Tisdale Boat Launch
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tisdale Boat Launch clear sky chart from 2005-11-06 to 2026-07-01.

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% 3 1 3 2 2 2 2 4 5% 67%	146627
	Night	9% 4 1 4 3 3 3 2 4 6% 63%	143185
Transparency	Day	22% 3 6% 20% 25% 24%	141544
	Night	25% 3 7% 19% 23% 21%	139257
Seeing	Day	8% 5% 14% 24% 28% 20%	17322
	Night	10% 4 17% 37% 29% 3	26605

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	18% 7% 3 7% 5% 5% 4 3 5% 6% 37%	4722
	11th to 20th	Day	12% 5% 2 5% 4 4 3 3 4 5% 53%	5336
	21st to end	Day	15% 6% 3 7% 5% 4 4 4 4 6% 42%	5843
February	1st to 10th	Day	18% 4 2 4 4 4 3 3 5% 6% 48%	1890
	11th to 20th	Day	13% 6% 2 6% 4 4 4 3 5% 7% 47%	1930
	21st to end	Day	13% 4 2 5% 3 4 3 4 5% 7% 50%	1730
March	1st to 10th	Day	12% 9% 3 7% 5% 4 4 3 4 7% 41%	4880
	11th to 20th	Day	13% 5% 2 5% 3 3 4 3 5% 7% 50%	5110
	21st to end	Day	13% 5% 2 5% 4 4 5% 4 6% 8% 44%	5741
April	1st to 10th	Day	10% 7% 2 5% 4 4 4 3 5% 6% 50%	2520
	11th to 20th	Day	8% 3 1 4 4 4 3 3 6% 5% 59%	2489
	21st to end	Day	4 4 1 3 3 3 3 3 5% 8% 64%	2520
May	1st to 10th	Day	4 3 1 3 2 2 2 2 3 6% 73%	7359
	11th to 20th	Day	1 1 1 2 1 1 1 1 2 5% 83%	8062
	21st to end	Day	2 1 1 1 1 2 2 2 3 6% 79%	8992
June	1st to 10th	Day	4 3 1 2 2 2 2 2 5% 7% 69%	2940
	11th to 20th	Day	1 1 2 1 1 1 2 3 4 83%	2940
	21st to end	Day	1 1 1 1 1 1 1 2 3 87%	2940
July	1st to 10th	Day	1 1 1 1 1 2 93%	6320
	11th to 20th	Day	1 1 1 1 1 1 1 2 2 90%	6217
	21st to end	Day	1 1 2 1 1 2 1 3 4 83%	6402
August	1st to 10th	Day	1 1 1 1 1 1 2 1 3 4 83%	5777
	11th to 20th	Day	1 1 1 1 1 1 2 3 90%	5543
	21st to end	Day	1 1 1 2 1 1 1 1 2 4 86%	5984
September	1st to 10th	Day	1 1 1 1 1 1 1 2 4 87%	2400
	11th to 20th	Day	2 2 1 2 2 2 2 2 4 5% 77%	2400
	21st to end	Day	3 2 1 2 2 1 1 2 3 4 80%	2130
October	1st to 10th	Day	2 2 1 2 1 2 3 2 3 5% 78%	3280
	11th to 20th	Day	4 3 1 3 2 2 2 3 4 5% 71%	3261
	21st to end	Day	5% 3 1 3 3 3 4 3 4 7% 64%	3558
November	1st to 10th	Day	9% 2 1 4 3 3 3 3 5% 7% 60%	1939
	11th to 20th	Day	12% 5% 2 5% 4 4 3 3 6% 8% 48%	1890
	21st to end	Day	10% 5% 2 5% 5% 3 4 3 4 5% 55%	1682
December	1st to 10th	Day	8% 4 1 5% 3 4 4 3 6% 9% 52%	2700
	11th to 20th	Day	24% 9% 4 11% 6% 5% 4 3 5% 5% 24%	3108
	21st to end	Day	23% 9% 3 7% 4 4 4 3 5% 7% 30%	4092
January	1st to 10th	Night	16% 6% 2 6% 4 4 4 3 5% 8% 40%	8172
	11th to 20th	Night	11% 5% 2 5% 3 3 4 3 4 5% 55%	7650
	21st to end	Night	15% 7% 2 6% 5% 4 4 3 4 5% 44%	8371
February	1st to 10th	Night	17% 4 1 4 3 4 4 3 5% 6% 50%	2730
	11th to 20th	Night	12% 5% 2 4 4 3 4 3 6% 8% 49%	2575
	21st to end	Night	13% 4 2 4 4 3 4 4 5% 7% 52%	2076
March	1st to 10th	Night	12% 7% 2 6% 4 4 4 3 4 7% 46%	5231
	11th to 20th	Night	14% 5% 1 4 3 3 3 3 5% 7% 53%	5110
