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 2025-01-22.

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 7% 5% 4 5% 4 6% 8% 37%	104978
	Night	15% 9% 3 7% 4 4 4 3 5% 6% 38%	104440
Transparency	Day	44% 4 11% 24% 15% 2	108633
	Night	46% 3 10% 23% 16% 2	108925
Seeing	Day	17% 7% 24% 26% 18% 9%	15773
	Night	18% 6% 26% 33% 16% 2	25683

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% 15% 7% 11% 5% 4 5% 3 4 6% 25%	2607
	11th to 20th	Day	15% 12% 4 13% 7% 7% 7% 4 4 4 22%	2610
	21st to end	Day	25% 18% 8% 10% 4 3 3 2 3 5% 18%	2959
February	1st to 10th	Day	17% 13% 7% 9% 5% 4 4 3 4 6% 28%	1900
	11th to 20th	Day	15% 10% 5% 10% 5% 4 4 3 5% 6% 31%	1848
	21st to end	Day	17% 13% 4 10% 4 4 3 3 4 6% 32%	1570
March	1st to 10th	Day	22% 16% 4 7% 4 3 3 3 3 5% 30%	3120
	11th to 20th	Day	13% 8% 3 5% 5% 4 4 3 5% 6% 43%	3374
	21st to end	Day	15% 10% 3 8% 5% 5% 5% 4 6% 7% 32%	3966
April	1st to 10th	Day	14% 10% 3 7% 5% 5% 4 4 5% 8% 35%	2280
	11th to 20th	Day	16% 9% 2 6% 5% 3 5% 4 5% 7% 38%	2254
	21st to end	Day	18% 8% 3 8% 4 4 4 3 5% 7% 35%	2441
May	1st to 10th	Day	19% 8% 3 7% 6% 4 5% 4 6% 9% 29%	4082
	11th to 20th	Day	20% 7% 2 6% 4 3 3 4 5% 7% 38%	4081
	21st to end	Day	9% 6% 3 8% 5% 5% 6% 5% 8% 8% 39%	4524
June	1st to 10th	Day	11% 6% 3 6% 5% 5% 6% 4 6% 8% 42%	2660
	11th to 20th	Day	8% 5% 2 6% 4 5% 5% 4 6% 8% 46%	2660
	21st to end	Day	9% 6% 2 6% 5% 5% 5% 4 7% 10% 41%	2660
July	1st to 10th	Day	13% 6% 2 7% 4 4 5% 4 6% 11% 39%	4440
	11th to 20th	Day	6% 4 2 5% 3 5% 5% 5% 7% 11% 48%	4440
	21st to end	Day	9% 7% 2 8% 6% 5% 6% 5% 8% 11% 34%	4629
August	1st to 10th	Day	8% 4 2 5% 4 4 6% 4 6% 10% 47%	4104
	11th to 20th	Day	8% 5% 2 6% 4 5% 5% 5% 8% 12% 41%	3861
	21st to end	Day	5% 4 2 5% 4 4 4 4 5% 9% 54%	4180
September	1st to 10th	Day	12% 5% 2 6% 5% 4 5% 4 5% 8% 45%	2242
	11th to 20th	Day	10% 6% 2 5% 3 4 4 4 6% 8% 48%	2090
	21st to end	Day	13% 5% 2 5% 4 4 4 3 4 7% 49%	2090
October	1st to 10th	Day	12% 5% 2 6% 4 4 4 2 4 7% 50%	2090
	11th to 20th	Day	12% 6% 2 5% 4 5% 5% 3 6% 6% 46%	1952
	21st to end	Day	18% 9% 3 8% 5% 4 4 3 5% 6% 36%	1881
November	1st to 10th	Day	8% 7% 2 4 4 3 5% 3 4 7% 52%	1762
	11th to 20th	Day	15% 10% 3 7% 4 4 4 3 6% 6% 38%	1800
	21st to end	Day	18% 11% 4 8% 5% 3 3 3 5% 6% 35%	1800
December	1st to 10th	Day	13% 11% 4 8% 3 4 3 3 4 5% 42%	2930
	11th to 20th	Day	14% 14% 6% 11% 4 6% 5% 4 4 5% 27%	3109
	21st to end	Day	24% 18% 6% 10% 5% 5% 4 3 5% 5% 17%	3982
January	1st to 10th	Night	17% 15% 7% 11% 4 4 4 3 5% 5% 25%	4568
	11th to 20th	Night	14% 16% 6% 13% 6% 6% 5% 3 4 5% 21%	4580
	21st to end	Night	25% 17% 5% 8% 4 4 3 3 4 4 24%	4718
February	1st to 10th	Night	20% 10% 5% 10% 6% 4 4 3 5% 5% 28%	2280
	11th to 20th	Night	14% 11% 5% 8% 5% 5% 4 4 5% 6% 33%	2218
	21st to end	Night	19% 11% 4 10% 5% 4 3 4 5% 6% 30%	1884
