Port Allegany
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Port Allegany clear sky chart from 2005-11-06 to 2026-05-02.

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	16% 12% 5% 10% 6% 5% 4 4 5% 6% 28%	131971
	Night	15% 14% 5% 11% 6% 4 4 3 4 5% 27%	130510
Transparency	Day	55% 6% 11% 18% 9% 1	135565
	Night	57% 6% 11% 16% 9% 1	135002
Seeing	Day	27% 19% 27% 16% 8% 3	16487
	Night	25% 17% 27% 21% 9% 1	26034

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	14% 19% 9% 23% 9% 3 3 2 3 3 13%	4661
	11th to 20th	Day	8% 19% 10% 23% 10% 6% 4 2 2 3 11%	5164
	21st to end	Day	15% 13% 7% 13% 9% 9% 6% 3 5% 5% 15%	5780
February	1st to 10th	Day	13% 19% 7% 13% 8% 6% 4 3 4 3 20%	1890
	11th to 20th	Day	12% 16% 8% 15% 7% 4 5% 3 4 5% 20%	1843
	21st to end	Day	18% 15% 4 13% 6% 3 3 3 4 6% 25%	1668
March	1st to 10th	Day	16% 14% 8% 9% 5% 3 3 2 4 5% 30%	5037
	11th to 20th	Day	12% 16% 7% 9% 4 3 3 3 4 6% 33%	5090
	21st to end	Day	16% 13% 5% 12% 6% 5% 4 4 4 4 28%	5600
April	1st to 10th	Day	17% 16% 4 9% 5% 4 4 3 5% 6% 28%	2520
	11th to 20th	Day	17% 14% 3 7% 5% 4 5% 4 6% 5% 31%	2494
	21st to end	Day	21% 11% 3 7% 5% 4 3 4 4 5% 34%	2667
May	1st to 10th	Day	27% 11% 3 7% 5% 5% 4 3 4 5% 26%	5901
	11th to 20th	Day	23% 12% 3 8% 5% 4 4 4 5% 7% 25%	6268
	21st to end	Day	20% 9% 3 7% 5% 6% 5% 4 5% 6% 31%	6949
June	1st to 10th	Day	17% 9% 2 7% 6% 4 5% 4 5% 8% 34%	2800
	11th to 20th	Day	16% 8% 3 8% 5% 5% 6% 4 7% 8% 31%	2800
	21st to end	Day	14% 7% 3 7% 6% 5% 5% 4 6% 7% 35%	2800
July	1st to 10th	Day	9% 6% 3 6% 6% 5% 6% 5% 7% 9% 38%	6360
	11th to 20th	Day	10% 8% 3 8% 5% 6% 7% 5% 8% 9% 31%	6360
	21st to end	Day	12% 6% 2 7% 5% 5% 5% 4 6% 7% 41%	6430
August	1st to 10th	Day	18% 9% 3 7% 5% 5% 4 4 7% 9% 29%	4234
	11th to 20th	Day	15% 7% 3 8% 6% 7% 6% 5% 7% 9% 26%	4174
	21st to end	Day	12% 7% 3 7% 4 5% 6% 4 6% 9% 36%	4345
September	1st to 10th	Day	18% 8% 2 5% 4 4 4 3 6% 7% 39%	2400
	11th to 20th	Day	13% 6% 3 7% 4 5% 4 4 5% 7% 43%	2358
	21st to end	Day	21% 9% 3 7% 4 5% 4 4 5% 7% 31%	2110
October	1st to 10th	Day	18% 9% 3 7% 5% 4 4 4 5% 7% 36%	2000
	11th to 20th	Day	21% 10% 3 8% 5% 5% 4 3 4 7% 31%	2000
	21st to end	Day	22% 17% 3 8% 5% 3 4 3 4 6% 26%	2200
November	1st to 10th	Day	14% 14% 3 7% 5% 4 5% 4 5% 7% 34%	1914
	11th to 20th	Day	16% 20% 5% 8% 5% 3 4 4 5% 6% 25%	1680
	21st to end	Day	18% 22% 6% 10% 6% 3 3 3 5% 6% 18%	1680
December	1st to 10th	Day	17% 25% 12% 18% 4 4 2 2 3 3 10%	2680
	11th to 20th	Day	18% 18% 8% 13% 7% 3 3 3 4 5% 19%	3066
	21st to end	Day	17% 24% 8% 13% 6% 4 4 2 4 4 15%	4048
January	1st to 10th	Night	13% 18% 9% 24% 10% 4 3 3 3 4 9%	8234
	11th to 20th	Night	9% 18% 10% 23% 11% 5% 4 2 4 4 10%	7717
	21st to end	Night	13% 16% 8% 15% 9% 9% 8% 2 3 3 15%	8401
February	1st to 10th	Night	13% 18% 6% 12% 8% 6% 4 3 4 5% 19%	2730
	11th to 20th	Night	12% 15% 7% 16% 8% 6% 5% 3 4 5% 18%	2663
