Fulton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fulton clear sky chart from 2005-11-06 to 2026-08-15.

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 7% 4 4 4 4 5% 7% 43%	143852
	Night	12% 8% 3 7% 4 4 4 3 5% 6% 44%	138338
Transparency	Day	38% 7% 13% 24% 16% 2	147450
	Night	39% 6% 12% 24% 17% 3	142819
Seeing	Day	17% 13% 29% 26% 13% 3	18125
	Night	17% 12% 31% 28% 12% 1	27862

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% 12% 4 11% 5% 4 4 3 4 5% 34%	4793
	11th to 20th	Day	7% 10% 4 8% 5% 6% 5% 3 5% 7% 42%	5310
	21st to end	Day	15% 13% 6% 9% 4 3 3 3 4 4 38%	5812
February	1st to 10th	Day	16% 12% 4 8% 5% 4 4 3 4 7% 34%	1890
	11th to 20th	Day	14% 10% 3 6% 5% 4 3 4 4 6% 39%	1923
	21st to end	Day	14% 10% 3 7% 4 4 3 4 4 5% 40%	1730
March	1st to 10th	Day	16% 10% 3 4 3 2 3 2 3 5% 49%	4925
	11th to 20th	Day	9% 7% 2 5% 3 3 3 3 5% 7% 52%	5090
	21st to end	Day	13% 11% 3 8% 5% 5% 5% 4 6% 8% 33%	5712
April	1st to 10th	Day	14% 9% 2 6% 5% 4 5% 3 5% 6% 43%	2520
	11th to 20th	Day	16% 9% 2 6% 4 3 4 3 5% 5% 42%	2494
	21st to end	Day	19% 8% 3 7% 4 4 4 3 5% 8% 34%	2520
May	1st to 10th	Day	15% 7% 3 7% 4 5% 5% 4 6% 8% 35%	7354
	11th to 20th	Day	13% 8% 3 7% 4 4 4 4 5% 7% 40%	8044
	21st to end	Day	17% 8% 3 7% 5% 4 5% 3 6% 6% 35%	9047
June	1st to 10th	Day	9% 4 2 5% 4 4 5% 5% 7% 10% 45%	2940
	11th to 20th	Day	8% 5% 2 5% 4 4 5% 4 7% 10% 46%	2940
	21st to end	Day	7% 4 2 5% 5% 5% 5% 4 7% 10% 47%	2940
July	1st to 10th	Day	9% 5% 2 6% 4 4 4 4 6% 10% 46%	8280
	11th to 20th	Day	6% 5% 2 7% 4 4 5% 4 7% 10% 46%	8066
	21st to end	Day	9% 5% 2 5% 4 4 5% 5% 8% 12% 41%	8337
August	1st to 10th	Day	5% 3 2 5% 4 4 5% 5% 8% 10% 50%	4364
	11th to 20th	Day	12% 5% 2 5% 4 4 5% 4 6% 7% 46%	4042
	21st to end	Day	5% 4 2 5% 4 4 4 4 6% 9% 53%	4312
September	1st to 10th	Day	10% 5% 2 5% 4 3 4 3 5% 7% 52%	2400
	11th to 20th	Day	9% 5% 2 5% 4 4 4 4 5% 8% 51%	2400
	21st to end	Day	9% 5% 2 5% 3 4 4 4 5% 7% 52%	2112
October	1st to 10th	Day	10% 5% 2 5% 4 4 4 3 4 5% 55%	2000
	11th to 20th	Day	15% 6% 2 5% 3 2 3 3 4 5% 53%	2000
	21st to end	Day	18% 8% 3 5% 3 3 3 2 3 5% 47%	2200
November	1st to 10th	Day	11% 7% 2 4 3 2 3 3 4 6% 53%	1934
	11th to 20th	Day	14% 8% 2 6% 3 3 3 3 5% 6% 47%	1890
	21st to end	Day	17% 11% 3 7% 3 4 3 2 4 5% 42%	1683
December	1st to 10th	Day	8% 10% 4 7% 4 3 2 3 4 6% 49%	2690
	11th to 20th	Day	11% 9% 5% 8% 4 3 4 3 5% 6% 42%	3088
	21st to end	Day	20% 21% 5% 11% 4 3 4 3 3 5% 21%	4070
January	1st to 10th	Night	13% 11% 6% 11% 5% 4 3 3 4 4 36%	8112
	11th to 20th	Night	9% 9% 4 12% 5% 5% 5% 4 4 4 40%	7680
	21st to end	Night	14% 12% 4 7% 5% 4 4 3 4 5% 36%	8402
February	1st to 10th	Night	14% 11% 3 8% 6% 4 4 4 5% 5% 35%	2730
	11th to 20th	Night	15% 9% 4 7% 5% 4 3 4 4 6% 39%	2582
	21st to end	Night	15% 10% 3 7% 4 3 3 2 5% 4 43%	2076
