Fort Griffin State Historic Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fort Griffin State Historic Site clear sky chart from 2005-11-06 to 2024-11-04.

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	8% 4 1 4 3 3 3 3 5% 6% 59%	101033
	Night	8% 4 1 4 3 3 3 3 5% 6% 61%	98103
Transparency	Day	26% 4 8% 23% 28% 12%	104877
	Night	24% 4 8% 22% 28% 15%	102386
Seeing	Day	9% 6% 23% 31% 24% 8%	15128
	Night	9% 6% 31% 39% 14% 1	25011

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	8% 7% 2 5% 4 2 3 2 4 4 60%	2847
	11th to 20th	Day	7% 6% 1 3 2 2 2 2 4 6% 66%	2850
	21st to end	Day	15% 8% 2 5% 3 3 3 2 3 5% 51%	3327
February	1st to 10th	Day	11% 6% 1 4 2 2 2 3 5% 6% 57%	1900
	11th to 20th	Day	10% 7% 2 5% 3 3 3 2 4 5% 55%	1849
	21st to end	Day	14% 7% 2 3 2 2 2 2 3 5% 58%	1570
March	1st to 10th	Day	13% 5% 1 4 3 3 3 3 5% 7% 54%	3244
	11th to 20th	Day	15% 5% 2 4 4 3 4 3 4 5% 52%	3480
	21st to end	Day	7% 6% 2 6% 5% 4 4 4 6% 6% 51%	3814
April	1st to 10th	Day	8% 4 1 4 3 4 3 3 5% 6% 58%	2099
	11th to 20th	Day	11% 5% 2 4 3 2 4 3 4 5% 57%	2254
	21st to end	Day	9% 4 1 4 4 3 3 2 5% 4 60%	2412
May	1st to 10th	Day	13% 4 2 5% 3 4 4 4 5% 6% 52%	4082
	11th to 20th	Day	13% 5% 2 5% 3 3 3 3 4 6% 54%	4082
	21st to end	Day	10% 4 2 6% 4 4 4 4 5% 7% 49%	4477
June	1st to 10th	Day	6% 3 1 5% 3 4 4 4 5% 8% 57%	2470
	11th to 20th	Day	4 2 1 4 3 4 4 4 5% 7% 62%	2470
	21st to end	Day	6% 2 1 3 3 4 3 3 5% 6% 63%	2470
July	1st to 10th	Day	7% 4 2 4 3 3 4 3 5% 8% 56%	4120
	11th to 20th	Day	3 2 1 3 3 3 3 4 6% 9% 63%	4120
	21st to end	Day	3 2 1 3 3 3 3 3 5% 8% 65%	4465
August	1st to 10th	Day	2 1 1 3 3 3 3 3 4 7% 72%	4089
	11th to 20th	Day	3 2 1 3 2 3 3 3 5% 8% 66%	3726
	21st to end	Day	4 2 1 3 2 3 4 3 5% 8% 65%	4180
September	1st to 10th	Day	11% 4 2 4 3 4 3 3 4 5% 56%	2100
	11th to 20th	Day	11% 5% 2 4 4 3 4 3 5% 7% 51%	2090
	21st to end	Day	9% 3 2 3 2 3 3 3 4 6% 62%	2090
October	1st to 10th	Day	5% 2 1 3 3 3 3 3 4 6% 66%	2090
	11th to 20th	Day	9% 3 1 3 2 2 3 2 4 4 68%	1995
	21st to end	Day	11% 4 1 3 2 2 2 2 3 3 68%	2090
November	1st to 10th	Day	8% 4 2 4 3 2 3 3 4 5% 63%	1755
	11th to 20th	Day	6% 3 1 3 3 2 3 2 5% 6% 65%	1710
	21st to end	Day	12% 4 1 5% 3 3 3 2 3 5% 59%	1710
December	1st to 10th	Day	11% 6% 2 4 3 3 3 3 4 6% 56%	1710
	11th to 20th	Day	9% 4 2 4 3 3 4 4 4 6% 56%	2161
	21st to end	Day	10% 6% 2 5% 4 3 3 2 3 3 60%	3135
January	1st to 10th	Night	11% 4 1 3 3 2 2 2 4 5% 63%	4108
	11th to 20th	Night	8% 5% 1 3 2 2 2 2 4 4 66%	4120
	21st to end	Night	12% 8% 2 4 3 3 3 2 4 5% 54%	4371
February	1st to 10th	Night	10% 5% 2 5% 3 3 3 3 4 5% 57%	2280
	11th to 20th	Night	11% 5% 2 5% 3 3 3 3 5% 5% 56%	2218
	21st to end	Night	11% 6% 2 4 2 3 3 2 4 4 62%	1884
March	1st to 10th	Night	9% 6% 2 5% 3 3 3 3 3 5% 58%	3616
