Vacaville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Vacaville clear sky chart from 2005-11-06 to 2024-11-05.

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	6% 3 1 3 2 2 3 3 4 6% 66%	105099
	Night	8% 4 1 4 3 3 3 3 4 7% 62%	102689
Transparency	Day	20% 3 8% 20% 25% 24%	104855
	Night	23% 4 9% 19% 22% 23%	102522
Seeing	Day	8% 6% 21% 32% 25% 9%	15314
	Night	9% 3 19% 41% 25% 3	24600

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	17% 8% 3 7% 4 4 3 4 5% 6% 38%	2612
	11th to 20th	Day	18% 9% 4 9% 6% 4 4 3 4 6% 35%	2860
	21st to end	Day	21% 8% 3 7% 5% 4 5% 4 5% 6% 32%	3146
February	1st to 10th	Day	14% 5% 3 6% 4 4 4 3 6% 5% 46%	1710
	11th to 20th	Day	12% 5% 2 5% 4 5% 4 4 5% 7% 46%	1745
	21st to end	Day	11% 5% 2 5% 4 4 4 3 6% 7% 49%	1570
March	1st to 10th	Day	10% 9% 3 10% 6% 5% 6% 5% 6% 7% 32%	3349
	11th to 20th	Day	9% 4 2 4 3 3 3 2 6% 6% 58%	3490
	21st to end	Day	11% 6% 2 6% 5% 4 5% 4 7% 8% 41%	3904
April	1st to 10th	Day	10% 7% 2 4 4 4 4 4 7% 7% 46%	2280
	11th to 20th	Day	8% 3 2 3 2 3 3 4 5% 8% 58%	2249
	21st to end	Day	3 3 1 3 3 3 4 3 5% 9% 64%	2280
May	1st to 10th	Day	5% 2 1 2 2 2 2 1 4 5% 76%	3945
	11th to 20th	Day	2 1 1 1 1 2 2 4 6% 79%	4247
	21st to end	Day	2 1 1 1 2 2 2 4 6% 79%	4813
June	1st to 10th	Day	3 3 1 2 2 3 3 3 5% 8% 67%	2660
	11th to 20th	Day	1 1 1 2 2 2 4 6% 82%	2660
	21st to end	Day	2 1 1 1 1 1 2 4 5% 83%	2660
July	1st to 10th	Day	1 1 1 2 3 92%	4420
	11th to 20th	Day	1 1 1 1 1 1 1 1 2 4 86%	4244
	21st to end	Day	1 1 1 1 1 2 5% 87%	4455
August	1st to 10th	Day	1 1 1 1 1 2 3 5% 7% 76%	4091
	11th to 20th	Day	1 1 1 2 3 4 88%	3843
	21st to end	Day	1 1 1 1 1 1 2 4 86%	4180
September	1st to 10th	Day	1 1 1 1 2 1 3 4 86%	2280
	11th to 20th	Day	1 2 1 2 2 2 2 3 5% 7% 74%	2280
	21st to end	Day	2 1 1 2 2 2 2 2 3 5% 80%	2021
October	1st to 10th	Day	1 2 1 3 2 2 2 2 4 6% 76%	3180
	11th to 20th	Day	3 2 1 2 2 2 2 2 4 6% 73%	3161
	21st to end	Day	4 2 1 4 3 4 3 3 4 7% 65%	3448
November	1st to 10th	Day	7% 4 1 4 3 3 4 3 5% 8% 59%	1825
	11th to 20th	Day	8% 6% 2 5% 4 5% 4 3 6% 6% 51%	1710
	21st to end	Day	9% 4 2 3 3 4 4 3 5% 7% 56%	1539
December	1st to 10th	Day	13% 6% 2 5% 3 4 4 3 5% 6% 47%	1520
	11th to 20th	Day	27% 10% 2 7% 4 3 2 3 4 6% 32%	1928
	21st to end	Day	19% 8% 3 7% 4 4 4 3 5% 8% 35%	2794
January	1st to 10th	Night	12% 7% 3 6% 4 3 4 3 5% 9% 45%	4331
	11th to 20th	Night	19% 7% 3 7% 4 4 4 4 5% 7% 35%	4110
	21st to end	Night	18% 8% 3 7% 4 4 4 4 5% 7% 35%	4521
February	1st to 10th	Night	15% 5% 2 5% 4 4 4 3 4 5% 50%	2470
	11th to 20th	Night	10% 4 2 5% 4 4 4 3 5% 8% 49%	2320
	21st to end	Night	12% 4 1 5% 3 3 3 2 4 8% 56%	1884
March	1st to 10th	Night	11% 7% 3 8% 5% 5% 4 4 6% 7% 40%	3521
	11th to 20th	Night	11% 4 1 3 2 3 3 2 4 5% 62%	3490
