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 2025-11-03.

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% 3 7% 5% 4 5% 4 6% 8% 40%	126789
	Night	13% 8% 3 7% 4 4 4 3 5% 7% 42%	123293
Transparency	Day	41% 5% 11% 23% 17% 3	130479
	Night	40% 4 10% 23% 19% 4	127674
Seeing	Day	16% 7% 22% 24% 20% 10%	16491
	Night	16% 6% 23% 31% 20% 3	26123

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% 5% 12% 5% 4 4 3 4 5% 32%	3617
	11th to 20th	Day	16% 7% 3 12% 3 3 4 3 4 5% 42%	3812
	21st to end	Day	19% 9% 5% 5% 3 3 3 3 5% 8% 38%	4943
February	1st to 10th	Day	18% 11% 3 8% 5% 4 3 3 4 6% 35%	2000
	11th to 20th	Day	19% 11% 4 8% 5% 3 4 2 4 5% 34%	1948
	21st to end	Day	19% 9% 3 6% 4 4 4 3 4 5% 38%	1650
March	1st to 10th	Day	15% 12% 4 9% 5% 4 4 3 4 5% 35%	4480
	11th to 20th	Day	12% 8% 2 6% 4 4 4 3 4 5% 47%	4745
	21st to end	Day	11% 8% 3 7% 5% 5% 4 4 5% 7% 42%	5798
April	1st to 10th	Day	13% 6% 2 6% 5% 5% 4 3 5% 7% 45%	2400
	11th to 20th	Day	13% 7% 3 6% 5% 4 4 4 5% 7% 44%	2374
	21st to end	Day	13% 8% 2 7% 5% 4 4 4 6% 8% 39%	2426
May	1st to 10th	Day	19% 8% 3 7% 5% 4 5% 5% 7% 9% 28%	5862
	11th to 20th	Day	15% 9% 3 10% 5% 5% 5% 4 6% 7% 31%	5861
	21st to end	Day	15% 8% 3 7% 5% 4 4 4 5% 7% 38%	6433
June	1st to 10th	Day	9% 5% 2 6% 5% 5% 5% 5% 7% 8% 41%	2600
	11th to 20th	Day	5% 4 2 6% 6% 5% 5% 5% 8% 10% 45%	2798
	21st to end	Day	5% 4 2 6% 5% 6% 7% 6% 9% 11% 40%	2800
July	1st to 10th	Day	7% 5% 2 6% 5% 5% 6% 5% 8% 11% 39%	6360
	11th to 20th	Day	7% 5% 2 7% 6% 6% 7% 6% 9% 13% 34%	6222
	21st to end	Day	11% 7% 3 7% 5% 5% 6% 5% 8% 11% 29%	6424
August	1st to 10th	Day	4 3 2 4 5% 5% 5% 4 7% 11% 50%	3987
	11th to 20th	Day	6% 4 2 7% 5% 5% 6% 5% 7% 10% 41%	3849
	21st to end	Day	6% 4 1 5% 4 4 4 4 6% 8% 53%	4312
September	1st to 10th	Day	11% 6% 2 6% 5% 6% 5% 5% 7% 7% 41%	2375
	11th to 20th	Day	12% 6% 2 5% 4 5% 5% 4 6% 7% 44%	2200
	21st to end	Day	11% 5% 2 5% 5% 3 4 3 6% 6% 50%	2200
October	1st to 10th	Day	11% 5% 2 5% 3 3 3 3 4 6% 56%	2200
	11th to 20th	Day	11% 6% 2 5% 3 3 4 2 4 6% 54%	2152
	21st to end	Day	16% 6% 2 5% 4 3 4 3 4 5% 47%	2005
November	1st to 10th	Day	13% 6% 1 4 3 3 3 3 4 6% 55%	1780
	11th to 20th	Day	14% 7% 3 5% 3 4 3 3 6% 6% 47%	1800
	21st to end	Day	14% 8% 3 6% 3 4 4 3 5% 7% 45%	1800
December	1st to 10th	Day	14% 9% 2 7% 3 4 4 3 5% 5% 45%	2930
	11th to 20th	Day	18% 11% 4 9% 5% 4 4 3 4 5% 32%	3373
	21st to end	Day	17% 11% 4 7% 6% 4 5% 4 6% 7% 29%	4273
January	1st to 10th	Night	15% 13% 4 9% 4 3 3 3 4 6% 36%	6348
	11th to 20th	Night	16% 10% 3 9% 4 3 3 2 3 4 43%	6151
	21st to end	Night	18% 11% 4 7% 3 3 3 3 4 5% 39%	6012
February	1st to 10th	Night	19% 9% 4 8% 6% 4 4 3 5% 6% 33%	2400
	11th to 20th	Night	22% 9% 4 7% 4 3 3 3 4 4 36%	2338
	21st to end	Night	22% 9% 3 6% 4 4 3 3 5% 5% 35%	1980
March	1st to 10th	Night	19% 11% 3 7% 4 4 4 3 5% 7% 34%	5373
