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 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% 11% 3 8% 5% 5% 4 4 5% 7% 31%	105028
	Night	18% 13% 4 9% 5% 4 4 3 5% 6% 28%	104007
Transparency	Day	52% 6% 12% 19% 9% 1	108633
	Night	57% 6% 11% 17% 8% 1	108490
Seeing	Day	20% 15% 27% 22% 11% 4	14661
	Night	23% 14% 27% 24% 11% 1	24175

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	19% 25% 8% 12% 7% 5% 4 3 4 4 11%	2565
	11th to 20th	Day	14% 23% 7% 21% 11% 6% 4 2 3 3 8%	2776
	21st to end	Day	22% 21% 7% 13% 7% 6% 5% 3 3 3 10%	3124
February	1st to 10th	Day	17% 19% 5% 15% 8% 5% 7% 4 4 4 13%	1710
	11th to 20th	Day	14% 18% 7% 14% 8% 6% 5% 4 3 5% 17%	1663
	21st to end	Day	21% 13% 5% 12% 8% 5% 4 4 5% 5% 18%	1486
March	1st to 10th	Day	19% 14% 4 8% 5% 4 4 3 4 6% 29%	3432
	11th to 20th	Day	10% 19% 5% 8% 5% 5% 4 4 5% 6% 29%	3480
	21st to end	Day	18% 11% 3 10% 6% 4 4 3 5% 6% 29%	3815
April	1st to 10th	Day	19% 14% 3 8% 4 5% 3 3 4 6% 31%	2258
	11th to 20th	Day	20% 10% 2 7% 4 4 4 3 5% 6% 34%	2274
	21st to end	Day	21% 10% 3 7% 5% 4 4 3 5% 5% 34%	2470
May	1st to 10th	Day	21% 10% 3 6% 5% 5% 4 4 6% 6% 31%	4108
	11th to 20th	Day	14% 10% 3 9% 5% 5% 5% 4 7% 8% 30%	4362
	21st to end	Day	12% 7% 2 6% 3 4 4 4 6% 7% 45%	4837
June	1st to 10th	Day	15% 8% 2 7% 5% 4 4 4 7% 7% 38%	2660
	11th to 20th	Day	13% 5% 2 6% 4 5% 4 4 7% 9% 40%	2660
	21st to end	Day	15% 6% 2 5% 4 3 5% 3 6% 8% 43%	2660
July	1st to 10th	Day	10% 5% 2 6% 4 4 5% 4 6% 9% 45%	4440
	11th to 20th	Day	13% 5% 2 6% 4 5% 4 4 7% 8% 42%	4440
	21st to end	Day	7% 5% 3 7% 4 4 6% 5% 8% 9% 43%	4480
August	1st to 10th	Day	17% 6% 2 6% 4 4 5% 3 6% 7% 39%	4104
	11th to 20th	Day	13% 6% 3 7% 5% 5% 6% 4 7% 11% 34%	4044
	21st to end	Day	12% 5% 2 5% 4 4 4 3 6% 9% 46%	4290
September	1st to 10th	Day	14% 7% 2 6% 4 4 4 4 5% 7% 42%	2280
	11th to 20th	Day	12% 4 2 6% 4 4 4 4 6% 8% 46%	2196
	21st to end	Day	15% 8% 3 7% 5% 6% 5% 5% 6% 8% 32%	2033
October	1st to 10th	Day	20% 8% 3 7% 6% 4 4 4 6% 6% 34%	1900
	11th to 20th	Day	21% 10% 3 8% 4 5% 5% 4 5% 6% 28%	1900
	21st to end	Day	26% 14% 3 10% 5% 5% 4 3 4 5% 22%	2090
November	1st to 10th	Day	15% 12% 3 9% 5% 5% 5% 4 5% 6% 32%	1745
	11th to 20th	Day	15% 15% 4 11% 5% 5% 5% 4 5% 5% 28%	1600
	21st to end	Day	21% 19% 5% 9% 5% 5% 5% 3 4 7% 18%	1600
December	1st to 10th	Day	22% 18% 7% 13% 7% 5% 5% 4 5% 4 11%	2600
	11th to 20th	Day	23% 21% 5% 10% 5% 4 4 3 4 5% 16%	2986
	21st to end	Day	23% 23% 5% 12% 7% 6% 4 3 3 4 12%	3960
January	1st to 10th	Night	20% 25% 7% 11% 6% 5% 4 3 3 3 13%	4514
	11th to 20th	Night	15% 22% 8% 20% 10% 6% 3 3 3 3 7%	4180
	21st to end	Night	25% 22% 6% 14% 6% 4 3 2 3 4 10%	4532
February	1st to 10th	Night	19% 20% 7% 13% 6% 4 4 3 5% 4 16%	2470
	11th to 20th	Night	16% 16% 6% 12% 7% 6% 5% 4 4 6% 18%	2403
	21st to end	Night	20% 15% 5% 13% 7% 4 4 3 4 5% 19%	1965
