Tufts Bay Campground
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tufts Bay Campground clear sky chart from 2005-11-06 to 2026-10-29.

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	8% 7% 3 8% 5% 5% 5% 4 6% 8% 40%	153681
	Night	7% 8% 4 9% 6% 5% 5% 4 6% 8% 37%	147160
Transparency	Day	41% 7% 16% 26% 10% 1	153389
	Night	43% 6% 16% 23% 10% 1	147037
Seeing	Day	12% 8% 27% 31% 18% 5%	18528
	Night	11% 7% 30% 37% 14% 1	27742

By Month

Percentage Cloud Cover NW (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	7% 11% 5% 13% 10% 9% 7% 4 5% 5% 24%	4125
	11th to 20th	Day	3 6% 3 12% 10% 8% 8% 6% 6% 9% 28%	4119
	21st to end	Day	4 10% 5% 11% 9% 7% 6% 4 6% 8% 30%	5046
February	1st to 10th	Day	8% 12% 6% 13% 7% 7% 7% 5% 6% 7% 24%	1797
	11th to 20th	Day	8% 12% 4 10% 8% 6% 6% 5% 5% 7% 30%	1845
	21st to end	Day	5% 10% 5% 13% 9% 8% 7% 6% 7% 7% 24%	1603
March	1st to 10th	Day	6% 11% 4 13% 8% 5% 5% 3 5% 7% 33%	4600
	11th to 20th	Day	3 12% 7% 17% 7% 5% 4 3 5% 7% 30%	5062
	21st to end	Day	7% 11% 6% 12% 7% 6% 5% 4 5% 7% 29%	5876
April	1st to 10th	Day	7% 9% 3 8% 6% 6% 6% 5% 8% 8% 35%	2520
	11th to 20th	Day	10% 12% 4 10% 6% 4 5% 4 6% 8% 30%	2570
	21st to end	Day	15% 9% 4 8% 4 4 4 3 5% 7% 37%	2903
May	1st to 10th	Day	12% 7% 2 5% 4 4 5% 4 6% 8% 43%	8224
	11th to 20th	Day	13% 8% 3 8% 5% 5% 6% 5% 7% 9% 31%	8191
	21st to end	Day	8% 5% 2 6% 4 5% 4 4 6% 9% 46%	9328
June	1st to 10th	Day	13% 7% 2 6% 4 5% 5% 5% 6% 8% 39%	3307
	11th to 20th	Day	17% 7% 2 6% 5% 5% 5% 5% 7% 8% 33%	3360
	21st to end	Day	10% 5% 2 5% 5% 5% 5% 4 7% 10% 42%	3351
July	1st to 10th	Day	5% 4 2 6% 4 5% 5% 4 7% 10% 49%	8820
	11th to 20th	Day	10% 5% 2 6% 5% 4 5% 4 7% 9% 43%	8820
	21st to end	Day	4 3 1 4 3 3 3 3 6% 7% 64%	9197
August	1st to 10th	Day	8% 5% 2 6% 4 4 4 4 6% 8% 50%	6462
	11th to 20th	Day	8% 4 2 5% 4 4 5% 4 7% 10% 46%	6206
	21st to end	Day	11% 5% 2 5% 3 3 4 3 5% 8% 53%	6374
September	1st to 10th	Day	9% 4 2 6% 4 4 5% 4 6% 8% 48%	2520
	11th to 20th	Day	13% 7% 2 6% 4 3 4 3 5% 8% 44%	2520
	21st to end	Day	9% 5% 2 4 3 3 3 3 4 8% 55%	2233
October	1st to 10th	Day	8% 7% 3 5% 3 4 3 4 6% 9% 49%	3370
	11th to 20th	Day	6% 7% 2 5% 5% 4 4 4 7% 11% 44%	3317
	21st to end	Day	7% 9% 4 7% 5% 5% 6% 4 6% 7% 40%	3210
November	1st to 10th	Day	14% 16% 4 7% 6% 5% 4 3 5% 5% 32%	1648
	11th to 20th	Day	6% 14% 5% 14% 7% 6% 5% 4 7% 6% 27%	1680
