Barrington
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Barrington clear sky chart from 2005-11-06 to 2024-01-16.

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	21% 10% 4 7% 6% 3 4 4 5% 6% 29%	75116
	Night	22% 11% 4 8% 6% 3 4 4 4 6% 27%	74681
Transparency	Day	55% 6% 11% 17% 9% 1	74827
	Night	59% 6% 10% 16% 8% 1	74505
Seeing	Day	26% 10% 24% 28% 11% 2	15926
	Night	27% 11% 25% 26% 10% 1	23718

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	20% 16% 6% 10% 9% 4 4 5% 5% 4 16%	1549
	11th to 20th	Day	24% 12% 5% 8% 7% 4 5% 4 6% 7% 17%	1666
	21st to end	Day	16% 10% 6% 11% 10% 5% 6% 4 5% 7% 20%	1782
February	1st to 10th	Day	21% 11% 7% 10% 9% 3 5% 6% 5% 5% 16%	1620
	11th to 20th	Day	19% 9% 6% 12% 9% 4 6% 4 5% 6% 20%	1573
	21st to end	Day	16% 11% 4 9% 9% 3 6% 4 6% 7% 26%	1426
March	1st to 10th	Day	18% 9% 4 9% 8% 4 6% 3 5% 6% 28%	1952
	11th to 20th	Day	17% 9% 3 7% 7% 4 4 4 5% 8% 34%	1980
	21st to end	Day	19% 8% 4 6% 5% 3 4 4 4 8% 34%	2178
April	1st to 10th	Day	25% 9% 4 6% 4 3 4 3 4 6% 31%	2081
	11th to 20th	Day	20% 7% 3 6% 5% 3 4 4 5% 5% 37%	2256
	21st to end	Day	23% 8% 3 5% 5% 2 3 4 4 7% 36%	2340
May	1st to 10th	Day	26% 10% 3 6% 6% 3 4 4 4 5% 28%	2340
	11th to 20th	Day	24% 8% 2 5% 4 3 4 3 4 8% 35%	2379
	21st to end	Day	23% 10% 3 6% 5% 3 4 4 5% 7% 31%	2724
June	1st to 10th	Day	28% 9% 3 5% 4 2 3 5% 5% 7% 30%	2520
	11th to 20th	Day	21% 10% 4 6% 5% 3 4 5% 5% 6% 33%	2638
	21st to end	Day	26% 12% 5% 7% 5% 2 4 4 5% 6% 25%	2700
July	1st to 10th	Day	23% 12% 5% 7% 4 3 5% 4 5% 7% 27%	2670
	11th to 20th	Day	24% 15% 6% 6% 5% 3 4 3 4 8% 22%	2449
	21st to end	Day	23% 12% 5% 9% 5% 3 4 4 5% 6% 26%	2548
August	1st to 10th	Day	18% 12% 4 8% 5% 3 4 4 5% 7% 31%	2327
	11th to 20th	Day	21% 11% 4 7% 5% 2 4 4 4 6% 31%	2304
	21st to end	Day	18% 9% 3 6% 4 3 3 4 5% 6% 39%	2517
September	1st to 10th	Day	15% 8% 4 5% 5% 2 3 4 4 6% 44%	2160
	11th to 20th	Day	18% 8% 3 5% 3 2 3 3 4 6% 44%	1988
	21st to end	Day	19% 8% 3 6% 4 2 3 3 5% 6% 41%	1980
October	1st to 10th	Day	20% 6% 2 5% 5% 3 4 5% 4 6% 40%	1805
	11th to 20th	Day	21% 8% 2 5% 5% 3 4 4 4 7% 37%	1800
	21st to end	Day	22% 8% 3 6% 7% 3 5% 5% 5% 6% 30%	1980
November	1st to 10th	Day	20% 8% 3 6% 5% 4 5% 5% 5% 7% 33%	1635
	11th to 20th	Day	21% 10% 5% 7% 7% 5% 4 5% 6% 7% 24%	1520
	21st to end	Day	19% 11% 6% 10% 9% 4 6% 5% 5% 5% 22%	1520
December	1st to 10th	Day	25% 14% 4 8% 9% 3 6% 5% 5% 5% 17%	1520
	11th to 20th	Day	30% 13% 4 8% 7% 4 4 5% 5% 6% 15%	1906
	21st to end	Day	23% 14% 6% 7% 5% 3 3 3 4 6% 25%	2783
January	1st to 10th	Night	22% 16% 7% 12% 8% 4 4 3 4 5% 15%	2611
	11th to 20th	Night	21% 14% 6% 9% 8% 4 5% 4 5% 8% 17%	2416
	21st to end	Night	16% 13% 8% 12% 10% 5% 5% 5% 6% 6% 15%	2574
February	1st to 10th	Night	21% 14% 7% 12% 9% 5% 5% 4 4 4 16%	2340
	11th to 20th	Night	20% 11% 5% 12% 9% 4 6% 5% 5% 5% 18%	2273
