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 2026-07-31.

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% 6% 2 6% 4 4 4 4 6% 8% 39%	138463
	Night	16% 7% 2 6% 4 4 4 3 5% 7% 41%	134554
Transparency	Day	41% 7% 12% 23% 15% 2	142022
	Night	40% 6% 12% 23% 16% 3	139081
Seeing	Day	21% 16% 28% 22% 10% 3	17139
	Night	19% 13% 29% 27% 10% 1	26407

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	13% 6% 2 6% 5% 5% 5% 4 6% 6% 41%	4661
	11th to 20th	Day	14% 9% 4 8% 4 4 4 3 5% 6% 39%	4889
	21st to end	Day	14% 6% 3 7% 4 5% 5% 4 6% 6% 38%	5780
February	1st to 10th	Day	14% 8% 3 7% 5% 5% 4 5% 6% 7% 37%	1890
	11th to 20th	Day	15% 8% 4 8% 4 4 4 3 5% 7% 38%	1952
	21st to end	Day	18% 10% 3 7% 4 4 4 3 5% 6% 38%	1730
March	1st to 10th	Day	21% 5% 2 5% 4 4 4 3 5% 6% 43%	4705
	11th to 20th	Day	12% 7% 2 6% 5% 5% 4 3 6% 7% 42%	5090
	21st to end	Day	17% 7% 2 5% 4 4 4 3 5% 6% 42%	5853
April	1st to 10th	Day	17% 7% 2 7% 5% 4 4 3 5% 8% 38%	2520
	11th to 20th	Day	15% 6% 3 6% 4 4 4 3 6% 7% 41%	2494
	21st to end	Day	16% 6% 2 5% 5% 5% 4 4 7% 7% 39%	2520
May	1st to 10th	Day	23% 6% 2 5% 4 4 4 4 6% 8% 33%	7630
	11th to 20th	Day	20% 7% 2 6% 4 4 4 3 6% 8% 35%	8221
	21st to end	Day	24% 7% 2 5% 3 4 4 3 6% 7% 35%	9060
June	1st to 10th	Day	12% 6% 2 5% 6% 4 4 5% 7% 9% 39%	2940
	11th to 20th	Day	14% 5% 2 6% 5% 5% 5% 5% 7% 9% 38%	2940
	21st to end	Day	12% 5% 2 6% 4 5% 5% 5% 7% 10% 41%	2940
July	1st to 10th	Day	8% 6% 2 6% 5% 5% 6% 5% 7% 11% 39%	6500
	11th to 20th	Day	11% 7% 3 7% 5% 5% 6% 5% 8% 11% 33%	6500
	21st to end	Day	11% 7% 3 6% 5% 4 5% 4 6% 9% 40%	6841
August	1st to 10th	Day	20% 6% 2 7% 4 5% 5% 4 6% 7% 33%	4234
	11th to 20th	Day	15% 5% 2 6% 4 4 5% 4 6% 9% 40%	3926
	21st to end	Day	13% 5% 2 4 3 4 4 3 6% 8% 48%	4312
September	1st to 10th	Day	16% 6% 2 6% 3 4 4 4 4 7% 45%	2400
	11th to 20th	Day	13% 5% 2 4 3 4 4 3 5% 8% 50%	2400
	21st to end	Day	20% 6% 3 8% 4 4 3 3 4 6% 38%	2145
October	1st to 10th	Day	18% 6% 2 5% 2 4 4 3 5% 7% 44%	2000
	11th to 20th	Day	16% 6% 2 7% 3 4 3 2 4 8% 45%	2000
	21st to end	Day	19% 5% 2 4 3 3 3 3 5% 7% 44%	2165
November	1st to 10th	Day	12% 7% 2 5% 3 3 3 3 4 7% 51%	1851
	11th to 20th	Day	16% 6% 2 5% 3 3 4 4 6% 8% 43%	1890
	21st to end	Day	16% 7% 2 5% 4 4 5% 4 6% 7% 41%	1690
December	1st to 10th	Day	14% 7% 2 7% 4 4 5% 4 6% 6% 40%	2680
	11th to 20th	Day	21% 9% 2 5% 3 3 3 3 5% 6% 40%	3066
	21st to end	Day	18% 7% 3 6% 5% 5% 4 4 6% 7% 36%	4048
January	1st to 10th	Night	12% 7% 3 7% 5% 5% 4 4 5% 8% 41%	8234
	11th to 20th	Night	14% 8% 2 6% 4 4 5% 3 6% 7% 41%	7979
	21st to end	Night	15% 7% 2 6% 4 3 3 3 5% 7% 44%	8401
February	1st to 10th	Night	16% 9% 2 5% 5% 4 5% 4 5% 6% 39%	2730
	11th to 20th	Night	17% 8% 3 7% 5% 4 4 4 5% 5% 38%	2554
	21st to end	Night	17% 8% 2 6% 4 4 4 3 5% 6% 40%	2076
March	1st to 10th	Night	17% 8% 3 6% 4 4 4 3 4 5% 42%	5352
