Allenford Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Allenford Observatory clear sky chart from 2005-11-06 to 2024-03-01.

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	16% 12% 5% 8% 6% 3 4 4 5% 6% 30%	78303
	Night	16% 14% 6% 10% 7% 3 4 4 4 5% 25%	81105
Transparency	Day	55% 6% 11% 18% 9% 1	78009
	Night	61% 6% 10% 15% 8% 1	80933
Seeing	Day	22% 12% 29% 23% 11% 4	14143
	Night	23% 11% 27% 27% 11% 1	23580

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	15% 23% 15% 13% 9% 3 5% 3 3 3 7%	2240
	11th to 20th	Day	11% 23% 11% 19% 15% 4 4 3 3 2 6%	2603
	21st to end	Day	18% 22% 11% 14% 8% 4 5% 3 3 3 8%	3124
February	1st to 10th	Day	14% 19% 7% 16% 12% 5% 5% 4 3 4 11%	1710
	11th to 20th	Day	13% 14% 8% 15% 11% 4 5% 5% 5% 5% 15%	1663
	21st to end	Day	15% 18% 7% 12% 7% 4 5% 5% 4 5% 18%	1532
March	1st to 10th	Day	15% 11% 5% 9% 9% 4 5% 5% 4 6% 28%	1913
	11th to 20th	Day	13% 12% 6% 9% 6% 4 6% 4 4 6% 29%	1980
	21st to end	Day	18% 10% 4 7% 7% 3 4 4 5% 6% 33%	2178
April	1st to 10th	Day	19% 13% 5% 7% 6% 3 4 3 5% 7% 29%	2069
	11th to 20th	Day	18% 10% 3 6% 5% 3 4 3 5% 6% 37%	2312
	21st to end	Day	20% 9% 4 6% 5% 2 4 4 5% 7% 34%	2340
May	1st to 10th	Day	17% 9% 2 6% 5% 3 4 4 5% 7% 38%	2340
	11th to 20th	Day	16% 8% 3 5% 5% 2 5% 3 5% 5% 42%	2387
	21st to end	Day	12% 5% 2 5% 5% 3 4 5% 6% 8% 45%	2725
June	1st to 10th	Day	14% 6% 3 5% 5% 3 4 6% 5% 8% 41%	2642
	11th to 20th	Day	12% 5% 2 6% 4 3 5% 5% 6% 8% 44%	2700
	21st to end	Day	15% 6% 3 5% 5% 3 4 4 6% 7% 43%	2700
July	1st to 10th	Day	10% 5% 2 4 4 2 5% 5% 6% 9% 50%	2700
	11th to 20th	Day	12% 5% 2 5% 4 3 5% 5% 6% 9% 45%	2632
	21st to end	Day	11% 5% 2 4 5% 3 5% 5% 6% 9% 44%	2547
August	1st to 10th	Day	12% 5% 2 4 4 3 4 5% 7% 9% 45%	2327
	11th to 20th	Day	12% 5% 3 5% 5% 3 5% 6% 5% 9% 44%	2303
	21st to end	Day	14% 6% 3 4 5% 3 5% 5% 6% 10% 41%	2561
September	1st to 10th	Day	14% 5% 3 7% 4 3 5% 5% 6% 8% 39%	2134
	11th to 20th	Day	13% 6% 3 5% 5% 2 5% 4 6% 9% 42%	1980
	21st to end	Day	17% 7% 3 7% 5% 4 5% 6% 5% 7% 34%	1980
October	1st to 10th	Day	20% 9% 3 7% 6% 3 5% 4 5% 7% 32%	1828
	11th to 20th	Day	27% 13% 5% 8% 7% 4 4 4 5% 5% 19%	1800
	21st to end	Day	31% 15% 4 8% 6% 3 3 3 4 5% 17%	1912
November	1st to 10th	Day	18% 18% 4 8% 8% 3 5% 4 5% 6% 21%	1639
	11th to 20th	Day	17% 20% 6% 9% 7% 3 5% 5% 4 7% 17%	1520
	21st to end	Day	21% 24% 9% 9% 7% 3 3 5% 4 5% 10%	1520
December	1st to 10th	Day	17% 28% 11% 15% 7% 3 4 3 2 3 6%	1520
	11th to 20th	Day	18% 24% 7% 15% 8% 3 4 3 4 4 9%	1811
	21st to end	Day	26% 24% 7% 14% 7% 3 3 3 3 3 7%	2431
January	1st to 10th	Night	16% 25% 12% 17% 9% 3 4 3 3 3 6%	4712
	11th to 20th	Night	15% 17% 10% 20% 14% 5% 5% 4 2 3 6%	4348
	21st to end	Night	17% 21% 10% 13% 9% 4 5% 4 4 4 10%	4532
February	1st to 10th	Night	13% 18% 8% 17% 12% 4 5% 4 3 4 12%	2470
	11th to 20th	Night	14% 14% 10% 15% 9% 4 5% 4 4 5% 18%	2403
