Newcastle Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Newcastle Observatory clear sky chart from 2005-11-06 to 2026-07-31.

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% 9% 3 7% 5% 4 4 4 5% 7% 36%	138703
	Night	16% 10% 3 7% 5% 4 4 4 5% 6% 35%	134280
Transparency	Day	48% 3 12% 23% 12% 1	142287
	Night	49% 3 12% 22% 13% 1	138784
Seeing	Day	21% 11% 30% 23% 11% 4	16626
	Night	21% 11% 29% 27% 11% 1	25890

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% 13% 5% 10% 4 4 4 4 5% 6% 29%	4661
	11th to 20th	Day	11% 21% 8% 15% 7% 5% 5% 3 4 4 17%	4844
	21st to end	Day	14% 16% 7% 13% 6% 5% 4 3 4 5% 23%	5780
February	1st to 10th	Day	15% 15% 6% 11% 7% 4 5% 4 5% 5% 24%	1890
	11th to 20th	Day	12% 16% 6% 11% 7% 6% 5% 3 4 5% 26%	1843
	21st to end	Day	18% 14% 5% 10% 6% 5% 4 3 5% 5% 27%	1630
March	1st to 10th	Day	19% 12% 4 8% 4 4 4 3 4 6% 32%	4968
	11th to 20th	Day	12% 12% 4 9% 5% 4 4 4 6% 7% 31%	5090
	21st to end	Day	20% 11% 2 6% 4 3 3 3 4 5% 39%	5627
April	1st to 10th	Day	18% 13% 3 8% 5% 5% 4 3 4 5% 31%	2520
	11th to 20th	Day	22% 9% 3 6% 4 3 4 2 4 6% 37%	2504
	21st to end	Day	20% 9% 3 6% 5% 5% 5% 3 5% 4 35%	2730
May	1st to 10th	Day	21% 8% 3 7% 4 4 4 4 5% 7% 33%	7854
	11th to 20th	Day	18% 7% 3 7% 5% 4 4 3 5% 7% 38%	8221
	21st to end	Day	19% 5% 2 5% 4 3 4 3 5% 7% 42%	9060
June	1st to 10th	Day	17% 6% 2 5% 4 5% 5% 4 7% 8% 37%	2940
	11th to 20th	Day	12% 5% 2 5% 4 5% 5% 5% 7% 9% 41%	2940
	21st to end	Day	16% 5% 2 6% 4 4 5% 4 6% 8% 40%	2940
July	1st to 10th	Day	11% 5% 2 6% 5% 4 5% 4 6% 9% 43%	6500
	11th to 20th	Day	11% 4 1 5% 4 4 5% 4 6% 9% 48%	6500
	21st to end	Day	7% 4 2 5% 4 4 5% 5% 7% 9% 48%	6849
August	1st to 10th	Day	17% 7% 3 6% 4 4 4 4 5% 7% 40%	4234
	11th to 20th	Day	14% 5% 2 5% 5% 5% 5% 4 6% 9% 40%	4174
	21st to end	Day	11% 5% 2 5% 4 4 5% 4 7% 9% 44%	4416
September	1st to 10th	Day	13% 5% 2 5% 5% 4 4 3 6% 7% 46%	2400
	11th to 20th	Day	10% 5% 2 5% 4 4 4 4 6% 7% 51%	2364
	21st to end	Day	15% 6% 2 6% 5% 4 5% 4 6% 7% 41%	2110
October	1st to 10th	Day	19% 6% 2 6% 5% 5% 4 4 5% 7% 38%	2000
	11th to 20th	Day	20% 9% 2 7% 5% 4 4 4 5% 6% 33%	2000
	21st to end	Day	23% 10% 3 8% 5% 4 4 3 5% 5% 29%	2200
November	1st to 10th	Day	15% 10% 3 6% 5% 5% 5% 4 6% 7% 36%	1760
	11th to 20th	Day	15% 13% 3 7% 6% 5% 4 4 6% 8% 29%	1680
	21st to end	Day	20% 13% 4 8% 5% 4 4 4 6% 7% 25%	1680
December	1st to 10th	Day	18% 17% 4 10% 6% 6% 5% 4 5% 5% 20%	2680
	11th to 20th	Day	19% 16% 5% 9% 4 4 4 3 4 5% 27%	3066
	21st to end	Day	25% 15% 5% 11% 4 4 3 3 4 5% 19%	4048
January	1st to 10th	Night	15% 15% 6% 10% 5% 5% 5% 4 5% 6% 26%	8234
	11th to 20th	Night	13% 17% 6% 12% 7% 5% 5% 3 5% 6% 21%	8038
	21st to end	Night	13% 13% 5% 11% 5% 4 5% 4 6% 5% 30%	8401
February	1st to 10th	Night	13% 16% 4 9% 6% 5% 6% 4 5% 5% 28%	2730
	11th to 20th	Night	15% 13% 5% 10% 6% 5% 5% 3 6% 6% 29%	2663
