Jackson
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Jackson clear sky chart from 2005-11-06 to 2025-03-27.

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% 7% 2 6% 4 4 4 4 6% 7% 43%	108871
	Night	13% 7% 2 6% 4 4 4 3 5% 7% 46%	110599
Transparency	Day	38% 6% 10% 23% 19% 4	112588
	Night	37% 5% 9% 23% 21% 5%	115022
Seeing	Day	15% 10% 23% 24% 20% 9%	15747
	Night	16% 8% 25% 30% 18% 3	25672

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	14% 11% 3 10% 4 3 3 3 4 5% 41%	3617
	11th to 20th	Day	15% 8% 2 7% 3 4 3 2 3 5% 49%	3966
	21st to end	Day	18% 8% 2 5% 4 4 3 3 4 6% 43%	4572
February	1st to 10th	Day	19% 11% 4 8% 4 3 3 3 4 5% 37%	2000
	11th to 20th	Day	20% 10% 3 7% 5% 3 3 3 3 5% 38%	1948
	21st to end	Day	20% 10% 3 7% 5% 4 3 2 5% 5% 36%	1650
March	1st to 10th	Day	18% 12% 4 8% 4 4 4 3 4 5% 34%	3220
	11th to 20th	Day	14% 7% 2 6% 4 4 4 3 5% 6% 44%	3444
	21st to end	Day	12% 7% 3 6% 6% 4 5% 3 5% 6% 42%	4225
April	1st to 10th	Day	12% 7% 3 6% 4 3 4 4 5% 6% 45%	2280
	11th to 20th	Day	16% 7% 3 6% 4 3 3 3 5% 6% 44%	2254
	21st to end	Day	12% 6% 2 7% 5% 5% 4 4 5% 7% 43%	2280
May	1st to 10th	Day	14% 7% 3 7% 5% 4 5% 4 7% 9% 37%	3879
	11th to 20th	Day	15% 7% 2 7% 4 5% 5% 4 6% 9% 37%	4081
	21st to end	Day	10% 7% 2 7% 5% 5% 6% 4 7% 9% 37%	4540
June	1st to 10th	Day	9% 5% 2 7% 4 5% 5% 4 7% 9% 42%	2660
	11th to 20th	Day	4 4 1 5% 4 5% 5% 5% 8% 10% 49%	2660
	21st to end	Day	5% 3 1 5% 4 5% 6% 6% 8% 12% 46%	2660
July	1st to 10th	Day	5% 5% 2 6% 6% 5% 6% 5% 9% 10% 40%	4440
	11th to 20th	Day	7% 7% 2 6% 5% 5% 5% 4 8% 12% 38%	4440
	21st to end	Day	14% 9% 3 8% 6% 6% 5% 4 6% 8% 31%	4429
August	1st to 10th	Day	3 3 1 4 4 4 4 4 7% 10% 56%	3785
	11th to 20th	Day	8% 5% 2 6% 4 5% 5% 4 8% 9% 45%	3729
	21st to end	Day	5% 4 2 5% 4 4 4 3 5% 8% 55%	4180
September	1st to 10th	Day	8% 5% 3 6% 5% 4 5% 4 6% 8% 46%	2280
	11th to 20th	Day	13% 5% 2 6% 4 4 5% 4 6% 8% 44%	2166
	21st to end	Day	11% 6% 2 5% 3 4 5% 3 4 7% 50%	2090
October	1st to 10th	Day	8% 3 2 4 3 3 4 3 5% 6% 59%	2071
	11th to 20th	Day	10% 5% 2 5% 2 3 3 3 5% 6% 55%	1900
	21st to end	Day	18% 6% 2 4 3 2 3 3 4 4 51%	2042
November	1st to 10th	Day	11% 6% 3 4 3 2 2 3 5% 6% 55%	1762
	11th to 20th	Day	14% 7% 2 5% 3 3 3 3 4 6% 51%	1800
	21st to end	Day	17% 8% 2 4 4 4 4 3 5% 6% 44%	1800
December	1st to 10th	Day	16% 9% 2 5% 3 3 3 2 4 4 47%	2930
	11th to 20th	Day	18% 10% 3 7% 5% 4 3 3 4 5% 39%	3109
	21st to end	Day	14% 12% 3 8% 4 5% 5% 4 5% 5% 33%	3982
January	1st to 10th	Night	17% 10% 3 9% 3 3 3 3 4 5% 39%	6348
	11th to 20th	Night	16% 9% 4 7% 4 3 3 2 3 4 46%	6010
	21st to end	Night	22% 8% 2 6% 3 3 3 2 4 5% 43%	6399
February	1st to 10th	Night	20% 11% 4 7% 4 3 4 3 4 4 37%	2400
	11th to 20th	Night	21% 8% 3 7% 4 4 4 3 4 5% 38%	2338
	21st to end	Night	19% 8% 2 6% 4 4 4 3 5% 4 41%	1980