	21st to end	Night	15% 16% 7% 11% 8% 3 5% 4 4 5% 22%	1918
March	1st to 10th	Night	14% 12% 6% 11% 8% 3 5% 4 4 4 29%	2041
	11th to 20th	Night	14% 13% 6% 9% 8% 3 4 4 4 4 32%	1979
	21st to end	Night	17% 11% 5% 7% 6% 3 4 4 5% 6% 33%	2178
April	1st to 10th	Night	20% 12% 4 8% 6% 2 5% 4 5% 6% 30%	1896
	11th to 20th	Night	18% 9% 4 6% 4 4 4 3 4 6% 38%	1606
	21st to end	Night	20% 10% 4 7% 6% 3 3 5% 4 6% 32%	1620
May	1st to 10th	Night	16% 7% 3 6% 5% 4 5% 4 4 8% 37%	1620
	11th to 20th	Night	15% 6% 3 5% 6% 2 5% 4 4 6% 42%	1505
	21st to end	Night	11% 4 2 5% 4 4 5% 6% 6% 8% 46%	1550
June	1st to 10th	Night	14% 6% 2 7% 6% 3 5% 4 5% 7% 41%	1314
	11th to 20th	Night	11% 6% 2 6% 5% 3 4 6% 7% 10% 42%	1260
	21st to end	Night	15% 4 2 6% 5% 3 4 5% 6% 8% 42%	1260
July	1st to 10th	Night	9% 4 1 3 4 3 4 4 6% 8% 54%	1260
	11th to 20th	Night	9% 5% 2 6% 4 2 7% 5% 6% 9% 45%	1321
	21st to end	Night	8% 5% 3 5% 6% 3 4 5% 7% 7% 48%	1771
August	1st to 10th	Night	10% 6% 3 5% 4 3 4 4 6% 8% 48%	1611
	11th to 20th	Night	9% 4 2 6% 6% 2 5% 5% 6% 8% 48%	1598
	21st to end	Night	13% 6% 2 7% 5% 2 4 5% 5% 7% 43%	1782
September	1st to 10th	Night	11% 4 2 6% 5% 3 4 5% 6% 8% 45%	1818
	11th to 20th	Night	13% 4 3 5% 4 3 4 5% 5% 7% 46%	1980
	21st to end	Night	16% 8% 3 6% 6% 3 5% 5% 4 7% 36%	1980
October	1st to 10th	Night	20% 8% 3 6% 6% 3 5% 4 5% 6% 34%	2132
	11th to 20th	Night	27% 12% 4 8% 6% 4 4 4 5% 6% 22%	2160
	21st to end	Night	28% 14% 4 9% 7% 3 4 4 4 5% 19%	2443
November	1st to 10th	Night	19% 17% 4 7% 6% 3 4 4 5% 5% 25%	2439
	11th to 20th	Night	18% 18% 6% 9% 8% 5% 4 5% 5% 5% 18%	2660
	21st to end	Night	23% 22% 7% 10% 7% 4 4 3 3 5% 14%	2660
December	1st to 10th	Night	20% 26% 12% 12% 6% 3 5% 4 2 3 7%	2660
	11th to 20th	Night	16% 22% 10% 14% 7% 3 5% 5% 4 4 11%	3382
	21st to end	Night	24% 23% 9% 15% 7% 3 4 3 3 3 7%	5236

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	81% 7% 8% 4	2241
	11th to 20th	Day	87% 4 4 3 2	2603
	21st to end	Day	82% 5% 7% 4 2	3124
February	1st to 10th	Day	77% 6% 6% 9% 1	1710
	11th to 20th	Day	71% 5% 9% 10% 4	1672
	21st to end	Day	68% 6% 9% 13% 4	1532
March	1st to 10th	Day	58% 5% 12% 17% 7% 1	1916
	11th to 20th	Day	56% 6% 10% 17% 10% 2	1980
	21st to end	Day	52% 4 11% 19% 12% 2	2178
April	1st to 10th	Day	57% 5% 11% 18% 10%	2069
	11th to 20th	Day	49% 3 9% 21% 15% 1	2312
	21st to end	Day	51% 5% 12% 19% 11% 2	2340
May	1st to 10th	Day	46% 4 9% 24% 13% 2	2340
	11th to 20th	Day	44% 5% 9% 25% 16% 2	2391
	21st to end	Day	37% 5% 15% 25% 15% 3	2725
June	1st to 10th	Day	40% 7% 10% 25% 16% 1	2642
	11th to 20th	Day	37% 6% 12% 26% 18% 1	2700
	21st to end	Day	40% 6% 12% 25% 14% 2	2700
July	1st to 10th	Day	31% 6% 15% 25% 20% 3	2626
	11th to 20th	Day	36% 6% 13% 31% 11% 2	2551
	21st to end	Day	37% 7% 13% 28% 14% 1	2405
August	1st to 10th	Day	34% 7% 17% 27% 13% 2	2314
