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 2024-11-02.

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% 7% 2 6% 4 4 4 4 5% 7% 39%	101280
	Night	18% 7% 2 6% 4 4 4 3 5% 6% 41%	97695
Transparency	Day	43% 6% 11% 22% 15% 2	101035
	Night	43% 6% 12% 22% 15% 2	97560
Seeing	Day	21% 14% 31% 22% 10% 3	14981
	Night	20% 10% 31% 29% 9% 1	24105

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 5% 3 3 4 3 5% 6% 47%	2517
	11th to 20th	Day	15% 9% 3 6% 6% 6% 5% 4 5% 6% 36%	2520
	21st to end	Day	22% 11% 4 8% 4 3 3 3 4 5% 33%	3002
February	1st to 10th	Day	18% 7% 3 6% 4 4 4 4 5% 6% 39%	1714
	11th to 20th	Day	15% 7% 3 6% 4 4 4 3 5% 5% 44%	1848
	21st to end	Day	20% 8% 2 5% 4 3 5% 3 5% 5% 39%	1570
March	1st to 10th	Day	27% 8% 3 5% 4 3 3 3 4 5% 35%	3116
	11th to 20th	Day	10% 5% 2 6% 6% 5% 5% 4 6% 7% 43%	3338
	21st to end	Day	21% 7% 2 5% 4 4 3 2 4 5% 43%	4133
April	1st to 10th	Day	18% 8% 3 6% 4 4 4 3 5% 7% 39%	2280
	11th to 20th	Day	17% 7% 2 6% 4 4 4 3 5% 7% 42%	2254
	21st to end	Day	20% 6% 2 5% 4 4 3 4 5% 7% 39%	2304
May	1st to 10th	Day	28% 8% 2 5% 3 3 4 3 5% 7% 30%	4106
	11th to 20th	Day	23% 8% 3 8% 5% 4 4 4 5% 7% 30%	4384
	21st to end	Day	14% 5% 2 5% 4 3 4 4 5% 9% 44%	4837
June	1st to 10th	Day	16% 6% 2 6% 5% 4 4 5% 8% 9% 36%	2660
	11th to 20th	Day	16% 6% 3 5% 5% 4 6% 4 6% 9% 36%	2660
	21st to end	Day	12% 6% 2 6% 6% 4 5% 5% 6% 9% 38%	2660
July	1st to 10th	Day	9% 7% 3 7% 5% 5% 6% 5% 7% 10% 35%	4440
	11th to 20th	Day	11% 6% 2 6% 4 5% 5% 5% 7% 10% 37%	4440
	21st to end	Day	14% 9% 3 8% 6% 5% 6% 4 6% 8% 32%	4814
August	1st to 10th	Day	20% 6% 2 7% 5% 6% 5% 4 7% 8% 31%	4169
	11th to 20th	Day	13% 6% 3 6% 4 4 4 4 6% 9% 41%	3730
	21st to end	Day	10% 6% 2 6% 4 4 4 4 6% 9% 46%	4180
September	1st to 10th	Day	15% 5% 2 6% 5% 5% 4 4 5% 6% 44%	2280
	11th to 20th	Day	13% 5% 2 5% 3 4 4 3 5% 7% 49%	2199
	21st to end	Day	18% 6% 3 6% 5% 5% 4 3 5% 6% 39%	2090
October	1st to 10th	Day	21% 7% 2 5% 4 3 4 3 5% 7% 41%	1982
	11th to 20th	Day	16% 5% 2 4 4 3 3 3 4 6% 49%	1900
	21st to end	Day	21% 4 2 4 3 4 3 4 4 7% 43%	1937
November	1st to 10th	Day	15% 6% 2 5% 3 3 2 3 5% 5% 52%	1681
	11th to 20th	Day	19% 6% 2 4 3 2 3 3 5% 6% 47%	1710
	21st to end	Day	15% 7% 2 5% 4 4 4 4 6% 6% 45%	1627
December	1st to 10th	Day	19% 8% 2 6% 4 4 2 4 6% 6% 39%	1520
	11th to 20th	Day	23% 5% 2 4 3 3 3 2 5% 7% 44%	1906
	21st to end	Day	18% 9% 3 9% 5% 5% 4 4 5% 7% 31%	2772
January	1st to 10th	Night	17% 6% 3 5% 3 3 3 3 5% 6% 47%	4429
	11th to 20th	Night	16% 8% 3 7% 4 4 4 3 4 5% 42%	4440
	21st to end	Night	24% 11% 2 5% 3 3 4 3 4 5% 34%	4651
