Frankfort
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Frankfort clear sky chart from 2005-11-06 to 2024-11-10.

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	14% 8% 3 7% 4 4 5% 4 6% 7% 38%	101713
	Night	14% 9% 3 7% 4 4 4 3 5% 7% 40%	97392
Transparency	Day	44% 4 10% 24% 16% 2	105424
	Night	43% 4 10% 24% 17% 3	101820
Seeing	Day	17% 9% 24% 25% 17% 9%	15223
	Night	18% 7% 24% 31% 17% 2	24712

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	15% 15% 7% 7% 4 5% 4 3 5% 6% 28%	2836
	11th to 20th	Day	17% 13% 5% 14% 5% 6% 4 3 4 5% 26%	2840
	21st to end	Day	28% 14% 8% 6% 3 4 3 2 4 4 23%	3124
February	1st to 10th	Day	18% 12% 4 9% 5% 4 3 3 4 5% 32%	1871
	11th to 20th	Day	18% 10% 3 9% 5% 4 4 3 5% 5% 34%	1848
	21st to end	Day	18% 13% 4 7% 4 4 4 3 6% 6% 31%	1570
March	1st to 10th	Day	25% 13% 4 6% 4 3 3 3 3 4 32%	3120
	11th to 20th	Day	14% 6% 3 6% 4 4 4 3 5% 7% 44%	3476
	21st to end	Day	15% 8% 3 8% 4 4 4 3 5% 8% 38%	3815
April	1st to 10th	Day	14% 8% 3 7% 4 4 4 4 5% 8% 39%	2262
	11th to 20th	Day	17% 8% 2 6% 4 4 5% 3 5% 6% 40%	2264
	21st to end	Day	17% 7% 2 6% 5% 4 5% 3 6% 6% 39%	2470
May	1st to 10th	Day	20% 8% 3 8% 5% 5% 5% 4 6% 7% 30%	4082
	11th to 20th	Day	19% 7% 2 7% 4 4 4 4 5% 6% 38%	4081
	21st to end	Day	11% 6% 2 7% 5% 5% 5% 5% 7% 10% 37%	4476
June	1st to 10th	Day	11% 4 2 7% 5% 5% 5% 4 5% 7% 43%	2470
	11th to 20th	Day	7% 5% 2 6% 5% 5% 6% 5% 7% 9% 44%	2595
	21st to end	Day	8% 6% 2 6% 5% 5% 5% 4 7% 10% 42%	2660
July	1st to 10th	Day	13% 6% 2 6% 4 5% 5% 4 7% 10% 38%	4440
	11th to 20th	Day	7% 4 2 5% 4 5% 5% 4 8% 11% 44%	4198
	21st to end	Day	14% 9% 3 9% 7% 7% 6% 5% 6% 8% 25%	4466
August	1st to 10th	Day	8% 5% 2 4 4 3 5% 4 7% 11% 46%	4104
	11th to 20th	Day	8% 5% 2 6% 5% 5% 6% 5% 8% 11% 40%	3956
	21st to end	Day	5% 3 2 6% 3 4 4 4 6% 8% 55%	4180
September	1st to 10th	Day	14% 5% 2 6% 3 5% 5% 4 5% 8% 43%	2174
	11th to 20th	Day	10% 5% 2 6% 4 4 5% 3 6% 7% 48%	2090
	21st to end	Day	15% 6% 2 5% 4 4 4 3 4 6% 47%	2090
October	1st to 10th	Day	10% 4 1 5% 3 4 5% 3 5% 8% 52%	2090
	11th to 20th	Day	12% 6% 2 6% 4 3 4 3 4 7% 48%	1965
	21st to end	Day	18% 5% 3 6% 3 4 5% 3 4 6% 43%	1940
November	1st to 10th	Day	13% 5% 2 4 4 3 4 3 2 6% 55%	1753
	11th to 20th	Day	15% 9% 3 6% 4 4 3 3 4 6% 42%	1710
	21st to end	Day	19% 9% 2 6% 4 3 4 3 6% 6% 39%	1710
December	1st to 10th	Day	22% 13% 4 7% 4 4 3 2 5% 4 31%	1710
	11th to 20th	Day	16% 12% 4 8% 5% 4 5% 4 5% 5% 32%	2153
	21st to end	Day	19% 16% 5% 8% 6% 4 5% 3 5% 6% 23%	3124
January	1st to 10th	Night	16% 16% 5% 9% 5% 4 4 3 5% 5% 27%	4109
	11th to 20th	Night	18% 15% 5% 12% 6% 4 3 2 3 3 28%	4120
	21st to end	Night	25% 14% 5% 7% 4 3 3 2 4 5% 27%	4532
February	1st to 10th	Night	21% 12% 4 7% 5% 4 4 3 5% 5% 29%	2307
	11th to 20th	Night	20% 10% 3 8% 4 4 4 4 4 5% 33%	2218
	21st to end	Night	22% 13% 3 8% 5% 3 4 3 3 6% 29%	1884
