Area 63
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Area 63 clear sky chart from 2005-11-06 to 2024-03-01.

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	8% 6% 3 7% 8% 5% 7% 7% 7% 9% 35%	78888
	Night	7% 5% 3 6% 6% 4 5% 6% 7% 10% 43%	80525
Transparency	Day	42% 10% 15% 17% 12% 4	78611
	Night	34% 10% 18% 21% 14% 4	80321
Seeing	Day	7% 3 13% 25% 28% 25%	14848
	Night	7% 3 14% 34% 31% 11%	25037

By Month

Percentage Cloud Cover SE (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	10% 7% 3 7% 6% 3 5% 5% 6% 9% 41%	2836
	11th to 20th	Day	16% 8% 2 7% 7% 4 5% 6% 6% 10% 31%	2840
	21st to end	Day	8% 6% 3 7% 7% 4 6% 6% 5% 7% 41%	3289
February	1st to 10th	Day	9% 6% 3 6% 5% 4 6% 4 6% 8% 43%	1900
	11th to 20th	Day	6% 3 2 5% 4 3 4 4 6% 9% 55%	1890
	21st to end	Day	5% 4 2 4 4 4 5% 6% 6% 9% 50%	1727
March	1st to 10th	Day	3 2 2 5% 6% 3 6% 6% 6% 9% 53%	1980
	11th to 20th	Day	6% 4 2 6% 5% 4 5% 5% 7% 9% 48%	1980
	21st to end	Day	4 4 2 5% 6% 4 6% 5% 4 8% 52%	2178
April	1st to 10th	Day	4 3 2 5% 6% 4 7% 6% 7% 11% 46%	1980
	11th to 20th	Day	6% 4 2 5% 7% 5% 7% 7% 7% 9% 41%	1986
	21st to end	Day	7% 3 2 5% 7% 4 6% 5% 6% 8% 47%	2160
May	1st to 10th	Day	4 2 2 4 6% 4 6% 6% 7% 8% 51%	2160
	11th to 20th	Day	9% 6% 3 7% 8% 4 6% 7% 7% 9% 34%	2245
	21st to end	Day	10% 6% 3 8% 8% 5% 7% 6% 6% 8% 31%	2531
June	1st to 10th	Day	14% 9% 4 10% 10% 6% 8% 8% 7% 7% 18%	2340
	11th to 20th	Day	9% 6% 3 10% 8% 7% 9% 8% 9% 9% 22%	2340
	21st to end	Day	8% 6% 4 10% 10% 6% 8% 8% 9% 9% 23%	2340
July	1st to 10th	Day	6% 7% 4 9% 10% 7% 9% 8% 9% 11% 21%	2340
	11th to 20th	Day	9% 7% 4 9% 9% 6% 9% 7% 7% 11% 23%	2340
	21st to end	Day	5% 6% 4 9% 10% 6% 9% 8% 9% 11% 22%	2547
August	1st to 10th	Day	6% 6% 4 8% 10% 6% 8% 9% 8% 11% 24%	2327
	11th to 20th	Day	5% 6% 2 8% 11% 7% 10% 8% 9% 13% 23%	2072
	21st to end	Day	8% 7% 4 10% 11% 7% 8% 8% 8% 9% 21%	2178
September	1st to 10th	Day	7% 6% 4 9% 11% 7% 8% 9% 8% 11% 21%	1980
	11th to 20th	Day	8% 7% 4 9% 10% 6% 9% 8% 8% 9% 23%	1980
	21st to end	Day	11% 9% 4 8% 10% 6% 8% 8% 6% 8% 21%	1980
October	1st to 10th	Day	7% 6% 3 8% 10% 5% 7% 7% 8% 10% 29%	1944
	11th to 20th	Day	7% 5% 3 6% 9% 5% 8% 7% 7% 8% 35%	1800
	21st to end	Day	8% 7% 3 6% 6% 4 6% 6% 5% 9% 40%	1980
November	1st to 10th	Day	7% 4 2 5% 5% 4 6% 5% 6% 8% 48%	1857
	11th to 20th	Day	8% 5% 3 5% 7% 5% 8% 6% 6% 7% 40%	1900
	21st to end	Day	6% 4 2 6% 7% 4 5% 7% 6% 9% 44%	1900
December	1st to 10th	Day	7% 5% 2 5% 5% 3 5% 5% 6% 8% 48%	1784
	11th to 20th	Day	7% 6% 3 5% 5% 3 5% 5% 7% 8% 45%	2153
	21st to end	Day	11% 5% 3 7% 7% 4 5% 7% 7% 10% 35%	3124
January	1st to 10th	Night	8% 6% 2 6% 6% 4 5% 6% 7% 9% 40%	4109
	11th to 20th	Night	16% 10% 4 8% 7% 4 5% 5% 6% 7% 30%	4120
	21st to end	Night	7% 6% 3 7% 6% 4 6% 6% 6% 8% 42%	4362
February	1st to 10th	Night	8% 6% 3 5% 4 3 5% 5% 6% 8% 48%	2280
