Ashby
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ashby clear sky chart from 2005-11-06 to 2024-02-20.

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	7% 5% 2 5% 4 3 4 4 5% 7% 53%	78345
	Night	7% 6% 2 5% 5% 3 4 4 5% 7% 51%	80901
Transparency	Day	31% 4 13% 28% 19% 4	78049
	Night	32% 4 14% 28% 18% 4	80719
Seeing	Day	11% 7% 31% 32% 16% 3	14749
	Night	10% 8% 37% 35% 9% 1	24896

By Month

Percentage Cloud Cover SW (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	2 6% 4 8% 6% 2 4 4 4 5% 55%	2538
	11th to 20th	Day	4 8% 3 5% 5% 3 5% 6% 7% 8% 46%	2540
	21st to end	Day	4 4 1 5% 4 3 4 4 6% 7% 58%	2794
February	1st to 10th	Day	6% 9% 5% 7% 6% 4 5% 5% 4 6% 43%	1796
	11th to 20th	Day	6% 7% 3 7% 5% 3 5% 4 4 7% 48%	1839
	21st to end	Day	6% 9% 3 4 4 2 3 5% 6% 7% 52%	1480
March	1st to 10th	Day	6% 6% 2 5% 3 2 4 5% 5% 8% 53%	1800
	11th to 20th	Day	8% 7% 3 6% 4 2 5% 4 5% 6% 49%	1872
	21st to end	Day	10% 9% 5% 6% 6% 3 5% 4 6% 8% 40%	2315
April	1st to 10th	Day	11% 6% 3 4 5% 2 4 4 5% 7% 48%	2160
	11th to 20th	Day	14% 7% 3 6% 5% 3 4 4 4 6% 44%	2131
	21st to end	Day	14% 7% 2 5% 5% 2 4 3 5% 7% 45%	2318
May	1st to 10th	Day	13% 5% 2 4 5% 3 4 4 5% 7% 46%	2340
	11th to 20th	Day	15% 7% 2 5% 5% 3 4 4 5% 8% 43%	2345
	21st to end	Day	13% 5% 3 5% 5% 3 5% 5% 5% 7% 43%	2724
June	1st to 10th	Day	6% 4 2 4 3 3 4 4 6% 9% 55%	2520
	11th to 20th	Day	8% 4 2 4 3 3 4 4 6% 9% 53%	2520
	21st to end	Day	3 2 1 3 3 3 4 4 5% 8% 63%	2520
July	1st to 10th	Day	7% 3 2 3 4 3 5% 6% 6% 9% 54%	2520
	11th to 20th	Day	4 2 1 3 3 3 4 5% 5% 9% 61%	2520
	21st to end	Day	5% 4 2 3 4 3 5% 6% 7% 9% 52%	2742
August	1st to 10th	Day	6% 4 1 4 5% 4 6% 6% 7% 9% 48%	2396
	11th to 20th	Day	4 3 2 3 4 2 4 5% 5% 9% 59%	2221
	21st to end	Day	6% 3 1 3 4 2 3 4 6% 7% 60%	2376
September	1st to 10th	Day	7% 3 2 4 3 2 3 4 4 6% 62%	2160
	11th to 20th	Day	6% 3 1 3 3 2 4 4 5% 6% 63%	2016
	21st to end	Day	8% 3 2 4 3 2 3 3 4 6% 62%	1980
October	1st to 10th	Day	12% 6% 2 4 2 2 3 3 4 7% 57%	1980
	11th to 20th	Day	9% 5% 1 5% 3 2 3 3 3 6% 59%	1757
	21st to end	Day	8% 6% 2 4 4 2 4 3 4 7% 56%	1782
November	1st to 10th	Day	5% 5% 2 4 4 2 3 3 6% 8% 58%	1673
	11th to 20th	Day	5% 5% 1 4 3 2 4 4 6% 7% 58%	1710
	21st to end	Day	6% 5% 3 4 3 2 4 4 5% 7% 57%	1710
