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 2024-10-25.

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% 10% 4 8% 5% 5% 5% 4 6% 7% 32%	101668
	Night	15% 11% 4 9% 5% 5% 4 4 5% 6% 33%	97107
Transparency	Day	49% 8% 13% 19% 10% 1	101433
	Night	49% 8% 13% 20% 10% 1	96961
Seeing	Day	19% 15% 31% 21% 10% 3	14644
	Night	19% 13% 32% 25% 10% 1	23737

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% 15% 5% 9% 7% 4 5% 4 4 6% 25%	2517
	11th to 20th	Day	10% 19% 8% 16% 9% 6% 5% 3 4 5% 15%	2724
	21st to end	Day	20% 20% 8% 12% 6% 5% 4 3 4 5% 15%	3124
February	1st to 10th	Day	14% 17% 4 15% 7% 7% 5% 4 5% 5% 18%	1710
	11th to 20th	Day	12% 16% 5% 14% 8% 5% 5% 4 5% 6% 21%	1663
	21st to end	Day	16% 15% 5% 11% 6% 5% 4 3 4 5% 24%	1458
March	1st to 10th	Day	17% 13% 5% 10% 5% 5% 3 3 4 5% 30%	3432
	11th to 20th	Day	11% 16% 6% 11% 6% 6% 5% 3 5% 5% 27%	3480
	21st to end	Day	16% 12% 3 8% 6% 4 4 3 5% 5% 35%	3815
April	1st to 10th	Day	17% 15% 4 9% 5% 4 4 3 6% 5% 28%	2247
	11th to 20th	Day	19% 11% 4 7% 4 3 3 3 5% 6% 34%	2333
	21st to end	Day	20% 11% 3 8% 4 4 3 3 4 6% 33%	2470
May	1st to 10th	Day	17% 9% 3 7% 4 4 4 4 5% 8% 33%	4108
	11th to 20th	Day	17% 10% 3 8% 5% 5% 5% 4 6% 7% 32%	4393
	21st to end	Day	12% 6% 2 6% 4 4 4 4 6% 7% 45%	4837
June	1st to 10th	Day	16% 7% 3 7% 5% 4 5% 4 7% 7% 35%	2660
	11th to 20th	Day	13% 6% 2 6% 5% 4 4 5% 7% 9% 39%	2665
	21st to end	Day	15% 6% 3 7% 5% 5% 5% 4 6% 8% 38%	2850
July	1st to 10th	Day	12% 5% 3 7% 5% 5% 6% 5% 7% 9% 37%	4550
	11th to 20th	Day	10% 5% 2 6% 5% 5% 6% 4 7% 9% 42%	4440
	21st to end	Day	9% 6% 2 6% 5% 5% 6% 4 8% 9% 40%	4537
August	1st to 10th	Day	15% 7% 2 7% 4 4 5% 4 7% 8% 36%	4104
	11th to 20th	Day	13% 7% 3 7% 5% 5% 5% 4 7% 9% 35%	4044
	21st to end	Day	11% 6% 2 6% 4 5% 5% 4 6% 9% 42%	4356
September	1st to 10th	Day	13% 6% 2 7% 5% 5% 5% 4 6% 7% 40%	2280
	11th to 20th	Day	11% 7% 2 6% 4 3 5% 4 6% 8% 43%	2171
	21st to end	Day	14% 8% 3 9% 6% 5% 4 4 5% 6% 36%	2048
October	1st to 10th	Day	18% 9% 3 7% 5% 5% 4 3 5% 6% 34%	1900
	11th to 20th	Day	20% 11% 4 8% 5% 4 5% 3 5% 6% 29%	1900
	21st to end	Day	25% 15% 3 8% 5% 4 4 4 5% 5% 21%	2027
November	1st to 10th	Day	14% 15% 3 8% 4 4 5% 4 6% 7% 30%	1587
	11th to 20th	Day	14% 15% 4 10% 7% 6% 5% 4 5% 7% 22%	1520
	21st to end	Day	18% 17% 6% 12% 6% 5% 5% 3 4 5% 19%	1520
December	1st to 10th	Day	15% 20% 7% 14% 6% 5% 6% 4 4 6% 13%	1520
	11th to 20th	Day	17% 15% 4 10% 7% 6% 5% 4 5% 6% 19%	1906
	21st to end	Day	25% 17% 6% 16% 7% 5% 4 3 3 3 11%	2772
January	1st to 10th	Night	16% 15% 6% 12% 7% 6% 5% 3 5% 6% 19%	4429
	11th to 20th	Night	12% 14% 7% 15% 10% 7% 6% 4 5% 5% 15%	4234
	21st to end	Night	18% 14% 7% 11% 9% 5% 4 3 5% 5% 17%	4532
February	1st to 10th	Night	13% 17% 5% 11% 7% 5% 5% 6% 5% 6% 21%	2470
	11th to 20th	Night	13% 14% 6% 11% 6% 6% 5% 4 6% 6% 24%	2403
