Oak Hummock Marsh Interpretive Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Oak Hummock Marsh Interpretive Center clear sky chart from 2005-11-06 to 2025-11-03.

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	11% 9% 3 9% 6% 5% 5% 4 6% 8% 35%	127353
	Night	9% 10% 4 10% 6% 5% 5% 4 6% 7% 33%	122972
Transparency	Day	46% 6% 15% 23% 8% 1	130753
	Night	49% 6% 14% 22% 9% 1	127661
Seeing	Day	14% 9% 30% 29% 14% 4	17666
	Night	15% 7% 31% 33% 13% 1	27545

By Month

Percentage Cloud Cover NE (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	6% 15% 6% 14% 7% 7% 8% 5% 6% 6% 19%	3178
	11th to 20th	Day	5% 12% 4 16% 9% 9% 9% 8% 9% 8% 11%	3152
	21st to end	Day	5% 15% 7% 16% 9% 8% 7% 4 6% 6% 17%	3974
February	1st to 10th	Day	8% 14% 6% 11% 9% 9% 8% 5% 7% 5% 19%	1705
	11th to 20th	Day	7% 9% 4 9% 7% 7% 8% 6% 8% 9% 26%	1754
	21st to end	Day	6% 13% 5% 10% 7% 7% 8% 5% 6% 8% 26%	1557
March	1st to 10th	Day	9% 11% 4 10% 8% 5% 5% 4 7% 8% 28%	4603
	11th to 20th	Day	8% 11% 5% 13% 10% 7% 5% 4 5% 7% 24%	4980
	21st to end	Day	9% 12% 6% 11% 6% 5% 5% 3 5% 6% 32%	5464
April	1st to 10th	Day	9% 11% 4 9% 6% 5% 4 4 6% 7% 36%	2444
	11th to 20th	Day	12% 11% 3 8% 6% 5% 5% 3 5% 6% 36%	2572
	21st to end	Day	14% 9% 3 7% 5% 4 5% 4 6% 7% 36%	2600
May	1st to 10th	Day	13% 7% 2 5% 4 4 4 3 5% 7% 46%	6114
	11th to 20th	Day	19% 8% 2 8% 4 5% 5% 4 6% 8% 32%	6660
	21st to end	Day	14% 6% 2 6% 4 3 4 3 4 6% 47%	7428
June	1st to 10th	Day	15% 7% 2 6% 6% 5% 5% 4 6% 7% 36%	3000
	11th to 20th	Day	15% 6% 3 6% 5% 5% 5% 4 7% 8% 35%	3000
	21st to end	Day	11% 7% 3 7% 5% 5% 6% 5% 8% 9% 36%	3000
July	1st to 10th	Day	8% 4 2 6% 5% 5% 5% 5% 7% 10% 43%	6799
	11th to 20th	Day	9% 5% 2 6% 4 5% 5% 4 7% 9% 44%	6800
	21st to end	Day	7% 4 2 6% 4 5% 5% 4 7% 9% 47%	7367
August	1st to 10th	Day	7% 4 2 6% 4 5% 5% 4 7% 9% 46%	4410
	11th to 20th	Day	11% 5% 2 5% 5% 5% 5% 4 5% 8% 46%	4171
	21st to end	Day	12% 6% 2 5% 4 4 4 4 6% 8% 45%	4675
September	1st to 10th	Day	10% 5% 2 5% 4 4 4 3 5% 8% 49%	2490
	11th to 20th	Day	14% 6% 3 8% 5% 6% 3 4 6% 8% 37%	2200
	21st to end	Day	14% 7% 3 6% 4 4 4 3 6% 8% 42%	2200
October	1st to 10th	Day	16% 10% 3 8% 4 4 4 3 5% 7% 36%	2035
	11th to 20th	Day	13% 14% 3 8% 5% 5% 4 4 5% 7% 32%	1955
	21st to end	Day	15% 15% 4 9% 6% 4 4 3 6% 8% 25%	1980
November	1st to 10th	Day	16% 16% 5% 9% 5% 4 4 3 6% 6% 26%	1599
	11th to 20th	Day	9% 16% 6% 13% 6% 5% 5% 3 4 7% 26%	1600
	21st to end	Day	13% 14% 6% 14% 6% 6% 4 4 4 6% 25%	1460
December	1st to 10th	Day	11% 16% 6% 14% 9% 5% 5% 4 7% 8% 15%	2290
	11th to 20th	Day	9% 13% 6% 13% 6% 5% 5% 6% 7% 8% 21%	2639
	21st to end	Day	8% 13% 6% 18% 8% 6% 5% 3 6% 6% 21%	3498
January	1st to 10th	Night	4 14% 7% 14% 8% 9% 8% 5% 6% 5% 21%	6787
	11th to 20th	Night	5% 13% 6% 14% 10% 9% 10% 9% 6% 4 14%	6753
	21st to end	Night	7% 17% 8% 14% 7% 6% 6% 4 6% 6% 19%	7002
February	1st to 10th	Night	8% 13% 5% 11% 8% 7% 7% 4 6% 7% 25%	2695
