Mansfield Dam
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mansfield Dam clear sky chart from 2005-11-06 to 2026-06-16.

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	12% 6% 2 5% 4 4 4 4 5% 7% 47%	137771
	Night	14% 6% 2 5% 3 3 3 3 5% 7% 50%	134630
Transparency	Day	36% 5% 10% 21% 19% 10%	141539
	Night	34% 5% 10% 19% 19% 12%	138929
Seeing	Day	14% 10% 25% 30% 18% 4	16983
	Night	15% 8% 28% 34% 13% 1	26921

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	13% 8% 2 5% 3 3 3 2 3 5% 51%	5289
	11th to 20th	Day	12% 5% 2 5% 3 3 3 3 5% 5% 56%	5310
	21st to end	Day	23% 8% 3 7% 3 3 2 2 3 5% 40%	6143
February	1st to 10th	Day	19% 8% 2 5% 3 3 3 2 4 4 46%	2100
	11th to 20th	Day	17% 7% 2 5% 3 3 3 3 4 6% 46%	2049
	21st to end	Day	18% 6% 2 4 3 2 3 2 3 5% 51%	1730
March	1st to 10th	Day	14% 7% 2 6% 3 3 3 3 4 6% 50%	5017
	11th to 20th	Day	15% 6% 2 6% 3 3 3 2 4 5% 51%	5090
	21st to end	Day	14% 7% 3 6% 3 3 4 3 5% 6% 46%	5583
April	1st to 10th	Day	15% 8% 2 6% 4 4 4 4 5% 6% 42%	2310
	11th to 20th	Day	16% 8% 3 7% 4 4 4 3 5% 5% 41%	2286
	21st to end	Day	16% 6% 2 5% 5% 4 4 3 5% 6% 43%	2685
May	1st to 10th	Day	21% 7% 2 6% 4 4 4 4 6% 7% 35%	7617
	11th to 20th	Day	13% 6% 2 6% 4 4 4 4 5% 8% 42%	7627
	21st to end	Day	13% 7% 3 7% 5% 5% 5% 5% 7% 8% 35%	8392
June	1st to 10th	Day	6% 5% 1 5% 4 4 6% 5% 7% 8% 49%	2730
	11th to 20th	Day	7% 4 1 5% 4 4 6% 5% 7% 9% 47%	2666
	21st to end	Day	6% 5% 2 5% 5% 6% 6% 5% 8% 9% 42%	2600
July	1st to 10th	Day	11% 6% 2 7% 5% 5% 5% 4 7% 9% 38%	5900
	11th to 20th	Day	4 4 2 5% 4 5% 6% 5% 8% 11% 46%	5900
	21st to end	Day	7% 5% 2 6% 5% 5% 5% 5% 7% 10% 44%	6422
August	1st to 10th	Day	1 1 1 2 2 3 3 3 4 8% 73%	4234
	11th to 20th	Day	3 2 1 4 3 3 4 4 6% 10% 60%	3911
	21st to end	Day	4 3 2 5% 4 4 6% 5% 7% 11% 50%	4115
September	1st to 10th	Day	9% 5% 2 6% 5% 4 5% 4 6% 7% 46%	2200
	11th to 20th	Day	11% 6% 2 6% 4 4 5% 4 6% 8% 44%	2200
	21st to end	Day	7% 4 2 5% 4 4 5% 4 5% 8% 53%	2200
October	1st to 10th	Day	6% 4 2 4 3 4 4 3 4 7% 59%	2200
	11th to 20th	Day	12% 4 1 5% 3 3 3 3 5% 6% 55%	2045
	21st to end	Day	11% 4 2 4 3 4 3 2 3 5% 59%	2200
November	1st to 10th	Day	14% 7% 2 5% 3 3 3 3 4 6% 49%	2058
	11th to 20th	Day	10% 5% 2 6% 4 4 3 3 5% 6% 53%	1974
	21st to end	Day	17% 7% 2 5% 3 3 4 2 4 5% 47%	1890
December	1st to 10th	Day	21% 9% 3 6% 4 3 3 2 3 4 42%	3030
	11th to 20th	Day	16% 7% 2 6% 4 4 4 3 5% 5% 44%	3481
	21st to end	Day	15% 5% 2 4 3 2 3 2 3 4 58%	4587
January	1st to 10th	Night	15% 6% 2 4 3 3 3 2 3 5% 54%	7634
	11th to 20th	Night	10% 3 1 3 2 2 2 3 5% 5% 64%	7680
	21st to end	Night	26% 8% 2 6% 3 3 3 2 4 5% 39%	8127
February	1st to 10th	Night	18% 7% 3 4 2 3 3 2 3 5% 50%	2520
	11th to 20th	Night	19% 7% 2 4 2 3 3 2 3 5% 49%	2458
	21st to end	Night	19% 6% 2 4 3 3 4 2 4 5% 48%	2076
March	1st to 10th	Night	16% 6% 2 5% 4 4 4 3 5% 6% 45%	5058