	21st to end	Night	15% 16% 6% 15% 7% 5% 4 3 4 4 22%	2136
March	1st to 10th	Night	16% 15% 5% 10% 9% 4 3 3 4 5% 25%	5020
	11th to 20th	Night	14% 16% 6% 8% 4 3 3 2 4 6% 33%	5089
	21st to end	Night	13% 14% 5% 11% 5% 4 4 3 5% 5% 31%	5573
April	1st to 10th	Night	18% 15% 4 9% 4 4 5% 4 4 5% 27%	2100
	11th to 20th	Night	18% 15% 3 6% 4 3 3 3 4 6% 34%	2075
	21st to end	Night	16% 12% 3 6% 4 4 5% 3 5% 7% 34%	1970
May	1st to 10th	Night	28% 12% 3 7% 4 4 4 2 3 5% 27%	4062
	11th to 20th	Night	22% 14% 3 6% 4 4 4 3 4 5% 31%	3621
	21st to end	Night	20% 13% 2 7% 4 4 4 3 5% 7% 32%	3926
June	1st to 10th	Night	14% 8% 2 7% 4 4 4 5% 7% 8% 36%	1600
	11th to 20th	Night	13% 7% 2 7% 4 5% 4 5% 7% 8% 38%	1600
	21st to end	Night	13% 7% 3 7% 3 4 4 5% 6% 7% 43%	1600
July	1st to 10th	Night	13% 8% 3 7% 5% 4 4 3 5% 8% 39%	3600
	11th to 20th	Night	12% 8% 2 6% 5% 5% 5% 4 7% 9% 39%	3600
	21st to end	Night	12% 6% 2 6% 4 4 4 4 5% 8% 46%	4418
August	1st to 10th	Night	18% 8% 2 7% 4 5% 5% 4 6% 7% 34%	2915
	11th to 20th	Night	18% 9% 3 6% 4 4 4 4 5% 7% 36%	2875
	21st to end	Night	11% 7% 2 6% 4 4 5% 4 5% 8% 43%	3520
September	1st to 10th	Night	14% 7% 2 6% 4 4 4 2 5% 7% 45%	2000
	11th to 20th	Night	13% 7% 2 5% 3 3 4 3 5% 6% 48%	2038
	21st to end	Night	20% 8% 3 7% 5% 4 4 3 4 6% 34%	2290
October	1st to 10th	Night	17% 8% 2 6% 4 4 4 3 4 6% 41%	2400
	11th to 20th	Night	19% 13% 3 6% 5% 4 3 3 5% 7% 33%	2400
	21st to end	Night	24% 15% 2 7% 5% 3 3 3 5% 5% 28%	2640
November	1st to 10th	Night	12% 14% 3 7% 4 4 4 4 5% 5% 38%	2599
	11th to 20th	Night	16% 19% 5% 8% 5% 5% 4 3 5% 6% 25%	2940
	21st to end	Night	15% 20% 7% 11% 5% 4 4 4 4 5% 20%	2940
December	1st to 10th	Night	15% 20% 12% 19% 6% 4 4 3 3 4 11%	4720
	11th to 20th	Night	18% 18% 8% 14% 5% 4 4 3 3 4 19%	5348
	21st to end	Night	18% 20% 9% 13% 7% 4 3 3 4 4 15%	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	77% 4 6% 9% 4	4662
	11th to 20th	Day	80% 3 5% 8% 4 1	5198
	21st to end	Day	71% 5% 9% 12% 4	5780
February	1st to 10th	Day	69% 5% 8% 12% 6% 1	1890
	11th to 20th	Day	67% 5% 7% 15% 6%	1852
	21st to end	Day	61% 4 10% 17% 6% 2	1668
March	1st to 10th	Day	56% 5% 12% 18% 9%	5040
	11th to 20th	Day	52% 5% 16% 17% 7% 2	5090
	21st to end	Day	57% 6% 7% 17% 12% 2	5600
April	1st to 10th	Day	57% 5% 10% 16% 11% 1	2520
	11th to 20th	Day	53% 7% 10% 16% 13% 1	2494
	21st to end	Day	52% 6% 8% 19% 13% 2	2667
May	1st to 10th	Day	60% 5% 8% 16% 8% 3	5910
	11th to 20th	Day	56% 8% 9% 17% 9% 1	6272
	21st to end	Day	50% 8% 11% 20% 11% 1	6949
June	1st to 10th	Day	48% 7% 12% 20% 13% 1	2800
	11th to 20th	Day	48% 8% 14% 18% 11% 1	2800
	21st to end	Day	44% 7% 14% 22% 12%	2800
July	1st to 10th	Day	41% 7% 14% 24% 14% 1	6290
	11th to 20th	Day	45% 7% 14% 21% 12%	6285
	21st to end	Day	40% 6% 11% 27% 15% 1	6245
August	1st to 10th	Day	50% 7% 14% 20% 9%	4221
