Burkes Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Burkes Observatory 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	19% 7% 3 6% 5% 3 5% 4 5% 7% 37%	74594
	Night	18% 8% 3 6% 5% 3 4 4 5% 7% 37%	75201
Transparency	Day	46% 6% 12% 21% 13% 2	74299
	Night	47% 6% 12% 21% 13% 2	75031
Seeing	Day	24% 15% 31% 20% 8% 2	14417
	Night	23% 12% 32% 26% 7%	23016

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	16% 9% 4 6% 6% 4 5% 4 5% 6% 36%	1517
	11th to 20th	Day	21% 10% 3 6% 7% 2 2 4 4 6% 35%	1488
	21st to end	Day	14% 10% 3 7% 6% 3 4 4 5% 6% 39%	1584
February	1st to 10th	Day	18% 11% 3 6% 5% 2 5% 5% 5% 5% 34%	1601
	11th to 20th	Day	13% 10% 5% 9% 6% 4 5% 4 5% 6% 33%	1697
	21st to end	Day	14% 10% 4 7% 6% 3 6% 6% 5% 6% 33%	1480
March	1st to 10th	Day	18% 10% 3 6% 6% 3 5% 4 5% 6% 35%	1797
	11th to 20th	Day	17% 8% 3 5% 5% 3 4 4 4 6% 40%	1964
	21st to end	Day	18% 8% 4 7% 5% 3 4 4 5% 4 39%	2196
April	1st to 10th	Day	22% 10% 4 6% 5% 3 4 3 5% 5% 32%	2160
	11th to 20th	Day	19% 7% 2 5% 5% 3 3 4 5% 8% 38%	2265
	21st to end	Day	24% 10% 3 6% 5% 2 4 4 4 6% 32%	2340
May	1st to 10th	Day	24% 7% 3 6% 4 3 5% 4 5% 7% 33%	2340
	11th to 20th	Day	21% 7% 2 6% 5% 4 4 5% 4 6% 35%	2326
	21st to end	Day	19% 5% 3 5% 5% 4 4 5% 6% 8% 37%	2747
June	1st to 10th	Day	24% 7% 3 6% 5% 3 5% 4 6% 7% 30%	2700
	11th to 20th	Day	19% 6% 3 5% 4 3 5% 5% 5% 7% 36%	2700
	21st to end	Day	25% 6% 3 5% 6% 3 5% 5% 6% 7% 29%	2700
July	1st to 10th	Day	15% 6% 2 5% 6% 3 5% 5% 6% 9% 38%	2535
	11th to 20th	Day	14% 5% 3 6% 6% 4 5% 6% 6% 8% 36%	2520
	21st to end	Day	14% 6% 2 7% 6% 4 6% 6% 6% 9% 35%	2744
August	1st to 10th	Day	15% 5% 2 5% 5% 4 6% 5% 7% 9% 37%	2334
	11th to 20th	Day	15% 6% 2 5% 6% 3 6% 5% 5% 9% 38%	2304
	21st to end	Day	13% 6% 2 5% 4 3 4 6% 5% 8% 44%	2530
September	1st to 10th	Day	11% 4 3 6% 6% 3 5% 4 6% 8% 46%	2098
	11th to 20th	Day	13% 6% 2 4 4 3 4 3 4 6% 52%	1980
	21st to end	Day	16% 6% 2 4 4 3 4 4 6% 8% 43%	1980
October	1st to 10th	Day	19% 6% 2 5% 6% 3 4 4 5% 6% 39%	1955
	11th to 20th	Day	20% 8% 2 4 5% 3 4 3 5% 7% 39%	1748
	21st to end	Day	25% 9% 3 7% 5% 3 4 4 4 4 33%	1782
November	1st to 10th	Day	18% 5% 2 6% 5% 3 5% 5% 5% 6% 40%	1671
	11th to 20th	Day	21% 6% 2 4 4 3 5% 4 5% 6% 39%	1710
	21st to end	Day	22% 7% 2 5% 3 3 4 3 3 6% 41%	1536
December	1st to 10th	Day	23% 9% 3 6% 6% 3 5% 4 4 5% 32%	1359
	11th to 20th	Day	22% 10% 3 5% 5% 2 3 3 4 5% 37%	1668
	21st to end	Day	26% 11% 3 5% 5% 3 4 4 4 5% 30%	2538
January	1st to 10th	Night	16% 10% 3 6% 5% 4 4 4 5% 6% 36%	2649
	11th to 20th	Night	16% 12% 5% 7% 6% 4 5% 5% 5% 6% 30%	2611
	21st to end	Night	11% 9% 4 6% 7% 3 5% 5% 5% 7% 38%	2772
February	1st to 10th	Night	16% 9% 4 7% 7% 4 5% 5% 6% 7% 30%	2358
	11th to 20th	Night	14% 10% 4 7% 5% 4 4 4 4 6% 36%	2147
	21st to end	Night	15% 11% 4 6% 6% 3 5% 4 4 5% 37%	1776
