Poole's Resort Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Poole's Resort Observatory clear sky chart from 2005-11-06 to 2024-08-30.

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	17% 10% 3 8% 5% 4 4 4 5% 7% 33%	95914
	Night	19% 11% 4 8% 5% 4 4 3 5% 6% 31%	93135
Transparency	Day	26% 51% 7% 11% 5%	95633
	Night	29% 51% 6% 9% 4	92970
Seeing	Day	23% 16% 30% 19% 9% 2	14301
	Night	25% 13% 29% 24% 8% 1	23395

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	17% 17% 6% 11% 6% 4 5% 3 5% 4 23%	2517
	11th to 20th	Day	15% 17% 8% 15% 6% 6% 4 3 5% 5% 17%	2520
	21st to end	Day	18% 21% 7% 12% 7% 5% 5% 3 4 4 15%	2964
February	1st to 10th	Day	16% 17% 4 13% 6% 5% 5% 3 5% 5% 21%	1710
	11th to 20th	Day	15% 16% 5% 11% 6% 5% 4 4 5% 5% 25%	1681
	21st to end	Day	20% 15% 4 10% 7% 5% 4 3 4 5% 22%	1570
March	1st to 10th	Day	22% 12% 4 10% 5% 3 4 3 4 4 29%	3138
	11th to 20th	Day	12% 17% 5% 10% 5% 4 4 3 5% 5% 29%	3480
	21st to end	Day	15% 9% 3 9% 5% 4 3 3 4 6% 39%	4022
April	1st to 10th	Day	21% 13% 4 7% 5% 4 3 3 4 5% 32%	2280
	11th to 20th	Day	22% 9% 3 6% 4 3 4 3 3 6% 37%	2254
	21st to end	Day	21% 11% 3 7% 4 4 4 4 5% 5% 32%	2357
May	1st to 10th	Day	22% 9% 2 7% 6% 5% 4 3 5% 7% 30%	4426
	11th to 20th	Day	16% 9% 3 8% 5% 4 4 4 6% 7% 34%	4398
	21st to end	Day	14% 6% 2 6% 4 4 5% 4 6% 9% 40%	4837
June	1st to 10th	Day	20% 7% 3 6% 5% 4 5% 3 5% 8% 32%	2660
	11th to 20th	Day	16% 6% 2 6% 5% 5% 5% 4 6% 8% 38%	2660
	21st to end	Day	17% 8% 2 7% 4 4 5% 4 6% 7% 35%	2660
July	1st to 10th	Day	11% 6% 2 6% 4 4 5% 5% 7% 9% 39%	4440
	11th to 20th	Day	13% 6% 2 6% 4 4 5% 4 7% 9% 41%	4440
	21st to end	Day	10% 6% 2 6% 4 5% 5% 5% 7% 10% 40%	4814
August	1st to 10th	Day	11% 7% 2 7% 4 4 5% 4 6% 7% 41%	2563
	11th to 20th	Day	12% 5% 2 6% 5% 5% 6% 4 7% 9% 38%	2390
	21st to end	Day	13% 6% 2 6% 5% 4 4 4 6% 9% 41%	2486
September	1st to 10th	Day	13% 6% 3 6% 4 4 4 4 5% 8% 42%	2160
	11th to 20th	Day	12% 7% 3 6% 4 5% 3 3 5% 7% 46%	2160
	21st to end	Day	17% 7% 2 6% 4 4 5% 4 5% 6% 39%	1923
October	1st to 10th	Day	22% 8% 3 7% 4 3 3 3 5% 7% 35%	1800
	11th to 20th	Day	21% 10% 3 8% 5% 4 6% 3 5% 6% 29%	1800
	21st to end	Day	27% 10% 3 8% 5% 4 4 3 4 5% 26%	1858
November	1st to 10th	Day	15% 10% 3 7% 5% 5% 4 5% 6% 7% 32%	1671
	11th to 20th	Day	16% 13% 4 9% 5% 6% 4 4 4 5% 31%	1557
	21st to end	Day	21% 14% 4 9% 6% 4 4 4 6% 6% 21%	1520
December	1st to 10th	Day	25% 17% 5% 10% 5% 4 4 4 5% 5% 17%	1520
	11th to 20th	Day	22% 17% 5% 10% 5% 4 4 3 4 5% 21%	1906
	21st to end	Day	28% 17% 5% 10% 6% 4 4 2 3 3 19%	2772
January	1st to 10th	Night	19% 17% 5% 11% 5% 5% 4 3 5% 4 22%	4429
	11th to 20th	Night	15% 16% 7% 14% 8% 6% 5% 3 4 4 18%	4440
	21st to end	Night	22% 17% 6% 10% 6% 5% 4 3 4 4 19%	4691
February	1st to 10th	Night	18% 15% 5% 13% 7% 5% 5% 3 4 5% 20%	2470