March	1st to 10th	Night	20% 14% 3 8% 5% 4 3 3 3 4 31%	3408
	11th to 20th	Night	20% 18% 4 7% 4 4 3 3 4 6% 26%	3479
	21st to end	Night	17% 9% 3 8% 4 4 4 3 5% 6% 39%	3817
April	1st to 10th	Night	21% 14% 3 7% 5% 3 4 3 5% 4 30%	1920
	11th to 20th	Night	19% 9% 3 8% 5% 4 4 4 5% 6% 34%	1870
	21st to end	Night	18% 10% 3 6% 4 4 5% 4 5% 7% 35%	1710
May	1st to 10th	Night	24% 10% 3 8% 4 3 4 3 5% 6% 31%	2833
	11th to 20th	Night	14% 7% 3 8% 6% 5% 5% 4 7% 9% 33%	2527
	21st to end	Night	13% 6% 3 5% 3 4 4 4 6% 8% 44%	2738
June	1st to 10th	Night	12% 9% 3 6% 6% 5% 6% 5% 7% 7% 36%	1520
	11th to 20th	Night	12% 5% 2 6% 5% 5% 5% 4 6% 8% 41%	1520
	21st to end	Night	15% 7% 2 5% 5% 4 4 5% 6% 8% 39%	1520
July	1st to 10th	Night	10% 6% 2 7% 5% 5% 5% 4 6% 9% 43%	2520
	11th to 20th	Night	13% 6% 2 6% 4 4 4 3 6% 8% 44%	2520
	21st to end	Night	10% 5% 2 6% 5% 4 5% 4 7% 7% 45%	3069
August	1st to 10th	Night	11% 8% 3 7% 5% 4 4 4 6% 8% 40%	2825
	11th to 20th	Night	14% 8% 3 7% 5% 5% 4 4 6% 7% 36%	2785
	21st to end	Night	9% 5% 2 6% 5% 4 6% 4 7% 9% 45%	3334
September	1st to 10th	Night	15% 6% 2 5% 4 3 4 3 5% 7% 44%	1900
	11th to 20th	Night	13% 5% 2 5% 3 3 3 3 4 8% 51%	1981
	21st to end	Night	17% 7% 3 7% 5% 4 5% 5% 6% 7% 35%	2147
October	1st to 10th	Night	18% 6% 3 7% 5% 5% 4 3 5% 7% 38%	2280
	11th to 20th	Night	22% 10% 3 8% 4 5% 4 4 5% 6% 29%	2280
	21st to end	Night	27% 9% 3 7% 4 5% 5% 4 5% 6% 26%	2508
November	1st to 10th	Night	18% 10% 3 7% 5% 4 3 3 5% 6% 36%	2548
	11th to 20th	Night	16% 13% 3 10% 6% 5% 4 3 5% 6% 28%	2800
	21st to end	Night	20% 15% 5% 10% 6% 5% 4 4 5% 6% 20%	2800
December	1st to 10th	Night	19% 22% 7% 14% 6% 4 4 4 5% 5% 11%	4580
	11th to 20th	Night	21% 23% 5% 11% 7% 5% 4 3 3 4 14%	5208
	21st to end	Night	25% 20% 5% 11% 6% 5% 4 3 4 4 13%	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	78% 8% 6% 5% 3	2566
	11th to 20th	Day	81% 8% 6% 4 1	2776
	21st to end	Day	80% 7% 9% 3 1	3124
February	1st to 10th	Day	76% 6% 10% 7% 1	1710
	11th to 20th	Day	71% 6% 9% 11% 3	1672
	21st to end	Day	67% 6% 11% 11% 4	1486
March	1st to 10th	Day	56% 6% 11% 20% 6%	3435
	11th to 20th	Day	54% 8% 18% 14% 6% 1	3480
	21st to end	Day	54% 9% 9% 20% 7% 1	3815
April	1st to 10th	Day	56% 5% 11% 18% 10% 1	2258
	11th to 20th	Day	50% 6% 11% 20% 12% 2	2274
	21st to end	Day	53% 5% 10% 17% 13% 2	2470
May	1st to 10th	Day	51% 6% 13% 18% 10% 2	4120
	11th to 20th	Day	49% 11% 13% 20% 7% 1	4366
	21st to end	Day	36% 7% 14% 25% 14% 3	4837
June	1st to 10th	Day	43% 8% 13% 20% 15% 1	2660
	11th to 20th	Day	40% 8% 15% 23% 12% 1	2660
	21st to end	Day	39% 8% 14% 25% 13% 1	2660
July	1st to 10th	Day	36% 5% 13% 29% 16% 2	4370
	11th to 20th	Day	38% 5% 14% 25% 16%	4365
	21st to end	Day	37% 7% 18% 22% 16% 1	4337
August	1st to 10th	Day	44% 7% 13% 23% 12% 1	4091
	11th to 20th	Day	45% 6% 17% 24% 7%	4083