	11th to 20th	Night	6% 4 1 3 4 3 4 5% 6% 9% 56%	2174
	21st to end	Night	4 2 2 3 4 2 4 5% 5% 9% 60%	1727
March	1st to 10th	Night	3 3 2 3 4 2 3 4 5% 8% 62%	1987
	11th to 20th	Night	6% 3 2 4 5% 2 4 4 6% 9% 56%	1980
	21st to end	Night	5% 3 2 4 3 2 5% 4 6% 9% 58%	2178
April	1st to 10th	Night	4 3 1 3 4 3 4 5% 7% 10% 57%	1980
	11th to 20th	Night	5% 3 2 4 5% 3 4 5% 6% 11% 52%	1923
	21st to end	Night	6% 3 1 4 4 3 5% 4 6% 8% 56%	1800
May	1st to 10th	Night	2 2 1 3 4 2 4 4 6% 9% 61%	1800
	11th to 20th	Night	6% 4 2 6% 6% 4 5% 6% 9% 11% 42%	1660
	21st to end	Night	7% 4 3 5% 5% 4 5% 7% 8% 10% 43%	1744
June	1st to 10th	Night	11% 8% 4 8% 7% 5% 6% 7% 8% 9% 26%	1620
	11th to 20th	Night	7% 5% 3 6% 6% 5% 7% 8% 9% 13% 32%	1620
	21st to end	Night	7% 6% 3 7% 7% 5% 8% 7% 8% 12% 30%	1620
July	1st to 10th	Night	5% 6% 3 6% 7% 5% 6% 8% 8% 12% 34%	1620
	11th to 20th	Night	5% 5% 3 7% 5% 4 7% 9% 10% 12% 34%	1620
	21st to end	Night	4 4 3 6% 8% 5% 8% 8% 8% 12% 35%	1771
August	1st to 10th	Night	5% 5% 2 7% 6% 5% 7% 8% 8% 14% 32%	1611
	11th to 20th	Night	5% 5% 2 5% 6% 5% 9% 9% 8% 13% 33%	1804
	21st to end	Night	8% 6% 4 8% 7% 4 7% 7% 9% 11% 29%	2178
September	1st to 10th	Night	5% 4 3 6% 6% 5% 7% 8% 11% 14% 33%	1980
	11th to 20th	Night	9% 6% 4 8% 7% 4 7% 6% 7% 11% 31%	1980
	21st to end	Night	9% 8% 3 8% 8% 5% 7% 7% 8% 10% 27%	1980
October	1st to 10th	Night	7% 7% 3 6% 6% 4 5% 7% 7% 9% 38%	2014
	11th to 20th	Night	8% 5% 2 6% 5% 3 6% 5% 7% 9% 44%	2160
	21st to end	Night	10% 5% 2 6% 6% 3 4 4 5% 9% 45%	2376
November	1st to 10th	Night	7% 5% 2 4 5% 3 5% 4 5% 8% 51%	2221
	11th to 20th	Night	8% 6% 3 5% 5% 4 5% 5% 7% 8% 45%	2280
	21st to end	Night	7% 5% 3 5% 5% 3 4 4 5% 9% 49%	2280
December	1st to 10th	Night	6% 4 2 6% 5% 3 5% 5% 5% 8% 52%	2392
	11th to 20th	Night	11% 4 2 4 4 2 4 4 5% 8% 50%	3042
	21st to end	Night	9% 8% 3 6% 6% 4 6% 6% 6% 9% 38%	4532

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	38% 7% 11% 22% 17% 5%	2837
	11th to 20th	Day	48% 8% 13% 17% 11% 3	2840
	21st to end	Day	39% 7% 9% 21% 18% 6%	3289
February	1st to 10th	Day	38% 5% 10% 23% 17% 6%	1900
	11th to 20th	Day	25% 6% 10% 26% 24% 10%	1900
	21st to end	Day	27% 7% 11% 20% 25% 10%	1727
March	1st to 10th	Day	24% 8% 11% 27% 23% 7%	1980
	11th to 20th	Day	31% 6% 11% 26% 19% 7%	1980
	21st to end	Day	30% 6% 11% 24% 20% 9%	2178
April	1st to 10th	Day	29% 9% 15% 26% 16% 5%	1980
	11th to 20th	Day	37% 8% 14% 22% 16% 4	1986
	21st to end	Day	31% 7% 12% 22% 22% 6%	2160
May	1st to 10th	Day	28% 6% 13% 23% 22% 7%	2160
	11th to 20th	Day	43% 9% 15% 21% 12% 1	2249
	21st to end	Day	48% 9% 14% 16% 12% 1	2531
June	1st to 10th	Day	61% 10% 16% 11% 3	2340
	11th to 20th	Day	52% 14% 20% 13% 1	2340
	21st to end	Day	54% 14% 21% 10% 1	2340
July	1st to 10th	Day	53% 16% 23% 7%	2275
	11th to 20th	Day	52% 14% 24% 9%	2271
	21st to end	Day	50% 16% 25% 9%	2405
