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 2026-10-29.

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	11% 8% 3 8% 5% 5% 5% 4 6% 8% 38%	149642
	Night	12% 9% 4 8% 5% 4 4 4 5% 7% 38%	142758
Transparency	Day	41% 7% 12% 25% 13% 1	153155
	Night	44% 6% 12% 23% 14% 2	147322
Seeing	Day	17% 11% 32% 24% 11% 4	18629
	Night	18% 10% 30% 28% 13% 1	28403

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% 12% 6% 12% 6% 6% 6% 4 6% 7% 26%	4691
	11th to 20th	Day	7% 10% 5% 11% 5% 5% 6% 6% 7% 7% 32%	4710
	21st to end	Day	10% 14% 6% 10% 6% 4 5% 3 4 6% 33%	5174
February	1st to 10th	Day	10% 14% 6% 10% 5% 4 5% 4 6% 8% 28%	1911
	11th to 20th	Day	12% 11% 4 8% 5% 5% 4 3 5% 6% 35%	2048
	21st to end	Day	11% 13% 5% 12% 5% 4 5% 4 6% 6% 29%	1730
March	1st to 10th	Day	13% 9% 3 7% 4 4 4 3 5% 6% 42%	4580
	11th to 20th	Day	10% 6% 3 8% 5% 5% 5% 4 5% 7% 41%	4769
	21st to end	Day	18% 12% 5% 11% 6% 5% 5% 4 5% 5% 25%	6099
April	1st to 10th	Day	16% 12% 4 8% 5% 5% 5% 5% 5% 5% 30%	2520
	11th to 20th	Day	15% 9% 3 8% 5% 5% 5% 4 6% 6% 34%	2494
	21st to end	Day	16% 9% 3 7% 5% 4 5% 4 5% 7% 34%	2667
May	1st to 10th	Day	12% 8% 3 8% 5% 5% 5% 5% 7% 8% 36%	7616
	11th to 20th	Day	12% 7% 3 7% 5% 5% 5% 5% 6% 7% 38%	8156
	21st to end	Day	14% 6% 2 6% 4 4 5% 4 6% 9% 41%	9047
June	1st to 10th	Day	9% 6% 2 7% 5% 4 4 5% 6% 8% 45%	2940
	11th to 20th	Day	10% 6% 2 5% 4 5% 5% 3 6% 9% 45%	2940
	21st to end	Day	8% 7% 3 6% 5% 5% 5% 4 7% 9% 41%	2940
July	1st to 10th	Day	9% 7% 3 7% 5% 4 5% 4 7% 9% 40%	8280
	11th to 20th	Day	5% 4 2 5% 4 4 5% 5% 7% 10% 49%	8280
	21st to end	Day	7% 5% 2 6% 4 5% 5% 5% 6% 9% 45%	8990
August	1st to 10th	Day	12% 6% 2 6% 4 4 5% 4 6% 9% 41%	6414
	11th to 20th	Day	12% 5% 3 7% 4 5% 5% 4 7% 9% 40%	5624
	21st to end	Day	7% 6% 3 7% 4 4 5% 4 7% 9% 44%	6080
September	1st to 10th	Day	10% 6% 2 6% 4 4 5% 5% 7% 8% 44%	2520
	11th to 20th	Day	11% 5% 2 5% 3 4 5% 3 5% 8% 49%	2384
	21st to end	Day	11% 6% 2 7% 5% 5% 4 4 6% 9% 41%	2310
October	1st to 10th	Day	11% 7% 3 6% 4 3 3 3 6% 7% 47%	2251
	11th to 20th	Day	17% 8% 3 8% 5% 5% 5% 4 6% 6% 34%	2061
	21st to end	Day	15% 9% 3 7% 5% 4 5% 4 5% 6% 36%	2052
November	1st to 10th	Day	11% 9% 4 7% 5% 5% 4 4 4 7% 41%	1852
	11th to 20th	Day	12% 11% 3 10% 6% 5% 5% 4 6% 7% 31%	1890
	21st to end	Day	17% 12% 3 6% 5% 4 4 3 4 6% 36%	1774
December	1st to 10th	Day	8% 9% 4 8% 6% 5% 5% 4 7% 8% 36%	2690
	11th to 20th	Day	12% 14% 4 11% 5% 5% 6% 5% 7% 8% 24%	3088
	21st to end	Day	21% 20% 7% 12% 5% 5% 4 3 4 4 15%	4070
January	1st to 10th	Night	11% 12% 6% 12% 6% 4 4 3 4 5% 33%	8232
	11th to 20th	Night	9% 13% 6% 13% 7% 6% 6% 4 6% 6% 23%	8280
	21st to end	Night	11% 14% 5% 9% 5% 5% 4 3 6% 6% 32%	9022
February	1st to 10th	Night	12% 14% 4 9% 6% 5% 4 3 5% 6% 32%	2709
	11th to 20th	Night	13% 10% 3 8% 4 4 4 4 5% 7% 39%	2458
	21st to end	Night	17% 11% 3 7% 4 4 4 3 5% 6% 36%	2076
