 23% 16% 2	2730
	11th to 20th	Day	36% 7% 13% 24% 18% 1	2666
	21st to end	Day	28% 9% 15% 29% 17% 3	2600
July	1st to 10th	Day	37% 9% 18% 27% 8% 1	5836
	11th to 20th	Day	24% 6% 17% 35% 17% 1	5831
	21st to end	Day	39% 9% 15% 25% 12% 1	6240
August	1st to 10th	Day	20% 7% 16% 28% 25% 4	4220
	11th to 20th	Day	34% 7% 16% 32% 9% 1	3957
	21st to end	Day	30% 8% 13% 27% 20% 3	4311
September	1st to 10th	Day	36% 7% 11% 20% 18% 8%	2400
	11th to 20th	Day	37% 7% 12% 18% 20% 6%	2336
	21st to end	Day	32% 6% 9% 19% 26% 8%	2115
October	1st to 10th	Day	16% 3 7% 12% 30% 32%	3260
	11th to 20th	Day	19% 3 4 18% 36% 20%	3240
	21st to end	Day	31% 4 5% 26% 27% 7%	3538
November	1st to 10th	Day	33% 4 8% 23% 24% 7%	2058
	11th to 20th	Day	31% 4 9% 20% 26% 11%	2100
	21st to end	Day	42% 3 6% 18% 26% 5%	1909
December	1st to 10th	Day	42% 3 6% 26% 19% 4	2690
	11th to 20th	Day	46% 4 4 20% 21% 4	3367
	21st to end	Day	45% 5% 7% 22% 17% 4	4587
January	1st to 10th	Night	40% 4 8% 26% 21% 2	7635
	11th to 20th	Night	25% 3 5% 20% 36% 12%	7680
	21st to end	Night	47% 3 6% 15% 21% 8%	8402
February	1st to 10th	Night	45% 3 7% 20% 18% 6%	2730
	11th to 20th	Night	45% 3 7% 19% 20% 6%	2559
	21st to end	Night	41% 4 7% 15% 24% 10%	1971
March	1st to 10th	Night	43% 5% 7% 13% 19% 13%	5029
	11th to 20th	Night	33% 4 7% 21% 19% 16%	5090
	21st to end	Night	39% 5% 9% 24% 20% 4	5588
April	1st to 10th	Night	35% 5% 10% 22% 19% 10%	2143
	11th to 20th	Night	33% 5% 10% 22% 21% 9%	2075
	21st to end	Night	36% 6% 11% 23% 21% 3	2100
May	1st to 10th	Night	48% 6% 11% 19% 12% 4	5809
	11th to 20th	Night	46% 6% 10% 20% 14% 4	5266
	21st to end	Night	49% 8% 14% 15% 10% 4	5805
June	1st to 10th	Night	27% 8% 15% 28% 20% 2	1890
	11th to 20th	Night	26% 5% 12% 32% 21% 4	1845
	21st to end	Night	20% 7% 14% 31% 24% 4	1800
July	1st to 10th	Night	33% 9% 18% 28% 11% 1	4035
	11th to 20th	Night	19% 7% 17% 37% 18% 1	4026
	21st to end	Night	32% 8% 15% 28% 17% 1	4320
August	1st to 10th	Night	13% 4 16% 31% 29% 7%	2916
	11th to 20th	Night	23% 6% 19% 36% 14% 2	3160
	21st to end	Night	24% 7% 13% 27% 27% 2	3586
September	1st to 10th	Night	27% 8% 12% 23% 22% 8%	2000
	11th to 20th	Night	33% 6% 10% 23% 21% 7%	2059
	21st to end	Night	26% 4 10% 20% 28% 11%	2264
October	1st to 10th	Night	15% 3 8% 13% 27% 35%	3920
	11th to 20th	Night	17% 2 4 16% 37% 24%	3899
	21st to end	Night	28% 3 4 23% 29% 13%	4252
November	1st to 10th	Night	31% 4 7% 20% 27% 10%	2460
	11th to 20th	Night	30% 4 8% 20% 26% 12%	2520
	21st to end	Night	37% 4 7% 19% 27% 6%	2699
December	1st to 10th	Night	37% 3 6% 29% 20% 4	4720
	11th to 20th	Night	47% 3 5% 18% 20% 8%	5049
	21st to end	Night	43% 4 8% 23% 19% 3	6633

