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 2024-04-03.

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	14% 6% 3 6% 5% 3 5% 5% 5% 7% 40%	79245
	Night	14% 7% 3 5% 5% 3 4 4 5% 7% 43%	80868
Transparency	Day	42% 7% 11% 21% 17% 3	78958
	Night	40% 6% 10% 21% 19% 4	80675
Seeing	Day	16% 9% 22% 24% 19% 10%	14287
	Night	17% 7% 24% 30% 19% 3	24166

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% 13% 4 8% 6% 3 5% 5% 4 5% 32%	2527
	11th to 20th	Day	21% 7% 3 10% 5% 2 3 3 3 5% 38%	2588
	21st to end	Day	24% 10% 4 5% 4 2 3 3 4 6% 36%	3476
February	1st to 10th	Day	20% 10% 4 6% 4 2 3 4 3 6% 37%	1900
	11th to 20th	Day	21% 9% 3 6% 6% 3 4 4 3 5% 37%	1848
	21st to end	Day	22% 9% 3 6% 4 2 4 4 3 5% 37%	1570
March	1st to 10th	Day	17% 9% 3 6% 5% 3 4 4 5% 6% 39%	1900
	11th to 20th	Day	20% 7% 3 6% 6% 3 4 4 5% 6% 36%	1974
	21st to end	Day	17% 6% 3 7% 6% 3 5% 5% 6% 7% 35%	2463
April	1st to 10th	Day	13% 5% 2 6% 5% 3 5% 4 5% 7% 46%	2184
	11th to 20th	Day	16% 6% 3 5% 5% 2 4 4 5% 6% 44%	2134
	21st to end	Day	14% 6% 3 6% 5% 3 4 5% 6% 8% 40%	2160
May	1st to 10th	Day	17% 5% 2 4 5% 3 5% 4 6% 8% 41%	2336
	11th to 20th	Day	13% 7% 3 7% 6% 3 4 4 6% 7% 39%	2301
	21st to end	Day	10% 5% 3 6% 6% 3 6% 6% 6% 11% 37%	2531
June	1st to 10th	Day	9% 6% 3 6% 6% 4 5% 5% 6% 10% 41%	2369
	11th to 20th	Day	5% 3 2 5% 6% 4 5% 7% 7% 11% 45%	2520
	21st to end	Day	5% 3 2 5% 6% 4 7% 6% 8% 10% 43%	2520
July	1st to 10th	Day	9% 4 3 7% 7% 4 7% 6% 8% 10% 34%	2520
	11th to 20th	Day	9% 5% 2 5% 6% 5% 6% 7% 7% 10% 37%	2495
	21st to end	Day	7% 4 2 5% 6% 5% 7% 8% 8% 11% 36%	2547
August	1st to 10th	Day	6% 4 3 6% 7% 5% 7% 7% 9% 10% 37%	2161
	11th to 20th	Day	10% 5% 3 6% 6% 4 6% 6% 7% 9% 39%	2125
	21st to end	Day	11% 5% 2 6% 6% 5% 5% 6% 7% 9% 39%	2376
September	1st to 10th	Day	10% 6% 2 6% 6% 4 5% 6% 6% 8% 42%	2153
	11th to 20th	Day	13% 5% 2 5% 6% 3 5% 5% 5% 7% 44%	1980
	21st to end	Day	11% 4 2 4 5% 2 4 4 6% 7% 52%	1980
October	1st to 10th	Day	12% 4 2 4 4 2 4 3 4 7% 54%	1980
	11th to 20th	Day	12% 5% 2 5% 4 3 3 4 4 7% 52%	1915
	21st to end	Day	17% 6% 2 5% 4 3 3 4 4 5% 46%	1828
November	1st to 10th	Day	12% 5% 2 4 3 2 3 3 4 5% 57%	1672
	11th to 20th	Day	15% 5% 3 4 3 3 4 3 5% 6% 50%	1710
	21st to end	Day	16% 7% 2 4 4 2 4 4 5% 6% 46%	1710
December	1st to 10th	Day	24% 8% 3 6% 4 2 4 4 4 5% 36%	1710
	11th to 20th	Day	16% 10% 4 5% 6% 3 5% 3 4 6% 38%	2153
	21st to end	Day	16% 10% 4 7% 6% 3 5% 4 6% 7% 32%	2929
January	1st to 10th	Night	19% 12% 3 5% 3 3 3 4 4 6% 38%	4428
	11th to 20th	Night	19% 10% 4 8% 6% 3 3 4 4 4 36%	4344
	21st to end	Night	23% 12% 4 5% 3 2 3 3 4 4 36%	4180
February	1st to 10th	Night	19% 11% 3 6% 6% 3 4 4 4 5% 34%	2280
	11th to 20th	Night	22% 9% 4 6% 5% 3 3 3 4 4 37%	2218
	21st to end	Night	25% 8% 3 6% 5% 3 4 4 4 6% 33%	1884
March	1st to 10th	Night	17% 7% 3 6% 4 3 4 4 5% 7% 41%	2280