	11th to 20th	Day	38% 7% 15% 27% 12%	2303
	21st to end	Day	40% 7% 15% 25% 12% 1	2561
September	1st to 10th	Day	42% 7% 13% 24% 12% 2	2134
	11th to 20th	Day	39% 5% 14% 29% 11%	1980
	21st to end	Day	47% 8% 12% 25% 7% 1	1980
October	1st to 10th	Day	53% 7% 10% 19% 10% 1	1828
	11th to 20th	Day	66% 6% 11% 12% 5% 1	1800
	21st to end	Day	71% 4 9% 12% 3	1912
November	1st to 10th	Day	64% 5% 10% 15% 6%	1639
	11th to 20th	Day	67% 7% 13% 8% 5%	1520
	21st to end	Day	75% 6% 10% 7% 1	1520
December	1st to 10th	Day	84% 4 6% 4 1	1520
	11th to 20th	Day	79% 5% 10% 6% 1	1810
	21st to end	Day	83% 5% 8% 4	2431
January	1st to 10th	Night	85% 5% 5% 4 1	4712
	11th to 20th	Night	84% 6% 6% 3 1	4348
	21st to end	Night	78% 6% 10% 4 2	4532
February	1st to 10th	Night	77% 5% 7% 10% 2	2470
	11th to 20th	Night	70% 5% 8% 12% 4	2405
	21st to end	Night	64% 5% 11% 13% 6%	1918
March	1st to 10th	Night	59% 4 11% 16% 8% 1	2051
	11th to 20th	Night	56% 5% 10% 17% 10% 2	1980
	21st to end	Night	53% 4 9% 19% 13% 2	2178
April	1st to 10th	Night	56% 4 9% 20% 11% 1	1896
	11th to 20th	Night	48% 3 9% 20% 18% 2	1606
	21st to end	Night	54% 5% 8% 17% 14% 2	1620
May	1st to 10th	Night	47% 5% 9% 22% 15% 3	1620
	11th to 20th	Night	43% 4 7% 24% 18% 3	1506
	21st to end	Night	34% 7% 14% 25% 16% 4	1551
June	1st to 10th	Night	42% 6% 10% 22% 18% 3	1314
	11th to 20th	Night	36% 7% 13% 25% 18% 1	1260
	21st to end	Night	38% 7% 12% 25% 15% 2	1260
July	1st to 10th	Night	27% 6% 11% 28% 23% 4	1225
	11th to 20th	Night	33% 7% 13% 30% 15% 2	1279
	21st to end	Night	33% 8% 14% 26% 17% 1	1672
August	1st to 10th	Night	35% 6% 14% 29% 14% 1	1600
	11th to 20th	Night	32% 8% 15% 27% 16% 2	1598
	21st to end	Night	40% 7% 13% 27% 12% 1	1782
September	1st to 10th	Night	34% 8% 12% 30% 14% 2	1818
	11th to 20th	Night	36% 6% 14% 30% 13%	1980
	21st to end	Night	46% 7% 14% 24% 8% 1	1980
October	1st to 10th	Night	52% 6% 10% 19% 12% 1	2132
	11th to 20th	Night	61% 7% 10% 16% 5%	2160
	21st to end	Night	68% 6% 9% 12% 5%	2443
November	1st to 10th	Night	60% 6% 10% 18% 5%	2439
	11th to 20th	Night	67% 6% 12% 10% 4 1	2660
	21st to end	Night	72% 6% 12% 9% 1	2660
December	1st to 10th	Night	82% 5% 7% 4 1	2660
	11th to 20th	Night	77% 5% 12% 6% 1	3382
	21st to end	Night	84% 5% 7% 4	5236

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	24% 19% 33% 17% 4 2	189
	11th to 20th	Day	23% 20% 35% 15% 6% 1	270
	21st to end	Day	27% 16% 30% 20% 7%	297
February	1st to 10th	Day	29% 23% 30% 15% 3	270
	11th to 20th	Day	21% 24% 39% 14% 2	270
	21st to end	Day	31% 24% 34% 9% 2	225
March	1st to 10th	Day	24% 17% 35% 17% 6% 1	356
	11th to 20th	Day	23% 15% 34% 21% 6% 1	420
	21st to end	Day	27% 12% 32% 20% 7% 1	462
April	1st to 10th	Day	25% 17% 29% 20% 9% 1	420
	11th to 20th	Day	30% 13% 27% 15% 9% 6%	412
	21st to end	Day	28% 9% 31% 22% 7% 2	420
May	1st to 10th	Day	26% 9% 30% 23% 9% 4	423