	21st to end	Night	10% 6% 2 6% 5% 4 5% 4 5% 7% 46%	3747
April	1st to 10th	Night	6% 5% 1 3 5% 4 5% 3 5% 7% 56%	1900
	11th to 20th	Night	7% 4 1 3 3 3 3 3 5% 6% 63%	1879
	21st to end	Night	4 2 1 2 2 2 2 3 5% 7% 68%	1900
May	1st to 10th	Night	2 1 1 1 1 2 2 1 3 6% 79%	3025
	11th to 20th	Night	1 1 2 1 1 2 2 3 5% 82%	2649
	21st to end	Night	1 1 1 1 1 1 1 4 6% 82%	2762
June	1st to 10th	Night	3 2 1 3 2 3 3 3 4 7% 70%	1520
	11th to 20th	Night	1 1 1 1 1 1 2 2 3 5% 83%	1520
	21st to end	Night	1 1 1 1 1 1 2 3 5% 82%	1520
July	1st to 10th	Night	1 1 1 1 3 92%	2540
	11th to 20th	Night	1 1 1 1 2 1 1 2 5% 84%	2718
	21st to end	Night	1 1 1 1 1 1 2 5% 9% 79%	3109
August	1st to 10th	Night	2 1 1 2 1 1 2 3 5% 9% 73%	2848
	11th to 20th	Night	1 1 1 2 3 6% 85%	2999
	21st to end	Night	1 1 1 1 1 1 1 3 6% 84%	3498
September	1st to 10th	Night	1 1 1 1 1 3 7% 84%	1900
	11th to 20th	Night	2 1 1 2 1 1 3 2 4 8% 75%	1900
	21st to end	Night	1 1 1 2 2 2 2 3 6% 80%	2155
October	1st to 10th	Night	2 1 1 2 2 2 2 2 4 6% 77%	3800
	11th to 20th	Night	2 1 1 3 2 2 3 2 4 7% 75%	3777
	21st to end	Night	4 2 1 3 3 3 4 3 5% 7% 66%	4121
November	1st to 10th	Night	6% 4 1 3 3 3 3 3 5% 8% 60%	2351
	11th to 20th	Night	7% 5% 2 4 3 3 3 3 5% 8% 57%	2470
	21st to end	Night	8% 4 2 4 3 2 4 4 4 6% 59%	2636
December	1st to 10th	Night	14% 5% 2 6% 4 3 3 3 4 6% 49%	2660
	11th to 20th	Night	25% 8% 2 5% 4 3 4 3 6% 6% 33%	3276
	21st to end	Night	16% 7% 3 7% 5% 4 5% 3 6% 6% 38%	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	46% 7% 12% 24% 8% 2	2612
	11th to 20th	Day	51% 5% 11% 15% 12% 6%	2860
	21st to end	Day	52% 6% 10% 17% 11% 4	3146
February	1st to 10th	Day	39% 4 8% 22% 19% 8%	1710
	11th to 20th	Day	36% 6% 10% 20% 20% 8%	1754
	21st to end	Day	33% 5% 11% 25% 19% 8%	1570
March	1st to 10th	Day	46% 8% 11% 16% 16% 3	3349
	11th to 20th	Day	27% 4 10% 28% 19% 12%	3490
	21st to end	Day	36% 9% 16% 22% 14% 3	3904
April	1st to 10th	Day	34% 6% 12% 22% 19% 7%	2280
	11th to 20th	Day	24% 5% 14% 25% 23% 9%	2252
	21st to end	Day	19% 4 13% 30% 28% 7%	2280
May	1st to 10th	Day	13% 2 9% 29% 25% 23%	3945
	11th to 20th	Day	8% 2 5% 30% 38% 17%	4250
	21st to end	Day	8% 2 10% 38% 29% 11%	4814
June	1st to 10th	Day	16% 4 10% 29% 29% 11%	2660
	11th to 20th	Day	6% 2 8% 23% 36% 24%	2660
	21st to end	Day	6% 1 3 14% 37% 39%	2660
July	1st to 10th	Day	2 1 2 6% 15% 74%	4351
	11th to 20th	Day	6% 1 3 8% 17% 66%	4170
	21st to end	Day	3 1 2 7% 26% 61%	4315
August	1st to 10th	Day	8% 2 2 11% 27% 49%	4076
	11th to 20th	Day	3 1 2 10% 42% 41%	3882
	21st to end	Day	5% 1 4 11% 39% 41%	4179
September	1st to 10th	Day	5% 1 3 8% 33% 51%	2280
	11th to 20th	Day	12% 2 6% 22% 41% 18%	2280
	21st to end	Day	10% 2 4 19% 35% 30%	2021
October	1st to 10th	Day	11% 2 4 12% 28% 43%	3180
