Fall River Pkwy Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fall River Pkwy Observatory clear sky chart from 2005-11-06 to 2024-12-02.

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% 6% 2 7% 5% 5% 6% 5% 7% 9% 38%	101259
	Night	9% 6% 2 7% 5% 5% 5% 4 7% 9% 41%	98312
Transparency	Day	37% 10% 16% 18% 14% 5%	105001
	Night	37% 9% 15% 18% 15% 6%	102709
Seeing	Day	10% 6% 19% 28% 24% 13%	15554
	Night	11% 5% 19% 31% 27% 6%	25618

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	11% 8% 2 7% 4 3 4 3 5% 7% 47%	2836
	11th to 20th	Day	14% 7% 3 7% 5% 5% 4 4 4 7% 40%	2840
	21st to end	Day	10% 7% 3 7% 5% 4 4 3 5% 8% 45%	3124
February	1st to 10th	Day	15% 8% 2 7% 4 4 4 3 4 6% 43%	1876
	11th to 20th	Day	13% 6% 2 5% 4 3 3 3 5% 6% 49%	1848
	21st to end	Day	13% 6% 3 5% 4 3 4 4 5% 7% 47%	1646
March	1st to 10th	Day	11% 10% 3 9% 5% 4 5% 3 7% 7% 37%	3435
	11th to 20th	Day	6% 4 2 5% 3 4 4 4 6% 9% 52%	3480
	21st to end	Day	14% 7% 2 6% 4 4 4 4 5% 8% 42%	3815
April	1st to 10th	Day	8% 5% 2 5% 4 4 5% 4 6% 8% 48%	2090
	11th to 20th	Day	8% 6% 3 7% 5% 5% 5% 4 6% 7% 45%	2144
	21st to end	Day	5% 4 1 5% 4 4 4 4 6% 10% 53%	2315
May	1st to 10th	Day	5% 3 2 4 4 4 5% 4 6% 10% 52%	4082
	11th to 20th	Day	8% 7% 3 7% 5% 5% 6% 5% 9% 9% 36%	4081
	21st to end	Day	5% 4 1 5% 4 5% 5% 5% 8% 12% 46%	4476
June	1st to 10th	Day	10% 6% 2 7% 5% 7% 7% 6% 9% 11% 30%	2470
	11th to 20th	Day	4 5% 2 7% 6% 6% 7% 6% 10% 12% 33%	2470
	21st to end	Day	7% 6% 3 8% 7% 8% 7% 7% 9% 10% 28%	2470
July	1st to 10th	Day	6% 6% 3 8% 7% 8% 9% 8% 10% 11% 24%	4120
	11th to 20th	Day	4 4 2 7% 7% 8% 9% 8% 11% 14% 25%	4120
	21st to end	Day	4 4 2 6% 7% 7% 9% 8% 11% 15% 27%	4466
August	1st to 10th	Day	11% 6% 3 9% 6% 7% 7% 6% 10% 11% 24%	4104
	11th to 20th	Day	5% 5% 2 6% 5% 6% 6% 5% 9% 13% 36%	4020
	21st to end	Day	8% 6% 2 8% 6% 7% 7% 6% 8% 10% 32%	3875
September	1st to 10th	Day	10% 9% 4 9% 7% 7% 7% 6% 8% 10% 24%	2090
	11th to 20th	Day	13% 7% 3 9% 7% 7% 7% 6% 8% 8% 24%	2090
	21st to end	Day	13% 8% 2 9% 5% 5% 5% 5% 7% 9% 32%	2090
October	1st to 10th	Day	12% 6% 3 7% 5% 5% 6% 4 6% 10% 36%	2043
	11th to 20th	Day	6% 5% 3 5% 4 5% 4 3 6% 8% 51%	1900
	21st to end	Day	9% 5% 2 5% 4 4 5% 3 5% 9% 49%	2090
November	1st to 10th	Day	11% 6% 3 7% 4 4 5% 3 5% 8% 45%	1957
	11th to 20th	Day	10% 7% 3 7% 4 4 5% 3 6% 7% 44%	2000
	21st to end	Day	12% 6% 2 8% 4 4 4 4 5% 6% 45%	1800
December	1st to 10th	Day	9% 5% 3 6% 5% 5% 5% 4 6% 8% 44%	1719
	11th to 20th	Day	14% 8% 3 5% 5% 5% 4 3 5% 7% 42%	2153
	21st to end	Day	15% 7% 3 8% 5% 4 4 3 4 5% 42%	3124
January	1st to 10th	Night	13% 9% 3 7% 4 4 4 3 5% 8% 42%	4109
	11th to 20th	Night	10% 9% 3 7% 5% 4 5% 5% 6% 8% 38%	4120
	21st to end	Night	11% 8% 3 8% 5% 4 5% 3 5% 6% 41%	4532
February	1st to 10th	Night	14% 7% 3 7% 5% 4 4 4 5% 6% 42%	2299
	11th to 20th	Night	13% 7% 2 7% 5% 5% 4 3 4 6% 46%	2218
	21st to end	Night	11% 6% 3 6% 5% 3 4 3 6% 7% 45%	1806
