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 2024-11-03.

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% 3 7% 5% 5% 5% 4 6% 8% 38%	101335
	Night	13% 9% 3 7% 5% 4 4 4 5% 7% 37%	97729
Transparency	Day	43% 7% 13% 23% 12% 1	101126
	Night	45% 6% 12% 22% 13% 2	97610
Seeing	Day	17% 10% 31% 25% 12% 4	15869
	Night	18% 9% 30% 29% 13% 1	25707

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% 15% 7% 11% 5% 4 5% 3 5% 6% 29%	2527
	11th to 20th	Day	11% 12% 6% 13% 5% 4 6% 6% 8% 8% 20%	2530
	21st to end	Day	17% 19% 9% 10% 5% 3 3 3 4 6% 21%	2787
February	1st to 10th	Day	11% 14% 6% 9% 5% 4 5% 4 6% 8% 28%	1729
	11th to 20th	Day	12% 10% 4 8% 5% 5% 5% 3 6% 6% 35%	1848
	21st to end	Day	11% 13% 5% 12% 5% 4 5% 4 5% 6% 29%	1570
March	1st to 10th	Day	12% 10% 3 7% 4 4 5% 4 5% 6% 40%	3120
	11th to 20th	Day	11% 6% 4 8% 6% 5% 5% 4 5% 7% 40%	3264
	21st to end	Day	19% 11% 4 10% 5% 4 5% 4 5% 5% 27%	4165
April	1st to 10th	Day	16% 12% 3 8% 4 5% 5% 5% 5% 5% 30%	2280
	11th to 20th	Day	15% 9% 3 7% 5% 5% 4 3 6% 7% 35%	2254
	21st to end	Day	17% 9% 3 7% 5% 4 5% 4 5% 6% 35%	2413
May	1st to 10th	Day	14% 8% 3 8% 4 5% 5% 5% 6% 7% 35%	4082
	11th to 20th	Day	13% 6% 3 6% 4 5% 4 4 6% 8% 41%	4360
	21st to end	Day	11% 7% 2 6% 4 4 5% 4 6% 9% 42%	4824
June	1st to 10th	Day	9% 6% 2 6% 5% 5% 4 4 6% 8% 45%	2660
	11th to 20th	Day	10% 6% 2 5% 4 4 4 3 6% 9% 46%	2660
	21st to end	Day	8% 7% 3 6% 5% 5% 5% 4 7% 9% 41%	2660
July	1st to 10th	Day	11% 7% 3 7% 5% 5% 5% 4 7% 9% 37%	4440
	11th to 20th	Day	5% 3 1 5% 4 4 5% 5% 8% 11% 50%	4440
	21st to end	Day	6% 6% 2 6% 5% 5% 5% 5% 6% 9% 45%	4813
August	1st to 10th	Day	9% 6% 2 6% 4 4 5% 5% 7% 9% 42%	4370
	11th to 20th	Day	9% 4 2 6% 4 5% 5% 4 7% 9% 46%	3822
	21st to end	Day	7% 6% 3 7% 5% 4 4 4 6% 8% 46%	4180
September	1st to 10th	Day	10% 5% 3 6% 3 4 4 4 7% 8% 45%	2280
	11th to 20th	Day	10% 5% 2 5% 4 4 5% 3 5% 8% 50%	2157
	21st to end	Day	11% 6% 2 7% 5% 5% 4 4 6% 9% 41%	2090
October	1st to 10th	Day	12% 7% 3 6% 4 4 3 3 6% 7% 45%	2037
	11th to 20th	Day	17% 8% 3 8% 5% 5% 5% 3 6% 6% 33%	1865
	21st to end	Day	16% 10% 3 7% 5% 4 5% 3 5% 6% 36%	1881
November	1st to 10th	Day	11% 9% 3 7% 5% 4 4 4 5% 7% 42%	1690
	11th to 20th	Day	12% 11% 3 10% 6% 5% 5% 4 6% 8% 30%	1710
	21st to end	Day	18% 10% 3 6% 4 4 4 3 4 5% 38%	1606
December	1st to 10th	Day	14% 12% 4 9% 6% 6% 5% 4 7% 8% 26%	1520
