Croft State Park
Clear Sky Chart
History

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

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	13% 6% 2 6% 4 4 4 4 6% 8% 43%	101223
	Night	15% 6% 2 6% 4 4 4 4 5% 7% 43%	97900
Transparency	Day	37% 7% 12% 20% 19% 5%	104952
	Night	39% 7% 10% 18% 20% 7%	102310
Seeing	Day	16% 8% 23% 25% 19% 9%	15203
	Night	16% 8% 23% 30% 20% 3	25253

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% 5% 2 4 2 3 3 3 4 7% 51%	2836
	11th to 20th	Day	15% 7% 2 4 3 2 3 3 3 3 53%	2840
	21st to end	Day	26% 6% 2 4 3 2 3 2 4 5% 44%	3124
February	1st to 10th	Day	15% 7% 2 6% 4 4 4 4 6% 6% 43%	1762
	11th to 20th	Day	21% 7% 2 4 4 3 3 3 4 5% 45%	1848
	21st to end	Day	19% 7% 3 7% 4 3 4 3 4 5% 40%	1570
March	1st to 10th	Day	24% 7% 2 5% 3 3 4 3 4 5% 41%	3433
	11th to 20th	Day	12% 4 2 5% 4 3 4 3 5% 6% 52%	3480
	21st to end	Day	21% 6% 1 5% 4 3 4 3 5% 6% 42%	3815
April	1st to 10th	Day	11% 5% 2 5% 4 3 5% 4 6% 8% 48%	2090
	11th to 20th	Day	13% 5% 2 5% 4 4 5% 4 6% 7% 47%	2220
	21st to end	Day	12% 5% 1 5% 4 4 3 3 6% 7% 49%	2470
May	1st to 10th	Day	11% 7% 2 7% 4 5% 6% 5% 7% 8% 38%	4082
	11th to 20th	Day	16% 7% 3 7% 5% 4 4 4 5% 8% 37%	4081
	21st to end	Day	8% 4 2 6% 4 5% 6% 5% 7% 10% 45%	4476
June	1st to 10th	Day	9% 6% 2 7% 5% 5% 6% 5% 8% 11% 36%	2470
	11th to 20th	Day	6% 4 2 6% 5% 6% 5% 5% 7% 11% 41%	2470
	21st to end	Day	7% 4 2 7% 6% 6% 6% 5% 9% 9% 40%	2470
July	1st to 10th	Day	7% 6% 2 8% 6% 6% 6% 6% 8% 11% 34%	4120
	11th to 20th	Day	7% 5% 2 6% 5% 5% 6% 5% 9% 12% 38%	4120
	21st to end	Day	10% 9% 4 8% 7% 7% 7% 6% 9% 11% 23%	4466
August	1st to 10th	Day	18% 7% 2 7% 5% 5% 5% 5% 7% 11% 27%	4104
	11th to 20th	Day	9% 5% 2 6% 4 5% 5% 5% 8% 11% 37%	4044
	21st to end	Day	6% 3 2 5% 4 4 5% 4 6% 8% 53%	4194
September	1st to 10th	Day	8% 5% 2 6% 5% 6% 4 5% 7% 8% 43%	2090
	11th to 20th	Day	15% 6% 2 6% 4 5% 4 4 5% 8% 41%	2090
	21st to end	Day	16% 6% 2 6% 5% 5% 5% 4 5% 5% 42%	2090
October	1st to 10th	Day	15% 4 2 4 2 2 2 3 4 6% 55%	2024
	11th to 20th	Day	13% 4 2 4 2 2 3 2 4 6% 59%	1900
	21st to end	Day	13% 5% 2 5% 3 3 3 2 3 5% 57%	2090
November	1st to 10th	Day	14% 5% 2 5% 3 3 3 2 4 6% 53%	1947
	11th to 20th	Day	14% 5% 2 4 4 3 4 3 4 5% 52%	1710
	21st to end	Day	16% 5% 2 5% 3 4 4 2 5% 5% 50%	1710
December	1st to 10th	Day	19% 8% 3 6% 3 4 4 3 4 7% 40%	1710
	11th to 20th	Day	17% 6% 2 4 3 2 3 3 4 5% 49%	2153
	21st to end	Day	20% 6% 2 4 4 3 3 3 4 7% 42%	3124
January	1st to 10th	Night	17% 5% 2 5% 3 3 3 3 4 5% 50%	4109
	11th to 20th	Night	12% 6% 2 6% 4 4 4 3 5% 5% 49%	4120
	21st to end	Night	24% 8% 2 4 3 2 2 2 3 4 45%	4532
February	1st to 10th	Night	15% 6% 2 5% 4 4 3 3 4 5% 48%	2413
	11th to 20th	Night	21% 7% 3 5% 4 4 3 3 4 3 44%	2218
	21st to end	Night	17% 7% 2 5% 4 4 3 4 4 6% 42%	1884
March	1st to 10th	Night	22% 8% 2 6% 4 4 4 3 5% 6% 36%	3418
