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 2025-01-07.

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% 9% 5% 4 4 4 5% 6% 28%	105026
	Night	16% 14% 5% 10% 5% 4 4 3 5% 6% 28%	104008
Transparency	Day	53% 7% 11% 19% 9% 1	108631
	Night	55% 6% 11% 17% 9% 1	108491
Seeing	Day	26% 18% 28% 17% 8% 3	14794
	Night	25% 17% 27% 21% 9% 1	24312

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% 23% 13% 12% 5% 3 3 2 3 4 18%	2565
	11th to 20th	Day	10% 20% 9% 20% 8% 4 4 2 3 4 16%	2786
	21st to end	Day	22% 18% 10% 14% 7% 5% 3 2 3 4 12%	3124
February	1st to 10th	Day	15% 19% 7% 12% 8% 6% 4 3 4 4 18%	1710
	11th to 20th	Day	12% 16% 7% 15% 7% 4 5% 3 4 5% 21%	1663
	21st to end	Day	19% 14% 4 13% 6% 3 4 3 4 6% 25%	1513
March	1st to 10th	Day	19% 15% 7% 8% 5% 3 3 3 4 6% 28%	3427
	11th to 20th	Day	10% 20% 8% 10% 5% 4 3 3 3 5% 29%	3480
	21st to end	Day	16% 12% 3 12% 6% 4 4 4 5% 5% 29%	3829
April	1st to 10th	Day	16% 16% 4 8% 5% 4 4 3 5% 6% 29%	2280
	11th to 20th	Day	18% 14% 3 7% 5% 4 5% 4 6% 5% 31%	2254
	21st to end	Day	21% 11% 3 7% 5% 5% 3 4 4 5% 33%	2413
May	1st to 10th	Day	25% 10% 3 7% 5% 4 4 3 4 6% 29%	4108
	11th to 20th	Day	21% 11% 4 8% 5% 5% 5% 4 5% 7% 25%	4362
	21st to end	Day	13% 7% 3 6% 5% 5% 5% 4 6% 7% 40%	4837
June	1st to 10th	Day	17% 9% 2 7% 6% 5% 5% 4 5% 8% 34%	2660
	11th to 20th	Day	14% 8% 3 8% 5% 5% 6% 4 7% 8% 32%	2660
	21st to end	Day	15% 7% 3 7% 6% 4 5% 4 7% 7% 35%	2660
July	1st to 10th	Day	10% 6% 3 6% 6% 6% 6% 5% 8% 10% 35%	4440
	11th to 20th	Day	10% 7% 2 7% 5% 6% 6% 5% 8% 9% 34%	4440
	21st to end	Day	10% 7% 3 8% 6% 5% 6% 4 7% 8% 36%	4472
August	1st to 10th	Day	19% 9% 3 8% 5% 5% 4 4 7% 9% 28%	4104
	11th to 20th	Day	15% 7% 3 8% 6% 7% 6% 5% 7% 9% 26%	4044
	21st to end	Day	12% 8% 3 7% 4 5% 6% 4 6% 9% 36%	4212
September	1st to 10th	Day	18% 8% 2 5% 4 4 4 3 6% 7% 38%	2280
	11th to 20th	Day	14% 6% 3 7% 4 5% 4 4 5% 7% 42%	2240
	21st to end	Day	21% 9% 3 8% 4 5% 4 4 5% 6% 31%	2005
October	1st to 10th	Day	19% 9% 3 7% 5% 4 4 4 5% 7% 33%	1900
	11th to 20th	Day	21% 9% 4 8% 5% 5% 4 3 4 6% 31%	1900
	21st to end	Day	22% 16% 3 8% 5% 4 4 3 4 6% 25%	2090
November	1st to 10th	Day	13% 14% 3 7% 5% 4 5% 4 5% 7% 34%	1822
	11th to 20th	Day	16% 19% 5% 9% 4 3 4 4 5% 6% 25%	1600
	21st to end	Day	18% 22% 5% 9% 6% 3 3 4 5% 6% 19%	1600
December	1st to 10th	Day	17% 25% 12% 19% 4 4 2 2 3 3 10%	2600
	11th to 20th	Day	19% 18% 8% 13% 7% 3 4 3 4 5% 18%	2986
	21st to end	Day	17% 24% 8% 12% 6% 4 4 3 4 4 15%	3960
January	1st to 10th	Night	15% 20% 11% 16% 5% 4 4 3 4 5% 14%	4514
	11th to 20th	Night	12% 19% 10% 18% 8% 5% 4 3 4 4 14%	4170
	21st to end	Night	21% 21% 8% 16% 8% 4 3 2 3 3 12%	4532
February	1st to 10th	Night	14% 19% 5% 11% 9% 5% 4 3 5% 5% 19%	2470
	11th to 20th	Night	13% 15% 6% 15% 7% 6% 5% 3 4 5% 19%	2403
	21st to end	Night	16% 15% 6% 15% 7% 5% 4 3 4 4 22%	1939