	11th to 20th	Day	20% 9% 28% 25% 14% 4	447
	21st to end	Day	17% 7% 28% 28% 16% 5%	485
June	1st to 10th	Day	15% 10% 32% 27% 13% 3	572
	11th to 20th	Day	13% 11% 30% 29% 12% 4	630
	21st to end	Day	18% 7% 34% 28% 10% 3	630
July	1st to 10th	Day	11% 6% 27% 33% 18% 5%	621
	11th to 20th	Day	16% 7% 29% 28% 13% 7%	606
	21st to end	Day	15% 5% 28% 31% 16% 6%	488
August	1st to 10th	Day	15% 5% 22% 32% 16% 9%	446
	11th to 20th	Day	14% 5% 18% 32% 21% 11%	439
	21st to end	Day	18% 7% 20% 29% 17% 8%	495
September	1st to 10th	Day	14% 9% 24% 28% 16% 8%	450
	11th to 20th	Day	11% 7% 23% 28% 21% 10%	450
	21st to end	Day	18% 10% 25% 25% 16% 6%	450
October	1st to 10th	Day	25% 13% 21% 24% 12% 5%	450
	11th to 20th	Day	28% 16% 30% 20% 4 2	450
	21st to end	Day	35% 14% 30% 16% 5%	427
November	1st to 10th	Day	32% 16% 29% 16% 6%	255
	11th to 20th	Day	29% 19% 28% 19% 3 2	180
	21st to end	Day	31% 23% 31% 13% 3	180
December	1st to 10th	Day	33% 13% 32% 17% 4	180
	11th to 20th	Day	32% 23% 27% 11% 7% 1	180
	21st to end	Day	40% 14% 32% 11% 2 1	198
January	1st to 10th	Night	24% 18% 30% 22% 6%	950
	11th to 20th	Night	29% 15% 30% 19% 7% 1	897
	21st to end	Night	20% 12% 32% 27% 8% 1	836
February	1st to 10th	Night	23% 17% 34% 22% 4	760
	11th to 20th	Night	21% 15% 32% 26% 6%	743
	21st to end	Night	24% 17% 34% 22% 3	628
March	1st to 10th	Night	20% 14% 34% 25% 6% 1	723
	11th to 20th	Night	22% 13% 33% 24% 6% 1	720
	21st to end	Night	23% 10% 30% 27% 9% 1	792
April	1st to 10th	Night	24% 12% 31% 27% 6%	720
	11th to 20th	Night	23% 11% 27% 26% 10% 2	542
	21st to end	Night	26% 8% 24% 30% 11% 1	540
May	1st to 10th	Night	21% 4 27% 34% 13% 1	540
	11th to 20th	Night	20% 7% 19% 40% 13% 1	444
	21st to end	Night	13% 3 27% 40% 16% 1	389
June	1st to 10th	Night	16% 6% 28% 37% 11% 2	360
	11th to 20th	Night	13% 7% 25% 40% 15% 1	360
	21st to end	Night	17% 4 22% 38% 19%	360
July	1st to 10th	Night	11% 4 17% 49% 18% 1	350
	11th to 20th	Night	12% 2 22% 37% 24% 1	401
	21st to end	Night	10% 3 20% 45% 22% 1	591
August	1st to 10th	Night	12% 2 18% 37% 30% 1	537
	11th to 20th	Night	12% 2 13% 39% 29% 4	534
	21st to end	Night	16% 4 19% 33% 25% 3	594
September	1st to 10th	Night	13% 6% 20% 35% 21% 5%	715
	11th to 20th	Night	14% 4 18% 39% 21% 5%	720
	21st to end	Night	19% 7% 22% 28% 20% 4	720
October	1st to 10th	Night	23% 7% 24% 29% 14% 2	720
	11th to 20th	Night	31% 11% 24% 24% 7% 1	720
	21st to end	Night	34% 13% 26% 23% 4 1	792
November	1st to 10th	Night	30% 11% 27% 23% 7% 1	740
	11th to 20th	Night	26% 18% 29% 18% 8% 1	760
	21st to end	Night	33% 14% 31% 18% 4	760
December	1st to 10th	Night	34% 17% 29% 15% 5%	760
	11th to 20th	Night	24% 17% 38% 17% 4 1	817
	21st to end	Night	34% 13% 31% 17% 3	1045

Page generated at 2024-02-27 06:30:18. Version ac07

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