Sea Rim State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sea Rim 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 7% 5% 5% 5% 4 7% 9% 39%	126782
	Night	13% 7% 2 6% 4 4 4 4 5% 8% 44%	124443
Transparency	Day	39% 6% 15% 20% 15% 6%	130390
	Night	38% 5% 13% 20% 17% 8%	128912
Seeing	Day	11% 5% 16% 26% 28% 13%	16290
	Night	13% 5% 18% 29% 28% 7%	26103

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	20% 10% 3 7% 4 3 3 2 4 5% 39%	4077
	11th to 20th	Day	15% 7% 3 6% 4 3 3 3 4 5% 47%	4080
	21st to end	Day	24% 9% 3 8% 4 3 3 3 5% 6% 32%	4488
February	1st to 10th	Day	18% 9% 3 8% 6% 3 3 4 5% 6% 34%	1800
	11th to 20th	Day	22% 9% 4 8% 3 3 3 2 4 5% 38%	2057
	21st to end	Day	21% 11% 3 7% 4 3 3 3 4 6% 35%	1815
March	1st to 10th	Day	20% 9% 3 8% 4 4 4 3 5% 7% 32%	4936
	11th to 20th	Day	16% 6% 2 7% 5% 5% 4 3 5% 6% 41%	4980
	21st to end	Day	18% 7% 3 7% 4 4 4 4 5% 5% 39%	5462
April	1st to 10th	Day	14% 8% 3 6% 5% 5% 4 3 5% 8% 39%	2250
	11th to 20th	Day	13% 7% 3 7% 5% 4 5% 5% 6% 7% 39%	2374
	21st to end	Day	9% 6% 2 6% 5% 4 5% 4 5% 9% 45%	2400
May	1st to 10th	Day	17% 8% 3 9% 6% 6% 6% 4 7% 8% 26%	5405
	11th to 20th	Day	10% 5% 2 7% 4 5% 5% 5% 7% 9% 41%	5538
	21st to end	Day	8% 6% 3 8% 5% 7% 7% 6% 9% 13% 29%	6434
June	1st to 10th	Day	5% 4 2 5% 5% 6% 6% 7% 10% 11% 39%	2600
	11th to 20th	Day	5% 4 2 6% 6% 6% 6% 6% 9% 12% 38%	2600
	21st to end	Day	7% 4 2 7% 7% 7% 7% 6% 10% 12% 31%	2600
July	1st to 10th	Day	7% 6% 2 6% 5% 5% 6% 7% 11% 15% 31%	5900
	11th to 20th	Day	6% 5% 2 8% 7% 7% 7% 6% 9% 12% 30%	5900
	21st to end	Day	8% 6% 2 8% 6% 6% 6% 5% 7% 10% 35%	6422
August	1st to 10th	Day	2 2 1 3 3 4 5% 5% 8% 12% 55%	4181
	11th to 20th	Day	3 3 1 4 4 5% 5% 6% 9% 13% 48%	3849
	21st to end	Day	8% 5% 2 8% 6% 6% 7% 6% 7% 9% 36%	4312
September	1st to 10th	Day	9% 6% 2 8% 6% 6% 6% 5% 8% 11% 35%	2356
	11th to 20th	Day	13% 7% 2 7% 5% 5% 5% 5% 7% 8% 37%	2200
	21st to end	Day	8% 5% 2 4 4 5% 5% 4 7% 9% 47%	2188
October	1st to 10th	Day	5% 4 2 4 4 4 4 3 5% 8% 56%	2000
	11th to 20th	Day	10% 3 1 3 3 4 4 3 5% 7% 56%	2000
	21st to end	Day	12% 4 2 4 3 3 3 2 4 7% 56%	2200
November	1st to 10th	Day	11% 6% 2 5% 4 3 5% 3 6% 6% 50%	2058
	11th to 20th	Day	11% 5% 2 5% 3 3 5% 3 6% 7% 50%	2100
	21st to end	Day	14% 7% 3 6% 4 4 3 3 5% 7% 44%	2100
December	1st to 10th	Day	21% 9% 3 7% 4 3 3 3 4 6% 38%	3178
	11th to 20th	Day	12% 7% 3 8% 5% 5% 5% 4 4 5% 42%	3454
	21st to end	Day	15% 7% 2 6% 4 3 4 3 4 5% 46%	4488
January	1st to 10th	Night	18% 7% 3 6% 4 3 4 3 5% 5% 43%	5888
	11th to 20th	Night	18% 8% 3 6% 4 3 3 2 4 5% 45%	5900
	21st to end	Night	27% 9% 3 7% 4 4 3 3 4 6% 30%	6490
February	1st to 10th	Night	18% 8% 3 6% 4 5% 4 3 4 6% 39%	2600
	11th to 20th	Night	19% 9% 3 6% 3 3 3 3 4 6% 41%	2243
	21st to end	Night	19% 11% 2 6% 4 4 3 3 5% 7% 37%	1815