March	1st to 10th	Night	15% 9% 3 6% 4 5% 4 3 4 5% 42%	5493
	11th to 20th	Night	10% 7% 3 5% 4 3 5% 4 6% 9% 46%	5438
	21st to end	Night	18% 11% 5% 11% 6% 5% 4 3 4 5% 29%	5072
April	1st to 10th	Night	16% 9% 3 7% 4 5% 5% 4 6% 8% 35%	2100
	11th to 20th	Night	18% 9% 3 8% 4 4 4 4 4 5% 37%	2075
	21st to end	Night	16% 8% 2 6% 4 5% 5% 3 6% 7% 38%	1953
May	1st to 10th	Night	14% 7% 3 6% 5% 4 4 4 6% 8% 39%	5237
	11th to 20th	Night	10% 7% 5% 6% 5% 4 5% 4 6% 8% 41%	4729
	21st to end	Night	14% 6% 3 7% 4 4 4 3 5% 7% 42%	5139
June	1st to 10th	Night	9% 5% 2 6% 5% 4 5% 4 6% 8% 46%	1680
	11th to 20th	Night	11% 6% 2 6% 5% 4 4 4 6% 9% 43%	1680
	21st to end	Night	9% 7% 3 7% 4 5% 5% 4 6% 8% 44%	1680
July	1st to 10th	Night	9% 7% 2 7% 4 5% 5% 4 6% 8% 42%	4708
	11th to 20th	Night	4 4 2 5% 3 3 3 4 7% 9% 54%	4707
	21st to end	Night	6% 5% 2 6% 4 4 4 4 7% 8% 49%	5117
August	1st to 10th	Night	14% 6% 2 6% 4 4 4 3 5% 7% 45%	3749
	11th to 20th	Night	9% 6% 3 8% 5% 4 5% 4 5% 9% 42%	4418
	21st to end	Night	6% 4 2 5% 4 5% 5% 4 6% 10% 50%	5046
September	1st to 10th	Night	8% 4 2 6% 3 5% 5% 3 6% 7% 51%	2100
	11th to 20th	Night	11% 4 2 4 3 4 4 3 5% 7% 53%	2214
	21st to end	Night	12% 7% 3 6% 4 4 4 3 4 7% 46%	2310
October	1st to 10th	Night	12% 5% 2 6% 3 4 4 4 5% 7% 49%	2367
	11th to 20th	Night	16% 8% 3 6% 4 3 4 3 5% 6% 42%	2558
	21st to end	Night	18% 7% 2 7% 5% 4 4 4 6% 8% 36%	2965
November	1st to 10th	Night	13% 8% 2 7% 4 4 4 3 4 6% 45%	2666
	11th to 20th	Night	14% 9% 3 7% 6% 5% 5% 4 5% 6% 35%	2730
	21st to end	Night	16% 10% 4 7% 5% 5% 4 3 5% 6% 36%	2841
December	1st to 10th	Night	11% 10% 3 7% 4 5% 4 4 5% 7% 41%	4720
	11th to 20th	Night	15% 15% 5% 10% 5% 5% 4 4 5% 6% 27%	5339
	21st to end	Night	20% 19% 6% 10% 6% 4 4 3 5% 5% 18%	7150

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	56% 6% 15% 15% 7%	4692
	11th to 20th	Day	48% 6% 11% 19% 14% 2	4710
	21st to end	Day	51% 5% 9% 23% 11%	5174
February	1st to 10th	Day	52% 7% 13% 17% 9% 1	1911
	11th to 20th	Day	48% 6% 11% 24% 9% 2	2058
	21st to end	Day	53% 7% 10% 18% 9% 2	1730
March	1st to 10th	Day	42% 5% 11% 25% 12% 5%	4580
	11th to 20th	Day	41% 6% 14% 25% 12% 2	4769
	21st to end	Day	58% 7% 13% 14% 7% 1	6101
April	1st to 10th	Day	53% 9% 9% 19% 11%	2520
	11th to 20th	Day	46% 9% 10% 21% 11% 3	2494
	21st to end	Day	47% 7% 14% 19% 12% 1	2667
May	1st to 10th	Day	40% 9% 11% 25% 13% 1	7651
	11th to 20th	Day	40% 9% 12% 24% 15% 1	8160
	21st to end	Day	37% 8% 11% 24% 16% 4	9061
June	1st to 10th	Day	35% 6% 14% 25% 17% 2	2940
	11th to 20th	Day	35% 8% 14% 24% 18% 2	2940
	21st to end	Day	37% 9% 14% 23% 15% 2	2940
July	1st to 10th	Day	37% 8% 13% 27% 13% 2	8211
	11th to 20th	Day	26% 8% 13% 33% 18% 1	8205
	21st to end	Day	33% 8% 14% 24% 20% 2	8794
August	1st to 10th	Day	37% 7% 13% 29% 13% 1	6399
	11th to 20th	Day	37% 9% 15% 30% 8%	5663
	21st to end	Day	33% 8% 14% 29% 15% 1	6079
