Dunceath Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dunceath Observatory clear sky chart from 2005-11-06 to 2024-04-25.

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% 6% 3 6% 6% 4 5% 5% 6% 8% 39%	83860
	Night	13% 6% 2 5% 5% 3 4 4 5% 8% 45%	85251
Transparency	Day	42% 7% 11% 17% 17% 6%	83590
	Night	37% 7% 11% 19% 18% 8%	85042
Seeing	Day	13% 8% 20% 24% 23% 12%	14098
	Night	14% 6% 22% 30% 22% 5%	23970

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	18% 9% 3 6% 5% 3 3 4 5% 6% 39%	2847
	11th to 20th	Day	15% 6% 3 4 4 2 2 3 3 5% 54%	2850
	21st to end	Day	24% 9% 3 5% 4 2 4 3 5% 5% 36%	3162
February	1st to 10th	Day	17% 9% 3 6% 5% 4 5% 4 4 5% 39%	1900
	11th to 20th	Day	19% 7% 3 5% 5% 3 4 4 3 5% 41%	1848
	21st to end	Day	18% 9% 3 6% 6% 3 4 3 6% 6% 37%	1575
March	1st to 10th	Day	24% 9% 3 7% 5% 3 5% 4 5% 8% 26%	3436
	11th to 20th	Day	15% 8% 3 7% 6% 4 5% 5% 7% 9% 32%	3480
	21st to end	Day	12% 7% 3 6% 6% 4 5% 5% 5% 6% 41%	3899
April	1st to 10th	Day	11% 6% 3 5% 5% 4 6% 4 6% 8% 41%	2280
	11th to 20th	Day	15% 7% 3 7% 5% 3 4 6% 5% 7% 38%	2254
	21st to end	Day	9% 6% 3 5% 6% 3 5% 6% 6% 8% 44%	2209
May	1st to 10th	Day	11% 6% 3 5% 6% 4 5% 5% 6% 9% 41%	2160
	11th to 20th	Day	10% 6% 3 4 5% 4 6% 6% 6% 8% 42%	2124
	21st to end	Day	7% 5% 3 6% 7% 4 7% 7% 8% 10% 36%	2337
June	1st to 10th	Day	9% 5% 3 7% 7% 5% 7% 10% 9% 10% 31%	2312
	11th to 20th	Day	4 5% 3 7% 8% 6% 8% 7% 8% 10% 35%	2340
	21st to end	Day	7% 6% 3 7% 8% 5% 9% 7% 8% 9% 30%	2340
July	1st to 10th	Day	8% 6% 3 8% 8% 6% 7% 9% 8% 10% 27%	2340
	11th to 20th	Day	7% 5% 3 8% 9% 5% 8% 7% 9% 10% 28%	2340
	21st to end	Day	9% 6% 4 7% 8% 6% 8% 6% 7% 9% 30%	2479
August	1st to 10th	Day	5% 4 2 8% 8% 5% 8% 6% 7% 10% 35%	2148
	11th to 20th	Day	11% 5% 2 7% 7% 6% 7% 8% 7% 9% 31%	2125
	21st to end	Day	13% 5% 3 6% 7% 5% 7% 6% 7% 9% 33%	2376
September	1st to 10th	Day	9% 5% 2 6% 6% 4 7% 7% 9% 9% 34%	2160
	11th to 20th	Day	13% 6% 2 5% 5% 4 5% 6% 6% 7% 41%	2160
	21st to end	Day	9% 6% 2 6% 5% 3 5% 4 5% 7% 50%	1961
October	1st to 10th	Day	6% 4 2 4 5% 3 5% 4 6% 8% 54%	1800
	11th to 20th	Day	10% 4 2 4 4 3 3 4 5% 7% 56%	1800
	21st to end	Day	11% 5% 2 4 4 2 4 5% 4 6% 54%	1980
November	1st to 10th	Day	10% 4 2 4 5% 3 5% 3 5% 7% 52%	1858
	11th to 20th	Day	10% 5% 3 5% 5% 3 3 4 5% 6% 51%	1900
	21st to end	Day	14% 6% 3 5% 5% 3 4 4 5% 7% 45%	1848
December	1st to 10th	Day	15% 8% 2 5% 5% 3 4 4 5% 6% 42%	1767
	11th to 20th	Day	16% 7% 4 6% 6% 4 4 4 4 5% 39%	2330
	21st to end	Day	17% 8% 2 6% 5% 3 4 4 5% 7% 40%	3135
January	1st to 10th	Night	18% 7% 2 4 4 2 3 4 4 6% 45%	4108
	11th to 20th	Night	16% 7% 2 4 3 2 3 3 4 5% 52%	4120
	21st to end	Night	26% 7% 2 4 3 2 2 2 4 7% 39%	4500
February	1st to 10th	Night	17% 7% 3 6% 5% 2 4 4 4 7% 41%	2280
	11th to 20th	Night	19% 6% 3 6% 5% 2 4 4 4 6% 42%	2218
	21st to end	Night	22% 8% 4 5% 5% 3 2 4 4 7% 37%	1884