	21st to end	Night	13% 5% 2 5% 3 4 4 4 5% 8% 45%	5476
April	1st to 10th	Night	7% 4 2 5% 4 4 3 4 5% 7% 55%	2100
	11th to 20th	Night	7% 4 2 3 3 3 3 3 4 7% 61%	2079
	21st to end	Night	5% 3 1 2 2 2 3 2 4 7% 68%	2100
May	1st to 10th	Night	4 3 1 3 2 2 3 2 3 4 72%	5585
	11th to 20th	Night	1 1 2 1 2 2 2 3 6% 80%	4800
	21st to end	Night	2 2 1 2 1 2 2 1 3 5% 80%	5181
June	1st to 10th	Night	4 2 2 2 2 3 3 4 6% 72%	1680
	11th to 20th	Night	1 1 1 1 2 2 2 3 5% 84%	1680
	21st to end	Night	1 1 1 1 2 2 2 2 3 3 84%	1680
July	1st to 10th	Night	1 1 1 1 1 1 2 92%	3640
	11th to 20th	Night	1 1 1 1 1 1 1 1 2 90%	3731
	21st to end	Night	1 1 1 1 2 2 3 4 85%	4472
August	1st to 10th	Night	2 1 1 2 1 1 1 1 2 3 84%	4035
	11th to 20th	Night	1 1 1 1 1 1 2 92%	4318
	21st to end	Night	1 1 1 1 1 2 1 2 3 85%	5015
September	1st to 10th	Night	1 1 1 1 1 1 2 4 88%	2000
	11th to 20th	Night	3 2 1 3 2 2 1 1 3 5% 79%	2000
	21st to end	Night	2 1 2 1 1 1 1 3 5% 83%	2263
October	1st to 10th	Night	2 2 1 2 2 2 2 2 3 4 79%	3920
	11th to 20th	Night	3 1 1 2 2 2 2 2 4 5% 76%	3897
	21st to end	Night	6% 2 1 3 2 2 3 3 4 7% 66%	4253
November	1st to 10th	Night	8% 4 1 4 3 3 3 3 5% 8% 58%	2578
	11th to 20th	Night	10% 4 1 4 3 4 3 3 5% 8% 54%	2730
	21st to end	Night	11% 5% 2 4 3 3 3 2 4 6% 57%	2935
December	1st to 10th	Night	9% 4 2 4 2 3 3 3 5% 7% 59%	4700
	11th to 20th	Night	23% 7% 3 7% 6% 4 5% 4 6% 8% 27%	5316
	21st to end	Night	25% 8% 3 7% 4 4 4 3 4 5% 32%	7106

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	47% 8% 11% 22% 9% 4	4723
	11th to 20th	Day	34% 4 5% 17% 22% 18%	5336
	21st to end	Day	43% 4 9% 16% 14% 13%	5843
February	1st to 10th	Day	38% 5% 9% 20% 19% 8%	1890
	11th to 20th	Day	37% 5% 10% 22% 19% 7%	1939
	21st to end	Day	34% 6% 10% 25% 19% 6%	1730
March	1st to 10th	Day	43% 6% 8% 21% 19% 4	4880
	11th to 20th	Day	34% 4 10% 25% 16% 10%	5110
	21st to end	Day	37% 5% 13% 28% 14% 3	5741
April	1st to 10th	Day	34% 4 10% 24% 20% 8%	2520
	11th to 20th	Day	27% 5% 11% 24% 23% 11%	2492
	21st to end	Day	19% 4 13% 29% 26% 8%	2520
May	1st to 10th	Day	16% 2 7% 25% 30% 21%	7359
	11th to 20th	Day	8% 2 4 23% 40% 24%	8065
	21st to end	Day	9% 2 7% 30% 38% 14%	8994
June	1st to 10th	Day	16% 3 9% 27% 30% 15%	2940
	11th to 20th	Day	7% 2 6% 20% 35% 29%	2940
	21st to end	Day	6% 2 2 13% 37% 41%	2940
July	1st to 10th	Day	3 1 1 7% 20% 68%	6252
	11th to 20th	Day	5% 1 1 5% 15% 73%	6142
	21st to end	Day	7% 2 3 17% 27% 44%	6217
August	1st to 10th	Day	11% 2 1 9% 28% 51%	4206
	11th to 20th	Day	5% 1 1 10% 40% 43%	4014
	21st to end	Day	7% 1 1 13% 38% 39%	4311
September	1st to 10th	Day	6% 1 2 10% 28% 53%	2400
	11th to 20th	Day	13% 3 5% 22% 39% 19%	2400
	21st to end	Day	11% 2 4 20% 31% 32%	2130
October	1st to 10th	Day	12% 3 3 12% 26% 44%	3280
