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 2026-05-17.

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	13% 8% 3 8% 5% 5% 5% 4 6% 8% 36%	131454
	Night	14% 9% 3 8% 5% 4 4 4 5% 7% 37%	131539
Transparency	Day	45% 4 11% 24% 14% 2	135066
	Night	46% 4 10% 23% 15% 2	136000
Seeing	Day	16% 8% 24% 25% 18% 8%	17550
	Night	18% 6% 26% 32% 16% 2	27433

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% 12% 6% 12% 6% 4 5% 3 5% 8% 24%	4691
	11th to 20th	Day	9% 12% 5% 13% 9% 7% 6% 4 4 5% 27%	4710
	21st to end	Day	17% 13% 6% 12% 7% 6% 5% 3 4 5% 22%	5492
February	1st to 10th	Day	17% 13% 7% 9% 5% 4 4 3 4 6% 28%	2100
	11th to 20th	Day	15% 11% 5% 10% 5% 5% 4 3 5% 6% 30%	2048
	21st to end	Day	16% 12% 4 11% 4 4 3 3 4 6% 33%	1730
March	1st to 10th	Day	19% 13% 5% 7% 4 4 3 3 3 4 34%	4580
	11th to 20th	Day	11% 9% 3 6% 5% 4 5% 3 6% 7% 41%	4938
	21st to end	Day	15% 11% 4 8% 5% 5% 5% 3 6% 7% 32%	5810
April	1st to 10th	Day	15% 10% 3 7% 5% 5% 4 4 5% 7% 34%	2520
	11th to 20th	Day	15% 9% 2 7% 5% 4 5% 4 5% 7% 37%	2494
	21st to end	Day	17% 8% 3 7% 4 4 4 4 5% 8% 36%	2698
May	1st to 10th	Day	19% 8% 3 8% 5% 4 5% 4 6% 8% 29%	5992
	11th to 20th	Day	19% 7% 2 7% 5% 4 4 3 6% 7% 36%	5939
	21st to end	Day	11% 6% 3 8% 5% 5% 6% 5% 8% 8% 34%	6495
June	1st to 10th	Day	11% 6% 3 6% 5% 5% 6% 4 6% 8% 43%	2800
	11th to 20th	Day	9% 6% 2 6% 5% 5% 5% 4 6% 9% 45%	2800
	21st to end	Day	9% 6% 2 6% 5% 5% 5% 4 7% 10% 41%	2800
July	1st to 10th	Day	10% 5% 2 6% 4 4 5% 4 6% 11% 42%	6360
	11th to 20th	Day	8% 5% 2 7% 5% 5% 6% 5% 7% 11% 39%	6360
	21st to end	Day	11% 7% 2 8% 6% 6% 6% 5% 7% 9% 33%	6657
August	1st to 10th	Day	7% 4 2 5% 4 4 6% 4 6% 10% 48%	4234
	11th to 20th	Day	8% 5% 2 6% 4 5% 5% 5% 8% 12% 41%	3985
	21st to end	Day	5% 4 2 5% 4 4 4 4 6% 9% 54%	4312
September	1st to 10th	Day	12% 5% 1 6% 5% 4 5% 4 5% 8% 46%	2360
	11th to 20th	Day	10% 6% 2 4 3 4 4 4 6% 8% 50%	2200
	21st to end	Day	13% 5% 2 5% 4 4 4 3 4 7% 49%	2200
October	1st to 10th	Day	12% 5% 2 6% 4 4 4 2 4 7% 50%	2200
	11th to 20th	Day	12% 6% 2 5% 4 5% 5% 3 6% 6% 46%	2055
	21st to end	Day	18% 9% 3 8% 5% 3 4 3 5% 6% 37%	1980
November	1st to 10th	Day	8% 7% 2 5% 4 3 5% 3 4 7% 52%	1852
	11th to 20th	Day	15% 10% 3 7% 4 4 4 3 6% 6% 38%	1890
	21st to end	Day	18% 11% 4 9% 5% 3 3 2 5% 5% 35%	1890
December	1st to 10th	Day	13% 11% 4 8% 3 4 3 3 4 5% 41%	3020
	11th to 20th	Day	14% 14% 5% 11% 4 6% 5% 4 4 5% 27%	3192
	21st to end	Day	24% 18% 6% 10% 5% 5% 4 3 5% 5% 17%	4070
January	1st to 10th	Night	14% 14% 6% 12% 6% 4 5% 4 5% 6% 25%	8232
	11th to 20th	Night	10% 14% 6% 14% 7% 6% 5% 4 4 5% 24%	8280
	21st to end	Night	17% 11% 4 8% 5% 5% 4 4 5% 6% 31%	8683
February	1st to 10th	Night	19% 10% 5% 10% 6% 4 4 3 5% 5% 28%	2520
	11th to 20th	Night	15% 11% 4 9% 5% 4 4 4 5% 6% 33%	2458
	21st to end	Night	18% 11% 4 10% 5% 3 3 4 5% 6% 31%	2076
