Moraine Valley Community College Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Moraine Valley Community College Observatory clear sky chart from 2005-11-06 to 2024-11-01.

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	13% 9% 3 8% 5% 4 4 4 6% 7% 36%	101246
	Night	14% 10% 4 7% 4 4 4 3 5% 6% 38%	97780
Transparency	Day	47% 4 12% 23% 13% 2	101035
	Night	47% 3 11% 22% 14% 2	97663
Seeing	Day	17% 12% 31% 24% 12% 4	15785
	Night	18% 11% 30% 29% 11% 1	25613

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	14% 14% 8% 10% 5% 5% 5% 3 5% 5% 27%	2527
	11th to 20th	Day	13% 16% 6% 14% 6% 5% 4 7% 8% 4 18%	2530
	21st to end	Day	20% 26% 6% 9% 4 3 3 2 4 5% 18%	2847
February	1st to 10th	Day	16% 14% 5% 10% 6% 5% 4 3 5% 5% 27%	1771
	11th to 20th	Day	14% 11% 5% 8% 6% 5% 4 3 5% 6% 34%	1848
	21st to end	Day	15% 14% 5% 9% 5% 4 4 4 5% 7% 29%	1570
March	1st to 10th	Day	16% 15% 4 8% 4 4 4 3 4 5% 34%	3120
	11th to 20th	Day	10% 7% 4 7% 6% 5% 5% 4 6% 7% 38%	3250
	21st to end	Day	19% 12% 6% 13% 6% 5% 5% 4 5% 5% 20%	4165
April	1st to 10th	Day	16% 14% 3 9% 5% 5% 4 3 5% 5% 31%	2280
	11th to 20th	Day	17% 9% 3 6% 5% 5% 5% 3 5% 6% 35%	2254
	21st to end	Day	20% 8% 3 8% 5% 4 4 4 6% 7% 33%	2393
May	1st to 10th	Day	17% 8% 2 7% 5% 5% 5% 4 6% 8% 34%	4082
	11th to 20th	Day	15% 7% 2 6% 4 4 4 4 5% 8% 41%	4257
	21st to end	Day	10% 6% 2 6% 4 4 5% 4 6% 8% 44%	4824
June	1st to 10th	Day	10% 6% 2 6% 4 4 5% 4 7% 7% 45%	2660
	11th to 20th	Day	9% 6% 2 6% 4 5% 4 4 7% 8% 45%	2660
	21st to end	Day	11% 6% 2 7% 6% 5% 5% 5% 8% 9% 36%	2660
July	1st to 10th	Day	11% 7% 3 8% 6% 5% 6% 5% 7% 8% 33%	4440
	11th to 20th	Day	7% 4 2 5% 4 4 5% 4 7% 10% 47%	4440
	21st to end	Day	8% 6% 2 7% 5% 5% 5% 4 7% 8% 40%	4813
August	1st to 10th	Day	9% 5% 3 6% 4 4 5% 5% 6% 8% 44%	4300
	11th to 20th	Day	9% 5% 2 6% 4 4 5% 4 6% 9% 44%	3765
	21st to end	Day	7% 5% 2 6% 4 5% 5% 3 6% 10% 48%	4180
September	1st to 10th	Day	12% 5% 1 6% 5% 4 4 3 5% 8% 46%	2280
	11th to 20th	Day	11% 5% 2 4 3 3 4 3 6% 8% 51%	2147
	21st to end	Day	11% 7% 2 6% 4 4 4 4 6% 8% 42%	2090
October	1st to 10th	Day	12% 7% 3 7% 4 4 4 3 5% 6% 46%	2060
	11th to 20th	Day	18% 9% 3 7% 5% 5% 3 4 4 6% 37%	1877
	21st to end	Day	20% 9% 3 7% 5% 4 3 4 5% 6% 35%	1881
November	1st to 10th	Day	13% 8% 3 5% 4 4 3 3 5% 6% 45%	1672
	11th to 20th	Day	16% 11% 3 8% 5% 5% 4 3 5% 7% 34%	1710
	21st to end	Day	18% 11% 3 9% 5% 3 4 2 3 5% 35%	1672
December	1st to 10th	Day	15% 14% 4 10% 6% 4 5% 3 4 5% 30%	1520
	11th to 20th	Day	13% 15% 5% 10% 5% 4 5% 3 5% 6% 28%	1918
	21st to end	Day	21% 22% 8% 13% 5% 5% 3 2 3 3 14%	2783
January	1st to 10th	Night	15% 15% 8% 11% 5% 4 4 3 4 4 28%	4428
	11th to 20th	Night	16% 18% 8% 12% 5% 4 4 5% 6% 4 18%	4440
	21st to end	Night	23% 18% 7% 9% 4 4 4 3 3 4 21%	4816
February	1st to 10th	Night	17% 14% 4 8% 6% 4 3 3 4 6% 31%	2409
