Water Valley Overlook
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Water Valley Overlook clear sky chart from 2005-11-06 to 2025-08-05.

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	13% 7% 3 7% 4 4 5% 4 6% 8% 40%	125669
	Night	14% 7% 3 6% 4 4 4 3 5% 7% 42%	122450
Transparency	Day	40% 7% 11% 22% 17% 4	129359
	Night	39% 5% 10% 22% 19% 5%	126831
Seeing	Day	16% 9% 23% 24% 19% 9%	16172
	Night	17% 8% 24% 30% 19% 3	25851

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	15% 12% 5% 10% 4 3 4 3 4 5% 34%	3617
	11th to 20th	Day	16% 6% 3 12% 3 3 3 2 3 5% 45%	3718
	21st to end	Day	20% 8% 3 5% 3 3 3 3 5% 7% 40%	4972
February	1st to 10th	Day	20% 11% 3 7% 4 3 3 3 3 6% 36%	2000
	11th to 20th	Day	21% 9% 3 7% 5% 4 4 3 4 5% 36%	1948
	21st to end	Day	21% 9% 3 6% 4 3 4 3 4 5% 38%	1650
March	1st to 10th	Day	18% 11% 3 8% 4 4 4 3 4 5% 36%	4480
	11th to 20th	Day	13% 7% 2 6% 4 4 3 3 4 5% 47%	4702
	21st to end	Day	13% 7% 2 7% 5% 4 4 4 5% 7% 43%	5868
April	1st to 10th	Day	13% 6% 2 6% 5% 4 4 4 5% 6% 45%	2400
	11th to 20th	Day	15% 6% 3 6% 4 3 3 3 5% 7% 44%	2374
	21st to end	Day	13% 7% 2 7% 5% 5% 5% 3 6% 8% 39%	2400
May	1st to 10th	Day	19% 8% 3 6% 5% 5% 6% 4 7% 9% 28%	5858
	11th to 20th	Day	16% 9% 4 9% 6% 5% 5% 4 5% 7% 30%	5861
	21st to end	Day	17% 8% 3 7% 4 4 4 4 5% 8% 38%	6433
June	1st to 10th	Day	9% 6% 3 6% 5% 4 5% 4 7% 10% 41%	2633
	11th to 20th	Day	6% 4 2 6% 5% 5% 6% 5% 7% 10% 44%	2800
	21st to end	Day	5% 4 2 6% 5% 6% 6% 5% 9% 11% 42%	2800
July	1st to 10th	Day	7% 4 2 7% 5% 6% 6% 5% 8% 11% 40%	6360
	11th to 20th	Day	8% 5% 2 6% 5% 6% 7% 6% 9% 12% 33%	6279
	21st to end	Day	12% 8% 2 7% 5% 5% 6% 5% 8% 10% 31%	6424
August	1st to 10th	Day	4 3 2 5% 4 4 5% 5% 7% 8% 53%	3846
	11th to 20th	Day	7% 5% 2 6% 5% 5% 5% 5% 7% 10% 43%	3729
	21st to end	Day	6% 4 2 5% 4 4 4 5% 5% 8% 53%	4180
September	1st to 10th	Day	10% 6% 2 7% 5% 4 6% 4 6% 8% 42%	2272
	11th to 20th	Day	13% 6% 2 6% 5% 4 5% 4 5% 7% 44%	2090
	21st to end	Day	11% 5% 2 5% 4 3 4 3 7% 7% 49%	2090
October	1st to 10th	Day	11% 4 2 5% 3 3 4 3 4 7% 55%	2090
	11th to 20th	Day	11% 5% 2 5% 3 3 3 3 4 7% 53%	2021
	21st to end	Day	17% 6% 2 5% 4 4 3 3 4 5% 48%	1929
November	1st to 10th	Day	13% 6% 2 4 3 3 3 3 4 5% 54%	1762
	11th to 20th	Day	15% 7% 2 4 3 4 3 2 4 6% 49%	1800
	21st to end	Day	15% 8% 2 5% 4 3 3 3 5% 6% 45%	1800
December	1st to 10th	Day	17% 7% 2 6% 3 3 4 3 4 5% 46%	2930
	11th to 20th	Day	23% 10% 4 7% 5% 3 4 3 3 5% 33%	3373
	21st to end	Day	19% 9% 4 7% 4 4 4 4 7% 7% 31%	4180
January	1st to 10th	Night	16% 12% 4 9% 3 3 3 3 4 6% 37%	6348
	11th to 20th	Night	17% 10% 3 9% 4 3 3 2 3 3 43%	6208
	21st to end	Night	19% 10% 3 6% 4 3 3 3 4 5% 39%	5984
February	1st to 10th	Night	19% 12% 3 7% 5% 4 4 3 5% 5% 33%	2400
	11th to 20th	Night	22% 10% 3 7% 4 4 3 2 4 4 36%	2338
	21st to end	Night	24% 8% 2 6% 4 4 3 3 5% 6% 35%	1980