March	1st to 10th	Night	19% 13% 3 7% 4 3 3 3 4 5% 38%	5493
	11th to 20th	Night	12% 6% 3 7% 4 4 4 3 5% 7% 47%	5242
	21st to end	Night	16% 9% 3 8% 4 5% 5% 4 4 7% 35%	5405
April	1st to 10th	Night	14% 8% 3 6% 5% 4 4 4 6% 7% 39%	2100
	11th to 20th	Night	14% 8% 3 7% 5% 4 4 3 5% 7% 40%	2075
	21st to end	Night	15% 6% 2 7% 4 5% 4 4 6% 7% 38%	1922
May	1st to 10th	Night	19% 9% 3 7% 6% 4 5% 4 5% 7% 30%	4123
	11th to 20th	Night	16% 7% 2 7% 4 4 4 4 6% 8% 38%	4086
	21st to end	Night	13% 7% 3 7% 5% 4 5% 4 7% 8% 37%	4345
June	1st to 10th	Night	10% 5% 3 6% 4 5% 4 4 5% 8% 47%	1600
	11th to 20th	Night	9% 5% 2 7% 5% 4 5% 4 6% 9% 46%	1600
	21st to end	Night	6% 3 2 5% 4 4 5% 4 7% 10% 49%	1600
July	1st to 10th	Night	8% 6% 2 6% 4 4 5% 4 6% 8% 47%	3618
	11th to 20th	Night	7% 5% 2 6% 5% 4 5% 5% 7% 9% 45%	3617
	21st to end	Night	9% 7% 2 6% 5% 5% 4 5% 8% 10% 40%	4201
August	1st to 10th	Night	8% 5% 2 7% 4 4 4 4 4 7% 51%	2915
	11th to 20th	Night	6% 4 2 6% 4 5% 6% 4 6% 8% 48%	3060
	21st to end	Night	4 3 2 4 4 4 4 4 6% 9% 57%	3586
September	1st to 10th	Night	11% 4 2 6% 4 3 3 4 5% 7% 50%	2020
	11th to 20th	Night	8% 4 1 5% 3 3 4 3 5% 7% 58%	2200
	21st to end	Night	13% 6% 2 6% 4 4 4 2 4 6% 49%	2200
October	1st to 10th	Night	9% 4 2 4 3 3 3 2 5% 6% 57%	2200
	11th to 20th	Night	15% 6% 2 5% 3 4 4 2 5% 6% 48%	2339
	21st to end	Night	17% 8% 3 7% 4 4 4 3 4 6% 40%	2860
November	1st to 10th	Night	11% 7% 3 5% 4 3 4 3 6% 6% 48%	2666
	11th to 20th	Night	14% 9% 3 6% 4 4 4 3 6% 7% 41%	2730
	21st to end	Night	18% 12% 3 9% 5% 4 4 3 5% 5% 32%	2730
December	1st to 10th	Night	16% 10% 4 8% 5% 4 3 3 5% 5% 39%	4380
	11th to 20th	Night	17% 12% 5% 11% 5% 5% 4 3 4 5% 28%	5227
	21st to end	Night	25% 17% 6% 10% 6% 4 4 3 4 4 17%	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	59% 4 11% 20% 6% 1	4692
	11th to 20th	Day	58% 5% 9% 15% 11% 2	4710
	21st to end	Day	65% 3 7% 17% 6% 3	5492
February	1st to 10th	Day	58% 3 9% 19% 10% 1	2100
	11th to 20th	Day	54% 3 10% 22% 10% 1	2058
	21st to end	Day	53% 2 9% 23% 9% 2	1730
March	1st to 10th	Day	55% 3 5% 19% 14% 3	4580
	11th to 20th	Day	42% 3 9% 30% 14% 1	4938
	21st to end	Day	52% 3 13% 20% 10% 2	5812
April	1st to 10th	Day	49% 3 11% 22% 14% 1	2520
	11th to 20th	Day	46% 3 11% 24% 12% 3	2494
	21st to end	Day	47% 3 11% 24% 12% 2	2698
May	1st to 10th	Day	52% 5% 12% 21% 9%	6027
	11th to 20th	Day	49% 3 11% 25% 11%	5943
	21st to end	Day	43% 6% 13% 23% 14% 2	6509
June	1st to 10th	Day	39% 5% 11% 26% 17% 3	2800
	11th to 20th	Day	36% 5% 12% 25% 20% 2	2800
	21st to end	Day	37% 5% 16% 22% 16% 4	2800
July	1st to 10th	Day	35% 5% 11% 28% 19% 2	6291
	11th to 20th	Day	36% 8% 15% 26% 14% 1	6285
	21st to end	Day	43% 8% 14% 21% 12% 2	6467
August	1st to 10th	Day	30% 7% 16% 33% 14% 1	4221
	11th to 20th	Day	33% 6% 13% 32% 14% 1	4024
	21st to end	Day	26% 5% 14% 33% 18% 4	4311