	11th to 20th	Night	18% 8% 3 6% 5% 3 5% 4 4 6% 38%	2204
	21st to end	Night	15% 7% 3 6% 6% 4 5% 5% 5% 7% 38%	2150
April	1st to 10th	Night	11% 6% 2 5% 4 3 4 5% 5% 7% 48%	1820
	11th to 20th	Night	15% 5% 2 4 5% 2 3 4 4 7% 49%	1775
	21st to end	Night	13% 6% 3 4 4 2 5% 5% 6% 8% 43%	1800
May	1st to 10th	Night	10% 5% 3 6% 5% 3 5% 4 5% 7% 48%	1621
	11th to 20th	Night	10% 5% 3 6% 5% 4 5% 5% 5% 8% 45%	1592
	21st to end	Night	7% 4 2 5% 6% 3 5% 6% 8% 10% 43%	1744
June	1st to 10th	Night	8% 5% 3 5% 5% 3 5% 5% 5% 11% 45%	1584
	11th to 20th	Night	3 2 1 4 5% 3 5% 4 7% 9% 56%	1440
	21st to end	Night	3 3 2 4 4 3 4 6% 8% 11% 52%	1440
July	1st to 10th	Night	7% 5% 2 6% 5% 4 5% 6% 8% 12% 40%	1440
	11th to 20th	Night	7% 4 2 4 5% 3 6% 6% 6% 14% 44%	1462
	21st to end	Night	5% 4 2 4 5% 3 6% 6% 9% 11% 45%	1771
August	1st to 10th	Night	5% 4 2 5% 5% 3 5% 6% 8% 11% 46%	1774
	11th to 20th	Night	7% 4 2 5% 5% 3 5% 6% 8% 10% 45%	1776
	21st to end	Night	8% 5% 3 6% 4 3 5% 5% 7% 11% 43%	1980
September	1st to 10th	Night	11% 6% 2 5% 5% 3 4 4 6% 7% 49%	1800
	11th to 20th	Night	9% 4 2 5% 5% 3 4 5% 6% 7% 50%	1967
	21st to end	Night	9% 4 2 4 3 3 4 4 5% 6% 56%	1980
October	1st to 10th	Night	10% 3 2 3 3 2 3 3 4 6% 60%	1980
	11th to 20th	Night	13% 6% 2 5% 5% 3 3 3 5% 6% 50%	2042
	21st to end	Night	15% 7% 2 5% 4 2 3 3 4 6% 49%	2526
November	1st to 10th	Night	10% 5% 3 5% 4 2 4 3 4 5% 55%	2406
	11th to 20th	Night	12% 5% 2 4 4 2 3 4 5% 8% 49%	2470
	21st to end	Night	18% 7% 2 5% 4 2 4 4 4 6% 46%	2470
December	1st to 10th	Night	20% 9% 3 6% 5% 2 4 4 4 6% 37%	2470
	11th to 20th	Night	17% 7% 2 5% 4 2 4 3 4 5% 47%	3042
	21st to end	Night	18% 11% 4 8% 5% 4 5% 5% 5% 6% 29%	4728

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	52% 4 8% 20% 14% 2	2528
	11th to 20th	Day	51% 4 7% 17% 20% 1	2588
	21st to end	Day	51% 3 8% 22% 14% 1	3476
February	1st to 10th	Day	50% 4 7% 19% 16% 3	1900
	11th to 20th	Day	51% 4 6% 20% 15% 4	1858
	21st to end	Day	51% 3 8% 15% 16% 6%	1570
March	1st to 10th	Day	46% 5% 7% 16% 18% 6%	1900
	11th to 20th	Day	49% 6% 9% 18% 15% 2	1974
	21st to end	Day	48% 6% 11% 21% 14% 1	2463
April	1st to 10th	Day	38% 6% 10% 23% 20% 4	2184
	11th to 20th	Day	41% 5% 7% 20% 21% 6%	2134
	21st to end	Day	41% 6% 10% 24% 16% 2	2160
May	1st to 10th	Day	41% 6% 10% 24% 15% 3	2336
	11th to 20th	Day	44% 7% 11% 22% 15% 1	2305
	21st to end	Day	40% 9% 13% 24% 13% 1	2531
June	1st to 10th	Day	37% 8% 13% 23% 18% 2	2369
	11th to 20th	Day	30% 10% 15% 25% 17% 3	2520
	21st to end	Day	33% 11% 15% 20% 17% 4	2520
July	1st to 10th	Day	39% 14% 15% 18% 11% 3	2451
	11th to 20th	Day	39% 10% 17% 21% 10% 3	2420
	21st to end	Day	36% 12% 17% 25% 9% 1	2405
August	1st to 10th	Day	36% 12% 17% 22% 11% 2	2148
	11th to 20th	Day	39% 10% 13% 21% 15% 2	2125
	21st to end	Day	40% 9% 12% 22% 14% 3	2376
