Providence
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Providence clear sky chart from 2005-11-06 to 2025-04-26.

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	17% 7% 2 6% 4 4 4 4 5% 7% 40%	113244
	Night	18% 8% 3 6% 4 4 4 3 5% 6% 41%	115370
Transparency	Day	26% 43% 6% 13% 10% 2	116838
	Night	27% 41% 6% 13% 11% 2	119940
Seeing	Day	24% 18% 32% 18% 6% 2	15647
	Night	23% 15% 33% 23% 6%	24698

By Month

Percentage Cloud Cover NE (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% 7% 2 8% 4 4 4 3 5% 6% 47%	3597
	11th to 20th	Day	15% 8% 2 6% 3 3 4 3 4 5% 48%	3570
	21st to end	Day	17% 9% 2 6% 4 3 4 3 4 4 43%	3960
February	1st to 10th	Day	19% 7% 2 5% 4 5% 5% 4 6% 6% 37%	1905
	11th to 20th	Day	14% 7% 2 5% 4 4 5% 4 5% 6% 42%	1948
	21st to end	Day	19% 8% 3 5% 3 4 4 4 5% 7% 38%	1650
March	1st to 10th	Day	22% 11% 3 5% 3 3 3 2 4 6% 38%	4476
	11th to 20th	Day	16% 9% 2 5% 4 4 4 4 5% 7% 42%	4768
	21st to end	Day	24% 9% 2 6% 4 4 4 4 5% 5% 32%	5780
April	1st to 10th	Day	20% 8% 3 6% 4 3 3 3 5% 7% 38%	2400
	11th to 20th	Day	18% 7% 3 5% 3 4 4 3 6% 7% 40%	2374
	21st to end	Day	21% 6% 2 7% 4 4 4 4 4 6% 39%	2534
May	1st to 10th	Day	27% 11% 3 7% 3 3 3 3 4 7% 29%	4106
	11th to 20th	Day	24% 9% 3 7% 5% 4 4 3 4 6% 32%	4107
	21st to end	Day	15% 5% 2 5% 4 4 4 3 5% 7% 45%	4837
June	1st to 10th	Day	18% 6% 2 6% 4 4 4 4 7% 9% 34%	2660
	11th to 20th	Day	16% 6% 2 6% 5% 4 5% 4 6% 9% 36%	2660
	21st to end	Day	15% 7% 2 6% 5% 4 5% 4 7% 9% 37%	2660
July	1st to 10th	Day	14% 6% 2 6% 5% 6% 6% 5% 8% 9% 34%	4440
	11th to 20th	Day	14% 6% 2 6% 4 5% 5% 5% 7% 10% 36%	4440
	21st to end	Day	19% 8% 2 7% 5% 5% 5% 4 6% 7% 32%	4814
August	1st to 10th	Day	17% 8% 3 8% 5% 5% 5% 4 6% 8% 30%	4117
	11th to 20th	Day	12% 6% 2 8% 5% 5% 6% 5% 6% 8% 38%	3953
	21st to end	Day	7% 4 2 6% 5% 5% 6% 5% 7% 9% 45%	4180
September	1st to 10th	Day	15% 7% 2 5% 4 4 4 4 5% 6% 45%	2275
	11th to 20th	Day	13% 6% 2 5% 3 3 3 3 4 6% 51%	2090
	21st to end	Day	19% 7% 2 6% 4 3 5% 3 4 6% 43%	2090
October	1st to 10th	Day	23% 6% 1 5% 3 4 3 3 4 5% 42%	2090
	11th to 20th	Day	15% 5% 2 5% 3 3 4 3 5% 6% 49%	1872
	21st to end	Day	18% 5% 2 6% 4 4 3 3 5% 5% 44%	1881
November	1st to 10th	Day	16% 6% 2 5% 4 3 3 3 4 5% 48%	1761
	11th to 20th	Day	18% 6% 2 4 3 3 3 3 4 7% 47%	1800
