Martin Creek Lake State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Martin Creek Lake State 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	12% 6% 2 6% 4 4 4 3 5% 7% 46%	127093
	Night	12% 6% 2 5% 4 3 3 3 5% 7% 50%	124197
Transparency	Day	37% 5% 10% 22% 19% 7%	130703
	Night	34% 4 10% 21% 22% 10%	128650
Seeing	Day	14% 8% 23% 26% 22% 7%	16591
	Night	14% 8% 25% 32% 18% 2	26418

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	17% 10% 3 5% 3 2 3 3 4 4 46%	4077
	11th to 20th	Day	14% 5% 1 4 3 2 3 3 5% 6% 54%	4080
	21st to end	Day	24% 10% 3 5% 3 2 3 2 3 3 43%	4488
February	1st to 10th	Day	21% 8% 4 7% 4 3 3 2 3 4 42%	1800
	11th to 20th	Day	21% 8% 3 6% 4 4 3 3 4 4 40%	1925
	21st to end	Day	20% 8% 3 6% 3 4 3 3 3 5% 41%	1815
March	1st to 10th	Day	18% 12% 3 8% 3 3 3 2 3 5% 40%	4936
	11th to 20th	Day	14% 6% 2 5% 3 3 3 3 4 6% 51%	4980
	21st to end	Day	16% 8% 3 7% 4 4 4 3 5% 6% 41%	5462
April	1st to 10th	Day	14% 7% 3 5% 4 4 4 3 4 7% 45%	2245
	11th to 20th	Day	14% 7% 3 5% 4 4 5% 4 6% 7% 41%	2374
	21st to end	Day	11% 6% 2 6% 5% 4 5% 4 6% 7% 44%	2400
May	1st to 10th	Day	16% 8% 3 7% 5% 5% 4 4 5% 7% 37%	5575
	11th to 20th	Day	13% 6% 2 8% 5% 4 5% 4 6% 7% 39%	5862
	21st to end	Day	11% 7% 2 7% 5% 5% 5% 4 7% 9% 39%	6434
June	1st to 10th	Day	7% 4 1 6% 6% 6% 6% 5% 7% 11% 40%	2600
	11th to 20th	Day	5% 3 2 6% 5% 6% 6% 5% 8% 10% 46%	2600
	21st to end	Day	5% 4 2 5% 5% 6% 5% 5% 8% 10% 45%	2600
July	1st to 10th	Day	8% 5% 2 7% 6% 6% 6% 5% 8% 11% 36%	5900
	11th to 20th	Day	5% 3 2 5% 4 4 5% 4 7% 10% 52%	5900
	21st to end	Day	10% 7% 2 6% 4 5% 5% 3 6% 8% 43%	6422
August	1st to 10th	Day	2 2 1 3 3 3 3 3 5% 8% 68%	4234
	11th to 20th	Day	4 3 1 3 3 3 4 4 7% 10% 58%	4007
	21st to end	Day	8% 4 2 6% 5% 5% 6% 5% 8% 9% 41%	4312
September	1st to 10th	Day	9% 5% 2 5% 4 5% 5% 5% 6% 8% 46%	2330
	11th to 20th	Day	12% 7% 2 5% 4 4 4 4 6% 7% 45%	2200
	21st to end	Day	7% 3 2 4 3 4 4 4 5% 7% 57%	2200
October	1st to 10th	Day	6% 3 1 4 3 4 3 2 4 6% 64%	2010
	11th to 20th	Day	12% 5% 2 4 3 3 3 3 4 6% 57%	2000
	21st to end	Day	14% 5% 2 4 3 2 3 2 4 5% 56%	2200
November	1st to 10th	Day	13% 5% 1 6% 3 3 3 3 5% 5% 52%	2058
	11th to 20th	Day	9% 6% 2 6% 3 4 3 3 5% 5% 54%	2100
	21st to end	Day	17% 7% 3 6% 4 3 3 3 4 5% 45%	1995
December	1st to 10th	Day	19% 5% 2 6% 3 3 2 2 4 5% 48%	3030
	11th to 20th	Day	18% 8% 3 6% 4 4 4 3 5% 6% 40%	3454
	21st to end	Day	16% 9% 3 7% 4 3 3 3 4 4 45%	4488
January	1st to 10th	Night	16% 6% 2 5% 3 2 3 2 4 4 53%	5888
	11th to 20th	Night	13% 5% 2 3 2 2 3 2 3 6% 59%	5900
	21st to end	Night	27% 9% 2 5% 3 3 3 2 3 3 40%	6490
February	1st to 10th	Night	17% 8% 2 5% 4 3 3 3 5% 6% 45%	2600
	11th to 20th	Night	20% 8% 3 5% 4 2 2 2 4 5% 44%	2374
	21st to end	Night	19% 7% 2 5% 3 3 4 2 4 5% 46%	1815
March	1st to 10th	Night	20% 8% 2 6% 4 3 3 3 4 6% 42%	4919