March	1st to 10th	Night	24% 11% 3 6% 6% 2 3 4 4 6% 30%	3429
	11th to 20th	Night	17% 8% 3 6% 6% 3 5% 4 5% 7% 36%	3480
	21st to end	Night	15% 6% 2 5% 5% 3 4 4 5% 6% 43%	3732
April	1st to 10th	Night	13% 6% 3 4 4 3 4 5% 5% 9% 44%	1900
	11th to 20th	Night	13% 6% 3 6% 5% 3 4 4 4 7% 46%	1875
	21st to end	Night	8% 4 1 4 4 3 5% 4 4 7% 55%	1850
May	1st to 10th	Night	8% 5% 2 5% 4 2 4 4 6% 9% 51%	1800
	11th to 20th	Night	8% 5% 3 3 5% 2 5% 5% 6% 10% 49%	1769
	21st to end	Night	7% 3 2 4 5% 4 6% 5% 7% 10% 47%	1938
June	1st to 10th	Night	7% 4 3 5% 5% 4 6% 6% 8% 10% 44%	1642
	11th to 20th	Night	3 3 2 4 5% 3 6% 6% 9% 13% 46%	1620
	21st to end	Night	6% 5% 3 5% 7% 4 6% 7% 10% 10% 38%	1620
July	1st to 10th	Night	4 6% 2 5% 6% 3 7% 7% 8% 12% 40%	1620
	11th to 20th	Night	6% 4 1 5% 5% 3 7% 8% 8% 13% 41%	1620
	21st to end	Night	6% 4 3 6% 7% 3 6% 6% 7% 13% 40%	1835
August	1st to 10th	Night	4 3 2 4 4 3 5% 6% 8% 15% 47%	1790
	11th to 20th	Night	5% 3 2 6% 6% 5% 6% 7% 7% 13% 39%	1776
	21st to end	Night	9% 5% 3 5% 5% 4 5% 6% 8% 11% 40%	1980
September	1st to 10th	Night	8% 5% 2 5% 5% 3 5% 6% 8% 10% 43%	1800
	11th to 20th	Night	9% 6% 3 5% 6% 3 5% 6% 6% 8% 44%	1800
	21st to end	Night	7% 5% 2 4 4 3 4 4 6% 7% 54%	1975
October	1st to 10th	Night	6% 4 1 4 3 2 3 3 5% 7% 60%	2160
	11th to 20th	Night	7% 5% 3 4 3 2 4 4 5% 5% 58%	2160
	21st to end	Night	11% 5% 2 4 4 2 4 3 4 6% 56%	2376
November	1st to 10th	Night	10% 4 2 4 4 3 4 3 5% 6% 57%	2220
	11th to 20th	Night	12% 5% 2 5% 4 2 3 3 3 6% 55%	2280
	21st to end	Night	15% 7% 2 4 4 3 3 3 4 7% 47%	2310
December	1st to 10th	Night	16% 7% 2 6% 4 2 3 3 5% 7% 45%	2390
	11th to 20th	Night	14% 8% 3 6% 5% 3 4 5% 5% 5% 42%	2862
	21st to end	Night	19% 10% 3 5% 4 2 3 4 3 5% 41%	4532

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	46% 5% 4 16% 23% 6%	2848
	11th to 20th	Day	35% 3 4 18% 30% 9%	2850
	21st to end	Day	51% 3 5% 13% 20% 9%	3162
February	1st to 10th	Day	47% 5% 8% 12% 17% 10%	1900
	11th to 20th	Day	45% 4 6% 14% 21% 10%	1858
	21st to end	Day	47% 5% 8% 16% 16% 9%	1575
March	1st to 10th	Day	56% 6% 9% 15% 10% 4	3436
	11th to 20th	Day	47% 7% 9% 18% 15% 4	3480
	21st to end	Day	43% 6% 8% 14% 22% 7%	3899
April	1st to 10th	Day	41% 6% 9% 17% 18% 9%	2280
	11th to 20th	Day	43% 6% 9% 18% 16% 9%	2254
	21st to end	Day	37% 6% 10% 19% 24% 4	2209
May	1st to 10th	Day	39% 6% 12% 20% 17% 6%	2160
	11th to 20th	Day	39% 7% 11% 24% 17% 2	2128
	21st to end	Day	39% 10% 15% 23% 13% 1	2337
June	1st to 10th	Day	43% 11% 14% 20% 11% 1	2312
	11th to 20th	Day	41% 11% 13% 21% 12% 2	2340
	21st to end	Day	45% 15% 14% 19% 6% 1	2340
July	1st to 10th	Day	48% 13% 19% 15% 5% 1	2276
	11th to 20th	Day	45% 14% 19% 17% 4 1	2271
	21st to end	Day	46% 11% 19% 16% 7% 1	2341
August	1st to 10th	Day	40% 13% 21% 18% 8%	2136
	11th to 20th	Day	45% 13% 18% 17% 6% 1	2125
	21st to end	Day	44% 11% 17% 17% 9% 2	2376
