Prompton State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Prompton State Park clear sky chart from 2005-11-06 to 2024-11-30.

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	16% 8% 3 7% 5% 5% 5% 4 6% 7% 33%	101650
	Night	16% 8% 3 7% 5% 4 4 4 6% 7% 35%	97963
Transparency	Day	47% 8% 12% 20% 11% 1	105171
	Night	45% 8% 13% 21% 12% 1	102531
Seeing	Day	25% 17% 28% 18% 9% 3	14902
	Night	23% 16% 28% 24% 9% 1	24127

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	12% 13% 6% 10% 6% 4 4 3 4 5% 31%	2517
	11th to 20th	Day	13% 12% 7% 14% 6% 6% 6% 3 4 5% 23%	2520
	21st to end	Day	20% 14% 6% 10% 6% 4 4 3 5% 5% 23%	3092
February	1st to 10th	Day	15% 11% 4 10% 7% 6% 6% 5% 5% 5% 26%	1710
	11th to 20th	Day	12% 10% 5% 9% 6% 5% 5% 4 6% 7% 31%	1764
	21st to end	Day	19% 11% 3 8% 7% 4 3 4 5% 5% 29%	1570
March	1st to 10th	Day	23% 12% 3 9% 5% 4 4 3 4 5% 29%	3116
	11th to 20th	Day	9% 10% 5% 9% 6% 5% 6% 4 7% 6% 34%	3475
	21st to end	Day	19% 10% 3 6% 5% 4 4 3 5% 6% 34%	4038
April	1st to 10th	Day	17% 12% 3 8% 5% 4 5% 4 4 6% 33%	2280
	11th to 20th	Day	16% 10% 3 7% 5% 4 4 4 5% 7% 35%	2254
	21st to end	Day	17% 8% 2 8% 6% 4 4 4 5% 6% 35%	2280
May	1st to 10th	Day	26% 8% 2 6% 4 4 4 3 5% 6% 31%	4251
	11th to 20th	Day	22% 9% 3 7% 5% 6% 5% 4 6% 6% 26%	4398
	21st to end	Day	13% 5% 2 5% 4 5% 6% 5% 7% 9% 40%	4837
June	1st to 10th	Day	15% 7% 2 7% 6% 6% 6% 5% 6% 9% 33%	2660
	11th to 20th	Day	15% 7% 2 7% 6% 5% 5% 5% 6% 9% 32%	2660
	21st to end	Day	13% 6% 3 8% 5% 5% 5% 5% 7% 9% 35%	2660
July	1st to 10th	Day	8% 6% 3 8% 6% 6% 7% 5% 7% 10% 35%	4440
	11th to 20th	Day	9% 6% 2 6% 5% 5% 6% 5% 9% 12% 36%	4440
	21st to end	Day	13% 8% 3 7% 6% 5% 6% 5% 6% 7% 33%	4814
August	1st to 10th	Day	22% 6% 3 7% 5% 5% 5% 4 6% 8% 29%	4141
	11th to 20th	Day	15% 6% 3 6% 5% 5% 6% 5% 7% 9% 34%	3804
	21st to end	Day	17% 5% 2 5% 3 4 5% 4 7% 8% 41%	4180
September	1st to 10th	Day	16% 6% 2 7% 4 5% 4 3 6% 7% 39%	2280
	11th to 20th	Day	14% 5% 3 5% 4 4 4 4 5% 8% 45%	2256
	21st to end	Day	19% 6% 2 6% 5% 4 4 4 6% 8% 35%	2075
October	1st to 10th	Day	18% 7% 2 7% 4 4 4 3 5% 8% 36%	1900
	11th to 20th	Day	15% 8% 3 6% 5% 5% 4 4 6% 7% 37%	1900
	21st to end	Day	20% 9% 3 7% 5% 5% 4 4 5% 7% 31%	1991
November	1st to 10th	Day	13% 8% 2 7% 4 3 4 4 4 7% 44%	1761
	11th to 20th	Day	15% 10% 3 7% 6% 4 4 3 5% 7% 35%	1790
	21st to end	Day	17% 9% 3 7% 6% 5% 5% 4 6% 7% 30%	1598
December	1st to 10th	Day	17% 14% 5% 8% 5% 5% 5% 5% 6% 6% 25%	1520
	11th to 20th	Day	22% 10% 5% 8% 5% 4 3 4 5% 6% 30%	1906
	21st to end	Day	18% 15% 6% 11% 7% 6% 5% 3 5% 5% 19%	2772
January	1st to 10th	Night	15% 9% 5% 9% 5% 5% 4 4 6% 8% 30%	4429
	11th to 20th	Night	14% 11% 4 13% 6% 5% 5% 4 5% 7% 26%	4440
	21st to end	Night	20% 12% 4 10% 7% 5% 5% 4 5% 5% 22%	4560
February	1st to 10th	Night	14% 10% 4 8% 6% 5% 4 4 5% 7% 33%	2470
	11th to 20th	Night	12% 9% 3 9% 7% 6% 5% 5% 7% 8% 30%	2301
