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 2025-01-07.

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 6% 7% 34%	105130
	Night	16% 10% 3 7% 5% 5% 5% 4 5% 7% 34%	103912
Transparency	Day	46% 7% 14% 22% 11% 1	108730
	Night	49% 7% 12% 20% 11% 1	108400
Seeing	Day	18% 10% 27% 27% 14% 4	14593
	Night	19% 10% 29% 28% 13% 2	24022

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	16% 14% 4 8% 6% 6% 4 3 5% 6% 29%	2565
	11th to 20th	Day	11% 20% 6% 15% 8% 5% 5% 4 5% 5% 17%	2652
	21st to end	Day	21% 18% 7% 11% 5% 5% 4 3 4 5% 18%	3124
February	1st to 10th	Day	15% 14% 4 13% 8% 6% 6% 3 5% 5% 21%	1710
	11th to 20th	Day	13% 14% 6% 12% 6% 5% 4 3 5% 6% 26%	1663
	21st to end	Day	18% 13% 5% 10% 5% 4 4 3 5% 4 28%	1470
March	1st to 10th	Day	20% 9% 3 9% 5% 4 4 4 5% 6% 31%	3415
	11th to 20th	Day	10% 14% 5% 10% 5% 6% 5% 4 5% 6% 30%	3480
	21st to end	Day	17% 8% 3 6% 4 4 4 3 5% 6% 41%	3830
April	1st to 10th	Day	18% 10% 3 8% 6% 4 6% 4 5% 6% 30%	2280
	11th to 20th	Day	19% 9% 3 7% 5% 3 4 3 5% 6% 36%	2276
	21st to end	Day	19% 9% 3 7% 5% 6% 4 4 5% 6% 34%	2470
May	1st to 10th	Day	17% 8% 4 7% 5% 5% 5% 3 6% 7% 33%	4191
	11th to 20th	Day	14% 10% 3 8% 5% 5% 5% 4 6% 8% 32%	4398
	21st to end	Day	11% 6% 2 6% 4 4 4 3 6% 9% 46%	4837
June	1st to 10th	Day	16% 6% 2 7% 4 5% 5% 5% 5% 9% 37%	2660
	11th to 20th	Day	12% 5% 2 5% 4 4 5% 5% 7% 9% 42%	2660
	21st to end	Day	13% 6% 2 6% 4 4 4 4 7% 8% 41%	2660
July	1st to 10th	Day	9% 5% 2 5% 4 4 5% 4 7% 11% 43%	4440
	11th to 20th	Day	10% 4 2 5% 4 4 5% 4 6% 9% 47%	4440
	21st to end	Day	6% 5% 2 6% 5% 5% 5% 5% 8% 9% 44%	4633
August	1st to 10th	Day	15% 8% 3 6% 4 4 5% 4 6% 8% 39%	4104
	11th to 20th	Day	11% 6% 2 6% 4 4 6% 5% 7% 10% 39%	4044
	21st to end	Day	9% 5% 2 6% 4 4 5% 4 7% 10% 44%	4290
September	1st to 10th	Day	13% 5% 2 5% 4 5% 5% 5% 5% 6% 45%	2280
	11th to 20th	Day	11% 5% 1 5% 3 3 4 4 6% 8% 49%	2228
	21st to end	Day	14% 5% 2 7% 4 5% 5% 4 6% 7% 41%	2014
October	1st to 10th	Day	17% 8% 3 6% 4 6% 6% 4 5% 7% 35%	1900
	11th to 20th	Day	18% 10% 3 7% 6% 5% 3 4 5% 7% 33%	1900
	21st to end	Day	22% 10% 3 9% 6% 5% 5% 3 5% 6% 27%	2090
November	1st to 10th	Day	15% 9% 3 9% 5% 5% 5% 4 6% 8% 32%	1680
	11th to 20th	Day	14% 11% 5% 9% 6% 5% 6% 4 7% 8% 27%	1600
	21st to end	Day	19% 14% 4 7% 6% 4 5% 4 6% 7% 24%	1600
December	1st to 10th	Day	18% 15% 5% 11% 8% 7% 5% 4 5% 5% 16%	2600
	11th to 20th	Day	19% 14% 5% 9% 5% 5% 5% 3 4 6% 25%	2986
	21st to end	Day	25% 16% 6% 11% 6% 4 4 3 4 4 16%	3960
January	1st to 10th	Night	18% 14% 5% 9% 5% 6% 5% 4 5% 6% 24%	4514
	11th to 20th	Night	15% 13% 4 12% 9% 6% 6% 4 6% 7% 17%	4308
	21st to end	Night	20% 14% 5% 9% 5% 5% 5% 3 4 6% 23%	4532
February	1st to 10th	Night	14% 16% 4 9% 7% 6% 5% 4 5% 5% 24%	2470
	11th to 20th	Night	14% 13% 5% 9% 7% 5% 4 4 5% 6% 28%	2403
	21st to end	Night	16% 10% 4 8% 5% 5% 5% 5% 5% 6% 29%	1984
