Davenport Beach
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Davenport Beach clear sky chart from 2005-11-06 to 2024-02-15.

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	9% 6% 2 4 4 2 4 4 5% 9% 50%	78499
	Night	11% 6% 2 4 4 2 4 4 5% 8% 50%	80608
Transparency	Day	29% 7% 12% 20% 20% 13%	78222
	Night	31% 8% 12% 18% 18% 13%	80407
Seeing	Day	10% 5% 12% 28% 32% 13%	14462
	Night	12% 5% 11% 26% 33% 14%	23971

By Month

Percentage Cloud Cover SW (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% 6% 2 5% 4 3 3 4 6% 7% 44%	2777
	11th to 20th	Day	18% 7% 3 5% 5% 3 4 5% 5% 7% 36%	2860
	21st to end	Day	22% 7% 3 5% 5% 3 5% 4 5% 8% 33%	3146
February	1st to 10th	Day	18% 6% 2 4 4 2 4 3 5% 7% 46%	1710
	11th to 20th	Day	13% 5% 2 4 5% 2 4 4 6% 8% 45%	1704
	21st to end	Day	14% 5% 2 4 4 3 4 5% 4 6% 48%	1480
March	1st to 10th	Day	16% 7% 3 5% 5% 2 4 4 6% 9% 38%	1953
	11th to 20th	Day	17% 5% 2 5% 5% 3 5% 5% 6% 8% 37%	1980
	21st to end	Day	12% 5% 2 3 4 3 5% 5% 5% 7% 50%	2203
April	1st to 10th	Day	13% 5% 2 4 4 3 4 5% 5% 7% 48%	2160
	11th to 20th	Day	8% 5% 2 4 3 2 3 4 6% 9% 54%	2129
	21st to end	Day	6% 4 2 4 4 2 4 5% 6% 9% 53%	2160
May	1st to 10th	Day	5% 5% 2 4 4 2 4 4 5% 10% 54%	2204
	11th to 20th	Day	5% 5% 2 4 3 2 4 4 5% 10% 55%	2308
	21st to end	Day	6% 8% 2 5% 5% 3 4 5% 5% 9% 47%	2723
June	1st to 10th	Day	5% 6% 3 4 5% 2 4 4 6% 10% 51%	2520
	11th to 20th	Day	3 5% 2 3 3 2 3 4 6% 10% 59%	2520
	21st to end	Day	3 5% 2 4 3 2 3 4 5% 11% 59%	2520
July	1st to 10th	Day	3 6% 2 4 3 3 4 6% 6% 11% 51%	2478
	11th to 20th	Day	3 7% 2 4 4 3 4 5% 6% 10% 52%	2340
	21st to end	Day	1 5% 2 5% 3 2 4 6% 8% 13% 51%	2546
August	1st to 10th	Day	2 7% 2 5% 4 3 4 5% 7% 12% 49%	2328
	11th to 20th	Day	1 5% 2 4 4 3 4 5% 5% 12% 55%	2173
	21st to end	Day	2 7% 2 4 3 3 4 5% 6% 14% 50%	2376
September	1st to 10th	Day	2 4 1 3 4 3 3 2 6% 9% 64%	2160
	11th to 20th	Day	4 6% 2 4 4 2 3 4 6% 10% 55%	2160
	21st to end	Day	4 3 1 2 2 2 3 2 5% 9% 68%	1907
October	1st to 10th	Day	3 3 1 3 4 3 3 3 4 7% 65%	1800
	11th to 20th	Day	6% 5% 2 3 4 3 3 3 4 8% 60%	1800
	21st to end	Day	8% 5% 2 4 3 2 3 4 4 8% 59%	1980
November	1st to 10th	Day	9% 3 2 3 4 2 5% 4 6% 8% 54%	1855
	11th to 20th	Day	10% 5% 2 3 4 2 4 5% 6% 6% 54%	1710
	21st to end	Day	11% 4 1 4 3 2 3 4 3 8% 58%	1587
December	1st to 10th	Day	14% 5% 2 5% 4 2 4 4 6% 7% 45%	1520
	11th to 20th	Day	28% 8% 2 4 4 2 3 4 5% 6% 33%	1928
	21st to end	Day	23% 6% 2 4 4 3 4 4 5% 7% 39%	2794
January	1st to 10th	Night	14% 7% 2 4 4 2 3 4 5% 6% 48%	4160
	11th to 20th	Night	20% 7% 2 5% 4 3 5% 6% 5% 7% 35%	4110
	21st to end	Night	21% 7% 3 5% 5% 3 4 4 5% 7% 34%	4521
February	1st to 10th	Night	18% 5% 2 3 3 2 4 4 4 5% 50%	2470
	11th to 20th	Night	12% 6% 2 4 3 2 4 5% 7% 9% 46%	2236
	21st to end	Night	13% 6% 2 4 3 2 4 3 6% 6% 50%	1776
March	1st to 10th	Night	18% 9% 3 6% 4 2 4 4 6% 6% 38%	2003
