Erie
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Erie clear sky chart from 2005-11-06 to 2026-06-01.

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% 12% 4 10% 5% 4 4 3 5% 6% 30%	132251
	Night	17% 15% 5% 11% 5% 4 4 3 4 5% 26%	130875
Transparency	Day	54% 6% 11% 18% 9% 1	135849
	Night	59% 6% 10% 16% 9% 1	135364
Seeing	Day	24% 16% 28% 21% 9% 2	16504
	Night	26% 15% 26% 22% 9% 1	26144

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	17% 24% 9% 28% 5% 3 2 2 3 2 6%	4938
	11th to 20th	Day	11% 23% 10% 21% 8% 5% 5% 3 3 4 8%	5246
	21st to end	Day	16% 17% 8% 18% 9% 7% 5% 3 4 3 10%	5780
February	1st to 10th	Day	17% 18% 5% 16% 10% 5% 4 2 3 4 14%	1890
	11th to 20th	Day	15% 18% 10% 15% 7% 5% 4 3 3 3 16%	1843
	21st to end	Day	19% 16% 5% 12% 5% 4 4 4 5% 5% 21%	1680
March	1st to 10th	Day	15% 15% 6% 12% 6% 3 3 2 4 5% 28%	5042
	11th to 20th	Day	13% 16% 5% 9% 5% 4 4 3 4 6% 30%	5090
	21st to end	Day	21% 14% 6% 10% 4 4 3 3 3 5% 26%	5586
April	1st to 10th	Day	18% 13% 3 7% 4 4 4 3 5% 7% 30%	2436
	11th to 20th	Day	19% 12% 3 6% 4 4 4 4 4 6% 34%	2576
	21st to end	Day	20% 9% 3 7% 4 4 4 3 5% 6% 35%	2730
May	1st to 10th	Day	20% 9% 3 8% 5% 4 4 4 5% 6% 31%	6018
	11th to 20th	Day	18% 8% 3 7% 4 4 4 3 6% 8% 34%	6118
	21st to end	Day	20% 7% 2 7% 4 4 5% 3 5% 6% 37%	7103
June	1st to 10th	Day	16% 6% 2 6% 4 4 4 3 6% 9% 41%	2800
	11th to 20th	Day	13% 6% 3 7% 4 4 5% 4 7% 9% 39%	2800
	21st to end	Day	14% 5% 1 5% 4 4 4 4 7% 9% 43%	2800
July	1st to 10th	Day	10% 5% 2 6% 4 4 4 4 7% 10% 44%	6360
	11th to 20th	Day	13% 6% 3 6% 4 4 4 3 6% 8% 43%	6021
	21st to end	Day	12% 5% 2 6% 4 4 4 4 5% 8% 47%	6424
August	1st to 10th	Day	15% 5% 2 7% 5% 5% 5% 4 6% 8% 38%	4234
	11th to 20th	Day	14% 6% 2 7% 5% 5% 5% 5% 7% 9% 34%	4174
	21st to end	Day	12% 5% 2 5% 4 5% 4 4 6% 9% 42%	4492
September	1st to 10th	Day	16% 7% 2 6% 3 4 4 3 6% 8% 42%	2400
	11th to 20th	Day	12% 5% 2 5% 5% 4 4 3 6% 7% 47%	2220
	21st to end	Day	18% 7% 3 8% 5% 4 5% 3 4 7% 35%	2192
October	1st to 10th	Day	19% 7% 2 7% 4 5% 4 4 5% 8% 36%	2000
	11th to 20th	Day	23% 10% 3 7% 5% 5% 4 3 5% 6% 29%	2000
	21st to end	Day	28% 13% 3 8% 5% 4 4 3 4 6% 22%	2200
November	1st to 10th	Day	18% 16% 4 7% 4 4 3 3 5% 7% 29%	1904
	11th to 20th	Day	17% 24% 3 8% 5% 4 5% 3 5% 6% 21%	1680
	21st to end	Day	22% 25% 5% 10% 5% 4 4 3 4 5% 13%	1680
December	1st to 10th	Day	19% 32% 11% 12% 5% 4 3 2 3 2 7%	2680
	11th to 20th	Day	21% 25% 9% 13% 4 3 4 3 3 3 11%	3066
	21st to end	Day	23% 23% 7% 16% 5% 4 4 3 3 3 10%	4048
January	1st to 10th	Night	16% 24% 11% 28% 4 3 2 2 2 2 6%	7952
	11th to 20th	Night	11% 22% 11% 21% 8% 6% 4 2 3 3 7%	7639
	21st to end	Night	17% 18% 7% 16% 8% 5% 4 3 4 5% 14%	8401
February	1st to 10th	Night	18% 21% 6% 14% 7% 4 3 2 3 4 17%	2730
	11th to 20th	Night	16% 19% 6% 15% 7% 5% 4 2 4 4 17%	2663
