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 2025-04-11.

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 6% 4 4 4 3 5% 7% 43%	113588
	Night	13% 9% 3 7% 4 4 4 3 5% 6% 44%	114885
Transparency	Day	38% 7% 12% 24% 17% 3	117227
	Night	39% 6% 11% 23% 18% 3	119388
Seeing	Day	17% 12% 28% 26% 13% 3	16143
	Night	17% 12% 31% 28% 12% 1	26141

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	13% 12% 5% 12% 5% 5% 4 3 5% 6% 31%	3691
	11th to 20th	Day	9% 11% 4 8% 4 7% 5% 3 4 5% 40%	4080
	21st to end	Day	15% 13% 6% 8% 4 3 3 3 4 5% 36%	4488
February	1st to 10th	Day	17% 12% 4 8% 5% 4 4 3 4 7% 33%	1800
	11th to 20th	Day	14% 10% 3 6% 5% 4 3 4 4 6% 39%	1829
	21st to end	Day	15% 11% 3 7% 4 4 3 4 4 5% 40%	1650
March	1st to 10th	Day	16% 10% 3 4 3 2 3 2 3 5% 50%	4818
	11th to 20th	Day	9% 7% 2 5% 3 3 3 3 5% 7% 52%	4980
	21st to end	Day	14% 11% 3 8% 5% 5% 5% 4 6% 8% 33%	5589
April	1st to 10th	Day	13% 9% 2 6% 5% 3 5% 3 5% 6% 43%	2400
	11th to 20th	Day	17% 9% 2 6% 4 3 4 3 5% 6% 42%	2254
	21st to end	Day	21% 7% 3 7% 4 4 4 3 5% 8% 34%	2280
May	1st to 10th	Day	14% 8% 3 7% 5% 5% 5% 4 7% 9% 34%	3945
	11th to 20th	Day	16% 9% 3 7% 4 4 4 3 5% 7% 37%	4303
	21st to end	Day	11% 6% 3 6% 5% 4 5% 4 6% 7% 45%	4824
June	1st to 10th	Day	8% 4 2 5% 4 5% 5% 5% 7% 10% 46%	2660
	11th to 20th	Day	8% 5% 2 5% 4 4 5% 4 6% 9% 48%	2660
	21st to end	Day	6% 4 2 4 5% 5% 5% 4 7% 10% 48%	2660
July	1st to 10th	Day	13% 6% 2 6% 4 4 5% 4 6% 9% 39%	4440
	11th to 20th	Day	5% 4 2 6% 4 4 5% 4 7% 10% 50%	4324
	21st to end	Day	8% 5% 2 5% 4 5% 6% 5% 9% 11% 41%	4465
August	1st to 10th	Day	5% 3 1 4 4 4 5% 5% 8% 10% 50%	4104
	11th to 20th	Day	13% 5% 2 5% 4 4 5% 4 6% 7% 45%	3864
	21st to end	Day	5% 4 2 5% 4 4 4 4 6% 9% 53%	4180
September	1st to 10th	Day	11% 5% 2 5% 4 3 4 3 5% 7% 51%	2280
	11th to 20th	Day	10% 5% 2 5% 4 4 4 3 5% 8% 52%	2280
	21st to end	Day	8% 5% 2 5% 4 4 4 4 5% 7% 52%	2007
October	1st to 10th	Day	11% 5% 2 5% 4 4 4 3 4 5% 55%	1900
	11th to 20th	Day	15% 7% 2 4 3 2 3 3 4 5% 53%	1900
	21st to end	Day	17% 8% 3 5% 3 3 3 2 3 5% 47%	2090
November	1st to 10th	Day	11% 7% 2 4 3 2 3 3 5% 6% 53%	1840
	11th to 20th	Day	14% 8% 2 5% 3 3 3 3 5% 6% 47%	1800
	21st to end	Day	16% 11% 2 6% 3 4 3 2 4 5% 43%	1603
December	1st to 10th	Day	8% 10% 4 6% 4 3 2 3 4 6% 50%	2610
	11th to 20th	Day	12% 9% 5% 8% 4 3 4 3 5% 6% 42%	3008
	21st to end	Day	20% 21% 5% 11% 4 3 4 2 3 4 21%	3982
January	1st to 10th	Night	14% 11% 7% 13% 5% 4 3 3 4 4 31%	6256
	11th to 20th	Night	11% 10% 4 13% 5% 5% 5% 4 4 4 35%	5900
	21st to end	Night	16% 13% 5% 7% 4 3 3 3 4 4 37%	6490
February	1st to 10th	Night	15% 11% 3 8% 6% 4 4 4 5% 5% 34%	2600
	11th to 20th	Night	15% 9% 4 7% 5% 4 3 3 4 5% 39%	2456
	21st to end	Night	15% 10% 3 7% 4 3 3 2 5% 4 43%	1980
March	1st to 10th	Night	18% 12% 3 5% 3 3 2 2 3 4 45%	5065