March	1st to 10th	Night	19% 10% 3 6% 4 3 3 3 5% 6% 37%	4919
	11th to 20th	Night	18% 9% 3 6% 4 3 3 3 4 5% 42%	4980
	21st to end	Night	16% 10% 2 6% 4 4 4 3 4 6% 42%	5467
April	1st to 10th	Night	16% 8% 2 6% 4 4 5% 4 5% 7% 41%	2149
	11th to 20th	Night	15% 5% 2 5% 3 4 3 4 6% 7% 47%	1975
	21st to end	Night	10% 5% 2 5% 4 4 4 4 6% 8% 47%	2000
May	1st to 10th	Night	22% 8% 3 8% 5% 4 4 3 7% 9% 28%	4490
	11th to 20th	Night	12% 5% 2 6% 4 4 4 4 6% 9% 44%	4345
	21st to end	Night	11% 7% 2 7% 4 5% 5% 5% 8% 12% 35%	4443
June	1st to 10th	Night	5% 3 2 4 4 4 4 4 7% 11% 53%	1800
	11th to 20th	Night	4 4 2 5% 5% 3 5% 5% 8% 14% 46%	1800
	21st to end	Night	5% 5% 2 6% 5% 5% 5% 5% 9% 13% 40%	1800
July	1st to 10th	Night	5% 5% 2 6% 5% 4 5% 4 6% 14% 44%	4078
	11th to 20th	Night	2 3 2 6% 5% 5% 7% 5% 9% 12% 42%	4077
	21st to end	Night	5% 5% 2 8% 5% 6% 5% 5% 7% 10% 42%	4449
August	1st to 10th	Night	2 1 1 2 2 3 3 4 6% 10% 66%	2974
	11th to 20th	Night	3 2 1 3 3 3 4 4 8% 14% 57%	3200
	21st to end	Night	6% 3 1 6% 5% 6% 6% 5% 9% 12% 40%	3586
September	1st to 10th	Night	8% 5% 2 7% 5% 5% 4 5% 7% 11% 43%	2037
	11th to 20th	Night	11% 5% 3 7% 5% 4 4 4 7% 9% 42%	2200
	21st to end	Night	8% 4 2 5% 3 3 4 3 6% 8% 54%	2200
October	1st to 10th	Night	5% 5% 2 4 4 3 3 3 5% 7% 59%	2390
	11th to 20th	Night	8% 4 1 3 3 3 4 2 5% 8% 59%	2400
	21st to end	Night	11% 4 1 3 3 2 2 2 4 6% 60%	2640
November	1st to 10th	Night	8% 5% 2 5% 3 3 4 3 5% 7% 53%	2460
	11th to 20th	Night	12% 5% 1 5% 3 3 3 2 4 6% 55%	2520
	21st to end	Night	12% 6% 3 7% 4 4 4 4 5% 7% 45%	2520
December	1st to 10th	Night	21% 10% 3 9% 4 4 3 3 4 7% 33%	4210
	11th to 20th	Night	12% 8% 3 9% 4 4 4 3 5% 6% 42%	4908
	21st to end	Night	15% 8% 3 6% 3 3 3 3 4 5% 46%	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	49% 3 4 19% 19% 6%	4078
	11th to 20th	Day	41% 2 5% 20% 23% 9%	4080
	21st to end	Day	54% 3 5% 14% 15% 10%	4488
February	1st to 10th	Day	50% 4 6% 15% 16% 9%	1800
	11th to 20th	Day	52% 3 7% 14% 16% 8%	2068
	21st to end	Day	53% 3 7% 14% 15% 7%	1815
March	1st to 10th	Day	54% 3 8% 12% 14% 9%	4936
	11th to 20th	Day	44% 3 9% 13% 17% 14%	4980
	21st to end	Day	46% 4 12% 17% 20% 2	5464
April	1st to 10th	Day	43% 4 12% 18% 15% 9%	2250
	11th to 20th	Day	42% 4 12% 19% 16% 8%	2374
	21st to end	Day	34% 4 14% 24% 20% 5%	2400
May	1st to 10th	Day	52% 4 14% 18% 9% 2	5440
	11th to 20th	Day	37% 6% 14% 22% 19% 3	5542
	21st to end	Day	41% 7% 18% 26% 8%	6447
June	1st to 10th	Day	30% 6% 22% 28% 14%	2600
	11th to 20th	Day	31% 7% 19% 30% 11% 1	2600
	21st to end	Day	37% 8% 25% 23% 7%	2600
July	1st to 10th	Day	33% 11% 35% 19% 2	5836
	11th to 20th	Day	41% 13% 28% 17% 2	5831
	21st to end	Day	41% 10% 21% 24% 3	6240
August	1st to 10th	Day	18% 6% 20% 44% 13%	4167
	11th to 20th	Day	22% 8% 39% 27% 3	3885
	21st to end	Day	40% 9% 17% 21% 12% 1	4311
