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 2024-01-17.

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% 7% 3 6% 5% 3 4 4 5% 7% 48%	74818
	Night	9% 8% 4 6% 6% 3 5% 5% 5% 7% 43%	75032
Transparency	Day	36% 5% 11% 22% 19% 7%	74521
	Night	41% 6% 12% 21% 16% 6%	74847
Seeing	Day	9% 7% 20% 27% 24% 13%	13226
	Night	11% 5% 22% 37% 22% 3	22397

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	18% 19% 7% 10% 7% 4 5% 3 4 4 20%	1519
	11th to 20th	Day	15% 16% 7% 12% 8% 4 5% 4 3 6% 18%	1488
	21st to end	Day	12% 15% 6% 12% 9% 3 5% 4 5% 6% 23%	1584
February	1st to 10th	Day	14% 12% 5% 8% 7% 4 5% 6% 5% 7% 28%	1544
	11th to 20th	Day	9% 12% 4 8% 6% 3 3 4 5% 7% 38%	1613
	21st to end	Day	8% 10% 4 7% 7% 4 5% 5% 5% 7% 37%	1480
March	1st to 10th	Day	12% 8% 4 5% 5% 3 5% 6% 7% 8% 38%	1800
	11th to 20th	Day	9% 8% 4 7% 7% 3 6% 5% 6% 8% 37%	1876
	21st to end	Day	8% 8% 4 7% 7% 4 7% 6% 8% 8% 34%	2354
April	1st to 10th	Day	9% 7% 4 7% 6% 4 6% 5% 6% 8% 39%	2160
	11th to 20th	Day	5% 7% 3 5% 6% 3 6% 5% 7% 9% 44%	2132
	21st to end	Day	5% 6% 3 5% 5% 3 5% 6% 6% 9% 48%	2351
May	1st to 10th	Day	4 4 2 4 5% 3 4 5% 6% 9% 54%	2520
	11th to 20th	Day	7% 5% 2 6% 6% 3 5% 6% 7% 10% 43%	2477
	21st to end	Day	7% 6% 3 6% 6% 4 5% 5% 7% 8% 46%	2723
June	1st to 10th	Day	9% 5% 3 6% 5% 3 5% 5% 6% 9% 46%	2520
	11th to 20th	Day	6% 4 2 4 5% 3 5% 5% 6% 8% 52%	2520
	21st to end	Day	3 3 2 3 4 2 3 4 4 7% 64%	2520
July	1st to 10th	Day	2 1 1 2 3 2 3 3 4 6% 73%	2520
	11th to 20th	Day	2 2 1 3 2 2 3 3 4 5% 75%	2520
	21st to end	Day	1 1 1 1 1 2 2 3 4 83%	2741
August	1st to 10th	Day	2 2 1 3 2 1 2 3 4 5% 75%	2507
	11th to 20th	Day	3 2 1 2 2 2 3 3 4 5% 75%	2368
	21st to end	Day	3 2 1 3 3 2 3 4 5% 8% 66%	2376
September	1st to 10th	Day	3 2 1 3 2 2 2 3 4 7% 71%	2160
	11th to 20th	Day	4 3 3 5% 5% 3 3 5% 5% 7% 58%	2126
	21st to end	Day	6% 5% 2 4 4 3 4 5% 6% 7% 55%	1980
October	1st to 10th	Day	7% 5% 2 5% 5% 3 4 4 6% 6% 54%	1811
	11th to 20th	Day	7% 4 2 5% 6% 3 5% 5% 6% 8% 49%	1777
	21st to end	Day	13% 7% 3 5% 5% 3 4 5% 5% 7% 43%	1782
November	1st to 10th	Day	13% 8% 4 7% 8% 4 6% 5% 5% 6% 35%	1674
	11th to 20th	Day	13% 10% 6% 10% 7% 4 5% 4 4 6% 31%	1536
	21st to end	Day	13% 11% 7% 8% 8% 5% 5% 5% 6% 6% 27%	1520
December	1st to 10th	Day	13% 14% 5% 12% 8% 4 5% 5% 5% 5% 25%	1520
	11th to 20th	Day	19% 16% 10% 12% 8% 4 5% 5% 5% 5% 13%	1925
	21st to end	Day	14% 18% 6% 11% 9% 4 6% 5% 5% 5% 17%	2794
January	1st to 10th	Night	19% 15% 5% 9% 7% 4 6% 4 5% 7% 19%	2646
	11th to 20th	Night	14% 11% 8% 11% 7% 4 5% 4 5% 8% 23%	2616
	21st to end	Night	11% 14% 6% 12% 8% 4 6% 5% 5% 6% 24%	2772
February	1st to 10th	Night	11% 13% 5% 7% 6% 3 6% 5% 6% 7% 32%	2415
	11th to 20th	Night	9% 8% 3 7% 7% 4 6% 5% 6% 7% 38%	2233
	21st to end	Night	8% 9% 4 6% 8% 4 6% 6% 8% 9% 33%	1776
March	1st to 10th	Night	9% 10% 4 7% 6% 3 5% 4 7% 8% 37%	2160
