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 2025-07-06.

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% 8% 3 8% 5% 5% 5% 4 6% 8% 39%	123161
	Night	7% 9% 4 10% 6% 5% 5% 4 6% 7% 37%	124322
Transparency	Day	41% 7% 17% 24% 9% 1	122911
	Night	44% 7% 16% 23% 9% 1	124218
Seeing	Day	12% 8% 27% 31% 18% 5%	16703
	Night	11% 7% 30% 36% 14% 1	26048

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	6% 12% 5% 13% 10% 9% 6% 5% 5% 5% 24%	3179
	11th to 20th	Day	3 8% 4 11% 8% 8% 9% 6% 6% 8% 29%	3159
	21st to end	Day	4 10% 5% 10% 8% 6% 6% 4 6% 8% 32%	3890
February	1st to 10th	Day	8% 13% 5% 13% 7% 7% 7% 5% 6% 7% 23%	1711
	11th to 20th	Day	8% 12% 4 10% 8% 6% 6% 5% 5% 7% 30%	1755
	21st to end	Day	5% 10% 5% 13% 8% 7% 7% 6% 7% 7% 24%	1529
March	1st to 10th	Day	6% 11% 4 13% 8% 5% 5% 3 5% 7% 33%	4500
	11th to 20th	Day	3 12% 7% 17% 7% 5% 4 3 5% 7% 30%	4953
	21st to end	Day	7% 11% 6% 12% 7% 6% 5% 4 5% 7% 30%	5749
April	1st to 10th	Day	6% 9% 3 8% 6% 6% 6% 5% 8% 8% 36%	2400
	11th to 20th	Day	11% 12% 4 10% 6% 4 5% 4 6% 8% 29%	2446
	21st to end	Day	15% 9% 3 8% 4 4 4 3 5% 6% 37%	2765
May	1st to 10th	Day	15% 8% 2 5% 4 4 5% 4 6% 7% 42%	6340
	11th to 20th	Day	11% 8% 3 8% 6% 6% 6% 6% 8% 9% 29%	6298
	21st to end	Day	10% 6% 2 6% 4 4 4 4 5% 8% 44%	7162
June	1st to 10th	Day	13% 7% 2 6% 4 5% 5% 4 6% 8% 40%	3150
	11th to 20th	Day	18% 7% 2 6% 5% 5% 5% 4 7% 8% 34%	3200
	21st to end	Day	9% 5% 2 5% 5% 4 5% 4 7% 10% 43%	3191
July	1st to 10th	Day	4 5% 2 6% 4 5% 5% 4 8% 9% 48%	4816
	11th to 20th	Day	7% 4 2 5% 4 4 4 4 7% 10% 49%	4740
	21st to end	Day	3 2 1 3 3 3 4 3 6% 7% 64%	4934
August	1st to 10th	Day	7% 4 2 6% 4 4 4 4 6% 8% 51%	4412
	11th to 20th	Day	6% 4 2 5% 4 4 5% 4 7% 10% 50%	4219
	21st to end	Day	11% 4 1 4 2 3 3 3 5% 7% 56%	4381
September	1st to 10th	Day	9% 5% 2 5% 4 4 5% 4 6% 8% 49%	2280
	11th to 20th	Day	13% 7% 2 6% 4 3 4 3 5% 8% 44%	2280
	21st to end	Day	10% 5% 2 4 4 4 3 3 4 8% 52%	2021
October	1st to 10th	Day	9% 7% 2 5% 3 4 4 3 6% 8% 49%	3170
	11th to 20th	Day	6% 6% 2 5% 4 4 4 4 8% 11% 45%	3119
	21st to end	Day	7% 9% 4 7% 5% 5% 6% 4 6% 8% 39%	3041
November	1st to 10th	Day	14% 17% 4 7% 6% 5% 4 3 4 5% 32%	1568
	11th to 20th	Day	6% 14% 5% 14% 7% 6% 5% 4 7% 6% 27%	1600
	21st to end	Day	9% 12% 6% 11% 7% 5% 7% 5% 5% 7% 26%	1546
December	1st to 10th	Day	6% 12% 3 13% 9% 8% 6% 4 6% 7% 26%	2158
	11th to 20th	Day	7% 13% 4 14% 10% 7% 6% 4 6% 7% 21%	2259
	21st to end	Day	3 7% 3 11% 7% 5% 5% 4 6% 7% 40%	3240
January	1st to 10th	Night	3 10% 6% 13% 9% 8% 8% 5% 7% 7% 24%	6766
	11th to 20th	Night	4 8% 5% 14% 9% 9% 9% 6% 7% 6% 24%	6739
	21st to end	Night	5% 10% 5% 13% 6% 5% 6% 4 6% 7% 33%	7081
February	1st to 10th	Night	8% 12% 4 11% 7% 6% 6% 6% 6% 8% 25%	2705
	11th to 20th	Night	5% 11% 4 12% 6% 7% 5% 4 7% 8% 30%	2532
	21st to end	Night	4 8% 4 10% 8% 6% 7% 5% 8% 9% 33%	2100
