Warwick
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Warwick clear sky chart from 2005-11-06 to 2025-04-26.

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	17% 7% 2 6% 4 4 4 3 5% 7% 40%	113243
	Night	17% 8% 2 6% 4 4 4 3 5% 6% 41%	115368
Transparency	Day	42% 7% 13% 21% 15% 3	116837
	Night	43% 6% 12% 21% 16% 3	119938
Seeing	Day	19% 16% 33% 22% 8% 2	15661
	Night	20% 14% 33% 24% 7% 1	24719

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	10% 7% 3 6% 4 4 4 3 6% 6% 48%	3597
	11th to 20th	Day	14% 8% 2 6% 4 3 4 3 4 5% 48%	3570
	21st to end	Day	18% 8% 3 6% 4 4 3 3 4 4 43%	3960
February	1st to 10th	Day	18% 8% 2 5% 3 5% 5% 3 6% 6% 38%	1915
	11th to 20th	Day	14% 7% 2 5% 5% 4 5% 4 5% 7% 42%	1948
	21st to end	Day	20% 7% 3 6% 4 4 4 4 4 6% 40%	1650
March	1st to 10th	Day	20% 11% 3 6% 3 3 3 2 4 6% 39%	4476
	11th to 20th	Day	15% 9% 2 5% 4 4 4 3 5% 6% 43%	4768
	21st to end	Day	22% 9% 3 7% 4 4 4 4 5% 5% 33%	5779
April	1st to 10th	Day	19% 8% 3 6% 4 3 3 3 6% 7% 38%	2400
	11th to 20th	Day	18% 7% 2 5% 3 3 5% 3 6% 7% 40%	2374
	21st to end	Day	20% 7% 2 6% 4 4 4 3 5% 6% 39%	2530
May	1st to 10th	Day	27% 11% 3 7% 3 3 3 3 4 6% 30%	4106
	11th to 20th	Day	24% 8% 3 8% 5% 5% 3 3 5% 6% 33%	4100
	21st to end	Day	15% 5% 1 5% 4 4 4 4 5% 8% 45%	4837
June	1st to 10th	Day	18% 6% 2 5% 5% 5% 5% 4 7% 8% 35%	2660
	11th to 20th	Day	14% 6% 2 5% 5% 5% 5% 4 7% 8% 37%	2660
	21st to end	Day	14% 6% 2 6% 4 5% 4 4 6% 10% 39%	2660
July	1st to 10th	Day	12% 7% 3 7% 5% 5% 6% 5% 7% 9% 35%	4440
	11th to 20th	Day	12% 6% 2 6% 5% 4 5% 4 7% 10% 38%	4440
	21st to end	Day	19% 7% 3 6% 5% 4 5% 4 6% 8% 32%	4814
August	1st to 10th	Day	17% 7% 3 8% 5% 5% 5% 4 6% 9% 31%	4113
	11th to 20th	Day	12% 6% 3 7% 5% 4 6% 4 6% 8% 39%	3949
	21st to end	Day	7% 4 2 5% 4 5% 6% 5% 7% 8% 45%	4180
September	1st to 10th	Day	14% 6% 3 5% 4 4 4 4 5% 6% 45%	2275
	11th to 20th	Day	13% 6% 2 5% 3 3 3 3 5% 6% 51%	2090
	21st to end	Day	19% 6% 2 6% 4 4 4 3 4 5% 43%	2090
October	1st to 10th	Day	23% 6% 2 5% 3 4 3 2 4 5% 42%	2090
	11th to 20th	Day	15% 6% 2 5% 3 3 3 3 5% 7% 48%	1875
	21st to end	Day	19% 5% 2 5% 4 4 4 3 5% 5% 45%	1881
November	1st to 10th	Day	16% 6% 2 5% 4 4 4 3 5% 5% 48%	1761
	11th to 20th	Day	17% 6% 2 4 3 3 4 3 5% 6% 47%	1800
	21st to end	Day	17% 6% 2 6% 4 3 4 3 4 5% 46%	1800
December	1st to 10th	Day	14% 8% 3 5% 3 3 3 3 4 6% 48%	2709
	11th to 20th	Day	19% 7% 2 5% 4 2 3 2 3 5% 50%	2986
	21st to end	Day	19% 10% 3 7% 4 4 3 2 3 5% 40%	3960
January	1st to 10th	Night	14% 5% 2 4 3 3 4 3 4 6% 52%	6349
	11th to 20th	Night	15% 9% 3 7% 4 4 3 3 4 4 43%	6315
	21st to end	Night	17% 9% 3 7% 4 5% 4 3 4 5% 38%	6996
February	1st to 10th	Night	17% 9% 3 5% 5% 4 4 3 4 5% 41%	2478
	11th to 20th	Night	17% 8% 3 6% 4 4 4 3 5% 6% 41%	2338
	21st to end	Night	17% 9% 2 6% 5% 4 4 3 5% 4 41%	1980
