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 2026-05-02.

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	15% 9% 3 8% 5% 5% 5% 4 5% 7% 34%	132062
	Night	15% 10% 3 8% 5% 5% 5% 4 5% 7% 33%	130413
Transparency	Day	47% 6% 13% 21% 11% 1	135648
	Night	50% 7% 11% 20% 11% 1	134913
Seeing	Day	18% 11% 27% 26% 13% 4	16266
	Night	19% 10% 29% 28% 12% 2	25723

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% 12% 4 10% 6% 6% 5% 3 5% 6% 27%	4661
	11th to 20th	Day	10% 20% 8% 17% 9% 6% 4 3 4 4 13%	4906
	21st to end	Day	13% 15% 7% 14% 6% 6% 5% 3 4 5% 21%	5780
February	1st to 10th	Day	15% 14% 5% 12% 8% 6% 6% 3 5% 5% 22%	1890
	11th to 20th	Day	14% 13% 6% 12% 7% 6% 4 3 5% 6% 25%	1843
	21st to end	Day	18% 13% 5% 11% 6% 5% 4 3 5% 4 27%	1620
March	1st to 10th	Day	20% 10% 4 9% 5% 4 4 3 4 5% 32%	5010
	11th to 20th	Day	11% 12% 4 9% 5% 6% 6% 4 5% 8% 30%	5090
	21st to end	Day	19% 9% 3 7% 4 4 4 3 5% 5% 36%	5601
April	1st to 10th	Day	18% 10% 4 9% 6% 4 6% 4 5% 6% 30%	2520
	11th to 20th	Day	20% 9% 3 7% 5% 3 4 3 5% 6% 36%	2518
	21st to end	Day	19% 9% 3 7% 5% 5% 5% 4 4 6% 34%	2730
May	1st to 10th	Day	19% 8% 3 8% 5% 5% 5% 3 5% 7% 31%	6026
	11th to 20th	Day	16% 10% 3 8% 5% 4 4 3 5% 8% 33%	6318
	21st to end	Day	17% 7% 3 7% 4 4 4 3 5% 8% 38%	6949
June	1st to 10th	Day	15% 6% 2 7% 4 5% 5% 5% 6% 9% 37%	2800
	11th to 20th	Day	12% 5% 2 5% 4 4 5% 5% 7% 9% 41%	2800
	21st to end	Day	13% 6% 2 6% 4 4 4 4 7% 8% 41%	2800
July	1st to 10th	Day	9% 6% 2 6% 5% 5% 5% 4 7% 10% 43%	6360
	11th to 20th	Day	9% 4 2 5% 4 4 5% 4 6% 9% 49%	6360
	21st to end	Day	6% 4 2 5% 4 5% 5% 5% 7% 9% 48%	6661
August	1st to 10th	Day	15% 7% 2 6% 4 4 5% 3 5% 8% 40%	4234
	11th to 20th	Day	11% 6% 2 6% 4 4 5% 5% 7% 10% 39%	4174
	21st to end	Day	9% 5% 2 6% 4 4 5% 4 6% 10% 44%	4426
September	1st to 10th	Day	13% 5% 2 5% 4 5% 5% 5% 5% 7% 46%	2400
	11th to 20th	Day	10% 5% 1 5% 3 3 5% 4 6% 8% 49%	2345
	21st to end	Day	14% 5% 2 7% 4 5% 5% 4 6% 7% 41%	2120
October	1st to 10th	Day	16% 8% 3 6% 4 5% 5% 4 5% 7% 37%	2000
	11th to 20th	Day	18% 10% 3 7% 6% 5% 3 4 5% 7% 33%	2000
	21st to end	Day	22% 10% 3 9% 6% 5% 5% 3 5% 6% 27%	2200
November	1st to 10th	Day	16% 8% 3 8% 5% 5% 5% 4 5% 8% 33%	1766
	11th to 20th	Day	14% 11% 4 9% 6% 5% 6% 4 6% 8% 27%	1680
	21st to end	Day	19% 14% 4 7% 6% 4 5% 4 6% 7% 24%	1680
December	1st to 10th	Day	18% 16% 5% 11% 8% 7% 5% 4 5% 5% 16%	2680
	11th to 20th	Day	19% 14% 5% 9% 5% 5% 5% 3 4 6% 25%	3066
	21st to end	Day	25% 16% 6% 11% 6% 4 4 3 4 4 17%	4048
January	1st to 10th	Night	15% 13% 5% 11% 6% 6% 5% 3 5% 6% 25%	8234
	11th to 20th	Night	12% 16% 6% 14% 8% 6% 5% 4 6% 6% 16%	7965
	21st to end	Night	12% 13% 5% 11% 6% 6% 6% 4 6% 7% 24%	8401
February	1st to 10th	Night	14% 15% 4 9% 6% 6% 5% 4 5% 6% 25%	2730
	11th to 20th	Night	14% 13% 5% 10% 7% 5% 5% 3 5% 6% 27%	2663
	21st to end	Night	15% 11% 4 8% 5% 5% 6% 5% 6% 6% 28%	2186
