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 2024-10-24.

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	7% 4 1 3 2 2 3 2 4 5% 66%	101095
	Night	9% 4 1 4 3 3 3 2 4 6% 62%	97862
Transparency	Day	22% 4 7% 18% 24% 24%	100849
	Night	24% 4 9% 19% 23% 22%	97697
Seeing	Day	8% 5% 17% 27% 28% 15%	15222
	Night	9% 4 18% 41% 26% 3	24500

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 6% 4 5% 5% 4 5% 5% 34%	2568
	11th to 20th	Day	20% 11% 4 9% 5% 4 4 3 3 5% 33%	2860
	21st to end	Day	23% 10% 3 8% 4 5% 4 3 5% 7% 28%	3146
February	1st to 10th	Day	16% 6% 3 6% 4 4 4 3 4 5% 47%	1710
	11th to 20th	Day	12% 5% 2 5% 4 4 4 3 4 8% 48%	1756
	21st to end	Day	13% 5% 2 4 3 5% 3 3 4 7% 51%	1570
March	1st to 10th	Day	12% 8% 4 9% 6% 5% 5% 4 6% 6% 34%	3317
	11th to 20th	Day	10% 5% 1 4 3 2 3 4 5% 7% 56%	3490
	21st to end	Day	12% 7% 2 7% 5% 5% 5% 5% 6% 7% 40%	3917
April	1st to 10th	Day	11% 7% 2 5% 3 3 4 4 5% 8% 48%	2280
	11th to 20th	Day	8% 4 1 4 3 3 4 3 5% 6% 58%	2249
	21st to end	Day	3 3 1 2 3 3 4 3 4 9% 64%	2280
May	1st to 10th	Day	5% 2 1 2 2 2 2 2 3 5% 76%	3922
	11th to 20th	Day	2 2 2 1 2 2 2 3 5% 80%	4301
	21st to end	Day	2 1 1 1 1 2 2 4 6% 79%	4813
June	1st to 10th	Day	4 3 1 2 2 2 3 3 4 7% 69%	2660
	11th to 20th	Day	1 1 1 1 2 2 2 4 5% 82%	2660
	21st to end	Day	2 1 1 1 1 2 1 3 3 85%	2660
July	1st to 10th	Day	1 1 1 1 2 93%	4420
	11th to 20th	Day	1 1 1 1 1 2 1 2 3 87%	4307
	21st to end	Day	1 1 1 1 1 2 3 89%	4455
August	1st to 10th	Day	1 1 1 2 1 2 2 2 5% 5% 78%	4091
	11th to 20th	Day	1 1 1 1 1 1 2 3 89%	3821
	21st to end	Day	1 1 1 1 1 1 1 2 3 88%	4180
September	1st to 10th	Day	1 1 1 1 1 1 2 3 88%	2280
	11th to 20th	Day	2 2 1 2 2 2 2 2 4 6% 76%	2280
	21st to end	Day	3 2 1 2 1 2 1 1 3 4 81%	2030
October	1st to 10th	Day	2 2 1 3 3 2 2 2 3 5% 75%	1900
	11th to 20th	Day	5% 2 1 3 2 2 3 2 4 5% 72%	1900
	21st to end	Day	6% 3 2 4 3 2 3 3 3 5% 67%	2011
November	1st to 10th	Day	9% 4 1 3 3 3 4 3 4 8% 59%	1760
	11th to 20th	Day	10% 6% 2 6% 4 4 3 4 5% 6% 51%	1710
	21st to end	Day	10% 4 1 5% 3 3 4 4 5% 7% 53%	1549
December	1st to 10th	Day	14% 7% 2 5% 4 5% 3 4 4 7% 45%	1520
	11th to 20th	Day	27% 10% 3 6% 4 4 3 2 5% 5% 31%	1928
	21st to end	Day	17% 8% 3 7% 5% 5% 4 4 5% 8% 33%	2794
January	1st to 10th	Night	13% 7% 3 7% 5% 4 4 4 5% 7% 41%	4375
	11th to 20th	Night	21% 8% 4 8% 4 4 4 3 5% 6% 33%	4110
	21st to end	Night	20% 8% 3 8% 4 4 5% 3 4 6% 33%	4521
February	1st to 10th	Night	15% 5% 2 4 4 3 3 3 4 5% 51%	2470
	11th to 20th	Night	11% 4 2 4 4 3 4 4 6% 7% 51%	2309
	21st to end	Night	13% 4 2 4 2 3 3 3 4 7% 56%	1884
March	1st to 10th	Night	13% 7% 3 7% 5% 4 4 4 5% 7% 41%	3555
	11th to 20th	Night	13% 3 1 3 2 2 3 2 3 5% 60%	3490
	21st to end	Night	13% 6% 2 6% 5% 4 5% 3 6% 7% 44%	3722
April	1st to 10th	Night	8% 5% 2 4 3 4 4 3 4 7% 55%	1900
	11th to 20th	Night	7% 4 1 3 4 2 3 3 5% 6% 62%	1879
	21st to end	Night	4 2 1 2 2 2 2 4 4 7% 70%	1900
May	1st to 10th	Night	2 1 1 1 1 1 2 2 4 6% 79%	3037
	11th to 20th	Night	2 1 1 1 1 2 1 2 5% 83%	2590