	11th to 20th	Day	12% 12% 4 10% 5% 4 6% 5% 7% 7% 28%	1918
	21st to end	Day	18% 21% 7% 13% 5% 5% 4 2 4 4 16%	2783
January	1st to 10th	Night	14% 14% 7% 10% 5% 4 3 3 4 5% 31%	4428
	11th to 20th	Night	13% 14% 6% 14% 7% 5% 6% 5% 6% 7% 17%	4440
	21st to end	Night	18% 18% 7% 10% 5% 4 3 3 5% 6% 23%	4876
February	1st to 10th	Night	12% 14% 4 9% 6% 5% 3 3 5% 7% 31%	2451
	11th to 20th	Night	13% 10% 3 8% 4 4 4 4 5% 7% 39%	2218
	21st to end	Night	18% 11% 3 7% 4 4 4 3 5% 6% 35%	1884
March	1st to 10th	Night	15% 10% 3 7% 4 4 4 3 4 5% 40%	3733
	11th to 20th	Night	10% 6% 3 5% 4 4 4 4 6% 8% 46%	3722
	21st to end	Night	20% 10% 5% 11% 6% 5% 4 3 4 4 28%	3466
April	1st to 10th	Night	15% 9% 2 7% 4 5% 5% 4 6% 8% 35%	1900
	11th to 20th	Night	18% 9% 3 8% 4 4 4 4 4 5% 37%	1875
	21st to end	Night	17% 9% 2 6% 4 4 4 3 6% 6% 38%	1767
May	1st to 10th	Night	15% 8% 3 7% 5% 4 5% 4 6% 8% 36%	2813
	11th to 20th	Night	15% 7% 2 5% 4 4 6% 4 7% 8% 36%	2540
	21st to end	Night	12% 8% 3 8% 4 4 4 3 4 7% 42%	2743
June	1st to 10th	Night	9% 4 2 6% 5% 4 5% 4 6% 8% 46%	1520
	11th to 20th	Night	11% 6% 2 5% 5% 4 4 4 6% 9% 44%	1520
	21st to end	Night	9% 6% 3 6% 4 5% 4 3 6% 9% 45%	1520
July	1st to 10th	Night	12% 7% 2 7% 4 5% 5% 4 7% 7% 39%	2530
	11th to 20th	Night	4 3 1 5% 4 3 4 5% 8% 10% 54%	2530
	21st to end	Night	5% 4 2 6% 4 4 5% 5% 8% 9% 48%	2750
August	1st to 10th	Night	9% 5% 2 4 4 4 4 3 6% 9% 50%	2564
	11th to 20th	Night	8% 5% 2 7% 4 4 4 4 5% 8% 49%	3003
	21st to end	Night	7% 4 2 5% 4 5% 4 4 6% 10% 50%	3476
September	1st to 10th	Night	8% 4 2 7% 3 4 4 3 5% 6% 52%	1900
	11th to 20th	Night	10% 4 2 4 4 4 4 3 5% 7% 53%	2003
	21st to end	Night	13% 7% 3 6% 4 3 4 3 4 7% 46%	2090
October	1st to 10th	Night	12% 5% 2 6% 3 4 4 4 5% 6% 48%	2141
	11th to 20th	Night	16% 8% 3 6% 4 3 5% 3 4 6% 42%	2314
	21st to end	Night	19% 8% 2 7% 5% 4 4 3 5% 7% 36%	2717
November	1st to 10th	Night	12% 7% 2 7% 4 4 4 3 4 6% 46%	2433
	11th to 20th	Night	14% 10% 3 7% 6% 5% 5% 4 5% 6% 35%	2470
	21st to end	Night	17% 9% 4 6% 5% 4 4 3 6% 6% 37%	2569
December	1st to 10th	Night	16% 11% 3 8% 5% 5% 5% 4 5% 7% 29%	2660
	11th to 20th	Night	14% 13% 4 9% 5% 5% 5% 4 5% 6% 29%	3279
	21st to end	Night	20% 18% 5% 9% 6% 4 4 3 5% 5% 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	44% 7% 11% 24% 11% 3	3120
	11th to 20th	Day	43% 6% 11% 26% 13% 2	3264
