South Tamworth Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the South Tamworth Observatory clear sky chart from 2005-11-06 to 2024-01-16.

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% 7% 3 6% 5% 3 5% 5% 5% 7% 37%	74828
	Night	16% 7% 3 5% 5% 3 5% 5% 5% 7% 39%	74968
Transparency	Day	45% 5% 12% 22% 13% 2	74533
	Night	45% 5% 12% 23% 13% 2	74797
Seeing	Day	23% 15% 29% 21% 9% 3	13786
	Night	22% 11% 26% 30% 10% 1	22774

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	13% 10% 3 5% 6% 4 5% 6% 5% 7% 37%	1517
	11th to 20th	Day	16% 9% 3 6% 6% 3 5% 4 6% 7% 35%	1486
	21st to end	Day	11% 7% 3 7% 8% 3 4 5% 6% 7% 39%	1584
February	1st to 10th	Day	14% 10% 3 6% 5% 4 6% 5% 5% 8% 33%	1590
	11th to 20th	Day	12% 7% 4 9% 6% 3 6% 5% 5% 7% 36%	1748
	21st to end	Day	15% 10% 5% 6% 6% 4 5% 5% 6% 5% 34%	1480
March	1st to 10th	Day	13% 8% 3 7% 6% 3 6% 6% 6% 7% 36%	1797
	11th to 20th	Day	15% 8% 3 7% 5% 3 5% 3 5% 6% 39%	1893
	21st to end	Day	15% 9% 4 6% 6% 3 4 4 4 6% 40%	2299
April	1st to 10th	Day	19% 9% 4 6% 5% 3 4 4 5% 6% 37%	2160
	11th to 20th	Day	16% 6% 3 6% 5% 3 5% 4 6% 7% 39%	2172
	21st to end	Day	21% 8% 3 7% 6% 3 5% 4 4 5% 33%	2340
May	1st to 10th	Day	22% 9% 2 7% 6% 3 4 4 5% 6% 31%	2340
	11th to 20th	Day	18% 7% 3 6% 5% 3 4 5% 5% 7% 37%	2402
	21st to end	Day	15% 7% 3 6% 6% 3 5% 5% 5% 7% 37%	2725
June	1st to 10th	Day	21% 8% 3 6% 6% 3 5% 5% 6% 7% 30%	2520
	11th to 20th	Day	17% 7% 3 6% 5% 4 5% 5% 6% 7% 37%	2520
	21st to end	Day	19% 7% 3 6% 6% 3 6% 6% 6% 8% 31%	2520
July	1st to 10th	Day	16% 6% 3 6% 6% 3 5% 6% 6% 9% 36%	2520
	11th to 20th	Day	12% 7% 3 6% 5% 3 6% 6% 8% 9% 35%	2520
	21st to end	Day	14% 5% 2 5% 6% 4 5% 6% 6% 9% 37%	2744
August	1st to 10th	Day	12% 5% 3 6% 5% 3 6% 6% 6% 9% 38%	2404
	11th to 20th	Day	13% 6% 2 6% 6% 3 5% 7% 6% 9% 38%	2304
	21st to end	Day	11% 4 2 4 6% 3 5% 4 6% 10% 45%	2390
September	1st to 10th	Day	12% 4 2 4 5% 3 4 5% 7% 9% 46%	2160
	11th to 20th	Day	13% 5% 3 4 3 3 4 4 3 7% 51%	1984
	21st to end	Day	15% 5% 1 4 5% 3 4 5% 5% 6% 46%	1980
October	1st to 10th	Day	22% 6% 3 5% 5% 3 4 4 4 6% 37%	1980
	11th to 20th	Day	16% 7% 2 4 6% 4 5% 5% 5% 6% 40%	1720
	21st to end	Day	24% 8% 3 6% 5% 3 4 4 4 5% 33%	1782
November	1st to 10th	Day	14% 6% 2 4 4 3 4 5% 6% 7% 44%	1671
	11th to 20th	Day	19% 5% 2 4 5% 4 5% 5% 6% 7% 40%	1710
	21st to end	Day	20% 7% 3 4 5% 3 4 5% 5% 6% 38%	1668
December	1st to 10th	Day	19% 10% 3 5% 5% 3 6% 6% 5% 7% 30%	1520
	11th to 20th	Day	21% 8% 2 5% 5% 3 4 4 4 6% 39%	1906
	21st to end	Day	23% 11% 3 5% 5% 3 5% 5% 6% 5% 30%	2772
January	1st to 10th	Night	13% 9% 3 5% 4 4 5% 6% 6% 8% 39%	2649
	11th to 20th	Night	15% 12% 4 6% 6% 3 5% 5% 6% 6% 33%	2602
	21st to end	Night	10% 8% 3 7% 6% 3 5% 6% 6% 8% 38%	2772
February	1st to 10th	Night	13% 9% 4 7% 5% 3 6% 6% 6% 8% 33%	2364
	11th to 20th	Night	10% 9% 3 6% 5% 3 5% 6% 6% 7% 39%	2098