	21st to end	Night	14% 13% 4 9% 5% 4 5% 4 5% 6% 31%	2175
March	1st to 10th	Night	17% 10% 3 9% 5% 5% 4 4 5% 5% 33%	5074
	11th to 20th	Night	12% 8% 3 7% 5% 5% 5% 4 6% 7% 38%	5089
	21st to end	Night	21% 8% 3 6% 3 3 3 3 4 5% 42%	5547
April	1st to 10th	Night	20% 9% 3 6% 5% 4 5% 4 6% 7% 33%	2100
	11th to 20th	Night	17% 8% 2 8% 5% 4 4 3 5% 6% 38%	2075
	21st to end	Night	17% 7% 3 7% 4 4 5% 5% 6% 6% 37%	1898
May	1st to 10th	Night	25% 7% 2 6% 4 4 4 4 5% 6% 33%	5043
	11th to 20th	Night	15% 6% 3 7% 4 5% 4 4 6% 7% 40%	4639
	21st to end	Night	19% 6% 2 6% 3 4 4 3 5% 7% 43%	5114
June	1st to 10th	Night	12% 6% 2 6% 5% 4 5% 5% 7% 7% 40%	1680
	11th to 20th	Night	9% 5% 2 7% 4 5% 5% 5% 6% 8% 45%	1680
	21st to end	Night	12% 7% 3 6% 4 4 4 3 6% 8% 42%	1680
July	1st to 10th	Night	9% 5% 2 6% 5% 4 5% 4 6% 9% 45%	3680
	11th to 20th	Night	11% 4 2 5% 4 4 4 3 5% 8% 51%	3680
	21st to end	Night	10% 4 2 4 4 3 4 3 5% 8% 53%	4206
August	1st to 10th	Night	11% 4 2 5% 4 4 5% 3 6% 8% 49%	2915
	11th to 20th	Night	13% 4 2 5% 4 4 4 3 5% 7% 51%	2875
	21st to end	Night	10% 4 2 4 3 4 4 4 6% 8% 52%	3449
September	1st to 10th	Night	11% 5% 1 6% 4 4 5% 3 6% 6% 49%	2000
	11th to 20th	Night	11% 4 1 4 3 3 4 4 5% 6% 55%	2033
	21st to end	Night	18% 5% 3 6% 4 4 4 3 3 6% 45%	2290
October	1st to 10th	Night	17% 6% 2 6% 4 4 4 3 5% 7% 43%	2400
	11th to 20th	Night	20% 7% 3 7% 6% 4 5% 4 5% 6% 35%	2400
	21st to end	Night	21% 8% 3 7% 4 4 4 4 5% 7% 33%	2640
November	1st to 10th	Night	17% 8% 2 6% 4 4 5% 4 6% 7% 38%	2754
	11th to 20th	Night	16% 12% 3 6% 5% 4 5% 4 6% 7% 31%	2940
	21st to end	Night	21% 11% 3 7% 5% 4 5% 5% 6% 8% 26%	2940
December	1st to 10th	Night	17% 15% 4 9% 5% 5% 4 4 6% 7% 24%	4720
	11th to 20th	Night	16% 17% 5% 8% 4 5% 4 3 5% 6% 26%	5348
	21st to end	Night	26% 15% 5% 11% 5% 4 4 4 4 5% 18%	7150

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	58% 2 12% 18% 9% 1	4662
	11th to 20th	Day	73% 2 9% 9% 6% 1	4875
	21st to end	Day	65% 2 11% 12% 9% 1	5780
February	1st to 10th	Day	63% 3 10% 18% 5% 1	1890
	11th to 20th	Day	62% 2 8% 16% 10% 1	1852
	21st to end	Day	62% 2 9% 18% 9% 1	1630
March	1st to 10th	Day	55% 2 11% 17% 15% 1	4971
	11th to 20th	Day	53% 2 17% 16% 10% 2	5090
	21st to end	Day	50% 2 7% 22% 18% 2	5627
April	1st to 10th	Day	55% 3 8% 20% 13% 2	2520
	11th to 20th	Day	51% 2 8% 22% 16% 1	2504
	21st to end	Day	52% 3 10% 19% 14% 2	2730
May	1st to 10th	Day	51% 3 11% 20% 11% 3	7863
	11th to 20th	Day	48% 3 12% 22% 15% 1	8225
	21st to end	Day	43% 2 12% 29% 13% 2	9061
June	1st to 10th	Day	44% 4 12% 22% 16% 1	2940
	11th to 20th	Day	38% 4 15% 28% 14% 1	2940
	21st to end	Day	41% 4 14% 25% 14% 1	2940
July	1st to 10th	Day	36% 5% 15% 29% 15% 1	6430
	11th to 20th	Day	32% 4 14% 34% 15% 1	6425
	21st to end	Day	31% 6% 15% 33% 14%	6656
August	1st to 10th	Day	44% 4 14% 24% 13% 1	4221
	11th to 20th	Day	39% 4 15% 31% 10%	4213
