South Fork Natural History Museum and Nature Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the South Fork Natural History Museum and Nature Center 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	16% 7% 2 6% 4 4 4 3 6% 7% 40%	101206
	Night	18% 8% 3 6% 4 4 4 3 5% 7% 38%	97948
Transparency	Day	23% 47% 7% 13% 9% 1	104782
	Night	25% 47% 7% 12% 9% 1	102461
Seeing	Day	18% 9% 26% 28% 15% 4	15150
	Night	20% 10% 27% 27% 13% 2	24158

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	16% 7% 3 6% 5% 4 4 3 5% 6% 41%	2517
	11th to 20th	Day	18% 9% 2 6% 5% 4 4 4 5% 5% 38%	2520
	21st to end	Day	22% 11% 4 8% 4 4 3 3 5% 4 32%	2816
February	1st to 10th	Day	18% 7% 2 6% 6% 4 5% 3 6% 7% 35%	1832
	11th to 20th	Day	15% 6% 2 7% 5% 4 4 3 4 7% 44%	1848
	21st to end	Day	20% 10% 2 5% 3 3 4 3 6% 6% 38%	1570
March	1st to 10th	Day	26% 7% 2 5% 3 3 3 3 4 6% 37%	3116
	11th to 20th	Day	10% 4 1 5% 4 4 4 4 6% 8% 51%	3273
	21st to end	Day	20% 9% 2 5% 4 4 4 3 6% 5% 39%	4129
April	1st to 10th	Day	18% 8% 2 5% 4 4 4 4 5% 7% 40%	2280
	11th to 20th	Day	18% 7% 2 5% 4 3 3 3 6% 7% 44%	2254
	21st to end	Day	18% 6% 2 5% 3 4 4 4 6% 6% 41%	2403
May	1st to 10th	Day	26% 11% 3 6% 4 3 3 3 4 6% 29%	4106
	11th to 20th	Day	23% 9% 3 7% 4 3 3 3 5% 7% 35%	4142
	21st to end	Day	13% 7% 2 6% 3 4 3 4 7% 9% 42%	4837
June	1st to 10th	Day	16% 5% 2 5% 5% 4 4 4 6% 7% 41%	2660
	11th to 20th	Day	13% 7% 2 5% 4 4 5% 5% 7% 9% 41%	2660
	21st to end	Day	11% 7% 2 5% 4 4 4 4 8% 9% 43%	2660
July	1st to 10th	Day	13% 9% 3 7% 5% 4 5% 4 7% 9% 35%	4440
	11th to 20th	Day	12% 6% 2 6% 5% 4 4 4 7% 9% 41%	4440
	21st to end	Day	17% 8% 2 6% 4 4 4 4 6% 8% 36%	4814
August	1st to 10th	Day	17% 7% 2 6% 5% 4 4 4 5% 9% 36%	4155
	11th to 20th	Day	10% 6% 2 6% 5% 4 4 3 6% 8% 46%	3791
	21st to end	Day	7% 3 1 5% 4 4 5% 4 6% 9% 52%	4180
September	1st to 10th	Day	13% 7% 2 6% 3 3 3 3 5% 8% 46%	2280
	11th to 20th	Day	11% 6% 2 4 3 3 3 3 5% 6% 53%	2119
	21st to end	Day	19% 7% 2 6% 4 4 4 4 5% 6% 40%	2090
October	1st to 10th	Day	21% 6% 2 5% 3 3 4 3 4 6% 43%	2090
	11th to 20th	Day	14% 7% 1 5% 4 3 3 4 5% 7% 47%	1881
	21st to end	Day	17% 6% 2 6% 4 4 4 3 5% 7% 41%	1881
November	1st to 10th	Day	15% 6% 2 4 3 3 4 3 4 7% 48%	1761
	11th to 20th	Day	16% 7% 2 5% 4 4 3 4 4 8% 44%	1710
	21st to end	Day	16% 8% 2 5% 3 3 5% 4 5% 6% 42%	1710
December	1st to 10th	Day	19% 8% 3 7% 5% 3 5% 4 5% 7% 34%	1563
	11th to 20th	Day	21% 8% 2 5% 3 2 3 3 4 6% 43%	1906
	21st to end	Day	19% 12% 3 7% 5% 4 3 3 5% 5% 33%	2772
January	1st to 10th	Night	18% 6% 2 5% 3 3 4 3 5% 7% 44%	4429
	11th to 20th	Night	18% 9% 3 8% 4 3 3 3 4 4 41%	4440
	21st to end	Night	23% 11% 3 8% 4 4 3 3 5% 5% 30%	4838
February	1st to 10th	Night	17% 9% 3 7% 5% 3 4 3 5% 6% 38%	2347
	11th to 20th	Night	18% 8% 3 5% 4 4 3 4 6% 7% 37%	2218
	21st to end	Night	21% 7% 2 5% 4 4 4 4 4 6% 39%	1884
