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 2025-02-25.

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	8% 4 1 3 3 2 3 2 4 5% 66%	112731
	Night	9% 4 1 4 3 3 3 2 4 5% 62%	114757
Transparency	Day	22% 4 7% 19% 24% 25%	112486
	Night	25% 4 8% 19% 23% 22%	114591
Seeing	Day	8% 5% 14% 24% 28% 20%	15513
	Night	10% 4 17% 37% 29% 3	24917

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% 7% 2 6% 5% 5% 4 3 4 6% 40%	3639
	11th to 20th	Day	15% 7% 3 6% 3 3 2 2 3 4 53%	4096
	21st to end	Day	19% 6% 2 6% 4 4 3 3 3 5% 44%	4510
February	1st to 10th	Day	19% 4 2 5% 4 3 3 3 5% 6% 48%	1800
	11th to 20th	Day	13% 6% 2 5% 4 4 4 3 5% 7% 48%	1836
	21st to end	Day	13% 5% 2 5% 3 3 3 3 5% 7% 50%	1611
March	1st to 10th	Day	15% 9% 3 8% 6% 5% 5% 4 5% 7% 35%	3316
	11th to 20th	Day	10% 4 2 4 3 3 3 3 4 6% 56%	3490
	21st to end	Day	15% 6% 2 6% 4 4 5% 3 6% 7% 41%	3917
April	1st to 10th	Day	11% 7% 2 5% 4 4 4 3 5% 6% 49%	2280
	11th to 20th	Day	9% 3 1 3 4 3 3 3 6% 6% 59%	2249
	21st to end	Day	3 3 1 3 3 3 2 3 5% 8% 65%	2280
May	1st to 10th	Day	5% 2 1 2 1 2 2 2 4 6% 75%	3972
	11th to 20th	Day	2 2 1 2 1 2 2 2 3 5% 80%	4330
	21st to end	Day	2 1 1 2 1 2 2 2 3 6% 78%	4813
June	1st to 10th	Day	4 3 1 2 3 3 2 3 5% 7% 67%	2660
	11th to 20th	Day	1 1 2 1 1 1 2 3 4 82%	2660
	21st to end	Day	2 1 1 1 1 2 2 2 3 86%	2660
July	1st to 10th	Day	1 1 1 1 1 2 93%	4420
	11th to 20th	Day	1 1 1 1 1 1 1 2 2 87%	4343
	21st to end	Day	1 1 1 1 1 1 2 3 88%	4455
August	1st to 10th	Day	2 2 1 2 2 1 2 2 4 6% 77%	4091
	11th to 20th	Day	1 1 1 1 1 1 2 3 89%	3851
	21st to end	Day	1 1 1 1 1 1 1 1 1 3 88%	4180
September	1st to 10th	Day	1 1 1 1 1 1 2 4 88%	2280
	11th to 20th	Day	2 2 1 2 2 2 2 2 4 5% 77%	2280
	21st to end	Day	3 2 2 2 1 1 2 3 4 81%	2024
October	1st to 10th	Day	2 1 1 2 1 2 3 2 3 5% 78%	3180
	11th to 20th	Day	4 3 1 3 2 2 2 3 4 5% 71%	3161
	21st to end	Day	5% 3 1 3 3 3 4 3 4 7% 64%	3448
November	1st to 10th	Day	9% 3 1 4 3 3 3 3 5% 7% 60%	1845
	11th to 20th	Day	11% 5% 2 5% 4 4 3 3 6% 8% 50%	1800
	21st to end	Day	11% 4 1 4 4 3 4 3 4 6% 55%	1602
December	1st to 10th	Day	9% 4 1 5% 3 3 4 3 6% 9% 53%	2620
	11th to 20th	Day	24% 9% 4 11% 6% 5% 4 3 5% 5% 24%	3028
	21st to end	Day	23% 9% 3 7% 4 5% 4 3 5% 8% 30%	4004
January	1st to 10th	Night	11% 5% 2 6% 4 4 5% 4 6% 9% 44%	6306
	11th to 20th	Night	15% 6% 2 6% 3 3 3 2 3 4 54%	5880
	21st to end	Night	17% 7% 2 6% 4 3 4 3 4 5% 47%	6468
February	1st to 10th	Night	17% 4 1 4 2 3 4 3 5% 6% 50%	2600
	11th to 20th	Night	11% 5% 2 4 3 3 4 3 6% 8% 51%	2449
	21st to end	Night	12% 4 2 4 4 3 4 4 5% 6% 53%	1937
March	1st to 10th	Night	15% 8% 2 7% 4 4 4 3 5% 7% 42%	3555
	11th to 20th	Night	14% 4 1 3 3 2 3 2 4 5% 60%	3490
	21st to end	Night	14% 5% 2 5% 4 4 5% 4 6% 8% 43%	3736
