Big Bend Community College
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Big Bend Community College clear sky chart from 2005-11-06 to 2025-01-07.

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	7% 7% 3 6% 4 4 4 3 5% 6% 50%	108996
	Night	9% 9% 3 7% 4 4 4 4 5% 7% 44%	108646
Transparency	Day	34% 4 10% 22% 19% 10%	108765
	Night	39% 5% 11% 21% 16% 7%	108523
Seeing	Day	9% 7% 20% 27% 24% 13%	14460
	Night	11% 5% 22% 37% 22% 3	23587

By Month

Percentage Cloud Cover NW (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% 20% 7% 12% 5% 4 4 2 4 5% 21%	2587
	11th to 20th	Day	18% 16% 5% 10% 6% 5% 5% 3 5% 6% 22%	2516
	21st to end	Day	23% 20% 7% 12% 5% 3 3 2 4 4 16%	2794
February	1st to 10th	Day	14% 13% 4 9% 6% 6% 5% 5% 5% 7% 27%	1629
	11th to 20th	Day	9% 12% 4 10% 5% 4 3 4 5% 7% 37%	1705
	21st to end	Day	7% 11% 3 9% 6% 5% 5% 4 5% 6% 37%	1570
March	1st to 10th	Day	8% 8% 3 6% 4 4 5% 5% 7% 9% 41%	3138
	11th to 20th	Day	5% 6% 2 6% 4 3 4 3 5% 7% 55%	3321
	21st to end	Day	7% 8% 3 8% 6% 6% 6% 5% 7% 8% 35%	4130
April	1st to 10th	Day	9% 9% 2 8% 6% 5% 5% 4 6% 7% 39%	2280
	11th to 20th	Day	5% 7% 2 6% 5% 5% 5% 4 7% 8% 45%	2252
	21st to end	Day	5% 6% 2 6% 5% 5% 5% 5% 6% 8% 47%	2482
May	1st to 10th	Day	8% 5% 1 3 3 3 3 3 5% 9% 56%	4420
	11th to 20th	Day	4 3 1 4 3 3 3 4 5% 8% 60%	4377
	21st to end	Day	6% 7% 3 7% 5% 5% 5% 4 6% 8% 45%	4813
June	1st to 10th	Day	9% 6% 2 6% 4 4 4 4 7% 8% 46%	2660
	11th to 20th	Day	6% 4 2 5% 4 4 5% 4 6% 7% 52%	2660
	21st to end	Day	3 3 1 4 3 3 3 4 4 7% 63%	2660
July	1st to 10th	Day	1 1 2 2 2 2 2 3 4 82%	4420
	11th to 20th	Day	1 1 1 2 2 2 2 2 3 3 81%	4420
	21st to end	Day	1 1 2 1 2 2 2 3 4 81%	4790
August	1st to 10th	Day	2 2 1 3 2 2 3 2 4 5% 75%	4401
	11th to 20th	Day	2 2 1 2 2 3 3 2 5% 7% 72%	4145
	21st to end	Day	3 4 2 4 3 3 3 2 4 6% 65%	4180
September	1st to 10th	Day	3 2 1 3 2 2 2 3 4 7% 71%	2280
	11th to 20th	Day	4 4 2 5% 4 4 4 4 5% 7% 57%	2244
	21st to end	Day	5% 4 2 5% 3 3 5% 4 6% 6% 57%	2090
October	1st to 10th	Day	5% 3 1 3 3 3 3 3 6% 8% 62%	3191
	11th to 20th	Day	5% 4 1 6% 5% 5% 6% 5% 6% 8% 47%	3111
	21st to end	Day	9% 6% 3 7% 4 4 5% 4 6% 7% 45%	3101
November	1st to 10th	Day	13% 9% 3 9% 7% 5% 5% 4 5% 6% 36%	1764
	11th to 20th	Day	13% 11% 5% 11% 7% 5% 5% 3 5% 6% 30%	1616