	11th to 20th	Night	12% 6% 2 5% 3 4 3 3 5% 7% 51%	4980
	21st to end	Night	14% 7% 2 7% 5% 3 4 3 4 6% 45%	5467
April	1st to 10th	Night	12% 5% 2 6% 4 3 4 4 5% 8% 48%	2155
	11th to 20th	Night	12% 6% 2 6% 4 4 4 4 4 6% 48%	1975
	21st to end	Night	11% 6% 2 5% 4 4 3 3 5% 6% 51%	2000
May	1st to 10th	Night	16% 8% 3 8% 5% 4 3 4 5% 8% 37%	4324
	11th to 20th	Night	13% 7% 2 7% 4 4 4 3 5% 7% 43%	4053
	21st to end	Night	11% 6% 2 6% 4 4 4 4 6% 8% 45%	4443
June	1st to 10th	Night	5% 3 1 4 3 4 4 5% 7% 11% 53%	1800
	11th to 20th	Night	4 3 1 3 4 3 4 4 6% 10% 58%	1800
	21st to end	Night	5% 3 1 4 4 4 4 5% 6% 10% 54%	1800
July	1st to 10th	Night	7% 4 2 6% 5% 6% 5% 5% 8% 12% 40%	4078
	11th to 20th	Night	4 2 1 3 3 3 5% 4 7% 12% 56%	4077
	21st to end	Night	9% 5% 3 5% 4 3 4 4 6% 10% 48%	4449
August	1st to 10th	Night	2 2 1 2 1 2 2 3 4 7% 74%	2926
	11th to 20th	Night	3 2 1 3 2 3 3 3 7% 11% 62%	3046
	21st to end	Night	4 4 2 5% 3 5% 6% 5% 7% 9% 50%	3586
September	1st to 10th	Night	7% 5% 2 5% 5% 4 3 4 5% 8% 52%	2065
	11th to 20th	Night	10% 4 2 5% 3 5% 4 3 5% 7% 51%	2200
	21st to end	Night	7% 3 1 5% 3 3 2 3 5% 6% 62%	2200
October	1st to 10th	Night	5% 3 1 3 3 3 3 2 5% 6% 65%	2369
	11th to 20th	Night	11% 4 1 3 2 3 3 3 4 5% 62%	2400
	21st to end	Night	13% 4 1 5% 2 2 2 2 4 5% 59%	2640
November	1st to 10th	Night	12% 5% 1 4 4 3 3 2 4 6% 57%	2460
	11th to 20th	Night	9% 5% 1 5% 4 4 3 3 4 6% 57%	2520
	21st to end	Night	14% 6% 2 5% 4 3 3 3 5% 6% 49%	2620
December	1st to 10th	Night	18% 6% 2 5% 4 3 3 3 4 5% 48%	4380
	11th to 20th	Night	16% 8% 3 6% 4 4 4 2 3 4 46%	4908
	21st to end	Night	14% 9% 2 5% 4 3 3 2 3 4 50%	6490

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% 2 6% 24% 22% 3	4078
	11th to 20th	Day	32% 3 5% 23% 28% 10%	4080
	21st to end	Day	49% 2 3 14% 20% 13%	4488
February	1st to 10th	Day	49% 3 5% 15% 18% 11%	1800
	11th to 20th	Day	48% 4 5% 16% 18% 8%	1935
	21st to end	Day	47% 3 5% 13% 20% 11%	1815
March	1st to 10th	Day	48% 3 5% 12% 20% 12%	4936
	11th to 20th	Day	35% 4 4 16% 21% 20%	4980
	21st to end	Day	44% 3 8% 21% 19% 5%	5464
April	1st to 10th	Day	41% 5% 8% 21% 17% 7%	2245
	11th to 20th	Day	41% 7% 9% 17% 19% 8%	2374
	21st to end	Day	38% 6% 10% 20% 23% 4	2400
May	1st to 10th	Day	46% 6% 11% 25% 10% 2	5610
	11th to 20th	Day	44% 4 11% 17% 21% 2	5866
	21st to end	Day	40% 7% 12% 23% 16% 2	6447
June	1st to 10th	Day	35% 9% 16% 25% 14% 1	2600
	11th to 20th	Day	31% 9% 14% 27% 16% 3	2600
	21st to end	Day	31% 8% 16% 28% 15% 2	2600
July	1st to 10th	Day	40% 6% 24% 22% 7%	5836
	11th to 20th	Day	27% 5% 19% 36% 12%	5831
	21st to end	Day	39% 5% 14% 30% 12%	6240
August	1st to 10th	Day	16% 5% 14% 34% 29% 3	4220
	11th to 20th	Day	21% 5% 20% 39% 13% 1	4046
	21st to end	Day	36% 7% 17% 23% 15% 1	4311
September	1st to 10th	Day	34% 8% 12% 19% 18% 9%	2330