	11th to 20th	Night	12% 4 1 3 2 3 3 3 6% 7% 55%	3480
	21st to end	Night	5% 7% 2 5% 4 3 4 4 6% 5% 55%	3817
April	1st to 10th	Night	6% 4 1 4 3 3 3 2 4 8% 60%	2076
	11th to 20th	Night	10% 3 2 4 3 3 4 3 5% 5% 57%	1877
	21st to end	Night	8% 4 1 3 2 2 2 3 5% 6% 63%	1767
May	1st to 10th	Night	14% 5% 2 5% 4 3 4 3 3 5% 52%	2823
	11th to 20th	Night	8% 4 2 5% 4 4 3 4 5% 6% 55%	2823
	21st to end	Night	9% 4 1 3 2 2 3 3 6% 7% 58%	3090
June	1st to 10th	Night	4 2 1 4 3 3 4 5% 7% 10% 57%	1710
	11th to 20th	Night	2 2 1 3 3 3 4 4 6% 9% 64%	1710
	21st to end	Night	4 2 1 3 3 3 3 3 5% 6% 67%	1710
July	1st to 10th	Night	5% 4 1 5% 3 3 3 3 6% 9% 58%	2850
	11th to 20th	Night	2 1 1 2 2 2 3 3 6% 11% 68%	2850
	21st to end	Night	2 1 1 3 3 3 3 3 5% 8% 68%	3098
August	1st to 10th	Night	1 1 2 2 2 2 2 5% 8% 74%	2836
	11th to 20th	Night	2 2 1 3 2 2 2 3 5% 8% 68%	3110
	21st to end	Night	3 3 1 3 3 3 4 3 5% 8% 64%	3487
September	1st to 10th	Night	9% 4 1 4 3 3 5% 3 4 6% 59%	2080
	11th to 20th	Night	10% 4 2 5% 4 3 3 3 5% 7% 54%	2090
	21st to end	Night	7% 3 1 4 2 3 2 3 5% 5% 63%	2090
October	1st to 10th	Night	6% 3 1 2 2 2 3 3 4 7% 67%	2090
	11th to 20th	Night	8% 3 1 3 2 2 2 2 3 5% 70%	2163
	21st to end	Night	9% 4 1 3 2 2 2 2 3 4 67%	2508
November	1st to 10th	Night	8% 4 1 3 2 2 2 2 4 5% 66%	2393
	11th to 20th	Night	4 3 1 4 3 3 4 3 5% 5% 66%	2470
	21st to end	Night	13% 4 1 3 3 3 3 3 4 6% 57%	2470
December	1st to 10th	Night	9% 4 1 4 3 3 3 2 4 6% 61%	2470
	11th to 20th	Night	9% 5% 2 4 3 3 3 3 5% 6% 57%	3036
	21st to end	Night	9% 5% 2 5% 3 3 3 3 4 5% 59%	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	30% 2 5% 18% 30% 15%	2848
	11th to 20th	Day	22% 2 7% 19% 36% 13%	2850
	21st to end	Day	38% 2 5% 19% 28% 9%	3327
February	1st to 10th	Day	29% 4 6% 20% 27% 15%	1900
	11th to 20th	Day	33% 3 5% 19% 25% 14%	1859
	21st to end	Day	32% 2 4 14% 27% 22%	1570
March	1st to 10th	Day	31% 3 6% 11% 27% 22%	3244
	11th to 20th	Day	36% 3 11% 17% 24% 9%	3480
	21st to end	Day	32% 5% 10% 20% 23% 11%	3814
April	1st to 10th	Day	26% 4 9% 21% 23% 16%	2099
	11th to 20th	Day	31% 4 7% 15% 24% 18%	2254
	21st to end	Day	28% 4 8% 19% 31% 10%	2412
May	1st to 10th	Day	33% 5% 8% 20% 18% 15%	4120
	11th to 20th	Day	33% 4 9% 21% 27% 7%	4086
	21st to end	Day	33% 6% 11% 22% 15% 13%	4489
June	1st to 10th	Day	24% 6% 13% 29% 22% 5%	2470
	11th to 20th	Day	20% 6% 10% 29% 27% 9%	2470
	21st to end	Day	21% 5% 11% 26% 27% 9%	2470
July	1st to 10th	Day	26% 5% 11% 34% 19% 5%	4056
	11th to 20th	Day	17% 5% 11% 32% 31% 5%	4051
	21st to end	Day	17% 5% 10% 31% 34% 4	4325
August	1st to 10th	Day	13% 4 10% 25% 39% 10%	4075
	11th to 20th	Day	17% 4 10% 33% 30% 6%	3762
	21st to end	Day	18% 5% 16% 29% 27% 4	4179
September	1st to 10th	Day	30% 5% 9% 20% 25% 12%	2100
	11th to 20th	Day	34% 6% 8% 19% 26% 9%	2090
