Newmarket
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Newmarket clear sky chart from 2005-11-06 to 2026-09-14.

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	14% 10% 4 9% 5% 5% 5% 4 5% 7% 32%	149957
	Night	14% 11% 4 9% 6% 5% 5% 4 5% 6% 32%	141072
Transparency	Day	49% 7% 12% 20% 10% 1	153551
	Night	49% 7% 13% 20% 11% 1	145566
Seeing	Day	20% 16% 31% 20% 9% 3	17050
	Night	19% 14% 32% 25% 9% 1	26078

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	15% 13% 5% 14% 9% 6% 6% 4 5% 6% 18%	4661
	11th to 20th	Day	9% 19% 9% 18% 9% 8% 5% 3 4 4 11%	5046
	21st to end	Day	12% 15% 7% 16% 8% 7% 6% 3 5% 5% 16%	5780
February	1st to 10th	Day	14% 17% 4 15% 7% 6% 4 4 4 5% 19%	1890
	11th to 20th	Day	12% 16% 6% 14% 8% 5% 5% 4 4 6% 20%	1843
	21st to end	Day	16% 16% 6% 10% 7% 5% 4 3 5% 5% 23%	1608
March	1st to 10th	Day	17% 12% 5% 10% 6% 5% 4 3 4 5% 29%	5042
	11th to 20th	Day	11% 13% 5% 11% 6% 6% 5% 3 5% 7% 28%	5090
	21st to end	Day	18% 15% 4 8% 5% 4 3 3 4 5% 32%	5586
April	1st to 10th	Day	17% 15% 4 10% 5% 4 4 3 6% 5% 27%	2483
	11th to 20th	Day	19% 12% 4 7% 4 3 3 3 5% 5% 34%	2581
	21st to end	Day	19% 11% 3 8% 5% 4 3 4 4 6% 33%	2730
May	1st to 10th	Day	18% 9% 3 8% 5% 4 4 3 5% 7% 33%	7642
	11th to 20th	Day	14% 9% 3 8% 5% 4 4 4 5% 7% 36%	8216
	21st to end	Day	17% 7% 2 6% 4 4 4 3 5% 6% 42%	9060
June	1st to 10th	Day	15% 7% 3 6% 5% 4 5% 4 7% 7% 37%	2940
	11th to 20th	Day	13% 6% 2 6% 5% 5% 4 6% 7% 9% 38%	2946
	21st to end	Day	14% 6% 3 7% 5% 5% 5% 4 6% 8% 38%	3150
July	1st to 10th	Day	12% 6% 3 7% 5% 6% 6% 4 7% 8% 37%	8501
	11th to 20th	Day	8% 4 2 6% 4 4 5% 4 6% 10% 47%	8280
	21st to end	Day	10% 5% 2 6% 4 5% 5% 4 6% 8% 44%	8466
August	1st to 10th	Day	17% 7% 3 7% 4 5% 5% 3 6% 6% 37%	6014
	11th to 20th	Day	11% 6% 2 7% 5% 5% 5% 4 7% 9% 38%	5951
	21st to end	Day	14% 7% 2 7% 5% 5% 5% 4 6% 8% 37%	6343
September	1st to 10th	Day	13% 6% 2 7% 5% 4 5% 4 6% 8% 40%	2520
	11th to 20th	Day	11% 6% 2 5% 4 3 5% 4 6% 8% 44%	2321
	21st to end	Day	14% 8% 3 8% 6% 5% 4 4 5% 6% 36%	2156
October	1st to 10th	Day	18% 9% 3 7% 4 5% 4 3 5% 6% 36%	2000
	11th to 20th	Day	20% 11% 4 8% 5% 4 5% 3 5% 6% 29%	2000
	21st to end	Day	24% 14% 3 8% 4 5% 4 4 6% 5% 21%	2200
November	1st to 10th	Day	15% 15% 4 8% 4 4 5% 4 5% 6% 29%	1757
	11th to 20th	Day	14% 15% 4 10% 7% 6% 5% 4 5% 7% 23%	1680
	21st to end	Day	17% 17% 6% 13% 7% 5% 5% 3 4 5% 18%	1680
December	1st to 10th	Day	16% 23% 7% 12% 6% 5% 6% 4 5% 5% 12%	2680
	11th to 20th	Day	17% 20% 5% 12% 6% 5% 4 4 4 5% 19%	3066
	21st to end	Day	21% 16% 6% 18% 6% 5% 4 3 4 4 12%	4048
January	1st to 10th	Night	13% 13% 6% 14% 8% 7% 5% 4 5% 6% 19%	8234
	11th to 20th	Night	10% 15% 7% 18% 11% 7% 6% 4 5% 4 12%	7837
	21st to end	Night	12% 13% 6% 12% 9% 6% 6% 4 6% 6% 20%	8401
February	1st to 10th	Night	12% 16% 5% 11% 6% 5% 5% 6% 5% 5% 23%	2730
	11th to 20th	Night	13% 14% 6% 11% 6% 6% 5% 4 6% 6% 23%	2663
