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Peach Mountain Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Peach Mountain Observatory clear sky chart from 2005-11-06 to 2024-11-06.

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	14% 10% 4 8% 5% 5% 5% 4 6% 7% 34%	100967
	Night	14% 11% 4 8% 5% 4 4 3 5% 7% 35%	98097
Transparency	Day	47% 7% 12% 21% 13% 1	104581
	Night	47% 6% 12% 21% 13% 1	102623
Seeing	Day	17% 11% 29% 23% 14% 6%	15579
	Night	19% 10% 29% 29% 12% 1	25529

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	16% 20% 6% 11% 5% 5% 5% 3 4 5% 21%	2527
	11th to 20th	Day	16% 18% 6% 12% 6% 7% 7% 4 5% 5% 13%	2530
	21st to end	Day	28% 21% 7% 10% 5% 3 3 2 3 4 14%	3001
February	1st to 10th	Day	14% 15% 5% 13% 8% 4 6% 4 6% 6% 21%	1710
	11th to 20th	Day	14% 12% 5% 14% 9% 4 5% 2 4 6% 25%	1827
	21st to end	Day	15% 16% 4 12% 6% 5% 3 3 5% 6% 25%	1570
March	1st to 10th	Day	17% 15% 5% 9% 5% 4 4 3 5% 5% 26%	3152
	11th to 20th	Day	13% 12% 4 9% 6% 5% 5% 3 5% 6% 33%	3480
	21st to end	Day	19% 13% 4 10% 6% 5% 5% 3 5% 6% 27%	3815
April	1st to 10th	Day	17% 12% 4 6% 6% 4 5% 4 5% 7% 30%	2243
	11th to 20th	Day	17% 9% 4 7% 5% 5% 4 4 5% 7% 35%	2380
	21st to end	Day	17% 10% 3 8% 5% 4 4 2 5% 6% 35%	2470
May	1st to 10th	Day	17% 9% 2 7% 4 4 5% 3 6% 7% 35%	4082
	11th to 20th	Day	15% 7% 3 7% 5% 5% 5% 4 6% 8% 35%	4081
	21st to end	Day	10% 6% 2 6% 4 5% 4 4 5% 8% 45%	4530
June	1st to 10th	Day	10% 6% 2 6% 5% 5% 5% 4 6% 9% 42%	2660
	11th to 20th	Day	10% 7% 3 6% 4 6% 5% 4 7% 8% 41%	2660
	21st to end	Day	9% 6% 2 7% 5% 5% 6% 5% 8% 9% 38%	2660
July	1st to 10th	Day	10% 7% 3 6% 5% 6% 6% 5% 7% 10% 37%	4440
	11th to 20th	Day	7% 4 2 5% 4 4 5% 4 6% 10% 48%	4440
	21st to end	Day	6% 6% 2 6% 6% 6% 5% 5% 7% 9% 41%	4602
August	1st to 10th	Day	11% 5% 2 6% 4 5% 5% 4 6% 9% 42%	4104
	11th to 20th	Day	10% 7% 2 7% 4 5% 5% 4 7% 9% 40%	4044
	21st to end	Day	7% 6% 2 6% 6% 5% 6% 4 7% 10% 41%	4414
September	1st to 10th	Day	10% 6% 2 7% 5% 5% 5% 4 5% 8% 42%	2171
	11th to 20th	Day	9% 5% 2 4 4 4 5% 4 6% 8% 48%	2090
	21st to end	Day	13% 7% 3 8% 4 4 6% 4 6% 8% 37%	2090
October	1st to 10th	Day	13% 7% 3 7% 5% 4 5% 4 5% 7% 42%	2062
	11th to 20th	Day	17% 8% 3 9% 6% 5% 4 4 5% 6% 33%	1900
	21st to end	Day	19% 10% 4 7% 5% 4 4 4 4 7% 30%	1905
November	1st to 10th	Day	11% 10% 4 8% 5% 4 4 4 5% 7% 39%	1717
	11th to 20th	Day	14% 14% 4 9% 5% 5% 4 3 5% 6% 30%	1710
	21st to end	Day	20% 12% 4 7% 6% 5% 4 4 5% 6% 28%	1710
December	1st to 10th	Day	13% 17% 7% 12% 7% 5% 5% 3 5% 6% 21%	1543
	11th to 20th	Day	15% 16% 7% 10% 5% 5% 5% 5% 6% 7% 21%	1864
	21st to end	Day	24% 21% 8% 12% 6% 4 4 3 3 4 11%	2783
January	1st to 10th	Night	16% 16% 7% 12% 6% 5% 4 3 5% 5% 23%	4428
	11th to 20th	Night	15% 16% 7% 15% 6% 5% 6% 4 5% 6% 14%	4440
	21st to end	Night	24% 18% 8% 11% 5% 4 3 2 3 4 16%	4656
February	1st to 10th	Night	17% 16% 5% 10% 8% 5% 5% 3 5% 5% 23%	2470
