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 2024-01-16.

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	6% 7% 3 6% 6% 4 6% 6% 8% 10% 38%	74749
	Night	5% 6% 3 6% 5% 3 6% 6% 8% 12% 40%	75055
Transparency	Day	36% 10% 14% 22% 14% 4	74446
	Night	33% 9% 17% 24% 13% 4	74880
Seeing	Day	15% 26% 32% 18% 8% 2	14407
	Night	11% 28% 28% 21% 10% 1	24082

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	1 4 3 6% 7% 3 7% 9% 11% 15% 34%	1329
	11th to 20th	Day	1 4 4 7% 8% 6% 7% 7% 10% 14% 33%	1389
	21st to end	Day	1 6% 3 7% 5% 5% 7% 8% 11% 15% 32%	1782
February	1st to 10th	Day	1 6% 4 8% 7% 7% 8% 7% 12% 16% 24%	1620
	11th to 20th	Day	1 5% 4 10% 9% 5% 8% 7% 11% 13% 27%	1575
	21st to end	Day	1 5% 5% 12% 9% 5% 8% 6% 12% 13% 23%	1356
March	1st to 10th	Day	2 4 4 9% 8% 5% 8% 8% 11% 13% 28%	1943
	11th to 20th	Day	4 8% 3 7% 7% 4 6% 7% 9% 13% 32%	1980
	21st to end	Day	5% 11% 5% 11% 9% 5% 7% 7% 9% 10% 21%	2178
April	1st to 10th	Day	6% 13% 5% 7% 6% 5% 6% 6% 9% 11% 25%	2114
	11th to 20th	Day	7% 12% 5% 8% 8% 5% 7% 7% 7% 9% 25%	2272
	21st to end	Day	12% 14% 4 8% 7% 4 5% 5% 6% 8% 28%	2340
May	1st to 10th	Day	11% 11% 4 7% 6% 4 7% 6% 7% 8% 29%	2370
	11th to 20th	Day	15% 12% 4 6% 6% 4 6% 6% 7% 8% 25%	2478
	21st to end	Day	19% 10% 3 8% 7% 4 6% 5% 6% 9% 23%	2724
June	1st to 10th	Day	12% 8% 3 7% 6% 4 6% 7% 7% 8% 30%	2682
	11th to 20th	Day	10% 7% 4 7% 8% 4 6% 6% 8% 9% 31%	2700
	21st to end	Day	5% 3 3 4 4 3 6% 6% 7% 9% 48%	2700
July	1st to 10th	Day	5% 3 2 3 5% 4 5% 8% 8% 10% 48%	2700
	11th to 20th	Day	3 2 2 3 4 3 6% 6% 6% 8% 57%	2700
	21st to end	Day	3 3 2 3 4 3 6% 6% 7% 8% 56%	2649
August	1st to 10th	Day	6% 5% 1 5% 6% 3 6% 5% 7% 8% 49%	2328
	11th to 20th	Day	7% 4 1 4 5% 3 5% 5% 5% 7% 54%	2299
	21st to end	Day	6% 4 2 4 5% 3 5% 5% 7% 7% 53%	2557
September	1st to 10th	Day	8% 4 1 3 4 2 4 5% 5% 7% 56%	2160
	11th to 20th	Day	9% 6% 2 5% 4 3 5% 5% 4 7% 50%	2024
	21st to end	Day	9% 6% 2 4 4 3 4 5% 6% 9% 48%	1980
October	1st to 10th	Day	11% 10% 3 6% 5% 2 5% 5% 5% 8% 39%	1801
	11th to 20th	Day	6% 9% 3 5% 4 2 5% 5% 8% 10% 43%	1800
	21st to end	Day	4 6% 3 7% 5% 5% 6% 6% 9% 12% 36%	1922
November	1st to 10th	Day	6% 6% 3 8% 5% 4 6% 7% 8% 11% 36%	1534
	11th to 20th	Day	2 5% 3 6% 6% 4 7% 6% 8% 16% 36%	1520
	21st to end	Day	1 5% 4 5% 6% 4 6% 7% 10% 13% 40%	1520
December	1st to 10th	Day	1 3 3 6% 7% 4 8% 7% 12% 14% 36%	1520
	11th to 20th	Day	1 5% 3 6% 7% 5% 6% 7% 11% 16% 34%	1761
	21st to end	Day	1 6% 3 7% 7% 4 6% 7% 8% 11% 40%	2442
January	1st to 10th	Night	1 3 2 7% 7% 4 7% 7% 11% 17% 35%	2836
	11th to 20th	Night	2 3 6% 7% 4 7% 7% 10% 16% 38%	2705
	21st to end	Night	1 5% 3 5% 6% 3 6% 9% 10% 17% 35%	2574
February	1st to 10th	Night	1 6% 5% 9% 8% 5% 6% 7% 11% 16% 25%	2340
	11th to 20th	Night	2 5% 4 7% 7% 4 7% 9% 9% 17% 30%	2272
	21st to end	Night	5% 4 11% 7% 5% 6% 7% 11% 13% 31%	1898