	11th to 20th	Day	17% 3 5% 25% 29% 21%	3261
	21st to end	Day	22% 3 7% 23% 31% 14%	3558
November	1st to 10th	Day	25% 5% 9% 28% 23% 11%	1939
	11th to 20th	Day	35% 5% 12% 23% 18% 7%	1890
	21st to end	Day	31% 5% 10% 21% 21% 11%	1682
December	1st to 10th	Day	29% 4 10% 28% 20% 9%	2700
	11th to 20th	Day	63% 4 7% 13% 11% 2	3108
	21st to end	Day	55% 4 11% 19% 9% 2	4092
January	1st to 10th	Night	44% 5% 15% 21% 11% 4	8172
	11th to 20th	Night	32% 5% 6% 17% 26% 14%	7650
	21st to end	Night	42% 4 8% 15% 17% 14%	8371
February	1st to 10th	Night	35% 4 8% 20% 20% 11%	2730
	11th to 20th	Night	34% 4 10% 22% 22% 9%	2577
	21st to end	Night	30% 6% 10% 22% 23% 9%	2076
March	1st to 10th	Night	38% 6% 10% 22% 20% 5%	5231
	11th to 20th	Night	32% 3 12% 23% 20% 10%	5110
	21st to end	Night	36% 6% 13% 26% 15% 3	5476
April	1st to 10th	Night	29% 4 12% 22% 22% 10%	2100
	11th to 20th	Night	25% 4 11% 27% 20% 13%	2079
	21st to end	Night	18% 4 12% 29% 29% 8%	2100
May	1st to 10th	Night	18% 3 6% 23% 30% 20%	5583
	11th to 20th	Night	9% 2 4 22% 37% 26%	4800
	21st to end	Night	10% 2 6% 29% 37% 17%	5182
June	1st to 10th	Night	15% 3 11% 26% 31% 15%	1680
	11th to 20th	Night	6% 2 5% 20% 33% 33%	1680
	21st to end	Night	9% 1 2 12% 31% 44%	1680
July	1st to 10th	Night	4 1 1 6% 21% 68%	3600
	11th to 20th	Night	6% 1 1 5% 12% 76%	3683
	21st to end	Night	6% 1 3 18% 26% 47%	4345
August	1st to 10th	Night	12% 2 1 7% 26% 53%	2929
	11th to 20th	Night	4 1 1 7% 39% 49%	3117
	21st to end	Night	7% 1 1 9% 35% 47%	3608
September	1st to 10th	Night	5% 1 2 8% 30% 54%	2000
	11th to 20th	Night	12% 2 4 19% 36% 27%	2000
	21st to end	Night	8% 2 4 18% 32% 37%	2263
October	1st to 10th	Night	12% 2 3 11% 20% 52%	3920
	11th to 20th	Night	12% 2 6% 27% 29% 23%	3897
	21st to end	Night	19% 2 5% 22% 30% 20%	4253
November	1st to 10th	Night	24% 5% 8% 25% 22% 15%	2578
	11th to 20th	Night	28% 5% 12% 26% 22% 9%	2730
	21st to end	Night	30% 4 8% 22% 24% 13%	2935
December	1st to 10th	Night	26% 4 8% 27% 22% 12%	4700
	11th to 20th	Night	54% 5% 9% 16% 13% 3	5316
	21st to end	Night	55% 5% 11% 16% 10% 3	7106

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	36% 5% 18% 22% 17% 2	220
	11th to 20th	Day	15% 8% 18% 23% 23% 13%	426
	21st to end	Day	16% 7% 18% 22% 23% 14%	473
February	1st to 10th	Day	20% 9% 13% 23% 23% 11%	430
	11th to 20th	Day	16% 10% 25% 23% 18% 7%	470
	21st to end	Day	13% 9% 20% 30% 20% 7%	446
March	1st to 10th	Day	17% 12% 25% 25% 14% 7%	540
	11th to 20th	Day	18% 9% 19% 21% 21% 11%	540
	21st to end	Day	15% 10% 23% 26% 19% 6%	594
April	1st to 10th	Day	13% 9% 19% 26% 19% 14%	540
	11th to 20th	Day	10% 8% 22% 26% 19% 14%	532
	21st to end	Day	5% 6% 18% 30% 23% 19%	540
May	1st to 10th	Day	8% 6% 21% 27% 23% 15%	543
