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 2024-08-30.

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	14% 9% 3 7% 5% 4 5% 4 6% 8% 37%	95468
	Night	15% 9% 3 7% 4 4 4 3 5% 6% 38%	93598
Transparency	Day	46% 4 11% 23% 14% 2	95227
	Night	47% 3 10% 23% 14% 2	93445
Seeing	Day	17% 7% 24% 26% 18% 9%	15290
	Night	18% 6% 25% 33% 16% 2	25077

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% 8% 11% 5% 4 5% 3 4 6% 25%	2527
	11th to 20th	Day	15% 12% 4 13% 7% 7% 7% 4 4 4 22%	2530
	21st to end	Day	25% 18% 8% 10% 5% 3 3 2 3 5% 18%	2951
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 6% 4 5% 6% 5% 7% 10% 44%	2457
	11th to 20th	Day	10% 5% 2 7% 4 5% 5% 5% 8% 10% 40%	2328
	21st to end	Day	6% 4 2 5% 4 4 5% 5% 6% 9% 49%	2485
September	1st to 10th	Day	13% 5% 2 6% 5% 4 5% 4 5% 8% 43%	2124
	11th to 20th	Day	11% 6% 2 5% 3 4 4 4 6% 8% 48%	1980
	21st to end	Day	12% 4 2 5% 4 4 4 3 4 7% 51%	1980
October	1st to 10th	Day	13% 5% 2 6% 4 4 4 2 5% 7% 48%	1980
	11th to 20th	Day	12% 7% 2 6% 4 5% 4 3 6% 6% 45%	1850
	21st to end	Day	19% 9% 3 8% 5% 4 4 4 5% 5% 35%	1782
November	1st to 10th	Day	8% 7% 2 4 4 3 5% 3 4 6% 53%	1672
	11th to 20th	Day	15% 9% 3 7% 4 4 4 3 6% 6% 38%	1710
	21st to end	Day	19% 11% 4 7% 5% 3 3 2 5% 6% 36%	1710
December	1st to 10th	Day	18% 13% 5% 9% 4 5% 4 3 4 6% 29%	1710
	11th to 20th	Day	14% 16% 6% 10% 4 5% 4 4 4 5% 30%	1980
	21st to end	Day	22% 19% 7% 9% 5% 4 4 3 4 5% 18%	2783
January	1st to 10th	Night	17% 15% 7% 11% 4 4 4 3 5% 5% 25%	4428
	11th to 20th	Night	14% 17% 6% 13% 6% 6% 5% 3 4 5% 21%	4440
	21st to end	Night	25% 17% 5% 8% 4 4 3 3 4 4 24%	4703
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	7% 4 2 6% 4 4 5% 5% 6% 8% 50%	1701
	11th to 20th	Night	6% 4 2 5% 4 5% 5% 4 7% 8% 50%	1789
	21st to end	Night	6% 3 2 4 4 4 3 3 6% 9% 55%	2080
September	1st to 10th	Night	12% 5% 2 6% 5% 3 4 4 5% 8% 48%	1818
	11th to 20th	Night	8% 4 1 5% 3 3 4 3 5% 7% 56%	1980
	21st to end	Night	11% 5% 2 6% 4 4 4 2 4 6% 52%	1980
October	1st to 10th	Night	9% 4 2 5% 3 4 3 2 6% 7% 55%	1980
	11th to 20th	Night	16% 6% 2 6% 3 5% 4 2 5% 6% 45%	2104
	21st to end	Night	17% 8% 3 7% 4 4 4 3 4 6% 40%	2574
November	1st to 10th	Night	11% 7% 3 5% 4 3 4 3 5% 6% 48%	2406
	11th to 20th	Night	14% 9% 3 6% 4 4 4 3 5% 7% 41%	2470
	21st to end	Night	18% 12% 3 8% 5% 4 4 3 5% 6% 33%	2470
December	1st to 10th	Night	18% 10% 5% 9% 6% 5% 4 3 5% 5% 31%	2470
	11th to 20th	Night	18% 12% 4 9% 4 4 4 3 4 6% 32%	3212
	21st to end	Night	23% 18% 6% 10% 6% 4 4 3 4 4 18%	4884

