Carpenter Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Carpenter Observatory clear sky chart from 2005-11-06 to 2024-10-20.

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% 39%	101222
	Night	17% 7% 2 6% 4 4 4 3 5% 7% 41%	97479
Transparency	Day	42% 7% 13% 22% 13% 2	100982
	Night	42% 7% 12% 23% 14% 2	97338
Seeing	Day	20% 15% 28% 22% 11% 3	14874
	Night	19% 13% 30% 28% 10% 1	24164

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% 7% 3 5% 5% 5% 4 3 6% 6% 42%	2517
	11th to 20th	Day	14% 11% 4 9% 5% 5% 5% 3 5% 7% 32%	2648
	21st to end	Day	20% 10% 4 8% 5% 4 4 3 4 5% 33%	3124
February	1st to 10th	Day	15% 8% 3 7% 6% 5% 4 5% 6% 7% 36%	1710
	11th to 20th	Day	14% 7% 4 8% 4 4 4 3 5% 7% 39%	1761
	21st to end	Day	18% 10% 3 7% 4 4 4 3 5% 5% 36%	1570
March	1st to 10th	Day	25% 6% 2 5% 4 4 4 3 5% 6% 35%	3201
	11th to 20th	Day	10% 6% 2 6% 6% 5% 5% 4 6% 7% 43%	3480
	21st to end	Day	21% 8% 2 5% 4 3 3 2 4 5% 43%	3993
April	1st to 10th	Day	16% 8% 2 6% 5% 4 4 3 5% 8% 38%	2280
	11th to 20th	Day	15% 6% 3 6% 4 4 3 3 6% 7% 42%	2254
	21st to end	Day	16% 6% 2 5% 5% 5% 4 4 7% 8% 39%	2280
May	1st to 10th	Day	27% 7% 2 6% 4 4 4 4 5% 7% 30%	4112
	11th to 20th	Day	25% 9% 3 7% 5% 4 4 3 5% 7% 27%	4398
	21st to end	Day	13% 5% 2 5% 3 4 5% 3 7% 9% 44%	4837
June	1st to 10th	Day	12% 6% 2 5% 6% 4 4 5% 8% 10% 38%	2660
	11th to 20th	Day	13% 6% 2 6% 5% 5% 5% 6% 7% 9% 38%	2660
	21st to end	Day	11% 4 2 6% 4 5% 5% 5% 7% 10% 41%	2660
July	1st to 10th	Day	7% 5% 2 7% 6% 6% 7% 5% 8% 11% 37%	4440
	11th to 20th	Day	9% 5% 2 6% 4 5% 5% 6% 7% 10% 40%	4440
	21st to end	Day	11% 8% 3 8% 6% 5% 6% 4 7% 8% 34%	4663
August	1st to 10th	Day	20% 6% 2 7% 4 5% 5% 5% 6% 7% 33%	4104
	11th to 20th	Day	15% 5% 2 6% 4 4 5% 4 6% 9% 41%	3804
	21st to end	Day	13% 6% 2 5% 3 4 4 3 6% 8% 47%	4180
September	1st to 10th	Day	16% 6% 2 6% 3 4 4 4 4 7% 44%	2280
	11th to 20th	Day	13% 5% 2 4 3 4 4 3 5% 8% 50%	2280
	21st to end	Day	21% 5% 3 8% 4 4 3 3 4 6% 38%	2038
October	1st to 10th	Day	18% 6% 2 5% 2 4 4 3 6% 7% 42%	1900
	11th to 20th	Day	16% 6% 2 6% 3 4 3 3 4 8% 45%	1890
	21st to end	Day	21% 6% 2 5% 4 3 3 3 5% 7% 41%	1949
November	1st to 10th	Day	13% 7% 2 5% 3 3 3 3 4 7% 50%	1671
	11th to 20th	Day	17% 6% 2 5% 3 3 4 3 5% 8% 44%	1710
	21st to end	Day	16% 6% 2 5% 4 4 5% 4 6% 7% 42%	1530
December	1st to 10th	Day	17% 8% 3 7% 4 5% 4 4 6% 7% 34%	1520
	11th to 20th	Day	20% 7% 2 6% 4 3 4 3 6% 7% 39%	1906
	21st to end	Day	18% 8% 3 7% 6% 5% 5% 4 6% 7% 31%	2772
January	1st to 10th	Night	16% 6% 3 7% 5% 4 4 3 4 7% 40%	4429
	11th to 20th	Night	17% 9% 2 6% 4 4 4 3 5% 7% 39%	4308
	21st to end	Night	23% 10% 3 7% 4 3 3 3 4 5% 35%	4532
February	1st to 10th	Night	17% 9% 2 5% 5% 4 5% 4 5% 6% 38%	2470
	11th to 20th	Night	16% 8% 3 7% 5% 4 4 4 5% 5% 39%	2305
	21st to end	Night	18% 7% 3 6% 4 4 4 3 5% 6% 39%	1884
