Vernon
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Vernon clear sky chart from 2005-11-06 to 2026-02-16.

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	8% 4 2 4 3 3 3 3 5% 6% 59%	131127
	Night	7% 4 2 4 3 3 3 3 5% 7% 61%	130086
Transparency	Day	26% 3 8% 24% 28% 12%	134921
	Night	25% 2 7% 23% 28% 15%	134356
Seeing	Day	10% 5% 23% 32% 24% 7%	16911
	Night	9% 5% 32% 39% 14% 1	26948

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	6% 5% 2 5% 4 3 3 3 4 5% 61%	5289
	11th to 20th	Day	5% 4 1 3 2 2 2 2 3 4 73%	5310
	21st to end	Day	14% 6% 2 4 3 3 3 2 4 6% 53%	6031
February	1st to 10th	Day	9% 6% 2 5% 3 3 3 2 4 6% 58%	2100
	11th to 20th	Day	10% 6% 2 5% 3 3 4 2 4 6% 55%	1999
	21st to end	Day	12% 7% 2 5% 3 3 2 2 4 4 58%	1650
March	1st to 10th	Day	11% 4 1 4 2 3 3 2 4 5% 59%	4629
	11th to 20th	Day	8% 4 2 4 3 3 3 3 4 6% 60%	4980
	21st to end	Day	6% 6% 2 5% 2 3 3 3 6% 8% 55%	5462
April	1st to 10th	Day	9% 4 1 3 3 3 3 2 4 6% 61%	2240
	11th to 20th	Day	14% 4 2 4 3 3 4 3 4 5% 55%	2374
	21st to end	Day	10% 4 1 4 3 3 3 3 5% 6% 56%	2565
May	1st to 10th	Day	15% 5% 2 5% 3 3 3 3 5% 6% 49%	5862
	11th to 20th	Day	10% 4 2 5% 3 3 3 3 4 6% 57%	5862
	21st to end	Day	10% 5% 2 6% 4 4 4 4 5% 7% 49%	6434
June	1st to 10th	Day	6% 4 1 5% 4 3 4 5% 6% 7% 55%	2600
	11th to 20th	Day	5% 3 1 4 3 4 4 4 5% 8% 59%	2600
	21st to end	Day	5% 3 1 3 3 3 3 3 6% 8% 63%	2600
July	1st to 10th	Day	9% 6% 2 5% 4 5% 4 4 6% 8% 46%	5900
	11th to 20th	Day	3 3 1 4 3 4 4 3 5% 8% 60%	5900
	21st to end	Day	2 2 1 2 3 2 4 3 5% 8% 68%	6422
August	1st to 10th	Day	3 2 1 3 3 3 3 2 5% 8% 66%	4234
	11th to 20th	Day	3 2 1 3 3 3 3 4 6% 9% 63%	3918
	21st to end	Day	4 3 1 4 3 3 4 3 5% 7% 66%	4312
September	1st to 10th	Day	10% 4 2 4 3 3 3 3 4 6% 59%	2227
	11th to 20th	Day	10% 5% 2 5% 4 4 4 3 5% 6% 52%	2200
	21st to end	Day	9% 3 1 3 3 3 4 2 4 6% 62%	2200
October	1st to 10th	Day	6% 3 1 3 3 3 4 3 4 7% 63%	2200
	11th to 20th	Day	10% 2 1 3 2 2 3 2 3 5% 67%	2085
	21st to end	Day	10% 4 1 3 3 2 2 2 3 4 65%	2200
November	1st to 10th	Day	8% 4 2 2 2 3 3 2 4 6% 64%	1864
	11th to 20th	Day	6% 3 1 2 2 2 3 2 4 6% 69%	1890
	21st to end	Day	11% 5% 1 3 2 2 2 2 3 6% 62%	1890
December	1st to 10th	Day	5% 5% 2 5% 4 3 3 3 5% 6% 60%	3030
	11th to 20th	Day	6% 3 1 4 3 3 3 3 4 5% 65%	3481
	21st to end	Day	10% 7% 2 6% 3 3 3 2 3 5% 55%	4587
January	1st to 10th	Night	9% 5% 2 5% 3 3 3 3 5% 5% 58%	7634
	11th to 20th	Night	3 2 1 3 2 2 2 2 3 5% 76%	7680
	21st to end	Night	13% 7% 2 5% 3 3 3 3 4 5% 53%	8240
February	1st to 10th	Night	10% 5% 2 4 3 3 3 3 4 5% 59%	2520
	11th to 20th	Night	10% 5% 2 4 3 3 3 3 4 7% 56%	2398
	21st to end	Night	8% 6% 2 5% 4 3 3 2 4 5% 58%	1980
March	1st to 10th	Night	7% 5% 2 4 3 3 3 3 4 6% 59%	5236
	11th to 20th	Night	7% 3 1 3 2 2 2 3 4 6% 67%	4980
