Beman Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Beman Observatory clear sky chart from 2005-11-06 to 2024-01-15.

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% 10% 4 7% 6% 4 5% 5% 5% 7% 33%	74876
	Night	15% 10% 4 7% 6% 3 4 4 5% 7% 33%	74916
Transparency	Day	49% 6% 12% 20% 11% 1	74581
	Night	50% 6% 12% 19% 11% 1	74732
Seeing	Day	18% 11% 28% 24% 14% 6%	14584
	Night	19% 9% 29% 30% 12% 1	24559

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	15% 15% 6% 11% 10% 5% 6% 5% 5% 6% 16%	1517
	11th to 20th	Day	15% 17% 8% 12% 10% 5% 6% 4 4 5% 14%	1472
	21st to end	Day	14% 20% 10% 11% 10% 4 4 4 3 5% 14%	1629
February	1st to 10th	Day	14% 14% 6% 12% 12% 5% 6% 4 4 4 18%	1652
	11th to 20th	Day	14% 12% 6% 13% 9% 4 5% 5% 4 4 24%	1748
	21st to end	Day	15% 15% 7% 11% 7% 4 5% 5% 4 5% 22%	1480
March	1st to 10th	Day	12% 11% 5% 8% 8% 5% 6% 5% 6% 6% 28%	1800
	11th to 20th	Day	13% 10% 5% 8% 6% 3 4 4 5% 6% 34%	1954
	21st to end	Day	18% 13% 4 7% 6% 3 4 4 5% 6% 29%	2205
April	1st to 10th	Day	18% 12% 5% 7% 6% 3 4 4 5% 6% 30%	2160
	11th to 20th	Day	16% 11% 3 6% 5% 3 5% 5% 4 8% 35%	2211
	21st to end	Day	17% 8% 3 7% 6% 4 5% 4 5% 7% 34%	2340
May	1st to 10th	Day	16% 8% 4 7% 6% 4 5% 5% 6% 7% 32%	2340
	11th to 20th	Day	19% 6% 3 7% 6% 4 4 5% 5% 6% 36%	2301
	21st to end	Day	11% 7% 2 5% 6% 3 5% 5% 6% 11% 39%	2641
June	1st to 10th	Day	10% 5% 2 5% 6% 4 5% 6% 7% 9% 42%	2520
	11th to 20th	Day	10% 5% 3 5% 5% 4 5% 5% 7% 8% 43%	2520
	21st to end	Day	9% 5% 2 6% 7% 3 6% 7% 8% 9% 38%	2520
July	1st to 10th	Day	7% 4 2 4 6% 3 5% 6% 7% 9% 47%	2520
	11th to 20th	Day	9% 5% 2 5% 5% 3 5% 5% 7% 8% 45%	2520
	21st to end	Day	7% 4 3 5% 5% 3 6% 6% 7% 11% 42%	2699
August	1st to 10th	Day	8% 6% 2 5% 6% 3 5% 7% 7% 10% 41%	2327
	11th to 20th	Day	10% 5% 3 5% 6% 5% 6% 6% 6% 9% 41%	2303
	21st to end	Day	10% 6% 2 6% 5% 4 4 6% 6% 9% 42%	2445
September	1st to 10th	Day	12% 7% 2 7% 6% 4 5% 4 5% 9% 40%	2098
	11th to 20th	Day	10% 5% 2 4 5% 3 5% 5% 5% 9% 46%	1980
	21st to end	Day	12% 7% 3 5% 6% 4 5% 5% 6% 8% 39%	1980
October	1st to 10th	Day	13% 7% 3 7% 6% 3 4 5% 5% 7% 41%	1980
	11th to 20th	Day	18% 9% 4 8% 5% 3 6% 5% 6% 6% 30%	1781
	21st to end	Day	20% 12% 4 8% 6% 3 5% 4 5% 6% 27%	1782
November	1st to 10th	Day	11% 11% 3 6% 5% 4 4 4 4 7% 40%	1672
	11th to 20th	Day	14% 15% 6% 10% 7% 3 5% 5% 4 6% 25%	1710
	21st to end	Day	19% 15% 7% 7% 6% 3 5% 3 4 7% 26%	1710
December	1st to 10th	Day	13% 17% 10% 10% 7% 3 6% 5% 4 5% 19%	1658
	11th to 20th	Day	13% 17% 9% 11% 7% 3 5% 5% 6% 6% 18%	1918
	21st to end	Day	20% 22% 8% 12% 9% 4 3 3 3 4 10%	2783
January	1st to 10th	Night	18% 13% 7% 11% 8% 4 5% 5% 5% 6% 19%	2648
	11th to 20th	Night	17% 14% 9% 11% 9% 4 4 4 4 6% 17%	2583
	21st to end	Night	14% 14% 10% 13% 10% 4 5% 5% 5% 6% 15%	2725
February	1st to 10th	Night	15% 17% 6% 10% 10% 4 5% 4 4 4 19%	2304
	11th to 20th	Night	13% 14% 6% 8% 8% 5% 5% 6% 5% 5% 25%	2098