	11th to 20th	Night	13% 12% 4 7% 5% 4 5% 3 5% 6% 37%	2218
	21st to end	Night	18% 12% 4 8% 5% 4 3 3 4 5% 34%	1884
March	1st to 10th	Night	17% 13% 3 6% 4 3 3 3 4 5% 38%	3733
	11th to 20th	Night	10% 6% 3 7% 5% 4 4 3 5% 6% 48%	3737
	21st to end	Night	20% 11% 6% 9% 5% 5% 4 3 4 5% 26%	3466
April	1st to 10th	Night	15% 10% 3 6% 4 4 4 3 5% 7% 38%	1900
	11th to 20th	Night	19% 8% 3 6% 4 4 3 4 4 6% 39%	1875
	21st to end	Night	17% 8% 3 8% 5% 4 4 4 5% 6% 35%	1786
May	1st to 10th	Night	16% 7% 3 7% 5% 4 5% 4 6% 7% 35%	2813
	11th to 20th	Night	15% 6% 2 6% 5% 5% 4 4 6% 8% 40%	2640
	21st to end	Night	10% 8% 2 7% 5% 4 4 4 5% 7% 44%	2743
June	1st to 10th	Night	9% 5% 2 5% 5% 4 4 4 6% 7% 49%	1520
	11th to 20th	Night	7% 6% 2 5% 5% 4 4 4 6% 10% 45%	1520
	21st to end	Night	11% 6% 3 6% 4 5% 6% 4 6% 9% 42%	1520
July	1st to 10th	Night	11% 5% 2 7% 5% 6% 6% 4 6% 8% 40%	2530
	11th to 20th	Night	6% 5% 2 5% 4 4 4 4 5% 7% 55%	2530
	21st to end	Night	5% 5% 2 6% 4 5% 6% 5% 7% 9% 45%	2750
August	1st to 10th	Night	7% 5% 2 7% 4 5% 5% 4 6% 8% 47%	2635
	11th to 20th	Night	8% 5% 2 5% 4 5% 4 4 5% 7% 52%	3061
	21st to end	Night	8% 5% 2 6% 3 3 4 3 5% 8% 52%	3476
September	1st to 10th	Night	10% 5% 2 7% 3 3 4 2 5% 7% 52%	1900
	11th to 20th	Night	8% 5% 2 4 3 3 4 3 5% 7% 55%	2014
	21st to end	Night	10% 6% 2 9% 3 3 4 5% 6% 7% 46%	2090
October	1st to 10th	Night	11% 5% 3 5% 4 4 3 3 5% 7% 50%	2118
	11th to 20th	Night	17% 8% 3 5% 4 3 4 2 3 6% 45%	2302
	21st to end	Night	20% 9% 3 6% 3 3 4 4 5% 7% 36%	2717
November	1st to 10th	Night	12% 8% 3 5% 4 3 3 3 5% 6% 47%	2413
	11th to 20th	Night	15% 10% 3 8% 5% 4 4 3 5% 6% 36%	2470
	21st to end	Night	17% 10% 3 7% 5% 4 3 3 5% 6% 37%	2503
December	1st to 10th	Night	16% 11% 4 10% 5% 4 5% 3 5% 6% 31%	2660
	11th to 20th	Night	15% 15% 4 9% 5% 4 4 3 4 6% 31%	3279
	21st to end	Night	24% 19% 6% 10% 5% 5% 4 3 4 5% 16%	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	60% 2 14% 17% 7%	2528
	11th to 20th	Day	66% 2 10% 13% 8%	2530
	21st to end	Day	71% 2 7% 14% 5%	2847
February	1st to 10th	Day	60% 4 11% 15% 9% 2	1771
	11th to 20th	Day	53% 3 10% 22% 10% 2	1858
	21st to end	Day	56% 4 11% 21% 7% 2	1570
March	1st to 10th	Day	54% 3 8% 22% 11% 2	3120
	11th to 20th	Day	44% 2 12% 30% 11% 1	3250
	21st to end	Day	67% 3 14% 13% 3	4165
April	1st to 10th	Day	55% 4 8% 20% 12%	2280
	11th to 20th	Day	49% 4 10% 22% 12% 4	2254
	21st to end	Day	51% 4 12% 19% 12% 2	2393
May	1st to 10th	Day	48% 4 10% 26% 11% 1	4120
	11th to 20th	Day	43% 3 11% 28% 14%	4261
	21st to end	Day	38% 3 12% 23% 21% 4	4837
June	1st to 10th	Day	36% 4 13% 27% 18% 2	2660
	11th to 20th	Day	36% 5% 11% 26% 20% 3	2660
	21st to end	Day	42% 6% 14% 22% 13% 3	2660
July	1st to 10th	Day	47% 5% 12% 21% 13% 2	4371
	11th to 20th	Day	31% 6% 16% 29% 17% 1	4365
	21st to end	Day	39% 6% 16% 17% 20% 2	4662
August	1st to 10th	Day	35% 6% 15% 28% 14% 1	4285
