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 2024-11-01.

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	7% 6% 2 8% 6% 6% 6% 5% 7% 10% 36%	100601
	Night	7% 6% 2 7% 5% 5% 5% 5% 7% 10% 42%	98298
Transparency	Day	40% 10% 17% 19% 11% 3	100409
	Night	34% 11% 19% 20% 12% 3	98160
Seeing	Day	7% 3 13% 25% 27% 25%	15828
	Night	7% 3 14% 34% 31% 11%	25926

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	9% 7% 3 7% 5% 4 4 4 6% 9% 41%	2836
	11th to 20th	Day	16% 8% 2 8% 6% 6% 5% 4 6% 9% 30%	2840
	21st to end	Day	8% 7% 3 8% 6% 6% 5% 4 6% 7% 41%	3289
February	1st to 10th	Day	9% 7% 2 7% 5% 6% 5% 4 6% 8% 43%	1900
	11th to 20th	Day	6% 3 1 5% 3 4 4 3 6% 9% 55%	1890
	21st to end	Day	5% 5% 2 4 4 6% 5% 5% 6% 9% 50%	1727
March	1st to 10th	Day	5% 4 2 8% 6% 7% 6% 6% 8% 11% 36%	3435
	11th to 20th	Day	4 3 1 5% 4 4 5% 4 7% 10% 53%	3480
	21st to end	Day	9% 4 1 5% 4 4 5% 3 5% 8% 51%	3815
April	1st to 10th	Day	4 3 1 6% 5% 6% 6% 4 7% 11% 47%	2090
	11th to 20th	Day	5% 5% 2 6% 6% 7% 5% 5% 7% 9% 42%	2098
	21st to end	Day	7% 3 2 6% 6% 5% 5% 5% 7% 7% 47%	2280
May	1st to 10th	Day	3 2 1 5% 4 5% 5% 4 6% 8% 56%	3765
	11th to 20th	Day	6% 5% 2 5% 5% 5% 6% 5% 7% 10% 45%	3983
	21st to end	Day	6% 4 2 6% 6% 6% 6% 4 7% 9% 44%	4476
June	1st to 10th	Day	14% 10% 4 11% 8% 8% 7% 6% 7% 7% 18%	2470
	11th to 20th	Day	9% 7% 3 12% 7% 9% 8% 7% 8% 9% 21%	2470
	21st to end	Day	8% 7% 4 12% 8% 8% 8% 6% 9% 9% 22%	2470
July	1st to 10th	Day	6% 7% 3 10% 7% 8% 8% 6% 9% 12% 24%	4120
	11th to 20th	Day	7% 7% 4 10% 8% 8% 7% 6% 8% 13% 23%	4120
	21st to end	Day	5% 6% 3 8% 8% 7% 8% 7% 9% 14% 26%	4466
August	1st to 10th	Day	4 6% 4 11% 9% 9% 8% 7% 8% 11% 22%	4104
	11th to 20th	Day	4 5% 2 8% 8% 8% 9% 7% 10% 14% 26%	3619
	21st to end	Day	5% 6% 3 10% 8% 8% 8% 6% 10% 12% 23%	3828
September	1st to 10th	Day	7% 6% 4 10% 9% 9% 8% 7% 8% 11% 21%	2090
	11th to 20th	Day	8% 8% 3 11% 8% 8% 9% 6% 8% 9% 22%	2090
	21st to end	Day	11% 9% 4 10% 8% 8% 7% 6% 7% 9% 22%	2090
October	1st to 10th	Day	8% 6% 3 10% 8% 7% 6% 5% 8% 9% 28%	2052
	11th to 20th	Day	7% 5% 3 8% 7% 7% 7% 6% 7% 9% 33%	1900
	21st to end	Day	8% 6% 3 7% 4 6% 6% 4 5% 9% 40%	2090
November	1st to 10th	Day	7% 5% 2 6% 5% 5% 6% 4 6% 8% 48%	1857
	11th to 20th	Day	8% 6% 2 6% 7% 6% 7% 5% 6% 7% 40%	1900
	21st to end	Day	6% 5% 2 7% 6% 5% 5% 5% 6% 9% 44%	1900
