Carlson R. Chambliss Astronomical Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Carlson R. Chambliss Astronomical Observatory clear sky chart from 2005-11-06 to 2024-12-06.

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	16% 7% 2 6% 4 4 4 4 6% 8% 38%	101640
	Night	17% 7% 2 6% 4 4 4 3 5% 7% 41%	98089
Transparency	Day	42% 7% 12% 23% 14% 2	105201
	Night	41% 6% 12% 23% 15% 2	102616
Seeing	Day	21% 15% 28% 22% 11% 4	14997
	Night	20% 12% 29% 28% 11% 1	24320

By Month

Percentage Cloud Cover NE (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	15% 8% 3 5% 5% 4 3 4 5% 7% 42%	2517
	11th to 20th	Day	14% 11% 5% 10% 6% 4 5% 3 5% 7% 30%	2616
	21st to end	Day	20% 10% 3 8% 5% 4 4 3 5% 5% 33%	3124
February	1st to 10th	Day	16% 8% 3 6% 6% 5% 5% 4 6% 6% 36%	1710
	11th to 20th	Day	15% 7% 3 7% 5% 4 4 4 6% 8% 37%	1764
	21st to end	Day	19% 10% 3 6% 5% 3 5% 4 5% 5% 34%	1570
March	1st to 10th	Day	25% 7% 2 5% 4 4 4 3 5% 6% 34%	3175
	11th to 20th	Day	11% 5% 2 6% 6% 5% 5% 4 6% 8% 43%	3480
	21st to end	Day	21% 8% 2 5% 3 3 3 3 4 6% 42%	4001
April	1st to 10th	Day	16% 8% 3 6% 5% 4 4 4 6% 8% 36%	2280
	11th to 20th	Day	16% 7% 2 7% 5% 4 4 4 5% 7% 40%	2254
	21st to end	Day	17% 6% 2 6% 4 4 4 4 6% 7% 39%	2280
May	1st to 10th	Day	28% 7% 2 5% 4 4 4 4 5% 7% 29%	4137
	11th to 20th	Day	24% 9% 3 8% 5% 5% 4 3 6% 6% 27%	4398
	21st to end	Day	13% 5% 2 5% 4 4 4 4 6% 9% 44%	4837
June	1st to 10th	Day	12% 6% 2 6% 5% 5% 5% 4 8% 9% 37%	2660
	11th to 20th	Day	14% 6% 2 5% 5% 5% 5% 5% 7% 9% 37%	2660
	21st to end	Day	11% 5% 2 5% 4 5% 6% 5% 6% 9% 40%	2660
July	1st to 10th	Day	7% 4 2 7% 6% 7% 6% 6% 8% 11% 36%	4440
	11th to 20th	Day	9% 6% 2 6% 4 5% 6% 5% 7% 10% 40%	4440
	21st to end	Day	12% 9% 3 8% 6% 5% 6% 4 6% 8% 34%	4698
August	1st to 10th	Day	20% 6% 3 7% 4 5% 5% 4 6% 8% 32%	4104
	11th to 20th	Day	13% 6% 2 6% 5% 5% 5% 4 6% 8% 40%	3800
	21st to end	Day	14% 6% 2 5% 3 4 4 3 6% 8% 46%	4180
September	1st to 10th	Day	16% 6% 3 4 4 4 5% 4 5% 6% 44%	2280
	11th to 20th	Day	13% 5% 1 4 4 3 3 4 4 8% 50%	2275
	21st to end	Day	20% 7% 2 7% 4 4 4 3 4 5% 39%	2047
October	1st to 10th	Day	19% 6% 1 5% 3 4 5% 3 5% 7% 41%	1900
	11th to 20th	Day	17% 4 2 6% 4 4 4 3 5% 6% 45%	1900
	21st to end	Day	19% 6% 2 5% 3 3 4 4 5% 6% 42%	2044
November	1st to 10th	Day	14% 7% 2 4 3 3 2 2 4 7% 51%	1761
	11th to 20th	Day	16% 6% 2 5% 4 3 4 4 6% 7% 45%	1800
	21st to end	Day	18% 5% 2 5% 3 4 5% 4 5% 8% 40%	1610
December	1st to 10th	Day	18% 9% 3 7% 5% 5% 4 4 6% 6% 34%	1560
	11th to 20th	Day	20% 8% 2 5% 4 4 4 4 6% 6% 37%	1906
	21st to end	Day	19% 8% 3 8% 5% 5% 5% 4 6% 6% 30%	2772
January	1st to 10th	Night	15% 7% 2 6% 5% 4 3 4 6% 7% 41%	4429
	11th to 20th	Night	17% 8% 3 7% 4 4 4 3 5% 6% 38%	4340
	21st to end	Night	24% 9% 2 6% 4 3 4 3 4 5% 35%	4532
February	1st to 10th	Night	16% 9% 3 6% 4 3 5% 4 4 6% 39%	2470
	11th to 20th	Night	17% 8% 3 6% 5% 4 4 4 5% 6% 39%	2301