March	1st to 10th	Night	20% 14% 2 7% 4 3 3 3 4 5% 34%	3733
	11th to 20th	Night	13% 6% 2 6% 3 4 4 3 4 6% 47%	3586
	21st to end	Night	17% 8% 3 8% 4 4 4 3 4 6% 40%	3694
April	1st to 10th	Night	13% 8% 4 6% 5% 4 4 4 6% 7% 39%	1900
	11th to 20th	Night	15% 8% 3 6% 4 4 3 3 5% 7% 41%	1875
	21st to end	Night	16% 6% 2 7% 4 5% 4 4 6% 7% 38%	1739
May	1st to 10th	Night	18% 11% 3 8% 6% 5% 5% 4 5% 7% 29%	2813
	11th to 20th	Night	19% 6% 2 6% 4 3 4 3 5% 7% 41%	2812
	21st to end	Night	9% 5% 2 6% 4 4 5% 4 7% 9% 44%	3029
June	1st to 10th	Night	9% 5% 3 5% 4 5% 4 4 6% 8% 48%	1520
	11th to 20th	Night	9% 5% 2 6% 4 4 5% 4 6% 9% 47%	1520
	21st to end	Night	6% 3 2 5% 4 4 5% 4 7% 10% 49%	1520
July	1st to 10th	Night	9% 6% 3 5% 3 4 4 4 6% 8% 48%	2530
	11th to 20th	Night	6% 3 2 4 3 4 4 4 6% 8% 56%	2530
	21st to end	Night	9% 7% 2 7% 5% 5% 4 4 8% 9% 39%	2926
August	1st to 10th	Night	8% 5% 2 7% 4 4 4 4 4 7% 51%	2825
	11th to 20th	Night	6% 5% 2 6% 4 5% 6% 4 6% 8% 48%	2964
	21st to end	Night	4 3 2 5% 4 4 4 4 6% 9% 57%	3476
September	1st to 10th	Night	11% 4 2 6% 4 3 4 4 5% 7% 49%	1919
	11th to 20th	Night	8% 4 1 5% 3 3 4 3 5% 7% 57%	2090
	21st to end	Night	13% 6% 2 6% 4 4 4 2 4 6% 50%	2090
October	1st to 10th	Night	9% 4 2 5% 3 3 3 2 5% 6% 57%	2090
	11th to 20th	Night	15% 6% 2 5% 3 4 4 2 5% 6% 47%	2222
	21st to end	Night	17% 7% 3 6% 4 4 4 3 4 6% 41%	2717
November	1st to 10th	Night	11% 7% 3 5% 4 3 4 3 5% 6% 48%	2536
	11th to 20th	Night	14% 9% 3 6% 4 4 4 3 6% 7% 40%	2600
	21st to end	Night	18% 12% 3 8% 5% 4 4 3 5% 6% 32%	2600
December	1st to 10th	Night	16% 9% 4 7% 5% 4 3 3 5% 5% 40%	4250
	11th to 20th	Night	17% 12% 5% 11% 5% 5% 4 3 4 5% 28%	5090
	21st to end	Night	25% 17% 6% 10% 6% 4 4 3 4 4 17%	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	61% 3 6% 21% 8%	2608
	11th to 20th	Day	64% 5% 10% 14% 7%	2610
	21st to end	Day	72% 2 7% 16% 3 1	2959
February	1st to 10th	Day	58% 3 8% 18% 11% 1	1900
	11th to 20th	Day	53% 4 10% 23% 10% 1	1858
	21st to end	Day	55% 2 9% 22% 9% 2	1570
March	1st to 10th	Day	59% 3 6% 19% 11% 2	3120
	11th to 20th	Day	42% 3 10% 29% 15% 1	3374
	21st to end	Day	52% 2 13% 23% 8% 1	3966
April	1st to 10th	Day	48% 3 11% 23% 14% 1	2280
	11th to 20th	Day	46% 3 11% 24% 13% 3	2254
	21st to end	Day	49% 3 11% 23% 12% 2	2441
May	1st to 10th	Day	52% 4 13% 24% 7%	4120
	11th to 20th	Day	47% 3 12% 26% 11%	4085
	21st to end	Day	40% 5% 12% 22% 19% 2	4537
June	1st to 10th	Day	39% 5% 11% 26% 16% 3	2660
	11th to 20th	Day	35% 4 12% 26% 21% 2	2660
	21st to end	Day	37% 5% 16% 23% 16% 4	2660
July	1st to 10th	Day	40% 5% 13% 24% 17% 2	4371
	11th to 20th	Day	28% 7% 15% 31% 18% 1	4365
	21st to end	Day	42% 7% 16% 18% 14% 3	4482
August	1st to 10th	Day	30% 7% 16% 32% 14% 1	4091
	11th to 20th	Day	33% 6% 13% 32% 15% 1	3900
	21st to end	Day	27% 5% 14% 32% 18% 4	4179
