Big Spy Mountain Overlook
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Big Spy Mountain Overlook clear sky chart from 2005-11-06 to 2024-03-08.

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% 7% 3 6% 6% 3 5% 5% 6% 7% 39%	78619
	Night	13% 6% 3 5% 5% 3 4 5% 5% 7% 43%	80922
Transparency	Day	42% 6% 11% 22% 15% 3	78340
	Night	39% 6% 11% 23% 17% 4	80720
Seeing	Day	21% 16% 26% 21% 12% 5%	14073
	Night	17% 14% 24% 28% 15% 2	24102

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% 7% 3 5% 5% 3 4 4 4 7% 44%	2836
	11th to 20th	Day	13% 10% 3 7% 6% 3 5% 5% 4 4 41%	2840
	21st to end	Day	19% 9% 3 7% 5% 3 4 3 4 5% 38%	3124
February	1st to 10th	Day	11% 8% 4 6% 6% 4 5% 4 5% 6% 40%	1710
	11th to 20th	Day	15% 7% 3 7% 6% 3 4 5% 6% 6% 38%	1663
	21st to end	Day	18% 8% 3 5% 6% 3 4 4 5% 5% 39%	1650
March	1st to 10th	Day	14% 6% 2 5% 4 2 4 4 5% 7% 47%	2057
	11th to 20th	Day	15% 9% 3 6% 6% 3 5% 5% 5% 7% 36%	1980
	21st to end	Day	15% 9% 4 8% 6% 3 5% 4 5% 5% 37%	2178
April	1st to 10th	Day	9% 7% 3 6% 5% 3 4 5% 5% 7% 45%	2094
	11th to 20th	Day	13% 6% 3 6% 5% 3 5% 4 4 7% 44%	2134
	21st to end	Day	16% 8% 3 5% 6% 4 5% 4 4 5% 40%	2229
May	1st to 10th	Day	15% 6% 3 7% 6% 4 5% 5% 6% 8% 34%	2340
	11th to 20th	Day	18% 8% 3 6% 6% 3 5% 6% 5% 8% 32%	2301
	21st to end	Day	14% 6% 3 6% 7% 4 5% 5% 6% 9% 35%	2553
June	1st to 10th	Day	12% 5% 2 5% 5% 3 5% 7% 7% 9% 40%	2520
	11th to 20th	Day	12% 5% 2 6% 6% 4 6% 6% 7% 10% 35%	2520
	21st to end	Day	9% 4 3 5% 6% 4 8% 7% 8% 10% 37%	2468
July	1st to 10th	Day	11% 6% 4 7% 6% 4 5% 6% 6% 10% 36%	2340
	11th to 20th	Day	7% 4 2 6% 7% 5% 9% 7% 9% 11% 33%	2340
	21st to end	Day	10% 7% 3 6% 7% 5% 7% 7% 8% 9% 30%	2547
August	1st to 10th	Day	13% 7% 3 6% 6% 4 6% 6% 7% 10% 32%	2327
	11th to 20th	Day	14% 6% 3 6% 7% 5% 7% 7% 6% 8% 31%	2290
	21st to end	Day	12% 7% 3 7% 6% 3 6% 7% 7% 9% 35%	2376
September	1st to 10th	Day	13% 6% 2 6% 5% 3 5% 5% 5% 7% 43%	2160
	11th to 20th	Day	15% 7% 3 6% 6% 3 3 6% 4 7% 40%	2032
	21st to end	Day	20% 7% 3 5% 5% 4 4 5% 5% 6% 35%	1948
October	1st to 10th	Day	15% 7% 2 5% 5% 3 4 4 5% 6% 45%	1800
	11th to 20th	Day	15% 6% 2 4 4 2 3 3 6% 6% 49%	1800
	21st to end	Day	14% 7% 2 5% 4 3 4 3 4 6% 48%	1980
November	1st to 10th	Day	12% 6% 2 4 4 2 3 3 4 6% 55%	1857
	11th to 20th	Day	14% 5% 2 5% 5% 2 4 5% 5% 7% 48%	1729
	21st to end	Day	14% 6% 3 5% 4 3 3 3 4 6% 49%	1520
December	1st to 10th	Day	15% 9% 3 7% 6% 3 5% 4 5% 6% 36%	1520
	11th to 20th	Day	15% 4 2 5% 4 2 3 3 4 6% 51%	1910
	21st to end	Day	17% 8% 3 6% 5% 3 5% 5% 6% 7% 35%	2946
January	1st to 10th	Night	12% 8% 2 4 5% 3 4 4 4 6% 47%	4109
	11th to 20th	Night	14% 9% 2 5% 4 3 4 4 4 6% 45%	4120
	21st to end	Night	19% 8% 3 5% 5% 3 4 4 4 5% 41%	4532
February	1st to 10th	Night	11% 7% 2 7% 6% 3 5% 5% 6% 7% 41%	2470
	11th to 20th	Night	18% 8% 3 6% 5% 3 4 4 4 6% 40%	2403
	21st to end	Night	13% 8% 3 4 5% 4 5% 6% 5% 8% 39%	1799