	21st to end	Night	17% 8% 3 8% 7% 4 5% 4 6% 6% 32%	1884
March	1st to 10th	Night	20% 13% 4 7% 4 4 3 3 5% 6% 29%	3724
	11th to 20th	Night	10% 9% 5% 7% 6% 5% 5% 4 6% 8% 35%	3480
	21st to end	Night	13% 10% 3 8% 5% 5% 5% 3 5% 5% 37%	3594
April	1st to 10th	Night	15% 11% 4 8% 7% 5% 4 3 6% 6% 31%	1900
	11th to 20th	Night	17% 8% 3 6% 4 4 5% 4 6% 7% 37%	1875
	21st to end	Night	19% 7% 2 7% 5% 4 4 3 5% 6% 38%	1900
May	1st to 10th	Night	27% 8% 3 6% 4 3 3 3 4 7% 32%	2717
	11th to 20th	Night	22% 10% 3 6% 5% 4 4 4 6% 6% 31%	2495
	21st to end	Night	13% 7% 3 7% 4 4 5% 4 7% 9% 38%	2738
June	1st to 10th	Night	16% 6% 2 6% 5% 5% 4 4 6% 7% 40%	1520
	11th to 20th	Night	13% 6% 2 5% 5% 4 4 4 6% 10% 42%	1520
	21st to end	Night	11% 4 1 4 4 5% 5% 4 8% 9% 45%	1520
July	1st to 10th	Night	9% 5% 3 7% 5% 6% 5% 5% 7% 8% 41%	2520
	11th to 20th	Night	12% 5% 2 5% 5% 4 5% 5% 7% 10% 40%	2520
	21st to end	Night	14% 7% 2 6% 4 4 4 4 6% 7% 41%	2739
August	1st to 10th	Night	21% 6% 2 7% 4 4 5% 5% 7% 8% 32%	2784
	11th to 20th	Night	18% 5% 2 6% 4 4 4 3 6% 7% 41%	2993
	21st to end	Night	14% 4 1 5% 3 4 4 4 5% 8% 48%	3476
September	1st to 10th	Night	14% 6% 2 5% 4 4 4 3 5% 8% 44%	1900
	11th to 20th	Night	13% 5% 2 5% 2 3 4 3 4 7% 51%	1924
	21st to end	Night	17% 6% 3 6% 4 5% 4 2 5% 7% 41%	2102
October	1st to 10th	Night	20% 6% 2 5% 4 4 4 3 5% 7% 40%	2280
	11th to 20th	Night	18% 8% 2 5% 4 4 4 3 5% 6% 43%	2280
	21st to end	Night	20% 9% 2 5% 4 4 4 4 5% 8% 35%	2605
November	1st to 10th	Night	11% 8% 3 6% 5% 4 4 3 6% 6% 45%	2537
	11th to 20th	Night	19% 8% 2 6% 4 4 4 3 6% 7% 38%	2606
	21st to end	Night	14% 8% 3 7% 5% 5% 5% 4 6% 7% 35%	2798
December	1st to 10th	Night	19% 9% 3 9% 5% 5% 5% 5% 6% 8% 27%	2660
	11th to 20th	Night	17% 10% 4 8% 5% 5% 5% 3 5% 6% 30%	3288
	21st to end	Night	21% 11% 5% 9% 5% 5% 5% 4 5% 7% 23%	4884

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	52% 8% 13% 21% 5% 1	2518
	11th to 20th	Day	60% 8% 9% 15% 5% 2	2520
	21st to end	Day	62% 7% 10% 16% 6%	3092
February	1st to 10th	Day	56% 9% 11% 15% 9%	1710
	11th to 20th	Day	50% 8% 10% 20% 11% 1	1773
	21st to end	Day	54% 6% 11% 19% 9% 1	1570
March	1st to 10th	Day	57% 6% 10% 17% 8% 1	3119
	11th to 20th	Day	44% 11% 14% 22% 8% 1	3475
	21st to end	Day	49% 6% 8% 15% 19% 3	4038
April	1st to 10th	Day	51% 6% 9% 21% 11% 3	2280
	11th to 20th	Day	47% 7% 11% 20% 13% 2	2254
	21st to end	Day	48% 8% 9% 20% 12% 4	2280
May	1st to 10th	Day	53% 6% 11% 18% 10% 2	4265
	11th to 20th	Day	54% 9% 11% 17% 7% 1	4402
	21st to end	Day	36% 10% 15% 23% 15% 1	4837
June	1st to 10th	Day	46% 8% 14% 19% 13%	2660
	11th to 20th	Day	46% 8% 14% 21% 9% 1	2660
	21st to end	Day	43% 9% 14% 25% 10%	2660
July	1st to 10th	Day	42% 10% 14% 22% 12% 1	4370
	11th to 20th	Day	37% 10% 17% 24% 12%	4365
	21st to end	Day	46% 8% 14% 18% 13% 1	4661
August	1st to 10th	Day	52% 7% 14% 18% 9%	4127