April	1st to 10th	Night	8% 4 2 5% 4 4 3 4 5% 7% 55%	1900
	11th to 20th	Night	8% 4 2 3 2 2 3 3 5% 6% 62%	1879
	21st to end	Night	5% 2 1 2 2 2 3 2 4 7% 71%	1900
May	1st to 10th	Night	3 1 1 2 1 2 2 2 4 5% 76%	2998
	11th to 20th	Night	2 1 1 1 2 2 2 2 3 4 82%	2562
	21st to end	Night	2 1 1 1 1 1 2 1 3 5% 82%	2762
June	1st to 10th	Night	4 2 2 2 2 3 3 4 6% 71%	1520
	11th to 20th	Night	1 1 1 1 2 2 2 3 5% 83%	1520
	21st to end	Night	1 1 1 1 2 2 2 2 3 3 84%	1520
July	1st to 10th	Night	1 1 1 1 1 94%	2540
	11th to 20th	Night	1 1 2 1 1 1 1 2 2 86%	2603
	21st to end	Night	1 1 1 1 1 1 2 3 88%	3109
August	1st to 10th	Night	3 2 1 2 1 2 2 2 3 5% 77%	2848
	11th to 20th	Night	1 1 1 1 1 2 3 91%	2994
	21st to end	Night	2 1 1 1 1 1 1 1 2 89%	3498
September	1st to 10th	Night	1 1 1 1 1 1 2 3 89%	1900
	11th to 20th	Night	3 2 1 3 2 2 1 1 3 5% 79%	1900
	21st to end	Night	1 1 1 1 1 1 1 3 5% 83%	2150
October	1st to 10th	Night	2 1 1 2 2 1 2 2 3 4 80%	3800
	11th to 20th	Night	2 1 1 2 2 2 2 2 4 5% 77%	3777
	21st to end	Night	6% 2 1 3 2 2 3 3 4 7% 66%	4121
November	1st to 10th	Night	8% 4 1 4 3 3 3 3 5% 7% 59%	2452
	11th to 20th	Night	9% 4 1 4 3 4 3 4 5% 8% 56%	2600
	21st to end	Night	11% 4 2 3 3 3 3 3 4 6% 58%	2795
December	1st to 10th	Night	9% 4 1 3 2 3 3 3 5% 7% 59%	4560
	11th to 20th	Night	23% 7% 3 7% 6% 4 5% 4 6% 8% 28%	5176
	21st to end	Night	25% 8% 3 7% 4 4 4 3 4 5% 32%	6952

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	44% 9% 11% 20% 10% 6%	3639
	11th to 20th	Day	38% 5% 6% 19% 19% 14%	4096
	21st to end	Day	42% 5% 7% 13% 18% 14%	4510
February	1st to 10th	Day	39% 5% 9% 20% 19% 8%	1800
	11th to 20th	Day	35% 6% 9% 22% 20% 8%	1845
	21st to end	Day	34% 5% 9% 27% 18% 6%	1611
March	1st to 10th	Day	47% 8% 11% 15% 16% 4	3316
	11th to 20th	Day	28% 5% 10% 25% 19% 13%	3490
	21st to end	Day	41% 6% 14% 22% 14% 3	3917
April	1st to 10th	Day	35% 4 11% 24% 19% 8%	2280
	11th to 20th	Day	26% 5% 11% 24% 24% 10%	2252
	21st to end	Day	18% 4 13% 29% 27% 9%	2280
May	1st to 10th	Day	12% 4 9% 26% 26% 23%	3972
	11th to 20th	Day	11% 2 5% 25% 36% 21%	4333
	21st to end	Day	10% 3 11% 33% 29% 15%	4814
June	1st to 10th	Day	17% 3 9% 27% 28% 15%	2660
	11th to 20th	Day	8% 2 7% 21% 34% 29%	2660
	21st to end	Day	7% 2 2 12% 37% 41%	2660
July	1st to 10th	Day	3 1 2 6% 16% 72%	4351
	11th to 20th	Day	7% 1 1 7% 18% 65%	4268
	21st to end	Day	5% 2 1 6% 26% 60%	4315
August	1st to 10th	Day	11% 2 1 9% 27% 51%	4076
	11th to 20th	Day	5% 1 1 10% 41% 43%	3890
	21st to end	Day	6% 1 1 13% 38% 40%	4179
September	1st to 10th	Day	5% 1 2 8% 28% 55%	2280
	11th to 20th	Day	12% 3 5% 22% 39% 19%	2280
	21st to end	Day	11% 2 4 21% 31% 32%	2024
October	1st to 10th	Day	11% 3 3 12% 26% 45%	3180
