Seawall Campground
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Seawall Campground 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	19% 10% 3 6% 4 4 4 3 5% 7% 36%	126594
	Night	19% 10% 3 7% 4 4 4 3 5% 6% 35%	124497
Transparency	Day	48% 5% 12% 21% 13% 2	130130
	Night	49% 4 12% 20% 13% 2	129050
Seeing	Day	23% 11% 27% 26% 11% 2	17319
	Night	24% 13% 27% 24% 10% 1	25644

By Month

Percentage Cloud Cover NE (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% 10% 3 7% 6% 5% 4 4 5% 7% 33%	3597
	11th to 20th	Day	15% 9% 3 6% 4 4 4 3 4 6% 39%	3570
	21st to end	Day	15% 11% 3 6% 4 4 3 3 5% 6% 40%	4164
February	1st to 10th	Day	18% 13% 3 6% 6% 5% 4 4 6% 8% 29%	1800
	11th to 20th	Day	15% 8% 3 7% 5% 4 4 4 6% 8% 33%	1843
	21st to end	Day	14% 10% 3 7% 6% 4 4 4 6% 6% 36%	1650
March	1st to 10th	Day	24% 11% 2 6% 4 4 4 3 5% 6% 31%	4562
	11th to 20th	Day	21% 10% 3 6% 4 4 3 2 5% 6% 37%	4980
	21st to end	Day	29% 8% 2 5% 4 3 4 4 5% 5% 30%	5466
April	1st to 10th	Day	21% 9% 2 6% 5% 3 3 3 4 6% 37%	2341
	11th to 20th	Day	21% 8% 2 4 3 4 3 2 5% 8% 39%	2564
	21st to end	Day	20% 7% 3 6% 4 4 4 3 4 6% 38%	2600
May	1st to 10th	Day	28% 11% 4 7% 4 3 4 3 4 5% 26%	5886
	11th to 20th	Day	19% 10% 3 8% 5% 4 4 3 5% 6% 34%	5861
	21st to end	Day	20% 12% 3 7% 4 4 4 3 5% 6% 32%	7020
June	1st to 10th	Day	22% 9% 3 7% 4 4 4 3 5% 7% 33%	3000
	11th to 20th	Day	19% 8% 2 5% 4 4 3 3 6% 8% 38%	3000
	21st to end	Day	25% 10% 3 6% 4 4 3 4 5% 6% 31%	3000
July	1st to 10th	Day	21% 12% 4 7% 4 4 5% 4 5% 7% 28%	6590
	11th to 20th	Day	17% 14% 3 7% 4 4 5% 4 5% 8% 30%	6360
	21st to end	Day	15% 7% 2 5% 3 4 5% 5% 5% 8% 41%	6704
August	1st to 10th	Day	20% 10% 3 7% 4 4 4 4 5% 7% 33%	4235
	11th to 20th	Day	17% 10% 3 7% 5% 4 4 3 5% 7% 36%	4175
	21st to end	Day	10% 6% 2 6% 3 3 4 3 5% 7% 51%	4675
September	1st to 10th	Day	12% 6% 2 5% 3 4 4 3 5% 8% 47%	2293
	11th to 20th	Day	12% 7% 2 4 3 4 4 3 3 6% 53%	2200
	21st to end	Day	17% 7% 2 6% 3 3 4 3 4 7% 44%	2200
October	1st to 10th	Day	16% 7% 2 5% 4 3 4 3 6% 6% 44%	2126
	11th to 20th	Day	17% 7% 2 6% 4 4 4 3 4 7% 43%	2000
	21st to end	Day	22% 9% 2 5% 3 2 4 3 5% 5% 40%	2003
November	1st to 10th	Day	17% 7% 2 6% 5% 3 4 3 5% 6% 42%	1851
	11th to 20th	Day	19% 6% 2 6% 3 3 4 3 5% 8% 41%	1832
	21st to end	Day	20% 10% 3 6% 3 3 4 3 6% 6% 36%	1680
December	1st to 10th	Day	20% 9% 2 4 3 3 3 2 5% 6% 42%	2601
	11th to 20th	Day	21% 8% 3 6% 4 3 4 3 4 5% 39%	2667
	21st to end	Day	20% 12% 2 7% 4 3 3 3 4 6% 36%	3498
January	1st to 10th	Night	13% 11% 3 7% 4 4 4 4 5% 7% 36%	6349
	11th to 20th	Night	14% 12% 4 11% 6% 5% 4 3 5% 6% 31%	6315
	21st to end	Night	14% 10% 3 8% 4 4 5% 4 5% 6% 37%	6790
February	1st to 10th	Night	19% 10% 4 7% 6% 5% 4 4 6% 7% 28%	2600
	11th to 20th	Night	15% 11% 3 7% 4 4 4 3 7% 6% 36%	2439
	21st to end	Night	16% 10% 3 7% 5% 4 5% 3 5% 6% 37%	1980
