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 2024-05-13.

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% 7% 3 7% 5% 4 5% 4 6% 7% 40%	83987
	Night	14% 8% 3 6% 4 4 4 3 5% 7% 43%	85523
Transparency	Day	42% 5% 10% 23% 17% 3	83700
	Night	41% 4 9% 23% 18% 4	85330
Seeing	Day	17% 7% 22% 24% 20% 11%	14427
	Night	17% 6% 23% 31% 20% 3	24240

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	13% 12% 5% 9% 6% 5% 5% 4 5% 5% 30%	2527
	11th to 20th	Day	20% 8% 3 10% 4 4 4 4 4 4 35%	2657
	21st to end	Day	22% 11% 6% 6% 3 3 3 2 4 6% 32%	3447
February	1st to 10th	Day	18% 11% 3 7% 5% 4 3 3 4 6% 35%	1900
	11th to 20th	Day	19% 11% 3 8% 5% 3 4 2 4 5% 35%	1848
	21st to end	Day	20% 10% 3 7% 4 4 4 3 4 5% 36%	1570
March	1st to 10th	Day	19% 14% 4 9% 5% 3 4 3 4 5% 31%	3120
	11th to 20th	Day	13% 7% 2 7% 4 4 4 3 4 6% 47%	3315
	21st to end	Day	12% 8% 2 6% 5% 6% 4 4 6% 6% 40%	4052
April	1st to 10th	Day	12% 6% 2 6% 5% 5% 4 3 5% 7% 45%	2280
	11th to 20th	Day	13% 7% 3 6% 5% 4 4 4 5% 6% 44%	2254
	21st to end	Day	13% 8% 2 7% 5% 4 4 3 6% 8% 40%	2304
May	1st to 10th	Day	15% 6% 2 5% 5% 4 4 4 6% 8% 40%	2470
	11th to 20th	Day	14% 8% 2 8% 5% 5% 4 3 5% 7% 39%	2329
	21st to end	Day	8% 6% 3 7% 6% 6% 5% 5% 7% 10% 39%	2531
June	1st to 10th	Day	9% 5% 2 7% 5% 5% 5% 5% 7% 8% 41%	2340
	11th to 20th	Day	5% 4 2 6% 6% 5% 5% 5% 8% 10% 46%	2518
	21st to end	Day	5% 4 2 6% 6% 6% 7% 6% 8% 11% 40%	2520
July	1st to 10th	Day	9% 6% 3 7% 7% 6% 6% 6% 8% 9% 33%	2520
	11th to 20th	Day	8% 5% 2 6% 6% 6% 7% 6% 7% 9% 37%	2466
	21st to end	Day	6% 5% 2 7% 6% 6% 7% 7% 10% 10% 34%	2547
August	1st to 10th	Day	6% 5% 3 6% 7% 8% 7% 5% 8% 12% 34%	2199
	11th to 20th	Day	9% 5% 3 8% 6% 5% 7% 4 7% 9% 37%	2125
	21st to end	Day	10% 6% 2 7% 5% 5% 6% 6% 7% 9% 38%	2376
September	1st to 10th	Day	10% 6% 2 6% 6% 6% 5% 5% 7% 8% 40%	2138
	11th to 20th	Day	13% 6% 2 5% 4 5% 5% 4 6% 7% 43%	1980
	21st to end	Day	11% 5% 1 5% 4 3 4 3 5% 6% 52%	1980
October	1st to 10th	Day	11% 5% 2 5% 3 3 3 3 4 6% 54%	1980
	11th to 20th	Day	12% 6% 2 5% 4 3 4 2 4 6% 52%	1938
	21st to end	Day	17% 6% 2 5% 4 3 4 3 4 5% 46%	1805
November	1st to 10th	Day	13% 5% 1 4 3 3 2 3 4 6% 58%	1672
	11th to 20th	Day	14% 7% 3 4 3 4 3 3 5% 6% 48%	1710
	21st to end	Day	14% 7% 3 5% 3 4 4 3 5% 7% 45%	1710
December	1st to 10th	Day	21% 11% 2 7% 3 3 4 3 5% 5% 35%	1710
	11th to 20th	Day	16% 9% 3 7% 5% 5% 4 4 5% 6% 38%	2153
	21st to end	Day	16% 11% 4 8% 6% 4 5% 4 5% 7% 30%	2996
January	1st to 10th	Night	17% 12% 3 6% 4 3 4 3 5% 6% 38%	4428
	11th to 20th	Night	17% 11% 4 9% 4 4 3 3 3 4 36%	4301
	21st to end	Night	21% 12% 5% 6% 3 3 3 2 4 6% 35%	4208
February	1st to 10th	Night	19% 9% 4 8% 6% 4 4 3 5% 6% 34%	2280
	11th to 20th	Night	21% 9% 3 7% 4 3 3 3 4 4 37%	2218
	21st to end	Night	23% 9% 3 6% 4 4 3 3 5% 5% 33%	1884
March	1st to 10th	Night	23% 10% 3 6% 5% 4 4 3 4 6% 33%	3733
