Tall Timbers
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tall Timbers clear sky chart from 2005-11-06 to 2024-12-24.

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% 6% 2 5% 4 4 4 4 6% 8% 43%	101559
	Night	14% 7% 2 6% 4 4 4 3 5% 7% 43%	98494
Transparency	Day	20% 47% 7% 14% 9% 2	105193
	Night	22% 47% 6% 13% 10% 2	102999
Seeing	Day	15% 4 16% 30% 25% 11%	15237
	Night	16% 6% 24% 32% 18% 3	24807

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	16% 6% 2 4 3 3 3 3 5% 6% 49%	2581
	11th to 20th	Day	14% 9% 3 6% 4 3 4 4 4 5% 43%	2840
	21st to end	Day	13% 11% 4 7% 4 3 4 3 5% 6% 39%	3124
February	1st to 10th	Day	14% 7% 2 6% 5% 4 5% 4 5% 8% 38%	1710
	11th to 20th	Day	19% 6% 2 4 3 4 4 3 5% 6% 45%	1770
	21st to end	Day	17% 8% 2 6% 5% 4 5% 4 6% 7% 38%	1570
March	1st to 10th	Day	22% 7% 2 5% 3 3 4 3 5% 8% 37%	3311
	11th to 20th	Day	11% 4 1 3 3 3 4 4 6% 8% 54%	3480
	21st to end	Day	21% 7% 2 5% 4 3 3 3 5% 6% 41%	3928
April	1st to 10th	Day	11% 6% 2 4 4 4 4 4 6% 8% 48%	2280
	11th to 20th	Day	10% 6% 2 5% 4 4 4 4 5% 6% 50%	2254
	21st to end	Day	14% 6% 2 5% 4 3 4 4 5% 7% 45%	2280
May	1st to 10th	Day	19% 7% 3 7% 4 4 5% 4 6% 9% 31%	3876
	11th to 20th	Day	19% 7% 2 6% 4 4 4 4 5% 9% 36%	4316
	21st to end	Day	10% 4 2 5% 4 4 5% 4 7% 10% 47%	4823
June	1st to 10th	Day	10% 5% 1 5% 4 4 5% 4 7% 10% 45%	2660
	11th to 20th	Day	9% 5% 1 4 4 4 5% 5% 8% 10% 46%	2660
	21st to end	Day	8% 4 2 4 5% 4 6% 5% 8% 10% 45%	2660
July	1st to 10th	Day	6% 4 2 5% 4 5% 5% 5% 8% 12% 44%	4440
	11th to 20th	Day	10% 5% 2 6% 5% 5% 5% 5% 8% 12% 38%	4320
	21st to end	Day	9% 5% 2 7% 6% 5% 6% 6% 9% 9% 36%	4466
August	1st to 10th	Day	13% 8% 3 7% 4 5% 5% 5% 8% 11% 32%	4104
	11th to 20th	Day	8% 6% 2 6% 5% 6% 5% 4 6% 9% 42%	3769
	21st to end	Day	9% 3 2 5% 3 3 4 3 6% 9% 52%	4180
September	1st to 10th	Day	12% 5% 2 6% 4 5% 4 4 6% 8% 45%	2280
	11th to 20th	Day	13% 6% 3 6% 4 3 4 3 5% 8% 47%	2280
	21st to end	Day	19% 8% 3 6% 3 3 3 3 6% 7% 39%	2024
October	1st to 10th	Day	15% 5% 2 6% 4 3 4 3 5% 6% 47%	1900
	11th to 20th	Day	16% 4 2 4 2 3 3 3 4 6% 53%	1900
	21st to end	Day	12% 5% 2 5% 3 3 3 3 5% 7% 51%	2090
November	1st to 10th	Day	13% 5% 2 4 3 3 3 2 5% 6% 53%	1832
	11th to 20th	Day	14% 5% 2 5% 3 4 4 3 5% 7% 49%	1800
	21st to end	Day	14% 5% 2 6% 3 3 3 3 4 6% 52%	1665
December	1st to 10th	Day	15% 7% 2 4 4 3 4 3 6% 8% 44%	1600
	11th to 20th	Day	15% 7% 2 5% 4 3 3 2 3 4 51%	1990
	21st to end	Day	16% 6% 2 6% 4 4 4 3 6% 7% 41%	2796
January	1st to 10th	Night	14% 8% 3 6% 4 3 4 3 5% 6% 45%	4361
	11th to 20th	Night	16% 8% 2 6% 3 4 4 3 4 6% 45%	4120
	21st to end	Night	18% 9% 3 6% 4 4 3 3 4 4 42%	4532
February	1st to 10th	Night	16% 8% 3 6% 4 3 4 4 5% 6% 43%	2470
	11th to 20th	Night	19% 7% 2 5% 4 4 4 2 5% 6% 42%	2293
	21st to end	Night	17% 8% 2 5% 4 3 3 3 5% 6% 45%	1884