March	1st to 10th	Night	26% 11% 3 6% 4 4 4 3 4 4 31%	5276
	11th to 20th	Night	16% 11% 3 6% 4 4 5% 4 6% 8% 31%	4979
	21st to end	Night	27% 9% 3 5% 4 4 4 3 4 5% 31%	5466
April	1st to 10th	Night	23% 11% 2 6% 4 4 4 3 4 5% 34%	2055
	11th to 20th	Night	21% 10% 3 6% 4 3 4 3 6% 7% 33%	1785
	21st to end	Night	24% 10% 3 6% 5% 4 3 4 5% 6% 33%	1800
May	1st to 10th	Night	29% 10% 3 9% 4 3 4 3 5% 6% 25%	4054
	11th to 20th	Night	24% 8% 2 7% 4 4 5% 3 6% 7% 30%	4033
	21st to end	Night	18% 12% 4 8% 6% 4 4 4 5% 7% 31%	3909
June	1st to 10th	Night	26% 9% 2 7% 3 3 5% 4 5% 8% 29%	1400
	11th to 20th	Night	20% 9% 3 6% 4 3 3 4 6% 7% 37%	1400
	21st to end	Night	26% 10% 3 6% 4 3 3 3 5% 6% 31%	1400
July	1st to 10th	Night	19% 12% 4 9% 5% 5% 5% 4 6% 7% 24%	3374
	11th to 20th	Night	19% 15% 3 8% 4 4 4 3 5% 6% 28%	3600
	21st to end	Night	13% 9% 3 7% 4 4 5% 4 6% 7% 38%	4102
August	1st to 10th	Night	23% 13% 4 7% 4 4 4 3 5% 6% 28%	2915
	11th to 20th	Night	19% 10% 3 6% 4 5% 6% 4 5% 7% 31%	2872
	21st to end	Night	10% 7% 3 7% 4 4 4 3 4 8% 46%	3223
September	1st to 10th	Night	14% 6% 2 5% 3 3 4 3 5% 7% 48%	2104
	11th to 20th	Night	16% 8% 2 4 3 2 3 3 4 6% 50%	2200
	21st to end	Night	17% 7% 2 5% 4 3 4 3 5% 7% 45%	2200
October	1st to 10th	Night	19% 6% 2 5% 3 3 3 3 5% 6% 43%	2273
	11th to 20th	Night	17% 7% 2 6% 3 3 4 3 6% 7% 43%	2400
	21st to end	Night	23% 8% 2 5% 4 3 4 3 4 7% 36%	2835
November	1st to 10th	Night	18% 7% 2 5% 4 3 4 3 5% 6% 43%	2667
	11th to 20th	Night	17% 9% 2 7% 4 4 4 3 6% 7% 38%	2785
	21st to end	Night	19% 9% 3 5% 4 4 4 3 6% 7% 36%	2940
December	1st to 10th	Night	20% 10% 2 7% 4 4 4 4 6% 6% 34%	4806
	11th to 20th	Night	24% 9% 2 4 3 3 3 3 5% 5% 39%	5697
	21st to end	Night	23% 11% 3 6% 3 3 3 3 4 5% 35%	7474

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	51% 4 12% 25% 7%	3598
	11th to 20th	Day	46% 4 14% 23% 11% 2	3600
	21st to end	Day	46% 6% 12% 17% 14% 5%	4164
February	1st to 10th	Day	54% 6% 13% 14% 11% 2	1800
	11th to 20th	Day	48% 7% 15% 16% 12% 2	1851
	21st to end	Day	47% 6% 13% 19% 11% 4	1650
March	1st to 10th	Day	55% 4 9% 10% 16% 6%	4566
	11th to 20th	Day	50% 4 15% 19% 10% 2	4980
	21st to end	Day	55% 3 8% 15% 16% 3	5466
April	1st to 10th	Day	50% 5% 9% 17% 16% 3	2341
	11th to 20th	Day	44% 5% 10% 24% 14% 3	2564
	21st to end	Day	47% 5% 9% 19% 17% 3	2600
May	1st to 10th	Day	60% 5% 11% 17% 6% 1	5897
	11th to 20th	Day	50% 6% 11% 21% 8% 2	5865
	21st to end	Day	52% 5% 13% 18% 12% 1	7020
June	1st to 10th	Day	51% 6% 11% 21% 11% 1	3000
	11th to 20th	Day	45% 6% 11% 20% 15% 2	3000
	21st to end	Day	54% 5% 10% 18% 11% 2	3000
July	1st to 10th	Day	55% 5% 11% 18% 11%	6520
	11th to 20th	Day	51% 7% 12% 20% 9% 1	6285
	21st to end	Day	41% 7% 13% 25% 14% 1	6511
August	1st to 10th	Day	52% 5% 11% 23% 9%	4222
	11th to 20th	Day	49% 4 18% 19% 10%	4214