	11th to 20th	Day	16% 3 5% 25% 29% 21%	3161
	21st to end	Day	21% 3 7% 23% 31% 14%	3448
November	1st to 10th	Day	25% 5% 8% 28% 22% 12%	1845
	11th to 20th	Day	33% 5% 12% 24% 19% 7%	1800
	21st to end	Day	30% 6% 10% 22% 20% 12%	1602
December	1st to 10th	Day	29% 4 10% 28% 20% 9%	2620
	11th to 20th	Day	63% 4 7% 13% 11% 2	3028
	21st to end	Day	55% 4 11% 19% 8% 2	4004
January	1st to 10th	Night	37% 6% 17% 21% 13% 5%	6306
	11th to 20th	Night	36% 5% 7% 18% 21% 13%	5880
	21st to end	Night	40% 4 8% 11% 20% 16%	6468
February	1st to 10th	Night	36% 4 8% 21% 20% 11%	2600
	11th to 20th	Night	32% 4 10% 22% 22% 9%	2451
	21st to end	Night	30% 6% 9% 23% 23% 8%	1937
March	1st to 10th	Night	41% 8% 13% 19% 16% 3	3555
	11th to 20th	Night	27% 4 8% 24% 23% 14%	3490
	21st to end	Night	36% 8% 13% 25% 13% 4	3736
April	1st to 10th	Night	30% 5% 12% 22% 22% 10%	1900
	11th to 20th	Night	24% 4 11% 29% 21% 12%	1879
	21st to end	Night	16% 4 13% 29% 30% 9%	1900
May	1st to 10th	Night	11% 5% 9% 24% 30% 22%	2998
	11th to 20th	Night	8% 2 5% 24% 37% 23%	2562
	21st to end	Night	8% 3 9% 37% 26% 17%	2762
June	1st to 10th	Night	15% 3 12% 27% 29% 14%	1520
	11th to 20th	Night	7% 3 6% 21% 33% 31%	1520
	21st to end	Night	9% 2 2 12% 31% 44%	1520
July	1st to 10th	Night	3 1 1 5% 16% 74%	2500
	11th to 20th	Night	8% 1 1 7% 15% 68%	2555
	21st to end	Night	4 1 6% 25% 63%	3011
August	1st to 10th	Night	12% 2 1 7% 25% 54%	2839
	11th to 20th	Night	4 1 1 6% 39% 49%	3021
	21st to end	Night	7% 1 1 9% 35% 47%	3498
September	1st to 10th	Night	5% 1 1 7% 30% 55%	1900
	11th to 20th	Night	11% 2 4 19% 37% 27%	1900
	21st to end	Night	7% 2 3 18% 32% 38%	2150
October	1st to 10th	Night	11% 2 3 10% 20% 53%	3800
	11th to 20th	Night	12% 2 6% 27% 29% 24%	3777
	21st to end	Night	19% 2 5% 23% 30% 21%	4121
November	1st to 10th	Night	25% 5% 8% 24% 22% 16%	2452
	11th to 20th	Night	26% 5% 12% 26% 22% 9%	2600
	21st to end	Night	29% 4 8% 21% 24% 13%	2795
December	1st to 10th	Night	25% 4 8% 27% 23% 13%	4560
	11th to 20th	Night	54% 5% 9% 17% 13% 3	5176
	21st to end	Night	54% 5% 12% 16% 10% 3	6952

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	37% 4 18% 22% 18% 2	200
	11th to 20th	Day	17% 9% 19% 23% 21% 11%	396
	21st to end	Day	18% 6% 18% 20% 23% 15%	440
February	1st to 10th	Day	22% 9% 14% 22% 23% 11%	400
	11th to 20th	Day	16% 10% 25% 23% 19% 8%	436
	21st to end	Day	14% 10% 20% 27% 21% 8%	399
March	1st to 10th	Day	18% 13% 24% 25% 12% 7%	460
	11th to 20th	Day	19% 9% 20% 20% 20% 12%	460
	21st to end	Day	16% 11% 25% 26% 18% 5%	506
April	1st to 10th	Day	14% 8% 19% 28% 18% 12%	460
	11th to 20th	Day	11% 8% 22% 26% 19% 14%	452
	21st to end	Day	4 7% 19% 28% 23% 20%	460
May	1st to 10th	Day	7% 6% 23% 28% 22% 13%	463
	11th to 20th	Day	6% 3 20% 25% 23% 23%	488
