Jamestown
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Jamestown clear sky chart from 2005-11-06 to 2024-07-16.

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% 13% 5% 10% 5% 4 4 3 5% 6% 27%	89809
	Night	17% 15% 5% 10% 5% 4 4 3 4 6% 26%	89695
Transparency	Day	57% 4 11% 18% 9% 1	89538
	Night	60% 4 10% 16% 8% 1	89519
Seeing	Day	26% 16% 28% 17% 9% 3	14147
	Night	26% 15% 25% 23% 10% 1	23654

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	14% 27% 11% 17% 6% 3 3 3 3 3 10%	2553
	11th to 20th	Day	10% 25% 10% 20% 8% 4 3 2 2 3 13%	2840
	21st to end	Day	22% 18% 11% 18% 8% 4 4 2 3 2 8%	3124
February	1st to 10th	Day	17% 20% 7% 16% 9% 5% 4 3 3 3 14%	1710
	11th to 20th	Day	13% 18% 8% 18% 8% 4 4 3 3 4 16%	1663
	21st to end	Day	18% 18% 5% 13% 7% 3 4 3 4 5% 21%	1513
March	1st to 10th	Day	20% 13% 6% 9% 5% 3 3 3 4 6% 28%	3432
	11th to 20th	Day	10% 22% 8% 10% 4 3 3 2 5% 5% 26%	3480
	21st to end	Day	19% 13% 6% 11% 4 3 3 3 5% 5% 27%	3815
April	1st to 10th	Day	16% 17% 4 8% 5% 4 4 4 4 6% 29%	2241
	11th to 20th	Day	20% 14% 2 6% 5% 4 3 4 5% 6% 31%	2272
	21st to end	Day	20% 13% 3 7% 4 4 4 3 4 5% 33%	2470
May	1st to 10th	Day	23% 10% 4 6% 5% 4 4 3 5% 6% 30%	4108
	11th to 20th	Day	16% 11% 4 8% 5% 5% 6% 4 6% 8% 27%	4265
	21st to end	Day	13% 6% 2 6% 5% 5% 5% 4 5% 7% 42%	4837
June	1st to 10th	Day	16% 7% 3 7% 4 5% 4 4 7% 8% 35%	2660
	11th to 20th	Day	14% 7% 3 7% 5% 5% 5% 4 6% 9% 35%	2660
	21st to end	Day	16% 7% 2 6% 5% 4 6% 4 7% 8% 36%	2660
July	1st to 10th	Day	10% 6% 2 5% 5% 6% 5% 4 7% 9% 41%	2660
	11th to 20th	Day	13% 7% 2 7% 5% 4 5% 5% 8% 9% 34%	2536
	21st to end	Day	12% 7% 3 7% 5% 5% 6% 6% 7% 8% 34%	2547
August	1st to 10th	Day	12% 5% 3 7% 4 5% 5% 5% 7% 9% 36%	2327
	11th to 20th	Day	13% 8% 3 7% 6% 6% 6% 5% 7% 10% 30%	2303
	21st to end	Day	14% 7% 3 6% 4 5% 5% 5% 7% 9% 34%	2444
September	1st to 10th	Day	19% 8% 3 7% 4 4 4 4 5% 8% 35%	2160
	11th to 20th	Day	15% 6% 3 6% 4 4 4 4 6% 8% 39%	2057
	21st to end	Day	18% 9% 3 9% 5% 5% 4 4 5% 7% 30%	1940
October	1st to 10th	Day	20% 9% 3 7% 5% 5% 4 3 6% 6% 31%	1800
	11th to 20th	Day	21% 12% 3 10% 5% 4 4 3 5% 5% 27%	1800
	21st to end	Day	25% 16% 4 8% 5% 5% 4 3 4 5% 21%	1980
November	1st to 10th	Day	13% 18% 4 9% 4 4 5% 3 5% 6% 29%	1714
	11th to 20th	Day	17% 21% 5% 10% 5% 3 3 3 5% 6% 21%	1520
	21st to end	Day	17% 27% 5% 11% 5% 4 3 4 5% 5% 16%	1520
December	1st to 10th	Day	18% 29% 9% 13% 5% 3 3 2 4 3 11%	1520
	11th to 20th	Day	16% 22% 9% 16% 5% 3 3 3 5% 6% 13%	1906
	21st to end	Day	23% 26% 9% 12% 5% 3 3 2 3 4 11%	2772
January	1st to 10th	Night	15% 24% 10% 20% 5% 4 3 2 3 3 9%	4388
	11th to 20th	Night	12% 21% 11% 19% 7% 5% 5% 3 3 4 10%	4120
	21st to end	Night	24% 20% 10% 16% 7% 3 3 2 2 2 10%	4532
February	1st to 10th	Night	17% 20% 6% 15% 9% 5% 3 2 4 3 16%	2470
	11th to 20th	Night	13% 17% 6% 18% 9% 5% 5% 3 4 4 16%	2403