December	1st to 10th	Day	5% 7% 3 6% 5% 2 5% 4 4 7% 52%	1530
	11th to 20th	Day	4 4 2 5% 4 3 4 4 5% 6% 59%	1926
	21st to end	Day	10% 13% 4 5% 4 2 4 4 3 6% 46%	2794
January	1st to 10th	Night	5% 9% 3 7% 7% 3 4 4 5% 6% 47%	4417
	11th to 20th	Night	2 7% 4 7% 5% 3 4 4 6% 9% 49%	4430
	21st to end	Night	3 5% 2 5% 6% 3 4 5% 6% 8% 53%	4873
February	1st to 10th	Night	7% 10% 3 7% 5% 2 5% 5% 6% 6% 43%	2400
	11th to 20th	Night	5% 8% 4 7% 5% 3 5% 5% 5% 8% 45%	2212
	21st to end	Night	5% 8% 3 6% 5% 2 5% 4 4 7% 50%	1776
March	1st to 10th	Night	8% 7% 3 4 5% 2 4 4 5% 6% 52%	2160
	11th to 20th	Night	8% 6% 3 5% 5% 2 4 4 5% 8% 51%	2087
	21st to end	Night	10% 7% 3 6% 6% 3 5% 5% 6% 8% 41%	2039
April	1st to 10th	Night	11% 6% 3 5% 5% 3 4 4 6% 8% 44%	1800
	11th to 20th	Night	12% 7% 3 5% 5% 3 4 4 4 6% 47%	1777
	21st to end	Night	14% 7% 2 5% 4 3 3 5% 6% 8% 43%	1640
May	1st to 10th	Night	12% 5% 3 7% 5% 3 4 5% 5% 7% 45%	1620
	11th to 20th	Night	15% 6% 3 5% 4 3 5% 5% 5% 6% 43%	1547
	21st to end	Night	15% 5% 2 5% 5% 3 6% 4 7% 8% 40%	1552
June	1st to 10th	Night	8% 4 2 3 4 3 4 6% 6% 10% 50%	1440
	11th to 20th	Night	10% 4 2 3 4 3 5% 6% 7% 8% 48%	1440
	21st to end	Night	6% 3 1 4 5% 3 4 6% 7% 10% 50%	1440
July	1st to 10th	Night	6% 3 2 4 4 3 5% 6% 7% 10% 50%	1440
	11th to 20th	Night	5% 2 1 4 4 3 3 5% 6% 9% 60%	1440
	21st to end	Night	4 4 2 5% 4 3 5% 5% 7% 10% 50%	1576
August	1st to 10th	Night	4 5% 2 6% 6% 3 7% 6% 7% 10% 46%	1543
	11th to 20th	Night	5% 3 1 3 4 2 4 4 6% 9% 58%	1678
	21st to end	Night	5% 3 2 3 4 3 4 4 6% 7% 60%	1980
September	1st to 10th	Night	8% 4 2 4 3 2 3 3 5% 6% 60%	1800
	11th to 20th	Night	8% 3 2 4 3 3 3 3 4 7% 61%	1944
	21st to end	Night	10% 3 1 4 3 2 3 3 4 5% 62%	1980
October	1st to 10th	Night	12% 6% 2 4 4 2 3 3 3 6% 56%	1980
	11th to 20th	Night	8% 5% 2 3 4 2 3 3 4 5% 61%	2182
	21st to end	Night	9% 6% 2 4 4 2 3 3 4 6% 57%	2574
November	1st to 10th	Night	5% 5% 2 3 3 2 3 4 7% 7% 58%	2405
	11th to 20th	Night	4 4 3 5% 5% 3 4 4 6% 7% 55%	2470
	21st to end	Night	5% 5% 2 3 4 2 5% 4 5% 8% 57%	2470
December	1st to 10th	Night	4 6% 3 5% 5% 3 4 4 5% 7% 54%	2645
	11th to 20th	Night	5% 5% 2 5% 3 2 4 4 5% 7% 58%	3271
	21st to end	Night	10% 11% 3 4 4 3 3 3 4 7% 47%	4873