	11th to 20th	Night	14% 13% 5% 10% 6% 4 5% 3 5% 5% 28%	2237
	21st to end	Night	18% 11% 4 11% 5% 4 4 3 6% 6% 28%	1884
March	1st to 10th	Night	16% 13% 4 7% 5% 4 3 3 5% 6% 35%	3701
	11th to 20th	Night	9% 8% 3 5% 5% 4 5% 4 6% 8% 43%	3480
	21st to end	Night	16% 10% 3 8% 5% 4 4 4 5% 6% 35%	3817
April	1st to 10th	Night	16% 9% 3 7% 6% 4 4 4 4 6% 36%	1952
	11th to 20th	Night	18% 9% 2 5% 5% 5% 4 4 6% 7% 36%	1747
	21st to end	Night	16% 9% 2 6% 5% 4 4 4 5% 6% 38%	1710
May	1st to 10th	Night	17% 9% 2 7% 5% 4 5% 4 5% 8% 34%	2813
	11th to 20th	Night	15% 7% 3 7% 4 4 4 3 4 6% 42%	2812
	21st to end	Night	10% 6% 2 6% 4 4 4 3 6% 8% 47%	3022
June	1st to 10th	Night	11% 6% 2 5% 4 4 5% 3 6% 8% 47%	1520
	11th to 20th	Night	10% 6% 2 6% 4 5% 4 4 6% 9% 43%	1520
	21st to end	Night	9% 5% 3 7% 3 4 4 3 6% 11% 46%	1520
July	1st to 10th	Night	8% 3 2 5% 5% 5% 5% 4 7% 10% 47%	2530
	11th to 20th	Night	9% 3 2 4 3 3 4 3 6% 8% 55%	2530
	21st to end	Night	5% 4 2 6% 5% 5% 5% 4 8% 9% 47%	2955
August	1st to 10th	Night	10% 6% 2 6% 3 4 4 3 5% 9% 47%	2825
	11th to 20th	Night	10% 6% 2 5% 4 4 4 4 6% 7% 49%	2785
	21st to end	Night	8% 6% 2 6% 5% 5% 4 4 5% 7% 47%	3238
September	1st to 10th	Night	9% 6% 2 6% 4 4 4 4 5% 7% 49%	1990
	11th to 20th	Night	9% 6% 2 4 4 3 4 2 5% 7% 54%	2090
	21st to end	Night	14% 6% 2 7% 4 4 5% 4 5% 6% 43%	2090
October	1st to 10th	Night	12% 7% 3 6% 4 4 4 3 4 6% 47%	2116
	11th to 20th	Night	19% 9% 3 8% 5% 4 4 3 5% 6% 35%	2280
	21st to end	Night	21% 9% 3 7% 4 5% 4 4 5% 6% 34%	2688
November	1st to 10th	Night	13% 9% 3 7% 4 4 4 3 5% 6% 42%	2483
	11th to 20th	Night	16% 11% 4 8% 5% 5% 5% 4 6% 7% 31%	2470
	21st to end	Night	18% 15% 4 8% 5% 4 4 3 5% 5% 29%	2470
December	1st to 10th	Night	16% 16% 6% 12% 6% 5% 5% 3 5% 6% 21%	2626
	11th to 20th	Night	14% 14% 5% 12% 6% 6% 5% 4 5% 6% 23%	3318
	21st to end	Night	27% 23% 6% 10% 5% 4 4 3 4 4 12%	4884

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	65% 6% 11% 13% 5%	2528
	11th to 20th	Day	70% 9% 12% 7% 3	2530
	21st to end	Day	75% 5% 9% 7% 3 1	3001
February	1st to 10th	Day	62% 6% 11% 13% 7%	1710
	11th to 20th	Day	61% 5% 9% 15% 9% 1	1837
	21st to end	Day	60% 5% 11% 15% 7% 1	1570
March	1st to 10th	Day	59% 6% 11% 17% 7% 1	3152
	11th to 20th	Day	49% 7% 14% 20% 8% 2	3480
	21st to end	Day	57% 5% 12% 14% 9% 2	3815
April	1st to 10th	Day	53% 5% 11% 19% 12%	2243
	11th to 20th	Day	48% 6% 11% 21% 12% 2	2380
	21st to end	Day	49% 6% 13% 17% 14% 1	2470
May	1st to 10th	Day	46% 8% 12% 22% 12% 1	4120
	11th to 20th	Day	44% 9% 14% 23% 10% 1	4085
	21st to end	Day	36% 6% 11% 20% 23% 4	4543
June	1st to 10th	Day	37% 7% 12% 27% 14% 3	2660
	11th to 20th	Day	38% 8% 12% 22% 17% 2	2660
	21st to end	Day	38% 9% 14% 21% 16% 2	2660
July	1st to 10th	Day	40% 7% 14% 20% 16% 2	4371
	11th to 20th	Day	30% 6% 13% 32% 18% 1	4365
	21st to end	Day	36% 9% 14% 19% 21% 1	4456
August	1st to 10th	Day	37% 7% 12% 25% 17% 1	4091
