Martinez
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Martinez clear sky chart from 2005-11-06 to 2024-01-12.

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	12% 5% 2 5% 5% 3 5% 5% 6% 8% 43%	74901
	Night	13% 5% 2 5% 5% 3 5% 5% 6% 7% 45%	74826
Transparency	Day	37% 8% 12% 19% 18% 5%	74624
	Night	37% 8% 11% 18% 19% 7%	74622
Seeing	Day	15% 9% 22% 24% 20% 10%	14074
	Night	15% 7% 23% 32% 21% 3	24193

By Month

Percentage Cloud Cover SE (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 4 4 2 4 4 6% 6% 46%	1706
	11th to 20th	Day	15% 6% 2 6% 5% 3 3 4 5% 6% 44%	1635
	21st to end	Day	17% 6% 3 4 5% 2 3 4 3 6% 46%	1782
February	1st to 10th	Day	15% 6% 3 6% 5% 3 4 6% 6% 7% 39%	1724
	11th to 20th	Day	19% 7% 2 4 4 3 3 3 4 6% 46%	1748
	21st to end	Day	19% 6% 2 5% 4 3 5% 4 5% 6% 43%	1480
March	1st to 10th	Day	13% 5% 2 5% 3 2 4 4 4 6% 52%	1980
	11th to 20th	Day	17% 5% 3 5% 6% 2 3 5% 5% 7% 44%	1980
	21st to end	Day	15% 5% 2 5% 4 3 5% 4 5% 7% 44%	2178
April	1st to 10th	Day	11% 4 2 5% 5% 3 5% 4 4 7% 50%	1980
	11th to 20th	Day	11% 5% 2 5% 5% 4 5% 4 5% 7% 47%	2051
	21st to end	Day	8% 3 1 4 4 3 4 5% 6% 9% 53%	2340
May	1st to 10th	Day	8% 4 2 4 4 3 4 5% 6% 8% 51%	2340
	11th to 20th	Day	11% 6% 3 6% 6% 4 5% 6% 7% 8% 39%	2301
	21st to end	Day	11% 4 3 6% 6% 4 5% 7% 7% 10% 38%	2531
June	1st to 10th	Day	10% 5% 3 6% 6% 3 6% 6% 8% 11% 36%	2340
	11th to 20th	Day	7% 4 2 4 5% 4 6% 6% 9% 11% 43%	2340
	21st to end	Day	6% 4 2 6% 6% 4 7% 7% 9% 12% 38%	2340
July	1st to 10th	Day	7% 5% 3 7% 8% 4 7% 7% 8% 10% 32%	2340
	11th to 20th	Day	8% 5% 2 6% 8% 5% 7% 7% 9% 10% 32%	2340
	21st to end	Day	7% 5% 2 6% 6% 4 9% 8% 9% 14% 30%	2547
August	1st to 10th	Day	8% 5% 2 6% 7% 6% 6% 8% 9% 13% 29%	2327
	11th to 20th	Day	11% 5% 2 7% 7% 5% 7% 9% 8% 10% 30%	2303
	21st to end	Day	13% 7% 3 7% 8% 5% 7% 6% 6% 10% 28%	2320
September	1st to 10th	Day	8% 5% 2 5% 6% 4 6% 6% 7% 9% 41%	1980
	11th to 20th	Day	14% 5% 2 4 5% 4 5% 6% 6% 9% 41%	1980
	21st to end	Day	15% 6% 3 6% 5% 3 4 4 4 6% 43%	1980
October	1st to 10th	Day	14% 5% 3 5% 4 2 3 4 3 5% 51%	1940
	11th to 20th	Day	12% 5% 1 4 4 2 3 3 4 6% 57%	1800
	21st to end	Day	12% 4 2 4 5% 2 4 4 3 4 56%	1980
November	1st to 10th	Day	13% 6% 2 4 4 2 3 4 4 6% 53%	1857
	11th to 20th	Day	14% 5% 3 3 2 2 3 3 4 6% 55%	1734
	21st to end	Day	15% 5% 2 5% 4 3 3 5% 4 7% 48%	1710
December	1st to 10th	Day	19% 6% 3 5% 5% 2 4 4 5% 7% 39%	1710
	11th to 20th	Day	16% 5% 2 4 4 3 3 3 4 6% 50%	2153
	21st to end	Day	21% 8% 2 4 4 2 3 4 4 6% 42%	3124
January	1st to 10th	Night	16% 6% 3 5% 4 3 3 4 4 6% 46%	2459
	11th to 20th	Night	16% 6% 2 4 4 3 4 4 6% 6% 45%	2365
	21st to end	Night	17% 6% 2 5% 3 3 3 4 4 4 48%	2574
February	1st to 10th	Night	16% 6% 2 6% 5% 3 4 4 5% 6% 44%	2232
	11th to 20th	Night	18% 6% 3 4 5% 3 4 3 4 5% 46%	2098
	21st to end	Night	15% 6% 3 5% 5% 3 4 4 5% 7% 45%	1773
