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 2025-07-06.

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 7% 5% 4 4 4 6% 7% 37%	119986
	Night	17% 7% 2 6% 4 4 4 3 5% 7% 39%	118814
Transparency	Day	45% 4 11% 23% 14% 2	123532
	Night	44% 3 12% 23% 15% 2	123429
Seeing	Day	26% 15% 28% 19% 9% 3	15713
	Night	23% 14% 27% 25% 9% 1	24900

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 11% 5% 4 4 4 5% 6% 37%	3597
	11th to 20th	Day	14% 10% 3 11% 5% 5% 4 4 5% 5% 33%	3570
	21st to end	Day	17% 9% 3 6% 4 4 5% 4 6% 5% 37%	4351
February	1st to 10th	Day	15% 8% 2 9% 6% 6% 5% 5% 6% 6% 33%	1800
	11th to 20th	Day	13% 9% 3 8% 5% 5% 5% 3 5% 6% 39%	1903
	21st to end	Day	18% 9% 3 7% 6% 4 4 3 5% 5% 36%	1650
March	1st to 10th	Day	22% 7% 3 7% 4 4 3 3 4 5% 38%	4476
	11th to 20th	Day	13% 7% 3 7% 5% 4 4 4 5% 8% 40%	4878
	21st to end	Day	19% 8% 2 5% 4 4 4 4 5% 6% 39%	5868
April	1st to 10th	Day	18% 9% 2 7% 5% 5% 4 3 5% 6% 36%	2400
	11th to 20th	Day	17% 8% 3 6% 4 4 4 3 4 7% 39%	2374
	21st to end	Day	18% 6% 3 7% 5% 5% 4 4 5% 6% 37%	2400
May	1st to 10th	Day	30% 7% 2 6% 4 4 4 4 5% 7% 28%	6018
	11th to 20th	Day	22% 8% 3 6% 4 4 5% 4 5% 6% 32%	6318
	21st to end	Day	21% 6% 2 5% 4 4 5% 5% 7% 8% 32%	6949
June	1st to 10th	Day	16% 5% 2 7% 7% 5% 4 5% 6% 9% 35%	2800
	11th to 20th	Day	17% 7% 2 6% 5% 5% 5% 4 6% 9% 34%	2800
	21st to end	Day	13% 7% 2 6% 5% 4 5% 4 6% 9% 37%	2800
July	1st to 10th	Day	10% 5% 3 8% 5% 6% 6% 5% 7% 9% 35%	4510
	11th to 20th	Day	11% 6% 3 6% 5% 5% 5% 5% 8% 10% 38%	4440
	21st to end	Day	15% 8% 2 8% 5% 5% 5% 5% 7% 8% 34%	4814
August	1st to 10th	Day	22% 5% 3 6% 5% 5% 5% 5% 7% 7% 31%	4205
	11th to 20th	Day	15% 5% 2 5% 4 5% 5% 5% 6% 8% 39%	3739
	21st to end	Day	14% 6% 2 5% 3 4 3 3 6% 9% 45%	4180
September	1st to 10th	Day	16% 6% 2 6% 4 3 4 3 5% 7% 43%	2280
	11th to 20th	Day	14% 5% 1 5% 3 4 5% 3 5% 6% 50%	2228
	21st to end	Day	19% 6% 2 6% 4 4 4 3 6% 6% 40%	2090
October	1st to 10th	Day	20% 7% 2 6% 4 4 4 4 4 6% 39%	1933
	11th to 20th	Day	15% 6% 2 6% 4 4 4 4 5% 8% 42%	1900
	21st to end	Day	22% 6% 2 5% 5% 4 4 5% 6% 6% 36%	1962
November	1st to 10th	Day	13% 6% 2 4 4 4 4 3 4 5% 51%	1761
	11th to 20th	Day	17% 7% 3 5% 4 3 4 4 6% 6% 42%	1800
	21st to end	Day	17% 8% 3 7% 5% 3 4 4 5% 7% 37%	1646
December	1st to 10th	Day	16% 8% 3 7% 4 4 5% 4 6% 8% 35%	2600
	11th to 20th	Day	21% 8% 3 5% 4 3 3 3 4 7% 38%	2986
	21st to end	Day	17% 9% 4 9% 5% 5% 4 3 6% 8% 30%	3960
January	1st to 10th	Night	12% 8% 3 9% 5% 4 5% 4 6% 8% 37%	6349
	11th to 20th	Night	12% 8% 3 11% 5% 4 5% 3 6% 7% 35%	6315
	21st to end	Night	16% 8% 2 6% 5% 4 5% 4 5% 6% 38%	6601
February	1st to 10th	Night	15% 8% 3 6% 5% 5% 4 4 5% 7% 38%	2600
	11th to 20th	Night	15% 8% 3 7% 4 4 5% 5% 6% 6% 37%	2383
	21st to end	Night	17% 9% 2 7% 4 4 4 4 5% 5% 38%	1980
March	1st to 10th	Night	20% 8% 3 6% 4 4 3 2 5% 6% 40%	5364
