Dixon
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dixon clear sky chart from 2005-11-06 to 2025-09-04.

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	12% 8% 3 8% 5% 4 5% 4 6% 7% 38%	126504
	Night	12% 9% 3 8% 5% 4 4 3 5% 6% 40%	122461
Transparency	Day	43% 5% 12% 24% 14% 2	130030
	Night	44% 4 11% 24% 15% 2	126998
Seeing	Day	16% 9% 28% 27% 15% 5%	17015
	Night	17% 9% 31% 31% 12% 1	26788

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	8% 12% 5% 18% 8% 7% 5% 3 4 5% 25%	3617
	11th to 20th	Day	8% 9% 5% 12% 7% 6% 6% 5% 7% 6% 29%	3638
	21st to end	Day	11% 14% 6% 12% 6% 3 4 3 5% 6% 29%	4488
February	1st to 10th	Day	13% 13% 5% 10% 6% 5% 4 4 5% 7% 28%	1800
	11th to 20th	Day	14% 10% 3 8% 5% 6% 4 3 5% 8% 35%	1835
	21st to end	Day	13% 11% 4 10% 5% 4 4 4 6% 6% 34%	1650
March	1st to 10th	Day	18% 9% 3 6% 3 2 3 2 4 5% 45%	4544
	11th to 20th	Day	9% 5% 3 6% 5% 4 4 4 5% 8% 47%	4980
	21st to end	Day	20% 11% 4 10% 5% 5% 5% 4 5% 6% 25%	5737
April	1st to 10th	Day	15% 13% 4 8% 5% 4 4 4 5% 6% 33%	2400
	11th to 20th	Day	16% 11% 3 7% 6% 4 5% 4 5% 6% 35%	2374
	21st to end	Day	20% 9% 3 7% 4 4 4 3 5% 7% 34%	2400
May	1st to 10th	Day	13% 8% 3 8% 5% 4 5% 4 6% 8% 37%	6057
	11th to 20th	Day	14% 6% 3 6% 4 5% 5% 4 5% 7% 42%	6319
	21st to end	Day	13% 7% 3 7% 5% 4 5% 4 7% 8% 37%	6935
June	1st to 10th	Day	9% 5% 2 6% 4 4 5% 5% 8% 8% 44%	2800
	11th to 20th	Day	9% 6% 2 6% 5% 4 5% 4 6% 8% 46%	2800
	21st to end	Day	10% 6% 3 7% 5% 5% 5% 4 6% 8% 41%	2800
July	1st to 10th	Day	8% 8% 3 8% 4 5% 5% 5% 7% 9% 38%	6360
	11th to 20th	Day	9% 6% 2 6% 5% 4 5% 4 7% 9% 44%	6360
	21st to end	Day	10% 7% 3 7% 5% 5% 5% 4 8% 9% 38%	6892
August	1st to 10th	Day	7% 5% 2 6% 4 4 5% 4 8% 12% 43%	4234
	11th to 20th	Day	10% 6% 2 5% 4 5% 5% 4 7% 9% 43%	4008
	21st to end	Day	8% 5% 2 6% 4 4 4 4 6% 9% 50%	4312
September	1st to 10th	Day	12% 5% 1 5% 4 5% 3 3 5% 8% 49%	2316
	11th to 20th	Day	10% 4 2 4 3 3 5% 3 4 9% 53%	2275
	21st to end	Day	10% 6% 2 6% 4 4 5% 4 5% 7% 47%	2043
October	1st to 10th	Day	11% 8% 2 5% 4 3 4 3 4 6% 50%	1900
	11th to 20th	Day	16% 8% 2 6% 4 4 4 3 4 7% 42%	1900
	21st to end	Day	18% 9% 3 6% 3 3 4 3 4 6% 41%	2013
November	1st to 10th	Day	11% 10% 3 6% 4 4 4 3 5% 7% 43%	1762
	11th to 20th	Day	14% 12% 4 7% 5% 4 4 3 5% 7% 35%	1755
	21st to end	Day	16% 11% 3 8% 4 4 4 3 4 6% 36%	1600
December	1st to 10th	Day	9% 9% 3 8% 4 3 3 3 5% 7% 47%	2610
	11th to 20th	Day	15% 11% 6% 14% 6% 6% 5% 3 5% 6% 23%	3008
	21st to end	Day	22% 22% 8% 12% 5% 3 3 2 3 4 15%	3982
January	1st to 10th	Night	11% 11% 6% 15% 5% 4 4 3 4 5% 32%	6348
	11th to 20th	Night	10% 13% 5% 11% 8% 6% 4 5% 6% 5% 26%	6337
	21st to end	Night	14% 13% 5% 11% 6% 4 4 3 4 4 33%	6490
February	1st to 10th	Night	14% 12% 5% 7% 5% 5% 4 3 5% 6% 34%	2600
	11th to 20th	Night	12% 10% 2 9% 5% 4 4 3 4 5% 41%	2450
	21st to end	Night	13% 11% 3 8% 4 4 4 3 4 5% 41%	1980