	11th to 20th	Day	13% 4 7% 25% 29% 22%	3161
	21st to end	Day	19% 4 8% 24% 31% 15%	3448
November	1st to 10th	Day	24% 5% 9% 28% 22% 11%	1825
	11th to 20th	Day	34% 5% 10% 25% 20% 6%	1710
	21st to end	Day	29% 4 11% 23% 24% 10%	1539
December	1st to 10th	Day	37% 5% 12% 22% 17% 8%	1520
	11th to 20th	Day	56% 5% 9% 12% 15% 4	1928
	21st to end	Day	47% 7% 13% 19% 12% 3	2794
January	1st to 10th	Night	37% 7% 18% 24% 10% 3	4331
	11th to 20th	Night	49% 7% 14% 13% 11% 7%	4110
	21st to end	Night	48% 6% 13% 15% 12% 5%	4521
February	1st to 10th	Night	36% 3 8% 21% 21% 10%	2470
	11th to 20th	Night	32% 4 10% 22% 21% 10%	2322
	21st to end	Night	30% 3 9% 28% 23% 7%	1884
March	1st to 10th	Night	40% 8% 16% 16% 17% 4	3521
	11th to 20th	Night	27% 3 8% 27% 22% 13%	3490
	21st to end	Night	35% 7% 13% 26% 14% 4	3747
April	1st to 10th	Night	28% 5% 14% 21% 22% 9%	1900
	11th to 20th	Night	23% 4 12% 29% 20% 13%	1879
	21st to end	Night	16% 3 12% 30% 31% 7%	1900
May	1st to 10th	Night	10% 2 9% 26% 32% 21%	3025
	11th to 20th	Night	7% 2 5% 22% 36% 27%	2649
	21st to end	Night	7% 2 9% 37% 29% 16%	2762
June	1st to 10th	Night	15% 4 10% 25% 32% 15%	1520
	11th to 20th	Night	7% 2 7% 19% 38% 28%	1520
	21st to end	Night	7% 2 3 11% 32% 44%	1520
July	1st to 10th	Night	3 1 5% 15% 76%	2500
	11th to 20th	Night	6% 1 2 7% 14% 70%	2669
	21st to end	Night	5% 1 1 8% 23% 63%	3011
August	1st to 10th	Night	10% 2 2 8% 22% 55%	2839
	11th to 20th	Night	3 1 2 7% 33% 54%	3026
	21st to end	Night	6% 1 2 8% 34% 48%	3498
September	1st to 10th	Night	5% 1 2 8% 28% 56%	1900
	11th to 20th	Night	10% 2 5% 19% 38% 25%	1900
	21st to end	Night	9% 2 4 18% 31% 37%	2155
October	1st to 10th	Night	10% 2 5% 11% 19% 53%	3800
	11th to 20th	Night	11% 3 7% 27% 27% 25%	3777
	21st to end	Night	18% 3 7% 21% 30% 22%	4121
November	1st to 10th	Night	23% 4 10% 26% 21% 16%	2351
	11th to 20th	Night	27% 3 12% 27% 22% 9%	2470
	21st to end	Night	27% 4 9% 22% 25% 13%	2636
December	1st to 10th	Night	37% 4 10% 20% 18% 11%	2660
	11th to 20th	Night	50% 5% 11% 15% 16% 3	3276
	21st to end	Night	45% 9% 13% 17% 13% 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	31% 5% 21% 24% 16% 3	227
	11th to 20th	Day	17% 6% 20% 31% 19% 7%	370
	21st to end	Day	16% 5% 19% 26% 27% 8%	407
February	1st to 10th	Day	17% 10% 20% 25% 22% 7%	370
	11th to 20th	Day	18% 10% 24% 25% 17% 6%	403
	21st to end	Day	13% 8% 28% 29% 16% 5%	382
March	1st to 10th	Day	18% 10% 26% 29% 12% 5%	460
	11th to 20th	Day	18% 6% 25% 24% 18% 8%	460
	21st to end	Day	14% 13% 26% 27% 17% 3	506
April	1st to 10th	Day	13% 8% 27% 25% 18% 8%	460
	11th to 20th	Day	9% 11% 30% 23% 18% 9%	452
	21st to end	Day	3 10% 27% 26% 24% 10%	460
May	1st to 10th	Day	5% 9% 30% 30% 21% 5%	463
