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 2024-03-18.

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% 4 7% 6% 3 5% 5% 6% 8% 36%	78536
	Night	14% 9% 4 7% 6% 3 4 4 5% 7% 37%	81299
Transparency	Day	45% 7% 13% 22% 11% 1	78237
	Night	47% 6% 12% 21% 12% 2	81119
Seeing	Day	17% 10% 31% 25% 13% 5%	14887
	Night	18% 9% 30% 29% 13% 1	24969

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	11% 14% 8% 9% 6% 3 5% 4 4 6% 29%	2527
	11th to 20th	Day	11% 11% 6% 13% 6% 4 5% 9% 8% 8% 20%	2530
	21st to end	Day	17% 18% 9% 9% 6% 3 3 4 4 6% 21%	2787
February	1st to 10th	Day	11% 12% 7% 9% 6% 3 5% 5% 6% 8% 29%	1729
	11th to 20th	Day	13% 10% 4 6% 6% 4 5% 4 5% 7% 36%	1848
	21st to end	Day	11% 12% 6% 11% 7% 3 5% 5% 5% 6% 29%	1570
March	1st to 10th	Day	14% 9% 4 8% 6% 4 5% 5% 4 6% 34%	1900
	11th to 20th	Day	12% 7% 4 7% 7% 3 5% 5% 5% 8% 37%	1918
	21st to end	Day	17% 11% 5% 7% 7% 3 5% 5% 6% 6% 28%	2376
April	1st to 10th	Day	16% 11% 5% 7% 5% 4 6% 6% 5% 6% 30%	2160
	11th to 20th	Day	16% 9% 3 7% 6% 4 4 5% 6% 7% 34%	2134
	21st to end	Day	17% 8% 3 6% 6% 3 5% 5% 4 7% 34%	2286
May	1st to 10th	Day	15% 9% 4 7% 6% 4 5% 6% 6% 8% 31%	2340
	11th to 20th	Day	16% 8% 3 6% 5% 3 5% 5% 5% 7% 36%	2454
	21st to end	Day	12% 7% 2 6% 6% 3 6% 4 7% 8% 40%	2725
June	1st to 10th	Day	9% 5% 2 5% 5% 3 4 5% 6% 8% 46%	2520
	11th to 20th	Day	11% 6% 3 4 4 3 4 4 6% 10% 46%	2520
	21st to end	Day	8% 6% 3 5% 6% 4 6% 5% 7% 9% 42%	2520
July	1st to 10th	Day	6% 4 2 4 5% 3 5% 4 6% 10% 50%	2520
	11th to 20th	Day	7% 4 2 5% 4 3 6% 6% 7% 9% 48%	2520
	21st to end	Day	5% 4 2 4 5% 3 6% 5% 7% 10% 48%	2743
August	1st to 10th	Day	7% 4 2 5% 5% 3 6% 6% 8% 11% 45%	2482
	11th to 20th	Day	8% 5% 3 5% 6% 3 6% 5% 6% 10% 44%	2179
	21st to end	Day	7% 5% 2 6% 5% 4 5% 5% 7% 9% 47%	2376
September	1st to 10th	Day	11% 6% 3 5% 4 3 4 6% 7% 7% 44%	2160
	11th to 20th	Day	11% 5% 2 4 4 3 5% 5% 5% 8% 49%	2044
	21st to end	Day	11% 6% 2 6% 5% 4 5% 5% 6% 9% 40%	1980
October	1st to 10th	Day	13% 7% 3 5% 5% 2 3 4 6% 7% 44%	1930
	11th to 20th	Day	18% 8% 4 7% 6% 4 5% 4 6% 6% 32%	1767
	21st to end	Day	17% 9% 4 7% 6% 4 5% 5% 5% 6% 35%	1782
November	1st to 10th	Day	11% 8% 4 6% 5% 3 4 5% 5% 7% 41%	1672
	11th to 20th	Day	12% 10% 4 9% 7% 3 6% 5% 6% 8% 31%	1710
	21st to end	Day	19% 10% 3 6% 4 3 5% 4 3 5% 38%	1606
December	1st to 10th	Day	14% 11% 4 8% 7% 5% 5% 4 7% 8% 26%	1520
	11th to 20th	Day	12% 11% 5% 8% 6% 3 6% 6% 7% 8% 28%	1918
	21st to end	Day	18% 20% 7% 12% 7% 4 4 3 4 4 16%	2783
January	1st to 10th	Night	14% 13% 7% 9% 6% 3 4 4 4 5% 31%	4428
	11th to 20th	Night	14% 14% 6% 12% 8% 4 6% 7% 6% 7% 17%	4440
	21st to end	Night	18% 17% 8% 8% 6% 3 4 3 4 6% 23%	4876
February	1st to 10th	Night	12% 13% 5% 8% 7% 4 4 4 5% 7% 32%	2451
	11th to 20th	Night	13% 9% 4 7% 5% 3 4 4 5% 8% 39%	2218
	21st to end	Night	18% 11% 3 6% 5% 2 4 4 5% 6% 35%	1884
