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 2024-12-09.

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	22% 12% 4 8% 5% 4 4 3 5% 6% 28%	102236
	Night	22% 13% 4 9% 5% 4 4 3 4 6% 26%	97578
Transparency	Day	56% 6% 10% 17% 9% 1	105826
	Night	59% 5% 10% 16% 9% 1	102065
Seeing	Day	26% 10% 24% 28% 11% 2	17191
	Night	26% 11% 25% 26% 11% 1	24875

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% 13% 5% 12% 6% 5% 5% 4 5% 5% 19%	2571
	11th to 20th	Day	20% 11% 6% 14% 6% 6% 6% 4 7% 6% 16%	2840
	21st to end	Day	22% 12% 5% 10% 6% 5% 4 4 5% 6% 21%	3124
February	1st to 10th	Day	22% 15% 5% 11% 8% 5% 4 5% 5% 5% 16%	1710
	11th to 20th	Day	18% 11% 5% 13% 8% 6% 5% 3 5% 6% 21%	1663
	21st to end	Day	16% 11% 4 10% 8% 5% 5% 3 5% 7% 27%	1513
March	1st to 10th	Day	28% 12% 4 8% 5% 4 4 3 4 5% 23%	3394
	11th to 20th	Day	16% 11% 3 9% 5% 4 4 4 5% 8% 30%	3480
	21st to end	Day	29% 11% 4 9% 5% 4 4 2 4 6% 24%	3816
April	1st to 10th	Day	25% 10% 4 6% 4 3 3 3 4 6% 32%	2197
	11th to 20th	Day	20% 8% 3 7% 4 4 4 3 4 5% 37%	2383
	21st to end	Day	22% 8% 2 6% 4 3 4 3 5% 7% 37%	2470
May	1st to 10th	Day	23% 9% 4 9% 6% 5% 5% 4 5% 6% 25%	4106
	11th to 20th	Day	23% 12% 3 8% 4 4 3 3 4 6% 29%	4229
	21st to end	Day	21% 13% 6% 8% 4 3 3 3 4 5% 29%	4836
June	1st to 10th	Day	27% 10% 2 6% 4 3 3 3 5% 7% 30%	2660
	11th to 20th	Day	20% 10% 3 6% 4 3 4 3 5% 6% 34%	2785
	21st to end	Day	26% 13% 4 8% 4 3 4 3 5% 5% 24%	2850
July	1st to 10th	Day	29% 17% 4 6% 3 3 3 2 4 5% 24%	4702
	11th to 20th	Day	30% 18% 5% 8% 4 3 3 2 3 6% 18%	4313
	21st to end	Day	21% 11% 4 10% 6% 4 4 3 4 6% 26%	4467
August	1st to 10th	Day	30% 15% 4 9% 4 3 3 2 4 5% 21%	4105
	11th to 20th	Day	18% 12% 5% 10% 5% 3 4 3 4 5% 31%	4045
	21st to end	Day	12% 8% 3 8% 5% 3 3 3 5% 6% 46%	4419
September	1st to 10th	Day	15% 9% 4 6% 4 3 3 3 4 6% 43%	2280
	11th to 20th	Day	17% 8% 3 6% 3 3 3 3 4 6% 44%	2098
	21st to end	Day	19% 9% 3 7% 3 3 3 3 4 6% 40%	2090
October	1st to 10th	Day	20% 6% 2 6% 4 4 5% 4 4 6% 39%	1905
	11th to 20th	Day	20% 7% 2 6% 4 4 4 3 5% 7% 37%	1900
	21st to end	Day	21% 9% 3 7% 6% 5% 4 4 5% 6% 31%	2089
November	1st to 10th	Day	20% 9% 2 7% 4 5% 4 4 5% 7% 33%	1723
	11th to 20th	Day	21% 11% 4 8% 6% 5% 5% 4 6% 7% 24%	1600
	21st to end	Day	19% 13% 5% 11% 7% 6% 5% 4 5% 4 21%	1600
December	1st to 10th	Day	24% 16% 4 9% 8% 4 5% 4 5% 5% 17%	1584
	11th to 20th	Day	30% 14% 4 9% 6% 5% 3 4 5% 5% 15%	1906
	21st to end	Day	23% 15% 5% 8% 5% 4 3 3 4 6% 25%	2783
January	1st to 10th	Night	18% 16% 7% 17% 6% 4 4 3 4 5% 16%	4365
	11th to 20th	Night	17% 14% 6% 13% 7% 5% 5% 3 5% 6% 18%	4120
	21st to end	Night	20% 15% 6% 14% 7% 5% 4 3 5% 5% 16%	4532
February	1st to 10th	Night	21% 16% 6% 13% 8% 6% 4 3 4 4 15%	2470