	11th to 20th	Night	14% 8% 3 5% 4 4 4 3 5% 7% 43%	5077
	21st to end	Night	17% 9% 3 7% 4 4 4 3 5% 6% 39%	5064
April	1st to 10th	Night	17% 9% 3 8% 5% 4 4 4 5% 6% 35%	2000
	11th to 20th	Night	19% 8% 2 6% 4 4 5% 3 5% 7% 37%	1975
	21st to end	Night	18% 8% 2 6% 4 4 3 3 5% 6% 41%	1998
May	1st to 10th	Night	33% 7% 2 4 4 3 3 3 5% 7% 28%	3964
	11th to 20th	Night	24% 9% 3 5% 3 4 4 3 4 6% 34%	3575
	21st to end	Night	21% 6% 3 6% 4 4 4 4 6% 8% 34%	3926
June	1st to 10th	Night	16% 6% 2 5% 5% 4 4 3 5% 7% 42%	1600
	11th to 20th	Night	14% 6% 2 5% 4 5% 4 4 5% 9% 42%	1600
	21st to end	Night	13% 4 2 5% 4 4 4 4 7% 9% 45%	1600
July	1st to 10th	Night	12% 5% 2 6% 5% 4 5% 4 7% 10% 39%	2560
	11th to 20th	Night	12% 6% 2 5% 4 5% 5% 4 6% 9% 41%	2520
	21st to end	Night	18% 7% 2 5% 4 5% 5% 4 6% 8% 37%	2739
August	1st to 10th	Night	22% 6% 2 6% 5% 4 4 3 6% 8% 34%	2719
	11th to 20th	Night	15% 7% 3 6% 4 4 4 3 5% 5% 43%	3058
	21st to end	Night	12% 5% 2 5% 3 3 4 3 5% 8% 50%	3476
September	1st to 10th	Night	15% 6% 2 5% 3 3 3 4 5% 8% 46%	1900
	11th to 20th	Night	14% 5% 1 4 3 4 4 2 4 7% 52%	1952
	21st to end	Night	18% 6% 3 5% 3 3 4 3 5% 6% 43%	2090
October	1st to 10th	Night	21% 6% 2 5% 4 4 3 3 3 6% 42%	2243
	11th to 20th	Night	18% 5% 2 5% 4 3 3 3 4 6% 48%	2280
	21st to end	Night	22% 7% 2 5% 3 3 3 3 5% 7% 40%	2635
November	1st to 10th	Night	13% 6% 2 5% 4 4 4 3 5% 7% 49%	2537
	11th to 20th	Night	18% 7% 2 5% 3 3 3 3 5% 6% 44%	2600
	21st to end	Night	15% 7% 2 6% 5% 4 4 3 6% 7% 41%	2750
December	1st to 10th	Night	14% 7% 3 8% 4 4 4 3 5% 7% 41%	4580
	11th to 20th	Night	24% 8% 2 5% 3 3 4 3 4 5% 38%	5208
	21st to end	Night	20% 10% 3 8% 5% 4 4 3 5% 6% 33%	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	45% 4 8% 29% 12% 2	3598
	11th to 20th	Day	51% 3 10% 21% 11% 4	3600
	21st to end	Day	48% 2 9% 25% 14% 1	4351
February	1st to 10th	Day	51% 4 10% 20% 14% 1	1800
	11th to 20th	Day	47% 4 8% 22% 17% 2	1912
	21st to end	Day	51% 2 10% 23% 12% 2	1650
March	1st to 10th	Day	48% 3 9% 20% 13% 7%	4479
	11th to 20th	Day	44% 2 13% 29% 9% 4	4878
	21st to end	Day	46% 3 9% 13% 24% 6%	5868
April	1st to 10th	Day	49% 4 7% 22% 14% 4	2400
	11th to 20th	Day	46% 3 11% 21% 16% 3	2374
	21st to end	Day	47% 3 8% 22% 15% 4	2400
May	1st to 10th	Day	56% 4 12% 16% 10% 2	6029
	11th to 20th	Day	52% 3 10% 21% 12% 1	6322
	21st to end	Day	48% 5% 11% 23% 12% 1	6949
June	1st to 10th	Day	45% 5% 12% 23% 15% 1	2800
	11th to 20th	Day	46% 4 12% 25% 11% 2	2800
	21st to end	Day	42% 6% 12% 26% 14% 1	2800
July	1st to 10th	Day	43% 7% 12% 22% 14% 1	4440
	11th to 20th	Day	39% 6% 16% 25% 14% 1	4365
	21st to end	Day	48% 5% 12% 19% 15% 1	4661
August	1st to 10th	Day	51% 4 13% 22% 10%	4191
	11th to 20th	Day	40% 6% 14% 29% 10%	3775
	21st to end	Day	36% 3 12% 33% 15% 1	4180