	11th to 20th	Night	16% 5% 2 5% 4 2 4 4 5% 8% 44%	1980
	21st to end	Night	14% 5% 2 4 4 3 3 3 4 7% 50%	2152
April	1st to 10th	Night	13% 5% 3 3 4 3 4 5% 5% 8% 47%	1800
	11th to 20th	Night	11% 5% 2 4 4 2 3 4 4 7% 55%	1779
	21st to end	Night	6% 6% 2 3 2 2 3 4 5% 11% 57%	1800
May	1st to 10th	Night	6% 6% 1 4 4 3 3 3 5% 9% 56%	1752
	11th to 20th	Night	4 7% 1 5% 5% 3 4 5% 5% 12% 51%	1584
	21st to end	Night	5% 10% 3 6% 4 2 3 4 4 11% 49%	1552
June	1st to 10th	Night	4 5% 3 4 4 2 4 4 6% 10% 54%	1440
	11th to 20th	Night	2 7% 1 4 3 2 4 4 4 8% 61%	1440
	21st to end	Night	3 5% 1 3 2 2 5% 4 5% 11% 59%	1440
July	1st to 10th	Night	2 10% 1 3 3 2 3 4 4 11% 57%	1477
	11th to 20th	Night	2 8% 2 5% 4 2 3 3 6% 10% 54%	1620
	21st to end	Night	2 9% 3 6% 6% 3 6% 6% 7% 12% 41%	1773
August	1st to 10th	Night	2 8% 2 5% 6% 3 5% 5% 6% 13% 46%	1611
	11th to 20th	Night	2 6% 2 6% 4 2 3 5% 5% 12% 52%	1728
	21st to end	Night	2 9% 3 4 3 2 3 5% 6% 12% 53%	1980
September	1st to 10th	Night	1 6% 2 2 3 2 4 4 4 8% 64%	1800
	11th to 20th	Night	4 7% 2 3 4 2 4 3 4 9% 58%	1800
	21st to end	Night	3 5% 1 3 2 1 2 3 3 8% 68%	2048
October	1st to 10th	Night	4 5% 3 4 3 1 2 2 4 6% 64%	2160
	11th to 20th	Night	6% 4 3 5% 3 2 3 3 5% 7% 59%	2160
	21st to end	Night	8% 4 2 3 4 2 2 3 4 7% 62%	2376
November	1st to 10th	Night	9% 4 2 4 3 2 3 3 4 7% 58%	2221
	11th to 20th	Night	10% 4 2 3 4 3 3 3 5% 9% 54%	2470
	21st to end	Night	8% 3 2 4 4 2 4 3 4 6% 60%	2591
December	1st to 10th	Night	16% 6% 2 4 4 2 3 3 4 6% 50%	2660
	11th to 20th	Night	28% 7% 3 4 4 2 3 4 5% 6% 34%	3276
	21st to end	Night	21% 7% 2 4 4 2 3 4 5% 7% 39%	4862

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	38% 10% 13% 26% 9% 4	2777
	11th to 20th	Day	47% 9% 11% 14% 10% 8%	2860
	21st to end	Day	49% 9% 10% 15% 12% 5%	3146
February	1st to 10th	Day	39% 5% 9% 19% 18% 10%	1710
	11th to 20th	Day	37% 6% 11% 19% 20% 7%	1713
	21st to end	Day	39% 6% 9% 22% 18% 7%	1480
March	1st to 10th	Day	45% 7% 10% 20% 14% 5%	1953
	11th to 20th	Day	45% 7% 11% 17% 17% 4	1980
	21st to end	Day	36% 9% 14% 21% 16% 4	2203
April	1st to 10th	Day	37% 6% 15% 19% 19% 4	2160
	11th to 20th	Day	28% 8% 16% 24% 18% 6%	2132
	21st to end	Day	27% 8% 15% 27% 19% 5%	2160
May	1st to 10th	Day	25% 7% 14% 23% 27% 5%	2204
	11th to 20th	Day	23% 8% 15% 24% 22% 7%	2311
	21st to end	Day	33% 9% 15% 21% 19% 3	2724
June	1st to 10th	Day	25% 9% 15% 22% 22% 7%	2520
	11th to 20th	Day	17% 8% 14% 23% 27% 12%	2520
	21st to end	Day	16% 5% 11% 18% 26% 23%	2520
July	1st to 10th	Day	15% 6% 13% 16% 23% 28%	2411
	11th to 20th	Day	19% 7% 12% 18% 16% 28%	2271
	21st to end	Day	13% 7% 11% 16% 25% 27%	2405
August	1st to 10th	Day	19% 7% 12% 17% 23% 22%	2312
	11th to 20th	Day	13% 6% 12% 17% 25% 27%	2173
	21st to end	Day	16% 8% 11% 20% 22% 22%	2376
September	1st to 10th	Day	13% 5% 9% 14% 23% 37%	2160
	11th to 20th	Day	20% 8% 12% 20% 25% 15%	2160
