CARMA
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the CARMA clear sky chart from 2005-11-06 to 2024-04-03.

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	2 2 1 3 3 2 3 4 5% 7% 69%	78964
	Night	1 3 1 3 3 2 3 3 5% 7% 69%	81189
Transparency	Day	14% 3 8% 20% 28% 27%	78672
	Night	14% 4 10% 24% 29% 21%	81004
Seeing	Day	4 11% 28% 32% 19% 6%	14322
	Night	2 4 23% 42% 26% 3	24028

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 2 1 2 2 2 3 4 7% 11% 64%	2539
	11th to 20th	Day	3 1 4 3 3 4 7% 7% 10% 57%	2540
	21st to end	Day	3 5% 1 3 3 2 3 4 7% 11% 57%	3178
February	1st to 10th	Day	2 3 1 3 3 2 3 4 5% 10% 66%	1900
	11th to 20th	Day	1 3 1 3 4 2 4 4 5% 9% 64%	1850
	21st to end	Day	4 1 3 3 2 4 3 5% 8% 65%	1570
March	1st to 10th	Day	1 2 1 3 4 2 4 5% 7% 9% 61%	1900
	11th to 20th	Day	1 3 1 3 4 3 4 5% 6% 11% 59%	1947
	21st to end	Day	1 3 1 2 3 2 4 5% 5% 9% 66%	2508
April	1st to 10th	Day	2 3 2 3 3 2 3 4 4 8% 67%	2185
	11th to 20th	Day	2 3 1 2 3 2 3 4 5% 7% 69%	2129
	21st to end	Day	1 2 1 2 2 2 3 3 5% 8% 70%	2160
May	1st to 10th	Day	2 3 1 4 4 2 3 3 5% 6% 68%	2321
	11th to 20th	Day	4 3 1 3 3 2 3 4 4 7% 66%	2301
	21st to end	Day	3 4 2 4 3 2 4 4 5% 7% 62%	2608
June	1st to 10th	Day	2 2 2 3 4 3 3 5% 5% 8% 63%	2520
	11th to 20th	Day	2 2 1 2 3 2 2 3 4 4 77%	2520
	21st to end	Day	1 2 1 2 3 2 2 3 3 4 77%	2520
July	1st to 10th	Day	2 2 1 2 3 2 4 4 5% 5% 71%	2520
	11th to 20th	Day	2 3 2 3 4 2 4 4 4 6% 67%	2520
	21st to end	Day	3 3 2 4 4 3 5% 5% 5% 6% 61%	2699
August	1st to 10th	Day	2 2 1 2 3 2 2 4 3 5% 73%	2149
	11th to 20th	Day	1 1 1 2 3 2 2 2 5% 5% 75%	2122
	21st to end	Day	2 2 1 2 2 1 2 3 3 5% 77%	2376
September	1st to 10th	Day	1 2 1 2 3 2 2 3 3 4 77%	2160
	11th to 20th	Day	2 1 1 1 2 1 2 2 3 4 82%	2044
	21st to end	Day	1 1 1 1 1 2 2 3 4 83%	1980
October	1st to 10th	Day	2 2 1 2 2 1 2 3 3 5% 78%	1980
	11th to 20th	Day	1 2 1 2 2 2 2 3 3 4 79%	1810
	21st to end	Day	1 1 2 1 2 3 5% 5% 79%	1872
November	1st to 10th	Day	2 1 1 2 2 3 3 4 6% 76%	1674
	11th to 20th	Day	1 1 1 2 1 1 2 3 4 5% 80%	1710
	21st to end	Day	2 2 1 1 2 3 3 4 5% 6% 72%	1710
December	1st to 10th	Day	2 2 1 2 2 2 3 5% 4 8% 69%	1710
	11th to 20th	Day	3 5% 2 4 4 3 4 5% 6% 11% 54%	1938
	21st to end	Day	2 5% 3 5% 4 2 4 5% 7% 10% 54%	2794
January	1st to 10th	Night	1 4 2 4 4 2 3 4 5% 7% 66%	4406
	11th to 20th	Night	4 2 4 3 2 3 4 5% 10% 63%	4416
	21st to end	Night	2 7% 3 4 3 2 4 5% 6% 9% 55%	4487
February	1st to 10th	Night	2 3 1 3 3 2 3 4 4 8% 67%	2280
	11th to 20th	Night	1 3 2 3 3 2 3 4 5% 8% 67%	2218
	21st to end	Night	1 3 1 4 2 2 3 4 4 8% 68%	1884
March	1st to 10th	Night	2 1 3 3 3 4 5% 5% 9% 64%	2280
	11th to 20th	Night	1 3 1 3 4 2 3 4 7% 9% 63%	2229