	21st to end	Day	12% 12% 6% 11% 7% 6% 4 4 6% 5% 26%	1600
December	1st to 10th	Day	10% 11% 6% 14% 7% 6% 5% 4 6% 6% 25%	2620
	11th to 20th	Day	17% 20% 9% 14% 6% 4 4 3 4 4 14%	3025
	21st to end	Day	15% 19% 6% 15% 8% 5% 4 3 5% 4 16%	4004
January	1st to 10th	Night	17% 18% 6% 10% 6% 6% 5% 3 6% 6% 17%	4490
	11th to 20th	Night	16% 12% 5% 10% 6% 4 5% 4 5% 8% 25%	4382
	21st to end	Night	18% 20% 8% 13% 5% 5% 4 3 4 5% 16%	4862
February	1st to 10th	Night	11% 14% 4 9% 6% 4 6% 4 6% 7% 31%	2549
	11th to 20th	Night	9% 9% 3 8% 6% 5% 5% 4 6% 7% 37%	2361
	21st to end	Night	7% 10% 3 8% 7% 5% 5% 5% 8% 8% 33%	1884
March	1st to 10th	Night	6% 8% 3 7% 5% 4 5% 4 8% 10% 40%	3736
	11th to 20th	Night	5% 6% 3 5% 4 3 3 3 4 6% 59%	3657
	21st to end	Night	6% 9% 3 8% 6% 6% 7% 6% 9% 9% 32%	3522
April	1st to 10th	Night	8% 11% 3 8% 5% 5% 5% 4 6% 6% 39%	1900
	11th to 20th	Night	6% 7% 2 6% 5% 5% 4 3 5% 6% 48%	1879
	21st to end	Night	6% 6% 3 7% 5% 5% 5% 5% 6% 9% 44%	1695
May	1st to 10th	Night	6% 5% 2 5% 4 3 3 3 5% 7% 57%	2540
	11th to 20th	Night	5% 3 2 4 3 3 3 3 6% 7% 62%	2516
	21st to end	Night	5% 3 2 6% 4 4 4 4 6% 8% 53%	2762
June	1st to 10th	Night	7% 5% 2 6% 5% 4 5% 4 5% 8% 50%	1520
	11th to 20th	Night	6% 4 1 4 4 4 3 5% 6% 7% 56%	1520
	21st to end	Night	4 3 1 4 3 4 4 3 6% 7% 60%	1520
July	1st to 10th	Night	1 1 1 1 1 2 2 3 4 84%	2540
	11th to 20th	Night	1 1 1 1 1 1 2 3 5% 83%	2540
	21st to end	Night	1 1 1 2 1 2 2 3 3 83%	2762
August	1st to 10th	Night	3 2 1 2 2 2 1 2 3 6% 77%	2529
	11th to 20th	Night	2 3 1 3 2 3 3 3 4 5% 70%	2683
	21st to end	Night	2 3 1 4 3 3 2 3 5% 5% 68%	3498
September	1st to 10th	Night	2 2 1 3 2 2 3 3 4 6% 72%	1900
	11th to 20th	Night	4 3 2 5% 4 4 4 4 6% 7% 59%	1935
	21st to end	Night	5% 4 1 4 3 3 3 3 6% 8% 60%	2090
October	1st to 10th	Night	5% 3 1 3 3 3 3 3 5% 9% 62%	3786
	11th to 20th	Night	6% 4 2 5% 3 4 6% 4 7% 8% 52%	3824
	21st to end	Night	10% 6% 2 6% 5% 5% 4 4 6% 7% 46%	4457
November	1st to 10th	Night	13% 8% 3 7% 4 5% 5% 4 7% 7% 37%	2535
	11th to 20th	Night	12% 10% 3 7% 6% 6% 5% 4 6% 7% 34%	2780
	21st to end	Night	12% 13% 4 9% 6% 5% 5% 4 5% 6% 30%	2800
December	1st to 10th	Night	7% 8% 6% 8% 5% 4 5% 6% 7% 8% 35%	4560
	11th to 20th	Night	18% 17% 8% 13% 6% 5% 5% 4 5% 5% 13%	5180
	21st to end	Night	17% 18% 4 11% 6% 5% 4 3 5% 5% 21%	6952