	11th to 20th	Night	12% 5% 2 5% 4 4 4 3 5% 6% 50%	5089
	21st to end	Night	15% 7% 3 6% 4 4 4 3 5% 6% 43%	5320
April	1st to 10th	Night	18% 7% 3 5% 4 5% 5% 3 5% 7% 38%	2100
	11th to 20th	Night	15% 6% 2 6% 5% 4 4 3 6% 7% 41%	2075
	21st to end	Night	19% 5% 2 5% 3 3 4 4 5% 6% 44%	2100
May	1st to 10th	Night	22% 7% 2 7% 4 4 4 4 6% 7% 32%	5311
	11th to 20th	Night	20% 8% 3 7% 4 4 3 4 6% 8% 34%	4639
	21st to end	Night	25% 6% 2 7% 4 3 4 3 5% 6% 34%	5114
June	1st to 10th	Night	15% 5% 2 6% 4 4 4 3 6% 8% 42%	1680
	11th to 20th	Night	13% 5% 2 6% 4 6% 5% 4 6% 9% 40%	1680
	21st to end	Night	12% 4 2 5% 4 4 5% 3 7% 11% 42%	1680
July	1st to 10th	Night	9% 6% 2 7% 5% 6% 6% 5% 6% 9% 39%	3680
	11th to 20th	Night	12% 8% 3 7% 6% 5% 6% 4 8% 10% 31%	3680
	21st to end	Night	12% 6% 2 6% 4 5% 4 4 5% 9% 43%	4226
August	1st to 10th	Night	20% 7% 3 5% 4 4 4 4 6% 8% 36%	2915
	11th to 20th	Night	14% 7% 3 7% 5% 5% 4 3 5% 6% 41%	3089
	21st to end	Night	12% 5% 2 5% 4 3 4 4 6% 8% 47%	3586
September	1st to 10th	Night	14% 6% 2 5% 4 4 3 3 5% 6% 48%	2000
	11th to 20th	Night	12% 5% 2 4 3 3 4 3 5% 7% 51%	2000
	21st to end	Night	20% 6% 2 5% 4 4 5% 4 5% 6% 39%	2249
October	1st to 10th	Night	19% 7% 2 5% 3 2 4 3 3 6% 45%	2400
	11th to 20th	Night	16% 5% 2 5% 3 3 3 2 5% 7% 48%	2400
	21st to end	Night	18% 6% 2 5% 3 3 3 4 4 6% 48%	2672
November	1st to 10th	Night	11% 5% 2 4 4 4 4 4 5% 7% 51%	2667
	11th to 20th	Night	15% 7% 2 6% 3 4 3 3 5% 6% 46%	2730
	21st to end	Night	15% 6% 2 6% 5% 4 4 3 5% 8% 43%	2928
December	1st to 10th	Night	13% 8% 3 7% 4 4 4 3 5% 6% 42%	4720
	11th to 20th	Night	22% 7% 2 5% 3 4 3 3 5% 6% 40%	5348
	21st to end	Night	19% 8% 3 7% 4 4 4 3 5% 6% 36%	7150

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% 5% 13% 25% 15% 1	4662
	11th to 20th	Day	45% 5% 11% 19% 15% 5%	4920
	21st to end	Day	44% 7% 13% 23% 13% 1	5780
February	1st to 10th	Day	45% 7% 13% 23% 11% 1	1890
	11th to 20th	Day	46% 6% 11% 23% 12% 2	1961
	21st to end	Day	49% 5% 10% 23% 10% 3	1730
March	1st to 10th	Day	41% 6% 10% 24% 13% 6%	4708
	11th to 20th	Day	38% 7% 13% 26% 11% 5%	5090
	21st to end	Day	42% 5% 11% 17% 20% 4	5853
April	1st to 10th	Day	43% 6% 11% 21% 14% 5%	2520
	11th to 20th	Day	40% 7% 13% 21% 15% 4	2494
	21st to end	Day	42% 7% 11% 22% 15% 4	2520
May	1st to 10th	Day	47% 8% 12% 21% 11% 1	7639
	11th to 20th	Day	44% 7% 12% 24% 12% 1	8225
	21st to end	Day	46% 7% 10% 23% 13% 1	9061
June	1st to 10th	Day	38% 8% 14% 22% 16% 1	2940
	11th to 20th	Day	41% 8% 15% 23% 11% 2	2940
	21st to end	Day	36% 9% 15% 24% 14% 1	2940
July	1st to 10th	Day	37% 11% 14% 21% 15% 1	6430
	11th to 20th	Day	41% 11% 16% 21% 9% 1	6425
	21st to end	Day	39% 7% 10% 21% 21% 1	6648
August	1st to 10th	Day	48% 8% 12% 22% 10%	4221
	11th to 20th	Day	38% 8% 11% 30% 12% 1	3964
	21st to end	Day	33% 7% 11% 28% 19% 2	4312