	21st to end	Night	13% 9% 3 5% 5% 3 6% 5% 5% 8% 38%	1776
March	1st to 10th	Night	13% 9% 4 6% 5% 3 5% 5% 5% 7% 40%	2150
	11th to 20th	Night	15% 8% 4 5% 6% 4 5% 5% 6% 6% 36%	2065
	21st to end	Night	15% 9% 3 6% 5% 3 4 4 5% 7% 40%	2052
April	1st to 10th	Night	18% 10% 3 5% 6% 3 5% 4 4 6% 37%	1800
	11th to 20th	Night	16% 6% 3 6% 7% 4 4 4 5% 8% 37%	1736
	21st to end	Night	22% 8% 2 5% 4 3 4 4 5% 6% 36%	1620
May	1st to 10th	Night	21% 9% 4 6% 5% 3 5% 4 5% 6% 32%	1620
	11th to 20th	Night	18% 6% 4 6% 5% 3 5% 5% 6% 7% 36%	1505
	21st to end	Night	17% 6% 3 5% 6% 3 4 4 6% 7% 37%	1550
June	1st to 10th	Night	20% 7% 3 6% 5% 3 5% 5% 6% 7% 34%	1440
	11th to 20th	Night	18% 7% 3 5% 4 3 4 5% 5% 8% 39%	1440
	21st to end	Night	17% 5% 2 5% 5% 4 5% 5% 7% 7% 38%	1440
July	1st to 10th	Night	17% 4 2 5% 5% 3 5% 5% 5% 8% 41%	1440
	11th to 20th	Night	14% 5% 2 5% 5% 3 4 5% 6% 9% 41%	1440
	21st to end	Night	14% 4 2 4 5% 3 5% 5% 5% 9% 44%	1574
August	1st to 10th	Night	14% 6% 2 5% 5% 3 4 4 5% 8% 44%	1514
	11th to 20th	Night	15% 6% 3 6% 5% 3 4 5% 5% 8% 40%	1596
	21st to end	Night	15% 5% 3 4 4 3 3 4 5% 8% 46%	1962
September	1st to 10th	Night	12% 5% 2 3 3 3 3 4 6% 7% 51%	1800
	11th to 20th	Night	15% 5% 2 4 4 2 4 4 3 6% 51%	1975
	21st to end	Night	15% 6% 2 4 3 3 4 5% 4 7% 46%	1980
October	1st to 10th	Night	20% 6% 2 6% 5% 2 5% 5% 5% 5% 39%	1980
	11th to 20th	Night	15% 6% 2 5% 5% 4 5% 5% 6% 8% 39%	2235
	21st to end	Night	23% 8% 3 5% 5% 3 5% 4 5% 6% 35%	2574
November	1st to 10th	Night	14% 6% 2 6% 5% 3 5% 5% 5% 7% 43%	2407
	11th to 20th	Night	16% 5% 3 6% 5% 3 4 5% 5% 7% 42%	2470
	21st to end	Night	16% 7% 3 5% 5% 3 4 5% 5% 6% 42%	2510
December	1st to 10th	Night	18% 9% 4 7% 5% 3 5% 3 5% 6% 34%	2660
	11th to 20th	Night	20% 8% 2 4 5% 3 4 5% 5% 6% 37%	3288
	21st to end	Night	22% 11% 3 7% 5% 3 4 5% 4 5% 32%	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	45% 4 11% 25% 14% 1	1518
	11th to 20th	Day	48% 6% 13% 18% 11% 3	1486
	21st to end	Day	44% 4 12% 22% 16% 2	1584
February	1st to 10th	Day	50% 4 15% 18% 10% 2	1590
	11th to 20th	Day	47% 6% 11% 19% 13% 4	1757
	21st to end	Day	52% 4 11% 17% 13% 3	1480
March	1st to 10th	Day	47% 5% 12% 19% 13% 5%	1800
	11th to 20th	Day	46% 4 11% 18% 17% 5%	1893
	21st to end	Day	47% 4 9% 18% 18% 5%	2299
April	1st to 10th	Day	48% 4 9% 21% 14% 4	2160
	11th to 20th	Day	44% 6% 12% 21% 16% 2	2172
	21st to end	Day	54% 5% 7% 17% 14% 3	2340
May	1st to 10th	Day	53% 4 8% 20% 13% 2	2340
	11th to 20th	Day	46% 6% 9% 21% 16% 3	2406
	21st to end	Day	45% 7% 13% 22% 12% 2	2725
June	1st to 10th	Day	51% 6% 12% 21% 9% 1	2520
	11th to 20th	Day	44% 5% 11% 22% 15% 3	2520
	21st to end	Day	49% 8% 12% 19% 11% 1	2520
July	1st to 10th	Day	42% 6% 13% 24% 14% 1	2450
	11th to 20th	Day	42% 6% 16% 26% 9% 1	2445
	21st to end	Day	39% 8% 15% 24% 13% 1	2591
August	1st to 10th	Day	41% 8% 16% 24% 11%	2390