	11th to 20th	Night	13% 7% 2 6% 4 3 4 4 4 6% 47%	3643
	21st to end	Night	14% 8% 3 7% 5% 4 4 4 5% 6% 40%	3608
April	1st to 10th	Night	12% 5% 2 6% 4 3 4 4 6% 7% 47%	1900
	11th to 20th	Night	14% 7% 2 4 4 3 3 4 4 6% 48%	1875
	21st to end	Night	12% 7% 2 7% 5% 4 4 3 5% 9% 44%	1873
May	1st to 10th	Night	10% 7% 2 7% 5% 3 5% 3 5% 6% 47%	1710
	11th to 20th	Night	9% 7% 2 6% 4 3 5% 4 6% 8% 45%	1619
	21st to end	Night	6% 5% 2 7% 6% 5% 5% 4 8% 10% 43%	1744
June	1st to 10th	Night	8% 6% 2 5% 5% 4 4 4 7% 8% 46%	1616
	11th to 20th	Night	3 4 1 4 4 3 4 4 6% 11% 55%	1440
	21st to end	Night	3 3 2 4 5% 5% 4 5% 9% 11% 49%	1440
July	1st to 10th	Night	8% 5% 3 6% 4 5% 6% 5% 7% 11% 40%	1440
	11th to 20th	Night	7% 4 1 5% 4 5% 6% 4 7% 13% 44%	1489
	21st to end	Night	4 4 2 6% 6% 5% 6% 6% 8% 11% 42%	1771
August	1st to 10th	Night	6% 4 2 6% 4 5% 4 4 8% 11% 45%	1735
	11th to 20th	Night	6% 5% 2 6% 4 5% 5% 4 8% 10% 45%	1776
	21st to end	Night	8% 5% 2 6% 5% 5% 5% 5% 6% 11% 44%	1980
September	1st to 10th	Night	11% 5% 2 5% 4 4 5% 4 5% 6% 49%	1804
	11th to 20th	Night	9% 5% 2 6% 4 4 4 3 6% 7% 48%	1980
	21st to end	Night	9% 4 2 4 3 4 3 3 6% 6% 56%	1980
October	1st to 10th	Night	9% 5% 2 4 3 3 3 3 4 6% 60%	1980
	11th to 20th	Night	14% 6% 2 5% 4 3 3 3 5% 6% 48%	2019
	21st to end	Night	15% 7% 2 5% 3 3 3 3 5% 6% 48%	2549
November	1st to 10th	Night	11% 5% 2 5% 4 3 3 3 5% 4 55%	2406
	11th to 20th	Night	12% 6% 2 5% 3 3 3 4 6% 8% 49%	2470
	21st to end	Night	15% 8% 2 5% 4 3 3 4 4 6% 45%	2470
December	1st to 10th	Night	20% 10% 3 6% 5% 3 3 3 5% 6% 35%	2470
	11th to 20th	Night	15% 9% 2 6% 3 3 4 3 4 5% 46%	3042
	21st to end	Night	16% 11% 5% 9% 5% 5% 5% 4 5% 5% 29%	4642

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	53% 4 5% 22% 13% 2	2528
	11th to 20th	Day	52% 4 6% 19% 18% 1	2657
	21st to end	Day	54% 3 6% 23% 13% 1	3447
February	1st to 10th	Day	51% 3 7% 21% 16% 3	1900
	11th to 20th	Day	53% 3 5% 21% 14% 4	1858
	21st to end	Day	51% 3 8% 17% 16% 5%	1570
March	1st to 10th	Day	56% 3 6% 14% 13% 8%	3120
	11th to 20th	Day	40% 3 8% 25% 18% 6%	3315
	21st to end	Day	43% 4 9% 27% 16% 1	4052
April	1st to 10th	Day	39% 5% 9% 24% 20% 3	2280
	11th to 20th	Day	41% 4 7% 21% 22% 6%	2254
	21st to end	Day	42% 4 9% 26% 16% 2	2304
May	1st to 10th	Day	41% 4 12% 26% 14% 2	2470
	11th to 20th	Day	43% 5% 12% 24% 15% 1	2333
	21st to end	Day	40% 6% 14% 26% 12% 2	2531
June	1st to 10th	Day	38% 6% 11% 25% 18% 2	2340
	11th to 20th	Day	31% 5% 17% 27% 18% 3	2518
	21st to end	Day	33% 8% 16% 23% 16% 4	2520
July	1st to 10th	Day	41% 7% 17% 20% 12% 3	2451
	11th to 20th	Day	39% 7% 17% 22% 11% 4	2391
	21st to end	Day	36% 8% 19% 25% 10% 2	2405
August	1st to 10th	Day	39% 7% 17% 24% 11% 1	2186
	11th to 20th	Day	40% 7% 13% 23% 15% 2	2125
	21st to end	Day	40% 5% 14% 24% 13% 3	2376