September	1st to 10th	Day	39% 7% 11% 20% 20% 3	2400
	11th to 20th	Day	32% 6% 10% 25% 23% 3	2400
	21st to end	Day	48% 6% 9% 16% 19% 2	2145
October	1st to 10th	Day	36% 5% 10% 20% 25% 5%	3260
	11th to 20th	Day	28% 5% 13% 27% 22% 6%	3240
	21st to end	Day	26% 4 14% 25% 27% 4	3479
November	1st to 10th	Day	34% 4 15% 24% 19% 4	1851
	11th to 20th	Day	38% 6% 12% 24% 18% 2	1890
	21st to end	Day	40% 7% 12% 29% 9% 2	1690
December	1st to 10th	Day	43% 5% 17% 24% 10% 2	2680
	11th to 20th	Day	45% 5% 14% 28% 8% 1	3066
	21st to end	Day	45% 7% 15% 20% 12% 1	4048
January	1st to 10th	Night	39% 6% 15% 23% 14% 3	8234
	11th to 20th	Night	39% 6% 12% 21% 17% 5%	8022
	21st to end	Night	39% 4 11% 27% 18% 2	8401
February	1st to 10th	Night	44% 5% 13% 25% 11% 2	2730
	11th to 20th	Night	46% 5% 10% 20% 16% 2	2556
	21st to end	Night	43% 6% 11% 22% 15% 3	2076
March	1st to 10th	Night	42% 6% 10% 22% 12% 7%	5362
	11th to 20th	Night	33% 7% 15% 28% 12% 5%	5090
	21st to end	Night	41% 5% 8% 17% 24% 4	5320
April	1st to 10th	Night	44% 5% 12% 20% 15% 4	2100
	11th to 20th	Night	40% 7% 12% 19% 19% 2	2075
	21st to end	Night	39% 6% 12% 21% 17% 5%	2100
May	1st to 10th	Night	49% 7% 11% 19% 12% 2	5318
	11th to 20th	Night	46% 9% 12% 22% 10% 1	4640
	21st to end	Night	49% 7% 9% 21% 12% 2	5115
June	1st to 10th	Night	38% 8% 10% 23% 20% 1	1680
	11th to 20th	Night	38% 9% 14% 23% 14% 2	1680
	21st to end	Night	35% 9% 15% 25% 14% 2	1680
July	1st to 10th	Night	40% 10% 14% 20% 14% 3	3640
	11th to 20th	Night	45% 10% 16% 19% 10% 1	3632
	21st to end	Night	36% 9% 12% 22% 20% 1	4104
August	1st to 10th	Night	45% 9% 17% 18% 10% 1	2904
	11th to 20th	Night	42% 7% 12% 23% 15% 1	3117
	21st to end	Night	33% 7% 12% 29% 18% 1	3586
September	1st to 10th	Night	37% 6% 11% 23% 20% 3	2000
	11th to 20th	Night	33% 6% 10% 24% 25% 3	2000
	21st to end	Night	44% 6% 9% 18% 20% 2	2249
October	1st to 10th	Night	42% 5% 10% 20% 21% 2	3920
	11th to 20th	Night	27% 5% 10% 29% 25% 4	3899
	21st to end	Night	27% 4 12% 31% 24% 3	4308
November	1st to 10th	Night	31% 6% 13% 26% 19% 4	2667
	11th to 20th	Night	40% 5% 10% 23% 18% 4	2730
	21st to end	Night	39% 5% 13% 27% 14% 1	2928
December	1st to 10th	Night	41% 4 14% 29% 11% 1	4720
	11th to 20th	Night	45% 4 13% 24% 12% 2	5348
	21st to end	Night	45% 7% 12% 19% 15% 1	7150

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	29% 28% 27% 12% 4 1	220
	11th to 20th	Day	38% 26% 26% 9% 2	264
	21st to end	Day	25% 32% 29% 10% 3 1	363
February	1st to 10th	Day	26% 26% 34% 11% 2 1	330
	11th to 20th	Day	30% 23% 37% 8% 2	439
	21st to end	Day	30% 23% 28% 17% 2	446
March	1st to 10th	Day	27% 22% 30% 17% 3	540
	11th to 20th	Day	27% 26% 29% 13% 4 1	540
	21st to end	Day	29% 23% 30% 13% 4 1	594
April	1st to 10th	Day	29% 20% 30% 15% 5% 1	540
	11th to 20th	Day	24% 23% 27% 16% 6% 2	532
	21st to end	Day	26% 16% 33% 18% 5% 2	540