March	1st to 10th	Night	19% 16% 4 10% 6% 4 3 3 4 5% 26%	3410
	11th to 20th	Night	16% 19% 7% 11% 5% 3 3 3 4 6% 24%	3479
	21st to end	Night	13% 13% 3 10% 5% 3 3 3 6% 5% 35%	3802
April	1st to 10th	Night	17% 15% 4 9% 5% 4 5% 4 4 6% 28%	1900
	11th to 20th	Night	18% 15% 3 6% 3 3 3 3 5% 6% 36%	1875
	21st to end	Night	16% 11% 3 7% 5% 4 5% 3 5% 6% 34%	1782
May	1st to 10th	Night	26% 11% 3 6% 4 4 4 2 4 6% 31%	2833
	11th to 20th	Night	20% 12% 3 6% 5% 5% 4 3 5% 6% 30%	2527
	21st to end	Night	14% 8% 2 7% 5% 4 4 3 5% 8% 40%	2738
June	1st to 10th	Night	13% 8% 2 7% 5% 4 4 5% 7% 9% 36%	1520
	11th to 20th	Night	11% 7% 2 7% 4 5% 4 5% 7% 8% 39%	1520
	21st to end	Night	13% 7% 3 7% 3 4 4 5% 6% 7% 42%	1520
July	1st to 10th	Night	13% 9% 3 7% 5% 4 5% 4 6% 6% 39%	2520
	11th to 20th	Night	11% 7% 2 6% 5% 4 4 4 6% 9% 43%	2520
	21st to end	Night	14% 6% 3 6% 4 4 4 4 6% 8% 41%	3077
August	1st to 10th	Night	18% 9% 3 7% 4 5% 5% 3 6% 7% 34%	2825
	11th to 20th	Night	18% 9% 3 6% 4 4 4 4 6% 7% 36%	2785
	21st to end	Night	11% 7% 2 6% 4 4 5% 4 5% 8% 43%	3412
September	1st to 10th	Night	15% 7% 2 7% 4 4 4 3 5% 7% 44%	1900
	11th to 20th	Night	13% 7% 2 5% 4 3 4 3 5% 6% 47%	1936
	21st to end	Night	20% 8% 3 7% 5% 4 4 3 4 6% 35%	2175
October	1st to 10th	Night	18% 9% 2 6% 4 4 4 3 4 6% 40%	2280
	11th to 20th	Night	19% 12% 3 6% 5% 4 3 3 5% 7% 32%	2280
	21st to end	Night	24% 14% 2 7% 5% 3 3 3 5% 6% 27%	2508
November	1st to 10th	Night	12% 14% 3 7% 4 4 4 4 5% 5% 39%	2472
	11th to 20th	Night	16% 19% 4 8% 5% 5% 4 4 4 6% 25%	2800
	21st to end	Night	15% 20% 6% 10% 5% 4 5% 4 5% 5% 21%	2800
December	1st to 10th	Night	15% 20% 12% 19% 6% 4 4 3 3 4 11%	4580
	11th to 20th	Night	18% 18% 8% 14% 5% 4 4 3 4 4 19%	5208
	21st to end	Night	18% 20% 9% 12% 7% 4 3 3 4 4 15%	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	71% 5% 7% 12% 4 1	2566
	11th to 20th	Day	72% 4 8% 11% 4	2786
	21st to end	Day	75% 5% 8% 8% 3 1	3124
February	1st to 10th	Day	70% 5% 9% 11% 5%	1710
	11th to 20th	Day	65% 5% 8% 15% 7%	1672
	21st to end	Day	61% 4 10% 17% 6% 2	1513
March	1st to 10th	Day	56% 5% 11% 21% 6%	3430
	11th to 20th	Day	56% 6% 14% 16% 6% 1	3480
	21st to end	Day	54% 7% 9% 20% 9% 2	3829
April	1st to 10th	Day	56% 5% 10% 17% 11% 1	2280
	11th to 20th	Day	52% 7% 10% 17% 13% 1	2254
	21st to end	Day	53% 6% 8% 18% 13% 2	2413
May	1st to 10th	Day	55% 6% 9% 21% 8% 1	4120
	11th to 20th	Day	54% 10% 12% 16% 7% 1	4366
	21st to end	Day	40% 8% 13% 24% 14% 1	4837
June	1st to 10th	Day	48% 7% 12% 19% 12% 1	2660
	11th to 20th	Day	47% 9% 14% 19% 11% 1	2660
	21st to end	Day	45% 8% 14% 23% 11%	2660
July	1st to 10th	Day	42% 8% 14% 23% 12% 1	4370
	11th to 20th	Day	42% 8% 14% 22% 14%	4365
	21st to end	Day	43% 7% 14% 24% 11% 1	4329
August	1st to 10th	Day	51% 7% 13% 20% 8%	4091
	11th to 20th	Day	49% 9% 15% 21% 5%	4083