	21st to end	Night	18% 9% 2 5% 4 4 3 4 4 6% 40%	1884
March	1st to 10th	Night	22% 10% 2 6% 4 3 4 3 4 5% 36%	3660
	11th to 20th	Night	11% 6% 2 5% 4 4 4 4 5% 6% 48%	3479
	21st to end	Night	17% 9% 3 6% 4 3 2 2 4 5% 45%	3631
April	1st to 10th	Night	18% 6% 3 6% 4 4 5% 4 6% 6% 38%	1900
	11th to 20th	Night	14% 7% 3 7% 5% 4 4 4 6% 7% 42%	1875
	21st to end	Night	20% 4 2 5% 4 4 4 3 6% 6% 43%	1900
May	1st to 10th	Night	26% 8% 2 6% 4 4 4 3 5% 7% 31%	2830
	11th to 20th	Night	25% 9% 3 8% 5% 4 4 3 5% 6% 29%	2495
	21st to end	Night	13% 6% 3 6% 4 4 5% 3 6% 9% 41%	2738
June	1st to 10th	Night	16% 6% 2 7% 4 3 3 3 6% 8% 42%	1520
	11th to 20th	Night	12% 6% 2 5% 5% 4 4 5% 7% 8% 42%	1520
	21st to end	Night	12% 4 2 6% 4 4 4 3 8% 10% 43%	1520
July	1st to 10th	Night	8% 6% 3 7% 7% 6% 7% 5% 7% 9% 38%	2520
	11th to 20th	Night	9% 6% 2 7% 4 5% 7% 5% 7% 10% 38%	2520
	21st to end	Night	14% 8% 2 6% 4 4 5% 4 6% 8% 39%	2851
August	1st to 10th	Night	20% 7% 3 7% 5% 4 5% 4 6% 8% 33%	2825
	11th to 20th	Night	15% 7% 3 7% 5% 4 4 4 5% 6% 41%	2997
	21st to end	Night	13% 5% 2 4 3 3 5% 4 5% 8% 48%	3476
September	1st to 10th	Night	14% 7% 2 5% 4 3 3 3 4 7% 47%	1900
	11th to 20th	Night	12% 5% 2 5% 3 4 4 3 5% 6% 52%	1905
	21st to end	Night	20% 6% 2 6% 4 4 4 3 5% 6% 42%	2128
October	1st to 10th	Night	20% 7% 2 5% 3 3 3 4 4 7% 43%	2280
	11th to 20th	Night	16% 5% 2 4 3 3 3 3 5% 6% 48%	2280
	21st to end	Night	19% 7% 2 4 2 3 4 3 4 6% 46%	2552
November	1st to 10th	Night	12% 5% 2 5% 3 4 4 3 5% 6% 52%	2537
	11th to 20th	Night	16% 7% 3 5% 5% 3 3 3 3 7% 46%	2600
	21st to end	Night	15% 6% 2 5% 4 4 4 3 5% 8% 42%	2785
December	1st to 10th	Night	19% 7% 2 7% 4 4 5% 4 5% 6% 36%	2737
	11th to 20th	Night	19% 7% 2 6% 4 4 4 4 6% 6% 39%	3288
	21st to end	Night	19% 8% 3 7% 5% 4 4 3 5% 6% 35%	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	42% 5% 15% 26% 10% 2	2518
	11th to 20th	Day	52% 7% 11% 18% 11% 1	2616
	21st to end	Day	52% 7% 12% 20% 8% 1	3124
February	1st to 10th	Day	45% 8% 14% 20% 12% 1	1710
	11th to 20th	Day	44% 6% 12% 24% 13% 2	1773
	21st to end	Day	50% 5% 11% 21% 11% 3	1570
March	1st to 10th	Day	48% 7% 10% 26% 8% 2	3178
	11th to 20th	Day	35% 9% 12% 28% 13% 3	3480
	21st to end	Day	44% 5% 10% 18% 19% 3	4001
April	1st to 10th	Day	44% 6% 11% 21% 14% 5%	2280
	11th to 20th	Day	42% 6% 11% 22% 15% 4	2254
	21st to end	Day	41% 7% 11% 21% 15% 5%	2280
May	1st to 10th	Day	52% 8% 11% 18% 10% 2	4149
	11th to 20th	Day	55% 8% 11% 16% 8% 1	4402
	21st to end	Day	34% 8% 13% 27% 15% 2	4837
June	1st to 10th	Day	40% 9% 13% 23% 13% 2	2660
	11th to 20th	Day	41% 9% 15% 23% 10% 2	2660
	21st to end	Day	37% 10% 14% 25% 14% 1	2660
July	1st to 10th	Day	39% 10% 14% 22% 13% 1	4370
	11th to 20th	Day	36% 10% 16% 24% 13% 1	4365
	21st to end	Day	47% 7% 10% 18% 16% 1	4548
August	1st to 10th	Day	49% 8% 12% 21% 9%	4091
	11th to 20th	Day	39% 7% 12% 29% 12% 1	3838