	21st to end	Night	13% 13% 5% 12% 5% 5% 5% 4 5% 6% 27%	1992
March	1st to 10th	Night	16% 11% 4 8% 6% 5% 5% 3 4 6% 32%	3408
	11th to 20th	Night	12% 13% 4 9% 5% 4 4 3 5% 6% 34%	3479
	21st to end	Night	15% 8% 3 10% 5% 4 4 3 5% 5% 38%	3817
April	1st to 10th	Night	19% 13% 3 7% 5% 4 5% 3 5% 5% 31%	1933
	11th to 20th	Night	16% 9% 3 7% 5% 4 4 3 5% 6% 38%	1813
	21st to end	Night	15% 11% 3 8% 5% 4 4 4 5% 7% 35%	1710
May	1st to 10th	Night	17% 8% 2 7% 5% 4 4 3 5% 7% 39%	2833
	11th to 20th	Night	15% 8% 2 6% 4 5% 4 3 6% 8% 38%	2497
	21st to end	Night	10% 6% 2 5% 4 4 4 3 5% 8% 50%	2738
June	1st to 10th	Night	14% 6% 2 7% 4 4 5% 5% 5% 7% 41%	1520
	11th to 20th	Night	10% 5% 3 5% 6% 4 5% 4 7% 9% 42%	1504
	21st to end	Night	12% 7% 2 6% 5% 4 4 4 5% 8% 43%	1330
July	1st to 10th	Night	7% 5% 2 6% 4 4 4 4 6% 8% 50%	2391
	11th to 20th	Night	13% 4 2 4 4 4 4 3 5% 8% 52%	2520
	21st to end	Night	7% 5% 2 4 4 4 5% 4 7% 8% 50%	3014
August	1st to 10th	Night	10% 6% 3 5% 5% 4 4 3 5% 7% 49%	2825
	11th to 20th	Night	13% 6% 2 5% 3 3 3 3 6% 8% 48%	2785
	21st to end	Night	11% 6% 2 5% 4 4 4 3 5% 8% 48%	3266
September	1st to 10th	Night	9% 6% 2 6% 4 4 5% 4 5% 7% 46%	1900
	11th to 20th	Night	12% 4 2 4 4 4 3 2 5% 6% 53%	2004
	21st to end	Night	16% 8% 3 6% 4 4 4 4 4 7% 41%	2130
October	1st to 10th	Night	16% 8% 3 7% 5% 4 4 3 5% 6% 39%	2280
	11th to 20th	Night	18% 9% 3 8% 5% 5% 4 4 5% 6% 33%	2280
	21st to end	Night	22% 11% 3 8% 5% 4 4 4 5% 6% 26%	2435
November	1st to 10th	Night	18% 10% 3 6% 4 3 4 4 6% 7% 34%	2483
	11th to 20th	Night	17% 13% 4 8% 6% 5% 5% 4 6% 7% 27%	2660
	21st to end	Night	18% 15% 5% 9% 6% 5% 5% 4 6% 5% 22%	2660
December	1st to 10th	Night	18% 16% 6% 11% 6% 5% 5% 4 5% 5% 18%	2660
	11th to 20th	Night	14% 18% 6% 11% 6% 5% 5% 4 5% 6% 18%	3288
	21st to end	Night	26% 18% 5% 13% 5% 5% 5% 4 4 5% 11%	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	56% 10% 16% 13% 5%	2518
	11th to 20th	Day	70% 8% 9% 10% 3	2724
	21st to end	Day	71% 8% 9% 9% 3 1	3124
February	1st to 10th	Day	65% 7% 10% 13% 4 1	1710
	11th to 20th	Day	60% 7% 10% 15% 6% 1	1672
	21st to end	Day	61% 7% 10% 14% 7% 1	1458
March	1st to 10th	Day	54% 8% 13% 16% 9%	3435
	11th to 20th	Day	54% 9% 11% 19% 7% 1	3480
	21st to end	Day	47% 7% 12% 19% 13% 2	3815
April	1st to 10th	Day	56% 6% 11% 17% 9% 1	2247
	11th to 20th	Day	49% 6% 11% 20% 14% 1	2333
	21st to end	Day	51% 7% 10% 17% 12% 3	2470
May	1st to 10th	Day	46% 9% 13% 18% 13% 1	4120
	11th to 20th	Day	48% 10% 13% 20% 9% 1	4397
	21st to end	Day	36% 8% 14% 23% 17% 3	4837
June	1st to 10th	Day	44% 8% 14% 18% 15% 1	2660
	11th to 20th	Day	39% 8% 14% 22% 16% 1	2665
	21st to end	Day	43% 8% 14% 22% 13% 1	2850
July	1st to 10th	Day	40% 8% 15% 22% 15% 1	4480
	11th to 20th	Day	35% 8% 15% 32% 10% 1	4365
	21st to end	Day	37% 10% 14% 23% 16% 1	4392
August	1st to 10th	Day	44% 8% 14% 22% 11% 1	4091
