Port Jervis
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Port Jervis clear sky chart from 2005-11-06 to 2026-10-29.

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 6% 7% 37%	149796
	Night	17% 7% 3 6% 4 4 4 3 5% 7% 39%	142285
Transparency	Day	44% 4 12% 23% 14% 2	153299
	Night	44% 4 12% 24% 15% 2	146871
Seeing	Day	26% 16% 28% 19% 9% 3	17457
	Night	23% 14% 27% 25% 9% 1	26564

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% 9% 3 10% 6% 5% 5% 4 5% 6% 36%	4661
	11th to 20th	Day	14% 10% 3 10% 5% 5% 4 3 5% 5% 37%	4650
	21st to end	Day	15% 8% 2 5% 4 5% 5% 4 6% 6% 40%	5637
February	1st to 10th	Day	15% 8% 2 9% 6% 6% 5% 4 6% 6% 34%	1890
	11th to 20th	Day	14% 9% 3 8% 5% 5% 4 3 5% 6% 38%	2001
	21st to end	Day	17% 9% 3 7% 5% 4 4 3 5% 5% 36%	1730
March	1st to 10th	Day	22% 7% 3 6% 4 4 3 3 4 5% 38%	4576
	11th to 20th	Day	13% 7% 3 7% 5% 4 4 4 5% 8% 40%	4985
	21st to end	Day	18% 8% 2 5% 4 4 4 4 5% 6% 39%	5997
April	1st to 10th	Day	18% 9% 2 7% 5% 4 4 3 5% 6% 36%	2520
	11th to 20th	Day	17% 7% 3 6% 4 4 4 3 5% 8% 39%	2494
	21st to end	Day	18% 6% 3 7% 5% 5% 4 4 5% 7% 37%	2520
May	1st to 10th	Day	26% 6% 2 6% 4 4 4 4 5% 7% 32%	7811
	11th to 20th	Day	19% 7% 3 6% 4 4 4 4 5% 7% 37%	8221
	21st to end	Day	23% 7% 2 5% 4 4 5% 5% 7% 8% 30%	9060
June	1st to 10th	Day	15% 5% 2 7% 6% 5% 4 4 6% 9% 36%	2940
	11th to 20th	Day	17% 7% 1 6% 5% 5% 5% 4 6% 9% 35%	2940
	21st to end	Day	14% 7% 2 6% 5% 4 5% 4 6% 9% 37%	2940
July	1st to 10th	Day	14% 6% 2 7% 4 5% 5% 5% 6% 9% 36%	8280
	11th to 20th	Day	11% 5% 2 6% 5% 5% 5% 4 8% 11% 37%	8280
	21st to end	Day	16% 6% 2 6% 4 4 4 4 5% 8% 41%	8993
August	1st to 10th	Day	17% 6% 3 8% 6% 6% 6% 5% 8% 9% 28%	6160
	11th to 20th	Day	14% 5% 2 5% 4 5% 5% 4 6% 9% 42%	5497
	21st to end	Day	14% 6% 2 5% 3 4 4 4 7% 10% 42%	6080
September	1st to 10th	Day	15% 6% 2 7% 4 3 4 3 5% 7% 43%	2520
	11th to 20th	Day	14% 5% 1 5% 3 3 4 3 6% 6% 50%	2462
	21st to end	Day	19% 6% 2 7% 4 4 4 3 6% 6% 38%	2310
October	1st to 10th	Day	18% 6% 2 6% 4 4 4 4 4 6% 41%	2137
	11th to 20th	Day	16% 6% 2 6% 4 4 4 3 5% 8% 42%	2100
	21st to end	Day	20% 6% 2 5% 5% 4 4 5% 6% 6% 38%	2141
November	1st to 10th	Day	13% 6% 2 4 4 4 4 3 4 5% 50%	1851
	11th to 20th	Day	17% 7% 3 6% 4 3 4 4 6% 6% 41%	1890
	21st to end	Day	17% 8% 3 7% 5% 4 4 4 5% 7% 36%	1728
December	1st to 10th	Day	16% 8% 3 7% 5% 4 5% 4 6% 8% 35%	2680
	11th to 20th	Day	21% 8% 3 5% 4 3 4 3 5% 7% 39%	3066
	21st to end	Day	17% 9% 4 9% 5% 5% 4 3 6% 7% 30%	4048
January	1st to 10th	Night	12% 10% 3 10% 6% 5% 5% 4 6% 7% 33%	8234
	11th to 20th	Night	12% 9% 3 11% 5% 5% 4 3 6% 7% 34%	8235
	21st to end	Night	13% 8% 2 6% 6% 4 4 4 5% 7% 41%	8540
February	1st to 10th	Night	15% 8% 3 6% 5% 5% 4 4 5% 7% 39%	2730
	11th to 20th	Night	15% 8% 3 7% 4 4 5% 5% 6% 6% 37%	2505
	21st to end	Night	16% 10% 2 7% 4 4 4 4 5% 6% 38%	2076