September	1st to 10th	Day	38% 10% 11% 21% 17% 3	2153
	11th to 20th	Day	38% 8% 10% 21% 20% 3	1980
	21st to end	Day	31% 6% 11% 24% 22% 6%	1980
October	1st to 10th	Day	32% 4 8% 23% 27% 5%	1980
	11th to 20th	Day	34% 4 8% 22% 25% 8%	1915
	21st to end	Day	41% 4 7% 19% 24% 6%	1828
November	1st to 10th	Day	31% 3 8% 21% 30% 6%	1672
	11th to 20th	Day	36% 3 7% 22% 25% 7%	1710
	21st to end	Day	40% 4 7% 23% 21% 6%	1710
December	1st to 10th	Day	50% 4 6% 20% 16% 3	1710
	11th to 20th	Day	48% 4 8% 20% 18% 2	2150
	21st to end	Day	50% 5% 11% 21% 10% 2	2929
January	1st to 10th	Night	48% 3 7% 24% 17% 1	4428
	11th to 20th	Night	52% 4 7% 16% 17% 5%	4344
	21st to end	Night	53% 3 6% 21% 15% 2	4180
February	1st to 10th	Night	53% 3 10% 17% 16% 2	2280
	11th to 20th	Night	51% 4 6% 18% 17% 5%	2219
	21st to end	Night	53% 3 8% 15% 16% 5%	1884
March	1st to 10th	Night	43% 4 9% 14% 21% 9%	2280
	11th to 20th	Night	47% 5% 8% 20% 16% 3	2204
	21st to end	Night	45% 5% 11% 22% 15% 2	2150
April	1st to 10th	Night	36% 4 12% 24% 21% 4	1820
	11th to 20th	Night	37% 3 9% 20% 22% 9%	1775
	21st to end	Night	37% 6% 10% 25% 19% 2	1800
May	1st to 10th	Night	37% 6% 9% 24% 21% 3	1621
	11th to 20th	Night	36% 9% 16% 21% 17% 2	1593
	21st to end	Night	33% 10% 14% 25% 15% 3	1745
June	1st to 10th	Night	34% 7% 13% 24% 18% 3	1584
	11th to 20th	Night	21% 8% 17% 33% 18% 3	1440
	21st to end	Night	24% 10% 18% 27% 17% 4	1440
July	1st to 10th	Night	34% 11% 19% 20% 14% 3	1400
	11th to 20th	Night	28% 9% 20% 26% 12% 5%	1414
	21st to end	Night	29% 12% 17% 28% 13% 1	1672
August	1st to 10th	Night	29% 10% 17% 28% 15% 1	1763
	11th to 20th	Night	29% 12% 18% 22% 16% 3	1776
	21st to end	Night	33% 10% 14% 26% 13% 5%	1980
September	1st to 10th	Night	33% 8% 12% 25% 18% 5%	1800
	11th to 20th	Night	32% 8% 12% 19% 27% 3	1967
	21st to end	Night	28% 6% 10% 23% 26% 7%	1980
October	1st to 10th	Night	26% 5% 8% 24% 28% 9%	1980
	11th to 20th	Night	36% 4 7% 21% 22% 9%	2042
	21st to end	Night	37% 4 6% 22% 25% 6%	2526
November	1st to 10th	Night	33% 4 7% 22% 26% 8%	2406
	11th to 20th	Night	33% 4 7% 21% 28% 7%	2470
	21st to end	Night	41% 4 6% 22% 22% 5%	2470
December	1st to 10th	Night	49% 5% 8% 17% 17% 3	2470
	11th to 20th	Night	41% 3 7% 22% 23% 4	3044
	21st to end	Night	53% 5% 11% 17% 12% 3	4728

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	26% 15% 40% 12% 7%	270
	11th to 20th	Day	28% 20% 33% 13% 4 2	270
	21st to end	Day	23% 18% 38% 18% 4	297
February	1st to 10th	Day	29% 17% 33% 17% 3 1	270
	11th to 20th	Day	33% 19% 34% 12% 2 1	270
	21st to end	Day	40% 16% 33% 7% 4	225
March	1st to 10th	Day	28% 16% 32% 19% 6%	270
	11th to 20th	Day	23% 17% 35% 19% 5% 1	344
	21st to end	Day	23% 14% 34% 22% 7% 1	506
April	1st to 10th	Day	19% 14% 29% 24% 11% 2	428
	11th to 20th	Day	18% 14% 28% 25% 12% 2	412
	21st to end	Day	19% 12% 28% 25% 12% 4	420