	11th to 20th	Day	42% 9% 15% 26% 7%	3842
	21st to end	Day	39% 7% 12% 31% 10% 1	4180
September	1st to 10th	Day	43% 7% 12% 22% 14% 1	2280
	11th to 20th	Day	37% 6% 12% 22% 21% 1	2256
	21st to end	Day	46% 6% 13% 19% 15% 1	2075
October	1st to 10th	Day	45% 6% 8% 21% 18% 2	3160
	11th to 20th	Day	38% 5% 10% 25% 18% 4	3140
	21st to end	Day	34% 6% 18% 27% 13% 3	3255
November	1st to 10th	Day	40% 7% 13% 23% 16% 2	1761
	11th to 20th	Day	47% 7% 12% 20% 12% 2	1790
	21st to end	Day	51% 7% 15% 19% 7% 1	1598
December	1st to 10th	Day	57% 8% 16% 11% 7% 1	1520
	11th to 20th	Day	55% 6% 16% 17% 5%	1906
	21st to end	Day	66% 7% 9% 13% 5%	2772
January	1st to 10th	Night	49% 8% 15% 20% 7% 2	4429
	11th to 20th	Night	54% 10% 14% 16% 5% 1	4440
	21st to end	Night	61% 8% 9% 15% 6% 1	4560
February	1st to 10th	Night	49% 8% 14% 19% 9% 1	2470
	11th to 20th	Night	49% 9% 12% 18% 10% 2	2303
	21st to end	Night	50% 7% 10% 20% 11% 2	1884
March	1st to 10th	Night	54% 7% 11% 17% 10% 1	3734
	11th to 20th	Night	43% 11% 16% 22% 8% 1	3481
	21st to end	Night	46% 7% 8% 19% 17% 3	3594
April	1st to 10th	Night	52% 7% 10% 18% 11% 2	1900
	11th to 20th	Night	46% 7% 11% 21% 15%	1875
	21st to end	Night	45% 7% 10% 19% 15% 3	1900
May	1st to 10th	Night	53% 7% 10% 21% 8% 1	2723
	11th to 20th	Night	50% 10% 15% 16% 8% 1	2496
	21st to end	Night	39% 11% 14% 22% 13% 1	2739
June	1st to 10th	Night	41% 7% 12% 24% 16%	1520
	11th to 20th	Night	38% 7% 20% 25% 9% 1	1520
	21st to end	Night	32% 11% 19% 25% 13%	1520
July	1st to 10th	Night	39% 9% 18% 18% 16% 1	2480
	11th to 20th	Night	37% 9% 16% 25% 12% 1	2472
	21st to end	Night	41% 7% 14% 21% 16% 1	2651
August	1st to 10th	Night	47% 9% 16% 20% 7%	2774
	11th to 20th	Night	41% 7% 15% 26% 10%	3021
	21st to end	Night	33% 7% 13% 33% 14%	3476
September	1st to 10th	Night	37% 8% 13% 25% 16% 1	1900
	11th to 20th	Night	33% 7% 12% 25% 23% 1	1924
	21st to end	Night	43% 6% 11% 22% 18% 1	2102
October	1st to 10th	Night	44% 7% 10% 23% 16% 1	3800
	11th to 20th	Night	33% 6% 13% 23% 20% 4	3779
	21st to end	Night	34% 6% 17% 27% 15% 1	4291
November	1st to 10th	Night	39% 6% 12% 22% 18% 2	2537
	11th to 20th	Night	44% 6% 14% 20% 14% 2	2606
	21st to end	Night	45% 8% 16% 22% 9%	2798
December	1st to 10th	Night	52% 9% 15% 17% 6%	2660
	11th to 20th	Night	52% 7% 14% 17% 8% 1	3288
	21st to end	Night	58% 9% 13% 15% 5%	4884

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	32% 27% 26% 14% 1 1	180
	11th to 20th	Day	39% 27% 24% 9% 1	180
	21st to end	Day	28% 31% 29% 7% 5%	288
February	1st to 10th	Day	32% 29% 31% 6% 1	270
	11th to 20th	Day	37% 27% 30% 5% 1	371
	21st to end	Day	37% 23% 28% 9% 2	382
March	1st to 10th	Day	33% 20% 29% 14% 3	460
	11th to 20th	Day	33% 24% 25% 14% 3 1	460
	21st to end	Day	33% 25% 26% 10% 4 2	506
April	1st to 10th	Day	32% 25% 26% 12% 4 1	460
	11th to 20th	Day	29% 25% 27% 10% 8% 2	452
	21st to end	Day	29% 21% 30% 13% 5% 2	460
