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 2026-04-02.

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% 11% 6% 5% 4 3 5% 6% 27%	131541
	Night	15% 15% 6% 12% 6% 4 4 3 4 5% 25%	130269
Transparency	Day	58% 4 10% 18% 9% 1	135136
	Night	61% 4 10% 16% 8% 1	134760
Seeing	Day	27% 17% 28% 17% 9% 3	16297
	Night	26% 15% 25% 23% 10% 1	25920

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	15% 21% 9% 29% 7% 2 2 2 2 3 7%	4753
	11th to 20th	Day	9% 22% 10% 23% 9% 8% 3 2 2 2 8%	5246
	21st to end	Day	15% 15% 7% 17% 12% 9% 6% 3 3 3 10%	5780
February	1st to 10th	Day	16% 19% 7% 16% 8% 6% 4 3 3 3 15%	1890
	11th to 20th	Day	13% 18% 8% 19% 9% 4 4 3 3 4 15%	1843
	21st to end	Day	17% 19% 5% 14% 7% 3 4 3 4 5% 20%	1669
March	1st to 10th	Day	17% 14% 7% 12% 6% 3 3 2 3 5% 28%	5042
	11th to 20th	Day	12% 18% 7% 10% 4 4 3 3 4 6% 30%	5090
	21st to end	Day	21% 14% 6% 11% 4 3 3 2 4 4 26%	5586
April	1st to 10th	Day	16% 17% 4 8% 5% 4 4 4 4 6% 28%	2370
	11th to 20th	Day	20% 15% 2 6% 5% 4 3 4 5% 6% 31%	2393
	21st to end	Day	19% 13% 3 7% 4 4 4 3 4 5% 34%	2600
May	1st to 10th	Day	23% 11% 4 8% 5% 5% 4 3 5% 5% 28%	5888
	11th to 20th	Day	19% 12% 3 8% 5% 4 5% 4 5% 7% 27%	6129
	21st to end	Day	20% 8% 3 7% 4 5% 4 4 5% 7% 34%	6949
June	1st to 10th	Day	16% 7% 3 7% 4 4 4 3 7% 8% 35%	2800
	11th to 20th	Day	15% 7% 3 8% 5% 5% 5% 4 6% 9% 33%	2800
	21st to end	Day	15% 7% 2 6% 5% 4 5% 4 7% 8% 37%	2800
July	1st to 10th	Day	9% 6% 3 6% 5% 6% 6% 5% 7% 10% 38%	6360
	11th to 20th	Day	11% 8% 3 8% 5% 5% 5% 4 7% 9% 34%	6205
	21st to end	Day	11% 6% 2 7% 5% 5% 5% 5% 6% 7% 42%	6424
August	1st to 10th	Day	16% 7% 3 7% 5% 5% 5% 5% 6% 8% 33%	4234
	11th to 20th	Day	14% 8% 4 8% 6% 6% 7% 5% 8% 10% 26%	4174
	21st to end	Day	12% 7% 2 6% 5% 5% 5% 5% 7% 11% 36%	4425
September	1st to 10th	Day	17% 8% 2 7% 4 4 4 4 5% 8% 37%	2400
	11th to 20th	Day	14% 5% 3 6% 4 4 4 4 6% 8% 41%	2285
	21st to end	Day	19% 9% 4 9% 5% 5% 4 4 6% 7% 29%	2155
October	1st to 10th	Day	19% 8% 3 7% 4 5% 4 4 6% 7% 34%	2000
	11th to 20th	Day	20% 12% 3 10% 5% 4 5% 3 5% 5% 28%	2000
	21st to end	Day	24% 16% 4 8% 5% 5% 4 3 4 5% 22%	2200
November	1st to 10th	Day	14% 17% 4 9% 4 4 5% 3 5% 6% 29%	1897
	11th to 20th	Day	17% 22% 5% 11% 5% 3 3 3 5% 5% 21%	1680
	21st to end	Day	18% 27% 6% 11% 5% 4 3 3 4 5% 14%	1680
December	1st to 10th	Day	17% 31% 12% 15% 5% 3 2 2 3 3 6%	2680
	11th to 20th	Day	18% 22% 8% 17% 7% 3 2 2 3 4 12%	3066
	21st to end	Day	20% 24% 9% 14% 6% 4 4 2 3 4 10%	4048
January	1st to 10th	Night	13% 21% 10% 31% 8% 4 2 2 2 2 6%	8137
	11th to 20th	Night	9% 20% 11% 25% 9% 6% 4 2 3 3 7%	7639
	21st to end	Night	15% 17% 8% 15% 9% 7% 7% 3 3 4 11%	8401
February	1st to 10th	Night	16% 19% 6% 16% 8% 6% 4 3 4 4 16%	2730
	11th to 20th	Night	13% 17% 7% 19% 9% 5% 5% 3 4 4 15%	2663