	21st to end	Day	18% 7% 2 5% 4 3 4 3 4 5% 45%	1800
December	1st to 10th	Day	15% 8% 2 5% 3 3 3 3 4 6% 48%	2703
	11th to 20th	Day	19% 6% 2 6% 3 2 2 3 3 5% 49%	2986
	21st to end	Day	19% 10% 3 7% 4 3 3 2 4 5% 39%	3960
January	1st to 10th	Night	14% 6% 1 5% 3 3 4 3 4 6% 51%	6349
	11th to 20th	Night	14% 10% 3 8% 4 4 3 3 4 4 43%	6315
	21st to end	Night	16% 9% 3 7% 4 4 4 3 5% 5% 38%	6996
February	1st to 10th	Night	17% 8% 3 6% 5% 4 4 3 5% 6% 40%	2487
	11th to 20th	Night	17% 8% 3 6% 5% 3 3 4 5% 5% 41%	2338
	21st to end	Night	17% 9% 3 7% 4 3 4 3 4 4 41%	1980
March	1st to 10th	Night	23% 9% 2 4 3 4 3 3 5% 5% 38%	5364
	11th to 20th	Night	17% 10% 3 6% 4 3 4 3 5% 6% 40%	5191
	21st to end	Night	25% 9% 2 5% 4 4 4 4 5% 4 34%	5150
April	1st to 10th	Night	19% 9% 2 6% 5% 3 5% 3 5% 6% 37%	2000
	11th to 20th	Night	19% 8% 2 6% 4 4 4 4 5% 6% 38%	1975
	21st to end	Night	20% 7% 2 7% 4 3 3 3 4 6% 41%	1762
May	1st to 10th	Night	24% 10% 3 8% 5% 4 4 3 5% 7% 27%	2834
	11th to 20th	Night	24% 9% 3 8% 5% 5% 5% 3 6% 7% 26%	2813
	21st to end	Night	18% 6% 2 5% 5% 4 4 4 6% 7% 40%	2739
June	1st to 10th	Night	16% 7% 3 8% 4 4 4 3 6% 7% 37%	1520
	11th to 20th	Night	18% 6% 2 6% 5% 4 4 3 5% 8% 39%	1520
	21st to end	Night	16% 7% 2 5% 4 4 4 5% 7% 9% 38%	1520
July	1st to 10th	Night	15% 7% 3 6% 5% 4 6% 5% 7% 10% 33%	2520
	11th to 20th	Night	15% 8% 3 5% 4 3 5% 5% 6% 9% 37%	2520
	21st to end	Night	18% 9% 3 8% 5% 4 4 4 6% 7% 31%	2739
August	1st to 10th	Night	21% 7% 3 7% 5% 4 5% 4 7% 8% 29%	2780
	11th to 20th	Night	9% 7% 3 7% 5% 7% 6% 6% 6% 8% 35%	2870
	21st to end	Night	8% 5% 2 4 4 3 3 3 5% 8% 55%	3476
September	1st to 10th	Night	13% 5% 3 6% 5% 4 5% 4 5% 6% 43%	1905
	11th to 20th	Night	15% 6% 1 5% 3 3 3 3 4 6% 52%	2090
	21st to end	Night	18% 9% 2 6% 4 4 4 3 3 5% 41%	2090
October	1st to 10th	Night	20% 7% 3 5% 4 3 4 3 4 7% 41%	2090
	11th to 20th	Night	15% 5% 2 4 4 3 4 3 5% 7% 48%	2304
	21st to end	Night	20% 7% 2 6% 4 3 4 3 4 6% 41%	2717
November	1st to 10th	Night	14% 5% 2 5% 4 4 3 4 5% 5% 49%	2537
	11th to 20th	Night	18% 7% 2 5% 3 3 3 3 4 5% 47%	2600
	21st to end	Night	16% 6% 2 4 3 3 4 4 5% 7% 46%	2600
December	1st to 10th	Night	18% 8% 2 5% 3 3 3 2 4 5% 47%	4475
	11th to 20th	Night	23% 8% 2 5% 3 3 3 3 4 5% 42%	5208
	21st to end	Night	17% 11% 3 7% 4 3 3 2 4 5% 41%	6996