	21st to end	Day	25% 4 8% 20% 28% 16%	2090
October	1st to 10th	Day	13% 3 5% 15% 37% 27%	3480
	11th to 20th	Day	18% 3 7% 20% 31% 20%	3300
	21st to end	Day	16% 2 3 27% 39% 14%	3428
November	1st to 10th	Day	24% 3 8% 24% 26% 15%	1755
	11th to 20th	Day	21% 3 6% 23% 31% 15%	1710
	21st to end	Day	31% 2 5% 21% 27% 15%	1710
December	1st to 10th	Day	31% 4 6% 21% 28% 10%	1710
	11th to 20th	Day	31% 3 9% 17% 28% 13%	2159
	21st to end	Day	32% 2 4 22% 26% 14%	3135
January	1st to 10th	Night	26% 2 5% 20% 34% 13%	4108
	11th to 20th	Night	23% 3 7% 20% 30% 18%	4120
	21st to end	Night	34% 2 7% 16% 28% 13%	4371
February	1st to 10th	Night	30% 3 6% 18% 26% 17%	2280
	11th to 20th	Night	30% 4 7% 17% 24% 17%	2218
	21st to end	Night	28% 3 5% 16% 25% 24%	1884
March	1st to 10th	Night	30% 4 4 12% 22% 27%	3616
	11th to 20th	Night	29% 3 11% 25% 20% 12%	3480
	21st to end	Night	29% 5% 8% 20% 29% 9%	3817
April	1st to 10th	Night	24% 5% 9% 20% 22% 21%	2076
	11th to 20th	Night	28% 5% 10% 17% 21% 19%	1877
	21st to end	Night	22% 3 11% 24% 29% 10%	1767
May	1st to 10th	Night	36% 5% 7% 16% 20% 16%	2850
	11th to 20th	Night	30% 5% 11% 22% 23% 9%	2824
	21st to end	Night	25% 6% 12% 22% 24% 11%	3099
June	1st to 10th	Night	20% 7% 16% 30% 23% 5%	1710
	11th to 20th	Night	16% 6% 13% 29% 28% 9%	1710
	21st to end	Night	19% 5% 10% 26% 27% 12%	1710
July	1st to 10th	Night	22% 6% 11% 35% 21% 4	2805
	11th to 20th	Night	12% 3 8% 37% 32% 8%	2796
	21st to end	Night	15% 4 11% 33% 33% 3	2999
August	1st to 10th	Night	10% 3 6% 26% 44% 11%	2826
	11th to 20th	Night	15% 3 12% 31% 31% 9%	3140
	21st to end	Night	18% 5% 18% 28% 25% 5%	3487
September	1st to 10th	Night	27% 4 9% 22% 25% 14%	2080
	11th to 20th	Night	30% 5% 11% 20% 23% 10%	2090
	21st to end	Night	23% 4 6% 20% 28% 19%	2090
October	1st to 10th	Night	11% 2 7% 13% 34% 34%	3480
	11th to 20th	Night	15% 3 7% 20% 31% 24%	3584
	21st to end	Night	17% 3 4 21% 42% 15%	4120
November	1st to 10th	Night	23% 3 7% 21% 26% 19%	2393
	11th to 20th	Night	20% 4 6% 23% 29% 18%	2470
	21st to end	Night	30% 3 5% 16% 30% 16%	2470
December	1st to 10th	Night	26% 3 7% 22% 29% 14%	2470
	11th to 20th	Night	29% 3 6% 20% 27% 16%	3037
	21st to end	Night	29% 3 5% 17% 29% 17%	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	10% 13% 38% 30% 9%	270
	11th to 20th	Day	15% 11% 30% 31% 11% 1	270
	21st to end	Day	13% 10% 40% 26% 10% 1	297
February	1st to 10th	Day	15% 12% 37% 26% 9%	270
	11th to 20th	Day	17% 11% 40% 23% 8%	270
	21st to end	Day	22% 13% 39% 21% 4	225
March	1st to 10th	Day	17% 11% 35% 30% 7%	270
	11th to 20th	Day	19% 11% 37% 26% 6% 1	270
	21st to end	Day	12% 14% 42% 23% 8% 1	297
April	1st to 10th	Day	11% 14% 42% 22% 10% 1	279
	11th to 20th	Day	14% 14% 46% 20% 6%	452
	21st to end	Day	12% 12% 38% 27% 10% 1	592