March	1st to 10th	Night	22% 14% 3 6% 4 4 3 3 4 5% 33%	3733
	11th to 20th	Night	15% 6% 2 5% 3 3 4 3 5% 6% 48%	3483
	21st to end	Night	15% 8% 2 7% 5% 5% 4 4 6% 6% 40%	3817
April	1st to 10th	Night	13% 7% 2 5% 5% 5% 5% 5% 6% 7% 41%	1933
	11th to 20th	Night	16% 7% 3 6% 4 4 4 3 5% 6% 42%	1863
	21st to end	Night	16% 7% 3 6% 5% 4 4 3 5% 6% 40%	1710
May	1st to 10th	Night	20% 9% 4 8% 5% 5% 5% 4 6% 7% 27%	2813
	11th to 20th	Night	18% 6% 2 5% 4 3 4 4 7% 8% 39%	2812
	21st to end	Night	9% 5% 2 6% 5% 4 5% 4 7% 11% 42%	3079
June	1st to 10th	Night	9% 4 2 6% 3 5% 4 3 6% 10% 48%	1710
	11th to 20th	Night	6% 5% 2 5% 4 4 3 5% 7% 10% 50%	1577
	21st to end	Night	6% 4 1 5% 3 5% 5% 3 8% 11% 47%	1520
July	1st to 10th	Night	8% 5% 2 7% 5% 5% 4 4 6% 9% 46%	2530
	11th to 20th	Night	7% 4 2 5% 4 4 4 3 6% 9% 52%	2747
	21st to end	Night	12% 9% 4 10% 5% 5% 6% 4 7% 8% 31%	3087
August	1st to 10th	Night	7% 4 2 5% 4 4 4 4 6% 11% 50%	2825
	11th to 20th	Night	6% 6% 2 6% 5% 5% 6% 4 6% 9% 44%	2870
	21st to end	Night	4 3 1 3 3 3 4 3 6% 9% 62%	3476
September	1st to 10th	Night	11% 5% 2 4 3 5% 4 3 5% 8% 50%	1985
	11th to 20th	Night	9% 5% 2 5% 3 4 4 3 4 7% 53%	2090
	21st to end	Night	12% 6% 3 5% 4 3 3 2 5% 5% 52%	2090
October	1st to 10th	Night	9% 4 1 6% 4 3 4 2 5% 6% 57%	2090
	11th to 20th	Night	14% 5% 2 5% 4 4 4 3 5% 6% 48%	2213
	21st to end	Night	17% 7% 2 6% 4 3 3 3 4 5% 45%	2655
November	1st to 10th	Night	12% 6% 2 5% 4 3 4 3 5% 5% 50%	2530
	11th to 20th	Night	15% 9% 3 5% 4 4 3 3 5% 6% 44%	2470
	21st to end	Night	17% 10% 2 6% 5% 3 4 3 5% 6% 40%	2470
December	1st to 10th	Night	22% 10% 3 7% 4 3 3 3 5% 6% 33%	2470
	11th to 20th	Night	19% 12% 5% 8% 5% 3 3 3 4 6% 34%	3042
	21st to end	Night	18% 16% 5% 10% 6% 5% 5% 4 4 6% 21%	4532

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% 2 11% 18% 10% 1	2837
	11th to 20th	Day	63% 2 8% 19% 7% 1	2840
	21st to end	Day	66% 1 6% 21% 5% 1	3124
February	1st to 10th	Day	55% 3 7% 23% 10% 2	1871
	11th to 20th	Day	54% 3 7% 22% 12% 3	1858
	21st to end	Day	55% 3 8% 21% 10% 3	1570
March	1st to 10th	Day	57% 2 7% 19% 10% 5%	3120
	11th to 20th	Day	40% 3 11% 26% 19% 1	3476
	21st to end	Day	46% 3 12% 26% 12% 1	3815
April	1st to 10th	Day	43% 3 12% 25% 14% 3	2262
	11th to 20th	Day	46% 3 8% 23% 16% 3	2264
	21st to end	Day	46% 4 11% 25% 12% 2	2470
May	1st to 10th	Day	53% 5% 13% 20% 9%	4120
	11th to 20th	Day	48% 3 12% 23% 13%	4085
	21st to end	Day	41% 5% 14% 19% 19% 2	4489
June	1st to 10th	Day	40% 5% 10% 26% 18% 2	2470
	11th to 20th	Day	34% 6% 15% 25% 18% 2	2595
	21st to end	Day	37% 6% 14% 21% 18% 4	2660
July	1st to 10th	Day	42% 4 13% 22% 17% 1	4371
	11th to 20th	Day	32% 5% 12% 35% 14% 2	4126
	21st to end	Day	55% 5% 11% 16% 11% 1	4324
August	1st to 10th	Day	30% 6% 14% 36% 13% 1	4091
	11th to 20th	Day	36% 4 11% 32% 15% 2	3995
	21st to end	Day	27% 5% 11% 35% 19% 3	4179