	11th to 20th	Night	11% 6% 2 6% 4 4 4 4 5% 6% 49%	5213
	21st to end	Night	14% 7% 3 8% 5% 4 4 3 5% 7% 41%	5160
April	1st to 10th	Night	12% 5% 2 7% 4 3 4 4 6% 7% 46%	2000
	11th to 20th	Night	14% 7% 2 4 4 3 4 4 5% 6% 49%	1975
	21st to end	Night	11% 7% 2 7% 5% 4 4 3 5% 9% 43%	1971
May	1st to 10th	Night	13% 10% 3 9% 5% 5% 5% 4 6% 7% 32%	4033
	11th to 20th	Night	13% 9% 3 9% 6% 4 5% 4 6% 7% 33%	4032
	21st to end	Night	13% 7% 3 7% 5% 5% 5% 4 6% 8% 37%	4421
June	1st to 10th	Night	8% 6% 2 5% 5% 4 4 4 7% 8% 45%	1794
	11th to 20th	Night	4 4 2 4 4 3 4 5% 6% 11% 53%	1600
	21st to end	Night	4 3 2 4 5% 5% 3 4 8% 11% 50%	1600
July	1st to 10th	Night	7% 4 2 6% 4 5% 6% 5% 8% 11% 43%	3618
	11th to 20th	Night	6% 4 2 6% 4 5% 6% 5% 8% 15% 39%	3744
	21st to end	Night	7% 7% 3 8% 6% 5% 6% 5% 8% 12% 31%	4427
August	1st to 10th	Night	4 3 1 4 3 3 3 3 5% 9% 61%	3144
	11th to 20th	Night	4 3 2 5% 4 4 5% 4 8% 12% 49%	3200
	21st to end	Night	5% 3 1 5% 4 4 4 4 6% 9% 56%	3586
September	1st to 10th	Night	10% 5% 2 5% 4 4 5% 4 5% 6% 50%	2005
	11th to 20th	Night	9% 5% 2 6% 4 4 4 3 6% 7% 48%	2200
	21st to end	Night	11% 5% 2 4 4 3 3 3 6% 6% 53%	2200
October	1st to 10th	Night	8% 5% 2 4 3 2 3 2 4 6% 62%	2200
	11th to 20th	Night	13% 6% 2 5% 4 3 3 3 5% 6% 52%	2244
	21st to end	Night	14% 7% 2 5% 3 3 3 3 4 6% 49%	2833
November	1st to 10th	Night	12% 6% 2 5% 4 3 3 3 5% 4 53%	2563
	11th to 20th	Night	13% 7% 2 5% 3 3 3 4 6% 8% 48%	2600
	21st to end	Night	15% 8% 2 5% 4 3 3 4 4 6% 46%	2600
December	1st to 10th	Night	17% 10% 3 8% 4 3 3 2 4 5% 41%	4250
	11th to 20th	Night	21% 10% 3 6% 3 3 3 2 4 4 41%	4822
	21st to end	Night	17% 11% 5% 9% 5% 5% 5% 4 5% 5% 29%	6656

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	54% 3 9% 20% 13% 2	3618
	11th to 20th	Day	46% 3 4 22% 24% 1	3812
	21st to end	Day	46% 3 6% 23% 17% 5%	4943
February	1st to 10th	Day	51% 3 8% 21% 15% 3	2000
	11th to 20th	Day	54% 3 5% 20% 14% 4	1958
	21st to end	Day	49% 3 8% 18% 17% 6%	1650
March	1st to 10th	Day	52% 3 5% 14% 17% 9%	4480
	11th to 20th	Day	40% 3 7% 22% 20% 8%	4745
	21st to end	Day	41% 4 9% 28% 17% 1	5800
April	1st to 10th	Day	39% 5% 10% 24% 20% 3	2400
	11th to 20th	Day	41% 4 7% 22% 21% 6%	2374
	21st to end	Day	42% 4 10% 26% 16% 2	2426
May	1st to 10th	Day	50% 6% 14% 20% 9% 1	5897
	11th to 20th	Day	52% 5% 14% 20% 10%	5865
	21st to end	Day	45% 5% 8% 23% 17% 2	6447
June	1st to 10th	Day	38% 6% 12% 24% 18% 2	2600
	11th to 20th	Day	32% 5% 16% 26% 19% 3	2798
	21st to end	Day	33% 8% 16% 22% 16% 4	2800
July	1st to 10th	Day	35% 7% 19% 27% 11% 1	6291
	11th to 20th	Day	38% 8% 23% 24% 6% 1	6147
	21st to end	Day	45% 7% 22% 20% 5% 1	6240
August	1st to 10th	Day	25% 6% 16% 33% 19% 1	3974
	11th to 20th	Day	34% 6% 15% 28% 15% 2	3885
	21st to end	Day	28% 5% 11% 31% 24% 2	4311
