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 2025-03-12.

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% 6% 2 6% 4 4 5% 4 6% 8% 43%	108686
	Night	14% 6% 2 6% 4 4 4 3 5% 7% 45%	110338
Transparency	Day	23% 43% 7% 13% 11% 3	112326
	Night	24% 41% 6% 14% 12% 4	114837
Seeing	Day	16% 11% 25% 26% 17% 6%	15646
	Night	16% 8% 28% 32% 14% 1	25437

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	15% 5% 2 4 3 3 3 3 4 4 56%	3982
	11th to 20th	Day	13% 6% 2 5% 3 3 3 3 4 5% 54%	4060
	21st to end	Day	11% 8% 3 7% 5% 4 4 3 4 5% 46%	4466
February	1st to 10th	Day	13% 8% 2 6% 5% 4 5% 4 5% 7% 41%	1800
	11th to 20th	Day	21% 6% 3 3 4 4 4 2 4 6% 44%	1878
	21st to end	Day	17% 7% 3 5% 5% 4 5% 4 5% 8% 39%	1650
March	1st to 10th	Day	21% 10% 2 6% 3 3 4 2 5% 6% 36%	3506
	11th to 20th	Day	11% 5% 2 5% 3 2 3 3 4 6% 55%	3491
	21st to end	Day	18% 7% 2 5% 3 3 4 3 4 7% 43%	3877
April	1st to 10th	Day	13% 5% 2 4 3 3 3 3 5% 7% 52%	2280
	11th to 20th	Day	10% 5% 2 6% 4 4 4 4 5% 7% 49%	2254
	21st to end	Day	12% 7% 3 6% 5% 4 4 3 5% 7% 45%	2280
May	1st to 10th	Day	11% 7% 3 8% 6% 6% 6% 4 7% 9% 34%	3815
	11th to 20th	Day	19% 7% 2 7% 5% 5% 5% 4 6% 8% 33%	4108
	21st to end	Day	8% 5% 2 6% 3 5% 5% 4 6% 10% 47%	4823
June	1st to 10th	Day	10% 5% 2 6% 5% 5% 6% 4 6% 10% 41%	2660
	11th to 20th	Day	8% 5% 2 6% 5% 5% 5% 5% 7% 11% 41%	2660
	21st to end	Day	8% 5% 3 6% 5% 5% 6% 4 7% 12% 39%	2660
July	1st to 10th	Day	7% 4 2 6% 5% 6% 6% 6% 9% 12% 38%	4377
	11th to 20th	Day	11% 7% 3 8% 6% 5% 6% 4 7% 10% 34%	4120
	21st to end	Day	9% 8% 3 8% 6% 6% 6% 6% 7% 9% 30%	4466
August	1st to 10th	Day	16% 9% 4 9% 6% 6% 6% 5% 7% 9% 23%	4104
	11th to 20th	Day	9% 7% 3 8% 5% 5% 6% 6% 8% 10% 34%	3742
	21st to end	Day	6% 4 2 6% 4 5% 6% 5% 8% 10% 42%	4180
September	1st to 10th	Day	13% 6% 2 6% 5% 5% 5% 3 7% 9% 39%	2280
	11th to 20th	Day	13% 7% 3 6% 5% 5% 5% 4 5% 8% 40%	2280
	21st to end	Day	20% 7% 2 7% 5% 5% 4 3 5% 6% 35%	2012
October	1st to 10th	Day	16% 6% 2 5% 4 3 3 3 4 7% 46%	1900
	11th to 20th	Day	14% 6% 2 4 3 3 3 3 4 5% 52%	1900
	21st to end	Day	11% 5% 2 5% 4 4 4 3 4 6% 53%	2090
November	1st to 10th	Day	13% 6% 2 5% 4 4 4 3 4 5% 51%	1925
	11th to 20th	Day	14% 6% 2 5% 3 3 3 3 4 6% 52%	1800
	21st to end	Day	14% 5% 1 4 3 4 4 3 4 5% 53%	1710
December	1st to 10th	Day	11% 5% 2 6% 4 3 3 3 4 5% 53%	2600
	11th to 20th	Day	14% 8% 3 7% 4 4 3 3 4 4 46%	2990
	21st to end	Day	13% 5% 2 6% 4 3 4 3 5% 7% 48%	3960
January	1st to 10th	Night	12% 7% 2 5% 3 3 3 3 4 5% 53%	5958
	11th to 20th	Night	14% 6% 2 5% 3 3 3 2 4 4 53%	5900
	21st to end	Night	15% 7% 3 6% 3 3 3 3 4 5% 48%	6490
February	1st to 10th	Night	17% 7% 2 5% 4 3 4 3 5% 6% 44%	2600
	11th to 20th	Night	22% 7% 3 5% 3 3 4 3 5% 5% 40%	2407
	21st to end	Night	15% 7% 2 5% 4 3 3 3 4 5% 48%	1980
March	1st to 10th	Night	24% 8% 3 7% 4 4 4 3 5% 5% 34%	3564
