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 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	11% 9% 3 8% 6% 5% 5% 4 6% 8% 35%	101929
	Night	10% 10% 4 9% 6% 5% 5% 4 6% 7% 34%	97337
Transparency	Day	46% 7% 16% 23% 7%	105350
	Night	47% 7% 14% 23% 8% 1	102003
Seeing	Day	14% 9% 30% 29% 14% 4	16273
	Night	15% 7% 31% 33% 13% 1	26191

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	8% 16% 5% 12% 8% 9% 7% 5% 5% 5% 20%	2218
	11th to 20th	Day	5% 10% 5% 20% 12% 11% 8% 5% 7% 7% 11%	2220
	21st to end	Day	7% 18% 6% 17% 8% 7% 6% 4 5% 5% 16%	2764
February	1st to 10th	Day	7% 14% 6% 11% 8% 8% 8% 5% 8% 5% 19%	1619
	11th to 20th	Day	8% 10% 5% 10% 7% 7% 8% 6% 8% 9% 25%	1664
	21st to end	Day	6% 13% 5% 9% 6% 7% 8% 5% 6% 8% 26%	1481
March	1st to 10th	Day	12% 10% 4 10% 10% 5% 5% 4 6% 8% 25%	3207
	11th to 20th	Day	8% 11% 6% 13% 11% 7% 5% 4 5% 7% 23%	3480
	21st to end	Day	8% 14% 7% 13% 7% 5% 4 3 5% 6% 30%	3814
April	1st to 10th	Day	9% 11% 4 9% 5% 5% 4 4 5% 7% 36%	2321
	11th to 20th	Day	12% 11% 3 8% 6% 5% 5% 3 5% 6% 36%	2442
	21st to end	Day	14% 8% 3 7% 5% 4 5% 4 6% 7% 36%	2470
May	1st to 10th	Day	17% 9% 3 6% 4 4 5% 3 5% 7% 37%	4264
	11th to 20th	Day	21% 8% 2 8% 4 4 4 3 5% 7% 33%	4636
	21st to end	Day	20% 8% 3 7% 5% 4 4 3 5% 6% 35%	5173
June	1st to 10th	Day	15% 7% 2 7% 6% 5% 5% 4 6% 7% 36%	2850
	11th to 20th	Day	16% 6% 3 6% 5% 5% 5% 4 7% 8% 35%	2850
	21st to end	Day	11% 7% 3 7% 5% 5% 6% 5% 8% 9% 36%	2850
July	1st to 10th	Day	9% 4 2 6% 5% 5% 6% 5% 8% 11% 39%	4750
	11th to 20th	Day	9% 4 1 5% 3 4 5% 4 7% 10% 49%	4750
	21st to end	Day	6% 4 2 5% 5% 5% 5% 4 6% 9% 51%	5126
August	1st to 10th	Day	7% 4 2 6% 4 5% 5% 4 7% 9% 46%	4274
	11th to 20th	Day	11% 5% 2 5% 5% 5% 5% 4 5% 8% 46%	4041
	21st to end	Day	12% 6% 2 5% 4 4 4 4 6% 8% 45%	4532
September	1st to 10th	Day	10% 5% 2 5% 4 4 3 3 5% 8% 50%	2366
	11th to 20th	Day	13% 6% 3 8% 5% 6% 3 4 5% 8% 38%	2090
	21st to end	Day	15% 7% 3 6% 4 4 4 3 6% 8% 41%	2090
October	1st to 10th	Day	17% 11% 3 8% 4 4 4 3 5% 7% 35%	1933
	11th to 20th	Day	12% 14% 3 8% 5% 5% 4 4 5% 7% 32%	1857
	21st to end	Day	15% 15% 5% 9% 6% 5% 4 4 6% 8% 25%	1881
November	1st to 10th	Day	16% 16% 5% 9% 4 4 4 3 6% 6% 26%	1558
	11th to 20th	Day	8% 15% 6% 13% 7% 5% 5% 4 4 7% 27%	1520
	21st to end	Day	13% 14% 5% 13% 6% 6% 4 4 4 6% 25%	1387
December	1st to 10th	Day	8% 16% 6% 15% 11% 5% 6% 4 6% 7% 17%	1330
	11th to 20th	Day	9% 15% 7% 15% 6% 6% 6% 5% 6% 6% 19%	1679
	21st to end	Day	10% 12% 4 11% 6% 7% 6% 4 7% 7% 26%	2442
January	1st to 10th	Night	5% 15% 6% 12% 8% 9% 8% 5% 6% 6% 21%	4737
	11th to 20th	Night	5% 13% 5% 16% 12% 11% 9% 5% 5% 5% 13%	4750
	21st to end	Night	8% 17% 8% 15% 7% 6% 6% 4 5% 5% 19%	4901
February	1st to 10th	Night	8% 13% 5% 11% 8% 7% 7% 4 6% 7% 26%	2561
	11th to 20th	Night	7% 10% 3 8% 7% 7% 6% 5% 8% 8% 33%	2403