March	1st to 10th	Night	20% 10% 3 7% 4 3 3 3 5% 5% 37%	3853
	11th to 20th	Night	13% 8% 2 5% 4 3 3 4 5% 6% 49%	3765
	21st to end	Night	13% 7% 2 7% 5% 4 4 4 6% 7% 42%	3542
April	1st to 10th	Night	11% 6% 2 6% 4 3 3 4 5% 8% 47%	1900
	11th to 20th	Night	15% 6% 2 4 3 2 3 3 5% 8% 47%	1875
	21st to end	Night	10% 7% 3 6% 5% 4 4 4 5% 7% 46%	1900
May	1st to 10th	Night	18% 8% 3 6% 4 4 3 3 5% 8% 40%	3016
	11th to 20th	Night	11% 8% 3 7% 4 4 4 3 5% 7% 44%	2812
	21st to end	Night	8% 6% 2 6% 5% 6% 4 4 7% 10% 41%	3000
June	1st to 10th	Night	8% 6% 2 7% 6% 4 5% 4 6% 10% 41%	1520
	11th to 20th	Night	4 3 1 4 3 4 3 4 8% 9% 58%	1520
	21st to end	Night	3 2 1 4 4 4 4 5% 8% 12% 53%	1520
July	1st to 10th	Night	6% 5% 2 6% 5% 5% 7% 5% 9% 10% 42%	2530
	11th to 20th	Night	4 4 1 4 4 5% 5% 4 7% 12% 49%	2530
	21st to end	Night	9% 9% 4 8% 6% 4 5% 4 5% 9% 37%	3124
August	1st to 10th	Night	2 2 1 4 3 4 3 3 6% 8% 64%	3144
	11th to 20th	Night	3 3 2 6% 3 4 4 5% 6% 10% 54%	3100
	21st to end	Night	4 3 1 4 4 3 4 4 6% 9% 59%	3476
September	1st to 10th	Night	8% 4 1 7% 4 3 3 4 6% 7% 53%	1900
	11th to 20th	Night	9% 6% 2 6% 5% 3 3 4 5% 7% 51%	1995
	21st to end	Night	10% 4 2 5% 3 3 3 2 5% 7% 57%	2090
October	1st to 10th	Night	8% 3 2 4 3 3 2 3 5% 6% 62%	2105
	11th to 20th	Night	11% 5% 1 4 2 3 4 2 4 6% 58%	2280
	21st to end	Night	16% 6% 2 4 3 3 4 2 4 5% 51%	2555
November	1st to 10th	Night	12% 5% 2 4 3 3 3 3 5% 5% 55%	2536
	11th to 20th	Night	10% 5% 2 5% 4 3 4 3 5% 7% 52%	2600
	21st to end	Night	15% 7% 2 5% 3 4 3 3 4 6% 48%	2600
December	1st to 10th	Night	18% 7% 2 5% 4 3 3 2 4 5% 47%	4250
	11th to 20th	Night	19% 9% 3 6% 3 3 3 3 4 5% 43%	5090
	21st to end	Night	16% 10% 3 9% 5% 5% 5% 4 5% 5% 34%	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	47% 3 11% 22% 16% 1	3618
	11th to 20th	Day	40% 5% 5% 24% 25% 1	3966
	21st to end	Day	43% 3 7% 19% 23% 6%	4572
February	1st to 10th	Day	50% 3 8% 21% 16% 2	2000
	11th to 20th	Day	50% 4 7% 18% 16% 4	1958
	21st to end	Day	50% 4 8% 16% 16% 6%	1650
March	1st to 10th	Day	53% 5% 6% 13% 15% 8%	3220
	11th to 20th	Day	39% 6% 8% 24% 17% 6%	3444
	21st to end	Day	42% 5% 10% 22% 20% 1	4225
April	1st to 10th	Day	39% 5% 9% 22% 21% 3	2280
	11th to 20th	Day	41% 4 7% 20% 20% 6%	2254
	21st to end	Day	40% 6% 10% 25% 18% 1	2280
May	1st to 10th	Day	42% 8% 11% 23% 15% 1	3914
	11th to 20th	Day	41% 9% 14% 22% 13% 1	4085
	21st to end	Day	39% 11% 11% 25% 14% 1	4553
June	1st to 10th	Day	36% 9% 13% 21% 18% 2	2660
	11th to 20th	Day	27% 8% 15% 28% 19% 3	2660
	21st to end	Day	28% 10% 17% 25% 17% 4	2660
July	1st to 10th	Day	35% 9% 17% 28% 10% 2	4371
	11th to 20th	Day	35% 8% 15% 32% 9% 2	4365
	21st to end	Day	50% 8% 11% 23% 7% 1	4288
August	1st to 10th	Day	22% 7% 17% 29% 23% 2	3773
	11th to 20th	Day	32% 6% 18% 23% 17% 2	3765
	21st to end	Day	28% 5% 11% 28% 25% 3	4179
September	1st to 10th	Day	34% 9% 10% 25% 18% 5%	2280
