Indiana Dunes State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Indiana Dunes State Park clear sky chart from 2005-11-06 to 2024-03-28.

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 7% 6% 3 4 5% 5% 7% 34%	78681
	Night	16% 12% 5% 7% 6% 3 4 4 5% 6% 32%	81364
Transparency	Day	48% 6% 12% 20% 11% 2	78382
	Night	51% 7% 10% 19% 11% 2	81184
Seeing	Day	18% 11% 30% 24% 13% 4	14834
	Night	20% 12% 29% 26% 12% 1	24881

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% 17% 13% 11% 8% 4 4 4 5% 4 15%	2527
	11th to 20th	Day	14% 17% 9% 14% 9% 5% 6% 10% 5% 3 9%	2530
	21st to end	Day	23% 24% 6% 9% 5% 3 3 3 3 6% 15%	2783
February	1st to 10th	Day	15% 14% 7% 10% 8% 4 4 5% 4 6% 23%	1818
	11th to 20th	Day	14% 12% 4 10% 9% 3 4 4 5% 5% 30%	1848
	21st to end	Day	15% 15% 6% 11% 5% 3 4 4 4 6% 28%	1570
March	1st to 10th	Day	17% 12% 5% 9% 6% 3 3 4 5% 6% 29%	1900
	11th to 20th	Day	13% 10% 5% 8% 7% 3 5% 5% 5% 7% 34%	1971
	21st to end	Day	18% 12% 5% 9% 6% 3 4 5% 5% 5% 27%	2422
April	1st to 10th	Day	15% 10% 5% 6% 5% 3 4 5% 5% 7% 34%	2160
	11th to 20th	Day	16% 11% 3 6% 4 3 4 4 4 8% 37%	2134
	21st to end	Day	18% 9% 4 6% 5% 3 4 5% 6% 7% 33%	2304
May	1st to 10th	Day	16% 9% 4 6% 6% 3 5% 5% 6% 9% 33%	2340
	11th to 20th	Day	18% 9% 3 5% 5% 3 4 4 4 7% 38%	2337
	21st to end	Day	11% 6% 3 6% 6% 3 5% 6% 6% 9% 40%	2725
June	1st to 10th	Day	9% 5% 3 5% 6% 3 4 5% 6% 8% 46%	2520
	11th to 20th	Day	9% 5% 2 5% 5% 3 5% 6% 6% 8% 46%	2520
	21st to end	Day	10% 5% 2 5% 6% 3 5% 6% 7% 9% 41%	2520
July	1st to 10th	Day	8% 5% 2 5% 4 3 5% 5% 6% 9% 48%	2520
	11th to 20th	Day	9% 4 3 4 5% 3 5% 5% 6% 10% 48%	2520
	21st to end	Day	6% 4 2 5% 5% 4 5% 6% 7% 10% 46%	2743
August	1st to 10th	Day	7% 4 2 5% 5% 4 5% 5% 7% 10% 46%	2391
	11th to 20th	Day	8% 5% 2 5% 6% 4 5% 5% 6% 9% 45%	2201
	21st to end	Day	8% 4 2 4 4 3 4 5% 6% 9% 51%	2376
September	1st to 10th	Day	11% 5% 3 5% 5% 3 5% 4 6% 7% 45%	2160
	11th to 20th	Day	11% 5% 2 4 4 4 4 5% 6% 9% 46%	2002
	21st to end	Day	11% 6% 4 5% 5% 3 5% 5% 6% 9% 41%	1980
October	1st to 10th	Day	14% 7% 3 5% 5% 3 4 4 5% 6% 44%	1980
	11th to 20th	Day	20% 9% 3 7% 6% 3 4 4 5% 6% 33%	1765
	21st to end	Day	22% 10% 4 7% 5% 4 5% 4 5% 7% 27%	1782
November	1st to 10th	Day	13% 10% 3 6% 4 3 5% 5% 6% 6% 40%	1672
	11th to 20th	Day	17% 14% 6% 7% 7% 3 4 4 5% 6% 27%	1710
	21st to end	Day	19% 14% 6% 9% 5% 3 4 4 4 5% 29%	1710
December	1st to 10th	Day	15% 18% 7% 11% 7% 4 4 4 4 5% 22%	1539
	11th to 20th	Day	13% 19% 8% 11% 7% 3 4 4 6% 5% 21%	1918
	21st to end	Day	21% 21% 8% 13% 8% 4 4 4 3 4 11%	2783
January	1st to 10th	Night	17% 20% 10% 10% 7% 3 4 4 4 4 18%	4428
	11th to 20th	Night	16% 21% 9% 13% 7% 3 5% 8% 4 3 11%	4440
	21st to end	Night	24% 18% 8% 10% 6% 4 4 3 3 5% 15%	4884
February	1st to 10th	Night	18% 13% 6% 8% 7% 3 5% 4 4 6% 25%	2359
	11th to 20th	Night	15% 11% 6% 8% 8% 4 5% 5% 5% 5% 29%	2218
