Buehler Trust Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Buehler Trust Observatory clear sky chart from 2005-11-06 to 2024-03-18.

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	17% 6% 3 5% 5% 3 5% 5% 5% 7% 40%	78565
	Night	18% 7% 3 5% 4 3 4 4 5% 6% 42%	81212
Transparency	Day	29% 37% 8% 15% 10% 2	78270
	Night	29% 35% 8% 15% 10% 1	81041
Seeing	Day	21% 14% 31% 22% 10% 3	14075
	Night	20% 10% 31% 28% 9% 1	23377

By Month

Percentage Cloud Cover NE (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% 7% 2 4 4 2 4 4 5% 6% 47%	2517
	11th to 20th	Day	16% 9% 3 5% 7% 4 6% 4 5% 6% 36%	2520
	21st to end	Day	22% 11% 4 7% 5% 2 3 4 4 5% 33%	3002
February	1st to 10th	Day	18% 7% 3 6% 4 3 5% 4 5% 7% 39%	1714
	11th to 20th	Day	15% 6% 3 5% 5% 3 4 4 5% 5% 45%	1848
	21st to end	Day	20% 8% 3 5% 4 3 5% 5% 5% 6% 39%	1570
March	1st to 10th	Day	15% 6% 3 5% 5% 3 4 4 5% 7% 42%	1897
	11th to 20th	Day	15% 6% 2 5% 6% 3 6% 4 6% 7% 40%	1968
	21st to end	Day	19% 7% 3 5% 4 3 4 4 5% 6% 39%	2357
April	1st to 10th	Day	18% 7% 3 5% 4 3 4 4 5% 6% 40%	2160
	11th to 20th	Day	17% 6% 3 5% 4 3 4 4 5% 7% 43%	2134
	21st to end	Day	21% 6% 2 4 5% 3 4 5% 5% 8% 39%	2182
May	1st to 10th	Day	24% 5% 3 5% 5% 2 4 5% 5% 7% 35%	2340
	11th to 20th	Day	20% 6% 2 5% 5% 3 5% 5% 5% 8% 36%	2464
	21st to end	Day	16% 6% 2 5% 5% 2 5% 5% 5% 8% 41%	2725
June	1st to 10th	Day	17% 5% 2 5% 5% 3 5% 6% 7% 10% 36%	2520
	11th to 20th	Day	16% 6% 3 5% 5% 3 5% 6% 6% 9% 35%	2520
	21st to end	Day	12% 5% 2 6% 6% 3 5% 6% 6% 10% 39%	2520
July	1st to 10th	Day	11% 6% 3 6% 6% 4 6% 6% 6% 9% 38%	2520
	11th to 20th	Day	10% 5% 3 5% 5% 3 6% 6% 8% 10% 39%	2520
	21st to end	Day	12% 6% 3 6% 7% 3 6% 6% 6% 9% 36%	2744
August	1st to 10th	Day	10% 6% 2 6% 6% 5% 6% 6% 8% 8% 37%	2377
	11th to 20th	Day	12% 6% 3 6% 6% 4 5% 6% 6% 9% 37%	2126
	21st to end	Day	13% 6% 3 5% 5% 3 5% 5% 6% 9% 40%	2376
September	1st to 10th	Day	15% 5% 2 5% 6% 3 5% 4 5% 7% 43%	2160
	11th to 20th	Day	13% 4 2 5% 3 3 4 3 5% 7% 50%	2084
	21st to end	Day	17% 5% 3 5% 6% 3 5% 4 5% 6% 41%	1980
October	1st to 10th	Day	22% 6% 2 4 4 3 3 3 4 7% 41%	1878
	11th to 20th	Day	16% 6% 2 4 4 3 3 4 4 7% 47%	1800
	21st to end	Day	22% 4 2 4 4 3 4 4 5% 6% 42%	1836
November	1st to 10th	Day	15% 6% 2 5% 3 2 3 4 4 5% 51%	1671
	11th to 20th	Day	19% 6% 2 3 4 2 3 4 5% 6% 47%	1710
