Galveston Island State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Galveston Island 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	12% 6% 2 6% 4 4 5% 4 7% 9% 41%	100958
	Night	13% 6% 2 6% 4 4 4 4 6% 8% 44%	98144
Transparency	Day	36% 9% 16% 20% 14% 5%	104631
	Night	35% 7% 14% 20% 16% 7%	102598
Seeing	Day	12% 4 15% 26% 29% 14%	14760
	Night	14% 4 15% 30% 29% 8%	24589

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	18% 10% 3 7% 4 3 4 3 5% 6% 37%	2847
	11th to 20th	Day	15% 7% 2 6% 4 3 4 2 4 6% 47%	2850
	21st to end	Day	23% 9% 3 6% 4 3 4 4 5% 7% 33%	3135
February	1st to 10th	Day	20% 10% 2 6% 4 4 3 4 4 5% 36%	1782
	11th to 20th	Day	22% 11% 3 5% 4 3 4 3 3 5% 38%	1920
	21st to end	Day	22% 9% 3 7% 3 4 3 2 4 5% 37%	1727
March	1st to 10th	Day	22% 10% 3 8% 5% 5% 5% 4 6% 7% 25%	3436
	11th to 20th	Day	19% 9% 3 8% 6% 5% 5% 3 6% 6% 30%	3480
	21st to end	Day	14% 6% 2 6% 4 3 4 3 5% 6% 47%	3814
April	1st to 10th	Day	17% 8% 3 6% 4 3 4 3 5% 7% 39%	2090
	11th to 20th	Day	14% 7% 3 6% 5% 4 4 3 6% 7% 40%	2231
	21st to end	Day	10% 6% 2 6% 5% 4 4 4 5% 7% 47%	2280
May	1st to 10th	Day	18% 8% 3 8% 5% 4 5% 4 6% 8% 32%	3765
	11th to 20th	Day	13% 7% 2 7% 4 5% 5% 3 7% 8% 39%	4008
	21st to end	Day	9% 5% 2 6% 5% 6% 6% 6% 9% 11% 33%	4477
June	1st to 10th	Day	4 4 2 4 4 5% 5% 5% 9% 11% 48%	2470
	11th to 20th	Day	5% 4 1 4 4 5% 4 6% 10% 13% 44%	2470
	21st to end	Day	8% 4 2 5% 5% 5% 6% 6% 10% 12% 39%	2470
July	1st to 10th	Day	8% 4 2 6% 5% 5% 6% 6% 8% 11% 38%	4120
	11th to 20th	Day	5% 6% 3 9% 6% 7% 8% 6% 9% 11% 29%	4120
	21st to end	Day	10% 7% 2 8% 6% 6% 6% 5% 8% 11% 32%	4465
August	1st to 10th	Day	2 1 1 2 2 3 3 3 6% 10% 66%	4104
	11th to 20th	Day	3 2 1 3 2 4 5% 5% 10% 15% 51%	3791
	21st to end	Day	6% 4 2 6% 5% 6% 6% 5% 8% 11% 40%	4166
September	1st to 10th	Day	10% 5% 2 7% 5% 5% 6% 5% 7% 10% 37%	2090
	11th to 20th	Day	14% 6% 2 6% 5% 5% 5% 4 7% 8% 38%	2090
	21st to end	Day	8% 6% 2 6% 4 4 4 3 6% 7% 50%	2090
October	1st to 10th	Day	6% 4 1 5% 3 3 3 3 6% 8% 56%	1952
	11th to 20th	Day	10% 5% 2 4 3 4 4 3 5% 7% 55%	1900
	21st to end	Day	11% 4 2 5% 3 3 3 3 4 5% 57%	2090
November	1st to 10th	Day	10% 5% 2 6% 4 3 4 4 6% 7% 49%	1898
	11th to 20th	Day	13% 5% 2 5% 4 4 4 4 5% 7% 47%	1900
	21st to end	Day	16% 7% 3 6% 5% 4 4 3 5% 7% 42%	1900
December	1st to 10th	Day	17% 6% 3 6% 3 4 4 4 4 7% 42%	1734
	11th to 20th	Day	14% 7% 2 6% 4 4 4 4 5% 8% 40%	2161
	21st to end	Day	17% 7% 2 6% 4 4 4 4 5% 6% 41%	3135
January	1st to 10th	Night	20% 9% 3 7% 4 4 4 3 5% 6% 36%	4108
	11th to 20th	Night	16% 8% 2 6% 4 3 3 3 4 6% 46%	4120
	21st to end	Night	24% 9% 3 6% 3 3 3 3 5% 8% 33%	4532
February	1st to 10th	Night	19% 10% 3 6% 4 4 4 3 5% 6% 38%	2413
	11th to 20th	Night	20% 10% 2 4 3 2 4 2 4 6% 43%	2146
	21st to end	Night	20% 9% 3 5% 3 4 3 4 5% 5% 39%	1727
March	1st to 10th	Night	24% 11% 3 6% 3 3 4 4 5% 6% 31%	3419