March	1st to 10th	Night	18% 8% 3 6% 4 3 3 3 4 4 44%	5338
	11th to 20th	Night	10% 6% 2 7% 4 4 4 3 4 8% 49%	4980
	21st to end	Night	18% 13% 5% 10% 5% 5% 4 3 5% 5% 26%	5192
April	1st to 10th	Night	16% 10% 3 6% 4 4 4 3 4 6% 41%	2000
	11th to 20th	Night	16% 10% 2 7% 4 4 3 3 5% 6% 41%	1975
	21st to end	Night	16% 9% 3 7% 6% 3 4 3 5% 7% 38%	2000
May	1st to 10th	Night	17% 7% 3 7% 5% 3 4 3 5% 6% 39%	3833
	11th to 20th	Night	11% 5% 2 6% 5% 5% 5% 4 6% 7% 43%	3596
	21st to end	Night	12% 7% 3 5% 5% 4 4 3 5% 8% 43%	3942
June	1st to 10th	Night	7% 6% 2 6% 4 4 4 4 7% 7% 50%	1600
	11th to 20th	Night	9% 6% 2 6% 4 4 4 4 7% 10% 44%	1600
	21st to end	Night	10% 5% 2 5% 4 5% 4 4 6% 8% 47%	1600
July	1st to 10th	Night	10% 6% 3 7% 4 4 5% 5% 7% 9% 41%	3618
	11th to 20th	Night	7% 4 2 6% 4 4 4 3 5% 9% 52%	3617
	21st to end	Night	8% 7% 3 6% 5% 5% 5% 4 6% 9% 43%	3962
August	1st to 10th	Night	5% 3 2 5% 4 4 4 4 7% 9% 54%	2926
	11th to 20th	Night	6% 5% 2 6% 3 4 4 4 6% 8% 53%	3044
	21st to end	Night	7% 4 2 5% 4 4 4 4 5% 8% 53%	3586
September	1st to 10th	Night	9% 5% 2 4 3 3 3 2 5% 7% 56%	1930
	11th to 20th	Night	10% 4 2 3 4 4 4 4 6% 8% 52%	1900
	21st to end	Night	7% 5% 2 5% 5% 4 3 3 6% 7% 52%	2121
October	1st to 10th	Night	11% 5% 2 5% 4 3 3 3 3 6% 54%	2280
	11th to 20th	Night	14% 7% 2 6% 4 4 3 3 4 6% 48%	2280
	21st to end	Night	18% 8% 3 7% 4 4 4 3 4 5% 39%	2584
November	1st to 10th	Night	12% 7% 2 5% 4 3 3 3 5% 6% 51%	2536
	11th to 20th	Night	14% 9% 3 8% 4 4 4 3 5% 6% 40%	2641
	21st to end	Night	16% 9% 3 7% 5% 4 4 3 4 6% 39%	2800
December	1st to 10th	Night	8% 7% 3 7% 4 4 4 3 5% 6% 48%	4580
	11th to 20th	Night	15% 13% 5% 9% 4 4 4 3 5% 6% 32%	5199
	21st to end	Night	22% 19% 6% 12% 5% 5% 4 3 4 4 15%	6996

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	62% 4 9% 18% 6%	3618
	11th to 20th	Day	54% 3 10% 14% 16% 3	3638
	21st to end	Day	57% 3 13% 19% 7%	4488
February	1st to 10th	Day	55% 4 13% 20% 7% 1	1800
	11th to 20th	Day	49% 4 12% 23% 11% 2	1844
	21st to end	Day	50% 5% 11% 23% 10% 2	1650
March	1st to 10th	Day	43% 4 9% 28% 14% 2	4544
	11th to 20th	Day	36% 4 10% 34% 16% 1	4980
	21st to end	Day	59% 4 14% 17% 6% 1	5739
April	1st to 10th	Day	52% 4 12% 22% 10%	2400
	11th to 20th	Day	49% 4 10% 22% 13% 1	2374
	21st to end	Day	50% 5% 10% 21% 12% 2	2400
May	1st to 10th	Day	44% 5% 10% 22% 17% 1	6095
	11th to 20th	Day	41% 6% 10% 27% 13% 3	6323
	21st to end	Day	43% 6% 11% 25% 14% 2	6949
June	1st to 10th	Day	34% 7% 15% 26% 17% 2	2800
	11th to 20th	Day	36% 5% 12% 23% 21% 3	2800
	21st to end	Day	39% 6% 13% 25% 15% 2	2800
July	1st to 10th	Day	39% 6% 13% 29% 12% 1	6291
	11th to 20th	Day	36% 7% 14% 28% 15% 1	6285
	21st to end	Day	39% 8% 18% 20% 14% 1	6696
August	1st to 10th	Day	31% 7% 18% 29% 14% 1	4220
	11th to 20th	Day	36% 6% 15% 26% 15% 1	4047
	21st to end	Day	31% 6% 13% 31% 16% 2	4311