February	1st to 10th	Night	17% 8% 3 6% 4 4 3 3 4 5% 42%	2464
	11th to 20th	Night	16% 8% 3 6% 4 4 4 4 4 6% 41%	2218
	21st to end	Night	19% 8% 2 5% 5% 4 3 3 4 5% 42%	1884
March	1st to 10th	Night	25% 9% 3 5% 4 4 3 3 4 5% 36%	3724
	11th to 20th	Night	12% 7% 2 5% 4 4 4 4 5% 6% 47%	3617
	21st to end	Night	19% 9% 2 6% 4 3 3 3 3 6% 42%	3498
April	1st to 10th	Night	19% 7% 2 6% 4 4 4 3 6% 7% 38%	1900
	11th to 20th	Night	19% 7% 2 6% 3 3 5% 3 5% 6% 41%	1875
	21st to end	Night	20% 7% 2 6% 4 3 4 3 4 7% 42%	1874
May	1st to 10th	Night	26% 10% 3 7% 4 3 3 3 5% 6% 29%	2834
	11th to 20th	Night	24% 10% 3 6% 4 4 3 3 4 5% 34%	2538
	21st to end	Night	16% 7% 2 6% 3 4 4 3 6% 7% 42%	2738
June	1st to 10th	Night	17% 6% 2 4 4 4 5% 4 5% 8% 41%	1520
	11th to 20th	Night	13% 6% 3 5% 4 4 4 4 6% 10% 41%	1520
	21st to end	Night	12% 4 2 5% 5% 4 5% 4 6% 10% 42%	1520
July	1st to 10th	Night	10% 5% 3 7% 5% 6% 5% 5% 7% 9% 38%	2520
	11th to 20th	Night	13% 7% 2 5% 4 4 6% 4 8% 10% 36%	2520
	21st to end	Night	19% 8% 2 5% 4 4 5% 4 6% 7% 36%	2739
August	1st to 10th	Night	23% 6% 3 6% 4 5% 5% 4 5% 7% 32%	2711
	11th to 20th	Night	14% 7% 2 7% 5% 5% 4 4 5% 7% 39%	3097
	21st to end	Night	10% 5% 2 5% 3 3 4 4 5% 7% 52%	3476
September	1st to 10th	Night	15% 7% 2 5% 4 4 3 4 5% 6% 45%	1900
	11th to 20th	Night	14% 6% 1 4 3 3 3 3 4 7% 52%	1981
	21st to end	Night	18% 7% 2 6% 4 4 3 3 4 6% 45%	2090
October	1st to 10th	Night	20% 7% 2 6% 4 3 3 3 4 6% 42%	2194
	11th to 20th	Night	16% 5% 2 5% 3 3 3 3 4 6% 50%	2280
	21st to end	Night	21% 7% 2 5% 3 3 4 3 4 6% 44%	2660
November	1st to 10th	Night	14% 5% 2 5% 3 3 4 4 5% 5% 51%	2431
	11th to 20th	Night	20% 6% 2 4 3 2 3 3 4 5% 48%	2470
	21st to end	Night	14% 6% 2 5% 4 3 3 3 5% 7% 47%	2550
December	1st to 10th	Night	20% 7% 2 6% 4 3 3 3 5% 6% 40%	2660
	11th to 20th	Night	20% 7% 2 5% 4 4 4 4 5% 5% 42%	3288
	21st to end	Night	20% 10% 3 6% 3 4 4 3 5% 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	38% 4 10% 32% 13% 3	2518
	11th to 20th	Day	48% 5% 12% 21% 13% 2	2520
	21st to end	Day	54% 4 8% 21% 10% 2	3002
February	1st to 10th	Day	45% 5% 13% 23% 13% 2	1714
	11th to 20th	Day	42% 4 9% 24% 17% 3	1857
	21st to end	Day	46% 5% 11% 21% 14% 3	1570
March	1st to 10th	Day	51% 4 11% 22% 10% 2	3119
	11th to 20th	Day	34% 9% 12% 29% 15% 2	3338
	21st to end	Day	44% 4 7% 16% 24% 5%	4133
April	1st to 10th	Day	44% 6% 10% 20% 16% 5%	2280
	11th to 20th	Day	42% 5% 11% 21% 18% 3	2254
	21st to end	Day	43% 6% 9% 21% 17% 4	2304
May	1st to 10th	Day	53% 6% 12% 15% 12% 2	4120
	11th to 20th	Day	51% 8% 12% 18% 9% 2	4388
