Chamberlain Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Chamberlain 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% 7% 3 5% 5% 3 5% 5% 5% 7% 42%	74768
	Night	13% 7% 3 6% 5% 3 4 4 5% 7% 44%	75026
Transparency	Day	41% 5% 12% 25% 15% 2	74475
	Night	41% 4 11% 25% 17% 3	74841
Seeing	Day	15% 8% 26% 27% 18% 6%	14485
	Night	17% 8% 29% 31% 14% 2	24441

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	12% 12% 6% 9% 5% 3 5% 4 5% 6% 34%	1517
	11th to 20th	Day	16% 11% 6% 9% 6% 3 4 3 5% 6% 31%	1553
	21st to end	Day	13% 11% 5% 9% 6% 2 4 3 4 6% 37%	1782
February	1st to 10th	Day	16% 10% 5% 7% 5% 3 4 5% 5% 7% 33%	1620
	11th to 20th	Day	15% 10% 4 6% 6% 4 5% 4 5% 8% 34%	1739
	21st to end	Day	17% 10% 4 7% 5% 3 4 4 5% 5% 38%	1480
March	1st to 10th	Day	15% 8% 4 5% 5% 3 4 4 4 5% 41%	1801
	11th to 20th	Day	18% 9% 4 5% 5% 3 4 4 5% 6% 35%	1980
	21st to end	Day	20% 11% 4 7% 6% 3 5% 5% 5% 6% 28%	2304
April	1st to 10th	Day	12% 6% 2 6% 5% 4 5% 4 6% 8% 42%	2160
	11th to 20th	Day	16% 9% 3 5% 6% 3 4 4 4 6% 41%	2134
	21st to end	Day	17% 6% 4 5% 6% 3 4 4 5% 6% 39%	2160
May	1st to 10th	Day	16% 6% 3 6% 5% 3 5% 5% 7% 9% 36%	2240
	11th to 20th	Day	17% 5% 2 4 6% 4 4 6% 6% 7% 39%	2443
	21st to end	Day	11% 5% 3 6% 6% 4 7% 6% 7% 8% 39%	2725
June	1st to 10th	Day	8% 4 2 4 5% 3 5% 5% 6% 10% 48%	2520
	11th to 20th	Day	8% 4 2 4 5% 3 5% 6% 6% 9% 48%	2520
	21st to end	Day	5% 3 2 4 5% 4 6% 6% 7% 11% 46%	2520
July	1st to 10th	Day	9% 3 1 5% 5% 4 5% 7% 8% 11% 42%	2520
	11th to 20th	Day	5% 3 1 4 5% 3 5% 5% 6% 10% 51%	2520
	21st to end	Day	7% 4 1 4 5% 3 6% 5% 6% 9% 49%	2653
August	1st to 10th	Day	8% 5% 2 5% 6% 4 5% 6% 8% 10% 43%	2315
	11th to 20th	Day	9% 5% 2 5% 6% 4 6% 6% 7% 9% 41%	2125
	21st to end	Day	7% 4 2 4 4 3 4 6% 6% 8% 51%	2376
September	1st to 10th	Day	14% 5% 2 4 3 3 4 3 5% 8% 49%	2160
	11th to 20th	Day	9% 4 2 5% 5% 3 3 5% 5% 8% 52%	2124
	21st to end	Day	7% 5% 2 4 5% 2 4 5% 5% 7% 54%	1980
October	1st to 10th	Day	11% 5% 2 4 4 3 4 4 4 6% 54%	1814
	11th to 20th	Day	16% 5% 3 4 4 2 3 4 4 6% 49%	1800
	21st to end	Day	18% 7% 3 5% 4 3 3 3 5% 4 46%	1936
November	1st to 10th	Day	11% 4 2 4 4 2 3 4 4 8% 53%	1672
	11th to 20th	Day	14% 8% 3 5% 3 2 3 4 4 6% 47%	1710
	21st to end	Day	16% 10% 5% 6% 5% 4 4 3 4 6% 39%	1644
December	1st to 10th	Day	13% 11% 4 7% 5% 3 5% 5% 4 6% 39%	1520
	11th to 20th	Day	14% 9% 4 6% 5% 3 5% 5% 5% 6% 37%	1918
	21st to end	Day	21% 14% 5% 7% 6% 3 5% 4 4 6% 24%	2783
January	1st to 10th	Night	13% 9% 5% 7% 5% 4 5% 4 5% 5% 38%	2648
	11th to 20th	Night	16% 10% 4 9% 6% 3 4 4 4 6% 35%	2498
	21st to end	Night	14% 11% 4 8% 6% 3 4 4 5% 6% 34%	2574
February	1st to 10th	Night	16% 11% 6% 7% 5% 3 4 4 5% 5% 34%	2340
	11th to 20th	Night	16% 7% 4 7% 5% 3 4 4 5% 6% 40%	2106
	21st to end	Night	17% 10% 4 7% 6% 2 3 3 4 5% 40%	1776
