Fort Erie
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fort Erie 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% 4 9% 5% 5% 4 4 5% 6% 30%	131975
	Night	17% 13% 4 10% 6% 5% 4 3 5% 6% 27%	130507
Transparency	Day	54% 5% 12% 19% 9% 1	135569
	Night	59% 5% 10% 16% 8% 1	134999
Seeing	Day	20% 15% 27% 22% 12% 4	16345
	Night	23% 14% 27% 24% 11% 1	25885

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	18% 21% 7% 15% 6% 5% 4 3 4 5% 12%	4661
	11th to 20th	Day	12% 24% 8% 21% 11% 7% 5% 2 3 2 5%	5140
	21st to end	Day	15% 16% 7% 16% 11% 10% 6% 4 4 3 9%	5780
February	1st to 10th	Day	17% 19% 5% 15% 8% 5% 7% 4 4 4 13%	1890
	11th to 20th	Day	14% 19% 7% 14% 8% 6% 5% 4 3 5% 16%	1843
	21st to end	Day	20% 14% 5% 12% 8% 5% 5% 4 5% 5% 17%	1638
March	1st to 10th	Day	17% 14% 6% 11% 6% 4 3 3 4 5% 27%	5042
	11th to 20th	Day	11% 16% 4 8% 5% 5% 5% 4 5% 6% 31%	5090
	21st to end	Day	21% 12% 4 9% 6% 4 4 3 5% 5% 27%	5586
April	1st to 10th	Day	19% 14% 3 8% 4 5% 3 3 4 6% 30%	2496
	11th to 20th	Day	20% 11% 3 7% 4 4 4 3 5% 6% 33%	2516
	21st to end	Day	21% 10% 3 7% 5% 4 4 3 5% 5% 34%	2730
May	1st to 10th	Day	23% 10% 3 7% 5% 5% 5% 4 5% 6% 28%	5901
	11th to 20th	Day	17% 10% 3 9% 5% 4 4 3 6% 8% 31%	6268
	21st to end	Day	21% 8% 3 6% 3 4 4 4 5% 6% 36%	6949
June	1st to 10th	Day	15% 8% 2 7% 5% 4 4 4 7% 7% 38%	2800
	11th to 20th	Day	12% 5% 3 7% 5% 5% 5% 4 7% 9% 39%	2800
	21st to end	Day	14% 6% 2 5% 4 3 5% 3 6% 9% 43%	2800
July	1st to 10th	Day	10% 6% 2 6% 4 4 5% 4 6% 9% 45%	6360
	11th to 20th	Day	13% 6% 3 6% 4 5% 4 4 7% 8% 41%	6360
	21st to end	Day	9% 5% 2 6% 4 4 5% 4 6% 8% 47%	6452
August	1st to 10th	Day	16% 6% 2 6% 4 4 5% 3 6% 7% 40%	4234
	11th to 20th	Day	13% 6% 3 7% 5% 5% 5% 4 7% 11% 34%	4174
	21st to end	Day	11% 5% 2 6% 4 4 4 3 6% 9% 45%	4426
September	1st to 10th	Day	14% 7% 2 5% 4 4 4 4 5% 7% 43%	2400
	11th to 20th	Day	11% 4 2 6% 4 4 4 4 6% 8% 47%	2311
	21st to end	Day	15% 8% 3 7% 5% 6% 5% 4 6% 8% 32%	2140
October	1st to 10th	Day	19% 8% 3 6% 6% 4 4 3 6% 6% 36%	2000
	11th to 20th	Day	21% 10% 3 8% 4 5% 5% 4 5% 7% 29%	2000
	21st to end	Day	26% 14% 3 10% 4 5% 4 3 4 5% 22%	2200
November	1st to 10th	Day	16% 12% 3 9% 5% 5% 5% 4 5% 6% 32%	1834
	11th to 20th	Day	15% 15% 3 11% 5% 5% 5% 4 5% 5% 28%	1680
	21st to end	Day	21% 19% 4 9% 5% 5% 5% 4 4 6% 18%	1680
December	1st to 10th	Day	21% 18% 7% 13% 7% 5% 5% 4 5% 4 11%	2680
	11th to 20th	Day	22% 21% 5% 10% 5% 5% 4 3 4 5% 16%	3066
	21st to end	Day	23% 23% 6% 12% 7% 6% 4 3 3 4 12%	4048
January	1st to 10th	Night	18% 21% 7% 13% 6% 4 4 3 3 4 16%	8234
	11th to 20th	Night	13% 22% 9% 22% 10% 7% 4 3 3 3 7%	7741
	21st to end	Night	17% 18% 6% 17% 10% 8% 5% 3 4 4 10%	8401
February	1st to 10th	Night	18% 19% 6% 13% 6% 5% 4 3 4 4 17%	2730
	11th to 20th	Night	16% 16% 6% 13% 7% 5% 5% 3 4 6% 18%	2663
	21st to end	Night	19% 17% 6% 13% 7% 4 4 3 4 5% 18%	2165