December	1st to 10th	Day	7% 6% 2 6% 4 4 5% 4 7% 7% 48%	1784
	11th to 20th	Day	7% 7% 2 6% 5% 4 6% 4 7% 8% 44%	2153
	21st to end	Day	11% 5% 3 8% 6% 6% 5% 6% 7% 10% 35%	3124
January	1st to 10th	Night	8% 6% 2 8% 5% 5% 5% 4 7% 10% 40%	4109
	11th to 20th	Night	16% 10% 4 9% 6% 5% 4 4 6% 7% 29%	4120
	21st to end	Night	7% 6% 3 8% 5% 5% 5% 5% 7% 8% 41%	4362
February	1st to 10th	Night	8% 6% 2 5% 4 5% 4 4 7% 8% 48%	2280
	11th to 20th	Night	6% 4 1 3 4 4 4 3 6% 9% 56%	2174
	21st to end	Night	4 3 1 4 3 3 4 4 5% 9% 60%	1727
March	1st to 10th	Night	8% 6% 2 8% 6% 5% 5% 4 7% 7% 42%	3418
	11th to 20th	Night	5% 3 1 5% 4 3 4 3 7% 10% 54%	3480
	21st to end	Night	9% 5% 2 5% 3 3 4 3 5% 8% 53%	3817
April	1st to 10th	Night	4 3 1 4 4 4 4 4 7% 9% 56%	2090
	11th to 20th	Night	5% 3 2 5% 4 3 4 4 7% 11% 53%	2031
	21st to end	Night	6% 3 2 4 4 4 4 3 6% 8% 56%	1900
May	1st to 10th	Night	7% 4 1 5% 3 4 3 3 6% 7% 58%	3130
	11th to 20th	Night	4 3 1 5% 4 4 3 4 7% 10% 54%	2922
	21st to end	Night	6% 4 2 5% 4 4 4 4 7% 8% 51%	3079
June	1st to 10th	Night	11% 9% 3 9% 6% 6% 6% 6% 8% 9% 27%	1710
	11th to 20th	Night	7% 6% 3 7% 5% 6% 7% 6% 9% 13% 31%	1710
	21st to end	Night	6% 7% 3 8% 6% 7% 7% 6% 9% 12% 30%	1710
July	1st to 10th	Night	5% 8% 3 9% 7% 6% 6% 6% 9% 12% 32%	2840
	11th to 20th	Night	4 6% 3 9% 6% 7% 8% 7% 9% 11% 30%	2840
	21st to end	Night	4 6% 3 8% 7% 7% 7% 6% 9% 11% 32%	3087
August	1st to 10th	Night	4 5% 2 9% 6% 7% 6% 6% 9% 14% 33%	2825
	11th to 20th	Night	6% 6% 3 9% 6% 7% 8% 7% 9% 12% 27%	3171
	21st to end	Night	5% 4 3 9% 6% 7% 7% 7% 12% 14% 27%	3828
September	1st to 10th	Night	5% 5% 3 7% 6% 7% 7% 7% 11% 13% 31%	2090
	11th to 20th	Night	9% 6% 4 9% 6% 7% 6% 5% 7% 10% 30%	2090
	21st to end	Night	9% 8% 3 9% 7% 7% 6% 5% 8% 10% 27%	2090
October	1st to 10th	Night	8% 7% 3 8% 5% 5% 6% 5% 7% 8% 36%	2126
	11th to 20th	Night	9% 5% 2 7% 4 4 6% 4 7% 9% 42%	2280
	21st to end	Night	10% 5% 2 7% 5% 4 4 3 5% 9% 45%	2508
November	1st to 10th	Night	7% 5% 2 5% 4 4 5% 3 5% 8% 51%	2228
	11th to 20th	Night	8% 6% 2 6% 5% 5% 4 4 7% 8% 45%	2280
	21st to end	Night	7% 6% 2 6% 5% 4 4 3 5% 9% 49%	2280
December	1st to 10th	Night	6% 5% 2 6% 5% 4 4 4 6% 8% 52%	2392
	11th to 20th	Night	10% 5% 2 5% 4 3 4 3 6% 8% 50%	3042
	21st to end	Night	9% 8% 3 7% 5% 5% 5% 4 6% 9% 37%	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	35% 12% 14% 21% 14% 4	3435