	11th to 20th	Night	11% 5% 2 5% 3 3 3 3 5% 7% 52%	3480
	21st to end	Night	19% 5% 2 6% 4 4 3 4 4 6% 43%	3817
April	1st to 10th	Night	12% 6% 2 5% 4 4 3 3 6% 7% 49%	2090
	11th to 20th	Night	13% 5% 2 5% 4 2 3 4 5% 7% 50%	1924
	21st to end	Night	10% 6% 2 5% 4 3 5% 3 4 6% 51%	1710
May	1st to 10th	Night	13% 7% 3 7% 4 3 4 4 6% 8% 40%	2813
	11th to 20th	Night	17% 7% 2 6% 4 4 5% 3 5% 9% 38%	2812
	21st to end	Night	9% 4 2 6% 4 5% 5% 5% 8% 11% 41%	3079
June	1st to 10th	Night	11% 6% 2 6% 6% 6% 7% 5% 9% 9% 34%	1710
	11th to 20th	Night	10% 6% 2 6% 5% 5% 6% 5% 7% 9% 38%	1710
	21st to end	Night	7% 6% 2 7% 6% 7% 6% 6% 7% 10% 36%	1710
July	1st to 10th	Night	10% 7% 3 9% 7% 7% 7% 6% 7% 9% 27%	2840
	11th to 20th	Night	8% 6% 2 7% 5% 5% 6% 6% 11% 14% 31%	2840
	21st to end	Night	12% 11% 4 10% 6% 7% 6% 6% 9% 10% 20%	3087
August	1st to 10th	Night	17% 10% 4 8% 5% 4 6% 5% 8% 9% 24%	2825
	11th to 20th	Night	11% 8% 3 8% 7% 6% 6% 6% 7% 10% 28%	2785
	21st to end	Night	6% 4 2 6% 5% 5% 6% 4 7% 8% 46%	3424
September	1st to 10th	Night	10% 5% 2 7% 4 5% 4 4 6% 8% 43%	2090
	11th to 20th	Night	16% 8% 2 6% 4 6% 4 4 6% 8% 36%	2090
	21st to end	Night	15% 7% 2 6% 4 4 4 3 5% 6% 44%	2090
October	1st to 10th	Night	14% 5% 1 5% 3 3 4 3 4 7% 50%	2154
	11th to 20th	Night	15% 4 2 5% 3 2 3 3 4 6% 54%	2280
	21st to end	Night	13% 4 1 4 3 3 3 2 3 5% 58%	2508
November	1st to 10th	Night	14% 6% 2 5% 2 3 3 3 4 5% 53%	2347
	11th to 20th	Night	14% 6% 2 4 4 3 3 3 4 6% 52%	2477
	21st to end	Night	16% 4 2 5% 4 4 4 3 5% 7% 47%	2470
December	1st to 10th	Night	19% 7% 2 5% 4 4 4 4 4 5% 42%	2470
	11th to 20th	Night	17% 6% 2 5% 3 2 3 2 4 5% 52%	3042
	21st to end	Night	21% 5% 2 5% 4 4 4 3 6% 7% 40%	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% 4 6% 25% 23% 7%	2837
	11th to 20th	Day	36% 4 6% 17% 31% 6%	2840
	21st to end	Day	43% 4 5% 17% 25% 6%	3124
February	1st to 10th	Day	40% 4 9% 21% 20% 5%	1762
	11th to 20th	Day	43% 4 6% 18% 22% 6%	1858
	21st to end	Day	45% 6% 7% 15% 21% 7%	1570
March	1st to 10th	Day	46% 5% 7% 17% 15% 9%	3433
	11th to 20th	Day	32% 6% 8% 14% 29% 12%	3480
	21st to end	Day	43% 6% 8% 19% 22% 3	3815
April	1st to 10th	Day	32% 6% 10% 19% 26% 6%	2090
	11th to 20th	Day	35% 6% 10% 18% 21% 10%	2220
	21st to end	Day	33% 6% 11% 25% 20% 5%	2470
May	1st to 10th	Day	40% 9% 16% 19% 13% 2	4120
	11th to 20th	Day	44% 8% 11% 21% 15% 1	4085
	21st to end	Day	30% 10% 17% 22% 19% 2	4489
June	1st to 10th	Day	39% 10% 16% 24% 9% 2	2470
	11th to 20th	Day	33% 10% 19% 24% 14% 1	2470
	21st to end	Day	36% 12% 16% 20% 14% 3	2470
July	1st to 10th	Day	40% 11% 19% 18% 9% 2	4055
	11th to 20th	Day	35% 12% 27% 19% 5% 1	4051
	21st to end	Day	50% 12% 17% 14% 5% 1	4324
August	1st to 10th	Day	49% 9% 17% 20% 6%	4091
	11th to 20th	Day	37% 10% 19% 19% 13% 2	4083
	21st to end	Day	27% 9% 15% 27% 18% 4	4194