	21st to end	Night	1 3 1 3 3 2 4 4 5% 8% 67%	2090
April	1st to 10th	Night	2 2 2 3 3 2 3 3 5% 6% 69%	1820
	11th to 20th	Night	1 2 1 3 3 2 2 2 4 7% 73%	1779
	21st to end	Night	1 2 1 2 2 2 2 4 4 7% 72%	1800
May	1st to 10th	Night	3 3 2 3 3 2 3 3 5% 7% 68%	1638
	11th to 20th	Night	2 2 1 3 4 2 3 3 4 5% 70%	1594
	21st to end	Night	3 3 1 4 3 2 3 3 5% 6% 67%	1664
June	1st to 10th	Night	2 2 1 2 3 2 3 3 4 6% 71%	1440
	11th to 20th	Night	1 1 1 1 2 2 3 2 4 5% 79%	1440
	21st to end	Night	1 1 1 2 1 1 2 2 3 6% 80%	1440
July	1st to 10th	Night	1 1 2 3 2 3 4 3 6% 76%	1440
	11th to 20th	Night	2 1 1 2 3 2 3 3 5% 6% 72%	1440
	21st to end	Night	3 2 1 4 3 2 3 4 6% 7% 65%	1612
August	1st to 10th	Night	2 2 1 3 2 2 3 3 4 5% 73%	1788
	11th to 20th	Night	1 1 1 2 2 2 3 4 4 81%	1780
	21st to end	Night	2 1 1 1 2 2 3 3 4 4 78%	1980
September	1st to 10th	Night	1 1 1 1 1 1 1 2 3 4 84%	1800
	11th to 20th	Night	1 1 2 1 1 1 2 2 4 84%	1916
	21st to end	Night	1 2 1 1 1 1 2 2 2 4 83%	1980
October	1st to 10th	Night	2 2 1 2 2 1 2 2 3 4 79%	1980
	11th to 20th	Night	1 1 1 2 2 1 2 2 3 5% 80%	2146
	21st to end	Night	1 1 1 2 1 2 2 4 5% 81%	2484
November	1st to 10th	Night	1 1 1 1 2 2 3 6% 82%	2405
	11th to 20th	Night	1 1 2 2 1 2 2 4 8% 76%	2470
	21st to end	Night	2 1 1 2 3 2 3 3 4 9% 71%	2470
December	1st to 10th	Night	1 2 2 3 3 2 4 4 6% 8% 67%	2470
	11th to 20th	Night	1 6% 1 4 3 2 4 5% 7% 11% 55%	3261
	21st to end	Night	3 4 1 4 4 3 5% 6% 7% 11% 52%	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	11% 6% 14% 37% 29% 3	2539
	11th to 20th	Day	15% 7% 21% 25% 25% 7%	2540
	21st to end	Day	18% 5% 18% 29% 25% 5%	3178
February	1st to 10th	Day	14% 3 11% 29% 28% 15%	1900
	11th to 20th	Day	16% 4 8% 25% 36% 11%	1860
	21st to end	Day	15% 3 11% 32% 29% 11%	1570
March	1st to 10th	Day	16% 5% 8% 30% 30% 11%	1900
	11th to 20th	Day	18% 3 9% 28% 28% 14%	1947
	21st to end	Day	13% 3 13% 30% 30% 10%	2508
April	1st to 10th	Day	16% 2 10% 29% 27% 16%	2185
	11th to 20th	Day	14% 3 9% 21% 34% 20%	2132
	21st to end	Day	11% 3 8% 28% 35% 15%	2160
May	1st to 10th	Day	15% 3 5% 19% 39% 18%	2321
	11th to 20th	Day	18% 2 5% 20% 38% 17%	2304
	21st to end	Day	20% 3 7% 20% 34% 16%	2608
June	1st to 10th	Day	16% 4 8% 13% 29% 30%	2520
	11th to 20th	Day	11% 2 4 10% 27% 47%	2520
	21st to end	Day	11% 2 3 5% 22% 57%	2520
July	1st to 10th	Day	14% 3 4 6% 14% 58%	2451
	11th to 20th	Day	16% 4 6% 10% 17% 47%	2445
	21st to end	Day	19% 6% 6% 12% 18% 39%	2549
August	1st to 10th	Day	13% 3 5% 7% 18% 55%	2135
	11th to 20th	Day	9% 3 5% 6% 22% 54%	2122
	21st to end	Day	10% 2 3 6% 22% 57%	2376
September	1st to 10th	Day	11% 3 3 8% 18% 57%	2160
	11th to 20th	Day	8% 2 3 10% 31% 46%	2044
	21st to end	Day	7% 1 3 11% 38% 41%	1980