March	1st to 10th	Night	18% 12% 3 5% 3 3 2 2 3 4 44%	5179
	11th to 20th	Night	12% 8% 2 4 3 3 3 3 5% 5% 51%	5090
	21st to end	Night	15% 12% 4 8% 5% 4 4 3 4 6% 35%	5458
April	1st to 10th	Night	12% 8% 3 6% 4 4 3 3 4 6% 46%	2100
	11th to 20th	Night	13% 9% 3 5% 3 3 4 3 5% 7% 45%	2075
	21st to end	Night	18% 8% 3 5% 4 3 4 4 4 7% 41%	2100
May	1st to 10th	Night	17% 9% 3 6% 4 4 4 3 5% 7% 37%	5501
	11th to 20th	Night	11% 7% 2 6% 4 3 4 4 5% 9% 45%	4830
	21st to end	Night	16% 7% 3 7% 4 4 4 4 6% 7% 36%	5139
June	1st to 10th	Night	8% 4 2 4 3 4 4 4 6% 8% 51%	1680
	11th to 20th	Night	6% 5% 2 6% 4 3 4 5% 6% 11% 49%	1680
	21st to end	Night	5% 3 1 4 3 4 4 4 7% 10% 55%	1680
July	1st to 10th	Night	8% 5% 2 6% 4 4 4 3 5% 10% 49%	4708
	11th to 20th	Night	6% 4 2 5% 4 4 4 4 6% 10% 51%	4903
	21st to end	Night	5% 4 2 6% 4 5% 5% 5% 7% 10% 46%	5770
August	1st to 10th	Night	4 3 1 3 3 3 3 4 6% 9% 61%	3016
	11th to 20th	Night	11% 5% 2 5% 3 3 4 3 5% 7% 51%	3100
	21st to end	Night	5% 3 1 3 3 3 4 3 6% 9% 59%	3586
September	1st to 10th	Night	11% 4 2 3 3 3 3 3 4 8% 56%	2000
	11th to 20th	Night	8% 5% 2 5% 4 4 4 3 7% 8% 52%	2000
	21st to end	Night	8% 5% 2 5% 4 4 4 2 5% 7% 55%	2265
October	1st to 10th	Night	8% 4 2 4 3 3 3 3 5% 5% 60%	2400
	11th to 20th	Night	14% 5% 2 5% 3 3 3 2 4 5% 53%	2400
	21st to end	Night	17% 8% 2 5% 3 3 3 3 4 5% 48%	2640
November	1st to 10th	Night	11% 5% 2 5% 3 3 4 2 5% 5% 55%	2582
	11th to 20th	Night	11% 7% 3 7% 4 3 3 3 4 6% 50%	2730
	21st to end	Night	17% 9% 3 6% 4 3 3 3 4 5% 43%	2935
December	1st to 10th	Night	9% 9% 3 6% 4 4 3 3 5% 5% 48%	4720
	11th to 20th	Night	15% 11% 4 7% 3 3 3 3 5% 6% 41%	5339
	21st to end	Night	23% 18% 6% 9% 4 4 3 3 3 4 24%	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	51% 6% 10% 21% 10% 2	4794
	11th to 20th	Day	42% 5% 11% 22% 15% 4	5310
	21st to end	Day	50% 4 10% 16% 16% 3	5812
February	1st to 10th	Day	51% 5% 11% 21% 11% 1	1890
	11th to 20th	Day	46% 5% 11% 20% 14% 4	1932
	21st to end	Day	45% 5% 9% 23% 15% 4	1730
March	1st to 10th	Day	40% 3 7% 22% 24% 4	4925
	11th to 20th	Day	31% 5% 10% 24% 24% 6%	5090
	21st to end	Day	46% 9% 14% 24% 6%	5714
April	1st to 10th	Day	42% 6% 11% 24% 16% 1	2520
	11th to 20th	Day	44% 5% 10% 24% 14% 3	2494
	21st to end	Day	47% 7% 13% 20% 13% 1	2520
May	1st to 10th	Day	43% 9% 14% 21% 13%	7389
	11th to 20th	Day	42% 8% 10% 22% 16% 2	8048
	21st to end	Day	47% 8% 10% 20% 15% 1	9061
June	1st to 10th	Day	31% 10% 16% 27% 15% 2	2940
	11th to 20th	Day	30% 9% 14% 25% 18% 4	2940
	21st to end	Day	30% 9% 16% 25% 16% 4	2940
July	1st to 10th	Day	33% 7% 15% 25% 18% 1	8211
	11th to 20th	Day	31% 9% 17% 25% 16% 2	7991
	21st to end	Day	32% 9% 23% 29% 7% 1	8155
August	1st to 10th	Day	25% 8% 18% 34% 14% 1	4350
	11th to 20th	Day	36% 7% 14% 27% 16% 1	4081
	21st to end	Day	26% 7% 16% 33% 14% 3	4311