March	1st to 10th	Night	17% 9% 3 5% 5% 3 4 4 4 4 42%	2160
	11th to 20th	Night	19% 8% 4 7% 4 2 4 4 5% 7% 37%	1994
	21st to end	Night	21% 9% 3 5% 5% 3 5% 5% 5% 7% 32%	2050
April	1st to 10th	Night	11% 7% 3 4 5% 3 4 5% 5% 7% 47%	1800
	11th to 20th	Night	14% 6% 2 5% 5% 3 4 4 5% 8% 44%	1775
	21st to end	Night	18% 6% 4 7% 5% 2 4 4 4 6% 40%	1800
May	1st to 10th	Night	16% 7% 2 5% 4 2 4 4 6% 7% 42%	1718
	11th to 20th	Night	13% 7% 4 5% 4 3 4 4 4 6% 45%	1448
	21st to end	Night	9% 5% 2 7% 6% 3 5% 6% 6% 9% 41%	1551
June	1st to 10th	Night	8% 4 3 4 4 3 4 5% 6% 9% 50%	1440
	11th to 20th	Night	6% 4 2 4 4 2 5% 4 6% 9% 53%	1440
	21st to end	Night	5% 3 2 4 5% 3 4 6% 6% 10% 52%	1440
July	1st to 10th	Night	9% 3 2 4 4 2 4 5% 7% 10% 50%	1440
	11th to 20th	Night	5% 3 2 4 5% 4 5% 3 5% 10% 55%	1440
	21st to end	Night	6% 4 2 5% 5% 3 5% 5% 6% 8% 51%	1661
August	1st to 10th	Night	7% 3 1 4 4 2 5% 5% 6% 9% 53%	1623
	11th to 20th	Night	7% 5% 2 6% 4 2 5% 5% 6% 7% 52%	1776
	21st to end	Night	5% 3 1 4 4 3 4 5% 5% 8% 58%	1980
September	1st to 10th	Night	11% 4 2 5% 3 3 4 3 4 8% 53%	1800
	11th to 20th	Night	9% 3 2 5% 4 3 4 4 6% 7% 52%	1817
	21st to end	Night	9% 3 2 4 4 2 4 5% 5% 6% 57%	1980
October	1st to 10th	Night	9% 3 1 4 5% 2 4 4 5% 7% 56%	2142
	11th to 20th	Night	14% 6% 2 4 3 2 3 3 5% 6% 51%	2160
	21st to end	Night	19% 7% 2 5% 4 2 3 4 4 5% 45%	2418
November	1st to 10th	Night	9% 5% 2 4 4 2 4 5% 4 6% 56%	2406
	11th to 20th	Night	12% 7% 3 5% 4 2 3 3 5% 7% 49%	2470
	21st to end	Night	18% 8% 3 5% 3 2 4 3 5% 5% 43%	2532
December	1st to 10th	Night	16% 10% 4 6% 5% 4 5% 4 5% 7% 34%	2660
	11th to 20th	Night	17% 8% 3 6% 5% 3 4 3 4 6% 42%	3279
	21st to end	Night	20% 19% 5% 8% 6% 4 5% 4 4 4 21%	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	52% 3 10% 21% 13% 1	1518
	11th to 20th	Day	55% 4 10% 24% 7%	1553
	21st to end	Day	50% 3 12% 24% 10% 2	1782
February	1st to 10th	Day	51% 4 13% 22% 9% 1	1620
	11th to 20th	Day	49% 4 10% 22% 12% 2	1749
	21st to end	Day	50% 4 8% 22% 13% 3	1480
March	1st to 10th	Day	45% 4 9% 27% 13% 2	1801
	11th to 20th	Day	50% 4 11% 19% 12% 2	1980
	21st to end	Day	56% 4 12% 18% 8% 1	2304
April	1st to 10th	Day	40% 4 13% 27% 16% 1	2160
	11th to 20th	Day	46% 3 9% 25% 14% 3	2134
	21st to end	Day	46% 4 12% 24% 12% 1	2160
May	1st to 10th	Day	44% 6% 15% 25% 9% 1	2240
	11th to 20th	Day	43% 6% 13% 24% 14% 1	2447
	21st to end	Day	41% 6% 15% 22% 13% 2	2725
June	1st to 10th	Day	32% 5% 15% 29% 17% 3	2520
	11th to 20th	Day	31% 6% 14% 24% 23% 3	2520
	21st to end	Day	30% 6% 18% 24% 17% 4	2520
July	1st to 10th	Day	34% 7% 15% 28% 13% 4	2451
	11th to 20th	Day	27% 6% 16% 29% 20% 3	2445
	21st to end	Day	31% 5% 14% 31% 17% 2	2506
August	1st to 10th	Day	34% 6% 14% 29% 16% 1	2301
	11th to 20th	Day	36% 5% 15% 27% 15% 1	2125
	21st to end	Day	29% 5% 14% 26% 20% 6%	2376