March	1st to 10th	Night	14% 10% 4 7% 7% 4 5% 4 5% 5% 34%	2280
	11th to 20th	Night	12% 6% 4 4 5% 3 5% 5% 6% 8% 43%	2220
	21st to end	Night	19% 9% 5% 7% 6% 4 4 4 4 6% 33%	1980
April	1st to 10th	Night	15% 8% 3 6% 5% 4 5% 5% 6% 8% 35%	1800
	11th to 20th	Night	19% 9% 3 6% 5% 3 4 4 4 5% 37%	1775
	21st to end	Night	17% 9% 3 5% 5% 3 5% 4 6% 6% 38%	1674
May	1st to 10th	Night	16% 7% 3 6% 6% 3 5% 6% 6% 8% 33%	1620
	11th to 20th	Night	17% 8% 2 5% 5% 2 5% 4 6% 7% 39%	1437
	21st to end	Night	12% 6% 3 7% 6% 3 4 4 5% 9% 41%	1551
June	1st to 10th	Night	10% 4 2 5% 6% 3 5% 5% 6% 8% 47%	1440
	11th to 20th	Night	12% 5% 3 4 5% 4 4 4 5% 9% 45%	1440
	21st to end	Night	9% 6% 3 5% 5% 3 5% 4 5% 9% 46%	1440
July	1st to 10th	Night	7% 4 2 4 4 3 4 5% 7% 9% 51%	1440
	11th to 20th	Night	6% 3 2 5% 4 3 3 5% 8% 9% 52%	1440
	21st to end	Night	6% 4 2 4 4 2 5% 6% 7% 9% 51%	1575
August	1st to 10th	Night	5% 4 2 4 5% 3 6% 5% 7% 9% 51%	1453
	11th to 20th	Night	7% 4 2 5% 4 3 3 5% 6% 10% 51%	1718
	21st to end	Night	8% 3 2 4 4 3 5% 4 6% 8% 52%	1980
September	1st to 10th	Night	9% 4 2 6% 5% 3 5% 4 5% 7% 50%	1800
	11th to 20th	Night	11% 4 2 4 4 3 4 4 4 7% 54%	1897
	21st to end	Night	13% 6% 3 6% 4 2 4 4 3 7% 46%	1980
October	1st to 10th	Night	13% 6% 2 5% 4 3 5% 5% 5% 6% 47%	2028
	11th to 20th	Night	17% 8% 3 6% 4 3 4 4 4 6% 41%	2192
	21st to end	Night	20% 7% 2 5% 6% 3 4 4 5% 7% 36%	2574
November	1st to 10th	Night	12% 7% 3 6% 4 3 5% 4 4 6% 46%	2406
	11th to 20th	Night	14% 9% 3 7% 7% 4 5% 5% 5% 6% 35%	2470
	21st to end	Night	17% 8% 4 5% 5% 4 4 4 6% 7% 37%	2569
December	1st to 10th	Night	16% 11% 4 7% 6% 4 5% 5% 5% 7% 30%	2660
	11th to 20th	Night	14% 12% 4 8% 6% 3 5% 5% 5% 7% 29%	3279
	21st to end	Night	21% 18% 6% 8% 7% 3 4 4 5% 6% 19%	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	57% 7% 14% 17% 5%	2528
	11th to 20th	Day	60% 8% 13% 16% 3	2530
	21st to end	Day	65% 5% 8% 17% 4	2787
February	1st to 10th	Day	52% 7% 14% 17% 9% 1	1729
	11th to 20th	Day	48% 7% 12% 23% 9% 2	1858
	21st to end	Day	54% 7% 10% 18% 9% 2	1570
March	1st to 10th	Day	51% 7% 12% 20% 8% 2	1900
	11th to 20th	Day	46% 6% 12% 22% 12% 2	1918
	21st to end	Day	56% 7% 13% 18% 6% 1	2376
April	1st to 10th	Day	52% 9% 10% 18% 11%	2160
	11th to 20th	Day	47% 8% 10% 21% 11% 3	2134
	21st to end	Day	49% 7% 13% 18% 12% 1	2286
May	1st to 10th	Day	49% 7% 13% 23% 8%	2340
	11th to 20th	Day	46% 8% 12% 22% 12% 1	2458
	21st to end	Day	41% 10% 12% 22% 14% 2	2725
June	1st to 10th	Day	35% 6% 14% 26% 16% 2	2520
	11th to 20th	Day	34% 8% 14% 24% 19% 2	2520
	21st to end	Day	37% 9% 14% 23% 15% 2	2520
July	1st to 10th	Day	29% 8% 13% 32% 15% 3	2451
	11th to 20th	Day	30% 9% 14% 27% 18% 2	2445
	21st to end	Day	29% 9% 16% 28% 14% 3	2591
August	1st to 10th	Day	31% 8% 15% 30% 13% 2	2467
	11th to 20th	Day	34% 9% 15% 28% 13% 1	2179
	21st to end	Day	32% 8% 13% 25% 19% 2	2376