	21st to end	Night	19% 13% 6% 9% 6% 2 4 3 3 4 30%	1884
March	1st to 10th	Night	16% 13% 6% 7% 6% 4 5% 5% 4 5% 30%	2280
	11th to 20th	Night	12% 8% 4 6% 5% 3 4 5% 5% 7% 41%	2209
	21st to end	Night	20% 11% 5% 7% 5% 3 4 4 4 6% 30%	2102
April	1st to 10th	Night	14% 10% 5% 6% 5% 3 4 5% 5% 7% 36%	1800
	11th to 20th	Night	18% 9% 3 5% 6% 4 4 4 4 5% 38%	1775
	21st to end	Night	18% 8% 4 7% 6% 3 4 4 4 6% 36%	1656
May	1st to 10th	Night	18% 8% 4 5% 5% 3 5% 5% 5% 7% 35%	1620
	11th to 20th	Night	19% 7% 2 6% 4 3 4 5% 5% 8% 38%	1554
	21st to end	Night	10% 6% 2 6% 5% 4 6% 5% 7% 7% 42%	1551
June	1st to 10th	Night	9% 5% 2 5% 5% 2 4 4 6% 10% 48%	1440
	11th to 20th	Night	8% 5% 3 6% 5% 3 4 5% 6% 9% 46%	1440
	21st to end	Night	9% 6% 3 5% 6% 3 5% 6% 5% 8% 42%	1440
July	1st to 10th	Night	7% 3 2 4 6% 2 5% 5% 6% 9% 51%	1440
	11th to 20th	Night	8% 4 3 3 4 2 5% 6% 5% 8% 52%	1440
	21st to end	Night	5% 3 1 4 5% 4 5% 5% 8% 10% 49%	1575
August	1st to 10th	Night	7% 3 2 4 5% 3 4 5% 8% 11% 49%	1546
	11th to 20th	Night	8% 3 2 4 4 3 5% 4 6% 9% 51%	1696
	21st to end	Night	8% 4 2 5% 5% 3 4 4 5% 7% 52%	1980
September	1st to 10th	Night	12% 5% 2 5% 4 3 4 3 5% 7% 49%	1800
	11th to 20th	Night	10% 5% 3 5% 4 2 3 4 4 7% 52%	1939
	21st to end	Night	11% 6% 2 5% 5% 3 6% 5% 5% 7% 45%	1980
October	1st to 10th	Night	13% 6% 2 4 5% 4 4 4 5% 6% 47%	1980
	11th to 20th	Night	21% 9% 2 6% 4 2 4 4 4 6% 38%	2189
	21st to end	Night	24% 11% 3 6% 5% 2 4 3 4 6% 32%	2574
November	1st to 10th	Night	14% 12% 4 7% 4 3 4 4 4 6% 39%	2406
	11th to 20th	Night	15% 16% 4 9% 6% 3 4 4 5% 6% 28%	2470
	21st to end	Night	19% 13% 5% 9% 6% 2 4 4 4 6% 29%	2470
December	1st to 10th	Night	17% 17% 7% 10% 8% 3 5% 3 4 5% 21%	2636
	11th to 20th	Night	15% 18% 8% 12% 6% 3 4 4 4 6% 20%	3279
	21st to end	Night	24% 20% 7% 9% 7% 4 5% 3 4 4 13%	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	70% 8% 10% 9% 4	2528
	11th to 20th	Day	72% 11% 9% 7% 1	2530
	21st to end	Day	71% 4 9% 12% 3	2783
February	1st to 10th	Day	62% 6% 12% 12% 7% 1	1818
	11th to 20th	Day	55% 6% 11% 19% 9% 1	1858
	21st to end	Day	58% 5% 11% 17% 6% 2	1570
March	1st to 10th	Day	56% 6% 11% 19% 8% 1	1900
	11th to 20th	Day	48% 6% 12% 22% 10% 1	1971
	21st to end	Day	59% 5% 13% 18% 5% 1	2422
April	1st to 10th	Day	49% 6% 11% 22% 12%	2160
	11th to 20th	Day	46% 5% 11% 21% 13% 3	2134
	21st to end	Day	50% 5% 14% 16% 13% 2	2304
May	1st to 10th	Day	48% 6% 14% 23% 9% 1	2340
	11th to 20th	Day	47% 5% 12% 22% 13% 1	2341
	21st to end	Day	41% 7% 12% 23% 15% 2	2725
June	1st to 10th	Day	36% 6% 11% 25% 19% 2	2520
	11th to 20th	Day	35% 5% 12% 25% 20% 3	2520
	21st to end	Day	38% 8% 17% 20% 16% 2	2520
July	1st to 10th	Day	32% 7% 14% 26% 18% 4	2451
	11th to 20th	Day	32% 6% 16% 28% 16% 2	2445
	21st to end	Day	32% 8% 16% 25% 16% 3	2591
August	1st to 10th	Day	31% 7% 17% 30% 14% 2	2376
