Fieldon Hill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fieldon Hill Observatory clear sky chart from 2005-11-06 to 2024-01-14.

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	12% 7% 3 6% 5% 3 4 4 5% 7% 42%	74752
	Night	13% 8% 3 6% 5% 3 4 4 5% 7% 43%	75019
Transparency	Day	41% 4 12% 25% 15% 2	74460
	Night	41% 4 11% 25% 17% 3	74832
Seeing	Day	15% 10% 26% 27% 17% 5%	14497
	Night	16% 9% 30% 30% 13% 1	24451

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	12% 11% 5% 9% 6% 3 4 4 5% 6% 34%	1517
	11th to 20th	Day	15% 12% 6% 9% 7% 3 5% 3 4 5% 31%	1565
	21st to end	Day	13% 11% 6% 9% 6% 3 4 4 4 5% 36%	1782
February	1st to 10th	Day	16% 10% 5% 9% 6% 3 3 5% 5% 7% 32%	1620
	11th to 20th	Day	16% 8% 4 6% 6% 4 5% 5% 5% 7% 35%	1712
	21st to end	Day	17% 12% 3 6% 5% 3 3 4 4 5% 37%	1480
March	1st to 10th	Day	14% 10% 4 5% 5% 3 4 4 5% 6% 39%	1826
	11th to 20th	Day	18% 11% 3 7% 4 4 4 4 5% 5% 35%	1980
	21st to end	Day	21% 10% 4 7% 6% 4 5% 5% 4 6% 28%	2289
April	1st to 10th	Day	12% 6% 3 6% 6% 3 5% 4 5% 8% 43%	2160
	11th to 20th	Day	17% 9% 4 6% 4 2 4 4 4 5% 41%	2134
	21st to end	Day	18% 7% 3 5% 6% 4 4 4 4 7% 38%	2160
May	1st to 10th	Day	16% 6% 3 6% 5% 3 4 6% 6% 9% 36%	2219
	11th to 20th	Day	17% 5% 3 5% 6% 4 5% 5% 6% 7% 39%	2478
	21st to end	Day	10% 6% 3 6% 6% 3 6% 6% 6% 8% 39%	2725
June	1st to 10th	Day	7% 4 3 5% 5% 3 4 5% 6% 10% 48%	2520
	11th to 20th	Day	8% 4 2 4 4 3 5% 5% 8% 8% 49%	2520
	21st to end	Day	6% 3 2 4 5% 4 6% 6% 8% 10% 46%	2520
July	1st to 10th	Day	9% 4 2 4 4 4 6% 5% 6% 12% 44%	2520
	11th to 20th	Day	4 3 2 4 5% 3 5% 5% 7% 10% 51%	2520
	21st to end	Day	8% 4 2 5% 5% 2 5% 5% 6% 10% 48%	2627
August	1st to 10th	Day	7% 4 3 5% 6% 4 6% 5% 7% 9% 43%	2328
	11th to 20th	Day	9% 5% 2 6% 5% 4 6% 5% 8% 9% 42%	2135
	21st to end	Day	8% 3 2 5% 4 3 4 5% 7% 8% 50%	2376
September	1st to 10th	Day	13% 5% 2 4 4 3 4 4 5% 8% 50%	2160
	11th to 20th	Day	9% 5% 2 3 5% 3 4 4 6% 8% 51%	2142
	21st to end	Day	6% 4 2 5% 4 3 3 4 5% 8% 55%	1966
October	1st to 10th	Day	11% 5% 2 4 4 3 4 3 5% 6% 54%	1800
	11th to 20th	Day	15% 7% 3 5% 3 2 3 3 4 6% 50%	1800
	21st to end	Day	18% 7% 3 4 5% 3 3 3 3 5% 46%	1957
November	1st to 10th	Day	11% 6% 2 4 4 2 4 3 5% 6% 53%	1672
	11th to 20th	Day	15% 7% 3 5% 4 2 3 4 4 7% 45%	1710
	21st to end	Day	15% 10% 4 7% 4 4 3 3 4 6% 41%	1611
December	1st to 10th	Day	12% 12% 4 6% 5% 2 4 4 5% 7% 39%	1520
	11th to 20th	Day	14% 8% 5% 7% 5% 3 4 4 5% 6% 38%	1918
	21st to end	Day	20% 14% 4 9% 6% 3 5% 4 4 5% 24%	2783
January	1st to 10th	Night	13% 10% 4 8% 6% 3 4 5% 5% 6% 38%	2648
	11th to 20th	Night	16% 10% 5% 8% 6% 2 4 4 4 5% 36%	2465
	21st to end	Night	13% 11% 5% 8% 6% 3 4 4 5% 6% 35%	2574
February	1st to 10th	Night	15% 12% 6% 8% 6% 3 4 4 4 6% 33%	2340
	11th to 20th	Night	15% 9% 3 7% 5% 3 4 4 5% 6% 39%	2132
