Fort Meigs Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fort Meigs Observatory clear sky chart from 2005-11-06 to 2025-02-06.

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	14% 10% 4 8% 5% 5% 5% 4 6% 7% 33%	108711
	Night	15% 11% 4 8% 5% 4 4 3 5% 6% 34%	109636
Transparency	Day	47% 8% 12% 20% 12% 1	112354
	Night	48% 7% 12% 20% 12% 1	114133
Seeing	Day	17% 12% 29% 23% 13% 5%	15854
	Night	19% 10% 29% 28% 12% 1	25773

By Month

Percentage Cloud Cover SE (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	13% 17% 7% 18% 6% 4 4 3 4 5% 17%	3617
	11th to 20th	Day	14% 18% 5% 14% 9% 6% 8% 3 3 3 16%	3679
	21st to end	Day	22% 17% 8% 13% 5% 4 5% 3 4 4 16%	4466
February	1st to 10th	Day	16% 16% 5% 12% 7% 6% 4 4 5% 5% 21%	1755
	11th to 20th	Day	15% 12% 4 12% 8% 6% 5% 3 5% 5% 25%	1830
	21st to end	Day	18% 13% 4 10% 5% 5% 3 4 5% 7% 26%	1570
March	1st to 10th	Day	20% 16% 4 10% 6% 4 4 3 4 5% 24%	3184
	11th to 20th	Day	14% 12% 3 8% 5% 5% 5% 3 5% 7% 35%	3480
	21st to end	Day	20% 12% 4 9% 4 5% 5% 4 5% 6% 27%	3815
April	1st to 10th	Day	14% 11% 4 8% 7% 5% 6% 4 6% 5% 30%	2211
	11th to 20th	Day	17% 8% 3 7% 5% 5% 4 4 6% 8% 34%	2385
	21st to end	Day	19% 8% 3 7% 4 4 4 3 5% 7% 35%	2470
May	1st to 10th	Day	18% 9% 3 8% 5% 4 5% 4 6% 7% 31%	4082
	11th to 20th	Day	18% 7% 3 6% 5% 5% 5% 5% 5% 8% 34%	4081
	21st to end	Day	10% 5% 2 7% 5% 4 5% 5% 6% 8% 42%	4476
June	1st to 10th	Day	12% 6% 2 6% 5% 6% 5% 5% 7% 8% 39%	2589
	11th to 20th	Day	10% 6% 2 6% 5% 4 5% 4 6% 8% 43%	2660
	21st to end	Day	11% 6% 2 7% 5% 5% 6% 5% 7% 9% 38%	2660
July	1st to 10th	Day	11% 6% 3 7% 5% 5% 5% 4 6% 10% 39%	4440
	11th to 20th	Day	7% 4 2 6% 4 5% 5% 5% 7% 11% 45%	4440
	21st to end	Day	7% 6% 2 7% 6% 6% 5% 5% 7% 9% 41%	4467
August	1st to 10th	Day	10% 5% 2 6% 5% 4 5% 4 6% 9% 43%	4104
	11th to 20th	Day	9% 5% 2 6% 5% 5% 6% 5% 8% 10% 39%	4044
	21st to end	Day	8% 5% 2 6% 4 5% 5% 4 7% 11% 42%	4418
September	1st to 10th	Day	13% 6% 2 6% 4 4 4 4 6% 7% 44%	2147
	11th to 20th	Day	9% 6% 2 5% 5% 4 4 3 7% 8% 47%	2090
	21st to end	Day	17% 8% 2 6% 3 3 4 3 5% 8% 41%	2090
October	1st to 10th	Day	11% 6% 2 6% 5% 5% 4 4 5% 7% 44%	2057
	11th to 20th	Day	17% 9% 2 7% 5% 4 4 3 5% 6% 38%	1900
	21st to end	Day	18% 10% 3 7% 5% 5% 5% 5% 6% 7% 31%	1945
November	1st to 10th	Day	12% 8% 3 6% 4 4 5% 3 6% 7% 42%	1762
	11th to 20th	Day	17% 14% 3 8% 5% 5% 4 4 3 6% 32%	1800
	21st to end	Day	20% 13% 5% 7% 5% 5% 5% 3 6% 6% 27%	1800
December	1st to 10th	Day	14% 15% 6% 12% 7% 6% 4 3 4 6% 23%	2930
	11th to 20th	Day	19% 18% 6% 10% 5% 4 5% 4 5% 5% 19%	3285
	21st to end	Day	26% 20% 7% 11% 5% 4 4 3 3 4 13%	3982
January	1st to 10th	Night	15% 16% 6% 16% 6% 5% 4 3 4 4 21%	6348
	11th to 20th	Night	13% 18% 8% 13% 7% 6% 6% 4 4 4 16%	6295
	21st to end	Night	21% 15% 7% 10% 5% 4 4 3 4 5% 22%	6490
February	1st to 10th	Night	17% 15% 5% 10% 7% 4 4 3 4 6% 24%	2536