	11th to 20th	Day	49% 9% 14% 22% 6%	4213
	21st to end	Day	42% 7% 12% 29% 9% 1	4345
September	1st to 10th	Day	44% 6% 11% 23% 15% 1	2400
	11th to 20th	Day	40% 7% 10% 25% 17% 1	2358
	21st to end	Day	53% 6% 10% 18% 12% 1	2110
October	1st to 10th	Day	42% 7% 11% 21% 17% 1	3260
	11th to 20th	Day	46% 6% 12% 17% 15% 4	3240
	21st to end	Day	46% 5% 14% 24% 10% 1	3538
November	1st to 10th	Day	49% 7% 11% 18% 12% 3	1914
	11th to 20th	Day	61% 4 11% 16% 6% 2	1680
	21st to end	Day	68% 6% 9% 13% 4 1	1680
December	1st to 10th	Day	81% 3 6% 7% 2	2680
	11th to 20th	Day	68% 5% 9% 14% 4	3066
	21st to end	Day	72% 6% 9% 9% 4	4048
January	1st to 10th	Night	78% 5% 6% 8% 3	8234
	11th to 20th	Night	78% 4 7% 6% 4	7758
	21st to end	Night	74% 4 7% 9% 5% 1	8401
February	1st to 10th	Night	66% 5% 9% 12% 7%	2730
	11th to 20th	Night	68% 5% 9% 13% 5%	2665
	21st to end	Night	64% 5% 10% 12% 8% 1	2136
March	1st to 10th	Night	61% 5% 13% 15% 6%	5030
	11th to 20th	Night	51% 6% 16% 18% 6% 3	5090
	21st to end	Night	53% 6% 9% 16% 15% 2	5573
April	1st to 10th	Night	58% 6% 9% 15% 11% 1	2100
	11th to 20th	Night	50% 7% 11% 19% 11% 2	2075
	21st to end	Night	48% 7% 11% 20% 12% 2	1970
May	1st to 10th	Night	60% 5% 8% 15% 9% 3	4069
	11th to 20th	Night	53% 9% 11% 17% 9%	3622
	21st to end	Night	50% 8% 10% 18% 11% 3	3927
June	1st to 10th	Night	42% 8% 13% 22% 14% 1	1600
	11th to 20th	Night	40% 10% 14% 22% 12% 1	1600
	21st to end	Night	38% 9% 14% 26% 13% 1	1600
July	1st to 10th	Night	44% 5% 12% 25% 14% 1	3560
	11th to 20th	Night	40% 7% 16% 25% 12% 1	3552
	21st to end	Night	36% 7% 12% 26% 20% 1	4288
August	1st to 10th	Night	47% 8% 14% 23% 8% 1	2904
	11th to 20th	Night	45% 7% 14% 26% 8%	2902
	21st to end	Night	37% 7% 13% 33% 9% 1	3520
September	1st to 10th	Night	39% 7% 13% 25% 14% 3	2000
	11th to 20th	Night	35% 7% 14% 26% 17% 2	2038
	21st to end	Night	50% 6% 13% 18% 12% 1	2290
October	1st to 10th	Night	44% 6% 9% 22% 18% 1	3920
	11th to 20th	Night	44% 5% 13% 19% 14% 6%	3899
	21st to end	Night	43% 4 16% 24% 12% 1	4252
November	1st to 10th	Night	46% 6% 12% 20% 13% 2	2599
	11th to 20th	Night	60% 6% 11% 14% 7% 2	2940
	21st to end	Night	64% 7% 11% 14% 4 1	2940
December	1st to 10th	Night	77% 6% 8% 7% 2	4720
	11th to 20th	Night	69% 4 9% 13% 5%	5348
	21st to end	Night	72% 6% 8% 10% 4	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% 30% 22% 8% 4	220
	11th to 20th	Day	40% 30% 24% 3 2	315
	21st to end	Day	37% 26% 31% 6% 1	363
February	1st to 10th	Day	36% 29% 26% 7% 1	330
	11th to 20th	Day	40% 28% 29% 3 1	330
	21st to end	Day	41% 26% 27% 6%	384
March	1st to 10th	Day	36% 26% 25% 10% 2	540
	11th to 20th	Day	35% 24% 28% 10% 2 1	540
	21st to end	Day	36% 25% 25% 10% 2 1	594
April	1st to 10th	Day	36% 25% 23% 12% 3 1	540
	11th to 20th	Day	32% 25% 24% 11% 6% 2	532
	21st to end	Day	29% 19% 34% 12% 5%	540