	11th to 20th	Night	6% 9% 3 8% 6% 7% 6% 6% 8% 8% 33%	2533
	21st to end	Night	6% 12% 4 12% 6% 6% 7% 4 5% 7% 32%	2090
March	1st to 10th	Night	8% 12% 4 10% 6% 5% 6% 4 6% 7% 31%	5253
	11th to 20th	Night	6% 10% 3 8% 6% 4 5% 4 6% 8% 38%	4979
	21st to end	Night	11% 12% 4 9% 5% 4 4 3 5% 6% 37%	5467
April	1st to 10th	Night	11% 8% 3 7% 5% 4 4 4 6% 7% 41%	1953
	11th to 20th	Night	13% 10% 4 8% 5% 4 4 4 6% 6% 36%	1779
	21st to end	Night	12% 9% 3 9% 5% 5% 5% 5% 6% 6% 37%	1800
May	1st to 10th	Night	14% 8% 2 6% 4 4 4 3 5% 6% 43%	3846
	11th to 20th	Night	17% 6% 2 5% 5% 5% 5% 4 7% 9% 35%	3252
	21st to end	Night	13% 5% 2 5% 3 3 3 3 4 7% 52%	3470
June	1st to 10th	Night	11% 7% 2 6% 4 4 5% 5% 8% 8% 40%	1400
	11th to 20th	Night	14% 6% 2 4 4 4 5% 4 6% 8% 41%	1400
	21st to end	Night	10% 4 2 6% 4 5% 5% 4 8% 10% 43%	1400
July	1st to 10th	Night	7% 3 1 5% 4 5% 5% 4 6% 8% 52%	3180
	11th to 20th	Night	6% 4 2 6% 4 4 4 4 7% 10% 48%	3180
	21st to end	Night	6% 4 1 4 4 4 5% 5% 6% 10% 51%	3504
August	1st to 10th	Night	6% 4 2 5% 5% 4 4 4 7% 10% 49%	2748
	11th to 20th	Night	8% 3 1 5% 3 4 4 4 6% 9% 51%	2888
	21st to end	Night	9% 5% 2 7% 4 4 4 3 5% 9% 48%	3234
September	1st to 10th	Night	8% 4 2 6% 4 3 4 4 7% 6% 52%	1906
	11th to 20th	Night	14% 4 2 7% 4 4 4 4 5% 8% 44%	2200
	21st to end	Night	15% 6% 2 6% 4 4 3 4 4 7% 44%	2200
October	1st to 10th	Night	16% 9% 3 6% 4 4 4 3 5% 8% 38%	2345
	11th to 20th	Night	15% 10% 4 8% 4 5% 5% 4 5% 6% 33%	2441
	21st to end	Night	14% 13% 3 8% 5% 4 5% 3 5% 7% 32%	2860
November	1st to 10th	Night	13% 13% 5% 10% 6% 5% 4 4 5% 7% 28%	2743
	11th to 20th	Night	11% 15% 6% 12% 6% 4 4 4 5% 5% 27%	2800
	21st to end	Night	12% 15% 6% 13% 7% 5% 4 3 5% 5% 24%	2936
December	1st to 10th	Night	8% 17% 6% 15% 11% 7% 6% 4 6% 5% 14%	4900
	11th to 20th	Night	8% 14% 5% 14% 6% 5% 5% 5% 6% 7% 25%	5568
	21st to end	Night	7% 12% 5% 18% 9% 7% 6% 4 5% 5% 22%	7480

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	64% 6% 9% 16% 6%	3179
	11th to 20th	Day	66% 5% 8% 15% 6%	3180
	21st to end	Day	66% 5% 12% 14% 3	3974
February	1st to 10th	Day	62% 7% 11% 12% 8% 1	1705
	11th to 20th	Day	51% 7% 15% 20% 7%	1763
	21st to end	Day	54% 8% 13% 17% 7%	1557
March	1st to 10th	Day	52% 6% 17% 16% 9%	4605
	11th to 20th	Day	57% 7% 14% 16% 6%	4980
	21st to end	Day	51% 6% 13% 21% 9%	5464
April	1st to 10th	Day	45% 7% 13% 23% 10%	2444
	11th to 20th	Day	47% 5% 12% 22% 11% 1	2572
	21st to end	Day	45% 7% 16% 23% 7% 1	2600
May	1st to 10th	Day	37% 5% 14% 26% 17%	6125
	11th to 20th	Day	50% 6% 9% 24% 11% 1	6664
	21st to end	Day	37% 6% 9% 22% 22% 4	7428
June	1st to 10th	Day	44% 8% 14% 23% 10% 1	3000
	11th to 20th	Day	43% 9% 16% 22% 10%	3000
	21st to end	Day	42% 10% 19% 21% 8%	3000
July	1st to 10th	Day	35% 6% 24% 28% 7%	6726
	11th to 20th	Day	35% 5% 20% 35% 5%	6719
	21st to end	Day	34% 5% 22% 34% 5%	7154