	21st to end	Night	16% 15% 6% 17% 8% 4 4 3 3 4 20%	2134
March	1st to 10th	Night	17% 16% 6% 10% 8% 4 3 2 4 4 25%	5018
	11th to 20th	Night	14% 14% 7% 9% 4 4 3 3 4 6% 33%	5089
	21st to end	Night	15% 14% 7% 10% 5% 4 3 3 5% 5% 28%	5588
April	1st to 10th	Night	17% 17% 4 9% 4 4 4 4 5% 5% 28%	2052
	11th to 20th	Night	18% 13% 3 6% 3 4 4 3 5% 6% 34%	1973
	21st to end	Night	14% 12% 4 7% 5% 4 4 4 5% 6% 34%	1800
May	1st to 10th	Night	26% 12% 3 6% 4 3 4 3 4 6% 29%	4053
	11th to 20th	Night	18% 10% 4 8% 5% 4 4 3 4 6% 35%	3760
	21st to end	Night	20% 9% 2 6% 3 3 3 3 6% 8% 38%	3926
June	1st to 10th	Night	13% 6% 3 8% 6% 4 4 4 6% 9% 37%	1600
	11th to 20th	Night	15% 7% 2 6% 4 5% 4 4 7% 8% 38%	1600
	21st to end	Night	14% 7% 2 6% 4 4 4 4 6% 9% 41%	1600
July	1st to 10th	Night	11% 8% 3 6% 5% 4 4 3 6% 10% 40%	3600
	11th to 20th	Night	11% 6% 3 6% 5% 4 4 4 7% 9% 40%	3738
	21st to end	Night	10% 6% 2 6% 4 4 4 4 6% 8% 45%	4428
August	1st to 10th	Night	11% 8% 3 8% 4 5% 4 4 6% 8% 38%	2915
	11th to 20th	Night	15% 8% 3 7% 4 5% 5% 4 6% 8% 36%	2875
	21st to end	Night	9% 6% 3 6% 4 4 5% 4 6% 9% 44%	3439
September	1st to 10th	Night	14% 7% 2 6% 4 3 4 3 6% 7% 44%	2000
	11th to 20th	Night	12% 6% 2 5% 3 3 4 3 4 7% 49%	2110
	21st to end	Night	20% 8% 3 7% 4 5% 5% 4 6% 7% 33%	2245
October	1st to 10th	Night	17% 8% 3 6% 5% 5% 4 3 5% 6% 39%	2400
	11th to 20th	Night	20% 11% 3 7% 5% 4 4 3 5% 7% 30%	2400
	21st to end	Night	26% 12% 3 7% 5% 4 3 3 5% 5% 27%	2640
November	1st to 10th	Night	15% 17% 3 7% 4 3 3 3 5% 5% 33%	2618
	11th to 20th	Night	17% 19% 5% 8% 6% 5% 4 4 5% 5% 21%	2940
	21st to end	Night	17% 23% 7% 10% 5% 4 4 3 4 5% 18%	2940
December	1st to 10th	Night	15% 24% 12% 16% 6% 5% 4 2 3 3 9%	4720
	11th to 20th	Night	18% 24% 9% 14% 6% 4 3 3 3 3 13%	5348
	21st to end	Night	19% 23% 8% 14% 7% 4 3 3 3 4 11%	7150

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	85% 2 6% 6% 2	4754
	11th to 20th	Day	85% 2 5% 6% 3	5280
	21st to end	Day	80% 2 8% 7% 3	5780
February	1st to 10th	Day	76% 3 8% 9% 4	1890
	11th to 20th	Day	74% 3 7% 11% 5%	1852
	21st to end	Day	67% 3 9% 14% 5% 1	1669
March	1st to 10th	Day	61% 3 12% 19% 6%	5045
	11th to 20th	Day	58% 3 16% 17% 6% 1	5090
	21st to end	Day	62% 3 6% 18% 11% 1	5586
April	1st to 10th	Day	59% 3 10% 17% 11% 1	2370
	11th to 20th	Day	53% 5% 9% 20% 10% 2	2393
	21st to end	Day	54% 3 10% 18% 13% 2	2600
May	1st to 10th	Day	58% 5% 7% 18% 8% 3	5897
	11th to 20th	Day	56% 5% 9% 20% 10% 1	6133
	21st to end	Day	50% 5% 11% 20% 12% 2	6949
June	1st to 10th	Day	47% 5% 11% 21% 14% 1	2800
	11th to 20th	Day	47% 7% 13% 22% 11% 1	2800
	21st to end	Day	44% 6% 13% 23% 14%	2800
July	1st to 10th	Day	40% 6% 12% 24% 17% 1	6290
	11th to 20th	Day	45% 6% 12% 20% 16%	6130
	21st to end	Day	40% 6% 11% 25% 17% 1	6240
August	1st to 10th	Day	47% 6% 13% 22% 11%	4221