	11th to 20th	Night	14% 14% 5% 10% 5% 5% 4 4 4 6% 28%	2233
	21st to end	Night	21% 13% 4 9% 4 4 4 4 4 6% 28%	1884
March	1st to 10th	Night	19% 13% 4 7% 4 4 3 2 3 5% 35%	3669
	11th to 20th	Night	11% 7% 2 6% 5% 5% 5% 3 5% 7% 43%	3480
	21st to end	Night	17% 9% 4 8% 5% 4 4 3 5% 6% 35%	3817
April	1st to 10th	Night	16% 10% 3 6% 5% 4 4 4 6% 6% 35%	1986
	11th to 20th	Night	18% 8% 2 6% 5% 4 5% 3 5% 6% 37%	1744
	21st to end	Night	17% 8% 3 6% 4 4 4 3 5% 7% 37%	1710
May	1st to 10th	Night	18% 8% 3 8% 5% 5% 5% 3 6% 7% 31%	2813
	11th to 20th	Night	18% 8% 2 6% 3 4 4 3 6% 7% 40%	2812
	21st to end	Night	11% 5% 2 5% 5% 4 5% 4 5% 9% 46%	3079
June	1st to 10th	Night	11% 5% 2 5% 4 5% 5% 5% 5% 7% 45%	1587
	11th to 20th	Night	10% 5% 3 6% 4 5% 4 5% 7% 8% 44%	1520
	21st to end	Night	11% 4 1 5% 4 4 5% 5% 6% 10% 44%	1520
July	1st to 10th	Night	9% 4 2 4 4 4 4 4 6% 10% 49%	2530
	11th to 20th	Night	8% 4 2 4 4 4 4 4 7% 10% 49%	2530
	21st to end	Night	6% 5% 2 6% 4 5% 5% 5% 6% 10% 45%	3082
August	1st to 10th	Night	13% 6% 3 6% 4 4 5% 3 5% 9% 43%	2825
	11th to 20th	Night	9% 5% 2 5% 4 4 4 5% 6% 7% 49%	2785
	21st to end	Night	8% 4 2 6% 4 4 5% 4 5% 8% 49%	3236
September	1st to 10th	Night	10% 6% 2 6% 4 3 3 4 5% 6% 50%	2014
	11th to 20th	Night	10% 4 2 6% 4 3 3 2 6% 7% 54%	2090
	21st to end	Night	14% 7% 3 6% 5% 4 4 3 5% 6% 45%	2090
October	1st to 10th	Night	13% 6% 2 5% 4 4 4 3 5% 7% 48%	2123
	11th to 20th	Night	17% 9% 3 6% 4 4 5% 3 5% 6% 39%	2280
	21st to end	Night	20% 8% 3 6% 4 4 4 3 5% 6% 36%	2650
November	1st to 10th	Night	13% 9% 3 6% 4 4 4 3 5% 7% 44%	2536
	11th to 20th	Night	16% 11% 3 8% 4 5% 4 4 6% 7% 33%	2600
	21st to end	Night	20% 13% 4 8% 6% 4 4 3 5% 6% 26%	2600
December	1st to 10th	Night	13% 12% 6% 12% 6% 5% 5% 3 5% 6% 26%	4250
	11th to 20th	Night	16% 18% 7% 10% 5% 5% 4 4 4 5% 22%	4896
	21st to end	Night	27% 18% 6% 10% 5% 4 4 3 4 5% 14%	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	67% 7% 9% 13% 3	3618
	11th to 20th	Day	72% 6% 9% 6% 7%	3679
	21st to end	Day	73% 5% 8% 9% 5%	4466
February	1st to 10th	Day	63% 7% 12% 13% 5%	1755
	11th to 20th	Day	59% 7% 10% 16% 7%	1840
	21st to end	Day	54% 7% 15% 15% 6% 2	1570
March	1st to 10th	Day	60% 8% 10% 16% 5%	3184
	11th to 20th	Day	46% 8% 16% 21% 7% 1	3480
	21st to end	Day	56% 9% 14% 15% 6%	3815
April	1st to 10th	Day	51% 9% 11% 16% 12%	2211
	11th to 20th	Day	47% 8% 12% 20% 12% 2	2385
	21st to end	Day	48% 6% 12% 21% 10% 2	2470
May	1st to 10th	Day	47% 9% 13% 21% 9% 1	4120
	11th to 20th	Day	43% 11% 14% 21% 10% 1	4085
	21st to end	Day	35% 10% 12% 18% 20% 5%	4489
June	1st to 10th	Day	39% 9% 12% 24% 13% 3	2589
	11th to 20th	Day	36% 8% 14% 21% 17% 3	2660
	21st to end	Day	39% 10% 14% 19% 15% 4	2660
July	1st to 10th	Day	39% 8% 13% 21% 17% 2	4371
	11th to 20th	Day	28% 9% 15% 29% 18% 2	4365
	21st to end	Day	35% 9% 14% 17% 21% 3	4325
August	1st to 10th	Day	35% 9% 16% 25% 15% 1	4091