August	1st to 10th	Day	33% 5% 20% 31% 10%	4394
	11th to 20th	Day	36% 5% 22% 31% 5%	4210
	21st to end	Day	37% 5% 24% 29% 6%	4674
September	1st to 10th	Day	33% 6% 19% 32% 8% 1	2490
	11th to 20th	Day	44% 9% 18% 25% 4	2200
	21st to end	Day	40% 6% 17% 30% 7%	2200
October	1st to 10th	Day	43% 5% 14% 30% 8%	3308
	11th to 20th	Day	44% 5% 12% 28% 11%	3161
	21st to end	Day	50% 5% 19% 20% 5%	3190
November	1st to 10th	Day	59% 7% 13% 18% 4 1	1599
	11th to 20th	Day	58% 9% 13% 15% 4	1600
	21st to end	Day	61% 7% 16% 13% 3	1460
December	1st to 10th	Day	66% 7% 13% 7% 6%	2290
	11th to 20th	Day	58% 5% 14% 15% 7%	2640
	21st to end	Day	63% 7% 8% 16% 5%	3498
January	1st to 10th	Night	62% 7% 9% 13% 8%	6787
	11th to 20th	Night	68% 5% 7% 16% 4	6800
	21st to end	Night	64% 4 12% 14% 5%	7002
February	1st to 10th	Night	57% 5% 13% 16% 9%	2695
	11th to 20th	Night	45% 8% 16% 23% 8%	2534
	21st to end	Night	51% 7% 12% 21% 10%	2090
March	1st to 10th	Night	50% 6% 13% 17% 9% 4	5264
	11th to 20th	Night	41% 7% 15% 24% 12% 1	4980
	21st to end	Night	48% 5% 9% 25% 13% 1	5467
April	1st to 10th	Night	40% 5% 13% 24% 16% 2	1953
	11th to 20th	Night	48% 5% 8% 23% 14% 2	1779
	21st to end	Night	44% 6% 12% 24% 12% 2	1800
May	1st to 10th	Night	40% 6% 10% 24% 19%	3855
	11th to 20th	Night	44% 6% 12% 25% 11% 2	3253
	21st to end	Night	33% 6% 8% 23% 24% 6%	3470
June	1st to 10th	Night	37% 10% 15% 22% 15%	1400
	11th to 20th	Night	39% 7% 15% 24% 13% 2	1400
	21st to end	Night	34% 9% 22% 26% 9% 1	1400
July	1st to 10th	Night	30% 6% 22% 33% 9% 1	3145
	11th to 20th	Night	31% 4 20% 37% 6% 1	3138
	21st to end	Night	29% 5% 26% 33% 7% 1	3403
August	1st to 10th	Night	30% 5% 16% 33% 15%	2740
	11th to 20th	Night	29% 5% 26% 31% 9%	2915
	21st to end	Night	34% 5% 19% 33% 9%	3234
September	1st to 10th	Night	30% 7% 17% 31% 13%	1906
	11th to 20th	Night	39% 7% 19% 25% 9% 1	2200
	21st to end	Night	40% 7% 14% 29% 10% 1	2200
October	1st to 10th	Night	38% 5% 11% 32% 12% 1	3839
	11th to 20th	Night	44% 5% 12% 28% 11%	3977
	21st to end	Night	45% 5% 16% 29% 5%	4610
November	1st to 10th	Night	56% 7% 15% 16% 6% 1	2743
	11th to 20th	Night	58% 9% 14% 14% 5%	2800
	21st to end	Night	62% 6% 14% 12% 4	2936
December	1st to 10th	Night	70% 6% 12% 9% 3	4900
	11th to 20th	Night	58% 5% 13% 12% 12%	5566
	21st to end	Night	62% 6% 9% 16% 7%	7480

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	12% 5% 34% 30% 16% 3	300
	11th to 20th	Day	12% 7% 31% 33% 14% 2	300
	21st to end	Day	15% 8% 31% 27% 15% 4	330
February	1st to 10th	Day	14% 10% 32% 32% 10% 2	300
	11th to 20th	Day	10% 10% 34% 27% 15% 4	300
	21st to end	Day	10% 7% 39% 31% 12% 1	249
March	1st to 10th	Day	15% 10% 30% 27% 16% 2	300
	11th to 20th	Day	11% 11% 35% 27% 14% 2	300
	21st to end	Day	14% 7% 32% 31% 14% 2	330
April	1st to 10th	Day	13% 9% 31% 34% 10% 4	544
	11th to 20th	Day	17% 12% 30% 27% 13% 1	690