September	1st to 10th	Day	32% 6% 12% 24% 21% 5%	2400
	11th to 20th	Day	31% 6% 11% 28% 22% 3	2400
	21st to end	Day	30% 7% 11% 25% 23% 4	2112
October	1st to 10th	Day	20% 3 6% 18% 44% 9%	3260
	11th to 20th	Day	23% 3 6% 21% 38% 9%	3240
	21st to end	Day	35% 4 8% 24% 27% 2	3538
November	1st to 10th	Day	32% 6% 13% 24% 22% 4	1934
	11th to 20th	Day	38% 4 9% 24% 20% 4	1890
	21st to end	Day	45% 4 10% 26% 14% 1	1683
December	1st to 10th	Day	37% 4 14% 30% 15% 1	2690
	11th to 20th	Day	43% 5% 13% 25% 13% 1	3085
	21st to end	Day	66% 5% 11% 11% 6%	4070
January	1st to 10th	Night	52% 4 12% 22% 9%	8113
	11th to 20th	Night	47% 4 8% 23% 15% 3	7680
	21st to end	Night	51% 4 12% 18% 14% 2	8402
February	1st to 10th	Night	50% 6% 11% 20% 12% 2	2730
	11th to 20th	Night	45% 5% 10% 21% 15% 3	2583
	21st to end	Night	43% 3 10% 23% 17% 3	2076
March	1st to 10th	Night	44% 4 7% 21% 21% 3	5179
	11th to 20th	Night	35% 5% 8% 22% 25% 5%	5090
	21st to end	Night	49% 7% 11% 22% 9% 1	5458
April	1st to 10th	Night	38% 6% 11% 25% 18% 3	2100
	11th to 20th	Night	38% 6% 10% 24% 16% 5%	2075
	21st to end	Night	43% 5% 11% 23% 17% 1	2100
May	1st to 10th	Night	44% 8% 14% 21% 12% 1	5531
	11th to 20th	Night	35% 8% 12% 24% 17% 4	4831
	21st to end	Night	44% 9% 12% 17% 17% 1	5149
June	1st to 10th	Night	28% 8% 15% 28% 17% 3	1680
	11th to 20th	Night	28% 8% 12% 27% 23% 3	1680
	21st to end	Night	23% 8% 18% 27% 18% 6%	1680
July	1st to 10th	Night	30% 7% 15% 28% 19% 1	4670
	11th to 20th	Night	26% 9% 16% 29% 18% 2	4858
	21st to end	Night	29% 9% 22% 32% 8%	5641
August	1st to 10th	Night	19% 7% 19% 34% 19% 1	3006
	11th to 20th	Night	32% 6% 14% 27% 18% 3	3127
	21st to end	Night	21% 6% 20% 33% 17% 4	3586
September	1st to 10th	Night	28% 6% 13% 23% 24% 7%	2000
	11th to 20th	Night	29% 7% 11% 25% 23% 5%	2000
	21st to end	Night	29% 5% 9% 25% 27% 4	2265
October	1st to 10th	Night	16% 3 7% 20% 45% 8%	3920
	11th to 20th	Night	23% 3 7% 23% 32% 12%	3899
	21st to end	Night	35% 4 7% 26% 26% 3	4252
November	1st to 10th	Night	32% 5% 12% 27% 19% 6%	2582
	11th to 20th	Night	36% 4 9% 25% 22% 4	2730
	21st to end	Night	44% 4 11% 24% 15% 2	2935
December	1st to 10th	Night	38% 5% 11% 33% 14% 1	4720
	11th to 20th	Night	44% 4 12% 22% 17% 1	5341
	21st to end	Night	65% 5% 12% 12% 5% 1	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% 21% 37% 14% 2	330
	11th to 20th	Day	32% 24% 33% 10% 1	330
	21st to end	Day	22% 24% 40% 12% 2	363
February	1st to 10th	Day	28% 21% 36% 14% 2	330
	11th to 20th	Day	26% 28% 32% 12% 2	330
	21st to end	Day	31% 21% 35% 12% 1	273
March	1st to 10th	Day	22% 25% 42% 11% 1	330
	11th to 20th	Day	30% 19% 35% 14% 2	330
	21st to end	Day	32% 23% 33% 11% 2	415
April	1st to 10th	Day	24% 17% 36% 17% 5% 1	540
	11th to 20th	Day	27% 20% 31% 17% 5%	532
	21st to end	Day	26% 15% 36% 19% 4 1	540