March	1st to 10th	Night	17% 10% 4 8% 6% 5% 5% 4 5% 5% 32%	5047
	11th to 20th	Night	12% 8% 3 7% 5% 5% 5% 4 6% 8% 37%	5089
	21st to end	Night	21% 7% 2 5% 4 4 3 3 4 6% 40%	5572
April	1st to 10th	Night	19% 10% 3 7% 5% 4 5% 4 5% 7% 33%	2100
	11th to 20th	Night	16% 8% 3 8% 4 5% 5% 4 4 6% 37%	2069
	21st to end	Night	17% 8% 3 7% 4 5% 5% 4 5% 8% 35%	1890
May	1st to 10th	Night	25% 8% 3 6% 4 3 4 3 5% 6% 33%	3934
	11th to 20th	Night	14% 7% 2 7% 5% 5% 7% 3 6% 8% 36%	3575
	21st to end	Night	18% 5% 3 6% 4 4 4 4 5% 7% 39%	3926
June	1st to 10th	Night	12% 6% 3 6% 5% 5% 6% 4 6% 7% 40%	1600
	11th to 20th	Night	9% 6% 2 7% 5% 4 5% 5% 7% 10% 43%	1600
	21st to end	Night	11% 6% 3 6% 4 5% 3 4 6% 8% 42%	1600
July	1st to 10th	Night	7% 6% 2 7% 4 5% 5% 4 7% 9% 44%	3600
	11th to 20th	Night	10% 5% 2 6% 4 4 4 4 5% 9% 49%	3600
	21st to end	Night	9% 4 2 5% 3 3 4 4 6% 8% 52%	4188
August	1st to 10th	Night	10% 5% 2 6% 4 4 4 4 5% 8% 48%	2915
	11th to 20th	Night	12% 5% 2 6% 4 4 4 3 5% 7% 50%	2875
	21st to end	Night	10% 5% 2 5% 3 4 4 4 6% 9% 48%	3439
September	1st to 10th	Night	11% 5% 2 5% 4 4 5% 3 6% 6% 49%	2000
	11th to 20th	Night	10% 5% 1 4 3 4 4 4 6% 6% 54%	2050
	21st to end	Night	17% 6% 2 6% 4 4 4 3 4 6% 43%	2280
October	1st to 10th	Night	14% 6% 2 7% 5% 4 4 4 5% 7% 41%	2400
	11th to 20th	Night	19% 9% 3 7% 5% 4 4 4 5% 7% 34%	2400
	21st to end	Night	20% 8% 3 7% 4 5% 5% 4 6% 6% 32%	2640
November	1st to 10th	Night	16% 8% 3 6% 4 4 5% 4 6% 6% 37%	2747
	11th to 20th	Night	16% 11% 3 7% 6% 5% 5% 4 6% 8% 29%	2940
	21st to end	Night	20% 12% 4 7% 5% 5% 5% 5% 6% 8% 24%	2940
December	1st to 10th	Night	16% 15% 4 10% 5% 5% 5% 5% 6% 7% 21%	4720
	11th to 20th	Night	18% 15% 4 9% 5% 5% 5% 4 6% 6% 24%	5348
	21st to end	Night	26% 14% 5% 10% 6% 5% 5% 3 4 5% 16%	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% 7% 12% 14% 8%	4662
	11th to 20th	Day	75% 9% 6% 6% 4	4938
	21st to end	Day	65% 6% 9% 12% 7%	5780
February	1st to 10th	Day	64% 7% 10% 14% 4 1	1890
	11th to 20th	Day	60% 6% 10% 16% 7% 1	1852
	21st to end	Day	59% 5% 11% 18% 6%	1620
March	1st to 10th	Day	52% 5% 12% 17% 13% 1	5013
	11th to 20th	Day	49% 5% 19% 16% 9% 2	5090
	21st to end	Day	49% 3 10% 21% 16% 1	5601
April	1st to 10th	Day	50% 6% 12% 19% 12% 2	2520
	11th to 20th	Day	48% 5% 10% 22% 14% 2	2518
	21st to end	Day	49% 4 12% 20% 12% 3	2730
May	1st to 10th	Day	50% 7% 11% 16% 12% 4	6035
	11th to 20th	Day	49% 10% 9% 16% 15% 1	6322
	21st to end	Day	43% 5% 13% 24% 13% 2	6949
June	1st to 10th	Day	42% 7% 13% 21% 15% 1	2800
	11th to 20th	Day	35% 7% 15% 27% 14% 2	2800
	21st to end	Day	37% 6% 16% 25% 15% 1	2800
July	1st to 10th	Day	34% 6% 15% 28% 16% 1	6290
	11th to 20th	Day	30% 6% 14% 34% 16% 1	6285
	21st to end	Day	30% 8% 15% 33% 14%	6470
August	1st to 10th	Day	41% 6% 15% 24% 14% 1	4221
	11th to 20th	Day	37% 6% 17% 30% 10%	4213
