Thompson Grove Picnic Area
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Thompson Grove Picnic Area 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	5% 4 1 4 3 3 3 3 5% 7% 61%	104958
	Night	5% 4 1 4 3 3 4 3 5% 7% 59%	102806
Transparency	Day	22% 4 10% 22% 27% 15%	104707
	Night	24% 5% 10% 22% 26% 14%	102647
Seeing	Day	7% 7% 27% 34% 20% 5%	15393
	Night	7% 7% 35% 39% 12% 1	25347

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	5% 7% 3 5% 4 3 3 3 4 6% 59%	2538
	11th to 20th	Day	3 3 1 4 3 4 4 3 5% 7% 64%	2586
	21st to end	Day	5% 6% 2 5% 3 3 4 4 5% 6% 57%	3306
February	1st to 10th	Day	3 7% 2 5% 4 3 3 3 4 7% 58%	1900
	11th to 20th	Day	3 7% 3 6% 4 3 2 3 4 6% 59%	1849
	21st to end	Day	3 4 1 4 3 3 4 3 4 6% 65%	1570
March	1st to 10th	Day	3 4 1 4 2 3 3 2 4 6% 67%	3130
	11th to 20th	Day	8% 5% 2 5% 3 3 3 3 5% 6% 58%	3249
	21st to end	Day	5% 7% 2 4 3 3 3 3 6% 7% 57%	4157
April	1st to 10th	Day	4 4 1 3 2 2 3 4 4 6% 66%	2280
	11th to 20th	Day	8% 4 1 5% 3 3 3 3 4 6% 60%	2251
	21st to end	Day	7% 4 2 3 3 2 4 3 4 8% 60%	2280
May	1st to 10th	Day	8% 4 1 4 3 2 3 4 5% 6% 60%	4083
	11th to 20th	Day	8% 4 2 4 4 4 3 3 5% 6% 58%	4082
	21st to end	Day	5% 2 1 2 3 2 3 3 5% 7% 66%	4489
June	1st to 10th	Day	5% 2 1 3 3 3 4 4 8% 9% 57%	2642
	11th to 20th	Day	4 2 1 3 3 3 4 3 6% 7% 65%	2660
	21st to end	Day	5% 3 1 5% 4 3 5% 4 6% 9% 56%	2660
July	1st to 10th	Day	5% 3 1 4 4 4 4 4 6% 9% 55%	4430
	11th to 20th	Day	2 2 1 3 4 4 4 4 7% 10% 60%	4430
	21st to end	Day	4 3 1 4 3 4 5% 5% 7% 9% 55%	4577
August	1st to 10th	Day	6% 4 2 5% 4 4 4 4 7% 10% 51%	3784
	11th to 20th	Day	4 2 1 3 2 3 5% 4 7% 9% 59%	3726
	21st to end	Day	3 3 1 4 3 4 5% 4 7% 9% 57%	4180
September	1st to 10th	Day	8% 3 1 3 2 3 4 4 5% 6% 61%	2280
	11th to 20th	Day	7% 4 2 4 2 3 3 3 5% 6% 61%	2137
	21st to end	Day	6% 3 1 3 2 2 2 2 4 5% 68%	2090
October	1st to 10th	Day	5% 3 1 2 2 2 2 2 3 5% 72%	3480
	11th to 20th	Day	7% 4 2 4 2 3 3 2 4 6% 65%	3228
	21st to end	Day	4 3 1 1 1 1 2 1 2 5% 78%	3201
November	1st to 10th	Day	4 3 1 3 2 2 2 2 5% 5% 71%	1736
	11th to 20th	Day	2 4 1 3 2 2 3 3 4 5% 72%	1710
	21st to end	Day	6% 6% 2 3 2 2 2 2 3 5% 66%	1710
December	1st to 10th	Day	2 5% 2 4 2 3 4 3 4 7% 63%	1710
	11th to 20th	Day	5% 4 1 3 4 3 3 4 5% 7% 62%	2043
	21st to end	Day	4 5% 2 6% 3 3 3 3 4 6% 62%	2794
January	1st to 10th	Night	3 6% 2 7% 5% 4 4 4 5% 6% 56%	4417
	11th to 20th	Night	2 5% 1 4 3 3 4 4 5% 6% 62%	4400
	21st to end	Night	3 6% 2 5% 4 3 3 3 4 7% 60%	4357
February	1st to 10th	Night	4 6% 2 5% 3 4 3 3 5% 5% 61%	2280
	11th to 20th	Night	5% 7% 2 7% 4 4 3 3 5% 7% 54%	2218
	21st to end	Night	6% 5% 1 2 2 2 3 3 7% 6% 63%	1884
March	1st to 10th	Night	4 4 1 3 2 2 2 2 4 6% 69%	3734
	11th to 20th	Night	7% 6% 2 6% 4 4 4 3 5% 6% 54%	3718
