Franklin
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Franklin clear sky chart from 2005-11-06 to 2026-07-16.

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% 6% 2 6% 4 4 5% 4 6% 8% 42%	137605
	Night	13% 6% 2 6% 4 4 4 3 5% 7% 44%	135119
Transparency	Day	26% 36% 8% 15% 12% 3	141202
	Night	27% 35% 7% 15% 13% 4	139593
Seeing	Day	16% 11% 25% 25% 16% 6%	17476
	Night	16% 9% 28% 32% 14% 1	27137

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% 5% 2 4 3 3 3 3 4 5% 54%	5171
	11th to 20th	Day	13% 6% 2 4 3 3 3 3 3 4 56%	5280
	21st to end	Day	13% 8% 3 7% 4 4 4 3 4 5% 45%	5780
February	1st to 10th	Day	13% 8% 2 6% 5% 4 5% 4 5% 7% 42%	1890
	11th to 20th	Day	21% 6% 3 4 4 4 4 2 3 6% 43%	1975
	21st to end	Day	18% 7% 3 5% 5% 4 4 4 5% 7% 38%	1730
March	1st to 10th	Day	18% 9% 2 6% 4 4 4 3 5% 6% 39%	4992
	11th to 20th	Day	11% 6% 2 6% 3 3 3 3 4 6% 53%	5090
	21st to end	Day	13% 6% 2 5% 3 4 4 3 5% 7% 47%	5678
April	1st to 10th	Day	12% 5% 2 5% 3 3 3 3 5% 7% 51%	2520
	11th to 20th	Day	10% 5% 1 5% 4 4 4 4 5% 7% 50%	2494
	21st to end	Day	11% 7% 3 6% 5% 4 4 3 6% 7% 44%	2520
May	1st to 10th	Day	13% 6% 3 7% 5% 5% 5% 4 6% 9% 38%	7112
	11th to 20th	Day	15% 7% 2 6% 4 4 4 3 5% 8% 41%	7681
	21st to end	Day	15% 7% 3 7% 4 4 4 4 5% 8% 39%	9045
June	1st to 10th	Day	9% 5% 2 6% 4 5% 6% 4 6% 10% 42%	2940
	11th to 20th	Day	9% 5% 2 6% 5% 5% 5% 5% 7% 11% 41%	2940
	21st to end	Day	7% 5% 2 6% 5% 5% 6% 4 8% 12% 40%	2940
July	1st to 10th	Day	8% 5% 2 6% 5% 5% 6% 6% 9% 12% 37%	6407
	11th to 20th	Day	9% 7% 3 9% 7% 6% 7% 5% 8% 11% 29%	5965
	21st to end	Day	7% 6% 2 7% 6% 6% 7% 6% 8% 12% 33%	6424
August	1st to 10th	Day	16% 9% 4 9% 6% 6% 6% 5% 7% 9% 23%	4234
	11th to 20th	Day	10% 7% 3 8% 5% 5% 6% 5% 8% 10% 33%	3862
	21st to end	Day	6% 4 2 6% 4 5% 6% 5% 8% 10% 43%	4312
September	1st to 10th	Day	13% 6% 2 5% 5% 5% 5% 3 7% 9% 40%	2400
	11th to 20th	Day	14% 7% 3 6% 5% 5% 5% 4 5% 8% 39%	2400
	21st to end	Day	20% 7% 3 7% 5% 5% 4 4 5% 6% 35%	2117
October	1st to 10th	Day	16% 6% 2 5% 4 3 3 3 4 7% 47%	2000
	11th to 20th	Day	14% 6% 2 4 3 3 3 3 5% 5% 52%	2000
	21st to end	Day	12% 5% 2 5% 3 3 3 3 4 5% 53%	2200
November	1st to 10th	Day	13% 6% 2 4 4 4 4 3 4 5% 51%	2023
	11th to 20th	Day	14% 6% 2 5% 3 3 3 3 4 6% 53%	1890
	21st to end	Day	13% 5% 2 4 3 4 4 3 4 5% 53%	1795
December	1st to 10th	Day	12% 5% 2 6% 4 3 4 3 4 5% 52%	2680
	11th to 20th	Day	14% 8% 3 7% 3 4 3 3 4 4 46%	3070
	21st to end	Day	13% 5% 2 6% 4 3 4 3 5% 7% 48%	4048
January	1st to 10th	Night	11% 7% 2 5% 3 3 4 3 5% 6% 51%	7717
	11th to 20th	Night	13% 6% 2 5% 3 3 3 2 4 4 55%	7680
	21st to end	Night	17% 7% 3 6% 3 3 3 2 4 5% 47%	8401
February	1st to 10th	Night	17% 7% 2 5% 4 3 4 3 5% 6% 44%	2730
	11th to 20th	Night	22% 7% 2 5% 3 3 4 3 5% 5% 39%	2530
	21st to end	Night	16% 7% 2 6% 4 3 3 3 4 5% 46%	2076