	21st to end	Night	18% 12% 5% 9% 7% 3 4 4 5% 7% 26%	1776
March	1st to 10th	Night	15% 11% 4 6% 7% 4 4 4 5% 6% 35%	2160
	11th to 20th	Night	14% 8% 3 6% 6% 3 4 4 6% 7% 40%	2004
	21st to end	Night	19% 9% 4 7% 6% 3 3 4 5% 6% 33%	2165
April	1st to 10th	Night	14% 10% 4 7% 5% 3 5% 5% 6% 7% 36%	1800
	11th to 20th	Night	18% 9% 3 6% 4 4 5% 4 5% 6% 37%	1697
	21st to end	Night	16% 9% 3 7% 5% 3 4 4 5% 8% 37%	1620
May	1st to 10th	Night	17% 9% 4 6% 7% 4 5% 4 5% 8% 32%	1620
	11th to 20th	Night	20% 7% 2 4 4 3 4 5% 5% 7% 39%	1592
	21st to end	Night	10% 5% 3 5% 6% 3 5% 5% 7% 10% 41%	1630
June	1st to 10th	Night	10% 6% 2 4 4 2 5% 3 6% 10% 47%	1440
	11th to 20th	Night	11% 5% 2 5% 5% 2 5% 3 7% 10% 45%	1440
	21st to end	Night	8% 5% 3 5% 6% 3 4 6% 6% 10% 46%	1440
July	1st to 10th	Night	6% 3 2 4 4 3 4 5% 7% 10% 51%	1440
	11th to 20th	Night	8% 4 2 4 4 3 3 4 6% 8% 54%	1440
	21st to end	Night	6% 3 2 5% 5% 3 5% 5% 6% 9% 51%	1616
August	1st to 10th	Night	8% 4 2 4 5% 3 4 5% 6% 9% 51%	1611
	11th to 20th	Night	8% 4 2 5% 6% 3 4 5% 7% 9% 48%	1598
	21st to end	Night	9% 5% 2 4 4 3 4 5% 5% 8% 51%	1908
September	1st to 10th	Night	10% 6% 3 5% 5% 3 4 5% 5% 9% 47%	1844
	11th to 20th	Night	11% 5% 2 4 4 2 3 3 4 8% 53%	1980
	21st to end	Night	14% 6% 3 5% 5% 3 4 4 5% 7% 44%	1980
October	1st to 10th	Night	15% 7% 2 6% 4 3 4 4 4 7% 44%	1980
	11th to 20th	Night	18% 10% 4 7% 6% 3 4 4 4 6% 33%	2177
	21st to end	Night	23% 9% 4 6% 6% 3 4 4 5% 6% 31%	2574
November	1st to 10th	Night	13% 10% 3 6% 6% 3 4 4 4 6% 40%	2406
	11th to 20th	Night	14% 14% 4 9% 6% 3 4 7% 6% 6% 27%	2470
	21st to end	Night	18% 13% 6% 8% 6% 4 3 4 5% 7% 27%	2470
December	1st to 10th	Night	16% 16% 8% 12% 7% 4 5% 5% 4 6% 17%	2517
	11th to 20th	Night	15% 15% 7% 13% 8% 4 5% 5% 4 6% 19%	3279
	21st to end	Night	26% 20% 7% 10% 6% 3 4 4 4 5% 12%	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	69% 6% 11% 11% 3	1518
	11th to 20th	Day	73% 5% 10% 8% 4	1472
	21st to end	Day	73% 4 9% 10% 3	1629
February	1st to 10th	Day	69% 6% 8% 12% 6%	1652
	11th to 20th	Day	64% 5% 8% 14% 8% 1	1758
	21st to end	Day	64% 5% 10% 13% 6% 1	1480
March	1st to 10th	Day	55% 7% 12% 18% 8% 1	1800
	11th to 20th	Day	50% 6% 11% 18% 13% 2	1954
	21st to end	Day	55% 5% 11% 19% 9% 1	2205
April	1st to 10th	Day	55% 5% 9% 20% 10%	2160
	11th to 20th	Day	49% 6% 11% 19% 14% 2	2211
	21st to end	Day	49% 6% 12% 16% 14% 2	2340
May	1st to 10th	Day	51% 6% 12% 20% 10% 1	2340
	11th to 20th	Day	49% 6% 10% 20% 14% 2	2305
	21st to end	Day	40% 7% 14% 24% 13% 1	2641
June	1st to 10th	Day	36% 8% 11% 28% 14% 2	2520
	11th to 20th	Day	37% 6% 14% 23% 18% 2	2520
	21st to end	Day	38% 9% 14% 21% 15% 2	2520
July	1st to 10th	Day	31% 8% 13% 26% 18% 4	2451
	11th to 20th	Day	35% 7% 12% 25% 18% 2	2445
	21st to end	Day	33% 8% 14% 24% 19% 2	2549
August	1st to 10th	Day	35% 9% 15% 27% 12% 2	2314