	21st to end	Day	9% 12% 6% 11% 7% 5% 7% 5% 6% 6% 26%	1623
December	1st to 10th	Day	6% 12% 3 13% 9% 8% 6% 4 6% 7% 26%	2224
	11th to 20th	Day	7% 13% 4 14% 10% 8% 6% 4 6% 7% 21%	2319
	21st to end	Day	3 7% 3 11% 7% 5% 5% 5% 6% 7% 40%	3311
January	1st to 10th	Night	4 10% 6% 14% 9% 7% 7% 5% 7% 7% 24%	8768
	11th to 20th	Night	3 7% 4 13% 9% 8% 8% 6% 8% 7% 28%	8779
	21st to end	Night	4 11% 5% 13% 7% 5% 6% 4 7% 8% 30%	9159
February	1st to 10th	Night	8% 12% 5% 11% 7% 6% 6% 6% 6% 8% 25%	2840
	11th to 20th	Night	5% 11% 4 11% 6% 7% 5% 4 7% 8% 31%	2662
	21st to end	Night	4 8% 4 10% 8% 6% 7% 5% 7% 9% 32%	2202
March	1st to 10th	Night	4 9% 5% 12% 8% 6% 6% 4 7% 9% 29%	5494
	11th to 20th	Night	6% 11% 4 10% 8% 6% 5% 5% 6% 8% 30%	5139
	21st to end	Night	8% 11% 5% 13% 7% 6% 6% 4 6% 8% 26%	5329
April	1st to 10th	Night	7% 9% 3 6% 5% 5% 6% 4 5% 9% 42%	2100
	11th to 20th	Night	10% 12% 4 9% 6% 5% 5% 5% 5% 8% 31%	1999
	21st to end	Night	12% 9% 3 7% 5% 5% 5% 4 6% 8% 35%	1717
May	1st to 10th	Night	12% 7% 2 6% 4 4 4 4 5% 6% 46%	4724
	11th to 20th	Night	16% 11% 3 9% 5% 4 5% 4 6% 7% 30%	4702
	21st to end	Night	9% 6% 2 6% 4 5% 5% 4 7% 9% 43%	4844
June	1st to 10th	Night	12% 5% 2 5% 6% 5% 4 4 6% 9% 43%	1309
	11th to 20th	Night	15% 6% 2 6% 6% 5% 5% 5% 7% 9% 34%	1260
	21st to end	Night	10% 5% 2 6% 3 4 4 4 6% 9% 48%	1264
July	1st to 10th	Night	6% 5% 2 5% 3 4 5% 4 7% 10% 49%	4140
	11th to 20th	Night	6% 5% 2 5% 5% 5% 5% 4 7% 8% 48%	4140
	21st to end	Night	4 3 1 4 3 3 4 4 6% 9% 59%	4890
August	1st to 10th	Night	4 3 2 4 3 4 4 5% 6% 8% 56%	3708
	11th to 20th	Night	6% 3 1 5% 4 4 5% 4 7% 10% 50%	3858
	21st to end	Night	9% 4 2 5% 4 4 4 4 6% 7% 52%	4773
September	1st to 10th	Night	9% 4 2 5% 4 4 3 3 6% 7% 52%	2100
	11th to 20th	Night	11% 6% 3 5% 4 3 4 4 6% 8% 46%	2100
	21st to end	Night	9% 5% 1 3 3 3 3 4 5% 8% 55%	2383
October	1st to 10th	Night	10% 6% 2 7% 3 4 4 3 5% 8% 47%	4040
	11th to 20th	Night	5% 6% 2 5% 3 4 4 3 6% 8% 53%	4018
	21st to end	Night	7% 10% 3 7% 4 5% 4 4 6% 8% 43%	4762
November	1st to 10th	Night	14% 13% 4 10% 6% 4 5% 4 4 5% 31%	2870
	11th to 20th	Night	6% 12% 5% 14% 7% 6% 5% 4 6% 7% 29%	2940
	21st to end	Night	8% 12% 6% 11% 6% 5% 5% 4 6% 8% 28%	2993
December	1st to 10th	Night	7% 15% 6% 15% 8% 7% 6% 4 5% 6% 22%	5180
	11th to 20th	Night	7% 13% 5% 13% 9% 8% 7% 5% 7% 7% 20%	6093
	21st to end	Night	3 7% 3 12% 8% 6% 5% 4 5% 6% 43%	7881