	11th to 20th	Day	5% 5% 28% 29% 23% 10%	488
	21st to end	Day	2 7% 24% 31% 26% 10%	529
June	1st to 10th	Day	4 6% 25% 34% 22% 8%	490
	11th to 20th	Day	1 8% 22% 39% 25% 5%	490
	21st to end	Day	1 3 23% 39% 29% 6%	490
July	1st to 10th	Day	1 1 15% 45% 30% 7%	486
	11th to 20th	Day	1 13% 43% 33% 9%	484
	21st to end	Day	1 1 13% 44% 32% 10%	531
August	1st to 10th	Day	2 2 14% 44% 29% 9%	487
	11th to 20th	Day	1 3 18% 37% 28% 13%	477
	21st to end	Day	1 1 13% 38% 32% 15%	539
September	1st to 10th	Day	1 2 12% 36% 35% 15%	490
	11th to 20th	Day	2 6% 18% 33% 28% 13%	490
	21st to end	Day	2 3 18% 32% 29% 14%	490
October	1st to 10th	Day	2 6% 19% 27% 28% 18%	490
	11th to 20th	Day	6% 6% 18% 27% 27% 17%	490
	21st to end	Day	7% 5% 20% 27% 27% 13%	539
November	1st to 10th	Day	8% 5% 22% 23% 29% 13%	397
	11th to 20th	Day	11% 6% 17% 30% 27% 9%	270
	21st to end	Day	11% 5% 18% 35% 28% 3	189
December	1st to 10th	Day	21% 5% 19% 28% 18% 9%	180
	11th to 20th	Day	21% 5% 19% 29% 22% 5%	180
	21st to end	Day	21% 5% 25% 24% 21% 4	198
January	1st to 10th	Night	18% 3 16% 36% 21% 5%	760
	11th to 20th	Night	15% 5% 16% 39% 21% 5%	760
	21st to end	Night	17% 4 16% 35% 25% 3	836
February	1st to 10th	Night	17% 6% 16% 37% 21% 3	760
	11th to 20th	Night	13% 5% 23% 32% 23% 4	744
	21st to end	Night	13% 7% 21% 38% 20% 2	628
March	1st to 10th	Night	16% 6% 21% 33% 23% 2	760
	11th to 20th	Night	16% 5% 19% 35% 23% 2	760
	21st to end	Night	12% 5% 25% 39% 17% 1	836
April	1st to 10th	Night	8% 5% 24% 43% 18% 2	760
	11th to 20th	Night	9% 6% 27% 35% 19% 3	751
	21st to end	Night	4 4 27% 41% 22% 2	760
May	1st to 10th	Night	5% 3 29% 39% 22% 2	670
	11th to 20th	Night	3 2 22% 47% 24% 2	455
	21st to end	Night	3 3 27% 46% 20%	411
June	1st to 10th	Night	4 2 24% 49% 20%	380
	11th to 20th	Night	1 2 26% 54% 17%	380
	21st to end	Night	1 1 27% 51% 21%	380
July	1st to 10th	Night	1 1 16% 61% 22%	370
	11th to 20th	Night	1 15% 55% 27% 2	467
	21st to end	Night	1 1 13% 54% 29% 2	624
August	1st to 10th	Night	2 19% 49% 28% 3	567
	11th to 20th	Night	1 16% 50% 30% 2	673
	21st to end	Night	1 13% 48% 36% 1	836
September	1st to 10th	Night	1 1 12% 48% 36% 3	760
	11th to 20th	Night	2 1 18% 45% 30% 4	760
	21st to end	Night	2 2 16% 40% 36% 5%	760
October	1st to 10th	Night	3 3 14% 42% 32% 6%	760
	11th to 20th	Night	4 3 17% 38% 32% 5%	760
	21st to end	Night	6% 3 18% 35% 31% 8%	836
November	1st to 10th	Night	7% 4 18% 32% 34% 5%	760
	11th to 20th	Night	9% 2 16% 39% 28% 5%	760
	21st to end	Night	10% 5% 16% 40% 24% 5%	760
December	1st to 10th	Night	16% 6% 16% 35% 22% 5%	760
	11th to 20th	Night	22% 4 16% 34% 22% 3	760
	21st to end	Night	19% 7% 20% 33% 20% 1	836

Page generated at 2024-11-02 23:11:15. Version ac07

Copyright © 2024 Attilla Danko.