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	32% 4 11% 31% 21% 1	2539
	11th to 20th	Day	34% 6% 15% 27% 16% 3	2540
	21st to end	Day	26% 3 23% 31% 12% 4	2794
February	1st to 10th	Day	42% 6% 14% 22% 13% 4	1796
	11th to 20th	Day	37% 4 13% 25% 16% 5%	1849
	21st to end	Day	31% 5% 14% 29% 16% 5%	1480
March	1st to 10th	Day	30% 5% 13% 28% 22% 3	1800
	11th to 20th	Day	35% 5% 13% 25% 19% 3	1872
	21st to end	Day	43% 6% 16% 22% 11% 2	2315
April	1st to 10th	Day	36% 5% 16% 26% 14% 4	2160
	11th to 20th	Day	41% 5% 12% 23% 15% 3	2134
	21st to end	Day	40% 3 13% 26% 17% 1	2318
May	1st to 10th	Day	38% 4 15% 30% 12% 1	2340
	11th to 20th	Day	41% 5% 19% 27% 8% 1	2349
	21st to end	Day	40% 6% 16% 24% 12% 2	2724
June	1st to 10th	Day	27% 5% 20% 32% 14% 2	2520
	11th to 20th	Day	28% 5% 15% 30% 18% 5%	2520
	21st to end	Day	19% 5% 12% 32% 26% 5%	2520
July	1st to 10th	Day	27% 5% 11% 31% 21% 5%	2451
	11th to 20th	Day	20% 5% 11% 28% 25% 11%	2445
	21st to end	Day	26% 6% 13% 28% 23% 5%	2590
August	1st to 10th	Day	30% 7% 16% 27% 14% 6%	2380
	11th to 20th	Day	22% 5% 14% 30% 22% 7%	2221
	21st to end	Day	22% 5% 10% 26% 27% 10%	2376
September	1st to 10th	Day	23% 4 9% 27% 23% 13%	2160
	11th to 20th	Day	22% 4 9% 29% 27% 9%	2016
	21st to end	Day	25% 3 8% 31% 28% 5%	1980
October	1st to 10th	Day	30% 3 10% 25% 27% 4	1980
	11th to 20th	Day	29% 3 9% 30% 22% 7%	1757
	21st to end	Day	30% 3 13% 28% 20% 6%	1782
November	1st to 10th	Day	25% 4 14% 30% 21% 6%	1673
	11th to 20th	Day	26% 3 12% 29% 25% 5%	1710
	21st to end	Day	27% 4 13% 31% 21% 4	1710
December	1st to 10th	Day	33% 4 13% 28% 18% 4	1530
	11th to 20th	Day	25% 4 16% 40% 14% 2	1924
	21st to end	Day	42% 3 9% 29% 15% 2	2794
January	1st to 10th	Night	38% 3 12% 29% 16% 1	4417
	11th to 20th	Night	32% 5% 18% 28% 15% 2	4430
	21st to end	Night	30% 4 18% 31% 16% 1	4873
February	1st to 10th	Night	40% 5% 13% 27% 12% 3	2400
	11th to 20th	Night	37% 4 15% 26% 14% 4	2212
	21st to end	Night	35% 3 14% 27% 17% 5%	1776
March	1st to 10th	Night	33% 4 11% 28% 20% 3	2160
	11th to 20th	Night	33% 4 11% 27% 22% 3	2087
	21st to end	Night	41% 5% 17% 25% 11% 2	2039
April	1st to 10th	Night	37% 6% 16% 21% 16% 4	1800
	11th to 20th	Night	38% 5% 14% 25% 15% 3	1777
	21st to end	Night	40% 5% 14% 28% 12% 1	1640
May	1st to 10th	Night	39% 6% 16% 26% 13% 1	1620
	11th to 20th	Night	41% 6% 18% 25% 9% 1	1548
	21st to end	Night	41% 8% 19% 21% 9% 2	1552
June	1st to 10th	Night	28% 7% 23% 27% 12% 2	1440
	11th to 20th	Night	32% 6% 19% 25% 12% 5%	1440
	21st to end	Night	27% 7% 16% 29% 18% 3	1440
July	1st to 10th	Night	29% 5% 18% 30% 15% 3	1400
	11th to 20th	Night	22% 5% 12% 30% 22% 8%	1392
	21st to end	Night	27% 7% 16% 27% 18% 4	1488
August	1st to 10th	Night	32% 8% 20% 24% 12% 4	1535
	11th to 20th	Night	24% 5% 15% 33% 18% 6%	1678
	21st to end	Night	23% 6% 10% 28% 25% 9%	1980
September	1st to 10th	Night	25% 4 10% 25% 27% 9%	1800
	11th to 20th	Night	26% 3 11% 28% 25% 8%	1944
	21st to end	Night	26% 3 8% 31% 26% 6%	1980
October	1st to 10th	Night	32% 3 9% 27% 24% 4	1980
	11th to 20th	Night	26% 4 10% 29% 22% 9%	2182
	21st to end	Night	29% 3 12% 26% 21% 9%	2574
November	1st to 10th	Night	24% 4 14% 29% 23% 6%	2405
	11th to 20th	Night	28% 3 13% 28% 23% 5%	2470
	21st to end	Night	26% 3 11% 31% 24% 4	2470
December	1st to 10th	Night	29% 4 15% 28% 19% 4	2645
	11th to 20th	Night	27% 4 14% 37% 17% 2	3272
	21st to end	Night	38% 4 11% 30% 14% 2	4873