	21st to end	Night	13% 13% 5% 12% 5% 5% 5% 4 6% 6% 26%	2194
March	1st to 10th	Night	15% 11% 5% 10% 6% 6% 5% 3 5% 6% 29%	5018
	11th to 20th	Night	9% 10% 4 9% 5% 5% 5% 5% 7% 7% 34%	5089
	21st to end	Night	18% 9% 4 11% 5% 4 4 3 5% 5% 34%	5588
April	1st to 10th	Night	18% 12% 3 8% 5% 4 5% 3 6% 5% 30%	2137
	11th to 20th	Night	16% 9% 3 7% 5% 4 4 3 5% 5% 38%	2006
	21st to end	Night	15% 10% 3 7% 5% 4 4 4 5% 6% 36%	1890
May	1st to 10th	Night	19% 8% 3 6% 4 4 4 3 5% 7% 37%	5257
	11th to 20th	Night	14% 7% 2 7% 5% 5% 5% 3 6% 7% 39%	4641
	21st to end	Night	17% 7% 2 5% 3 3 3 3 4 7% 46%	5114
June	1st to 10th	Night	13% 6% 2 7% 4 4 5% 4 5% 8% 42%	1680
	11th to 20th	Night	10% 5% 2 6% 5% 4 5% 4 7% 9% 42%	1662
	21st to end	Night	11% 7% 2 7% 5% 4 4 4 5% 8% 44%	1470
July	1st to 10th	Night	8% 6% 2 7% 4 4 4 4 6% 8% 47%	4447
	11th to 20th	Night	10% 4 1 5% 3 4 4 3 5% 9% 51%	4680
	21st to end	Night	11% 5% 2 5% 3 4 4 3 6% 8% 49%	5596
August	1st to 10th	Night	13% 8% 3 6% 5% 4 4 3 5% 6% 45%	4135
	11th to 20th	Night	12% 5% 2 6% 3 3 3 3 5% 7% 50%	4095
	21st to end	Night	13% 7% 2 6% 4 4 4 3 6% 8% 43%	4734
September	1st to 10th	Night	9% 6% 2 6% 4 4 5% 4 5% 8% 47%	2100
	11th to 20th	Night	11% 4 2 4 4 4 3 2 5% 5% 55%	2141
	21st to end	Night	16% 8% 3 6% 4 4 3 3 4 7% 42%	2242
October	1st to 10th	Night	15% 7% 3 7% 5% 4 4 3 5% 6% 41%	2400
	11th to 20th	Night	18% 9% 3 8% 5% 5% 4 3 5% 6% 33%	2400
	21st to end	Night	21% 9% 3 8% 5% 4 4 4 5% 6% 29%	2640
November	1st to 10th	Night	18% 12% 3 6% 4 3 5% 3 6% 7% 33%	2753
	11th to 20th	Night	16% 14% 4 8% 6% 5% 5% 4 6% 6% 26%	2940
	21st to end	Night	18% 16% 5% 10% 6% 5% 5% 4 6% 5% 21%	2940
December	1st to 10th	Night	15% 17% 6% 12% 7% 6% 6% 4 6% 6% 16%	4720
	11th to 20th	Night	14% 18% 7% 13% 6% 5% 5% 4 5% 5% 19%	5348
	21st to end	Night	21% 18% 5% 15% 5% 5% 5% 4 4 5% 12%	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	59% 8% 14% 12% 6%	4662
	11th to 20th	Day	74% 6% 8% 8% 3	5080
	21st to end	Day	68% 6% 10% 9% 7%	5780
February	1st to 10th	Day	65% 7% 9% 14% 4 1	1890
	11th to 20th	Day	62% 6% 10% 15% 6% 1	1852
	21st to end	Day	62% 7% 10% 14% 6% 1	1608
March	1st to 10th	Day	55% 6% 13% 14% 11%	5045
	11th to 20th	Day	52% 7% 14% 19% 6% 2	5090
	21st to end	Day	53% 6% 10% 18% 13% 1	5586
April	1st to 10th	Day	56% 6% 10% 17% 10% 1	2483
	11th to 20th	Day	50% 6% 10% 20% 13% 1	2581
	21st to end	Day	51% 7% 11% 17% 12% 2	2730
May	1st to 10th	Day	49% 7% 13% 17% 11% 4	7651
	11th to 20th	Day	46% 8% 11% 19% 16% 1	8220
	21st to end	Day	41% 6% 10% 26% 14% 2	9061
June	1st to 10th	Day	43% 8% 14% 19% 16% 1	2940
	11th to 20th	Day	39% 8% 14% 22% 15% 1	2946
	21st to end	Day	42% 8% 14% 23% 13% 1	3150
July	1st to 10th	Day	42% 8% 15% 23% 12% 1	8432
	11th to 20th	Day	30% 6% 13% 35% 15% 1	8205
	21st to end	Day	35% 8% 13% 29% 14%	8279
August	1st to 10th	Day	46% 7% 13% 17% 14% 2	6001