	11th to 20th	Day	38% 8% 10% 31% 12% 1	4083
	21st to end	Day	37% 7% 13% 29% 12% 2	4413
September	1st to 10th	Day	39% 8% 14% 22% 14% 2	2171
	11th to 20th	Day	32% 7% 11% 31% 16% 1	2090
	21st to end	Day	43% 8% 11% 24% 14%	2090
October	1st to 10th	Day	31% 5% 10% 31% 21% 1	3426
	11th to 20th	Day	40% 5% 11% 24% 19%	3140
	21st to end	Day	46% 4 13% 24% 12% 2	3117
November	1st to 10th	Day	45% 6% 13% 22% 14% 1	1717
	11th to 20th	Day	55% 5% 12% 19% 8% 2	1710
	21st to end	Day	56% 6% 13% 17% 7%	1710
December	1st to 10th	Day	65% 5% 11% 15% 4	1543
	11th to 20th	Day	61% 7% 14% 14% 4	1861
	21st to end	Day	78% 5% 8% 6% 3	2783
January	1st to 10th	Night	62% 6% 11% 15% 6% 1	4428
	11th to 20th	Night	68% 6% 12% 9% 5%	4440
	21st to end	Night	72% 5% 9% 10% 3 1	4656
February	1st to 10th	Night	62% 7% 10% 13% 6% 1	2470
	11th to 20th	Night	57% 5% 11% 17% 9% 1	2238
	21st to end	Night	56% 4 13% 17% 8% 2	1884
March	1st to 10th	Night	49% 5% 13% 24% 7% 1	3701
	11th to 20th	Night	36% 7% 15% 21% 20% 1	3480
	21st to end	Night	49% 6% 13% 21% 11% 1	3817
April	1st to 10th	Night	48% 6% 10% 21% 14% 1	1952
	11th to 20th	Night	46% 6% 11% 18% 18% 1	1747
	21st to end	Night	46% 6% 12% 18% 15% 3	1710
May	1st to 10th	Night	47% 6% 11% 21% 13% 2	2840
	11th to 20th	Night	42% 7% 10% 26% 13% 2	2813
	21st to end	Night	32% 9% 13% 21% 21% 4	3030
June	1st to 10th	Night	34% 7% 12% 27% 18% 3	1520
	11th to 20th	Night	35% 8% 14% 24% 17% 2	1520
	21st to end	Night	33% 7% 13% 27% 20% 1	1520
July	1st to 10th	Night	32% 6% 13% 29% 14% 6%	2490
	11th to 20th	Night	27% 6% 13% 31% 22% 2	2482
	21st to end	Night	30% 9% 18% 18% 23% 2	2861
August	1st to 10th	Night	35% 6% 13% 28% 17% 1	2814
	11th to 20th	Night	32% 7% 10% 37% 12% 2	2812
	21st to end	Night	35% 7% 11% 30% 16% 1	3238
September	1st to 10th	Night	33% 7% 12% 27% 19% 2	1990
	11th to 20th	Night	29% 6% 10% 30% 22% 2	2090
	21st to end	Night	40% 7% 12% 27% 14% 1	2090
October	1st to 10th	Night	26% 5% 9% 33% 26% 1	3532
	11th to 20th	Night	42% 4 11% 23% 19%	3779
	21st to end	Night	39% 4 10% 32% 14% 1	4426
November	1st to 10th	Night	42% 6% 11% 24% 15% 1	2483
	11th to 20th	Night	51% 6% 14% 19% 9% 1	2470
	21st to end	Night	56% 6% 12% 18% 7%	2470
December	1st to 10th	Night	64% 6% 10% 13% 6%	2626
	11th to 20th	Night	60% 7% 13% 14% 6% 1	3320
	21st to end	Night	76% 5% 10% 6% 3	4884

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	23% 18% 36% 16% 6% 1	270
	11th to 20th	Day	25% 14% 43% 15% 3 1	270
	21st to end	Day	30% 14% 34% 16% 4 1	297
February	1st to 10th	Day	23% 22% 36% 14% 4 1	270
	11th to 20th	Day	27% 20% 36% 14% 3	270
	21st to end	Day	24% 28% 35% 12% 1	225
March	1st to 10th	Day	23% 22% 35% 17% 2	289
	11th to 20th	Day	24% 11% 35% 22% 7%	460
	21st to end	Day	27% 14% 32% 19% 6% 1	506
April	1st to 10th	Day	19% 16% 35% 21% 8% 1	460
	11th to 20th	Day	25% 18% 31% 13% 7% 5%	452