March	1st to 10th	Night	12% 6% 3 5% 5% 2 4 4 4 5% 51%	1980
	11th to 20th	Night	15% 5% 2 3 5% 3 5% 4 5% 7% 46%	1980
	21st to end	Night	12% 5% 2 5% 4 3 5% 5% 6% 7% 45%	2178
April	1st to 10th	Night	11% 4 2 4 5% 3 4 5% 5% 6% 51%	1980
	11th to 20th	Night	12% 4 2 4 4 3 4 3 4 8% 52%	1865
	21st to end	Night	9% 3 2 4 4 3 4 4 5% 7% 54%	1626
May	1st to 10th	Night	7% 4 2 4 5% 3 5% 5% 7% 7% 51%	1620
	11th to 20th	Night	9% 4 2 6% 6% 4 6% 6% 9% 10% 40%	1592
	21st to end	Night	9% 5% 3 6% 6% 4 6% 6% 7% 8% 42%	1744
June	1st to 10th	Night	12% 7% 3 5% 6% 3 6% 8% 6% 11% 34%	1620
	11th to 20th	Night	7% 4 2 6% 6% 3 5% 6% 8% 11% 42%	1620
	21st to end	Night	7% 4 2 6% 6% 4 6% 7% 10% 12% 35%	1620
July	1st to 10th	Night	8% 5% 3 5% 6% 4 6% 7% 8% 12% 33%	1620
	11th to 20th	Night	7% 5% 3 5% 7% 5% 6% 8% 10% 14% 31%	1620
	21st to end	Night	7% 5% 3 6% 7% 5% 6% 8% 9% 11% 35%	1771
August	1st to 10th	Night	8% 5% 3 5% 9% 5% 6% 8% 10% 11% 31%	1611
	11th to 20th	Night	11% 6% 3 6% 7% 4 5% 6% 8% 13% 31%	1598
	21st to end	Night	12% 7% 3 6% 8% 3 5% 5% 6% 11% 33%	2011
September	1st to 10th	Night	10% 4 2 5% 6% 4 5% 6% 8% 9% 40%	1980
	11th to 20th	Night	12% 6% 2 7% 6% 4 5% 4 5% 7% 41%	1980
	21st to end	Night	13% 5% 2 5% 5% 3 5% 4 6% 6% 45%	1980
October	1st to 10th	Night	13% 6% 2 4 5% 2 4 3 4 6% 52%	2017
	11th to 20th	Night	12% 4 2 3 4 2 3 3 4 5% 57%	2160
	21st to end	Night	11% 4 2 4 5% 2 4 3 4 6% 56%	2376
November	1st to 10th	Night	12% 5% 2 4 3 2 3 3 4 5% 56%	2221
	11th to 20th	Night	14% 5% 2 4 4 2 4 3 3 6% 52%	2441
	21st to end	Night	14% 4 2 4 4 2 4 4 5% 7% 50%	2470
December	1st to 10th	Night	17% 5% 2 4 4 3 4 4 5% 7% 44%	2470
	11th to 20th	Night	17% 5% 2 3 3 2 3 3 3 4 52%	3042
	21st to end	Night	19% 7% 3 5% 5% 3 4 4 5% 6% 38%	4532

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	37% 7% 9% 18% 24% 5%	1707
	11th to 20th	Day	40% 6% 7% 19% 21% 6%	1635
	21st to end	Day	41% 3 5% 18% 26% 7%	1782
February	1st to 10th	Day	42% 5% 10% 20% 17% 7%	1724
	11th to 20th	Day	40% 5% 5% 20% 23% 7%	1758
	21st to end	Day	42% 5% 9% 15% 19% 9%	1480
March	1st to 10th	Day	35% 4 8% 18% 22% 12%	1980
	11th to 20th	Day	40% 7% 11% 17% 17% 8%	1980
	21st to end	Day	40% 6% 10% 21% 19% 5%	2178
April	1st to 10th	Day	34% 6% 10% 20% 23% 8%	1980
	11th to 20th	Day	35% 6% 10% 19% 20% 10%	2051
	21st to end	Day	27% 7% 12% 26% 24% 4	2340
May	1st to 10th	Day	28% 8% 14% 23% 21% 5%	2340
	11th to 20th	Day	39% 10% 16% 18% 16% 2	2305
	21st to end	Day	38% 10% 13% 22% 15% 2	2531
June	1st to 10th	Day	38% 12% 18% 19% 12% 1	2340
	11th to 20th	Day	30% 13% 20% 24% 12% 1	2340
	21st to end	Day	33% 13% 19% 20% 12% 3	2340
July	1st to 10th	Day	40% 14% 18% 16% 8% 3	2275
	11th to 20th	Day	40% 14% 21% 16% 6% 3	2271
	21st to end	Day	37% 15% 22% 18% 7% 1	2405
August	1st to 10th	Day	41% 17% 17% 19% 6% 1	2314
	11th to 20th	Day	44% 14% 17% 17% 7% 1	2303
	21st to end	Day	48% 12% 16% 14% 8% 1	2320