March	1st to 10th	Night	2 5% 3 7% 6% 4 7% 7% 9% 14% 36%	2016
	11th to 20th	Night	3 6% 4 6% 5% 3 5% 6% 9% 15% 39%	1980
	21st to end	Night	3 11% 5% 9% 7% 4 7% 5% 9% 11% 29%	2178
April	1st to 10th	Night	8% 10% 4 6% 6% 4 6% 6% 8% 10% 33%	1846
	11th to 20th	Night	5% 9% 4 8% 7% 4 7% 7% 8% 11% 30%	1633
	21st to end	Night	12% 11% 3 7% 5% 2 5% 5% 6% 8% 36%	1620
May	1st to 10th	Night	10% 11% 4 5% 6% 3 6% 6% 7% 9% 33%	1589
	11th to 20th	Night	15% 13% 4 5% 5% 3 5% 5% 6% 8% 32%	1417
	21st to end	Night	19% 10% 3 6% 6% 3 5% 6% 6% 9% 26%	1552
June	1st to 10th	Night	14% 7% 3 6% 6% 6% 7% 7% 6% 8% 31%	1274
	11th to 20th	Night	14% 7% 3 5% 7% 3 5% 6% 6% 8% 37%	1260
	21st to end	Night	6% 4 2 4 5% 2 5% 5% 6% 8% 53%	1260
July	1st to 10th	Night	7% 4 2 5% 4 3 4 5% 7% 8% 52%	1260
	11th to 20th	Night	3 3 1 5% 5% 2 4 4 6% 7% 59%	1260
	21st to end	Night	5% 3 2 4 5% 3 4 5% 6% 7% 56%	1663
August	1st to 10th	Night	6% 5% 2 6% 5% 4 4 5% 7% 8% 48%	1611
	11th to 20th	Night	5% 4 2 4 5% 3 5% 4 7% 8% 52%	1602
	21st to end	Night	8% 4 2 5% 5% 3 4 6% 6% 8% 49%	1797
September	1st to 10th	Night	9% 6% 2 4 4 2 4 5% 4 5% 55%	1800
	11th to 20th	Night	9% 6% 2 4 4 3 5% 6% 6% 9% 48%	1934
	21st to end	Night	10% 6% 2 4 3 2 4 4 6% 8% 51%	1980
October	1st to 10th	Night	12% 9% 3 6% 4 3 4 5% 6% 8% 42%	2158
	11th to 20th	Night	7% 8% 2 4 5% 3 4 5% 7% 10% 45%	2160
	21st to end	Night	4 5% 2 6% 6% 4 5% 6% 7% 13% 41%	2433
November	1st to 10th	Night	5% 5% 2 6% 5% 3 5% 6% 10% 15% 38%	2526
	11th to 20th	Night	1 4 2 4 4 3 7% 7% 11% 16% 39%	2660
	21st to end	Night	1 5% 3 6% 6% 3 6% 6% 10% 16% 40%	2660
December	1st to 10th	Night	3 3 7% 5% 3 7% 8% 12% 16% 36%	2660
	11th to 20th	Night	1 5% 2 6% 5% 3 6% 6% 9% 16% 42%	3427
	21st to end	Night	5% 3 6% 5% 3 5% 6% 7% 13% 46%	5214

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	30% 15% 20% 23% 10% 1	1329
	11th to 20th	Day	35% 12% 19% 21% 12% 2	1389
	21st to end	Day	33% 12% 20% 22% 11% 2	1782
February	1st to 10th	Day	39% 16% 19% 18% 7% 1	1620
	11th to 20th	Day	41% 13% 18% 20% 6% 2	1584
	21st to end	Day	44% 14% 11% 17% 11% 4	1356
March	1st to 10th	Day	37% 15% 18% 20% 9% 1	1943
	11th to 20th	Day	36% 11% 18% 21% 11% 1	1980
	21st to end	Day	50% 12% 16% 16% 6% 1	2178
April	1st to 10th	Day	44% 12% 14% 21% 7% 1	2114
	11th to 20th	Day	49% 10% 15% 18% 7%	2275
	21st to end	Day	52% 7% 14% 19% 7%	2340
May	1st to 10th	Day	47% 8% 12% 25% 7% 1	2370
	11th to 20th	Day	51% 8% 15% 19% 6%	2482
	21st to end	Day	55% 8% 18% 15% 4	2724
June	1st to 10th	Day	46% 9% 18% 20% 6%	2682
	11th to 20th	Day	42% 10% 12% 20% 13% 3	2700
	21st to end	Day	26% 9% 15% 26% 21% 4	2700
July	1st to 10th	Day	24% 9% 12% 27% 22% 6%	2626
	11th to 20th	Day	20% 7% 9% 24% 24% 16%	2619
	21st to end	Day	20% 8% 7% 19% 29% 16%	2501
August	1st to 10th	Day	29% 6% 10% 24% 21% 10%	2313
	11th to 20th	Day	25% 7% 7% 27% 23% 9%	2299