	11th to 20th	Night	19% 12% 4 12% 9% 5% 6% 4 5% 6% 19%	2403
	21st to end	Night	14% 13% 4 11% 6% 6% 5% 3 4 6% 27%	1938
March	1st to 10th	Night	26% 12% 3 10% 6% 4 3 3 3 3 25%	3445
	11th to 20th	Night	16% 12% 5% 11% 6% 4 4 4 5% 7% 28%	3479
	21st to end	Night	32% 10% 4 7% 3 3 3 2 3 4 27%	3816
April	1st to 10th	Night	24% 12% 4 7% 5% 4 3 2 5% 5% 29%	1982
	11th to 20th	Night	25% 10% 2 5% 4 3 3 3 4 6% 35%	1744
	21st to end	Night	23% 9% 3 7% 4 3 3 2 5% 8% 33%	1710
May	1st to 10th	Night	24% 13% 4 7% 5% 4 4 3 5% 6% 25%	2834
	11th to 20th	Night	25% 12% 4 8% 4 3 4 3 4 6% 28%	2666
	21st to end	Night	21% 17% 5% 7% 4 3 3 2 4 5% 29%	2749
June	1st to 10th	Night	26% 13% 3 7% 4 3 4 4 4 6% 28%	1520
	11th to 20th	Night	19% 12% 3 8% 4 3 4 3 5% 5% 34%	1406
	21st to end	Night	30% 14% 3 7% 4 3 3 2 5% 5% 23%	1330
July	1st to 10th	Night	33% 15% 3 7% 3 4 4 3 4 5% 20%	2230
	11th to 20th	Night	32% 21% 5% 8% 4 3 2 3 3 3 15%	2649
	21st to end	Night	24% 13% 4 9% 5% 4 3 3 5% 5% 26%	3087
August	1st to 10th	Night	25% 18% 4 9% 4 2 3 3 4 5% 24%	2825
	11th to 20th	Night	23% 13% 5% 8% 3 4 3 3 4 6% 30%	2782
	21st to end	Night	13% 10% 3 7% 4 3 3 3 4 7% 42%	3236
September	1st to 10th	Night	16% 10% 3 6% 3 4 3 3 5% 6% 41%	1900
	11th to 20th	Night	20% 6% 2 5% 4 3 4 3 5% 6% 42%	2080
	21st to end	Night	22% 8% 3 6% 4 3 4 2 4 6% 37%	2090
October	1st to 10th	Night	21% 8% 3 7% 3 3 3 3 5% 7% 38%	2275
	11th to 20th	Night	18% 6% 2 6% 4 4 4 4 5% 8% 39%	2280
	21st to end	Night	22% 10% 3 8% 5% 4 4 3 5% 5% 32%	2508
November	1st to 10th	Night	18% 9% 3 7% 4 4 4 3 4 7% 37%	2571
	11th to 20th	Night	18% 13% 4 9% 7% 5% 5% 4 5% 7% 23%	2800
	21st to end	Night	19% 14% 5% 10% 6% 4 5% 4 6% 6% 22%	2800
December	1st to 10th	Night	24% 15% 5% 9% 7% 6% 4 3 5% 6% 16%	2779
	11th to 20th	Night	26% 16% 5% 11% 6% 5% 4 3 4 5% 16%	3293
	21st to end	Night	23% 13% 5% 10% 5% 4 4 3 4 4 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	66% 7% 14% 11% 2	2572
	11th to 20th	Day	67% 8% 12% 10% 3	2840
	21st to end	Day	64% 8% 12% 12% 3	3124
February	1st to 10th	Day	70% 6% 10% 9% 5%	1710
	11th to 20th	Day	65% 6% 10% 13% 5%	1671
	21st to end	Day	57% 7% 12% 16% 7% 2	1513
March	1st to 10th	Day	64% 4 10% 15% 6% 1	3398
	11th to 20th	Day	49% 10% 15% 16% 9% 1	3480
	21st to end	Day	63% 5% 8% 15% 9% 1	3816
April	1st to 10th	Day	54% 5% 10% 17% 13% 1	2197
	11th to 20th	Day	48% 5% 12% 21% 14% 1	2383
	21st to end	Day	48% 5% 11% 19% 16% 2	2470
May	1st to 10th	Day	56% 11% 11% 16% 5% 1	4120
	11th to 20th	Day	54% 8% 10% 17% 9% 1	4233
	21st to end	Day	55% 8% 10% 14% 12% 1	4836
June	1st to 10th	Day	54% 6% 9% 21% 9% 1	2660
	11th to 20th	Day	50% 7% 10% 18% 12% 3	2785
	21st to end	Day	62% 6% 9% 14% 8% 1	2850
July	1st to 10th	Day	64% 4 7% 13% 11% 1	4628
	11th to 20th	Day	71% 4 5% 13% 6%	4237