	21st to end	Day	42% 7% 12% 29% 9% 1	4212
September	1st to 10th	Day	45% 6% 11% 21% 15% 1	2280
	11th to 20th	Day	41% 7% 10% 24% 17% 1	2240
	21st to end	Day	53% 6% 10% 18% 12% 1	2005
October	1st to 10th	Day	43% 7% 11% 21% 16% 1	3160
	11th to 20th	Day	46% 6% 13% 17% 15% 4	3140
	21st to end	Day	46% 5% 14% 24% 10% 1	3428
November	1st to 10th	Day	48% 7% 12% 18% 13% 3	1822
	11th to 20th	Day	60% 4 11% 16% 6% 2	1600
	21st to end	Day	67% 6% 9% 13% 5% 1	1600
December	1st to 10th	Day	81% 4 6% 7% 2	2600
	11th to 20th	Day	69% 5% 9% 13% 4	2986
	21st to end	Day	72% 6% 9% 9% 4	3960
January	1st to 10th	Night	71% 6% 9% 11% 3	4514
	11th to 20th	Night	73% 6% 9% 9% 2 1	4170
	21st to end	Night	78% 4 6% 9% 3	4532
February	1st to 10th	Night	66% 6% 10% 12% 6%	2470
	11th to 20th	Night	66% 6% 9% 14% 5%	2405
	21st to end	Night	64% 5% 10% 12% 8% 1	1939
March	1st to 10th	Night	60% 6% 11% 18% 5%	3420
	11th to 20th	Night	58% 7% 13% 15% 6% 1	3480
	21st to end	Night	47% 6% 10% 20% 15% 2	3802
April	1st to 10th	Night	57% 6% 9% 16% 11%	1900
	11th to 20th	Night	49% 7% 11% 19% 11% 2	1875
	21st to end	Night	48% 7% 11% 19% 13% 2	1782
May	1st to 10th	Night	55% 6% 10% 19% 8% 1	2840
	11th to 20th	Night	51% 12% 13% 16% 7% 1	2528
	21st to end	Night	40% 10% 12% 20% 14% 4	2739
June	1st to 10th	Night	41% 8% 14% 22% 13% 1	1520
	11th to 20th	Night	38% 11% 14% 23% 12% 2	1520
	21st to end	Night	39% 9% 13% 26% 13% 1	1520
July	1st to 10th	Night	45% 6% 12% 20% 16% 1	2480
	11th to 20th	Night	36% 7% 17% 25% 14% 1	2472
	21st to end	Night	40% 8% 12% 24% 16% 1	2979
August	1st to 10th	Night	47% 8% 14% 23% 7% 1	2814
	11th to 20th	Night	45% 7% 14% 26% 7%	2812
	21st to end	Night	37% 7% 13% 32% 9% 1	3412
September	1st to 10th	Night	40% 7% 13% 24% 14% 3	1900
	11th to 20th	Night	36% 7% 13% 24% 18% 2	1936
	21st to end	Night	49% 6% 13% 19% 12% 1	2175
October	1st to 10th	Night	45% 7% 9% 21% 17% 1	3800
	11th to 20th	Night	44% 6% 13% 18% 13% 6%	3779
	21st to end	Night	43% 4 16% 24% 12% 1	4120
November	1st to 10th	Night	46% 6% 13% 20% 13% 2	2472
	11th to 20th	Night	59% 6% 11% 14% 8% 2	2800
	21st to end	Night	63% 7% 11% 15% 4 1	2800
December	1st to 10th	Night	77% 6% 8% 7% 2	4580
	11th to 20th	Night	69% 4 9% 13% 4	5208
	21st to end	Night	72% 6% 8% 10% 4	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	34% 28% 24% 8% 4 1	192
	11th to 20th	Day	37% 31% 26% 4 2	257
	21st to end	Day	32% 28% 32% 7% 1	297
February	1st to 10th	Day	36% 33% 25% 7%	270
	11th to 20th	Day	38% 29% 29% 3 1	270
	21st to end	Day	42% 26% 25% 6%	325
March	1st to 10th	Day	34% 26% 26% 11% 3	460
	11th to 20th	Day	31% 25% 29% 11% 3 2	460
	21st to end	Day	35% 24% 26% 11% 3 1	506
April	1st to 10th	Day	33% 24% 24% 14% 3 1	460
	11th to 20th	Day	31% 23% 25% 12% 7% 2	452
	21st to end	Day	29% 19% 33% 12% 6%	460
