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 2025-07-06.

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% 9% 3 8% 5% 5% 5% 4 6% 8% 37%	119843
	Night	13% 9% 4 8% 5% 4 4 3 5% 7% 38%	119162
Transparency	Day	42% 7% 12% 24% 13% 2	123401
	Night	44% 6% 12% 22% 14% 2	123745
Seeing	Day	17% 11% 31% 25% 12% 4	16769
	Night	18% 10% 30% 28% 13% 1	26655

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	9% 11% 6% 12% 6% 5% 6% 4 6% 7% 28%	3617
	11th to 20th	Day	8% 10% 6% 11% 5% 5% 5% 5% 7% 7% 31%	3620
	21st to end	Day	13% 16% 7% 8% 4 3 3 3 4 6% 33%	4000
February	1st to 10th	Day	11% 14% 6% 10% 5% 4 5% 4 6% 8% 28%	1820
	11th to 20th	Day	12% 11% 4 8% 5% 5% 5% 3 5% 6% 35%	1948
	21st to end	Day	11% 13% 5% 12% 5% 4 5% 4 5% 6% 30%	1650
March	1st to 10th	Day	13% 9% 3 7% 4 4 4 3 5% 6% 42%	4480
	11th to 20th	Day	10% 6% 3 8% 5% 5% 5% 4 5% 7% 41%	4666
	21st to end	Day	18% 12% 5% 11% 6% 5% 5% 4 5% 5% 25%	5967
April	1st to 10th	Day	16% 13% 4 8% 4 5% 5% 5% 5% 5% 30%	2400
	11th to 20th	Day	15% 9% 3 7% 5% 5% 5% 4 6% 6% 35%	2374
	21st to end	Day	16% 9% 3 7% 5% 4 5% 4 5% 7% 35%	2540
May	1st to 10th	Day	14% 9% 3 7% 4 4 5% 4 6% 7% 37%	5862
	11th to 20th	Day	13% 7% 3 7% 5% 5% 5% 5% 7% 8% 37%	6266
	21st to end	Day	14% 6% 2 5% 4 4 5% 4 6% 9% 41%	6935
June	1st to 10th	Day	9% 6% 2 6% 5% 4 4 5% 6% 8% 46%	2800
	11th to 20th	Day	10% 6% 2 5% 4 4 5% 3 6% 9% 45%	2800
	21st to end	Day	8% 7% 3 6% 5% 5% 5% 4 7% 9% 41%	2800
July	1st to 10th	Day	11% 7% 3 7% 5% 5% 5% 4 7% 10% 37%	4511
	11th to 20th	Day	5% 3 1 5% 4 4 5% 5% 8% 11% 50%	4440
	21st to end	Day	6% 6% 2 6% 5% 5% 5% 5% 6% 9% 45%	4813
August	1st to 10th	Day	9% 6% 2 6% 4 4 5% 5% 7% 9% 42%	4370
	11th to 20th	Day	9% 4 2 6% 4 5% 5% 4 7% 9% 46%	3822
	21st to end	Day	7% 6% 3 7% 5% 4 4 4 6% 8% 46%	4180
September	1st to 10th	Day	10% 5% 3 6% 3 4 4 4 7% 8% 45%	2280
	11th to 20th	Day	10% 5% 2 5% 4 4 5% 3 5% 8% 50%	2157
	21st to end	Day	11% 6% 2 7% 5% 5% 4 4 6% 9% 41%	2090
October	1st to 10th	Day	12% 7% 3 6% 4 4 3 3 6% 7% 45%	2037
	11th to 20th	Day	17% 8% 3 8% 5% 5% 5% 3 6% 6% 33%	1865
	21st to end	Day	16% 10% 3 7% 5% 4 5% 3 5% 6% 35%	1881
November	1st to 10th	Day	11% 9% 3 7% 5% 4 4 4 5% 7% 41%	1762
	11th to 20th	Day	12% 12% 3 10% 6% 5% 5% 4 6% 7% 30%	1800
	21st to end	Day	18% 11% 3 6% 5% 4 4 3 3 6% 37%	1690
December	1st to 10th	Day	8% 9% 3 8% 6% 5% 5% 4 7% 8% 36%	2610
	11th to 20th	Day	12% 14% 4 11% 5% 5% 6% 5% 7% 8% 24%	3008
	21st to end	Day	21% 20% 7% 12% 5% 5% 4 3 4 4 15%	3982
January	1st to 10th	Night	10% 12% 6% 11% 6% 5% 4 3 5% 5% 34%	6348
	11th to 20th	Night	11% 13% 5% 13% 7% 5% 6% 5% 6% 6% 23%	6360
	21st to end	Night	14% 15% 6% 9% 4 4 3 3 5% 6% 32%	6974
February	1st to 10th	Night	12% 14% 4 9% 6% 5% 3 3 5% 6% 31%	2580
	11th to 20th	Night	13% 10% 3 8% 4 4 4 4 5% 7% 38%	2338
	21st to end	Night	18% 11% 3 7% 4 4 4 3 5% 6% 36%	1980