March	1st to 10th	Night	20% 8% 3 6% 4 4 3 2 5% 6% 40%	5484
	11th to 20th	Night	14% 8% 3 5% 4 4 4 3 5% 7% 43%	5189
	21st to end	Night	17% 9% 3 7% 4 4 4 3 5% 6% 38%	5177
April	1st to 10th	Night	18% 9% 2 8% 5% 4 4 4 5% 6% 35%	2100
	11th to 20th	Night	18% 8% 2 6% 4 4 5% 4 5% 7% 37%	2075
	21st to end	Night	19% 8% 2 6% 3 4 3 3 5% 6% 41%	2098
May	1st to 10th	Night	28% 6% 2 5% 4 4 4 3 5% 8% 31%	5142
	11th to 20th	Night	21% 8% 2 5% 3 4 4 4 5% 7% 37%	4639
	21st to end	Night	22% 8% 3 7% 5% 4 4 3 5% 7% 32%	5114
June	1st to 10th	Night	16% 6% 2 5% 4 4 4 3 5% 7% 43%	1680
	11th to 20th	Night	14% 6% 2 5% 4 5% 4 4 5% 9% 42%	1680
	21st to end	Night	13% 4 2 5% 4 4 4 4 7% 9% 45%	1680
July	1st to 10th	Night	16% 5% 2 6% 4 4 4 4 6% 9% 39%	4680
	11th to 20th	Night	12% 6% 2 6% 4 5% 5% 4 6% 10% 39%	4680
	21st to end	Night	15% 5% 2 5% 3 4 4 4 6% 7% 45%	5084
August	1st to 10th	Night	19% 7% 3 7% 5% 5% 5% 4 6% 8% 33%	3984
	11th to 20th	Night	15% 5% 2 6% 4 4 5% 4 6% 6% 43%	4489
	21st to end	Night	13% 5% 2 5% 3 4 4 3 5% 7% 48%	5045
September	1st to 10th	Night	16% 6% 2 5% 3 4 3 4 5% 8% 46%	2100
	11th to 20th	Night	14% 5% 2 4 3 4 4 2 4 6% 52%	2158
	21st to end	Night	19% 7% 3 5% 3 3 4 3 5% 6% 41%	2310
October	1st to 10th	Night	20% 6% 2 5% 4 3 3 3 3 6% 45%	2479
	11th to 20th	Night	18% 5% 2 5% 3 3 3 3 4 6% 48%	2520
	21st to end	Night	20% 7% 2 4 3 3 3 3 5% 7% 42%	2875
November	1st to 10th	Night	13% 6% 2 5% 4 4 4 3 5% 7% 48%	2667
	11th to 20th	Night	18% 7% 2 4 4 3 3 4 5% 6% 44%	2730
	21st to end	Night	15% 7% 2 6% 5% 4 4 3 7% 7% 41%	2888
December	1st to 10th	Night	14% 7% 3 8% 4 4 4 3 6% 7% 41%	4720
	11th to 20th	Night	23% 8% 2 5% 4 3 4 3 4 5% 38%	5348
	21st to end	Night	20% 10% 3 8% 5% 4 4 3 5% 6% 33%	7150

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	46% 5% 9% 26% 12% 2	4662
	11th to 20th	Day	48% 3 9% 20% 14% 5%	4680
	21st to end	Day	43% 3 11% 25% 17% 1	5637
February	1st to 10th	Day	50% 4 10% 20% 15% 1	1890
	11th to 20th	Day	48% 4 8% 22% 17% 2	2010
	21st to end	Day	50% 3 10% 23% 12% 2	1730
March	1st to 10th	Day	48% 3 9% 20% 13% 7%	4579
	11th to 20th	Day	44% 2 13% 28% 9% 4	4985
	21st to end	Day	46% 4 9% 13% 23% 6%	5997
April	1st to 10th	Day	49% 4 7% 22% 15% 4	2520
	11th to 20th	Day	45% 3 12% 21% 16% 3	2494
	21st to end	Day	47% 3 9% 22% 15% 4	2520
May	1st to 10th	Day	51% 5% 11% 19% 13% 1	7823
	11th to 20th	Day	47% 4 11% 24% 13% 1	8225
	21st to end	Day	50% 5% 13% 21% 11% 1	9061
June	1st to 10th	Day	44% 5% 11% 24% 15% 1	2940
	11th to 20th	Day	45% 4 12% 25% 12% 2	2940
	21st to end	Day	42% 5% 12% 26% 13% 1	2940
July	1st to 10th	Day	44% 8% 13% 20% 14% 1	8210
	11th to 20th	Day	37% 7% 15% 29% 12%	8205
	21st to end	Day	40% 5% 11% 24% 18% 1	8795
August	1st to 10th	Day	51% 7% 13% 18% 10%	6146
	11th to 20th	Day	37% 6% 17% 31% 8%	5533
	21st to end	Day	36% 5% 14% 31% 13% 1	6080