May	1st to 10th	Day	32% 21% 25% 14% 6% 2	463
	11th to 20th	Day	26% 18% 29% 15% 8% 3	487
	21st to end	Day	19% 15% 29% 21% 12% 5%	529
June	1st to 10th	Day	21% 17% 31% 21% 9% 2	490
	11th to 20th	Day	18% 15% 27% 25% 13% 2	490
	21st to end	Day	17% 18% 33% 22% 8% 2	490
July	1st to 10th	Day	14% 9% 30% 26% 16% 5%	485
	11th to 20th	Day	12% 13% 28% 26% 15% 5%	484
	21st to end	Day	14% 11% 32% 27% 12% 4	532
August	1st to 10th	Day	15% 8% 26% 28% 15% 7%	486
	11th to 20th	Day	18% 9% 28% 26% 12% 8%	479
	21st to end	Day	16% 11% 29% 24% 12% 7%	539
September	1st to 10th	Day	20% 14% 23% 22% 14% 7%	490
	11th to 20th	Day	15% 7% 25% 24% 19% 9%	490
	21st to end	Day	28% 16% 23% 17% 12% 4	490
October	1st to 10th	Day	23% 14% 25% 19% 15% 4	490
	11th to 20th	Day	29% 20% 27% 14% 8% 2	490
	21st to end	Day	34% 20% 27% 15% 4	539
November	1st to 10th	Day	26% 19% 30% 15% 8% 2	422
	11th to 20th	Day	37% 22% 28% 12% 2 1	200
	21st to end	Day	40% 21% 32% 7% 1	200
December	1st to 10th	Day	38% 31% 22% 6% 2 2	200
	11th to 20th	Day	42% 23% 29% 5% 2	200
	21st to end	Day	36% 26% 30% 5% 2	220
January	1st to 10th	Night	30% 27% 31% 10% 3	785
	11th to 20th	Night	30% 24% 30% 14% 2	760
	21st to end	Night	28% 27% 30% 14% 1	836
February	1st to 10th	Night	31% 24% 30% 14% 1	760
	11th to 20th	Night	29% 31% 29% 10% 1	743
	21st to end	Night	32% 27% 28% 12% 2	628
March	1st to 10th	Night	26% 26% 31% 15% 2	760
	11th to 20th	Night	31% 23% 25% 17% 4	760
	21st to end	Night	25% 23% 31% 15% 5% 1	836
April	1st to 10th	Night	26% 23% 30% 17% 3	760
	11th to 20th	Night	30% 16% 28% 19% 7% 1	751
	21st to end	Night	22% 14% 33% 26% 5%	642
May	1st to 10th	Night	25% 13% 24% 28% 10% 1	570
	11th to 20th	Night	18% 12% 31% 33% 7%	393
	21st to end	Night	16% 7% 27% 32% 18% 1	411
June	1st to 10th	Night	13% 9% 31% 33% 13% 1	380
	11th to 20th	Night	15% 9% 23% 41% 12%	380
	21st to end	Night	12% 8% 32% 34% 13% 1	380
July	1st to 10th	Night	14% 4 24% 38% 18% 2	370
	11th to 20th	Night	10% 2 24% 41% 23% 1	368
	21st to end	Night	14% 3 22% 40% 19% 2	614
August	1st to 10th	Night	13% 3 20% 39% 23% 1	567
	11th to 20th	Night	17% 5% 18% 32% 26% 3	564
	21st to end	Night	13% 7% 20% 33% 24% 3	798
September	1st to 10th	Night	18% 8% 24% 29% 19% 2	760
	11th to 20th	Night	17% 6% 21% 26% 27% 3	760
	21st to end	Night	22% 12% 22% 23% 18% 3	760
October	1st to 10th	Night	22% 11% 26% 23% 17% 2	760
	11th to 20th	Night	27% 15% 29% 21% 7% 1	760
	21st to end	Night	33% 14% 31% 18% 4	836
November	1st to 10th	Night	21% 18% 32% 23% 6%	780
	11th to 20th	Night	31% 19% 28% 16% 6% 1	800
	21st to end	Night	30% 22% 30% 14% 4 1	800
December	1st to 10th	Night	33% 27% 26% 11% 3	800
	11th to 20th	Night	31% 25% 27% 15% 3	800
	21st to end	Night	32% 24% 30% 13% 1	880

Page generated at 2025-01-04 03:24:02. Version ac07

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