	21st to end	Day	57% 7% 9% 17% 10%	4325
August	1st to 10th	Day	67% 5% 6% 14% 8%	4092
	11th to 20th	Day	56% 5% 10% 22% 7%	4084
	21st to end	Day	40% 5% 10% 25% 19% 1	4419
September	1st to 10th	Day	42% 5% 9% 25% 17% 2	2280
	11th to 20th	Day	43% 5% 10% 21% 18% 2	2098
	21st to end	Day	45% 5% 9% 23% 17% 2	2090
October	1st to 10th	Day	45% 5% 12% 26% 12% 1	3165
	11th to 20th	Day	40% 4 12% 23% 20% 1	3140
	21st to end	Day	44% 4 11% 27% 10% 3	3415
November	1st to 10th	Day	51% 7% 12% 20% 9% 1	1723
	11th to 20th	Day	59% 7% 12% 15% 6%	1600
	21st to end	Day	65% 7% 12% 12% 3	1600
December	1st to 10th	Day	69% 7% 9% 12% 4	1584
	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	70% 7% 10% 10% 2	4365
	11th to 20th	Night	66% 8% 11% 12% 4	4120
	21st to end	Night	71% 7% 10% 9% 3	4532
February	1st to 10th	Night	73% 5% 9% 9% 4	2470
	11th to 20th	Night	66% 6% 9% 14% 5%	2406
	21st to end	Night	59% 5% 12% 15% 8% 1	1938
March	1st to 10th	Night	65% 4 9% 11% 10% 1	3454
	11th to 20th	Night	55% 7% 14% 14% 9% 1	3480
	21st to end	Night	63% 3 9% 14% 10% 2	3816
April	1st to 10th	Night	57% 4 8% 15% 13% 2	1982
	11th to 20th	Night	50% 4 10% 22% 12% 2	1744
	21st to end	Night	51% 5% 9% 21% 12% 2	1710
May	1st to 10th	Night	57% 8% 12% 17% 5%	2840
	11th to 20th	Night	58% 7% 8% 18% 8% 1	2667
	21st to end	Night	57% 6% 10% 19% 7% 1	2750
June	1st to 10th	Night	57% 6% 7% 22% 8% 1	1520
	11th to 20th	Night	52% 5% 9% 20% 13% 1	1406
	21st to end	Night	62% 6% 8% 13% 9% 1	1330
July	1st to 10th	Night	67% 3 7% 13% 9%	2195
	11th to 20th	Night	76% 4 4 8% 7% 2	2601
	21st to end	Night	60% 5% 9% 16% 9% 1	2989
August	1st to 10th	Night	64% 3 9% 16% 8%	2813
	11th to 20th	Night	56% 4 11% 22% 6%	2809
	21st to end	Night	43% 4 10% 24% 18%	3235
September	1st to 10th	Night	45% 5% 8% 24% 16% 3	1900
	11th to 20th	Night	43% 6% 9% 22% 19% 2	2080
	21st to end	Night	49% 5% 7% 22% 17% 1	2090
October	1st to 10th	Night	47% 5% 12% 23% 12% 1	3795
	11th to 20th	Night	37% 5% 12% 23% 22% 1	3779
	21st to end	Night	45% 4 9% 27% 15% 1	4120
November	1st to 10th	Night	50% 6% 12% 21% 10% 1	2571
	11th to 20th	Night	60% 7% 11% 16% 6%	2800
	21st to end	Night	63% 7% 13% 13% 4	2800
December	1st to 10th	Night	70% 6% 10% 11% 3	2779
	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% 17% 35% 19% 3	370
	21st to end	Day	22% 16% 34% 23% 4	407
February	1st to 10th	Day	28% 15% 35% 18% 3	370
	11th to 20th	Day	24% 23% 31% 19% 3	366
	21st to end	Day	21% 17% 35% 23% 5% 1	355
March	1st to 10th	Day	23% 18% 34% 22% 3	460
	11th to 20th	Day	23% 22% 24% 27% 4	460
	21st to end	Day	24% 13% 32% 21% 7% 2	506
April	1st to 10th	Day	30% 12% 28% 23% 6%	460
	11th to 20th	Day	24% 10% 30% 32% 3 1	452
	21st to end	Day	24% 9% 28% 28% 10% 1	460