September	1st to 10th	Day	41% 4 11% 24% 18% 2	2280
	11th to 20th	Day	36% 3 9% 25% 25% 2	2228
	21st to end	Day	45% 3 9% 22% 19% 2	2090
October	1st to 10th	Day	41% 3 7% 21% 24% 3	3206
	11th to 20th	Day	33% 4 9% 28% 23% 3	3140
	21st to end	Day	31% 3 17% 27% 18% 4	3213
November	1st to 10th	Day	37% 3 12% 25% 19% 3	1761
	11th to 20th	Day	42% 3 10% 25% 18% 3	1800
	21st to end	Day	46% 4 13% 26% 10% 2	1646
December	1st to 10th	Day	46% 5% 15% 25% 9% 1	2600
	11th to 20th	Day	46% 3 14% 22% 13% 2	2986
	21st to end	Day	52% 4 9% 20% 14% 1	3960
January	1st to 10th	Night	44% 4 10% 25% 15% 2	6349
	11th to 20th	Night	45% 4 14% 21% 13% 4	6360
	21st to end	Night	47% 2 11% 19% 17% 4	6601
February	1st to 10th	Night	46% 3 14% 23% 12% 1	2600
	11th to 20th	Night	46% 4 10% 20% 17% 3	2385
	21st to end	Night	47% 3 7% 24% 16% 3	1980
March	1st to 10th	Night	46% 3 11% 20% 16% 4	5374
	11th to 20th	Night	42% 3 16% 25% 11% 4	5078
	21st to end	Night	47% 3 6% 18% 22% 4	5064
April	1st to 10th	Night	49% 3 9% 21% 15% 3	2000
	11th to 20th	Night	48% 4 9% 21% 18% 1	1975
	21st to end	Night	45% 2 9% 24% 17% 4	1998
May	1st to 10th	Night	56% 3 12% 17% 11% 1	3970
	11th to 20th	Night	52% 4 12% 18% 14% 1	3576
	21st to end	Night	50% 4 12% 24% 9% 1	3927
June	1st to 10th	Night	43% 4 10% 25% 18% 1	1600
	11th to 20th	Night	40% 4 16% 29% 10% 1	1600
	21st to end	Night	35% 5% 16% 28% 15% 1	1600
July	1st to 10th	Night	39% 7% 16% 20% 14% 3	2520
	11th to 20th	Night	38% 6% 15% 27% 13% 1	2472
	21st to end	Night	44% 5% 14% 19% 17% 2	2651
August	1st to 10th	Night	48% 6% 16% 21% 9% 1	2709
	11th to 20th	Night	42% 4 14% 30% 10%	3088
	21st to end	Night	33% 4 11% 34% 16% 1	3476
September	1st to 10th	Night	37% 4 12% 28% 18% 1	1900
	11th to 20th	Night	34% 3 10% 26% 25% 2	1952
	21st to end	Night	42% 3 8% 24% 22% 1	2090
October	1st to 10th	Night	43% 4 9% 24% 20% 1	3750
	11th to 20th	Night	30% 2 10% 29% 25% 4	3779
	21st to end	Night	32% 3 15% 30% 18% 1	4334
November	1st to 10th	Night	37% 4 11% 24% 21% 2	2537
	11th to 20th	Night	42% 3 10% 23% 19% 3	2600
	21st to end	Night	41% 3 15% 29% 11% 1	2750
December	1st to 10th	Night	43% 3 13% 32% 9% 1	4580
	11th to 20th	Night	49% 2 12% 20% 15% 2	5208
	21st to end	Night	53% 3 10% 19% 13% 2	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	36% 25% 27% 11% 2 1	200
	11th to 20th	Day	41% 25% 25% 8% 1 1	200
	21st to end	Day	31% 26% 31% 7% 5%	305
February	1st to 10th	Day	35% 25% 29% 9% 2	300
	11th to 20th	Day	35% 27% 27% 9% 1	451
	21st to end	Day	32% 24% 30% 12% 2	414
March	1st to 10th	Day	31% 22% 29% 13% 5%	500
	11th to 20th	Day	31% 23% 28% 14% 3 1	500
	21st to end	Day	35% 19% 31% 10% 4 1	550
April	1st to 10th	Day	37% 21% 24% 12% 5% 1	500
	11th to 20th	Day	32% 23% 26% 12% 6% 2	492
	21st to end	Day	31% 18% 33% 13% 4 2	500
May	1st to 10th	Day	38% 15% 22% 15% 7% 2	503