September	1st to 10th	Day	36% 4 10% 28% 18% 4	2360
	11th to 20th	Day	32% 3 10% 30% 21% 3	2200
	21st to end	Day	36% 3 8% 25% 26% 2	2200
October	1st to 10th	Day	23% 3 8% 31% 33% 2	3590
	11th to 20th	Day	31% 4 9% 27% 27% 2	3323
	21st to end	Day	40% 2 9% 24% 24% 1	3180
November	1st to 10th	Day	34% 3 11% 31% 17% 4	1852
	11th to 20th	Day	46% 3 9% 23% 15% 4	1890
	21st to end	Day	53% 2 9% 23% 12% 1	1890
December	1st to 10th	Day	47% 3 9% 27% 13%	3020
	11th to 20th	Day	60% 4 8% 19% 8% 1	3189
	21st to end	Day	70% 3 10% 11% 5%	4070
January	1st to 10th	Night	61% 3 11% 18% 7%	8233
	11th to 20th	Night	62% 3 8% 13% 11% 2	8280
	21st to end	Night	55% 3 10% 22% 9% 1	8683
February	1st to 10th	Night	58% 2 11% 20% 8% 1	2520
	11th to 20th	Night	53% 3 10% 21% 12% 1	2459
	21st to end	Night	54% 3 11% 19% 11% 2	2076
March	1st to 10th	Night	52% 2 6% 26% 12% 3	5493
	11th to 20th	Night	38% 3 10% 28% 20% 1	5242
	21st to end	Night	50% 3 9% 28% 8% 1	5405
April	1st to 10th	Night	44% 3 11% 26% 13% 2	2100
	11th to 20th	Night	44% 3 10% 21% 17% 5%	2075
	21st to end	Night	44% 4 10% 26% 13% 3	1922
May	1st to 10th	Night	54% 4 11% 20% 9% 3	4150
	11th to 20th	Night	44% 4 12% 27% 13% 1	4087
	21st to end	Night	43% 6% 15% 22% 12% 3	4353
June	1st to 10th	Night	35% 4 10% 25% 22% 3	1600
	11th to 20th	Night	35% 4 11% 25% 21% 4	1600
	21st to end	Night	29% 6% 17% 24% 20% 4	1600
July	1st to 10th	Night	33% 7% 11% 27% 19% 4	3580
	11th to 20th	Night	33% 8% 16% 28% 15% 1	3572
	21st to end	Night	37% 7% 15% 26% 13% 3	4078
August	1st to 10th	Night	32% 5% 14% 35% 13% 1	2904
	11th to 20th	Night	32% 6% 13% 31% 18% 1	3087
	21st to end	Night	24% 5% 13% 31% 23% 4	3586
September	1st to 10th	Night	34% 3 10% 26% 20% 6%	2020
	11th to 20th	Night	27% 4 8% 30% 27% 4	2200
	21st to end	Night	37% 3 8% 23% 24% 4	2200
October	1st to 10th	Night	20% 2 7% 24% 43% 3	3590
	11th to 20th	Night	27% 3 7% 25% 35% 3	3810
	21st to end	Night	35% 3 7% 25% 25% 5%	4610
November	1st to 10th	Night	37% 3 8% 26% 22% 3	2666
	11th to 20th	Night	43% 2 8% 25% 18% 3	2730
	21st to end	Night	54% 3 9% 22% 12% 1	2730
December	1st to 10th	Night	48% 3 11% 26% 12%	4380
	11th to 20th	Night	59% 3 10% 18% 10% 1	5229
	21st to end	Night	72% 3 9% 12% 5%	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	22% 15% 30% 25% 7% 1	330
	11th to 20th	Day	20% 19% 34% 22% 4	330
	21st to end	Day	26% 12% 35% 21% 6%	363
February	1st to 10th	Day	23% 11% 38% 22% 7%	330
	11th to 20th	Day	23% 13% 37% 19% 7%	330
	21st to end	Day	24% 10% 40% 20% 5%	273
March	1st to 10th	Day	21% 16% 39% 19% 5%	330
	11th to 20th	Day	26% 11% 36% 19% 6% 1	466
	21st to end	Day	27% 13% 34% 19% 7% 1	594
April	1st to 10th	Day	20% 13% 32% 24% 9% 2	540
	11th to 20th	Day	18% 14% 29% 23% 12% 4	532
	21st to end	Day	20% 9% 37% 22% 9% 3	540
May	1st to 10th	Day	20% 10% 29% 26% 10% 4	543
