Harrington Beach State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Harrington Beach State Park clear sky chart from 2005-11-06 to 2025-11-03.

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% 8% 3 7% 5% 4 5% 4 6% 8% 39%	126811
	Night	13% 9% 3 7% 5% 4 4 4 5% 7% 38%	123478
Transparency	Day	43% 5% 12% 25% 13% 2	130311
	Night	45% 5% 11% 23% 15% 2	128052
Seeing	Day	15% 4 19% 33% 23% 6%	17296
	Night	18% 7% 25% 31% 17% 3	27109

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	10% 11% 5% 11% 5% 5% 5% 5% 7% 7% 29%	3617
	11th to 20th	Day	10% 9% 3 10% 5% 4 7% 7% 7% 7% 30%	3620
	21st to end	Day	13% 14% 6% 8% 5% 3 4 3 5% 7% 33%	3982
February	1st to 10th	Day	11% 12% 6% 11% 6% 4 4 5% 6% 7% 29%	1785
	11th to 20th	Day	12% 11% 4 8% 6% 5% 5% 4 5% 5% 36%	1948
	21st to end	Day	11% 11% 4 10% 5% 4 4 5% 5% 7% 33%	1650
March	1st to 10th	Day	13% 7% 3 6% 4 4 4 4 6% 6% 44%	4480
	11th to 20th	Day	11% 6% 2 7% 5% 5% 5% 3 5% 7% 43%	4652
	21st to end	Day	21% 10% 4 9% 5% 4 4 3 5% 6% 29%	5967
April	1st to 10th	Day	16% 12% 3 6% 5% 4 5% 5% 6% 6% 32%	2400
	11th to 20th	Day	16% 8% 3 7% 5% 5% 5% 4 5% 6% 35%	2374
	21st to end	Day	17% 9% 2 8% 5% 5% 4 4 6% 6% 34%	2562
May	1st to 10th	Day	15% 7% 3 7% 4 4 4 3 5% 7% 42%	5862
	11th to 20th	Day	12% 9% 4 7% 4 5% 5% 4 6% 7% 37%	6309
	21st to end	Day	15% 6% 2 5% 4 4 4 4 6% 8% 42%	6935
June	1st to 10th	Day	10% 5% 2 6% 6% 4 5% 4 7% 7% 44%	2800
	11th to 20th	Day	11% 7% 2 6% 5% 5% 4 4 6% 9% 41%	2800
	21st to end	Day	8% 6% 2 5% 4 4 5% 5% 7% 10% 44%	2800
July	1st to 10th	Day	10% 5% 2 7% 5% 4 5% 4 7% 10% 41%	6360
	11th to 20th	Day	6% 4 2 5% 4 4 5% 4 7% 10% 49%	6360
	21st to end	Day	7% 5% 2 6% 4 4 5% 4 7% 9% 46%	6924
August	1st to 10th	Day	10% 5% 2 5% 5% 6% 5% 4 6% 9% 44%	4533
	11th to 20th	Day	10% 4 2 5% 4 4 4 4 5% 7% 51%	3992
	21st to end	Day	8% 5% 2 7% 4 4 5% 4 6% 8% 47%	4312
September	1st to 10th	Day	10% 5% 3 6% 4 5% 4 4 6% 8% 47%	2400
	11th to 20th	Day	11% 5% 2 6% 4 3 4 3 5% 8% 49%	2266
	21st to end	Day	11% 7% 2 7% 4 4 5% 4 6% 8% 43%	2200
October	1st to 10th	Day	13% 5% 3 6% 4 4 4 3 6% 6% 46%	2146
	11th to 20th	Day	19% 8% 3 7% 5% 5% 4 4 7% 7% 31%	1945
	21st to end	Day	15% 8% 2 8% 5% 4 4 4 5% 6% 37%	1980
November	1st to 10th	Day	12% 7% 4 7% 5% 4 4 4 5% 7% 42%	1780
	11th to 20th	Day	11% 12% 3 8% 7% 5% 6% 4 7% 8% 31%	1800
	21st to end	Day	17% 11% 3 8% 4 4 3 3 5% 8% 35%	1670
December	1st to 10th	Day	11% 10% 4 6% 6% 5% 5% 4 7% 9% 33%	2610
	11th to 20th	Day	13% 14% 4 8% 6% 6% 6% 5% 7% 7% 24%	3008
	21st to end	Day	21% 18% 6% 11% 5% 4 4 4 5% 5% 16%	3982
January	1st to 10th	Night	11% 11% 6% 11% 5% 4 4 3 5% 5% 34%	6348
	11th to 20th	Night	12% 13% 4 12% 7% 5% 7% 6% 6% 5% 24%	6360
	21st to end	Night	12% 14% 5% 8% 5% 4 4 4 5% 6% 32%	6996
February	1st to 10th	Night	13% 13% 5% 8% 6% 5% 5% 4 6% 5% 31%	2611
	11th to 20th	Night	12% 10% 4 8% 5% 4 5% 3 5% 5% 39%	2338