September	1st to 10th	Day	39% 6% 11% 21% 18% 5%	2375
	11th to 20th	Day	38% 6% 9% 24% 21% 3	2200
	21st to end	Day	34% 4 10% 25% 22% 5%	2200
October	1st to 10th	Day	21% 3 5% 18% 43% 9%	3590
	11th to 20th	Day	24% 2 6% 24% 29% 15%	3483
	21st to end	Day	31% 3 6% 24% 29% 8%	3217
November	1st to 10th	Day	33% 3 8% 23% 28% 5%	1780
	11th to 20th	Day	37% 3 6% 23% 24% 6%	1800
	21st to end	Day	40% 3 6% 26% 21% 5%	1800
December	1st to 10th	Day	42% 3 5% 28% 21% 2	2930
	11th to 20th	Day	55% 3 7% 19% 13% 3	3370
	21st to end	Day	53% 4 10% 24% 8% 2	4273
January	1st to 10th	Night	50% 3 9% 21% 16% 1	6348
	11th to 20th	Night	47% 2 5% 20% 22% 4	6151
	21st to end	Night	49% 2 4 22% 18% 5%	6012
February	1st to 10th	Night	53% 3 9% 18% 16% 1	2400
	11th to 20th	Night	53% 3 6% 18% 16% 4	2339
	21st to end	Night	51% 3 7% 17% 17% 5%	1980
March	1st to 10th	Night	50% 4 5% 16% 19% 6%	5373
	11th to 20th	Night	36% 4 7% 20% 19% 14%	5213
	21st to end	Night	44% 3 8% 26% 17% 2	5160
April	1st to 10th	Night	36% 4 10% 25% 21% 3	2000
	11th to 20th	Night	36% 3 8% 22% 22% 8%	1975
	21st to end	Night	39% 4 11% 27% 18% 2	1971
May	1st to 10th	Night	49% 5% 14% 20% 11% 1	4060
	11th to 20th	Night	50% 6% 15% 17% 12% 1	4033
	21st to end	Night	43% 6% 13% 24% 14% 1	4429
June	1st to 10th	Night	33% 7% 15% 25% 17% 3	1794
	11th to 20th	Night	25% 5% 17% 32% 18% 3	1600
	21st to end	Night	25% 7% 17% 32% 15% 4	1600
July	1st to 10th	Night	33% 7% 20% 27% 12% 1	3580
	11th to 20th	Night	31% 8% 26% 28% 6% 2	3699
	21st to end	Night	43% 8% 23% 19% 6% 1	4297
August	1st to 10th	Night	20% 6% 12% 39% 22% 1	3133
	11th to 20th	Night	25% 6% 22% 30% 15% 1	3230
	21st to end	Night	24% 6% 12% 32% 24% 3	3586
September	1st to 10th	Night	34% 5% 12% 25% 19% 5%	2005
	11th to 20th	Night	34% 4 11% 22% 26% 2	2200
	21st to end	Night	31% 5% 10% 24% 25% 7%	2200
October	1st to 10th	Night	19% 3 5% 20% 40% 12%	3590
	11th to 20th	Night	22% 2 4 22% 31% 19%	3652
	21st to end	Night	26% 3 6% 25% 29% 11%	4571
November	1st to 10th	Night	35% 3 6% 22% 25% 8%	2563
	11th to 20th	Night	35% 3 6% 22% 28% 7%	2600
	21st to end	Night	40% 3 7% 24% 22% 5%	2600
December	1st to 10th	Night	47% 3 6% 17% 25% 2	4250
	11th to 20th	Night	47% 3 4 23% 20% 3	4824
	21st to end	Night	56% 4 7% 22% 9% 2	6656

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	22% 16% 39% 15% 7%	300
	11th to 20th	Day	26% 18% 37% 15% 3 1	300
	21st to end	Day	21% 13% 45% 18% 3	330
February	1st to 10th	Day	28% 15% 35% 17% 5% 1	300
	11th to 20th	Day	33% 17% 37% 10% 2 1	300
	21st to end	Day	32% 17% 37% 10% 4	249
March	1st to 10th	Day	26% 14% 36% 18% 5%	300
	11th to 20th	Day	25% 15% 34% 18% 7% 1	395
	21st to end	Day	21% 13% 36% 21% 8% 1	550
April	1st to 10th	Day	19% 14% 30% 24% 11% 1	500
	11th to 20th	Day	19% 13% 29% 25% 12% 1	492
	21st to end	Day	20% 11% 29% 24% 13% 4	500