	11th to 20th	Night	13% 5% 2 5% 4 4 3 3 3 6% 52%	3498
	21st to end	Night	18% 6% 2 5% 3 2 3 3 4 5% 49%	3754
April	1st to 10th	Night	13% 6% 2 5% 4 4 4 3 5% 6% 46%	1900
	11th to 20th	Night	12% 6% 2 6% 4 3 4 3 4 7% 50%	1875
	21st to end	Night	13% 4 2 7% 3 3 4 3 5% 6% 49%	1900
May	1st to 10th	Night	14% 8% 3 8% 5% 5% 5% 3 6% 8% 36%	3108
	11th to 20th	Night	20% 7% 3 6% 4 4 4 4 5% 7% 36%	2782
	21st to end	Night	9% 5% 2 6% 5% 4 4 3 6% 10% 44%	2732
June	1st to 10th	Night	10% 5% 2 6% 5% 4 5% 4 8% 12% 40%	1520
	11th to 20th	Night	10% 5% 1 7% 4 5% 6% 4 5% 12% 41%	1520
	21st to end	Night	7% 6% 2 5% 5% 5% 5% 5% 8% 9% 42%	1520
July	1st to 10th	Night	7% 5% 2 7% 5% 5% 6% 5% 9% 11% 37%	2577
	11th to 20th	Night	10% 7% 3 8% 5% 5% 6% 5% 7% 10% 34%	2840
	21st to end	Night	16% 9% 3 9% 5% 5% 5% 4 6% 8% 29%	3087
August	1st to 10th	Night	20% 7% 3 8% 5% 4 5% 5% 6% 9% 28%	2825
	11th to 20th	Night	8% 7% 3 8% 5% 5% 6% 4 6% 10% 38%	3054
	21st to end	Night	7% 5% 2 5% 4 4 5% 4 8% 9% 45%	3476
September	1st to 10th	Night	11% 6% 2 6% 3 3 4 4 7% 8% 45%	1900
	11th to 20th	Night	13% 6% 2 7% 5% 4 3 4 5% 6% 44%	1900
	21st to end	Night	19% 8% 3 7% 4 5% 4 3 5% 7% 35%	2165
October	1st to 10th	Night	14% 6% 2 6% 4 3 4 4 5% 6% 48%	2280
	11th to 20th	Night	14% 6% 2 5% 4 4 3 3 4 4 52%	2280
	21st to end	Night	13% 5% 2 5% 4 3 3 3 4 6% 54%	2508
November	1st to 10th	Night	15% 6% 2 5% 3 3 3 3 4 5% 51%	2371
	11th to 20th	Night	16% 6% 2 5% 3 3 3 3 5% 6% 49%	2600
	21st to end	Night	12% 5% 2 5% 4 4 3 3 5% 6% 50%	2686
December	1st to 10th	Night	10% 5% 2 6% 4 4 4 3 4 6% 52%	4580
	11th to 20th	Night	16% 7% 3 9% 5% 4 4 4 5% 5% 38%	5205
	21st to end	Night	12% 5% 2 5% 4 4 4 3 5% 7% 48%	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	24% 26% 1 16% 20% 13%	3983
	11th to 20th	Day	24% 26% 3 12% 28% 7%	4060
	21st to end	Day	31% 28% 5% 20% 13% 3	4466
February	1st to 10th	Day	17% 62% 4 10% 6% 1	1800
	11th to 20th	Day	20% 61% 3 7% 7% 3	1887
	21st to end	Day	17% 61% 4 7% 8% 2	1650
March	1st to 10th	Day	38% 39% 6% 6% 7% 5%	3506
	11th to 20th	Day	16% 39% 4 15% 18% 8%	3491
	21st to end	Day	25% 39% 10% 12% 12% 3	3877
April	1st to 10th	Day	13% 64% 3 8% 9% 2	2280
	11th to 20th	Day	13% 65% 4 10% 6% 2	2254
	21st to end	Day	14% 64% 6% 8% 5% 2	2280
May	1st to 10th	Day	31% 41% 11% 12% 4 1	3850
	11th to 20th	Day	31% 40% 8% 16% 5%	4112
	21st to end	Day	18% 40% 11% 17% 12% 2	4837
June	1st to 10th	Day	15% 65% 4 9% 6% 1	2660
	11th to 20th	Day	10% 66% 7% 11% 6% 1	2660
	21st to end	Day	12% 64% 7% 10% 7%	2660
July	1st to 10th	Day	24% 41% 16% 11% 7% 2	4308
	11th to 20th	Day	32% 39% 16% 11% 2	4051
	21st to end	Day	34% 39% 7% 10% 9% 1	4324
August	1st to 10th	Day	40% 39% 10% 10% 2	4091
	11th to 20th	Day	26% 40% 9% 17% 8%	3778
	21st to end	Day	18% 38% 8% 22% 12% 1	4180
