Hoover
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hoover clear sky chart from 2005-11-06 to 2024-01-16.

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	13% 6% 3 5% 5% 3 5% 5% 6% 8% 42%	74836
	Night	12% 5% 2 5% 5% 3 4 5% 5% 7% 46%	74967
Transparency	Day	40% 5% 11% 20% 19% 5%	74564
	Night	37% 5% 10% 21% 21% 7%	74759
Seeing	Day	15% 9% 22% 24% 20% 10%	13427
	Night	14% 7% 22% 30% 22% 4	23483

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	19% 7% 3 5% 4 3 3 3 4 5% 43%	1706
	11th to 20th	Day	20% 9% 3 5% 4 2 3 3 4 5% 42%	1751
	21st to end	Day	17% 6% 3 5% 4 3 3 3 4 6% 46%	1980
February	1st to 10th	Day	19% 10% 3 6% 4 3 4 4 4 6% 38%	1800
	11th to 20th	Day	23% 7% 2 4 4 2 4 4 4 5% 39%	1748
	21st to end	Day	20% 9% 4 5% 6% 3 3 4 3 5% 37%	1480
March	1st to 10th	Day	15% 7% 3 6% 5% 2 3 4 4 5% 46%	1800
	11th to 20th	Day	16% 9% 3 6% 5% 3 5% 5% 5% 7% 37%	1893
	21st to end	Day	14% 7% 3 6% 6% 2 4 5% 5% 8% 40%	2290
April	1st to 10th	Day	11% 5% 3 5% 4 3 4 4 5% 7% 48%	2160
	11th to 20th	Day	12% 5% 3 6% 5% 3 4 4 5% 7% 46%	2134
	21st to end	Day	8% 3 2 4 6% 3 4 5% 5% 8% 50%	2160
May	1st to 10th	Day	11% 5% 2 4 5% 3 4 5% 6% 7% 49%	2290
	11th to 20th	Day	10% 4 2 5% 5% 3 5% 5% 6% 10% 44%	2301
	21st to end	Day	9% 5% 2 5% 6% 3 5% 4 6% 9% 45%	2531
June	1st to 10th	Day	10% 6% 3 6% 6% 4 5% 7% 8% 10% 34%	2340
	11th to 20th	Day	6% 4 2 4 5% 3 7% 7% 7% 11% 44%	2340
	21st to end	Day	7% 5% 2 5% 6% 3 7% 6% 7% 10% 42%	2340
July	1st to 10th	Day	9% 5% 2 7% 7% 4 8% 7% 8% 11% 32%	2340
	11th to 20th	Day	8% 5% 2 6% 7% 4 8% 9% 10% 12% 30%	2340
	21st to end	Day	7% 4 2 6% 7% 5% 8% 8% 8% 11% 33%	2474
August	1st to 10th	Day	7% 4 2 5% 7% 4 7% 8% 9% 12% 34%	2148
	11th to 20th	Day	11% 5% 2 7% 7% 5% 7% 7% 7% 10% 33%	2125
	21st to end	Day	12% 5% 3 6% 7% 4 6% 7% 7% 10% 32%	2376
September	1st to 10th	Day	10% 4 3 6% 6% 3 7% 7% 5% 8% 41%	2120
	11th to 20th	Day	13% 6% 2 5% 5% 3 5% 5% 5% 7% 43%	1980
	21st to end	Day	11% 5% 2 4 6% 3 4 4 5% 6% 52%	1980
October	1st to 10th	Day	9% 4 2 5% 4 3 5% 4 5% 5% 54%	1980
	11th to 20th	Day	10% 4 2 4 4 2 3 3 5% 6% 55%	1980
	21st to end	Day	13% 5% 2 4 4 3 4 3 4 5% 54%	1870
November	1st to 10th	Day	12% 5% 3 4 4 3 3 3 4 5% 54%	1672
	11th to 20th	Day	14% 5% 3 4 3 3 4 4 4 6% 53%	1710
	21st to end	Day	14% 6% 2 4 5% 2 5% 4 4 7% 45%	1710
December	1st to 10th	Day	21% 7% 3 5% 5% 3 4 4 4 6% 39%	1710
	11th to 20th	Day	18% 8% 3 5% 6% 3 4 4 3 4 42%	2153
	21st to end	Day	18% 10% 5% 6% 4 3 4 4 5% 7% 35%	3124
January	1st to 10th	Night	17% 8% 3 5% 4 3 3 4 4 5% 46%	2459
	11th to 20th	Night	17% 9% 5% 5% 5% 3 4 3 4 6% 40%	2316
	21st to end	Night	17% 7% 3 4 5% 2 4 4 4 5% 45%	2376
February	1st to 10th	Night	18% 7% 2 6% 4 3 4 4 4 7% 42%	2160
	11th to 20th	Night	20% 7% 3 5% 5% 2 3 3 4 5% 44%	2098
	21st to end	Night	20% 6% 2 4 5% 3 4 5% 5% 7% 39%	1776