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	66% 6% 9% 12% 7% 1	2587
	11th to 20th	Day	62% 6% 15% 14% 3	2540
	21st to end	Day	74% 5% 12% 7% 2	2794
February	1st to 10th	Day	56% 8% 17% 15% 5%	1629
	11th to 20th	Day	48% 6% 15% 19% 10% 1	1714
	21st to end	Day	46% 6% 16% 21% 9% 2	1570
March	1st to 10th	Day	37% 6% 13% 26% 17% 2	3138
	11th to 20th	Day	30% 4 12% 42% 12%	3321
	21st to end	Day	43% 7% 16% 20% 12% 2	4130
April	1st to 10th	Day	42% 5% 14% 23% 14% 2	2280
	11th to 20th	Day	35% 5% 15% 23% 17% 5%	2252
	21st to end	Day	34% 5% 13% 25% 19% 4	2482
May	1st to 10th	Day	25% 4 7% 25% 33% 8%	4420
	11th to 20th	Day	20% 5% 7% 33% 27% 7%	4380
	21st to end	Day	36% 5% 14% 28% 15% 2	4814
June	1st to 10th	Day	35% 5% 9% 24% 22% 5%	2660
	11th to 20th	Day	29% 4 11% 29% 21% 6%	2660
	21st to end	Day	21% 4 8% 29% 27% 11%	2660
July	1st to 10th	Day	9% 1 3 15% 28% 43%	4351
	11th to 20th	Day	10% 1 4 10% 24% 51%	4345
	21st to end	Day	9% 2 4 18% 35% 32%	4639
August	1st to 10th	Day	14% 2 4 16% 36% 29%	4384
	11th to 20th	Day	14% 3 7% 35% 32% 10%	4187
	21st to end	Day	22% 3 8% 27% 32% 9%	4179
September	1st to 10th	Day	15% 3 9% 27% 32% 15%	2280
	11th to 20th	Day	25% 4 12% 25% 25% 8%	2244
	21st to end	Day	27% 4 15% 32% 18% 5%	2090
October	1st to 10th	Day	21% 3 12% 37% 25% 2	3191
	11th to 20th	Day	34% 5% 18% 27% 16% 1	3111
	21st to end	Day	38% 5% 14% 27% 12% 5%	3101
November	1st to 10th	Day	50% 7% 13% 20% 9% 1	1764
	11th to 20th	Day	55% 5% 15% 16% 7% 1	1616
	21st to end	Day	60% 7% 15% 11% 7% 1	1600
December	1st to 10th	Day	59% 6% 14% 16% 5%	2620
	11th to 20th	Day	76% 4 7% 9% 4	3028
	21st to end	Day	71% 5% 11% 10% 3	4004
January	1st to 10th	Night	66% 7% 11% 10% 4	4490
	11th to 20th	Night	56% 7% 17% 16% 3	4420
	21st to end	Night	72% 7% 12% 7% 2 1	4862
February	1st to 10th	Night	53% 6% 18% 16% 7% 1	2549
	11th to 20th	Night	44% 7% 18% 20% 10%	2363
	21st to end	Night	45% 7% 16% 21% 11% 1	1884
March	1st to 10th	Night	36% 6% 11% 29% 16% 2	3736
	11th to 20th	Night	28% 3 8% 42% 18% 1	3658
	21st to end	Night	44% 7% 16% 26% 7%	3522
April	1st to 10th	Night	42% 6% 13% 24% 13% 1	1900
	11th to 20th	Night	35% 4 9% 27% 19% 5%	1879
	21st to end	Night	35% 6% 10% 26% 19% 5%	1695
May	1st to 10th	Night	28% 4 5% 21% 36% 8%	2540
	11th to 20th	Night	21% 5% 6% 30% 33% 5%	2516
	21st to end	Night	27% 6% 16% 37% 12% 2	2762
June	1st to 10th	Night	33% 3 9% 25% 25% 6%	1520
	11th to 20th	Night	27% 6% 8% 30% 24% 6%	1520
	21st to end	Night	22% 3 7% 27% 29% 12%	1520
July	1st to 10th	Night	7% 2 3 14% 26% 48%	2500
	11th to 20th	Night	7% 2 3 10% 21% 58%	2492
	21st to end	Night	8% 2 2 14% 35% 40%	2674
August	1st to 10th	Night	13% 1 3 9% 40% 34%	2521
	11th to 20th	Night	18% 2 5% 27% 34% 13%	2707
	21st to end	Night	18% 3 5% 27% 31% 16%	3498
September	1st to 10th	Night	14% 3 7% 26% 28% 22%	1900
	11th to 20th	Night	23% 5% 10% 23% 27% 12%	1935
	21st to end	Night	23% 4 11% 32% 22% 9%	2090
October	1st to 10th	Night	20% 3 8% 38% 30% 1	3786
	11th to 20th	Night	30% 4 15% 27% 21% 3	3824
	21st to end	Night	38% 4 10% 30% 16% 2	4457
November	1st to 10th	Night	45% 7% 15% 21% 10% 2	2535
	11th to 20th	Night	48% 8% 16% 19% 8% 1	2780
	21st to end	Night	53% 7% 16% 16% 7% 1	2800
December	1st to 10th	Night	43% 9% 19% 24% 4	4560
	11th to 20th	Night	74% 6% 12% 6% 2	5176
	21st to end	Night	65% 6% 11% 12% 5%	6952