	21st to end	Night	18% 14% 6% 16% 8% 4 3 3 3 4 21%	1938
March	1st to 10th	Night	21% 16% 4 10% 6% 4 3 2 3 4 28%	3408
	11th to 20th	Night	17% 16% 8% 11% 5% 4 2 2 4 5% 25%	3479
	21st to end	Night	15% 13% 6% 10% 5% 4 3 3 4 5% 32%	3817
April	1st to 10th	Night	16% 17% 4 8% 4 4 4 4 5% 5% 29%	1938
	11th to 20th	Night	18% 12% 3 6% 4 4 4 3 5% 6% 35%	1873
	21st to end	Night	14% 12% 4 7% 5% 5% 4 4 5% 7% 34%	1710
May	1st to 10th	Night	25% 10% 3 6% 4 3 4 3 5% 6% 31%	2833
	11th to 20th	Night	15% 9% 4 8% 4 4 5% 4 5% 7% 35%	2624
	21st to end	Night	14% 6% 2 5% 3 4 3 3 6% 9% 44%	2738
June	1st to 10th	Night	13% 6% 3 8% 6% 4 4 4 6% 9% 37%	1520
	11th to 20th	Night	14% 7% 2 6% 4 5% 4 4 7% 8% 40%	1520
	21st to end	Night	14% 7% 2 6% 4 4 4 4 6% 8% 40%	1520
July	1st to 10th	Night	9% 6% 2 6% 6% 4 4 3 6% 9% 45%	1520
	11th to 20th	Night	11% 5% 2 5% 5% 3 4 4 7% 8% 45%	1542
	21st to end	Night	11% 6% 2 5% 5% 5% 5% 5% 6% 9% 40%	1771
August	1st to 10th	Night	9% 5% 2 6% 4 4 4 4 7% 9% 45%	1611
	11th to 20th	Night	12% 6% 3 6% 3 5% 6% 4 8% 9% 39%	1598
	21st to end	Night	12% 7% 2 6% 4 4 5% 4 6% 9% 42%	1894
September	1st to 10th	Night	15% 8% 2 6% 4 3 4 3 6% 7% 42%	1800
	11th to 20th	Night	14% 6% 2 5% 4 4 4 3 4 7% 47%	1898
	21st to end	Night	19% 7% 2 7% 4 5% 5% 4 6% 6% 35%	2020
October	1st to 10th	Night	17% 9% 3 6% 5% 5% 4 3 5% 6% 37%	2160
	11th to 20th	Night	21% 12% 3 8% 5% 4 4 3 5% 7% 28%	2160
	21st to end	Night	27% 12% 3 7% 5% 5% 3 3 4 5% 25%	2376
November	1st to 10th	Night	15% 16% 3 7% 4 4 4 3 5% 5% 33%	2362
	11th to 20th	Night	17% 19% 4 8% 6% 5% 4 5% 5% 5% 22%	2660
	21st to end	Night	17% 23% 7% 10% 5% 4 4 3 4 5% 19%	2660
December	1st to 10th	Night	19% 27% 9% 11% 5% 4 4 3 3 3 11%	2660
	11th to 20th	Night	17% 24% 9% 15% 6% 4 3 2 3 4 13%	3288
	21st to end	Night	23% 24% 8% 13% 6% 4 4 3 3 4 9%	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	80% 2 8% 8% 2	2554
	11th to 20th	Day	78% 2 7% 10% 3	2840
	21st to end	Day	85% 1 7% 4 2 1	3124
February	1st to 10th	Day	77% 2 9% 8% 4	1710
	11th to 20th	Day	74% 3 7% 11% 5%	1672
	21st to end	Day	67% 3 9% 14% 5% 2	1513
March	1st to 10th	Day	60% 3 10% 22% 5%	3435
	11th to 20th	Day	61% 3 15% 15% 5% 1	3480
	21st to end	Day	59% 3 8% 19% 10% 1	3815
April	1st to 10th	Day	58% 3 11% 17% 11% 1	2241
	11th to 20th	Day	53% 5% 9% 20% 11% 2	2272
	21st to end	Day	55% 3 10% 18% 13% 2	2470
May	1st to 10th	Day	55% 4 8% 22% 9% 2	4120
	11th to 20th	Day	55% 5% 12% 20% 8% 1	4269
	21st to end	Day	41% 5% 13% 23% 15% 3	4837
June	1st to 10th	Day	47% 5% 11% 22% 13% 1	2660
	11th to 20th	Day	46% 7% 13% 22% 12% 1	2660
	21st to end	Day	45% 6% 12% 23% 13%	2660
July	1st to 10th	Day	40% 6% 12% 24% 16% 2	2590
	11th to 20th	Day	44% 7% 13% 22% 14%	2461
	21st to end	Day	45% 7% 13% 21% 13% 1	2405
August	1st to 10th	Day	42% 7% 14% 27% 10%	2314