	21st to end	Day	15% 6% 2 4 4 3 4 5% 6% 6% 45%	1627
December	1st to 10th	Day	20% 7% 2 5% 5% 3 3 4 6% 6% 39%	1520
	11th to 20th	Day	23% 4 3 4 3 2 3 3 4 7% 45%	1906
	21st to end	Day	18% 8% 4 7% 6% 4 5% 5% 5% 7% 31%	2772
January	1st to 10th	Night	17% 6% 3 4 3 2 3 3 5% 6% 47%	4429
	11th to 20th	Night	16% 8% 3 6% 5% 3 4 4 4 5% 42%	4440
	21st to end	Night	24% 11% 3 5% 4 2 4 4 4 5% 34%	4651
February	1st to 10th	Night	17% 8% 3 5% 4 3 4 4 4 5% 43%	2464
	11th to 20th	Night	16% 7% 3 6% 4 3 5% 4 4 6% 41%	2218
	21st to end	Night	19% 7% 3 5% 5% 3 4 3 4 5% 42%	1884
March	1st to 10th	Night	18% 6% 3 4 4 3 4 4 4 6% 45%	2270
	11th to 20th	Night	17% 8% 2 4 5% 2 5% 4 4 6% 44%	2153
	21st to end	Night	18% 7% 2 6% 5% 2 3 5% 4 7% 41%	1998
April	1st to 10th	Night	19% 7% 2 5% 5% 3 4 4 5% 7% 39%	1800
	11th to 20th	Night	19% 6% 2 4 4 2 5% 4 5% 7% 41%	1775
	21st to end	Night	21% 6% 2 5% 4 2 3 4 4 6% 42%	1776
May	1st to 10th	Night	22% 7% 3 7% 5% 3 5% 4 4 5% 35%	1620
	11th to 20th	Night	19% 8% 3 5% 4 3 4 4 4 6% 39%	1444
	21st to end	Night	17% 6% 3 4 3 3 4 4 6% 8% 41%	1550
June	1st to 10th	Night	18% 5% 3 4 4 3 5% 5% 5% 8% 41%	1440
	11th to 20th	Night	14% 5% 3 5% 5% 3 5% 5% 6% 10% 40%	1440
	21st to end	Night	12% 4 2 4 6% 3 5% 5% 6% 10% 44%	1440
July	1st to 10th	Night	12% 4 2 6% 6% 4 5% 5% 7% 8% 40%	1440
	11th to 20th	Night	12% 6% 2 4 4 4 5% 6% 7% 10% 39%	1440
	21st to end	Night	12% 4 2 4 4 3 5% 5% 7% 10% 42%	1574
August	1st to 10th	Night	9% 5% 2 5% 5% 3 6% 6% 6% 8% 44%	1539
	11th to 20th	Night	11% 6% 2 8% 7% 4 6% 6% 6% 8% 36%	1774
	21st to end	Night	14% 5% 3 5% 5% 3 4 5% 5% 8% 43%	1980
September	1st to 10th	Night	16% 6% 2 5% 5% 3 4 5% 5% 6% 44%	1800
	11th to 20th	Night	15% 6% 2 3 4 2 3 3 3 7% 53%	1876
	21st to end	Night	17% 6% 2 5% 5% 2 3 4 4 6% 46%	1980
October	1st to 10th	Night	21% 6% 2 6% 4 2 3 4 4 6% 42%	2078
	11th to 20th	Night	17% 5% 2 4 4 2 4 4 4 6% 48%	2160
	21st to end	Night	22% 7% 2 5% 3 2 4 3 4 6% 43%	2520
November	1st to 10th	Night	14% 4 3 4 4 2 4 5% 5% 5% 51%	2407
	11th to 20th	Night	21% 5% 2 4 3 2 3 3 4 5% 48%	2470
	21st to end	Night	14% 5% 3 4 5% 3 4 4 5% 7% 47%	2550
December	1st to 10th	Night	20% 6% 2 5% 5% 3 3 4 5% 6% 40%	2660
	11th to 20th	Night	20% 7% 2 4 4 3 4 4 5% 5% 42%	3288
	21st to end	Night	20% 9% 3 5% 4 3 5% 4 4 5% 36%	4884