	21st to end	Day	26% 7% 8% 25% 24% 11%	2557
September	1st to 10th	Day	25% 6% 7% 24% 27% 11%	2160
	11th to 20th	Day	31% 7% 9% 25% 23% 5%	2024
	21st to end	Day	30% 7% 12% 29% 18% 4	1980
October	1st to 10th	Day	41% 7% 13% 23% 14% 2	1801
	11th to 20th	Day	35% 7% 18% 23% 14% 3	1800
	21st to end	Day	31% 15% 17% 23% 12% 2	1922
November	1st to 10th	Day	38% 9% 15% 23% 11% 4	1534
	11th to 20th	Day	32% 13% 19% 24% 10% 2	1520
	21st to end	Day	30% 10% 19% 23% 15% 3	1520
December	1st to 10th	Day	32% 12% 22% 18% 11% 4	1520
	11th to 20th	Day	32% 13% 29% 19% 6% 1	1760
	21st to end	Day	32% 11% 10% 24% 10% 13%	2442
January	1st to 10th	Night	29% 14% 21% 25% 10% 2	2836
	11th to 20th	Night	29% 13% 20% 23% 10% 4	2705
	21st to end	Night	29% 12% 20% 24% 13% 2	2574
February	1st to 10th	Night	42% 13% 16% 20% 8% 1	2340
	11th to 20th	Night	36% 12% 21% 22% 8% 2	2273
	21st to end	Night	38% 12% 15% 19% 13% 3	1898
March	1st to 10th	Night	34% 12% 18% 23% 11% 2	2016
	11th to 20th	Night	32% 9% 20% 26% 11% 2	1980
	21st to end	Night	45% 10% 18% 21% 6% 1	2178
April	1st to 10th	Night	42% 9% 16% 22% 10% 1	1846
	11th to 20th	Night	42% 9% 17% 23% 9% 1	1633
	21st to end	Night	45% 6% 19% 22% 7%	1620
May	1st to 10th	Night	43% 9% 14% 27% 7%	1589
	11th to 20th	Night	48% 7% 16% 21% 7%	1418
	21st to end	Night	51% 7% 21% 15% 5%	1552
June	1st to 10th	Night	45% 11% 19% 18% 6% 1	1274
	11th to 20th	Night	42% 9% 12% 23% 11% 2	1260
	21st to end	Night	26% 7% 17% 28% 18% 4	1260
July	1st to 10th	Night	27% 7% 12% 29% 20% 5%	1225
	11th to 20th	Night	22% 5% 11% 28% 22% 13%	1218
	21st to end	Night	25% 4 11% 22% 26% 11%	1571
August	1st to 10th	Night	30% 6% 13% 27% 17% 7%	1602
	11th to 20th	Night	25% 7% 11% 29% 21% 7%	1602
	21st to end	Night	29% 7% 9% 25% 22% 7%	1797
September	1st to 10th	Night	29% 4 9% 21% 26% 10%	1800
	11th to 20th	Night	31% 6% 12% 26% 21% 4	1934
	21st to end	Night	29% 5% 11% 31% 21% 2	1980
October	1st to 10th	Night	39% 7% 14% 23% 15% 2	2158
	11th to 20th	Night	33% 7% 16% 25% 17% 3	2160
	21st to end	Night	30% 10% 19% 24% 14% 3	2433
November	1st to 10th	Night	32% 10% 18% 24% 12% 4	2526
	11th to 20th	Night	26% 13% 22% 26% 11% 2	2660
	21st to end	Night	28% 10% 20% 27% 12% 4	2660
December	1st to 10th	Night	31% 13% 20% 21% 11% 3	2660
	11th to 20th	Night	28% 10% 27% 26% 8% 1	3428
	21st to end	Night	29% 7% 13% 27% 11% 12%	5214

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	14% 40% 27% 12% 5% 2	180
	11th to 20th	Day	15% 43% 23% 9% 4 4	180
	21st to end	Day	9% 48% 33% 6% 2 2	264
February	1st to 10th	Day	17% 49% 29% 6%	240
	11th to 20th	Day	15% 45% 30% 6% 2 1	240
	21st to end	Day	19% 37% 30% 9% 5%	222
March	1st to 10th	Day	13% 42% 34% 8% 2	420
	11th to 20th	Day	13% 37% 32% 13% 5% 1	420
	21st to end	Day	18% 31% 34% 13% 3 1	462
April	1st to 10th	Day	25% 32% 32% 10% 1	420
	11th to 20th	Day	18% 37% 29% 12% 3	412