	21st to end	Day	33% 6% 13% 36% 10% 1	4426
September	1st to 10th	Day	35% 8% 15% 30% 11% 1	2400
	11th to 20th	Day	31% 6% 15% 32% 14% 1	2345
	21st to end	Day	40% 7% 16% 26% 10% 1	2120
October	1st to 10th	Day	37% 5% 14% 29% 14% 1	3260
	11th to 20th	Day	38% 6% 18% 24% 14% 1	3240
	21st to end	Day	48% 7% 16% 21% 8% 1	3538
November	1st to 10th	Day	47% 7% 14% 21% 10% 1	1766
	11th to 20th	Day	54% 8% 15% 15% 8% 1	1680
	21st to end	Day	59% 6% 14% 16% 4	1680
December	1st to 10th	Day	68% 7% 12% 10% 2	2680
	11th to 20th	Day	61% 8% 11% 11% 8%	3066
	21st to end	Day	71% 6% 7% 11% 4	4048
January	1st to 10th	Night	59% 7% 11% 16% 6%	8234
	11th to 20th	Night	68% 12% 5% 9% 5%	8008
	21st to end	Night	60% 10% 8% 13% 8%	8401
February	1st to 10th	Night	61% 7% 11% 16% 5% 1	2730
	11th to 20th	Night	59% 5% 10% 17% 8%	2665
	21st to end	Night	56% 6% 12% 18% 7% 1	2186
March	1st to 10th	Night	53% 5% 10% 17% 12% 3	5057
	11th to 20th	Night	44% 6% 16% 21% 11% 1	5090
	21st to end	Night	46% 4 8% 21% 18% 2	5572
April	1st to 10th	Night	51% 5% 10% 19% 13% 1	2100
	11th to 20th	Night	48% 6% 9% 20% 16% 2	2069
	21st to end	Night	46% 6% 11% 21% 14% 2	1890
May	1st to 10th	Night	52% 6% 11% 13% 13% 5%	3941
	11th to 20th	Night	46% 9% 10% 20% 13% 2	3576
	21st to end	Night	44% 6% 11% 22% 15% 2	3927
June	1st to 10th	Night	42% 7% 10% 23% 16% 3	1600
	11th to 20th	Night	36% 7% 12% 23% 21% 3	1600
	21st to end	Night	39% 7% 14% 24% 16% 1	1600
July	1st to 10th	Night	35% 6% 14% 23% 20% 2	3560
	11th to 20th	Night	34% 5% 12% 32% 17% 1	3552
	21st to end	Night	30% 6% 12% 30% 22% 1	4064
August	1st to 10th	Night	35% 5% 14% 29% 15% 2	2904
	11th to 20th	Night	34% 5% 15% 31% 13% 1	2902
	21st to end	Night	33% 6% 12% 34% 14% 1	3439
September	1st to 10th	Night	34% 6% 14% 30% 14% 2	2000
	11th to 20th	Night	30% 6% 13% 33% 17% 1	2050
	21st to end	Night	43% 5% 10% 27% 13% 1	2280
October	1st to 10th	Night	35% 5% 10% 27% 23% 1	3920
	11th to 20th	Night	43% 5% 14% 30% 8%	3899
	21st to end	Night	41% 6% 14% 28% 10% 1	4252
November	1st to 10th	Night	45% 6% 13% 21% 13% 1	2747
	11th to 20th	Night	52% 8% 13% 17% 10% 1	2940
	21st to end	Night	59% 7% 14% 15% 4	2940
December	1st to 10th	Night	62% 7% 14% 14% 4	4720
	11th to 20th	Night	61% 8% 11% 13% 7%	5348
	21st to end	Night	71% 7% 10% 9% 5%	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	24% 20% 32% 17% 7% 1	220
	11th to 20th	Day	27% 25% 32% 12% 4 1	267
	21st to end	Day	23% 23% 31% 19% 4	363
February	1st to 10th	Day	24% 22% 34% 15% 4	330
	11th to 20th	Day	24% 22% 36% 17% 1	330
	21st to end	Day	27% 22% 34% 16% 1	336
March	1st to 10th	Day	23% 16% 35% 21% 5%	540
	11th to 20th	Day	22% 19% 32% 21% 5% 1	540
	21st to end	Day	27% 14% 32% 18% 7% 1	594
April	1st to 10th	Day	23% 16% 32% 23% 6% 1	540
	11th to 20th	Day	25% 15% 28% 20% 8% 3	532
	21st to end	Day	23% 11% 35% 22% 8% 1	540