	21st to end	Night	14% 11% 6% 10% 7% 4 6% 4 4 7% 26%	1827
March	1st to 10th	Night	19% 10% 5% 9% 7% 4 5% 5% 5% 5% 27%	1994
	11th to 20th	Night	20% 9% 4 8% 8% 3 4 4 4 6% 29%	1979
	21st to end	Night	18% 9% 3 6% 5% 3 5% 4 5% 6% 35%	2178
April	1st to 10th	Night	25% 10% 4 6% 6% 3 4 3 5% 5% 28%	1878
	11th to 20th	Night	25% 8% 3 4 5% 3 4 4 3 6% 35%	1652
	21st to end	Night	24% 8% 3 6% 5% 3 4 3 5% 9% 32%	1620
May	1st to 10th	Night	26% 9% 3 7% 5% 3 5% 4 5% 6% 27%	1620
	11th to 20th	Night	27% 10% 3 6% 4 3 4 3 4 6% 31%	1511
	21st to end	Night	25% 12% 3 6% 4 3 4 3 5% 6% 28%	1550
June	1st to 10th	Night	26% 11% 3 6% 5% 2 4 5% 4 6% 28%	1440
	11th to 20th	Night	20% 11% 4 7% 4 2 4 4 4 5% 33%	1332
	21st to end	Night	30% 13% 3 6% 4 2 3 3 4 6% 24%	1260
July	1st to 10th	Night	23% 15% 4 6% 4 3 6% 4 4 7% 26%	1266
	11th to 20th	Night	26% 15% 6% 7% 6% 4 4 5% 4 6% 18%	1507
	21st to end	Night	26% 13% 5% 8% 5% 3 3 4 5% 5% 23%	1770
August	1st to 10th	Night	20% 12% 4 7% 5% 2 3 3 4 6% 32%	1612
	11th to 20th	Night	23% 13% 5% 7% 4 3 4 4 3 6% 29%	1596
	21st to end	Night	19% 10% 3 5% 5% 2 4 3 5% 8% 36%	1838
September	1st to 10th	Night	16% 9% 3 6% 4 3 3 3 4 6% 41%	1800
	11th to 20th	Night	21% 6% 2 4 5% 2 4 4 5% 7% 41%	1970
	21st to end	Night	22% 8% 3 5% 4 3 3 3 4 7% 38%	1980
October	1st to 10th	Night	21% 7% 3 6% 4 2 3 4 4 7% 38%	2155
	11th to 20th	Night	19% 6% 3 5% 4 3 3 5% 5% 8% 39%	2160
	21st to end	Night	23% 9% 3 7% 6% 3 4 4 5% 5% 31%	2376
November	1st to 10th	Night	19% 8% 4 6% 5% 3 4 4 4 6% 36%	2439
	11th to 20th	Night	18% 11% 5% 9% 8% 4 4 5% 5% 8% 23%	2660
	21st to end	Night	19% 13% 5% 9% 7% 3 5% 5% 6% 6% 22%	2660
December	1st to 10th	Night	25% 14% 5% 8% 8% 4 5% 4 4 7% 16%	2660
	11th to 20th	Night	26% 15% 6% 9% 7% 3 4 4 4 5% 17%	3293
	21st to end	Night	23% 12% 6% 8% 6% 3 5% 4 4 5% 24%	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	72% 6% 9% 9% 3	1550
	11th to 20th	Day	68% 7% 12% 12% 1	1666
	21st to end	Day	66% 7% 10% 14% 3	1782
February	1st to 10th	Day	69% 5% 11% 10% 5%	1620
	11th to 20th	Day	66% 6% 11% 13% 5%	1581
	21st to end	Day	58% 7% 12% 16% 7% 1	1426
March	1st to 10th	Day	58% 4 11% 17% 8% 2	1956
	11th to 20th	Day	49% 6% 12% 19% 12% 2	1980
	21st to end	Day	50% 5% 12% 19% 12% 2	2178
April	1st to 10th	Day	54% 5% 10% 16% 13% 1	2081
	11th to 20th	Day	48% 5% 12% 21% 13% 1	2256
	21st to end	Day	50% 5% 11% 19% 14% 2	2340
May	1st to 10th	Day	59% 5% 8% 19% 8% 2	2340
	11th to 20th	Day	49% 6% 8% 20% 15% 2	2383
	21st to end	Day	54% 7% 11% 18% 9% 1	2724
June	1st to 10th	Day	54% 6% 9% 21% 9% 1	2520
	11th to 20th	Day	52% 7% 9% 17% 12% 3	2638
	21st to end	Day	61% 6% 9% 14% 8% 1	2700
July	1st to 10th	Day	56% 7% 10% 15% 9% 2	2596
	11th to 20th	Day	62% 6% 8% 17% 6% 1	2373
	21st to end	Day	57% 8% 9% 18% 7% 1	2406
August	1st to 10th	Day	51% 8% 11% 20% 10% 1	2314