September	1st to 10th	Day	36% 9% 14% 19% 19% 3	2090
	11th to 20th	Day	39% 9% 12% 16% 20% 3	2090
	21st to end	Day	43% 5% 10% 19% 17% 6%	2090
October	1st to 10th	Day	28% 3 7% 20% 32% 11%	3362
	11th to 20th	Day	19% 3 6% 17% 31% 25%	3140
	21st to end	Day	27% 3 4 24% 24% 17%	3428
November	1st to 10th	Day	33% 5% 7% 18% 28% 9%	1947
	11th to 20th	Day	34% 5% 7% 21% 25% 9%	1710
	21st to end	Day	37% 4 7% 20% 24% 7%	1710
December	1st to 10th	Day	45% 4 7% 21% 17% 5%	1710
	11th to 20th	Day	36% 4 7% 19% 23% 10%	2150
	21st to end	Day	41% 6% 7% 22% 22% 3	3124
January	1st to 10th	Night	36% 4 7% 19% 27% 7%	4109
	11th to 20th	Night	36% 5% 8% 16% 28% 7%	4120
	21st to end	Night	44% 3 5% 16% 25% 6%	4532
February	1st to 10th	Night	40% 4 8% 19% 22% 7%	2413
	11th to 20th	Night	45% 4 6% 16% 23% 7%	2219
	21st to end	Night	42% 5% 9% 16% 21% 7%	1884
March	1st to 10th	Night	46% 8% 10% 14% 15% 7%	3418
	11th to 20th	Night	31% 5% 8% 15% 26% 14%	3480
	21st to end	Night	42% 5% 7% 18% 20% 8%	3817
April	1st to 10th	Night	35% 6% 9% 17% 26% 7%	2090
	11th to 20th	Night	33% 5% 9% 20% 23% 10%	1924
	21st to end	Night	34% 5% 10% 25% 22% 5%	1710
May	1st to 10th	Night	40% 8% 13% 21% 15% 2	2840
	11th to 20th	Night	42% 9% 14% 20% 15% 1	2813
	21st to end	Night	30% 11% 15% 27% 16% 2	3087
June	1st to 10th	Night	40% 10% 17% 20% 12% 2	1710
	11th to 20th	Night	38% 10% 17% 21% 12% 2	1710
	21st to end	Night	39% 13% 18% 14% 13% 4	1710
July	1st to 10th	Night	49% 11% 17% 15% 7% 2	2795
	11th to 20th	Night	36% 15% 25% 19% 3 2	2786
	21st to end	Night	56% 13% 15% 12% 4 1	2988
August	1st to 10th	Night	53% 9% 18% 15% 4	2814
	11th to 20th	Night	48% 11% 17% 15% 8%	2812
	21st to end	Night	33% 9% 13% 25% 19% 2	3424
September	1st to 10th	Night	37% 9% 15% 18% 17% 4	2090
	11th to 20th	Night	43% 8% 13% 16% 17% 2	2090
	21st to end	Night	40% 7% 11% 18% 18% 6%	2090
October	1st to 10th	Night	30% 6% 8% 20% 29% 8%	3596
	11th to 20th	Night	22% 3 5% 18% 27% 25%	3779
	21st to end	Night	28% 3 4 21% 27% 17%	4120
November	1st to 10th	Night	34% 4 7% 18% 25% 11%	2347
	11th to 20th	Night	35% 3 6% 17% 26% 12%	2477
	21st to end	Night	36% 4 7% 19% 27% 7%	2470
December	1st to 10th	Night	44% 5% 8% 18% 20% 6%	2470
	11th to 20th	Night	35% 4 8% 17% 25% 10%	3044
	21st to end	Night	42% 5% 8% 21% 20% 3	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	21% 20% 34% 21% 3	270
	11th to 20th	Day	26% 19% 32% 18% 5%	270
	21st to end	Day	22% 19% 39% 16% 4	297
February	1st to 10th	Day	20% 21% 35% 18% 6%	270
	11th to 20th	Day	36% 17% 32% 12% 3	270
	21st to end	Day	26% 23% 35% 13% 3	225
March	1st to 10th	Day	22% 14% 34% 21% 8% 2	458
	11th to 20th	Day	20% 14% 38% 22% 5% 1	460
	21st to end	Day	20% 15% 38% 20% 6% 1	506
April	1st to 10th	Day	17% 15% 33% 22% 12% 1	460
	11th to 20th	Day	16% 12% 31% 27% 13% 2	452
	21st to end	Day	16% 10% 29% 24% 15% 6%	460