March	1st to 10th	Night	23% 9% 2 4 3 4 4 3 4 6% 39%	5364
	11th to 20th	Night	17% 10% 3 6% 4 4 3 3 4 6% 41%	5191
	21st to end	Night	24% 10% 2 6% 4 4 4 3 5% 5% 34%	5150
April	1st to 10th	Night	19% 9% 3 6% 4 5% 4 3 5% 6% 37%	2000
	11th to 20th	Night	19% 8% 2 6% 4 3 4 3 5% 6% 39%	1975
	21st to end	Night	20% 7% 3 7% 4 3 3 3 4 5% 41%	1766
May	1st to 10th	Night	26% 9% 3 7% 5% 3 4 3 5% 6% 28%	2834
	11th to 20th	Night	25% 9% 3 8% 5% 5% 4 3 5% 6% 26%	2813
	21st to end	Night	17% 7% 2 6% 4 4 4 4 6% 8% 39%	2747
June	1st to 10th	Night	17% 7% 3 7% 5% 4 4 4 6% 7% 38%	1520
	11th to 20th	Night	17% 7% 2 5% 5% 4 4 3 6% 8% 39%	1520
	21st to end	Night	15% 8% 2 5% 4 3 4 4 6% 10% 39%	1520
July	1st to 10th	Night	14% 8% 3 7% 5% 5% 6% 5% 6% 10% 32%	2520
	11th to 20th	Night	14% 7% 2 6% 4 4 5% 5% 7% 9% 37%	2520
	21st to end	Night	18% 8% 3 7% 5% 4 5% 4 6% 8% 31%	2739
August	1st to 10th	Night	21% 7% 2 7% 5% 4 6% 4 7% 9% 29%	2784
	11th to 20th	Night	9% 7% 3 7% 6% 6% 7% 6% 7% 8% 36%	2875
	21st to end	Night	8% 4 1 5% 3 4 3 3 5% 7% 56%	3476
September	1st to 10th	Night	13% 6% 3 7% 5% 4 4 4 5% 6% 44%	1905
	11th to 20th	Night	14% 6% 2 5% 3 3 3 2 4 7% 51%	2090
	21st to end	Night	19% 8% 3 6% 4 3 4 3 4 5% 41%	2090
October	1st to 10th	Night	20% 6% 2 6% 4 3 4 3 4 6% 42%	2090
	11th to 20th	Night	15% 4 2 4 4 4 4 3 5% 7% 49%	2299
	21st to end	Night	20% 6% 3 5% 4 4 3 2 5% 6% 41%	2717
November	1st to 10th	Night	14% 6% 2 5% 4 4 4 3 4 5% 49%	2537
	11th to 20th	Night	17% 7% 2 5% 3 3 4 3 3 6% 47%	2600
	21st to end	Night	16% 6% 2 4 3 3 4 3 5% 7% 47%	2600
December	1st to 10th	Night	17% 9% 2 5% 4 3 3 2 4 4 49%	4466
	11th to 20th	Night	23% 8% 2 5% 3 3 3 2 4 4 43%	5208
	21st to end	Night	16% 10% 4 7% 4 3 3 2 4 5% 42%	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	36% 5% 8% 27% 21% 4	3598
	11th to 20th	Day	39% 6% 10% 21% 17% 8%	3600
	21st to end	Day	45% 5% 9% 21% 19% 2	3960
February	1st to 10th	Day	45% 6% 15% 18% 14% 3	1915
	11th to 20th	Day	42% 6% 11% 23% 15% 4	1957
	21st to end	Day	45% 6% 12% 19% 15% 3	1650
March	1st to 10th	Day	45% 5% 12% 14% 12% 11%	4479
	11th to 20th	Day	38% 7% 15% 27% 11% 2	4768
	21st to end	Day	52% 5% 8% 14% 16% 6%	5779
April	1st to 10th	Day	43% 7% 12% 18% 16% 3	2400
	11th to 20th	Day	43% 7% 9% 20% 18% 3	2374
	21st to end	Day	44% 8% 10% 19% 15% 4	2530
May	1st to 10th	Day	54% 9% 14% 12% 9% 1	4120
	11th to 20th	Day	50% 9% 15% 15% 9% 2	4104
	21st to end	Day	36% 10% 15% 21% 18% 2	4837
June	1st to 10th	Day	43% 10% 15% 20% 11% 1	2660
	11th to 20th	Day	41% 9% 15% 21% 13% 1	2660
	21st to end	Day	40% 10% 15% 22% 13% 1	2660
July	1st to 10th	Day	44% 9% 13% 18% 14% 1	4370
	11th to 20th	Day	40% 8% 17% 23% 11% 1	4365
	21st to end	Day	47% 8% 14% 17% 13% 2	4661
August	1st to 10th	Day	49% 8% 17% 19% 7%	4099
	11th to 20th	Day	40% 8% 15% 27% 9% 1	3988
	21st to end	Day	32% 8% 17% 25% 17% 2	4180
