Mahoning Valley Cortese Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mahoning Valley Cortese Observatory 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	15% 11% 4 10% 5% 5% 5% 4 5% 7% 29%	131983
	Night	16% 12% 5% 10% 5% 4 4 3 5% 6% 29%	131151
Transparency	Day	53% 6% 11% 20% 10% 1	135615
	Night	54% 5% 11% 19% 11% 1	135589
Seeing	Day	23% 16% 28% 19% 11% 4	16586
	Night	22% 13% 28% 25% 11% 1	26405

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	17% 21% 7% 23% 5% 4 3 2 3 4 11%	5258
	11th to 20th	Day	11% 21% 9% 19% 9% 6% 4 2 3 3 11%	5280
	21st to end	Day	18% 19% 7% 13% 9% 6% 5% 3 4 4 13%	5780
February	1st to 10th	Day	16% 19% 5% 12% 7% 4 4 2 4 4 21%	1890
	11th to 20th	Day	15% 16% 7% 14% 8% 5% 4 3 4 5% 20%	1864
	21st to end	Day	17% 18% 4 12% 4 4 4 4 5% 6% 22%	1730
March	1st to 10th	Day	18% 12% 5% 12% 5% 3 4 3 4 6% 28%	4994
	11th to 20th	Day	12% 10% 5% 10% 5% 5% 4 3 4 6% 35%	5090
	21st to end	Day	19% 12% 5% 10% 5% 4 4 3 4 6% 29%	5586
April	1st to 10th	Day	16% 13% 4 7% 5% 5% 4 4 5% 7% 30%	2380
	11th to 20th	Day	17% 11% 3 7% 5% 5% 5% 3 5% 6% 32%	2623
	21st to end	Day	20% 10% 3 7% 5% 4 4 3 4 6% 34%	2730
May	1st to 10th	Day	20% 9% 4 9% 5% 5% 5% 4 5% 6% 28%	5992
	11th to 20th	Day	18% 9% 3 8% 5% 4 5% 4 5% 8% 30%	5991
	21st to end	Day	18% 7% 2 6% 5% 5% 5% 4 6% 7% 34%	6846
June	1st to 10th	Day	14% 6% 3 7% 5% 6% 5% 5% 6% 7% 36%	2800
	11th to 20th	Day	13% 7% 3 8% 6% 5% 4 3 6% 8% 37%	2800
	21st to end	Day	12% 6% 2 6% 4 5% 6% 5% 7% 9% 39%	2800
July	1st to 10th	Day	7% 6% 3 6% 5% 5% 5% 5% 7% 10% 42%	6048
	11th to 20th	Day	9% 6% 3 7% 6% 6% 5% 5% 8% 10% 35%	5900
	21st to end	Day	10% 6% 2 7% 5% 5% 5% 4 7% 8% 40%	6424
August	1st to 10th	Day	14% 7% 3 7% 5% 5% 6% 5% 7% 9% 32%	4234
	11th to 20th	Day	11% 7% 3 7% 5% 5% 7% 5% 7% 10% 33%	4174
	21st to end	Day	8% 5% 3 7% 6% 6% 6% 4 6% 10% 39%	4550
September	1st to 10th	Day	13% 6% 3 6% 4 4 4 3 5% 7% 43%	2340
	11th to 20th	Day	10% 5% 2 6% 5% 4 4 3 7% 8% 44%	2200
	21st to end	Day	19% 9% 3 7% 4 3 5% 4 4 6% 37%	2200
October	1st to 10th	Day	14% 6% 3 7% 5% 4 5% 4 6% 7% 40%	2040
	11th to 20th	Day	21% 10% 3 7% 5% 4 4 3 5% 6% 33%	2000
	21st to end	Day	22% 10% 4 8% 4 5% 5% 3 6% 6% 28%	2200
November	1st to 10th	Day	12% 9% 3 8% 5% 4 5% 4 5% 7% 37%	1886
	11th to 20th	Day	18% 16% 4 7% 6% 4 4 3 5% 5% 27%	1801
	21st to end	Day	18% 17% 6% 10% 6% 4 5% 3 6% 5% 19%	1680
December	1st to 10th	Day	19% 17% 8% 12% 6% 5% 5% 4 4 4 16%	2680
	11th to 20th	Day	23% 20% 6% 10% 6% 3 3 3 4 4 17%	3070
	21st to end	Day	26% 21% 6% 14% 6% 5% 3 2 3 3 9%	4122
January	1st to 10th	Night	15% 19% 8% 23% 5% 4 4 3 4 4 11%	7635
	11th to 20th	Night	11% 20% 10% 18% 9% 6% 6% 3 3 4 12%	7680
	21st to end	Night	18% 17% 7% 12% 6% 5% 5% 3 4 5% 18%	8401
February	1st to 10th	Night	19% 16% 5% 12% 7% 5% 4 3 5% 5% 21%	2730
	11th to 20th	Night	16% 14% 7% 13% 7% 6% 4 3 4 5% 20%	2640