	11th to 20th	Night	14% 14% 6% 11% 6% 4 4 4 5% 6% 27%	2384
	21st to end	Night	19% 14% 5% 9% 6% 4 4 3 4 4 27%	1884
March	1st to 10th	Night	20% 12% 3 8% 5% 4 4 3 4 5% 32%	3697
	11th to 20th	Night	20% 17% 4 8% 5% 4 3 3 4 6% 26%	3479
	21st to end	Night	17% 12% 3 8% 5% 3 3 3 3 5% 38%	3609
April	1st to 10th	Night	22% 11% 2 8% 4 3 3 3 4 6% 34%	1900
	11th to 20th	Night	21% 8% 3 6% 5% 4 4 3 4 6% 36%	1875
	21st to end	Night	22% 9% 3 8% 5% 4 3 4 4 6% 33%	1836
May	1st to 10th	Night	23% 9% 3 8% 4 4 4 4 5% 6% 29%	2514
	11th to 20th	Night	19% 9% 3 7% 4 5% 4 3 5% 6% 34%	2495
	21st to end	Night	14% 7% 2 6% 4 4 5% 4 5% 9% 41%	2738
June	1st to 10th	Night	16% 9% 3 7% 5% 4 5% 4 6% 8% 32%	1520
	11th to 20th	Night	13% 5% 2 6% 4 5% 5% 4 6% 8% 42%	1520
	21st to end	Night	18% 7% 2 6% 4 4 6% 4 6% 8% 35%	1520
July	1st to 10th	Night	13% 7% 3 7% 5% 5% 4 4 6% 8% 38%	2520
	11th to 20th	Night	14% 6% 2 6% 4 4 4 3 7% 8% 43%	2520
	21st to end	Night	10% 6% 2 6% 4 4 5% 4 7% 7% 43%	2739
August	1st to 10th	Night	9% 7% 3 6% 4 4 5% 5% 7% 8% 42%	1592
	11th to 20th	Night	12% 7% 3 7% 5% 3 4 4 6% 8% 41%	1712
	21st to end	Night	11% 5% 3 6% 4 5% 5% 4 7% 7% 43%	2080
September	1st to 10th	Night	12% 6% 3 7% 4 4 4 3 6% 7% 45%	1800
	11th to 20th	Night	14% 6% 1 5% 3 3 4 3 6% 8% 47%	1800
	21st to end	Night	16% 6% 2 6% 4 4 3 4 6% 7% 41%	2033
October	1st to 10th	Night	20% 8% 2 7% 4 4 5% 4 5% 7% 35%	2160
	11th to 20th	Night	20% 7% 3 9% 5% 5% 5% 4 5% 6% 31%	2160
	21st to end	Night	26% 9% 3 8% 5% 4 4 3 5% 5% 27%	2497
November	1st to 10th	Night	19% 10% 3 7% 4 4 3 3 5% 6% 36%	2407
	11th to 20th	Night	18% 11% 3 8% 5% 5% 5% 4 5% 6% 32%	2622
	21st to end	Night	22% 13% 3 8% 5% 4 5% 4 5% 6% 23%	2660
December	1st to 10th	Night	22% 16% 5% 11% 6% 4 4 4 5% 5% 19%	2660
	11th to 20th	Night	22% 16% 4 9% 5% 4 3 3 5% 4 26%	3288
	21st to end	Night	31% 14% 4 11% 5% 3 4 3 4 4 16%	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	41% 40% 7% 7% 3 1	2518
	11th to 20th	Day	47% 40% 9% 3 2	2520
	21st to end	Day	48% 41% 6% 4 1	2964
February	1st to 10th	Day	25% 65% 3 5% 2	1710
	11th to 20th	Day	22% 64% 3 7% 4	1690
	21st to end	Day	23% 65% 3 4 4 1	1570
March	1st to 10th	Day	36% 41% 6% 11% 5%	3141
	11th to 20th	Day	34% 41% 11% 7% 7% 1	3480
	21st to end	Day	28% 40% 8% 16% 7% 1	4022
April	1st to 10th	Day	21% 65% 3 5% 5% 1	2280
	11th to 20th	Day	18% 66% 3 7% 5% 1	2254
	21st to end	Day	19% 65% 3 7% 5% 1	2357
May	1st to 10th	Day	33% 43% 7% 14% 3	4440
	11th to 20th	Day	31% 44% 9% 13% 3	4402
	21st to end	Day	25% 43% 8% 17% 7%	4837
June	1st to 10th	Day	18% 65% 3 8% 5%	2660
	11th to 20th	Day	15% 66% 5% 9% 4 1	2660
	21st to end	Day	16% 64% 5% 9% 5% 1	2660
July	1st to 10th	Day	27% 35% 8% 21% 8%	4370
	11th to 20th	Day	26% 35% 10% 23% 5%	4365
	21st to end	Day	26% 36% 10% 21% 8%	4661