	21st to end	Night	5% 6% 2 4 2 4 3 3 5% 7% 59%	3481
April	1st to 10th	Night	4 3 1 3 2 3 3 3 5% 7% 66%	1900
	11th to 20th	Night	7% 4 1 4 4 4 4 3 5% 7% 56%	1877
	21st to end	Night	8% 4 2 3 2 4 3 3 5% 8% 58%	1900
May	1st to 10th	Night	7% 4 1 4 3 3 3 2 4 6% 63%	2887
	11th to 20th	Night	11% 4 1 4 3 3 3 4 5% 7% 54%	2823
	21st to end	Night	7% 4 1 4 4 4 4 3 5% 6% 59%	3098
June	1st to 10th	Night	4 3 1 5% 4 4 4 4 7% 10% 55%	1533
	11th to 20th	Night	3 3 1 3 3 3 4 4 7% 7% 62%	1520
	21st to end	Night	4 3 1 5% 4 4 6% 5% 7% 10% 51%	1520
July	1st to 10th	Night	6% 3 1 3 3 4 5% 5% 9% 11% 51%	2540
	11th to 20th	Night	3 4 2 6% 4 3 4 4 7% 13% 51%	2540
	21st to end	Night	6% 4 2 5% 5% 5% 5% 5% 8% 10% 45%	2979
August	1st to 10th	Night	8% 4 2 6% 5% 5% 5% 5% 8% 9% 43%	3155
	11th to 20th	Night	5% 3 2 5% 4 5% 6% 6% 9% 13% 44%	3113
	21st to end	Night	3 3 1 7% 6% 6% 6% 6% 8% 9% 44%	3487
September	1st to 10th	Night	6% 3 1 4 3 4 4 4 7% 7% 57%	1900
	11th to 20th	Night	7% 4 1 4 2 3 3 4 6% 7% 59%	2042
	21st to end	Night	6% 3 1 3 2 2 2 2 4 6% 69%	2090
October	1st to 10th	Night	5% 2 1 3 2 2 3 3 4 5% 70%	3480
	11th to 20th	Night	9% 3 1 3 2 3 3 2 5% 6% 62%	3681
	21st to end	Night	5% 3 1 2 2 1 2 2 4 5% 74%	4324
November	1st to 10th	Night	5% 3 1 3 2 2 2 2 3 7% 70%	2503
	11th to 20th	Night	2 3 1 3 2 2 3 2 4 5% 74%	2470
	21st to end	Night	5% 5% 1 3 3 2 3 3 4 6% 64%	2470
December	1st to 10th	Night	3 5% 2 4 3 3 3 3 5% 7% 63%	2470
	11th to 20th	Night	4 4 1 4 3 3 3 3 5% 7% 63%	3142
	21st to end	Night	3 5% 2 5% 3 4 5% 4 5% 6% 58%	4873

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	27% 5% 6% 24% 30% 7%	2539
	11th to 20th	Day	19% 3 13% 27% 29% 9%	2586
	21st to end	Day	27% 4 8% 24% 30% 7%	3306
February	1st to 10th	Day	27% 3 10% 22% 24% 14%	1900
	11th to 20th	Day	27% 4 7% 22% 25% 15%	1859
	21st to end	Day	20% 4 5% 18% 31% 22%	1570
March	1st to 10th	Day	18% 3 4 18% 27% 29%	3130
	11th to 20th	Day	27% 5% 7% 21% 30% 10%	3249
	21st to end	Day	25% 4 8% 24% 28% 11%	4157
April	1st to 10th	Day	18% 4 8% 22% 28% 20%	2280
	11th to 20th	Day	25% 4 7% 21% 24% 18%	2254
	21st to end	Day	23% 4 10% 26% 25% 12%	2280
May	1st to 10th	Day	24% 4 10% 21% 18% 23%	4083
	11th to 20th	Day	27% 5% 9% 24% 22% 14%	4086
	21st to end	Day	18% 5% 12% 19% 22% 24%	4489
June	1st to 10th	Day	20% 7% 17% 25% 20% 11%	2642
	11th to 20th	Day	17% 5% 8% 20% 27% 23%	2660
	21st to end	Day	23% 6% 11% 24% 22% 14%	2660
July	1st to 10th	Day	25% 5% 12% 25% 24% 7%	4361
	11th to 20th	Day	18% 5% 16% 23% 30% 8%	4355
	21st to end	Day	23% 5% 13% 24% 27% 8%	4431
August	1st to 10th	Day	27% 6% 18% 23% 18% 8%	3772
	11th to 20th	Day	20% 5% 12% 23% 30% 10%	3762
	21st to end	Day	22% 5% 15% 26% 26% 6%	4179
September	1st to 10th	Day	23% 5% 11% 22% 23% 15%	2280
	11th to 20th	Day	24% 4 9% 19% 27% 18%	2137
