Paxton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Paxton clear sky chart from 2005-11-06 to 2026-03-03.

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	12% 9% 3 8% 5% 5% 5% 4 6% 7% 36%	130844
	Night	13% 9% 4 8% 5% 4 4 3 5% 6% 38%	130572
Transparency	Day	45% 6% 12% 22% 14% 2	134391
	Night	45% 5% 11% 22% 15% 2	135100
Seeing	Day	16% 11% 28% 25% 15% 6%	17446
	Night	17% 10% 30% 29% 12% 1	27415

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	12% 13% 5% 15% 7% 4 4 3 6% 6% 24%	4691
	11th to 20th	Day	8% 11% 6% 15% 8% 8% 5% 4 6% 5% 23%	4710
	21st to end	Day	15% 17% 5% 11% 8% 5% 4 3 4 5% 25%	5473
February	1st to 10th	Day	16% 12% 4 10% 6% 5% 4 3 5% 5% 29%	1984
	11th to 20th	Day	15% 11% 4 9% 6% 5% 4 3 5% 7% 31%	2048
	21st to end	Day	14% 14% 6% 10% 4 3 4 2 5% 6% 32%	1730
March	1st to 10th	Day	18% 15% 4 8% 4 3 3 2 3 4 38%	4500
	11th to 20th	Day	7% 10% 4 6% 5% 4 5% 4 6% 9% 42%	4685
	21st to end	Day	16% 13% 5% 9% 5% 5% 4 3 5% 6% 28%	5967
April	1st to 10th	Day	16% 11% 4 7% 5% 4 4 4 6% 7% 34%	2400
	11th to 20th	Day	16% 9% 3 6% 5% 5% 5% 4 5% 7% 36%	2374
	21st to end	Day	20% 8% 3 8% 5% 4 4 4 5% 6% 35%	2472
May	1st to 10th	Day	18% 8% 3 7% 5% 5% 5% 5% 6% 9% 30%	5862
	11th to 20th	Day	15% 7% 3 7% 4 4 5% 4 5% 7% 38%	5998
	21st to end	Day	11% 7% 3 8% 5% 5% 5% 4 6% 9% 38%	6935
June	1st to 10th	Day	10% 5% 3 6% 4 5% 5% 4 7% 8% 43%	2800
	11th to 20th	Day	8% 5% 2 7% 5% 4 5% 4 6% 8% 46%	2800
	21st to end	Day	9% 6% 2 7% 5% 4 5% 5% 7% 9% 41%	2800
July	1st to 10th	Day	10% 5% 2 6% 4 5% 6% 5% 8% 11% 39%	6360
	11th to 20th	Day	8% 6% 2 7% 5% 6% 6% 5% 8% 11% 36%	6360
	21st to end	Day	10% 7% 2 7% 6% 6% 5% 4 8% 9% 36%	6924
August	1st to 10th	Day	6% 4 2 6% 4 4 5% 4 6% 9% 50%	4297
	11th to 20th	Day	8% 5% 2 6% 4 4 5% 4 8% 11% 41%	3849
	21st to end	Day	5% 4 2 5% 4 4 5% 4 7% 11% 49%	4312
September	1st to 10th	Day	10% 5% 2 6% 4 4 4 4 6% 7% 47%	2400
	11th to 20th	Day	10% 5% 2 5% 3 3 4 4 5% 7% 51%	2265
	21st to end	Day	11% 5% 2 6% 4 5% 5% 4 6% 7% 47%	2200
October	1st to 10th	Day	11% 6% 2 6% 4 5% 4 3 5% 6% 47%	2166
	11th to 20th	Day	16% 7% 2 6% 4 3 4 4 5% 8% 42%	2000
	21st to end	Day	17% 9% 3 7% 5% 4 4 4 6% 6% 35%	1992
November	1st to 10th	Day	12% 7% 2 5% 4 3 3 4 5% 7% 49%	1852
	11th to 20th	Day	16% 12% 3 6% 4 5% 3 3 4 5% 38%	1890
	21st to end	Day	17% 11% 3 10% 5% 4 3 2 4 4 36%	1890
December	1st to 10th	Day	9% 11% 5% 8% 5% 3 3 3 4 6% 42%	2700
	11th to 20th	Day	13% 15% 5% 13% 6% 5% 6% 4 5% 6% 23%	3088
	21st to end	Day	25% 19% 6% 13% 5% 5% 4 3 4 4 12%	4070
January	1st to 10th	Night	13% 14% 6% 12% 5% 4 4 3 4 5% 30%	8232
	11th to 20th	Night	10% 13% 6% 13% 8% 6% 6% 3 4 5% 25%	8280
	21st to end	Night	16% 12% 6% 9% 5% 4 4 3 4 5% 32%	8726
February	1st to 10th	Night	16% 12% 4 9% 6% 5% 4 3 4 5% 30%	2634
	11th to 20th	Night	14% 11% 3 9% 5% 4 5% 3 5% 6% 34%	2458