September	1st to 10th	Day	38% 9% 19% 17% 14% 3	2356
	11th to 20th	Day	41% 7% 15% 20% 15% 3	2200
	21st to end	Day	31% 5% 15% 25% 15% 9%	2188
October	1st to 10th	Day	21% 3 7% 16% 21% 31%	3260
	11th to 20th	Day	19% 3 6% 24% 37% 10%	3240
	21st to end	Day	25% 3 8% 15% 39% 10%	3538
November	1st to 10th	Day	34% 4 10% 23% 20% 8%	2058
	11th to 20th	Day	32% 5% 11% 19% 21% 12%	2100
	21st to end	Day	40% 4 9% 20% 18% 8%	2100
December	1st to 10th	Day	48% 3 8% 18% 18% 4	3178
	11th to 20th	Day	43% 5% 6% 17% 19% 10%	3452
	21st to end	Day	41% 3 6% 18% 23% 9%	4488
January	1st to 10th	Night	45% 3 6% 20% 19% 8%	5888
	11th to 20th	Night	44% 2 3 18% 23% 10%	5900
	21st to end	Night	56% 3 4 13% 14% 10%	6490
February	1st to 10th	Night	47% 3 7% 12% 20% 11%	2600
	11th to 20th	Night	45% 3 7% 17% 18% 9%	2243
	21st to end	Night	47% 4 9% 14% 15% 10%	1815
March	1st to 10th	Night	47% 3 9% 16% 15% 10%	4919
	11th to 20th	Night	45% 3 8% 13% 14% 16%	4980
	21st to end	Night	44% 3 10% 16% 20% 7%	5467
April	1st to 10th	Night	43% 4 9% 19% 16% 9%	2149
	11th to 20th	Night	38% 3 11% 21% 15% 12%	1975
	21st to end	Night	34% 4 13% 23% 20% 6%	2000
May	1st to 10th	Night	51% 4 13% 20% 8% 3	4520
	11th to 20th	Night	36% 5% 13% 26% 18% 4	4346
	21st to end	Night	38% 6% 20% 28% 8% 1	4452
June	1st to 10th	Night	24% 5% 21% 34% 15%	1800
	11th to 20th	Night	26% 7% 19% 32% 14% 1	1800
	21st to end	Night	34% 7% 26% 25% 7%	1800
July	1st to 10th	Night	31% 8% 39% 21% 2	4035
	11th to 20th	Night	30% 10% 37% 20% 2	4026
	21st to end	Night	37% 8% 21% 29% 5%	4320
August	1st to 10th	Night	14% 5% 21% 44% 16%	2964
	11th to 20th	Night	17% 7% 40% 33% 4	3230
	21st to end	Night	33% 12% 21% 22% 11% 1	3586
September	1st to 10th	Night	35% 8% 21% 19% 13% 4	2037
	11th to 20th	Night	38% 6% 17% 20% 16% 4	2200
	21st to end	Night	30% 5% 14% 24% 19% 8%	2200
October	1st to 10th	Night	21% 4 7% 16% 20% 32%	3910
	11th to 20th	Night	16% 4 6% 27% 30% 17%	3899
	21st to end	Night	20% 2 6% 14% 42% 16%	4252
November	1st to 10th	Night	31% 4 11% 22% 23% 9%	2460
	11th to 20th	Night	32% 3 8% 20% 25% 11%	2520
	21st to end	Night	39% 4 9% 20% 19% 9%	2520
December	1st to 10th	Night	53% 3 7% 17% 16% 5%	4210
	11th to 20th	Night	40% 6% 8% 16% 19% 12%	4909
	21st to end	Night	42% 3 6% 16% 26% 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	22% 10% 33% 25% 9%	300
	11th to 20th	Day	16% 10% 32% 30% 11% 1	300
	21st to end	Day	20% 11% 34% 27% 7% 1	330
February	1st to 10th	Day	22% 6% 34% 28% 10%	300
	11th to 20th	Day	26% 13% 30% 27% 5%	300
	21st to end	Day	21% 9% 39% 26% 5%	249
March	1st to 10th	Day	18% 8% 38% 29% 7%	300
	11th to 20th	Day	18% 13% 41% 22% 5% 1	300
	21st to end	Day	15% 11% 31% 35% 8% 1	330
April	1st to 10th	Day	13% 11% 32% 32% 11%	350
	11th to 20th	Day	16% 10% 32% 24% 17% 1	492
	21st to end	Day	10% 6% 25% 38% 18% 2	500