	11th to 20th	Day	50% 8% 14% 22% 7%	4213
	21st to end	Day	41% 7% 11% 30% 11% 1	4425
September	1st to 10th	Day	46% 5% 11% 24% 13% 1	2400
	11th to 20th	Day	40% 7% 10% 28% 15%	2285
	21st to end	Day	54% 5% 10% 21% 9% 1	2155
October	1st to 10th	Day	44% 5% 12% 22% 16% 1	3260
	11th to 20th	Day	50% 4 14% 17% 12% 4	3240
	21st to end	Day	52% 4 14% 22% 8% 1	3538
November	1st to 10th	Day	55% 5% 10% 17% 10% 2	1897
	11th to 20th	Day	65% 4 10% 15% 6% 2	1680
	21st to end	Day	73% 3 10% 9% 3 1	1680
December	1st to 10th	Day	86% 2 5% 6% 1	2680
	11th to 20th	Day	78% 3 9% 9% 1	3066
	21st to end	Day	80% 2 9% 7% 2	4048
January	1st to 10th	Night	89% 1 5% 4 1	8137
	11th to 20th	Night	84% 2 6% 4 2	7680
	21st to end	Night	80% 2 7% 8% 3	8401
February	1st to 10th	Night	74% 2 8% 11% 4	2730
	11th to 20th	Night	74% 4 7% 10% 4	2665
	21st to end	Night	70% 3 8% 12% 7% 1	2134
March	1st to 10th	Night	64% 3 10% 18% 5%	5028
	11th to 20th	Night	53% 3 13% 21% 7% 2	5090
	21st to end	Night	58% 4 7% 15% 13% 2	5588
April	1st to 10th	Night	58% 5% 10% 16% 10% 1	2052
	11th to 20th	Night	52% 4 11% 20% 12% 2	1973
	21st to end	Night	50% 5% 12% 20% 11% 3	1800
May	1st to 10th	Night	58% 4 8% 15% 11% 4	4060
	11th to 20th	Night	51% 6% 12% 20% 9% 1	3761
	21st to end	Night	46% 6% 10% 24% 11% 3	3927
June	1st to 10th	Night	44% 6% 11% 22% 15% 2	1600
	11th to 20th	Night	42% 7% 13% 23% 14% 2	1600
	21st to end	Night	40% 6% 14% 26% 13% 1	1600
July	1st to 10th	Night	41% 5% 12% 25% 14% 2	3560
	11th to 20th	Night	40% 6% 14% 26% 14% 1	3690
	21st to end	Night	36% 6% 12% 22% 22% 1	4297
August	1st to 10th	Night	44% 6% 13% 27% 9% 1	2904
	11th to 20th	Night	44% 7% 15% 26% 8%	2902
	21st to end	Night	37% 5% 14% 33% 10% 1	3439
September	1st to 10th	Night	40% 5% 12% 28% 14% 2	2000
	11th to 20th	Night	36% 4 14% 28% 17% 1	2110
	21st to end	Night	51% 5% 11% 20% 11% 1	2245
October	1st to 10th	Night	45% 5% 8% 23% 20% 1	3920
	11th to 20th	Night	49% 4 11% 17% 15% 3	3899
	21st to end	Night	46% 3 14% 24% 12% 1	4252
November	1st to 10th	Night	53% 5% 10% 21% 10% 2	2618
	11th to 20th	Night	65% 3 10% 13% 6% 3	2940
	21st to end	Night	70% 3 10% 12% 3 1	2940
December	1st to 10th	Night	82% 3 7% 6% 2	4720
	11th to 20th	Night	77% 3 7% 10% 2	5348
	21st to end	Night	78% 3 8% 9% 2	7150

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	37% 27% 25% 8% 3	235
	11th to 20th	Day	35% 34% 24% 5% 2 1	330
	21st to end	Day	35% 26% 29% 8% 1	363
February	1st to 10th	Day	38% 24% 29% 8% 2	330
	11th to 20th	Day	37% 31% 28% 5%	330
	21st to end	Day	39% 24% 31% 5% 1	328
March	1st to 10th	Day	33% 24% 28% 12% 3	540
	11th to 20th	Day	36% 21% 29% 10% 3 1	540
	21st to end	Day	38% 21% 25% 11% 4 1	594
April	1st to 10th	Day	35% 21% 26% 14% 4 1	504
	11th to 20th	Day	34% 21% 21% 13% 8% 2	492
	21st to end	Day	30% 17% 31% 16% 4 1	500