May	1st to 10th	Day	21% 8% 27% 25% 14% 4	503
	11th to 20th	Day	17% 6% 24% 25% 18% 9%	527
	21st to end	Day	14% 5% 19% 26% 22% 15%	573
June	1st to 10th	Day	14% 1 20% 22% 24% 19%	530
	11th to 20th	Day	6% 2 15% 28% 33% 16%	728
	21st to end	Day	7% 2 15% 32% 27% 19%	730
July	1st to 10th	Day	10% 2 10% 27% 31% 20%	721
	11th to 20th	Day	10% 1 9% 24% 33% 23%	658
	21st to end	Day	8% 3 8% 23% 32% 26%	576
August	1st to 10th	Day	8% 1 8% 26% 37% 20%	526
	11th to 20th	Day	11% 1 9% 29% 34% 16%	519
	21st to end	Day	13% 1 6% 22% 35% 23%	583
September	1st to 10th	Day	12% 2 11% 27% 33% 16%	530
	11th to 20th	Day	15% 2 8% 23% 31% 21%	530
	21st to end	Day	16% 5% 15% 26% 27% 12%	530
October	1st to 10th	Day	15% 2 16% 30% 27% 10%	530
	11th to 20th	Day	12% 8% 29% 30% 17% 4	482
	21st to end	Day	24% 7% 31% 27% 9% 2	363
November	1st to 10th	Day	18% 8% 30% 27% 13% 3	306
	11th to 20th	Day	17% 10% 38% 25% 9%	300
	21st to end	Day	20% 10% 35% 19% 14% 3	300
December	1st to 10th	Day	27% 15% 32% 22% 4 1	300
	11th to 20th	Day	21% 14% 37% 19% 9%	300
	21st to end	Day	24% 15% 35% 22% 4	330
January	1st to 10th	Night	22% 13% 32% 28% 5%	1000
	11th to 20th	Night	26% 13% 32% 24% 5%	908
	21st to end	Night	21% 9% 42% 26% 3	880
February	1st to 10th	Night	23% 10% 36% 27% 4	800
	11th to 20th	Night	27% 14% 32% 25% 3	783
	21st to end	Night	28% 13% 35% 23% 2	660
March	1st to 10th	Night	22% 10% 34% 27% 6%	800
	11th to 20th	Night	20% 10% 33% 28% 8% 1	800
	21st to end	Night	19% 9% 34% 29% 9%	754
April	1st to 10th	Night	15% 10% 32% 32% 10%	600
	11th to 20th	Night	16% 10% 32% 32% 9% 2	593
	21st to end	Night	14% 7% 32% 34% 12% 1	600
May	1st to 10th	Night	15% 3 31% 32% 17% 2	600
	11th to 20th	Night	12% 3 23% 35% 22% 4	591
	21st to end	Night	9% 2 15% 38% 30% 5%	650
June	1st to 10th	Night	12% 1 13% 37% 31% 6%	600
	11th to 20th	Night	5% 2 10% 37% 41% 6%	600
	21st to end	Night	4 1 10% 36% 40% 9%	600
July	1st to 10th	Night	9% 1 5% 31% 44% 10%	585
	11th to 20th	Night	9% 1 5% 28% 44% 12%	582
	21st to end	Night	6% 1 6% 27% 50% 9%	657
August	1st to 10th	Night	9% 1 3 27% 50% 10%	597
	11th to 20th	Night	6% 1 7% 40% 39% 8%	594
	21st to end	Night	9% 1 5% 30% 46% 9%	660
September	1st to 10th	Night	11% 2 8% 31% 43% 5%	605
	11th to 20th	Night	12% 1 9% 29% 42% 6%	800
	21st to end	Night	13% 3 13% 32% 35% 5%	800
October	1st to 10th	Night	11% 3 14% 35% 30% 6%	800
	11th to 20th	Night	17% 4 23% 34% 20% 2	800
	21st to end	Night	18% 5% 27% 32% 17% 2	880
November	1st to 10th	Night	14% 6% 23% 38% 17% 3	789
	11th to 20th	Night	16% 8% 31% 32% 12% 1	800
	21st to end	Night	20% 8% 28% 33% 11% 1	800
December	1st to 10th	Night	26% 9% 29% 28% 7% 1	800
	11th to 20th	Night	22% 7% 31% 32% 8% 1	800
	21st to end	Night	26% 9% 31% 28% 5%	955

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