	11th to 20th	Day	54% 6% 10% 18% 10% 1	2304
	21st to end	Day	45% 6% 12% 22% 15% 1	2517
September	1st to 10th	Day	41% 6% 10% 25% 17% 2	2160
	11th to 20th	Day	44% 6% 10% 22% 18% 2	1988
	21st to end	Day	45% 5% 8% 23% 17% 2	1980
October	1st to 10th	Day	44% 6% 12% 24% 11% 2	1805
	11th to 20th	Day	48% 5% 13% 23% 10% 1	1800
	21st to end	Day	54% 6% 12% 17% 10% 1	1980
November	1st to 10th	Day	52% 7% 12% 19% 9% 1	1635
	11th to 20th	Day	59% 7% 12% 16% 6%	1520
	21st to end	Day	65% 7% 12% 13% 3	1520
December	1st to 10th	Day	70% 7% 9% 11% 4	1520
	11th to 20th	Day	71% 6% 10% 9% 4	1905
	21st to end	Day	63% 7% 15% 12% 3	2783
January	1st to 10th	Night	72% 6% 9% 11% 2	2611
	11th to 20th	Night	67% 7% 13% 10% 3	2416
	21st to end	Night	70% 6% 11% 11% 3	2574
February	1st to 10th	Night	73% 5% 10% 9% 3	2340
	11th to 20th	Night	67% 6% 9% 13% 5%	2276
	21st to end	Night	59% 6% 12% 15% 7% 1	1827
March	1st to 10th	Night	60% 6% 11% 14% 9% 1	2003
	11th to 20th	Night	57% 4 11% 14% 12% 1	1980
	21st to end	Night	51% 5% 10% 20% 12% 2	2178
April	1st to 10th	Night	57% 5% 8% 15% 13% 3	1878
	11th to 20th	Night	50% 4 10% 21% 13% 2	1652
	21st to end	Night	52% 4 10% 21% 11% 1	1620
May	1st to 10th	Night	56% 5% 9% 19% 9% 1	1620
	11th to 20th	Night	55% 4 5% 20% 14% 1	1512
	21st to end	Night	56% 6% 10% 17% 9% 1	1551
June	1st to 10th	Night	57% 6% 7% 22% 7% 1	1440
	11th to 20th	Night	53% 5% 8% 18% 13% 2	1332
	21st to end	Night	61% 6% 8% 13% 10% 1	1260
July	1st to 10th	Night	58% 5% 11% 17% 9% 1	1231
	11th to 20th	Night	67% 6% 7% 14% 6% 1	1459
	21st to end	Night	62% 5% 10% 15% 7% 1	1672
August	1st to 10th	Night	54% 5% 9% 20% 11%	1600
	11th to 20th	Night	58% 5% 9% 18% 10% 1	1596
	21st to end	Night	48% 5% 10% 22% 15%	1838
September	1st to 10th	Night	45% 5% 8% 24% 15% 3	1800
	11th to 20th	Night	44% 6% 8% 22% 18% 2	1970
	21st to end	Night	48% 5% 7% 22% 17% 1	1980
October	1st to 10th	Night	48% 5% 10% 22% 13% 2	2155
	11th to 20th	Night	45% 6% 12% 26% 10% 1	2160
	21st to end	Night	56% 5% 9% 18% 10% 1	2376
November	1st to 10th	Night	51% 7% 12% 20% 10% 1	2439
	11th to 20th	Night	60% 7% 11% 16% 5%	2660
	21st to end	Night	63% 7% 13% 13% 4	2660
December	1st to 10th	Night	70% 6% 11% 11% 3	2660
	11th to 20th	Night	72% 6% 7% 11% 3	3295
	21st to end	Night	65% 6% 12% 14% 3 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	31% 17% 32% 18% 2	370
	11th to 20th	Day	26% 16% 36% 19% 3	356
	21st to end	Day	21% 17% 36% 22% 4 1	374
February	1st to 10th	Day	28% 16% 37% 18% 1	340
	11th to 20th	Day	25% 22% 30% 19% 3	336
	21st to end	Day	21% 16% 37% 22% 4 1	322
March	1st to 10th	Day	22% 18% 35% 22% 3	420
	11th to 20th	Day	22% 22% 25% 26% 4	420
	21st to end	Day	22% 12% 34% 23% 8% 2	462
April	1st to 10th	Day	31% 13% 28% 22% 6%	420
	11th to 20th	Day	24% 10% 30% 32% 3 1	412