March	1st to 10th	Night	4 9% 5% 12% 8% 6% 6% 4 7% 9% 28%	5374
	11th to 20th	Night	6% 11% 4 10% 8% 6% 6% 5% 6% 8% 30%	5028
	21st to end	Night	8% 11% 5% 13% 7% 6% 6% 4 6% 8% 27%	5214
April	1st to 10th	Night	7% 9% 2 6% 5% 5% 6% 4 6% 9% 42%	2000
	11th to 20th	Night	10% 12% 4 8% 6% 5% 5% 5% 6% 8% 32%	1903
	21st to end	Night	12% 10% 3 7% 5% 5% 6% 4 6% 8% 35%	1635
May	1st to 10th	Night	15% 9% 2 6% 4 4 3 3 5% 5% 43%	3640
	11th to 20th	Night	17% 9% 3 8% 5% 4 5% 4 6% 7% 31%	3618
	21st to end	Night	11% 7% 2 7% 4 4 4 3 6% 7% 44%	3708
June	1st to 10th	Night	12% 5% 2 5% 6% 4 4 4 6% 9% 44%	1247
	11th to 20th	Night	15% 5% 2 6% 7% 5% 5% 5% 7% 9% 35%	1200
	21st to end	Night	9% 5% 2 5% 3 4 4 4 6% 10% 49%	1204
July	1st to 10th	Night	7% 4 2 4 4 5% 5% 4 8% 11% 47%	2255
	11th to 20th	Night	4 3 1 3 3 4 4 4 6% 8% 59%	2220
	21st to end	Night	2 2 1 3 3 3 4 4 6% 9% 64%	2624
August	1st to 10th	Night	6% 4 2 5% 3 3 4 4 5% 7% 57%	2528
	11th to 20th	Night	3 3 1 5% 4 4 5% 4 7% 9% 53%	2618
	21st to end	Night	7% 4 2 4 3 4 4 4 6% 7% 55%	3285
September	1st to 10th	Night	9% 4 2 5% 4 4 4 3 6% 7% 52%	1900
	11th to 20th	Night	11% 6% 3 4 4 3 4 4 6% 8% 47%	1900
	21st to end	Night	10% 6% 2 3 3 3 3 4 5% 8% 53%	2157
October	1st to 10th	Night	11% 7% 3 7% 3 3 4 3 5% 8% 47%	3800
	11th to 20th	Night	5% 5% 2 5% 3 4 4 3 6% 8% 54%	3778
	21st to end	Night	8% 9% 3 7% 4 5% 4 4 6% 8% 42%	4513
November	1st to 10th	Night	14% 13% 4 10% 6% 5% 5% 3 4 5% 31%	2730
	11th to 20th	Night	6% 12% 5% 14% 7% 6% 5% 4 6% 7% 29%	2800
	21st to end	Night	8% 12% 6% 12% 6% 5% 5% 4 6% 8% 28%	2850
December	1st to 10th	Night	7% 15% 6% 15% 8% 6% 6% 4 5% 6% 22%	5026
	11th to 20th	Night	7% 13% 5% 13% 9% 8% 7% 5% 6% 7% 20%	5933
	21st to end	Night	3 7% 3 12% 8% 6% 5% 3 5% 6% 43%	7711

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% 15% 5%	3179
	11th to 20th	Day	50% 8% 14% 18% 10% 1	3180
	21st to end	Day	48% 8% 24% 17% 3	3890
February	1st to 10th	Day	58% 7% 13% 15% 7%	1711
	11th to 20th	Day	52% 7% 14% 17% 9% 1	1764
	21st to end	Day	55% 8% 13% 18% 6%	1529
March	1st to 10th	Day	51% 6% 22% 15% 6%	4500
	11th to 20th	Day	54% 8% 15% 18% 5%	4954
	21st to end	Day	49% 9% 14% 22% 6%	5749
April	1st to 10th	Day	41% 9% 17% 22% 11%	2400
	11th to 20th	Day	52% 7% 14% 18% 8% 1	2446
	21st to end	Day	47% 6% 15% 23% 9% 1	2765
May	1st to 10th	Day	40% 5% 12% 25% 15% 3	6340
	11th to 20th	Day	46% 10% 15% 20% 9%	6302
	21st to end	Day	35% 9% 16% 26% 12% 2	7162
June	1st to 10th	Day	40% 8% 15% 25% 11% 1	3150
	11th to 20th	Day	46% 9% 15% 22% 8% 1	3200
	21st to end	Day	35% 10% 20% 27% 7% 1	3191
July	1st to 10th	Day	28% 9% 24% 27% 10% 1	4742
	11th to 20th	Day	30% 7% 16% 34% 12%	4659
	21st to end	Day	19% 6% 16% 40% 16% 3	4778
August	1st to 10th	Day	31% 7% 20% 29% 12% 1	4396
	11th to 20th	Day	29% 7% 16% 36% 11% 1	4261
	21st to end	Day	28% 5% 19% 32% 15% 1	4380