	21st to end	Day	35% 7% 11% 26% 19% 2	4837
June	1st to 10th	Day	40% 9% 13% 21% 15% 2	2660
	11th to 20th	Day	43% 9% 11% 23% 12% 2	2660
	21st to end	Day	39% 8% 13% 22% 16% 1	2660
July	1st to 10th	Day	41% 10% 12% 21% 14% 1	4370
	11th to 20th	Day	38% 9% 16% 21% 14% 1	4365
	21st to end	Day	48% 8% 11% 16% 15% 2	4661
August	1st to 10th	Day	48% 8% 14% 20% 9%	4155
	11th to 20th	Day	37% 8% 14% 28% 13% 1	3766
	21st to end	Day	34% 6% 11% 28% 19% 2	4180
September	1st to 10th	Day	40% 7% 10% 21% 19% 3	2280
	11th to 20th	Day	34% 5% 11% 23% 24% 3	2199
	21st to end	Day	45% 6% 8% 19% 18% 4	2090
October	1st to 10th	Day	43% 5% 10% 22% 17% 3	1982
	11th to 20th	Day	36% 5% 12% 25% 21% 2	1900
	21st to end	Day	42% 5% 10% 22% 19% 3	1937
November	1st to 10th	Day	36% 4 11% 23% 22% 3	1681
	11th to 20th	Day	39% 4 10% 23% 21% 4	1710
	21st to end	Day	38% 5% 13% 30% 12% 2	1627
December	1st to 10th	Day	45% 5% 14% 21% 14% 1	1520
	11th to 20th	Day	41% 4 15% 23% 13% 3	1906
	21st to end	Day	50% 8% 10% 23% 8%	2772
January	1st to 10th	Night	39% 4 11% 31% 12% 4	4429
	11th to 20th	Night	45% 4 13% 23% 12% 2	4440
	21st to end	Night	52% 4 8% 22% 12% 2	4651
February	1st to 10th	Night	44% 5% 12% 25% 13% 2	2464
	11th to 20th	Night	45% 4 10% 19% 18% 5%	2220
	21st to end	Night	44% 5% 7% 24% 16% 4	1884
March	1st to 10th	Night	50% 5% 10% 21% 11% 3	3734
	11th to 20th	Night	36% 5% 14% 25% 17% 3	3618
	21st to end	Night	45% 3 8% 15% 21% 7%	3498
April	1st to 10th	Night	45% 5% 11% 20% 16% 4	1900
	11th to 20th	Night	44% 5% 10% 20% 19% 2	1875
	21st to end	Night	43% 5% 9% 21% 19% 4	1874
May	1st to 10th	Night	56% 6% 10% 17% 10% 1	2840
	11th to 20th	Night	53% 7% 14% 14% 11% 2	2539
	21st to end	Night	40% 7% 14% 24% 13% 3	2739
June	1st to 10th	Night	41% 6% 11% 21% 20% 2	1520
	11th to 20th	Night	39% 8% 13% 27% 12% 1	1520
	21st to end	Night	35% 8% 15% 25% 16% 1	1520
July	1st to 10th	Night	41% 9% 16% 18% 14% 2	2480
	11th to 20th	Night	41% 9% 14% 22% 12% 1	2472
	21st to end	Night	44% 8% 14% 15% 18% 2	2651
August	1st to 10th	Night	50% 9% 15% 16% 9% 1	2701
	11th to 20th	Night	41% 9% 12% 27% 10% 1	3127
	21st to end	Night	31% 6% 12% 31% 19% 1	3476
September	1st to 10th	Night	40% 7% 10% 24% 19% 1	1900
	11th to 20th	Night	33% 6% 10% 23% 25% 3	1981
	21st to end	Night	42% 5% 9% 22% 22% 2	2090
October	1st to 10th	Night	44% 5% 12% 22% 15% 3	2194
	11th to 20th	Night	35% 5% 13% 27% 18% 2	2280
	21st to end	Night	42% 4 11% 23% 18% 2	2660
November	1st to 10th	Night	35% 6% 11% 22% 22% 4	2431
	11th to 20th	Night	40% 4 9% 24% 19% 5%	2470