September	1st to 10th	Day	17% 61% 9% 7% 5% 2	2280
	11th to 20th	Day	19% 60% 5% 8% 6% 2	2280
	21st to end	Day	24% 59% 3 10% 3	2012
October	1st to 10th	Day	20% 38% 6% 15% 18% 3	3160
	11th to 20th	Day	11% 36% 3 11% 30% 9%	3140
	21st to end	Day	8% 36% 4 21% 19% 11%	3428
November	1st to 10th	Day	18% 55% 4 12% 8% 2	1925
	11th to 20th	Day	17% 56% 3 9% 12% 4	1800
	21st to end	Day	15% 56% 3 12% 11% 2	1710
December	1st to 10th	Day	22% 35% 4 19% 15% 5%	2600
	11th to 20th	Day	31% 32% 8% 13% 12% 4	2986
	21st to end	Day	27% 26% 9% 22% 16%	3960
January	1st to 10th	Night	26% 26% 2 14% 22% 10%	5958
	11th to 20th	Night	25% 25% 2 15% 27% 5%	5900
	21st to end	Night	29% 28% 4 19% 16% 4	6490
February	1st to 10th	Night	16% 61% 6% 10% 6% 1	2600
	11th to 20th	Night	21% 61% 2 7% 7% 2	2409
	21st to end	Night	15% 61% 2 11% 7% 4	1980
March	1st to 10th	Night	40% 40% 5% 8% 6% 2	3564
	11th to 20th	Night	19% 39% 4 11% 18% 10%	3498
	21st to end	Night	24% 39% 4 19% 11% 3	3754
April	1st to 10th	Night	15% 65% 4 6% 9% 1	1900
	11th to 20th	Night	14% 65% 4 9% 6% 2	1875
	21st to end	Night	14% 64% 5% 10% 6% 1	1900
May	1st to 10th	Night	31% 40% 12% 11% 5% 1	3138
	11th to 20th	Night	31% 40% 7% 18% 4	2783
	21st to end	Night	22% 40% 11% 16% 10% 1	2739
June	1st to 10th	Night	14% 66% 7% 8% 5% 1	1520
	11th to 20th	Night	10% 66% 7% 9% 7%	1520
	21st to end	Night	12% 64% 5% 11% 7% 1	1520
July	1st to 10th	Night	25% 43% 13% 13% 4 1	2536
	11th to 20th	Night	33% 39% 14% 12% 2	2786
	21st to end	Night	40% 37% 5% 8% 10%	2988
August	1st to 10th	Night	39% 38% 11% 10% 2	2814
	11th to 20th	Night	25% 40% 12% 16% 8%	3084
	21st to end	Night	18% 37% 7% 20% 16% 1	3476
September	1st to 10th	Night	15% 60% 10% 7% 6% 1	1900
	11th to 20th	Night	18% 60% 4 9% 8% 2	1900
	21st to end	Night	24% 60% 6% 7% 3	2165
October	1st to 10th	Night	24% 37% 7% 16% 14% 2	3800
	11th to 20th	Night	12% 36% 2 12% 24% 13%	3779
	21st to end	Night	9% 36% 4 23% 16% 12%	4120
November	1st to 10th	Night	20% 55% 4 10% 10% 2	2371
	11th to 20th	Night	16% 56% 3 9% 10% 6%	2600
	21st to end	Night	15% 56% 3 12% 11% 2	2686
December	1st to 10th	Night	21% 35% 3 18% 17% 6%	4580
	11th to 20th	Night	36% 32% 5% 11% 10% 6%	5208
	21st to end	Night	27% 26% 10% 22% 13% 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	21% 28% 33% 13% 5%	283
	11th to 20th	Day	19% 28% 37% 14% 2	300
	21st to end	Day	22% 21% 41% 14% 3	330
February	1st to 10th	Day	18% 25% 38% 15% 4	300
	11th to 20th	Day	30% 22% 32% 14% 3	426
	21st to end	Day	23% 20% 33% 21% 4	414
March	1st to 10th	Day	22% 21% 32% 18% 6%	500
	11th to 20th	Day	21% 18% 35% 20% 5% 1	464
	21st to end	Day	20% 18% 35% 19% 6% 2	506
April	1st to 10th	Day	20% 17% 35% 19% 8% 1	460
	11th to 20th	Day	14% 16% 31% 23% 12% 3	452
	21st to end	Day	17% 15% 30% 27% 10% 2	460
May	1st to 10th	Day	14% 14% 33% 26% 11% 2	463