	11th to 20th	Day	34% 5% 11% 33% 16% 1	3802
	21st to end	Day	32% 5% 12% 28% 20% 3	4179
September	1st to 10th	Day	36% 4 12% 24% 19% 4	2280
	11th to 20th	Day	31% 5% 11% 30% 21% 3	2147
	21st to end	Day	39% 5% 9% 27% 19% 1	2090
October	1st to 10th	Day	39% 4 11% 26% 17% 2	2060
	11th to 20th	Day	49% 3 10% 23% 15% 1	1877
	21st to end	Day	51% 3 10% 23% 10% 2	1881
November	1st to 10th	Day	39% 3 15% 24% 17% 2	1672
	11th to 20th	Day	50% 4 12% 22% 12% 1	1710
	21st to end	Day	53% 3 10% 23% 10%	1672
December	1st to 10th	Day	56% 3 13% 20% 7% 1	1520
	11th to 20th	Day	57% 3 11% 20% 7% 1	1915
	21st to end	Day	78% 3 7% 9% 3	2783
January	1st to 10th	Night	61% 2 10% 18% 8% 1	4428
	11th to 20th	Night	68% 2 11% 12% 6%	4440
	21st to end	Night	68% 2 9% 15% 6%	4816
February	1st to 10th	Night	56% 3 10% 18% 11% 2	2409
	11th to 20th	Night	50% 3 10% 22% 14% 1	2219
	21st to end	Night	54% 3 9% 20% 11% 3	1884
March	1st to 10th	Night	50% 3 11% 24% 10% 3	3733
	11th to 20th	Night	39% 3 10% 28% 18% 2	3737
	21st to end	Night	61% 2 10% 20% 6% 1	3466
April	1st to 10th	Night	46% 3 12% 25% 13% 2	1900
	11th to 20th	Night	47% 3 8% 22% 17% 4	1875
	21st to end	Night	49% 4 9% 21% 14% 2	1786
May	1st to 10th	Night	48% 3 12% 22% 13% 2	2840
	11th to 20th	Night	42% 4 14% 29% 10% 1	2641
	21st to end	Night	40% 4 11% 18% 21% 6%	2751
June	1st to 10th	Night	34% 4 13% 26% 20% 3	1520
	11th to 20th	Night	33% 4 13% 25% 23% 2	1520
	21st to end	Night	39% 6% 14% 22% 17% 2	1520
July	1st to 10th	Night	41% 5% 16% 22% 11% 5%	2490
	11th to 20th	Night	28% 5% 14% 28% 23% 2	2482
	21st to end	Night	33% 6% 17% 19% 22% 4	2662
August	1st to 10th	Night	34% 6% 15% 28% 16% 1	2626
	11th to 20th	Night	31% 5% 14% 28% 20% 1	3090
	21st to end	Night	30% 4 12% 33% 17% 4	3476
September	1st to 10th	Night	32% 3 12% 27% 24% 3	1900
	11th to 20th	Night	29% 3 8% 30% 27% 2	2014
	21st to end	Night	37% 4 10% 30% 17% 2	2090
October	1st to 10th	Night	34% 5% 9% 30% 21% 2	2118
	11th to 20th	Night	42% 2 8% 26% 20% 2	2302
	21st to end	Night	49% 3 10% 24% 13% 1	2717
November	1st to 10th	Night	39% 3 9% 27% 19% 3	2413
	11th to 20th	Night	49% 3 11% 23% 13% 1	2470
	21st to end	Night	50% 3 12% 24% 11%	2503
December	1st to 10th	Night	54% 4 11% 21% 9% 1	2660
	11th to 20th	Night	56% 3 12% 19% 10% 1	3281
	21st to end	Night	73% 2 8% 12% 4	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	22% 17% 36% 20% 4	270
	11th to 20th	Day	26% 21% 33% 16% 3 1	270
	21st to end	Day	25% 18% 34% 19% 2 1	297
February	1st to 10th	Day	24% 20% 40% 14% 2	270
	11th to 20th	Day	26% 22% 33% 17% 3	270
	21st to end	Day	25% 19% 41% 12% 2	225
March	1st to 10th	Day	21% 27% 39% 11% 2	270
	11th to 20th	Day	25% 20% 34% 16% 5%	305
	21st to end	Day	29% 18% 29% 17% 5% 1	506
April	1st to 10th	Day	25% 18% 32% 18% 7%	460
	11th to 20th	Day	23% 21% 25% 20% 9% 1	452
	21st to end	Day	24% 17% 34% 17% 7% 1	460