	11th to 20th	Day	23% 6% 20% 33% 14% 4	3480
	21st to end	Day	30% 6% 10% 28% 17% 9%	3815
April	1st to 10th	Day	28% 8% 15% 27% 16% 5%	2090
	11th to 20th	Day	35% 8% 14% 22% 17% 4	2098
	21st to end	Day	31% 7% 12% 22% 22% 6%	2280
May	1st to 10th	Day	22% 7% 14% 31% 23% 4	3800
	11th to 20th	Day	28% 11% 16% 35% 9%	3987
	21st to end	Day	31% 10% 16% 29% 13% 1	4489
June	1st to 10th	Day	59% 11% 16% 11% 3	2470
	11th to 20th	Day	53% 13% 19% 13% 2	2470
	21st to end	Day	54% 13% 21% 10% 1	2470
July	1st to 10th	Day	48% 14% 25% 13%	4055
	11th to 20th	Day	50% 13% 30% 7%	4051
	21st to end	Day	42% 17% 30% 10%	4324
August	1st to 10th	Day	50% 15% 24% 9% 2	4091
	11th to 20th	Day	42% 16% 30% 13%	3656
	21st to end	Day	48% 16% 29% 7% 1	3828
September	1st to 10th	Day	51% 18% 19% 11%	2090
	11th to 20th	Day	53% 15% 20% 10% 2	2090
	21st to end	Day	56% 13% 14% 12% 4 1	2090
October	1st to 10th	Day	47% 11% 14% 15% 10% 3	2052
	11th to 20th	Day	44% 9% 13% 18% 13% 4	1900
	21st to end	Day	39% 6% 9% 19% 19% 7%	2090
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% 7% 13% 22% 31% 8%	1727
March	1st to 10th	Night	37% 11% 13% 21% 14% 4	3418
	11th to 20th	Night	21% 9% 23% 29% 15% 3	3480
	21st to end	Night	27% 8% 12% 23% 25% 6%	3817
April	1st to 10th	Night	21% 7% 18% 33% 16% 5%	2090
	11th to 20th	Night	24% 7% 18% 25% 22% 4	2031
	21st to end	Night	24% 7% 15% 28% 22% 4	1900
May	1st to 10th	Night	21% 9% 17% 36% 14% 3	3160
	11th to 20th	Night	22% 9% 23% 34% 12%	2923
	21st to end	Night	24% 11% 18% 31% 15%	3087
June	1st to 10th	Night	49% 12% 20% 16% 2	1710
	11th to 20th	Night	40% 15% 26% 17% 2	1710
	21st to end	Night	42% 17% 28% 11% 2	1710
July	1st to 10th	Night	41% 15% 31% 13%	2795
	11th to 20th	Night	40% 18% 34% 7%	2786
	21st to end	Night	40% 15% 31% 14% 1	2988
August	1st to 10th	Night	38% 13% 32% 14% 3	2814
	11th to 20th	Night	43% 17% 31% 10%	3200
	21st to end	Night	39% 17% 37% 6% 1	3828
September	1st to 10th	Night	38% 19% 30% 12% 1	2090
	11th to 20th	Night	45% 16% 24% 12% 2	2090
	21st to end	Night	47% 16% 19% 12% 6%	2090
October	1st to 10th	Night	41% 12% 19% 16% 10% 2	2126
	11th to 20th	Night	35% 8% 18% 20% 16% 2	2280
	21st to end	Night	36% 7% 13% 19% 18% 7%	2508
November	1st to 10th	Night	29% 6% 14% 22% 20% 9%	2228
	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% 30% 6%	382