	11th to 20th	Day	23% 5% 26% 24% 15% 8%	551
	21st to end	Day	13% 4 23% 27% 20% 13%	596
June	1st to 10th	Day	13% 5% 21% 30% 22% 9%	730
	11th to 20th	Day	11% 4 19% 31% 24% 11%	730
	21st to end	Day	11% 3 22% 28% 24% 11%	730
July	1st to 10th	Day	13% 1 10% 28% 27% 21%	721
	11th to 20th	Day	8% 2 14% 34% 28% 14%	718
	21st to end	Day	10% 3 9% 30% 31% 17%	679
August	1st to 10th	Day	9% 2 11% 22% 35% 21%	526
	11th to 20th	Day	13% 2 10% 29% 29% 17%	519
	21st to end	Day	7% 2 9% 26% 35% 21%	583
September	1st to 10th	Day	11% 2 12% 25% 35% 14%	530
	11th to 20th	Day	10% 2 9% 22% 34% 22%	530
	21st to end	Day	15% 5% 18% 24% 24% 14%	530
October	1st to 10th	Day	11% 4 18% 34% 24% 10%	530
	11th to 20th	Day	10% 10% 33% 26% 17% 4	470
	21st to end	Day	26% 9% 34% 23% 7% 1	363
November	1st to 10th	Day	12% 13% 31% 28% 12% 4	330
	11th to 20th	Day	18% 17% 31% 20% 12% 1	330
	21st to end	Day	24% 9% 35% 23% 8% 1	330
December	1st to 10th	Day	18% 15% 36% 23% 5% 2	330
	11th to 20th	Day	19% 11% 38% 25% 6% 1	330
	21st to end	Day	27% 14% 33% 21% 5% 1	363
January	1st to 10th	Night	22% 12% 33% 28% 5%	1050
	11th to 20th	Night	24% 11% 35% 26% 4	1050
	21st to end	Night	21% 10% 37% 29% 4	1035
February	1st to 10th	Night	25% 9% 36% 28% 3	840
	11th to 20th	Night	20% 12% 36% 28% 3	823
	21st to end	Night	25% 10% 37% 26% 2	692
March	1st to 10th	Night	23% 11% 34% 27% 5%	840
	11th to 20th	Night	20% 10% 34% 29% 7%	840
	21st to end	Night	23% 7% 32% 32% 5% 1	844
April	1st to 10th	Night	17% 9% 36% 30% 8%	630
	11th to 20th	Night	17% 7% 34% 30% 11%	623
	21st to end	Night	19% 4 39% 28% 9% 1	630
May	1st to 10th	Night	20% 5% 32% 33% 10% 1	630
	11th to 20th	Night	17% 4 22% 33% 21% 3	609
	21st to end	Night	11% 3 20% 39% 25% 2	650
June	1st to 10th	Night	12% 1 19% 44% 23% 2	600
	11th to 20th	Night	11% 2 15% 44% 26% 2	600
	21st to end	Night	7% 2 16% 41% 32% 3	600
July	1st to 10th	Night	10% 2 5% 38% 37% 9%	585
	11th to 20th	Night	8% 2 9% 41% 34% 6%	582
	21st to end	Night	10% 2 8% 41% 36% 3	657
August	1st to 10th	Night	9% 1 7% 38% 41% 4	597
	11th to 20th	Night	7% 1 9% 39% 39% 5%	594
	21st to end	Night	7% 2 8% 35% 43% 6%	660
September	1st to 10th	Night	13% 1 9% 37% 36% 5%	620
	11th to 20th	Night	9% 1 10% 35% 39% 6%	800
	21st to end	Night	15% 4 15% 35% 26% 3	800
October	1st to 10th	Night	11% 3 19% 38% 25% 5%	800
	11th to 20th	Night	18% 6% 27% 32% 17% 2	800
	21st to end	Night	21% 6% 33% 30% 9% 1	880
November	1st to 10th	Night	14% 8% 29% 35% 14% 2	820
	11th to 20th	Night	18% 11% 33% 29% 9% 1	840
	21st to end	Night	25% 9% 27% 32% 6% 1	840
December	1st to 10th	Night	23% 8% 35% 28% 5%	840
	11th to 20th	Night	25% 7% 32% 29% 7% 1	977
	21st to end	Night	30% 11% 30% 26% 3	1155

Page generated at 2026-05-14 01:59:00. Version ac07

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