	21st to end	Day	57% 7% 14% 15% 5% 2	4165
April	1st to 10th	Day	52% 9% 9% 19% 11%	2280
	11th to 20th	Day	46% 8% 10% 21% 12% 3	2254
	21st to end	Day	48% 7% 13% 18% 13% 1	2413
May	1st to 10th	Day	44% 8% 11% 22% 14% 1	4120
	11th to 20th	Day	38% 8% 14% 25% 13% 1	4364
	21st to end	Day	36% 10% 12% 22% 17% 3	4837
June	1st to 10th	Day	35% 6% 14% 25% 17% 2	2660
	11th to 20th	Day	34% 8% 14% 24% 19% 2	2660
	21st to end	Day	37% 9% 14% 23% 15% 2	2660
July	1st to 10th	Day	41% 8% 12% 25% 12% 2	4371
	11th to 20th	Day	25% 9% 17% 33% 16% 1	4365
	21st to end	Day	33% 9% 16% 21% 18% 3	4662
August	1st to 10th	Day	35% 7% 14% 30% 12% 1	4355
	11th to 20th	Day	31% 9% 13% 35% 11% 1	3861
	21st to end	Day	34% 8% 13% 24% 20% 1	4179
September	1st to 10th	Day	34% 8% 12% 28% 16% 2	2280
	11th to 20th	Day	31% 7% 12% 33% 16% 2	2157
	21st to end	Day	38% 8% 12% 29% 13% 1	2090
October	1st to 10th	Day	37% 5% 12% 31% 14% 1	2037
	11th to 20th	Day	49% 6% 11% 21% 11% 1	1865
	21st to end	Day	49% 6% 10% 23% 10% 1	1881
November	1st to 10th	Day	42% 5% 14% 24% 14% 1	1690
	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	46% 7% 11% 25% 9% 3	3733
	11th to 20th	Night	34% 6% 13% 27% 17% 3	3722
	21st to end	Night	59% 6% 8% 16% 10% 1	3466
April	1st to 10th	Night	46% 7% 10% 21% 15% 1	1900
	11th to 20th	Night	49% 5% 6% 18% 18% 4	1875
	21st to end	Night	45% 6% 12% 20% 16% 2	1767
May	1st to 10th	Night	43% 7% 12% 20% 15% 3	2840
	11th to 20th	Night	41% 8% 14% 24% 12% 1	2541
	21st to end	Night	41% 5% 10% 18% 17% 8%	2751
June	1st to 10th	Night	33% 8% 11% 28% 17% 2	1520
	11th to 20th	Night	36% 6% 10% 24% 21% 3	1520
	21st to end	Night	37% 7% 13% 25% 16% 3	1520
July	1st to 10th	Night	41% 7% 13% 21% 12% 5%	2490
	11th to 20th	Night	22% 7% 16% 36% 16% 3	2482
	21st to end	Night	30% 8% 15% 20% 24% 3	2662
August	1st to 10th	Night	31% 7% 14% 28% 19% 2	2555
	11th to 20th	Night	32% 6% 12% 34% 16% 1	3030
	21st to end	Night	28% 7% 13% 28% 20% 3	3476
September	1st to 10th	Night	32% 6% 11% 25% 23% 3	1900
	11th to 20th	Night	29% 6% 10% 35% 18% 2	2003
	21st to end	Night	39% 5% 9% 30% 16% 2	2090
October	1st to 10th	Night	35% 6% 11% 29% 17% 2	2141
	11th to 20th	Night	43% 5% 13% 21% 17% 1	2314
	21st to end	Night	48% 5% 12% 22% 11% 1	2717
November	1st to 10th	Night	39% 5% 12% 25% 17% 3	2433