	21st to end	Night	16% 12% 4 9% 5% 3 4 3 5% 6% 35%	2076
March	1st to 10th	Night	16% 13% 5% 6% 4 3 3 2 4 5% 38%	5398
	11th to 20th	Night	11% 7% 3 7% 5% 4 3 3 5% 7% 45%	5315
	21st to end	Night	17% 9% 4 10% 5% 5% 4 4 6% 6% 29%	4962
April	1st to 10th	Night	13% 9% 3 7% 4 5% 4 3 5% 6% 40%	2000
	11th to 20th	Night	16% 8% 3 6% 5% 4 4 3 4 6% 41%	1975
	21st to end	Night	18% 8% 3 6% 5% 5% 5% 3 5% 7% 36%	1926
May	1st to 10th	Night	18% 11% 3 8% 5% 4 4 3 5% 7% 33%	4033
	11th to 20th	Night	14% 7% 2 6% 4 4 4 3 6% 9% 40%	3886
	21st to end	Night	13% 9% 3 7% 4 5% 4 4 6% 7% 37%	3942
June	1st to 10th	Night	10% 5% 2 6% 4 3 4 4 5% 7% 49%	1600
	11th to 20th	Night	8% 5% 2 6% 4 4 4 4 6% 8% 48%	1600
	21st to end	Night	7% 5% 2 7% 4 5% 4 4 7% 11% 43%	1600
July	1st to 10th	Night	10% 5% 2 6% 4 4 5% 4 7% 10% 44%	3618
	11th to 20th	Night	5% 5% 2 6% 4 5% 5% 4 8% 10% 46%	3617
	21st to end	Night	8% 7% 3 8% 5% 5% 5% 4 6% 8% 42%	3947
August	1st to 10th	Night	6% 4 2 5% 4 4 4 4 7% 9% 51%	2852
	11th to 20th	Night	6% 5% 2 6% 4 5% 5% 3 7% 9% 49%	3200
	21st to end	Night	6% 4 2 6% 3 4 4 3 5% 8% 54%	3586
September	1st to 10th	Night	11% 4 2 5% 4 3 3 3 5% 7% 54%	2000
	11th to 20th	Night	8% 4 1 4 4 3 4 3 5% 7% 57%	2114
	21st to end	Night	10% 6% 2 6% 4 4 5% 4 6% 6% 47%	2200
October	1st to 10th	Night	11% 5% 2 5% 3 4 3 3 4 5% 55%	2230
	11th to 20th	Night	14% 7% 2 5% 3 3 3 2 5% 6% 50%	2400
	21st to end	Night	18% 8% 3 6% 5% 3 4 3 4 6% 40%	2846
November	1st to 10th	Night	10% 7% 3 7% 3 3 4 3 5% 6% 49%	2666
	11th to 20th	Night	12% 9% 3 7% 5% 4 4 3 5% 6% 42%	2730
	21st to end	Night	17% 12% 4 9% 4 3 3 3 4 5% 35%	2730
December	1st to 10th	Night	12% 9% 3 8% 4 4 4 3 5% 6% 43%	4704
	11th to 20th	Night	16% 11% 5% 9% 6% 5% 4 3 4 5% 32%	5339
	21st to end	Night	26% 17% 7% 11% 5% 4 4 3 4 4 16%	7150

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	59% 4 14% 16% 6% 1	4692
	11th to 20th	Day	62% 4 8% 12% 12% 2	4710
	21st to end	Day	63% 3 10% 17% 6% 1	5473
February	1st to 10th	Day	56% 4 12% 17% 8% 2	1984
	11th to 20th	Day	54% 5% 10% 21% 9% 1	2058
	21st to end	Day	53% 5% 10% 21% 9% 2	1730
March	1st to 10th	Day	53% 3 7% 19% 16% 3	4500
	11th to 20th	Day	38% 5% 10% 34% 12% 1	4685
	21st to end	Day	55% 7% 13% 16% 8% 1	5969
April	1st to 10th	Day	49% 6% 12% 21% 12%	2400
	11th to 20th	Day	46% 6% 11% 22% 11% 4	2374
	21st to end	Day	50% 5% 13% 19% 11% 2	2472
May	1st to 10th	Day	48% 8% 11% 21% 11% 1	5897
	11th to 20th	Day	44% 7% 11% 24% 12% 2	6002
	21st to end	Day	40% 7% 12% 22% 16% 3	6949
June	1st to 10th	Day	35% 9% 13% 23% 17% 3	2800
	11th to 20th	Day	34% 7% 11% 24% 20% 4	2800
	21st to end	Day	38% 8% 14% 22% 16% 3	2800
July	1st to 10th	Day	37% 7% 13% 28% 14% 2	6291
	11th to 20th	Day	39% 8% 15% 25% 13% 1	6285
	21st to end	Day	42% 7% 15% 22% 12% 1	6728
August	1st to 10th	Day	30% 7% 17% 31% 15% 1	4282
	11th to 20th	Day	33% 7% 16% 27% 16% 1	3885