September	1st to 10th	Day	32% 8% 17% 25% 15% 3	2280
	11th to 20th	Day	39% 7% 16% 26% 10% 2	2280
	21st to end	Day	32% 5% 15% 32% 14% 2	2021
October	1st to 10th	Day	33% 5% 21% 31% 9% 2	3170
	11th to 20th	Day	31% 5% 17% 37% 10%	3119
	21st to end	Day	42% 6% 18% 29% 5%	3041
November	1st to 10th	Day	54% 6% 15% 18% 7% 1	1568
	11th to 20th	Day	55% 9% 15% 16% 5%	1600
	21st to end	Day	55% 9% 17% 17% 3	1546
December	1st to 10th	Day	55% 10% 18% 13% 4	2158
	11th to 20th	Day	62% 8% 20% 7% 4	2260
	21st to end	Day	42% 5% 12% 23% 13% 4	3240
January	1st to 10th	Night	55% 8% 15% 17% 5%	6766
	11th to 20th	Night	55% 7% 13% 14% 10%	6780
	21st to end	Night	47% 8% 23% 19% 3	7081
February	1st to 10th	Night	54% 7% 13% 18% 8%	2705
	11th to 20th	Night	48% 8% 14% 18% 12% 1	2533
	21st to end	Night	43% 8% 16% 23% 9%	2100
March	1st to 10th	Night	48% 7% 22% 18% 4	5374
	11th to 20th	Night	48% 8% 18% 18% 6%	5028
	21st to end	Night	53% 7% 13% 19% 8%	5214
April	1st to 10th	Night	38% 7% 17% 23% 15% 1	2000
	11th to 20th	Night	49% 7% 12% 20% 10% 2	1903
	21st to end	Night	46% 7% 13% 22% 10% 1	1635
May	1st to 10th	Night	42% 5% 11% 22% 18% 3	3640
	11th to 20th	Night	50% 8% 12% 17% 12% 1	3618
	21st to end	Night	35% 9% 14% 25% 15% 2	3708
June	1st to 10th	Night	34% 6% 15% 30% 15% 1	1247
	11th to 20th	Night	43% 8% 15% 22% 12% 1	1200
	21st to end	Night	30% 8% 20% 30% 11% 1	1204
July	1st to 10th	Night	29% 7% 26% 30% 8%	2220
	11th to 20th	Night	22% 7% 14% 43% 15%	2178
	21st to end	Night	17% 5% 14% 45% 16% 3	2541
August	1st to 10th	Night	26% 7% 20% 32% 14% 2	2520
	11th to 20th	Night	25% 6% 16% 37% 14% 1	2642
	21st to end	Night	27% 6% 13% 35% 18% 1	3285
September	1st to 10th	Night	31% 6% 13% 26% 18% 6%	1900
	11th to 20th	Night	33% 8% 15% 28% 13% 3	1900
	21st to end	Night	29% 6% 12% 33% 17% 3	2157
October	1st to 10th	Night	37% 5% 18% 31% 10%	3800
	11th to 20th	Night	29% 4 16% 37% 14% 1	3778
	21st to end	Night	40% 5% 13% 34% 8% 1	4513
November	1st to 10th	Night	54% 7% 13% 18% 7% 1	2730
	11th to 20th	Night	53% 8% 18% 16% 5%	2800
	21st to end	Night	52% 9% 17% 19% 3	2850
December	1st to 10th	Night	62% 7% 16% 11% 3	5026
	11th to 20th	Night	61% 7% 18% 10% 3	5931
	21st to end	Night	43% 4 10% 27% 12% 4	7711

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% 27% 32% 21% 6%	200
	11th to 20th	Day	11% 8% 30% 28% 22% 1	200
	21st to end	Day	8% 11% 29% 34% 16% 2	306
February	1st to 10th	Day	12% 11% 32% 32% 11% 2	300
	11th to 20th	Day	8% 6% 30% 32% 18% 6%	300
	21st to end	Day	7% 6% 26% 34% 22% 4	249
March	1st to 10th	Day	11% 9% 28% 33% 17% 2	300
	11th to 20th	Day	8% 12% 31% 31% 14% 3	480
	21st to end	Day	11% 9% 32% 31% 15% 2	550
April	1st to 10th	Day	7% 14% 33% 30% 13% 3	500
	11th to 20th	Day	14% 15% 33% 26% 9% 3	492
	21st to end	Day	16% 9% 27% 33% 13% 2	665
May	1st to 10th	Day	12% 8% 25% 28% 21% 5%	703