March	1st to 10th	Night	12% 5% 2 5% 5% 4 4 5% 5% 6% 48%	2064
	11th to 20th	Night	19% 6% 2 5% 5% 3 4 5% 6% 7% 38%	1980
	21st to end	Night	15% 7% 3 6% 6% 3 4 4 5% 6% 42%	2178
April	1st to 10th	Night	12% 7% 3 5% 5% 3 4 4 6% 8% 42%	1864
	11th to 20th	Night	12% 7% 3 4 3 2 4 5% 4 9% 47%	1775
	21st to end	Night	16% 5% 2 6% 5% 3 4 4 5% 7% 43%	1746
May	1st to 10th	Night	15% 5% 4 5% 4 3 5% 5% 6% 8% 40%	1620
	11th to 20th	Night	16% 8% 3 6% 5% 3 4 5% 5% 7% 36%	1592
	21st to end	Night	15% 6% 3 6% 4 3 4 4 5% 9% 41%	1718
June	1st to 10th	Night	10% 6% 2 5% 4 3 6% 6% 6% 10% 42%	1440
	11th to 20th	Night	10% 7% 2 6% 4 3 5% 7% 6% 8% 43%	1440
	21st to end	Night	9% 4 2 4 5% 3 4 5% 7% 10% 47%	1484
July	1st to 10th	Night	9% 6% 3 5% 6% 3 5% 4 7% 9% 42%	1620
	11th to 20th	Night	6% 3 2 4 5% 4 5% 7% 8% 13% 45%	1620
	21st to end	Night	6% 5% 3 5% 5% 5% 6% 5% 8% 11% 40%	1771
August	1st to 10th	Night	10% 6% 3 7% 6% 3 6% 7% 6% 9% 38%	1611
	11th to 20th	Night	12% 8% 3 6% 6% 4 5% 5% 7% 7% 39%	1598
	21st to end	Night	10% 6% 2 5% 7% 3 6% 5% 7% 9% 38%	1973
September	1st to 10th	Night	12% 6% 3 5% 4 3 4 5% 6% 7% 47%	1800
	11th to 20th	Night	12% 7% 2 5% 5% 3 4 4 6% 8% 44%	1924
	21st to end	Night	20% 9% 2 6% 5% 3 3 4 4 6% 39%	2011
October	1st to 10th	Night	14% 7% 3 6% 4 2 4 3 5% 5% 45%	2160
	11th to 20th	Night	13% 6% 3 5% 4 3 5% 4 5% 6% 48%	2160
	21st to end	Night	14% 5% 2 4 4 3 4 4 5% 6% 51%	2376
November	1st to 10th	Night	12% 8% 3 6% 4 2 2 3 3 5% 52%	2221
	11th to 20th	Night	13% 5% 3 5% 5% 2 4 4 4 6% 50%	2446
	21st to end	Night	13% 5% 3 4 5% 3 4 4 5% 6% 48%	2660
December	1st to 10th	Night	16% 8% 3 7% 5% 4 4 4 4 5% 41%	2660
	11th to 20th	Night	13% 6% 3 7% 5% 3 4 4 4 6% 45%	3285
	21st to end	Night	15% 5% 2 5% 6% 4 6% 5% 6% 7% 38%	4692

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	39% 6% 5% 26% 18% 6%	2837
	11th to 20th	Day	47% 4 6% 18% 20% 5%	2840
	21st to end	Day	48% 4 7% 20% 17% 3	3124
February	1st to 10th	Day	44% 5% 10% 23% 16% 3	1710
	11th to 20th	Day	45% 5% 9% 19% 17% 4	1672
	21st to end	Day	47% 4 9% 18% 16% 5%	1650
March	1st to 10th	Day	37% 4 10% 23% 21% 4	2057
	11th to 20th	Day	47% 7% 8% 17% 16% 6%	1980
	21st to end	Day	48% 7% 8% 20% 13% 5%	2178
April	1st to 10th	Day	37% 5% 12% 21% 18% 7%	2094
	11th to 20th	Day	39% 5% 11% 22% 18% 5%	2134
	21st to end	Day	46% 5% 10% 22% 13% 4	2229
May	1st to 10th	Day	46% 8% 13% 19% 12% 2	2340
	11th to 20th	Day	48% 8% 15% 19% 8% 2	2305
	21st to end	Day	44% 8% 15% 23% 9% 1	2553
June	1st to 10th	Day	38% 9% 15% 25% 13% 1	2520
	11th to 20th	Day	41% 9% 16% 20% 13% 1	2520
	21st to end	Day	38% 10% 15% 24% 11% 1	2468
July	1st to 10th	Day	43% 9% 14% 19% 13% 2	2275
	11th to 20th	Day	38% 11% 16% 21% 12% 1	2271
	21st to end	Day	45% 9% 13% 20% 11% 1	2405
August	1st to 10th	Day	45% 9% 16% 22% 8%	2314
	11th to 20th	Day	47% 9% 13% 20% 10% 1	2290