	21st to end	Night	16% 13% 3 7% 4 4 3 3 6% 6% 35%	1980
March	1st to 10th	Night	15% 7% 2 5% 4 4 4 3 5% 6% 44%	5373
	11th to 20th	Night	11% 6% 2 6% 4 4 5% 4 6% 8% 44%	5348
	21st to end	Night	18% 12% 4 8% 5% 5% 4 3 4 5% 31%	4964
April	1st to 10th	Night	17% 10% 3 6% 5% 3 4 4 4 6% 38%	2000
	11th to 20th	Night	20% 9% 2 6% 4 3 4 3 5% 5% 39%	1975
	21st to end	Night	17% 7% 2 6% 4 3 4 3 6% 7% 40%	1836
May	1st to 10th	Night	15% 6% 3 7% 4 4 4 3 6% 8% 39%	4033
	11th to 20th	Night	11% 7% 5% 8% 4 4 5% 5% 6% 7% 38%	3602
	21st to end	Night	18% 7% 3 6% 4 4 4 3 4 7% 40%	3942
June	1st to 10th	Night	11% 5% 2 7% 4 4 4 4 5% 9% 45%	1600
	11th to 20th	Night	13% 5% 2 7% 5% 4 4 3 6% 8% 42%	1600
	21st to end	Night	9% 6% 3 6% 4 4 5% 4 6% 6% 47%	1600
July	1st to 10th	Night	9% 5% 2 6% 5% 4 5% 4 6% 9% 44%	3618
	11th to 20th	Night	6% 4 2 5% 4 4 5% 3 6% 8% 53%	3617
	21st to end	Night	6% 4 2 6% 4 4 4 4 6% 9% 50%	3947
August	1st to 10th	Night	10% 4 2 6% 4 4 4 3 6% 9% 48%	2623
	11th to 20th	Night	9% 5% 2 6% 4 4 5% 3 6% 8% 48%	3040
	21st to end	Night	8% 4 2 5% 4 5% 5% 4 6% 8% 50%	3586
September	1st to 10th	Night	9% 4 2 5% 5% 3 5% 3 5% 7% 52%	2000
	11th to 20th	Night	10% 4 2 5% 4 4 4 3 5% 7% 53%	2113
	21st to end	Night	13% 6% 2 6% 4 4 3 3 6% 6% 46%	2200
October	1st to 10th	Night	13% 6% 2 6% 3 4 3 3 5% 6% 49%	2250
	11th to 20th	Night	18% 8% 2 6% 3 4 4 4 6% 6% 40%	2455
	21st to end	Night	19% 8% 3 6% 4 4 4 4 6% 7% 36%	2860
November	1st to 10th	Night	12% 9% 3 5% 4 4 5% 4 4 6% 45%	2563
	11th to 20th	Night	14% 11% 3 8% 6% 4 5% 4 5% 6% 34%	2600
	21st to end	Night	16% 10% 3 6% 5% 5% 5% 3 5% 6% 35%	2725
December	1st to 10th	Night	12% 11% 3 7% 3 3 4 3 6% 8% 40%	4580
	11th to 20th	Night	16% 17% 5% 8% 5% 5% 4 4 5% 5% 26%	5199
	21st to end	Night	21% 17% 5% 9% 5% 5% 4 3 5% 6% 19%	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	53% 5% 14% 20% 7%	3618
	11th to 20th	Day	50% 10% 8% 15% 16% 2	3620
	21st to end	Day	53% 5% 9% 20% 14%	3982
February	1st to 10th	Day	53% 8% 10% 19% 9% 1	1785
	11th to 20th	Day	49% 5% 11% 22% 11% 2	1958
	21st to end	Day	51% 5% 11% 20% 11% 2	1650
March	1st to 10th	Day	40% 4 13% 24% 13% 6%	4480
	11th to 20th	Day	41% 4 15% 24% 14% 2	4652
	21st to end	Day	57% 3 12% 17% 11% 1	5969
April	1st to 10th	Day	50% 6% 13% 20% 11% 1	2400
	11th to 20th	Day	49% 5% 10% 21% 13% 3	2374
	21st to end	Day	49% 6% 15% 17% 11% 2	2562
May	1st to 10th	Day	43% 4 11% 25% 15% 2	5897
	11th to 20th	Day	42% 8% 10% 24% 14% 1	6313
	21st to end	Day	40% 5% 10% 28% 15% 3	6949
June	1st to 10th	Day	37% 6% 12% 28% 15% 3	2800
	11th to 20th	Day	39% 5% 14% 24% 16% 1	2800
	21st to end	Day	34% 7% 16% 26% 16% 2	2800
July	1st to 10th	Day	40% 3 13% 33% 10% 1	6291
	11th to 20th	Day	31% 3 15% 35% 15% 1	6285
	21st to end	Day	34% 4 16% 25% 18% 2	6728
August	1st to 10th	Day	37% 4 17% 29% 12% 1	4518