	21st to end	Night	17% 9% 4 7% 5% 2 3 3 5% 5% 40%	1776
March	1st to 10th	Night	16% 10% 4 6% 4 3 4 3 3 5% 42%	2147
	11th to 20th	Night	19% 8% 3 6% 5% 3 4 4 6% 6% 37%	1980
	21st to end	Night	21% 10% 4 7% 5% 3 5% 4 5% 7% 30%	2066
April	1st to 10th	Night	11% 7% 3 5% 6% 3 4 4 5% 7% 46%	1800
	11th to 20th	Night	13% 8% 2 4 4 3 5% 4 5% 7% 44%	1775
	21st to end	Night	19% 7% 3 6% 4 3 3 3 5% 6% 41%	1800
May	1st to 10th	Night	16% 6% 2 5% 5% 3 4 4 6% 8% 42%	1736
	11th to 20th	Night	14% 7% 3 6% 4 3 4 3 5% 7% 44%	1416
	21st to end	Night	10% 5% 3 6% 6% 3 5% 6% 5% 9% 42%	1551
June	1st to 10th	Night	7% 5% 2 5% 3 3 4 5% 7% 8% 51%	1440
	11th to 20th	Night	7% 4 2 3 5% 3 5% 4 6% 10% 52%	1440
	21st to end	Night	5% 4 2 5% 4 3 5% 5% 7% 9% 51%	1440
July	1st to 10th	Night	9% 4 2 4 5% 3 4 4 5% 10% 51%	1440
	11th to 20th	Night	5% 2 2 4 4 3 5% 5% 5% 9% 55%	1440
	21st to end	Night	6% 4 2 5% 5% 3 4 5% 6% 10% 50%	1687
August	1st to 10th	Night	7% 3 2 4 3 3 5% 5% 5% 9% 53%	1611
	11th to 20th	Night	7% 5% 2 5% 5% 3 4 4 6% 8% 52%	1763
	21st to end	Night	5% 3 2 4 4 3 4 4 6% 8% 57%	1980
September	1st to 10th	Night	11% 5% 1 4 3 3 4 3 5% 6% 54%	1800
	11th to 20th	Night	9% 4 2 4 4 3 4 5% 5% 7% 53%	1800
	21st to end	Night	7% 5% 2 4 4 2 4 4 5% 7% 56%	1990
October	1st to 10th	Night	9% 4 2 4 4 2 4 4 4 6% 57%	2160
	11th to 20th	Night	14% 5% 2 4 4 2 3 4 5% 7% 50%	2160
	21st to end	Night	17% 8% 2 4 4 2 4 3 4 4 45%	2398
November	1st to 10th	Night	10% 5% 3 4 3 2 4 4 4 6% 56%	2406
	11th to 20th	Night	12% 6% 3 5% 5% 2 3 4 5% 7% 49%	2470
	21st to end	Night	18% 8% 3 5% 4 2 3 3 4 6% 43%	2565
December	1st to 10th	Night	15% 10% 4 7% 7% 3 4 4 5% 6% 34%	2660
	11th to 20th	Night	16% 9% 5% 6% 4 2 4 3 4 6% 41%	3279
	21st to end	Night	19% 20% 6% 8% 7% 3 4 4 3 4 21%	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	51% 3 10% 20% 14% 1	1518
	11th to 20th	Day	55% 4 11% 23% 7%	1565
	21st to end	Day	51% 3 13% 22% 9% 2	1782
February	1st to 10th	Day	53% 3 12% 22% 10% 1	1620
	11th to 20th	Day	49% 4 12% 20% 14% 2	1722
	21st to end	Day	49% 4 10% 22% 13% 3	1480
March	1st to 10th	Day	46% 4 9% 25% 13% 2	1826
	11th to 20th	Day	51% 4 11% 20% 12% 2	1980
	21st to end	Day	56% 4 13% 17% 9% 1	2289
April	1st to 10th	Day	41% 4 11% 27% 16%	2160
	11th to 20th	Day	46% 3 9% 24% 14% 3	2134
	21st to end	Day	47% 4 12% 22% 13% 1	2160
May	1st to 10th	Day	44% 6% 15% 25% 9% 1	2219
	11th to 20th	Day	43% 6% 12% 23% 14% 1	2482
	21st to end	Day	41% 7% 14% 22% 14% 2	2725
June	1st to 10th	Day	31% 5% 14% 30% 17% 2	2520
	11th to 20th	Day	31% 5% 14% 25% 23% 3	2520
	21st to end	Day	30% 6% 18% 25% 17% 4	2520
July	1st to 10th	Day	33% 6% 15% 30% 13% 4	2451
	11th to 20th	Day	27% 6% 17% 29% 19% 3	2445
	21st to end	Day	30% 5% 15% 32% 16% 2	2481
August	1st to 10th	Day	36% 6% 14% 29% 15% 1	2314
	11th to 20th	Day	37% 6% 15% 27% 14% 1	2135