	11th to 20th	Day	48% 7% 14% 22% 8%	2303
	21st to end	Day	44% 8% 12% 24% 11% 2	2444
September	1st to 10th	Day	48% 5% 12% 22% 12% 1	2160
	11th to 20th	Day	42% 7% 10% 26% 14% 1	2057
	21st to end	Day	52% 5% 10% 22% 9% 1	1940
October	1st to 10th	Day	52% 5% 13% 16% 12% 2	1800
	11th to 20th	Day	59% 4 14% 15% 7% 1	1800
	21st to end	Day	67% 3 9% 13% 7% 1	1980
November	1st to 10th	Day	55% 5% 11% 16% 11% 2	1714
	11th to 20th	Day	64% 4 10% 15% 6% 2	1520
	21st to end	Day	71% 3 11% 10% 3 1	1520
December	1st to 10th	Day	80% 2 8% 9% 2	1520
	11th to 20th	Day	74% 3 12% 9% 2 1	1906
	21st to end	Day	82% 1 10% 7% 1	2772
January	1st to 10th	Night	82% 2 7% 7% 2	4388
	11th to 20th	Night	80% 3 9% 6% 2	4120
	21st to end	Night	83% 2 6% 7% 2	4532
February	1st to 10th	Night	74% 2 9% 10% 4	2470
	11th to 20th	Night	73% 4 7% 11% 4	2405
	21st to end	Night	69% 3 8% 13% 7% 1	1938
March	1st to 10th	Night	61% 3 9% 22% 4	3418
	11th to 20th	Night	63% 3 10% 17% 6% 1	3480
	21st to end	Night	55% 3 8% 18% 13% 2	3817
April	1st to 10th	Night	57% 5% 11% 17% 10%	1938
	11th to 20th	Night	52% 4 11% 20% 12% 2	1873
	21st to end	Night	50% 5% 12% 19% 11% 3	1710
May	1st to 10th	Night	53% 5% 10% 19% 11% 2	2840
	11th to 20th	Night	48% 7% 15% 21% 8% 1	2625
	21st to end	Night	37% 7% 11% 26% 14% 5%	2739
June	1st to 10th	Night	44% 6% 12% 22% 15% 1	1520
	11th to 20th	Night	41% 7% 13% 23% 14% 2	1520
	21st to end	Night	41% 6% 13% 27% 12% 1	1520
July	1st to 10th	Night	38% 6% 12% 23% 18% 3	1480
	11th to 20th	Night	35% 6% 14% 27% 16% 2	1494
	21st to end	Night	38% 7% 16% 23% 16% 1	1672
August	1st to 10th	Night	35% 6% 16% 32% 10% 1	1600
	11th to 20th	Night	40% 7% 17% 27% 9% 1	1598
	21st to end	Night	39% 4 16% 26% 13% 2	1894
September	1st to 10th	Night	42% 5% 13% 26% 12% 2	1800
	11th to 20th	Night	38% 4 14% 26% 17% 1	1898
	21st to end	Night	49% 5% 12% 21% 12% 1	2020
October	1st to 10th	Night	48% 5% 11% 20% 15% 1	2160
	11th to 20th	Night	56% 4 13% 16% 10% 1	2160
	21st to end	Night	63% 4 10% 15% 7% 1	2376
November	1st to 10th	Night	52% 5% 11% 20% 10% 2	2362
	11th to 20th	Night	64% 3 11% 14% 6% 3	2660
	21st to end	Night	69% 4 11% 13% 3 1	2660
December	1st to 10th	Night	80% 2 7% 8% 2	2660
	11th to 20th	Night	77% 3 10% 8% 2	3288
	21st to end	Night	81% 2 8% 7% 1	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	34% 28% 25% 9% 3	191
	11th to 20th	Day	33% 33% 25% 6% 2 1	270
	21st to end	Day	32% 26% 31% 9% 1	297
February	1st to 10th	Day	40% 24% 29% 6% 1	270
	11th to 20th	Day	36% 32% 26% 5%	270
	21st to end	Day	42% 21% 30% 6% 1	274
March	1st to 10th	Day	33% 23% 28% 12% 3	460
	11th to 20th	Day	33% 21% 32% 11% 3 1	460
	21st to end	Day	36% 22% 24% 12% 5% 1	506
April	1st to 10th	Day	33% 21% 27% 14% 4 1	460
	11th to 20th	Day	34% 21% 21% 13% 9% 2	452
	21st to end	Day	30% 17% 32% 15% 5% 1	460