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	27% 27% 4 21% 18% 3	3598
	11th to 20th	Day	27% 27% 6% 17% 15% 7%	3600
	21st to end	Day	35% 29% 6% 13% 15% 2	3960
February	1st to 10th	Day	18% 62% 7% 8% 5% 1	1905
	11th to 20th	Day	19% 61% 2 8% 9% 2	1957
	21st to end	Day	16% 62% 5% 10% 7% 1	1650
March	1st to 10th	Day	38% 29% 7% 8% 8% 10%	4479
	11th to 20th	Day	29% 31% 10% 21% 8% 1	4768
	21st to end	Day	42% 30% 3 11% 9% 5%	5780
April	1st to 10th	Day	21% 62% 3 7% 6% 1	2400
	11th to 20th	Day	16% 63% 3 8% 9% 1	2374
	21st to end	Day	18% 63% 3 8% 6% 1	2534
May	1st to 10th	Day	37% 42% 9% 7% 5%	4120
	11th to 20th	Day	37% 41% 10% 8% 4	4111
	21st to end	Day	23% 42% 6% 15% 14% 1	4837
June	1st to 10th	Day	15% 65% 4 9% 6%	2660
	11th to 20th	Day	14% 65% 5% 10% 5% 1	2660
	21st to end	Day	14% 64% 4 9% 8%	2660
July	1st to 10th	Day	29% 40% 8% 13% 10% 1	4370
	11th to 20th	Day	27% 38% 11% 14% 9% 1	4365
	21st to end	Day	35% 37% 7% 11% 8% 1	4661
August	1st to 10th	Day	34% 40% 10% 12% 4	4103
	11th to 20th	Day	27% 40% 8% 20% 5%	3992
	21st to end	Day	16% 41% 10% 20% 12% 1	4180
September	1st to 10th	Day	15% 61% 4 11% 8%	2275
	11th to 20th	Day	16% 60% 4 9% 10% 2	2090
	21st to end	Day	19% 60% 3 9% 8% 1	2090
October	1st to 10th	Day	24% 38% 6% 15% 15% 3	3480
	11th to 20th	Day	16% 37% 3 17% 24% 3	3088
	21st to end	Day	16% 37% 9% 20% 16% 2	3081
November	1st to 10th	Day	18% 57% 6% 9% 9% 1	1761
	11th to 20th	Day	16% 57% 4 8% 13% 3	1800
	21st to end	Day	16% 57% 4 14% 6% 2	1800
December	1st to 10th	Day	24% 36% 9% 21% 10%	2703
	11th to 20th	Day	27% 32% 9% 11% 15% 6%	2986
	21st to end	Day	37% 27% 5% 16% 11% 4	3960
January	1st to 10th	Night	23% 27% 6% 28% 14% 2	6349
	11th to 20th	Night	33% 27% 8% 16% 12% 5%	6360
	21st to end	Night	38% 29% 6% 11% 12% 4	6996
February	1st to 10th	Night	18% 62% 5% 8% 5% 1	2487
	11th to 20th	Night	18% 61% 3 6% 11% 2	2340
	21st to end	Night	18% 61% 3 8% 7% 2	1980
March	1st to 10th	Night	37% 30% 6% 10% 11% 6%	5374
	11th to 20th	Night	32% 30% 12% 14% 9% 2	5192
	21st to end	Night	41% 30% 3 7% 14% 5%	5150
April	1st to 10th	Night	22% 62% 3 7% 5% 2	2000
	11th to 20th	Night	17% 63% 5% 6% 8% 1	1975
	21st to end	Night	17% 63% 4 8% 7% 1	1762
May	1st to 10th	Night	35% 45% 8% 10% 2	2840
	11th to 20th	Night	40% 42% 9% 7% 2	2814
	21st to end	Night	25% 42% 9% 15% 8%	2740
June	1st to 10th	Night	15% 65% 4 9% 7%	1520
	11th to 20th	Night	15% 65% 4 10% 6%	1520
	21st to end	Night	13% 64% 5% 11% 6% 1	1520
July	1st to 10th	Night	31% 40% 7% 12% 10%	2480
	11th to 20th	Night	28% 39% 11% 15% 8%	2472
	21st to end	Night	35% 38% 7% 10% 10% 1	2651
August	1st to 10th	Night	37% 40% 7% 9% 5% 1	2770
	11th to 20th	Night	28% 42% 8% 17% 4	2897
	21st to end	Night	13% 39% 11% 20% 16%	3476
September	1st to 10th	Night	16% 60% 4 12% 7% 1	1905
	11th to 20th	Night	16% 60% 3 9% 11% 1	2090
	21st to end	Night	21% 60% 3 8% 7%	2090
October	1st to 10th	Night	25% 39% 8% 17% 10% 2	3480
	11th to 20th	Night	11% 37% 4 17% 27% 3	3827
	21st to end	Night	18% 37% 7% 21% 15% 2	4467
November	1st to 10th	Night	18% 57% 5% 10% 9% 2	2537
	11th to 20th	Night	17% 56% 4 9% 12% 3	2600
	21st to end	Night	16% 57% 5% 14% 6% 2	2600
December	1st to 10th	Night	27% 35% 7% 20% 10%	4475
	11th to 20th	Night	33% 31% 9% 9% 16% 2	5208
	21st to end	Night	35% 28% 5% 15% 14% 3	6996

