Colebrook
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Colebrook clear sky chart from 2005-11-06 to 2024-01-27.

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	18% 12% 5% 9% 7% 4 5% 4 5% 6% 26%	74904
	Night	17% 13% 5% 10% 7% 4 5% 4 4 5% 25%	75142
Transparency	Day	60% 5% 10% 17% 8% 1	74609
	Night	62% 5% 9% 16% 7% 1	74971
Seeing	Day	30% 18% 27% 16% 7% 2	13686
	Night	27% 17% 24% 22% 9% 1	22690

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	13% 14% 10% 18% 10% 6% 5% 5% 4 3 12%	1517
	11th to 20th	Day	13% 18% 7% 13% 12% 4 4 4 5% 4 16%	1520
	21st to end	Day	9% 13% 9% 14% 11% 4 7% 4 4 4 21%	1632
February	1st to 10th	Day	13% 17% 8% 14% 11% 5% 7% 3 3 3 16%	1530
	11th to 20th	Day	10% 15% 10% 16% 11% 5% 6% 4 3 4 17%	1748
	21st to end	Day	11% 17% 7% 15% 9% 5% 6% 4 4 4 19%	1480
March	1st to 10th	Day	12% 16% 8% 11% 9% 4 5% 4 3 4 22%	1797
	11th to 20th	Day	14% 14% 7% 9% 8% 4 4 4 3 4 29%	1882
	21st to end	Day	15% 16% 7% 12% 7% 3 4 2 2 4 27%	2314
April	1st to 10th	Day	19% 17% 6% 10% 6% 2 3 3 3 4 26%	2160
	11th to 20th	Day	17% 14% 5% 7% 6% 3 4 4 4 4 33%	2181
	21st to end	Day	22% 16% 4 8% 5% 3 4 4 4 6% 24%	2340
May	1st to 10th	Day	24% 13% 4 6% 5% 2 4 4 5% 5% 29%	2340
	11th to 20th	Day	22% 10% 4 7% 5% 3 3 5% 3 5% 32%	2464
	21st to end	Day	19% 7% 3 7% 6% 4 5% 6% 7% 8% 27%	2725
June	1st to 10th	Day	27% 10% 4 6% 5% 4 5% 5% 5% 7% 23%	2520
	11th to 20th	Day	21% 7% 3 5% 6% 3 5% 5% 6% 7% 32%	2520
	21st to end	Day	23% 8% 4 7% 6% 4 6% 6% 6% 6% 25%	2520
July	1st to 10th	Day	18% 6% 3 6% 6% 3 5% 6% 7% 8% 31%	2520
	11th to 20th	Day	15% 7% 3 7% 6% 4 7% 6% 6% 9% 28%	2520
	21st to end	Day	19% 7% 3 6% 6% 4 7% 6% 6% 9% 27%	2744
August	1st to 10th	Day	18% 7% 2 7% 6% 4 6% 6% 7% 8% 29%	2449
	11th to 20th	Day	16% 7% 3 7% 6% 4 6% 6% 7% 9% 28%	2304
	21st to end	Day	19% 8% 3 5% 5% 4 4 5% 5% 8% 34%	2408
September	1st to 10th	Day	18% 7% 3 6% 5% 3 5% 4 5% 6% 37%	2160
	11th to 20th	Day	19% 7% 3 5% 4 3 4 3 5% 6% 41%	1998
	21st to end	Day	18% 9% 3 6% 6% 2 4 5% 5% 8% 34%	1980
October	1st to 10th	Day	23% 12% 4 6% 5% 3 4 4 5% 6% 27%	1980
	11th to 20th	Day	16% 16% 5% 8% 5% 4 4 4 6% 6% 26%	1689
	21st to end	Day	23% 22% 5% 7% 5% 3 4 3 3 4 21%	1782
November	1st to 10th	Day	16% 18% 6% 7% 5% 4 4 4 4 5% 27%	1671
	11th to 20th	Day	17% 17% 8% 12% 6% 4 4 4 4 5% 21%	1710
	21st to end	Day	16% 16% 7% 13% 6% 3 5% 4 5% 5% 19%	1601
December	1st to 10th	Day	16% 22% 9% 14% 8% 3 3 3 4 4 14%	1520
	11th to 20th	Day	16% 18% 8% 12% 7% 3 4 3 4 4 20%	1906
	21st to end	Day	21% 18% 7% 13% 9% 4 5% 4 3 3 14%	2772
January	1st to 10th	Night	12% 18% 8% 17% 11% 5% 7% 5% 3 3 11%	2649
	11th to 20th	Night	13% 16% 8% 14% 11% 5% 6% 5% 4 4 13%	2660
	21st to end	Night	9% 14% 8% 14% 11% 6% 8% 6% 4 4 16%	2868
February	1st to 10th	Night	12% 14% 7% 15% 13% 6% 6% 4 3 5% 15%	2430