	21st to end	Night	2 1 1 1 1 2 2 3 5% 83%	2762
June	1st to 10th	Night	4 1 3 2 3 3 2 3 7% 71%	1520
	11th to 20th	Night	1 1 1 2 2 2 1 2 4 84%	1520
	21st to end	Night	2 1 1 1 1 1 1 1 2 3 86%	1520
July	1st to 10th	Night	1 1 1 1 1 94%	2540
	11th to 20th	Night	1 1 1 2 1 1 2 1 2 3 86%	2653
	21st to end	Night	1 1 1 1 1 1 1 2 5% 87%	3109
August	1st to 10th	Night	2 2 1 2 2 2 2 2 4 5% 77%	2848
	11th to 20th	Night	1 1 1 1 1 2 3 89%	3022
	21st to end	Night	2 1 1 1 1 1 1 2 2 88%	3498
September	1st to 10th	Night	1 1 1 1 1 1 2 3 88%	1900
	11th to 20th	Night	2 2 1 2 2 2 2 2 3 5% 78%	1900
	21st to end	Night	1 1 1 2 1 1 1 2 3 5% 82%	2145
October	1st to 10th	Night	3 2 1 2 2 2 2 2 4 5% 75%	2280
	11th to 20th	Night	3 2 1 2 2 2 2 3 5% 6% 73%	2280
	21st to end	Night	5% 2 1 4 2 3 2 2 4 6% 69%	2412
November	1st to 10th	Night	7% 4 1 3 3 3 3 3 6% 8% 59%	2317
	11th to 20th	Night	9% 4 2 4 3 2 3 3 5% 7% 58%	2470
	21st to end	Night	9% 4 2 4 3 3 3 3 4 6% 59%	2626
December	1st to 10th	Night	15% 6% 2 5% 4 3 3 2 4 6% 49%	2660
	11th to 20th	Night	23% 8% 2 6% 4 3 3 3 6% 7% 33%	3276
	21st to end	Night	18% 7% 3 7% 5% 5% 5% 4 5% 6% 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%	1765
	21st to end	Day	34% 5% 9% 25% 19% 7%	1570
March	1st to 10th	Day	48% 8% 10% 15% 15% 3	3317
	11th to 20th	Day	28% 5% 11% 27% 17% 12%	3490
	21st to end	Day	39% 8% 14% 23% 13% 3	3917
April	1st to 10th	Day	35% 5% 12% 23% 19% 7%	2280
	11th to 20th	Day	25% 6% 13% 24% 23% 9%	2252
	21st to end	Day	19% 5% 12% 29% 27% 8%	2280
May	1st to 10th	Day	13% 3 8% 28% 25% 23%	3922
	11th to 20th	Day	9% 3 5% 27% 39% 16%	4304
	21st to end	Day	9% 4 10% 34% 30% 14%	4814
June	1st to 10th	Day	17% 3 10% 27% 29% 14%	2660
	11th to 20th	Day	7% 2 8% 21% 34% 27%	2660
	21st to end	Day	7% 2 3 12% 38% 39%	2660
July	1st to 10th	Day	3 1 2 6% 15% 74%	4351
	11th to 20th	Day	7% 1 3 8% 16% 66%	4232
	21st to end	Day	3 2 2 7% 25% 61%	4315
August	1st to 10th	Day	9% 2 3 9% 26% 51%	4076
	11th to 20th	Day	3 2 2 10% 42% 42%	3859
	21st to end	Day	6% 1 2 11% 39% 41%	4179
September	1st to 10th	Day	5% 2 2 8% 30% 53%	2280
	11th to 20th	Day	13% 2 5% 22% 40% 18%	2280
	21st to end	Day	11% 2 4 19% 35% 30%	2030
October	1st to 10th	Day	14% 3 6% 17% 30% 29%	1900
	11th to 20th	Day	16% 4 9% 20% 25% 25%	1900
	21st to end	Day	20% 3 8% 21% 27% 19%	2011
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%	2311
	21st to end	Night	29% 5% 9% 26% 23% 8%	1884
March	1st to 10th	Night	42% 7% 16% 16% 15% 4	3555
	11th to 20th	Night	27% 4 8% 25% 22% 14%	3490
	21st to end	Night	37% 6% 14% 25% 14% 4	3722
April	1st to 10th	Night	29% 5% 13% 22% 22% 9%	1900
	11th to 20th	Night	23% 4 12% 28% 21% 11%	1879
	21st to end	Night	15% 5% 13% 30% 29% 8%	1900
May	1st to 10th	Night	9% 4 10% 25% 31% 20%	3037
	11th to 20th	Night	7% 2 6% 25% 40% 19%	2590
	21st to end	Night	7% 2 9% 39% 29% 14%	2762
June	1st to 10th	Night	15% 4 10% 26% 31% 14%	1520
	11th to 20th	Night	7% 2 7% 21% 34% 29%	1520
	21st to end	Night	7% 1 3 11% 33% 43%	1520
July	1st to 10th	Night	3 1 1 5% 15% 75%	2500
