Halfmoon Campground
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Halfmoon Campground clear sky chart from 2005-11-06 to 2026-04-02.

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	5% 6% 3 7% 5% 5% 6% 5% 8% 10% 41%	140296
	Night	4 6% 2 7% 5% 5% 6% 5% 8% 11% 42%	138934
Transparency	Day	32% 8% 13% 24% 18% 5%	135002
	Night	30% 8% 15% 26% 16% 4	135234
Seeing	Day	18% 26% 31% 17% 7% 1	17375
	Night	14% 28% 27% 20% 9% 1	27030

By Month

Percentage Cloud Cover SW (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	3 3 8% 6% 7% 8% 8% 12% 14% 31%	4124
	11th to 20th	Day	2 1 7% 8% 10% 8% 6% 10% 11% 37%	4472
	21st to end	Day	3 2 7% 4 5% 6% 6% 9% 12% 47%	5844
February	1st to 10th	Day	1 8% 3 9% 7% 8% 7% 6% 12% 14% 24%	1890
	11th to 20th	Day	1 5% 4 12% 8% 7% 7% 6% 10% 13% 27%	1845
	21st to end	Day	1 5% 4 12% 7% 7% 6% 5% 12% 13% 27%	1586
March	1st to 10th	Day	2 7% 5% 8% 4 5% 6% 5% 7% 11% 41%	4976
	11th to 20th	Day	1 9% 3 8% 6% 6% 6% 5% 8% 10% 38%	5110
	21st to end	Day	3 13% 5% 11% 7% 7% 7% 6% 9% 11% 21%	5607
April	1st to 10th	Day	5% 15% 4 8% 5% 6% 6% 5% 9% 11% 26%	2362
	11th to 20th	Day	6% 12% 5% 9% 7% 7% 7% 5% 7% 9% 27%	2528
	21st to end	Day	11% 15% 4 9% 6% 5% 5% 4 6% 7% 27%	2600
May	1st to 10th	Day	9% 16% 4 8% 5% 4 5% 4 6% 8% 31%	5966
	11th to 20th	Day	11% 12% 3 8% 5% 6% 6% 5% 8% 9% 26%	6298
	21st to end	Day	10% 7% 2 7% 5% 5% 5% 4 7% 9% 38%	6925
June	1st to 10th	Day	11% 9% 3 8% 5% 6% 5% 6% 7% 8% 32%	2980
	11th to 20th	Day	9% 8% 3 8% 7% 5% 6% 5% 8% 9% 32%	3000
	21st to end	Day	5% 4 2 5% 4 5% 6% 5% 7% 9% 49%	3000
July	1st to 10th	Day	3 3 2 5% 5% 6% 6% 6% 8% 8% 48%	6779
	11th to 20th	Day	5% 2 1 2 3 3 5% 5% 7% 9% 59%	6780
	21st to end	Day	3 3 1 5% 4 5% 7% 6% 8% 9% 50%	6645
August	1st to 10th	Day	4 5% 1 5% 4 5% 6% 5% 8% 10% 48%	5779
	11th to 20th	Day	4 3 1 4 4 4 5% 4 6% 8% 57%	5798
	21st to end	Day	8% 5% 2 5% 3 4 5% 4 6% 7% 52%	6425
September	1st to 10th	Day	8% 4 1 4 3 3 5% 3 5% 7% 57%	2400
	11th to 20th	Day	8% 7% 2 6% 4 4 5% 4 5% 7% 47%	2248
	21st to end	Day	8% 6% 1 5% 3 3 4 4 6% 8% 51%	2200
October	1st to 10th	Day	6% 7% 2 5% 3 3 3 3 4 6% 59%	3271
	11th to 20th	Day	4 7% 2 5% 3 3 3 4 6% 9% 53%	3250
	21st to end	Day	3 7% 3 7% 4 5% 5% 5% 8% 11% 43%	3438
November	1st to 10th	Day	5% 6% 3 8% 4 6% 7% 5% 9% 11% 37%	1698
	11th to 20th	Day	2 5% 3 7% 6% 7% 6% 5% 8% 15% 36%	1680