September	1st to 10th	Day	35% 5% 10% 25% 21% 3	2316
	11th to 20th	Day	29% 5% 12% 31% 20% 3	2275
	21st to end	Day	35% 6% 10% 29% 18% 2	2043
October	1st to 10th	Day	24% 2 5% 31% 36% 1	3160
	11th to 20th	Day	28% 3 12% 23% 30% 4	3140
	21st to end	Day	40% 3 9% 29% 14% 4	3290
November	1st to 10th	Day	41% 5% 13% 26% 14% 3	1762
	11th to 20th	Day	49% 4 14% 21% 12% 1	1755
	21st to end	Day	50% 4 14% 22% 9% 1	1600
December	1st to 10th	Day	39% 3 13% 36% 8% 1	2610
	11th to 20th	Day	62% 3 12% 14% 7% 2	3005
	21st to end	Day	74% 3 8% 11% 3	3982
January	1st to 10th	Night	55% 3 11% 22% 9%	6348
	11th to 20th	Night	58% 3 12% 12% 14% 1	6337
	21st to end	Night	56% 3 10% 19% 12% 1	6490
February	1st to 10th	Night	52% 4 10% 21% 12% 1	2600
	11th to 20th	Night	46% 4 11% 24% 14% 1	2451
	21st to end	Night	46% 4 10% 23% 14% 3	1980
March	1st to 10th	Night	44% 3 8% 25% 17% 3	5338
	11th to 20th	Night	35% 4 9% 30% 18% 3	4980
	21st to end	Night	59% 5% 12% 16% 8% 1	5192
April	1st to 10th	Night	45% 4 10% 25% 15% 2	2000
	11th to 20th	Night	45% 4 9% 23% 16% 4	1975
	21st to end	Night	47% 5% 11% 21% 13% 2	2000
May	1st to 10th	Night	45% 5% 10% 19% 18% 2	3860
	11th to 20th	Night	38% 6% 13% 23% 17% 3	3597
	21st to end	Night	38% 6% 10% 30% 15% 1	3950
June	1st to 10th	Night	32% 5% 14% 27% 20% 3	1600
	11th to 20th	Night	34% 5% 11% 25% 20% 4	1600
	21st to end	Night	35% 7% 14% 22% 19% 4	1600
July	1st to 10th	Night	38% 6% 13% 27% 15% 2	3580
	11th to 20th	Night	29% 6% 13% 31% 19% 1	3572
	21st to end	Night	35% 8% 18% 23% 14% 2	3847
August	1st to 10th	Night	25% 7% 17% 33% 16% 2	2916
	11th to 20th	Night	29% 6% 17% 31% 17% 1	3071
	21st to end	Night	29% 6% 12% 31% 18% 5%	3586
September	1st to 10th	Night	29% 4 11% 26% 26% 3	1930
	11th to 20th	Night	31% 4 10% 30% 20% 4	1900
	21st to end	Night	30% 4 10% 29% 23% 3	2121
October	1st to 10th	Night	24% 3 6% 31% 34% 3	3800
	11th to 20th	Night	28% 3 9% 23% 33% 4	3779
	21st to end	Night	46% 3 8% 22% 18% 4	4244
November	1st to 10th	Night	35% 4 13% 26% 19% 4	2536
	11th to 20th	Night	45% 3 12% 24% 14% 2	2641
	21st to end	Night	47% 4 10% 27% 11% 1	2800
December	1st to 10th	Night	37% 4 13% 35% 11% 1	4580
	11th to 20th	Night	54% 4 12% 22% 8% 1	5201
	21st to end	Night	72% 4 8% 11% 4	6996

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	20% 12% 31% 29% 6% 2	300
	11th to 20th	Day	19% 15% 40% 20% 5% 1	300
	21st to end	Day	18% 13% 39% 24% 5% 1	330
February	1st to 10th	Day	21% 13% 37% 25% 4	300
	11th to 20th	Day	21% 19% 33% 21% 6% 1	300
	21st to end	Day	21% 15% 42% 18% 4	249
March	1st to 10th	Day	18% 18% 41% 18% 5%	300
	11th to 20th	Day	19% 17% 34% 21% 7% 2	300
	21st to end	Day	28% 16% 31% 18% 5% 1	450
April	1st to 10th	Day	25% 16% 32% 20% 7% 1	500
	11th to 20th	Day	22% 19% 28% 20% 10% 1	492
	21st to end	Day	24% 12% 34% 21% 9% 1	500