March	1st to 10th	Night	16% 7% 2 4 4 3 4 3 5% 6% 46%	2160
	11th to 20th	Night	15% 5% 3 5% 4 2 5% 6% 5% 7% 42%	2066
	21st to end	Night	14% 5% 2 5% 4 3 5% 5% 5% 7% 45%	2080
April	1st to 10th	Night	11% 4 2 5% 4 3 5% 5% 6% 8% 47%	1800
	11th to 20th	Night	13% 5% 2 5% 3 2 4 4 5% 7% 51%	1775
	21st to end	Night	10% 4 2 4 5% 3 4 3 5% 7% 54%	1800
May	1st to 10th	Night	9% 4 1 4 4 3 4 5% 5% 9% 52%	1666
	11th to 20th	Night	9% 5% 2 4 6% 3 5% 6% 6% 9% 45%	1592
	21st to end	Night	6% 3 2 4 5% 3 5% 6% 8% 10% 48%	1744
June	1st to 10th	Night	6% 5% 3 5% 6% 4 7% 7% 8% 11% 38%	1620
	11th to 20th	Night	4 3 1 3 3 2 6% 6% 8% 11% 52%	1620
	21st to end	Night	5% 4 2 5% 5% 4 5% 5% 8% 11% 44%	1620
July	1st to 10th	Night	6% 5% 2 6% 6% 4 8% 6% 8% 11% 39%	1620
	11th to 20th	Night	6% 4 3 5% 6% 3 5% 6% 8% 12% 41%	1620
	21st to end	Night	5% 4 2 6% 6% 4 7% 7% 7% 11% 42%	1839
August	1st to 10th	Night	5% 3 1 5% 5% 3 5% 7% 9% 14% 42%	1790
	11th to 20th	Night	8% 5% 2 6% 5% 4 6% 6% 8% 10% 41%	1776
	21st to end	Night	10% 5% 2 6% 7% 3 6% 6% 6% 8% 40%	1980
September	1st to 10th	Night	8% 4 2 6% 7% 3 5% 4 6% 10% 44%	1822
	11th to 20th	Night	10% 4 2 4 6% 4 4 5% 5% 8% 47%	1980
	21st to end	Night	7% 5% 2 5% 5% 2 4 4 5% 7% 55%	1980
October	1st to 10th	Night	7% 4 2 4 4 2 3 3 4 6% 61%	1980
	11th to 20th	Night	11% 4 2 4 4 2 3 5% 4 6% 55%	1980
	21st to end	Night	14% 5% 2 4 3 2 3 3 3 4 55%	2482
November	1st to 10th	Night	11% 4 2 3 4 2 4 3 4 5% 58%	2406
	11th to 20th	Night	11% 6% 2 4 3 2 3 3 4 5% 54%	2470
	21st to end	Night	13% 6% 1 5% 4 3 5% 4 5% 6% 48%	2470
December	1st to 10th	Night	18% 7% 2 5% 5% 3 4 3 4 7% 41%	2470
	11th to 20th	Night	17% 7% 3 4 4 2 4 3 4 4 47%	3042
	21st to end	Night	19% 8% 3 6% 5% 3 4 4 6% 7% 34%	4532

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	45% 2 7% 18% 24% 5%	1707
	11th to 20th	Day	46% 3 6% 19% 21% 5%	1751
	21st to end	Day	41% 3 5% 21% 25% 6%	1980
February	1st to 10th	Day	48% 2 7% 20% 18% 4	1800
	11th to 20th	Day	49% 3 4 19% 18% 7%	1758
	21st to end	Day	50% 4 6% 11% 21% 7%	1480
March	1st to 10th	Day	41% 3 8% 17% 21% 10%	1800
	11th to 20th	Day	48% 4 10% 15% 17% 5%	1893
	21st to end	Day	43% 4 9% 21% 20% 3	2290
April	1st to 10th	Day	36% 4 11% 22% 19% 8%	2160
	11th to 20th	Day	38% 4 6% 20% 24% 7%	2134
	21st to end	Day	32% 5% 9% 26% 26% 3	2160
May	1st to 10th	Day	34% 5% 10% 24% 23% 4	2290
	11th to 20th	Day	36% 5% 16% 25% 15% 3	2305
	21st to end	Day	37% 6% 11% 24% 18% 3	2531
June	1st to 10th	Day	42% 8% 14% 21% 14% 1	2340
	11th to 20th	Day	31% 9% 18% 26% 15% 2	2340
	21st to end	Day	35% 8% 18% 25% 11% 4	2340
July	1st to 10th	Day	40% 11% 19% 19% 9% 2	2275
	11th to 20th	Day	41% 12% 20% 17% 9% 1	2271
	21st to end	Day	40% 10% 21% 20% 9% 1	2336
August	1st to 10th	Day	36% 11% 20% 25% 6% 1	2136
	11th to 20th	Day	43% 8% 18% 17% 10% 3	2125
	21st to end	Day	44% 9% 15% 19% 10% 4	2376