March	1st to 10th	Night	20% 11% 3 6% 4 4 3 3 5% 7% 34%	5373
	11th to 20th	Night	13% 6% 2 5% 4 3 4 3 5% 6% 48%	5256
	21st to end	Night	16% 7% 2 7% 4 4 4 3 5% 6% 41%	5103
April	1st to 10th	Night	12% 7% 2 6% 4 3 4 3 5% 7% 47%	2000
	11th to 20th	Night	15% 6% 2 5% 4 3 3 3 4 7% 48%	1975
	21st to end	Night	12% 7% 2 5% 4 4 5% 4 6% 8% 43%	2000
May	1st to 10th	Night	15% 9% 4 8% 6% 5% 5% 4 6% 7% 33%	4034
	11th to 20th	Night	15% 9% 4 9% 5% 4 4 4 6% 6% 33%	4032
	21st to end	Night	14% 8% 3 8% 5% 4 4 4 6% 8% 37%	4421
June	1st to 10th	Night	9% 5% 3 6% 4 4 5% 4 6% 11% 44%	1760
	11th to 20th	Night	4 3 1 4 4 3 5% 3 8% 9% 55%	1600
	21st to end	Night	3 3 2 5% 4 4 5% 5% 8% 11% 52%	1600
July	1st to 10th	Night	7% 5% 2 6% 4 5% 5% 5% 8% 10% 41%	3618
	11th to 20th	Night	6% 4 2 5% 5% 4 5% 5% 8% 16% 40%	3678
	21st to end	Night	8% 7% 3 8% 5% 5% 6% 5% 9% 13% 32%	4427
August	1st to 10th	Night	3 2 1 4 3 3 3 3 6% 8% 61%	3167
	11th to 20th	Night	5% 3 1 5% 4 3 5% 5% 8% 11% 50%	3100
	21st to end	Night	5% 3 2 4 3 3 4 4 6% 9% 57%	3476
September	1st to 10th	Night	10% 7% 2 5% 4 4 3 4 6% 7% 49%	1900
	11th to 20th	Night	10% 5% 2 6% 4 4 4 4 6% 7% 49%	2077
	21st to end	Night	10% 5% 2 5% 3 4 4 3 5% 6% 54%	2090
October	1st to 10th	Night	9% 4 2 4 3 3 3 3 4 6% 61%	2090
	11th to 20th	Night	12% 6% 2 5% 4 3 3 3 5% 6% 52%	2156
	21st to end	Night	15% 7% 2 5% 3 3 3 3 4 6% 50%	2667
November	1st to 10th	Night	12% 5% 3 6% 4 3 4 3 4 5% 53%	2536
	11th to 20th	Night	13% 6% 2 5% 4 3 3 3 6% 8% 48%	2600
	21st to end	Night	17% 8% 2 5% 3 3 4 3 4 5% 46%	2600
December	1st to 10th	Night	19% 9% 3 7% 3 3 3 2 4 4 43%	4250
	11th to 20th	Night	25% 8% 2 5% 3 2 3 3 3 4 42%	4822
	21st to end	Night	22% 10% 5% 8% 4 4 4 4 4 5% 29%	6784

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	51% 4 11% 19% 13% 2	3618
	11th to 20th	Day	45% 3 6% 21% 25% 1	3718
	21st to end	Day	44% 3 8% 22% 18% 5%	4972
February	1st to 10th	Day	51% 4 7% 20% 15% 3	2000
	11th to 20th	Day	52% 4 6% 20% 15% 4	1958
	21st to end	Day	49% 3 8% 16% 17% 7%	1650
March	1st to 10th	Day	51% 4 5% 14% 17% 9%	4480
	11th to 20th	Day	39% 4 7% 22% 19% 9%	4702
	21st to end	Day	41% 5% 9% 27% 17% 1	5870
April	1st to 10th	Day	39% 6% 10% 22% 20% 4	2400
	11th to 20th	Day	40% 5% 7% 21% 21% 6%	2374
	21st to end	Day	42% 6% 10% 24% 16% 2	2400
May	1st to 10th	Day	49% 9% 13% 18% 10% 1	5893
	11th to 20th	Day	51% 8% 12% 19% 9%	5865
	21st to end	Day	44% 6% 9% 22% 16% 2	6447
June	1st to 10th	Day	37% 8% 13% 23% 18% 2	2633
	11th to 20th	Day	32% 10% 14% 24% 18% 2	2800
	21st to end	Day	33% 11% 15% 20% 16% 4	2800
July	1st to 10th	Day	33% 12% 17% 26% 11% 1	6291
	11th to 20th	Day	36% 12% 21% 24% 5% 1	6204
	21st to end	Day	44% 10% 21% 20% 5%	6240
August	1st to 10th	Day	23% 8% 15% 31% 20% 2	3833
	11th to 20th	Day	32% 9% 14% 27% 16% 2	3765
	21st to end	Day	28% 8% 10% 27% 25% 2	4179