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	26% 9% 20% 24% 20% 1	192
	11th to 20th	Day	25% 7% 17% 31% 15% 6%	180
	21st to end	Day	26% 3 20% 26% 20% 5%	198
February	1st to 10th	Day	19% 8% 26% 28% 14% 3	289
	11th to 20th	Day	16% 11% 26% 25% 17% 5%	385
	21st to end	Day	11% 13% 26% 28% 18% 4	382
March	1st to 10th	Day	13% 10% 28% 28% 15% 6%	460
	11th to 20th	Day	12% 11% 20% 27% 21% 8%	460
	21st to end	Day	12% 12% 26% 29% 15% 5%	506
April	1st to 10th	Day	12% 11% 28% 23% 18% 8%	460
	11th to 20th	Day	8% 14% 29% 27% 14% 8%	452
	21st to end	Day	6% 10% 24% 31% 19% 11%	460
May	1st to 10th	Day	7% 8% 20% 31% 24% 10%	463
	11th to 20th	Day	10% 8% 16% 28% 25% 14%	488
	21st to end	Day	7% 5% 17% 26% 27% 18%	529
June	1st to 10th	Day	8% 8% 20% 24% 25% 16%	490
	11th to 20th	Day	5% 8% 26% 32% 19% 10%	490
	21st to end	Day	3 3 15% 30% 28% 21%	490
July	1st to 10th	Day	2 2 12% 34% 32% 18%	486
	11th to 20th	Day	1 3 15% 27% 35% 19%	484
	21st to end	Day	1 2 11% 24% 38% 24%	531
August	1st to 10th	Day	2 4 10% 25% 33% 26%	487
	11th to 20th	Day	2 2 10% 23% 34% 29%	477
	21st to end	Day	4 4 16% 26% 28% 22%	539
September	1st to 10th	Day	3 3 13% 28% 33% 20%	490
	11th to 20th	Day	6% 4 19% 23% 30% 19%	490
	21st to end	Day	8% 8% 17% 28% 28% 12%	490
October	1st to 10th	Day	9% 5% 23% 25% 24% 14%	490
	11th to 20th	Day	8% 7% 19% 25% 28% 13%	465
	21st to end	Day	15% 7% 22% 31% 18% 6%	330
November	1st to 10th	Day	15% 10% 21% 34% 18% 3	300
	11th to 20th	Day	17% 10% 28% 25% 14% 6%	207
	21st to end	Day	17% 5% 20% 30% 21% 8%	200
December	1st to 10th	Day	17% 7% 19% 28% 20% 11%	200
	11th to 20th	Day	20% 5% 27% 30% 16% 3	200
	21st to end	Day	20% 7% 26% 28% 17% 2	220
January	1st to 10th	Night	24% 6% 25% 30% 14% 1	784
	11th to 20th	Night	19% 3 22% 37% 18% 2	760
	21st to end	Night	16% 3 21% 39% 19% 2	836
February	1st to 10th	Night	18% 5% 28% 33% 14% 2	760
	11th to 20th	Night	12% 5% 27% 37% 18% 2	744
	21st to end	Night	11% 9% 27% 36% 16% 2	628
March	1st to 10th	Night	13% 6% 22% 40% 16% 2	760
	11th to 20th	Night	10% 5% 26% 37% 20% 2	760
	21st to end	Night	11% 7% 29% 37% 15% 1	836
April	1st to 10th	Night	11% 6% 25% 35% 21% 2	760
	11th to 20th	Night	9% 7% 32% 31% 17% 4	751
	21st to end	Night	7% 6% 30% 37% 17% 3	555
May	1st to 10th	Night	6% 8% 29% 35% 20% 2	380
	11th to 20th	Night	9% 6% 18% 34% 30% 3	374
	21st to end	Night	6% 3 20% 41% 26% 4	411
June	1st to 10th	Night	8% 4 21% 39% 26% 2	380
	11th to 20th	Night	6% 8% 28% 40% 16% 2	380
	21st to end	Night	5% 2 26% 40% 24% 3	380
July	1st to 10th	Night	3 1 18% 44% 32% 2	370
	11th to 20th	Night	2 3 19% 43% 31% 1	368
	21st to end	Night	1 1 14% 40% 39% 4	416
August	1st to 10th	Night	3 2 14% 36% 40% 5%	378
	11th to 20th	Night	3 2 12% 35% 40% 8%	484
	21st to end	Night	3 3 16% 36% 37% 5%	836
September	1st to 10th	Night	2 3 16% 41% 32% 6%	760
	11th to 20th	Night	5% 3 15% 32% 39% 7%	760
	21st to end	Night	7% 4 20% 34% 31% 4	760
October	1st to 10th	Night	12% 3 16% 39% 28% 2	760
	11th to 20th	Night	9% 4 21% 35% 26% 4	760
	21st to end	Night	13% 5% 24% 39% 16% 4	836
November	1st to 10th	Night	16% 6% 21% 43% 13% 1	780
	11th to 20th	Night	17% 8% 25% 33% 15% 2	800
	21st to end	Night	17% 5% 18% 37% 20% 3	800
December	1st to 10th	Night	16% 4 19% 41% 17% 4	800
	11th to 20th	Night	21% 5% 21% 39% 13% 1	800
	21st to end	Night	22% 6% 24% 38% 9% 1	880

Page generated at 2025-01-04 00:24:04. Version ac07

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