September	1st to 10th	Day	38% 4 10% 27% 18% 4	2242
	11th to 20th	Day	33% 3 10% 29% 21% 4	2090
	21st to end	Day	36% 3 8% 26% 24% 2	2090
October	1st to 10th	Day	23% 3 8% 31% 33% 2	3480
	11th to 20th	Day	31% 4 9% 27% 27% 2	3220
	21st to end	Day	40% 2 9% 24% 24% 1	3081
November	1st to 10th	Day	34% 3 11% 30% 18% 4	1762
	11th to 20th	Day	46% 3 9% 23% 15% 4	1800
	21st to end	Day	52% 2 9% 23% 13% 1	1800
December	1st to 10th	Day	47% 3 9% 28% 14%	2930
	11th to 20th	Day	60% 4 8% 19% 8% 1	3106
	21st to end	Day	70% 3 10% 12% 5%	3982
January	1st to 10th	Night	62% 2 10% 17% 8%	4568
	11th to 20th	Night	67% 2 9% 14% 7% 1	4580
	21st to end	Night	66% 2 8% 16% 8%	4718
February	1st to 10th	Night	59% 2 11% 19% 8% 1	2280
	11th to 20th	Night	52% 3 10% 21% 13% 1	2219
	21st to end	Night	56% 2 11% 18% 11% 2	1884
March	1st to 10th	Night	55% 2 7% 24% 11% 1	3733
	11th to 20th	Night	38% 3 11% 26% 21% 2	3586
	21st to end	Night	48% 2 10% 30% 9% 1	3694
April	1st to 10th	Night	44% 3 11% 26% 13% 3	1900
	11th to 20th	Night	44% 2 9% 21% 18% 5%	1875
	21st to end	Night	45% 4 10% 24% 14% 3	1739
May	1st to 10th	Night	56% 3 11% 21% 7% 2	2840
	11th to 20th	Night	43% 3 13% 28% 12% 1	2813
	21st to end	Night	35% 5% 15% 25% 16% 4	3037
June	1st to 10th	Night	35% 4 11% 26% 21% 3	1520
	11th to 20th	Night	33% 4 11% 25% 22% 5%	1520
	21st to end	Night	29% 6% 16% 25% 20% 4	1520
July	1st to 10th	Night	34% 5% 10% 27% 18% 5%	2490
	11th to 20th	Night	25% 6% 14% 33% 21% 2	2482
	21st to end	Night	39% 6% 15% 24% 13% 4	2833
August	1st to 10th	Night	33% 5% 14% 34% 13% 1	2814
	11th to 20th	Night	32% 6% 13% 30% 18% 1	2991
	21st to end	Night	25% 5% 13% 30% 23% 4	3476
September	1st to 10th	Night	34% 3 11% 25% 20% 7%	1919
	11th to 20th	Night	27% 4 9% 29% 27% 5%	2090
	21st to end	Night	37% 3 8% 24% 23% 4	2090
October	1st to 10th	Night	20% 2 7% 24% 43% 3	3480
	11th to 20th	Night	27% 3 7% 25% 36% 2	3693
	21st to end	Night	34% 3 7% 25% 25% 5%	4467
November	1st to 10th	Night	38% 3 8% 25% 22% 3	2536
	11th to 20th	Night	44% 2 9% 24% 18% 4	2600
	21st to end	Night	54% 3 9% 22% 12% 1	2600
December	1st to 10th	Night	47% 3 11% 26% 12%	4250
	11th to 20th	Night	59% 3 10% 18% 10% 1	5092
	21st to end	Night	72% 3 9% 12% 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	23% 15% 30% 25% 7% 1	300
	11th to 20th	Day	21% 17% 34% 24% 5%	300
	21st to end	Day	29% 10% 33% 21% 6%	300
February	1st to 10th	Day	24% 11% 38% 21% 7%	270
	11th to 20th	Day	23% 13% 36% 20% 8%	270
	21st to end	Day	27% 8% 40% 21% 4	225
March	1st to 10th	Day	23% 16% 36% 21% 5%	270
	11th to 20th	Day	26% 10% 35% 20% 7% 1	393
	21st to end	Day	28% 12% 33% 18% 8% 1	506
April	1st to 10th	Day	18% 13% 31% 26% 10% 2	460
	11th to 20th	Day	19% 12% 28% 23% 13% 4	452
	21st to end	Day	21% 10% 37% 20% 8% 4	460
May	1st to 10th	Day	21% 10% 27% 27% 11% 5%	463