	11th to 20th	Day	33% 3 15% 37% 11% 1	4031
	21st to end	Day	36% 4 15% 26% 19% 1	4311
September	1st to 10th	Day	36% 6% 13% 29% 15% 2	2400
	11th to 20th	Day	34% 5% 14% 31% 15% 1	2266
	21st to end	Day	38% 5% 13% 31% 13%	2200
October	1st to 10th	Day	25% 3 7% 41% 23% 2	3497
	11th to 20th	Day	40% 4 10% 27% 20% 1	3148
	21st to end	Day	42% 3 11% 29% 14% 1	3180
November	1st to 10th	Day	42% 5% 14% 24% 13% 1	1780
	11th to 20th	Day	51% 6% 14% 20% 8% 1	1800
	21st to end	Day	50% 5% 14% 24% 7%	1670
December	1st to 10th	Day	48% 7% 18% 21% 6% 1	2610
	11th to 20th	Day	56% 5% 11% 17% 9% 1	3005
	21st to end	Day	70% 4 6% 13% 7%	3982
January	1st to 10th	Night	53% 5% 7% 22% 12% 1	6348
	11th to 20th	Night	60% 8% 7% 9% 15% 1	6360
	21st to end	Night	53% 4 13% 18% 12%	6996
February	1st to 10th	Night	53% 6% 9% 19% 12% 1	2611
	11th to 20th	Night	48% 5% 10% 23% 13% 2	2339
	21st to end	Night	50% 6% 11% 19% 12% 2	1980
March	1st to 10th	Night	43% 3 14% 24% 13% 3	5373
	11th to 20th	Night	38% 4 14% 25% 16% 3	5348
	21st to end	Night	57% 3 9% 17% 13% 1	4964
April	1st to 10th	Night	48% 5% 9% 20% 17% 1	2000
	11th to 20th	Night	48% 4 7% 21% 16% 4	1975
	21st to end	Night	43% 5% 13% 23% 14% 2	1836
May	1st to 10th	Night	43% 5% 12% 20% 18% 2	4060
	11th to 20th	Night	42% 7% 12% 21% 16% 2	3603
	21st to end	Night	46% 3 8% 24% 13% 6%	3950
June	1st to 10th	Night	35% 6% 11% 29% 18% 2	1600
	11th to 20th	Night	38% 5% 10% 25% 19% 3	1600
	21st to end	Night	36% 7% 14% 23% 18% 3	1600
July	1st to 10th	Night	38% 2 13% 32% 11% 3	3580
	11th to 20th	Night	29% 3 14% 34% 18% 2	3572
	21st to end	Night	31% 3 16% 24% 23% 2	3832
August	1st to 10th	Night	34% 4 15% 26% 19% 2	2614
	11th to 20th	Night	35% 4 12% 32% 16% 1	3067
	21st to end	Night	33% 4 12% 27% 21% 4	3586
September	1st to 10th	Night	31% 6% 10% 28% 22% 2	2000
	11th to 20th	Night	31% 5% 9% 36% 18% 2	2113
	21st to end	Night	38% 5% 9% 31% 15% 1	2200
October	1st to 10th	Night	27% 3 7% 41% 22% 1	3679
	11th to 20th	Night	37% 3 12% 27% 19% 2	3991
	21st to end	Night	43% 4 9% 26% 18%	4610
November	1st to 10th	Night	39% 6% 11% 25% 17% 2	2563
	11th to 20th	Night	50% 6% 11% 20% 11% 2	2600
	21st to end	Night	50% 6% 15% 21% 8% 1	2725
December	1st to 10th	Night	43% 5% 17% 26% 6% 3	4580
	11th to 20th	Night	61% 4 9% 12% 11% 2	5201
	21st to end	Night	67% 5% 8% 14% 7%	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	17% 9% 30% 34% 9% 2	300
	11th to 20th	Day	14% 9% 34% 31% 11%	300
	21st to end	Day	19% 6% 29% 33% 11% 1	330
February	1st to 10th	Day	15% 8% 35% 31% 9% 2	300
	11th to 20th	Day	16% 10% 35% 29% 10%	300
	21st to end	Day	18% 6% 37% 35% 3 1	249
March	1st to 10th	Day	14% 6% 37% 33% 9%	300
	11th to 20th	Day	18% 6% 31% 29% 14% 2	339
	21st to end	Day	26% 4 26% 31% 11% 1	550
April	1st to 10th	Day	24% 5% 28% 30% 13%	500
	11th to 20th	Day	20% 5% 27% 31% 14% 4	492