May	1st to 10th	Day	10% 10% 36% 34% 9% 1	653
	11th to 20th	Day	13% 6% 28% 34% 14% 4	675
	21st to end	Day	9% 5% 31% 34% 16% 5%	734
June	1st to 10th	Day	7% 1 14% 44% 27% 6%	680
	11th to 20th	Day	4 2 17% 47% 25% 5%	680
	21st to end	Day	4 1 10% 37% 37% 11%	680
July	1st to 10th	Day	6% 1 5% 34% 38% 16%	671
	11th to 20th	Day	3 1 6% 31% 43% 16%	668
	21st to end	Day	2 5% 26% 47% 20%	739
August	1st to 10th	Day	2 4 29% 46% 18%	674
	11th to 20th	Day	5% 1 5% 26% 45% 17%	477
	21st to end	Day	4 1 5% 29% 41% 20%	539
September	1st to 10th	Day	12% 1 4 20% 40% 24%	310
	11th to 20th	Day	5% 1 6% 26% 40% 22%	300
	21st to end	Day	12% 2 7% 26% 35% 17%	300
October	1st to 10th	Day	3 2 10% 38% 34% 13%	300
	11th to 20th	Day	9% 5% 29% 37% 17% 4	300
	21st to end	Day	15% 7% 26% 31% 17% 3	330
November	1st to 10th	Day	14% 8% 26% 33% 18% 3	279
	11th to 20th	Day	12% 9% 29% 27% 18% 4	270
	21st to end	Day	17% 12% 31% 28% 10% 3	270
December	1st to 10th	Day	14% 8% 34% 31% 10% 2	270
	11th to 20th	Day	9% 9% 40% 31% 11%	270
	21st to end	Day	17% 10% 40% 24% 9%	297
January	1st to 10th	Night	10% 8% 37% 36% 9%	950
	11th to 20th	Night	11% 10% 33% 38% 7%	950
	21st to end	Night	11% 10% 35% 37% 6%	949
February	1st to 10th	Night	13% 9% 41% 33% 4	760
	11th to 20th	Night	13% 10% 42% 32% 4	744
	21st to end	Night	14% 14% 48% 21% 3	628
March	1st to 10th	Night	12% 12% 40% 32% 4	694
	11th to 20th	Night	14% 11% 40% 31% 5%	570
	21st to end	Night	7% 13% 47% 30% 4	627
April	1st to 10th	Night	7% 11% 55% 25% 3	570
	11th to 20th	Night	10% 12% 48% 28% 2	563
	21st to end	Night	7% 11% 48% 29% 5%	570
May	1st to 10th	Night	9% 8% 49% 30% 5%	570
	11th to 20th	Night	7% 6% 37% 39% 10% 1	561
	21st to end	Night	7% 5% 41% 34% 13% 1	617
June	1st to 10th	Night	4 2 27% 47% 19% 1	570
	11th to 20th	Night	2 2 31% 56% 8%	570
	21st to end	Night	5% 2 18% 53% 20% 2	570
July	1st to 10th	Night	5% 1 8% 48% 35% 2	555
	11th to 20th	Night	3 7% 53% 35% 2	552
	21st to end	Night	2 5% 53% 38% 2	624
August	1st to 10th	Night	2 5% 54% 37% 1	567
	11th to 20th	Night	5% 1 8% 45% 39% 2	564
	21st to end	Night	4 1 6% 43% 42% 4	627
September	1st to 10th	Night	10% 1 10% 43% 33% 3	570
	11th to 20th	Night	11% 1 11% 48% 28% 2	570
	21st to end	Night	9% 2 14% 48% 26% 2	570
October	1st to 10th	Night	7% 2 24% 43% 24% 1	570
	11th to 20th	Night	10% 4 29% 42% 14% 1	643
	21st to end	Night	11% 7% 31% 36% 14% 1	836
November	1st to 10th	Night	10% 4 30% 41% 14% 1	885
	11th to 20th	Night	4 9% 34% 42% 11% 1	950
	21st to end	Night	15% 7% 36% 30% 12% 1	950
December	1st to 10th	Night	12% 6% 34% 40% 7%	950
	11th to 20th	Night	14% 7% 35% 36% 7%	950
	21st to end	Night	11% 7% 39% 35% 7%	1045

Page generated at 2024-11-01 21:47:43. Version ac07

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