September	1st to 10th	Day	39% 8% 14% 18% 17% 5%	2120
	11th to 20th	Day	40% 7% 10% 19% 20% 4	1980
	21st to end	Day	33% 5% 9% 23% 23% 8%	1980
October	1st to 10th	Day	32% 4 9% 20% 25% 10%	1980
	11th to 20th	Day	30% 3 7% 24% 28% 8%	1980
	21st to end	Day	34% 3 4 18% 31% 10%	1870
November	1st to 10th	Day	34% 3 5% 17% 29% 12%	1672
	11th to 20th	Day	34% 2 5% 20% 27% 11%	1710
	21st to end	Day	40% 3 7% 18% 24% 8%	1710
December	1st to 10th	Day	47% 4 8% 16% 19% 6%	1710
	11th to 20th	Day	47% 2 5% 17% 23% 5%	2150
	21st to end	Day	49% 3 6% 20% 20% 2	3124
January	1st to 10th	Night	41% 4 7% 19% 24% 5%	2459
	11th to 20th	Night	47% 4 5% 19% 20% 5%	2316
	21st to end	Night	43% 3 4 19% 25% 7%	2376
February	1st to 10th	Night	44% 3 6% 19% 20% 7%	2160
	11th to 20th	Night	45% 3 5% 19% 19% 9%	2099
	21st to end	Night	45% 4 7% 15% 19% 9%	1776
March	1st to 10th	Night	39% 3 6% 17% 23% 12%	2160
	11th to 20th	Night	41% 5% 11% 17% 20% 6%	2066
	21st to end	Night	38% 4 8% 25% 20% 5%	2080
April	1st to 10th	Night	35% 5% 11% 22% 20% 8%	1800
	11th to 20th	Night	34% 4 7% 22% 22% 11%	1775
	21st to end	Night	32% 4 10% 25% 23% 6%	1800
May	1st to 10th	Night	30% 5% 11% 24% 25% 5%	1666
	11th to 20th	Night	34% 7% 19% 20% 17% 3	1593
	21st to end	Night	28% 8% 13% 27% 19% 4	1745
June	1st to 10th	Night	35% 10% 14% 22% 17% 1	1620
	11th to 20th	Night	23% 7% 22% 29% 16% 3	1620
	21st to end	Night	31% 9% 17% 23% 17% 4	1620
July	1st to 10th	Night	37% 9% 21% 20% 10% 3	1575
	11th to 20th	Night	33% 11% 24% 21% 9% 2	1566
	21st to end	Night	32% 11% 24% 23% 10% 1	1737
August	1st to 10th	Night	28% 9% 23% 30% 9% 1	1778
	11th to 20th	Night	36% 10% 21% 17% 11% 4	1776
	21st to end	Night	40% 7% 15% 21% 12% 5%	1980
September	1st to 10th	Night	36% 6% 16% 19% 17% 5%	1822
	11th to 20th	Night	35% 7% 12% 20% 21% 6%	1980
	21st to end	Night	29% 5% 9% 25% 24% 8%	1980
October	1st to 10th	Night	26% 5% 8% 22% 25% 13%	1980
	11th to 20th	Night	31% 4 6% 22% 26% 12%	1980
	21st to end	Night	35% 2 5% 16% 29% 13%	2482
November	1st to 10th	Night	30% 3 7% 18% 27% 14%	2406
	11th to 20th	Night	33% 2 5% 19% 27% 14%	2470
	21st to end	Night	37% 3 7% 20% 24% 9%	2470
December	1st to 10th	Night	43% 3 9% 18% 21% 5%	2470
	11th to 20th	Night	41% 3 7% 15% 29% 6%	3044
	21st to end	Night	47% 4 5% 21% 20% 3	4532

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% 23% 31% 17% 4	270
	11th to 20th	Day	27% 18% 31% 17% 6%	255
	21st to end	Day	24% 23% 39% 11% 1 1	264
February	1st to 10th	Day	26% 22% 38% 12% 2	240
	11th to 20th	Day	39% 15% 31% 14%	240
	21st to end	Day	29% 18% 42% 11% 1	198
March	1st to 10th	Day	25% 21% 33% 15% 5% 1	240
	11th to 20th	Day	23% 17% 37% 15% 7% 1	333
	21st to end	Day	23% 16% 31% 20% 10%	462
April	1st to 10th	Day	19% 13% 31% 24% 12% 1	420
	11th to 20th	Day	17% 14% 31% 24% 12% 2	412
	21st to end	Day	12% 10% 31% 29% 14% 3	420