	21st to end	Day	35% 5% 13% 36% 10% 1	4416
September	1st to 10th	Day	38% 5% 13% 32% 11% 1	2400
	11th to 20th	Day	33% 3 14% 34% 16% 1	2364
	21st to end	Day	42% 4 15% 27% 11%	2110
October	1st to 10th	Day	38% 3 13% 31% 13% 1	3260
	11th to 20th	Day	40% 4 16% 24% 15% 1	3240
	21st to end	Day	48% 5% 16% 21% 9%	3538
November	1st to 10th	Day	48% 4 13% 24% 12% 1	1760
	11th to 20th	Day	52% 4 15% 17% 10% 1	1680
	21st to end	Day	60% 3 13% 17% 6%	1680
December	1st to 10th	Day	67% 3 14% 11% 4	2680
	11th to 20th	Day	61% 4 11% 14% 10%	3066
	21st to end	Day	69% 3 8% 12% 7%	4048
January	1st to 10th	Night	60% 3 12% 16% 9%	8234
	11th to 20th	Night	66% 2 10% 14% 8% 1	8082
	21st to end	Night	56% 3 11% 15% 14% 1	8401
February	1st to 10th	Night	59% 3 10% 21% 6% 1	2730
	11th to 20th	Night	58% 3 9% 20% 10% 1	2665
	21st to end	Night	54% 3 11% 23% 9% 1	2175
March	1st to 10th	Night	54% 2 9% 18% 13% 4	5084
	11th to 20th	Night	46% 3 15% 23% 12% 2	5090
	21st to end	Night	47% 2 7% 22% 20% 3	5547
April	1st to 10th	Night	51% 3 9% 21% 15% 2	2100
	11th to 20th	Night	48% 3 9% 21% 18% 2	2075
	21st to end	Night	47% 4 10% 21% 16% 2	1898
May	1st to 10th	Night	53% 2 9% 17% 15% 4	5050
	11th to 20th	Night	44% 3 13% 24% 14% 2	4640
	21st to end	Night	43% 2 11% 26% 15% 2	5115
June	1st to 10th	Night	42% 4 10% 25% 16% 3	1680
	11th to 20th	Night	36% 4 12% 24% 21% 3	1680
	21st to end	Night	39% 4 13% 27% 15% 2	1680
July	1st to 10th	Night	35% 5% 16% 23% 20% 1	3640
	11th to 20th	Night	33% 4 12% 33% 18% 1	3632
	21st to end	Night	31% 5% 12% 32% 19% 1	4085
August	1st to 10th	Night	35% 3 15% 29% 16% 2	2904
	11th to 20th	Night	35% 3 16% 32% 13% 2	2902
	21st to end	Night	30% 4 13% 36% 15% 1	3449
September	1st to 10th	Night	35% 4 14% 31% 14% 1	2000
	11th to 20th	Night	30% 3 13% 35% 18% 1	2033
	21st to end	Night	43% 3 10% 29% 14% 1	2290
October	1st to 10th	Night	34% 2 10% 29% 24% 1	3920
	11th to 20th	Night	43% 3 13% 32% 10%	3899
	21st to end	Night	41% 4 15% 28% 11% 1	4252
November	1st to 10th	Night	46% 3 13% 24% 14% 1	2754
	11th to 20th	Night	52% 3 12% 21% 11% 1	2940
	21st to end	Night	57% 4 15% 18% 6%	2940
December	1st to 10th	Night	60% 3 15% 17% 5%	4720
	11th to 20th	Night	60% 4 11% 14% 10% 1	5348
	21st to end	Night	70% 2 11% 11% 6%	7150

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	25% 18% 33% 15% 6% 2	220
	11th to 20th	Day	29% 23% 29% 15% 3 1	255
	21st to end	Day	25% 21% 31% 18% 3	363
February	1st to 10th	Day	27% 22% 35% 14% 2	330
	11th to 20th	Day	25% 27% 33% 15% 1	330
	21st to end	Day	32% 19% 36% 13%	346
March	1st to 10th	Day	24% 19% 34% 19% 4	540
	11th to 20th	Day	29% 18% 30% 18% 4 1	540
	21st to end	Day	33% 12% 33% 15% 6% 1	594
April	1st to 10th	Day	26% 17% 34% 16% 6% 1	540
	11th to 20th	Day	32% 14% 27% 17% 7% 3	532
	21st to end	Day	25% 11% 39% 16% 8% 1	540