September	1st to 10th	Day	38% 8% 11% 22% 20% 1	2275
	11th to 20th	Day	32% 6% 12% 24% 22% 3	2090
	21st to end	Day	44% 6% 8% 19% 20% 2	2090
October	1st to 10th	Day	38% 5% 10% 23% 19% 5%	3480
	11th to 20th	Day	29% 4 9% 26% 29% 4	3091
	21st to end	Day	31% 4 14% 29% 19% 3	3081
November	1st to 10th	Day	39% 6% 13% 20% 20% 2	1761
	11th to 20th	Day	37% 5% 12% 20% 22% 4	1800
	21st to end	Day	42% 5% 11% 27% 12% 3	1800
December	1st to 10th	Day	39% 4 13% 27% 16% 1	2709
	11th to 20th	Day	41% 3 14% 17% 19% 6%	2986
	21st to end	Day	48% 6% 9% 20% 14% 4	3960
January	1st to 10th	Night	33% 4 10% 31% 19% 3	6349
	11th to 20th	Night	44% 4 11% 20% 15% 6%	6360
	21st to end	Night	48% 6% 10% 18% 15% 5%	6996
February	1st to 10th	Night	46% 5% 12% 22% 13% 2	2478
	11th to 20th	Night	44% 5% 10% 19% 17% 4	2340
	21st to end	Night	46% 5% 9% 21% 15% 4	1980
March	1st to 10th	Night	47% 4 10% 16% 14% 7%	5374
	11th to 20th	Night	45% 7% 16% 19% 11% 2	5192
	21st to end	Night	51% 5% 6% 11% 21% 6%	5150
April	1st to 10th	Night	47% 5% 10% 19% 15% 4	2000
	11th to 20th	Night	45% 6% 11% 17% 19% 2	1975
	21st to end	Night	46% 5% 10% 20% 14% 5%	1766
May	1st to 10th	Night	56% 10% 13% 13% 8% 1	2840
	11th to 20th	Night	56% 10% 13% 13% 7% 2	2814
	21st to end	Night	43% 12% 15% 18% 11% 1	2748
June	1st to 10th	Night	45% 8% 13% 19% 13% 1	1520
	11th to 20th	Night	43% 7% 13% 24% 13% 1	1520
	21st to end	Night	42% 8% 15% 24% 11% 1	1520
July	1st to 10th	Night	49% 8% 12% 18% 12% 1	2480
	11th to 20th	Night	42% 10% 16% 23% 9% 1	2472
	21st to end	Night	50% 7% 14% 15% 12% 2	2651
August	1st to 10th	Night	51% 10% 13% 16% 8% 1	2774
	11th to 20th	Night	41% 11% 15% 25% 8%	2902
	21st to end	Night	27% 6% 17% 28% 21% 1	3476
September	1st to 10th	Night	41% 7% 10% 23% 17% 2	1905
	11th to 20th	Night	34% 6% 12% 22% 23% 2	2090
	21st to end	Night	46% 7% 8% 17% 19% 3	2090
October	1st to 10th	Night	40% 5% 12% 24% 16% 3	3480
	11th to 20th	Night	26% 4 9% 26% 32% 4	3822
	21st to end	Night	32% 4 12% 27% 21% 3	4467
November	1st to 10th	Night	38% 6% 13% 21% 19% 3	2537
	11th to 20th	Night	41% 5% 9% 22% 19% 4	2600
	21st to end	Night	38% 5% 15% 27% 13% 2	2600
December	1st to 10th	Night	41% 4 12% 27% 16% 1	4466
	11th to 20th	Night	46% 4 12% 16% 19% 2	5208
	21st to end	Night	45% 5% 10% 20% 18% 3	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	22% 26% 34% 16% 4	200
	11th to 20th	Day	21% 30% 37% 10% 4	200
	21st to end	Day	19% 26% 38% 12% 4	220
February	1st to 10th	Day	24% 23% 36% 15% 1	440
	11th to 20th	Day	26% 25% 38% 9% 1	496
	21st to end	Day	22% 23% 37% 14% 3	414
March	1st to 10th	Day	25% 22% 33% 17% 2	500
	11th to 20th	Day	21% 23% 37% 16% 2 1	500
	21st to end	Day	26% 20% 37% 12% 5% 1	550
April	1st to 10th	Day	25% 24% 32% 14% 5%	500
	11th to 20th	Day	24% 22% 37% 13% 3	492
	21st to end	Day	24% 18% 35% 16% 5% 2	480