May	1st to 10th	Day	13% 9% 26% 31% 16% 5%	423
	11th to 20th	Day	9% 5% 24% 30% 22% 11%	447
	21st to end	Day	12% 5% 15% 30% 21% 16%	485
June	1st to 10th	Day	13% 4 15% 29% 24% 15%	450
	11th to 20th	Day	6% 4 14% 23% 29% 23%	450
	21st to end	Day	9% 4 12% 24% 30% 21%	450
July	1st to 10th	Day	9% 2 6% 24% 34% 24%	445
	11th to 20th	Day	7% 2 7% 20% 32% 32%	444
	21st to end	Day	7% 2 8% 19% 35% 28%	488
August	1st to 10th	Day	7% 2 7% 25% 31% 27%	446
	11th to 20th	Day	10% 2 6% 28% 34% 20%	439
	21st to end	Day	15% 2 9% 23% 31% 20%	495
September	1st to 10th	Day	9% 3 9% 31% 33% 15%	450
	11th to 20th	Day	12% 4 14% 25% 33% 12%	450
	21st to end	Day	11% 3 15% 30% 32% 9%	450
October	1st to 10th	Day	11% 5% 23% 30% 25% 6%	450
	11th to 20th	Day	13% 7% 25% 33% 21% 1	450
	21st to end	Day	19% 13% 22% 30% 14% 2	314
November	1st to 10th	Day	18% 10% 32% 25% 11% 4	270
	11th to 20th	Day	17% 15% 38% 24% 6%	270
	21st to end	Day	15% 16% 38% 22% 9% 1	270
December	1st to 10th	Day	28% 16% 29% 23% 3	270
	11th to 20th	Day	24% 15% 38% 16% 5% 1	270
	21st to end	Day	26% 18% 34% 19% 4	297
January	1st to 10th	Night	20% 15% 35% 24% 5% 1	760
	11th to 20th	Night	21% 16% 30% 25% 8%	741
	21st to end	Night	20% 14% 36% 27% 4	792
February	1st to 10th	Night	22% 11% 34% 29% 4	720
	11th to 20th	Night	24% 13% 33% 26% 4	703
	21st to end	Night	22% 15% 35% 25% 3	592
March	1st to 10th	Night	19% 12% 32% 32% 5%	720
	11th to 20th	Night	17% 13% 34% 25% 10% 1	720
	21st to end	Night	16% 12% 33% 28% 10%	694
April	1st to 10th	Night	12% 11% 36% 28% 14%	540
	11th to 20th	Night	14% 10% 32% 29% 14% 2	533
	21st to end	Night	12% 9% 27% 35% 16% 2	540
May	1st to 10th	Night	9% 6% 27% 32% 22% 4	540
	11th to 20th	Night	10% 4 22% 33% 26% 5%	531
	21st to end	Night	7% 2 11% 35% 37% 7%	584
June	1st to 10th	Night	10% 1 10% 38% 35% 7%	540
	11th to 20th	Night	5% 1 10% 26% 46% 13%	540
	21st to end	Night	5% 1 8% 29% 43% 14%	540
July	1st to 10th	Night	7% 2 3 26% 45% 16%	525
	11th to 20th	Night	6% 1 4 21% 47% 21%	522
	21st to end	Night	7% 1 6% 23% 48% 15%	591
August	1st to 10th	Night	5% 1 2 25% 49% 17%	537
	11th to 20th	Night	9% 2 5% 30% 45% 9%	534
	21st to end	Night	12% 2 6% 26% 42% 12%	594
September	1st to 10th	Night	9% 2 7% 32% 40% 9%	562
	11th to 20th	Night	12% 3 11% 29% 37% 7%	720
	21st to end	Night	8% 2 13% 33% 40% 4	720
October	1st to 10th	Night	10% 3 21% 33% 28% 6%	720
	11th to 20th	Night	12% 5% 24% 35% 23% 2	720
	21st to end	Night	17% 7% 21% 33% 20% 2	792
November	1st to 10th	Night	13% 6% 19% 38% 19% 4	740
	11th to 20th	Night	14% 9% 28% 34% 13% 2	760
	21st to end	Night	16% 10% 28% 32% 12% 1	760
December	1st to 10th	Night	21% 11% 27% 30% 9% 1	760
	11th to 20th	Night	25% 9% 28% 29% 9%	760
	21st to end	Night	25% 11% 29% 28% 6%	836

Page generated at 2024-01-13 00:38:11. Version ac07

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