September	1st to 10th	Day	34% 4 9% 30% 18% 5%	2160
	11th to 20th	Day	31% 4 8% 27% 26% 3	2124
	21st to end	Day	29% 5% 8% 31% 23% 3	1980
October	1st to 10th	Day	32% 4 9% 25% 26% 3	1814
	11th to 20th	Day	37% 3 9% 24% 23% 4	1800
	21st to end	Day	43% 2 8% 28% 16% 3	1936
November	1st to 10th	Day	31% 3 13% 27% 21% 5%	1672
	11th to 20th	Day	38% 3 9% 25% 19% 4	1710
	21st to end	Day	48% 4 9% 26% 13%	1644
December	1st to 10th	Day	48% 4 12% 24% 11%	1520
	11th to 20th	Day	48% 3 10% 24% 12% 3	1915
	21st to end	Day	62% 3 11% 15% 8% 1	2783
January	1st to 10th	Night	49% 3 9% 24% 14% 1	2648
	11th to 20th	Night	53% 3 8% 26% 10%	2498
	21st to end	Night	51% 3 12% 22% 11% 1	2574
February	1st to 10th	Night	54% 4 10% 20% 11% 1	2340
	11th to 20th	Night	46% 4 10% 22% 16% 2	2107
	21st to end	Night	49% 2 10% 23% 13% 3	1776
March	1st to 10th	Night	45% 4 8% 23% 16% 2	2160
	11th to 20th	Night	47% 5% 10% 22% 13% 3	1994
	21st to end	Night	52% 4 12% 22% 9% 1	2050
April	1st to 10th	Night	37% 4 11% 27% 17% 3	1800
	11th to 20th	Night	39% 3 11% 24% 19% 4	1775
	21st to end	Night	46% 4 8% 23% 17% 3	1800
May	1st to 10th	Night	41% 6% 13% 23% 15% 2	1718
	11th to 20th	Night	41% 5% 12% 24% 17% 2	1449
	21st to end	Night	38% 6% 15% 21% 16% 4	1552
June	1st to 10th	Night	30% 5% 15% 28% 20% 3	1440
	11th to 20th	Night	27% 5% 12% 28% 24% 5%	1440
	21st to end	Night	27% 6% 15% 29% 17% 7%	1440
July	1st to 10th	Night	29% 5% 14% 32% 15% 5%	1400
	11th to 20th	Night	25% 5% 14% 33% 19% 3	1392
	21st to end	Night	29% 5% 13% 30% 21% 2	1569
August	1st to 10th	Night	26% 7% 15% 33% 17% 2	1613
	11th to 20th	Night	31% 5% 12% 29% 22% 1	1776
	21st to end	Night	24% 5% 14% 27% 24% 5%	1980
September	1st to 10th	Night	32% 3 10% 27% 21% 7%	1800
	11th to 20th	Night	29% 3 9% 29% 24% 5%	1817
	21st to end	Night	28% 4 9% 25% 29% 4	1980
October	1st to 10th	Night	29% 3 11% 26% 26% 5%	2142
	11th to 20th	Night	34% 3 7% 28% 22% 6%	2160
	21st to end	Night	42% 3 8% 22% 21% 4	2418
November	1st to 10th	Night	30% 4 11% 26% 22% 6%	2406
	11th to 20th	Night	37% 2 9% 28% 21% 4	2470
	21st to end	Night	43% 3 10% 26% 17% 1	2532
December	1st to 10th	Night	50% 4 11% 23% 12% 1	2660
	11th to 20th	Night	45% 3 10% 26% 14% 1	3281
	21st to end	Night	66% 4 8% 13% 7% 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	22% 16% 36% 20% 6%	270
	11th to 20th	Day	29% 15% 36% 17% 3	252
	21st to end	Day	19% 19% 45% 14% 4	264
February	1st to 10th	Day	27% 16% 42% 12% 4	240
	11th to 20th	Day	25% 23% 29% 19% 4	240
	21st to end	Day	27% 14% 41% 17% 1	198
March	1st to 10th	Day	20% 16% 43% 19% 3	240
	11th to 20th	Day	31% 15% 31% 16% 6%	240
	21st to end	Day	32% 13% 32% 18% 6%	390
April	1st to 10th	Day	16% 12% 40% 21% 9% 1	420
	11th to 20th	Day	20% 13% 29% 24% 12% 2	412
	21st to end	Day	24% 12% 31% 22% 9% 2	420