	11th to 20th	Night	16% 6% 2 4 3 3 3 3 4 4 51%	5090
	21st to end	Night	19% 8% 2 6% 3 3 3 2 4 6% 44%	5588
April	1st to 10th	Night	15% 6% 2 5% 4 4 4 3 5% 6% 45%	2310
	11th to 20th	Night	18% 7% 3 5% 4 4 3 3 4 6% 43%	2283
	21st to end	Night	17% 9% 2 4 3 3 3 3 3 7% 45%	1928
May	1st to 10th	Night	24% 8% 3 6% 4 4 3 3 5% 7% 34%	5266
	11th to 20th	Night	10% 7% 3 6% 4 4 4 3 6% 8% 45%	5265
	21st to end	Night	14% 7% 2 7% 4 4 5% 4 7% 9% 37%	5793
June	1st to 10th	Night	6% 4 1 3 3 3 4 3 6% 10% 58%	1890
	11th to 20th	Night	6% 3 2 4 3 3 4 4 6% 9% 57%	1845
	21st to end	Night	7% 4 2 4 4 3 3 4 5% 9% 55%	1800
July	1st to 10th	Night	9% 5% 2 6% 4 4 4 5% 7% 10% 43%	4078
	11th to 20th	Night	4 3 1 4 3 3 4 3 7% 13% 54%	4077
	21st to end	Night	6% 5% 2 5% 4 4 4 4 7% 11% 47%	4449
August	1st to 10th	Night	1 1 1 2 2 3 2 5% 8% 76%	2926
	11th to 20th	Night	3 2 1 3 2 3 3 3 6% 11% 62%	3141
	21st to end	Night	4 3 1 4 3 4 5% 4 6% 10% 56%	3785
September	1st to 10th	Night	8% 5% 2 5% 4 4 4 4 6% 7% 51%	2200
	11th to 20th	Night	9% 6% 2 6% 4 5% 4 4 6% 8% 48%	2200
	21st to end	Night	9% 3 1 4 3 4 4 3 6% 8% 55%	2200
October	1st to 10th	Night	6% 3 1 3 2 3 3 3 4 7% 64%	2200
	11th to 20th	Night	12% 4 1 4 3 3 3 3 5% 5% 58%	2332
	21st to end	Night	14% 4 1 3 3 3 3 2 3 4 61%	2640
November	1st to 10th	Night	14% 6% 1 5% 3 2 3 2 4 5% 54%	2460
	11th to 20th	Night	11% 5% 2 4 3 3 3 2 5% 6% 57%	2642
	21st to end	Night	17% 6% 2 5% 3 3 4 3 4 6% 47%	2730
December	1st to 10th	Night	19% 8% 3 6% 3 3 4 3 4 5% 42%	4380
	11th to 20th	Night	19% 9% 3 5% 3 2 2 3 3 4 47%	4946
	21st to end	Night	16% 6% 2 4 2 2 2 2 3 4 57%	6633

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	37% 3 5% 23% 23% 9%	5290
	11th to 20th	Day	32% 2 4 16% 27% 19%	5310
	21st to end	Day	48% 3 4 12% 22% 11%	6143
February	1st to 10th	Day	41% 5% 5% 13% 21% 15%	2100
	11th to 20th	Day	41% 4 8% 17% 19% 11%	2059
	21st to end	Day	38% 3 5% 18% 20% 15%	1730
March	1st to 10th	Day	35% 4 6% 17% 17% 20%	5017
	11th to 20th	Day	36% 6% 5% 9% 16% 28%	5090
	21st to end	Day	39% 6% 8% 18% 21% 8%	5585
April	1st to 10th	Day	44% 5% 7% 16% 15% 13%	2310
	11th to 20th	Day	44% 7% 7% 13% 18% 11%	2286
	21st to end	Day	41% 6% 7% 19% 18% 8%	2685
May	1st to 10th	Day	48% 5% 11% 20% 13% 3	7655
	11th to 20th	Day	40% 5% 10% 18% 22% 6%	7631
	21st to end	Day	42% 8% 13% 24% 11% 2	8405
June	1st to 10th	Day	30% 8% 14% 27% 18% 3	2730
	11th to 20th	Day	32% 7% 14% 26% 17% 5%	2666
	21st to end	Day	35% 11% 13% 23% 17% 3	2600
July	1st to 10th	Day	42% 5% 18% 29% 5% 1	5836
	11th to 20th	Day	30% 4 19% 32% 14% 1	5831
	21st to end	Day	34% 6% 17% 26% 15% 2	6240
August	1st to 10th	Day	12% 4 12% 40% 30% 1	4220
	11th to 20th	Day	20% 5% 22% 39% 12% 3	3949
	21st to end	Day	27% 7% 21% 25% 18% 2	4114
September	1st to 10th	Day	36% 8% 10% 21% 15% 10%	2200
