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 2026-07-31.

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% 8% 42%	137612
	Night	13% 7% 2 6% 4 4 4 3 5% 7% 45%	135562
Transparency	Day	39% 6% 11% 22% 18% 4	141290
	Night	38% 5% 10% 23% 20% 5%	139963
Seeing	Day	16% 10% 23% 24% 19% 8%	17668
	Night	16% 8% 25% 30% 18% 3	27372

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% 11% 3 9% 4 3 3 3 4 5% 39%	4691
	11th to 20th	Day	13% 7% 2 6% 4 3 3 2 3 4 53%	5168
	21st to end	Day	19% 7% 2 6% 5% 4 3 3 4 5% 41%	5922
February	1st to 10th	Day	18% 10% 4 7% 4 3 3 3 4 5% 38%	2100
	11th to 20th	Day	20% 10% 3 7% 5% 3 3 3 3 6% 38%	2048
	21st to end	Day	19% 10% 3 7% 5% 4 3 2 5% 5% 37%	1730
March	1st to 10th	Day	16% 13% 4 8% 4 4 4 3 4 5% 35%	4580
	11th to 20th	Day	13% 8% 2 6% 4 4 4 3 5% 6% 46%	4887
	21st to end	Day	11% 8% 3 7% 5% 4 4 3 5% 7% 44%	6086
April	1st to 10th	Day	13% 6% 2 5% 4 4 4 4 5% 7% 45%	2520
	11th to 20th	Day	15% 6% 3 6% 4 3 3 3 5% 6% 45%	2494
	21st to end	Day	12% 6% 2 7% 5% 5% 4 5% 5% 7% 41%	2520
May	1st to 10th	Day	15% 7% 3 8% 5% 4 5% 5% 7% 8% 33%	7217
	11th to 20th	Day	12% 8% 3 8% 5% 5% 5% 4 6% 8% 35%	7626
	21st to end	Day	18% 10% 3 8% 5% 5% 5% 4 6% 7% 28%	8511
June	1st to 10th	Day	8% 5% 2 7% 4 5% 6% 4 7% 9% 42%	2940
	11th to 20th	Day	4 5% 2 5% 5% 5% 5% 5% 8% 10% 48%	2940
	21st to end	Day	5% 4 2 4 4 5% 6% 6% 8% 11% 45%	2940
July	1st to 10th	Day	5% 5% 2 7% 6% 5% 6% 5% 8% 10% 41%	6500
	11th to 20th	Day	6% 5% 2 6% 5% 6% 6% 6% 9% 14% 36%	6500
	21st to end	Day	10% 6% 2 6% 5% 6% 6% 5% 8% 12% 35%	6503
August	1st to 10th	Day	3 3 1 4 4 4 4 4 7% 10% 56%	3905
	11th to 20th	Day	8% 4 2 6% 4 5% 4 4 7% 10% 45%	3849
	21st to end	Day	5% 4 2 5% 4 4 4 3 5% 8% 55%	4312
September	1st to 10th	Day	8% 5% 2 6% 5% 4 5% 4 6% 9% 46%	2400
	11th to 20th	Day	13% 5% 2 6% 3 4 5% 4 6% 8% 45%	2280
	21st to end	Day	11% 6% 2 6% 3 4 5% 3 4 6% 50%	2200
October	1st to 10th	Day	9% 3 2 4 3 3 3 3 5% 6% 59%	2180
	11th to 20th	Day	10% 5% 2 5% 2 3 4 3 5% 6% 56%	2000
	21st to end	Day	18% 5% 2 4 3 2 3 3 3 4 51%	2149
November	1st to 10th	Day	11% 6% 3 4 3 2 2 3 5% 6% 55%	1852
	11th to 20th	Day	13% 7% 2 5% 3 3 3 3 4 7% 51%	1890
	21st to end	Day	16% 8% 2 4 4 4 4 3 5% 6% 44%	1890
December	1st to 10th	Day	16% 9% 3 6% 3 3 3 2 4 4 47%	3020
	11th to 20th	Day	18% 10% 3 7% 5% 4 3 3 4 5% 40%	3192
	21st to end	Day	14% 12% 3 8% 4 6% 5% 4 5% 5% 33%	4070
January	1st to 10th	Night	18% 9% 2 8% 3 3 3 3 4 5% 41%	8232
	11th to 20th	Night	13% 8% 3 6% 4 3 3 2 3 4 51%	7818
	21st to end	Night	21% 8% 3 7% 4 4 3 3 4 5% 39%	8283
February	1st to 10th	Night	19% 11% 3 6% 4 3 4 3 4 5% 38%	2520
	11th to 20th	Night	21% 8% 3 7% 4 4 4 3 4 5% 38%	2458
	21st to end	Night	19% 8% 2 6% 4 4 4 3 5% 4 41%	2076
March	1st to 10th	Night	17% 10% 3 7% 4 3 4 3 5% 6% 37%	5493