	11th to 20th	Day	41% 6% 16% 25% 11% 1	2304
	21st to end	Day	35% 5% 15% 26% 18% 2	2390
September	1st to 10th	Day	34% 7% 14% 30% 14% 1	2160
	11th to 20th	Day	34% 3 9% 31% 20% 3	1984
	21st to end	Day	38% 5% 12% 26% 18% 2	1980
October	1st to 10th	Day	48% 4 11% 21% 14% 2	1980
	11th to 20th	Day	43% 4 13% 29% 10% 1	1720
	21st to end	Day	52% 4 12% 19% 11% 2	1782
November	1st to 10th	Day	38% 5% 15% 26% 14% 2	1671
	11th to 20th	Day	42% 4 13% 21% 17% 3	1710
	21st to end	Day	46% 4 17% 20% 11% 1	1668
December	1st to 10th	Day	53% 5% 12% 20% 9% 1	1520
	11th to 20th	Day	47% 5% 8% 21% 17% 2	1906
	21st to end	Day	56% 4 10% 19% 9% 2	2772
January	1st to 10th	Night	43% 5% 13% 24% 13% 2	2649
	11th to 20th	Night	51% 5% 13% 19% 9% 2	2602
	21st to end	Night	43% 6% 11% 20% 17% 3	2772
February	1st to 10th	Night	48% 5% 13% 19% 13% 2	2364
	11th to 20th	Night	43% 5% 11% 23% 15% 3	2100
	21st to end	Night	45% 5% 12% 21% 13% 4	1776
March	1st to 10th	Night	44% 5% 9% 24% 15% 3	2160
	11th to 20th	Night	47% 5% 10% 20% 14% 4	2066
	21st to end	Night	44% 4 9% 18% 19% 5%	2052
April	1st to 10th	Night	49% 4 9% 20% 15% 3	1800
	11th to 20th	Night	46% 5% 9% 24% 15% 1	1736
	21st to end	Night	48% 4 11% 19% 13% 3	1620
May	1st to 10th	Night	53% 5% 8% 20% 13% 2	1620
	11th to 20th	Night	47% 6% 10% 19% 13% 4	1506
	21st to end	Night	45% 6% 16% 22% 10% 2	1551
June	1st to 10th	Night	48% 7% 12% 20% 12%	1440
	11th to 20th	Night	44% 7% 14% 19% 14% 2	1440
	21st to end	Night	44% 8% 15% 23% 10% 1	1440
July	1st to 10th	Night	39% 7% 17% 22% 14% 1	1400
	11th to 20th	Night	38% 7% 18% 25% 12%	1392
	21st to end	Night	37% 6% 16% 29% 12% 1	1486
August	1st to 10th	Night	39% 6% 14% 28% 13% 1	1504
	11th to 20th	Night	41% 7% 15% 24% 13%	1596
	21st to end	Night	36% 6% 13% 29% 16% 1	1962
September	1st to 10th	Night	31% 7% 15% 31% 16% 1	1800
	11th to 20th	Night	35% 5% 10% 28% 20% 2	1975
	21st to end	Night	37% 5% 11% 30% 14% 2	1980
October	1st to 10th	Night	45% 6% 12% 22% 13% 2	1980
	11th to 20th	Night	43% 4 14% 28% 10% 1	2235
	21st to end	Night	51% 4 12% 20% 11% 2	2574
November	1st to 10th	Night	40% 6% 11% 26% 15% 2	2407
	11th to 20th	Night	42% 5% 10% 25% 16% 2	2470
	21st to end	Night	43% 5% 15% 25% 11% 1	2510
December	1st to 10th	Night	52% 4 12% 22% 9% 1	2660
	11th to 20th	Night	47% 6% 12% 19% 15% 1	3288
	21st to end	Night	56% 4 9% 21% 10% 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	27% 18% 29% 19% 7%	180
	11th to 20th	Day	30% 23% 24% 18% 3 2	172
	21st to end	Day	16% 24% 34% 19% 6% 1	176
February	1st to 10th	Day	29% 24% 29% 15% 3	272
	11th to 20th	Day	26% 21% 32% 19% 2	416
	21st to end	Day	29% 17% 30% 20% 3	346
March	1st to 10th	Day	28% 15% 32% 21% 3	420
	11th to 20th	Day	28% 22% 30% 13% 6% 1	420
	21st to end	Day	25% 18% 31% 17% 6% 3	462
April	1st to 10th	Day	31% 17% 27% 17% 7% 2	420
	11th to 20th	Day	27% 21% 26% 15% 8% 2	412