	11th to 20th	Day	34% 10% 14% 29% 12% 1	4083
	21st to end	Day	33% 9% 14% 31% 12% 2	4417
September	1st to 10th	Day	38% 9% 13% 21% 17% 3	2147
	11th to 20th	Day	33% 7% 12% 28% 19% 1	2090
	21st to end	Day	40% 8% 13% 22% 16% 1	2090
October	1st to 10th	Day	28% 6% 14% 31% 20% 1	3421
	11th to 20th	Day	39% 5% 11% 26% 19%	3140
	21st to end	Day	41% 6% 13% 24% 16% 1	3182
November	1st to 10th	Day	41% 7% 12% 24% 16% 1	1762
	11th to 20th	Day	54% 6% 10% 17% 11% 1	1800
	21st to end	Day	57% 6% 13% 17% 7%	1800
December	1st to 10th	Day	61% 8% 16% 12% 3	2930
	11th to 20th	Day	65% 7% 11% 14% 3	3282
	21st to end	Day	75% 6% 7% 8% 4	3982
January	1st to 10th	Night	64% 7% 8% 16% 5%	6348
	11th to 20th	Night	69% 6% 10% 8% 6%	6295
	21st to end	Night	64% 6% 13% 10% 7%	6490
February	1st to 10th	Night	61% 7% 12% 15% 5% 1	2536
	11th to 20th	Night	55% 6% 11% 19% 8% 1	2234
	21st to end	Night	56% 7% 11% 16% 8% 2	1884
March	1st to 10th	Night	51% 6% 11% 24% 8%	3669
	11th to 20th	Night	36% 9% 17% 21% 16% 1	3480
	21st to end	Night	47% 8% 13% 23% 8% 1	3817
April	1st to 10th	Night	47% 7% 13% 17% 14% 2	1986
	11th to 20th	Night	45% 7% 11% 17% 17% 2	1744
	21st to end	Night	45% 6% 12% 20% 15% 3	1710
May	1st to 10th	Night	49% 10% 10% 17% 13% 1	2840
	11th to 20th	Night	42% 9% 13% 24% 12% 1	2813
	21st to end	Night	31% 9% 12% 26% 19% 3	3087
June	1st to 10th	Night	35% 8% 12% 25% 17% 3	1587
	11th to 20th	Night	34% 9% 13% 25% 16% 3	1520
	21st to end	Night	32% 10% 14% 24% 19% 1	1520
July	1st to 10th	Night	30% 8% 12% 27% 17% 6%	2490
	11th to 20th	Night	27% 8% 17% 27% 18% 2	2482
	21st to end	Night	30% 10% 18% 19% 18% 4	2984
August	1st to 10th	Night	37% 8% 14% 24% 15% 2	2814
	11th to 20th	Night	31% 9% 12% 29% 18% 1	2812
	21st to end	Night	32% 8% 13% 29% 17% 2	3236
September	1st to 10th	Night	34% 7% 13% 23% 19% 4	2014
	11th to 20th	Night	29% 6% 12% 27% 25% 2	2090
	21st to end	Night	40% 7% 12% 22% 17% 2	2090
October	1st to 10th	Night	24% 5% 10% 30% 31% 1	3539
	11th to 20th	Night	36% 5% 11% 27% 21%	3779
	21st to end	Night	36% 5% 9% 32% 16% 2	4363
November	1st to 10th	Night	41% 6% 12% 25% 16% 1	2536
	11th to 20th	Night	48% 8% 13% 19% 11% 2	2600
	21st to end	Night	58% 6% 12% 18% 6%	2600
December	1st to 10th	Night	57% 7% 14% 16% 5%	4250
	11th to 20th	Night	62% 8% 12% 12% 5% 1	4898
	21st to end	Night	71% 7% 10% 8% 5%	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	20% 24% 33% 18% 4 1	300
	11th to 20th	Day	21% 22% 42% 11% 4	300
	21st to end	Day	28% 16% 33% 18% 4	330
February	1st to 10th	Day	29% 18% 37% 12% 3 1	285
	11th to 20th	Day	26% 18% 36% 18% 2	270
	21st to end	Day	27% 22% 39% 10% 3	225
March	1st to 10th	Day	23% 19% 35% 17% 5%	308
	11th to 20th	Day	24% 13% 38% 19% 6% 1	460
	21st to end	Day	29% 16% 31% 17% 6%	506
April	1st to 10th	Day	18% 19% 32% 20% 10% 1	460
	11th to 20th	Day	20% 22% 27% 19% 9% 3	452