May	1st to 10th	Day	17% 11% 35% 27% 8% 2	636
	11th to 20th	Day	22% 12% 26% 24% 13% 4	725
	21st to end	Day	14% 10% 28% 28% 13% 6%	789
June	1st to 10th	Day	9% 7% 25% 34% 20% 5%	730
	11th to 20th	Day	11% 5% 30% 32% 18% 4	730
	21st to end	Day	12% 7% 29% 31% 15% 5%	730
July	1st to 10th	Day	10% 3 15% 32% 26% 13%	721
	11th to 20th	Day	11% 3 22% 33% 21% 9%	718
	21st to end	Day	8% 2 21% 36% 26% 6%	794
August	1st to 10th	Day	8% 2 20% 34% 26% 10%	726
	11th to 20th	Day	12% 4 16% 30% 28% 11%	617
	21st to end	Day	9% 4 18% 31% 28% 10%	583
September	1st to 10th	Day	15% 6% 19% 27% 24% 9%	502
	11th to 20th	Day	8% 3 17% 36% 26% 10%	490
	21st to end	Day	12% 7% 30% 26% 19% 7%	443
October	1st to 10th	Day	17% 9% 27% 26% 16% 5%	300
	11th to 20th	Day	19% 18% 32% 19% 11%	300
	21st to end	Day	30% 13% 30% 21% 5% 2	330
November	1st to 10th	Day	16% 12% 38% 20% 11% 3	300
	11th to 20th	Day	20% 15% 34% 21% 8% 2	300
	21st to end	Day	23% 13% 34% 24% 6%	300
December	1st to 10th	Day	15% 14% 41% 22% 6% 2	300
	11th to 20th	Day	19% 14% 36% 23% 8%	300
	21st to end	Day	28% 14% 35% 20% 4	330
January	1st to 10th	Night	15% 13% 37% 27% 8%	1000
	11th to 20th	Night	17% 13% 38% 26% 6% 1	1000
	21st to end	Night	19% 12% 37% 26% 6%	1100
February	1st to 10th	Night	20% 12% 37% 26% 5%	1000
	11th to 20th	Night	19% 12% 37% 27% 5%	896
	21st to end	Night	20% 11% 43% 22% 4 1	660
March	1st to 10th	Night	22% 11% 36% 24% 6% 1	791
	11th to 20th	Night	17% 11% 34% 31% 6%	600
	21st to end	Night	25% 11% 37% 22% 4 1	660
April	1st to 10th	Night	21% 13% 37% 25% 4	600
	11th to 20th	Night	21% 13% 31% 28% 7% 1	593
	21st to end	Night	21% 10% 32% 30% 8%	600
May	1st to 10th	Night	18% 7% 35% 32% 8% 1	600
	11th to 20th	Night	18% 8% 28% 33% 13%	591
	21st to end	Night	13% 3 29% 36% 17% 1	650
June	1st to 10th	Night	10% 4 24% 46% 16% 1	600
	11th to 20th	Night	11% 3 30% 41% 14% 1	600
	21st to end	Night	12% 4 29% 38% 17% 1	600
July	1st to 10th	Night	10% 2 13% 41% 30% 4	585
	11th to 20th	Night	7% 2 20% 43% 25% 4	582
	21st to end	Night	8% 2 16% 43% 30% 1	657
August	1st to 10th	Night	6% 2 15% 43% 32% 3	597
	11th to 20th	Night	6% 2 12% 44% 30% 5%	594
	21st to end	Night	9% 2 12% 48% 26% 4	660
September	1st to 10th	Night	12% 2 18% 39% 25% 4	579
	11th to 20th	Night	12% 2 20% 36% 26% 5%	570
	21st to end	Night	10% 6% 26% 35% 22% 2	746
October	1st to 10th	Night	14% 6% 27% 33% 20% 1	760
	11th to 20th	Night	18% 12% 31% 28% 11%	760
	21st to end	Night	22% 11% 32% 27% 7%	836
November	1st to 10th	Night	16% 8% 40% 26% 9%	780
	11th to 20th	Night	20% 12% 37% 25% 6%	841
	21st to end	Night	21% 13% 34% 26% 7%	1000
December	1st to 10th	Night	19% 11% 39% 24% 6%	1000
	11th to 20th	Night	23% 9% 33% 29% 5%	1000
	21st to end	Night	28% 13% 32% 25% 3	1100

Page generated at 2025-09-01 00:51:06. Version ac07

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