Vallejo Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Vallejo Observatory clear sky chart from 2005-11-06 to 2024-11-08.

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% 4 2 4 3 3 3 3 5% 7% 60%	105095
	Night	8% 5% 2 6% 4 3 3 3 5% 7% 55%	102752
Transparency	Day	24% 4 8% 20% 24% 21%	104853
	Night	28% 5% 10% 19% 21% 17%	102583
Seeing	Day	8% 10% 27% 34% 17% 4	15378
	Night	10% 5% 19% 38% 25% 4	24665

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% 10% 3 8% 4 5% 4 4 5% 7% 35%	2669
	11th to 20th	Day	18% 10% 5% 9% 4 5% 3 2 4 6% 33%	2860
	21st to end	Day	20% 9% 3 7% 5% 5% 5% 4 5% 7% 30%	3146
February	1st to 10th	Day	15% 6% 2 7% 4 4 5% 3 4 6% 45%	1710
	11th to 20th	Day	13% 8% 3 6% 4 4 4 4 5% 8% 42%	1737
	21st to end	Day	13% 5% 3 5% 4 4 4 3 5% 6% 48%	1570
March	1st to 10th	Day	11% 8% 4 10% 6% 6% 6% 4 6% 7% 30%	3379
	11th to 20th	Day	9% 5% 2 4 4 3 3 3 5% 6% 55%	3490
	21st to end	Day	11% 6% 2 7% 4 5% 5% 4 7% 9% 38%	3881
April	1st to 10th	Day	11% 7% 2 5% 5% 4 3 4 7% 8% 45%	2280
	11th to 20th	Day	8% 4 2 5% 3 3 4 4 5% 7% 56%	2249
	21st to end	Day	3 4 2 3 3 3 3 3 5% 10% 61%	2280
May	1st to 10th	Day	5% 3 1 2 2 2 2 2 3 5% 74%	3955
	11th to 20th	Day	2 2 1 2 2 2 2 2 4 7% 73%	4192
	21st to end	Day	2 2 1 3 2 2 2 2 4 6% 75%	4813
June	1st to 10th	Day	3 4 1 4 2 4 3 3 5% 7% 63%	2660
	11th to 20th	Day	1 2 1 2 2 2 3 3 4 7% 75%	2660
	21st to end	Day	1 2 1 2 2 2 2 2 4 5% 76%	2660
July	1st to 10th	Day	1 1 2 2 2 1 2 2 4 84%	4420
	11th to 20th	Day	1 1 1 2 2 3 2 2 4 6% 76%	4179
	21st to end	Day	1 1 3 2 2 2 2 4 5% 78%	4455
August	1st to 10th	Day	1 2 1 3 2 3 4 4 7% 8% 65%	4091
	11th to 20th	Day	1 1 2 2 2 2 2 3 5% 80%	3851
	21st to end	Day	1 2 1 3 2 2 3 2 4 5% 74%	4180
September	1st to 10th	Day	2 1 3 2 2 2 2 3 5% 77%	2280
	11th to 20th	Day	2 4 2 5% 2 3 3 3 3 8% 65%	2280
	21st to end	Day	2 2 1 2 2 2 2 2 4 6% 74%	2010
October	1st to 10th	Day	1 2 1 3 2 2 3 3 4 6% 72%	3180
	11th to 20th	Day	4 4 2 5% 3 2 2 2 5% 6% 65%	3161
	21st to end	Day	4 4 1 5% 3 4 4 3 6% 8% 58%	3448
November	1st to 10th	Day	8% 4 2 4 3 3 3 3 5% 7% 58%	1882
	11th to 20th	Day	9% 8% 3 7% 4 4 4 3 5% 7% 47%	1710
	21st to end	Day	10% 6% 1 4 4 3 4 4 5% 7% 53%	1535
December	1st to 10th	Day	13% 7% 3 6% 4 3 3 4 5% 7% 44%	1520
	11th to 20th	Day	23% 12% 3 8% 5% 4 3 3 4 5% 30%	1928
	21st to end	Day	19% 9% 3 7% 5% 4 4 4 5% 8% 32%	2794
January	1st to 10th	Night	14% 7% 3 8% 4 4 4 3 5% 6% 42%	4277
	11th to 20th	Night	18% 9% 4 9% 5% 5% 4 3 5% 7% 32%	4110
	21st to end	Night	21% 10% 3 8% 5% 4 4 3 4 6% 32%	4521
February	1st to 10th	Night	14% 6% 2 5% 4 4 3 3 4 6% 48%	2470
	11th to 20th	Night	11% 7% 2 6% 4 3 4 3 5% 8% 47%	2328
	21st to end	Night	11% 6% 1 4 3 4 4 3 5% 7% 52%	1884
March	1st to 10th	Night	12% 9% 3 9% 5% 4 4 3 5% 7% 38%	3490