	21st to end	Night	19% 17% 6% 14% 5% 4 4 3 4 4 21%	2124
March	1st to 10th	Night	19% 16% 4 9% 6% 3 3 2 4 5% 27%	5018
	11th to 20th	Night	14% 17% 5% 8% 3 3 4 3 5% 6% 34%	5089
	21st to end	Night	16% 16% 5% 10% 5% 4 4 3 4 4 30%	5588
April	1st to 10th	Night	19% 16% 5% 8% 4 4 4 3 4 5% 28%	2184
	11th to 20th	Night	20% 11% 3 7% 4 4 4 3 6% 6% 32%	2010
	21st to end	Night	15% 11% 3 6% 5% 5% 5% 4 5% 7% 34%	1890
May	1st to 10th	Night	23% 10% 3 7% 5% 4 4 4 5% 6% 29%	4143
	11th to 20th	Night	15% 7% 3 8% 5% 5% 5% 4 6% 7% 35%	3993
	21st to end	Night	20% 7% 2 5% 3 3 4 4 6% 9% 38%	4014
June	1st to 10th	Night	12% 7% 3 6% 6% 5% 4 4 7% 8% 40%	1600
	11th to 20th	Night	12% 7% 3 7% 6% 4 4 4 6% 7% 41%	1600
	21st to end	Night	13% 6% 2 6% 5% 4 5% 4 7% 8% 40%	1600
July	1st to 10th	Night	11% 6% 2 7% 5% 4 5% 4 6% 9% 41%	3600
	11th to 20th	Night	12% 6% 2 6% 4 5% 5% 4 7% 8% 41%	3921
	21st to end	Night	9% 5% 2 6% 4 4 5% 4 5% 8% 47%	4428
August	1st to 10th	Night	11% 6% 3 8% 5% 5% 5% 4 7% 8% 39%	2915
	11th to 20th	Night	16% 8% 3 7% 5% 4 5% 3 5% 6% 37%	2875
	21st to end	Night	10% 6% 2 6% 5% 5% 5% 4 6% 9% 42%	3371
September	1st to 10th	Night	14% 7% 3 5% 3 3 4 4 5% 7% 45%	2000
	11th to 20th	Night	13% 5% 2 6% 3 3 3 3 5% 7% 49%	2175
	21st to end	Night	17% 8% 3 7% 4 5% 5% 4 6% 6% 35%	2206
October	1st to 10th	Night	20% 8% 2 6% 4 3 4 3 5% 6% 39%	2400
	11th to 20th	Night	25% 9% 3 7% 5% 4 4 3 5% 5% 29%	2400
	21st to end	Night	30% 11% 3 7% 3 3 4 3 4 5% 27%	2640
November	1st to 10th	Night	20% 15% 4 7% 4 4 3 3 5% 6% 31%	2608
	11th to 20th	Night	20% 22% 3 8% 5% 4 4 3 5% 5% 20%	2940
	21st to end	Night	23% 26% 6% 7% 4 3 3 3 4 3 18%	2940
December	1st to 10th	Night	17% 32% 10% 10% 5% 3 4 3 3 3 10%	4720
	11th to 20th	Night	18% 28% 9% 12% 4 3 3 2 4 4 12%	5348
	21st to end	Night	22% 23% 6% 12% 6% 4 4 3 4 5% 12%	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	86% 3 6% 4 1	4939
	11th to 20th	Day	80% 4 8% 5% 2	5280
	21st to end	Day	78% 5% 7% 7% 3	5780
February	1st to 10th	Day	75% 4 8% 9% 4	1890
	11th to 20th	Day	74% 5% 6% 11% 5%	1852
	21st to end	Day	65% 6% 10% 13% 4 2	1680
March	1st to 10th	Day	57% 6% 14% 18% 4	5045
	11th to 20th	Day	54% 7% 15% 18% 5% 2	5090
	21st to end	Day	59% 7% 6% 18% 8% 1	5586
April	1st to 10th	Day	55% 6% 12% 17% 10%	2436
	11th to 20th	Day	52% 6% 10% 20% 11% 2	2576
	21st to end	Day	50% 5% 10% 20% 12% 2	2730
May	1st to 10th	Day	52% 7% 9% 19% 9% 4	6027
	11th to 20th	Day	49% 7% 13% 21% 9% 1	6122
	21st to end	Day	46% 7% 12% 20% 12% 3	7103
June	1st to 10th	Day	42% 6% 13% 24% 14% 1	2800
	11th to 20th	Day	41% 8% 14% 24% 13% 1	2800
	21st to end	Day	37% 8% 14% 25% 15% 1	2800
July	1st to 10th	Day	34% 7% 14% 26% 17% 1	6290
	11th to 20th	Day	38% 8% 14% 25% 16%	5949
	21st to end	Day	35% 7% 13% 26% 18%	6240
August	1st to 10th	Day	41% 9% 15% 23% 12%	4221
	11th to 20th	Day	42% 9% 16% 25% 7% 1	4213