September	1st to 10th	Day	38% 9% 11% 21% 17% 5%	2272
	11th to 20th	Day	38% 8% 9% 21% 20% 3	2090
	21st to end	Day	33% 6% 12% 23% 21% 6%	2090
October	1st to 10th	Day	21% 4 5% 16% 43% 11%	3480
	11th to 20th	Day	23% 3 7% 23% 29% 15%	3339
	21st to end	Day	30% 3 6% 22% 30% 8%	3154
November	1st to 10th	Day	33% 4 8% 21% 28% 6%	1762
	11th to 20th	Day	37% 4 7% 21% 25% 6%	1800
	21st to end	Day	39% 4 7% 24% 21% 5%	1800
December	1st to 10th	Day	42% 4 5% 27% 20% 2	2930
	11th to 20th	Day	54% 4 7% 19% 13% 3	3370
	21st to end	Day	50% 5% 11% 24% 8% 2	4180
January	1st to 10th	Night	50% 3 9% 20% 16% 1	6348
	11th to 20th	Night	47% 3 6% 17% 22% 4	6208
	21st to end	Night	48% 3 5% 21% 17% 5%	5984
February	1st to 10th	Night	53% 4 10% 17% 15% 2	2400
	11th to 20th	Night	53% 4 6% 17% 16% 4	2339
	21st to end	Night	51% 3 8% 16% 18% 5%	1980
March	1st to 10th	Night	50% 4 7% 15% 18% 6%	5373
	11th to 20th	Night	36% 4 7% 20% 19% 14%	5256
	21st to end	Night	44% 4 8% 24% 18% 3	5103
April	1st to 10th	Night	37% 4 12% 23% 21% 4	2000
	11th to 20th	Night	37% 3 9% 21% 22% 8%	1975
	21st to end	Night	38% 6% 11% 25% 18% 2	2000
May	1st to 10th	Night	49% 9% 12% 19% 11% 1	4061
	11th to 20th	Night	50% 8% 14% 16% 12% 1	4033
	21st to end	Night	43% 8% 11% 23% 13% 1	4429
June	1st to 10th	Night	35% 7% 13% 24% 18% 3	1760
	11th to 20th	Night	23% 8% 16% 32% 19% 3	1600
	21st to end	Night	24% 10% 18% 28% 17% 4	1600
July	1st to 10th	Night	32% 11% 19% 26% 11% 1	3580
	11th to 20th	Night	28% 11% 25% 29% 5% 2	3633
	21st to end	Night	41% 11% 23% 19% 6% 1	4297
August	1st to 10th	Night	19% 7% 12% 38% 23% 1	3156
	11th to 20th	Night	23% 9% 20% 30% 16% 1	3130
	21st to end	Night	22% 8% 12% 31% 24% 3	3476
September	1st to 10th	Night	33% 8% 11% 24% 19% 5%	1900
	11th to 20th	Night	33% 7% 12% 19% 26% 2	2077
	21st to end	Night	30% 6% 10% 23% 25% 6%	2090
October	1st to 10th	Night	18% 4 7% 18% 40% 13%	3480
	11th to 20th	Night	21% 3 4 21% 31% 20%	3577
	21st to end	Night	25% 4 7% 25% 28% 12%	4392
November	1st to 10th	Night	35% 4 7% 21% 25% 8%	2536
	11th to 20th	Night	33% 4 8% 20% 28% 7%	2600
	21st to end	Night	40% 4 6% 23% 22% 5%	2600
December	1st to 10th	Night	46% 4 6% 17% 25% 2	4250
	11th to 20th	Night	47% 3 6% 22% 20% 3	4824
	21st to end	Night	56% 4 9% 20% 9% 2	6784

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% 15% 39% 12% 7%	300
	11th to 20th	Day	26% 20% 36% 13% 3 2	300
	21st to end	Day	22% 18% 38% 17% 3	330
February	1st to 10th	Day	29% 18% 32% 17% 3 1	300
	11th to 20th	Day	33% 21% 33% 11% 2 1	300
	21st to end	Day	36% 16% 35% 10% 4	249
March	1st to 10th	Day	28% 18% 31% 18% 5%	300
	11th to 20th	Day	24% 19% 35% 17% 5% 1	378
	21st to end	Day	23% 15% 34% 21% 7% 1	550
April	1st to 10th	Day	22% 16% 28% 22% 10% 2	500
	11th to 20th	Day	20% 15% 29% 24% 11% 1	492
	21st to end	Day	19% 12% 29% 25% 11% 4	500