	11th to 20th	Night	11% 5% 2 4 3 3 3 2 4 6% 57%	3490
	21st to end	Night	11% 8% 3 8% 5% 4 4 3 5% 6% 43%	3772
April	1st to 10th	Night	8% 6% 2 6% 5% 4 3 3 6% 7% 51%	1900
	11th to 20th	Night	7% 5% 2 4 4 3 3 3 4 7% 59%	1879
	21st to end	Night	4 3 1 4 3 3 3 3 5% 8% 63%	1900
May	1st to 10th	Night	4 2 1 4 2 2 2 2 3 4 74%	3002
	11th to 20th	Night	1 2 1 5% 3 3 3 3 5% 8% 66%	2707
	21st to end	Night	2 1 1 3 2 2 2 2 3 4 76%	2762
June	1st to 10th	Night	3 3 1 4 4 3 4 3 5% 10% 59%	1520
	11th to 20th	Night	1 1 1 3 3 3 3 2 5% 7% 72%	1520
	21st to end	Night	1 2 2 3 2 3 3 3 4 7% 71%	1520
July	1st to 10th	Night	1 1 2 3 2 2 2 3 4 80%	2540
	11th to 20th	Night	1 2 1 4 4 4 4 3 5% 6% 67%	2785
	21st to end	Night	1 1 1 7% 5% 5% 4 4 6% 7% 59%	3109
August	1st to 10th	Night	2 3 1 5% 5% 4 4 5% 6% 9% 54%	2848
	11th to 20th	Night	1 1 3 3 3 3 2 5% 6% 72%	2993
	21st to end	Night	2 2 1 5% 3 3 2 2 4 7% 68%	3498
September	1st to 10th	Night	1 2 3 2 2 3 3 5% 7% 72%	1900
	11th to 20th	Night	3 4 2 6% 3 4 3 3 5% 7% 61%	1900
	21st to end	Night	1 2 1 4 3 3 3 3 4 7% 69%	2164
October	1st to 10th	Night	2 2 1 3 3 2 3 2 4 6% 71%	3800
	11th to 20th	Night	3 5% 3 7% 3 2 2 2 4 6% 63%	3777
	21st to end	Night	5% 4 2 4 3 3 4 3 5% 7% 60%	4121
November	1st to 10th	Night	6% 5% 1 6% 4 3 4 2 4 8% 56%	2356
	11th to 20th	Night	9% 6% 3 5% 3 3 4 3 5% 7% 51%	2470
	21st to end	Night	9% 5% 1 4 4 4 4 3 5% 6% 56%	2641
December	1st to 10th	Night	14% 6% 3 6% 4 4 3 3 4 6% 45%	2660
	11th to 20th	Night	24% 8% 3 7% 4 4 4 4 6% 7% 30%	3276
	21st to end	Night	17% 8% 3 8% 6% 5% 5% 4 5% 7% 33%	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% 11% 27% 7% 2	2669
	11th to 20th	Day	53% 3 13% 14% 11% 6%	2860
	21st to end	Day	53% 5% 11% 16% 11% 4	3146
February	1st to 10th	Day	40% 4 7% 21% 20% 8%	1710
	11th to 20th	Day	40% 4 9% 19% 21% 6%	1746
	21st to end	Day	38% 4 9% 24% 19% 7%	1570
March	1st to 10th	Day	51% 6% 12% 17% 13% 2	3379
	11th to 20th	Day	30% 4 12% 30% 13% 11%	3490
	21st to end	Day	40% 7% 16% 23% 12% 2	3881
April	1st to 10th	Day	37% 4 13% 22% 19% 4	2280
	11th to 20th	Day	28% 4 15% 26% 21% 7%	2252
	21st to end	Day	21% 3 15% 30% 26% 4	2280
May	1st to 10th	Day	15% 2 9% 33% 23% 18%	3955
	11th to 20th	Day	12% 2 6% 31% 35% 12%	4195
	21st to end	Day	13% 2 14% 34% 33% 4	4814
June	1st to 10th	Day	20% 5% 11% 29% 27% 8%	2660
	11th to 20th	Day	9% 3 10% 23% 38% 17%	2660
	21st to end	Day	11% 3 4 16% 34% 33%	2660
July	1st to 10th	Day	6% 2 2 7% 15% 68%	4351
	11th to 20th	Day	8% 4 3 8% 17% 59%	4107
	21st to end	Day	7% 5% 2 7% 28% 51%	4315
August	1st to 10th	Day	13% 4 3 11% 27% 42%	4076
	11th to 20th	Day	7% 3 2 10% 43% 34%	3890
	21st to end	Day	10% 4 3 14% 35% 33%	4179
September	1st to 10th	Day	10% 3 2 10% 32% 43%	2280
	11th to 20th	Day	19% 4 5% 24% 34% 14%	2280
	21st to end	Day	13% 2 4 22% 34% 25%	2010