	11th to 20th	Day	6% 6% 20% 24% 22% 23%	568
	21st to end	Day	4 4 14% 26% 27% 25%	617
June	1st to 10th	Day	3 3 13% 24% 35% 21%	570
	11th to 20th	Day	2 5% 12% 27% 35% 19%	570
	21st to end	Day	3 10% 27% 34% 27%	570
July	1st to 10th	Day	1 5% 28% 40% 26%	527
	11th to 20th	Day	1 5% 21% 42% 32%	524
	21st to end	Day	1 4 20% 44% 32%	575
August	1st to 10th	Day	2 1 5% 22% 41% 30%	527
	11th to 20th	Day	1 2 4 20% 41% 33%	517
	21st to end	Day	1 1 4 17% 38% 39%	583
September	1st to 10th	Day	1 1 7% 20% 42% 30%	530
	11th to 20th	Day	3 3 8% 24% 31% 31%	530
	21st to end	Day	3 2 15% 24% 29% 27%	530
October	1st to 10th	Day	4 6% 15% 22% 25% 29%	530
	11th to 20th	Day	6% 5% 15% 21% 26% 27%	530
	21st to end	Day	11% 7% 15% 21% 28% 19%	583
November	1st to 10th	Day	10% 6% 17% 21% 26% 20%	415
	11th to 20th	Day	12% 5% 17% 26% 26% 14%	330
	21st to end	Day	13% 6% 12% 26% 29% 14%	220
December	1st to 10th	Day	18% 9% 15% 17% 24% 16%	220
	11th to 20th	Day	20% 4 15% 26% 23% 12%	220
	21st to end	Day	22% 10% 21% 21% 20% 5%	242
January	1st to 10th	Night	20% 6% 19% 31% 22% 3	840
	11th to 20th	Night	15% 5% 16% 37% 23% 4	840
	21st to end	Night	18% 5% 15% 34% 25% 3	924
February	1st to 10th	Night	19% 4 15% 38% 22% 2	840
	11th to 20th	Night	14% 7% 23% 33% 20% 3	824
	21st to end	Night	13% 6% 22% 40% 18% 2	692
March	1st to 10th	Night	16% 5% 22% 34% 20% 2	840
	11th to 20th	Night	15% 5% 20% 33% 25% 2	840
	21st to end	Night	14% 6% 23% 35% 20% 1	924
April	1st to 10th	Night	9% 5% 22% 39% 23% 2	840
	11th to 20th	Night	8% 6% 24% 34% 25% 3	831
	21st to end	Night	6% 5% 20% 40% 26% 3	840
May	1st to 10th	Night	5% 4 26% 38% 24% 2	725
	11th to 20th	Night	3 4 21% 43% 28% 1	451
	21st to end	Night	4 5% 21% 41% 29% 1	455
June	1st to 10th	Night	5% 3 22% 43% 27% 1	420
	11th to 20th	Night	1 3 25% 49% 22%	420
	21st to end	Night	2 2 20% 44% 30% 1	420
July	1st to 10th	Night	1 15% 52% 31% 1	390
	11th to 20th	Night	1 13% 55% 30% 1	427
	21st to end	Night	1 1 10% 43% 43% 2	657
August	1st to 10th	Night	3 1 13% 44% 37% 3	597
	11th to 20th	Night	1 1 8% 46% 40% 4	704
	21st to end	Night	1 7% 40% 49% 3	880
September	1st to 10th	Night	1 2 9% 38% 47% 4	800
	11th to 20th	Night	3 1 11% 38% 41% 6%	800
	21st to end	Night	2 2 15% 34% 39% 8%	800
October	1st to 10th	Night	5% 4 13% 38% 33% 7%	800
	11th to 20th	Night	5% 3 16% 37% 35% 5%	800
	21st to end	Night	8% 4 15% 35% 30% 8%	880
November	1st to 10th	Night	9% 5% 17% 30% 33% 5%	820
	11th to 20th	Night	12% 2 17% 39% 27% 3	840
	21st to end	Night	12% 5% 15% 36% 28% 3	840
December	1st to 10th	Night	15% 6% 16% 32% 24% 6%	840
	11th to 20th	Night	24% 5% 14% 31% 24% 3	840
	21st to end	Night	22% 7% 19% 31% 19% 1	924

Page generated at 2026-06-27 23:10:48. Version ac07

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