	21st to end	Day	16% 10% 34% 27% 11% 2	700
May	1st to 10th	Day	14% 13% 33% 27% 12% 1	703
	11th to 20th	Day	21% 11% 28% 25% 13% 3	725
	21st to end	Day	18% 10% 24% 28% 15% 4	789
June	1st to 10th	Day	17% 12% 29% 24% 13% 5%	730
	11th to 20th	Day	16% 10% 32% 29% 10% 2	730
	21st to end	Day	12% 8% 28% 32% 15% 5%	730
July	1st to 10th	Day	8% 8% 29% 28% 17% 10%	721
	11th to 20th	Day	13% 8% 28% 29% 17% 5%	718
	21st to end	Day	7% 5% 29% 33% 19% 8%	794
August	1st to 10th	Day	8% 8% 29% 29% 19% 7%	726
	11th to 20th	Day	10% 5% 25% 32% 20% 8%	715
	21st to end	Day	12% 8% 27% 31% 18% 4	803
September	1st to 10th	Day	10% 9% 32% 32% 15% 2	620
	11th to 20th	Day	19% 8% 38% 25% 8% 3	330
	21st to end	Day	19% 8% 31% 30% 11% 1	330
October	1st to 10th	Day	19% 11% 28% 29% 9% 3	330
	11th to 20th	Day	18% 12% 35% 25% 9% 2	330
	21st to end	Day	26% 10% 28% 23% 12% 1	363
November	1st to 10th	Day	25% 9% 27% 26% 11% 1	306
	11th to 20th	Day	18% 10% 39% 24% 9% 1	300
	21st to end	Day	17% 11% 36% 29% 6%	300
December	1st to 10th	Day	15% 7% 35% 28% 14% 1	300
	11th to 20th	Day	14% 10% 37% 29% 8% 1	300
	21st to end	Day	12% 8% 29% 32% 15% 4	330
January	1st to 10th	Night	13% 6% 34% 31% 15% 2	1000
	11th to 20th	Night	15% 8% 32% 33% 12% 1	1000
	21st to end	Night	14% 7% 32% 34% 12% 1	1100
February	1st to 10th	Night	13% 7% 30% 36% 14% 1	1000
	11th to 20th	Night	10% 6% 30% 37% 15% 3	979
	21st to end	Night	11% 8% 35% 30% 15% 2	770
March	1st to 10th	Night	13% 8% 31% 32% 16% 1	755
	11th to 20th	Night	12% 7% 39% 29% 12% 1	600
	21st to end	Night	18% 7% 28% 31% 13% 3	660
April	1st to 10th	Night	14% 6% 30% 36% 12% 2	600
	11th to 20th	Night	16% 7% 30% 36% 11% 1	593
	21st to end	Night	15% 8% 32% 34% 11% 1	600
May	1st to 10th	Night	19% 9% 31% 30% 11% 1	600
	11th to 20th	Night	17% 7% 32% 31% 12% 1	591
	21st to end	Night	18% 7% 29% 33% 12% 1	650
June	1st to 10th	Night	14% 7% 31% 32% 16%	600
	11th to 20th	Night	15% 6% 30% 36% 13% 1	600
	21st to end	Night	11% 6% 23% 40% 20% 1	600
July	1st to 10th	Night	7% 3 26% 40% 22% 2	585
	11th to 20th	Night	8% 4 26% 40% 21% 2	582
	21st to end	Night	8% 2 23% 42% 21% 3	657
August	1st to 10th	Night	7% 4 21% 46% 21% 2	597
	11th to 20th	Night	9% 2 23% 40% 23% 3	594
	21st to end	Night	11% 6% 22% 39% 21% 1	660
September	1st to 10th	Night	11% 5% 32% 33% 17% 3	600
	11th to 20th	Night	16% 6% 27% 38% 14%	600
	21st to end	Night	16% 7% 35% 29% 13% 1	600
October	1st to 10th	Night	22% 8% 33% 30% 7% 1	745
	11th to 20th	Night	20% 7% 33% 30% 10%	841
	21st to end	Night	20% 9% 31% 30% 9% 1	1100
November	1st to 10th	Night	19% 9% 35% 25% 12% 1	986
	11th to 20th	Night	18% 10% 36% 25% 9% 2	1000
	21st to end	Night	19% 9% 39% 26% 6% 1	1000
December	1st to 10th	Night	12% 8% 31% 34% 12% 2	1000
	11th to 20th	Night	16% 9% 35% 30% 9% 2	1000
	21st to end	Night	18% 7% 29% 30% 13% 2	1100

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