March	1st to 10th	Night	25% 12% 3 6% 4 3 3 3 4 5% 34%	3724
	11th to 20th	Night	12% 6% 2 7% 5% 3 4 3 6% 7% 45%	3685
	21st to end	Night	24% 8% 2 5% 4 3 4 3 4 5% 38%	3498
April	1st to 10th	Night	19% 8% 2 6% 4 4 4 3 6% 6% 39%	1900
	11th to 20th	Night	17% 8% 2 7% 3 3 3 4 5% 6% 43%	1875
	21st to end	Night	20% 7% 3 6% 4 2 4 3 4 7% 39%	1777
May	1st to 10th	Night	22% 14% 5% 9% 4 3 3 3 4 6% 27%	2834
	11th to 20th	Night	25% 10% 3 7% 5% 4 5% 4 5% 7% 25%	2766
	21st to end	Night	17% 9% 3 6% 4 4 4 4 7% 7% 35%	2738
June	1st to 10th	Night	17% 9% 2 7% 5% 2 5% 3 5% 8% 37%	1520
	11th to 20th	Night	17% 6% 2 4 4 4 3 4 6% 10% 40%	1520
	21st to end	Night	13% 7% 3 6% 5% 4 5% 4 6% 9% 38%	1520
July	1st to 10th	Night	15% 12% 4 7% 4 4 5% 4 5% 8% 31%	2520
	11th to 20th	Night	13% 7% 3 6% 5% 4 5% 5% 7% 10% 35%	2520
	21st to end	Night	17% 9% 3 7% 5% 5% 4 3 6% 8% 33%	2739
August	1st to 10th	Night	21% 8% 3 7% 4 5% 5% 5% 7% 7% 30%	2730
	11th to 20th	Night	9% 6% 3 7% 5% 5% 5% 4 7% 8% 40%	3032
	21st to end	Night	8% 4 2 5% 3 3 3 3 6% 8% 55%	3476
September	1st to 10th	Night	14% 7% 2 6% 4 4 4 4 5% 6% 42%	1900
	11th to 20th	Night	14% 6% 2 4 3 3 3 3 5% 7% 50%	2060
	21st to end	Night	18% 8% 3 6% 6% 4 4 3 5% 6% 38%	2090
October	1st to 10th	Night	19% 8% 3 6% 4 4 4 3 4 5% 40%	2090
	11th to 20th	Night	16% 6% 2 5% 3 3 3 3 5% 7% 48%	2293
	21st to end	Night	19% 8% 3 7% 4 4 3 3 5% 5% 39%	2717
November	1st to 10th	Night	14% 6% 2 6% 4 4 4 3 5% 6% 46%	2537
	11th to 20th	Night	19% 7% 3 5% 4 4 4 3 5% 5% 42%	2477
	21st to end	Night	15% 6% 2 6% 5% 4 4 4 6% 8% 43%	2470
December	1st to 10th	Night	21% 8% 4 6% 5% 4 4 3 5% 6% 33%	2612
	11th to 20th	Night	19% 8% 3 7% 4 4 3 3 5% 6% 38%	3288
	21st to end	Night	20% 11% 3 6% 4 4 4 3 4 6% 36%	4884

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	29% 37% 5% 18% 9% 1	2518
	11th to 20th	Day	26% 40% 7% 18% 8% 1	2520
	21st to end	Day	38% 41% 4 12% 4 1	2816
February	1st to 10th	Day	18% 65% 7% 7% 3	1832
	11th to 20th	Day	17% 63% 2 9% 8% 1	1857
	21st to end	Day	16% 65% 5% 7% 4 2	1570
March	1st to 10th	Day	34% 41% 7% 10% 7% 2	3119
	11th to 20th	Day	13% 41% 9% 26% 10% 1	3273
	21st to end	Day	30% 40% 5% 11% 11% 3	4129
April	1st to 10th	Day	18% 65% 3 7% 6% 1	2280
	11th to 20th	Day	14% 65% 3 8% 9%	2254
	21st to end	Day	15% 65% 3 8% 7% 1	2403
May	1st to 10th	Day	37% 43% 9% 7% 4 1	4120
	11th to 20th	Day	34% 41% 11% 10% 3	4146
	21st to end	Day	22% 42% 6% 17% 13% 1	4837
June	1st to 10th	Day	15% 65% 4 9% 7%	2660
	11th to 20th	Day	13% 66% 4 9% 7% 1	2660
	21st to end	Day	12% 64% 4 11% 9%	2660
July	1st to 10th	Day	33% 39% 6% 10% 11% 1	4370
	11th to 20th	Day	27% 39% 11% 15% 8% 1	4365
	21st to end	Day	33% 37% 9% 11% 9% 1	4661
August	1st to 10th	Day	33% 38% 10% 14% 4	4141
	11th to 20th	Day	23% 39% 10% 23% 5%	3829
	21st to end	Day	15% 39% 11% 22% 13%	4180