	21st to end	Day	42% 10% 17% 20% 9% 2	2376
September	1st to 10th	Day	40% 7% 13% 19% 18% 4	2160
	11th to 20th	Day	43% 6% 6% 25% 17% 3	2032
	21st to end	Day	48% 7% 8% 18% 18% 2	1948
October	1st to 10th	Day	40% 5% 8% 27% 16% 5%	1800
	11th to 20th	Day	36% 3 10% 26% 20% 4	1800
	21st to end	Day	39% 4 7% 26% 20% 5%	1980
November	1st to 10th	Day	33% 4 8% 23% 27% 5%	1857
	11th to 20th	Day	36% 4 10% 20% 22% 8%	1729
	21st to end	Day	37% 4 9% 24% 23% 3	1520
December	1st to 10th	Day	47% 6% 9% 20% 15% 4	1520
	11th to 20th	Day	35% 4 7% 25% 21% 7%	1906
	21st to end	Day	46% 5% 10% 23% 14% 2	2946
January	1st to 10th	Night	36% 6% 6% 24% 23% 4	4109
	11th to 20th	Night	39% 6% 7% 21% 21% 6%	4120
	21st to end	Night	46% 4 6% 23% 16% 5%	4532
February	1st to 10th	Night	40% 6% 11% 23% 17% 2	2470
	11th to 20th	Night	45% 4 7% 19% 18% 6%	2405
	21st to end	Night	43% 5% 10% 23% 14% 5%	1799
March	1st to 10th	Night	37% 6% 10% 24% 19% 5%	2064
	11th to 20th	Night	44% 7% 7% 20% 19% 3	1980
	21st to end	Night	43% 7% 10% 20% 15% 5%	2178
April	1st to 10th	Night	39% 5% 13% 20% 18% 5%	1864
	11th to 20th	Night	34% 6% 14% 21% 20% 5%	1775
	21st to end	Night	41% 5% 11% 25% 15% 3	1746
May	1st to 10th	Night	41% 8% 14% 21% 13% 3	1620
	11th to 20th	Night	46% 8% 13% 22% 9% 2	1593
	21st to end	Night	40% 8% 17% 26% 9% 1	1719
June	1st to 10th	Night	36% 9% 13% 29% 12% 1	1440
	11th to 20th	Night	38% 9% 17% 23% 13% 2	1440
	21st to end	Night	31% 10% 17% 25% 16% 3	1484
July	1st to 10th	Night	38% 10% 15% 20% 14% 3	1575
	11th to 20th	Night	28% 12% 21% 26% 12% 1	1566
	21st to end	Night	34% 9% 18% 27% 12%	1672
August	1st to 10th	Night	40% 8% 18% 23% 9% 1	1600
	11th to 20th	Night	41% 8% 14% 24% 12% 1	1598
	21st to end	Night	39% 9% 18% 22% 9% 3	1973
September	1st to 10th	Night	36% 7% 15% 21% 17% 4	1800
	11th to 20th	Night	36% 8% 11% 26% 17% 3	1924
	21st to end	Night	47% 6% 8% 20% 16% 3	2011
October	1st to 10th	Night	40% 4 11% 26% 16% 3	2160
	11th to 20th	Night	37% 5% 7% 26% 21% 4	2160
	21st to end	Night	34% 4 9% 23% 25% 5%	2376
November	1st to 10th	Night	36% 4 7% 22% 24% 7%	2221
	11th to 20th	Night	36% 4 8% 22% 24% 6%	2446
	21st to end	Night	37% 5% 8% 24% 21% 5%	2660
December	1st to 10th	Night	45% 5% 8% 23% 15% 3	2660
	11th to 20th	Night	40% 5% 7% 19% 22% 7%	3288
	21st to end	Night	42% 6% 9% 23% 19% 2	4692

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	32% 32% 21% 12% 3	270
	11th to 20th	Day	37% 28% 27% 8% 1	270
	21st to end	Day	31% 32% 29% 7% 1	297
February	1st to 10th	Day	27% 33% 31% 9% 1	270
	11th to 20th	Day	45% 24% 26% 4	270
	21st to end	Day	36% 25% 23% 14% 1	342
March	1st to 10th	Day	29% 24% 27% 16% 4	448
	11th to 20th	Day	27% 26% 27% 14% 5% 1	420
	21st to end	Day	24% 24% 30% 15% 7%	462
April	1st to 10th	Day	24% 27% 25% 15% 9%	420
	11th to 20th	Day	24% 16% 28% 18% 11% 3	412
	21st to end	Day	26% 20% 27% 16% 8% 2	420