	11th to 20th	Day	38% 8% 18% 28% 8%	5990
	21st to end	Day	42% 7% 15% 28% 8%	6343
September	1st to 10th	Day	38% 8% 15% 27% 9% 1	2520
	11th to 20th	Day	35% 8% 14% 29% 13%	2321
	21st to end	Day	46% 7% 14% 24% 9%	2156
October	1st to 10th	Day	40% 7% 14% 26% 13% 1	3260
	11th to 20th	Day	43% 7% 15% 21% 13%	3240
	21st to end	Day	55% 8% 14% 17% 6%	3538
November	1st to 10th	Day	52% 9% 13% 18% 8% 1	1757
	11th to 20th	Day	57% 10% 12% 13% 7% 1	1680
	21st to end	Day	66% 7% 12% 13% 2	1680
December	1st to 10th	Day	72% 9% 10% 8% 2	2680
	11th to 20th	Day	65% 8% 11% 10% 6%	3066
	21st to end	Day	73% 8% 6% 8% 5%	4048
January	1st to 10th	Night	59% 8% 15% 14% 4	8234
	11th to 20th	Night	69% 7% 11% 8% 4	7878
	21st to end	Night	59% 8% 12% 11% 10%	8401
February	1st to 10th	Night	59% 8% 10% 17% 5%	2730
	11th to 20th	Night	58% 8% 11% 17% 6%	2665
	21st to end	Night	54% 7% 14% 17% 7%	2194
March	1st to 10th	Night	53% 6% 11% 18% 10% 2	5028
	11th to 20th	Night	43% 8% 18% 21% 8% 2	5090
	21st to end	Night	48% 6% 12% 18% 14% 2	5588
April	1st to 10th	Night	54% 5% 11% 19% 11% 1	2137
	11th to 20th	Night	47% 6% 10% 20% 15% 2	2006
	21st to end	Night	46% 6% 12% 19% 15% 2	1890
May	1st to 10th	Night	45% 7% 11% 17% 15% 5%	5264
	11th to 20th	Night	42% 8% 12% 21% 15% 2	4642
	21st to end	Night	39% 7% 11% 27% 16% 2	5115
June	1st to 10th	Night	38% 7% 12% 24% 18% 2	1680
	11th to 20th	Night	36% 7% 13% 22% 20% 2	1662
	21st to end	Night	38% 7% 14% 23% 16% 1	1470
July	1st to 10th	Night	34% 6% 16% 27% 15% 1	4407
	11th to 20th	Night	30% 5% 13% 33% 18% 1	4632
	21st to end	Night	32% 7% 12% 29% 19% 1	5468
August	1st to 10th	Night	41% 6% 12% 23% 15% 4	4124
	11th to 20th	Night	32% 6% 16% 34% 10% 1	4122
	21st to end	Night	39% 6% 15% 29% 10% 1	4734
September	1st to 10th	Night	34% 7% 17% 29% 13% 1	2100
	11th to 20th	Night	29% 6% 13% 34% 17% 1	2141
	21st to end	Night	42% 8% 12% 27% 11% 1	2242
October	1st to 10th	Night	32% 6% 10% 28% 23% 1	3920
	11th to 20th	Night	43% 6% 16% 22% 12%	3899
	21st to end	Night	42% 8% 16% 25% 9%	4252
November	1st to 10th	Night	48% 6% 14% 21% 9% 1	2753
	11th to 20th	Night	55% 9% 13% 15% 8% 1	2940
	21st to end	Night	60% 10% 15% 12% 2	2940
December	1st to 10th	Night	66% 9% 12% 10% 3	4720
	11th to 20th	Night	64% 9% 9% 12% 7%	5348
	21st to end	Night	71% 9% 10% 8% 3	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	21% 25% 33% 16% 4	220
	11th to 20th	Day	25% 29% 28% 13% 4 1	294
	21st to end	Day	25% 24% 34% 15% 2	363
February	1st to 10th	Day	27% 24% 35% 11% 3	330
	11th to 20th	Day	26% 25% 41% 7% 1	330
	21st to end	Day	33% 24% 34% 10%	289
March	1st to 10th	Day	25% 20% 37% 15% 4	540
	11th to 20th	Day	26% 22% 32% 16% 4 1	540
	21st to end	Day	31% 20% 30% 15% 4 1	594
April	1st to 10th	Day	28% 21% 33% 12% 6%	540
	11th to 20th	Day	31% 20% 25% 15% 6% 3	532
	21st to end	Day	24% 18% 34% 16% 6% 1	540