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	61% 6% 12% 14% 7%	4125
	11th to 20th	Day	49% 7% 15% 18% 10% 1	4140
	21st to end	Day	50% 7% 20% 16% 7%	5046
February	1st to 10th	Day	58% 7% 13% 15% 7%	1797
	11th to 20th	Day	52% 7% 14% 17% 10%	1854
	21st to end	Day	56% 8% 13% 18% 6%	1603
March	1st to 10th	Day	51% 6% 22% 15% 6%	4600
	11th to 20th	Day	54% 8% 16% 18% 5%	5063
	21st to end	Day	50% 9% 14% 22% 6%	5876
April	1st to 10th	Day	42% 9% 17% 22% 10%	2520
	11th to 20th	Day	51% 7% 16% 18% 7% 1	2570
	21st to end	Day	47% 6% 14% 24% 8% 1	2903
May	1st to 10th	Day	38% 5% 11% 28% 16% 2	8224
	11th to 20th	Day	45% 8% 13% 21% 11%	8195
	21st to end	Day	33% 8% 14% 29% 14% 1	9328
June	1st to 10th	Day	41% 8% 14% 24% 11% 1	3307
	11th to 20th	Day	45% 8% 15% 22% 8% 1	3360
	21st to end	Day	36% 10% 20% 26% 7% 1	3351
July	1st to 10th	Day	29% 7% 24% 30% 10%	8746
	11th to 20th	Day	37% 5% 14% 32% 10% 2	8739
	21st to end	Day	20% 5% 17% 38% 18% 3	8999
August	1st to 10th	Day	32% 6% 18% 30% 12% 1	6446
	11th to 20th	Day	33% 6% 18% 35% 8%	6248
	21st to end	Day	31% 4 16% 32% 16% 1	6373
September	1st to 10th	Day	33% 7% 17% 27% 14% 2	2520
	11th to 20th	Day	38% 6% 16% 28% 10% 2	2520
	21st to end	Day	30% 5% 14% 33% 15% 2	2233
October	1st to 10th	Day	33% 5% 20% 32% 9% 1	3370
	11th to 20th	Day	32% 5% 16% 36% 11%	3317
	21st to end	Day	42% 6% 18% 29% 6%	3210
November	1st to 10th	Day	54% 6% 14% 18% 7% 1	1648
	11th to 20th	Day	55% 9% 15% 16% 5%	1680
	21st to end	Day	55% 8% 17% 17% 4	1623
December	1st to 10th	Day	56% 10% 18% 12% 4	2224
	11th to 20th	Day	62% 8% 20% 7% 3	2320
	21st to end	Day	42% 5% 13% 23% 13% 4	3311
January	1st to 10th	Night	56% 7% 14% 15% 7%	8769
	11th to 20th	Night	51% 6% 16% 16% 11%	8820
	21st to end	Night	48% 7% 20% 18% 7%	9159
February	1st to 10th	Night	54% 7% 13% 18% 8%	2840
	11th to 20th	Night	48% 7% 13% 19% 12%	2663
	21st to end	Night	44% 8% 16% 23% 9%	2202
March	1st to 10th	Night	48% 7% 23% 18% 4	5494
	11th to 20th	Night	48% 8% 19% 18% 6%	5139
	21st to end	Night	53% 7% 13% 19% 8%	5329
April	1st to 10th	Night	39% 7% 17% 23% 14% 1	2100
	11th to 20th	Night	49% 6% 13% 20% 10% 2	1999
	21st to end	Night	46% 7% 13% 23% 10% 1	1717
May	1st to 10th	Night	38% 4 10% 28% 18% 2	4724
	11th to 20th	Night	52% 7% 11% 20% 11% 1	4702
	21st to end	Night	33% 9% 13% 28% 16% 1	4848
June	1st to 10th	Night	36% 6% 14% 29% 15% 1	1309
	11th to 20th	Night	44% 8% 15% 21% 11% 1	1260
	21st to end	Night	32% 8% 19% 30% 10% 1	1264
July	1st to 10th	Night	30% 6% 25% 30% 7% 1	4105
	11th to 20th	Night	32% 5% 14% 37% 11% 1	4098
	21st to end	Night	22% 5% 17% 36% 19% 2	4783
August	1st to 10th	Night	24% 6% 23% 32% 13% 2	3700
	11th to 20th	Night	27% 6% 21% 35% 10% 1	3882
	21st to end	Night	31% 5% 12% 30% 20% 1	4773
September	1st to 10th	Night	31% 6% 13% 29% 16% 5%	2100
	11th to 20th	Night	34% 7% 15% 29% 12% 3	2100
	21st to end	Night	28% 6% 12% 35% 18% 3	2383
October	1st to 10th	Night	36% 4 17% 31% 10%	4040
	11th to 20th	Night	30% 4 16% 35% 15% 1	4018
	21st to end	Night	39% 5% 13% 33% 8% 1	4762
November	1st to 10th	Night	54% 7% 13% 18% 7% 1	2870
	11th to 20th	Night	52% 8% 18% 17% 6%	2940
	21st to end	Night	51% 8% 16% 20% 3	2993
December	1st to 10th	Night	62% 7% 16% 11% 3	5180
	11th to 20th	Night	61% 7% 18% 10% 3	6091
	21st to end	Night	43% 4 10% 26% 12% 4	7881

