Cerro Alto Campground
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cerro Alto Campground clear sky chart from 2005-11-06 to 2024-02-10.

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% 4 2 3 3 2 3 4 4 6% 63%	78468
	Night	6% 5% 2 4 4 2 3 4 4 6% 59%	80524
Transparency	Day	22% 4 9% 21% 26% 19%	78189
	Night	25% 4 9% 20% 24% 17%	80326
Seeing	Day	6% 7% 20% 36% 25% 6%	14504
	Night	6% 3 13% 36% 35% 7%	24190

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	8% 4 2 5% 5% 3 5% 5% 6% 7% 51%	2713
	11th to 20th	Day	11% 8% 3 5% 5% 3 4 5% 7% 7% 44%	2860
	21st to end	Day	12% 8% 3 6% 6% 3 5% 6% 5% 9% 37%	3146
February	1st to 10th	Day	13% 6% 2 4 3 2 3 4 5% 6% 54%	1758
	11th to 20th	Day	9% 5% 3 5% 4 2 4 4 5% 7% 53%	1750
	21st to end	Day	11% 6% 3 4 3 2 4 4 6% 6% 51%	1480
March	1st to 10th	Day	10% 7% 2 7% 6% 3 4 6% 5% 7% 43%	1862
	11th to 20th	Day	10% 6% 3 5% 5% 4 5% 4 6% 8% 45%	1980
	21st to end	Day	9% 4 2 4 4 3 4 5% 4 8% 54%	2268
April	1st to 10th	Day	9% 6% 2 4 3 2 4 4 6% 7% 54%	2160
	11th to 20th	Day	6% 4 2 4 4 2 3 4 5% 7% 60%	2129
	21st to end	Day	6% 3 2 3 3 2 3 4 4 6% 64%	2160
May	1st to 10th	Day	4 4 1 3 3 2 2 3 4 6% 68%	2160
	11th to 20th	Day	2 2 1 2 3 2 4 3 4 7% 70%	2206
	21st to end	Day	3 4 2 3 3 2 3 3 4 7% 67%	2723
June	1st to 10th	Day	3 3 1 2 3 2 3 3 4 8% 69%	2520
	11th to 20th	Day	1 2 1 2 2 1 2 2 3 5% 81%	2520
	21st to end	Day	1 1 2 2 1 2 2 2 5% 82%	2520
July	1st to 10th	Day	1 1 1 2 1 2 2 4 7% 79%	2520
	11th to 20th	Day	2 1 1 2 2 1 2 3 4 5% 77%	2347
	21st to end	Day	1 1 1 1 2 1 3 4 4 8% 73%	2546
August	1st to 10th	Day	1 2 1 2 3 1 3 3 3 7% 75%	2239
	11th to 20th	Day	1 1 1 2 2 1 2 3 2 5% 81%	2122
	21st to end	Day	1 1 1 2 2 2 2 2 3 6% 78%	2376
September	1st to 10th	Day	1 1 1 1 1 1 2 2 2 5% 83%	2160
	11th to 20th	Day	2 1 1 2 2 1 2 2 2 5% 80%	2160
	21st to end	Day	1 2 1 2 2 1 2 4 4 5% 75%	1973
October	1st to 10th	Day	3 2 1 3 3 1 3 3 4 6% 73%	1800
	11th to 20th	Day	3 3 1 4 3 1 3 3 4 5% 71%	1800
	21st to end	Day	3 3 2 4 3 2 2 4 3 6% 69%	1980
November	1st to 10th	Day	6% 3 2 3 4 1 3 3 4 6% 66%	1793
	11th to 20th	Day	5% 4 1 3 3 2 4 4 5% 6% 63%	1710
	21st to end	Day	7% 4 2 4 4 2 4 4 4 5% 61%	1710
December	1st to 10th	Day	8% 5% 3 6% 5% 2 4 4 5% 7% 51%	1595
	11th to 20th	Day	21% 7% 2 7% 4 2 3 4 4 6% 38%	1928
	21st to end	Day	13% 9% 2 5% 5% 3 4 5% 5% 8% 41%	2794
January	1st to 10th	Night	8% 6% 2 5% 4 3 4 3 4 7% 54%	4220
	11th to 20th	Night	11% 9% 3 5% 5% 3 4 4 5% 7% 44%	4110
	21st to end	Night	15% 8% 2 5% 5% 3 5% 5% 4 7% 41%	4521
February	1st to 10th	Night	10% 6% 2 4 4 2 4 3 3 5% 56%	2404
	11th to 20th	Night	8% 4 2 3 3 2 4 4 5% 7% 59%	2098
	21st to end	Night	10% 5% 2 5% 4 2 3 3 4 7% 56%	1776
March	1st to 10th	Night	10% 7% 3 5% 4 3 4 5% 4 8% 47%	2095
	11th to 20th	Night	8% 5% 2 4 5% 3 4 5% 6% 6% 49%	1980
