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 2024-12-09.

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% 9% 5% 4 4 4 5% 7% 28%	101629
	Night	17% 14% 5% 10% 5% 4 4 3 5% 6% 27%	98144
Transparency	Day	55% 5% 11% 19% 9% 1	105235
	Night	58% 4 11% 18% 9% 1	102626
Seeing	Day	26% 17% 28% 17% 9% 3	14665
	Night	26% 15% 25% 23% 10% 1	24197

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% 5% 2 6% 5% 6% 6% 5% 7% 11% 36%	4440
	11th to 20th	Day	11% 7% 2 7% 5% 4 5% 4 8% 9% 36%	4327
	21st to end	Day	9% 7% 3 8% 5% 5% 6% 5% 7% 7% 38%	4466
August	1st to 10th	Day	17% 7% 3 7% 5% 5% 5% 5% 6% 8% 32%	4104
	11th to 20th	Day	14% 8% 4 8% 6% 6% 7% 5% 8% 10% 25%	4044
	21st to end	Day	13% 7% 2 6% 5% 5% 5% 5% 7% 11% 35%	4290
September	1st to 10th	Day	18% 8% 2 7% 4 4 4 4 5% 8% 36%	2280
	11th to 20th	Day	14% 5% 3 6% 4 4 4 4 6% 8% 40%	2171
	21st to end	Day	19% 9% 4 9% 5% 5% 4 4 5% 7% 29%	2047
October	1st to 10th	Day	20% 9% 3 7% 5% 5% 4 4 6% 7% 32%	1900
	11th to 20th	Day	20% 12% 3 10% 5% 4 4 3 5% 5% 28%	1900
	21st to end	Day	24% 16% 4 8% 5% 5% 4 3 4 5% 22%	2090
November	1st to 10th	Day	13% 17% 4 9% 4 4 5% 3 5% 6% 30%	1805
	11th to 20th	Day	17% 22% 5% 10% 5% 4 3 3 5% 5% 21%	1600
	21st to end	Day	18% 27% 5% 11% 5% 4 3 4 5% 5% 15%	1600
December	1st to 10th	Day	17% 29% 10% 13% 5% 3 3 2 4 3 10%	1584
	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	12% 8% 3 7% 5% 4 4 3 6% 9% 40%	2520
	11th to 20th	Night	11% 6% 2 5% 5% 4 4 4 7% 9% 43%	2616
	21st to end	Night	10% 6% 2 6% 5% 5% 5% 5% 6% 8% 42%	3087
August	1st to 10th	Night	12% 8% 3 8% 4 5% 4 4 6% 7% 37%	2825
	11th to 20th	Night	15% 8% 3 8% 4 5% 5% 4 6% 8% 35%	2785
	21st to end	Night	9% 6% 3 6% 4 4 5% 4 6% 9% 44%	3334
September	1st to 10th	Night	15% 8% 2 6% 4 3 4 3 6% 6% 43%	1900
	11th to 20th	Night	13% 6% 2 5% 4 3 4 3 4 7% 48%	2004
	21st to end	Night	20% 8% 3 7% 4 5% 5% 4 5% 6% 33%	2133
October	1st to 10th	Night	17% 9% 3 6% 5% 5% 4 3 5% 6% 37%	2280
	11th to 20th	Night	20% 12% 3 7% 5% 4 4 3 5% 7% 29%	2280
	21st to end	Night	26% 12% 3 7% 5% 4 3 3 5% 5% 27%	2508
November	1st to 10th	Night	15% 16% 3 7% 5% 3 3 3 5% 5% 34%	2490
	11th to 20th	Night	18% 19% 4 8% 6% 5% 4 4 5% 5% 21%	2800
	21st to end	Night	17% 23% 7% 10% 5% 4 4 3 4 5% 18%	2800
December	1st to 10th	Night	19% 27% 10% 12% 5% 4 4 2 3 3 11%	2779
	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	41% 6% 12% 24% 15% 1	4370
	11th to 20th	Day	42% 6% 11% 22% 17%	4252
	21st to end	Day	43% 7% 12% 23% 15% 1	4324
August	1st to 10th	Day	48% 6% 12% 22% 11%	4091
	11th to 20th	Day	50% 8% 14% 22% 6%	4083
	21st to end	Day	41% 7% 11% 29% 11% 1	4290
September	1st to 10th	Day	46% 5% 11% 23% 13% 1	2280
	11th to 20th	Day	41% 7% 10% 26% 15% 1	2171
	21st to end	Day	54% 5% 10% 21% 9% 1	2047