	21st to end	Day	1 6% 2 6% 5% 5% 6% 6% 10% 13% 40%	1680
December	1st to 10th	Day	2 1 6% 5% 6% 6% 5% 11% 10% 47%	2700
	11th to 20th	Day	4 2 6% 6% 6% 6% 6% 11% 15% 38%	2837
	21st to end	Day	1 5% 2 10% 7% 6% 6% 7% 9% 10% 36%	3575
January	1st to 10th	Night	3 2 8% 5% 7% 6% 7% 13% 15% 33%	8768
	11th to 20th	Night	1 1 6% 6% 6% 7% 6% 10% 14% 41%	8532
	21st to end	Night	3 2 6% 5% 5% 6% 6% 11% 11% 45%	8370
February	1st to 10th	Night	1 7% 5% 10% 6% 7% 7% 6% 11% 15% 25%	2730
	11th to 20th	Night	1 5% 3 10% 6% 6% 6% 7% 9% 16% 30%	2662
	21st to end	Night	5% 4 11% 6% 6% 5% 6% 11% 14% 32%	2218
March	1st to 10th	Night	1 7% 3 6% 4 5% 6% 5% 8% 12% 44%	5137
	11th to 20th	Night	1 8% 3 7% 5% 5% 5% 5% 7% 11% 42%	5110
	21st to end	Night	2 12% 4 10% 6% 7% 6% 6% 9% 11% 26%	5610
April	1st to 10th	Night	7% 12% 3 7% 5% 6% 5% 5% 8% 10% 34%	2061
	11th to 20th	Night	5% 10% 3 9% 6% 5% 7% 5% 8% 10% 31%	1816
	21st to end	Night	11% 12% 3 8% 5% 3 5% 4 6% 8% 35%	1800
May	1st to 10th	Night	8% 13% 5% 8% 5% 4 4 4 6% 7% 37%	4013
	11th to 20th	Night	12% 10% 4 7% 5% 4 4 4 6% 10% 34%	3617
	21st to end	Night	9% 8% 2 6% 5% 5% 5% 5% 7% 9% 39%	3972
June	1st to 10th	Night	13% 6% 2 6% 6% 6% 7% 6% 7% 8% 33%	1415
	11th to 20th	Night	13% 8% 2 7% 6% 4 5% 5% 6% 8% 37%	1400
	21st to end	Night	6% 4 2 4 4 3 4 5% 7% 8% 53%	1400
July	1st to 10th	Night	4 2 1 5% 4 4 5% 5% 9% 8% 53%	3180
	11th to 20th	Night	5% 3 1 5% 4 4 5% 4 6% 7% 56%	3180
	21st to end	Night	6% 5% 2 6% 4 5% 5% 4 8% 9% 47%	4208
August	1st to 10th	Night	5% 7% 1 6% 4 4 5% 5% 7% 10% 46%	4033
	11th to 20th	Night	3 3 1 5% 4 5% 6% 4 8% 8% 53%	4051
	21st to end	Night	7% 4 2 6% 3 4 4 4 5% 6% 54%	4550
September	1st to 10th	Night	8% 6% 2 4 3 3 4 4 4 6% 56%	2000
	11th to 20th	Night	9% 6% 2 5% 4 5% 6% 4 6% 9% 46%	2150
	21st to end	Night	9% 6% 2 4 3 3 4 3 6% 8% 54%	2200
October	1st to 10th	Night	6% 5% 1 4 2 3 4 3 5% 6% 60%	3918
	11th to 20th	Night	5% 8% 2 5% 3 3 4 4 7% 8% 51%	3898
	21st to end	Night	3 6% 2 6% 4 5% 5% 5% 7% 11% 46%	4361
November	1st to 10th	Night	4 6% 2 6% 5% 5% 5% 5% 10% 15% 38%	2800
	11th to 20th	Night	1 5% 2 5% 4 5% 7% 6% 11% 15% 40%	2940
	21st to end	Night	1 5% 2 6% 5% 5% 5% 5% 10% 15% 39%	2940
December	1st to 10th	Night	2 2 5% 5% 4 5% 5% 9% 14% 49%	4710
	11th to 20th	Night	4 2 6% 5% 6% 7% 6% 9% 15% 40%	5561
	21st to end	Night	5% 3 8% 5% 6% 6% 6% 9% 12% 41%	7623

