Fall River State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fall River State Park clear sky chart from 2005-11-06 to 2025-11-18.

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	11% 6% 2 6% 4 4 4 3 5% 7% 49%	127055
	Night	10% 5% 2 5% 3 3 3 3 5% 7% 53%	123599
Transparency	Day	34% 5% 11% 26% 20% 4	130706
	Night	31% 5% 11% 26% 22% 5%	128011
Seeing	Day	13% 9% 27% 29% 17% 4	16980
	Night	13% 9% 32% 34% 13% 1	26799

By Month

Percentage Cloud Cover SE (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	15% 8% 3 7% 5% 4 3 3 4 7% 42%	4077
	11th to 20th	Day	8% 8% 3 8% 6% 6% 4 3 4 5% 45%	4080
	21st to end	Day	12% 11% 3 6% 3 4 3 2 3 5% 47%	4488
February	1st to 10th	Day	15% 9% 3 7% 5% 4 3 2 4 6% 43%	1800
	11th to 20th	Day	11% 7% 3 8% 4 4 4 3 5% 6% 46%	1867
	21st to end	Day	10% 8% 3 6% 3 4 5% 4 5% 7% 45%	1660
March	1st to 10th	Day	10% 7% 2 6% 3 3 3 3 3 5% 54%	4936
	11th to 20th	Day	8% 6% 1 4 3 3 3 3 5% 7% 57%	4980
	21st to end	Day	11% 8% 4 8% 5% 4 4 3 6% 7% 39%	5462
April	1st to 10th	Day	12% 7% 2 5% 4 3 3 3 4 7% 48%	2220
	11th to 20th	Day	15% 7% 2 6% 4 4 3 3 5% 6% 44%	2394
	21st to end	Day	18% 9% 3 6% 4 4 3 4 5% 5% 40%	2600
May	1st to 10th	Day	18% 8% 2 6% 4 4 4 2 4 5% 42%	5862
	11th to 20th	Day	12% 6% 2 5% 4 3 4 3 5% 7% 50%	5862
	21st to end	Day	19% 6% 2 6% 4 3 4 3 6% 7% 39%	6434
June	1st to 10th	Day	6% 4 1 5% 5% 4 5% 4 6% 10% 50%	2600
	11th to 20th	Day	8% 4 2 5% 4 4 5% 3 6% 9% 51%	2600
	21st to end	Day	6% 3 2 3 4 4 4 4 6% 8% 57%	2600
July	1st to 10th	Day	8% 4 2 6% 4 5% 5% 4 7% 8% 46%	5900
	11th to 20th	Day	8% 4 2 5% 4 4 4 4 6% 9% 50%	5900
	21st to end	Day	5% 4 2 6% 5% 6% 6% 5% 7% 10% 44%	6422
August	1st to 10th	Day	6% 3 2 5% 4 3 4 4 6% 8% 54%	4234
	11th to 20th	Day	7% 4 2 7% 4 4 4 4 5% 8% 50%	4171
	21st to end	Day	6% 3 2 4 3 4 4 3 5% 8% 59%	4492
September	1st to 10th	Day	13% 4 1 5% 4 2 4 3 4 6% 53%	2266
	11th to 20th	Day	10% 5% 2 6% 3 4 4 3 5% 7% 50%	2200
	21st to end	Day	9% 4 2 5% 3 4 4 3 4 6% 57%	2200
October	1st to 10th	Day	8% 5% 2 6% 4 4 4 3 5% 6% 53%	2066
	11th to 20th	Day	10% 3 1 3 3 2 3 3 5% 6% 61%	2000
	21st to end	Day	16% 6% 2 4 3 3 3 2 4 5% 53%	2200
November	1st to 10th	Day	9% 6% 1 4 2 2 3 3 4 6% 60%	2000
	11th to 20th	Day	9% 5% 1 4 3 3 3 2 3 6% 58%	1863
