Smith Mountain Lake State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Smith Mountain Lake State Park clear sky chart from 2005-11-06 to 2024-11-05.

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	14% 5% 2 6% 4 4 4 4 6% 8% 43%	100707
	Night	15% 5% 2 6% 4 4 4 4 5% 7% 44%	98273
Transparency	Day	38% 8% 12% 22% 16% 4	104356
	Night	37% 7% 11% 22% 18% 5%	102762
Seeing	Day	17% 10% 24% 24% 18% 7%	15160
	Night	17% 8% 26% 30% 17% 2	25460

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	17% 4 1 4 3 4 3 3 5% 6% 49%	2836
	11th to 20th	Day	14% 7% 2 5% 5% 4 3 3 5% 6% 46%	2840
	21st to end	Day	21% 7% 3 6% 3 4 3 3 4 4 41%	3124
February	1st to 10th	Day	13% 7% 2 6% 4 4 6% 4 6% 7% 41%	1710
	11th to 20th	Day	19% 5% 1 5% 3 4 3 4 6% 7% 42%	1677
	21st to end	Day	20% 6% 3 5% 4 4 4 3 5% 7% 39%	1673
March	1st to 10th	Day	22% 7% 3 5% 3 3 3 3 5% 7% 38%	3435
	11th to 20th	Day	11% 4 1 4 3 4 3 3 5% 7% 54%	3480
	21st to end	Day	20% 7% 2 6% 4 4 4 3 4 6% 39%	3815
April	1st to 10th	Day	11% 5% 2 4 4 4 4 4 5% 7% 50%	2180
	11th to 20th	Day	13% 6% 2 5% 4 3 4 3 5% 6% 49%	2254
	21st to end	Day	16% 5% 2 6% 5% 5% 4 3 5% 7% 43%	2363
May	1st to 10th	Day	15% 5% 2 7% 6% 5% 6% 5% 6% 8% 34%	4082
	11th to 20th	Day	21% 6% 2 7% 4 4 5% 4 6% 8% 35%	4081
	21st to end	Day	9% 3 1 5% 5% 5% 5% 4 7% 9% 47%	4476
June	1st to 10th	Day	11% 4 2 5% 5% 4 5% 4 7% 9% 45%	2470
	11th to 20th	Day	9% 4 2 6% 5% 4 5% 5% 7% 11% 41%	2470
	21st to end	Day	8% 5% 2 6% 5% 5% 5% 5% 8% 9% 42%	2470
July	1st to 10th	Day	6% 4 2 6% 5% 6% 5% 5% 9% 12% 38%	4120
	11th to 20th	Day	8% 6% 3 7% 5% 5% 6% 6% 7% 13% 36%	4120
	21st to end	Day	12% 8% 3 9% 7% 6% 6% 5% 8% 8% 28%	4466
August	1st to 10th	Day	14% 7% 3 7% 5% 5% 5% 5% 8% 11% 32%	4104
	11th to 20th	Day	9% 4 2 6% 4 5% 6% 5% 7% 10% 41%	4026
	21st to end	Day	8% 4 1 5% 3 4 4 3 6% 11% 50%	4180
September	1st to 10th	Day	13% 5% 2 5% 4 3 4 4 5% 7% 49%	2280
	11th to 20th	Day	14% 6% 2 6% 4 4 3 4 5% 8% 44%	2095
	21st to end	Day	24% 5% 2 5% 4 4 3 4 5% 7% 37%	2081
October	1st to 10th	Day	18% 5% 2 3 2 4 2 2 4 6% 52%	1900
	11th to 20th	Day	16% 4 1 4 2 3 3 3 4 7% 53%	1900
	21st to end	Day	13% 5% 2 5% 3 3 3 3 4 6% 54%	2090
November	1st to 10th	Day	13% 4 1 4 3 3 3 3 4 5% 56%	1898
	11th to 20th	Day	14% 6% 2 4 3 4 4 3 4 6% 51%	1788
	21st to end	Day	14% 4 1 5% 3 3 4 3 5% 8% 50%	1591
December	1st to 10th	Day	16% 7% 2 6% 4 6% 5% 5% 6% 7% 39%	1520
	11th to 20th	Day	15% 5% 2 4 3 3 3 2 4 6% 54%	1988
	21st to end	Day	20% 5% 2 5% 4 4 4 5% 6% 8% 37%	3124
January	1st to 10th	Night	14% 6% 2 5% 3 3 4 3 5% 6% 50%	4109
	11th to 20th	Night	16% 6% 2 5% 4 3 3 3 4 7% 47%	4120
	21st to end	Night	23% 6% 2 6% 3 4 3 3 4 5% 42%	4532
February	1st to 10th	Night	15% 6% 2 5% 4 3 4 4 5% 7% 44%	2470
	11th to 20th	Night	20% 6% 2 5% 4 3 3 3 5% 5% 44%	2386
	21st to end	Night	16% 7% 2 6% 4 4 5% 3 5% 6% 43%	1780