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	11% 5% 28% 31% 20% 5%	220
	11th to 20th	Day	11% 10% 30% 27% 20% 1	220
	21st to end	Day	9% 11% 28% 33% 16% 2	337
February	1st to 10th	Day	12% 10% 33% 32% 11% 2	330
	11th to 20th	Day	10% 6% 28% 31% 18% 6%	330
	21st to end	Day	7% 6% 28% 35% 21% 4	273
March	1st to 10th	Day	11% 9% 28% 33% 17% 2	330
	11th to 20th	Day	8% 13% 32% 30% 13% 3	519
	21st to end	Day	12% 9% 32% 31% 14% 2	594
April	1st to 10th	Day	8% 14% 33% 30% 13% 3	540
	11th to 20th	Day	14% 15% 32% 27% 9% 3	532
	21st to end	Day	16% 10% 26% 32% 14% 2	713
May	1st to 10th	Day	12% 8% 25% 29% 21% 5%	753
	11th to 20th	Day	12% 8% 25% 31% 18% 6%	775
	21st to end	Day	13% 8% 22% 29% 21% 6%	844
June	1st to 10th	Day	12% 12% 28% 28% 15% 4	780
	11th to 20th	Day	17% 10% 30% 27% 13% 3	780
	21st to end	Day	11% 8% 22% 30% 23% 6%	780
July	1st to 10th	Day	8% 4 20% 37% 25% 6%	771
	11th to 20th	Day	12% 4 26% 29% 23% 7%	768
	21st to end	Day	5% 5% 24% 30% 26% 10%	849
August	1st to 10th	Day	10% 5% 20% 35% 21% 9%	776
	11th to 20th	Day	9% 6% 19% 34% 24% 7%	685
	21st to end	Day	12% 5% 23% 30% 22% 8%	627
September	1st to 10th	Day	14% 6% 28% 29% 18% 5%	570
	11th to 20th	Day	17% 8% 22% 34% 17% 3	570
	21st to end	Day	13% 10% 26% 32% 16% 3	417
October	1st to 10th	Day	16% 6% 29% 25% 20% 4	360
	11th to 20th	Day	12% 8% 33% 28% 17% 3	360
	21st to end	Day	13% 11% 37% 26% 12% 2	387
November	1st to 10th	Day	18% 8% 33% 26% 10% 4	330
	11th to 20th	Day	12% 12% 32% 31% 12% 1	330
	21st to end	Day	9% 9% 33% 36% 10% 3	330
December	1st to 10th	Day	8% 9% 31% 35% 13% 4	286
	11th to 20th	Day	10% 10% 40% 32% 8%	220
	21st to end	Day	10% 2 31% 35% 17% 5%	242
January	1st to 10th	Night	8% 8% 34% 37% 12% 1	1050
	11th to 20th	Night	10% 10% 34% 36% 9% 1	1050
	21st to end	Night	11% 8% 38% 32% 10% 1	1155
February	1st to 10th	Night	12% 7% 29% 36% 15% 1	950
	11th to 20th	Night	9% 8% 30% 37% 15% 1	824
	21st to end	Night	5% 4 24% 41% 20% 4	692
March	1st to 10th	Night	10% 6% 31% 38% 13% 1	840
	11th to 20th	Night	9% 6% 33% 38% 13% 1	840
	21st to end	Night	13% 6% 30% 38% 11% 2	798
April	1st to 10th	Night	11% 9% 28% 38% 13% 1	630
	11th to 20th	Night	15% 10% 33% 34% 8%	623
	21st to end	Night	16% 8% 31% 34% 10%	630
May	1st to 10th	Night	14% 7% 24% 39% 16% 1	630
	11th to 20th	Night	16% 6% 28% 31% 18% 1	621
	21st to end	Night	17% 5% 24% 34% 17% 3	570
June	1st to 10th	Night	13% 7% 29% 32% 17% 2	420
	11th to 20th	Night	17% 6% 25% 38% 13% 2	420
	21st to end	Night	11% 3 24% 41% 18% 2	420
July	1st to 10th	Night	7% 3 21% 43% 25% 1	410
	11th to 20th	Night	9% 4 24% 41% 20% 2	408
	21st to end	Night	3 5% 24% 44% 22% 2	595
August	1st to 10th	Night	7% 4 22% 42% 22% 3	627
	11th to 20th	Night	6% 2 21% 43% 26% 2	624
	21st to end	Night	8% 5% 26% 36% 24% 1	693
September	1st to 10th	Night	12% 5% 24% 39% 19% 1	630
	11th to 20th	Night	12% 6% 21% 42% 18% 1	630
	21st to end	Night	10% 6% 31% 39% 12% 1	761
October	1st to 10th	Night	15% 6% 27% 36% 15% 1	840
	11th to 20th	Night	10% 7% 32% 36% 14% 2	840
	21st to end	Night	14% 10% 33% 35% 8%	1141
November	1st to 10th	Night	21% 7% 33% 32% 7% 1	1025
	11th to 20th	Night	11% 9% 34% 34% 12% 1	1050
	21st to end	Night	12% 7% 39% 33% 8% 1	1050
December	1st to 10th	Night	10% 6% 34% 34% 14% 2	1050
	11th to 20th	Night	12% 9% 33% 34% 11% 1	1050
	21st to end	Night	11% 5% 30% 39% 12% 3	1155

Page generated at 2026-10-26 02:37:48. Version ac07

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