March	1st to 10th	Night	22% 8% 3 5% 4 3 4 3 4 6% 38%	3524
	11th to 20th	Night	14% 4 2 4 3 4 4 4 5% 7% 49%	3480
	21st to end	Night	16% 9% 3 6% 3 3 3 3 3 5% 47%	3702
April	1st to 10th	Night	15% 7% 2 6% 4 4 4 3 5% 7% 43%	1900
	11th to 20th	Night	11% 6% 2 5% 4 4 4 3 5% 8% 48%	1875
	21st to end	Night	17% 5% 2 5% 4 4 4 3 5% 7% 44%	1900
May	1st to 10th	Night	19% 9% 2 7% 5% 4 4 3 5% 6% 34%	3048
	11th to 20th	Night	21% 8% 2 7% 4 4 5% 4 5% 6% 34%	2573
	21st to end	Night	10% 5% 2 6% 3 5% 4 4 6% 9% 45%	2732
June	1st to 10th	Night	12% 5% 1 5% 4 5% 5% 5% 6% 12% 40%	1520
	11th to 20th	Night	11% 6% 2 6% 4 5% 5% 4 7% 10% 41%	1520
	21st to end	Night	8% 4 2 6% 6% 5% 5% 4 8% 9% 44%	1520
July	1st to 10th	Night	7% 3 2 7% 6% 6% 5% 6% 8% 10% 41%	2520
	11th to 20th	Night	9% 5% 2 6% 6% 5% 5% 4 8% 11% 38%	2636
	21st to end	Night	10% 8% 4 8% 6% 5% 5% 5% 7% 8% 33%	3087
August	1st to 10th	Night	14% 8% 3 7% 5% 4 5% 3 7% 11% 33%	2825
	11th to 20th	Night	9% 7% 3 8% 5% 5% 6% 4 7% 9% 38%	3026
	21st to end	Night	9% 5% 2 5% 3 4 4 4 5% 7% 52%	3476
September	1st to 10th	Night	13% 5% 3 6% 4 5% 4 3 5% 7% 46%	1900
	11th to 20th	Night	10% 5% 2 5% 3 4 4 4 7% 8% 47%	1900
	21st to end	Night	20% 8% 3 6% 4 3 4 4 5% 6% 37%	2151
October	1st to 10th	Night	16% 6% 2 6% 3 4 4 3 4 6% 45%	2280
	11th to 20th	Night	17% 5% 2 4 4 3 4 3 4 5% 51%	2280
	21st to end	Night	15% 5% 2 4 3 3 3 3 5% 6% 51%	2508
November	1st to 10th	Night	12% 6% 3 6% 3 3 3 3 4 6% 52%	2463
	11th to 20th	Night	16% 7% 2 5% 3 4 4 2 5% 5% 48%	2600
	21st to end	Night	12% 5% 2 4 3 4 4 3 5% 7% 51%	2730
December	1st to 10th	Night	16% 7% 3 5% 4 3 3 3 6% 6% 43%	2800
	11th to 20th	Night	17% 7% 3 6% 3 4 3 2 5% 7% 43%	3425
	21st to end	Night	13% 8% 3 6% 4 4 4 4 6% 8% 41%	4933

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	22% 37% 4 23% 12% 3	2582
	11th to 20th	Day	27% 37% 5% 12% 15% 4	2840
	21st to end	Day	30% 41% 7% 14% 7% 1	3124
February	1st to 10th	Day	16% 65% 5% 9% 4 1	1710
	11th to 20th	Day	16% 64% 3 8% 7% 2	1779
	21st to end	Day	18% 65% 5% 4 6% 1	1570
March	1st to 10th	Day	33% 43% 6% 9% 7% 3	3311
	11th to 20th	Day	13% 41% 5% 20% 17% 4	3480
	21st to end	Day	27% 41% 6% 12% 12% 2	3928
April	1st to 10th	Day	14% 66% 3 10% 7% 1	2280
	11th to 20th	Day	12% 66% 5% 9% 7% 1	2254
	21st to end	Day	13% 65% 5% 9% 5% 2	2280
May	1st to 10th	Day	33% 44% 7% 12% 3 1	3911
	11th to 20th	Day	28% 43% 8% 16% 3	4320
	21st to end	Day	16% 44% 9% 16% 13% 2	4837
June	1st to 10th	Day	13% 66% 5% 10% 5% 1	2660
	11th to 20th	Day	9% 67% 6% 10% 8%	2660
	21st to end	Day	10% 64% 7% 11% 7% 1	2660
July	1st to 10th	Day	20% 41% 19% 11% 7% 3	4370
	11th to 20th	Day	27% 39% 14% 17% 3	4245
	21st to end	Day	28% 38% 9% 12% 11% 1	4324
August	1st to 10th	Day	31% 39% 12% 15% 3	4091
	11th to 20th	Day	21% 40% 9% 21% 9%	3806
	21st to end	Day	14% 38% 11% 20% 16% 1	4180