	11th to 20th	Day	34% 7% 16% 27% 16% 2	2201
	21st to end	Day	30% 7% 14% 26% 19% 4	2376
September	1st to 10th	Day	37% 6% 13% 24% 16% 4	2160
	11th to 20th	Day	34% 5% 13% 28% 17% 2	2002
	21st to end	Day	38% 7% 11% 25% 18% 2	1980
October	1st to 10th	Day	39% 7% 11% 25% 16% 2	1980
	11th to 20th	Day	51% 6% 10% 21% 12% 1	1765
	21st to end	Day	56% 6% 11% 18% 8% 1	1782
November	1st to 10th	Day	42% 7% 14% 21% 15% 1	1672
	11th to 20th	Day	57% 6% 10% 18% 8% 1	1710
	21st to end	Day	58% 6% 10% 19% 7%	1710
December	1st to 10th	Day	65% 7% 9% 13% 6%	1539
	11th to 20th	Day	64% 5% 11% 17% 4	1915
	21st to end	Day	78% 6% 8% 7% 2	2783
January	1st to 10th	Night	67% 8% 9% 12% 4	4428
	11th to 20th	Night	73% 9% 8% 7% 2	4440
	21st to end	Night	71% 6% 8% 11% 4	4884
February	1st to 10th	Night	60% 6% 10% 15% 8% 2	2359
	11th to 20th	Night	54% 7% 10% 19% 10% 1	2219
	21st to end	Night	58% 6% 8% 17% 9% 2	1884
March	1st to 10th	Night	56% 6% 10% 20% 8% 1	2280
	11th to 20th	Night	42% 6% 14% 22% 14% 3	2209
	21st to end	Night	56% 6% 11% 19% 8% 1	2102
April	1st to 10th	Night	47% 6% 12% 21% 13% 1	1800
	11th to 20th	Night	49% 5% 7% 19% 17% 3	1775
	21st to end	Night	50% 6% 10% 18% 14% 3	1656
May	1st to 10th	Night	48% 6% 11% 23% 11% 1	1620
	11th to 20th	Night	45% 6% 11% 21% 16% 1	1555
	21st to end	Night	40% 7% 14% 20% 16% 3	1552
June	1st to 10th	Night	30% 7% 14% 27% 20% 2	1440
	11th to 20th	Night	34% 6% 12% 24% 21% 2	1440
	21st to end	Night	38% 8% 15% 22% 14% 3	1440
July	1st to 10th	Night	29% 8% 14% 28% 17% 4	1400
	11th to 20th	Night	28% 8% 13% 26% 22% 4	1392
	21st to end	Night	26% 9% 17% 25% 18% 5%	1487
August	1st to 10th	Night	28% 7% 16% 31% 17% 1	1537
	11th to 20th	Night	29% 7% 17% 25% 20% 2	1696
	21st to end	Night	31% 7% 10% 27% 21% 5%	1980
September	1st to 10th	Night	35% 5% 12% 23% 18% 6%	1800
	11th to 20th	Night	31% 6% 8% 28% 24% 2	1939
	21st to end	Night	36% 7% 10% 27% 18% 3	1980
October	1st to 10th	Night	37% 7% 9% 25% 20% 2	1980
	11th to 20th	Night	47% 6% 8% 22% 16% 1	2189
	21st to end	Night	53% 5% 11% 21% 10% 1	2574
November	1st to 10th	Night	46% 6% 8% 22% 16% 2	2406
	11th to 20th	Night	54% 9% 10% 18% 9% 1	2470
	21st to end	Night	57% 6% 11% 20% 7%	2470
December	1st to 10th	Night	64% 7% 8% 14% 6% 1	2636
	11th to 20th	Night	60% 11% 10% 14% 4	3281
	21st to end	Night	74% 6% 8% 8% 3	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	24% 19% 34% 18% 3	270
	11th to 20th	Day	30% 15% 37% 13% 3 1	270
	21st to end	Day	26% 19% 36% 18% 2	297
February	1st to 10th	Day	22% 26% 34% 14% 4	270
	11th to 20th	Day	24% 25% 32% 15% 3	270
	21st to end	Day	24% 27% 37% 11% 1	225
March	1st to 10th	Day	25% 24% 34% 16% 1	270
	11th to 20th	Day	24% 18% 34% 18% 6% 1	341
	21st to end	Day	30% 17% 29% 18% 6%	490
April	1st to 10th	Day	24% 15% 35% 19% 6% 1	420
	11th to 20th	Day	22% 20% 31% 17% 7% 4	412
	21st to end	Day	24% 15% 34% 17% 9% 1	420