August	1st to 10th	Day	16% 62% 8% 10% 5%	2549
	11th to 20th	Day	17% 63% 6% 10% 4	2390
	21st to end	Day	16% 61% 7% 11% 5%	2486
September	1st to 10th	Day	13% 65% 7% 11% 4 1	2160
	11th to 20th	Day	12% 63% 5% 11% 8%	2160
	21st to end	Day	15% 64% 5% 11% 5%	1923
October	1st to 10th	Day	19% 63% 4 9% 4 1	1800
	11th to 20th	Day	19% 64% 7% 8% 2	1800
	21st to end	Day	25% 63% 4 7% 2	1858
November	1st to 10th	Day	25% 60% 6% 6% 2	1671
	11th to 20th	Day	23% 60% 5% 10% 2	1557
	21st to end	Day	26% 61% 6% 4 3	1520
December	1st to 10th	Day	29% 60% 6% 4 1	1520
	11th to 20th	Day	36% 51% 8% 4 1	1906
	21st to end	Day	45% 38% 5% 10% 2	2772
January	1st to 10th	Night	41% 41% 10% 6% 2	4429
	11th to 20th	Night	46% 39% 7% 5% 2	4440
	21st to end	Night	47% 42% 5% 4 1	4691
February	1st to 10th	Night	26% 65% 3 4 2	2470
	11th to 20th	Night	21% 64% 4 7% 4	2386
	21st to end	Night	21% 64% 4 7% 4	1884
March	1st to 10th	Night	32% 42% 5% 15% 6%	3707
	11th to 20th	Night	38% 41% 9% 6% 5% 1	3480
	21st to end	Night	31% 39% 5% 14% 9% 1	3609
April	1st to 10th	Night	21% 64% 3 8% 4	1900
	11th to 20th	Night	18% 66% 3 6% 7% 1	1875
	21st to end	Night	19% 65% 4 6% 6% 1	1836
May	1st to 10th	Night	36% 42% 7% 11% 3	2520
	11th to 20th	Night	35% 43% 8% 11% 3	2496
	21st to end	Night	26% 41% 6% 14% 13%	2739
June	1st to 10th	Night	16% 66% 4 8% 5% 1	1520
	11th to 20th	Night	16% 65% 3 8% 8% 1	1520
	21st to end	Night	17% 64% 4 9% 6% 1	1520
July	1st to 10th	Night	31% 36% 7% 16% 10% 1	2480
	11th to 20th	Night	27% 35% 8% 26% 4	2472
	21st to end	Night	26% 36% 10% 19% 8%	2651
August	1st to 10th	Night	14% 62% 9% 9% 5%	1582
	11th to 20th	Night	21% 62% 5% 10% 4	1712
	21st to end	Night	14% 61% 6% 14% 5%	2080
September	1st to 10th	Night	13% 64% 7% 11% 5%	1800
	11th to 20th	Night	13% 63% 5% 12% 6% 1	1800
	21st to end	Night	13% 64% 5% 12% 6%	2033
October	1st to 10th	Night	17% 64% 4 9% 5% 1	2160
	11th to 20th	Night	18% 64% 6% 8% 3 1	2160
	21st to end	Night	24% 63% 5% 6% 3	2497
November	1st to 10th	Night	23% 59% 7% 7% 3	2407
	11th to 20th	Night	22% 60% 6% 8% 4	2622
	21st to end	Night	25% 61% 5% 7% 2	2660
December	1st to 10th	Night	29% 60% 4 5% 1	2660
	11th to 20th	Night	34% 50% 6% 8% 3	3288
	21st to end	Night	46% 38% 7% 8% 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	26% 23% 31% 13% 7%	180
	11th to 20th	Day	36% 17% 31% 15% 2 1	180
	21st to end	Day	25% 23% 34% 15% 4	252
February	1st to 10th	Day	32% 29% 30% 9% 1	270
	11th to 20th	Day	30% 28% 35% 8%	288
	21st to end	Day	36% 19% 30% 13% 2	382
March	1st to 10th	Day	26% 21% 31% 17% 5%	460
	11th to 20th	Day	28% 22% 32% 14% 4	460
	21st to end	Day	34% 20% 26% 14% 6% 1	506
April	1st to 10th	Day	32% 18% 29% 15% 5%	460
	11th to 20th	Day	31% 21% 25% 13% 7% 3	452
	21st to end	Day	30% 20% 28% 13% 6% 2	460
May	1st to 10th	Day	23% 18% 31% 20% 6% 2	463