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	28% 26% 9% 27% 9% 1	2518
	11th to 20th	Day	37% 27% 9% 17% 9% 1	2520
	21st to end	Day	45% 25% 7% 16% 6% 1	3002
February	1st to 10th	Day	29% 34% 8% 17% 10% 1	1714
	11th to 20th	Day	28% 37% 8% 16% 10% 2	1857
	21st to end	Day	31% 35% 8% 14% 10% 2	1570
March	1st to 10th	Day	27% 35% 9% 18% 9% 1	1900
	11th to 20th	Day	28% 37% 9% 15% 10% 2	1968
	21st to end	Day	29% 37% 6% 13% 12% 3	2357
April	1st to 10th	Day	27% 37% 7% 14% 11% 4	2160
	11th to 20th	Day	29% 36% 8% 14% 10% 3	2134
	21st to end	Day	27% 38% 8% 13% 11% 3	2182
May	1st to 10th	Day	31% 37% 6% 12% 12% 2	2340
	11th to 20th	Day	29% 39% 7% 13% 10% 3	2468
	21st to end	Day	25% 40% 10% 14% 10% 2	2725
June	1st to 10th	Day	26% 40% 11% 13% 8% 1	2520
	11th to 20th	Day	30% 40% 9% 15% 5% 2	2520
	21st to end	Day	28% 39% 10% 14% 8% 1	2520
July	1st to 10th	Day	29% 40% 9% 14% 9% 1	2450
	11th to 20th	Day	23% 40% 11% 16% 9% 2	2445
	21st to end	Day	27% 41% 9% 12% 10% 1	2591
August	1st to 10th	Day	26% 41% 10% 14% 8% 1	2363
	11th to 20th	Day	28% 39% 9% 14% 10% 1	2126
	21st to end	Day	30% 39% 6% 13% 11% 2	2376
September	1st to 10th	Day	27% 38% 7% 13% 12% 3	2160
	11th to 20th	Day	21% 37% 9% 16% 16% 2	2084
	21st to end	Day	28% 38% 6% 13% 13% 3	1980
October	1st to 10th	Day	27% 37% 6% 17% 12%	1878
	11th to 20th	Day	26% 38% 9% 17% 9% 1	1800
	21st to end	Day	29% 38% 6% 14% 11% 1	1836
November	1st to 10th	Day	20% 41% 7% 16% 14% 2	1671
	11th to 20th	Day	25% 40% 8% 14% 11% 2	1710
	21st to end	Day	26% 41% 8% 17% 8% 1	1627
December	1st to 10th	Day	27% 41% 9% 15% 7% 1	1520
	11th to 20th	Day	30% 32% 11% 16% 9% 2	1906
	21st to end	Day	38% 30% 9% 18% 5%	2772
January	1st to 10th	Night	29% 26% 10% 26% 8% 2	4429
	11th to 20th	Night	34% 26% 10% 18% 9% 2	4440
	21st to end	Night	43% 24% 7% 18% 7% 1	4651
February	1st to 10th	Night	29% 35% 8% 16% 10% 1	2464
	11th to 20th	Night	30% 36% 8% 12% 11% 3	2220
	21st to end	Night	30% 35% 5% 17% 11% 2	1884
March	1st to 10th	Night	26% 35% 10% 17% 9% 2	2280
	11th to 20th	Night	30% 37% 8% 15% 9% 2	2154
	21st to end	Night	27% 37% 7% 13% 12% 4	1998
April	1st to 10th	Night	29% 37% 7% 13% 11% 3	1800
	11th to 20th	Night	32% 37% 6% 12% 13% 1	1775
	21st to end	Night	27% 38% 7% 13% 12% 3	1776
May	1st to 10th	Night	33% 37% 6% 11% 11% 2	1620
	11th to 20th	Night	29% 39% 7% 11% 13% 3	1445
	21st to end	Night	24% 39% 12% 13% 9% 2	1551
June	1st to 10th	Night	27% 38% 9% 13% 11% 1	1440
	11th to 20th	Night	26% 40% 10% 17% 6% 1	1440
	21st to end	Night	24% 42% 11% 15% 9%	1440
July	1st to 10th	Night	28% 40% 10% 12% 8% 2	1400
	11th to 20th	Night	24% 43% 9% 15% 8% 1	1392
	21st to end	Night	20% 43% 11% 13% 11% 2	1486
August	1st to 10th	Night	24% 41% 11% 13% 10% 1	1529
	11th to 20th	Night	29% 39% 9% 14% 8%	1774
	21st to end	Night	29% 39% 8% 12% 10% 1	1980
September	1st to 10th	Night	28% 39% 7% 13% 12% 1	1800
	11th to 20th	Night	22% 36% 7% 17% 16% 2	1876
	21st to end	Night	26% 37% 6% 15% 15% 1	1980
October	1st to 10th	Night	28% 38% 7% 16% 10% 1	2078
	11th to 20th	Night	27% 38% 9% 16% 10% 1	2160
	21st to end	Night	30% 38% 8% 15% 10% 1	2520
November	1st to 10th	Night	19% 42% 7% 14% 14% 3	2407
	11th to 20th	Night	26% 39% 6% 16% 11% 2	2470
	21st to end	Night	25% 40% 8% 18% 9%	2550
December	1st to 10th	Night	26% 41% 9% 15% 9% 1	2660
	11th to 20th	Night	29% 33% 10% 13% 13% 2	3288
	21st to end	Night	36% 29% 11% 16% 8%	4884