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	7% 7% 41% 29% 11% 4	270
	11th to 20th	Day	11% 12% 35% 33% 7% 1	270
	21st to end	Day	7% 10% 48% 22% 9% 3	297
February	1st to 10th	Day	11% 9% 53% 22% 4	270
	11th to 20th	Day	9% 10% 51% 21% 7% 1	267
	21st to end	Day	10% 13% 49% 22% 6%	198
March	1st to 10th	Day	10% 11% 36% 28% 14%	240
	11th to 20th	Day	12% 7% 40% 27% 10% 4	240
	21st to end	Day	14% 11% 40% 26% 7% 2	401
April	1st to 10th	Day	15% 17% 34% 25% 9%	420
	11th to 20th	Day	18% 17% 35% 21% 8% 1	412
	21st to end	Day	19% 11% 27% 29% 13% 2	578
May	1st to 10th	Day	17% 8% 29% 30% 12% 3	603
	11th to 20th	Day	20% 7% 27% 28% 17% 2	625
	21st to end	Day	17% 7% 29% 29% 13% 4	679
June	1st to 10th	Day	7% 5% 24% 31% 25% 7%	630
	11th to 20th	Day	9% 6% 33% 34% 15% 2	630
	21st to end	Day	6% 3 30% 35% 21% 4	630
July	1st to 10th	Day	8% 4 21% 39% 23% 5%	621
	11th to 20th	Day	5% 2 21% 42% 25% 5%	618
	21st to end	Day	8% 1 17% 45% 25% 4	684
August	1st to 10th	Day	8% 2 20% 40% 23% 7%	626
	11th to 20th	Day	6% 2 24% 40% 24% 4	535
	21st to end	Day	4 3 25% 36% 25% 7%	495
September	1st to 10th	Day	7% 4 26% 36% 21% 5%	450
	11th to 20th	Day	5% 3 20% 39% 24% 9%	306
	21st to end	Day	11% 7% 26% 31% 20% 4	270
October	1st to 10th	Day	17% 7% 23% 27% 21% 6%	270
	11th to 20th	Day	10% 14% 32% 28% 15% 1	270
	21st to end	Day	13% 12% 36% 24% 13% 2	297
November	1st to 10th	Day	9% 9% 39% 24% 16% 3	270
	11th to 20th	Day	7% 10% 38% 34% 9% 3	270
	21st to end	Day	10% 7% 39% 33% 7% 4	270
December	1st to 10th	Day	10% 8% 46% 28% 9%	270
	11th to 20th	Day	9% 10% 43% 29% 8%	270
	21st to end	Day	16% 12% 42% 21% 7% 1	297
January	1st to 10th	Night	8% 12% 40% 29% 10% 1	950
	11th to 20th	Night	7% 14% 43% 29% 6%	950
	21st to end	Night	9% 11% 43% 30% 7%	1045
February	1st to 10th	Night	12% 11% 45% 27% 4	803
	11th to 20th	Night	9% 8% 49% 27% 6%	742
	21st to end	Night	9% 9% 51% 27% 4 1	592
March	1st to 10th	Night	13% 9% 40% 33% 6%	720
	11th to 20th	Night	12% 8% 41% 31% 7% 1	647
	21st to end	Night	12% 10% 40% 31% 7%	594
April	1st to 10th	Night	14% 14% 38% 29% 5%	540
	11th to 20th	Night	15% 11% 44% 26% 3	533
	21st to end	Night	17% 11% 32% 32% 7%	540
May	1st to 10th	Night	13% 8% 36% 33% 11% 1	540
	11th to 20th	Night	19% 5% 33% 30% 12% 1	531
	21st to end	Night	17% 6% 33% 33% 11%	584
June	1st to 10th	Night	9% 4 35% 35% 16% 2	540
	11th to 20th	Night	12% 7% 37% 37% 7% 1	540
	21st to end	Night	5% 3 30% 49% 12% 1	540
July	1st to 10th	Night	7% 2 29% 44% 16% 1	525
	11th to 20th	Night	6% 2 29% 52% 11% 1	522
	21st to end	Night	6% 1 27% 49% 16% 1	591
August	1st to 10th	Night	7% 3 21% 52% 15% 1	537
	11th to 20th	Night	5% 1 28% 52% 14%	534
	21st to end	Night	6% 3 28% 49% 14%	594
September	1st to 10th	Night	10% 3 27% 48% 11% 1	540
	11th to 20th	Night	9% 5% 28% 42% 14% 1	540
	21st to end	Night	12% 3 34% 41% 9% 1	540
October	1st to 10th	Night	16% 6% 31% 36% 11%	540
	11th to 20th	Night	11% 8% 33% 37% 11% 1	742
	21st to end	Night	12% 9% 35% 35% 8% 1	990
November	1st to 10th	Night	8% 7% 40% 37% 8% 1	925
	11th to 20th	Night	6% 12% 41% 33% 7% 1	950
	21st to end	Night	8% 7% 40% 36% 8% 1	950
December	1st to 10th	Night	6% 14% 46% 27% 7%	950
	11th to 20th	Night	8% 11% 43% 31% 6%	950
	21st to end	Night	12% 13% 39% 29% 5% 1	1045

Page generated at 2024-02-17 04:28:35. Version ac07

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