	11th to 20th	Day	19% 7% 26% 29% 15% 5%	487
	21st to end	Day	17% 3 21% 30% 21% 8%	529
June	1st to 10th	Day	12% 4 22% 32% 25% 5%	490
	11th to 20th	Day	10% 6% 18% 32% 24% 10%	490
	21st to end	Day	9% 6% 16% 37% 26% 7%	490
July	1st to 10th	Day	9% 2 10% 33% 31% 14%	485
	11th to 20th	Day	8% 1 12% 35% 32% 12%	484
	21st to end	Day	8% 2 16% 38% 26% 9%	532
August	1st to 10th	Day	14% 3 15% 31% 27% 11%	486
	11th to 20th	Day	13% 3 13% 26% 31% 13%	479
	21st to end	Day	9% 3 11% 32% 28% 17%	539
September	1st to 10th	Day	14% 3 15% 26% 24% 18%	490
	11th to 20th	Day	15% 3 17% 27% 25% 13%	490
	21st to end	Day	24% 9% 18% 24% 18% 6%	490
October	1st to 10th	Day	19% 6% 18% 24% 24% 10%	490
	11th to 20th	Day	15% 8% 26% 29% 18% 3	490
	21st to end	Day	14% 10% 27% 27% 16% 6%	539
November	1st to 10th	Day	17% 8% 28% 30% 14% 4	478
	11th to 20th	Day	18% 15% 29% 26% 11% 2	400
	21st to end	Day	18% 16% 25% 26% 13% 2	310
December	1st to 10th	Day	22% 14% 41% 16% 7% 1	200
	11th to 20th	Day	21% 16% 36% 20% 9% 1	200
	21st to end	Day	21% 14% 34% 18% 11% 1	220
January	1st to 10th	Night	19% 16% 37% 24% 4	800
	11th to 20th	Night	19% 14% 35% 25% 7%	800
	21st to end	Night	18% 13% 40% 28% 2	880
February	1st to 10th	Night	21% 13% 37% 26% 4	800
	11th to 20th	Night	25% 15% 40% 18% 2	783
	21st to end	Night	20% 15% 38% 24% 3	660
March	1st to 10th	Night	17% 15% 36% 28% 5%	800
	11th to 20th	Night	20% 12% 39% 23% 5%	767
	21st to end	Night	20% 11% 38% 27% 5%	836
April	1st to 10th	Night	17% 13% 43% 23% 4	760
	11th to 20th	Night	14% 11% 38% 26% 11%	751
	21st to end	Night	15% 8% 35% 36% 6%	760
May	1st to 10th	Night	15% 10% 32% 34% 8%	751
	11th to 20th	Night	17% 6% 25% 40% 11% 1	544
	21st to end	Night	13% 1 17% 46% 21% 1	411
June	1st to 10th	Night	11% 3 18% 46% 22% 1	380
	11th to 20th	Night	8% 3 19% 45% 23% 2	380
	21st to end	Night	9% 3 16% 48% 24% 1	380
July	1st to 10th	Night	10% 2 12% 47% 26% 3	400
	11th to 20th	Night	7% 1 10% 40% 39% 4	552
	21st to end	Night	8% 3 17% 40% 30% 2	624
August	1st to 10th	Night	12% 2 11% 41% 30% 4	567
	11th to 20th	Night	11% 3 11% 44% 29% 3	719
	21st to end	Night	11% 2 10% 35% 36% 5%	836
September	1st to 10th	Night	13% 3 12% 37% 30% 6%	760
	11th to 20th	Night	15% 3 14% 33% 29% 5%	760
	21st to end	Night	21% 5% 17% 35% 20% 1	760
October	1st to 10th	Night	15% 4 19% 32% 26% 4	760
	11th to 20th	Night	17% 7% 25% 33% 17% 1	760
	21st to end	Night	15% 6% 26% 33% 17% 3	836
November	1st to 10th	Night	17% 7% 24% 35% 14% 3	780
	11th to 20th	Night	19% 9% 29% 34% 10%	800
	21st to end	Night	15% 10% 30% 33% 11% 2	800
December	1st to 10th	Night	21% 11% 33% 30% 7%	800
	11th to 20th	Night	16% 9% 34% 34% 8%	800
	21st to end	Night	17% 12% 33% 31% 7%	880

Page generated at 2025-03-09 08:08:47. Version ac07

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