September	1st to 10th	Day	14% 61% 8% 9% 6% 1	2280
	11th to 20th	Day	16% 61% 4 10% 7% 2	2280
	21st to end	Day	23% 59% 3 10% 3 1	2024
October	1st to 10th	Day	21% 38% 5% 13% 19% 4	3160
	11th to 20th	Day	12% 37% 3 15% 25% 9%	3140
	21st to end	Day	8% 36% 6% 21% 20% 10%	3428
November	1st to 10th	Day	17% 55% 5% 11% 9% 3	1832
	11th to 20th	Day	15% 57% 4 9% 12% 3	1800
	21st to end	Day	15% 56% 3 14% 10% 1	1665
December	1st to 10th	Day	20% 57% 4 11% 5% 2	1600
	11th to 20th	Day	19% 46% 5% 16% 10% 4	1986
	21st to end	Day	27% 39% 9% 17% 8%	2796
January	1st to 10th	Night	26% 37% 5% 16% 12% 4	4361
	11th to 20th	Night	26% 37% 3 17% 14% 3	4120
	21st to end	Night	31% 40% 3 15% 10% 1	4532
February	1st to 10th	Night	16% 65% 5% 10% 4 1	2470
	11th to 20th	Night	17% 64% 2 8% 8% 2	2295
	21st to end	Night	15% 64% 4 9% 5% 2	1884
March	1st to 10th	Night	34% 42% 4 11% 7% 1	3524
	11th to 20th	Night	16% 42% 5% 18% 16% 3	3480
	21st to end	Night	24% 41% 4 14% 14% 4	3702
April	1st to 10th	Night	16% 65% 3 7% 9% 1	1900
	11th to 20th	Night	13% 66% 4 9% 7% 1	1875
	21st to end	Night	15% 66% 4 8% 6% 1	1900
May	1st to 10th	Night	33% 42% 7% 12% 4 1	3078
	11th to 20th	Night	32% 43% 7% 15% 3	2574
	21st to end	Night	19% 44% 9% 16% 11% 1	2739
June	1st to 10th	Night	15% 66% 5% 8% 6% 1	1520
	11th to 20th	Night	12% 67% 5% 8% 7% 1	1520
	21st to end	Night	11% 66% 5% 9% 7% 2	1520
July	1st to 10th	Night	25% 43% 14% 10% 7% 1	2480
	11th to 20th	Night	26% 39% 18% 15% 3	2588
	21st to end	Night	33% 40% 8% 11% 8%	2988
August	1st to 10th	Night	33% 39% 10% 14% 3	2814
	11th to 20th	Night	24% 40% 11% 16% 9%	3055
	21st to end	Night	16% 38% 5% 19% 22%	3476
September	1st to 10th	Night	15% 62% 8% 9% 5% 2	1900
	11th to 20th	Night	16% 60% 4 10% 8% 2	1900
	21st to end	Night	23% 61% 5% 8% 3	2151
October	1st to 10th	Night	24% 38% 7% 13% 13% 5%	3800
	11th to 20th	Night	11% 37% 5% 15% 23% 8%	3779
	21st to end	Night	8% 36% 5% 24% 18% 9%	4120
November	1st to 10th	Night	17% 56% 4 11% 9% 2	2463
	11th to 20th	Night	17% 57% 3 9% 10% 5%	2600
	21st to end	Night	13% 57% 5% 11% 12% 2	2730
December	1st to 10th	Night	21% 57% 4 11% 5% 2	2800
	11th to 20th	Night	22% 47% 4 12% 11% 3	3428
	21st to end	Night	26% 39% 9% 18% 7% 1	4933

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% 4 23% 40% 13% 1	198
	11th to 20th	Day	17% 6% 32% 34% 11%	270
	21st to end	Day	19% 5% 22% 38% 16% 1	297
February	1st to 10th	Day	16% 5% 19% 44% 13% 3	270
	11th to 20th	Day	24% 7% 26% 35% 8% 1	378
	21st to end	Day	21% 7% 26% 36% 9% 1	382
March	1st to 10th	Day	17% 6% 28% 34% 13% 2	460
	11th to 20th	Day	16% 6% 24% 39% 12% 3	460
	21st to end	Day	18% 5% 23% 37% 14% 3	506
April	1st to 10th	Day	14% 6% 25% 35% 17% 3	460
	11th to 20th	Day	9% 4 20% 38% 22% 6%	452
	21st to end	Day	16% 4 21% 31% 23% 4	460
May	1st to 10th	Day	16% 5% 18% 31% 24% 5%	463