	11th to 20th	Night	20% 9% 3 8% 5% 5% 5% 4 5% 6% 30%	3480
	21st to end	Night	11% 6% 2 5% 4 4 5% 3 5% 7% 48%	3817
April	1st to 10th	Night	14% 7% 3 6% 5% 4 4 4 5% 8% 41%	2090
	11th to 20th	Night	14% 7% 2 5% 4 3 4 3 6% 8% 44%	1895
	21st to end	Night	11% 6% 3 6% 4 4 5% 3 5% 7% 45%	1900
May	1st to 10th	Night	22% 8% 2 7% 4 4 4 3 6% 7% 33%	3130
	11th to 20th	Night	13% 5% 2 5% 4 4 4 3 6% 7% 44%	2890
	21st to end	Night	10% 5% 2 6% 5% 5% 5% 5% 8% 12% 38%	3090
June	1st to 10th	Night	4 4 1 4 3 4 4 3 6% 10% 57%	1710
	11th to 20th	Night	5% 4 2 4 4 3 4 5% 8% 11% 50%	1710
	21st to end	Night	5% 4 2 5% 5% 7% 5% 5% 8% 13% 40%	1710
July	1st to 10th	Night	5% 5% 2 6% 5% 4 4 4 7% 13% 45%	2850
	11th to 20th	Night	2 3 2 7% 6% 6% 7% 6% 9% 13% 38%	2850
	21st to end	Night	6% 6% 3 7% 6% 6% 6% 5% 7% 12% 36%	3098
August	1st to 10th	Night	1 1 1 2 2 2 2 3 5% 8% 73%	2836
	11th to 20th	Night	2 2 1 3 3 3 4 4 7% 15% 56%	3037
	21st to end	Night	4 3 1 4 4 4 5% 5% 8% 14% 47%	3476
September	1st to 10th	Night	7% 5% 2 6% 5% 5% 5% 5% 7% 11% 41%	2084
	11th to 20th	Night	13% 6% 3 6% 5% 4 5% 4 6% 8% 41%	2090
	21st to end	Night	9% 4 2 5% 4 3 4 3 6% 8% 52%	2090
October	1st to 10th	Night	5% 3 2 5% 4 3 4 3 5% 8% 57%	2209
	11th to 20th	Night	10% 3 1 4 3 3 3 3 5% 6% 59%	2280
	21st to end	Night	10% 5% 2 4 3 3 3 3 5% 5% 59%	2508
November	1st to 10th	Night	9% 5% 2 5% 4 3 3 4 5% 6% 53%	2280
	11th to 20th	Night	14% 5% 2 5% 4 4 4 3 5% 6% 50%	2280
	21st to end	Night	15% 6% 2 6% 4 4 5% 4 4 6% 43%	2280
December	1st to 10th	Night	19% 7% 3 5% 4 3 3 3 4 7% 42%	2441
	11th to 20th	Night	15% 8% 2 6% 4 4 5% 4 5% 7% 41%	3036
	21st to end	Night	16% 8% 3 7% 4 4 4 3 4 6% 42%	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	47% 6% 7% 16% 17% 8%	2848
	11th to 20th	Day	34% 9% 10% 20% 16% 10%	2850
	21st to end	Day	50% 5% 6% 14% 16% 8%	3135
February	1st to 10th	Day	49% 6% 8% 15% 13% 10%	1782
	11th to 20th	Day	49% 5% 9% 13% 16% 7%	1930
	21st to end	Day	48% 6% 11% 14% 13% 8%	1727
March	1st to 10th	Day	52% 12% 12% 12% 10% 2	3436
	11th to 20th	Day	50% 11% 13% 10% 12% 4	3480
	21st to end	Day	35% 8% 14% 18% 20% 4	3814
April	1st to 10th	Day	42% 8% 11% 17% 14% 8%	2090
	11th to 20th	Day	41% 8% 13% 16% 13% 8%	2231
	21st to end	Day	34% 8% 14% 21% 18% 5%	2280
May	1st to 10th	Day	45% 13% 15% 14% 9% 4	3800
	11th to 20th	Day	37% 11% 12% 20% 16% 4	4012
	21st to end	Day	33% 16% 18% 26% 6% 1	4489
June	1st to 10th	Day	25% 12% 21% 29% 14%	2470
	11th to 20th	Day	26% 11% 20% 29% 13% 1	2470
	21st to end	Day	33% 14% 21% 26% 6%	2470
July	1st to 10th	Day	37% 8% 32% 21% 2	4056
	11th to 20th	Day	45% 12% 25% 16% 3	4051
	21st to end	Day	44% 11% 23% 20% 2	4325
August	1st to 10th	Day	14% 7% 21% 45% 14%	4090
	11th to 20th	Day	19% 10% 42% 26% 3	3828
	21st to end	Day	35% 13% 19% 23% 9% 1	4165