March	1st to 10th	Night	18% 9% 3 8% 6% 5% 5% 3 5% 5% 33%	3422
	11th to 20th	Night	15% 10% 4 8% 5% 5% 5% 3 5% 6% 34%	3479
	21st to end	Night	17% 6% 2 4 4 4 3 3 5% 6% 45%	3801
April	1st to 10th	Night	19% 10% 3 6% 4 4 4 4 5% 6% 34%	1900
	11th to 20th	Night	16% 7% 3 7% 4 4 5% 4 4 6% 38%	1870
	21st to end	Night	17% 9% 3 7% 4 5% 5% 4 5% 8% 34%	1710
May	1st to 10th	Night	19% 7% 3 5% 4 4 4 3 5% 7% 38%	2747
	11th to 20th	Night	14% 8% 2 7% 5% 5% 7% 4 6% 8% 35%	2495
	21st to end	Night	10% 5% 2 6% 3 4 4 4 5% 8% 48%	2738
June	1st to 10th	Night	12% 6% 3 6% 5% 5% 6% 4 6% 8% 40%	1520
	11th to 20th	Night	9% 6% 2 7% 5% 3 5% 5% 7% 10% 43%	1520
	21st to end	Night	12% 6% 3 6% 5% 5% 3 4 6% 8% 42%	1520
July	1st to 10th	Night	7% 5% 2 6% 4 5% 5% 4 7% 9% 47%	2520
	11th to 20th	Night	11% 5% 1 5% 4 4 3 4 5% 9% 50%	2520
	21st to end	Night	9% 4 2 4 3 3 4 4 6% 8% 52%	2917
August	1st to 10th	Night	11% 5% 2 6% 4 4 4 4 5% 8% 48%	2825
	11th to 20th	Night	12% 5% 2 6% 4 4 4 3 5% 7% 49%	2785
	21st to end	Night	10% 5% 2 5% 4 4 4 4 6% 8% 48%	3334
September	1st to 10th	Night	12% 5% 2 5% 4 4 5% 3 6% 6% 48%	1900
	11th to 20th	Night	11% 5% 1 4 3 4 4 4 6% 6% 53%	1947
	21st to end	Night	16% 7% 2 6% 4 4 4 3 4 6% 43%	2166
October	1st to 10th	Night	15% 6% 2 7% 5% 4 4 4 5% 7% 40%	2280
	11th to 20th	Night	19% 9% 3 7% 5% 4 4 4 5% 7% 33%	2280
	21st to end	Night	20% 9% 3 7% 5% 5% 5% 4 6% 6% 31%	2508
November	1st to 10th	Night	17% 7% 2 6% 4 4 5% 4 6% 6% 38%	2613
	11th to 20th	Night	16% 11% 3 7% 5% 5% 5% 4 6% 8% 30%	2800
	21st to end	Night	20% 11% 3 7% 5% 5% 5% 5% 6% 8% 25%	2800
December	1st to 10th	Night	17% 15% 4 11% 5% 5% 5% 5% 6% 7% 21%	4580
	11th to 20th	Night	18% 15% 4 9% 5% 5% 5% 4 6% 6% 24%	5208
	21st to end	Night	26% 14% 5% 10% 6% 5% 5% 3 5% 5% 16%	6996

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	57% 9% 16% 11% 6% 1	2566
	11th to 20th	Day	71% 13% 7% 5% 4	2652
	21st to end	Day	70% 7% 10% 9% 3 1	3124
February	1st to 10th	Day	65% 7% 10% 13% 3 1	1710
	11th to 20th	Day	58% 6% 11% 16% 8% 1	1672
	21st to end	Day	58% 5% 12% 18% 7%	1470
March	1st to 10th	Day	52% 6% 12% 20% 9%	3418
	11th to 20th	Day	50% 5% 16% 17% 10% 1	3480
	21st to end	Day	43% 4 13% 23% 16% 2	3830
April	1st to 10th	Day	49% 6% 13% 19% 11% 2	2280
	11th to 20th	Day	47% 5% 10% 21% 15% 2	2276
	21st to end	Day	48% 4 12% 20% 13% 3	2470
May	1st to 10th	Day	47% 7% 13% 18% 14% 2	4203
	11th to 20th	Day	47% 11% 12% 19% 9% 1	4402
	21st to end	Day	33% 6% 15% 27% 16% 3	4837
June	1st to 10th	Day	42% 7% 14% 21% 14% 1	2660
	11th to 20th	Day	35% 7% 15% 26% 15% 2	2660
	21st to end	Day	37% 6% 17% 25% 14% 1	2660
July	1st to 10th	Day	32% 6% 15% 29% 16% 1	4370
	11th to 20th	Day	31% 6% 15% 37% 11%	4365
	21st to end	Day	32% 9% 17% 27% 16% 1	4485
August	1st to 10th	Day	41% 6% 15% 23% 14% 1	4091
	11th to 20th	Day	37% 6% 17% 29% 10%	4083