	21st to end	Day	28% 7% 14% 31% 15% 4	4311
September	1st to 10th	Day	35% 6% 12% 25% 19% 4	2400
	11th to 20th	Day	31% 5% 11% 25% 24% 5%	2265
	21st to end	Day	35% 5% 10% 24% 24% 2	2200
October	1st to 10th	Day	27% 3 7% 25% 35% 3	3530
	11th to 20th	Day	30% 4 10% 23% 30% 2	3240
	21st to end	Day	42% 4 8% 23% 22% 2	3192
November	1st to 10th	Day	35% 5% 14% 25% 17% 4	1852
	11th to 20th	Day	48% 4 10% 22% 13% 3	1890
	21st to end	Day	53% 4 11% 20% 11% 1	1890
December	1st to 10th	Day	45% 3 11% 29% 10% 1	2700
	11th to 20th	Day	61% 5% 10% 18% 5% 1	3085
	21st to end	Day	76% 5% 8% 7% 4	4070
January	1st to 10th	Night	57% 5% 11% 20% 7%	8233
	11th to 20th	Night	62% 3 8% 13% 12% 2	8280
	21st to end	Night	56% 3 10% 21% 10% 1	8726
February	1st to 10th	Night	56% 5% 11% 17% 9% 2	2634
	11th to 20th	Night	50% 4 11% 22% 11% 2	2459
	21st to end	Night	51% 4 11% 20% 11% 2	2076
March	1st to 10th	Night	49% 4 9% 23% 11% 4	5398
	11th to 20th	Night	38% 5% 11% 26% 17% 3	5315
	21st to end	Night	53% 7% 10% 21% 7% 1	4962
April	1st to 10th	Night	43% 6% 11% 23% 14% 2	2000
	11th to 20th	Night	44% 5% 9% 22% 17% 4	1975
	21st to end	Night	48% 5% 11% 21% 11% 4	1926
May	1st to 10th	Night	51% 6% 10% 18% 12% 3	4060
	11th to 20th	Night	40% 7% 12% 25% 14% 2	3887
	21st to end	Night	43% 7% 12% 21% 14% 3	3950
June	1st to 10th	Night	33% 6% 12% 28% 18% 4	1600
	11th to 20th	Night	32% 6% 12% 26% 21% 4	1600
	21st to end	Night	34% 6% 17% 23% 17% 4	1600
July	1st to 10th	Night	35% 5% 13% 29% 14% 3	3580
	11th to 20th	Night	31% 7% 16% 27% 18% 1	3572
	21st to end	Night	38% 7% 16% 22% 14% 3	3832
August	1st to 10th	Night	27% 7% 18% 30% 16% 2	2843
	11th to 20th	Night	30% 7% 15% 28% 18% 1	3230
	21st to end	Night	28% 5% 12% 34% 18% 4	3586
September	1st to 10th	Night	30% 6% 9% 28% 21% 6%	2000
	11th to 20th	Night	27% 5% 9% 26% 29% 5%	2114
	21st to end	Night	35% 6% 8% 24% 24% 3	2200
October	1st to 10th	Night	20% 3 7% 30% 37% 3	3646
	11th to 20th	Night	26% 3 8% 26% 33% 3	3899
	21st to end	Night	37% 4 8% 22% 24% 5%	4596
November	1st to 10th	Night	35% 5% 11% 27% 19% 4	2666
	11th to 20th	Night	44% 4 11% 24% 15% 2	2730
	21st to end	Night	51% 4 9% 23% 12% 1	2730
December	1st to 10th	Night	42% 3 12% 30% 12% 1	4704
	11th to 20th	Night	55% 4 12% 18% 11% 1	5341
	21st to end	Night	71% 4 9% 10% 5%	7150

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	21% 17% 33% 20% 8%	330
	11th to 20th	Day	23% 22% 39% 12% 4	330
	21st to end	Day	23% 21% 34% 18% 4	363
February	1st to 10th	Day	22% 16% 37% 20% 5%	330
	11th to 20th	Day	23% 18% 39% 15% 4	330
	21st to end	Day	24% 18% 44% 12% 2	273
March	1st to 10th	Day	20% 22% 38% 17% 2	306
	11th to 20th	Day	25% 19% 36% 16% 4	326
	21st to end	Day	30% 16% 31% 15% 7% 1	550
April	1st to 10th	Day	24% 13% 34% 21% 7% 1	500
	11th to 20th	Day	22% 19% 29% 18% 11% 1	492
	21st to end	Day	22% 15% 33% 21% 7% 2	500