	11th to 20th	Day	37% 7% 12% 20% 17% 8%	2200
	21st to end	Day	27% 4 10% 23% 24% 11%	2200
October	1st to 10th	Day	14% 3 6% 13% 27% 37%	3270
	11th to 20th	Day	19% 3 5% 17% 32% 25%	3240
	21st to end	Day	28% 2 3 21% 34% 11%	3538
November	1st to 10th	Day	35% 4 8% 19% 26% 9%	2058
	11th to 20th	Day	32% 3 8% 20% 26% 12%	2100
	21st to end	Day	42% 4 6% 17% 24% 7%	1995
December	1st to 10th	Day	41% 2 7% 20% 25% 6%	3030
	11th to 20th	Day	46% 2 5% 14% 22% 10%	3452
	21st to end	Day	44% 2 5% 16% 27% 5%	4488
January	1st to 10th	Night	36% 2 6% 24% 27% 5%	5888
	11th to 20th	Night	29% 3 5% 19% 33% 12%	5900
	21st to end	Night	51% 2 4 13% 18% 12%	6490
February	1st to 10th	Night	41% 3 7% 18% 18% 13%	2600
	11th to 20th	Night	44% 3 6% 18% 20% 9%	2374
	21st to end	Night	42% 4 7% 14% 18% 14%	1815
March	1st to 10th	Night	45% 4 4 12% 22% 13%	4919
	11th to 20th	Night	34% 4 7% 15% 19% 21%	4980
	21st to end	Night	42% 4 8% 19% 20% 7%	5467
April	1st to 10th	Night	34% 6% 11% 20% 18% 11%	2155
	11th to 20th	Night	37% 5% 9% 19% 19% 12%	1975
	21st to end	Night	33% 6% 9% 21% 25% 6%	2000
May	1st to 10th	Night	46% 5% 10% 22% 13% 4	4354
	11th to 20th	Night	42% 5% 13% 17% 21% 3	4054
	21st to end	Night	35% 6% 15% 26% 13% 5%	4452
June	1st to 10th	Night	23% 9% 16% 29% 20% 2	1800
	11th to 20th	Night	21% 6% 17% 31% 20% 5%	1800
	21st to end	Night	25% 7% 16% 26% 24% 3	1800
July	1st to 10th	Night	36% 5% 26% 26% 6%	4035
	11th to 20th	Night	22% 5% 25% 33% 15% 1	4026
	21st to end	Night	33% 5% 18% 32% 10% 2	4320
August	1st to 10th	Night	11% 4 14% 34% 31% 5%	2916
	11th to 20th	Night	17% 5% 18% 45% 12% 3	3073
	21st to end	Night	28% 6% 18% 25% 20% 2	3586
September	1st to 10th	Night	31% 6% 13% 22% 19% 10%	2065
	11th to 20th	Night	31% 7% 12% 22% 19% 9%	2200
	21st to end	Night	23% 4 10% 22% 28% 13%	2200
October	1st to 10th	Night	13% 3 5% 14% 20% 43%	3876
	11th to 20th	Night	16% 2 4 17% 33% 28%	3899
	21st to end	Night	26% 2 4 18% 34% 16%	4252
November	1st to 10th	Night	30% 3 9% 20% 27% 12%	2460
	11th to 20th	Night	30% 4 8% 19% 25% 14%	2520
	21st to end	Night	37% 3 7% 18% 23% 11%	2620
December	1st to 10th	Night	41% 3 6% 17% 28% 6%	4380
	11th to 20th	Night	44% 2 8% 13% 23% 11%	4909
	21st to end	Night	40% 2 6% 17% 28% 7%	6490

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	24% 18% 38% 15% 5%	300
	11th to 20th	Day	26% 15% 39% 15% 5% 1	300
	21st to end	Day	26% 20% 36% 15% 2	330
February	1st to 10th	Day	29% 17% 35% 15% 4	300
	11th to 20th	Day	35% 19% 36% 9% 1	300
	21st to end	Day	32% 19% 38% 10% 2	249
March	1st to 10th	Day	30% 17% 33% 16% 5%	300
	11th to 20th	Day	19% 27% 36% 14% 3	300
	21st to end	Day	18% 23% 39% 16% 3	330
April	1st to 10th	Day	23% 16% 39% 17% 5%	345
	11th to 20th	Day	23% 14% 30% 23% 9% 1	492
	21st to end	Day	15% 14% 34% 27% 9% 2	500