	21st to end	Day	14% 5% 9% 21% 32% 18%	1907
October	1st to 10th	Day	18% 4 12% 19% 25% 22%	1800
	11th to 20th	Day	22% 7% 10% 18% 21% 22%	1800
	21st to end	Day	25% 5% 11% 19% 20% 20%	1980
November	1st to 10th	Day	28% 6% 12% 24% 21% 10%	1855
	11th to 20th	Day	31% 6% 11% 22% 22% 8%	1710
	21st to end	Day	29% 4 12% 18% 26% 11%	1587
December	1st to 10th	Day	37% 6% 12% 18% 15% 11%	1520
	11th to 20th	Day	53% 6% 10% 13% 13% 5%	1928
	21st to end	Day	45% 7% 12% 21% 11% 4	2794
January	1st to 10th	Night	36% 10% 16% 24% 10% 3	4160
	11th to 20th	Night	46% 10% 14% 12% 9% 8%	4110
	21st to end	Night	49% 10% 10% 13% 11% 7%	4521
February	1st to 10th	Night	38% 4 10% 17% 18% 13%	2470
	11th to 20th	Night	34% 8% 11% 18% 22% 7%	2238
	21st to end	Night	34% 6% 13% 27% 15% 5%	1776
March	1st to 10th	Night	45% 7% 12% 16% 13% 5%	2003
	11th to 20th	Night	39% 6% 10% 19% 19% 6%	1980
	21st to end	Night	36% 8% 14% 20% 16% 6%	2152
April	1st to 10th	Night	35% 9% 16% 19% 16% 5%	1800
	11th to 20th	Night	30% 8% 13% 25% 17% 7%	1779
	21st to end	Night	23% 8% 17% 27% 19% 7%	1800
May	1st to 10th	Night	26% 7% 12% 21% 23% 10%	1752
	11th to 20th	Night	25% 12% 15% 19% 22% 6%	1585
	21st to end	Night	29% 14% 15% 20% 20% 3	1552
June	1st to 10th	Night	22% 12% 13% 23% 22% 8%	1440
	11th to 20th	Night	19% 8% 12% 18% 26% 17%	1440
	21st to end	Night	18% 9% 8% 18% 23% 24%	1440
July	1st to 10th	Night	15% 10% 10% 12% 23% 30%	1435
	11th to 20th	Night	19% 9% 10% 17% 16% 28%	1566
	21st to end	Night	24% 13% 11% 15% 15% 22%	1674
August	1st to 10th	Night	25% 12% 12% 17% 16% 18%	1602
	11th to 20th	Night	18% 8% 10% 15% 23% 26%	1728
	21st to end	Night	18% 12% 9% 16% 20% 24%	1980
September	1st to 10th	Night	13% 7% 8% 13% 23% 36%	1800
	11th to 20th	Night	20% 8% 9% 21% 25% 17%	1800
	21st to end	Night	14% 5% 8% 20% 31% 22%	2048
October	1st to 10th	Night	20% 7% 9% 15% 23% 26%	2160
	11th to 20th	Night	22% 7% 9% 19% 19% 23%	2160
	21st to end	Night	23% 6% 8% 20% 22% 22%	2376
November	1st to 10th	Night	26% 5% 10% 25% 20% 14%	2221
	11th to 20th	Night	28% 6% 12% 22% 22% 9%	2470
	21st to end	Night	28% 5% 10% 20% 24% 14%	2591
December	1st to 10th	Night	37% 6% 10% 18% 17% 13%	2660
	11th to 20th	Night	52% 5% 10% 14% 14% 5%	3276
	21st to end	Night	44% 10% 13% 17% 11% 4	4862

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	28% 3 16% 26% 21% 7%	327
	11th to 20th	Day	17% 2 13% 29% 29% 9%	370
	21st to end	Day	15% 2 13% 31% 30% 10%	407
February	1st to 10th	Day	19% 3 16% 25% 25% 12%	370
	11th to 20th	Day	13% 9% 19% 27% 27% 5%	390
	21st to end	Day	10% 6% 21% 33% 25% 5%	346
March	1st to 10th	Day	21% 5% 19% 30% 20% 5%	420
	11th to 20th	Day	23% 3 16% 26% 23% 9%	420
	21st to end	Day	12% 5% 21% 37% 19% 6%	462
April	1st to 10th	Day	14% 6% 18% 35% 21% 5%	420
	11th to 20th	Day	11% 7% 21% 34% 19% 8%	412
	21st to end	Day	9% 5% 23% 30% 21% 12%	420
