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 2024-11-04.

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	9% 8% 3 7% 5% 5% 5% 4 6% 8% 40%	105360
	Night	7% 8% 3 9% 6% 5% 5% 4 6% 8% 39%	102217
Transparency	Day	40% 8% 17% 25% 9% 1	105110
	Night	41% 7% 16% 24% 10% 1	102113
Seeing	Day	12% 8% 27% 30% 18% 5%	15827
	Night	11% 7% 30% 36% 14% 1	25124

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% 13% 5% 11% 10% 8% 6% 4 4 5% 27%	2219
	11th to 20th	Day	4 8% 4 11% 9% 10% 12% 7% 6% 8% 22%	2199
	21st to end	Day	4 11% 4 9% 8% 6% 5% 4 6% 8% 34%	2708
February	1st to 10th	Day	8% 13% 6% 13% 6% 7% 6% 5% 6% 7% 24%	1625
	11th to 20th	Day	8% 13% 4 10% 8% 6% 6% 5% 5% 6% 29%	1665
	21st to end	Day	5% 10% 5% 13% 8% 7% 7% 5% 7% 7% 24%	1455
March	1st to 10th	Day	7% 13% 5% 12% 8% 6% 6% 4 5% 6% 29%	3130
	11th to 20th	Day	4 11% 6% 12% 5% 4 4 3 6% 8% 36%	3457
	21st to end	Day	6% 9% 5% 12% 7% 5% 5% 5% 6% 8% 31%	4010
April	1st to 10th	Day	7% 8% 3 8% 6% 6% 6% 5% 8% 8% 36%	2280
	11th to 20th	Day	11% 12% 4 10% 6% 4 5% 4 6% 8% 29%	2322
	21st to end	Day	15% 9% 3 8% 4 4 4 4 5% 6% 36%	2627
May	1st to 10th	Day	20% 10% 2 5% 4 4 4 3 6% 7% 34%	4430
	11th to 20th	Day	7% 6% 3 7% 5% 6% 6% 5% 8% 9% 36%	4388
	21st to end	Day	13% 7% 2 8% 5% 5% 5% 5% 6% 9% 35%	4996
June	1st to 10th	Day	14% 7% 2 6% 4 5% 5% 4 6% 8% 39%	2992
	11th to 20th	Day	18% 7% 2 6% 5% 5% 5% 4 7% 8% 34%	3040
	21st to end	Day	9% 5% 2 5% 5% 4 5% 4 7% 10% 43%	3032
July	1st to 10th	Day	4 5% 2 6% 4 5% 5% 4 8% 9% 48%	4740
	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% 6% 3 3 5% 5% 31%	1512
	11th to 20th	Day	6% 13% 4 13% 7% 6% 5% 4 7% 6% 28%	1520
	21st to end	Day	9% 12% 6% 11% 7% 5% 6% 5% 6% 7% 27%	1469
December	1st to 10th	Day	6% 15% 4 12% 9% 7% 6% 5% 6% 6% 25%	1254
	11th to 20th	Day	6% 11% 5% 13% 9% 7% 6% 4 5% 7% 27%	1439
	21st to end	Day	4 9% 3 8% 5% 5% 5% 4 6% 7% 44%	2254
January	1st to 10th	Night	4 10% 6% 14% 8% 6% 6% 5% 7% 8% 26%	4726
	11th to 20th	Night	4 7% 4 15% 10% 9% 9% 6% 6% 6% 23%	4699
	21st to end	Night	6% 12% 4 10% 6% 5% 5% 4 6% 7% 35%	4954
February	1st to 10th	Night	7% 13% 5% 11% 7% 6% 5% 6% 6% 8% 26%	2570
	11th to 20th	Night	6% 11% 5% 12% 6% 7% 5% 4 7% 8% 30%	2402
	21st to end	Night	4 8% 4 10% 8% 6% 7% 5% 8% 9% 31%	1998
March	1st to 10th	Night	6% 11% 4 13% 8% 6% 6% 4 7% 8% 27%	3734
	11th to 20th	Night	5% 10% 4 8% 6% 6% 6% 5% 6% 9% 35%	3505
	21st to end	Night	6% 8% 5% 12% 7% 6% 6% 5% 7% 9% 29%	3637
April	1st to 10th	Night	7% 9% 2 6% 5% 5% 6% 4 5% 9% 42%	1900
	11th to 20th	Night	11% 12% 4 9% 6% 4 5% 5% 6% 7% 31%	1807
	21st to end	Night	12% 10% 3 7% 5% 5% 5% 4 6% 8% 35%	1553
May	1st to 10th	Night	21% 11% 3 7% 4 3 3 3 5% 5% 34%	2540
	11th to 20th	Night	13% 8% 3 6% 4 4 4 4 7% 7% 39%	2518
	21st to end	Night	15% 7% 2 8% 4 5% 5% 3 6% 8% 37%	2582
June	1st to 10th	Night	12% 5% 2 5% 6% 5% 4 4 6% 9% 43%	1185
	11th to 20th	Night	16% 5% 2 6% 7% 5% 5% 5% 7% 9% 34%	1140
	21st to end	Night	9% 4 2 5% 3 4 4 4 6% 10% 49%	1144
July	1st to 10th	Night	7% 4 2 4 4 5% 5% 4 8% 11% 46%	2220
	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	15% 13% 4 10% 6% 4 5% 3 4 5% 30%	2639
	11th to 20th	Night	6% 12% 5% 14% 7% 6% 5% 4 6% 7% 29%	2660
	21st to end	Night	8% 12% 6% 11% 6% 5% 5% 4 6% 8% 29%	2707
December	1st to 10th	Night	7% 12% 5% 12% 9% 6% 6% 4 6% 6% 27%	2924
	11th to 20th	Night	8% 12% 5% 13% 7% 7% 6% 5% 6% 7% 24%	3753
	21st to end	Night	4 7% 3 7% 5% 4 4 3 5% 6% 52%	5397

