Davis
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Davis clear sky chart from 2005-11-06 to 2024-02-20.

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	8% 4 2 3 3 2 3 3 4 6% 62%	78510
	Night	10% 4 2 4 3 2 3 3 4 6% 59%	80708
Transparency	Day	25% 4 8% 19% 24% 19%	78225
	Night	27% 4 9% 19% 22% 18%	80514
Seeing	Day	8% 5% 17% 27% 29% 14%	14234
	Night	9% 4 18% 40% 26% 3	23679

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	20% 9% 3 5% 5% 3 5% 5% 5% 5% 35%	2568
	11th to 20th	Day	20% 11% 4 7% 6% 3 4 4 3 5% 33%	2860
	21st to end	Day	23% 9% 4 7% 5% 4 4 5% 5% 6% 28%	3146
February	1st to 10th	Day	16% 5% 3 6% 4 3 4 3 3 6% 47%	1710
	11th to 20th	Day	13% 4 2 4 5% 3 5% 4 4 8% 48%	1747
	21st to end	Day	14% 4 2 3 3 3 4 4 3 7% 51%	1480
March	1st to 10th	Day	13% 6% 3 6% 5% 4 4 4 6% 7% 41%	1901
	11th to 20th	Day	15% 6% 2 5% 5% 2 3 5% 6% 7% 42%	1980
	21st to end	Day	12% 4 2 4 4 3 5% 5% 5% 8% 48%	2232
April	1st to 10th	Day	12% 6% 3 4 4 2 4 5% 5% 8% 47%	2160
	11th to 20th	Day	8% 3 2 4 4 2 4 4 5% 6% 59%	2129
	21st to end	Day	4 3 1 2 3 2 4 4 4 9% 64%	2160
May	1st to 10th	Day	4 2 1 3 3 1 2 3 4 7% 69%	2230
	11th to 20th	Day	3 3 1 2 3 2 2 4 4 7% 69%	2427
	21st to end	Day	3 2 1 2 3 2 3 4 5% 8% 68%	2723
June	1st to 10th	Day	4 3 1 2 3 1 3 3 4 7% 69%	2520
	11th to 20th	Day	1 1 1 1 1 2 2 4 5% 82%	2520
	21st to end	Day	2 1 1 1 1 2 1 3 4 85%	2520
July	1st to 10th	Day	1 1 1 1 1 2 2 3 89%	2520
	11th to 20th	Day	1 1 1 1 1 1 1 2 3 88%	2459
	21st to end	Day	1 1 1 1 1 1 2 2 3 4 85%	2546
August	1st to 10th	Day	2 1 1 1 1 2 2 3 4 83%	2328
	11th to 20th	Day	1 1 1 1 1 2 2 3 4 85%	2183
	21st to end	Day	1 1 1 1 1 1 2 2 3 88%	2376
September	1st to 10th	Day	1 1 1 1 1 2 2 3 88%	2160
	11th to 20th	Day	3 2 1 2 2 2 3 3 6% 76%	2160
	21st to end	Day	3 2 1 2 2 2 1 2 3 4 81%	1924
October	1st to 10th	Day	2 2 1 2 3 2 3 3 3 5% 74%	1800
	11th to 20th	Day	5% 2 1 3 2 2 3 3 4 5% 71%	1800
	21st to end	Day	6% 3 2 3 3 2 3 3 3 5% 67%	1980
November	1st to 10th	Day	9% 4 2 3 3 2 4 4 4 7% 59%	1760
	11th to 20th	Day	10% 6% 2 5% 5% 3 4 4 5% 6% 51%	1710
	21st to end	Day	10% 3 2 4 4 3 4 5% 5% 7% 54%	1549
December	1st to 10th	Day	14% 7% 2 4 5% 3 3 5% 4 7% 45%	1520
	11th to 20th	Day	27% 9% 4 6% 4 3 4 3 5% 5% 31%	1928
	21st to end	Day	17% 7% 3 6% 6% 3 4 5% 5% 8% 33%	2794
January	1st to 10th	Night	13% 6% 3 6% 6% 3 4 5% 5% 7% 41%	4375
	11th to 20th	Night	21% 8% 4 7% 5% 3 4 4 5% 6% 33%	4110
	21st to end	Night	20% 8% 4 7% 5% 3 5% 4 4 6% 34%	4521
February	1st to 10th	Night	16% 5% 2 4 4 2 3 4 4 6% 51%	2470
	11th to 20th	Night	11% 4 2 4 4 2 5% 4 5% 7% 51%	2302
	21st to end	Night	13% 4 2 3 2 2 3 4 4 7% 55%	1776
March	1st to 10th	Night	15% 5% 2 5% 5% 2 4 4 5% 6% 46%	2057
	11th to 20th	Night	15% 4 2 4 4 2 4 4 4 7% 48%	1980