May	1st to 10th	Day	13% 8% 26% 33% 18% 3	503
	11th to 20th	Day	10% 5% 19% 37% 26% 4	583
	21st to end	Day	8% 3 16% 39% 29% 5%	789
June	1st to 10th	Day	6% 1 9% 33% 36% 14%	730
	11th to 20th	Day	7% 2 9% 30% 39% 13%	730
	21st to end	Day	9% 2 5% 24% 41% 19%	730
July	1st to 10th	Day	6% 2 4 19% 42% 26%	721
	11th to 20th	Day	6% 1 1 17% 44% 31%	718
	21st to end	Day	6% 1 3 17% 45% 27%	794
August	1st to 10th	Day	3 1 1 11% 52% 32%	699
	11th to 20th	Day	5% 1 2 8% 42% 42%	519
	21st to end	Day	12% 2 4 14% 35% 33%	583
September	1st to 10th	Day	10% 1 6% 17% 41% 25%	486
	11th to 20th	Day	12% 1 5% 19% 37% 26%	330
	21st to end	Day	11% 1 6% 22% 41% 19%	330
October	1st to 10th	Day	6% 2 7% 32% 38% 14%	330
	11th to 20th	Day	10% 2 10% 33% 34% 11%	330
	21st to end	Day	13% 7% 18% 30% 26% 6%	363
November	1st to 10th	Day	14% 4 18% 30% 30% 5%	330
	11th to 20th	Day	13% 5% 19% 41% 18% 4	330
	21st to end	Day	16% 9% 29% 28% 15% 3	330
December	1st to 10th	Day	21% 7% 23% 27% 16% 6%	330
	11th to 20th	Day	16% 7% 26% 38% 11% 1	321
	21st to end	Day	21% 8% 30% 26% 14% 2	330
January	1st to 10th	Night	21% 8% 28% 34% 10%	1000
	11th to 20th	Night	20% 8% 27% 35% 10% 1	1000
	21st to end	Night	22% 6% 28% 35% 9%	1100
February	1st to 10th	Night	21% 6% 29% 34% 9%	1000
	11th to 20th	Night	23% 12% 25% 31% 10%	688
	21st to end	Night	21% 8% 32% 32% 6%	495
March	1st to 10th	Night	19% 8% 29% 32% 12%	600
	11th to 20th	Night	18% 8% 26% 36% 12% 1	600
	21st to end	Night	12% 6% 27% 37% 16% 1	660
April	1st to 10th	Night	17% 8% 24% 36% 15%	600
	11th to 20th	Night	16% 8% 25% 36% 16% 1	593
	21st to end	Night	11% 5% 27% 37% 18% 1	600
May	1st to 10th	Night	12% 6% 23% 42% 17%	600
	11th to 20th	Night	9% 3 19% 41% 25% 2	591
	21st to end	Night	7% 3 12% 37% 35% 6%	650
June	1st to 10th	Night	5% 1 4 31% 50% 9%	600
	11th to 20th	Night	4 1 6% 25% 52% 11%	600
	21st to end	Night	6% 1 6% 17% 51% 19%	600
July	1st to 10th	Night	6% 2 4 12% 49% 27%	585
	11th to 20th	Night	3 1 2 9% 48% 38%	582
	21st to end	Night	3 1 3 10% 58% 26%	657
August	1st to 10th	Night	2 1 1 5% 59% 33%	597
	11th to 20th	Night	4 2 7% 55% 32%	594
	21st to end	Night	8% 1 2 14% 51% 23%	660
September	1st to 10th	Night	8% 2 5% 15% 48% 23%	600
	11th to 20th	Night	10% 2 4 18% 51% 15%	600
	21st to end	Night	11% 1 6% 22% 48% 12%	600
October	1st to 10th	Night	6% 3 9% 28% 47% 8%	790
	11th to 20th	Night	9% 2 15% 34% 35% 6%	800
	21st to end	Night	12% 5% 14% 34% 30% 4	880
November	1st to 10th	Night	10% 3 17% 33% 32% 5%	820
	11th to 20th	Night	14% 5% 18% 38% 25% 1	840
	21st to end	Night	13% 4 29% 34% 16% 2	840
December	1st to 10th	Night	21% 6% 22% 32% 18% 1	945
	11th to 20th	Night	18% 8% 24% 35% 14%	1036
	21st to end	Night	21% 7% 26% 34% 12%	1100

Page generated at 2025-12-15 00:13:50. Version ac07

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