	11th to 20th	Day	24% 20% 29% 18% 7% 2	527
	21st to end	Day	23% 11% 27% 24% 11% 3	573
June	1st to 10th	Day	21% 12% 32% 22% 11% 2	530
	11th to 20th	Day	25% 12% 25% 25% 12% 1	530
	21st to end	Day	18% 10% 32% 27% 10% 1	530
July	1st to 10th	Day	15% 8% 29% 28% 15% 5%	505
	11th to 20th	Day	15% 5% 27% 30% 20% 2	484
	21st to end	Day	16% 9% 34% 25% 14% 2	532
August	1st to 10th	Day	14% 7% 26% 32% 14% 6%	486
	11th to 20th	Day	18% 6% 24% 29% 17% 5%	479
	21st to end	Day	15% 9% 28% 26% 13% 8%	539
September	1st to 10th	Day	22% 10% 22% 24% 15% 7%	490
	11th to 20th	Day	17% 8% 24% 23% 17% 11%	490
	21st to end	Day	25% 9% 27% 23% 11% 5%	490
October	1st to 10th	Day	27% 12% 22% 21% 14% 4	490
	11th to 20th	Day	20% 16% 30% 20% 11% 2	490
	21st to end	Day	28% 15% 30% 19% 8% 1	472
November	1st to 10th	Day	21% 16% 29% 23% 9% 2	395
	11th to 20th	Day	29% 21% 23% 22% 6% 1	400
	21st to end	Day	33% 20% 30% 13% 4	246
December	1st to 10th	Day	33% 23% 28% 12% 4 1	200
	11th to 20th	Day	41% 22% 24% 12% 3	200
	21st to end	Day	31% 22% 29% 14% 4	220
January	1st to 10th	Night	24% 25% 33% 15% 3	800
	11th to 20th	Night	28% 19% 28% 21% 4	800
	21st to end	Night	22% 21% 34% 20% 2	880
February	1st to 10th	Night	25% 19% 34% 20% 2	800
	11th to 20th	Night	27% 25% 33% 13% 2	783
	21st to end	Night	30% 21% 31% 15% 4	660
March	1st to 10th	Night	28% 21% 32% 16% 4	800
	11th to 20th	Night	25% 23% 27% 21% 4 1	800
	21st to end	Night	23% 21% 33% 18% 4 1	880
April	1st to 10th	Night	28% 18% 32% 18% 5%	800
	11th to 20th	Night	27% 17% 30% 22% 5%	791
	21st to end	Night	25% 16% 28% 23% 7%	798
May	1st to 10th	Night	32% 12% 25% 24% 8%	562
	11th to 20th	Night	24% 12% 28% 29% 7% 1	394
	21st to end	Night	19% 7% 24% 36% 14% 1	433
June	1st to 10th	Night	19% 6% 23% 39% 13% 1	400
	11th to 20th	Night	18% 5% 29% 33% 16%	400
	21st to end	Night	13% 4 24% 45% 14% 1	400
July	1st to 10th	Night	16% 4 16% 43% 18% 2	380
	11th to 20th	Night	14% 4 23% 42% 17% 1	368
	21st to end	Night	14% 4 21% 42% 18% 1	416
August	1st to 10th	Night	14% 2 21% 40% 22% 1	500
	11th to 20th	Night	16% 3 16% 38% 24% 2	723
	21st to end	Night	17% 4 19% 35% 23% 2	836
September	1st to 10th	Night	19% 5% 24% 31% 18% 3	760
	11th to 20th	Night	19% 6% 20% 28% 21% 5%	760
	21st to end	Night	21% 6% 22% 32% 18% 2	760
October	1st to 10th	Night	26% 9% 21% 25% 17% 2	760
	11th to 20th	Night	22% 12% 25% 31% 10%	760
	21st to end	Night	27% 14% 29% 23% 8%	836
November	1st to 10th	Night	18% 16% 30% 27% 9% 1	780
	11th to 20th	Night	25% 18% 27% 22% 8% 1	800
	21st to end	Night	22% 18% 30% 22% 7% 1	800
December	1st to 10th	Night	27% 19% 29% 20% 5%	800
	11th to 20th	Night	26% 22% 26% 22% 4	800
	21st to end	Night	29% 18% 31% 19% 3	880

Page generated at 2025-07-03 01:30:16. Version ac07

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