	11th to 20th	Night	9% 15% 8% 15% 12% 5% 8% 5% 2 4 17%	2098
	21st to end	Night	11% 16% 6% 11% 9% 5% 7% 3 4 5% 22%	1776
March	1st to 10th	Night	12% 16% 9% 12% 8% 4 5% 4 4 5% 22%	2150
	11th to 20th	Night	15% 14% 6% 10% 7% 4 6% 4 4 4 27%	2075
	21st to end	Night	17% 15% 6% 11% 6% 3 4 3 3 4 28%	2039
April	1st to 10th	Night	19% 15% 5% 9% 7% 4 4 4 4 5% 25%	1800
	11th to 20th	Night	18% 13% 5% 7% 6% 3 4 4 4 6% 31%	1728
	21st to end	Night	23% 12% 4 6% 6% 3 4 4 5% 5% 27%	1620
May	1st to 10th	Night	22% 12% 4 6% 6% 3 4 4 5% 6% 29%	1620
	11th to 20th	Night	19% 8% 2 6% 6% 3 4 5% 4 8% 33%	1445
	21st to end	Night	19% 8% 3 5% 5% 4 5% 4 5% 7% 34%	1550
June	1st to 10th	Night	27% 8% 3 6% 4 3 4 4 4 6% 29%	1440
	11th to 20th	Night	19% 6% 3 6% 5% 4 5% 4 6% 7% 35%	1440
	21st to end	Night	20% 7% 3 6% 6% 4 5% 6% 6% 6% 30%	1440
July	1st to 10th	Night	15% 6% 3 5% 7% 3 5% 6% 5% 8% 36%	1440
	11th to 20th	Night	15% 6% 3 5% 5% 4 5% 6% 7% 8% 37%	1440
	21st to end	Night	15% 7% 2 6% 5% 4 6% 5% 6% 7% 36%	1574
August	1st to 10th	Night	15% 6% 2 6% 5% 3 5% 5% 6% 8% 39%	1470
	11th to 20th	Night	16% 8% 3 6% 5% 3 5% 5% 6% 8% 35%	1596
	21st to end	Night	17% 7% 2 5% 5% 3 4 4 4 7% 42%	1946
September	1st to 10th	Night	17% 6% 3 5% 5% 3 4 5% 5% 6% 41%	1800
	11th to 20th	Night	18% 7% 2 5% 5% 2 3 4 4 6% 44%	1962
	21st to end	Night	19% 8% 2 5% 4 2 4 3 5% 7% 40%	1980
October	1st to 10th	Night	20% 12% 2 5% 6% 4 5% 5% 4 6% 32%	1980
	11th to 20th	Night	19% 15% 3 7% 7% 4 5% 4 4 5% 27%	2267
	21st to end	Night	23% 17% 5% 7% 5% 3 5% 5% 5% 6% 20%	2574
November	1st to 10th	Night	18% 17% 5% 9% 6% 3 4 4 5% 5% 25%	2407
	11th to 20th	Night	15% 15% 8% 12% 7% 3 3 3 4 6% 25%	2470
	21st to end	Night	16% 16% 9% 12% 11% 3 4 3 3 4 19%	2576
December	1st to 10th	Night	18% 20% 10% 14% 8% 4 4 4 3 4 12%	2660
	11th to 20th	Night	17% 19% 8% 15% 10% 3 4 3 4 4 13%	3288
	21st to end	Night	21% 17% 7% 15% 8% 3 4 4 3 3 15%	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	77% 3 7% 10% 3	1518
	11th to 20th	Day	72% 4 6% 11% 6% 2	1520
	21st to end	Day	68% 3 8% 12% 8% 1	1632
February	1st to 10th	Day	75% 3 5% 10% 6% 1	1530
	11th to 20th	Day	74% 3 7% 10% 5% 1	1757
	21st to end	Day	69% 5% 6% 11% 7% 2	1480
March	1st to 10th	Day	68% 4 7% 12% 6% 3	1800
	11th to 20th	Day	61% 4 9% 12% 11% 2	1882
	21st to end	Day	65% 3 5% 15% 10% 2	2314
April	1st to 10th	Day	64% 3 8% 14% 9% 2	2160
	11th to 20th	Day	56% 3 8% 20% 12% 1	2181
	21st to end	Day	63% 4 8% 15% 7% 3	2340
May	1st to 10th	Day	58% 4 7% 20% 11% 1	2340
	11th to 20th	Day	55% 5% 9% 20% 10% 1	2468
	21st to end	Day	52% 8% 12% 18% 9%	2725
June	1st to 10th	Day	61% 6% 10% 18% 5% 1	2520
	11th to 20th	Day	51% 6% 10% 22% 10% 1	2520
	21st to end	Day	58% 6% 10% 18% 7%	2520
July	1st to 10th	Day	48% 7% 15% 21% 9%	2450
	11th to 20th	Day	51% 8% 14% 22% 6%	2445
	21st to end	Day	54% 8% 12% 20% 6%	2591