	21st to end	Day	26% 8% 27% 27% 11% 1	420
May	1st to 10th	Day	30% 9% 28% 26% 7% 1	423
	11th to 20th	Day	22% 6% 30% 30% 10% 1	525
	21st to end	Day	32% 4 20% 30% 12% 2	680
June	1st to 10th	Day	32% 4 18% 33% 12% 2	630
	11th to 20th	Day	23% 4 22% 35% 16% 1	630
	21st to end	Day	31% 4 20% 33% 11% 1	630
July	1st to 10th	Day	30% 3 12% 35% 17% 2	620
	11th to 20th	Day	30% 4 12% 33% 19% 3	547
	21st to end	Day	24% 3 13% 36% 22% 2	488
August	1st to 10th	Day	20% 4 15% 36% 21% 4	446
	11th to 20th	Day	28% 3 15% 31% 17% 5%	439
	21st to end	Day	21% 5% 17% 31% 22% 4	495
September	1st to 10th	Day	19% 3 17% 36% 22% 3	450
	11th to 20th	Day	23% 6% 24% 26% 16% 5%	450
	21st to end	Day	23% 3 25% 31% 14% 5%	450
October	1st to 10th	Day	23% 7% 23% 29% 16% 2	363
	11th to 20th	Day	22% 10% 24% 33% 10% 3	360
	21st to end	Day	26% 12% 26% 25% 10% 1	396
November	1st to 10th	Day	20% 17% 25% 27% 10% 1	365
	11th to 20th	Day	24% 21% 28% 20% 7%	370
	21st to end	Day	26% 19% 27% 23% 5% 1	370
December	1st to 10th	Day	32% 15% 28% 21% 4	370
	11th to 20th	Day	34% 19% 28% 16% 2	370
	21st to end	Day	28% 20% 30% 18% 2 1	407
January	1st to 10th	Night	31% 18% 29% 18% 4	832
	11th to 20th	Night	27% 17% 30% 22% 4	744
	21st to end	Night	23% 18% 35% 20% 4	792
February	1st to 10th	Night	29% 19% 31% 19% 2	720
	11th to 20th	Night	25% 21% 33% 17% 4	703
	21st to end	Night	18% 15% 37% 23% 6% 1	592
March	1st to 10th	Night	24% 13% 36% 23% 3	720
	11th to 20th	Night	22% 12% 33% 23% 9% 1	720
	21st to end	Night	22% 12% 31% 25% 7% 1	792
April	1st to 10th	Night	29% 11% 28% 27% 5%	618
	11th to 20th	Night	26% 6% 34% 27% 6% 1	534
	21st to end	Night	29% 4 25% 27% 13% 2	540
May	1st to 10th	Night	30% 5% 25% 29% 8% 2	540
	11th to 20th	Night	30% 5% 22% 31% 11% 1	532
	21st to end	Night	30% 4 17% 32% 15% 2	583
June	1st to 10th	Night	31% 3 20% 29% 16%	540
	11th to 20th	Night	23% 5% 16% 38% 18% 1	432
	21st to end	Night	34% 3 14% 30% 18% 2	360
July	1st to 10th	Night	29% 2 12% 37% 19% 1	356
	11th to 20th	Night	32% 2 9% 35% 19% 2	522
	21st to end	Night	30% 5% 9% 37% 18% 2	590
August	1st to 10th	Night	27% 4 11% 32% 22% 4	538
	11th to 20th	Night	27% 2 15% 30% 23% 4	532
	21st to end	Night	23% 3 13% 32% 23% 5%	594
September	1st to 10th	Night	19% 5% 15% 38% 20% 3	540
	11th to 20th	Night	24% 3 18% 30% 21% 4	710
	21st to end	Night	25% 5% 20% 30% 14% 6%	720
October	1st to 10th	Night	25% 6% 22% 30% 16% 1	720
	11th to 20th	Night	22% 9% 28% 26% 13% 3	720
	21st to end	Night	28% 12% 25% 26% 8%	792
November	1st to 10th	Night	23% 12% 26% 28% 10% 1	755
	11th to 20th	Night	24% 18% 27% 24% 8%	850
	21st to end	Night	25% 18% 29% 19% 7% 1	850
December	1st to 10th	Night	33% 15% 28% 19% 5%	850
	11th to 20th	Night	32% 21% 28% 16% 3	850
	21st to end	Night	28% 20% 30% 19% 3 1	935

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