	21st to end	Day	25% 24% 29% 17% 5% 1	420
May	1st to 10th	Day	20% 20% 32% 21% 6% 2	453
	11th to 20th	Day	28% 13% 25% 19% 11% 3	625
	21st to end	Day	23% 14% 24% 21% 15% 3	679
June	1st to 10th	Day	15% 18% 27% 23% 13% 3	630
	11th to 20th	Day	19% 27% 30% 17% 7% 1	630
	21st to end	Day	7% 15% 33% 30% 12% 2	630
July	1st to 10th	Day	7% 12% 34% 28% 14% 4	621
	11th to 20th	Day	4 17% 35% 30% 13% 1	618
	21st to end	Day	4 11% 39% 30% 13% 2	580
August	1st to 10th	Day	11% 14% 39% 26% 8% 1	447
	11th to 20th	Day	10% 12% 37% 30% 9% 3	437
	21st to end	Day	7% 18% 39% 23% 11% 3	495
September	1st to 10th	Day	9% 18% 41% 24% 7% 1	450
	11th to 20th	Day	15% 22% 35% 21% 4 2	450
	21st to end	Day	20% 24% 29% 19% 7% 1	450
October	1st to 10th	Day	20% 23% 30% 14% 12% 1	271
	11th to 20th	Day	14% 34% 33% 11% 6% 2	270
	21st to end	Day	19% 37% 29% 9% 5% 2	297
November	1st to 10th	Day	23% 34% 27% 11% 3 1	270
	11th to 20th	Day	13% 47% 31% 7% 3	270
	21st to end	Day	16% 36% 34% 11% 3	270
December	1st to 10th	Day	18% 45% 22% 9% 6% 1	270
	11th to 20th	Day	16% 46% 28% 8% 2	216
	21st to end	Day	17% 40% 28% 9% 5% 1	198
January	1st to 10th	Night	8% 41% 31% 14% 4 1	950
	11th to 20th	Night	7% 46% 29% 11% 5% 1	872
	21st to end	Night	7% 49% 28% 10% 5% 1	792
February	1st to 10th	Night	9% 47% 25% 14% 5%	720
	11th to 20th	Night	8% 42% 31% 13% 6% 1	704
	21st to end	Night	10% 32% 34% 16% 7% 1	592
March	1st to 10th	Night	7% 33% 35% 18% 7% 1	720
	11th to 20th	Night	9% 31% 29% 22% 7% 2	720
	21st to end	Night	11% 25% 30% 24% 8% 1	792
April	1st to 10th	Night	16% 24% 32% 19% 8% 1	586
	11th to 20th	Night	12% 25% 36% 20% 7% 1	533
	21st to end	Night	19% 17% 27% 23% 11% 2	540
May	1st to 10th	Night	19% 16% 26% 27% 11% 1	540
	11th to 20th	Night	23% 10% 18% 29% 18% 2	531
	21st to end	Night	23% 10% 21% 28% 15% 2	584
June	1st to 10th	Night	14% 15% 19% 31% 18% 2	374
	11th to 20th	Night	18% 17% 29% 26% 10%	360
	21st to end	Night	9% 9% 20% 43% 19% 1	360
July	1st to 10th	Night	7% 4 20% 39% 28% 2	350
	11th to 20th	Night	3 8% 27% 45% 16% 1	348
	21st to end	Night	6% 4 27% 40% 21% 2	577
August	1st to 10th	Night	9% 5% 26% 39% 20% 2	537
	11th to 20th	Night	7% 6% 25% 38% 22% 2	534
	21st to end	Night	8% 10% 24% 34% 22% 2	594
September	1st to 10th	Night	11% 10% 24% 34% 19% 2	540
	11th to 20th	Night	14% 7% 24% 32% 17% 4	674
	21st to end	Night	15% 16% 24% 26% 16% 3	720
October	1st to 10th	Night	16% 16% 25% 27% 13% 2	720
	11th to 20th	Night	13% 29% 27% 18% 9% 3	720
	21st to end	Night	14% 30% 31% 16% 8% 2	792
November	1st to 10th	Night	15% 35% 30% 14% 5% 1	861
	11th to 20th	Night	10% 45% 30% 12% 2	950
	21st to end	Night	7% 38% 35% 14% 4	950
December	1st to 10th	Night	10% 40% 32% 13% 4 1	950
	11th to 20th	Night	10% 48% 29% 10% 3 1	950
	21st to end	Night	9% 45% 26% 12% 7%	1045

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