September	1st to 10th	Day	40% 12% 16% 15% 12% 4	2160
	11th to 20th	Day	40% 9% 13% 15% 16% 6%	2160
	21st to end	Day	35% 6% 10% 21% 19% 9%	1961
October	1st to 10th	Day	27% 6% 10% 21% 23% 13%	1800
	11th to 20th	Day	29% 5% 7% 17% 29% 14%	1800
	21st to end	Day	31% 4 7% 15% 28% 15%	1980
November	1st to 10th	Day	32% 4 7% 19% 27% 10%	1858
	11th to 20th	Day	35% 4 6% 16% 26% 13%	1900
	21st to end	Day	40% 5% 7% 16% 22% 11%	1848
December	1st to 10th	Day	42% 5% 8% 19% 17% 8%	1767
	11th to 20th	Day	47% 5% 6% 13% 23% 7%	2328
	21st to end	Day	44% 6% 7% 17% 23% 3	3135
January	1st to 10th	Night	40% 4 6% 14% 26% 9%	4108
	11th to 20th	Night	35% 4 5% 19% 25% 12%	4120
	21st to end	Night	47% 3 5% 17% 20% 8%	4500
February	1st to 10th	Night	44% 4 7% 16% 19% 9%	2280
	11th to 20th	Night	43% 5% 5% 15% 19% 12%	2219
	21st to end	Night	47% 4 9% 15% 14% 12%	1884
March	1st to 10th	Night	54% 6% 9% 13% 12% 6%	3429
	11th to 20th	Night	47% 7% 9% 16% 16% 5%	3480
	21st to end	Night	41% 5% 9% 19% 20% 6%	3732
April	1st to 10th	Night	37% 7% 9% 18% 18% 11%	1900
	11th to 20th	Night	39% 5% 9% 18% 18% 11%	1875
	21st to end	Night	28% 7% 11% 22% 26% 7%	1850
May	1st to 10th	Night	29% 6% 12% 26% 20% 7%	1800
	11th to 20th	Night	31% 7% 15% 25% 20% 3	1770
	21st to end	Night	30% 9% 16% 27% 16% 1	1939
June	1st to 10th	Night	32% 12% 19% 24% 13% 1	1642
	11th to 20th	Night	27% 11% 20% 26% 14% 2	1620
	21st to end	Night	35% 12% 19% 24% 9%	1620
July	1st to 10th	Night	34% 13% 26% 19% 6% 1	1575
	11th to 20th	Night	31% 16% 27% 20% 4 1	1566
	21st to end	Night	32% 15% 26% 21% 7%	1733
August	1st to 10th	Night	23% 13% 34% 22% 8%	1778
	11th to 20th	Night	35% 14% 25% 20% 6% 1	1776
	21st to end	Night	36% 12% 22% 17% 9% 4	1980
September	1st to 10th	Night	32% 11% 20% 18% 12% 6%	1800
	11th to 20th	Night	37% 10% 16% 16% 15% 6%	1800
	21st to end	Night	30% 7% 12% 24% 17% 11%	1975
October	1st to 10th	Night	24% 6% 11% 21% 24% 14%	2160
	11th to 20th	Night	28% 5% 7% 21% 25% 14%	2160
	21st to end	Night	30% 4 6% 16% 24% 19%	2376
November	1st to 10th	Night	30% 4 8% 19% 26% 13%	2220
	11th to 20th	Night	33% 4 7% 14% 26% 16%	2280
	21st to end	Night	39% 4 6% 18% 21% 12%	2310
December	1st to 10th	Night	40% 5% 8% 21% 20% 6%	2390
	11th to 20th	Night	44% 4 6% 12% 20% 13%	2863
	21st to end	Night	47% 4 7% 16% 19% 7%	4532

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	25% 18% 33% 17% 6% 1	270
	11th to 20th	Day	21% 19% 36% 19% 5%	270
	21st to end	Day	28% 20% 36% 13% 2	297
February	1st to 10th	Day	26% 23% 27% 19% 5%	270
	11th to 20th	Day	30% 19% 31% 15% 4	270
	21st to end	Day	20% 29% 40% 9% 2	225
March	1st to 10th	Day	24% 21% 31% 20% 4	270
	11th to 20th	Day	25% 19% 35% 16% 4	270
	21st to end	Day	16% 21% 34% 21% 8% 1	344
April	1st to 10th	Day	17% 16% 34% 24% 9% 1	460
	11th to 20th	Day	21% 15% 31% 21% 11% 1	452