March	1st to 10th	Night	18% 14% 5% 9% 6% 5% 4 3 4 4 28%	5018
	11th to 20th	Night	16% 14% 3 6% 4 4 4 3 5% 7% 33%	5089
	21st to end	Night	18% 11% 4 9% 5% 4 4 3 5% 5% 33%	5588
April	1st to 10th	Night	21% 13% 4 8% 6% 4 4 2 5% 4 29%	2122
	11th to 20th	Night	19% 10% 3 8% 4 4 4 4 5% 6% 33%	2070
	21st to end	Night	18% 9% 3 6% 4 5% 5% 4 5% 7% 35%	1890
May	1st to 10th	Night	26% 12% 4 8% 4 3 4 3 4 5% 28%	4062
	11th to 20th	Night	14% 7% 3 8% 6% 5% 5% 4 6% 8% 34%	3621
	21st to end	Night	19% 8% 3 7% 3 4 4 4 5% 7% 36%	3926
June	1st to 10th	Night	12% 9% 3 6% 6% 5% 5% 5% 7% 7% 36%	1600
	11th to 20th	Night	12% 5% 2 6% 5% 5% 5% 4 6% 8% 41%	1600
	21st to end	Night	15% 6% 2 5% 5% 4 4 5% 6% 8% 40%	1600
July	1st to 10th	Night	11% 5% 2 7% 4 4 4 4 6% 10% 42%	3600
	11th to 20th	Night	11% 6% 2 6% 5% 4 4 4 6% 8% 43%	3600
	21st to end	Night	11% 5% 2 6% 4 4 5% 4 6% 7% 48%	4396
August	1st to 10th	Night	11% 8% 3 7% 5% 4 4 4 6% 8% 41%	2915
	11th to 20th	Night	14% 8% 3 7% 5% 5% 4 4 6% 7% 37%	2875
	21st to end	Night	9% 5% 2 6% 5% 4 6% 4 6% 9% 45%	3439
September	1st to 10th	Night	14% 6% 2 5% 4 3 4 3 5% 8% 45%	2000
	11th to 20th	Night	12% 5% 2 5% 3 3 3 3 5% 8% 52%	2085
	21st to end	Night	17% 8% 3 7% 5% 4 4 5% 6% 7% 35%	2260
October	1st to 10th	Night	18% 6% 3 7% 5% 5% 4 3 5% 7% 40%	2400
	11th to 20th	Night	22% 10% 3 8% 4 5% 4 4 5% 6% 30%	2400
	21st to end	Night	26% 9% 3 7% 4 5% 5% 4 5% 6% 27%	2640
November	1st to 10th	Night	18% 10% 3 7% 5% 4 4 3 5% 6% 36%	2679
	11th to 20th	Night	16% 14% 4 10% 6% 5% 4 3 5% 6% 27%	2940
	21st to end	Night	20% 16% 5% 10% 6% 5% 4 4 5% 6% 20%	2940
December	1st to 10th	Night	19% 22% 7% 14% 6% 4 4 3 5% 5% 11%	4720
	11th to 20th	Night	21% 23% 5% 12% 7% 5% 4 3 4 4 14%	5348
	21st to end	Night	25% 20% 5% 11% 6% 5% 4 3 4 4 13%	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	78% 4 6% 7% 4	4662
	11th to 20th	Day	86% 5% 4 3 1	5174
	21st to end	Day	81% 4 8% 5% 1	5780
February	1st to 10th	Day	75% 6% 10% 8% 1	1890
	11th to 20th	Day	71% 6% 9% 11% 3	1852
	21st to end	Day	68% 6% 11% 11% 4	1638
March	1st to 10th	Day	60% 4 13% 17% 6%	5045
	11th to 20th	Day	53% 5% 18% 16% 6% 1	5090
	21st to end	Day	59% 6% 7% 20% 7% 1	5586
April	1st to 10th	Day	57% 5% 10% 18% 9% 1	2496
	11th to 20th	Day	51% 5% 10% 20% 11% 2	2516
	21st to end	Day	52% 5% 11% 19% 12% 2	2730
May	1st to 10th	Day	56% 5% 11% 16% 9% 3	5910
	11th to 20th	Day	50% 9% 10% 20% 11% 1	6272
	21st to end	Day	48% 5% 12% 22% 11% 2	6949
June	1st to 10th	Day	43% 8% 12% 20% 15% 1	2800
	11th to 20th	Day	41% 8% 15% 23% 12% 1	2800
	21st to end	Day	39% 8% 14% 24% 14% 1	2800
July	1st to 10th	Day	37% 4 13% 29% 17% 1	6290
	11th to 20th	Day	41% 4 14% 25% 16% 1	6285
	21st to end	Day	36% 5% 15% 26% 17%	6267
August	1st to 10th	Day	43% 7% 14% 23% 13% 1	4221
	11th to 20th	Day	45% 6% 17% 25% 8%	4213