May	1st to 10th	Day	24% 20% 30% 16% 7% 3	423
	11th to 20th	Day	22% 15% 30% 20% 11% 3	447
	21st to end	Day	19% 8% 27% 22% 18% 7%	485
June	1st to 10th	Day	14% 10% 30% 26% 14% 6%	450
	11th to 20th	Day	14% 9% 27% 27% 16% 7%	450
	21st to end	Day	9% 12% 30% 30% 14% 5%	450
July	1st to 10th	Day	12% 6% 20% 31% 21% 9%	445
	11th to 20th	Day	7% 4 21% 36% 21% 11%	444
	21st to end	Day	13% 6% 21% 30% 20% 10%	488
August	1st to 10th	Day	15% 7% 22% 25% 22% 10%	446
	11th to 20th	Day	12% 6% 22% 26% 22% 11%	439
	21st to end	Day	12% 5% 19% 28% 20% 16%	495
September	1st to 10th	Day	14% 6% 19% 25% 22% 14%	450
	11th to 20th	Day	16% 6% 19% 30% 20% 9%	450
	21st to end	Day	27% 10% 21% 23% 15% 4	450
October	1st to 10th	Day	20% 10% 22% 29% 16% 5%	450
	11th to 20th	Day	18% 18% 24% 24% 14% 2	450
	21st to end	Day	20% 18% 32% 19% 8% 2	495
November	1st to 10th	Day	18% 15% 31% 24% 10% 2	455
	11th to 20th	Day	25% 21% 26% 20% 7% 1	321
	21st to end	Day	28% 17% 35% 14% 4 1	180
December	1st to 10th	Day	27% 26% 32% 11% 3 1	180
	11th to 20th	Day	28% 23% 29% 17% 2 1	180
	21st to end	Day	28% 22% 33% 14% 4	249
January	1st to 10th	Night	21% 26% 30% 19% 3	760
	11th to 20th	Night	24% 21% 29% 23% 4	760
	21st to end	Night	20% 23% 32% 23% 2	836
February	1st to 10th	Night	18% 21% 31% 27% 3	760
	11th to 20th	Night	27% 27% 28% 16% 1	743
	21st to end	Night	23% 21% 34% 19% 2	628
March	1st to 10th	Night	18% 22% 32% 24% 4 1	751
	11th to 20th	Night	27% 20% 25% 21% 7% 1	720
	21st to end	Night	20% 17% 31% 26% 5%	792
April	1st to 10th	Night	18% 23% 31% 23% 6%	720
	11th to 20th	Night	17% 18% 28% 25% 11% 1	711
	21st to end	Night	21% 11% 30% 29% 9% 1	666
May	1st to 10th	Night	18% 12% 25% 27% 16% 1	540
	11th to 20th	Night	18% 8% 27% 31% 14% 2	531
	21st to end	Night	17% 3 17% 32% 27% 4	558
June	1st to 10th	Night	9% 3 20% 45% 22% 2	360
	11th to 20th	Night	11% 6% 19% 34% 28% 2	360
	21st to end	Night	9% 5% 18% 42% 23% 3	404
July	1st to 10th	Night	12% 2 17% 30% 31% 8%	525
	11th to 20th	Night	6% 1 12% 34% 41% 7%	522
	21st to end	Night	7% 3 15% 36% 34% 5%	591
August	1st to 10th	Night	12% 1 13% 35% 34% 5%	537
	11th to 20th	Night	14% 3 13% 31% 34% 6%	534
	21st to end	Night	14% 3 13% 31% 35% 5%	785
September	1st to 10th	Night	14% 3 12% 30% 32% 7%	720
	11th to 20th	Night	14% 4 14% 32% 29% 6%	720
	21st to end	Night	23% 8% 18% 28% 21% 3	720
October	1st to 10th	Night	17% 10% 17% 29% 22% 5%	720
	11th to 20th	Night	16% 14% 23% 29% 15% 2	720
	21st to end	Night	17% 13% 26% 30% 13% 2	792
November	1st to 10th	Night	16% 12% 27% 30% 13% 3	740
	11th to 20th	Night	19% 16% 24% 29% 10% 1	760
	21st to end	Night	18% 18% 25% 28% 10% 1	760
December	1st to 10th	Night	21% 21% 29% 22% 7%	760
	11th to 20th	Night	15% 19% 29% 31% 6%	760
	21st to end	Night	19% 20% 27% 31% 3	836

Page generated at 2024-03-05 07:23:59. Version ac07

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