	11th to 20th	Night	11% 7% 2 5% 4 3 3 4 5% 6% 50%	5336
	21st to end	Night	13% 7% 3 7% 4 4 4 3 5% 7% 44%	5083
April	1st to 10th	Night	12% 7% 2 5% 4 3 4 3 5% 8% 46%	2100
	11th to 20th	Night	14% 6% 2 5% 4 3 4 3 5% 8% 47%	2075
	21st to end	Night	11% 7% 3 6% 5% 4 4 3 5% 7% 45%	2100
May	1st to 10th	Night	18% 10% 3 7% 4 4 3 3 5% 7% 37%	5622
	11th to 20th	Night	12% 8% 3 9% 5% 4 5% 3 5% 7% 40%	5234
	21st to end	Night	17% 10% 3 8% 5% 5% 4 4 6% 7% 29%	5617
June	1st to 10th	Night	8% 6% 2 7% 6% 4 5% 4 7% 11% 41%	1680
	11th to 20th	Night	4 4 1 4 3 4 3 3 7% 9% 56%	1680
	21st to end	Night	3 2 1 4 4 4 4 5% 8% 13% 53%	1680
July	1st to 10th	Night	6% 5% 2 6% 5% 5% 6% 5% 8% 9% 43%	3698
	11th to 20th	Night	3 3 1 5% 4 5% 6% 5% 9% 14% 44%	3697
	21st to end	Night	6% 6% 3 7% 5% 4 5% 4 7% 14% 38%	4561
August	1st to 10th	Night	2 2 1 4 3 4 3 3 6% 8% 64%	3244
	11th to 20th	Night	3 3 2 6% 3 4 4 5% 6% 10% 54%	3200
	21st to end	Night	4 3 1 4 4 3 4 4 6% 9% 58%	3586
September	1st to 10th	Night	8% 4 1 7% 4 3 3 4 6% 7% 53%	2000
	11th to 20th	Night	8% 5% 2 6% 5% 3 3 4 5% 7% 51%	2100
	21st to end	Night	10% 4 2 5% 3 3 3 2 5% 6% 57%	2200
October	1st to 10th	Night	7% 3 2 4 3 3 2 3 5% 5% 62%	2216
	11th to 20th	Night	11% 5% 1 4 2 2 4 2 4 6% 59%	2400
	21st to end	Night	17% 6% 2 4 3 3 4 2 4 5% 50%	2690
November	1st to 10th	Night	12% 6% 2 4 3 3 3 3 5% 5% 55%	2666
	11th to 20th	Night	10% 5% 2 5% 4 3 4 3 5% 7% 52%	2730
	21st to end	Night	16% 8% 2 5% 3 4 3 3 4 6% 47%	2730
December	1st to 10th	Night	18% 7% 2 5% 4 3 3 2 4 5% 47%	4380
	11th to 20th	Night	19% 9% 3 6% 3 3 3 3 4 5% 44%	5227
	21st to end	Night	16% 10% 3 8% 5% 5% 4 4 5% 5% 34%	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	48% 3 11% 24% 13% 1	4692
	11th to 20th	Day	37% 4 5% 22% 32% 1	5168
	21st to end	Day	46% 3 7% 19% 20% 5%	5922
February	1st to 10th	Day	50% 3 8% 21% 16% 2	2100
	11th to 20th	Day	50% 4 7% 19% 16% 4	2058
	21st to end	Day	49% 4 8% 16% 17% 7%	1730
March	1st to 10th	Day	52% 4 5% 16% 15% 9%	4580
	11th to 20th	Day	39% 5% 7% 21% 20% 8%	4887
	21st to end	Day	41% 4 9% 24% 21% 1	6088
April	1st to 10th	Day	39% 5% 9% 23% 21% 3	2520
	11th to 20th	Day	40% 4 8% 21% 20% 6%	2494
	21st to end	Day	41% 6% 10% 24% 17% 1	2520
May	1st to 10th	Day	45% 7% 13% 19% 15% 1	7252
	11th to 20th	Day	45% 7% 14% 17% 15% 2	7630
	21st to end	Day	51% 8% 10% 19% 10% 2	8525
June	1st to 10th	Day	36% 9% 13% 22% 19% 2	2940
	11th to 20th	Day	29% 8% 15% 27% 18% 3	2940
	21st to end	Day	28% 9% 17% 25% 17% 3	2940
July	1st to 10th	Day	35% 8% 16% 27% 13% 1	6431
	11th to 20th	Day	34% 9% 22% 28% 6% 1	6425
	21st to end	Day	40% 8% 22% 24% 6%	6320
August	1st to 10th	Day	22% 7% 17% 30% 23% 2	3893
	11th to 20th	Day	32% 6% 19% 24% 17% 2	3885
	21st to end	Day	27% 5% 11% 28% 26% 3	4311
September	1st to 10th	Day	33% 9% 10% 26% 18% 4	2400
