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 2024-11-06.

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% 8% 40%	101196
	Night	13% 7% 3 6% 4 4 4 3 5% 7% 43%	97833
Transparency	Day	40% 5% 10% 24% 18% 3	104928
	Night	38% 4 10% 24% 19% 5%	102240
Seeing	Day	17% 7% 22% 24% 20% 11%	15152
	Night	16% 6% 23% 31% 20% 3	24829

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	17% 7% 2 7% 4 4 4 4 6% 9% 35%	4082
	11th to 20th	Day	16% 8% 3 7% 4 4 4 3 6% 8% 37%	4081
	21st to end	Day	10% 7% 3 7% 5% 5% 4 4 6% 9% 40%	4476
June	1st to 10th	Day	10% 5% 2 7% 5% 5% 5% 5% 7% 8% 41%	2470
	11th to 20th	Day	5% 4 2 5% 6% 5% 5% 5% 8% 10% 46%	2658
	21st to end	Day	5% 4 2 6% 6% 6% 7% 6% 8% 11% 40%	2660
July	1st to 10th	Day	7% 5% 2 6% 6% 6% 6% 6% 8% 11% 38%	4440
	11th to 20th	Day	9% 5% 2 6% 5% 6% 6% 5% 8% 11% 36%	4344
	21st to end	Day	16% 10% 4 9% 6% 6% 6% 5% 7% 8% 25%	4466
August	1st to 10th	Day	3 3 2 4 4 5% 5% 4 7% 11% 51%	3864
	11th to 20th	Day	6% 4 2 7% 5% 5% 6% 5% 7% 10% 41%	3729
	21st to end	Day	6% 4 1 5% 4 4 4 4 6% 8% 53%	4180
September	1st to 10th	Day	11% 6% 2 6% 6% 6% 5% 4 7% 7% 40%	2256
	11th to 20th	Day	13% 6% 2 5% 4 5% 5% 4 6% 7% 43%	2090
	21st to end	Day	11% 5% 1 5% 4 3 4 3 6% 6% 50%	2090
October	1st to 10th	Day	10% 5% 2 5% 3 3 3 3 4 6% 56%	2090
	11th to 20th	Day	11% 6% 2 5% 3 3 4 2 4 6% 53%	2045
	21st to end	Day	16% 6% 2 5% 4 3 4 3 4 5% 48%	1905
November	1st to 10th	Day	12% 5% 1 4 3 3 3 2 4 6% 57%	1717
	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	13% 9% 3 8% 4 4 4 3 5% 7% 41%	2813
	11th to 20th	Night	12% 8% 2 7% 5% 3 4 4 5% 7% 43%	2812
	21st to end	Night	6% 5% 2 7% 5% 5% 5% 4 7% 9% 43%	3079
June	1st to 10th	Night	8% 7% 2 5% 5% 4 4 4 8% 8% 45%	1705
	11th to 20th	Night	4 4 1 4 4 3 4 4 6% 11% 55%	1520
	21st to end	Night	4 3 2 4 5% 5% 3 4 9% 11% 49%	1520
July	1st to 10th	Night	6% 4 2 5% 4 5% 6% 6% 8% 12% 41%	2530
	11th to 20th	Night	8% 4 2 6% 3 4 5% 4 7% 12% 44%	2618
	21st to end	Night	10% 10% 4 9% 7% 6% 6% 5% 7% 8% 28%	3087
August	1st to 10th	Night	4 3 1 4 3 3 3 3 5% 9% 61%	3047
	11th to 20th	Night	4 3 2 5% 4 4 5% 5% 8% 11% 49%	3100
	21st to end	Night	5% 3 1 5% 3 4 4 4 6% 9% 56%	3476
September	1st to 10th	Night	10% 6% 2 5% 4 4 5% 4 5% 6% 49%	1905
	11th to 20th	Night	10% 5% 2 6% 4 4 4 3 6% 7% 47%	2090
	21st to end	Night	10% 5% 2 4 3 4 3 3 6% 6% 54%	2090
October	1st to 10th	Night	8% 5% 2 4 3 3 3 3 4 6% 61%	2090
	11th to 20th	Night	14% 6% 2 5% 4 3 3 3 5% 6% 51%	2132
	21st to end	Night	14% 7% 2 5% 3 3 3 3 4 6% 50%	2691
November	1st to 10th	Night	11% 6% 2 5% 4 3 4 3 5% 4 54%	2483
	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	45% 5% 12% 23% 13% 1	4120
	11th to 20th	Day	45% 4 13% 25% 13%	4085
	21st to end	Day	40% 6% 10% 24% 20% 1	4489
June	1st to 10th	Day	39% 6% 11% 25% 17% 2	2470
	11th to 20th	Day	31% 5% 16% 26% 19% 3	2658
	21st to end	Day	33% 7% 16% 22% 16% 4	2660
July	1st to 10th	Day	37% 7% 20% 27% 8% 2	4371
	11th to 20th	Day	38% 6% 19% 27% 8% 2	4269
	21st to end	Day	55% 6% 13% 19% 7% 1	4324
August	1st to 10th	Day	24% 6% 16% 33% 19% 1	3851
	11th to 20th	Day	34% 6% 15% 27% 15% 2	3765
	21st to end	Day	28% 5% 11% 31% 24% 2	4179