	21st to end	Day	33% 7% 13% 36% 10% 1	4290
September	1st to 10th	Day	35% 8% 15% 29% 11% 1	2280
	11th to 20th	Day	32% 6% 15% 32% 15% 1	2228
	21st to end	Day	40% 7% 16% 27% 10%	2014
October	1st to 10th	Day	37% 5% 15% 29% 13% 1	3160
	11th to 20th	Day	38% 6% 18% 24% 14% 1	3140
	21st to end	Day	48% 7% 16% 22% 7% 1	3428
November	1st to 10th	Day	47% 7% 14% 21% 10% 1	1680
	11th to 20th	Day	54% 7% 15% 16% 8% 1	1600
	21st to end	Day	59% 6% 14% 16% 4	1600
December	1st to 10th	Day	69% 7% 13% 9% 2	2600
	11th to 20th	Day	61% 8% 11% 11% 8%	2986
	21st to end	Day	71% 7% 6% 11% 4	3960
January	1st to 10th	Night	62% 10% 13% 11% 4	4514
	11th to 20th	Night	67% 18% 6% 7% 3 1	4308
	21st to end	Night	66% 10% 9% 10% 4 1	4532
February	1st to 10th	Night	62% 8% 10% 15% 4 1	2470
	11th to 20th	Night	59% 6% 10% 16% 8% 1	2405
	21st to end	Night	55% 6% 13% 18% 7% 1	1984
March	1st to 10th	Night	53% 5% 10% 22% 8% 1	3432
	11th to 20th	Night	49% 7% 13% 20% 11% 1	3480
	21st to end	Night	40% 5% 9% 24% 19% 3	3801
April	1st to 10th	Night	50% 5% 10% 20% 13% 2	1900
	11th to 20th	Night	48% 6% 9% 19% 17% 2	1870
	21st to end	Night	47% 6% 11% 20% 15% 2	1710
May	1st to 10th	Night	46% 7% 12% 17% 16% 2	2754
	11th to 20th	Night	45% 10% 12% 20% 10% 2	2496
	21st to end	Night	32% 7% 13% 25% 21% 3	2739
June	1st to 10th	Night	42% 7% 10% 22% 16% 2	1520
	11th to 20th	Night	36% 7% 12% 22% 21% 3	1520
	21st to end	Night	39% 7% 13% 24% 16% 1	1520
July	1st to 10th	Night	32% 6% 14% 25% 21% 2	2480
	11th to 20th	Night	33% 5% 13% 34% 14% 1	2472
	21st to end	Night	29% 7% 15% 30% 17% 1	2824
August	1st to 10th	Night	35% 5% 13% 29% 15% 2	2814
	11th to 20th	Night	34% 5% 15% 32% 12% 1	2812
	21st to end	Night	33% 6% 12% 34% 14% 1	3334
September	1st to 10th	Night	35% 7% 14% 28% 14% 2	1900
	11th to 20th	Night	30% 6% 13% 32% 18% 1	1947
	21st to end	Night	43% 5% 11% 27% 13% 1	2166
October	1st to 10th	Night	35% 5% 10% 26% 23% 1	3800
	11th to 20th	Night	43% 6% 14% 30% 8%	3779
	21st to end	Night	41% 6% 15% 28% 10% 1	4120
November	1st to 10th	Night	45% 6% 13% 21% 13% 1	2613
	11th to 20th	Night	51% 8% 13% 17% 10% 1	2800
	21st to end	Night	58% 8% 15% 15% 4	2800
December	1st to 10th	Night	63% 7% 14% 14% 3	4580
	11th to 20th	Night	61% 8% 11% 13% 7%	5208
	21st to end	Night	70% 7% 10% 8% 5%	6996

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	23% 19% 31% 17% 8% 1	192
	11th to 20th	Day	24% 23% 33% 14% 5% 1	218
	21st to end	Day	22% 20% 33% 22% 4	297
February	1st to 10th	Day	22% 24% 35% 15% 4	270
	11th to 20th	Day	21% 21% 40% 17% 1	270
	21st to end	Day	28% 21% 32% 18% 1	282
March	1st to 10th	Day	22% 13% 38% 21% 5%	460
	11th to 20th	Day	19% 19% 33% 23% 5% 1	460
	21st to end	Day	26% 12% 33% 20% 8% 1	506
April	1st to 10th	Day	20% 13% 33% 26% 7% 1	460
	11th to 20th	Day	25% 13% 30% 21% 9% 4	452
	21st to end	Day	23% 10% 33% 24% 8% 2	460