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	58% 7% 14% 14% 7%	2219
	11th to 20th	Day	57% 10% 14% 15% 4 1	2220
	21st to end	Day	46% 9% 19% 22% 5%	2708
February	1st to 10th	Day	58% 7% 13% 16% 6%	1625
	11th to 20th	Day	54% 7% 14% 16% 9% 1	1674
	21st to end	Day	55% 8% 13% 17% 6%	1455
March	1st to 10th	Day	54% 7% 20% 13% 6%	3130
	11th to 20th	Day	45% 11% 20% 18% 6%	3458
	21st to end	Day	47% 10% 17% 20% 6%	4010
April	1st to 10th	Day	41% 9% 17% 22% 10%	2280
	11th to 20th	Day	52% 7% 15% 18% 7% 2	2322
	21st to end	Day	47% 6% 15% 22% 8% 1	2627
May	1st to 10th	Day	47% 7% 16% 22% 7% 1	4430
	11th to 20th	Day	36% 12% 16% 23% 12%	4392
	21st to end	Day	40% 12% 20% 20% 7% 1	4996
June	1st to 10th	Day	41% 8% 15% 24% 11% 1	2992
	11th to 20th	Day	45% 9% 15% 22% 8% 1	3040
	21st to end	Day	34% 11% 20% 27% 7% 1	3032
July	1st to 10th	Day	28% 9% 24% 27% 10% 1	4666
	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	55% 6% 14% 18% 7% 1	1512
	11th to 20th	Day	53% 9% 15% 16% 5%	1520
	21st to end	Day	54% 9% 17% 17% 3	1469
December	1st to 10th	Day	57% 9% 15% 14% 5%	1254
	11th to 20th	Day	55% 8% 21% 10% 6%	1440
	21st to end	Day	38% 6% 15% 21% 14% 6%	2254
January	1st to 10th	Night	51% 10% 19% 16% 4	4726
	11th to 20th	Night	58% 7% 15% 14% 6% 1	4740
	21st to end	Night	46% 9% 19% 22% 4	4954
February	1st to 10th	Night	53% 7% 14% 19% 7%	2570
	11th to 20th	Night	49% 8% 14% 17% 11% 1	2403
	21st to end	Night	44% 8% 15% 23% 9%	1998
March	1st to 10th	Night	50% 9% 19% 19% 4	3734
	11th to 20th	Night	41% 11% 23% 18% 7%	3505
	21st to end	Night	47% 9% 17% 18% 9%	3637
April	1st to 10th	Night	38% 7% 17% 23% 14% 1	1900
	11th to 20th	Night	50% 7% 12% 19% 10% 3	1807
	21st to end	Night	46% 8% 14% 22% 10% 1	1553
May	1st to 10th	Night	51% 6% 13% 21% 9% 1	2540
	11th to 20th	Night	39% 10% 13% 20% 17% 2	2518
	21st to end	Night	39% 12% 17% 24% 9%	2582
June	1st to 10th	Night	36% 6% 15% 29% 14% 1	1185
	11th to 20th	Night	44% 8% 14% 21% 12% 1	1140
	21st to end	Night	30% 8% 20% 30% 11% 1	1144
July	1st to 10th	Night	29% 7% 26% 29% 7%	2185
	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	55% 7% 13% 17% 7% 1	2639
	11th to 20th	Night	52% 8% 18% 16% 6%	2660
	21st to end	Night	50% 9% 18% 20% 4	2707
December	1st to 10th	Night	56% 7% 15% 16% 6%	2924
	11th to 20th	Night	57% 9% 16% 14% 4	3751
	21st to end	Night	33% 5% 13% 27% 15% 6%	5397