May	1st to 10th	Day	19% 16% 37% 22% 5% 1	656
	11th to 20th	Day	19% 13% 29% 26% 11% 2	775
	21st to end	Day	15% 11% 32% 25% 11% 4	844
June	1st to 10th	Day	10% 7% 26% 35% 17% 6%	780
	11th to 20th	Day	10% 6% 27% 39% 15% 3	780
	21st to end	Day	8% 9% 32% 35% 13% 3	780
July	1st to 10th	Day	11% 4 18% 32% 28% 8%	771
	11th to 20th	Day	7% 5% 23% 35% 25% 5%	768
	21st to end	Day	8% 4 19% 36% 27% 5%	849
August	1st to 10th	Day	9% 3 20% 43% 22% 4	776
	11th to 20th	Day	10% 3 22% 35% 25% 6%	632
	21st to end	Day	9% 2 17% 34% 30% 9%	583
September	1st to 10th	Day	10% 5% 17% 33% 28% 6%	530
	11th to 20th	Day	7% 3 19% 34% 27% 10%	530
	21st to end	Day	10% 10% 25% 29% 20% 5%	392
October	1st to 10th	Day	13% 7% 35% 28% 15% 2	330
	11th to 20th	Day	20% 20% 28% 23% 8%	330
	21st to end	Day	32% 21% 29% 17% 2	363
November	1st to 10th	Day	15% 17% 38% 20% 8% 2	330
	11th to 20th	Day	21% 20% 32% 21% 5% 1	330
	21st to end	Day	31% 15% 28% 23% 3	330
December	1st to 10th	Day	19% 21% 37% 15% 6% 2	330
	11th to 20th	Day	23% 20% 36% 17% 3 1	330
	21st to end	Day	25% 27% 34% 13% 1	363
January	1st to 10th	Night	18% 19% 39% 19% 5%	1050
	11th to 20th	Night	21% 21% 36% 18% 4	1050
	21st to end	Night	18% 19% 39% 21% 2	1155
February	1st to 10th	Night	21% 18% 38% 20% 2	1050
	11th to 20th	Night	22% 18% 37% 21% 2	948
	21st to end	Night	23% 19% 38% 17% 2	692
March	1st to 10th	Night	24% 15% 40% 19% 2	707
	11th to 20th	Night	23% 15% 34% 24% 4	630
	21st to end	Night	26% 17% 36% 18% 3	693
April	1st to 10th	Night	16% 18% 40% 22% 4	630
	11th to 20th	Night	19% 16% 34% 24% 6%	623
	21st to end	Night	21% 10% 39% 24% 5%	630
May	1st to 10th	Night	17% 8% 36% 31% 7%	630
	11th to 20th	Night	16% 9% 27% 34% 13% 1	621
	21st to end	Night	13% 7% 29% 32% 17% 2	683
June	1st to 10th	Night	9% 5% 22% 40% 23% 2	630
	11th to 20th	Night	6% 3 27% 42% 20% 1	630
	21st to end	Night	4 3 30% 45% 16% 2	630
July	1st to 10th	Night	10% 3 13% 36% 33% 4	615
	11th to 20th	Night	5% 2 19% 39% 33% 2	612
	21st to end	Night	6% 2 17% 42% 31% 2	690
August	1st to 10th	Night	6% 4 14% 44% 30% 2	627
	11th to 20th	Night	8% 1 15% 40% 33% 2	606
	21st to end	Night	7% 2 14% 40% 35% 3	660
September	1st to 10th	Night	13% 3 18% 37% 25% 5%	600
	11th to 20th	Night	10% 3 16% 39% 28% 5%	600
	21st to end	Night	10% 6% 23% 34% 22% 4	730
October	1st to 10th	Night	9% 6% 28% 32% 21% 4	800
	11th to 20th	Night	16% 12% 35% 27% 10%	800
	21st to end	Night	22% 15% 33% 23% 7%	880
November	1st to 10th	Night	14% 12% 38% 29% 8%	820
	11th to 20th	Night	16% 16% 37% 24% 7%	840
	21st to end	Night	24% 14% 34% 23% 5%	1045
December	1st to 10th	Night	20% 16% 37% 22% 4	1050
	11th to 20th	Night	24% 14% 34% 24% 3	1050
	21st to end	Night	25% 18% 34% 21% 1	1155

Page generated at 2026-08-12 02:37:17. Version ac07

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