September	1st to 10th	Day	37% 13% 14% 16% 16% 4	1980
	11th to 20th	Day	38% 9% 13% 17% 20% 4	1980
	21st to end	Day	42% 6% 10% 17% 18% 7%	1980
October	1st to 10th	Day	36% 5% 7% 20% 24% 8%	1940
	11th to 20th	Day	29% 4 8% 23% 28% 8%	1800
	21st to end	Day	31% 6% 5% 16% 30% 13%	1980
November	1st to 10th	Day	33% 5% 8% 16% 25% 13%	1857
	11th to 20th	Day	32% 5% 7% 21% 23% 12%	1734
	21st to end	Day	37% 5% 9% 20% 21% 9%	1710
December	1st to 10th	Day	43% 7% 9% 16% 19% 6%	1710
	11th to 20th	Day	37% 4 7% 19% 24% 9%	2150
	21st to end	Day	42% 6% 8% 18% 23% 3	3124
January	1st to 10th	Night	40% 5% 7% 18% 23% 6%	2459
	11th to 20th	Night	39% 5% 8% 19% 22% 8%	2365
	21st to end	Night	40% 4 5% 18% 23% 10%	2574
February	1st to 10th	Night	41% 4 10% 17% 19% 9%	2232
	11th to 20th	Night	40% 5% 7% 17% 22% 9%	2099
	21st to end	Night	39% 6% 10% 15% 18% 12%	1773
March	1st to 10th	Night	36% 5% 9% 15% 23% 12%	1980
	11th to 20th	Night	37% 6% 11% 17% 21% 8%	1980
	21st to end	Night	37% 8% 10% 19% 19% 8%	2178
April	1st to 10th	Night	32% 6% 9% 19% 22% 10%	1980
	11th to 20th	Night	32% 6% 7% 21% 23% 11%	1865
	21st to end	Night	28% 7% 11% 24% 23% 7%	1626
May	1st to 10th	Night	28% 8% 15% 23% 19% 7%	1620
	11th to 20th	Night	36% 12% 17% 17% 16% 1	1593
	21st to end	Night	37% 10% 10% 22% 18% 2	1745
June	1st to 10th	Night	42% 11% 16% 18% 12% 1	1620
	11th to 20th	Night	34% 11% 19% 24% 11% 1	1620
	21st to end	Night	35% 15% 22% 16% 10% 3	1620
July	1st to 10th	Night	38% 15% 21% 13% 9% 4	1575
	11th to 20th	Night	37% 17% 23% 17% 5% 2	1566
	21st to end	Night	36% 17% 22% 18% 6% 1	1672
August	1st to 10th	Night	41% 18% 18% 18% 6%	1600
	11th to 20th	Night	41% 13% 19% 18% 7% 1	1598
	21st to end	Night	44% 12% 18% 15% 9% 1	2011
September	1st to 10th	Night	36% 12% 17% 16% 13% 5%	1980
	11th to 20th	Night	41% 9% 12% 18% 17% 4	1980
	21st to end	Night	39% 7% 12% 18% 18% 5%	1980
October	1st to 10th	Night	33% 6% 10% 18% 26% 7%	2017
	11th to 20th	Night	30% 4 10% 21% 25% 11%	2160
	21st to end	Night	30% 4 7% 18% 28% 14%	2376
November	1st to 10th	Night	30% 5% 8% 16% 25% 15%	2221
	11th to 20th	Night	35% 4 7% 15% 24% 15%	2441
	21st to end	Night	35% 5% 9% 17% 25% 10%	2470
December	1st to 10th	Night	38% 7% 10% 19% 20% 6%	2470
	11th to 20th	Night	37% 4 8% 17% 26% 9%	3044
	21st to end	Night	44% 6% 7% 20% 20% 4	4532

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	20% 22% 41% 15% 3	270
	11th to 20th	Day	20% 21% 31% 22% 6%	245
	21st to end	Day	20% 28% 33% 14% 4 1	264
February	1st to 10th	Day	18% 22% 39% 17% 5%	240
	11th to 20th	Day	33% 17% 37% 11% 2	240
	21st to end	Day	25% 19% 36% 16% 5%	198
March	1st to 10th	Day	17% 16% 33% 24% 10%	420
	11th to 20th	Day	18% 15% 38% 21% 8%	420
	21st to end	Day	18% 14% 38% 20% 9% 1	462
April	1st to 10th	Day	16% 15% 30% 26% 13% 1	420
	11th to 20th	Day	14% 14% 26% 25% 17% 4	412