May	1st to 10th	Day	19% 8% 26% 30% 12% 4	463
	11th to 20th	Day	17% 5% 23% 34% 17% 4	487
	21st to end	Day	11% 4 23% 34% 22% 6%	529
June	1st to 10th	Day	16% 6% 26% 34% 16% 2	490
	11th to 20th	Day	13% 7% 22% 34% 21% 3	490
	21st to end	Day	17% 7% 21% 35% 17% 4	490
July	1st to 10th	Day	9% 4 19% 36% 26% 7%	485
	11th to 20th	Day	13% 4 20% 33% 23% 7%	484
	21st to end	Day	8% 3 23% 42% 19% 5%	532
August	1st to 10th	Day	12% 3 18% 34% 24% 8%	486
	11th to 20th	Day	10% 4 19% 32% 27% 8%	479
	21st to end	Day	11% 4 23% 36% 20% 7%	539
September	1st to 10th	Day	11% 6% 23% 28% 22% 9%	490
	11th to 20th	Day	10% 3 18% 31% 23% 15%	490
	21st to end	Day	16% 7% 26% 29% 16% 6%	490
October	1st to 10th	Day	21% 8% 26% 24% 16% 5%	490
	11th to 20th	Day	18% 16% 31% 24% 9% 2	490
	21st to end	Day	25% 16% 29% 22% 8%	539
November	1st to 10th	Day	21% 17% 27% 25% 9% 1	303
	11th to 20th	Day	19% 21% 36% 19% 5% 2	200
	21st to end	Day	28% 13% 36% 19% 5%	200
December	1st to 10th	Day	23% 19% 34% 19% 6% 1	200
	11th to 20th	Day	26% 24% 32% 16% 3 1	200
	21st to end	Day	29% 17% 36% 16% 2	220
January	1st to 10th	Night	23% 18% 37% 16% 6%	785
	11th to 20th	Night	27% 15% 33% 21% 4	760
	21st to end	Night	21% 13% 36% 25% 5% 1	836
February	1st to 10th	Night	22% 17% 40% 19% 3	760
	11th to 20th	Night	21% 16% 37% 23% 4	743
	21st to end	Night	21% 15% 38% 22% 4	628
March	1st to 10th	Night	20% 12% 36% 26% 5%	760
	11th to 20th	Night	21% 14% 34% 25% 5% 1	760
	21st to end	Night	19% 10% 33% 27% 11% 1	836
April	1st to 10th	Night	22% 9% 32% 29% 7%	760
	11th to 20th	Night	18% 10% 33% 26% 12% 1	746
	21st to end	Night	19% 7% 30% 30% 13% 1	570
May	1st to 10th	Night	20% 4 24% 33% 15% 3	523
	11th to 20th	Night	15% 3 27% 39% 15% 1	374
	21st to end	Night	11% 3 19% 39% 25% 2	411
June	1st to 10th	Night	13% 3 23% 42% 17% 2	380
	11th to 20th	Night	9% 3 23% 43% 20% 2	380
	21st to end	Night	12% 3 21% 43% 20% 1	380
July	1st to 10th	Night	5% 3 16% 51% 23% 3	370
	11th to 20th	Night	12% 3 17% 38% 29% 2	368
	21st to end	Night	11% 2 14% 46% 24% 3	519
August	1st to 10th	Night	11% 2 15% 38% 30% 4	567
	11th to 20th	Night	10% 3 14% 36% 32% 5%	564
	21st to end	Night	12% 4 19% 35% 27% 3	746
September	1st to 10th	Night	13% 4 19% 34% 25% 4	760
	11th to 20th	Night	13% 4 17% 32% 28% 8%	760
	21st to end	Night	18% 6% 20% 27% 23% 5%	760
October	1st to 10th	Night	19% 5% 28% 26% 19% 3	760
	11th to 20th	Night	23% 11% 28% 27% 10% 1	760
	21st to end	Night	22% 12% 31% 27% 7%	836
November	1st to 10th	Night	22% 10% 26% 30% 11% 1	780
	11th to 20th	Night	21% 15% 33% 23% 7% 2	800
	21st to end	Night	25% 12% 34% 22% 7%	800
December	1st to 10th	Night	27% 15% 34% 20% 4	800
	11th to 20th	Night	24% 14% 37% 21% 4 1	800
	21st to end	Night	30% 14% 36% 18% 2	880

Page generated at 2025-01-04 03:24:03. Version ac07

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