March	1st to 10th	Night	24% 7% 3 6% 4 4 3 4 5% 5% 35%	3418
	11th to 20th	Night	11% 4 1 4 3 3 3 3 6% 6% 54%	3480
	21st to end	Night	17% 6% 2 5% 3 3 3 3 4 5% 48%	3817
April	1st to 10th	Night	15% 6% 2 6% 4 3 4 3 5% 6% 45%	1999
	11th to 20th	Night	14% 5% 2 6% 3 3 3 3 6% 6% 50%	1875
	21st to end	Night	16% 4 2 5% 4 3 4 3 6% 8% 45%	1833
May	1st to 10th	Night	16% 7% 2 7% 4 5% 5% 4 5% 8% 37%	2813
	11th to 20th	Night	23% 7% 2 6% 4 3 3 3 4 6% 37%	2812
	21st to end	Night	11% 4 2 5% 4 4 3 4 7% 10% 47%	3079
June	1st to 10th	Night	9% 4 1 6% 4 4 5% 5% 7% 12% 41%	1710
	11th to 20th	Night	11% 4 2 5% 4 4 5% 4 7% 9% 46%	1710
	21st to end	Night	8% 3 2 5% 5% 4 5% 4 8% 11% 45%	1710
July	1st to 10th	Night	6% 4 2 7% 5% 6% 6% 5% 8% 10% 41%	2840
	11th to 20th	Night	9% 6% 2 5% 5% 5% 6% 5% 7% 11% 38%	2840
	21st to end	Night	11% 9% 3 9% 6% 5% 6% 5% 7% 9% 30%	3087
August	1st to 10th	Night	17% 7% 2 6% 4 5% 5% 4 8% 10% 30%	2825
	11th to 20th	Night	8% 4 2 6% 5% 5% 6% 5% 8% 10% 41%	2785
	21st to end	Night	8% 4 2 6% 4 4 5% 4 6% 9% 48%	3461
September	1st to 10th	Night	11% 6% 2 7% 4 4 5% 3 6% 6% 46%	1900
	11th to 20th	Night	16% 6% 2 6% 4 4 4 3 6% 7% 41%	2080
	21st to end	Night	24% 7% 3 7% 4 4 3 3 5% 5% 37%	2099
October	1st to 10th	Night	18% 5% 2 4 4 3 3 3 4 7% 47%	2280
	11th to 20th	Night	14% 5% 2 5% 4 4 3 3 4 6% 51%	2280
	21st to end	Night	14% 3 1 3 3 3 3 2 4 6% 56%	2508
November	1st to 10th	Night	13% 6% 2 5% 3 3 3 3 4 5% 53%	2280
	11th to 20th	Night	14% 5% 1 4 3 3 4 4 5% 5% 53%	2389
	21st to end	Night	14% 4 2 5% 3 3 4 4 5% 7% 50%	2584
December	1st to 10th	Night	18% 7% 3 5% 4 4 4 3 5% 6% 43%	2660
	11th to 20th	Night	16% 6% 2 5% 4 4 4 3 4 6% 47%	3190
	21st to end	Night	19% 5% 2 6% 4 4 5% 5% 6% 9% 35%	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	34% 5% 9% 29% 18% 6%	2837
	11th to 20th	Day	39% 4 7% 20% 25% 5%	2840
	21st to end	Day	47% 5% 6% 21% 18% 3	3124
February	1st to 10th	Day	40% 7% 12% 22% 18% 3	1710
	11th to 20th	Day	40% 5% 9% 23% 17% 5%	1686
	21st to end	Day	44% 5% 13% 14% 18% 5%	1673
March	1st to 10th	Day	45% 6% 9% 21% 13% 6%	3435
	11th to 20th	Day	29% 7% 9% 25% 20% 10%	3480
	21st to end	Day	45% 6% 9% 19% 17% 3	3815
April	1st to 10th	Day	31% 7% 11% 23% 19% 8%	2180
	11th to 20th	Day	35% 6% 12% 23% 19% 6%	2254
	21st to end	Day	41% 7% 12% 22% 15% 4	2363
May	1st to 10th	Day	45% 10% 13% 18% 12% 2	4120
	11th to 20th	Day	48% 8% 10% 23% 10% 1	4085
	21st to end	Day	30% 11% 16% 22% 17% 4	4489
June	1st to 10th	Day	34% 10% 16% 26% 14% 1	2470
	11th to 20th	Day	36% 10% 15% 21% 15% 2	2470
	21st to end	Day	35% 12% 15% 22% 15% 2	2470
July	1st to 10th	Day	35% 13% 20% 16% 10% 5%	4055
	11th to 20th	Day	38% 10% 19% 24% 9% 1	4051
	21st to end	Day	50% 11% 12% 18% 10%	4324
August	1st to 10th	Day	45% 9% 16% 23% 5% 1	4091
	11th to 20th	Day	35% 11% 17% 26% 10% 1	4065
	21st to end	Day	29% 7% 19% 29% 15% 2	4180