	11th to 20th	Day	42% 8% 16% 24% 10%	4083
	21st to end	Day	36% 7% 14% 32% 10% 1	4356
September	1st to 10th	Day	39% 9% 15% 26% 10% 1	2280
	11th to 20th	Day	36% 8% 14% 28% 13%	2171
	21st to end	Day	46% 8% 14% 24% 8%	2048
October	1st to 10th	Day	49% 7% 13% 19% 11% 1	1900
	11th to 20th	Day	54% 8% 13% 17% 7% 1	1900
	21st to end	Day	62% 8% 11% 14% 5%	2027
November	1st to 10th	Day	51% 9% 14% 18% 8% 1	1587
	11th to 20th	Day	57% 11% 12% 13% 7% 1	1520
	21st to end	Day	65% 8% 13% 13% 2	1520
December	1st to 10th	Day	69% 10% 10% 9% 2	1520
	11th to 20th	Day	62% 11% 13% 12% 3	1906
	21st to end	Day	76% 8% 7% 8% 1	2772
January	1st to 10th	Night	61% 9% 14% 12% 3	4429
	11th to 20th	Night	65% 10% 12% 9% 2	4234
	21st to end	Night	65% 10% 11% 10% 3 1	4532
February	1st to 10th	Night	61% 9% 10% 17% 4	2470
	11th to 20th	Night	57% 8% 12% 16% 6%	2405
	21st to end	Night	54% 8% 14% 17% 7%	1992
March	1st to 10th	Night	51% 7% 12% 22% 7% 1	3418
	11th to 20th	Night	45% 10% 14% 21% 9% 2	3480
	21st to end	Night	40% 8% 14% 23% 14% 2	3817
April	1st to 10th	Night	53% 5% 11% 19% 11% 1	1933
	11th to 20th	Night	47% 7% 9% 20% 15% 2	1813
	21st to end	Night	47% 7% 12% 18% 15% 2	1710
May	1st to 10th	Night	42% 8% 13% 18% 16% 3	2840
	11th to 20th	Night	42% 10% 14% 21% 11% 2	2498
	21st to end	Night	29% 9% 14% 25% 20% 2	2739
June	1st to 10th	Night	39% 8% 12% 23% 16% 2	1520
	11th to 20th	Night	37% 7% 13% 22% 20% 2	1504
	21st to end	Night	38% 8% 14% 23% 16% 1	1330
July	1st to 10th	Night	31% 6% 15% 26% 19% 3	2351
	11th to 20th	Night	31% 5% 14% 35% 14% 1	2472
	21st to end	Night	29% 9% 15% 31% 15% 1	2918
August	1st to 10th	Night	35% 6% 13% 29% 15% 2	2814
	11th to 20th	Night	33% 6% 18% 30% 12% 1	2812
	21st to end	Night	34% 7% 13% 33% 12% 1	3266
September	1st to 10th	Night	34% 7% 17% 27% 14% 1	1900
	11th to 20th	Night	30% 6% 13% 33% 18% 1	2004
	21st to end	Night	41% 8% 12% 27% 11%	2130
October	1st to 10th	Night	45% 8% 11% 19% 16% 1	2280
	11th to 20th	Night	50% 8% 14% 20% 8%	2280
	21st to end	Night	56% 9% 12% 15% 9%	2435
November	1st to 10th	Night	47% 6% 14% 22% 10% 1	2483
	11th to 20th	Night	54% 9% 13% 15% 8% 1	2660
	21st to end	Night	58% 10% 16% 12% 2	2660
December	1st to 10th	Night	65% 10% 12% 11% 3	2660
	11th to 20th	Night	64% 10% 11% 13% 3	3288
	21st to end	Night	73% 10% 9% 6% 2	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	21% 22% 33% 19% 5% 1	180
	11th to 20th	Day	22% 29% 29% 14% 5% 1	240
	21st to end	Day	22% 23% 37% 15% 3	297
February	1st to 10th	Day	23% 26% 37% 11% 3	270
	11th to 20th	Day	23% 24% 43% 8% 1	270
	21st to end	Day	33% 25% 31% 11%	239
March	1st to 10th	Day	23% 19% 38% 16% 4	460
	11th to 20th	Day	21% 22% 35% 17% 4 1	460
	21st to end	Day	28% 19% 31% 17% 4 1	506
April	1st to 10th	Day	25% 20% 35% 14% 7%	460
	11th to 20th	Day	30% 19% 25% 15% 7% 3	452