May	1st to 10th	Day	7% 6% 19% 31% 29% 9%	423
	11th to 20th	Day	8% 4 19% 31% 28% 10%	448
	21st to end	Day	9% 8% 16% 25% 27% 15%	485
June	1st to 10th	Day	9% 5% 12% 32% 32% 10%	450
	11th to 20th	Day	5% 5% 15% 31% 33% 11%	450
	21st to end	Day	6% 6% 7% 30% 40% 11%	450
July	1st to 10th	Day	8% 6% 5% 22% 41% 17%	446
	11th to 20th	Day	7% 6% 6% 19% 42% 20%	444
	21st to end	Day	4 6% 3 21% 43% 24%	487
August	1st to 10th	Day	6% 8% 6% 26% 40% 13%	447
	11th to 20th	Day	6% 5% 4 24% 38% 23%	437
	21st to end	Day	6% 7% 2 21% 43% 21%	495
September	1st to 10th	Day	3 3 6% 24% 44% 20%	450
	11th to 20th	Day	7% 6% 6% 30% 34% 16%	450
	21st to end	Day	6% 5% 8% 22% 40% 20%	450
October	1st to 10th	Day	4 6% 11% 25% 33% 20%	450
	11th to 20th	Day	6% 4 9% 22% 34% 25%	450
	21st to end	Day	9% 4 8% 30% 32% 17%	495
November	1st to 10th	Day	8% 3 14% 25% 34% 16%	451
	11th to 20th	Day	9% 4 10% 29% 34% 13%	270
	21st to end	Day	9% 1 8% 33% 36% 12%	212
December	1st to 10th	Day	17% 4 11% 28% 29% 11%	180
	11th to 20th	Day	16% 2 19% 24% 30% 8%	180
	21st to end	Day	19% 2 19% 29% 23% 8%	198
January	1st to 10th	Night	18% 4 13% 28% 27% 10%	760
	11th to 20th	Night	17% 3 11% 27% 29% 13%	760
	21st to end	Night	17% 4 9% 30% 32% 9%	836
February	1st to 10th	Night	19% 4 13% 26% 27% 10%	760
	11th to 20th	Night	15% 5% 16% 30% 24% 9%	722
	21st to end	Night	14% 6% 20% 31% 24% 5%	592
March	1st to 10th	Night	20% 7% 14% 27% 26% 6%	720
	11th to 20th	Night	17% 4 13% 29% 29% 8%	720
	21st to end	Night	16% 5% 17% 32% 24% 5%	792
April	1st to 10th	Night	13% 6% 17% 33% 25% 6%	720
	11th to 20th	Night	13% 9% 17% 30% 24% 8%	711
	21st to end	Night	9% 5% 18% 32% 23% 14%	720
May	1st to 10th	Night	9% 5% 15% 30% 31% 11%	672
	11th to 20th	Night	8% 7% 11% 27% 32% 15%	522
	21st to end	Night	11% 8% 12% 27% 27% 15%	389
June	1st to 10th	Night	7% 4 10% 33% 35% 13%	360
	11th to 20th	Night	6% 4 9% 30% 42% 9%	360
	21st to end	Night	5% 6% 4 22% 47% 16%	360
July	1st to 10th	Night	8% 7% 3 17% 43% 22%	385
	11th to 20th	Night	9% 3 2 14% 41% 31%	522
	21st to end	Night	11% 7% 3 11% 42% 27%	591
August	1st to 10th	Night	9% 9% 2 19% 42% 20%	537
	11th to 20th	Night	7% 5% 2 18% 46% 22%	660
	21st to end	Night	6% 6% 5% 14% 45% 24%	792
September	1st to 10th	Night	6% 4 3 18% 44% 26%	720
	11th to 20th	Night	6% 4 5% 23% 45% 18%	720
	21st to end	Night	5% 2 8% 20% 41% 24%	720
October	1st to 10th	Night	8% 4 8% 27% 33% 20%	720
	11th to 20th	Night	8% 3 8% 19% 39% 22%	720
	21st to end	Night	10% 4 7% 25% 33% 22%	792
November	1st to 10th	Night	10% 3 11% 26% 34% 17%	740
	11th to 20th	Night	12% 2 8% 28% 37% 13%	760
	21st to end	Night	9% 2 11% 33% 34% 11%	760
December	1st to 10th	Night	16% 4 11% 30% 30% 8%	760
	11th to 20th	Night	21% 4 13% 28% 27% 7%	760
	21st to end	Night	18% 4 19% 30% 23% 6%	836

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