September	1st to 10th	Day	35% 9% 12% 20% 20% 4	2280
	11th to 20th	Day	40% 6% 10% 22% 19% 2	2095
	21st to end	Day	47% 8% 9% 17% 18% 2	2081
October	1st to 10th	Day	33% 4 8% 18% 29% 8%	3160
	11th to 20th	Day	24% 3 6% 24% 28% 15%	3140
	21st to end	Day	24% 4 10% 25% 24% 12%	3428
November	1st to 10th	Day	31% 5% 9% 22% 27% 6%	1898
	11th to 20th	Day	35% 5% 8% 22% 21% 8%	1788
	21st to end	Day	32% 5% 10% 24% 25% 4	1591
December	1st to 10th	Day	44% 8% 9% 18% 17% 4	1520
	11th to 20th	Day	33% 4 8% 25% 23% 7%	1984
	21st to end	Day	40% 8% 12% 25% 13% 2	3124
January	1st to 10th	Night	35% 5% 8% 25% 23% 4	4109
	11th to 20th	Night	38% 5% 8% 20% 25% 5%	4120
	21st to end	Night	45% 5% 7% 23% 15% 6%	4532
February	1st to 10th	Night	38% 6% 10% 24% 19% 3	2470
	11th to 20th	Night	43% 4 8% 19% 19% 6%	2388
	21st to end	Night	41% 6% 10% 23% 15% 6%	1780
March	1st to 10th	Night	48% 7% 9% 19% 14% 4	3418
	11th to 20th	Night	28% 7% 9% 20% 25% 11%	3480
	21st to end	Night	38% 5% 9% 24% 19% 5%	3817
April	1st to 10th	Night	39% 6% 10% 19% 21% 5%	1999
	11th to 20th	Night	34% 6% 9% 23% 21% 6%	1875
	21st to end	Night	35% 7% 12% 25% 18% 4	1833
May	1st to 10th	Night	44% 9% 13% 21% 11% 2	2840
	11th to 20th	Night	48% 6% 10% 22% 13% 1	2813
	21st to end	Night	29% 10% 18% 26% 13% 4	3087
June	1st to 10th	Night	33% 11% 16% 25% 15%	1710
	11th to 20th	Night	32% 11% 18% 21% 16% 2	1710
	21st to end	Night	30% 12% 16% 21% 17% 4	1710
July	1st to 10th	Night	36% 13% 19% 18% 12% 3	2795
	11th to 20th	Night	37% 11% 22% 22% 8% 1	2786
	21st to end	Night	48% 11% 14% 19% 8%	2988
August	1st to 10th	Night	45% 10% 17% 21% 7% 1	2814
	11th to 20th	Night	34% 9% 18% 27% 11% 1	2812
	21st to end	Night	31% 8% 12% 35% 11% 2	3461
September	1st to 10th	Night	37% 9% 12% 20% 16% 6%	1900
	11th to 20th	Night	41% 8% 10% 20% 20% 2	2080
	21st to end	Night	49% 6% 8% 18% 16% 3	2099
October	1st to 10th	Night	38% 5% 8% 18% 24% 6%	3800
	11th to 20th	Night	25% 3 7% 22% 30% 13%	3779
	21st to end	Night	21% 3 7% 29% 27% 12%	4120
November	1st to 10th	Night	34% 4 10% 20% 25% 7%	2280
	11th to 20th	Night	32% 5% 9% 21% 24% 8%	2389
	21st to end	Night	33% 4 9% 25% 22% 6%	2584
December	1st to 10th	Night	43% 5% 8% 24% 17% 3	2660
	11th to 20th	Night	38% 5% 8% 22% 21% 6%	3192
	21st to end	Night	41% 7% 12% 21% 18% 2	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	24% 26% 29% 16% 5% 1	270
	11th to 20th	Day	28% 20% 38% 12% 2	270
	21st to end	Day	25% 21% 38% 13% 3	297
February	1st to 10th	Day	19% 23% 36% 17% 6%	270
	11th to 20th	Day	33% 25% 30% 9% 3 1	270
	21st to end	Day	27% 17% 34% 17% 3	328
March	1st to 10th	Day	24% 15% 33% 20% 8% 1	460
	11th to 20th	Day	21% 19% 34% 20% 6% 1	460
	21st to end	Day	25% 12% 36% 22% 5%	506
April	1st to 10th	Day	18% 20% 31% 20% 9% 2	460
	11th to 20th	Day	19% 15% 26% 24% 12% 4	452
	21st to end	Day	19% 12% 34% 23% 10% 2	460