	11th to 20th	Night	8% 7% 4 6% 7% 4 5% 6% 6% 8% 39%	2082
	21st to end	Night	7% 9% 4 7% 6% 4 6% 6% 7% 10% 33%	2001
April	1st to 10th	Night	9% 9% 5% 7% 5% 4 5% 5% 6% 7% 39%	1800
	11th to 20th	Night	7% 7% 3 6% 6% 3 5% 4 5% 6% 48%	1779
	21st to end	Night	6% 6% 3 6% 6% 3 5% 6% 6% 10% 44%	1607
May	1st to 10th	Night	5% 3 2 4 5% 2 5% 5% 6% 9% 53%	1440
	11th to 20th	Night	8% 4 3 5% 5% 3 6% 5% 7% 9% 46%	1416
	21st to end	Night	5% 3 2 6% 6% 3 5% 7% 7% 7% 48%	1552
June	1st to 10th	Night	7% 4 3 5% 6% 3 6% 5% 5% 8% 49%	1440
	11th to 20th	Night	6% 4 2 3 5% 3 4 5% 5% 7% 56%	1440
	21st to end	Night	4 3 1 4 3 3 4 3 6% 8% 61%	1440
July	1st to 10th	Night	2 2 1 2 2 1 3 4 5% 7% 71%	1440
	11th to 20th	Night	2 1 1 1 2 2 2 3 3 6% 76%	1440
	21st to end	Night	1 1 2 1 2 3 3 4 83%	1576
August	1st to 10th	Night	3 2 1 2 2 1 2 2 3 5% 78%	1432
	11th to 20th	Night	2 1 1 2 2 1 3 3 4 6% 75%	1526
	21st to end	Night	2 2 1 2 3 2 3 4 5% 6% 70%	1980
September	1st to 10th	Night	2 2 1 2 3 1 3 3 4 6% 72%	1800
	11th to 20th	Night	4 3 2 4 4 3 4 4 6% 7% 60%	1833
	21st to end	Night	5% 4 2 3 4 2 3 3 5% 8% 59%	1980
October	1st to 10th	Night	9% 5% 2 5% 4 3 4 4 5% 7% 53%	2146
	11th to 20th	Night	7% 5% 2 5% 4 3 6% 5% 5% 7% 51%	2182
	21st to end	Night	10% 6% 3 6% 6% 4 5% 4 6% 7% 44%	2574
November	1st to 10th	Night	13% 8% 3 6% 5% 4 5% 5% 6% 7% 37%	2405
	11th to 20th	Night	12% 9% 3 7% 7% 4 5% 5% 6% 7% 35%	2641
	21st to end	Night	12% 11% 5% 8% 6% 4 6% 5% 5% 7% 31%	2660
December	1st to 10th	Night	13% 12% 7% 9% 7% 3 5% 6% 6% 7% 27%	2660
	11th to 20th	Night	16% 15% 9% 13% 7% 4 5% 5% 5% 5% 16%	3280
	21st to end	Night	15% 18% 5% 8% 8% 4 5% 5% 5% 6% 21%	4862

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	68% 6% 11% 9% 4 1	1519
	11th to 20th	Day	69% 7% 12% 10% 2	1488
	21st to end	Day	64% 6% 15% 10% 4 1	1584
February	1st to 10th	Day	55% 8% 17% 15% 5% 1	1544
	11th to 20th	Day	47% 6% 16% 20% 10% 1	1622
	21st to end	Day	46% 6% 16% 21% 10% 1	1480
March	1st to 10th	Day	43% 6% 16% 24% 10% 1	1800
	11th to 20th	Day	46% 5% 12% 26% 11%	1876
	21st to end	Day	45% 7% 17% 21% 9% 1	2354
April	1st to 10th	Day	43% 5% 13% 23% 14% 2	2160
	11th to 20th	Day	35% 5% 15% 23% 17% 4	2132
	21st to end	Day	33% 5% 13% 25% 19% 4	2351
May	1st to 10th	Day	25% 3 11% 33% 23% 3	2520
	11th to 20th	Day	34% 6% 11% 27% 18% 3	2480
	21st to end	Day	35% 5% 12% 27% 18% 3	2724
June	1st to 10th	Day	35% 5% 9% 25% 22% 5%	2520
	11th to 20th	Day	29% 4 11% 30% 21% 6%	2520
	21st to end	Day	21% 4 8% 29% 27% 11%	2520
July	1st to 10th	Day	14% 2 6% 24% 33% 20%	2451
	11th to 20th	Day	14% 2 5% 18% 34% 26%	2445
	21st to end	Day	8% 3 3 15% 42% 29%	2589
August	1st to 10th	Day	14% 3 6% 22% 33% 23%	2490
	11th to 20th	Day	13% 3 6% 25% 36% 17%	2368
	21st to end	Day	17% 4 7% 29% 34% 9%	2376
September	1st to 10th	Day	15% 3 10% 27% 31% 14%	2160