	11th to 20th	Day	11% 8% 25% 32% 18% 6%	725
	21st to end	Day	14% 8% 22% 28% 21% 6%	789
June	1st to 10th	Day	12% 11% 29% 28% 15% 4	730
	11th to 20th	Day	18% 11% 29% 26% 13% 3	730
	21st to end	Day	10% 8% 23% 31% 23% 6%	730
July	1st to 10th	Day	8% 3 21% 35% 25% 7%	697
	11th to 20th	Day	11% 4 25% 29% 24% 7%	668
	21st to end	Day	5% 6% 24% 30% 25% 10%	739
August	1st to 10th	Day	9% 4 21% 36% 22% 9%	676
	11th to 20th	Day	9% 6% 19% 33% 25% 8%	593
	21st to end	Day	12% 4 24% 31% 21% 7%	539
September	1st to 10th	Day	14% 7% 28% 29% 18% 4	490
	11th to 20th	Day	17% 8% 23% 32% 17% 2	490
	21st to end	Day	15% 9% 28% 30% 15% 3	352
October	1st to 10th	Day	16% 6% 27% 24% 22% 5%	300
	11th to 20th	Day	9% 8% 33% 28% 19% 3	300
	21st to end	Day	12% 10% 40% 25% 12% 2	330
November	1st to 10th	Day	20% 8% 31% 26% 11% 4	300
	11th to 20th	Day	13% 11% 32% 30% 13% 1	300
	21st to end	Day	10% 9% 34% 35% 9% 3	300
December	1st to 10th	Day	7% 9% 31% 35% 14% 4	260
	11th to 20th	Day	8% 10% 41% 32% 9% 1	200
	21st to end	Day	10% 1 29% 36% 18% 5%	220
January	1st to 10th	Night	8% 8% 34% 37% 12% 1	1000
	11th to 20th	Night	11% 9% 35% 36% 9% 1	1000
	21st to end	Night	11% 9% 38% 32% 10% 1	1100
February	1st to 10th	Night	12% 6% 30% 36% 15% 1	905
	11th to 20th	Night	9% 8% 30% 37% 14% 2	784
	21st to end	Night	5% 4 23% 42% 21% 5%	660
March	1st to 10th	Night	9% 6% 32% 38% 14% 1	800
	11th to 20th	Night	9% 6% 33% 38% 14% 1	800
	21st to end	Night	12% 6% 30% 38% 12% 2	760
April	1st to 10th	Night	10% 9% 29% 39% 14% 1	600
	11th to 20th	Night	15% 10% 34% 33% 8%	593
	21st to end	Night	17% 8% 30% 35% 10%	600
May	1st to 10th	Night	14% 6% 25% 38% 17% 1	600
	11th to 20th	Night	15% 6% 28% 31% 19% 1	591
	21st to end	Night	18% 6% 23% 34% 17% 3	542
June	1st to 10th	Night	13% 7% 29% 32% 17% 2	400
	11th to 20th	Night	17% 7% 25% 37% 13% 2	400
	21st to end	Night	10% 4 24% 42% 18% 2	400
July	1st to 10th	Night	7% 3 21% 43% 24% 1	380
	11th to 20th	Night	8% 4 24% 42% 20% 2	368
	21st to end	Night	3 5% 24% 43% 23% 2	538
August	1st to 10th	Night	7% 4 23% 41% 23% 3	567
	11th to 20th	Night	6% 2 20% 41% 29% 2	564
	21st to end	Night	8% 4 26% 36% 24% 1	627
September	1st to 10th	Night	12% 5% 24% 38% 20% 1	570
	11th to 20th	Night	13% 6% 21% 42% 18% 1	570
	21st to end	Night	11% 6% 31% 37% 13% 1	689
October	1st to 10th	Night	16% 6% 26% 34% 17% 1	760
	11th to 20th	Night	10% 6% 32% 36% 14% 2	760
	21st to end	Night	14% 9% 34% 34% 9%	1045
November	1st to 10th	Night	21% 7% 33% 32% 8% 1	975
	11th to 20th	Night	11% 9% 33% 34% 12% 2	1000
	21st to end	Night	12% 8% 39% 33% 8% 1	1000
December	1st to 10th	Night	10% 6% 33% 34% 14% 2	1000
	11th to 20th	Night	12% 9% 33% 35% 11% 1	1000
	21st to end	Night	11% 5% 30% 39% 13% 3	1100

Page generated at 2025-07-02 23:30:16. Version ac07

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