	21st to end	Day	33% 5% 12% 28% 21% 1	4675
September	1st to 10th	Day	34% 6% 13% 27% 19% 1	2293
	11th to 20th	Day	34% 5% 11% 26% 21% 2	2200
	21st to end	Day	40% 5% 10% 26% 18% 1	2200
October	1st to 10th	Day	44% 4 14% 24% 13% 1	3464
	11th to 20th	Day	32% 3 9% 34% 21%	3240
	21st to end	Day	35% 3 17% 24% 18% 3	3215
November	1st to 10th	Day	43% 5% 15% 22% 13% 1	1851
	11th to 20th	Day	43% 5% 10% 23% 16% 3	1832
	21st to end	Day	49% 5% 16% 21% 7% 1	1680
December	1st to 10th	Day	45% 4 15% 22% 12% 1	2601
	11th to 20th	Day	49% 4 15% 15% 12% 6%	2667
	21st to end	Day	50% 6% 12% 17% 11% 3	3498
January	1st to 10th	Night	47% 4 14% 25% 9% 1	6349
	11th to 20th	Night	54% 4 14% 18% 9% 1	6360
	21st to end	Night	47% 5% 12% 18% 15% 4	6790
February	1st to 10th	Night	55% 6% 12% 13% 11% 2	2600
	11th to 20th	Night	48% 7% 11% 18% 14% 2	2442
	21st to end	Night	48% 4 11% 20% 13% 4	1980
March	1st to 10th	Night	58% 3 7% 11% 13% 8%	5285
	11th to 20th	Night	49% 5% 21% 16% 8% 1	4980
	21st to end	Night	56% 3 6% 16% 17% 2	5466
April	1st to 10th	Night	53% 4 8% 14% 17% 4	2055
	11th to 20th	Night	50% 4 9% 21% 15% 2	1785
	21st to end	Night	53% 4 9% 18% 14% 3	1800
May	1st to 10th	Night	60% 4 13% 14% 8% 1	4060
	11th to 20th	Night	52% 7% 13% 18% 9% 1	4034
	21st to end	Night	53% 6% 13% 19% 9%	3910
June	1st to 10th	Night	54% 6% 9% 21% 8% 1	1400
	11th to 20th	Night	46% 7% 12% 21% 12% 2	1400
	21st to end	Night	54% 5% 8% 20% 10% 2	1400
July	1st to 10th	Night	59% 5% 10% 19% 8%	3335
	11th to 20th	Night	57% 4 12% 17% 9%	3552
	21st to end	Night	44% 5% 15% 23% 12% 1	3981
August	1st to 10th	Night	59% 4 10% 19% 8%	2903
	11th to 20th	Night	51% 5% 14% 21% 9%	2899
	21st to end	Night	38% 4 11% 25% 21% 1	3223
September	1st to 10th	Night	36% 6% 12% 27% 18% 1	2104
	11th to 20th	Night	37% 4 10% 26% 21% 2	2200
	21st to end	Night	40% 4 9% 28% 18% 1	2200
October	1st to 10th	Night	40% 4 13% 25% 16% 2	3715
	11th to 20th	Night	32% 4 11% 29% 24% 1	3899
	21st to end	Night	41% 3 9% 29% 15% 3	4573
November	1st to 10th	Night	43% 5% 12% 24% 15% 1	2667
	11th to 20th	Night	46% 5% 13% 20% 14% 2	2785
	21st to end	Night	49% 5% 16% 17% 11% 1	2940
December	1st to 10th	Night	50% 4 10% 25% 11%	4806
	11th to 20th	Night	48% 3 14% 17% 15% 2	5698
	21st to end	Night	51% 5% 11% 16% 15% 1	7474

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	25% 30% 27% 13% 5%	200
	11th to 20th	Day	28% 23% 28% 16% 6% 1	200
	21st to end	Day	20% 21% 36% 18% 5%	307
February	1st to 10th	Day	25% 21% 33% 16% 4	400
	11th to 20th	Day	23% 26% 37% 12% 2	441
	21st to end	Day	23% 18% 32% 24% 3	414
March	1st to 10th	Day	26% 18% 34% 19% 3	500
	11th to 20th	Day	23% 19% 33% 20% 4	500
	21st to end	Day	29% 16% 29% 19% 6% 1	550
April	1st to 10th	Day	29% 15% 32% 19% 4 1	500
	11th to 20th	Day	26% 14% 33% 20% 6% 1	492
	21st to end	Day	25% 7% 36% 24% 8% 1	500