May	1st to 10th	Day	21% 18% 30% 19% 9% 3	543
	11th to 20th	Day	19% 14% 31% 23% 9% 4	567
	21st to end	Day	18% 14% 29% 24% 11% 4	617
June	1st to 10th	Day	14% 16% 33% 25% 10% 1	570
	11th to 20th	Day	15% 15% 30% 26% 11% 2	576
	21st to end	Day	18% 12% 35% 25% 9% 2	780
July	1st to 10th	Day	10% 8% 30% 32% 16% 4	644
	11th to 20th	Day	12% 8% 30% 29% 14% 7%	564
	21st to end	Day	8% 10% 31% 34% 12% 5%	620
August	1st to 10th	Day	11% 8% 29% 29% 15% 8%	566
	11th to 20th	Day	11% 9% 26% 27% 21% 7%	559
	21st to end	Day	14% 9% 30% 24% 16% 7%	627
September	1st to 10th	Day	14% 11% 28% 26% 15% 8%	570
	11th to 20th	Day	8% 8% 26% 25% 22% 12%	542
	21st to end	Day	15% 11% 32% 23% 14% 5%	530
October	1st to 10th	Day	21% 14% 27% 19% 15% 4	530
	11th to 20th	Day	22% 21% 34% 15% 7% 2	530
	21st to end	Day	28% 17% 34% 17% 4	583
November	1st to 10th	Day	26% 22% 28% 18% 6%	298
	11th to 20th	Day	26% 25% 30% 15% 3 1	220
	21st to end	Day	30% 22% 36% 10% 2	220
December	1st to 10th	Day	24% 24% 36% 12% 4	220
	11th to 20th	Day	31% 23% 30% 12% 4	220
	21st to end	Day	29% 23% 35% 11% 1 1	242
January	1st to 10th	Night	21% 23% 36% 15% 4	840
	11th to 20th	Night	25% 19% 33% 19% 4	840
	21st to end	Night	19% 15% 40% 20% 6%	924
February	1st to 10th	Night	21% 19% 39% 20% 1	840
	11th to 20th	Night	23% 18% 37% 20% 2	823
	21st to end	Night	20% 22% 37% 18% 3	692
March	1st to 10th	Night	20% 20% 37% 20% 3	840
	11th to 20th	Night	22% 20% 34% 19% 5% 1	840
	21st to end	Night	21% 17% 34% 21% 6%	924
April	1st to 10th	Night	26% 15% 35% 21% 3	840
	11th to 20th	Night	19% 16% 36% 21% 7% 1	762
	21st to end	Night	19% 13% 34% 26% 7%	630
May	1st to 10th	Night	18% 9% 31% 30% 11% 1	630
	11th to 20th	Night	16% 9% 32% 32% 10% 1	416
	21st to end	Night	14% 7% 30% 34% 15% 1	455
June	1st to 10th	Night	14% 8% 34% 33% 11%	420
	11th to 20th	Night	12% 9% 31% 35% 13%	420
	21st to end	Night	13% 8% 28% 39% 11%	420
July	1st to 10th	Night	6% 6% 28% 42% 18% 1	410
	11th to 20th	Night	9% 7% 27% 38% 19% 1	408
	21st to end	Night	8% 5% 27% 40% 18% 1	638
August	1st to 10th	Night	11% 4 20% 38% 27% 1	627
	11th to 20th	Night	7% 6% 19% 42% 24% 3	624
	21st to end	Night	12% 6% 26% 34% 20% 2	778
September	1st to 10th	Night	10% 8% 28% 32% 19% 4	840
	11th to 20th	Night	12% 6% 23% 31% 24% 5%	813
	21st to end	Night	17% 9% 23% 31% 16% 3	800
October	1st to 10th	Night	17% 10% 30% 26% 16% 1	800
	11th to 20th	Night	22% 15% 32% 23% 8% 1	800
	21st to end	Night	26% 13% 35% 22% 4	880
November	1st to 10th	Night	24% 14% 31% 22% 8%	820
	11th to 20th	Night	22% 20% 32% 19% 6% 1	840
	21st to end	Night	25% 17% 33% 21% 4	840
December	1st to 10th	Night	26% 17% 37% 17% 3	840
	11th to 20th	Night	22% 21% 38% 17% 3	840
	21st to end	Night	30% 16% 38% 15% 2	924

Page generated at 2026-09-11 04:11:53. Version ac07

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