	21st to end	Day	13% 6% 2 4 3 2 2 2 4 5% 56%	1800
December	1st to 10th	Day	6% 6% 2 5% 3 3 3 3 4 6% 60%	2940
	11th to 20th	Day	9% 6% 2 5% 4 4 4 3 4 5% 55%	3391
	21st to end	Day	16% 14% 6% 9% 4 4 4 3 4 5% 31%	4488
January	1st to 10th	Night	13% 8% 3 7% 4 3 3 2 4 6% 46%	5888
	11th to 20th	Night	7% 6% 3 7% 5% 5% 5% 3 4 5% 50%	5900
	21st to end	Night	14% 9% 3 6% 3 2 3 2 3 4 51%	6490
February	1st to 10th	Night	11% 9% 3 6% 5% 4 3 3 5% 6% 45%	2600
	11th to 20th	Night	13% 8% 3 6% 4 4 4 3 4 6% 48%	2435
	21st to end	Night	11% 6% 2 5% 3 2 3 3 5% 7% 52%	1968
March	1st to 10th	Night	12% 7% 2 5% 3 3 3 2 4 5% 55%	4919
	11th to 20th	Night	7% 3 1 3 3 3 4 3 4 6% 62%	4980
	21st to end	Night	12% 6% 2 5% 4 4 4 4 5% 7% 47%	5467
April	1st to 10th	Night	11% 5% 2 5% 4 3 3 3 5% 6% 53%	2180
	11th to 20th	Night	12% 6% 2 6% 4 3 3 3 4 7% 50%	1951
	21st to end	Night	16% 6% 2 5% 5% 3 3 3 5% 6% 47%	1800
May	1st to 10th	Night	18% 7% 2 6% 3 3 2 2 4 6% 46%	4053
	11th to 20th	Night	15% 6% 2 5% 3 3 4 2 4 7% 51%	4053
	21st to end	Night	19% 5% 1 4 2 3 2 2 4 7% 50%	4443
June	1st to 10th	Night	5% 4 2 4 3 4 5% 4 7% 9% 53%	1800
	11th to 20th	Night	4 5% 2 4 3 3 4 5% 6% 11% 52%	1800
	21st to end	Night	6% 2 2 4 3 4 4 4 6% 8% 58%	1800
July	1st to 10th	Night	6% 4 2 5% 4 4 4 3 6% 9% 53%	4078
	11th to 20th	Night	5% 4 2 5% 3 4 4 3 6% 11% 54%	4077
	21st to end	Night	5% 4 2 7% 4 5% 5% 5% 8% 10% 46%	4449
August	1st to 10th	Night	3 2 1 3 3 4 4 4 6% 9% 59%	2926
	11th to 20th	Night	7% 3 2 5% 4 4 4 4 6% 8% 53%	2888
	21st to end	Night	4 2 1 3 3 3 3 3 4 8% 64%	3411
September	1st to 10th	Night	10% 3 2 4 3 3 2 3 5% 5% 59%	2130
	11th to 20th	Night	10% 4 1 5% 3 3 5% 4 6% 6% 52%	2200
	21st to end	Night	7% 3 2 4 2 3 3 3 5% 6% 61%	2200
October	1st to 10th	Night	9% 4 2 5% 3 3 3 3 4 6% 58%	2312
	11th to 20th	Night	11% 4 2 3 3 3 2 2 4 6% 60%	2400
	21st to end	Night	14% 5% 2 4 3 3 3 3 4 4 56%	2640
November	1st to 10th	Night	9% 4 1 4 3 2 3 2 4 5% 62%	2513
	11th to 20th	Night	9% 6% 1 4 3 3 4 3 5% 6% 58%	2692
	21st to end	Night	13% 7% 2 4 3 2 3 3 3 5% 56%	2600
December	1st to 10th	Night	6% 4 1 4 3 3 3 2 4 6% 63%	4250
	11th to 20th	Night	10% 5% 2 5% 3 3 3 3 4 6% 56%	4816
	21st to end	Night	19% 9% 4 7% 4 4 4 3 4 5% 38%	6490