March	1st to 10th	Night	15% 12% 5% 7% 5% 2 4 4 4 5% 36%	2150
	11th to 20th	Night	16% 10% 4 6% 5% 3 5% 5% 4 7% 35%	1994
	21st to end	Night	18% 8% 3 6% 5% 3 4 3 4 5% 39%	2156
April	1st to 10th	Night	23% 10% 4 5% 4 2 3 5% 4 6% 33%	1800
	11th to 20th	Night	20% 5% 3 6% 6% 4 4 4 6% 7% 36%	1643
	21st to end	Night	27% 9% 3 6% 3 3 4 4 5% 6% 31%	1620
May	1st to 10th	Night	22% 8% 4 6% 5% 2 4 6% 6% 7% 31%	1620
	11th to 20th	Night	21% 6% 4 7% 6% 3 5% 5% 5% 7% 31%	1582
	21st to end	Night	18% 7% 3 6% 5% 3 4 4 5% 8% 37%	1524
June	1st to 10th	Night	21% 10% 3 6% 6% 4 5% 5% 5% 6% 30%	1260
	11th to 20th	Night	16% 7% 3 6% 6% 2 4 4 5% 9% 38%	1260
	21st to end	Night	23% 7% 3 6% 4 3 5% 4 6% 8% 31%	1260
July	1st to 10th	Night	15% 5% 3 5% 5% 3 5% 6% 6% 9% 37%	1420
	11th to 20th	Night	14% 7% 2 5% 6% 3 4 4 7% 9% 38%	1440
	21st to end	Night	16% 5% 2 5% 5% 3 5% 6% 6% 9% 38%	1574
August	1st to 10th	Night	12% 5% 3 5% 5% 3 4 6% 7% 8% 41%	1585
	11th to 20th	Night	14% 8% 2 6% 6% 3 5% 5% 7% 8% 37%	1596
	21st to end	Night	13% 6% 2 5% 5% 2 4 4 5% 7% 48%	1822
September	1st to 10th	Night	14% 4 2 4 3 2 5% 5% 4 8% 49%	1862
	11th to 20th	Night	17% 6% 2 4 3 2 4 3 3 6% 51%	1980
	21st to end	Night	17% 5% 2 4 4 2 4 4 4 7% 46%	1980
October	1st to 10th	Night	19% 7% 2 5% 5% 3 5% 5% 4 6% 39%	2004
	11th to 20th	Night	18% 5% 2 6% 5% 4 5% 5% 4 8% 39%	2209
	21st to end	Night	25% 9% 2 5% 4 3 4 4 5% 6% 33%	2574
November	1st to 10th	Night	18% 7% 3 6% 5% 2 4 4 4 6% 41%	2407
	11th to 20th	Night	18% 6% 2 5% 5% 3 5% 4 5% 8% 38%	2470
	21st to end	Night	17% 8% 3 5% 5% 3 4 4 6% 7% 38%	2641
December	1st to 10th	Night	22% 10% 4 6% 4 3 4 4 5% 5% 32%	2816
	11th to 20th	Night	23% 8% 3 5% 4 4 3 4 4 6% 37%	3531
	21st to end	Night	25% 10% 3 5% 4 2 4 3 4 5% 34%	5108

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	49% 4 12% 19% 15% 1	1518
	11th to 20th	Day	51% 6% 11% 19% 10% 2	1488
	21st to end	Day	46% 6% 11% 19% 17% 2	1584
February	1st to 10th	Day	50% 5% 12% 18% 12% 2	1601
	11th to 20th	Day	51% 5% 11% 18% 12% 2	1706
	21st to end	Day	50% 6% 10% 18% 11% 5%	1480
March	1st to 10th	Day	51% 4 11% 17% 13% 3	1800
	11th to 20th	Day	45% 4 9% 21% 16% 5%	1964
	21st to end	Day	47% 6% 8% 18% 16% 5%	2196
April	1st to 10th	Day	54% 4 9% 16% 13% 5%	2160
	11th to 20th	Day	45% 5% 10% 22% 15% 2	2265
	21st to end	Day	53% 5% 9% 18% 12% 4	2340
May	1st to 10th	Day	51% 5% 8% 20% 13% 3	2340
	11th to 20th	Day	50% 6% 8% 19% 15% 2	2330
	21st to end	Day	44% 8% 15% 20% 12% 2	2747
June	1st to 10th	Day	52% 6% 12% 20% 9% 1	2700
	11th to 20th	Day	46% 6% 12% 19% 16% 2	2700
	21st to end	Day	53% 7% 14% 16% 9% 1	2700
July	1st to 10th	Day	41% 8% 15% 23% 13% 1	2465
	11th to 20th	Day	43% 7% 15% 25% 10% 1	2445
	21st to end	Day	44% 7% 15% 23% 10% 1	2591
August	1st to 10th	Day	42% 7% 17% 26% 9%	2320
	11th to 20th	Day	42% 8% 15% 23% 12%	2304