March	1st to 10th	Day	3 4 25% 41% 23% 4	460
	11th to 20th	Day	6% 3 25% 34% 29% 4	460
	21st to end	Day	5% 2 19% 35% 32% 7%	506
April	1st to 10th	Day	3 4 26% 35% 27% 6%	460
	11th to 20th	Day	5% 4 24% 31% 27% 9%	452
	21st to end	Day	4 4 16% 36% 31% 10%	460
May	1st to 10th	Day	4 2 8% 33% 38% 16%	463
	11th to 20th	Day	10% 2 14% 26% 28% 20%	487
	21st to end	Day	9% 2 6% 22% 30% 32%	529
June	1st to 10th	Day	16% 4 5% 19% 28% 29%	490
	11th to 20th	Day	10% 2 6% 18% 25% 39%	490
	21st to end	Day	6% 2 2 10% 24% 54%	490
July	1st to 10th	Day	5% 2 1 7% 23% 62%	485
	11th to 20th	Day	7% 2 1 8% 26% 56%	484
	21st to end	Day	6% 1 1 12% 25% 55%	532
August	1st to 10th	Day	6% 1 4 10% 26% 53%	486
	11th to 20th	Day	4 1 1 8% 27% 58%	479
	21st to end	Day	8% 2 5% 16% 27% 41%	539
September	1st to 10th	Day	7% 2 4 9% 26% 52%	490
	11th to 20th	Day	7% 1 3 12% 29% 48%	490
	21st to end	Day	10% 3 3 14% 33% 36%	490
October	1st to 10th	Day	8% 2 11% 28% 35% 16%	490
	11th to 20th	Day	8% 4 10% 29% 33% 15%	490
	21st to end	Day	9% 3 15% 33% 31% 10%	539
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	4 4 26% 47% 18% 1	760
	11th to 20th	Night	7% 3 23% 49% 18% 1	760
	21st to end	Night	5% 4 23% 48% 20%	836
April	1st to 10th	Night	4 3 18% 51% 22% 1	760
	11th to 20th	Night	6% 3 22% 46% 22% 1	751
	21st to end	Night	6% 3 16% 51% 23% 1	760
May	1st to 10th	Night	3 2 12% 46% 34% 3	760
	11th to 20th	Night	6% 2 11% 44% 32% 5%	632
	21st to end	Night	7% 1 6% 29% 47% 9%	617
June	1st to 10th	Night	12% 2 4 21% 47% 14%	570
	11th to 20th	Night	7% 2 2 12% 48% 28%	570
	21st to end	Night	5% 2 2 9% 47% 35%	570
July	1st to 10th	Night	5% 3 1 5% 44% 42%	555
	11th to 20th	Night	5% 3 1 7% 43% 42%	552
	21st to end	Night	5% 1 1 7% 41% 45%	624
August	1st to 10th	Night	6% 1 1 7% 47% 38%	567
	11th to 20th	Night	6% 2 2 7% 44% 38%	704
	21st to end	Night	9% 2 4 17% 41% 28%	836
September	1st to 10th	Night	7% 2 4 11% 43% 33%	760
	11th to 20th	Night	9% 2 4 15% 41% 28%	760
	21st to end	Night	11% 2 6% 19% 41% 21%	760
October	1st to 10th	Night	11% 3 7% 34% 37% 8%	760
	11th to 20th	Night	10% 2 9% 34% 37% 9%	760
	21st to end	Night	12% 2 14% 38% 30% 5%	836
November	1st to 10th	Night	8% 1 19% 40% 29% 3	743
	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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