	21st to end	Night	13% 3 2 4 3 2 4 4 5% 6% 54%	2123
April	1st to 10th	Night	8% 5% 2 4 3 3 5% 4 4 7% 55%	1800
	11th to 20th	Night	8% 3 1 3 4 2 3 3 5% 7% 62%	1779
	21st to end	Night	4 2 1 2 2 2 3 4 4 7% 70%	1800
May	1st to 10th	Night	4 2 1 2 2 2 2 3 5% 7% 71%	1727
	11th to 20th	Night	3 1 1 2 2 1 3 3 4 8% 72%	1462
	21st to end	Night	3 2 1 2 1 3 3 4 7% 74%	1552
June	1st to 10th	Night	4 1 3 2 2 3 3 3 7% 71%	1440
	11th to 20th	Night	1 1 2 1 2 2 2 4 84%	1440
	21st to end	Night	2 1 1 1 2 1 2 2 2 3 86%	1440
July	1st to 10th	Night	1 1 1 1 1 1 2 2 90%	1440
	11th to 20th	Night	1 1 1 1 1 1 1 1 1 2 89%	1497
	21st to end	Night	1 1 1 1 1 1 2 3 6% 83%	1773
August	1st to 10th	Night	2 1 1 2 2 1 2 1 2 4 82%	1611
	11th to 20th	Night	1 1 2 1 2 2 3 5% 83%	1715
	21st to end	Night	1 1 1 1 1 1 1 3 4 86%	1980
September	1st to 10th	Night	1 1 1 1 1 1 1 2 3 88%	1800
	11th to 20th	Night	2 2 1 2 2 1 2 2 2 5% 79%	1800
	21st to end	Night	1 1 1 2 2 1 1 2 3 5% 81%	2031
October	1st to 10th	Night	3 2 1 2 2 2 2 3 4 5% 75%	2160
	11th to 20th	Night	4 2 1 2 2 2 2 4 5% 6% 72%	2160
	21st to end	Night	5% 2 1 3 3 2 2 3 4 6% 70%	2376
November	1st to 10th	Night	7% 4 1 3 3 2 3 3 5% 8% 59%	2317
	11th to 20th	Night	9% 4 2 4 3 2 3 4 5% 7% 58%	2470
	21st to end	Night	10% 4 1 3 4 2 3 4 4 6% 59%	2626
December	1st to 10th	Night	15% 6% 2 4 5% 2 4 3 4 6% 49%	2660
	11th to 20th	Night	24% 8% 3 5% 5% 2 3 4 6% 7% 33%	3276
	21st to end	Night	18% 7% 3 6% 6% 4 5% 5% 5% 7% 35%	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	49% 8% 11% 23% 7% 1	2568
	11th to 20th	Day	55% 6% 9% 13% 12% 5%	2860
	21st to end	Day	54% 8% 10% 15% 10% 3	3146
February	1st to 10th	Day	41% 5% 8% 22% 18% 7%	1710
	11th to 20th	Day	36% 6% 11% 21% 19% 7%	1756
	21st to end	Day	34% 5% 9% 24% 20% 8%	1480
March	1st to 10th	Day	42% 6% 11% 21% 15% 5%	1901
	11th to 20th	Day	40% 5% 10% 23% 16% 6%	1980
	21st to end	Day	35% 7% 13% 20% 19% 6%	2232
April	1st to 10th	Day	36% 5% 12% 22% 18% 7%	2160
	11th to 20th	Day	25% 6% 13% 24% 23% 9%	2132
	21st to end	Day	19% 5% 12% 29% 27% 8%	2160
May	1st to 10th	Day	17% 3 10% 26% 30% 13%	2230
	11th to 20th	Day	16% 4 8% 29% 30% 12%	2430
	21st to end	Day	15% 5% 15% 31% 25% 10%	2724
June	1st to 10th	Day	17% 3 10% 27% 28% 14%	2520
	11th to 20th	Day	7% 2 8% 22% 33% 27%	2520
	21st to end	Day	7% 2 3 13% 39% 37%	2520
July	1st to 10th	Day	4 2 4 10% 27% 54%	2451
	11th to 20th	Day	5% 1 3 13% 27% 51%	2384
	21st to end	Day	6% 2 3 10% 24% 55%	2405
August	1st to 10th	Day	9% 3 3 13% 32% 42%	2312
	11th to 20th	Day	5% 2 2 13% 35% 42%	2183
	21st to end	Day	5% 1 2 13% 37% 43%	2376
September	1st to 10th	Day	5% 2 3 8% 30% 52%	2160
	11th to 20th	Day	12% 2 5% 22% 40% 19%	2160
	21st to end	Day	11% 2 4 20% 34% 29%	1924
October	1st to 10th	Day	14% 3 7% 18% 31% 27%	1800