	11th to 20th	Day	38% 7% 14% 26% 12% 2	2303
	21st to end	Day	36% 7% 12% 26% 16% 3	2445
September	1st to 10th	Day	41% 6% 15% 22% 15% 2	2098
	11th to 20th	Day	33% 7% 13% 30% 16% 1	1980
	21st to end	Day	41% 6% 13% 24% 16%	1980
October	1st to 10th	Day	43% 6% 9% 26% 14% 2	1980
	11th to 20th	Day	53% 6% 11% 20% 9% 1	1781
	21st to end	Day	58% 6% 11% 16% 8% 1	1782
November	1st to 10th	Day	44% 6% 12% 22% 14% 1	1672
	11th to 20th	Day	60% 5% 10% 17% 7% 1	1710
	21st to end	Day	61% 4 14% 15% 5% 1	1710
December	1st to 10th	Day	66% 6% 11% 12% 4 1	1658
	11th to 20th	Day	66% 6% 13% 13% 3	1915
	21st to end	Day	78% 5% 8% 6% 3	2783
January	1st to 10th	Night	65% 6% 9% 14% 5% 1	2648
	11th to 20th	Night	68% 5% 12% 10% 5%	2583
	21st to end	Night	70% 6% 10% 10% 5% 1	2725
February	1st to 10th	Night	68% 5% 9% 12% 5% 1	2304
	11th to 20th	Night	60% 6% 9% 18% 8% 1	2099
	21st to end	Night	58% 4 13% 16% 7% 2	1776
March	1st to 10th	Night	51% 5% 12% 22% 9% 1	2160
	11th to 20th	Night	44% 6% 13% 21% 15% 2	2004
	21st to end	Night	52% 5% 9% 22% 10% 2	2165
April	1st to 10th	Night	46% 7% 11% 22% 13% 1	1800
	11th to 20th	Night	47% 5% 10% 18% 17% 2	1697
	21st to end	Night	45% 6% 12% 20% 14% 3	1620
May	1st to 10th	Night	51% 5% 12% 20% 11% 2	1620
	11th to 20th	Night	44% 6% 11% 18% 19% 2	1593
	21st to end	Night	36% 8% 16% 24% 14% 2	1631
June	1st to 10th	Night	33% 7% 11% 29% 17% 3	1440
	11th to 20th	Night	35% 6% 15% 25% 17% 2	1440
	21st to end	Night	33% 8% 15% 26% 16% 2	1440
July	1st to 10th	Night	27% 8% 13% 27% 21% 5%	1400
	11th to 20th	Night	28% 6% 14% 28% 21% 2	1392
	21st to end	Night	28% 8% 16% 24% 21% 4	1526
August	1st to 10th	Night	29% 6% 16% 31% 16% 2	1600
	11th to 20th	Night	32% 6% 14% 29% 16% 3	1598
	21st to end	Night	31% 6% 11% 26% 22% 3	1908
September	1st to 10th	Night	35% 7% 11% 26% 18% 2	1844
	11th to 20th	Night	31% 4 10% 33% 20% 1	1980
	21st to end	Night	39% 6% 12% 26% 16% 1	1980
October	1st to 10th	Night	41% 5% 10% 25% 18% 1	1980
	11th to 20th	Night	51% 6% 11% 19% 13% 1	2177
	21st to end	Night	54% 6% 10% 21% 9% 1	2574
November	1st to 10th	Night	46% 5% 11% 23% 14% 1	2406
	11th to 20th	Night	53% 8% 13% 17% 8% 1	2470
	21st to end	Night	57% 6% 13% 18% 5%	2470
December	1st to 10th	Night	67% 7% 9% 11% 6%	2517
	11th to 20th	Night	66% 6% 12% 12% 4	3281
	21st to end	Night	75% 6% 10% 7% 2	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	22% 14% 37% 20% 5% 1	270
	11th to 20th	Day	21% 17% 44% 12% 5% 1	252
	21st to end	Day	25% 16% 38% 16% 5%	264
February	1st to 10th	Day	25% 22% 34% 18% 1	240
	11th to 20th	Day	28% 19% 39% 14% 1	240
	21st to end	Day	24% 30% 34% 10% 1	198
March	1st to 10th	Day	23% 22% 40% 11% 4	240
	11th to 20th	Day	21% 13% 35% 23% 8%	394
	21st to end	Day	27% 14% 31% 20% 6% 2	462
April	1st to 10th	Day	24% 13% 32% 22% 8%	420
	11th to 20th	Day	26% 17% 28% 18% 8% 4	412