	21st to end	Day	18% 4 7% 21% 32% 18%	2090
October	1st to 10th	Day	16% 3 4 16% 38% 22%	3480
	11th to 20th	Day	24% 2 8% 18% 31% 16%	3228
	21st to end	Day	14% 2 3 16% 43% 23%	3201
November	1st to 10th	Day	16% 2 8% 19% 34% 21%	1736
	11th to 20th	Day	15% 3 6% 27% 34% 16%	1710
	21st to end	Day	24% 2 5% 17% 29% 24%	1710
December	1st to 10th	Day	20% 4 10% 28% 26% 11%	1710
	11th to 20th	Day	22% 3 7% 23% 32% 14%	2041
	21st to end	Day	23% 4 10% 21% 25% 17%	2794
January	1st to 10th	Night	29% 5% 7% 26% 27% 6%	4417
	11th to 20th	Night	21% 4 12% 26% 27% 10%	4400
	21st to end	Night	25% 4 12% 22% 30% 7%	4357
February	1st to 10th	Night	24% 4 9% 21% 30% 12%	2280
	11th to 20th	Night	30% 4 8% 21% 25% 13%	2218
	21st to end	Night	20% 4 5% 20% 32% 20%	1884
March	1st to 10th	Night	18% 3 4 18% 24% 31%	3734
	11th to 20th	Night	29% 5% 9% 19% 24% 14%	3718
	21st to end	Night	23% 6% 9% 25% 25% 12%	3481
April	1st to 10th	Night	18% 5% 8% 23% 27% 20%	1900
	11th to 20th	Night	26% 5% 9% 22% 22% 16%	1877
	21st to end	Night	25% 5% 13% 23% 21% 13%	1900
May	1st to 10th	Night	23% 5% 12% 19% 15% 25%	2887
	11th to 20th	Night	28% 7% 14% 21% 18% 12%	2824
	21st to end	Night	25% 6% 11% 15% 16% 26%	3099
June	1st to 10th	Night	23% 8% 17% 26% 16% 10%	1533
	11th to 20th	Night	19% 5% 14% 19% 24% 19%	1520
	21st to end	Night	25% 6% 14% 26% 16% 13%	1520
July	1st to 10th	Night	26% 6% 16% 28% 18% 6%	2500
	11th to 20th	Night	25% 6% 17% 24% 24% 5%	2492
	21st to end	Night	31% 6% 13% 23% 19% 8%	2886
August	1st to 10th	Night	36% 6% 15% 20% 19% 5%	3144
	11th to 20th	Night	28% 5% 13% 26% 23% 5%	3143
	21st to end	Night	33% 5% 14% 23% 21% 4	3487
September	1st to 10th	Night	25% 7% 14% 20% 23% 12%	1900
	11th to 20th	Night	23% 6% 11% 20% 24% 16%	2042
	21st to end	Night	19% 4 8% 20% 33% 15%	2090
October	1st to 10th	Night	17% 3 6% 17% 36% 21%	3480
	11th to 20th	Night	24% 2 7% 20% 27% 18%	3681
	21st to end	Night	16% 2 3 19% 42% 19%	4324
November	1st to 10th	Night	17% 2 7% 20% 31% 23%	2503
	11th to 20th	Night	14% 3 5% 24% 36% 16%	2470
	21st to end	Night	22% 2 6% 19% 28% 23%	2470
December	1st to 10th	Night	22% 3 10% 26% 28% 11%	2470
	11th to 20th	Night	22% 4 6% 21% 33% 14%	3143
	21st to end	Night	23% 6% 9% 22% 28% 12%	4873

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	9% 5% 31% 40% 13% 2	270
	11th to 20th	Day	8% 9% 35% 34% 11% 3	270
	21st to end	Day	5% 9% 33% 31% 19% 3	297
February	1st to 10th	Day	5% 11% 44% 29% 10% 1	270
	11th to 20th	Day	7% 10% 44% 28% 8% 3	270
	21st to end	Day	7% 12% 47% 31% 3	225
March	1st to 10th	Day	3 11% 40% 31% 13% 1	270
	11th to 20th	Day	12% 11% 31% 31% 12% 2	270
	21st to end	Day	12% 17% 38% 22% 8% 1	498
April	1st to 10th	Day	7% 14% 43% 26% 9% 1	460
	11th to 20th	Day	10% 18% 42% 23% 7% 1	452