	11th to 20th	Night	12% 8% 2 4 3 3 3 3 5% 5% 51%	4980
	21st to end	Night	15% 12% 4 9% 5% 4 4 3 4 6% 34%	5340
April	1st to 10th	Night	12% 8% 3 6% 4 4 4 3 4 6% 47%	2000
	11th to 20th	Night	13% 9% 3 5% 4 3 4 3 5% 7% 45%	1881
	21st to end	Night	18% 7% 3 5% 4 3 4 4 5% 7% 40%	1900
May	1st to 10th	Night	16% 9% 2 5% 4 4 3 3 6% 9% 39%	2954
	11th to 20th	Night	13% 9% 3 6% 4 4 4 4 5% 8% 42%	2584
	21st to end	Night	10% 5% 2 5% 3 4 4 4 6% 8% 47%	2743
June	1st to 10th	Night	8% 4 1 4 3 4 4 4 6% 8% 52%	1520
	11th to 20th	Night	5% 5% 2 6% 4 3 4 4 6% 11% 49%	1520
	21st to end	Night	4 3 1 4 3 4 4 4 7% 10% 56%	1520
July	1st to 10th	Night	11% 6% 2 6% 4 4 4 3 5% 10% 44%	2530
	11th to 20th	Night	4 3 1 3 3 3 4 4 6% 11% 59%	2642
	21st to end	Night	5% 5% 2 6% 4 5% 5% 5% 7% 10% 46%	3098
August	1st to 10th	Night	4 3 1 3 3 3 3 4 6% 9% 61%	2836
	11th to 20th	Night	11% 6% 2 5% 4 3 4 3 5% 7% 51%	2969
	21st to end	Night	5% 3 1 4 3 3 4 3 6% 9% 59%	3476
September	1st to 10th	Night	11% 4 2 3 3 2 3 3 3 8% 57%	1900
	11th to 20th	Night	8% 5% 2 5% 4 3 4 3 7% 7% 52%	1900
	21st to end	Night	7% 5% 2 5% 4 4 4 3 5% 7% 55%	2151
October	1st to 10th	Night	8% 4 2 4 3 3 3 3 5% 5% 60%	2280
	11th to 20th	Night	14% 6% 2 5% 3 3 3 2 4 5% 53%	2280
	21st to end	Night	16% 9% 2 5% 3 3 3 3 4 5% 48%	2508
November	1st to 10th	Night	11% 5% 2 5% 3 3 3 2 4 5% 56%	2456
	11th to 20th	Night	12% 7% 3 7% 4 3 3 3 4 6% 49%	2600
	21st to end	Night	16% 9% 2 6% 4 3 3 3 4 5% 44%	2795
December	1st to 10th	Night	9% 9% 3 6% 4 4 3 3 5% 5% 49%	4580
	11th to 20th	Night	15% 11% 4 7% 3 3 3 3 5% 6% 41%	5199
	21st to end	Night	23% 18% 6% 9% 4 4 3 3 3 4 23%	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	53% 6% 10% 18% 10% 2	3692
	11th to 20th	Day	45% 5% 11% 20% 14% 4	4080
	21st to end	Day	51% 4 9% 14% 18% 3	4488
February	1st to 10th	Day	53% 5% 11% 20% 11% 1	1800
	11th to 20th	Day	46% 5% 11% 19% 15% 3	1838
	21st to end	Day	45% 4 9% 23% 15% 4	1650
March	1st to 10th	Day	39% 4 7% 23% 24% 4	4818
	11th to 20th	Day	31% 5% 10% 24% 24% 6%	4980
	21st to end	Day	47% 9% 15% 23% 6%	5591
April	1st to 10th	Day	42% 6% 10% 24% 16% 1	2400
	11th to 20th	Day	43% 5% 10% 24% 15% 3	2254
	21st to end	Day	48% 6% 13% 19% 13% 1	2280
May	1st to 10th	Day	43% 10% 15% 20% 11% 1	3980
	11th to 20th	Day	45% 8% 11% 23% 12% 1	4307
	21st to end	Day	36% 9% 11% 24% 19% 1	4837
June	1st to 10th	Day	30% 10% 16% 28% 15% 2	2660
	11th to 20th	Day	30% 9% 14% 25% 18% 4	2660
	21st to end	Day	28% 10% 17% 25% 16% 4	2660
July	1st to 10th	Day	40% 7% 13% 23% 14% 2	4371
	11th to 20th	Day	28% 8% 14% 31% 17% 2	4249
	21st to end	Day	32% 11% 20% 25% 11% 1	4325
August	1st to 10th	Day	25% 8% 18% 35% 14% 1	4090
	11th to 20th	Day	37% 7% 13% 25% 16% 1	3903
	21st to end	Day	26% 8% 16% 33% 13% 3	4179
September	1st to 10th	Day	32% 6% 11% 24% 21% 5%	2280