	21st to end	Night	20% 14% 4 12% 5% 4 4 3 4 5% 24%	2076
March	1st to 10th	Night	21% 14% 4 9% 5% 4 3 3 4 5% 29%	5078
	11th to 20th	Night	14% 11% 4 8% 4 4 4 4 5% 6% 37%	5090
	21st to end	Night	18% 12% 4 9% 5% 4 5% 3 5% 5% 32%	5588
April	1st to 10th	Night	18% 13% 4 8% 4 4 5% 3 6% 5% 29%	2239
	11th to 20th	Night	15% 10% 3 7% 4 4 5% 4 5% 7% 33%	1963
	21st to end	Night	15% 9% 2 7% 5% 5% 5% 4 6% 8% 36%	1890
May	1st to 10th	Night	25% 10% 3 7% 5% 4 5% 3 5% 5% 27%	4123
	11th to 20th	Night	16% 9% 3 6% 4 4 4 3 5% 7% 37%	4122
	21st to end	Night	17% 6% 2 6% 4 4 4 4 6% 9% 38%	4249
June	1st to 10th	Night	9% 6% 2 8% 6% 4 5% 5% 7% 7% 41%	1600
	11th to 20th	Night	10% 6% 2 8% 5% 4 4 4 6% 9% 42%	1600
	21st to end	Night	10% 6% 2 6% 4 5% 5% 4 7% 9% 42%	1600
July	1st to 10th	Night	9% 6% 3 7% 4 4 5% 4 6% 8% 43%	3892
	11th to 20th	Night	10% 5% 2 6% 5% 5% 5% 4 7% 10% 41%	4057
	21st to end	Night	8% 5% 2 6% 4 4 4 4 6% 8% 48%	4427
August	1st to 10th	Night	11% 9% 4 7% 5% 4 4 3 6% 7% 39%	2915
	11th to 20th	Night	13% 7% 3 7% 4 5% 4 3 5% 6% 43%	2875
	21st to end	Night	8% 5% 2 6% 5% 5% 6% 5% 6% 8% 44%	3313
September	1st to 10th	Night	12% 6% 2 5% 4 3 4 4 5% 7% 48%	2057
	11th to 20th	Night	10% 5% 2 5% 4 4 4 4 5% 8% 52%	2200
	21st to end	Night	16% 7% 3 6% 5% 5% 4 3 5% 6% 39%	2200
October	1st to 10th	Night	15% 5% 2 6% 4 3 4 4 5% 7% 45%	2360
	11th to 20th	Night	18% 7% 2 7% 5% 4 5% 4 5% 7% 37%	2400
	21st to end	Night	22% 9% 3 7% 4 4 3 4 5% 6% 33%	2640
November	1st to 10th	Night	13% 9% 3 6% 4 4 4 4 5% 8% 39%	2631
	11th to 20th	Night	17% 15% 4 8% 5% 5% 4 3 4 6% 28%	2817
	21st to end	Night	20% 18% 4 8% 5% 5% 4 3 5% 5% 24%	2940
December	1st to 10th	Night	16% 19% 8% 11% 6% 5% 4 3 4 5% 17%	4720
	11th to 20th	Night	19% 21% 8% 11% 5% 4 3 2 4 4 19%	5345
	21st to end	Night	25% 19% 6% 12% 5% 4 4 3 4 5% 13%	7058

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 8% 7% 3	5259
	11th to 20th	Day	79% 3 6% 7% 4	5280
	21st to end	Day	75% 4 6% 11% 3	5780
February	1st to 10th	Day	67% 4 9% 14% 7%	1890
	11th to 20th	Day	68% 4 7% 14% 7%	1873
	21st to end	Day	62% 5% 10% 16% 6% 2	1730
March	1st to 10th	Day	57% 4 11% 20% 7%	4994
	11th to 20th	Day	50% 6% 13% 23% 7% 2	5090
	21st to end	Day	56% 5% 8% 18% 12% 1	5586
April	1st to 10th	Day	53% 4 12% 17% 12% 1	2380
	11th to 20th	Day	52% 5% 11% 18% 12% 2	2623
	21st to end	Day	51% 5% 10% 21% 11% 2	2730
May	1st to 10th	Day	54% 6% 9% 18% 9% 4	6027
	11th to 20th	Day	50% 7% 10% 21% 10% 1	5995
	21st to end	Day	46% 6% 11% 20% 13% 3	6861
June	1st to 10th	Day	45% 6% 11% 25% 12% 1	2800
	11th to 20th	Day	44% 5% 14% 21% 14% 1	2800
	21st to end	Day	39% 7% 14% 24% 15% 2	2800
July	1st to 10th	Day	36% 6% 12% 27% 16% 2	5983
	11th to 20th	Day	39% 7% 14% 24% 15% 1	5831
	21st to end	Day	39% 7% 11% 22% 20% 1	6240
August	1st to 10th	Day	45% 7% 15% 22% 11%	4221