August	1st to 10th	Day	51% 8% 16% 20% 6%	2435
	11th to 20th	Day	49% 8% 16% 19% 7%	2304
	21st to end	Day	49% 6% 12% 22% 11% 1	2408
September	1st to 10th	Day	46% 7% 13% 23% 10%	2160
	11th to 20th	Day	44% 4 11% 26% 14% 1	1998
	21st to end	Day	49% 5% 13% 22% 10% 1	1980
October	1st to 10th	Day	56% 5% 11% 19% 8%	1980
	11th to 20th	Day	58% 5% 13% 17% 5%	1689
	21st to end	Day	68% 4 8% 12% 7% 1	1782
November	1st to 10th	Day	62% 4 9% 16% 8% 1	1671
	11th to 20th	Day	67% 5% 7% 11% 7% 3	1710
	21st to end	Day	66% 5% 12% 13% 3	1601
December	1st to 10th	Day	75% 3 7% 10% 4	1520
	11th to 20th	Day	69% 4 6% 13% 9% 1	1906
	21st to end	Day	77% 4 4 9% 6%	2772
January	1st to 10th	Night	79% 4 6% 8% 4	2649
	11th to 20th	Night	76% 5% 6% 9% 3 1	2660
	21st to end	Night	71% 5% 6% 10% 6% 1	2868
February	1st to 10th	Night	74% 4 7% 9% 6% 1	2430
	11th to 20th	Night	74% 4 5% 11% 5% 1	2100
	21st to end	Night	68% 4 6% 12% 9% 1	1776
March	1st to 10th	Night	67% 3 6% 15% 7% 2	2160
	11th to 20th	Night	62% 4 9% 12% 10% 2	2076
	21st to end	Night	62% 3 6% 18% 9% 3	2039
April	1st to 10th	Night	63% 4 7% 14% 10% 1	1800
	11th to 20th	Night	54% 5% 8% 20% 12%	1728
	21st to end	Night	59% 5% 9% 15% 10% 2	1620
May	1st to 10th	Night	58% 3 7% 20% 11% 1	1620
	11th to 20th	Night	51% 6% 10% 20% 12% 1	1446
	21st to end	Night	49% 7% 14% 20% 9% 1	1551
June	1st to 10th	Night	57% 5% 9% 20% 7%	1440
	11th to 20th	Night	49% 6% 11% 23% 9% 2	1440
	21st to end	Night	53% 9% 12% 20% 6%	1440
July	1st to 10th	Night	45% 9% 14% 21% 10%	1400
	11th to 20th	Night	43% 9% 15% 27% 7%	1392
	21st to end	Night	47% 8% 14% 21% 9%	1486
August	1st to 10th	Night	42% 8% 18% 27% 5%	1460
	11th to 20th	Night	46% 8% 17% 20% 9%	1596
	21st to end	Night	43% 6% 14% 25% 11%	1946
September	1st to 10th	Night	44% 6% 14% 26% 9%	1800
	11th to 20th	Night	43% 5% 13% 27% 11% 1	1962
	21st to end	Night	45% 5% 12% 26% 10% 2	1980
October	1st to 10th	Night	53% 6% 9% 20% 11% 1	1980
	11th to 20th	Night	60% 5% 12% 18% 6%	2267
	21st to end	Night	65% 6% 9% 12% 7% 1	2574
November	1st to 10th	Night	63% 3 10% 16% 7% 1	2407
	11th to 20th	Night	63% 4 8% 15% 8% 2	2470
	21st to end	Night	70% 5% 9% 11% 5%	2576
December	1st to 10th	Night	78% 4 7% 8% 3	2660
	11th to 20th	Night	77% 3 5% 8% 7%	3288
	21st to end	Night	76% 5% 6% 9% 5%	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	26% 23% 35% 14% 2	180
	11th to 20th	Day	35% 22% 31% 9% 2 1	180
	21st to end	Day	25% 27% 32% 12% 4	188
February	1st to 10th	Day	41% 28% 23% 7% 1	222
	11th to 20th	Day	32% 30% 28% 9% 2	416
	21st to end	Day	34% 24% 27% 12% 2	346
March	1st to 10th	Day	32% 26% 27% 11% 4	420
	11th to 20th	Day	33% 25% 25% 12% 4 1	420
	21st to end	Day	33% 22% 24% 13% 7% 2	462
April	1st to 10th	Day	42% 18% 23% 10% 6% 1	420
	11th to 20th	Day	35% 22% 24% 10% 7% 2	412
	21st to end	Day	36% 21% 26% 10% 5% 2	420