	11th to 20th	Day	20% 2 15% 31% 24% 9%	487
	21st to end	Day	18% 3 8% 23% 31% 17%	529
June	1st to 10th	Day	11% 3 8% 30% 28% 19%	490
	11th to 20th	Day	10% 1 9% 30% 35% 16%	490
	21st to end	Day	9% 2 11% 26% 35% 17%	490
July	1st to 10th	Day	9% 3 6% 24% 35% 24%	485
	11th to 20th	Day	4 2 4 20% 44% 26%	484
	21st to end	Day	10% 2 6% 24% 40% 18%	532
August	1st to 10th	Day	12% 2 5% 24% 38% 19%	486
	11th to 20th	Day	9% 2 9% 23% 38% 19%	479
	21st to end	Day	10% 3 6% 24% 34% 23%	539
September	1st to 10th	Day	14% 2 8% 23% 30% 23%	490
	11th to 20th	Day	13% 3 8% 22% 33% 20%	490
	21st to end	Day	25% 4 14% 24% 24% 9%	490
October	1st to 10th	Day	19% 4 11% 27% 24% 15%	490
	11th to 20th	Day	16% 4 17% 28% 26% 9%	490
	21st to end	Day	13% 5% 22% 30% 23% 7%	539
November	1st to 10th	Day	16% 4 22% 28% 23% 7%	432
	11th to 20th	Day	15% 7% 29% 32% 16% 3	400
	21st to end	Day	13% 8% 27% 26% 20% 5%	265
December	1st to 10th	Day	15% 6% 24% 39% 16% 2	200
	11th to 20th	Day	20% 5% 25% 31% 20% 1	200
	21st to end	Day	18% 5% 22% 35% 17% 3	204
January	1st to 10th	Night	19% 12% 36% 28% 5%	760
	11th to 20th	Night	19% 10% 32% 31% 8%	760
	21st to end	Night	19% 12% 35% 31% 3	836
February	1st to 10th	Night	18% 8% 35% 33% 6%	760
	11th to 20th	Night	22% 12% 38% 24% 3	743
	21st to end	Night	19% 10% 33% 33% 4 1	628
March	1st to 10th	Night	16% 7% 35% 34% 7% 1	760
	11th to 20th	Night	19% 8% 33% 30% 9% 1	760
	21st to end	Night	18% 6% 31% 36% 8% 1	836
April	1st to 10th	Night	19% 6% 34% 31% 9%	760
	11th to 20th	Night	14% 5% 26% 39% 15% 1	751
	21st to end	Night	20% 5% 24% 38% 13% 1	760
May	1st to 10th	Night	17% 4 25% 36% 15% 2	717
	11th to 20th	Night	17% 5% 21% 38% 18% 1	426
	21st to end	Night	14% 2 11% 30% 39% 4	411
June	1st to 10th	Night	11% 2 15% 36% 32% 4	380
	11th to 20th	Night	13% 2 10% 42% 29% 5%	380
	21st to end	Night	8% 2 13% 42% 32% 4	380
July	1st to 10th	Night	9% 2 9% 32% 41% 8%	370
	11th to 20th	Night	6% 6% 33% 45% 9%	432
	21st to end	Night	7% 2 11% 36% 38% 6%	624
August	1st to 10th	Night	11% 2 8% 40% 33% 6%	567
	11th to 20th	Night	12% 3 10% 34% 33% 7%	703
	21st to end	Night	13% 2 8% 32% 36% 10%	836
September	1st to 10th	Night	16% 2 9% 30% 34% 9%	760
	11th to 20th	Night	12% 3 10% 29% 38% 8%	760
	21st to end	Night	23% 5% 14% 30% 25% 3	760
October	1st to 10th	Night	19% 5% 15% 28% 25% 8%	760
	11th to 20th	Night	19% 7% 24% 29% 19% 2	760
	21st to end	Night	18% 8% 25% 29% 17% 3	836
November	1st to 10th	Night	15% 7% 24% 32% 17% 4	780
	11th to 20th	Night	18% 9% 30% 30% 13% 1	800
	21st to end	Night	14% 11% 29% 34% 11% 2	800
December	1st to 10th	Night	19% 9% 33% 27% 10% 2	800
	11th to 20th	Night	18% 8% 39% 27% 9%	800
	21st to end	Night	18% 9% 31% 33% 9%	851

Page generated at 2024-12-21 04:13:50. Version ac07

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