	11th to 20th	Day	37% 8% 12% 20% 18% 5%	2200
	21st to end	Day	29% 8% 10% 20% 19% 15%	2200
October	1st to 10th	Day	16% 4 6% 12% 25% 37%	3590
	11th to 20th	Day	21% 3 8% 19% 29% 20%	3311
	21st to end	Day	26% 3 4 20% 32% 14%	3538
November	1st to 10th	Day	36% 6% 9% 16% 22% 12%	2058
	11th to 20th	Day	34% 4 8% 18% 21% 15%	1974
	21st to end	Day	42% 4 6% 16% 20% 13%	1890
December	1st to 10th	Day	48% 2 6% 16% 19% 9%	3030
	11th to 20th	Day	42% 5% 7% 11% 23% 13%	3479
	21st to end	Day	32% 3 5% 16% 28% 16%	4587
January	1st to 10th	Night	35% 2 5% 19% 24% 13%	7635
	11th to 20th	Night	24% 2 4 18% 30% 22%	7680
	21st to end	Night	49% 3 3 11% 21% 12%	8127
February	1st to 10th	Night	38% 5% 6% 13% 21% 18%	2520
	11th to 20th	Night	40% 3 7% 17% 19% 14%	2458
	21st to end	Night	40% 4 6% 13% 20% 17%	2076
March	1st to 10th	Night	38% 5% 7% 16% 18% 15%	5058
	11th to 20th	Night	37% 6% 7% 10% 15% 25%	5090
	21st to end	Night	42% 6% 7% 17% 19% 9%	5588
April	1st to 10th	Night	39% 6% 9% 17% 15% 15%	2310
	11th to 20th	Night	42% 6% 10% 13% 16% 14%	2283
	21st to end	Night	41% 5% 10% 18% 17% 9%	1928
May	1st to 10th	Night	50% 5% 9% 19% 13% 4	5293
	11th to 20th	Night	38% 6% 11% 19% 19% 9%	5266
	21st to end	Night	43% 6% 17% 24% 8% 2	5805
June	1st to 10th	Night	22% 8% 17% 29% 22% 3	1890
	11th to 20th	Night	23% 7% 17% 28% 20% 5%	1845
	21st to end	Night	26% 9% 17% 28% 17% 3	1800
July	1st to 10th	Night	37% 6% 25% 26% 5% 1	4035
	11th to 20th	Night	24% 5% 24% 34% 12% 1	4026
	21st to end	Night	33% 5% 21% 25% 12% 4	4320
August	1st to 10th	Night	9% 4 14% 45% 28% 1	2916
	11th to 20th	Night	19% 5% 30% 32% 12% 2	3169
	21st to end	Night	23% 9% 22% 27% 16% 2	3785
September	1st to 10th	Night	31% 7% 14% 23% 17% 8%	2200
	11th to 20th	Night	34% 8% 14% 24% 15% 6%	2200
	21st to end	Night	27% 6% 14% 22% 17% 13%	2200
October	1st to 10th	Night	15% 4 7% 14% 20% 40%	3590
	11th to 20th	Night	19% 3 9% 17% 31% 20%	3792
	21st to end	Night	26% 3 4 19% 32% 17%	4252
November	1st to 10th	Night	33% 5% 8% 17% 23% 14%	2460
	11th to 20th	Night	30% 5% 8% 20% 21% 16%	2642
	21st to end	Night	39% 5% 8% 16% 18% 15%	2730
December	1st to 10th	Night	47% 3 6% 16% 18% 10%	4380
	11th to 20th	Night	43% 3 7% 9% 22% 17%	4947
	21st to end	Night	34% 3 4 15% 28% 15%	6633

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% 16% 37% 19% 5%	330
	11th to 20th	Day	23% 18% 33% 19% 6% 1	330
	21st to end	Day	22% 24% 31% 18% 4	363
February	1st to 10th	Day	25% 16% 35% 20% 4	330
	11th to 20th	Day	25% 22% 38% 13% 2	330
	21st to end	Day	26% 22% 37% 14% 1	273
March	1st to 10th	Day	24% 20% 39% 15% 2	330
	11th to 20th	Day	21% 25% 35% 15% 4	330
	21st to end	Day	15% 21% 40% 18% 5% 1	363
April	1st to 10th	Day	23% 19% 39% 15% 3	330
	11th to 20th	Day	20% 23% 37% 16% 5%	324
	21st to end	Day	21% 16% 38% 19% 5%	705