May	1st to 10th	Day	24% 10% 34% 21% 8% 4	543
	11th to 20th	Day	18% 10% 30% 27% 11% 4	567
	21st to end	Day	16% 9% 30% 26% 14% 4	617
June	1st to 10th	Day	19% 11% 31% 25% 11% 2	570
	11th to 20th	Day	15% 9% 29% 28% 15% 3	570
	21st to end	Day	18% 8% 29% 29% 12% 4	570
July	1st to 10th	Day	11% 4 25% 35% 19% 6%	565
	11th to 20th	Day	14% 4 27% 32% 16% 7%	564
	21st to end	Day	10% 5% 31% 35% 14% 5%	616
August	1st to 10th	Day	13% 3 27% 30% 19% 8%	526
	11th to 20th	Day	13% 2 25% 30% 21% 8%	519
	21st to end	Day	12% 5% 27% 32% 17% 8%	583
September	1st to 10th	Day	14% 7% 25% 27% 19% 8%	530
	11th to 20th	Day	11% 3 22% 26% 24% 14%	530
	21st to end	Day	17% 7% 31% 25% 14% 6%	530
October	1st to 10th	Day	20% 9% 28% 22% 16% 5%	530
	11th to 20th	Day	22% 14% 33% 22% 7% 2	530
	21st to end	Day	30% 15% 29% 20% 7%	583
November	1st to 10th	Day	26% 14% 28% 23% 8% 1	331
	11th to 20th	Day	24% 22% 31% 18% 4 1	220
	21st to end	Day	28% 17% 35% 16% 3 1	220
December	1st to 10th	Day	26% 17% 36% 15% 4 1	220
	11th to 20th	Day	30% 20% 35% 12% 3	220
	21st to end	Day	33% 18% 32% 14% 2	242
January	1st to 10th	Night	25% 18% 35% 16% 6%	840
	11th to 20th	Night	29% 17% 29% 20% 5% 1	840
	21st to end	Night	22% 14% 35% 23% 5% 1	924
February	1st to 10th	Night	23% 17% 38% 20% 2	840
	11th to 20th	Night	22% 18% 36% 22% 3	823
	21st to end	Night	23% 18% 36% 20% 4	692
March	1st to 10th	Night	21% 16% 34% 25% 4	840
	11th to 20th	Night	23% 14% 37% 21% 4 1	840
	21st to end	Night	22% 13% 33% 25% 7% 1	924
April	1st to 10th	Night	26% 11% 33% 25% 5%	840
	11th to 20th	Night	21% 13% 32% 23% 9% 1	831
	21st to end	Night	21% 8% 31% 28% 11%	638
May	1st to 10th	Night	24% 6% 27% 29% 12% 2	557
	11th to 20th	Night	15% 6% 30% 37% 11%	414
	21st to end	Night	14% 5% 25% 36% 18% 2	455
June	1st to 10th	Night	14% 4 26% 40% 16% 1	420
	11th to 20th	Night	12% 5% 25% 38% 19% 1	420
	21st to end	Night	12% 5% 23% 41% 17%	420
July	1st to 10th	Night	7% 3 18% 50% 20% 1	410
	11th to 20th	Night	11% 2 18% 42% 25% 1	408
	21st to end	Night	12% 1 19% 45% 20% 2	544
August	1st to 10th	Night	11% 2 17% 38% 28% 4	597
	11th to 20th	Night	10% 3 14% 37% 31% 4	594
	21st to end	Night	13% 3 22% 34% 25% 4	795
September	1st to 10th	Night	13% 3 22% 35% 23% 4	800
	11th to 20th	Night	13% 4 19% 32% 26% 7%	800
	21st to end	Night	20% 6% 20% 30% 21% 5%	800
October	1st to 10th	Night	20% 6% 26% 26% 20% 3	800
	11th to 20th	Night	23% 10% 30% 27% 9% 1	800
	21st to end	Night	25% 10% 31% 27% 7%	880
November	1st to 10th	Night	22% 12% 26% 28% 11% 1	820
	11th to 20th	Night	22% 15% 32% 22% 7% 1	840
	21st to end	Night	27% 12% 31% 24% 6%	840
December	1st to 10th	Night	28% 15% 31% 21% 5%	840
	11th to 20th	Night	24% 16% 35% 20% 5%	840
	21st to end	Night	32% 14% 34% 17% 3	924

Page generated at 2026-07-28 03:25:26. Version ac07

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