	21st to end	Day	30% 4 14% 27% 19% 6%	2376
September	1st to 10th	Day	34% 4 10% 29% 19% 5%	2160
	11th to 20th	Day	31% 4 9% 28% 25% 4	2142
	21st to end	Day	29% 4 10% 31% 23% 3	1966
October	1st to 10th	Day	32% 3 10% 27% 25% 4	1800
	11th to 20th	Day	38% 2 9% 25% 23% 4	1800
	21st to end	Day	43% 3 8% 27% 16% 3	1957
November	1st to 10th	Day	32% 3 13% 27% 21% 5%	1672
	11th to 20th	Day	39% 4 9% 25% 19% 4	1710
	21st to end	Day	47% 3 10% 27% 13%	1611
December	1st to 10th	Day	46% 4 13% 25% 12%	1520
	11th to 20th	Day	47% 3 11% 25% 11% 3	1915
	21st to end	Day	62% 4 10% 15% 8% 1	2783
January	1st to 10th	Night	48% 4 9% 24% 13% 2	2648
	11th to 20th	Night	52% 3 9% 26% 10%	2465
	21st to end	Night	51% 4 12% 21% 11% 1	2574
February	1st to 10th	Night	54% 3 10% 20% 11% 2	2340
	11th to 20th	Night	47% 3 10% 22% 16% 3	2133
	21st to end	Night	48% 3 11% 24% 12% 3	1776
March	1st to 10th	Night	46% 3 8% 24% 16% 2	2147
	11th to 20th	Night	49% 3 11% 22% 13% 3	1980
	21st to end	Night	55% 5% 12% 20% 9% 1	2066
April	1st to 10th	Night	38% 4 11% 27% 17% 4	1800
	11th to 20th	Night	39% 3 11% 24% 19% 4	1775
	21st to end	Night	46% 4 8% 22% 18% 2	1800
May	1st to 10th	Night	40% 5% 14% 23% 15% 2	1736
	11th to 20th	Night	41% 5% 11% 24% 17% 2	1417
	21st to end	Night	37% 6% 16% 20% 17% 4	1552
June	1st to 10th	Night	28% 5% 15% 29% 20% 3	1440
	11th to 20th	Night	28% 5% 12% 27% 25% 4	1440
	21st to end	Night	27% 5% 15% 28% 18% 7%	1440
July	1st to 10th	Night	30% 6% 14% 32% 14% 5%	1400
	11th to 20th	Night	25% 6% 13% 32% 21% 3	1392
	21st to end	Night	28% 5% 13% 31% 20% 2	1593
August	1st to 10th	Night	28% 5% 16% 33% 16% 2	1601
	11th to 20th	Night	30% 4 13% 29% 23% 1	1763
	21st to end	Night	24% 5% 13% 28% 23% 6%	1980
September	1st to 10th	Night	32% 3 10% 26% 22% 8%	1800
	11th to 20th	Night	30% 4 8% 27% 25% 6%	1800
	21st to end	Night	28% 4 9% 27% 28% 4	1990
October	1st to 10th	Night	29% 4 10% 25% 27% 5%	2160
	11th to 20th	Night	34% 3 7% 28% 21% 6%	2160
	21st to end	Night	43% 3 8% 21% 21% 4	2398
November	1st to 10th	Night	31% 4 12% 26% 21% 6%	2406
	11th to 20th	Night	36% 3 8% 29% 21% 4	2470
	21st to end	Night	44% 3 10% 26% 16% 1	2565
December	1st to 10th	Night	52% 3 11% 23% 11% 1	2660
	11th to 20th	Night	45% 3 10% 26% 15% 1	3281
	21st to end	Night	68% 3 8% 13% 7% 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	19% 21% 37% 18% 6%	270
	11th to 20th	Day	29% 19% 34% 16% 2	249
	21st to end	Day	15% 22% 44% 16% 3	264
February	1st to 10th	Day	24% 18% 41% 14% 3	240
	11th to 20th	Day	23% 21% 33% 18% 3	240
	21st to end	Day	26% 19% 37% 16% 2	198
March	1st to 10th	Day	20% 22% 39% 18% 1	240
	11th to 20th	Day	30% 13% 35% 18% 4	240
	21st to end	Day	31% 14% 33% 17% 5%	375
April	1st to 10th	Day	16% 15% 38% 22% 8% 1	420
	11th to 20th	Day	21% 15% 31% 20% 13%	412
	21st to end	Day	23% 15% 32% 22% 7% 1	420