	11th to 20th	Day	37% 7% 10% 20% 23% 4	2280
	21st to end	Day	34% 5% 10% 20% 24% 7%	2200
October	1st to 10th	Day	17% 3 7% 16% 41% 16%	3557
	11th to 20th	Day	20% 3 5% 23% 33% 16%	3240
	21st to end	Day	29% 3 4 24% 34% 7%	3451
November	1st to 10th	Day	32% 4 8% 24% 26% 7%	1852
	11th to 20th	Day	35% 3 8% 22% 25% 7%	1890
	21st to end	Day	41% 4 7% 22% 22% 4	1890
December	1st to 10th	Day	42% 3 6% 28% 19% 2	3020
	11th to 20th	Day	48% 3 7% 21% 16% 4	3189
	21st to end	Day	50% 5% 10% 24% 11% 1	4070
January	1st to 10th	Night	47% 3 11% 23% 14% 2	8233
	11th to 20th	Night	39% 3 6% 18% 29% 4	7818
	21st to end	Night	49% 3 7% 19% 18% 5%	8283
February	1st to 10th	Night	50% 4 9% 18% 18% 2	2520
	11th to 20th	Night	50% 3 7% 19% 16% 5%	2459
	21st to end	Night	45% 5% 8% 17% 19% 6%	2076
March	1st to 10th	Night	47% 5% 7% 15% 18% 8%	5493
	11th to 20th	Night	35% 4 7% 22% 18% 14%	5336
	21st to end	Night	39% 5% 9% 22% 21% 3	5083
April	1st to 10th	Night	36% 5% 11% 23% 19% 5%	2100
	11th to 20th	Night	35% 4 9% 22% 23% 7%	2075
	21st to end	Night	37% 5% 12% 25% 19% 3	2100
May	1st to 10th	Night	47% 5% 11% 21% 14% 1	5652
	11th to 20th	Night	45% 5% 13% 21% 12% 3	5235
	21st to end	Night	52% 8% 10% 18% 10% 2	5627
June	1st to 10th	Night	35% 9% 11% 20% 23% 2	1680
	11th to 20th	Night	23% 6% 15% 32% 21% 4	1680
	21st to end	Night	22% 9% 18% 29% 18% 5%	1680
July	1st to 10th	Night	33% 9% 17% 26% 14% 2	3660
	11th to 20th	Night	26% 8% 23% 32% 8% 2	3652
	21st to end	Night	37% 6% 23% 25% 8%	4432
August	1st to 10th	Night	17% 6% 10% 41% 24% 1	3232
	11th to 20th	Night	22% 8% 20% 30% 18% 2	3230
	21st to end	Night	22% 6% 13% 29% 26% 4	3586
September	1st to 10th	Night	29% 8% 10% 25% 22% 7%	2000
	11th to 20th	Night	31% 7% 12% 19% 28% 4	2100
	21st to end	Night	29% 4 9% 26% 25% 7%	2200
October	1st to 10th	Night	16% 4 6% 16% 40% 18%	3619
	11th to 20th	Night	18% 3 4 18% 37% 20%	3899
	21st to end	Night	27% 3 5% 27% 24% 13%	4338
November	1st to 10th	Night	32% 4 7% 24% 27% 7%	2666
	11th to 20th	Night	31% 4 7% 23% 24% 11%	2730
	21st to end	Night	40% 4 6% 22% 23% 5%	2730
December	1st to 10th	Night	41% 3 8% 23% 23% 2	4380
	11th to 20th	Night	45% 3 6% 23% 20% 3	5229
	21st to end	Night	50% 5% 10% 22% 11% 3	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	25% 20% 35% 16% 4	330
	11th to 20th	Day	27% 20% 38% 12% 2 1	330
	21st to end	Day	23% 23% 40% 9% 3	363
February	1st to 10th	Day	26% 21% 34% 14% 4 1	330
	11th to 20th	Day	34% 25% 32% 6% 3	330
	21st to end	Day	32% 22% 33% 9% 4	273
March	1st to 10th	Day	26% 21% 35% 13% 5%	330
	11th to 20th	Day	28% 21% 37% 13% 2	330
	21st to end	Day	23% 18% 35% 18% 6%	581
April	1st to 10th	Day	20% 17% 31% 24% 7% 1	540
	11th to 20th	Day	21% 17% 30% 23% 9% 1	532
	21st to end	Day	17% 15% 29% 23% 13% 2	540
May	1st to 10th	Day	20% 15% 27% 25% 10% 3	543