	11th to 20th	Day	17% 4 9% 20% 24% 26%	1800
	21st to end	Day	21% 3 8% 20% 27% 20%	1980
November	1st to 10th	Day	25% 5% 10% 26% 24% 11%	1760
	11th to 20th	Day	35% 6% 10% 24% 19% 6%	1710
	21st to end	Day	29% 8% 11% 23% 21% 9%	1549
December	1st to 10th	Day	39% 7% 10% 21% 16% 7%	1520
	11th to 20th	Day	57% 5% 9% 11% 15% 3	1928
	21st to end	Day	48% 7% 15% 17% 10% 2	2794
January	1st to 10th	Night	42% 7% 16% 24% 9% 3	4375
	11th to 20th	Night	52% 6% 12% 13% 11% 7%	4110
	21st to end	Night	50% 6% 12% 16% 12% 5%	4521
February	1st to 10th	Night	37% 4 8% 22% 20% 9%	2470
	11th to 20th	Night	32% 5% 10% 22% 22% 9%	2304
	21st to end	Night	30% 5% 9% 26% 23% 8%	1776
March	1st to 10th	Night	39% 5% 14% 18% 18% 6%	2057
	11th to 20th	Night	36% 5% 8% 22% 21% 8%	1980
	21st to end	Night	32% 5% 12% 22% 22% 7%	2123
April	1st to 10th	Night	30% 5% 14% 20% 22% 9%	1800
	11th to 20th	Night	23% 4 11% 27% 22% 12%	1779
	21st to end	Night	16% 5% 13% 29% 29% 8%	1800
May	1st to 10th	Night	14% 5% 10% 23% 35% 14%	1727
	11th to 20th	Night	13% 3 10% 31% 29% 14%	1462
	21st to end	Night	12% 4 14% 32% 27% 11%	1552
June	1st to 10th	Night	16% 4 10% 26% 31% 14%	1440
	11th to 20th	Night	7% 2 8% 21% 33% 29%	1440
	21st to end	Night	8% 1 3 12% 34% 41%	1440
July	1st to 10th	Night	5% 1 3 10% 28% 55%	1400
	11th to 20th	Night	6% 1 2 10% 23% 58%	1449
	21st to end	Night	6% 2 2 9% 26% 56%	1674
August	1st to 10th	Night	9% 3 2 12% 29% 45%	1602
	11th to 20th	Night	6% 2 3 10% 32% 48%	1715
	21st to end	Night	6% 2 2 10% 31% 49%	1980
September	1st to 10th	Night	5% 2 2 7% 31% 53%	1800
	11th to 20th	Night	10% 3 5% 19% 39% 25%	1800
	21st to end	Night	8% 2 5% 19% 32% 34%	2031
October	1st to 10th	Night	13% 3 7% 19% 28% 30%	2160
	11th to 20th	Night	14% 3 8% 18% 29% 29%	2160
	21st to end	Night	17% 3 6% 22% 28% 24%	2376
November	1st to 10th	Night	23% 5% 9% 24% 22% 16%	2317
	11th to 20th	Night	26% 4 11% 27% 23% 9%	2470
	21st to end	Night	27% 5% 9% 21% 27% 12%	2626
December	1st to 10th	Night	37% 6% 10% 21% 18% 10%	2660
	11th to 20th	Night	49% 7% 10% 14% 16% 4	3276
	21st to end	Night	48% 7% 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	35% 5% 17% 21% 18% 4	196
	11th to 20th	Day	17% 7% 19% 22% 24% 11%	370
	21st to end	Day	16% 5% 19% 23% 23% 14%	407
February	1st to 10th	Day	18% 9% 16% 20% 25% 12%	370
	11th to 20th	Day	18% 11% 20% 22% 18% 10%	406
	21st to end	Day	14% 10% 24% 27% 19% 7%	346
March	1st to 10th	Day	16% 10% 24% 28% 16% 6%	420
	11th to 20th	Day	19% 8% 20% 24% 17% 11%	420
	21st to end	Day	15% 11% 24% 25% 19% 6%	462
April	1st to 10th	Day	15% 9% 22% 27% 17% 10%	420
	11th to 20th	Day	10% 9% 26% 27% 15% 13%	412
	21st to end	Day	4 7% 22% 27% 25% 14%	420
May	1st to 10th	Day	5% 7% 24% 30% 23% 11%	423