March	1st to 10th	Night	19% 6% 2 6% 4 4 4 3 4 5% 42%	5078
	11th to 20th	Night	12% 5% 2 5% 5% 4 4 3 4 6% 51%	5090
	21st to end	Night	14% 6% 2 5% 4 3 4 3 4 6% 49%	5495
April	1st to 10th	Night	13% 6% 2 5% 4 4 4 4 5% 7% 46%	2100
	11th to 20th	Night	11% 5% 2 5% 3 3 4 3 4 7% 52%	2075
	21st to end	Night	12% 4 2 7% 3 4 4 3 5% 6% 49%	2100
May	1st to 10th	Night	12% 8% 3 7% 5% 5% 5% 4 7% 9% 35%	5797
	11th to 20th	Night	16% 7% 3 6% 4 4 4 3 5% 7% 43%	5176
	21st to end	Night	19% 8% 3 7% 4 4 4 3 5% 8% 35%	5108
June	1st to 10th	Night	9% 5% 2 6% 5% 5% 5% 4 8% 11% 41%	1680
	11th to 20th	Night	10% 5% 1 8% 4 5% 6% 4 5% 11% 40%	1680
	21st to end	Night	7% 5% 2 5% 5% 5% 5% 5% 7% 10% 43%	1680
July	1st to 10th	Night	8% 6% 3 7% 5% 5% 6% 5% 9% 12% 35%	3765
	11th to 20th	Night	10% 8% 3 8% 6% 6% 7% 5% 8% 11% 27%	4102
	21st to end	Night	12% 7% 3 8% 5% 5% 5% 5% 8% 9% 33%	4427
August	1st to 10th	Night	21% 7% 3 8% 5% 4 5% 5% 6% 9% 28%	2915
	11th to 20th	Night	9% 7% 4 8% 5% 5% 6% 4 6% 10% 38%	3152
	21st to end	Night	7% 5% 2 6% 4 5% 5% 4 8% 9% 45%	3586
September	1st to 10th	Night	11% 6% 2 6% 3 3 4 4 7% 8% 45%	2000
	11th to 20th	Night	13% 7% 2 7% 5% 4 3 4 5% 6% 44%	2000
	21st to end	Night	19% 9% 3 7% 5% 5% 4 3 5% 6% 35%	2280
October	1st to 10th	Night	13% 6% 2 6% 4 3 4 3 5% 6% 49%	2400
	11th to 20th	Night	15% 6% 2 5% 4 4 3 2 3 4 51%	2400
	21st to end	Night	13% 5% 2 4 4 3 3 3 4 5% 53%	2640
November	1st to 10th	Night	15% 6% 2 5% 3 3 3 3 4 4 52%	2493
	11th to 20th	Night	15% 6% 2 5% 3 3 3 3 5% 6% 49%	2730
	21st to end	Night	12% 5% 2 5% 4 4 4 3 5% 6% 50%	2821
December	1st to 10th	Night	11% 5% 2 6% 4 4 4 3 4 6% 52%	4720
	11th to 20th	Night	16% 7% 3 8% 5% 4 4 4 5% 5% 39%	5345
	21st to end	Night	12% 5% 2 5% 4 4 4 3 5% 7% 49%	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	26% 20% 8% 18% 17% 10%	5172
	11th to 20th	Day	26% 20% 2 11% 31% 10%	5280
	21st to end	Day	34% 22% 5% 21% 14% 4	5780
February	1st to 10th	Day	18% 59% 4 10% 8% 2	1890
	11th to 20th	Day	22% 58% 3 7% 8% 3	1984
	21st to end	Day	19% 58% 4 8% 8% 2	1730
March	1st to 10th	Day	38% 28% 5% 10% 12% 7%	4992
	11th to 20th	Day	23% 27% 5% 16% 20% 9%	5090
	21st to end	Day	26% 28% 11% 14% 16% 5%	5678
April	1st to 10th	Day	15% 58% 5% 10% 10% 2	2520
	11th to 20th	Day	14% 59% 5% 12% 7% 2	2494
	21st to end	Day	16% 59% 6% 11% 6% 2	2520
May	1st to 10th	Day	34% 24% 13% 16% 12% 1	7144
	11th to 20th	Day	31% 23% 11% 21% 14%	7685
	21st to end	Day	37% 24% 9% 16% 13% 2	9061
June	1st to 10th	Day	16% 59% 5% 10% 8% 1	2940
	11th to 20th	Day	12% 60% 9% 12% 6% 1	2940
	21st to end	Day	13% 58% 8% 13% 7%	2940
July	1st to 10th	Day	30% 30% 16% 16% 7% 2	6338
	11th to 20th	Day	39% 32% 18% 9% 1	5896
	21st to end	Day	32% 31% 10% 17% 10% 1	6240
August	1st to 10th	Day	41% 38% 10% 10% 1	4221
	11th to 20th	Day	27% 39% 9% 17% 8%	3898
	21st to end	Day	19% 37% 8% 22% 13%	4312