September	1st to 10th	Day	41% 4 12% 24% 18% 2	2520
	11th to 20th	Day	36% 3 9% 25% 24% 3	2462
	21st to end	Day	46% 4 10% 21% 18% 2	2310
October	1st to 10th	Day	40% 3 7% 22% 24% 3	3410
	11th to 20th	Day	34% 4 9% 27% 22% 4	3340
	21st to end	Day	31% 3 16% 27% 19% 4	3392
November	1st to 10th	Day	37% 3 12% 25% 19% 3	1851
	11th to 20th	Day	42% 3 9% 24% 18% 3	1890
	21st to end	Day	46% 4 13% 26% 10% 1	1728
December	1st to 10th	Day	46% 5% 15% 25% 9% 1	2680
	11th to 20th	Day	46% 3 14% 22% 13% 2	3066
	21st to end	Day	52% 4 9% 20% 14% 1	4048
January	1st to 10th	Night	48% 4 11% 22% 12% 2	8234
	11th to 20th	Night	47% 4 12% 20% 13% 4	8280
	21st to end	Night	43% 3 10% 22% 19% 3	8540
February	1st to 10th	Night	45% 3 13% 23% 13% 2	2730
	11th to 20th	Night	46% 4 10% 20% 17% 3	2507
	21st to end	Night	47% 3 8% 24% 16% 3	2076
March	1st to 10th	Night	46% 2 11% 20% 16% 4	5494
	11th to 20th	Night	42% 3 16% 25% 11% 4	5190
	21st to end	Night	47% 3 6% 17% 22% 4	5177
April	1st to 10th	Night	49% 3 10% 20% 15% 3	2100
	11th to 20th	Night	47% 4 9% 21% 18% 1	2075
	21st to end	Night	45% 2 8% 24% 17% 4	2098
May	1st to 10th	Night	52% 4 13% 18% 12% 1	5148
	11th to 20th	Night	47% 4 12% 23% 12% 1	4640
	21st to end	Night	52% 4 11% 23% 9% 1	5115
June	1st to 10th	Night	41% 4 10% 25% 19% 1	1680
	11th to 20th	Night	40% 4 15% 29% 10% 1	1680
	21st to end	Night	35% 5% 16% 28% 14% 1	1680
July	1st to 10th	Night	42% 7% 16% 20% 14% 2	4640
	11th to 20th	Night	39% 7% 14% 27% 12% 1	4632
	21st to end	Night	37% 5% 13% 28% 17% 1	4967
August	1st to 10th	Night	48% 7% 14% 20% 9% 1	3974
	11th to 20th	Night	40% 5% 17% 30% 7%	4519
	21st to end	Night	36% 5% 13% 31% 14% 1	5045
September	1st to 10th	Night	38% 4 12% 28% 17% 1	2100
	11th to 20th	Night	34% 3 10% 26% 25% 2	2158
	21st to end	Night	44% 3 8% 23% 21% 1	2310
October	1st to 10th	Night	41% 3 9% 25% 20% 1	3986
	11th to 20th	Night	30% 2 10% 28% 25% 4	4019
	21st to end	Night	32% 3 15% 30% 18% 2	4574
November	1st to 10th	Night	36% 4 12% 24% 21% 2	2667
	11th to 20th	Night	41% 3 10% 23% 20% 3	2730
	21st to end	Night	42% 3 14% 29% 11% 1	2888
December	1st to 10th	Night	42% 3 13% 32% 9% 1	4720
	11th to 20th	Night	49% 2 12% 20% 15% 2	5348
	21st to end	Night	53% 3 10% 19% 13% 2	7150

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	35% 26% 28% 10% 1	220
	11th to 20th	Day	43% 25% 23% 7% 1	220
	21st to end	Day	34% 26% 30% 6% 4	336
February	1st to 10th	Day	33% 25% 30% 9% 3	330
	11th to 20th	Day	35% 27% 27% 9% 1	489
	21st to end	Day	31% 27% 29% 11% 2	446
March	1st to 10th	Day	32% 21% 29% 13% 4	540
	11th to 20th	Day	33% 22% 28% 14% 3 1	540
	21st to end	Day	35% 21% 30% 9% 4 1	594
April	1st to 10th	Day	38% 21% 24% 11% 5% 1	540
	11th to 20th	Day	31% 22% 28% 12% 6% 2	532
	21st to end	Day	30% 17% 34% 13% 4 2	540