May	1st to 10th	Day	29% 18% 33% 15% 4	463
	11th to 20th	Day	20% 17% 40% 17% 5% 1	487
	21st to end	Day	16% 11% 35% 28% 8% 2	529
June	1st to 10th	Day	17% 11% 37% 25% 9% 2	490
	11th to 20th	Day	13% 13% 37% 27% 8% 1	490
	21st to end	Day	15% 11% 36% 29% 7% 1	490
July	1st to 10th	Day	15% 8% 28% 34% 14% 2	485
	11th to 20th	Day	12% 7% 27% 37% 15% 2	484
	21st to end	Day	14% 8% 35% 33% 9% 1	532
August	1st to 10th	Day	12% 8% 32% 35% 11% 3	486
	11th to 20th	Day	16% 6% 27% 34% 14% 4	479
	21st to end	Day	11% 6% 32% 30% 14% 7%	539
September	1st to 10th	Day	17% 9% 27% 27% 15% 4	490
	11th to 20th	Day	14% 9% 28% 26% 16% 7%	490
	21st to end	Day	22% 9% 32% 25% 9% 3	490
October	1st to 10th	Day	24% 11% 27% 22% 11% 5%	490
	11th to 20th	Day	16% 17% 31% 22% 11% 2	441
	21st to end	Day	22% 16% 30% 22% 9% 1	429
November	1st to 10th	Day	14% 18% 36% 22% 8% 2	395
	11th to 20th	Day	21% 24% 32% 18% 5%	400
	21st to end	Day	23% 21% 32% 18% 6% 1	400
December	1st to 10th	Day	21% 20% 36% 17% 5%	270
	11th to 20th	Day	28% 26% 32% 12% 3 1	200
	21st to end	Day	21% 19% 39% 14% 6% 2	220
January	1st to 10th	Night	20% 22% 39% 16% 3	800
	11th to 20th	Night	27% 22% 33% 16% 3	800
	21st to end	Night	18% 25% 35% 19% 2	880
February	1st to 10th	Night	22% 20% 38% 20% 1	800
	11th to 20th	Night	24% 22% 40% 12% 1	783
	21st to end	Night	23% 21% 36% 18% 2	660
March	1st to 10th	Night	23% 20% 35% 19% 4	800
	11th to 20th	Night	21% 16% 39% 21% 3 1	800
	21st to end	Night	25% 15% 38% 18% 4	880
April	1st to 10th	Night	23% 18% 35% 21% 3	800
	11th to 20th	Night	20% 16% 39% 21% 4	791
	21st to end	Night	23% 14% 36% 21% 5%	592
May	1st to 10th	Night	26% 11% 31% 25% 6%	570
	11th to 20th	Night	21% 12% 40% 22% 4 1	562
	21st to end	Night	22% 5% 28% 36% 8% 1	420
June	1st to 10th	Night	19% 7% 28% 36% 9% 1	380
	11th to 20th	Night	19% 6% 28% 38% 9%	380
	21st to end	Night	19% 6% 26% 39% 10%	380
July	1st to 10th	Night	16% 5% 27% 38% 14% 1	370
	11th to 20th	Night	15% 4 22% 43% 14% 1	368
	21st to end	Night	15% 2 27% 42% 14%	416
August	1st to 10th	Night	13% 4 28% 43% 12%	539
	11th to 20th	Night	12% 3 27% 39% 18%	616
	21st to end	Night	14% 4 21% 38% 19% 3	836
September	1st to 10th	Night	15% 4 29% 34% 16% 2	760
	11th to 20th	Night	16% 6% 26% 30% 18% 4	760
	21st to end	Night	23% 7% 26% 29% 13% 2	760
October	1st to 10th	Night	23% 10% 27% 25% 13% 2	760
	11th to 20th	Night	18% 12% 34% 24% 11% 2	760
	21st to end	Night	21% 13% 37% 20% 8%	836
November	1st to 10th	Night	17% 13% 35% 24% 10% 1	780
	11th to 20th	Night	21% 20% 34% 19% 6%	800
	21st to end	Night	19% 21% 33% 22% 5% 1	800
December	1st to 10th	Night	25% 19% 32% 20% 4 1	800
	11th to 20th	Night	23% 21% 36% 17% 3 1	800
	21st to end	Night	22% 20% 36% 18% 4	880

Page generated at 2025-04-23 09:25:04. Version ac07

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