	21st to end	Night	6% 12% 4 12% 6% 6% 7% 4 5% 7% 32%	1989
March	1st to 10th	Night	11% 11% 3 11% 7% 5% 5% 4 6% 7% 29%	3641
	11th to 20th	Night	5% 9% 3 8% 6% 4 5% 4 6% 8% 42%	3479
	21st to end	Night	9% 13% 5% 9% 5% 4 5% 4 5% 6% 35%	3817
April	1st to 10th	Night	10% 8% 3 6% 5% 4 4 4 6% 8% 42%	1856
	11th to 20th	Night	13% 10% 4 8% 5% 4 4 4 6% 6% 36%	1689
	21st to end	Night	11% 9% 3 8% 5% 5% 5% 5% 6% 6% 38%	1710
May	1st to 10th	Night	19% 9% 3 6% 4 3 4 4 6% 7% 36%	2686
	11th to 20th	Night	18% 5% 2 5% 4 4 4 4 6% 7% 41%	2266
	21st to end	Night	18% 7% 2 6% 3 3 3 3 4 6% 45%	2414
June	1st to 10th	Night	12% 7% 2 6% 4 4 5% 4 8% 8% 40%	1330
	11th to 20th	Night	14% 6% 2 4 4 4 5% 4 6% 8% 41%	1330
	21st to end	Night	10% 4 2 6% 4 5% 4 3 8% 10% 43%	1330
July	1st to 10th	Night	8% 3 1 4 4 5% 5% 4 6% 8% 52%	2220
	11th to 20th	Night	5% 3 1 4 3 3 4 3 7% 11% 54%	2220
	21st to end	Night	5% 4 1 4 4 4 5% 5% 7% 10% 52%	2435
August	1st to 10th	Night	6% 4 2 5% 5% 4 4 4 7% 10% 49%	2664
	11th to 20th	Night	8% 3 1 5% 3 4 4 4 6% 10% 51%	2798
	21st to end	Night	9% 5% 2 7% 4 4 4 3 5% 9% 48%	3135
September	1st to 10th	Night	9% 4 2 6% 4 4 4 4 6% 6% 52%	1810
	11th to 20th	Night	13% 4 2 7% 4 4 4 4 5% 8% 45%	2090
	21st to end	Night	16% 6% 3 7% 4 4 3 4 4 7% 42%	2090
October	1st to 10th	Night	17% 10% 3 6% 4 4 4 3 5% 7% 38%	2228
	11th to 20th	Night	15% 10% 4 7% 5% 5% 5% 4 5% 6% 34%	2319
	21st to end	Night	14% 13% 4 8% 5% 5% 5% 3 5% 7% 32%	2717
November	1st to 10th	Night	14% 13% 4 10% 6% 5% 4 4 5% 7% 28%	2680
	11th to 20th	Night	10% 15% 6% 12% 7% 4 4 4 5% 5% 27%	2660
	21st to end	Night	12% 15% 6% 12% 8% 5% 4 4 5% 6% 25%	2789
December	1st to 10th	Night	7% 12% 5% 13% 10% 7% 6% 4 7% 7% 21%	2850
	11th to 20th	Night	9% 16% 6% 13% 6% 6% 6% 4 5% 6% 23%	3518
	21st to end	Night	8% 11% 3 12% 8% 7% 6% 4 6% 6% 27%	5225

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	63% 7% 12% 14% 3	2219
	11th to 20th	Day	70% 6% 11% 10% 3	2220
	21st to end	Day	67% 7% 9% 13% 4	2764
February	1st to 10th	Day	61% 7% 12% 12% 8% 1	1619
	11th to 20th	Day	52% 7% 15% 19% 7%	1673
	21st to end	Day	54% 8% 12% 18% 8%	1481
March	1st to 10th	Day	55% 7% 15% 18% 5%	3209
	11th to 20th	Day	58% 9% 12% 16% 5%	3480
	21st to end	Day	53% 8% 14% 18% 7%	3814
April	1st to 10th	Day	45% 7% 13% 24% 10%	2321
	11th to 20th	Day	47% 6% 12% 22% 11% 2	2442
	21st to end	Day	45% 7% 16% 23% 7% 1	2470
May	1st to 10th	Day	44% 7% 13% 25% 10% 1	4275
	11th to 20th	Day	50% 7% 10% 21% 11% 1	4640
	21st to end	Day	48% 8% 12% 22% 10%	5173
June	1st to 10th	Day	44% 8% 15% 22% 10% 1	2850
	11th to 20th	Day	43% 10% 15% 22% 10%	2850
	21st to end	Day	42% 10% 18% 21% 8%	2850
July	1st to 10th	Day	36% 8% 24% 26% 6%	4676
	11th to 20th	Day	29% 6% 21% 37% 6%	4669
	21st to end	Day	30% 6% 21% 36% 7%	4963
August	1st to 10th	Day	33% 5% 20% 31% 10%	4258
	11th to 20th	Day	36% 5% 22% 31% 5%	4080