	21st to end	Day	35% 6% 11% 29% 17% 2	4180
September	1st to 10th	Day	40% 7% 11% 20% 20% 3	2280
	11th to 20th	Day	33% 6% 11% 24% 24% 3	2275
	21st to end	Day	48% 5% 9% 17% 20% 2	2047
October	1st to 10th	Day	39% 4 9% 20% 23% 5%	3160
	11th to 20th	Day	29% 4 11% 28% 22% 5%	3140
	21st to end	Day	27% 4 15% 24% 26% 4	3346
November	1st to 10th	Day	34% 4 14% 25% 19% 3	1761
	11th to 20th	Day	39% 6% 10% 25% 18% 2	1800
	21st to end	Day	40% 7% 13% 30% 9% 2	1610
December	1st to 10th	Day	49% 6% 16% 18% 10% 1	1560
	11th to 20th	Day	45% 6% 16% 24% 8% 1	1906
	21st to end	Day	51% 7% 13% 21% 7%	2772
January	1st to 10th	Night	41% 5% 14% 26% 11% 3	4429
	11th to 20th	Night	45% 7% 13% 24% 10% 2	4340
	21st to end	Night	50% 5% 10% 24% 9% 1	4532
February	1st to 10th	Night	44% 6% 13% 25% 10% 2	2470
	11th to 20th	Night	45% 5% 11% 19% 16% 3	2303
	21st to end	Night	44% 5% 10% 21% 16% 4	1884
March	1st to 10th	Night	49% 5% 8% 24% 11% 2	3670
	11th to 20th	Night	34% 7% 12% 29% 15% 2	3480
	21st to end	Night	42% 4 7% 18% 22% 5%	3631
April	1st to 10th	Night	44% 6% 11% 22% 14% 3	1900
	11th to 20th	Night	41% 7% 11% 20% 20% 2	1875
	21st to end	Night	39% 6% 12% 22% 17% 5%	1900
May	1st to 10th	Night	52% 7% 9% 20% 10% 2	2837
	11th to 20th	Night	54% 10% 12% 14% 10% 1	2496
	21st to end	Night	38% 10% 12% 23% 13% 3	2739
June	1st to 10th	Night	40% 7% 11% 22% 19% 2	1520
	11th to 20th	Night	36% 11% 14% 25% 14% 1	1520
	21st to end	Night	35% 9% 14% 28% 13% 1	1520
July	1st to 10th	Night	40% 11% 15% 17% 15% 3	2480
	11th to 20th	Night	39% 8% 15% 24% 13% 1	2472
	21st to end	Night	42% 9% 13% 18% 18% 1	2760
August	1st to 10th	Night	47% 9% 17% 17% 10% 1	2814
	11th to 20th	Night	43% 6% 12% 23% 15% 1	3025
	21st to end	Night	34% 7% 11% 29% 19% 1	3476
September	1st to 10th	Night	37% 6% 10% 23% 20% 3	1900
	11th to 20th	Night	33% 6% 9% 24% 25% 3	1905
	21st to end	Night	43% 6% 8% 20% 21% 2	2128
October	1st to 10th	Night	42% 5% 10% 21% 20% 2	3800
	11th to 20th	Night	28% 4 9% 29% 25% 5%	3779
	21st to end	Night	27% 3 12% 32% 22% 3	4200
November	1st to 10th	Night	33% 5% 14% 24% 20% 4	2537
	11th to 20th	Night	41% 4 9% 25% 17% 4	2600
	21st to end	Night	40% 5% 13% 28% 13% 1	2785
December	1st to 10th	Night	47% 6% 13% 21% 12% 1	2737
	11th to 20th	Night	44% 6% 13% 22% 13% 2	3288
	21st to end	Night	47% 7% 14% 23% 8%	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% 28% 28% 15% 4 1	180
	11th to 20th	Day	32% 25% 31% 10% 2	207
	21st to end	Day	22% 30% 30% 12% 4 1	297
February	1st to 10th	Day	25% 27% 32% 13% 3 1	270
	11th to 20th	Day	28% 24% 36% 11% 1	372
	21st to end	Day	32% 20% 28% 18% 3	382
March	1st to 10th	Day	27% 20% 29% 19% 4	460
	11th to 20th	Day	25% 27% 30% 13% 4 2	460
	21st to end	Day	29% 22% 29% 13% 6% 1	506
April	1st to 10th	Day	25% 25% 28% 16% 5% 1	460
	11th to 20th	Day	21% 25% 28% 16% 7% 3	452
	21st to end	Day	27% 15% 33% 17% 4 3	460