	21st to end	Day	36% 7% 14% 25% 17% 2	2530
September	1st to 10th	Day	35% 7% 15% 26% 15% 1	2098
	11th to 20th	Day	34% 5% 10% 29% 21% 3	1980
	21st to end	Day	38% 6% 12% 28% 16% 1	1980
October	1st to 10th	Day	44% 5% 11% 23% 14% 1	1955
	11th to 20th	Day	44% 6% 15% 25% 9% 1	1748
	21st to end	Day	53% 5% 10% 18% 12% 1	1782
November	1st to 10th	Day	43% 6% 14% 22% 14% 2	1671
	11th to 20th	Day	43% 6% 11% 20% 16% 3	1710
	21st to end	Day	45% 4 17% 23% 10% 1	1536
December	1st to 10th	Day	54% 6% 11% 19% 10% 1	1359
	11th to 20th	Day	49% 5% 10% 19% 15% 2	1668
	21st to end	Day	56% 6% 9% 19% 7% 2	2538
January	1st to 10th	Night	47% 6% 12% 21% 12% 1	2649
	11th to 20th	Night	54% 7% 13% 16% 9% 2	2611
	21st to end	Night	45% 5% 10% 22% 15% 2	2772
February	1st to 10th	Night	52% 5% 12% 18% 11% 2	2358
	11th to 20th	Night	49% 4 10% 20% 15% 2	2149
	21st to end	Night	49% 5% 9% 19% 14% 4	1776
March	1st to 10th	Night	50% 5% 8% 20% 14% 3	2160
	11th to 20th	Night	49% 6% 12% 15% 15% 3	1995
	21st to end	Night	46% 6% 9% 19% 17% 3	2156
April	1st to 10th	Night	52% 5% 8% 16% 16% 3	1800
	11th to 20th	Night	46% 6% 9% 21% 16% 1	1643
	21st to end	Night	53% 6% 11% 15% 12% 3	1620
May	1st to 10th	Night	51% 6% 9% 19% 13% 2	1620
	11th to 20th	Night	50% 8% 10% 19% 11% 2	1583
	21st to end	Night	47% 7% 12% 22% 11% 1	1525
June	1st to 10th	Night	53% 5% 13% 19% 9% 1	1260
	11th to 20th	Night	43% 6% 15% 20% 14% 2	1260
	21st to end	Night	51% 7% 14% 17% 9% 1	1260
July	1st to 10th	Night	41% 8% 17% 22% 11% 1	1380
	11th to 20th	Night	40% 8% 16% 26% 11%	1392
	21st to end	Night	42% 9% 17% 22% 9% 1	1486
August	1st to 10th	Night	38% 9% 16% 28% 8%	1575
	11th to 20th	Night	42% 9% 16% 22% 11%	1596
	21st to end	Night	35% 6% 13% 27% 17% 1	1822
September	1st to 10th	Night	33% 7% 15% 30% 14% 1	1862
	11th to 20th	Night	35% 5% 11% 29% 19% 1	1980
	21st to end	Night	40% 5% 11% 29% 14% 2	1980
October	1st to 10th	Night	44% 7% 12% 23% 13% 1	2004
	11th to 20th	Night	42% 7% 13% 26% 11% 1	2209
	21st to end	Night	51% 5% 12% 19% 12% 1	2574
November	1st to 10th	Night	43% 7% 12% 23% 14% 1	2407
	11th to 20th	Night	43% 5% 11% 23% 16% 2	2470
	21st to end	Night	45% 6% 16% 19% 13% 2	2641
December	1st to 10th	Night	53% 5% 10% 20% 11% 1	2816
	11th to 20th	Night	49% 5% 10% 19% 16% 1	3532
	21st to end	Night	52% 5% 13% 18% 11% 1	5108

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	29% 16% 33% 17% 6%	180
	11th to 20th	Day	30% 22% 30% 13% 4 1	172
	21st to end	Day	21% 23% 34% 18% 5%	176
February	1st to 10th	Day	31% 13% 32% 21% 2	321
	11th to 20th	Day	26% 23% 34% 15% 3	394
	21st to end	Day	22% 22% 34% 18% 4	346
March	1st to 10th	Day	29% 20% 33% 15% 3	420
	11th to 20th	Day	26% 20% 35% 14% 4 1	420
	21st to end	Day	28% 22% 26% 15% 6% 2	462
April	1st to 10th	Day	34% 22% 26% 13% 5% 1	420
	11th to 20th	Day	31% 23% 28% 11% 6% 1	412