	21st to end	Day	10% 14% 29% 29% 17% 2	437
May	1st to 10th	Day	12% 9% 28% 32% 16% 3	423
	11th to 20th	Day	11% 3 23% 29% 24% 9%	447
	21st to end	Day	6% 3 16% 33% 29% 13%	485
June	1st to 10th	Day	9% 3 13% 31% 28% 15%	602
	11th to 20th	Day	6% 2 13% 30% 38% 12%	630
	21st to end	Day	9% 2 11% 25% 31% 22%	630
July	1st to 10th	Day	6% 2 9% 22% 40% 21%	621
	11th to 20th	Day	6% 2 5% 22% 39% 27%	618
	21st to end	Day	9% 2 7% 20% 39% 24%	617
August	1st to 10th	Day	3 1 6% 18% 35% 37%	446
	11th to 20th	Day	8% 1 4 13% 39% 35%	439
	21st to end	Day	13% 3 6% 21% 30% 27%	495
September	1st to 10th	Day	9% 1 6% 21% 43% 20%	450
	11th to 20th	Day	12% 2 10% 22% 37% 17%	450
	21st to end	Day	12% 3 9% 27% 33% 15%	426
October	1st to 10th	Day	6% 4 20% 39% 23% 8%	270
	11th to 20th	Day	8% 7% 20% 34% 21% 11%	270
	21st to end	Day	18% 12% 22% 30% 14% 4	297
November	1st to 10th	Day	15% 4 26% 36% 16% 3	270
	11th to 20th	Day	16% 12% 31% 24% 16% 1	270
	21st to end	Day	14% 19% 33% 23% 8% 3	270
December	1st to 10th	Day	20% 12% 31% 25% 10% 2	270
	11th to 20th	Day	23% 13% 37% 22% 5%	270
	21st to end	Day	25% 16% 32% 20% 6% 1	297
January	1st to 10th	Night	23% 9% 36% 26% 6%	950
	11th to 20th	Night	21% 10% 32% 29% 9%	950
	21st to end	Night	23% 12% 33% 26% 6%	1026
February	1st to 10th	Night	20% 12% 36% 27% 5%	760
	11th to 20th	Night	23% 14% 30% 28% 6%	743
	21st to end	Night	25% 16% 35% 22% 2	628
March	1st to 10th	Night	17% 13% 32% 32% 6%	580
	11th to 20th	Night	18% 9% 33% 32% 8%	570
	21st to end	Night	16% 9% 35% 30% 10%	627
April	1st to 10th	Night	18% 9% 34% 29% 10% 1	570
	11th to 20th	Night	16% 10% 33% 30% 10% 1	563
	21st to end	Night	9% 5% 29% 40% 16% 1	555
May	1st to 10th	Night	11% 3 27% 41% 17% 1	540
	11th to 20th	Night	12% 3 19% 41% 24% 2	531
	21st to end	Night	7% 2 15% 38% 33% 6%	584
June	1st to 10th	Night	7% 2 9% 36% 41% 5%	540
	11th to 20th	Night	2 1 9% 36% 42% 10%	540
	21st to end	Night	7% 1 7% 27% 42% 15%	540
July	1st to 10th	Night	4 1 4 25% 47% 19%	525
	11th to 20th	Night	5% 1 3 20% 47% 24%	522
	21st to end	Night	5% 1 5% 19% 52% 17%	591
August	1st to 10th	Night	5% 1 3 21% 49% 21%	537
	11th to 20th	Night	4 3 19% 51% 22%	534
	21st to end	Night	10% 1 5% 21% 44% 19%	594
September	1st to 10th	Night	9% 1 4 27% 45% 14%	540
	11th to 20th	Night	10% 2 9% 26% 43% 10%	540
	21st to end	Night	9% 1 10% 33% 41% 6%	696
October	1st to 10th	Night	8% 2 16% 36% 35% 4	720
	11th to 20th	Night	8% 4 22% 37% 27% 3	720
	21st to end	Night	13% 7% 23% 34% 21% 3	792
November	1st to 10th	Night	11% 5% 20% 40% 20% 3	740
	11th to 20th	Night	13% 8% 28% 35% 14% 1	760
	21st to end	Night	19% 8% 27% 30% 15% 1	760
December	1st to 10th	Night	19% 9% 26% 32% 13%	760
	11th to 20th	Night	20% 9% 32% 31% 8%	797
	21st to end	Night	26% 11% 28% 27% 8%	1045

Page generated at 2024-04-22 08:25:40. Version ac07

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