Fort Erie Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fort Erie Observatory clear sky chart from 2005-11-06 to 2024-09-14.

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%	100895
	Night	18% 13% 4 9% 5% 4 4 3 5% 6% 29%	96980
Transparency	Day	52% 7% 12% 19% 9% 1	100662
	Night	57% 7% 11% 16% 8% 1	96833
Seeing	Day	23% 17% 28% 20% 9% 3	14331
	Night	23% 15% 27% 24% 10% 1	23717

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%	2517
	11th to 20th	Day	14% 23% 7% 21% 11% 6% 4 2 3 3 8%	2775
	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%	2261
	11th to 20th	Day	20% 10% 2 7% 4 4 4 3 5% 6% 34%	2271
	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%	4366
	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% 7% 9% 43%	4484
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% 45%	4287
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%	2122
	21st to end	Day	15% 8% 3 6% 5% 6% 5% 5% 6% 8% 33%	1924
October	1st to 10th	Day	20% 9% 3 7% 6% 4 4 3 5% 6% 33%	1800
	11th to 20th	Day	22% 10% 4 8% 5% 5% 5% 4 5% 6% 27%	1800
	21st to end	Day	27% 15% 3 10% 4 5% 4 3 3 5% 21%	1980
November	1st to 10th	Day	16% 12% 3 8% 5% 5% 5% 4 5% 5% 32%	1657
	11th to 20th	Day	16% 15% 4 11% 5% 4 4 4 5% 6% 28%	1520
	21st to end	Day	22% 19% 4 8% 5% 4 5% 3 4 7% 18%	1520
December	1st to 10th	Day	21% 20% 6% 11% 6% 6% 4 4 4 4 13%	1520
	11th to 20th	Day	21% 22% 5% 12% 5% 4 4 4 4 5% 14%	1906
	21st to end	Day	26% 26% 6% 10% 5% 4 3 2 3 3 11%	2772
January	1st to 10th	Night	20% 25% 7% 11% 6% 5% 4 3 3 3 13%	4429
	11th to 20th	Night	15% 22% 8% 20% 10% 6% 3 3 3 3 7%	4184
	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%	1919
	11th to 20th	Night	19% 9% 3 8% 5% 4 4 4 5% 6% 34%	1874
	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%	2512
	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	11% 5% 2 6% 5% 4 5% 4 7% 7% 45%	3052
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%	3335
September	1st to 10th	Night	15% 6% 2 5% 4 3 4 3 5% 7% 44%	1900
	11th to 20th	Night	13% 5% 1 5% 3 3 3 3 5% 8% 51%	1912
	21st to end	Night	17% 7% 2 6% 5% 4 4 5% 6% 7% 37%	2035
October	1st to 10th	Night	19% 6% 3 7% 5% 5% 4 3 5% 7% 38%	2160
	11th to 20th	Night	22% 10% 4 8% 4 5% 5% 4 5% 6% 28%	2160
	21st to end	Night	28% 9% 3 7% 4 5% 5% 4 5% 5% 24%	2376
November	1st to 10th	Night	18% 10% 3 7% 5% 4 3 3 5% 6% 36%	2415
	11th to 20th	Night	16% 13% 3 9% 6% 5% 5% 3 5% 6% 28%	2660
	21st to end	Night	20% 15% 4 10% 6% 5% 4 4 5% 6% 20%	2660
December	1st to 10th	Night	22% 20% 5% 11% 7% 4 4 3 5% 5% 14%	2660
	11th to 20th	Night	19% 22% 6% 11% 7% 5% 4 3 4 4 16%	3288
	21st to end	Night	30% 19% 5% 10% 5% 4 4 3 4 4 11%	4884

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	2518
	11th to 20th	Day	81% 8% 6% 4 1	2775
	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	2261
	11th to 20th	Day	50% 6% 11% 20% 12% 2	2271
	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	4370
	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	4341
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	4287
September	1st to 10th	Day	42% 8% 14% 24% 12% 1	2280
	11th to 20th	Day	36% 8% 14% 29% 14% 1	2122
	21st to end	Day	48% 7% 14% 21% 10% 1	1924
October	1st to 10th	Day	51% 8% 13% 16% 11% 1	1800
	11th to 20th	Day	58% 7% 14% 15% 6% 1	1800
	21st to end	Day	68% 4 11% 10% 6% 1	1980
November	1st to 10th	Day	55% 7% 11% 17% 8% 2	1657
	11th to 20th	Day	58% 8% 15% 13% 5% 2	1520
	21st to end	Day	68% 6% 12% 10% 3	1520
December	1st to 10th	Day	74% 9% 8% 8% 1	1520
	11th to 20th	Day	76% 8% 9% 6% 1	1906
	21st to end	Day	80% 6% 8% 6%	2772
January	1st to 10th	Night	76% 10% 7% 6% 1	4429
	11th to 20th	Night	80% 9% 6% 3 1	4184
	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	1919
	11th to 20th	Night	51% 6% 10% 18% 14% 2	1874
	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	2513
	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% 16% 2	2955
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	3335
September	1st to 10th	Night	38% 8% 13% 25% 14% 2	1900
	11th to 20th	Night	34% 6% 14% 28% 17% 2	1912
	21st to end	Night	44% 9% 13% 21% 12% 1	2035
October	1st to 10th	Night	48% 6% 12% 19% 14% 1	2160
	11th to 20th	Night	57% 7% 13% 14% 8%	2160
	21st to end	Night	63% 7% 10% 13% 6% 1	2376
November	1st to 10th	Night	52% 6% 11% 19% 10% 2	2415
	11th to 20th	Night	59% 8% 12% 13% 6% 2	2660
	21st to end	Night	65% 8% 13% 11% 3	2660
December	1st to 10th	Night	74% 8% 11% 6% 1	2660
	11th to 20th	Night	73% 8% 10% 7% 2	3288
	21st to end	Night	78% 7% 8% 6%	4884