October	1st to 10th	Day	45% 6% 13% 21% 15% 1	3160
	11th to 20th	Day	50% 4 14% 16% 12% 4	3140
	21st to end	Day	51% 4 14% 22% 8% 1	3428
November	1st to 10th	Day	55% 5% 11% 17% 11% 2	1805
	11th to 20th	Day	64% 4 10% 15% 6% 2	1600
	21st to end	Day	72% 3 11% 10% 3 1	1600
December	1st to 10th	Day	80% 2 7% 8% 2	1584
	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	43% 6% 12% 22% 15% 2	2480
	11th to 20th	Night	37% 5% 15% 27% 15% 1	2568
	21st to end	Night	38% 7% 14% 23% 18% 1	2988
August	1st to 10th	Night	45% 5% 13% 28% 9% 1	2814
	11th to 20th	Night	45% 7% 15% 26% 7%	2812
	21st to end	Night	37% 5% 14% 33% 10% 1	3334
September	1st to 10th	Night	41% 5% 12% 26% 14% 2	1900
	11th to 20th	Night	37% 4 14% 26% 18% 1	2004
	21st to end	Night	52% 5% 11% 20% 11% 1	2133
October	1st to 10th	Night	45% 5% 8% 22% 19% 1	3800
	11th to 20th	Night	50% 4 11% 16% 15% 3	3779
	21st to end	Night	46% 3 15% 24% 12% 1	4120
November	1st to 10th	Night	52% 5% 10% 21% 10% 2	2490
	11th to 20th	Night	65% 3 10% 13% 6% 3	2800
	21st to end	Night	70% 4 11% 13% 3 1	2800
December	1st to 10th	Night	80% 3 7% 8% 2	2779
	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% 10% 29% 26% 16% 6%	484
	21st to end	Day	14% 8% 34% 23% 15% 6%	532
August	1st to 10th	Day	14% 9% 27% 24% 16% 9%	486
	11th to 20th	Day	18% 10% 24% 25% 14% 9%	479
	21st to end	Day	16% 11% 25% 27% 14% 8%	539
September	1st to 10th	Day	19% 12% 24% 21% 16% 8%	490
	11th to 20th	Day	13% 7% 26% 22% 22% 11%	490
	21st to end	Day	22% 16% 26% 18% 14% 4	490
October	1st to 10th	Day	24% 12% 28% 17% 15% 4	490
	11th to 20th	Day	30% 18% 28% 15% 7% 2	490
	21st to end	Day	37% 17% 26% 16% 3	539
November	1st to 10th	Day	31% 18% 27% 17% 5% 2	378
	11th to 20th	Day	39% 23% 27% 9% 3 1	200
	21st to end	Day	38% 22% 34% 7%	200
December	1st to 10th	Day	40% 25% 25% 7% 3 1	196
	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% 3 19% 37% 25% 2	425
	21st to end	Night	14% 4 16% 40% 25% 1	624
August	1st to 10th	Night	13% 4 14% 39% 28% 2	567
	11th to 20th	Night	15% 6% 15% 30% 32% 2	564
	21st to end	Night	14% 4 19% 32% 27% 4	746
September	1st to 10th	Night	19% 7% 19% 30% 21% 4	760
	11th to 20th	Night	16% 6% 15% 31% 27% 4	760
	21st to end	Night	25% 10% 19% 25% 17% 4	760
October	1st to 10th	Night	24% 8% 24% 25% 18% 2	760
	11th to 20th	Night	31% 11% 27% 22% 7% 1	760
	21st to end	Night	37% 10% 30% 19% 4	836
November	1st to 10th	Night	28% 14% 25% 24% 8%	780
	11th to 20th	Night	33% 19% 24% 17% 5% 1	800
	21st to end	Night	34% 21% 26% 15% 4	800
December	1st to 10th	Night	36% 26% 24% 11% 3	795
	11th to 20th	Night	32% 26% 25% 14% 3	760
	21st to end	Night	33% 23% 29% 13% 2	836

Page generated at 2024-12-06 03:54:50. Version ac07

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