May	1st to 10th	Day	18% 14% 39% 24% 5%	753
	11th to 20th	Day	18% 11% 31% 29% 10% 2	775
	21st to end	Day	16% 8% 30% 33% 12% 2	844
June	1st to 10th	Day	7% 4 22% 38% 24% 4	780
	11th to 20th	Day	9% 3 22% 45% 17% 4	756
	21st to end	Day	6% 3 19% 36% 28% 7%	730
July	1st to 10th	Day	8% 3 12% 42% 27% 8%	721
	11th to 20th	Day	5% 1 9% 43% 36% 5%	718
	21st to end	Day	5% 2 9% 37% 40% 7%	794
August	1st to 10th	Day	2 1 6% 42% 38% 11%	726
	11th to 20th	Day	6% 1 6% 42% 36% 8%	558
	21st to end	Day	5% 2 8% 34% 35% 16%	464
September	1st to 10th	Day	8% 4 10% 30% 38% 11%	330
	11th to 20th	Day	8% 1 9% 31% 43% 8%	330
	21st to end	Day	9% 2 12% 39% 30% 8%	330
October	1st to 10th	Day	4 3 16% 42% 28% 6%	330
	11th to 20th	Day	10% 6% 28% 35% 18% 4	330
	21st to end	Day	18% 15% 25% 27% 12% 3	363
November	1st to 10th	Day	19% 10% 28% 32% 8% 4	330
	11th to 20th	Day	17% 10% 33% 28% 11% 2	330
	21st to end	Day	22% 20% 32% 17% 8% 1	330
December	1st to 10th	Day	19% 11% 38% 21% 8% 3	330
	11th to 20th	Day	22% 13% 36% 21% 7% 1	330
	21st to end	Day	16% 15% 38% 23% 7% 1	363
January	1st to 10th	Night	19% 11% 34% 29% 7%	1050
	11th to 20th	Night	20% 13% 31% 30% 6%	1050
	21st to end	Night	22% 13% 30% 29% 5%	1060
February	1st to 10th	Night	24% 12% 32% 28% 5%	840
	11th to 20th	Night	26% 15% 33% 24% 2	824
	21st to end	Night	23% 16% 39% 21% 1	692
March	1st to 10th	Night	25% 13% 36% 23% 3	646
	11th to 20th	Night	20% 12% 37% 27% 4	630
	21st to end	Night	18% 13% 43% 24% 2	693
April	1st to 10th	Night	16% 14% 40% 27% 3	630
	11th to 20th	Night	22% 15% 38% 21% 4	623
	21st to end	Night	21% 11% 40% 21% 7%	630
May	1st to 10th	Night	17% 12% 40% 27% 4	630
	11th to 20th	Night	15% 9% 34% 31% 10% 1	621
	21st to end	Night	13% 6% 37% 32% 12%	683
June	1st to 10th	Night	7% 2 28% 44% 18% 2	630
	11th to 20th	Night	6% 2 37% 43% 12% 1	615
	21st to end	Night	7% 2 23% 45% 21% 2	600
July	1st to 10th	Night	8% 2 16% 45% 24% 4	585
	11th to 20th	Night	3 1 16% 52% 25% 2	582
	21st to end	Night	4 2 15% 51% 24% 3	657
August	1st to 10th	Night	1 12% 56% 26% 4	597
	11th to 20th	Night	5% 1 12% 52% 26% 3	594
	21st to end	Night	5% 1 7% 49% 32% 6%	660
September	1st to 10th	Night	8% 2 11% 43% 31% 6%	600
	11th to 20th	Night	11% 2 10% 42% 32% 3	600
	21st to end	Night	10% 1 17% 38% 33% 2	600
October	1st to 10th	Night	6% 2 15% 46% 28% 4	600
	11th to 20th	Night	13% 4 27% 37% 19% 2	732
	21st to end	Night	16% 9% 27% 29% 18% 1	880
November	1st to 10th	Night	14% 6% 25% 39% 15% 1	820
	11th to 20th	Night	13% 8% 30% 35% 13% 1	962
	21st to end	Night	20% 11% 29% 28% 11% 1	1050
December	1st to 10th	Night	19% 9% 32% 31% 9%	1050
	11th to 20th	Night	23% 10% 31% 30% 6%	1050
	21st to end	Night	19% 12% 30% 32% 7%	1155

Page generated at 2026-06-13 01:31:38. Version ac07

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