	21st to end	Day	4 5% 15% 25% 26% 25%	529
June	1st to 10th	Day	4 3 15% 24% 32% 23%	490
	11th to 20th	Day	2 5% 12% 27% 36% 18%	490
	21st to end	Day	2 9% 27% 35% 27%	490
July	1st to 10th	Day	1 5% 27% 42% 26%	486
	11th to 20th	Day	1 5% 21% 42% 31%	484
	21st to end	Day	1 3 20% 45% 31%	531
August	1st to 10th	Day	2 1 5% 23% 41% 28%	487
	11th to 20th	Day	1 2 4 19% 41% 33%	477
	21st to end	Day	1 5% 18% 38% 38%	539
September	1st to 10th	Day	1 6% 19% 43% 30%	490
	11th to 20th	Day	2 4 9% 25% 31% 29%	490
	21st to end	Day	2 2 15% 24% 29% 28%	490
October	1st to 10th	Day	3 6% 15% 22% 24% 30%	490
	11th to 20th	Day	6% 5% 15% 20% 26% 29%	490
	21st to end	Day	10% 7% 15% 21% 29% 18%	539
November	1st to 10th	Day	10% 6% 18% 21% 25% 19%	381
	11th to 20th	Day	10% 6% 15% 26% 28% 15%	300
	21st to end	Day	15% 5% 13% 28% 28% 13%	200
December	1st to 10th	Day	20% 9% 16% 17% 22% 17%	200
	11th to 20th	Day	20% 4 16% 27% 23% 11%	200
	21st to end	Day	22% 10% 20% 22% 21% 5%	220
January	1st to 10th	Night	18% 6% 18% 32% 22% 3	800
	11th to 20th	Night	16% 5% 17% 38% 20% 4	800
	21st to end	Night	18% 5% 16% 33% 26% 4	880
February	1st to 10th	Night	20% 4 15% 37% 22% 2	800
	11th to 20th	Night	13% 7% 22% 34% 21% 3	784
	21st to end	Night	12% 7% 22% 39% 18% 2	646
March	1st to 10th	Night	18% 5% 21% 34% 20% 2	760
	11th to 20th	Night	16% 5% 19% 33% 24% 2	760
	21st to end	Night	15% 7% 24% 35% 19% 1	836
April	1st to 10th	Night	9% 5% 22% 39% 23% 2	760
	11th to 20th	Night	9% 7% 23% 33% 25% 3	751
	21st to end	Night	6% 5% 19% 40% 27% 3	760
May	1st to 10th	Night	4 4 27% 37% 25% 2	656
	11th to 20th	Night	3 3 21% 43% 29% 1	407
	21st to end	Night	3 5% 21% 39% 30% 1	411
June	1st to 10th	Night	5% 3 20% 42% 27% 2	380
	11th to 20th	Night	1 2 24% 49% 23% 1	380
	21st to end	Night	2 2 18% 46% 32% 1	380
July	1st to 10th	Night	1 13% 53% 32% 1	370
	11th to 20th	Night	1 12% 55% 31% 1	405
	21st to end	Night	1 1 9% 43% 44% 2	624
August	1st to 10th	Night	3 1 13% 44% 37% 2	567
	11th to 20th	Night	1 1 8% 46% 40% 4	668
	21st to end	Night	1 7% 40% 49% 3	836
September	1st to 10th	Night	1 1 9% 38% 48% 4	760
	11th to 20th	Night	3 1 11% 39% 41% 5%	760
	21st to end	Night	2 2 16% 33% 39% 8%	760
October	1st to 10th	Night	4 4 13% 38% 33% 8%	760
	11th to 20th	Night	4 3 16% 37% 35% 5%	760
	21st to end	Night	7% 4 15% 35% 30% 8%	836
November	1st to 10th	Night	9% 5% 17% 31% 33% 5%	780
	11th to 20th	Night	11% 2 17% 40% 28% 3	800
	21st to end	Night	13% 5% 16% 37% 27% 3	800
December	1st to 10th	Night	16% 6% 16% 33% 23% 6%	800
	11th to 20th	Night	25% 5% 14% 31% 24% 2	800
	21st to end	Night	21% 7% 20% 32% 20% 1	880

Page generated at 2025-02-22 03:51:38. Version ac07

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