March	1st to 10th	Night	17% 12% 4 8% 5% 4 3 3 4 5% 36%	3418
	11th to 20th	Night	6% 5% 1 5% 4 4 4 4 7% 11% 49%	3480
	21st to end	Night	12% 8% 3 6% 4 3 4 3 5% 6% 47%	3817
April	1st to 10th	Night	7% 6% 2 5% 4 4 5% 3 6% 8% 49%	2090
	11th to 20th	Night	8% 6% 2 5% 4 4 4 4 5% 7% 51%	1984
	21st to end	Night	6% 4 1 4 4 4 4 5% 8% 9% 53%	1878
May	1st to 10th	Night	4 3 2 4 4 4 5% 4 8% 9% 54%	2813
	11th to 20th	Night	8% 6% 2 7% 5% 4 5% 5% 7% 9% 41%	2812
	21st to end	Night	4 3 1 4 4 4 4 4 7% 10% 55%	3079
June	1st to 10th	Night	8% 5% 2 6% 4 6% 5% 6% 9% 12% 37%	1710
	11th to 20th	Night	5% 5% 2 6% 6% 5% 7% 6% 9% 13% 37%	1710
	21st to end	Night	7% 5% 2 8% 5% 6% 6% 5% 9% 13% 33%	1710
July	1st to 10th	Night	5% 5% 3 9% 6% 7% 6% 6% 9% 13% 30%	2840
	11th to 20th	Night	4 4 2 8% 6% 6% 7% 5% 11% 15% 31%	2840
	21st to end	Night	5% 6% 3 7% 6% 7% 8% 7% 11% 14% 26%	3087
August	1st to 10th	Night	10% 6% 3 8% 6% 7% 6% 6% 9% 11% 27%	2825
	11th to 20th	Night	4 4 2 6% 5% 5% 6% 5% 8% 12% 42%	2785
	21st to end	Night	7% 6% 3 8% 5% 5% 6% 4 7% 11% 38%	3752
September	1st to 10th	Night	10% 8% 3 9% 6% 7% 7% 6% 7% 10% 26%	2090
	11th to 20th	Night	12% 7% 3 7% 7% 7% 7% 6% 9% 10% 25%	2090
	21st to end	Night	9% 6% 3 8% 5% 6% 5% 4 7% 10% 37%	2090
October	1st to 10th	Night	12% 7% 3 7% 5% 5% 5% 3 5% 8% 40%	2135
	11th to 20th	Night	6% 4 2 5% 3 4 4 4 5% 8% 54%	2280
	21st to end	Night	8% 5% 2 6% 4 4 4 4 7% 6% 51%	2508
November	1st to 10th	Night	10% 6% 2 7% 4 4 4 3 6% 8% 46%	2341
	11th to 20th	Night	12% 7% 2 7% 5% 4 4 3 5% 7% 46%	2400
	21st to end	Night	11% 7% 2 6% 4 4 5% 3 5% 7% 44%	2595
December	1st to 10th	Night	11% 6% 2 5% 4 4 4 4 7% 9% 45%	2495
	11th to 20th	Night	12% 8% 3 7% 4 3 4 3 4 6% 45%	3042
	21st to end	Night	14% 8% 3 7% 5% 4 5% 3 6% 7% 38%	4532

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	38% 5% 7% 17% 23% 11%	2837
	11th to 20th	Day	43% 6% 6% 14% 19% 11%	2840
	21st to end	Day	37% 7% 9% 18% 17% 12%	3124
February	1st to 10th	Day	42% 6% 8% 14% 20% 9%	1876
	11th to 20th	Day	36% 5% 8% 18% 22% 12%	1858
	21st to end	Day	36% 6% 10% 17% 19% 11%	1646
March	1st to 10th	Day	43% 8% 11% 19% 14% 5%	3435
	11th to 20th	Day	26% 8% 15% 19% 21% 11%	3480
	21st to end	Day	39% 6% 9% 21% 16% 8%	3815
April	1st to 10th	Day	32% 6% 12% 21% 19% 11%	2090
	11th to 20th	Day	35% 7% 11% 20% 18% 8%	2144
	21st to end	Day	25% 7% 14% 24% 24% 7%	2315
May	1st to 10th	Day	23% 11% 13% 31% 17% 4	4120
	11th to 20th	Day	38% 11% 14% 24% 12% 2	4085
	21st to end	Day	25% 11% 16% 31% 16% 1	4489
June	1st to 10th	Day	42% 12% 17% 19% 9%	2470
	11th to 20th	Day	36% 14% 20% 24% 6%	2470
	21st to end	Day	43% 14% 22% 15% 6%	2470
July	1st to 10th	Day	42% 17% 27% 14% 1	4055
	11th to 20th	Day	37% 18% 36% 7% 2	4051
	21st to end	Day	34% 20% 33% 11% 2	4324
August	1st to 10th	Day	46% 14% 29% 11% 1	4091
	11th to 20th	Day	32% 13% 25% 21% 10%	4059