	11th to 20th	Day	38% 7% 9% 19% 23% 4	2166
	21st to end	Day	34% 5% 10% 21% 23% 7%	2090
October	1st to 10th	Day	17% 3 7% 16% 41% 16%	3448
	11th to 20th	Day	20% 3 5% 23% 33% 16%	3140
	21st to end	Day	28% 3 5% 24% 34% 7%	3344
November	1st to 10th	Day	32% 3 8% 24% 26% 7%	1762
	11th to 20th	Day	36% 3 7% 21% 25% 8%	1800
	21st to end	Day	41% 4 7% 22% 22% 4	1800
December	1st to 10th	Day	41% 3 6% 28% 19% 2	2930
	11th to 20th	Day	49% 3 7% 22% 15% 4	3106
	21st to end	Day	50% 5% 10% 23% 11% 1	3982
January	1st to 10th	Night	48% 4 9% 19% 17% 2	6348
	11th to 20th	Night	44% 4 6% 18% 24% 4	6010
	21st to end	Night	46% 3 5% 22% 20% 4	6399
February	1st to 10th	Night	51% 4 9% 17% 17% 3	2400
	11th to 20th	Night	50% 4 7% 19% 16% 5%	2339
	21st to end	Night	46% 5% 8% 17% 19% 6%	1980
March	1st to 10th	Night	48% 5% 8% 13% 17% 8%	3853
	11th to 20th	Night	36% 5% 9% 22% 19% 9%	3765
	21st to end	Night	41% 6% 10% 19% 23% 1	3542
April	1st to 10th	Night	35% 6% 11% 23% 20% 5%	1900
	11th to 20th	Night	36% 4 8% 20% 23% 8%	1875
	21st to end	Night	36% 5% 11% 26% 19% 3	1900
May	1st to 10th	Night	42% 8% 10% 22% 15% 2	3046
	11th to 20th	Night	38% 7% 14% 25% 14% 1	2813
	21st to end	Night	35% 10% 13% 28% 14% 2	3008
June	1st to 10th	Night	36% 9% 11% 21% 21% 2	1520
	11th to 20th	Night	21% 6% 15% 32% 22% 4	1520
	21st to end	Night	21% 9% 17% 28% 19% 5%	1520
July	1st to 10th	Night	32% 10% 18% 27% 10% 2	2490
	11th to 20th	Night	25% 8% 15% 37% 11% 4	2482
	21st to end	Night	45% 7% 14% 22% 12%	3025
August	1st to 10th	Night	17% 6% 10% 40% 25% 1	3132
	11th to 20th	Night	22% 8% 19% 30% 18% 2	3130
	21st to end	Night	21% 6% 14% 30% 25% 4	3476
September	1st to 10th	Night	29% 8% 10% 25% 21% 7%	1900
	11th to 20th	Night	31% 6% 12% 18% 28% 4	1995
	21st to end	Night	28% 4 9% 27% 25% 7%	2090
October	1st to 10th	Night	16% 4 6% 16% 41% 18%	3508
	11th to 20th	Night	18% 3 4 18% 37% 21%	3779
	21st to end	Night	26% 3 6% 28% 24% 13%	4203
November	1st to 10th	Night	32% 4 6% 23% 28% 7%	2536
	11th to 20th	Night	32% 4 7% 22% 25% 11%	2600
	21st to end	Night	39% 4 6% 22% 24% 6%	2600
December	1st to 10th	Night	40% 3 8% 24% 23% 2	4250
	11th to 20th	Night	45% 3 5% 24% 20% 3	5092
	21st to end	Night	50% 5% 10% 22% 10% 3	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	25% 20% 36% 15% 4	300
	11th to 20th	Day	27% 20% 37% 12% 2 1	300
	21st to end	Day	22% 22% 41% 10% 4	330
February	1st to 10th	Day	27% 22% 32% 14% 4 1	300
	11th to 20th	Day	35% 24% 31% 7% 3	300
	21st to end	Day	32% 22% 34% 9% 3	249
March	1st to 10th	Day	27% 20% 35% 13% 5%	300
	11th to 20th	Day	27% 20% 36% 14% 2	300
	21st to end	Day	23% 18% 35% 18% 7%	518
April	1st to 10th	Day	19% 17% 32% 23% 8% 1	460
	11th to 20th	Day	22% 15% 29% 24% 10% 1	452
	21st to end	Day	18% 15% 29% 23% 13% 3	460
May	1st to 10th	Day	19% 13% 26% 26% 12% 3	463