May	1st to 10th	Day	12% 12% 37% 31% 7% 1	569
	11th to 20th	Day	16% 7% 28% 32% 14% 3	725
	21st to end	Day	12% 8% 26% 34% 16% 5%	789
June	1st to 10th	Day	8% 2 17% 37% 30% 6%	730
	11th to 20th	Day	5% 2 17% 40% 29% 7%	730
	21st to end	Day	5% 1 13% 33% 35% 13%	730
July	1st to 10th	Day	8% 1 12% 29% 37% 13%	721
	11th to 20th	Day	5% 1 7% 27% 45% 15%	718
	21st to end	Day	7% 1 7% 29% 43% 14%	794
August	1st to 10th	Day	5% 2 6% 24% 46% 17%	726
	11th to 20th	Day	7% 1 5% 25% 45% 16%	616
	21st to end	Day	12% 1 7% 21% 40% 20%	583
September	1st to 10th	Day	10% 1 8% 25% 41% 15%	460
	11th to 20th	Day	7% 1 12% 30% 33% 17%	330
	21st to end	Day	10% 2 13% 36% 28% 12%	330
October	1st to 10th	Day	5% 2 20% 40% 24% 8%	330
	11th to 20th	Day	9% 8% 29% 33% 16% 5%	330
	21st to end	Day	22% 11% 27% 24% 13% 3	363
November	1st to 10th	Day	17% 7% 33% 25% 16% 2	330
	11th to 20th	Day	12% 10% 34% 33% 8% 2	330
	21st to end	Day	19% 17% 34% 21% 7% 2	330
December	1st to 10th	Day	20% 13% 38% 20% 7% 2	330
	11th to 20th	Day	24% 15% 33% 21% 7% 1	321
	21st to end	Day	22% 19% 37% 16% 5% 1	330
January	1st to 10th	Night	21% 10% 35% 27% 7%	1000
	11th to 20th	Night	22% 14% 32% 25% 6%	1000
	21st to end	Night	23% 13% 32% 27% 4	1100
February	1st to 10th	Night	23% 12% 35% 27% 4	1000
	11th to 20th	Night	26% 15% 35% 21% 3	819
	21st to end	Night	23% 14% 39% 19% 4	495
March	1st to 10th	Night	20% 12% 35% 27% 5%	600
	11th to 20th	Night	16% 16% 36% 28% 4 1	600
	21st to end	Night	15% 13% 41% 25% 6%	660
April	1st to 10th	Night	14% 15% 39% 27% 6%	600
	11th to 20th	Night	14% 15% 36% 26% 9%	593
	21st to end	Night	13% 10% 37% 31% 8% 1	600
May	1st to 10th	Night	12% 9% 36% 30% 12%	600
	11th to 20th	Night	13% 7% 32% 30% 16% 2	591
	21st to end	Night	9% 5% 27% 39% 18% 3	650
June	1st to 10th	Night	4 1 14% 44% 33% 4	600
	11th to 20th	Night	3 2 15% 46% 30% 3	600
	21st to end	Night	6% 1 12% 37% 38% 7%	600
July	1st to 10th	Night	5% 1 9% 40% 37% 8%	585
	11th to 20th	Night	3 1 6% 37% 47% 5%	582
	21st to end	Night	4 1 8% 37% 41% 9%	657
August	1st to 10th	Night	4 1 5% 38% 47% 7%	597
	11th to 20th	Night	5% 1 4 39% 45% 6%	594
	21st to end	Night	9% 1 5% 35% 46% 6%	660
September	1st to 10th	Night	8% 2 8% 32% 44% 7%	600
	11th to 20th	Night	12% 1 7% 30% 44% 6%	600
	21st to end	Night	7% 2 10% 43% 34% 5%	600
October	1st to 10th	Night	6% 2 15% 40% 34% 4	769
	11th to 20th	Night	12% 5% 25% 36% 21% 2	800
	21st to end	Night	16% 9% 25% 31% 18% 2	880
November	1st to 10th	Night	12% 5% 25% 40% 17% 1	820
	11th to 20th	Night	12% 8% 30% 38% 11% 1	840
	21st to end	Night	17% 11% 32% 28% 11%	940
December	1st to 10th	Night	18% 12% 33% 30% 7%	1050
	11th to 20th	Night	21% 10% 32% 30% 6%	1036
	21st to end	Night	20% 13% 31% 30% 6%	1100

Page generated at 2025-12-15 00:13:54. Version ac07

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