September	1st to 10th	Day	36% 9% 12% 26% 16% 2	2160
	11th to 20th	Day	32% 7% 12% 33% 14% 2	2044
	21st to end	Day	38% 8% 12% 29% 12% 1	1980
October	1st to 10th	Day	39% 5% 13% 30% 13% 1	1930
	11th to 20th	Day	51% 6% 11% 20% 11% 1	1767
	21st to end	Day	50% 6% 11% 22% 10% 1	1782
November	1st to 10th	Day	42% 5% 14% 24% 14% 1	1672
	11th to 20th	Day	51% 6% 15% 20% 8% 1	1710
	21st to end	Day	51% 4 14% 24% 7%	1606
December	1st to 10th	Day	55% 7% 18% 12% 7% 1	1520
	11th to 20th	Day	51% 8% 15% 19% 6% 1	1915
	21st to end	Day	72% 4 8% 12% 4	2783
January	1st to 10th	Night	56% 5% 13% 18% 7%	4428
	11th to 20th	Night	67% 5% 12% 12% 4	4440
	21st to end	Night	64% 5% 12% 15% 4	4876
February	1st to 10th	Night	52% 7% 12% 17% 11% 2	2451
	11th to 20th	Night	44% 5% 14% 22% 13% 1	2219
	21st to end	Night	50% 5% 11% 20% 11% 3	1884
March	1st to 10th	Night	51% 6% 12% 20% 9% 2	2280
	11th to 20th	Night	38% 7% 14% 24% 15% 3	2220
	21st to end	Night	54% 5% 10% 20% 10% 1	1980
April	1st to 10th	Night	46% 8% 10% 21% 15% 1	1800
	11th to 20th	Night	49% 5% 6% 18% 18% 4	1775
	21st to end	Night	45% 6% 13% 19% 16% 2	1674
May	1st to 10th	Night	45% 8% 12% 23% 11% 1	1620
	11th to 20th	Night	44% 7% 11% 22% 14% 2	1438
	21st to end	Night	42% 5% 12% 23% 16% 2	1552
June	1st to 10th	Night	32% 8% 12% 28% 18% 2	1440
	11th to 20th	Night	36% 6% 10% 24% 21% 3	1440
	21st to end	Night	36% 7% 13% 26% 15% 3	1440
July	1st to 10th	Night	28% 8% 15% 28% 18% 4	1400
	11th to 20th	Night	26% 7% 14% 30% 19% 4	1392
	21st to end	Night	26% 8% 15% 27% 19% 5%	1487
August	1st to 10th	Night	29% 7% 15% 30% 16% 3	1444
	11th to 20th	Night	29% 7% 16% 32% 17% 1	1718
	21st to end	Night	29% 7% 11% 29% 21% 3	1980
September	1st to 10th	Night	34% 6% 12% 24% 22% 3	1800
	11th to 20th	Night	30% 6% 10% 36% 16% 2	1897
	21st to end	Night	39% 4 9% 31% 15% 1	1980
October	1st to 10th	Night	37% 6% 12% 28% 16% 2	2028
	11th to 20th	Night	44% 5% 13% 20% 17% 1	2192
	21st to end	Night	48% 5% 13% 22% 10% 1	2574
November	1st to 10th	Night	39% 5% 12% 24% 17% 3	2406
	11th to 20th	Night	48% 6% 14% 19% 10% 1	2470
	21st to end	Night	48% 6% 16% 21% 8% 1	2569
December	1st to 10th	Night	53% 7% 14% 18% 7% 1	2660
	11th to 20th	Night	54% 7% 13% 18% 7% 1	3281
	21st to end	Night	66% 5% 11% 13% 4	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	20% 17% 34% 24% 5%	270
	11th to 20th	Day	20% 20% 33% 21% 5% 1	270
	21st to end	Day	24% 11% 37% 19% 9%	297
February	1st to 10th	Day	17% 20% 40% 17% 6%	270
	11th to 20th	Day	21% 25% 34% 16% 4	270
	21st to end	Day	21% 21% 43% 12% 3	225
March	1st to 10th	Day	19% 25% 41% 12% 3	270
	11th to 20th	Day	24% 17% 36% 17% 6% 1	287
	21st to end	Day	27% 12% 30% 22% 7% 2	462
April	1st to 10th	Day	23% 13% 35% 22% 6%	420
	11th to 20th	Day	23% 18% 28% 18% 10% 2	412
	21st to end	Day	26% 10% 29% 22% 11% 2	420