September	1st to 10th	Day	15% 61% 5% 11% 7%	2280
	11th to 20th	Day	15% 60% 4 9% 11% 1	2119
	21st to end	Day	21% 60% 4 8% 6%	2090
October	1st to 10th	Day	20% 38% 7% 14% 17% 4	3480
	11th to 20th	Day	13% 37% 6% 16% 26% 2	3110
	21st to end	Day	17% 37% 11% 19% 14% 2	3081
November	1st to 10th	Day	18% 56% 7% 9% 9% 1	1761
	11th to 20th	Day	15% 59% 4 10% 10% 1	1710
	21st to end	Day	15% 60% 6% 13% 5% 1	1710
December	1st to 10th	Day	21% 60% 6% 6% 7%	1563
	11th to 20th	Day	23% 48% 7% 8% 13% 2	1906
	21st to end	Day	35% 38% 6% 16% 5%	2772
January	1st to 10th	Night	25% 38% 7% 22% 6% 2	4429
	11th to 20th	Night	29% 37% 9% 15% 9% 1	4440
	21st to end	Night	41% 41% 4 9% 5%	4838
February	1st to 10th	Night	17% 65% 5% 9% 3 1	2347
	11th to 20th	Night	17% 64% 3 7% 8% 1	2220
	21st to end	Night	17% 65% 3 7% 6% 2	1884
March	1st to 10th	Night	39% 41% 4 11% 5% 1	3734
	11th to 20th	Night	19% 41% 11% 16% 10% 1	3686
	21st to end	Night	32% 40% 3 6% 14% 3	3498
April	1st to 10th	Night	18% 65% 3 7% 6% 1	1900
	11th to 20th	Night	14% 66% 5% 8% 7% 1	1875
	21st to end	Night	18% 64% 3 8% 6% 1	1777
May	1st to 10th	Night	38% 42% 8% 8% 3 1	2840
	11th to 20th	Night	39% 43% 8% 7% 2	2767
	21st to end	Night	27% 42% 9% 14% 8% 1	2739
June	1st to 10th	Night	16% 65% 2 8% 7% 1	1520
	11th to 20th	Night	13% 65% 4 11% 6%	1520
	21st to end	Night	14% 64% 3 11% 7% 1	1520
July	1st to 10th	Night	37% 38% 6% 11% 9%	2480
	11th to 20th	Night	29% 40% 11% 14% 6%	2472
	21st to end	Night	36% 36% 10% 8% 10% 1	2651
August	1st to 10th	Night	37% 39% 10% 10% 4 1	2720
	11th to 20th	Night	24% 40% 12% 19% 5%	3060
	21st to end	Night	13% 38% 10% 24% 15%	3476
September	1st to 10th	Night	16% 61% 4 12% 6% 1	1900
	11th to 20th	Night	15% 59% 4 9% 11% 1	2060
	21st to end	Night	23% 60% 4 7% 6%	2090
October	1st to 10th	Night	24% 38% 7% 18% 11% 2	3480
	11th to 20th	Night	12% 37% 5% 16% 27% 3	3803
	21st to end	Night	16% 37% 9% 19% 17% 1	4467
November	1st to 10th	Night	18% 57% 5% 10% 8% 1	2537
	11th to 20th	Night	17% 60% 4 8% 9% 2	2477
	21st to end	Night	16% 60% 5% 13% 5% 1	2470
December	1st to 10th	Night	22% 60% 5% 8% 5%	2612
	11th to 20th	Night	24% 49% 7% 9% 11% 1	3288
	21st to end	Night	33% 38% 8% 13% 8%	4884

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% 19% 33% 21% 6% 1	180
	11th to 20th	Day	19% 23% 38% 16% 4	180
	21st to end	Day	22% 12% 38% 18% 9% 1	213
February	1st to 10th	Day	24% 13% 37% 23% 4	392
	11th to 20th	Day	21% 18% 38% 21% 2	456
	21st to end	Day	23% 15% 34% 21% 7% 1	382
March	1st to 10th	Day	20% 13% 37% 25% 6%	460
	11th to 20th	Day	17% 14% 40% 22% 7% 1	460
	21st to end	Day	22% 13% 36% 21% 7% 1	506
April	1st to 10th	Day	23% 12% 33% 22% 9% 1	460
	11th to 20th	Day	21% 10% 29% 31% 9% 1	452
	21st to end	Day	23% 9% 27% 31% 8% 2	460
May	1st to 10th	Day	24% 9% 29% 26% 10% 1	463