	21st to end	Day	36% 8% 13% 30% 12% 1	4492
September	1st to 10th	Day	41% 7% 14% 24% 13% 1	2400
	11th to 20th	Day	37% 7% 13% 28% 15%	2220
	21st to end	Day	50% 6% 11% 22% 10% 1	2192
October	1st to 10th	Day	40% 7% 15% 23% 14% 1	3260
	11th to 20th	Day	48% 5% 14% 20% 11% 2	3240
	21st to end	Day	49% 6% 14% 23% 7% 1	3538
November	1st to 10th	Day	55% 6% 10% 18% 10% 2	1904
	11th to 20th	Day	64% 5% 10% 13% 6% 2	1680
	21st to end	Day	75% 4 8% 8% 4	1680
December	1st to 10th	Day	84% 4 6% 5% 1	2680
	11th to 20th	Day	78% 5% 7% 9% 1	3066
	21st to end	Day	80% 5% 8% 6% 1	4048
January	1st to 10th	Night	87% 3 5% 4 1	7952
	11th to 20th	Night	83% 3 7% 4 2	7680
	21st to end	Night	74% 5% 8% 9% 3	8401
February	1st to 10th	Night	73% 5% 9% 10% 3	2730
	11th to 20th	Night	72% 5% 8% 11% 4	2665
	21st to end	Night	67% 5% 9% 11% 6% 1	2124
March	1st to 10th	Night	59% 5% 12% 17% 7%	5028
	11th to 20th	Night	51% 6% 12% 21% 9% 1	5090
	21st to end	Night	55% 7% 9% 16% 12% 1	5588
April	1st to 10th	Night	58% 6% 9% 16% 10% 1	2184
	11th to 20th	Night	53% 5% 10% 18% 12% 2	2010
	21st to end	Night	49% 6% 10% 21% 10% 3	1890
May	1st to 10th	Night	55% 6% 8% 14% 11% 6%	4150
	11th to 20th	Night	48% 7% 12% 21% 10% 1	3994
	21st to end	Night	43% 7% 12% 23% 13% 2	4015
June	1st to 10th	Night	41% 8% 10% 23% 15% 3	1600
	11th to 20th	Night	41% 6% 12% 23% 16% 2	1600
	21st to end	Night	41% 7% 13% 23% 15% 1	1600
July	1st to 10th	Night	38% 7% 12% 24% 16% 3	3560
	11th to 20th	Night	37% 8% 13% 24% 17% 2	3871
	21st to end	Night	33% 8% 13% 21% 24% 1	4297
August	1st to 10th	Night	41% 7% 12% 28% 12% 1	2904
	11th to 20th	Night	46% 8% 13% 23% 9% 1	2902
	21st to end	Night	36% 8% 16% 28% 11% 1	3371
September	1st to 10th	Night	38% 7% 12% 27% 15% 2	2000
	11th to 20th	Night	34% 6% 14% 26% 19% 1	2175
	21st to end	Night	49% 6% 11% 19% 14% 1	2206
October	1st to 10th	Night	39% 7% 10% 23% 19% 1	3920
	11th to 20th	Night	51% 5% 11% 16% 15% 2	3899
	21st to end	Night	46% 4 14% 22% 13% 1	4252
November	1st to 10th	Night	55% 5% 11% 19% 9% 2	2608
	11th to 20th	Night	66% 5% 10% 12% 5% 2	2940
	21st to end	Night	71% 4 10% 11% 3 1	2940
December	1st to 10th	Night	80% 5% 9% 4 1	4720
	11th to 20th	Night	77% 4 9% 8% 1	5348
	21st to end	Night	75% 6% 9% 9% 1	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	34% 29% 27% 7% 3	270
	11th to 20th	Day	35% 32% 24% 6% 2	330
	21st to end	Day	30% 30% 29% 10% 1 1	363
February	1st to 10th	Day	30% 26% 32% 11% 1	330
	11th to 20th	Day	35% 25% 33% 7%	330
	21st to end	Day	34% 24% 34% 7%	283
March	1st to 10th	Day	28% 25% 33% 10% 4	540
	11th to 20th	Day	30% 23% 33% 12% 1 1	540
	21st to end	Day	35% 20% 28% 14% 3 1	594
April	1st to 10th	Day	26% 22% 33% 15% 3 1	540
	11th to 20th	Day	31% 19% 27% 15% 7% 2	532
	21st to end	Day	26% 15% 35% 18% 5% 1	540