	21st to end	Night	5% 5% 2 5% 3 4 4 3 5% 7% 57%	5467
April	1st to 10th	Night	8% 4 1 4 3 3 3 2 4 6% 60%	2155
	11th to 20th	Night	11% 3 1 3 3 4 4 3 5% 7% 57%	1977
	21st to end	Night	10% 3 2 4 3 4 3 3 5% 6% 57%	1834
May	1st to 10th	Night	15% 5% 2 4 3 3 4 3 4 5% 53%	4053
	11th to 20th	Night	7% 4 2 4 4 3 3 3 5% 7% 57%	4053
	21st to end	Night	10% 4 2 5% 3 3 4 3 5% 6% 55%	4443
June	1st to 10th	Night	4 2 1 4 3 3 3 4 7% 12% 57%	1800
	11th to 20th	Night	3 3 1 4 3 3 3 3 7% 10% 59%	1800
	21st to end	Night	3 3 2 4 4 3 3 2 5% 7% 65%	1800
July	1st to 10th	Night	6% 6% 3 7% 5% 3 5% 3 6% 9% 48%	4078
	11th to 20th	Night	3 2 1 3 2 3 4 3 7% 11% 62%	4077
	21st to end	Night	2 2 1 3 3 3 4 4 6% 8% 65%	4449
August	1st to 10th	Night	1 2 1 2 3 3 4 3 5% 8% 69%	2926
	11th to 20th	Night	3 2 1 3 3 3 4 4 6% 10% 61%	3137
	21st to end	Night	3 2 1 3 2 3 3 4 6% 9% 63%	3597
September	1st to 10th	Night	8% 4 1 4 3 3 3 3 5% 7% 58%	2170
	11th to 20th	Night	8% 4 2 7% 3 4 3 3 5% 8% 52%	2200
	21st to end	Night	8% 3 1 4 3 3 3 3 5% 6% 61%	2200
October	1st to 10th	Night	6% 3 1 4 3 3 3 3 4 6% 64%	2200
	11th to 20th	Night	7% 3 2 4 2 2 2 2 3 4 69%	2293
	21st to end	Night	9% 3 1 4 2 2 2 2 3 5% 67%	2640
November	1st to 10th	Night	8% 4 1 2 2 3 2 2 3 4 69%	2650
	11th to 20th	Night	5% 2 1 3 2 3 3 3 4 6% 68%	2730
	21st to end	Night	9% 4 1 3 3 3 3 2 4 6% 62%	2730
December	1st to 10th	Night	7% 4 1 3 2 3 3 3 4 5% 64%	4380
	11th to 20th	Night	5% 4 1 4 3 3 3 2 4 6% 65%	4946
	21st to end	Night	10% 5% 2 5% 3 3 3 3 4 5% 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	28% 1 4 29% 29% 9%	5290
	11th to 20th	Day	18% 1 5% 19% 46% 12%	5310
	21st to end	Day	35% 2 6% 21% 25% 11%	6031
February	1st to 10th	Day	29% 2 5% 22% 31% 10%	2100
	11th to 20th	Day	33% 2 6% 25% 23% 11%	2009
	21st to end	Day	32% 2 3 16% 29% 18%	1650
March	1st to 10th	Day	29% 2 5% 12% 24% 28%	4629
	11th to 20th	Day	28% 1 7% 16% 26% 22%	4980
	21st to end	Day	29% 2 8% 28% 25% 8%	5464
April	1st to 10th	Day	26% 3 8% 22% 27% 15%	2240
	11th to 20th	Day	32% 3 6% 19% 24% 15%	2374
	21st to end	Day	29% 3 9% 24% 27% 8%	2565
May	1st to 10th	Day	37% 3 9% 23% 18% 11%	5900
	11th to 20th	Day	30% 2 8% 20% 25% 15%	5866
	21st to end	Day	35% 4 9% 25% 16% 11%	6447
June	1st to 10th	Day	27% 5% 14% 30% 18% 7%	2600
	11th to 20th	Day	22% 4 10% 26% 29% 8%	2600
	21st to end	Day	20% 4 12% 26% 28% 9%	2600
July	1st to 10th	Day	35% 5% 9% 23% 22% 6%	5836
	11th to 20th	Day	22% 4 11% 26% 30% 7%	5831
	21st to end	Day	14% 3 13% 34% 30% 5%	6240
August	1st to 10th	Day	17% 2 8% 25% 31% 16%	4220
	11th to 20th	Day	17% 4 11% 31% 27% 10%	3956
	21st to end	Day	20% 4 12% 31% 28% 6%	4311
September	1st to 10th	Day	28% 3 7% 23% 27% 13%	2227
	11th to 20th	Day	33% 4 8% 22% 26% 8%	2200