March	1st to 10th	Night	15% 9% 3 6% 4 5% 4 3 4 5% 42%	5373
	11th to 20th	Night	9% 7% 3 5% 4 3 4 4 6% 9% 46%	5320
	21st to end	Night	18% 11% 5% 11% 6% 5% 4 3 4 5% 28%	4962
April	1st to 10th	Night	15% 9% 3 7% 4 5% 5% 4 6% 8% 36%	2000
	11th to 20th	Night	18% 9% 3 7% 4 4 4 4 4 5% 37%	1975
	21st to end	Night	16% 9% 3 6% 4 4 5% 3 6% 6% 38%	1860
May	1st to 10th	Night	17% 8% 3 7% 5% 4 4 4 5% 7% 37%	4033
	11th to 20th	Night	12% 8% 5% 6% 5% 4 5% 4 6% 7% 40%	3643
	21st to end	Night	16% 7% 3 7% 4 3 4 3 4 7% 41%	3942
June	1st to 10th	Night	9% 5% 2 6% 5% 4 5% 4 6% 8% 46%	1600
	11th to 20th	Night	11% 6% 2 6% 5% 4 4 4 6% 9% 43%	1600
	21st to end	Night	9% 7% 3 7% 4 5% 4 4 6% 9% 44%	1600
July	1st to 10th	Night	12% 7% 2 7% 4 5% 5% 4 7% 7% 39%	2570
	11th to 20th	Night	4 3 1 5% 4 3 4 5% 8% 10% 54%	2530
	21st to end	Night	5% 4 2 6% 4 4 5% 5% 8% 9% 48%	2750
August	1st to 10th	Night	9% 5% 2 4 4 4 4 3 6% 9% 50%	2564
	11th to 20th	Night	8% 5% 2 7% 4 4 4 4 5% 8% 49%	3003
	21st to end	Night	7% 4 2 5% 4 5% 4 4 6% 10% 50%	3476
September	1st to 10th	Night	8% 4 2 7% 3 4 4 3 5% 6% 52%	1900
	11th to 20th	Night	10% 4 2 4 4 4 4 3 5% 7% 53%	2003
	21st to end	Night	13% 7% 3 6% 4 3 4 3 4 7% 46%	2090
October	1st to 10th	Night	12% 5% 2 6% 3 4 4 4 5% 6% 48%	2141
	11th to 20th	Night	16% 8% 3 6% 4 3 5% 3 4 6% 42%	2314
	21st to end	Night	19% 7% 2 7% 5% 4 4 3 5% 7% 36%	2717
November	1st to 10th	Night	12% 8% 2 7% 4 4 4 3 4 6% 46%	2536
	11th to 20th	Night	14% 10% 3 7% 6% 5% 5% 4 5% 6% 34%	2600
	21st to end	Night	16% 10% 4 7% 5% 4 4 3 6% 6% 36%	2705
December	1st to 10th	Night	11% 9% 3 7% 4 5% 4 4 5% 7% 41%	4580
	11th to 20th	Night	15% 15% 5% 10% 5% 5% 4 4 5% 6% 27%	5199
	21st to end	Night	20% 19% 6% 10% 6% 4 4 3 5% 5% 18%	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	54% 6% 13% 18% 8%	3618
	11th to 20th	Day	51% 7% 12% 13% 14% 3	3620
	21st to end	Day	53% 5% 9% 21% 13%	4000
February	1st to 10th	Day	53% 7% 13% 16% 9% 1	1820
	11th to 20th	Day	49% 7% 11% 23% 9% 2	1958
	21st to end	Day	53% 7% 10% 18% 10% 2	1650
March	1st to 10th	Day	42% 5% 11% 25% 12% 5%	4480
	11th to 20th	Day	41% 6% 14% 25% 12% 2	4666
	21st to end	Day	58% 7% 12% 14% 7% 1	5969
April	1st to 10th	Day	53% 9% 9% 19% 11%	2400
	11th to 20th	Day	46% 8% 10% 21% 12% 3	2374
	21st to end	Day	48% 7% 14% 18% 12% 1	2540
May	1st to 10th	Day	42% 8% 11% 23% 13% 2	5897
	11th to 20th	Day	40% 10% 13% 24% 13% 1	6270
	21st to end	Day	37% 9% 11% 27% 13% 2	6949
June	1st to 10th	Day	35% 6% 14% 26% 17% 2	2800
	11th to 20th	Day	35% 8% 14% 24% 18% 2	2800
	21st to end	Day	37% 9% 13% 23% 16% 2	2800
July	1st to 10th	Day	40% 8% 12% 25% 12% 2	4442
	11th to 20th	Day	25% 9% 17% 33% 16% 1	4365
	21st to end	Day	33% 9% 16% 21% 18% 3	4662
August	1st to 10th	Day	35% 7% 14% 30% 12% 1	4355
	11th to 20th	Day	31% 9% 13% 35% 11% 1	3861
	21st to end	Day	34% 8% 13% 24% 20% 1	4179