October	1st to 10th	Day	13% 3 4 12% 29% 39%	3180
	11th to 20th	Day	18% 6% 6% 24% 27% 20%	3161
	21st to end	Day	21% 6% 7% 25% 27% 14%	3448
November	1st to 10th	Day	26% 4 9% 28% 21% 12%	1882
	11th to 20th	Day	36% 5% 9% 22% 21% 6%	1710
	21st to end	Day	30% 4 10% 22% 23% 10%	1535
December	1st to 10th	Day	38% 3 12% 21% 18% 7%	1520
	11th to 20th	Day	55% 5% 8% 13% 14% 4	1928
	21st to end	Day	50% 5% 13% 18% 11% 3	2794
January	1st to 10th	Night	40% 7% 19% 23% 8% 3	4277
	11th to 20th	Night	52% 4 14% 13% 9% 7%	4110
	21st to end	Night	54% 4 12% 13% 11% 6%	4521
February	1st to 10th	Night	38% 4 8% 22% 20% 9%	2470
	11th to 20th	Night	36% 4 11% 21% 21% 8%	2330
	21st to end	Night	33% 5% 10% 29% 18% 5%	1884
March	1st to 10th	Night	46% 6% 17% 15% 14% 3	3490
	11th to 20th	Night	30% 4 13% 23% 19% 11%	3490
	21st to end	Night	41% 5% 17% 23% 11% 3	3772
April	1st to 10th	Night	33% 4 16% 21% 21% 5%	1900
	11th to 20th	Night	27% 4 13% 29% 18% 9%	1879
	21st to end	Night	20% 3 15% 32% 25% 6%	1900
May	1st to 10th	Night	16% 2 10% 29% 29% 14%	3002
	11th to 20th	Night	16% 3 11% 29% 27% 14%	2707
	21st to end	Night	13% 2 19% 35% 28% 3	2762
June	1st to 10th	Night	21% 7% 11% 25% 27% 9%	1520
	11th to 20th	Night	12% 3 9% 20% 37% 17%	1520
	21st to end	Night	13% 3 4 17% 33% 29%	1520
July	1st to 10th	Night	8% 2 3 6% 16% 65%	2500
	11th to 20th	Night	12% 6% 4 7% 16% 54%	2734
	21st to end	Night	12% 9% 4 6% 23% 45%	3011
August	1st to 10th	Night	18% 6% 4 10% 29% 33%	2839
	11th to 20th	Night	10% 5% 2 8% 43% 32%	3020
	21st to end	Night	14% 4 3 12% 37% 29%	3498
September	1st to 10th	Night	11% 3 3 10% 31% 42%	1900
	11th to 20th	Night	20% 5% 7% 23% 29% 16%	1900
	21st to end	Night	14% 3 4 21% 31% 26%	2164
October	1st to 10th	Night	15% 3 4 12% 21% 45%	3800
	11th to 20th	Night	20% 7% 5% 25% 22% 22%	3777
	21st to end	Night	22% 5% 6% 23% 25% 18%	4121
November	1st to 10th	Night	27% 4 11% 26% 18% 13%	2356
	11th to 20th	Night	31% 6% 10% 25% 20% 8%	2470
	21st to end	Night	28% 5% 10% 22% 24% 12%	2641
December	1st to 10th	Night	40% 4 9% 18% 18% 11%	2660
	11th to 20th	Night	52% 6% 10% 14% 15% 3	3276
	21st to end	Night	49% 7% 14% 16% 11% 3	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	27% 10% 28% 19% 12% 3	258
	11th to 20th	Day	19% 11% 20% 32% 15% 3	370
	21st to end	Day	13% 10% 25% 31% 19% 3	407
February	1st to 10th	Day	17% 11% 22% 29% 19% 2	370
	11th to 20th	Day	17% 16% 27% 23% 15% 3	399
	21st to end	Day	13% 15% 24% 31% 14% 3	382
March	1st to 10th	Day	18% 17% 30% 22% 11% 3	460
	11th to 20th	Day	17% 15% 26% 21% 15% 5%	460
	21st to end	Day	13% 18% 31% 26% 10% 2	506
April	1st to 10th	Day	14% 15% 32% 25% 10% 4	460
	11th to 20th	Day	12% 18% 29% 24% 11% 5%	452
	21st to end	Day	6% 18% 29% 29% 13% 5%	460
May	1st to 10th	Day	9% 14% 30% 34% 11% 1	463