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	32% 12% 17% 27% 12%	4125
	11th to 20th	Day	33% 10% 14% 19% 17% 7%	4472
	21st to end	Day	24% 7% 18% 27% 21% 3	5844
February	1st to 10th	Day	39% 15% 18% 17% 10% 1	1890
	11th to 20th	Day	39% 12% 17% 21% 8% 3	1854
	21st to end	Day	39% 13% 12% 20% 13% 3	1586
March	1st to 10th	Day	32% 8% 9% 23% 20% 7%	4976
	11th to 20th	Day	30% 9% 15% 31% 14% 1	5110
	21st to end	Day	47% 8% 18% 20% 6% 1	5607
April	1st to 10th	Day	43% 12% 14% 21% 9% 1	2362
	11th to 20th	Day	47% 10% 15% 20% 8%	2531
	21st to end	Day	52% 7% 14% 18% 9%	2600
May	1st to 10th	Day	47% 5% 9% 26% 11% 2	5966
	11th to 20th	Day	45% 9% 15% 20% 9% 1	6302
	21st to end	Day	36% 7% 16% 29% 10% 2	6926
June	1st to 10th	Day	44% 9% 18% 21% 8% 1	2980
	11th to 20th	Day	40% 11% 13% 19% 14% 3	3000
	21st to end	Day	24% 9% 14% 27% 22% 4	3000
July	1st to 10th	Day	22% 8% 10% 25% 28% 8%	6706
	11th to 20th	Day	17% 5% 6% 25% 29% 18%	6699
	21st to end	Day	23% 9% 9% 17% 29% 12%	6453
August	1st to 10th	Day	28% 6% 11% 21% 22% 12%	4208
	11th to 20th	Day	22% 7% 6% 30% 27% 7%	4197
	21st to end	Day	23% 6% 6% 29% 24% 11%	4632
September	1st to 10th	Day	24% 6% 7% 26% 28% 10%	2400
	11th to 20th	Day	32% 7% 9% 26% 22% 5%	2248
	21st to end	Day	27% 6% 12% 28% 21% 6%	2200
October	1st to 10th	Day	25% 6% 9% 22% 28% 10%	3271
	11th to 20th	Day	26% 5% 16% 32% 18% 4	3250
	21st to end	Day	28% 10% 13% 25% 21% 3	3438
November	1st to 10th	Day	36% 9% 15% 25% 12% 4	1698
	11th to 20th	Day	31% 12% 19% 25% 10% 2	1680
	21st to end	Day	29% 10% 19% 25% 15% 2	1680
December	1st to 10th	Day	24% 8% 23% 22% 18% 4	2700
	11th to 20th	Day	26% 10% 31% 22% 9% 1	2836
	21st to end	Day	31% 10% 10% 23% 16% 9%	3575
January	1st to 10th	Night	28% 9% 15% 30% 17% 1	8769
	11th to 20th	Night	27% 8% 18% 25% 16% 6%	8532
	21st to end	Night	27% 7% 15% 24% 22% 5%	8370
February	1st to 10th	Night	42% 12% 16% 19% 10% 2	2730
	11th to 20th	Night	35% 11% 20% 21% 10% 3	2663
	21st to end	Night	34% 12% 16% 21% 15% 3	2218
March	1st to 10th	Night	31% 9% 9% 27% 18% 5%	5137
	11th to 20th	Night	29% 7% 20% 31% 11% 1	5110
	21st to end	Night	46% 6% 19% 20% 8% 1	5610
April	1st to 10th	Night	42% 9% 15% 23% 11% 1	2061
	11th to 20th	Night	41% 8% 16% 24% 9% 1	1816
	21st to end	Night	45% 6% 18% 22% 8%	1800
May	1st to 10th	Night	43% 7% 13% 25% 11% 1	4010
	11th to 20th	Night	42% 7% 14% 28% 7% 2	3618
	21st to end	Night	36% 8% 17% 28% 11%	3972
June	1st to 10th	Night	43% 10% 18% 20% 8% 1	1415
	11th to 20th	Night	41% 10% 13% 23% 12% 3	1400
	21st to end	Night	25% 7% 17% 28% 20% 4	1400
July	1st to 10th	Night	20% 6% 8% 37% 25% 4	3145
	11th to 20th	Night	21% 6% 8% 22% 28% 15%	3138
	21st to end	Night	28% 6% 11% 24% 21% 9%	4088
August	1st to 10th	Night	29% 6% 13% 24% 18% 10%	2928
	11th to 20th	Night	26% 8% 9% 30% 21% 5%	2928
	21st to end	Night	24% 5% 6% 32% 26% 7%	3274
September	1st to 10th	Night	28% 4 9% 23% 26% 9%	2000
	11th to 20th	Night	32% 6% 12% 27% 19% 3	2150
	21st to end	Night	27% 5% 10% 31% 23% 4	2200
October	1st to 10th	Night	23% 5% 8% 26% 28% 10%	3918
	11th to 20th	Night	28% 5% 14% 26% 20% 6%	3898
	21st to end	Night	25% 8% 12% 27% 22% 6%	4361
November	1st to 10th	Night	30% 10% 17% 26% 13% 4	2800
	11th to 20th	Night	25% 13% 22% 27% 12% 2	2940
	21st to end	Night	27% 9% 20% 28% 12% 4	2940
December	1st to 10th	Night	21% 8% 20% 28% 20% 3	4710
	11th to 20th	Night	26% 9% 26% 29% 9% 2	5562
	21st to end	Night	29% 7% 12% 28% 15% 9%	7623