May	1st to 10th	Day	32% 19% 27% 13% 7% 2	463
	11th to 20th	Day	24% 14% 28% 22% 9% 3	487
	21st to end	Day	18% 13% 29% 22% 12% 6%	529
June	1st to 10th	Day	22% 15% 30% 22% 10% 2	490
	11th to 20th	Day	18% 13% 29% 23% 14% 3	490
	21st to end	Day	20% 12% 33% 24% 8% 2	490
July	1st to 10th	Day	13% 8% 29% 24% 19% 7%	485
	11th to 20th	Day	14% 9% 29% 26% 17% 5%	465
	21st to end	Day	15% 8% 34% 23% 14% 5%	488
August	1st to 10th	Day	12% 8% 28% 25% 17% 10%	446
	11th to 20th	Day	18% 8% 24% 26% 15% 9%	439
	21st to end	Day	17% 11% 25% 25% 14% 8%	495
September	1st to 10th	Day	19% 12% 24% 22% 16% 7%	450
	11th to 20th	Day	13% 7% 26% 23% 21% 9%	450
	21st to end	Day	20% 16% 26% 18% 15% 4	450
October	1st to 10th	Day	26% 11% 28% 16% 15% 4	450
	11th to 20th	Day	31% 19% 28% 15% 6% 1	450
	21st to end	Day	39% 17% 25% 15% 3	495
November	1st to 10th	Day	31% 17% 26% 18% 5% 3	347
	11th to 20th	Day	40% 22% 24% 9% 3 1	180
	21st to end	Day	36% 21% 37% 7%	180
December	1st to 10th	Day	41% 25% 23% 7% 3 1	180
	11th to 20th	Day	38% 26% 27% 8% 1	180
	21st to end	Day	37% 24% 32% 6%	198
January	1st to 10th	Night	32% 24% 30% 9% 4	760
	11th to 20th	Night	32% 25% 26% 14% 3	760
	21st to end	Night	27% 25% 30% 16% 3	836
February	1st to 10th	Night	32% 21% 29% 17%	760
	11th to 20th	Night	28% 25% 33% 12% 2	743
	21st to end	Night	32% 24% 28% 13% 3	628
March	1st to 10th	Night	30% 21% 28% 17% 4	760
	11th to 20th	Night	32% 19% 24% 19% 5%	760
	21st to end	Night	26% 19% 30% 19% 5% 1	836
April	1st to 10th	Night	29% 16% 30% 21% 4	760
	11th to 20th	Night	29% 13% 28% 21% 7% 1	749
	21st to end	Night	23% 10% 29% 31% 6% 1	570
May	1st to 10th	Night	25% 10% 21% 31% 13% 1	570
	11th to 20th	Night	18% 9% 28% 35% 9%	451
	21st to end	Night	16% 7% 27% 29% 19% 2	411
June	1st to 10th	Night	17% 5% 29% 34% 14% 1	380
	11th to 20th	Night	18% 9% 22% 38% 14%	380
	21st to end	Night	18% 6% 27% 34% 14% 1	380
July	1st to 10th	Night	11% 5% 19% 42% 21% 4	370
	11th to 20th	Night	15% 4 18% 36% 25% 2	414
	21st to end	Night	14% 4 16% 40% 24% 1	591
August	1st to 10th	Night	13% 3 15% 39% 28% 2	537
	11th to 20th	Night	14% 5% 16% 31% 32% 3	534
	21st to end	Night	15% 4 19% 31% 26% 4	706
September	1st to 10th	Night	20% 6% 19% 30% 21% 4	720
	11th to 20th	Night	17% 7% 16% 31% 25% 4	720
	21st to end	Night	24% 10% 20% 25% 18% 4	720
October	1st to 10th	Night	24% 8% 24% 25% 17% 2	720
	11th to 20th	Night	32% 11% 28% 22% 6% 1	720
	21st to end	Night	39% 10% 29% 18% 3	792
November	1st to 10th	Night	29% 13% 25% 25% 8%	740
	11th to 20th	Night	33% 19% 25% 17% 6% 1	760
	21st to end	Night	33% 22% 26% 16% 4	760
December	1st to 10th	Night	36% 25% 24% 11% 3	760
	11th to 20th	Night	32% 26% 25% 14% 3	760
	21st to end	Night	33% 23% 29% 13% 2	836

Page generated at 2024-07-13 10:19:51. Version ac07

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