	21st to end	Night	9% 5% 2 5% 4 2 3 3 4 6% 57%	2087
April	1st to 10th	Night	7% 5% 2 4 4 2 4 3 5% 8% 58%	1800
	11th to 20th	Night	5% 4 2 4 3 1 3 3 4 5% 66%	1779
	21st to end	Night	4 5% 3 4 3 2 3 3 3 7% 64%	1800
May	1st to 10th	Night	3 4 2 4 3 2 2 3 5% 8% 64%	1800
	11th to 20th	Night	3 3 2 3 4 3 3 3 5% 8% 64%	1680
	21st to end	Night	3 4 3 5% 4 2 3 4 4 7% 62%	1552
June	1st to 10th	Night	3 2 2 3 4 2 4 4 5% 8% 64%	1440
	11th to 20th	Night	1 3 2 2 3 2 2 2 4 7% 71%	1440
	21st to end	Night	1 2 1 3 3 2 1 2 3 6% 77%	1440
July	1st to 10th	Night	1 1 4 4 2 3 4 5% 6% 71%	1440
	11th to 20th	Night	1 1 1 2 3 1 3 4 4 5% 74%	1608
	21st to end	Night	1 2 1 2 3 2 4 4 6% 10% 65%	1773
August	1st to 10th	Night	1 2 1 2 3 2 3 2 5% 8% 71%	1700
	11th to 20th	Night	1 1 1 2 2 2 3 3 4 6% 77%	1780
	21st to end	Night	1 1 3 3 2 3 3 4 6% 75%	1980
September	1st to 10th	Night	2 2 1 2 2 2 2 2 2 4 80%	1800
	11th to 20th	Night	2 2 1 3 2 1 3 2 3 4 77%	1800
	21st to end	Night	1 2 1 2 2 1 2 2 3 4 80%	1981
October	1st to 10th	Night	3 3 1 3 3 2 3 3 4 5% 71%	2160
	11th to 20th	Night	3 3 2 4 3 2 3 3 4 5% 68%	2160
	21st to end	Night	3 4 2 3 3 2 3 2 4 5% 69%	2376
November	1st to 10th	Night	4 4 1 3 3 2 3 3 4 6% 67%	2283
	11th to 20th	Night	4 3 2 3 3 2 4 4 4 7% 64%	2470
	21st to end	Night	4 4 2 4 3 2 4 4 5% 6% 60%	2470
December	1st to 10th	Night	10% 5% 2 4 4 2 4 4 5% 6% 54%	2583
	11th to 20th	Night	19% 9% 3 5% 5% 3 4 4 5% 7% 37%	3276
	21st to end	Night	13% 8% 4 6% 5% 3 4 5% 5% 8% 38%	4862

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	28% 6% 14% 33% 15% 4	2713
	11th to 20th	Day	37% 6% 13% 20% 14% 10%	2860
	21st to end	Day	40% 8% 12% 18% 14% 8%	3146
February	1st to 10th	Day	32% 3 7% 20% 21% 17%	1758
	11th to 20th	Day	30% 4 9% 22% 24% 11%	1760
	21st to end	Day	32% 5% 12% 21% 22% 8%	1480
March	1st to 10th	Day	38% 7% 11% 17% 19% 8%	1862
	11th to 20th	Day	35% 6% 12% 21% 18% 9%	1980
	21st to end	Day	28% 6% 15% 26% 18% 7%	2268
April	1st to 10th	Day	29% 5% 12% 26% 19% 9%	2160
	11th to 20th	Day	24% 4 13% 26% 24% 8%	2132
	21st to end	Day	20% 6% 12% 26% 28% 8%	2160
May	1st to 10th	Day	18% 3 12% 24% 32% 11%	2160
	11th to 20th	Day	15% 4 11% 29% 31% 11%	2209
	21st to end	Day	18% 4 14% 31% 28% 6%	2724
June	1st to 10th	Day	16% 5% 10% 26% 29% 14%	2520
	11th to 20th	Day	9% 2 8% 19% 37% 25%	2520
	21st to end	Day	9% 2 5% 18% 32% 35%	2520
July	1st to 10th	Day	7% 1 4 15% 33% 39%	2451
	11th to 20th	Day	11% 3 6% 14% 33% 33%	2277
	21st to end	Day	10% 3 7% 18% 31% 30%	2405
August	1st to 10th	Day	12% 2 5% 15% 30% 36%	2223
	11th to 20th	Day	8% 2 4 16% 36% 34%	2122
	21st to end	Day	10% 1 4 16% 36% 33%	2376
September	1st to 10th	Day	7% 2 4 15% 30% 42%	2160
	11th to 20th	Day	10% 2 5% 21% 37% 25%	2160
	21st to end	Day	11% 2 8% 17% 37% 25%	1973