September	1st to 10th	Day	40% 6% 11% 21% 17% 5%	2256
	11th to 20th	Day	39% 6% 10% 23% 20% 3	2090
	21st to end	Day	34% 3 11% 25% 22% 5%	2090
October	1st to 10th	Day	21% 3 6% 18% 43% 10%	3480
	11th to 20th	Day	24% 2 6% 24% 30% 14%	3376
	21st to end	Day	31% 3 6% 24% 29% 8%	3117
November	1st to 10th	Day	30% 3 8% 24% 29% 5%	1717
	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	43% 5% 13% 24% 14% 1	2840
	11th to 20th	Night	41% 5% 16% 21% 17% 1	2813
	21st to end	Night	35% 6% 15% 26% 17% 1	3087
June	1st to 10th	Night	34% 6% 14% 25% 17% 3	1705
	11th to 20th	Night	23% 5% 17% 33% 18% 3	1520
	21st to end	Night	26% 7% 17% 31% 15% 4	1520
July	1st to 10th	Night	32% 7% 22% 28% 9% 2	2490
	11th to 20th	Night	29% 7% 19% 34% 8% 3	2570
	21st to end	Night	52% 7% 13% 19% 8% 1	2988
August	1st to 10th	Night	19% 6% 12% 39% 23% 1	3036
	11th to 20th	Night	25% 6% 22% 30% 15% 1	3130
	21st to end	Night	23% 6% 13% 32% 24% 3	3476
September	1st to 10th	Night	35% 5% 11% 25% 19% 5%	1905
	11th to 20th	Night	35% 4 11% 22% 26% 2	2090
	21st to end	Night	30% 4 10% 25% 24% 7%	2090
October	1st to 10th	Night	19% 3 6% 20% 41% 12%	3480
	11th to 20th	Night	22% 2 4 21% 31% 19%	3540
	21st to end	Night	25% 3 6% 26% 29% 12%	4429
November	1st to 10th	Night	34% 3 6% 23% 26% 8%	2483
	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% 5% 22% 26% 19% 10%	487
	21st to end	Day	13% 3 18% 27% 23% 16%	529
June	1st to 10th	Day	14% 1 18% 22% 24% 20%	490
	11th to 20th	Day	6% 2 14% 28% 33% 17%	678
	21st to end	Day	7% 2 16% 33% 25% 17%	680
July	1st to 10th	Day	10% 2 11% 26% 30% 21%	671
	11th to 20th	Day	10% 1 9% 25% 31% 24%	611
	21st to end	Day	9% 3 9% 24% 30% 25%	532
August	1st to 10th	Day	8% 1 7% 26% 37% 21%	486
	11th to 20th	Day	12% 1 10% 29% 33% 15%	479
	21st to end	Day	14% 1 4 20% 36% 24%	539
September	1st to 10th	Day	12% 1 10% 27% 33% 17%	490
	11th to 20th	Day	16% 2 8% 23% 30% 21%	490
	21st to end	Day	16% 4 14% 27% 27% 12%	490
October	1st to 10th	Day	15% 2 16% 29% 27% 11%	490
	11th to 20th	Day	13% 8% 31% 28% 16% 4	445
	21st to end	Day	24% 7% 29% 28% 10% 2	330
November	1st to 10th	Day	17% 7% 30% 29% 14% 4	285
	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 22% 36% 23% 5%	561
	21st to end	Night	9% 2 14% 38% 32% 6%	617
June	1st to 10th	Night	13% 1 13% 36% 32% 6%	570
	11th to 20th	Night	5% 1 10% 37% 41% 6%	570
	21st to end	Night	5% 1 11% 37% 39% 8%	570
July	1st to 10th	Night	10% 1 5% 31% 43% 10%	555
	11th to 20th	Night	9% 1 6% 29% 43% 12%	552
	21st to end	Night	7% 1 6% 28% 49% 9%	624
August	1st to 10th	Night	8% 1 3 28% 50% 10%	567
	11th to 20th	Night	7% 1 7% 41% 38% 7%	564
	21st to end	Night	10% 1 4 29% 47% 10%	627
September	1st to 10th	Night	11% 2 7% 30% 43% 5%	575
	11th to 20th	Night	13% 1 10% 29% 41% 6%	760
	21st to end	Night	12% 3 13% 32% 35% 5%	760
October	1st to 10th	Night	11% 3 15% 34% 30% 7%	760
	11th to 20th	Night	18% 4 24% 34% 19% 2	760
	21st to end	Night	17% 5% 26% 32% 17% 2	836
November	1st to 10th	Night	13% 6% 23% 38% 17% 3	764
	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

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