	21st to end	Day	37% 4 12% 34% 11% 1	4290
September	1st to 10th	Day	42% 8% 14% 24% 12% 1	2280
	11th to 20th	Day	36% 7% 14% 29% 13% 1	2196
	21st to end	Day	49% 7% 14% 20% 9% 1	2033
October	1st to 10th	Day	43% 5% 13% 26% 13% 1	3160
	11th to 20th	Day	47% 4 16% 20% 12% 1	3140
	21st to end	Day	53% 3 14% 23% 7%	3428
November	1st to 10th	Day	55% 6% 11% 17% 8% 2	1745
	11th to 20th	Day	58% 8% 14% 13% 5% 2	1600
	21st to end	Day	69% 6% 11% 10% 3	1600
December	1st to 10th	Day	78% 5% 10% 6% 1	2600
	11th to 20th	Day	74% 5% 10% 9% 2	2986
	21st to end	Day	78% 5% 8% 8% 2	3960
January	1st to 10th	Night	76% 10% 7% 6% 1	4514
	11th to 20th	Night	80% 9% 6% 3 1	4180
	21st to end	Night	81% 7% 6% 4 1	4532
February	1st to 10th	Night	73% 6% 10% 9% 2	2470
	11th to 20th	Night	69% 6% 10% 12% 3	2405
	21st to end	Night	68% 6% 10% 11% 5%	1965
March	1st to 10th	Night	58% 5% 10% 20% 6%	3418
	11th to 20th	Night	59% 7% 13% 14% 6% 1	3480
	21st to end	Night	47% 5% 11% 22% 13% 1	3817
April	1st to 10th	Night	57% 5% 9% 19% 10% 1	1920
	11th to 20th	Night	51% 6% 10% 18% 14% 2	1870
	21st to end	Night	49% 6% 11% 18% 14% 2	1710
May	1st to 10th	Night	53% 7% 9% 17% 10% 3	2840
	11th to 20th	Night	45% 10% 17% 20% 8% 1	2528
	21st to end	Night	36% 7% 12% 24% 19% 2	2739
June	1st to 10th	Night	44% 9% 10% 22% 14% 1	1520
	11th to 20th	Night	40% 7% 13% 21% 18% 1	1520
	21st to end	Night	42% 7% 14% 22% 13% 2	1520
July	1st to 10th	Night	41% 4 11% 24% 17% 3	2480
	11th to 20th	Night	40% 4 14% 27% 14% 1	2472
	21st to end	Night	37% 6% 17% 22% 15% 2	2971
August	1st to 10th	Night	41% 6% 14% 26% 11% 1	2814
	11th to 20th	Night	47% 6% 15% 24% 8%	2812
	21st to end	Night	37% 5% 13% 32% 13% 1	3334
September	1st to 10th	Night	38% 8% 13% 25% 14% 2	1900
	11th to 20th	Night	34% 5% 13% 28% 18% 1	1981
	21st to end	Night	47% 8% 12% 20% 11% 1	2147
October	1st to 10th	Night	45% 4 9% 25% 17% 1	3800
	11th to 20th	Night	51% 4 13% 19% 13%	3779
	21st to end	Night	48% 4 15% 24% 8% 1	4120
November	1st to 10th	Night	51% 6% 10% 20% 10% 2	2548
	11th to 20th	Night	59% 7% 12% 13% 6% 2	2800
	21st to end	Night	66% 8% 13% 11% 3	2800
December	1st to 10th	Night	78% 5% 11% 5% 1	4580
	11th to 20th	Night	77% 5% 7% 9% 2	5208
	21st to end	Night	76% 5% 7% 9% 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	27% 26% 30% 10% 6% 2	192
	11th to 20th	Day	27% 29% 29% 12% 3 1	252
	21st to end	Day	24% 26% 29% 16% 4	297
February	1st to 10th	Day	29% 26% 31% 11% 2	270
	11th to 20th	Day	26% 29% 35% 10%	270
	21st to end	Day	29% 25% 35% 10% 1	277
March	1st to 10th	Day	23% 20% 35% 17% 3 2	460
	11th to 20th	Day	24% 20% 34% 17% 5% 1	460
	21st to end	Day	28% 14% 32% 19% 6% 1	506
April	1st to 10th	Day	23% 22% 31% 18% 6% 1	460
	11th to 20th	Day	26% 21% 25% 17% 9% 3	452
	21st to end	Day	25% 15% 31% 21% 7% 2	460
May	1st to 10th	Day	26% 13% 27% 21% 10% 3	463