May	1st to 10th	Day	32% 21% 26% 13% 6% 2	507
	11th to 20th	Day	28% 17% 29% 15% 8% 3	527
	21st to end	Day	22% 15% 28% 20% 11% 4	573
June	1st to 10th	Day	22% 17% 31% 20% 8% 2	530
	11th to 20th	Day	21% 15% 27% 23% 12% 2	530
	21st to end	Day	16% 17% 33% 23% 8% 2	530
July	1st to 10th	Day	13% 9% 30% 27% 15% 5%	525
	11th to 20th	Day	13% 13% 27% 27% 15% 5%	524
	21st to end	Day	14% 11% 32% 28% 12% 4	576
August	1st to 10th	Day	14% 8% 27% 28% 16% 7%	526
	11th to 20th	Day	18% 8% 27% 27% 13% 7%	519
	21st to end	Day	16% 11% 31% 23% 13% 7%	583
September	1st to 10th	Day	20% 15% 22% 22% 15% 8%	530
	11th to 20th	Day	14% 6% 25% 25% 20% 10%	530
	21st to end	Day	28% 15% 24% 17% 12% 4	530
October	1st to 10th	Day	22% 14% 25% 20% 15% 5%	530
	11th to 20th	Day	29% 22% 27% 14% 7% 2	530
	21st to end	Day	35% 19% 27% 15% 3	583
November	1st to 10th	Day	26% 20% 29% 15% 8% 2	454
	11th to 20th	Day	40% 20% 27% 10% 1 1	220
	21st to end	Day	40% 21% 31% 6% 1	220
December	1st to 10th	Day	40% 30% 21% 5% 2 1	220
	11th to 20th	Day	43% 23% 27% 5% 2	220
	21st to end	Day	39% 26% 29% 5% 2	242
January	1st to 10th	Night	30% 28% 31% 10% 2	840
	11th to 20th	Night	31% 26% 29% 13% 2	840
	21st to end	Night	29% 28% 28% 13% 1	924
February	1st to 10th	Night	31% 23% 31% 14%	840
	11th to 20th	Night	30% 30% 30% 10% 1	823
	21st to end	Night	32% 27% 28% 12% 2	692
March	1st to 10th	Night	28% 26% 31% 14% 2	840
	11th to 20th	Night	32% 23% 26% 16% 3	840
	21st to end	Night	27% 23% 31% 15% 4 1	924
April	1st to 10th	Night	29% 23% 29% 16% 3	840
	11th to 20th	Night	30% 16% 28% 19% 6% 1	831
	21st to end	Night	23% 14% 32% 26% 5%	710
May	1st to 10th	Night	25% 13% 24% 28% 9%	603
	11th to 20th	Night	19% 12% 31% 32% 7%	414
	21st to end	Night	18% 7% 27% 30% 17% 1	433
June	1st to 10th	Night	14% 9% 30% 34% 12% 1	400
	11th to 20th	Night	16% 9% 24% 40% 12%	400
	21st to end	Night	12% 8% 32% 35% 14% 1	400
July	1st to 10th	Night	13% 4 24% 38% 18% 2	390
	11th to 20th	Night	11% 3 23% 41% 22% 1	388
	21st to end	Night	14% 3 22% 40% 19% 2	647
August	1st to 10th	Night	13% 3 21% 39% 23% 2	597
	11th to 20th	Night	17% 5% 17% 32% 26% 3	594
	21st to end	Night	13% 7% 20% 34% 23% 3	840
September	1st to 10th	Night	17% 8% 24% 29% 19% 2	800
	11th to 20th	Night	16% 6% 20% 27% 28% 3	800
	21st to end	Night	23% 11% 22% 24% 18% 3	800
October	1st to 10th	Night	21% 11% 26% 23% 17% 2	800
	11th to 20th	Night	27% 15% 30% 21% 7% 1	800
	21st to end	Night	34% 14% 31% 18% 4	880
November	1st to 10th	Night	22% 17% 32% 22% 6%	820
	11th to 20th	Night	32% 19% 27% 16% 5% 1	840
	21st to end	Night	31% 22% 29% 14% 3	840
December	1st to 10th	Night	33% 26% 26% 11% 3	840
	11th to 20th	Night	31% 25% 27% 14% 3	840
	21st to end	Night	33% 24% 30% 13% 1	924

Page generated at 2026-04-29 02:21:43. Version ac07

Copyright © 2026 Attilla Danko.