	21st to end	Day	12% 10% 25% 28% 20% 6%	420
May	1st to 10th	Day	9% 12% 29% 29% 15% 6%	423
	11th to 20th	Day	15% 3 17% 30% 21% 13%	447
	21st to end	Day	15% 4 14% 26% 26% 15%	485
June	1st to 10th	Day	12% 2 14% 30% 28% 14%	450
	11th to 20th	Day	8% 3 18% 23% 25% 24%	450
	21st to end	Day	7% 3 14% 32% 26% 18%	450
July	1st to 10th	Day	8% 2 8% 24% 31% 27%	445
	11th to 20th	Day	9% 1 6% 25% 35% 24%	444
	21st to end	Day	7% 1 7% 27% 37% 21%	488
August	1st to 10th	Day	12% 2 13% 25% 30% 19%	446
	11th to 20th	Day	10% 3 9% 21% 37% 20%	439
	21st to end	Day	12% 3 10% 26% 28% 21%	495
September	1st to 10th	Day	8% 4 11% 27% 32% 18%	450
	11th to 20th	Day	16% 2 13% 26% 30% 13%	450
	21st to end	Day	18% 3 15% 28% 24% 12%	450
October	1st to 10th	Day	16% 5% 20% 28% 22% 8%	450
	11th to 20th	Day	11% 5% 23% 28% 23% 10%	450
	21st to end	Day	14% 8% 25% 27% 21% 5%	495
November	1st to 10th	Day	18% 6% 25% 27% 20% 4	455
	11th to 20th	Day	17% 13% 39% 20% 9% 1	294
	21st to end	Day	12% 16% 34% 23% 13% 2	270
December	1st to 10th	Day	26% 14% 33% 19% 8% 1	270
	11th to 20th	Day	21% 15% 39% 15% 8% 2	270
	21st to end	Day	29% 16% 33% 14% 6% 2	297
January	1st to 10th	Night	20% 13% 34% 27% 6%	760
	11th to 20th	Night	18% 12% 31% 31% 8%	728
	21st to end	Night	20% 11% 40% 25% 4	792
February	1st to 10th	Night	17% 12% 34% 29% 7%	720
	11th to 20th	Night	22% 12% 35% 29% 2	703
	21st to end	Night	19% 14% 34% 29% 4	592
March	1st to 10th	Night	13% 12% 36% 33% 7%	720
	11th to 20th	Night	17% 11% 34% 29% 9% 1	720
	21st to end	Night	14% 13% 35% 29% 9%	792
April	1st to 10th	Night	12% 13% 32% 32% 11%	720
	11th to 20th	Night	14% 11% 28% 32% 14% 1	711
	21st to end	Night	10% 5% 27% 41% 16%	546
May	1st to 10th	Night	10% 7% 27% 38% 18% 1	540
	11th to 20th	Night	10% 4 25% 37% 21% 4	531
	21st to end	Night	11% 2 11% 34% 38% 4	584
June	1st to 10th	Night	14% 2 15% 35% 30% 5%	540
	11th to 20th	Night	7% 2 12% 33% 34% 11%	540
	21st to end	Night	8% 2 12% 35% 39% 5%	540
July	1st to 10th	Night	11% 1 8% 31% 40% 9%	525
	11th to 20th	Night	8% 3 5% 30% 47% 7%	522
	21st to end	Night	7% 1 7% 35% 42% 8%	591
August	1st to 10th	Night	9% 1 9% 32% 40% 9%	537
	11th to 20th	Night	13% 2 5% 31% 41% 7%	534
	21st to end	Night	13% 2 11% 29% 38% 7%	697
September	1st to 10th	Night	9% 3 10% 32% 40% 6%	720
	11th to 20th	Night	13% 2 12% 29% 39% 4	720
	21st to end	Night	16% 3 13% 30% 33% 4	720
October	1st to 10th	Night	15% 4 16% 34% 25% 6%	720
	11th to 20th	Night	13% 5% 20% 33% 25% 3	720
	21st to end	Night	12% 7% 24% 32% 23% 2	792
November	1st to 10th	Night	13% 6% 23% 34% 20% 3	740
	11th to 20th	Night	17% 10% 27% 32% 13% 1	760
	21st to end	Night	15% 9% 26% 32% 17% 1	760
December	1st to 10th	Night	18% 11% 28% 31% 11% 1	760
	11th to 20th	Night	20% 8% 28% 31% 13% 1	760
	21st to end	Night	26% 12% 26% 28% 8%	836

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