May	1st to 10th	Day	24% 12% 33% 20% 9% 2	423
	11th to 20th	Day	22% 9% 33% 21% 13% 2	483
	21st to end	Day	14% 7% 29% 29% 14% 6%	679
June	1st to 10th	Day	11% 6% 30% 32% 17% 4	630
	11th to 20th	Day	11% 7% 31% 30% 18% 3	630
	21st to end	Day	13% 6% 32% 32% 13% 5%	630
July	1st to 10th	Day	10% 4 23% 28% 23% 11%	621
	11th to 20th	Day	11% 5% 24% 32% 20% 7%	618
	21st to end	Day	9% 4 26% 36% 19% 6%	684
August	1st to 10th	Day	9% 1 17% 34% 26% 12%	510
	11th to 20th	Day	8% 4 25% 31% 23% 9%	439
	21st to end	Day	12% 3 20% 34% 23% 8%	495
September	1st to 10th	Day	15% 5% 22% 31% 21% 6%	450
	11th to 20th	Day	12% 5% 17% 32% 22% 11%	450
	21st to end	Day	16% 12% 20% 26% 19% 7%	450
October	1st to 10th	Day	17% 7% 29% 29% 15% 3	450
	11th to 20th	Day	23% 20% 30% 20% 6%	293
	21st to end	Day	34% 13% 36% 14% 2	297
November	1st to 10th	Day	15% 15% 40% 21% 7% 2	270
	11th to 20th	Day	26% 17% 34% 18% 4	270
	21st to end	Day	31% 13% 40% 14% 2	270
December	1st to 10th	Day	22% 23% 34% 15% 6%	270
	11th to 20th	Day	21% 23% 38% 14% 3	270
	21st to end	Day	25% 24% 38% 12% 1	297
January	1st to 10th	Night	24% 21% 35% 18% 3	950
	11th to 20th	Night	25% 19% 34% 17% 4 1	950
	21st to end	Night	24% 17% 36% 20% 3	1045
February	1st to 10th	Night	26% 14% 37% 20% 3	835
	11th to 20th	Night	22% 19% 35% 21% 4	743
	21st to end	Night	27% 18% 37% 15% 3	628
March	1st to 10th	Night	23% 16% 36% 20% 6% 1	760
	11th to 20th	Night	18% 12% 39% 25% 6%	760
	21st to end	Night	25% 12% 30% 27% 6%	667
April	1st to 10th	Night	20% 15% 34% 23% 6% 1	540
	11th to 20th	Night	23% 12% 30% 25% 8% 2	533
	21st to end	Night	22% 9% 31% 29% 8% 1	540
May	1st to 10th	Night	22% 6% 33% 28% 11% 1	540
	11th to 20th	Night	22% 3 27% 33% 15% 1	531
	21st to end	Night	12% 5% 22% 37% 22% 3	584
June	1st to 10th	Night	11% 4 22% 41% 21% 1	540
	11th to 20th	Night	11% 4 26% 37% 19% 2	540
	21st to end	Night	11% 5% 24% 38% 20% 2	540
July	1st to 10th	Night	9% 1 15% 38% 30% 7%	525
	11th to 20th	Night	9% 3 19% 38% 26% 5%	522
	21st to end	Night	7% 2 18% 41% 31% 2	591
August	1st to 10th	Night	7% 2 12% 44% 30% 5%	537
	11th to 20th	Night	9% 4 14% 38% 30% 6%	534
	21st to end	Night	10% 3 17% 38% 27% 4	594
September	1st to 10th	Night	13% 5% 17% 35% 26% 3	540
	11th to 20th	Night	10% 7% 17% 34% 27% 5%	679
	21st to end	Night	13% 7% 25% 29% 22% 4	720
October	1st to 10th	Night	16% 7% 28% 29% 20% 2	720
	11th to 20th	Night	25% 15% 30% 22% 8%	720
	21st to end	Night	29% 16% 29% 20% 6%	792
November	1st to 10th	Night	21% 16% 33% 18% 10% 1	740
	11th to 20th	Night	23% 22% 32% 18% 5%	760
	21st to end	Night	27% 17% 33% 18% 5%	760
December	1st to 10th	Night	26% 20% 35% 17% 3	926
	11th to 20th	Night	24% 18% 36% 20% 2	950
	21st to end	Night	30% 18% 35% 15% 2	1045

Page generated at 2024-03-24 22:37:01. Version ac07

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