	21st to end	Day	24% 3 6% 22% 32% 12%	2200
October	1st to 10th	Day	14% 2 6% 15% 39% 25%	3590
	11th to 20th	Day	19% 2 5% 22% 33% 18%	3377
	21st to end	Day	18% 1 4 28% 37% 11%	3538
November	1st to 10th	Day	24% 2 5% 23% 31% 15%	1864
	11th to 20th	Day	19% 2 6% 25% 35% 14%	1890
	21st to end	Day	27% 2 5% 21% 31% 14%	1890
December	1st to 10th	Day	26% 2 5% 37% 23% 7%	3030
	11th to 20th	Day	24% 1 8% 18% 35% 14%	3479
	21st to end	Day	34% 2 5% 26% 24% 9%	4587
January	1st to 10th	Night	30% 2 4 30% 28% 7%	7635
	11th to 20th	Night	14% 1 7% 21% 38% 19%	7680
	21st to end	Night	35% 1 5% 19% 28% 11%	8240
February	1st to 10th	Night	30% 2 6% 21% 28% 14%	2520
	11th to 20th	Night	30% 2 7% 22% 24% 15%	2398
	21st to end	Night	30% 2 3 18% 25% 22%	1980
March	1st to 10th	Night	27% 2 3 14% 22% 31%	5236
	11th to 20th	Night	21% 1 5% 19% 20% 33%	4980
	21st to end	Night	28% 2 7% 22% 31% 10%	5467
April	1st to 10th	Night	27% 2 8% 19% 25% 19%	2155
	11th to 20th	Night	27% 3 9% 20% 24% 17%	1977
	21st to end	Night	29% 3 8% 24% 27% 9%	1834
May	1st to 10th	Night	35% 3 11% 20% 18% 13%	4080
	11th to 20th	Night	27% 3 9% 18% 25% 19%	4054
	21st to end	Night	31% 3 12% 20% 18% 16%	4452
June	1st to 10th	Night	20% 4 18% 32% 18% 7%	1800
	11th to 20th	Night	21% 4 14% 27% 27% 8%	1800
	21st to end	Night	21% 3 9% 27% 28% 13%	1800
July	1st to 10th	Night	33% 4 10% 29% 19% 4	4035
	11th to 20th	Night	17% 3 10% 32% 29% 8%	4026
	21st to end	Night	17% 3 11% 34% 30% 5%	4320
August	1st to 10th	Night	14% 2 7% 26% 33% 18%	2916
	11th to 20th	Night	18% 3 11% 29% 29% 10%	3165
	21st to end	Night	17% 4 13% 33% 27% 7%	3597
September	1st to 10th	Night	26% 3 9% 21% 27% 14%	2170
	11th to 20th	Night	31% 3 10% 21% 25% 11%	2200
	21st to end	Night	24% 3 5% 22% 29% 17%	2200
October	1st to 10th	Night	14% 2 5% 15% 36% 28%	3590
	11th to 20th	Night	22% 2 5% 18% 33% 21%	3727
	21st to end	Night	17% 2 3 25% 37% 15%	4252
November	1st to 10th	Night	21% 1 5% 23% 31% 18%	2650
	11th to 20th	Night	19% 3 4 24% 35% 17%	2730
	21st to end	Night	26% 2 4 21% 32% 15%	2730
December	1st to 10th	Night	25% 2 4 29% 31% 9%	4380
	11th to 20th	Night	24% 2 5% 21% 33% 16%	4947
	21st to end	Night	31% 2 5% 25% 27% 10%	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	11% 7% 38% 32% 11% 2	330
	11th to 20th	Day	12% 13% 32% 30% 12% 1	330
	21st to end	Day	12% 7% 37% 31% 11% 2	363
February	1st to 10th	Day	14% 7% 35% 35% 9% 1	330
	11th to 20th	Day	11% 10% 43% 30% 7%	315
	21st to end	Day	20% 8% 37% 28% 6% 1	249
March	1st to 10th	Day	13% 10% 38% 30% 9% 1	300
	11th to 20th	Day	17% 10% 38% 24% 9% 2	300
	21st to end	Day	12% 9% 42% 26% 9% 1	330
April	1st to 10th	Day	13% 11% 41% 23% 12% 1	340
	11th to 20th	Day	15% 14% 42% 25% 5%	492
	21st to end	Day	14% 9% 38% 28% 9% 2	665