May	1st to 10th	Day	19% 9% 32% 27% 11% 1	423
	11th to 20th	Day	19% 7% 28% 25% 17% 4	589
	21st to end	Day	13% 5% 27% 30% 16% 8%	679
June	1st to 10th	Day	8% 5% 19% 33% 25% 10%	630
	11th to 20th	Day	9% 3 21% 33% 26% 7%	630
	21st to end	Day	6% 5% 26% 34% 21% 8%	630
July	1st to 10th	Day	11% 1 13% 28% 31% 17%	621
	11th to 20th	Day	7% 3 14% 35% 31% 11%	618
	21st to end	Day	9% 2 15% 32% 31% 11%	684
August	1st to 10th	Day	8% 2 13% 36% 29% 12%	613
	11th to 20th	Day	12% 4 11% 28% 32% 12%	439
	21st to end	Day	9% 2 12% 29% 35% 13%	495
September	1st to 10th	Day	14% 4 14% 32% 24% 12%	450
	11th to 20th	Day	9% 3 12% 31% 32% 13%	450
	21st to end	Day	9% 6% 23% 29% 25% 9%	450
October	1st to 10th	Day	12% 7% 24% 37% 14% 5%	284
	11th to 20th	Day	15% 17% 31% 26% 9% 1	270
	21st to end	Day	31% 12% 30% 20% 7%	297
November	1st to 10th	Day	14% 10% 36% 21% 14% 5%	270
	11th to 20th	Day	20% 15% 34% 18% 11% 3	270
	21st to end	Day	27% 11% 30% 25% 6% 1	270
December	1st to 10th	Day	13% 14% 44% 18% 7% 4	270
	11th to 20th	Day	20% 13% 37% 26% 3	270
	21st to end	Day	25% 18% 38% 15% 4	297
January	1st to 10th	Night	17% 14% 38% 25% 6%	950
	11th to 20th	Night	21% 13% 37% 23% 5%	923
	21st to end	Night	19% 13% 39% 26% 2	990
February	1st to 10th	Night	22% 14% 37% 23% 4	900
	11th to 20th	Night	19% 15% 38% 26% 2	711
	21st to end	Night	24% 14% 34% 25% 2	592
March	1st to 10th	Night	22% 12% 38% 23% 5%	720
	11th to 20th	Night	26% 9% 33% 26% 6%	554
	21st to end	Night	27% 9% 30% 29% 5%	594
April	1st to 10th	Night	16% 11% 38% 28% 7%	540
	11th to 20th	Night	17% 9% 35% 29% 10% 1	533
	21st to end	Night	22% 5% 37% 27% 8%	540
May	1st to 10th	Night	18% 6% 31% 34% 10% 1	540
	11th to 20th	Night	17% 3 24% 39% 15% 1	531
	21st to end	Night	10% 4 23% 41% 19% 3	584
June	1st to 10th	Night	9% 2 19% 39% 29% 1	540
	11th to 20th	Night	9% 2 18% 46% 22% 3	540
	21st to end	Night	6% 3 20% 43% 26% 2	540
July	1st to 10th	Night	11% 1 7% 34% 38% 8%	525
	11th to 20th	Night	5% 1 13% 43% 34% 4	522
	21st to end	Night	7% 2 13% 39% 37% 3	591
August	1st to 10th	Night	8% 2 9% 44% 35% 3	537
	11th to 20th	Night	8% 2 9% 42% 34% 5%	534
	21st to end	Night	5% 1 10% 39% 39% 6%	594
September	1st to 10th	Night	12% 2 14% 35% 32% 6%	540
	11th to 20th	Night	9% 3 15% 34% 34% 6%	557
	21st to end	Night	10% 5% 22% 31% 27% 4	720
October	1st to 10th	Night	12% 2 26% 32% 24% 4	720
	11th to 20th	Night	18% 9% 30% 30% 12% 1	720
	21st to end	Night	23% 9% 32% 29% 6% 1	792
November	1st to 10th	Night	12% 7% 39% 31% 10% 1	740
	11th to 20th	Night	16% 13% 35% 29% 7% 1	760
	21st to end	Night	24% 10% 33% 26% 7%	822
December	1st to 10th	Night	22% 10% 35% 27% 5% 1	950
	11th to 20th	Night	23% 8% 33% 30% 6%	950
	21st to end	Night	28% 14% 32% 24% 2	1045

Page generated at 2024-01-12 06:31:50. Version ac07

Copyright 2024 Attilla Danko