September	1st to 10th	Day	18% 58% 9% 9% 5% 2	2400
	11th to 20th	Day	21% 57% 5% 9% 7% 2	2400
	21st to end	Day	26% 57% 4 10% 3	2117
October	1st to 10th	Day	20% 37% 6% 15% 19% 3	3260
	11th to 20th	Day	12% 35% 3 11% 30% 9%	3240
	21st to end	Day	9% 35% 4 21% 19% 12%	3538
November	1st to 10th	Day	19% 53% 4 14% 9% 2	2023
	11th to 20th	Day	17% 53% 3 11% 13% 4	1890
	21st to end	Day	16% 54% 3 13% 11% 3	1795
December	1st to 10th	Day	23% 34% 4 20% 15% 4	2680
	11th to 20th	Day	31% 31% 8% 13% 12% 4	3066
	21st to end	Day	27% 26% 9% 22% 16%	4048
January	1st to 10th	Night	28% 21% 8% 17% 18% 7%	7718
	11th to 20th	Night	27% 20% 2 14% 28% 8%	7680
	21st to end	Night	34% 22% 4 19% 15% 6%	8401
February	1st to 10th	Night	17% 58% 6% 10% 7% 1	2730
	11th to 20th	Night	22% 58% 3 8% 7% 2	2532
	21st to end	Night	18% 58% 2 11% 7% 4	2076
March	1st to 10th	Night	36% 29% 6% 11% 12% 7%	5078
	11th to 20th	Night	25% 28% 5% 12% 18% 12%	5090
	21st to end	Night	27% 28% 8% 19% 13% 5%	5495
April	1st to 10th	Night	17% 59% 5% 8% 9% 1	2100
	11th to 20th	Night	15% 59% 5% 12% 7% 2	2075
	21st to end	Night	16% 58% 6% 12% 7% 1	2100
May	1st to 10th	Night	36% 24% 13% 17% 8% 1	5827
	11th to 20th	Night	32% 23% 10% 23% 11%	5177
	21st to end	Night	41% 23% 8% 15% 10% 2	5115
June	1st to 10th	Night	16% 60% 7% 8% 8% 2	1680
	11th to 20th	Night	14% 61% 8% 10% 7%	1680
	21st to end	Night	13% 58% 6% 14% 8% 1	1680
July	1st to 10th	Night	31% 32% 14% 16% 7% 1	3726
	11th to 20th	Night	40% 33% 15% 9% 1	4051
	21st to end	Night	36% 28% 10% 14% 13%	4297
August	1st to 10th	Night	40% 37% 11% 10% 2	2904
	11th to 20th	Night	26% 39% 12% 15% 8%	3182
	21st to end	Night	19% 37% 7% 20% 16% 1	3586
September	1st to 10th	Night	16% 58% 11% 9% 5% 1	2000
	11th to 20th	Night	20% 57% 5% 10% 8% 2	2000
	21st to end	Night	26% 57% 7% 7% 3	2280
October	1st to 10th	Night	24% 36% 7% 16% 15% 2	3920
	11th to 20th	Night	14% 35% 2 12% 24% 13%	3899
	21st to end	Night	10% 35% 4 23% 16% 12%	4252
November	1st to 10th	Night	20% 52% 4 10% 11% 2	2493
	11th to 20th	Night	17% 53% 3 9% 11% 6%	2730
	21st to end	Night	16% 54% 3 13% 12% 2	2821
December	1st to 10th	Night	22% 34% 3 18% 17% 6%	4720
	11th to 20th	Night	36% 32% 5% 11% 10% 6%	5348
	21st to end	Night	27% 26% 10% 23% 13% 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	20% 28% 34% 13% 5%	312
	11th to 20th	Day	19% 29% 37% 13% 2	330
	21st to end	Day	22% 22% 40% 13% 2	363
February	1st to 10th	Day	18% 26% 38% 15% 3	330
	11th to 20th	Day	29% 22% 32% 14% 3	463
	21st to end	Day	24% 20% 31% 20% 4	446
March	1st to 10th	Day	22% 20% 32% 20% 5%	540
	11th to 20th	Day	21% 18% 34% 20% 5% 1	540
	21st to end	Day	19% 18% 38% 18% 6% 1	594
April	1st to 10th	Day	19% 17% 35% 20% 8% 1	540
	11th to 20th	Day	14% 17% 33% 23% 11% 3	532
	21st to end	Day	15% 14% 31% 27% 11% 2	540