September	1st to 10th	Day	35% 9% 13% 28% 15% 2	2520
	11th to 20th	Day	32% 7% 12% 32% 15% 2	2384
	21st to end	Day	38% 7% 12% 29% 13%	2310
October	1st to 10th	Day	24% 3 8% 43% 21% 1	3602
	11th to 20th	Day	35% 7% 10% 27% 20% 1	3277
	21st to end	Day	41% 5% 9% 29% 12% 3	3252
November	1st to 10th	Day	43% 5% 14% 24% 14% 1	1852
	11th to 20th	Day	52% 6% 14% 20% 8% 1	1890
	21st to end	Day	52% 4 14% 24% 6%	1774
December	1st to 10th	Day	44% 6% 22% 21% 6% 1	2690
	11th to 20th	Day	54% 8% 13% 17% 7% 1	3085
	21st to end	Day	72% 5% 7% 12% 5%	4070
January	1st to 10th	Night	53% 5% 12% 21% 9%	8233
	11th to 20th	Night	59% 5% 11% 11% 12% 1	8280
	21st to end	Night	52% 5% 13% 20% 10%	9022
February	1st to 10th	Night	52% 6% 12% 18% 11% 2	2709
	11th to 20th	Night	45% 5% 13% 23% 13% 1	2459
	21st to end	Night	48% 5% 11% 22% 11% 3	2076
March	1st to 10th	Night	43% 6% 12% 24% 12% 3	5493
	11th to 20th	Night	35% 5% 13% 30% 13% 4	5438
	21st to end	Night	57% 6% 9% 15% 12% 1	5072
April	1st to 10th	Night	46% 7% 10% 21% 15% 1	2100
	11th to 20th	Night	49% 5% 7% 19% 17% 4	2075
	21st to end	Night	44% 6% 13% 21% 15% 2	1953
May	1st to 10th	Night	41% 6% 11% 24% 16% 2	5264
	11th to 20th	Night	39% 7% 13% 24% 16% 2	4730
	21st to end	Night	41% 5% 8% 21% 18% 7%	5149
June	1st to 10th	Night	34% 8% 11% 27% 19% 2	1680
	11th to 20th	Night	36% 6% 11% 23% 21% 3	1680
	21st to end	Night	37% 7% 13% 24% 16% 3	1680
July	1st to 10th	Night	38% 7% 14% 26% 13% 3	4670
	11th to 20th	Night	24% 6% 14% 31% 23% 2	4662
	21st to end	Night	29% 8% 13% 27% 22% 2	5002
August	1st to 10th	Night	38% 6% 12% 26% 17% 1	3740
	11th to 20th	Night	38% 8% 14% 29% 12%	4445
	21st to end	Night	28% 7% 13% 34% 16% 2	5046
September	1st to 10th	Night	32% 6% 12% 26% 21% 2	2100
	11th to 20th	Night	30% 6% 10% 34% 18% 2	2214
	21st to end	Night	39% 5% 9% 30% 16% 1	2310
October	1st to 10th	Night	25% 4 8% 38% 24% 1	3796
	11th to 20th	Night	36% 5% 11% 24% 22% 2	4081
	21st to end	Night	41% 5% 10% 25% 17% 2	4715
November	1st to 10th	Night	41% 5% 11% 24% 16% 2	2666
	11th to 20th	Night	48% 6% 14% 20% 10% 2	2730
	21st to end	Night	50% 6% 15% 21% 8%	2841
December	1st to 10th	Night	43% 6% 17% 25% 7% 3	4720
	11th to 20th	Night	57% 7% 11% 16% 9% 1	5341
	21st to end	Night	67% 5% 10% 13% 5%	7150

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% 17% 35% 22% 4	330
	11th to 20th	Day	19% 25% 33% 18% 4 1	330
	21st to end	Day	25% 15% 37% 16% 7%	363
February	1st to 10th	Day	18% 20% 41% 16% 5%	330
	11th to 20th	Day	22% 26% 33% 15% 3	330
	21st to end	Day	22% 22% 42% 11% 2	273
March	1st to 10th	Day	22% 25% 39% 12% 2	330
	11th to 20th	Day	27% 19% 34% 14% 5% 1	362
	21st to end	Day	27% 15% 32% 19% 6% 2	594
April	1st to 10th	Day	25% 16% 34% 19% 5%	540
	11th to 20th	Day	24% 20% 28% 17% 9% 2	532
	21st to end	Day	25% 13% 31% 21% 10% 1	540