	11th to 20th	Day	31% 6% 10% 27% 22% 3	2280
	21st to end	Day	30% 7% 11% 26% 23% 3	2007
October	1st to 10th	Day	19% 3 6% 18% 44% 9%	3160
	11th to 20th	Day	23% 3 6% 21% 38% 9%	3140
	21st to end	Day	35% 4 8% 24% 27% 2	3428
November	1st to 10th	Day	32% 5% 13% 23% 22% 5%	1840
	11th to 20th	Day	38% 5% 9% 23% 21% 4	1800
	21st to end	Day	44% 5% 10% 27% 14% 1	1603
December	1st to 10th	Day	36% 4 14% 30% 16% 1	2610
	11th to 20th	Day	43% 5% 13% 24% 13% 1	3005
	21st to end	Day	67% 5% 10% 11% 6%	3982
January	1st to 10th	Night	57% 4 10% 20% 9% 1	6256
	11th to 20th	Night	53% 5% 8% 20% 12% 3	5900
	21st to end	Night	51% 4 10% 18% 15% 2	6490
February	1st to 10th	Night	51% 6% 10% 18% 12% 2	2600
	11th to 20th	Night	46% 5% 11% 20% 15% 3	2457
	21st to end	Night	44% 4 10% 23% 16% 3	1980
March	1st to 10th	Night	44% 4 7% 21% 21% 3	5065
	11th to 20th	Night	35% 5% 8% 22% 25% 5%	4980
	21st to end	Night	50% 7% 11% 22% 9% 1	5340
April	1st to 10th	Night	38% 5% 11% 25% 18% 3	2000
	11th to 20th	Night	38% 6% 9% 24% 17% 5%	1881
	21st to end	Night	43% 6% 10% 22% 17% 1	1900
May	1st to 10th	Night	39% 10% 18% 18% 14% 1	2984
	11th to 20th	Night	39% 10% 13% 26% 11% 1	2585
	21st to end	Night	31% 11% 16% 20% 21% 2	2751
June	1st to 10th	Night	27% 9% 16% 28% 18% 3	1520
	11th to 20th	Night	27% 8% 11% 27% 23% 3	1520
	21st to end	Night	22% 8% 18% 27% 19% 7%	1520
July	1st to 10th	Night	36% 7% 11% 29% 15% 2	2490
	11th to 20th	Night	18% 7% 15% 38% 20% 2	2594
	21st to end	Night	30% 9% 20% 27% 13% 1	2999
August	1st to 10th	Night	19% 7% 19% 34% 19% 1	2826
	11th to 20th	Night	33% 6% 13% 27% 18% 3	2996
	21st to end	Night	21% 7% 20% 33% 16% 4	3476
September	1st to 10th	Night	27% 6% 13% 24% 24% 7%	1900
	11th to 20th	Night	29% 7% 11% 24% 24% 5%	1900
	21st to end	Night	29% 5% 9% 26% 27% 4	2151
October	1st to 10th	Night	16% 3 7% 20% 45% 8%	3800
	11th to 20th	Night	23% 3 7% 22% 33% 12%	3779
	21st to end	Night	34% 4 8% 25% 26% 3	4120
November	1st to 10th	Night	31% 5% 12% 27% 19% 6%	2456
	11th to 20th	Night	37% 4 8% 24% 22% 4	2600
	21st to end	Night	43% 4 11% 24% 16% 2	2795
December	1st to 10th	Night	37% 5% 10% 33% 14% 1	4580
	11th to 20th	Night	44% 4 12% 22% 17% 1	5201
	21st to end	Night	66% 5% 12% 12% 5% 1	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	26% 21% 36% 15% 2	300
	11th to 20th	Day	31% 23% 34% 11% 1	300
	21st to end	Day	21% 23% 40% 13% 2	330
February	1st to 10th	Day	29% 21% 35% 14% 2	300
	11th to 20th	Day	26% 28% 31% 12% 2	300
	21st to end	Day	31% 22% 34% 12% 2	249
March	1st to 10th	Day	21% 23% 44% 11% 1	300
	11th to 20th	Day	29% 19% 35% 15% 2	300
	21st to end	Day	33% 22% 32% 11% 2	380
April	1st to 10th	Day	23% 17% 36% 19% 5% 1	500
	11th to 20th	Day	27% 17% 32% 18% 6%	452
	21st to end	Day	27% 14% 35% 19% 4 1	460