May	1st to 10th	Day	32% 19% 28% 13% 7% 2	503
	11th to 20th	Day	26% 14% 27% 22% 8% 3	527
	21st to end	Day	20% 13% 28% 21% 12% 5%	573
June	1st to 10th	Day	22% 15% 31% 21% 10% 2	530
	11th to 20th	Day	19% 14% 29% 22% 13% 3	530
	21st to end	Day	19% 12% 33% 24% 9% 2	530
July	1st to 10th	Day	13% 8% 28% 26% 19% 6%	525
	11th to 20th	Day	14% 10% 28% 27% 16% 6%	524
	21st to end	Day	15% 8% 32% 25% 15% 6%	576
August	1st to 10th	Day	13% 9% 27% 25% 17% 9%	526
	11th to 20th	Day	18% 10% 24% 26% 14% 8%	519
	21st to end	Day	16% 11% 25% 26% 14% 8%	583
September	1st to 10th	Day	19% 12% 23% 21% 18% 8%	530
	11th to 20th	Day	12% 6% 25% 22% 24% 11%	530
	21st to end	Day	21% 16% 27% 18% 15% 4	530
October	1st to 10th	Day	23% 12% 28% 18% 15% 4	530
	11th to 20th	Day	29% 19% 29% 14% 6% 2	530
	21st to end	Day	38% 16% 27% 16% 3	583
November	1st to 10th	Day	32% 18% 27% 16% 5% 2	410
	11th to 20th	Day	40% 21% 26% 9% 3 1	220
	21st to end	Day	39% 21% 34% 6%	220
December	1st to 10th	Day	40% 25% 25% 7% 2	220
	11th to 20th	Day	39% 25% 27% 7% 1	220
	21st to end	Day	38% 23% 31% 7% 1	242
January	1st to 10th	Night	33% 25% 30% 9% 4	840
	11th to 20th	Night	32% 26% 27% 13% 2	840
	21st to end	Night	27% 26% 29% 15% 2	924
February	1st to 10th	Night	32% 21% 29% 18%	840
	11th to 20th	Night	29% 25% 32% 12% 1	823
	21st to end	Night	31% 25% 28% 13% 3	692
March	1st to 10th	Night	30% 21% 29% 17% 3	840
	11th to 20th	Night	32% 19% 24% 19% 5%	840
	21st to end	Night	27% 19% 30% 18% 5% 1	924
April	1st to 10th	Night	31% 16% 29% 21% 3	805
	11th to 20th	Night	30% 13% 28% 21% 7% 1	789
	21st to end	Night	23% 11% 29% 31% 6% 1	600
May	1st to 10th	Night	26% 10% 21% 31% 12% 1	600
	11th to 20th	Night	19% 9% 28% 35% 8%	475
	21st to end	Night	17% 7% 28% 28% 18% 2	433
June	1st to 10th	Night	18% 5% 28% 35% 14% 1	400
	11th to 20th	Night	18% 9% 22% 37% 14%	400
	21st to end	Night	17% 5% 27% 34% 16% 1	400
July	1st to 10th	Night	10% 4 18% 43% 20% 4	390
	11th to 20th	Night	14% 4 18% 37% 25% 2	448
	21st to end	Night	13% 4 16% 40% 26% 1	657
August	1st to 10th	Night	12% 4 15% 39% 28% 2	597
	11th to 20th	Night	14% 5% 15% 31% 32% 3	594
	21st to end	Night	14% 4 19% 32% 27% 4	785
September	1st to 10th	Night	19% 7% 19% 30% 22% 4	800
	11th to 20th	Night	15% 6% 14% 32% 28% 4	800
	21st to end	Night	25% 10% 19% 25% 18% 4	800
October	1st to 10th	Night	23% 8% 24% 25% 19% 2	800
	11th to 20th	Night	30% 10% 29% 23% 7% 1	800
	21st to end	Night	37% 10% 30% 20% 4	880
November	1st to 10th	Night	30% 14% 25% 24% 7%	820
	11th to 20th	Night	33% 19% 24% 17% 5% 1	840
	21st to end	Night	35% 21% 26% 15% 4	840
December	1st to 10th	Night	36% 25% 24% 12% 3	840
	11th to 20th	Night	33% 26% 25% 14% 3	840
	21st to end	Night	34% 22% 29% 13% 2	924

Page generated at 2026-03-30 02:18:43. Version ac07

Copyright © 2026 Attilla Danko.