May	1st to 10th	Day	12% 11% 34% 22% 16% 5%	463
	11th to 20th	Day	16% 5% 20% 26% 23% 10%	487
	21st to end	Day	14% 4 19% 26% 24% 14%	529
June	1st to 10th	Day	10% 4 16% 31% 27% 11%	490
	11th to 20th	Day	9% 4 14% 28% 28% 18%	490
	21st to end	Day	9% 3 15% 32% 24% 17%	490
July	1st to 10th	Day	9% 2 9% 24% 32% 25%	485
	11th to 20th	Day	8% 1 6% 30% 33% 21%	484
	21st to end	Day	7% 3 8% 33% 32% 17%	532
August	1st to 10th	Day	16% 2 13% 24% 28% 16%	486
	11th to 20th	Day	12% 3 9% 30% 27% 19%	479
	21st to end	Day	12% 2 9% 24% 30% 23%	539
September	1st to 10th	Day	9% 3 12% 27% 32% 18%	490
	11th to 20th	Day	18% 3 15% 20% 28% 17%	490
	21st to end	Day	21% 4 19% 25% 25% 7%	490
October	1st to 10th	Day	18% 4 19% 26% 23% 10%	490
	11th to 20th	Day	11% 7% 24% 29% 22% 6%	490
	21st to end	Day	18% 8% 19% 30% 19% 6%	539
November	1st to 10th	Day	21% 8% 23% 27% 18% 4	485
	11th to 20th	Day	17% 14% 35% 22% 9% 2	270
	21st to end	Day	11% 11% 33% 29% 12% 3	270
December	1st to 10th	Day	25% 13% 33% 21% 7%	270
	11th to 20th	Day	23% 14% 29% 23% 10% 1	270
	21st to end	Day	27% 14% 30% 19% 8% 2	297
January	1st to 10th	Night	20% 16% 32% 25% 6%	760
	11th to 20th	Night	20% 16% 30% 30% 5%	760
	21st to end	Night	21% 14% 35% 27% 2	836
February	1st to 10th	Night	19% 13% 32% 33% 3	760
	11th to 20th	Night	25% 13% 38% 22% 2	743
	21st to end	Night	21% 14% 39% 24% 3	628
March	1st to 10th	Night	19% 12% 32% 32% 6%	760
	11th to 20th	Night	19% 13% 35% 25% 8% 1	760
	21st to end	Night	18% 11% 34% 29% 8%	836
April	1st to 10th	Night	15% 15% 33% 28% 9%	760
	11th to 20th	Night	15% 13% 29% 28% 15%	738
	21st to end	Night	13% 5% 29% 35% 17% 1	570
May	1st to 10th	Night	10% 9% 29% 34% 18%	570
	11th to 20th	Night	14% 6% 20% 36% 22% 2	561
	21st to end	Night	14% 2 13% 31% 35% 5%	617
June	1st to 10th	Night	13% 1 14% 38% 30% 5%	570
	11th to 20th	Night	11% 2 16% 30% 32% 10%	570
	21st to end	Night	8% 1 14% 32% 39% 6%	570
July	1st to 10th	Night	10% 2 8% 31% 40% 9%	555
	11th to 20th	Night	10% 2 7% 27% 44% 10%	552
	21st to end	Night	9% 2 9% 32% 40% 8%	624
August	1st to 10th	Night	15% 2 7% 28% 38% 9%	567
	11th to 20th	Night	14% 2 8% 30% 39% 7%	564
	21st to end	Night	12% 1 9% 25% 45% 8%	727
September	1st to 10th	Night	11% 3 11% 30% 39% 7%	760
	11th to 20th	Night	19% 3 14% 25% 35% 5%	760
	21st to end	Night	17% 4 17% 32% 29% 2	760
October	1st to 10th	Night	15% 4 18% 29% 29% 5%	760
	11th to 20th	Night	16% 6% 23% 31% 21% 2	760
	21st to end	Night	15% 7% 22% 33% 21% 2	836
November	1st to 10th	Night	17% 5% 23% 35% 18% 2	780
	11th to 20th	Night	16% 11% 28% 32% 12% 1	763
	21st to end	Night	16% 9% 27% 35% 13% 1	760
December	1st to 10th	Night	22% 11% 26% 33% 8%	760
	11th to 20th	Night	19% 11% 28% 32% 11%	760
	21st to end	Night	25% 10% 25% 31% 8%	836

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