May	1st to 10th	Day	42% 16% 25% 11% 5% 1	423
	11th to 20th	Day	30% 18% 32% 15% 5% 1	447
	21st to end	Day	26% 20% 28% 19% 6% 1	485
June	1st to 10th	Day	34% 14% 31% 13% 6%	450
	11th to 20th	Day	25% 17% 28% 20% 9% 2	450
	21st to end	Day	24% 16% 34% 14% 8% 2	450
July	1st to 10th	Day	22% 13% 31% 25% 8% 2	445
	11th to 20th	Day	18% 11% 36% 22% 9% 2	444
	21st to end	Day	21% 12% 33% 26% 6% 2	488
August	1st to 10th	Day	20% 11% 30% 22% 13% 2	446
	11th to 20th	Day	18% 10% 32% 22% 13% 5%	439
	21st to end	Day	26% 13% 22% 22% 12% 5%	495
September	1st to 10th	Day	24% 13% 24% 21% 12% 6%	450
	11th to 20th	Day	26% 11% 22% 19% 15% 7%	450
	21st to end	Day	23% 13% 24% 22% 11% 6%	450
October	1st to 10th	Day	29% 16% 23% 17% 12% 3	450
	11th to 20th	Day	30% 16% 28% 13% 10% 2	388
	21st to end	Day	38% 18% 23% 15% 6%	396
November	1st to 10th	Day	34% 17% 26% 17% 5%	365
	11th to 20th	Day	32% 24% 25% 13% 5% 1	370
	21st to end	Day	36% 20% 26% 13% 3 1	261
December	1st to 10th	Day	36% 23% 24% 14% 4	180
	11th to 20th	Day	36% 23% 29% 8% 3	180
	21st to end	Day	40% 19% 30% 10% 2 1	198
January	1st to 10th	Night	26% 24% 33% 15% 3	760
	11th to 20th	Night	27% 26% 27% 16% 4	760
	21st to end	Night	21% 26% 31% 17% 4 1	820
February	1st to 10th	Night	26% 27% 29% 16% 2	720
	11th to 20th	Night	25% 27% 29% 16% 3	703
	21st to end	Night	26% 23% 30% 19% 2	592
March	1st to 10th	Night	28% 20% 30% 19% 3	720
	11th to 20th	Night	31% 20% 25% 18% 6% 1	720
	21st to end	Night	29% 21% 23% 18% 8% 1	792
April	1st to 10th	Night	35% 21% 23% 17% 5%	720
	11th to 20th	Night	30% 17% 25% 21% 7%	664
	21st to end	Night	33% 17% 25% 19% 6%	540
May	1st to 10th	Night	29% 16% 28% 19% 8% 1	540
	11th to 20th	Night	23% 15% 25% 28% 8% 1	384
	21st to end	Night	24% 9% 26% 30% 10% 1	389
June	1st to 10th	Night	31% 8% 22% 27% 11% 1	360
	11th to 20th	Night	24% 9% 20% 31% 16%	360
	21st to end	Night	23% 9% 18% 38% 11% 1	360
July	1st to 10th	Night	17% 6% 24% 36% 16% 1	350
	11th to 20th	Night	17% 6% 21% 38% 18% 1	348
	21st to end	Night	18% 4 19% 41% 18% 1	394
August	1st to 10th	Night	19% 4 16% 39% 21%	396
	11th to 20th	Night	18% 7% 21% 33% 20% 1	532
	21st to end	Night	22% 6% 19% 32% 18% 2	758
September	1st to 10th	Night	20% 8% 21% 33% 16% 2	720
	11th to 20th	Night	23% 8% 19% 26% 22% 2	720
	21st to end	Night	25% 9% 23% 24% 16% 3	720
October	1st to 10th	Night	28% 11% 20% 26% 14% 1	720
	11th to 20th	Night	31% 17% 19% 20% 11% 2	720
	21st to end	Night	36% 18% 22% 19% 5%	792
November	1st to 10th	Night	32% 17% 23% 19% 8%	740
	11th to 20th	Night	28% 22% 24% 17% 8% 2	760
	21st to end	Night	31% 22% 24% 17% 5% 1	760
December	1st to 10th	Night	33% 24% 25% 13% 5%	760
	11th to 20th	Night	33% 24% 24% 15% 4	760
	21st to end	Night	36% 20% 26% 15% 2	836

Page generated at 2024-01-24 09:37:27. Version ac07

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