	21st to end	Day	13% 15% 39% 22% 10% 1	460
May	1st to 10th	Day	7% 11% 35% 33% 12% 2	629
	11th to 20th	Day	10% 8% 28% 34% 18% 3	675
	21st to end	Day	7% 9% 36% 35% 12% 2	734
June	1st to 10th	Day	6% 5% 25% 35% 24% 5%	680
	11th to 20th	Day	5% 4 31% 38% 19% 3	680
	21st to end	Day	5% 4 21% 43% 22% 5%	680
July	1st to 10th	Day	5% 2 16% 38% 31% 7%	671
	11th to 20th	Day	3 12% 36% 39% 10%	668
	21st to end	Day	5% 1 7% 37% 41% 9%	726
August	1st to 10th	Day	3 2 14% 33% 38% 10%	487
	11th to 20th	Day	5% 1 13% 41% 31% 9%	477
	21st to end	Day	4 1 12% 45% 29% 9%	539
September	1st to 10th	Day	7% 16% 41% 29% 7%	490
	11th to 20th	Day	4 3 17% 40% 28% 7%	347
	21st to end	Day	10% 3 22% 29% 27% 9%	300
October	1st to 10th	Day	15% 5% 18% 30% 26% 6%	300
	11th to 20th	Day	7% 6% 30% 30% 21% 7%	300
	21st to end	Day	12% 8% 28% 28% 18% 6%	330
November	1st to 10th	Day	9% 9% 30% 30% 21% 1	291
	11th to 20th	Day	5% 8% 31% 36% 15% 5%	270
	21st to end	Day	10% 13% 32% 24% 14% 6%	270
December	1st to 10th	Day	3 6% 37% 36% 14% 3	270
	11th to 20th	Day	8% 8% 37% 35% 12%	270
	21st to end	Day	10% 10% 43% 30% 6%	297
January	1st to 10th	Night	6% 7% 37% 40% 10% 1	950
	11th to 20th	Night	6% 8% 35% 37% 12% 1	933
	21st to end	Night	4 5% 42% 38% 10% 1	836
February	1st to 10th	Night	5% 9% 44% 34% 7% 1	760
	11th to 20th	Night	8% 9% 51% 27% 6%	744
	21st to end	Night	10% 8% 51% 27% 4	628
March	1st to 10th	Night	6% 11% 45% 33% 4	760
	11th to 20th	Night	9% 11% 36% 36% 7% 1	717
	21st to end	Night	6% 15% 49% 26% 4	627
April	1st to 10th	Night	6% 12% 48% 29% 4	570
	11th to 20th	Night	7% 12% 50% 28% 3	563
	21st to end	Night	10% 10% 45% 30% 5%	570
May	1st to 10th	Night	8% 9% 45% 33% 5%	570
	11th to 20th	Night	10% 7% 35% 37% 11% 1	561
	21st to end	Night	7% 7% 46% 32% 8%	617
June	1st to 10th	Night	4 5% 35% 44% 11%	570
	11th to 20th	Night	3 5% 46% 40% 6%	570
	21st to end	Night	5% 2 32% 49% 13%	570
July	1st to 10th	Night	5% 1 20% 52% 21%	555
	11th to 20th	Night	4 2 15% 52% 27% 1	552
	21st to end	Night	7% 1 13% 52% 27%	624
August	1st to 10th	Night	3 1 14% 50% 30% 2	567
	11th to 20th	Night	7% 2 14% 52% 24% 1	564
	21st to end	Night	5% 1 19% 48% 26% 1	627
September	1st to 10th	Night	6% 1 21% 54% 18% 1	570
	11th to 20th	Night	7% 2 32% 45% 13% 1	570
	21st to end	Night	6% 5% 27% 46% 14% 1	570
October	1st to 10th	Night	12% 3 31% 41% 12% 1	570
	11th to 20th	Night	6% 6% 33% 40% 12% 2	702
	21st to end	Night	8% 7% 32% 34% 16% 3	952
November	1st to 10th	Night	6% 5% 32% 42% 13% 2	963
	11th to 20th	Night	4 8% 37% 38% 13% 1	950
	21st to end	Night	8% 7% 33% 37% 14% 1	950
December	1st to 10th	Night	5% 7% 35% 40% 12% 1	950
	11th to 20th	Night	8% 8% 38% 36% 10% 1	950
	21st to end	Night	8% 12% 38% 33% 8% 1	1045

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