	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% 19% 34% 16% 5% 1	298
	21st to end	Day	27% 13% 31% 21% 7% 2	506
April	1st to 10th	Day	24% 15% 35% 21% 6%	460
	11th to 20th	Day	23% 19% 28% 18% 10% 2	452
	21st to end	Day	26% 11% 29% 22% 11% 2	460
May	1st to 10th	Day	22% 12% 31% 26% 8% 2	463
	11th to 20th	Day	21% 8% 34% 25% 10% 3	649
	21st to end	Day	16% 7% 32% 25% 14% 7%	734
June	1st to 10th	Day	11% 8% 32% 31% 14% 4	680
	11th to 20th	Day	15% 6% 31% 31% 12% 5%	680
	21st to end	Day	14% 7% 31% 32% 14% 3	680
July	1st to 10th	Day	9% 4 26% 31% 21% 10%	671
	11th to 20th	Day	9% 5% 30% 31% 16% 8%	668
	21st to end	Day	6% 3 30% 38% 16% 7%	739
August	1st to 10th	Day	9% 3 26% 32% 20% 10%	649
	11th to 20th	Day	10% 4 22% 27% 23% 13%	479
	21st to end	Day	10% 4 21% 35% 22% 9%	539
September	1st to 10th	Day	13% 5% 26% 29% 22% 7%	490
	11th to 20th	Day	11% 2 23% 31% 21% 12%	490
	21st to end	Day	17% 9% 26% 24% 17% 7%	490
October	1st to 10th	Day	18% 10% 26% 26% 17% 4	437
	11th to 20th	Day	24% 17% 28% 23% 6% 1	300
	21st to end	Day	25% 15% 37% 16% 5% 1	330
November	1st to 10th	Day	16% 13% 40% 21% 8% 2	276
	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% 36% 26% 8% 1	751
	21st to end	Night	24% 7% 27% 31% 9% 1	627
April	1st to 10th	Night	20% 11% 34% 27% 7%	570
	11th to 20th	Night	26% 9% 31% 23% 9% 1	563
	21st to end	Night	22% 8% 29% 31% 11% 1	570
May	1st to 10th	Night	18% 9% 28% 35% 8% 1	570
	11th to 20th	Night	20% 5% 29% 32% 15% 1	561
	21st to end	Night	16% 5% 22% 34% 21% 3	617
June	1st to 10th	Night	12% 3 25% 39% 19% 2	570
	11th to 20th	Night	14% 3 31% 32% 19% 1	570
	21st to end	Night	12% 3 24% 39% 19% 2	570
July	1st to 10th	Night	9% 2 17% 38% 30% 4	555
	11th to 20th	Night	7% 2 22% 39% 26% 4	552
	21st to end	Night	7% 1 17% 46% 27% 2	624
August	1st to 10th	Night	9% 1 15% 44% 28% 3	567
	11th to 20th	Night	9% 2 16% 37% 32% 5%	564
	21st to end	Night	8% 2 17% 41% 29% 3	627
September	1st to 10th	Night	10% 3 21% 34% 26% 6%	570
	11th to 20th	Night	12% 4 19% 32% 28% 5%	673
	21st to end	Night	15% 8% 23% 27% 22% 4	760
October	1st to 10th	Night	15% 6% 26% 32% 19% 3	760
	11th to 20th	Night	21% 10% 33% 25% 10%	760
	21st to end	Night	25% 9% 31% 26% 9% 1	836
November	1st to 10th	Night	17% 11% 35% 25% 10% 1	749
	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

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