September	1st to 10th	Day	34% 8% 12% 28% 16% 2	2280
	11th to 20th	Day	31% 7% 12% 33% 16% 2	2157
	21st to end	Day	38% 8% 12% 29% 13% 1	2090
October	1st to 10th	Day	24% 4 8% 42% 21% 1	3388
	11th to 20th	Day	35% 7% 10% 28% 19% 1	3081
	21st to end	Day	42% 5% 9% 29% 12% 3	3081
November	1st to 10th	Day	43% 5% 14% 24% 13% 1	1762
	11th to 20th	Day	52% 6% 14% 19% 8% 1	1800
	21st to end	Day	52% 4 14% 24% 7%	1690
December	1st to 10th	Day	43% 6% 23% 21% 6% 1	2610
	11th to 20th	Day	54% 9% 13% 17% 7% 1	3005
	21st to end	Day	71% 5% 7% 12% 5%	3982
January	1st to 10th	Night	52% 5% 11% 21% 11%	6348
	11th to 20th	Night	61% 4 11% 10% 13% 1	6360
	21st to end	Night	54% 5% 15% 17% 10%	6974
February	1st to 10th	Night	52% 7% 12% 17% 11% 2	2580
	11th to 20th	Night	45% 5% 13% 23% 13% 1	2339
	21st to end	Night	49% 5% 11% 21% 11% 3	1980
March	1st to 10th	Night	43% 5% 12% 24% 12% 3	5373
	11th to 20th	Night	34% 5% 13% 31% 14% 3	5320
	21st to end	Night	57% 6% 9% 15% 12% 1	4962
April	1st to 10th	Night	45% 7% 10% 21% 15% 1	2000
	11th to 20th	Night	48% 5% 7% 19% 17% 4	1975
	21st to end	Night	44% 6% 13% 20% 16% 2	1860
May	1st to 10th	Night	45% 6% 12% 18% 16% 2	4060
	11th to 20th	Night	41% 7% 14% 20% 15% 3	3644
	21st to end	Night	43% 5% 9% 23% 14% 5%	3950
June	1st to 10th	Night	33% 8% 11% 28% 18% 2	1600
	11th to 20th	Night	36% 6% 11% 24% 20% 3	1600
	21st to end	Night	37% 7% 12% 25% 16% 3	1600
July	1st to 10th	Night	41% 7% 13% 22% 12% 5%	2530
	11th to 20th	Night	22% 7% 16% 36% 16% 3	2482
	21st to end	Night	30% 8% 15% 20% 24% 3	2662
August	1st to 10th	Night	31% 7% 14% 28% 19% 2	2555
	11th to 20th	Night	32% 6% 12% 34% 16% 1	3030
	21st to end	Night	28% 7% 13% 28% 20% 3	3476
September	1st to 10th	Night	32% 6% 11% 25% 23% 3	1900
	11th to 20th	Night	29% 6% 10% 35% 18% 2	2003
	21st to end	Night	39% 5% 9% 30% 16% 2	2090
October	1st to 10th	Night	25% 4 8% 38% 24% 1	3570
	11th to 20th	Night	36% 5% 11% 24% 22% 1	3837
	21st to end	Night	42% 5% 10% 25% 17% 2	4467
November	1st to 10th	Night	40% 5% 12% 25% 16% 2	2536
	11th to 20th	Night	49% 6% 14% 19% 10% 2	2600
	21st to end	Night	49% 6% 16% 21% 8% 1	2705
December	1st to 10th	Night	42% 6% 18% 25% 7% 3	4580
	11th to 20th	Night	57% 7% 11% 15% 9% 1	5201
	21st to end	Night	67% 5% 10% 13% 5%	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	20% 17% 35% 23% 5%	300
	11th to 20th	Day	20% 22% 33% 19% 4 1	300
	21st to end	Day	25% 13% 37% 17% 8%	330
February	1st to 10th	Day	18% 20% 40% 16% 5%	300
	11th to 20th	Day	21% 26% 34% 16% 3	300
	21st to end	Day	22% 22% 42% 12% 2	249
March	1st to 10th	Day	20% 25% 40% 12% 2	300
	11th to 20th	Day	25% 19% 35% 15% 5% 1	330
	21st to end	Day	27% 13% 32% 20% 6% 2	550
April	1st to 10th	Day	24% 16% 34% 21% 5%	500
	11th to 20th	Day	24% 19% 27% 17% 10% 2	492
	21st to end	Day	26% 12% 30% 21% 10% 1	500