	11th to 20th	Day	25% 4 12% 24% 26% 9%	2126
	21st to end	Day	28% 4 15% 31% 18% 4	1980
October	1st to 10th	Day	30% 4 12% 34% 18% 2	1811
	11th to 20th	Day	32% 5% 19% 31% 12% 1	1777
	21st to end	Day	41% 5% 15% 25% 13% 1	1782
November	1st to 10th	Day	50% 7% 13% 19% 9% 1	1674
	11th to 20th	Day	55% 5% 15% 16% 7% 1	1536
	21st to end	Day	59% 6% 15% 12% 7% 1	1520
December	1st to 10th	Day	63% 5% 12% 13% 7%	1520
	11th to 20th	Day	76% 6% 8% 6% 4	1928
	21st to end	Day	69% 6% 12% 9% 4	2794
January	1st to 10th	Night	64% 7% 13% 11% 4 1	2646
	11th to 20th	Night	62% 7% 15% 13% 3	2616
	21st to end	Night	60% 8% 16% 12% 3 1	2772
February	1st to 10th	Night	51% 6% 18% 16% 7% 1	2415
	11th to 20th	Night	43% 8% 19% 20% 10%	2235
	21st to end	Night	44% 7% 15% 21% 11% 1	1776
March	1st to 10th	Night	44% 5% 14% 26% 11% 1	2160
	11th to 20th	Night	43% 5% 11% 29% 12% 1	2083
	21st to end	Night	44% 7% 14% 25% 9%	2001
April	1st to 10th	Night	43% 6% 12% 24% 14% 1	1800
	11th to 20th	Night	36% 4 8% 28% 19% 5%	1779
	21st to end	Night	36% 6% 10% 25% 19% 5%	1607
May	1st to 10th	Night	27% 4 8% 29% 27% 5%	1440
	11th to 20th	Night	34% 5% 10% 26% 21% 5%	1416
	21st to end	Night	30% 6% 10% 31% 18% 4	1552
June	1st to 10th	Night	33% 3 9% 25% 25% 5%	1440
	11th to 20th	Night	27% 6% 9% 30% 23% 5%	1440
	21st to end	Night	22% 3 8% 27% 29% 12%	1440
July	1st to 10th	Night	13% 3 6% 21% 32% 25%	1400
	11th to 20th	Night	11% 3 5% 17% 33% 31%	1392
	21st to end	Night	6% 3 2 12% 39% 38%	1488
August	1st to 10th	Night	13% 2 4 15% 36% 30%	1424
	11th to 20th	Night	13% 3 5% 19% 38% 22%	1526
	21st to end	Night	14% 4 5% 24% 36% 17%	1980
September	1st to 10th	Night	13% 3 7% 27% 28% 22%	1800
	11th to 20th	Night	22% 5% 10% 22% 28% 12%	1833
	21st to end	Night	23% 4 11% 31% 22% 9%	1980
October	1st to 10th	Night	31% 4 9% 28% 26% 2	2146
	11th to 20th	Night	32% 5% 12% 30% 19% 3	2182
	21st to end	Night	39% 6% 12% 27% 14% 2	2574
November	1st to 10th	Night	45% 8% 15% 21% 10% 2	2405
	11th to 20th	Night	47% 8% 17% 19% 8% 1	2641
	21st to end	Night	52% 7% 16% 17% 7% 1	2660
December	1st to 10th	Night	56% 7% 14% 17% 5%	2660
	11th to 20th	Night	70% 7% 12% 7% 3	3276
	21st to end	Night	63% 6% 13% 10% 6% 1	4862

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% 22% 22% 1	180
	11th to 20th	Day	24% 6% 17% 31% 16% 6%	172
	21st to end	Day	25% 3 21% 26% 20% 5%	176
February	1st to 10th	Day	19% 9% 27% 30% 13% 2	264
	11th to 20th	Day	16% 10% 26% 25% 17% 5%	353
	21st to end	Day	11% 12% 25% 31% 17% 4	346
March	1st to 10th	Day	14% 9% 30% 27% 14% 6%	420
	11th to 20th	Day	13% 12% 20% 28% 21% 6%	420
	21st to end	Day	13% 13% 26% 29% 15% 5%	462
April	1st to 10th	Day	12% 11% 28% 24% 17% 8%	420
	11th to 20th	Day	8% 14% 30% 26% 13% 9%	412
	21st to end	Day	7% 9% 25% 30% 19% 10%	420
May	1st to 10th	Day	6% 8% 20% 32% 24% 10%	423