	11th to 20th	Day	15% 6% 25% 27% 19% 8%	487
	21st to end	Day	11% 4 22% 30% 22% 12%	567
June	1st to 10th	Day	10% 4 18% 28% 25% 15%	680
	11th to 20th	Day	5% 2 14% 31% 33% 14%	680
	21st to end	Day	7% 2 17% 34% 27% 13%	680
July	1st to 10th	Day	7% 2 13% 28% 31% 20%	671
	11th to 20th	Day	8% 3 11% 24% 35% 19%	668
	21st to end	Day	7% 3 11% 27% 33% 19%	677
August	1st to 10th	Day	7% 3 9% 29% 35% 17%	486
	11th to 20th	Day	10% 2 15% 30% 33% 10%	479
	21st to end	Day	10% 1 9% 20% 39% 21%	539
September	1st to 10th	Day	8% 3 13% 29% 35% 12%	490
	11th to 20th	Day	12% 3 11% 24% 33% 17%	490
	21st to end	Day	17% 6% 13% 29% 23% 11%	490
October	1st to 10th	Day	8% 4 20% 31% 28% 9%	471
	11th to 20th	Day	9% 13% 38% 27% 12% 2	300
	21st to end	Day	21% 14% 32% 23% 9% 2	330
November	1st to 10th	Day	17% 8% 31% 31% 11% 2	300
	11th to 20th	Day	12% 16% 35% 28% 7% 1	300
	21st to end	Day	26% 13% 28% 20% 11% 2	300
December	1st to 10th	Day	26% 19% 29% 18% 7% 1	300
	11th to 20th	Day	26% 17% 32% 17% 8%	300
	21st to end	Day	27% 18% 37% 15% 4	330
January	1st to 10th	Night	23% 15% 34% 24% 4	1000
	11th to 20th	Night	24% 17% 33% 21% 4	1000
	21st to end	Night	22% 12% 39% 24% 2	1061
February	1st to 10th	Night	27% 14% 34% 22% 4	800
	11th to 20th	Night	27% 17% 33% 21% 2	783
	21st to end	Night	23% 18% 35% 22% 2	660
March	1st to 10th	Night	22% 14% 32% 28% 5%	800
	11th to 20th	Night	24% 12% 35% 25% 4 1	710
	21st to end	Night	17% 12% 34% 29% 9%	647
April	1st to 10th	Night	15% 12% 36% 28% 9% 1	570
	11th to 20th	Night	18% 10% 31% 30% 10% 1	563
	21st to end	Night	13% 8% 36% 31% 11% 2	570
May	1st to 10th	Night	15% 8% 25% 36% 15% 1	570
	11th to 20th	Night	12% 5% 24% 36% 19% 4	561
	21st to end	Night	8% 2 19% 37% 30% 4	617
June	1st to 10th	Night	11% 3 13% 38% 29% 6%	570
	11th to 20th	Night	5% 1 11% 36% 43% 4	570
	21st to end	Night	4 1 11% 39% 38% 7%	570
July	1st to 10th	Night	6% 3 8% 32% 41% 11%	555
	11th to 20th	Night	7% 1 9% 26% 45% 12%	552
	21st to end	Night	7% 2 7% 29% 44% 11%	624
August	1st to 10th	Night	5% 7% 31% 48% 8%	567
	11th to 20th	Night	7% 1 7% 38% 41% 5%	564
	21st to end	Night	8% 1 7% 30% 44% 10%	627
September	1st to 10th	Night	9% 1 8% 35% 42% 5%	570
	11th to 20th	Night	9% 2 12% 32% 39% 7%	665
	21st to end	Night	11% 3 14% 36% 32% 4	760
October	1st to 10th	Night	8% 4 16% 36% 31% 4	760
	11th to 20th	Night	14% 6% 23% 36% 19% 2	760
	21st to end	Night	19% 7% 28% 30% 15% 1	836
November	1st to 10th	Night	15% 7% 26% 33% 16% 2	780
	11th to 20th	Night	13% 10% 33% 34% 10% 1	800
	21st to end	Night	20% 10% 29% 29% 11% 1	800
December	1st to 10th	Night	25% 12% 30% 27% 7%	800
	11th to 20th	Night	22% 12% 29% 30% 7%	930
	21st to end	Night	25% 14% 31% 25% 5%	1100

Page generated at 2025-03-24 08:04:25. Version ac07

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