May	1st to 10th	Day	21% 14% 31% 24% 8% 2	543
	11th to 20th	Day	21% 10% 33% 24% 9% 3	747
	21st to end	Day	16% 8% 33% 24% 12% 6%	844
June	1st to 10th	Day	11% 9% 34% 31% 13% 4	780
	11th to 20th	Day	15% 9% 31% 29% 11% 5%	780
	21st to end	Day	13% 7% 34% 30% 13% 3	780
July	1st to 10th	Day	9% 4 27% 31% 20% 9%	771
	11th to 20th	Day	9% 6% 30% 32% 17% 7%	768
	21st to end	Day	7% 4 31% 37% 15% 6%	849
August	1st to 10th	Day	9% 4 26% 32% 20% 10%	746
	11th to 20th	Day	11% 4 23% 27% 23% 11%	559
	21st to end	Day	9% 4 24% 34% 21% 8%	627
September	1st to 10th	Day	13% 6% 26% 28% 21% 7%	570
	11th to 20th	Day	13% 2 23% 30% 20% 11%	570
	21st to end	Day	17% 9% 27% 24% 16% 8%	570
October	1st to 10th	Day	17% 10% 29% 26% 16% 3	511
	11th to 20th	Day	23% 17% 30% 23% 6% 1	360
	21st to end	Day	21% 14% 40% 18% 6% 1	387
November	1st to 10th	Day	19% 16% 38% 19% 7% 2	330
	11th to 20th	Day	22% 19% 37% 15% 7%	330
	21st to end	Day	25% 14% 41% 17% 3 1	330
December	1st to 10th	Day	18% 22% 37% 16% 6% 1	330
	11th to 20th	Day	23% 19% 34% 18% 5% 2	330
	21st to end	Day	29% 21% 34% 13% 4	363
January	1st to 10th	Night	19% 17% 36% 23% 5%	1050
	11th to 20th	Night	21% 17% 35% 20% 6% 1	1050
	21st to end	Night	20% 12% 37% 26% 5%	1155
February	1st to 10th	Night	20% 16% 36% 23% 6%	1029
	11th to 20th	Night	19% 16% 35% 25% 5%	823
	21st to end	Night	23% 16% 36% 20% 5%	692
March	1st to 10th	Night	19% 14% 33% 25% 8% 1	840
	11th to 20th	Night	18% 14% 35% 26% 7% 1	830
	21st to end	Night	24% 8% 28% 30% 8% 1	693
April	1st to 10th	Night	21% 13% 33% 26% 7%	630
	11th to 20th	Night	26% 9% 31% 23% 9% 1	623
	21st to end	Night	21% 8% 29% 31% 10% 1	630
May	1st to 10th	Night	18% 9% 29% 34% 9% 1	630
	11th to 20th	Night	18% 7% 29% 31% 14% 1	621
	21st to end	Night	16% 6% 23% 34% 20% 3	683
June	1st to 10th	Night	12% 3 25% 40% 19% 2	630
	11th to 20th	Night	14% 4 32% 31% 18% 1	630
	21st to end	Night	12% 3 25% 40% 19% 2	630
July	1st to 10th	Night	8% 2 19% 38% 29% 4	615
	11th to 20th	Night	7% 3 21% 40% 25% 4	612
	21st to end	Night	7% 2 18% 47% 24% 2	690
August	1st to 10th	Night	9% 1 16% 44% 27% 3	627
	11th to 20th	Night	9% 2 16% 37% 31% 5%	624
	21st to end	Night	8% 2 19% 40% 28% 3	693
September	1st to 10th	Night	9% 4 22% 33% 26% 6%	630
	11th to 20th	Night	12% 4 19% 31% 29% 5%	744
	21st to end	Night	14% 8% 23% 28% 23% 4	840
October	1st to 10th	Night	15% 6% 27% 32% 18% 2	840
	11th to 20th	Night	21% 10% 33% 26% 10%	840
	21st to end	Night	23% 9% 31% 27% 10% 1	913
November	1st to 10th	Night	19% 12% 35% 24% 10% 1	820
	11th to 20th	Night	21% 17% 34% 22% 6% 1	840
	21st to end	Night	23% 13% 36% 22% 5%	951
December	1st to 10th	Night	22% 16% 35% 21% 5%	1050
	11th to 20th	Night	22% 14% 34% 23% 6% 1	1050
	21st to end	Night	30% 13% 35% 20% 3	1155

Page generated at 2026-10-26 03:37:46. Version ac07

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