May	1st to 10th	Day	12% 5% 35% 37% 10% 1	703
	11th to 20th	Day	15% 4 29% 34% 15% 3	725
	21st to end	Day	11% 5% 27% 35% 18% 4	789
June	1st to 10th	Day	7% 2 15% 42% 28% 5%	730
	11th to 20th	Day	6% 2 19% 44% 24% 5%	730
	21st to end	Day	5% 1 12% 42% 34% 7%	730
July	1st to 10th	Day	6% 2 6% 34% 39% 14%	721
	11th to 20th	Day	4 1 6% 33% 43% 14%	718
	21st to end	Day	3 1 3 29% 48% 16%	794
August	1st to 10th	Day	5% 1 5% 32% 44% 13%	726
	11th to 20th	Day	6% 1 6% 34% 37% 16%	565
	21st to end	Day	5% 1 6% 29% 42% 18%	583
September	1st to 10th	Day	12% 1 3 26% 39% 19%	357
	11th to 20th	Day	7% 1 6% 29% 38% 19%	330
	21st to end	Day	12% 2 8% 27% 37% 14%	330
October	1st to 10th	Day	4 1 18% 34% 31% 13%	330
	11th to 20th	Day	9% 4 26% 37% 21% 3	330
	21st to end	Day	19% 7% 21% 31% 18% 4	363
November	1st to 10th	Day	15% 4 29% 29% 20% 3	330
	11th to 20th	Day	12% 7% 26% 34% 18% 4	330
	21st to end	Day	17% 8% 32% 27% 13% 4	330
December	1st to 10th	Day	10% 5% 40% 31% 14% 1	330
	11th to 20th	Day	8% 7% 34% 35% 15% 2	330
	21st to end	Day	18% 8% 35% 28% 9% 2	363
January	1st to 10th	Night	9% 6% 38% 37% 9%	1050
	11th to 20th	Night	8% 9% 35% 40% 8%	1050
	21st to end	Night	10% 6% 38% 39% 7%	1097
February	1st to 10th	Night	12% 7% 41% 33% 7%	840
	11th to 20th	Night	13% 9% 42% 32% 4	804
	21st to end	Night	12% 10% 43% 32% 3	660
March	1st to 10th	Night	11% 11% 40% 33% 5%	740
	11th to 20th	Night	15% 10% 42% 27% 7%	600
	21st to end	Night	8% 11% 46% 31% 4	660
April	1st to 10th	Night	9% 10% 51% 26% 5%	600
	11th to 20th	Night	11% 9% 51% 26% 3	593
	21st to end	Night	12% 8% 46% 29% 6%	600
May	1st to 10th	Night	10% 6% 46% 31% 7%	600
	11th to 20th	Night	11% 4 40% 34% 10% 1	591
	21st to end	Night	7% 4 37% 39% 11% 1	650
June	1st to 10th	Night	5% 2 29% 45% 18% 1	600
	11th to 20th	Night	3 2 34% 52% 9%	600
	21st to end	Night	3 1 23% 49% 22% 1	600
July	1st to 10th	Night	5% 1 11% 46% 34% 3	585
	11th to 20th	Night	3 1 10% 51% 33% 2	582
	21st to end	Night	3 6% 49% 40% 2	657
August	1st to 10th	Night	1 8% 54% 35% 2	597
	11th to 20th	Night	5% 1 9% 50% 34% 1	594
	21st to end	Night	4 9% 46% 37% 4	660
September	1st to 10th	Night	9% 2 12% 43% 32% 3	600
	11th to 20th	Night	10% 16% 45% 26% 2	600
	21st to end	Night	9% 2 18% 43% 27% 2	600
October	1st to 10th	Night	7% 3 24% 44% 22% 1	600
	11th to 20th	Night	9% 4 31% 43% 12% 1	693
	21st to end	Night	10% 8% 31% 36% 15% 1	880
November	1st to 10th	Night	10% 4 33% 39% 13% 2	1010
	11th to 20th	Night	6% 6% 34% 43% 11% 1	1050
	21st to end	Night	12% 8% 34% 35% 12% 1	1050
December	1st to 10th	Night	12% 6% 32% 41% 9%	1050
	11th to 20th	Night	12% 6% 35% 39% 8%	1050
	21st to end	Night	12% 5% 37% 39% 7%	1155

Page generated at 2026-02-13 00:42:13. Version ac07

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