	11th to 20th	Day	6% 14% 33% 32% 15% 1	488
	21st to end	Day	4 10% 30% 38% 16% 2	529
June	1st to 10th	Day	6% 10% 33% 36% 13% 2	490
	11th to 20th	Day	2 11% 34% 39% 11% 1	490
	21st to end	Day	6% 32% 43% 17% 1	490
July	1st to 10th	Day	1 4 29% 50% 15% 1	486
	11th to 20th	Day	1 3 23% 50% 22% 1	484
	21st to end	Day	1 1 27% 50% 19% 2	531
August	1st to 10th	Day	2 5% 28% 48% 15% 2	487
	11th to 20th	Day	1 5% 27% 44% 19% 3	477
	21st to end	Day	1 3 22% 46% 24% 3	539
September	1st to 10th	Day	1 4 23% 44% 23% 6%	490
	11th to 20th	Day	2 10% 24% 41% 16% 7%	490
	21st to end	Day	2 7% 24% 34% 26% 7%	490
October	1st to 10th	Day	3 6% 26% 33% 22% 10%	490
	11th to 20th	Day	5% 8% 22% 29% 27% 9%	490
	21st to end	Day	8% 8% 24% 28% 26% 6%	539
November	1st to 10th	Day	9% 10% 21% 24% 31% 6%	436
	11th to 20th	Day	8% 9% 16% 34% 27% 7%	270
	21st to end	Day	13% 5% 25% 35% 18% 3	187
December	1st to 10th	Day	17% 11% 23% 27% 16% 6%	180
	11th to 20th	Day	18% 13% 22% 29% 16% 2	180
	21st to end	Day	21% 10% 27% 27% 14% 1	198
January	1st to 10th	Night	19% 5% 14% 33% 24% 5%	760
	11th to 20th	Night	16% 5% 14% 38% 21% 5%	760
	21st to end	Night	17% 5% 14% 36% 24% 4	836
February	1st to 10th	Night	17% 6% 14% 37% 21% 4	760
	11th to 20th	Night	13% 8% 18% 34% 22% 5%	744
	21st to end	Night	15% 7% 20% 33% 22% 3	628
March	1st to 10th	Night	18% 9% 19% 31% 21% 3	760
	11th to 20th	Night	16% 8% 19% 32% 23% 3	760
	21st to end	Night	13% 9% 26% 34% 17% 1	836
April	1st to 10th	Night	11% 8% 26% 36% 17% 3	760
	11th to 20th	Night	10% 11% 26% 32% 18% 3	751
	21st to end	Night	6% 8% 30% 34% 20% 2	760
May	1st to 10th	Night	6% 6% 26% 39% 21% 2	660
	11th to 20th	Night	3 4 22% 45% 23% 2	487
	21st to end	Night	3 7% 27% 42% 19% 2	411
June	1st to 10th	Night	4 5% 28% 45% 17% 1	380
	11th to 20th	Night	1 5% 26% 51% 16%	380
	21st to end	Night	2 3 27% 46% 22%	380
July	1st to 10th	Night	1 1 17% 58% 23% 1	370
	11th to 20th	Night	2 1 16% 52% 25% 4	506
	21st to end	Night	2 2 18% 46% 30% 3	624
August	1st to 10th	Night	4 2 17% 45% 28% 3	567
	11th to 20th	Night	1 2 21% 45% 28% 3	667
	21st to end	Night	2 1 16% 46% 30% 4	836
September	1st to 10th	Night	1 1 15% 45% 33% 5%	760
	11th to 20th	Night	4 3 19% 43% 27% 4	760
	21st to end	Night	2 3 15% 40% 34% 6%	760
October	1st to 10th	Night	4 4 15% 37% 33% 6%	760
	11th to 20th	Night	6% 6% 15% 34% 32% 6%	760
	21st to end	Night	8% 4 12% 34% 33% 9%	836
November	1st to 10th	Night	8% 6% 15% 31% 33% 6%	770
	11th to 20th	Night	12% 3 14% 37% 29% 6%	760
	21st to end	Night	12% 4 13% 38% 27% 5%	760
December	1st to 10th	Night	16% 5% 14% 36% 24% 5%	760
	11th to 20th	Night	23% 6% 14% 33% 21% 3	760
	21st to end	Night	20% 6% 21% 32% 19% 1	836

Page generated at 2024-11-05 05:15:54. Version ac07

Copyright © 2024 Attilla Danko.