	21st to end	Day	25% 14% 32% 19% 8% 2	460
May	1st to 10th	Day	21% 13% 33% 19% 12% 3	463
	11th to 20th	Day	18% 12% 30% 22% 12% 7%	487
	21st to end	Day	12% 7% 30% 24% 19% 8%	529
June	1st to 10th	Day	12% 8% 29% 32% 15% 4	609
	11th to 20th	Day	11% 9% 30% 31% 15% 4	680
	21st to end	Day	13% 6% 31% 30% 15% 5%	680
July	1st to 10th	Day	9% 5% 23% 33% 20% 11%	671
	11th to 20th	Day	9% 6% 24% 32% 19% 11%	668
	21st to end	Day	8% 4 24% 29% 25% 10%	533
August	1st to 10th	Day	10% 4 17% 30% 26% 13%	486
	11th to 20th	Day	10% 5% 22% 30% 22% 12%	479
	21st to end	Day	10% 2 20% 29% 27% 13%	539
September	1st to 10th	Day	13% 6% 19% 30% 21% 11%	490
	11th to 20th	Day	10% 3 19% 25% 29% 14%	490
	21st to end	Day	18% 11% 23% 23% 17% 7%	490
October	1st to 10th	Day	12% 9% 28% 26% 19% 8%	490
	11th to 20th	Day	18% 18% 31% 22% 10% 2	490
	21st to end	Day	25% 15% 35% 19% 6% 1	394
November	1st to 10th	Day	13% 18% 33% 22% 10% 3	300
	11th to 20th	Day	24% 22% 27% 21% 4 1	300
	21st to end	Day	27% 18% 37% 16% 2	300
December	1st to 10th	Day	24% 23% 31% 16% 7%	300
	11th to 20th	Day	21% 25% 34% 16% 4	300
	21st to end	Day	27% 22% 32% 16% 2	330
January	1st to 10th	Night	23% 17% 35% 20% 5%	1000
	11th to 20th	Night	26% 15% 37% 18% 4 1	974
	21st to end	Night	23% 15% 37% 21% 3	880
February	1st to 10th	Night	26% 13% 34% 23% 3	781
	11th to 20th	Night	22% 14% 34% 27% 2	743
	21st to end	Night	25% 17% 37% 19% 2	628
March	1st to 10th	Night	21% 12% 33% 27% 7%	760
	11th to 20th	Night	18% 16% 37% 24% 6% 1	760
	21st to end	Night	22% 13% 31% 27% 7%	836
April	1st to 10th	Night	19% 15% 36% 25% 4	656
	11th to 20th	Night	19% 13% 34% 25% 7% 1	563
	21st to end	Night	20% 9% 35% 26% 8% 1	570
May	1st to 10th	Night	21% 6% 31% 32% 10% 1	570
	11th to 20th	Night	20% 5% 29% 31% 14% 1	561
	21st to end	Night	10% 3 27% 37% 21% 2	617
June	1st to 10th	Night	12% 4 27% 41% 15%	570
	11th to 20th	Night	12% 4 25% 41% 18% 1	570
	21st to end	Night	12% 3 24% 37% 21% 2	570
July	1st to 10th	Night	9% 3 17% 41% 27% 3	555
	11th to 20th	Night	9% 3 20% 40% 23% 5%	552
	21st to end	Night	6% 2 16% 45% 29% 2	624
August	1st to 10th	Night	8% 3 14% 43% 29% 3	567
	11th to 20th	Night	11% 2 16% 35% 31% 4	564
	21st to end	Night	9% 2 17% 36% 33% 4	627
September	1st to 10th	Night	12% 5% 18% 33% 27% 5%	684
	11th to 20th	Night	9% 4 17% 33% 34% 3	760
	21st to end	Night	16% 7% 22% 32% 21% 3	760
October	1st to 10th	Night	14% 8% 25% 31% 19% 3	760
	11th to 20th	Night	19% 16% 28% 26% 10% 2	760
	21st to end	Night	24% 13% 30% 26% 7%	836
November	1st to 10th	Night	16% 14% 33% 26% 10% 2	780
	11th to 20th	Night	22% 15% 34% 22% 7% 1	800
	21st to end	Night	25% 14% 33% 22% 6%	800
December	1st to 10th	Night	22% 18% 35% 21% 4 1	800
	11th to 20th	Night	25% 14% 35% 21% 4	835
	21st to end	Night	30% 13% 33% 20% 3	1100

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