May	1st to 10th	Day	23% 15% 30% 21% 8% 2	463
	11th to 20th	Day	20% 13% 33% 22% 11% 3	585
	21st to end	Day	14% 11% 34% 24% 12% 5%	734
June	1st to 10th	Day	11% 10% 33% 28% 12% 5%	680
	11th to 20th	Day	12% 8% 34% 26% 16% 3	680
	21st to end	Day	13% 11% 35% 26% 10% 4	680
July	1st to 10th	Day	10% 5% 25% 32% 17% 11%	671
	11th to 20th	Day	12% 6% 29% 30% 15% 8%	668
	21st to end	Day	8% 7% 27% 34% 18% 6%	739
August	1st to 10th	Day	7% 4 26% 32% 20% 10%	605
	11th to 20th	Day	10% 5% 21% 30% 24% 10%	479
	21st to end	Day	7% 4 21% 39% 21% 8%	539
September	1st to 10th	Day	14% 6% 23% 31% 21% 5%	490
	11th to 20th	Day	10% 4 19% 33% 24% 9%	490
	21st to end	Day	14% 11% 25% 28% 17% 5%	490
October	1st to 10th	Day	17% 8% 29% 26% 15% 4	460
	11th to 20th	Day	21% 23% 31% 19% 5% 1	300
	21st to end	Day	30% 15% 35% 16% 3	330
November	1st to 10th	Day	14% 17% 37% 23% 6% 3	270
	11th to 20th	Day	24% 19% 35% 16% 6% 1	270
	21st to end	Day	26% 11% 40% 19% 3	270
December	1st to 10th	Day	21% 24% 34% 16% 4	270
	11th to 20th	Day	21% 17% 41% 17% 3	270
	21st to end	Day	27% 22% 37% 12% 2	297
January	1st to 10th	Night	21% 17% 35% 22% 4	950
	11th to 20th	Night	23% 18% 34% 20% 4 1	950
	21st to end	Night	22% 14% 34% 26% 4	1045
February	1st to 10th	Night	23% 13% 37% 22% 4	889
	11th to 20th	Night	21% 16% 34% 25% 3	743
	21st to end	Night	23% 19% 36% 19% 3	628
March	1st to 10th	Night	23% 14% 36% 21% 6%	760
	11th to 20th	Night	16% 13% 39% 25% 6% 1	760
	21st to end	Night	26% 13% 29% 25% 7% 1	627
April	1st to 10th	Night	21% 13% 35% 24% 6%	570
	11th to 20th	Night	23% 13% 32% 23% 8% 1	563
	21st to end	Night	22% 10% 32% 26% 8%	570
May	1st to 10th	Night	18% 8% 36% 29% 8%	570
	11th to 20th	Night	18% 4 29% 34% 14% 1	561
	21st to end	Night	14% 6% 27% 34% 19%	617
June	1st to 10th	Night	11% 4 26% 44% 14% 1	570
	11th to 20th	Night	10% 6% 28% 42% 13% 1	570
	21st to end	Night	12% 5% 26% 39% 17% 1	570
July	1st to 10th	Night	8% 3 18% 39% 27% 4	555
	11th to 20th	Night	7% 5% 21% 40% 25% 3	552
	21st to end	Night	5% 2 20% 47% 24% 2	624
August	1st to 10th	Night	6% 2 14% 47% 27% 3	567
	11th to 20th	Night	8% 3 14% 40% 31% 4	564
	21st to end	Night	9% 2 17% 39% 30% 3	627
September	1st to 10th	Night	11% 4 19% 33% 28% 4	570
	11th to 20th	Night	8% 5% 18% 36% 28% 4	684
	21st to end	Night	12% 8% 24% 34% 21% 3	760
October	1st to 10th	Night	14% 6% 26% 35% 17% 2	760
	11th to 20th	Night	20% 14% 30% 26% 9%	760
	21st to end	Night	25% 13% 30% 24% 8%	836
November	1st to 10th	Night	16% 14% 38% 20% 10% 2	743
	11th to 20th	Night	19% 18% 34% 23% 5% 1	760
	21st to end	Night	22% 12% 39% 21% 6%	793
December	1st to 10th	Night	21% 16% 37% 22% 4	950
	11th to 20th	Night	23% 14% 35% 24% 4	950
	21st to end	Night	31% 16% 32% 19% 2	1045

Page generated at 2024-10-29 10:20:47. Version ac07

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