March	1st to 10th	Night	21% 10% 3 6% 4 4 3 3 4 5% 37%	3637
	11th to 20th	Night	11% 6% 2 6% 4 5% 5% 3 5% 6% 47%	3479
	21st to end	Night	16% 8% 3 6% 4 3 3 2 4 5% 46%	3638
April	1st to 10th	Night	17% 7% 3 5% 4 5% 5% 4 5% 7% 38%	1900
	11th to 20th	Night	15% 7% 2 6% 5% 4 4 3 6% 7% 42%	1875
	21st to end	Night	19% 5% 2 5% 4 3 4 4 5% 6% 44%	1900
May	1st to 10th	Night	26% 7% 2 6% 4 4 4 3 5% 7% 31%	2857
	11th to 20th	Night	24% 9% 3 8% 4 4 3 4 5% 6% 28%	2495
	21st to end	Night	13% 6% 3 7% 4 3 5% 4 6% 10% 41%	2738
June	1st to 10th	Night	15% 6% 2 6% 4 4 4 3 6% 9% 42%	1520
	11th to 20th	Night	12% 5% 2 5% 4 6% 5% 5% 6% 10% 41%	1520
	21st to end	Night	12% 4 1 5% 4 5% 5% 3 7% 11% 43%	1520
July	1st to 10th	Night	8% 5% 2 7% 5% 6% 6% 6% 7% 9% 39%	2520
	11th to 20th	Night	9% 6% 2 6% 6% 5% 6% 4 8% 10% 38%	2520
	21st to end	Night	14% 7% 2 6% 5% 5% 5% 4 6% 8% 38%	2886
August	1st to 10th	Night	20% 7% 3 5% 4 4 4 4 6% 8% 35%	2825
	11th to 20th	Night	14% 7% 3 7% 5% 5% 4 3 5% 6% 41%	2993
	21st to end	Night	12% 5% 2 5% 4 3 4 4 6% 8% 47%	3476
September	1st to 10th	Night	15% 6% 2 5% 4 4 3 3 5% 6% 47%	1900
	11th to 20th	Night	13% 5% 2 4 3 3 4 2 5% 7% 52%	1900
	21st to end	Night	21% 5% 2 5% 4 4 5% 3 5% 6% 41%	2136
October	1st to 10th	Night	19% 7% 2 5% 3 3 4 3 3 6% 44%	2280
	11th to 20th	Night	16% 5% 2 5% 3 4 3 3 5% 7% 48%	2275
	21st to end	Night	19% 6% 2 5% 3 3 3 4 3 6% 45%	2404
November	1st to 10th	Night	11% 5% 2 4 4 4 4 4 5% 6% 51%	2407
	11th to 20th	Night	16% 7% 2 6% 4 3 3 3 5% 6% 46%	2470
	21st to end	Night	14% 5% 2 5% 4 4 4 3 5% 8% 44%	2648
December	1st to 10th	Night	20% 7% 2 7% 4 5% 5% 3 5% 6% 36%	2660
	11th to 20th	Night	17% 7% 2 6% 4 5% 4 3 6% 6% 39%	3288
	21st to end	Night	18% 8% 3 7% 5% 4 5% 4 5% 7% 34%	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	41% 6% 15% 25% 11% 2	2518
	11th to 20th	Day	51% 7% 12% 17% 12% 2	2648
	21st to end	Day	52% 8% 12% 20% 8% 1	3124
February	1st to 10th	Day	46% 7% 13% 21% 11% 1	1710
	11th to 20th	Day	45% 6% 11% 24% 13% 2	1770
	21st to end	Day	50% 5% 10% 21% 10% 3	1570
March	1st to 10th	Day	47% 7% 11% 26% 8% 2	3204
	11th to 20th	Day	35% 9% 13% 26% 14% 3	3480
	21st to end	Day	45% 4 10% 19% 19% 3	3993
April	1st to 10th	Day	43% 7% 11% 21% 14% 5%	2280
	11th to 20th	Day	40% 7% 12% 21% 15% 4	2254
	21st to end	Day	41% 7% 11% 21% 16% 4	2280
May	1st to 10th	Day	52% 8% 10% 18% 10% 2	4124
	11th to 20th	Day	53% 9% 13% 16% 8% 1	4402
	21st to end	Day	33% 9% 14% 26% 16% 2	4837
June	1st to 10th	Day	39% 9% 14% 23% 14% 1	2660
	11th to 20th	Day	40% 9% 15% 23% 10% 3	2660
	21st to end	Day	36% 10% 15% 24% 14% 1	2660
July	1st to 10th	Day	37% 11% 15% 21% 13% 2	4370
	11th to 20th	Day	36% 10% 16% 24% 13% 1	4365
	21st to end	Day	46% 8% 11% 18% 16% 1	4514
August	1st to 10th	Day	48% 8% 12% 22% 9%	4091
	11th to 20th	Day	38% 8% 11% 30% 12% 1	3842