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	21% 29% 29% 17% 3	180
	11th to 20th	Day	28% 25% 36% 9% 3	180
	21st to end	Day	20% 24% 38% 11% 6% 2	265
February	1st to 10th	Day	28% 20% 38% 11% 2	274
	11th to 20th	Day	24% 22% 35% 17% 2	456
	21st to end	Day	27% 18% 35% 16% 4	382
March	1st to 10th	Day	23% 22% 31% 20% 3	460
	11th to 20th	Day	21% 23% 33% 17% 5% 1	449
	21st to end	Day	28% 20% 31% 15% 6% 1	462
April	1st to 10th	Day	25% 20% 32% 14% 7% 1	420
	11th to 20th	Day	22% 19% 34% 15% 8% 2	412
	21st to end	Day	30% 17% 33% 14% 4 2	420
May	1st to 10th	Day	31% 19% 27% 15% 5% 2	423
	11th to 20th	Day	23% 13% 36% 19% 7% 1	447
	21st to end	Day	21% 8% 26% 28% 14% 3	485
June	1st to 10th	Day	17% 10% 32% 25% 13% 3	450
	11th to 20th	Day	20% 13% 31% 24% 11% 1	450
	21st to end	Day	14% 12% 31% 26% 15% 2	450
July	1st to 10th	Day	14% 6% 25% 32% 19% 4	445
	11th to 20th	Day	11% 4 28% 32% 21% 3	444
	21st to end	Day	14% 7% 28% 33% 15% 2	488
August	1st to 10th	Day	11% 7% 24% 35% 15% 7%	446
	11th to 20th	Day	15% 5% 23% 32% 20% 5%	439
	21st to end	Day	13% 6% 29% 28% 17% 6%	495
September	1st to 10th	Day	18% 8% 27% 24% 16% 7%	450
	11th to 20th	Day	18% 6% 29% 24% 13% 11%	450
	21st to end	Day	21% 10% 32% 20% 11% 6%	450
October	1st to 10th	Day	27% 8% 27% 20% 14% 4	450
	11th to 20th	Day	19% 16% 29% 23% 11% 2	450
	21st to end	Day	26% 13% 32% 19% 9% 1	423
November	1st to 10th	Day	16% 13% 31% 24% 12% 3	365
	11th to 20th	Day	25% 17% 30% 22% 5% 1	370
	21st to end	Day	18% 20% 34% 21% 5% 1	287
December	1st to 10th	Day	23% 26% 30% 14% 7%	180
	11th to 20th	Day	31% 22% 33% 13% 2	180
	21st to end	Day	28% 18% 35% 12% 7% 1	198
January	1st to 10th	Night	19% 15% 41% 21% 4	760
	11th to 20th	Night	25% 15% 33% 23% 3	760
	21st to end	Night	21% 15% 38% 24% 2	836
February	1st to 10th	Night	23% 12% 37% 26% 2	760
	11th to 20th	Night	22% 16% 41% 19% 1	743
	21st to end	Night	25% 16% 35% 21% 4	628
March	1st to 10th	Night	23% 14% 37% 21% 5%	760
	11th to 20th	Night	22% 14% 37% 22% 4 1	752
	21st to end	Night	22% 13% 38% 21% 5%	792
April	1st to 10th	Night	22% 16% 36% 21% 5%	720
	11th to 20th	Night	22% 14% 35% 24% 5%	711
	21st to end	Night	23% 12% 33% 25% 5% 1	696
May	1st to 10th	Night	24% 12% 33% 23% 8%	540
	11th to 20th	Night	23% 10% 33% 28% 5%	383
	21st to end	Night	21% 5% 21% 40% 12% 1	389
June	1st to 10th	Night	20% 4 28% 36% 12%	360
	11th to 20th	Night	15% 5% 29% 38% 12%	360
	21st to end	Night	11% 3 24% 51% 11%	360
July	1st to 10th	Night	12% 4 23% 40% 19% 1	350
	11th to 20th	Night	13% 4 19% 44% 20% 1	348
	21st to end	Night	15% 2 20% 47% 13% 2	394
August	1st to 10th	Night	10% 2 22% 44% 20% 2	465
	11th to 20th	Night	15% 4 17% 40% 23% 1	710
	21st to end	Night	15% 4 18% 40% 21% 2	792
September	1st to 10th	Night	17% 4 23% 36% 18% 2	720
	11th to 20th	Night	18% 4 23% 33% 18% 4	720
	21st to end	Night	20% 5% 25% 34% 15% 2	720
October	1st to 10th	Night	23% 8% 27% 26% 14% 2	720
	11th to 20th	Night	19% 10% 28% 32% 10%	720
	21st to end	Night	24% 10% 34% 23% 8%	792
November	1st to 10th	Night	16% 9% 32% 29% 12% 1	740
	11th to 20th	Night	23% 12% 33% 25% 7%	760
	21st to end	Night	19% 14% 34% 26% 6% 1	760
December	1st to 10th	Night	24% 13% 33% 24% 5% 1	760
	11th to 20th	Night	23% 13% 35% 26% 3	760
	21st to end	Night	24% 13% 36% 26% 2	836

Page generated at 2024-03-15 14:01:46. Version ac07

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