	21st to end	Day	23% 13% 32% 18% 11% 2	460
May	1st to 10th	Day	24% 13% 30% 20% 11% 3	463
	11th to 20th	Day	18% 9% 31% 21% 14% 7%	487
	21st to end	Day	14% 8% 23% 27% 20% 8%	557
June	1st to 10th	Day	12% 7% 29% 31% 17% 4	680
	11th to 20th	Day	12% 8% 31% 28% 18% 4	680
	21st to end	Day	11% 9% 30% 29% 16% 6%	680
July	1st to 10th	Day	8% 5% 21% 29% 25% 11%	671
	11th to 20th	Day	10% 6% 26% 28% 21% 9%	668
	21st to end	Day	9% 4 23% 31% 24% 9%	616
August	1st to 10th	Day	9% 4 19% 29% 24% 16%	486
	11th to 20th	Day	13% 5% 17% 28% 26% 11%	479
	21st to end	Day	10% 3 22% 28% 25% 11%	539
September	1st to 10th	Day	13% 5% 22% 24% 22% 14%	490
	11th to 20th	Day	10% 3 17% 25% 28% 16%	490
	21st to end	Day	17% 11% 22% 23% 19% 8%	490
October	1st to 10th	Day	16% 9% 27% 26% 15% 7%	490
	11th to 20th	Day	19% 16% 29% 26% 9% 1	490
	21st to end	Day	29% 16% 32% 17% 6%	354
November	1st to 10th	Day	15% 18% 34% 24% 8% 1	285
	11th to 20th	Day	21% 22% 33% 18% 5% 1	270
	21st to end	Day	27% 18% 38% 13% 4	270
December	1st to 10th	Day	24% 21% 32% 15% 7% 1	191
	11th to 20th	Day	24% 20% 41% 11% 4	227
	21st to end	Day	27% 23% 33% 15% 2	297
January	1st to 10th	Night	22% 15% 35% 21% 5% 1	950
	11th to 20th	Night	26% 14% 34% 21% 5% 1	950
	21st to end	Night	21% 12% 36% 27% 5%	908
February	1st to 10th	Night	26% 11% 36% 23% 3	760
	11th to 20th	Night	22% 15% 35% 24% 4	743
	21st to end	Night	25% 14% 38% 21% 3	628
March	1st to 10th	Night	21% 12% 35% 25% 6% 1	760
	11th to 20th	Night	17% 17% 36% 24% 5% 1	760
	21st to end	Night	24% 11% 31% 27% 7%	836
April	1st to 10th	Night	19% 14% 36% 27% 4	622
	11th to 20th	Night	23% 10% 34% 25% 7% 1	563
	21st to end	Night	22% 8% 33% 29% 9%	570
May	1st to 10th	Night	20% 8% 31% 31% 10% 1	570
	11th to 20th	Night	21% 4 29% 32% 13% 1	561
	21st to end	Night	12% 4 25% 36% 21% 2	617
June	1st to 10th	Night	12% 4 24% 44% 15% 1	570
	11th to 20th	Night	12% 3 22% 44% 18%	570
	21st to end	Night	10% 3 22% 43% 21% 1	570
July	1st to 10th	Night	8% 3 15% 41% 28% 5%	555
	11th to 20th	Night	11% 3 17% 40% 26% 3	552
	21st to end	Night	4 1 19% 47% 27% 1	624
August	1st to 10th	Night	8% 2 16% 41% 29% 3	567
	11th to 20th	Night	9% 3 18% 38% 29% 4	564
	21st to end	Night	9% 1 16% 38% 31% 3	627
September	1st to 10th	Night	11% 5% 19% 34% 26% 5%	660
	11th to 20th	Night	11% 3 18% 32% 31% 5%	760
	21st to end	Night	15% 8% 20% 31% 21% 5%	760
October	1st to 10th	Night	15% 7% 27% 32% 16% 3	760
	11th to 20th	Night	22% 12% 29% 27% 9% 1	760
	21st to end	Night	24% 13% 33% 23% 6%	836
November	1st to 10th	Night	18% 12% 30% 27% 11% 1	764
	11th to 20th	Night	22% 14% 35% 21% 7% 1	760
	21st to end	Night	25% 13% 33% 23% 5%	760
December	1st to 10th	Night	23% 16% 35% 20% 6%	760
	11th to 20th	Night	23% 13% 38% 22% 4	907
	21st to end	Night	33% 12% 34% 20% 2	1045

Page generated at 2024-11-03 13:19:03. Version ac07

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