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	42% 5% 11% 25% 15% 2	4078
	11th to 20th	Day	40% 4 10% 22% 19% 4	4080
	21st to end	Day	42% 3 9% 21% 20% 5%	4488
February	1st to 10th	Day	44% 4 11% 25% 11% 4	1800
	11th to 20th	Day	39% 5% 11% 25% 15% 3	1876
	21st to end	Day	38% 5% 9% 22% 19% 7%	1660
March	1st to 10th	Day	34% 3 6% 20% 24% 13%	4936
	11th to 20th	Day	27% 4 9% 21% 24% 15%	4980
	21st to end	Day	42% 7% 11% 28% 10% 1	5464
April	1st to 10th	Day	35% 5% 13% 24% 18% 5%	2220
	11th to 20th	Day	41% 4 10% 23% 17% 4	2394
	21st to end	Day	45% 6% 10% 25% 13% 1	2600
May	1st to 10th	Day	45% 5% 9% 18% 20% 2	5900
	11th to 20th	Day	33% 7% 10% 23% 23% 4	5866
	21st to end	Day	44% 7% 11% 19% 18% 2	6447
June	1st to 10th	Day	28% 10% 17% 26% 17% 2	2600
	11th to 20th	Day	31% 6% 12% 29% 19% 2	2600
	21st to end	Day	22% 6% 17% 28% 21% 5%	2600
July	1st to 10th	Day	32% 7% 12% 26% 20% 3	5836
	11th to 20th	Day	31% 6% 12% 31% 19% 2	5831
	21st to end	Day	30% 8% 18% 31% 13%	6240
August	1st to 10th	Day	27% 6% 14% 26% 23% 5%	4220
	11th to 20th	Day	33% 6% 16% 26% 17% 2	4210
	21st to end	Day	24% 5% 16% 36% 14% 5%	4491
September	1st to 10th	Day	32% 5% 12% 24% 20% 7%	2266
	11th to 20th	Day	33% 5% 11% 26% 22% 3	2200
	21st to end	Day	30% 5% 9% 22% 29% 5%	2200
October	1st to 10th	Day	21% 4 8% 17% 41% 11%	3365
	11th to 20th	Day	15% 3 6% 31% 32% 12%	3240
	21st to end	Day	28% 3 8% 27% 27% 7%	3538
November	1st to 10th	Day	26% 4 9% 32% 23% 6%	2000
	11th to 20th	Day	28% 4 9% 28% 26% 6%	1863
	21st to end	Day	32% 3 10% 29% 23% 3	1800
December	1st to 10th	Day	28% 3 8% 38% 21% 1	2940
	11th to 20th	Day	32% 5% 7% 32% 21% 2	3389
	21st to end	Day	55% 5% 9% 22% 8% 1	4488
January	1st to 10th	Night	40% 4 11% 29% 14% 2	5888
	11th to 20th	Night	34% 6% 10% 24% 21% 5%	5900
	21st to end	Night	38% 2 9% 21% 23% 5%	6490
February	1st to 10th	Night	41% 4 12% 24% 15% 4	2600
	11th to 20th	Night	39% 4 11% 26% 17% 3	2436
	21st to end	Night	32% 4 9% 24% 22% 8%	1968
March	1st to 10th	Night	33% 4 6% 23% 26% 8%	4919
	11th to 20th	Night	22% 4 8% 19% 34% 12%	4980
	21st to end	Night	35% 6% 15% 28% 14% 2	5467
April	1st to 10th	Night	31% 5% 11% 23% 23% 7%	2180
	11th to 20th	Night	35% 5% 12% 23% 20% 6%	1951
	21st to end	Night	37% 6% 14% 22% 17% 4	1800
May	1st to 10th	Night	40% 6% 13% 22% 17% 3	4080
	11th to 20th	Night	34% 6% 11% 23% 19% 7%	4054
	21st to end	Night	34% 6% 14% 25% 18% 3	4452
June	1st to 10th	Night	26% 8% 18% 28% 18% 2	1800
	11th to 20th	Night	24% 8% 16% 29% 20% 3	1800
	21st to end	Night	23% 7% 14% 30% 22% 5%	1800
July	1st to 10th	Night	27% 6% 15% 29% 21% 3	4035
	11th to 20th	Night	24% 5% 12% 37% 20% 2	4026
	21st to end	Night	29% 8% 17% 34% 11% 1	4320
August	1st to 10th	Night	20% 6% 15% 31% 19% 9%	2916
	11th to 20th	Night	28% 7% 15% 28% 20% 3	2915
	21st to end	Night	19% 5% 14% 37% 20% 5%	3411
September	1st to 10th	Night	27% 5% 11% 27% 20% 10%	2130
	11th to 20th	Night	30% 6% 11% 24% 23% 5%	2200
	21st to end	Night	23% 5% 9% 26% 31% 6%	2200
October	1st to 10th	Night	17% 3 7% 14% 45% 14%	3780
	11th to 20th	Night	19% 3 6% 24% 34% 15%	3899
	21st to end	Night	27% 3 8% 26% 31% 6%	4252
November	1st to 10th	Night	26% 3 9% 30% 25% 7%	2513
	11th to 20th	Night	28% 4 8% 26% 29% 5%	2692
	21st to end	Night	32% 4 9% 26% 24% 5%	2600
December	1st to 10th	Night	24% 3 12% 40% 19% 1	4250
	11th to 20th	Night	32% 3 8% 29% 23% 4	4817
	21st to end	Night	47% 5% 9% 25% 11% 3	6490