May	1st to 10th	Day	20% 9% 28% 29% 11% 4	507
	11th to 20th	Day	17% 7% 24% 33% 16% 4	527
	21st to end	Day	13% 6% 23% 33% 20% 5%	573
June	1st to 10th	Day	16% 6% 27% 33% 15% 2	530
	11th to 20th	Day	12% 8% 24% 34% 20% 3	530
	21st to end	Day	16% 8% 22% 34% 16% 4	530
July	1st to 10th	Day	9% 4 22% 35% 24% 6%	525
	11th to 20th	Day	13% 4 21% 34% 22% 7%	524
	21st to end	Day	8% 4 24% 41% 18% 4	576
August	1st to 10th	Day	12% 3 19% 36% 23% 7%	526
	11th to 20th	Day	11% 4 19% 33% 26% 8%	519
	21st to end	Day	11% 4 23% 36% 19% 7%	583
September	1st to 10th	Day	12% 7% 22% 28% 22% 9%	530
	11th to 20th	Day	10% 3 17% 32% 24% 14%	530
	21st to end	Day	16% 7% 26% 30% 15% 5%	530
October	1st to 10th	Day	20% 8% 25% 25% 17% 5%	530
	11th to 20th	Day	18% 16% 32% 23% 8% 2	530
	21st to end	Day	25% 16% 29% 21% 8% 1	583
November	1st to 10th	Day	23% 17% 28% 24% 8% 1	329
	11th to 20th	Day	20% 21% 35% 19% 4 1	220
	21st to end	Day	29% 14% 36% 17% 4	220
December	1st to 10th	Day	22% 19% 35% 18% 5%	220
	11th to 20th	Day	26% 24% 33% 15% 2	220
	21st to end	Day	30% 19% 35% 14% 2	242
January	1st to 10th	Night	23% 19% 38% 15% 6%	840
	11th to 20th	Night	28% 16% 33% 19% 4	840
	21st to end	Night	21% 15% 35% 24% 5% 1	924
February	1st to 10th	Night	21% 17% 40% 19% 3	840
	11th to 20th	Night	21% 17% 36% 23% 3	823
	21st to end	Night	22% 16% 38% 21% 4	692
March	1st to 10th	Night	21% 13% 36% 25% 4	840
	11th to 20th	Night	21% 15% 34% 25% 4 1	840
	21st to end	Night	20% 11% 33% 25% 10% 1	924
April	1st to 10th	Night	23% 10% 33% 28% 6%	840
	11th to 20th	Night	19% 11% 32% 27% 11% 1	825
	21st to end	Night	19% 8% 30% 30% 12%	630
May	1st to 10th	Night	22% 5% 24% 33% 14% 3	553
	11th to 20th	Night	15% 4 27% 39% 14% 1	394
	21st to end	Night	12% 3 20% 39% 24% 2	433
June	1st to 10th	Night	12% 3 25% 42% 17% 2	400
	11th to 20th	Night	10% 3 23% 43% 19% 2	400
	21st to end	Night	12% 3 22% 43% 20% 1	400
July	1st to 10th	Night	5% 3 15% 51% 23% 3	390
	11th to 20th	Night	11% 3 16% 38% 29% 2	388
	21st to end	Night	11% 3 15% 45% 24% 3	547
August	1st to 10th	Night	10% 2 14% 38% 31% 4	597
	11th to 20th	Night	10% 3 14% 36% 33% 5%	594
	21st to end	Night	12% 4 20% 36% 26% 3	785
September	1st to 10th	Night	12% 4 20% 34% 26% 4	800
	11th to 20th	Night	12% 3 17% 33% 28% 7%	800
	21st to end	Night	18% 7% 20% 28% 23% 5%	800
October	1st to 10th	Night	18% 5% 28% 27% 20% 3	800
	11th to 20th	Night	23% 11% 29% 26% 10% 1	800
	21st to end	Night	22% 12% 32% 28% 6%	880
November	1st to 10th	Night	22% 11% 26% 30% 10% 1	820
	11th to 20th	Night	20% 16% 34% 23% 6% 1	840
	21st to end	Night	26% 12% 33% 22% 6%	840
December	1st to 10th	Night	27% 15% 34% 20% 4	840
	11th to 20th	Night	24% 15% 36% 21% 4 1	840
	21st to end	Night	31% 14% 35% 17% 2	924

Page generated at 2026-04-29 02:21:43. Version ac07

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