September	1st to 10th	Day	39% 5% 10% 22% 19% 6%	2174
	11th to 20th	Day	36% 4 9% 25% 23% 4	2090
	21st to end	Day	38% 5% 7% 24% 23% 3	2090
October	1st to 10th	Day	21% 3 5% 29% 39% 3	3480
	11th to 20th	Day	27% 3 8% 29% 31% 3	3244
	21st to end	Day	32% 2 8% 30% 22% 6%	3177
November	1st to 10th	Day	34% 2 8% 29% 23% 4	1753
	11th to 20th	Day	44% 2 8% 23% 18% 5%	1710
	21st to end	Day	46% 3 8% 23% 18% 2	1710
December	1st to 10th	Day	58% 2 9% 21% 9% 1	1710
	11th to 20th	Day	55% 3 8% 19% 14% 1	2150
	21st to end	Day	63% 3 9% 16% 7% 1	3124
January	1st to 10th	Night	59% 3 8% 17% 11% 1	4109
	11th to 20th	Night	63% 2 7% 19% 9% 2	4120
	21st to end	Night	60% 3 8% 19% 9% 1	4532
February	1st to 10th	Night	56% 3 9% 21% 9% 1	2307
	11th to 20th	Night	54% 3 7% 22% 13% 1	2219
	21st to end	Night	58% 2 10% 14% 12% 3	1884
March	1st to 10th	Night	56% 2 6% 22% 12% 2	3733
	11th to 20th	Night	38% 3 10% 28% 17% 3	3483
	21st to end	Night	45% 3 10% 26% 14% 1	3817
April	1st to 10th	Night	41% 4 10% 24% 18% 3	1933
	11th to 20th	Night	43% 3 7% 20% 19% 6%	1863
	21st to end	Night	45% 4 11% 24% 13% 3	1710
May	1st to 10th	Night	56% 4 11% 20% 8% 2	2840
	11th to 20th	Night	43% 5% 14% 26% 11% 1	2813
	21st to end	Night	34% 7% 13% 25% 17% 3	3087
June	1st to 10th	Night	32% 4 13% 29% 17% 5%	1710
	11th to 20th	Night	29% 6% 15% 24% 21% 5%	1577
	21st to end	Night	30% 6% 18% 24% 16% 6%	1520
July	1st to 10th	Night	36% 6% 11% 26% 18% 3	2490
	11th to 20th	Night	29% 5% 12% 35% 17% 2	2696
	21st to end	Night	49% 6% 12% 20% 12% 1	2988
August	1st to 10th	Night	29% 5% 15% 36% 13% 2	2814
	11th to 20th	Night	35% 6% 10% 31% 16% 2	2897
	21st to end	Night	19% 4 14% 35% 22% 5%	3476
September	1st to 10th	Night	33% 5% 12% 23% 21% 6%	1985
	11th to 20th	Night	31% 4 10% 25% 26% 4	2090
	21st to end	Night	35% 4 7% 24% 24% 5%	2090
October	1st to 10th	Night	22% 3 6% 21% 45% 3	3480
	11th to 20th	Night	26% 2 7% 26% 34% 4	3673
	21st to end	Night	32% 2 6% 22% 30% 7%	4368
November	1st to 10th	Night	36% 3 7% 25% 24% 4	2530
	11th to 20th	Night	42% 2 7% 22% 22% 5%	2470
	21st to end	Night	46% 2 9% 25% 16% 2	2470
December	1st to 10th	Night	53% 3 10% 21% 12% 1	2470
	11th to 20th	Night	53% 3 8% 22% 13% 2	3044
	21st to end	Night	65% 3 9% 15% 7%	4532

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	24% 19% 32% 18% 7% 1	270
	11th to 20th	Day	28% 21% 31% 16% 4	270
	21st to end	Day	26% 16% 40% 14% 3	297
February	1st to 10th	Day	24% 16% 39% 16% 4	270
	11th to 20th	Day	31% 20% 34% 11% 3 1	270
	21st to end	Day	32% 16% 37% 11% 3	225
March	1st to 10th	Day	26% 19% 38% 13% 4	270
	11th to 20th	Day	22% 15% 38% 18% 7%	456
	21st to end	Day	26% 14% 34% 18% 8%	506
April	1st to 10th	Day	20% 15% 28% 24% 11% 1	460
	11th to 20th	Day	21% 14% 27% 21% 13% 4	452
	21st to end	Day	20% 10% 32% 26% 8% 3	460