May	1st to 10th	Day	36% 15% 27% 13% 7% 2	463
	11th to 20th	Day	24% 16% 30% 20% 8% 2	487
	21st to end	Day	19% 13% 28% 23% 13% 3	529
June	1st to 10th	Day	21% 14% 32% 21% 9% 3	490
	11th to 20th	Day	19% 15% 26% 25% 13% 2	490
	21st to end	Day	16% 13% 36% 22% 11% 2	490
July	1st to 10th	Day	13% 7% 31% 27% 18% 4	485
	11th to 20th	Day	10% 8% 28% 33% 17% 3	484
	21st to end	Day	15% 10% 36% 24% 11% 4	532
August	1st to 10th	Day	14% 9% 27% 26% 18% 6%	486
	11th to 20th	Day	15% 8% 25% 29% 17% 5%	479
	21st to end	Day	17% 8% 29% 24% 14% 9%	539
September	1st to 10th	Day	21% 12% 21% 21% 18% 7%	490
	11th to 20th	Day	14% 8% 27% 23% 17% 11%	490
	21st to end	Day	24% 12% 27% 21% 13% 3	490
October	1st to 10th	Day	26% 13% 23% 19% 14% 6%	490
	11th to 20th	Day	21% 18% 29% 23% 7% 2	490
	21st to end	Day	29% 19% 26% 18% 7% 1	486
November	1st to 10th	Day	23% 19% 24% 20% 11% 2	395
	11th to 20th	Day	30% 22% 28% 16% 4 1	390
	21st to end	Day	37% 21% 31% 10% 3	200
December	1st to 10th	Day	32% 30% 23% 9% 6% 1	180
	11th to 20th	Day	39% 23% 26% 9% 2	180
	21st to end	Day	31% 26% 27% 14% 2	198
January	1st to 10th	Night	26% 24% 32% 15% 2	760
	11th to 20th	Night	28% 21% 30% 19% 3	760
	21st to end	Night	22% 25% 34% 16% 3	836
February	1st to 10th	Night	28% 19% 33% 18% 2	760
	11th to 20th	Night	27% 27% 33% 13% 1	743
	21st to end	Night	31% 22% 30% 14% 3	628
March	1st to 10th	Night	27% 22% 32% 16% 3	760
	11th to 20th	Night	28% 23% 29% 17% 4	760
	21st to end	Night	23% 24% 31% 16% 5%	836
April	1st to 10th	Night	25% 22% 31% 19% 3	760
	11th to 20th	Night	24% 18% 32% 19% 6% 1	751
	21st to end	Night	25% 17% 31% 22% 6%	760
May	1st to 10th	Night	29% 14% 27% 22% 8%	505
	11th to 20th	Night	21% 9% 34% 27% 8% 1	374
	21st to end	Night	17% 7% 26% 37% 13% 1	411
June	1st to 10th	Night	17% 9% 23% 36% 14% 1	380
	11th to 20th	Night	15% 8% 27% 36% 14%	380
	21st to end	Night	11% 6% 23% 46% 13%	380
July	1st to 10th	Night	12% 6% 20% 39% 21% 1	370
	11th to 20th	Night	13% 4 20% 45% 17% 1	368
	21st to end	Night	15% 5% 20% 41% 19%	416
August	1st to 10th	Night	15% 2 22% 39% 21% 2	539
	11th to 20th	Night	16% 4 14% 41% 22% 3	682
	21st to end	Night	16% 6% 18% 34% 25% 1	836
September	1st to 10th	Night	18% 7% 24% 28% 20% 2	760
	11th to 20th	Night	16% 5% 22% 29% 23% 5%	760
	21st to end	Night	21% 10% 23% 29% 15% 2	760
October	1st to 10th	Night	24% 12% 22% 23% 17% 1	760
	11th to 20th	Night	23% 12% 28% 29% 8%	760
	21st to end	Night	27% 16% 30% 21% 6%	836
November	1st to 10th	Night	18% 16% 32% 25% 9% 1	780
	11th to 20th	Night	27% 18% 27% 21% 6% 1	800
	21st to end	Night	22% 21% 33% 19% 5% 1	800
December	1st to 10th	Night	29% 21% 30% 16% 4	760
	11th to 20th	Night	25% 23% 31% 18% 3	760
	21st to end	Night	28% 23% 31% 17% 2	836

Page generated at 2024-11-27 17:30:55. Version ac07

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