	11th to 20th	Day	41% 7% 12% 29% 9% 1	4213
	21st to end	Day	37% 8% 13% 29% 11% 2	4550
September	1st to 10th	Day	39% 5% 12% 24% 16% 3	2340
	11th to 20th	Day	36% 6% 14% 26% 16% 1	2200
	21st to end	Day	47% 5% 10% 23% 13% 1	2200
October	1st to 10th	Day	33% 6% 13% 28% 19% 1	3326
	11th to 20th	Day	47% 6% 9% 21% 13% 4	3240
	21st to end	Day	42% 5% 13% 25% 14% 1	3538
November	1st to 10th	Day	46% 5% 12% 22% 14% 1	1886
	11th to 20th	Day	57% 5% 10% 18% 7% 3	1801
	21st to end	Day	65% 7% 9% 14% 6%	1680
December	1st to 10th	Day	69% 6% 11% 11% 2	2680
	11th to 20th	Day	72% 4 8% 13% 3	3066
	21st to end	Day	81% 3 8% 7% 2	4122
January	1st to 10th	Night	77% 5% 7% 8% 3	7636
	11th to 20th	Night	76% 5% 8% 9% 3	7680
	21st to end	Night	69% 3 9% 13% 6%	8401
February	1st to 10th	Night	65% 5% 9% 15% 5%	2730
	11th to 20th	Night	66% 5% 8% 16% 5%	2642
	21st to end	Night	63% 4 8% 15% 9% 1	2076
March	1st to 10th	Night	57% 4 12% 19% 9%	5078
	11th to 20th	Night	45% 7% 15% 23% 10% 1	5090
	21st to end	Night	52% 6% 9% 19% 14% 1	5588
April	1st to 10th	Night	54% 7% 10% 17% 12% 2	2239
	11th to 20th	Night	49% 5% 13% 18% 13% 2	1963
	21st to end	Night	45% 6% 11% 21% 14% 3	1890
May	1st to 10th	Night	57% 5% 9% 15% 9% 5%	4150
	11th to 20th	Night	44% 7% 10% 24% 13% 2	4123
	21st to end	Night	41% 6% 13% 24% 14% 2	4256
June	1st to 10th	Night	40% 7% 10% 25% 16% 3	1600
	11th to 20th	Night	38% 6% 14% 23% 16% 3	1600
	21st to end	Night	36% 8% 13% 24% 18% 1	1600
July	1st to 10th	Night	37% 6% 12% 25% 19% 2	3849
	11th to 20th	Night	36% 8% 14% 27% 14% 1	4006
	21st to end	Night	33% 6% 12% 20% 26% 1	4297
August	1st to 10th	Night	43% 6% 12% 24% 14% 1	2904
	11th to 20th	Night	40% 6% 11% 29% 12% 1	2902
	21st to end	Night	35% 8% 13% 28% 14% 2	3313
September	1st to 10th	Night	35% 5% 11% 28% 17% 4	2057
	11th to 20th	Night	29% 6% 14% 28% 21% 2	2200
	21st to end	Night	44% 5% 11% 21% 18% 1	2200
October	1st to 10th	Night	33% 5% 9% 28% 23% 1	3854
	11th to 20th	Night	41% 6% 11% 23% 16% 3	3899
	21st to end	Night	38% 4 12% 29% 16% 1	4252
November	1st to 10th	Night	42% 6% 11% 24% 14% 3	2631
	11th to 20th	Night	57% 4 10% 18% 8% 3	2817
	21st to end	Night	62% 5% 11% 17% 5% 1	2940
December	1st to 10th	Night	67% 5% 12% 11% 4	4720
	11th to 20th	Night	69% 4 10% 14% 2	5348
	21st to end	Night	74% 5% 10% 10% 1	7058

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	32% 27% 29% 8% 3	330
	11th to 20th	Day	35% 28% 27% 7% 2	330
	21st to end	Day	33% 31% 26% 9% 2	363
February	1st to 10th	Day	30% 25% 34% 8% 2	330
	11th to 20th	Day	33% 31% 29% 5% 1	330
	21st to end	Day	30% 33% 31% 6%	273
March	1st to 10th	Day	26% 25% 34% 11% 5%	513
	11th to 20th	Day	29% 22% 32% 11% 5% 1	540
	21st to end	Day	33% 21% 28% 14% 3	594
April	1st to 10th	Day	29% 22% 28% 14% 6% 1	540
	11th to 20th	Day	30% 18% 27% 16% 8% 2	532
	21st to end	Day	27% 18% 31% 18% 5% 2	540