	11th to 20th	Day	16% 11% 28% 27% 14% 3	487
	21st to end	Day	14% 8% 30% 28% 15% 5%	529
June	1st to 10th	Day	17% 16% 27% 29% 11% 1	490
	11th to 20th	Day	12% 13% 23% 31% 17% 3	490
	21st to end	Day	16% 10% 31% 29% 11% 3	490
July	1st to 10th	Day	9% 8% 21% 34% 23% 5%	485
	11th to 20th	Day	13% 9% 25% 29% 19% 5%	484
	21st to end	Day	9% 8% 28% 32% 17% 6%	532
August	1st to 10th	Day	12% 6% 22% 31% 21% 8%	486
	11th to 20th	Day	14% 6% 23% 29% 21% 8%	479
	21st to end	Day	11% 7% 25% 30% 18% 8%	539
September	1st to 10th	Day	14% 8% 24% 28% 18% 8%	490
	11th to 20th	Day	10% 6% 19% 26% 24% 15%	490
	21st to end	Day	16% 15% 26% 21% 16% 6%	490
October	1st to 10th	Day	20% 12% 26% 19% 17% 6%	490
	11th to 20th	Day	24% 18% 30% 19% 7% 2	490
	21st to end	Day	32% 20% 24% 17% 6%	539
November	1st to 10th	Day	23% 18% 32% 18% 8% 1	342
	11th to 20th	Day	29% 27% 25% 15% 4 2	200
	21st to end	Day	34% 26% 29% 11% 1	200
December	1st to 10th	Day	31% 26% 27% 12% 6%	200
	11th to 20th	Day	33% 23% 25% 17% 3	200
	21st to end	Day	30% 30% 24% 12% 3 1	220
January	1st to 10th	Night	31% 24% 28% 12% 5%	785
	11th to 20th	Night	32% 23% 27% 14% 3	760
	21st to end	Night	24% 17% 36% 18% 5%	836
February	1st to 10th	Night	28% 24% 29% 16% 3	760
	11th to 20th	Night	26% 21% 32% 18% 3	743
	21st to end	Night	28% 20% 32% 18% 2	628
March	1st to 10th	Night	23% 17% 33% 22% 5%	760
	11th to 20th	Night	26% 17% 30% 20% 6% 1	760
	21st to end	Night	24% 12% 34% 20% 9% 1	836
April	1st to 10th	Night	26% 15% 30% 24% 4	760
	11th to 20th	Night	24% 14% 29% 22% 9% 1	746
	21st to end	Night	23% 9% 27% 30% 9% 1	570
May	1st to 10th	Night	21% 9% 23% 32% 13% 2	570
	11th to 20th	Night	13% 9% 26% 42% 10% 1	393
	21st to end	Night	13% 6% 27% 31% 21% 2	411
June	1st to 10th	Night	14% 6% 30% 35% 15% 1	380
	11th to 20th	Night	14% 7% 24% 37% 17% 1	380
	21st to end	Night	14% 8% 25% 38% 14%	380
July	1st to 10th	Night	8% 4 22% 42% 21% 2	370
	11th to 20th	Night	12% 4 26% 36% 20% 2	368
	21st to end	Night	11% 3 24% 36% 23% 2	606
August	1st to 10th	Night	11% 4 17% 39% 25% 3	567
	11th to 20th	Night	10% 6% 18% 33% 30% 3	564
	21st to end	Night	12% 5% 21% 34% 25% 3	746
September	1st to 10th	Night	16% 7% 19% 33% 21% 4	760
	11th to 20th	Night	14% 5% 19% 27% 28% 7%	760
	21st to end	Night	20% 10% 21% 28% 17% 4	760
October	1st to 10th	Night	21% 8% 27% 23% 18% 2	760
	11th to 20th	Night	26% 18% 24% 23% 8% 2	760
	21st to end	Night	31% 16% 29% 20% 5%	836
November	1st to 10th	Night	23% 15% 30% 23% 8% 1	780
	11th to 20th	Night	24% 22% 29% 16% 7% 1	800
	21st to end	Night	28% 23% 30% 16% 5%	800
December	1st to 10th	Night	35% 24% 24% 13% 4	800
	11th to 20th	Night	32% 25% 26% 15% 3	800
	21st to end	Night	35% 18% 28% 16% 2	880

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

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