May	1st to 10th	Day	37% 17% 23% 14% 6% 2	543
	11th to 20th	Day	23% 20% 31% 18% 7% 2	567
	21st to end	Day	24% 12% 28% 23% 10% 3	617
June	1st to 10th	Day	20% 13% 31% 23% 11% 2	570
	11th to 20th	Day	26% 12% 26% 24% 11% 1	570
	21st to end	Day	19% 10% 33% 27% 10% 1	570
July	1st to 10th	Day	15% 7% 29% 30% 15% 5%	565
	11th to 20th	Day	15% 6% 28% 29% 20% 2	564
	21st to end	Day	16% 8% 33% 27% 13% 3	620
August	1st to 10th	Day	14% 7% 25% 32% 16% 6%	566
	11th to 20th	Day	17% 7% 24% 30% 17% 5%	559
	21st to end	Day	15% 10% 29% 26% 13% 7%	627
September	1st to 10th	Day	20% 11% 24% 25% 14% 6%	570
	11th to 20th	Day	16% 8% 24% 24% 18% 10%	570
	21st to end	Day	25% 9% 27% 22% 12% 5%	570
October	1st to 10th	Day	25% 12% 23% 21% 14% 5%	570
	11th to 20th	Day	23% 16% 29% 19% 11% 2	570
	21st to end	Day	26% 14% 31% 19% 8% 1	537
November	1st to 10th	Day	21% 18% 28% 22% 8% 2	425
	11th to 20th	Day	29% 21% 22% 23% 5%	430
	21st to end	Day	34% 22% 29% 12% 4	268
December	1st to 10th	Day	33% 23% 29% 11% 4	220
	11th to 20th	Day	41% 22% 24% 11% 2	220
	21st to end	Day	32% 24% 28% 13% 4	242
January	1st to 10th	Night	24% 24% 34% 16% 3	840
	11th to 20th	Night	29% 20% 28% 20% 4	840
	21st to end	Night	23% 22% 34% 19% 2	924
February	1st to 10th	Night	25% 19% 34% 20% 2	840
	11th to 20th	Night	27% 24% 33% 13% 1	823
	21st to end	Night	30% 21% 31% 15% 3	692
March	1st to 10th	Night	28% 20% 32% 16% 3	840
	11th to 20th	Night	25% 23% 27% 20% 4	840
	21st to end	Night	23% 21% 33% 18% 4 1	924
April	1st to 10th	Night	29% 18% 31% 17% 5%	840
	11th to 20th	Night	26% 17% 31% 21% 5%	831
	21st to end	Night	25% 16% 29% 24% 6%	838
May	1st to 10th	Night	31% 12% 26% 23% 7%	590
	11th to 20th	Night	24% 12% 28% 29% 7%	414
	21st to end	Night	20% 7% 24% 35% 13% 1	455
June	1st to 10th	Night	18% 6% 24% 39% 13% 1	420
	11th to 20th	Night	18% 5% 29% 32% 15%	420
	21st to end	Night	13% 4 24% 45% 13%	420
July	1st to 10th	Night	16% 4 17% 43% 18% 2	410
	11th to 20th	Night	13% 4 24% 41% 16% 1	408
	21st to end	Night	14% 4 21% 42% 18% 1	460
August	1st to 10th	Night	14% 2 19% 42% 22% 1	554
	11th to 20th	Night	16% 3 17% 39% 23% 2	800
	21st to end	Night	18% 4 19% 35% 22% 2	924
September	1st to 10th	Night	20% 6% 23% 32% 18% 3	840
	11th to 20th	Night	18% 7% 20% 29% 22% 5%	840
	21st to end	Night	21% 6% 22% 32% 17% 2	840
October	1st to 10th	Night	24% 9% 22% 26% 17% 2	840
	11th to 20th	Night	23% 13% 25% 30% 9%	840
	21st to end	Night	26% 13% 29% 24% 8%	913
November	1st to 10th	Night	20% 15% 30% 26% 8% 1	820
	11th to 20th	Night	26% 18% 26% 22% 7% 1	840
	21st to end	Night	23% 18% 29% 23% 7% 1	840
December	1st to 10th	Night	26% 19% 29% 20% 5%	840
	11th to 20th	Night	27% 22% 26% 22% 3	840
	21st to end	Night	30% 18% 30% 19% 3	924

Page generated at 2026-10-26 04:37:48. Version ac07

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