	21st to end	Night	37% 5% 13% 29% 15% 2	2550
December	1st to 10th	Night	44% 5% 13% 22% 14% 2	2660
	11th to 20th	Night	44% 4 12% 20% 16% 4	3288
	21st to end	Night	49% 6% 12% 21% 12% 1	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% 34% 16% 5% 1	460
	21st to end	Day	28% 21% 30% 15% 6% 1	506
April	1st to 10th	Day	27% 20% 32% 13% 7% 1	460
	11th to 20th	Day	23% 21% 33% 15% 7% 2	452
	21st to end	Day	28% 17% 33% 16% 4 2	460
May	1st to 10th	Day	31% 19% 26% 16% 6% 2	463
	11th to 20th	Day	23% 13% 34% 21% 8% 1	487
	21st to end	Day	20% 9% 28% 28% 14% 2	529
June	1st to 10th	Day	17% 10% 33% 25% 12% 3	490
	11th to 20th	Day	18% 12% 31% 26% 12% 1	490
	21st to end	Day	15% 12% 31% 26% 14% 2	490
July	1st to 10th	Day	14% 6% 27% 31% 19% 4	485
	11th to 20th	Day	11% 4 29% 33% 21% 3	484
	21st to end	Day	14% 8% 29% 32% 16% 2	532
August	1st to 10th	Day	13% 7% 25% 34% 15% 7%	486
	11th to 20th	Day	15% 5% 23% 33% 19% 5%	479
	21st to end	Day	12% 7% 29% 29% 16% 7%	539
September	1st to 10th	Day	17% 9% 27% 24% 17% 7%	490
	11th to 20th	Day	17% 5% 28% 26% 13% 11%	490
	21st to end	Day	22% 10% 31% 21% 10% 5%	490
October	1st to 10th	Day	25% 8% 28% 20% 14% 4	490
	11th to 20th	Day	18% 16% 30% 22% 11% 2	490
	21st to end	Day	25% 12% 32% 20% 10% 2	458
November	1st to 10th	Day	16% 14% 31% 24% 12% 3	369
	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	23% 15% 37% 21% 4 1	760
	21st to end	Night	23% 14% 38% 21% 5%	836
April	1st to 10th	Night	22% 16% 36% 21% 4	760
	11th to 20th	Night	22% 14% 34% 24% 5%	751
	21st to end	Night	22% 12% 34% 25% 5% 1	734
May	1st to 10th	Night	24% 13% 33% 23% 7%	570
	11th to 20th	Night	23% 10% 33% 28% 5%	404
	21st to end	Night	21% 5% 22% 40% 11% 1	411
June	1st to 10th	Night	19% 5% 28% 37% 12%	380
	11th to 20th	Night	14% 5% 30% 39% 12%	380
	21st to end	Night	11% 3 26% 49% 10%	380
July	1st to 10th	Night	12% 4 24% 40% 19% 1	370
	11th to 20th	Night	13% 4 20% 43% 20% 1	368
	21st to end	Night	16% 3 20% 46% 13% 1	416
August	1st to 10th	Night	12% 3 22% 43% 19% 2	492
	11th to 20th	Night	15% 4 17% 39% 23% 1	750
	21st to end	Night	15% 4 19% 39% 21% 2	836
September	1st to 10th	Night	16% 5% 24% 36% 18% 2	760
	11th to 20th	Night	17% 4 22% 34% 18% 4	760
	21st to end	Night	21% 5% 24% 33% 15% 1	760
October	1st to 10th	Night	23% 8% 27% 26% 14% 2	760
	11th to 20th	Night	18% 10% 30% 31% 11% 1	760
	21st to end	Night	23% 10% 33% 25% 8%	836
November	1st to 10th	Night	16% 9% 33% 28% 12% 1	748
	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 2024-10-30 13:19:24. Version ac07

Copyright © 2024 Attilla Danko.