May	1st to 10th	Day	28% 16% 32% 18% 4 1	543
	11th to 20th	Day	24% 13% 28% 26% 7% 2	567
	21st to end	Day	18% 10% 30% 28% 11% 3	617
June	1st to 10th	Day	18% 15% 29% 29% 7% 2	530
	11th to 20th	Day	16% 12% 26% 30% 14% 2	530
	21st to end	Day	16% 9% 32% 31% 10% 2	530
July	1st to 10th	Day	11% 8% 25% 34% 18% 4	525
	11th to 20th	Day	16% 8% 27% 28% 15% 4	524
	21st to end	Day	11% 6% 30% 33% 16% 4	576
August	1st to 10th	Day	11% 9% 26% 31% 18% 6%	526
	11th to 20th	Day	15% 8% 20% 34% 17% 6%	519
	21st to end	Day	14% 8% 27% 30% 18% 4	583
September	1st to 10th	Day	17% 12% 21% 26% 19% 5%	530
	11th to 20th	Day	11% 5% 23% 31% 22% 8%	530
	21st to end	Day	20% 12% 30% 22% 12% 4	530
October	1st to 10th	Day	22% 13% 24% 23% 15% 4	530
	11th to 20th	Day	28% 18% 31% 16% 6% 1	530
	21st to end	Day	37% 18% 29% 15% 2	583
November	1st to 10th	Day	32% 21% 27% 15% 4 1	387
	11th to 20th	Day	38% 21% 28% 9% 4	220
	21st to end	Day	38% 22% 32% 8%	220
December	1st to 10th	Day	39% 26% 25% 8% 2 1	220
	11th to 20th	Day	37% 27% 27% 10%	220
	21st to end	Day	38% 25% 26% 10% 1	242
January	1st to 10th	Night	33% 28% 27% 9% 3	840
	11th to 20th	Night	33% 23% 30% 13% 1	840
	21st to end	Night	26% 24% 31% 15% 3	924
February	1st to 10th	Night	30% 23% 29% 17% 2	840
	11th to 20th	Night	27% 26% 31% 13% 2	823
	21st to end	Night	29% 25% 31% 14% 1	692
March	1st to 10th	Night	27% 19% 32% 19% 4	840
	11th to 20th	Night	28% 19% 31% 18% 5%	840
	21st to end	Night	28% 16% 28% 22% 6% 1	924
April	1st to 10th	Night	26% 16% 32% 20% 5%	840
	11th to 20th	Night	27% 12% 33% 21% 7% 1	766
	21st to end	Night	23% 11% 31% 27% 7% 1	630
May	1st to 10th	Night	26% 9% 23% 32% 10% 1	630
	11th to 20th	Night	19% 7% 30% 34% 9% 1	570
	21st to end	Night	17% 7% 25% 32% 16% 3	455
June	1st to 10th	Night	16% 5% 31% 33% 15% 1	400
	11th to 20th	Night	15% 7% 28% 34% 17% 1	400
	21st to end	Night	15% 6% 25% 38% 15% 1	400
July	1st to 10th	Night	11% 5% 20% 38% 21% 5%	390
	11th to 20th	Night	12% 6% 21% 33% 25% 3	525
	21st to end	Night	12% 5% 18% 41% 22% 1	657
August	1st to 10th	Night	12% 4 21% 37% 22% 3	597
	11th to 20th	Night	14% 5% 16% 35% 26% 4	594
	21st to end	Night	15% 6% 19% 31% 24% 4	743
September	1st to 10th	Night	18% 7% 19% 32% 20% 5%	800
	11th to 20th	Night	14% 6% 16% 32% 26% 5%	800
	21st to end	Night	21% 10% 22% 28% 15% 4	800
October	1st to 10th	Night	22% 9% 24% 26% 17% 2	800
	11th to 20th	Night	31% 15% 27% 19% 7% 1	800
	21st to end	Night	37% 16% 27% 18% 2	880
November	1st to 10th	Night	32% 15% 27% 20% 6%	820
	11th to 20th	Night	35% 20% 28% 11% 4 1	840
	21st to end	Night	38% 21% 28% 9% 3	840
December	1st to 10th	Night	40% 23% 26% 8% 3	840
	11th to 20th	Night	36% 27% 25% 11% 2	840
	21st to end	Night	35% 23% 30% 11% 1	924

Page generated at 2026-05-29 01:53:29. Version ac07

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