	21st to end	Day	34% 7% 11% 27% 19% 2	4180
September	1st to 10th	Day	40% 7% 11% 20% 20% 3	2280
	11th to 20th	Day	32% 6% 11% 24% 23% 3	2280
	21st to end	Day	47% 5% 9% 17% 20% 2	2038
October	1st to 10th	Day	40% 6% 13% 22% 17% 2	1900
	11th to 20th	Day	38% 5% 12% 24% 19% 2	1890
	21st to end	Day	42% 5% 12% 23% 16% 2	1949
November	1st to 10th	Day	35% 4 14% 25% 18% 4	1671
	11th to 20th	Day	39% 6% 12% 23% 18% 2	1710
	21st to end	Day	39% 7% 13% 30% 9% 2	1530
December	1st to 10th	Day	48% 7% 15% 18% 11% 1	1520
	11th to 20th	Day	44% 6% 15% 26% 8% 1	1906
	21st to end	Day	49% 8% 15% 19% 8% 1	2772
January	1st to 10th	Night	41% 7% 14% 25% 11% 3	4429
	11th to 20th	Night	44% 6% 14% 24% 10% 2	4308
	21st to end	Night	50% 5% 10% 25% 9% 1	4532
February	1st to 10th	Night	45% 6% 13% 25% 10% 2	2470
	11th to 20th	Night	46% 5% 10% 20% 17% 2	2307
	21st to end	Night	44% 6% 11% 21% 15% 4	1884
March	1st to 10th	Night	48% 7% 10% 22% 12% 2	3647
	11th to 20th	Night	33% 8% 13% 30% 14% 2	3480
	21st to end	Night	41% 5% 8% 18% 23% 5%	3638
April	1st to 10th	Night	44% 6% 12% 21% 15% 4	1900
	11th to 20th	Night	40% 7% 12% 19% 20% 3	1875
	21st to end	Night	39% 7% 12% 21% 17% 5%	1900
May	1st to 10th	Night	52% 8% 9% 19% 10% 2	2864
	11th to 20th	Night	53% 11% 13% 12% 10% 1	2496
	21st to end	Night	37% 10% 13% 23% 14% 3	2739
June	1st to 10th	Night	39% 8% 11% 23% 19% 1	1520
	11th to 20th	Night	36% 9% 15% 24% 14% 1	1520
	21st to end	Night	34% 9% 15% 26% 14% 2	1520
July	1st to 10th	Night	38% 11% 16% 17% 14% 4	2480
	11th to 20th	Night	37% 9% 17% 23% 12% 1	2472
	21st to end	Night	41% 9% 13% 18% 17% 1	2794
August	1st to 10th	Night	45% 9% 18% 18% 9% 1	2814
	11th to 20th	Night	42% 6% 13% 23% 15% 1	3021
	21st to end	Night	33% 8% 12% 29% 18% 1	3476
September	1st to 10th	Night	37% 6% 11% 22% 20% 3	1900
	11th to 20th	Night	32% 6% 10% 23% 26% 3	1900
	21st to end	Night	44% 6% 9% 19% 20% 2	2136
October	1st to 10th	Night	42% 6% 12% 23% 16% 2	2280
	11th to 20th	Night	36% 5% 12% 28% 17% 2	2275
	21st to end	Night	40% 5% 11% 26% 17% 2	2404
November	1st to 10th	Night	32% 6% 13% 26% 19% 5%	2407
	11th to 20th	Night	40% 5% 10% 23% 18% 4	2470
	21st to end	Night	38% 5% 13% 28% 14% 1	2648
December	1st to 10th	Night	48% 5% 13% 21% 13% 1	2660
	11th to 20th	Night	44% 6% 13% 21% 13% 2	3288
	21st to end	Night	45% 9% 15% 22% 9%	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	27% 26% 29% 13% 4 1	180
	11th to 20th	Day	33% 25% 29% 10% 3	216
	21st to end	Day	23% 31% 31% 11% 3 1	297
February	1st to 10th	Day	26% 26% 33% 11% 3 1	270
	11th to 20th	Day	27% 24% 38% 9% 2	368
	21st to end	Day	32% 22% 26% 17% 2	382
March	1st to 10th	Day	26% 22% 30% 18% 3	460
	11th to 20th	Day	25% 29% 28% 13% 4 1	460
	21st to end	Day	29% 22% 30% 15% 4 1	506
April	1st to 10th	Day	26% 22% 30% 15% 5% 1	460
	11th to 20th	Day	23% 23% 27% 17% 6% 3	452