September	1st to 10th	Day	40% 6% 12% 22% 17% 3	2138
	11th to 20th	Day	39% 6% 10% 23% 20% 3	1980
	21st to end	Day	32% 3 10% 27% 23% 6%	1980
October	1st to 10th	Day	32% 3 8% 25% 27% 5%	1980
	11th to 20th	Day	35% 3 7% 22% 25% 8%	1938
	21st to end	Day	40% 4 6% 21% 24% 5%	1805
November	1st to 10th	Day	30% 3 8% 24% 30% 6%	1672
	11th to 20th	Day	37% 3 6% 23% 25% 6%	1710
	21st to end	Day	40% 3 6% 25% 21% 5%	1710
December	1st to 10th	Day	51% 3 6% 21% 16% 3	1710
	11th to 20th	Day	46% 4 9% 21% 18% 2	2150
	21st to end	Day	52% 5% 9% 21% 10% 3	2996
January	1st to 10th	Night	47% 3 7% 25% 16% 1	4428
	11th to 20th	Night	52% 3 5% 19% 16% 5%	4301
	21st to end	Night	53% 2 5% 23% 15% 2	4208
February	1st to 10th	Night	53% 2 8% 18% 17% 1	2280
	11th to 20th	Night	52% 3 6% 19% 16% 4	2219
	21st to end	Night	53% 3 8% 16% 15% 5%	1884
March	1st to 10th	Night	54% 4 7% 13% 16% 7%	3733
	11th to 20th	Night	38% 4 8% 23% 16% 11%	3643
	21st to end	Night	45% 3 8% 24% 19% 1	3608
April	1st to 10th	Night	35% 5% 10% 25% 22% 3	1900
	11th to 20th	Night	37% 3 8% 21% 22% 9%	1875
	21st to end	Night	38% 4 10% 27% 19% 2	1873
May	1st to 10th	Night	37% 4 11% 26% 20% 2	1710
	11th to 20th	Night	36% 7% 17% 22% 16% 2	1620
	21st to end	Night	34% 6% 17% 26% 15% 2	1745
June	1st to 10th	Night	33% 6% 15% 25% 18% 3	1616
	11th to 20th	Night	23% 5% 18% 34% 17% 3	1440
	21st to end	Night	25% 7% 18% 32% 15% 4	1440
July	1st to 10th	Night	34% 7% 19% 23% 14% 3	1400
	11th to 20th	Night	29% 7% 20% 26% 14% 5%	1441
	21st to end	Night	31% 8% 17% 28% 13% 2	1672
August	1st to 10th	Night	30% 8% 16% 31% 14% 1	1724
	11th to 20th	Night	32% 7% 20% 23% 16% 2	1776
	21st to end	Night	34% 6% 14% 27% 14% 4	1980
September	1st to 10th	Night	35% 5% 12% 26% 18% 4	1804
	11th to 20th	Night	34% 4 11% 22% 26% 2	1980
	21st to end	Night	28% 5% 9% 25% 26% 7%	1980
October	1st to 10th	Night	26% 3 8% 25% 29% 9%	1980
	11th to 20th	Night	37% 4 7% 21% 23% 9%	2019
	21st to end	Night	38% 3 4 23% 26% 6%	2549
November	1st to 10th	Night	34% 3 6% 23% 27% 8%	2406
	11th to 20th	Night	34% 3 6% 22% 28% 7%	2470
	21st to end	Night	40% 3 7% 24% 22% 5%	2470
December	1st to 10th	Night	50% 3 8% 19% 16% 3	2470
	11th to 20th	Night	41% 3 6% 23% 23% 4	3044
	21st to end	Night	55% 5% 7% 19% 12% 2	4642

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% 41% 14% 7%	270
	11th to 20th	Day	29% 16% 36% 14% 3 1	270
	21st to end	Day	22% 13% 43% 19% 4	297
February	1st to 10th	Day	29% 13% 35% 18% 5% 1	270
	11th to 20th	Day	33% 15% 37% 11% 2 1	270
	21st to end	Day	36% 18% 34% 9% 4	225
March	1st to 10th	Day	26% 12% 38% 19% 6%	270
	11th to 20th	Day	25% 13% 34% 19% 7% 1	360
	21st to end	Day	22% 12% 35% 22% 8% 1	506
April	1st to 10th	Day	19% 13% 29% 25% 12% 2	460
	11th to 20th	Day	20% 12% 29% 26% 12% 2	452
	21st to end	Day	20% 11% 28% 24% 13% 4	460
May	1st to 10th	Day	20% 8% 27% 26% 15% 5%	463