May	1st to 10th	Day	19% 14% 37% 23% 6% 1	565
	11th to 20th	Day	18% 14% 27% 27% 12% 2	675
	21st to end	Day	14% 11% 32% 26% 13% 5%	734
June	1st to 10th	Day	9% 5% 26% 37% 18% 6%	680
	11th to 20th	Day	8% 4 28% 41% 16% 3	680
	21st to end	Day	7% 9% 32% 35% 14% 3	680
July	1st to 10th	Day	12% 4 17% 30% 29% 8%	671
	11th to 20th	Day	7% 5% 22% 36% 26% 4	668
	21st to end	Day	9% 4 19% 35% 28% 5%	739
August	1st to 10th	Day	8% 3 19% 43% 22% 4	676
	11th to 20th	Day	11% 3 22% 34% 23% 6%	566
	21st to end	Day	9% 2 17% 32% 31% 9%	539
September	1st to 10th	Day	11% 5% 17% 32% 28% 7%	490
	11th to 20th	Day	8% 3 20% 35% 25% 9%	490
	21st to end	Day	11% 11% 26% 30% 19% 4	359
October	1st to 10th	Day	14% 8% 35% 26% 15% 3	300
	11th to 20th	Day	20% 20% 28% 24% 7%	300
	21st to end	Day	31% 20% 29% 18% 2	330
November	1st to 10th	Day	16% 14% 37% 22% 8% 2	300
	11th to 20th	Day	21% 21% 30% 21% 6% 1	300
	21st to end	Day	29% 16% 28% 24% 3	300
December	1st to 10th	Day	18% 22% 36% 16% 6% 2	300
	11th to 20th	Day	23% 20% 36% 17% 3 1	300
	21st to end	Day	26% 28% 32% 13% 1	330
January	1st to 10th	Night	18% 18% 39% 19% 5%	1000
	11th to 20th	Night	21% 21% 36% 19% 4	1000
	21st to end	Night	18% 19% 40% 22% 2	1100
February	1st to 10th	Night	22% 18% 38% 20% 3	1000
	11th to 20th	Night	22% 18% 36% 21% 2	902
	21st to end	Night	23% 19% 38% 17% 2	660
March	1st to 10th	Night	23% 16% 40% 19% 3	673
	11th to 20th	Night	23% 14% 35% 24% 4	600
	21st to end	Night	27% 17% 36% 18% 3	660
April	1st to 10th	Night	16% 18% 40% 23% 4	600
	11th to 20th	Night	18% 16% 34% 25% 7%	565
	21st to end	Night	21% 10% 39% 24% 6%	570
May	1st to 10th	Night	17% 8% 34% 33% 8% 1	570
	11th to 20th	Night	17% 7% 27% 35% 13% 1	561
	21st to end	Night	13% 6% 29% 32% 18% 2	617
June	1st to 10th	Night	8% 4 21% 40% 24% 2	570
	11th to 20th	Night	6% 3 26% 43% 21% 1	570
	21st to end	Night	4 3 29% 45% 16% 2	570
July	1st to 10th	Night	11% 3 14% 36% 31% 5%	555
	11th to 20th	Night	5% 2 19% 40% 33% 2	552
	21st to end	Night	7% 2 16% 41% 32% 2	624
August	1st to 10th	Night	6% 4 13% 44% 32% 2	567
	11th to 20th	Night	8% 1 15% 40% 32% 3	564
	21st to end	Night	7% 1 15% 39% 34% 3	627
September	1st to 10th	Night	12% 3 18% 37% 25% 5%	570
	11th to 20th	Night	10% 3 16% 39% 27% 5%	570
	21st to end	Night	10% 6% 24% 34% 21% 4	693
October	1st to 10th	Night	10% 7% 28% 31% 21% 4	760
	11th to 20th	Night	17% 12% 35% 27% 9%	760
	21st to end	Night	21% 15% 33% 24% 7%	836
November	1st to 10th	Night	13% 11% 37% 29% 9%	780
	11th to 20th	Night	16% 16% 36% 24% 7%	800
	21st to end	Night	22% 14% 35% 23% 5%	995
December	1st to 10th	Night	20% 15% 37% 23% 4 1	1000
	11th to 20th	Night	24% 13% 34% 25% 3	1000
	21st to end	Night	26% 18% 34% 21% 2	1100

Page generated at 2025-04-08 08:17:28. Version ac07

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