	21st to end	Day	40% 14% 21% 24% 1	3875
September	1st to 10th	Day	49% 14% 17% 12% 7% 1	2090
	11th to 20th	Day	51% 14% 16% 13% 6%	2090
	21st to end	Day	44% 9% 15% 16% 14% 2	2090
October	1st to 10th	Day	49% 7% 9% 11% 15% 8%	3394
	11th to 20th	Day	28% 5% 6% 17% 32% 11%	3140
	21st to end	Day	24% 6% 6% 21% 33% 9%	3428
November	1st to 10th	Day	36% 6% 10% 20% 18% 10%	1957
	11th to 20th	Day	39% 6% 8% 16% 21% 10%	2000
	21st to end	Day	39% 5% 10% 19% 20% 7%	1800
December	1st to 10th	Day	36% 7% 14% 22% 16% 5%	1719
	11th to 20th	Day	40% 7% 10% 15% 20% 7%	2150
	21st to end	Day	44% 6% 7% 17% 18% 9%	3124
January	1st to 10th	Night	40% 5% 7% 14% 21% 13%	4109
	11th to 20th	Night	43% 6% 7% 16% 19% 10%	4120
	21st to end	Night	41% 8% 10% 15% 15% 12%	4532
February	1st to 10th	Night	41% 7% 9% 14% 18% 11%	2299
	11th to 20th	Night	39% 5% 8% 18% 18% 12%	2219
	21st to end	Night	36% 5% 11% 19% 17% 12%	1806
March	1st to 10th	Night	49% 6% 11% 15% 12% 6%	3418
	11th to 20th	Night	28% 7% 15% 23% 17% 10%	3480
	21st to end	Night	38% 6% 10% 17% 19% 11%	3817
April	1st to 10th	Night	32% 6% 14% 19% 17% 11%	2090
	11th to 20th	Night	32% 7% 10% 23% 20% 9%	1984
	21st to end	Night	24% 8% 14% 28% 21% 5%	1878
May	1st to 10th	Night	21% 12% 18% 29% 16% 4	2840
	11th to 20th	Night	33% 12% 18% 25% 10% 2	2813
	21st to end	Night	21% 8% 17% 33% 19% 1	3087
June	1st to 10th	Night	35% 11% 24% 21% 9%	1710
	11th to 20th	Night	35% 13% 23% 23% 7%	1710
	21st to end	Night	37% 15% 24% 17% 5% 1	1710
July	1st to 10th	Night	42% 14% 27% 15% 1	2795
	11th to 20th	Night	36% 20% 33% 9% 2	2786
	21st to end	Night	40% 16% 29% 14% 1	2988
August	1st to 10th	Night	44% 15% 30% 10% 2	2814
	11th to 20th	Night	30% 14% 26% 20% 10%	2812
	21st to end	Night	37% 12% 25% 23% 3	3752
September	1st to 10th	Night	47% 14% 19% 13% 5% 1	2090
	11th to 20th	Night	50% 13% 16% 15% 7%	2090
	21st to end	Night	40% 11% 14% 19% 15% 2	2090
October	1st to 10th	Night	50% 8% 9% 12% 12% 9%	3564
	11th to 20th	Night	27% 4 6% 17% 36% 10%	3779
	21st to end	Night	22% 6% 8% 20% 33% 11%	4120
November	1st to 10th	Night	35% 7% 11% 19% 17% 11%	2341
	11th to 20th	Night	38% 6% 8% 17% 21% 9%	2400
	21st to end	Night	37% 5% 11% 19% 18% 9%	2595
December	1st to 10th	Night	34% 7% 17% 21% 15% 6%	2495
	11th to 20th	Night	40% 5% 9% 17% 21% 8%	3044
	21st to end	Night	44% 7% 11% 16% 18% 5%	4532

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% 10% 45% 27% 7%	270
	11th to 20th	Day	6% 11% 35% 35% 11% 1	270
	21st to end	Day	15% 17% 37% 27% 4	297
February	1st to 10th	Day	15% 14% 33% 29% 9% 1	270
	11th to 20th	Day	14% 13% 40% 26% 8%	270
	21st to end	Day	11% 8% 39% 33% 9%	301
March	1st to 10th	Day	10% 13% 31% 32% 13% 1	460
	11th to 20th	Day	10% 10% 32% 30% 14% 3	460
	21st to end	Day	12% 8% 34% 30% 14% 2	506
April	1st to 10th	Day	10% 11% 33% 30% 14% 3	460
	11th to 20th	Day	10% 10% 25% 34% 15% 6%	452