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%	2528
	11th to 20th	Day	65% 5% 10% 14% 6%	2530
	21st to end	Day	72% 2 7% 16% 3 1	2951
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	34% 5% 14% 30% 15% 2	2444
	11th to 20th	Day	38% 5% 14% 27% 16% 1	2328
	21st to end	Day	30% 5% 12% 28% 17% 7%	2485
September	1st to 10th	Day	39% 4 10% 27% 16% 4	2124
	11th to 20th	Day	34% 3 10% 28% 20% 3	1980
	21st to end	Day	34% 3 8% 27% 26% 2	1980
October	1st to 10th	Day	37% 3 11% 25% 22% 3	1980
	11th to 20th	Day	39% 2 9% 25% 22% 3	1850
	21st to end	Day	51% 2 9% 23% 14% 1	1782
November	1st to 10th	Day	33% 3 11% 30% 18% 4	1672
	11th to 20th	Day	46% 3 9% 23% 16% 4	1710
	21st to end	Day	51% 2 9% 23% 13% 1	1710
December	1st to 10th	Day	59% 3 9% 19% 10%	1710
	11th to 20th	Day	58% 3 6% 21% 10% 1	1977
	21st to end	Day	70% 3 9% 12% 6%	2783
January	1st to 10th	Night	62% 2 10% 17% 8%	4428
	11th to 20th	Night	67% 2 9% 15% 7%	4440
	21st to end	Night	66% 2 8% 16% 8%	4703
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	32% 5% 14% 31% 17% 2	1690
	11th to 20th	Night	30% 5% 14% 29% 20% 2	1789
	21st to end	Night	26% 4 14% 28% 21% 6%	2080
September	1st to 10th	Night	35% 3 11% 25% 18% 7%	1818
	11th to 20th	Night	28% 4 9% 31% 25% 4	1980
	21st to end	Night	35% 3 8% 25% 24% 4	1980
October	1st to 10th	Night	30% 3 11% 27% 26% 4	1980
	11th to 20th	Night	41% 3 6% 25% 22% 3	2104
	21st to end	Night	46% 3 9% 24% 16% 3	2574
November	1st to 10th	Night	37% 3 8% 25% 22% 4	2406
	11th to 20th	Night	44% 2 9% 24% 19% 3	2470
	21st to end	Night	53% 3 9% 22% 12% 1	2470
December	1st to 10th	Night	56% 3 10% 21% 10% 1	2470
	11th to 20th	Night	55% 2 9% 21% 13% 1	3214
	21st to end	Night	71% 2 8% 12% 6%	4884

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% 13% 30% 26% 7% 1	270
	11th to 20th	Day	23% 15% 33% 24% 5%	270
	21st to end	Day	29% 10% 33% 21% 6%	297
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%	532
September	1st to 10th	Day	13% 2 11% 26% 34% 14%	450
	11th to 20th	Day	11% 2 10% 23% 34% 20%	450
	21st to end	Day	13% 5% 19% 25% 24% 14%	450
October	1st to 10th	Day	12% 3 20% 37% 19% 9%	450
	11th to 20th	Day	11% 9% 36% 27% 14% 2	396
	21st to end	Day	30% 7% 33% 25% 5% 1	297
November	1st to 10th	Day	12% 12% 29% 29% 14% 4	270
	11th to 20th	Day	17% 15% 30% 22% 14% 1	270
	21st to end	Day	24% 7% 34% 24% 10% 1	270
December	1st to 10th	Day	21% 13% 36% 22% 6% 3	270
	11th to 20th	Day	20% 10% 36% 26% 7% 1	270
	21st to end	Day	26% 14% 32% 22% 5% 1	297
January	1st to 10th	Night	22% 11% 33% 29% 5%	950
	11th to 20th	Night	25% 9% 34% 26% 5%	950
	21st to end	Night	22% 9% 34% 30% 4	937
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 8% 32% 45% 7%	624
September	1st to 10th	Night	14% 1 9% 35% 36% 5%	558
	11th to 20th	Night	10% 2 10% 34% 39% 6%	720
	21st to end	Night	14% 3 16% 36% 27% 3	720
October	1st to 10th	Night	11% 3 20% 37% 24% 5%	720
	11th to 20th	Night	19% 6% 27% 32% 16% 1	720
	21st to end	Night	22% 5% 32% 31% 9% 1	792
November	1st to 10th	Night	14% 7% 27% 35% 15% 2	740
	11th to 20th	Night	18% 10% 31% 29% 10% 1	760
	21st to end	Night	24% 9% 26% 33% 7% 1	760
December	1st to 10th	Night	24% 7% 34% 28% 6% 1	760
	11th to 20th	Night	25% 6% 31% 30% 7% 1	883
	21st to end	Night	29% 10% 29% 27% 4	1045

Page generated at 2024-08-27 09:49:37. Version ac07

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