May	1st to 10th	Day	21% 10% 33% 25% 9% 2	503
	11th to 20th	Day	22% 10% 25% 26% 13% 5%	586
	21st to end	Day	11% 9% 32% 25% 14% 9%	789
June	1st to 10th	Day	11% 8% 25% 31% 19% 5%	730
	11th to 20th	Day	11% 5% 28% 30% 21% 5%	730
	21st to end	Day	10% 8% 30% 30% 17% 5%	730
July	1st to 10th	Day	10% 3 17% 31% 22% 17%	721
	11th to 20th	Day	8% 4 20% 33% 25% 11%	718
	21st to end	Day	10% 3 17% 33% 27% 9%	794
August	1st to 10th	Day	5% 2 15% 34% 28% 15%	621
	11th to 20th	Day	8% 3 18% 30% 30% 12%	519
	21st to end	Day	5% 2 15% 32% 33% 13%	583
September	1st to 10th	Day	10% 6% 18% 27% 29% 9%	530
	11th to 20th	Day	8% 4 13% 28% 30% 17%	530
	21st to end	Day	13% 8% 25% 23% 20% 12%	530
October	1st to 10th	Day	13% 5% 26% 30% 20% 6%	496
	11th to 20th	Day	13% 21% 28% 27% 9% 2	330
	21st to end	Day	29% 15% 33% 17% 6% 1	363
November	1st to 10th	Day	13% 15% 35% 23% 10% 4	330
	11th to 20th	Day	24% 18% 32% 17% 8% 1	330
	21st to end	Day	25% 13% 35% 23% 4	330
December	1st to 10th	Day	15% 19% 43% 16% 6% 1	330
	11th to 20th	Day	18% 17% 40% 20% 4 1	330
	21st to end	Day	28% 18% 35% 16% 3	363
January	1st to 10th	Night	22% 14% 39% 22% 3	1050
	11th to 20th	Night	21% 18% 38% 19% 4	1050
	21st to end	Night	20% 15% 38% 23% 3	1155
February	1st to 10th	Night	24% 13% 36% 23% 3	954
	11th to 20th	Night	20% 17% 35% 25% 3	823
	21st to end	Night	23% 14% 40% 20% 3	692
March	1st to 10th	Night	21% 15% 35% 24% 4	809
	11th to 20th	Night	17% 15% 38% 24% 6% 1	780
	21st to end	Night	23% 11% 37% 24% 4	660
April	1st to 10th	Night	18% 13% 38% 26% 5%	600
	11th to 20th	Night	19% 13% 36% 24% 9%	593
	21st to end	Night	23% 10% 34% 27% 7% 1	600
May	1st to 10th	Night	18% 8% 37% 30% 8%	600
	11th to 20th	Night	17% 6% 29% 34% 13% 2	591
	21st to end	Night	11% 6% 28% 35% 18% 2	650
June	1st to 10th	Night	12% 4 25% 43% 15%	600
	11th to 20th	Night	11% 4 26% 43% 17% 1	600
	21st to end	Night	8% 4 26% 41% 21% 1	600
July	1st to 10th	Night	11% 2 15% 35% 33% 4	585
	11th to 20th	Night	5% 3 19% 42% 28% 4	582
	21st to end	Night	6% 3 13% 44% 32% 2	657
August	1st to 10th	Night	7% 3 12% 44% 31% 4	597
	11th to 20th	Night	6% 2 12% 45% 31% 4	594
	21st to end	Night	6% 2 14% 37% 37% 3	660
September	1st to 10th	Night	13% 3 15% 38% 28% 4	600
	11th to 20th	Night	8% 4 14% 39% 31% 4	714
	21st to end	Night	13% 7% 21% 31% 27% 3	800
October	1st to 10th	Night	14% 5% 22% 37% 20% 3	800
	11th to 20th	Night	18% 11% 30% 29% 12%	800
	21st to end	Night	22% 13% 36% 24% 6%	880
November	1st to 10th	Night	14% 9% 43% 25% 8% 1	820
	11th to 20th	Night	16% 16% 35% 26% 6% 1	840
	21st to end	Night	23% 16% 31% 24% 6%	840
December	1st to 10th	Night	21% 13% 39% 24% 3	1034
	11th to 20th	Night	23% 13% 32% 26% 6%	1050
	21st to end	Night	30% 14% 33% 20% 2	1155

Page generated at 2026-02-28 00:40:19. Version ac07

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