October	1st to 10th	Day	13% 4 9% 21% 24% 30%	1800
	11th to 20th	Day	17% 3 7% 19% 28% 26%	1800
	21st to end	Day	18% 3 8% 15% 28% 29%	1980
November	1st to 10th	Day	21% 3 8% 20% 29% 19%	1793
	11th to 20th	Day	21% 4 11% 18% 26% 20%	1710
	21st to end	Day	26% 4 6% 18% 25% 21%	1710
December	1st to 10th	Day	32% 4 10% 17% 21% 16%	1595
	11th to 20th	Day	47% 6% 8% 16% 15% 9%	1928
	21st to end	Day	38% 7% 13% 22% 14% 5%	2794
January	1st to 10th	Night	29% 6% 13% 26% 21% 4	4220
	11th to 20th	Night	36% 7% 11% 22% 12% 11%	4110
	21st to end	Night	41% 6% 12% 16% 15% 9%	4521
February	1st to 10th	Night	31% 4 7% 18% 23% 16%	2404
	11th to 20th	Night	26% 4 9% 23% 25% 13%	2099
	21st to end	Night	30% 5% 9% 23% 24% 9%	1776
March	1st to 10th	Night	35% 5% 13% 22% 16% 8%	2095
	11th to 20th	Night	32% 6% 12% 19% 22% 9%	1980
	21st to end	Night	28% 6% 14% 23% 22% 7%	2087
April	1st to 10th	Night	27% 5% 14% 26% 18% 11%	1800
	11th to 20th	Night	22% 3 13% 29% 24% 10%	1779
	21st to end	Night	21% 5% 10% 27% 29% 8%	1800
May	1st to 10th	Night	19% 4 13% 24% 27% 13%	1800
	11th to 20th	Night	18% 3 12% 28% 27% 11%	1682
	21st to end	Night	22% 5% 14% 25% 27% 7%	1552
June	1st to 10th	Night	18% 5% 13% 23% 28% 14%	1440
	11th to 20th	Night	14% 3 7% 21% 32% 24%	1440
	21st to end	Night	10% 3 4 18% 32% 34%	1440
July	1st to 10th	Night	10% 3 3 17% 29% 37%	1400
	11th to 20th	Night	12% 2 6% 18% 30% 32%	1555
	21st to end	Night	13% 4 5% 21% 29% 27%	1674
August	1st to 10th	Night	13% 2 5% 18% 33% 30%	1691
	11th to 20th	Night	8% 2 3 18% 33% 35%	1780
	21st to end	Night	11% 1 4 19% 32% 34%	1980
September	1st to 10th	Night	11% 2 3 13% 27% 45%	1800
	11th to 20th	Night	11% 3 6% 18% 33% 29%	1800
	21st to end	Night	10% 2 6% 17% 37% 28%	1981
October	1st to 10th	Night	15% 3 6% 23% 22% 30%	2160
	11th to 20th	Night	19% 4 8% 17% 27% 26%	2160
	21st to end	Night	19% 2 6% 16% 30% 26%	2376
November	1st to 10th	Night	18% 4 8% 20% 27% 22%	2283
	11th to 20th	Night	19% 4 11% 18% 26% 21%	2470
	21st to end	Night	24% 5% 10% 17% 22% 22%	2470
December	1st to 10th	Night	29% 4 9% 17% 21% 19%	2583
	11th to 20th	Night	47% 5% 9% 15% 16% 8%	3276
	21st to end	Night	41% 8% 12% 19% 14% 6%	4862

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	19% 12% 26% 28% 12% 1	289
	11th to 20th	Day	12% 9% 28% 35% 15% 1	370
	21st to end	Day	10% 11% 26% 33% 17% 2	407
February	1st to 10th	Day	15% 10% 24% 30% 18% 4	394
	11th to 20th	Day	11% 11% 28% 30% 17% 3	415
	21st to end	Day	9% 15% 28% 34% 11% 3	346
March	1st to 10th	Day	13% 17% 29% 33% 8%	420
	11th to 20th	Day	14% 11% 30% 32% 11% 1	420
	21st to end	Day	9% 18% 29% 31% 12% 1	462
April	1st to 10th	Day	13% 10% 29% 31% 15% 4	420
	11th to 20th	Day	7% 14% 29% 33% 14% 3	412
	21st to end	Day	4 11% 30% 31% 18% 5%	420