	21st to end	Day	37% 5% 24% 29% 6%	4531
September	1st to 10th	Day	32% 7% 19% 32% 9% 1	2366
	11th to 20th	Day	43% 9% 18% 25% 4	2090
	21st to end	Day	41% 7% 17% 28% 7%	2090
October	1st to 10th	Day	43% 5% 14% 30% 8%	3206
	11th to 20th	Day	43% 5% 12% 28% 11%	3063
	21st to end	Day	50% 5% 19% 20% 6%	3091
November	1st to 10th	Day	58% 7% 12% 18% 4 1	1558
	11th to 20th	Day	57% 10% 13% 15% 4	1520
	21st to end	Day	60% 7% 16% 14% 3	1387
December	1st to 10th	Day	65% 8% 14% 10% 3	1330
	11th to 20th	Day	62% 7% 15% 12% 4	1680
	21st to end	Day	53% 10% 12% 18% 7%	2442
January	1st to 10th	Night	59% 10% 12% 14% 5%	4737
	11th to 20th	Night	70% 7% 8% 12% 2	4750
	21st to end	Night	66% 6% 11% 13% 4	4901
February	1st to 10th	Night	57% 6% 13% 16% 9%	2561
	11th to 20th	Night	46% 8% 16% 22% 9%	2404
	21st to end	Night	50% 7% 12% 21% 10%	1989
March	1st to 10th	Night	51% 7% 12% 22% 8%	3652
	11th to 20th	Night	36% 10% 17% 25% 12% 1	3480
	21st to end	Night	47% 7% 11% 25% 10% 1	3817
April	1st to 10th	Night	39% 5% 13% 23% 16% 2	1856
	11th to 20th	Night	47% 5% 9% 21% 15% 2	1689
	21st to end	Night	44% 6% 12% 24% 11% 2	1710
May	1st to 10th	Night	44% 8% 12% 23% 13%	2695
	11th to 20th	Night	40% 7% 14% 27% 9% 3	2267
	21st to end	Night	39% 8% 12% 28% 12% 1	2414
June	1st to 10th	Night	37% 10% 16% 22% 14%	1330
	11th to 20th	Night	40% 7% 15% 23% 14% 2	1330
	21st to end	Night	33% 9% 22% 26% 9% 1	1330
July	1st to 10th	Night	29% 7% 22% 33% 8% 1	2185
	11th to 20th	Night	25% 6% 22% 39% 8% 1	2178
	21st to end	Night	27% 5% 23% 36% 8% 1	2358
August	1st to 10th	Night	30% 5% 16% 34% 14%	2656
	11th to 20th	Night	28% 5% 26% 31% 9%	2825
	21st to end	Night	34% 5% 19% 32% 9%	3135
September	1st to 10th	Night	31% 7% 17% 31% 13%	1810
	11th to 20th	Night	37% 7% 19% 26% 10% 1	2090
	21st to end	Night	41% 7% 14% 28% 9% 1	2090
October	1st to 10th	Night	39% 5% 11% 32% 12%	3722
	11th to 20th	Night	43% 5% 13% 29% 10%	3855
	21st to end	Night	45% 5% 16% 30% 5%	4467
November	1st to 10th	Night	56% 7% 15% 15% 6% 1	2680
	11th to 20th	Night	58% 9% 14% 14% 5%	2660
	21st to end	Night	61% 7% 14% 13% 5%	2789
December	1st to 10th	Night	60% 8% 16% 13% 4	2850
	11th to 20th	Night	60% 7% 15% 13% 5%	3516
	21st to end	Night	54% 8% 12% 17% 9%	5225

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% 6% 35% 30% 15% 3	270
	11th to 20th	Day	11% 8% 30% 34% 15% 2	270
	21st to end	Day	15% 6% 29% 29% 16% 4	297
February	1st to 10th	Day	14% 9% 32% 34% 10% 2	270
	11th to 20th	Day	11% 10% 34% 26% 14% 4	270
	21st to end	Day	10% 6% 39% 31% 14% 1	225
March	1st to 10th	Day	15% 10% 30% 28% 15% 2	270
	11th to 20th	Day	11% 10% 33% 27% 15% 3	270
	21st to end	Day	14% 7% 30% 33% 14% 2	297
April	1st to 10th	Day	13% 9% 31% 34% 10% 4	501
	11th to 20th	Day	16% 12% 30% 26% 14% 1	640
	21st to end	Day	15% 10% 36% 26% 11% 2	650