	21st to end	Day	23% 10% 35% 20% 11% 1	420
May	1st to 10th	Day	24% 13% 27% 24% 9% 4	423
	11th to 20th	Day	22% 10% 26% 23% 11% 8%	447
	21st to end	Day	15% 7% 25% 27% 19% 7%	595
June	1st to 10th	Day	12% 7% 30% 32% 14% 5%	630
	11th to 20th	Day	13% 6% 26% 31% 18% 5%	630
	21st to end	Day	12% 7% 30% 32% 14% 5%	630
July	1st to 10th	Day	8% 4 20% 30% 24% 14%	621
	11th to 20th	Day	11% 6% 25% 28% 21% 9%	618
	21st to end	Day	9% 3 25% 33% 22% 8%	640
August	1st to 10th	Day	9% 4 17% 28% 23% 19%	446
	11th to 20th	Day	12% 4 16% 27% 30% 11%	439
	21st to end	Day	9% 5% 22% 27% 24% 13%	495
September	1st to 10th	Day	16% 6% 18% 26% 23% 11%	450
	11th to 20th	Day	9% 4 18% 27% 28% 14%	450
	21st to end	Day	15% 12% 20% 25% 18% 10%	450
October	1st to 10th	Day	16% 8% 27% 27% 13% 8%	450
	11th to 20th	Day	20% 18% 26% 30% 6% 1	414
	21st to end	Day	29% 15% 36% 14% 4 1	297
November	1st to 10th	Day	15% 19% 35% 23% 6% 2	270
	11th to 20th	Day	23% 21% 33% 17% 6%	270
	21st to end	Day	29% 15% 41% 12% 3	270
December	1st to 10th	Day	26% 23% 34% 11% 6%	270
	11th to 20th	Day	22% 21% 39% 15% 3	270
	21st to end	Day	23% 25% 35% 15% 2	297
January	1st to 10th	Night	22% 14% 37% 22% 5% 1	950
	11th to 20th	Night	24% 14% 35% 22% 5% 1	923
	21st to end	Night	19% 12% 35% 29% 5%	943
February	1st to 10th	Night	26% 11% 38% 22% 3	720
	11th to 20th	Night	20% 15% 35% 26% 3	703
	21st to end	Night	26% 12% 40% 20% 3	592
March	1st to 10th	Night	21% 11% 36% 24% 7% 1	720
	11th to 20th	Night	16% 13% 37% 27% 6% 1	720
	21st to end	Night	23% 10% 32% 27% 7%	779
April	1st to 10th	Night	16% 12% 37% 29% 6% 1	540
	11th to 20th	Night	21% 9% 36% 25% 8% 1	533
	21st to end	Night	21% 7% 34% 30% 8% 1	540
May	1st to 10th	Night	22% 6% 30% 31% 9% 1	540
	11th to 20th	Night	22% 5% 29% 30% 13% 1	531
	21st to end	Night	13% 2 26% 37% 19% 2	584
June	1st to 10th	Night	11% 4 24% 42% 18%	540
	11th to 20th	Night	14% 3 24% 40% 19% 1	540
	21st to end	Night	10% 2 23% 42% 22% 2	540
July	1st to 10th	Night	8% 2 16% 40% 29% 5%	525
	11th to 20th	Night	9% 3 17% 44% 23% 3	522
	21st to end	Night	8% 1 16% 46% 28% 1	591
August	1st to 10th	Night	9% 2 11% 45% 30% 3	537
	11th to 20th	Night	9% 1 15% 40% 29% 6%	534
	21st to end	Night	12% 2 17% 36% 29% 4	594
September	1st to 10th	Night	11% 3 18% 38% 23% 6%	584
	11th to 20th	Night	11% 4 17% 35% 29% 4	720
	21st to end	Night	17% 5% 22% 30% 22% 5%	720
October	1st to 10th	Night	18% 6% 24% 32% 19% 2	720
	11th to 20th	Night	23% 12% 28% 28% 8% 1	720
	21st to end	Night	27% 12% 30% 25% 6%	792
November	1st to 10th	Night	20% 10% 28% 31% 10% 1	740
	11th to 20th	Night	22% 13% 36% 24% 5% 1	760
	21st to end	Night	24% 12% 33% 27% 4	760
December	1st to 10th	Night	23% 14% 37% 21% 6%	807
	11th to 20th	Night	23% 14% 38% 22% 4	950
	21st to end	Night	30% 13% 35% 21% 1	1045

Page generated at 2024-01-12 07:31:46. Version ac07

Copyright 2024 Attilla Danko