	21st to end	Day	5% 5% 28% 34% 21% 8%	460
May	1st to 10th	Day	5% 4 24% 38% 21% 9%	463
	11th to 20th	Day	7% 3 19% 34% 26% 11%	487
	21st to end	Day	8% 2 12% 26% 33% 19%	529
June	1st to 10th	Day	13% 2 9% 30% 29% 17%	490
	11th to 20th	Day	5% 1 11% 25% 32% 26%	490
	21st to end	Day	7% 1 5% 24% 34% 29%	490
July	1st to 10th	Day	5% 2 4 16% 33% 39%	485
	11th to 20th	Day	4 1 3 13% 40% 40%	484
	21st to end	Day	7% 2 5% 17% 40% 30%	532
August	1st to 10th	Day	11% 1 5% 17% 35% 31%	486
	11th to 20th	Day	7% 1 2 15% 39% 36%	479
	21st to end	Day	12% 2 4 21% 33% 28%	539
September	1st to 10th	Day	13% 3 7% 18% 33% 25%	490
	11th to 20th	Day	15% 3 8% 28% 31% 14%	490
	21st to end	Day	13% 2 10% 27% 32% 16%	490
October	1st to 10th	Day	17% 4 20% 32% 21% 6%	490
	11th to 20th	Day	8% 5% 20% 36% 26% 6%	490
	21st to end	Day	9% 4 19% 37% 27% 4	539
November	1st to 10th	Day	15% 6% 23% 31% 20% 5%	495
	11th to 20th	Day	15% 8% 28% 32% 14% 3	500
	21st to end	Day	13% 11% 31% 35% 9% 1	300
December	1st to 10th	Day	10% 10% 32% 31% 16% 1	273
	11th to 20th	Day	17% 11% 29% 33% 7% 2	270
	21st to end	Day	15% 9% 27% 37% 11% 1	297
January	1st to 10th	Night	14% 10% 34% 31% 10% 1	760
	11th to 20th	Night	12% 8% 28% 37% 13% 2	760
	21st to end	Night	16% 10% 34% 33% 7%	836
February	1st to 10th	Night	16% 7% 31% 34% 12% 1	760
	11th to 20th	Night	16% 8% 32% 35% 8%	743
	21st to end	Night	14% 6% 31% 42% 6%	628
March	1st to 10th	Night	10% 8% 30% 41% 11%	760
	11th to 20th	Night	10% 7% 29% 39% 14% 1	760
	21st to end	Night	11% 6% 30% 38% 15% 1	836
April	1st to 10th	Night	9% 6% 31% 40% 14% 1	760
	11th to 20th	Night	11% 7% 26% 36% 19% 1	751
	21st to end	Night	7% 3 22% 45% 22% 1	738
May	1st to 10th	Night	7% 2 17% 44% 27% 3	570
	11th to 20th	Night	6% 2 17% 37% 32% 7%	561
	21st to end	Night	7% 1 9% 30% 45% 9%	617
June	1st to 10th	Night	11% 2 8% 31% 40% 9%	570
	11th to 20th	Night	6% 2 7% 25% 43% 16%	570
	21st to end	Night	9% 2 5% 22% 46% 15%	570
July	1st to 10th	Night	7% 1 4 19% 45% 23%	555
	11th to 20th	Night	7% 2 14% 50% 27%	552
	21st to end	Night	5% 1 4 19% 54% 16%	624
August	1st to 10th	Night	8% 1 3 17% 51% 20%	567
	11th to 20th	Night	6% 1 3 14% 51% 26%	564
	21st to end	Night	11% 2 6% 19% 42% 19%	826
September	1st to 10th	Night	12% 2 6% 21% 44% 15%	760
	11th to 20th	Night	15% 3 7% 24% 42% 9%	760
	21st to end	Night	13% 2 9% 26% 40% 10%	760
October	1st to 10th	Night	16% 2 16% 29% 33% 5%	760
	11th to 20th	Night	7% 5% 15% 36% 31% 5%	760
	21st to end	Night	10% 4 17% 34% 32% 4	836
November	1st to 10th	Night	13% 4 22% 33% 24% 4	780
	11th to 20th	Night	16% 7% 23% 32% 20% 2	800
	21st to end	Night	13% 6% 28% 34% 19% 1	800
December	1st to 10th	Night	13% 8% 24% 31% 22% 2	768
	11th to 20th	Night	13% 8% 26% 32% 19% 2	760
	21st to end	Night	16% 7% 22% 37% 17% 1	836

Page generated at 2024-11-29 10:43:06. Version ac07

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