May	1st to 10th	Day	23% 11% 30% 26% 9% 2	423
	11th to 20th	Day	22% 8% 34% 24% 10% 3	600
	21st to end	Day	16% 7% 31% 24% 15% 7%	679
June	1st to 10th	Day	10% 7% 33% 32% 14% 4	630
	11th to 20th	Day	16% 6% 29% 32% 13% 5%	630
	21st to end	Day	13% 6% 30% 33% 14% 3	630
July	1st to 10th	Day	8% 3 24% 32% 23% 11%	621
	11th to 20th	Day	9% 5% 29% 32% 17% 8%	618
	21st to end	Day	6% 3 31% 38% 15% 7%	684
August	1st to 10th	Day	9% 2 25% 32% 20% 11%	601
	11th to 20th	Day	10% 4 20% 27% 24% 14%	439
	21st to end	Day	10% 4 21% 34% 22% 9%	495
September	1st to 10th	Day	14% 4 25% 29% 22% 7%	450
	11th to 20th	Day	12% 2 23% 31% 20% 12%	450
	21st to end	Day	17% 9% 25% 24% 18% 8%	450
October	1st to 10th	Day	20% 8% 25% 26% 17% 4	400
	11th to 20th	Day	26% 17% 28% 22% 6% 1	270
	21st to end	Day	25% 15% 36% 16% 5% 1	297
November	1st to 10th	Day	16% 13% 40% 21% 8% 2	270
	11th to 20th	Day	18% 19% 40% 16% 8%	270
	21st to end	Day	25% 11% 41% 19% 3 1	270
December	1st to 10th	Day	21% 18% 39% 15% 7% 1	270
	11th to 20th	Day	22% 16% 35% 19% 6% 2	270
	21st to end	Day	27% 20% 35% 14% 3	297
January	1st to 10th	Night	19% 16% 36% 24% 5%	950
	11th to 20th	Night	21% 15% 34% 21% 7% 1	950
	21st to end	Night	20% 11% 36% 28% 5%	1045
February	1st to 10th	Night	20% 15% 35% 24% 6%	931
	11th to 20th	Night	19% 15% 36% 25% 5%	743
	21st to end	Night	24% 15% 36% 20% 5%	628
March	1st to 10th	Night	19% 12% 34% 25% 9% 1	760
	11th to 20th	Night	17% 13% 35% 27% 8% 1	744
	21st to end	Night	24% 8% 26% 31% 10% 2	594
April	1st to 10th	Night	20% 11% 34% 27% 8%	540
	11th to 20th	Night	27% 8% 31% 24% 10% 2	533
	21st to end	Night	22% 7% 29% 31% 11% 1	540
May	1st to 10th	Night	18% 9% 29% 35% 9% 1	540
	11th to 20th	Night	20% 5% 29% 30% 15% 1	531
	21st to end	Night	16% 4 22% 33% 21% 3	584
June	1st to 10th	Night	11% 3 24% 39% 20% 2	540
	11th to 20th	Night	14% 3 29% 33% 20% 1	540
	21st to end	Night	12% 2 24% 40% 20% 2	540
July	1st to 10th	Night	8% 1 17% 38% 32% 4	525
	11th to 20th	Night	7% 2 22% 39% 26% 4	522
	21st to end	Night	7% 1 17% 46% 26% 2	591
August	1st to 10th	Night	9% 1 15% 44% 29% 3	537
	11th to 20th	Night	9% 2 14% 37% 33% 5%	534
	21st to end	Night	9% 2 17% 39% 30% 3	594
September	1st to 10th	Night	10% 2 21% 34% 26% 6%	540
	11th to 20th	Night	12% 4 20% 31% 28% 5%	637
	21st to end	Night	16% 8% 23% 26% 23% 4	720
October	1st to 10th	Night	16% 5% 25% 32% 20% 3	720
	11th to 20th	Night	21% 10% 33% 25% 11%	720
	21st to end	Night	25% 9% 31% 26% 9% 1	792
November	1st to 10th	Night	17% 11% 35% 25% 10% 1	740
	11th to 20th	Night	21% 16% 34% 22% 6% 1	760
	21st to end	Night	22% 12% 36% 23% 6%	859
December	1st to 10th	Night	23% 15% 35% 21% 5%	950
	11th to 20th	Night	22% 13% 34% 25% 6% 1	950
	21st to end	Night	29% 13% 35% 20% 3	1045

Page generated at 2024-03-15 13:01:44. Version ac07

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