May	1st to 10th	Day	21% 13% 32% 25% 8% 2	503
	11th to 20th	Day	21% 8% 33% 25% 10% 3	698
	21st to end	Day	16% 8% 33% 24% 13% 6%	789
June	1st to 10th	Day	11% 9% 33% 30% 13% 4	730
	11th to 20th	Day	15% 6% 31% 31% 12% 5%	730
	21st to end	Day	13% 7% 33% 31% 13% 3	730
July	1st to 10th	Day	9% 4 26% 32% 21% 9%	697
	11th to 20th	Day	9% 5% 30% 31% 16% 8%	668
	21st to end	Day	6% 3 30% 38% 16% 7%	739
August	1st to 10th	Day	9% 3 26% 32% 20% 10%	649
	11th to 20th	Day	10% 4 22% 27% 23% 13%	479
	21st to end	Day	10% 4 21% 35% 22% 9%	539
September	1st to 10th	Day	13% 5% 26% 29% 22% 7%	490
	11th to 20th	Day	11% 2 23% 31% 21% 12%	490
	21st to end	Day	17% 9% 26% 24% 17% 7%	490
October	1st to 10th	Day	18% 10% 26% 26% 17% 4	437
	11th to 20th	Day	24% 17% 28% 23% 6% 1	300
	21st to end	Day	25% 15% 37% 16% 5% 1	330
November	1st to 10th	Day	17% 15% 40% 20% 7% 2	300
	11th to 20th	Day	20% 20% 39% 15% 7%	300
	21st to end	Day	25% 13% 40% 18% 3 1	300
December	1st to 10th	Day	19% 21% 38% 15% 7% 1	300
	11th to 20th	Day	23% 18% 34% 19% 5% 2	300
	21st to end	Day	29% 19% 33% 14% 4	330
January	1st to 10th	Night	18% 17% 36% 24% 5%	1000
	11th to 20th	Night	21% 16% 35% 21% 7% 1	1000
	21st to end	Night	20% 12% 36% 27% 5%	1100
February	1st to 10th	Night	20% 16% 35% 23% 6%	980
	11th to 20th	Night	19% 16% 36% 25% 5%	783
	21st to end	Night	24% 15% 37% 20% 5%	660
March	1st to 10th	Night	19% 13% 34% 25% 9% 1	800
	11th to 20th	Night	17% 14% 35% 26% 7% 1	790
	21st to end	Night	24% 8% 27% 30% 9% 1	660
April	1st to 10th	Night	21% 11% 34% 27% 7%	600
	11th to 20th	Night	26% 9% 31% 24% 9% 1	593
	21st to end	Night	22% 8% 29% 31% 10% 1	600
May	1st to 10th	Night	19% 9% 29% 34% 9% 1	600
	11th to 20th	Night	19% 5% 29% 31% 15% 1	591
	21st to end	Night	16% 5% 22% 34% 20% 3	650
June	1st to 10th	Night	11% 3 25% 40% 19% 2	600
	11th to 20th	Night	14% 3 32% 32% 19% 1	600
	21st to end	Night	12% 3 25% 40% 19% 2	600
July	1st to 10th	Night	9% 2 18% 38% 30% 4	570
	11th to 20th	Night	7% 2 22% 39% 26% 4	552
	21st to end	Night	7% 1 17% 46% 27% 2	624
August	1st to 10th	Night	9% 1 15% 44% 28% 3	567
	11th to 20th	Night	9% 2 16% 37% 32% 5%	564
	21st to end	Night	8% 2 17% 41% 29% 3	627
September	1st to 10th	Night	10% 3 21% 34% 26% 6%	570
	11th to 20th	Night	12% 4 19% 32% 28% 5%	673
	21st to end	Night	15% 8% 23% 27% 22% 4	760
October	1st to 10th	Night	15% 6% 26% 32% 19% 3	760
	11th to 20th	Night	21% 10% 33% 25% 10%	760
	21st to end	Night	25% 9% 31% 26% 9% 1	836
November	1st to 10th	Night	18% 11% 35% 24% 10% 1	780
	11th to 20th	Night	21% 16% 34% 22% 6% 1	800
	21st to end	Night	22% 13% 36% 22% 6%	905
December	1st to 10th	Night	22% 16% 35% 21% 5%	1000
	11th to 20th	Night	23% 14% 34% 24% 6% 1	1000
	21st to end	Night	29% 13% 34% 20% 3	1100

Page generated at 2025-07-03 00:30:18. Version ac07

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