May	1st to 10th	Day	18% 12% 25% 28% 13% 4	423
	11th to 20th	Day	15% 7% 23% 28% 16% 11%	447
	21st to end	Day	12% 3 18% 29% 22% 16%	485
June	1st to 10th	Day	11% 5% 17% 22% 25% 20%	479
	11th to 20th	Day	6% 3 16% 27% 31% 17%	630
	21st to end	Day	7% 3 17% 32% 27% 15%	630
July	1st to 10th	Day	9% 2 12% 30% 27% 21%	621
	11th to 20th	Day	9% 4 10% 26% 30% 23%	593
	21st to end	Day	8% 1 10% 25% 33% 23%	488
August	1st to 10th	Day	7% 2 10% 25% 35% 20%	446
	11th to 20th	Day	10% 1 11% 29% 36% 13%	439
	21st to end	Day	13% 2 8% 20% 37% 20%	495
September	1st to 10th	Day	10% 2 10% 26% 35% 16%	450
	11th to 20th	Day	15% 2 9% 24% 30% 20%	450
	21st to end	Day	14% 4 16% 27% 28% 10%	450
October	1st to 10th	Day	12% 3 20% 28% 25% 12%	450
	11th to 20th	Day	14% 12% 29% 29% 13% 3	385
	21st to end	Day	25% 12% 24% 26% 10% 2	297
November	1st to 10th	Day	19% 11% 28% 29% 10% 3	270
	11th to 20th	Day	17% 14% 36% 23% 9% 1	270
	21st to end	Day	22% 14% 29% 19% 13% 3	270
December	1st to 10th	Day	28% 17% 29% 21% 6%	270
	11th to 20th	Day	20% 17% 34% 19% 9% 1	270
	21st to end	Day	25% 19% 35% 18% 3	297
January	1st to 10th	Night	24% 15% 30% 27% 5%	950
	11th to 20th	Night	28% 16% 30% 22% 4	912
	21st to end	Night	21% 11% 41% 24% 2	836
February	1st to 10th	Night	25% 13% 33% 26% 3	760
	11th to 20th	Night	28% 15% 30% 25% 3	743
	21st to end	Night	31% 16% 32% 20% 1	628
March	1st to 10th	Night	22% 13% 32% 27% 5%	760
	11th to 20th	Night	21% 12% 34% 25% 7% 1	760
	21st to end	Night	20% 9% 33% 30% 8%	687
April	1st to 10th	Night	14% 11% 32% 32% 10% 1	546
	11th to 20th	Night	18% 10% 29% 32% 10% 2	533
	21st to end	Night	15% 7% 32% 31% 13% 1	540
May	1st to 10th	Night	13% 5% 32% 32% 18% 1	540
	11th to 20th	Night	12% 4 24% 32% 24% 3	531
	21st to end	Night	9% 2 15% 39% 31% 6%	584
June	1st to 10th	Night	11% 2 14% 33% 34% 5%	540
	11th to 20th	Night	4 1 12% 37% 40% 6%	540
	21st to end	Night	4 1 13% 35% 39% 8%	540
July	1st to 10th	Night	8% 2 9% 26% 42% 12%	525
	11th to 20th	Night	7% 11% 27% 43% 12%	522
	21st to end	Night	6% 1 8% 30% 46% 9%	591
August	1st to 10th	Night	7% 1 5% 27% 50% 10%	537
	11th to 20th	Night	8% 1 7% 39% 40% 4	534
	21st to end	Night	10% 1 6% 28% 46% 9%	594
September	1st to 10th	Night	11% 2 10% 30% 43% 5%	540
	11th to 20th	Night	11% 2 12% 29% 39% 6%	707
	21st to end	Night	10% 3 18% 31% 34% 5%	720
October	1st to 10th	Night	12% 4 17% 32% 31% 5%	720
	11th to 20th	Night	17% 6% 22% 35% 18% 1	720
	21st to end	Night	18% 7% 25% 32% 17% 2	792
November	1st to 10th	Night	13% 6% 23% 38% 19% 2	740
	11th to 20th	Night	14% 9% 31% 32% 12% 1	760
	21st to end	Night	22% 8% 27% 31% 12% 1	760
December	1st to 10th	Night	24% 13% 28% 28% 7%	760
	11th to 20th	Night	23% 8% 30% 31% 8% 1	760
	21st to end	Night	27% 11% 30% 27% 5%	954

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