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	28% 30% 23% 12% 5% 2	180
	11th to 20th	Day	27% 30% 26% 12% 4 1	252
	21st to end	Day	26% 24% 27% 19% 4	297
February	1st to 10th	Day	31% 27% 28% 11% 3	270
	11th to 20th	Day	29% 33% 28% 9% 1	270
	21st to end	Day	39% 19% 29% 11% 1	279
March	1st to 10th	Day	26% 21% 31% 16% 5% 1	460
	11th to 20th	Day	31% 17% 33% 15% 4 1	460
	21st to end	Day	31% 20% 25% 17% 5% 2	506
April	1st to 10th	Day	25% 23% 28% 17% 6% 1	460
	11th to 20th	Day	31% 21% 22% 15% 7% 3	452
	21st to end	Day	30% 17% 29% 16% 7% 2	460
May	1st to 10th	Day	27% 15% 29% 17% 8% 4	463
	11th to 20th	Day	20% 14% 31% 21% 11% 3	487
	21st to end	Day	17% 13% 31% 23% 10% 5%	529
June	1st to 10th	Day	23% 14% 32% 22% 8% 1	490
	11th to 20th	Day	15% 16% 30% 25% 10% 3	490
	21st to end	Day	21% 15% 30% 24% 8% 2	490
July	1st to 10th	Day	11% 10% 27% 31% 18% 4	485
	11th to 20th	Day	16% 12% 29% 25% 13% 5%	484
	21st to end	Day	11% 9% 34% 28% 12% 5%	532
August	1st to 10th	Day	16% 9% 24% 28% 15% 8%	486
	11th to 20th	Day	13% 9% 28% 26% 16% 8%	479
	21st to end	Day	14% 8% 31% 24% 15% 7%	539
September	1st to 10th	Day	16% 13% 23% 24% 16% 8%	490
	11th to 20th	Day	12% 8% 22% 25% 22% 11%	463
	21st to end	Day	19% 16% 26% 21% 12% 6%	450
October	1st to 10th	Day	26% 12% 24% 18% 14% 6%	450
	11th to 20th	Day	27% 22% 27% 18% 5% 1	450
	21st to end	Day	37% 19% 24% 14% 6%	495
November	1st to 10th	Day	26% 19% 30% 16% 7% 1	315
	11th to 20th	Day	33% 26% 26% 10% 2 3	180
	21st to end	Day	33% 28% 24% 11% 3	180
December	1st to 10th	Day	32% 26% 30% 8% 4 1	180
	11th to 20th	Day	33% 28% 23% 14% 2	180
	21st to end	Day	35% 30% 23% 10% 2 1	198
January	1st to 10th	Night	32% 24% 26% 13% 4	760
	11th to 20th	Night	32% 24% 26% 15% 3	760
	21st to end	Night	25% 21% 31% 17% 6%	836
February	1st to 10th	Night	28% 26% 28% 15% 3	760
	11th to 20th	Night	26% 23% 30% 17% 3	743
	21st to end	Night	29% 23% 28% 17% 2	628
March	1st to 10th	Night	24% 18% 30% 22% 6%	760
	11th to 20th	Night	28% 17% 30% 20% 5% 1	760
	21st to end	Night	24% 14% 31% 22% 7% 1	836
April	1st to 10th	Night	26% 16% 32% 22% 3	760
	11th to 20th	Night	24% 16% 29% 23% 7% 1	750
	21st to end	Night	24% 9% 31% 29% 8%	570
May	1st to 10th	Night	22% 11% 22% 31% 12% 2	570
	11th to 20th	Night	16% 7% 30% 37% 9%	391
	21st to end	Night	14% 10% 25% 34% 16% 1	411
June	1st to 10th	Night	14% 8% 32% 32% 13% 1	380
	11th to 20th	Night	14% 9% 27% 36% 12%	380
	21st to end	Night	18% 7% 32% 32% 11%	380
July	1st to 10th	Night	10% 6% 25% 41% 17% 1	370
	11th to 20th	Night	13% 7% 29% 33% 18% 1	368
	21st to end	Night	13% 4 25% 39% 17% 2	602
August	1st to 10th	Night	12% 4 20% 40% 22% 2	567
	11th to 20th	Night	11% 6% 21% 34% 26% 3	564
	21st to end	Night	13% 5% 24% 31% 24% 2	747
September	1st to 10th	Night	17% 8% 21% 33% 18% 3	760
	11th to 20th	Night	15% 5% 22% 28% 25% 5%	736
	21st to end	Night	19% 11% 24% 27% 16% 4	720
October	1st to 10th	Night	20% 11% 27% 24% 16% 2	720
	11th to 20th	Night	28% 16% 25% 22% 8% 1	720
	21st to end	Night	34% 14% 26% 22% 4	792
November	1st to 10th	Night	24% 16% 27% 24% 9% 1	740
	11th to 20th	Night	24% 22% 29% 16% 8% 1	760
	21st to end	Night	28% 22% 28% 17% 5%	760
December	1st to 10th	Night	35% 23% 22% 15% 4	760
	11th to 20th	Night	29% 27% 25% 16% 3	760
	21st to end	Night	35% 20% 28% 16% 2	836

Page generated at 2024-09-11 10:00:02. Version ac07

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