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	31% 26% 27% 14% 3	200
	11th to 20th	Day	29% 29% 34% 7% 3	200
	21st to end	Day	27% 25% 34% 11% 1 1	220
February	1st to 10th	Day	33% 24% 30% 11% 1	433
	11th to 20th	Day	33% 29% 30% 6% 2	496
	21st to end	Day	30% 23% 33% 11% 3	414
March	1st to 10th	Day	33% 21% 32% 12% 2	500
	11th to 20th	Day	30% 26% 29% 11% 3 1	500
	21st to end	Day	31% 24% 31% 8% 4 2	550
April	1st to 10th	Day	35% 23% 26% 11% 5% 1	500
	11th to 20th	Day	31% 25% 29% 12% 3 1	492
	21st to end	Day	27% 21% 30% 18% 2 2	480
May	1st to 10th	Day	33% 23% 29% 12% 3	463
	11th to 20th	Day	24% 17% 40% 14% 3 1	487
	21st to end	Day	19% 16% 35% 22% 5% 2	529
June	1st to 10th	Day	23% 14% 33% 21% 8% 1	490
	11th to 20th	Day	16% 19% 37% 21% 6% 1	490
	21st to end	Day	19% 13% 38% 22% 7% 1	490
July	1st to 10th	Day	18% 11% 31% 27% 12% 1	485
	11th to 20th	Day	18% 8% 32% 29% 11% 3	484
	21st to end	Day	15% 11% 38% 26% 9% 1	532
August	1st to 10th	Day	14% 10% 34% 30% 9% 2	486
	11th to 20th	Day	15% 9% 33% 29% 11% 3	479
	21st to end	Day	12% 10% 35% 24% 13% 5%	539
September	1st to 10th	Day	19% 11% 29% 23% 13% 4	490
	11th to 20th	Day	18% 12% 27% 24% 12% 7%	490
	21st to end	Day	24% 11% 34% 19% 7% 4	490
October	1st to 10th	Day	28% 12% 27% 19% 9% 5%	490
	11th to 20th	Day	20% 17% 33% 18% 10% 3	440
	21st to end	Day	25% 18% 30% 17% 7% 2	429
November	1st to 10th	Day	22% 16% 33% 17% 9% 2	395
	11th to 20th	Day	27% 21% 32% 15% 6%	400
	21st to end	Day	27% 22% 30% 15% 6% 1	400
December	1st to 10th	Day	24% 28% 31% 12% 5%	264
	11th to 20th	Day	34% 25% 33% 7% 2 1	200
	21st to end	Day	25% 25% 32% 14% 2 2	220
January	1st to 10th	Night	23% 20% 36% 17% 3	800
	11th to 20th	Night	30% 19% 34% 15% 2	800
	21st to end	Night	22% 22% 35% 17% 3	880
February	1st to 10th	Night	25% 19% 36% 19% 1	800
	11th to 20th	Night	28% 22% 36% 13% 1	783
	21st to end	Night	25% 22% 33% 17% 3	660
March	1st to 10th	Night	26% 19% 35% 17% 3	800
	11th to 20th	Night	22% 22% 36% 17% 3	800
	21st to end	Night	28% 19% 34% 16% 3	880
April	1st to 10th	Night	26% 20% 34% 17% 3	800
	11th to 20th	Night	24% 20% 34% 18% 4	791
	21st to end	Night	24% 18% 38% 17% 3	588
May	1st to 10th	Night	29% 14% 31% 20% 4	570
	11th to 20th	Night	23% 16% 37% 22% 2	562
	21st to end	Night	21% 7% 36% 29% 6%	412
June	1st to 10th	Night	17% 10% 33% 31% 9%	380
	11th to 20th	Night	21% 6% 37% 29% 6%	380
	21st to end	Night	19% 4 36% 34% 6% 1	380
July	1st to 10th	Night	16% 4 33% 38% 9%	370
	11th to 20th	Night	15% 4 33% 38% 9% 1	368
	21st to end	Night	16% 4 30% 41% 9%	416
August	1st to 10th	Night	15% 5% 34% 37% 9%	535
	11th to 20th	Night	13% 5% 30% 39% 12%	611
	21st to end	Night	15% 6% 25% 37% 16% 2	836
September	1st to 10th	Night	18% 6% 31% 34% 11% 1	760
	11th to 20th	Night	18% 7% 28% 28% 17% 3	760
	21st to end	Night	25% 7% 28% 27% 11% 2	760
October	1st to 10th	Night	25% 10% 26% 25% 12% 2	760
	11th to 20th	Night	19% 11% 35% 23% 12% 1	760
	21st to end	Night	24% 15% 33% 21% 7%	836
November	1st to 10th	Night	18% 15% 33% 24% 9% 1	780
	11th to 20th	Night	23% 18% 35% 18% 6%	800
	21st to end	Night	23% 20% 32% 21% 4 1	800
December	1st to 10th	Night	26% 17% 35% 17% 5%	800
	11th to 20th	Night	28% 18% 32% 20% 2	800
	21st to end	Night	26% 19% 34% 18% 3	880

Page generated at 2025-04-23 09:25:03. Version ac07

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