May	1st to 10th	Day	17% 13% 32% 25% 10% 3	463
	11th to 20th	Day	19% 6% 24% 26% 16% 8%	487
	21st to end	Day	16% 4 20% 28% 24% 9%	529
June	1st to 10th	Day	11% 5% 23% 32% 20% 9%	490
	11th to 20th	Day	10% 5% 18% 29% 26% 12%	490
	21st to end	Day	9% 4 18% 33% 26% 10%	490
July	1st to 10th	Day	11% 2 12% 27% 32% 16%	485
	11th to 20th	Day	5% 2 10% 28% 39% 15%	484
	21st to end	Day	10% 2 15% 31% 27% 15%	532
August	1st to 10th	Day	13% 3 21% 20% 29% 13%	486
	11th to 20th	Day	10% 3 15% 27% 26% 18%	479
	21st to end	Day	11% 2 8% 27% 31% 21%	539
September	1st to 10th	Day	14% 3 13% 24% 28% 18%	490
	11th to 20th	Day	17% 3 14% 22% 28% 16%	490
	21st to end	Day	29% 6% 19% 26% 16% 5%	490
October	1st to 10th	Day	22% 5% 16% 28% 23% 7%	490
	11th to 20th	Day	14% 13% 20% 25% 23% 4	490
	21st to end	Day	14% 10% 27% 30% 15% 4	539
November	1st to 10th	Day	18% 10% 26% 29% 14% 4	472
	11th to 20th	Day	18% 16% 29% 22% 13% 1	348
	21st to end	Day	15% 20% 27% 25% 10% 2	213
December	1st to 10th	Day	23% 18% 34% 18% 7% 1	180
	11th to 20th	Day	22% 13% 33% 23% 9% 1	204
	21st to end	Day	24% 15% 32% 18% 9% 2	297
January	1st to 10th	Night	21% 16% 34% 25% 3	760
	11th to 20th	Night	18% 15% 34% 30% 3	760
	21st to end	Night	20% 13% 41% 24% 2	836
February	1st to 10th	Night	19% 14% 38% 27% 3	760
	11th to 20th	Night	24% 16% 41% 19% 1	743
	21st to end	Night	20% 13% 40% 24% 3	628
March	1st to 10th	Night	17% 13% 36% 29% 4	760
	11th to 20th	Night	20% 13% 35% 23% 8% 1	760
	21st to end	Night	18% 11% 35% 31% 5%	836
April	1st to 10th	Night	18% 17% 33% 26% 6%	760
	11th to 20th	Night	15% 10% 34% 29% 12%	751
	21st to end	Night	17% 6% 33% 35% 9%	693
May	1st to 10th	Night	15% 8% 34% 27% 15%	570
	11th to 20th	Night	19% 5% 24% 32% 18% 2	561
	21st to end	Night	16% 1 15% 33% 31% 4	617
June	1st to 10th	Night	11% 2 16% 40% 30% 2	570
	11th to 20th	Night	11% 1 14% 33% 36% 4	570
	21st to end	Night	8% 2 15% 43% 30% 3	570
July	1st to 10th	Night	10% 1 10% 34% 38% 7%	555
	11th to 20th	Night	6% 2 7% 36% 43% 6%	552
	21st to end	Night	8% 1 11% 42% 33% 4	624
August	1st to 10th	Night	14% 2 10% 36% 35% 4	567
	11th to 20th	Night	12% 2 9% 34% 39% 4	564
	21st to end	Night	11% 1 11% 30% 40% 7%	821
September	1st to 10th	Night	14% 2 10% 30% 37% 7%	760
	11th to 20th	Night	18% 2 13% 29% 34% 5%	760
	21st to end	Night	27% 4 17% 28% 22% 2	760
October	1st to 10th	Night	20% 5% 18% 28% 25% 5%	760
	11th to 20th	Night	16% 8% 24% 32% 17% 2	760
	21st to end	Night	16% 7% 26% 37% 13% 2	836
November	1st to 10th	Night	16% 7% 27% 34% 14% 2	760
	11th to 20th	Night	15% 11% 32% 31% 11% 1	760
	21st to end	Night	16% 11% 31% 32% 11% 1	760
December	1st to 10th	Night	22% 12% 35% 26% 6%	760
	11th to 20th	Night	17% 10% 38% 30% 5%	760
	21st to end	Night	21% 12% 33% 29% 4	836

Page generated at 2024-11-03 02:11:20. Version ac07

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