	21st to end	Day	29% 21% 29% 12% 7% 2	420
May	1st to 10th	Day	32% 20% 27% 15% 4 2	423
	11th to 20th	Day	22% 19% 33% 18% 7% 2	447
	21st to end	Day	21% 14% 33% 23% 7% 2	485
June	1st to 10th	Day	23% 15% 34% 19% 7% 2	450
	11th to 20th	Day	19% 16% 31% 23% 8% 2	450
	21st to end	Day	20% 14% 34% 18% 12% 2	450
July	1st to 10th	Day	20% 9% 31% 24% 14% 3	445
	11th to 20th	Day	15% 6% 34% 29% 13% 3	444
	21st to end	Day	15% 8% 36% 28% 11% 3	488
August	1st to 10th	Day	11% 12% 28% 27% 17% 4	446
	11th to 20th	Day	18% 9% 29% 23% 16% 6%	439
	21st to end	Day	15% 9% 28% 28% 15% 5%	495
September	1st to 10th	Day	17% 9% 25% 25% 18% 6%	450
	11th to 20th	Day	20% 11% 24% 22% 13% 10%	450
	21st to end	Day	15% 13% 28% 24% 13% 6%	450
October	1st to 10th	Day	28% 14% 20% 20% 14% 5%	450
	11th to 20th	Day	21% 16% 25% 23% 13% 3	391
	21st to end	Day	34% 13% 23% 24% 5% 1	396
November	1st to 10th	Day	23% 15% 26% 27% 8% 2	365
	11th to 20th	Day	28% 17% 25% 20% 9% 1	370
	21st to end	Day	30% 16% 29% 19% 6% 1	328
December	1st to 10th	Day	25% 27% 23% 16% 8% 1	180
	11th to 20th	Day	31% 19% 33% 13% 4	180
	21st to end	Day	31% 18% 30% 18% 3 1	198
January	1st to 10th	Night	21% 12% 34% 29% 4	760
	11th to 20th	Night	24% 14% 28% 29% 5%	744
	21st to end	Night	17% 17% 32% 28% 5% 1	792
February	1st to 10th	Night	21% 15% 34% 28% 2	720
	11th to 20th	Night	19% 18% 38% 21% 4	703
	21st to end	Night	20% 17% 32% 26% 4	592
March	1st to 10th	Night	24% 13% 32% 27% 4	720
	11th to 20th	Night	23% 15% 30% 26% 6%	720
	21st to end	Night	23% 14% 27% 26% 10% 1	792
April	1st to 10th	Night	25% 14% 28% 28% 6%	720
	11th to 20th	Night	21% 15% 28% 28% 7%	672
	21st to end	Night	28% 13% 24% 28% 7%	540
May	1st to 10th	Night	28% 8% 26% 28% 9% 1	540
	11th to 20th	Night	22% 10% 31% 27% 10%	444
	21st to end	Night	21% 6% 21% 35% 15% 1	389
June	1st to 10th	Night	22% 6% 25% 36% 10% 1	360
	11th to 20th	Night	20% 6% 22% 37% 14% 1	360
	21st to end	Night	21% 4 23% 38% 13% 1	360
July	1st to 10th	Night	18% 3 19% 42% 17%	350
	11th to 20th	Night	17% 1 20% 40% 20% 2	348
	21st to end	Night	15% 3 16% 47% 18% 1	394
August	1st to 10th	Night	16% 3 16% 41% 23% 1	440
	11th to 20th	Night	17% 5% 23% 33% 19% 2	532
	21st to end	Night	17% 4 18% 36% 21% 4	774
September	1st to 10th	Night	15% 5% 22% 36% 20% 2	720
	11th to 20th	Night	19% 7% 19% 30% 21% 4	720
	21st to end	Night	18% 7% 23% 31% 18% 3	720
October	1st to 10th	Night	23% 10% 18% 29% 17% 2	720
	11th to 20th	Night	21% 10% 24% 31% 13% 1	720
	21st to end	Night	30% 13% 22% 27% 7%	792
November	1st to 10th	Night	20% 12% 27% 30% 9% 2	740
	11th to 20th	Night	22% 15% 29% 26% 7% 1	760
	21st to end	Night	22% 18% 24% 29% 6%	760
December	1st to 10th	Night	26% 13% 30% 25% 6% 1	760
	11th to 20th	Night	25% 15% 27% 29% 4	760
	21st to end	Night	27% 15% 28% 28% 3	836

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