	21st to end	Day	24% 17% 33% 17% 7% 1	460
May	1st to 10th	Day	20% 15% 30% 21% 10% 3	463
	11th to 20th	Day	19% 12% 29% 26% 10% 4	487
	21st to end	Day	15% 12% 29% 27% 12% 5%	529
June	1st to 10th	Day	14% 16% 31% 27% 10% 1	490
	11th to 20th	Day	14% 14% 29% 28% 13% 2	495
	21st to end	Day	18% 11% 33% 27% 9% 2	680
July	1st to 10th	Day	11% 8% 30% 29% 18% 4	556
	11th to 20th	Day	12% 7% 28% 30% 15% 7%	484
	21st to end	Day	8% 8% 31% 35% 13% 6%	532
August	1st to 10th	Day	11% 7% 28% 28% 16% 9%	486
	11th to 20th	Day	11% 8% 24% 27% 23% 8%	479
	21st to end	Day	13% 9% 29% 25% 17% 7%	539
September	1st to 10th	Day	13% 9% 28% 26% 16% 8%	490
	11th to 20th	Day	8% 8% 26% 24% 21% 13%	490
	21st to end	Day	14% 12% 31% 22% 15% 6%	490
October	1st to 10th	Day	22% 13% 28% 18% 14% 4	490
	11th to 20th	Day	21% 20% 34% 16% 7% 2	490
	21st to end	Day	29% 18% 31% 18% 4	514
November	1st to 10th	Day	22% 23% 28% 20% 7%	248
	11th to 20th	Day	23% 26% 30% 17% 3 1	180
	21st to end	Day	29% 20% 37% 11% 2	180
December	1st to 10th	Day	23% 23% 36% 14% 4	180
	11th to 20th	Day	28% 23% 31% 13% 4 1	180
	21st to end	Day	26% 22% 39% 11% 2	198
January	1st to 10th	Night	22% 21% 36% 15% 5% 1	760
	11th to 20th	Night	24% 18% 33% 20% 4 1	760
	21st to end	Night	19% 14% 41% 21% 6%	836
February	1st to 10th	Night	21% 18% 39% 21% 1	760
	11th to 20th	Night	22% 17% 38% 20% 3	743
	21st to end	Night	20% 21% 37% 18% 4	628
March	1st to 10th	Night	19% 19% 38% 21% 4	760
	11th to 20th	Night	21% 19% 35% 19% 5% 1	760
	21st to end	Night	20% 16% 35% 22% 7%	836
April	1st to 10th	Night	25% 15% 35% 22% 3	760
	11th to 20th	Night	18% 16% 36% 21% 8% 1	689
	21st to end	Night	20% 13% 34% 25% 8%	570
May	1st to 10th	Night	18% 7% 31% 32% 11% 1	570
	11th to 20th	Night	16% 7% 32% 34% 11% 1	376
	21st to end	Night	11% 7% 29% 36% 16% 1	411
June	1st to 10th	Night	14% 7% 34% 34% 11%	380
	11th to 20th	Night	12% 8% 31% 36% 14% 1	380
	21st to end	Night	13% 8% 28% 39% 12%	380
July	1st to 10th	Night	6% 6% 28% 41% 19% 1	370
	11th to 20th	Night	9% 6% 27% 37% 20% 1	368
	21st to end	Night	7% 5% 27% 41% 19% 1	577
August	1st to 10th	Night	11% 4 21% 37% 27% 1	567
	11th to 20th	Night	7% 5% 17% 43% 25% 3	564
	21st to end	Night	12% 5% 26% 34% 21% 2	704
September	1st to 10th	Night	11% 8% 27% 32% 19% 4	760
	11th to 20th	Night	13% 6% 23% 31% 23% 5%	760
	21st to end	Night	17% 10% 23% 31% 16% 3	760
October	1st to 10th	Night	18% 10% 30% 25% 15% 1	760
	11th to 20th	Night	22% 14% 31% 24% 8% 1	760
	21st to end	Night	27% 13% 33% 22% 4	812
November	1st to 10th	Night	23% 13% 32% 23% 9% 1	740
	11th to 20th	Night	22% 18% 33% 20% 6% 1	760
	21st to end	Night	24% 16% 34% 22% 4	760
December	1st to 10th	Night	27% 16% 38% 16% 3	760
	11th to 20th	Night	21% 19% 39% 18% 3 1	760
	21st to end	Night	30% 15% 37% 16% 2	836

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