May	1st to 10th	Day	18% 13% 26% 25% 13% 4	503
	11th to 20th	Day	15% 10% 23% 27% 15% 10%	527
	21st to end	Day	13% 7% 20% 28% 19% 13%	573
June	1st to 10th	Day	11% 6% 19% 23% 23% 18%	563
	11th to 20th	Day	7% 3 17% 26% 31% 15%	730
	21st to end	Day	7% 3 17% 30% 28% 16%	730
July	1st to 10th	Day	8% 2 12% 31% 27% 19%	721
	11th to 20th	Day	8% 4 10% 27% 31% 21%	689
	21st to end	Day	9% 2 10% 24% 33% 22%	576
August	1st to 10th	Day	8% 2 11% 26% 34% 19%	502
	11th to 20th	Day	9% 1 15% 28% 34% 13%	479
	21st to end	Day	12% 2 8% 21% 37% 21%	539
September	1st to 10th	Day	11% 3 12% 27% 32% 15%	490
	11th to 20th	Day	15% 2 9% 26% 29% 19%	490
	21st to end	Day	16% 5% 17% 27% 26% 10%	490
October	1st to 10th	Day	11% 3 20% 29% 26% 11%	490
	11th to 20th	Day	13% 12% 29% 29% 15% 3	421
	21st to end	Day	23% 11% 26% 27% 11% 2	330
November	1st to 10th	Day	20% 11% 28% 29% 10% 2	300
	11th to 20th	Day	18% 15% 35% 23% 9% 1	300
	21st to end	Day	22% 14% 30% 18% 13% 3	300
December	1st to 10th	Day	27% 17% 31% 20% 5%	300
	11th to 20th	Day	23% 17% 32% 19% 8% 1	300
	21st to end	Day	25% 18% 35% 18% 3	330
January	1st to 10th	Night	24% 14% 30% 27% 4	1000
	11th to 20th	Night	27% 16% 31% 22% 4	959
	21st to end	Night	21% 11% 41% 25% 2	880
February	1st to 10th	Night	25% 13% 33% 26% 3	800
	11th to 20th	Night	28% 15% 30% 23% 3	783
	21st to end	Night	30% 15% 33% 21% 2	660
March	1st to 10th	Night	22% 14% 33% 27% 5%	800
	11th to 20th	Night	22% 12% 34% 25% 6% 1	800
	21st to end	Night	20% 9% 34% 29% 8%	723
April	1st to 10th	Night	16% 12% 31% 31% 9% 1	600
	11th to 20th	Night	18% 10% 30% 32% 9% 1	593
	21st to end	Night	15% 8% 33% 31% 13% 1	600
May	1st to 10th	Night	14% 6% 31% 32% 17% 1	600
	11th to 20th	Night	13% 4 24% 33% 23% 3	591
	21st to end	Night	10% 2 17% 38% 28% 5%	650
June	1st to 10th	Night	11% 3 16% 33% 33% 5%	600
	11th to 20th	Night	5% 2 12% 37% 39% 6%	600
	21st to end	Night	4 1 12% 35% 40% 9%	600
July	1st to 10th	Night	8% 3 9% 28% 42% 11%	585
	11th to 20th	Night	7% 1 10% 28% 44% 11%	582
	21st to end	Night	7% 2 7% 30% 45% 9%	657
August	1st to 10th	Night	7% 1 7% 27% 49% 9%	579
	11th to 20th	Night	7% 1 8% 40% 40% 4	564
	21st to end	Night	10% 1 6% 28% 47% 9%	627
September	1st to 10th	Night	11% 2 11% 30% 41% 5%	570
	11th to 20th	Night	12% 2 12% 29% 39% 6%	747
	21st to end	Night	11% 3 18% 30% 33% 5%	760
October	1st to 10th	Night	11% 4 16% 33% 31% 5%	760
	11th to 20th	Night	16% 7% 22% 36% 19% 1	760
	21st to end	Night	17% 6% 25% 32% 17% 2	836
November	1st to 10th	Night	14% 6% 23% 37% 18% 2	780
	11th to 20th	Night	15% 10% 31% 32% 12% 1	800
	21st to end	Night	22% 9% 26% 31% 12% 1	800
December	1st to 10th	Night	24% 13% 28% 28% 7%	800
	11th to 20th	Night	24% 8% 30% 31% 7% 1	800
	21st to end	Night	28% 11% 30% 27% 4	1005

Page generated at 2025-08-02 00:32:24. Version ac07

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