	11th to 20th	Day	11% 7% 15% 28% 26% 13%	448
	21st to end	Day	7% 4 17% 26% 27% 19%	485
June	1st to 10th	Day	7% 6% 21% 24% 25% 17%	450
	11th to 20th	Day	5% 8% 26% 32% 19% 10%	450
	21st to end	Day	4 2 15% 30% 27% 21%	450
July	1st to 10th	Day	2 2 12% 33% 33% 18%	446
	11th to 20th	Day	1 3 16% 29% 34% 18%	444
	21st to end	Day	1 2 10% 24% 38% 24%	487
August	1st to 10th	Day	2 4 11% 23% 34% 26%	447
	11th to 20th	Day	3 2 9% 23% 34% 29%	437
	21st to end	Day	3 4 16% 26% 29% 22%	495
September	1st to 10th	Day	4 3 14% 29% 34% 17%	450
	11th to 20th	Day	6% 5% 18% 23% 30% 20%	450
	21st to end	Day	8% 8% 17% 28% 28% 12%	450
October	1st to 10th	Day	9% 5% 23% 25% 24% 14%	450
	11th to 20th	Day	9% 7% 19% 24% 27% 14%	427
	21st to end	Day	16% 7% 23% 30% 16% 7%	297
November	1st to 10th	Day	14% 10% 21% 36% 16% 3	270
	11th to 20th	Day	18% 10% 25% 25% 15% 7%	187
	21st to end	Day	16% 5% 22% 31% 18% 8%	180
December	1st to 10th	Day	18% 7% 21% 28% 18% 8%	180
	11th to 20th	Day	17% 5% 28% 31% 17% 2	180
	21st to end	Day	19% 7% 26% 27% 18% 3	198
January	1st to 10th	Night	23% 6% 26% 29% 14% 1	760
	11th to 20th	Night	18% 3 22% 37% 18% 2	748
	21st to end	Night	16% 3 21% 39% 19% 3	792
February	1st to 10th	Night	18% 5% 29% 33% 14% 2	720
	11th to 20th	Night	12% 5% 27% 36% 18% 2	704
	21st to end	Night	11% 8% 27% 36% 15% 2	592
March	1st to 10th	Night	13% 6% 23% 40% 16% 2	720
	11th to 20th	Night	10% 5% 26% 37% 20% 2	720
	21st to end	Night	11% 7% 29% 37% 14% 1	792
April	1st to 10th	Night	12% 5% 25% 35% 21% 2	720
	11th to 20th	Night	10% 6% 32% 31% 18% 4	711
	21st to end	Night	8% 5% 31% 37% 17% 3	527
May	1st to 10th	Night	6% 7% 31% 34% 20% 2	360
	11th to 20th	Night	9% 5% 18% 33% 31% 3	354
	21st to end	Night	6% 3 20% 41% 26% 5%	389
June	1st to 10th	Night	8% 3 21% 40% 26% 2	360
	11th to 20th	Night	5% 8% 28% 40% 16% 2	360
	21st to end	Night	5% 2 25% 39% 25% 3	360
July	1st to 10th	Night	3 1 17% 44% 32% 2	350
	11th to 20th	Night	2 3 20% 43% 30% 1	348
	21st to end	Night	1 1 14% 41% 39% 4	394
August	1st to 10th	Night	3 2 13% 35% 42% 5%	358
	11th to 20th	Night	3 1 11% 34% 41% 8%	458
	21st to end	Night	3 3 16% 36% 37% 5%	792
September	1st to 10th	Night	3 3 17% 41% 31% 5%	720
	11th to 20th	Night	5% 3 15% 31% 40% 7%	720
	21st to end	Night	7% 3 20% 33% 31% 5%	720
October	1st to 10th	Night	12% 3 17% 38% 28% 2	720
	11th to 20th	Night	10% 4 21% 34% 26% 5%	720
	21st to end	Night	13% 5% 24% 38% 17% 4	792
November	1st to 10th	Night	16% 6% 21% 43% 13% 1	740
	11th to 20th	Night	17% 7% 25% 32% 16% 3	760
	21st to end	Night	16% 6% 19% 37% 20% 2	760
December	1st to 10th	Night	16% 4 20% 41% 16% 3	760
	11th to 20th	Night	20% 5% 21% 39% 14% 1	760
	21st to end	Night	21% 6% 23% 38% 10% 1	836

Page generated at 2024-01-14 06:54:58. Version ac07

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