May	1st to 10th	Day	20% 11% 29% 25% 11% 5%	463
	11th to 20th	Day	18% 7% 25% 26% 16% 8%	487
	21st to end	Day	13% 4 21% 29% 21% 13%	529
June	1st to 10th	Day	13% 4 19% 26% 25% 12%	490
	11th to 20th	Day	8% 4 18% 33% 26% 11%	615
	21st to end	Day	10% 5% 21% 31% 21% 12%	680
July	1st to 10th	Day	14% 3 13% 25% 23% 23%	671
	11th to 20th	Day	8% 3 17% 26% 27% 18%	533
	21st to end	Day	13% 3 11% 30% 27% 16%	532
August	1st to 10th	Day	12% 3 13% 25% 27% 20%	486
	11th to 20th	Day	11% 3 13% 33% 27% 14%	479
	21st to end	Day	9% 3 8% 26% 32% 23%	539
September	1st to 10th	Day	14% 2 12% 28% 28% 16%	490
	11th to 20th	Day	11% 2 10% 27% 33% 18%	490
	21st to end	Day	17% 6% 17% 23% 26% 10%	490
October	1st to 10th	Day	12% 3 16% 35% 24% 10%	490
	11th to 20th	Day	13% 12% 28% 28% 14% 5%	490
	21st to end	Day	20% 8% 37% 22% 12% 1	389
November	1st to 10th	Day	16% 7% 30% 32% 11% 4	297
	11th to 20th	Day	23% 13% 30% 23% 10% 1	270
	21st to end	Day	23% 9% 32% 26% 9%	270
December	1st to 10th	Day	23% 19% 29% 21% 7% 1	270
	11th to 20th	Day	19% 14% 39% 19% 8%	270
	21st to end	Day	28% 19% 31% 16% 5%	297
January	1st to 10th	Night	24% 15% 32% 25% 4	760
	11th to 20th	Night	29% 14% 32% 22% 4	760
	21st to end	Night	24% 11% 37% 25% 2	836
February	1st to 10th	Night	29% 11% 32% 26% 3	760
	11th to 20th	Night	27% 11% 37% 23% 2	743
	21st to end	Night	29% 12% 38% 19% 2	628
March	1st to 10th	Night	24% 11% 33% 27% 5%	760
	11th to 20th	Night	25% 9% 35% 25% 6%	760
	21st to end	Night	22% 12% 29% 30% 7%	836
April	1st to 10th	Night	16% 10% 33% 33% 9%	603
	11th to 20th	Night	18% 8% 32% 29% 11% 1	563
	21st to end	Night	18% 6% 34% 32% 9% 1	570
May	1st to 10th	Night	20% 5% 27% 32% 15% 1	570
	11th to 20th	Night	16% 6% 17% 39% 19% 4	561
	21st to end	Night	9% 3 17% 37% 28% 6%	617
June	1st to 10th	Night	10% 2 14% 43% 27% 3	570
	11th to 20th	Night	8% 2 12% 42% 32% 4	570
	21st to end	Night	6% 2 14% 46% 28% 3	570
July	1st to 10th	Night	12% 2 10% 29% 37% 10%	555
	11th to 20th	Night	8% 1 9% 36% 39% 6%	552
	21st to end	Night	12% 2 8% 38% 35% 6%	624
August	1st to 10th	Night	10% 1 7% 35% 43% 5%	567
	11th to 20th	Night	7% 3 7% 40% 38% 5%	564
	21st to end	Night	7% 1 5% 36% 43% 7%	627
September	1st to 10th	Night	13% 1 8% 35% 37% 6%	655
	11th to 20th	Night	12% 3 10% 32% 39% 6%	760
	21st to end	Night	14% 4 15% 36% 29% 3	760
October	1st to 10th	Night	11% 3 18% 35% 28% 5%	760
	11th to 20th	Night	16% 6% 25% 35% 16% 2	760
	21st to end	Night	21% 6% 29% 30% 13% 1	836
November	1st to 10th	Night	15% 7% 25% 34% 17% 2	779
	11th to 20th	Night	18% 9% 32% 29% 11% 1	760
	21st to end	Night	21% 10% 26% 31% 11% 1	760
December	1st to 10th	Night	28% 9% 29% 28% 7%	760
	11th to 20th	Night	26% 9% 32% 26% 7% 1	760
	21st to end	Night	29% 12% 28% 26% 4	836

Page generated at 2024-11-07 06:55:45. Version ac07

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