	21st to end	Day	37% 4 12% 35% 11% 1	4426
September	1st to 10th	Day	41% 7% 13% 26% 12% 1	2400
	11th to 20th	Day	35% 7% 13% 30% 13% 1	2311
	21st to end	Day	49% 6% 14% 20% 9% 1	2140
October	1st to 10th	Day	42% 5% 12% 27% 13% 1	3260
	11th to 20th	Day	47% 4 16% 20% 12% 1	3240
	21st to end	Day	53% 3 14% 22% 8% 1	3538
November	1st to 10th	Day	56% 6% 11% 18% 8% 1	1834
	11th to 20th	Day	58% 7% 14% 14% 5% 2	1680
	21st to end	Day	70% 6% 11% 10% 3	1680
December	1st to 10th	Day	78% 5% 9% 7% 1	2680
	11th to 20th	Day	74% 5% 10% 9% 2	3066
	21st to end	Day	78% 5% 8% 7% 2	4048
January	1st to 10th	Night	76% 5% 6% 10% 3	8234
	11th to 20th	Night	84% 5% 4 4 2	7782
	21st to end	Night	81% 4 6% 6% 2	8401
February	1st to 10th	Night	74% 5% 9% 10% 2	2730
	11th to 20th	Night	69% 6% 10% 12% 3	2665
	21st to end	Night	69% 5% 9% 11% 5%	2165
March	1st to 10th	Night	61% 4 10% 17% 7% 1	5028
	11th to 20th	Night	52% 5% 15% 19% 8% 2	5090
	21st to end	Night	54% 4 10% 18% 12% 1	5588
April	1st to 10th	Night	59% 4 9% 18% 9% 1	2122
	11th to 20th	Night	51% 5% 11% 19% 13% 1	2070
	21st to end	Night	49% 6% 10% 20% 13% 2	1890
May	1st to 10th	Night	59% 6% 7% 14% 10% 5%	4069
	11th to 20th	Night	47% 8% 14% 20% 10% 1	3622
	21st to end	Night	47% 5% 11% 22% 14% 2	3927
June	1st to 10th	Night	44% 8% 10% 22% 14% 2	1600
	11th to 20th	Night	41% 7% 13% 21% 17% 1	1600
	21st to end	Night	42% 7% 14% 21% 14% 2	1600
July	1st to 10th	Night	40% 3 12% 26% 17% 2	3560
	11th to 20th	Night	40% 3 13% 27% 16% 1	3552
	21st to end	Night	36% 4 14% 23% 21% 2	4266
August	1st to 10th	Night	41% 6% 14% 26% 11% 1	2904
	11th to 20th	Night	47% 5% 15% 24% 8%	2902
	21st to end	Night	37% 4 13% 32% 13% 1	3439
September	1st to 10th	Night	38% 7% 13% 26% 14% 2	2000
	11th to 20th	Night	33% 5% 13% 30% 17% 1	2085
	21st to end	Night	47% 8% 12% 20% 12% 1	2260
October	1st to 10th	Night	44% 4 8% 25% 18% 1	3920
	11th to 20th	Night	51% 4 13% 19% 13%	3899
	21st to end	Night	48% 4 15% 24% 8% 1	4252
November	1st to 10th	Night	52% 6% 10% 21% 10% 2	2679
	11th to 20th	Night	60% 7% 12% 13% 6% 2	2940
	21st to end	Night	67% 8% 12% 11% 3	2940
December	1st to 10th	Night	78% 5% 11% 5% 1	4720
	11th to 20th	Night	77% 5% 7% 9% 2	5348
	21st to end	Night	76% 5% 7% 9% 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	26% 25% 32% 10% 5% 1	220
	11th to 20th	Day	26% 29% 29% 12% 3 1	309
	21st to end	Day	23% 28% 30% 15% 4	363
February	1st to 10th	Day	27% 23% 31% 15% 3	330
	11th to 20th	Day	26% 26% 34% 12% 1	330
	21st to end	Day	30% 22% 35% 12% 1	331
March	1st to 10th	Day	24% 19% 35% 17% 4 1	540
	11th to 20th	Day	24% 19% 34% 17% 5% 1	540
	21st to end	Day	28% 13% 31% 20% 6% 1	594
April	1st to 10th	Day	24% 21% 30% 19% 6% 1	540
	11th to 20th	Day	26% 20% 25% 18% 9% 3	532
	21st to end	Day	24% 13% 30% 24% 8% 1	540
May	1st to 10th	Day	27% 12% 28% 21% 9% 3	507