September	1st to 10th	Day	37% 15% 17% 17% 11% 3	2090
	11th to 20th	Day	41% 12% 12% 19% 14% 2	2090
	21st to end	Day	32% 8% 15% 20% 15% 9%	2090
October	1st to 10th	Day	21% 4 8% 17% 18% 32%	3238
	11th to 20th	Day	22% 4 7% 24% 33% 10%	3140
	21st to end	Day	24% 3 6% 20% 36% 10%	3428
November	1st to 10th	Day	32% 8% 12% 20% 21% 6%	1898
	11th to 20th	Day	36% 7% 13% 16% 19% 10%	1900
	21st to end	Day	42% 6% 9% 18% 16% 8%	1900
December	1st to 10th	Day	40% 8% 12% 20% 14% 5%	1734
	11th to 20th	Day	41% 8% 11% 14% 18% 9%	2159
	21st to end	Day	41% 8% 9% 15% 17% 10%	3135
January	1st to 10th	Night	46% 8% 8% 12% 14% 12%	4108
	11th to 20th	Night	38% 6% 8% 16% 22% 11%	4120
	21st to end	Night	50% 5% 6% 14% 16% 9%	4532
February	1st to 10th	Night	46% 6% 9% 10% 17% 11%	2413
	11th to 20th	Night	43% 5% 9% 15% 17% 11%	2146
	21st to end	Night	46% 6% 10% 13% 17% 9%	1727
March	1st to 10th	Night	51% 8% 12% 15% 10% 4	3419
	11th to 20th	Night	52% 10% 11% 13% 10% 5%	3480
	21st to end	Night	33% 8% 13% 15% 25% 6%	3817
April	1st to 10th	Night	40% 7% 11% 18% 15% 9%	2090
	11th to 20th	Night	36% 8% 13% 18% 13% 12%	1895
	21st to end	Night	36% 7% 12% 22% 16% 6%	1900
May	1st to 10th	Night	46% 11% 14% 15% 9% 5%	3160
	11th to 20th	Night	36% 8% 12% 21% 15% 7%	2891
	21st to end	Night	33% 12% 20% 26% 8% 1	3099
June	1st to 10th	Night	22% 7% 20% 33% 18%	1710
	11th to 20th	Night	24% 8% 19% 31% 17% 2	1710
	21st to end	Night	32% 10% 23% 25% 9%	1710
July	1st to 10th	Night	30% 7% 37% 24% 3	2805
	11th to 20th	Night	35% 9% 32% 21% 4	2796
	21st to end	Night	41% 11% 25% 21% 2	2999
August	1st to 10th	Night	12% 6% 17% 51% 15%	2826
	11th to 20th	Night	18% 7% 39% 32% 4	3066
	21st to end	Night	27% 14% 24% 25% 10% 1	3476
September	1st to 10th	Night	34% 12% 21% 19% 11% 3	2084
	11th to 20th	Night	40% 10% 14% 19% 15% 2	2090
	21st to end	Night	30% 8% 15% 22% 18% 7%	2090
October	1st to 10th	Night	21% 4 8% 17% 17% 32%	3690
	11th to 20th	Night	18% 3 7% 25% 33% 14%	3779
	21st to end	Night	20% 3 7% 17% 39% 15%	4120
November	1st to 10th	Night	31% 6% 14% 22% 19% 8%	2280
	11th to 20th	Night	35% 6% 11% 21% 18% 9%	2280
	21st to end	Night	40% 7% 10% 20% 17% 7%	2280
December	1st to 10th	Night	42% 6% 10% 20% 14% 7%	2441
	11th to 20th	Night	42% 7% 9% 14% 15% 13%	3037
	21st to end	Night	43% 7% 8% 14% 21% 8%	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% 7% 31% 26% 10% 1	270
	11th to 20th	Day	19% 9% 28% 34% 10% 1	270
	21st to end	Day	19% 10% 35% 27% 9%	297
February	1st to 10th	Day	24% 8% 31% 27% 9% 1	270
	11th to 20th	Day	24% 7% 34% 27% 7% 1	270
	21st to end	Day	23% 7% 44% 24% 2	225
March	1st to 10th	Day	19% 3 36% 34% 7% 1	270
	11th to 20th	Day	19% 7% 42% 22% 7% 1	270
	21st to end	Day	15% 7% 39% 32% 7%	297
April	1st to 10th	Day	15% 10% 39% 27% 9% 1	270
	11th to 20th	Day	19% 9% 31% 24% 15% 2	429
	21st to end	Day	13% 5% 28% 35% 17% 2	460