	11th to 20th	Day	17% 4 23% 26% 20% 11%	456
	21st to end	Day	13% 2 16% 26% 25% 18%	485
June	1st to 10th	Day	14% 1 16% 21% 26% 22%	450
	11th to 20th	Day	6% 1 14% 28% 33% 18%	628
	21st to end	Day	7% 2 16% 33% 25% 18%	630
July	1st to 10th	Day	11% 1 10% 24% 31% 23%	621
	11th to 20th	Day	11% 1 8% 24% 32% 25%	564
	21st to end	Day	8% 2 7% 24% 32% 27%	488
August	1st to 10th	Day	9% 1 7% 25% 37% 22%	446
	11th to 20th	Day	13% 1 6% 29% 35% 16%	439
	21st to end	Day	15% 1 4 20% 36% 23%	495
September	1st to 10th	Day	12% 1 9% 26% 34% 18%	450
	11th to 20th	Day	16% 1 8% 23% 31% 22%	450
	21st to end	Day	14% 4 13% 27% 28% 13%	450
October	1st to 10th	Day	16% 1 17% 29% 26% 11%	450
	11th to 20th	Day	14% 8% 31% 29% 14% 4	408
	21st to end	Day	26% 7% 26% 27% 10% 2	297
November	1st to 10th	Day	18% 6% 29% 29% 14% 4	270
	11th to 20th	Day	15% 10% 40% 26% 9%	270
	21st to end	Day	20% 10% 34% 19% 14% 3	270
December	1st to 10th	Day	28% 15% 29% 23% 4 1	270
	11th to 20th	Day	19% 14% 38% 19% 10%	270
	21st to end	Day	23% 16% 36% 21% 4	297
January	1st to 10th	Night	23% 13% 32% 27% 5%	950
	11th to 20th	Night	26% 13% 31% 24% 5%	863
	21st to end	Night	21% 10% 41% 25% 3	836
February	1st to 10th	Night	23% 10% 36% 28% 4	760
	11th to 20th	Night	26% 13% 32% 26% 3	743
	21st to end	Night	29% 13% 34% 22% 2	628
March	1st to 10th	Night	22% 10% 33% 28% 6%	760
	11th to 20th	Night	20% 10% 33% 28% 8% 1	760
	21st to end	Night	19% 9% 33% 29% 9%	717
April	1st to 10th	Night	15% 10% 32% 32% 11%	570
	11th to 20th	Night	16% 10% 31% 32% 9% 2	563
	21st to end	Night	15% 6% 32% 34% 12% 1	570
May	1st to 10th	Night	14% 3 31% 32% 18% 2	570
	11th to 20th	Night	12% 2 23% 36% 23% 5%	540
	21st to end	Night	9% 2 12% 37% 34% 6%	584
June	1st to 10th	Night	12% 1 12% 35% 33% 6%	540
	11th to 20th	Night	5% 1 10% 38% 40% 6%	540
	21st to end	Night	4 1 11% 37% 39% 8%	540
July	1st to 10th	Night	10% 1 4 30% 44% 11%	525
	11th to 20th	Night	10% 1 6% 27% 43% 13%	522
	21st to end	Night	6% 1 6% 28% 50% 9%	591
August	1st to 10th	Night	9% 1 3 28% 50% 10%	537
	11th to 20th	Night	7% 1 6% 40% 39% 7%	534
	21st to end	Night	10% 1 4 29% 46% 10%	594
September	1st to 10th	Night	12% 2 7% 29% 45% 5%	544
	11th to 20th	Night	12% 1 10% 30% 41% 6%	720
	21st to end	Night	11% 2 13% 32% 36% 5%	720
October	1st to 10th	Night	11% 3 16% 33% 30% 7%	720
	11th to 20th	Night	18% 4 25% 33% 18% 2	720
	21st to end	Night	18% 5% 26% 32% 16% 2	792
November	1st to 10th	Night	13% 5% 23% 38% 17% 3	740
	11th to 20th	Night	15% 8% 31% 33% 13% 1	760
	21st to end	Night	20% 8% 27% 33% 11% 1	760
December	1st to 10th	Night	26% 9% 28% 29% 7% 1	760
	11th to 20th	Night	21% 7% 31% 32% 8% 1	760
	21st to end	Night	26% 9% 31% 28% 5%	907

Page generated at 2024-05-10 11:39:06. Version ac07

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