October	1st to 10th	Day	9% 2 5% 15% 34% 35%	1980
	11th to 20th	Day	10% 2 3 13% 36% 37%	1810
	21st to end	Day	7% 1 4 19% 41% 27%	1872
November	1st to 10th	Day	10% 2 8% 24% 35% 21%	1674
	11th to 20th	Day	7% 2 7% 28% 41% 15%	1710
	21st to end	Day	12% 2 9% 26% 33% 17%	1710
December	1st to 10th	Day	14% 4 12% 29% 28% 14%	1710
	11th to 20th	Day	22% 6% 11% 28% 25% 7%	1938
	21st to end	Day	20% 8% 15% 27% 23% 7%	2794
January	1st to 10th	Night	16% 5% 14% 36% 26% 4	4406
	11th to 20th	Night	15% 5% 18% 35% 20% 6%	4416
	21st to end	Night	21% 7% 17% 30% 20% 5%	4487
February	1st to 10th	Night	16% 4 12% 28% 26% 14%	2280
	11th to 20th	Night	15% 5% 9% 28% 32% 11%	2219
	21st to end	Night	14% 3 11% 30% 33% 9%	1884
March	1st to 10th	Night	15% 3 10% 33% 28% 11%	2280
	11th to 20th	Night	14% 4 13% 28% 32% 10%	2229
	21st to end	Night	15% 4 11% 34% 30% 6%	2090
April	1st to 10th	Night	16% 3 10% 31% 27% 12%	1820
	11th to 20th	Night	12% 2 9% 29% 33% 15%	1779
	21st to end	Night	12% 3 9% 33% 32% 11%	1800
May	1st to 10th	Night	17% 2 6% 25% 36% 14%	1638
	11th to 20th	Night	16% 3 6% 23% 38% 15%	1595
	21st to end	Night	17% 3 9% 22% 34% 14%	1664
June	1st to 10th	Night	13% 3 8% 16% 33% 27%	1440
	11th to 20th	Night	9% 3 5% 13% 29% 42%	1440
	21st to end	Night	8% 1 4 8% 28% 52%	1440
July	1st to 10th	Night	10% 2 4 9% 17% 58%	1400
	11th to 20th	Night	12% 3 7% 12% 20% 47%	1392
	21st to end	Night	17% 4 8% 13% 22% 37%	1522
August	1st to 10th	Night	13% 3 3 9% 20% 51%	1779
	11th to 20th	Night	7% 2 4 9% 27% 51%	1780
	21st to end	Night	9% 2 2 9% 26% 52%	1980
September	1st to 10th	Night	6% 2 3 9% 27% 54%	1800
	11th to 20th	Night	8% 1 3 12% 32% 44%	1916
	21st to end	Night	8% 1 2 11% 35% 42%	1980
October	1st to 10th	Night	10% 1 5% 16% 35% 33%	1980
	11th to 20th	Night	10% 1 3 16% 39% 31%	2146
	21st to end	Night	7% 2 5% 17% 43% 27%	2484
November	1st to 10th	Night	6% 1 8% 25% 38% 21%	2405
	11th to 20th	Night	9% 2 10% 26% 36% 17%	2470
	21st to end	Night	12% 2 9% 23% 39% 14%	2470
December	1st to 10th	Night	14% 5% 11% 30% 26% 13%	2470
	11th to 20th	Night	20% 6% 15% 30% 24% 6%	3261
	21st to end	Night	21% 8% 15% 29% 21% 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	7% 7% 32% 33% 16% 4	180
	11th to 20th	Day	1 7% 30% 34% 18% 9%	180
	21st to end	Day	6% 11% 22% 33% 23% 6%	416
February	1st to 10th	Day	6% 11% 29% 31% 18% 5%	460
	11th to 20th	Day	5% 13% 31% 36% 12% 3	455
	21st to end	Day	6% 9% 32% 39% 12% 2	382
March	1st to 10th	Day	5% 14% 36% 32% 10% 3	460
	11th to 20th	Day	5% 17% 30% 29% 15% 3	460
	21st to end	Day	6% 20% 35% 30% 8% 2	506
April	1st to 10th	Day	8% 18% 29% 27% 15% 3	429
	11th to 20th	Day	11% 18% 28% 30% 12% 2	412
	21st to end	Day	6% 19% 34% 23% 12% 7%	420