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% 13% 38% 18% 4	330
	11th to 20th	Day	25% 18% 41% 14% 2 1	330
	21st to end	Day	24% 22% 36% 14% 4	363
February	1st to 10th	Day	30% 14% 35% 16% 5% 1	330
	11th to 20th	Day	29% 24% 33% 11% 3	330
	21st to end	Day	34% 20% 32% 12% 3	273
March	1st to 10th	Day	28% 14% 36% 18% 3 1	330
	11th to 20th	Day	29% 22% 34% 11% 3	330
	21st to end	Day	24% 18% 41% 15% 2	363
April	1st to 10th	Day	24% 18% 33% 16% 9%	495
	11th to 20th	Day	27% 15% 29% 21% 7% 1	532
	21st to end	Day	22% 13% 34% 20% 9% 2	540
May	1st to 10th	Day	20% 12% 31% 27% 8% 1	556
	11th to 20th	Day	16% 8% 32% 28% 13% 2	775
	21st to end	Day	13% 7% 29% 30% 16% 5%	844
June	1st to 10th	Day	12% 4 19% 31% 26% 8%	780
	11th to 20th	Day	8% 5% 18% 36% 25% 8%	756
	21st to end	Day	5% 3 16% 38% 29% 8%	730
July	1st to 10th	Day	6% 2 14% 35% 32% 11%	721
	11th to 20th	Day	7% 2 9% 33% 37% 12%	718
	21st to end	Day	8% 2 8% 31% 37% 14%	794
August	1st to 10th	Day	6% 1 8% 39% 35% 10%	726
	11th to 20th	Day	14% 2 7% 30% 34% 13%	566
	21st to end	Day	11% 2 6% 27% 36% 18%	583
September	1st to 10th	Day	11% 2 10% 27% 36% 14%	530
	11th to 20th	Day	13% 2 11% 24% 34% 16%	466
	21st to end	Day	13% 5% 15% 38% 22% 7%	330
October	1st to 10th	Day	6% 2 28% 38% 22% 4	330
	11th to 20th	Day	14% 8% 34% 26% 15% 2	330
	21st to end	Day	25% 12% 29% 24% 8% 2	363
November	1st to 10th	Day	19% 13% 32% 23% 12% 2	330
	11th to 20th	Day	16% 12% 39% 25% 7% 1	330
	21st to end	Day	26% 15% 31% 20% 7% 1	330
December	1st to 10th	Day	24% 15% 34% 20% 6% 1	330
	11th to 20th	Day	29% 13% 34% 16% 7% 1	330
	21st to end	Day	30% 13% 36% 18% 3	363
January	1st to 10th	Night	24% 12% 30% 30% 4	1050
	11th to 20th	Night	22% 15% 34% 26% 4	1050
	21st to end	Night	22% 13% 35% 26% 3	1155
February	1st to 10th	Night	25% 13% 31% 25% 5%	1050
	11th to 20th	Night	24% 16% 35% 23% 2	924
	21st to end	Night	25% 15% 34% 23% 3	587
March	1st to 10th	Night	25% 10% 31% 30% 5%	630
	11th to 20th	Night	22% 14% 33% 27% 4	630
	21st to end	Night	17% 12% 37% 29% 5%	693
April	1st to 10th	Night	18% 12% 36% 26% 7%	630
	11th to 20th	Night	17% 12% 32% 29% 9% 1	623
	21st to end	Night	16% 8% 37% 29% 10%	630
May	1st to 10th	Night	16% 5% 28% 40% 9% 1	630
	11th to 20th	Night	16% 8% 26% 32% 15% 2	621
	21st to end	Night	11% 5% 23% 35% 23% 3	683
June	1st to 10th	Night	7% 3 13% 39% 35% 4	630
	11th to 20th	Night	5% 3 13% 41% 34% 3	615
	21st to end	Night	5% 1 9% 39% 39% 7%	600
July	1st to 10th	Night	5% 2 8% 36% 42% 8%	585
	11th to 20th	Night	4 2 5% 33% 46% 9%	582
	21st to end	Night	4 1 4 34% 46% 10%	657
August	1st to 10th	Night	5% 2 5% 37% 44% 7%	597
	11th to 20th	Night	8% 2 4 35% 44% 7%	594
	21st to end	Night	8% 1 6% 32% 44% 8%	660
September	1st to 10th	Night	8% 2 8% 36% 41% 7%	600
	11th to 20th	Night	11% 1 11% 32% 40% 5%	600
	21st to end	Night	10% 4 13% 33% 35% 5%	664
October	1st to 10th	Night	10% 3 15% 37% 32% 4	800
	11th to 20th	Night	14% 5% 23% 38% 20% 1	800
	21st to end	Night	20% 7% 26% 29% 16% 1	880
November	1st to 10th	Night	14% 7% 26% 34% 17% 1	820
	11th to 20th	Night	13% 10% 29% 36% 13%	840
	21st to end	Night	20% 10% 29% 29% 11% 1	917
December	1st to 10th	Night	21% 10% 32% 31% 6%	1050
	11th to 20th	Night	25% 9% 30% 30% 6%	1050
	21st to end	Night	25% 12% 29% 28% 6%	1155

Page generated at 2026-06-13 01:31:40. Version ac07

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