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	19% 12% 34% 28% 7% 1	300
	11th to 20th	Day	22% 16% 38% 20% 3	300
	21st to end	Day	14% 10% 46% 25% 4 1	330
February	1st to 10th	Day	22% 17% 35% 22% 3 1	300
	11th to 20th	Day	18% 16% 41% 21% 4	300
	21st to end	Day	16% 19% 40% 19% 5%	249
March	1st to 10th	Day	19% 18% 35% 23% 5%	300
	11th to 20th	Day	24% 15% 35% 19% 7%	300
	21st to end	Day	23% 16% 40% 16% 5%	330
April	1st to 10th	Day	17% 22% 36% 21% 4	320
	11th to 20th	Day	19% 17% 36% 22% 5%	512
	21st to end	Day	23% 14% 35% 19% 7% 1	700
May	1st to 10th	Day	16% 12% 36% 26% 10% 1	703
	11th to 20th	Day	18% 12% 29% 26% 13% 3	725
	21st to end	Day	16% 11% 29% 25% 15% 4	789
June	1st to 10th	Day	5% 5% 22% 35% 24% 8%	730
	11th to 20th	Day	8% 4 26% 40% 18% 4	730
	21st to end	Day	5% 5% 26% 42% 19% 3	730
July	1st to 10th	Day	7% 3 16% 32% 30% 11%	721
	11th to 20th	Day	5% 3 13% 39% 33% 8%	718
	21st to end	Day	8% 2 10% 34% 35% 11%	794
August	1st to 10th	Day	7% 3 17% 37% 30% 7%	726
	11th to 20th	Day	8% 2 15% 35% 33% 7%	715
	21st to end	Day	8% 2 12% 33% 36% 10%	698
September	1st to 10th	Day	12% 1 14% 31% 33% 8%	396
	11th to 20th	Day	6% 2 18% 38% 26% 10%	330
	21st to end	Day	15% 4 22% 33% 20% 7%	330
October	1st to 10th	Day	11% 6% 27% 28% 19% 9%	330
	11th to 20th	Day	8% 8% 44% 28% 11% 1	330
	21st to end	Day	26% 9% 33% 21% 8% 2	363
November	1st to 10th	Day	15% 11% 32% 26% 13% 2	330
	11th to 20th	Day	15% 13% 38% 20% 12% 2	321
	21st to end	Day	17% 14% 36% 24% 9%	300
December	1st to 10th	Day	10% 12% 42% 22% 11% 2	300
	11th to 20th	Day	16% 15% 35% 25% 8% 1	300
	21st to end	Day	17% 21% 37% 22% 3	330
January	1st to 10th	Night	12% 12% 39% 30% 8%	1000
	11th to 20th	Night	14% 13% 40% 27% 6%	1000
	21st to end	Night	12% 12% 40% 30% 5%	1100
February	1st to 10th	Night	16% 14% 39% 27% 4	1000
	11th to 20th	Night	16% 15% 37% 29% 2	881
	21st to end	Night	15% 14% 40% 27% 5%	648
March	1st to 10th	Night	13% 12% 40% 31% 4	600
	11th to 20th	Night	18% 12% 35% 29% 5%	600
	21st to end	Night	19% 14% 40% 23% 3	660
April	1st to 10th	Night	14% 14% 40% 26% 6%	600
	11th to 20th	Night	16% 15% 38% 26% 5%	593
	21st to end	Night	17% 12% 38% 27% 6% 1	600
May	1st to 10th	Night	17% 8% 37% 32% 7% 1	600
	11th to 20th	Night	15% 6% 31% 32% 16%	591
	21st to end	Night	12% 6% 29% 32% 18% 2	650
June	1st to 10th	Night	7% 3 22% 42% 26% 1	600
	11th to 20th	Night	6% 3 27% 48% 17%	600
	21st to end	Night	6% 2 33% 43% 15% 1	600
July	1st to 10th	Night	7% 2 14% 44% 31% 2	585
	11th to 20th	Night	3 1 16% 47% 32% 2	582
	21st to end	Night	7% 1 13% 44% 32% 3	657
August	1st to 10th	Night	6% 1 16% 48% 28% 2	597
	11th to 20th	Night	6% 2 13% 48% 30% 2	594
	21st to end	Night	5% 1 13% 41% 37% 2	660
September	1st to 10th	Night	11% 1 18% 43% 26% 2	600
	11th to 20th	Night	11% 2 21% 39% 24% 3	600
	21st to end	Night	9% 4 22% 41% 21% 4	600
October	1st to 10th	Night	11% 3 27% 36% 21% 2	712
	11th to 20th	Night	13% 7% 39% 32% 8% 1	800
	21st to end	Night	18% 12% 31% 29% 9% 1	880
November	1st to 10th	Night	11% 9% 37% 31% 10% 1	873
	11th to 20th	Night	12% 13% 35% 32% 8% 1	1036
	21st to end	Night	17% 11% 32% 32% 8%	1000
December	1st to 10th	Night	13% 10% 37% 32% 7% 1	1000
	11th to 20th	Night	18% 10% 36% 31% 5%	1000
	21st to end	Night	17% 14% 33% 30% 5%	1100

Page generated at 2025-11-14 23:55:56. Version ac07

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