May	1st to 10th	Day	17% 13% 34% 25% 9% 2	423
	11th to 20th	Day	18% 10% 29% 25% 15% 3	624
	21st to end	Day	13% 7% 28% 30% 14% 8%	679
June	1st to 10th	Day	8% 6% 19% 33% 25% 8%	630
	11th to 20th	Day	10% 3 23% 35% 23% 6%	630
	21st to end	Day	6% 7% 27% 35% 19% 6%	630
July	1st to 10th	Day	10% 2 13% 28% 31% 16%	621
	11th to 20th	Day	6% 3 17% 37% 29% 8%	618
	21st to end	Day	9% 1 17% 33% 31% 8%	684
August	1st to 10th	Day	8% 1 16% 37% 28% 11%	626
	11th to 20th	Day	12% 3 12% 30% 32% 10%	449
	21st to end	Day	9% 2 14% 29% 32% 13%	495
September	1st to 10th	Day	12% 3 18% 30% 27% 10%	450
	11th to 20th	Day	9% 2 15% 32% 28% 13%	450
	21st to end	Day	7% 8% 24% 29% 26% 7%	436
October	1st to 10th	Day	12% 9% 26% 35% 14% 4	270
	11th to 20th	Day	16% 18% 34% 22% 9% 1	270
	21st to end	Day	28% 18% 27% 21% 6%	297
November	1st to 10th	Day	10% 13% 37% 24% 13% 3	270
	11th to 20th	Day	19% 19% 31% 21% 9% 1	270
	21st to end	Day	22% 16% 33% 22% 7% 1	270
December	1st to 10th	Day	11% 19% 41% 19% 7% 3	270
	11th to 20th	Day	19% 19% 35% 24% 4	270
	21st to end	Day	26% 20% 38% 13% 4	297
January	1st to 10th	Night	17% 16% 40% 23% 5%	950
	11th to 20th	Night	21% 16% 36% 21% 5%	918
	21st to end	Night	18% 16% 40% 25% 2	990
February	1st to 10th	Night	22% 13% 39% 24% 2	900
	11th to 20th	Night	20% 16% 38% 23% 3	737
	21st to end	Night	23% 16% 35% 23% 3	592
March	1st to 10th	Night	20% 17% 37% 23% 3	707
	11th to 20th	Night	22% 10% 36% 26% 6%	540
	21st to end	Night	26% 10% 34% 25% 4	594
April	1st to 10th	Night	16% 14% 38% 26% 6%	540
	11th to 20th	Night	15% 12% 36% 27% 9% 1	533
	21st to end	Night	23% 7% 36% 27% 6%	540
May	1st to 10th	Night	18% 7% 32% 34% 9%	540
	11th to 20th	Night	17% 6% 26% 35% 15% 1	531
	21st to end	Night	10% 6% 24% 39% 20% 2	584
June	1st to 10th	Night	9% 2 23% 37% 28% 1	540
	11th to 20th	Night	8% 3 21% 46% 20% 2	540
	21st to end	Night	6% 2 24% 43% 23% 2	540
July	1st to 10th	Night	10% 1 10% 37% 35% 7%	525
	11th to 20th	Night	6% 1 14% 44% 31% 3	522
	21st to end	Night	6% 2 14% 39% 36% 4	591
August	1st to 10th	Night	8% 2 9% 43% 36% 3	537
	11th to 20th	Night	9% 1 12% 40% 34% 5%	534
	21st to end	Night	4 1 13% 37% 40% 4	594
September	1st to 10th	Night	12% 1 17% 37% 27% 5%	540
	11th to 20th	Night	10% 1 13% 39% 32% 4	540
	21st to end	Night	8% 6% 24% 32% 25% 4	720
October	1st to 10th	Night	11% 5% 26% 32% 22% 4	720
	11th to 20th	Night	16% 11% 33% 29% 11% 1	720
	21st to end	Night	22% 12% 33% 26% 7% 1	792
November	1st to 10th	Night	13% 9% 38% 30% 10%	740
	11th to 20th	Night	16% 14% 36% 28% 6%	760
	21st to end	Night	22% 12% 35% 25% 6%	855
December	1st to 10th	Night	21% 13% 36% 24% 5% 1	950
	11th to 20th	Night	23% 10% 31% 30% 5%	950
	21st to end	Night	27% 16% 34% 21% 2	1045

Page generated at 2024-01-11 03:22:43. Version ac07

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