May	1st to 10th	Day	28% 18% 28% 17% 6% 2	543
	11th to 20th	Day	22% 15% 32% 21% 9% 2	567
	21st to end	Day	24% 10% 26% 24% 14% 3	617
June	1st to 10th	Day	14% 14% 31% 24% 14% 3	570
	11th to 20th	Day	19% 12% 29% 26% 12% 2	570
	21st to end	Day	14% 12% 29% 28% 13% 4	570
July	1st to 10th	Day	12% 5% 24% 34% 19% 7%	565
	11th to 20th	Day	7% 7% 26% 33% 22% 6%	564
	21st to end	Day	10% 7% 29% 34% 16% 4	616
August	1st to 10th	Day	12% 5% 26% 29% 20% 8%	526
	11th to 20th	Day	14% 5% 21% 33% 19% 7%	519
	21st to end	Day	12% 7% 23% 31% 18% 9%	583
September	1st to 10th	Day	17% 10% 21% 26% 18% 8%	530
	11th to 20th	Day	15% 5% 23% 30% 18% 10%	530
	21st to end	Day	23% 13% 25% 22% 14% 3	530
October	1st to 10th	Day	22% 8% 25% 22% 16% 6%	530
	11th to 20th	Day	20% 15% 30% 21% 13% 2	530
	21st to end	Day	20% 15% 35% 19% 9% 2	564
November	1st to 10th	Day	17% 17% 29% 25% 10% 3	425
	11th to 20th	Day	20% 23% 30% 21% 6%	430
	21st to end	Day	27% 19% 34% 16% 4	230
December	1st to 10th	Day	27% 24% 33% 11% 4 1	220
	11th to 20th	Day	28% 25% 31% 11% 3	220
	21st to end	Day	25% 26% 27% 14% 6% 1	242
January	1st to 10th	Night	20% 21% 38% 18% 3	840
	11th to 20th	Night	26% 20% 30% 22% 3	840
	21st to end	Night	19% 20% 39% 19% 2	924
February	1st to 10th	Night	22% 18% 36% 23% 2	840
	11th to 20th	Night	26% 22% 36% 15% 1	823
	21st to end	Night	24% 20% 35% 18% 2	692
March	1st to 10th	Night	22% 20% 32% 22% 3	840
	11th to 20th	Night	24% 20% 33% 19% 5%	840
	21st to end	Night	21% 19% 36% 20% 4	924
April	1st to 10th	Night	23% 20% 33% 19% 4	840
	11th to 20th	Night	18% 18% 34% 23% 6%	831
	21st to end	Night	22% 13% 32% 27% 6%	840
May	1st to 10th	Night	25% 11% 30% 27% 7%	656
	11th to 20th	Night	18% 10% 32% 33% 7%	414
	21st to end	Night	18% 7% 26% 37% 11% 1	455
June	1st to 10th	Night	15% 8% 25% 37% 15%	420
	11th to 20th	Night	13% 7% 28% 41% 10%	420
	21st to end	Night	13% 3 25% 45% 14% 1	420
July	1st to 10th	Night	11% 3 20% 45% 19% 1	410
	11th to 20th	Night	9% 2 22% 41% 24% 1	408
	21st to end	Night	10% 5% 20% 40% 24% 1	551
August	1st to 10th	Night	12% 2 17% 41% 26% 2	597
	11th to 20th	Night	14% 5% 16% 36% 26% 2	718
	21st to end	Night	14% 3 20% 37% 23% 2	880
September	1st to 10th	Night	15% 4 25% 33% 20% 3	800
	11th to 20th	Night	13% 6% 17% 37% 24% 4	800
	21st to end	Night	22% 6% 20% 32% 19% 1	800
October	1st to 10th	Night	22% 8% 24% 27% 18% 3	800
	11th to 20th	Night	20% 11% 27% 30% 12%	800
	21st to end	Night	21% 12% 31% 26% 9%	880
November	1st to 10th	Night	16% 11% 32% 29% 11% 1	820
	11th to 20th	Night	20% 18% 29% 26% 7% 1	840
	21st to end	Night	18% 18% 32% 25% 6%	840
December	1st to 10th	Night	25% 17% 33% 20% 5%	840
	11th to 20th	Night	21% 17% 34% 24% 4	840
	21st to end	Night	23% 16% 34% 25% 3	924

Page generated at 2026-07-28 03:25:27. Version ac07

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