May	1st to 10th	Day	30% 18% 28% 16% 5% 3	543
	11th to 20th	Day	25% 13% 31% 20% 8% 4	567
	21st to end	Day	19% 12% 28% 22% 15% 5%	617
June	1st to 10th	Day	18% 11% 35% 23% 11% 2	530
	11th to 20th	Day	19% 11% 26% 27% 13% 4	530
	21st to end	Day	16% 8% 32% 25% 15% 4	530
July	1st to 10th	Day	11% 6% 23% 29% 21% 9%	525
	11th to 20th	Day	14% 6% 27% 28% 17% 8%	524
	21st to end	Day	12% 6% 27% 30% 17% 9%	576
August	1st to 10th	Day	12% 8% 20% 31% 20% 10%	526
	11th to 20th	Day	15% 7% 25% 25% 18% 9%	519
	21st to end	Day	10% 7% 23% 29% 22% 8%	583
September	1st to 10th	Day	13% 11% 21% 25% 20% 10%	530
	11th to 20th	Day	11% 4 19% 31% 23% 13%	530
	21st to end	Day	25% 10% 25% 21% 14% 6%	530
October	1st to 10th	Day	14% 11% 28% 22% 20% 4	530
	11th to 20th	Day	25% 17% 32% 17% 7% 2	530
	21st to end	Day	28% 19% 28% 19% 5%	583
November	1st to 10th	Day	21% 23% 29% 15% 9% 2	364
	11th to 20th	Day	34% 18% 29% 14% 5%	283
	21st to end	Day	33% 18% 38% 10% 1	220
December	1st to 10th	Day	31% 25% 30% 11% 2 1	220
	11th to 20th	Day	30% 27% 31% 10% 2	220
	21st to end	Day	35% 23% 30% 10% 2	261
January	1st to 10th	Night	27% 22% 36% 12% 3	840
	11th to 20th	Night	30% 23% 30% 14% 3	840
	21st to end	Night	26% 24% 30% 18% 3	924
February	1st to 10th	Night	29% 19% 29% 21% 2	840
	11th to 20th	Night	26% 20% 35% 16% 2	823
	21st to end	Night	29% 18% 35% 15% 3	692
March	1st to 10th	Night	25% 17% 33% 20% 4	840
	11th to 20th	Night	26% 18% 30% 21% 6%	840
	21st to end	Night	25% 16% 33% 21% 5% 1	924
April	1st to 10th	Night	26% 15% 32% 21% 5%	840
	11th to 20th	Night	22% 14% 35% 20% 8% 1	719
	21st to end	Night	18% 11% 36% 28% 7%	630
May	1st to 10th	Night	22% 10% 27% 33% 8%	630
	11th to 20th	Night	18% 8% 27% 33% 12% 1	621
	21st to end	Night	14% 4 27% 32% 20% 2	567
June	1st to 10th	Night	10% 4 35% 38% 13% 1	400
	11th to 20th	Night	13% 5% 25% 42% 15% 1	400
	21st to end	Night	12% 6% 27% 34% 20% 1	400
July	1st to 10th	Night	8% 3 16% 41% 27% 5%	510
	11th to 20th	Night	9% 3 21% 36% 27% 3	582
	21st to end	Night	10% 3 17% 40% 28% 2	657
August	1st to 10th	Night	9% 3 16% 41% 27% 3	597
	11th to 20th	Night	12% 4 14% 36% 29% 4	594
	21st to end	Night	12% 2 19% 34% 29% 4	711
September	1st to 10th	Night	15% 5% 19% 32% 26% 4	800
	11th to 20th	Night	11% 4 15% 37% 29% 5%	800
	21st to end	Night	19% 8% 22% 28% 20% 4	800
October	1st to 10th	Night	18% 7% 25% 26% 21% 3	800
	11th to 20th	Night	21% 12% 31% 25% 9% 2	800
	21st to end	Night	29% 12% 28% 24% 7%	880
November	1st to 10th	Night	20% 13% 30% 27% 10% 1	820
	11th to 20th	Night	26% 19% 30% 18% 6% 1	840
	21st to end	Night	30% 19% 31% 16% 5%	840
December	1st to 10th	Night	30% 19% 30% 16% 5%	840
	11th to 20th	Night	27% 23% 29% 18% 4	840
	21st to end	Night	31% 18% 31% 19% 2	924

Page generated at 2026-05-29 01:53:24. Version ac07

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