	11th to 20th	Day	16% 7% 27% 26% 17% 7%	567
	21st to end	Day	14% 5% 23% 28% 19% 10%	659
June	1st to 10th	Day	10% 4 19% 29% 24% 13%	780
	11th to 20th	Day	6% 3 17% 31% 31% 13%	780
	21st to end	Day	7% 2 17% 33% 27% 13%	780
July	1st to 10th	Day	7% 2 12% 29% 31% 20%	771
	11th to 20th	Day	7% 3 11% 25% 36% 18%	768
	21st to end	Day	6% 3 11% 28% 34% 18%	777
August	1st to 10th	Day	7% 3 9% 29% 35% 16%	526
	11th to 20th	Day	9% 2 14% 29% 35% 11%	519
	21st to end	Day	10% 1 10% 22% 37% 20%	583
September	1st to 10th	Day	8% 3 13% 30% 34% 12%	530
	11th to 20th	Day	11% 3 11% 25% 33% 17%	530
	21st to end	Day	18% 7% 13% 30% 22% 10%	530
October	1st to 10th	Day	8% 4 19% 32% 27% 9%	510
	11th to 20th	Day	9% 12% 36% 29% 12% 2	330
	21st to end	Day	21% 14% 34% 21% 8% 2	363
November	1st to 10th	Day	18% 8% 32% 29% 10% 2	330
	11th to 20th	Day	12% 16% 37% 28% 7% 1	330
	21st to end	Day	26% 13% 29% 19% 10% 2	330
December	1st to 10th	Day	26% 19% 31% 18% 6% 1	330
	11th to 20th	Day	25% 16% 34% 17% 8%	330
	21st to end	Day	28% 17% 37% 15% 3	363
January	1st to 10th	Night	23% 15% 34% 24% 4	1050
	11th to 20th	Night	24% 18% 34% 21% 3	1050
	21st to end	Night	23% 13% 39% 24% 2	1114
February	1st to 10th	Night	26% 13% 36% 22% 4	840
	11th to 20th	Night	28% 17% 33% 21% 2	823
	21st to end	Night	23% 18% 35% 22% 2	692
March	1st to 10th	Night	21% 14% 33% 27% 5%	840
	11th to 20th	Night	24% 12% 35% 25% 4 1	746
	21st to end	Night	17% 12% 34% 28% 8%	693
April	1st to 10th	Night	15% 12% 37% 27% 8%	630
	11th to 20th	Night	17% 10% 33% 29% 10%	623
	21st to end	Night	13% 8% 35% 31% 12% 2	630
May	1st to 10th	Night	16% 8% 25% 36% 14% 1	630
	11th to 20th	Night	12% 6% 26% 35% 18% 3	621
	21st to end	Night	11% 2 19% 36% 27% 4	683
June	1st to 10th	Night	11% 3 14% 39% 28% 5%	630
	11th to 20th	Night	6% 1 13% 36% 40% 3	630
	21st to end	Night	4 2 12% 37% 40% 6%	630
July	1st to 10th	Night	6% 2 8% 31% 42% 11%	615
	11th to 20th	Night	6% 1 9% 26% 46% 11%	612
	21st to end	Night	6% 2 7% 29% 45% 11%	687
August	1st to 10th	Night	5% 7% 33% 48% 8%	597
	11th to 20th	Night	7% 1 7% 38% 42% 6%	594
	21st to end	Night	7% 2 7% 31% 43% 10%	660
September	1st to 10th	Night	9% 1 9% 35% 41% 5%	600
	11th to 20th	Night	9% 2 12% 33% 39% 7%	700
	21st to end	Night	11% 3 14% 36% 31% 5%	800
October	1st to 10th	Night	8% 4 17% 37% 30% 4	800
	11th to 20th	Night	14% 6% 22% 37% 20% 2	800
	21st to end	Night	20% 7% 29% 29% 14% 1	880
November	1st to 10th	Night	15% 7% 26% 34% 16% 2	820
	11th to 20th	Night	12% 10% 34% 34% 10% 1	840
	21st to end	Night	20% 11% 29% 28% 11% 1	840
December	1st to 10th	Night	25% 12% 31% 27% 6%	840
	11th to 20th	Night	22% 12% 30% 30% 6%	977
	21st to end	Night	25% 14% 32% 24% 5%	1155

Page generated at 2026-07-28 02:25:25. Version ac07

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