May	1st to 10th	Day	7% 16% 35% 25% 13% 3	423
	11th to 20th	Day	10% 13% 26% 29% 18% 4	448
	21st to end	Day	7% 14% 27% 29% 18% 5%	485
June	1st to 10th	Day	5% 13% 27% 30% 18% 8%	450
	11th to 20th	Day	3 14% 30% 28% 18% 7%	450
	21st to end	Day	2 12% 27% 32% 20% 7%	450
July	1st to 10th	Day	2 8% 27% 34% 21% 8%	446
	11th to 20th	Day	3 5% 21% 35% 24% 11%	444
	21st to end	Day	3 5% 26% 32% 23% 11%	487
August	1st to 10th	Day	2 8% 34% 31% 17% 8%	447
	11th to 20th	Day	1 7% 25% 32% 22% 13%	437
	21st to end	Day	2 4 32% 31% 22% 10%	495
September	1st to 10th	Day	3 8% 25% 34% 20% 10%	450
	11th to 20th	Day	4 10% 28% 33% 20% 4	450
	21st to end	Day	2 8% 28% 35% 23% 4	450
October	1st to 10th	Day	3 9% 31% 27% 23% 6%	450
	11th to 20th	Day	3 7% 25% 36% 24% 5%	450
	21st to end	Day	2 9% 23% 34% 23% 9%	387
November	1st to 10th	Day	2 5% 23% 34% 29% 6%	270
	11th to 20th	Day	3 6% 20% 37% 23% 11%	270
	21st to end	Day	3 4 23% 34% 30% 6%	270
December	1st to 10th	Day	2 3 28% 42% 19% 6%	270
	11th to 20th	Day	1 11% 27% 32% 21% 8%	185
	21st to end	Day	4 10% 31% 32% 21% 3	198
January	1st to 10th	Night	3 4 28% 38% 21% 5%	760
	11th to 20th	Night	1 2 33% 42% 17% 5%	760
	21st to end	Night	3 5% 31% 39% 18% 3	836
February	1st to 10th	Night	4 6% 28% 39% 20% 3	760
	11th to 20th	Night	2 5% 28% 42% 20% 2	744
	21st to end	Night	3 6% 35% 43% 12% 1	628
March	1st to 10th	Night	2 4 33% 44% 14% 3	760
	11th to 20th	Night	3 6% 27% 39% 23% 3	760
	21st to end	Night	3 7% 32% 42% 15% 1	836
April	1st to 10th	Night	4 6% 28% 42% 19% 1	728
	11th to 20th	Night	3 9% 28% 39% 18% 3	711
	21st to end	Night	2 6% 29% 38% 23% 3	720
May	1st to 10th	Night	4 6% 29% 44% 16% 2	558
	11th to 20th	Night	3 5% 27% 40% 24% 1	531
	21st to end	Night	5% 7% 22% 41% 24% 1	502
June	1st to 10th	Night	3 3 19% 44% 28% 3	360
	11th to 20th	Night	1 3 15% 51% 29% 1	360
	21st to end	Night	1 1 13% 54% 30% 1	360
July	1st to 10th	Night	1 3 49% 44% 3	350
	11th to 20th	Night	2 3 46% 47% 3	348
	21st to end	Night	2 1 7% 44% 44% 2	430
August	1st to 10th	Night	2 2 13% 46% 35% 2	714
	11th to 20th	Night	1 1 9% 47% 39% 3	712
	21st to end	Night	2 8% 45% 43% 3	792
September	1st to 10th	Night	2 1 10% 41% 42% 4	720
	11th to 20th	Night	1 1 11% 48% 35% 4	720
	21st to end	Night	1 1 14% 38% 42% 4	720
October	1st to 10th	Night	2 1 19% 43% 31% 4	720
	11th to 20th	Night	2 3 16% 43% 30% 5%	720
	21st to end	Night	1 4 20% 36% 31% 8%	792
November	1st to 10th	Night	1 1 22% 41% 30% 6%	740
	11th to 20th	Night	1 2 23% 46% 24% 4	760
	21st to end	Night	3 2 24% 42% 26% 3	760
December	1st to 10th	Night	3 3 26% 47% 18% 4	760
	11th to 20th	Night	2 3 31% 44% 17% 3	760
	21st to end	Night	4 4 33% 39% 18% 1	836

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