	11th to 20th	Day	17% 11% 28% 27% 14% 3	527
	21st to end	Day	16% 8% 29% 27% 14% 5%	573
June	1st to 10th	Day	17% 15% 28% 29% 11% 1	530
	11th to 20th	Day	12% 13% 23% 32% 17% 3	530
	21st to end	Day	15% 10% 30% 30% 11% 4	530
July	1st to 10th	Day	8% 8% 21% 35% 24% 5%	525
	11th to 20th	Day	13% 9% 24% 29% 19% 5%	524
	21st to end	Day	9% 8% 27% 32% 18% 6%	576
August	1st to 10th	Day	11% 6% 21% 30% 25% 8%	526
	11th to 20th	Day	14% 6% 21% 29% 22% 9%	519
	21st to end	Day	11% 7% 25% 29% 19% 9%	583
September	1st to 10th	Day	13% 9% 24% 26% 18% 10%	530
	11th to 20th	Day	10% 5% 18% 25% 26% 16%	530
	21st to end	Day	16% 14% 25% 21% 18% 6%	530
October	1st to 10th	Day	19% 12% 24% 20% 18% 7%	530
	11th to 20th	Day	24% 16% 30% 21% 7% 2	530
	21st to end	Day	32% 19% 24% 18% 7%	583
November	1st to 10th	Day	24% 18% 32% 18% 8% 1	371
	11th to 20th	Day	29% 26% 25% 15% 5% 1	220
	21st to end	Day	34% 25% 29% 11% 1	220
December	1st to 10th	Day	31% 24% 28% 12% 5%	220
	11th to 20th	Day	31% 23% 28% 16% 2	220
	21st to end	Day	31% 29% 24% 12% 2 1	242
January	1st to 10th	Night	30% 24% 28% 13% 5%	840
	11th to 20th	Night	32% 23% 28% 14% 3	840
	21st to end	Night	23% 18% 37% 17% 5%	924
February	1st to 10th	Night	27% 23% 29% 17% 3	840
	11th to 20th	Night	26% 20% 32% 19% 3	823
	21st to end	Night	28% 19% 33% 19% 2	692
March	1st to 10th	Night	23% 17% 33% 23% 5%	840
	11th to 20th	Night	26% 16% 30% 21% 5%	840
	21st to end	Night	24% 13% 33% 21% 8% 1	924
April	1st to 10th	Night	26% 14% 31% 24% 4	840
	11th to 20th	Night	25% 14% 28% 23% 9% 1	826
	21st to end	Night	23% 9% 27% 32% 9%	630
May	1st to 10th	Night	22% 8% 23% 33% 12% 1	603
	11th to 20th	Night	13% 9% 26% 41% 10%	414
	21st to end	Night	15% 6% 27% 31% 20% 2	433
June	1st to 10th	Night	14% 6% 29% 36% 16% 1	400
	11th to 20th	Night	14% 7% 24% 38% 17% 1	400
	21st to end	Night	14% 8% 25% 38% 16% 1	400
July	1st to 10th	Night	8% 4 21% 43% 21% 3	390
	11th to 20th	Night	12% 4 25% 36% 22% 2	388
	21st to end	Night	12% 3 23% 36% 24% 2	638
August	1st to 10th	Night	11% 4 17% 39% 27% 3	597
	11th to 20th	Night	10% 6% 17% 34% 30% 3	594
	21st to end	Night	12% 5% 21% 35% 24% 3	785
September	1st to 10th	Night	15% 7% 19% 33% 21% 5%	800
	11th to 20th	Night	13% 5% 18% 27% 31% 7%	800
	21st to end	Night	20% 9% 20% 29% 18% 4	800
October	1st to 10th	Night	20% 8% 27% 24% 19% 3	800
	11th to 20th	Night	25% 18% 25% 23% 8% 2	800
	21st to end	Night	30% 15% 30% 21% 5%	880
November	1st to 10th	Night	24% 15% 30% 23% 7% 1	820
	11th to 20th	Night	24% 23% 29% 17% 7% 1	840
	21st to end	Night	28% 22% 30% 16% 4	840
December	1st to 10th	Night	35% 24% 24% 13% 4	840
	11th to 20th	Night	31% 25% 27% 15% 3	840
	21st to end	Night	35% 18% 29% 16% 2	924

Page generated at 2026-04-29 02:21:42. Version ac07

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