May	1st to 10th	Day	29% 19% 25% 17% 6% 3	463
	11th to 20th	Day	23% 15% 30% 21% 9% 2	487
	21st to end	Day	18% 9% 28% 25% 15% 5%	529
June	1st to 10th	Day	15% 14% 31% 23% 13% 3	490
	11th to 20th	Day	18% 11% 28% 25% 14% 3	490
	21st to end	Day	13% 12% 33% 26% 13% 4	490
July	1st to 10th	Day	12% 4 24% 31% 21% 8%	485
	11th to 20th	Day	7% 6% 26% 33% 23% 5%	484
	21st to end	Day	11% 7% 30% 32% 15% 4	532
August	1st to 10th	Day	13% 5% 22% 32% 19% 8%	486
	11th to 20th	Day	13% 6% 21% 34% 19% 7%	479
	21st to end	Day	14% 6% 24% 28% 18% 10%	539
September	1st to 10th	Day	19% 9% 21% 24% 20% 7%	490
	11th to 20th	Day	14% 5% 23% 28% 20% 10%	490
	21st to end	Day	25% 14% 22% 21% 14% 4	490
October	1st to 10th	Day	24% 8% 26% 21% 15% 6%	490
	11th to 20th	Day	19% 15% 28% 23% 12% 3	490
	21st to end	Day	21% 16% 31% 18% 12% 1	514
November	1st to 10th	Day	16% 16% 30% 24% 11% 3	395
	11th to 20th	Day	21% 20% 32% 23% 5% 1	400
	21st to end	Day	27% 22% 31% 15% 5%	210
December	1st to 10th	Day	31% 21% 31% 12% 5% 1	190
	11th to 20th	Day	32% 26% 25% 13% 4	180
	21st to end	Day	26% 22% 31% 15% 5% 2	198
January	1st to 10th	Night	19% 19% 39% 20% 3	760
	11th to 20th	Night	25% 16% 32% 24% 3	760
	21st to end	Night	19% 18% 37% 24% 2	836
February	1st to 10th	Night	23% 17% 34% 25% 2	760
	11th to 20th	Night	24% 21% 38% 16% 1	743
	21st to end	Night	25% 18% 36% 19% 2	628
March	1st to 10th	Night	22% 19% 32% 23% 4	760
	11th to 20th	Night	24% 18% 33% 20% 5% 1	760
	21st to end	Night	22% 15% 38% 20% 5%	836
April	1st to 10th	Night	22% 19% 34% 20% 5%	760
	11th to 20th	Night	19% 15% 35% 24% 7%	751
	21st to end	Night	22% 13% 32% 27% 7%	760
May	1st to 10th	Night	24% 10% 29% 28% 7% 1	580
	11th to 20th	Night	20% 7% 32% 32% 8% 1	374
	21st to end	Night	18% 7% 20% 40% 14% 1	411
June	1st to 10th	Night	16% 6% 26% 35% 18%	380
	11th to 20th	Night	13% 6% 25% 42% 13% 1	380
	21st to end	Night	11% 4 25% 46% 14%	380
July	1st to 10th	Night	11% 4 19% 41% 22% 2	370
	11th to 20th	Night	8% 3 21% 40% 26% 2	368
	21st to end	Night	12% 3 18% 42% 23% 2	479
August	1st to 10th	Night	13% 3 14% 42% 26% 2	567
	11th to 20th	Night	14% 5% 16% 36% 27% 2	686
	21st to end	Night	15% 3 18% 37% 25% 2	836
September	1st to 10th	Night	16% 4 25% 32% 20% 2	760
	11th to 20th	Night	15% 4 17% 35% 24% 5%	760
	21st to end	Night	23% 5% 20% 31% 19% 2	760
October	1st to 10th	Night	22% 7% 24% 26% 18% 3	760
	11th to 20th	Night	18% 11% 26% 33% 11% 1	760
	21st to end	Night	23% 11% 29% 27% 9%	836
November	1st to 10th	Night	14% 11% 35% 28% 12% 1	780
	11th to 20th	Night	20% 16% 29% 27% 7% 1	800
	21st to end	Night	18% 16% 33% 27% 6%	800
December	1st to 10th	Night	25% 14% 34% 21% 5% 1	783
	11th to 20th	Night	21% 15% 33% 25% 6%	760
	21st to end	Night	23% 13% 34% 27% 3	836

Page generated at 2024-12-03 06:45:10. Version ac07

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