	11th to 20th	Day	17% 17% 34% 21% 9% 2	487
	21st to end	Day	16% 16% 30% 25% 11% 2	529
June	1st to 10th	Day	25% 14% 31% 21% 8% 1	490
	11th to 20th	Day	16% 13% 34% 24% 10% 3	490
	21st to end	Day	21% 15% 32% 21% 9% 2	490
July	1st to 10th	Day	14% 9% 31% 28% 16% 2	485
	11th to 20th	Day	16% 10% 30% 28% 13% 4	484
	21st to end	Day	13% 10% 35% 28% 12% 2	532
August	1st to 10th	Day	16% 9% 28% 27% 16% 4	486
	11th to 20th	Day	15% 8% 25% 29% 17% 6%	479
	21st to end	Day	14% 10% 33% 23% 14% 6%	532
September	1st to 10th	Day	15% 12% 31% 25% 10% 6%	450
	11th to 20th	Day	13% 10% 26% 24% 17% 10%	450
	21st to end	Day	19% 12% 28% 23% 15% 3	450
October	1st to 10th	Day	26% 17% 24% 17% 12% 5%	450
	11th to 20th	Day	26% 20% 30% 17% 5% 2	450
	21st to end	Day	36% 15% 27% 17% 4	434
November	1st to 10th	Day	26% 20% 29% 17% 7% 1	365
	11th to 20th	Day	30% 14% 34% 14% 6% 1	217
	21st to end	Day	27% 23% 35% 12% 2	180
December	1st to 10th	Day	35% 23% 23% 15% 4	180
	11th to 20th	Day	31% 24% 33% 10% 2	180
	21st to end	Day	34% 20% 30% 13% 3	198
January	1st to 10th	Night	34% 17% 28% 17% 4	760
	11th to 20th	Night	30% 19% 28% 19% 4	760
	21st to end	Night	24% 16% 32% 21% 6%	836
February	1st to 10th	Night	27% 21% 33% 17% 2	760
	11th to 20th	Night	24% 18% 37% 18% 3	743
	21st to end	Night	28% 18% 31% 20% 3	628
March	1st to 10th	Night	28% 15% 32% 22% 4	760
	11th to 20th	Night	29% 16% 32% 19% 4 1	760
	21st to end	Night	26% 14% 34% 19% 7%	836
April	1st to 10th	Night	28% 14% 33% 23% 3	760
	11th to 20th	Night	27% 18% 30% 19% 6% 1	751
	21st to end	Night	27% 10% 31% 22% 9%	696
May	1st to 10th	Night	26% 9% 27% 27% 9% 1	380
	11th to 20th	Night	14% 11% 35% 32% 7%	374
	21st to end	Night	14% 9% 35% 29% 11% 1	411
June	1st to 10th	Night	20% 8% 28% 35% 8% 1	380
	11th to 20th	Night	13% 11% 28% 33% 13% 1	380
	21st to end	Night	19% 8% 27% 32% 13% 1	380
July	1st to 10th	Night	13% 5% 28% 38% 15%	370
	11th to 20th	Night	13% 5% 28% 35% 19% 1	368
	21st to end	Night	14% 4 26% 42% 12% 1	416
August	1st to 10th	Night	13% 4 26% 37% 20%	458
	11th to 20th	Night	17% 4 18% 36% 21% 3	588
	21st to end	Night	13% 6% 26% 36% 17% 2	832
September	1st to 10th	Night	17% 7% 27% 32% 15% 2	720
	11th to 20th	Night	18% 7% 22% 29% 21% 4	720
	21st to end	Night	18% 11% 26% 25% 18% 2	720
October	1st to 10th	Night	26% 12% 27% 19% 14% 2	720
	11th to 20th	Night	24% 15% 28% 25% 8%	720
	21st to end	Night	34% 12% 29% 22% 3	792
November	1st to 10th	Night	27% 14% 30% 21% 8%	740
	11th to 20th	Night	26% 18% 31% 16% 9%	760
	21st to end	Night	34% 17% 27% 15% 6%	760
December	1st to 10th	Night	34% 19% 27% 18% 3	760
	11th to 20th	Night	30% 17% 33% 17% 2 1	760
	21st to end	Night	34% 17% 29% 17% 2	836

Page generated at 2024-08-27 09:49:42. Version ac07

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