May	1st to 10th	Day	26% 12% 32% 23% 5% 2	503
	11th to 20th	Day	18% 8% 34% 29% 10% 2	527
	21st to end	Day	27% 5% 28% 26% 12% 1	682
June	1st to 10th	Day	24% 5% 28% 28% 13% 2	730
	11th to 20th	Day	25% 4 21% 32% 15% 4	730
	21st to end	Day	28% 3 21% 33% 12% 2	730
July	1st to 10th	Day	25% 4 18% 35% 16% 3	625
	11th to 20th	Day	22% 4 19% 33% 20% 3	524
	21st to end	Day	18% 2 19% 38% 20% 3	576
August	1st to 10th	Day	13% 3 21% 36% 23% 3	526
	11th to 20th	Day	19% 4 18% 32% 20% 8%	519
	21st to end	Day	16% 4 19% 37% 19% 5%	583
September	1st to 10th	Day	15% 2 22% 37% 19% 4	530
	11th to 20th	Day	18% 6% 24% 26% 17% 8%	530
	21st to end	Day	18% 6% 26% 29% 17% 4	530
October	1st to 10th	Day	16% 10% 25% 30% 16% 4	489
	11th to 20th	Day	18% 11% 30% 26% 13% 1	420
	21st to end	Day	29% 10% 30% 23% 8%	462
November	1st to 10th	Day	19% 18% 32% 25% 5% 1	425
	11th to 20th	Day	25% 18% 31% 19% 6% 1	430
	21st to end	Day	27% 20% 29% 19% 5%	430
December	1st to 10th	Day	26% 16% 35% 18% 4 1	380
	11th to 20th	Day	29% 25% 31% 12% 4	214
	21st to end	Day	27% 20% 28% 21% 4	220
January	1st to 10th	Night	24% 24% 30% 18% 4	800
	11th to 20th	Night	28% 22% 29% 16% 5%	800
	21st to end	Night	19% 25% 35% 17% 4	880
February	1st to 10th	Night	26% 22% 34% 16% 3	800
	11th to 20th	Night	23% 28% 31% 16% 3 1	783
	21st to end	Night	23% 17% 36% 19% 4	660
March	1st to 10th	Night	25% 18% 36% 20% 2	800
	11th to 20th	Night	22% 18% 29% 23% 8%	800
	21st to end	Night	25% 14% 33% 22% 6% 1	880
April	1st to 10th	Night	30% 12% 32% 21% 5%	800
	11th to 20th	Night	26% 8% 32% 27% 7%	601
	21st to end	Night	28% 9% 26% 27% 10% 1	600
May	1st to 10th	Night	27% 4 29% 27% 11% 2	600
	11th to 20th	Night	26% 6% 26% 31% 10% 1	592
	21st to end	Night	24% 5% 23% 32% 14% 2	540
June	1st to 10th	Night	30% 5% 18% 33% 13% 2	400
	11th to 20th	Night	24% 3 18% 34% 20% 3	400
	21st to end	Night	34% 2 15% 32% 17% 2	400
July	1st to 10th	Night	22% 3 16% 39% 19% 1	390
	11th to 20th	Night	25% 2 13% 36% 22% 3	388
	21st to end	Night	22% 2 14% 37% 23% 2	512
August	1st to 10th	Night	21% 1 15% 38% 22% 2	598
	11th to 20th	Night	21% 3 15% 35% 24% 2	592
	21st to end	Night	18% 3 16% 35% 25% 4	660
September	1st to 10th	Night	17% 2 19% 38% 21% 3	779
	11th to 20th	Night	20% 5% 20% 30% 20% 6%	800
	21st to end	Night	19% 6% 23% 30% 19% 3	800
October	1st to 10th	Night	23% 7% 22% 28% 18% 2	800
	11th to 20th	Night	21% 12% 27% 25% 14% 2	800
	21st to end	Night	28% 12% 31% 21% 8%	880
November	1st to 10th	Night	22% 13% 30% 25% 8% 1	820
	11th to 20th	Night	23% 21% 29% 20% 7% 1	870
	21st to end	Night	26% 19% 32% 16% 6% 1	950
December	1st to 10th	Night	30% 17% 32% 16% 4	950
	11th to 20th	Night	28% 24% 29% 15% 4 1	936
	21st to end	Night	29% 19% 32% 16% 4	983

Page generated at 2025-12-15 01:13:56. Version ac07

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