August	1st to 10th	Day	49% 16% 25% 10% 1	2314
	11th to 20th	Day	47% 18% 26% 9%	2072
	21st to end	Day	55% 16% 21% 8% 1	2178
September	1st to 10th	Day	52% 17% 19% 11%	1980
	11th to 20th	Day	53% 15% 20% 10% 2	1980
	21st to end	Day	57% 13% 14% 10% 4 1	1980
October	1st to 10th	Day	46% 11% 15% 15% 10% 3	1944
	11th to 20th	Day	43% 9% 12% 18% 13% 4	1800
	21st to end	Day	40% 7% 9% 18% 18% 8%	1980
November	1st to 10th	Day	32% 7% 14% 20% 18% 10%	1857
	11th to 20th	Day	40% 7% 10% 20% 15% 7%	1900
	21st to end	Day	34% 8% 13% 20% 21% 4	1900
December	1st to 10th	Day	33% 5% 13% 24% 21% 4	1784
	11th to 20th	Day	34% 6% 12% 20% 19% 9%	2150
	21st to end	Day	41% 8% 15% 18% 14% 3	3124
January	1st to 10th	Night	37% 8% 14% 22% 16% 4	4109
	11th to 20th	Night	52% 8% 12% 17% 9% 3	4120
	21st to end	Night	37% 7% 11% 21% 17% 6%	4362
February	1st to 10th	Night	32% 7% 13% 24% 19% 5%	2280
	11th to 20th	Night	24% 5% 12% 27% 22% 9%	2175
	21st to end	Night	20% 6% 13% 23% 30% 8%	1727
March	1st to 10th	Night	20% 6% 12% 30% 24% 7%	1987
	11th to 20th	Night	24% 6% 16% 30% 19% 5%	1980
	21st to end	Night	23% 7% 12% 28% 24% 6%	2178
April	1st to 10th	Night	21% 7% 18% 33% 16% 5%	1980
	11th to 20th	Night	25% 7% 18% 24% 21% 4	1923
	21st to end	Night	24% 7% 15% 28% 22% 4	1800
May	1st to 10th	Night	18% 7% 15% 34% 21% 6%	1800
	11th to 20th	Night	31% 11% 21% 22% 15%	1661
	21st to end	Night	32% 11% 19% 23% 15%	1745
June	1st to 10th	Night	50% 12% 20% 15% 2	1620
	11th to 20th	Night	39% 16% 27% 17% 2	1620
	21st to end	Night	42% 17% 28% 11% 2	1620
July	1st to 10th	Night	39% 18% 31% 11%	1575
	11th to 20th	Night	35% 17% 36% 12% 1	1566
	21st to end	Night	37% 16% 33% 13% 1	1672
August	1st to 10th	Night	38% 15% 31% 15% 1	1600
	11th to 20th	Night	37% 20% 32% 11%	1804
	21st to end	Night	43% 17% 29% 10% 2	2178
September	1st to 10th	Night	36% 19% 32% 12% 1	1980
	11th to 20th	Night	45% 16% 24% 12% 2	1980
	21st to end	Night	48% 16% 19% 11% 6%	1980
October	1st to 10th	Night	39% 12% 20% 16% 10% 2	2014
	11th to 20th	Night	34% 8% 18% 21% 17% 2	2160
	21st to end	Night	35% 8% 13% 19% 18% 7%	2376
November	1st to 10th	Night	29% 6% 14% 21% 20% 9%	2221
	11th to 20th	Night	36% 7% 10% 26% 16% 6%	2280
	21st to end	Night	32% 7% 12% 22% 22% 5%	2280
December	1st to 10th	Night	28% 7% 14% 29% 18% 4	2392
	11th to 20th	Night	30% 6% 11% 23% 20% 9%	3044
	21st to end	Night	39% 9% 17% 18% 15% 2	4532

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	9% 7% 30% 33% 18% 3	270
	11th to 20th	Day	11% 6% 29% 33% 17% 4	270
	21st to end	Day	12% 8% 33% 34% 12% 1	297
February	1st to 10th	Day	7% 9% 23% 35% 21% 4	270
	11th to 20th	Day	6% 4 23% 38% 21% 8%	312
	21st to end	Day	5% 5% 18% 38% 29% 6%	382
March	1st to 10th	Day	3 3 25% 40% 25% 4	420
	11th to 20th	Day	6% 3 24% 33% 29% 5%	420
	21st to end	Day	3 2 19% 34% 35% 7%	462