	11th to 20th	Day	24% 3 24% 24% 15% 8%	487
	21st to end	Day	13% 3 22% 27% 22% 14%	551
June	1st to 10th	Day	13% 4 21% 30% 22% 9%	680
	11th to 20th	Day	11% 3 19% 32% 24% 11%	680
	21st to end	Day	12% 3 23% 28% 24% 11%	680
July	1st to 10th	Day	14% 1 10% 28% 26% 21%	671
	11th to 20th	Day	8% 1 14% 33% 29% 15%	668
	21st to end	Day	10% 2 10% 31% 31% 16%	630
August	1st to 10th	Day	10% 2 10% 23% 36% 20%	486
	11th to 20th	Day	14% 2 10% 30% 29% 15%	479
	21st to end	Day	7% 2 9% 25% 35% 21%	539
September	1st to 10th	Day	12% 2 11% 26% 36% 13%	490
	11th to 20th	Day	10% 2 10% 23% 34% 21%	490
	21st to end	Day	15% 5% 20% 24% 24% 13%	490
October	1st to 10th	Day	11% 4 19% 36% 22% 9%	490
	11th to 20th	Day	10% 10% 35% 26% 15% 4	433
	21st to end	Day	28% 8% 33% 24% 7% 1	330
November	1st to 10th	Day	12% 12% 30% 29% 13% 4	300
	11th to 20th	Day	18% 16% 32% 21% 12% 1	300
	21st to end	Day	23% 8% 36% 23% 9% 1	300
December	1st to 10th	Day	19% 15% 36% 22% 5% 3	300
	11th to 20th	Day	20% 11% 37% 25% 6% 1	300
	21st to end	Day	27% 14% 31% 22% 5% 1	330
January	1st to 10th	Night	22% 12% 33% 28% 5%	1000
	11th to 20th	Night	24% 10% 35% 26% 5%	1000
	21st to end	Night	22% 9% 35% 30% 4	943
February	1st to 10th	Night	26% 8% 35% 28% 3	760
	11th to 20th	Night	19% 12% 37% 29% 3	743
	21st to end	Night	26% 10% 36% 26% 3	628
March	1st to 10th	Night	22% 10% 34% 28% 6%	760
	11th to 20th	Night	20% 9% 34% 29% 7% 1	760
	21st to end	Night	23% 6% 32% 32% 6% 1	764
April	1st to 10th	Night	16% 8% 36% 31% 8%	570
	11th to 20th	Night	18% 5% 32% 31% 13% 1	563
	21st to end	Night	21% 4 39% 27% 8% 1	570
May	1st to 10th	Night	20% 4 30% 34% 11% 1	570
	11th to 20th	Night	18% 3 20% 33% 22% 3	561
	21st to end	Night	10% 3 19% 40% 27% 2	617
June	1st to 10th	Night	11% 1 18% 45% 23% 2	570
	11th to 20th	Night	11% 2 15% 44% 26% 2	570
	21st to end	Night	7% 1 16% 42% 31% 3	570
July	1st to 10th	Night	10% 2 6% 39% 35% 9%	555
	11th to 20th	Night	8% 1 9% 41% 34% 6%	552
	21st to end	Night	10% 2 8% 42% 35% 3	624
August	1st to 10th	Night	10% 1 6% 38% 41% 4	567
	11th to 20th	Night	7% 1 10% 40% 37% 5%	564
	21st to end	Night	7% 2 9% 33% 44% 7%	627
September	1st to 10th	Night	13% 1 9% 36% 36% 5%	589
	11th to 20th	Night	9% 1 10% 35% 39% 6%	760
	21st to end	Night	15% 4 16% 36% 26% 3	760
October	1st to 10th	Night	11% 3 19% 38% 24% 5%	760
	11th to 20th	Night	18% 6% 27% 31% 17% 2	760
	21st to end	Night	21% 5% 33% 31% 10% 1	836
November	1st to 10th	Night	14% 7% 28% 34% 14% 2	780
	11th to 20th	Night	18% 11% 32% 29% 10% 1	800
	21st to end	Night	25% 9% 27% 32% 7% 1	800
December	1st to 10th	Night	23% 8% 35% 28% 6% 1	800
	11th to 20th	Night	25% 6% 32% 29% 7% 1	930
	21st to end	Night	30% 11% 29% 27% 4	1100

Page generated at 2025-01-19 03:06:45. Version ac07

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