May	1st to 10th	Day	15% 14% 35% 24% 10% 2	543
	11th to 20th	Day	18% 8% 27% 29% 14% 4	567
	21st to end	Day	19% 5% 22% 29% 19% 7%	617
June	1st to 10th	Day	12% 5% 24% 29% 24% 5%	570
	11th to 20th	Day	10% 6% 20% 32% 22% 9%	570
	21st to end	Day	8% 5% 16% 37% 28% 6%	570
July	1st to 10th	Day	10% 2 11% 33% 32% 13%	565
	11th to 20th	Day	8% 2 12% 34% 32% 13%	544
	21st to end	Day	8% 2 15% 37% 26% 11%	576
August	1st to 10th	Day	14% 4 16% 31% 25% 10%	526
	11th to 20th	Day	13% 4 13% 27% 30% 13%	519
	21st to end	Day	9% 3 13% 32% 27% 15%	583
September	1st to 10th	Day	15% 4 17% 26% 22% 16%	530
	11th to 20th	Day	16% 4 17% 26% 24% 12%	530
	21st to end	Day	25% 9% 18% 25% 18% 6%	530
October	1st to 10th	Day	18% 6% 18% 24% 23% 11%	530
	11th to 20th	Day	16% 11% 25% 28% 17% 3	530
	21st to end	Day	15% 11% 28% 26% 15% 6%	583
November	1st to 10th	Day	16% 9% 29% 30% 13% 4	516
	11th to 20th	Day	18% 15% 29% 26% 10% 2	430
	21st to end	Day	17% 16% 27% 26% 12% 2	335
December	1st to 10th	Day	23% 14% 41% 15% 6% 1	220
	11th to 20th	Day	20% 14% 37% 20% 8%	220
	21st to end	Day	21% 17% 33% 18% 10% 1	242
January	1st to 10th	Night	19% 16% 37% 24% 4	840
	11th to 20th	Night	19% 15% 35% 24% 6%	840
	21st to end	Night	18% 13% 40% 27% 2	924
February	1st to 10th	Night	21% 13% 37% 25% 4	840
	11th to 20th	Night	25% 15% 40% 18% 2	823
	21st to end	Night	20% 16% 38% 23% 3	692
March	1st to 10th	Night	18% 15% 35% 28% 4	840
	11th to 20th	Night	20% 13% 39% 23% 5%	840
	21st to end	Night	19% 12% 40% 25% 4	924
April	1st to 10th	Night	17% 14% 43% 22% 4	840
	11th to 20th	Night	14% 11% 39% 26% 10%	831
	21st to end	Night	14% 8% 35% 36% 6%	840
May	1st to 10th	Night	15% 10% 34% 33% 8%	830
	11th to 20th	Night	16% 6% 27% 41% 10% 1	602
	21st to end	Night	15% 3 19% 44% 19% 1	455
June	1st to 10th	Night	10% 3 20% 46% 21%	420
	11th to 20th	Night	8% 4 22% 43% 21% 2	420
	21st to end	Night	8% 3 16% 47% 25% 1	420
July	1st to 10th	Night	10% 2 12% 48% 26% 2	444
	11th to 20th	Night	7% 2 10% 39% 37% 5%	597
	21st to end	Night	8% 3 16% 40% 31% 2	657
August	1st to 10th	Night	13% 3 11% 40% 29% 4	597
	11th to 20th	Night	12% 3 11% 43% 29% 3	757
	21st to end	Night	11% 2 11% 36% 35% 5%	880
September	1st to 10th	Night	13% 3 13% 37% 29% 5%	800
	11th to 20th	Night	16% 3 14% 33% 29% 5%	800
	21st to end	Night	22% 5% 17% 35% 20% 1	800
October	1st to 10th	Night	15% 4 19% 32% 26% 4	800
	11th to 20th	Night	18% 8% 25% 33% 16% 1	800
	21st to end	Night	16% 7% 26% 32% 16% 3	880
November	1st to 10th	Night	17% 7% 25% 34% 14% 2	820
	11th to 20th	Night	18% 10% 30% 33% 9%	840
	21st to end	Night	14% 11% 30% 33% 11% 1	840
December	1st to 10th	Night	21% 10% 32% 30% 6%	840
	11th to 20th	Night	16% 9% 34% 34% 8%	840
	21st to end	Night	16% 12% 35% 31% 6%	924

Page generated at 2026-07-13 03:14:54. Version ac07

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