	11th to 20th	Day	6% 3 25% 28% 25% 13%	448
	21st to end	Day	4 5% 19% 26% 29% 17%	485
June	1st to 10th	Day	4 6% 20% 27% 29% 14%	450
	11th to 20th	Day	1 5% 17% 32% 38% 8%	450
	21st to end	Day	1 2 16% 32% 36% 14%	450
July	1st to 10th	Day	1 1 9% 39% 38% 12%	446
	11th to 20th	Day	1 7% 34% 41% 17%	444
	21st to end	Day	9% 33% 40% 17%	487
August	1st to 10th	Day	2 2 11% 34% 37% 14%	447
	11th to 20th	Day	10% 30% 38% 22%	437
	21st to end	Day	1 9% 27% 43% 21%	495
September	1st to 10th	Day	1 2 7% 28% 42% 21%	450
	11th to 20th	Day	4 3 12% 29% 34% 19%	450
	21st to end	Day	3 3 15% 25% 33% 21%	450
October	1st to 10th	Day	2 7% 16% 25% 26% 24%	450
	11th to 20th	Day	5% 4 15% 22% 30% 25%	450
	21st to end	Day	8% 5% 16% 24% 27% 20%	495
November	1st to 10th	Day	8% 5% 19% 20% 28% 19%	356
	11th to 20th	Day	10% 5% 17% 21% 34% 14%	270
	21st to end	Day	11% 2 15% 32% 27% 12%	194
December	1st to 10th	Day	18% 7% 18% 19% 24% 13%	180
	11th to 20th	Day	18% 5% 20% 27% 19% 11%	180
	21st to end	Day	20% 6% 21% 29% 19% 6%	198
January	1st to 10th	Night	18% 5% 19% 33% 22% 4	760
	11th to 20th	Night	16% 5% 15% 37% 24% 3	760
	21st to end	Night	17% 4 16% 33% 26% 3	836
February	1st to 10th	Night	18% 5% 16% 36% 23% 2	760
	11th to 20th	Night	13% 5% 22% 35% 22% 3	742
	21st to end	Night	14% 6% 24% 35% 19% 2	592
March	1st to 10th	Night	17% 6% 20% 35% 20% 2	720
	11th to 20th	Night	16% 6% 18% 35% 23% 1	720
	21st to end	Night	14% 5% 25% 36% 19% 1	792
April	1st to 10th	Night	10% 4 23% 41% 20% 1	720
	11th to 20th	Night	9% 6% 26% 37% 19% 3	711
	21st to end	Night	6% 4 25% 42% 22% 2	720
May	1st to 10th	Night	5% 3 28% 40% 23% 1	647
	11th to 20th	Night	4 2 22% 50% 22% 1	400
	21st to end	Night	4 2 26% 46% 21%	389
June	1st to 10th	Night	4 2 24% 49% 21% 1	360
	11th to 20th	Night	1 2 26% 51% 21%	360
	21st to end	Night	1 1 22% 53% 23% 1	360
July	1st to 10th	Night	1 15% 61% 23%	350
	11th to 20th	Night	1 14% 60% 23% 1	405
	21st to end	Night	1 1 9% 58% 29% 2	591
August	1st to 10th	Night	2 1 15% 54% 26% 1	537
	11th to 20th	Night	1 14% 51% 31% 2	647
	21st to end	Night	1 11% 49% 38% 1	792
September	1st to 10th	Night	1 2 9% 48% 38% 2	720
	11th to 20th	Night	2 1 16% 43% 33% 4	720
	21st to end	Night	1 2 16% 39% 36% 6%	720
October	1st to 10th	Night	4 3 15% 39% 33% 6%	720
	11th to 20th	Night	4 3 17% 36% 35% 5%	720
	21st to end	Night	6% 3 15% 35% 31% 9%	792
November	1st to 10th	Night	8% 4 16% 34% 33% 5%	740
	11th to 20th	Night	9% 2 18% 39% 28% 4	760
	21st to end	Night	10% 5% 16% 38% 26% 5%	760
December	1st to 10th	Night	16% 6% 17% 34% 22% 5%	760
	11th to 20th	Night	23% 5% 14% 33% 24% 3	760
	21st to end	Night	19% 8% 20% 32% 19% 1	836

Page generated at 2024-02-17 03:28:39. Version ac07

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