May	1st to 10th	Day	7% 8% 32% 30% 20% 4	423
	11th to 20th	Day	3 10% 22% 40% 19% 6%	448
	21st to end	Day	6% 12% 23% 35% 19% 5%	485
June	1st to 10th	Day	5% 4 20% 35% 28% 7%	450
	11th to 20th	Day	2 4 20% 38% 28% 9%	450
	21st to end	Day	1 2 16% 37% 34% 10%	450
July	1st to 10th	Day	8% 45% 36% 10%	446
	11th to 20th	Day	2 3 37% 41% 17%	444
	21st to end	Day	6% 39% 40% 15%	487
August	1st to 10th	Day	1 1 14% 42% 34% 8%	447
	11th to 20th	Day	1 2 6% 37% 38% 16%	437
	21st to end	Day	2 1 8% 40% 39% 11%	495
September	1st to 10th	Day	1 2 10% 36% 40% 10%	450
	11th to 20th	Day	3 3 14% 40% 34% 6%	450
	21st to end	Day	1 5% 13% 35% 38% 6%	450
October	1st to 10th	Day	1 6% 22% 40% 26% 4	450
	11th to 20th	Day	4 5% 22% 38% 28% 4	450
	21st to end	Day	3 6% 19% 38% 30% 5%	495
November	1st to 10th	Day	5% 7% 22% 36% 26% 5%	389
	11th to 20th	Day	7% 7% 19% 40% 22% 5%	270
	21st to end	Day	7% 5% 24% 35% 26% 3	270
December	1st to 10th	Day	8% 10% 28% 35% 16% 2	215
	11th to 20th	Day	9% 13% 20% 33% 22% 3	180
	21st to end	Day	15% 15% 27% 29% 12% 3	198
January	1st to 10th	Night	14% 5% 19% 38% 19% 4	760
	11th to 20th	Night	11% 3 19% 43% 21% 4	760
	21st to end	Night	14% 3 17% 42% 20% 4	836
February	1st to 10th	Night	14% 6% 12% 39% 25% 4	758
	11th to 20th	Night	9% 5% 19% 39% 23% 4	704
	21st to end	Night	11% 7% 18% 43% 18% 3	592
March	1st to 10th	Night	12% 6% 19% 41% 19% 3	720
	11th to 20th	Night	9% 5% 18% 38% 25% 5%	720
	21st to end	Night	9% 5% 21% 38% 23% 3	792
April	1st to 10th	Night	9% 4 18% 41% 26% 2	720
	11th to 20th	Night	6% 6% 20% 37% 26% 5%	711
	21st to end	Night	5% 5% 22% 34% 27% 8%	720
May	1st to 10th	Night	4 3 17% 37% 33% 7%	720
	11th to 20th	Night	4 3 12% 37% 37% 7%	618
	21st to end	Night	3 2 16% 39% 32% 7%	389
June	1st to 10th	Night	3 2 9% 38% 43% 6%	360
	11th to 20th	Night	2 2 8% 31% 50% 7%	360
	21st to end	Night	1 3 32% 52% 11%	360
July	1st to 10th	Night	1 1 21% 64% 13%	350
	11th to 20th	Night	1 1 9% 64% 25%	511
	21st to end	Night	2 1 12% 61% 24%	591
August	1st to 10th	Night	1 3 26% 55% 14%	626
	11th to 20th	Night	1 2 22% 61% 14%	712
	21st to end	Night	1 1 22% 61% 16%	792
September	1st to 10th	Night	1 1 3 22% 59% 14%	720
	11th to 20th	Night	2 1 5% 35% 45% 12%	720
	21st to end	Night	1 1 8% 30% 49% 11%	720
October	1st to 10th	Night	4 1 8% 38% 42% 7%	720
	11th to 20th	Night	4 3 9% 39% 40% 6%	720
	21st to end	Night	5% 2 9% 41% 34% 9%	792
November	1st to 10th	Night	5% 4 13% 41% 33% 5%	740
	11th to 20th	Night	5% 2 15% 45% 27% 6%	760
	21st to end	Night	5% 4 17% 44% 26% 4	760
December	1st to 10th	Night	11% 5% 16% 41% 24% 3	760
	11th to 20th	Night	14% 4 17% 42% 20% 2	760
	21st to end	Night	11% 6% 23% 40% 17% 3	836

Page generated at 2024-02-07 03:11:58. Version ac07

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