	11th to 20th	Day	19% 5% 28% 33% 14% 2	487
	21st to end	Day	18% 3 17% 33% 23% 7%	529
June	1st to 10th	Day	15% 3 19% 35% 23% 4	490
	11th to 20th	Day	14% 3 22% 36% 20% 5%	490
	21st to end	Day	16% 3 18% 35% 23% 5%	490
July	1st to 10th	Day	15% 3 12% 36% 26% 8%	485
	11th to 20th	Day	10% 2 14% 34% 30% 10%	484
	21st to end	Day	14% 3 18% 38% 25% 3	532
August	1st to 10th	Day	14% 4 14% 32% 28% 8%	486
	11th to 20th	Day	15% 2 14% 32% 28% 8%	479
	21st to end	Day	10% 3 19% 32% 24% 11%	539
September	1st to 10th	Day	17% 4 18% 29% 22% 10%	490
	11th to 20th	Day	15% 4 22% 27% 22% 11%	490
	21st to end	Day	24% 5% 24% 28% 15% 4	490
October	1st to 10th	Day	25% 8% 20% 23% 18% 7%	490
	11th to 20th	Day	15% 10% 28% 27% 16% 4	470
	21st to end	Day	22% 11% 31% 24% 10% 3	429
November	1st to 10th	Day	15% 11% 29% 27% 15% 3	395
	11th to 20th	Day	21% 16% 32% 22% 9%	370
	21st to end	Day	18% 16% 30% 24% 11% 1	370
December	1st to 10th	Day	21% 17% 37% 16% 9%	223
	11th to 20th	Day	23% 24% 27% 23% 3	180
	21st to end	Day	24% 15% 33% 20% 7% 1	198
January	1st to 10th	Night	21% 19% 36% 20% 4	760
	11th to 20th	Night	27% 17% 33% 19% 4	760
	21st to end	Night	21% 18% 37% 22% 3	836
February	1st to 10th	Night	22% 13% 40% 22% 3	760
	11th to 20th	Night	23% 18% 40% 16% 3	743
	21st to end	Night	24% 17% 34% 20% 6%	628
March	1st to 10th	Night	22% 14% 32% 25% 6%	760
	11th to 20th	Night	20% 11% 35% 27% 6% 1	760
	21st to end	Night	23% 9% 35% 23% 9% 1	836
April	1st to 10th	Night	23% 8% 32% 30% 7% 1	760
	11th to 20th	Night	19% 9% 30% 31% 11% 1	751
	21st to end	Night	22% 6% 28% 30% 12% 2	637
May	1st to 10th	Night	23% 6% 25% 30% 13% 3	570
	11th to 20th	Night	22% 5% 28% 33% 11% 1	541
	21st to end	Night	21% 1 16% 32% 25% 4	411
June	1st to 10th	Night	21% 2 18% 32% 25% 2	380
	11th to 20th	Night	19% 2 16% 38% 23% 2	380
	21st to end	Night	16% 2 14% 42% 24% 2	380
July	1st to 10th	Night	13% 2 14% 39% 29% 3	370
	11th to 20th	Night	12% 3 13% 37% 29% 5%	368
	21st to end	Night	15% 3 12% 40% 27% 3	416
August	1st to 10th	Night	10% 2 13% 43% 27% 4	511
	11th to 20th	Night	13% 3 12% 36% 31% 5%	709
	21st to end	Night	12% 3 14% 33% 29% 8%	836
September	1st to 10th	Night	18% 3 18% 31% 24% 7%	760
	11th to 20th	Night	16% 4 18% 30% 24% 8%	760
	21st to end	Night	20% 4 23% 29% 19% 3	760
October	1st to 10th	Night	23% 8% 21% 27% 16% 5%	760
	11th to 20th	Night	20% 10% 28% 27% 13% 3	760
	21st to end	Night	23% 10% 33% 22% 11% 1	836
November	1st to 10th	Night	16% 11% 30% 27% 14% 2	780
	11th to 20th	Night	23% 16% 30% 21% 9% 1	763
	21st to end	Night	18% 18% 31% 23% 8% 1	760
December	1st to 10th	Night	25% 16% 31% 21% 6% 1	760
	11th to 20th	Night	22% 20% 32% 21% 5%	760
	21st to end	Night	24% 16% 36% 21% 3	836

Page generated at 2024-11-08 06:44:46. Version ac07

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