	11th to 20th	Night	7% 1 2 6% 14% 69%	2605
	21st to end	Night	4 1 1 6% 25% 63%	3011
August	1st to 10th	Night	10% 3 2 7% 24% 54%	2839
	11th to 20th	Night	3 1 2 7% 37% 50%	3050
	21st to end	Night	7% 1 2 8% 33% 49%	3498
September	1st to 10th	Night	5% 2 2 7% 30% 55%	1900
	11th to 20th	Night	11% 3 5% 19% 38% 24%	1900
	21st to end	Night	8% 1 5% 19% 32% 35%	2145
October	1st to 10th	Night	12% 3 7% 18% 27% 33%	2280
	11th to 20th	Night	13% 3 7% 19% 29% 28%	2280
	21st to end	Night	17% 4 6% 22% 28% 24%	2412
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% 21% 22% 18% 10%	409
	21st to end	Day	13% 10% 23% 28% 19% 7%	382
March	1st to 10th	Day	16% 10% 26% 27% 15% 6%	460
	11th to 20th	Day	18% 9% 21% 22% 18% 11%	460
	21st to end	Day	15% 11% 24% 26% 18% 5%	506
April	1st to 10th	Day	14% 9% 22% 27% 17% 11%	460
	11th to 20th	Day	10% 9% 25% 27% 16% 14%	452
	21st to end	Day	4 7% 22% 27% 25% 14%	460
May	1st to 10th	Day	6% 6% 25% 31% 22% 10%	463
	11th to 20th	Day	6% 2 23% 27% 27% 14%	488
	21st to end	Day	3 5% 18% 27% 30% 17%	529
June	1st to 10th	Day	4 5% 20% 28% 30% 13%	490
	11th to 20th	Day	1 5% 17% 32% 37% 8%	490
	21st to end	Day	1 1 16% 33% 36% 13%	490
July	1st to 10th	Day	1 1 8% 39% 37% 14%	486
	11th to 20th	Day	1 8% 33% 41% 17%	484
	21st to end	Day	1 10% 33% 39% 17%	531
August	1st to 10th	Day	2 1 11% 33% 38% 14%	487
	11th to 20th	Day	1 11% 30% 36% 20%	477
	21st to end	Day	1 9% 27% 40% 23%	539
September	1st to 10th	Day	1 1 7% 29% 41% 21%	490
	11th to 20th	Day	3 3 12% 29% 33% 19%	490
	21st to end	Day	2 3 14% 24% 34% 22%	490
October	1st to 10th	Day	2 6% 14% 26% 27% 24%	490
	11th to 20th	Day	5% 5% 14% 22% 28% 25%	490
	21st to end	Day	8% 5% 16% 24% 28% 19%	508
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	744
	21st to end	Night	13% 6% 23% 36% 19% 2	628
March	1st to 10th	Night	17% 7% 20% 35% 19% 2	760
	11th to 20th	Night	16% 7% 18% 34% 24% 1	760
	21st to end	Night	14% 6% 25% 37% 18% 1	836
April	1st to 10th	Night	10% 5% 24% 40% 20% 1	760
	11th to 20th	Night	9% 6% 25% 37% 20% 3	751
	21st to end	Night	5% 4 24% 43% 22% 2	760
May	1st to 10th	Night	4 4 28% 40% 22% 1	682
	11th to 20th	Night	3 2 21% 51% 21% 1	422
	21st to end	Night	4 2 26% 47% 21%	411
June	1st to 10th	Night	4 2 24% 49% 21% 1	380
	11th to 20th	Night	1 2 27% 50% 20%	380
	21st to end	Night	1 1 23% 53% 22% 1	380
July	1st to 10th	Night	1 14% 62% 23%	370
	11th to 20th	Night	1 14% 59% 24% 1	429
	21st to end	Night	1 1 10% 57% 29% 2	624
August	1st to 10th	Night	2 1 16% 54% 26% 1	567
	11th to 20th	Night	1 15% 52% 30% 2	684
	21st to end	Night	1 1 12% 48% 37% 2	836
September	1st to 10th	Night	1 2 10% 48% 38% 2	760
	11th to 20th	Night	2 2 17% 44% 32% 4	760
	21st to end	Night	1 2 16% 39% 36% 6%	760
October	1st to 10th	Night	3 3 15% 39% 34% 6%	760
	11th to 20th	Night	4 3 17% 36% 34% 5%	760
	21st to end	Night	6% 3 15% 36% 31% 9%	804
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 2024-10-20 23:20:05. Version ac07

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