May	1st to 10th	Day	15% 5% 26% 35% 17% 2	463
	11th to 20th	Day	11% 2 18% 42% 22% 4	627
	21st to end	Day	7% 2 16% 43% 28% 4	734
June	1st to 10th	Day	6% 1 6% 36% 38% 13%	680
	11th to 20th	Day	8% 1 6% 32% 40% 13%	680
	21st to end	Day	9% 3 5% 24% 40% 20%	680
July	1st to 10th	Day	8% 3 1 20% 44% 25%	671
	11th to 20th	Day	6% 1 2 15% 43% 32%	668
	21st to end	Day	6% 2 2 15% 48% 27%	739
August	1st to 10th	Day	2 1 1 12% 49% 34%	676
	11th to 20th	Day	4 1 1 6% 46% 42%	517
	21st to end	Day	12% 2 1 12% 36% 36%	538
September	1st to 10th	Day	13% 2 4 15% 35% 31%	300
	11th to 20th	Day	10% 2 17% 43% 27%	300
	21st to end	Day	10% 2 2 17% 46% 23%	300
October	1st to 10th	Day	7% 1 3 35% 39% 14%	300
	11th to 20th	Day	10% 2 8% 33% 32% 15%	300
	21st to end	Day	14% 5% 20% 28% 25% 8%	330
November	1st to 10th	Day	15% 2 13% 37% 27% 7%	282
	11th to 20th	Day	17% 2 18% 39% 19% 5%	270
	21st to end	Day	20% 6% 28% 31% 13% 2	270
December	1st to 10th	Day	20% 5% 20% 30% 17% 8%	270
	11th to 20th	Day	22% 8% 26% 33% 10% 1	270
	21st to end	Day	21% 4 30% 28% 14% 3	297
January	1st to 10th	Night	22% 6% 24% 33% 14% 1	950
	11th to 20th	Night	20% 6% 26% 37% 11%	950
	21st to end	Night	22% 7% 26% 34% 10%	1045
February	1st to 10th	Night	25% 6% 25% 33% 10%	893
	11th to 20th	Night	24% 7% 23% 34% 11%	672
	21st to end	Night	25% 9% 25% 33% 8%	471
March	1st to 10th	Night	21% 6% 25% 34% 13% 1	570
	11th to 20th	Night	17% 8% 23% 36% 15% 1	570
	21st to end	Night	14% 4 25% 38% 17% 2	627
April	1st to 10th	Night	16% 7% 24% 38% 14%	570
	11th to 20th	Night	18% 6% 22% 36% 17%	563
	21st to end	Night	13% 4 23% 40% 18% 1	570
May	1st to 10th	Night	13% 4 22% 43% 18%	570
	11th to 20th	Night	11% 2 16% 44% 24% 3	561
	21st to end	Night	6% 2 10% 40% 36% 5%	617
June	1st to 10th	Night	4 2 3 32% 50% 8%	570
	11th to 20th	Night	5% 2 2 29% 51% 11%	570
	21st to end	Night	6% 1 3 20% 50% 19%	570
July	1st to 10th	Night	7% 2 2 12% 51% 26%	555
	11th to 20th	Night	3 1 1 9% 52% 36%	552
	21st to end	Night	3 2 1 10% 56% 28%	624
August	1st to 10th	Night	2 1 7% 61% 30%	567
	11th to 20th	Night	5% 1 1 5% 55% 33%	564
	21st to end	Night	8% 1 1 12% 50% 28%	627
September	1st to 10th	Night	8% 1 3 14% 48% 26%	570
	11th to 20th	Night	16% 1 3 17% 43% 20%	570
	21st to end	Night	10% 1 5% 21% 48% 16%	570
October	1st to 10th	Night	6% 1 5% 27% 50% 11%	689
	11th to 20th	Night	9% 3 10% 33% 37% 8%	760
	21st to end	Night	11% 5% 15% 33% 30% 7%	836
November	1st to 10th	Night	11% 2 12% 34% 34% 6%	760
	11th to 20th	Night	16% 3 17% 36% 27% 1	760
	21st to end	Night	15% 5% 23% 36% 18% 3	760
December	1st to 10th	Night	21% 6% 17% 33% 20% 3	921
	11th to 20th	Night	20% 6% 21% 37% 15% 1	950
	21st to end	Night	23% 6% 23% 33% 14% 1	1045

Page generated at 2024-11-03 01:11:26. Version ac07

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