	21st to end	Day	19% 3 22% 36% 17% 3	500
May	1st to 10th	Day	18% 3 21% 40% 16% 2	503
	11th to 20th	Day	19% 3 17% 33% 24% 5%	715
	21st to end	Day	15% 2 13% 35% 26% 9%	789
June	1st to 10th	Day	11% 2 13% 39% 30% 6%	730
	11th to 20th	Day	14% 1 12% 40% 25% 7%	730
	21st to end	Day	12% 2 12% 40% 29% 6%	730
July	1st to 10th	Day	8% 1 7% 31% 40% 13%	721
	11th to 20th	Day	9% 2 9% 34% 36% 10%	718
	21st to end	Day	6% 1 8% 40% 37% 8%	794
August	1st to 10th	Day	8% 2 8% 34% 36% 12%	709
	11th to 20th	Day	11% 1 8% 30% 36% 15%	519
	21st to end	Day	9% 2 9% 34% 34% 11%	583
September	1st to 10th	Day	12% 4 12% 31% 31% 10%	530
	11th to 20th	Day	12% 2 10% 28% 34% 15%	530
	21st to end	Day	15% 5% 17% 29% 24% 10%	530
October	1st to 10th	Day	18% 4 18% 28% 26% 7%	476
	11th to 20th	Day	20% 7% 26% 33% 12% 2	330
	21st to end	Day	20% 7% 26% 34% 11% 2	363
November	1st to 10th	Day	14% 6% 26% 35% 17% 2	306
	11th to 20th	Day	16% 10% 34% 27% 12%	300
	21st to end	Day	24% 7% 29% 31% 9%	300
December	1st to 10th	Day	19% 9% 36% 25% 11%	300
	11th to 20th	Day	20% 10% 36% 24% 9% 2	300
	21st to end	Day	26% 10% 32% 24% 6% 2	330
January	1st to 10th	Night	19% 14% 36% 24% 7%	1000
	11th to 20th	Night	22% 12% 34% 25% 6% 1	1000
	21st to end	Night	19% 11% 35% 27% 8%	1100
February	1st to 10th	Night	19% 10% 35% 30% 5% 1	988
	11th to 20th	Night	17% 11% 37% 26% 8%	783
	21st to end	Night	24% 8% 33% 29% 5%	660
March	1st to 10th	Night	18% 6% 30% 34% 11% 1	800
	11th to 20th	Night	14% 8% 32% 33% 12% 1	800
	21st to end	Night	22% 4 24% 36% 13% 1	662
April	1st to 10th	Night	22% 7% 28% 32% 10% 1	600
	11th to 20th	Night	25% 4 22% 33% 13% 3	593
	21st to end	Night	20% 3 21% 38% 17% 1	600
May	1st to 10th	Night	18% 3 17% 42% 18% 2	600
	11th to 20th	Night	18% 3 17% 33% 25% 4	591
	21st to end	Night	14% 2 13% 34% 29% 8%	650
June	1st to 10th	Night	13% 2 11% 43% 25% 7%	600
	11th to 20th	Night	15% 1 12% 40% 27% 6%	600
	21st to end	Night	10% 2 12% 40% 32% 5%	600
July	1st to 10th	Night	9% 2 5% 32% 42% 10%	585
	11th to 20th	Night	7% 1 8% 38% 36% 10%	582
	21st to end	Night	7% 2 9% 38% 39% 6%	657
August	1st to 10th	Night	7% 1 7% 38% 38% 8%	597
	11th to 20th	Night	9% 2 10% 35% 33% 11%	594
	21st to end	Night	10% 3 11% 35% 37% 5%	660
September	1st to 10th	Night	10% 3 16% 33% 30% 9%	600
	11th to 20th	Night	10% 3 16% 27% 33% 12%	713
	21st to end	Night	16% 4 19% 28% 25% 8%	800
October	1st to 10th	Night	17% 4 21% 31% 23% 5%	800
	11th to 20th	Night	22% 8% 27% 29% 13% 1	800
	21st to end	Night	23% 9% 27% 29% 11% 2	880
November	1st to 10th	Night	16% 8% 32% 31% 11% 2	789
	11th to 20th	Night	20% 11% 33% 27% 8%	800
	21st to end	Night	21% 11% 34% 28% 6%	925
December	1st to 10th	Night	22% 14% 35% 24% 5%	1000
	11th to 20th	Night	24% 13% 34% 21% 7% 1	1000
	21st to end	Night	29% 10% 31% 25% 4	1100

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