	21st to end	Day	33% 18% 29% 14% 5% 1	420
May	1st to 10th	Day	32% 16% 31% 17% 4	423
	11th to 20th	Day	25% 19% 33% 15% 6% 1	447
	21st to end	Day	22% 17% 36% 18% 7%	507
June	1st to 10th	Day	27% 13% 32% 19% 8% 1	630
	11th to 20th	Day	21% 16% 27% 23% 12% 1	630
	21st to end	Day	26% 10% 28% 27% 8% 2	630
July	1st to 10th	Day	19% 11% 34% 26% 9% 1	460
	11th to 20th	Day	15% 9% 38% 24% 11% 3	444
	21st to end	Day	14% 7% 38% 29% 9% 3	488
August	1st to 10th	Day	14% 8% 35% 29% 13% 2	446
	11th to 20th	Day	17% 7% 29% 28% 15% 4	439
	21st to end	Day	18% 10% 32% 25% 12% 3	495
September	1st to 10th	Day	14% 11% 33% 25% 13% 4	450
	11th to 20th	Day	20% 10% 29% 22% 12% 7%	450
	21st to end	Day	17% 14% 29% 22% 11% 6%	450
October	1st to 10th	Day	20% 17% 23% 24% 13% 3	437
	11th to 20th	Day	26% 13% 29% 19% 10% 2	360
	21st to end	Day	32% 13% 29% 19% 5% 1	396
November	1st to 10th	Day	25% 13% 29% 22% 9% 1	365
	11th to 20th	Day	30% 14% 31% 20% 5% 1	370
	21st to end	Day	29% 16% 28% 21% 5%	370
December	1st to 10th	Day	27% 16% 36% 15% 5%	209
	11th to 20th	Day	34% 20% 34% 9% 2	180
	21st to end	Day	34% 18% 29% 14% 5% 1	198
January	1st to 10th	Night	22% 16% 34% 25% 3	760
	11th to 20th	Night	24% 17% 35% 20% 4	747
	21st to end	Night	17% 17% 38% 24% 4	792
February	1st to 10th	Night	23% 14% 35% 25% 3	720
	11th to 20th	Night	23% 17% 38% 19% 2	703
	21st to end	Night	21% 15% 36% 25% 3	592
March	1st to 10th	Night	24% 15% 36% 23% 2	720
	11th to 20th	Night	21% 17% 35% 21% 6%	720
	21st to end	Night	24% 15% 31% 23% 6% 1	792
April	1st to 10th	Night	30% 15% 33% 20% 3	720
	11th to 20th	Night	23% 16% 34% 22% 4	579
	21st to end	Night	32% 12% 30% 21% 4	540
May	1st to 10th	Night	25% 12% 31% 27% 4	540
	11th to 20th	Night	23% 13% 38% 21% 4	521
	21st to end	Night	20% 7% 34% 32% 6% 1	389
June	1st to 10th	Night	25% 8% 30% 31% 6%	360
	11th to 20th	Night	20% 5% 28% 38% 10%	360
	21st to end	Night	25% 3 29% 38% 6%	360
July	1st to 10th	Night	18% 3 31% 38% 9%	350
	11th to 20th	Night	16% 3 27% 41% 13% 1	348
	21st to end	Night	16% 4 24% 42% 13% 1	394
August	1st to 10th	Night	13% 6% 28% 40% 13%	511
	11th to 20th	Night	16% 5% 27% 38% 13% 1	532
	21st to end	Night	16% 6% 26% 38% 13% 1	634
September	1st to 10th	Night	17% 4 31% 35% 12% 1	720
	11th to 20th	Night	19% 7% 29% 29% 15% 3	720
	21st to end	Night	20% 8% 30% 29% 13% 2	720
October	1st to 10th	Night	22% 8% 27% 31% 13%	720
	11th to 20th	Night	22% 10% 29% 29% 9% 1	720
	21st to end	Night	30% 14% 29% 22% 5%	792
November	1st to 10th	Night	24% 11% 30% 26% 8% 1	740
	11th to 20th	Night	22% 15% 31% 24% 8% 1	760
	21st to end	Night	24% 17% 30% 24% 5%	841
December	1st to 10th	Night	28% 12% 36% 19% 5%	850
	11th to 20th	Night	25% 15% 35% 21% 3	850
	21st to end	Night	29% 15% 32% 20% 3	899

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