May	1st to 10th	Day	29% 8% 27% 28% 7% 1	463
	11th to 20th	Day	21% 7% 28% 31% 11% 1	570
	21st to end	Day	31% 4 20% 31% 12% 2	735
June	1st to 10th	Day	30% 4 19% 33% 11% 2	680
	11th to 20th	Day	22% 3 20% 36% 17% 1	680
	21st to end	Day	33% 4 19% 32% 11% 1	680
July	1st to 10th	Day	31% 3 12% 34% 18% 2	670
	11th to 20th	Day	31% 4 12% 32% 19% 2	593
	21st to end	Day	24% 3 12% 35% 23% 3	532
August	1st to 10th	Day	22% 5% 14% 34% 20% 4	486
	11th to 20th	Day	27% 4 14% 31% 19% 6%	479
	21st to end	Day	20% 4 16% 33% 22% 6%	539
September	1st to 10th	Day	19% 3 18% 35% 21% 4	490
	11th to 20th	Day	23% 6% 22% 24% 19% 6%	490
	21st to end	Day	22% 3 24% 31% 15% 4	490
October	1st to 10th	Day	22% 7% 22% 29% 17% 3	393
	11th to 20th	Day	21% 10% 24% 32% 10% 2	390
	21st to end	Day	24% 12% 26% 27% 10% 1	429
November	1st to 10th	Day	19% 17% 27% 26% 10% 1	395
	11th to 20th	Day	25% 20% 29% 20% 7%	400
	21st to end	Day	27% 18% 27% 22% 5% 1	400
December	1st to 10th	Day	32% 15% 28% 22% 4	394
	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% 18% 30% 21% 4	760
	21st to end	Night	24% 17% 35% 20% 4	836
February	1st to 10th	Night	29% 19% 30% 19% 3	760
	11th to 20th	Night	24% 21% 33% 18% 3	743
	21st to end	Night	19% 15% 36% 24% 6% 1	628
March	1st to 10th	Night	24% 14% 35% 23% 4	760
	11th to 20th	Night	22% 12% 33% 23% 9% 1	760
	21st to end	Night	24% 13% 30% 25% 7% 1	836
April	1st to 10th	Night	28% 11% 28% 28% 5%	652
	11th to 20th	Night	27% 6% 33% 27% 6% 1	564
	21st to end	Night	28% 4 25% 28% 12% 2	570
May	1st to 10th	Night	30% 5% 25% 30% 9% 2	570
	11th to 20th	Night	30% 5% 21% 31% 11% 1	562
	21st to end	Night	29% 4 17% 33% 15% 2	616
June	1st to 10th	Night	31% 3 21% 29% 16%	570
	11th to 20th	Night	22% 5% 16% 38% 18% 1	456
	21st to end	Night	34% 2 13% 30% 18% 2	380
July	1st to 10th	Night	30% 2 11% 36% 19% 1	377
	11th to 20th	Night	33% 3 9% 34% 18% 2	552
	21st to end	Night	30% 5% 9% 37% 18% 1	623
August	1st to 10th	Night	27% 4 10% 31% 23% 4	568
	11th to 20th	Night	27% 2 15% 30% 23% 4	562
	21st to end	Night	22% 3 13% 32% 23% 7%	627
September	1st to 10th	Night	19% 5% 15% 38% 19% 3	570
	11th to 20th	Night	23% 3 17% 30% 22% 5%	750
	21st to end	Night	25% 5% 19% 31% 14% 6%	760
October	1st to 10th	Night	25% 6% 21% 30% 17% 1	760
	11th to 20th	Night	21% 9% 28% 25% 14% 2	760
	21st to end	Night	27% 12% 25% 26% 9%	836
November	1st to 10th	Night	22% 12% 28% 28% 10% 1	797
	11th to 20th	Night	24% 18% 27% 23% 7%	900
	21st to end	Night	26% 18% 29% 19% 7% 1	900
December	1st to 10th	Night	32% 15% 28% 19% 5%	893
	11th to 20th	Night	32% 21% 28% 16% 3	850
	21st to end	Night	28% 20% 30% 19% 3 1	935

Page generated at 2024-12-06 04:54:47. Version ac07

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