May	1st to 10th	Day	15% 13% 32% 27% 11% 1	653
	11th to 20th	Day	20% 11% 27% 25% 13% 3	675
	21st to end	Day	19% 11% 25% 27% 15% 3	734
June	1st to 10th	Day	17% 12% 29% 23% 13% 6%	680
	11th to 20th	Day	17% 11% 32% 28% 10% 3	680
	21st to end	Day	12% 7% 27% 33% 16% 6%	680
July	1st to 10th	Day	8% 8% 29% 27% 17% 11%	671
	11th to 20th	Day	13% 8% 27% 29% 18% 6%	668
	21st to end	Day	7% 5% 30% 32% 18% 8%	739
August	1st to 10th	Day	8% 8% 29% 29% 19% 7%	676
	11th to 20th	Day	10% 5% 25% 32% 20% 8%	665
	21st to end	Day	12% 8% 28% 31% 17% 4	748
September	1st to 10th	Day	10% 9% 32% 33% 15% 2	576
	11th to 20th	Day	16% 8% 40% 24% 8% 3	300
	21st to end	Day	21% 9% 31% 29% 10%	300
October	1st to 10th	Day	21% 12% 27% 27% 9% 3	300
	11th to 20th	Day	16% 11% 36% 26% 9% 2	300
	21st to end	Day	26% 10% 28% 23% 12% 1	330
November	1st to 10th	Day	24% 9% 27% 27% 10% 2	291
	11th to 20th	Day	15% 10% 41% 24% 9% 1	270
	21st to end	Day	17% 12% 38% 28% 5%	270
December	1st to 10th	Day	14% 6% 35% 28% 15% 1	270
	11th to 20th	Day	13% 11% 37% 30% 8% 1	270
	21st to end	Day	12% 8% 28% 33% 15% 4	297
January	1st to 10th	Night	13% 6% 34% 30% 15% 2	950
	11th to 20th	Night	15% 7% 32% 32% 12% 1	950
	21st to end	Night	14% 7% 32% 34% 12% 1	1045
February	1st to 10th	Night	13% 7% 29% 36% 14% 1	950
	11th to 20th	Night	11% 7% 30% 36% 14% 3	929
	21st to end	Night	11% 7% 35% 30% 15% 2	733
March	1st to 10th	Night	14% 7% 29% 32% 17% 1	717
	11th to 20th	Night	12% 7% 39% 28% 12% 1	570
	21st to end	Night	18% 7% 28% 31% 14% 3	627
April	1st to 10th	Night	14% 6% 31% 35% 12% 2	570
	11th to 20th	Night	16% 7% 30% 35% 12% 1	563
	21st to end	Night	14% 8% 32% 34% 11% 1	570
May	1st to 10th	Night	20% 9% 29% 31% 10% 1	570
	11th to 20th	Night	17% 7% 32% 31% 13% 1	561
	21st to end	Night	19% 7% 29% 32% 11% 1	617
June	1st to 10th	Night	15% 7% 30% 32% 16%	570
	11th to 20th	Night	15% 6% 30% 34% 13% 1	570
	21st to end	Night	11% 5% 22% 41% 20% 1	570
July	1st to 10th	Night	7% 3 26% 40% 22% 2	555
	11th to 20th	Night	8% 3 26% 39% 22% 2	552
	21st to end	Night	8% 2 23% 42% 22% 4	624
August	1st to 10th	Night	7% 4 22% 46% 20% 2	567
	11th to 20th	Night	8% 2 23% 40% 23% 3	564
	21st to end	Night	11% 5% 23% 39% 20% 1	627
September	1st to 10th	Night	11% 4 31% 34% 17% 2	570
	11th to 20th	Night	15% 6% 27% 38% 13%	570
	21st to end	Night	17% 7% 36% 29% 11%	570
October	1st to 10th	Night	22% 8% 32% 30% 7% 1	708
	11th to 20th	Night	19% 7% 34% 30% 10%	799
	21st to end	Night	19% 9% 31% 30% 9% 1	1045
November	1st to 10th	Night	19% 9% 35% 25% 12% 1	963
	11th to 20th	Night	17% 10% 37% 25% 9% 2	950
	21st to end	Night	19% 9% 39% 26% 6% 1	950
December	1st to 10th	Night	11% 8% 31% 35% 12% 2	950
	11th to 20th	Night	16% 10% 34% 30% 9% 2	950
	21st to end	Night	18% 7% 30% 30% 13% 2	1045

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