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% 37% 24% 10% 4 1	220
	11th to 20th	Day	24% 42% 21% 6% 3 3	235
	21st to end	Day	17% 42% 32% 6% 2 1	363
February	1st to 10th	Day	24% 44% 25% 6% 1	330
	11th to 20th	Day	19% 42% 30% 6% 2 1	330
	21st to end	Day	30% 34% 25% 7% 4	302
March	1st to 10th	Day	19% 40% 31% 8% 2 1	540
	11th to 20th	Day	23% 32% 29% 12% 4 1	540
	21st to end	Day	24% 30% 31% 11% 3 1	594
April	1st to 10th	Day	25% 32% 33% 9% 1	505
	11th to 20th	Day	19% 35% 32% 11% 3	492
	21st to end	Day	27% 26% 27% 15% 5% 1	500
May	1st to 10th	Day	20% 20% 33% 20% 6% 2	537
	11th to 20th	Day	30% 15% 25% 18% 10% 3	725
	21st to end	Day	22% 15% 25% 21% 14% 2	789
June	1st to 10th	Day	16% 19% 29% 21% 12% 3	730
	11th to 20th	Day	21% 27% 29% 16% 6% 1	730
	21st to end	Day	11% 17% 32% 27% 11% 2	730
July	1st to 10th	Day	9% 14% 35% 26% 13% 3	721
	11th to 20th	Day	5% 18% 36% 28% 12% 1	718
	21st to end	Day	5% 14% 38% 28% 12% 2	678
August	1st to 10th	Day	12% 17% 39% 24% 7% 1	527
	11th to 20th	Day	12% 15% 36% 26% 8% 2	517
	21st to end	Day	9% 21% 37% 21% 9% 2	583
September	1st to 10th	Day	9% 18% 40% 25% 7% 1	530
	11th to 20th	Day	18% 22% 34% 20% 4 2	530
	21st to end	Day	20% 25% 28% 20% 6% 1	530
October	1st to 10th	Day	23% 24% 30% 12% 10% 1	331
	11th to 20th	Day	18% 34% 31% 10% 5% 2	330
	21st to end	Day	25% 34% 26% 8% 4 1	363
November	1st to 10th	Day	29% 32% 24% 10% 4 1	330
	11th to 20th	Day	21% 42% 28% 7% 2	330
	21st to end	Day	21% 37% 29% 9% 3	330
December	1st to 10th	Day	28% 41% 19% 7% 5% 1	330
	11th to 20th	Day	27% 41% 23% 7% 2	263
	21st to end	Day	26% 38% 24% 7% 4	242
January	1st to 10th	Night	14% 40% 29% 13% 4	1050
	11th to 20th	Night	13% 44% 27% 10% 5% 1	982
	21st to end	Night	12% 47% 26% 10% 4 1	924
February	1st to 10th	Night	14% 44% 24% 13% 5%	840
	11th to 20th	Night	11% 41% 31% 12% 5% 1	824
	21st to end	Night	17% 32% 30% 14% 6% 1	692
March	1st to 10th	Night	11% 33% 33% 16% 6% 1	840
	11th to 20th	Night	15% 29% 28% 20% 6% 2	840
	21st to end	Night	15% 24% 29% 23% 7% 1	924
April	1st to 10th	Night	17% 25% 32% 18% 7% 1	654
	11th to 20th	Night	13% 25% 36% 19% 6% 1	593
	21st to end	Night	21% 18% 27% 23% 11% 2	600
May	1st to 10th	Night	19% 16% 27% 27% 10% 1	600
	11th to 20th	Night	23% 12% 18% 28% 17% 2	591
	21st to end	Night	22% 11% 23% 28% 15% 2	650
June	1st to 10th	Night	14% 15% 22% 29% 17% 2	415
	11th to 20th	Night	19% 17% 30% 25% 10%	400
	21st to end	Night	10% 10% 22% 41% 17% 1	400
July	1st to 10th	Night	7% 6% 23% 36% 26% 2	390
	11th to 20th	Night	4 9% 29% 43% 14% 1	388
	21st to end	Night	7% 6% 27% 39% 19% 2	642
August	1st to 10th	Night	10% 6% 28% 37% 18% 2	597
	11th to 20th	Night	7% 8% 27% 36% 19% 2	594
	21st to end	Night	9% 11% 26% 33% 20% 2	660
September	1st to 10th	Night	11% 10% 24% 34% 19% 2	600
	11th to 20th	Night	15% 9% 25% 32% 16% 4	750
	21st to end	Night	16% 17% 25% 25% 15% 3	800
October	1st to 10th	Night	17% 18% 26% 25% 12% 2	800
	11th to 20th	Night	17% 29% 26% 17% 8% 3	800
	21st to end	Night	17% 31% 29% 14% 8% 2	880
November	1st to 10th	Night	18% 35% 28% 13% 5% 1	955
	11th to 20th	Night	15% 43% 29% 11% 2	1050
	21st to end	Night	12% 38% 33% 13% 4	1050
December	1st to 10th	Night	15% 39% 29% 12% 4 1	1050
	11th to 20th	Night	16% 45% 27% 9% 3 1	1050
	21st to end	Night	16% 43% 23% 11% 6%	1155

Page generated at 2026-03-30 00:18:42. Version ac07

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