April	1st to 10th	Day	3 4 25% 33% 28% 6%	420
	11th to 20th	Day	5% 4 23% 31% 28% 9%	412
	21st to end	Day	4 4 15% 34% 32% 11%	420
May	1st to 10th	Day	4 2 8% 33% 37% 16%	423
	11th to 20th	Day	10% 2 13% 25% 29% 22%	447
	21st to end	Day	9% 2 6% 22% 28% 32%	485
June	1st to 10th	Day	17% 4 4 19% 27% 29%	450
	11th to 20th	Day	8% 2 5% 16% 26% 43%	450
	21st to end	Day	5% 2 2 10% 25% 56%	450
July	1st to 10th	Day	5% 2 1 6% 22% 64%	445
	11th to 20th	Day	7% 2 1 7% 27% 56%	444
	21st to end	Day	6% 1 1 12% 25% 56%	488
August	1st to 10th	Day	5% 1 2 9% 26% 57%	446
	11th to 20th	Day	4 1 1 8% 28% 58%	439
	21st to end	Day	8% 3 5% 15% 27% 42%	495
September	1st to 10th	Day	7% 2 4 9% 26% 52%	450
	11th to 20th	Day	6% 1 3 12% 27% 50%	450
	21st to end	Day	11% 2 3 12% 35% 36%	450
October	1st to 10th	Day	7% 1 10% 29% 37% 16%	450
	11th to 20th	Day	8% 4 9% 28% 35% 16%	450
	21st to end	Day	9% 3 13% 32% 32% 11%	495
November	1st to 10th	Day	7% 4 18% 30% 29% 12%	455
	11th to 20th	Day	9% 3 22% 32% 26% 8%	460
	21st to end	Day	5% 2 22% 34% 31% 6%	460
December	1st to 10th	Day	8% 5% 20% 33% 29% 5%	344
	11th to 20th	Day	9% 4 21% 35% 19% 11%	270
	21st to end	Day	6% 5% 23% 33% 25% 8%	297
January	1st to 10th	Night	8% 5% 21% 46% 19% 2	760
	11th to 20th	Night	9% 4 25% 43% 19% 1	760
	21st to end	Night	8% 4 29% 46% 13%	836
February	1st to 10th	Night	10% 5% 23% 47% 15% 1	760
	11th to 20th	Night	7% 3 25% 45% 18% 1	743
	21st to end	Night	4 4 21% 51% 19%	628
March	1st to 10th	Night	3 4 26% 47% 19% 1	723
	11th to 20th	Night	7% 3 22% 49% 18% 1	720
	21st to end	Night	4 4 22% 49% 21%	792
April	1st to 10th	Night	4 3 18% 50% 23% 1	720
	11th to 20th	Night	6% 3 21% 47% 23% 1	711
	21st to end	Night	6% 3 16% 51% 23% 1	720
May	1st to 10th	Night	3 2 12% 46% 35% 3	720
	11th to 20th	Night	6% 2 10% 44% 34% 5%	599
	21st to end	Night	7% 1 6% 29% 48% 10%	584
June	1st to 10th	Night	13% 1 4 20% 47% 15%	540
	11th to 20th	Night	6% 2 1 11% 50% 30%	540
	21st to end	Night	5% 2 2 9% 46% 35%	540
July	1st to 10th	Night	5% 2 1 4 44% 43%	525
	11th to 20th	Night	4 3 1 7% 44% 41%	522
	21st to end	Night	5% 1 1 7% 40% 46%	591
August	1st to 10th	Night	6% 1 6% 47% 39%	537
	11th to 20th	Night	6% 2 2 8% 44% 39%	666
	21st to end	Night	9% 2 4 16% 40% 28%	792
September	1st to 10th	Night	6% 2 4 11% 43% 34%	720
	11th to 20th	Night	9% 2 4 15% 41% 28%	720
	21st to end	Night	12% 2 5% 19% 42% 21%	720
October	1st to 10th	Night	10% 3 7% 35% 38% 8%	720
	11th to 20th	Night	10% 2 8% 34% 38% 9%	720
	21st to end	Night	12% 2 13% 37% 32% 5%	792
November	1st to 10th	Night	8% 1 19% 40% 29% 3	740
	11th to 20th	Night	9% 3 16% 43% 25% 4	760
	21st to end	Night	9% 2 18% 44% 26% 1	760
December	1st to 10th	Night	7% 2 17% 43% 30% 1	760
	11th to 20th	Night	10% 3 17% 40% 28% 3	760
	21st to end	Night	7% 3 19% 43% 27% 1	836

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