	21st to end	Day	27% 15% 33% 17% 4 3	460
May	1st to 10th	Day	29% 18% 25% 19% 7% 2	463
	11th to 20th	Day	23% 15% 31% 22% 9% 2	487
	21st to end	Day	18% 9% 27% 26% 16% 3	529
June	1st to 10th	Day	14% 14% 32% 23% 13% 3	490
	11th to 20th	Day	17% 10% 29% 28% 14% 2	490
	21st to end	Day	13% 13% 29% 28% 13% 3	490
July	1st to 10th	Day	11% 5% 24% 33% 19% 8%	485
	11th to 20th	Day	7% 6% 25% 34% 23% 5%	484
	21st to end	Day	10% 7% 31% 32% 17% 4	532
August	1st to 10th	Day	12% 5% 26% 29% 20% 8%	486
	11th to 20th	Day	14% 5% 22% 32% 20% 6%	479
	21st to end	Day	12% 6% 23% 31% 18% 10%	539
September	1st to 10th	Day	18% 10% 21% 26% 18% 8%	490
	11th to 20th	Day	15% 5% 23% 29% 18% 10%	490
	21st to end	Day	24% 13% 25% 20% 14% 3	490
October	1st to 10th	Day	23% 9% 25% 22% 16% 5%	490
	11th to 20th	Day	18% 15% 31% 22% 13% 2	486
	21st to end	Day	21% 15% 35% 18% 9% 1	480
November	1st to 10th	Day	18% 14% 28% 25% 11% 3	365
	11th to 20th	Day	19% 21% 31% 22% 6% 1	370
	21st to end	Day	22% 18% 36% 18% 4 1	190
December	1st to 10th	Day	25% 25% 33% 12% 4 1	180
	11th to 20th	Day	28% 24% 32% 12% 3 1	180
	21st to end	Day	24% 27% 27% 16% 5% 2	198
January	1st to 10th	Night	20% 20% 38% 19% 3	760
	11th to 20th	Night	25% 18% 30% 23% 3	760
	21st to end	Night	18% 20% 39% 20% 2	836
February	1st to 10th	Night	22% 18% 35% 23% 2	760
	11th to 20th	Night	24% 23% 37% 14% 1	743
	21st to end	Night	25% 21% 35% 17% 3	628
March	1st to 10th	Night	21% 20% 33% 22% 4	760
	11th to 20th	Night	24% 20% 33% 18% 5%	760
	21st to end	Night	21% 17% 37% 20% 5%	836
April	1st to 10th	Night	23% 20% 34% 19% 4	760
	11th to 20th	Night	18% 17% 35% 23% 7%	751
	21st to end	Night	22% 13% 32% 26% 6%	760
May	1st to 10th	Night	24% 11% 30% 27% 8%	594
	11th to 20th	Night	19% 9% 32% 33% 7%	374
	21st to end	Night	15% 6% 27% 39% 12% 1	411
June	1st to 10th	Night	15% 8% 24% 37% 16%	380
	11th to 20th	Night	12% 7% 27% 43% 11%	380
	21st to end	Night	12% 2 25% 47% 13% 1	380
July	1st to 10th	Night	11% 3 21% 45% 18% 1	370
	11th to 20th	Night	9% 2 22% 40% 25% 1	368
	21st to end	Night	11% 4 19% 42% 24% 1	501
August	1st to 10th	Night	11% 2 18% 41% 25% 2	567
	11th to 20th	Night	14% 5% 17% 36% 27% 2	682
	21st to end	Night	14% 3 20% 37% 24% 2	836
September	1st to 10th	Night	15% 4 26% 33% 20% 3	760
	11th to 20th	Night	13% 5% 17% 35% 25% 4	760
	21st to end	Night	22% 6% 21% 31% 19% 1	760
October	1st to 10th	Night	23% 8% 24% 27% 16% 3	760
	11th to 20th	Night	19% 11% 28% 31% 11% 1	759
	21st to end	Night	23% 12% 31% 25% 9%	792
November	1st to 10th	Night	15% 11% 33% 29% 12% 1	740
	11th to 20th	Night	19% 17% 29% 27% 7% 1	760
	21st to end	Night	17% 17% 33% 26% 6%	760
December	1st to 10th	Night	25% 16% 32% 20% 5% 1	760
	11th to 20th	Night	19% 16% 35% 25% 4	760
	21st to end	Night	22% 15% 35% 25% 2	836

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