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% 4 27% 32% 21% 6%	180
	11th to 20th	Day	12% 8% 27% 28% 23% 1	180
	21st to end	Day	9% 11% 28% 33% 17% 2	275
February	1st to 10th	Day	13% 12% 29% 33% 12% 1	270
	11th to 20th	Day	9% 7% 31% 31% 16% 6%	270
	21st to end	Day	8% 6% 26% 34% 22% 4	225
March	1st to 10th	Day	11% 10% 29% 33% 15% 2	270
	11th to 20th	Day	9% 12% 32% 31% 14% 3	441
	21st to end	Day	11% 8% 32% 30% 16% 2	506
April	1st to 10th	Day	8% 14% 34% 28% 12% 3	460
	11th to 20th	Day	15% 15% 32% 26% 9% 3	452
	21st to end	Day	16% 10% 27% 33% 13% 1	617
May	1st to 10th	Day	13% 8% 25% 27% 22% 5%	653
	11th to 20th	Day	9% 8% 25% 33% 19% 7%	675
	21st to end	Day	14% 9% 23% 27% 21% 6%	734
June	1st to 10th	Day	13% 10% 29% 29% 15% 4	680
	11th to 20th	Day	19% 11% 29% 26% 13% 3	680
	21st to end	Day	9% 8% 24% 30% 23% 6%	680
July	1st to 10th	Day	8% 3 21% 35% 25% 7%	671
	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% 28% 27% 12% 4	279
	11th to 20th	Day	13% 11% 31% 31% 13% 1	270
	21st to end	Day	9% 10% 32% 36% 10% 3	270
December	1st to 10th	Day	7% 8% 30% 35% 15% 5%	234
	11th to 20th	Day	7% 10% 42% 31% 9% 1	180
	21st to end	Day	11% 2 31% 33% 18% 6%	198
January	1st to 10th	Night	8% 8% 34% 37% 12% 1	950
	11th to 20th	Night	11% 9% 34% 36% 9% 1	950
	21st to end	Night	11% 9% 36% 33% 11% 1	1045
February	1st to 10th	Night	12% 6% 29% 37% 15% 1	860
	11th to 20th	Night	10% 8% 31% 36% 13% 2	744
	21st to end	Night	5% 4 23% 42% 21% 5%	628
March	1st to 10th	Night	10% 6% 32% 36% 14% 1	760
	11th to 20th	Night	9% 6% 33% 37% 14% 1	760
	21st to end	Night	12% 6% 30% 39% 11% 2	722
April	1st to 10th	Night	10% 9% 29% 38% 13% 1	570
	11th to 20th	Night	15% 10% 33% 33% 8%	563
	21st to end	Night	17% 9% 31% 35% 9%	570
May	1st to 10th	Night	15% 6% 25% 37% 16% 1	570
	11th to 20th	Night	13% 6% 28% 32% 20% 1	561
	21st to end	Night	18% 6% 23% 32% 17% 3	515
June	1st to 10th	Night	14% 7% 28% 32% 17% 2	380
	11th to 20th	Night	17% 7% 25% 36% 14% 2	380
	21st to end	Night	10% 3 23% 44% 18% 2	380
July	1st to 10th	Night	8% 3 21% 43% 25% 1	370
	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% 31% 8% 1	943
	11th to 20th	Night	11% 9% 33% 34% 12% 2	950
	21st to end	Night	12% 8% 39% 32% 8% 1	950
December	1st to 10th	Night	10% 6% 33% 34% 15% 2	950
	11th to 20th	Night	12% 9% 32% 35% 11% 1	950
	21st to end	Night	11% 5% 30% 38% 13% 2	1045

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